Field of the Invention

The present invention relates to processes for the production of bicyclic polyhydroxylated alkaloids comprising the cyclisation of intermediates having three or more free hydroxyl groups. In particular, the invention provides processes for the synthesis of polyhydroxylated pyrroiizidine or indolizidine alkaloids comprising the cyclisation of pyrrolidine or piperidine intermediates having three or more free hydroxyl groups.

Background to the Invention

Alkaloids

The term alkaloid is used sensu stricto to define any basic, organic, nitrogenous compound which occurs naturally in an organism (particularly in a plant). However, unless otherwise indicated, the term alkaloid is used herein sensu lato to define a broader grouping of compounds which include not only the naturally occurring alkaloids, but also their synthetic and semi-synthetic analogues and derivatives.

Most known alkaloids are phytochemicals, present as secondary metabolites in plant tissues (where they may play a role in defence), but some occur as secondary metabolites in the tissues of animals, microorganisms and fungi. There is growing evidence that the standard techniques for screening microbial cultures are inappropriate for detecting many classes of alkaloids (particularly polar alkaloids: see below) and that microbes (including bacteria and fungi, particularly the filamentous representatives) will prove to be an important source of alkaloids as screening techniques become more sophisticated.

Structurally, alkaloids exhibit great diversity. Many alkaloids are small molecules, with molecular weights below 250 Daltons. The skeletons may be derived from amino acids, though some are derived from other groups (such as steroids). Others can be considered as sugar analogues. It is becoming apparent (see Watson ef a/. (2001 ) Phytochemistry 56: 265-295) that the water soluble fractions of medicinal plants and microbial cultures contain many interesting novel polar alkaloids, including many carbohydrate analogues. Such analogues include a rapidly growing number of so-called polyhydroxylated alkaloids.

Most alkaloids are classified structurally on the basis of the configuration of the N-heterocycle. Examples of some important alkaloids and their structures are set out in Kutchan (1995) The Plant Cell 7:1059-1070. Watson et al. (2001) Phytochemistry 56: 265-295 have classified a comprehensive range of polyhydroxylated alkaloids inter alia as piperidine, pyrroiine, pyrrolidine, pyrroiizidine, indolizidine and nortropanes alkaloids (see Figs. 1-7 of Watson et al. (2001), the disclosure of which is incorporated herein by reference).

Watson ef a/. (2001), ibidem also show that a functional classification of at least some alkaloids is possible on the basis of their glycosidase inhibitory profile: many polyhydroxylated alkaloids are potent and highly selective glycosidase inhibitors. These alkaloids can mimic the number, position and configuration of hydroxyl groups present in pyranosyl or furanosyl moieties and so bind to the active site of a cognate glycosidase, thereby inhibiting it. This area is reviewed in Legler (1990) Adv. Carbohydr. Chem. Biochem. 48: 319-384 and in Asano et al. (1995) J. Med. Chem. 38: 2349-2356.

It has long been recognized that many alkaloids are pharmacologically active, and humans have been using alkaloids (typically in the form of plant extracts) as poisons, narcotics, stimulants and medicines for thousands of years. The therapeutic applications of polyhydroxylated alkaloids have been comprehensively reviewed in Watson et al. (2001), ibidem: applications include cancer therapy, immune stimulation, the treatment of diabetes, the treatment of infections (especially viral infections), therapy of glycosphingolipid lysosomal storage diseases and the treatment of autoimmune disorders (such as arthritis and sclerosis).

Both natural and synthetic mono- and bi-cyclic nitrogen analogues of carbohydrates are known to have potential as chemotherapeutic agents. Alexine (1) and australine (2) were the first pyrrolizidine alkaloids to be isolated with a carbon substituent at C-3, rather than the more common C-1 substituents characteristic of the necine family of pyrrolizidines.

Alexine (1)

Australine (2)

The alexines occur in all species of the genus Alexa and also in the related species Castanospermum australe. Stereoisomers of alexine, including 1 ,7a-diepialexine (3), have also been isolated (Nash et al. (1990) Phytochemistry (29) 111) and synthesised (Choi ef al. (1991) Tetrahedron Letters (32) 5517 and Denmark and Cottell (2001) J. Org. Chem. (66) 4276-4284).

1, 7a-diβpialexine (3)

Because of the reported weak in vitro antiviral properties of one 7,7a-diepialexine (subsequently defined as 1 ,7a-diepialexine), there has been some interest in the isolation of the natural products and the synthesis of analogues.

As an indolizidine alkaloid (and so structurally distinct from the pyrrolizidine alexines), swainsonine (4) is a potent and specific inhibitor of α-mannosidase and is reported to have potential as an antimetastic, tumour anti¬ proliferative and immunoregulatory agent (see e.g. US5650413, WO00/37465, WO93/09117).

Swainsonine (4)

Another indolizidine alkaloid, castanospermine (5), is a potent α-glucosidase inhibitor. This compound, along with certain 6-O-acyl derivatives (such as that known as Celgosivir or Bucast (6)), has been reported to exhibit anti-viral and antimetastatic activities.

Castanospermine (5)

Bucast (6)

The effect of variation in the size of the six-membered ring of swainsonine on its glycosidase inhibitory activity has been studied: pyrrolizidine derivatives (so-called "ring contracted swainsonines") have been synthesised. However, these synthetic derivatives (1S, 2R, 7R, 7aR)-1 ,2,7-trihydroxypyrrolizidine (7) and the 7S-epimer (8)) were shown to have much weaker inhibitory activity relative to swainsonine itself (see US5075457).

1S, ZR, 7R, 7a(R)-1,2,7-trihydroxypyrrolizidine (7)

Another compound, (1S, 2R, 6S, 7R1 7ar)-1 ,2,6,7-tetrahydroxypyrrolizidine (9) is an analogue of 1 ,8- diepiswainsonine and described as a "useful" inhibitor of glycosidase enzymes in EP0417059.

(1S, 2R1 6S, 7R, 7ar)-1,2,6,7-tetrahydroxypyrrolizidine (9) Casuarine, (1 R,2R,3R,6S,7S,7aR)-3-(hydroxymethyl)-1 ,2,6,7-tetrahydroxypyrrolizidine (10) (also known as casuarin) is a highly oxygenated bicyclic pyrrolizidine alkaloid that can be regarded as a more highly oxygenated analogue of the 1 ,7a-diepialexine (shown in 3) or as a C(3) hydroxymethyl-substituted analogue of the 1α,2α,6α,7α,7a(S)-1,2,6,7-tetrahydroxypyrrolizidine (shown in 9).

Casuarine (10)

Casuarine can be isolated from several botanical sources, including the bark of Casuarina equisetifolia (Casuarinaceae), the leaves and bark of Eugenia jambolana (Myrtaceae) and Syzygium guineense (Myrtaceae) (see e.g. Nash et al. (1994) Tetrahedron Letters (35) 7849-52).

Casuarina equisetifolia wood, bark and leaves have been claimed to be useful against diarrhoea, dysentery and colic (Chopra et a/. (1956) Glossary of Indian Medicinal Plants, Council of Scientific and Industrial Research (India), New Delhi, p. 55) and a sample of bark has recently been prescribed in Western Samoa for the treatment of breast cancer. An African plant containing casuarine (identified as Syzygium guineense) has been reported to be beneficial in the treatment of AIDS patients (see Wormald et a/. (1996) Carbohydrate Letters (2) 169-74).

The casuarine-6-α-glucoside (casuarine-6-α-D-glucopyranose, 11) has also been isolated from the bark and leaves of Eugenia jambolana (Wormald et al. (1996) Carbohydrate Letters (2) 169-74).

Casuarine-6-α-D-glucopyranose (11)

Eugenia jambolana is a well known tree in India for the therapeutic value of its seeds, leaves and fruit against diabetes and bacterial infections. Its fruit have been shown to reduce blood sugar levels in humans and aqueous extracts of the bark are claimed to affect glycogenosis and glycogen storage in animals (Wormald et al. (1996) Carbohydrate Letters (2) 169-74). Thus, polyhydroxylated alkaloids (especially polyhydroxy pyrrolizidine and indolizidines alkaloids) have great potential as therapeutic agents. However, they are often present in only small quantities in natural sources and are difficult to purify.

There is therefore a need for processes for the chemical synthesis of polyhydroxylated alkaloids (and polyhydroxylated pyrrolizidine and indolizidines alkaloids in particular) in order to exploit their therapeutic potential and to permit the systematic comparison and evaluation of structure-function relationships.

Synthesis of polvhvdroxylated alkaloids

The synthesis of polyhydroxylated alkaloids is technically challenging, principally because of the problems associated with unwanted side reactions arising from the hydroxyl groups: the more hydroxyl groups in the structure, the greater the difficulty.

This problem has been tackled by protecting or differentiating the reactivity of the oxygen functions. Bell et al. (1997) Tetrahedron Letters 38(33): 5869-72 describe the synthesis of four diastereoisomers of casuarine from eight carbon sugar lactones by reduction of open chain azidodimesylates by Suzuki-Takaoka reduction to allow the formation of the pyrrolizidine nucleus by bicyclisation (Bell et al. (1997) Tetrahedron Letters 38(33): 5869- 72). However, the use of heavily protected intermediates limits the flexibility of the scheme: it cannot be readily adapted to other pyrrolizidines because the requirement for selective protection, deprotection and activation leads to cumbersome and lengthy schemes, whilst the use of starting materials possessing the correct hydroxyl configurations is limited by their availability.

Another approach is based on tandem [4+2]/[3+2] nitroalkene cycloadditions. It has been used for the synthesis of several pyrrolizidine and indolizidines alkaloids with up to four contiguous stereogenic centres (see Denmark and Hurd (1999) Organic Letters 1(8): 1311-14). The method was later extended by the same workers to the synthesis of (+)-casuarine by the intermolecular [3+2] cycloaddition of a suitable substituted dipolarophile and a flexible, heavily substituted nitronate. However, the synthesis is not readily adaptable to other stereoisomers, is lengthy and the overall yield is modest (20%).

There is therefore a need for generally applicable, efficient and flexible processes for the synthesis of polyhydroxylated alkaloids.

It has now been discovered that the synthesis of polyhydroxylated pyrrolizidine and indolizidine alkaloids can be achieved without protecting all of the free hydroxyl groups, so permitting considerably shortened synthetic schemes. Moreover, the use of intermediates having free hydroxyl groups provides a hitherto unexploited mechanism for controlling the product distribution, stereospecificity and yield via complex formation at the free hydroxyl groups. Summary of the Invention

According to the invention there is provided a process for the production of a polyhydroxylated bicyclic (for example pyrrolizidine, indolizidine or quinolizidine) alkaloid comprising the cyclisation of a pyrrolidine or piperidine intermediate having three or more free hydroxyl groups.

The application of a cyclisation step to an intermediate having three or more free hydroxyl groups may eliminate the need for selective protection, deprotection and/or activation at these sites. Thus, shortened synthetic schemes may be employed whilst retaining good yields. Moreover, the free hydroxyl groups can be exploited to control the product distribution and/or stereospecificity and/or yield of the alkaloid products (as described infra).

The alkaloids produced according to the processes of the invention preferably have at least 3, 4, 5, 6 or 7 free hydroxyl groups on the ring system nucleus. Most preferred are alkaloid products having 3, 4 or 5 free hydroxyl groups on the ring system nucleus. The alkaloids produced according to the processes of the invention are preferably polar and/or water-soluble.

The invention finds particular application in the synthesis of polyhydroxylated pyrrolizidine alkaloids, for example having the formula:

wherein R1, R2, R3 and R4 are independently selected from hydrogen, hydroxyl, straight or branched, linear or cyclic, unsubstituted or substituted, saturated or unsaturated acyl, ether, alkyl, alkenyl, alkynyl and aryl groups, primary, secondary and tertiary amines, imines, sulphides, thiols, halides (e.g. chlorine, fluorine, iodine and bromine), phosphates, phosphonates, phosphinates, metal, nitrile, nitro, azido, sulphone, sulphoxide and sulphydryl groups, or a pharmaceutically acceptable salt or derivative thereof, and wherein the cyclisation is of a pyrrolidine intermediate.

In another preferred embodiment, the invention finds particular application in the synthesis of polyhydroxylated indolizidine alkaloids, for example having the formula: wherein R1, R2, R3, R4 and R5 are independently selected from hydrogen, hydroxyl, straight or branched, linear or cyclic, unsubstituted or substituted, saturated or unsaturated acyl, ether, alkyl, alkenyl, alkynyl and aryl groups, primary, secondary and tertiary amines, imines, sulphides, thiols, halides (e g chlorine, fluorine, iodine and bromine), phosphates, phosphonates, phosphinates, metal, nitrile, nitro, azido, sulphone, sulphoxide and sulphydryl groups, or a pharmaceutically acceptable salt or derivative thereof, and wherein the cyclisation is of a pyrrolidine or pipeπdine intermediate

Any suitable means of cyclisation may be employed according to the invention Preferred is base-catalysed cyclisation

The pyrrolidine or piperidine intermediate cyclised according to the invention may be produced by any convenient synthetic technique Particularly preferred are pyrrolidine or piperidine intermediates produced by azide reduction In such embodiments, the pyrrolidine or piperidine intermediates may be produced as the direct products of the azide reduction or indirectly via a lactam intermediate

Detailed Description of the Invention

Definitions

Where used herein and unless specifically indicated otherwise, the following terms are intended to have the following meanings in addition to any broader (or narrower) meanings the terms might enjoy in the art

As used herein, the term alkaloid, as applied to the products of the processes of the invention, is used to define the synthetic or semi-synthetic counterpart of any basic, organic, nitrogenous compound which occurs naturally in an organism (particularly in a plant), together with analogues and derivatives thereof

As used herein, the term bicyclic polyhydroxylated alkaloid defines a class of highly oxygenated alkaloids having a double or fused ring nucleus (ι e having two or more cyclic rings in which two or more atoms are common to two adjoining rings) Typically, such alkaloids have at least 3, 4, 5, 6 or 7 (preferably 3, 4 or 5) free hydroxyl groups on the ring system nucleus

As used herein, the term polyhydroxylated pyrrolidine alkaloid defines a highly oxygenated alkaloid (e g having at least 3, 4, 5, 6 or 7 (preferably 3, 4 or 5) free hydroxyl groups on the ring system nucleus) that comprises the nucleus

As used herein, the term polyhydroxylated indolizidine alkaloid defines a highly oxygenated alkaloid (e g having at least 3, 4, 5, 6 or 7 (preferably 3, 4 or 5) free hydroxyl groups on the ring system nucleus) that comprises the nucleus

As used herein, the term polyhydroxylated quinolizidine alkaloid defines a highly oxygenated alkaloid (e.g. having at least 3, 4, 5, 6 or 7 (preferably 3, 4, 5 or 6) free hydroxyl groups on the ring system nucleus) that comprises the nucleus:

As used herein, the term heteroatom defines an atom of any element other than carbon or hydrogen. Preferred heteroatoms are boron, nitrogen, oxygen, phosphorus, sulfur and selenium.

As used herein, the term polar, as applied to alkaloids, is used to define alkaloids which exhibit high solubility in polar solvents (which have an electric dipole moment and so display hydrophilicity) relative to non-polar solvents (which exhibit hydrophobicity). The polar alkaloids of the invention may therefore be soluble in water.

The terms derivative and pharmaceutically acceptable derivative as applied to the alkaloids of the invention define compounds which are obtained (or obtainable) by chemical derivatization of the parent alkaloids of the invention. The pharmaceutically acceptable derivatives are therefore suitable for administration to or use in contact with the tissues of humans without undue toxicity, irritation or allergic response (i.e. commensurate with a reasonable benefit/risk ratio). Preferred derivatives are those obtained (or obtainable) by alkylatioπ, esterification or acylation of the parent alkaloids. The derivatives may be immunomodulatory perse, or may be inactive until processed in vivo. In the latter case, the derivatives of the invention act as pro-drugs. Particularly preferred pro-drugs are ester derivatives which are esterified at one or more of the free hydroxyls and which are activated by hydrolysis in vivo. The pharmaceutically acceptable derivatives of the invention retain some or all of the immunomodulatory activity of the parent compound. In some cases, the immunomodulatory activity is increased by derivatization. Derivatization may also augment other biological activities of the alkaloid, for example bioavailability and/or glycosidase inhibitory activity and/or glycosidase inhibitory profile. For example, derivatization may increase glycosidase Inhibitory potency ancf/or specificity.

The term pharmaceutically acceptable salt as applied to the alkaloids of the invention defines any non-toxic organic or inorganic acid addition salt of the free base alkaloid which are suitable for use in contact with the tissues of humans and lower animals without undue toxicity, irritation, allergic response and which are commensurate with a reasonable benefiVrisk ratio. Suitable pharmaceutically acceptable salts are well known in the art. Examples are the salts with inorganic acids (for example hydrochloric, hydrobromic, sulphuric and phosphoric acids), organic carboxylic acids (for example acetic, propionic, glycolic, lactic, pyruvic, malonic, succinic, fumaric, malic, tartaric, citric, ascorbic, maleic, hydroxymaleic, dihydroxymafeic, benzoic, phenylacetfc, 4-aminobenzoic, 4-hydroxybenzoic, anthranilic, cinnamic, salicylic, 2-phenoxybenzoic, 2-acetoxybenzoic and mandelic acid) and organic sulfonic acids (for example methanesulfonic acid and p-toluenesulfonic acid). The drugs of the invention may also be converted into salts by reaction with an alkali metal halide, for example sodium chloride, sodium iodide or lithium iodide. Preferably, the alkaloids of the invention are converted into their salts by reaction with a stoichiometric amount of sodium chloride in the presence of a solvent such as acetone.

These salts and the free base compounds can exist in either a hydrated or a substantially anhydrous form. Crystalline forms of the alkaloids of the invention are also contemplated and in general the acid addition salts of the alkaloids are crystalline materials which are soluble in water and various hydrophilic organic solvents and which in comparison to their free base forms, demonstrate higher melting points and an increased solubility.

In its broadest aspect, the present invention contemplates all optical isomers, racemic forms and diastereoisomers of the alkaloid products. Those skilled in the art will appreciate that, owing to the asymmetrically substituted carbon atoms present in the alkaloids of the invention, the pyrrolidine and indolizidine alkaloids may be produced in optically active and racemic forms. Thus, references to the pyrrolizidine and indolizidine alkaloid products of the present invention encompass the products as a mixture of diastereoisomers, as individual diastereoisomers, as a mixture of enantiomers as well as in the form of individual enantiomers.

Polvhydroxylated alkabid products

A wide range of bicyclic polyhydroxylated alkaloid products may be synthesised using the processes of the invention.

For example, the bicyclic polyhydroxylated alkaloids produced according to the invention may have a pyrrolizidine nucleus. Such 5+5 alkaloids are based on a bicyclic nucleus derived from two fused pyrrolidine rings with N at the bridgehead, thus:

V-N^/

Examples of such bicyclic polyhydroxylated pyrrolizidine alkaloids include those listed in Figure 5 of Watson ef a/. (2001) Phytochemistry 56: 265-295 (see page 274), the content of which is incorporated herein by reference.

The bicyclic polyhydroxylated alkaloid produced according to the invention may have an indolizidine nucleus. Such 6+5 alkaloids are based on a bicyclic nucleus derived from fused piperidine and pyrrolidine rings with N at the bridgehead, thus: Examples of such bicyclic polyhydroxylated indolizidine alkaloids include those listed in Figure 6 of Watson ef a/. (2001) Phytochetnistry 56: 265-295 (see page 275), the content of which is incorporated herein by reference.

The bicyclic polyhydroxylated alkaloid produced according to the invention may have a quinolizidine nucleus. Such 6+6 alkaloids are based on a bicyclic nucleus derived from fused piperidine rings with N at the bridgehead, thus:

The bicyclic polyhydroxylated alkaloids produced according to the processes of the invention may have at least 3, 4, 5, 6 or 7 free hydroxyl groups on the ring system nucleus. Preferably, the alkaloids have 3, 4, 5 or 6 free hydroxyl groups on the ring system nucleus. Thus, the number of hydroxyl groups present are typically sufficient to render the alkaloid molecule polar and/or soluble in polar solvents (e.g. water).

The nuclei of the bicyclic polyhydroxylated alkaloids produced according to the processes of the invention may have groups or substituents other than hydroxyl groups on the ring system nucleus. Such groups/substituents include those selected from hydrogen, straight or branched, linear or cyclic, unsubstituted or substituted, saturated or unsaturated acyl, ether, alkyl, alkenyl, alkynyl and aryl groups.

Ether groups include epoxides, acetals (including glycosidyl moieties, e.g. glucosidyl moieties) and hemiacetals. Hemiacetal groups include cyclic hemiacetals (for example, polyhydroxylated cyclic hemiacetal sugars).

Acyl groups include aldehydes and ketones (including polyhydroxylated aldehyde and ketone sugars, which may be aldose or ketose). Other acyl groups include carboxylic acids and carboxylic acid derivatives. The latter include acid halides, acid anhydrides, esters, amides and imides.

Aryl groups include 5-, 6- and 7-membered single-ring aromatic groups that may include from zero to four heteroatoms, for example, benzene, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine and pyrimidine.

Aryl groups containing heteroatoms include, for example, thiophene, thianthrene, furan, pyran, isobenzofuran, chromene, xanthene, phenoxathiin, pyrrole, imidazole, pyrazole, isothiazole, isoxazole, pyridine, pyrazine, pyrimidine, pyridazine, indolizine, isoindole, indole, indazole, purine, quinolizine, isoquinoline, quinoline, phthalazine, naphthyridine, quinoxaline, qum' azoline, cinnoline, pteridine, carbazole, carboline, phenanthήdine, acridine, pyrimidine, phenanthroline, phenazine, phenarsazine, phenothiazine, furazan, phenoxazine, pyrrolidine, oxolane, thiolane, oxazole, piperidine, piperazine, morpholine, lactones, lactams such as azetidinones and pyrrolidinones, sultams and sultones.

The aryl groups may also include polycyclic ring systems having two or more cyclic rings in which two or more carbons are common to two adjoining rings (the rings are "fused rings") wherein at least one of the rings is aromatic (e.g. the other cyclic rings can be cycloalkyls, cycloalkenyls, cycloalkynyls, aryls and/or heterocyclyls).

Other graups/substituents include primary, secondary and tertiary amines, imines, sulphides, thiols, halides (e.g. chlorine, fluorine, iodine and bromine), phosphates, phosphonates, phosphinates, metal, nitrile, nitro, azido, sulphone, sulphoxide and sulphydryl groups.

Pyrrolizidine alkaloid products

The pyrrolidine alkaloid products of the processes of the invention may have the formula:

wherein R1, R2, R3 and R4 are independently selected from hydrogen, hydroxyl, straight or branched, linear or cyclic, unsubstituted or substituted, saturated or unsaturated acyl, ether, alkyl, alkenyl, alkynyl and aryl groups, primary, secondary and tertiary amines, imines, sulphides, thiols, halides (e.g. chlorine, fluorine, iodine and bromine), phosphates, phosphonates, phosphinates, metal, nitrile, nitro, azido, sulphone, sulphoxide and sulphydryl groups, or a pharmaceutically acceptable salt or derivative thereof.

Suitable ether groups include epoxides, acetals (including glycosidyl moieties, e.g. glucosidyl moieties) and hemiacetals. Hemiacetal groups include cyclic hemiacetals (for example, polyhydroxylated cyclic hemiacetal sugars).

Suitable acyl groups include aldehydes and ketones (including polyhydroxylated aldehyde and ketone sugars, which may be aldose or fcetose). Other acyl groups include carboxylic acids and carboxylic acid derivatives. The latter include acid halides, acid anhydrides, esters, amides and imides.

Suitable aryl groups include 5-, 6- and 7-membered single-ring aromatic groups that may include from zero to four heteroatoms, for example, benzene, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine and pyrimidine. Exemplary aryl groups containing heteroatoms include, for example, thiophene, thianthrene, furan, pyran, isobenzofuran, chromene, xanthene, phenoxathiin, pyrrole, imidazole, pyrazole, isothiazole, isoxazole, pyridine, pyrazine, pyrimidine, pyridazine, indolizine, isoindole, indole, indazole, purine, quinolizine, isoquinoline, quinoiine, phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline, pteridine, carbazole, carboline, phenanthridine, acridine, pyrimidine, phenanthroline, phenazine, phenarsazine, phenothiazine, furazan, phenoxazine, pyrrolidine, oxolane, thiolane, oxazole, piperidine, piperazine, morpholine, lactones, lactams such as azetidinones and pyrrolidinones, sultams and sultones. The aryl groups may also include polycyclic ring systems having two or more cyclic rings in which two or more carbons are common to two adjoining rings (the rings are "fused rings") wherein at least one of the rings is aromatic (e.g. the other cyclic rings can be cycloalkyls, cycloalkenyls, cycloalkynyls, aryls and/or heterocyclyls).

In preferred embodiments, any or all of R1, R2, R3 and R4 is a saccharide moiety and the alkaloid product is a glycoside. Thus, particularly preferred are compounds in which any or all of R1, R2, R3 and R4 is a glucoside c arabinoside moiety.

Preferably, the pyrrolizidine alkaloid products of the processes of the invention have the formula:

wherein R is selected from the group comprising hydrogen, straight or branched, linear or cyclic, unsubstituted or substituted, saturated or unsaturated acyl, ether, alkyl, alkenyl, alkynyl and aryl groups, or a pharmaceutically acceptable salt or derivative thereof.

In preferred embodiments, the pyrrolizidine ring bears a saccharide moiety and the alkaloid product is a glycoside. Thus, particularly preferred are compounds in which R is a glucoside or arabinoside moiety.

The derivative may be an acyl derivative. For example, the alkaloid may be: (a) peracylated; or (b) acylated at C-3 hydroxymethyl; or (c) acylated at C-6; (d) acylated at C-3 hydroxymethyl and C-6.

The acyl derivative may be alkanoyl or aroyl. Preferred are alkanoyl derivatives selected from acetyl, propanoyl or butanoyl. Preferred is 6-O-butanoylcasuarine having the formula:

or a pharmaceutically acceptable salt or derivative thereof.

Yet other preferred pyrrolizidine alkaloid products have the formula:

wherein R is selected from the group comprising hydrogen, straight or branched, unsubstituted or substituted, linear or cyclic, saturated or unsaturated acyl, ether, alkyl, alkenyl, alkynyl and aryl groups, or a pharmaceutically acceptable salt or derivative thereof.

In another particularly preferred embodiment the pyrrolizidine alkaloid product is 1R,2R,3R,6S,7S,7aR)-3- (hydroxymethyl)-1,2,6,7-tetrahydroxypyrrolizidirre (casuarirte), wherein R is hydrogen and having the formula:

or a pharmaceutically acceptable salt or derivative thereof.

The other embodiments, the pyrrolizidine alkaloid product is casuarine glycoside, or a pharmaceutically acceptable salt or derivative thereof. In such embodiments, the alkaloid is preferably casuarine-6-α-D- g/ucoside of the formula:

or a pharmaceutically acceptable salt or derivative thereof.

Other preferred pyrrolizidine alkaloid products include those selected from: (a) 3,7-d/ep/-casuarine; (b) 7-ep/-casuarine; (c) 3,6,7-/r/ep/-casuarine; (d) 6,7-cfep/-casuarine; (e) 3-ep/-casuarine; (f) 3,7-d/ep/-casuarine-6-α-D-g]ucoside; (g) 7-ep/-casuarine-6-α-D-glucoside; (h) 3,6,7-fr/ep/-casuarine-6-α-D-glucoside; (i) 6,7-d/ep/-casuarine-6-α-D-glucoside; and (j) 3-ep/-casuarine-6-α-D-g)ucoside, or a pharmaceutically acceptable salt or derivative thereof.

As mentioned infra, the invention contemplates diastereomers of the compounds of the invention. Particularly preferred are diastereomers selected from 3,7-αfep/-casuarine (12), 7-ep/-casuarine (13), 3,6,7-triepi-casuarine (14), 6,7-α7ep/-casuarine (15) and 3-ep/-casuarine (16), as well as pharmaceutically acceptable salts and derivatives thereof.

CH2OH

3, 7-diepi-casuarine (12)

7-epicasuarine (13)

CH2OH

3,6, 7-triepi-casuarine (14)

6, 7-diepi-casuaήne (15)

CH2OH

3-epi-casuarine (16)

Other preferred diastereomers are selected from 3,7-d/ep/-casuarine-6-α-D-glucoside (17), 7-ep/-casuarine-6-α- D-glucoside (18), 3,6,7-f/7'ep/-casuarine-6-α-D-glucoside (19), 6,7-cfep/-casuarine-6-α-D-glucoside (20) and 3- ep/-casuarine-6-α-D-glucoside (21 ), as well as pharmaceutically acceptable salts and derivatives thereof.

3, 7-diepi-casuarine-β-α-D-glucoside (17)

7-epi-casuarine-6-α-D-glucoside (18)

3,6, 7-triepi-casuahne-6-a-D-glucoslde (19)

6, J-diepi-casuarine-β-a-D-glucoside (20)

3-epi-casuarine-6-a-D-glucoside (21) Other preferred diastereomers include 7a epimers selected from 3,7,7a-tr/ep/-casuarine, 7,7a-diep/-casuarine, 3,6,7, 7a-fefraep/-casuarine, 6,7,7a-triep/-casuarine and 3,7a-diep/-casuarine, as well as pharmaceutically acceptable salts and derivatives thereof.

Indolizidine alkaloid products The indolizidine alkaloid products of the processes of the invention may have the formula: wherein R1, R2, R3, R4 and R5 are independently selected from hydrogen, hydroxyl, straight or branched, linear or cyclic, unsubstituted or substituted, saturated or unsaturated acyl, ether, alkyl, alkenyl, alkynyl and aryl groups, primary, secondary and tertiary amines, imines, sulphides, thiols, halides (e.g. chlorine, fluorine, iodine and bromine), phosphates, phosphonates, phosphinates, metal, nitrile, nitro, azido, sulphone, sulphoxide and sulphydryl groups, or a pharmaceutically acceptable salt or derivative thereof.

Suitable ether groups include epoxides, acetals (including glycosidyl moieties, e.g. glucosidyl moieties) and hemiacetals. Hemiacetal groups include cyclic hemiacetals (for example, polyhydroxylated cyclic hemiacetal sugars).

Suitable acyl groups include aldehydes and ketones (including polyhydroxylated aldehyde and ketone sugars, which may be aldose or ketose). Other acyl groups include carboxylic acids and carboxylic acid derivatives. The latter include acid halides, acid anhydrides, esters, amides and imides.

Suitable aryl groups include 5-, 6- and 7-membered single-ring aromatic groups that may include from zero to four heteroatoms, for example, benzene, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine and pyrimidine. Exemplary aryl groups containing heteroatoms include, for example, thiophene, thianthrene, furan, pyran, isobenzofuran, chromene, xanthene, phenoxathiin, pyrrole, imidazole, pyrazole, isothiazole, isoxazole, pyridine, pyrazine, pyrimidine, pyridazine, indolizine, isoindole, indole, indazole, purine, quinolizine, isoquinoline, quinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline, pteridine, carbazole, carboline, phenanthridine, acridine, pyrimidine, phenanthroline, phenazine, phenarsazine, phenothiazine, furazan, phenoxazine, pyrrolidine, oxolane, thiolane, oxazole, piperidine, piperazine, morpholine, lactones, lactams such as azetidinones and pyrrolidinones, sultams and sultones. The aryl groups may also include polycyclic ring systems having two or more cyclic rings in which two or more carbons are common to two adjoining rings (the rings are "fused rings") wherein at least one of the rings is aromatic (e.g. the other cyclic rings can be cycloalkyls, cycloalkenyls, cycloalkynyls, aryls and/or heterocyclyls).

In preferred embodiments, any or all of R1, R2, R3 and R4 is a saccharide moiety and the alkaloid product is a glycoside. Thus, particularly preferred are compounds in which any or all of R1, R2, R3 and R4 is a glucoside or arabinoside moiety.

Thus, the indolizidine products obtainable by the processes of the invention include swainsonine (4), castanospermine (5), Bucast (6) and various derivatives and salts thereof.

Preferably, the indolizidine alkaloid products of the processes of the invention have the formula:

wherein R1 is selected from the group comprising hydrogen, straight or branched, unsubstituted or substituted, linear or cyclic, saturated or unsaturated acyl, ether, alkyl (e g cycloalkyl), alkenyl, alkynyl and aryl groups and R2 and R3 are selected from hydrogen, hydroxy and alkoxy, or a pharmaceutically acceptable salt or derivative thereof

Preferably, the indolizidine product has the formula

wherein R1 is selected from the group comprising hydrogen, straight or branched, unsubstituted or substituted, linear or cyclic, saturated or unsaturated acyl, ether, alkyl (e g cycloalkyl), alkenyl, alkynyl and aryl groups and R2 is selected from hydrogen, hydroxy and alkoxy, or a pharmaceutically acceptable salt or derivative thereof

More preferably, they have the formula

wherein R1 is selected from the group comprising hydrogen, straight or branched, unsubstituted or substituted, linear or cyclic, saturated or unsaturated acyl, ether, alkyl (e g cycloalkyl), alkenyl, alkynyl and aryl groups and R2 is selected from hydrogen, hydroxy and alkoxy, or a pharmaceutically acceptable salt or derivative thereof

Particularly preferred are indolizidine alkaloid products having the formula

or a pharmaceutically acceptable salt or derivative thereof

More preferably, the indolizidine alkaloid product has the formula

or a pharmaceutically acceptable salt or derivative thereof.

Pyrrolidine and piperidine intermediates for cvclisation

The pyrrolidine or piperidine intermediates for cyclisation in the processes of the invention are preferably generated from carbon skeleton precursors having: (a) an N function; and (b) two electrophilic carbon atoms susceptible to nucleophilic attack by the N function. Preferably, the N function and electrophilic carbon atoms have the following configuration (relative spacing):

(a) i, i +3 and i +8 (for pyrrolizidine products); or (b) i, i +3 and i +7 (for pyrrolizidine and indolizidine products).

Suitable N functions include amino groups or precursors thereto (for example, azides or lactams).

The electrophilic carbon atoms may be carbonyl carbons and/or carbon atoms furnished with leaving groups. Any suitable leaving group may be employed, but preferred are sulphonate leaving groups (e.g. triflates, mesylates and tosylates). Thus, one preferred class of carbon skeleton precursors suitable for use in a process for the production of a range of different polyhydroxylated pyrrolizidine alkaloids are the ditosylateheptahydroxyazidooctanes.

It should be noted that the two electrophilic carbon atoms need not both be present simultaneously in any single precursor. Rather, they may be elaborated sequentially, the second being provided (for example via the addition of a leaving group) after the first has been subject to nucleophilic attack by the N function (which may be coincident with the creation of a first (5- or 6-membered) ring (and the formation of the pyrrolidine or piperidine intermediate or precursor thereof).

In preferred embodiments, the carbon skeleton precursors are linear polyhydroxy alkanes (e.g. heptane, octane or nonane), precursors thereto or derivatives thereof. However, it is important to note that any hydroxyl groups on the carbon skeleton precursors and/or the pyrrolidine or piperidine intermediates may be partially or fully protected during part of the synthesis, provided that the pyrrolidine or piperidine intermediate on which the cyclisation step is performed comprises at least 3 free hydroxyl groups. Thus, in some embodiments, the pyrrolidine or piperidine intermediates are partially or fully protected during some of the synthesis and deprotected prior to the cyclisation step. Such temporary protection may comprise, for example, the addition of temporary trimethyl silyl group(s).

The carbon skeleton precursors may be generated by any suitable techniques, including Kiliani chain extension(s) and/or Wittig reaction(s). Such techniques per se are known in the art and do not form part of the present invention. However, while the synthesis of acetonides of octonolactones (which are suitable carbon skeleton precursors for use according to the invention: see Example 9 below) by Kiliani chain extension is described in Bell et a/. (1996) Tetrahedron: Asymmetry 7(2): 595-606 and the products used in schemes for the production of four diastereoisomers of casuarine (Bell et al. (1997) Tetrahedron Letters 38(33): 5869-72), the use of the Wittig reaction to elaborate appropriate carbon skeleton precursors is not precedented and may provide short access to a wide variety of different stereoisomers (see Example 4, below).

Azide reduction

In embodiments where an azide group provides the N function, the synthetic steps leading up to the formation of the pyrrolidine or piperidine intermediates may comprise an azide reduction step.

Any suitable reducing agent may be used to perform the reduction. Particularly preferred is catalytic hydrogenation (e.g. with a metal catalyst such as palladium) and sodium hydrogen telluride reduction (Suzuki- Takaoka procedure). The latter procedure is particularly preferred in circumstances where steric hindrance from adjacent protected groups prevents efficient catalytic hydrogenation.

When employed, the azide reduction step may effect the formation of a first ring and may therefore elaborate, directly or indirectly (e.g. via a lactam), the pyrrolidine or piperidine intermediate. In cases where azide reduction produces a lactam intermediate, the pyrrolidine or piperidine is conveniently derived therefrom by reduction. Any of a wide range of reducing agents may be employed for this step: preferred is borane reduction at elevated temperature.

Cvclisation

The cyclisation of the pyrrolidine or piperidine intermediate may be effected by any suitable method. Preferred is base-catalysed cyclisation.

In embodiments where base catalysed cyclisation is employed, any base may be used. Preferred are water- soluble bases, for example sodium acetate. However, solid phase cyclisation may be achieved using polymer- bound bases (for example in conjunction with ion-exchange media).

In some embodiments, the cyclisation step may terminate the synthesis. However, in many applications the cyclisations are followed by further reactions and/or processing, particularly in embodiments where the alkaloid product is to be used in a pharmaceutical composition. For example, the product of the cyclisation may be subject to derivitization, crystallization, purification (e.g. by chromatography) and/or admixture with various pharmaceutical excipients.

Complex formation at free hvdroxyl groups

The presence of free hydroxyl groups on the pyrrolidine or piperidine intermediates of the invention permit complex formation with various complexiπg agents during (or prior to) the cyclisation step.

Such complexing agents include metal ions (e.g. anions such as Na+ or Mg++ and Al+++), complex ions (such a borates) and zeolites. Complex formation at the free hydroxyl residues during or before the cyclisation step may be exploited to induce conformational restrictions/constraints and so lead to specific cyclisations, permitting a further means of control over the product distribution prfile, stereospecificity and yield

Exemplification

The invention will now be described with reference to specific Examples These are merely exemplary and for illustrative purposes only they are not intended to be limiting in any way to the scope of the monopoly claimed or to the invention described These examples constitute the best mode currently contemplated for practicing the invention

Example 1 Synthesis of 3,7-dιep;-casuarιne (12) Reaction scheme

General Experimental

All reactions were carried out under an atmosphere of argon at room temperature using anhydrous solvents unless otherwise stated. Anhydrous solvents were purchased from Fluka Chemicals and were used as supplied. Reagents were supplied from Aldrich, Fluka and Fisher and were used as supplied. Thin layer chromatography (TIc) was performed on aluminium sheets pre-coated with Merck 60 F254 silica gel and were visualised under ultra-violet light and staining using 6% phosphomolybdic acid in ethanol. Silica gel chromatography was carried out using Sorbsil C60 40/60 silica gel under a positive atmosphere. Amberlite IR- 120, strongly acidic ion-exchange resin was prepared by soaking the resin in 2M hydrochloric acid for at least two hours followed by elution with distilled water until the eluant reached pH 5. Dowex 50WX8-100 was prepared by soaking the resin with 2IW hydrochloric acid for at least two hours followed by elution with distilled water until neutral. Infrared spectra were recorded on a Perkin-Elmer 1750 IR Fourier Transform spectrophotometer using thin films on sodium chloride plates. Only characteristic peaks are recorded. Optical rotations were measured on a Perkin-Elmer 241 polarimeter with a path length of 1dm. Concentrations are quoted in g/100mL. Nuclear magnetic resonance spectra were recorded on a Bruker DQX 400 spectrometer in the stated deuterated solvent. All spectra were recorded at ambient temperature. Chemical shifts (δ) are quoted in ppm and are relative to residual solvent as standard. Proton spectra (5H) were recorded at 400 MHz and carbon spectra (δc) at 100 MHz.

2.3:5.6:7.8-Tri-0-isopropylidene-D-ervf/7ro-L-te/o-octono -1.4-lactone (QcI 5.6:7,8-Di-0-isopropylidene-D-e/yf/7ro-Uaa/acfo-octono-1 ,4-lactone (QbI

Sodium cyanide (7.02 g, 142 mmol) was added to a stirred solution of D-g/ycero-D-gu/o-heptose (Qa, 21 g, 100 mmol) in water (300 ml). The reaction mixture was stirred at room temperature for 48 h, heated at reflux for 48 h and passed through a column containing Amberlite IR-120 (strongly acidic ion-exchange resin, 300 ml). The eluent was concentrated under reduced pressure and the residue dried in vacuo for 24 hours. The resulting foam was treated with acetone (500 ml) and sulphuric acid (5.4 ml) in the presence of anhydrous copper sulphate (10 g, 62 mmol) at room temperature for 48 h. T.l.c analysis indicated the presence of two major products (ethyl acetate:cyclohexane, 1 :1; Rf 0.72, 0.18). The reaction mixture was filtered and the filtrate was treated with sodium bicarbonate (50 g) for 24 h at room temperature. Solid residues were removed by filtration and the filtrate was concentrated under reduced pressure. The resulting crude yellow syrup was purified by silica gel chromatography providing 2,3:5,6:7,8-tri-O-isopropylidene-D-eryfftro-L-ra/o-octono-1, 4-lactone Qc as a colourless syrup (Rf 0.72; 7.672 g; 21 %;) and 5,6:7,8-di-O-isopropylidene-D-θΛ|/fήro-L-ga/acfo-ocfono-1 ,4- lactone Qb as a clear oil (Rf 0.18; 8.105 g; 25 %) 2,3:5,6:7,8-tri-O-isopropylidene-D-e/yfftro-L-fa/o-octono-1 ,4- lactone Qc : δH (CDCI3) 1.29, 1.33, 1.35, 1.38, 1.42, 1.48 (6 x s, 18H, 3 x C(CHs)2), 3.93-3.99 (m, 2H, H-8a, H- 7), 4.03-4.07 (m, 2H, H-5, H-Q), 4.15 (dd, 1 H, J8a,8b 8.7 J8b,7 6.1 , H-8b), 4.75-4.78 (m, 3H, H-2, H-3, H-4); δc (CDCI3) 25.23, 25.51, 26.00, 26.71, 26.73, 27.16 (3 x C(CH3)2), 67.93, 74.93, 76.33, 76.69, 78.65, 79.40, 80.06, 109.95, 110.72, 113.19, 174.27; vmaχ (film) 1793. 5,6:7,8-di-O-isopropylidene-D-e/yf/?ro-L-ga/acfo-octono-1 ,4- lactone Qb : δH (de-acetone) 1.28, 1.32, 1.34, 1.35 (4s, 12H1 2 x C(CHa)2), 3.92 (1H, m, H-8a), 3.98 (m, 1 H, H- 7), 4.14 (m, 2H, H-5, H-8b), 4.23-4.25 (m, 2H, H-4, H-6), 4.35-4.40 (m, 2H, H-2, H-3); δc (de-acetone) 25.31 , 25.87, 26.72, 27.31 , 68.06, 75.15, 75.23, 77.51, 78.05, 78.41 , 79.01 , 110.06, 110.31 , 174.25; vmax (film) 1793, 3541. 2.3:5,6-Di-0-isopropylidene-D-e/yfftro-L-fa/o-octono-1 ,4-lactone Qd

A solution of 2,3:5,6:7,8-tri-0-isopropylidene-D-e/yfrVσ-L-fa/o-octono-1, 4-lactone (Qc, 3.8 g, 10.6 mmo!) was treated with acetic acid:water (2:3, 100 ml) at 50 0C for 2 h. T.l.c analysis (ethyl acetate:cyclohexane, 1:1) indicated the disappearance of the starting material (Rf 0.72) and the presence of a more polar compound (Rf 0.15). The solvent was removed under reduced pressure and the residue was purified by silica gel chromatography (ethyl acetaexyclohexane, 1 :1 to 3:1) yielding 2,3:5,6-di-O-isopropylidene-D-eryfftro-L-fa/o- octono-1,4-lactone Qd as a clear oil (3.23 g, 94 %): 6H (CD3OD) 1.28, 1.38, , 1.43 (3 x s, 12H, 2 x C(CHa)2), 3.59 (dd, 1H, Jβa,7 5.40 J8a,8b 11.41 , H-8a), 3.66-3.69 (m, 1H, H-7), 3.74 (dd, 1 H, J8b,7 2.90 Hz, H-8b), 4.01 (app t, 1H, J6J 7.62 Hz, H-Q), 4.24 (dd, 1H, J5,β 8.17 Hz J5,4 0.89 Hz, H-5), 4.79-4.81 (m, 2H, H-3, H-A), 4.89-4.91 (m, 1H, H-2); δc (CD3OD) 24.62, 25.42, 26.05, 26.49, 63.86, 73.81 , 75.40, 75.91, 79.18, 79.90, 80.78, 110.53, 113.09, 175.76; vmax (film) 1791 , 3478; [α]D -35.7 (c 1 , CHCI3).

8-0-terf-Butyldimethylsilyl-2,3:5.6-di-0-isopropylidene-D -ervftro-L-te/o-octono-1.4-lactone Qe

To a solution of 2,3:5, 6-di-0-isopropylidene-D-e^/7ro-L-fa/o-octoπo-1,4-lactoπe (Qd, 3.18 g, 10 mmol) in N1N- dimethylformamide (40 ml) was added fe/t-butyldimethylsilyl chloride (1.808 g, 12 mmol) and imidazole (1.361 g, 20 mmol). The reaction mixture was stirred at room temperature for 16 h after which t.l.c. analysis (ethyl acetatexyclohexane, 1 :1) showed no starting material (Rf 0.15) and the formation of one major product (Rf 0.63). The solvent was removed under reduced pressure and the residue was partitioned between ethyl acetate and brine. The aqueous layer was extracted with ethyl acetate and the combined organic layers were dried (MgSO4), filtered and the solvent removed. The resulting pale oil was purified by silica gel chromatography (ethyl acetatexyclohexane, 0:1 to 1 :2) to give 8-0-terf-butyldimethylsilyl-2,3:5,6-di-0-isopropylidene-D-er κfhro- L-fafo-octono-1,4-lactone Qe as a clear oil (3.612 g, 85%): 5H (CDCI3) 0.04 (br s, 6H, 2 x CW3), 0.86 (s, 9H, C(CHs)3), 1.23, 1.30, 1.32, 1.41 (4 x s, 12H, 2 x C(CHs)2), 3.63-3.67 (m, 2H, H-8a, H-7), 3.76 (br d, 1H, H-8b), 3.96 (app t, J5J 8.21 J6,5 7.98, H-6), 4.08 (br d, 1H, H-5), 4.72 (br s, 2H, H-2, H-3), 4.78 (br s, 1H, H-4); δc (CDCI3) -5.52, -5.45, 18.25, 25.51 , 25.80, 25.93, 26.68, 27.18, 63.95, 72.97, 74.88, 74.93, 78.71 , 79.63, 79.87, 110.34, 113.00, 174.42; vmax (film) 1794, 3570; [α]D -20.1 (c 1 , CHCI3).

7-Azido-8-0-tert-butyldimethylsilyl-7-deoxy-2.3:5,6-di-0- isopropylidene-L-f/7reo-L-fa/o-octono-1 ,4-lactone Qf

A solution of 8-0-ferf-butyldimethylsilyl-2,3:5,6-di-0-isopropylidene-D-er /fΛro-L-tø/o-octono-1 ,4-lactone (Qe, 3.5 g, 8.2 mmol) in a pyridine:dichloromethane mixture (1:4, 25 ml) was cooled to -300C. Trifluoromethanesulfonic anhydride (3.5 g, 2.09 ml, 12.4 mmol) was added portion-wise and the mixture was stirred for 2 h. T.l.c analysis (ethyl acetatexyclohexane, 1 :3) indicated the disappearance of starting material (Rf 0.38) and the presence of a less polar product (Rf 0.48). The reaction mixture was concentrated under reduced pressure and the residue was partitioned between ethyl acetate and 0.5 M hydrochloric acid. The organic layer was washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. The resulting crude pale orange residue was treated with sodium azide (807 mg, 12.4 mmol) in Λ/,Λ/-dimethylformamide (25 ml) for 16 h. T.l.c. analysis (ethyl acetate:cyclohexane, 1 :4) indicated the disappearance of the intermediate triflate (Rf 0.42) and the presence of a more polar compound (Rf 0.40). The reaction solvent was removed in vacuo and the residue was partitioned between ethyl acetate and brine. The aqueous layer was extracted with ethyl acetate and the combined organic layers were dried (MgSO4), filtered and concentrated in vacuo. The resulting crude residue was purified by silica gel chromatography (ethyl acetate:cyclohexane, 0:1 to 1:4) providing 7-azido-8-O-ferf-butyldimethylsilyl-7- deoxy-2,3:5,6-di-0-isopropylidene-L-fΛreo-L-fa/o-octono-1 ,4-lactone Qf as a colourless oil (3.026 g, 81%): 5H (CDCI3) 0.11 (2 x s, 6H, 2 x CH3), 0.91 (s, 9H, C(CHa)3), 1-30, 1.38, 1.41, 1.47 (4 x s, 12H, 2 x C(CHs)2), 3.41- 3.45 (m, 1H, H-7), 3.87 (dd, 1H, J8a,7 5.37 Hz J8a,βb 10.81 Hz, H-8a), 3.92 (dd, 1H, JBbJ 7.32 Hz, H-8b), 4.19-4.24 (m, 2H, H-5, H-6), 4.61 (br s, 1 H, H-4), 4.75-4.79 (m, 2H, H-2, H-3); δc (CDCI3) -5.59, -5.56, 18.14, 25.54, 25.73, 26.09, 26.71 , 26.98, 61.61 , 63.19, 67.94, 74.84, 74.94, 75.47, 78.36, 78.66, 110.90, 113.37, 174.02; vmax (film) 1796, 2111 ; [α]D +36.7 (c 1 , CHCI3).

7-Azido-8-O-teft-butyldimethylsilyl-7-deoxy-2,3:5,6-di-O- isopropylidene-L-f/7reo-L-fa/o-octitol Qq

7-azido-8-0-ferf-butyldimethylsilyl-7-deoxy-2,3:5,6-di-0- isopropylidene-L-f/?reo-L-fa/o-octono-1 ,4-lactone (Qf, 3.00 g, 6.6 mmol) was dissolved in tetrahydrofuran (40 ml) and was cooled to 0 0C. Lithium borohydride (216 mg, 9.9 mmol) was added and the mixture was stirred at 0 0C to room temperature for 24 h. T.l.c. analysis (ethyl acetate:cyclohexane, 1:1) indicated the disappearance of the starting material (Rf 0.76) and the presence of a more polar compound (Rf 0.45). The reaction was quenched through the addition of ammonium chloride (sat. aq.) and the partitioned between ethyl acetate and brine. The aqueous layer was extracted with ethyl acetate (2 x) and the combined organic layers were dried (MgSO4), filtered and the solvent removed. The resulting crude residue was purified by silica gel chromatography (ethyl acetate:cyclohexane, 1:3 to 1:1) affording 7-azido-8-0-fert-butyldimethylsilyl-7-deoxy-2,3:5,6-di-0-iso propylidene-L-f/7reo-L-fa/o-octitol Qg as a colourless syrup (2.476 g, 82 %): δH (CDCI3) 0.10 (s, 6H, 2 x CH3), 0.91 (s, 9H, C(CH3)3), 1.36, 1.41 , 1.42, 1.48 (4 x s, 12H, 2 x C(CHs)2), 3.43-3.47 (m, 1H, H-7), 3.66 (br d, 1 H, H-4), 3.79-3.92 (m, 4H, H-1 , H-1a, H-8, H-8a), 4.10-4.14 (m, 2H, H-2, H-3), 4.30-4.38 (m, 2H, H-5, H-6); δG (CDCI3) -5.61 , -5.51 , 18.14, 25.18, 25.71, 26.87, 27.07, 27.86, 60.65, 62.39, 63.66, 67.62, 75.90, 76.91 , 77.18, 77.49, 108.63, 110.16; vmax (film) 2109, 3536; [α]D +46.6 (c 1 , CHCI3).

7-Azido-8-0-te/t-butyldimethylsilyl-7-deoxy-2,3:5.6-di-0- isopropylidene-1 ,4-di-0-methanesulphonyl-L-f/7reo-L- fa/o-octitol Qh

7-Azido-8-0-ferf-butyldimethylsilyl-7-deoxy-2,3:5,6-di-0- isopropylidene-L-fΛreo-L-fato-octitol (Qg, 2.4 g, 5.3 mmol) was dissolved in pyridine (20 ml) and was added to a solution of 4-dimethylamino pyridine (64 mg, 0.53 mmol) and methanesulfonyl chloride (4.814 g, 3.253 ml, 42 mmol) in pyridine (20 ml) and stirred for 2 h. T.l.c analysis (ethyl acetatexyclohexane, 1 :2, double elution) revealed the disappearance of starting material (Rf 0.33) and the presence of a more hydrophobic product (Rf 0.43). The solvent was removed under educed pressure and the residue was partitioned between ethyl acetate and brine. The aqueous layer was extracted with ethyl acetate and the combined organic layers were dried (MgSO4), filtered and concentrated under reduced pressure. The resulting crude residue was purified by silica gel chromatography (ethyl acetate:cyclohexane, 1 :2) giving 7-azido-8-0-fert-butyldimethylsilyl-7-deoxy-2,3:5,6-di-0-iso propylidene-1 ,4-di- O-methanesulfonyl-L-fhreo-L-fa/o-octitol Qh as a colourless oil (2.973 g, 92 %): 5H (CDCI3) 0.11, 0.12 (2 x s, 6H, 2 x CH3), 0.91 (s, 9H, C(CHs)3), 1.41 , 1.44, 1.46, 1.56 (4 x s, 12H, 2 x C(CHs)2), 3.08 (s, 3H, SO2CH3), 3.21 (s, 3H, SO2CH3), 3.49 (ddd, 1 H, J7,e 2.82 Hz, J7,β 5.46 Hz, J7,8a 7.94 Hz, H-7), 3.87-3.97 (m, 2H, H-8, H-8a), 4.19 (dd, 1H, J6,5 2.30 Hz, H-6), 4.24-4.31 (m, 2H, H-1 , H-5), 4.36 (dd, 1 H, J3,4 2.96 Hz, J3|2 6.62 Hz, H-3), 4.49-4.53 (m, 1H, H-2), 4.69 (dd, 1H, Ju,2 2.39 Hz, J13|1 10.83 Hz, H-1a), 5.11 (app t, 1H, H-4); δc (CDCI3) - 5.56, 18.18, 25.76, 26.24, 26.78, 26.89, 27.56, 37.75, 39.02, 60.90, 63.57, 70.44, 76.00, 76.07, 76.46, 77.18, 77.32, 109.01 , 110.68; vmax (film) 2113; [α]D -16.2 (c 1 , CHCI3).

7-Azido-7-deoxy-1.4-di-0-methanesulphonyl-L-f/7reo-L-fa/o -octitol Qi

7-Azido-8-0-fe/t-butyldimethylsilyl-7-deoxy-2,3:5,6-di-0- isppropylidene-1 ,4-di-0-methanesulfonyl-L-fhreo-L- fa/o-octitol (Qh, 2.9O g, 4.7 mmol) was treated with a trifluroacetic acid:water mixture (1:1 , 40 ml) for 3 h. T.l.c. analysis (ethyl acetate) showed the disappearance of starting material (Rf 0.9) and the presence of a more polar product (Rf 0.12). The solvent was removed under reduced pressure and the residue was co-evaporated with toluene and dried under vacuum. Purification by silica gel chromatography (ethyl acetate:cylcohexane, 1 :1 to 1:0) yielded 7-azido-7-deoxy-1,4-di-0-methanesulphonyl-L-f/?reo-L-fa/o-oc titol Qi as a colourless oil (1.677 g, 85 %): δH (CD3OD) 3.12 (s, 3H, SO2CH3), 3.21 (s, 3H, SO2CH3), 3.61-3.71 (m, 2H, H-7, H-8), 3.78-3.82 (m, 2H, H-6, H-8a), 3.98-4.05 (m, 2H, H-2, H-3), 4.11-4.13 (m, 1H, H-5), 4.34 (dd, 1 H, J1l2 4.87 Hz, Ji,1a 10.44 Hz, H-1 ), 4.45 (dd, 1 H, J1a,2 1.87 Hz, H-1a), 5.00 (dd, 1 H, J4.3 1.91 Hz, J4,s 6.15 Hz, H-4); δc (Cp3OD) 36.17, 38.11 , 61.84, 66.62, 69.09, 70.33, 70.45, 71.08, 72.55, 86.41 ; vmax (film) 2113; [α]D -9.1 (c 1 , H2O).

(1 R,2R,3S,6S,7R,7aRV3-(Hvdroxymethyl1-1 ,2,6,7-tetrahvdroxypyrrolizidine Qi [3,7-d/ep/-Casuarine]

7-Azido-7-deoxy-1 ,4-di-O-methanesulphonyl-L-fft/Bo-L-fa/o-octitol (Qi, 1.6 g, 3.78 mmol) was dissolved in water (30 ml) and was treated with 10 % palladium on carbon (400 mg) under an atmosphere of hydrogen for 16 h. T.l.c analysis (ethyl acetate:methanol, 9:1) indicated the disappearance of starting material (Rf 0.75) and the presence of a more polar product (Rf 0.05). Palladium was removed by filtration and the filtrate was treated with sodium acetate (930 mg, 11.34 mmol) at 60 0C for 16 h. The reaction mixture was cooled and the solvent removed in vacuo. The crude brown oil was purified by ion-exchange chromatography (Dowex 50WX8-100, H+ form, eluting with 2M ammonium hydroxide) to afford (1R,2R,3S,6S,7R,7aR)-3-(hydroxymethyl)-1 ,2,6,7- tetrahydroxypyrrolizidine [3,7-d/ep/-Casuarine] Qj as a brown glass (671 mg, 87%): 5n (D2O) 2.81-2.92 (m, 2H, H-5, H-5a), 3.16 (dd, 1H, J3|2 5.91 Hz, J3|8 10.74 Hz, H-3), 3.30 (app t, 1H, J 3.78 Hz, H-7a), 3.76 (dd, 1H, J8,8a 6.35 Hz, H-8), 3.87 (dd, 1 H, H-8a), 4.01 (d, 1H, J2,i 3.55 Hz, H-2), 4.04-4.12 (m, 2H, H-6, H-7), 4.29 (app t, 1H, H-1 ); δc (D2O) 49.32, 57.29, 63.78, 70.41 , 72.59, 72.65, 74.47, 78.25; [α]D -21.1 (c 0.5, H2O).

Example 2

The ring closure described above may be defined as a "1 , 4,7 ring closure": the pyrrolidine intermediate (not shown) for cyclisation in the process of Example 1 is generated from a carbon skeleton precursor Qi having two electrophilic carbon atoms and an N function at positions 1 , 4 and 7, respectively.

This relative spacing may be reversed, whilst preserving the same relative spacing of i, i +3 and i +6, so that the carbon skeleton precursor has an N function and two electrophilic carbon atoms at positions 2, 5 and 8, respectively. Such a "2, 5, 8 ring closure" reaction scheme is shown below:

Modification of the reaction scheme described in Example 1 in this way may permit access to a different range of products by changing the stereoisomeric specificity.

Example 3: Synthesis of 3-epicasuarine

Experimental

Methyl 3,4:5, 6-di-O-isopropylidene-D-qluconate 2

Compound 2 was prepared according to a literature procedure (Regeling ef a/. (1987) Reel. Trav. Chim. Pays- Bas (106) : 461). D-glucono-1 ,5-lactone 1 (10.0 g, 56 mmol) was suspended in 2,2-dimethoxypropane (20 ml), MeOH (2 ml) and acetone (6 ml). After addition of para-toluenesulphoπic acid (150 mg), the mixture was stirred at room temperature overnight under a nitrogen atmosphere. Then, solid NaHCO3 (1.0 g) was added to the clear yellow solution and the resulting mixture was filtered over celite. After evaporation of the solvents in vacuo, the residue was redissolved in DCM (100 ml) and washed with water (100 ml). The organic layer was subsequently dried on Na2SO4. Column chromatography (EtOAc/cyclohexane 1/3 v/v) afforded the product as a clear, colourless oil (12.80 g, 79%). Rf 0.71 (EtOAc/cyclohexane 1/1 v/v); [α]D -2.0 (c, 0.72 in CHCI3) [Lit. -1.7 (c, 1.18 in CHCI3)5]; δH (400 MHz, CDCI3) 1.38, 1.40, 1.42, 1.47 (12H, 4 x s, C(CH3)2), 3.08 (1 H, d, OH, J 9.1 Hz), 3.88 (3H, s, OCH3), 4.03 (1 H, dd, H-6', J 3.4 Hz, 8.2 Hz), 4.10 (1 H1 m, H-4), 4.14 (1H, m, H-5), 4.19 (1H, dd, H-6, J 5.8 Hz, 8.2 Hz), 4.26 (1 H, dd, H-3, J 1.6 Hz, 7.6 Hz), 4.38 (1H, dd, H-2, J 1.6 Hz, 9.2 Hz); δc (100 MHz, CDCI3) 25.7, 27.0, 27.1 , 27.6 (C(CHs)2), 53.1 (OCH3), 68.3 (C-6), 69.9 (C-2), 76.9 (C-4), 77.5 (C-5), 81.3 (C-3), 110.3, 110.5 (C(CHa)2), 173.4 (C=O); MS m/z (ESI +ve) 310.95 (M+Na+).

Methyl 3,4:5.6-di-0-isopropylidene-2-0-trifluoromethanesulphonyl-D- gluconate 3

Compound 3 was prepared according to a literature procedure (Taillefumier et al. (1996) Carbohydrate Lett. (2) : 39). Methyl 3,4:5,6-di-0-isopropylidene-D-gluconate 2 (11.5 g, 39.6 mmol) was dissolved in DCM (120 ml) and dry pyridine (4.8 ml, 59 mmol) was added. The resulting solution was cooled to -1O0C, after which trifluoromethanesulphonic anhydride (7.4 ml, 44 mmol) was added dropwise. After stirring at -1O0C for 30 minutes under a nitrogen atmosphere, the light orange reaction mixture was washed with 1M HCI (100 ml), and pH 7 buffer (100 ml). After drying on NaZSO4, the product was obtained as an off-white solid (15.06 g, 90%). Rf 0.37 (EtOAc/cyclohexane 1/3 v/v); [α]D +43.7 (c, 0.89 in CHCI3) [Lit. +44.2 (c, 1.10 in CHCI3)5]; δH (400 MHz, CDCI3) 1.36, 1.40, 1.41 (12H, 3 x s, C(CH3)2), 3.87 (1H, dd, H-6', J 7.2 Hz, 8.6 Hz), 3.90 (1 H, m, H-4), 3.91 (3H, s, OCH3), 4.08 (1 H, m, H-5), 4.20 (1H, dd, H-6, J 6.2 Hz, 8.6 Hz), 4.55 (1H, dd, H-3, J 1.9 Hz, 7.6 Hz), 5.33 (1 H, d, H-2, J 1.9 Hz); δc (100 MHz, CDCI3) 25.0, 26.1 , 27.2 (C(CHs)2), 54.5 (OCH3), 68.1 (C-6), 76.9, 77.0, 79.3, 80.5 (C-2, C-3, C-4, C-5), 110.2, 111.4 (C(CH3)2), 115.2 (CF3, q, JC,F 319 Hz), 165.4 (C=O); MS m/z (ESI +ve) 455.20 (M+Na+). Methyl 2-azido-2-deoxy-3.4:5.6-di-O-isopropylidene-D-mannonate 4

Methyl 3,4:5,6-di-O-isopropylidene-2-O-trifluoromethanesulphonyl-D- gluconate 3 (15.1 g, 35.7 mmol) was dissolved in DMF (30 ml) and NaNe (2.55 g, 39.2 mmol) was added. The resulting mixture was stirred at room temperature under a nitrogen atmosphere. Then, the solvent was evaporated in vacuo and the residue was redissolved in EtOAc (100 ml). After washing with water (100 ml) and drying on Na2SCU, the crude product was subjected to column chromatography (EtOAc/cyclohexane 1/4 v/v), yielding the product as a clear, colourless oil (10.96 g, 97%). Rf 0.36 (EtOAc/cyclohexane 1/3 v/v); [α]D +21.5 (c, 0.69 in CHCI3) [Lit. +21.3 (c, 1.30 in CHCI3)6]; vmax (film) 2114 cm"1 (N3), 1754 cm"1 (C=O); δH (400 MHz, CDCI3) 1.33, 1.37, 1.41 , 1.46 (12H, 4 x s, C(CWs)2), 3.81 (3H, s, OCW3), 3.97 (1H, dd, H-6', J 4.8 Hz, 8.0 Hz), 4.04 (2H, m, H-4, H-5), 4.15 (1H, dd, H-6, J 5.2 Hz, 8.0 Hz), 4.31 (1 H, d, H-2, J 3.5 Hz), 4.38 (1H, dd, H-3, J 3.5 Hz, 6.6 Hz); δc (100 MHz, CDCl3) 25.3, 26.4, 26.9, 27.3 (C(CH3)2), 52.6 (OCH3), 63.0 (C-2), 67.6 (C-6), 76.8 (C-5), 77.6 (C-4), 80.7 (C-3), 110.0, 110.4 (C(CHs)2), 167.7 (C=O); MS m/z (ESI +ve) 316.21 (M+H+), 288.01 (M-N2+H+); for Ci3H21N3O6 calcd. C 49.52, H 6.71 , N 13.33, found C 49.44, H 6.69, N 13.12.

Methyl 4-azido-2,3,4-trideoxy-5.6:7,8-di-0-isopropylidene-D-manno-o ct-2-enoate 6

A solution of methyl 2-azido-2-deoxy-3,4:5,6-di-O-isopropylidene-D-mannonate 4 (10.96 g, 34.8 mmol) was dissolved in toluene (200 ml) was cooled to -780C, after which a 1.5M solution of DIBAL-H in toluene (35 ml) was added dropwise. The resulting mixture was stirred for three hours at -78°C under a nitrogen atmosphere. The excess hydride was quenched by dropwise addition of MeOH (10 ml) and the reaction mixture was allowed to warm to room temperature. Then, methyl (triphenylphosphoranylidene)acetate 5 (12.8 g, 38.3 mmol) was added in one portion and the resulting mixture was stirred at room temperature overnight under a nitrogen atmosphere. The solvents were evaporated in vacuo, after which Et2O (100 ml) and 2M NaOH (100 ml) were added. The layers were separated, and the organic phase was dried on Na2SO4. After filtration and evaporation of the volatiles, the resulting white solid was triturated with petroleum ether 40-60 and the solids were removed by filtration. Column chromatography (EtOAc/cyclohexane 1/6 v/v) afforded the product as a white solid (8.95 g, 75%). Rf 0.89 (EtOAc/cyclohexane 1/1 v/v); m.p. 45-46 0C; [α]D +35.5 (c, 0.71 in CHCI3); vmax (film) 2095 cm"1 (N3), 1725 cm"1 (C=O); 5H (400 MHz, CDCI3) 1.36, 1.38, 1.51 (12H, 3 x s, C(CH3)2), 3.73 (1H, m, H-7), 3.78 (3H, s, OCH3), 3.93 (1H, dd, H-8\J 5.2 Hz, 8.4 Hz), 4.05 (1H, m, H-7), 4.14 (1H, dd, H-8, J 4.0 Hz, 8.4 Hz), 4.17 (1H, dd, H-5, J 3.0 Hz, 3.6 Hz), 4.33 (1 H, ddd, H-4, J 1.2 Hz, 3.6 Hz, 7.2 Hz), 6.11 (1 H, dd, H-2, J 1.2 Hz, 15.6 Hz), 6.96 (1 H, dd, H-3, J 7.2 Hz, 15.2 Hz); δc (100 MHz, CDCI3) 25.1 , 26.4, 26.9, 27.2 (C(CH3)2), 51.8 (OCH3), 63.1 (C-4), 67.7 (C-8), 76.8 (C-7), 78.3 (C-6), 81.4 (C-5), 109.9, 110.6 (C(CH3)2), 125.2 (C-2), 140.3 (C-3), 165.7 (C=O); HRMS m/z (ESI +ve): Found 683.3251 (2M+H+); C30H47N6Oi2 requires 683.325; for Ci5H23N3O6 calcd. C 52.78, H 6.79, N 12.31 , found C 52.78, H 6.78, N 12.10.

Methyl 4-azido-4-deoxy-5.6:7,8-di-O-isopropylidene-D-e/vtf)/O-L-aff fO-octonate 7a and methyl 4-azido-4-deoxy- 5,6:7,8-di-0-isopropylidene-D-e/vfftro-L-q/uco-octonate 7b

Methyl 4-azido-2,3,4-trideoxy-5,6:7,8-di-0-isopropylidene-D-eAyfftr o-L-manno-oct-2-enoate 6 (6.85 g, 20.0 mmol) was dissolved in a mixture of acetone (50 ml) and water (10 ml), after which N-methylmorpholiπe oxide (4.69 g, 40.0 mmol) and OSO4 (50 mg) were added. The resulting mixture was stirred overnight at room temperature under a nitrogen atmosphere. Subsequently, EtOAc (100 ml) and 5% NaHCO3 (100 ml) were added and the layers were separated. The organic layer was dried on Na2Sθ4 and after filtration and evaporation, the crude material was subjected to column chromatography (EtOAc/cyclohexane 1/1 v/v), affording an inseparable 4/1 mixture of the products 7a and 7b as a white solid (5.37 g, 72%). Rf 0.36 (EtOAc/cyclohexane 1/3 v/v); m.p. 119-122 0C; vmax (film) 3465 cm"1 (OH), 2111 cm"1 (N3), 1748 cm'1 (C=O); δH (400 MHz, CDCI3) 1.35, 1.38, 1.40, 1.43, 1.47, 1.52 (15.0H, 6 x s, maj/min C(CHa)2), 2.91 (0.25H, min (C- 3)OH), 3.03 (1.00H, maj (C-2)OH), 3.19 (0.25H, min (C-2)OH), 3.73 (1.00H, dd, maj H-3), 3.81 (3.25H, m, maj OCH3, min (C-3)OH), 3.85 (0.75H, s, min OCH3), 3.95 (0.25H, m, min H-4), 4.05 (4.00H, m, maj H-6, maj H-7, maj H-8', min H-3, min H-6, min H-7, min H-8'), 4.24 (2.50H, maj H-4, maj-H-8, min H-5, min H-8), 4.48 (1.25H, m, maj H-2, min H-2), 4.55 (1.00H, m, maj H-5); δc (100 MHz, CDCI3) 25.0, 25.7, 26.9, 27.2 (maj C(CH3)2), 25.4, 26.5, 27.3 (min C(CH3)2), 52.5 (maj OCH3), 52.8 (min OCH3), 61.5 (maj C-4), 65.0 (min C-4), 68.0 (min C- 8), 68.6 (maj C-8), 70.9, 71.1 (maj C-2, C-3), 71.1, 71.3 (min C-2, C-3), 76.9 (maj C-6), 77.0 (min C-6), 77.5 (maj C-7), 78.6 (min C-7), 80.2 (min C-5), 80.7 (maj C-5), 110.0, 110.1 , 110.3 (maj/min C(CH3)2), 173.1 (min C=O), 173.3 (maj C=O); HRMS m/z (ESI +ve): Found 398.1528 (M+Na+); Ci5H25N3O8Na requires 398.1539; for Ci5H25N3O8 calcd. C 47.99, H 6.71 , N 11.19, found C 48.49, H 6.79, N 10.67. S.B^.S-O-diisoproDylidene-Σ.S-di-O-tert-butyldimethylsilyl- D-erv'^ro-L-atfro-octono- v -lactam 8

A 4/1 mixture of methyl 4-azido-4-deoxy-5,6:7,8-di-Q-isopropylidene-D-e/yf/7ro-L-a/f ro-octonate 7a and methyl 4-azido-4-deoxy-5,6:7,8-di-0-isopropylidene-D-e/yf/7ro-L-g/u co-octonate 7b (5.28 g, 14.07 mmol) was dissolved in THF (50 ml) and 20% Pd(OH)2 on carbon (150 mg) was added. The resulting mixture was stirred for 48 hours at room temperature under a hydrogen atmosphere. The catalyst was removed by filtration over celite which was rinsed with THF. After evaporation of the solvent in vacuo, the residue was redissolved in toluene (200 ml). This mixture was stirred at reflux temperature for three hours under a nitrogen atmosphere. The solvent was removed in vacuo and the residue was redissolved in THF (50 ml) after which imidazole (4.22 g, 62.04 mmol) and TBDMS-CI (4.68 g, 31.02 mmol) were added. The resulting mixture was stirred overnight at reflux temperature under a nitrogen atmosphere. Subsequently, the solvents were removed in vacuo and the reaction mixture was redissolved in DCM (50 ml) and washed with 1M HCI (50 ml), 5% NaHCO3 (50 ml), and brine (50 ml). After drying on Na2SO4 and column chromatography (EtOAc/cyclohexane 1/6 v/v), the product was obtained as a clear, colourless oil (5.41 g, 70%). Rf 0.48 (EtOAc/cyclohexane 1/4 v/v); [CC]D +1.8 (c, 1.59 in CHCI3); vmax (film) 1725 cm"1 (C=O); δH (400 MHz, CDCI3) 0.18, 0.20 (12H, 2 x s, SiCH3), 0.95 (18H, s, SiC(CHs)3), 1.36, 1.38, 1.40, 1.46 (12H, 4 x s, C(CHs)2), 3.27 (1 H, dd, H-4, J 8.3 Hz, 6.8 Hz), 3.62 (1H, app. t, H-6, J 8.1 Hz), 3.76 (1H, app. t, H-5, J 8.2 Hz), 3.99 (2H, m, H-7, H-8'), 4.20 (2H, m, H-3, H-8), 4.28 (1 H, d, H- 2, J 8.1 Hz); δc (100 MHz, CDCI3) -5.1, -4.6 (SiCH3), 18.4 (SiC(CH3)3), 24.9 (SiC(CHs)3), 26.6, 26.7 (C(CHs)2), 27.5 (C-4), 26.8 (C-8), 75.8 (C-2), 76.5 (C-3), 79.5 (C-7), 81.7 (C-6), 83.5 (C-5), 109.8, 110.4 (C(CH3)2), 172.5 (C=O); HRMS m/z (ESI +ve): Found 546.3265 (M+H+); C26H52NO7Si2 requires 546.3282; for C26H5INO7Si3 calcd. C 57.21, H 9.42, N 2.57, found C 57.20, H 9.68, N 2.26.

δ.e-O-isopropylidene-Σ.S-di-O-te/f-butyldimethylsilyl-D -e/yffjro-L-a/fro-octono-v-lactam 9

S.δJ.δ-O-diisopropylidene^S-di-O-fer^butyldimethylsilyl-D- eAyfftro-L-a/fro-octono-γ-lactam 8 (3.76 g, 6.89 mmol) was dissolved in MeOH (6 ml), HOAc (12 ml), and water (2 ml). The resulting mixture was stirred at reflux temperature for 5 hours under a nitrogen atmosphere. Then, solid NaHCOe was added until all acetic acid was neutralized. Et2O (100 ml) and water (50 ml) were added and the layers were separated. After drying on Na2SO4 the product was obtained as a clear, colourless oil (2.39 g, 69%) and was used without further purification. Rf 0.17 (EtOAc/cyclohexane 1/1 v/v); [α]D +2.9 (c, 0.41 in CHCI3); vmax (film) 3336 cm"1 (OH), 1701 cm"1 (C=O); δH (400 MHz, CDCI3) 0.14, 0.17, 0.19 (12H, 3 x s, SiCH3), 0.91 , 0.92 (18H, 2 x s, SiC(CWa)3), 1.36, 1.40 (6H, 2 x s, C(CHs)2), 2.98 (1H, br. s, OW), 3.37 (1H, dd, H-4, J 2.8 Hz, 9.2 Hz), 3.66 (1H, dd, H-6, J 7.2 Hz, 15.2 Hz), 3.73 (2H, m, H-7, H-81), 3.82 (1H, dd, H-5, J 7.2 Hz, 9.2 Hz), 3.87 (1H, dd, H-8, J 5.6 Hz, 13.2 Hz), 4.04 (1H, d, H-2, J 2.8 Hz), 4.26 (1 H, app. t, H-3, J 2.8 Hz), 4.99 (1 H, s, OH), 7.48 (1 H, s, NH); δc (100 MHz, CDCI3) -4.8, -4.7, -4.4, -4.2 (SiCH3), 17.9, 18.1 (SiC(CH3)3), 25.8 (SiC(CH3)3), 26.6, 26.8 (C(CHs)2), 63.4 (C-4), 64.7 (C-8), 72.9 (C-7), 77.9 (C-7), 80.9 (C-6), 82.0 (C-5), 109.1 (C(CH3)2), 175.3 (C=O); HRMS m/z (ESI +ve): Found 506.2970 (M+H+); C23H48NOySi2 requires 506.2969; for C23H47NO7Si2 calcd. C 54.62, H 9.37, N 2.77, found C 54.85, H 9.64, N 2.54.

S.e-O-isopropylidene^-O-methanesulphonyl-Σ.S.S-tri-O-fer t-butyldimethylsilyl-D-e/Yfhro-L-a/fro-octono-v-lactam 10

δ^-O-isopropylidene^.S-di-O-tert-butyldimethylsilyl-D-eA yfhro-L-a/frfo-octono-γ-lactam 9 (2.39 g, 4.73 mmol) was dissolved in dry pyridine (10 ml) and TBDMS-CI (784 mg, 5.20 mmol) was added. The resulting mixture was stirred at room temperature for 5 hours under a nitrogen atmosphere. DCM (100 ml) was added, and the mixture was washed with 1M HCI (100 ml), 5% NaHCO3 (50 ml), and brine (50 ml). After drying on Na2SO4, the solvents were evaporated in vacuo until a volume of 10 ml remained. Then, triethylamine (1.0 ml, 7.1 mmol) and methanesulphonyl chloride (439 μl, 5.68 mmol) were added. The resulting mixture was stirred for 30 minutes at room temperature under a nitrogen atmosphere. After washing with 1M HCI (10 ml), 5% NaHCO3 (10 ml), and brine (10 ml), the organic phase was dried on Na2SO4. Column chromatography (EtOAc/cyclohexane 1/4 v/v) then yielded the product as a clear, colourless oil (2.18 g, 66%). Rf 0.23 (EtOAc/cyclohexane 1/4 v/v); [α]D +28.9 (c, 0.37 in CHCI3); vmax (film) 1720 cm"1 (C=O); δH (400 MHz, CDCI3) 0.11 , 0.12, 0.17, 0.18 (18H, 4 x s, SiCH3), 0.87, 0.90, 0.91 , 0.92, 0.92 (27H, 5 x s (SiC(CH3)3), 1.40, 1.46 (6H, 2 x s, C(CHs)2), 3.09 (3H, s, SO2CH3), 3.41 (1H, d, H-4, J 8.0 Hz), 3.81 (1H, dd, H-8', J 4.0 Hz, 12.0 Hz), 3.85 (1H, s, H-2), 3.93 (1H, dd, H-8, J 7.1 Hz, 12.0 Hz), 4.07 (1H, app. t, H-5, J 8.0 Hz), 4.16 (1 H, dd, H-6, J 3.7 Hz, 8.0 Hz), 4.23 (1H, s, H-3), 4.64 (1 H, ddd, H-7, J 3.7 Hz, 4.0 Hz, 7.1 Hz), 6.09 (1H, s, NH); δc (100 MHz, CDCI3) -5.5, -5.5, -5.2, -4.8, -4.7, -4.4 (SiCH3), 17.8, 18.0, 18.2, 18.3 (SiC(CHs)3), 25.7, 25.7, 25.8 (SiC(CHs)3), 26.9, 27.1 (C(CHs)2), 38.4 (SO2CH3), 61.5 (C-8), 65.5 (C-4), 76.0 (C-6), 77.3 (C-3), 78.1 (C-2), 79.2 (C-5), 82.0 (C-7), 110.4, 110.5 (C(CHa)2), 175.0 (C=O); HRMS m/z (ESI +ve): Found 698.3615 (M+H+); C3oH64Nθ9SSi3 requires 698.3210.

octal 11

5,6-0-isopropylidene-7-0-methanesulphonyl-2,3,84ri-0-ferf -butyldimethylsilyl-D-er/f/7ro-L-a/fro-octono-Y-lactam 10 (2.87 g, 4.11 mmol) was dissolved in THF (40 ml) and a 1M solution of BH3 in THF (21 ml) was added. The resulting mixture was stirred at reflux temperature for 1 hour under a nitrogen atmosphere. Then, the reaction mixture was allowed to cool to room temperature, after which MeOH (5 ml) was added cautiously. The solvents were removed by evaporation in vacuo and after column chromatography (EtOAc/cyclohexane 1/8 v/v), the product was obtained as a clear, colourless oil (1.60 g, 57%). [α]D -67.1 (c, 0.38 in CHCI3); vmax (film) 3394 cm"1 (NH); δH (400 MHz, CDCI3) 0.10, 0.11 , 0.11, 0.12, 0.17, 0.18 (18H, 6 x s, SiCH3), 0.90, 0.92, 0.94 (27H, 3 x s, SiC(CWs)3), 1.39, 1.44 (6H, 2 x s, C(CWs)2), 3.06 (1H, dd, H-4, J 6.4, 8.5), 3.25 (3H, s, SO2CW3), 3.63 (1H, app. d, H-V, J 10.4), 3.90 (2H, m, H-1 , H-8'), 4.04 (1H, dd, H-8, J 2.0, 12.0), 4.16 (1 H, br. m, H-3), 4.28 (1 H, dd, H-6, J 6.3, 9.2), 4.43 (1 H, dd, H-5, J 6.3, 8.5), 4.66 (1H, ddd, H-7, J 2.0, 7.6, 9.2), 4.85 (1 H, ddd, H-2, J 2.8, 8.0, 10.4), 5.06 (1H, br. s, NH); δc (100 MHz, CDCI3) -5.5, -5.4, -4.9, -4.8, -4.8, -4.7 (SiCH3), 17.7, 18.3, 18.4 (SiC(CH3)s), 25.6, 25.8, 25.9, 26.0 (SiC(CHs)3), 26.5, 27.1 (C(CH3)2), 39.2 (SO2CH3), 63.8 (C-8), 75.1 (C-4), 76.0 (C-6), 76.2 (C-1), 77.2 (C-5), 77.8 (C-3), 85.0 (C-7), 92.9 (C-2), 110.4 (C(CH3)2); HRMS m/z (ESI +ve): Found 684.3804 (M+H+); C30H66NO8SSi3 requires 684.3817.

1 ,4-dideoxy-1 ,4-imino-7-O-methanesulphonyl-D-en/f/?ro-L-a/fro-octol 12

1 ,4-dideoxy-1 ,4-imino-5,6-0-isopropylidene-7-0-methanesulphonyl-8-0-fe/if -butyldimethylsilyl-D-e/yfΛΛo-L-a/fro- octol 11 (1.18 g, 1.72 mmol) was dissolved in TFA (4.5 ml) and water (0.5 ml). The resulting mixture was stirred for 3 hours at reflux temperature under a nitrogen atmosphere. The solvents were evaporated in vacuo and the residue was co-evaporated with toluene, yielding the product as a clear, light brown oil (978 mg) which was used without further purification. δH (400 MHz, D2O) 3.19 (3H, s, SO2CH3), 3.35 (1 H, dd, H-1', J 2.1 Hz, 12.4 Hz), 3.49 (1H, dd, H-1 , J 4.0 Hz, 12.4 Hz), 3.64 (1H, dd, H-4, J 3.6 Hz, 6.5 Hz), 3.85 (1H, dd, H-8\ J 5.2 Hz, 13.2 Hz), 3.98 (2H, m, H-6, H-8), 4.10 (1H, dd, H-5, J 1.2 Hz, 6.5 Hz), 4.28 (1 H, app. p, H-2, J 2.1 Hz, 4.0 Hz, 3.6 Hz), 4.34 (1 H, app. t, H-3, J 3.6 Hz), 4.80 (1H, m, H-7); δc (100 MHz, D2O) 27.5 (SO2CH3), 39.9 (C-1), 49.4 (C-8), 56.0 (C-5), 56.7 (C-4), 57.8 (C-6), 64.0 (C-2), 65.1 (C-3), 71.0 (C-7); MS m/z (ESI +ve): 301.82 (M+H+).

3-epicasuarine 13

i ^-dideoxy-i ^-imino^-O-methanesulphonyl-D-e/yfhro-L-a/fro-octol 12 was dissolved in water (20 ml) and 423 mg (5.16 mmol) NaOAc was added. The resulting mixture was stirred overnight at room temperature under a nitrogen atmosphere. The solvents were removed in vacuo and the residue was subjected to ion-exchange chromatography on Amberlite CG120 (H+) using 1M NH4OH as eluent affording the product as a light brown oil (314 mg, 89%). [α]D +5.8 (c, 0.69 in CHCI3); δH (400 MHz, D2O) 2.96 (3H, app. d, H-7a, H-5), 3.13 (1H, ddd, H- 3, J 3.2 Hz, J 6.4 Hz, 7.2 Hz), 3.79 (1 H, dd, H-8', J 7.2 Hz, 11.8 Hz), 3.85 (1 H, dd, H-8, J 6.4 Hz, 11.8 Hz), 3.89 (1H, app. t, H-7, J 7.8 Hz), 3.96 (1 H, app. q, H-6, J 7.8 Hz), 4.04 (1H, dd, H-2, J 1.4 Hz, 3.2 Hz), 4.13 (1H, app. t, H-1 , J 1.4 Hz); δc (100 MHz, D2O) 60.8 (C-5), 66.5 (C-8), 73.4 (C-3), 75.0 (C-7a), 75.3 (C-6), 76.2 (C-7), 76.5 (C-2), 77.2 (C-1); HRMS m/z (ESI +ve): Found 206.1030 (M+H+); C8Hi6NO5 requires 206.1028.

Results

The opening stages of the synthesis of 3-epicasuarine are outlined in Scheme 1. The first step was the ring opening and concomitant acetonide protection of D-glucono-δ-lactone 1 according to a known procedure1. Thus, treatment of 1 with 2,2-dimethoxypropane in a mixture of acetone and methanol in the presence of a catalytic amount of para-toluenesulphonic acid afforded ester 2 in 79% yield. Then, the required nitrogen centre was introduced by nucleophilic displacement of triflate ester 3 which was formed by reaction of 2 with trifluoromethanesulphonic anhydride in the presence of pyridine. The substitution reaction with sodium azide in DMF to yield azide 4 proceeded with near quantitative yield.

Scheme 1 Synthesis of azide 4 from D-glucono-δ-lactone 1

In the next steps two additional carbon centres with attached hydroxyl groups were introduced (Scheme 2) In order to achieve this, the methyl ester of 4 was first reduced to the corresponding aldehyde, using DIBAL-H at - 78°C to avoid over-reduction to the alcohol The crude aldehyde was used directly in the subsequent Wittig reaction with methyl (trιphenylphosphoranylιdene)acetate 5 After column chromatography, the major E-isomer 6 was isolated in 75% yield A slight amount (approximately 9%) of the Z-isomer was also formed, but could not be isolated in pure form The double bond of 6 was then subjected to bishydroxylation using a catalytic amount of osmιum(VIII)tetroxιde and NMO as the stoichiometric co-oxidant This afforded a 4 1 mixture of isomers 7a and 7b, which could not be separated at this point

75%

ratio 7a 7b 4 1

Scheme 2 Synthesis of octonates 7a and 7b

After this, the first ring of the casuarine framework was formed as outlined in Scheme 3 The azido groups in 7a and 7b (which were used as a mixture) were reduced using a catalytic hydrogenolysis On heating the resulting amines formed five membered lactams on expulsion of methanol These were too polar to be conveniently purified, and were used crudely in the next step, a protection reaction using TBDMS-CI and imidazole as the base. At this stage, the two diastereomers could be separated and the major isomer 8 was obtained in 70% over three steps.

Scheme 3: Synthesis of TBDMS protected lactam 8.

In order to form the second ring of the casuarine framework, the hydroxyl group at the 7-position had to be furnished with a good leaving group (Scheme 4). First, the terminal acetonide was selectively removed with 60% acetic acid, affording mono-acetonide 9 in 69%. Then, the primary hydroxyl group of 9 was protected using TBMDS-Cl and pyridine as the base. At this point, a mesylate leaving group could be introduced using mesyl chloride and triethylamine. This yielded mesylate 10 in 66% yield over two steps.

Scheme 4: Synthesis of mesylate 10. The stage was now set for the formation of the second ring of the casuarine framework (Scheme 5). The lactam ring in mesylate 10 was reduced using borane at elevated temperature to afford pyrrolidine 11. Then, all protecting groups were removed by refluxing in a mixture of TFA and water (9/1 v/v), after which cyclisation was achieved using sodium acetate as the base. This led to formation of 3-epicasuarine 13 and a minor amount of a molecule which was identified by GCMS and NMR as casuarine. The final product was purified using ion- exchange techniques. The overall yield was 6.0%, corresponding to 82.9% yield per step.

1. TFA/H2O 9/1 v/v 2. NaOAc, H2O 89%

Scheme 5: Formation of 3-epicasuarine 13.

The stereochemical identity of 3-epicasuarine 13 was demonstrated by NOE difference experiments, which showed strong contacts between H-2 and H-3, and between H-1 and H-7 (Figure 1). Furthermore, comparison of the optical rotation of 13 ([α]D +5.8) with the value for 3,6,7-triepicasuarine ([α]D -20.32) which would be the product eventually resulting from 7b clearly showed that the final product indeed evolved from 7a, leading to 3- epicasuarine.

Figure 1 NOE contacts in 3-epιcasuaπne 13

GCMS analysis of the material after acidic ion exchange chromatography (not shown) showed that the product was of good purity The presence in this trace of a small amount of casuaπne resulting from retention in the final nucleophilic substitution is further evidence of the stereochemistry of the product

Example 4 Synthesis of casuaπne

Experimental

δ.e-O-isopropylidene-Σ.S.δ-tri-O-fθrt-butyldimethylsi lyl-D-e/yfftro-L-a/fro-octono-v-lactam 14

5,6 7,8-0-dιιsopropylιdene-2,3-dι-0-terf-butyldιmethylsιly l-D-eo/tøro-L-a/fro-octono-γ-lactam 8 (2 70 g, 4 76 mmol) was dissolved in MeOH (1 5 ml), HOAc (6 ml), and water (0 5 ml) The resulting mixture was stirred at reflux temperature for 5 hours under a nitrogen atmosphere After that, EtOAc (60 ml) and 2M NaOH (60 ml) were added and the layers were separated The organic layer was dried on Na2SO4 and the solvents were evaporated The residue was redissolved in pyridine (10 ml) and TBDMS-Cl (860 mg, 5 71 mmol) was added The resulting solution was stirred overnight at room temperature under a nitrogen atmosphere Then, DCM (60 ml) was added and the resulting mixture was washed with 2M HCI (60 ml), satd NaHCO3 (60 ml) and brine (60 ml) The organic layer was dried on Na2SO4 and after column chromatography (EtOAc/cyclohexane 1/6 v/v), the product was obtained as a clear colourless oil (2 38 g, 81 %) Rf 0 35 (EtOAc/cyclohexane 1/4 v/v), [αb +13.5 (c, 0.65 in CHCI3); vmax (film) 3306 cm"1 (OH), 1716 cm"1 (C=O); δH (400 MHz, CDCI3) 0.10, 0.10, 0.12, 0.17, 0.19 (18H1 5 x s, SiCH3), 0.90, 0.91 , 0.92 (27H, 3 x s, SiC(CH3)3), 1.34, 1.37 (6H, 2 x s, C(CHs)2), 3.07 (1H, d, OH, J 2.8 Hz), 3.35 (1H, dd, H-4, J 9.0 Hz, 2.0 Hz), 3.50 (1H, app. t, H-6, J 3.8 Hz), 3.60 (2H, br. m, H- 7, H-8), 3.80 (1 H, dd, H-5, J 9.0 Hz, 7.6 Hz), 3.85 (1H, dd, H-8", J 2.8 Hz, 9.6 Hz), 3.97 (1H, d, H-2, J 2.8 Hz), 4.27 (1H1 app. t, J 2.8 Hz); δc (100 MHz, CDCI3) -5.5, -4.9, -4.7, -4.5, -4.2 (SiCH3), 17.9, 18.2, 18.2 (SiC(CH3)3), 25.6, 25.8, 25.8 (SiC(CHa)3), 26.7 (C(CH3)2), 63.1 (C-4), 64.6 (C-8), 71.9 (C-7), 77.5 (C-3), 77.7 (C-2), 80.7 (C- 6), 82.4 (C-5), 108.8 (C(CHs)2), 174.4 (C=O); HRMS m/z (ESI +ve): Found 620.3857 (M+H+); C29H82NO7Si3 requires 620.3834; for C23H6INO7Si3 calcd. C 56.17, H 9.92, N 2.26, found C 56.09, H 10.05, N 2.25.

5,6-0-isopropylidene-2,3,8-tri-0-fert-butyldimethylsilyl- L-(/?reo-L-a/fro-octono-v-lactam 15

δ.e-O-isopropylidene^.S.δ-tπ-O-fert-butyldimethylsilyl -D-er/fΛro-L-a/fΛO-octono-γ-lactam 14 (2.38 g, 3.83 mmol) was dissolved in dry DCM (10 ml). The solution was cooled to -50°C and pyridine (1.87 ml, 23.0 mmol) was added. Then, trifluoromethanesulphonic anhydride (1.29 ml, 7.66 mmol) was added dropwise after which the reaction mixture was stirred for five hours under a nitrogen atmosphere while slowly warming to O0C. DCM (40 ml) and 1 M HCI (50 ml) were added and the layers were separated. The organic layer was washed with pH 7 buffer (50 ml) and dried on Na2SO<i. Then, the solvent was evaporated, the residue was redissolved in dry 2- butanone (10 ml), and cesium trifluoroacetate (922 mg, 3.75 mmol) was added. The resulting mixture was stirred overnight at 5O0C under a nitrogen atmosphere. Then, K2CO3 (500 mg) was added and the mixture was stirred for 15 minutes. The solvent was evaporated, the residue was redissolved in EtOAc (50 ml) and washed with water (50 ml). After drying on Na2Sθ4 and purification by column chromatography (EtOAc/cyclohexane 1/4 v/v), the product was obtained as a light yellow oil (469 mg, 20%). Rf 0.25 (EtOAc/cyclohexane 1/4 v/v); [a]D +11.1 (c, 0.55 in CHCI3); vmax (film) 3269 cm'1 (OH), 1715 cm"1 (C=O); δH (400 MHz, CDCI3) 0.09, 0.10, 0.12, 0.12, 0.17, 0.17 (18H, 6 x s, SiCH3), 0.90, 0.90, 0.91 (27H, 3 x s, SiC(CH3)3), 1.38, 1.40 (6H, 2 x s, C(CHs)2), 2.66 (1H, d, OH, J 3.6 Hz), 3.42 (1 H, dd, H-4, J 1.6 Hz, 8.0 Hz), 3.64 (1H, dd, H-8, J 6.2 Hz, 9.8 Hz), 3.76 (2H, m, H-7, H-8'), 3.92 (1H, d, H-2, J 2.4 Hz), 3.94 (1H, app. t, H-6, J 3.8 Hz), 4.04 (1H, app. t, H-5, J 8.0 Hz), 4.17 (1H, app. s, H-3), 6.36 (1 H, br. s, NH); δc (100 MHz, CDCI3) -5.4, -5.3, -4.9, -4.7, -4.5, -4.3 (SiCH3), 17.9, 18.1, 18.3 (SiC(CHs)3), 25.7, 25.7, 25.9 (SiC(CHs)3), 26.9, 27.0 (C(CH3)2), 63.7 (C-4), 63.8 (C-8), 71.3 (C-7), 76.8 (C- 3), 77.1 (C-5), 77.5 (C-2), 79.3 (C-6), 109.0 (C(CH3)2), 174.5 (C=O); HRMS m/z (ESI +ve): Found 642.3685 (M+Na+); C29H6INO7Si3Na requires 642.3654. δ.β-O-isopropylidene-y-O-methanesulphonyl^.S.δ-tri-O-tert -butyldimethylsilyl-L-fftreo-L-affro-octono-γ-lactam 16

δ.δ-O-isopropylidene-Σ.S.δ-tri-O-feΛ^utyldimethylsil yl-L-tøreo-L-a/fro-octono-γ-lactam 15 (452 mg, 0.73 mmol) was dissolved in DCM (10 ml) after which triethylamine (308 μl, 2.19 mmol) and methanesulphonyl chloride (69 μl, 0.88 mmol) were added. The resulting mixture was stirred for two hours at room temperature under a nitrogen atmosphere. Subsequently, DCM (40 ml) was added and the reaction mixture was washed with 1M HCI (50 ml), satd. NaHCO3 (50 ml) and brine (50 ml). The organic layer was dried on Na2SO4. Column chromatography (EtOAc/cyclohexane 1/4 v/v) yielded the product as a light yellow oil (461 mg, 90%). Rf 0.37 (EtOAc/cyclohexane 1/4 v/v); [α]D +6.0 (c, 0.57 in CHCI3); vmaχ (film) 1715 cm"1 (C=O), 1177 cm"1 (SO3); δH (400 MHz, CDCI3) 0.11, 0.11, 0.12, 0.14, 0.18, 0.18 (18H, 6 x s, SiCH3), 0.87, 0.89, 0.91 (27H, 3 x s, SiC(CH3)3), 1.38, 1.40 (6H, 2 x s, C(CH3)2), 3.50 (1 H, app. d, H-4, J 6.4 Hz), 3.88 (3H, m, H-5, H-8, H-8'), 4.03 (2H, m, H-3, H-6), 4.24 (1 H, app. s, H-2), 4.66 (1 H, m, H-7), 6.61 (1H, br. s, NH); δc (100 MHz, CDCI3) -5.4, -5.4, -5.1 , -4.8, - 4.7, -4.4 (SiCH3), 17.8, 18.2, 18.3 (SiC(CHs)3), 25.7, 25.8, 25.9 (SiC(CH3)3), 27.1 (C(CH3)2), 38.8 (SO2CH3), 62.9 (C-8), 64.5 (C-4), 75.7 (C-2), 77.4, 77.6 (C-3, C-5, C-6), 82.9 (C-7), 109.5 (C(CH3)2), 174.9 (C=O); HRMS m/z (ESI +ve): Found 720.3432 (M+Na+); C30H83NO9SSi3Na requires 720.3429.

i ^-dideoxy-i ^-imino-δ.δ-O-isopropylidene^-O-methanesulphonyl-δ-O-tert -butyldimethylsilyl-L-fήreo-L-affro- octol 17

δ.δ-O-isopropylidene^-O-methanesulphonyl^.S.δ-tri-O-fe rt-butyldimethylsilyl-L-frjreo-L-a/fro-octono-γ-lactam 16 (411 mg, 0.59 mmol) was dissolved in THF (5 ml) and a 1M solution of BH3 in THF (5.9 ml) was added. The resulting mixture was stirred at reflux temperature for one hour under a nitrogen atmosphere. Then, MeOH (5 ml) was added cautiously, after which the solvents were evaporated. After column chromatography (EtOAc/cyclohexane 1/8 v/v), the product was obtained as a clear, colourless oil (231 mg, 57%). Rf 0.60 (EtOAc/cyclohexane 1/4 v/v); [α]D -8.5 (c, 1.32 in CHCI3); vmax (film) 3487 cm"1 (NH), 1358 cm"1 (B-N), 1771 cm" 1 (SO3); δH (400 MHz, CDCl3) 0.07, 0.08, 010, 0-11 , 0.17, 0.18 (18H, 6 x s, SiCH3), 0.88, 0.90, 0.93 (27H, 3 x s, SiC(CH3)3), 1.39, 1.43 (6H, 2 x s, C(CH3)2), 3.08 (1H, app. dd, H-4, J 6.8 Hz, 9.6 Hz), 3.15 (3H, s, SO2CH3), 3.44 (1H, app. d, H-1 , J 8.8 Hz), 3.86 (2H, m, H-3, H-8), 4.03 (1H, dd, H-8', J 8.8 Hz, 11.6 Hz), 4.07 (1 H, dd, H- 6, J 7.4 Hz, 8.2 Hz), 4.24 (1 H, dd, H-5, J 8.2 Hz, 9.6 Hz), 4.27 (1H, app. s, H-2), 4.71 (1H, br. s, NH), 4.85 (1H, app. dt, H-V, J 2.4 Hz, 8.4 Hz), 5.09 (1H, app. d, H-7, J 7.6 Hz); δc (100 MHz, CDCI3) -5.4, -5.0, -4.9, -4.8, -4.8, -4.7 (SiCH3), 17.9, 18.1 , 18.5 (SlC(CH3)3), 25.6, 25.7, 25.8, 25.9, 26.1, 26.9 (SiC(CH3)s), 26.9 (C(CH3)2), 38.8 (SO2CH3), 64.1 (C-8), 74.8 (C-5), 75.5 (C-4), 76.4 (C-2), 77.2 (C-3), 80.1 (C-6), 82.2 (C-7), 93.0 (C-1), 109.0 (C(CHs)2); HRMS m/z (ESl +ve): Found 684.3810 (M+H+); C30H6SNO8SSi3 requires 684.3817.

1 ,4-dideoxy-1 ,4-imino-7-0-methanesulphonyl-L-tøreo-L-a/fro-octol 18

1 ,4-dideoxy-1 ,4-imino-5,6-0-isopropylidene-7-0-methanesulphonyl-8-0-terf- butyldimethylsilyl-L-fhreo-L-a/fΛθ- octol 17 (138 mg, 0.20 mmol) was dissolved in a mixture of TFA (1.8 ml) and water (0.2 ml). This solution was then stirred for five hours at reflux temperature under a nitrogen atmosphere. Then, the solvents were evaporated, the residue was redissolved in water (10 ml) and washed with EtOAc (10 ml). The water layer was subsequently evaporated to dryness yielding the product as a brown oil (105 mg) which was used without further purification. 5H (400 MHz, D2O) 3.18 (3H, s, SO2CH3), 3.29 (1H, dd, H-1 , J 2.8 Hz, 12.4 Hz), 3.47 (1H, dd, H-1', J 3.2 Hz, 12.4 Hz), 3.66 (1 H, app. t, H-4, J 5.2 Hz), 3.78 (1 H, dd, H-8, J 5.8 Hz, 13.3 Hz), 3.85 (1H, dd, H-8', J 3.2 Hz, 13.3 Hz), 3.92 (1 H, dd, H-6, J 4.2 Hz, 5.8 Hz), 4.02 (1H, dd, H-5, J 4.2 Hz, 5.4 Hz), 4.25 (2H, m, H-2, H-3), 4.76 (1H, m, H-7); δc (100 MHz, D2O) 38.2 (SO2CH3), 50.4 (C-1), 60.8 (C-8), 66.4 (C-4), 67.5 (C-5), 69.2 (C-6), 74.7, 75.5 (C-2, C-3), 84.3 (C-7); MS m/z (ESI +ve): 301.76 (M+H+).

Casuarine 19

1 ,4-dideoxy-1 ,4-imino-7-O-methanesulphonyl-L-fΛreo-L-a/fro-octol 18 (105 mg) was dissolved in water (5 ml) and sodium acetate (49 mg, 0.6 mmol) was added. The resulting mixture was stirred at room temperature for three hours under a nitrogen atmosphere. The solvents were removed in vacuo and the residue was subjected to ion-exchange chromatography on Amberlite CG120 (H+) using 1M NH4OH as eluent yielding the product as a brown oil (37 mg, 91%). δH (400 MHz, D2O) 2.89 (1H, dd, H-5, J 3.0 Hz, 12.4 Hz), 3.00 (2H, m, H-3, H-7a), 3.22 (1H, dd, H-5', J 3.8 Hz, 12.4 Hz), 3.54 (1H, dd, H-8, J 6.4 Hz, 12.0 Hz), 3.71 (2H, m, H-2, H-81), 4.12 (3H, m, H-1, H-6, H-7); MS m/z (ESI +ve) 205.95 (M+H+).

Results

Scheme 6: Projected synthesis of casuarine.

_Λ r Λ

Firstly, a synthesis of casuarine was envisaged, which started out from the known compound 5,6- isopropylidene-L-gulonolactone (Scheme 6). This can be converted to a sulfonate ester which is then substituted with an excess of sodium azide under thermodynamic control. Although the ratio of the two azide products in the crude reaction mixture is in favour of the desired L-gulono stereochemistry, the yield in all conditions investigated was disappointing. Attempts to accomplish the next step, a DIBAL-H reduction followed by a Wittig reaction, were unsuccessful. In view of these results, a different strategy was devised which started from lactam 8 obtained in the 3-epicasuarine synthesis described above. After acidolysis of the terminal acetonide, the primary hydroxy! group was selectively protected using TBDMS-CI and pyridine, affording alcohol 14 (Scheme 7).

Scheme 7: Synthesis of alcohol 14.

The remaining hydroxyl group in 14 was then epimerised by furnishing it with a triflate leaving group followed by substitution using cesium trifluoroacetate. After basic hydrolysis of the resulting trifluoroacetate, epimer 15 was obtained in 20% yield (Scheme 8). This low yield was mainly caused by the temperamental synthesis of the triflate. It is thought that optimisation of this step can lead to improvement of the overall yield of the epimerisation.

Scheme 8: Epimerisation affording alcohol 15.

The remainder of the synthesis was analogous to the route to 3-epicasuarine (Scheme 9). Thus, the hydroxyl group in 15 was furnished with a good leaving group, yielding mesylate 16 in 90% yield. Then, the lactam was reduced using borane, and the protecting groups were removed by treatment with TFA affording precursor 18. Cyclisation using sodium acetate as the base yielded casuarine 19. The overall yield was 2.2%, corresponding to an efficiency of 79.9% per step.

Scheme 9: Synthesis of casuarine 19.

The 1H NMR spectrum of 19 obtained after purification by acidic ion exchange was in accordance with the literature (Nash ef a/. (1994) Tetrahedron Lett. 35 : 7849). A GCMS trace (not shown) clearly indicated that the product was of good purity. Example 5: Synthesis of indolizidines and/or pyrrolidines from glucosamine using Wittiα reaction

Reagents: i TfN3, CuSO4; ii Ph3P=CHCO2(Bu, Δ; iii 1 mol% OsO4, NMO/Ad mix; iv H2, Pd/C; TFA / H2O 9/1 v/v; v TsCI, pyridine; vi BH3.DMS, Δ; then NaOAc.

Treatment of glucosamine A with triflic azide in the presence of copper sulfate give the azide B which with a Wittig extension gives C. C may undergo hydroxylation with osmium tetraoxide, and the stereochemistry of the formation of the diol can be controlled by Sharpless Admix to give either D or E. Reduction of D and cyclisation to the lactam F which would selectively undergo tosylation at the primary alcohol function to afford H. Similarly E would give G and I. Borane reduction of H followed by treatment with sodium acetate as base would allow the direct formation of the indolizidiπe L or alternatively prior cyclization to the epoxide J which would afford the pyrrolizidine Wl. A similar sequence of reactions on I would give P by direct cyclisation or N via the epoxide K.

In the above schemes, direct cyclisation or indirect via the epoxides (to yield indolizidines and pyrrolizidines, respectively) may be selectively driven by optimisation of reaction parameters, including pH, metal ion content and/or reactant concentrations. Thus, ring formation on displacement of the tosylate is either direct formation of the six-membered ring (to give the indolizidine) or the formation of an epoxide in competition - in the latter the epoxide is later opened by the nitrogen to yield the pyrrolizidine.

Example 6: Alternative schemes for the synthesis of indolizidines and/or pyrrolidines

Scheme 1

Scheme 2

Example 7: Synthesis of 7a-epi-(+Vcasuarine

7a-epi-(+)-casuarιn Reagents: i Ph3P=CO2'Bu, Δ; ii 1mol% OsO4, NMO; iii TFA / H2O 9/1 v/v; iv acetone, cat. H2SO4; v TBDMS-CI, imidazole, Δ; vi HOAc / H2O 1/1 v/v, Δ; vii TBDMS-CI, pyridine; viii cone, ammonia, dioxane; ix Ms-Cl, Et3N; x BH3-DMS, THF, Δ; xi TFA / H2O 9/1 v/v; xii NaOAc, H2O. Example 8: Synthesis of 3,7a-diepi-(+Vcasuarine

Reagents: i Ph3P=CO2^Bu, Δ; ii 1mol% OsO4, NMO; iii TFA / H2O 9/1 v/v; iv acetone, cat. H2SO4; v TBDMS-CI, imidazole, Δ; vi HOAc / H2O 1/1 v/v, Δ; vii TBDMS-CI, pyridine; viii cone, ammonia, dioxane; ix Ms-Cl, Et3N; x BH3-DMS, THF, Δ; xi TFA / H2O 9/1 v/v; xii NaOAc, H2O.

Example 9: Large scale synthesis of 3,7-diep/-casuarine (12)

Synthesis of 3,7-diep/-casuarine (12) optimised for the production of 10Og of product utilises as the starting material the seven-carbon building block α-D-glucoheptonic γ-lactone 1. About two to three kilogrammes of this material are required, which is commercially available.

(a) Scheme 1 : Reduction to the lactol

1 2 The reduction of 1 to the lactol 2 with sodium borohydride has been achieved on a scale up to 0.5Kg scale and this reaction is quantitative by 13C NMR (Scheme 1). To date 4 Kg of lactone 1 have been reduced. Over¬ reduction is possible if the reaction is not kept below - pH 5.

(b) Scheme 2: Kiliani reaction

The lactol 2 is used directly in the Kiliani homologation to the eight-carbon lactone. The Kiliani reaction is routinely carried out on ~360g batches of the crude lactol 2. Treatment with sodium cyanide affords the octonolactone which when treated with acetone under acidic conditions generates approximately a 1 :1 mixture of di- and triacetonides, 4 and 3 respectively (Scheme 2).

Rather than filtering the crude Kiliani mixture through an ion exchange resin (Amberlite IR-120), adding the resin directly to the reaction mixture and stirring the two together for >30 minutes ensures better contact between the resin and product. The resin is then filtered.

The combined yield of 3 and 4 is typically in the 40% region (-17% of triacetonide 3 and -23% of diacetonide 4). Hence each 10Og of γ-lactone 1 affords approximately 3Og of triacetonide 3. Initially the yield of triacetonide 3 from the acetonide reaction (step iii) was much lower than anticipated. It was discovered that upon scale up the reaction was not reaching completion. NMR clearly showed that the lower running diactonide product was in fact a mixture of three co-running diacetonides. This mixture comprises of the expected diacetonide product 4 and two precursors of the triacetonide 3 which have failed to be fully protected under the reaction conditions. However, treating this mixture of diacetonides with further sulphuric acid and cupric sulphate in acetone afforded pure diacetone 4 and further triacetonide 3, thus raising the overall yield. (c) Scheme 3 Introduction of azide

IV 50% aq AcOH V TBDMS Cl DMF 550C Imidazole -3O0C to RT

ine O0C

[Sl] = TBDMS

Tπacetonide 3 can be brought through the synthesis in 5Og batches Deprotection with 40% aqueous acetic acid affords the 7,8-dιol 5 in 77-94% yield This compound can be selectively silylated in 86-93 % yield on up to 8Og scale It was found that conducting the reaction at twice the concentration with less silylating reagent and at lower temperature gave an increased yield for this transformation The silyl compound 6 is treated with triflic anhydride to afford the triflate, which after aqueous workup is washed through a small 'plug' of silica to remove polar residues The tπflate is then stirred with sodium azide to give the fully protected derivative 7 in 66-81% yield over the two steps (Scheme 3) The silyl compound 6 is routinely brought through these two steps in 30- 4Og batches

The crude Kiliani product is essentially insoluble in acetone Yields can be improved by stirring the reaction with an overhead motor this significantly increases the mixing of both the crude Kiliani product and the cupric sulfate and also decreases the reaction time Further improvement in yield can be achieved by concentrating the crude Kiliani product with toluene to form a 'crispy foam' This foam can then be ground up in a pestle and mortar to a fine solid thereby increasing the surface area of lactone in the reaction This also significantly decreases reaction times Heating the reaction to reflux (75-8O0C) not only speeds up the reaction but also allows a smaller volume of acetone to be employed (typically 1-2L for each 10Og of starting lactone)

It was also found that as the scale of the reaction increases it becomes more difficult to push the reaction to completion The formation/degradation of acetonides is usually an equilibrium process yet despite the addition of excess cupric sulfate to remove any water produced the acetonides fail to fully protect under the reaction conditions A simple 're-extraction' protocol circumvents this problem after neutralization (with sodium bicarbonate) the crude mixture of acetonides is filtered and concentrated and the crude orange gum then stirred in acetone with further cupric sulfate and sulfuric acid (at room temperature) for ~24h The acetonides are then neutralized for a second time (with further sodium bicarbonate) This simple second acetonide formation increases the yield of recovered tπacetonide 3 (after chromatography) With regard to step iv (selective acid catalysed removal of the primary acetonide), this reaction is carried out on a scale up to 6Og It has been found that the best yields are obtained when 40% aqueous acetic acid is used at a temperature of 5O0C Raising the concentration to 50% and/or increasing the temperature to 55-6O0C generally result in slightly lower yields Over-deprotection occurs with extended reaction times

With regard to step v (selective silylation of the primary alcohol), it was found this reaction gives better yields when the concentration is doubled and the temperature lowered initially to -4O0C, then raised slowly to room temperature Under these conditions only 1 05 equivalents of TBDMS-CI are required and only traces (if any) of dι-sιlylated product are seen This reaction is carried out up to 8Og scale

With regard to steps vι and vιι (triflation/azide displacement reaction), this two-stage process becomes more capricious as the scale increases Low yields may be due to small amounts of triflic acid being carried through to the azide displacement and in turn promoting side reactions Introducing a sodium bicarbonate wash into the aqueous work-up (of the inflate) helps to remove any triflic acid Washing the crude triflate through a small plug of silica removes any other polar residues, which could interfere with the azide displacement

Care must be taken during scheme 3 to avoid problems arising from the fact that the acetonide reaction is water sensitive (both the tπflation and azide displacement are water sensitive) and the crude Kiliani product is very hygroscopic

With regard to step ιx (mesylation of the diol 8), it was found that 6 equivalents of mesyl chloride are sufficient if the reaction concentration is kept to less than 5ml solvent (pyridine) per gram of starting material A 0 5M HCI wash helps to remove any traces of pyridine and stirring the organic phase with sodium bicarbonate for -1 hour removes excess mesyl chloride any unremoved mesyl chloride will be converted to methanesufonic acid and may interfere with the cyclisation (step xιι)

(d) Scheme 4 Synthesis of the di-mesylate

[Si] VHi LiBH4 THF ix MsCI pyridine O0C to RT DMAP O0C tO RT Ms0

The azide can be reduced to the diol 8 with lithium borohydride (up to 5Og scale) in 75-85% yield Subsequent treatment with methanesulphonyl chloride in pyridine affords the fully protected derivative 9 in 75-90% yield (Scheme 4) (e) Scheme 5 Ring closure

[Si] xi H2 Pd/C water

10 11

then

Treatment of the di-mesyl compound 9 with 25% aqueous tπfluoroacetic acid over a 12 hour period afforded the crude alcohol 10 without any formation of by-products The alcohol 10 is clean by NMR and is therefore not purified This deprotection can be routinely carried out on ~30g batches of di-mesyl compound 9.

Treatment of 10 with hydrogen and catalytic palladium affords the amine 11, which is also used directly in the next and final step Treatment of amine 11 with sodium acetate at 600C gives 3,7-dιep/-casuarιne 12 as an impure orange gum, which can be purified on acidic ion exchange resin (DOWEX® 50WX8-200) to afford a mixture of 3,7-diep;-casuarιne (12) and a very minor isomer (3,7,7a-trιepιcasuarιne or 3,7a-diepιcasuarιne) see Scheme 5

This three-step protocol gives a combined 66-87% yield over the three steps

The product, 3,7-dιep/-casuaπne 12, can be further purified by crystallization (if desired) Alternatively, anion exchange chromatography (e g using Dowex 1 in hydroxide form) may be employed

The overall reaction scheme is shown below (Scheme 6), where 3,7-dιep;-casuarιne 12 is shown as MNL24 (f) Scheme 6 Outline of route

iv 50% aq AcOH, 5O0C

vi Tf2O1 Pyridine, „ v τ TqBnDuMsS.-πCI1 Π DΛMΛPF

DCM1 -300C to RT Imidazole, -4O0C to RT

VIi NaN3, DMF [Si] = TBDMS

ViIi LiBH41 THF κ MsC, pyridine,

O0C to RT DMAP, O0C to RT Msθ *-Ajy.s.OrS. ~~t..

x 25% aq TFA

Pd/C, water

10 Example 10: Synthesis of D-casuarine

Scheme 1: Reagents and conditions i) benzaldehyde, cone. HCl. ii) TBS-CI, imidazole, DMAP (cat.), DMF. iii) 1. Tf2O, pyridine, DCM; 2. NaN3, DMF, PPTS. iv) DiBAL-H, DCM, -78 0C. v) Ph3P=C(H)CO2'Bu, THF, Δ. vi) (DHQ)2-PYR (1%), K2OsO4 (1%), MeSO2NH2, K3Fe(CN)6, K2CO3, fBu-OH:H2O (1 :1). vii) 1. TFA:H2O (9:1); 2. 2,2-DMP, MeOH, acetone, PTSA (cat.), 50 0C. viii) 1. HOAc:H2O:dioxane (2:1 :1), 50 0C. ix) LiBH4 (2M in THF), THF, O 0C - RT. x) MsCI, DMAP (cat.), pyridine, xi) 1. TFA:H2O (9:1 ); 2. H2, 10% Pd/C, dioxane:H2O (1 :1); 3. NaOAc, H2O, 50 0C.

3,5-O-Benzylidene-L-gulono-v-lactone 1.2

This compound was prepared using a modified literature procedure (see Crawford, T. C. US Patent 1978, US 4,111,958). L-gulono-γ-lactone 1.1 (25.0 g, 140 mmol) was dissolved in benzaldehyde (200 ml) and cone. HCI (15 ml) was added. This reaction mixture was stirred overnight. The thick crystalline mass was then filtered and the crystals were washed with Et2O (2 x 50 ml) to afford the product (25.3 g, 68%) as a white solid.

M. p. 187 0C {Lit. 188-189 °C[3]}; [α]D +59.1 (c 1.00, DMF) {Lit. [α]D +61.1 (DMF)[1]}; δH (cf-DMSO, 400 MHz) 3.41 (1H, br. s, OH), 3.63 (2H, d, H-6a, H-6b, J6,s 6.7 Hz), 4.18 (1H, m, H-5), 4.46 (1H, s, H-4), 4.73 (2H, s, H-2, H-3), 5.07 (1 H, br. s, OH), 5.74 (1 H, s, ArCH), 7.5-8.0 (5H, m, ArH). δc ((/-DMSO, 50 MHz) 60.0 (C-6), 69.6, 70.9, 75.1 , 76.4 (C-2, C-3, C-4, C-5), 98.4 (ArCH), 126.8, 128.3, 129.5, 135.0 (ArC), 173.6 (C=O). 3.5-O-Benzylidene-6-O-ferf-butyldimetrιylsilyl-L-qulono-γ- laGtone 1.3

3,5-O-Benzylidene-L-gulono-γ-lactone 1.2 (20.00 g, 75.1 mmol), imidazole (15.34 g, 225.3 mmol) and DMAP (275 mg, 2.25 mmol) were dissolved in DMF (150 ml). After cooling the solution to 0 0C, a solution of TBS-CI (12.45 g, 82.6 mmol) in DMF (100 ml) was added dropwise. The reaction mixture was stirred at room temperature overnight. Workup as above.

Rf (EtOAc/cyclohexane, 1/1 v/v) = 0.37; m.p. 174-175 0C; [α]D +56.6 (c 0.65 g/100 ml, CHCI3) {Lit. [α]D +56 (CHCI3)); v 3356 (OH), 1786 (C=O); δH (400 MHz, CDCI3) 0.09 (6H, s, SiCH3), 0.90 (9H, s, SiC(CH3)3), 2.79 (1 H, d, OH, Jo»,2 10.4 Hz), 3.88 (1 H, dd, H-6a, J6a,eb 9.6 Hz, J6a,5 5.6 Hz), 3.98 (1 H, dd, H-6b, Jβb.βa 9-6 Hz, J6b,5 8.4 Hz), 4.16 (1 H, m, H-5), 4.42 (1 H, app. t, H-4, J 1.8 Hz), 4.59 (1H, dd, H-2, J2|OH 10.4 Hz, J2,3 4.0 Hz), 4.74 (1 H, dd, H-3, J3,2 4.0 Hz, J3|4 2.0 Hz), 5.64 (1 H, s, ArCH), 7.38 (5H, m, ArH); δc (100 MHz, CDCI3) -5.5 (SiCH3), 18.3 (SiC(CHs)3), 25.8 (SiC(CH3)3), 26.9 (C(CH3)2), 60.7 (C-6), 69.0 (C-4), 71.7 (C-2), 73.7 (C-3), 76.4 (C-5), 99.5 (ArCH), 126.3, 128.4, 129.6, 136.4 (ArC), 174.7 (C=O); HRMS m/z (ESI +ve) observed 381.1731 [M+H+], C-IgH2EiO6Si requires 381.1733; for Ci9H28O6Si calcd. C 59.97 H 7.42, found C 59.89 H 7.15.

2-Azido-3.5-O-benzylidene-6-O-fe/f-butyldimethylsilyl-2-d eoxy-L-qulono-γ-lactone 1.4

S.δ-O-Benzylidene-δ-O-ferf-butyldimethylsilyl-L-gulono- γ-lactone 1.3 (15.59 g, 40.97 mmol) was dissolved in DCM (150 ml) and pyridine (7.36 ml, 90.14 mmol) was added. This solution was cooled to -20 0C and Tf2O (7.58 ml, 45.07 mmol) was added dropwise. The reaction mixture was then stirred at -20 0C for one hour, after which it was washed with 0.5M HCI (150 ml) and brine (150 ml). After drying on Na2SO4 the solvent was evaporated and the residue was redissolved in DMF (100 ml). After adding NaN3 (7.99 g, 122.9 mmol), the reaction mixture was stirred at room temperature for one hour. Then, PPTS (11.33 g, 45.07 mmol) was added and the reaction mixture was stirred overnight at 50 0C. After that, the solvent was evaporated and the residue was redissolved in EtOAc (150 ml), washed with brine (150 ml) and dried on Na2SO4. Column chromatography (EtOAc/cyclohexane, 1/4 v/v) yielded the product (10.63 g, 64%) as a crystalline solid.

Rf (EtOAc/cyclohexane, 1/2 v/v) = 0.39; m.p. 90 0C; v 2116 (N3), 1785 (C=O); δH (400 MHz, CDCI3) 0.10 (6H, s, SiCH3), 0.91 (9H, s, SiC(CH3)3), 3.89 (1H, dd, H-6a, J6a,6b 9.8 Hz, Jβa,s 5.8 Hz), 3.96 (1H, dd, H-6b, Jβbea 9.8 Hz, J6b,5 8.4 Hz), 4.08 (1H, d, H-2, J2]3 4.4 Hz), 4.19 (1 H, m, H-5), 4.30 (1H, app. t, H-4, J 2.0 Hz), 4.81 (1 H, dd, H- 3, J3,2 4.4 Hz, J3,4 2.0 Hz), 5.63 (1H, s, ArCH), 7.40 (5H, m, ArH); δc (100 MHz, CDCI3) -5.5 (SiCH3), 18.3 (SiC(CHs)3), 26.9 (SiC(CHs)3), 60.8 (C-6), 61.7 (C-2), 70.4 (C-4), 71.8 (C-3), 76.3 (C-5), 99.6 (ArCH), 126.2, 128.4, 129.0, 136.25 (ArC), 170.6 (C=O).

Methyl 4-azido-5,7-O-benzylidene-8-teff-butyldimethylsilyl-2,3.4-tr ideoxy-D-αu/o-oct-2-enoate 1.6

2-Azido-3,5-0-benzylidene-6-0-ferf-butyldimethylsilyl-2-d eoxy-L-gulono-χ-lactone 1.4 (3.83 g, 9.44 mmol) was dissolved in DCM (100 ml) and cooled to O0C. After dropwise addition of a 1.5M solution of DiBAL-H in toluene (9.44 ml), the mixture was stirred at O0C for three hours, after which IR clearly showed the disappearance of the C=O absorption of the starting material at 1785 cm"1. Cautiously, 0.5M HCI (100 ml) was added and the layers were separated, after which the organic fraction was dried on Na2SO-*. After filtration and evaporation of the solvent, 2-Azido-3,5-0-benzylidene-6-0-tert-butyldimethylsilyl-2-deox y-L-gulose 1.5 was obtained which was used without purification. (Methoxycarbonylmethyl)triphenylphosphonium bromide (4.30 g, 10.38 mrnol) was dissolved in DCM (50 ml) and shaken gently with 2M NaOH (50 ml) for 5 minutes. The layers were separated and the organic layer was dried on Na2SO*). After filtration and evaporation of the solvent, the crude phosphorous ylid was redissolved in dioxan (100 ml) and added to crude 2-Azido-3,5-O-benzylidene-6-O-fert- butyldimethylsilyl-2-deoxy-L-gulose 5. The resulting solution was stirred overnight at room temperature. After evaporation of the solvent, the crude material was triturated with pet. ether 40-60. After filtration, the filtrate was evaporated to dryness, and column chromatography (EtOAc/cyclohexane, 1/4 v/v) afforded the product (3.43 g, 78%) as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) = 0.67; [α]D +12.8 (c 0.20 g/100 ml, CHCI3); v 3443 (OH), 2109 (N3), 1728 (C=O); δH (400 MHz, CDCI3) 0.10, 0.11 (6H, 2 x s, SiCH3), 0.92 (9H, s, SiC(CHs)3), 2.74 (1 H, OH, JoH.β 9.6 Hz), 3.71 (1 H, dd, H-5, J5,4 1.0 Hz, J5,6 5.4 Hz), 3.77 (3H, s, OCH3), 3.93 (4H, m, H-6, H-7, H-8a, H-8b), 4.53 (1H, m, H-4), 5.58 (1H, s, ArCH), 6.20 (1H, dd, H-2, J2A 1.4 Hz, J2,3 11.8 Hz), 7.03 (1H, dd, H-3, J3|4 6.0 Hz, J3,2 11.8 Hz), 7.46 (5H, m, ArH); δc (100 MHz, CDCI3) -5.4, -5.4 (SiCH3), 25.9 (SiC(CHs)3), 26.9 (SiC(CH3)3), 51.6 (OCH3), 52.3 (C-5), 60.7 (C-4), 62.9 (C-8), 79.8, 81.0 (C-6, C-7), 101.1 (ArCH), 124.0 (C-2), 125.9, 128.2, 129.1, 133.4 (ArC), 142.6 (C-3), 166.4 (C=O); HRMS m/z (ESI +ve) observed 486.2033 [M+Na+], C22H33N3O6SiNa requires 486.2036.

Methyl 5 J-O-benzylidene-δ-O-ferf-butyldimethylsilyl-L-atfro-L-frtre o-octonate 1.7

Potassium ferricyanide (6.38 g, 19.38 mmol), potassium carbonate (2.68 g, 19.38 mmol), methane sulphonamide (614 mg, 6.46 mmol), potassium osmate dihydrate (24 mg, 0.0646 mmol) and (DHQ)2PHAL (57 mg, 0.0646 mmol) were dissolved in a mixture of fert-butanol (30 ml) and water (30 ml). The resulting mixture was stirred for 10 minutes at O0C after which methyl 4-azido-5,7-O-benzylidene-8-fert-butyldimethylsilyl-2,3,4- trideoxy-D-gu/o-oct-2-enoate 1.6 (2.98 g, 6.46 mmol) was added as a solution in DCM (2 ml) and fert-butanol (2 ml). The resulting mixture was stirred for six hours at O0C up to room temperature. Then, a satd. solution of NaHSO3 (30 ml) in water was added and the crude product was extracted with EtOAc (2 x 60 ml) and dried on Na2SO4. Column chromatography (EtOAc/cyclohexane, 1/2 v/v) afforded the product (2.02 g, 63%) as a clear, pale yellow oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) = 0.18; [α]D +16.2 (c 0.46 g/100 ml, CHCI3); δH (400 MHz, C6D6) 0.18, 0.19 (6H, 2 x s, Si(CHs)2), 1.07 (9H, s, SiC(CHa)3), 2.80 (1H, br. s, 6-OH), 3.36 (1H, d, 2-OH, JOH,2 7.6 Hz), 3.42 (3H, s, OCH3), 3.65 (3H, m, H-5, H-7, 3-OH), 3.85 (1H, m, H-6), 3.87 (1 H, dd, H-8a, JaaJ 5.2 Hz, J8a,8b 10.4 Hz), 3.92 (1 H, dd, H-8b, J8b,7 6.2 Hz, J8b|8a 10.4 Hz), 4.21 (1H, app. t, H-4, J 8.4 Hz), 4.30 (1 H, d, H-3, J 8.8 Hz), 4.54 (1H, dd, H-2, J2,z 1.4 Hz, J2,OH 7.6 Hz), 5.28 (1H, s, ArCH), 7.22 (3H, m, ArH), 7.54 (2H, m, ArH); δc (100 MHz, C6D6) -5.2, -5.1 (Si(CH3).), 18.7 (SiC(CH3)3), 26.2 (SiC(CHs)3), 52.3 (OCH3), 61.5 (C-4), 63.2 (C-8), 64.1 (C-6), 71.8 (C-2), 74.1 (C-3), 80.6, 82.5 (C-5, C-7), 101.5 (ArCH), 126.4, 128.7, 129.6, 137.8 (ArC), 173.5 (C=O); HRMS m/z (ESI +ve) 798.2273 [M+H+], C22H36N3O8Si requires 798.2271; for C22H35N3O8Si calcd. C 53.10 H 7.09 N 8.44, found C 53.26 H 7.11 N 8.39. Methyl 4-azido-4-deoxy-2.3:5,6:7, δ-tri-O-isopropylidene-L-affro-L-fήreo-octonate 1.8

Tert-butyi 5,7-O-benzylidene-8-O-te/f-butyldimethylsilyl-L-a/fro-L-f/7r eo-octonate 1.7 (2.80 g, 5.19 mmol) was dissolved in TFA (4.5 ml) and water (0.5 ml) and the resulting mixture was stirred for 3 hours at room temperature. The solvents were evaporated and the residue was dried carefully in vacuo. The crude deprotected material was then redissolved in 2,2-DMP (32 ml), acetone (11.2 ml) and methanol (7.2 ml). After addition of PTSA monohydrate (150 mg), the resulting mixture was stirred for 48 hours at 50 0C. The reaction mixture was neutralised by addition of NaHCCb (s), and after filtration and evaporation, column chromatography (EtOAc/cyclohexane, 1/3 v/v) afforded the product (1.36 g, 63%) as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) = 0.49; [α]D -28.3 (c 0.54 g/100 ml, CHCI3); v 2109 (N3), 1747 (C=O); δH (400 MHz, CDCI3) 1.39, 1.40, 1.43, 1.44, 1.46, 1.55 (18H, 6 x s, C(CH3)2), 3.79 (3H, s, OCH3), 3.91-4.02 (4H, m, H- 4, H-5, H-6, H-8a), 4.08 (1H, app. t, H-8b, J 7.4 Hz), 4.23 (1H, app. dt, H-7, J 3.6 Hz, J 6.8 Hz), 4.58 (1H, dd, H- 3, J3,4 3.4 Hz, J3,2 6.7 Hz), 4.64 (1 H, d, H-2, J2,3 6.7 Hz); δc (100 MHz, CDCI3) 25.4, 25.7, 26.2, 26.5, 26.8, 27.2 (C(CHa)2), 52.5 (OCH3), 64.3 (C-4), 66.1 (C-8), 75.1 (C-5/6), 75.1 (C-7), 75.2 (C-2), 79.2 (C-3), 79.9 (C-5/6), 109.7, 110.3, 111.9 (C(CHs)2), 171.3 (C=O); HRMS e/z (ESI +ve) 416.2035 [M+H+], C18H30N3Os requires 416.2033; for Ci8H29N3O8 calcd. C 52.04 H 7.04 N 10.11 , found C 52.12 H 7.11 N 10.32.

Methyl 4-azido-8-terf-butyldimethylsilyl-4-deoxy-2.3:5.6-di-0-isopr opylidene-L-a/fro-L-^reo-octonate 1.9

Methyl 4-azido-4-deoxy-2,3:5,6:7,8-tri-0-isopropylidene-L-a/fro-L-f ftreo-octonate 1.8 (921 mg, 2.22 mmol) was dissolved in a mixture of acetic acid (10 ml), H2O (5 ml) and dioxane (5 ml), which was stirred for 6 hours at 5O0C. The solvents were evaporated and the residue was redissolved EtOAc (10 ml), washed with satd. NaHCO3 (10 ml) and dried on Na2Sθ4. The crude diol was dissolved in pyridine (5 ml) after which TBS-CI (401 mg, 2.66 mmol) was added. The resulting mixture was stirred overnight at room temperature. After evaporation of the solvent, the crude product was redissolved in DCM (25 ml) and washed with 1 M HCI (25 ml), satd. NaHCO3 (25 ml) and brine (25 ml). The organic fraction was dried on Na2Sθ4 and purified by column chromatography (EtOAc/cyclohexane, 1/4 v/v), yielding the product (686 mg, 63%) as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/1 v/v) = 0.71; [α]D -25.9 (c 0.36 g/100 ml, CHCI3); v 3450 (OH), 2112 (N3), 1749 (C=O); δH (400 MHz, CDCI3) 0.10 (6H, s, Si(CHo)2), 0.92 (9H, s, SiC(CHs)3), 0.40, 0.42, 0.43, 0.46 (12H, 4 x s, C(CH3)2), 2.29 (1H, d, OH, JQHJ 7.7 Hz), 3.63 (1H, dd, H-8a, JSa,ab 9.6 Hz, JBa,7 6.4 Hz), 3.70-3.80 (2H, m, H-7, H-8b), 3.78 (3H, s, OCH3), 3.93 (1H, dd, H-4, J4|3 3.8 Hz, J4|5 7.9 Hz), 4.07 (1H, app. t, H-5, J 7.8 Hz), 4.13 (1H, dd, H-6, J6,5 7.7 Hz, J6|7 1.3 Hz), 4.56 (1H, dd, H-3, J3|4 3.8 Hz, J3|2 6.6 Hz), 4.63 (1 H, d, H-2, J2|3 6.6 Hz); δo (100 MHz, CDCI3) -5.5, -5.4 (Si(CHs)2), 18.2 (SiC(CH3)3), 25.4, 26.5, 26.8, 27.0 (C(CHa)2), 25.8 (SiC(CHs)3), 52.5 (OCH3), 64.5 (C-8), 64.6 (C-4), 69.9 (C-7), 74.4 (C-5), 75.3 (C-2), 79.1 (C-3), 79.2 (C-6), 110.0, 111.9 (C(CHs)2), 171.3 (C=O); HRMS m/z (EΞSI +ve) 512.2404 [M+Na+], C2i H39N3O6SiNa requires 512.2404; for C2iHs9N3O8Si calcd. C 51.51 H 8.03 N 8.58, found C 51.72 H 7.89 N 8.11.

4-Azido-8-terf-butyldimethylsilyl-4-deoxy-2,3:5,6-di-0-is opropylidene-L-affro-L-fftreo-octitol 1.10

Methyl 4-azido-8-terf-butyldimethylsilyl-4-deoxy-2,3:5,6-di-0-isopr opylidene-L-a/fro-L-f/7reo-octonate 1.9 (686 mg, 1.40 mmol) was dissolved in THF (5 ml) and cooled to O0C. After dropwise addition of a 2M solution of LiBhU in THF (1.40 ml), the reaction mixture was allowed to stir overnight at O0C up to room temperature. After adding 1M HCI (10 ml) cautiously, the product was extracted with DCM (2 x 10 ml). The organic fraction was dried on Na2SCU and after purification by column chromatography (EtOAc/cyclohexane, 1/2 v/v) the product (439 mg, 68%) was obtained as a clear colourless oil.

Rf (EtOAc/cyclohexane, 1/1 v/v) = 0.59; v 3427 (OH), 2113 (N3); δπ (400 MHz, CDCI3) 0.09, 0.13 (6H, 2 x s, Si(CHs)2), 0.92 (9H, s, SiC(CHs)3), 1.43, 1.45, 1.48 (12H, 3 x s, C(CHs)2), 2.08 (1 H, br. t, 1-OH, J 5.8 Hz), 2.33 (1H, d, 7-OH, JOH,7 7.6 Hz), 3.69-3.76 (4H, br. m, H-1a, H-7, H-8a, H-8b), 3.83 (1H, br. m, H-1b), 3.92 (1 H, app. t, H-4, J 6.4 Hz), 4.01 (1H, app. t, H-5, J 6.8 Hz), 4.10 (1H, app. t, H-3, J 7.2 Hz), 4.19 (2H, m, H-2, H-6); δc (100 MHz, CDCI3) -5.4, -5.3 (Si(CH3)2), 18.2 (SiC(CHs)3), 25.8 (SiC(CHs)3), 26.7, 26.9, 26.9, 27.1 (C(CHs)2), 63.0 (C-1), 64.4 (C-8), 64.5 (C-4), 69.9 (C-7), 75.4 (C-3), 76.2 (C-5), 78.3, 78.9 (C-2, C-6), 109.6, 110.1 (C(CHs)2); HRMS m/z (ESI +ve) 462.2640 [M+H+], C20H40N3O7Si requires 462.2636; for C20H39N3O7Si calcd. C 52.04 H 8.52 N 9.10, found C 51.87 H 8.22 N 8.98.

4-Azido-8-tert-butyldimethylsilyl-4-deoxy-2,3:5,6-di-0-is opropylidene-1 ,7-di-0-methanesulfonyl-L-a/fro-L-f/?reo- octitol 1.11

4-Azido-8-fert-butyldimethylsilyl-4-deoxy-2,3:5,6-di-0-is opropylidene-L-a/fro-L-f/7reo-octitol 1.10 (258 mg, 0.56 mmol) was dissolved in pyridine (5 ml) and cooled to O0C after which mesyl chloride (348 μl, 4.48 mmol) and DMAP (6.8 mg, 0.056 mmol) were added. The resulting mixture was stirred overnight at room temperature. The solvent was evaporated, after which the residue was redissolved in DCM (20 ml) and washed with 1M HCl (20 ml), satd. NaHCO3 (20 ml) and brine (20 ml). After drying on Na2SO4, column chromatography (EtOAc/cyclohexane, 1/2 v/v) yielded the product (333 mg, 96%) as a clear, light yellow oil.

Rf (EtOAc/cyclohexane, 1/1 v/v) = 0.74; [α]D -7.8 (c 0.27 g/100 ml, CHCI3); v 3419 (OH), 2114 (N3); δH (400 MHz, CDCI3) 0.11 , 0.12 (6H, 2 x s, Si(CH3)2), 0.92 (9H, s, SiC(CH3)3), 1.42, 1.43, 1.44, 1.50 (12H, 4 x s, C(CHs)2), 3.08, 3.12 (6H, 2 x s, SO2CH3), 3.87 (1H, dd, H-8a, J8a,8b 10.8 Hz, J8a,7 5.6 Hz), 3.98 (3H, m, H-8b, H- 4, H-5), 4.15 (1H, dd, H-3, J 4.4 Hz, J 7.4 Hz), 4.29 (2H, m, H-6, H-1a), 4.39 (1H, m, H-2), 4.49 (1H, dd, H-1b, J1b,2 2.0 Hz, Jib,ia 11.6 Hz), 4.78 (1H, app. t, H-7, J 6.0 Hz); HRMS m/z (ESI +ve) 640.2012 [M+Na+], C22H43N3O1IS2SiNa requires 640.2006; for C22H43N3OnS2Si calcd. C 42.77 H 7.02 N 6.80, found C 42.35 H 6.95 N 6.56.

Casuarine 1.12

4-Azido-8-fert-butyldimethylsilyl-4-deoxy-2,3:5,6-di-O-is opropylidene-1,7-di-O-methanesulfonyl-L-a/fro-L-f/?reo- octitol 1.11 (328 mg, 0.53 mmol) was dissolved in a mixture of TFA (1.8 ml) and H2O (0.2 ml) and the resulting solution was stirred for 2 hours at room temperature. The solvents were evaporated and the residue was redissolved in H2O (2 ml) and dioxane (2 ml). After addition of 10% Pd/C (10 mg), the mixture was stirred overnight under a hydrogen atmosphere. After filtration over Celite®, the solvents were evaporated. The crude deprotected material was dissolved in water (5 ml) and NaOAc (153 mg, 1.86 mmol) was added. After stirring for 24 hours at 5O0C, the solvent was evaporated and the crude material was subjected to ion exchange chromatography (Dowex 50X8-H+, elution with 2M NH4OH) to afford the product (78.2 mg, 72%) as a brown oil. Example 11 Synthesis of 6,7-d;ep/-L-casuarιne

Scheme 2 reagents and conditions ι) benzaldehyde, cone HCI π) TBS-CI, imidazole, DMAP (cat ), DMF in) 1 Tf2O, pyridine, DCM, 2 NaN3, DMF, PPTS ιv) DiBAL-H, DCM, -78 0C v) Ph3P=C(H)CO2(Bu, THF, Δ vι) (DHQ)2-PHAL (1%), K2OsO4 (1%), MeSO2NH2, K3Fe(CN)6, K2CO3, fBu-OH H2O (1 1 ) vιι) 1 TFA H2O (9 1), 2 2,2-DMP, MeOH, acetone, PTSA (cat ), 50 0C vin) 1 HOAc H2O dioxane (2 1 1 ), 50 0C ιx) LiBH4 (2M in THF), THF, O 0C - RT x) MsCI, DMAP (cat ), pyridine xι) 1 TFA H2O (9 1), 2 H2, 10% Pd/C, dioxane H2O (1 1), 3 NaOAc, H2O, 50 0C

3,5-0-Benzylιdene-D-qιιlonolactone 22

D-gulonolactone 2.1 (25 O g, 140 mmol) was suspended in benzaldehyde (200 ml) and 37% hydrochloric acid (15 ml) was added The resulting mixture was stirred overnight at room temperature Diethyl ether (200 ml) was then added and the crystal mass was filtered After washing the crystals with copious diethyl ether and drying in vacuo, the product (25 1 g, 67%) was obtained as white crystals

[α]D -58 2 (c O 79, DMF) {Lit [α]D +61 1 (DMF) for the enantiomeric ]}, m p 188 0C {Lit 188-189 0C for the enantiomer}, δH (400 MHz, cf-DMSO) 3 60 (2H, d, H-6a, H-6b, J 6 6 Hz), 4 16 (1H, app t, H-5, J 6 6 Hz), 4 34 (1H, s, H-4), 4.70 (2H, s, H-2, H-3), 5.71 (1 H, s, Ar-CH), 7.37 (3H, m, ArH), 7.43 (2H, m, ArH); δH (100 MHz, d6- DMSO) 60.5 (C-6), 70.1 (C-4), 71.4, 75.6 (C-2, C-3), 76.9 (C-5), 98.9 (Ar-CH), 127.3, 128.8, 129.7, 138.6 (ArC), 176.7 (C=O).

3.5-0-Benzylidene-6-0-ferf-butyldimethylsilyl-D-αulonola ctoπe 2.3

3,5-O-Benzylidene-D-gulonolactone 2.2 (6.92 g, 25.99 mmol), imidazole (5.31 g, 77.97 mmol) and DMAP (64 mg, 0.52 mmol) were dissolved in DMF (150 ml). After cooling to -20 0C, a solution of TBS-Cl (3.92 g, 25.99 mmol) in DMF (100 ml) was added dropwise. The resulting mixture was stirred overnight at -20 0C up to room temperature. The solvent was evaporated and the residue redissolved in EtOAc (150 ml). After washing with 1M HCI (150 ml), satd. NaHCO3 (150 ml) and brine (150 ml), the organic layer was dried on Na2SO^ After evaporation and trituration with cold pet. ether 40-60 (150 ml), the product (7.78 g, 79%) was obtained as a white solid.

[α]D -58.9 (c 0.69, CHCI3); v 3363 (OH), 1787 (CO); δH (400 MHz, cf-DMSO) 0.06, 0.07 (6H, 2 x s, Si(CH3)2), 0.88 (9H, s, SiC(CHa)3), 3.79 (2H, m, H-6a, H-6b), 4.23 (1H, app. t, H-5, J 6.2 Hz), 4.42 (1H, s, H-4), 4.72 (2H, m, H-2, H-3), 5.73 (1H, s, Ar-CH), 5.99 (1H, d, OH, J0R2 7.2 Hz), 7.37 (3H, m, ArH), 7.44 (2H, m, ArH); δc (100 MHz, cf-DMSO) -4.6, -4.5 (Si(CHs)2), 18.9 (SiC(CH3)3), 26.6 (SiC(CHs)3), 62.2 (C-6), 69.9 (C-4), 71.4, 75.6 (C- 2, C-3), 76.4 (C-5), 98.7 (Ar-CH), 127.2, 128.8, 129.7, 138.5 (ArC), 176.7 (C=O).

2-Azido-3.5-O-benzylidene-6-O-ferf-butyldimethylsilyl-2-d eoxy-D-qulonolactone 2.4

S.S-O-Benzylidene-e-O-fert-butyldimethylsilyl-D-gulonolac tone 2.3 (7.78 g, 20.44 mmol) and pyridine (4.00 ml, 49.06 mmol) were dissolved in DCM (100 ml). After cooling to -20 0C, trifluoromethanesulfonic anhydride (4.13 ml, 24.53 mmol) was added in portions. The mixture was stirred at -20 0C for one hour, followed by washing with 1M HCI (100 ml) and brine (100 ml). After drying on Na2Sθ4, the solvent was evaporated and the residue was redissolved in DMF (100 ml). Sodium azide (3.98 g, 61.32 mmol) was added and the mixture was stirred at room temperature for one hour after which PPTS (5.14 g, 20.44 mmol) was added. The reaction mixture was then stirred for 48 hours at room temperature. The solvent was evaporated and the residue was redissolved in EtOAc (150 ml), washed with water (150 ml), and dried on Na2SO^ After column chromatography (EtOAc/cyclohexane, 1/4 v/v), the product (3.96 g, 48%) was obtained as a crystalline solid.

Rf (EtOAc/cyclohexane, 1/2 v/v) 0.41; [α]D -99.0 (c 1.94, CHCI3); v 2115 (N3), 1783 (CO); δH (400 MHz, CDCI3) 0.11 (6H, s, Si(CHs)2), 0.92 (9H, s, SiC(CHs)3), 3.90 (1H, dd, H-6a, J6a,5 6.2 Hz, Jβa,6b 9.4 Hz), 3.95 (1H, app. t, H-6b, J 9.0 Hz), 4.07 (1H, d, H-2, J2|3 4.0 Hz), 4.18 (1H, app. t, H-5, J 7.0 Hz), 4.41 (1 H, s, H-4), 4.79 (1H, m, H-3), 5.63 (1H, s, Ar-CH), 7.38 (3H, m, ArH), 7.48 (2H, m, ArH); δc (100 MHz, CDCI3) -5.5, -5.4 (Si(CH3)2), 18.3 (SiC(CH3)3), 25.8, 26.9 (SiC(CHa)3), 60.9 (C-6), 61.7 (C-2), 70.5 (C-4), 75.1 (C-3), 76.4 (C-5), 99.5 (Ar-CH), 126.2, 128.4, 129.5, 136.4 (ArC), 170.8 (C=O).

Methyl 4-azido-5,7-0-benzylidene-6-0-teff-butyldimethylsilyl-2.3.4- trideoxy-D-gu/o-oct-2-enoate 2.5

2-Azido-3,5-O-benzylidene-6-O-terf-butyldimethylsilyl-2-d eoxy-D-gulonolactone 2.4 (3.96 g, 9.77 mmol) was dissolved in DCM (50 ml). This solution was cooled to 0 0C after which a 1.5M solution of DiBAL-H in toluene (9.77 ml) was added. The resulting mixture was stirred at 0 0C for 45 minutes. After addition of 1M HCI (50 ml), the layers were separated and the organic fraction was dried on Na2SO4 and the solvents were evaporated. (Methoxycarbonylmethyl)triphenylphosphoπium bromide (4.87 g, 11.72 mmol) was dissolved in DCM (50 ml) and shaken gently with 2M NaOH (50 ml) for five minutes. The organic layer was dried on Na2SO4 and the solvent was evaporated. The ylid was then dissolved in dioxane (50 ml) and added to the crude lactol. The resulting mixture was stirred overnight at room temperature. After evaporation of the solvent and column chromatography (EtOAc/cyclohexane, 1/4 v/v), the product (3.63 g, 80%) was obtained as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) 0.72; [α]D -17.0 (c 0.91 , CHCI3); v 3445 (OH), 2109 (N3), 1727 (CO); δH (400 MHz, CDCI3) 0.11, 0.12 (6H, 2 x s, SiCW3J2), 0.93 (9H1 s, SiC(CHs)3), 2.75 (1H, d, OH, JQH.6 10.0 Hz), 3.71 (1H, app. t, H-5, J 9.0 Hz), 3.78 (3H, s, OCH3), 3.88-3.96 (4H, m, H-6, H-7, H-8a, H-8b), 4.52 (1 H, dd, H-4, J4,3 6.2 Hz, J4,5 8.8 Hz), 5.58 (1H, s, Ar-CH), 6.20 (1H, d, H-2, J2|3 15.8 Hz), 7.03 (1H, dd, H-3, J3,2 15.8 Hz, J3ι4 6.2 Hz), 7.37 (3H, m, ArH), 7.46 (2H, m, ArH); D0 (100 MHz, CDCI3) -5.4, -5.4 (Si(CHs)2), 18.3 (SiC(CHs)3), 25.9 (SiC(CHs)3), 51.8 (OCH3), 60.8 (C-4), 62.5 (C-8), 63.0, 79.8 (C-6, C-7), 81.1 (C-5), 101.1 (Ar-CH), 124.1 (C-2), 125.9, 128.2, 129.1, 137.0 (ArC), 142.6 (C-3), 166.1 (C=O).

4-Azido-5.7-0-ben2Vlidene-8-0-feff-butyldimethylsilyl-4-d eoxy-D-q/tJco-D-fhreo-octono-γ-lactone 2.6

Methyl 4-azido-5,7-O-benzylidene-6-O-terf-butyIdimethylsilyl-2,3,4- trideoxy-D-gu/o-oct-2-enoate 2.5 (2.32 g, 5.00 mmol) was dissolved in a mixture of tert-butanol (25 ml) and water (25 ml) and potassium ferricyanide (4.94, 15.0 mmol), potassium carbonate (2.07 g, 15.0 mmol), methanesulfonamide (476 mg, 5.00 mmol) and (DHQ)2PHAL (39 mg, 0.050 mmol) were added. The resulting mixture was stirred for 10 minutes at 0 0C, after which potassium osmate (18 mg, 0.050 mmol) was added. The reaction mixture was stirred overnight at 0 0C up to room temperature. Satd. NaHSO3 (25 ml) and EtOAc (50 ml) were added and the layers were separated. The aqueous layer was re-extracted with EtOAc (50 ml) and the combined organic fractions were dried on Na2SO4. Column chromatography (EtOAc/cyclohexane, 1/2 v/v) yielded the product (1.19 g, 48%) as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) 0.14; [α]D +7.3 (c 0.63, CHCI3); v 3446 (OH), 2116 (N3), 1740 (CO); δH (400 MHz, CDCI3) 0.11 , 0.12 (6H, 2 x s, Si(CH3)2), 0.93 (9H, s, SiC(CH3)3), 2.76 (1 H, d, 6-OH, J0H,6 9-6 Hz), 2.93 (1H, d, 2-OH, JOH,2 9.6 Hz), 3.19 (1H, d, 3-OH, JOH,3 4.8 Hz), 3.86 (3H, s, OCH3), 3.89-3.98 (4H, br. m, H-6, H- 7, H-8a, H-8b), 4.06 (2H, app. s, H-4, H-5), 4.23 (1H, dd, H-2, J2]3 3.2 Hz, J3,Λ 9.6 Hz), 4.39 (1H, app. t, H-3, J 4.0 Hz), 5.64 (1 H, s, Ar-CH), 7.38 (3H, m, ArH), 7.48 (2H, m, ArH); Dc (100 MHz, CDCI3) -5.4, -5.4 (Si(CHs)2), 18.3 (SiC(CH3)s), 25.8 (SiC(CHs)3), 53.2 (OCH3), 61.8 (C-4/5), 62.6 (C-8), 63.5 (C-6/7), 70.3 (C-2), 72.0 (C-3), 78.6 (C-4/5), 79.9 (C-6/7), 101.1 (Ar-CH), 126.0, 128.3, 129.2, 137.2 (ArC), 173.4 (C=O).

Methyl 4-azido-4-deoxy-2,3:5,6:7,8-tri-0-isopropylidene-D-q/oco-D-f hreo-octonate 2.7

4-Azido-5,7-O-benzylidene-8-O-terf-butyldimethylsilyl-4-d eoxy-D-g/uco-D-tf7reo-octono-γ-lactone 2.6 (1.17 g, 2.35 mmol) was dissolved in TFA (4.5 ml) and water (0.5 ml). This solution was stirred for three hours at room temperature, after which the solvents were evaporated to dryness. The residue was redissolved in a mixture of 2,2-dimethoxypropane (8.0 ml), acetone (2.8 ml) and methanol (1.8 ml). After addition of para-toluenesulfonic acid (50 mg), the reaction mixture was stirred overnight at 50 0C. Solid NaHCO3 was added to neutralize, and after filtration and evaporation column chromatography (EtOAc/cyclohexane, 1/3 v/v) afforded the product (240 mg, 25%) as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) 0.41 ; [α]D -41.4 (c 0.82, CHCI3); v 2113 (N3), 1763 (CO); δH (400 IVIHz, CDCI3) 1.39, 1.42, 1.45, 1.56 (18H, 4 x s, C(CH3J2J1 4.43 (1 H, dd, H-4, J4,3 3.0 Hz, J4|5 8.4 Hz), 3.80 (3H, s, OCH3), 3.94 (1H, app. t, H-8a, J 7.8 Hz), 4.09 (2H, m, H-8b, H-6), 4.28 (2H, m, H-5, H-7), 4.54 (1H, dd, H-3, J3|4 3.0 Hz, J3|2 7.6 Hz), 4.59 (1H, d, H-2, Jz,3 7.6 Hz); δc (100 MHz, CDCI3) 25.7, 26.2, 26.4, 27.1, 27.4 (C(CH3)2), 52.5 (OCH3), 62.7 (C-4), 66.0 (C-8), 75.0 (C-5/7), 75.9 (C-2), 76.2 (C-5/7), 78.6 (C-3), 79.4 (C-6), 109.7, 110.5, 112.0 (C(CHs)2), 170.6 (C=O).

Methyl 4-azido-8-tert-butyldimethylsilyl-4-deoxy-2,3:5,6-di-0-isopr opylidene-D-q/uco-D-^reo-octonate 2.8

Methyl 4-azido-4-deoxy-2,3:5,6:7,8-tri-0-isopropylidene-D-g/uco-D-t f7reo-octonate 2.7 (222 mg, 0.53 mmol) was dissolved in a mixture of acetic acid (5.0 ml), dioxane (2.5 ml) and water (2.5 ml). The resulting solution was stirred overnight at 50 0C after which the solvents were evaporated. The residue was redissolved in EtOAc (20 ml), washed with water (20 ml) and dried on Na2SO4. The solvent was evaporated and the residue was redissolved in pyridine (5.0 ml) after which TBS-CI (121 mg, 0.80 mmol) was added. The resulting mixture was stirred overnight at room temperature. The solvent was evaporated and the residue was redissolved in EtOAc (10 ml), washed with 1M HCI (10 ml), satd. NaHCO3 (10 ml) and brine (10 ml), and dried on Na2SO4. Column chromatography (EtOAc/cyclohexane, 1/4 v/v) yielded the product (164 mg, 63%) as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) 0.41 ; [α]D -45.4 (c 1.25, CHCI3); v 3445 (OH), 2113 (N3), 1756 (CO); δH (400 MHz, CDCI3) 0.06 (6H, s, Si(CW3J2), 0.89 (9H, s, SiC(CW3J3), 1.39, 1.41, 1.49 (12H, 3 x s, C(CWs)2), 2.33 (1H, s, OH, JOH,7 7.6 Hz), 3.46 (1H, dd, H-4, J4,3 3.4 Hz, J4|5 8.0 Hz), 3.63 (1 H, dd, H-8a, J8a,8b 10.0 Hz, JSaj 6.0 Hz), 3.70 (1H, dd, H-8b, J8b,8a 10.0 Hz, J8b,7 6.2 Hz), 3.77 (3H, s, OCH3), 3.79 (1 H, m, H-7), 4.18 (1H, dd, H-6, J6,? 2.0 Hz, J6,? 6.8 Hz), 4.31 (1H, app. t, H-5, J 7.6 Hz), 4.48 (1H, dd, H-3, J3,4 3.4 Hz, J3,2 7.6 Hz), 4.56 (1 H, d, H-2, J2,3 7.6 Hz); δc (100 MHz, CDCI3) -5.5, -5.4 (Si(CH3J2), 18.3 (SiC(CH3J3), 25.8 (SiC(CH3J3), 25.7, 26.4, 26.9, 27.0, 27.0 (C(CH3J2), 52.5 (OCH3), 63.0 (C-4), 64.6 (C-8), 70.0 (C-7), 75.7 (C-5), 75.9 (C-2), 78.6 (C-3), 79.1 (C-6), 110.0, 111.9 (C(CHs)2), 170.6 (C=O).

4-Azido-8-tert-butyldimethylsilyl-4-deoxy-2,3:5.6-di-0-is opropylidene-D-g/uco-D-f/7reo-octitol 2.9

Methyl 4-azido-4-deoxy-2,3:5,6-di-O-isopropylidene-D-g/uco-D-f/?reo -octonate 2.8 (147 mg, 0.30 mmol) was dissolved in THF (5.0 ml). The solution was cooled to 0 0C and a 2M solution of LiBH4 in THF (300 μl) was added. The resulting mixture was stirred for eight hours at room temperature, after which the solvent was evaporated. The residue was redissolved in DCM (10 ml), washed with satd. NH4CI (10 ml) and dried on Na2SO4. After column chromatography (EtOAc/cyclohexane, 1/1 v/v), the product (108 mg, 78%) was obtained as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) 0.23; [α]D -40.6 (c 0.69, CHCI3); v 3446 (OH), 2112 (N3); δH (400 MHz, CDCI3) 0.07 (6H, s, Si(CH3J2, 0.89 (9H, s, SiC(CW3J3), 0.41, 0.42, 0.44 (12H, 3 x s, C(CW3J2), 2.42 (2H, br. d, 1-OW, 7- OW, J 6.8 Hz), 3.43 (1H, dd, H-4, J4|5 3.9 Hz, J4,3 7.0 Hz), 3.63 (1 H, dd, H-8a, J8a,7 6.0 Hz, J8a,8b 10.0 Hz), 3.70 (2H, m, H-8b, H-1a), 3.81 (2H, m, H-1b, H-7), 4.14 (1H, dd, H-5, JBA 3.9 Hz, J5,β 8.0 Hz), 4.18 (2H, m, H-2, H- 6), 4.24 (1H, app. t, H-3, J 7.2 Hz); δc (100 MHz, CDCI3) -5.4, -5.3 (Si(CH3)2), 18.3 (SiC(CH3)3), 25.9 (SiC(CHs)3), 26.8, 27.0, 27.1, 27.2 (C(CH3)2), 61.9 (C-1), 63.7 (C-4), 64.8 (C-8), 69.9 (C-7), 76.1 (C-5), 77.7 (C- 3), 78.2, 78.6 (C-2, C-6).

4-Azido-8-fe/f-butyldimethylsilyl-4-deoxy-2.3:5,6-di-O-is opropylidene-1 ,7-di-O-methanesulphonyl-D-q/uco-D- f/7reo-octitol 2.10

4-Azido-8-terf-butyldimethylsilyl-4-deoxy-2,3:5,6-di-0-is opropylidene-D-g/uco-D-f/7reo-octitol 2.9 (100 mg, 0.22 mmol) and DMAP (2.7 mg, 0.022 mmol) were dissolved in pyridine (5.0 ml). After cooling to 0 0C, methanesulphonyl chloride (136 μl, 1.76 mmol) was added and the resulting mixture was stirred overnight at room temperature. The solvent was evaporated and the residue was redissolved in EtOAc (5 ml), washed with 1M HCI (5 ml), satd. NaHCO3 (5 ml), water (5 ml) and brine (5 ml), and dried on Na2SO4. Column chromatography (EtOAc/cyclohexane, 1/2 v/v) afforded the product (108 mg, 79%) as a clear, light yellow oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) 0.33; [α]D -33.0 (σ 0.78, CHCI3); v 2113 (N3), 1360 (OSO2), 1175 (OSO2); δH (400 MHz, CDCI3) 0.07, 0.10 (6H, 2 x s, Si(CH3)2), 0.90 (9H, s, SiC(CH3)3), 1.40, 1.41 (6H, 2 x s, C(CH3)2), 3.08 (3H, s, SCH3), 3.11 (3H, s, SCH3), 3.83 (2H, m, H-4, H-8a), 3.98 (1 H, dd, H-8b, J8b,sa 112 Hz, J8.,? 8.0 Hz), 4.11 (1H, dd, H-3/5, J 2.6 Hz, J 7.8 Hz), 4.29-4.37 (5H, m, H-2, H-3/5, H-6, H-1a, H-1b), 5.01 (1 H, app. dd, H-7, J 4.0 Hz, J 8.4 Hz); δc (100 MHz, CDCI3) -5.6, -5.3 (Si(CH3)2), 18.4 (SiC(CHs)3), 25.8 (SiC(CH3)3), 26.5, 26.7, 26.9, 26.9 (C(CHa)2), 37.7, 38.8 (SCH3), 61.7 (C-4), 63.8 (C-8), 67.9, 75.6, 76.1 , 76.4 (C-2, C-3, C-5, C-6), 77.8 (C-1), 81.1 (C-7), 110.2, 110.6 (C(CHs)2).

6.7-tf/epAcasuarine 2.11

4-Azido-8-ferf-butyldimethyIsilyl-4-deoxy-2,3:5,6-di-0-is opropylidene-1 ,7-di-0-methanesulphonyl-D-g/t/co-D- fftreo-octitol 2.10 (100 mg, 0.16 mmol) was dissolved in a mixture of TFA (1.8 ml) and water (0.2 ml) and stirred for three hours at room tempature. The solvents were evaporated and the residue redissolved in a mixture of dioxane (1.0 ml) and water (1.0 ml). After addition of 10% palladium on carbon (10 mg), the mixture was stirred overnight at room temperature under a hydrogen atmosphere. Then, the reaction mixture was filtered over celite® and the solvents were removed by evaporation. The crude product was redissolved in water (2.0 ml) and sodium acetate (39 mg, 0.48 mmol) was added. The resulting solution was stirred overnight at 50 0C. After evaporation of the solvent, the crude material was subjected to ion exchange chromatography (Amberlyst CG120-H+) and eluted with 2M ammonia yielding the product (23.9 mg, 73%) as a brown solid.

[α]D +8.0 (c 0.70, H2O) {Lit. [α]D +8.4 (c 0.89, H2O)[I]); δH (400 MHz, D2O) 2.62 (1 H, m, H-3), 2.80 1H, dd, H-5a, Jsa.sb 12.0 Hz, Jsa.s 4.0 Hz), 2.95 (1H, app. d, H-5b, J5b,5a 12.0 Hz), 3.31 (1H, dd, H-7a, JTaj 3.6 Hz, J7s,i 7.2 Hz), 3.50 (1H, dd, H-8a, Jβa.sb 11.8 Hz, J8a,3 6.6 Hz), 3.69 (1H, dd, H-8b, J8b,8a 11.8 Hz, J8b,3 3.4 Hz), 3.81 (1H, app. t, H-2, J 8.6 Hz), 4.04 (1H, br. s, H-7), 4.18 (1H, app. t, H-1 , J 7.6 Hz), 4.23 (1H, br. s, H-6); δc (100 MHz, D2O) 58.6 (C-5), 62.9 (C-8), 69.2 (C-7a), 71.1 (C-3), 73.2 (C-1), 74.2 (C-7), 77.8 (C-6), 79.1 (C-2). Example 12 Synthesis of L-casuarine

Scheme 3 reagents and conditions ι) (DHQD)2-PHAL (1%), K2OsO4 (1%), MeSO2NH2, K3Fe(CN)6, K2CO3, fBu- OH H2O (1 1) H) 1 TFA H2O (9 1), 2 2,2-DMP, MeOH, acetone, PTSA (cat ), 50 0C in) 1 HOAc H2O dioxane (2 1 1), 50 0C IV) LiBH4 (2M in THF), THF, 0 0C - RT v) MsCI1 DMAP (cat ), pyridine vι) 1 TFA H2O (9 1), 2 H2, 10% Pd/C, dioxane H2O (1 1), 3 NaOAc, H2O, 50 0C

Methyl 4-azιdo-5,7-0-benzylιdene-8-0-terf-butyldιmethylsιlyl-4- deoxy-D-f/?reo-D-atfro-octonate 3 1

Potassium carbonate (3 24 g, 23 46 mmol), K3Fe(CN)β (7 72 g, 23 46 mmol), methane sulfonamide (744 mg, 7 82 mmol), (DHQD)2-PHAL (183 mg, 3%) and potassium osmate (86 mg, 3%) were suspended in a mixture of terf-butanol (40 ml) and water (40 ml) After cooling to O 0C and stirring for 10 minutes, a solution of methyl 4- azido-5,7-O-benzylidene-6-O-ferf-butyldimethylsilyl-2,3,4-tn deoxy-D-gu/o-oct-2-enoate 2.5 (3 63 g, 7 82 mmol) in dichloromethane (4 O ml) was added dropwise The resulting mixture was stirred for 4 hours at O 0C Satd Na2SO3 (20 ml) was added, and the crude product was extracted with EtOAc (100 ml) The organic fraction was dried on Na2SO4 and subjected to column chromatography (EtOAc/cyclohexane 1/2 v/v) to afford the product (2 21 g, 57%) as a white foam

Rf (EtOAc/cyclohexane, 1/2 v/v) = 0 19, [α]D -15 0 (c 041 g/100 ml, CHCI3), v 3474 (OH), 2116 (N3), 1746 (C=O), δH (400 MHz, CDCI3) ???, Dc (100 MHz, CDCI3) -5 4, -54 (Si(CH3J2), 184 (SιC(CH3)3), 25 8 (Si(C(CH 3)3), 52 8 (OCH3), 61 7 (C-4), 63 7 (C-8), 71 2 (C-2), 73 6 (C-3), 80 0, 824 (C-5, C-7), 101 6 (Ar-CH), 126 0, 1284, 129 5, 136 6 (ArC), 173 2 (C=O) Methyl 4-azido-4-deoxy-2.3:5,6:7.8-tri-0-isopropylidene-D-tf)reo-D- a/fr-o-octonate 3.2

Methyl 4-azido-5,7-0-beπzylidene-8-0-terf-butyldimethylsilyl-4-deo xy-D-fftreo-D-a#ro-octoπate 3.1 (2.21 g, 4.44 mmol) was dissolved in a mixture of TFA (4.5 ml) and water (0.5 ml) and stirred for three hours at room temperature. Then, the solvents were evaporated and the residue was dried in vacuo and redissolved in a mixture of 2,2-DMP (16 ml), acetone (5.6 ml) and methanol (3.6 ml). After addition of camphor sulfonic acid (100 mg), the mixture was stirred for 48 hours at 50 0C. Solid NaHCC>3 was added to neutralize the acid and after filtration the solvents were evaporated. Column chromatography (EtOAc/cyclohexane, 1/3 v/v) yielded the product (1.16 g, 63 %) as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/2 v/v)=0.45; [α]D +25.7 (c 0.93 g/100 ml, CHCI3); v 2111 (N3), 1745 (C=O); δH (400 MHz, CDCI3) 1.39, 1.40, 1.42, 1.44, 1.46, 1.54 (18H, 6 x s, C(CHs)2), 1.39 (3H, s, OCH3), 3.91-4.02 (4H, br. m, H-4, H-5, H-6, H-8a), 4.07 (1H, app. t, H-8b, J 7.6 Hz), 4.22 (1 H, app. dt, H-7, J 3.3 Hz, J 6.9 Hz), 4.58 (1 H, dd, H-3, J3,4 3.2 Hz, J3|2 6.8 Hz), 4.64 (1 H, d, H-2, J2|3 6.8 Hz); δc (100 MHz, CDCI3) 25.4, 25.7, 26.2, 26.5, 26.8, 27.2 (C(CHs)2), 52.5 (OCH3), 64.3 (C-4), 66.1 (C-8), 75.1 (C-5/6), 75.1 (C-7), 75.2 (C-2), 79.2 (C-3), 79.9 (C- 5/6), 109.7, 110.3, 111.9 (C(CHs)2), 171.3 (C=O).

Methyl 4-azido-8-tert-butyldimethylsilyl-4-deoxy-2.3:5,6-di-0-isopr opylidene-D-atfro-D-f/;reo-octonate 3.3

Methyl 4-azido-4-deoxy-2,3:5,6:7,8-tri-0-isopropylidene-D-a/frø-D- fftreo-octonate 3.2 (1.05 mg, 2.52 mmol) was dissolved in a mixture of acetic acid (5.0 ml), H2O (2.5 ml) and dioxane (2.5 ml), which was stirred overnight at 5O0C. The solvents were evaporated and the residue was redissolved EtOAc (10 ml), washed with satd. NaHCO3 (10 ml) and dried on Na2Sθ4. The crude diol was dissolved in pyridine (10 ml) after which TBS-CI (455 mg, 3.02 mmol) was added. The resulting mixture was stirred overnight at room temperature. After evaporation of the solvent, the crude product was redissolved in EtOAc (25 ml) and washed with 1M HCI (25 ml), satd. NaHCO3 (25 ml) and brine (25 ml). The organic fraction was dried on Na2Sθ4 and purified by column chromatography (EtOAc/cyclohexane, 1/3 v/v), yielding the product (990 mg, 81%) as a clear, colourless oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) = 0.37; δH (400 MHz, CDCI3) 0.09 (6H, s, Si(CH3)2), 0.91 (9H, s, SiC(CHs)3), 0.40, 0.42, 0.46, 0.54 (12H, 4 x s, C(CH3)2), 2.30 (1H, d, OH, J0H1? 8.0 Hz), 3.63 (1H, dd, H-8a, J8a,8b 9.4 Hz, Jβa,7 6.6 Hz), 3.70-3.80 (2H, m, H-7, H-8b), 3.78 (3H, s, OCH3), 3.93 (1H, dd, H-4, J4,3 3.6 Hz, J4,5 7.8 Hz), 4.07 (1H, app. t, H-5, J 7.8 Hz), 4.13 (1H, br. d, H-6, J6,5 7.8 Hz), 4.56 (1H, dd, H-3, _/3,4 3.6 Hz, J3,2 6.1 Hz), 4.63 (1 H, d, H-2, J2,s 6.1 Hz); δc (100 MHz, CDCI3) -5.4, -5.4 (Si(CH3)2), 18.3 (SiC(CHs)3), 25.5, 26.6, 26.8, 27.0 (C(CHs)2), 25.8 (SiC(CH3)s), 52.5 (OCH3), 64.5 (C-8), 64.6 (C-4), 69.9 (C-7), 74.4 (C-5), 75.3 (C-2), 79.1 (C-3), 79.2 (C-6), 110.0, 111.9 (C(CHs)2), 171.3 (C=O).

4-Azido-8-terf-butyldimethylsilyl-4-deoxy-2.3:5,6-di-0-is opropylidene-D-atfrø-D-f/7Λeo-octitol 3.4

Methyl 4-azido-8-tert-butyldimethylsilyl-4-deoxy-2,3:5,6-di-0-isopr opylidene-D-a/fro-D-f/7reo-octonate 3.3 (877 mg, 1.79 mmol) was dissolved in THF (5 ml) and cooled to O0C. After dropwise addition of a 2M solution of LiBH4 in THF (1.79 ml), the reaction mixture was allowed to stir overnight at O0C up to room temperature. After adding 1M HCI (10 ml) cautiously, the product was extracted with DCM (2 x 10 ml). The organic fraction was dried on Na2SO4 and after purification by column chromatography (EtOAc/cyclohexane, 1/2 v/v) the product (683 mg, 83%) was obtained as a clear colourless oil.

Rf (EtOAc/cyclohexane, 1/1 v/v) = 0.27; δH (400 MHz, CDCI3) 0.09 (6H, s, Si(CH3)2), 0.91 (9H, s, SiC(CH3)s), 1.43, 1.46, 1.48 (12H, 3 x s, C(CH3)2), 2.10 (1 H, br. t, 1-OH, J 6.6 Hz), 2.33 (1H, d, 7-OH, JOHJ 7.6 Hz), 3.62- 3.75 (4H, br. m, H-1a, H-7, H-8a, H-8b), 3.85 (1 H, br. m, H-1b), 3.92 (1H, app. t, H-4, J 6.4 Hz), 4.01 (1H, app. t, H-5, J 6.8 Hz), 4.09 (1 H, app. t, H-3, J 7.4 Hz), 4.19 (2H, m, H-2, H-6); δc (100 MHz, CDCI3) -5.4, -5.4 (Si(CHs)2), 18.2 (SiC(CHa)3), 25.8 (SiC(CHs)3), 26.7, 26.9, 26.9, 27.1 (C(CHs)2), 63.0 (C-1), 64.4 (C-8), 64.5 (C- 4), 69.9 (C-7), 75.4 (C-3), 76.2 (C-5), 78.3, 78.9 (C-2, C-6), 109.9, 110.1 (C(CHs)2).

4-Azido-8-ferf-butyldimethylsilyl-4-deoxy-2,3:5,6-di-0-is opropylidene-1,7-di-Q-methanesulfonyl-D-atfro-D-f/7reo- octitol 3.5

4-Azido-8-tert-butyldimethylsilyl-4-deoxy-2,3:5,6-di-0-is opropylidene-D-a/fro-D-fΛreo-octitol 3.4 (666 mg, 1.44 mmol) was dissolved in pyridine (5 ml) and cooled to O0C after which mesyl chloride (893 μl, 11.52 mmol) and DMAP (35 mg, 0.29 mmol) were added. The resulting mixture was stirred overnight at room temperature. The solvent was evaporated, after which the residue was redissolved in EtOAc (20 ml) and washed with 1M HCl (20 ml), satd. NaHCO3 (20 ml) and brine (20 ml). After drying on Na2SO4, column chromatography (EtOAc/cyclohexane, 1/2 v/v) yielded the product (928 mg, 100%) as a clear, light yellow oil.

Rf (EtOAc/cyclohexane, 1/2 v/v) = 0.39; δH (400 MHz, CDCI3) 0.10, 0.12 (6H, 2 x s, Si(CHs)2), 0.92 (9H, s, SiC(CHs)3), 1.42, 1.44, 1.50 (12H, 3 x s, C(CHs)2), 3.08, 3.12 (6H, 2 x s, SO2CH3), 3.86 (1 H, dd, H-8a J8a,8b10.6 Hz, J8a,7 5.8 Hz), 3.98 (3H, m, H-8b, H-4, H-5), 4.14 (1 H, dd, H-3, J 4.6 Hz, J 7.4 Hz), 4.28 (2H, m, H-6, H-1a), 4.38 (1H, m, H-2), 4.47 (1H, dd, H-1b Ju,2 2.4 Hz, J1a,1b 11.2 Hz), 4.77 (1H, app. t, H-7, J 5.6 Hz); δc (400 MHz, CDCI3) -5.5, -5.4 (Si(CH3)2), 18.3 (SiC(CHs)3), 25.8 (SiC(CH3)3), 26.6, 26.7, 26.7, 26.9, 27.1 (C(CH3)2), 37.6, 38.7 (SO2CH3), 62.6 (C-8), 63.9 (C-4/5), 69.4 (C-1), 74.6 (C-4/5), 75.7 (C-2), 76.1 (C-3), 77.5 (C-6), 79.9 (C-7), 110.8, 111.0 (C(CHs)2).

L-Casuarine 3.6

4-Azido-8-tert-butyldimethylsilyl-4-deoxy-2,3:5,6-di-O-is opropylidene-1,7-di-O-methanesulfonyl-D-a/fro-D-f/7Λeo- octitol 3.5 (909 mg, 1.47 mmol) was dissolved in a mixture of TFA (3.6 ml) and H2O (0.4 ml) and the resulting solution was stirred for 2 hours at room temperature. The solvents were evaporated and the residue was redissolved in H2O (2 ml) and dioxane (2 ml). After addition of 10% Pd/C (10 mg), the mixture was stirred overnight under a hydrogen atmosphere. After filtration over Celite®, the solvents were evaporated. The crude deprotected material was dissolved in water (5 ml) and NaOAc (362 mg, 4.41 mmol) was added. After stirring for 24 hours at 5O0C, the solvent was evaporated and the crude material was subjected to ion exchange chromatography (Dowex 50X8-H+, elution with 2M NH4OH) to afford the product (200 mg, 66%) as a brown oil.

δH (400 MHz, D2O) 3.01 (1H, dd, H-5), 3.17 (2H, m, H-3, H-7a), 3.37 (1 H, dd, H-51), 3.70 (1H, dd, H-8), 3.87 (2H, m, H-2, H-81), 4.28 (3H, H-1, H-6, H-7); δc (100 MHz, D2O) 58.7 (C-5), 62.7 (C-8), 70.7 (C-3), 73.0 (C-7a), 76.6 (C-2), 77.7 (C-6), 78.0 (C-1), 79.3 (C-7). Equivalents

The foregoing description details presently preferred embodiments of the present invention. Numerous modifications and variations in practice thereof are expected to occur to those skilled in the art upon consideration of these descriptions. Those modifications and variations are intended to be encompassed within the claims appended hereto.