BACKGROUND OF THE INVENTION

Substituted 1,2,3-aminodiols are used as intermediates in the synthesis of biologically active renin inhibitors. Of particular interest is [2S- (2R*,3S*,4R*) ] -2-amino-1-cyclohexyl-6-methyl-3,4- heptanediol which has been utilized as a key intermediate in the synthesis of biologically active renin inhibitors as disclosed in J. R. Luly, et al, Journal of Medicinal Chemistry 31:2264-2276 (1988); J. J. Plattner, et al, Journal of Medicinal Chemistry 31:2277-2288 (1988); G. J. Hanson, et al, Biochemical and Biophysical Research Communications 160:1-5 (1989) ; H. L. Sham, et al, Journal of Chemical Society. Chemical Communications 666-667 (1990) ; T. D. Ocain and M. Abou-Gharbia, Druσs of the Future 16:37-51 (1991); and . R. Baker and S. C. Condon, Tetrahedron Letters 33:1577-1580 (1992).

Renin is a proteolytic enzyme synthesized and stored principally in the juxtaglomerular apparatus of the kidney. Inhibitors of renin are useful for treating renin-associated hypertension, congestive heart failure, glaucoma, hyperaldosteronism, diseases caused by retroviruses including HTLV I, II, and III, as well as diagnostic tools for determining the presence of renin-associated hypertension or hyperaldosteronism. Many of the renin inhibitors under development as antihypertensive agents use substituted 1,2,3-aminodiols such as [2S- (2R*,3S*,4R*) ] -2-amino-l- cyclohexyl-6-methyl-3,4-heptanediol as their C-terminal component.

J. R. Luly, et al, Journal of Medicinal Chemistry 31:2264-2276 (1988) disclosed a process for preparing

[2S- (2R*,3S*,4R*) ] -2-amino-1-cyclohexyl-6-methyl-3,4- heptanediol involving a multi-step synthesis which proceeded in low yield. This process suffers from several major disadvantages besides the low yield. The process utilizes a ittig reaction step using isoamyltriphenylphosphonium bromide, a very expensive reagent. This step results in a mixture of diastereomers and a byproduct that is expensive to dispose as waste. Also, the process requires osmium tetroxide which is highly toxic, expensive, and undesirable to use in a large-scale synthesis. Additionally, the overall process proceeds in low yield particularly as a result of the isolation and purification of the correct diastereomer from the reaction mixture.

Other investigators have sought to overcome the disadvantages associated with the osmylation oxidation process (J. R. Luly, Journal of Organic Chemistry 53:6109-6112 (1988); J. L. Wood, et al, Tetrahedron Letters 31:6329-6330 (1990); W. R. Baker and

S. L. Condon, Tetrahedron Letters 33:1581-1584 (1992); and M. F. Chan and C.-N. Hsiao, 203rd National American Chemical Society Meeting Organic Chemistry Division. Abstract 464 (April 1992)). Thus, we have surprisingly and unexpectedly found an improved process to prepare substituted 1,2,3- aminodiols and in particular [2S- (2R*,3S*,4R*) ] -2- amino-1-cyclohexyl-6-methyl-3,4-heptanediol. This process is accomplished in a series of reactions joining two inexpensive fragments in a stereochemically controlled manner which results in a high overall yield of highly enriched diastereomerically pure material.

The object of the present invention is an improved process for preparing substituted 1,2,3-aminodiols by using a novel synthetic scheme. The present method utilizes inexpensive starting materials, requires minimal purifications of intermediates, and affords

higher yields compared to the previous method. In addition the present process avoids the use of expensive and toxic osmium tetroxide and phosphonium Wittig reagents. The chemistry of the new process is more amenable to large-scale production and unexpectedly reduces the overall cost significantly compared to the previously mentioned osmylation method.

SUMMARY OF THE INVENTION

Accordingly, a first aspect of the present invention is an improved process for the preparation of a highly diastereomerically enriched compound of Formula I

and pharmaceutically acceptable acid addition salts thereof wherein R is hydrogen or a nitrogen atom protecting group; R ¹ is alkyl, arylalkyl, or cycloalkylmethyl; and R ³ is alkyl or arylalkyl, which comprises:

(a) treating a highly enantiomerically enriched compound of Formula VI

wherein R ^a is a nitrogen atom protecting group and R ¹ is as defined above with a cyanide reagent in a solvent to afford by crystallization a diastereomerically pure compound of Formula V

wherein R ^a and R ¹ are as defined above; (b) treating a compound of Formula V with an acid to afford a highly diastereomerically enriched compound of Formula IV

•HX

wherein X is a halogen or HS0 ₄ and R ¹ is as defined above;

(c) treating a compound of Formula IV with a base followed by a nitrogen atom protecting reagent to afford a highly diastereomerically enriched compound of Formula III

wherein R ^a and R ¹ are as defined above; (d) treating a compound of Formula III with a compound of formula

R ² -H

wherein R ² is NR|, wherein R ⁵ is alkyl or -CH ₂ -aryl or a carboxylic acid activating group to afford a highly diastereomerically enriched compound of Formula Ilia

wherein R ^a , R ¹ , and R ² are as defined above;

(e) treating either a compound of Formula III or Formula Ilia with a compound of Formula VII

R ³ -M VII

wherein M is lithium, MgX ^a , or MgR ³ wherein X ^a is a halogen and R ³ is as defined above in a solvent to afford a diastereomerically enriched compound of Formula II

wherein R ^a , R ¹ , and R ³ are as defined above; (f) treating a compound of Formula II with a reducing metal hydride in a solvent to afford a highly diastereomerically enriched compound of Formula la

wherein R ^a , R ¹ , and R ³ are as defined above;

(g) treating a compound of Formula la in which R ^a is a carbamate nitrogen atom protecting group with a base to afford a highly diastereomerically enriched compound of Formula lb

wherein R ¹ and R ³ are as defined above; and (h) treating a compound of Formula la or a compound of Formula lb with a deprotecting reagent in a solvent to afford a highly diastereomerically enriched compound of Formula I.

A second aspect of the present invention is an improved process for the preparation of a diastereomerically enriched compound of Formula II

wherein R ^a is a nitrogen atom protecting group; R ¹ is alkyl, arylalkyl, or cycloalkylmethyl; and R ³ is alkyl or arylalkyl, which comprises:

(a) treating a highly enantiomerically enriched compound of Formula VI

wherein R ^a and R ¹ are as defined above with a cyanide reagent in a solvent to afford by crystallization a diastereomerically pure compound of Formula V

wherein R ^a and R ¹ are as defined above;

(b) treating a compound of Formula V with an acid to afford a highly diastereomerically enriched compound of Formula IV

wherein X is a halogen or HS0 ₄ and R ¹ is as defined above;

(c) treating a compound of Formula IV with a base followed by a nitrogen atom protecting reagent to afford a highly diastereomerically enriched compound of Formula III

wherein R ^a and R ¹ are as defined above;

(d) treating a compound of Formula III with a compound of formula

R ² -H

wherein R ² is NR|, wherein R ⁵ is alkyl or -CH ₂ -aryl or a carboxylic acid activating group to afford a highly diastereomerically enriched compound of Formula Ilia

wherein R ^a , R ¹ , and R ² are as defined above; and (e) treating either a compound of Formula III or Formula Ilia with a compound of Formula VII

R ^J -M VII

wherein M is lithium, MgX ^a , or MgR ³ wherein X ^a is a halogen and R ³ is as defined above in a solvent to afford a diastereomerically enriched compound of Formula II.

A third aspect of the present invention is an improved process for the preparation of a highly diastereomerically enriched compound of Formula Ilia

wherein R ^a is a nitrogen atom protecting group, R ¹ is alkyl, arylalkyl, or cycloalkylmethyl and R ² is NR ,

wherein R ⁵ is alkyl or -CH ₂ -aryl or a carboxylic acid activating group which comprises: (a) treating a highly enantiomerically enriched compound of Formula VI

wherein R ^a and R ¹ are as defined above with a cyanide reagent in a solvent to afford by crystallization a diastereomerically pure compound of Formula V

wherein R ^a and R ¹ are as defined above;

(b) treating a compound of Formula V with an acid to afford a highly diastereomerically enriched compound of Formula IV

wherein X is a halogen or HS0 ₄ and R ¹ is as defined above;

(c) treating a compound of Formula IV with a base followed by a nitrogen atom protecting reagent to afford a highly diastereomerically enriched compound of Formula III

wherein R ^a and R ¹ are as defined above; and

(d) treating a compound of Formula III with a compound of formula

R ² -H

wherein R ² is as defined above to afford a highly diastereomerically enriched compound of Formula Ilia.

A fourth aspect of the present invention is an improved process for the preparation of a highly diastereomerically enriched compound of Formula III

wherein R ^a is a nitrogen atom protecting group, and R ¹ is alkyl, arylalkyl, or cycloalkylmethyl, which comprises:

(a) treating a highly enantiomerically enriched compound of Formula VI

wherein R ^a and R ¹ are as defined above with a cyanide reagent in a solvent to afford by crystallization a diastereomerically pure compound of Formula V

wherein R ^a and R ¹ are as defined above; (b) treating a compound of Formula V with an acid to afford a highly diastereomerically enriched compound of Formula IV

•HX

wherein X is a halogen or HS0 ₄ and R ¹ is as defined above; and (c) treating a compound of Formula IV with a base followed by a nitrogen atom protecting reagent to afford a highly diastereomerically enriched compound of Formula III.

A fifth aspect of the present invention is an improved process for the preparation of a highly diastereomerically enriched compound of Formula IV

•HX

wherein X is a halogen or HS0 ₄ and R ¹ is alkyl, arylalkyl, or cycloalkylmethyl which comprises: (a) treating a highly enantiomerically enriched compound of Formula VI

wherein R ^a is a nitrogen atom protecting group and R ¹ is as defined above with a cyanide reagent in a solvent to afford by crystallization a diastereomerically pure compound of Formula V

wherein R ^a and R ¹ are as defined above; and

(b) treating a compound of Formula V with an acid to afford a highly diastereomerically enriched compound of Formula IV.

A sixth aspect of the present invention is an improved process for the preparation of a diastereomerically pure compound of Formula V

wherein R ^a is a nitrogen atom protecting group, and R ¹ is alkyl, arylalkyl, or cycloalkylmethyl, which comprises treating a highly enantiomerically enriched compound of Formula VI

wherein R ^a and R ¹ are as defined above with a cyanide reagent in a solvent to afford by crystallization a diastereomerically pure compound of Formula V.

A seventh aspect of the present invention is an improved process for the preparation of a highly diastereomerically enriched compound of Formula I

and pharmaceutically acceptable acid addition salts thereof wherein R is hydrogen or a nitrogen atom protecting group; R ¹ is alkyl, arylalkyl, or cycloalkylmethyl; and R ³ is alkyl or arylalkyl, which comprises:

(a) treating a highly diastereomerically enriched compound of Formula IVa

or pharmaceutically acceptable acid addition salts thereof wherein R ¹ is as defined above with a nitrogen atom protecting reagent to afford a highly diastereomerically enriched compound of Formula III

wherein R ^a is a nitrogen atom protecting group and R ¹ is as defined above;

(b) treating a compound of Formula III with a compound of formula

R ² -H

wherein R ² is NR , wherein R ⁵ is alkyl or -CH ₂ -aryl or a carboxylic acid activating group to afford a highly diastereomerically enriched compound of Formula Ilia

wherein R ^a , R ¹ , and R ² are as defined above;

(c) treating either a compound of Formula III or Formula Ilia with a compound of Formula VII

R ³ -M VII

wherein M is lithium, MgX ^a , or MgR ³ wherein X ^a is a halogen and R ³ is as defined above in a solvent to afford a diastereomerically enriched compound of Formula II

wherein R ^a , R ¹ , and R ³ are as defined above; (d) treating a compound of Formula II with a reducing metal hydride in a solvent to afford a highly diastereomerically enriched compound of Formula la

wherein R ^a , R ¹ , and R ³ are as defined above; (e) treating a compound-of Formula la in which R ^a is a carbamate nitrogen atom protecting group with a base to afford a highly diastereomerically enriched compound of Formula lb

wherein R ¹ and R ³ are as defined above; and

(f) treating a compound of Formula la or a compound of Formula lb with a deprotecting reagent in a solvent to

afford a highly diastereomerically enriched compound of Formula I.

DETAILED DESCRIPTION OF THE INVENTION

In this invention, the term "alkyl" means a straight or branched hydrocarbon group having from 1 to 12 carbon atoms and includes, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, undecyl, dodecyl, and the like.

The term "cycloalkyl" means a saturated hydro- carbon ring which contains from 3 to 12 carbon atoms, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, adamantyl, and the like.

The term "cycloalkylmethyl" means a saturated hydrocarbon ring attached to a methyl group. The saturated hydrocarbon ring contains from 3 to 12 carbon atoms. Examples of such are cyclopropylmethyl, cyclopentylmethyl, cyclohexylmethyl, adamantylmethyl, and the like.

The terms "alkoxy" and "thioalkoxy" are 0-alkyl or S-alkyl as defined above for alkyl.

The term "aryl" means an aromatic group which is a phenyl group, unsubstituted or substituted by 1 to 4 substituents selected from alkyl as defined above, alkoxy as defined above, thioalkoxy as defined above,

-NH-A wherein A is an alkyl group as defined above or a nitrogen atom protecting group as defined hereinafter, -N-A wherein A is as defined above,

A -N-alkyl wherein R ^a is a nitrogen atom protecting

R ^a group and alkyl is as defined above.

The term "arylalkyl" means an aryl group as defined above attached to an alkyl group as defined above.

The term "acyl" means an alkyl group as defined above attached to a carbonyl group which is attached to the parent molecular residue, for example acetyl, pivaloyl, and the like.

The term "aroyl" means an aryl group as defined above attached to a carbonyl group, for example benzoyl, and the like.

The term "alkali metal" is a metal in Group IA of the periodic table and includes, for example, lithium, sodium, potassium, and the like.

The term "alkaline-earth metal" is a metal in Group IIA of the periodic table and includes, for example, calcium, magnesium, and the like.

"Halogen" is fluorine, chlorine, bromine, or iodine.

The term "nitrogen atom protecting group" means those groups used to protect nitrogen atoms against undesirable reactions during synthetic procedures such as an acyl group, for example, acetyl, pivaloyl, and the like; an aroyl group, for example, benzoyl, and the like; a carbamate group, for example, tertiary butyloxycarbonyl, ethyloxycarbonyl, benzyloxycarbonyl, and the like.

The term "carboxylic acid activating group" means a substituent which augments the electrophilic character of the carboxyl carbon atom such as, for example, anhydrides, activated esters, methoxy methyl amides, imidazole amides, and the like.

The term "diastereomerically pure compound" means a compound consisting of at least 95% of a single diastereomer as determined using conventional nuclear magnetic resonance (NMR) methodology for single diastereomer analysis.

The term "highly diastereomerically enriched compound" means a compound consisting of not less than 90% [area % high performance liquid chromatography (HPLC) ] of a single diastereomer and not more than 2% (area % of chiral HPLC) of another diastereomer. The term "highly enantiomerically enriched compound" means a compound consisting of not less than 90% (area % HPLC) of a single enantiomer and not more than 2% (area % chiral HPLC) of another enantiomer. The term "diastereomerically enriched compound" means a compound that can be expressed in a % term of more of one diastereomer than the other diastereomer(s) .

A compound of Formula I is capable of further forming a pharmaceutically acceptable acid addition salt. All of these forms are within the scope of the present invention.

Pharmaceutically acceptable acid addition salts of a compound of Formula I include salts derived from nontoxic inorganic acids such as hydrochloric, nitric, phosphoric, sulfuric, hydrobromic, hydriodic, phosphorous, and the like, as well as the salts derived from nontoxic organic acids such as aliphatic mono- and dicarboxylic acids, phenyl-substituted alkanoic acids, hydroxy alkanoic acids, alkanedioic acids, aromatic acids, aliphatic and aromatic sulfonic acids, etc. Such salts thus include sulfate, pyrosulf te, bisulfate, sulfite, bisulfite, nitrate, phosphate, monohydrogenphosphate, dihydrogenphosphate, metaphosphate, pyrophosphate, chloride, bromide, iodide, acetate, propionate, caprylate, isobutyrate, oxalate, malonate, succinate, suberate, sebacate, fumarate, maleate, mandelate, benzoate, chlorobenzoate, methylbenzoate, dinitrobenzoate, phthalate, benzenesulfonate, toluenesulfonate, phenylacetate, citrate, lactate, maleate, tartrate, methanesulfonate, and the like. Also contemplated are salts of amino

acids such as arginate and the like and gluconate and galacturonate (see, for example, S. M. Bergs, et al, "Pharmaceutical Salts," Journal of Pharmaceutical Science 66:1-19 (1977)). The acid addition salts of said basic compounds are prepared by contacting the free base form with a sufficient amount of the desired acid to produce the salt in the conventional manner. The free base form may be regenerated by contacting the salt form with a base and isolating the free base in the conventional manner. The free base forms differ from their respective salt forms somewhat in certain physical properties such as solubility in polar solvents, but otherwise the salts are equivalent to their respective free bases for purposes of the present invention.

Certain of the compounds of the present invention can exist in unsolvated forms as well as solvated forms, including hydrated forms. In general, the solvated forms, including hydrated forms, are equivalent to unsolvated forms and are intended to be encompassed within the scope of the present invention. Certain of the compounds of the present invention possess one or more chiral centers and each center may exist in the R(D) or S(L) configuration. The present invention is a stereoselective synthetic method to prepare diastereomerically pure, highly diastereo¬ merically enriched and diastereomerically enriched compounds.

The process of the present invention is a new, improved, economical,and commercially feasible method for preparing highly diastereomerically enriched substituted 1,2,3-aminodiols.

The process of the present invention is outlined in the following Scheme I:

SCHEME I

VI V IV

lb

A diastereomerically pure compound of Formula V wherein R ¹ is alkyl, arylalkyl, or cycloalkylmethyl, R ^a is a nitrogen atom protecting group such as an acyl group, for example, acetyl, pivaloyl, and the like; an aroyl group, for example, benzoyl and the like; a carbamate group, for example, tertiary butyloxy- carbonyl, ethyloxycarbonyl, benzyloxycarbonyl, and the like, is prepared from a highly enantiomerically enriched compound of Formula VI, wherein R ^a and R ¹ are as defined above by reaction with a cyanide reagent such as, for example, acetone cyanohydrin, sodium cyanide, potassium cyanide, trimethylsilylcyanide, and the like in a solvent such as, for example, heptane, methylene chloride, and the like with or without the use of a catalyst. Preferably, the reaction is carried out with acetone cyanohydrin in heptane in the presence of a phase transfer catalyst (tetrabutyl ammonium iodide) .

Alternatively, a compound of Formula V is prepared from a compound of Formula VI by treatment with an alkali metal bisulfite such as, for example, sodium bisulfite, potassium bisulfite, and the like, in a solvent such as, for example, methylene chloride and the like to afford the bisulfite addition product in situ followed by the addition of a cyano anion equivalent reagent such as an alkali cyanide, for example, sodium cyanide and the like. Preferably, the reaction is carried out with sodium bisulfite and sodium cyanide in methylene chloride. The cyanohydrin of Formula V can be isolated as a diastereomerically pure crystalline solid by crystallization from a nonpolar, nonaromatic solvent such as, for example, a straight or branched alkane, for example, pentane, hexane, heptane, octane, nonane, decane, and the like, a cycloalkane, for example, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, and the like, or an alkyl

substituted cycloalkane, for example, methylcyclo- pentane, methylcyclohexane, dimethylcyclohexane, n-butylcyclohexane, tertiary-butylcyclohexane. isopropylcyclohexane, and the like, and water system or optionally not isolated and converted directly to a compound of Formula IV. Preferably, the cyanohydrin of Formula V is isolated.

A highly diastereomerically enriched compound of Formula IV wherein X is a halogen such as, for example, chlorine, bromine, and the like, or a sulfate such as HS0 ₄ , and R ¹ is as defined above is prepared from a compound of Formula V by hydrolysis with an acid such as, for example, concentrated aqueous hydrochloric acid and the like at about 40°C to about the reflux temperature of the solvent for about 3 to 24 hours. Preferably, the reaction is carried out with concentrated aqueous hydrochloric acid at about 80°C to about the reflux temperature of the solvent for about 3 to 6 hours. A highly diastereomerically enriched compound of Formula III wherein R ^a and R ¹ are as defined above is prepared from a compound of Formula IVa by reaction with a nitrogen atom protecting reagent using conventional methodology, for example, in the case wherein R ^a is ethyloxycarbonyl a compound of

Formula IVa is reacted with ethyl chloroformate in the presence of a base, such as, for example, sodium hydroxide and the like to afford a compound of Formula III. Alternatively, a pharmaceutically acceptable acid addition salt of a compound of

Formula IV is converted to a compound of Formula III by removal of the pharmaceutically acceptable acid addition salt by conventional methodology such as, for example, use of a base, for example, sodium hydroxide and the like and subsequent reaction with a nitrogen atom protecting reagent as described above.

A highly diastereomerically enriched compound of Formula Ilia wherein R ² is NR ₂ , wherein R ⁵ is alkyl or -CH ₂ -aryl, or other suitable carboxylic acid activating group and R ^a and R ¹ are as defined above is prepared from a compound of Formula III and a compound of formula

R ² -H

wherein R ² is as defined above using conventional methodology to convert carboxylic acid into an amide, an ester, or activated acyl moiety such as, for example, an anhydride, activated ester, and the like. A diastereomerically enriched compound of Formula II wherein R ³ is alkyl or arylalkyl, R ^a and R ¹ are as defined above is prepared from either a compound of Formula III or Ilia by reaction with a compound of Formula VII.

R ³ -M VII

wherein M is lithium, MgX ^a , or MgR ³ wherein X ^a is a halogen and R ³ is as defined above in a solvent such as, for example, diethyl ether, heptane, methyl tertiary butyl ether, toluene, tetrahydrofuran, and the like at about -78°C to about 25°C and subsequently deaggregating the lithium aggregates with a reagent such as, for example, tetramethylethylenedia ine, N,N- dimethylaminopropane, lithium chloride, lithium bromide, and the like. Preferably, the reaction is carried out on a compound of Formula III using isobutyllithium in toluene at about -15°C to -5°C and deaggregating with a combination of lithium bromide and tetrahydrofuran. A highly diastereomerically enriched compound of

Formula la, wherein R ^a , R ¹ , and R ³ are as defined above, is prepared from a compound of Formula II by reduction

with a reducing metal hydride reagent such as, for example, sodium borohydride, sodium triacetoxyboro- hydride, and the like in a solvent such as, for example, acetonitrile, toluene, tetrahydrofuran, heptane, and the like. Preferably, the reaction is carried out with sodium triacetoxyborohydride in an acetonitrile/heptane mixture.

A compound of Formula lb wherein R ¹ and R ³ are as defined above is prepared from a compound of Formula la, in which R ^a is a carbamate nitrogen atom protecting group by incomplete hydrolysis using a base in a solvent such as, for example, methanol. Preferably the reaction is carried out with potassium hydroxide in aqueous methanol. A highly diastereomerically enriched compound of

Formula I wherein R, R ¹ , and R ³ are as defined above is prepared from either a compound of Formula la or Formula lb by reaction with a deprotecting reagent in a solvent such as, for example, by complete hydrolysis using an acid, for example, trifluoroacetic acid, hydrochloric acid, and the like; or a base, for example, sodium hydroxide, potassium hydroxide, and the like; and a solvent, for example, aqueous methanol, and the like. Preferably, the reaction is carried out with potassium hydroxide in aqueous methanol.

Thus, the asymmetric synthesis of compounds of the present invention is based upon starting from an enantiomerically pure nitrogen protected amino acid. The chiral purity is maintained through the formation of the aldehyde, Compound VI. The aldehyde enantiomeric purity is controlled by reaction conditions and used in situ to prepare the cyanohydrin, Compound V.

The cyanohydrin is isolated by a selective crystallization procedure to afford a pure diastereomer, as determined by NMR and HPLC techniques. This sets two stereocenters. The beta amino chiral

center cannot be epimerized throughout the remaining synthetic sequence. The alpha hydroxy carbon chiral center can be epimerized under catalytic basic conditions. The stereochemistry of the two chiral centers is maintained through the acidic hydrolysis to Compound IV, the amine protection to Compound III and the ketone formation to Compound II steps.

The alpha hydroxy carbon hydrogen of the ketone substrate Compound II, could epimerize, but the beta amino chiral center could not. Thus, the potential to get two of the four possible diastereomers at the ketone reduction step exists. The reduction of the ketone (a prochiral center) gives the other two possible resulting hydroxy chiral centers. The selective reduction conditions disclosed in the present invention affords highly diastereomerically enriched production of the desired aminodiol. A combination of NMR and HPLC conditions were used to verify the purity of the diastereomers of both the ketone and the aminodiol substrates.

In all cases, the minimum chiral purity of the highly diastereomerically enriched compounds is not less than 90% (area % HPLC) and not more than 2% (area % chiral HPLC) of another enantiomer or diastereomer for the final aminodiol.

Enantiomerically enriched is defined as any compound that can be expressed in % term of more of one enantiomer than the other. Diasteriomerically enriched is defined as any compound that can be expressed in a % term of more of one diastereomer than the other(s) .

The exact method of determining % diastereomeric excess (de) and % enantiomeric excess (ee) is disclosed in Synthesis of Optically Active o_-Amino Acids by R. M. Williams, Pergamon Press (1989) . A compound of Formula VI is known and capable of being prepared by methods known in the art (J. Boger, et al, Journal of Medicinal Chemistry 28:1779 (1985)

and J. R. Luly, et al, Journal of Organic Chemistry 52:1487 (1987) ) .

J. R. Luly, et al, Journal of Medicinal Chemistry 31:2264-2276 (1988); J. J. Plattner, et al, Journal of Medicinal Chemistry 31:2277-2288 (1988); G. J. Hanson, et al, Biochemical and Biophysical Research Communications 160:1-5 (1989); H. L. Sham, et al, Journal of Chemical Society Chemical Communications 666-667 (1990) ; T. D. Ocain and M. Abou-Gharbia Drugs of the Future 16:37-51 (1991); and W. R. Baker and S. L. Condon Tetrahedron Letters 33:1577-1580 (1992) disclose the use of substituted 1,2,3-aminodiols in the preparation of biologically active renin inhibitors. The following examples are illustrative to show the present process, the preparation of starting materials, and the use of [2S- (2R*,3S*,4R*) ] -2-amino-l- cyclohexyl-6-methyl-3,4-hepanediol in the preparation of [IS- (1R*,2S*,3R*)] -N- (4-morpholinylsulfonyl) -L- phenylalanyl-3- (2-amino-4-thiazolyl) -N- [1-cyclohexylmethyl) -2,3-dihydroxy-5-methylhexyl] -L- alaninamide disclosed in European Patent Application 0399556 and J. T. Repine, et al, Journal of Medicinal Chemistry 35:1032 (1992), useful as a renin inhibitor.

EXAMPLE 1

T2S- (2R*.3S*.4R*) 1 -2-Amino-l-cvclohexyl-6-methyl-3.4- heptanediol

(a) Preparation of fR- (R*.S*) 1 -l-cγclohexylmethyl-2- cyano-2-hydroxycarbamic acid. 1.1-dimethylethyl ester Method A: The (S) - (2-cyclohexyl-1-formyl- ethyl) carbamic acid, 1,1-dimethylethyl ester (47.6 g) (J. Boger, et al, Journal of Medicinal Chemistry 28:1779 (1985) and J. R. Luly, et al, Journal of Organic Chemistry 52:1487 (1987)) is dissolved in 520 rtiL of methylene chloride. The reaction mixture is cooled to 0°C and a solution of sodium bisulfite (47.6 g) in 160 mL water is added. The mixture is

allowed to stir at 0°C for 90 minutes, 15.6 g sodium cyanide is added as a solid, and the reaction mixture is stirred for another 90 minutes. The mixture is diluted with 1200 mL ethyl acetate/hexane (1:1), washed three times with 1000 mL water, dried over magnesium sulfate, filtered, and the solvent removed in vacuo. The resulting diastereomerically enriched [R-(R*,S*)]- 1-cyclohexylmethyl-2-cyano-2-hydroxycarbamic acid, 1,1-dimethylethyl ester can be used as an oil or crystallized diastereomerically pure from heptane/water. The crystalline material is used to obtain the following physical characteristics: ^ ^• H NMR (200 MHz, deuterated chloroform (CDC1 ₃ ) : δ 4.84 (d, 1H) , 4.60 (m, 2H) , 3.82 (m, 1H) , 1.80-0.90 (m, 13H) , 1.45 (s, 9H) ;

[α]J ⁵ = -50.8° (c = 1.0, methanol (MeOH) ) .

The other diastereomer [R- (R*,R*) ] -1-cyclohexyl¬ methyl-2-cyano-2-hydroxycarbamic acid, 1,1-dimethyl¬ ethyl ester, forms upon extended exposure to catalytic amounts of base (e.g., potassium cyanide). This is observed by a doubling of peaks in both ¹³ C NMR and HPLC data.

¹³ C NMR of [R-(R*,R*)] diastereomer (100.6 MHz, CDCL ₃ ) : δ 157.7, 118.2, 81.3, 67.3, 52.2, 38.0, 33.8, 33.9, 32.3, 28.3, 26.2, 26.0, 25.8.

¹³ C NMR of desired [R-(R*,S*)] diastereomer (100.6 MHz, CDCL ₃ ) : δ 156.4, 118.6, 81.0, 64.7, 51.4, 36.3, 33.9, 33.8, 32.2, 28.2, 26.3, 26.1, 25.9. HPLC (Column: Supelco DB, C-18, 5 μm, 250 x 4.6 mm; mobile phase: CH ₃ CN/H ₂ 0, 40/60; Rl detection (40°C) ; sample size: 23 mg/5 mL 100% CH ₃ CN) ; Rf: [R-(R*,R*)] 27.5 min, [R-(R*,S*)] 28.9 min; flow rate: 1.5 mL/min. Method B: Potassium cyanide (0.40 g) , tetra- butylammonium iodide (0.38 g) , water (50 mL) , and acetone cyanohydrin (9.48 g) is added to a (S) - (2- cyclohexyl-1-formylethyl)carbamic acid, 1,1-dimethyl¬ ethyl ester (J. Boger, et al, Journal of Medicinal

Chemistry 28:1779 (1985) and J. R. Luly, et al, Journal of Organic Chemistry 52:1487 (1987)) solution (ca. 125 mL heptane) . The reaction mixture is stirred overnight at 25°C. The organic layer is separated and washed four times with water. The resulting slurry is filtered and dried to obtain 31.1 g of the diastereomerically pure [R- (R*,S*) ] -1- (cyclohexyl- methyl) -2-cyano-2-hydroxycarbamic acid, 1,1-dimethyl- ethyl ester as a white crystalline solid. This material is identical in all respects to that prepared by Method A.

(b) Preparation of fR- (R*,S*) -β-amino-Q.-hydroxycγclo- hexanebutanoic acid, monohydrochloride

Method A: The [R- (R*,S*) ] -1- (cyclohexylmethyl) -2- cyano-2-hydroxycarbamic acid, 1,1-dimethylethyl ester (9.2 g) , and concentrated aqueous hydrochloric acid (100 mL) are heated to reflux for a minimum of 2 hours and cooled to 25°C. The resulting solids are isolated by filtration and washed with diethyl ether to obtain 5.3 g of the [R- (R*,S*) ] -jS-amino-α-hydroxycyclohexane¬ butanoic acid, monohydrochloride salt as a white crystalline solid. The crystalline material is used to obtain the following physical characteristics: ¹ H NMR (200 MHz, CDC1 ₃ ) : δ 4.20 (d, 1H, J = 3.4 Hz), 3.49 (m, 1H) , 1.50-0.69 (m, 13H) ;

¹³ C NMR (50.3 MHz, CDC1 ₃ ) : δ 177.5, 72.6, 54.2, 39.6,

36.2, 35.8, 35.4, 29.1, 28.9, 28.7;

IR (cm ^-1 ) 1728, 1072; m.p. 210°C-212°C;

[α.] ⁵ = -13.4° (c = 1.08, water). Method B: The [R- (R*,S*) ] -1- (cyclohexylmethyl) -2- cyano-2-hydroxycarbamic acid, 1,1-dimethyl ester (177.1 g) and 1.25 L of concentrated aqueous hydrochloric acid are heated at 80°C for 3 hours and cooled to 0°C. The resulting slurry is filtered and dried to afford 132.8 g of the [R- (R*,S*) ] -S-amino-α- hydroxycyclohexanebutanoic acid, monohydrochloride salt

as a white crystalline solid. This material is identical in all respects to that prepared by Method A.

(c) Preparation of fR- (R*.S*) 1 - β- \ (ethoxycarbonyl) amino! -α-hydroxycyclohexanebutanoic acid The [R- (R*,S*) ] -3-amino-a;-hydroxycyclohexane- butanoic acid, monohydrochloride salt (10 kg) is dissolved in 33.6 L of water and cooled to 5°C. The pH is adjusted to about 9.5 using IN sodium hydroxide (roughly 85 L) , maintaining the temperature about 5°C. Ethyl chloroformate (5.0 kg) is added. The pH of the reaction mixture is maintained at about 9.5 by the addition of more IN sodium hydroxide. The reaction mixture is stirred at 5°C for 2 to 3 hours. The solution is washed once with toluene (90 L) to remove impurities and hydrochloric acid is added to the water layer, adjusting the pH to about 2.0. The reaction mixture is extracted by washing the reaction mixture two times with .toluene (90 L) . The toluene layers are combined and partially concentrated to obtain 10.5 kg of the [R- (R*,S*) ] -β- [ (ethoxycarbonyl)amino] -α-hydroxy- cyclohexanebutanoic acid as a solution. A sample is isolated by removing excess solvents under vacuum and affords the following physical characteristics: ^X H NMR (200 MHz, CDC1 ₃ ) : δ 5.51 (d, 1H, J = 9.7 Hz), 4.20-4.00 (m, 2H) , 4.15 (q, 2H, J = 6.7 Hz), 1.16 (t, 3H, J = 6.7 Hz) ;

¹³ C NMR (50.3 MHz, CDC1 ₃ ) : β 175.1, 157.1, 72.1, 61.0, 51.1, 39.8, 34.3, 33.7, 32.9, 26.6, 26.5, 14.4.

(d) Preparation of TR- (R*.S*) 1 -l- (cyclohexylmethyl) -2- hydroxy-5-methyl-3-oxocarbamic acid, ethyl ester

Solid anhydrous lithium bromide (7.6 kg) is added to a 50% solution of [R- (R*,S*) ] -β- [ (ethyloxycarbonyl) amino] -α.-hydroxycyclohexylbutanoic acid (10.5 kg in toluene) and cooled to 10°C. Tetrahydrofuran (12.6 kg) is added to the mixture maintaining the temperature below 30°C. The mixture is stirred until the solids are dissolved and cooled to -10°C. The isobutyl

lithium (11.3 kg, 176.4 mol, 24.5% solution in heptane) is added slowly. After the addition is complete, the solution is warmed to 10°C and stirred for 1 to 3 hours. The reaction is quenched by addition to a solution of ammonium chloride (30 kg in 90 L of water) at 0°C. The resulting organic layer is separated and concentrated. Acetonitrile (85 L) is added and the solution is partially concentrated to obtain 10.5 kg of the [R- (R*,S*)] -1- (cyclohexylmethyl) -2-hydroxy-5- methyl-3-oxocarbamic acid, ethyl ester. The ketone is isolated by removing excess solvents under vacuum and gives the following physical characteristics: ^X E NMR (200 MHz, CDC1 ₃ ) : δ 4.87 (d, 1H, J = 10.1 Hz), 4.31 (m, 1H) , 4.03 (s, 1H) , 4.01 (q, 2H, J = 7.1 Hz), 2.53 (m, 2H) , 2.17 (m, 1H) , 1.90-0.80 (m, 11H) , 1.19 (t, 3H, J = 6.9 Hz) , 0.93 (d, 6H, J = 6.7 Hz); ¹³ C NMR (50.3 MHz, CDC1 ₃ ) : δ 210.0, 156.1, 78.5, 60.9, 50.0, 46.6, 40.8, 34.2, 33.5, 33.0, 26.5, 26.2, 26.1, 24.5, 22.5, 22.4, 14.5. (e) Preparation of TlS- (IR* .2S* ,3R*) 1 -1- (cyclohexyl¬ methyl) -2.3-dihydroxy-5-methylcarbamic acid, ethyl ester

Sodium triacetoxyborohydride (6.7 kg) is dissolved in 16 L of toluene. A solution of 10.0 kg of [R- (R*,S*)] -l- (cyclohexylmethyl) -2-hydroxy-5-methyl-3- oxocarbamic acid, ethyl ester in acetonitrile (16.0 kg) is added, maintaining the temperature about 20°C-24°C. The reaction mixture is stirred for 4 hours and cooled to 5°C. A sodium bicarbonate solution (5.4 kg in 60 L water) is cooled to 15°C-20°C and added slowly to the reaction mixture, maintaining the temperature at about 10°C. The reaction mixture is stirred for 15 minutes and filtered to collect the white solids. The solids are rinsed three times with 10 L heptane, one time with 10 L water, and dried at 30°C-40°C under vacuum for 5 hours to obtain 7.1 kg of the highly diastereomerically enriched [IS- (1R*,2S*,3R*) ] -1-

(cyclohexylmethyl) -2,3-dihydroxy-5-methylcarbamic acid, ethyl ester as a white crystalline solid. The crystalline diol material is used to obtain the following physical characteristics: ^X E NMR (200 MHz, CDC1 ₃ ) : δ 4.81 (d, 1H, J = 9.3 Hz), 4.07 (m, 4H) , 3.35 (br s, 1H) , 3.19 (br d, 1H) , 2.25 (br s, 1H) , 1.89 (m, 1H) , 1.79-1.64 (m, 15H) , 1.23 (t, 3H, J = 7.0 Hz), 0.93 (d, 3H, J = 6.6 Hz), 0.87 (d, 3H, J = 6.5 Hz) ; ¹³ C NMR (50.3 MHz, CDC1 ₃ ): δ 157.5, 77.5, 69.6, 61.3, 48.6, 42.3, 39.9, 34.3, 33.8, 32.8, 26.5, 26.2, 26.1, 24.5, 23.9, 21.6, 14.5.

A mixture of the two possible reduction diastereomers is prepared by using sodium borohydride in methanol as the reducing agent. The two diastereomers form in about 60/40 ratio as determined from a doubling of peaks in both ¹³ C NMR and HPLC data. This ratio is dependent upon the reducing agent and solvent used. The ratio of undesired/desired diastereomer is found to be: 60/40 using sodium borohydride in methanol; 18/82 using sodium borohydride in tetrahydrofuran; 1/100 using sodium triacetoxy- borohydride in both tetrahydrofuran and in a mixture of heptane-acetonitrile. ¹³ C NMR (for other diastereomer) (50.3 MHz, CDCL ₃ ) : δ 156.5, 76.7, 70.3, 60.8, 49.3, 42.1, 40.9, 34.1, 34.0, 32.9, 26.5, 26.1, 26.0, 24.4, 23.8, 21.4, 14.6. HPLC (Column: Ultrasphere C-18, 5 μm, 250 x 4.6 mm; mobile phase: CH ₃ CN/H ₂ 0, 45/55; Rl detection (40°C) ; sample size: 27.9 mg/5 mL mobile phase; flow rate: 1.5 mL/min) ; Rf: [IS- (IR*,2S*,3S*) ] 16.6 min, [IS- (1R*,2S*,3R*) ] 17.6 min.

(f) Preparation of f2S- (2R*.3S*,4R*) 1 -2-amino-1-cyclo¬ hexyl-6-methyl-3.4-heptanediol The [IS- (1R*,2S*,3R*) ] -1- (cyclohexylmethyl) -2,3- dihydroxy-5-methylcarbamic acid, ethyl ester (7.1 kg) is dissolved in 19 L methanol and 20 L water. A

solution of potassium hydroxide (11.2 kg (45% aqueous) in 37 L water) is added slowly to the diol solution, maintaining the temperature at about 35°C. The mixture is heated to reflux for 8 hours, cooled to 15°C, and stirred for 1 hour after crystals are noted. The solids are collected by filtration, rinsed with a methanol solution (3 L in 12 L water) , followed by 20 L water, and dried at 35°C under vacuum for 5 hours to obtain 5.1 kg of [2S- (2R*,3S*,4R*) ] -2-amino-l- cyclohexyl-6-methyl-3,4-heptanediol as a white crystalline solid. The crystalline material is used to obtain the following physical characteristics: ¹ H NMR (200 MHz, CDC1 ₃ ): δ 3.77 (dt, IH, J = 9.5 Hz, J = 3.6 Hz), 3.23 (dd, IH, J = 2.2 Hz, J = 3.6 Hz), 3.04 (dt, IH, J = 2.1 Hz, J = 6.7 Hz), 1.70-0.80 (m, 16H) , 0.96 (d, 3H, J = 6.6 Hz), 0.92 (d, 3H, J = 6.5 Hz) ;

¹³ C NMR (50.3 MHz, CDC1 ₃ ) : δ 74.5, 73.3, 48.4, 43.7, 43.3, 34.1, 33.8, 32.9, 26.5, 26.3, 26.1, 24.8, 23.5, 22.0.

HPLC (Column: Supelco DB C-18, 5 μm, 250 x 4.6 mm; mobile phase: CH ₃ CN/aqueous 0.1 M Octanesulfonic acid sodium salt, 3.0 pH adjusted with H ₃ P0 ₄ or NH ₄ OH-plus- 2 L triethylamine/L, 35/65; Rl detection (40°C) ; flow rate 1.5 mL/min; sample size: 2.63 mg/mL mobile phase); Rf: [2S- (2R*,3S*,4S) ] 9.8 min, [2S- (2R*,3S*,4R*) ] 11.0 min.

Chiral HPLC Tetra-O-acetyl-jδ-D-glucopyranosyl isothiocyanate (GITC) derivatization method (Column: Supelco DB C-18, 5 μ , 250 x 4.6 mm; mobile phase:

CH ₃ CN/H ₂ 0, 50/50; flow rate 1.5 mL/min; UV detection (214 nm) ; sample preparation: 72 mg GITC in 3.0 mL CH ₃ CN, 1.0-1.3 mg sample in 0.15 mL mobile phase. Take 0.15 mL of each solution and stir at room temperature for 30 minutes. Dilute to 3.0 mL with mobile phase and inject -20 μl>) ; Rf: 17.2 min [2S- (2R*,3S*,4R*) ] .

EXAMPLE 2 riS- (1R*.2S*.3R*)1 -N- (4-Morpholinylsulfonyl) -L- phenylalanyl-3- (2-amino-4-thiazolyl) -N- Tl- cyclohexylmethyl) -2.3-dihydroxy-5-methylhexyl1 -L- alaninamide

1-N-Hydroxybenzotriazole, 190.6 g, 395.0 g of [2S- (2R*,3S*,4R*) ] -2-amino-1-cyclohexyl-6-methyl- 3,4-heptanediol (Example 1), 682.4 g (1.62 mol) of N- (4-morpholinylsulfonyl) -L-phenylalanyl-3- (2-amino-4- thiazolyl) -L-alanine (European Published Patent

Application 0399556 and J. T. Repine, et al, Journal of Medicinal Chemistry 35:1032 (1992)) and 20 L of ethyl acetate are charged into a 50 L reactor and the slurry is stirred. Triethylamine, 107.1 g with 0.5 L of ethyl acetate, is added to the mixture and stirred for 1 hour at 30°C. A solution of 300.0 g of dicyclohexylcarbodiimide dissolved in 2.5 L of ethyl acetate is added to the reaction mixture over 15 to 30 minutes. The slurry is warmed to 35°C to 40°C and stirred at that temperature for 48 hours, cooled to 25°C, and the solids removed by filtration. The filtrate is washed with 0.5 N aqueous hydrochloric acid solution (4 L) , saturated sodium bicarbonate solution (4 x 4 L) , and water (2 L) . The solution is concentrated to a thick slurry under vacuum, chilled to 5°C, and the crude product solid collected by filtration and dried under vacuum at 40°C. The crude product and 4 L of isopropanol are charged into a 12 L reactor and the slurry is heated to 45°C. Water, 1 L, is added and heating continued to 60°C. The solution is cooled slowly to crystallize the product and then chilled to 10°C. The slurry is filtered and the cake is washed with cold isopropanol. After drying at 40°C under vacuum, 770 g of [IS- (1R*,2S*,3R*) ] -N- (4- morpholinylsulfonyl) -L-phenylalanyl-3- (2-amino-4- thiazolyl) -N- [ (1-cyclohexylmethyl) -2,3-dihydroxy-5- methylhexyl] -L-alaninamide is obtained as white needles

of >99% purity by HPLC; mass spectrum (fast atom bombardment): 709.2 M ⁺ .