2, 5-disubstituted 3-mercaptopentanoic acid The present invention relates to novel compounds, and pharmaceutically acceptable salts thereof, which inhibit basic carboxypeptidases, more specifically carboxypeptidase U, and thus can be used in the prevention and treatment of diseases wherein inhibition of carboxypeptidase U is beneficial, such as thrombosis and hypercoagulability in blood and tissue, atherosclerosis, adhesions, dermal scarring, cancer, fibrotic conditions, inflammatory diseases and those conditions which benefit from maintaining or enhancing bradykinin levels in the body. In further aspects, the invention relates to compounds of the invention for use in therapy; to processes for preparation of such new compounds; to pharmaceutical compositions containing at least one compound of the invention, or a pharmaceutically acceptable salt thereof, as active ingredient; and to the use of the active compounds in the manufacture of medicaments for the medical use indicated above.

Fibrinolysis is the result of a series of enzymatic reactions resulting in the degradation of fibrin by plasmin. The activation of plasminogen is the central process in fibrinolysis. The cleavage of plasminogen to produce plasmin is accomplished by the plasminogen activators, tissue-type plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-PA). Initial plasmin degradation of fibrin generates carboxy- terminal lysine residues that serve as high affinity binding sites for plasminogen. Since plasminogen bound to fibrin is much more readily activated to plasmin than free plasminogen this mechanism provides a positive feedback regulation of fibrinolysis.

One of the endogenous inhibitors to fibrinolysis is carboxypeptidase U (CPU).

CPU is also known as plasma carboxypeptidase B, active thrombin activatable fibrinolysis inhibitor (TAFIa), carboxypeptidase R and inducible carboxypeptidase activity. CPU is formed during coagulation and fibrinolysis from its precursor proCPU by the action of proteolytic enzymes, such as thrombin, thrombin-thrombomodulin complex or plasmin.

CPU cleaves basic amino acids at the carboxy-terminal of fibrin fragments. The loss of carboxy-terminal lysines and thereby of lysine binding sites for plasminogen then serves to inhibit fibrinolysis. By inhibiting the loss of lysine binding sites for plasminogen and thus increase the rate of plasmin formation, effective inhibitors of carboxypeptidase U are expected to facilitate fibrinolysis.

2-Mercaptomethyl-3-guanidinoethylthiopropanoic acid is reported as a carboxypeptidase N inhibitor. More recently, this compound has been shown to inhibit CPU, Hendriks, D. et al., Biochimica et Biophysica Acta, 1034 (1990) 86-92.

Guanidinoethylmercaptosuccinic acid is reported as a carboxypeptidase N inhibitor.

More recently, this compound has been shown to inhibit CPU, Eaton, D. L., et al., The Journal of Biological Chemistry, 266 (1991) 21833-21838.

CPU inhibitors are disclosed in WO 00/66550, WO 00/66557, WO 03/013526 and WO 03/027128 and a pharmaceutical formulation containing a CPU inhibitor and a thrombin inhibitor is disclosed in WO 00/66152. Inhibitors of plasma carboxypeptidase B are disclosed in WO 01/19836. Inhibitors of TAFIa are disclosed in WO 02/14285.

It has now been found that compounds of formula (1) are particularly effective as inhibitors of carboxypeptidase U and are thereby useful as medicaments for the treatment or prophylaxis of conditions wherein inhibition of carboxypeptidase U is beneficial.

Thus, the present invention provides a compound of formula (I) : wherein: Rl is phenyl {optionally substituted by halogen, hydroxy, cyano, Cl alkyl (itself optionally mono-substituted by cyano, hydroxy or phenyl), C1-4 alkoxy (itself optionally substituted by tetrahydrofuranyl), CF3, OCF3, methylenedioxy, C (O) R3, S (O) 2R4, phenyl (itself optionally substituted by halogen), phenoxy (itself optionally substituted by halogen) or tetrahydrofuranyloxy}, naphthyl, pyridinyl, 1, 2,3, 4-tetrahydropyrimidin-2, 4- dione-yl (optionally substituted by Cl 4 alkyl) or tetrahydrothienyl; R2 is aminopyridinyl, aminothiazolyl or 3-azabicyclo [3.2. 1] octyl; R3 is hydroxy, Cl 4 alkoxy (itself optionally substituted by phenyl (itself optionally substituted by halogen) or pyridinyl), NR5R6 or an N-linked 5-or 6-membered heterocyclic ring {unsubstituted or mono-substituted by hydroxy, oxo, Cl 4 alkyl (itself optionally substituted by hydroxy or NHphenyl), C02 (CI alkyl) or phenyl (itself optionally substituted by halogen)} ;

R4 is NR 7R 8or an N-linked 5-or 6-membered heterocyclic ring {unsubstituted; mono- substituted by hydroxy, oxo, Cl alkyl (itself optionally substituted by hydroxy or NHphenyl), CO2 (Czx alkyl) or phenyl (itself optionally substituted by halogen); or fused to a benzene ring which is optionally substituted by Ci-4 alkoxy} ; R5, R6, le and R8 are, independently, hydrogen, Clx alkyl {optionally substituted by halogen, cyano, hydroxy, phenyl (itself optionally substituted by halogen or methylenedioxy), pyridinyl, COaH or C02 (Czx alkyl)} or C24 alkenyl ; provided that when Rl is 6-aminopyridin-3-yl then R2 is substituted phenyl, naphthyl, pyridinyl, 1, 2,3, 4-tetrahydropyrimidin-2,4-dione-yl (optionally substituted by CI-4 alkyl) or tetrahydrothienyl; or a pharmaceutically acceptable salt or solvate thereof, or a solvate of such a salt.

The compounds of formula (I) exist in isomeric forms and the present invention covers all such forms and mixtures thereof in all proportions. Both the pure enantiomers, racemic mixtures and equal and unequal mixtures of two enantiomers are within the scope of the present invention. It should also be understood that all the diastereomeric forms possible are within the scope of the invention.

The term Ci-4 alkyl denotes a straight or branched alkyl group having 1 to 4 carbon atoms in the chain. Examples of alkyl include methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl and tert-butyl.

The term Ci-4 alkoxy denotes an alkyl-O-group, where alkyl is straight or branched chain and examples include methoxy and ethoxy.

Halogen includes fluoro, chloro, bromo and iodo (but is, for example, fluoro or chloro).

An N-linked 5-or 6-membered heterocyclic ring is, for example, a pyrrolidinyl, piperidinyl or piperazinyl ring.

In one particular aspect the present invention provides a compound of formula (I) wherein RI is phenyl {optionally substituted by halogen, hydroxy, cyano, Cl alkyl (itself optionally mono-substituted by cyano or hydroxy), Ci-4 alkoxy, CF3, OCF3, methylenedioxy, C (O) NH2, S (0) 2NH2 or phenyl (itself optionally substituted by halogen)}, pyridinyl or tetrahydrothienyl; R2 is aminopyridinyl, aminothiazolyl or 3- azabicyclo [3.2. 1] octyl; provided that when R2 is 6-aminopyridin-3-yl then Rl is substituted

phenyl, pyridinyl or tetrahydrothienyl; or a pharmaceutically acceptable salt or solvate thereof, or a solvate of such a salt.

In another aspect the invention provides a compound of formula (I) wherein Rl is phenyl {optionally substituted (for example carrying 1 or 2 substituents) by halogen, hydroxy, cyano, Cl4 alkyl (itself optionally mono-substituted by cyano, hydroxy or phenyl), Cl alkoxy, CF3, OCF3, methylenedioxy, phenoxy (itself optionally substituted by halogen), tetrahydrofuranyloxy or tetrahydrofuranylmethoxy}, naphthyl, pyridinyl or tetrahydrothienyl.

In yet another aspect the present invention provides a compound of formula (I) wherein Rl is phenyl {substituted (for example mono-substituted) by halogen, hydroxy, cyano, CI-4 alkyl (itself optionally mono-substituted by cyano or hydroxy), CI. alkoxy (for example methoxy), CF3 or methylenedioxy} or tetrahydrothienyl.

In a still further aspect the present invention provides a compound of formula (I) wherein R'is phenyl {mono-substituted by halogen (for example chloro or fluoro), hydroxy, cyano, Cl 1 alkyl (mono-substituted by cyano), CF3 or methylenedioxy} or tetrahydrothienyl.

Aminopyridinyl is, for example, 6-aminopyridin-3-yl. Aminothiazolyl is, for example, 2-aminothiazol-5-yl. 3-Azabicyclo [3.2. 1] octyl is, for example, 3- azabicyclo [3.2. 1] oct-8-yl.

In a further aspect the present invention provides a compound of formula (I) wherein R2 is aminopyridine (for example 6-aminopyridin-3-yl).

The compounds of the present invention can be prepared by adaptation of methods described in the literature (for example WO 00/66557), or by using or adapting the methods of Examples 1,26 or 51 below. It will be appreciated that when adapting methods of the literature or Examples 1,26 or 51 functional groups of intermediate compounds may need to be protected by protecting groups. The preparations of certain intermediates are presented in Schemes 1 and 2.

For example a compound of formula (I) can be prepared by reacting a compound of formula (II) :

wherein Ru ils as defined above or includes a group that can be subsequently reacted to form the group Rl, R* is a suitable protecting group (such as a Cl 6 alkyl group (for example tert-butyl) ) and R2 is as defined above or the amine function of R2 can be protected (for example by a tert-butoxycarbonyl group), with a thiol of formula L-SH, wherein L is a suitable protecting group (for example 4-methoxybenzyl), in the presence of a suitable catalyst (for example sodium hydride) and in a suitable solvent (for example N, N-dimethyl formamide) to form a compound of formula (III) : and, optionally reacting the functional group on Rl (for example Rl might include an acid group that can be coupled with an amino function to form an amide in the presence of a catalyst (such as HATU)), and subsequently removing the protecting groups as necessary.

Functional groups which it is desirable to protect include hydroxy, carboxylate and amino groups. Suitable protecting groups for hydroxy include trialkylsilyl or diarylalkyl- silyl (for example tert-butyldimethylsilyl, tert-butyldiphenylsilyl or trimethylsilyl), tetrahydropyranyl, methoxymethyl, benzyloxymethyl and 4-methoxybenzyl. Suitable protecting groups for carboxylate include ethyl, tert-butyl and benzyl esters. Suitable protecting groups for amino include tert-butyloxycarbonyl, 2,4, 6-trimethoxybenzyl and benzyloxycarbonyl. The use of protecting groups is described in'Protective Groups in Organic Synthesis', third edition, T. W. Greene & P. G. M. Wutz, Wiley-Interscience (1999).

The protective group may also be a polymer resin such as Wang resin or a 2-chorotrityl chloride resin.

The compounds of the invention are inhibitors of carboxypeptidase U and are thus expected to be useful in those conditions where inhibition of carboxypeptidase U is beneficial, such as in the treatment or prophylaxis of thrombosis and hypercoagulability in blood and tissues, atherosclerosis, adhesions, dermal scarring, cancer, fibrotic conditions, inflammatory diseases and those conditions which benefit from maintaining or enhancing bradykinin levels in the body of mammals, such as man.

In a further aspect of the invention a compound of formula (I), or a pharmaceutically acceptable salt or solvate thereof, or a solvate of such a salt, is used in the

in the treatment or prophylaxis of thrombosis. In another aspect of the invention a compound of formula (I), or a pharmaceutically acceptable salt or solvate thereof, or a solvate of such a salt, is used in method of manufacturing a medicament for the treatment or prophylaxis of thrombosis.

It is known that hypercoagulability may lead to thrombo-embolic diseases.

Conditions associated with hypercoagulability and thrombo-embolic diseases which may be mentioned include protein C resistance and inherited or aquired deficiences in antithrombin III, protein C, protein S and heparin cofactor II. Other conditions known to be associated with hypercoagulability and thrombo-embolic disease include circulatory and septic shock, circulating antiphospholipid antibodies, hyperhomocysteinemia, heparin induced thrombocytopenia and defects in fibrinolysis. The compounds of the invention are thus indicated both in the therapeutic and/or prophylactic treatment of these conditions.

Other disease states which may be mentioned include the therapeutic and/or prophylactic treatment of venous thrombosis and pulmonary embolism, arterial thrombosis (for example in myocardial infarction, unstable angina, thrombosis-based stroke and peripheral arterial thrombosis) and systemic embolism usually from the atrium during atrial fibrillation or from the left ventricle after transmural myocardial infarction.

The compounds of the invention are further indicated in the treatment of conditions where there is an undesirable excess of proCPU/CPU.

Moreover, the compounds of the invention are expected to have utility in prophylaxis of re-occlusion and restenosis (that is, thrombosis) after thrombolysis, percutaneous trans-luminal intervention (PTI) and coronary bypass operations; the prevention of re-thrombosis after microsurgery and vascular surgery in general.

Further indications include the therapeutic and/or prophylactic treatment of disseminated intravascular coagulation caused by bacteria, multiple trauma, intoxication or any other mechanism, fibrinolytic treatment when blood is in contact with foreign surfaces in the body, such as vascular grafts, vascular stents, vascular catheters, mechanical and biological prosthetic valves or any other medical device, and fibrinolytic treatment when blood is in contact with medical devices outside the body, such as during cardiovascular surgery using a heart-lung machine or in haemodialysis.

Furthermore, the compounds of the invention are expected to have utility in prophylaxis of atherosclerotic progression and transplant rejection in patients subject to organ transplantation, for example renal transplantation.

The compounds of the invention are also expected to have utility in inhibiting tumor maturation and progression.

Moreover, the compounds of the invention are expected to have utility in treatment of any condition in which fibrosis is a contributing factor. Such fibrotic conditions include cystic fibrosis, pulmonary fibrotic disease eg chronic obstructive pulmonary disease (COPD), adult respiratory distress syndrome (ARDS), fibromuscular dysplasia, fibrotic lung disease and fibrin deposits in the eye during opthalmic surgery.

The compounds of the invention are also expected to have utility in treatment of inflammation. In particular the invention may be used for the treatment or prevention of inflammatory diseases such as asthma, arthritis, endometriosis, inflammatory bowel diseases, psoriasis and atopic dermatitis.

The compounds of the invention are also expected to have utility in treatment of neurodegenerative diseases such as Alzheimer and Parkinsons.

The compounds of the invention are also expected to have utility in treatment of conditions known to benefit from maintaining or enhancing bradykinin levels. Such conditions include hypertension, angina, heart failure, pulmonary hypertension, renal failure and organ failure.

The compounds of the invention may also be combined and/or co-administered with any antithrombotic agent with a different mechanism of action, such as an anticoagulant (for example a vitamin K antagonist, an unfractionated or low molecular weight heparin, a synthetic heparin fragment such as fondaparinux, a thrombin inhibitor, a factor Xa inhibitor or other coagulation factor/enzyme inhibitor, a recombinant coagulation factor such as a recombinant human activated protein C) or an antiplatelet agent (such as acetylsalicylic acid, dipyridamole, ticlopidine, clopidogrel or other ADP-receptor [such as a P2Y12 or P2Y1] antagonist, a thromboxane receptor and/or synthetase inhibitor, a fibrinogen receptor antagonist, a prostacyclin mimetic or a phosphodiesterase inhibitor).

The compounds of the invention may further be combined and/or coadministered with thrombolytics such as tissue plasminogen activator (natural, recombinant or modified), streptokinase, urokinase, prourokinase, anisoylated plasminogen-streptokinase activator

complex (APSAC), animal salivary gland plasminogen activators, and the like, in the treatment of thrombotic diseases, in particular myocardial infarction, ischaemic stroke and massive pulmonary embolism.

The compounds of the invention should have a selectivity for carboxypeptidase U over carboxypeptidase N of>100 : 1, for example >1000 : 1, using the assay described below.

The inhibiting effect of the compounds of the present invention was estimated using the assay described in: Dirk Hendriks, Simon Schare and Marc van Sande, Clinical Chemistry, 31,1936-1939 (1985); and Wei Wang, Dirk F. Hendriks, Simon S. Scharpe, The Journal of Biological Chemistry, 269,15937-15944 (1994).

Thus, the present invention provides a compound of formula (I), or a pharmaceutically acceptable salt or solvate thereof, or a solvate of such a salt, as hereinbefore defined for use in therapy.

In a further aspect, the present invention provides the use of a compound of formula (I), or a pharmaceutically acceptable salt or solvate thereof, or a solvate of such a salt, as hereinbefore defined in the manufacture of a medicament for use in therapy.

In the context of the present invention, the term"therapy"includes"prophylaxis" unless there are specific indications to the contrary. The terms"therapeutic"and "therapeutically"should be understood accordingly.

The invention also provides a method of treating a condition where inhibition of carboxypeptidase U is beneficial in a mammal suffering from, or at risk of, said condition, which comprises administering to the mammal a therapeutically effective amount of a compound of formula (I), or a pharmaceutically acceptable salt or solvate thereof, or a solvate of such a salt, as hereinbefore defined.

For the above-mentioned therapeutic uses the dosage administered will vary with the compound employed, the mode of administration, the treatment desired and the disorder indicated.

The compounds of formula (I) and pharmaceutically acceptable salts, solvates or solvates of salts thereof may be used on their own but will generally be administered in the form of a pharmaceutical composition in which the formula (I) compound, salt, solvate or solvate of salt (active ingredient) is in association with a pharmaceutically acceptable adjuvant, diluent or carrier. Depending on the mode of administration, the pharmaceutical

composition will, for example, comprise from 0.05 to 99 % w (per cent by weight), such as from 0.05 to 80 % w, for example from 0.10 to 70 % w, such as from 0.10 to 50 % w, of active ingredient, all percentages by weight being based on total composition.

The present invention thus also provides a pharmaceutical composition comprising a compound of formula (1), or a pharmaceutically acceptable salt or solvate thereof, or a solvate of such a salt, as hereinbefore defined, in association with a pharmaceutically acceptable adjuvant, diluent or carrier.

The invention further provides a process for the preparation of a pharmaceutical composition of the invention which comprises mixing a compound of formula (I), or a pharmaceutically acceptable salt or solvate thereof, or a solvate of such a salt, as hereinbefore defined, with a pharmaceutically acceptable adjuvant, diluent or carrier.

Also included in the invention are derivatives of compounds of formula (I) which have the biological function of compounds of formula (I), such as prodrugs. Prodrugs are, for example, (pivaloyloxy) methyl esters and [ (ethoxycarbonyl) oxy] methyl esters of carboxylic acids.

The following Examples illustrate the invention.

EXAMPLES General Experimental Procedures Mass spectra were recorded on a VG Platform II or a Micromass ZQ mass spectrometer equipped with an electrospray interface (LC-MS). High resolution mass spectra were recorded on a Micromass LCT mass spectrometer equipped with an electrospray interface (LC-HRMS). IH NMR measurements were performed on Varian UNITY plus 400,500 and 600 spectrometers, operating at'H frequencies of 400,500 and 600 MHz respectively. NMR spectra were recorded in DMSO, D20, CD3CN or mixtures thereof. Chemical shifts are given in ppm with the solvent as internal standard.

Chromatography separations were performed using Merck Silica gel 60 (0.063-0. 200 mm).

The compounds named below were named using ACD/Name version 6. 06/ 11 June 2002 available from advanced chemistry development inc. , Canada.

EXAMPLE 1 This Example illustrates the preparation of 2- [ (6-aminopyridin-3-yl) methyl] -5- (1,1'-biphenyl-3-yl)-3-mercaptopentanoic acid (a) 3- (1, 1'-Biphenyl-3-vDpropanal To a solution of 3-iodo-1, 1'-biphenyl (0.964 g, 3.44 mmol) and tetrabutylammonium chloride (0.956g, 3.44 mmol) in dry DMF (3 mL) was added allyl alcohol (0.351 mL, 5.16 mmol), sodium hydrogencarbonate (0.723 g, 8.60 mmol), and palladium (II) acetate (31 mg, 0.14 mmol), and the mixture was stirred at room temperature for 18 h. The reaction mixture was then diluted with EtOAc and the solid material filtered off (elite). The filtrate was washed with water three times, dried (Na2S04) and concentrated. Flash chromatography (heptan/tert-butyl methyl ether, 4: 1) of the residue gave 3- (1, 1'-biphenyl-3-yl) propanal (0.601 g, 83%).

(b) tert-Butyl 5-(1,1'-biphenyl-3-yl)-2-({6-[(tert-butoxycarbonyl)amino]pyr idin-3- yl} methyl) pent-2-enoate A solution of tert-butyl 3-{6-[(tert-butoxycarbonyl) amino] pyridin-3-yl} -2- (diethoxyphosphoryl) propanoate (1.058 g, 2.31 mmol) in dry THF (4 mL) was added to a solution of sodium hydride (0.111 g, 60% in mineral oil, 2.77 mmol) in dry THF (3 mL) at 0 °C and the mixture was stirred at 0 °C for 60 min. To this mixture a solution of 3- (1, 1'- biphenyl-3-yl) propanal (0.582 g, 2.77 mmol) in dry THF (3 mL) was added, and the reaction mixture was allowed to attain room temperature over 22 h. EtOAc was then added, and the organic phase was washed with saturated aqueous NH4C1 and water, dried (Na2SO4) and concentrated. Flash chromatography (toluene/EtOAc, 15: 1) of the residue gave tert-butyl 5-(1,1'-biphenyl-3-yl)-2-({6-[(tert-butoxycarbonyl)amino] pyridin-3- yl} methyl) pent-2-enoate (1.105 g, 93%) as amixture of E/Z-isomers.

(c) tert-ButYl 5-(1,1'-biphenyl-3-yl)-2-({6-[(tert-butoxycarbonyl)amino]pyr idin-3- yl} methvl)-3-r (4-methoxybenzvl) thio') pentanoate A solution of 4-methoxy-a-toluenethiol (0. 58 mL, 4.17 mmol) in dry, degassed DMF (2 mL) was treated at room temperature with a catalytic amount of sodium hydride

(60% in mineral oil), followed by a solution of tert-butyl 5- (1, 1'-biphenyl-3-yl)-2- ( {6- [ (tert-butoxycarbonyl) amino] pyridin-3-yl} methyl) pent-2-enoate (1.073 g, 2.08 mmol) in dry, degassed DMF (5 mL). After 20 h at room temperature the reaction mixture was diluted with EtOAc and washed with water three times. The organic layer was dried (Na2SO4), concentrated, and subjected to flash chromatography (heptan/EtOAc, 3: 1 and toluene/EtOAc 12: 1) to give tert-butyl 5-(1,1'-biphenyl-3-yl)-2-({6-[(tert- butoxycarbonyl) amino] pyridin-3-yl} methyl)-3- [ (4-methoxybenzyl) thio] pentanoate (1.251 g, 90%) (d) 2-r (6-Aminopvridin-3-yl) methvll-5-(1, 1'-biphenyl-3-yl)-3-mercaptoPentanoic acid tert-Butyl 5-(1,1'-biphenyl-3-yl)-2-({6-[(tert-butoxycarbonyl) amino] pyridin-3- yl} methyl)-3- [ (4-methoxybenzyl) thio] pentanoate (0.669 g, 1.00 mmol) was dissolved in triethylsilane (0.75 mL) and trifluoroacetic acid (6.0 mL). The solution was heated to 60 °C for 3h and then concentrated. Purification of the residue by reversed-phase HPLC (C-8 column, linear gradient 40% 100% of MeCN in 5% aqueous MeCN containing 0.15% trifluoroacetic acid) gave the title diastereomeric compound as the trifluoroacetic salt (0.342g, 68%) after freeze-drying.

'H NMR (400 MHz, CD3CN/D20) : 8 7.70 (dd, J= 2.1, 9.2 Hz, 0. 5H), 7.66 (dd, J= 2.1, 9.2 Hz, 0.5 Hz), 7.61-7. 58 (m, 2H), 7.53-7. 51 (m, 1H), 7.46-7. 41 (m, 4H), 7.38-7. 32 (m, 2H), 7.22-7. 16 (m, 1H), 6.88 (d, J= 9.1 Hz, 0. 5H), 6.84 (d, J= 9.1 Hz, 0. 5H), 3.10-2. 74 (m, 6H), 2.17-2. 04 (m, 1H), 1.91-1. 78 (m, lH). 13C NMR (101 MHz, CD3CN/D20) : 6 175.3, 174.9, 153.0, 146.0, 145.8, 142.3, 141.1, 140.9, 134.0, 133.9, 129.4, 129.2, 127.9, 127.9, 127.8, 127.3, 127.2, 127.1, 124.9, 124.8, 124.4, 124.1, 113.9, 113.8, 53. 6, 53. 0, 41.3, 40.5, 37.9, 33.1, 33.0, 31.2, 30.3. HRMS (ESI) calculated for C23H25N202S 393.1637 (M+H) +, found 393.1650.

EXAMPLE 2 2-[(6-Aminopyridin-3-yl)methyl]-3-mercapto-5-(1-naphthyl) pentanoic acid was synthesised according to the procedure for Example 1.

1H NMR (400 MHz, CDC13): 6 8. 14-8.10 (d, 1H), 7.93-7. 89 (d, 1H), 7.80-7. 54 (m, 1H), 7.67-7. 35 (m, 6H), 6. 83-6. 77 (m, 1H), 3.52-3. 35 (m, 1H), 3.22-3. 12 (m, 2H), 2.90-2. 80 (m,

3H), 2.25-2. 13 (m, 1H), 2.05-1. 87 (m, 1H). HRMS (ESI) calculated for C21H23N2O2S 367.1480 (M+H) +, found 367.1497.

EXAMPLE 3 2- [ (6-Aminopyridin-3-yl) methyl]-5- (3-cyanophenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 1.

1H NMR (400 MHz, CD3CN/D20) : 6 7.73 (dd, J= 2. 2,9. 3 Hz, 0. 5H), 7.70 (dd, J= 2. 2,9. 3 Hz, 0. 5H), 7.58-7. 40 (m, SH), 6.90 (d, J= 9.1 Hz, 0. 5H), 6.88 (d, J= 9.3 Hz, 0. 5H), 2.99- 2.88 (m, 2H), 2.82-2. 71 (m, 4H), 2.12-2. 00 (m, 1H), 1.88-1. 74 (m, 1H).

3CNMR (101 MHz, CD3CN/D20) : 8 175.5, 174.9, 153.0, 146.0, 145.8, 143.1, 133.9, 132.4, 132.3, 130.3, 130.3, 129.8, 124.3, 124.0, 119.4, 113.9, 113.9, 111.6, 53.8, 52. 8, 41.1, 40.2, 37.4, 32.5, 32.5, 31.1, 30.5. HRMS (ESI) calcd for C18H2oN302S 342.1276 (M+H) +, found 342.1277 EXAMPLE 4 5- [3- (Aminocarbonyl) phenyl]-2- [ (6-aminopyridin-3-yl) methyl] -3- mercaptopentanoic acid was synthesised according to the procedure for Example 1, starting from 3-iodo-N-(2, 4,6-trimethoxybenzyl) benzamide. 3-iodo-N- (2, 4,6- trimethoxybenzyl) benzamid was synthesised from 3-iodobenzoic acid using standard procedures.

1H NMR (400 MHz, CD3CN/D20) : 8 7.72-7. 67 (m, 1H), 7.65-7. 61 (m, 2H), 7.52-7. 49 (m, 1H), 7.42-7. 35 (m, 2H), 6.89 (d, J= 9.3 Hz, 0.7H), 6.85 (d, J= 9.1 Hz, 0.3H), 3.00-2. 87 (m, 2H), 2.81-2. 72 (m, 4H), 2.13-2. 00 (m, 1H), 1.90-1. 86 (m, 1H).

13C NMR (101 MHz, CD3CN/D20) : 8 175.7, 175.1, 171.5, 161.7, 161.4, 153.0, 146.0, 145.8, 142.1, 142.0, 133.9, 133.4, 132.7, 129.1, 127.8, 127.7, 125.5, 124.3, 124.0, 114.0, 113.9, 53.7, 52.6, 41.0, 39.9, 37.7, 37.6, 32. 8, 32.7, 31.0, 30.4. HRMS (ESI) calcd for C18H22N303S 360.1382 (M+H) +, found 360. 1378.

EXAMPLE 5 2-[(6-Aminopyridin-3-yl) methyl]-5-[2-fluoro-4-(trifluoromethyl) phenyl]-3- mercaptopentanoic acid was synthesised according to the procedure for Example 1.

'H NMR (400 MHz, CD3CN/D20) : 8 7.75-7. 71 (m, 1H), 7.56 (d, J = 1. 6H, 1H), 7. 47-7. 35 (m, 3H), 6.91 (d, J= 9.3 Hz, 1 H), 3.04-2. 91 (m, 1H), 2.88-2. 74 (m, 4H).

3C NMR (101 MHz, CD3CN/D20) : 8 175. 4, 174.9, 162.0, 161.4, 159.6, 153.0, 146.0, 145.9, 134.0, 133.2, 133.0, 129.9, 124.2, 124.0, 121.4, 114.0, 113.9, 112.8, 112.6, 53.8, 53.0, 41.5, 40. 8, 36.3, 36.2, 31.2, 30.6, 26.5. HRMS (ESI) calcd for C18Hl9F4N202S 403.1103 (M+H)+, found 403. 1137.

EXAMPLE 6 2- [ (6-Aminopyridin-3-yl) methyl]-5- (3-chlorophenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 1.

1H NMR (500 MHz, CD3CN/D20) : 8 7.75 (dd, 0. 5H), 7.72 (dd, 0.5 H), 7.56 (d, 0. 5H), 7.54 (d, 0.5 H), 7.30-7. 10 (m, 4H), 6.92 (d, 0. 5H), 6.91 (d, 0. 5H), 3.02-2. 65 (m, 6H), 2.10- 2.00 (m, 1H), 1. 88-1. 74 (m, 1H). MS (ESI) 351.1 (M+H) +.

EXAMPLE 7 2- [ (6-Aminopyridin-3-yl) methyl]-5- (1, 3-benzodioxol-5-yl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 1. lH NMR (400 MHz, CD3CN/D20) : 8 7.72 (dd, 1H), 7.69 (d, 0. 5H), 7.55 (s, 0. 5H), 7.53 (s, 0. 5H), 6.89 (m, 1H), 6.77-6. 60 (m, 3H), 5.88 (s, 2H), 3.0-2. 70 (m, 5H), 2.58-2. 68 (m, 1H), 1.92-2. 08 (m, 1H), 1.69-1. 81 (m, 1H). HRMS (ESI) calculated for Cl8H2oN204S 361.1222 (M+H) +, found 361.1236.

EXAMPLE 8 2- [ (6-Aminopyridin-3-yl) methyl]-3-mercapto-5-pyridin-2-ylpentanoic acid was synthesised according to the procedure for Example 1, starting from 3-pyridin-2- ylpropanal.

1H NMR (600 MHz, D20) 8 ppm 1.90-2. 37 (m, 2 H), 2.70-2. 98 (m, 3 H), 3.05-3. 11 (m, 1 H), 3.12-3. 24 (m, 1 H), 3.32-3. 41 (m, 1 H), 6.89 (d, 1 H), 7.57 (s, 1 H), 7.75 (dd, 1 H), 7.80-7. 85 (m, 1 H), 7. 88 (d, 1 H), 8. 39-8. 46 (m, 1 H), 8.54-8. 60 (m, 1 H).

MS (ESI) 318.2 (M+H) +.

EXAMPLE 9 2- [ (6-Aminopyridin-3-yl) methyl]-3-mercapto-5- (3, 4,5-trimethoxyphenyl) pentanoic acid was synthesised according to the procedure for Example 1.

'H NMR (600 MHz,, CD3CN/D2O) 5ppm 1.71-1. 87 (m, 1H), 1.98-2. 10 (m, 1H), 2.58- 2.70 (m, 1H), 2.73-2. 87 (m, 4H), 2.90 (d, 0. 5H), 2. 88-3. 02 (m, 0. 5H), 3.65 (s, 3H), 3.75 (s, 3H), 3.75 (s, 3H), 6.48 (s, 1H), 6.49 (s, 1H), 6.88 (d, 0. 5H), 6.89 (d, 0. 5H), 7.52 (d, 1H), 7.67-7. 72 (m, 1H). MS (ESI) 407.2 (M+H) +.

EXAMPLE 10 2-[(6-Aminopyridin-3-yl)methyl]-3-mercapto-5-pyridin-3-ylpen tanoic acid was synthesised according to the procedure for Example 1, starting from 3-pyridin-3- ylpropanal.

'H NMR (600 MHz, CD3CN/D2O) 8 ppm 1. 78-1. 90 (m, 1H), 2.03-2. 19 (m, 1H), 2.71-2. 78 (m, 1H), 2.78-3. 02 (m, 4H), 3. 07-3. 18 (m, 1H), 6.90 (d, 1H), 7.56 (s, 1H), 7.73-7. 76 (m, 1H), 7.91-7. 95 (m, 1H), 8.40-8. 44 (m, 1H), 8. 55-8. 59 (m, 2H).

MS (ESI) 318. 2 (M+H) +.

EXAMPLE 11 2- [ (6-Aminopyridin-3-yl) methyl]-5- [4- (cyanomethyl) phenyl] -3-mercaptopentanoic acid was synthesised according to the procedure for Example 1.

'H NMR (500 MHz, CD3CN/D20) : 5 7.99 (dd, 0. 5H), 7.96 (dd, 0. 5H), 7.81 (d, 0. 5H), 7.80 (d, 0. 5H), 7.56-7. 46 (m, 4H), 7.17 (d, 0. 5H), 7.15 (d, 0. 5H), 4.11 (s, 2H), 3.26-2. 97 (m, 6H), 2.40-2. 25 (m, 1H), 2.17-2. 02 (m, 1H). MS (ESI) 356.2 (M+H) +.

EXAMPLE 12 2-[(6-Aminopyridin-3-yl) methyl]-5-(2-hydroxyphenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 1, starting from 1-iodo-2- [ (4- methoxybenzyl) oxy] benzene. 1-iodo-2- [ (4-methoxybenzyl) oxy] benzene was synthesised from 2-iodophenol using standard procedures.

IH NMR (500 MHz, 90% CD3CN/D20) 8 ppm 1.72-1. 87 (m, 1 H), 2.00-2. 15 (m, 1 H), 2.60-2. 75 (m, 1 H), 2.77-2. 94 (m, 4.6 H), 3.06-3. 11 (m, 0.4 H), 6.75-6. 81 (m, 2 H), 6.90-

6.94 (m, 1H), 7. 02-7. 13 (m, 2 H), 7.56 (d, 0.6 H), 7.57 (d, 0.4 H), 7.75 (dd, 0.6 H), 7.77 (dd, 0.4 H). MS (ESI) 333.2 (M+H) +.

EXAMPLE 13 2-[(6-Aminopyridin-3-yl)methyl]-5-[4-(aminosulfonyl) phenyl] -3- mercaptopentanoic acid was synthesised according to the procedure for Example 1, starting from 4-iodo-N (2, 4,6-trimethoxybenzyl) benzenesulfonamide. 4-iodo-N-(2, 4,6- trimethoxybenzyl) benzenesulfonamide was synthesised from 4-iodobenzenesulfonyl chloride using standard procedures.

1H NMR (500 MHz, 75% CD3CN/D20) 8 ppm 1.79-1. 92 (m, 1 H), 2.04-2. 18 (m, 1 H), 2.76-2. 88 (m, 4 H), 2.90-3. 07 (m, 2 H), 6.92 (d, 0.5 H), 6.93 (d, 0. 5 H), 7.40 (d, 1 H), 7.42 (d, 1 H), 7.57 (d, 0.5 H), 7.58 (d, 0.5 H), 7.72-7. 81 (m, 3 H). MS (ESI) 396.1 (M+H) +.

EXAMPLE 14 2- [ (6-Aminopyridin-3-yl) methyl]-3-mercapto-5- (4-methoxyphenyl) pentanoic acid was synthesised according to the procedure for Example 1.

IH NMR (500 MHz, 75% CD3CN/D2O) 8 ppm 1.73-1. 85 (m, 1 H), 1.99-2. 11 (m, 1 H), 2.61-2. 72 (m, 1 H), 2.75-2. 95 (m, 4.5 H), 2. 98-3. 04 (m, 0.5 H), 3.75 (s, 1.5 H), 3.76 (s, 1.5 H), 6.82-6. 88 (m, 2 H), 6.92 (d, 0. 5 H), 6.93 (d, 0. 5 H), 7.12 (d, 0. 5 H), 7.15 (d, 0. 5 H), 7.56 (s, 0.5 H), 7.58 (s, 0.5), 7.72-7. 78 (m, 1 H). MS (ESI) 347.2 (M+H) +.

EXAMPLE 15 2- [ (6-Aminopyridin-3-yl) methyl]-5- (4-hydroxyphenyl)-3-mercaptopentanoic acid was synthesized from 2- [ (6-aminopyridin-3-yl) methyl]-3-mercapto-5- (4- methoxyphenyl) pentanoic acid using standard conditions for the methoxy group hydrolysis (concentrated aqueous hydrochloric acid at reflux under argon for 24 h).

1H NMR (500 MHz, 25% CD3CN in D20) 8 ppm 1.73-1. 85 (m, 1 H), 1.94-2. 09 (m, 1 H), 2.59-2. 68 (m, 1 H), 2.75-2. 87 (m, 4 H), 2.90 (d, 0.5 H), 2.98-3. 03 (m, 0.5 H), 6.71-6. 76 (m, 2 H), 6.90-6. 95 (m, 1 H), 7.00-7. 07 (m, 2 H), 7.54-7. 57 (m, 1 H), 7. 71-7. 76 (m, 1 H). MS (ESI) 333.2 (M+H) +.

EXAMPLE 16 2- [ (6-Aminopyridin-3-yl) methyl]-3-mercapto-5- [4- (trifluoromethoxy) phenyl] - pentanoic acid was synthesised according to the procedure for Example 1.

1H NMR (500 MHz, CD3CN/D20) 8 ppm 1. 76-1. 88 (m, 1 H), 2.01-2. 14 (m, 1 H), 2.66- 3.07 (m, 6 H), 6.94 (d, 1 H), 7.16-7. 25 (m, 2 H), 7.26-7. 34 (m, 2 H), 7.59 (d, 1 H), 7.78 (dd, 1 H). MS (ESI) 401.3 (M+H) +.

EXAMPLE 17 2- [ (6-Aminopyridin-3-yl) methyl]-5- (1, 3-dimethyl-2, 4-oxo-1, 2,3, 4- tetrahydropyrimidin-5-yl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 1.

'H NMR (500 MHz, CD3CN/D20) 6 ppm 1.57-1. 76 (m, 1 H), 1.92-2. 06 (m, 1 H), 2.31- 2.45 (m, 1 H), 2.53-2. 63 (m, 1 H), 2.75-3. 07 (m, 4 H), 3.22 (s, 1.5 H), 3.23 (s, 1.5 H) 3.30 (s, 1.5 H), 3.30 (s, 1.5 H), 6.94 (d, 1 H), 7.30 (s, 0.5 H), 7. 32 (s, 0.5 H), 7.59-7. 64 (m, 1 H), 7.80 (dd, 1 H). MS (ESI) 379.2 (M+H) +.

EXAMPLE 18 2- [(6-Aminopyridin-3-yl) methyl]-3-mercapto-5-(tetrahydro-2-thienyl) pentanoic acid was synthesised according to the procedure for Example 1, starting from 3-thien-2- ylpropanal.

1H NMR (500 MHz,, 90% CD3CN/D2O) S ppm 1. 48-1. 60 (m, 3 H), 1.70-1. 90 (m, 3 H), 2.00-2. 10 (m, 2 H), 2.70-3. 10 (m, 6 H), 3.25-3. 33 (m, 1 H), 6.92 (d, 1 H), 7.59 (s, 1 H), 7.78 (dd, 1 H). MS (ESI) 327.3 (M+H) +.

EXAMPLE 19 2- [ (6-Aminopyridin-3-yl) methyl]-5- [3- (hydroxymethyl) phenyl]-3- mercaptopentanoic acid was synthesised according to the procedure for Example 1, starting from 1-iodo-3- { [ (4-methoxybenzyl) oxy] methyl} benzene. 1-iodo-3-{ [(4- methoxybenzyl) oxy] methyl} benzene was synthesized from (3-iodophenyl) methanol using standard procedures.

1H NMR (500 MHz, CD3CN/D2O) 8 ppm 1.94-2. 10 (m, 1 H), 2.21-2. 37 (m, 1 H), 2.78- 3.24 (m, 6 H), 4.77 (s, 1 H), 4.78 (s, 1 H), 7.09 (d, 0.5 H), 7.12 (d, 0.5 H), 7.34-7. 44 (m, 3

H), 7.48-7. 54 (m, 1 H), 7.73 (d, 0. 5H), 7.74 (d, 0. 5H), 7.91 (dd, 0. 5H), 7.96 (dd, 0. 5H). MS (ESI) 347.3 (M+H) +.

EXAMPLE 20 2-[(6-Aminopyridin-3-yl) methyl]-5-[2-(2, 4-dichlorophenoxy) phenyl]-3- mercaptopentanoic acid was synthesised according to the procedure for Example 1.

'H NMR (400 MHz, CDC13) : 8 7.64 (d, 1H), 7.51 (d, 1 H), 7.40 (d, 1H), 7.27 (m, 1H), 7. 18-7. 04 (m, 3H), 7.78-7. 69 (m, 3H), 3.15-2. 92 (m, 2H), 2. 87-2. 65 (m, 4H), 2.21-2. 08 (m, 1H), 1.89-1. 75 (m, 1H). HRMS (ESI) calculated for C23H22C12N203S 477. 0806 (M+H) +, found 477.0170..

EXAMPLE 21 2- [ (6-Aminopyridin-3-yl) methyl]-5- (3, 5-dimethylphenyl) -3-mercaptopentanoic acid was synthesised according to the procedure for Example 1. lH NMR (500 MHz, CD3CN/D20) 5 ppm 1.72-1. 85 (m, 1 H), 1.97-2. 11 (m, 1 H), 2.23 (s, 3 H), 2.24 (s, 3 H), 2.57-2. 66 (m, 1 H), 2.75-2. 87 (m, 4 H), 2.90 (d, 0.5 H), 2.99-3. 05 (m, 0. 5 H), 6.78-6. 85 (m, 3 H), 6.88-6. 94 (m, lH), 7.54 (d, 0. 5 H), 7.56 (d, 0. 5 H), 7.71 (dd, 0.5 H), 7.73 (d, 0.5 H). MS (ESI) 345.2 (M+H) +.

EXAMPLE 22 2- [ (6-Aminopyridin-3-yl) methyl]-3-mercapto-5- (4-propylphenyl) pentanoic acid was synthesised according to the procedure for Example 1.

'H NMR (500 MHz, CD3CN/D20) 8 ppm 0.84 (t, 3 H), 1.49-1. 58 (m, 2 H), 1.70-1. 81 (m, 1 H), 1.96-2. 04 (m, 1 H), 2.50 (t, 2 H), 2.60-2. 70 (m, 1 H), 2.71-2. 93 (m, 4 H), 2.93-3. 01 (m, 1 H), 6.88 (d, 1 H), 7.07-7. 10 (m, 4 H), 7.54 (d, 1 H), 7.71 (dd, 1 H). MS (ESI) 359.2 (M+H) +.

EXAMPLE 23 2- [ (6-Aminopyridin-3-yl) methyl]-5- (4-benzylphenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 1 starting from (4- iodophenyl) (phenyl) methanone.

IH NMR (500 MHz, 80% CD3CN/D20) 8 ppm 1.72-1. 82 (m, 1 H), 2.00-2. 10 (m, I H), 2. 72-2. 62 (m, 1 H), 2.78-3. 04 (m, 5H), 3.9 (s, 2 H), 6.90 (d, H), 7.08-7. 29 (m, 9H), 7.55 (d, 1 H), 7.73 (dd, 1 H). HRMS (ESI) calculated for C24H27N202S 407.1793 (M+H) +, found 407. 1804.

EXAMPLE 24 2-[(2-Amino-1, 3-thiazol-5-yl) methyl] -3-mercapto-5-phenylpentanoic acid was synthesised according to the procedure for Example 1 starting from tert-butyl 3-{2-[(tert- butoxycarbonyl) amino]-1,3-thiazol-5-yl}-2-(diethoxyphosphoryl) propanoate. Tert-butyl 3- {2-[(tert-butoxycarbonyl)amino]-1,3-thiazol-5-yl}-2-(diethox yphosphoryl)propanoate was synthesised as shown in Scheme 1.

IH NMR (500 MHz, 90% CD3CN/D2O) 8 ppm 1. 78-1. 90 (m, 1H), 2.00-2. 11 (m, 1H), 2.68-2. 77 (m, 1H), 2. 78-3. 2 (m, 4. 5H), 3.05-3. 11 (m, 0. 5H), 6.85-6. 88 (m, 1H), 7.16-7. 33 (m, 5H). MS (ESI) 323.2 (M+H) \ EXAMPLE 25 2- (3-Azabicyclo [3.2. 1] oct-8-ylmethyl)-3-mercapto-5-phenylpentanoic acid was synthesised according to the procedure for Example 1 starting from tert-butyl 8- [3-tet-t- butoxy-2- (diethoxyphosphoryl) -3-oxopropyl]-3-azabicyclo [3.2. 1] octane-3-carboxylate.

Tert-butyl 8- [3-tert-butoxy-2- (diethoxyphosphoryl)-3-oxopropyl]-3- azabicyclo [3.2. 1] octane-3-carboxylate was synthesised as shown in Scheme 2.

'H NMR (400 MHz, CD3CN/D2O) : b 7.90-7. 80 (m, 2H), 7. 80-7. 70 (m, 3H), 3.80-3. 60 (m, 2H), 3.60-3. 35 (m, 4H), 3.35-3. 18 (m, 1H), 3.18-3. 00 (m, 1H), 2.90-1. 80 (m, 11H). MS (ESI) 333.5 (M+H)+.

EXAMPLE 26 This Example illustrates the preparation of 2-[(6-aminopyndin-3-yl) methyl]-3- mercapto-5-(3-{[methyl (2-phenylethyl) amino] carbonyl}phenyl)pentanoic acid.

(a) 3-{5-tert-butoxy-4-({6-[(tert-butoxycarbonyl)amino]pyridin-3 -yl}methyl)-3-[(4- methoxvbenzvl) thiol-5-oxopentyl} benzoic acid

KOH (5 mL of a 1M solution in ethanol) was added to a solution of ethyl 3-{5-tert- butoxy-4- ( {6- [ (tert-butoxycarbonyl) amino] pyridin-3-yllmethyl)-3- [ (4- methoxybenzyl) thio] -5-oxopentyl} benzoate (0.27 g, 0.406 mmol, synthesised according to the procedure for Example 1) in ethanol (2 mL), and the mixture was stirred at room temperature for 2 h and then at 50 °C for 2 h. The reaction mixture was then diluted with diethyl ether and water. The organic phase was extracted with 0. 1M aqueous KOH and the combined aqueous phase was acidified (pH 5) using 3M aqueous HC1. The aqueous phase was then extracted with diethyl ether and the organic phase was washed with brine, dried and concentrated. Purification of the residue by reversed-phase HPLC (C-8 column, linear gradient 40%- 100% of MeCN in 5% aqueous MeCN containing 0.1 M ammonium acetate) gave a residue that was dissolved in toluene and water and concentrated to give 3- {5-tert-butoxy-4-({6-[(tert-butoxycarbonyl)amino]pyridin-3-y l}methyl)-3-[(4- methoxybenzyl) thio]-5-oxopentyl} benzoic acid (0.12 g, 54%).

(b) tert-butyl-2-({6-[(tert-butoxycarbonyl)amino]pyridin-3-yl}me thyl)-3-[(4- methoxybenzvl) thio1-5- (3-,rmethvl (2-phenvlethyl) aminolcarbonylphenyllpentanoate N-methylphenethylamine (20 N. L, 0.14 mmoL), HATU (55 mg, 0.15 mmoL) and iPr2EtN (46 L, 0.26 mmoL) was added to a solution of 3-{5-tert-butoxy-4-({6-[(tert- butoxycarbonyl) amino] pyridin-3-yl} methyl)-3- [ (4-methoxybenzyl) thio] -5- oxopentyl} benzoic acid (84 mg, 0.132 mmol) in DMF (2 mL) under argon at 0 °C. The reaction mixture was stirred for 2 h and was then quenched with ice. Diethylether and water was added and the aqueous phase was extracted diethyl ether. The combined organic phase was dried and concentrated. Flash chromatography (heptan/EtOAc, 3: 1) gave tert- butyl 2-({6-[(tert-butoxycarbonyl) amino] pyridin-3-yl} methyl)-3- [ (4-methoxybenzyl) thio] - 5-(3-{[methyl (2-phenylethyl) amino] carbonyl} phenyl) pentanoate (81 mg, 81. 4 %).

(c) 2-[(6-aminopyridin-3-yl)methyl]-3-mercapto-5-(3-{[methyl (2- phenylethyl) phenyl') pentanoic acid tert-butyl 2-({6-[(tert-butoxycarbonyl) amino] pyridin-3-yl} methyl)-3- [ (4- methoxybenzyl) thio]-5- (3- { [methyl (2-phenylethyl) amino] carbonyl} phenyl) pentanoate (80 mg, 0.106 mmol) was dissolved in triethylsilane (0.4 mL) and trifluoroacetic acid (3.0 mL). The solution was heated to 60 °C for 1 h and was then concentrated. Purification of

the residue by reversed-phase HPLC (C-8 column, linear gradient 20% @ 100% of MeCN in 5% aqueous MeCN containing 0.15% trifluoroacetic acid) gave the title diastereomeric compound as the trifluoroacetic salt (64 mg, 100 %) after freeze-drying.

'H NMR (400 MHz, CD3CN/D20) : 8 7.76-6. 63 (m, 12 H), 3.71 (m, 1H), 3.40 (m, 1H), 3.21-2. 54 (m, 11H), 2.12-1. 63 (m, 2H). HRMS (ESI) calcd for C27H3lN303S 478.2164 (M+H) +, found 478. 2133.

EXAMPLE 27 3- [5- (6-Aminopyridin-3-yl)-4-carboxy-3-mercaptopentyl] benzoic acid was synthesised according to the procedure for Example 26 starting from 3- {5-tert-butoxy-4- ({6-[(tert-butoxycarbonyl) amino] pyridin-3-yl} methyl)-3- [ (4-methoxybenzyl) thio] -5- oxopentyl} benzoic acid.

IH NMR (400 MHz, D20) : 8 8.05-8. 01 (dd, 1H), 8.01-7. 99 (s, l H), 7.90-7. 86 (dd, 1H), 7.73-7. 70 (s, 1H), 7.68-7. 58 (m, 2H), 7.08-7. 04 (d, 1H), 3.18-3. 08 (m, 1H), 3.06-2. 90 (m, 5H), 2.36-2. 26 (m, 1H), 2.14-2. 04 (m, 1H). HRMS (ESI) calculated for ClsH2oN204S 361.1222 (M+H) +, found 361.1212.

EXAMPLE 28 2- [ (6-Aminopyridin-3-yl) methyl]-5- [3- (3, 4-dihydroisoquinolin-2 ( lI)- ylcarbonyl) phenyl] -3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (500 MHz, CD3CN/D20) : # 7.73 (m, 1H), 7.52 (s, 1H), 7.44-7. 11 (m, 8H), 6.90 (m, 1H), 4.81 (s, 1H), 4.54 (s, 1H), 3.89 (br, 1H), 3.57 (br, 1H), 2.99-2. 65 (m, 8H), 2.09 (m, 1H), 1.85 (m, 1H). HRMS (ESI) calcd for C27H29N303S 476.2008 (M+H) +, found 476.2002.

EXAMPLE 29 2-[(6-Aminopyridin-3-yl) methyl]-5-{3-[(6, 7-dimethoxy-3,4-dihydroisoquinolin- 2 (lH)-yl) carbonyl] phenyl}-3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (400 MHz, CD3CN/D20): 6 7. 68 (m, 1H), 7.49 (s, 1H), 7. 38-7. 22 (m, 4H), 6.90- 6.72 (m, 2. 5H), 6.47 (s, 0. 5H), 4.69 (s, 1H), 4.44 (s, 1H), 3.96-3. 46 (m, 8H), 3.01-2. 59 (m,

8H), 2.17-1. 67 (m, 2H). HRMS (ESI) calcd for C29H33N305S 536.2219 (M+H) +, found 536.2248.

EXAMPLE 30 2- [(6-Aminopyridin-3-yl)methyl]-3-mercapto-5-{3-[(2-pyridin-2- ylethoxy) carbonyl] phenyl} pentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (400 MHz, CD3CN/D20): 5 8.64 (d, 1H), 8.46 (dd, 1H), 7.98 (d, 1H), 7.88 (dd, 1H), 7.77-7. 64 (m, 3H), 7.58-7-31 (m, 3H), 6.89 (dd, 1H), 4.65 (t, 2H), 3.50 (t, 2H), 2.99- 2.62 (m, 6H), 2.03 (m, 1H), 1.79 (m, 1H). HRMS (ESI) calcd for C25H27N304S 466.1803 (M+H) +, found 466.1813.

EXAMPLE 31 2- [ (6-Aminopyridin-3-yl) methyl]-5- (3-1 [2- (2, 6- dichlorophenyl) ethoxy] carbonyl} phenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (400 MHz, CD3CN/D20): 8 7.69 (m, 3H), 7.51 (s, 1H), 7.38-7. 28 (m, 4H), 7.12 (m, 1H), 6.84 (m, 1H), 4.48 (m, 2H), 3.62 (m, 0. 5H), 3.31 (m, 2H), 3.10 (m, 0. 5H), 2. 98- 2.53 (m, 5H), 2.0 (m, 1H), 1.75 (m, 1H). HRMS (ESI) calcd for C26H26C12N204S 533.1069 (M+H) +, found 533.1071.

EXAMPLE 32 2-[(6-Aminopyridin-3-yl)methyl]-5-[3-(ethoxycarbonyl) phenyl] -3- mercaptopentanoic acid was synthesised according to the procedure for Example 26 starting from ethyl 3- {5-tert-butoxy-4-({6-[(tert-butoxycarbonyl) amino] pyridin-3- yl}methyl)-3-[(4-methoxybenzyl)thio]-5-oxopentyl}benzoate.

IH NMR (500 MHz, CD3CN/D20): 8 7.90 (d, 1H), 7.87 (s, 1H), 7.74 (d, 1H), 7.58 (s, 1H), 7.53 (d, 1H), 7.48 (t, 1H), 6.91 (d, 1H), 4.41 (q, 2H), 2.95-3. 03 (m, 1H), 2.95-2. 82 (m, 4H), 2.75-2. 80 (m, 1H), 2.14-2. 23 (m, 1H), 1.95-2. 03 (m, 1H), 1.41 (t, 3H). HRMS (ESI) calculated for C20H25N2O4S 389.1535 (M+H) +, found 389.1555.

EXAMPLE 33 2-[(6-Aminopyridin-3-yl)methyl]-5-(3- { [ (2-fluoroethyl) amino] carbonyl} phenyl)-3- mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (500 MHz, 10% CD3CN in D2O) : 8 7.95 (dd, 0. 5H), 7.90 (dd, 0.5 H), 7. 86-7. 81 (m, 2H), 7.75 (dd, 0. 5H), 7.73 (dd, 0. 5H), 7.70-7. 60 (m, 2H), 7.13 (d, 0. 5H), 7.07 (d, 0. 5H), 4.89-4. 86 (m, 1H), 4.8-4. 76 (m, 1H), 3.91-3. 94 (m, 1H), 3. 85-3. 89 (m, 1H), 3.25- 3.12 (m, 2. 5H), 3.11-2. 98 (m, 3H), 2.92-2. 97 (m, 0. 5H), 2.41-2. 24 (m, 1H), 2.21-2. 01 (m, 1H). HRMS (ESI) calculated for C2oH25FN303S 406.1600 (M+H) +, found 406.1560.

EXAMPLE 34 2-[(6-Aminopyridin-3-yl) methyl]-5- {3-[(dimethylamino) carbonyl] phenyl}-3- mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (500 MHz, 5% CD3CN/D20) : 8 7.77 (dd, 0. 5H), 7.72 (dd, 0. 5H), 7.52-7. 54 (m, 1H), 7.45-7. 32 (m, 2H), 7.25-7. 29 (m, 2H), 6.91 (d, 0. 5H), 6.93 (d, 0. 5H), 3.07 (s, 3H), 2.95 (two s, 3H), 3.05-2. 71 (m, 6H), 2.19-2. 0 (m, 1H), 1.99-1. 82 (m, 1H). HRMS (ESI) calculated for C2oH26N303S 388.1695 (M+H) +, found 388. 1683.

EXAMPLE 35 2- [ (6-Aminopyridin-3-yl) methyl] -3-mercapto-5- {3- [ (vinylamino) carbonyl] phenyl} pentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (500 MHz, 10% CD3CN/D2O) : 5 7.71 (two dd, 1H), 7.53 (two dd, 0. 5H), 6.89 (m, 1H), 6.77-6. 60 (m, 3H), 5. 88 (s, 2H), 3.0-2. 70 (m, 5H), 2.62 (m, 1H), 2.00 (m, 1H), 1.75 (m, 1H). HRMS (ESI) calculated for C20H24N303S 386. 1538 (M+H) +, found 386.1470.

EXAMPLE 36 2- [ (6-Aminopyridin-3-yl) methyl]-5- [3- ( { [2- (1, 3-benzodioxol-5- yl) ethyl] amino} carbonyl) phenyl] -3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (500 MHz, 20% CD3CN/D20) 8 ppm 1. 88-2. 06 (m, 1 H), 2.10-2. 27 (m, 1 H), 2.79-3. 11 (m, 8 H), 3.68 (t, 2 H), 6.00 (s, 2 H), 6.85 (m, 1 H), 6.90 (m, 2 H), 6.96 (d, 0.7 H), 7.01 (d, 0. 3 H), 7.47 (m, 1.2H), 7.51 (m, 0. 6 H), 7.56 (s, 0. 7 H), 7. 58 (s, 0. 3 H), 7.62 (s,

2 H), 7.76 (d, 0.7 H), 7.81 (d, 0.3 H). HRMS (ESI) calculated for C27H29N305S 508.1906 (M+H) +, found 508.1935.

EXAMPLE 37 2-[(6-Aminopyridin-3-yl) methyl]-5- {3-[(dibenzylamino) carbonyl] phenyl}-3- mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (500 MHz, , 50% CD3CN/D2O) 8 ppm 2.28-2. 40 (m, 1 H), 2.52-2. 63 (m, 1 H), 3.25-3. 53 (m, 6 H), 4.99 (s, 2 H), 5.23 (s, 2 H), 7.46 (d, 0.4 H), 7.48 (d, 0.6 H), 7.71 (d, 2 H), 7.83-8. 00 (m, 12 H), 8.08 (s, 1 H), 8.25 (dd, 0.4 H), 8.28 (dd, 0.6 H).

HRMS (ESI) calculated for C32H33N303S 540.2321 (M+H) +, found 540.2340.

EXAMPLE 38 2-[(6-Aminopyridin-3-yl)methyl]-5-(3-{[(2- hydroxyethyl) (methyl) amino] carbonyl} phenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (500 MHz, 50% CD3CN/D2O) 6 ppm 1.71-2. 11 (m, 2 H), 2.67-2. 96 (m, 6 H), 2.89 (s, 1.5 H), 3.01 (s, 1.5 H), 3.34 (q, 1 H), 3.52-3. 57 (m, 1 H), 3.59 (t, 1 H), 3.77 (t, 1 H), 6.74-6. 86 (m, 1 H), 7.12-7. 41 (m, 4 H), 7.45 (s, 1 H) 7.58-7. 63 (m, 0.5 H), 7.65-7. 69 (m, 0.5 H). HRMS (ESI) calculated for C2lH28N304S 418. 1800 (M+H) +, found 418.1752.

EXAMPLE 39 2-[(6-Aminopyridin-3-yl)methyl]-5-{3-[(3-hydroxypyrrolidin-1 - yl) carbonyl] phenyl}-3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (400 MHz, CD3CN/D20) : 8 8.35-8. 15 (m, 1H), 8.05 (br s, 1H), 8.00-7. 75 (m, 4H), 7.50-7. 35 (m, 1H), 6.16 (brm, 0. 5H), 6.02 (brm, 0. 5H), 5.02 (brm, 0. 5H), 4. 88 (br m, 0. 5H), 4.50-3. 60 (m, 4H), 3.55-3. 20 (m, 7H), 3.0-2. 2 (m, 4H). HRMS (ESI) calculated for C22H28N304S 430. 1829 (M+H) +, found 430.1801.

EXAMPLE 40 2- [ (6-Aminopyridin-3-yl) methyl]-5- (3- { [4- (4-chlorophenyl) piperazin-1- yl] carbonyl} phenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

IH NMR (400 MHz, CD3CN) : 8 7.75-7. 67 (m, 1H), 7.52-7. 47 (dd, 1 H), 7.40-7. 28 (m, 5H), 7.12-7. 07 (m, 3H), 6.90-6. 84 (m, 1H), 4.00-3. 50 (m, 4H), 3.40-3. 20 (m, 4H), 3.03-2. 90 (m, 1H), 2.87-2. 70 (m, 5H), 2.17-2. 03 (m, 1H), 1.97-1. 89 (m, 1H). HRMS (ESI) calculated for C28H31ClN4 03S 539.1884 (M+H) +, found 539.1868.

EXAMPLE 41 2- [ (6-Aminopyridin-3-yl) methyl]-5- (3- { [benzyl (methyl) amino] carbonyl} phenyl)- 3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

'H NMR (400 MHz, CD3CN) : 8 7.75-7. 18 (m, llH), 6.88-6. 80 (d, 1 H), 4. 80-4. 70 (s, 1H), 4.53-4. 45 (s, 1H), 3.00-2. 95 (m, 1H), 2.93-2. 90 (s, 3H), 2.88-2. 78 (m, 5H), 2.05-2. 00 (m, 1H), 1.99-1. 94 (m, 1H). HRMS (ESI) calculated for C26H29N303S 464. 2008 (M+H) +, found 464. 1972.

EXAMPLE 42 2- [ (6-Aminopyridin-3-yl) methyl]-3-mereapto-5- [3- (pyrrolidin-l- ylcarbonyl) phenyl] pentanoic acid was synthesised according to the procedure for Example 26.

'H NMR (500 MHz, 95% CD3CN in D2O) : 8 7.75 (dd, 0. 5H), 7.69 (dd, 0.5 H), 7.51-7. 54 (m, 1H), 7.44-7. 30 (m, 4H), 6.91 (d, 0. 5H), 6.87 (d, 0. 5H), 3.53 (t, 2H), 3.30-3. 40 (m, 2H), 3.00-2. 79 (m, 5. 5H), 2.67-2. 74 (m, 0. 5H), 2.18-1. 8 (m, 6H). HRMS (ESI) calculated for C22H28N303S 414.1851 (M+H) +, found 414. 1837.

EXAMPLE 43 2- [ (6-Aminopyridin-3-yl) methyl]-5- (3- { [4-(ethoxycarbonyl) piperidin-1- yl] carbonyl} phenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

IH NMR (500 MHz, CD3CN/D2O) : 8 1.28 (t, 3H), 1.59-1. 79 (m, 2H), 1.86-1. 96 (m, 2H), 2.0-2. 22 (m, 2H), 2.68-2. 75 (m, 1H), 2.80-3. 12 (m, 7H), 3.13-3. 25 (m, 1H), 3.65 (d, 1H),

4.18 (q, 2H), 4.40-4. 48 (m, 1H), 6.95-7. 00 (m, 1H), 7.27-7. 31 (m, 2H), 7.36-7. 48 (m, 2H), 7.60 (s, 1H), 7.78 (dd, 0. 5H), 7.82 (dd, 0. 5H). HRMS (ESI) calculated for C26H34N305S 500.2219 (M+H) +, found 500.2233.

EXAMPLE 44 2- [ (6-Aminopyridin-3-yl) methyl]-5- (3- { [4-(hydroxymethyl) piperidin-1- yl] carbonyl} phenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (400MHz, CD3CN): 8 7.65-7. 71 (dd, 1H), 7.49-7. 52 (d, 1H), 7.18-7. 36 (m, 4H), 6.82-6. 85 (dd, 1H), 3.41-3. 47 (m, 4H), 2.77-3. 10 (m, 7H), 2.0-2. 1 (m, 2H), 1.68-1. 92 (m, 5H). HRMS (ESI) calculated for C24H32N304S 458. 2114 (M+H) +, found 458. 2097.

EXAMPLE 45 2- [ (6-Aminopyridin-3-yl) methyl]-3-mercapto-5- { 3- [ (3-oxopiperazin-1- yl) carbonyl] phenyl} pentanoic acid was synthesised according to the procedure for Example 26.

'H NMR (500 MHz, CD3CN/D20) 5 ppm 1.77-1. 90 (m, 1H), 1.99-2. 12 (m, 1H), 2.75-3. 0 (m, 6H), 3.25-3. 58 (m, 4H), 3.80-4. 10 (m, 1H), 4.2 (s, 1H), 6.89 (d, 0. 5H), 6.91 (d, 0. 5H), 7.24-7. 29 (m, 2H), 7.31-7. 42 (m, 2H), 7.52 (s, 1H), 7.71 (dd, 0. 4H), 7.74 (dd, 0. 6H).

HRMS (ESI) calculated for C22H27N404S 443.1753 (M+H) +, found 443.1766.

EXAMPLE 46 2-[(6-Aminopyridin-3-yl)methyl]-5-(3-{ [benzyl (3-ethoxy-3- oxopropyl) amino] carbonyl} phenyl) -3-mercaptopentanoic acid was synthesised according to the procedure for Example 26.

1H NMR (500 MHz, CD3CN/D20) 8 ppm 1.06 (t, 1H), 1.19 (t, 2H), 1.67-1. 88 (m, 1H), 1.90-2. 15 (m, 1H), 2.40-3. 0 (m, 8H), 3.40-3. 58 (m, 0.7H), 3.58-3. 66 (m, 1.3H), 3.91 (q, 0. 7H), 4.07 (q, 1.3H), 4.47 (s, 1.3H), 4.69 (s, 0.7H), 6.80-6. 92 (m, 1H), 7.1-7. 4 (m, 9H), 7.46 (s, 0.7H), 7.50 (s, 0.3H), 7.60-7. 74 (m, 1H). HRMS (ESI) calculated for C30H36N305S 550.2376 (M+H) +, found 550.2361.

EXAMPLE 47 2- [ (6-Aminopyridin-3-yl) methyl]-5- (3- { [ (cyanomethyl) (methyl) amino]- sulfonyl} phenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 1, starting from N-(cyanomethyl)-3-iodo-N-methylbenzenesulfonamide. N- (cyanomethyl)-3-iodo-N-methylbenzenesulfonamide was synthesised from 3- iodobenzenesulfonyl chloride using standard procedures.

'H NMR (500 MHz, CD3CN/D20) : 8 7.79 (dd, 0. 5H), 7.76 (dd, 0. 5H), 7.74-7. 69 (m, 2H), 7.64-7. 54 (m, 3H), 6.95 (d, 0. 5H), 6.94 (d, 0. 5H), 4.29 (s, 2H), 3.11-3. 00 (m, 2H), 2. 86 (s, 3H), 2.98-2. 78 (m, 4H), 2.20-2. 09 (m, 1H), 1.95-1. 83 (m, 1H). HRMS (ESI) calculated for C20H25N204S2 449.1317 (M+H) +, found 449.1329.

EXAMPLE 48 2-[(6-Aminopyridin-3-yl) methyl]-5-(3-{ [(2S)-2-(anilinomethyl) pyrrolidin-1- yl] sulfonyl} phenyl)-3-mercaptopentanoic acid was synthesised according to the procedure for Example 1, starting from N- (l (2S)-1- [ (3-iodophenyl) sulfonyl] pyrrolidin-2- yl} methyl) aniline. N (22-1-[(3-iodophenyl) sulfonyl] pyrrolidin-2-yl} methyl) aniline was synthesised from 3-iodobenzenesulfonyl chloride using standard procedures.

1H NMR (500 MHz, CD30D) : 8 7.71 (dd, J = 2.1, 9.1 Hz, 1H), 7.59-7. 45 (m, 7H), 7. 31- 7.29 (m, 3H), 6.89 (d, J= 9.3 Hz, 1H), 3.83-3. 75 (m, 1H), 3.53 (ddd, J= 3.1, 6.0, 13.0 Hz, 1H), 3.44-3. 36 (m, 2H), 3.26-3. 18 (m, 1H), 3.00-2. 70 (m, 6H), 2.05-1. 97 (m, 1H), 1.82- 1.65 (m, 3H), 1.57-1. 50 (m, 1H), 1.42-1. 32 (m, 1H). HRMS (ESI) calculated for C28H34N404S2 555.2100 (M+H) +, found 555.2032.

EXAMPLE 49 2-[(6-Aminopyridin-3-yl) methyl]-3-mercapto-5-{3-[(methylamino) sulfonyl]- phenyl} pentanoic acid was synthesised according to the procedure for Example 1, starting <BR> <BR> <BR> from N-(2-furylmethyl)-3-iodo-N-methylbenzenesulfonamide. N-(2-furylmethyl)-3-iodo- N-methylbenzenesulfonamide was synthesised from 3-iodobenzenesulfonyl chloride using standard procedures.

'H NMR (500 MHz, CD30D) : 8 7. 85 (dd, J= 2.1, 9.1 Hz, 1H), 7.69-7. 65 (m, 3H), 7. 51- 7.50 (m, 2H), 6.94 (dd, J= 0.5, 9.1 Hz, 1H), 3.12-3. 07 (m, 2H), 3.00-2. 96 (m, 1H), 2.93-

2.77 (m, 3H), 2.51 (s, 3H), 2.16-2. 10 (m, 1H), 1.91-1. 83 (m, 1H). HRMS (ESI) calculated for C18H23N3O4S2 410.1208 (M+H)+, found 410.1207.

EXAMPLE 50 2- [ (6-Aminopyridin-3-yl) methyl]-3-mercapto-5- (3- { [methyl (2- phenylethyl) amino] sulfonyl} phenyl) pentanoic acid was synthesised according to the procedure for Example 1, starting from 3-iodo-N-methyl-N-(2- phenylethyl) benzenesulfonamide. 3-iodo-N-methyl-N-(2-phenylethyl)benzenesulfonamide was synthesised from 3-iodobenzenesulfonyl chloride using standard procedures.

IH NMR (400 MHz, CDC13) : 8 7.64 (s, 1H), 7.54-7. 57 (d, 3H), 7.39-7. 40 (d, 3H), 7.24- 7.27 (t, 3H), 7.14-7. 20 (m, 3H), 6.75 (s, 2H), 3.23-3. 27 (t, 2H), 2.96-3. 03 (m, 3H), 2.80- 2. 84 (t, 3H), 2.72 (s, 3H), 2.07 (s, 1H), 1.69-1. 80 (dd, 1H), 1.53-1. 55 (d, 1H). MS (ESI) 514.3 (M+H) +.

EXAMPLE 51 This Example illustrates the preparation of 2-[(6-aminopyridin-3-yl) methyl] -3- mercapto-5- [3- (tetrahydrofuran-3-yloxy) phenyl] pentanoic acid.

(a) tert-butyl(3-iodophenoxy)dimethylsilane Imidazole (7.8 g, 115 mmol) was added to a solution of 3-iodophenol (12.7 g, 58 mmol) and tert-butyl (chloro) dimethylsilane (9.9 g, 65 mmol) in dichloromethane (80 mL) at 0 °C. The reaction mixture was stirred at rt overnight. The suspension was washed three times with water and once with brine, dried and concentrated to give crude tert-butyl (3- iodophenoxy) dimethylsilane (20 g, 93%).

(b) tert-butyl 2-({6-[(tert-butoxycarbonyl)amino]pyridin-3-yl}methyl)-5-(3- hydroxyphenyl)-3-[(4-methoxybenzyl)thio]pentanoate Glacial acetic acid (190 L, 3.3 mmoL) was added to a solution of tert-butyl 2-({6- [ (tert-butoxycarbonyl) amino] pyridin-3-yl} methyl)-5- (3- { [tert- butyl (dimethyl) silyl] oxy} phenyl)-3- ( (4-methoxybenzyl) thio] pentanoate (800 mg, 0.89 mmol, synthesised according to the procedure for Example 1, starting from tert-butyl (3- iodophenoxy) dimethylsilane) in dry THF (10 mL). Tetrabutylammonium fluoride

trihydrate (489 mg, 1.5 mmol) was added and the mixture was stirred for 12 h at room temperature. EtOAc (150 mL) was added and the solution was washed with saturated aqueous NaHC03, water and brine, dried and concentrated. Flash chromatography (CH2Cl2/EtOAc, 10: 1) gave tert-butyl 2-({6-[(tert-butoxycarbonyl) amino] pyridin-3- yl} methyl)-5- (3-hydroxyphenyl)-3- [ (4-methoxybenzyl) thio] pentanoate (660 mg, 98 %).

(c) tert-butyl 2-({6-[(tert-butoxycarbonyl)amino]pyridin-3-yl}methyl)-3-[(4 - methoxYbenzyl) thiol-5-[3-(tekahydrofuran-3-yloxy) phenyllpentanoate 1, 1'-azobis (N, N-dimethylformamide) (134 mg, 0.78 mmol) was added to a solution of tri-n-butylphosphine (221 pL, 0.89 mmol) in toluene (2 mL). Tetrahydrofuran-3-ol (36 µL, 44 mmol) and tert-butyl 2-({6-[(tert-butoxycarbonyl) amino] pyridin-3-yl} methyl)-5- (3-hydroxyphenyl)-3- [ (4-methoxybenzyl) thio] pentanoate (154 mg, 0.25 mmol) was added sequentially. The reaction mixture was stirred for 12 h at 80 °C. Toluene (100 mL) was added and the mixture was washed with brine, dried and concentrated. Flash chromatography (toluene/EtOAc, 100: 0 to 70: 30) gave tert-butyl 2-({6-[(tert- butoxycarbonyl) amino] pyridin-3-yl} methyl)-3- [ (4-methoxybenzyl) thio]-5- [3- (tetrahydrofuran-3-yloxy) phenyl] pentanoate (75 mg, 35 %).

(d) 2- (6-aminopyridin-3-vl) meth-3-mercapto-5- [3- (tetrahydrofuran-3- vloxv ! phenyllpentanoic acid 2-[(6-aminopyridin-3-yl)methyl]-3-mercapto-5-[3-(tetrahydrof uran-3- yloxy) phenyl] pentanoic acid was synthesised according to the procedure for Example 1, starting from tert-butyl 2-({6-[(tert-butoxycarbonyl) amino] pyridin-3-yl} methyl)-3- [ (4- methoxybenzyl) thio]-5- [3- (tetrahydrofuran-3-yloxy) phenyl] pentanoate.

1H NMR (500 MHz, CD3CN/D20 (1 : 1) : 6 7.72 (dd, 1H), 7.53 (d, 1H), 7.22 (dd, 1H), 6.90 (d, 1H), 6.83 (d, 1H), 6.76-6. 72 (m, 2H), 4.98 (m, 1H), 3.93-3. 79 (m, 4H), 2.99-2. 84 (m, 3H), 2.83-2. 66 (m, 3H), 2.27-2. 18 (m, 1H), 2.07-1. 96 (m, 2H), 1. 83-1. 73 (m, 1H). HRMS (ESI) calculated for C2lH27N204S 403.1692 (M+H) +, found 403. 1698.

EXAMPLE 52 2- [ (6-Aminopyridin-3-yl) methyl]-3-mercapto-5- [3- (tetrahydrofuran-3-ylmethoxy)- phenyl] pentanoic acid was synthesised according to the procedure for Example 51.

IH NMR (400 MHz, CD3CN) : # 7.75-7. 69 (d, 1H), 7.58-7. 56 (s, 1 H), 7.25-7. 18 (m, 1H), 6.88-6. 75 (m, 4H), 3. 98-3. 58 (m, 6H), 3.10-3. 00 (m, 1H), 2.95-2. 82 (m, 3H), 2.74-2. 65 (m, 2H), 2.13-2. 03 (m, 1H), 1.98-1. 66 (m, 4H). MS (ESI) 417.9 (M+H) +.

EXAMPLE 53 The activities of certain Examples in the assay described in: Dirk Hendriks, Simon Schare and Marc van Sande, Clinical Chemistry, 31,1936-1939 (1985) are presented in Table I below.

TABLE I Example No. IC50 6 0. 8 pm 7 0. 8 1M 11 0. 8 UM : 18 1. 0 pm 24 6.3 µM 25 4. 0 pM 28 0.8 µM Example No. IC5o 31 0.6 µM 33 0. 6 MM 41 0. 6 pM 42 0. 6 µM 43 2. 0 FM 47 1. 0 Jim Abbreviations HOAc = acetic acid HOAc = acetic acid MeOH = methanol MeOH = methanol min = minutes min = minutes rt = room temperature rt = room temperature DMF = dimethylformamide TFA = trifluoroacetic acid DMSO = dimethyl sulfoxide THF = tetrahydrofuran EtOAc = ethyl acetate h = hour DBU = 1, 8-diazabicyclo [5. 4. 0] undec-7-ene HATU = 0- (7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate

SCHEME 1 NHBOC NHBOC 1. tBuOzCCH2PO (OEt) N= b*enzene/pipeddine s reflux ! 16 h 2. NaCNBH3/HOAc (EtO) OP o< EtOH/0°C-rt/72 h COOtBu "1g% COOtBu SCHEME 2