Thrombin is a serine protease present in blood plasma in the form of a precursor, prothrombin. Thrombin plays a central role in the mechanism of blood coagulation by converting the solution plasma protein, fibrinogen, into insoluble fibrin.
Edwards et al., J. Amer. Chem. Soc., (1992) vol. 114, pp. 1854-63, describes peptidyl xcex1-ketobenzoxazoles, which are reversible inhibitors of the serine proteases human leukocyte elastase and porcine pancreatic elastase. European Publication 363 284 describes analogs of peptidase substrates in which the nitrogen atom of the scissile amide group of the substrate peptide has been replaced by hydrogen or a substituted carbonyl moiety. Australian Publication 86245677 also describes peptidase inhibitors having an activated electrophilic ketone moiety such as fluoromethylene ketone or xcex1-keto carboxyl derivatives. R. J. Brown et al., J. Med. Chem., Vol. 37, pages 1259-1261 (1994) describes orally active, non-peptidic inhibitors of human leukocyte elastase which contain trifluoromethylketone and pyridinone moieties. H. Mack et al., J. Enzyme Inhibition, Vol. 9, pages 73-86 (1995) describes rigid amidino-phenylalanine thrombin inhibitors which contain a pyridinone moiety as a central core structure. U.S. Pat. Nos. 5,536,708, 5,672,582, 5,510,369 and 5,741,485 describe proline-based thrombin inhibitors having cyclohexylamino end groups. The present invention includes thrombin inhibitors having phenyl ring end groups substituted with aminomethyl moieties, which have been found to provide therapeutically effective thrombin inhibitors having desirable potency and pharmacokinetic properties.
The invention includes compounds for inhibiting loss of blood platelets, inhibiting formation of blood platelet aggregates, inhibiting formation of fibrin, inhibiting thrombus formation, and inhibiting embolus formation in a mammal, comprising a compound of the invention in a pharmaceutically acceptable carrier. These compounds may optionally include anticoagulants, antiplatelet agents, and thrombolytic agents. The compounds can be added to blood, blood products, or mammalian organs in order to effect the desired inhibitions.
The invention also includes a compound for preventing or treating unstable angina, refractory angina, myocardial infarction, transient ischemic attacks, atrial fibrillation, thrombotic stroke, embolic stroke, deep vein thrombosis, disseminated intravascular coagulation, ocular build up of fibrin, and reocclusion or restenosis of recanalized vessels, in a mammal, comprising a compound of the invention in a pharmaceutically acceptable carrier. These compounds may optionally include anticoagulants, antiplatelet agents, and thrombolytic agents.
The invention also includes a method for reducing the thrombogenicity of a surface in a mammal by attaching to the surface, either covalently or noncovalently, a compound of the invention.
Compounds of the invention are useful as thrombin inhibitors and have therapeutic value in for example, preventing coronary artery disease.
This invention includes compounds of the general formula 
or a pharmaceutically acceptable salt thereof, wherein
R1 and R2 are independently selected from the group consisting of
1) hydrogen,
2) C1-6 alkyl,
3) C1-6 alkyl substituted with one, two or three members, same or different, selected from the group consisting of
i) hydroxyl,
ii) halogen,
iii) C3,
iv) phenyl,
v) phenyl, substituted with one, two or three members, same or different, selected from the group consisting of
a) hydroxyl,
b) halogen,
c) CF3,
d) C1-6 alkyl,
e) C1-4 alkoxyl,
f) amino,
g) C1-4 alkylamino, and
h) CH3C(O)NHxe2x80x94,
vi) pyridyl,
vii) pyridyl substituted with one or two members, same or different, selected from the group consisting of
a) halogen,
b) C1-4 alkoxyl, and
c) C1-6 alkyl,
viii) pyridyl N-oxide
ix) pyridyl N-oxide substituted with one or two members, same or different, selected from the group consisting of
a) halogen,
b) C1-4 alkoxyl, and
c) C1-6 alkyl,
x) C3-6 cycloalkyl, and
xi) C3-6 cycloalkyl substituted with C1-4 alkyl or halogen,
4) Cxe2x89xa1Cxe2x80x94R8,
5) phenyl,
6) phenyl substituted with one, two or three members, same or different, selected from the group consisting of
i) hydroxyl,
ii) halogen,
iii) CF3,
iv) C 1-6 alkyl,
v) C1-4 alkoxyl,
vi) amino,
vii) C1-4 alkylamino, and
viii) CH3C(O)NHxe2x80x94,
7) pyridyl,
8) pyridyl substituted with one or two members, same or different, selected from the group consisting of
i) halogen,
ii) C1-4 alkoxyl, and
iii) C1-6 alkyl,
9) pyridyl N-oxide,
10) pyridyl N-oxide substituted with one or two members, same or different, selected from the group consisting of
i) halogen,
ii) C1-4 alkoxyl, and
iii) C1-6 alkyl,
11) C3-6 cycloalkyl, and
12) C3-6 cycloalkyl substituted with C1-4 alkyl or halogen;
R3 is hydrogen or halogen;
R4 is halogen;
R8 is selected from the group consisting of
1) hydrogen,
2) C1-6 alkyl,
3) C3-6 cycloalkyl, and
4) C3-6 cycloalkyl substituted with C1-4 alkyl or halogen,
provided that when R3 is hydrogen, R4 is Cl.
In a class of compounds or pharmaceutically acceptable salts thereof of the invention, R3 is hydrogen or F, and R4 is Cl or F, provided that when R3 is hydrogen, R4 is Cl.
In a subclass of the class of compounds or pharmaceutically acceptable salts thereof, R2 is hydrogen or C1-6 alkyl.
In a group of this subclass or pharmaceutically acceptable salts thereof, R1 is
1) C1-6 alkyl, unsubstituted or substituted with one, two, or three members, same or different, selected from the group consisting of
i) cyclopropyl, and
ii) cyclopropyl substituted with C1-4 alkyl,
Cxe2x89xa1CC(CH3)3, or
phenyl substituted with Cl.
Examples of this group of compounds are listed below: 
1(3,3-Dimethyl-2(R)-hydroxybutanoyl)azetidine-2(S)-N-(2-aminomethyl-5-chlorobenzyl)carboxamide (1) 
1-(4,4-Dimethyl-2(R)-hydroxypentanoyl)azetidine-2(S)-N-(2-aminomethyl-5-chlorobenzyl)carboxamide (2) 
1-(3-(1-Methylcyclopropyl)-2(R)-hydroxypropanoyl)azetidine-2(S)-N-(2-aminomethyl-5-chlorobenzyl)carboxamide (3) 
1-(3(S)-Cyclopropyl-2(R)-hydroxybutanoyl)azetidine-2(S)-N-(2-aminomethyl-5-chlorobenzyl)carboxamide (4) 
1-(3-Cyclopropyl-3-methyl-2(R)-hydroxybutanoyl)azetidine-2(S)-N-(2-aminomethyl-5-chlorobenzyl)carboxamide (5) 
1-(3(R)-Cyclopropyl-2(R)-hydroxybutanoyl)azetidine-2(S)-N-(2-aminomethyl-5-chlorobenzyl)carboxamide (4) 
1-(2-hydroxy-2,5,5-trimethyl-3-hexynoyl)azetidine-2(S)-N-(2-aminomethyl-5-chlorobenzyl)carboxamide (7) 
1-(2(R)-hydroxy(3-chlorophenyl)acetyl)azetidine-2(S)-N-(2-aminomethyl-5-chlorobenzyl)carboxamide (8) 
1-(3-Cyclopropyl-3-methyl-2(R)-hydroxybutanoyl)azetidine-2(S)-N-(2-aminomethyl-6-fluoro-5-chlorobenzyl)carboxamide (9) 
1-(3,3-Dimethyl-2(R)-hydroxybutanoyl)azetidine-2(S)-N-(2-aminomethyl-5,6-difluorobenzyl)carboxamide (10)
The compounds of the present invention, may have chiral centers and occur as racemates, racemic mixtures and as individual diastereomers, or enantiomers with all isomeric forms being included in the present invention. The compounds of the present invention may also have polymorphic crystalline forms, with all polymorphic crystalline forms being, included in the present invention.
When any variable occurs more than one time in any constituent or in formula I, its definition on each occurrence is independent of its definition at every other occurrence. Also, combinations of substituents and/or variables are permissible only if such combinations result in stable compounds.
Some abbreviations that may appear in this application are as follows:
As used herein except where noted, xe2x80x9calkylxe2x80x9d is intended to include both branched- and straight-chain saturated aliphatic hydrocarbon groups having the specified number of carbon atoms (Me is methyl, Et is ethyl, Pr is propyl, Bu is butyl); xe2x80x9calkoxylxe2x80x9d represents a linear or branched alkyl group of indicated number of carbon atoms attached through an oxygen bridge; xe2x80x9chalogenxe2x80x9d, as used herein, means fluoro, chloro, bromo and iodo; and xe2x80x9ccounterionxe2x80x9d is used to represent a small, single negatively-charged species, such as chloride, bromide, hydroxide, acetate, trifluoroacetate, perchlorate, nitrate, benzoate, maleate, sulfate, tartrate, hemitartrate, benzene sulfonate, and the like.
The term xe2x80x9cC3-6 cycloalkylxe2x80x9d is intended to include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl, and the like.
The term xe2x80x9carylxe2x80x9d as used herein except where noted, represents a stable 6- to 10-membered mono- or bicyclic ring system such as phenyl, or naphthyl. The aryl ring can be unsubstituted or substituted with one or more of C1-4 lower alkyl; hydroxy; alkoxy; halogen; amino.
The pyridyl N-oxide portion of the compounds of the invention are structurally depicted using conventional representations 
which have equivalent meanings.
In this specification methyl substituents may be represented by 
For example, the structures 
have equivalent meanings.
The pharmaceutically-acceptable salts of the compounds of Formula I (in the form of water- or oil-soluble or dispersible products) include the conventional non-toxic salts such as those derived from inorganic acids, e.g. hydrochloric, hydrobromoic, sulfuric, sulfamic, phosphoric, nitric and the like, or the quaternary ammonium salts which are formed, e.g., from inorganic or organic acids or bases. Examples of acid addition salts include acetate, adipate, alginate, aspartate, benzoate, benzenesulfonate, bisulfate, butyrate, citrate, camphorate, camphorsulfonate, cyclopentanepropionate, digluconate, dodecylsulfate, ethanesulfonate, fumarate, glucoheptanoate, glycerophosphate, hemisulfate, heptanoate, hexanoate, hydrochloride, hydrobromide, hydroiodide, 2-hydroxyethanesulfonate, lactate, maleate, methanesulfonate, 2-naphthalenesulfonate, nicotinate, nitrate, oxalate, pamoate, pectinate, persulfate, 3-phenylpropionate, picrate, pivalate, propionate, succinate, sulfate, tartrate, thiocyanate, tosylate, and undecanoate. Base salts include ammonium salts, alkali metal salts such as sodium and potassium salts, alkaline earth metal salts such as calcium and magnesium salts, salts with organic bases such as dicyclohexylamine salts, N-methyl-D-glucamine, and salts with amino acids such as arginine, lysine, and so forth. Also, the basic nitrogen-containing groups may be quaternized with such agents as lower alkyl halides, such as methyl, ethyl, propyl, and butyl chloride, bromides and iodides; dialkyl sulfates like dimethyl, diethyl, dibutyl; and diamyl sulfates, long chain halides such as decyl, lauryl, myristyl and stearyl chlorides, bromides and iodides, aralkyl halides like benzyl and phenethyl bromides and others.
Thrombin Inhibitorsxe2x80x94Therapeutic Usesxe2x80x94Method of Using
Anticoagulant therapy is indicated for the treatment and prevention of a variety of thrombotic conditions, particularly coronary artery and cerebrovascular disease. Those experienced in this field are readily aware of the circumstances requiring anticoagulant therapy. The term xe2x80x9cpatientxe2x80x9d used herein is taken to mean mammals such as primates, including humans, sheep, horses, cattle, pigs, dogs, cats, rats, and mice.
Thrombin inhibition is useful not only in the anticoagulant therapy of individuals having thrombotic conditions, but is useful whenever inhibition of blood coagulation is required such as to prevent coagulation of stored whole blood and to prevent coagulation in other biological samples for testing or storage. Thus, the thrombin inhibitors can be added to or contacted with any medium containing or suspected of containing thrombin and in which it is desired that blood coagulation be inhibited, e.g., when contacting the mammal""s blood with material selected from the group consisting of vascular grafts, stents, orthopedic prosthesis, cardiac prosthesis, and extracorporeal circulation systems.
Compounds of the invention are useful for treating or preventing venous thromboembolism (e.g. obstruction or occlusion of a vein by a detached thrombus; obstruction or occlusion of a lung artery by a detached thrombus), cardiogenic thromboembolism (e.g. obstruction or occlusion of the heart by a detached thrombus), arterial thrombosis (e.g. formation of a thrombus within an artery that may cause infarction of tissue supplied by the artery), atherosclerosis (e.g. arteriosclerosis characterized by irregularly distributed lipid deposits) in mammals, and for lowering the propensity of devices that come into contact with blood to clot blood.
Examples of venous thromboembolism which may be treated or prevented with compounds of the invention include obstruction of a vein, obstruction of a lung artery (pulmonary embolism), deep vein thrombosis, thrombosis associated with cancer and cancer chemotherapy, thrombosis inherited with thrombophilic diseases such as Protein C deficiency, Protein S deficiency, antithrombin III deficiency, and Factor V Leiden, and thrombosis resulting from acquired thrombophilic disorders such as systemic lupus erythematosus (inflammatory connective tissue disease). Also with regard to venous thromboembolism, compounds of the invention are useful for maintaining patency of indwelling catheters.
Examples of cardiogenic thromboembolism which may be treated or prevented with compounds of the invention include thromboembolic stroke (detached thrombus causing neurological affliction related to impaired cerebral blood supply), cardiogenic thromboembolism associated with atrial fibrillation (rapid, irregular twitching of upper heart chamber muscular fibrils), cardiogenic thromboembolism associated with prosthetic heart valves such as mechanical heart valves, and cardiogenic thromboembolism associated with heart disease.
Examples of arterial thrombosis include unstable angina (severe constrictive pain in chest of coronary origin), myocardial infarction (heart muscle cell death resulting from insufficient blood supply), ischemic heart disease (local anemia due to obstruction (such as by arterial narrowing) of blood supply), reocclusion during or after percutaneous transluminal coronary angioplasty, restenosis after percutaneous transluminal coronary angioplasty, occlusion of coronary artery bypass grafts, and occlusive cerebrovascular disease. Also with regard to arterial thrombosis, compounds of the invention are useful for maintaining patency in arteriovenous cannulas.
Examples of atherosclerosis include arteriosclerosis.
Examples of devices that come into contact with blood include vascular grafts, stents, orthopedic prosthesis, cardiac prosthesis, and extracorporeal circulation systems
The thrombin inhibitors of the invention can be administered in such oral forms as tablets, capsules (each of which includes sustained release or timed release formulations), pills, powders, granules, elixers, tinctures, suspensions, syrups, and emulsions. Likewise, they may be administered in intravenous (bolus or infusion), intraperitoneal, subcutaneous, or intramuscular form, all using forms well known to those of ordinary skill in the pharmaceutical arts. An effective but non-toxic amount of the compound desired can be employed as an anti-aggregation agent. For treating ocular build up of fibrin, the compounds may be administered intraocularly or topically as well as orally or parenterally.
The thrombin inhibitors can be administered in the form of a depot injection or implant preparation which may be formulated in such a manner as to permit a sustained release of the active ingredient. The active ingredient can be compressed into pellets or small cylinders and implanted subcutaneously or intramuscularly as depot injections or implants. Implants may employ inert materials such as biodegradable polymers or synthetic silicones, for example, Silastic, silicone rubber or other polymers manufactured by the Dow-Corning Corporation.
The thrombin inhibitors can also be administered in the form of liposome delivery systems, such as small unilamellar vesicles, large unilamellar vesicles and multilamellar vesicles. Liposomes can be formed from a variety of phospholipids, such as cholesterol, stearylamine or phosphatidylcholines.
The thrombin inhibitors may also be delivered by the use of monoclonal antibodies as individual carriers to which the compound molecules are coupled. The thrombin inhibitors may also be coupled with soluble polymers as targetable drug carriers. Such polymers can include polyvinlypyrrolidone, pyran copolymer, polyhydroxy-propyl-methacrylamide-phenol, polyhydroxyethyl-aspartamide-phenol, or polyethyleneoxide-polylysine substituted with palmitoyl residues. Furthermore, the thrombin inhibitors may be coupled to a class of biodegradable polymers useful in achieving controlled release of a drug, for example, polylactic acid, polyglycolic acid, copolymers of polylactic and polyglycolic acid, polyepsilon caprolactone, polyhydroxy butyric acid, polyorthoesters, polyacetals, polydihydropyrans, polycyanoacrylates and cross linked or amphipathic block copolymers of hydrogels.
The dosage regimen utilizing the thrombin inhibitors is selected in accordance with a variety of factors including type, species, age, weight, sex and medical condition of the patient; the severity of the condition to be treated; the route of administration; the renal and hepatic function of the patient; and the particular compound or salt thereof employed. An ordinarily skilled physician or veterinarian can readily determine and prescribe the effective amount of the drug required to prevent, counter, or arrest the progress of the condition.
Oral dosages of the thrombin inhibitors, when used for the indicated effects, will range between about 0.01 mg per kg of body weight per day (mg/kg/day) to about 30 mg/kg/day, preferably 0.025-7.5 mg/kg/day, more preferably 0. 1-2.5 mg/kg/day, and most preferably 0.1-0.5 mg/kg/day (unless specified otherwise, amounts of active ingredients are on free base basis). For example, an 80 kg patient would receive between about 0.8 mg/day and 2.4 g/day, preferably 2-600 mg/day, more preferably 8-200 mg/day, and most preferably 8-40 mg/kg/day. A suitably prepared medicament for once a day administration would thus contain between 0.8 mg and 2.4 g, preferably between 2 mg and 600 mg, more preferably between 8 mg and 200 mg, and most preferably 8 mg and 40 mg, e.g., 8 mg, 10 mg, 20 mg and 40 mg. Advantageously, the thrombin inhibitors may be administered in divided doses of two, three, or four times daily. For administration twice a day, a suitably prepared medicament would contain between 0.4 mg and 4 g, preferably between 1 mg and 300 mg, more preferably between 4 mg and 100 mg, and most preferably 4 mg and 20 mg, e.g., 4 mg, 5 mg, 10 mg and 20 mg.
Intravenously, the patient would receive the active ingredient in quantities sufficient to deliver between 0.025-7.5 mg/kg/day, preferably 0.1-2.5 mg/kg/day, and more preferably 0.1-0.5 mg/kg/day. Such quantities may be administered in a number of suitable ways, e.g. large volumes of low concentrations of active ingredient during one extended period of time or several times a day, low volumes of high concentrations of active ingredient during a short period of time, e.g. once a day. Typically, a conventional intravenous formulation may be prepared which contains a concentration of active ingredient of between about 0.01-1.0 mg/ml, e.g. 0.1 mg/ml, 0.3 mg/ml, and 0.6 mg/ml, and administered in amounts per day of between 0.01 ml/kg patient weight and 10.0 ml/kg patient weight, e.g. 0.1 ml/kg, 0.2 ml/kg, 0.5 ml/kg. In one example, an 80 kg patient, receiving 8 ml twice a day of an intravenous formulation having a concentration of active ingredient of 0.5 mg/ml, receives 8 mg of active ingredient per day. Glucuronic acid, L-lactic acid, acetic acid, citric acid or any pharmaceutically acceptable acid/conjugate base with reasonable buffering capacity in the pH range acceptable for intravenous administration may be used as buffers. The choice of appropriate buffer and pH of a formulation, depending on solubility of the drug to be administered, is readily made by a person having ordinary skill in the art.
The compounds can also be administered in intranasal form via topical use of suitable intranasal vehicles, or via transdermal routes, using those forms of transdermal skin patches well known to those of ordinary skill in that art. To be administered in the form of a transdermal delivery system, the dosage administration will, or course, be continuous rather than intermittent throughout the dosage regime.
The thrombin inhibitors are typically administered as active ingredients in admixture with suitable pharmaceutical diluents, excipients or carriers (collectively referred to herein as xe2x80x9ccarrierxe2x80x9d materials) suitably selected with respect to the intended form of administration, that is, oral tablets, capsules, elixers, syrups and the like, and consistent with convention pharmaceutical practices.
For instance, for oral administration in the form of a tablet or capsule, the active drug component can be combined with an oral, non-toxic, pharmaceutically acceptable, inert carrier such as lactose, starch, sucrose, glucose, methyl cellulose, magnesium stearate, dicalcium phosphate, calcium sulfate, mannitol, sorbitol and the like; for oral administration in liquid form, the oral drug components can be combined with any oral, non-toxic, pharmaceutically acceptable inert carrier such as ethanol, glycerol, water and the like. Moreover, when desired or necessary, suitable binders, lubricants, distintegrating agents and coloring agents can also be incorporated into the mixture. Suitable binders include starch, gelatin, natural sugars such as glucose or beta-lactose, corn-sweeteners, natural and synthetic gums such as acacia, tragacanth or sodium alginate, carboxymethylcellulose, polyethylene glycol, waxes and the like. Lubricants used in these dosage forms include sodium oleate, sodium stearate, magnesium stearate, sodium benzoate, sodium acetate, sodium chloride and the like. Disintegrators include, without limitation, starch methyl cellulose, agar, bentonite, xanthan gum and the like.
The thrombin inhibitors can also be co-administered with suitable anti-platelet agents, including, but not limited to, fibrinogen receptor antagonists (e.g. to treat or prevent unstable angina or to prevent reocclusion after angioplasty and restenosis), anticoagulants such as aspirin, thrombolytic agents such as plasminogen activators or streptokinase to achieve synergistic effects in the treatment of various vascular pathologies, or lipid lowering agents including antihypercholesterolemics (e.g. HMG CoA reductase inhibitors such as lovastatin, HMG CoA synthase inhibitors, etc.) to treat or prevent atherosclerosis. For example, patients suffering from coronary artery disease, and patients subjected to angioplasty procedures, would benefit from coadministration of fibrinogen receptor antagonists and thrombin inhibitors. Also, thrombin inhibitors enhance the efficiency of tissue plasminogen activator-mediated thrombolytic reperfusion. Thrombin inhibitors may be administered first following thrombus formation, and tissue plasminogen activator or other plasminogen activator is administered thereafter.
Typical doses of thrombin inhibitors of the invention in combination with other suitable anti-platelet agents, anticoagulation agents, or thrombolytic agents may be the same as those doses of thrombin inhibitors administered without coadministration of additional anti-platelet agents, anticoagulation agents, or thrombolytic agents, or may be substantially less that those doses of thrombin inhibitors administered without coadministration of additional anti-platelet agents, anticoagulation agents, or thrombolytic agents, depending on a patient""s therapeutic needs.
Unless other wise stated, all NMR determinations were made using 400 MHz field strength. 
Compounds of the present invention are synthesized using procedures and chemical intermediates which are well known to those of ordinary skill in the art. The compounds of the present invention are essentially comprised of three subunits, referred to as the P1, P2 and P3 subunits, which are connected together by two amide bonds. The central subunit, the P2 subunit, is an amino acid. This P2 amino acid is connected at its carboxy end via an amide bond to the P1 subunit, a benzylamine derivative, and this P2 amino acid is connected at its amino end via an amide bond to the P3 subunit which is a hydroxy acid. Standard amino acid coupling procedures and protecting group chemistry enables synthesis of the final compounds in either direction, i.e., the P2-P1 amide bond may be formed first, followed by formation of the P3-P2 amide bond, or the P3-P2 amide bond may be formed first, followed by formation of the P2-P1 amide bond. Standard protecting group chemistry may be employed, if necessary, in the P1 and P3 subunits to allow selective amide bond formation between the various subunits. After the subunits have been connected via the two amide bonds to give a P3-P2-P1 structure, any additional protecting groups that may present in the P1 and or P3 subunits can be removed using standard procedures to give final compounds. Scheme 1 shows a synthesis in which the P1 and P2 amide bond is formed first, and the P3 amide bond is formed last. These P1 subunits are comprised of a halogen-substituted, mono-protected bis-benzylamine derivative. A synthesis of such a bis-benzylamine derivative is shown in Scheme 1. Bromo ester 1 is cyanated to give an ortho-cyano ester, 2. Both the ester and cyano groups are then reduced to give an amino alcohol which is protected on nitrogen to give intermediate 3. The alcohol in 3 is then converted to an azide, 4, and the azido group is reduced to give the mono-protected bis-benzylamine derivative 5. The amino group in 5 is then acylated with N-protected azetitdine-2-carboxylic acid and the azetitine protecting group is removed to give 6. The azetidine nitrogen in 6 is then acylated with a hydroxy ester, and the remaining benzylamine protecting group is removed to give final compound 7. The hydroxy acid used in this sequence can be made in several ways. Scheme 2 shows two methods. The first method involves addition of an organometallic (R1-M) to an oxalate ester to give alpha keto ester 9. Addition of a second organometallic (R2-M) or hydride reagent to keto ester 9, followed by ester hydrolysis, gives hydroxy acid 10. Another way of making hydroxy acids for use in Scheme 1 involves deprotonation of ester 11, and oxidation of the resulting ester enolate with a reagent such as an oxaziridine to give hydroxy ester 12. Saponification of the ester in 12 gives hydroxy acid 13.