Process for the preparation of epothilone analogs

Abstract

The present invention relates to a process for the preparation of epothilone analogs by initially forming novel ring-opened epothilones and carrying out a macrolactamization reaction thereon. The subject process is amenable to being carried out in a single reaction vessel without isolation of the intermediate compound and provides at least about a three-fold increase in yield over prior processes for preparing the desired epothilone analogs.

Description

FIELD OF THE INVENTION

[0002] The present invention relates to an improved process for the preparation of certain epothilone analogs, including novel intermediates, which is characterized by a significantly enhanced yield.

BACKGROUND OF THE INVENTION

[0003] Epothilones are macrolide compounds that find utility in the pharmaceutical field. For example, epothilones A and B having the structures: 1

[0004] may be found to exert microtubule-stabilizing effects similar to paclitaxel (TAXOL®) and hence cytotoxic activity against rapidly proliferating cells, such as, tumor cells or other hyperproliferative cellular disease, see Hofle, G., et al., Angew. Chem. Int. Ed. Engl., Vol. 35, No.13/14, 1567-1569 (1996); WO93/10121 published May 27, 1993; and WO97/19086 published May 29, 1997.

[0005] Derivatives and analogs of epothilones A and B have been synthesized and may be used to treat a variety of cancers and other abnormal proliferative diseases. Such analogs are disclosed in Hofle et al., Id.; Nicolaou, K. C., et al., Angew. Chem. Int. Ed. Engl., Vol. 36, No. 19, 2097-2103 (1997); and Su, D. -S., et al., Angew. Chem. Int. Ed. Engl. Vol. 36, No. 19, 2093-2097 (1997).

[0006] Analogs of the epothilones that have been found to have advantageous activity are represented by the following structure 2

[0007] wherein Q, and R1 through R6 have the meanings given herein below.

[0008] An improved synthesis for these analogs involving novel intermediates is provided in accordance with the present invention.

SUMMARY OF THE INVENTION

[0009] The present invention is directed to a process for the preparation of compounds represented by formulas I and II wherein Q, Z, and R1 through R6 are as defined below. 3

[0010] The compounds represented by formula I are novel intermediates for the preparation of epothilone analogs that are useful in the treatment of a variety of cancers and other abnormal proliferative diseases. Compounds represented by formula I may be utilized to prepare epothilone analogs represented by formula II which are useful as anticancer agents.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The process of the present invention provides an advantageous synthesis for the compounds represented by formula II including the preparation of novel ring opened epothilone intermediate compounds represented by formula I. 4

[0012] As used in formulas I and II, and throughout the specification, the meaning of the symbol Q is: 5

[0013] M is selected from the group consisting of oxygen, sulfur, NR8, and CR9R10;

[0014] Z is selected from the group consisting of 6

[0015] R1-R5, R7, and R11-R15 are selected from the group consisting of hydrogen, alkyl, substituted alkyl, aryl, substituted aryl and heterocyclo, and wherein R1 and R2 are alkyl, they can be joined to form a cycloalkyl;

[0016] R6 is selected from the group consisting of hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, cycloalkyl, heterocyclo and substituted heterocyclo;

[0017] R8 is selected from the group consisting of hydrogen, alkyl, substituted alkyl, R11C═O, R12OC═O and R13SO2;

[0018] R9 and R10 are selected from the group consisting of hydrogen, halogen, alkyl, substituted alkyl, aryl, heterocyclo, hydroxy, R14C═O, and R15OC═O; and

[0019] R16, R17, and R18 are independently selected from the group consisting of alkyl, aryl, and aralkyl.

[0020] The process of the present invention is advantageous in that only two steps are required to prepare the epothilone analogs from the epothilone starting material, for example, epothilone B. Two further distinct advantages of the process of the present invention are that the yields of crystallized compounds represented by formula II are significantly higher than those previously realized utilizing the free acid of the compound represented by formula I as the intermediate compound, and the fact that the preparation of the intermediate is amendable to being carried out in one step. A further advantage of this process is that it can progress from the epothilone starting material to the epothilone represented by formula II without the need to isolate and purify an intermediate. Those skilled in the art will immediately recognize the economic benefits of such a process.

[0021] Definitions

[0022] The following are definitions of various terms used herein to describe this invention. These definitions apply to the terms as they are used throughout this specification, unless otherwise limited in specific instances, either individually or as part of a larger group.

[0023] The term “epothilone”, as used herein, denotes compounds containing an epothilone core and a side chain group as defined herein. The term “epothilone core”, as used herein, denotes a moiety containing the core structure (with the numbering of ring system positions used herein shown): 7

[0024] wherein the substituents are as defined herein and where

[0025] X is selected from the group consisting of C═O, CH2 and CHOR19;

[0026] B1 and B2 are selected from the group consisting of OR20 and OCOR21 ;

[0027] R19 and R20 are selected from the group consisting of hydrogen, alkyl, substituted alkyl, trialkylsilyl, alkyldiarylsilyl, and dialkylarylsilyl; and

[0028] R21 is selected from the group consisting of hydrogen, alkyl, substituted alkyl, aryl, and heterocyclo.

[0029] The term “side chain group” refers to substituent G as defined by the following formula

Ym—A—

[0030] where

[0031] A is optionally substituted alkenyl;

[0032] Y is an optionally substituted ring system containing one to three rings and at least one carbon to carbon double bond in at least one ring; and

[0033] m is zero or 1.

[0034] The term “alkyl” refers to optionally substituted straight- or branched-chain saturated hydrocarbon groups having from 1 to 20 carbon atoms, preferably from 1 to 7 carbon atoms. The expression “lower alkyl” refers to optionally substituted alkyl groups having from 1 to 4 carbon atoms.

[0035] The term “substituted alkyl” refers to an alkyl group substituted by, for example, one to four substituents, such as, halo, trifluoromethyl, trifluoromethoxy, hydroxy, alkoxy, cycloalkyoxy, heterocylooxy, oxo, alkanoyl, aryl, aryloxy, aralkyl, alkanoyloxy, amino, alkylamino, arylamino, aralkylamino, cycloalkylamino, heterocycloamino, disubstituted amino in which the two substituents on the amino group are selected from alkyl, aryl, aralkyl, alkanoylamino, aroylamino, aralkanoylamino, substituted alkanoylamino, substituted arylamino, substituted aralkanoylamino, thiol, alkylthio, arylthio, aralkylthio, cycloalkylthio, heterocyclothio, alkylthiono, arylthiono, aralkylthiono, alkylsulfonyl, arylsulfonyl, aralkylsulfonyl, sulfonamido (e.g. SO2NH2), substituted sulfonamido, nitro, cyano, carboxy, carbamyl (e.g. CONH2), substituted carbamyl (e.g. CONH alkyl, CONH aryl, CONH aralkyl or instances where there are two substituents on the nitrogen selected from alkyl, aryl or aralkyl), alkoxycarbonyl, aryl, substituted aryl, guanidino and heterocyclos, such as, indolyl, imidazolyl, furyl, thienyl, thiazolyl, pyrrolidyl, pyridyl, pyrimidyl and the like. Wherein, as noted above, the substituents themselves are further substituted, such further substituents are selected from the group consisting of halogen, alkyl, alkoxy, aryl and aralkyl. The definitions given herein for alkyl and substituted alkyl apply as well to the alkyl portion of alkoxy groups.

[0036] The term “alkenyl” refers to optionally substituted unsaturated aliphatic hydrocarbon groups having from one to nine carbons and one or more double bonds. Substituents may include one or more substituent groups as described above for substituted alkyl.

[0037] The term “halogen” or “halo” refers to fluorine, chlorine, bromine and iodine.

[0038] The term “ring system” refers to an optionally substituted ring system containing one to three rings and at least one carbon to carbon double bond in at least one ring. Exemplary ring systems include, but are not limited to, an aryl or a partially or fully unsaturated heterocyclic ring system, which may be optionally substituted.

[0039] The term “aryl” refers to monocyclic or bicyclic aromatic hydrocarbon groups having from 6 to 12 carbon atoms in the ring portion, for example, phenyl, naphthyl, biphenyl and diphenyl groups, each of which may be substituted.

[0040] The term “aralkyl” refers to an aryl group bonded to a larger entity through an alkyl group, such as benzyl.

[0041] The term “substituted aryl” refers to an aryl group substituted by, for example, one to four substituents such as alkyl; substituted alkyl, halo, trifluoromethyl, trifluoromethoxy, hydroxy, alkoxy, cycloalkyloxy, heterocyclooxy, alkanoyl, alkanoyloxy, amino, alkylamino, dialkylamino, aralkylamino, cycloalkylamino, heterocycloamino, alkanoylamino, thiol, alkylthio, cycloalkylthio, heterocyclothio, ureido, nitro, cyano, carboxy, carboxyalkyl, carbamyl, alkoxycarbonyl, alkylthiono, arylthiono, alkysulfonyl, sulfonamido, aryloxy and the like. The substituent may be further substituted by one or more members selected from the group consisting of halo, hydroxy, alkyl, alkoxy, aryl, substituted alkyl, substituted aryl and aralkyl.

[0042] The term “cycloalkyl” refers to optionally substituted saturated cyclic hydrocarbon ring systems, preferably containing 1 to 3 rings and 3 to 7 carbons per ring, which may be further fused with an unsaturated C3-C7 carbocyclic ring. Exemplary groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclodecyl, cyclododecyl, and adamantyl. Exemplary substituents include one or more alkyl groups as described above, or one or more of the groups described above as substituents for alkyl groups.

[0043] The terms “heterocycle”, “heterocyclic” and “heterocyclo” refer to an optionally substituted, unsaturated, partially saturated, or fully saturated, aromatic or nonaromatic cyclic group, for example, which is a 4 to 7 membered monocyclic, 7 to 11 membered bicyclic, or 10 to 15 membered tricyclic ring system, which has at least one heteroatom in at least one carbon atom-containing ring. Each ring of the heterocyclic group containing a heteroatom may have 1, 2 or 3 heteroatoms selected from nitrogen atoms, oxygen atoms and sulfur atoms, where the nitrogen and sulfur heteroatoms may also optionally be oxidized and the nitrogen heteroatoms may also optionally be quaternized. The heterocyclic group may be attached at any heteroatom or carbon atom.

[0044] Exemplary monocyclic heterocyclic groups include pyrrolidinyl, pyrrolyl, indolyl, pyrazolyl, oxetanyl, pyrazolinyl, imidazolyl, imidazolinyl, imidazolidinyl, oxazolyl, oxazolidinyl, isoxazolinyl, isoxazolyl, thiazolyl, thiadiazolyl, thiazolidinyl, isothiazolyl, isothiazolidinyl, furyl, tetrahydrofuryl, thienyl, oxadiazolyl, piperidinyl, piperazinyl, 2-oxopiperazinyl, 2-oxopiperidinyl, 2-oxopyrrolidinyl, 2-oxazepinyl, azepinyl, 4-piperidonyl, pyridyl, N-oxo-pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, tetrahydropyranyl, tetrahydrothiopyranyl, tetrahydrothiopyranyl sulfone, morpholinyl, thiomorpholinyl, thiomorpholinyl sulfoxide, thiomorpholinyl sulfone, 1,3-dioxolane and tetrahydro-1,1-dioxothienyl, dioxanyl, isothiazolidinyl, thietanyl, thiiranyl, triazinyl, and triazolyl, and the like.

[0045] Exemplary bicyclic heterocyclic groups include benzothiazolyl, benzoxazolyl, benzothienyl, quinuclidinyl, quinolinyl, quinolinyl-N-oxide, tetrahydroisoquinolinyl, isoquinolinyl, benzimidazolyl, benzopyranyl, indolizinyl, benzofuryl, chromonyl, coumarinyl, cinnolinyl, quinoxalinyl, indazolyl, pyrrolopyridyl, furopyridinyl (such as furo[2,3-c]pyridinyl, furo[3,1-b]pyridinyl] or furo[2,3-b]pyridinyl), dihydroisoindolyl, dihydroquinazolinyl (such as 3,4-dihydro-4-oxo-quinazolinyl), benzisothiazolyl, benzisoxazolyl, benzodiazinyl, benzofurazanyl, benzothiopyranyl, benzotriazolyl, benzpyrazolyl, dihydrobenzofuryl, dihydrobenzothienyl, dihydrobenzothiopyranyl, dihydrobenzothiopyranyl sulfone, dihydrobenzopyranyl, indolinyl, isochromanyl, isoindolinyl, naphthyridinyl, phthalazinyl, piperonyl, purinyl, pyridopyridyl, quinazolinyl, tetrahydroquinolinyl, thienofuryl, thienopyridyl, thienothienyl, and the like.

[0046] Exemplary substituents for the terms “ring system,” “heterocycle,” “heterocyclic,” and “heterocyclo” include one or more substituent groups as described above for substituted alkyl or substituted aryl, and smaller heterocyclos, such as, epoxides, aziridines and the like.

[0047] The term “alkanoyl” refers to —C(O)-alkyl.

[0048] The term “substituted alkanoyl” refers to —C(O)-substituted alkyl.

[0049] The term “heteroatoms” shall include oxygen, sulfur and nitrogen.

[0050] The compounds represented by formula II form salts with a variety of organic and inorganic acids. Such salts include those formed with hydrogen chloride, hydrogen bromide, methanesulfonic acid, hydroxyethanesulfonic acid, sulfuric acid, acetic acid, trifluoroacetic acid, maleic acid, benzenesulfonic acid, toluenesulfonic acid and various others as are recognized by those of ordinary skill in the art of pharmaceutical compounding. Such salts are formed by reacting a compound represented by formula II in an equivalent amount of the acid in a medium in which the salt precipitates or in an aqueous medium followed by evaporation.

[0051] In addition, zwitterions (“inner salts”) can be formed and are included within the term salts as used herein.

[0052] The compounds represented by formulae I and II above may exist as multiple optical, geometric, and stereoisomers. While the compounds shown herein are depicted for one optical orientation, included within the present invention are all isomers and mixtures thereof.

[0053] Use and Utility

[0054] The invention is a process by which compounds represented by formula II above that are microtubule-stabilizing agents are produced. The compounds, and thus the process, are useful in the treatment of a variety of cancers and other proliferative diseases including, but not limited to, the following;

[0055] carcinoma, including that of the bladder, breast, colon, kidney, liver, lung, ovary, pancreas, stomach, cervix, thyroid and skin, including squamous cell carcinoma;

[0056] hematopoietic tumors of lymphoid lineage, including leukemia, acute lymphocytic leukemia, acute lymphoblastic leukemia, B-cell lymphoma, T-cell lymphoma, Hodgkins lymphoma, non-Hodgkins lymphoma, hairy cell lymphoma and Burketts lymphoma;

[0057] hematopoietic tumors of myeloid lineage, including acute and chronic myelogenous leukemias and promyelocytic leukemia;

[0058] tumors of mesenchymal origin, including fibrosarcoma and rhabdomyoscarcoma;

[0059] other tumors, including melanoma, seminoma, teratocarcinoma, neuroblastoma and glioma;

[0060] tumors of the central and peripheral nervous system, including astrocytoma, neuroblastoma, glioma, and schwannomas;

[0061] tumors of mesenchymal origin, including fibrosarcoma, rhabdomyoscaroma, and osteosarcoma; and

[0062] other tumors, including melanoma, xeroderma pigmentosum, keratoacanthoma, seminoma, thyroid follicular cancer and teratocarcinoma.

[0063] The compounds produced by the invention as represented by formula II above will also inhibit angiogenesis, thereby affecting the growth of tumors and providing treatment of tumors and tumor-related disorders. Such anti-angiogenesis properties of the compounds represented by formula II will also be useful in the treatment of other conditions responsive to anti-angiogenesis agents including, but not limited to, certain forms of blindness related to retinal vascularization, arthritis, especially inflammatory arthritis, multiple sclerosis, restinosis and psoriasis.

[0064] Compounds produced by the invention as represented by formula II will induce or inhibit apoptosis, a physiological cell death process critical for normal development and homeostasis. Alterations of apoptotic pathways contribute to the pathogenesis of a variety of human diseases. Compounds represented by formula II, as modulators of apoptosis, will be useful in the treatment of a variety of human diseases with aberrations in apoptosis including, but not limited to, cancer and precancerous lesions, immune response related diseases, viral infections, degenerative diseases of the musculoskeletal system and kidney disease.

[0065] Without wishing to be bound to any mechanism or morphology, the compounds produced by the invention as represented by formula II may also be used to treat conditions other than cancer or other proliferative diseases. Such conditions include, but are not limited to viral infections such as herpesvirus, poxvirus, Epstein-Barr virus, Sindbis virus and adenovirus; autoimmune diseases such as systemic lupus erythematosus, immune mediated glomerulonephritis, rheumatoid arthritis, psoriasis, inflammatory bowel diseases and autoimmune diabetes mellitus; neurodegenerative disorders such as Alzheimer's disease, AIDS-related dementia, Parkinson's disease, amyotrophic lateral sclerosis, retinitis pigmentosa, spinal muscular atrophy and cerebellar degeneration; AIDS; myelodysplastic syndromes; aplastic anemia; ischemic injury associated myocardial infarctions; stroke and reperfusion injury; restenosis; arrhythmia; atherosclerosis; toxin-induced or alcohol induced liver diseases; hematological diseases such as chronic anemia and aplastic anemia; degenerative diseases of the musculoskeletal system such as osteoporosis and arthritis; aspirin-sensitive rhinosinusitis; cystic fibrosis; multiple sclerosis; kidney diseases; and cancer pain.

[0066] General Methods of Preparation

[0067] The novel open-ring intermediates represented by formula I can be prepared from an epothilone starting material represented by formula III in Scheme 1 wherein Q, Z, and R1 through R6 are as defined above. The epothilone starting materials represented by formula III are known compounds, see, for example, Hofle, G., et al., Angew. Chem. Int. Ed. Engl., Vol. 35, No.13/14, 1567-1569 (1996); WO93/10121 published May 27, 1993; and WO97/19086 published May 29, 1997; Nicolaou, K. C., et al., Angew Chem. Int. Ed. Engl., Vol. 36, No. 19, 2097-2103 (1997); and Su, D. -S., et al., Angew Chem. Int. Ed. Engl., Vol. 36, No. 19, 2093-2097 (1997).

[0068] As illustrated in Scheme 1, the epothilone starting material III is reacted with a suitable azide donor agent and a reducing agent in the presence of a phase transfer catalyst and a palladium catalyst under mildly acidic conditions, i.e. a pH not below about 5.5, preferably from pH 6.0 to 6.5, most preferably about 6.5, in a suitable mixed solvent system comprising water and an organic solvent such as THF, DMF and the like. The reaction is conducted at ambient temperature for an extended period, e.g. in excess of twelve hours.

[0069] The epothilone starting material for this invention can be any epothilone comprising an epothilone core and side chain as defined herein. Preferably the starting material is a compound represented by formula III in Scheme 1. 8

[0070] Suitable azide donor agents for this reaction include metal azides, for example lithium or sodium azide, tetraalkylammonium azides, for example, tetrabutylammonium azide, trialkylsilyl azides, for example trimethylsilyl azide, and the like. Preferred azide donors are sodium azide and tetrabutyl ammonium azide. An especially preferred azide donor is tetrabutylammounium azide.

[0071] Suitable reducing agents are trialkylphosphine, triarylphosphine, tri(alkyl/aryl)phosphine, trialkylarsine, triarylarsine, tri(alkyl/aryl)arsine and mixtures thereof. Preferred reducing agents are trimethyl phosphine, triethyl phosphine, tributyl phosphine, triphenyl phosphine, and tripropyl phosphine. An especially preferred reducing agent is trimethyl phosphine (PME3).

[0072] Suitable phase transfer catalysts or agents may include any quaternary onium salt and their corresponding anions. Suitable phase transfer agents include tetraalkylonium, tetrararylonium, tetraaralkylonium, and any combination of these types of onium substituents. More specifically the phase transfer catalyst may include tetraalkylammonium halides such as tetrabutylammonium chloride or benzyltriethylammonium chloride. An especially preferred phase transfer agent is tetrabutylammonium chloride. The onium substituent may be ammonium, phosphonium, or arsonium. Exemplary anions for these quartenary salts include, but are not limited to, halides, hydroxyl, cyano, phosphate, sulfate and the like. Other suitable phase transfer catalysts or agents are described in Yuri Goldberg, Phase Transfer Catalysis, Gordon and Breach Science Publishers, 1992, Chapter 1 and the references cited therein, the full text of which is incorporated herein by reference.

[0073] The palladium catalyst for the reaction shown in Scheme 1 may be, for example, palladium acetate, palladium chloride, palladium tetrakis-(triphenyl-phosphine), palladium tetrakis-(triphenylarsine), tris-(dibenzylideneacetone)-dipalladium(0)chloroform adduct (Pd2(dba)3.CHCl3 and the like. A preferred catalyst is tris-(dibenzylideneacetone)-dipalladium(0)chloroform adduct (Pd2(dba)3.CHCl3). Tris-(dibenzylideneacetone)-dipalladium is also a useful catalyst in the reaction illustrated in Scheme 1. The chemistry of the palladium catalysts is known, see for example, I. J. Tsuji, Palladium Reagents and Catalysts: Innovations in Organic Synthesis, New York, Wiley and Sons, 1995, the full text of which is incorporated herein by reference.

[0074] Suitable buffering agents to maintain the pH within the desired range include a mild acid or acidic salt, such as acetic acid, sodium biphosphate and, preferably, ammonium chloride.

[0075] As shown in Scheme 2, epothilone analogs represented by formula II are prepared from the novel open-ring intermediates represented by formula I by macrolactamization utilizing a suitable macrolactamization or coupling agent in a mixed organic solvent system, such as THF/DMF. 9

[0076] Macrolactamization agents for the reaction include 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI), or EDCI in combination with 1-hydroxy-7-azabenzotriazole (HOAT) or 1-hydroxy-7-benzotriazole hydrate (HOBT), other carbodiimides such as dicyclohexylcarbodiimide and diisopropylcarbodiimide, O-benzotriazol-1-yl-N,N,N′,N′-bis(tetramethylene)uronium hexafluorophosphate (HBTu/DMAP), O-(7-azabenzotriazol)-1-yl-N,N,N′,N′-bis(tetramethylene)uronium hexafluorophosphate (HATu/DMAP), benzotriazole-1-yloxy-tris(bimethylamino)phosphonium hexafluorophosphate (BOP), N,N-dimethyl-4-aminopyridine (DMAP), K2CO3, diisopropylamine, triethylamine and the like. A preferred macrolactamization agent includes 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI) in combination with 1-hydroxy-7-benzotriazole (HOBT). Examples of other suitable macrolactamization agents can be found in J. M. Humphrey and A. R. Chamberlin, Chem. Rev. 97, 2243-2266, (1997), the full text of which is incorporated herein by reference.

[0077] The cyclization reaction as shown in Scheme 2 is carried out in the cold, i.e. a temperature of from about 0° C. to about −20° C., preferably from about −5° C. to −10° C.

[0078] The reaction of Scheme 2 is carried out in mildly alkaline conditions with a mild base such as K2CO3, triethylamine, diisopropylamine and the like, preferably with K2CO3, to inhibit the production of any unwanted by-products.

[0079] Scheme 3 below illustrates a preferred embodiment of the invention. The synthesis of the compounds represented by formula II from the starting epothilone material, epothilone B represented by formula III, is sequentially reacted without isolation of the novel intermediate represented by formula I as illustrated. 10

[0080] It has been found in accordance with the present invention that the compounds represented by formula II can be prepared in significantly improved yields in comparison to prior methods. Typically, the instant process produces about three fold increase in yield.

[0081] All references cited herein are incorporated by reference as if set forth at length herein.

[0082] The following non-limiting examples serve to illustrate the practice of the invention.

EXAMPLE 1

[0083] (βS,εR,ζS,ηS,2R,3S)-3-[(2S,3E)-2-amino-3-methyl-4-(2-methyl-4-thiazolyl)-3-butenyl]-β,ζ-dihydroxy-γ,γ,ε,η,2-pentamethyl-δ-oxooxiraneundecanoic acid, tetrabutylammonium salt (1:1). 11

[0084] In a 250 mL round bottom flask there was combined epothilone B (3.87 g), sodium azide (NaN3) (0.99 g, 2.0 equivalent), tetrabuytlammonium chloride (Bu4NCl) (2.3 g, 1.1 equivalents), ammonium chloride (NH4Cl) (0.82 g, 2.0 equivalents) and tetrahydrofuran (THF) (60 mL). The resulting suspension was degassed with argon and there was added thereto water (1.37 g, 10 equivalents, pre-degassed), trimethyl phosphine (PMe3) (15.2 mL, 1.0M solution in THF, 2.0 equivalents). The reaction temperature of the mixture was equilibrated to 25° C. before the addition of tris-(dibenzylideneacetone)-dipalladium(0)chloroform adduct (Pd2(dba)3.CHCl3) (158 mg, 0.02 equivalents). The resulting solution was magneticly stirred under an argon atmosphere for 19 hours and water (30 mL) and ethyl acetate (EtOAc) (30 mL) were added thereto. The two layers of the resulting mixture were separated and the aqueous layer extracted three times with 25 mL portions of ethyl acetate. The combined ethyl acetate layer was back extracted with three 15 mL portions of water. The resulting combined aqueous layer was saturated with sodium chloride (NaCl) and the pH thereof adjusted to from 6 to 6.5 with sodium phosphate monobasic (NaH2PO4). The resulting suspension was extracted with five 25 mL portions of dichloromethane (CH2Cl2) and the extracts were combined and dried over sodium sulfate. The suspension was filtered and the filtrate concentrated to provide 5.6 g of the amino acid salt in 96% yield with a HPLC area of 93%.

EXAMPLE 2

[0085] [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-7,11-Dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione. 12

[0086] The amino acid salt formed in Example 1 (4.18 g) was dissolved in a one to one mixture of tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) (270 mL) and the resulting solution was cooled to −5° C. There was added potassium carbonate(K2CO3) (0.75 g, 1.0 equivalent) and the mixture stirred for five minutes before the addition of 1-hydroxy-7-benzotriazole hydrate (HOBt) (0.88 g, 1.2 equivalents) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI) (2.09 g, 2.0 equivalents). The resulting mixture was stirred at −5° C. for two hours, 0° C. for eight hours and 10° C. for two hours. There was then added ethyl acetate (ETOAc) (500 mL) and the resulting organic layer was washed with five 120 mL portions of water. The combined aqueous layer was washed three times with 100 mL portions of ethyl acetate. The combined organic layer was back extracted with three portions (100 mL each) of water, 100 mL of brine, and dried over magnesium sulfate) (MgSO4). Filtration followed by concentration provided 2.50 g of crude [1S-1R*,3R*(E),7R*,10S*,-11R*,12R*,16S*]]-7,11-Dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione as a white solid in 92.7% yield with an HPLC AP of 94.75. The product was passed through a pad of silica gel by means of a solution of ethyl acetate/cyclohexane/triethyl amine (Et3N) (3/7/0.04) and crystallized from a mixture of ethyl acetate and cyclohexane to give 1.6 g of purified product in 56% yield from epothilone B with a HPLC area of 99.0%.

EXAMPLE 3

[0087] [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-7,11-Dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione. 13

[0088] To a jacketed 125 mL round bottom flask, fitted with a mechanical stirrer, there was combined epothilone-B (5.08 g), tetrabutyammonium azide (Bu4NN3) (3.55 g, 1.25 equivalents), ammonium chloride (1.07 g, 2 eq), water (1.8 ml, 10 equivalents), tetrahydrofuran (THF) (15 ml), and N,N-dimethylformamide (DMF) (15 ml). The mixture was inerted by sparging nitrogen subsurface for 15 minutes. In a second flask was charged tetrahydrofuran (70 ml), followed by trimethylphosphine (PMe3) (1.56 ml, 1.5 equivalents), then tris(dibenzilidineacetone)-dipalladium(0)-chloroform adduct (Pd2(dba)3.CHCl3)(0.259 g, 0.025 equivalents). The catalyst mixture was stirred for 20 minutes at ambient temperature, then added to the epothilone-B mixture. The combined mixture was stirred for 4.5 hours at 30° C. The completed reaction mixture was then filtered to remove solid ammonium chloride (NH4Cl). The filtrate contained (βS,εR,ζS,ηS,2R,3S)-3-[(2S,3E)-2-amino-3-methyl-4-(2-methyl-4-thiazolyl)-3-butenyl]-β,ζ-dihydroxy-γ,γ,ε,η,2-pentamethyl-δ-oxooxxiraneundecanoic acid, tetrabutylammonium salt (1:1) with a HPLC area of 94.1%.

[0089] In a 500 mL flask there was combined 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDCI) (3.82 g, 2 equivalents), 1-hydroxy-7-benzotriazole hydrate (HOBt) (1.68 g, 1.1 equivalents), potassium carbonate (1.38 g, 1 equivalent), N,N-dimethylformamide (DMF) (40 ml) and tetrahydrofuran (THF) (160 ml). The mixture was warmed to 35° C. and the filtrate from above was added thereto, dropwise over a period of three hours. This mixture was then stirred for an additional 1 hour at 35° C. Vacuum distillation was then applied to the reaction mixture to reduce the volume thereof to about 80 mL. The resulting solution was partitioned between 100 mL of ethyl acetate and 100 mL of water. The aqueous layer was then back-extracted with 100 ml ethyl acetate. The combined organic layers were extracted with 50 ml water and then 20 mL brine. The resulting product solution was filtered through a Zeta Plus® pad and then stripped to an oil. The crude oil was chromatographed on silica gel 60 (35 ml silica per gram of theoretical product) with an eluent comprised of 88% dichloromethane (CH2Cl2), 10% ethyl acetate (EtOAc) and 2% triethylamine (Et3N). The fractions were analyzed by HPLC, the purest of which were combined and stripped to give the purified solid. The resulting solid was slurried in ethyl acetate (32 ml) for 40 minutes at 75° C., then cyclohexane (C6H12) (16 ml) was added, and the mixture cooled to 5° C. The purified solid was collected on filter paper, washed with cold ethyl acetate/cyclohexane, and dried. The yield was 1.72 g (38% yield) of the white solid product, [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-7,11-dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione, with a HPLC area of 99.2%.

EXAMPLE 4

[0090] [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-7,11-Dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione. 14

[0091] In another embodiment of the invention the title compound can be prepared in a single reaction vessel without isolating the intermediate salt (represented as formula I) as follows.

[0092] In a 25 mL round bottom flask is combined epothilone B (3.87 g), sodium azide (NaN3) (0.99 g, 2.0 equivalents), tetrabutylammonium chloride (Bu4NCl) (2.3 g, 1.1 equivalents), ammonium chloride (NH4Cl) (0.82 g, 2.0 equivalents) and tetrahydrofuran (THF) (60 mL). The resulting suspension is degassed with argon and there is added thereto water (1.37 g, 10 equivalents, pre-degassed), and trimethylphosphine (PMe3) (15.2 mL, 1.0M solution in THF, 2.0 equivalents). The reaction temperature of the mixture is equilibrated to 25° C. before the addition of tris(dibenzilidineacetone)-dipalladium(0)-chloroform adduct (Pd2(dba)3.CHCl3) (158 mg, 0.02 equivalents). The resulting solution is stirred under an argon atmosphere for seventeen hours. The temperature of the reaction solution is cooled to −5° C. There is added potassium carbonate (K2CO3) (0.75 g, 1.0 equivalent) and the mixture is stirred for five minutes before the addition of 1-hydroxy-7-benzotriazole hydrate (HOBt) (0.88 g, 1.2 equivalents) and 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDCI) (2.09 g, 2.0 equivalents). The resulting mixture is stirred at −5° C. for two hours, 0° C. for eight hours and 10° C. for two hours. Ethyl acetate (500 mL) is added and the resulting organic layer is washed with five 120 mL portions of water. The combined aqueous layer is back extracted three times with 100 mL portions of ethyl acetate. The combined organic layers are then washed with 100 mL of brine and dried over magnesium sulfate (MgSO4). Filtration followed by concentration provides about 2.50 g of the named product as a white solid. The product is passed through a pad of silica gel by means of a solution of ethyl acetate/cyclohexane/triethylamine (Et3N) (3/7/0.04) and crystallized from a mixture of ethyl acetate and cyclohexane to give about 1.6 g of purified product.

EXAMPLE 5

[0093] Tetrabutylammonium azide (Bu4NN3).

[0094] To a 50 mL round bottom flask, fitted with a magnetic stirring bar, there was combined tetrabutylammonium chloride (Bu4NCl.H2O) (7.78 g, 1.4 equivalents) sodium azide (1.82 g 1.4 equivalents) in DMF 14 mL. The mixture was stirred for 72 h at 20-21° C. The reaction was diluted with THF (28 mL) and the solids were filtered off and washed with THF (12 mL).

EXAMPLE 6

[0095] Tetrabutylammonium azide (Bu4NN3).

[0096] To a 50 mL round bottom flask, fitted with a magnetic stirring bar, there was combined tetrabutylammonium chloride (Bu4NCl.H2O) (8.7 g, 1.4 equivalents) sodium azide (2.03 g 1.4 equivalents) in DMF 14 mL. The mixture was stirred for 7 h at 30° C. h. The reaction was diluted with THF (28 mL) and the solids were filtered off and washed with THF (12 mL).

EXAMPLE 7

[0097] [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-7,11-Dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione. 15

[0098] To a 100 mL round bottom flask, fitted with a mechanical stirrer, there was combined epothilone-B (10.15 g), solution of tetrabutylammonium azide (Bu4NN3) (56 ml, 1.25 equivalents) in DMF and THF, ammonium chloride (2.14 g, 2 eq), water (3.6 ml, 10 equivalents), and N,N-dimethylformamide (DMF) (6 ml). The mixture was inerted by sparging nitrogen subsurface for 30 minutes. In a second flask was charged tetrahydrofuran (40 ml), followed by trimethylphosphine (PMe3) (3 ml, 1.5 equivalents), then tris(dibenzilidineacetone)-dipalladium(0)-chloroform adduct (Pd2(dba)3.CHCl3)(0.345 g, 0.017 equivalents). The catalyst mixture was stirred for 20 minutes at ambient temperature, then added to the epothilone-B mixture. The combined mixture was stirred for 18 hours at 31-35° C. The completed reaction mixture was then filtered to remove solid ammonium chloride (NH4Cl). The filtrate contained (βS,εR,ζS,ηS,2R, 3S)-3-[(2S,3E)-2-amino-3-methyl-4-(2-methyl-4-thiazolyl)-3-butenyl]-β,ζ-dihydroxy-γ,γ,ε,η,2-pentamethyl-δ-oxooxirane-undecanoic acid, tetrabutylammonium salt (1:1).

[0099] In a 250 mL flask there was combined 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDCI) (7.64 g, 2 equivalents), 1-hydroxy-7-benzotriazole hydrate (HOBt) (3.06 g, 1 equivalent), potassium carbonate (1.41 g, 0.5 equivalent), N,N-dimethylformamide (DMF) (40 ml) and tetrahydrofuran (THF) (24 ml). The mixture was warmed to 35° C. and the filtrate from above was added thereto, slowly over a period of four hours. The resulting solution was then partitioned between 80 mL of ethyl acetate and 210 mL of water. The aqueous layer was then back-extracted with 2×80 ml ethyl acetate. The combined organic layers were extracted with 120 ml water and dried over sodium sulfate. The resulting product solution was stirred over Darco KRB (1 g) for 2 h. The crude solution was filtered through a pad of florisil (3 g of florisil per gram of input). The column was rinsed with ethyl acetate (60 mL). The combined filtrate was concentrated under vacuo to a final volume of ˜100 mL below 30° C. The resulting slurry in ethyl acetate was heated for 30 minutes at 71° C., then heptane (C7H16) (50 ml) was added, and the mixture cooled to 21° C. The purified solid was collected on filter paper, washed with ethyl acetate/heptane, and dried. The yield was 4.4 g (44% yield) of the white solid product, [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-7,11-dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione, with a HPLC area of 98.3%.

EXAMPLE 8

[0100] [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-7,11-Dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione. 16

[0101] To a 100 mL round bottom flask, fitted with a mechanical stirrer, there was combined epothilone-B (5.1 g), solution of tetrabutylammonium azide (Bu4NN3) (29 ml, 1.30 equivalents) in DMF and THF, ammonium chloride (1.07 g, 2 eq), water (1.8 ml, 10 equivalents), and N,N-dimethylformamide (DMF) (3 ml). The mixture was inerted by sparging nitrogen subsurface for 30 minutes. In a second flask was charged tetrahydrofuran (20 ml), followed by trimethylphosphine (PMe3) (1.5 ml, 1.5 equivalents), then tris(dibenzilidineacetone)-dipalladium(0)-chloroform adduct (Pd2(dba)3.CHCl3)(0.175 g, 0.017 equivalents). The catalyst mixture was stirred for 20 minutes at ambient temperature, then added to the epothilone-B mixture. The combined mixture was stirred for 18 hours at 31-35° C. The completed reaction mixture was then filtered to remove solid ammonium chloride (NH4Cl), followed by a zeta pad (R53SP or R51 SP) filtration. The filtrate contained (βS,εR,ζS,ηS,2R,3S)-3-[(2S,3E)-2-amino-3-methyl-4-(2-methyl-4-thiazolyl)-3-butenyl]-β,ζ-dihydroxy-γ,γ,ε,η,2-pentamethyl-δ-oxooxxiraneundecanoic acid, tetrabutylammonium salt (1:1).

[0102] In a 100 mL flask there was combined 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDCI) (3.9 g, 2 equivalents), 1-hydroxy-7-benzotriazole hydrate (HOBt) (1.52 g, 1 equivalent), potassium carbonate (0.67 g, 0.5 equivalent), N,N-dimethylformamide (DMF) (20 ml) and tetrahydrofuran (THF) (12 ml). The mixture was warmed to 35° C. and the filtrate from above was added thereto, slowly over a period of four hours. The resulting solution was then partitioned between 25 mL of ethyl acetate and 100 mL of water. The aqueous layer was then back-extracted with 2×25 ml ethyl acetate. The combined organic layers were extracted with 60 ml water. The resulting product solution was filtered through a zeta pad (R53SP or R51 SP). The crude solution was diluted with 1 part of cyclohexane and 1% v/v of triethylamine was added. This solution was filtered through a pad of silica gel (5 g of florisil per gram of input). The column was rinsed with 2:1 ethyl acetate:cyclohexane (400 mL) containing 1% v/v triethylamine. After discarding the first 100 ml, the filtrate was concentrated under vacuo to a final volume of ˜50 mL below 30° C. Cyclohexane (20 to 30 mL) was added and the resulting slurry was heated for 30 minutes at 71° C. Finally the mixture was cooled to 21° C. The purified solid was collected on filter paper, washed with ethyl acetate/cyclohexane, and dried. The yield was 5.1 g (51% yield) of the white solid product, [1S-[1R*,3R*(E),7R*,10S*,11R*, 12R*, 16S*]]-7,11-dihydroxy-8,8,10,12,16-pentamethyl -3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione, with a HPLC area of 99.2%.

EXAMPLE 9

[0103] [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-7,11-Dihydroxy-8,8,10,12,16-pentamethyl -3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione. 17

[0104] Sodium azide (NaN3, 10.20 g) was stirred with 12.5 mL of water for about 15 minutes in a Morton flask and 70 mL of dimethylformamide (DMF) was added to the resulting aqueous slurry. The agitation was continued for an additional 15 minutes and solid tetrabutylammoniun chloride (TBACl, 43.6 g) was added to the mixture. The agitation was continued for an additional 24 h. The tetrabutylammonium azide (TBA-N3) concentration was measured by HPLC analysis. The TBA-N3 formation was very fast and substantial concentration was observed as early as 15 minutes after addition of TBACl. Tetrahydrofuran (THF, 140 mL) was added to the rich TBA-N3 solution. The slurry was filtered on a Buchner funnel and the residue was washed with 60 mL of additional THF and combined with the rich filtrate. The TBA-N3 content was analyzed by HPLC.

EXAMPLE 10

[0105] [1S-[1R*,3R*(E),7R*,10S*,11R*,12R*,16S*]]-7,11-Dihydroxy-8,8,10,12,16-pentamethyl-3-[1-methyl-2-(2-methyl-4-thiazolyl)ethenyl]-4-aza-17-oxabicyclo[14.1.0]heptadecane-5,9-dione. 18

[0106] Sodium azide (NaN3, 3.04 g) was stirred with 4 mL of water, for about 15 minutes, in a 100 mL flask, at 15-33° C. Solid tetrabutylammoniun chloride (TBACl, 13.05 g) was added to the mixture and stirred for 15-45 minutes. Dimethylformamide (DMF, 21 mL) was added and the mixture stirred at 18-33° C., until the supernatant showed >90% azide by HPLC determination. Tetrahydrofuran (THF, 42 mL) was added and the slurry was filtered. The residual solids were washed with 18 mL of THF. The rich tetrabutylammonium azide (TBA-N3) solution was quantitated for azide by HPLC and the KF measured prior to use.

Claims

1. A compound represented by the formula

2. A compound in accordance with claim 1 wherein said compound has the formula

3. A compound in accordance with claim 2 wherein said compound has the structure

4. A process for preparing a compound represented by the formula

5. A process in accordance with claim 4 for preparing a compound represented by the formula

6. A process in accordance with claim 5, wherein said epothilone starting material is epothilone B, and said compound of formula IV is represented by the structure

7. A process for preparing a compound represented by the formula

8. A process in accordance with claim 7 for preparing a compound represented by the formula

9. A process in accordance with claim 8, wherein said epothilone starting material is epothilone B, and said compound of formula IV is represented by the structure

10. A process in accordance with claim 7, wherein said azide donor is tetrabutylammonium azide.

11. A process for the preparation of an epothilone represented by the formula

12. A process in accordance with claim 11 wherein said intermediate is represented by the formula

13. A process in accordance with claim 12 wherein said epothilone represented by formula II has the structure

14. A process in accordance with claim 11 wherein said coupling agent comprises 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxy-7-benzotriazole hydrate.

15. A process for the preparation of an epothilone represented by the formula

16. A process in accordance with claim 15 wherein said intermediate is represented by the formula

17. A process in accordance with claim 16 wherein said epothilone starting material is epothilone B, said intermediate compound represented by formula I has the structure

18. A process for the preparation of an epothilone represented by the formula

19. A process in accordance with claim 18 wherein said intermediate is represented by the formula

20. A process in accordance with claim 19 wherein said epothilone starting material is epothilone B, said intermediate compound represented by formula IV has the structure

21. A process in accordance with claim 15 wherein said azide donor agent is selected from the group consisting of lithium azide, sodium azide, tetraalkylammonium azide and trialkylsilyl azide, said reducing agent is selected from the group consisting of a trialkylphosphine, triarylphosphine, trialkylarsine, triarylarsine, and mixtures thereof, said phase transfer catalyst is selected from the group consisting of tetraalkylonium, tetraarylonium, tetraaralkylonium salts and mixtures thereof, said palladium catalyst is selected from the group consisting of palladium acetate, palladium chloride, palladium tetrakis-(triphenylphosphine), palladium tetrakris-(triphenylarsine) and tris-(dibenzylideneacetone)-dipalladium(0)chloroform adduct.

22. A process in accordance with claim 21 wherein the azide donor agent is sodium azide, the reducing agent is trimethylphosphine, the phase transfer catalyst is tetrabutylammonium chloride, and the palladium catalyst is tris-(dibenzylideneacetone)-dipalladium(0)chlorofrom adduct.

23. A process in accordance with claim 15 wherein said macrolactamization coupling agent comprises one or more members selected from the group consisting of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxy-7-benzotriazole hydrate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxy-7-azabenzotriazole hydrate, dicyclohexylcarbodiimide, diisopropylcarbodiimide, diphenylphosphoryl azide, O-benzotriazol-1-yl-N,N,N′,N′-bis(tetramethylene)uronium hexafluorophosphate, O-(7-azabenzotriazol)-1-yl-N,N,N′,N′-bis(tetramethylene)uronium hexafluorophosphate, benzotriazol-1-yloxy-tris(bimethylamino)phosphonium hexafluorophosphate, N,N-dimethyl-4-aminopyridine, K2CO3, diisopropylamine, and triethylamine.

24. A process in accordance with claim 23 where said coupling agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxy-7-benzotriazole hydrate.

25. A process in accordance with claim 18 wherein said azide donor agent is selected from the group consisting of lithium azide, sodium azide, tetraalkylammonium azide and trialkylsilyl azide, said buffering agent is selected from the group consisting of mild acids and acidic salts, said palladium catalyst is selected from the group consisting of palladium acetate, palladium chloride, palladium tetrakis-(triphenylphosphine), palladium tetrakris-(triphenylarsine) and tris-(dibenzylideneacetone)-dipalladium(0)chloroform adduct, and said reducing agent is selected from the group consisting of a trialkylphosphine, triarylphosphine, trialkylarsine, triarylarsine, and mixtures thereof.

26. A process in accordance with claim 25 wherein the azide donor agent is tetrabutylammonium azide, the buffering agent is ammonium chloride, the palladium catalyst is tris-(dibenzylideneacetone)-dipalladium(0)chlorofrom adduct, and the reducing agent is trimethylphosphine.

27. A process in accordance with claim 18 wherein said macrolactamization coupling agent comprises one or more members selected from the group consisting of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxy-7-benzotriazole hydrate, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxy-7-azabenzotriazole hydrate, dicyclohexylcarbodiimide, diisopropylcarbodiimide, diphenylphosphoryl azide, O-benzotriazol-1-yl-N,N,N′,N′-bis (tetramethylene)uronium hexafluorophosphate, O-(7-azabenzotriazol)-1-yl-N,N,N′,N′-bis(tetramethylene)uronium hexafluorophosphate, benzotriazol-1-yloxy-tris(bimethylamino)phosphonium hexafluorophosphate, N,N-dimethyl-4-aminopyridine, K2CO3, diisopropylamine, and triethylamine.

28. A process in accordance with claim 27 where said coupling agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxy-7-benzotriazole hydrate.