PROCESS FOR THE PREPARATION OF CONJUGATES USEFUL IN THE TREATMENT OF PROSTATE CANCER

Abstract: The present invention is directed to the improved synthesis of compounds of formula (I) which may be useful in the treatment of prostate cancer.

Description: TITLE OF THE INVENTION PROCESS FOR THE PREPARATION OF CONJUGATES USEFUL IN THE TREATMENT OF PROSTATE CANCER BACKGROUND OF THE INVENTION In 1994 cancer of the prostate gland is expected to be diagnosed in 200,000 men in the U.S. and 38,000 American males will die from this disease (Garnick, M.B. (1994). The Dilemmas of Prostate Cancer. Scientific American, April:72-81). Thus, prostate cancer is the most frequently diagnosed malignancy (other than that of the skin) in U.S. men and the second leading cause of cancer- related deaths (behind lung cancer) in that group. Compositions useful in the treatment of prostatic cancer and related conditions are described in United States Patent Nos. 5,599,686, 5,866,679 and 5,948,750, and United States Patent Applications Serial No. 08/950,805, filed 14th October 1997(PCT Publ.No. WO 98/18493). Said compositions comprise chemical conjugates comprising known cytotoxic agents and oligopeptides having amino acid sequences that are selectively proteolytically cleaved by free prostate specific antigen and that include a cyclic amino acid having a hydrophilic substituent. The oligopeptide moieties are selected from oligomers that are selectively recognised by free prostate specific antigen (PSA) and are capable of being proteolytically cleaved by the enzymatic activity thereof. Ideally, the cytotoxic activity of the cytotoxic agent is greatly reduced or absent when the intact oligopeptide containing the PSA proteolytic cleavage site is bonded directly, or through a chemical linker, to the cytotoxic agent. Also ideally, the cytotoxic activity of the cytotoxic agent increases significantly, or is restored completely, upon proteolytic cleavage of the attached oligopeptide at the cleavage site. Anthracycline antibiotics, in particular doxorubicin, are among the cytotoxic agents that were described in the published patent applications as preferably incorporated into such conjugates, which may be referred to as PSA conjugates. It is the object of this invention to provide an efficient, scaleable and reproducible process for the preparation of PSA conjugates having an anthracycline antibiotic moiety as the cytotoxic agent and having the cleavable oligopeptide directly attached, via the C-terminus amino acid, to the glycosyl amine of the anthracycline antibiotic moiety. Another object of this invention is to provide intermediate compounds useful in the preparation of such PSA conjugates. SUMMARY OF THE INVENTION A chemical process for the preparation of a PSA conjugate which comprises an anthracycline antibiotic and an oligopeptide, having an amino acid sequence that is selectively proteolytically cleaved by free prostate specific antigen (PSA) is disclosed. Such conjugates are useful in the treatment of prostatic cancer and benign prostatic hyperplasia (BPH). DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a process for the preparation of compounds as illustrated by formula I: or a pharmaceutically acceptable salt thereof wherein oligopeptide is an oligopeptide which is selectively recognized by the free prostate specific antigen (PSA) and is capable of being proteolytically cleaved by the enzymatic activity of the free prostate specific antigen, Ra is -CH3, -CH2OH, -CH2OCO(CH2)3CH3, or -CH2OCOCH(OC2H5)2; Rb is -OCH3, -OH or -H; Rd is -OH, -OTHP or -H; and Re is -OH or -H, provided that Re is not -OH when Rd is -OH or -OTHP; R is selected from: a) acetyl; e) hydrogen; Rl and R2 are independently selected from: a) hydrogen, b) unsubstituted or substituted aryl, unsubstituted or substituted heterocycle, C3-C10 cycloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, halogen, C1-C6 perfluoroalkyl, R3O-, R3C(O)NR3-, (R3) 2 NC(0)-, R32N-C(NR3)-, R4S(O) m NH, CN, NO2, R3C(O)-, N3, -N(R3) 2 , or R40C(0)NR3-, c) unsubstituted C1-C6 alkyl, d) substituted Ci-Cβ alkyl wherein the substituent on the substituted Ci- C(, alkyl is selected from unsubstituted or substituted aryl, unsubstituted or substituted heterocyclic, C3-C10 cycloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, R O-, R4S(O) m NH, R3C(0)NR3-, (R3) NC(O)-, R32N-C(NR3)-, CN, R3C(O)-, N3, -N(R3)2, and R40C(0)-NR3-; or Rl and R2 are combined to form -(CH2)s- wherein one of the carbon atoms is optionally replaced by a moiety selected from: O, S(O) m , -NC(O)-, NH and -N(COR4)-; R3 is selected from: hydrogen, aryl, substituted aryl, heterocycle, substituted heterocycle, C1-C6 alkyl and C3-C10 cycloalkyl; R4 is selected from: aryl, substituted aryl, heterocycle, substituted heterocycle, C1-C6 alkyl and C3-C10 cycloalkyl; m is 0, 1 or 2; n is 1, 2, 3 or 4; p is zero or an integer between 1 and 100; q is 0 or 1, provided that if p is zero, q is 1; r is an integer between 1 and 10; and s is 3, 4 or 5. The process comprises the step of preparing the compound of the formula la: m nus or a salt thereof; wherein oligopeptide, R, R a , Rb, Rd nd Re are described as above R' is selected from: a) R, b) a protected precursor to R, and c) an N-terminus protecting group; by mixing an oligopeptide of the formula A: N-terminus J wherein oligopeptide and R' are described as above, or a salt thereof; with an anthracycline antibiotic of the formula B: B or a salt thereof; wherein R a , Rb, Rd and R are as described hereinabove, in the presence of a carboxyl activating agent and, optionally, in the presence of a base. In an embodiment of the instant process, if R' is a protected precursor to R or an N-terminus protecting group, the process further comprises the step of removing the protecting group to produce the compound of the formula I. In an embodiment of the instant process, the oligopeptide of formula A is mixed with a salt of the anthracycline antibiotic of the formula B in the presence of a carboxyl activating agent and a base. In an embodiment of the instant process, the carboxyl activating agent is selected from dicyclohexylcarbodiimide (DCC), N-ethyl-N-(3- dimethylaminopropyl)- carbodiimide (EDC), and 1,3-diisopropylcarbodiimide (DIC). In a preferred embodiment, the carboxyl activating agent is EDC. In an embodiment of the instant process, the base is selected from 2,4,6-collidine, lutidine, pyridine, triethyl amine and (iPr)2NEt. In a preferred embodiment, the base is 2,4,6-collidine. It has been suφrisingly discovered that use 2,4,6-collidine as the base in the instant process for the formation of the compound of the formula la results in lower epimerization of the C-terminus amino acid moiety than when other bases previously described are utilized. In a further embodiment of the instant process, the mixing of the compounds of formula A and formula B is additionally in the presence of an additive. In a preferred further embodiment of the instant process the additive is selected from HOAt, HOBt, HOPO or a combination thereof. In a preferred embodiment of the further embodiment of the instant process, the additive is HOAt. In a secondpreferred embodiment of the further embodiment of the instant process, the additive is a combination of HOPO and HOAt. In a further embodiment of the instant process, the oligopeptide of the formula A is mixed with the anthracycline antibiotic of the formula B in the presence of a carboxyl activating agent, an additive and a base. In a preferred further embodiment of the instant process, the oligopeptide of the formula A is mixed with the anthracycline antibiotic of the formula B in the presence of an additive and a base, and a carboxyl activating agent is thereafter added to the mixture. It has been surprisingly discovered that when the carboxyl activating agent is added last to a preformed mixture of the process components the amount of epimerization that occurs at the C-terminus amino acid of the oligopeptide moiety in the compound of formula la is less than when the base is added last to the reaction mixture. In a more preferred further embodiment of the instant process, the oligopeptide of the formula A is mixed with the anthracycline antibiotic of the formula B in the presence of an additive and a base, and a carboxyl activating agent is thereafter added to the mixture in two or more portions. In an embodiment of the instant invention, the anthracycline antibiotic is doxorubicin (Ra is -CH2OH, Rb is -OCH3, Re is H and Rd is -OH). In another embodiment of the instant invention, R is selected from: a) acetyl; and b) In another embodiment of the instant invention, R is and R' is In another embodiment of the instant invention, R is and R' is and the process further comprises the step of removing the protecting group by contacting the compound of formula la with piperidine. In a preferred embodiment of the instant invention, the oligopeptide comprises an oligomer selected from: a) 4-HypXaaSerTyrGln|SerSer (SEQ._D.NO.: 1), b) 4-HypXaaSerTyrGln|SerAla (SEQ.ID.NO.: 2), c) Ala-4-HypXaaSerTyrTyr|Ser (SEQ.ID.NO.: 3), d) AlaAsn4-HypXaaSerTyrGln|Ser (SEQ.ID.NO.: 4), e) 4-HypXaaSerTyrGln|SerSerThr (SEQ.ID.NO.: 5), f) 4-HypTyrGln|SerSerTlιr (SEQ.ID.NO.: 6), g) 4-HypXaaSerTyrGln|SerSerSer (SEQ.ID.NO.: 7), h) 4-HypTyrGln|SerSerSer (SEQ.ID.NO.: 8), i) 4-HypXaaLysTyrGln|SerSerSer (SEQ.ID.NO.: 9), j) 4-HypXaahArgTyrGln|SerSerSer (SEQ.ID.NO.: 10), k) 4-HypXaaSerTyrGln|SerSerLeu (SEQ.ID.NO.: 11); 1) 4-HypTyrGln|SerSerLeu (SEQ.ID.NO.: 12); m) 4-HypXaaSerTyrGln|SerLeu (SEQ.ID.NO.: 13); n) 4-HypTyrGln|SerLeu (SEQ.ID.NO.: 14); p) 4-HypXaaSerTyrGln|SerNle (SEQ.ID.NO.: 15); q) 4-HypTyrGln|SerNle (SEQ.ID.NO.: 16); r) 4-HypXaaSerTyrGln|SerTIC (SEQ.ID.NO.: 17); s) 4-HypTyrGln|SerTIC (SEQ.ID.NO. : 18); t) 4-HypXaaSerChgGln|SerLeu (SEQ.ID.NO.: 19); u) 4-HypChgGln|SerLeu (SEQ.ID.NO.: 20); v) 4-HypXaaSerChgGln|SerNle (SEQ.ID.NO.: 21); w) 4-HypChgGln|SerNle (SEQ.ID.NO.: 22); x) 4-HypXaaSerChgGln|SerTIC (SEQ.ID.NO.: 23); y) 4-HypChgGln|SerTIC (SEQ.ID.NO.: 24); z) AlaSerTyrGln|SerSerLeu (SEQ.ID.NO.: 25); aa) SerhArgChgGln| SerLeu (SEQ.ID.NO.: 26); bb) hArgSerSerTyrGlnlSerNle (SEQ.ID.NO.: 27); cc) hArgAlaSerChgGln|SerLeu (SEQ.ID.NO.: 28); dd) hArgSerSerTyrGln|SerLeu (SEQ.ID.NO.: 29); ee) hArgSerSerChg|SerLeu (SEQ.ID.NO.: 30); fit) SerhArgChgGln|SerLeu (SEQ.ID.NO.: 31); gg) hArgTyrGln|SerLeu (SEQ.ID.NO.: 32); hh) hArgSerSerChgGlnlSerLeu (SEQ.ID.NO.: 33); ii) SerhArgTyrGln|SerLeu (SEQ.ID.NO.: 34); jj) SerSerTyrGln|SerLeu (SEQ.ID.NO.: 35); kk) SerSerSerChgGln|SerLeu (SEQ.ID.NO.: 36); 11) 3PAL-SerSerChgGln|SerLeu (SEQ.ID.NO.: 37); mm) SerSerChgGln|SerLeu (SEQ.ID.NO.: 38); nn) SerSerSerChgGln|Ser(dLeu) (SEQ.ID.NO.: 39); oo) SerSerSerChgGln|SerVal (SEQ.ID.NO.: 40); pp) ProSerSerChgGln|SerVal (SEQ.ID.NO.: 41); qq) GlySerSerChgGln|SerLeu (SEQ.ID.NO.: 42); rr) hSerSerSerChgGln|SerLeu (SEQ.ID.NO.: 43); ss) hArgSerSerChgGln|SerNle (SEQ.ID.NO.: 44); tt) hArgTyrGln|SerSerSerLeu (SEQ.ID.NO.: 45); uu) LysTyrGln|SerSerSerLeu (SEQ.ID.NO.: 46); w) SerTyrGln|SerSerSerLeu (SEQ.ID.NO.: 47); ww) SerSerChgGln-Ser(dLeu) (SEQ.ID.NO.: 48); xx) 3PAL-SerSerChgGln-Ser(dLeu) (SEQ.ID.NO.: 49); and yy) AlaSerChgGln-SerLeu (SEQ.ID.NO.: 50). wherein 4-Hyp is 4-hydroxyproline, Xaa is any amino acid, hArg is homoarginine, hSer is homoserine, TIC is l,2,3,4-tetrahydro-3-isoquinoline carboxylic acid, Cha is cyclohexylalanme and Chg is cyclohexylglycine. Preferably Xaa in the more preferred embodiment is selected from Ala, Ser and He. In a preferred embodiment the present invention is directed to a process for the preparation of the compound of formula 4: (SEQ.ID.NO.: 51) or a pharmaceutically acceptable salt thereof; which comprises the step of mixing an oligopeptide of the formula 2a: 2a (SEQ.ID.NO.: 51) wherein R" is -OH or a protected precursor to -OH; or a salt thereof; with an anthracycline antibiotic of the formula 1 : or a salt thereof; in the presence of a carboxyl activating agent and, optionally, in the presence of a base, to form a compound of the formula 3a: (SEQ.ID.NO.: 51) or a salt thereof. In a further embodiment of this preferred embodiment, the process further comprises the step of converting R" to a -OH moiety. In a more preferred embodiment, the present invention is directed to a process for the preparation of the compound of formula 4: (SEQ.ID.NO.: 51) or a pharmaceutically acceptable salt thereof; which comprises the steps of: a) mixing an oligopeptide of the formula 2: (SEQ.ID.NO.: 52) or a salt thereof; with an anthracycline antibiotic of the formula 1: or a salt thereof; in the presence of a carboxyl activating agent and, optionally, in the presence of a base, to form a compound of the formula 3: (SEQ.ID.NO.: 52) or a salt thereof. In a further embodiment of the more preferred embodiment of the instant process, the oligopeptide of the formula 2 is added to the reaction mixture that comprises a solvent, in particular DMF, at about -6°C to about -3°C to form a first slurry and the anthracycline antibiotic of the formula 1 is added to that slurry to form a second slurry. It has been surprisingly discovered that maintaining such a low temperature for addition of the oligopeptide to the reaction mixture and then adding the doxorubicin to the slurry at low temperature avoids the formation of a gel in the reaction mixture which is detrimental to a large scale preparation of the compound of the formula 3. In a second further embodiment of the more preferred embodiment of the instant process, the anthracycline antibiotic of the formula 1 is mixed in a solvent, in particular DMF, with a carboxyl activating agent, and optionally a base, to form a first slurry, which is then cooled to about -6°C to about -3°C and the oligopeptide of the formula 2 is added to that slurry to form a second slurry. In an embodiment of the further embodiments of the instant process, the oligopeptide of formula 1 is mixed with a salt of the anthracycline antibiotic of the formula 2 in the presence of a carboxyl activating agent and a base. Preferably, the salt of the anthracycline antibiotic of the formula 2 is the hydrochloride salt. In an embodiment of the further embodiments of the instant process, the process further comprises the step of removing the fluorenylmethoxy protecting group of the compound of formula 3 to produce the compound of the formula 4. In a further embodiment of the instant process, the step of removing the fluorenylmethoxy protecting group of the compound of formula 3 comprises contacting the compound of formula 3 with piperidine. The phrase "oligomers that comprise an amino acid sequence" as used hereinabove, and elsewhere in the Detailed Description of the Invention, describes oligomers of from about 3 to about 100 amino acids residues which include in their amino acid sequence the specific amino acid sequence decribed and which are therefore proteolytically cleaved within the amino acid sequence described by free PSA. Preferably, the oligomer is from 5 to 10 amino acid residues. Thus, for example, the following oligomer: hArgSer4-HypChgGln|SerLeu (SEQ.ID.NO.: 53); comprises the amino acid sequence: 4-HypChgGln|SerLeu (SEQ.ID.NO.: 54); and would therefore come within the instant invention. The inclusion of the symbol "|" within an amino acid sequence indicates the point within that sequence where the oligopeptide is proteolytically cleaved by free PSA. The compounds of the present invention may have asymmetric centers and occur as racemates, racemic mixtures, and as individual diastereomers, with all possible isomers, including optical isomers, being included in the present invention. Unless otherwise specified, named amino acids are understood to have the natural "L" stereoconfiguration. When any variable (e.g. aryl, heterocycle, R3 etc.) occurs more than one time in any constituent, its definition on each occurence is independent of every other occurence. For example, HO(CRlR2)2- represents HOCH2CH2-, HOCH2CH(OH)-, HOCH(CH3)CH(OH)-, etc. Also, combinations of substituents and/or variables are permissible only if such combinations result in stable compounds. The following abbreviations are utilized in the specification and tables to denote the indicated amino acids and moieties: hR or hArg: homoarginine hY or hTyr: homotyrosine Cha: cyclohexylalanme Amf: 4-aminomethylphenylalanine DPL: 2-(4,6-dimethylpyrimidinyl)lysine (imidazolyl)K: N'-(2-imidazolyl)lysine Me2PO3-Y: O-dimethylphosphotyrosine O-Me-Y: O-methyltyrosine TIC: 1 ,2,3,4-tetrahydro-3-isoquinoline carboxylic acid DAP: 1 ,3-diaminopropane TFA: trifluoroacetic acid AA: acetic acid 3PAL 3-pyridyl-alanine 4-Hyp 4-hydroxyproline Abu alpha-aminobutyric acid Thi thienylalanine Boc/BOC t-Butoxycarbonyl; DMAc dimethylacetamide DMF Dimethylformamide; DMSO Methyl sulfoxide; EDC l-(3-dimethylaminopropyl)-3-ethyl-carbodiimide; EtOAc Ethyl acetate; EtOH Ethanol; FAB Fast atom bombardment; HOAt 1 -Hydroxy-7-azabenzotriazole HOBt 1-Hydroxybenzotriazole hydrate; HOPO 2-hydroxypyridine-N-oxide HPLC High-performance liquid chromatography; IPAc isopropylacetate MeOH methanol RPLC Reverse Phase Liquid Chromatography TFA Trifluoroacetic acid; THF Tetrahydrofuran. As used herein, "alkyl" and the alkyl portion of aralkyl and similar terms, is intended to include both branched and straight-chain saturated aliphatic hydrocarbon groups having the specified number of carbon atoms; "alkoxy" represents an alkyl group of indicated number of carbon atoms attached through an oxygen bridge. As used herein, "cycloalkyl" is intended to include non-aromatic cyclic hydrocarbon groups having the specified number of carbon atoms. Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and the like. "Alkenyl" groups include those groups having the specified number of carbon atoms and having one or several double bonds. Examples of alkenyl groups include vinyl, allyl, isopropenyl, pentenyl, hexenyl, heptenyl, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, 1-propenyl, 2-butenyl, 2-methyl-2-butenyl, isoprenyl, farnesyl, geranyl, geranylgeranyl and the like. "Alkynyl" groups include those groups having the specified number of carbon atoms and having one triple bonds. Examples of alkynyl groups include acetylene, 2-butynyl, 2-pentynyl, 3-pentynyl and the like. "Halogen" or "halo" as used herein means fiuoro, chloro, bromo and iodo. As used herein, "aryl," and the aryl portion of aralkyl and aroyl, is intended to mean any stable monocyclic or bicyclic carbon ring of up to 7 members in each ring, wherein at least one ring is aromatic. Examples of such aryl elements include phenyl, naphthyl, tetrahydronaphthyl, indanyl, biphenyl, phenanthryl, anthryl or acenaphthyl. The term heterocycle or heterocyclic, as used herein, represents a stable 5- to 7-membered monocyclic or stable 8- to 11-membered bicyclic heterocyclic ring which is either saturated or unsaturated, and which consists of carbon atoms and from one to four heteroatoms selected from the group consisting of N, O, and S, and including any bicyclic group in which any of the above-defined heterocyclic rings is fused to a benzene ring. The heterocyclic ring may be attached at any heteroatom or carbon atom which results in the creation of a stable structure. Examples of such heterocyclic elements include, but are not limited to, azepinyl, benzimidazolyl, benzisoxazolyl, benzofurazanyl, benzopyranyl, benzothiopyranyl, benzofuryl, benzothiazolyl, benzothienyl, benzoxazolyl, chromanyl, cinnolinyl, dihydrobenzofuryl, dihydrobenzothienyl, dihydrobenzothiopyranyl, dihydrobenzothiopyranyl sulfone, furyl, imidazolidinyl, imidazolinyl, imidazolyl, indolinyl, indolyl, isochromanyl, isoindolinyl, isoquinolinyl, isothiazolidinyl, isothiazolyl, isothiazolidinyl, moφholinyl, naphthyridinyl, oxadiazolyl, 2- oxoazepinyl, oxazolyl, 2-oxopiperazinyl, 2-oxopiperdinyl, 2-oxopyrrolidinyl, piperidyl, piperazinyl, pyridyl, pyrazinyl, pyrazolidinyl, pyrazolyl, pyridazinyl, pyrimidinyl, pyrrolidinyl, pyrrolyl, quinazolinyl, quinolinyl, quinoxalinyl, tetrahydrofuryl, tetrahydroisoquinolinyl, tetrahydroquinolinyl, thiamorpholinyl, thiamoφholinyl sulfoxide, thiazolyl, thiazolinyl, thienofuryl, thienothienyl, and thienyl. As used herein in the terms "substituted Cl -8 alkyl", "substituted aryl" and "substituted heterocycle" include moieties containing from 1 to 3 substituents in addition to the point of attachment to the rest of the compound. Such additional substituents are selected from F, Cl, Br, CF3, NH2, N(Ci-C6 alkyl)2, NO2, CN, (C1 - C6 alkyl)O-, -OH, (C1-C6 alkyl)S(O) m -, (C1-C6 alkyl)C(O)NH-, H2N-C(NH)-, (Cl - C6 alkyl)C(O)-, (C1-C6 alkyl)OC(O)-, N3, (C1-C6 alkyl)OC(O)NH- and C1-C20 alkyl. The term "an integer between 1 and 10" represents the numbers 1 and 10 as well as those integers between those numbers. The term "an integer between 1 and 100" represents the numbers 1 and 100 as well as those integers between those numbers. When Rl and R are combined to form -(CH2)s-, the cyclic moieties and heteroatom-containing cyclic moieties so defined include, but are not limited to: As used herein, the term "PEG" represents certain polyethylene glycol containing substituents having the designated number of ethyleneoxy subunits. Thus the term PEG(2) represents and the term PEG(6) represents As used herein, the term "(2R)(2,3-dihydroxypropionyl)" represents the following structure: As used herein, the term "(2R,3S) 2,3,4-trihydroxybutanoyl" represents the following structure: HO The following compounds are specific examples of a oligopeptide- cytotoxic agent conjugate that may be prepared by the process of the instant invention: wherein X is: O HO V ^ SerSerSerChgGlnSerLeu-^- (SEQ.ID.NO.: 63), OH O HO. SerSerSerChgGlnSerLeu— f- (SEQ.ID.NO.: 64), or an optical isomer or pharmaceutically acceptable salt thereof. Other PSA conjugate compounds that may be prepared by the process of the instant invention include, but are not limited to, the compounds described in the following patents and patent publications: U.S. Pat. No. 5,599,686, issued February 4, 1997; U.S. Pat. No. 5,866,679, issued February 2, 1999; WO 96/00503 (January 11, 1996); USSN 08/468,161 filed on June 6, 1997; WO 98/10651 (March 19, 1998); USSN 08/926,412 filed on September 9, 1997; and U.S. Pat. No. 5,948,750, issued September 7, 1999; WO 98/18493 (May 7, 1998); USSN 08/950,805, filed on October 14, 1997. The pharmaceutically acceptable salts of the conjugates that may be prepared by the process of this invention and salts of Compounds of the formulae A, B, 1, 2a and 3a utilized in the instant processes include the conventional non-toxic salts of the compounds, e.g., non-toxic inorganic or organic acids. For example, such conventional non-toxic salts include those derived from inorganic acids such as hydrochloric, hydrobromic, sulfuric, sulfamic, phosphoric, nitric and the like; and the salts prepared from organic acids such as acetic, propionic, succinic, glycolic, stearic, lactic, malic, tartaric, citric, ascorbic, palmoic, maleic, hydroxymaleic, phenylacetic, glutamic, benzoic, salicylic, sulfanilic, 2-acetoxybenzoic, fumaric, toluenesulfonic, methanesulfonic, ethane disulfonic, oxalic, isethionic, trifluoroacetic and the like. With respect to the conjugates described herein which comprise a N- terminus blocking group on the peptide which contains a carboxylic acid moiety, a pharmaceutically acceptable salt may take the form -COOM, where M is a negative charge, which is balanced by a counterion, e.g., an alkali metal cation such as sodium or potassium. Other pharmaceutically acceptable counterions may be calcium, magnesium, zinc, ammonium, or alkylammonium cations such as tetramethylammonium, tetrabutylammonium, choline, triethylhydroammonium, meglumine, triethanolhydroammonium and the like. For the puφose of the process of the instant invention, the carboxyl activating agent may be selected from the group including, but not limited to, 2-(lH- benzotriazol-l-yl)-l,l,3,3-tetramethyluronium hexafluorophosphate (known as HBTU), 1 -hydroxybenzotriazole hydrate (known as HOBt), dicyclohexylcarbodiimide (DCC), N-ethyl-N-(3-dimethylaminopropyl)- carbodiimide (EDC), diphenylphosphorylazide (DPP A), benzotriazol-1-yl-oxy-tris- (dimethylamino)phosphonium hexafluorophosphate (BOP), 1,3- diisopropylcarbodiimide (DIC) and the like, used in combination or singularly. Preferably the carboxyl activating agent is selected from EDC, DIC and DCC. Most preferably the carboxyl activating agent is EDC. The coupling reaction of the a ine moiety to the carboxyl terminus may also comprise a base, such as 2,4,6-collidine, lutidine, pyridine, triethyl amine, Hϋnig's base ((iPr)2NEt) and the like. Preferably the base is selected from 2,4,6- collidine and lutidine. Most preferably the base is 2,4,6-collidine. The coupling reaction may also comprise an additive, such as l-hydroxy-7-azabenzotriazole (HOAt), 1 -hydroxybenzotriazole (HOBt), 2-hydroxypyridine-N-oxide, (HOPO), N- hydroxysuccinimide, pyridine N-oxide and the like, or combinations thereof. Preferably the additive is selected from HOAt, HOPO, HOBt or combinations thereof. More preferably the additive is HOAt. Also, more preferable the additive is a combination of HOPO and HOAt. The coupling reaction may also comprise a solvent. Such a solvent may be selected from N,N-dimethylformamide (DMF), N,N- dimethylacetamide (DM Ac), N-methylpiperidone (NMP), aqueous THF, and the like. Preferably the solvent is selected from a polar aprotic organic solvent, such as DMF, DMAc, NMP and the like. Most preferably, the solvent is DMF. One skilled in the art understands that in the synthesis of compounds of the invention, one may need to protect various reactive functionalities on the starting compounds and intermediates while a desired reaction is carried out on other portions of the molecule. After the desired reactions are complete, or at any desired time, normally such protecting groups will be removed by, for example, hydrolytic or hydrogenolytic means. Such protection and deprotection steps are conventional in organic chemistry. One skilled in the art is referred to Protective Groups in Organic Chemistry, McOmie, ed., Plenum Press, NY, NY (1973); and, Protective Groups in Organic Synthesis, Greene, ed., John Wiley & Sons, NY, NY (1981) for the teaching of protective groups which may be useful in the preparation of compounds of the present invention. By way of example only, useful amino-protecting groups may include, for example, Ci-Cio alkanoyl groups such as formyl, acetyl, dichloroacetyl, propionyl, hexanoyl, 3,3-diethylhexanoyl, γ-chlorobutryl, and the like; Cl-CiO alkoxycarbonyl and C5-C15 aryloxycarbonyl groups such as tert-butoxycarbonyl, benzyloxycarbonyl, allyloxycarbonyl, 4-nitrobenzyloxycarbonyl, fluorenylmethyloxycarbonyl and cinnamoyloxycarbonyl; halo-(Ci-Cιo)- alkoxycarbonyl such as 2,2,2-trichloroethoxycarbonyl; and C1 -C15 arylalkyl and alkenyl group such as benzyl, phenethyl, allyl, trityl, and the like. Other commonly used amino-protecting groups are those in the form of enamines prepared with β-keto- esters such as methyl or ethyl acetoacetate. Useful carboxy-protecting groups may include, for example, C1-C10 alkyl groups such as methyl, tert-butyl, decyl; halo-Ci-Cio alkyl such as 2,2,2- trichloroethyl, and 2-iodoethyl; C5-C15 arylalkyl such as benzyl, 4-methoxybenzyl, 4- nitrobenzyl, triphenylmethyl, diphenylmethyl; C1-C10 alkanoyloxymethyl such as acetoxymethyl, propionoxymethyl and the like; and groups such as phenacyl, 4- halophenacyl, allyl, dimethylallyl, tri-(Cι-C3 alkyl)silyl, such as trimethylsilyl, β-p- toluenesulfonylethyl, β-p-nitrophenylthio-ethyl, 2,4,6-trimethylbenzyl, β- methylthioethyl, phthalimidomethyl, 2,4-dinitro-phenylsulphenyl, 2-nitrobenzhydryl and related groups. Similarly, useful hydroxy protecting groups may include, for example, the formyl group, the chloroacetyl group, the benzyl group, the benzhydryl group, the trityl group, the 4-nitrobenzyl group, the trimethylsilyl group, the phenacyl group, the tert-butyl group, the methoxymethyl group, the tetrahydropyranyl group, and the like. With respect to the preferred embodiment of an oligopeptide combined with the anthracycline antibiotic doxorubicin, the following Reaction Schemes illustrate the synthesis of the conjugates of the instant invention. Other bases than piperidine are useful in the deprotection illustrated in Reaction Scheme IV, including dimethyl amine, diethyl, amine, pyrrohdine, quinuclidine and the like. Preferably piperidine is utilized. REACTION SCHEME I N-terminus REACTION SCHEME I (continued) deprotection (R' is not R) R — oligopeptide N-terminus REACTION SCHEME us N-terminus REACTION SCHEME REACTION SCHEME III (continued) piperidine N-terminus REACTION SCHEME IV e REACTION SCHEME IV (continued) Reaction Schemes V-VUI below illustrate other methods for the preparation of the PSA conjugates, in particular, the preparation of the compound of formula 4. Thus, as shown in Reaction Scheme V, an unblocked glutaryl peptide 5 may be prepared by methods well known in the art and coupled to the amine moiety of the anthracycline cytotoxic agent as described above. Specific preparation of the compound of formula 4 is illustrated in Reaction Scheme VI. Alternatively, as illustrated in Reaction Scheme VII, a bis-blocked peptide 6 may be prepared by methods well known in the art and selectively deprotected to provide the benzyl ester analog of the compound of formula 2. After coupling to the anthracycline cytotoxic agent as described above, deprotection of the acid moiety can be accomplished by catalytic hydrogenation, thereby avoiding prolonged exposure of compound 4 to a base. Other carboxylic acid protecting groups that may be useful include t-butyl, sillyl and the like. It is known that the anthracyclines are chemically sensitive to base. In yet another embodiment, the cleavable peptide portion of the instant conjugate may be attached in two or more fragments, as ilustrated in Reaction Scheme VIII. Such a synthetic strategy might allow more flexibility in selection and use of blocking groups. The particular selection of which peptide fragment to attach first that is shown in the scheme is illustrative only and is not meant to limiting. REACTION SCHEME V N-terminus REACTION SCHEME VI REACTION SCHEME VII REACTION SCHEME VII (continued REACTION SCHEME Vm REACTION SCHEME VIII (continued) REACTION SCHEME Vm (continued) One skilled in the art will appreciate that although specific reagents and reaction conditions are outlined in the following examples, modification can be made which are meant to be encompassed by the spirit and scope of the invention. The following preparations and examples, therefore, are provided to further illustrate the invention, and are not limiting. Unless otherwise indicated, all amino acids described in the examples have the natural (L) stereoconfiguration. EXAMPLE 1 Preparation N-( N'-(Fm-Glutaryl)-trans-4-hvdroxy-L-prolinyl-alanyl)serine Step 1 : N-Boc-trans-4-hvdroxy-L-proline A solution of trans-4-hydroxy-L-proline (3.0 kg, 22.88 M) in 1 M aqueous sodium hydroxide (25.2 L) and tert-butanol (12.0 L) was treated with a solution of di-tert-butyldicarbonate (5.09 kg) in tert-butanol (6.0 L) at 20°C over 20 minutes. Upon complete addition, the resulting solution was stirred at 20°C for 2 hours. The solution was extracted with hexane (2 x 15.0 L) and then acidified to pH 1 to 1.5 by cautious addition of a solution of potassium hydrogen sulphate (3.6 kg) in water (15.0 L). The mixture was extracted with ethyl acetate (3 x l5.0 L). The combined ethyl acetate extracts were washed with water (2 x 1.0 L) and dried by azeotropic distillation at atmospheric pressure (final KF of ethyl acetate solution <0.1%). The ethyl acetate solution was then concentrated by atmospheric distillation to a volume of 15.0 L, diluted with hexane (8.0 L), seeded and stirred at 20°C for 1 hour. Hexane (22.5 L) was added over 2 hours, the slurry was cooled to 0°C for 1 hour and the solid collected by filtration. The product was washed with cold (0°C) 2:1 hexane/ethyl acetate (15.0 L) and dried in vacuo at 45 °C to afford the title compound as a white crystalline solid. Step 2: N-Boc-trans-4-hvdroxy-L-proline Pentafluorophenyl ester Boc-trans-4-hydroxy-L-proline (3.5 kg) (prepared as described in Step 1) and pentafluorophenol (3.06 kg) were dissolved in ethyl acetate (52 L). The solution was treated with a solution of dicyclohexylcarbodiimide (3.43 kg) in ethyl acetate (8 L) and the mixture was stirred at room temperature for 2 hours. The resulting slurry was cooled to 0°C, filtered and the solids washed with ethyl acetate (15 L). The filtrate was evaporated at atmospheric pressure to a volume of 10 L and diluted with hexane (100 L). The resulting mixture was stirred at room temperature overnight and then cooled to 0°C for 1 hour. The solid was collected by filtration, washed with cold (°C) 10:1 hexane/ethyl acetate (15 L) and dried at 45 °C in vacuo to afford the title compound as a white crystalline solid. Step 3: N-(trans-4-hvdroxy-L-prolinyl-alanyl)serine hydrochloride N-alanylserine (1.5 kg, 8.515 M) and Boc-trans-4-hydroxy-L-proline (3.72 kg) (prepared as described in step 2) were heated at 50°C in dimethylformamide (15 L) for 3 hours. The solution was cooled to 20°C, treated with concentrated hydrochloric acid (7.5 L) and stirred at room temperature for 24 hours. The resulting slurry was diluted with isopropanol (30 L), stirred at room temperature for 30 minutes and then cooled to 0°C for 1 hour. The solid was collected by filtration and washed with isopropanol (20 L). The solid was dried in vacuo at 40°C to afford the title compound as a white crystalline solid. Step 4: Fluorenylmethyl Glutarate 9-Fluorenyl methanol (2.0 kg), glutaric anhydride (2.33 kg) and sodium bicarbonate (1.71 kg) were stirred together in N-methylpyrrolidinone (8.0 L) at room temperature for 72 hours. The slurry was filtered and the solids washed with isopropyl acetate (2 x 10.0 L). The filtrate was washed with 1.0 M hydrochloric acid (3 x 10.0 L). The organic layer was extracted with 1.0 M aqueous sodium hydroxide (3 x 8.0 L). The combined basic extracts were covered with isopropyl acetate (20.0 L) and acidified to pH 2 with 2.0 M hydrochloric acid (12.5 L). The phases were separated and the aqueous phase was extracted with isopropyl acetate (10.0 L). The combined organic phases were washed with water (10.0 L) and dried by azeotropic distillation at <60°C under reduced pressure (KF <0.05%). The solution was then concentrated under reduced pressure (<60°C) to a volume of 7.0 L. The solution was diluted with hexane (6.0 L), seeded and stirred at room temperature for 30 minutes. The resulting slurry was diluted by addition of hexane (42.0 L) over 40 minutes. The slurry was cooled to 0°C for 1 hour and the solid collected by filtration and washed with cold (0°C) 8:1 hexane/iPAC (20.0 L). The solid was dried in vacuo at 45°C to afford the title compound as a pale cream solid. Step 5: Fluorenylmethyl Glutarate Pentafluorophenyl Ester Fluorenylmethyl glutarate (2.5k g) (prepared as described in Step 4) and pentafluorophenol (1.63 kg) were dissolved in ethyl acetate (25 L). The solution was treated with a solution of dicyclohexylcarbodiimide (1.83 kg) in ethyl acetate (7.5 L) and the mixture was stirred at 20°C overnight. The resulting slurry was filtered and the solids were washed through with ethyl acetate (10 L). The filtrate was evaporated at atmospheric pressure to a volume of 7.5 L and diluted with hexane (75 L). The slurry was filtered at 60-65°C then allowed to cool to room temperature and stirred overnight. The slurry was cooled to 0°C for 1 hour, the solid collected by filtration and washed with 10:1 hexane/ethyl acetate (15 L). The solid was dried in vacuo at 45 °C to afford the title compound as a white crystalline solid. Step 6: N-( N'-(Fm-Glutaryl)-trans-4-hvdroxy-L-prolinyl-alanyl)serine N-(trans-4-hydroxy-L-prolinyl-alanyl)serine hydrochloride_(2.3 kg) (prepared as described in Step 3) was suspended in dimethylformamide (22 L) and the slurry was treated with N-ethylmorpholine (911 ml) followed by a solution of fluorenylmethyl glutarate pentafluorophenyl ester (3.5 kg) (prepared as described in Step 5) in dimethylformamide (14 L). The mixture was heated at 50°C for 3 hours and the resulting solution evaporated to residue under reduced pressure. The residue was partitioned between water (80 L) and tert-butyl methyl ether (34 L). The phases were separated and the aqueous layer was extracted with tert-butyl methyl ether (34 L). The aqueous solution was seeded and stirred at room temperature overnight. The solid was collected by filtration (slow) and washed with water (25 L). The damp filter cake was dissolved in isopropanol (90 L) with warming and the solution concentrated to half volume by distillation at atmospheric pressure. Additional portions of isopropanol (3 x 45 L) were added and the batch was concentrated to ca half volume by atmospheric distillation after addition of each portion (Final KF of liquors <0.5%). The slurry was diluted with isopropanol (23 L), stirred at 20°C overnight, cooled to 0°C for 1 hour and the solid collected by filtration. The cake was washed with isopropanol (20 L) and the solid dried in vacuo at 45 °C to afford the crude product as a white solid. Step 7: Recrystallisation of N-( N'-(Fm-Glutaryl)-trans-4-hydroxy-L-prolinyl- alanvDserine N-(N'-(Fm-Glutaryl)-trans-4-hydroxy-L-prolinyl-alanyl)serine (3.4 kg) (prepared as described in Step 6) was dissolved in methanol (51 L) at reflux. The solution was filtered and concentrated by atmospheric distillation to a volume of 17 L (5 ml/g). The solution was diluted with ethyl acetate (102 L) allowed to cool to 20°C and stirred overnight. The resulting slurry was cooled to 0°C for 1 hour and the solid was collected by filtration. The cake was washed with cold (0°C) 10:1 ethyl acetate/methanol (20 L) and dried in vacuo at 45°C to afford the product as a white solid. EXAMPLE 2 Preparation N-(cyclohexylglycyl-glutaminyl-serinyl)leucine benzyl ester hydrochloride (SEQ.ID.NO.: 65) Step 1: N-(serinyl)leucine benzyl ester hydrochloride Leucine benzyl ester p-tosylate (1000 g) and HOBt (412 g) were slurried in isopropyl acetate (12 L). The mixture was cooled to 0°C in an ice-bath and a slurry of sodium bicarbonate (469.7 g) in water (1 L), N-BOC-L-serine (573.6 g) in water (2 L) and EDC.HC1 (560.2 g) in water (2 L) were added. The mixture was allowed to warm to 20°C over 30 minutes and aged at 20°C for 2 hours (<1 A% Leu- OBn remaining). If the reaction was not complete after 2 hours, further NaHCO3 and EDC.HC1 were added. The phases were separated and the organic layer was washed sequentially with saturated sodium bicarbonate (2 x 3.75 L), 0.5 M sodium hydrogen sulphate (2 x 3.75 L) and water (2 x 2.5 L). The wet, isopropyl acetate solution was concentrated under reduced pressure to 3 L and the water content checked. (KF = 0.12%. It is important that this solution is dry prior to the addition of hydrogen chloride in isopropyl acetate). The solution was transferred to a 20 L round bottom flask under a nitrogen atmosphere and cooled to 0°C. To the solution was added 3.6 M HCI in isopropyl acetate (7 L, 10 mol equiv. HCI). The product began to crystallise after 5 minutes. The reaction was aged at 0°C for 1 hr, and then allowed to warm to room temperature. The slurry was cooled to 0-5°C, diluted with heptane (2.5 L) and aged at 0°C for 30 minutes. The product was collected by filtration, washed with cold isopropyl acetate/heptane (4:1) (2.5 L) and dried in vacuo at 35°C, with a nitrogen sweep. Step 2: N-(N'-(Boc)-glutaminyl-serinyl)leucine benzyl ester N-(serinyl)leucine benzyl ester hydrochloride (350 g) (prepared as described in Step 1), HOBt (157.7 g) and N-Boc-L-glutamine (262.5 g) were slurried in DMF (2.5 L) and the mixture was cooled to 0°C. N-Ethylmorpholine (245.5 g) and EDC. HCI (214 g) were added and the mixture was aged at 0°C for 2.5 hours. Water (14.7 L) was added over 20 minutes and the white slurry aged at 0°C for 1 hour. The product collected by filtration and washed with water (3.2 L). The cake was dried in the fume-hood overnight. The isolated N-BOC-Gln-Ser-Leu-OBn, which contained DMF and HOBt, was combined with a second batch of identical size, and swished in water (12 L) at 20°C for 1 hour. The product was collected by filtration, washed with water (2.5 L) and air-dried in a fume-hood over the weekend. The batch was dried in vacuo, at 42°C, with a nitrogen bleed. Step 3: N-(glutaminyl-serinyl)leucine benzyl ester hydrochloride N-(N'-(Boc)-glutaminyl-serinyl)leucine benzyl ester (715 g, 1.33 M) (prepared as described in Step 2) was suspended in iPAC (3.5 L) at room temperature. To the slurry was added a 3.8 M solution of HCI in iPAC (3.5 L, 13.3 M) whereupon all the solids dissolved. After a short time, the product crystallised. The mixture was stirred at room temperature for 3.75 hours when HPLC showed complete reaction. The slurry was diluted with iPAC (4.0 L), stirred for 1 hour at room temperature and the solid collected by filtration under nitrogen. The product is very hygroscopic in the presence of excess HCI and must be collected under dry nitrogen. The cake was washed with iPAC (4.0 L), the solid dried on the filter under nitrogen for 2 hours and then dried in vacuo at 45°C. Step 4: N-(N'-(Boc)-cyclohexylglycylglutaminyl-serinyl)leucine benzyl ester (SEQ.ID.NO.: 66) N-(glutaminyl-serinyl)leucine benzyl ester hydrochloride (2.6 kg) (prepared as described in Step 3), N-Boc-L-cyclohexylglycine (1.414 kg) and HOBt hydrate (168 g) were dissolved in DMF (13.0 L). N-ethylmorpholine (1.266 kg, 11.0 M) and EDC hydrochloride (1.265 kg) were added and the mixture stirred at 20°C for 3 hours. The solution was diluted with ethyl acetate (13.0 L) and water (26.0 L) added. The product precipitated and the slurry was stirred at room temperature for 1 hour. The solid was collected by filtration, washed with 1 : 1 ethyl acetate/water (60 L) dried on the filter under nitrogen for 24 hours and dried in vacuo at 45°. The title compound was obtained as a white solid. Step 5: N-(cyclohexylglycyl-glutaminyl-serinyl)leucine benzyl ester hydrochloride (SEQ.ID.NO.: 65) N-(N'-(Boc)-cyclohexylglycylglutaminyl-serinyl)leucine_benzyl ester (1850 g) (prepared as described in Step 4) was slurried in isopropyl acetate (3.2 L). The slurry was cooled to 0°C in an ice bath and 3.8 M HCl/isopropyl acetate (3.7 L, 11.4 mol equiv.) was added over 5 minutes, maintaining the temperature between 8 and 10°C. The starting material had dissolved after 15-20 minutes. The solution was seeded and the reaction aged at 8-10°C for 2 hrs, (< 1 A% N-Boc-tetrapeptide-OBn remaining). The batch was filtered, under a nitrogen blanket, washed with cold (10°C) isopropyl acetate (4 x 3 L) then dried on the filter under nitrogen. The solid was dried in vacuo, at 40°C. The crude N-(cyclohexylglycyl-glutaminyl-serinyl)leucine benzyl ester hydrochloride (2.2 Kg) was slurried in methanol (22.3 L) at room temperature. The batch was stirred for 1 hour and then ethyl acetate (44.6 L) was added over 30 minutes. The batch was cooled to 0-5°C, aged for one hour, then filtered and washed with cold (0-5°C) methanol/ethyl acetate (6 L, 1 :2). The solid was dried on the filter, under nitrogen, for 45 minutes and then dried in vacuo, at 40°C, with a nitrogen sweep. The N-(cyclohexylglycyl-glutaminyl-serinyl)leucine benzyl ester hydrochloride (1.478 Kg) was slurried in methanol (14.8 L) at room and the batch stirred for lhr. Ethyl acetate (29.6 L) was added over 30 minutes, the batch was cooled to 0-5°C and aged for an hour. The solid collected by filtration, washed with cold (0-5°C) methanol/ethyl acetate (4.5 L, 1:2), dried on the filter for 45 minutes, under nitrogen, and then dried under vacuum, at 40°C. This material was then utilized in subsequent reactions. EXAMPLE 3 Preparation N-(N'-(Fm-Glutaryl)-trans-4-hydroxy-L-prolinyl-alanyl-serine- cvclohexylglvcyl-glutaminyl-serinvDleucine (heptapeptide 2) (SEQ.ID.NO.: 52) Step 1: N-(N'-(Fm-Glutaryl)-trans-4-hydroxy-L-prolinyl-alanyl-serine- cyclohexylglycyl-glutaminyl-serinyl)leucine benzyl_ester (SEQ.ID.NO.: 67) N-(cyclohexylglycyl-glutaminyl-serinyl)leucine benzyl ester hydrochloride (500 g) (prepared as described in Example 2), N-( N'-(Fm-Glutaryl)- trans-4-hydroxy-L-prolinyl-alanyl)serine (490 g) (prepared as described in Example 1) and HOAt (160 g) were slurried in DMF (8.2 L) and cooled to 2°C in an ice bath. N- ethylmorpholine (135 ml) was added followed by EDC.HC1 (210 g). The mixture was stirred at 0 - 2°C for 2 hours and sampled. HPLC showed 0.2A% tetrapeptide remaining. The reaction mixture was diluted with ethyl acetate (4 L) and transferred to a 30-gallon glass vessel through a 5μ in-line filter. The flask and lines were rinsed with ethyl acetate/DMF (1:1, 500 ml) and ethyl acetate (4 L). Water (16.4 L) was added over 25 minutes (temperature 11°C to 23 °C) and the mixture stirred slowly, at 20°C, for 30 minutes. The product was collected by filtration, washed with water (3 L), ethyl acetate (1 L) and water (2x3 L), then dried on the filter under nitrogen, and dried in vacuo at 45 °C. Step 2: N-(N'-(Fm-Glutaryl)-trans-4-hydroxy-L-prolinyl-alanyl-serine- cvclohexylglvcyl-glutaminyl-serinvPleucine (SEQ.ID.NO.: 52) N-( N'-(Fm-Glutaryl)-trans-4-hydroxy-L-prolinyl-alanyl-serine- cyclohexylglycyl-glutaminyl-serinyl)leucine benzyl ester (1.1 Kg) (prepared as described in Step 1) was dissolved in dimethylacetamide (7.8 L) containing methanesulphonic acid (93.5 ml). 5% Pd/C (110 g, 10 wt%), slurried in DMA (1.0 L), was added and the mixture hydrogenated at atmospheric pressure for 1 hour 40 minutes. The reaction mixture was sampled: HPLC showed no starting material remaining. The reaction mixture was filtered through a pre-wetted (DMA) pad of hyflo (500 g) to remove the catalyst. The hyflo pad washed with DMA (2.2 L) and then ethyl acetate (5.5 L). The filtrate was diluted with ethyl acetate (5.5 L) and stirred for 15 minutes. Water (44 L) was added over 40 minutes and the batch age for 1 hour. The solid collected by filtration, washed with water (1x10 L, 3x20 L), dried on the filter under a nitrogen blanket and dried in vacuo at 45°C. Step 3: N-(N'-(Fm-Glutaryl)-trans-4-hydroxy-L-prolinyl-alanyl-serine- cyclohexylglvcyl-glutaminyl-serinyDleucine Swish Purification Crude N-(N'-(Fm-Glutaryl)-trans-4-hydroxy-L-prolinyl-alanyl-serine- cyclohexylglycyl-glutaminyl-serinyl)leucine (2.58 kg) (prepared as described in Step 2) was sieved. The solid (2.56 Kg) was swished in ethyl acetate for 3 hours. The solid was collected by filtration, washed with ethyl acetate (26 L), dried on the filter under nitrogen and dried in vacuo at 40°C. EXAMPLE 4 Preparation of [N-Glutaryl(OFm)-(4-trans-L-Hyp)]-Ala-Ser-Chg-Gln-Ser-Leu-Dox Compound 3 (SEQ.ID.NO.: 54) To a 3 necked, 12 L round bottom flask equipped with mechanical stirrer, thermocouple, and nitrogen inlet was charged DMF (5.1 L) and HOAt (43.4 g, 319 mmoles, 1.2 equivalents). The yellow solution was inerted with nitrogen and warmed to 40°C. Heptapeptide 2 (357.34 g, 266 mmoles) was added portion-wise to the warm solution; after stirring for 30 minutes at 40°C, a light yellow, opaque, homogeneous mixture resulted. The mixture was cooled to room temperature, Doxorubicin 1 was added (158.9 g, 274 mmoles, 1.03 equivalents), and the red slurry was further cooled to -5°C. One equivalent of 2,4,6-collidine (35 ml) was added followed by 0.8 equivalents of EDC (40.8 g, 213 mmoles) followed by the remaining two equivalents of 2,4,6-collidine (70 ml). The red slurry was aged at -5°C to -3°C. After aging for a total of 3 hours, conversion had reached 90 A % Compound 3, 2.5 A% peptide 1 and the reaction was warmed to 0°C. Aging for another 2 hours reduced peptide level to 0.73 A% and the reaction was quenched as follows. In a 50 L, 4 necked round bottom flask equipped with a mechanical stirrer, thermocouple, and nitrogen inlet, was charged K2HPO4 (67.9 g), KH2PO4 (283 g), and water (13 L) to give a 0.19 M pH 6.3 buffer solution. The buffer solution was inerted with nitrogen, cooled to 15-18°C, and the cold reaction mixture (-1°C) was added to the buffer via an addition funnel over 60 minutes maintaining the slurry temperature at 15-18°C. After complete addition, the red slurry was aged 15 minutes at 18°C, and filtered. The filter cake was displacement washed with water (1 X 6 L), followed by slurry washing with water (6 X 6 L), and dried in vacuo at room temperature with a nitrogen sweep. After drying for 48 hours, 402 g (96 % yield based on weight) of red solid was obtained. The solid was assayed to have an HPLC purity of 93.54 A%. EXAMPLE 4 A Alternate Preparation of [N-Glutaryl(OFm)-(4-trans-L-Hyp)]-Ala-Ser-Chg-Gln-Ser- Leu-Dox Compound 3 (SEQ.ID.NO.: 54) DMF (400 mL) was charged to a IL RB flask and degassed by N2 sparge while cooling to -6°C. The peptide (19.97 g, 19.06 mmol) and HOAt (3.12 g, 22.9 mmol) were then charged as solids to the cold DMF. A slurry of doxorubicin- HC1 (11.05 g, 19.06 mmol) in degassed DMF (50 mL) was charged by vacuum, followed by two rinses (2 x 25 mL) of the slurry flask. 2,4,6-collidine was charged followed by a portion of EDC (2.92 g, 0.8 eq.). After 1.3 h, a second charge of EDC (2.19 g, 0.6 eq) was made. After a total age of 7.4 h the clear red solution was queched by dropwise addition to a pH 6.2 phosphate buffer (1350 mL) at 16-17 °C over 1.3 h. The resulting slurry was filtered and the filter cake was then washed with water (2000 mL). The filter cake was dried under a N2 stream giving 28.7g red powder (95.6%, uncorrected for purity). EXAMPLE 4B Alternate Preparation of [N-Glutaryl(OFm)-(4-trans-L-Hyp)]-Ala-Ser-Chg-Gln-Ser- Leu-Pox Compound 3 (SEQ.ID.NO.: 54) A 1 L, 4 neck round bottom flask was set up and 20.0 g of DoxorubicinΗCl (20.0 g, 34.5 mmol) was added in a glovebox. The flask was then equipped with a truebore stirrer, N 2 inlet/vacuum inlet, and a thermocouple. DMF (472 mL) and water (4.7 mL) were premixed (20 °C) and then charged to form a red slurry. The 2,4,6-collidine (12.5 g, 103 mmol) and 2-HOPO (4.6 g, 41.4 mmol) were then, respectively, charged at ambient temperature and allowed to mix for 10 minutes. The slurry was then cooled to -5 °C and the heptapeptide 2 (40.6 g, 35.3 mmol) was charged. It was stirred for 30 minutes at that temperature. The first, 0.8 equivalent of the EDC'HCl (5.3 g) was charged, and the solution allowed to mix for -90 minutes. The reaction was monitored by HPLC . After 90 minutes had elapsed, the remaining 0.6 equivalents of EDC # HC1 (3.96 g) was added, the cooling bath was removed and the reaction was allowed to mix overnight at room temperature (21-22 °C). The prepared buffer solution (1.20 L of the following buffer: 10.9 g K 2 HPO 4 , 43.54 g KH 2 PO 4 ; pH 6.05) was added to a 3-L round bottom flask equipped with a truebore stirrer, N 2 inlet and thermocouple. The reaction solution was transferred to a 1-L addition funnel while, concurrently, the temperature of the buffer was reduced to 15-18 °C. The reaction solution was added to the buffer over 1-1.5 hours, while maintaining the temperature between 15-18 °C. A precipitate resulted. The precipitated material was filtered and washed with water (2.30 L). After drying overnight at 22 °C under N 2 and house vacuum, the solid (53.0 g) was assayed and was 91.5 A%, 88.1 wt.%. The yield after correction for purity was 86%. EXAMPLE 4C Alternate Preparation of [N-Glutaryl(OFm)-(4-trans-L-Hyp)]-Ala-Ser-Chg-Gln-Ser- Leu-Pox Compound 3 (SEQ.ID.NO.: 54) A 3L, 4 neck round bottom flask was set up and, concurrently, 20.0 grams of Doxorubicin Φ HC1 (34.5 mmol) was added in a glovebox to a sealed beaker or Erlenmeyer flask. The 3L flask was then equipped with a truebore stirrer, N 2 inlet/vacuum inlet, and a thermocouple. DMF (472 mL) and water (4.7 mL) were premixed (20 °C) and then partially charged (approximately V 2 the volume) to the 3L vessel. 2-HOPO (4.6 g, 41.4 mmol) and HOAt (0.47 g, 3.45 mmol) were then, respectively, charged and allowed to mix for 10 minutes or until dissolved. One- quarter of the wet DMF was then added to the DoxΗCl to form a slurry, and this was then added to the 3L vessel. Finally, the 2,4,6-collidine (12.5 g, 103 mmol) was added to the 3L vessel which was then cooled to -5 °C and the heptapeptide 2 (40.6 g , 35.3 mmol) was charged. After stirring for 30 minutes the first, 0.8 equivalents of the EDC»HC1 was charged (5.3 g), followed by the final quarter of solvent. The resulting slurry was stirred for about 90 minutes and then the remaining 0.6 equivalents of EDCΗCl (3.96 g) was added. The cooling bath was removed and the reaction was allowed to mix overnight at room temperature (21-22 °C). Ethyl acetate (354 mL) was then added to the reaction solution at 20 °C. The temperature of the reaction solution was reduced to 15-18 °C. The pH6 buffer solution (1.20 L of water, 10.9 g K 2 HPO 4 , 43.54 g KH 2 PO 4 ) was added slowly to the reaction solution over 1 hour, while maintaining the temperature between 15 and l8 °C. The precipitated material was filtered through a 600 mL medium sintered glass funnel, washed with water. (2.3 L) and the cake was dried overnight on the filter at ambient temperature under N 2 . The solid (54.5g) was assayed at 89.7 A%. The yield, after correction for purity, was 90.0%. EXAMPLE 5 Preparation of [N-Glutaryl-(4-trans-L-Hyp)]-Ala-Ser-Chg-Gln-Ser-Leu-Dox Piperidinium salt Compound 4 (SEQ.ID.NO.: 51) To a 3 necked, 12 L round bottom flask equipped with mechanical stirrer, thermocouple, and nitrogen inlet was charged Compound 3 (399 g, 253.5 mmoles, TG 1.4 %) and DMF (3.55 L). The red solution was inerted with nitrogen, cooled to 1°C, and a solution of piperidine (40 mL, 404 mmoles, 1.6 eq.) in DMF (400 mL) was added drop-wise over 70 minutes maintaining the batch temperature at 0-2°C. The reaction was monitored by HPLC. After aging 1.5 hours at 0-2°C, conversion had reached 92.4 %. Additional piperidine was charged after 2 hours reaction time (2.5 mL piperidine in 25 mL DMF); after aging another 2 hours, conversion had reached 98.1 % and the reaction was quenched as follows. In a 22 L, 3 necked round bottom flask equipped with mechanical stirrer, thermocouple, and nitrogen inlet was charged isopropyl acetate (12.1 L), inerted with nitrogen, and cooled to 0-5°C. To the cold i-PAc was added the cold (2°C) reaction mixture via nitrogen pressure cannulation over 40 minutes. The resulting pink slurry was aged at 0-5°C for thirty minutes then filtered under nitrogen. The cake was displacement washed with i-PAc (2 x 4 L) then slurry washed with i-PAc (3 x 4 L). All washes were done under a nitrogen blanket. The solid was dried in vacuo at room temperature with a nitrogen sweep for 24 hours to give 369.05 g of an orange solid. The solid was assayed by HPLC, 87 A %. EXAMPLE 6 Preparative HPLC purification of [N-G_utaryl-(4-trans-L-Hyp)]-Ala-Ser-Chg-Gln-Ser- Leu-Dox Piperidinium salt Compound 4 (SEQ.ID.NO.: 51) The crude piperidine salt was purified by preparative HPLC on C-18 silica gel, eluting with a 0.1% aqueous ammonium acetate/acetonitrile gradient (100%NH4θ Ac to 55 % NH4O Ac over 80 min) . The rich cuts that were >97% pure were pooled and rechromatographed on C-18 silica gel using a 2% aqueous HOAc/acetonitrile gradient (100% aqueous HO Ac to 40% aqueous HO Ac over 60 min). The fractions that were >98% pure were pooled and lyophilized, providing the pure free acid 4. EXAMPLE 6A Alternate Preparation of [N-Glutaryl-(4-trans-L-Hyp)]-Ala-Ser-Chg-Gln-Ser-Leu-Dox Compound 4 (SEQ.ID.NO.: 51) To a solution of the heptapeptide 2 (1.09 g, 0.99 mmol) in DMF at 0 °C was added solid quinuclidine (0.34 g, 3.00 mmol). The solution was stirred at 0 °C for 0.5 h, and at 20 °C for 2.0 h, respectively. An aliquot was taken and assayed by LC to show no heptapeptide 2 remained, indicating that conversion to the diacid was complete. To this solution of [N-Glutaryl-(4-trans-L-Hyp)]-Ala-Ser-Chg-Gln- Ser-Leu was added 2,4,6-collidine (0.50 mL, 3.78 mmol), HOAt (0.163 g, 3.00 mmol) and Doxorubicin » HCl (0.58 g, 1.00 mmol), resulting in a slurry. The slurry was cooled to 0 °C and solid EDC » HC1 (0.20 g, 1.04 mmol) was introduced in one portion. The reaction was aged for 2.5 h at 0 °C to lead to a homogenous solution that was assayed by LC to show the formation of Compound 4 in 78% yield. EXAMPLE 6B Alternate Preparation of [N-Glutaryl-(4-trans-L-Hyp)]-Ala-Ser-Chg-Gln-Ser-Leu-Dox Compound 4 (SEQ.ID.NO.: 51) To a solution of the heptapeptide 2 (1.09 g, 0.99 mmol) in DMF at 0°C was added a solid quinuclidine (0.34 g, 3.00 mmol). The solution was stirred at 0°C for 0.5 h, and at 20°C for 2.0 h, respectively. An aliquot was taken and assayed by LC to show no heptapeptide 2 remained, indicating that conversion to the diacid was complete. To a portion of the solution of [N-Glutaryl-(4-trans-L-Hyp)]-Ala-Ser- Chg-Gln-Ser-Leu (ca. 0.497 mmol) was added 2,4,6-collidine (0.123 mL, 0.934 mmol), 2-HOPO (52 mg, 0.467 mmol) and Doxorubicin*HCl (092 mg, 0.159 mmol) at 20°C, resulting in a slurry. The slurry was cooled to 0°C and solid EDCΗCl (100 mg, 0.524 mmol) was introduced in one portion. The reaction was aged for 2.0 h at 0°C and then assayed by LC to show the formation of Compound 4 in 93.9% yield and no remaining doxorubicin. Alternative Preparation of N-(N'-(Fm-Glutaryl)-trans-4-hydroxy-L-prolinyl-alanyl- serine-cvclohexylglycyl-glutaminyl-serinyl)leucine (SEQ.ID.NO.: 52) Fm-Glutaryl-Hyp-Ala-Ser-Chg-Gln-Ser-Leu-OBn (prepared as described in Step 1 or Alternate Step 1) (200 g) was dissolved in dimethylacetamide (1.9 L) at 45-50°C. 5% Pd/C (20 g, 10 wt%) slurried in DMA (100 ml) was added and the slurry was cooled to -5 to -10°C. The mixture was hydrogenated at atmospheric pressure maintaining the temperature between -10 and -5°C for 5.5 hours. The mixture was filtered while cold through a pre- wetted pad of Hyflo. The filtrate was diluted with ethyl acetate (2.5 L) and water (8.0 L) was added. The batch was aged for a further 1 hour and the solid was collected by filtration. The cake was washed with water and sucked down on the filter and then dried in vacuo at 45 °C with a nitrogen sweep.

Claims: WHAT IS CLAIMED IS: 1. A process for the preparation of a compound of formula I: N-terminus or a pharmaceutically acceptable salt thereof wherein oligopeptide is an oligopeptide which is selectively recognized by the free prostate specific antigen (PSA) and is capable of being proteolytically cleaved by the enzymatic activity of the free prostate specific antigen, Ra is -CH3, -CH2OH, -CH2OCO(CH2)3CH3, or -CH2OCOCH(OC2H5)2; Rb is -OCH3, -OH or -H; Rd is -OH, -OTHP or -H; and Re is -OH or -H, provided that Re is not -OH when Rd is -OH or -OTHP; R is selected from: a) acetyl; e) hydrogen; Rl and R2 are independently selected from: a) hydrogen, b) unsubstituted or substituted aryl, unsubstituted or substituted heterocycle, C3-C10 cycloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, halogen, C1-C6 perfluoroalkyl, R3θ-, R3C(O)NR3-, (R3)2NC(O)-, R32N-C(NR3)-, R4S(O) m NH, CN, NO2, R3C(O)-, N3, -N(R3) 2 , or R4OC(O)NR3-, c) unsubstituted C1-C alkyl, d) substituted C1-C6 alkyl wherein the substituent on the substituted C1-C6 alkyl is selected from unsubstituted or substituted aryl, unsubstituted or substituted heterocyclic, C3-C10 cycloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, R3θ-, R4S(O) m NH, R3C(O)NR3-, (R3) 2 NC(O)-, R3 2 N-C(NR3)-, CN, R3C(O)-, N3, -N(R3) 2 , and R4OC(O)-NR3-; or Rl and R2 are combined to form -(CH2)s- wherein one of the carbon atoms is optionally replaced by a moiety selected from: O, S(O)m > -NC(O)-, NH and -N(C0R4)-; R3 is selected from: hydrogen, aryl, substituted aryl, heterocycle, substituted heterocycle, C1-C6 alkyl and C3-C10 cycloalkyl; R4 is selected from: aryl, substituted aryl, heterocycle, substituted heterocycle, Ci-Cβ alkyl and C3-C 10 cycloalkyl; m is 0, 1 or 2; n is 1, 2, 3 or 4; p is zero or an integer between 1 and 100; q is 0 or 1, provided that if p is zero, q is 1; r is an integer between 1 and 10; and s is 3, 4 or 5; that comprises the step of preparing the compound of the formula la: -term nus or a salt thereof; wherein oligopeptide, R, Ra, Rb 5 Rd and R e are described as above R' is selected from: a) R as described above, b) a protected precursor to R, and c) an N-terminus protecting group; by mixing an oligopeptide of the formula A: N-terminus wherein oligopeptide and R' are described as above; or a salt thereof; with an anthracycline antibiotic of the formula B: B wherein Ra, Rb ; Rd and Re are as described hereinabove, or a salt thereof; in the presence of a carboxyl activating agent and, optionally, in the presence of a base. 2. The process according to Claim 1 wherein R' is a protected precursor to R or an N-terminus protecting group and wherein the process further comprises the step of removing the protecting group to produce the compound of the formula I. 3. The process according to Claim 1 wherein the oligopeptide of formula A is mixed with a salt of the anthracycline antibiotic of the formula B in the presence of a carboxyl activating agent and a base. 4. The process according to Claim 1 wherein the carboxyl activating agent comprises dicyclohexylcarbodiimide (DCC), N-ethyl-N-(3- dimethylaminopropyl)-carbodiimide (EDC), or 1,3-diisopropylcarbodiimide (DIC). 5. The process according to Claim 4 wherein the carboxy activating agent is EDC. 6. The process according to Claim 3 wherein the base comprises 2,4,6-collidine, lutidine, pyridine, triethyl amine or (iPr)2NEt. 7. The process according to Claim 6 wherein the base is 2,4,6- collidine. 8. The process according to Claim 1 wherein the mixing of the compounds of formula A and formula B is additionally in the presence of an additive. 9. The process according to Claim 8 wherein the additive is selected from HOAt, HOBt, HOPO or a combination thereof. 10. The process according to Claim 9 wherein the additive is a combination of HOPO and HOAt. 11. The process according to Claim 8 wherein the oligopeptide of the formula A is mixed with the anthracycline antibiotic of the formula B in the presence of an additive and a base, and a carboxyl activating agent is thereafter added to the mixture. 12. The process according to Claim 11 wherein the oligopeptide of the formula A is mixed with the anthracycline antibiotic of the formula B in the presence of an additive and a base, and a carboxyl activating agent is thereafter added to the mixture in two or more portions. 13. The process according to Claim 1 wherein the anthracycline antibiotic is doxorubicin (Ra is -CH2OH, Rb is -OCH3, Re is H and Rd is -OH). 14. The process according to Claim 1 wherein R is selected from: a) acetyl; and cording to Claim 1 wherein R is and R' is 16. The process according to Claim 1 wherein R is and R' is and wherein the process further comprises the step of removing the protecting group contacting the compound of formula la with a base selected from piperidine, dimethyl amine, diethyl amine, pyrrohdine and quinuclidine. 17. The process according to Claim 16 wherein the compound of formula la is contacted with piperidine. 18. A process for the preparation of the compound of formula 4: (SEQ.ID.NO.: 51) or a pharmaceutically acceptable salt thereof; which comprises the step of mixing an oligopeptide of the formula 2a: 2a wherein R" is -OH or a protected precursor to -OH; or a salt thereof; with an anthracycline antibiotic of the formula 1 : or a salt thereof, in the presence of a carboxyl activating agent and, optionally in the presence of a base, to form a compound of the formula 3a (SEQ.ID.NO.: 53) or a salt thereof. 19. The process according to Claim 18 which further comprises the step of converting R" to an -OH moiety. 20. The process according to Claim 18 wherein the carboxyl activating agent comprises dicyclohexylcarbodiimide (DCC), N-ethyl-N-(3- dimethylaminopropyl)- carbodiimide (EDC), or 1,3-diisopropylcarbodiimide (DIC). 21. The process according to Claim 20 wherein the carboxy activating agent is EDC. 22. The process according to Claim 18 wherein the oligopeptide of formula 2a is mixed with a salt of the anthracycline antibiotic of the formula 1 in the presence of a carboxyl activating agent and a base. 23. The process according to Claim 22 wherein the base comprises 2,4,6-collidine, lutidine, pyridine, triethyl amine or (iPr)2NEt. 24. The process according to Claim 23 wherein the base is 2,4,6- collidine. 25. The process according to Claim 18 wherein the mixing of the compounds of formula 2a and formula 1 is additionally in the presence of an additive. 26. The process according to Claim 25 wherein the additive is selected from HOAt, HOBt, HOPO or a combination thereof 27. The process according to Claim 26 wherein the additive is a combination of HOPO and HOAt. 28. The process according to Claim 25 wherein the oligopeptide of the formula 2a is mixed with the anthracycline antibiotic of the formula 1 in the presence of an additive and a base, and a carboxyl activating agent is thereafter added to the mixture. 29. The process according to Claim 28 wherein the oligopeptide of the formula 2a is mixed with the anthracycline antibiotic of the formula 1 in the presence of an additive and a base, and a carboxyl activating agent is thereafter added to the mixture in two or more portions. 30. A process for the preparation of the compound of formula 4: (SEQ.ID.NO.: 51) or a pharmaceutically acceptable salt thereof; which comprises the step of mixing an oligopeptide of the formula 2: (SEQ.ID.NO.: 52) or a salt thereof; with an anthracycline antibiotic of the formula 1 : or a salt thereof; in the presence of a carboxyl activating agent and a base to form a compound of the formula 3: (SEQ.ID.NO.: 54) or a salt thereof. 31. The process according to Claim 30 which comprises adding the oligopeptide of the formula 2 to a reaction mixture that comprises a solvent at a temperature from about -6°C to about -3°C to form a first slurry and the anthracycline antibiotic of the formula 1 is added to the first slurry to form a second slurry. 32. The process according to Claim 31 wherein the solvent is DMF. 33. The process according to Claim 30 which further comprises the step of removing the fluorenylmethoxy protecting group of the compound of formula 3 to produce the compound of the formula 4. 34. The process according to Claim 33 which comprises the removing the fluorenylmethoxy protecting group of the compound of formula 3 by contacting the compound of formula 3 with a base selected from piperidine, dimethyl amine, diethyl amine, pyrrohdine and quinuclidine. 35. The process according to Claim 34 wherein the compound of formula 3 is contacted with piperidine. 36. The process according to Claim 30 wherein the carboxyl activating agent comprises dicyclohexylcarbodiimide (DCC), N-ethyl-N-(3- dimethylaminopropyl)- carbodiimide (EDC), or 1,3-diisopropylcarbodiimide (DIC). 37. The process according to Claim 34 wherein the carboxy activating agent is EDC. 38. The process according to Claim 30 wherein the base comprises 2,4,6-collidine, lutidine, pyridine, triethyl amine or (iPr^NEt. 39. The process according to Claim 37 wherein the base is 2,4,6- collidine. 40. The process according to Claim 30 wherein the mixing of the compounds of formula A and formula B is additionally in the presence of an additive. 41. The process according to Claim 40 wherein the additive is selected from HOAt, HOBt, HOPO or a combination thereof 42. The process according to Claim 41 wherein the additive is a combination of HOPO and HOAt. 43. The process according to Claim 30 wherein the oligopeptide of the formula 2 is mixed with the anthracycline antibiotic of the formula 1 in the presence of an additive and a base, and a carboxyl activating agent is thereafter added to the mixture. 44. The process according to Claim 43 wherein the oligopeptide of the formula 2 is mixed with the anthracycline antibiotic of the formula 1 in the presence of an additive and a base, and a carboxyl activating agent is thereafter added to the mixture in two or more portions.

Inventors: LIEBERMAN DAVID R, LYNCH JOSEPH E, ROBBINS MICHAEL A, SHI YAO-JUN, LIEBERMAN, DAVID, R., LYNCH, JOSEPH, E., ROBBINS, MICHAEL, A., SHI, YAO-JUN
Applicants: LIEBERMAN DAVID R, LYNCH JOSEPH E, MERCK & CO INC, ROBBINS MICHAEL A, SHI YAO JUN, LIEBERMAN, DAVID, R., LYNCH, JOSEPH, E., MERCK & CO., INC., ROBBINS, MICHAEL, A., SHI, YAO-JUN
Application year: 2000
Main classification: A61K47
IPC codes: A61K38, A61K47, A61P35, C07K1