Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D498/00—Heterocyclic compounds containing in the condensed system at least one hetero ring having nitrogen and oxygen atoms as the only ring hetero atoms
  • C07D498/12—Heterocyclic compounds containing in the condensed system at least one hetero ring having nitrogen and oxygen atoms as the only ring hetero atoms in which the condensed system contains three hetero rings
  • C07D498/18—Bridged systems
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K47/00—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
  • A61K47/50—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates
  • A61K47/51—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent
  • A61K47/68—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment
  • A61K47/6801—Drug-antibody or immunoglobulin conjugates defined by the pharmacologically or therapeutically active agent
  • A61K47/6803—Drugs conjugated to an antibody or immunoglobulin, e.g. cisplatin-antibody conjugates
  • A61K47/68033—Drugs conjugated to an antibody or immunoglobulin, e.g. cisplatin-antibody conjugates the drug being a maytansine
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P31/00—Antiinfectives, i.e. antibiotics, antiseptics, chemotherapeutics
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P31/00—Antiinfectives, i.e. antibiotics, antiseptics, chemotherapeutics
  • A61P31/12—Antivirals
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P35/00—Antineoplastic agents
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P37/00—Drugs for immunological or allergic disorders
  • A61P37/02—Immunomodulators
  • A61P37/06—Immunosuppressants, e.g. drugs for graft rejection
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P43/00—Drugs for specific purposes, not provided for in groups A61P1/00-A61P41/00

Definitions

• the present invention relates to a process for preparing and purifying cytotoxic agents. More specifically, the invention relates a process for preparing and purifying cytotoxic agents comprising thiol-containing maytansinoids. These cytotoxic agents can be used as therapeutic agents by linking them to a cell binding agent, through the thiol group, and then delivering them to a specific cell population in a targeted fashion.
• Cytotoxic drugs such as methotrexate, daunorubicin, doxorubicin, vincristine, vinblastine, melphalan, mitomycin C, and chlorambucil have been conjugated to a variety of murine monoclonal antibodies.
• the drug molecules were linked to the antibody molecules through an intermediary carrier molecule such as serum albumin (Garnett et al., 46 Cancer Res.
• One of the cleavable linkers that has been employed for the preparation of antibody-drug conjugates is an acid-labile linker based on cis-aconitic acid that takes advantage of the acidic environment of different intracellular compartments such as the endosomes encountered during receptor mediated endocytosis and the lysosomes.
• Shen and Ryser introduced this method for the preparation of conjugates of daunorubicin with macromolecular carriers (102 Biochem. Biophys. Res. Commun. 1048-1054 (1981)).
• Yang and Reisfeld used the same technique to conjugate daunorubicin to an anti- melanoma antibody (80 J Natl. Cane. Inst. 1154-1159 (1988)). Dillman et al.
• Another major drawback with existing antibody-drug conjugates is their inability to deliver a sufficient concentration of drug to the target site because of the limited number of targeted antigens and the relatively moderate cytotoxicity of cancerostatic drugs like methotrexate, daunorubicin and vincristine.
• cancerostatic drugs like methotrexate, daunorubicin and vincristine.
• an antibody conjugate of doxorubicin was evaluated in human clinical trials, and found to be ineffective (Tolcher et al., 17 J Clinical Oncol. 478-484 (1999)).
• linkage of a large number of drug molecules either directly to the antibody or through a polymeric carrier molecule becomes necessary.
• such heavily modified antibodies often display impaired binding to the target antigen and fast in vivo clearance from the blood stream.
• Maytansinoids are highly cytotoxic drugs. Maytansine was first isolated by Kupchan et al. from the east African shrub Maytenus serrata and
• the naturally occurring and synthetic C-3 esters can be classified into two groups:
• Esters of group (b) were found to be much more cytotoxic than esters 110 of group (a).
• Maytansine is a mitotic inhibitor. Treatment of L1210 cells in vivo with maytansine has been reported to result in 67% of the cells accumulating in mitosis. Untreated control cells were reported to demonstrate a mitotic index ranging from between 3.2 to 5.8% (Sieber et al., 43 Comparative
• maytansine has also been shown to be active. Tumor growth in the P388 lymphocytic leukemia system was shown to be inhibited over a
• U.S. Pat. Nos. 5,208,020 and 5,416,064 disclose that a thiol-containing maytansinoid may be produced by first converting a maytansinoid bearing an ester group into maytansinol, then esterifying the resulting maytansinol with N-methyl-E-alanine or N-methyl-Z-cysteine derivatives to yield disulfide- containing maytansinoids, followed by cleavage of the disulfide group with
• maytansinol is first derived from maytansine or other esters of maytansinol by reduction, such as with lithium aluminum
• the next step in the process is the conversion of maytansinol to
• the object of the present invention is to provide an improved process for the preparation and purification of thiol-containing maytansinoids that reduces the complexity of the process, allows scalability and improves the 200 yield.
• the present invention provides a process for 205 preparing a thiol-containing maytansinoid comprising the steps of:
• a reducing agent selected from the group consisting of lithium trimethoxyaluminum hydride (LiAl(OMe) 3 H), lithium triethoxyaluminum hydride (LiAl(OEt) 3 H), lithium tripropoxyaluminum hydride (LiAl(OPr) H),
• sodium trimethoxyaluminum hydride NaAl(OMe) 3 H
• sodium triethoxyaluminum hydride NaAl(OEt) 3 H
• sodium tripropoxyaluminum hydride NaAl(OPr) 3 H
• the reducing agent in (1) is lithium trimethoxyaluminum hydride.
• the reducing agent in (1) is used in a concentration of
• the reducing agent in (1) is used in a concentration of from about 7.5 to 30 equivalents per mole of the maytansinoid C-3 ester. Most preferably, the reducing agent in (1) is used in a concentration from about 10 to 20 equivalents per mole of the maytansinoid C-3 ester.
• the reductive hydrolysis in (1) is conducted at a temperature of from about -80°C to 0°C. More preferably, the reductive hydrolysis in (1) is conducted at a temperature of from about -45°C to -27.5°C. Most preferably, the reductive hydrolysis in (1) is conducted at a temperature of from about -35°C to -30°C.
• the reducing agent in (1) is added over a period of from about 5 to 40 minutes. More preferably, the reducing agent in (1) is added over a period of from about 7 to 20 minutes. Most preferably, the reducing agent in (1) is added over a period of from about 8 to 12 minutes.
• the maytansinol is purified in (2) by chromatography.
• the maytansinol is purified in (2) by chromatography where the chromatography is silica gel column chromatography, preparative thin- layer chromatography on silica gel or cyano-bonded silica HPLC column chromatography.
• the maytansinol is purified in (2) by chromatography where the chromatography is silica gel column 245 chromatography.
• the purification in (2) is performed at ambient temperature.
• the maytansinol in (2) is purified to a purity of about 95%.
• the carboxylic acid in (3) is selected from the group consisting of N-methyl-N-methyldithioacetyl-I-alanine, N-methyl-N-(3- 250 methyldithio-propanoyl)-Z-alanine, N-methyl-N-(3-methyldithio-butanoyl)- - alanine, N-methyl-N-(4-methyldithio-butanoyl)-__.-alanine, N-methyl-N-(5- methyldithio-pentanoyl)-Z-alanine, N-methyl-N-(3-phenyldithio-propanoyl)- - alanine, N-methyl-N- [3 -(4-nitrophenyldithio)-propanoyl]E-alanine, N-acetyl- N-methyl-methyldithiocysteine and N-acetyl-N
• the esterification in (3) is conducted at ambient temperature.
• the esterification in (3) further comprises the use of 260 dicyclohexylcarbodiimide and zinc chloride.
• the separating in (4) is carried out by passing the reaction mixture over a cyano-bonded silica HPLC column.
• the separating in (4) is carried out at about 25°C.
• the reduction in (5) uses dithiothreitol as the reducing 265 agent.
• the reduction in (5) is carried out in a mixture of ethyl acetate-methanol-aqueous buffer which is capable of keeping buffer salts, dithiothreitol, unreduced maytansinoids and reduced maytansinoids in solution. More preferably, the mixture of ethyl acetate-methanol-aqueous
• 270 buffer is 1 : 1.5 : 1 , v/v/v, ethyl acetate:methanol:aqueous buffer.
• the concentration of the thiol-containing maytansinoid is such that the thiol-containing maytansinoid remains soluble in ethyl acetate- methanol-aqueous buffer.
• the concentration of the thiol-containing maytansinoid is about 4 g/L.
• the reduction in (5) is carried out in an oxygen-free atmosphere.
• the reduction in (5) is carried out at about 25°C.
• the purification of the thiol-containing maytansinoid in (6) is by chromatography. More preferably, the chromatography is by a cyano- 280 bonded HPLC column. Most preferably, the chromatography is by a cyano- bonded HPLC column equilibrated and run in an organic solvent.
• the organic solvent is a mixture of hexanes:2-propanol:ethyl acetate, more preferably the solvent is a 78.0:5.5:16.5, v/v/v, mixture of hexanes:2- propanol: ethyl acetate.
• Fig. 1 shows the reduction of ansamitocins la-e to yield maytansinol
• Fig. 2a shows the conversion of the ⁇ -mercapto-carboxylic acids 3a-e to the respective methyl-dithio derivatives 4a-e.
• Fig. 2b shows the conversion of the ⁇ -mercapto-carboxylic acid 3b to the respective aryl-dithio derivatives 5a-b.
• Fig. 2c shows the conversion of the methyl-dithio derivatives 4a-e and the aryl-dithio derivatives 5a-b to N ⁇ methyl-E-alanine derivatives 6a-g containing a disulfide group.
• Fig. 3 a shows the conversion of N-methylcysteine and N- methylhomocysteine (7a-b) to the respective disulfide derivatives 8a-b.
• Fig. 3b shows the acylation of the disulfide derivatives 8a-b to N- methyl-E-cysteine derivatives 9a-b containing a disulfide group.
• Fig. 4 shows the esterification of maytansinol (2) with the N-methyl-Z-
• alanine derivatives 6a-g containing a disulfide group to yield the disulfide- containing maytansinoid stereoisomers 10, from which the L-isomers are separated via chromatography to yield the disulfide-containing maytansinoid L-isomers lOa-g, which in turn are reduced to yield the thiol-containing maytansinoids lla-g.
• FIG. 5 shows the esterification of maytansinol (2) with the N-methyl-E- cysteine derivatives 9a-b containing a disulfide group to yield the disulfide- containing maytansinoid stereoisomers 12, from which the L-isomers are separated via chromatography to yield the disulfide-containing maytansinoid L-isomers 12a-b, which in turn are reduced to yield the thiol-containing
• This invention is based on the synthesis of thiol-containing maytansinoid derivatives that retain high cytotoxicity and that can be effectively linked to cell binding agents.
• the art reveals that the existing 315 methods for producing thiol-containing maytansinoids are complex, non- scalable and produce low product yield.
• the present invention overcomes these problems by disclosing a novel process for producing thiol-containing maytansinoids that reduces the complexity of the process, allows scalability and improves product yield.
• the invention provides a novel process for the production of thiol-containing maytansinoids, useful agents for the elimination of diseased or abnormal cells that are to be killed or lysed, such as tumor cells (particularly solid tumor cells), virus infected cells, microorganism infected cells, parasite infected cells, autoimmune cells (cells that produce
• thiol-containing maytansinoids can be chemically linked to a cell binding agent while keeping a high cytotoxicity either in bound form or in
• High cytotoxicity is defined as exhibiting a toxicity having an IC 5 o ⁇ the inhibiting concentration of a toxic substance that leaves a surviving fraction of 0.5 ⁇ of about 10 "8 M or less when measured in vitro with KB cells upon a 24 hour exposure time to the drug.
• Cell binding agents may be of any kind presently known, or that become known and include peptides and non-peptides. Generally, these can be antibodies (especially monoclonal antibodies), lymphokines, hormones, growth factors, nutrient-transport molecules (such as transferrin), or any other
• maytansinoids include maytansinol and 345 maytansinol analogues.
• suitable maytansinol analogues include those having a modified aromatic ring and those having modifications at other positions.
• Specific examples of suitable analogues of maytansinol having a modified aromatic ring, and the process for their production, include: 350 (1) C-19-dechloro (U.S. Pat. No. 4,256,746) (prepared by lithium aluminum hydride reduction of ansamitocin P-2);
• linking group In order to link the maytansinoid to the cell binding agent, a linking group is used. 375 Suitable linking groups are well known in the art and include disulfide groups, thioether groups, acid labile groups, photolabile groups, peptidase labile groups and esterase labile groups. Preferred are disulfide groups and thioether groups.
• the linking group is part of a 380 chemical moiety that is covalently bound to the maytansinoid through disclosed methods.
• the chemical moiety is covalently bound to the maytansinoid via an ester linkage.
• the linkage position is expected to be useful as the linkage position, depending upon the type of link. For example, for forming an 385 ester linkage, the C-3 position having a hydroxyl group, the C-14 position modified with hydroxymethyl, the C-15 position modified with hydroxy and the C-20 position having a hydroxy group are all expected to be useful.
• C-3 position is preferred and the C-3 position of maytansinol is especially preferred.
• 390 Also preferred is an N-methyl-E-alanine-containing C-3 ester of maytansinol and an N-methyl-E-cysteine-containing C-3 ester of maytansinol or their analogues.
• the present invention recites a process for the preparation and purification of a thiol-containing maytansinoid that positions the linking group 395 at C-3 of maytansinol.
• Step 1 Synthesis of Maytansinol (2) from an Ester-Bearing Maytansinoid
• the first step in the preparation and purification of thiol-containing maytansinoids involves the reductive hydrolysis of a maytansinoid C-3 ester into maytansinol (2).
• the maytansinoid C-3 ester is maytansine or ansamitocin P-
• ansamitocin P-3 (lc). Maytansine can obtained as described by Kupchan et al, 42 J Org. Chem. 2349-2357 (1977). The microbiological preparation of ansamitocin P-3 (lc) is described in US Pat. No. 4,450,234 and in Hatano et al., 48 Agric. Biol. Chem. 1721-1729 (1984).
• the anhydrous solvent is tetrahydrofuran (THF), 2- methoxyethyl ether, dioxane or di-ethyl ether, although other solvents can be used. More preferably, the anhydrous solvent is tefrahydrofuran. Preferably, 20 to 30 mL of the anhydrous solvent is used per gram of ester, more preferably 25 mL/g.
• the inert gas is argon, nitrogen or helium, although other gases can be used. More preferably, the inert gas is argon.
• the solution is maintained at between about 0 to -80°C, more preferably between about -30 to -50°C, most preferably between about -35 to - 45°C, in a dry ice-acetone bath.
• a reducing agent is also cooled, and then transferred into the chilled solution of the maytansinoid C-3 ester.
• the reaction is maintained under an inert gas atmosphere, at a low temperature, and stirred.
• the reducing agent is lithium trimethoxyaluminum hydride (LiAl(OMe) H), lithium triethoxyaluminum hydride (LiAl(OEt) 3 H), lithium tripropoxyaluminum hydride (LiAl(OPr) 3 H), sodium trimethoxyaluminum hydride (NaAl(OMe) 3 H), sodium triethoxyaluminum hydride (NaAl(OEt) 3 H) or sodium tripropoxyaluminum hydride (NaAl(OPr) 3 H). More preferably, the reducing agent is lithium trimethoxyaluminum hydride (LiAl(OMe) 3 H).
• the reducing agent is cooled to about -30 to -40°C in a dry ice- acetone bath.
• the cooled reducing agent is transferred into the chilled solution of the maytansinoid C-3 ester via a canula.
• the inert gas is argon, nitrogen or helium, although other gases can be used. More preferably, the inert gas is argon.
• the reducing agent is used in a concentration of from about 5 to 100 equivalents per mole of the maytansinoid C-3 ester, more preferably from about 7.5 to 30 equivalents per mole, most preferably from about 10 to 20 equivalents per mole.
• the reducing agent is added to the chilled solution of maytansinoid C-3 ester over a time period ranging from about 5 to 40 minutes, more preferably from about 7 to 20 minutes, most preferably from about 8 to 12 minutes.
• the reaction is maintained under an inert gas atmosphere at a temperature range of from about -25°C to -80°C, more preferably from about -27°C to -45°C, most preferably from about -30°C to -35°C.
• the reaction is stirred between about 30 min and three hours, more preferably for about three hours.
• the amount of reducing agent used, the temperature maintained during the reaction, the length of the time period over which the reducing agent is added and the reaction time are each dependent on the other. For example, the lower the amount of the reducing agent, the longer the reaction time. Similarly, the lower the temperature, the larger the excess of reducing agent required and the longer the time required for completion of the reaction. Moreover, the slower the rate the reducing agent is added, the longer reaction time required for completion of the reaction.
• the reaction is quenched by the addition of saturated sodium chloride solution, water or ammonium chloride solution, more preferably by the addition of saturated sodium chloride solution.
• the reaction is quenched using between about 20 to 40 mL of the solution per gram of maytansinoid ester used.
• the reaction is extracted with ethyl acetate, dichloromethane, toluene, chloroform or ether, more preferably with ethyl acetate.
• the reaction is extracted at the rate of between about 4 x 80 to 4 x 200 mL/g maytansinoid ester used.
• the combined ethyl acetate extracts are dried over sodium sulfate or magnesium sulfate, more preferably sodium sulfate, and filtered.
• the crude maytansinol (2) may be purified, if required, by chromatography.
• the crude maytansinol (2) may be purified by dissolving it in a minimum volume of ethyl acetate, dichloro methane, ether, chloroform or toluene, more preferably ethyl acetate, and purified via silica gel column chromatography using dichloromethane, chloroform, ethyl acetate or toluene, more preferably dichloromethane.
• the crude maytansinol (2) may be purified by dissolving it in a minimum volume of ethyl acetate, dichloro methane, ether, chloroform or toluene, more preferably ethyl acetate, and purified via silica gel column chromatography using dichloromethane, chloroform, ethyl acetate or toluene, more preferably dichloromethane.
• the crude maytansinol (2) may be purified by dissolving it in a minimum volume of e
• 475 maytansinol (2) is eluted with a step gradient starting with dichloromethane or ethyl acetate, or a mixture of dichloromethane: ethyl acetate:alcohol, chloroform:ethyl acetate or toluene:ethyl acetate, preferably 77:23:0, v/v/v, dichloromethane:ethyl acetate:alcohol.
• the concentration of alcohol is slowly increased from 0 to about 20%, preferably from 0 to about 10%.
• the purification may be performed at ambient temperature.
• the purification is performed at a temperature of about 20°C and 25°C.
• the alcohol is methanol, ethanol, n-propanol, iso-propanol, n-, iso-, sec-, or tert-butanol,
• the crude maytansinol (2) may be purified using a cyano-bonded silica HPLC column that is run in normal phase, using organic solvents in the mobile phase.
• the crude maytansinol (2) is dissolved in ethyl acetate, ethyl acetate:isopropanol:hexane (mobile phase)
• the cyano-bonded HPLC column that is used for the separation is one having cyanopropyl and cyano-di-isopropyl groups stably bonded to the silica backbone.
• Such columns are available under the trade names DiazemTM, ZorbaxTM,
• the organic solvent used in the mobile phase is hexanes:2-propanol:dichloromethane:ethyl acetate.
• the concentration of each constituent of the organic solvent is in the range 65-75:2-4:15-20:5-10, v/v/v/v, respectively. More preferably, the concentration of each element of the organic solvent is
• maytansinol (2) purified by this process is at least 90% pure, more preferably at least 95% pure.
• maytansinol (2) of less than 90% purity is used in the following steps, additional purification steps may be required.
• the reduction reaction may yield small amounts of undesired side products, in addition to the maytansinol (2).
• purification may be required to remove the contaminants.
• the side products are not generated, such as where the precise times, temperatures, and amounts are established, then the
• Step 2 Synthesis of Esters of Maytansinol (2) Having a Linking Group
• the maytansinol (2) from Step 1 is next esterified with disulfide- containing N-methyl-Z-alanine derivatives 6a-g or N-methyl-i-cysteine derivatives 9a-b, in the presence of dicyclohexylcarbodiimide (DCC) and zinc
• N-methyl-Z-alanine may be prepared as described in the literature (see, Fu, S. J. & Birnbaum, S. M., 75 J. Amer. Chem. Soc. 918 (1953)), or is
• the N-methyl-Z-alanine derivatives containing a disulfide group are N-methyl-N-methyldithioacetyl-Z-alanine, N-methyl-N-(3- methyldithio-propanoyl)-Z-alanine, N-methyl-N-(4-methylditl ⁇ io-butanoyl)-Z- alanine, N-methyl-N-(3-methyldithio-butanoyl)-Z-alanine, N-methyl-N-(5-
• These disulfide-containing derivatives 9a-b will be condensed with maytansinol (2) to form maytansinoids containing disulfide-linking groups 12a-b.
• N-methyl-Z-cysteine can be prepared as described in Undheim and
• N-methyl-Z-cysteine derivatives containing a disulfide group are N-acetyl-N-methyl-methyldithiocysteine (9a) and N-acetyl-N- methyl-methyldithiohomocysteine (9b) .
• racemic versions of 6a- g and 9a-b i.e. a D, L-mixture
• the N-methyl-Z-alanine or N-methyl-Z-cysteine derivative containing a disulfide group is N-methyl-N-(methyldithio-propanoyl)-Z- alanine (6b) and N-acetyl-N-methyl-methyldithiocysteine (9a), respectively.
• the solution of the disulfide-containing derivative comprises dry methylene chloride, tetrahydrofuran, or ether, preferably dry methylene chloride, using between about 10 to 50 mL/gram maytansinol, preferably 20 mL/gram.
• the inert gas is argon, nitrogen or helium, although other gases can be used. More preferably, the inert gas is argon.
• the DCC or EDC is in methylene chloride, tetrahydrofuran or ether, preferably methylene chloride, using about 10 to 15 mL per gram DCC or EDC, preferably 12 mL/g.
• the DCC or EDC solution is added at the rate of about 5 to 7 moles/mole of maytansinol.
• the ZnCl 2 is about 1 M, and it is used at between about 1.2 to 1.5 moles/mole of
• 580 maytansinol, preferably 1.25 moles, in ether or methylene chloride, preferably ether.
• maytansinol is in methylene chloride, tetrahydrofuran or ether, more preferably methylene chloride, using about 10 to 120 mL solvent per gram of maytansinol, preferably 100 mL/g.
• the reaction mixture is stirred at between 4 to 30°C, preferably room temperature, for between 1 to 24 hours,
• the separation can be conducted using silica gel chromatography, but the process is not easily converted to an industrial scale. Separation can also be accomplished through other, less desirable, means such as HPLC using chiral columns or silica columns.
• the 600 separation are those that have cyanopropyl and cyano-di-isopropyl groups stably bonded to the silica backbone.
• Such columns are available under the trade names DiazemTM, ZorbaxTM, MonochromTM, and KromasilTM, among others.
• the organic solvent used in the mobile phase is hexanes:2- propanol: ethyl acetate.
• the yield of the separation is greater than
• the desired L-isomer has a retention time of about 36 to 46 min, preferably 42 min, while the D-isomer elutes at about 50 to 60 minutes, preferably 56 min.
• the esterification is carried out at about 25°C.
• the L- aminoacyl maytansinol esters obtained from Step 2 are dissolved in a solution comprising a solvent and an alcohol. This mixture is stirred under an inert gas atmosphere, and treated with a solution of dithiothreitol or dithioerythritol, in
• EDTA ethylenediaminetetraacetic acid
• the solvent the L-aminoacyl maytansinol esters obtained is obtained
• the alcohol the L-aminoacyl maytansinol esters obtained from Step 2 are dissolved in is methanol or ethanol, more preferably methanol, using from about 90 to 120 mL alcohol per
• the reaction between L-aminoacyl maytansinol esters and dithiothreitol is in a mixture of ethyl acetate:methanol:aqueous buffer which is capable of keeping the buffer salts, dithiothreitol and maytansinoids (reduced and non-reduced forms) in solution. More preferably, the reaction between L-aminoacyl maytansinol esters and
• dithiothreitol is in a 1 : 5 : 1 mixture of ethyl acetate :methanol : aqueous buffer.
• the concentration of L-aminoacyl maytansinol esters used in Step 3 is less than about 4 g/L such that the L-aminoacyl maytansinol esters remain solubilized.
• the reduction reaction is carried out in an oxygen-free
• the inert gas is argon, nitrogen or helium, although other gases can be used. More preferably, the inert gas is argon.
• the reduction reaction is carried out at between 4 to 30°C, more preferably at room temperature. One of ordinary skill in the art will understand that the reaction can be carried out at lower temperatures, however,
• the solution containing the L-aminoacyl maytansinol esters is treated with dithiothreitol, dithioerythritol or a phosphine reagent such as tris (2-carboxyethyl) phosphine (TCEP), more preferably dithiothreitol, using about 2 to 3 moles reducing agent per mole maytansinoid, preferably 2.5
• potassium phosphate buffer sodium phosphate buffer or triethanolamine buffer, preferably potassium phosphate buffer, the buffer at a concentration between about 20 to 100 mM, preferably 50 mM, using 60 to 80 mL of the buffered DTT per gram maytansinoid, preferably 72 mL/g, and containing from about 1 to 10 mM, preferably 2 mM,
• EDTA ethylenediaminetetraacetic acid
• the completed reaction is treated with a 0.2 M solution of potassium phosphate buffer, sodium phosphate buffer or triethanolamine buffer, more preferably potassium phosphate buffer, using from about 120 to 160 mL buffer per gram maytansinoid, preferably 144 mL/g, and containing
• the extraction is with ethyl acetate, dichloro methane, or ether, more preferably ethyl acetate, using 200 to 500 mL per gram maytansinoid, preferably 300 mL/g, repeated three times.
• the combined organic layers are washed with a saturated sodium chloride solution, water or a saturated ammonium chloride
• 665 solution more preferably a saturated sodium chloride solution, using 40 to 100 mL per gram maytansinoid, preferably 50 mL/g, and then dried over sodium sulfate or magnesium sulfate, preferably sodium sulfate.
• the cyano-bonded HPLC columns that are used for the separation are those that have cyanopropyl and cyano-di-isopropyl groups
• the organic solvent used in the mobile phase is hexanes:2-pro ⁇ anol: ethyl acetate. More preferably, the organic solvent used in the mobile phase is a 78.0:5.5:16.5 (v/v/v) mixture of hexanes:2-propanol: ethyl acetate.
• the flow rate is 150 mL/min.
• the yield of the separation is greater than 75%, and product is at least about 90% pure, more preferably, at least about 95% pure.
• the desired thiol-containing maytansinoids l la-d and 13a-b have a retention time of 16 min, within a range from about 14 to 18 min.
• N-methyl-L-alanine-containing maytansinoid derivatives taught by the present invention are represented by formulas (I) - (IV):
• Z represents H or SR, wherein R represents a methyl, linear alkyl, branched alkyl, cyclic alkyl, simple or substituted aryl or heterocyclic group; represents an integer of 1 to 10; and may represents a maytansinoid.
• Rj and R which may be the same or different, represents H, 690 CH 3 or CH CH ;
• Z represents H or SR, wherein R represents methyl, linear alkyl, branched alkyl, cyclic alkyl, simple or substituted aryl, or heterocyclic;
• m represents 0, 1, 2 or 3; and may represents a maytansinoid.
• Z represents H or SR, wherein R represents methyl, linear alkyl, branched alkyl, cyclic alkyl, simple or substituted aryl, or heterocyclic; p represents an integer of 3 to 8; and may represents a maytansinoid.
• Z represents H or SR, wherein R represents methyl, linear alkyl, branched alkyl, cyclic alkyl, simple or substituted aryl or heterocyclic; q represents an integer from 1 to 10; Y represents Cl or H; and X represents H or CH 3 .
• N-methyl-Z-cysteine-containing maytansinoid
• Z represents H or SR, wherein R represents methyl, linear alkyl, branched alkyl, cyclic alkyl, simple or substituted aryl, or heterocyclic; o represents 1 or 2; q represents 0 or an integer of 1 to 10; and may represents a maytansinoid.
• Z represents H or SR, wherein R represents methyl, linear 715 alkyl, branched alkyl, cyclic alkyl, simple or substituted aryl or heterocyclic; o represents 1 or 2; q represents 0 or an integer of 1 to 10; Y represents Cl or H; and X represents H or CH 3 .
• linear alkyls examples include methyl, ethyl, propyl, butyl, pentyl and hexyl.
• branched alkyls examples include isopropyl, isobutyl, sec-butyl, tert. -butyl, isopentyl and 1-ethyl-propyl.
• cyclic alkyls examples include cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl.
• Examples of simple aryls include phenyl and naphthyl. 725
• Examples of substituted aryls include aryls such as those described above substituted with alkyl groups, with halogens, such as Cl, Br, F, nitro groups, amino groups, sulfonic acid groups, carboxylic acid groups, hydroxy groups and alkoxy groups.
• heterocyclics are compounds wherein the heteroatoms are 730 selected from O, N and S, and include pyrrollyl, pyridyl, f ryl and thiophene.
• room temperature and “ambient temperature” mean environmental temperature or uncontrolled temperature.
• optical purity means that the purity exceeds 98%.
• ranges 735 are specified herein, e.g. temperature, time, concentration etc., the range includes all specific values within the range, as well as subranges falling within the broad range. Where values are stated to be “about” a specific value, or range of values, it is to be understood that statistically insignificant variations in those values are included as well. 740 EXAMPLES
• 5-Mercaptopentanoic acid (3d) was prepared by a modification of a literature method (Kl im et al, 37 J Org.
• N-methyl-N-methyldithioacetoyl-Z-alanine (6a).
• l-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (2.99 g, 15.6 mmol) and triethylamine (1.58 g, 15.6 mmol) in dry CH 2 C1 2 (40 mL) at 0°C was added a solution of methyldithio-acetic acid (Singh et al., 104 Anal.
• reaction mixture was stirred for fifteen minutes at -15°C and then warmed to room temperature and stirred for an additional period of 2.5 hours.
• 1 M HCl (10 mL) was added and the reaction mixture was extracted with ethyl acetate (4 x 50 mL). The combined organic layers were dried with ⁇ a 2 SO , filtered, and evaporated under reduced pressure.
• the crude mixture was purified by
• Methyldithio-N-methylcysteine (8a) A solution of N-methylcysteine (7a) (Undhein, K., & Eidem, A., 23 Ada Chem. Scandinavica 3129-3133 (1970)) (1.5 g, 11.1 mmol) in H O (20 mL) was stirred at room temperature,
• N-methylhomocysteine (7b) can be made by the method previously described for N-methylcysteine (Undhein, K., & Eidem, A., 23 Acta Chem. Scandinavica 3129-3133 (1970)).
• N-acetyl-N-methyl-methyldithiohomocysteine (9b).
• One of ordinary skill in the art will understand how to make N-acetyl-N-methyl- methyldithiohomocysteine (8b) based on the method for making N-acetyl-N-
• Step 1 Reduction of Ansamitocin P-3 (lc) into Maytansinol
• Ansanmitocin P-3 (lc) was converted into maytansinol (2) by reductive hydrolysis.
• Ansamitocin P-3 (lc) (3.2 g, 5.0 mmol) was dissolved in anhydrous THF (80 mL), and the solution was placed under an argon 1000 atmosphere, and cooled in a dry ice-acetone bath to -40°C.
• 1015 maytansinol (2) .
• the crude product was dissolved in ethyl acetate and loaded onto a silica gel column packed in dichloromethane.
• the column was eluted with a step gradient starting with a mixture of dichloromethane: ethyl acetate:methanol (77:23:0, v/v/v) and slowly increasing the concentration of
• the maytansinol was further purified by HPLC as follows.
• a KromasilTM cyano preparative HPLC column 250 mm x 50 mm, 10 micron
• the compound 10a can be more efficiently purified using a DiazemTM cyano HPLC column (250 mm x 10 mm, 10 micron particle size) equilibrated in a mixture of hexanes:2-propanol:ethyl acetate (17:2:6, v/v/v) at a flow rate of 4.7 mL/min.
• the mixture can be further purified using a DiazemTM cyano
• HPLC column 250 mm x 50 mm, 10 micron particle size was equilibrated in a mixture of hexanes:2-propanol:ethyl acetate (17:2:6, v/v/v) at a flow rate of 150 mL/min as described above for (10b).
• the completed reaction mixture was treated with a solution of 0.2 M potassium phosphate buffer (250 mL), pH 6.0, containing 2 mM EDTA, and then extracted with ethyl acetate (3 x 600 mL).
• the organic layers were
• the crude thiol-containing maytansinoid lib was purified by HPLC using a preparative DiazemTM cyano HPLC column (250 mm x 50 mm, 10

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