United States Patent
`Holton
`
`119
`
`|
`
`[54] METAL ALKOXIDES
`
`{75]
`
`Inventor:
`
`Robert A. Holton, Tallahassee, Fla.
`
`[73] Assignee:
`
`Florida State University, Tallahassee,
`Fla.
`
`[21] Appl. No.: 862,778
`
`[22] Filed:
`
`Apr. 3, 1992
`
`[63}
`
`Related U.S. Application Data
` Continuation-in-part of Ser. No. 763,805, Sep. 23, 1991,
`abandoned.
`
`[SU]
`
`Int. CLS wesc CO7D 305/14; CO7F 5/02;
`CO7F 7/02
`[52] U.S. Ch. eecccscccccccscssssssssssseeeseee 549/213; 549/214;
`549/510; 549/511
`[58] Field of Search ................ 549/214, 510, 511, 213
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,814,470
`4,857,653
`4,924,011
`4,924,012
`4,942,184
`5,015,744
`
`3/1989 Colinet al.ee 514/449
`8/1989 Colin etal. ....
`sesnseeenoness 349/511
`
`
`5/1990 Denis et al.
`...
`sitsessenseses 849/510
`5/1990 Colinet al. oes 849/510
`
`7/1990 Haugwitz et al. oc. 514/449
`-S/1991 Holton wc essserseseeennees 349/510
`
`FOREIGN PATENT DOCUMENTS
`
`7/1987 European Pat. Off.
`253738
`7/1987 European Pat. Off.
`253739
`336840 4/1989 European Pat. Off.
`336841
`4/1989 European Pat. Off.
`
`.
`.
`.
`.
`
`OTHER PUBLICATIONS
`
`Denis and Greene, “A Highly Efficient, Practical Ap-
`proach to Natural Taxol”, J. Am. Chem. Soc. 1988, 110,
`5917-5919.
`
`ATOMA
`
`5,229,526
`Jul. 20, 1993
`
`US005229526A °
`[11] Patent Number:
`
`[45] Date of Patent:
`
`Holton et al., “A Synthesis of Taxusin”, J. Am. Chem.
`Soc., 1988, 110, pp. 6558-6560.
`Holton, “Synthesis of the Taxane Ring System”, J. Am.
`Chem. Soc., 1984, 106, pp. 5731-5732.
`Mukerjee et al, “8-Lactams: Retrospect and Pros-
`pect”, Tetrahedron vol. 34, Report No. 52, pp.
`1731-1767 (1978).
`Waniet al., “Plant Antitumor Agents. VI. The Isolation
`and Structure of Taxol, a Novel Antileukemic and Anti-
`tumor Agent from Taxus brevifolia”, J. Am. Chem. Soc.
`93:9, May 5, 1971, pp. 2325-2327.
`
`Primary Examiner—C. Warren Ivy
`Assistant Examiner—Ba K. Trinh
`Attorney, Agent, or Firm—Senniger, Powers, Leavitt &
`Roedel
`
`ABSTRACT
`[57]
`A metal alkoxide having the following formula:
`
`@)
`
`wherein T] is hydrogen or a hydroxy protecting group,
`Z is —OT2, or —OCOCH3, T2 is hydrogen or a hy-
`droxy protecting group, and M is selected from the
`group comprising Group JA, NAandtransition met-
`als are useful in the preparation ofbiologically active
`derivatives of baccatin HI and 10-deacetyl baccatin
`IH.
`-
`
`15 Claims, No Drawings
`
`Sanofi Exh. 2003
`Neptunev. Aventis
`IPR2019-00136
`
`Sanofi Exh. 2003
`Neptune v. Aventis
`IPR2019-00136
`
`

`

`1
`
`METAL ALKOXIDES
`
`5,229,526
`
`ay)
`
`5
`
`10
`
`20
`
`25
`
`30
`
`35
`
`45
`
`30
`
`55
`
`REFERENCE TO RELATED APPLICATIONS
`
`This application is a continuation-in-part application
`of U.S. Ser. No. 07/763,805, filed Sep. 23, 1991, now
`abandoned.
`
`BACKGROUNDOF THE INVENTION
`
`The present invention is directed to novel metal al-
`koxides useful in the preparation of derivatives of bac-
`catin IIT and 10-deacety] baccatin III such as taxol,
`taxotere and other taxane derivatives which havebio-
`
`logical activity.
`The taxane family of terpenes, of which taxol is a
`member, has attracted considerable interest in both the
`biological and chemical arts. Taxol is a promising can-
`cer chemotherapeutic agent with a broad spectrum of
`antileukemic and tumor-inhibiting activity. Taxol has
`the following structure:
`
`(1)
`
`Ce6HsCONH
`
`CeH5 3
`
`taxol is currently
`Because of this promising activity,
`undergoingclinical trials in both France and the United
`States.
`
`The supply of taxol for these clinical trials is pres-
`ently being provided by the bark from Taxus brevifolia
`(Western Yew). However,taxol is found only in minute
`quantities in the bark of these slow growing evergreens,
`causing considerable concern that the limited supply of
`taxol will not meet the demand. Consequently, chemists
`in recent years have expendedtheir energiesin trying to
`find a viable synthetic route for the preparation of tax-
`ols. So far, the results have not been entirely satisfac-
`tory.
`One synthetic route that has been proposed is di-
`rected to the synthesis of the tetracyclic taxane nucleus
`from commodity chemicals. A synthesis of the taxol
`congenertaxusin has been reported by Holton,et al. in
`JACS 110, 6558 (1988). Despite the progress made in
`this approach,thefinal total synthesis of taxol is, never-
`theless, likely to be a multi-step, tedious, and costly
`process.
`Analternate approach to the preparation oftaxol has
`been described by Greene, et al.
`in JACS 110, 5917
`(1988), and involves the use of a congener of taxol,
`10-deacety! baccatin IIT which has the structure of
`formula IE shown below:
`
`10-deacety] baccatin III is more readily available than
`taxol since it can be obtained from the needles of Taxus
`baccata. According to the method of Greene et al.,
`10-deacetylbaccatin ITI is converted to taxol by attach-
`ment of the C-10 acetyl group and by attachmentof the
`C-13 B-amidoester side chain through the esterification
`of the C-13 alcohol with a B-amido carboxylic acid unit.
`Although this approach requires relatively few steps,
`the synthesis of the B-amido carboxylic acid unit is a
`multi-step process which proceedsin low yield, and the
`coupling reaction is tedious and also proceeds in low
`yield. However, this coupling reaction is a key step
`which is required in every contemplated synthesis of
`taxol or biologically active derivative of taxol, since it
`has been shown by Wani,et al. in JACS 93, 2325 (1971)
`that the presence of the B-amidoester side chain at C13
`is required for anti-tumoractivity.
`More recently, it has been reported in Colin et al.
`U.S. Pat. No. 4,814,470 that taxol derivatives of the
`formula III below, havean activity significantly greater
`than that of taxol (1).
`
`aa)
`
`co—O
`
`2';CH—R"”
`
`CeHs—CH—-R”™”
`3!
`
`
`
`OCOCH;
`
`R' represents hydrogenor acetyl and one of R” and R’”
`represents hydroxy and the other represents tert-butox-
`ycarbonylamino and. their stereoisomeric forms, and
`mixtures thereof.
`According to Colin et al., U.S. Pat. No. 4,418,470, the
`products of general formula (III) are obtained by the
`action of the sodium salt of tert-butyl] N-chlorocarba-
`mate on a product of general formula:
`
`qv)
`
`(e)
`4
`
`OCOOCH2Ch
`
` Ta
`OCOCsHs OCOCH;
`
`CoHs
`
`65
`
`in which R’ denotes an acetyl or 2,2,2-trichloroethox-
`ycarbony] radical, followed by the replacement of the
`2,2,2-trichloroethoxycarbonyl group or groups by hy-
`
`

`

`5,229,526
`
`4
`
`3
`drogen. It is reported by Denis et al. in U.S. Pat. No.
`4,924,011, however, that this process leads to a mixture
`of isomers whichhasto be separated and,as a result, not
`all the baccatin III or 10-deactylbaccatin III employed
`for the preparation of the product of general formula
`(IV) can be converted to a product of general formula
`(IH).
`In an effort to improve upon the Colin et al. process,
`Denis et al. disclose a different process for preparing
`derivatives of baccatin III or of 10-deactylbaccatin III
`of general formula
`
`R'O
`
` ro oR
`
`OH
`OCOCs.Hs OCOCH;
`CéHs— CH—NHCOOC(CH)3
`
`v)
`
`15
`
`20
`
`in which R' denotes hydrogen or acetyl wherein an acid
`of general formula:
`
`25
`
`OR;
`
`CeHs
`
`(VI)
`
`30
`
`is con-
`is a hydroxy-protecting group,
`in which Ry;
`densed with a taxane derivative of general formula:
`
`35
`
`SUMMARYOF THE INVENTION
`
`Among the objects of the present invention, there-
`fore, is the provision of activated baccatin HI and 10-
`deacetyl baccatin III derivatives which permit attach-
`ment of the 8-amidoester side chain in high yield, the
`provision of such derivatives which permit the use of a
`racemic mixture of side chain precursor, eliminating the
`need for the expensive, time-consuming process of sepa-
`rating the precursor into its respective isomeric forms,
`and the provision of such derivatives which permit the
`preparation of taxanes having greater variety in the
`side-chain.
`.
`Briefly, therefore, the present invention is directed to
`a metal alkoxide having the formula:
`
`Q)
`
`is hydrogen or a hydroxy protecting
`wherein T,
`group, Z is —OT2, or —OCOCH3, T2 is hydrogen
`or a hydroxy protecting group, and M is a metal,
`preferably, Li, Mg, Na, K or Ti.
`Other objects and features of this invention will be in
`part apparent and in part pointed out hereinafter.
`
`DETAILED DESCRIPTION
`
`Metal alkoxides (1) are activated derivatives of bacca-
`tin ITI and/or 10-deacetyl baccatin III and have particu-
`lar utility in a process for the preparation of taxol, tax-
`otere and other biologically active taxane derivatives.
`In accordance with the present invention, metal alkox-
`ides (1) are reacted with 8-lactam (2) to form a B-amido
`ester intermediate. The intermediate is then converted
`to a biologically active taxane derivative.
`B-lactam (2) has the general formula:
`
`Rs
`
`J Oo
`NZ c
`Rett
`R3 R2
`
`eR,
`
`Q)
`
`wherein
`R1 is —ORg6, —SR7, or —NRgRo;
`R2 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or
`heteroaryl;
`.
`R3 and Rgare independently hydrogen,alkyl, alkenyl,
`alkynyl, aryl, heteroaryl, or acyl, provided, how-
`ever, that R3 and Ry are not both acyl;
`Rs
`is —CORjo, —COOR)9, —COSR)o,
`—CONRsRio0, —SO2R11, or —POR72R43;
`Regis alkyl, alkenyl, alkynyl, aryl, heteroaryl, or hy-
`droxy protecting group;
`R7 is alkyl, alkenyl, alkynyl, aryl, heteroary], or sulf-
`hydry] protecting group;
`Rg is hydrogen, alkyl, alkenyl, alkynyl, aryl, or
`heteroary];
`Rg is an amino protecting group;
`
`45
`
`50
`
`65
`
`R20
`
`oO
`4
`
`(VI)
`
`
`
`HO--
`
`roH °
`i
`OCOCH;
`OCOC.sH5
`
`in which R32is an acetyl hydroxy-protecting group and
`R3 is a hydroxy-protecting group, and the protecting
`groups Ri, R3 and, where appropriate, R2 are then re-
`placed by hydrogen. However, this method employs
`relatively harsh conditions, proceeds with poor conver-
`sion, and provides less than optimalyields.
`A major difficulty remaining in the synthesis of taxol
`and other potential anti-tumor agentsis the lack of bac-
`catin IT] and 10-deacetyl baccatin III derivatives which
`have been activated at the C-13 oxygen. Development
`of such derivatives would permit attachment of the
`8-amidoester side chain in high yield and thus,facilitate
`the synthesis of taxol as well as related anti-tumor
`agents having a modified set of nuclear substituents or a
`modified C-13 side chain.
`Another majordifficulty encountered in the synthesis
`of taxol is that known processes for the attachment of
`the B-amido ester side chain at C-13 are generally not
`sufficiently diastereoselective. Therefore the side chain
`precursor must be prepared in optically active form to
`obtain the desired diastereomer during attachment.
`
`

`

`5,229,526
`
`5
`Ryo is alkyl, alkenyl, alkynyl, aryl, or heteroary];
`Ry;
`is alkyl, alkenyl, alkynyl,
`aryl, heteroaryl,
`—OR 10, or —NRsR14;
`Rj2 and Rj3are independently alkyl, alkenyl, alkynyl,
`aryl, heteroaryl], —OR jo, or —NRgRj4; and
`Ry4 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or
`heteroaryl.
`In accordance with the present invention, Rs of B-
`lactam (2) is preferably —COR jo with Rio being aryl,
`p-substituted phenyl, or lower alkoxy, and most prefera-
`bly, phenyl, methoxy, ethoxy,
`tert-butoxy (“tBuO”;
`(CH3)3CO—) or
`
`* C
`
`wherein X is Cl, Br, F, CH30—, or NO?—. Preferably
`R2and Rgare hydrogen or lower alkyl. R3 is preferably
`aryl, most preferably, naphthyl, phenyl,
`
`©
`» OC
`
`Oo
`
`oO
`
`Ph
`
`wherein X is as previously defined, Me is methyl] and Ph
`is phenyl. Preferably, Ry is selected from —ORg¢, —SR7
`or —NRsRo wherein Re, R7 and Ro, are hydroxy, sulf-
`hydryl, and amine protecting groups, respectively, and
`Rg is hydrogen,alkyl, alkenyl, alkynyl, aryl, or heteroa-
`ryl. Most preferably, Rj is —ORg¢ wherein R¢is triethyl-
`silyl] (“TES”), 1-ethoxyethyl (“EE”) or 2,2,2-trichloro-
`ethoxymethyl.
`The 8-lactam aikyl groups, either alone or with the
`various substituents defined hereinabove are preferably
`loweralkyl containing from one to six carbon atomsin
`the principal chain and up to 15 carbon atoms. They
`may be straight or branched chain and include methyl,
`
`6
`ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, aryl,
`hexyl, and the like.
`.
`The B-lactam alkeny! groups, either alone or with the
`various substituents defined hereinabove are preferably
`loweralkenyl containing from two to six carbon atoms
`in the principal chain and up to 15 carbon atoms. They
`may be straight or branched chain and include ethenyl,
`propenyl, isopropenyl, butenyl, isobutenyl, aryl, hex-
`enyl, and the like.
`The £-lactam alkynyl groups,either alone or with the
`various substituents defined hereinabove are preferably
`lower alkynyl containing from two to six carbon atoms
`in the principal chain and up to 15 carbon atoms. They
`maybestraight or branched chain and include ethynyl,
`propynyl, butynyl, isobutynyl, aryl, hexyny!, and the
`like.
`The 8-lactam aryl moieties described, either alone or
`with various substituents, contain from 6 to 15 carbon
`atoms and include phenyl, a-naphthy! or B-naphthy],
`etc. Substituents include alkanoxy, protected hydroxy,
`halogen, alkyl, aryl, alkenyl, acyl, acyloxy, nitro,
`amino, amido, etc. Phenyl is the more preferred aryl.
`As noted above, R of £-lactam (2) may be -OR¢ with
`Re being alkyl, acyl, ethoxyethy! (“EE”), triethylsilyl
`(“TES”), 2,2,2-trichloroethoxymethyl, or other hy-
`droxyl protecting group such as acetals and ethers, i.e.,
`methoxymethy!
`(“MOM”), benzyloxymethyl]; esters,
`such as acetates; carbonates, such as methyl carbonates;
`and alkyl and ary] silyl such as triethylsilyl, trimethyl-
`silyl, dimethyl-t-butylsilyl, dimethylarylsilyl, dimethy]-
`heteroarylsilyl, and triisopropylsily], and the like. A
`variety of protecting groupsfor the hydroxyl group and
`the synthesis thereof may be found in “Protective
`Groups in Organic Synthesis” by T. W. Greene, John
`Wiley and Sons, 1981. The hydroxyl protecting group
`selected should be easily removed under conditions that
`are sufficiently mild, e.g., in 48% HF,acetonitrile, pyri-
`dine, or 0.5% HCl/water/ethanol, and/or zinc, acetic
`acid so as not to disturb the ester linkage or other sub-
`stituents of the taxol intermediate.
`Also as noted previously, R7 may be a sulfhydryl
`protecting group and Rg maybe an amine protecting
`group. Sulfhydryl protecting groups include hemithioa-
`cetals such as 1-ethoxyethyl and methoxymethy], thio-
`esters, or thiocarbonates. Amine protecting groupsin-
`clude carbamates, for example, 2,2,2-trichloroethylcar-
`bamate or tertbutylcarbamate. A variety of sulfhydryl}
`and amine protecting groups may be found in the
`above-identified text by T. W. Greene.
`The £-lactams(2) can be prepared from readily avail-
`able materials, as is illustrated in schemes A and B be-
`low:
`
`10
`
`15
`
`25
`
`30
`
`35
`
`45
`
`50
`
`Scheme A
`
`OCH3
`
`CH30.
`
`

`

`7
`
`5,229,526
`
`-continued
`
`8
`
`i
`
`Ar
`
`5
`|
`
`ae?
`“OEE
`
`<—
`
`HL
`
`Ar*
`
`y
`_|
`
`2°
`“OEE
`
`HL
`y 2°
`,
`<<_ |
`Ar”
`“OAc
`
`Scheme B
`
`
`
`OLi
`?
`H
`=
`(
`
`
`TESO ort —>|TEsO OEt Nn 2?
`*
`_|
`\;
`‘Tt
`
`ArCHO
`
`N“TMS 1
`[
`i> Ar
`
`OTES
`
`Ar
`
`oO
`ll
`
`Ar
`
`“OTES
`
`reagents: (a) triethylamine, CH2Cl2, 25° C., 18 h; (b) 4
`equiv ceric ammonium nitrate, CH3CN, —10° C., 10
`min; (c) KOH, THF, H20,0° C., 30 min; (d) ethyl vinyl
`ether, THF, toluene sulfonic acid (cat.), 0° C., 1.5 h;(e)
`n-butyllithium, ether, —78° C., 10 min; benzoyl chlo-
`ride, —78° C., 1 h; (f) lithium diisopropy! amide, THF
`—78° C. to —50° C.; (g) lithium hexamethyldisilazide,
`THF —78° C. to 0° C.; (h) THF, —78° C. to 25° C., 12
`h.
`
`In
`The starting materials are readily available.
`scheme A, a-Acyloxy acetyl chloride is prepared from
`glycolic acid, and, in the presence of a tertiary amine,it
`cyclocondenses with imines prepared from aldehydes
`and p-methoxyaniline to give 1-p-methoxyphenyl-3-
`acyloxy-4-arylazetidin-2-ones. The p-methoxyphenyl
`group can be readily removed through oxidation with
`ceric ammonium nitrate, and the acyloxy group can be
`hydrolyzed under standard conditions familiar to those
`experiencedin the art to provide 3-hydroxy-4-arylazeti-
`din-2-ones. The 3-hydroxyl group is protected with
`l-ethoxyethyl, but may be protected with variety of
`standard protecting groups such as the triethylsilyl
`group orothertrialky] (or aryl) silyl groups. In Scheme
`B, ethyl-a-triethylsilyloxyacetate is readily prepared
`from glycolic acid.
`The racemic 8-lactams may be resolved into the pure
`enantiomersprior to protection by recrystallization of
`the corresponding 2-methoxy-2-(trifluoromethy!) phen-
`ylacetic esters. However, the reaction described herein-
`below in which the 8-amidoester side chain is attached
`has the advantage of being highly diastereoselective,
`thus permitting the use of a racemic mixture of side
`chain precursor.
`The 3-(1-ethoxyethoxy)-4-phenylazetidin-2-one of
`Scheme A and the 3-(1-triethylsily])-4-phenylazetidin-
`2-one of Scheme B can be converted to B-lactam (2), by
`treatment with a base, preferably n-butyllithium, and an
`acy! chloride, sulfonyl chloride, phosphinyl chloride,
`phosphoryl chloride or an alkyl chloroformate at — 78°
`C.orless.
`Preferably, the metal alkoxides are prepared by react-
`ing an alcohol having two to four rings of the taxane
`nucleus and a C-13 hydroxyl] group with an organome-
`tallic compoundin a suitable solvent. Most preferably,
`
`30
`
`35
`
`45
`
`55
`
`60
`
`65
`
`CsH5N
`30
`
`the alcohol is a protected baccatin III, in particular,
`7-O-triethylsilyl baccatin IIT (which can be obtained as
`described by Greene,et al. in JACS 110, 5917 (1988) or
`by other routes) or 7,10-bis-O-triethylsilyl baccatin III.
`As reported in Greeneet al., 10-deacetyl baccatin II
`is converted to 7-O-triethylsilyl-10-deacetyl baccatin
`III according to the following reaction scheme:
`
`.HO
`
`oO
`
`(C2H5)3SiCl
`
`(4a)
`
`Underwhatis reported to be carefully optimized condi-
`tions, 10-deacety] baccatin II] is reacted with 20 equiva-
`lents of (C2Hs)3SiCl at 23° C. under an argon atmo-
`sphere for 20 hours in the presence of 50 ml of pyridi-
`ne/mmol of 10-deacety] baccatin IN to provide 7-trie-
`thylsilyl-10-deacety] baccatin III (4a) as a reaction
`product in 84-86% yield after purification.
`The reaction product (4a) is then acetylated with 5
`equivalents of CH3COCI and 25 mLof pyridine/mmol
`of 4a at 0° C. under an argon atmosphere for 48 hours to
`provide 86% yield of 7-O-triethylsily] baccatin HI (4b)
`as reported by Greene,et al. in JACS 110, 5917 at 5918
`(1988).
`
`

`

`5,229,526
`
`9
`Alternatively, 7-triethylsilyl-10-deacetyl baccatin III
`(4a) can be protected at C-10 oxygen with an acid labile
`hydroxyl protecting group. For example, treatment of
`(4a) with n-butyllithium in THF followed by triethylsi-
`lyl chloride (1.1 mol equiv.) at 0° C. gives 7,10-bis-O-
`triethyisilyl baccatin HE (4c) in 95% yield. Also, (4a)
`can be converted to 7-O-treithylsilyl-10-(1-ethoxyethy])
`baccatin IE] (4d) in 90% yield by treatment with excess
`ethyl vinyl ether and a catalytic amount of methane
`sulfonic acid. These preparations are illustrated in the 10
`reaction scheme below.
`
`5
`
`CH3CH2CH2CH)Li + HO-
`
`10
`
`z
`
`CH3
`
` CH3 pccHs)s
`
`OCOCsHs
`
`
`
`OSi(C2Hs)3
`HO om
`
`
`
`? OCcOcH; ©
`OCOC.Hs
`
`(4b)
`
`CH:COCI_
`
`/CsHsN
`
`OSi(C2H5)3
`oO
`
`4a
`
`n-Buli
`(GHeysicr > HO
`
`(4c)
` OSi(C2H5)3
`
`(CAT)CH3S03H \C2H30C2H5
`
`(4d)
`
`The 7-O-triethylsily] baccatin ITI derivatives (4b, 4c
`or 4d) are reacted with an organometallic compound
`such as n-butyllithium in a solvent such as tetrahydrofu- 65
`ran (THF), to form the metal alkoxide 13-O-lithium-7-
`O-triethylsily! baccatin II derivative (5b, 5c or 5d) as
`shownin the following reaction scheme:
`
`

`

`3,229,526
`
`11
`-continued
`
`CH3
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`30
`
`55
`
`65
`
`CH3CH2CH2CH3 + LiO--
`
`(5b) Z = —OCOCH3
`(Sc) Z = —OSi(C2H5)3
`(5d) Z = —OEE
`
` OH i
`
`.
`
`»
`/
`;
`ococH; °
`|
`OCOCEHs
`
`As shownin the following reaction scheme, the 13-O-
`lithium-7-O-triethylsilyl baccatin If] derivative (5b, 5c,
`or 5d) reacts with 8-lactam (2) to provide an intermedi-
`ate (6b, 6c, or 6d) in which the C-7 and C-2’ hydroxyl
`groups are protected with a triethylsily] group. The
`triethylsily] and ethoxyethyi groups are then hydro-
`lyzed under mild conditions so as not to disturb the ester
`linkage or the taxane substituents.
`The 7-O-triethylsilyl baccatin III derivatives (4b, 4c
`or 4d) are reacted with an organometallic compound
`such as n-butyllithium in a solvent such as tetrahydrofu-
`tan (THF), to form the metal alkoxide 13-O-lithium-7-
`O-triethylsilyl baccatin III derivative (5b, 5c or 5d) as
`shownin the following reaction scheme:
`
`CH3CH2CH)>CH2Li + HO--
`
`
`
`CH3 pcrtishs
`
`
` OH
`
`i
`»
`~¢
`i;
`=o
`;
`| OCOcH;
`OCOC56H5
`
`rn
`
`z
`
`CH
`
`oO
`
`4 CH3 OSi(C2H5)3
`
`ii
`
`.i
`
`f
`! OCOCH;
`OCOC.6Hs
`(5b) Z = —OCOCHS
`(Sc) Z = —OSi(C2Hs)a
`(5d) Z = —OEE
`
`CH3CH2CH2CH3 + LiO--
`
`As shownin the following reaction scheme, the 13-O-
`lithium-7-O-triethylsily] baccatin HI derivative (5b, 5c,
`or 5d) reacts with 8-lactam (2) to provide an intermedi-
`ate (6b, 6c, or 6d) in which the C-7 and C-2’ hydroxyl
`groups are protected with a triethylsilyl group. The
`triethylsilyl and ethoxyethyl groups are then hydro-
`lyzed under mild conditionsso as not to disturb the ester
`linkage or the taxane substituents.
`
`12
`
`
`
`
`
`b-d
`
`ZZ
`
`= —OCOCH3
`=
`= OSi(C2H5)3
`Z=
`—OEE
`
`6 b
`
`,
`c,
`d,
`
`wherein Tj is a hydroxy protecting group; M is a metal;
`Ph is phenyl]; Ac is acetyl; and Rj to Rs are as previously
`defined.
`Metal substituent, M, of metal alkoxide (3) is a Group
`IA,ITA,IIA,lanthanide or actinide elementora transi-
`tion, Group IIIA, IVA, VA or VIA metal. Preferably,
`it is a Group IA, IIA ortransition metal, and most pref-
`erably, it is lithium, magnesium, sodium, potassium or
`titanium.
`Both the conversion of the alcohol to the metal alkox-
`ide and the ultimate synthesis of the taxane derivative
`can take place in the same reaction vessel. Preferably,
`the 8-lactam is added to the reaction vessel after forma-
`tion therein of the metal alkoxide.
`The organometallic compound n-butyllithium is pref-
`erably used to convert baccatin III or 10-deacetyl bac-
`catin III to the corresponding metal alkoxide, but other
`sources of metallic substituent such as lithium diisopro-
`pyl amide, other lithium or magnesium amides, ethy]-
`magnesium bromide, methylmagnesium bromide, other
`organolithium compounds, other organomagnesium
`compounds, organosodium, organotitanium or or-
`ganopotassium may also be used. Organometallic com-
`pounds are readily available, or may be prepared by
`available methods including reduction of organic ha-
`lides with metal. For example, buty] bromide can be
`reacted with lithium metal in diethyl ether to give a
`solution of n-butyllithium in the following manner:
`
`CH3CH2CH2CH)Br + 2Li =o CH3CH)CH)CH2Li + LiBr
`
`

`

`5,229,526
`
`13
`Although THFis the preferred solvent for the reac-
`tion mixture, other ethereal solvents, such as dimeth-
`oxyethane, or aromatic solvents ‘mayalso be suitable.
`Certain solvents, including some halogenated solvents
`and somestraight-chain hydrocarbons in which the
`reactants are too poorly soluble, are not suitable. Other
`solvents are not appropriate for other reasons. For ex-
`ample, esters are not appropriate for use with certain
`organometallic compoundssuch as n-butyllithium due
`to incompatibility therewith.
`Although the reaction scheme disclosed herein is
`ideally directed to the synthesis of taxol, taxotere, and
`other taxane derivatives exemplified herein, it can be
`used with modifications in either the B-lactam or the
`tetracyclic metal alkoxide to produce other compounds.
`Thus, the B-lactam and the tetracyclic metal alkoxide
`can be derived from natural or unnatural sources, to
`prepare other synthetic taxols,
`taxol derivatives, 10-
`deacetyltaxols, and the enantiomers and diastereomers
`thereof contemplated within the present invention.
`The process of the invention also has the important
`advantage of being highly diastereoselective. Therefore
`racemic mixtures of the side chain precursors may be
`used. Substantial cost savings may be realized because
`there is no need to resolve racemic £-lactamsinto their
`pure enantiomers. Additional cost savings may bereal-
`ized becauseless side chain precursor,e.g., 60-70% less,
`is required relative to prior processes.
`The following examples illustrate the invention.
`EXAMPLE1
`
`Preparation of 2'-ethoxyethyl-7-triethylsilyl taxol, and
`subsequently taxol, from racemic B-lactam
`To a solution of 7-triethylsily] baccatin ITI (20 mg,
`0.028 mmol) in 1 ml of THF at —78° C. was added
`dropwise 0.17 ml of a 0.164M solution of nBuLiin hex-
`ane. After 30 min at —78° C., a solution of cis-1-benz-
`oy]-3-(1-ethoxyethoxy)-4-phenylazetidin-2-one’
`(47.5
`mg, 0.14 mmol) in 1 ml of THF was added dropwise to
`the mixture. The solution was allowed to slowly warm
`(over 1.5 h) to 0° C. and wasthenstirred at 0° C. for 1
`h and 1 mi of a 10% solution of ACOH in THF was
`added. The mixture was partitioned between saturated
`aqueous NaHCO; and 60/40 ethyl acetate/hexane.
`Evaporation of the organic layer gave a residue which
`was purified by flash chromatography to give 23 mg
`(80%) of (2’R,3’S)-2’-ethoxyethyl-7-triethylsilyl
`taxol
`and 3.5 mg 13%) of 2',3’-epi(2’S,3’R)-2'-ethoxyethy]-7-
`triethylsily] taxol.
`A 5 mg sample of (2’R,3’S)-2'-ethoxyethyl-7-triethyl-
`silyl taxol wasdissolved in 2 ml ofethanol, and 0.5 ml of
`0.5% aqueous HCI solution was added. The mixture
`wasstirred at 0° C. for 30 h and diluted with 50 ml of
`ethyl acetate. The solution was extracted with 20 ml of
`saturated aqueous sodium bicarbonate solution, dried
`over sodium sulfate and concentrated. The residue was
`purified by flash chromatography to provide 4.5 mg
`(ca.90%) taxol, which was identical with an authentic
`sample in all respects.
`A 5 mg sample of 2’,3'-epi(2’S,3’R)-2'’-ethoxyethy!-7-
`triethylsily! taxol was dissolved’ in 2 ml of ethanol and
`0.5 ml of 0.5% aqueous HCl solution was added. The
`mixture wasstirred at 0° C. for 30 h and diluted with 5
`ml of ethyl acetate. The solution was extracted with 20
`ml of saturated aqueous sodium bicarbonate solution,
`dried over sodium sulfate and concentrated. The resi-
`
`14
`due was purified by flash chromatography to provide
`4.5 mg (ca.90%) of 2’,3'-epitaxol.
`EXAMPLE2
`
`Preparation of 2’,7-(bis)triethylsily] taxol, and
`subsequently taxol, from racemic. B-lactam
`To a solution of 7-triethylsilyl baccatin IIT (100 mg,
`0.143 mmol) in 1 ml of THF at —45° C. was added
`dropwise 0.087 ml of a 1.63M solution of nBuLiin hex-
`ane. After I h at —45° C., a solution of cis-1-benzoyl-3-
`triethylsilyloxy)-4-phenylazetidin-2-one (274 mg, 0.715
`mmol) in 1 ml of THF was added dropwise to the mix-
`ture. The solution was allowed to warm to 0° C. and
`held at 0° C. for 1h. One ml of a 10% solution of ACOH
`in THF was added. The mixture waspartitioned be-
`tween saturated aqueous NaHCO; and 60/40 ethyl
`acetate/hexane. Evaporation of the organic layer gave
`a residue which was purified by flash chromatography
`followed by recrystallization to give 131 mg (85%) of
`(2'R,3'S)-2',7-(bis)triethylsilyl taxol and 15 mg (10%) of
`2',3'-epi(2'S,3’R)-2',7-(bis)triethylsily! taxol.
`To a solution of 121.3 mg (0.112 mmol) of (2’R,3’S)-
`2',7-(bis)triethylsilyE taxol in 6 ml] of acetonitrile and 0.3
`ml of pyridine at 0° C. wasadded 0.9 ml of 48% aqueous
`HF. The mixture was stirred at 0° C. for 8 h, then at 25°
`C. for 6 h. The mixture was partitioned between satu-
`rated aqueous sodium bicarbonate and ethyl acetate.
`Evaporation of the ethyl acetate solution gave 113 mg
`of material which was purified by flash chromatogra-
`phy and recrystallization to give 94 mg (98%) taxol,
`which was identical with an authentic sample in all
`respects.
`To a solution of 5 mg of (2’R,3’S)-2',7-(bis)triethylsi-
`ly! taxol] in 0.5 ml of acetonitrile and 0.03 ml of pyridine
`at O° C. was added 0.09 mi of 48% aqueous HF. The
`mixture wasstirred at 0° C. for 8 h, then at 25° C.for 6
`h. The mixture waspartitioned between saturated aque-
`ous sodium bicarbonate and ethy! acetate. Evaporation
`of the ethyl acetate solution gave 5 mg of material
`which was purified by flash chromatography and re-
`crystallization to give 4.6 mg (ca.95%)of 2',3’-epitaxol.
`EXAMPLE3
`
`Preparation of taxotere
`To a solution of 7,10-bis-triethylsilyl baccatin ITI (200
`mg, 0.248 mmol)) in 2 mL of THF at —45° C. was
`added dropwise 0.174 mL of a 1.63M solution of nBuLi
`in hexane. After 0.5 h at —45° C., a solution of cis-1-
`(tert-butoxycarbony])-3-triethylsilyloxy-4-phenylazeti-
`din-2-one (467 mg, 1.24 mmol) in 2 mL of THF was
`added dropwise to the mixture. The solution was
`warmed to 0° C, and kept at that temperature for 1 h
`before 1 mL of a 10% solution of ACOH in THF was
`added. The mixture was partitioned between saturated
`aqueous NaHCO; and 60/40 ethyl acetate/hexane.
`Evaporation of the organic layer gave a residue which
`was purified by filtration throughsilica gel to give 280
`mg of crude 2',7,10-tris-triethylsilyl taxotere.
`To a solution of 280 mg ofthe crude product obtained
`from the previous reaction in 12 mL of acetonitrile and
`0.6 mL of pyridine at 0° C. was added 1.8 mL of 48%
`aqueous HF. The mixture was stirred at 0° C. for 3 h,
`then at 25° C. for 13 h, and partitioned between satu-
`rated aqueous sodium bicarbonate and ethyl acetate.
`Evaporation of the ethyl acetate solution gave 215 mg
`of material which was purified by flash chromatogra-
`phy to give 190 mg (95%) of taxotere, which wasre-
`
`10
`
`15
`
`25
`
`30
`
`45
`
`60
`
`65
`
`

`

`15
`crystallized from methanol/water. All analytical and
`spectral data were identical with that reported for tax-
`otere in U.S. Pat. No. 4,814,470.
`
`EXAMPLE4
`
`
`
`wherein Np? is
`
`Preparation of 3’-desphenyl-3’-(2-naphthyl) taxol
`To a solution of 7-triethylsilyl baccatin III (200 mg,
`0.286 mmol) in 2 mL of THF at —45° C. was added
`dropwise 0.174 mL of a 1.63M solution of nBuLi in
`hexane. After 0.5 h at —45° C., a solution ofcis-1-benz-
`oyl-3-triethylsilyloxy-4-(2-naphthy])azetidin-2-one (620
`mg, 1.43 mmol) in 2 mL of THF was added dropwise to
`the mixture. The solution was warmed to 0° C. and kept
`at that temperature for 1 h before 1 mL of a 10% solu-
`tion of AcOH in THF was added. The mixture was
`partitioned between saturated aqueous NaHCO3 and
`60/40 ethyl acetate/hexane. Evaporation of the organic
`layer gave a residue which was purified by filtration
`throughsilica gel to give 320 mg of a mixture contain-
`ing
`(2'R,3’S)-2',7-(bis)triethylsilyl-3’-desphenyl-3'-(2-
`naphthyl) taxol and a small amount of the (2’'S,3’R)
`isomer.
`To a solution of 320 mg (0.283 mmol) of the mixture
`obtained from the previous reaction in 18 mL ofaceto-
`nitrile and 0.93 mL of pyridine at 0° C. was added 2.8
`mL of 48% aqueous HF. The mixture wasstirred at 0°
`C. for 3 h, then at 25° C. for 13 h, and partitioned be-
`tween saturated aqueous sodium bicarbonate and ethyl
`acetate. Evaporation of the ethyl acetate solution gave
`255 mg of material which was purified by flash chroma-
`tography to give 166 mg (64%) of 3’-desphenyl-3'-(2-
`naphthyl) taxol, which was recrystallized from me-
`thanol/water.
`,
`m.p 164°-165° C.; [a]25~q—52.6° (c 0.005, CHCls).
`1H NMR (CDCh, 300 MHz) 88.14 (d, J=7.3 Hz, 2H,
`benzoate ortho), 7.96 (m, 1H, aromatic), 7.90 (m, 1H,
`aromatic), 7.85 (m, 2H, aromatic), 7.76 (m, 2H, aro-
`matic), 7.60 (m, 3H, aromatic), 7.52 (m, 4H, aromatic),
`7.41 (m, 2H, aromatic), 7.01 (d, J=8.8 Hz, 1H, NH),
`6.27 (s, 1H, H10), 6.26 (dd, J=9.2, 9.2 Hz, 1H, H13),
`5.97 (dd, J=8.8, 2.5 Hz, 1H, H3’), 5.68 (d, J=7.1 Hz,
`1H, H2 £), 4.93 (m, 1H, H5), 4.92 (m, fH, H2’), 4.39 (m,
`1H, H7), 4.30 (d, J=8.5 Hz, 1H, H20 a), 4.20 (d, J=8.5
`Hz, 1H, H20 §), 3.81 (d, J=7.1 Hz, 1H, H3), 3.60 (d,
`J=5 Hz, 1H, 2’'OH), 2.48 (m, 1H, H6 a), 2.45 (br, 1H, 7
`OH), 2.39 (s, 3H, 4Ac), 2.30 (m, 2H, H14), 2.24 (s, 3H,
`10Ac), 1.83 (m, 1H, H6 £8), 1.82 (brs, 3H, Me18), 1.68 (s,
`
`5,229,526
`
`16
`1H, 10H), 1.68 (s, 3H, Me19), 1.24 (s, 3H, Me17), 1.14 (s,
`3H, Mel6).
`
`EXAMPLE5
`
`
`
`wherein Np}is
`
`Preparation of 3'-desphenyl-3'-(i-naphthy]) taxol
`To a solution of 7-triethylsily! baccatin III (200 mg,
`0.286 mmol) in 2 mL of THF at —45° C. was added
`dropwise 0.174 mL of a 1.63M solution of nBuLi in
`hexane. After 0.5 h at —45° C., a solution ofcis-1-benz-
`oyl-3-triethylsilyloxy-4-(1-naphthyl)azetidin-2-one (620
`mg, 1.43 mmol) in 2 mL of THF was added dropwise to
`the mixture. The solution was warmedto 0° C. and kept
`at that temperature for 1 h before 1 mL of a 10% solu-
`tion of AcOH in THF was added. The mixture was
`partitioned between saturated aqueous NaHCO; and
`60/40 ethyl acetate/hexane. Evaporation of the organic
`layer gave a residue which was purified by filtration
`throughsilica gel to give 325 mg of a mixture contain-
`ing
`(2'R,3’S)-2',7-(bis)triethylsilyl-3'-despheny]-3’-(1-
`naphthyl) taxol and a small amount of the (2’S,3’R)
`isomer.
`To a solution of 325 mg (0.287 mmol) of the mixture
`obtained from the previous reaction in 18 mL of aceto-
`nitrile and 0.93 mL of pyridine at 0° C. was added 2.8
`mL of 48% aqueous HF. The mixture wasstirred at 0°
`C. for 3 h, then at 25° C. for13 h, and partitioned be-
`tween saturated aqueous sodium bicarbonate and ethyl
`acetate. Evaporation of the ethyl acetate solution gave
`260 mg of material which was purified by flash chroma-
`tography to give 166 mg (64%)of 3’-(1-naphthy])taxol,
`which was recrystallized from methanol/water.
`m.p. 164°-165° C.; [a]25n4—52.6° (c 0.005, CHCIs).
`1H NMR (CDCl3, 300 MHz) 68.11 (d, J=7.1 Hz, 2H,
`benzoate ortho), 8.11 (m