US005319112A
`United States Patent 19
`5,319,112
`[11] Patent Number:
`
`[45] Date of Patent: Jun. 7, 1994
`Kingston et al.
`
`AUNAAA
`
`(54 METHOD FOR THE CONVERSION OF
`CEPHALOMANNINE TO TAXOL AND FOR
`THE PREPARATION OF N-ACYL ANALOGS
`OF TAXOL
`
`[75]
`
`Inventors: David G. I. Kingston, Blacksburg;
`Anthony A. Molinero,
`Christiansburg, both of Va.
`
`(73] Assignee:
`
`Virgnia Tech Intellectual Properties,
`Inc., Blacksburg, Va.
`
`[21] Appl. No.: 931,319
`
`[22] Filed:
`Aug. 18, 1992
`[51]
`Tint, C05 ooocccsesssssesssssessscssesssssssssesseee C07D 305/14
`[52] U.S. CU. ceccssssseseesssssccsssenssaseseseee 549/510; 549/511
`[58] Field of Search ......ccsssssssssssssesssseeee 549/510, 511
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`......cess 349/510
`6/1980 Miller et al.
`4,206,221
`3/1989 Colin etal. ......
`sees
`.- 549/510
`4,814,470
`8/1989 Colin etal.......
`w+ 549/510
`4,857,653
`5/1990 Colin et al.
`.» 549/510
`4,924,012
`
`5/1991 Holton......
`.. 549/510
`5,015,744
`
`5,059,699 10/1991 Kingston et
`....ssesseree 549/510
`al.
`
`FOREIGN PATENT DOCUMENTS
`
`0400971 12/1990 European Pat. Off.
`
`.
`
`OTHER PUBLICATIONS
`
`Kingston et al., “The Chemistry of Taxol, A Clinically
`Useful, Anti-Cancer Agent”, J. Nat. Prod., 53, 1-12
`(1990).
`Deutschet al., “Synthesis of Congeners and Prodrugs3.
`Water-Soluble Prodrugs of Taxol With Potent Antitu-
`mor Activity”, J. Med. Chem., 32,788-792 (1989).
`Mangatalet al., “Application of the Vicinal Oxyamina-
`tion Reaction with Asymmetric Induction to the Hemi-
`synthesis of Taxol and Analogues”, Tetrahedron, 45,
`4177-4190 (1989).
`Deniset al., “A Highly Efficient, Practical Approach to
`Natural Taxol’, J. Am. Chem. Soc., 110, 5917-5919
`(1988).
`Magri et al., J. Org. Chem., 51, 30-39, (1986).
`Mathewetal., ‘Synthesis and Evaluation of Some Wa-
`ter-Soluble Prodrugs and Derivatives of Taxol with
`Tease
`
`Antitumor Activity”, J. Med. Chem., 35, 145-151
`(1992).
`Swindell et al., “Biologically Active Taxol Analogs
`With Deleted A-Ring Side-Chain Substituents and
`Variable C-2' Configurations”, J. Med. Chem., 34,
`1176-1184 (1991).
`Powell et al., “Cephalomannine; A New Antitumor
`Alkaloid for Cephalotaxus manni?’, Chem. Comm.,
`102-104 (1979).
`McGuireet al., “Taxol: A Unique Antineoplastic Agent
`with Significant Activity in Advanced Ovarian Epithe-
`lial Neoplasms”, Ann. Int. Med., 111, 273-279 (1989).
`Holmeset al., “Phase II Trial of Taxol, an Active Drug
`in the Treatment of Metastatic Breast Cancer”, J. Nat.
`Can. Inst., 24, 1791-1805 (1991).
`Rowinskyet al., “Taxol: Twenty Years Later, the Story
`Unfolds”, J. Nat. Can. Inst., 24, 1778-1781 (1991).
`Gueritte-Voegelein et
`al.,
`“Chemical Studies of
`10-Deacety! Baccatin III. Hemisynthesis of Taxol De-
`rivatives”, Tetrahedron, 42, 4451-4460 (1986).
`Kingston, “The Chemistry of Taxol”, Pharmac. Ther.,
`52, 1-34 (1991).
`(List continued on next page.)
`
`Primary Examiner—C. Warren Ivy
`Assistant Examiner—Ba K. Trinh
`Attorney, Agent, or Firm—Mason, Fenwick & Lawrence
`
`ABSTRACT
`[57]
`The natural product cephalomannine can be converted
`to the important anticancer natural product taxol by a
`simple process involving the steps of hydrogenation,
`benzoylation at the C-2'-position, protection of the C-7
`position, and reaction with oxaly! chloride, followed by
`reaction with diphenylcarbodiimide and deprotection.
`The same process can be applied to mixtures of taxol
`and cephalomannine, thus obviating the need for the
`separation of these closely related compounds. In addi-
`tion, the selection of an acylating reagent other than the
`benzoyl group allows the preparation of taxol analogs
`with other N-acyl] substituents.
`
`12 Claims, 6 Drawing Sheets
`
`Sanofi Exh. 2004
`Neptunev. Aventis
`IPR2019-00136
`
`Sanofi Exh. 2004
`Neptune v. Aventis
`IPR2019-00136
`
`

`

`5,319,112
`
`Page 2
`
`OTHER PUBLICATIONS
`
`Ringel et al., “Studies with RP 56976 (Taxotere): A
`Semisynthetic Analogue of Taxol”, J. Nat. Can., Inst.,
`4, 288-291 (1991).
`Gueritte-Voegelein et al., “Relationships Between the
`Structure of Taxol Analogues and Their Antimitotic
`Activity”, J. Med. Chem., 34, 992-998 (1991).
`
`Miller et al., “Antileukemic Alkaloids from Taxus Wal-
`lichiana Zucc.”, J. Org. Chem., 46, 1469-1474 (1981).
`Shiozaki et al., “Cleavage and Some Modifications of
`the 7-Amide Group of the Cephamycins”, Tetrahe-
`dron, 36, 2735-2740 (1980).
`Shiozaki et al., “A New Method for Cleavage 7-Amide
`Group of Cephalosporins”, Tetrahedron Lett., 46,
`4059-4062 (1977).
`
`

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`U.S.PatentJune7,1994Sheet4of65,319,112
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`U.S.PatentJune7,1994Sheet6of65,319,112
`
`
`

`

`1
`
`5,319,112
`
`METHOD FOR THE CONVERSION OF
`
`CEPHALOMANNINE TO TAXOL AND FOR THE
`
`PREPARATION OF N-ACYL ANALOGS OF TAXOL
`
`FIELD OF THE INVENTION
`
`The present invention relates to taxol, taxol conge-
`ners, taxol analogues, and methods for making same.
`The invention relates more particularly to the synthesis
`of taxol or taxol congeners from natural products hav-
`ing portions of the taxol structure.
`
`BACKGROUNDOF THE INVENTION
`
`Taxol is a naturally occurring diterpenoid which has
`
`demonstrated great potential as an anti-cancer drug.
`Taxol, shown below as compound1, can be isolated
`from the bark of the western yew, Taxus brevifolia, and
`is also found in several other yew species such as 7.
`baccata and T. cuspidata. For further information re-
`garding taxol,
`see Kingston et al., U.S. Pat. No.
`5,059,699. Ail patents, articles, and other documents
`cited herein are incorporated by reference as if repro-
`duced in ful! below.
`
`
`
`15
`
`25
`
`30
`
`Since taxol is very scarce, a procedure to make taxol
`from cephalomannine would prove valuable becauseit
`would increase the supply of taxol, while also avoiding
`the need to separate cephalomannine from taxol.
`No previous work on a direct conversion of cephalo-
`mannineto taxol has been reported. An indirect route is
`available through the work of Magri et al., in Journal of
`Organic Chemistry, Vol. 51, p. 3239, 1986, who reported
`that taxol can be converted to baccatin JII, shown
`below as compound 3, by treatment with tetrabutylam-
`monium borohydride in dichloromethane. It has been
`surprisingly discovered that this process works equally
`well with cephalomannine, so a pathway exists to pre-
`pare baccatin III 3 from cephalomannine.
`
`
`
`oO
`
` HO
`
`=
`:
`OH : =. 0
`Oo
`i
`x
`
`ZO
`
`. CH
`ql
`Oo
`
`Taxol almost always co-occurs with the closely re-
`lated compound cephalomannine, shown below as com-
`pound 2. Due to their close structural similarity, the
`separation of taxol from cephalomannineis a very diffi-
`‘cult one. See Waniet al., “Plant Antitumor Agents. VI.
`The Isolation and Structure of Taxol, A Novel Antileu-
`kemic and Antitumor Agent from Taxus brevifolia,” J.
`Am. Chem. Soc. 93, 2325(1971); Powell et al., “Cephalo-
`mannine; A New Antitumor Alkaloid from Ceph-
`alotaxus mannii,” J. Chem. Soc. Chem. Commun.
`
`102(1979); Miller et al., ‘““Antileukemic Alkaloids from
`Taxus wallichiana Zucc,” J. Org. Chem. 46, 1469(1981).
`
`50
`
`55
`
`65
`
`Baccatin III 3 can be converted to taxol by one of
`several published pathways. See Hoiton, R., “Method
`for Preparation of Taxol Using an Oxazinone,” U.S.
`Pat. No. 5,015,744; Denis et al., “Highly Efficient Prac-
`tical Approach to Natural Taxol,” J. Am. Chem. Soc.
`110, 5917(1988); Mangatal et al., “Application of the
`Vicinal Oxyamination Reaction with Asymmetric In-
`duction to the Hemisynthesis of Taxol and Analogues,”
`Tetrahedron 45, 4177(1989).
`Hence, cephalomannine can be converted to taxol
`through baccatin II 3, by treatment of cephalomannine
`with, by way of non-limiting example, tetrabutylam-
`monium borohydride in the presence of dichlorometh-
`ane. However,this process requires the synthesis of the
`B-phenylisoserine side-chain of taxol
`in enantiomeri-
`cally pure form, and the coupling of the side-chain to
`baccatin III 3 does not proceed quantitatively.
`Because of the promising clinical activity of taxol
`against various types of cancer, the preparation of ana-
`logues of taxol is an important endeavor, especially in
`
`

`

`3
`view of the previously mentioned limited supply of
`taxol. See McGuire et al., “Taxol: A Unique Antineo-
`plastic Agent with Significant Activity in Advanced
`Ovarian Epithelial Neoplasms,” Ann. Intern. Med. 111:
`273-279 (1989); Holmesetal., “Phase II Trials of Taxol,
`an Active Drug in the Treatment of Metastatic Breast
`Cancer,” J. Natl. Cancer Inst. 83: 1797-1805 (1991).
`It is believed that the preparation of taxol analogues
`will result in the synthesis of compounds with compara-
`ble or greater potency than taxol (thus reducing the
`need for the drug), superior bioavailability, or having
`less undesirable side effects. Indeed, the synthesis of the
`taxol analogue taxotere, which differs from taxol only in
`the nature of the N-acy] substituent and the absence of
`the 10-acetyl group,
`indicates the usefulness of this
`approach, since taxotere is reported to be approxi-
`mately twice as active as taxol in someassays (although
`taxol is believed to be moreeffective in other systems
`than taxotere). See Guéritte-Voegelein et al., “Chemical
`Studies of 10-Deacetylbaccatin III. Hemisynthesis of
`Taxol Derivatives,” Tetrahedron 42: 4451-4460 (1986);
`Ringel et al., “Studies with R P56976 (Taxotere) A
`Semisynthetic Analogue of Taxol,” J. Natl Cancer Inst.
`83:288-291 (1991).
`A large number of taxol analogs have antitumor
`properties as shownbytheir ability to inhibit the disas-
`sembly of microtubules. See “Relationships between the
`Structure of Taxol Analogues and Their Antimitotic
`Activity,” Journal of Medicinal Chemistry, Vol. 34, pp.
`992-998 (1991); “Biologically Active Taxol Analogues
`with Deleted A-Ring Side Chain Substituents and Vari-
`able C-2' Configurations,” Journal ofMedicinal Chemis-
`try, Vol. 34, pp. 1176-1184, (1991); “Synthesis and Eval-
`uation of Some Water-Soluble Prodrugs and Deriva-
`tives of Taxol with Antitumor Activity,” Journal of 35
`Medicinal Chemistry, Vol. 35, pp. 145-151, (1992). The
`foregoing articles demonstrate the effectiveness of taxol
`analogs as antitumor agents.
`There is also a need for a method to quickly deter-
`mine the biological activities of new compounds or
`pharmaceutical compounds having bioactivities or
`structures similar to taxol. The short supply and expense
`of taxol makes impractical the use of taxol as a standard
`in determining the bioactivities of other compounds;
`thus, it is highly desirable that a range of other stan-
`dards with known biological activities be available to
`determine the bioactivity of taxol derivatives and other
`compoundsrelative to taxol. Useful standards should be
`derivatives of taxol, or the standards should be com-
`pounds which have similar structures to taxol, but
`which are more readily available or which can be syn-
`thesized easier than taxol. At present, some derivatives,
`which do not exhibit the same high biological activity
`as taxol, are thrown away; this waste would be elimi-
`nated by a method which usestaxol derivatives, which
`havesignificantly less biological activity than taxol, as
`standards in bioactivity testing, rather than utilizing
`more taxol, which is already in short supply and very
`expensive. Further, it is critical in the commercial ex-
`ploitation of taxol and taxol congeners that the efficacy
`of taxol and taxol congeners designated for commercial
`sale be subjected to rigid quality standards. It is un-
`desireable to use taxol in quality testing due to its short
`supply, and therefore, it is desirable to develop quality
`or activity screening protocols whichutilize taxol ana-
`logs.
`Thus, there is a need for taxol derivatives having a
`range of in vivo and in vitro activities, and there is a
`
`4
`need for taxol derivatives or compoundshaving similar
`biological activities to taxol. There is a corresponding
`need for methods to prepare taxol derivatives and taxol
`congeners.
`There is also a need to prepare taxol from naturally
`occurring mixtures, and more particularly, there is a
`need to convert cephalomannine, or mixtures compris-
`ing cephalomannine, to taxol.
`There is also need for better methods of treating
`cancer, and moreparticularly of treating cancer with
`taxol analogs.
`OBJECTS OF THE INVENTION
`
`Therefore, it is a primary object of the present inven-
`tion to convert cephalomannine, or a mixture compris-
`ing cephalomannine, to taxol.
`It is another object of the present invention to pre-
`pare analogsoftaxol.
`It is a further object of this invention to develop a
`new method for preparing taxol and taxol congeners.
`It is yet another object of the present invention to
`prepare intermediates that can be directly converted to
`taxol or taxol congeners.
`It is a further object of the present invention to use
`taxol analogs to treat cancer.
`It is a still further object of this invention to produce
`taxol from a naturally occurring mixture.
`It is yet another object of the present invention to
`develop taxol analogs suitable for use in commercial
`quality control and screening of taxol and analogs of
`taxol.
`
`SUMMARYOF THE INVENTION
`
`These and other objects are achieved by the present
`invention as more fully described herein by reference to
`preferred non-limiting embodiments. In a first embodi-
`ment, a mixture of cephalomannine 2 and taxol
`1
`is
`converted to taxol
`1 by substituting the 2-methyl-2-
`butenoyl moiety on the C-13 side chain of cephaloman-
`nine with a benzoyl group; more specifically, a pre-
`ferred process comprises the steps of (1) hydrogenation,
`(2) benzoylation, (3) protection of the C-7 hydroxyl
`groupas its trichloroethyloxycarbony] (‘‘troc”) or other
`protecting group (4) reaction with oxalyl chloride fol-
`lowedby addition of water, (5) reaction with diphenyl-
`carbodiimide, and (6) removal of the protective group
`by reduction withzinc and acetic acid (troc) or hydro-
`lysis (TES). In a second embodiment, pure cephaloman-
`nine is converted to pure taxol by the same reaction
`sequence.
`In a third embodiment, either taxol, taxol congeners,
`or cephalomannine can be converted to an N-debenz-
`oyl-N-(alkyloxalate) analog or an N-debenzoyl-N-(N’-
`alkyloxamido) analog or the corresponding aryl analogs
`by the sequence of(1) hydrogenation (if necessary), (2)
`protection of the C-2’ and C-7 hydroxyl groupsas their
`2,2,2-trichloroethyloxycarbonyl (“‘troc”’) or other pro-
`tecting group derivative, and (3) reaction with oxalyl
`chloride followed by the addition of an appropriate
`alcohol or amine. The protective groups can be subse-
`quently removed.
`In a fourth embodiment, either taxol, taxol congeners
`or hydrogenated cephalomannine can be converted to
`any desired N-acyl analog by the sequence of(1) acyla-
`tion with a desired acylation reagent, (2) protection of
`the C-7 hydroxyl group as its 2,2,2-trichloroethylox-
`ycarbonyl (“troc’”’) or other protecting group deriva-
`tive, (3) reaction with oxaly] chloride followed by addi-
`
`5,319,112
`
`20
`
`25
`
`40
`
`45
`
`30
`
`55
`
`60
`
`65
`
`

`

`5
`tion of water, (4) reaction with diphenylcarbodiimide,
`during which the acyl group at C-2' migrates to the
`amino group at the 3’ position, and (5) removal of the
`protective group at C-7.
`In a sixth embodiment an intermediate, useful for its
`ability to be directly converted to taxol or taxol conge-
`ners, can be prepared from taxol, taxol congeners or
`hydrogenated cephalomannine by the sequence of(1)
`acylation, (2) protection of the C-7 hydroxyl group as
`its troc or other protecting group derivative, and (3)
`reaction with oxalyl chloride.
`In a seventh embodiment, anti-neoplastic, N-oxalyl-
`containing taxol derivatives are prepared.
`DEFINITIONS
`
`The terms used herein have the meanings as conven-
`tionally used in the chemical arts, unless the meaning is
`clearly indicated to be otherwise either by context or by
`specific language of the present disclosure. Definitions
`incorporate those used in standard texts, such as but not
`limited to Grant & Hackh’s Chemical Dictionary, Sth
`edition, McGraw-Hill, 1987.
`Taxol analogs are broadiy defined herein as those
`analogs having the basic structure of taxol (see 1),
`which are substituted at the C-2, C-4, C-7, C-10, C-2',
`and C-3’ positions by substituents which may include,
`but are not limited to H, hydroxy, alkoxy, amido, and
`ester (RCO?) wherein R is hydrogen,an alkali metal, an
`alkyl, an alkenyl, an alkynyl, an aminio, or an aryl.
`In the present invention the term iminio ion refers to
`the moiety:
`
`wherein Z is a counterion, preferably but not limited to
`cl-.
`The term alkyl refers to straight-chain or branched
`hydrocarbons which when incorporated into taxol
`compounds do not substantially destroy the properties
`of chemical stability, water solubility and biological
`activity; and in some preferable embodiments alkyl
`refers to the lower alkyls containing from oneto six
`carbon atomsin the principal chain and up to 10 carbon
`atoms; the lower alkyls may be straight or branched
`chain and include methy], ethyl, propyl, isopropyl, bu-
`tyl, isobutyl, tert-butyl, and the like.
`The term alkyi also refers to the substituted alkyl
`groups which do not substantially destroy the proper-
`ties of water solubility, chemical stability and biological
`activity including, but not limited to, the alkyl groups
`discussed above which have substituents such as halo,
`e.g., chloro, bromo;nitro; sulfate; sulfonyloxy; carboxy;
`carboxylate, e.g., —COO-—; phosphate, e.g., —OP(O)-
`(OH)2, —OP(OMKOR)}OH), —OP(O)2(OH)—, and the
`like; carbo-lower-alkoxy, e.g., carbomethoxy, carbe-
`thoxy; amino; mono- and di-loweralkylamino,e.g., me-
`thylamino, dimethylamino, carboxamide; sulfonamide;
`diethylamino, methylethylamino;
`amide;
`alkylsilyl,
`siloxy,
`lower-alkoxy, e.g., methoxy, ethoxy;
`lower-
`alkanoyloxy, e.g., acetoxy; alkenyl, alkynyl; aryl; ary]-
`oxy; and combinations of these, e.g., alkylbenzenesul-
`fonates.
`
`5,319,112
`
`6
`The term aryl refers to aryls with the same substitu-
`ents discussed above for the substituted alkyls and also
`includes, but is not limited to, lower alkyl, e.g. methyl,
`ethyl, butyl, etc., provided the substituents do not sub-
`stantially destroy the properties of chemical stability,
`water solubility, and biological activity.
`
`DESCRIPTION OF THE DRAWINGS
`
`FIG.1 illustrates steps in a preferred embodiment of
`the present invention involving the conversion of ceph-
`alomannine to taxol wherein a mixture of cephaloman-
`nine and taxol is hydrogenated and the hydroxyl group
`at the C-2’ position is benzoylated.
`FIG.2 illustrates a further step in the conversion of
`cephalomannine to taxol wherein the hydroxy] groupat
`the C-7 position is protected by the reaction with 2,2,2-
`trichloroethyloxycarbonyl chloride.
`FIG.3 illustrates a further step in the conversion of
`cephalomannine to taxol wherein an iminio salt
`is
`formed by the addition of oxalyl chloride.
`FIG.4 illustrates a further step in the conversion of
`cephalomannine to taxol wherein an oxamic acid deriv-
`ative is formed by the addition of water.
`FIG.5 illustrates a further step in the conversion of
`cephalomannine to taxol wherein. reaction of the ox-
`amic acid derivative with diphenylcarbodiimide, fol-
`lowed by removalof the protecting group by treatment
`with zinc and acetic acid produces taxol.
`FIG.6 illustrates a reaction using a model compound,
`which demonstrates the formation of a stable oxalyl
`heterocyclic derivative of taxol.
`
`DETAILED DESCRIPTION OF THE
`INVENTION CONVERSION OF A MIXTURE OF
`CEPHALOMANNINE AND TAXOL TO TAXOL
`
`With reference to FIGS. 1-5, a mixture of cephalo-
`mannine 2 and taxol
`1] (about 1:1) is hydrogenated at
`room temperature over a platinum catalyst
`in ethyl
`acetate solution to give a mixture of taxol and dihy-
`drocephalomannine 4 in quantitative yield. Compound
`4 below
`
`10
`
`15
`
`25
`
`30
`
`35
`
`45
`
`
`
` °
`Osaneo=(,\
`
`is a mixture of diastereomers at the 2’-position. The
`mixture was then benzoylated at the 2'-position bytreat-
`ment with one equivalent of benzoic acid in the pres-
`ence of an activating agent, which in a preferred em-
`bodiment comprises dicyclohexylcarbodiimide and 4-
`dimethylaminopyridine to yield a mixture of 2’-benzo-
`ates 5. Mixture 5, comprising the compounds 5 and 5’,
`was then
`
`65
`
`

`

`5,319,112
`
`5
`
`5
`
`10
`
`15
`
`3
`
` 8
`
`-continued
`T
`“o
`
`O
`
`OH
`
`OH
`
`O
`t
`
`o
`
`7 0 A
`
`
`
`u
`
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`
`oO
`
`CH3
`
`tl
`
`NH
`
`:
`
`0 {
`
`5°
`
`converted to its 7-trichloroethyl oxycarbony! deriva-
`tive 6, shown below by reaction with 2,2,2-trichloroe-
`20 thyloxycarbonyl chloride and pyridine in methylene
`chloride. Purification of mixture 6 by flash chromatog-
`raphy gavea purified mixture in 85% yield based on the
`original mixture.
`
`
`
` \
`
`°
`
`Oune
`
`4
`
`Q&
`
`o=(
`
`65
`
`Reaction of mixture 6 with excess oxalyl chloride at
`room temperature in benzene gave the mixture of iminio
`compounds 7 and 7’ below.
`.
`
`

`

`5,319,112
`
`Compounds 7 and 7’ appeared as a white crystalline
`precipitate over a period of 18 hoursif the reaction was
`cooled, but were also formedin solution over 5 hours at 35
`room temperature. More information on the reaction of
`amides with oxalyl chloride can be found in Chiozakiet
`al. “A New Method for the Cleavage of 7-Amide
`Group of Cephalosporins,” Tetrahedron Letters 46, 4059
`(1977). Reaction of mixture 7 with water yielded the 40
`oxamic acid derivative 8 as a single pure substance in
`
`65% yield from mixture 6.
`
`
`
`If the cephalomannine portion of the mixture is not
`hydrogenated first, reaction takes a different course.
`This can be illustrated by a model compound. Thus,
`treatment of the methy! ester 9 (R=PhCO)with oxalyl
`chloride yielded the iminium salt 10. Reaction of 10
`with methanol, however, yielded in part the ether 11, 65
`formed by Michael addition of methano! to the ap-
`unsaturated iminium salt. Similarly reaction of the non-
`hydrogenated cephalomannine-iminio ion with water
`
`would not form the oxamic acid derivative in good
`yield.
`
`t
`SyNH
`
`:
`
`Oo
`
`9
`
`‘
`
`11
`
`

`

`5,319,112
`
`11
`Conversion of oxamic acid 8 to taxol is accomplished
`by treatment with diphenylcarbodiimide. For more
`information on this type of reaction, see Shiozaki etal.
`in “Cleavage and Some Modifications of the 7-Amide
`Group of the Cephamycins,” Tetrahedron 36, 2735
`(1980), which discusses reaction of compounds with an
`oxamic acid moiety with diphenylcarbodiimide. Thus
`
`12
`the
`bis(2,2,2-trichloroethoxycarbonyl) derivative of
`aforementioned compounds. This derivative is then
`converted as previously described to the 2’,7-bis(2,2,2-
`trichloroethoxycarbonyl) analog of the iminio ion 7.
`Treatment of the iminio compound with methanol con-
`verted it to the N-debenzoyl-N-(methyloxalyl) taxol
`analog 14. The use of other alcohols, ROH,in the
`
`14
`
`Ch3C
`
`reaction of 8 with diphenylcarbodiimide in methylene ,
`chloride for 96 hours at room temperature yielded the *
`protected taxol derivative shown below as 13. It is be-
`lieved that the reaction proceedsinitially to produce the
`amino taxol derivative shown as 12 in FIG.5, and that
`O-acyl—N-acyl transfer occurs spontaneously to pro-
`duce 13. Conversion of 13 to taxol 1 was achieved by
`treatment with zinc and acetic acid, as previously de-
`scribed for similar compounds.
`
`5 quench process allows for the synthesis of analogs of
`° compound 14, where the choice of alkoxy group at the
`2” position of the C-13 side-chain is made by selection
`of the appropriate quench alcohol. Thecritical feature
`of this reaction is the presence of the nucleophilic OH
`group. Although,in a preferred embodiment, R is CH3,
`the quench alcohol R-OH,may include, but is not lim-
`ited to, any alkyl, arene, aryl or substituted alkyl or aryl.
`Illustrative, non-limiting examples of R are phenyl,
`
`30
`
`
`
`13
`
`NH
`
`
`
`CONVERSION OF CEPHALOMANNINE TO
`TAXOL
`
`Application of the reaction sequence described above
`to pure cephalomannine will yield pure taxol, since the
`reaction proceeds on a mixture of taxol and cephalo-
`mannineto yield a single pure product. In fact, experi-
`ments indicate that cephalomannine actually reacts
`somewhat more readily than taxol in this process.
`
`55
`
`PREPARATION OF ALKYL OXALATE
`ANALOGS OF TAXOL
`
`Either pure taxol, hydrogenated cephalomannine, or
`a mixture comprising either or both of these compounds
`is protected at the 2’ and 7 positions by a protecting
`group, and then converted as described previously to
`the 2',7-protected analog of the iminio ion 7. For exam-
`ple, use of the 2,2,2-trichloroethoxycarbony] (‘“‘troc’’)
`protecting group results in formation of the 2’,7-
`
`65
`
`methylphenyl, methoxyphenyl, hydroxyphenyl, trime-
`thoxyphenyl, chlorophenyl, nitrophenyl, aminophenyl,
`phenacetyl, methyl, ethyl, and t-butyl. If the quench
`alcohol in the above reaction is replaced by a metal
`hydroxide, or if the acidic proton of the oxamic acid
`derivative is replaced by ion exchange, then R can also
`be a metal such as sodium or potassium. In preferred
`embodiments, analogs of compound 14 are useful as
`anticancer agents when provided in an antineoplasti-
`cally effective amount, although this may require de-
`protection of the C-2’ and/or C-7 position to optimize
`such bioactivity.
`:
`An alternative preparation of analogs such as 14 is by
`quenching the iminio derivative with water to yield the
`ditroc analog 8, followed by treatmentof this acid with
`an alcoho! such as methanol and dilute mineral acid or
`dicyclohexylcarbodiimide (DCC). This alternate proce-
`dure is preferred for alcohols other than methanol.
`
`

`

`13
`The protecting group at the C-2’ and C-7 positions
`can be removed by reaction with the appropriate rea-
`gent. For example, reaction of 14 with Zn in acetic acid
`
`14
`example, reaction of 16 with zinc in acetic acid converts
`it to the taxol analog 17.
`
`5,319,112
`
`converts it to the taxo! analog 15.
`
`Analogs of compounds14, 15, 16, and 17 that have an
`20 acyl groupat the C-2’ position are obtained by the reac-
`tion of taxol or cephalomannineor a mixture containing
`either or both of these compounds with an acylating
`REARon:SorTAxOD mpe
`reagent (e.g. benzoic acid, See FIG. 1). The resulting
`compound, 18, is shown below. See also, Holton, U.S.
`Either pure taxol, hydrogenated cephalomannine, or
`a mixture comprising either or both of these compounds 25 Pat. No. 5,015,744, which shows other taxol analogs,
`is protected at the 2’ and 7 positions by a protecting
`acylated at the 2’ position or the 2’ and 7 position, which
`group and then converted as described previously to
`it has been discovered are suitable for use as starting
`the 2’,7-protected analog of the iminio ion 7. For exam-
`materials for producing the oxalate and oxamido deriva-
`ple, use of the 2,2,2-trichloroethoxycarbony] protecting
`tives of the present invention. The most reactive hy-
`group results in formation of the 2',7-bis(2,2,2-trichloro- 30 droxyl group at the 2’ position will be acylated in pref-
`ethoxycarbonyl) analog of the iminio ion 7. Treatment
`erence to the other hydroxyl groups on the taxol or
`of this hydrogenated compound with an amine, such as
`cephalomanninestructure. As shownin the synthesis of
`by way of non-limiting example, aniline, forms the N-
`14, where the acylating reagent is 2,2,2-trichloroethy!
`debenzoyl-N-(N’-phenyloxamide)
`analog
`16 where
`chloroformate, conditions for acylating both positions
`R=Ph.
`35 are readily available.
`
`16
`
`CCly
`
`
`
`Cih3C
`
`Appropriate acylating reagents include, but are not
`The use of other amines in the quench process allows
`limited to: carboxylic acids, carboxylic esters, anhy-
`the synthesis of any desired amide analog of compound
`16, where the choice of amide, C(O)NHR,is made by 55 drides, cyclic anhydrides, amides,
`lactams,
`lactones,
`the selection of the appropriate amine. Thus, R can be,
`acid halides (also known as acyl halides), isocyanates
`but is not limited to, any alkyl, alkene, alkyne, aryl or
`and the substituted derivatives of these compounds.
`substituted alkyl, alkene, alkyne, or aryl. Preferred ana-
`Acylation reactions sometimes require activating agents
`logs of compound 16 are useful as anticancer agents,
`such as tertiary amines and n-butyllithium. Numerous
`when administered in an antineoplastically effective 60 additional acylating reagents and activating agents not
`amount.
`specifically recited here can also be used in the present
`Analternate preparation of analogs such as 16 is by
`invention.
`quenching the iminio derivative with water to yield the
`CONVERSION OF TAXOL OR
`ditroc analog of 8, followed by treatment of this acid
`with an amine in the presence of DCC. This alternate 65 CEPHALOMANNINE ‘TO N-ACYL ANALOGS
`procedure is preferred for amines other than aniline.
`OF TAXOL
`The protecting group at the 2’ and 7 positions can be
`The method of the present invention as described
`removed by reaction with the appropriate reagent. For
`abovecan be used to prepare N-acyl taxol analogs. For
`
`

`

`15
`example, treatment of taxol with a desired acylating
`reagent will convert it to a 2’-acyltaxol derivative 18.
`
`16
`18 at the C-7 position with 2,2,2-trichloroethylchloro-
`formate will yield the protected
`
`5,319,112
`
`19
`
`Protection of
`
`derivative 19, and treatment of 19 with oxalyl chloride
`followed by wateras previously described will yield the
`oxamic acid derivative 20, where R is any desired aryl,
`
`18
`
`20
`21 by deoxyalylation 21
`
`loweralkyl, alkenyl or alkynyl or substituted aryl or
`substituted alkyl group. By way of non-limiting exam-
`ples, R is phenyl, hydroxyphenyi, methylphenyl, me-
`thoxyphenyl,
`trimethoxyphenyi, chlorophenyl, nitro-
`phenyl, acylphenyl, phenacetyl, methyl, ethyl, and
`45 ethynyl. Treatment of 20 with diphenylcarbodiimide,as
`previously described, will yield the N-acyl derivative
`
`65
`
`followed by O-acyl—N-acyl transfer. Deprotection at
`C-7 with zinc and acetic acid will then yield the N-acyl
`
`

`

`17
`taxol analog 22. The sameset of reactions could also be
`carried
`
`5,319,112
`
`
`
`
`
`oO
`
`24
`
`O
`
`OR2
`
`“4
`
`24
`
`Ry; = TCEM,R2- troc or other protecting groups
`
`out using hydrogenated cephalomannine in place of
`taxol,
`resulting in compounds 20-22 and the 2”- 20
`isobutylated analogs of 18 and 19.
`N-acyl taxol analogs are important analogs of taxol
`for anticancer treatment. The present invention pro-
`vides a simple way of preparing such analogs from taxol
`or cephalomannine without removing the side-chain.
`PREPARATION OF TAXOTERE FROM
`CEPHALOMANNINE
`
`compound 24 can then be reacted with di-t-butyl dicar-
`bonate to yield the 10-acety] taxotere derivative 25. The
`10-acetyl group of 25 can be hydrolyzed under mild
`base conditions to yield 26, and deprotection of 26 by
`zinc and acetic acid will yield taxotere 27. Alterna-
`tively, 25 can be deprotected first with zinc and acetic
`25 cid to yield 10-acetyl taxotere 28, and this can be hy-
`drolyzed under very mild conditions with methanolic
`sodium bicarbonate to yield taxotere 27.
`
`Hydrogenation of cephalomannine 2, to its dihydro
`y
`derivative 4 can be followed by protection as the 2’-tri- 30
`chloroethoxy methyl ether (TCEM)-7-troc derivative oY
`23. Other protecting groups can also be used in place of
`NH
`the TCEM andtroc derivatives. Treatment of 23 or
`i
`other 2’,7 protected analogs with oxaly! chloride fol-
`lowed by an aqueous
`
`35
`
`
`
`°
`ll
`
`oO
`
`OH?
`oO
`S
`
`AU °
`5
`oO
`CH;
`
`ll
`Oo
`
`OCH2CCI3
`
`55
`
`25 R = TCEMortroc or other protecting group, R’ = CH3;CO
`60 26 R = TCEM ortroc or other protecting group, R' = H
`27 R=H,R'=H
`28 R =H, R’ = CH3CO
`
`quench and subsequent reaction with diphenylcarbodii-
`mide as previously described would give the amino
`derivative 24.
`
`65
`
`EXAMPLES
`The following nonlimiting examples provide specific
`synthetic methods for the conversion of a mixture of
`taxol and cephalomannine into pure taxol or N-acyl
`
`oO
`
`AOo
`
`Oo
`
`i
`
`Ow
`
`OCH?CCl3
`
`
`
`

`

`19
`analogsof taxol. Other methods and materials similar or
`equivalent to those described herein can be used in the
`practice or testing of the present
`invention. Proton
`NMRdata for selected compounds is shown in Tables
`1-3.
`
`Example 1
`Hydrogenation of taxol/cephalomannine
`A 262 mg quantity of an approximately 50/50 mixture
`of taxol and cephalomannine was dissolved in 10 mL of 10
`ethyl acetate in a 100 mL round bottom flask with mag-
`netic stirring. Then 20 mg of PtO2 was added and the
`flask was attached to a hydrogenation apparatus. After
`flushing the flask five times with hydrogen gas, the
`solution was stirred at room temperature. After 1 hour,
`the flask was removed from the hydrogenation appara-
`tus and the solution filtered through Celite to-remove
`the catalyst. The resulting solution was evaporated to
`dryness under vacuum. Theresult was 262 mg (100%)
`of a mixture of taxol and dihydrocephalomannine. No
`further puri