AU6051500A

AU6051500A - C-2 hydroxyl protected-n-acyl(2r,3s)-3-phenylisoserine activated esters and methods for production thereof

Info

Publication number: AU6051500A
Application number: AU60515/00A
Authority: AU
Inventors: Madhavi C. Chander; James D Mcchesney; Jan Zygmunt
Original assignee: Tapestry Pharmaceuticals Inc
Current assignee: Tapestry Pharmaceuticals Inc
Priority date: 1999-06-21
Filing date: 2000-06-16
Publication date: 2001-01-09
Also published as: JP2003502401A; EP1192126A1; TR200103747T2; CA2375343A1; NO20016165D0; NO20016165L; WO2000078707A1

Description

WO 00/78707 PCT/US00/16617 C-2 HYDROXYL PROTECTED-N-ACYL(2R,3S)-3-PHENYLISOSERINE ACTIVATED ESTERS AND METHODS FOR PRODUCTION THEREOF FIELD OF THE INVENTION This invention generally relates to the synthesis of paclitaxel from precursor compounds. More particularly, though, this invention concerns the semi-synthesis of paclitaxel using a protected baccatin III backbone which is esterified with suitably protected side chain activated esters to produce an intermediate that may be converted to paclitaxel. BACKGROUND OF THE INVENTION The chemical compound referred to in the literature as taxol, and more recently "paclitaxel", has received increasing attention in the scientific and medical community due to its demonstration of anti-tumor activity. Paclitaxel has been approved for the chemotherapeutic treatment of several different varieties of tumors, and the clinical trials indicate that paclitaxel promises a broad range of potent anti-leukemic and tumor-inhibiting activity. As is known, paclitaxel is a naturally occurring taxane diterpenoid having the formula and numbering system as follows: AcO O OH O Ph NH 0 H H 0 Ph O OH OAc OH OCOPh (Formula 1) 10 9 19 7 18 11 15 6 3 5 17 13 4 O 2 2 14 0 (Numbering System) WO 00/78707 PCT/US00/16617 2 While the paclitaxel molecule is found in several species of yew (genus Taxus, family Taxaceae), the concentration of this compound is very low. Moreover, these evergreens are slow-growing. Thus, a danger exists that the increasing use of paclitaxel as an effective anti-cancer agent will deplete natural resources in the form of the yew trees. Indeed, while the bark of the yew trees typically exhibit the highest concentration of paclitaxel, the production of 1 kilogram of paclitaxel requires approximately 16,000 pounds of bark. Thus, the long term prospects for the availability of paclitaxel through isolation is discouraging. The paclitaxel compound, of course, is built upon the baccatin III backbone, and there are a variety of other taxane compounds, such as baccatin Ill, cephalommanine, 10-deacetylbaccatin III, etc., some of which are more readily extracted in higher yields from the yew tree. Indeed, a relatively high concentration of 10-deacetylbaccatin Ill can be extracted from the leaves of the yew as a renewable resource. Typically, however, these other taxane compounds present in the yew tree do not exhibit the degree of anti-tumor activity shown by the paclitaxel compound. Since the paclitaxel compound appears so promising as a chemotherapeutic agent, organic chemists have spent substantial time and resources in attempting to synthesize the paclitaxel molecule. A more promising route to the creation of significant quantities of the paclitaxel compound has been proposed by the semi-synthesis of paclitaxel by the attachment of the A-ring side chain to the C-13 position of the naturally occurring baccatin III backbone derived from the various taxanes present in the yew. See, Denis et al, "Highly Efficient, Practical Approach to Natural Taxol", Journal of the American Chemical Society, page 5917 (1988). In that article, the partial synthesis of paclitaxel from 10-deacetylbaccatin III is described. The most straightforward implementation of partial synthesis of paclitaxel requires convenient access to chiral, non-racemic side chains and derivatives, an abundant natural source of baccatin III or closely related WO 00/78707 PCT/US00/16617 3 diterpenoid substances, and an effective means of joining the two. Of particular interest then is the condensation of baccatin III or 10 deacetylbaccatin Ill with the paclitaxel A-ring side chain. However, the esterification of these two units is difficult because of the hindered C-13 hydroxyl of baccatin III located within the concave region of the hemispherical taxane skeleton. For example, Greene and Gueritte Voegelein reported only a 50% conversion after 100 hours in one partial synthesis of paclitaxel. J. Am. Chem. Soc., 1988, 110, 5917. In U.S. Patent No. 4,929,011 issued May 8, 1990 to Denis et al entitled "Process for Preparing Taxol", the semi-synthesis of paclitaxel from the condensation of a (2R,3S) side chain acid of the general formula: O Ph NH P C0 2 H Ph C2 OP1 (Formula 2) wherein P 1 is a hydroxyl protecting group with a taxane derivative of the general formula of: AcO O

OP

2 sIH 0H _ H = 0 HO"' E OH : OAc OCOPh (Formula 3) wherein P 2 is a hydroxyl protecting group is described wherein the condensation product is subsequently processed to remove the P 1 and P 2 protecting groups. In Denis et al, the (2R, 3S) 3-phenylisoserine derivative, with the exception of the P 1 protecting group, is the A-ring side chain for the paclitaxel molecule. The P 2 protecting group on the baccatin III backbone is, for example, a trimethylsilyl or a trialkylsilyl radical.

WO 00/78707 PCT/US00/16617 4 An alternative semi-synthesis of paclitaxel is described in U.S. Patent No. 5,770,745 to Swindell et al. Swindell et al. discloses semi-synthesis of paclitaxel from a baccatin Ill backbone by the condensation with a side chain having the general formula: O

R

1 0 NH RIO") NH Ph -' CO 2 H OP S (Formula 4) wherein R 1 is alkyl, olefinic or aromatic or PhCH 2 and P 1 is a hydroxyl protecting group. The side chain in Swindell et al is distinct from the side chain attachment used in Denis et al, above, in that the nitrogen is protected as a carbamate. Preferably, the A-ring side chain is benzyloxycarbonyl (CBZ) protected. After esterification, the CBZ protecting group is removed and replaced by PhCO to lead to paclitaxel. This process generated higher yields than that described in Denis et al. In Swindell et al., the preferred masking groups were selected to be trichloroethoxymethyl or trichloroethoxycarbonyl. Benzyloxymethyl (BOM) was, however, disclosed as a possible side chain hydroxyl protecting group for the 3-phenylisoserine side chain, but, according to the processes described therein, the BOM protecting group could not be removed from the more encumbered C-2 hydroxyl in the attached 3-phenylisoserine side chain. The use of the BOM protected side chain was not extensively investigated, for that reason. Subsequently, it has been shown in U.S. Patent No. 5,675,025 to Sisti et al., issued October 7, 1997, that the BOM group could be removed from the more encumbered C-2 hydroxyl in the attached 3-phenylisoserine side chain. U.S. Patent No. 4,924,012, issued May 8, 1990 to Colin et al discloses a process for preparing derivatives of baccatin III and of 10- WO 00/78707 PCT/US00/16617 5 deacetylbaccatin III, by condensation of an acid with a derivative of a baccatin III or of 10-deacetylbaccatin III, with the subsequent removal of protecting groups by acid hydrolysis. Several syntheses of TAXOTERE® (Registered to Rhone-Poulenc Sante) and related compounds have been reported in the Journal of Organic Chemistry: 1986, 51, 46; 1990, 55, 1957; 1991, 56, 1681; 1991, 56, 6939; 1992, 57, 4320; 1992, 57, 6387; and 993, 58, 255; also, U.S. Patent No. 5,015,744 issued May 14, 1991 to Holton describes such a synthesis. Additional techniques for the synthesis of paclitaxel and paclitaxel analogues are discussed in U.S. Patent No. 5,688,977 to Sisti et al., U.S. Patent No. 5,750,737 to Sisti et al., U.S. Patent No. 5,684,175 to Sisti et al. and U.S. Patent No. 5,750,736 to Sisti. Despite the advances made in the semi-synthesis of the paclitaxel molecule in the above-described processes, there remains a need for more efficient protocols for the synthesis of paclitaxel in order to increase efficiencies in yields and production rates. There remains such a need for semi-synthesis that may be implemented into commercial processes. There is a further need for efficient protocols for the synthesis of paclitaxel analogs, intermediates and various A-ring side chain structures. SUMMARY OF THE INVENTION It is an object of the present invention to provide new C-2 hydroxyl protected-N-Acyl (2R,3S)-3-phenylisoserine activated esters and production processes therefore, that are useful in the semi-synthesis of paclitaxel. Another object of the present invention is to provide a new and useful process for the production of an hydrogenatable benzyl-type protected side chain which may be readily attached to a protected baccatin III backbone during the semi-synthesis of paclitaxel. Still a further object of the present invention is to provide N-CBZ protected C-2 hydroxyl-benzyl protected (2R,3S)-3-phenylisoserine activated esters and production methods therefor.

WO 00/78707 PCT/US00/16617 6 Still a further object of the present invention is to develop efficient cost effective processes for the production of N-CBZ protected C-2 hydroxyl benzyl protected (2R,3S)-3-phenylisoserine activated esters. According to the present invention, then, a chemical compound is provided having the formula: O R, NH 0 Ph - O- Z

OP

1 wherein Pi is a hydroxyl protecting group, R 1 may be an alkyl group, an olefinic group, an aromatic group, an O-alkyl group, an O-olefinic group, or an O-aromatic group, and Z may be a substituted phenyl moiety or an N imido moiety. R, is preferably Ph, PhCH 2 , O-Ph or O-CH 2 Ph, and P 1 is preferably benzyl, benzyloxymethyl or benzoyl. Z may be a phenyl moiety having the formula:

R

2

R

3 / R4

R

6

R

5 such that the chemical compound has the formula: O 0 R I NH O R2 R3 Phj 0 R 4

OP

1 R6 Rs WO 00/78707 PCT/US00/16617 7 where each of R 2 to R6 is H or an electron withdrawing group. Exemplary electron withdrawing groups include NO 2 or halogens, such as F. It is preferred that at least one of R 2 to R 6 is a halogen or NO 2 . A preferred embodiment is where P 1 is benzyloxymethyl; R 2 , R 3 , R 5 , and Re are H; R 4 is NO 2 ; and R 1 is OCH 2 Ph. Also preferred is where P 1 is benzyloxymethyl; R 2 , R 3 , R 4 , R 5 and R 6 are F; and R 1 is OCH 2 Ph. It is further preferred where Pi is benzyloxymethyl; R 2 and R 4 are NO 2 ; R 3 , Rs, and R6 are H; and R 1 is OCH 2 Ph. Z may alternatively be a heterocyclic N-imido moiety, preferably having 5 to 7 atoms in the ring, and alternatively substituted with at least one electron withdrawing group, such as a nitro or a halogen group. The N-imido moiety may be substituted with a plurality of the same or different electron withdrawing groups. In particular, Z may be succinimido, phthalimido, 5 norbornene-2,3-dicarboxyimido, and maleimido moieties and substituted derivatives thereof. The present invention is also directed to a process for producing an ester derivative useful in the production of paclitaxel, paclitaxel analogues and their intermediates. The process comprises the step of reacting a first compound of the general formula: O R NH ph

C

0 2

R

1 o Ph

OP

1 wherein Ri is an alkyl group, an olefinic group, an aromatic group, an O-alkyl group, an O-olefinic group, or an O-aromatic group; P 1 is a hydroxyl protecting group; and Rio is H or CO 2 X, where X is an alkyl group, an olefinic group or an aromatic group, with a second compound of the general formula:

HO-Z

WO 00/78707 PCT/US00/16617 8 wherein Z is selected from the group consisting of a substituted phenyl moiety and an N-imido moiety, to give a third compound of the general formula: 0 R, NH 0 Ph O- Z

OP

1 wherein R 1 is an alkyl group, an olefinic group, an aromatic group, an O-alkyl group, an O-olefinic group, or an O-aromatic group; P 1 is a hydroxyl protecting group; and Z is selected from the group consisting of a substituted phenyl moiety and an N-imido moiety. When Rio is H, the step of reacting may be conducted in the presence of THF and a carbodiimide, such as dicyclohexylcarbodiimide. When Rio is CO 2 X, X may particularly be

-CH

2 CH(CH3) 2 , and the step of reacting may be conducted in the presence of N-methyl morpholine and THF. The first compound may be formed by reacting a compound having the formula: 0 Ri NH - C0 2 H Ph CO2

OP

1 with a compound having the formula Cl-C0O 2 X to give the first compound. The second compound may be one having the formula: WO 00/78707 PCT/US00/16617 9 R 2

R

3 HO R4

R

6 R5 wherein each of R 2 to R 6 is selected from the group consisting of H and an electron withdrawing group. In particular, each of R 2 to R 6 may be H, halogen or NO 2 with at least one of R 2 to R 6 being halogen or NO 2 . R, may particularly be Ph, PhCH 2 , O-Ph or O-CH 2 Ph, and P 1 may be benzyl, benzyloxymethyl or benzoyl. Alternatively, the second compound may be one where Z may be a heterocyclic N-imido moiety, such as one having 5 to 7 atoms in the ring. In particular, Z may be succinimido, phthalimido, 5 norbornene-2,3-dicarboxyimido, or maleimido moieties and substituted derivatives thereof. These and other objects of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of the exemplary embodiments. DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS The present disclosure is broadly directed to a chemical process for the efficient production of paclitaxel, intermediates and precursors therefor. More specifically, the present invention concerns the semi-synthesis of paclitaxel by esterifying suitably protected 3-phenylisoserine activated esters having protecting groups at C-2 to the C-13 hydroxyl of 7-O-protected baccatin III. More particularly, the present invention preferably utilizes CBZ protection at the C-7 site of the baccatin III. The general process described herein involves the production of C-7 CBZ baccatin III, the production of a suitably protected 3-phenylisoserine activated ester having a suitable protecting group at C-2, the condensation of the two compounds, and the subsequent deprotection, acylation, deprotection of the condensation product to form paclitaxel.

WO 00/78707 PCT/US00/16617 10 A. Production of C7-CBZ Protected Baccatin III According to the present invention, two alternative routes are described which appear in copending Application Serial No. 08/922,684, now U.S. Patent No. X,XXX,XXX to Sisti et al., for producing C7-CBZ protected baccatin Ill. On one hand, baccatin III can be protected at the C-7 site to yield C-7 CBZ baccatin Ill. On the other hand, 10-deacetylbaccatin III (10-DAB) can be directly converted to C-7 CBZ baccatin III without going through a baccatin III intermediate. Production from baccatin III is advantageous for its yield and simplicity. The method using 10 deacetylbaccatin Ill has an advantage since 10-deacetylbaccatin Ill is much more naturally abundant, and thus less expensive, than baccatin III; however, this alternative method has a reduced yield. Route 1 (Using baccatin III) C-7 CBZ baccatin Ill has the formula: AcO 0 OCO 2

CH

2 Ph O" 9\HH OH : - OAc OCOPh and can be synthesized from baccatin Ill according to the following reaction: WO 00/78707 PCT/US00/16617 11 AcO O OH 1H H 0 H' 1 ' : t ==l 0 HO"0 HO OH0 A OH OAc OCOPh AcO O OCO 2

CH

2 Ph _ OH HO " OH E = - OAc OCOPh Reaction I Baccatin III is dissolved in THF (tetrahydrofuran) to form a first solution, which is cooled under a nitrogen atmosphere to a reduced temperature of less than -200C. n-Butyl lithium (1.6 M in hexane) is then added dropwise to the first solution to form a second solution, which is stirred for approximately five minutes at the reduced temperature. This creates the C-7 lithium alkoxide of baccatin Ill. Benzyl chloroformate (CBZ-CI) is added dropwise to the second solution to form a third solution which is then stirred and allowed to warm to 00C over approximately one (1) hour. The third solution is quenched with cold saturated ammonium chloride to eliminate any excess n butyl lithium and CBZ-CI, and the mixture is concentrated under vacuum to yield a first residue. This first residue is next taken up in ethyl acetate and washed once with water to remove unwanted salts. Next, the organic layer is washed with brine. The organic layer is then dried and concentrated under vacuum to yield a second residue. The second residue is recrystallized or column chromatographed with ethyl acetate: hexane to give C-7 CBZ baccatin Ill as a white solid.

WO 00/78707 PCT/US00/16617 12 Instead of using n-butyl lithium, it should be appreciated that other alkali bases may be used, especially potassium hydride and sodium hydride, to form the C-7 metal alkoxide of baccatin III, to the extent understood by the ordinarily skilled artisan. Route 2 (Using 10-deacetylbaccatin III) Alternatively, C-7 CBZ baccatin III can be synthesized directly from 1 0-deacetylbaccatin III as follows: HO 0 OH HH HO ""9HO OH = - OAc OCOPh AcO O OCO 2

CH

2 Ph HO MEH O H OAc OCOPh Reaction II Here, 10-DAB Ill is dissolved in THF to form a first solution which is cooled to a reduced temperature of less than -200C, and preferably to -400C, under a nitrogen atmosphere. At least two equivalents of n-butyl lithium (1.6 M in hexane) are then added dropwise to the first solution to form a second solution which is then stirred for approximately five minutes at the reduced temperature. Preferably, acetyl chloride (one equivalent) is added to the second solution to form a third solution which is stirred at the reduced temperature for approximately thirty minutes. Alternatively, acetic anhydride (one equivalent) may possibly be used in place of the acetyl chloride to acylate the 10-DAB III. In either case, benzyl chloroformate (one equivalent) WO 00/78707 PCT/US00/16617 13 is next added, and this fourth solution is stirred for an additional thirty minutes at the reduced temperature and then warmed to 0oC over thirty minutes. The fourth solution is then quenched with cold saturated ammonium chloride at the reduced temperature to remove any excess n butyl lithium, acetyl chloride and CBZ-Cl; this mixture is then warmed to room temperature. The solvent is removed under vacuum to yield an initial residue, which is taken up in ethyl acetate and washed with water to remove unwanted salts. The organic layer is then washed with brine, dried and concentrated under vacuum to yield a final residue. The final residue is chromatographed (silica gel hexanes:ethyl acetate) to yield C-7 CBZ baccatin Ill. It is important to note that this method represents a direct synthesis of C-7 CBZ baccatin Ill from 10-DAB Ill, as the intermediate formed in this reaction is a C-7 lithium alkoxide of baccatin III, that is, the intermediate is not baccatin III itself. While both Routes 1 and 2 specifically are directed to the production of derivatives of baccatin III, it should be apparent to the ordinarily skilled person that baccatin III analogs can be produced from the Route 2 process simply by substituting the appropriate acid chloride to the second solution in Route 2. This would result in the formation of analogues with different alkyl groups, for example, at C-10. It should now be appreciated that both Route 1 and Route 2 to the production of C-7 CBZ baccatin III can be expressed as a generalized method. This method starts with a step of dissolving a starting compound selected from the group consisting of baccatin III and 10-deacetylbaccatin III in a first solvent to form a first solution. The first solution is then cooled to a temperature of -200C or less. Thereafter, an alkyl lithium base is added to the first solution thereby to form an intermediate compound having a lithium alkoxide at the C-7 position thereof. Next, as would be required for the 10 DAB Ill starting compound, the method includes selectively acylating, at the C-10 position, any of the first intermediate compound present in the first solution where the intermediate compound does not already have an acetyl WO 00/78707 PCT/US00/16617 14 group at the C-10 position thereby to produce a second solution of C-7 lithium alkoxide of baccatin Ill. Of course, where the starting compound is baccatin III, the C-10 position already has an acetyl group. In any event, the method includes a step of thereafter adding CBZ-CI to the second solution to form a third solution of C-7 CBZ baccatin III. B. Production of N-Acyl C-2 Hydroxyl Protected (2R,3S)-3 Phenylisoserine A-Ring Side Chain Activated Esters The second precursor necessary for the semi-synthesis of paclitaxel according to the present invention is the N-acyl C-2 hydroxyl protected (2R,3S) phenylisoserine side chain activated ester having the general formula: 0 R NH Ph= C0 2

R

2 OP wherein R 1 is an alkyl group, an olefinic group, an aromatic group, Ph, PhCH 2 , an O-alkyl group, an O-olefinic group, an O-aromatic group, O-Ph, or

O-CH

2 Ph. P 1 is a hydroxyl protecting group and R 2 can be an N-imido group or a phenyl ring substituted with one or more electron withdrawing groups. Imido groups contemplated by the present invention include such groups as succinimido, phthalimido, 5-norbornene-2,3-dicarboxyimido, or derivatives thereof such as a maleimido group or succinimido group substituted at the 3 and/or 4 positions, or other heterocyclic imido groups, preferably having 5 to 7 atoms in the ring, alternatively substituted with chloro, fluoro, nitro or other groups. The preferred hydroxyl protecting group is a benzyloxymethyl (BOM) protecting group. Benzyl has also been demonstrated to be suitable as has benzoyl, and other protecting groups are believed suitable as well. The preferred N-Acyl group is benzyloxycarbonyl (CBZ). Other protecting groups WO 00/78707 PCT/US00/16617 15 and acyl groups (having alkyl, olefinic, and aromatic substituents and variations thereon) may be substituted, to the extent understood by the ordinarily skilled artisan. The starting compound to produce the desired side chain is (2R,3S) 3-phenylisoserine ethyl ester to produce the preferred N-CBZ protected (2R,3S)-3-phenylisoserine ethyl ester according to the reaction: 0

NH

2 Ph O NH - CBZ-CI Ph

CO

2 Et P hCO 2 Et P Na 2

CO

3 OH Et 2 0:H 2 0 OH Reaction III Here, (2R,3S)-3-phenylisoserine ethyl ester was alternatively dissolved in either equal parts diethyl ether:water or equal parts methyl t-butyl ether:water and the solution was cooled to 00C. The sodium carbonate was then added to the solution and benzylchloroformate was added dropwise over an interval of about five minutes and the resulting mixture stirred at 00C for approximately one hour. After the one hour stirring, the solution was then poured into water and extracted with methylene chloride or ethyl acetate, as desired. The organic layer is separated, dried and reduced under vacuum to residue. The residue was then recrystallized from ethyl acetate:hexane to result in N-CBZ (2R,3S)-3-phenylisoserine ethyl ester having the formula: 0 Ph O NH Ph - C0 2 Et OH Ph" H (Formula 5) The N-CBZ (2R,3S)-3-phenylisoserine ethyl ester was next protected by the hydrogenatable benzyl-type protecting group, in several ways. For WO 00/78707 PCTUS00/16617 16 example, one route to the desired hydrogenatable benzyl protected side chain is as follows: O 0 Ph 0 NH Ph 0 NH - BOM-CI SCO 2 Et Ph2Et Ph n-BuLi = ZZ OH THF, -78 0 C OBOM Reaction IV Here, the CBZ (2R,3S)-3-phenylisoserine ethyl ester is dissolved in anhydrous THF under a nitrogen atmosphere and cooled to a reduced temperature such as -400C or -780C, for example, in a dry ice/acetone bath followed by the dropwise addition of an alkylithium agent, such as n-butyl lithium, although it is desirable that the alkylithium agent be a straight chain alkyl. In any event, the reaction is best done at a temperature no greater than 00C. The resulting mixture was stirred for about ten minutes. Benzyloxymethyl chloride (BOM-CI) was then added dropwise over an interval of about five minutes and the mixture stirred for approximately two to five hours at the reduced temperature. Thereafter, the solution was warmed to oC and quenched with water. The resulting mixture is reduced under vacuum to residue, and this residue is thereafter taken up in ethyl acetate and washed with water and brine. The organic layer may then be dried and reduced under vacuum and the residue recrystallized from ethyl acetate:hexane or chromatographed with ethyl acetate:hexane to give the compound: 0 Ph 0 NH h C0 2 Et Ph ( o u 6 OBOM (Formula 6) WO 00/78707 PCT/US00/16617 17 Another route in the production of the compound according to formula 6 is accomplished by dissolving the compound N-CBZ (2R,3S)-3 phenylisoserine ethyl ester in anhydrous methylene chloride. Thereafter, a tertiary amine base, such as diisopropylethylamine, is added along with BOM-CI and the mix is refluxed for twenty-four hours. While this reaction route will produce N-CBZ, C-2 [hydroxyl] protected (2R,3S)-3 phenylisoserine ethyl ester, the reaction proceeds much slower than the preferred route, discussed above. In either instance, the resulting protected (2R,3S)-3-phenylisoserine ethyl ester compound of formula 6 may simply be converted to the N-CBZ C 2 0-BOM-protected (2R,3S) phenylisoserine intermediate by the reaction: 0 0 '__ "'kPh 0 ) NH Ph 0 NH - LiOH S CO 2 Et Ph " 0 2 H Ph - EtOH:H 2 0 = -BOM OBOM Reaction V Here, the protected (2R,3S)-3-phenylisoserine ethyl ester is dissolved in ethanol/water (ratio 8:1). Lithium hydroxide (or other suitable alkali hydroxide) is added to the solution and the resulting mixture stirred for approximately three hours in order to saponify the compound. The mixture is then acidified (1N HCI) and extracted with ethyl acetate. The resulting organic layer is separated, dried and reduced under vacuum. The residue acid is then isolated for use without further purification. This produces the desired side chain having the general formula: WO 00/78707 PCT/US00/16617 18 0 Ph 0 NH P CO 2 H OBOM OBOM (Formula 7) Benzyl itself is another example of a hydrogenatable benzyl protecting group that may be used instead of BOM. The compound of the formula: 0 Ph 0 NH Ph CO 2 Et OBn OBn (Formula 8) was therefore produced as above with the substitution of benzyl bromide for BOM-CI in Reaction IV according to the reaction 0 0 Ph 0O NH Ph 0 NH - C BnBr, THF : C02Et 1 ',",,CO 2 E t Ph C 2 n-BuLi Ph C OH OBn Reaction VI Here, the CBZ protected (2R,3S)-3-phenylisoserine ethyl ester is dissolved in anhydrous THF under a nitrogen atmosphere and cooled to a reduced temperature such as -400C or -780C, for example, in a dry ice/acetone bath followed by the dropwise addition of an alkylithium agent, such as n-butyl lithium, although it is desirable that the alkylithium agent be a straight chain alkyl. The resulting mixture was stirred for about ten minutes. Benzyl WO 00/78707 PCT/US00/16617 19 bromide (BnBr) was then added dropwise over an interval of about five minutes and the mixture stirred for approximately two to five hours at the reduced temperature. Thereafter, the solution was warmed to 0OC and quenched with water. The resulting mixture is reduced under vacuum to residue, and this residue is thereafter taken up in ethyl acetate and washed with water and brine. The organic layer may then be dried and reduced under vacuum and the residue recrystallized from ethyl acetate:hexane or chromatographed with ethyl acetate:hexane to give the compound of Formula 8. Alternatively, the compound of Formula 8 may be obtained according to the reaction: O O Ph 0 NH Ph 0 NH NaH,DMF Ph

CO

2 Et - Ph

CO

2 H BnBr Ph OH OBn Reaction VII Here, to a stirred solution of NaH in anhydrous DMF under N 2 was added the compound of Formula 5 dissolved in DMF over five minutes. The mixture was then stirred at 0oC for one half hour, after which time benzyl bromide (1.1 equivalents) was added dropwise over five minutes and the reaction stirred for two hours. The mixture was then quenched with H 2 0. Thereafter, a selected one of diethyl ether and methyl t-butyl ether was added. The organic layer was then washed with four portions of H 2 0, brine, and then dried and reduced under vacuum to produce the compound of Formula 8. Formula 8 may then be readily converted into: WO 00/78707 PCT/US00/16617 20 0 Ph 0 NH h" 0 2 H Ph CO2H OBn OBn (Formula 9) by the process of Reaction V, above. N-CBZ C-2-OBOM protected (2R,3S)-3-phenylisoserine (Formula 7) may be converted into its corresponding activated esters by one of two routes, although it should be appreciated that other esterification methods known in scientific literature may be used to produce the activated ester, to the extent understood by the ordinarily skilled artisan. Further, it should be appreciated that the methods are applicable to C-2 and C-3N variations of Formula 7, to the extent understood by the ordinarily skilled artisan. In the first route N-CBZ-C-2-OBOM protected (2R,3S)-3 phenylisoserine is mixed with 1.2 equivalents of dicyclohexylcarbodiimide or other suitable carbodiimide and 1.2 equivalents of either p-nitrophenol, pentaflurophenol, 2,4-dinitrophenol (or other substituted phenols, to the extent understood by the ordinarily skilled artisan) or N-hydroxy succinimide (or other N-hydroxy imides, to the extent understood by the ordinarily skilled artisan) in THF and stirred for several hours at room temperature. The preferred substituted phenol is p-nitrophenol. The preferred N-hydroxy imide is N-hydroxy succinimide. It should be appreciated that the substituted phenols and N-hydroxy imides contemplated by the present invention are either readily available or may be synthesized from readily available starting materials according to procedures known in the art. The resulting mixture is diluted with ethyl acetate, cooled to 0OC for several hours, stirred for an additional several minutes and filtered. The filtrate is then washed with 1N HCI, water, 20% aqueous NaHCO 3 , water, brine, dried over sodium sulfate and reduced in vacuo to a residue. The WO 00/78707 PCT/US00/16617 21 residue may then be column chromatographed and/or recrystallized from ethyl acetate:heptane. Exemplary reactions of the first route are as follows: 0 Ph 0 NH Ph - CO 2H O OBOM Ph 0 NH 0 + DCC P

NO

2 ~Ph THF / \ OBOM HO / \ NO 2 (Formula 10) Reaction VIII 0 Ph 0 NH Ph -CO2H O 0 2 N OBOM Ph 0 NH 0 DCC Ph O / NO 2 THF OBOM HO NO 2 (Formula 11) Reaction IX WO 00/78707 PCT/US00/16617 22 0 Ph 0 NH Ph CO2H 0 F F OBOM OBOM Ph 0 NH 0 F + F DCC Ph OF F F Ph - = 0 F THF OBOM F F HO F F F (Formula 12) Reaction X 0 Ph 0 NH Ph C 0 OBOM 0 Ph 0 NH 0 +DCC 0 O-N Ph THF 08C0 HO-N (Formula 13) Reaction XI In the second route, a mixed anhydride of N-CBZ-C-2-OBOM 3 phenylisoserine may be reacted with either p-nitrophenol, pentaflurophenol, 2,4-dinitrophenol (or other substituted phenols, to the extent understood by the ordinarily skilled artisan) or N-hydroxy succinimide (or other N-hydroxy imides, to the extent understood by the ordinarily skilled artisan) to afford the corresponding activated esters. It is contemplated that mixed anhydrides having alkyl, olefinic, aromatic or other appropriate radicals might be used, to the extent understood by the ordinarily skilled artisan.

WO 00/78707 PCT/US00/16617 23 To a solution of N-CBZ-C-2-OBOM-3-phenylisoserine in THF cooled to -150 to -200C under nitrogen was added 1.5 equivalents of i-butyl chloroformate followed by 1.5 equivalents of N-methyl morpholine. The resulting mixture was stirred for several minutes followed by addition of 1.5 equivalents of either p-nitrophenol, pentaflurophenol, 2,4-dinitrophenol (or other substituted phenols, to the extent understood by the ordinarily skilled artisan) or N-hydroxy succinimide (or other N-hydroxy imides, to the extent understood by the ordinarily skilled artisan). The mixture was then stirred for several minutes between -150 to 00C then one hour at between 0OC to 250C. After which time the mixture was diluted with ethyl acetate, washed with water and brine, dried over sodium sulfate and reduced in vacuo to a residue. The residue was then purified by column chromatography and/or recrystallization from heptane:ethyl acetate. o Ph 0 H -= J CHs h CO 2 H + Ci 0 CH 3 : OH 3 OBOM CH3 u mN-Methyl Morpholine THF -15 to 250 C HO Oz 0 2 N + 0 HO / 0

HO

S+ F F [Formula 10] [Formula 11] [Formula 12] [Formula 13] Reaction XII WO 00/78707 PCT/US00/16617 24 Reactions VIII, IX, X, XI and XII may be generalized by the following reaction XIII: O O R NH R NH O Riop 1 Ph " 0 0Phi," O-Z OP, OP, + HO-Z Reaction XIII where Pi is a hydroxyl protecting group such as BOM or benzyl; R 1 is an alkyl group, an olefinic group, an aromatic group (such as Ph, PhCH 2 ), an O alkyl group, an O-olefinic group, or an O-aromatic group (such as O-Ph or O

CH

2 Ph); Rio is H or CO 2 X, where X is an alkyl group, an olefinic group, or an aromatic group; and Z is either a substituted phenyl moiety such as:

R

2 R3 * R4 R6 R 5 wherein each of R 2 to R 6 is selected from the group consisting of H and an electron withdrawing group (such as a halogen or NO 2 ), or Z is an N-imido moiety, including but not limited to succinimido, phthalimido, 5-norbornene 2,3-dicarboxyimido, maleimido or derivatives thereof such as a maleimido group or succinimido group substituted at the 3 and/or 4 positions, or other heterocyclic imido groups, preferably having 5 to 7 atoms in the ring, alternatively substituted with chloro, fluoro, nitro or other groups.

WO 00/78707 PCT/US00/16617 25 C. Condensation of C-7 CBZ Baccatin Ill with the Side Chain Activated Esters The side chain activated esters (Formulas 10, 11, 12 or 13, or other variations to the extent understood by the ordinarily skilled artisan) as well as the C-7 CBZ baccatin III may now be condensed. This condensation may proceed in the presence of an appropriate lithium base (e.g., lithium hexamethyl disalizane or n-BuLi) in THF at 00C according to the reaction: AcO 0 OCBZ 0 Ph 0O NH Ph - 000 ph~ c 0 2R , HO'\'H-: H_'/0 Ph0H 6BoM OAc LiN(SiMe3) 2 AcO 0 OCBZ O Ph O NH 0 H Ph O =H 0 _z OH OBOM- OAc OBz (Formula 14) Reaction XV wherein R 1 is p-nitrophenyl (Formula 10), 2,4-dinitrophenyl (Formula 11), pentaflurophenyl (Formula 12), or other substituted phenyl groups, or N succinimido (Formula 13), or other N-imido groups. Here, C-7 CBZ baccatin III (1.0 equivalent) and the activated ester (Formula 10, 11, 12, 13 or others as discussed, 1.5 equivalents) are dissolved in anhydrous THF under nitrogen and brought to OoC. It should be WO 00/78707 PCT/US00/16617 26 noted that other temperatures, including ambient temperature, have been shown to be suitable as well. To this is then added a suitable lithium basein this case lithium hexamethyl disalizane, but n-butyl lithium can also be employed. This presumably generates the C-13 lithium alkoxide of C-7 CBZ baccatin III in analogous fashion to the C-13 lithium alkoxide of C-7 TES baccatin III as described by Holton (U.S. Patent No. 5,229,526 and U.S. Patent No. 5,274,124). The mixture is then stirred for a period of time, preferably several hours, although time periods as short as thirty minutes have been employed. The mixture is then diluted with a 1:1 mixture of ethyl acetate and 1N HCl, the organic phase collected and washed with water and brine, dried over sodium sulfate and reduced in vacuo to a residue. The residue could then be purified by column chromatography (ethyl acetate/heptane) or recrystallization (diethyl ether or methyl t-butyl ether or ethyl acetate/heptane) to afford the coupled product of Formula 14. AcO O OCBZ 0 P h O) N H 0 /H P hO OBOM OAc OBz C-7 TES baccatin III can also be used in place of C-7-CBZ baccatin III to yield Formula 15. AcO O OTES 0 Ph O N H 0 H Ph O OH OBOM OAc OBz (Formula 15) WO 00/78707 PCT/US00/16617 27 The synthesis of C-7 TES baccatin Ill has been described (see Denis et al in "A Highly Efficient, Practical Approach to Natural Taxol," J. Am. Chem. Soc., 1988, p. 5917 and Kant et al in "A Chemoselective Approach to Functionalize the C-10 Position of 10-deacetyl Baccatin Ill. Synthesis and Biological Properties of Novel Taxol Analogs", Tetrahedron Letters, Vol. 35, No. 31, 1994, p. 5543). Other C-7 protected baccatin III compounds may also be used, to the extent understood by the ordinarily skilled artisan. The conversion of Formula 14 to paclitaxel has been previously described (Sisti et al, S.N. 08/719,488 now U.S. Patent No. 5,750,737) and may be accomplished as follows: D. Deprotections and Acylations to Form Paclitaxel from Formula 14 The compound according to Formula 14 may now be converted into paclitaxel by removing the nitrogen and C-7 CBZ groups, putting the benzoyl group onto the nitrogen, and finally removing the C-2' benzyl-type protecting group. Removal of the CBZ groups, and subsequent addition of the benzoyl group to the nitrogen are accomplished as follows (BOM is shown as the protecting group at the C-2' hydroxyl site, although benzyl could also be used): WO 00/78707 PCT/US00/16617 28 AcO O OCO 2

CH

2 Ph 0 Ph O J"NH O0 H Ph 0 OH : = 00 POCOPh AcO O OH (Frmla16 P h N H O H 0 Ph O H : OH : Ph O O OAc OCOPh (Formula 16) Reaction XVI Here, the coupled product of Formula 14 is dissolved in isopropanol to which the Pearlman's catalyst is added. The resulting mixture is hydrogenated at 40 psi for twenty-four hours, although alternatively, the mixture can be stirred under one atmosphere of hydrogen for twenty-four hours. Alternatively, the mixture can be hydrogenated at 1 atm of hydrogen in the presence of at least one equivalent of tri-fluroacetic acid resulting in the TFA salt of the resultant amine. Thereafter, the mixture is filtered through diatomaceous earth and reduced under vacuum to residue. Preferably, the residue is taken up in toluene and anhydrous potassium carbonate added. Alternatively, the residue may be taken up in ethyl acetate or toluene and a tertiary amine base, such as triethylamine, is added. In either case, benzoyl chloride is then added dropwise, and the mixture stirred for two hours. The resulting mixture is then washed with water and finally WO 00/78707 PCT/US00/16617 29 brine. The resulting organic phase is then separated, dried, and concentrated under vacuum to yield C-2'-BOM paclitaxel (Formula 16). Finally, the C-2'-BOM is removed according to the following reaction: AcO O OH 0 P h ) ,N H O H Ph 0 = H : OH PH 0 0 OAc Ph O O OCOPh AcO 0 OH O Ph N H O H Ph _O _ I H P hOH 0 O = OAc OH OCOPh Reaction XVII The BOM protected paclitaxel is dissolved in isopropanol to which Pearlman's catalyst is added. This mixture is hydrogenated for twenty-four hours under 40 psi hydrogen or twenty-four hours under one atmosphere of hydrogen in the presence of tri-fluroacetic acid to yield paclitaxel. The conversion of Formula 15 to paclitaxel has been previously described (Sisti et al, U.S. Patent No. 5,675,025, Oct. 7, 1997) and may be accomplished as follows: E. Deprotections and Acylation to Form Paclitaxel from Formula 15 The compound according to Formula 15 may now be converted into paclitaxel by removing the CBZ protecting group and acylating the side chain, removing the TES protecting group and removing the hydrogenatable WO 00/78707 PCT/US00/16617 30 benzyl protecting group. Here, several convenient routes have been found although in general, it is necessary to deprotect the C-7 site by removing the TES protecting group prior to deprotecting the C-2' site with the hydrogenatable benzyl protecting group. If the TES protecting group is not removed first, it is believed difficult at best to remove the hydrogenatable protecting group in a later processing step. In any event, the preferred route of producing paclitaxel is to first remove the CBZ protecting group according to the reaction: 0 Ph O NH 0H O BM .K OH~ iAcO O NOTES Ph O O OH OAc OBOM OCOPh 1. 2. AcO O OTES O PhKNH O0 Ph 0 O 0 OH - OAc OBOM OCOPh 1. Pearlmans Cat., 1 Atm H2, iPrOH 2. Benzoyl Chloride, EtOAc, TEA Reaction XVIII Here, the coupled product of Formula 15 is dissolved in isopropanol to which the Pearlman's catalyst is added. The resulting mixture is stirred under one atmosphere of hydrogen for twenty-four hours. Thereafter, the mixture is filtered through diatomaceous earth and reduced under vacuum to residue. The residue may then be taken up in ethyl acetate or toluene and a tertiary amine base, such as triethylamine is added. Benzoyl chloride was added WO 00/78707 PCT/US00/16617 31 dropwise, and the mixture stirred for two hours. The resulting mixture was then washed with dilute aqueous solution of NaHCO3, water, and finally brine. The resulting organic phase was then separated, dried and reduced under vacuum to yield the CBZ deprotected/acylated compound: AcO O OTES 0 Ph NH O H Ph O OH OAc OBOM OCOPh (Formula 17) Next, the compound of Formula 17 is deprotected at C-7 according to the reaction: AcO O OTES 0 Ph NH 0 H Ph 0" H1 O OH OAc OBOM OCOPh HF 40%

CH

3 CN nAcO O OH 0 Ph ]NH 0 Ph H \0 O - OH OAc OBOM OCOPh Reaction XIX Here, the compound of Formula 17 was dissolved in acetonitrile (CH 3 CN) at 00C. Hydrofluoric acid (40% aqueous) was then added and the mixture WO 00/78707 PCT/US00/16617 32 stirred for ten hours while being held at 00C. Thereafter, the mixture is diluted with ethyl acetate, saturated aqueous solution of NaHCO 3 , water and finally brine. The organic phase was separated, dried and reduced under vacuum to produce a deprotected product at the C-7 position according to the formula: AcO O OH O Ph NH O Ph O OH OAc OBOM OCOPh (Formula 18) Finally, the compound of Formula 18 is deprotected at C-2' to remove the hydrogenatable benzyl-type (BOM) protecting group and to liberate the C-2' hydroxy group thereby resulting in the desired paclitaxel. This is accomplished according to the reaction: AcO O OH O Ph I"NH O Ph OH OAc OBOM OCOPh Pearlmans Cat.

H

2 40 psi, iPrOH 24 h. PACLITAXEL Alternatively, the compound of Formula 15 may first be dissolved in

CH

3 CN at 00C and hydrofluoric acid (40% aqueous) added to deprotect the compound at the C-7 site by removing the TES protecting group. This results in a compound according to the Formula 19: WO 00/78707 PCT/US00/16617 33 AcO O OH 0 Ph O NH 0 Ph 0 OH OAc OBOM OCOPh (Formula 19) Next, the CBZ protecting group may be removed in a manner similar to that described above. Here, the compound of Formula 19 is dissolved in isopropanol and Pearlman's catalyst was added along with trifluoroacetic acid (TFA) (one equivalent). The mixture was held at 40 psi of hydrogen at room temperature for approximately four days. This removes the CBZ protecting group and forms the C-2' BOM protected paclitaxel compound as a TFA salt. The mixture was filtered through diatomaceous earth and reduced under vacuum. Next, a base plus an acylating agent was added to the residue. Specifically, the TFA salt of the C-2' BOM protected compound was dissolved in pyridine and either benzoyl chloride or benzoic anhydride was added. The resulting product is: AcO O OH 0 Ph NH 0 Ph - 0 : OH OAc OBOM OCOPh (Formula 16) The compound of Formula 16 is dissolved in isopropyl alcohol and placed in a Parr bottle and Pearlman's catalyst was added. The mixture was hydrogenated for twenty-four hours at 40 psi of hydrogen. Thereafter, the mixture was filtered through diatomaceous earth and the eluent reduced under vacuum. The residue may then be column chromatographed WO 00/78707 PCT/US00/16617 34 according to any desired technique or recrystallized from ethyl acetate:hexane for the final paclitaxel product. Accordingly, the present invention has been described with some degree of particularity directed to the exemplary embodiments of the present invention. It should be appreciated, though, that the present invention is defined by the following claims construed in light of the prior art so that modifications or changes may be made to the exemplary embodiments of the present invention without departing from the inventive concepts contained herein.

Claims

1. A chemical compound having the formula: 0 R, NH 0 Ph O- Z OP 1 wherein P 1 is a hydroxyl protecting group; R 1 is an alkyl group, an olefinic group, an aromatic group, an O-alkyl group, an O-olefinic group, or an O aromatic group; and wherein Z is selected from the group consisting of a substituted phenyl moiety and an N-imido moiety.

2. A chemical compound according to claim 1 wherein R 1 is selected from the group consisting of Ph, PhCH 2 , O-Ph and O-CH 2 Ph.

3. A chemical compound according to claim 1 wherein P 1 is selected from the group consisting of benzyl, benzyloxymethyl and benzoyl.

4. A chemical compound according to claim 1 wherein R, is O-CH 2 Ph and P 1 is benzyloxymethyl.

5. A chemical compound according to claim 1, wherein Z is a substituted phenyl moiety having the formula: R 2 R3 * R4 R 6 R 5 wherein each of R 2 to Re is selected from the group consisting of H and an electron withdrawing group.

6. A chemical compound according to claim 5 wherein each of R 2 to R 6 is selected from the group consisting of H, halogen and NO 2 ; with at least one R 2 to R 6 being one of the group consisting of halogen and NO 2 . WO 00/78707 PCT/US00/16617 36

7. A chemical compound according to claim 6 wherein said halogen is F.

8. A chemical compound according to claim 6 wherein P 1 is selected from the group consisting of benzyl, benzyloxymethyl and benzoyl; R 2 , R 3 , Rs, and R6 are H; R 4 is NO 2 ; and R 1 is OCH 2 Ph.

9. A chemical compound according to claim 6 wherein P 1 is selected from the group consisting of benzyl, benzyloxymethyl and benzoyl; R 2 , R 3 , R 4 , R 5 and R 6 are F; and R 1 is OCH 2 Ph

10. A chemical compound according to claim 6 wherein P 1 is selected from the group consisting of benzyl, benzyloxymethyl and benzoyl; R 2 and R4 are NO 2 ; R 3 , Rs, and R 6 are H; and R, is OCH 2 Ph.

11. A chemical compound according to claim 1 wherein Z is a heterocyclic N-imido moiety having 5 to 7 atoms in the ring.

12. A chemical compound according to claim 1 wherein Z is a heterocyclic N-imido moiety substituted with at least one electron withdrawing group.

13. A chemical compound according to claim 12 wherein said electron withdrawing group is selected from the group consisting of a halogen and a nitro group.

14. A chemical compound according to claim 12 wherein said heterocyclic N-imido moiety is substituted with a plurality of electron withdrawing groups, wherein a first electron withdrawing group substituted on said heterocyclic N-imido moiety is of a type different from a second electron withdrawing group substituted on said heterocyclic N-imido moiety.

15. A chemical compound according to claim 1 wherein Z is selected from the group consisting of succinimido, phthalimido, 5 norbornene-2,3-dicarboxyimido, and maleimido moieties and substituted derivatives thereof.

16. A chemical compound according to claim 1 wherein Z is an N imido moiety selected from the group consisting of Formulas 1 to 5, as follows: WO 00/78707 PCT/US00/16617 37 O R2 -N R 3 R4 R5 Formula 1 0 0 R2 -N CR3 o o Formula 2 0 R2 R, R3 - N R7 R6 9 R 4 0 R2 R3 N R4 O R5 Formula 4 0 -N (C Y 2)n 0 Formula 5 wherein R 2 to R 9 and Y are each selected from the group consisting of H and an electron withdrawing group; and n is an integer.

17. A chemical compound according to claim 16 wherein Z is the WO 00/78707 PCT/US00/16617 38 N-imido moiety of Formula 5 where n has an integer value of 2 to 4.

18. A chemical compound according to claim 16 wherein R 2 to R 9 and Y are each an electron withdrawing group selected from the group consisting of a halogen and a nitro group.

19. A chemical process to form an ester derivative useful in the production of paclitaxel, paclitaxel analogues and their intermediates comprising the step of reacting a first compound of the general formula: O Ri NH Ph- C0 2 R o OP op 1 wherein Ri is an alkyl group, an olefinic group, an aromatic group, an O-alkyl group, an O-olefinic group, or an O-aromatic group; P 1 is a hydroxyl protecting group; and Rio is H or CO 2 X, where X is an alkyl group, an olefinic group or an aromatic group, with a second compound of the general formula: HO-Z wherein Z is selected from the group consisting of a substituted phenyl moiety and an N-imido moiety, to give a third compound of the general formula: 0 R, NH O Ph O- Z OP 1 wherein Ri is an alkyl group, an olefinic group, an aromatic group, an O-alkyl group, an O-olefinic group, or an O-aromatic group; P 1 is a hydroxyl protecting group; and Z is selected from the group consisting of a substituted phenyl moiety and an N-imido moiety. WO 00/78707 PCT/US00/16617 39

20. A chemical process according to claim 19 wherein Rio is H and the step of reacting is conducted in the presence of THF and a carbodiimide.

21. A chemical process according to claim 20 wherein the carbodiimide is dicyclohexylcarbodiimide.

22. A chemical process according to claim 19 wherein Ro 10 is CO 2 X, where X is an alkyl group, an olefinic group or an aromatic group.

23. A chemical process according to claim 22 wherein X is -CH 2 CH(CH3) 2 .

24. A chemical process according to claim 22 wherein the step of reacting is conducted in the presence of N-methyl morpholine and THF.

25. A chemical process according to claim 22 wherein the first compound is formed by reacting a compound having the formula: O R NH Ph CO 2 H OPPh oP 1 with a compound having the formula CI-CO 2 X to give the first compound.

26. A chemical process according to claim 19 wherein said second compound has the formula: R 2 R 3 HO R4 R6 R 5 wherein each of R 2 to R 6 is selected from the group consisting of H and an electron withdrawing group.

27. A chemical process according to claim 26 wherein each of R2 to R 6 is selected from the group consisting of H, halogen and NO 2 with at least one R 2 to R 6 being one of the group consisting of halogen and NO 2 ; R 1 WO 00/78707 PCT/US00/16617 40 is selected from the group consisting of Ph, PhCH 2 , O-Ph and O-CH 2 Ph; and P 1 is selected from the group consisting of benzyl, benzyloxymethyl and benzoyl.

28. A chemical process according to claim 19 wherein Z is a heterocyclic N-imido moiety having 5 to 7 atoms in the ring.

29. A chemical process according to claim 19 wherein Z is an N imido moiety selected from the group consisting of succinimido, phthalimido, 5-norbornene-2,3-dicarboxyimido, and maleimido moieties and substituted derivatives thereof.