IL105572A - Production of 2',3'-dideoxy-2', 3'-didehydronucleosides - Google Patents

Description

o>t>DiN>^ i :η-ι-τ>π-ρ-τ-3' ,2* ->ορ Ν7>-τ-3' ,2* mon Production of 2 ' , 3 ' -dideoxy-2 ' , 31 -didehydronucleosides BRISTOL-MYERS SQUIBB COMPANY C: 89206/7 PRODUCTION OF 2 ' , 3 ' -DIDEOXY-2 ' , 3 ' -DIDEHYDRONUCLEOSIDES BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to improved processes to produc 2 ' , 3 ' -dideoxy-2 , ' 3 ' -didehydronucleosides .

DESCRIPTION OF THE BACKGROUND AND RELATED REFERENCES Acquired immunodeficiency syndrome (AIDS) is the resul of an infection by human immunodeficiency virus(es) '(HIV).

This retrovirus shows a specific tropism for the 2 helper/inducer T cells leading to their depletion. The resultant immunosuppression predisposes -HIV patients to life-threatening opportunistic infections.

Although at present there is no cure for AIDS, one nucleoside derivative, 3 ' -azido-3 ' -deoxythymidine (AZT, RetrovirTM), has already proved to be an efficacious agent in the treatment of AIDS in clinical trials and has been licensed by the appropriate regulatory agency for use in 3 patients with AIDS. A number of other chemical and biological agents have been reported to have biological activity against HIV. 2 ' , 3 ' -Dideoxycytidine (ddC), 2 ' , 3 ' -dideoxyadenosine (ddA),4 2 ' , 3 ' -dideoxy-2 ' , 3 ' -didehydrocyt dine (d4C),^ suramine and its analogs ribavarin,'' foscarnet,® HPA-23,^ d-penicillamine, castanospermine, ^ fusidic acid,^ 13 3 ' -azidoguanosine (AZG) , and 3 ' - luoro-3 '-deoxythymidine (FDDT) 14 are all reported to be active against HIV.

A number of reports have appeared in the literature which have shown that 2 ' , 3 ' -dideoxy-21 , 3 ' -didehydrothymidine (d4T) possesses in vitro activity against HIV in several cell lines. ^ 2' ,3' -dideoxy-2' , 3 ' -didehydrothymidine (d4T) has been prepared by Horwitz et al. by two different routes. ' The first; of these synthetic routes involves subjecting the 3 ' , 5 ' -anhydro derivative of thymidine to elimination reaction conditions. The second of these routes involves subjecting the 5 ' -O-protected 2,3'-anhydro nucleoside derivative of thymidine to ring-opening elimination reaction conditions.

The use of anhydro nucleosides as intermediates for nucleoside synthesis is well precedented in the literature in the art to which the present invention pertains. 18 With the recent discovery of the potency of 2',3'-dideoxy-2 ' , 3 ' -didehydrothy idine (d4T) as an anti-HIV agent, a process which allows 2 ' , 3 ' -dideoxy-2 ' , 3 ' -didehyd'ro-nucleosides, including d4T, to be prepared cheaply on a large scale becomes important.

The Horwitz route to produce d4T from the 31 , 5 ' -anhydro compound^ is not feasible on a large scale because complete removal of the large volume of DMSO used in scale-up of the Horwitz procedure is very difficult to achieve and requires high vacuum (0.01 mmHg and heating for the temperature range of about 40-50°C) for an extended period of time. These conditions lead to cleavage of the glycosidic bond to give thymine as an undesired side product. ,Also, prolonged exposure to basic conditions, which are required when solvents other than DMSO (e.g. THF, DMF) are used leads to decomposition of d4T to, again, give thymine as an undesired side product.

The alternative Horwitz procedure requires protection of the 5' -OH position before formation of the 2 , 5 ' -anhydro- nucleoside. This 2, 5 ' -anhydronucleoside can be opened to give the 5 ' -O-protected nucleoside.

The desired 2, 3' -anhydro nucleoside can be prepared directly by reacting thymidine with diethyl- ( 2-chloro-l , 1-2-trifluoroethyl ) a •mine .19 SUMMARY OF THE INVENTION This specification is divided out of the parent specification IL 89693. This invention is a process for producing 2',3'-dideoxy-2',3'-didehydronucleosides of the formula in high yields and on a relatively large scale.

DETAILED DESCRIPTION OF THE INVENTION This invention provides a process for producing a 2',3-dideoxy didehydronucleoside represented by the formula wherein B is a member selected from a purine base represented by the structural formula wherein R and R may be the same or different and are selected from hydrogen, hydroxy, halo (F, CI, Br), amino, monoalkylamino, di alky 1 amino , alkoxy and cyano groups wherein the alkyl moiety is selected from C-^-C-j alkyl groups; and : unsubsti tuted and substituted pyrimidine base represented by the structural formula wherein R is selected from hydroxy, amino and sulfhydryl 4 groups; R is selected from hydroxy, amino and sulfhydryl groups and R^ is selected from hydrogen, C^-C^ alkyl, C2~C alkenyl , C-2~C3 n l°alkenyl having from 1 to 5 halo groups as defined herein, C2~C3 alkynyl, alkoxy wherein the alkyl moiety has 1-3 carbon atoms, cyano and halo (F, Cl , Br and I) comprising the steps of (a) reacting a starting ribonucleoside represented by the formula with a- hydroxy protecting group reagent effective to selectively protect the 5 ' -hydroxyl (primary hydroxyl) group; (b) reacting with 51 -OH-protected ribonucleoside from step (a) with a reagent selected from 1 , 1 - thi ocarbodi mi ca-zole and thiophosgene under anhydrous conditions to obtain a reactive intermediate represented by the formula (c) subjecting the intermediate from step (6) to an elimination reaction by treatment with ?(OEt)^ in a polar solvent at an elevated temperature of about 140-175°C for about 0.5-4 hrs; and (d) deproterting the resulting 5 ' -O-protecting group by treatment under mild acid hydrolysis conditions.

As is described above, this invention concerns a process to produce 21 , 3 ' -dideoxy-2 ' , 3 ' -didehydronucleosides wherein the starting material is a ribonucleoside and wherein the base component B is derived from a member selected from the group of bases as described above. Preferably, the base is a pyrimidine base including one of the group of uracil and thymine.

When derived from purine bases, representati e of B are the following: 6-aminopurin-9-yl 2- aininopurin-9-yl 2 , 6-diaminopurin-9-yl 2- amino- 6-hydroxypurin-9-yl (guanin-9-yl) 6-hydroxypurin-9-yl In addition to the above, the B component may be 2-halopurin-9-yl , 6-halopurin-9- 1 , or 2 , 6-dihalopurin-9-yl , in which event the base component need not be activated, for example, completely silylated, in order to undergo the condensation or coupling reaction in -step (e).

When derived from pyrimidine bases, representative of B are the following: 2 , -dihydroxyprimidin-l-yl 5-methyl-2 , 4-dihydroxypyrimidin-l-yl 5-eth l-2 , -aminopyrimidin-l-yl 2-hydroxy-4-aminopyrimidin- 1-yl 5-vinyl-2 , -dihydroxypyrimidin-l-yl 5-halovinyl-2 , 4-dihydroxypyrimidin-l-yl 5-haloethyl-2 , 4-dihydroxypyrimidin-l-yl 5-haloethyl-2 , -dihydroxypyrimidin-l-yl The above-mentioned 5-methyl and 5-ethyl substituents are representative of 5-alkyl substituents and the 5-vinyl substituent is representative of 5-alkenyl substituents.

Examples of halo-groups on the 5-halovinyl (or 5-haloalkenyl ) group include 1 to 4 F, CI, and Br groups.

In the process according to this invention, the first step involves reacting a starting ribonucleoside with one of any conventional hydroxy protecting groups effective to- selectively protect the 5'-hydroxyl group (i.e., the primary hydroxyl group as distinguished from the sugar-ring-bound secondary hydroxy groups). The second step involves reacting the 5'-0 protected ribonucleoside with one of 1 , 1-t iocarbonyldiimdazole and thiophosgene under anhydrous conditions to obtain a reactive thiocarbonate . intermediate represented by the formula s The next step involves subjecting the reactive intermediate to an elimination reaction by treatment with P(OEt).j in a polar solvent at an elevated temperature of about 140-175 C for about 0.5-4 hrs. Finally, the fourth and last step involves deprotecting the resulting 5 ' -O-protecting group of the reactive thiocarbonate intermediate by treatment under mild acid hydrolysis conditions.

SCHEME I illustrates schematically a typical, representative process according to the present invention, proceeding from a starting ribonucleoside through thiocarbonate reactive intermediate.

SCHEME I Thus, the process according to this invention is useful for the preparation of a variety of 2 ' 3 ' -dideoxy-2 ' , 3 ' -didehydronucleosides, especially pyrimidine and purine nucleosides, having antiviral, antimetabolic, and antineoplastic activity as well as activity against human immunodef ciency viruses.

The following examples illustrate but a few representative embodiments of the processes according to this invention and are set forth to teach those skilled in the pertinent art how to practice this invention and are not to be construed as limiting in scope. All parts and percentages are by weight and temperatures are in degrees Celsius unless otherwise specified. 1- ( 5 ' -O-trityl-2 ' , 3 ' -thiocarbonylribofuranosyl )uracil 5 ' -O-Trityluridine (10.6 gm. , 22mM) was added to a dry 250mL round-bottomed flask under an argon atomosphere. Dry tetrahydrofuran (110 mL) was added and -the reaction mixture stirred until it became homogeneous. When - 1 , 1-thiocarbonyl- diimidazole (4.3 gm. , 27 mM) was added to the solution the reaction became yellow and was then allowed to stir at room temperature for 72 hrs. The solvent was removed in vacuo and the resulting syrup flash chromatographed on silica with ethyl acetate/hexane (75:25) as eluent. The produce was isolated and then recrystallized from absolute ethanol to give an off white powder (.8. gm. , 77%). ½ NMR (360 Mhz , CDC13) 8.9 (br 6, lH, NH) , 7.3 (m,16H, 3xC6H5,H6), 5.7 (d, 1H, H5), 5.6 (m, 2H, H2 ' , H3 ' ) , 5.4 (m, 1H, HI'), 3.4 (q, 2H, H5' ) . 5 ' O-Trityl-2 ' , 3 ' -dideoxy-2 ' , 31 -didehydrouridine l-( 5 ' -O-Trityl-2 ' , 3 ' -thiocarbonylribofuranosyl )uracil (6.0 gm., 11.5mM.) was added to triethyl phosphite (30 mL). The triethyl phosphite had been preheated to 160eC. The reaction mixture was heated at 160°C for lhr. The solvent was then removed in vacuo and then the resultant glassy solid was flash chromatographed on silica with ethyl ace¾ate/hexane (75:25) as eluent. The desired product was isolated from the column and then recrystallized from ethyl acetate/hexane and then collected as a white solid (2.0gm.40%). M~.p. 188-191°C. ½ NMR (360 Mhz, CDC13 ) 8.95 (br2, 1H, NH), 8.00 (d, 1H, H6), 7.5 (m, 15H, 3xCgH5), 7.2 (m, 1H, HI') 6.7, (m, 1H, H2 ' ) , 6.05 (m.lH, H3 ' ) , 5.2 (dd, H, H5), 5.10 (br s, 1H, H4'), 3.6 (m, 2H, H5 * ) .

References 1. (a) Barre-Sinoussi , F; Chermann, J.C. Rey, R. ; Nugeyre, M.T.; Chamaret, S.; Gruest, C.; Dauguet, C . ; Axler-Blin, C. ; Rouzioux, C; Rozenbaum, W. ; Montagnier, L. Science (Washington, D.C.) 1983, 220, 868-871. (b) Broder, S.; Gallo, R.C. N. Engl. J. Med. 1984, 311, 1292-1297. (c) Broder, S; Gallo, R.C. Annu. Rev. Immunol. 1985, 3^ 321-336.

. Popovic, M. ; Sarngadharan, M. G.; Read E.; Gallo, R. C. Science (Washington D. C. ) 1984, 224, 497-500. (b) Gallo, R. C. ; Sarngadharan, M. G. ; Popovic, M. ; Shaw, G. M. ; Hahn, B . ; Wong-Stahl, F. ; Robert-Guroff, M. ; Salahaddian, Z., Markham, P.D. Prog. Allergy 1986, 37, 1-45.

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. Mitsuya, H. ; Broder, S. Proc. Natl. Acad. Sci. U.S.A. 1986, 83, 1911-1915. . (a) Lin, T. S.; Shinazi, R. ; Chen, M. S.; Kinney- Thomas, E . ; Prusoff, W. H. Biochem. Pharmacol. 1987, 36, 311. (b) Balzarini, J.; Pauwels, R. ; Herdewijn, P.; De Clercq, E.; Cooney, D. A.; Kang, G-J.; Dalai, M. ; Johns, D.G.; Broder, S. Biochem. Biophys. Res.

Comm. 1986, 140, 735.

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J. J. A er. Med. Assoc. 1987, 258, 1347. (a) Balzarini, J.; Mitsuya, H.; De Clercq, E . ; Broder, S. Int. J. Med. , 1986, 37 451. (b) McCormick, J.B.; Getchell, J.B Mitchell, S.W.; Hicks, D.R. Lancet 1984, ii, 1367. (a) Sarin, P. S.; Taguchi , Y. Sun, D. ; Thornton, A.; Gallo, R.C.; Oberg, B. Biochem. Pharmacol. 1985, 3 , 4075. (b) Sandstrom, E. G. Kaplan, J. C; Byington, R. E.; Hirsch, M. B. Lancet 1985, i., 480.

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A.; Fox, J. J.; Armstrong, D. 27th ICAAC 1987, Abstract 368, pl61. i (a) Lin, T. S.; Chen, M. S . ; Gao, Y-S.; Ghazzouli, I.; Prusoff¾, W. H. J. Med. Chem. 1987, 30, 440. (b) Lin, t. S.; Shinazi, R. F. ; Prusoff, W. H. Biochem.

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Claims (3)

105572/3

1. . A process for producing a 2 ' , 3 ' -dideoxy-2 ' , 3 ' didehydronucleoside represented by the formula wherein B is a member selected from a purine base represented by the structural formula wherein R and R may be the same or different and are selected from hydrogen, hydroxy, halo (E, CI, Br), amino, monoalkylamino, d alky lamino , alkoxy and cyano groups wherein the alkyl moiety is selected from C.-C-j alkyl groups; and ■ unsubsti tuted and substituted pyrimidine base represented by the structural formual wherein R is selected from hydroxy, amino and sulfhydryl 4 groups; R is selected from hydroxy, amino and sulfhydryl groups and R^ is selected from hydrogen, C.-C^ alkyl, C2~C alkenyl, C2~C3 haloalkenyl having from 1 to 5 halo groups as defined herein, 2~C3 alkynyl, alkoxy wherein the alkyl moiety has 1-3 carbon atoms, cyano and halo (F, Cl , Br and I) - - comprising the steps of / (a) reacting a starting ribonucleoside represented by the formula - 15a - 105572/2 with a hydroxy protecting group reagent effective to selectively protect the 5'-hydroxyl (primary hydroxyl) group; (b) reacting with 5 ' -OH-protected ribonucleoside from step (a) with a reagent selected from 1 , 1-thiocarbodiimidazole and thiophosgene under anhydrous conditions to obtain a reactive intermediate represented by the formula s (c) subjecting the intermediate from step (b) to an elimination reaction by treatment with P(0Et)3 in a polar solvent at an elevated temperature of about 140-175 °C for aboiit 0.5 - k hrs ; and (d) deprotecting the resulting 5 ' -0-protecting group by treatment under mild acid hydrolysis conditions. - 16 - 105572/2

2. A process according to claim 1 wherein said pyrimidine base is selected from uridine and 5-methyl uridine.

3. A process for producing 2 ' -3 ' -dideoxy-2 ' -3 ' - didehydronucleoside according to claim 1 substantially as described herein with reference to the exmples. the Applicants, REINHOLD COHN AND PARTNERS - 17 -