Synthesis of carbocyclic analogs of 2',3'-dideoxysangivamycin, 2',3'-dideoxytoyocamycin, and 2',3'-dideoxytriciribine.

Syntheses and antiviral activity of new carbocyclic analogs of 2', 3'-dideoxysangivamycin, 2',3'-dideoxytoyocamycin and 2',3'-dideoxytriciribine is described. The key intermediate, carbocyclic 4-chloro-5-iodopyrrolopyrimidine. was synthesized in good yield via a novel iodination method using I2 and CF3COOAg. This carbocyclic 4-chloro-5-iodopyrrolopyrimidine then allowed for a concise synthesis of the desired 4,5-disubstituted carbocyclic nucleosides.

Synthesis and antiviral evaluation of halogenated beta-D- and -L-erythrofuranosylbenzimidazoles.

A series of 2-substituted benzimidazole D- and L-erythrofuranosyl nucleosides were synthesized and tested for activity against herpesviruses and for cytotoxicity. The D-nucleosides 2,5, 6-trichloro-1-(beta-D-erythrofuranosyl)benzimidazole (8a) and 2-bromo-5,6-dichloro-1-(beta-D-erythrofuranosyl)benzimidazole (8b) were prepared by coupling 1,2,3-tri-O-acetyl-beta-D-erythrofuranose (D-6) with the appropriate benzimidazole, followed by removal of the acetyl protecting groups. The 2-isopropylamino (9), 2-cyclopropylamino (10), and 2-mercaptobenzyl (11) derivatives were synthesized by nucleophilic displacements of the C-2 chlorine in the benzimidazole moiety of 8a. The D-nucleoside 4-bromo-5, 6-dichloro-2-isopropylamino-1-(beta-D-erythrofuranosyl)benzimid azo le (17) was prepared by coupling D-6 with the appropriate benzimidazole. The L-erythrofuranosyl derivatives, 5, 6-dichloro-2-isopropylamino-1-(beta-L-erythrofuranosyl)benzimid azo le (21a), its 2-cyclopropylamino analogue (21b), and the 2-isopropylamino analogue (25), were prepared by coupling L-6 with the appropriate benzimidazole. Several of these new derivatives had very good activity against HCMV in plaque and yield reduction assays (IC(50) = 0.05-19 microM against the Towne strain of HCMV) and DNA hybridization assays. Very little activity was observed against other herpesviruses. This pattern is similar to the antiviral activity profile observed for the corresponding ribofuranosides 2,5, 6-trichloro-1-(beta-D-ribofuranosyl)benzimidazole (4a), its 2-bromo analogue (4b), and the 2-cyclopropylamino analogue (4c). In comparison, 8a was 15-fold more active against HCMV than 4a, and 8b was 4-fold more active against HCMV than 4b. The 5, 6-dichloro-2-isopropylamino-1-(beta-L-erythrofuranosyl)benzimid azo le (21a) was less active than 4c, which is now in clinical trials for HCMV infection. Both 8a,b had comparable HCMV activity to 4c. Mode of action studies with the D-erythrose analogues established that 8b acted by inhibition of viral DNA processing whereas 9 and 10 may act via a different mechanism. The lack of a 5'-hydroxymethyl group in all members of this series established that antiviral activity occurred without 5'-phosphorylation, a feature required for the activity of most nucleoside analogues.

Synthesis of fluorosugar analogues of 2,5,6-trichloro-1-(beta-D-ribofuranosyl)benzimidazole as antivirals with potentially increased glycosidic bond stability.

The metabolic instability in vivo of the glycosidic bond of 2,5, 6-trichloro-1-(beta-D-ribofuranosyl)benzimidazole (TCRB) prompted us to design and synthesize the hitherto unreported fluorinated benzimidazole nucleosides 2,5, 6-trichloro-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)benzimidazole , 2,5, 6-trichloro-1-(3-deoxy-3-fluoro-beta-D-xylofuranosyl)benzimidazole, and 2-bromo-5, 6-dichloro-1-(2-deoxy-2-fluoro-beta-D-ribofuranosyl)benzimidazole. TCRB was converted into the 2',5'-ditrityl and 3',5'-ditrityl derivatives, which were fluorinated with DAST and deprotected to yield 2,5, 6-trichloro-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)benzimidazole and 2,5, 6-trichloro-1-(3-deoxy-3-fluoro-beta-D-xylofuranosyl)benzimidazole. The resulting low overall yield (5%) of 2,5, 6-trichloro-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)benzimidazole encouraged us to develop an alternative route. The heterocycle 2,5, 6-trichlorobenzimidazole was condensed with 1-bromo-3, 5-di-O-benzoyl-2-deoxy-2-fluoro-alpha-D-arabinofuranose to give, after deprotection, 2,5, 6-trichloro-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)benzimidazole in a 50% overall yield. The 2'-deoxy-2'-fluoro-beta-D-ribofuranosyl compounds were prepared using 2'-deoxy-2'-fluorouridine, N-deoxyribofuranosyl transferase, and 5,6-dichlorobenzimidazole. Functionalization of the C2 position then gave the desired derivatives. Antiviral and cytotoxicity testing revealed that the deoxy fluoro arabinofuranosyl, xylofuranosyl, and ribofuranosyl derivatives were less active against human cytomegalovirus and more cytotoxic than TCRB.

Studies designed to increase the stability and antiviral activity (HCMV) of the active benzimidazole nucleoside, TCRB.

The potent activity of 2,5,6-trichloro-1-(beta-D-ribofuranosyl)benzimidazole (TCRB) against Human Cytomegalovirus with the concomitant low cellular toxicity at concentrations that inhibit viral growth prompted considerable interest in this research area. This interest was moderated by the pharmacokinetic studies of TCRB in rats and monkeys that revealed the instability of TCRB in vivo. These studies suggested that the instability was due to a cleavage of the glycosidic bond in vivo which released the heterocycle (2,5,6-trichlorobenzimidazole) into the bloodstream. This prompted us to initiate synthetic studies designed to increase the stability of the glycosidic bond of TCRB and BDCRB. Several synthetic approaches to address this and other problems are presented.

Synthesis and antiviral activity of certain 5'-modified analogs of 2,5,6-trichloro-1-(beta-D-ribofuranosyl)benzimidazole.

A series of 5'-modified 2,5,6-trichlorobenzimidazole ribonucleosides has been synthesized and tested for activity against two human herpesviruses and for cytotoxicity. The 5'-methoxy, 5'-ethoxy, and 5'-butoxy analogs of 2,5,6-trichloro-1-(beta-D-ribofuranosyl)benzimidazole (TCRB) were prepared by coupling the appropriate 5-O-alkyl-1,2,3-tri-O-acetyl-beta-D-ribose derivatives with 2,5,6-trichlorobenzimidazole followed by removal of the protecting groups. The 5'-deoxy-5'-fluoro, -5'-chloro, -5'-bromo, -5'-iodo, -5'-azido, and -5'-thiomethyl derivatives were synthesized in a similar fashion. All of these 5'-modified derivatives had significant activity against HCMV in plaque and yield reduction assays (IC50's = 0.5-14.2 microM) but had little activity (IC50's > 100 microM) against HSV-1. This pattern in similar to the antiviral activity profile observed for TCRB. The 5'-halogenated derivatives were more active than the other 5'-modified derivatives with antiviral activity well separated from cytotoxicity. In general, cytotoxicity of all the 5'-modified derivatives was greater in human foreskin fibroblasts (HFF cells) than in L1210 or KB tumor cells. These results indicate that the viral target tolerates significant modifications of TCRB at the 5'-position without adversely affecting activity against HCMV, whereas the 5'-modifications increased cytotoxicity in human diploid cells.