Synthesis and antiviral activity of novel isonucleoside analogs.

A series of branched-chain sugar isonucleosides was synthesized and evaluated for antiviral activity against herpesviruses. The preparation of homochiral [3S-(3 alpha, 4 beta, 5 alpha)]-2-amino-1, 9-dihydro-9-[tetrahydro-4,5-bis(hydroxymethyl)-3-furanyl]-6H-purin-6-one (7, BMS-181,164) and related compounds was stereospecifically achieved starting from 1,2-isopropylidene-D-xylofuranose (10). An efficient two-step reduction of the anomeric center of bis-acetate 18 involved formation of the chloride intermediate 19, followed by diisobutylaluminum hydride reduction. Tosylation of the resulting alcohol 20 provided the key intermediate 21, which was coupled with a variety of nucleobase anions. Several members of this new class of compounds possess activity against herpes simplex virus types 1 and 2 (HSV-1 and -2), varicella-zoster virus (VZV), and human cytomegalovirus (HCMV). Compound 7 exhibits potent and selective activity against thymidine kinase encoding herpesviruses, in particular, HSV-1 and HSV-2. Evaluation of compound 7 for inhibition of WI-38 cell growth indicated an ID50 of > 700 microM. Although the antiherpetic activity in vitro of 7 is less than that of acyclovir (1), compound 7 displays superior efficacy in mouse model infections. The (bromovinyl)uridine analog 8 (BMS-181,165) also exhibits selective activity against HSV-1 and VZV, with no cytostatic effect on WI-38 cell growth at > 800 microM. Compound 8 is active against simian varicella virus and is efficacious in the corresponding monkey model.

Synthesis and antiviral activity of 1-cyclobutyl-5-(2-bromovinyl)uracil nucleoside analogues and related compounds.

A series of racemic (1 alpha (E), 2 beta, 3 alpha)-1-[2,3-bis(hydroxymethyl)cyclobutyl]-5-(2-halovinyl)uracils was synthesized and evaluated in cell culture. The bromovinyl, iodovinyl, and chlorovinyl analogues, 13, 15, and 16, respectively, are all potent inhibitors of varicella zoster virus (VZV), but are less inhibitory to the replication of human cytomegalovirus (HCMV) and herpes simplex viruses 1 and 2 (HSV-1, HSV-2). The excellent anti-VZV activities of 13, 15, and 16 coupled with their virtual inability to inhibit WI-38 cell growth indicate high in vitro therapeutic indices. VZV thymidine kinase readily converts these compounds to their respective monophosphates but not to their corresponding diphosphates. Compound 13a, the (1'R) enantiomer of the bromovinyl analogue 13, was also synthesized, and its potency is comparable to that of the racemate. A lower homologue 14, (1 alpha (E),2 beta, 3 alpha)-1-[2-hydroxy-3-(hydroxymethyl)cyclobutyl]-5- (2-bromovinyl)uracil, was found to be inactive against VZV, HCMV, HSV-1, and HSV-2.

Selective activity and cellular pharmacology of (1R-1 alpha,2 beta,3 alpha)-9-[2,3-bis(hydroxymethyl)cyclobutyl]guanine in herpesvirus-infected cells.

The cycloburtane nucleoside analog (1R-1 alpha,2 beta,3 alpha)-9-[2,3-bis(hydroxymethyl)cyclobutyl]guanine [(R)-BHCG or SQ 34,514] was recently synthesized and shown to be the active enantiomer of (+/-)-BHCG (SQ 33,054), a potent inhibitor of several strains of herpesviruses [J. Med. Chem 34:1415-1421 (1991); Antiviral Res. 13:41-52 (1990)]. In plaque reduction assays, (R)-BHCG was about 1000 times more active than its S-enantiomer on herpes simplex virus type I (HSV-1) and over 200 times more active against a thymidine kinase-deficient mutant HSV-1 and human cytomegalovirus (HCMV). We now show that both (R)-BHCG and (S)-BHCG are efficiently phosphorylated to their mono-, di-, and triphosphates by HSV-1-infected cells, in a manner similar to that of acyclovir [Proc. Natl. Acad. Sci. USA 74:5716-5720 (1977)]. The uptake of both enantiomers was greatly increased upon infection; however, (S)-BHCG was taken up to about twice the extent of (R)-BHCG and accumulated primarily as the mono- and diphosphates. (R)-BHCG accumulated primarily as the triphosphate, and accumulation was linear with both time and added drug concentration. The triphosphate had an apparent half-life of about 10 hr. Metabolic studies using HCMV-infected cells showed only a small degree of phosphorylation of (R)-BHCG and none of (S)-BHCG. When cells were labeled with 25 microM (R)-BHCG, the amount of (R)-BHCG triphosphate formed was less than 0.5 pmol/10(6) cells. Interestingly, the ED50 value of (R)-BHCG is about 100-fold higher against HCMV than against HSV-1, and the relative levels of (R)-BHCG triphosphate formed in cells infected by the two viruses are roughly proportional to the antiviral activities.

(+-)-(1 alpha,2 beta,3 alpha)-9-[2,3-bis(hydroxymethyl)-cyclobutyl] guanine [(+-)-BHCG or SQ 33,054]: a potent and selective inhibitor of herpesviruses.

(+-)-(1 alpha,2 beta,3 alpha)-9-[2,3-bis(hydroxymethyl)cyclobutyl] guanine [(+-)-BHCG or SQ 33,054] is a newly synthesized nucleoside analog with potent and selective antiviral activity against members of the herpesvirus group, including human cytomegalovirus. The activity against a thymidine kinase deficient HSV-2 mutant was 25-fold poorer than against the parent virus, suggesting that phosphorylation is an important prerequisite for antiviral activity against HSV-2. (+-)-BHCG is readily phosphorylated by purified HSV-1 thymidine kinase, and BHCG triphosphate synthesized enzymatically is a selective inhibitor of HSV-1 DNA polymerase. (+-)-BHCG did not inhibit host cell growth at concentrations at least 1000-fold higher than HSV-2 inhibitory concentrations. Subcutaneous administration of (+-)-BHCG was protective against HSV-1 systemic infections in mice. BHCG is an exciting antiviral agent and represents a new class of nucleoside analogs.