6-Hydrazinopurine 2'-methyl ribonucleosides and their 5'-monophosphate prodrugs as potent hepatitis C virus inhibitors.

A series of 6-hydrazinopurine 2'-methyl ribonucleosides was synthesized and tested for its inhibitory activity against the hepatitis C virus (HCV). The lack of antiviral activity of these nucleosides was associated with a poor affinity for adenosine kinase, which prompted us to synthesize several of their 5'-monophosphate prodrugs. Some of these prodrugs exhibited more than 1000-fold improvement in anti-HCV activity when compared to their parent nucleosides (EC(50) of 24 nM vs 92 microM for the parent).

Cyclic monophosphate prodrugs of base-modified 2'-C-methyl ribonucleosides as potent inhibitors of hepatitis C virus RNA replication.

A new series of heterobase-modified 2'-C-methyl ribonucleosides was synthesized and tested as inhibitors of hepatitis C virus (HCV) RNA replication. The nucleosides showed a weak inhibitory activity in a HCV replicon system (EC(50)=92 microM) and did not exhibit any cytotoxicity (CC(50)>300 microM). Cyclic monophosphate (cMP) prodrugs of the same nucleosides were synthesized and also tested in the HCV replicon system. Prodrugs exhibited strong potency (EC(50)=0.008 microM) without significant cytotoxicity (CC(50)>50 microM).

Structure-activity relationship (SAR) studies of quinoxalines as novel HCV NS5B RNA-dependent RNA polymerase inhibitors.

From chemical compound library screening using an HCV NS5B RNA-dependent RNA polymerase enzymatic assay, we identified a substituted quinoxaline hit with an IC(50) of 5.5 microM. A series of substituted quinoxaline amide derivatives were synthesized based on the hit's pharmacophore, and a good structure-activity relationship was observed. Computer modeling analysis was employed to help comprehend the SAR.

MDPSCL2: a new protecting group for chemoselective synthesis of 2'-O-alkylated guanosines.

An improved strategy for the synthesis of 2'-O-methyl-guanosine (6) and 2'-MOE-guanosine (8) is reported. The regioselectivity of the alkylation was attained using a novel silicon-based protecting group, methylene-bis (diisopropyl-silylchloride) (MDPSCl2, 2). The alkylation proceeded in a chemoselective manner using NaHMDS as the base and MeCl or MOE-Br as the appropriate electrophiles.

Novel synthesis of 2'-O-methylguanosine.

An efficient and chemoselective synthesis of 2'-O-methylguanosine (6) has been accomplished in high yield without protection of the guanine base. The salient feature of the synthesis of 6 lies in the application of methylene-bis-(diisopropylsilyl chloride), (MDPSCl(2), 2) as a new 3',5'-O-protecting group for nucleosides. Use of CH(3)Cl as a weak electrophile and NaHMDS as a mild base was crucial to the success of the 2'-O-methylation of 3',5'-O-protected guanosine.

Synthesis of 2'-O-methoxyethylguanosine using a novel silicon-based protecting group.

A short and efficient synthesis of 2'-O-methoxyethylguanosine (8) is described. Central to this strategy is the development of a novel silicon-based protecting group (MDPSCl(2), 2) used to protect the 3',5'-hydroxyl groups of the ribose. Silylation of guanosine with 2 proceeded with excellent regioselectivity and in 79% yield. Alkylation of the 2'-hydroxyl group of 6 proceeded with methoxyethyl bromide and NaHMDS and afforded compound 7 in 85% yield, without any noticeable cleavage of the silyl protecting group and without the need to protect the guanine base moiety. Finally, deprotection of 7 was achieved using TBAF and produced 8 in 97% yield.