title: Design, synthesis, and antiviral activity of certain 2,5,6-trihalo-1-(beta-D-ribofuranosyl)benzimidazoles.
abstract: A new series of 2-substituted 5,6-dichlorobenzimidazole ribonucleosides has been synthesized and tested for activity against two human herpes viruses and for cytotoxicity. 2,5,6-Trichloro-1-(beta-D-ribofuranosyl)benzimidazole (TCRB) was prepared by ribosylation of the heterocycle 2,5,6-trichlorobenzimidazole followed by a removal of the protecting groups. The 2-bromo derivative (BDCRB) was made in a similar fashion from 2-bromo-5,6-dichlorobenzimidazole. In contrast, the 2-iodo derivative presented a more difficult problem since the appropriate heterocycle was unavailable. This prompted us to prepare the 2-amino derivative followed by nonaqueous diazotization and removal of the blocking groups. Biological evaluation revealed marked differences in the activities of these compounds and the closely related known compound 5,6-dichloro-1-(beta-D-ribofuranosyl)benzimidazole (DRB). DRB was weakly active against both human cytomegalovirus (HCMV) and herpes simplex virus type 1 (HSV-1), (IC50's = 42 and 30 microM, respectively) but was cytotoxic to uninfected human foreskin fibroblasts and KB cells in the same dose range. Similar results were obtained with the heterocycle 2,5,6-trichlorobenzimidazole. In marked contrast, the ribonucleoside of 2,5,6-trichlorobenzimidazole (TCRB) was active against HCMV (IC50 = 2.9 microM, plaque assay; IC90 = 1.4 microM, yield assay) but only weakly active against HSV-1 (IC50 = 102 microM, plaque assay). Little to no cytotoxicity was observed in HFF and KB cells at concentrations up to 100 microM. By changing the substituent at the 2-position from chlorine to bromine (BDCRB), a 4-fold increase in activity against HCMV was observed without any significant increase in cytotoxicity. In contrast, the 2-I and 2-NH2 derivatives were only weakly active against HCMV and HSV-1 with activity not well-separated from cytotoxicity. These data establish that for maximum activity against HCMV with separation from cytotoxicity, ribose is preferred at the 1-position and that Cl or Br is apparently preferred at the 2-position. The activity and selectivity of both TCRB and BDCRB were better than that observed with either ganciclovir or foscarnet.
authors.affiliation: Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor 48109-1065, USA.
authors.forename: L B
authors.initials: LB
authors.lastname: Townsend
authors.forename: R V
authors.initials: RV
authors.lastname: Devivar
authors.forename: S R
authors.initials: SR
authors.lastname: Turk
authors.forename: M R
authors.initials: MR
authors.lastname: Nassiri
authors.forename: J C
authors.initials: JC
authors.lastname: Drach
mesh_terms: D000998:Antiviral Agents / Q000138:chemical synthesis* / Q000494:pharmacology; D001562:Benzimidazoles / Q000138:chemical synthesis* / Q000494:pharmacology; D003587:Cytomegalovirus / Q000187:drug effects; D015195:Drug Design; D018259:Herpesvirus 1, Human / Q000187:drug effects; D006801:Humans; D007624:KB Cells; D013329:Structure-Activity Relationship
chemical_list: D000998:Antiviral Agents; D001562:Benzimidazoles