Respiratory syncytial virus fusion inhibitors. Part 6: an examination of the effect of structural variation of the benzimidazol-2-one heterocycle moiety.

The effect of structural variation of the benzimidazol-2-one ring of RSV fusion inhibitors related to BMS-433771 (1) was examined in conjunction with side chain modifications and the introduction of an aminomethyl substituent at the 5-position of the core benzimidazole moiety. Replacement of the benzimidazol-2-one moiety with benzoxazole, oxindole, quinoline-2-one, quinazolin-2,4-dione and benzothiazine derivatives provided a series of potent RSV fusion inhibitors 4. However, the intrinsic potency of 6,6-fused ring systems was generally less than that of comparably substituted 5,6-fused heterocycles of the type found in BMS-433771 (1). The introduction of an aminomethyl substituent to the benzimidazole ring enhanced antiviral activity in the 6,6-fused ring systems.