Benzimidazole condensed ring systems. <b>1</b>. Syntheses and biological investigations of some substituted pyrido[1,2‐<i>a</i>]benzimidazoles

Abstract

Abstract The synthesis of some substituted 3‐hydroxy‐1‐oxo‐1 H,5H ‐pyrido[1,2‐ a ]benzimidazole‐4‐carbonitriles and 4‐ethyl carboxylates 3 and their 0‐ and N ‐dialkyl derivatives 5,6 is described. 3‐Ethoxy‐5‐ethyl‐2‐phenyl‐1 H,5H ‐pyrido[1,2‐ a ]benzimidazol‐1‐one 7 was obtained during the course of ethylating the parent ester 3t with triethyl phosphate. Chlorination of 3 with phosphorus oxychloride afforded the corresponding 1,3‐dichloropyrido[1,2‐ a ]benzimidazoles 8 which were converted to a variety of azido, amino, morpholino and methoxy derivatives of the system. The synthesis of the indolopyridobenzimidazole 15 is also described. Two compounds exhibited in vitro antibacterial activity. Many compounds were screened for antileukemic, antimicrobial, herbicidal and plant antifungal potencies but were inactive.