Syntheses are described for several unfused heterobicycles including 4,5′- and 2,4′-bithiazoles, 5-(thiazol-4′ and 5′-yl)-1,3,4- thiadiazoles , 5-(thien-2′-yl)-, 5-(furan-2′ and 3′-yl)-, thiadiazoles and related oxadiazoles, all with side chains containing dialkylamine terminal groups. The activities of these compounds as amplifiers of phleomycin -G are reported.