[Synthesis and H2-antagonistic action of N,N-substituted 1,3,4-oxadiazole-2,5-diamine. 30. H2-antihistaminics].

The semicarbazides 1 and 5a-c were transformed in high yields into the biureas 3a, b and the thiobiureas 10a-c and 11a-c by addition to appropriate iso(thio)cyanates and subsequently cyclisized to the N,N'-substituted 1,3,4-oxadiazole-2,5-diamines by means of elimination of water or hydrogen sulphide. The synthesized compounds were tested for H2-antagonistic activity at the isolated spontaneously beating guinea-pig atrium, where especially 4a, b and 12c showed pronounced H2-antagonistic action.