8-Chlorodibenz [b, f][1, 4] oxazepine-10 (11H)-carboxylic acid, 2-[1-oxo-3-(4-pyridinyl) propyl] hydrazide, monohydrochloride (1, SC-51089) is a functional PGE2 antagonist selective for the EP1 receptor subtype with antinociceptive activity. 1, 2 Analogues of SC- 51089, in which the diacylhydrazine moiety has been replaced with 2, 4-disubstituted- oxazoles and-thiazoles, are described.