Synthesis of some new biologically active 1,3,4-oxadiazolyl nitroindoles and a modified Fischer indole synthesis of ethyl nitro indole-2-carboxylates

An efficient and modified synthesis of ethyl-4-nitro/5-nitro/6-nitro and 7-nitroindole-2-carboxylates is described. Carbohydrazides of corresponding ethyl nitroindole-2-carboxylates underwent smooth one-step transformation to 1,3,4-oxadiazolyl nitroindoles (4a-l) on reaction with aromatic carboxylic acids in the presence of phosphorus oxychloride. An alternate method to synthesize 1,3,4-oxadiazolyl nitroindoles is also described. Among the newly synthesized 1,3,4-oxadiazolyl nitroindoles, a few compounds are studied for anti-inflammatory activity.