7-Hydroxy-(E)-3-phenylmethylene-chroman-4-one analogues as efflux pump inhibitors against Mycobacterium smegmatis mc² 155.

Efflux pump (EP) induces resistance in mycobacteria and hence could be explored as a new target for the discovery of anti-TB agents. In search for efflux pump inhibitors from natural products, bonducellin, a homoisoflavonoid was isolated from Caesalpinia digyna roots and evaluated for modulation and EP inhibitory activity. Bonducellin showed modulation in the MIC of EtBr by eight fold at a concentration of 62.5 mg/L and also showed significant EP inhibitory activity. A synthetic scheme was designed to prepare analogues of 7-hydroxy-(E)-3-phenylmethylene-chroman-4-one by modification at the phenylmethylene-ring and the synthesized compounds were evaluated in accumulation and efflux assays. Analogues 1, 7-11, 13-15, 17 and 19 were found to be good modulators and decreased the MIC of EtBr by ≥4 fold at sub-inhibitory concentration. The compounds 8, 13 and 17 were the most potent inhibitors of ethidium bromide efflux in Mycobacterium smegmatis mc(2) 155.