Putative role of uttronin (degalactotigonin) in cytotoxicity of uttroside B in HepG2 cells

Abstract

Uttroside B from Solanum nigrum Linn. exhibited potent cytotoxicity against HepG2 cells with an IC50 of 0.5 μM; interestingly, its congeners uttroside A and uttronin exhibited the same level of activity. We hypothesized that spirocyclization is the critical step for the activity of uttroside A or B that results in the formation of uttronin. To support our hypothesis, an uttroside B analogue was synthesized that cannot undergo spirocyclization, which resulted in a loss of cytotoxic activity. Mass spectral analysis of the supernatant from the cells treated with uttroside B further supported the spirocyclization of uttroside B to uttronin.