Elucidation of the Structure of Pseudorubriflordilactone B by Chemical Synthesis.

Rubriflordilactone B () is a schinortriterpenoid isolated by Sun and colleagues, which possesses a tetrasubstituted benzene moiety and eight stereocenters. The previous synthesis of by Li and co-workers uncovered the existence of its naturally occurring stereoisomer "pseudorubriflordilactone B". Here we report a collaborative study by the two groups that elucidates the structure of pseudorubriflordilactone B to be 16,17-bis--rubriflordilactone B (). Chemical synthesis served as an important tool in the structure determination. Taking advantage of a modular synthetic route, we systematically "mutated" the configurations of C-23, C-22, C-20, and C-16/C-17 located at the right-hand domain of , and thus prepared its 15 stereoisomers for spectrum comparison. The H NMR spectra of synthetic in deuterated chloroform and pyridine were identical to those of authentic pseudorubriflordilactone B, respectively. This synthetic sample displayed anti-HIV activity (EC = 0.288 μM) in vitro.