Synthesis, optical resolution, absolute configuration, and osteogenic activity of cis-pterocarpans

A convenient synthesis of natural and synthetic pterocarpans was achieved in three steps. Optical resolution of the respective enantiomers was accomplished by analytical and semi-preparative HPLC on a chiral stationary phase. For medicarpin and its synthetic derivative 9-demethoxymedicarpin, the absolute configuration was confirmed by a combination of experimental LC-ECD coupling and quantum-chemical ECD calculations. (-)-Medicarpin and (-)-9-demethoxymedicarpin are both 6aR,11aR-configured, and consequently the corresponding enantiomers, (+)-medicarpin and (+)-9-demethoxymedicarpin, possess the 6aS, 11aS-configuration. A comparative mechanism study for osteogenic (bone forming) activity of medicarpin (racemic versus enantiomerically pure material) revealed that (+)-(6aS, 11aS)-medicarpin (6a) significantly increased the bone morphogenetic protein-2 (BMP2) expression and the level of the bone-specific transcription factor Runx-2 mRNA, while the effect was opposite for the other enantiomer, (-)-(6aR, 11aR)-medicarpin (6a), and for the racemate, (+/-)-medicarpin, the combined effect of both the enantiomers on transcription levels was observed.