Four new selaginellin derivatives from Selaginella pulvinata: mechanism of racemization process in selaginellins with quinone methide. Issue 10 (11th March 2015) - Cao, Yuan
Abstract: Nine selaginellin derivatives, including a novel isoquinoline-type selaginellin named selaginisoquinoline A (1 ), and three ethoxy selaginellins P–R (2 –4 ), were isolated from the plant of Selaginella pulvinata . Their structures were determined by extensive spectroscopic analyses, and single-crystal X-ray diffraction, as well as CD calculations. Selaginisoquinoline A (1 ) is a racemate due to quinone methide-phenol tautomerism; while in the case of selaginellins P–R (2 –4 ), whose tautomerism was blocked by alkylation of C10–OH, the interesting racemization process is induced by axial chirality and molecular rotation, thus existing as a pair of slowly interconverting enantiomers. Compounds3, 5 and9 showed moderate cytotoxicity against BGC-823 human gastric cancer cell line. All compounds, including four enantiomers, exhibited good antifungal activities against four pathogenic fungi cell lines with MIC80 values in the range of 4–32 μg/mL. Graphical abstract: