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(±)-Quassidines I and J, Two Pairs of Cytotoxic Bis-β-carboline Alkaloid Enantiomers from Picrasma quassioides

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posted on 2015-01-23, 00:00 authored by Wei-Hua Jiao, Guo-Dong Chen, Hao Gao, Jing Li, Bin-Bin Gu, Ting-Ting Xu, Hao-Bing Yu, Guo-Hua Shi, Fan Yang, Xin-Sheng Yao, Hou-Wen Lin
(±)-Quassidines I (1) and J (2), two pairs of new bis-β-carboline alkaloid enantiomers, were isolated from the stems of Picrasma quassioides. Their structures were determined by the analysis of spectroscopic data, including HRESIMS and 2D NMR, and confirmed by single-crystal X-ray diffraction analysis. The racemic mixtures of 1 and 2 were resolved into two pairs of enantiomers, (+)-S-1a and (−)-R-1b and (+)-S-2a and (−)-R-2b, by HPLC using a chiral Daicel IB-3 column, respectively, which represents the first successful example to resolve bis-β-carboline racemic mixtures. The absolute configurations of the two pairs of enantiomers were determined by comparison between the calculated and experimental ECD spectra. The cytotoxicity evaluation revealed that (+)-S-1a and (+)-S-2a showed more potent cytotoxicity against human cervical HeLa and gastric MKN-28 cancer cell lines with IC50 values of 4.03–6.30 μM than their enantiomers with IC50 values of 9.64–12.3 μM; however, the two (+)-S-quassidines showed similar activities to their enantiomers against the mouse melanoma B-16 cancer cell line.

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