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(±)-Homocrepidine A, a Pair of Anti-inflammatory Enantiomeric Octahydroindolizine Alkaloid Dimers from Dendrobium crepidatum

Hu, Yang, Zhang, Chaofeng, Zhao, Xin, Wang, Yue, Feng, Deqiang, Zhang, Mian, Xie, Haifeng
Journal of natural products 2016 v.79 no.1 pp. 252-256
Dendrobium, X-ray diffraction, alkaloids, anti-inflammatory activity, enantiomers, high performance liquid chromatography, inducible nitric oxide synthase, inhibitory concentration 50, macrophages, nitric oxide, piperidines
A pair of racemic indolizidine enantiomers, (±)-homocrepidine A (1), and a piperidine derivative, homocrepidine B (2), were isolated from Dendrobium crepidatum along with the known alkaloid crepidine (3). The racemic mixture of 1 was separated into a pair of enantiomers, (+)-1 and (−)-1, by HPLC using a chiral chromatographic substrate, which represents the first successful example of resolving indolizidine racemic mixtures. The absolute configurations of (+)-1 and (−)-1 were assigned from single-crystal X-ray diffraction data. The evaluation of anti-inflammatory activity with LPS-induced RAW 264.7 macrophages revealed that (+)-1 strongly inhibited the production of nitric oxide (IC₅₀, 3.6 μM) and significantly decreased the expression of inducible nitric oxide synthase, while (−)-1 and (±)-1 only had moderate inhibitory effects (IC₅₀, 22.8 and 14.7 μM). Compound 2 showed moderate anti-inflammatory activity (IC₅₀, 27.6 μM).