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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).