Bioactive Bibenzyl Enantiomers From the Tubers of Bletilla striata.

Six new bibenzyls (three pairs of enantiomers), bletstrins D-F (1-3), were isolated from the ethyl acetate-soluble (EtOAc) extract of tubers of Bletilla striata (Thunb.) Rchb f. Their structures, including absolute configurations, were determined by 1D/2D NMR spectroscopy, optical rotation value, and experimental electronic circular dichroism (ECD) data analyses, respectively. Compounds 1-3 possess a hydroxyl-substituted chiral center on the aliphatic bibenzyl bridge, which represented the first examples of natural bibenzyl enantiomers from the genus of Bletilla. The antibacterial, antitumor necrosis factor (anti-TNF-α), and neuroprotective effects of the isolates have been evaluated. Compounds 3a and 3b were effective against three Gram-positive bacteria with minimum inhibitory concentrations (MICs) of 52-105 µg/ml. Compounds 2a and 2b exhibited significant inhibitory effects on TNF-α-mediated cytotoxicity in L929 cells with IC50 values of 25.7 ± 2.3 µM and 21.7 ± 1.7 µM, respectively. Subsequently, the possible anti-TNF-α mechanism of 2 was investigated by molecular docking simulation. Furthermore, the neuroprotective activities were tested on the H2O2-induced PC12 cell injury model, and compounds 2b, 3a, and 3b (10 µM) could obviously protect the cells with the cell viabilities of 57.86 ± 2.08%, 64.82 ± 2.84%, and 64.11 ± 2.52%, respectively.

Antibacterial stilbenes from the tubers of Bletilla striata.

Three new bibenzyl derivatives (bletstrins A-C, 1-3), including two bibenzyls that have hydroxyl-substituted chiral centers on the aliphatic bibenzyl bridge, along with eighteen known stilbenoids (4-21) were isolated from the tubers of Bletilla striata. The structures of new compounds were elucidated by the use of 1D/2D NMR spectroscopic data. The absolute configurations of bletitrins A and B were determined by optical rotation value. Compounds 13-16 were isolated from the Orchidaceae for the first time. Most of the isolated compounds were evaluated for their antibacterial activities against three gram-positive bacterial strains and one gram-negative bacterial strain. Compounds 4, 10, 12, 14, 15, 16 and 18 showed potent inhibitory activities, with MICs of (6-52 µg/mL) against S. aureus ATCC 6538.