Dengratiols E-G, three bioactive pairs of enantiomeric bibenzyl dimers from Dendrobium gratiosissimum.

Three pairs of enantiomeric bibenzyl dimers, (±)-dengratiols E-G [(±)-1-3], were obtained through various chromatographic techniques including chiral HPLC, from the ethanol extract of Dendrobium gratiosissimum. Their structures were elucidated to be R-(+)-1 and S-(-)-1, R-(+)-2 and S-(-)-2, and αR, α'R-(-)-3 and αS, α'S-(+)-3 on the basis of the extensive spectroscopic data and ECD analyses, respectively. The isolated enantiomerically pure along with their racemic forms showed moderate cytotoxicity against human HCT116, U87-MG, HepG2, BGC823, and PC9 cancer cell lines (IC50 9.25-48.01 µM). Enantiomers (+)-1 and (-)-1, and their racemate (±)-1 showed antiviral effects against HIV-1 with IC50 values of 12.26, 6.01, and 4.47 µM, respectively. Enantiomers (+)-2, and (-)-2 and their racemic form showed significant protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with IC50 values of 5.07, 3.11, and 4.37 µM, respectively.