A methanol extract prepared from Dendrobium signatum (Orchidaceae) showed significant free radical scavenging activity in the DPPH assay. Subsequent chemical study led to the isolation of 5 pure compounds, including a new compound, named dendrosignatol, together with 4 known compounds 3,4-dihydroxy-5,4´-dimethoxybibenzyl, dendrocandin B, dendrocandin I and dendrofalconerol A. Their structures were determined through by analysis of spectroscopic data (UV, IR, MS NMR). The DPPH radical scavenging activities of the isolated compounds were evaluated, and their IC50 values were determined to be 13.05, 8.29, 12.91, 62.49 and 9.43 µM, respectively. Quercetin (IC50 6.57 µM) and Trolox® (IC50 10.95 µM) were used as positive controls. In addition, these compounds were further investigated for their activity against superoxide radicals. Their IC50 values were found to be 51.17, 13.85, 58.23, 9.30 and 15.32 µM, respectively (Trolox® IC50 319.61 µM).

Thesis (M.Sc. in Pharm.)--Chulalongkorn University, 2015