Thesis (M.Sc. in Pharm)--Chulalongkorn University, 2013

Phytochemical study of a MeOH extract prepared from the whole plant of Dendrobium williamsonii Rchb.f. led to the isolation of six known compounds, namely, tetratriacontanyl-p-coumarate, trans-docosanoylferulate, 3,3´-dihydroxy-4,5-dimethoxybibenzyl, moscatilin, apigenin and vanillic acid. Their structures were determined by means of spectroscopic analysis (UV, IR, MS, and NMR), as well as by comparison with previously reported data. These compounds were evaluated for 2.2–diphenyl-1-picryhydrazyl (DPPH) free radical scavenging activity. 3,3´-Dihydroxy-4,5-dimethoxybibenzyl, moscatilin and apigenin exhibited moderate DPPH free radical scavenging activitiy with IC50 values of 19.56 + 1.30, 8.56 + 1.24 and 19.34 + 1.19 µM, respectively. Vitamin C and quercetin were used as positive controls with IC50 values of 42.46 + 2.31 and 8.34 + 0.47 µM, respectively. In addition, the isolates were evaluated for cytotoxicity and anti-herpes simplex activity. 3,3´-Dihydroxy-4,5-dimethoxybibenzyl and moscatilin showed cytotoxicity against KB cell line (oral human epidermal carcinoma). Moreover, 3,3´-dihydroxy-4,5-dimethoxybibenzyl showed weak activity against herpes simplex type 1 and type 2.