Phenolic Constituents with Antioxidative, Tyrosinase Inhibitory and Anti-aging Activities from Dendrobium loddigesii Rolfe

Aqueous ethanol extracts of powdered stems of Dendrobium loddigesii afforded three new phenolics including threo-7-O-ethyl-9-O-(4-hydroxyphenyl)propionyl-guaiacylglycerol (1), (R)-4,5,4'-trihydroxy-3,3',α-trimethoxybibenzyl (2) and (S)-5,5',7-trihydroxy-3',4'-dimethoxyflavanone (3), together with eleven known analogues. Their structures were determined by extensive spectroscopic analysis. To identify natural antioxidants, whitening, and anti-aging agents, the abilities of these phenolics were assessed to scavenge the 1,2-diphenyl-2-picrylhydrazyl (DPPH) radical, their abilities to inhibit tyrosinase production, and their abilities to stimulate collagen production by human dermal fibroblasts-adult (HDFa) assay. It was found that compounds 1, 4-8, 13 and 14 exhibited significant DPPH radical scavenging activities, compound 10 exhibited tyrosinase inhibitory activity (IC₅₀ 37.904 μg/mL), and compound 9 showed significant collagen production with an EC₅₀ value of 3.182 μg/mL. These results suggest that phenolic constituents from D. loddigesii may be candidate antioxidants, skin-whitening and/or anti-aging agents.