Three New Bibenzyl Derivatives from Dendrobium Candidum

Three new compounds were isolated from the stems of Dendrobium candidum: (S)-3,4,4'-trihydroxy-5,alpha-dimethoxybibenzyl (1), named dendrocandin C; (S)-3,4,4'-trihydroxy-5-methoxy-alpha-ethoxybibenzyl (2), named dendrocandin D; and 3,3',4,4'-tetrahydroxy-5-methoxybibenzyl (3), named dendrocandin E. Their structures were elucidated by 1D- and 2D-NMR spectroscopy and mass spectroscopy. The isolated compounds exhibited potent antioxidant activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging test, with IC(50) values of 34.2, 34.5, and 15.6 microM for compounds 1, 2, and 3, respectively. Vitamin C was used as positive control with IC(50) 23.2 microM.