Carolignans from the Aerial Parts of Euphorbia sikkimensis and Their Anti-HIV Activity

Seven new carolignans, including two pairs of enantiomers (+/-)-erythro-7'-methylcarolignan E (1a/1b) and (+/-)-threo-7'-methylcarolignan E (2a/2b), (+)-threo-carolignan E (3a), (+)-elythro-carolignan E (4a), and (-)-erythrocarolignan Z (5), together with four known lignans (3b, 4b, 6, and 7) and six polyphenols (8-13) were isolated from the aerial parts of Euphorbia sikkimensis. The structures of the new compounds were elucidated by spectroscopic analysis, and their absolute configurations were determined by electronic circular dichroism calculations. Seven of the isolates were examined for anti-HIV effects, and compounds 1a and 1b showed moderate anti-HIV activity with EC50 values of 6.3 and 5.3 mu M.