Abstract
Nine new sesquiterpenes, i.e., dendronobilins A–I (1–9), with copacamphane‐type (1), picrotoxane‐type (2–6), muurolene‐type (7), alloaromadendrane‐type (8), and cyclocopacamphane‐type (9) skeletons, were isolated from the 60% EtOH extract of the stems of Dendrobium nobile. Their structures were established as (1__R__,2__R,4__S,5__S__,6__S__,8__S,9__R)‐2,8‐dihydroxycopacamphan‐15‐one (1), (2__β__,3__β__,4__β__,5__β__)‐2,4,11‐trihydroxypicrotoxano‐3(15)‐lactone (2), (2__β__,3__β__,5__β__,9__α__,11__β__)‐2,11‐epoxy‐9,11,13‐trihydroxypicrotoxano‐3(15)‐lactone (3), (2__β__,3__β__,5__β__,12__R__*)‐2,11,13‐trihydroxypicrotoxano‐3(15)‐lactone (4), (2__β__,3__β__,5__β__,12__S__*)‐2,11,13‐trihydroxypicrotoxano‐3(15)‐lactone (5), (2__β__,3__β__,5__β__,9__α__)‐9,10‐cyclo‐2,11,13‐trihydroxypicrotoxano‐3(15)‐lactone (6), (9__β__,10__α__)‐muurol‐4‐ene‐9,10,11‐triol (7), (10__α__)‐alloaromadendrane‐10,12,14‐triol (8), and (5__β__)‐cyclocopacamphane‐5,12,15‐triol (9) on the basis of spectroscopic analysis. The absolute configuration of compound 1 was tentatively assigned as (1__R__,2__R__,4__S__,5__S__,6__S__,8__S__,9__R__) according to its CD spectrum and the octant rule. Compounds 1 and 4–9 were inactive in our preliminary in vitro immunomodulatory bioassay.