Four new stilbenoids from the orchids Coelogyne ochracea and Coelogyne cristata

摘要

The orchid Coelogyne ochracea Lindl. was earlier chemically investigated by two Indian groups of workers who reported the isolation of six new stilbenoids, viz. coelonin [2,7-dihydroxy-4-methoxy-9,10-dihydrophenanthrene], ochrolide, ochrone A, ochrone B, ochrolic acid and ochrolone, besides the known stilbenoids batatasin-III, coelogin, coeloginin and flaccidinin. Further chemical investigation of this orchid by the present investigators has resulted in the isolation of yet two new stilbenoids, designated ochracinone and ochracinanthrone, besides 3,4,5-trimethoxybenzaldehyde and four known stilbenoids, other than those reported earlier, viz. batatasin-III-dimethylether, flavidin, oxoflavidin and flavanthrin. The orchid Coelogyne cristata Lindl. was also earlier chemically investigated in our laboratory yielding the first pair of 9,10-dihydrophenanthropyran and pyrone, coelogin and coeloginin, and later two new phenanthrene derivatives coeloginanthrin and coeloginanthridin. Further investigation of this orchid by the present investigators afforded yet two new stilbenoids, designated coeloginone and coeloginanthrone. The structures of the four new stilbenoids ochracinone, ochracinanthrone, coeloginone and coeloginanthrone were established as 6-hydroxy-2,7,8-trimethoxy-9,10-dihydro-5H-phenanthro[4,5-bcd]pyran-5-one, 6-hydroxy-2,7,8-trimethoxy-5H-phenanthro[4,5-bcd]pyran-5-one, 2,6,7,8-tetramethoxy-9,10-dihydro-5H-phenanthro[4,5-bcd]pyran-5-one and 2,6,7,8-tetramethoxy-5H-phenanthro[4,5-6cd]pyran-5-one, respectively, from spectral and chemical evidence. Detailed 2D NMR [1-bond ~1H-~(13)C (HMQC) and 2- and 3-bond ~1H-~(13)C (HMBC) correlations] spectral studies carried out on coeloginone established unambiguous assignments of all the carbon resonances of the compound and partly those of its other three congeners.