Stilbenoids and flavonoids from the orchids Coelogyne uniflora, lone paleacea and Acrochoene punctata

Department of Chemistry, University College of Science, 92 Acharya Prafulla Chandra Road, Kolkata-700 009, India

Manuscript received 12 June 2001. accepted 23 August 2001

The orchid Coelogyne uniflora afforded earlier a steroidal ester, uniflorin. Further investigation of this orchid has now resulted in the isolation of two new phenanthropyrone derivatives, unifloranthrone and uniflorinanthrone, besides flavidin (la), flavidinin (lc), isoflvidinin (1d) and oxoflavidin (le). The structures of unifloranthrone and uniflorinanthrone were established as 2,7-dihydroxy­5H-phenanthro[4,5-bcd]pyran-5-one (2a) and 2,7-dimethoxy-5H-phenanthro[4,5-bcd]pyran-5-one (2c), respectively, from spectral and chemical evidence. Chemical investigation of the orchid Ione Paleacea yielded two flavanone derivatives, 5,7-dihydroxy-6-methoxy­2-phenyl-2,3-dihydro-4H-1-benzopyran-4-one (3a) and 5,7-dihydroxy-6-methoxy-2-(4'-hydroxyphenyI)-2,3-dihydro-4H-1-benzopyran-­4-one (3c), besides the known stilbenoids, 3-hydroxy-5-methoxybibenzyl (4a), batatasin-III (4c) and gigantol (4e). The orchid Acrochoene punctata afforded two known bibenzyl derivatives, viz. 3,4'-dihydroxy-5-methoxybibenzyl (4f) and 4,4'-dihydroxy-3,5- dimethoxybibenzyl (4g). Additional NMR spectral evidence was provided for further confirmation of the structures of 3a, 3c, 4a and 4g.