Mitrariosides, Five Bitter Labdane Glycosides from Mitraria coccinea (Gesneriaceae)

From Mitraria coccinea Cav. (Gesneriaceae), five strongly bitter labdane glycosides named mitrariosides A 1 , A 2 , B, C and D ( 1 — 5 ) were obtained. The structures were deduced by chemical and spectroscopic evidence (COSY, 13 C‐ 1 H CORR, NOESY and MS‐FAB) and found to be: mitrarioside A 1 ( 1 ): (6 S )‐19‐(β‐ D ‐galactopyranosyloxy)‐6‐hydroxy‐15‐(α‐ L rhamno‐pyranosyloxy)labda‐8(17),13‐diene, mitrarioside A 2 ( 2 ): (6 S )‐19‐(β‐ D ‐glucopyranosyloxy)‐6‐hydroxy‐15‐(α‐ L ‐rhamnopyranosyloxy)labda‐8(17),13‐diene, mitrarioside B ( 3 ):(6 S )‐19‐(β‐ D ‐glucopyranosyloxy)‐6‐hydroxy‐15‐(β‐ D ‐glucopyranosyloxy)‐labda‐8(17),13‐diene, mitrarioside C ( 4 ): (6 S )‐19‐(β‐ D ‐glucopyranosyloxy)‐6,15‐dihydroxylabda‐8(17), 13‐diene, and mitrarioside D ( 5 ): (6 S )‐19‐(α‐ L ‐rhamnopyranosyloxy)‐6,15‐dihydroxy‐labda‐8(17),13‐diene. The known compounds acteoside and calceolarioside C were also isolated.