[Studies on the alkaloids of Erythrina plants]

The alkaloidal components of eight Erythrina plants (Leguminosae), E. arborescence Roxb., E. orientalis (L.) Murr, E. crysta-galli Linn, E. crysta-galli (L.) cv. Maruba Deiko H. Murata, E. x bidwilli Lindl, E. poeppigiana (Walp) O. F. Cook, E. glauca Willd, and E. variegata L. were examined. As a result of this study, five new oxo-erythrinan alkaloids, erythrinine (8), 11-hydroxyerysotrine (9), erysotramidine (10), erytharbine (11), crystamidine (12) and a di-benz[d,f]azonine type alkaloid, erybidine (2), were isolated respectively. Two tetrahydroprotoberberine type alkaloids, scoulerine (4) and coreximine (5), were also isolated from E. orientalis (L.) Murr. A new synthetic route to erythrinan alkaloids was developed, via the cis -C/D-ring fused 15-methoxy-16-hydroxyerythrinan-2, 8-dione (49) as a key intermediate, from the enol methyl derivative (48) which was obtained by Birch reduction of the benzyl amide (47). The total synthesis of (+/-)-erysotramidine (10), an oxo-erythrinan alkaloid, including a novel ring cleavage of the aza-tricyclo[3.2.0.0] compound (70) with phenylselenyl chloride is described.