Constituents of two Japanese species of Ophiorrhiza (Rubiaceae) were studied. Ophiorrhiza kuroiwai Mak. was found to contain four known alkaloids, i.e. harman (I), camptothecin (II), 9-methoxycamptothecin (III), 10-methoxycamptothecin (IV), and three new alkaloids, i.e. lyalosidic acid (V), ophiorine A (VI) and ophiorine B(VII). From O. japonica Bl. three known alkaloids, i.e. harman (I), lyaloside (VIII), and 6-hydroxyharman (XVI), and six new compounds, i.e. lyalosidic acid (V), ophiorine A (VI), ophiorine B (VII), 10-hydroxylyalosidic acid (XVII), ophiorine A-methyl ester (XIV), and ophiorine B-methyl ester (XV), were isolated. Synthesis of lyaloside (VIII) using L-tryptophan (IX) and secologanin (X) was made. Interconversion between ophiorines A, B and lyaloside (VIII) was also carried out. Action of emulsin on lyalosidic acid (V) or lyaloside (VIII) was found to give rise to harman (I) as the result of a facile fragmentation of the intermediary hydrolysis product. Similarly, 6-hydroxyharman (XVI) was given from 10-hydroxylyalosidic acid (XVII). These results suggest a possibility that harmans widely distributing in Rubiaceous plants accompanying monoterpenoid indole alkaloids may be secondarily formed from β-carboline type monoterpenoid indole alkaloids through this or similar mechanisms.
