Alkaloids from Melodinus suaveolens

Two new quinoline alkaloids, 14,15--epoxyscandine (3) and meloscine N-oxide (6), along with six known alkaloids scandine (1), scandine N-oxide (2), meloscandonine (4), meloscine (5), tubotaiwine (7), polyneuridine (8) were isolated from the twigs and leaves of Melodinus suaveolens.The structures of the new compounds were elucidated on the basis of spectroscopic methods and circular dichroism experiments.The genus Melodinus (Apocynaceae) comprises 53 species mainly distributed in tropical or subtropical Asia and Australia. 1 This genus has been regarded as a rich source of monoterpenoid indole alkaloids, which originate from the condensation of tryptophan with secologanin. 2Up to now, more than 100 monomeric and dimeric indole alkaloids as well as quinoline alkaloids have been isolated from Melodinus sp.The interesting chemical significance of the Melodinus plants prompted us to initiate a phytochemical study on the twigs and leaves of Melodinus suaveolens, which led to the isolation of two new quinoline alkaloids, 14,15--epoxyscandine (3) and meloscine N-oxide (6), along with six known alkaloids scandine (1), 3 scandine N-oxide (2), 3 meloscandonine (4), 4 meloscine (5), 5 tubotaiwine (7), 6 and polyneuridine (8). 7