New indole alkaloids from Kopsia. Alkaloid variation in Kopsia singapurensis

Five new indole alkaloids, viz., kopsiloscine G (2), kopsidarine (4), kopsimaline F (6), kopsidine C N-oxide (7), and aspidophylline B (9), in addition to 17 other known alkaloids, were obtained from the leaf and stem-bark extract of the Malaysian Kopsia singapurensis. The structures were determined by using NMR and MS analysis. The results are compared with the alkaloidal composition of another sample of K. singapurensis, collected from the same location but at a different time of the year, as well as with other samples of K. singapurensis collected from different locations.