Study on chemical constituents from Kopsia singapurensis (Apocynaceae) yielded four new aspidofractinines:
Singaporentine A (1), N(1)-formylkopsininic acid (2), N(1)-formylkopsininic acid-N(4)-oxide (3), 15-hydroxykopsamine
(4); a new aspidospermatan: 14α-hydroxy-N(4)-methylcondylocarpine (5) and a new akuamiline: singaporentinidine (6)
together with 18 known indole alkaloids from different parts of the plant. The structures of these compounds were
elucidated by combination of various spectroscopic methods.