of Oncinotis tenuiloba STAPF, two novel polyamine alkaloids, oncinotin-11-one (5) and oncinotin-12-one (6), were isolated. Peracetylation of 6 provided the N-acetyl derivative 11 as well as N,N′-diacetylinandenin-10-en-12-one (12) due to a β-elimination-type side reaction resulting in ring enlargement of 11 (Scheme 1). Deuteration of 12 yielded 13, showing the same retention time as N,N′-diacetylinandenin-12-one