Oncinotine‐Type Spermidine Alkaloids from Oncinotis tenuiloba . Transformation of N ‐acetyloncinotin‐12‐one to N , N ′‐diacetylinandenin‐12‐one

From extracts of Oncinotis tenuiloba S TAPF , 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 ( 14 ), when co‐HPLC was performed together with different keto‐isomeric N , N ′‐diacetylinandeninones. Structure elucidation was extended by Schmidt degradation of 6 and N , N ′‐diacetyl(10,11‐ 2 H 2 )inandenin‐12‐one ( 13 ); the degradation products were identified by GC and ESI‐MS. The structure of 5 was proposed on the basis of spectroscopic means. Comparison of the spectroscopic data of 5 with those obtained from synthetic material as well as co‐HPLC of the N ‐acetyl derivative 20 together with the corresponding synthetic compound revealed the identity of the substances and confirmed the structure of 5 . Additionally, oncinotine ( 2 ) and neooncinotine ( 3 ) were isolated, separated, and identified with authentic samples by co‐HPLC of their N ‐acetyl derivatives 8 and 9 , respectively.