Kopsia tenuis

It is of interest to compare the alkaloidal composition of the Indonesian L eugenefolia which gave besides leuconolam, 21-O-methylleuconolam and rhazinilam-N-oxide, yohimbine, P-yohimbine, and the diazaspiroleuconolam compound, leuconoxine (17S) [136], which has since then also been obtained from the North Borneo species, Kopsia tenuis [19], A similar diazaspiroleuconolam derivative 176 has been obtained via a facile acid-induced ring-reclosure reaction of leuconolam, while the base-induced reaction gave the meloscine-type derivative 177 [127,128]. 

Tenuiphylline (319) [189] was obtained in minute amounts from Kopsia tenuis. The FABMS showed a MH peak at m/z 717 and high resolution measurements provided the formula C42H44N4O7. The UV spectrum indicated the presence of dihydroindole chromophores... 

ISO), which occurs in the same plant. Such a provenance leads inevitably to the revised stereochemistry 160) shown in 213. Initially 180), the structure postulated had the 18,19 and 16,17 two-carbon chains transposed. Lapidilectine B (214), from the leaves of the same plant, has suffered oxidative removal of C-21, followed by lactonization of a hydroxyl group generated at C-7 with the C-16 carboxyl group. Four more new alkaloids, from the same plant, are closely related structurally these are isolapidilectine (16-epilapidilectine A, 215), lapidilectam (3-oxolapidilectine A, 216), and the epimeric 15-hydroxy-14,15-dihydro-derivatives, lapidilectinol (217) and epi-lapidilectinol (218) 160). Another lapidilectine derivative, lO-methoxy-3-oxolapidilectine B (219), is a constituent alkaloid of Kopsia tenuis Leenh. and Steenis, a previously uninvestigated species from North Borneo 181). 

Tenuiphylline (574) was isolated in minute amounts, together with the ten-uisines (vide infra) from Kopsia tenuis occurring in Malaysian Borneo (360). The FABMS showed a MH peak at mjz 111 and high-resolution measurements provided the formula C42H44N4O7. The UV spectrum indicated the presence of dihydroindole chromophores and the IR spectrum indicated the presence of hydroxyl, urethane, ester, and lactone funetions. In view of the small amount obtained, definitive structure elucidation of tenuiphylline required resort to 600 MHz NMR spectra since extensive overlap was encountered with lower field instruments. 

Alkaloid from leaves of Kopsia tenuis (Apocynaceae). [a]p -90 (c, 0.092 in CHCI3). 

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