Koichiro Koyama

Alsmaphorazines A and B, Novel Indole Alkaloids from Alstonia pneumatophora

Two novel indole alkaloids, alsmaphorazines A and B, were isolated from the leaves of Alstonia pneumatophora (Apocynaceae), and their structures were determined on the basis of the 2D NMR and MS spectral analysis. These alkaloids possessed a new skeleton consisting of an 1,2-oxazinane and an isoxazolidine chromophore. The absolute configuration of alsmaphorazine B was determined by using CD spectral analysis. Alsmaphorazine A inhibited the NO production in the LPS-stimulated J774.1 cells dose-dependently without affecting the cell viability.

Alpneumines A–H, new anti-melanogenic indole alkaloids from Alstonia pneumatophora

Eight new indole alkaloids, alpneumines A-H (1-8) were isolated from the Malaysian Alstonia pneumatophora (Apocynaceae) and their structures were determined by MS and 2D NMR spectroscopic methods. Alpneumines E and G (5 and 7), vincamine, and apovincamine showed anti-melanogenesis in B16 mouse melanoma cells.

Biscarpamontamines A and B, an aspidosperma-iboga bisindole alkaloid and an aspidosperma-aspidosperma bisindole alkaloid, from Tabernaemontana sphaerocarpa.

Two new bisindole alkaloids, biscarpamontamine A (1), possessing an aspidosperma-iboga-type skeleton, and biscarpamontamine B (2), having an aspidosperma-aspidosperma-type skeleton, were isolated from stems of Tabernaemontana sphaerocarpa, and their structures were elucidated on the basis of spectroscopic data analysis. The absolute configuration of biscarpamontamine B (2) was established by comparison of its CD spectrum and with that of vobtusine (3). Biscarpamontamine B (2) showed potent cytotoxicity against various human cancer cell lines.

Alasmontamine A, a first tetrakis monoterpene indole alkaloid from Tabernaemontana elegans

A novel tetrakis monoterpene indole alkaloid, alasmontamine A (1) consisting of bis-vobtusine-type skeletons, was isolated from the leaves of Tabernaemontana elegans. The structure including the relative stereochemistry was elucidated on the basis of spectroscopic data. Alasmontamine A (1) exhibited moderate cell growth inhibitory activity against HL-60 cells.

Alstilobanines A-E, new indole alkaloids from Alstonia angustiloba.

Five new alkaloids, alstilobanines A (1)-E (5) were isolated from Alstonia angustiloba (Apocynaceae) and their structures were determined by MS and 2D NMR spectral analysis. Alstilobanines A-E showed a moderate vasorelaxant activity against phenylephrine-induced contraction of isolated rat aorta.