Koichiro Koyama

Koichiro Koyama; Yusuke Hirasawa; Alfarius Eko Nugroho; Takahiro Hosoya; Teh Chin Hoe; Kit-Lam Chan; Hiroshi Morita

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.

Koichiro Koyama; Yusuke Hirasawa; Takahiro Hosoya; Teh Chin Hoe; Kit-Lam Chan; Hiroshi Morita

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.

Kazumasa Zaima; Tomoko Hirata; Takahiro Hosoya; Yusuke Hirasawa; Koichiro Koyama; Abdul Rahman; Idha Kusumawati; Noor Cholies Zaini; Motoo Shiro; Hiroshi Morita

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.

Yusuke Hirasawa; Saori Miyama; Takahiro Hosoya; Koichiro Koyama; Abdul Rahman; Idha Kusumawati; Noor Cholies Zaini; Hiroshi Morita

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.

Koichiro Koyama; Yusuke Hirasawa; Kazumasa Zaima; Teh Chin Hoe; Kit-Lam Chan; Hiroshi Morita

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.

Hiroshi Morita; Shiori Oshimi; Yusuke Hirasawa; Koichiro Koyama; Toshio Honda; Wiwied Ekasari; Gunawan Indrayanto; Noor Cholies Zaini

Hiroshi Morita; Koichiro Koyama; Yoshikazu Sugimoto; Jun'ichi Kobayashi

Chee Yan Choo; Yusuke Hirasawa; Chiaki Karimata; Koichiro Koyama; Mitsuhiro Sekiguchi; Jun'ichi Kobayashi; Hiroshi Morita

Koichiro Koyama; Hiroshi Morita; Yusuke Hirasawa; Tomohiro Hoshino; Yutaro Obara; Norimichi Nakahata; Jun'ichi Kobayashi

Yusuke Hirasawa; Tomoyuki Tanaka; Koichiro Koyama; Hiroshi Morita