Kiyotaka Koyama

Two prenylated retrochalcones from Glycyrrhiza inflata

Two new chalcones, licochalcones C and D, were isolated from the root of Glycyrrhiza inflata (Leguminosae) together with three known chalcones echinatin, licochalcones A and B. Their structures were elucidated as 4,4′-dihydroxy-2-methoxy-3-prenylchalcone and 2-methoxy-3′-prenyl-3,4,4′-trihydroxychalcone, respectively, on a spectroscopic basis. All chalcones obtained from this plant are retrochalcones and lack an oxygen-functionality at the 2′-position. The biogenesis of retrochalcones is briefly discussed in relation to the chemotaxonomy of the genus Glycyrrhiza.

Anti-emetic principles of Pogostemon cablin (Blanco) Benth.

Bioassay-guided fractionation of anti-emetic extracts and constituents of 8 traditional Chinese herbal drugs was performed. Twenty extracts described in Table 1 showed anti-emetic activity on copper sulfate induced-emesis in young chicks. From the n-hexane extract of Pogostemon cablin, patchouli alcohol (1), pogostol (2), stigmast-4-en-3-one (3), retusin (4), and pachypodol (5) were tested and exhibited anti-emetic effects.

Six new 10-pheynl-[11]cytochalasans, cytochalasins N - S from phomopsis SP.

Abstract From Phomopsis sp. (68-GO-164) six new cytochalasans named cytochalasins N, O, P, Q, R and S were isolated, together with the four known compounds, epoxycytochalasins H and J and cytochalasins H and J. The structures ( 5 – 10 ) of the new compounds as 10-phenyl-[11]cytochalasans were determined from spectral data, especially 1 H and 13 C NMR, and by chemical correlation with known compounds. Cytochalasins P, Q, R and S ( 7 – 10 ) have novel diol-type structures in the cyclohexane part of the molecules.

The sesquiterpenoid carcinogen of bracken fern, and some analogues, from the pteridaceae

Abstract Ptaquiloside, the sesquiterpenoid carcinogen of Pteridium aquilinum, was isolated from Pteris cretica and Histiopteris incisa. Three new sesquiterpene glycosides of the illudane type, analogues of ptaquiloside, were isolated from Hypolepis punctata and Dennstaedtia hirsta. They are named hypolosides A, B and C, and characterized as compounds related to pterosin Z.

Pyridone alkaloids from a marine-derived fungus, Stagonosporopsis cucurbitacearum, and their activities against azole-resistant Candida albicans.

Four new 4-hydroxy-2-pyridone alkaloids, didymellamides A-D (1-4), were isolated from the marine-derived fungus Stagonosporopsis cucurbitacearum. The structures of 1-4 were elucidated from spectroscopic data (NMR, MS, and IR), and the absolute configuration of 1 was determined by X-ray diffraction analysis. Didymellamide A (1) exhibited antifungal activity against azole-resistant Candida albicans.

Chemical constituents of a marine fungus, Arthrinium sacchari.

Three new diterpenes, myrocin D (1), libertellenone E (2), and libertellenone F (3), and a new isocoumarin, decarboxyhydroxycitrinone (4), were isolated from the marine fungus Arthrinium sacchari, together with three known compounds (5-7). The structures of 1-4 were elucidated from spectroscopic data (NMR, MS, IR), and the absolute configurations of 1-3 were determined by X-ray diffraction analysis. The antiangiogenic activity of these compounds was evaluated by measuring their antiproliferation effects on human umbilical vein endothelial cells (HUVECs) and human umbilical artery endothelial cells (HUAECs). Compounds 4-7 showed inhibitory activity.

Structure-antiemetic-activity of some diarylheptanoids and their analogues

The structure-activity relationship of diarylheptanoids and their analogues inhibitory of emesis induced by copper sulfate in young chicks was investigated by testing 19 compounds. The compounds are 5 diarylheptanoids isolated from Alpinia katsumadai (Zingiberacea), 5 chemical derivatives of them, 6 analogues isolated from Zingiber officinale rhizome (Zingiberaceae), and 3 analogues available on the market. Among them, two types of essential functional structure of diarylheptanoids and their analogues showed the inhibitory effects against emesis.

Antiangiogenic Metabolites from a Marine-Derived Fungus, Hypocrea vinosa

The aims of this study were to investigate the role of tyrosine kinase in intracellular signaling and to search for lead compounds with tyrosine kinase inhibitory activity from metabolites of marine-derived fungi. We initially prepared 400 extracts from 200 species of marine fungi and then subjected them to a tyrosine kinase screening assay using human umbilical vein endothelial cell lysate. Tyrosine kinase inhibitory activity was observed among certain metabolites of Hypocrea vinosa. We isolated one known compound, SC2051 (1), as well as two new compounds, hypochromins A (2) and B (3), which have a bis(naphtho-gamma-pyrone) skeleton. Compounds 1-3 showed tyrosine kinase inhibitory activity, with IC(50) values of 42.1, 58.7, and 18.0 microMu, respectively. Furthermore, compounds 1-3 exhibited inhibitory effects on proliferation, migration, and tubule formation.

β-Secretase (BACE-1) inhibitory effect of biflavonoids

Here, we describe amentoflavone-type biflavonoids, which were isolated from natural sources and were found to inhibit beta-secretase (BACE-1). The structure-activity relationship was studied, and compounds 1-8, 10, 17, and 18 showed BACE-1 inhibitory activity. Among these compounds, 2,3-dihydroamentoflavone 17 and 2,3-dihydro-6-methylginkgetin 18 exhibited potent inhibitory effects with IC(50) values of 0.75 and 0.35 microM, respectively.

Mutagenicity of ptaquiloside, the carcinogen in bracken, and its related illudane-type sesquiterpenes I. Mutagenicity in Salmonella typhimurium

Ptaquiloside, a potent carcinogen of an illudane-type sesquiterpene glycoside isolated from Pteridium aquilinum, and its related compounds, hypolosides having the same nucleus isolated from the Pteridaceae, exhibited marked mutagenicity in the modified Ames test with Salmonella typhimurium TA98 and TA100 using a preincubation at pH 8.5. Illudins M and S, sesquiterpenes of the same illudane type from basidiomycetes, also exhibited mutagenicity. The structural requirements for mutagenicity are discussed.