Yukio Ogihara

Studies on fungal metabolites—XXXI: Anthraquinonoid colouring matters of Penicillium islandicum sopp and some other fungi (−)luteoskyrin, (−)rubroskyrin, (+)rugulosin and their related compounds

Abstract The structures of (+)rugulosin, (−)luteoskyrin and (−)rubroskyrin have been reexamined by NMR and new structures 18, 19 and 20 proposed respectively. Their absolute structures were established on the basis of the X-ray analysis of (+)dibromodehydrotetrahydrorugulosin (27). The minor analogous metabolites, (−)4a-oxyluteoskyrin (31) of P. islandicum and (+)4a-oxyrugulosin (32) of P. brunneum, have been formulated. On oxidation of (−)luteoskyrin and (+)rugulosin with pertrifluoroacetic acid (−)4a,4a′-dioxyluteoskyrin (33) and (+>4a,4a′-dioxyrugulosin (34) were formed, while with MnO2 (+)4a,4a′-dehydrorugulosin (35) was obtained. The structures of lumiluteoskyrin (37), and deoxylumiluteoskyrin (38), photooxidation products of luteoskyrin and deoxyluteoskyrin, respectively, have been elucidated.

A new sapogenin in the saponins of Zizyphus jujuba, Hovenia dulcis and Bacopa monniera

Abstract Acid hydrolysis of the saponin of the seeds of Zizyphus jujuba afforded ebelin lactone, which yielded the sapogenin, jujubogenin, on Smith-de Mayo degradation. The mechanism of conversion of jujubogenin into ebelin lactone has been elucidated. Hovenoside G of Hovenia dulcis and bacoside A of Bacopa monniera which produce ebelin lactone on acid hydrolysis have also been found to yield jujubogenin on Smith-de Mayo degradation.

Studies on fungal metabolites—XXXII: A renewed investigation on (−) flavoskyrin and its analogues

Abstract 1-Oxo-1,2,3,4-tetrahydroanthraquinone ( 4a ), and its 8-hydroxy-( 4b ) and 8-hydroxy-6- methyl ( 4c ) derivatives were dimerized to the compounds formulated as ( 6a ), ( 6b ) and ( 6e ), respectively. The structure of 6a was confirmed by X-ray crystallographic analysis. By the analogy with these dimers and NMR spectral analysis, a revised structure ( 7 ) was proposed for (−) flavoskyrin, a yellow metabolite of Penicillium islandicum NRRL 1175. A biosynthetic scheme involving Diels-Alder type cyclo-addition (π4s + π2s) was proposed for (−) flavoskyrin.

New peptide alkaloids from Hovenia dulcis and H. tomentella

Abstract From the root bark of Hovenia dulcis Thunb. and H. tommentella (Makino) Nakai (Rhamnaceae), three peptide alkaloids, frangulanine, hovenins- A and - B have been isolated. Hovenin- A has been shown to be des- N -methylfrangulanine (II).