Yoshinori Fujimoto

(S)-citramalic acid, a useful chiral synthon for the synthesis of 15-deoxy-16(S)-hydroxy-16-methylprostaglandins

(S)-Citramalic acid, a readily available microbial metabolite has been efficiently transformed into (2S)-2-methyl-2-hydroxy-1-hexanol (7), an important chiral synthon for the synthesis of 15-deoxy-16(S)-hydroxy-16-methylprostaglandins.

3β-Hydroxy-5β-cholest-7-en-6-one as an intermediate of 20-hydroxyecdysone biosynthesis in a hairy root culture of Ajuga reptans var. atropurpurea

[3α-2H]-, [4α-2H]- and [4β-2H]-Cholesterols and [3α-2H]- and [5-2H]-3β-hydroxy-5β-cholest-7-en-6-ones were converted with a hairy root culture of Ajuga reptans var. atropurpurea into 20-hydroxyecdysone, in which the deuterium atoms retained their original positions, thus strongly suggesting that 3β-hydroxy-5β-cholest-7-en-6-one is an obligatory intermediate in the biosynthesis of ecdysteroids in the plant.

Studies on the structure and stereochemistry of cytotoxic furanonaphthoquinones from Tabebuia impetiginosa: 5- and 8-hydroxy-2-(1-hydroxyethyl)naphtho[2,3-b]furan-4,9-diones

Chemical investigation of the bark of Tabebuia impetiginosa(Bignoniaceae) afforded cytotosic furanonaphthoquinones, including 5-hydroxy-2-(1-hydroxyethyl)naphtho[2,3-b]furan-4.9 dione and its 8-hydroxy isomer. The position of the phenolic group in these two compounds was established by X-ray crystallography. The furanonaphthoquinones were found to be mixtures of both enantiomers in diffferent proportions, i.e., (for the 5-hydroxyisomer)R:S1:23 and (for the 8-hydroxy isomer)R:S 3:1. The synthesis of the racemic naphthofurans, their optical resolution into enantiomerically pure forms, and the determination of their absolute stereochemistry are described. The structure of kigelinone was also established to be that of the 5-hydroxy isomer, not the 8-hydroxy one, through this study.

C-25 prochirality in the fragmentation reaction catalysed by fucosterol epoxide lyase from the silkworm, Bombyx mori

The fate of the diastereotopic methyl groups on the prochiral C-25 centre of fucosterol epoxide and isofucosterol epoxide during enzymatic conversion into desmosterol has been investigated. Incubation of stereospecifically 13C-labelled fucosterol (24R, 28R)-epoxides and isofucosterol (24R, 28S)-epoxides with a cell-free preparation obtained from the guts of larvae of the silkworm, Bombyx mori, followed by 13C NMR analysis of the product has shown that the reaction is stereospecific, where the pro-S and pro-R methyl groups of the epoxides turn stereospecifically into (Z)- and (E)-methyl groups of desmosterol, respectively.

Stereochemistry of the hydrogen addition to C-25 of desmosterol by sterol-Δ24-reductase of the silkworm, Bombyx mori

The C-25 stereochemistry of the reaction catalysed by sterol-Δ24-reductase from the insect, B. mori, has been investigated by the use of 13C NMR spectroscopy; incubation of isopropylidene (E)-methyl-13C labelled desmosterol afforded cholesterol with the label at pro-R-methyl of the isopropyl group, and the results indicated the C-25 hydrogen was introduced stereospecifically from the si-face of the double bond.

Stereochemical assignment of C-24 and C-25 of amarasterone A, a putative biosynthetic intermediate of cyasterone.

A C29 phytoecdysteroid named amarasterone A (1) has been isolated from Cyathula capitata (Amaranthaceae), Leuzea carthamoides (Asteraceae), and Microsorum scolopendria (Polypodiaceae). We recently isolated amarasterone A from C. officinalis. Amarasterone A has been postulated as a biosynthetic intermediate of cyasterone in Cyathula sp. The stereochemistry at the C-24 and C-25 positions of these amarasterone A samples was investigated by comparing the NMR spectroscopic data with those of stereodefined model compounds, (24R,25S)-, (24R,25R)-, (24S,25S)-, and (24S,25R)-isomers of (20R,22R)-3β-methoxystigmast-5-ene-20,22,26-triol (2a-d), which were synthesized in the present study. Amarasterone A isolated from Cyathula officinalis was determined to be the (24R,25S)-isomer (1a), while amarasterone A from L. carthamoides was found to be the (24R,25R)-isomer (1b). Amarasterone A from M. scolopendria was found to be a mixture of 1a and 1b. The biosynthesis of cyasterone in Cyathula sp. is discussed on the basis of the identical C-24 configuration of sitosterol and amarasterone A.

Structure of 8-hydroxy-2-(1-hydroxyethyl)naphtho[2,3-b]furan-4,9-dione

C 14 H 10 O 5 cristallise dans P2 1 2 1 2 1 avec a=6,851, b=35,89, c=4,618 A, Z=4; affinement jusqua R=0,068. Le groupement hydroxyl phenolique participe a une liaison hydrogene intramoleculaire avec le groupement carbonyl; et le groupement hydroxyl ethanolique forme une liaison hydrogene et connecte les molecules le long de laxe c