Toshihide Yamada

Triterpenoid glycosides from leaves of Ilex cornuta

Abstract Two new triterpene glycosides have been isolated from the methanol extract of leaves of Ilex cornuta . Their structures were established as pomolic acid 3β- O -α- l -2-acetoxyarabinopyranosyl-28- O -β- d -glucopyranoside and 29-hydroxyoleanolic acid 3β- O -α- l -arabinopyranosyl-28- O -β- d -glucopyranoside on the basis of spectroscopic data and chemical evidence. Adenosine was identified as the active principle of the methanol extract which is responsible for the increase of coronary blood flow in the isolated blood-perfused dog heart preparation.

Tag-Assisted Liquid-Phase Peptide Synthesis Using Hydrophobic Benzyl Alcohols as Supports

A soluble tag-assisted liquid-phase peptide synthesis was successfully established based on simple hydrophobic benzyl alcohols, which can be easily prepared from naturally abundant materials. Excellent precipitation yields can be obtained at each step, combining the best properties of solid-phase and liquid-phase techniques. This approach can also be applied efficiently to fragment couplings, allowing chemical synthesis of several bioactive peptides.

Three flavone glycosides from citrus sudachi

Abstract Three flavone glycosides, sudachiins B, C and D, were isolated from the green peel of Citrus sudachi . On the basis of UV, 1 H NMR and 13 C NMR spectral data sudachiins B and C were identified as sudachiin A 6″- (3-hydroxy-3-methyl)glutarateand 7- O -β-D-glucosyl sudachitin 6″-(3-hydroxy-3-methyl)glutarate, respectively. Sudachiin D was found to be a unique glycoside in which sudachiin A and 7- O -β-D-glucosylsudachitin were esterified at their 6″-positions with 3-hydroxy-3-methylglutaric acid.

Triterpenoids from the rhizome of Alisma plantago-aquatica

Abstract Two new protostane-type triterpenes have been isolated from the methanol extract of the rhizome of Alisma plantago-aquatica . Their structures have been elucidated as 16β-methoxyalisol B monoacetate and 16β-hydroxyalisol B monoacetate mainly on the basis of spectroscopic data.

Revised structure of a natural flavone from Artemisia lanata

Abstract The structure of a natural flavone from Artemisia lanata , thought to be 3,5-dihydroxy-7,8,3′,4′-tetramethoxyflavone, is revised to 5,3′-dihydroxy-3,6,7,4′-tetramethoxyflavone on the basis of spectral data.

Oxidative rearrangement of 2′-hydroxychalcones having no substituent at the 3′- and 5′-positions with thallium(III) nitrate in methanol

Oxidation of 2′-hydroxychalcones with no substituents at the 3′-and 5′-positions with thallium(III) nitrate (TTN) in methanol has been studied in detail and the following results obtained. (1) 2′-Hydroxy-4,6′-dimethoxychalcones (1b and 2b) have increased reactivity over their methyl ethers as a result of participation of the 6′-methoxy oxygen atom; the reactivity of 2′-hydroxy-4,4′-dimethoxychalcone 3b however was decreased. (2) The reactions were greatly affected by the substituents on the A and B rings and formed the corresponding 1,2-diaryl-3,3-dimethoxypropan-1-ones (acetal) and/or 2-(α-methoxybenzyl)coumaranones (coumaranone): the oxidative rearrangement was greatly accelerated by methoxy groups at the 4- and/or 2-positions to give an acetal as a main product. (3) Formation of the coumaranone was observed only when the 2′-hydroxychalcones had a methoxy group at the 6′-position and a B ring with weaker electron-donating nature. (4) The ratio of the coumaranones formed in the reaction of 2 with no substituent at the 4′-position was lower than that of 1 which formed quickly a cyclic TTN complex between the 2′-hydroxy and the neighbouring carbonyl groups. Only the reaction of 2′-hydroxy-6′-methoxychalcone 2a afforded the acetal and coumaranone together with a large amount of thallium compounds which were converted into a mixture of the corresponding isoflavone and aurone by treatment with hydrochloric acid. From these results, the mechanism of the reaction was proposed as shown in Schemes 2 and 3.