Miyuki Hirata

Antibacterial activity of isoflavonoids isolated from Erythrina variegata against methicillin‐resistant Staphylococcus aureus

Aims: To screen 16 isoflavonoids isolated from Erythrina variegata (Leguminosae) for their antibacterial activity against methicillin‐resistant Staphylococcus aureus (MRSA).

Antibacterial property of isoflavonoids isolated from Erythrina variegata against cariogenic oral bacteria

The antibacterial property of 7 compounds, isolated from Erythrina variegata (Leguminosae) by repeated silica gel column chromatography, against cariogenic oral bacteria was investigated. Extensive spectroscopic study revealed that all were isoflavonoids. Among them, 3,9-dihydroxy-2,10-di(gamma,gamma-dimethylallyl)-6a,11a-dehydropterocarpan (erycristagallin) showed the highest antibacterial activity against mutans streptococci, other oral streptococci, Actinomyces and Lactobacillus species with a minimum inhibitory concentration (MIC) range of 1.56-6.25 microg/ml, followed by 3,6a-dihydroxy-9-methoxy-2,10-di(gamma,gamma-dimethylallyl)pterocarpan (erystagallinA) and 9-hydroxy-3-methoxy-2-gamma,gamma-dimethylallylpterocarpan (orientanol B) (MIC range: 3.13-12.5 microg/ml). The antibacterial effect of erycristagallin to mutans streptococci was based on a bactericidal action. Erycristagallin (6.25 microg/ml: MIC) completely inhibited incorporation of radio-labelled thymidine into Streptococcus mutans cells. Incorporation of radio-labelled glucose into bacterial cells was also strongly inhibited at MIC, and 1/2 MIC of the compound reduced the incorporation approximately by half. The findings indicate that erycristagallin has a potential as potent phytochemical agent for prevention of dental caries by inhibiting the growth of cariogenic bacteria and by interfering with incorporation of glucose responsible for production of organic acids.

Three new isoflavonoids from Erythrina variegata

Three new isoflavonoids, eryvarins C-E, together with fourteen known compounds were isolated from the roots of Erythrina variegata (Leguminosae) and their structures were elucidated on the basis of spectroscopic evidence.

Four new isoflavonoids and a new 2-arylbenzofuran from the roots of Erythrina variegata

Two new isoflavonoids, eryvarins S (1) and T (2), and a new 2-arylbenzofuran, eryvarin U (3), together with nine known compounds, were isolated from the roots of Erythrina variegata. Their structures were established on the basis of spectroscopic analysis. Eryvarin U is a rare naturally-occurring 2-arylbenzofuran. The antibacterial activity of these three new compounds against 13 strains of methicillin-resistant Staphylococcus aureus (MRSA) was examined in which eryvarin U showed the highest antibacterial activity.

Eryvarins F and G, two 3-phenoxychromones from the roots of Erythrina variegata

Two 3-phenoxychromones, eryvarins F and G, were isolated from the roots of Erythrina variegata. Their structures were established to be 3-(2,4-dihydroxyphenoxy)-7-hydroxy-6,8-di(3,3-dimethylallyl)chromen-4-one and 3-(2,4-dihydroxyphenoxy)-8-(3,3-dimethylallyl)-2,2-dimethylpyrano[5,6:6,7]chromen-4-one on the basis of spectroscopic and chemical evidence. Eryvarins F and G are unusual 3-phenoxychromone derivatives with two isoprenoid groups.

Phenolic constituents from stem bark of Erythrina poeppigiana and their inhibitory activity on human glyoxalase I

A novel isoflavone, erythgianin A (1), along with nine known compounds 2–10, was isolated from the stem bark of Erythrinapoeppigiana (Leguminosae). The unusual isoflavone structure of 1, possessing a highly oxidized 3″,4″-dihydroxy-2″-hydroxymethyl-2″-methyl-2″,3″-dihydropyrano substituent, was determined on the basis of spectroscopic analyses. All of the isolated compounds were evaluated for their in vitro inhibitory activity toward human glyoxalase I. Among the isolates, isolupalbigenin (10) with two prenyl groups showed the highest inhibitory activity.

Theoretical studies on the configuration of a chalcanol derivative

The relative configuration of a naturally occurring monobenzoylated diol was assigned to erythro by comparing the weighted average of calculated 1H NMR coupling constants with the experimental values.