High-throughput screening of microbial extracts using rat hepatic microsomal glucose-6-phosphatase (G6Pase) led us to find thielavin B as a G6Pase inhibitor with inhibition of glucose output from glucagon-stimulated hepatocytes. Further searching for more potent analogs identified 11 new thielavins F-P in addition to the known thielavins A and B from a fungus Chaetomium carinthiacum ATCC 46463. Thielavin G showed the strongest activity as a G6Pase inhibitor (IC50=0.33μM), while the IC50 of thielavin B was 5.5μM. According to the structureactivity relationship, including authentic thielavins C, D and 3 partial hydrolysates from thielavins A and B, 3 benzoic acid-units and carboxylic acid functions are essential for G6Pase inhibition.
New antibiotics, miyakamides A1, A2, B1, and B2, were isolated from the cultured broth of Aspergillus flavus Link var. columnaris FKI-0739 together with known compounds, parasiticolide A, hydroxyaspergillic acid, and kojic acid. The structure of miyakamide A1 is N-acetyl-L-phenylalanyl-N-methyl-L-phenylalanyl-(αZ)-α, β-didehydrotryptamine, and miyakamide A2 is E isomer of A1 at didehydrotryptamine. The structure of miyakamide B1 is N-acetyl-L-tyrosyl-N-methyl-L-phenylalanyl-(αZ)-α, β-didehydrotryptamine, and B2 is E isomer of B1. Both miyakamides A1 and B1 existed as equilibrium isomers in solvents, and this isomerism was associated with cis-trans rotation of the amide bond between two amino acids. Conformational isomerism between two amino acids of miyakamides A2 and B2 is cis-form. Miyakamides showed growth inhibitory activity against brine shrimp, Artemia salina.
C-4 sterol methyl oxidase encoded by the ERG25 gene is a key enzyme in the ergosterol biosynthetic pathway in fungi. ERG25p contains three histidine clusters common to nonheme iron binding enzymes and endoplasmic reticulum retrieval signal. In order to characterize ERG25p, we generated a series of temperature-sensitive(ts) erg25 mutants by random mutagenesis. One of the resulting mutants, the mERG25 strain, accumulated 4, 4-dimethlzymosterol at the nonpermissive temperature. Sequence analysis of the mERG25 mutant indicated three amino acid substitutions in ERG25p, namely N48D, V133A, and F135S. These results indicate that the ERG25 gene product is a new antifungal target.
PF1163A and B are a pair of antifungal agents isolated from a fermentation broth of Penicillium sp. PF1163A inhibited ergosterol synthesis in Saccharomyces cerevisiae, resulting in an accumulation of 4, 4-dimethylzymosterol and a decrease of ergosterol. The ERG25 strain overexpressing the ERG25 gene was resistant to PF1163A. ERG25p is a C-4 sterol methyl oxidase known to be essential for the viability of yeast and fungi because of the known role of ERG25 gene disruption in S. cerevisiae-led lethality. ERG25p is the enzyme responsible for the first step in the removal of the two methyl groups at the C-4 position of sterol. From the results obtained here, we conclude that PF1163A is a novel natural antifungal that inhibits C-4 sterol methyl oxidase.
A series of 7-aminothiadiazolylcephalosporins having a 1-(substituted)-1H-imidazo[4, 5-b]pyridinium group at the C-3' position of the cephem nucleus were synthesized and evaluated for in vitro antibacterial activities. Among the cephalosporins prepared in this study, 7β-[2-(5-amino-1, 2, 4-thiadiazol-3-yl)-2(Z)-ethoxyiminoacetamido]-3-[1-(3-methylaminopropyl)-1H-imidazo[4, 5-b]pyridinium-4-yl]methyl-3-cephem-4-carboxylate sulfate (S-3578) showed extremely potent broad spectrum activity against both Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative bacteria including Pseudomonas aeruginosa, and good water solubility.
Chemical derivation methods to prepare 26-acyloxy and 26-hydroxymilbemycins, which had been reported as natural products, milbemycins α9, α10, α11, α12, α14, α15, α20, α21, α22, α23, α26, α27 from milbemycins A3, A4 were reported. Δ2, 3, Δ4, 26-Milbemycins A3, A4, which had also been reported as natural products, were further prepared from milbemycins A3, A4. Their acaricidal activities were also assessed against the organophosphorus-sensitive two-spotted spider mite (Tetranychus urticae) on primary leaves of cowpea plants (Vigna sinesis Savi species) by spraying.