Analysis of Streptomyces avermitilis genes required for avermectin biosynthesis utilizing a novel integration vector.

An integration vector for gene analysis in Streptomyces has been constructed. This vector replicates in Escherichia coli, and integrates into Streptomyces by homologous recombination between a cloned fragment and the genome. To overcome methylation-specific restriction barriers, an E. coli mutant triply defective in DNA methylation was constructed as a source for the integration plasmids. The frequency of integration of pVE616 derivatives into the Streptomyces avermitilis genome was proportional to the size of the cloned DNA. Derivatives of pVE616, containing fragments from pVE650, a plasmid with a 24-kb insert of S. avermitilis DNA, were used in complementation analyses of seven S. avermitilis mutants defective in glycosylation of avermectin (Av). Three complementation groups, located in a 7-kb region, were identified. Derivatives of pVE616, containing fragments from the 18-kb of DNA adjacent to the glycosylation region, were integrated into an Av producer. Av produced from the integrants was substantially reduced, indicating that the 18 kb also encodes gene products which are involved in Av biosynthesis.

Candelalides A-C: novel diterpenoid pyrones from fermentations of Sesquicillium candelabrum as blockers of the voltage-gated potassium channel Kv1.3.

[figure: see text] Blockers of the voltage-gated potassium channel Kv1.3 are potential immunosuppressants. Candelalides A-C are three novel diterpenoid pyrones that block this channel. The structure, stereochemistry, and activity against Kv1.3 are described.

Stability and kinetics of degradation of imipenem in aqueous solution.

In weakly acidic solution, the broad-spectrum antibiotic imipenem undergoes complex oligomerization initiated by intermolecular carboxyl group attack on the beta-lactam group. In weakly alkaline solution, intermolecular reaction between the beta-lactam and formimidoyl groups occurs instead. Both beta-lactam and formimidoyl groups also hydrolyze at pH-dependent rates. Complex decomposition schemes were determined in kinetic studies at pH 4.0 and 9.0-9.5 using HPLC and mathematical models. The rates of the several initial reactions, calculated as functions of pH and imipenem concentration by fitting the models to kinetic data, fully account for imipenem decomposition rates throughout the neutral pH range.

The preparation of zaragozic acid A analogues by directed biosynthesis.

Zaragozic acid A analogues are produced by an unidentified sterile fungus when it is exogenously supplied with 2-thiophenecarboxylic acid, 3-thiophenecarboxylic acid, 2-furoic acid, 2-fluorobenzoic acid, 3-fluorobenzoic acid, or 4-fluorobenzoic acid. The analogues carry 2-thiophenyl, 3-thiophenyl, 2-furyl, o-fluorophenyl, m-fluorophenyl, or p-fluorophenyl group, respectively, at C-6' of the C-1 alkyl side chain replacing the phenyl group of natural zaragozic acid A. All the new analogues of zaragozic acid A possess picomolar inhibitory activity against squalene synthase in vitro.

HIV-1 protease inhibitory activity of L-694,746, a novel metabolite of L-689,502.

L-689,502 is a potent inhibitor of HIV-1 protease activity in vitro. Microbial biotransformations of L-689,502 by cultures belonging to the genus Streptomyces sp. were performed. Extracts of culture broths were examined for the production of metabolites of L-689,502 that could inhibit HIV-1 protease activity. One culture, MA 6804 (Streptomyces lavendulae, ATCC 55095), produced L-694,746 that, while being structurally related to L-689,502, is a novel metabolite and a potent inhibitor of HIV-1 protease.