Henry Joshua

Avermectins, New Family of Potent Anthelmintic Agents: Isolation and Chromatographic Properties

The avermectins, a family of new anthelmintic agents, were isolated from the mycelia of Streptomyces avermitilis. Four closely related major components and four homologous minor components were separated from the complex. Solvent extraction, solvent partition, and adsorption methods were used to isolate and purify the complex; novel partition chromatography systems using Sephadex LH-20 were used to separate the components. A reverse-phase high-pressure liquid chromatography assay for the quantitative determination of all components was used extensively to monitor the purification methods.

Determination of aflatoxins by reversed-phase high-performance liquid chromatography with post-column in-line photochemical derivatization and fluorescence detection

Abstract Post-column in-line photochemical derivatization permits fluorescence detection of all four common aflatoxins B1, B2, G1 and G2. Chromatographic evidence indicates that the photolysis causes the hydration of the non-fluorescent B1 and G1 components to the B2a and G2a components respectively. Analysis of naturally contaminated corn samples show no interfering peaks and permits the determination of 1 and 0.25 ppb (w/w) of B1 and B2, respectively.

Inhibition of procine kidney “enkephalinase” by substituted-N-carboxymethyl dipeptides

Abstract A design effective for generating inhibitors of angiotensin converting enzyme has been successfully extended to inhibitors of another Zn ++ peptidase. A series of potent inhibitors for the zinc metalloendopeptidase associated with porcine kidney microsomes has been developed. Most contain the (S)-N-(1-carboxy-3-phenylpropyl)-L-Phe-X backbone. The most effective inhibitors with ID 50 values in the 10 −7 M range at pH 7.5 and 22°C were those where X = glycine, β-alanine, γ-amino butyric acid. A simple nomenclature designating substituted N-carboxy-methyl amino acid derivatives as -[N]- sharing amino acid derivatives is described.

Isolation, structure determination and squalene synthase activity of L-731,120 and L-731,128, alkyl citrate analogs of zaragozic acids A and B

Abstract Two new alkyl citrates, L-731,120 and L-731,128, with alkyl chains corresponding to those of zaragozic acids A and B, were isolated as minor components of large scale fungal fermentations producing zaragozic acid A and B. They are submicromolar inhibitors of squalene synthase in vitro .