Laszlo R. Treiber

Normal-phase high-performance liquid chromatography with relay gradient elution I. Description of the method

Abstract The utility of normal-phase HPLC with relay gradient elution covering the entire practical range of polarity from hexane through water is demonstrated. The separations have been carried out on a LiChrospher 100 Diol column. Analytes without appreciable UV absorbance have been detected by means of an evaporative light-scattering detector. The method presented is suitable for the classification of sample components according to their polarity. The potential utility of the technique in programs such as profiling, classification and screening of biological materials, metabolic studies and preparative-scale isolation is discussed.

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.

Oxidative photochemical decarboxylation of zaragozic acid A

A unique decomposition reaction of the novel squalene synthase inhibitors called zaragozic acids has been studied. Under very mild conditions, e.g. by merely exposing their solutions to air and visible light at ambient temperature, these compounds, characterized by the 2,8-dioxabicyclo[3.2.1]octane-4,6,7-trihydroxy-3,4,5-tricarboxylic acid core, rapidly decompose. As relatively stable intermediates in the cascade of decomposition, the biologically active 2,8-dioxabicyclo[3.2.1]octane-6,7-dihydroxy-4-keto-5-caroxylic acid (or 3,4-decarboxy-4-dehydro) derivatives of these compounds have been isolated in ca. 20% yield. Derivatization on the highly reactive 4-carbonyl group yields stable derivatives, several of which are potent inhibitors of squalene synthase. Further decomposition results in the elimination of C3 and C4 atoms and the carboxylic acid on C5, the oxidation of C5 to carboxylic acid and the liberation of the oxo group on C1. Specific results obtained with zaragozic acid A, a key representative of the family of these potent cholesterol-lowering agents, are presented in this study.

Quantitative analysis of cephamycin C in fermentation broths by means of thin-layer spectrodensitometry

A method has been developed that consists of one-dimensional thin-layer chromatography of the samples on pre-coated silica gel 60F254 plates followed by an in situ spectrophotometric evaluation of the chromatograms at 273 nm. Statistical evaluations showed a linear calibration (r2 greater than 0.999) for the range of 0.2-20 microgram/spot. The relative standard deviations for broth samples containing 1.505 and 12.47 microgram Cephamycin C per spot were 3.61 and 1.07%, respectively. The recovery was virtually quantitative: 97.6%. The correlation with a liquid chromatographic method was quite acceptable with r2 = 0.99124 and b = 0.998 (slope).

Quantitative thin-layer chromatography in accelerated stability studies for prediction of inherent sensitivity of drugs toward oxygen

This paper discusses a novel technique for studying the inherent sensitivity of materials toward oxygen and the utility of quantitative thin-layer chromatography, as a tool in such studies. The degradation generally followed first order kinetics up to about 60% decomposition, indicating that the usual kinetic treatment applied to homogeneous systems can be used. The method can also detect degradation products, in many cases adding a considerable diagnostic element to its predictive value. Among the model compounds tested testosterone was the most stable with ca. 95% recovery following a 190-h exposure to air on standard silica gel plates. The half-life time of the other model substances under similar experimental conditions was estimated by means of direct measurements or by extrapolation, and found to range from approximately 300 h to 1 h 10 min with cortisone marking the upper value and cholesta-3,5-diene the lower one.