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PubMedDate not supplied

Stereoselective metabolism of benzo[a]pyrene and 7-methylbenzo[a]pyrene by liver microsomes from sprague-Dawley rats pretreated with polychlorinated biphenyls.

The dihydrodiols formed from the metabolism of benzo[a]pyrene (BaP) and 7-methylbenzo[a]pyrene (7-MBaP) by liver microsomes from male Sprague-Dawley rats treated with polychlorinated biphenyls (PCBs, Aroclor 1254) have been examined by circular dichroism (CD) spectropolarimetry. Comparisons with optically pure enantiomers obtained via high performance liquid chromatography (HPLC) resolution of diastereomeric di-(-)-menthoxyacetates indicated that the trans-4,5-, 7,8- and 9,10-dihydrodiols formed from BaP metabolism are predominantly R,R-enantiomers with optical purities greater than 98%. The major enantiomers of the metabolically formed 7-MBaP-trans-4,5- and 9,10-dihydrodiols and 7-hydroxymethyl-BaP-trans-9,10-dihydrodiol have Cotton effects very similar to those of BaP-4R,5R- and 9R,10R-dihydrodiols, respectively. These 7-MBaP-trans-4,5- and 9,10-dihydrodiol metabolites therefore contain predominantly the R,R-enantiomers. The optical purity of metabolically formed 7-MBaP-trans-4,5-dihydrodiol was determined to be 30.8% enriched in (-)-enantiomer. The optical purity of the 9,10-dihydrodiol was not determined due to the lack of synthetic standards. The major trans-7,8-dihydrodiol enantiomer formed from 7-MBaP metabolism is a (+)-enantiomer (optical purity 60.4%) which has Cotton effects opposite in sign to that of the (-)-7R,8R-dihydrodiol formed from BaP metabolism. The results indicate that a methyl substituent on a polycyclic aromatic hydrocarbon may alter the stereoselective properties of the microsomal drug-metabolizing enzyme systems toward the substrate molecule.

Animals↗
PubMed1975

ORD and CD studies of saturated glycerides.

A convenient method for transforming 3-acyl-sn-glycerols into 1-acyl-2,3-diacyl'-sn-glycerols, antipodes of 1,2-diacyl'=3-acyl-sn-glycerols, of relatively high optical purity, via the 1,2-dimesyl-3-acyl-sn-glycerols has been worked out. ORD and CD curves of optically active triglycerides and also some mono- and diglycerides have been studied in detail. The curo 200 nm or below. A Cotton effect from the n yeilds ets* transtition of the ester chromophore was observed at 215-220 nm, which was negative for triglyceritical rotations could be observed in triglycerides with very small differences in chain length, such as 1,2-dilauroyl-3-myristoyl-sn-glycerol.

Circular Dichroism↗
PubMedDate not supplied

Digestion and absorption of trioleoyl-thioglycerol in the rat.

A triacylglycerol analogue, rac-1,2-di-O-oleoyl-3-S-oleoyl-3-thioglycerol, was fed to rats and chyle acylglycerols were analyzed. Triacylglycerol was the dominating chyle lipid but X-triacyl-1-thioglycerol constituted approx. 6% of total chyle lipids. Its identity was verified by ultraviolet and mass spectra and its stereochemical structure by ORD and CD. The proportions of triacyl-1-thio-sn-glycerol/triacyl-3-thio-sn-glycerol were 63/37 and 78/22 in two experiments. Possible reasons for this stereospecificity are discussed. The study shows that the stereochemical configuration of lipids isolated from biological material can be assessed by ORD and CD.

Animals↗