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At least 1,783 records · Page 99Linked to original sources
PubMed1986

Solution structure of d-GAATTCGAATTC by 2D NMR. A new approach to determination of sugar geometries in DNA segments.

A new approach based on the correlated spectroscopy (COSY) in 2D NMR has been described for determination of sugar geometries in oligonucleotides. Under the usual low resolution conditions employed in COSY, the intensities of cross peaks depend on the magnitudes of coupling constants. There are five vicinal coupling constants in a deoxyribose ring which are sensitive to the sugar geometry. The presence, absence and rough comparison of relative intensities of COSY cross peaks arising from such coupling constants enable one to fix the sugar conformation to a fair degree of precision. The methodology has been applied to d-GAATTCGAATTC. It is observed that ten out of the twelve nucleotide units in this sequence exhibit a rare O1'-endo geometry. The EcoRI cleavage sites (between G and A) in the dodecanucleotide show an interesting variation in the conformation with the two sugars attached to the Gs acquiring a geometry between C2'-endo and C4'-endo.

Carbohydrate Conformation↗
PubMed1990

Influence of hyperalimentation on rat hepatic microsomal fluidity and function.

Total parenteral nutrition with an amino acid-glucose solution has previously been shown to decrease rat hepatic drug metabolism compared with drug metabolic activity observed in rats receiving the same solution enterally and chow-fed animals. Because changes in membrane fluidity and lipid composition are reported to influence activity of a number of liver enzymes, effects of parenteral and enteral nutrition on hepatic microsomal membrane fluidity and lipid composition were assessed and compared with hepatic mixed-function oxidase activity. Both parenteral and enteral hyperalimentation produced a significant decrease in microsomal membrane fluidity (fluorescence anisotropy = 0.155 +/- 0.003 in both experimental groups versus 0.129 +/- 0.003 for microsomes from chow-fed animals). However, meperidine demethylase activity was significantly decreased compared with chow-fed experiments only in hepatic microsomes from parenterally hyperalimented animals, whereas ethoxyresorufin deethylase activity was significantly reduced only in the enteral-nutrition group. Inclusion of lipid in the parenterally administered hyperalimentation solution normalized microsomal membrane fluidity and lipid profile to those of chow-fed animals but did not increase hepatic meperidine demethylation. Both parenteral and enteral nutrition produce significant changes in physical state and lipid composition of rat hepatic microsomal membranes, but these changes are not responsible for the altered hepatic drug metabolism observed during hyperalimentation.

Animals↗
PubMed1995

Evaluation of an optically active crown ether for the chiral separation of di- and tripeptides.

The direct optical resolution of a number of di- and tripeptides was achieved by capillary zone electrophoresis using an enantioselective crown ether as buffer additive. The protonated primary amines form inclusion complexes with the crown ether. Chiral resolution is based on different stability constants of the diastereomeric complexes thereby changing the electrophoretic mobilities of the enantiomers. Enantioselectivity is strongly affected by the distance between the amine functionality and the chiral carbon atom. This effect was studied using di- and tripeptides especially synthesized for this purpose. In general, baseline resolution was obtained for those peptides with the amine group located as far as four bonds from the stereogenic center. Additionally, tripeptides possessing two chiral centers were separated to investigate the potential of the chiral selector for the analysis of complex analytes with related structures. Experimental factors such as crown ether concentration, buffer pH and temperature also show a strong influence on the resolution. These factors can be successfully employed for method optimization.

Amino Acid Sequence↗
PubMed1983

5-chloro-5 beta-cholestane, the first simple 5 beta-chlorosteroid.

The life, times, and the main achievements in the steroid field of Julius Mauthner are briefly described. Three attempts by the author to isolate and to characterise 5-chloro-5 beta-cholestane are enumerated; the last attempt was successful, and furnished 5-chloro-5 beta-cholestane in two polymorphic forms: m.p. 72-75 degrees C, [alpha]20D + 37 degrees (labile above 0 degrees C) and m.p. 94-95 degrees C, [alpha]20D + 34 degrees (stable up to 75 degrees C). Possible mechanisms of the spontaneous, solid-state dehydrochlorination above 0 degrees C of the polymorph, m.p. 72-75 degrees C, are discussed.

Cholestanes↗
PubMed1983

Recent developments in corticoid synthesis.

In an attempt to improve the industrial manufacture of corticoids starting from desoxycholic acid, two major tasks had to be accomplished: (1) selective transposition of a 12 alpha-oxygen function to the 11-position. (2) Degradation of the side chain by three carbon atoms. The most convenient solution to the first problem included protection of the 3 alpha-hydroxyl, then dehydrating the 12 alpha-alcohol via its mesylate, and treatment of the resulting delta 11-12-alkene with PDC and iodine, to obtain the 12 alpha-iodo-11-ketone in very high yield. After reductive dehalogenation and saponification, the resulting acid proved to be suitable for solving our second problem. Oxidative decarboxylation with lead tetraacetate leads to an olefin, the double bond of which could be shifted along the side chain to produce the corresponding delta 20-22-isomer. Ozonolytic cleavage of the C--C double bond in this position made the 20-ketone 19 readily accessible. The latter plays a key role in the production of various corticoid drugs, since most of them are derived from this very compound, e.g. cortisol.

Adrenal Cortex Hormones↗
PubMed1984

Metabolism of steroid acetates by Streptomyces albus.

Fermentation of 16-dehydropregnenolone acetate (1a) with Streptomyces albus yielded 16-dehydropregnenolone (1b) and 16-dehydroprogesterone (IIa). Similar incubation of pregnenolone acetate (Ic) with the strain afforded pregnenolone (Id), progesterone (IIb) and 20 alpha-hydroxy progesterone (IIc) while dehydroepiandrosterone acetate (IIIa) under the conditions was converted to dehydroepiandrosterone (IIIb), androstenedione (IVa) and testosterone (IVc). The strain was also capable of converting testosterone acetate (IVb) having the 17-acetoxy function in the 5-membered D-ring to testosterone (IVc) and androstenedione (IVa). All the products were identified by the application of various chemical and spectrometric techniques.

Androgens↗