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At least 1,279 records · Page 71Linked to original sources
PubMed1975

Inotropic and electrophysiological actions of verapamil and D 600 in mammalian myocardium. II. Pattern of inotropic effects of the optical isomers.

On isotonically contracting cat papillary muscles analysis, a comparison of the effects of the optical isomers of verapamil and D 600 and the racemic drugs was performed. 1. (-)-verapamil (0.2-3.0 mug/mo) and (-)-D-600 (0.1 mug/ml-3.0 mug/ml) leave the steady state contraction amplitudes nearly unchanged at 6/min, but produce a strong depression at 60/min. (-)-D 600 is about 8 times as effective as (-)-verapamil. The (+)-isomers exert only a moderate negative inotropic effect (particularly at low frequencies). 2. Increase of [Ca2+]O does not restitute the normal amplitude-frequency relationship during exposure to either the (-)-isomers or the (+)-isomers. 3. The (-)-isomers lead to typical biphasic staircases after step changes of frequency. A fast negative staircase occurs first followed by a rather slowly developing positive staircase. In contrast, the (+)-isomers have little influence on the usual staircase pattern. 4. The strength-interval relationship for single test contractions elicited after frequent conditioning stimulation indicated that the (-)-isomers probably slow the restitution of intracellular Ca-reavailability. The (+)-isomers have no such effects. 5. The effects produced by the (+/-)-compounds correspond qualitatively to those of the (-)-isomers. 6. The very different patterns of inotropic actions observed indicate that the (-)- and (+)-isomers of verapamil and D 600 probably interfere with cardiac excitation-contraction coupling at different sites.

Animals↗
PubMed1993

No decreased erythrocyte deformability in type 1 (insulin-dependent) diabetes, either by filtration or by ektacytometry.

A lower erythrocyte deformability, which causes impairment of the microcirculation, is postulated to contribute to diabetic organ complications. Erythrocyte deformability was measured in four groups of type 1 (insulin-dependent) diabetic subjects and 30 controls by filtration and ektacytometry. Twenty-five patients without organ complications, 21 with microalbuminuria, 13 with overt nephropathy and 12 with leg ulceration were studied. No decreased erythrocyte deformability was found in any of the diabetic groups with either technique, and neither did the total group of 71 diabetic subjects have a lower erythrocyte deformability when compared with the controls. In order to imitate local conditions in the kidney, erythrocyte deformability was also measured in hyperosmolar solutions. Again no differences were found between the diabetic groups separately or as a whole and the controls. Furthermore no correlation was found between erythrocyte deformability and the plasma glucose or glycosylated haemoglobin level.

Adult↗
PubMed1985

Melanin biosynthesis and the metabolism of flaviolin and 2-hydroxyjuglone in Wangiella dermatitidis.

Melanin biosynthesis in the human pathogen Wangiella dermatitidis was inhibited by tricyclazole, causing pentaketide melanin metabolites to accumulate in the cultures. One of these metabolites, scytalone, was racemic and thus different than the (+)-enantiomer from Verticillium dahliae. An albino mutant of W. dermatitidis metabolized scytalone to a pigment ultrastructurally identical to wild-type melanin. Cell-free homogenates of the wild type carried out typical reductive and dehydrative reactions with known melanin intermediates and the reductive reactions were inhibited by tricyclazole. Other reductive and dehydrative reactions that utilize flaviolin and 2-hydroxyjuglone were studied anaerobically with homogenates from both the wild type and the albino mutant. The homogenates converted flaviolin to 5-hydroxyscytalone and products identical to those obtained from 2-hydroxyjuglone. The albino, in culture, carried out the same reactions with 2-hydroxyjuglone but metabolized flaviolin to a number of unknown colored products apparently through oxidative reactions. Similarities between the melanin pathway and the flaviolin and 2-hydroxyjuglone branch pathways are discussed and tricyclazole is shown to inhibit reductive reactions with naphthols in the three pathways.

Melanins↗
PubMed1996

Total synthesis of glycononaosyl ceramide with a sialyl dimeric Le(x)-sequence.

The first total synthesis of glycononaosyl ceramide with a sialyl dimeric Le(x) sequence 1 is described. Regio- and stereo-selective glycosylations of sialyl donors 6,7,8 with the suitably protected Le(x) trisaccharide acceptors 9,10 beta were performed to give the expected tetrasaccharides 15 and 21, which were converted into the corresponding donors 20 and 22. Boron trifluoride etherate-promoted glycosylation of 20 with pentasaccharide acceptor 11 afforded regioselectively the expected nonasaccharide 23. After replacing benzyl groups of 23 by acetyl groups, the anomeric acetate was transformed into the alpha-trichloroacetimidate 27. The crucial coupling between 27 and (2S, 3R, 4E-3-O-benzoyl-2-N-tetracosanoylsphingenine 3 was executed to afford completely protected beta-glycoside 28. Finally, selective cleavage of the methyl ester and N,O-deprotection of 28 gave the target ganglioside 1.

Carbohydrate Sequence↗
PubMed1996

Synthesis of deoxygalactose-containing sialyl Le(X) ganglioside analogues to elucidate the structure necessary for selectin recognition.

Sialyl Lewis X ganglioside analogues containing 4-deoxy-, 6-deoxy-, and 4,6-dideoxy-D-galactopyranose in place of D-galactopyranose have been synthesized. Glycosylations of 2-(trimethylsilyl)ethyl 2,6-di-O-benzyl-beta-D-galactopyranoside and 2-(trimethylsilyl)ethyl beta-D-fucopyranoside with the phenyl 2-thioglycoside derivative of sialic acid, using N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) as the promoter in acetonitrile, gave the desired 2-(trimethylsilyl)ethyl sialyl-alpha-2-->3)-beta-D-galactopyranoside and -beta-D-fucopyranoside, respectively. The sialylgalactose derivative obtained was then modified to 4-deoxy and 4,6-dideoxy derivatives. These were converted, by O-benzoylation, transformation of the 2-(trimethylsilyl)ethyl group to trichloroacetimidates, and introduction of the methylthio group with methylthiomethylsilane, into the corresponding glycosyl donors, which were then coupled with 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl)-(1->3)-O-(2-acetamido-6-O- benzyl-2-deoxy-beta-D-glucopyranosyl)-(1->3)-2,4,6-tri-O-benzyl-beta-D- galactopyranoside in the presence of dimethyl(methylthio)sulfonium triflate (DMTST). The resulting pentasaccharides were each converted to the corresponding alpha-trichloroacetimidates, which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol, gave the desired sphingosine derivatives. Selective reduction of the azide group, N-acylation with octadecanoic acid, O-deacylation, and saponification of the methyl ester afforded the target compounds.

Animals↗
PubMedDate not supplied

Investigations of electron helicity in optically active molecules using polarized beams of electrons and positrons.

We will discuss one possible correlation between the origin of optical activity in biological molecules and the helicity of beta particles emitted in nuclear beta decay. This correlation is based on the supposition of Hrasko and Garay that electrons in optically active molecules possess helicity. Positronium formation experiments are significantly more sensitive to this particular effect than radiolysis experiments although no experiments of any type to date have obtained the sensitivity that our preliminary calculations indicate is necessary. We discuss a new experiment in which positronium is formed in vacuum with a low energy polarized positron beam. An improvement of up to 10(4) in sensitivity to the effect is possible.

Electrons↗
PubMedDate not supplied

Beta irradiation may induce stereoselectivity in the crystallization of optical isomers.

A novel approach has been introduced to detect the manifestation of symmetry breaking weak interactions at molecular level. In the racemic conglomerate crystallization of D,L-sodium-ammonium tartrate the effect of 32P irradiation was studied by measuring the weight and optical purity of the crystalline phase as well as the size distribution of the crystallites. The high number of independent experiments (over 1000) permitted statistical analysis of the results. The following observations have been made: 1. Beta irradiation influences the crystallization process, irradiated samples yield more crystalline material. 2. The effect involves presumably crystal seed formation because from the irradiated solutions more and smaller crystallites are formed. 3. The presence of beta particles induces stereoselective crystallization, the crystalline phase shows optical activity characteristic of the "unnatural" L-isomer. 4. The above changes are attributed to the beta irradiation as the magnitude of the effects depends on the amount of added radioactivity. Optically active contaminants are highly unlikely sources of the differences between irradiated and control series. 5. In the absence of 32P the tartrate enantiomers have equal probability to form crystals, i.e., the contribution of mixing of weak interaction into the electromagnetic one is not measurable in this system.

Crystallization↗
PubMedDate not supplied

Reflections on the origin of optical asymmetry on earth.

The importance of optical purity, which was stressed in an earlier review, is reassessed in the light of recent evidence concerning the optical configuration of amino acids in biological systems. The most significant fact to emerge in recent years that bear on the origin of optical asymmetry is the experimental evidence for the Salam-Weinberg theory. However, the problem remains: is the effect of PNC-interactions too small to be detectable, and if it is so small, can it be of any significance? In view of the contradictory and confusing nature of the evidence on the induction of optical activity, it is suggested that the Bremen Symposium should agree on some experimental protocols.

Amino Acids↗
PubMedDate not supplied

Amplification of optical activity by crystallization in the presence of tailor-made additives. The "inversion rule".

Experiments are described in which enantiomerically pure dimers, trimers and oligomers, generated from non chiral monomers by crystallization and topochemical reaction in suitably designed chiral crystals, induce preferential crystallization of the parent monomer in the enatiomorphous chiral phase of opposite absolute configuration. (We coin the term "inversion rule" for this effect). A general mechanism of amplification of optical activity by crystallization is proposed on the basis of these results, involving selective adsorption of resolved impurities on the surface of chiral crystals of similar stereochemistry, resulting in a decrease of the growth rate of the affected enantiomer and consequent preferential crystallization of the antipode. The implications of this mechanism to the generation and amplification of chirality in a closed system are discussed.

Crystallization↗
PubMedDate not supplied

Experiments on the abiotic amplification of optical activity.

Our earlier experiments are briefly reviewed, involving the abiotic generation of optical activity by exposure of DL-amino acids to various "chiral" physical forces. The enantiomeric enrichments so obtained were low, however, and additional experiments were undertaken with the objective of abiotically enhancing such small enantiomeric excesses. D not equal to L Mixtures of leucine N-carboxy anhydride gave enantiomerically enriched polymers on partial polymerization, while valine NCA mixtures behaved oppositely. Leucine polymers were also found to hydrolyze stereoselectively, providing for additional enantiomeric enhancement. A repetitive sequence of partial polymerization-hydrolysis steps is suggested as a possible mechanism for the abiotic genesis of optically enriched polypeptides on the primitive Earth.

Amino Acids↗
PubMedDate not supplied

Enantiomer enrichment in early peptides.

The two main ordered conformations of polypeptides, the alpha-helix and the beta-sheet, were considered as possible asymmetric supports for stereoselective processes leading to the enrichment in one enantiomer. alpha-Helices can accommodate residues of both chirality distributed in the same chain, whereas the formation of beta-sheets arises from the association of chain segments containing at least seven residues of the same chirality. When the residue composition departs from the racemic mixture, one handedness of the helix is favored, whereas the beta-sheet nuclei become predominantly of a unique chirality. Taking into account these observations, processes of enrichment specific for alpha- amd beta-structures were envisaged theoretically theoretically as well as experimentally.

Biological Evolution↗
PubMedDate not supplied

Critical evaluation of mathematical models for the amplification of chirality.

The main types of models related to the origin of biological asymmetry are reviewed and new models are proposed. It is shown that in polymerization (in contrast to Yamagata's hypothesis) only a temporary amplification of asymmetry occurs. Models have been constructed in which always the same enantiomer survives, independently of any fluctuations or asymmetric initial conditions. Therefore, the question of the "by chance" or the causal origin of biological asymmetry remains still open, although with a slight preference for a causal origin.

Catalysis↗