Acid L (acid + l)

Distribution by Scientific Domains
Medical Sciences50%
Chemistry50%

Kinds of Acid L

  • amino acid l
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    Selected Abstracts

    A Novel Proline-Valinol Thioamide Small Organic Molecule for a Highly Enantioselective Direct Aldol Reaction

    ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009
    Bing Wang
    Abstract A new prolinethioamide compound 4, prepared from readily available natural amino acid L -proline and amino alcohol L -valinol, has been found to be an active catalyst for the direct aldol reaction of various aldehydes with acetone, cyclohexanone or cyclopentanone at 0,°C. Using only 2,mol% loading of this organocatalyst, the reaction could give high enantioselectivity with up to 96% enantiomeric excess for the reaction of 2-nitrobenzaldehyde with acetone. And as for the cyclohexanone, the excellent diastereoselectivity (anti/syn: 99/1) and enantioselectivity (99% ee) could be achieved when reacted with 3-nitrobenzaldehyde in water in the presence of this thioamide 4. This structurally simple catalyst is a highly efficient prolinethioamide derivative, and the terminal hydroxy group in this catalyst is a primary alcohol which is different from the previously reported prerequisite secondary or tertiary alcohol of prolinamides. Our results suggest a new strategy in the design of diversiform organic catalysts for direct asymmetric aldol reactions and related transformations. [source]

    How to Spoil the Taste of Insect Prey?

    CHEMBIOCHEM, Issue 12 2010
    A Novel Feeding Deterrent against Ants Released by Larvae of the Alder Leaf Beetle, Agelastica alni
    Abstract Chemical defense of leaf beetle larvae (Chrysomelidae) against enemies is provided by secretions containing a wide range of deterrent compounds or by unpalatable hemolymph constituents. Here we report a new, very strong feeding deterrent against ants released by larvae of the alder leaf beetle Agelastica alni when attacked. The larvae release a defensive fluid from openings of pairwise, dorsolaterally located tubercles on the first to the eighth abdominal segments. The fluid, consisting of hemolymph and probably a glandular cell secretion, has previously been shown to contain a very stable, non-volatile feeding deterrent. The major deterrent component was isolated by repeated HPLC separation and analyzed by NMR and MS. The compound proved to be ,- L -glutamyl- L -2-furylalanine (1), a novel dipeptide containing the unusual amino acid L -2-furylalanine. This amino acid, although synthetically well known, has not previously been reported from natural sources. The absolute configuration of the natural compound was elucidated by enantioselective gas chromatography after derivatization. The structure of the dipeptide was verified by the synthesis of several isomeric dipeptides. In bioassays a concentration of 1 ,g,,L,1 was sufficient to deter polyphagous Myrmica rubra ants from feeding. [source]

    Asymmetric dimethylarginine (ADMA): the silent transition from an ,uraemic toxin' to a global cardiovascular risk molecule

    EUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 2 2005
    D. Fliser
    Abstract Endothelial dysfunction as a result of reduced bioavailability of nitric oxide (NO) plays a central role in the process of atherosclerotic vascular disease. In endothelial cells NO is synthesized from the amino acid l -arginine by the action of the NO synthase (NOS), which can be blocked by endogenous inhibitors such as asymmetric dimethylarginine (ADMA). Acute systemic administration of ADMA to healthy subjects significantly reduces NO generation, and causes an increase in systemic vascular resistance and blood pressure. Increased plasma ADMA levels as a result of reduced renal excretion have been associated with atherosclerotic complications in patients with terminal renal failure. However, a significant relationship between ADMA and traditional cardiovascular risk factors such as advanced age, high blood pressure and serum LDL-cholesterol, has been documented even in individuals without manifest renal dysfunction. As a consequence, the metabolism of ADMA by the enzyme dimethylarginine dimethylaminohydrolase (DDAH) has come into the focus of cardiovascular research. It has been proposed that dysregulation of DDAH with consecutive increase in plasma ADMA concentration and chronic NOS inhibition is a common pathophysiological pathway in numerous clinical conditions. Thus, ADMA has emerged as a potential mediator of atherosclerotic complications in patients with coronary heart disease, peripheral vascular disease, stroke, etc., being the culprit and not only an innocent biochemical marker of the atherosclerotic disease process. [source]

    The alpha-amino group of l -arginine mediates its antioxidant effect

    EUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 2 2001
    S. Wallner
    Antioxidant effects may constitute part of the possible antiatherogenic effects of the amino acid l -arginine. These antioxidant properties were further characterized in a model of lipoprotein oxidation. Oxidation of lipoproteins in unfractionated human serum was continuously monitored by a fluorescent probe. The antioxidant effects of l -arginine, N -,-acetyl-arginine and vitamin E in combination with l -arginine were measured after initiation of free radical generation with either copper or 2,2,-azobis(2-amidinopropane) hydrochloride (AAPH). The half-time of the fast propagation rate for copper-induced lipoprotein oxidation increased after incubation with l -arginine in a dose-dependent manner (P < 0·01). N -,-acetyl-arginine did not show such effects. Vitamin E and l -arginine show different effects on copper-induced oxidation, the former increasing only lag-time, the latter increasing only propagation rate, and do not have reciprocal effects. In contrast to copper-induced oxidation, l -arginine increased the lag-time of AAPH-induced lipoprotein oxidation (P < 0·01), with no effect on the propagation rate at physiological concentrations. Again, N -,-acetyl-arginine did not show any antioxidant effects. Our experiments provide further evidence that mechanisms other than serving as a substrate for the NO-synthase could be involved in the antiatherosclerotic effect of l -arginine. In addition, our experiments clearly show, that the antioxidant effect of l -arginine is due to a chemical moiety different from that serving as the substrate for NO biosynthesis. [source]

    Causes of hair loss and the developments in hair rejuvenation

    INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 1 2002
    D. H. Rushton
    Synopsis Hair is considered to be a major component of an individual's general appearance. The psychological impact of hair loss results in a measurably detrimental change in self-esteem and is associated with images of reduced worth. It is not surprising that both men and women find hair loss a stressful experience. Genetic hair loss is the major problem affecting men and by the age of 50, up to 50% will be affected. Initial attempts to regenerate the lost hair have centred on applying a topical solution of between 2% to 5% minoxidil; however, the results proved disappointing. Recently, finasteride, a type II 5, reductase inhibitor has been found to regrow a noticeable amount of hair in about 40% of balding men. Further developments in treatments have lead to the use of a dual type I and type II inhibitor where 90% of those treated regrow a noticeable amount of hair. In women the major cause of hair loss before the age of 50 is nutritional, with 30% affected. Increased and persistent hair shedding (chronic telogen effluvium) and reduced hair volume are the principle changes occurring. The main cause appears to be depleted iron stores, compromised by a suboptimal intake of the essential amino acid l -lysine. Correction of these imbalances stops the excessive hair loss and returns the hair back to its former glory. However, it can take many months to redress the situation. Résumé Les cheveux sont considérés comme étant une composante majeure de l'aspect général d'un individu. L'impact psychologique de la perte des cheveux conduit à une diminution mesurable de l'estime de soi et s'associe à des images de contexte négatif. Il n'est pas surprenant que les hommes comme les femmes ressentent la perte de cheveux comme une expérience stressante. La perte génétique des cheveux est le problème principal qui touche les hommes et autour de l'âge de 50 ans, jusqu'à 50% seront concernés. Les premières tentatives de régénération des cheveux perdus se sont focalisées sur l'application topique d'une solution comprenant entre 2% et 5% de minoxidil; cependant, les résultats se sont avérés décevants. Récemment, le finastéride, un inhibiteur de la 5,-réductase de type II s'est avéré permettre la repousse d'une quantité significative de cheveux chez environ 40% des hommes dégarnis. Les développements ultérieurs des traitements ont conduit à l'utilisation d'un inhibiteur associant type I et type II pour lequel 90% des personnes traitées constatent une repousse significative des cheveux. Chez les femmes la cause principale de la perte des cheveux avant l'âge de 50 ans est d'origine nutritionnelle, avec 30% de la population affectée. Une perte de cheveux persistante et croissante (telogen effluvium chronique) et un volume des cheveux réduit sont les principaux effets qui se produisent. La cause principale semble être des réserves de fer épuisées, associées à une prise insuffisante de l'acide aminé essentiel L-lysine. La correction de ces déséquilibres stoppe la perte excessive de cheveux et rend aux cheveux leur éclat d'antan. Cependant, plusieurs mois peuvent être nécessaires pour redresser la situation. [source]

    Modelling of the hydrolysis of sorghum straw at atmospheric pressure

    JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 5 2002
    Simón J Téllez-Luis
    Abstract Sorghum straw is a renewable, cheap and widespread resource. The acid hydrolysis of sorghum straw to obtain xylose solutions could be a good alternative for this abundant resource. The H2SO4 hydrolysis of sorghum straw at two different temperatures (80 and 100,°C) and three H2SO4 concentrations (2, 4 and 6%) using a solid/liquid ratio of 1:10 (w/w) was studied. Kinetic parameters of mathematical models for predicting the concentrations of xylose, glucose, acetic acid and furfural were determined. The activation energy of the release reaction was 183.3,kJ,mol,1 for xylose and 185.8,kJ mol,1 for glucose. The optimal conditions found were 6% H2SO4 at 100,°C for 60,min, which allow one to obtain a solution with 18.27,g xylose l,1, 6.78,g glucose l,1, 0.7,g furfural l,1 and 1.35,g acetic acid l,1. It is concluded that this process has potential for utilisation of this renewable lignocellulosic resource. © 2002 Society of Chemical Industry [source]