Search results for "Esteri"

The Catalytic Mechanism of Carboxylesterases: A Computational Study

2014

The catalytic mechanism of carboxylesterases (CEs, EC 3.1.1.1) is explored by computational means. CEs hydrolyze ester, amide, and carbamate bonds found in xenobiotics and endobiotics. They can also perform transesterification, a reaction important, for instance, in cholesterol homeostasis. The catalytic mechanisms with three different substrates (ester, thioester, and amide) have been established at the M06-2X/6-311++G**//B3LYP/6-31G* level of theory. It was found that the reactions proceed through a mechanism involving four steps instead of two as is generally proposed: (i) nucleophilic attack of serine to the substrate, forming the first tetrahedral intermediate, (ii) formation of the ac…

Synthesis of dehydrodipeptide esters and their evaluation as inhibitors of cathepsin C

2015

The procedures for the synthesis of esters of dehydropeptides containing C-terminal (Z)-dehydrophenylalanine and dehydroalanine have been elaborated. These esters appeared to be moderate or weak inhibitors of cathepsin C, with some of them exhibiting slow-binding behavior. As shown by molecular modeling, they are rather bound at the surface of the enzyme and are not submersed in its binding cavities. Electronic supplementary material The online version of this article (doi:10.1007/s00044-015-1366-0) contains supplementary material, which is available to authorized users.

On the structure of passifloricin A: asymmetric synthesis of the delta-lactones of (2Z,5S,7R,9S,11S)- and (2Z,5R,7R,9S,11S)tetrahydroxyhexacos-2-enoi…

2003

Stereoselective syntheses of the delta-lactone of (2Z,5S,7R,9S,11S)-tetrahydroxyhexacos-2-enoic acid, the structure reported for passifloricin A, and of its (5R)-epimer are described. The creation of all stereogenic centers relied upon Brown's asymmetric allylation methodology. The lactone ring was created via ring-closing metathesis. The NMR data of both synthetic products, however, were different from those of the natural product. The published structure of passifloricin A is thus erroneous and will require further synthetic work to be unambiguously assigned. [structure: see text]

Selective Formal Transesterification of Fluorinated 2-(Trimethylsilyl)ethyl α-Imino Esters Mediated by TBAF

2008

The scope of the transesterification reaction between beta-fluorinated alpha-imino esters and various electrophiles in the presence of TBAF as fluorine source is described. The reaction is highly selective for alkyl iodides, bromides, and mesylates, while alkyl chlorides react at a significantly slower rate and tosylates do not react under the reaction conditions. This methodology represents a simple and useful alternative for the preparation of a wide variety of fluorinated alpha-imino esters.

1978

Synthesis and characterization of polymeric derivatives of the folic acid antagonist, Methotrexate, N-[4-(N-methyl-2,4-diamino-6-pteridinylmethylamino)benzoyl] glutamic acid (1a), a widely used antitumor agent, are described. Derivatives of poly(L-lysine), poly(iminoethylene), poly(vinyl alcohol), and carboxymethylcellulose with various contents (3–15 mole-%) of substituted repeating units were prepared by polymer-analogous amidation and transesterification of the dimethyl ester of 1a and with N-[2-(N-methylmorpholinio)ethyl]carbodiimide p-toluenesulfonate as coupling reagent. By nucleophilic addition reactions of the pteridinyl amino groups under mild conditions, 1a was bound without cross…

Water-Blown Polyisocyanurate Foams From Vegetable Oil Polyols

2008

Polyols with the hydroxyl value OHV from 290 to 318 mg KOH/g are synthesized from rapeseed, sunflower seed, flaxseed, or coconut oils by the way of their: (1) transesterification with triethanolamine or (2) amidization with diethanolamine. The influence of water as the blowing agent on the storage stability of the polyol premix system is assessed from values of the polyol premix system pH, acid value, and variations in such parameters as cream and gel time. Water-blown polyisocyanurate (PIR) foams (150 · II × 300; II—isocyanate index) characterized by good mechanical characteristics, dimensional stability at 70°C and at relative humidity RH = 95% as well as by a very low water absorbance, …

Über die polykondensation von diäthylphosphit mit aliphastischen diolen

1973

Die Umesterungsreaktion von Diathylphosphit mit linearen Diolen HO–(CH2)x–OH (x = 2–6 und 8) wurde untersucht. Ihre Bilanz zeigte, das neben der angestrebten Umesterungsreaktion in teilweise sehr erheblichem Umfang auch Atherstrukturen gebildet werden. Diese bis jetzt in diesem Zusammenhang noch nicht beschriebene Reaktion verlauft sehr wahrscheinlich im Sinn einer direkten Alkylierung der alkoholischen OH-Gruppen durch die Phosphitestergruppen, denn sie erfordert keinen Katalysator. Die Estergruppen gehen dabei in saure P-OH-Gruppen uber, die unter den angewendeten Bedingungen nicht mehr ohne weiteres zur Kondensation mit den Diolen befahigt sind. Das Verhaltnis von unerwunschter Atherbild…

"IL RUOLO DELLE BANCHE LOCALI NEI PROCESSI DI INTERNAZIONALIZZAZIONE DELLE PMI MARCHIGIANE"

2008

Questo lavoro contiene un'analisi empirica per valutare il grado di diffusione nell'operatività delle banche operanti nella Regione Marche, dei prodotti/servizi finanziari avanzati per facilitare una maggiore visibilità delle PMI nei mercati internazionali. L'analisi delle componenti di offerta è stata effettuata tramite la somministrazione di un questionario di un questionario contenuto in un lavoro precedentemente pubblicato dall’ABI a cura del Prof. Fabrizio Onida che però aveva come oggetto di riferimento non soltanto piccole banche ma anche filiali estere di banche commerciali locali, banche estere, intermediari finanziari non bancari (ad esempio società internazionali di leasing e fac…

Calidad nutricional y bioaccesibilidad de derivados de frutas y vegetales al aplicar tecnologías térmicas y no térmicas (pulsos eléctricos, descargas…

2016

RESUMEN El consumo de una dieta variada y rica en frutas y hortalizas ayuda a prevenir y a tratar ciertas enfermedades crónicas. La elaboración de nuevas bebidas a base de derivados de frutas y vegetales ricas en compuestos bioactivos, puede ayudar al incremento del consumo de estos alimentos y por tanto contribuir a la prevención de diferentes problemas de salud. Por otra parte, la industria alimentaria muestra gran interés en la utilización de Stevia rebaudiana Bertoni como educolorante natural acalórico, como estrategia nutricional con el fin de disminuir la ingesta de azúcar. Además, la stevia contiene sustancias minerales, vitaminas, polifenoles y otros compuestos antioxidantes. En est…

Recovery of aliphatic low-molecular-mass carboxylic acids from hardwood kraft black liquor

2015

Abstract During alkaline pulping of wood, substantial amounts of carbohydrates-derived aliphatic carboxylic acids (formic and acetic acids together with various hydroxy acids) are formed and dissolved into the cooking liquor (“black liquor”). These acids with low heating values are considered to be potential feedstocks for the chemical industry but, due to many factors, their straightforward recovery as free acids from black liquor (pH 13–14) is difficult. In this paper, we outlined the partial recovery of volatile formic and acetic acids from the acidified birch ( Betula pendula ) kraft black liquor (pH approximately 2.5) by distillation, and the partial recovery of significant low-molecul…