Search results for "ACYLATION"
showing 10 items of 87 documents
Lipase-catalysed preparation of acyl derivatives of the germacranolide cnicin
2009
Several acyl derivatives of cnicin were obtained through lipase-catalysed acylation and alcoholysis reactions. In most reactions lipases showed a regioselective behaviour affording only one product. Longer chain acyl derivatives were prepared at lower temperature than the used in lipase-catalysed reactions, to preclude side products formation. The enzymatic approach let to prepare a family of novel acetyl and fatty acid derivatives of cnicin which are not obtainable following traditional organic synthetic procedures. Fil: Monsalve, Leandro Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad de Microanálisis…
New heterogeneous catalysts for greener routes in the synthesis of fine chemicals
2007
Abstract New strong Lewis acid SnTf-MCM-41 and SnTf-UVM-7 catalysts with unimodal and bimodal pore systems were prepared in a two-step synthesis in which the triflic acid (Tf) was incorporated to previously synthesized mesoporous tin-containing silicas. The Sn incorporation inside the pore walls was carried out through the Atrane method. The SnTf-UVM-7 catalysts were prepared by aggregating nanometric mesoporous particles defining a hierarchic textural-type additional pore system. Following these procedures, catalysts with different Si/Sn ratios—21.8 to 50.8 for SnTf-MCM-41 and 18.4 for SnTf-UVM-7—were prepared. These new materials were tested in the acylation of aromatic sulfonamides using…
Characterization of Acylating and Deacylating Activities of an Extracellular Phospholipase A2 in a Water-Restricted Environment
1994
The behavior of porcine pancreatic phospholipase A2 (ppPLA2) in monophasic low-water media has been explored, for the first time, in a systematic manner. It has been investigated how a number of variables can modulate both acylating and deacylating activities of the enzyme, and several interesting, unexpected results are presented. Among the most relevant, when placing ppPLA2 in the water-restricted environment, are the following: (i) it displays a remarkable alteration of its specificity toward the substrate polar head relative to all-water medium; (ii) it is quite severely inhibited by lysophosphatidylcholine (LPC), which has important implications, particularly concerning its acylation a…
Regioselective acylation of aminoresorcinarenes
2007
Abstract The acid catalyzed hydrolytic cleavage of the oxazine rings in the readily available tetraoxazine derivatives of resorcinarenes results in tetraaminoresorcinarenes. A similar process applied to C2-symmetrical bisoxazine resorcinarene tetratosylates affords C2v-symmetrical resorcinarenediamines. The mild acylation of these resorcinareneamines with BOC-anhydride or para-nitrophenyl ester proceeds selectively at the nitrogen atoms without affecting the hydroxyl groups. Most of the resulting resorcinareneamides are thus obtained in preparative yields and can be easily purified by simple crystallizations. In the crystalline state the compounds obtained are found to bind chloride anions …
Presence and coding properties of 2'-O-methyl-5-carbamoylmethyluridine (ncm5Um) in the wobble position of the anticodon of tRNA(Leu) (U*AA) from brew…
1992
AbstractThe unknown modified nucleoside U* has been isolated by enzymatic and HPLC protocols from tRNALeu(U*AA) recently discovered in brewer's yeast. The pure U* nucleoside has been characterized by electron impact mass spectroscopy, and comparison of its chromatographic and UV-absorption properties with those of appropriate synthetic compounds. The structure of U* was established as 2′-O-methyl-5-carbamoylmethyluridine (ncm5Um). The yeast tRNALeu (U*AA) is the only tRNA so far sequenced which has been shown to contain ncm5Um. The location of such a modified uridine at the first position of the anticodon restricts the decoding property to A of the leucine UUA codon.
The Reactions of Electron-Rich Heterocycles with Derivatives of Orthocarboxylic Acids; VIII. Proton Acid-Catalyzed Acylation of Indoles by 2-Alkoxy-1…
1987
In acid-catalyzed reactions with 3-unsubstituted indoles 1, 2-alkoxy-1,3-dioxolanes 2a-c behave as acyl equivalents. Depending on the substitution patterns of the reaction partners, the 1,3-dioxolanium ions 3a-c, generated in situ from the cyclic ortho esters by the action of sulfosalicylic acid, react to form tris-(3-indolyl)alkanes 6 and 9, bis-(3-indolyl)ethenes 7, or 3-benzoylindoles 8. Analogous reactivity was observed with related acyclic ortho esters. Reaktionen elektronenreicher Heterocyclen mit Orthocarbonsaure-Derivaten; VIII. Protonsaurekatalysierte Acylierung von Indolen mit 2-Alkoxy-1,3-dioxolanen 2-Alkoxy-1,3-dioxolane 2a-c reagieren als Acylaquivalente mit 3-unsubstituierten …
Studien zum Vorgang der Wasserstoffübertragung, 67. Endioldiester durch acylierende elektroreduktive Dimerisierung von Carbonsäurechloriden mit Lithi…
1983
Aromatische, aliphatische und aromatisch-aliphatische Carbonsaurechloride (und Anhydride) werden mit Lithiumamalgam (Li/Hg) durch acylierende reduktive Dimerisierung in wechselnden Ausbeuten (meist 70%) in cis- und/oder trans-Endioldiester 1–10 ubergefuhrt. Der Einflus des Losungsmittels auf den Reaktionsverlauf wird untersucht. Aus 2,2′-Diphensauredichlorid entsteht das Phenanthrenderivat 7, aus Phthaloyldichlorid Phthalid 8. Li/Hg wandelt Diphenyl-phosphinylchlorid in Tetraphenyldiphosphandioxid (15) um. Auf die Bestimmung der Halbstufenpotentiale von 12 Saurechloriden und vier 1,2-Diketonen grundet sich die Formulierung des Reaktionsmechanismus. 1,2-Diketone sind Zwischenprodukte der acy…
Veresterung und Veretherung sterisch gehinderter Kohlenhydrat‐Hydroxylfunktionen mit dem System Triphenylphosphan/Azodicarbonsäureester
1979
Die 6-0-Benzoyl-3-0-Benzyl-1,2-0-isopropyliden-α-D-glucofuranose (11) reagiert unter der Einwirkung von Azodicarbonsaure-diethylester (2) (DEAD) und Triphenylphosphan (1) mit p- Nitro benzoesaure, Benzoesaure, p-Toluolsulfonsaure- und Mesitylensulfonsaure-methylester sterisch nicht einheitlich. Es bildet sich das erwartete Substitutions-(L-ido)-Produkt (unter Inversion an C-5), aber daneben auch das D-gluco-Epimere; fur dessen Bildung wird ein Acylierungsmechanismus diskutiert. – Die Reaktion der 1,2:5,6-Di-O-isopropyliden α-D-glucofuranose(7) mit dem Reagenzsystem 1/2 und Arylsulfonsaure-methylesters bleibt auf der Alkoxyphosphoniumsalze 8 stehen. Durch Umsetzung mit Alkoholat erhalt man a…
Influence of cyclization and acyl substitution on the inotropic effects of adenine nucleotides.
1973
This study was designed to further elucidate relevance and mechanism of the positive inotropic action of cyclic N6-2′-O-dibutyryl-AMP (DB-c-AMP). For this purpose the effects of cyclic N6-monobutyryl-AMP (N6-MB-c-AMP), noncyclic N6-2′-O-3′-O-tributyryl-5′-AMP (TB-AMP), c-AMP, adenosine and various adenine nucleotides (ATP, ADP, AMP) on myocardial contractile force (CF) were investigated and compared to that of DB-c-AMP. The experiments were performed on isolated, electrically driven (frequency 2 Hz) rat left auricles, i.e. on a preparation in which DB-c-AMP consistently produced positive inotropic effects. The following results were obtained: From the failure of non-cyclic TB-AMP to increas…
Catalytic activity of rare-earth-supported catalysts in Friedel–Crafts acylations
1999
Abstract Friedel–Crafts acylations are catalysed by rare-earth-supported catalysts. The preparation, characterization and performance of these solid catalysts in a test acylation reaction and in a variety of syntheses of aromatic ketones are reported. In contrast to the reactions using AlCl3, the experimental conditions are non-polluting and the final work-up does not require any aqueous treatment.