- A REMARKABLE ENHANCEMENT OF THE RATE OF ESTER THIOLYSIS BY SYNTHETIC AMPHIPHILE VESICLES
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Cationic surfactant vesicles accelerate the rate of thiolysis of p-nitrophenyl octanoate by n-heptyl-mercaptan by several million fold in the pH range from 4 to 6, providing an efficient system for ester thiolysis in aqueous solution that is functional even at pH4, i.e. more than 6 pH units below the pKa of the SH group.Analysis of the data in terms of an ion exchange formalism implies that this rate acceleration is due primarily to concentration of the reagents in the dimensionally-restricted environment provided by the vesicle, coupled with small contributions from enhanced dissociation and reactivity of the nucleophile at the vesicle surface(s).
- Cuccovia, Iolanda M.,Quina, Frank H.,Chaimovich, Hernan
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Read Online
- One for Many: A Universal Reagent for Acylation Processes
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This work describes acylation reactions facilitated by a type of heterocycle-based acyl transfer agent, 2-acyloxypyridazinone. Reactions of 2-acyloxypyridazinone with carboxylic acids yield mixed carbonic anhydride intermediates, which are reactive and could be coupled with a wide range of substrates including acids, amines, alcohols, and thiols. The wide substrate scope, ease of operation (no additive or catalyst), storage and handling stability, and atom-efficiency from recycling the heterocycle carrier make the reported acylating agent attractive for acylation-based coupling reactions.
- Moon, Hyun Kyung,Sung, Gi Hyeon,Kim, Bo Ram,Park, Jong Keun,Yoon, Yong-Jin,Yoon, Hyo Jae
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supporting information
p. 1725 - 1730
(2016/06/09)
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- Hydrolysis of hydrophobic esters in a bicontinuous microemulsion catalysed by lipase B from Candida antarctica
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Selective enzyme-catalysed biotransformations offer great potential in organic chemistry. However, special requirements are needed to achieve optimum enzyme activity and stability. A bicontinuous microemulsion is proposed as reaction medium because of its
- Steudle, Anne K.,Subinya, Mireia,Nestl, Bettina M.,Stubenrauch, Cosima
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p. 2691 - 2700
(2015/01/30)
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- Enzyme mediated-transesterification of verbascoside and evaluation of antifungal activity of synthesised compounds
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Enzymatic acylation of verbascoside, a polyhydroxylated natural product, has been reported in this study using five different commercial lipases and taking p-nitrophenyl alkanoates as acyl donors. Out of these enzymes, the immobilised Candida antarctica lipase B was found as the enzyme of choice. Mono-and di-acylated products were formed, with mono as major product indicating high regioselective nature of such transformations. A series of acyl esters of verbascoside have been synthesised by this enzymatic transesterification methodology. The lipophilicity of the synthesised analogues was also checked. The analogues were further subjected to synergistic antifungal activity with amphotericin B (AmB) against Candida albicans. Fourfold reduction in minimum inhibitory concentration of AmB was observed with few synthesised analogues such as verbascoside 4″-octanoate (3b), verbascoside 4″-palmitate (3d) and verbascoside 4″,4′-dipalmitate (4d) at a concentration of 0.5 g/mL.
- Khazir, Jabeena,Ali, Intizar,Khan, Inshad Ali,Sampath Kumar, Halmuthur Mahabalarao
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p. 727 - 734
(2015/09/23)
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- Ytterbium triflate catalysed Friedel-Crafts reaction using carboxylic acids as acylating reagents under solvent-free conditions
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The Friedel-Crafts acylation of 1-naphthol and phenol derivatives with carboxylic acids were investigated by using a catalytic amount of metal-triflate, in particular Yb(OTf)3, under solvent-free conditions. Both aliphatic and aromatic carboxylic acids reacted easily to afford the corresponding hydroxyaryl ketones.
- Jin, Can,Li, Jie,Su, Weike
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experimental part
p. 607 - 611
(2011/02/26)
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- Stable gene variants of lipases
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The present invention relates to the generation and production of novel thermostable, organic solvent stable and pH tolerant lipase gene variants. The invention also relates to methods of selecting lipase variants for high temperatures and for their purification.
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- Inhibition of the Hydrolysis of p-Nitrophenyl Esters by Association with an Erythromycin A Derivative
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The alkaline hydrolysis of p-nitrophenyl esters (1) of an homologous series of straight chain acids and derivatives of naphthoic acids was studied in the presence of the antibiotic erythromycin A (E) and its hydrolysis product (Z).While (E) does not affect the hydrolysis of 1, (Z) inhibits this reaction.The observed pseudo-first-order rate constants decrease as the Z concentration increases and they tend to a minimum value.This inhibition is ascribed to the formation of a host-guest complex between Z and 1.It is suggested that the attack of an external HO- at the carbonyl ester group is hindered by steric and electrostatic effects.The association constants and the second-order rate constants for the complexed esters were calculated.The inhibition tends to be complete for esters of alkyl chains with an add number of carbon atoms.Such a trend is probably related to the geometric requirements of inclusion.
- Barra, Monica,Rossi, Rita H. de
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p. 1758 - 1772
(2007/10/02)
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- A Simple and Mild Esterification Method for Carboxylic Acids Using Mixed Carboxylic-Carbonic Anhydrides
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A simple and mild esterification method using mixed carboxylic-carbonic anhydrides has been developed.Simple aliphatic carboxylic esters are prepared in high yields by the reaction of acids with equimolar amounts of chloroformates (2,2,2-trichloroethyl chloroformate is an exception) and triethylamine in the presence of a catalytic amount of 4-(dimethylamino)pyridine.Although aromatic acids give a mixture of the ester, the acid anhydride, and the carbonate under normal conditions utilized in this study, it is found that increasing the amount of 4-(dimethylamino)pyridine drastically decreases the formation of the acid anhydride and the carbonate, affording a satisfactory yield of the ester.This method reaches a limit with sterically hindered acids and the formation of the acid anhydride and the carbonate is favored.
- Kim, Sunggak,Lee, Jae In,Kim, Youn Chul
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p. 560 - 565
(2007/10/02)
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