122020-03-5Relevant articles and documents
An Adverse Effect of Higher Catalyst Loading and Longer Reaction Time on Enantioselectivity in an Organocatalytic Multicomponent Reaction
Khopade, Tushar M.,Mete, Trimbak B.,Arora, Jyotsna S.,Bhat, Ramakrishna G.
supporting information, p. 6036 - 6040 (2018/04/27)
An enantioselective organocatalytic multicomponent reaction of aldehydes, ketones, and Meldrum's acid has been developed. A cinchona-based primary amine (1 mol %) catalyses the multicomponent reaction via the formation of the Knoevenagel product and a chiral enamine to form enantiopure δ-keto Meldrum's acids in a tandem catalytic pathway. An adverse effect of higher catalyst loading and longer reaction time on enantioselectivity was studied. This mild protocol provides an easy access to enantiopure carboxylic acids, esters and amides and the method is scalable on a gram quantity. DFT calculations were carried out on the proposed reaction mechanism and they were in close agreement with the experimental results.
β-substituted β-phenylpropionyl chymotrypsins. Structural and stereochemical features in stable acyl enzymes
Reed,Katzenellenbogen
, p. 1162 - 1176 (2007/10/02)
In order to develop effective alternate substrate inhibitors for serine proteases, we have prepared a series of β-substituted β-phenylpropionic acid esters related to some systems known to form stable acyl enzymes with α-chymotrypsin. Some of these compounds were prepared in enantiomerically pure form by asymmetric synthesis. Acyl enzyme species were generated from chymotrypsin by reaction with the active esters, and the progress of deacylation was monitored by the proflavin displacement assay. In some cases, it was possible to distinguish two different deacylation rates that correspond to the two enantiomers. β-Phenylpropionic acyl enzymes with β-substituents that are nonpolar were not especially stable, but a number of the polar derivatives and particularly the acylamino derivatives showed slow rates of deacylation (k(d) less than 0.005 min-1), with three systems showing deacylation enantioselectivities in the range of 500-1500. These results are consistent with a model in which additional stabilization of the acyl enzyme and enantioselectivity in the deacylation process derives from an additional hydrogen bond between the acyl enzyme species (as an acceptor) and the enzyme (as a donor). A number of active site residues that might be involved in this hydrogen bond are discussed.
