Rhodium(II)-catalyzed stereocontrolled synthesis of dihydrofuran-3-imines from 1-Tosyl-1,2,3-triazoles

Rhodium(II) acetate catalyzes the denitrogenative transformation of 5-substituted and 4,5-disubstituted 1-sulfonyl-1,2,3-triazoles with pendent allyl and propargyl ether motifs to oxonium ylides that undergo [2,3]-sigmatropic rearrangement to give substituted dihydrofuran-3-imines in high yield and diastereoselectivity

Enzymatic Reaction Mechanisms, pp ranca

ABSTRACT: The mechanism of the argininosuccinate lyase reaction has been probed by the measurement of the effects of isotopic substitution a t the reaction centers. A primary deuterium isotope effect of 1.0 on both Vand V / K is obtained with (2S,3R)-argininosuccinate-3-d, while a primary 15N isotope effect on V / K of 0.9964 f 0.0003 is observed. The 15N isotope effect on the equilibrium constant is 1.018 f 0.001. The proton that is abstracted from C-3 of argininosuccinate is unable to exchange with the solvent from the enzyme-intermediate complex but is rapidly exchanged with solvent from the enzyme-fumaratearginine complex. A deuterium solvent isotope effect of 2.0 is observed on the V,,, of the forward reaction. These and other data have been interpreted to suggest that argininosuccinate lyase catalyzes the cleavage of argininosuccinate via a carbanion intermediate. The proton abstraction step is not rate limiting, but the inverse 15N primary isotope effect and the solvent deuterium isotope effect suggest that protonation of the guanidino group and carbon-nitrogen bond cleavage of argininosuccinate are kinetically significant. Argininsuccinate lyase catalyzes the cleavage of argininosuccinate to arginine and fumarate. The enzyme is found in the liver where it functions in the biosynthesis of urea. The enzyme from bovine liver has been shown by Lusty and Ratner (1972) to be a tetramer of four identical subunits. No external cofactor is involved, and the enzyme apparently does not require metal ions for catalytic activity. The details of the catalytic events leading to the chemical transformation of argininosuccinate to fumarate and arginine are largely unknown. Ratner and co-workers have shown that the reaction involves the trans elimination of arginine and the pro-R hydrogen at C-3 of argininosuccinate (Hoberman et al., 1965). The kinetic mechanism of the reaction is random In this paper we report on our efforts to determine the magnitude and the timing of the bond-breaking steps in the conversion of argininosuccinate to arginine and fumarate. Th

STRENDA DB : enabling the validation and sharing of enzyme kinetics data

Standards for reporting enzymology data (STRENDA) DB is a validation and storage system for enzyme function data that incorporates the STRENDA Guidelines. It provides authors who are preparing a manuscript with a user‐friendly, web‐based service that checks automatically enzymology data sets entered in the submission form that they are complete and valid before they are submitted as part of a publication to a journal

Target selection and annotation for the structural genomics of the amidohydrolase and enolase superfamilies

To study the substrate specificity of enzymes, we use the amidohydrolase and enolase superfamilies as model systems; members of these superfamilies share a common TIM barrel fold and catalyze a wide range of chemical reactions. Here, we describe a collaboration between the Enzyme Specificity Consortium (ENSPEC) and the New York SGX Research Center for Structural Genomics (NYSGXRC) that aims to maximize the structural coverage of the amidohydrolase and enolase superfamilies. Using sequence- and structure-based protein comparisons, we first selected 535 target proteins from a variety of genomes for high-throughput structure determination by X-ray crystallography; 63 of these targets were not previously annotated as superfamily members. To date, 20 unique amidohydrolase and 41 unique enolase structures have been determined, increasing the fraction of sequences in the two superfamilies that can be modeled based on at least 30% sequence identity from 45% to 73%. We present case studies of proteins related to uronate isomerase (an amidohydrolase superfamily member) and mandelate racemase (an enolase superfamily member), to illustrate how this structure-focused approach can be used to generate hypotheses about sequence–structure–function relationships