O-succinylbenzoyl-CoA (OSB-CoA) synthetase (EC 6.2.1.26) catalyzes the ATP-dependent condensation of o-succinylbenzoate (OSB) and CoA to form OSB-CoA, the fourth step of the menaquinone biosynthetic pathway in Bacillus anthracis. Gene knockout studies have highlighted this enzyme as a potential target for the discovery of new antibiotics. Here we report the first studies on the kinetic mechanism of B. anthracis OSB-CoA synthetase, classifying it as an ordered Bi Uni Uni Bi ping-pong mechanism. Through a series of pre-steady-state and steady-state kinetic studies in conjunction with direct-binding studies, it is demonstrated that CoA, the last substrate to bind, strongly activates the first half-reaction after the first round of turnover. The activation of the first-half reaction is most likely achieved by CoA stabilizing conformations of the enzyme in the ‘F’ form, which slowly isomerize back to the E form. Thus, the kinetic mechanism of OSB-CoA synthetase may be more accurately described as an ordered Bi Uni Uni Bi Iso ping-pong mechanism. The substrate specificity of OSB-CoA synthetase was probed using a series of OSB analogs with alterations in the carboxylate groups. OSB-CoA shows a strong preference for OSB over all of the analogs tested as none were active except 4-(2-trifluoromethylphenyl)-4-oxobutyric acid which exhibited a 100-fold decrease in kcat/Km. Based on an understanding of OSB-CoA synthetase’s kinetic mechanism and substrate specificity, a reaction intermediate analog of OSB-AMP, 5’-O-(N-(2-trifluoromethylphenyl)-4-oxobutyl) adenosine sulfonamide (TFMP-butyl-AMS), was designed and synthesized. This inhibitor was found to be an uncompetitive inhibitor to CoA and a mixed-type inhibitor to ATP and OSB with low micromolar inhibition constants. Collectively, these results should serve as an important forerunner to more detailed and extensive inhibitor design studies aimed at developing lead compounds against the OSB-CoA synthetase class of enzymes.

Here we review the equatorial β-directing effects of electron-withdrawing protecting groups at remote positions of mannopyranosyl donors, mannuronate donors, rhamnopyranosyl donors, and 2,6-dideoxyglucopyranosyl donors. We discuss the equatorial α-directing effect of an electron-withdrawing group at the N-5 position of sialyl donors. The proposed mechanism and origin of some of the equatorial β-directing effects are described. We also review the effects of potentially participating, electron-withdrawing protecting groups at remote positions of glycopyranosyl and glycofuranosyl donors on the glycosylation stereochemistries. Further, we present substantial evidence in favor of the remote participation by the electron-withdrawing protecting groups and also include reports that are opposed to remote participation.

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Effects of potentially participating groups at remote positions of glycopyranosyl and glycofuranosyl donors on the glycosylation stereochemistry are reviewed. Substantial evidences in favor of the remote participation by protecting groups are presented and also included are a few reports opposed to the remote participation. A. IntroductionT h e p r o t e c t i n g g r o u p s i n t h e o l i g o s a c c h a r i d e synthesis are used to selectively block interfering functions as well as influence the reactivity and stereoselectivity in the glycosylation steps. The anchimeric assistance of a neighboring participating group such as an acyl group at the O-2 position of the glycosyl donor has been one of the most useful strategies for the stereoselective formation of 1,2-trans glycosides (1−5). The carbonyl functionality at the O-2 position of the glycosyl donor can attack an incipient oxonium ion to give a dioxonium ion. Nucleophilic attack by an acceptor to the opposite face of the dioxonium ion provides the 1,2-trans glycoside. When potentially participating groups are located at remote positions other than the O-2 position of glycosyl donors, the existence of the remote participation by the remote protecting groups in the glycosylation step has been controversial. Although numerous examples for glycosylations with glycosyl donors possessing potentially participating groups at remote positions can be found in the literature, most of them do not provide any information on the remote participation by protecting groups in glycosylations. There have been reports both in favor of and opposed to the remote participation by protecting groups in glycosylations. Herein we review the effects of potentially participating protecting groups at remote positions of glycopyranosyl and glycofuranosyl donors on the glycosylation stereochemistry. Further, we present substantial evidence in favor of the remote participation by protecting groups and also include a few reports that are opposed to remote participation.