Catalysis stereoelectronic effect

Key words. Recognition, hydrogen bonding, molecular clefts, convergent functionality, concerted catalysis, stereoelectronic effects. 

From this work, an important feature to be noted was the influence of stereoelectronic effects toward cleavage of / -1,4 (cellobiose) and a-1,4 linkage (maltose)/131 In the presence of zeolites, there is insufficient space inside the channels for conformational changes both in ground and transition states. In such a way, maltose is hydrolysed faster than cellobiose compared with homogeneous or macroporous ion-exchange resin catalysis/71... 

Intermolecular acid catalysis using a series of mainly carboxylic acids involves reaction of N-protonated naphthyl sulphamate with carboxylate anions in the rate-determining step. The / nuc value for attack (0.33) is similar to that reported by the same group for the reaction of phenolate ions with tertiary amine sulphonate (0.23). Stereoelectronic effects are suggested as governing the type of mechanism operating in these systems. 

The importance of TS stabihzation is engraved in physical organic chemistry. It also permeates biochemistry as one of the pillars of enzyme catalysis. In order to fuUy understand the role of this phenomenon, let s apply the Curtin-Hammett principle to the classic case of two rapidly interconverting conformers of different stability and reactivity through the prism of stereoelectronic effects. 

Figure 9.1 TS stabilization can overcome unfavorable ground state properties ("orthogonal stereoelectronic catalysis" - (a)) or amplify a ground state stereoelectronic effect ("parallel stereoelectronic catalysis" - (b)).

The mechanistic studies of enzyme catalysis constitute a very large field where rapid progress has been fueled by the recent advances in X-ray crystallography techniques and new spectroscopic methods. We will restrict ourselves to a small number of illustrative examples and refer the reader to an earher thorough discussion of stereoelectronic effects in biomolecules by Gorenstein. ... 

A unique advantage of the new structures relevant to their significance as enzyme models is the possibility of exploring stereoelectronic effects at carboxyl oxygen. Unlike the situation with acyl carbon, reaction trajectories and lone pair orientation at carboxyl oxygen have been difficult to assess. Candour [19] has pointed out that in most enzymes where the carboxylate appears at the active site, the more basic syn lone pair is involved in catalysis. (Scheme 10). 

Figure 3.17 Molecular mechanisms giving rise to enhanced hydrolysis rates of glycosides with carboxylic acid groups. In the case of salicyl fi-glucoside, frontside nucleophilic attack is stereoelectronically prohibited and distinction between specific acid catalysis of the hydrolysis of the anion and intramolecular general acid catalysis was made on the basis of solvent isotope effects in related systems. ...

Stereoelectronic Control in Hydrolysis of Cyclic Guanidinium Ions Journal of the American Chemical Society, 123, 4446-4450. (c) Perrin, C. L., Fabian, M. A., Brunckova, J., Ohta, B. K. (1999). Absence of Reverse Anomeric Effect in GlycosyUmidazoles. Journal of the American Chemical Society, 121, 6911-6918. (d) Perrin, C. L. Engler, R. E., Young, D. B. (2000). Bifunctional Catalysis and Apparent Stereoelectronic Control in Hydrolysis of Cyclic Imidatonium Ions. Journal of the American Chemical Society, 122, 4877 881. 

Vidhani, D. V., Krafft, M. E., Alabugin, I. V. (2014). Rh(I)-Catalyzed Transformation of Propargyl Vinyl Ethers into , Z)-Dienals Stereoelectronic Role of trans Effect in a Metal-Mediated PericycUc Process and a Shift from Homogeneous to Heterogeneous Catalysis During a One-Pot Reaction. Journal of Organic Chemistry, 79, 352-364. 

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