Is There a Generalized Reverse Anomeric Effect? Substituent and Solvent Effects on the Configurational Equilibria of Neutral and Protonated N-Arylglucopyranosylamines and N-Aryl-5-thioglucopyranosylamines† Export

@article{dfg:revano, abstract = {doi: 10.1021/jo991520j The effects of substitution and solvent on the configurational equilibria of neutral and protonated N-(4-Y-substituted-phenyl) peracetylated 5-thioglucopyranosylamines (Y = OMe, H, CF3, NO2) 14 and N-(4-Y-substituted-phenyl) peracetylated glucopyranosylamines (Y = OMe, H, NO2) 911 are described. The configurational equilibria were determined by direct integration of the resonances of the individual isomers in the 1H NMR spectra after equilibration of both alpha- and beta-isomers. The equilibrations of the neutral compounds 14 in CD3OD, CD3NO2, and (CD3)2CO were achieved by HgCl2 catalysis and those of the neutral compounds 911 in CD2Cl2 and CD3OD by triflic acid catalysis. The equilibrations of the protonated compounds in both the sulfur series (solvents, CD3OD, CD3NO2, (CD3)2CO, CDCl3, and CD2Cl2) and oxygen series (solvents, CD2Cl2 and CD3OD) were achieved with triflic acid. The substituent and solvent effects on the equilibria are discussed in terms of steric and electrostatic effects and orbital interactions associated with the endo-anomeric effect. A generalized reverse anomeric effect does not exist in neutral or protonated N-aryl-5-thioglucopyranosylamines and N-arylglucopyranosylamines. The anomeric effect ranges from 0.85 kcal mol-1 in 2 to 1.54 kcal mol-1 in 10. The compounds 14 and 911 show an enhanced endo-anomeric effect upon protonation, ranging from 1.73 kcal mol-1 in 2 to 2.57 kcal mol-1 in 10. We estimate the increase in the anomeric effect upon protonation of 10 to be approximately 1.0 kcal mol-1. However, this effect is offset by steric effects due to the associated counterion which we estimate to be approximately 1.2 kcal mol-1. The values of Keq(axialequatorial) in protonated 14 increase in the order OMe < H < CF3 < NO2, in agreement with the dominance of steric effects (due to the counterion) over the endo-anomeric effect. The values of Keq(axialequatorial) in protonated 911 show the trend OMe > H < NO2 that is explained by the balance of the endo-anomeric effect and steric effects in the individual compounds. The trends in the values of the C1H1 coupling constants for 14 and the corresponding deacetylated compounds 58 as a function of substituent and alpha- or beta-configuration are discussed in terms of the Perlin effect and the interplay of the endo- and exo-anomeric effects.}, author = {Randell, Karla D. and Johnston, Blair D. and Green, David F. and Pinto, Mario B.}, citeulike-article-id = {3859018}, citeulike-linkout-0 = {http://dx.doi.org/10.1021/jo991520j}, citeulike-linkout-1 = {http://pubs.acs.org/doi/abs/10.1021/jo991520j}, day = {1}, doi = {10.1021/jo991520j}, journal = {The Journal of Organic Chemistry}, keywords = {carbohydrate, conformational, preferences}, month = {January}, number = {1}, pages = {220--226}, posted-at = {2009-01-07 23:21:22}, priority = {0}, title = {Is There a Generalized Reverse Anomeric Effect? Substituent and Solvent Effects on the Configurational Equilibria of Neutral and Protonated N-Arylglucopyranosylamines and N-Aryl-5-thioglucopyranosylamines{\dag}}, url = {http://dx.doi.org/10.1021/jo991520j}, volume = {65}, year = {2000} }

TY - JOUR ID - dfg:revano L3 - citeulike-article-id:3859018 N2 - doi: 10.1021/jo991520j The effects of substitution and solvent on the configurational equilibria of neutral and protonated N-(4-Y-substituted-phenyl) peracetylated 5-thioglucopyranosylamines (Y = OMe, H, CF3, NO2) 14 and N-(4-Y-substituted-phenyl) peracetylated glucopyranosylamines (Y = OMe, H, NO2) 911 are described. The configurational equilibria were determined by direct integration of the resonances of the individual isomers in the 1H NMR spectra after equilibration of both alpha- and beta-isomers. The equilibrations of the neutral compounds 14 in CD3OD, CD3NO2, and (CD3)2CO were achieved by HgCl2 catalysis and those of the neutral compounds 911 in CD2Cl2 and CD3OD by triflic acid catalysis. The equilibrations of the protonated compounds in both the sulfur series (solvents, CD3OD, CD3NO2, (CD3)2CO, CDCl3, and CD2Cl2) and oxygen series (solvents, CD2Cl2 and CD3OD) were achieved with triflic acid. The substituent and solvent effects on the equilibria are discussed in terms of steric and electrostatic effects and orbital interactions associated with the endo-anomeric effect. A generalized reverse anomeric effect does not exist in neutral or protonated N-aryl-5-thioglucopyranosylamines and N-arylglucopyranosylamines. The anomeric effect ranges from 0.85 kcal mol-1 in 2 to 1.54 kcal mol-1 in 10. The compounds 14 and 911 show an enhanced endo-anomeric effect upon protonation, ranging from 1.73 kcal mol-1 in 2 to 2.57 kcal mol-1 in 10. We estimate the increase in the anomeric effect upon protonation of 10 to be approximately 1.0 kcal mol-1. However, this effect is offset by steric effects due to the associated counterion which we estimate to be approximately 1.2 kcal mol-1. The values of Keq(axialequatorial) in protonated 14 increase in the order OMe < H < CF3 < NO2, in agreement with the dominance of steric effects (due to the counterion) over the endo-anomeric effect. The values of Keq(axialequatorial) in protonated 911 show the trend OMe > H < NO2 that is explained by the balance of the endo-anomeric effect and steric effects in the individual compounds. The trends in the values of the C1H1 coupling constants for 14 and the corresponding deacetylated compounds 58 as a function of substituent and alpha- or beta-configuration are discussed in terms of the Perlin effect and the interplay of the endo- and exo-anomeric effects. IS - 1 JF - The Journal of Organic Chemistry EP - 226 TI - Is There a Generalized Reverse Anomeric Effect? Substituent and Solvent Effects on the Configurational Equilibria of Neutral and Protonated N-Arylglucopyranosylamines and N-Aryl-5-thioglucopyranosylamines† VL - 65 SP - 220 KW - carbohydrate KW - conformational KW - preferences AU - Randell, Karla AU - Johnston, Blair AU - Green, David AU - Pinto, Mario PY - 2000/01/01/ UR - http://dx.doi.org/10.1021/jo991520j ER -