Conformational preferences in glycosylamines. implications for the exo-anomeric effect.
The conformational preferences about the C-N bond in N-(4-methoxyphenyl)-2,3,4,6-tetra-O-acetyl-alpha (1) and beta-D-glucopyranosylamine (2), in the solid state and in solution, have been investigated. The crystal structure of the axially substituted alpha anomer (1) indicates a conformational preference about the C-1-N bond in which nN-->sigma*C-O exo-anomeric interactions may be expressed, although this conformational preference is not displayed in solution. The solution conformation relieves steric interactions that result from expression of the exo-anomeric effect in the solid-state conformation. The conformational preference in the equatorially substituted beta anomer (2) both in solution and in the solid state is similar and permits expression of nN-->sigma*C-O exo-anomeric interactions. The structural data for 1 and 2 indicate significant differences in O-5-C-1-N-1 bond angles but insignificant differences in each of the O-5-C-1 or C-1-N-1 bond lengths. The J(C-1-H-1 coupling constants in 1 and 2 indicate a greater coupling constant for the alpha anomer that is consistent with a dominant nO-->sigma*C-H orbital interaction in the beta anomer that weakens the C-1-H-1 bond.
Department of Chemistry and Biochemistry, Simon Fraser University, Burnaby, BC, Canada.
R J
RJ
Batchelor
D F
DF
Green
B D
BD
Johnston
B O
BO
Patrick
B M
BM
Pinto
D000107:Acetylation; D002236:Carbohydrate Conformation; D018360:Crystallography, X-Ray; D005944:Glucosamine / Q000031:analogs & derivatives* / Q000737:chemistry*; D008958:Models, Molecular; D012996:Solutions; D013237:Stereoisomerism
C430286:N-(4-methoxyphenyl)-2,3,4,6-tetra-O-acetyl-glucopyranosylamine; D012996:Solutions; D005944:Glucosamine