Der einfluss des anomeren effektes auf furanosekonformationen. Röntgenstrukturanalyse fünf isomerer methyl-3,6-anhydrohexofuranoside

Add time:08/17/2019    Source:sciencedirect.com

X-Ray crystallographic analysis of five isomeric methyl 3,6-anhydrohexofuranosides, methyl 3,6-anhydro-β-d-glucofuranoside (1), methyl 3,6-anhydro-α-l-idofuranoside (2), methyl 3,6-anhydro-β-d-mannofuranoside (3), methyl 3,6-anhydro-α-d-glucofuranoside (5), and methyl 3,6-anhydro-α-d-mannofuranoside (7), showed that the anomeric effect determines the conformation of the furanoid ring, which resulted in the quasi-axial orientation of the aglycon in all cases. Thus, 2 adopts an almost ideal E2 conformation, whereas 1 and 3 having the same R configuration at the anomeric center showed conformations of the furanoid ring intermediate between E2 and 1T2. Of the anomers 5 and 7 having an S configuration at C-1, 7 showed a related but opposite geometry, intermediate between 2E and 2T1, and 5 had a oT1 conformation, slightly distorted into oE. The anhydroring of all compounds showed a C-6 endo orientation, with the exception of 7, in which C-6 is exo oriented. These results from compounds in the solid state were compared with the conformations of the same compounds in solution, as deduced by 1H-n.m.r. spectroscopy.

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