Specific spectral assignments for acetoxyl-group resonances in proton magnetic resonance spectra of methyl β- D-glucopyranoside tetraacetate and related derivatives

Abstract

Methyl β- D-glucopyranoside tetraacetates ( 1) having a trideuterioacetyl group at O-2 ( 1a), O-3, ( 1b), O-4 ( 1c), and O-6 ( 1d) were synthesized by unambiguous routes to permit assignment of each individual acetoxyl-group signal in the p.m.r. spectrum of 1. The 6-acetoxyl resonance appears at lower field than signals of the other acetoxyl groups in carbon tetrachloride, chloroform- d, and methyl sulfoxide- d 6, but in pyridine- d 5 and benzene- d 6, the 2-acetoxyl-group signal appears at lower field. The acetoxyl resonances of methyl 2,3,4-tri- O-acetyl-6- O-trityl-β- D-glucopyranoside ( 2), methyl 2,3,4-tri- O-acetyl-β- D-glucopyranoside ( 3), methyl 2,3-di- O-acetyl-4,6- O-benzylidene-β- D-glucopyranoside ( 5), methyl 2,3-di- O-acetyl-β- D-glucopyranoside ( 6), methyl 2,3,6-tri- O-acetyl-β- D-glucopyranoside ( 7), and methyl 2,3-di- O-acetyl-6- O-trityl-β- D-glucopyranoside ( 12) were assigned similarly after synthesis of the 2-(trideuterioacetyl) ( 2a, 3a, 5a, 6a, 7a, and 12a), 3-(trideuterioacetyl) ( 2b, 3b, 5b, 6b, 7b, and 12b), 4-(trideuterioacetyl) ( 2c and 3c), and 6-(trideuterioacetyl) ( 7c) analogues. In chloroform- d and benzene- d 6, the 4-acetoxyl resonance appeared at about 0.3 p.p.m. to higher field than the other acetoxyl-group signals of 2. In chloroform- d and methyl sulfoxide- d 6, the 3-acetoxyl resonance is observed at highest field in compounds 1, 3, and 5. In all of these instances, the 4-hydroxyl group is substituted by an acetyl or benzylidene group. When no 4-substituent is present (compounds 6, 7, and 12), the 3-acetoxyl group resonates at lower field than the other acetoxyl groups.