Sensitivity of 1JC1-H1 Magnitudes to Anomeric Stereochemistry in 2,3-Anhydro-O-furanosides

Abstract
The magnitude of the one-bond coupling constant between C1 and H1 in 2,3-anhydro-O-furanosides has been shown to be sensitive to the stereochemistry at the anomeric center. A panel of 24 compounds was studied and in cases where the anomeric hydrogen is trans to the epoxide moiety, 1JC1-H1 = 163−168 Hz; and when this hydrogen is cis to the oxirane ring, 1JC1-H1 = 171−174 Hz. In contrast, for 2,3-anhydro-S-glycosides, the size of the 1JC1-H1 is not sensitive to C1 stereochemistry. Computational studies on all four methyl 2,3-anhydro-O-furanosides (5−8) demonstrated that 1JC1-H1 was inversely proportional to the length of the C1−H1 bond. A previously reported equation, which relates C1−H1 bond distance and atomic charges to 1JC1-H1 magnitudes, could be used to accurately predict the J values in the α-lyxo (5) and β-ribo (8) isomers. In contrast, with the β-lyxo (6) and α-ribo isomers (7), this equation underestimated the size of these coupling constants by 10−20 Hz.

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