| Abstract
| - Methyl β-d-ribofuranoside 5 andmethyl 2-deoxy-β-d-erythro-pentofuranoside(methyl 2-deoxy-β-d-ribofuranoside) 6 were synthesized with single sites of13C-enrichment at each carbon, and a complete set of13C−1Hand 13C−13C spin-coupling constants (37couplings in 5, 41 couplings in 6) in thesemolecules were obtained by 1Dand 2D NMR spectroscopy. 2JCHcoupling signs were determined from the observation of relativecross-peakdisplacements in 2D TOCSY data. The13C−1H couplings (one-, two-, and three-bond)were interpreted in structuraland conformational terms with assistance from conformational models of5 and 6 based on conventionaltwo-statepseudorotational analysis of 3JHHvalues (PSEUROT) and on theoretical predictions of conformationalenergies andJCH values obtained from ab initiomolecular orbital calculations on the ten envelope and planarconformers ofβ-d-ribofuranose 4 and2-deoxy-β-d-erythro-pentofuranose(2-deoxy-β-d-ribofuranose) 3. Acomparison of theoreticalJCH values in 3 and 4allowed an assessment of the effect of C2 structure (C2 oxyvs C2 deoxy) on coupling magnitudesand signs. Results show that the behavior of relatedJCH values in 5 and 6 maydiffer, especially when C2 is involvedas a coupled nucleus. In addition, several1JCH,2JCH, and3JCH values inβ-d-ribo and2-deoxy-β-d-ribo rings werefound to be sensitive to furanose ring and hydroxymethyl groupconformation; in the deoxyribo ring, thepresenceof diastereotopic protons at C2 produces paired13C−1H coupling pathways involvingH2R and H2S that arecomplementary, and differences in the resulting pairedJCH values are, in some instances, sensitive toring conformation.JCC values inβ-d-ribo and2-deoxy-β-d-ribo rings also reflectdifferences in ring structure and geometry, althoughfewer (e.g., 2JC3,C5,3JC1,C5,3JC2,C5) appear useful asconformational probes. The correlations drawn betweenringstructure/conformation andJCH/JCC magnitude andsign in 5 and 6 will be useful in anticipatedapplications of thesecouplings to assess furanose ring conformation/dynamics in DNA and RNAoligomers and in other biomoleculescontaining β-d-ribo and2-deoxy-β-d-ribo rings.
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