13C−1H and 13C−13C Spin Couplings in [2‘-13C]2‘-Deoxyribonucleosides: Correlations with Molecular Structure

2‘-Deoxyribonucleosides (2‘-deoxyadenosine ( 1 ), 2‘-deoxycytidine ( 2 ), thymidine (3 )) singly enriched with 13 C at C2‘ have been prepared and used to obtain one-, two-, and three-bond 13 C− 1 H and 13 C− 13 C spin-coupling constants involving C2‘. Coupling data are interpreted with assistance from complementary 3 J HH data (PSEUROT analysis), furanose structural parameters obtained from molecular orbital calculations, structure-coupling correlations found for J CH and J CC in carbohydrates, and calculated J values. Spin couplings in 1 − 3 involving C1‘ and C2‘ are also compared to corresponding values in ribonucleosides in order to assess the effects of nucleoside structure and conformation on J values within the furanose ring. 1 J C2 ‘,H2 ‘ R and 1 J C2 ‘,H2 ‘ S in 1 − 3 and 1 J C2 ‘,H2 ‘ in ribonucleosides depend on C−H bond orientation; 1 J C1 ‘,H1 ‘ in 1 − 3 and in ribonucleosides exhibits a similar dependence. The latter couplings appear to be essentially unaffected by N -glycoside torsion. 1 J CC values depend on the number and distribution of electronegative substituents on the C−C fragment. A modified projection curve is proposed to aid in the interpretation of 2 J C2 ‘,H1 ‘ values; the presence of N substitution at C1‘ causes a shift to more negative couplings relative to the O -substituted analog. In contrast, 2 J C1 ‘,H2 ‘ is essentially unaffected by the same change in the electronegative substituent at C1‘. 2 J CC values within the furanose ring are determined by two coupling pathways; in one case ( i.e., 2 J C1 ‘,C3 ‘ ), the observed coupling is shown to be the algebraic sum of the two couplings arising from each pathway. 3 J CH and 3 J CC values depend in general on appropriate molecular dihedral angles as expected (Karplus relationships); however, 3 J C2 ‘,H4 ‘ values exhibit unexpected behavior, thus suggesting potential limitations in its use as a structural probe.