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

Abstract

2‘-Deoxyribonucleosides (2‘-deoxyadenosine (1), 2‘-deoxycytidine (2), thymidine (3)) singly enriched with 13C at C2‘ have been prepared and used to obtain one-, two-, and three-bond 13C−1H and 13C−13C 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.

Intrinsic Conformational Properties of Deoxyribonucleosides: Implicated Role for Cytosine in the Equilibrium Among the A, B, and Z Forms of DNA

“…It is worth noting that NMR data represent averages over a large number of different conformers, reflecting the flexibility of all the furanose substituents. NMR-based conformational analysis of the deoxyribose in nucleosides is still an area of active research (Bandyopadhyay et al, 1997). The results presented in Table 2 show the conformations of the nucleosides in their north and south energy minima to be in the vicinity of the conformations that occur in A and B DNA, respectively.…”

A new single grating spectrograph for ultraviolet Raman scattering studies

“…As our test sample for evaluating a resonant scattering scenario, we have therefore chosen the purine nucleoside dA, which has been shown by NMR studies to favor the S conformation (71% at 25°C) in aqueous solution. 89 At pH D 7, it exhibits a relatively strong electronic absorption (ε 260 D 15 200 l mol 1 cm 1 ) 90 at 260 nm (450 cm 1 Stokes wavenumber shift with respect to 257-nm excitation), being sufficiently close to the selected Raman excitation wavelength.…”

2′‐Deoxy‐2′‐α‐C‐(hydroxymethyl)adenosine as Potential anti‐HCV Agent

“…[19][20] In our case, we measured on the non 1 H-decoupled 13 C spectrum a value of 165.9 Hz for 1 J C1,H1 , characteristic for adenosine (β-anomer) (literature value for adenosine is 165.6 Hz). [21] Finally, the nucleoside 14 was deprotected to afford the desired modified adenosine 8. The order in which the functions are deprotected is important.…”

“…6 Hz). [21] Finally, the nucleoside 14 was deprotected to afford the desired modified adenosine 8. The order in which the functions are deprotected is important.…”