DETERMINATION OF THE BACKBONE TORSION ANGLE-EPSILON IN NUCLEIC-ACIDS

The multiplet structure of cross peaks in double-quantum-filtered COSY NMR spectra is analysed for those resonances that include passive het eronuclear couplings. Interestingly, the cross peak involving the suga r-ring protons H2' and H3' in nucleic acids display an E.COSY-type app earance exclusively when the backbone torsion angle epsilon (C4'-C3'-0 3'-P) adopts a gauche(-) conformation. This observation allows an unam biguous analysis of the conformation around epsilon, without the knowl edge of (3)J(CP) coupling constants.