Conformational analysis of a ribopentandeolde tetraphosphate in aqueous solution. A two-dimensional NMR study at 500 MHZ1

Abstract
The 30 ribose proton resonances of the pentaribonucleoside tetraphosphate m62AUm62AUm62A have been assigned unequivocally by means of spin-echo-correlated spectroscopy, 2D J-resolved spectroscopy and Nuclear Overhauser difference spectroscopy, carried out at 500 MHz. A detailed comparison of the conforma-tional properties of the title compound with its constituent fragments m62AUm62AUm62AUm62A, m62AU and the relevant monomers is given. Chemical shift data indicate the existence of a doubly “bulged out” con-former, in which the two interior U-fragments are not involved in regular nearest neighbour stacking interactions. The coupling constants of the ribose-ring are interpreted in terms of the N/S equilibrium, and population distributions along the backbone angles β and are presented. The combined data suggest a strong similarity between the 5′-terminal triplets in m62AUm62AUm62A, m62-AUm62AU and m62AUm62A2

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