Measurement of (2)J(H,C)- and (3)J(H,C)-coupling constants by alpha/beta selective HC(C)H-TOCSY

A new heteronuclear NMR pulse sequence for the measurement of (n)J(C,H) cou pling constants, the alpha/beta selective HC(C)H-TOCSY, is described. It is shown that the (SE)-E-3 element (Meissner et al., 1997a,b) can be used to obtain spin state selective coherence transfer in molecules, in which adjac ent CH moieties are labeled with C-13. Application of the alpha/beta select ive HC(C)H-TOCSY to a 10nt RNA tetraloop 5'-CGCUUUUGCG-3', in which the fou r uridine residues are C-13 labeled in the sugar moiety, allowed measuremen t of two bond and three bond J(C,H) coupling constants, which provide addit ional restraints to characterize the sugar ring conformation of RNA in case s of conformational averaging.