Simplified multiplet pattern HSQC-TOCSY experiment for accurate determination of long-range heteronuclear coupling constants

A new two-dimensional pulse sequence for accurately determining heteronucle ar coupling constants is presented. It is derived from HSQC and HECADE tech niques with B-0 gradient coherence selection. The main feature of the propo sed method is spectra with only one component of the IS doublet; i.e., the final result is equivalent to a selective broadband excitation of either S- alpha or S-beta spin states and a preservation of these states during the e ntire experiment. The effect is obtained by an appropriate combination of i n- and antiphase coherences. It is demonstrated that heteronuclear single-b ond as well as long-range coupling constants and their relative signs are r eadily evaluated. The proposed sequence is equally or less sensitive to a v ariation of heteronuclear one-bond couplings than previously published, clo sely related sequences. The new method is applied to a peptide sample for d etermination of (3)J(N,H beta). (C) 1999 Academic Press.