Selective J-resolved-HMQC-1 and -2, new methods for measuring proton-proton coupling constants in strongly coupled spin systems.

Efficient pulse sequences for measuring (1)H-(1)H coupling constants (JHH) in strongly coupled spin systems, named selective J-resolved-HMQC-1 and -2, have been developed. In the strongly coupled spin systems such as -CH2-CHA(OH)-CHB(OH)-CH2-, measurements of (3)JHAHB are generally difficult owing to the complicated splitting caused by the adjacent CH2 protons. For easier and accurate measurements of (3)JHAHB in such a spin system, a selective excitation pulse is incorporated into the J-resolved HMQC pulse sequence. In the proposed methods, only two strongly coupled protons, HA and HB which are excited by a selective pulse, are observed as J-resolved HMQC signals. The cross peaks of HA and HB appear as doublets owing to (3)JHAHB along the F1 dimension in the selective J-resolved HMQC-1 and -2 experiments. The efficiency of the proposed pulse sequences has been demonstrated in application to the stereochemical studies of the complicated natural product, monazomycin.