"Perfect Echo" HMQC: Sensitivity and resolution enhancement by broadband homonuclear decoupling

Homonuclear H-1-H-1 J-modulation leads to J-multiplets in F-1 dimension of 2D H-1-C-13 HMQC spectra. This hampers unambiguous signal assignment for overcrowded C-13 spectra. Broadband homonuclear decoupling has been achieved in the indirect t(1) evolution period by incorporating blocks of perfect echo. This method of perfect echo HMQC demonstrates better resolution and sensitivity than conventional HMQC spectra. The results on Cyclosporine demonstrate that the method is very efficient for refocusing geminal couplings in weakly coupled -(CH2)-C-13 groups. Partial refocusing of vicinal couplings is also observed for -(CH)-C-13 and -(CH3)-C-13 groups. Interpretation of the result based on product operator formalism is also given. Comparison of pe-HMQC, HMQC and HSQC reveals that the F-1 linewidth of pe-HMQC is much narrower than HMQC and very close to that of HSQC for CH2 groups. (C) 2013 Elsevier Inc. All rights reserved.