Homonuclear long-range correlation spectra from HMBC experiments by covariance processing

We present a newapplication of covariance nuclear magnetic resonance processing based on 1H–13C-HMBC experiments which provides an effective way for establishing indirect 1H–1H and 13C–13C nuclear spin connectivity at natural isotope abundance. Themethod, which identifies correlated spin networks in terms of covariance between one-dimensional traces from a single decoupledHMBC experiment, derives 13C–13C as well as 1H–1H spin connectivity maps from the two-dimensional frequency domain heteronuclear longrange correlation data matrix. The potential and limitations of this novel covariance NMR application are demonstrated on two compounds: eugenyl-b-D-glucopyranoside and an emodin-derivative.