ONE-DIMENSIONAL INVERSE-DETECTED METHODS FOR MEASUREMENT OF LONG-RANGE PROTON-CARBON COUPLING-CONSTANTS - APPLICATION TO SACCHARIDES

Several inverse-detected one-dimensional methods for measurement of long-range heteronuclear coupling constants are proposed. A double-INEPT-type polarization transfer is used in these sequences. An initial transfer via one-bond couplings is followed by modulation of the single-quantum carbon magnetization by long-range heteronuclear couplings and a final back-transfer of the carbon magnetization to protons. Multiplets in pure antiphase with respect to the heteronuclear long-range couplings and additional in-phase splitting from proton-proton couplings are observed. Selection of a particular isotopomer, the subspectrum of which is coadded constructively during the course of the experiment, is achieved by a combined use of selective pulses and chemical-shift-selective filters, both applied in the C-13 or the H-1 frequency domains. Modifications are proposed which remove the undesirable effect of one-bond and passive long-range proton-carbon coupling constants. Signal intensities are analyzed theoretically and compared experimentally for various experimental schemes. The methods are illustrated on a peracetylated beta-cyclodextrin (M(r) = 2016 g/mol). The emphasis is placed on the measurement of interglycosidic heteronuclear long-range couplings, which proved to be useful in the conformational analysis of saccharides. (C) 1994 Academic Press, Inc.