APPLICATION OF HMBC AND HMQC-TOCSY NMR METHODS TO ASSIGN THE STRUCTURES OF BICYCLIC-PEPTIDE MIMETICS

The structures of representative bicyclic peptides are confirmed throu gh the NMR methods of HMBC and HMQC-TOCSY. Complete assignment of prot on and carbon resonances is afforded by these two-dimensional NMR meth ods. HMQC-TOCSY is especially useful for assigning spectra in molecule s having extensive proton spin systems and in establishing connectivit ies between protonated carbons. Long-range proton-carbon connectivitie s obtained by HMBC confirm structure in molecules containing heteroato ms or non-protonated carbons that interrupt proton spin systems.