Quantum mechanical calculation of coupling constants in the configurational analysis of flexible systems: determination of the configuration of Callipeltin A

An integrated NMR-quantum mechanical (QM) approach, relying on the comparison between calculated and experimental J-values, was applied to the analysis of the relative configuration of four amino acid units (known as AGDHE, D-aThr1, D-aThr2 and beta-OMeTyr) contained in callipeltin A, a cyclopeptide endowed with a powerful inhibitory activity on the cardiac sodium/calcium exchanger and also showing interesting antiviral and antifungal properties. In this paper we report the first example of the application of this method to a real case, which allowed the assignment of the relative configuration of the P-OMeTyr residue and the revision of the configuration of the Thr2 unit in callipeltin A.