Quantum Mechanical Calculation of Coupling Constants in the Configurational Analysis of Flexible Systems: Determination of the Configuration of Callipeltin A

Abstract

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, DaThr1, D-aThr2 and β-OMeTyr) contained in callipeltin A, a cyclopeptide endowed with a powerful inhibitory activity on the cardiac sodium/calcium exchanger and also showing

Quantum Mechanical Calculation of NMR Parameters in the Stereostructural Determination of Natural Products

“…They also suggest to calculate the probability of the stereostructural determination by using the theorem of Bayes. [47] The determination of configuration of callipeltin A (15) by our research group [50] is a particularly interesting application of the QM-J method [18] not only because it represented the first application to a real case but also because the structural reassignment was confirmed by total synthesis and spectral correlation of callipeltin A congeners. [51] Initially, for these potent antiviral marine peptides isolated from the sponges Callipelta sp.…”

Microbial Transformation of Marine Halogenated Sesquiterpenes

“…The biotransformation of pacifidiene(2) with M. plumbeus gave the metabolites 1 and 6. The molecular formula, C 15 H 20 Br 2 O 2 , of compound 6 was established based on13 C NMR, DEPT and MS [m/z: 392]. This formula suggests that oxygen was introduced in 2 in place of the chlorine atom.…”

Elucidating the Relative and Absolute Configuration of Organic Compounds by Quantum Mechanical Approaches

“…Conversely, J values are related to a confined region of the molecule and, if the spatial positions of the related atoms (e.g., two protons for 3 J H‐H , two carbons for 1 J C‐C , carbon and proton for 2,3 J C‐H , upon which these values depend) are strongly influenced by the spatial chemical arrangement of the substituents around a close and undefined stereocenter, they became highly diagnostic for the stereochemical determination. [6a], For these reasons, the conformers to be accounted can be in principle reduced only to those showing substantial geometrical differences around the precise molecular portion influencing the J predicted values. Indeed, different QM/NMR‐based approach examples have been reported focused on dissecting the case‐study molecules in small fragments related to the precise and most indicative molecular regions.…”