Computational NMR Spectroscopy of Organoarsenicals and the Natural Polyarsenic Compound Arsenicin A

Abstract

The (1)H and (13)C NMR chemical shifts and coupling constants of a series of organoarsenic compounds were calculated with DFT methods and compared with available experimental spectra. We show that non-relativistic methods successfully model the NMR spectra of these molecules; relativistic spin-orbit effects are small but appreciable for (13)C shifts, and their inclusion is beneficial. Application of the same methods of calculation to the intriguing natural polyarsenic compound arsenicin A allowed several viable alternative structures to be ruled out and thereby confirmed the previously suggested adamantane-like structure of arsenicin A. These results not only reinforce the known predictive power of DFT NMR calculations, but also open the way for the investigation of other naturally occurring molecules with unusual structures outside the scope of empirical methods.

Addressing the Stereochemistry of Complex Organic Molecules by Density Functional Theory-NMR: Vannusal B in Retrospective

“…8 These developments have been widely exploited to determine molecular structures, including those of natural substances, 9 with little if any recourse to empirical evidence; the latter strength is particularly critical whenever molecules with unusual or unprecedented constituents or connectivities are considered. Thus, high-level DFT calculations have aided the structure determination of arsenicin A 10 and clarified issues on the structure of hexacyclinol, 11,12 as well as helped in the structural revision of several other natural substances. 13 …”

STRUCTURAL REASSIGNMENT OF EPIERYTHRATIDINE, AN ALKALOID FROM Erythrinafusca, BASED ON NMR STUDIES AND COMPUTATIONAL METHODS

“…[10][11][12] These methods have been very important, together with total synthesis, 13 to determine the structures of unusual natural substances, 14,15 and differentiate diastereoisomers, 16 through calculations of proton-proton and proton-carbon J coupling constants as a tool for the assignment of the relative configurations of chiral organic compounds, an approach that agrees very well with the experimental data. [17][18] Moreover, extensive spectroscopic analyses and quantum mechanical (QM) methods have been used for the reassignment of some structures, 19 and can be very helpful to confirm both rigid and flexible molecular scaffolds.…”

Bioactive Poly(Arsenic) Compounds

“…DFT methods were also successfully applied to the simulation of NMR spectra of polyarsenic structures previously taken into account, due to the fact that such systems are ideally suited to the application of these calculations, since they are nonpolar and rigid. In particular, this theoretical approach was able to support the assignment for arsenicin A and offers a valid tool for the investigation of other naturally occurring molecules with similar structures (Tähtineen et al 2008).…”