Experimental and Theoretical Nuclear Magnetic Resonance Data from Tryptanthrin, an Alkaloid with Potential Activity Against Human Coronavirus

Coronaviruses belong to the subfamily Coronavirinae, which are large viruses with a single Ribonucleic acid tape and a nucleocapsid. In a recent study it was found that the molecule of tryptanthrin has antiviral potential against human coronavirus NL63. In this work, we used a combination of theoretical techniques with experimental nuclear magnetic resonance data to assist in the structural characterization of the Tryptanthrin molecule. Tryptanthrin was extracted from Couroupita guianensis leaves. The theoretical calculations of hydrogen-1, homonuclear spin–spin coupling constants and the quantum theory of atoms in molecules were performed employing density functional theory. Our results show that the hydrogen-1 chemical shifts calculated at the gaseous phase and solvent presented similar performance. The quantum theory of atoms in molecules calculations was able to quantify and qualify bonded interactions based on five topological parameters obtained at the analyzed bond critical point to tryptanthrin molecule. We obtained a satisfactory correlation between tryptanthrin delocalization index values and its experimental and calculated proton–proton coupling constants. In conclusion, the theoretical techniques used in this work in combination with NMR experimental data can be a useful tool in aiding the structural determination of organic compounds.