Computational 1H and 13C NMR of strychnobaillonine: On the way to larger molecules calculated at lower computational costs.

The 1H and 13C NMR chemical shifts of strychnobaillonine, a very large dimeric indole alkaloid, consisting of as many as 46 nonhydrogen atoms, were calculated with using the established earlier the most effective computational protocol, PBE0/pcSseg-2//pcseg-2. A very good result was achieved at this level, characterized by the root mean square deviation of only 0.14 ppm for protons and 2.4 ppm for carbons, which enabled the verification of the configurations of its all 13 asymmetrical centers. Essential deviations of the calculated and experimental 1H NMR spectrum of strychnobaillonine were established in several cases, which enabled the performance of some additional NMR assignments and reassignments of the originally proposed structure.