Computational ¹H and ¹³C NMR of the trimeric monoterpenoid indole alkaloid strychnohexamine: Selected spectral updates

Abstract

Very large trimeric indole alkaloid strychnohexamine, with empirical formula C 59 H 60 N 6 O (66 second-row atoms and 60 protons), has been subjected to the state-of-the-art computation of the 1 H and 13 C nuclear magnetic resonance (NMR) chemical shifts of its configurational isomers at each of the 14 asymmetric centers. Several spectral reassignments and corrections of 1 H and 13 C NMR spectra of this alkaloid were suggested based on the PBE0/pcSseg-2//pcseg-2 calculation of its NMR chemical shifts. Thus, all pairs of diastereotopic protons were assigned together with four aromatic carbon resonances of C-9 and C-11, C-9 00 , and C-11 00 . In addition, the unassigned chemical shifts of carbon C-23 00 and proton at C-3 0 in, accordingly, 13 C and 1 H NMR spectra were predicted.

Analytical and Structural Tools of Lipid Hydroperoxides: Present State and Future Perspectives

“…Quantum chemical calculations of NMR parameters have also been extensively used for the precise determination of diastereomerism of natural products with multiple asymmetric centers [ 138 , 141 , 142 , 143 , 158 , 159 , 160 , 161 ]. On the contrary, in the field of lipid hydroperoxides, only three papers have so far been reported [ 138 , 141 , 156 ].…”

Computational NMR of Carbohydrates: Theoretical Background, Applications, and Perspectives

“…As a further example of the DP4+ application, in a very recent paper by Semenov and Krivdin [ 59 ] the graphs of the probabilities for each candidate diastereomer of strychnohexamine 1 (shown in Figure 2 ) were presented as illustrated in Figure 3 . The latter were assigned based on the DP4+ results together with corresponding data provided by the Mean Absolute Error (MAE) and Corrected Mean Absolute Error (CMAE) analysis.…”

“…Element colors are as follows: protons—gray, carbons—dark yellow, nitrogens—blue, oxygen—red, while the chiral carbons are given in bright yellow. Reproduced from Semenov et al [ 59 ] with the permission of John Wiley and Sons.…”

“… Graphs of the DP4+ probability distribution for each diastereomer of strychnohexamine ( 1 ) together with the probabilities derived from the performed correlation analysis and the values of the resulting MAE and CMAE. Reproduced from Semenov et al [ 59 ] with the permission of John Wiley and Sons. …”

Simple and Versatile Scheme for the Stereochemical Identification of Natural Products and Diverse Organic Compounds with Multiple Asymmetric Centers

“…Calculations of 1 H and 13 C NMR isotropic magnetic shielding constants (and, accordingly, chemical shifts) were carried out at the DFT level with the DALTON package . In these calculations, we used the mPW1PW91/6-311G­(d,p) computational scheme, which was tested in one of our previous publications . In this scheme, the one-parameter hybrid functional mPW1PW91 (which is based on the Perdew–Wang exchange as modified by Adamo and Barone combined with PW91 correlation) was employed throughout in combination with Pople’s triple-ζ basis set 6-311G­(d,p) .…”