A C OCON Analysis of Proton‐Poor Heterocycles – Application ofCarbon Chemical Shift Predictions for the Evaluation of Structural Proposals

Abstract

The application of the new computer program COCON (Constitutions from Connectivities) to the 2D‐NMR data sets of three different complex natural products is described. The investigated compounds are proton‐poor and therefore underdetermined systems. For such molecules the number of possible constitutions and the computational speed of COCON are of interest. Our investigation is focused on how methods of 13C‐NMR chemical shift prediction can assist chemists with regard to refining the selection among the constitutions proposed by COCON.

Incorporation of 4J-HMBC and NOE Data into Computer-Assisted Structure Elucidation with WebCocon

“…In order to come to a conclusion, C NMR chemical shifts were calculated for the structural proposals [ 36 ] using three different calculation methods: NMRShiftDB [ 54 ] ( M-I ), DFT (GAMESS 2019 R2 [ 55 ], M-II ), and NMRPredict [ 56 ] ( M-III ). The results were compared to experimental values, as shown in Table 2 .…”

Theoretical NMR correlations based Structure Discussion

“…Most of these approaches have in common that they work only based on experimental NMR correlation data. COCON [ 1 , 4 , 23 , 24 ] has recently been extended with the capability to create a theoretical NMR correlation data set, based on a molecule's suggested constitution. The theoretical data set is used as input data for the structure elucidation software COCON.…”

“…For the small number of interesting constitutions a back-calculation on the carbon chemical shifts was made (ChemDraw v11), that were compared to the experimental values (see table 2 ). The last line in the table contains the sum of the absolute chemical shift differences for all carbons, exposing molecule 6 as the one that best fits the experimental data [ 24 , 27 , 28 ].…”

Ecological and Pharmacological Activities of Polybrominated Diphenyl Ethers (PBDEs) from the Indonesian Marine Sponge Lamellodysidea herbacea

“…In order to elucidate the correct regioisomers, the 1 H and 13 C NMR data were compared to existing NMR data in the literature (Tables 3 and 4). Furthermore, the structures of 1d and 2b were also verified through comparison with predicted 13 C NMR chemical shifts [43][44][45][46] using three different computational approaches: NMRPredict [47], NMRShiftDB [48], and CSEARCH [49]. The 13 C chemical shifts of compound 1d (this work) were compared to predicted values and literature data (the atom numbering of Bowden et al, 2000 [50] was used for all literature data).…”