[structure: see text] The computer-assisted constitutional assignment of ascomycin (1) is discussed. This example demonstrates that the NMR-based structure generator COCON is able to analyze data sets of organic molecules covering the full known range in size and complexity. The structural proposals of ascomycin were validated by calculating the 13C NMR chemical shifts using the computer program SpecEdit. The enhanced calculation time of COCON achieved by preorganizing the input data is also demonstrated for the data sets of aflatoxin B1 (2), 11-hydroxyrotenone (3), and haemoventosin (4).
The 2D NMR-guided computer program COCON can be extremely valuable for the constitutional analysis of unknown compounds, if its results are evaluated by neural network-assisted 13C NMR chemical shift and substructure analyses. As instructive examples, data sets of four differently complex marine natural products were thoroughly investigated. As a significant step towards a true automated structure elucidation, it is shown that the primary COCON output can be safely diminished to less than 1% of its original size without losing the correct structural proposal.
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.
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