These constraints and the ones resulting from fragment search shrink the chemical search space that would be otherwise too wide for practical applications. Together with a given molecular formula (MF) mainly determined by mass spectrometry (MS), the substructures and restrictions derived from 1D and 2D NMR spectra form the cornerstone of structure generation by CASE systems. The HSQC experiment indicates direct bonds between heavy atoms (non-hydrogen) and protons whereas HMBC and COSY spectra bear hints about long-range chemical shift correlations between protons and heavy atoms (HMBC) or between protons (COSY). The typical collection of NMR data used for computer-assisted structure elucidation (CASE) might contain 1D spectra such as 1H, 13C and DEPT as well as the 2D HSQC, HMBC and COSY spectra. Through-bond proximity relationships between atoms became available with the possibility of routinely recording two-dimensional (2D) NMR spectra.
Preliminarily to de novo structure elucidation by NMR, database lookup for an already known compound (dereplication) or for structure fragments has been included in several existing CASE systems using the spectral fingerprint of one-dimensional (1D) NMR experiments as a search key. NMR spectroscopy is the most widely used analytical method for the thorough identification of organic chemical compounds.
0 kommentar(er)
