Similarity search for a 1H-NMR spectroscopic data base

A similarity-search system is described for proton-NMR spectroscopy. In order to achieve fast retrieval of reference compounds, the ¹H-NMR spectra of the data base and of the unknown are encoded in a bitsring. The individual bits of the binary signature describe different features of the spectra. Part of the coupling information is coded in such a way that effects of magnetic field strength are taken into account. The encoding thus permits a fast search for identical and structurally similar reference compounds in the data base even when the spectra were recorded at different magnetic field strengths. Because the search consists of weighted comparison of bits, each of them describing different spectral features, a choice of different kinds of searches is possible with the same signature by selecting appropriate weight vectors. Thus specific spectroscopic features can be selected for the search. Such a context-sensitive similarity-search system allows, for example, a search for compounds having similar multiplicities or similar subspectra in a given (e.g., aromatic) region of the spectrum. Furthermore, by adjusting two “software knobs” which influence the normalization of the search results, the user can choose between the two extremes of forward and reverse search, and between an identity search, similarity search or classification search. The results were tested on a small library containing 550 spectra including some mixtures and duplicates recorded under different experimental conditions at 250 and 400 MHz.