A new approach to the use of commercial databases for the dereplication of purified natural products has been developed. This is based on searching a text file that links each structure with its molecular weight and an exact count of the number of methyl, methylene, and methine groups it contains. Analysis of such a text file, constructed from a database containing more than 126,000 natural product structures, revealed that these data, readily measured using MS and NMR spectroscopy, are highly discriminating. The identification of an alkaloid and a sesquiterpene using this new approach is described.
1 Functional human GABA B(1a,2) and GABA B(1b,2) B(1a,2) and GABA B(1b,2) respectively. 3 In competition binding assays the rank order was identical for both GABA B receptors. For known GABA B agonists the rank order was CGP274924SKF97541=CGP463814GABA4Baclo-fen and for GABA B antagonists the rank order was CGP54262A4CGP558454CGP524324 SCH 509114CGP511764CGP36742=CGP35348 52-OH Saclofen 5ABPA. 4 The allosteric e ect of calcium cations was also investigated. The e ect of removal of CaCl 2 from the binding assay conditions was ligand dependent to either cause a decrease in ligand a nity or to have no signi®cant e ect. However, these e ects were similar for both GABA B receptors. 5 A whole cell, scintillation proximity binding assay was used to determine agonist a nity at exclusively heterodimeric GABA B receptors. In competition assays, the rank order was the same for both GABA B(1a,2) and GABA B(1b,2) and consistent with that seen with cell membrane fractions. 6 These data suggest that, in terms of ligand binding, the currently identi®ed isoforms of the GABA B receptor are pharmacologically indistinguishable.
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