The Versatility of Boron

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Science  14 Apr 2000:
Vol. 288, Issue 5464, pp. 229
DOI: 10.1126/science.288.5464.229g

Combinatorial synthesis can be used to generate a mixture of compounds, commonly called a library, that then can be screened to identify promising drugs or catalysts. When isomeric reactants are used as building blocks, the analysis of the mixture by mass spectrometry becomes quite difficult because the masses of individual compounds, and even of fragments of compounds, can be virtually identical.

Nazarpack-Kandlousy et al. describe an approach for resolving this type of complexity. They attached substituted benzaldehydes containing boronic acid units in ortho, meta, or para positions to a central scaffold through oxime ether linkages (boronic acid compounds also are of interest for their ability to combine reversibly with the hydroxyl groups of carbohydrates). They sorted out the several possible isomers by labeling the boronic acid compounds with boron and deuterium isotopes and by selectively labeling some of the aminooxy groups of the scaffold with nitrogen-15. Mass spectrometry resolved the parent compounds, and a second round of ion fragmentation in the mass spectrometer resolved the pair of isomers due to the labeled nitrogen. This approach may be extended to more scaffold positions with the use of defined ratios of isotopes in the initial labeling reactions.—PDS

J. Am. Chem. Soc., in press.

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