NEW PROMISE IN COMBINATORIAL CHEMISTRY - SYNTHESIS, CHARACTERIZATION,AND SCREENING OF SMALL-MOLECULE LIBRARIES IN SOLUTION

Background: The increasing interest in combinatorial chemistry as a to ol for the development of therapeutics has led to many new methods of creating molecular libraries of potential lead compounds. Current meth ods have made it possible to develop libraries of several million comp ounds. As a result, the limiting factor in the screening of libraries has become the identification and characterization of active species. We have recently described a method for generating libraries of water- soluble compounds containing mixtures of 10(4) to 10(5) different smal l organic molecules by using generally applicable solution phase chemi stry. We set out to develop new methods to characterize and decode the se libraries. Results: Libraries were generated by condensing a multi- acid-chloride core molecule with various amines, producing molecules w ith functional groups about a rigid backbone. Composition and complexi ty of the libraries was evaluated using electrospray mass spectrometry to analyze model libraries containing up to 55 different molecules. T he number of peaks obtained in mass spectrometry is directly correlate d with the complexity of the library, and we were therefore able to de duce which of the expected compounds had in fact been formed in the li brary, and which of the building blocks in the library were not effici ently used. An iterative selection procedure Was developed using this information, which allowed the screening of libraries of up to 50,000 chemical species to produce a competitive inhibitor of the enzyme tryp sin. Conclusions: Our strategy for the identification of active specie s should be broadly applicable to other methods of generating complex libraries of small molecules. The selection from the library of a comp ound with desired biological properties augurs well for the potential value of generating and screening complex mixtures of small molecules in solution.