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Synthetic ligands discovered by in vitro selection.

The recognition and catalytic properties of biopolymers derive from an elegant evolutionary mechanism, whereby the genetic material encoding molecules with superior functional attributes survives a selective pressure and is propagated to subsequent generations. This process is routinely mimicked in vitro to generate nucleic-acid or peptide ligands and catalysts. Recent advances in DNA-programmed organic synthesis have raised the possibility that evolutionary strategies could also be used for small-molecule discovery, but the idea remains unproven. Here, using DNA-programmed combinatorial chemistry, a collection of 100 million distinct compounds is synthesized and subjected to selection for binding to the N-terminal SH3 domain of the proto-oncogene Crk. Over six generations, the molecular population converges to a small number of novel SH3 domain ligands. Remarkably, the hits bind with affinities similar to those of peptide SH3 ligands isolated from phage libraries of comparable complexity. The evolutionary approach has the potential to drastically simplify and accelerate small-molecule discovery.