Nonleadlikeness and leadlikeness in biochemical screening.

Biochemical assays have largely supplanted functional biological assays as drug screening tools in the early stages of drug discovery. The de-selection of compounds that are 'nonleadlike' binders (and bonders) and the proactive selection of those compounds that are 'leadlike' in their binding to the target are vital components of the screening effort. The physiochemical properties of leadlikeness and the surprising differences between those properties and the now classical definitions of druglikeness are becoming apparent.