Once a target, normally an enzyme or receptor, has been established and an assay for
activity has been developed, the medicinal chemistry team must discover, find, and
make compounds that interact with the target. Through the screening process, some
compounds emerge with sufficient activity to warrant further investigation. The active
compounds are then examined against a number of criteria, including complexity and
anticipated pharmacokinetic behavior. Compounds that satisfy the selection criteria are
called leads and advanced for further optimization of activity, selectivity, and biological
behavior. Occasionally, leads are found through other methods, such as serendipity
or clinical observations. This chapter describes techniques of discovering active compounds
through screening and selecting the most promising compounds as leads. The
overall process is collectively known as lead discovery