lead

https://doi.org/10.1351/goldbook.12677
Compound (or compound series) that satisfies predefined minimum criteria for further structure and activity optimization.
Note: Typically, a lead will demonstrate appropriate activity, selectivity, tractable structure-activity relationship and have confirmed activity in a relevant cell-based assay.
Source:
PAC, 2013, 85, 1725. (Glossary of terms used in medicinal chemistry. Part II (IUPAC Recommendations 2013)) on page 1739 [Terms] [Paper]