Determining how much, if any, affinity gain was realized upon macrocyclization in a given experimental example from the literature can be complicated. Once an inhibitor discovery program has identified an initial macrocyclic compound with promising affinity, further modification of the structure is typically required to achieve the optimal degree of conformational preorganization, as well as to optimize the many other properties important for a drug such as selectivity, solubility, cell permeability, metabolic stability, etc. In published reports, the resulting fully optimized macrocyclic compound is rarely compared with an exact acyclic counterpart, as would be needed to isolate effects directly resulting from macrocyclization. Nonetheless, several kinase inhibitor discovery programs have reported affinity data for congeneric macrocycle/acyclic compound pairs generated at some stage during ligand discovery or optimization. These congeneric pairs provide insight into whether, and how much, affinity is gained by cyclizing compounds that bind at the nucleotide binding site of kinases.