Within this small set of refined hits, a pair of related analogues 1 and 2 warranted deeper investigation (Figure ). Both compounds contain a pteridine core and possess a 2,4diamino substitution pattern, analogous to that seen in many Type I kinase inhibitors. The compounds were of modest potency (47 -109 µM) and had low maximal inhibition (44 -54%) when evaluated in the ADP-Glo TM assay. This reduced efficacy explains why the compounds had been overlooked in our earlier HTS triage. Testing in the SPA assay revealed modest activity and maximal inhibition (23 -26 µM, 72 -76%). We thus undertook to profile this series more extensively (Table ).