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Updated: May 21, 2026

Assaying Protein Kinase Activity with Radiolabeled ATP
Published on: May 26, 2017
Contribution of indazolinone tautomers to kinase activity
Anil Vasudevan1, Mary K Verzal, Clara I Villamil
1Advanced Technology, Global Pharmaceutical Research and Development, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064, United States. Anil.Vasudevan@abbott.com
Abstract:
The design and synthesis of indazolinone containing kinase inhibitors are reported. Regioisomers that showed profound potency variation in previously-reported isoindolinone and aminoindazole systems were surprisingly found to have similar potencies in the case of the indazolinone chemical series. An interpretation using differential hinge hydrogen bonding and tautomeric equilibrium of indazolinone ring system is supported by quantum mechanics calculations. The equipotent inhibition of a representative kinase (KDR) by regioisomeric indazolinones 4 and 5 is clear evidence that in case of the indazolinone hinge, both tautomers are equally favored, and should be considered in design of inhibitors.
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