TBB is one of the most selective protein kinase inhibitors known, and when tested against a panel of 33 serine/threonine and tyrosine protein kinases, only three exhibited moderate inhibition by TBB, with Ki values one to two orders of magnitude higher than that for CK2.
A cell-permeable, selective inhibitor of casein kinase-2 (CK2) (IC 50 = 0.9 and 1.6 μ M for rat liver and human recombinant CK2 respectively). Exhibits modest discrimination between CK2 subunits, with K i values ranging from 80 nM to 210 nM. Acts in an ATP/GTP-competitive manner and displays one to two orders of magnitude selectivity over a panel of 33 protein kinases.
TBB binds to the Val66 residue of casein kinase-2 and inhibits the binding of ATP/GTP. TBB is cell permeable; it induces caspase-dependent apoptosis and degrades hematopoietic lineage cell-specific protein 1 in Jurkat cells.
The method reported in literature [39] was used with appropriate modifications. 1H-benzotriazole (32, 3 g) was dissolved in a mixture of 69% HNO3 (50 mL) and 100% HNO3 (3 mL). Subsequently, the solution was heated to 80 °C and Br2 (6 eq.) was added slowly and dropwise over a period of 1 hour. The reaction mixture was stirred vigorously at 60 °C for 48 h and then cooled to room temperature. Unreacted Br2 was trapped and removed by 20% aqueous Na2S2O5 solution (100 mL) under nitrogen protection.Next, the reaction mixture was poured into a mixture of ice-cold H2O (200 mL) and saturated aqueous Na2S2O5 solution (10 mL). The resulting orange precipitate was collected by filtration and washed sequentially with H2O (50 mL) and EtOH (50 mL). The crude product was purified by multiple washes with hot MeOH (50 mL) to afford a white solid 4,5,6,7-tetrabromo-1H-benzotriazole (TBBt, 34, 7.45 g, 17.14 mmol, 68% yield). The structure of the product was confirmed by high-resolution mass spectrometry (HRMS).1H NMR, 13C NMR and melting point data were in agreement with those reported in the literature.Properties of TBBt 34 are as follows: white solid; melting point 264-266 °C (MeOH) [literature value: 262-266 °C (acetic acid)][89]; HRMS (ESI-TOF) m/z: [M + H]+ C9H7Br5N3+ m/z calculated value: 435.6941, measured value: 435.6629.
[1] European Journal of Medicinal Chemistry, 2018, vol. 150, p. 307 - 333
[2] European Journal of Medicinal Chemistry, 2014, vol. 84, p. 364 - 374
[3] Journal of the American Chemical Society, 1957, vol. 79, p. 4395,4399
[4] Bioorganic and Medicinal Chemistry, 2009, vol. 17, # 4, p. 1573 - 1578
