Modern combinatorial chemistry is used to discover compounds with desired function by an alternative strategy, in which the biological target is directly involved in the choice of ligands assembled from a pool of smaller fragments. Herein, we present the first experimental result where the use of in situ click chemistry has been successfully applied to probe the ligand-binding site of Abl and the ability of this enzyme to form its inhibitor. Docking studies show that Abl is able to allow the in situ click chemistry between specific azide and alkyne fragments by binding to Abl-active sites. This report allows medicinal chemists to use protein-directed in situ click chemistry for exploring the conformational space of a ligand-binding pocket and the ability of the protein to guide its inhibitor. This approach can be a novel, valuable tool to guide drug design synthesis in the field of tyrosine kinases. KEYWORDS: ligand-binding site, Abl tyrosine kinase, click chemistry, drug design synthesis T he findings that Bcr-Abl (cytoplasmic tyrosine kinase) is the cause of the leukemic phenotype and that the tyrosine kinase activity of Abl is fundamental for Bcr-Abl-mediated transformation have made this kinase an important target for the development of specific therapies. In the recent past, advances in the selective inhibition of Bcr-Abl kinase activity led to the development of several active compounds, and in particular, imatinib mesylate (Gleevec) is the one that currently represents the front-line therapy of CML. Considering our interest in the discovery of new inhibitors of tyrosine kinases, 1−5 we have recently reported the design and preparation of a small collection of quality N-[2-methyl-5-(triazol-1-yl)phenyl]pyrimidin-2-amine derivatives. 6 The antiproliferative activity in the micromolar range pointed out the efficacy of the compound named FA030 (Figure 1, IC 50 = 0.89 μM on the K-562 cell line). This one showed a potent antienzymatic activity against recombinant Abl kinase (IC 50 = 0.9 ± 0.1 μM). The ADME prediction suggested no significant difference between the behavior exhibited by FA030 and that of imatinib that differs for an amide group in the place of the triazole ring. 6 Moreover, the binding mode was very similar to that of imatinib. FA030 seems to have six hydrogen bonds with the protein, and the majority of contacts are mediated by van der Waals interactions. The triazole ring is involved in two hydrogen bonds with the carbonyl groups of Asp 381 and His 361.Over the last years, target-guided in situ synthesis 7 has attracted our attention because it proved to be a captivating and efficient approach to drug discovery. We applied this strategy to the formation of bivalent compounds that are able to target the tubulin/microtubules dynamic system. 8 Thus, we successfully used tubulin as a target to influence the composition of the mixture of a dynamic combinatorial library by exploiting the disulfide bond exchange reaction. 9 In this scenario, we turned our attention to in situ click chemistry...

The design and the preparation of a small library of 1,4‐diphenyl‐1,2,3‐triazole derivatives is reported, with the aim to obtain a new class of Hedgehog pathway inhibitors. The smoothened protein is part of the hedgehog signaling pathway that is inhibited by the lead compound Vismodegib. Based on molecular modeling simulations, seven triazole derivatives of Vismodegib are synthesized and their biological effect on different endothelial, cancer, and cancer stem cell lines is reported.