Chemical synthesis of novel aminopyrimidin-4-yl-1H-pyrazole derivatives as spleen tyrosine kinase (SYK) inhibitors

Spleen tyrosine kinase (SYK) plays a pivotal role in immunoreceptor signalling pathways implicated in various cancers and autoimmune diseases. Inhibition of SYK has shown therapeutic potential by attenuating immune-mediated damage and suppressing tumour growth. This study reports the synthesis, characterization, and evaluation of a novel series of aminopyrimidin-4-yl-1H-pyrazole derivatives (31, 35, 36, 37, 39, 41, 44, 47 and 49) as selective SYK inhibitors. The chemically synthesized molecules were structurally confirmed using ¹H, ¹³C NMR and mass spectrometry techniques. Further, molecular docking studies revealed differential binding affinities with the SYK active site, highlighting molecule 44 as the lead candidate, displaying the lowest docking score and strongest interactions. Subsequent 200 ns molecular dynamics simulations confirmed the enhanced stability of 44 in complex with SYK, evidenced by consistent hydrogen bonding, minimal root-mean square deviation (RMSD), and compact protein folding relative to other ligands. Furthermore, binding free energy calculations corroborated the favourable energetic profile of 44. Also, principal component and free energy landscape analyses showed that 44 maintained a single, stable conformational state with limited flexibility. On the other hand, in vitro enzyme inhibition assays employing a luminescence-based kinase activity system demonstrated that several compounds, particularly 44, exhibited potent concentration and time-dependent inhibition of SYK inhibition activity. Kinetic characterization revealed that 44 functions via a non-competitive inhibition mechanism, suggesting allosteric binding outside the ATP substrate site. These integrative in silico and in vitro findings establish 44 as a promising lead molecule for SYK-targeted therapies, combining potent binding affinity, conformational stability, and effective enzyme inhibition. This work advances the design of novel small-molecule SYK inhibitors with potential applications in cancer and autoimmune disease treatment.