The immune system's main task is to protect the body from foreign objects. It consists of three lines of defense with increasing specificity against pathogens. Part of the innate immune system are the pattern recognition receptors (PRRs), which specifically recognize pathogen- or damage-associated molecular patterns (PAMPs and DAMPs). Toll-like receptors (TLRs) also belong to one of the PRR classes. In the master's thesis, we focused on the structurally similar intracellular endosomal receptors TLR7 and TLR8, whose activation causes the increased expression of inflammatory cytokines and type I interferons and the associated immune response, antiviral and antitumor activity. Therefore, TLR7 and TLR8 agonists are being investigated as potential drugs for the treatment of various diseases such as cancer, viral infections and asthma.
In the master's thesis, we designed and synthesized various structural analogs with isoxazolo[5,4-d]pyrimidin-4(5H)-one and quinazolin-4(3H)-one scaffold as potential dual agonists of TLR7 and TLR8 receptors. A six-step synthetic procedure was used for the synthesis of both series of compounds. In both cases, the main scaffold was synthesized first, followed by N-alkylation with various 2-bromo esters and reduction of the ester to alcohol. In case of low yields, synthetic procedures were optimized by changing the solvents and reaction conditions.
The synthesized compounds and some intermediates were tested biologically on HEK293 hTLR7 cell lines. Compounds that showed preliminary agonistic activity on TLR7 were also tested on HEK293 hTLR8 cell lines, and their EC50 values for TLR7 and TLR8 were determined. Compounds with isoxazolo[5,4-d]pyrimidin-4(5H)-one scaffold did not show any agonistic activity on neither TLR7 nor TLR8, while quinazolin-4(3H)-one derivatives were found to be agonists on both receptors. The most potent TLR7 agonist was compound 31 (EC50 = 1,70 µM), while the most potent TLR8 agonist was compound 30 (EC50 = 13,2 µM). The results of the biological tests showed that compounds 29, 30 and 31 are dual TLR7/8 agonists in low micromolar concentrations, and thus represent a good starting point for further research and optimization.
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