Design, Synthesis, And Structure-Activity-Relationship Of Tetrahydropyrido[4,3-d]Pyrimidine Derivatives As Potent Smoothened Inhibitors

The Hedgehog(Hh) signaling pathway plays a pivotal role in the regulation of cell proliferation and differentiation during embryonic development. However, uncontrolled activation of the Hh pathway leads to increase cell proliferation and tumour formation. In recent years, the scientists have paied more and more attention to the Hedgehog pathway. And the pharmaceutical companies and research institutions have been focus on targeting Hh pathway’s, especially targeting Smoothened’s(G protein-coupled receptor family), small molecule inhibitors. FDA approved the Hedgehog pathway antagonists Vismodegib and Sonidegib to treat to adult patients with basal cell carcinoma in 2012 and 2015, respectively.However, Vismodegib has poor physical-chemical properties(melting point 264°C, the solubility of 9.5 μg/mL at pH 6.5), and drug resistance was emergent following the treatment process. In response to these defects a new molecular skeleton was designed by the scaffold hopping principle, and SP3-hybridized carbon atom is introduced in the center of the molecule, in order to make the molecule more flexible and unsmooth. We obtained two types of anologues, the clogP value of the tetrahydroimidazo[1,2-a]pyrazine anologues was low, but the potency was not good; tetrahydrothiazolo[5,4-c]pyridine anologues had good activity and ideal physical-chemical properties, and the clogP value was relatively high. On this basis, we adopted the classic bioisostere principles and designed new skeleton compounds consisting of tetrahydropyrido[4,3-d]pyrimidine. New compounds were synthesized, and 14 compounds exhibited low nanomolar inhibition of Hh signaling, more potent than Vismodegib. The activity of the best compound 1-72 was twenty-fold more potent than that of Vismodegib. Compounds 1-11, 1-56 and 1-59 showed good physical-chemical properties, under the current experimental conditions, while the melting point was lower than that of Vismodegib and the solubility was improved more than twenty-fold at pH 6.5.The inhibitions of compounds 1-19, 1-21, 1-48, 1-59 and 1-72 on five major metabolic enzymes were tested, the IC50 of these compounds were all above 10 μM, and showed good safety in vitro. The compounds 1-11, 1-48, 1-52 and 1-56 showed moderate clearance in vitro on human liver microsomes stability test. Compounds 1-11, 1-56, 1-59 and 1-72 showed good pharmacokinetic profile with low clearance and good oral bioavailability(74 %, 53% and 110% for 1-56, 1-59 and 1-72, respectively).In summary, we have got new skeleton compounds with more potent activity and better physical-chemical properties than Vismodegib through scaffold hopping and classic bioisosterism principles. These compounds will be used for the further study on pharmacodynamics.