A Synthesis of Novel Pyrazolylthienopyrimidine Derivatives as IL-6/STAT3 Inhibitors

Abstract

The interleukin-6 (IL-6) as a pro-inflammatory cytokine with TNF-α and IL-8 plays a central role in the induction of inflammation as well as in the continuation of a chronic inflammatory immune response. And, an over-production of IL-6 have been found in inflammatory tissues of several diseases, such as rheumatoid arthritis, psoriasis, inflammatory bowel disease, osteoarthritis, multiple myeloma, and also in human atherosclerotic plaque. IL-6 binds to its receptor (IL-6R, a ligand-binding 80 kDa glycoprotein chain) and induces the homodimerization of a signal transducing glycoprotein 130 (gp130), leading to the activation of the Janus kinase (Jak)/signal transducer and signal activator of transcription-3 (STAT3). STAT3 is also frequently overexpressed or persistently activated in most tumors and cancer, and activated STAT3 was found to suppress tumorimmune surveillance. Therefore, the blockade of STAT3 activation pathway stimulated by IL-6 could be an attractive therapeutic target for discovery of new drugs and is currently under intense investigation. In the other hand, thienopyrimidine and their derivatives are an important class of the most biologically active compounds, having diverse activities such as antibacterial, analgesic, antitumor, antioxidant, P2Y12 platelet aggregation inhibitor, and Aurora kinase inhibitor. We have synthesized over the years thienopyrimidine derivatives of promising biological activity. As part of a programme to discover novel inhibitors using thienopyrimidines, some of these compounds were found to possess potent IL-6/STAT3 inhibition. This result encouraged us to prepare new thienopyrimidines having pyrazole moiety in attempt to improve the IL-6/STAT3 inhibitory activity. Pyrazoles have been also reported to have a wide range of biological properties. Moreover, incorporation of pyrazole moiety into other heterocycles gave various pharmacological activities. Although a lot of methodologies have been developed over the years, the regiocontrolled and practical synthesis of 1,5-pyrazoles over 1,3-pyrazole is still less literature precedent and remains a noteworthy challenge. To the best of our knowledge no report have so far made in the synthesis of regioselective pyrazolylthienopyrimidine by the one pot reaction of (E)-3-(dimethylamino)-1-phenylprop-2en-1-one 2 with 4-hydrazinothienopyrimidine 1. Herein we report the efficient synthesis and biological activity of novel pyrazolylthienopyrimidine derivatives, 3A and 3B, as IL-6/ STAT3 inhibitor. The required reactant 2 can be easily prepared by the reaction of acetophenone with N,N-dimethylformamide dimethyl acetal (DMFDMA) in refluxing xylene. The reactants, 1A and 1B, were also obtained according to the procedure we have previously reported. In our initial studies toward synthesis of substituted pyrazolylthienopyrimidine, (E)-3-(dimethylamino)-1-phenylprop-2-en-1-one (2a) was reacted with 4-hydrazinothieno[2,3-d]pyrimidine (1A) in THF at reflux for 10 h. It was found that three products from the reaction mixture were formed, respectively, 4-(5-phenyl1H-pyrazol-1-yl)thieno[2,3-d]pyrimidine (3Aa, 1,5-isomer, 35%), 4-(3-phenyl-1H-pyrazol-1-yl)thieno[2,3-d]pyrimidine (4Aa, 1,3-isomer, 20%) and 1,2-adduct (5Aa, 15%), as shown Table 1. Accordingly, reaction optimization for the regioselective formation of 1,5-isomer was investigated at the various conditions (catalyst, reaction temperature and solvent). When the same reaction was carried out in refluxing ethanol in the presence of 1 equiv HCl as a catalyst, 3Aa was obtained as a major product in optimum yield (65%, Table 1, entry 6) within 6 h. Next, as depicted in Table 2, the reaction of 1A with 2b-h Table 1. Optimization for the reaction of 1A with 2a