Design, synthesis and pharmacological evaluation of novel fused pyrimidine analogues as anticancer agents.
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Cancer is a multifaceted disease considered as the most serious health burden all over the world. Due to existing of limited anticancer drugs and detrimental side effects, the anticancer research has been challenging. An investigation on identifying novel potential drugs is highly required to treat this serious abnormal cell growth. Advanced potential anticancer drug entrants are crucially required to combat the drawbacks linked with current drugs or line of therapies. Extensive investigations are being carried out on synthetic manipulations of heterocyclic aromatic compounds (purines) for developing efficient and potent anticancer drugs. Besides, these manipulations also offer effective leads for further optimization. Therefore, this project is an effort in detecting a novel and potent anticancer leads based on bioisostere of purines called pyrazolopyrimidines. In this research project we have performed an comprehensive literature survey of structural isomers of pyrazolopyrimidines (pyrazolo[1,5-a]pyrimidine and pyrazolo[4,3-d]pyrimidine) for their synthetic approaches and biological activities with special emphasis on structure-activity relationship (SAR) studies. These SAR studies prompted us to implement the observed studies on one of the structural isomer of pyrazolopyrimidine called pyrazolo[3,4-d]pyrimidine. And further, we have synthesized some novel series of pyrazolo[3,4-d]pyrimidine derivatives with various substituents at C-4 and C-6 positions of the scaffold. A total 71 compounds comprising of phenethyl and pentane hybrids (7-43, Chapter 4), benzoyl hybrids (5a-5h, 6a-6d and 7a-7c, Chapter 5) and lastly phenylcarbamoyl acetamide hybrids (9a-9s, Chapter 6) have been synthesized by molecular hybridization approach as outlined in schemes of respective chapters. The completion of reaction and the purity of novel synthesized compounds were confirmed by chromatographic analysis. All the newly synthesized compounds displayed acceptable analysis for their anticipated structures, which were established based on physicochemical and spectral data (IR, 1 H NMR, 13C NMR and HRMS). All synthesized compounds were primarily evaluated for their in vitro anticancer activities at Laboratory of Growth Regulators, Centre of the Region Hana for Biotechnological and Agricultural Research, Palacky University & Institute of Experimental Botany ASCR, Slechtitelu 27, 78371 Olomouc, Czech Republic. From the systematic analysis of anticancer activity, results obtained following key observations were made. i. Structural isomers of fused pyrimidines have been looked upon for molecular changes in emerging drug like candidates. Pyrazolopyrimidine is a bioisostere of purines has acquired considerable importance due to its diverse, facile and general synthetic methodologies with great medicinal importance. Several analogs of this scaffold have emerged as a promising leads in the design of some novel pharmacologically active compounds with enhanced iii metabolic, pharmacokinetic and pharmacological profiles, representing that there is plenty scope for considering pyrazolopyrimidine as a structural framework for evolving effective leads. ii. Chapter 4: From the 37 novel phenethyl and alkyl pentane pyrazolo[3,4-d]pyrimidine derivatives synthesized and evaluated for CDK2/Cyclin E, Abl kinase inhibitory activity and anti-proliferative activity against K-562 (chronic myelogeneous leukemia) and MCF7 (breast adenocarcinoma) cell lines. From the tested results, compounds 11 (CDK: IC50 = 5.1 µM; Abl: ˃12.5 µM), 8 (CDK: IC50 = 7.8 µM; Abl: ˃25 µM) and 36 (CDK: IC50 = 8.8 µM; Abl: >25 µM) exhibited significant inhibitory activity. Further from this series, most of the synthesized compounds indicated prominent anti-proliferative effects with IC50 value ranging from 19.2 µM to 27.4 µM. Incorporation of monosubstituted phenyl groups at C-4 of the pyrazolo[3,4-d]pyrimidine nucleus had favored for most prominent anticancer activity. iii. Chapter 5: Among the 15 novel benzoyl hybrids synthesized and evaluated, compounds 5a and 6c displayed (CDK2: IC50 = 8.8 µM, 6.8 µM) commendable inhibitory activity and notable anti-proliferative activity ranging from 18.9 µM to 89.3 µM). Presence of heteroatom containing bicyclic moieties at C-4 of the nucleus enhanced both inhibitory and anti-proliferative activity. iv. Chapter 6: Of the 19 novel phenylcarbamoyl acetamide hybrids synthesized and tested, compounds 9a, 9c, 9g, 9m and 9p showed moderate enzymatic inhibitory activity with an IC50 value ˃12.5 µM against both CDK2 and Abl kinases while, remaining compounds of this series could not generate IC50 values due to solubility limit (IC50 = ˃25 µM to ˃100 µM).