Synthesis, Spectral Characterization and Biological Evaluation of New Substituted 2H-Pyrimido[2,1-b]benzothiazol-2-ones

Background: During the last years, condensed pyrimidine compounds have received much attention because of their immense biological properties. These compounds have gained too much interest as proven by large number of reviews and research articles published in the current years. The aim of this manuscript is to develop a one pot reaction for the synthesis of benzothiazole coupled pyrimidine compounds using alkynoic acids and substituted 2-aminobenzothiazoles under normal reaction conditions. Methods: Different 2-aminobenzothiazoles and substituted alkynoic acids have been used to synthesize 2H-Pyrimido[2,1-b]benzothiazol-2-ones via conjugate addition of the imino nitrogen of 2-aminobenzothiazoles to alkyne β-carbon atom of acetylenic acids followed by ring closure. The structural assignments of the synthesized compounds were made on the basis of elemental analysis and spectroscopic data (IR, 1H NMR, 13C NMR and Mass). The synthesized compounds were evaluated for their antioxidant (DPPH and ABTS assays) and antimicrobial activities (using broth microdilution method). Results: The synthesized compounds with different substituent’s were obtained in moderate to good yields (56-75%). Most of the compounds (6a, 7a, 8a) were found to be more active in DPPH and ABTS assays and have also showed significant antibacterial and antifungal activity. Conclusion: A series of novel compounds with high activity and low toxicity synthesized, showed excellent antioxidant activity due to presence of electron donating groups on the ring. Some of the synthesized compounds showed better antimicrobial activity as the electron withdrawing groups on the aromatic ring increases the activity. Thus, the synthesized compounds shall prove as future antioxidant and antimicrobial drugs with further research.