Novel ferrocene-pyrazolo[1,5-a]pyrimidine hybrids: A facile environment-friendly regioselective synthesis, structure elucidation, and their antioxidant, antibacterial, and anti-biofilm activities

It was observed that when two prominent bioactive compounds fused together, the new hybrid showed much more promising possessions Aiming this, here we have fused pyrazolo[1,5-a]pyrimidines with ferrocene, both of which are popularly known as the bio-active molecular core, employing a very simple and facile synthetic strategy using a mild acid KHSO4 as a catalyst under ultrasonic irradiation. The structures of these synthesized novel compounds were confirmed by their spectral and analytical data. The single-crystal X-ray crystallographic analysis of a selected compound reveals that the 7-ferrocenyl-pyrazolo[1,5-a]pyrimidine (C22H16ClFeN3) hybrid interestingly exists as a dimer and forms a triclinic crystal system with P-1 space group (no. 2), a = 7.554(3) angstrom, b = 13.650(6) angstrom, c = 18.444(8) angstrom, alpha = 96.938(7) degrees , beta = 90.034(7) degrees, gamma = 106.015(6) degrees, V = 1813.5(14) angstrom(3), Z = 4, mu(MoK alpha)= 0.990 mm(-1), wavelength = 0.71073 angstrom, D-calc = 1.515 g/cm(3) with 42808 measured reflection (4.452 degrees <= 2 theta <= 58.312 degrees), 9524 unique reflections (R-int = 0.1267, R-sigma = 0.1390) were used in all the calculations. The final R-1 obtained was 0.0570 (I>2 sigma(I)) with wR(2) = 0.1656 for all data. Most of the compounds exhibited encouraging antioxidant activities like compounds 3b-c, 3k-1 and 3n exhibited prominent nitric-oxide scavenging activities, while compounds 3a-d, 3g, 3k, 3n, and 3o are promising DPPH-scavengers. Compounds 3i-k and 3m exhibited antibacterial activities at MIC of 500 mu g/ mL, while 3p exhibited activities at MIC of 250 mu g/mL. Five of the compounds, 3i-k, 3m, and 3p, were found to possess anti-biofilm activities against both Gram-positive and Gram-negative bacteria.