Novel nano-size and crab-like biological-based glycoluril with sulfonic acid tags as a reusable catalyst: its application to the synthesis of new mono- and bis-spiropyrans and their in vitro biological studies

Abstract

Herein novel crab-like biological-based glycoluril with sulfonic acid tags, namely glycoluril tetrakis(butane-1-sulfonic acid) (GTBSA), was prepared in nano-size form and fully characterized via several techniques, such as ¹H and ¹³C NMR, Fourier transform infrared spectroscopy (FT-IR), CHNS analysis, mass spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential thermal gravimetric analysis (DTG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is proved that this novel nanostructured catalyst is an efficient catalyst for the synthesis of novel spiropyrans via the one-pot multi-component condensation of isatine, naphthalene-2,3-diol or 2,5-dihydroxycyclohexa-2,5-diene-1,4-dione, and malononitrile or 1,3-dicarbonyl compounds in refluxing water. The mild reaction conditions, easy work-up, good to excellent yields and reusability of the catalyst are the major advantages of the described procedure. Results from DPPH radical scavenging assays showed that the synthesized compounds have eminent antioxidant efficacies (IC₅₀ : 0.16 ± 0.01 to 0.55 ± 0.02 mg mL⁻¹). Moreover, the in vitro antibacterial activities of the compounds were assessed against 4 Gram-positive and Gram-negative bacterial strains via a disc diffusion method. The results showed that compounds 2S and 3S possess high suitability for E. coli growth inhibition, comparable to the positive control gentamicin.