Novel highly functionalized 1,4-naphthoquinone 2-iminothiazole hybrids: Synthesis, photophysical properties, crystal structure, DFT studies, and anti(myco)bacterial/antifungal activity

Abstract

In this paper, a series of novel highly functionalized 1,4-naphthoquinone 2-iminothiazole hybrids were synthesized via a cyclization reaction of 2,3-diaminonaphthalene-1,4-dione N-aroylthioureas and α-bromoketones in good to excellent yields (74–94%). The stereochemistry of one of the 1,4-naphthoquinone 2-iminothiazole products was characterized by single crystal X-ray diffraction technique. Photophysical properties of the compounds in DMSO, HAc and THF were determined by using UV-vis spectroscopy. The ground state geometries and the absorption spectra of the compounds were also determined using Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) at B3LYP/631 + g(d,p) level of theory. The computed results are consistent with experimental values. An antimicrobial screening was performed against various bacterial (S. aureus, B. subtilis, A. hydrophila, E. coli and A. baumannii), fungal (C. glabrata C. tropicalis and C. albicans) and mycobacterial (M. tuberculosis H37Rv) strains. The compounds exhibited moderate antibacterial (62.5–500 μg/mL) and antifungal (31.25–250 μg/mL) activities against the aforementioned bacterial and fungal strains. Two of the compounds, 7j (3.90 μg/mL) and 7l (1.96 μg/mL), exhibited a significant antimycobacterial activity against the M. tuberculosis H37Rv strain, when compared to the reference drugs (Isoniazid: 0.98 μg/mL, Ethambutol: 1.96 μg/mL). The results showed that these novel 1,4-naphthoquinone 2-iminothiazole hybrids can be considered as potential pharmacophore groups for the development of new antimycobacterial agents.