Antibiotics, Vol. 11, Pages 1750: Potential Nitrogen-Based Heterocyclic Compounds for Treating Infectious Diseases: A Literature Review

The thiazole derivatives (181189), such as 3-substituted-4-aryl-2-[(1-phenylethylidene)hydra-zono]-2,3-dihydrothiazoles and 4-Aryl-2-[2-(1-substituted ethylidene) hydra-zinyl]-thiazoles were prepared through the reaction of bromoacetophenones and (ethylidene)hydrazinecarbothioamides (Scheme 14 and Scheme 15) [30]. Compounds 192209 were evaluated against different Gram-positive and Gram-negative strains of bacteria such as K. pneumonia, P. aeruginosa, S. aureus, and E. coli using reference drugs. The results concluded that compounds 192, 194, 195, 200 and 205 had remarkable activity against E. coli. Furthermore, compounds 195, 192, 196, 200, 209 and 207 reported the promising antibacterial activity against K. pneumonia, which is greater than ciprofloxacin. Compounds 192, 194, 195, 200, 205 and 207 exhibited excellent activity against P. aeruginosa, which was higher as compared to ciprofloxacin. Moreover, 196, 200, 205, 207 and 209 displayed several folds of activity against S. aureus. It was indicated from the results that the existence of a phenyl ring at thiosemicarbazones is necessary for significant activity. Similarly, the allyl, benzyl and phenyl group on the N-position of thiazole (207, 209 and 205) was associated with a significantly high degree of activity [30]. Thirty thiazole derivatives (213242) were synthesized by Zha et al., 2019 as represented in Scheme 16. In vitro antibacterial studies of compounds were carried out against B. subtilis, S. aureus, K. pneumonia and E. coli. The results explained that compounds 231 and 232 demonstrated valuable activity against all the bacterial strains, while compounds 226 and 227 revealed good activity against E. coli, S. aureus and B. subtilis because of the existence of an electron-donating (-OCH3 and -OH) moiety in the molecule [31]. Similarly, Abdel-Galil et al., 2018 reported the synthesis of a series of scaffolds of heterocyclic compounds that contain thiazolidin-5-one and thiazole rings from 4-formylphenyl benzoate precursor (Scheme 17). Antibacterial activity of the synthesized compounds was performed against S. aureus and E. coli. The results reported that compounds 244, 245 and 248 exhibited dominant antibacterial activity against the S. aureus bacterial strain, while 6 displayed exceptional activity against E. coli. Moreover, compounds 251, 250 and 246 demonstrated acceptable activity across the positive strain and compounds 244 and 247 revealed good activity against the negative strain (Table 1). The existence of ethoxy, methyl, amino, azo, hydroxyl, or methoxy groups assimilated with phenylbenzoate, cyanoacetyl hydrazine, and carbamothioylhydrazone moiety in the derivatives of thiazole depicted excellent antibacterial activity. Furthermore, the presence of an electron-withdrawing group rather than an electron-donating group in compound 249 reduced the activity. The compound 248 showed the excellent antibacterial activity against S. aureus and E. coli bacterial strains, which may be due to the –CH3 group at the 4th position of thiazole [32]. The synthesis of thiazoles from allyl thiourea as given in Scheme 18 was carried out by Khare, et al., 2016. All the synthesized compounds (253258) exhibited moderate activity [33]. Beyzaei, et al., 2017 illustrated the synthesis of 4-thiazolylpyrazole (264269) compounds from the modified Hantzsch method, in the presence of catalyst MgO nanoparticles as represented in Scheme 19. An evaluation of the in vitro antibacterial activity of the synthesized compounds was also performed against 21 bacteria. Compounds 264 to 269 of 4-thiazolylpyrazoles exhibited inhibition activities against S. agalactiae, P. aeruginosa and S. pneumoniae. In comparison with the other compounds, thiazoles 265 and 269 were potent against eight pathogenic bacterial strains, and as such they appeared as one of the effective broad-spectrum agents [34]. Mohamed et al., 2018 reported the synthesis of thiazole derivatives as shown in Scheme 20 and observed that the derivative of 272 had greater antibacterial activity. This may be due to the thiazole’s molecular structure and also the existence of the NH group, which helps the adsorption of a compound onto the surface of bacteria, perforation into their cell membrane, and finally eradication of the membrane, causing the death of bacteria [35]. Seven unique derivatives of pleuromutilin with the moiety of thioether and thiazole-5-carboxamide (277283) were prepared by Wang et al., 2011 as represented in Scheme 21. The in vitro antibacterial activity of the synthesized compounds was evaluated against two positive strains of bacteria viz. S. aureus ATCC26112 and S. aureus SC. The compounds exhibited valuable activity against the bacteria and it can be examined that the bacterial strain of S. aureus was more susceptible than S. aureus [36].

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