Azo dyes are one of the most important classes of chromophores, which are usually characterized by nitrogen-nitrogen double bonds (–N=N–). Azo dyes have a variety of applications in scientific, industrial, and pharmaceutical fields.
Synthesis of Heterocycle-Containing Azo Dyes and Their Derivatives
Compared with the dyes derived from simple aromatic amines, the azo dyes doped with heterocycles showed enhanced coloring properties, tinctorial strength, thermal stability, and more positive solvatochromic behavior. Nowadays, the synthesis of heterocycle-containing azo dyes and their derivatives has attracted special attention because of their strong biological activities. Therefore, researchers have synthesized and reported various analogs of heterocycle-containing azo dyes and their derivatives by different methods.
Table 1. Some synthesis methodologies of azo dyes containing various heterocyclic moieties (Mezgebe K, Mulugeta E. 2022)
| azo dyes containing thiophene |
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| Schiff base-azo dye derivative |
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| azo dye derivatives incorporating pyrrole |
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| azo dye derivatives containing pyrrole |
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| azo dye derivatives containing imidazole |
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| azo-imidazole derivatives |
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Antibacterial Activity
One of the most exciting aspects of heterocycle-containing azo dyes and their derivatives is their strong antibacterial activity. Recent studies have shown that some azo dyes containing heterocycles have remarkable antibacterial properties. Some synthetic azo dyes show antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus pyogenus.
Table 1. Chemical structures of antibacterial active azo dye derivatives incorporating heterocyclic moieties. (Mezgebe K, Mulugeta E. 2022)
Antifungal Activity
In addition to antibacterial activity, heterocycle-containing azo dyes also showed significant antifungal activity. Scientists have found that the synthetic azo dyes have antifungal properties against two pathogenic strains, viz. A. flavus and C. albicans. These azo dyes show good antibacterial, anti-mycobacterial and anticancer activities, indicating that these compounds can effectively inhibit a variety of diseases.
Anti-Tuberculosis Activity
Another exciting discovery in the realm of heterocycle-containing azo dyes is their potential anti-tuberculosis activity. Tuberculosis is still one of the most dangerous infectious diseases in the world. Recent studies have shown that some heterocycle-containing azo dyes have anti-tuberculosis activity. These compounds show the prospect of being used as an adjuvant therapy for conventional tuberculosis treatment and potentially improve the therapeutic efficacy.
Conclusion
In addition to the antibacterial, antifungal, and anti-tuberculosis activities mentioned above, heterocycle-containing azo dyes have also shown a wide range of biological activities, such as anticancer activity, anti-inflammatory activity, antioxidant activity and so on. At present, researchers are also exploring the biological activity of various azo dyes by adding heterocyclic components in the synthesis, so that they have a wider range of applications, especially in the field of pharmaceuticals. In the process of synthesizing various azo dyes, heterocyclic compounds were added by diazotization coupling reaction, and then post-modification was carried out to improve their biological and pharmaceutical activity. Heterocycle-containing azo dyes and their derivatives make a great contribution to the discovery of new, effective, and bioactive drugs with broad-spectrum activity. Therefore, the synthesis of azo dyes with heterocyclic parts needs to be further studied to enhance their pharmacological activity and develop new drugs.
Reference
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Mezgebe K, Mulugeta E. Synthesis and pharmacological activities of azo dye derivatives incorporating heterocyclic scaffolds: a review. RSC Adv. 2022;12(40):25932-25946.
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