THIOPHENES : PROPERTIES, SYNTHESIS AND ITS BIOLOGICAL ACTIVITIES

Thiophene (C₄H₄S), a representative sulfur-containing five-membered heteroaromatic compound, has been pivotal in contemporary chemistry due to its distinctive electronic characteristics, structural adaptability, and pharmacological relevance. Its aromatic stabilization, elevated polarizability, and regioselective reactivity differentiate it from purely carbocyclic counterparts, facilitating its application in materials science, synthetic methodologies, and drug development. Foundational thiophene chemistry was established through classical reactions such as the Paal–Knorr, Fiesselmann, Gewald, and Hinsberg syntheses. More recent advancements encompass metal-catalyzed cyclizations, C–H functionalization techniques, and solvent-free mechanochemical approaches. These innovations have enhanced regioselectivity and yield efficiency while adhering to the principles of green and sustainable chemistry. In medicinal chemistry, thiophene serves as a bioisosteric replacement for phenyl groups, influencing lipophilicity, metabolic stability, and receptor binding affinity. A diverse array of thiophene derivatives exhibit a broad spectrum of biological activities, including antibacterial, antifungal, anticancer, antioxidant, anti-inflammatory, neuroactive, and antiparasitic effects, complemented by naturally occurring thiophenes isolated from botanical sources. Structure–activity relationship analyses underscore the significance of substitution at the α-positions, the presence of electron-donating substituents, and heteroaryl linkages in modulating biological potency. This review integrates synthetic and biological insights into thiophene chemistry, with a focus on its pharmacological properties, mechanistic aspects, absorption, distribution, metabolism, and excretion (ADME) considerations, as well as prospective avenues for future investigation.