Synthesis, crystal structures and antimicrobial activities of 3-methyl and 3-bromo substituted benzo[b]thiophene based thiosemicarbazones

A series of thiosemicarbazones (TSCs) (<b>L^1–5</b>) containing benzothiophen moiety were prepared via the reaction of 3-methyl/3-bromobenzo[b]thiophene-2-carboxaldehyde with appropriate thiosemicarbazides. The compounds were confirmed by elemental analysis, FT-IR, ¹H NMR, MALDI-TOF and single crystal X-Ray diffraction techniques. The compounds exist in the E conformation with respect to the azomethine C = N double bond as confirmed by their C8/C9/N1/N2 torsion angles being 178.4(2)° (<b>L¹</b>), – 175.2(5)/177.4(5)° (<b>L²</b>), 177.5(2)° (<b>L³</b>), 179.7(3)° (<b>L⁴</b>), and – 177.4(7)° (<b>L⁵</b>). These compounds were researched for their antibacterial activity against Gram-positive bacteria (<i>E. faecalis</i> and <i>S. aureus</i>), Gram-negative bacteria (<i>E. coli, P. aeruginosa</i> and <i>S. marcescens</i>) and antifungal activity against a yeast species <i>C. albicans</i>. The ligands possessed varying degrees of antimicrobial activity. Generally, the compounds demonstrated higher efficacy against gram-positive bacteria than gram-negative ones. The antifungal activity of the compounds against <i>C. albicans</i> was found to be lower in comparison to their activity against bacteria.