Studies on the biological activity of some nitrothiophenes

The biological activity of nineteen substituted thiophenes (3) have been assessed by evaluating the minimum inhibitory concentration required to inhibit the growth of E. coli, M. luteus and A. niger. The series displays a wide range of activities with 2-chloro-3,5-dinitrothiophene (3a) or 2-bromo-3,5-dinitrothiophene (3c) showing the highest activity against all three organisms, while the simplest compound of the series, 2-nitrothiophene (3s) shows the smallest activity in each case. The mode of action of 3a and 3c is thought to involve nucleophilic attack by intracellular thiols at the 2-position of the heterocyclic ring leading to displacement of halogen, but other active derivatives, such as 2,4-dinitrothiophene (3h) and 5-nitrothiophene-2-carbaldehyde (3d) which have no displaceable halogen or leaving group are thought to act by forming Meisenheimer complexes.