| Summary: | A series of novel macroacyclic Schiff base ligands and their Cu (II) complexes were synthesised via reacting dicarbonyls of varying chain lengths with <i>S</i>-methyl dithiocarbazate (SMDTC) and <i>S</i>-benzyl dithiocarbazate (SBDTC) followed by coordination with Cu (II) ions. X-ray crystal structures were obtained for compound <b>4</b>, an SBDTC-diacetyl analogue, and <b>Cu7</b>, an SMDTC-hexanedione Cu (II) complex. Anticancer evaluation of the compounds showed that <b>Cu1</b>, an SMDTC-glyoxal complex, demonstrated the highest cytotoxic activity against MCF-7 and MDA-MB-231 breast cancer cells with IC<sub>50</sub> values of 1.7 µM and 1.4 µM, respectively. There was no clear pattern observed between the effect of chain length and cytotoxic activity; however, SMDTC-derived analogues were more active than SBDTC-derived analogues against MDA-MB-231 cells. The antibacterial assay showed that <i>K. rhizophila</i> was the most susceptible bacteria to the compounds, followed by <i>S. aureus</i>. Compound <b>4</b> and the SMDTC-derived analogues <b>3</b>, <b>5</b>, <b>Cu7</b> and <b>Cu9</b> possessed the highest antibacterial activity. These active analogues were further assessed, whereby <b>3</b> possessed the highest antibacterial activity with an MIC of <24.4 µg/mL against <i>K. rhizophila</i> and <i>S. aureus</i>. Further antibacterial studies showed that at least compounds <b>4</b> and <b>5</b> were bactericidal. Thus, <b>Cu1</b> and <b>3</b> were the most promising anticancer and antibacterial agents, respectively.
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