Synthesis, crystal structure, theoretical studies and biological properties of three novel trigonal prismatic Co(II), Ni(II) and Cu(II) macroacyclic Schiff base complexes incorporating piperazine moiety

Recent advances in the synthesis of piperazine based ligands and metal complexes and their applications

The piperazine scaffold is a privileged structure frequently found in biologically active compounds. Piperazine nucleus is found in many marketed drugs in the realm of antidepressants (amoxapine), antipsychotics (bifeprunox), antihistamines (cyclizine and oxatomide), antifungals (itraconazole), antibiotics (ciprofloxacin), etc. This is one of the reasons why piperazine based compounds are gaining prominence in today's research. In addition to the ring carbons, substitution in the nitrogen atom of piperazine not only creates potential drug molecules but also makes it unique with versatile binding possibilities with metal ions. Piperazine ring-based compounds find their application in biological systems with antihistamine, anticancer, antimicrobial and antioxidant properties. They have also been successfully used in the field of catalysis and metal organic frameworks (MOFs). The present review focuses on the synthesis and application of different piperazine derivatives and their metal complexes having diverse applications.

Metal Complexes as Promising Agents for Biomedical Applications

Background::

In this review article, a brief overview of novel metallotherapeutic agents (with an emphasis on the complexes of essential biometals) promising for medical application is presented. We have also focused on the recent work carried out by our research team, specifically the development of redox-active antimicrobial complexes of sterically hindered diphenols with some essential biometals (copper, zinc, nickel).

Results::

The complexes of essential metals (manganese, iron, cobalt, nickel, copper, zinc) described in the review show diverse in vitro biological activities, ranging from antimicrobial and antiinflammatory to antiproliferative and enzyme inhibitory. It is necessary to emphasize that the type of organic ligands in these metal complexes seems to be responsible for their pharmacological activities. In the last decades, there has been a significant interest in synthesis and biological evaluation of metal complexes with redox-active ligands. A substantial step in the development of these redox-active agents is the study of their physicochemical and biological properties, including investigations in vitro of model enzyme systems, which can provide evidence on a plausible mechanism underlying the pharmacological activity. When considering the peculiarities of the pharmacological activity of the sterically hindered diphenol derivatives and their nickel(II), copper(II) and zinc(II) complexes synthesized, we took into account the following: (i) all these compounds are potential antioxidants and (ii) their antimicrobial activity possibly results from their ability to affect the electron-transport chain.

Conclusion::

We obtained novel data demonstrating that the level of antibacterial and antifungal activity in the series of the above-mentioned metal-based antimicrobials depends not only on the nature of the phenolic ligands and complexing metal ions, but also on the lipophilicity and reducing ability of the ligands and metal complexes, specifically regarding the potential biotargets of their antimicrobial action – ferricytochrome c and the superoxide anion radical. The combination of antibacterial, antifungal and antioxidant activity allows one to consider these compounds as promising substances for developing therapeutic agents with a broad spectrum of activities.

Phosphate and polyphosphate anion recognition by a dinuclear copper(ii) complex of an unsymmetrical squaramide

At pH = 7.4, ATP⁴⁻ is selectively removed from water containing PhPO₄²⁻, Haep⁻, AMP²⁻ and ADP³⁻ by the studied squaramide-based dicopper(ii) complex.