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Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents
Published on: May 28, 2014
Pyrazine functionalized Ag(I) and Au(I)-NHC complexes are potential antibacterial agents
G Roymahapatra1, S M Mandal, W F Porto
1School of Applied Sciences, Haldia Institute of Technology, Haldia -721657, WB, India.
Current Medicinal Chemistry
|June 12, 2012
Summary
Novel pyrazine-functionalized silver and gold complexes show potent antibacterial activity against antibiotic-resistant pathogens. These compounds also inhibit bacterial biofilm formation and damage cell walls, offering a new avenue for antimicrobial drug development.
Area of Science:
- Medicinal Chemistry
- Inorganic Chemistry
- Microbiology
Background:
- Antimicrobial resistance (AMR) is a global health crisis, necessitating novel antibiotics with unique mechanisms of action.
- Traditional antibiotics are becoming increasingly ineffective against resistant bacterial strains.
- There is an urgent need for new antimicrobial agents to combat multidrug-resistant bacteria.
Purpose of the Study:
- To synthesize and characterize a novel class of pyrazine-functionalized silver(I) and gold(I)-N-heterocyclic carbene (NHC) complexes.
- To evaluate the antibacterial efficacy of these novel complexes against human pathogens, including antibiotic-resistant strains.
- To investigate the mechanism of action, including biofilm inhibition and cellular damage.
Main Methods:
- Synthesis and structural elucidation of Ag(I) and Au(I)-NHC complexes with pyrazine ligands (L-1, L-2, L-3).
- In vitro antimicrobial activity testing against various bacterial pathogens.
- Biofilm inhibition assays using Gram-positive (Streptococcus mutans) and Gram-negative (Escherichia coli) bacteria.
- Assessment of bacterial cell wall damage and membrane permeability.
- Computational studies to correlate structure with reactivity and activity.
Main Results:
- Two specific complexes, chloro[2,6-bis(1-methylimidazol)pyrazine]gold(I) (2b) and chloro[2,6-bis(1-methylimidazol)pyrazine]silver(I) (2a), exhibited potent antimicrobial activity, surpassing conventional antibiotics.
- Complexes 2b and 2a effectively inhibited biofilm formation in both S. mutans and E. coli.
- These active complexes caused significant damage to bacterial cell walls and increased membrane permeability.
- Binding studies indicated strong interaction of 2b and 2a with peptidoglycan layers (Lys and Dap-type).
- Theoretical studies suggested higher reactivity of complexes 2b and 2a, correlating with their enhanced antibacterial effects.
Conclusions:
- Pyrazine-functionalized Ag(I) and Au(I)-NHC complexes represent a promising new class of antibacterial agents.
- Complexes 2a and 2b demonstrate significant potential for combating antibiotic-resistant bacteria and preventing biofilm formation.
- The observed mechanism involves bacterial cell wall and membrane disruption, offering a novel approach to antimicrobial therapy.
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The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the para position.
01:22Preparation of 1° Amines: Azide Synthesis
Direct alkylation of ammonia produces polyalkylated amines, along with a quaternary ammonium salt. To exclusively prepare primary amines, the azide synthesis method can be used.
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum...
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum...
01:26Physical Properties of Amines
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01:25Basicity of Heterocyclic Aromatic Amines
Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
01:19Structure of Amines
The hybridized nitrogen atom in amines possesses a lone pair of electrons and is bound to three substituents with a bond angle of around 108°, which is less than the tetrahedral angle of 109.5°. However, the C–N–H bond angle is slightly larger at 112°, with a carbon–nitrogen bond length of 147 pm. This carbon–nitrogen bond length of of amines is longer than the carbon–oxygen bond of alcohols (143 pm) but shorter than alkanes’ carbon–carbon bond (154 pm). These aspects are illustrated in Figure...
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