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. 2024 Dec 15;29(24):5917.
doi: 10.3390/molecules29245917.

Heteroleptic Coumarin-Based Silver(I) Complexes: Possible New Antimicrobial Agents

Erika Mooney  1   2 , Brendan Twamley  3 , Gordon Cooke  1   2 , Emma Caraher  1   2 , Matthias Tacke  4 , Fintan Kelleher  1   2 , Bernadette S Creaven  2   5
Affiliations

Heteroleptic Coumarin-Based Silver(I) Complexes: Possible New Antimicrobial Agents

Erika Mooney et al. Molecules. .

Abstract

Heteroleptic coumarin-based silver(I) complexes with improved solubility profiles were synthesised using either triphenylphosphine or an N-heterocyclic carbene as adduct ligands, and were fully characterised using IR and NMR spectroscopy, elemental analysis, and, where possible, X-ray crystallography. The triphenylphosphine adducts formed well-resolved structures, where the oxyacetate ligands asymmetrically chelated the silver(I) ion in a bidentate chelating mode, and the silver(I) ion was also bound to two triphenylphosphine ligands. The solubility profile and photostability of the adducts were considerably improved compared to those of previously isolated simple coumarin silver(I) complexes. Analysis of the coumarin N-heterocyclic carbene(NHC) silver(I) adduct indicated that it likely formed as a complex aggregate species with an overall stoichiometry of 1:1:1 coumarin:Ag(I):NHC. The Kirby Bauer assay and broth microdilution assays were used to assess the silver(I) complexes' and adducts' antimicrobial activity against pathogenic strains of Pseudomonas aeruginosa, Escherichia coli, and MRSA. Interestingly, the formation of more soluble complexes did not increase the activity of the silver(I) complexes and, in effect, made them less effective antimicrobial agents, particularly against Escherichia coli and Pseudomonas aeruginosa, although they retained their activity against MRSA.

Keywords: antimicrobial; coumarin; hybrid; photostability; silver(I).

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Chemical structures of silver(I) complexes (i) SBC3 and (ii) 2-(8-acetyl-2-oxo-2H-chromen-7-yl)oxyacetatesilver(I).
Scheme 1
Scheme 1
Synthetic protocols used toward the synthesis of bis-triphenylphosphino adducts (5 and 6) and substituted coumarin-7-oxyaceto-silver-NHC* complexes (11) R = -COCH3 for 5, 7, 9, and 11 and R = H for 6, 8, and 10.
Figure 2
Figure 2
General numbering system for the assignment of NMR spectra of 3–6.
Figure 3
Figure 3
Molecular structure of [bis-triphenylphosphino)-(8-acetyl-2-oxo-2H-chromen-7-oxyacetosilver(I)] (5) with displacement at 50% probability, hydrogen atoms and disordered solvent omitted for clarity. Heteroatoms labelled only. See Figure S3.3a.
Figure 4
Figure 4
Molecular structure of [bis-triphenylphosphino)-(2-oxo-2H-chromen-7-oxyacetosilver(I)] (6) with displacement at 50% probability, hydrogen atoms and solvent omitted for clarity. Heteroatoms labelled only. See Figure S3.4a.
Figure 5
Figure 5
Numbering system used for the assignment of the 1H and 13C NMR spectra of compounds 9 and 10, where R1 = -COCH3 for 9 (labelled C13 and C14) and = H for 10.
Figure 6
Figure 6
1H NMR spectrum of [(8-acetyl-C-7-oxyaceto)(Ag)(NHC)] (11) recorded in DMSO-d6.
Figure 7
Figure 7
The antimicrobial effects of (a) amikacin, (b) erythromycin, (c) triphenylphosphine (d) DMSO, (e) coumarin-3-COOAg (12), (f) coumarin-7-oxyacetoAg (4), (g) 8-acetylcoumarin-7-oxyacetoAg (3), (h) coumarin-7-oxyacetoAgTPP2 (6), and (i) 8-acetylcoumarin-7-oxyacetoAgTPP2 (5) on E. coli assessed by the micro broth dilution assay.
Figure 8
Figure 8
The antimicrobial effects of (a) amikacin, (b) erythromycin, (c) triphenylphosphine (d) DMSO, (e) coumarin-3-COOAg (12), (f) coumarin-7-oxyacetoAg (4), (g) 8-acetylcoumarin-7-oxyacetoAg (3), (h) coumarin-7-oxyacetoAgTPP2 (6) and (i) 8-acetylcoumarin-7-oxyacetoAgTPP2 (5) on P. aeruginosa assessed by the micro broth dilution assay.
Figure 9
Figure 9
The antimicrobial effects of (a) amikacin, (b) erythromycin, (c) triphenylphosphine (d) DMSO, (e) coumarin-3-COOAg (12), (f) coumarin-7-oxyacetoAg (4), (g) 8-acetylcoumarin-7-oxyacetoAg (3), (h) coumarin-7-oxyacetoAgTPP2 (6) and (i) 8-acetylcoumarin-7-oxyacetoAgTPP2 (5) on MRSA assessed by the micro broth dilution assay.
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