Novel small molecules for modulation of bacterial signaling pathways

Conventional treatments for bacterial infections target bacterial viability, an approach that exerts a strong selective survival pressure on bacteria, leading to the development of multidrug resistant mutants. The number of multidrug resistant strains is increasing exponentially, far outpacing the development of new antibiotics. The conventional antibiotics are no longer the magic bullets they were once thought to be and there is an urgent need to develop new antibiotics and/or novel strategies that do not induce bacterial resistance. Bacteria employ a population-dependent cell-to-cell communication system known as quorum sensing (QS) to express various pathogenic traits such as virulence factor production and biofilm formation. Therefore, QS inhibition is a promising novel strategy to selectively control multidrug-resistant pathogenic bacteria, without exerting evolutionary pressures and development of resistance. This project focused on the design and synthesis of novel QS inhibitors based on common QS signaling molecules, such as N-acylated L-homoserine lactones (AHLs), indoles, N-acetyl glucosamine and other heterocyclic systems derived from halogenated furanones (Fimbrolides). Indole and glucosamine-based amides and oxo-amides were synthesized as non-native AHL mimics by applying EDC, DCC or EDC/HOBt mediated amide coupling methods. On docking study, the indole-based AHL mimics showed strong binding affinity with P. aeruginosa LasR receptor, with compound 146d having highest docking scores of 61.58. The reactions of brominated furanones with hydrazines have been developed granting access to 5-membered aminopyrrolones and hydrazinyl furanones, as well as 6-membered pyridazinones with novel bromination patterns. The ratio of formation of these different heterocycles varied with the types of hydrazine, as well as with the numbers of equivalents of hydrazines used. The X-ray crystallography analysis, revealed the characteristic halogen bonding in addition to other interactions such as hydrogen bonding which might facilitate efficient binding to the bacterial QS receptor proteins (LasR). The alkyne analogues of fimbrolides were synthesized via Sonogashira coupling reactions where the reaction was favored at the C5 bromo methylene group over the C4 bromine substituent of fimbrolides. Applying the Suzuki coupling reaction, various mono and di-aryl substituted fimbrolide analogues were synthesized where the aryl substitution also favored at the C5 bromo methylene group over the C4 bromo substituent. The dimeric scaffolds of fimbrolides were synthesized as novel ring structures using diboronic acids. Two different types of monoamino substituted (4-bromo or 5-bromomethylene) fimbrolides were isolated as novel structures via Buchwald-Hartwig coupling reactions of fimbrolides with various secondary amines from a single reaction in a predictable fashion (2:1 regioisomeric ratio). The newly synthesized compounds were tested for their QS inhibitory (QSI) efficacy against the P. aeruginosa PAMH602 and E. coli MT102 strains in terms of inhibition of their green fluorescent protein (GFP) production i.e. QS inhibition. The alkyne based fimbrolides compounds exhibited the highest QSI (up to 97.6% QSI at 250 µM) effect against P. aeruginosa MH602 followed by glucosamine (up to QSI 79.1% and 97.5% at 2 mM concentration against P. aeruginosa MH602 and E. coli MT102 strain respectively) and the indole based AHL analogues (up to 65% QSI at 250 µM against P. aeruginosa MH602). The co-treatment of some potent QS inhibitory compounds with tobramycin also showed two-three fold enhanced P. aeruginosa biofilm inhibitory effect compared to single tobramycin treatment. These findings highlight the potential usefulness of synthesized compounds in this project with non-violent modes of action i.e. blocking bacterial communication, a key strategy for the development of future anti-QS antimicrobial compounds.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2015

Author dc:creator

• Biswas, Nripendra

• Pseudomonas aeruginosa
• Antibacterials
• Quorum sensing
• Indole
• Fimbrolides
• Biofilm

Statement dc:rights

• open access
• CC BY-NC-ND 3.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by-nc-nd/3.0/au/

Language dc:language

EN

Identifier

https://doi.org/10.26190/unsworks/18660

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/55402