Synthesis and stability of small molecule probes for Pseudomonas aeruginosa quorum sensing modulation

Abstract

The human pathogen Pseudomonas aeruginosa uses N-butyryl-L-homoserine lactone (BHL) and N-(3-oxododecanyl)-L-homoserine lactone (OdDHL) as small molecule intercellular signals in a phenomenon known as quorum sensing (QS). QS modulators are effective at attenuating P. aeruginosa virulence; therefore, they are a potential new class of antibacterial agent. The lactone in BHL and OdDHL is hydrolysed under physiological conditions. The hydrolysis proceeds at a rate faster than racemisation of the alpha-chiral centre. Non-hydrolysable, non-racemic analogues (small molecule probes) were designed and synthesised, replacing the lactone with a ketone. OdDHL analogues were found to be relatively unstable to decomposition unless they were difluorinated between the beta-keto amide. Stability studies on a non-hydrolysable, cyclohexanone analogue indicated that racemisation of the alpha-chiral centre was relatively slow. This analogue was assayed to show that the L-isomer is likely to be responsible for the QS autoinducing activity in P. aeruginosa and Serratia strain ATCC39006.

Comparative Analyses of N‐Acylated Homoserine Lactones Reveal Unique Structural Features that Dictate Their Ability to Activate or Inhibit Quorum Sensing

“…AHL B2 is unique, as this D-AHL displays strong agonistic activity and its L-stereoisomer, control AHL 5, is virtually inactive in LasR (but is a moderate to strong antagonist in LuxR and TraR, respectively). This trend is opposite to what has been observed for native AHL ligands, for which the Lstereoisomer is an active agonist and the D-stereoisomer is almost inactive; [17,20] we observed this latter trend in the current study for OOHL (1). The reasons behind this trend reversal for B2 remain unclear, and in view of the complex antagonistic activity trends displayed by the limited set of D enantiomers in library B, suggest that lactone stereochemistry will be an important feature to probe in the future design of AHL-derived QS modulators.…”

“…[18] The effect of lactone stereochemistry on R protein activation had only been examined for a limited set of native AHLs, [20] and to our knowledge, had yet to be examined in synthetic AHL antagonists. [17] (We note, however, that many synthetic AHLs have been tested in racemic form, or their reported stereochemistry was not explicit, which adds additional complexity to this analysis. [9][10][11][13][14][15][16]) Lastly, the roles of acyl group aromaticity and spacer length on ligand activity, specifically in our antagonists 8 and 9, were unknown.…”

“…[9][10][11][12][13][14][15][16][17][18][19] Structural modifications to the lactone ring, including inversion of stereochemistry, [20] and replacement of the lactone with different carbo-or heterocycles [9][10][11]17,[21][22][23] have been examined to a lesser degree. Four of the most effective AHL-derived antagonists of TraR, LasR, or LuxR reported to date are shown in Scheme 1: the C 7 AHL 4 active against TraR, [13] the 3-oxo-phenylbutanoyl-and phenylbutanoyl HLs (5 and 6) active against LuxR, [14] and the 2-aminophenol analogue of OdDHL 7 active against LasR.…”

Iron limitation enhances acyl homoserine lactone (AHL) production and biofilm formation in clinical isolates ofAcinetobacter baumannii

“…38 Briefly, a drop of the AHL previously extracted by LL-extraction method as described as the above section was placed on one of the KBr grid/ plates. Then, the second plate was placed on top and subjected to IR (Brauker Tensor 70 FT-IR Spector-photometer).…”

The 4-aza-S-ribosyl-L-homocysteine Derivatives and the Related Gamma-lactam and Azahemiacetal Analogs: Synthesis, Inhibition and Quorum Sensing Activity

“…Spring and co-workers described the total synthesis of 3-oxo-C 12 -AHL and also reported four 3-oxo-C 12 -AHL analogs 47-48b having various nonhydrolysable cyclic ketone and lactone rings along with changes at the acyl side chain as LasR inhibitors. 94,95 Cyclic ketones, 48a, 48b were found to reduce immunomodulatory responses (for e.g., TNFα factor and nitric oxide production) ( Figure 10). Muh et al screened a library of 200,000 compounds using ultra-high-throughput-cell based screening and identified two LasR inhibitors having a phenyl (49) and tetrazole ring (50) connected to 12 carbon aliphatic chain similar to 3-oxo-C 12 -AHL ( Figure 11).…”