Design, synthesis, and biological evaluation of benzoheterocyclic sulfoxide derivatives as quorum sensing inhibitors in Pseudomonas aeruginosa

Figures & data

Figure 1. The main three QS signalling networks in P. aeruginosa.

Figure 2. The design of the title compounds.

Scheme 1. The synthetic route of the title compounds.

Table 1. Biofilm inhibition rates of derivatives against the P. aeruginosa PAO1.

Entry	Compound.
	R”	Inhibition rate^a.b (%)
a	H	–4.75 ± 0.54	19.8 ± 0.70	12.84 ± 4.17
b	4-Cl	3.93 ± 1.07	39.18 ± 1.84	46.13 ± 0.72
c	3-Cl	16.64 ± 1.67	26.00 ± 0.69	13.77 ± 0.27
d	2-Cl	5.32 ± 2.00	24.25 ± 2.31	15.14 ± 2.25
e	4-F	–3.26 ± 0.76	15.94 ± 0.56	38.64 ± 0.32
f	4-Br	14.52 ± 3.50	26.06 ± 1.54	14.60 ± 1.23
g	4-Me	3.25 ± 0.55	31.39 ± 2.40	16.27 ± 1.68
h	4-napthyl	–8.59 ± 1.34	36.95 ± 0.57	9.95 ± 0.59
i	4-NO2	2.59 ± 0.05	7.74 ± 2.10	16.45 ± 1.69
j	4-CF3	–6.28 ± 1.07	26.24 ± 1.42	15.65 ± 0.84
k	3-MeO	6.15 ± 0.33	14.64 ± 3.12	15.85 ± 3.33
l	4-MeO	5.48 ± 0.32	20.99 ± 2.19	12.51 ± 1.41
Benzimidazole	16.78 ± 1.07

^aAll data represent mean ± SD from different experiments performed in triplicate.

^bThe concentration of compounds were 50 μM, benzimidazole used as positive control. We also tested other concentrations, and the data was supplemented in supporting information.

Table 2. Biofilm inhibition rates of derivatives against the P. aeruginosa PAO1.

Entry	Compound.
	R”	Inhibition rate^a.b (%)
a	H	19.11 ± 2.12	11.92 ± 0.58	13.44 ± 0.37
b	4-Cl	43.64 ± 2.49	19.93 ± 0.57	29.44 ± 0.39
c	4-Me	23.75 ± 0.52	9.52 ± 1.7	13.33 + 0.96
d	4- NO2	22.30 ± 3.69	12.38 ± 2.54	13.18 + 0.69
e	4-CF3	26.45 ± 1.21	22.07 ± 0.82	18.75 ± 0.52
f	4-F	19.09 ± 1.16	14.19 ± 1.83	28.56 ± 0.45
Benzimidazole	16.78 ± 1.07

^aAll data represent mean ± SD from different experiments performed in triplicate.

^bThe concentrations of compounds were 50 μM, benzimidazole used as positive control. We also tested other concentrations, the data supplemented in supporting information.

Figure 3. Effects of 6b on P. aeruginosa PAO1 biofilm growth and formation. (A) Biofilm inhibition at 50 μM of 5b, 5h, 6d, 7b, 9b for 24 h in microtiter plate. (B) Growth at different concentrations of 6b (50, 25, 12.5, 5, 2.5 μM) for 16 h. (C) CLSM images of biofilm formed for 24 h with 50 μM and 25 μM of 6b, and benzimidazole used as positive control (An equal amount of dimethyl sulfoxide solvent was set as control group). Data represents the average of three-independent determinations of triplicate samples.

Figure 4. The effects of 5b, 5h, 6d, 7b, 9b on QS system report strain (A) PAO1-lasB-gfp, (B) PAO1-rhlA-gfp, and (C) PAO1-pqsA-gfp. The experiments were done triplicate.

Figure 5. (A) Dose-dependent inhibition curves of 6b incubated with the QS monitors PAO1-lasB-gfp. (B) Growth at different concentrations of 6b (20, 10, 5, 2.5, 1.25 μM). (C) IC₅₀ values calculations were based on three biological replicates and performed by nonlinear fitting, using Graphpad Prism 6 software. The IC₅₀ values of 6b was 2.08 ± 0.25 μM for PAO1-lasB-gfp. The experiments were also done in triplicate.

Figure 6. Effects of 6b on the production of (A) elastase (B) pyocyanin (C) rhamnolipid at different concentrations (50, 25, 12.5 and 0 μM). Error bars are means ± SDs. * = p < 0.05 versus the control, ** = p < 0.01 versus the control, *** = p < 0.001 versus the control.

Figure 7. Predicted binding model of compounds (OdDHL, 6b) and LasR (PDB code: 2uv0). (A) The pocket surface view of interactions between OdDHL, 6b with receptor protein lasR; (B) Superposition of native docking of OdDHL and OdDHL in LasR X-ray crystal structure, showing as OdDHL in green, OdDHL in LasR X-ray crystal structure in orange; (C) Details of 6b binding. 6b was shown in blue. The Residues involved in interactions with compounds are depicted as sticks in black and named in red. The hydrogen bonds are shown as aqua dashed lines.