Tore Benneche

Furanones, potential agents for preventing Staphylococcus epidermidis biofilm infections?

OBJECTIVES Staphylococcus epidermidis is often associated with biofilm infections related to medical implants. The aim of the present study was to find furanones that decrease biofilm formation without irritative or genotoxic effects, or effects on S. epidermidis growth. METHODS After screening including bioluminescence and biofilm assays, 2 furanones out of 11 were chosen for further studies. MIC values of the two furanones were established to determine whether biofilm inhibition effects were ascribed to inhibition of bacterial growth. To further investigate interference with communication, the effect of the furanones was tested in the presence of the autoinducer-2 precursor (S)-4,5-dihydroxy-2,3-pentanedione. The furanones were tested for possible irritative effects by the Hens egg test chorioallantoic membrane procedure. Finally, potential genotoxic effects in mice were assessed by a membrane array, and effects on global gene expression were investigated by using a microarray representing 30,000 genes of the mouse genome. RESULTS From the bioluminescence assay, 4 furanones out of 11 were chosen for further biofilm analyses. Biofilm formation by S. epidermidis was significantly decreased by the four furanones tested at concentrations not affecting microbial growth. Two furanones were chosen for further studies: one that decreased biofilm statistically more than the others and one containing two bromo substituents. The two furanones were found to be non-irritative and non-genotoxic at the concentrations used. CONCLUSIONS Furanones may inhibit biofilm formation through interference with quorum sensing and thus represent promising agents for protecting surfaces from being colonized by S. epidermidis.

Stannylation reaction and cross-couplings in pyrimidines

Abstract Pyrimidines have been stannylated in the activated 4-position by thermal decar☐ylation of the corresponding car☐ylic organotin esters. The decar☐ylation can be catalyzed by bis(acetonitrile)palladium(II) dichloride. 4-Iodopyrimidines are 4-stannylated either by substitution reactions with tri-n-butyltin-copper or by coupling reaction with hexamethyl- or hexa-n-butyl-ditin and Pd(II) catalysis. The stannylated pyrimidines form new carbon-carbon bonds by Pd(II)-catalyzed cross-couplings, tert-Butyldimethylsilyl-, dimethylthexylsilyl- and tert-butyldiphenylsilyl-oxymethyl (tri-n-butyl)tin have been synthesized and used in Pd(II)-catalyzed cross-coupling reactions with 4-chloropyrimidines. The silyi groups were not cleaved off during exposure to fluoride ions in aqueous media but were readily removed by fluoride ions in THF to yield the 4-hydroxymethylpyrimidine.

A quorum sensing-disrupting brominated thiophenone with a promising therapeutic potential to treat luminescent vibriosis.

Vibrio harveyi is amongst the most important bacterial pathogens in aquaculture. Novel methods to control this pathogen are needed since many strains have acquired resistance to antibiotics. We previously showed that quorum sensing-disrupting furanones are able to protect brine shrimp larvae against vibriosis. However, a major problem of these compounds is that they are toxic toward higher organisms and therefore, they are not safe to be used in aquaculture. The synthesis of brominated thiophenones, sulphur analogues of the quorum sensing-disrupting furanones, has recently been reported. In the present study, we report that these compounds block quorum sensing in V. harveyi at concentrations in the low micromolar range. Bioluminescence experiments with V. harveyi quorum sensing mutants and a fluorescence anisotropy assay indicated that the compounds disrupt quorum sensing in this bacterium by decreasing the ability of the quorum sensing master regulator LuxR to bind to its target promoter DNA. In vivo challenge tests with gnotobiotic brine shrimp larvae showed that thiophenone compound TF310, (Z)-4-((5-(bromomethylene)-2-oxo-2,5-dihydrothiophen-3-yl)methoxy)-4-oxobutanoic acid, completely protected the larvae from V. harveyi BB120 when dosed to the culture water at 2.5 µM or more, whereas severe toxicity was only observed at 250 µM. This makes TF310 showing the highest therapeutic index of all quorum sensing-disrupting compounds tested thus far in our brine shrimp model system.

Pd(0)-catalyzed allylic alkylation in the synthesis of (±)carbovir.

Abstract Racemic carbovir 1 has been synthesized in 6 steps from the cyclopentanone 8 with a Pd(0)-catalyzed allylation as a key reaction.

A synthetic furanone potentiates the effect of disinfectants on Salmonella in biofilm

Aims:  To study a possible effect of a synthetic brominated furanone on biofilm formation and biofilm resistance to disinfectants in Salmonella enterica.

Trialkylalanes in palladium-catalyzed chemo- and regioselective alkylations

Abstract Carbosubstitution in halogenoazines with alkyl groups is readily effected under the influence of Pd-catalysis with alanes as the donor of the alkyl group.

Facile synthesis of 5-(alkylidene)thiophen-2(5H)-ones. A new class of antimicrobial agents

5-(Chloromethylene)- and 5-(bromoalkylidene)thiophen-2(5H)-ones are easily prepared from readily available 2-acyl-5-methoxythiophenes in one step by reaction with excess acetyl chloride or acetyl bromide. Other 5-(methylidene)thiophen-2(5H)-ones have been made from 5-(bromomethylene)thiophene-2(5H)-one by treatment with different nucleophiles. Eighteen thiophenones were tested for capacity to reduce biofilm formation by the marine bacterium V. harveyi. All but three compounds reduced biofilm formation markedly. For all effective compounds but one, the relative biofilm reducing capacity was greater than inhibition of bacterial planktonic growth.

Synthesis of 5-(bromomethylene)furan-2(5H)-ones and 3-(bromomethylene)isobenzofuran-1(3H)-ones as inhibitors of microbial quorum sensing

(E)- and (Z)-5-(Bromomethylene)furan-2(5H)-ones and (E)- and (Z)-3-(bromomethylene)isobenzofuran-1(3H)-ones have been prepared starting from commercially available maleic anhydrides and phthalic anhydrides, respectively. A debrominative decarboxylation or a bromodecarboxylation reaction is a key step in the synthesis. The furanones were investigated for their ability to interfere with microbial communication and biofilm formation by Staphylococcus epidermidis.

Thiophenones inhibit Staphylococcus epidermidis biofilm formation at nontoxic concentrations

Frequent use of medical implants has led Staphylococcus epidermidis to develop into an opportunistic pathogen. The virulence is mainly linked to biofilm formation. Infections associated with biofilms are difficult to treat owing to enhanced resistance to antibiotics. Therefore, new and alternative treatments are called for. Bacterial communication is one of the regulatory mechanisms suggested to be involved in coordinating biofilm formation. In this study, we compared three communication inhibitors for preventing in vitro biofilm formation: a synthetic furanone, and two synthetic thiophenones, which are sulphur analogues of furanones. Furanones naturally source from the red macro alga Delisea pulchra. We also investigated the effect of thiophenone on transcriptional levels of genes associated with biofilm formation. We found that thiophenones were more effective in inhibiting biofilm formation than furanone, also in presence of albumin. We furthermore found that the thiophenones inhibited biofilm formation and bacterial communication more than furanones, and were less cytotoxic. The expression of the icaC and the lrgB genes, which are associated with biofilm formation, were affected by the thiophenone.

PALLADIUM CATALYSIS IN BRIDGE-FORMING REACTIONS BETWEEN STEREOSELECTIVELY SUBSTITUTED GLYCINE AUXILIARIES

Abstract The disulfide bridge in cystine has formally been replaced by substitution of two α-alanines at the β-carbon into the 2,3-positions in 1,3-butadiene. The key reactions are stereoselective alkylation of lithiated (2S)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine with 2,3-dibromopropene. The alkene-alkene bond formation was effected by Pd-catalysis either with the 2′-bromoallyl products from the alkylation as substrate or with the corresponding amino acid appropriately protected.