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Background Quorum sensing is an extracellular bacterial communication system used in the density-dependent regulation of gene expression and development of biofilms. Biofilm formation has been implicated in the establishment of catheter-associated urinary tract infections and therefore quorum sensing inhibitors (QSIs) have been suggested as anti-biofilm catheter coating agents. The long-term effects of QSIs in uropathogens is, however, not clearly understood. Objectives We evaluated the effects of repeated exposure to the QSIs cinnamaldehyde, (Z)-4-bromo-5(bromomethylene)-2(5H)-furanone-C30 (furanone-C30) and 4-fluoro-5-hydroxypentane-2,3-dione (F-DPD) on antimicrobial susceptibility, biofilm formation and relative pathogenicity in eight uropathogenic Escherichia coli (UPEC) isolates. Methods MICs, MBCs and minimum biofilm eradication concentrations and antibiotic susceptibility were determined. Biofilm formation was quantified using crystal violet. Relative pathogenicity was assessed in a Galleria mellonella model. To correlate changes in phenotype to gene expression, transcriptomic profiles were created through RNA sequencing and variant analysis of genomes was performed in strain EC958. Results Cinnamaldehyde and furanone-C30 led to increases in susceptibility in planktonic and biofilm-associated UPEC. Relative pathogenicity increased after cinnamaldehyde exposure (4/8 isolates), decreased after furanone-C30 exposure (6/8 isolates) and varied after F-DPD exposure (one increased and one decreased). A total of 9/96 cases of putative antibiotic cross-resistance were generated. Exposure to cinnamaldehyde or F-DPD reduced expression of genes associated with locomotion, whilst cinnamaldehyde caused an increase in genes encoding fimbrial and afimbrial-like adhesins. Furanone-C30 caused a reduction in genes involved in cellular biosynthetic processes, likely though impaired ribonucleoprotein assembly. Conclusions The multiple phenotypic adaptations induced during QSI exposure in UPEC should be considered when selecting an anti-infective catheter coating agent.

N-Methyl carbamoylimidazole is a safe and practical alternative to methyl isocyanate for carbamoylation reactions. We have developed a new chemical route for its synthesis from methyl iodide and applied this to the synthesis of N-[11C]methyl carbamoylimidazole as a new [11C]synthon to radiolabel biomolecules for PET imaging research. N-[11C]methyl carbamoylimidazole was prepared from [11C]methyl iodide in 70–74% radiochemical yield (decay corrected) and can be used in situ for further reaction without purification. The reactivity of N-[11C]methyl carbamoylimidazole was demonstrated in a series of [11C]carbamoylation reactions. Electronic supplementary material The online version of this article (10.1007/s10967-018-5948-4) contains supplementary material, which is available to authorized users.

Inhibitors of the enzyme NQO2 (NRH: quinone oxidoreductase 2) are of potential use in cancer chemotherapy and malaria. We have previously reported that non-symmetrical furan amidines are potent inhibitors of NQO2 and here novel analogues are evaluated. The furan ring has been changed to other heterocycles (imidazole, N-methylimidazole, oxazole, thiophene) and the amidine group has been replaced with imidate, reversed amidine, N-arylamide and amidoxime to probe NQO2 activity, improve solubility and decrease basicity of the lead furan amidine. All compounds were fully characterised spectroscopically and the structure of the unexpected product N-hydroxy-4-(5-methyl-4-phenylfuran-2-yl)benzamidine was established by X-ray crystallography. The analogues were evaluated for inhibition of NQO2, which showed lower activity than the lead furan amidine. The observed structure-activity relationship for the furanamidine series with NQO2 was rationalized by preliminary molecular docking and binding mode analysis. In addition, the oxazole-amidine analogue inhibited the growth of Plasmodium\ud falciparum with an IC50 value of 0.3 M.

(NRH):quinone oxidoreductase 2 (NQO2) is associated with various processes involved in cancer initiation and progression probably via the production of ROS during quinone metabolism. Thus, there is a need to develop inhibitors of NQO2 that are active in vitro and in vivo. As part of a strategy to achieve this we have used the 4-aminoquinoline backbone as a starting point and synthesized 21 novel analogues. The syntheses utilised p-anisidine with Meldrum's acid and trimethyl orthoacetate or trimethyl orthobenzoate to give the 4-hydrazin-quinoline scaffold, which was derivatised with aldehydes or acid chlorides to give hydrazone or hydrazide analogues, respectively. The hydrazones were the most potent inhibitors of NQO2 in cell free systems, some with low nano-molar IC50 values. Structure-activity analysis highlighted the importance of a small substituent at the 2-position of the 4-aminoquinoline ring, to reduce steric hindrance and improve engagement of the scaffold within the NQO2 active site. Cytotoxicity and NQO2–inhibitory activity in vitro was evaluated using ovarian cancer SKOV-3 and TOV-112 cells (expressing high and low levels of NQO2, respectively). Generally, the hydrazones were more toxic than hydrazide analogues and further, toxicity is unrelated to cellular NQO2 activity. Pharmacological inhibition of NQO2 in cells was measured using the toxicity of CB1954 as a surrogate end-point. Both the hydrazone and hydrazide derivatives are functionally active as inhibitors of NQO2 in the cells, but at different inhibitory potency levels. In particular, 4-((2-(6-methoxy-2-methylquinolin-4-yl)hydrazono)methyl)phenol has the greatest potency of any compound yet evaluated (53 nM), which is 50-fold lower than its toxicity IC50. This compound and some of its analogues could serve as useful pharmacological probes to determine the functional role of NQO2 in cancer development and response to therapy.

NRH:quinone oxidoreductase 2 enzyme (NQO2) is a potential therapeutic target in cancer and neurodegenerative diseases, with roles in either chemoprevention or chemotherapy. Here we report the design, synthesis and evaluation of non-symmetrical furan-amidines and their analogues as novel selective NQO2 inhibitors with reduced adverse off-target effects, such as binding to DNA. A pathway for the synthesis of the non-symmetrical furan-amidines was established from the corresponding 1,4-diketones. The synthesized non-symmetrical furan-amidines and their analogues showed potent NQO2 inhibition activity with nano-molar IC50 values. The most active compounds were non-symmetrical furan-amidines with meta- and para-nitro substitution on the aromatic ring, with IC50 values of 15 nM. In contrast to the symmetric furan-amidines, which showed potent intercalation in the minor grooves of DNA, the synthesized non-symmetrical furan-amidines showed no affinity towards DNA, as demonstrated by DNA melting temperature experiments. In addition, Plasmodium parasites, which possess their own quinone oxidoreductase PfNDH2, were inhibited by the non-symmetrical furan-amidines, the most active possessing a para-fluoro substituent (IC50 9.6 nM). The high NQO2 inhibition activity and nanomolar antimalarial effect of some of these analogues suggest the lead compounds are worthy of further development and optimization as potential drugs for novel anti-cancer and antimalarial strategies.

The diethyl ester of [(18)F]ML-10 is a small molecule apoptotic PET probe for cancer studies. Here we report a novel multi-step synthesis of the diethyl ester of ML-10 in excellent yields via fluorination using Xtal-Fluor-E. In addition, a one-pot radiosynthesis of the diethyl ester of [(18)F]ML-10 from nucleophilic [(18)F]fluoride was completed in 23% radiochemical yield (decay corrected). The radiochemical purity of the product was ≥99%. The diethyl ester of [(18)F]ML-10 was used in vivo to detect apoptosis in the testes of mice. In parallel studies, the dansyl-ML-10 diethyl ester was prepared and used to detect apoptotic cells in an in vitro cell based assay.

Meta-iodobenzylguanidine (mIBG) has been radiolabelled at the no-carrier-added level with [124I] for a proof of concept study to assess the diagnostic accuracy of [124I]mIBG PET/CT in detecting metastatic deposits in patients diagnosed with metastatic neuroblastoma. Radiolabelling of mIBG was achieved via the iododesilylation reaction between [124I]sodium iodide and meta-trimethylsilylbenzylguanidine. [124I]mIBG was produced in 62–70 % radioiodide incorporation yield from [124I]sodium iodide. The average amount of formulated [124I]mIBG was 359 MBq (range 344–389 MBq) with an average specific radioactivity of 4.1 TBq μmol−1 (range 1.8–5.9 TBq μmol−1) at end of synthesis.

Meta-iodobenzylguanidine (mIBG) has been radiolabelled at the no-carrier-added level with [124I] for a proof of concept study to assess the diagnostic accuracy of [124I]mIBG PET/CT in detecting metastatic deposits in patients diagnosed with metastatic neuroblastoma. Radiolabelling of mIBG was achieved via the iododesilylation reaction between [124I]sodium iodide and meta-trimethylsilylbenzylguanidine. [124I]mIBG was produced in 62–70 % radioiodide incorporation yield from [124I]sodium iodide. The average amount of formulated [124I]mIBG was 359 MBq (range 344–389 MBq) with an average specific radioactivity of 4.1 TBq μmol−1 (range 1.8–5.9 TBq μmol−1) at end of synthesis.

The aromatic rings in 4-O-dabsyl-6-O-dansyl-myo-inositol-1,3,5-orthoformate (6) participate in electron transfer causing static quenching as detected by the absence of fluorescence. Upon addition of acid, the orthoformate lock is cleaved, with subsequent conformational change of the myo-inositol ring from penta-axial to the more stable penta-equatorial chair, which causes some increase in fluorescence due to spatial separation of fluorophore and a quencher and reduction in static quenching. In the case of 4,6-O-bisdansyl-myo-inositol-1,3,5-orthoformate (3), the acid-induced removal of the orthoformate lock leads to substantial change of fluorescence following spatial separation of two dansyl groups.

(S)-4,5-Dihydroxypentane-2,3-dione [(S)-DPD, (1)] is a precursor for , a quorum sensing signalling molecule for inter- and intra-species bacterial communication. The synthesis of its fluoro-analogue, 4-fluoro-5-hydroxypentane-2,3-dione () is reported. An intermediate in this route also enables a new, shorter synthesis of the native (S)-DPD. 4-Fluoro-DPD (2) completely inhibited bioluminescence and bacterial growth of Vibrio harveyi BB170 strain at 12.5 μM and 100 μM, respectively.

We do not need to rehearse the grim story of the global rise of antibiotic resistant microbes. But what if it were possible to control the rate with which antibiotic resistance evolves by de novo mutation? It seems that some bacteria may already do exactly that: they modify the rate at which they mutate to antibiotic resistance dependent on their biological environment. In our recent study [Krasovec, et al. Nat. Commun. (2014), 5, 3742] we find that this modification depends on the density of the bacterial population and cell-cell interactions (rather than, for instance, the level of stress). Specifically, the wild-type strains of Escherichia coli we used will, in minimal glucose media, modify their rate of mutation to rifampicin resistance according to the density of wild-type cells. Intriguingly, the higher the density, the lower the mutation rate (Figure 1). Why this novel density-dependent 'mutation rate plasticity' (DD-MRP) occurs is a question at several levels. Answers are currently fragmentary, but involve the quorum-sensing gene luxS and its role in the activated methyl cycle.

(S)-4,5-Dihydroxypentane-2,3-dione [(S)-DPD, (1)] is a precursor for , a quorum sensing signalling molecule for inter- and intra-species bacterial communication. The synthesis of its fluoro-analogue, 4-fluoro-5-hydroxypentane-2,3-dione () is reported. An intermediate in this route also enables a new, shorter synthesis of the native (S)-DPD. 4-Fluoro-DPD (2) completely inhibited bioluminescence and bacterial growth of Vibrio harveyi BB170 strain at 12.5 μM and 100 μM, respectively.

The diethyl ester of [(18)F]ML-10 is a small molecule apoptotic PET probe for cancer studies. Here we report a novel multi-step synthesis of the diethyl ester of ML-10 in excellent yields via fluorination using Xtal-Fluor-E. In addition, a one-pot radiosynthesis of the diethyl ester of [(18)F]ML-10 from nucleophilic [(18)F]fluoride was completed in 23% radiochemical yield (decay corrected). The radiochemical purity of the product was ≥99%. The diethyl ester of [(18)F]ML-10 was used in vivo to detect apoptosis in the testes of mice. In parallel studies, the dansyl-ML-10 diethyl ester was prepared and used to detect apoptotic cells in an in vitro cell based assay.

Novel anticancer drugs targeting key apoptosis regulators have been developed and are undergoing clinical trials. Pharmacodynamic biomarkers to define the optimum dose of drug that provokes tumor apoptosis are in demand; acquisition of longitudinal tumor biopsies is a significant challenge and minimally invasive biomarkers are required. Considering this, we have developed and validated a preclinical 'death-switch' model for the discovery of secreted biomarkers of tumour apoptosis using in vitro proteomics and in vivo evaluation of the novel imaging probe [(18)F]ML-10 for non-invasive detection of apoptosis using positron emission tomography (PET). The 'death-switch' is a constitutively active mutant caspase-3 that is robustly induced by doxycycline to drive synchronous apoptosis in human colorectal cancer cells in vitro or grown as tumor xenografts. Death-switch induction caused caspase-dependent apoptosis between 3 and 24 hours in vitro and regression of 'death-switched' xenografts occurred within 24 h correlating with the percentage of apoptotic cells in tumor and levels of an established cell death biomarker (cleaved cytokeratin-18) in the blood. We sought to define secreted biomarkers of tumor apoptosis from cultured cells using Discovery Isobaric Tag proteomics, which may provide candidates to validate in blood. Early after caspase-3 activation, levels of normally secreted proteins were decreased (e.g. Gelsolin and Midkine) and proteins including CD44 and High Mobility Group protein B1 (HMGB1) that were released into cell culture media in vitro were also identified in the bloodstream of mice bearing death-switched tumors. We also exemplify the utility of the death-switch model for the validation of apoptotic imaging probes using [(18)F]ML-10, a PET tracer currently in clinical trials. Results showed increased tracer uptake of [(18)F]ML-10 in tumours undergoing apoptosis, compared with matched tumour controls imaged in the same animal. Overall, the death-switch model represents a robust and versatile tool for the discovery and validation of apoptosis biomarkers.

The autoinducer (4S)-4,5-dihydroxypentane-2,3-dione ((S)-DPD, AI-2) facilitates chemical communication, termed 'quorum sensing', amongst a wide range of bacteria, The synthesis of (S)-DPD is challenging in part due to its instability. Herein we report a novel synthesis of (S)-DPD via (2S)-2,3-O-isopropylidene glyceraldehyde, through Wittig, dihydroxylation and oxidation reactions, with a complimentary asymmetric synthesis to a key precursor. Its enantiomer (R)-DPD, was prepared from d-mannitol via (2R)-2,3-O-isopropylideneglyceraldehyde. The synthesized enantiomers of DPD have AI-2 bioluminescence-inducing properties in the Vibrio harveyi BB170 strain.

2-O-tert-Butyldimethylsilyl-4,6-bis-O-pyrenoyl-myo-inositol-1,3,5-orthoformate (6) and 2-O-tert-butyldimethylsilyl-4-O-[4-(dimethylamino)benzoyl]-6-O-pyrenoyl-myo-inositol-1,3,5-orthoacetate (10) adopt conformationally restricted unstable chairs with five axial substituents. In the symmetrical diester 6, the two pi-stacked pyrenoyl groups are electron acceptor-donor partners, giving a strong intramolecular excimer emission. In the mixed ester 10, the pyrenoyl group is the electron acceptor and the 4-(dimethylamino)benzoyl ester is the electron donor, giving a strong intramolecular exciplex emission. The conformation of the mixed ester 10 was assessed using 1H NMR spectroscopy (1H-NOESY) and computational studies. which showed the minimum inter-centroid distance between the two aromatic systems to be approximately 3.9 A. Upon addition of acid, the orthoformate/orthoacetate trigger in 6 and 10 was cleaved, which caused a switch of the conformation of the myo-inositol ring to the more stable penta-equatorial chair, leading to separation of the aromatic ester groups and loss of excimer and exciplex fluorescence, respectively. This study provides proof of principle for the development of novel fluorescent molecular probes.

2-O-tert-Butyldimethylsilyl-4,6-bispyrenoyl-myo-inositol-1,3,5-orthoformate (1) and 2-O-tert-butyldimethylsilyl-4-[(4-di-methylamino)benzoyl]-6-pyrenoyl-myo-inositol-1,3,5-orthoacetate (2) adopt unstable chair conformations with five substituents axial, in which the aromatic esters participate in π-stacking, and give excimer and exciplex fluorescence, respectively. Upon addition of acid, the orthoformate/orthoacetate lock is cleaved, which allows the inositol ring to switch to the more stable pen-ta-equatorial chair conformation, with loss of exciplex/excimer fluorescence.

The intramolecular heterodimer probe 4-O-dabsyl-2-O-dansyl-myo-inositol-1,3,5-orthoformate undergoes biomimetic reduction of the azo bond in the dabsyl group to give a fluorescence emission band at 560 nm. This is attributed to the loss of energy transfer between the fluorophore (dansyl) and quencher (dabsyl) groups as a result of the formation of 4-O-(4-aminobenzene sulfonyl)-2-O-dansyl-myo-inositol-1,3,5-orthoformate.

Ester prodrugs have the potential to eliminate the gastrotoxicity associated with the carboxylic acid group of indomethacin. 4,6-Bis- O -2′-[1′-(4″-chlorobenzoyl)-5′-methoxy-2′-methyl-1′ H -indol-3′-acetyl]- myo -inositol-1,3,5-orthoacetate ( 2 ) was synthesised and evaluated as a COX-2 inhibitor. It adopts a conformationally restricted chair with two indomethacin groups in the sterically hindered 1,3-diaxial positions. Acid-induced cleavage of the orthoacetate lock of the prodrug leads to a ring flip of the myo -inositol ring with the two indomethacin groups now in 1,3-diequatorial positions. This increases the susceptibility of hydrolysis of the ester groups to release indomethacin under acidic conditions. The long half-life (152 min) of decomposition of ( 2 ) at ∼pH 1–2 suggests that it may bypass the stomach with minimal hydrolysis upon oral administration. Indomethacin ester ( 2 ) was completely stable at pH 4.0–8.5 over 24 h at 37 °C and showed comparable activity to indomethacin in a COX-2 assay (pH 8.0).