Identification of Substituted Amino Acid Hydrazides as Novel Anti-Tubercular Agents, Using a Scaffold Hopping Approach.

Discovery and development of new therapeutic options for the treatment of Mycobacterium tuberculosis (Mtb) infection, particularly drug-resistant strains, are urgently required to tackle the global burden of this disease. Herein, we reported the synthesis of a novel series of N-substituted amino acid hydrazides, utilising a scaffold hopping approach within a library of anti-tubercular agents. Efficacy and selectivity were evaluated against three strains of Mtb (wild-type, isoniazid-resistant and rifampicin-resistant), and cytotoxicity against macrophages in vitro. The antibacterial activity and therapeutic index of these molecules were significantly affected by modifications with the N-substituents. Introduction of a 3,5-dinitroaryl moiety demonstrated enhanced antibacterial activity against all three strains of Mtb. In contrast, the inclusion of an imidazo [1,2-a]pyridine-3-carboxy moiety resulted in enhanced activity towards isoniazid mono-resistant Mtb relative to wild-type Mtb. Consequently, this scaffold hopping approach showed significant promise for exemplification of novel molecules with specific activity profiles against drug-resistant tuberculosis.

Identification of Novel Benzoxa-[2,1,3]-diazole Substituted Amino Acid Hydrazides as Potential Anti-Tubercular Agents.

Discovery and development of new therapeutic options for the treatment of Mycobacterium tuberculosis (Mtb) infection are desperately needed to tackle the continuing global burden of this disease and the efficacy and cost limitations associated with current medicines. Herein, we report the synthesis of a series of novel benzoxa-[2,1,3]-diazole substituted amino acid hydrazides in a two-step synthesis and evaluate their inhibitory activity against Mtb and selected bacterial strains of clinical importance utilising an end point-determined REMA assay. Alongside this, their potential for undesired cytotoxicity against mammalian cells was assessed employing standard MTT assay methodologies. It has been demonstrated using modification at three sites (the hydrazine, amino acid, and the benzodiazole) it is possible to change both the antibacterial activity and cytotoxicity of these molecules whilst not affecting their microbial selectivity, making them attractive architectures for further exploitation as novel antibacterial agents.

Testing a chemical series inspired by plant stress oxylipin signalling agents for herbicide safening activity.

BACKGROUND: Herbicide safening in cereals is linked to a rapid xenobiotic response (XR), involving the induction of glutathione transferases (GSTs). The XR is also invoked by oxidized fatty acids (oxylipins) released during plant stress, suggesting a link between these signalling agents and safening. To examine this relationship, a series of compounds modelled on the oxylipins 12-oxophytodienoic acid and phytoprostane 1, varying in lipophilicity and electrophilicity, were synthesized. Compounds were then tested for their ability to invoke the XR in Arabidopsis and protect rice seedlings exposed to the herbicide pretilachlor, as compared with the safener fenclorim. RESULTS: Of the 21 compounds tested, three invoked the rapid GST induction associated with fenclorim. All compounds possessed two electrophilic carbon centres and a lipophilic group characteristic of both oxylipins and fenclorim. Minor effects observed in protecting rice seedlings from herbicide damage positively correlated with the XR, but did not provide functional safening. CONCLUSION: The design of safeners based on the characteristics of oxylipins proved successful in deriving compounds that invoke a rapid XR in Arabidopsis but not in providing classical safening in a cereal. The results further support a link between safener and oxylipin signalling, but also highlight species-dependent differences in the responses to these compounds. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Rational Development of Novel Activity Probes for the Analysis of Human Cytochromes P450.

The identification and quantification of functional cytochromes P450 (CYPs) in biological samples is proving important for robust analyses of drug efficacy and metabolic disposition. In this study, a novel CYP activity-based probe was rationally designed and synthesised, demonstrating selective binding of CYP isoforms. The dependence of probe binding upon the presence of NADPH permits the selective detection of functionally active CYP. This allows the detection and analysis of these enzymes using biochemical and proteomic methodologies and approaches.

The first intramolecular silene Diels-Alder reactions.

The synthesis of silaheterocycles through the first examples of an intramolecular silene Diels-Alder reaction is described.

Key role for a glutathione transferase in multiple-herbicide resistance in grass weeds.

Multiple-herbicide resistance (MHR) in black-grass (Alopecurus myosuroides) and annual rye-grass (Lolium rigidum) is a global problem leading to a loss of chemical weed control in cereal crops. Although poorly understood, in common with multiple-drug resistance (MDR) in tumors, MHR is associated with an enhanced ability to detoxify xenobiotics. In humans, MDR is linked to the overexpression of a pi class glutathione transferase (GSTP1), which has both detoxification and signaling functions in promoting drug resistance. In both annual rye-grass and black-grass, MHR was also associated with the increased expression of an evolutionarily distinct plant phi (F) GSTF1 that had a restricted ability to detoxify herbicides. When the black-grass A. myosuroides (Am) AmGSTF1 was expressed in Arabidopsis thaliana, the transgenic plants acquired resistance to multiple herbicides and showed similar changes in their secondary, xenobiotic, and antioxidant metabolism to those determined in MHR weeds. Transcriptome array experiments showed that these changes in biochemistry were not due to changes in gene expression. Rather, AmGSTF1 exerted a direct regulatory control on metabolism that led to an accumulation of protective flavonoids. Further evidence for a key role for this protein in MHR was obtained by showing that the GSTP1- and MDR-inhibiting pharmacophore 4-chloro-7-nitro-benzoxadiazole was also active toward AmGSTF1 and helped restore herbicide control in MHR black-grass. These studies demonstrate a central role for specific GSTFs in MHR in weeds that has parallels with similar roles for unrelated GSTs in MDR in humans and shows their potential as targets for chemical intervention in resistant weed management.

Preparation and complete (1) H and (13)C assignment of some pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione (PCUD) derivatives.

The preparation of a number of alkyl and alkoxy derivatives of pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione derivatives utilising a cheap, practical, low energy, 'green', single-pass continuous flow photochemical reactor is reported. Their (1)H and (13)C NMR spectra are fully assigned, revealing some general characteristics not previously reported for this class of compound, which should aid the assignment and prediction of the NMR spectra of PCUD derivatives.

The maize benzoxazinone DIMBOA reacts with glutathione and other thiols to form spirocyclic adducts.

Maize, wheat and other grasses synthesise large quantities of benzoxazinones and their glucosides, which act as antifeedant and allelopathic agents. These activities are probably due to the electrophilic nature of the aglycones, however, the mechanism of their action is unclear. In biological systems, glutathione (GSH) is the major electrophile-reactive compound so the reaction of the major maize benzoxazinone DIMBOA with GSH was studied. GSH reacts with DIMBOA to form eight isomeric mono-conjugates and eight isomeric di-conjugates. Through NMR studies with the model thiol 2-mercaptoethanol, these were structurally elucidated as unusual spirocycles. Similar reactivity was observed with proteins, with cysteinyl thiols being modified by DIMBOA. The thioether bonds formed were stable and not easily reduced to the parent thiol. DIMBOA can therefore readily deplete GSH levels and irreversibly inactivate enzymes with active-site cysteine residues, with clear implications for potentially toxic effects when young grasses are ingested, whether by insect pests or humans.

Transition metal-catalysed cross-coupling reactions of P-activated enols.

Transition metal catalysed cross-coupling reactions are ubiquitous in organic chemistry providing an impressive technique for C-C bond formation. Whilst many electrophilic partners have been described for these reactions, aryl and vinyl phosphates, phosphonates and phosphonites can offer advantages in terms of preparation, stability and reactivity profile. This critical review summarises the advances made to date utilising P-activated enols in metal-catalysed cross-coupling reactions (97 references).

The Arabidopsis phi class glutathione transferase AtGSTF2: binding and regulation by biologically active heterocyclic ligands.

The plant-specific phi class of glutathione transferases (GSTFs) are often highly stress-inducible and expressed in a tissue-specific manner, suggestive of them having important protective roles. To date, these functions remain largely unknown, although activities associated with the binding and transport of reactive metabolites have been proposed. Using a sensitive and selective binding screen, we have probed the Arabidopsis thaliana GSTFs for natural product ligands from bacteria and plants. Uniquely, when overexpressed in bacteria, family members GSTF2 and GSTF3 bound a series of heterocyclic compounds, including lumichrome, harmane, norharmane and indole-3-aldehyde. When screened against total metabolite extracts from A. thaliana, GSTF2 also selectively bound the indole-derived phytoalexin camalexin, as well as the flavonol quercetin-3-O-rhamnoside. In each case, isothermal titration calorimetry revealed high-affinity binding (typically Kd<1 µM), which was enhanced in the presence of glutathione and by the other heterocyclic ligands. With GSTF2, these secondary ligand associations resulted in an allosteric enhancement in glutathione-conjugating activity. Together with the known stress responsiveness of GSTF2 and its association with membrane vesicles, these results are suggestive of roles in regulating the binding and transport of defence-related compounds in planta.

Fluorescence quenched quinone methide based activity probes--a cautionary tale.

A carbamate linked quenching group coupled with a pro-quinone methide reactive core provides an effective tool for studying enzyme function without problems associated with background fluorescence from unreacted probe. However, the relatively slow fragmentation of the carbamate linkage in such a strategy may cause problems of loss of signal or a decoupling of enzyme activity and labelling.

Silenes in organic synthesis: a concise synthesis of (+/-) -epi-picropodophyllin.

A concise, seven step synthesis of the aryl tetralin lignan lactone epi-picropodophyllin from piperonal is described. The key steps are a silene diene Diels-Alder reaction and the Hosomi-Sakurai reaction of the resultant silacyclohexene.

Hosomi-Sakurai reactions of silacyclohexenes.

Silacyclic allyl silanes, derived from silene-diene Diels-Alder reactions, combine with acetals in the presence of Lewis acids to afford, following oxidation of the intermediate fluorosilane, either butane-1,4-diols or tetrahydronaphthalenes containing four contiguous chiral centres with moderate to good diastereoselectivity.

Silenes in organic synthesis: a short synthesis of prelactone B.

A sequence involving dihydroxylation and acid induced fragmentation of silene generated silacyclohexenes represents the key step in a concise synthetic route to beta-hydroxy-delta-lactones.

Hosomi-Sakurai reactions of silacyclic allyl silanes.

Substituted silacyclohexenes, generated through silene-diene [4 + 2] cycloaddition reactions, undergo Lewis acid promoted Sakurai type reactions with acetals to afford, following oxidation of the resultant fluorosilane, 1,4-diols with four contiguous chiral centres.