Synthesis and biological evaluation of 4-(aminomethyl)-1-hydroxypyrazole analogues of muscimol as γ-aminobutyric acid(a) receptor agonists.

A series of bioisosteric 4-(aminomethyl)-1-hydroxypyrazole (4-AHP) analogues of muscimol, a GABA(A) receptor agonist, has been synthesized and pharmacologically characterized at native and selected recombinant GABA(A) receptors. The unsubstituted 4-AHP analogue (2a) (EC(50) 19 µM, R(max) 69%) was a moderately potent agonist at human α(1)ß(2)γ(2) GABA(A) receptors, and in SAR studies substitutions in the 3- and/or 5-position were found to be detrimental to binding affinities. Ligand-receptor docking in an α(1)ß(2)γ(2) GABA(A) receptor homology model along with the obtained SAR indicate that 2a and muscimol share a common binding mode, which deviates from the binding mode of the structurally related antagonist series based on 4-(piperidin-4-yl)-1-hydroxypyrazole (4-PHP, 1). Selectivity for α(1)ß(2)γ(2) over ρ(1) GABA(A) receptors was observed for the 5-chloro, 5-bromo, and 5-methyl substituted analogues of 2a illustrating that even small differences in structure can give rise to subtype selectivity.

[18F]fluorination of an arylboronic ester using [18F]selectfluor bis(triflate): application to 6-[18F]fluoro-L-DOPA.

The Ag-mediated electrophilic [(18)F]fluorination of an arylboronic ester is reported. This new radiochemical transformation uses [(18)F]selectfluor bis(triflate) in acetone. The process gave 6-[(18)F]fluoro-L-DOPA with a RCY of 19 ± 12% and a specific activity of 2.6 ± 0.3 GBq µmol(-1).

Learning and perceptual similarity among cuticular hydrocarbons in ants.

Nestmate recognition in ants is based on perceived differences in a multi-component blend of hydrocarbons that are present on the insect cuticle. Although supplementation experiments have shown that some classes of hydrocarbons, such as methyl branched alkanes and alkenes, have a salient role in nestmate recognition, there was basically no information available on how ants detect and perceive these molecules. We used a new conditioning procedure to investigate whether individual carpenter ants could associate a given hydrocarbon (linear or methyl-branched alkane) to sugar reward. We then studied perceptual similarity between a hydrocarbon previously associated with sugar and a novel hydrocarbon. Ants learnt all hydrocarbon-reward associations rapidly and with the same efficiency, regardless of the structure of the molecules. Ants could discriminate among a large number of pairs of hydrocarbons, but also generalised. Generalisation depended both on the structure of the molecule and the animal's experience. For linear alkanes, generalisation was observed when the novel molecule was smaller than the conditioned one. Generalisation between pairs of methyl-alkanes was high, while generalisation between hydrocarbons that differed in the presence or absence of a methyl group was low, suggesting that chain length and functional group might be coded independently by the ant olfactory system. Understanding variations in perception of recognition cues in ants is necessary for the general understanding of the mechanisms involved in social recognition processes based on chemical cues.

Discovery of benzamide analogues as a novel class of 5-HT3 receptor agonists.

A 5-HT3 receptor agonist based on a benzamide scaffold was identified in a screening of a small commercial compound library, and an elaborate SAR study originating from this hit was performed. The design, synthesis, and functional characterisation of benzamide analogues at the 5-HT3A receptor yielded substantial information concerning the analogues as 5-HT3 receptor agonists. However, the potencies of the derived analogues were not significantly improved over that of the initial hit. The benzamide scaffold constitutes a novel type of 5-HT3 receptor agonist, as it does not possess a positively charged functionality, which is essential for the binding of all orthosteric ligands to the receptor. Preliminary investigations suggest that the compounds may exert their effects on 5-HT3 receptors by binding to an allosteric site in the receptor complex.

Identification of an ant queen pheromone regulating worker sterility.

The selective forces that shape and maintain eusocial societies are an enduring puzzle in evolutionary biology. Ordinarily sterile workers can usually reproduce given the right conditions, so the factors regulating reproductive division of labour may provide insight into why eusociality has persisted over evolutionary time. Queen-produced pheromones that affect worker reproduction have been implicated in diverse taxa, including ants, termites, wasps and possibly mole rats, but to date have only been definitively identified in the honeybee. Using the black garden ant Lasius niger, we isolate the first sterility-regulating ant queen pheromone. The pheromone is a cuticular hydrocarbon that comprises the majority of the chemical profile of queens and their eggs, and also affects worker behaviour, by reducing aggression towards objects bearing the pheromone. We further show that the pheromone elicits a strong response in worker antennae and that its production by queens is selectively reduced following an immune challenge. These results suggest that the pheromone has a central role in colony organization and support the hypothesis that worker sterility represents altruistic self-restraint in response to an honest quality signal.

Ants recognize foes and not friends.

Discriminating among individuals and rejecting non-group members is essential for the evolution and stability of animal societies. Ants are good models for studying recognition mechanisms, because they are typically very efficient in discriminating 'friends' (nest-mates) from 'foes' (non-nest-mates). Recognition in ants involves multicomponent cues encoded in cuticular hydrocarbon profiles. Here, we tested whether workers of the carpenter ant Camponotus herculeanus use the presence and/or absence of cuticular hydrocarbons to discriminate between nest-mates and non-nest-mates. We supplemented the cuticular profile with synthetic hydrocarbons mixed to liquid food and then assessed behavioural responses using two different bioassays. Our results show that (i) the presence, but not the absence, of an additional hydrocarbon elicited aggression and that (ii) among the three classes of hydrocarbons tested (unbranched, mono-methylated and dimethylated alkanes; for mono-methylated alkanes, we present a new synthetic pathway), only the dimethylated alkane was effective in eliciting aggression. Our results suggest that carpenter ants use a fundamentally different mechanism for nest-mate recognition than previously thought. They do not specifically recognize nest-mates, but rather recognize and reject non-nest-mates bearing odour cues that are novel to their own colony cuticular hydrocarbon profile. This begs for a reappraisal of the mechanisms underlying recognition systems in social insects.

Novel 5-substituted 1-pyrazolol analogues of ibotenic acid: synthesis and pharmacology at glutamate receptors.

5-Substituted 1-pyrazolol analogues of ibotenic acid have been synthesized and pharmacologically characterized on ionotropic and metabotropic glutamate receptors (iGluRs and mGluRs). The syntheses involved introduction of bromide, alkyls, phenyl and arylalkyls in the 5-position of 1-benzyloxypyrazole leading to 5-substituted (RS)-2-amino-(1-hydroxy-4-pyrazolyl)acetic acids (5a-l). The pharmacological activities of the synthesized analogues ranged from the 5-cyclopropylmethyl analogue (5f) with weak but selective affinity for NMDA receptors (IC(50)=35 microM), over the 5-n-propyl analogue (5c), which was a selective mGluR2 agonist (EC(50)=72 microM), to the 5-cyclohexylmethyl analogue (5g), which was a selective mGluR2 antagonist (K(i)=32 microM), and the 5-phenylethyl analogue (5j), which was a weak but apparently selective mGluR1 antagonist (K(i)=230 microM). This series of compounds afforded GluR ligands with a broad spectrum of pharmacological profiles, and showing potential for development of new compounds with subtype-selective activities at various GluRs.

Synthesis and pharmacology of glutamate receptor ligands: new isothiazole analogues of ibotenic acid.

The naturally occurring heterocyclic amino acid ibotenic acid (Ibo) and the synthetic analogue thioibotenic acid (Thio-Ibo) possess interesting but dissimilar pharmacological activity at ionotropic and metabotropic glutamate receptors (iGluRs and mGluRs). Therefore, a series of Thio-Ibo analogues was synthesized. The synthesis included introduction of substituents by Suzuki and Grignard reactions on 4-halogenated 3-benzyloxyisothiazolols, reduction of the obtained alcohols, followed by introduction of the amino acid moiety by use of 2-(N-tert-butoxycarbonylimino)malonic acid diethyl ester. The obtained Thio-Ibo analogues (1, 2a-g) were characterized in functional assays on recombinant mGluRs and in receptor binding assays on native iGluRs. At mGluRs, the activity at Group II was retained for compounds with small substituents (2a-2d), whereas the Group I and Group III receptor activities for all new compounds were lost. Detection of NMDA receptor affinity prompted further characterization, and two-electrode voltage-clamp recordings at recombinant NMDA receptor subtypes NR1/NR2A-D expressed in Xenopus oocytes were carried out for compounds with small substituents (chloro, bromo, methyl or ethyl, compounds 2a-d). This series of Thio-Ibo analogues defines a structural threshold for NMDA receptor activation and reveals that the individual subtypes have different steric requirements for receptor activation. The compounds 2a and 2c are the first examples of agonists discriminating individual NMDA subtypes.

Ibotenic acid and thioibotenic acid: a remarkable difference in activity at group III metabotropic glutamate receptors.

In this study, we have determined and compared the pharmacological profiles of ibotenic acid and its isothiazole analogue thioibotenic acid at native rat ionotropic glutamate (iGlu) receptors and at recombinant rat metabotropic glutamate (mGlu) receptors expressed in mammalian cell lines. Thioibotenic acid has a distinct pharmacological profile at group III mGlu receptors compared with the closely structurally related ibotenic acid; the former is a potent (low microm) agonist, whereas the latter is inactive. By comparing the conformational energy profiles of ibotenic and thioibotenic acid with the conformations preferred by the ligands upon docking to mGlu1 and models of the other mGlu subtypes, we propose that unlike other subtypes, group III mGlu receptor binding sites require a ligand conformation at an energy level which is prohibitively expensive for ibotenic acid, but not for thioibotenic acid. These studies demonstrate how subtle differences in chemical structures can result in profound differences in pharmacological activity.

First synthesis of racemic saphenamycin and its enantiomers. investigation of biological activity.

The natural antibiotic saphenamycin, 6-[1-(2-hydroxy-6-methyl-benzoyloxy)-ethyl]-phenazine-1-carboxylic acid, was synthesized from saphenic acid using temporary allyl protection of carboxy and phenoxy functionalities. Resolution of racemic saphenic acid was performed by crystallization of the corresponding (-)-brucine diastereomeric salts and the absolute configuration of (-)-brucinium (-)-saphenate was determined by X-ray crystallography to have R-configuration. This also proved to be the configuration of natural saphenic acid. Enantiomers of saphenamycin were obtained from resolved saphenic acid and screened against a range of skin flora and resistant Staphylococcus aureus strains. Biological activities of saphenamycin enantiomers were compared with that of the synthetic racemate as well as earlier reported activities of saphenamycin isolated from natural sources. No significant difference was observed in activity of the enantiomers of saphenamycin, which revealed that the chirality of saphenamycin has no consequences for the antibiotic activity. Saphenamycin proved to be a potent antibiotic against fusidic acid and rifampicin resistant S. aureus strains showing MIC of 0.1-0.2 microg/mL.