Peter J. Scammells

Biodegradable ionic liquids: Part I. Concept, preliminary targets and evaluation

The design, preparation and evaluation of biodegradable ionic liquids containing ester or amide groups in the alkyl side chain are presented. Factors improving the biodegradation of surfactants were successfully applied to ionic liquids. These novel ionic liquids can be prepared from readily available starting materials in high yield. The introduction of a group susceptible to enzymatic hydrolysis greatly improves the biodegradation (OECD 301D ‘Closed Bottle Test’) compared with the commonly used dialkylimidazolium ionic liquids, bmimBF4 and bmimPF6. For the 3-methyl-1-(alkyloxycarbonylmethyl)imidazolium bromide series, the greatest biodegradation was observed when alkyl = butyl, pentyl, hexyl and octyl. The corresponding amide analogs proved to be poorly biodegradable.

Ionic liquids : The neglected issues

There has been an explosion of interest in ionic liquids in the last five years that has resulted in the discovery of a vast number of new ionic liquids with a wide range of interesting applications. Although ionic liquids are invariably described as highly stable green solvents, thorough investigations quantifying their purity, stability, biodegradability, and toxicity have lagged behind the pace of other research in the area. This review addresses these key issues and summarizes the approaches that have been developed for recycling ionic liquids.

Biodegradable ionic liquids

Further research toward the discovery of biodegradable ionic liquids (ILs) is described herein. The biodegradability of the target ILs was evaluated using the ‘Closed Bottle’ and ‘CO2 Headspace’ tests (OECD 301D and ISO 14593). This research has identified the first ILs which can be classified as ‘readily biodegradable’ under aerobic conditions.

A novel mechanism of G protein-coupled receptor functional selectivity. Muscarinic partial agonist McN-A-343 as a bitopic orthosteric/allosteric ligand.

Many G protein-coupled receptors (GPCRs) possess allosteric binding sites distinct from the orthosteric site utilized by their cognate ligands, but most GPCR allosteric modulators reported to date lack signaling efficacy in their own right. McN-A-343 (4-(N-(3-chlorophenyl)carbamoyloxy)-2-butynyltrimethylammonium chloride) is a functionally selective muscarinic acetylcholine receptor (mAChR) partial agonist that can also interact allosterically at the M2 mAChR. We hypothesized that this molecule simultaneously utilizes both an allosteric and the orthosteric site on the M2 mAChR to mediate these effects. By synthesizing progressively truncated McN-A-343 derivatives, we identified two, which minimally contain 3-chlorophenylcarbamate, as pure allosteric modulators. These compounds were positive modulators of the orthosteric antagonist N-[3H]methylscopolamine, but in functional assays of M2 mAChR-mediated ERK1/2 phosphorylation and guanosine 5′-3-O-([35S]thio)triphosphate binding, they were negative modulators of agonist efficacy. This negative allosteric effect was diminished upon mutation of Y177A in the second extracellular (E2) loop of the M2 mAChR that is known to reduce prototypical allosteric modulator potency. Our results are consistent with McN-A-343 being a bitopic orthosteric/allosteric ligand with the allosteric moiety engendering partial agonism and functional selectivity. This finding suggests a novel and largely unappreciated mechanism of “directed efficacy” whereby functional selectivity may be engendered in a GPCR by utilizing an allosteric ligand to direct the signaling of an orthosteric ligand encoded within the same molecule.

Design and Preparation of Room-Temperature Ionic Liquids Containing Biodegradable Side Chains

Novel room-temperature ionic liquids with potential sites of enzymatic hydrolysis have been prepared and tested for biodegradable properties.

Biodegradable pyridinium ionic liquids: design, synthesis and evaluation

A range of ionic liquids (ILs) with a pyridinium cation were synthesised and their biodegradability was evaluated using the CO2 Headspace test (ISO 14593). ILs bearing an ester side chain moiety were prepared from either pyridine or nicotinic acid and showed high levels of biodegradation under aerobic conditions and can be classified as ‘readily biodegradable’. In contrast, pyridinium ILs with alkyl side chains showed significantly lower levels of biodegradability in the same test. The utility of the biodegradable IL 6c as a reaction solvent for the Diels–Alder reaction was also investigated.

Further investigation of the biodegradability of imidazolium ionic liquids

In continuation of our earlier investigations, this report presents a rationale behind the design of a series of imidazolium based ionic liquids and their biodegradation using the CO2 headspace test (ISO 14593 method, OECD 310). The effect on biodegradability of these salts through variation of the N-substituted side chains of imidazolium ions was examined further through incorporation of various functional groups and increased alkyl chain lengths. A series of anions containing moieties known to be biodegradable were also incorporated into a number of imidazolium based salts and examined in a similar fashion.

A Monod-Wyman-Changeux mechanism can explain G protein-coupled receptor (GPCR) allosteric modulation.

Background: The Monod-Wyman-Changeux (MWC) mechanism is the preeminent conformational selection model for allosteric proteins. Results: The novel allosteric ligand, BQCA, behaves according to a two-state MWC mechanism at the M1 muscarinic GPCR. Conclusion: Chemical biological properties of GPCR allosteric ligands can be rationalized by the MWC model. Significance: Application of our experimental framework to allosteric GPCR modulators can assist ligand classification and drug discovery. The Monod-Wyman-Changeux (MWC) model was initially proposed to describe the allosteric properties of regulatory enzymes and subsequently extended to receptors. Yet despite GPCRs representing the largest family of receptors and drug targets, no study has systematically evaluated the MWC mechanism as it applies to GPCR allosteric ligands. We reveal how the recently described allosteric modulator, benzyl quinolone carboxylic acid (BQCA), behaves according to a strict, two-state MWC mechanism at the M1 muscarinic acetylcholine receptor (mAChR). Despite having a low affinity for the M1 mAChR, BQCA demonstrated state dependence, exhibiting high positive cooperativity with orthosteric agonists in a manner that correlated with efficacy but negative cooperativity with inverse agonists. The activity of BQCA was significantly increased at a constitutively active M1 mAChR but abolished at an inactive mutant. Interestingly, BQCA possessed intrinsic signaling efficacy, ranging from near-quiescence to full agonism depending on the coupling efficiency of the chosen intracellular pathway. This latter cellular property also determined the difference in magnitude of positive cooperativity between BQCA and the orthosteric agonist, carbachol, across pathways. The lack of additional, pathway-biased, allosteric modulation by BQCA was confirmed in genetically engineered yeast strains expressing different chimeras between the endogenous yeast Gpa1 protein and human Gα subunits. These findings define a chemical biological framework that can be applied to the study and classification of allosteric modulators across different GPCR families.

Phosphonium ionic liquids: design, synthesis and evaluation of biodegradability

The biodegradability of a range of phosphonium ionic liquids (ILs) was assessed using the CO2 headspace test (ISO 14593). Tetraalkylphosphonium cations in which one of the alkyl substituents contained ester, ether, alcohol or alkene functionality in order to promote biodegradation were targeted. These cations were paired with halide, triflimide and octylsulfate anions. In contrast to previously studied dialkylimidazolium and alkylpridinium ILs with incorporated ester moieties and octylsulfate anions, the phosphonium ILs showed relatively low levels of biodegradability.

Allosteric modulators of the adenosine A1 receptor: synthesis and pharmacological evaluation of 4-substituted 2-amino-3-benzoylthiophenes.

A series of 4-substituted 2-amino-3-benzoylthiophenes was screened using a functional assay of A(1)AR-mediated phosphorylation of ERK1/2 in intact CHO cells to identify both potential agonistic effects as well the ability to allosterically modulate the activity of the orthosteric agonist, R-PIA. More detailed concentration-response experiments were subsequently performed on two compounds (9a and 9o) utilizing both the ERK1/2 assay as well as a second assay of [(35)S]GTPgammaS binding to activated G proteins.