Inhibition of N-type calcium channels by phenoxyaniline and sulfonamide analogues

Building on previous investigations, structural modifications to the neuronal calcium ion channel blocker MONIRO-1 and related compounds were conducted that included replacement of the amide linker with an aniline and isosteric sulfonamide moiety, and the previously used strategy of substitution of the guanidinium group with less hydrophilic amine functionalities. A comprehensive SAR study revealed a number of phenoxyaniline and sulfonamide compounds that were more potent or had similar potency for the CaV2.2 and CaV3.2 channel compared to MONIRO-1 when evaluated in a FLIPR-based intracellular calcium response assay. Cytotoxicity investigations indicated that the sulfonamide analogues were well tolerated by Cos-7 cells at dosages required to inhibit both calcium ion channels. The sulfonamide derivatives were the most promising CaV2.2 inhibitors developed by us to date due, possessing high stability in plasma, low toxicity (estimated therapeutic index > 10), favourable CNS MPO scores (4.0-4.4) and high potency and selectivity, thereby, making this class of compounds suitable candidates for future in vivo studies.

Antibacterial and Antibiofilm Activity of Endophytic Alternaria sp. Isolated from Eremophila longifolia

The threat to public health resulting from the emergence of antimicrobial resistance (AMR) is ever rising. One of the major bacterial pathogens at the forefront of this problem is methicillin-resistant Staphylococcus aureus, or MRSA, for which there is a great need to find alternative treatments. One of the most promising alternatives is endophytic fungi, which were shown to produce a vast array of bioactive compounds, including many novel antibacterial compounds. In this study, two endophytic Alternaria sp., EL 24 and EL 35, were identified from the leaves of Eremophila longifolia. Ethyl acetate (EtOAc) extracts of their culture filtrates were found to inhibit both methicillin-sensitive S. aureus ATCC 25923 and MRSA strains M173525 and M180920. The activity of each extract was shown to be greatly affected by the growth medium, with considerable reductions in minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) observed when tested in tryptic soy broth with glucose (TSBG) compared with Mueller-Hinton broth (MHB). Both extracts displayed significant (p ≤ 0.05) antibiofilm activity against all three S. aureus strains, the greatest of which was that of EL 35, which reduced biofilm formation by M180920 by 72%, while that of EL 24 resulted in a 57% reduction against ATCC 25923. Both extracts also disrupted established biofilms, of which the most effective was EL 35, which reduced the M180920 biofilm by 64%, while EL 24 also performed best against M180920, reducing biofilm by 54%. Gas chromatography-mass spectrometry (GC-MS) analysis of the EL 24 EtOAc extract revealed five known compounds. This study highlights the promise of endophytic fungi from Australian plants as a potential source of substances effective against important bacterial pathogens. Further understanding of the responsible compounds and their mechanisms could lead to the development of treatments effective against MRSA, as well as novel biofilm-resistant biomedical materials, contributing towards reducing the burden of AMR.

Inhibition of N-type calcium ion channels by tricyclic antidepressants - experimental and theoretical justification for their use for neuropathic pain

A number of tricyclic antidepressants (TCAs) are commonly prescribed off-label for the treatment of neuropathic pain. The blockade of neuronal calcium ion channels is often invoked to partially explain the analgesic activity of TCAs, but there has been very limited experimental or theoretical evidence reported to support this assertion. The N-type calcium ion channel (CaV2.2) is a well-established target for the treatment of neuropathic pain and in this study a series of eleven TCAs and two closely related drugs were shown to be moderately effective inhibitors of this channel when endogenously expressed in the SH-SY5Y neuroblastoma cell line. A homology model of the channel, which matches closely a recently reported Cryo-EM structure, was used to investigate via docking and molecular dynamics experiments the possible mode of inhibition of CaV2.2 channels by TCAs. Two closely related binding modes, that occur in the channel cavity that exists between the selectivity filter and the internal gate, were identified. The TCAs are predicted to position themselves such that their ammonium side chains interfere with the selectivity filter, with some, such as amitriptyline, also appearing to hinder the channel's ability to open. This study provides the most comprehensive evidence to date that supports the notion that the blockade of neuronal calcium ion channels by TCAs is at least partially responsible for their analgesic effect.

Cannabis and Cannabinoids

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Reduction Chemistry of Natural Pyrethrins and Preliminary Insecticidal Activity of Reduced Pyrethrins

The natural extract pyrethrum is an insecticidal oil derived from Tanacetum cinerariifolium that is commonly used in domestic and agricultural pesticides. The major constituents of the extract are the Pyrethrins, six esters that provide pyrethrum with its insecticidal properties. These Pyrethrins readily degrade through several environmental means and as such, there can be significant Pyrethrin losses during processing and long-term storage of pyrethrum-based insecticides. This work attempts to alleviate the effect of these degradative processes through the pursuit of stabilised Pyrethrins by chemically removing oxidatively sensitive functionality. Several reduced Pyrethrin analogues were produced and a method to convert the more sensitive Pyrethrins present in the pyrethrum concentrate into their respective more stable jasmolin counterparts, as a mixture with the over-reduced tetrahydropyrethrins, was developed. All other reduction processes abolished insecticidal activity against Lucilia cuprina larvae, whereas some isomerised analogues showed comparable potency with the individual natural pyrethrin esters. This work has revealed new insights into the structure–activity relationships in this unique class of insecticide.

The Chemistry of Cannabis and Cannabinoids

The science of cannabis and cannabinoids encompasses a wide variety of scientific disciplines and can appear daunting to newcomers to the field. The encroachment of folklore and ‘cannabis culture’ into scientific discussions can cloud the situation further. This Primer Review is designed to give a succinct overview of the chemistry of cannabis and cannabinoids. It is hoped that it will provide a useful resource for chemistry undergraduates, postgraduates and their instructors, and experienced chemists who require a comprehensive and up to date summary of the field. The Review begins with a brief overview of the history and botany of cannabis, then goes on to detail important aspects of the chemistry of phytocannabinoids, endocannabinoids and synthetic cannabinomimetics. Other natural constituents of the cannabis plant are then described including terpenes and terpenoids, polyphenolics, alkaloids, waxes and triglycerides, and important toxic contaminants. A discussion of key aspects of the pharmacology associated with cannabinoids and the endocannabinoid system then follows, with a focus on the cannabinoid receptors, CB1 and CB2. The medicinal chemistry of cannabis and cannabinoids is covered, highlighting the range of diseases targeted with cannabis and phytocannabinoids, as well as key aspects of phytocannabinoid metabolism, distribution, and delivery. The modulation of endocannabinoid levels through the inhibition of key endocannabinoid-degrading enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) is then discussed. The Review concludes with an assessment of the much touted ‘entourage effect’. References to primary literature and more specialised reviews are provided throughout.

The binding of boronated peptides to low affinity mammalian saccharides

A 54-member library of boronated octapeptides, with all but the boronated residue being proteinogenic, was tested for affinity to a set of saccharides commonly found on the terminus of mammalian glycans. After experimentation with a high-throughput dye-displacement assay, attention was focused on isothermal titration calorimetry as a tool to provide reliable affinity data, including enthalpy and entropy of binding. A small number of boronated peptides showed higher affinity and significant selectivity for N-acetylneuraminic acid over methyl-α-d-galactopyranoside, methyl-α/β-l-fucopyranoside and N-acetyl-d-glucosamine. Thermodynamic data showed that for most of the boronated peptides studied, saccharide binding was associated with a significant increase in entropy, presumably resulting from the displacement of semiordered water molecules from around the sugar and/or peptide.

Inhibition of human N- and T-type calcium channels by an ortho-phenoxyanilide derivative, MONIRO-1

BACKGROUND AND PURPOSE

Voltage-gated calcium channels are involved in nociception in the CNS and in the periphery. N-type (Ca_v 2.2) and T-type (Ca_v 3.1, Ca_v 3.2 and Ca_v 3.3) voltage-gated calcium channels are particularly important in studying and treating pain and epilepsy.

EXPERIMENTAL APPROACH

In this study, whole-cell patch clamp electrophysiology was used to assess the potency and mechanism of action of a novel ortho-phenoxylanilide derivative, MONIRO-1, against a panel of voltage-gated calcium channels including Ca_v 1.2, Ca_v 1.3, Ca_v 2.1, Ca_v 2.2, Ca_v 2.3, Ca_v 3.1, Ca_v 3.2 and Ca_v 3.3.

KEY RESULTS

MONIRO-1 was 5- to 20-fold more potent at inhibiting human T-type calcium channels, hCa_v 3.1, hCa_v 3.2 and hCa_v 3.3 (IC₅₀ : 3.3 ± 0.3, 1.7 ± 0.1 and 7.2 ± 0.3 μM, respectively) than N-type calcium channel, hCa_v 2.2 (IC₅₀ : 34.0 ± 3.6 μM). It interacted with L-type calcium channels Ca_v 1.2 and Ca_v 1.3 with significantly lower potency (IC₅₀  > 100 μM) and did not inhibit hCa_v 2.1 or hCa_v 2.3 channels at concentrations as high as 100 μM. State- and use-dependent inhibition of hCa_v 2.2 channels was observed, whereas stronger inhibition occurred at high stimulation frequencies for hCa_v 3.1 channels suggesting a different mode of action between these two channels.

CONCLUSIONS AND IMPLICATIONS

Selectivity, potency, reversibility and multi-modal effects distinguish MONIRO-1 from other low MW inhibitors acting on Ca_v channels involved in pain and/or epilepsy pathways. High-frequency firing increased the affinity for MONIRO-1 for both hCa_v 2.2 and hCa_v 3.1 channels. Such Ca_v channel modulators have potential clinical use in the treatment of epilepsies, neuropathic pain and other nociceptive pathophysiologies.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

Molecular Markers for Pyrethrin Autoxidation in Stored Pyrethrum Crop: Analysis and Structure Determination

Pyrethrum is a natural insecticide extracted from Tanacetum cinerariifolium. Six esters, the pyrethrins, are responsible for the extract's insecticidal activity. The oxidative degradation of pyrethrins through contact with aerial oxygen is a potential cause of pyrethrin losses during pyrethrum manufacture. Described here is the first investigation of the autoxidation chemistry of the six pyrethrin esters isolated from pyrethrum. It was found that pyrethrins I and II, the major pyrethrin esters present in pyrethrum, undergo autoxidation more readily than the minor pyrethrin esters, the jasmolins and cinerins. Chromatographic analysis of pyrethrin I and II autoxidation mixtures showed some correlation with a similar analysis performed on extracts from T. cinerariifolium crop, which had been stored for 12 weeks without added antioxidants. Two pyrethrin II autoxidation products were isolated, characterized, and shown to be present in extracts of stored T. cinerariifolium crop, confirming that autoxidation of pyrethrin esters does occur during crop storage.

Inhibition of N-type calcium channels by fluorophenoxyanilide derivatives

A set of fluorophenoxyanilides, designed to be simplified analogues of previously reported ω-conotoxin GVIA mimetics, were prepared and tested for N-type calcium channel inhibition in a SH-SY5Y neuroblastoma FLIPR assay. N-type or Ca_v2.2 channel is a validated target for the treatment of refractory chronic pain. Despite being significantly less complex than the originally designed mimetics, up to a seven-fold improvement in activity was observed.

The Synthesis of Enantiopure α-Fluoro and α,α-Difluoro-β3-Arginine Derivatives

The synthesis of a set of monofluorinated, difluorinated, and non-fluorinated N-acetylated-β3-arginine esters, potential inhibitors of trypsin-like proteases, is described. Elaboration to the target compounds from previously reported enantiopure precursors derived from 3-hydroxypropanal involved 6–7 steps and was achieved in 48–65 % overall yield. The α,α-difluoro-β3-arginine derivative was found to be particularly prone to hydrolysis. Three β3-arginine derivatives were tested for their ability to inhibit trypsin, the α,α-difluoro compound being assayed in the form of a carboxylate zwitterion.

Concise Synthesis of Enantiomerically Pure (1'S,2'R)- and (1'R,2'S)-2S-Amino-3-(2'-aminomethyl-cyclopropyl)propionic Acid: Two E-Diastereoisomers of 4,5-Methano-L-lysine

A concise synthesis of both E-isomers of 2S-amino-3-(2′-aminomethyl-cyclopropyl)propionic acid, new methano-l-lysines, is described. The synthetic route includes nine steps from l-methionine, with a key step involving the cyclopropanation of an intermediate E-allylic alcohol. The resultant hydroxymethylcyclopropanes were readily separated and converted into the title α-amino acids. The stereochemistry around the cyclopropane rings was deduced by conducting the cyclopropanation in the presence of N,N,N′,N′-tetramethyl-d-tartaric acid diamide butylboronate, a chiral controller which is known to favour the production of S-hydroxymethyl cyclopropanes from allylic alcohols.

The Synthesis of a Cubane-Substituted Dipeptide

Amino acids and peptides bearing cyclic hydrocarbon side-chains are of interest in the development of a wide range of bioactive molecules. The preparation of an amino acid and a dipeptide derivative bearing an unfunctionalised cubane substituent is described. Attempts to prepare a cubylalanine derivative via the corresponding dehydroalanine were unsuccessful due to the high sensitivity of this vinyl cubane compound. Conversely, the addition of cubyllithium to a (RS)-glyoxylate sulfinimine led to an effective synthesis of a cubylglycine derivative and a cubane-substituted dipeptide in diastereomerically pure form.

Enantioselective synthesis of α-fluoro-β(3)-amino esters: synthesis of enantiopure, orthogonally protected α-fluoro-β(3)-lysine

The scope of a tandem conjugate addition-fluorination sequence performed on α,β-unsaturated esters using the enantiopure lithium amide derived from (S)-N-benzyl-N-(α-methylbenzyl)amine, and the electrophilic fluorinating agent N-fluorobenzenesulfonimide has been investigated. Using this method, α-fluoro-β(3)-amino esters can be obtained in up to quantitative yield and 80:20 to >99:1 dr. This simple methodology does not rely on the use of α-amino acids from the chiral pool and thus provides the potential for the preparation of enantiopure α-fluoro-β(3)-amino acids with a wide variety of side chains. Its utility was demonstrated through the synthesis of orthogonally protected (2S,3S)-α-fluoro-β(3)-lysine.

Wood Protection Properties of Quaternary Ammonium Spiroborate Esters Derived from Alkyl Tartrates

Four new tetra-n-butylammonium spiroborates derived from dimethyl, diethyl, di-iso-propyl and di-n-butyl esters of l-tartaric acid have been prepared and their potential as environmentally benign wood protectants investigated. These compounds showed good activity in a no-choice cellulose paper bioassay with Coptotermes acinaciformis termites. The hydrolytic stability of these spiroborates is not high relative to other spiroborates, yet the tetra-n-butylammonium spiroborate derived from di-iso-propyl-l-tartrate showed remarkable permanence in timber in a demanding leaching test.

Quaternary Ammonium Spiroborate Esters and Mixed Anhydrides Derived from Aliphatic ?-Hydroxy Acids and Diacids and their Wood Protection Properties

The preparation of tetra-n-butylammonium spiroborates derived from the aliphatic α-hydroxy acids glycolic and (S)-(+)-mandelic acid, and the spiroborate mixed anhydrides derived from the dicarboxylic acids oxalic, malonic, succinic, and phthalic acid was investigated. The target ammonium spiroborates were obtained in pure form from glycolic, (S)-(+)-mandelic, and oxalic acids and were tested for their potential as wood preservatives. The spiroborates derived from glycolic acid and (S)-(+)-mandelic acid show promise and are worthy of further investigation. Useful information about the order of stability of the spiroborate mixed anhydrides derived from the dicarboxylic acids has been obtained and a new oxalato triborate related in structure to borax has been prepared and characterized by X-ray crystallography.

Foreword to Professor Athelstan L. J. Beckwith Special Issue

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Surgical treatment of complex distal humeral fractures: functional outcome after internal fixation using precontoured anatomic plates

HYPOTHESIS

Several studies have shown good results with internal fixation of distal humeral fractures; however, few have focused specifically on anatomic parallel plate fixation using the same implant and postoperative regimen. The purpose of this study was to determine the functional outcome after open reduction and internal fixation of these complex fractures using parallel precontoured anatomic plates.

MATERIALS AND METHODS

This was a retrospective single-surgeon series involving 16 patients (12 women, 4 men) treated with a double-column parallel plating technique. Clinical assessment included the Mayo Elbow Performance Score (MEPS) and Disabilities of the Arm, Shoulder and Hand Score (DASH). Mean age was 43 years (range, 20-78 years). Average follow-up was 35 months. Four fractures were AO type A and 12 were AO type C.

RESULTS

Union was achieved in all patients. There was no superficial or deep infection or hardware failure. Two patients required removal of plates for pain and prominence but not all screws could be completely removed. The mean flexion was 132 degrees and extension was 29 degrees . The mean DASH score was 46.1. Grip strength was 56% of the uninjured side. Mean flexion and extension force was 72% and 70%, respectively, of the uninjured elbow. The mean MEPS score was 72.3.

DISCUSSION

Anatomically precontoured parallel plates are effective in achieving bony union with low implant failure with acceptable functional outcomes. However, screw extraction can be difficult when the implant is removed.

Wood Protection Properties of Quaternary Ammonium Arylspiroborate Esters Derived from Naphthalene 2,3-Diol, 2,2'-Biphenol and 3-Hydroxy-2-naphthoic Acid

In continuation of a program aimed at developing a boron-based, high performing and environmentally benign wood preservative suitable for outdoor use, three lipophilic tetra-n-butylammonium spiroborates, tetra-n-butylammonium bis[naphthalene-2,3-diolato(2-)-O,O′]borate 4, tetra-n-butylammonium bis[2,2′-biphenolato(2-)-O,O′]borate 5 and tetra-n-butylammonium bis[3-hydroxy-2-naphthoato(2-)-O,O′]borate 6 were prepared and tested. The higher molecular weight and lipophilicity of these borates compared with related borates previously examined correlates, in the case of 5 and 6, with significantly enhanced leach resistance while termiticidal activity has been maintained. The racemic spiroborate derived from 2,2′-biphenol 5, in particular, appears to be close to an optimum balance between ease of synthesis, solubility, hydrolytic stability and termiticidal activity.

Carboxymethylated-kappa-casein: a convenient tool for the identification of polyphenolic inhibitors of amyloid fibril formation

Reduced and carboxymethylated-kappa-casein (RCM-kappa-CN) is a milk-derived amyloidogenic protein that readily undergoes nucleation-dependent aggregation and amyloid fibril formation via a similar pathway to disease-specific amyloidogenic peptides like amyloid beta (Abeta), which is associated with Alzheimer's disease. In this study, a series of flavonoids, many known to be inhibitors of Abeta fibril formation, were screened for their ability to inhibit RCM-kappa-CN fibrilisation, and the results were compared with literature data on Abeta inhibition. Flavonoids that had a high degree of hydroxylation and molecular planarity gave good inhibition of RCM-kappa-CN fibril formation. IC(50) values were between 10- and 200-fold higher with RCM-kappa-CN than literature results for Abeta fibril inhibition, however, with few exceptions, they showed a similar trend in potency. The convenience and reproducibility of the RCM-kappa-CN assay make it an economic alternative first screen for Abeta inhibitory activity, especially for use with large compound libraries.

Synthesis and Cav2.2 Binding Data for Non-Peptide Mimetics of ω-Conotoxin GVIA based on a 5-Amino-Anthranilamide Core

A simple and efficient method has been developed for the synthesis of two anthranilamide-based non-peptide mimetics of ω-conotoxin GVIA. These anthranilamide derivatives aim to mimic the K2, R17, and Y13 residues of the peptide. The synthetic route described enables the rapid synthesis of anthranilamide analogues with identical alkyl chain lengths. The target compounds show affinity to rat N-type voltage gated calcium channels (Cav2.2) with EC50 values of 42 and 75 μM.

The Preparation of Solid-Supported Peptide Boronic Acids Derived from 4-Borono-L-phenylalanine and their Affinity for Alizarin

A library of solid-supported pentapeptide diboronic acids, a ‘lysine series’ and an ‘arginine series’, has been efficiently prepared using N-Fmoc-4-pinacolatoborono-l-phenylalanine and standard solid phase peptide synthesis methods. A technique for measuring the affinity of the chromophoric diol, alizarin, to the solid-supported peptide boronic acids has been developed. Considerable variation in alizarin binding strengths, both within and between arginine and lysine series was observed, with association constants in the range 200–1100 M–1 being recorded. The selective binding characteristics of these boronic acid–peptide hybrids suggest their potential use in carbohydrate sensors and cell-specific diagnostics and therapeutics.

Ring expansion reactions of 4-amino-1,1-dioxo-[1,2,3,5]-thiatriazoles

An unusual ring-expansion reaction of 4-amino-1,1-dioxo-[1,2,3,5]-thiatriazoles has been identified that produces the relatively rare 5-amino-1,1-dioxo-[1,2,4,6]-thiatriazines and. Initial alkylation of the thiatriazole with alpha-halo-esters at N-3 produces alpha-substituted esters which, under basic reaction conditions, undergo opening of the thiatriazole ring and re-closure to a thiatriazine ring. Similar alkylations of with diethyl chloromalonate and ethyl dichloroacetate lead to the loss of SO2 and the production of triazine and triazole, apparently by an initial alkylation at N-5. The reaction of with phenacyl bromides or a phenacyl dibromide forms fully unsaturated 5-amino-1,1-dioxo-[1,2,4,6]-thiatriazines.

Approaches to selective peptidic inhibitors of factor Xa

Inhibitors of procoagulant enzymes, such as factor Xa (fXa) and thrombin, are important for treating thrombosis. Thrombin has complex pro- and anti-coagulant roles and thus fXa is thought to represent an ideal target. Discrete kcat and Km values for cleavage of a library of fluorescence-quenched substrates by fXa were determined. The results highlighted the low selectivity of fXa at its prime sites, and its poor efficiency compared with thrombin, creating a challenge for the design of fXa-specific peptidic inhibitors. We hypothesized that Km rather than kcat/Km values may be better indicators of inhibitor potential for a peptidic sequence, leading us to design peptide sequences for both fXa and thrombin in three forms: fluorescence-quenched substrates, standard alpha-peptides and peptides containing a beta-homoarginine at the cleavage site. Kinetic and competitive inhibition assays with both fXa and thrombin showed the fluorescence-quenched substrates to be the best inhibitors, while the inhibitory effect of the beta-homoarginine peptides varied for the two proteases. Importantly, fXa was inhibited to a much greater extent by the beta-peptides than the corresponding alpha-peptides, resulting in an increased selectivity for fXa inhibition over thrombin for those peptides containing a beta-amino acid at the cleavage site.

Improving the membrane permeability of sialic acid derivatives

The potential of boronic acids to improve the bioavailability of carbohydrate derived drugs was investigated through the study of the transport of four sialic acid derivatives through a lipophilic supported liquid membrane at departure phase pH's of 7.4, 8.5 and 10.0. It was found that facilitated transport did occur in most cases, but interestingly, and in contrast to that observed with monosaccharides such as d-fructose, the lipophilic ammonium salt, Aliquat 336, promoted fluxes than those of the boronic acid. The triol side chain of the sialic acid derivatives, combined with the amide at C5, appears to represent a previously unrecognised chloride binding domain which promotes extraction of these compounds into membranes containing Aliquat 336, leading to fluxes greater than those produced by boronic acids.

Quaternary Ammonium Arylspiroborate Esters as Organo-Soluble, Environmentally Benign Wood Protectants

As part of a larger project aimed at the development of leach resistant boron-based wood preservatives, the anti-fungal and termiticidal activities, and the resistance to leaching from timber, of three related tetra-n-butylammonium spiroborates, tetra-n-butylammonium bis(ortho-hydroxymethylphenolato)borate 2, tetra-n-butylammonium bis[catecholato(2–)-O,O′]borate 3, and tetra-n-butylammonium bis[salicylato(2−)-O,O']borate 4, have been examined. All three borates are found to be active against test organisms, with the following orders of activity being observed: 2 > 3 > 4 > boric acid against wood decay fungi, and 2 > 3 ≈ 4 > boric acid against termites. The most active compound in both assays 2 also has the highest calculated lipophilicity. In a test for permanence in wood, the following order of leach resistance is observed: 4 >> 3 ≈ 2 > boric acid. This order appears to correlate more closely with the stability constants of the borate esters, as determined using 11B NMR spectroscopy, rather than calculated lipophilicities.

Enhanced Anti-Fungal Activity of the Organo-Soluble Borate Ester, Tetra-n-butylammonium Bis(ortho-hydroxymethylphenolato)borate

The borate ester, tetra-n-butylammonium bis(ortho-hydroxymethylphenolato)borate, NBu4[B(o-hmp)2], was synthesized and characterized by NMR spectroscopy (1H, 13C, 11B), ES-MS, and X-ray crystallography. The anti-fungal activity of this compound, as well as its sodium salt, the parent phenol, tetra-n-butylammonium bromide, and boric acid were evaluated against two wood decay fungi. The tetraalkylammonium borate NBu4[B(o-hmp)2] shows the highest activity out of the compounds examined. This finding suggests that the formation of lipophilic borate esters is a promising approach for the development of leach-resistant, borate-based wood preservatives.

Transport of Alkali Halides through a Liquid Organic Membrane Containing a Ditopic Salt-Binding Receptor

A ditopic receptor is shown to have an impressive ability to recognize and extract the ion pairs of various alkali halides into organic solution. X-ray diffraction analysis indicates that the salts are bound in the solid state as contact ion pairs. Transport experiments, using a supported liquid membrane and high salt concentration in the source phase, show that the ditopic receptor can transport alkali halide salts up to 10-fold faster than a monotopic cation or anion receptor and 2-fold faster than a binary mixture of cation and anion receptors. All transport systems exhibit the same qualitative order of ion selectivity; that is, for a constant anion, the cation selectivity order is K+ > Na+ > Li+, and for a constant cation, the anion transport selectivity order is I- > Br- > Cl-. The data suggest that with a ditopic receptor, the polarity of the receptor-salt complex can be lowered if the salt is bound as an associated ion pair, which leads to a faster diffusion through the membrane and a higher maximal flux.

Synthesis and biological evaluation of nonpeptide mimetics of ω-conotoxin GVIA

A benzothiazole-derived compound (4a) designed to mimic the C(alpha)-C(beta) bond vectors and terminal functionalities of Lys2, Tyr13 and Arg17 in omega-conotoxin GVIA was synthesised, together with analogues (4b-d), which had each side-chain mimic systematically truncated or eliminated. The affinity of these compounds for rat brain N-type and P/Q-type voltage gated calcium channels (VGCCs) was determined. In terms of N-type channel affinity and selectivity, two of these compounds (4a and 4d) were found to be highly promising, first generation mimetics of omega-conotoxin. The fully functionalised mimetic (4a) showed low microM binding affinity to N-type VGCCs (IC(50)=1.9 microM) and greater than 20-fold selectivity for this channel sub-type over P/Q-type VGCCs, whereas the mimetic in which the guanidine-type side chain was truncated back to an amine (4d, IC(50)= 4.1 microM) showed a greater than 25-fold selectivity for the N-type channel.

Fructose-Permeable Liquid Membranes Containing Boronic Acid Carriers

Liquid membranes that contain boronic acids have potential application in environmentally benign industrial D-fructose production. This review describes our efforts to develop boronic acid carriers that promote high fluxes, that are resistant to leaching, and that are highly selective for fructose over other sugars. Considerable progress has been made with multidentate boronic acid carriers. Initial attempts to transport D-fructose as macrocyclic β-D-fructopyranose diesters appeared to suffer from competitive transport of macrocyclic α-D-glucofuranose diesters, and did not lead to high D-fructose selectivity. On the other hand, carriers that can bind multiple equivalents of D-fructose as tridentate β-D-fructofuranose esters have been much more effective. Unfortunately, D-fructose selectivity is still apparently limited by a competitive and boronic acid-independent non-selective ‘mobile fixed site relay’ transport process. However, further progress will be possible through improved carrier design, careful investigation of the various stages of the transport process, and the use of more industrially useful membrane configurations.