Angus Murray Macleod

Tachykinin NK1 receptor antagonists act centrally to inhibit emesis induced by the chemotherapeutic agent cisplatin in ferrets

These studies have compared the pharmacological profile of two non-peptide human type neurokinin1 (hNK1) receptor selective antagonists, L-741,671 and a quaternised compound L-743,310. In radioligand binding studies L-741,671 and L-743,310 had high affinity for ferret and cloned hNK1 receptors [Ki (nM) ferret 0.7 and 0.1; human 0.03 and 0.06, respectively] but low affinity for rodent NK1 receptors [Ki (nM) 64 and 17, respectively] suggesting that ferret receptors have hNK1-like binding pharmacology. Studies in vivo showed that L-741,671 and L-743,310 had equivalent functional activity in the periphery (ID50s of 1.6 and 2 micrograms/kg i.v., respectively) as measured by inhibition of plasma protein extravasation evoked in the oesophagus of guinea pigs by resiniferatoxin (7 nmol/kg i.v.). Using an in situ brain perfusion technique in anaesthetised rats, L-741,671 was shown to be much more brain penetrant than the quaternary compound L-743,310 which had an entry rate similar to the poorly brain penetrant plasma marker inulin. These compounds thus provided an opportunity to compare the anti-emetic effects of equi-active hNK1 receptor antagonists with and without brain penetration to central NK1 receptor sites. When tested against cisplatin-induced emesis in ferrets, L-741,671 (0.3, 1 and 3 mg/kg i.v.) produced marked dose-dependent inhibition of retching and vomiting but L-743,310 was inactive at 3 and 10 micrograms/kg i.v. In contrast, direct central injection of L-741,671 and L-743,310 (30 micrograms) into the vicinity of the nucleus tractus solitarius or L-743,310 (200 micrograms) intracisternally was shown to inhibit retching and vomiting induced by i.v. cisplatin. L-741,671 and L-743,310 had equivalent functional activity, at the same dose, against cisplatin-induced emesis when injected centrally. These observations indicated that had L-743,310 penetrated into the brain after systemic administration it would have been active in the cisplatin-induced emesis assay and so show that brain penetration is essential for the anti-emetic action of systemically administered NK1 receptor antagonists.

An inverse agonist selective for alpha5 subunit-containing GABAA receptors enhances cognition.

α5IA is a compound that binds with equivalent subnanomolar affinity to the benzodiazepine (BZ) site of GABAA receptors containing an α1, α2, α3, or α5 subunit but has inverse agonist efficacy selective for the α5 subtype. As a consequence, the in vitro and in vivo effects of this compound are mediated primarily via GABAA receptors containing an α5 subunit. In a mouse hippocampal slice model, α5IA significantly enhanced the θ burst-induced long-term potentiation of the excitatory postsynaptic potential in the CA1 region but did not cause an increase in the paroxysmal burst discharges that are characteristic of convulsant and proconvulsant drugs. These in vitro data suggesting that α5IA may enhance cognition without being proconvulsant were confirmed in in vivo rodent models. Hence, α5IA significantly enhanced performance in a rat hippocampal-dependent test of learning and memory, the delayed-matching-to-position version of the Morris water maze, with a minimum effective oral dose of 0.3 mg/kg, which corresponded to a BZ site occupancy of 25%. However, in mice α5IA was not convulsant in its own right nor did it potentiate the effects of pentylenetetrazole acutely or produce kindling upon chronic dosing even at doses producing greater than 90% occupancy. Finally, α5IA was not anxiogenic-like in the rat elevated plus maze nor did it impair performance in the mouse rotarod assay. Together, these data suggest that the GABAA α5-subtype provides a novel target for the development of selective inverse agonists with utility in the treatment of disorders associated with a cognitive deficit.

Chiral Base-Mediated Asymmetric Synthesis of Tricarbonyl(.eta.6-arene)chromium Complexes

Enantiomerically enriched tricarbonyl(η 6 -arene)chromium complexes can be obtained in up to 84% ee from the reaction of certain monosubstituted complexes with Me 3 SiCl, mediated by a chiral lithium amide base

A study of the synthesis and racemisation of a chiral lithiated tricarbonyl(η6-anisole)chromium complex

Abstract The non-racemic metallated complex derived from tricarbonyl(η 6 -anisole)chromium 1 , formed using the homochiral lithium amide base 2 , undergoes rapid racemisation by intermolecular proton transfer if the neutral chromium complex is present, this problem being minimised if the deprotonation is conducted in the presence of LiCl.

In vitro and in vivo properties of 3-tert-butyl-7-(5-methylisoxazol-3-yl)-2-(1-methyl-1H-1,2,4-triazol-5-ylmethoxy)-pyrazolo[1,5-d]-[1,2,4]triazine (MRK-016), a GABAA receptor alpha5 subtype-selective inverse agonist

3-tert-Butyl-7-(5-methylisoxazol-3-yl)-2-(1-methyl-1H-1,2,4-triazol-5-ylmethoxy)-pyrazolo[1,5-d][1,2,4]triazine (MRK-016) is a pyrazolotriazine with an affinity of between 0.8 and 1.5 nM for the benzodiazepine binding site of native rat brain and recombinant human α1-, α2-, α3-, and α5-containing GABAA receptors. It has inverse agonist efficacy selective for the α5 subtype, and this α5 inverse agonism is greater than that of the prototypic α5-selective compound 3-(5-methylisoxazol-3-yl)-6-[(1-methyl-1,2,3-triazol-4-hdyl)methyloxy]-1,2,4-triazolo[3,4-a]phthalazine (α5IA). Consistent with its greater α5 inverse agonism, MRK-016 increased long-term potentiation in mouse hippocampal slices to a greater extent than α5IA. MRK-016 gave good receptor occupancy after oral dosing in rats, with the dose required to produce 50% occupancy being 0.39 mg/kg and a corresponding rat plasma EC50 value of 15 ng/ml that was similar to the rhesus monkey plasma EC50 value of 21 ng/ml obtained using [11C]flumazenil positron emission tomography. In normal rats, MRK-016 enhanced cognitive performance in the delayed matching-to-position version of the Morris water maze but was not anxiogenic, and in mice it was not proconvulsant and did not produce kindling. MRK-016 had a short half-life in rat, dog, and rhesus monkey (0.3–0.5 h) but had a much lower rate of turnover in human compared with rat, dog, or rhesus monkey hepatocytes. Accordingly, in human, MRK-016 had a longer half-life than in preclinical species (∼3.5 h). Although it was well tolerated in young males, with a maximal tolerated single dose of 5 mg corresponding to an estimated occupancy in the region of 75%, MRK-016 was poorly tolerated in elderly subjects, even at a dose of 0.5 mg, which, along with its variable human pharmacokinetics, precluded its further development.

A novel series of non‐quaternary oxadiazoles acting as full agonists at muscarinic receptors

1 A novel series of non‐quaternary oxadiazole‐based muscarinic agonists demonstrated high affinity for muscarinic receptors. 2 These agonists possessed high efficacy in the nanomolar range at muscarinic receptors in the superior cervical ganglion, atrium and ileum but did not show selectivity across the tissue preparations. 3 Two amino oxadiazoles, one from a quinuclidine series (L‐660,863) and one from a 1‐azanorbornane series (L‐670,207) possessed a high ratio of potency for displacing the binding of [3H]‐N‐methylscopolamine ([3H]‐NMS) to potency for displacing the agonist [3H]‐oxotremorine‐M ([3H]‐oxo‐M) (NMS/oxo‐M ratio) predictive of high efficacy in the cortex. 4 The two azanorbornane derivatives L‐670,548 and L‐670,207 stimulated the turnover of phosphatidylinositol in the cortex with a potency higher than that obtained with any other known muscarinic agonist (ED50 0.26 and 0.18 μm respectively). 5 The maximum response obtained with L‐670,207 was greater than that observed for carbachol but was comparable to that of the natural ligand acetylcholine. 6 These oxadiazole muscarinic agonists are among the most potent and efficacious non‐quaternary muscarinic agonists ever described.

Dioxalanones as synthetic intermediates. Part 6. Synthesis of 3-deoxy-D-manno-2-octulosonic acid (KDO), 3-deoxy-D-arabino-2-heptulosonic acid (DAH) and 2-keto-3-deoxy-D-gluconic acid (KDG)

Abstract Three biosynthetically significant α-keto acids KDO ( 7 ), DAH ( 8 ) and KDG ( 9 ) have been synthesised via 5-ylidene-1,3-dioxalan-4-one intermediates formed by Wittig reactions of protected monosaccharide-derived aldehydes with the Wittig reagent ( 3 ).

Serine derived NK1 antagonists 2: a pharmacophore model for arylsulfonamide binding

Modifications to the spirocyclic aryl sulfonamide portion of serine derived NK1 antagonists allow a partial pharmacophore model to be developed.

Chemistry of 5-ylidene-1,3-dioxolan-4-ones. Syntheses of3-deoxy-D-arabino-2-heptulosonic acid (DAH) and3-deoxy-D-manno-2-octulosonic acid (KDO)

Abstract 3-Deoxy-D-arabino-2-heptulosonic acid and 3-deoxy-D-manno-2-octulosonic acid have been synthesised in chiral form from D-arabinose and D-mannose respectively, via 5-ylidene-1,3-dioxolan-4-one intermediates. The α-keto acid function in the products is liberated under mild basic hydrolysis conditions.

A small molecule mitigates hearing loss in a mouse model of Usher syndrome III

Usher syndrome type III (USH3) characterized by progressive deafness, variable balance disorder, and blindness is caused by destabilizing mutations in the gene encoding the clarin-1 protein (CLRN1). Here we report a novel strategy to mitigate hearing loss associated with a common USH3 mutation CLRN1N48K that involved a cell-based high-throughput screening of small molecules capable of stabilizing CLRN1N48K, a secondary screening to eliminate general proteasome inhibitors, and finally an iterative process to optimize structure activity relationships. This resulted in the identification of BF844. To test the efficacy of BF844, a mouse model was developed that mimicked the progressive hearing loss of USH3. BF844 effectively attenuated progressive hearing loss and prevented deafness in this model. Because the human CLRN1N48K mutation causes both hearing and vision loss, BF844 could in principle prevent both sensory deficiencies in USH3. Moreover, the strategy described here could help identify drugs for other protein-destabilizing monogenic disorders.