We record the optimization of a series of novel metabotropic glutamate

We record the optimization of a series of novel metabotropic glutamate receptor 5 (mGlu5) positive allosteric modulators (PAMs) from a 5 6 class of dihydropyrazolo[1 5 remained problematic for the series. or allosteric agonism 19 20 respectively suggesting that PAMs with lower cooperativity and devoid of allosteric agonism may be preferable for obtaining an improved therapeutic index. More recently we disclosed phenoxy-based tool compounds derived from a dihydrothiazolopyridone21 and napthyridinone22 series; these compounds include PAMs with low to moderate efficacy. Although CNS disposition was excellent optimized modulators maintained relatively high clearance in rat and dog and were notably less potent relative to picolinamide-based acetylenic PAMs which readily achieve sub-100 nM potency. Figure 1 Representative mGu5 PAMs with amide and non-amide hydrogen-bond acceptor (HBA) pharmacophores. ARHGEF7 As part of an effort to examine the common amide motif present within chemotypes 1-4 we were interested in determining if bicyclic acetylenic-based ketone 5 and alcohol 6 reported by Merz23 as potent mGlu5 PAMs (rat mGlu5 EC50 = 34 and 180 nM respectively) would serve as an alternate hydrogen-bond acceptor (HBA) pharmacophore within one of our non-acetylene ether-based scaffolds. Incorporation of a chiral hydroxyl moeity was TG 100801 particularly attractive as a means to add TG 100801 sp3 character as TG 100801 well as an opportunity to carry a hydrogen bond donor to enhance aqueous solubility a structural motif presently rare in mGlu5 PAMs. Although encouraged at the outset we were also cognizant of recent structure-activity relationships (SAR) in a picolinamide acetylene chemotype demonstrating that hydroxyl installation within an eastern amide either directly or through bioactivation uncovered an unexpected allosteric activity at mGlu5 a pharmacological profile associated with epileptiform activity and a target mediated AE liability.19 20 24 To test the viability of alternate HBA pharmacophores fragments like those found within the Merz tetralone scaffolds we utilized a recently developed 5 6 pyrazole lactam nucleus25 as a template to test this hypothesis. To this end we focused on target 11 which was envisioned to be synthesized via a Dieckmann condensation followed by Krapcho decarboxylation from key intermediate 9. Synthesis of the initial proof-of-concept target ketone 11 began with prepearation of known pyrazole ester 8 (Scheme 1). Subjection of phenoxyacetone to sodium ethoxide and addition of the resulting enolate to diethyl oxalate yielded β-diketone 7. Condensation with TG 100801 hydrazine afforded the desired pyrazole ester 8 which was transported ahead without purification. Sadly alkylation of 8 with ethyl 4-bromobutyrate and NaH in THF at 0 °C afforded specifically undesired regioisomer 9’. A display of bases and solvents (LiOH KOH K2CO3 Cs2CO3 KOtBu LHMDS; MeCN toluene DMSO DMF) exposed that K2CO3 in DMF had been ideal for alkylation of 8 yielding inside a 3:1 combination of regioisomers 9 and 9’ (69% isolated produce 9). With diester 9 at hand Dieckmann condensation (KOPd[P(rate of metabolism with expected hepatic clearance (CLHEP) = 46.1 mL min?1 kg?1 in rat and 15.2 mL min?1 kg?1 in human being. Plasma proteins binding experiments exposed that 11 was extremely unbound (21% unbound in rat plasma 23 unbound in human being plasma ) and steady in plasma from both varieties (4 hr incubation; 37 °C). Evaluation from the inhibition from the main cytochrome P450 (CYP) enzymes proven that 11 has moderate inhibitory activity at 1A2 (6.2 μM) with no activity observed against the other major CYPs tested (2C9 2000000 3 Dimethyl analog 12e displayed higher predicted clearance near hepatic blood flow (64.4 mL min?1 kg?1 in rat and 17.6 mL min?1 kg?1 in human) with TG 100801 a reduced yet attractive fraction unbound TG 100801 (7% unbound in rat plasma 10 unbound in human plasma). Like PAM 11 12 displayed modest inhibitory activity at 1A2 (7.3 μM). α-Aryl congener 12c the most potent mGlu5 PAM from this study as a racemic mixture (rat EC50 = 35 nM) was rapidly turned over (CLHEP = 61.6 mL min?1 kg?1 in rat and 16.0 mL min?1 kg?1 in human) and was moderate to highly bound across species (3.2% unbound in rat plasma 0.8% unbound in human.