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  • We also explored various nitrogen substituents with

    2022-08-11

    We also explored various nitrogen substituents with an aim toward modulating sterics and basicity within the ABH series. No glycine uptake inhibition was detected with non-basic bicycles (data not shown). Isopropyl was the best compromise between desired on-target effect and clearance, however, efflux was still problematic. We did see a favorable shift in the latter with cyclopropyl , but microsomal stability was dramatically worse. Lastly, as with pyridine , Azidobutyric acid NHS ester in log through nitrogen incorporation was unsuccessful. This change adversely impacted potency () and efflux () respectively. Intravenous and oral pharmacokinetic profiles of dimethylbenzamide were determined in Sprague Dawley rats (). Compared to in vitro results, a lower than expected in vivo clearance was observed, which may be indicative of an underlying saturation mechanism. Consequently, bioavailability was also high while volume of distribution was low. Consistent with MDR1 efflux results, the brain-to-plasma ratio was low in rat but, for reasons not well understood, higher in mouse (brain/plasma: 0.4; CD-1 mice dosed s.c.). This may be at least partially reflective of the lower plasma-protein binding observed in the latter species (mu PPB: 32% free). Additionally, when profiling for off-target pharmacology, only five out of 100 targets demonstrated moderate activity in an MDS Pharma panel (% inhib @ 10 μM): human: α (54), RXR- α (−5 4) & 5HT (62); rat: Ca channel L-type (65) & Na channel site-2 (70). Minimal inhibition (<20%) was observed for related targets such as adenosine, DAT, NET, and SERT transporters and the NMDA receptor. Activity against glycine transporter-2 (GlyT2) was also low (GlyT2 IC 3.8 μM). Compound was tested in a mouse MK801 locomotor activity assay to model the treatment of positive and negative symptoms of schizophrenia. Compound showed dose-dependent reversal of MK801-induced locomotor activity and a statistically significant dose response at 3 and 10 μmol/kg (p < 0.01). Furthermore, potency at 3 μmol/kg for was comparable to at a higher dose (10 μmol/kg) (). Compounds described herein were prepared using the general route described in , which involved addition of an aryl or heteroaryl Grignard or lithium alternative to a chiral or racemic sulfinamide followed by deprotection and acylation. Isoquinuclidine/done, ABH, or ABX core aldehydes were prepared from their respective acid or ester precursors, and these syntheses, along with those of the fully elaborated final products have been previously reported., , An example synthesis of isoquinuclidine is shown in . Amide was alkylated with iodomethane and then reduced at low temperature using lithium aluminum hydride to afford aldehyde directly. Lewis acid-mediated sulfinamide formation to give was followed by trimethylaluminum-assisted addition of phenyllithium (98% d.e.), amide reduction using catalytic RhH(CO)(PPh), and deprotection using methanolic HCl. Acid coupling then provided . Final products derived from racemic analogs of (isoquinuclidines, ABHs, or ABXs) could be resolved under chiral chromatography conditions using supercritical fluid chromatography (SFC) or reverse phase chiral chromatography as a final step. For chiral isoquinuclidine final compounds, stereochemistry was assigned based on a comparison of intermediate calculated VCD spectra (, red/upper; , green/lower) with that derived experimentally from the amine (prior to amide coupling) which afforded more active (blue). In summary, we have described modifications to a series of isoquinuclidine benzamides as part of an effort to develop a novel in vivo probe for inhibiting glycine uptake in an MK801 LMA assay. In addition to potency, lipophilicity and human microsomal clearance were parameters for optimization. Heteroatom incorporation into the benzamide portion of led to equipotent derivatives (, ) with reduced log. Conversion of the pendant phenyl ring into a 2-methylfuran or pyridine (–) was less well tolerated but still superior from a potency perspective to all but changes to the meta position. Modest improvements in predicted human CL could be had through changes in ring size and the -alkyl group of the isoquinuclidine itself, with ABH and ABX bicycles lacking an alkylated nitrogen (–, ) demonstrating the largest improvement in microsomal stability. Simultaneously achieving a low efflux ratio remained elusive. Dimethylbenzamide , after evaluation for rat pharmacokinetics, was tested in a mouse MK801 LMA assay and had a statistically significant attenuation of locomotor activity at 3 and 10 μmol/kg compared to control, with favorable comparison to . The results of further optimization, an investigation of clearance mechanisms, and conditioned avoidance response and novel object recognition data will be reported in due course.