Discovery of a potent, selective, and less flexible selective norepinephrine reuptake inhibitor (sNRI)

Study on Pyridine-Boryl Radical-Promoted, Ketyl Radical-Mediated Carbon-Carbon Bond-Forming Reactions

Ketyl radicals are synthetically versatile reactive species, but their applications have been hampered by harsh generation conditions employing highly reducing metals. Recently, the pyridine-boryl radical received wide attention as a promising organic reductant because of its mildness as well as convenience in handling. While probing the utility of the pyridine-boryl radical, our group observed facile pinacol coupling reactivity that had not been known at that time. This serendipitous finding was successfully rendered into a practical synthesis of tetraaryl-1,2-diols in up to 99% yield within 1 h. Subsequently, upon examinations of various reaction manifolds, a diastereoselective ketyl-olefin cyclization was accomplished to produce cycloalkanols such as trans-2-alkyl-1-indanols. Compared to the previous methods, the stereocontrolling ability was considerably enhanced by taking advantage of the structurally modifiable boryl group that would be present near the bond-forming site. In this full account, our synthetic efforts with the O-boryl ketyl radicals are disclosed in detail, covering the discovery, optimization, scope expansion, and mechanistic analysis, including density functional theory (DFT) calculations.

Stereochemical modulation of ketyl radical cyclization enabled by pyridine-boryl radicals: catalytic diastereoselective synthesis of trans-2-alkyl-1-indanols

Previously available ketyl radical cyclization conditions suffer from low and uncontrollable diastereoselectivity because of the absence of reagent-substrate interactions. In this report, stereochemical modulation was accomplished by taking advantage of the pyridine-boryl radical, which leaves the synthetically modifiable boronate moiety on the carbonyl oxygen near the reacting center during the stereo-determining cyclization step. In consequence, a catalytic diastereoselective synthesis of trans-2-substituted-1-indanols was achieved in the presence of a sterically congested six-membered diboronic ester and an efficient hydrogen atom donor.

Preclinical to clinical translation of CNS transporter occupancy of TD-9855, a novel norepinephrine and serotonin reuptake inhibitor

BACKGROUND

Monoamine reuptake inhibitors exhibit unique clinical profiles that reflect distinct engagement of the central nervous system (CNS) transporters.

METHODS

We used a translational strategy, including rodent pharmacokinetic/pharmacodynamic modeling and positron emission tomography (PET) imaging in humans, to establish the transporter profile of TD-9855, a novel norepinephrine and serotonin reuptake inhibitor.

RESULTS

TD-9855 was a potent inhibitor of norepinephrine (NE) and serotonin 5-HT uptake in vitro with an inhibitory selectivity of 4- to 10-fold for NE at human and rat transporters. TD-9855 engaged norepinephrine transporters (NET) and serotonin transporters (SERT) in rat spinal cord, with a plasma EC50 of 11.7 ng/mL and 50.8 ng/mL, respectively, consistent with modest selectivity for NET in vivo. Accounting for species differences in protein binding, the projected human NET and SERT plasma EC50 values were 5.5 ng/mL and 23.9 ng/mL, respectively. A single-dose, open-label PET study (4-20mg TD-9855, oral) was conducted in eight healthy males using the radiotracers [(11)C]-3-amino-4- [2-[(di(methyl)amino)methyl]phenyl]sulfanylbenzonitrile for SERT and [(11)C]-(S,S)-methylreboxetine for NET. The long pharmacokinetic half-life (30-40 h) of TD-9855 allowed for sequential assessment of SERT and NET occupancy in the same subject. The plasma EC50 for NET was estimated to be 1.21 ng/mL, and at doses of greater than 4 mg the projected steady-state NET occupancy is high (>75%). After a single oral dose of 20mg, SERT occupancy was 25 (±8)% at a plasma level of 6.35 ng/mL.

CONCLUSIONS

These data establish the CNS penetration and transporter profile of TD-9855 and inform the selection of potential doses for future clinical evaluation.

Silylation-based kinetic resolution of monofunctional secondary alcohols

The nucleophilic small molecule catalyst (-)-tetramisole was found to catalyze the kinetic resolution of monofunctional secondary alcohols via enantioselective silylation. Optimization of this new methodology allows for selectivity factors up to 25 utilizing commercially available reagents and mild reaction conditions.

1-(Indolin-1-yl)-1-phenyl-3-propan-2-olamines as potent and selective norepinephrine reuptake inhibitors

Efforts to identify new selective and potent norepinephrine reuptake inhibitors (NRIs) for multiple indications by structural modification of the previous 3-(arylamino)-3-phenylpropan-2-olamine scaffold led to the discovery of a novel series of 1-(indolin-1-yl)-1-phenyl-3-propan-2-olamines (9). Investigation of the structure-activity relationships revealed that small alkyl substitution at the C3 position of the indoline ring enhanced selectivity for the norepinephrine transporter (NET) over the serotonin transporter (SERT). Several compounds bearing a 3,3-dimethyl group on the indoline ring, 9k, 9o,p, and 9s,t, exhibited potent inhibition of NET (IC(50) = 2.7-6.5 nM) and excellent selectivity over both serotonin and dopamine transporters. The best example from this series, 9p, a potent and highly selective NRI, displayed oral efficacy in a telemetric rat model of ovariectomized-induced thermoregulatory dysfunction, a mouse p-phenylquinone (PPQ) model of acute visceral pain, and a rat spinal nerve ligation (SNL) model of neuropathic pain.

Structure-activity relationships of norepinephrine reuptake inhibitors with benzothiadiazine dioxide or dihydrosulfostyril cores

Two related series of selective norepinephrine reuptake inhibitors were synthesized based on 3,4-dihydro-1H-2,1,3-benzothiadiazine 2,2-dioxide or 3,4-dihydrosulfostyril cores, and screened for monoamine reuptake inhibition. Structure-activity relationships were determined for the series' in vitro potency and selectivity versus serotonin or dopamine transporter inhibition, and analogs based on both cores were identified as potent and selective NRIs. The 3,4-dihydrosulfostyril series was further tested for microsome stability, and compound 16j, which was optimized for both potency and stability, showed efficacy in an in vivo model of thermoregulatory dysfunction.

1- or 3-(3-Amino-2-hydroxy-1-phenyl propyl)-1,3-dihydro-2H-benzimidazol-2-ones: potent, selective, and orally efficacious norepinephrine reuptake inhibitors

Sequential structural modifications of the aryloxypropanamine template (e.g., atomoxetine, 2) led to a novel series of 1-(3-amino-2-hydroxy-1-phenyl propyl)-1,3-dihydro-2H-benzimidazol-2-ones as selective norepinephrine reuptake inhibitors (NRIs). In general, this series of compounds potently blocked the human norepinephrine transporter (hNET) while exhibiting selectivity at hNET against both the human serotonin (hSERT) and dopamine transporters (hDAT). Numerous compounds (e.g., 19-22) had low nonamolar hNET potency with IC(50) values of 7-10 nM and excellent selectivity (>500 fold) at hNET over hSERT and hDAT. Several compounds, such as 20 and 22, were tested in a telemetric rat model of ovariectomized-induced thermoregulatory dysfunction and were efficacious at oral doses of 3 mg/kg in reducing the tail skin temperature. In addition, compound 20 was also studied in the rat hot plate and spinal nerve ligation (SNL) models of acute and neuropathic pain, respectively, and was orally efficacious at doses of 3-10 mg/kg.

Recent advances in the understanding of the interaction of antidepressant drugs with serotonin and norepinephrine transporters

The biogenic monoamine transporters are integral membrane proteins that perform active transport of extracellular dopamine, serotonin and norepinephrine into cells. These transporters are targets for therapeutic agents such as antidepressants, as well as addictive substances such as cocaine and amphetamine. Seminal advances in the understanding of the structure and function of this transporter family have recently been accomplished by structural studies of a bacterial transporter, as well as medicinal chemistry and pharmacological studies of mammalian transporters. This feature article focuses on antidepressant drugs that act on the serotonin and/or the norepinephrine transporters. Specifically, we focus on structure-activity relationships of these drugs with emphasis on relationships between their molecular properties and the current knowledge of transporter structure.