The novel antiepileptic drug, (R)-N-benzyl 2-acetamido-3-methoxypropionamide ((R)-lacosamide, Vimpat® ((R)-1)), was recently approved in the US and Europe for adjuvant treatment of partial-onset seizures in adults. (R)-1 preferentially enhances slow inactivation of voltage-gated Na+ currents, a pharmacological process relevant in the hyperexcitable neuron. We have advanced a strategy to identify lacosamide binding partners by attaching affinity bait (AB) and chemical reporter (CR) groups to (R)-1 to aid receptor detection and isolation. We showed that select lacosamide AB and AB&CR derivatives exhibited excellent activities similar to (R)-1 in the maximal electroshock seizure model in rodents. Here, we examined the effect of these lacosamide AB and AB&CR derivatives and compared them with (R)-1 on Na+ channel function in CNS catecholaminergic (CAD) cells. Using whole-cell patch clamp electrophysiology, we demonstrated that the test compounds do not affect the Na+ channel fast inactivation process, that they were far better modulators of slow inactivation than (R)-1, and that modulation of the slow inactivation process was stereospecific. The lacosamide AB agents that contained either an electrophilic isothiocyanate ((R)-5) or a photolabile azide ((R)-8) unit upon AB activation gave modest levels of permanent Na+ channel slow inactivation, providing initial evidence that these compounds may have covalently reacted with their cognate receptor(s). Our findings support the further use of these agents to delineate the (R)-1–mediated Na+ channel slow inactivation process.

We recently reported that merging key structural pharmacophores of the anticonvulsant drugs lacosamide (a functionalized amino acid) with safinamide (an α-aminoamide) resulted in novel compounds with anticonvulsant activities superior to that of either drug alone. Here, we examined the effects of six such chimeric compounds on Na+-channel function in central nervous system catecholaminergic (CAD) cells. Using whole-cell patch clamp electrophysiology, we demonstrated that these compounds affected Na+ channel fast and slow inactivation processes. Detailed electrophysiological characterization of two of these chimeric compounds that contained either an oxymethylene ((R)-7) or a chemical bond ((R)-11) between the two aromatic rings showed comparable effects on slow inactivation, use-dependence of block, development of slow inactivation, and recovery of Na+ channels from inactivation. Both compounds were equally effective at inducing slow inactivation; (R)-7 shifted the fast inactivation curve in the hyperpolarizing direction greater than (R)-11, suggesting that in the presence of (R)-7, a larger fraction of the channels are in an inactivated state. None of the chimeric compounds affected veratridine- or KCl-induced glutamate release in neonatal cortical neurons. There was modest inhibition of KCl-induced calcium influx in cortical neurons. Finally, a single intraperitoneal administration of (R)-7, but not (R)-11, completely reversed mechanical hypersensitivity in a tibial-nerve injury model of neuropathic pain. The strong effects of (R)-7 on slow and fast inactivation of Na+ channels may contribute to its efficacy and provide a promising novel therapy for neuropathic pain, in addition to its antiepileptic potential.

The structure-activity relationship (SAR) for the N-benzyl group in the clinical antiepileptic agent (R)-lacosamide ((R)-N-benzyl 2-acetamido-3-methoxypropionamide, (R)-3) has been explored. Forty-three compounds were prepared and then evaluated at the National Institute of Neurological Disorders and Stroke Anticonvulsant Screening Program for seizure protection in the maximal electroshock (MES) and subcutaneous Metrazol models. Comparing activities for two series of substituted aryl regioisomers (2′, 3′, 4′) showed that 4′-modified derivatives had the highest activity. Significantly, structural latitude existed at the 4′-site. The SAR indicated that non-bulky 4′-substituted (R)-3 derivatives exhibited superb activity, independent of their electronic properties. Activities in the MES test of several compounds were either comparable with or exceeded that of (R)-3, and surpassed the activities observed for the traditional antiepileptic agents phenytoin, phenobarbital, and valproate.Epilepsy, a major neurological disorder that affects all populations, 1 describes the types of recurrent seizures produced by paroxysmal, excessive, synchronous neuronal discharges in the brain. 2,3 In the United States alone, over 2 million people suffer from epilepsy and its sequelae; 340,000 are children. 4 For many of these individuals, the disabilities and associated neuropsychological and behavioral factors adversely affect their quality of life. The lifestyle restrictions plus the large expense for treatment, lost productivity, and rehabilitation result in a huge cost to society. 4 The treatment mainstay for patients with epileptic disorders has been the long-term and consistent administration of anticonvulsant drugs. 5,6 Unfortunately, current medications are ineffective for approximately one-third of these patients. 7 Many continue to have seizures, while others experience disturbing side effects (e.g., drowsiness, dizziness, nausea, liver damage). 8 Thus, there is a need for more efficacious drugs that function by different pharmacological pathways.CORRESPONDING AUTHOR: Division of Medicinal Chemistry and Natural Products, UNC Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina 27599-7568 and Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, hkohn@email.unc.edu, Telephone: 919-843-8112, Fax number: 919-966-0204. Supporting Information Available: Synthetic procedures for the intermediates leading to the preparation of (R)-4, 7-31, 33-39, 60, and 61, and (S)-11, 21, 23, 26, 28, 29, 34, and 38, elemental analyses, 1 H and 13 C NMR spectra of compounds evaluated in this study. This material is available free of charge via the internet at http://pubs.acs.org. NIH Public AccessAuthor Manuscript J Med Chem. Author manuscript; available in PMC 2011 February 11. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptIn 1985, we discovered a novel class of anticonvulsant agents, termed functionalized amino acids (FAA, a 1). ...

Abstract(R)-Lacosamide ((R)-2, (R)-N-benzyl 2-acetamido-3-methoxypropionamide), has recently gained regulatory approval for the treatment of partial-onset seizures in adults. Whole animal pharmacological studies have documented that (R)-2 function is unique. A robust strategy is advanced for the discovery of interacting proteins associated with function and toxicity of (R)-2 through the use of (R)-2 analogs, 3, that contain "affinity bait (AB)" and "chemical reporter (CR)" functional groups. In 3, covalent modification of the interacting proteins proceeds at the AB moiety, and detection or isolation of the selectively captured protein occurs through the bioorthogonal CR group upon reaction with an appropriate probe. We report the synthesis, pharmacological evaluation, and interrogation of the mouse soluble brain proteome using 3 where the AB group is an isothiocyanate moiety. One compound, (R)-N-(4-isothiocyanato)benzyl 2-acetamido-3-(prop-2-ynyloxy) propionamide ((R)-9), exhibited excellent seizure protection in mice and, like (R)-2, anticonvulsant activity principally resided in the (R)-stereoisomer. Several proteins were preferentially labeled by (R)-9 compared with (S)-9, including collapsin response mediator protein 2.