Brivaracetam | SV2A Protein Modulators| Sodium Channel Antagonists | Treatment for Partial-Onset Seizures

Brivaracetam {[2S]-2-[(4R)-2-oxo-4-propylpyrrolidinyl] butanamide} is a 2-pyrrolidone derivative with high affinity for synaptic vesicle glycoprotein 2a (SV2A). It is the newest member of UCB’s family of racetam compounds, and chemically is a 4-n-propyl analogue of its predecessor Levetiracetam [1]. Brivaracetam is a highly selective, reversible and water soluble SV2A ligand.

The birth of Brivaracetam is credited to the discovery of synaptic vesicle protein 2A (SV2A) as the principal site involved in the antiepileptic effect of Levetiracetam. This stimulated UCB to search for analogues with higher affinity for SV2A than Levetiracetam. While the exact role of SV2A is unknown, there is a high correlation between binding affinity at SV2A and antiepileptic activity [1, 2].

Brivaracetam: 2D and 3D Structure. There is a possibility of intramolecular hydrogen bond.

Brivaracetam was identified after a primary in vitro screening of over 10000 compounds, a secondary screening of 900 compounds in the mouse audiogenic seizure model, and a tertiary screening of 30 drug candidates in various other epilepsy models [2].

Brivaracetam has been extensively evaluated and compared to levetiracetam in a wide variety of in vitro and in vivo preclinical models of seizures and epilepsy. This assessment has demonstrated that brivaracetam exerts a more potent seizure protection than levetiracetam and, in several models, complete seizure suppression.

Brivaracetam binds to SV2A in the brain (pK_i = 7.1) with greater selectivity and 15- to 30-fold higher affinity than Levetiracetam (pK_i = 6.1), as demonstrated in preclinical models, and has demonstrated efficacy in reducing the frequency of partial onset seizures in clinical trials.

Since Brivaracetam is differentiated from Levetiracetam not only in potency but also in efficacy in several preclinical models of epilepsy, it has been postulated that either additional mechanisms of action for Brivaracetam might exist besides binding to SV2A, or alternatively that the binding of Brivaracetam to SV2A might lead to a qualitatively different functional response. The compound has been found to possess some inhibitory activity at neuronal voltage dependent sodium channels (albeit at high concentrations), on which Levetiracetam is inactive, and to reverse the inhibitory effects of a number of negative allosteric modulators, such as zinc and β-carbolines, on γ-aminobutyric acid (GABA)- and glycinegated currents [3].

Oral Brivaracetam has been approved in the EU on 14 Jan 2016 and by US FDA on 18 Feb 2016, as an adjunctive treatment for partial-onset seizures with or without secondary generalization (spreading to both sides of the brain after the initial seizure) in patients aged 16 or more years.

Epilepsy: Causes, Treatments and SV2A

Epilepsy, a common neurological disorder characterized by recurrent spontaneous seizures, is a major health problem that affects 1% of the population worldwide. Despite progress in understanding the pathogenesis of epileptic seizures, the cellular basis of human epilepsy remains a mystery and, in the absence of specific etiological comprehension, approaches to drug therapy are still directed toward the control of symptoms, i.e., suppression of seizures. Chronic administration of antiepileptic drugs (AEDs) is the treatment of choice in epilepsy. The goal of current therapy with an AED is to keep the patient free of seizures without inducing significant adverse effects [4].

Synaptic vesicle protein 2 (SV2) is an integral transmembrane glycoprotein expressed in neurons and endocrine cells. In neurons, SV2 is localized to synaptic vesicles and has been proposed to function as a modulator of Ca2⁺-dependent neurotransmitter release.

SV2 has three isoforms, A, B, and C, with SV2A being the most widely expressed in the brain. Of the three known isoforms, SV2A is ubiquitously expressed in the rat brain, whereas SV2B, although widely expressed, is undetectable in several groups of neurons in the hippocampus, central gray nuclei, and cerebellum. SV2C has a much more restricted distribution being found mostly in the basal ganglia, midbrain, and brainstem [5].

The exact function of SV2A, however, still remains elusive. SV2A was identified as the specific binding site for Levetiracetam, a second generation antiepileptic drug. Levetiracetam reduces presynaptic glutamate release particularly in neurons with a sustained and high frequency firing, and it was shown that the antiepileptic efficacy of Levetiracetam and its derivatives correlates with their binding affinity to SV2A.

Recently it was proved that human SV2A, when expressed in yeast, functions as a galactose transporter. Moreover, the antiepileptic drug Levetiracetam, which specifically binds to SV2A inhibits the galactose-dependent growth of SV2A-expressing yeast cells [5].

Brivaracetam Activity in Experimental Models of Seizure and Epilepsy

In in vitro models of epileptic activity in rat hippocampal slices, Brivaracetam (1-10 µM) inhibited epileptiform responses induced by a high potassium/low calcium ions perfusion fluid or by addition of 5 µM bicuculline methiodide (BMI) to the normal perfusion liquid. In particular, Brivaracetam (3.2 µM) reduced the occurrence of spontaneous bursts, while Levetiracetam (32 µM) was inactive against spontaneous bursts [1].

Brivaracetam shows potent activity in many in vivo models of seizures and epilepsy. For example:

a: Unlike Levetiracetam, Brivaracetam is effective in inhibiting seizures induced in the classical maximal electroshock and pentylenetetrazole seizure tests, albeit at relatively high doses.

b: Audiogenic seizure-susceptible mice were better protected against clonic convulsions induced by acoustic stimuli when treated with Brivaracetam than with levetiracetam [ED₅₀ values = 2.4 versus 30 mg/kg, intraperitoneally (i.p.)].

d: In corneally kindled mice (3 mA, 3 s, twice daily), Brivaracetam provided more potent protection than Levetiracetam against secondarily generalized motor seizures (ED₅₀ = 1.2 versus 7.3 mg/kg, i.p.). In the corneal kindling development model, pretreatment of mice twice daily with Brivaracetam (0.21-6.8 mg/kg, i.p.) prior to corneal stimulation (3 mA, 3 s, twice daily) also resulted in a more potent and persistent inhibition of kindling development than observed with Levetiracetam.

e: In hippocampal-kindled rats, a model of localization-related epilepsy, brivaracetam provided more potent protection against seizures than levetiracetam (minimal active dose = 0.21 versus 54 mg/kg, oral).

The activity profile of Brivaracetam in these models is suggestive of broad-spectrum efficacy against partial and generalized seizure types [1].

Dosages and Approvals:

Brivaracetam (Tradename: Briviact) is discovered and developed at UCB Pharma, which has a history of launching racetam derivatives having anticonvulsant (antiepileptic) properties. Brivaracetam is available as tablets (10, 25, 50, 75 and 100 mg), an oral solution (10 mg/ml) and a solution for injection or infusion (drip) into a vein (10 mg/ml). The recommended starting dose is either 25 mg twice a day or 50 mg twice a day, depending on the patient’s condition. The dose can then be adjusted according to the patient’s needs up to a maximum of 100 mg twice a day. Briviact can be given by injection or by infusion (drip) into a vein if it cannot be given by mouth [6].

Reported Activities for Brivaracetam:

The affinity of Brivaracetam for rat SV2A (80 nM) was about 15 fold higher than that of Levetiracetam (1250 nM) and this was further confirmed in human cerebral cortex with affinity values for Brivaracetam and Levetiracetam of 50 nM and 1585 nM respectively. The binding affinity (pK_i) for human synaptic vesicle protein 2A (hSV2A) of Brivaracetam was 7.1; as compared to 6.1 for Levetiracetam [1].

Brivaracetam inhibited voltage-gated sodium channel currents (IC₅₀ = 7 uM) as compared to Levetiracetam, which was inactive even at up to 1 mM in the same assay. Reversal of the activity was seen in high voltage activated calcium channel currents, where Levetiracetam has an IC₅₀ value of 13.9 uM; and Brivaracetam was inactive even at 1 mM.

Brivaracetam was profiled at 10 µM (a concentration greater than100 fold higher than its affinity for SV2A) against a panel of more than 55 targets comprising receptors, enzymes, ion channels and transporters. This panel included targets potentially involved in epilepsy such as GABAA (GABA and benzodiazepine binding sites), glycine, kainate, AMPA and NMDA receptors, L-type and N-type calcium channels, ATP and voltage dependent potassium channels, tetrodotoxin sensitive sodium channels, GABA transporter, glutamic acid decarboxylase (GAD) and the ryanodine receptor. Other targets screened were mostly G-protein coupled receptors (subtypes of adenosine, adrenergic, canabinoid, dopamine, histamine, opioid, muscarinic, neurokinine and serotonine receptors), transporters (adenosine, noradrenaline, dopamine and GABA) and enzymes (acetylcholinesterase, monoamine oxidase A and B). Brivaracetam did not bind, inhibit or activate any of the aforementioned targets.

Saturation curves indicated that [³H]ucb 34714 binds to an homogenous population of binding sites that have the characteristics of SV2A. Results from SV2A KO mice indisputably showed that [³H]ucb 34714, at concentrations up to 600 nM (the highest concentration tested) only labels SV2A proteins, as no specific binding for [³H]ucb 34714 could be observed in the brains of SV2A-/- KO mice [3].

Activities for Brivaracetam

 pK_i (Binding affinity for S2VA(h)) = 7.1

IC₅₀ (Inhibition of voltage-gated sodium channel currents) = 7 uM

Summary

Common name: UCB-34714; UCB 34714; UCB34714; Brivaracetam; Rikelta

Trademarks: Briviact

Molecular Formula: C11H20N2O2

CAS Registry Number: 357336-20-0

CAS Name: (2S)-2-[(4R)-2-oxo-4-propylpyrrolidin-1-yl] butanamide

Molecular Weight: 212.15

SMILES: CCCC1CC(=O)N(C1)C(CC)C(=O)N

InChI Key: MSYKRHVOOPPJKU-BDAKNGLRSA-N

InChI: InChI=1S/C11H20N2O2/c1-3-5-8-6-10(14)13(7-8)9(4-2)11(12)15/h8-9H,3-7H2,1-2H3,(H2,12,15)/t8-,9+/m1/s1

Mechanism of Action: SV2A Protein Modulators; Sodium Channel Antagonists

Activity: Antiepileptic drugs; Neuroprotectants; Non-opioid Aanalgesics; Nootropics; Treatment for Partial-Onset Seizures

Status: Launched 2016 (US, EU)

Chemical Class: Pyrrolidinones; Amides; Small-molecules; Racetam Compounds

Originator: UCB Pharma

Brivaracetam Synthesis

US8338621: The patent reports process to prepare racemic Brivaracetam. UCB has provided an insight to what Brivaracetam industrial process could be.

A mixture of powdered potassium carbonate (3.8 g, 27.6 mmol, 5 equiv.), ethyl-4-amino-3-propyl butyrate (1.65 g, 8.3 mmol, 1.5 equiv.) and substantially optically pure (S)-2-bromo butyric methyl ester (1.0 g, 5.5 mmol, 1 equiv.) in acetonitrile (25 ml, 25 vol.) was stirred overnight at room temperature. The resulting mixture was filtered and the filtrate evaporated to dryness leading to the intermediate as yellow oil. The crude residue was dissolved in toluene (20 ml) and 0.1 g of hydroxypyridine was added. The resulting solution was heated at 80 °C. overnight. After cooling to room temperature, 5 ml of a 1M NaOH solution were added and toluene was evaporated under reduced pressure. The resulting aqueous solution was washed with ethyl acetate (2×20 ml) and acidified to pH=2 by addition of a 1N HCl solution. The acidic aqueous solution was extracted twice with 20 ml of ethyl acetate. The combined organic layers were dried (MgSO₄) and concentrated to dryness leading to crude acidic intermediate. The latter was dissolved in THF (10 ml) and triethylamine was added. The resulting solution was cooled to 0 °C and 0.2 ml of ethychloroformate was added. The mixture was stirred 1 h and 0.5 ml of liquid ammonia was added at room temperature followed by K₂CO₃ (0.24 g, 1.7 mmol) and 1M aqueous HCl (12 ml). The reaction mixture was extracted twice with ethylacetate (2×20 ml), and combined organic layers were dried (MgSO₄) and evaporated leading 0.38 g (1.8 mmol, 32%) of (S)-2-[4-propyl-2-oxopyrrolidin-1-yl]butyramide.

J Med Chem 2004, 47(3), 530-549: In a 2-L, three-necked flask under argon, n-PrMgBr (2.0 M in ether, 820 mL, 1.64 mol) is added dropwise to a suspension of CuI (159.4 g, 0.82 mol) in dry Et₂O (450 mL) cooled at -20 °C. After 0.5 h, the solution is cooled to -40 °C, and TMSCl (89.09 g, 0.82 mol) is added dropwise followed by 2,3-furanone (68.9 g, 0.82 mol) dissolved in dry Et₂O (addition time: 0.5 h). The suspension is allowed to warm to room temperature and hydrolyzed with saturated ammonium chloride. The aqueous layer is extracted with AcOEt (3x), washed with water, dried over magnesium sulfate, and evaporated to dryness to afford the 4-n-propylbutyrolactone (103 g). It is used in the next step without further purification.

In a three-necked flask, under argon, TMSI (51 mL) is added to a solution of the 4-n-propylbutyrolactone (103.04 g, 0.805 mol) in CH₂Cl₂ (820 mL) cooled at 0 °C. The solution is stirred for 2 h at room temperature and hydrolyzed with 1 N HCl (870 mL) and then Na₂S₂O₃ (10% w/w, 300 mL). The aqueous layer is extracted with CH₂Cl₂, and the combined organic phase is washed with brine, dried over magnesium sulfate, and concentrated in vacuo to afford the crude 3-(iodomethyl) hexanoic acid (148.48 g). It is used in the next step without further purification. In a three-necked flask fitted with a reflux condenser, under argon, a solution of thionyl chloride (138 g, 1.16 mol) and the crude 3-iodomethyl-hexanoic acid (148.48 g) in benzene (150 mL) is stirred for 24 h at room temperature. The solvents are evaporated in vacuo and the residue is distilled (0.32 mmHg, T_eb = 85-90 °C) to afford the crude 3-(iodomethyl)hexanoic acid chloride 82a (120 g) contaminated by iodine. In a three-necked flask, under argon, the 3-(iodomethyl)hexanoic acid chloride (119.5 g, 0.43 mol) in CH₂Cl₂ (640 mL) is added dropwise to a mechanically stirred suspension of molecular sieves (72 g), powdered KOH (72.8 g), anhydrous Na₂SO₄ (72.8 g), tetra-n-butylammonium bromide (7.0 g, 0.02 mol), and S-2-aminobutyramide (66.6 g, 0.65 mol) in CH₂Cl₂ (1500 mL) cooled at 0 °C. The solution is stirred for 5 h at -5 °C, powdered KOH is added (15.6 g), and the stirring is continued overnight at -5 °C. The reaction mixture is filtered on Hyflocel and the solvent is evaporated in vacuo. The crude reaction mixture is purified successively by chromatography on silica gel (AcOEt-i-PrOH 97/03 (v/v)) and preparative chromatography on a chiral stationary phase (hexanes-EtOH) to afford the two isomers after recrystallization in i-Pr₂O. 

WO2001062726A2: The patent reports synthesis for Levetiracetam and provides insight on synthesizing various derivatives. This work is important as this one of the early work where UCB has reported synthesis of its future pipeline.

Step 1 - Reductive amination: In a three neck flask, under argon, 4-n-propyl-hydroxyfuranone (35.5 g, 0.25 mol) is added a solution of S-2-aminobutyramide (28.1 g, 0.275 mol.) in toluene (355 ml) at 18 °C. The solution is stirred for 0.5 h at this temperature and a precipitate appears. The reaction mixture is stirred for 2 h and NaOH 4N (37.5 ml) is added dropwise to the suspension followed by an aqueous solution of NaBH₄ (6.2 g, 0.16 mol.) in water (62 ml). After 1h, the reaction mixture is carefully quenched with AcOH (30 ml), heated to 50 °C for 3 h and cooled to room temperature overnight. NaOH 50% w/w is added (20 ml) and the aqueous phase is extracted with toluene (2x). The organic phases are combined, washed with brine and concentrated in vacuo to afford the crude unsaturated pyrrolidone (43.4 g) as orange oil which is used in the next step without any further purification. It can be recrystallyzed into a white solid (Mp = 72.9 °C).

Step 2 : Hydrogenolysis: In a three necked flask, under argon, an aqueous solution of HCOONH₄ (8 g, 0.126 mol.) is added by portions to a suspension of the crude unsaturated pyrrolidone (22 g, 0.105 mol.) and 10% Pd/C (1.1 g) in water (220 ml) heated at 50 °C. The suspension is stirred for 3 h at 50 °C, cooled to room temperature and stirred overnight. After 18 h, the suspension is heated at 50 °C and an aqueous solution of HCOONH₄ (8 g, 0.126 mol.) is added by portions. After 1.5 h a third portion of an aqueous solution of HCOONH₄ (8 g, 0.126 mol.) is added. The suspension is stirred for 0.5 h at 50 °C and 10% Pd/C (1.1 g) is added. The suspension is stirred for 5 h at this temperature and left overnight without stirring at room temperature. The reaction mixture is filtered over celite, washed with water (30 ml) and the aqueous layer is extracted with AcOEt (3x). The combined organic phases are washed with brine and concentrated in vacuo to afford the crude pyrrolidone as white crystals (18.1 g). The two diastereoisomers are separated by preparative HPLC on chiral phase (EtOH/heptane : 1/1) to afford, after recrystallisation in iPr₂O, the two pyrrolidones 158 (9.5 g) and 159 (7.2 g) as white solids.

Identifications:

1H NMR (Estimated) for Brivaracetam

Sideeffects: Treatment-emergent adverse events (AEs) that occurred in greater than 5% of Brivaracetam recipients included somnolence, dizziness, headache and fatigue. The median onset time of adverse events was about 1 h and their duration appeared to be short. The incidence of adverse events decreased with subsequent administrations of Brivaracetam. There was no indication of haematological or liver toxicity. No clinically significant changes in laboratory parameters or vital signs were observed in any treatment group.

Others: Brivaracetam contains two chiral centers. The chiral center linking the butanamide moiety to the pyrrolidone ring is highly stereoselective for binding to SV2A, with the R configuration (UCB-100230-1) being more than 3000 fold less potent than the S conformation (Brivaracetam). The second chiral center located on position 4 of the pyrrolidone conferred less stereoselectivity, with only a ratio of 5 in favor of Brivaracetam (R conformation) compared to UCB-34713 (S conformation).

Bivaracetam Analogs

Brivaracetam (2.1-68 mg/kg, i.p.) has been compared with gabapentin (30 or 60 mg/kg) in the mononeuropathic (chronic constriction injury) model and in the streptozotocin-induced diabetic model of neuropathic pain. In both models, Brivaracetam showed significant activity, increasing vocalization thresholds and displaying dose-dependent antihyperalgesia.

References:

1. von Rosenstiel P.; et. al. The Treatment of Epilepsy, Third Edition. Chap 35, 2009, Blackwell Publishing Ltd. (FMO only)

2. Rogawki, M. A. Brivaracetam: a rational drug discovery success story. Br J Pharmacol 2008, 154(8), 1555-1557. (free article)

3. Gillard, M.; et. al. Binding characteristics of brivaracetam, a selective, high affinity SV2A ligand in rat, mouse and human brain: relationship to anti-convulsant properties. Eur J Pharmacol 2011, 664(1-3), 36-44. (FMO only)

4. Kenda, B. M.; et. al. Discovery of 4-substituted pyrrolidone butanamides as new agents with significant antiepileptic activity. J Med Chem 2004, 47(3), 530-549. (FMO only)

5. Madeo, M.; et. al. The human synaptic vesicle protein, SV2A, functions as a galactose transporter in Saccharomyces cerevisiae. J Biol Chem 2014, 289(48), 33066-33071. (free article)

6. Brivaracetam Approval EU, US.

7. Surtees, J.; et. al. Process for the preparation of 2-oxo-1-pyrrolidine derivatives. US8338621B2

8. Differding, E.; et. al. 2-oxo-1-pyrrolidine derivatives, processes for preparing them and their uses. WO2001062726A2

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