(R)-Mephenytoin ((-)-Mephenytoin) is the R-enantiomer of mephenytoin. Mephenytoin is an anticonvulsant (antiepileptic/antiseizure).

Physicochemical Properties

Molecular Formula	C12H14N2O2
Molecular Weight	218.25
Exact Mass	218.106
CAS #	71140-51-7
Related CAS #	Mephenytoin;50-12-4;(S)-Mephenytoin;70989-04-7
PubChem CID	119127
Appearance	Typically exists as solid at room temperature
Density	1.154g/cm3
Melting Point	137-138ºC
Index of Refraction	1.541
LogP	1.74
Hydrogen Bond Donor Count	1
Hydrogen Bond Acceptor Count	2
Rotatable Bond Count	2
Heavy Atom Count	16
Complexity	310
Defined Atom Stereocenter Count	1
SMILES	CCC1(C(=O)N(C(=O)N1)C)C2=CC=CC=C2
InChi Key	GMHKMTDVRCWUDX-GFCCVEGCSA-N
InChi Code	InChI=1S/C12H14N2O2/c1-3-12(9-7-5-4-6-8-9)10(15)14(2)11(16)13-12/h4-8H,3H2,1-2H3,(H,13,16)/t12-/m1/s1
Chemical Name	(5R)-5-ethyl-3-methyl-5-phenylimidazolidine-2,4-dione
Synonyms	(R)-Mephenytoin; 71140-51-7; (R)-(-)-Mephenytoin; R-Mephenytoin; (-)-Mephenytoin; (5r)-5-ethyl-3-methyl-5-phenylimidazolidine-2,4-dione; Mephenytoin, (-)-; (R)-5-Ethyl-3-methyl-5-phenylimidazolidine-2,4-dione;
HS Tariff Code	2934.99.9001
Storage	Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month
Shipping Condition	Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Biological Activity

Targets	CYP2C9
ln Vitro	In order to produce 5-phenyl-5-ethylhydantoin (nirvanol), (R)-mephenytoin can be N-demethylated by the cytochrome P450 (CYP) isoform CYP2C9[1]. The metabolism of mephenytoin to its two major metabolites, 4-OH-mephenytoin (4-OH-M) and 5-phenyl-5-ethylhydantoin (nirvanol) was studied in human liver microsomes by a reversed phase HPLC assay. Because of preferential hydroxylation of S-mephenytoin in vivo, microsomes (5-300 micrograms protein) were incubated separately with S- and R-mephenytoin. After addition of phenobarbital as internal standard, the incubation mixture was extracted with dichloromethane. The residue remaining after evaporation was dissolved in water and injected on a 60 X 4.6-mm reversed-phase column (5 mu-C-18). Elution with acetonitrile/methanol/sodium perchlorate (20 mM, pH 2.5) led to almost baseline separation of mephenytoin, metabolites, and phenobarbital. Quantitation was performed by uv-absorption at 204 nm by the internal standard method. Propylene glycol was found to be the best solvent for mephenytoin, but inhibited the reaction noncompetitively. 4-OH-M and nirvanol could be detected at concentrations in the incubation mixture as low as 40 and 80 nM, respectively. The rates of metabolite formation were linear with time and protein concentration. The reaction was found to be substrate stereoselective. At substrate concentrations below 0.5 mM S-mephenytoin was preferentially hydroxylated to 4-OH-M, while R-mephenytoin was preferentially demethylated to nirvanol at all substrate concentrations tested (25-1600 microM). These data provide a mechanistic explanation for the stereospecific pharmacokinetics in vivo. The dependence of both metabolic relations on NADPH and the inhibition by CO suggest that they are mediated by cytochrome P-450-type monooxygenases[1].
Enzyme Assay	Previous biochemical studies have suggested that tolbutamide and mephenytoin are metabolized by the same cytochrome P450 enzyme. Conversely, clinical studies indicate the involvement of different P450 forms in tolbutamide and mephenytoin metabolism. Our objective was to elucidate further those P450 enzymes responsible for hydroxylation of these two drugs. We studied both tolbutamide and (S)-mephenytoin hydroxylation in microsomes from 38 different normal adult human livers, and found large variability in the rates of metabolism for both reactions (1.75-47.4 nmol/mg/hr for hydroxytolbutamide formation and 0.1-7.2 nmol/mg/hr for 4-hydroxymephenytoin formation). No significant correlation was found between the two activities. However, both reactions shared common inhibitors in vitro, including inhibition by antikidney-liver-microsome autoantibodies (Meier and Meyer, Biochemistry 26: 8466-8474, 1987) and by teniposide. Two human liver cDNAs for P450s of the CYP2C subfamily designated IIC8 and IIC9 (S. Kimura, J. Pastewka, H. V. Gelboin and F. J. Gonzalez, Nucl. Acids Res. 15: 10053-10054, 1987), were functionally expressed in human HepG2 and TK- cells using a vaccinia virus vector. Interestingly, tolbutamide was hydroxylated by both expressed P450s. Only IIC9 catalyzed the 4-hydroxylation of (R)-mephenytoin and neither enzyme metabolized (S)-mephenytoin. We conclude that tolbutamide and (R)-mephenytoin are both metabolized by the same P450 enzyme, IIC9, and that tolbutamide is hydroxylated by an additional highly related enzyme, IIC8, contributing to the lack of correlation of the two hydroxylase activities among human liver microsomes and indicating the absence of a monogenically controlled polymorphism for tolbutamide[2].
References	[1]. Assay of mephenytoin metabolism in human liver microsomes by high-performance liquid chromatography. Anal Biochem. 1985 Dec;151(2):286-91. [2]. Tolbutamide and mephenytoin hydroxylation by human cytochrome P450s in the CYP2C subfamily. J Pharmacol Exp Ther. 1990 Jan;252(1):442-7.

Solubility Data

Solubility (In Vitro)

DMSO: 220 mg/mL (1008.02 mM)

Solubility (In Vivo)

Solubility in Formulation 1: ≥ 5.5 mg/mL (25.20 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 55.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly. Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution. Solubility in Formulation 2: ≥ 5.5 mg/mL (25.20 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 55.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.  (Please use freshly prepared in vivo formulations for optimal results.)

Preparing Stock Solutions		1 mg	5 mg	10 mg
	1 mM	4.5819 mL	22.9095 mL	45.8190 mL
	5 mM	0.9164 mL	4.5819 mL	9.1638 mL
	10 mM	0.4582 mL	2.2910 mL	4.5819 mL

*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.