Carbamate derivatives of felbamate as potential anticonvulsant agents

Article abstract of DOI:10.1007/s00044-009-9208-6

Several monocarbamate compounds derived from felbamate were synthesized and 11 target compounds (1, 4, and 6-14) were initially evaluated in mice MES and PTZ models in our laboratory. Carbamate compounds with varying substituents on the oxygen (1-4) gave anticonvulsant activity with a wide range of ED ₅₀ in MES test from <20 mg/kg (2) to >300 mg/kg (4) and compounds with different groups on the nitrogen (5-14) also were quite active in the range of 15 mg/kg (14) to 170.5 mg/kg (6). This suggested that the spatial limitation in the MES model seemed flexible especially on the nitrogen end. All tested compounds showed some activity against mice scPTZ test, but none had the ED₅₀ value <50 mg/kg. Ten selected compounds (1 and 6-14) for subsequent pharmacological evaluation in NIH all gave positive mice MES activity except 8 and 9, which were unexpectedly active in rats after further evaluations. Among the compounds, 1, 8, and 9 advanced to the quantitative study and 1 and 9 provided the highest PI values, 15 and 21, respectively, in the rat oral MES test.

Full text of DOI:10.1007/s00044-009-9208-6

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2010) 19:498–513
DOI 10.1007/s00044-009-9208-6
ORIGINAL RESEARCH
Carbamate derivatives of felbamate as potential
anticonvulsant agents
Ching-Hsin Kung Æ Chul-Hoon Kwon
Received: 25 September 2008 / Accepted: 15 April 2009 / Published online: 15 May 2009
¨
Ó Birkhauser Boston 2009
Abstract Several monocarbamate compounds derived from felbamate were syn-
thesized and 11 target compounds (1, 4, and 6–14) were initially evaluated in mice
MES and PTZ models in our laboratory. Carbamate compounds with varying
substituents on the oxygen (1–4) gave anticonvulsant activity with a wide range of
ED50 in MES test from \20 mg/kg (2) to [300 mg/kg (4) and compounds with
different groups on the nitrogen (5–14) also were quite active in the range of 15 mg/
kg (14) to 170.5 mg/kg (6). This suggested that the spatial limitation in the MES
model seemed flexible especially on the nitrogen end. All tested compounds showed
some activity against mice scPTZ test, but none had the ED50 value\50 mg/kg. Ten
selected compounds (1 and 6–14) for subsequent pharmacological evaluation in
NIH all gave positive mice MES activity except 8 and 9, which were unexpectedly
active in rats after further evaluations. Among the compounds, 1, 8, and 9 advanced
to the quantitative study and 1 and 9 provided the highest PI values, 15 and 21,
respectively, in the rat oral MES test.
Keywords Carbamate ꢀ Felbamate ꢀ Anticonvulsant
Introduction
Many carbamate compounds have demonstrated potential therapeutic uses.
Meprobamate, an anxiolytic dicarbamate compound (Fig. 1) has been known to
Electronic supplementary material The online version of this article
(doi:10.1007/s00044-009-9208-6) contains supplementary material, which is available to authorized
users.
C.-H. Kung ꢀ C.-H. Kwon (&)
Department of Pharmaceutical Sciences, College of Pharmacy and Allied Health Professions,
St. John’s University, 8000 Utopia Parkway, 11439 Jamaica, NY, USA
e-mail: kwonc@stjohns.edu

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499
O
O
O
O
O
O
O
NH2
NH2
NH2
NH2
O
Felbamate
Meprobamate
O
OH
N
H
O
BURAMATE
Fig. 1 Felbamate, meprobamate, and buramate
possess anticonvulsant activity, and the search for additional anticonvulsant
carbamates continued through 1960 s. The duration of action of these carbamate-
related compounds was typically very short, and this has led to their discontinuance
as therapeutic agents (Murray and Kier, 1977). According to the SAR of those
dicarbamates, derivatives with two alkyl groups attached at C-2 possess stronger
muscle paralyzing action, whereas the presence of a phenyl group at the 2 position
enhance anticonvulsant activity (Ludwing et al., 1969). For example, felbamate, 2-
phenyl-1,3-propanediol dicarbamate, despite its structural similarity to meprobam-
ate, lacks anxiolytic properties and provides higher anticonvulsant activity in some
cases (Ludwing et al., 1969; Kupferberg, 1995). Felbamate was approved by the
United States FDA in 1993 as a new anticonvulsant drug. Its clinical use has been
rather limited subsequent to the finding of significant toxicological issues of
felbamate, i.e., aplastic anemia and hepatotoxicity (Frey and Bartels, 1997). 3-
Carbamoyl-2-phenyl propionaldehyde is a likely intermediate in the metabolism of
felbamate to its principal metabolite, 3-carbamoyl-2-phenyl propionic acid, and the
aldehyde intermediate would undergo a cascade of chemical reactions responsible
for the toxic properties of the parent drug, felbamate (Ludwing et al., 1969;
Thompson et al., 1996; Fig. 2). The aldehyde undergoes a b-elimination to a,b
unsaturated aldehyde (2-phenylpropenal), which is known to be toxic or a reversible
cyclization process forms a urethane compound as a reservoir. These intermediates
have been identified as urinary metabolites in humans (Thompson et al., 2000;
Dieckhaus et al., 2001) (see Scheme 1).
A felbamate analog that cannot undergo b-elimination by having a methyl
substituent at the prochiral carbon was reported with ED50 of 102 mg/kg in the mice
MES test by oral administration (Ludwing et al., 1969). A compound with a fluorine
substituent on the same carbon of felbamate structure also has been suggested
(Dieckhaus and Macdonald, 2001), and successfully synthesized with supportive
results in metabolic stability tests (Parker et al., 2005). Besides the replacement of

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O
O
O
O
NH2
NH2
OH
O
NH2
O
H
H
HO
N
O
O
O
O
O
O
NH2
2-phenylpropenal
(Atropaldehyde)
Urethane
Fig. 2 Felbamate metabolic pathway and toxic species
O
Cl
O
+
R
OH
R
O
O
O
R1NH2
(1), (2)
O
O
R
O
R1
+
R1NH2
R
N
H
O
Cl
(3), (4), (5), (6)
Scheme 1 Synthesis of Carbamate derivatives
the hydrogen to avoid the formation of toxic metabolite, other methods may apply as
well. The oxygen in one of the carbamate moieties may be replaced by another atom,
such as nitrogen or carbon. Limited SAR information is available for monocarbamate
analogs that lack the possibility of cascade metabolic pathway to form toxic species
as with felbamate (Yamagami et al., 1982; Tanaka et al., 1985). N-methyl or N,N-
dimethyl substituted benzyl carbamates were more potent than unsubstituted benzyl
carbamate, whereas N,N-dimethyl substitution decreases anticonvulsant activity in
phenylethyl or phenylpropyl carbamates (Tanaka et al., 1985). Among those
compounds, phenyl ethyl carbamate (Fig. 3) was the most potent. Interestingly,
carbamates with a hydroxyl group in structure, e.g., the mono-decarbamylated
alcohol of felbamate were found to be active in convulsion protection (Ludwing
et al., 1969). The hydroxylated carbamates are structurally similar to buramate
(Fig. 1), a hypnotic and anesthetic/CNS depressant (Aurousseau, 1960; Hazard et al.,
1951).

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501
O
R1
R2
OH
R1
O
N
R2
7
8
H
R1
R2
OH
OH
H
1
9
10
H
H
2
3
OH
OH
11
12
H
4
5
6
OH
OH
H
CH3
13
14
OH
H
Fig. 3 Structures of carbamate compounds
In this report, a series of monocarbamates with or without hydroxyethyl group on
the nitrogen were synthesized. They were (R,S)-2-phenylbutyl carbamate 1, phenyl
ethyl carbamate 2, benzyl carbamate 3, phenyl carbamate 4, benzyl N-methyl
carbamate 5, dibenzoyl carbamate 6, O-benzyl-N-(2-hydroxy ethyl) carbamate 7,
(S)-O-benzyl-N-2-hydroxy-1-methyl ethyl carbamate 8, (R)-O-benzyl-N-2-
hydroxy-1-methyl ethyl carbamate 9, and the racemic mixture 15, and (S)-O-
benzyl-N-1-hydroxy methyl propyl carbamate 10, (R)-O-benzyl-N-1-hydroxy
methyl propyl carbamate, 11, (R,S)-O-benzyl-N-(1-hydroxy methyl butyl) carba-
mate 12, (S)-O-benzyl-N-1-benzyl-2-hydroxy ethyl carbamate 13, (R)-O-benzyl-N-
1-benzyl-2-hydroxy ethyl carbamate 14. The compounds were evaluated for their
potential anticonvulsant activity in both MES and scPTZ animal-seizure models. On
the basis of the preliminary pharmacological results, further studies were conducted
for the chosen compounds in different models (see Scheme 2).
Chemistry
2-Phenyl butyl carbamate (1) was prepared via the nucleophilic substitution with the
corresponding phenyl carbonate according to Wang and Merrifield (1969) and

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O
O
R
R
OH
O
Cl
O
N
H
OH
+
H2N
(7 - 15)
Scheme 2 Synthesis of Hydroxy ethyl carbamate compounds
O
O
O
Cl
+
O
O
OH
Fig. 4 Intermediate in the synthesis of (1)
Sieber and Iselin (1968). In short, 2-phenyl butyl alcohol was initially treated with
phenyl chloroformate in basic organic solvent under low temperature (-5°C) to
form its corresponding arylalkyl phenyl carbonates in excellent yield (Fig. 4). The
carbonate then reacted with excess ammonia to produce this branched aryl alkyl
carbamate. The other carbamate compounds (3, 4, 5, 6) and benzyl N-hydroxyl alkyl
carbamates (7–15) were synthesized by following basically the same procedure by
reacting benzyl chloroformate (for 3, 5, 6, 7–15) or phenyl chloroformate (for 4)
with ammonia (for 3, 4), methylamine (for 5), benzylamine (for 6), or different
hydroxyl alkyl amines.
Experimental section
Chemistry
Melting points were determined on a Thomas-Hoover capillary melting point
apparatus and were uncorrected. Microanalyses were performed by Atlantic
Microlab, Inc., Norcross, GA. The following instruments were used: IR, Perkin-
Elmer Model 281 or Perkin-Elmer FT-IR Spectrometer SPECTRUM 1000; 1H
NMR, Varian EM-360-L CW, 60 MHz (Me4Si as internal standard) or Bruker-
400 MHz (Me4Si as internal standard); polarimeter, Perkin-Elmer Model 241. Silica
gel GF plates (250 lm, 10 9 20 cm2, Analtech) were used for thin-layer
chromatography (TLC). All chemicals and solvents were reagent grade and were
purchased from commercial vendors. Compounds 2, 3, 4, and 5 were purchased
from Sigma-Aldrich (St. Louis, MO) and were used directly for the anticonvulsant
tests.
O-2-Phenyl-butyl-O0-phenyl carbonate
Phenyl chloroformate (5 ml, 0.04 mol) in 20 ml of CH2Cl2 was added drop wise
into a solution of 5 g (0.033 mol) of ( )-b-ethyl-phenethyl alcohol and 4 ml

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(0.05 mol) of pyridine in 80 ml of CH2Cl2 under ice bath temperature with stirring
for 1 hour. After stirring overnight at room temperature, the mixture was poured into
crushed ice and diluted with 100 ml of methylene chloride. The organic phase was
separated, washed with water three times (3 9 250 ml), dried over anhydrous
sodium sulfate, and then evaporated in vacuo at 30°C to give a thick, colorless, oily
liquid. TLC Rf = 0.73 in CH2Cl2/Hexane (1:1). This was used for the subsequent
step without further purification.
2-Phenylbutyl carbamate (1)
Crude O-2-phenyl-butyl-O0-phenyl carbonate prepared above was dissolved in
40 ml DMF and then 17 ml of ammonia (2.0 M solution in Ethanol, 0.034 mol) was
added to the solution at room temperature with stirring. Additional ammonia was
added after 6 hours and every 12 hours until the starting carbonate compound
disappeared as visualized on TLC plate. A total of 50 ml of ammonia (2.0 M
solution in ethanol, 0.1 mol) was added. The mixture was evaporated in vacuo to the
half of its volume, and then 150 ml of water was added slowly. After keeping at 0°C
overnight, the product was filtered to give 5.97 g (92.3% yield) of white crystalline
product. mp 104–106°C; TLC Rf = 0.39 in CH2Cl2; TLC Rf = 0.13 in CH2Cl2/
Hexane (1:1); IR (SPECTRUM 1000, KBr, cm-1) 1686 (C=O), 2899, 2970 (alkyl),
3027, 3062, 3085 (ArH), 3326, 3411 (NH); 1H NMR (CDCl3) d 0.63–1.07
(t, J = 7 Hz, 3H, CH3), 1.43–2.00 (fused m, 2H, CH2), 2.60–3.10 (m, 1H, CH),
4.10–4.40 (d, J = 7 Hz, 2H, OCH2), 4.40–4.90 (br, 2H, NH2), 7.21 (s, 5H, ArH).
Anal. (C11H15NO2), C, H, N.
N,O-Dibenzyl carbamate (6)
Benzyl chloroformate (3.8 ml, 25 mmol) in 15 ml of CH2Cl2 was added gradually
into a solution of benzylamine (2.73 ml, 25 mmol) and pyridine (3 ml, 37.5 mmol)
in 25 ml of CH2Cl2 in 100-ml round-bottom flask at ice bath temperature with
stirring for 0.5 hours. After stirring overnight at room temperature, the mixture was
poured into crushed ice and diluted with 50 ml of CH2Cl2. The organic phase was
separated, washed with water three times (3 9 200 ml), dried over anhydrous
sodium sulfate, and then evaporated in vacuo to concentrated liquid. This liquid was
diluted in 100 ml of ethyl acetate, washed with acidic water three times
(3 9 200 ml, pH 1–2), dried over anhydrous sodium sulfate, and then evaporated
in vacuo to half of its volume and crystallized at 0°C to give 2.58 g (42.9% yield) of
1
white crystalline product. mp 60–61.5°C; TLC Rf = 0.71 in CH2Cl2; H NMR
(CDCl3) d 4.25–4.50 (d, J = 6 Hz, 2H, NCH2), 5.10 (s, 2H, OCH2), 7.23, 7.30 (2 s,
10H, ArH). Anal. (C15H15NO2), C, H, N.
O-Benzyl-N-(2-hydroxy ethyl) carbamate (7)
Benzyl chloroformate (3 ml, 20 mmol) in 10 ml of THF was added into the mixture
of ethanolamine (1.22 ml, 20 mmol) and pyridine (2.5 ml, 30 mmol) in 25 ml of
THF at ice bath temperature. After stirring overnight at room temperature, 75 ml of

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Med Chem Res (2010) 19:498–513
water and 50 ml of EtOAc were added into the reaction mixture in a separatory
funnel. The organic phase was washed with water three times, with acidic water (pH
1) three times, then separated and dried over anhydrous sodium sulfate. Evaporation
in vacuo gave a thick liquid. The liquid solidified when the liquid-containing, round-
bottomed flask was placed on dry ice. The crude solid product was purified
by preparative TLC to give 1.82 g (46.7% yield) of crystalline compound. mp 61–
62°C; TLC Rf = 0.31 in CH2Cl2; TLC Rf = 0.50 in EtOAc/ CH2Cl2 (1:1); TLC
1
Rf = 0.70 in EtOAc; H NMR (CDCl3) d 3.15–3.50 (t, J = 4.5 Hz, 2H, OCH2),
3.50–3.85 (m, 2H, NCH2), 5.10 (s, 2H, OCH2), 7.33 (s, 5H, ArH). Anal.
(C10H13NO3), C, H, N.
O-Benzyl-N-(1S)-2-hydroxy-1-methyl ethyl carbamate (8)
Benzyl chloroformate (2.0 ml, 13 mmol) in 10 ml of THF was added gradually into
a solution of (S)-(?)-2-amino-1-propanol (1 g, 13 mmol) and pyridine (1.2 ml,
14.5 mmol) in 25 ml of THF in a 100-ml round-bottom flask at ice bath temperature
with stirring. After stirring overnight at room temperature, 50 ml of 10% NaOH in
water was added and the mixture was kept stirring for additional 0.5 hours. The
mixture was then evaporated in vacuo, and the residue was diluted with CH2Cl2
(100 ml). The organic layer was separated and washed with acidic water (pH 1)
three times. This organic layer was separated again and evaporated in vacuo to give
a thick liquid. The liquid was then placed in a Petri dish and exposed to air
overnight to give a crude solid. Further purification by preparative TLC (solvent
system EtOAc: CH2Cl2 = 1:9) provided 555 mg (20.9% yield) of crystalline
compound. mp 80–82°C; [a]2D3 = -4.6 (c = 1.0, MeOH); TLC Rf = 0.53 in
EtOAc/CH2Cl2 (1:2); 1H NMR (CDCl3) d 1.03–1.43 (m, 3H, CH3), 3.43–4.17
(fused m, 3H, OCH2, NCH), 5.10 (s, 2H, OCH2), 7.37 (s, 5H, ArH). Anal.
(C11H15NO3), C, H, N.
O-Benzyl-N-(1R)-2-hydroxy-1-methyl ethyl carbamate (9) was prepared from
(R)-(–)-2-amino-1-propanol (1.0 g, 13 mmol) according to the procedure for 8 to
give 564 mg (21.5% yield) of crystalline compound. mp 80–82°C; [a]D23 = ?5.0
(c = 1.0, MeOH); TLC Rf = 0.53 in EtOAc/ CH2Cl2 (1:2); Anal. (C11H15NO3), C,
H, N.
O-Benzyl-N-(1S)-1-hydroxymethyl propyl carbamate (10) was prepared from
(S)-(?)-2-amino-1-butanol (1.0 g, 11 mmol) according to the procedure for 8 to
give 590 mg (24.1% yield) of crystalline compound. mp 64–66°C; [a]2D3 = -27.3
(c = 1.0, MeOH); TLC Rf = 0.56 in EtOAc/ CH2Cl2 (1:2); Anal. (C12H17NO3), C,
H, N.
O-Benzyl-N-(1R)-1-hydroxymethyl propyl carbamate (11) was prepared from
(R)-(–)-2-amino-1-butanol (1.0 g, 11 mmol) according to the procedure for 8 to
give 741 mg (30.2% yield) of crystalline compound. mp 65–67°C; [a]2D3 = ?26.5
1
(c = 1.0, MeOH); TLC Rf = 0.56 in EtOAc/ CH2Cl2 (1:2); H NMR [Bruker-
400 MHz] (CDCl3) d 0.96–1.00 (t, J = 7.2 Hz, 3H, CH3), 1.45–1.52 (m, 1H, CH2),
1.56–1.64 (m, 1H, CH2), 1.66 (s, exchangeable H), 2.22 (s, exchangeable H), 3.62
(fused s, 2H, OCH2), 3.71 (fused s, 1H, NCH), 5.13 (s, 2H, OCH2), 7.38 (s, 5H,
ArH). Anal. (C12H17NO3), C, H, N.

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(R,S)-O-Benzyl-N-(1-Hydroxymethyl butyl) carbamate (12)
Benzyl chloroformate (1.5 ml, 9.7 mmol) in 10 ml of THF was added gradually into
a solution of dl-2-amino-1-pentanol (1.0 g, 9.7 mmol) and pyridine (1.2 ml,
14.5 mmol) in 25 ml of THF in a 100 ml round bottom flask at ice bath temperature
with stirring for 0.5 hours. After stirring overnight at room temperature, 50 ml of
10% NaOH aqueous solution was added and kept stirring for additional 5 hours. The
mixture was concentrated in vacuo, and then EtOAc (50 ml) was added. The
separated organic layer was washed with acidic water (pH 1) three times. The
organic layer was evaporated in vacuo to give a thick liquid. The liquid solidified
upon cooling to give 1.363 g of white solid. Recrystallization of the solid with
CH2Cl2 and Hexane provided 1.01 g (44% yield) white crystalline compound. mp
1
71–72°C; TLC Rf = 0.58 in EtOAc/CH2Cl2 (1:2); H NMR (CDCl3) d 0.70–1.17
(m, 3H, CH3), 1.17–1.63 (fused m, 4H, CH2CH2), 3.46–3.80 (fused m, 3H, OCH2,
NCH), 5.07 (s, 2H, OCH2), 7.30 (s, 5H, ArH). Anal. (C13H19NO3), C, H, N.
O-Benzyl-N-(1S)-1-Benzyl-2-hydroxy ethyl carbamate (13) was prepared from
(S)-(-)-2-amino-3-phenyl-1-propanol (1.0 g, 6.6 mmol) according to the procedure
for 8 to give 1.50 g (80.0% yield) of crystalline compound. mp 91–93°C; [a]D23
=
-43.9 (c = 1.0, MeOH); TLC Rf = 0.72 in EtOAc/ CH2Cl2 (1:2); Anal. (C17H19
NO3), C, H, N.
O-Benzyl-N-(1R)-1-Benzyl-2-hydroxy ethyl carbamate (14) was prepared
from (R)-(?)-2-amino-3-phenyl-1-propanol (1.0 g, 6.6 mmol) according to the
procedure for 8 to give 1.30 g (70% yield) of crystalline compound. mp 90.5–
92.5°C; [a]2D3 = ?42.8 (c = 1.0, MeOH); TLC Rf = 0.72 in EtOAc/ CH2Cl2 (1:2);
1H NMR (CDCl3) d 2.70–3.05 (m, 2H, ArCH2), 3.45–3.75 (fused s, 2H, OCH2),
3.75–4.17 (fused m, 1H, NCH), 5.10 (s, 2H, OCH2), 7.27 (s, 5H, ArH), 7.37 (s, 5H,
ArH). Anal. (C17H19NO3), C, H, N.
(R,S)-O-Benzyl- N-2-Hydroxy-1-methyl ethyl carbamate (15) was prepared
by physically mixing 8 and 9 (1:1 ratio) thoroughly.
Pharmacological evaluations
Adult, male, Swiss-Webster mice (20–25 g, Taconic Farms, Germantown, NY)
were used. The mice were housed in an environmentally controlled room (12-hour
light/dark cycle, lights on 7:00 a.m.; 35–45% humidity; 20–30°C) with food and
water available ad libitum, except when removed from cages for testing. Drugs used
for antiepileptic testing were dissolved in normal saline or suspended in 30% PEG
(polyethylene glycol) (Porter et al., 1984). All test drugs were injected intraper-
itoneally in a volume of 10 ml/kg. Dose–response characteristics were determined
from at least three groups of mice (4–8 mice per group) for each drug tested. The
drugs were screened against 1) chemically induced seizures utilizing pentylenetet-
razole as the convulsant (subcutaneous pentylenetetrazole seizure threshold test;
scMET test), and 2) electrically induced seizures using a 50-mA current (maximal
electroshock seizure test; MES test). All tests were performed at 0.5 hours after drug
administration.

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In the scMET test, pentylenetetrazole was administered subcutaneously in a loose
fold of skin on the back of the neck in dose of 85 mg/kg (the convulsant dose, CD97)
(Porter et al., 1984). The animals were observed for 30 minutes after injection of
pentylenetetrazole, and absence of clonic spasms persisting for at least 5 seconds
was considered that the compound can elevate the pentylenetetrazole-induced
seizure threshold. In the MES test, corneal electrodes primed with a drop of
electrolyte solution (0.9% sodium chloride) were applied to the eyes and an
electrical stimulus (50 mA) was delivered for 0.2 seconds by an electroshock
equipment (Electroshock Unit Model 11A, IITC, Landing, NJ). Abolition of the
hind-leg tonic-extensor component (hind-leg tonic extension does not exceed a 90°
angle to the plane of the body) was considered that the compound can prevent MES-
induced seizure spread (Porter et al., 1984).
Further pharmacological evaluation data for selected compounds were provided
by NIH-ADD program, i.e., mice ip for MES, scMET, and TOX; rat po for MES,
scMET, and TOX; rat ip for MES, PTZ, TOX, and Flexible Format.
Results and discussion
2-Phenyl butyl carbamate (1) is a close structural analog of felbamate, but it has
only one carbamate moiety and therefore cannot undergo b-elimination upon the
expected metabolic decarbamylation. Its potential anticonvulsant activity was
evaluated and compared with those of several other carbamates, including felbamate
(Table 1). In general, all compounds showed some protection against seizures in
animal models. In MES test, 1 was essentially as potent as felbamate, although not
as potent as the unsubstituted phenylethyl carbamate 2 or benzyl carbamate 3. The
N-methyl substituted 5 was just as potent as 3; however, the corresponding benzyl
substituted compound 6 was less potent. Shortening the distance between the
carbamate and phenyl ring by one carbon (compound 4) also resulted in reduction of
potency. Among the compounds, 1 and 6 were selected and tested by the NIH-ADD
program; 6 showed activity only at 300-mg/kg dose in MES test with no activity in
PTZ test up to 300 mg/kg. On the other hand, 1 showed activity comparable to that
produced in our laboratory. Calculated TD50 value from NIH was 114.3 mg/kg in
mice rotorod test. Subsequent testing in rats by oral administration, 1 exhibited a
potent activity with ED50 of 21.0 mg/kg in MES and ED50 of [40 mg/kg in PTZ
tests. Furthermore, 1 did not show any toxicity up to 320 mg/kg in rats at the highest
dose tested. This provided the PI (protection index) better than 15 for MES test and
around 8 for PTZ test in rats. Compound 1, when tested in rats by intraperitoneal
administration, exhibited a slightly better activity (ED50 = 16.1 mg/kg) in MES test
but there was a substantially greater toxic profile by this route (TD50 = 50.5 mg/
kg). Preliminary Hippocampal Kindling screen in rats (ip) was also performed for
1. At 100 mg/kg, 1 did not show activity at which felbamate is also inactive.
Toxicity was however observed for 1 at 300 mg/kg and therefore testing could not
be carried out.
2-Hydroxyethyl benzylcarbamate 7 is structurally identical to buramate (benzyl
2-hydroxyethylcarbamate) except the order of carbamate is reversed. Compound 7

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also is related to 3-hydroxy-2-phenylpropyl carbamate, the mono-decarbamylated
alcohol metabolite of felbamate, which was reported to be active with the ED50 of
154 mg/kg in MES test in mice by oral administration (Ludwing et al., 1969).
Several 2-substituted benzyl 1-hydroxy-2-ylcarbamates (7–15) were synthesized
and tested for their potential anticonvulsant activity profiles. The unsubstituted
benzyl 1-hydroxy-2-ylcarbamate 7 exhibited a potent activity with ED50 of
25.2 mg/kg in MES test and 170.5 mg/kg in PTZ test. 2-Methyl substituted
individual stereoisomers 8 and 9 were less potent than 7 with no difference in
activity between the isomers. 2-Ethyl isomers 10 and 11 were even less potent with
some differences in activity between the isomers. The racemic mixture of 2-propyl
substituted isomer 12 was roughly equipotent to 8 and 9. On the other hand, 2-
benzyl isomers 13 and 14 showed significant activity with ED50 of 33.5 mg/kg in
MES test for the S isomer 13 and 14.9 mg/kg for the R isomer 14. Both isomers
gave some protection at different dose in mice PTZ tests, but activity was not dose-
dependant, therefore, ED50 values could not be calculated. The 2-substituted benzyl
1-hydroxy-2-ylcarbamates (7–15) were subsequently tested by the NIH-ADD
program. All compounds showed activity at 300 mg/kg in MES test with the
exception of 8 and 9, even though both were potently active in MES test in mice by
intraperitoneal administration in our lab. In PTZ test, only 12 showed activity at the
dose of 300 mg/kg. Although 8 and 9 were inactive at up to 300 mg/kg dose in both
MES and PTZ tests, they showed noticeable toxicity (data not shown). The
individual stereo isomers 8, 9, 10, and 11 were tested further in rats by oral
administration; interestingly, 10 provided 3/4 protections, but 11 protected only 1/4
in MES test at 30 mg/kg. Compound 8 protected 4/4 and 9 protected 2/4.
Subsequent quantitative testing showed the R isomer 9 was more potent with the
ED50 of 23.9 mg/kg in MES with the TD50 of [500 mg/kg, thus providing the PI
[20. Toxicity and preliminary Hippocampal Kindling screen in rats by intraperi-
toneal administration were performed for 9. At 100 mg/kg, 9 did not show activity,
and toxicity was observed at 300 mg/kg, therefore, testing could not be done.
Furthermore, Flexible Format in rats (ip) was evaluated for 8 and 9. R isomer 9
provided substantial activity at 30 minutes, whereas the activity of S isomer 8
disappeared at earlier stage at 10 minutes (Table 2). This may explain the difference
in the ED50 values in rat MES oral activity between the two isomers (see Table 3).
In summary, 11 of the listed 14 target compounds (1, 4, and 6–14) in Table 1
were evaluated in mice MES and PTZ models in our laboratory and literature data
were cited for the remaining 3 (2, 3, and 5). Carbamate compounds with substituents
on the oxygen in different sizes and lengths (1–4) all gave some anticonvulsant
activity with a wide range of ED50 in MES test from\20 mg/kg (2) to[300 mg/kg
(4). Compounds with different groups on the nitrogen (5–14) also were quite active
in the range of 15 mg/kg (14) to 170.5 mg/kg (6). This suggested the spatial
limitation seemed flexible especially on the nitrogen end. All tested compounds
showed some activity against mice scPTZ test, but none had the ED50 value
\50 mg/kg. Selected ten compounds (1 and 6–14) were subsequently submitted to
NIH for further pharmacological evaluation. They all gave positive mice MES
activity except 8 and 9, which were unexpectedly active in rats after further
evaluations. Among the compounds, 1, 8, and 9 advanced to the quantitative study

512
Med Chem Res (2010) 19:498–513
Table 2 NIH results of Flexible Format—Rats IP
5 min
10 min
15 min
30 min
60 min
S isomer 8
(20 mg/kg)
R isomer 9
(20 mg/kg)
MES
TOX
MES
TOX
3/4
0/4
1/4
0/4
1/4
0/4
0/4
0/4
0/4
0/4
1/4
0/4
0/4
0/4
2/4
0/4
1/4
0/4
0/4
0/4
No. of animals affected / no. of animals being tested
Table 3 ED50, TD50, and PI comparison of potential compounds (NIH rats PO)
#
Structure
ED50 (mg/kg)
TD50 (mg/kg)
PI
1
MES 20.98
[320
MES [ 15.3
PTZ [ 40
PTZ (8)
O
NH2
O
8
9
MES 67.58
[360
[500
MES [ 5.3
O
O
PTZ [ 125
PTZ (2.88)
OH
O
O
N
H
MES 23.85
MES [ 21
PTZ [ 250
PTZ (2)
OH
N
H
and 1 and 9 provided the highest PI values 15 and 21, respectively, in the rat oral
MES test.
Acknowledgment The authors thank James P. Stables at the NINDS of the NIH for conducting some of
the tests through the Anticonvulsant Screening Program.
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