Synthesis and anticonvulsant activity of (R)- and (S)-3-(Carbobenzyloxy- amino-1-glutarimidooxy)esters

Article abstract of DOI:10.14233/ajchem.2013.15202

A series of (R)- and (S)-3-carbobenzyloxy-amino-1-glutarimidooxy-esters (5a-e) ((R)-and (S)-methyl-1-(3-carbobenzyloxy-amino-I glutarimidooxy)acetate (5a), (R)-and (S)-ethyl-1-(3-carbobenzyloxy-amino-glutarimidooxy)acetate (5b), (R)- and (S)-ethyl-1-(3-carbo-benzyloxy-amino-glutarimidooxy)propionate (5c), (R)- and (S)-methyl-2-(3-carbobenzyloxy-amino-glutarimidooxy)butyrate (5d), (R)- and (S)-ethyl-2-(3-carbobenzyloxy-amino-glutarimidooxy)butyrate (5e) were synthesized and investigated their anticonvulsant activities.

Full text of DOI:10.14233/ajchem.2013.15202

Asian Journal of Chemistry; Vol. 25, No. 14 (2013), 8125-8127
http://dx.doi.org/10.14233/ajchem.2013.15202
Synthesis and Anticonvulsant Activity of (R)- and
(S)-3-(Carbobenzyloxy-amino-1-glutarimidooxy)esters
DO-HUN LEE
Department of Chemistry, Dong-A University, Busan 604-714, South Korea
Corresponding author: Tel: +82 51 2001053; E-mail: dohlee@dau.ac.kr
(Received: 25 January 2013; Accepted: 5 August 2013)
AJC-13887
A series of (R)- and (S)-3-carbobenzyloxy-amino-1-glutarimidooxy-esters (5a-e) ((R)-and (S)-methyl-1-(3-carbobenzyloxy-amino-
glutarimidooxy)acetate (5a), (R)-and (S)-ethyl-1-(3-carbobenzyloxy-amino-glutarimidooxy)acetate (5b), (R)- and (S)-ethyl-1-(3-carbo-
benzyloxy-amino-glutarimidooxy)propionate (5c), (R)- and (S)-methyl-2-(3-carbobenzyloxy-amino-glutarimidooxy)butyrate (5d), (R)-
and (S)-ethyl-2-(3-carbobenzyloxy-amino-glutarimidooxy)butyrate (5e) were synthesized and investigated their anticonvulsant activities.
Key Words: Epilepsy, Glutamic acid, (R)- and (S)-Glutarimidooxy ester, Anticonvulsant activity, ED50.
we tried examining the structural similarities of currently
available anticonvulsant compounds, known to act by different
pharmacological mechanisms each other. From the studies of
structural similarities of anticonvulsants, we find out the
interesting facts that anticonvulsant compounds included the
common structural moieties such as NH-CO-C-N and imide
in their structures and also some MNDA antagonist, showing
anticonvulsive effect, had structural similarity to glutamic acid,
known as excitatory amino acid, in view of bioisoster. So we
thought that the new anticonvulsants could be possibly deve-
loped from the glutamic acid in view of their structural sences.
And we designed the following imides such asA, having afore-
said common structures such as NH-CO-C-N, imide and
aminocarbonyl of GABA in their structure originated from
glutamic acid as shown in Scheme-I.
INTRODUCTION
Epilepsy is a common and diverse set of chronic neuro-
logical disorders characterized by seizures1. Epileptic seizures
result from abnormal, excessive or hypersyn chronous neuronal
activity in the brain. Epilepsy is usually controlled, but not
cured, with medication. However, over 30 % of people with
epilepsy do not have seizure control even with the best avail-
able medications2-6. Futheremore, the antiepileptic drug
presently used in clinical practics suffer from a broad range
of adverse side effects including sedation, tetratogenecity,
cognitive dulling and liver toxicity.And clinically the epilepsy
consists of various forms of seizure, so that there is a need for
combination and repeat therapy to control the such complex
convulsion. Owing to this multitherapy, there is a danger of
toxic and troublesome side effect7-10. Consequently, there is a
need for the development of new antiepileptic compound
having broader clinical spectrum and lower toxic side effects.
Recently, there has been many trials for the development of
new typed anticonvulsant compounds including derivatives
of various amino acids such as alanine derivatives and N-
benzoyl and N-phenyl glycine amide and structural modifica-
tion of currently used drug such as hydantoin, succinimdes
O
N
C
N
N----CO----C----N
O
CO2H
CO2H
Glutamic acid
N
R
HN
H2N
and glutarimides and various GABA related compounds11-15
.
O
R
But these compounds had some limitation in clinical use
that some drug showed anticonvulsant effect only in maximal
electric shock seizure test (MES) or pentylene-tetrazole induced
seizure test (PTZ). So we were interested in the development
of new anticonvulsant compounds of broad spectrum. In con-
nection with the studies for the development of anticonvulsants,
α
N-acyl- -aminoglutarimide
Scheme-I: Structure of N-acyl-α-aminoglutarimide
Usually the stereoisomers exhibited different pharmaco-
logical activities, so we tried preparing all the (R)- and (S)-
compounds in order to investigate the pharmacological

8126 Lee
Asian J. Chem.
differences between their stereoisomers. The compounds (1a-d)
could be prepared from the corresponding (R)- or (S)-glutamic
acid in moderate yields by known chemical reactions as shown
in Scheme-II.
hydrochloride (0.83 g, 12 mmol) in H2O (2 mL) with Na2CO3
(0.64 g) was stirred at 0 ºC for 1 h. The reaction solution was
concentrated in vacuo. The white crystal (2.47 g, 89 %) was
recrystallized by solution of ethanol and EtOAc. (R)-3-Carbo-
benzyloxy-amino-1-hydroxy glutarimide (4): yield 89 %; m.p.
136-137 ºC; Rf 0.46 (TLC eluent; benzene: THF: formic acid
= 15:5:2, v/v/v) ; IR (KBr, νmax, cm-1): 1700, 1750, 1820, 3100,
O
CO2
CO2H
H
CO2H
CO2H
i)
ii)
O
HN
HN
1
O
H2N
3300 ; H NMR (DMSO-d6): δ 1.73~1.85 (m, CH2, 2H),
O
OCH2Ph
O
OCH2Ph
2
2.18~2.25 (m, CH2, 2H), 3.86~3.89 (m, CH2, 1H), 5.00 (s,
CH2, 2H), 7.35 (s, ph, 5H). (S)-3-carbobenzyloxy-amino-1-
hydroxy-glutarimide (4): yield 2.36 g (89 %). The IR and 1H
NMR spectra of (S)-4 were identical with the IR and 1H NMR
spectra of (R)-4. The typical experimental procedure for syn-
thesis of (R)-methyl-1-(3-carbobenzyloxy-amino-glutarimido-
oxy)-acetate. A mixture of synthesized (R)-3-carbobenzyloxy-
amino-1-hydroxyglutarimide (4) (0.55 g, 2.0 mmol) and
BrCH2CO2CH3 (0.37 g, 2.4 mmol) with NaH (0.096 g, 2.4
mmol) and DMF 10 mL were stirred at room temperature for
5 h. After EtOAc (200 mL) was added, The reaction mixture
was added saturated NaHCO3 solution (50 mL), 5 % HCl
(50mL) and H2O (50 mL) Then the confined organic layers
were concentrated in vacuo. The obtained (R)-methyl-1-(3-
carbobenzyloxy-amino-glutarimidooxy)acetate (5a) (0.53 g,
75 %) was recrystallized with EtOAc and n-hexane. (R)-Methyl-
1-(3-carbobenzyloxy-amino-glutarimidooxy)acetate (5a): yield
75 %; Rf : 0.24 (TLC eluent; EtOAc: n-hexane = 1:1, v/v); IR
1
3
O
O
iv)
iii)
N
OR
N
OH
HN
HN
O
O
O
OCH2Ph
O
OCH2Ph
5a-e
4
5a : (R)- and (S)- , R= -CH2CO2CH3
5b : (R)- and (S)- , R= -CH2CO2C2H5
i) ClCOOCH2Ph, NaOH
iii) NH2OH, HCl, Na2CO3
ii) O(COCH3)2
iv) BrR, NaH
5c : (R)- and (S)- , R= -CH(CH3)CO2CH3
5d : (R)- and (S)- , R= -CH(C2H5)CO2CH3
5e : (R)- and (S)- , R= -CH(C2H5)CO2C2H5
Scheme-II: Synthetic pathway
EXPERIMENTAL
Melting points were determined on a Büchi 510 capillary
melting point apparatus and uncorrected. Infrared spectra were
recorded on a Perkin-Elmer 683 spectrophotometer. NMR
spectra were recorded on a Varian XL-300 or Bruker AC 200
FT-NMR spectrometer in CDCl3 containing Me4Si as an
internal reference. Mass spectra were obtained by using JEOL
JMS DX 303 or HP 5892 Mass Spectrometer. (R)-3-carbobenzyl-
oxyamino glutamic acid (2): To a solution of (R)-glutamic acid
(1) 5.88 g, 40 mmol) and NaOH (1.60 g, 40 mmol) in H2O (16
mL) and acetone (32 mL) at 0 ºC was added solution of carbo-
benzyloxy chloride (6.82 g, 40 mmol) and NaOH (1.6 0g, 40
mmol) in H2O (16 mL) and acetone (17 mL). The reaction
mixture was stirred at room temperature for 7 h. After reaction
solution was concentrated in vacuo, it was carefully acidified
(pH = 2) with conc HCl. Then the white solid was obtained in
good yield (9.60 g, 86 %). (R)-3-carbobenzyloxy-amino-
glutamic acid (2): yield 86 %; m.p. 122-123 ºC; Rf 0.46 (TLC
eluent; benzene: THF: formic acid = 15:5:2, v/v/v); IR (KBr,
1
(KBr, νmax, cm-1): 3350, 3000, 2900, 1750, 1250 ; H NMR
(DMSO-d6): 1.93 (m, CH2, 2H), 2.45~2.63 (m, CH2, 2H), 3.76
~3.78 (s, CH3, 3H), 4.37 (m, CH2, 2H), 4.55~4.64 (m, CH,
1H), 5.11~5.17 (m, CH2, 2H), 7.45 (s, ph, 5H). (S)-methyl-1-
(3-carbobenzyloxy-amino-glutarimidooxy)acetate (5a): yield,
1
0.49 g (70 %). The IR and H NMR spectra of (S)-5a were
identical with the IR and 1H NMR spectra of (R)-5a. (R)-Ethyl-
1-(3-carbobenzyloxy-amino-glutarimidooxy)acetate (5b): yield
67 % Rf : 0.25 (T.L.C eluent ; EtOAc: n-hexane = 1:1, v/v) ; IR
1
(KBr, νmax, cm-1): 1200, 1750, 3000, 2900, 3350 ; H NMR
(DMSO-d6): 1.24~1.31 (m, CH3, 3H), 2.04~2.11 (m, CH2,
2H), 2.48~2.58 (m, CH2, 2H), 4.17~4.27 (m, CH2, 2H), 4.47
(m, CH2, 2H), 4.57~4.62 (m, CH, 1H), 5.08~5.13 (m, CH2,
2H), 7.33 (s, ph, 5H). (S)-ethyl-2-(3- carbobenzyloxy-amino-
glutarimidooxy)-acetate (5b): yield 70 %. The IR and 1H NMR
spectra of (S)-5b were identical with the IR and 1H NMR spectra
of (R)-5b. (R)-Ethyl-2-(3-carbobenzyloxy-amino-
glutarimidooxy)propionate ( 5c): Yield 62 % Rf 0.17 (TLC
eluent ; EtOAc : n-hexane = 1 : 2, v/v) ; IR (KBr, νmax, cm-1):
3300, 3000, 2900, 1750, 1200; 1H NMR (DMSO-d6): δ 1.13
~1.23 (m, CH3, 3H), 1.29~1.39 (m, CH3, 3H), 1.77~1.81 (m,
CH2, 2H), 2.35 (s, CH2, 2H), 3.92 (s, CH2, 2H), 4.08~4.15 (m,
CH, 1H), 4.41~4.44 (m, CH, 1H), 5.00 (s, CH2, 2H), 7.34 (s,
ph, 5H). (S)-ethyl-1-(3-carbobenzyloxy- amino-glutarimido-
oxy)propionate (5c): yield 66 %. The IR and 1H NMR spectra
of (S)-5c were identical with the IR and 1H NMR spectra of
(R)-5c. (R)-Methyl-2-(3- carbobenzyloxy-amino-glutarimido-
oxy)butyrate (5d): yield 77 % Rf 0.36 (T.L.C eluent; EtOAc:
n-hexane = 1:1, v/v); IR (KBr, νmax, cm-1): 3350, 3000, 2900,
1750, 1250; 1H NMR (DMSO-d6): 0.97-1.07 (m, CH3, 3H),
1.34~1.39 (m, CH2, 2H), 1.79~1.93 (m, CH2, 2H), 2.50~2.61
(m, CH2, 2H), 3.51 (s, CH3, 3H), 4.01 (s, CH, 1H), 4.42~4.45
1
νmax, cm-1): 3400, 3300, 3100, 1750, 1700, 1680; H NMR
(DMSO-d6): δ 1.70~2.00 (m, CH2, 2H), 2.20~2.40 (m, CH2, 2H),
4.00~4.20 (m, CH, 1H), 5.03 (s, CH2, 2H), 7.30 (s, ph, 5H).
(S)-3-carbobenzyloxy-amino-aspartic acid (2): yield 80 %; the
IR and 1H NMR spectra of (S)-2 was identical with the IR and
1H NMR spectra of (R)-2. (R)-3-carbobenzyloxy-amino-
glutamic anhydride (3): A mixture of synthesized (R)-2 (5 g,
18 mmol) and acetic anhydride (50 mL) was stirred at room
temperature for 2 h. The reaction mixture was concentrated in
vacuo. After concentrating added 100 mL diethyl ether . Then
the white solid was obtained in good yield (4.38 g, 94 %)
m.p.: 96-97 ºC; Rf: 0.8 (T.L.C eluent; EtOAc); IR (KBr, νmax
,
cm-1): 1700, 1750, 1820, 3300. (S)-3-carbobenzyloxy-amino-
glutamic anhydride (3): m.p. 130-131 ºC ; The IR and 1H NMR
spectra of (S)-3 was identical with the IR and 1H NMR spectra
of (R)-3. (R)-3-carbobenzyloxy-amino-1-hydroxyglutarimide
(4): A mixture of synthesized (R)-3-carbobenzyloxy-amino-
glutamic anhydride (3) (2.63 g, 10 mmol) and hydroxylamine

Vol. 25, No. 14 (2013)
Synthesis and Anticonvulsant Activity of 3-(Carbobenzyloxy-amino-1-glutarimidooxy)esters 8127
(m, CH, 1H), 5.02~5.13 (m, CH2, 2H), 7.46 (s, ph, 5H). (S)-
Methyl-2-(3-carbobenzyloxy-amino-glutarimidooxy)butyrate
(5d): yield 76 %. The IR and 1H NMR spectra of (S)-5d were
identical with the IR and 1H NMR spectra of (R)-5d. (R)-Ethyl-
2-(3-carbobenzyloxy-amino-glutarimidooxy)butyrate (5e):
yield 71 % Rf: 0.30 (TLC eluent ; EtOAc: n-hexane = 1:2, v/v);
IR (KBr, νmax, cm-1): 3350, 3000, 2900, 1750, 1200; 1H NMR
(DMSO-d6): δ 0.97~1.03 (m, CH3, 3H), 1.25~1.35 (m, CH3, 3H),
1.88~2.01 (m, CH2, 2H), 2.45~2.54 (m, CH2, 2H), 2.79~2.90
(m, CH2, 2H), 3.50 (s, CH, 1H), 4.20~4.27 (m, CH2, 2H), 4.46
~4.52 (m, CH, 1H), 5.13 (s, CH2, 2H), 7.45 (s, ph, 5H). (S)-
Ethyl-2-(3-carbobenzyloxy-amino- glutarimidooxy)butyrate
(5e): yield 69 %. The IR and 1H NMR spectra of (S)-5e were
identical with the IR and 1H NMR spectra of (R)-5e.
ACKNOWLEDGEMENTS
This work was supported by a grant of Dong-A University
(2013).
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RESULTS AND DISCUSSION
From our standpoint about structural property of the
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(R)- and (S)-methyl-1-(3-carbobenzyloxy-amino-glutarimido-
oxy)acetate (5a), (R)- and (S)-ethyl-1-(3-carbobenzyloxy-
amino-glutarimidooxy)acetate (5b), (R)- and (S)-ethyl-1-(3-
carbobenzyloxy-amino-glutarimidooxy)propionate (5e), (R)-
and (S)-methyl-2-(3-carbobenzyloxy-amino-glutarimidooxy)-
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glutarimidooxy)butyrate (5e). All products gave satisfactory
spectral data. So the compounds 5a-e were submitted to the
following anticonvulsant tests. It was reported that MES test
was correlated to generalized tonic clonic seizure and PTZ
test to generalized absence seizure. So the primary anticon-
vulsant activity of (S)-N-Cbz-α-amino-glutarimidoxy acetic
acid ester are very meaningful for the clinical prediction of
anticonvulsant drug candidates. Therefore we investigated the
anticonvulsant activity for those compounds ((R)-5a-e and (S)-
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pentylenetetrazole induced seizure test (PTZ test). The results
of anticonvulsant activity are summarized in Table-1.
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TABLE-1
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PRIMARY ANTICONVULSANT ACTIVITY OF (S)-N-Cbz-
α-AMINO-GLUTARIMIDOXY ACETIC ACID ESTER
5a-e AGAINST THE STRYCHNINE TEST
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a
Compound
Config
R
ED50
5a
5b
5c
S
S
S
S
S
-CH CO CH3
2
45.8
53.5
69.2
161.7
98.3
2
-CH CO2C2H
2
5
-CH(CH3)CO2CH3
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5d
-CH(C2H )CO2CH
5
3
5e
-CH(C2H5)CO2C2H
5
aAll compounds were dissolved in polyethyleneglycol and
administered i.p to ICR male mice. Dos was denoted in mg/kg. cThe
Str. test: Subcutaneous strychnine (1.20 mg/kg) 0.5
administration of test compound.
h post
We continue to synthesize their analogs and evaluate their
anticonvulsant activities in order to develop more active anti-
convulsant compounds and define the structure-activity rela-
tionship more distinctly.