Synthesis and anticonvulsant activities of N-benzyl (2R)-2-acetamido-3-oxysubstituted propionamide derivatives

Article abstract of DOI:10.1016/j.bmc.2008.08.055

Lacosamide has been submitted for regulatory approval in the United States and Europe for the treatment of epilepsy. Previous synthetic methods did not permit the elaboration of the structure-activity relationship (SAR) for the 3-oxy site in lacosamide. We report an expedient five-step stereospecific synthesis for N-benzyl (2R)-2-acetamido-3-oxysubstituted propionamide analogs beginning with d-serine methyl ester. The procedure incorporated alkyl (e.g. methyl, primary, secondary, and tertiary) and aryl groups at this position. The SAR for the 3-oxy site showed maximal activity in animal seizure models for small 3-alkoxy substituents.

Full text of DOI:10.1016/j.bmc.2008.08.055

Bioorganic & Medicinal Chemistry 16 (2008) 8968–8975
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and anticonvulsant activities of N-benzyl
(2R)-2-acetamido-3-oxysubstituted propionamide derivatives
Pierre Morieux a, James P. Stables b, Harold Kohn a,c,
*
a Division of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North Carolina, Campus Box 7360, Chapel Hill, NC 27599-7360, USA
b Epilepsy Branch, National Institute of Neurological Disorders and Stroke, National Institute of Health, 6001 Executive Boulevard, Suite 2106, Rockville, MD 20852, USA
c Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599-3290, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Lacosamide has been submitted for regulatory approval in the United States and Europe for the treatment
of epilepsy. Previous synthetic methods did not permit the elaboration of the structure–activity relation-
ship (SAR) for the 3-oxy site in lacosamide. We report an expedient five-step stereospecific synthesis for
Received 3 May 2008
Revised 13 August 2008
Accepted 22 August 2008
Available online 28 August 2008
N-benzyl (2R)-2-acetamido-3-oxysubstituted propionamide analogs beginning with
D-serine methyl
ester. The procedure incorporated alkyl (e.g. methyl, primary, secondary, and tertiary) and aryl groups
at this position. The SAR for the 3-oxy site showed maximal activity in animal seizure models for small
3-alkoxy substituents.
Keywords:
Amino acid N-benzylamides
Aziridine ring opening
Anticonvulsants
Ó 2008 Elsevier Ltd. All rights reserved.
Diethoxytriphenylphosphorane
Structure–activity relationship
1. Introduction
O
O
Lacosamide (VimpatÒ, (R)-1) is an emerging neurological agent
that has shown therapeutic efficacy for the treatment of partial sei-
zures. It has been submitted for regulatory approval in the United
States and Europe under the sponsorship of UCB Pharma.1,2 Evalu-
ation of 1 in animal seizure models at the National Institutes of
Neurological Disorders and Stroke’s (NINDS) Anticonvulsant
Screening Program (ASP) showed that it exhibited potent anticon-
vulsant activity in the maximal electroshock seizure (MES) test in
mice (ip) and rats (po).3
H
N
N
H
O
(R)-1
R
O
R
O
3
O
O
H
N
H
N
N
H
N
H
2
O
O
)-
In 1996, we reported an expeditious three-step synthesis of (R)-
5
6
7
R= CH2CH3
R= CH2CHCH2
(
R
1 from D
-serine (Scheme 1).3 The 3-methoxy unit was installed by a
Williamson-type ether synthesis using MeI and Ag2O. Using race-
mic 4 and either EtI or allyl iodide in place of MeI gave the corre-
sponding O-substituted derivatives 5 and 6, respectively.3 Efforts
to extend the synthesis to other O-substituted analogs led to
appreciably lower yields of the desired ethers.4 This synthetic
impediment prevented our determining the structure–activity
relationship (SAR) for the 3-oxy substituent. We report herein an
expedient stereospecific synthesis of (R)-N-benzyl-2-acetamido-
3-oxysubstituted propionamides (7) and document the importance
of the 3-oxy substituent for anticonvulsant activity within this no-
vel class of agents.
2. Results and discussion
2.1. Synthesis
We sought a general and efficient procedure to prepare 7 that
would permit different substituents at the 3-oxy site. Okawa and
coworkers demonstrated that N-Cbz-substituted aziridines
underwent ring opening with alcohols and thiols using catalytic
amounts of BF3ꢀEt2O to give the corresponding 3-substituted deriva-
tives 9.5,6Similar procedures have been used by Larsson and Carlson,7
8
* Corresponding author. Tel.: +1 919 843 8112; fax: +1 919 843 7835.
E-mail address: harold_kohn@unc.edu (H. Kohn).
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.08.055

P. Morieux et al. / Bioorg. Med. Chem. 16 (2008) 8968–8975
8969
D
-serine stereochemical series.3 Accordingly, we converted 13a and
R'
X
O
13b to methyl and ethyl (2R)-N-(acetyl)aziridine-2-carboxylates
(14a and 14b) in 94% yield with acetic anhydride, Et3N, and a cata-
lytic amount of DMAP. Treatment of 14a and 14b with MeOH, the
primary alcohols, EtOH and diethylene glycol monomethyl ether
(DEGME), the secondary alcohol, iPrOH, the tertiary alcohol, tert-
BuOH, and phenol with one equivalent of BF3ꢀEt2O gave the
corresponding aziridine ring-opening products (15a,b–20a,b) in
50–60% isolated yield. The alcohols produced little differences in
yields. Conversion of esters 15a,b–20a,b to the N-benzyl amides 1,
27–31, respectively, followed established procedures. First, we
hydrolyzed methyl (ethyl) esters 15–20 with stoichiometric
amounts of LiOH (1.0–1.1 equiv) at 0 °C to provide the free acids
21–26 upon workup. Under these conditions we detected little or
no racemization. Coupling acids 21–26 with benzylamine and 4-
R'-XH
BF3 Et2O
∗
OR
∗
Cbz
OR
N
N
H
Cbz
O
8
9
and Zavada and coworkers.8 The synthetic utility of the Okawa pro-
cedure was hampered by the time required by the five-step synthe-
sis of 8 from the desired serine ester hydrochloride.5 In 1989, van
Boom reported a solution to this problem.9 Utilizing Evans’ one-step
cyclodehydration conversion of 2-amino alcohols to aziridines with
diethoxytriphenylphosphorane (DTPP),10 treatment of 10 with
DTPP provided the unsubstituted (2S)-aziridine-2-carboxylates 11.
OH
OBn
O
(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium
chlo-
O
P
EtO
Ph
OEt
Ph
ride (DMTMM)12 provided the amides 1, 27–31, respectively. After
column purification and subsequent recrystallization we saw that
the spectral and analytical data for 1, 27–31 were in agreement
with their proposed structures. Adding the chiral resolving agent
(R)-(ꢁ)-mandelic acid to a CDCl3 solution of each amide showed
only one signal for the acetamide methyl resonance consistent with
the expected enantiopurity of the products.3,13
P
OBn
+
+
+ 2 EtOH
Ph
Ph
H2N
Ph
Ph
N
H
O
DTPP
10
11
Thus, we treated D-serine methyl ester (12) with DTTP to give the
desired methyl (2R)-aziridine-2-carboxylate (13a) along with the
corresponding ethyl ester 13b in 50–60% total yield (Scheme 2).
The production of the ethyl ester 13b was surprising. The amount
of ethyl ester varied with each reaction and appeared to increase
with increasing reaction time, and increasing amounts of DTPP.11
Since the ester group was hydrolyzed to the acid in a subsequent
step to permit amide coupling, we used the binary mixture of esters
without separation. With an expedient route to 13, we evaluated
the generality of the BF3ꢀEt2O catalyzed alcohol ring-opening reac-
tion for this set of aziridines. We restricted our studies to the (R)-
stereoisomer since we have shown that the pharmacological activ-
ity for this class of substituted amino acids principally resided in the
2.2. Pharmacological activity
Compounds 1 and 27–31 were tested for anticonvulsant activ-
ity by the NIH and NINDS’s Anticonvulsant Screening Program
(ASP) using the procedures described by Stables and Kupferberg.14
The pharmacological data are summarized in Table 1, along with
similar results obtained for 1 and the established antiepileptic
agents phenytoin, valproate, and phenobarbital. We observed that
the N-benzyl (2R)-3-alkoxysubstituted 2-acetamidopropionamides
1, 27, and 29–31 exhibited moderate-to-excellent anticonvulsant
activity in the MES-seizure test in mice (ip). Among the 3-alkoxy-
substituted derivatives, activity improved with a coinciding de-
crease of the 3-alkoxy group’s size. Thus, the MES ED50 values
declined from a range between 30 mg/kg and 100 mg/kg for the
tert-butoxy analog 30, down to 23 mg/kg for 29, to 7.9 mg/kg for
27 and finally to 4.5 mg/kg for the O-methoxy compound 1. The
anticonvulsant activities for 1 and 27 exceeded that of phenytoin.15
Paralleling this increase, we observed a neurological toxicity in-
crease in the rotorod test16 similar to earlier findings.3 Introduction
of a 3-phenoxy unit in place of the 3-methoxy group in 1 to give 31
led to a marked activity reduction in the MES test (ED50 >100 mg/
kg but still <300 mg/kg). Finally, the polyether 28 exhibited neither
anticonvulsant nor neurological activity at the dose evaluated (up
OH
OH
OH
OH
O
Ac2O
H2N
N
AcOH
H
O
O
(R)-2
(R)-3
NMM
IBCF
PhCH2NH2
CH3I
O
OH
H
O
O
Ag2O
H
N
Ph
N
Ph
N
N
H
H
O
O
(R
)-1
(R)-3
Scheme 1. Three-step synthesis of (R)-lacosamide (1).
O
O
OH
Ac2O, NEt3
cat. DMAP
OR
DTPP
OR
O
N
O
H2N
N
H
O
12
(R
)-
(R
)-13 a R = Me
b R = Et
(R
)-14 a R = Me
b R = Et
O
R'H
BF3 Et2O
R'
O
R'
R'
O
1) LiOH
2) H+
PhCH2NH2
O
OR
O
O
H
N
OR
N
OH
Ph
N
DMTMM
N
H
N
H
H
O
O
(R
)-14 a R = Me
b R = Et
(
(
(
(
(
(
R
)-15 R' = OMe: a R = Me; b R = Et
)- R' = OEt: R = Me; R = Et
(
R
)-21 R' = OMe
)-22 R' = OEt
(
(
(
(
(
(
R
)-1 R' = OMe
)-27 R' = OEt
)-28 R' = DEGME
)-29 R' = Oi-Pr
16
a
b
(
R
R
R
R
R
R
R
R
R
R
R
17
(
R
)-23 R' = DEGME
)- R' = DEGME: a R = Me; b R = Et
18
a
b
(R )-24 R' = Oi-Pr
)- R' = Oi-Pr: R = Me; R = Et
19
a
b
25
)- R' = Otert-Bu
30
31
)- R' = Otert-Bu: R = Me; R = Et
(
R
)-
)-
R' = Otert-Bu
R' = OPh
20
a
b
26
(R )- R' = OPh
)- R' = OPh: R = Me; R = Et
Scheme 2. Synthesis of N-benzyl-(2R)-2-acetamido-3-oxysubstituted propionamide derivatives.

8970
P. Morieux et al. / Bioorg. Med. Chem. 16 (2008) 8968–8975
Table 1
eter. The high-resolution mass spectrum was performed on a
Bruker Apex-Q 12 Tesla FTICR by Dr. M. Crowe at the University
of North Carolina—Chapel Hill. Microanalysis was provided by
Atlantic Microlab, Inc. (Norcross, GA).
Pharmacological data for N-benzyl (2R)-2-acetamido-3-oxysubstituted propiona-
mides derivatives
R
O
O
H
4.2. Synthesis of diethoxytriphenylphosphorane (DTPP)
N
N
H
O
Triphenylphosphine (110.00 g, 419 mmol) was dissolved in
anhydrous toluene (500 mL) and the solvent was evaporated. The
solid was redissolved in a 1:1 mixture of anhydrous CH2Cl2
(350 mL) and THF (350 mL) and cooled at ꢁ78 °C (dry ice/acetone
bath). While stirring, Br2 (21.5 mL, 419 mmol) was added all at
once with a syringe and the reaction was stirred at ꢁ78 °C
(10 min). Commercial NaOEt (96%, 59.35 g, 838 mmol) was added
portionwise over 5 min, and then anhydrous EtOH (44 mL,
838 mmol) was added dropwise to the formed suspension. The
reaction was stirred at ꢁ78 °C (90 min), and allowed to warm to
room temperature. The supernatant was decanted and filtered over
Compound #
R
Mice (ip)a
Tox,c TD50
MES,b ED50
PId
6
(R)-1e
(R)-27
CH3
4.5 [0.5]
27 [0.25]
(26–28)
44 [0.25]
(37–54)
>300 [0.5]
77 [0.25]
(66–96)
>100, <300
[0.5]
(3.7–5.5)
7.9 [0.25]
(5.3–10.4)
CH2CH3
5.6
(R)-28
(R)-29
CH2CH2OCH2CH2OCH3 >300 [0.5]
CH(CH3)2
—
3.3
23 [0.25]
(20–26)
>30, <100 [0.5]
(R)-30
C(CH3)3
—
a
Celite bed. The remaining suspension was centrifuged at
(R)-31
C6H5
—
>100, <300
[0.5]
9.5 [2]
(8.1–10)
22 [1]
(15–23)
270 [0.25]
(250–340)
>30, <100 [0.5]
—
1600 rpm for 15 min. The supernatant layers obtained from both
fractions were combined and evaporated at 30 °C. Hexanes
(500 mL) were added to the oily residue and the mixture was sha-
ken for 5 min. The triphenylphosphine oxide (TPPO) was filtered,
and the solvent removed in vacuo. Additional hexanes (500 mL)
were added to the solid and the flask was let stand on ice for
20 min. Additional TPPO was filtered and the solvent evaporated
to yield DTPP as a white to pale yellow solid (66.42 g, 45% yield,
Phenytoinf
Phenobarbitalf
Valproatef
56 [2]
6.9
3.2
1.6
(53–72)
69 [0.5]
(63–73)
430 [0.25]
(370–450)
—
—
a
The compounds were administered intraperitoneally.
MES = maximal electroshock seizure test in mg/kg. Numbers in parentheses are
b
90% pure by wt): 1H NMR (CDCl3)
d 0.75 (t, J = 7.0 Hz,
95% confidence intervals. The dose effect data was obtained at the ‘time of peak’
effect (indicated in hours in the brackets).
P(OCH2CH3)2), 2.53 (app q, J = 7.0 Hz, P(OCH2CH3)2), 7.39–7.47
(m, 9 ArH), 8.04–8.12 (m, 6 ArH); 13C NMR (CDCl3) 16.4 (d,
J = 5.1 Hz, P(OCH2CH3)2), 57.5 (d, J = 6.8 Hz, P(OCH2CH3)2), 127.8,
129.4, 132.7 (15 ArC), 139.2 (d, J = 173.0 Hz, 3 ArC). The DTPP ob-
tained under these conditions was 85–95% pure by weight and
was contaminated with TPPO (1H NMR analysis).
c
Tox = neurologic toxicity determined from rotorod test in mice. Numbers in
parentheses are 95% confidence intervals. The dose effect data was obtained at the
‘time of peak’ effect (indicated in hours in the brackets).
d
PI = protective index (TD50/ED50).
Ref. 3.
Refs. 15 and 18.
e
f
4.3. General procedure to generate
12)
D-serine methyl ester ((R)-
to 300 mg/kg). We hypothesize that the loss of neurological activ-
ity is due to the inability of this hydrophilic derivative to cross the
blood brain barrier. No N-benzyl-3-oxysubstituted 2-acetamido-
propionamides 1 and 27–31 showed detectable activity in the
pentylenetetrazole test (scMet) in mice (data not shown), which
is in agreement with similar test results observed for this class of
compounds.3
D-Serine methyl ester hydrochloride (1 equiv) was suspended in
acetonitrile ([C] ꢂ 1 M) and Et3N (1.5 equiv) was added. After stir-
ring at room temperature (1 h), the salts were filtered and rinsed
with EtOAc and an equal volume of EtOAc was added. The mixture
was stirred at 0 °C (10 min), the solids filtered, and then approxi-
mately two thirds of the solvent volume removed in vacuo. The
remaining reaction mixture was stirred at 0 °C (10 min), filtered,
and the solvent removed. The resulting oil was dissolved in aceto-
nitrile and the solvent evaporated to remove excess Et3N. The pre-
ceding step was repeated until Et3N could not be detected, yielding
3. Conclusions
We have established a convenient, general, stereospecific syn-
thetic method for the preparation of N-benzyl-3-oxysubstituted
2-acetamidopropionamides (7). The route takes advantage of a ra-
pid and short synthesis of 14 using readily available DTPP.10 Key to
the preparation of these compounds is the BF3ꢀEt2O ring opening of
aziridine 14 with alcohols and phenol. Little differences in the
yields for ring opening were observed when we varied the size
and nucleophilicity of the alcohol or phenol.
the free amine of
that solidified upon standing overnight. (R)-12 was best used as an
oil since solid (R)-12 did not readily dissolve in organic solvents.
D
-serine methyl ester as a pale yellow oil (ꢂ90%)
4.4. Synthesis of (R)-methyl N-acetylaziridine-carboxylate ((R)-
14a) and (R)-ethyl N-acetylaziridine-carboxylate ((R)-14b)
4. Experimental
To a solution of D-serine methyl ester (41.30 g, 347 mmol) in
acetonitrile (500 mL) was added DTPP (86% by wt, 142.00 g,
346 mmol). The solution was stirred at room temperature (24 h).
The solvent was removed in vacuo, the residue dissolved in mini-
mal amount of CH2Cl2 (250 mL), and extracted with aqueous
0.1 M H2SO4 until the pH of the aqueous phase remained acidic
(3ꢃ 150 mL). The combined aqueous layers were washed with
EtOAc (3ꢃ 200 mL), basified (pH ꢂ 10) with solid Na2CO3, satu-
rated with NaCl until the solution became cloudy, and extracted
with EtOAc (6ꢃ 200 mL). The combined organic layers were dried
(Na2SO4) and evaporated to give a crude yellow liquid. Bulb-to-
4.1. General methods
Melting points were determined with a Thomas-Hoover melt-
ing point apparatus and are uncorrected. Infrared spectra (IR) were
run on a ATI Mattson Genesis Series FTIRTM spectrometer. Absorp-
tion values are expressed in wave-numbers (cmꢁ1). Optical rota-
tions were obtained on a Jasco P-1030 polarimeter. Proton (1H
NMR, 300 MHz) and carbon (13C NMR, 75 MHz) nuclear magnetic
resonance spectra were taken on a Varian Gemini 2000 spectrom-

P. Morieux et al. / Bioorg. Med. Chem. 16 (2008) 8968–8975
8971
bulb distillation of the liquid at 80 °C under vacuum (6 mm Hg)
yielded an approximately 9:1 molar mixture of (R)-13a and (R)-
13b as a colorless liquid (24.60 g, 69%). The mixture was directly
dissolved in CH2Cl2 (500 mL) and Et3 N (33.4 mL, 239 mmol) and
DMAP (1.46 g, 12 mmol) were successively added. While stirring
at room temperature (water bath), Ac2O (22.6 mL, 239 mmol)
was added dropwise over 15 min and the reaction was then al-
lowed to proceed at room temperature (45 min). The reaction
was successively washed with a 10% aqueous citric acid solution
(500 mL), and brine (500 mL), dried (Na2SO4), and the solvents
were removed in vacuo to yield an approximately 9:1 molar mix-
ture of a colorless residue (32.80 g, 94%) that was used without fur-
ther purification: Rf = 0.38 ((R)-14a), 0.39 ((R)-14b) (2:1 hexanes/
EtOAc). Spectral data for (R)-14a (ꢂ90 mol percent based on 1H
NMR integrations): 1H NMR (CDCl3) d 2.16 (s, CH3C(O)), 2.49 (dd,
J = 1.8, 7.0 Hz, NCHH0CH), 2.58 (dd, J = 3.0, 7.0 Hz, CHCOOCH3),
3.15 (dd, J = 1.8, 3.0 Hz, NCHH0CH), 3.80 (s, CO2CH3); 13C NMR
(CDCl3) d 23.8 (CH3C(O)), 31.0 (NCH2CH), 34.5 (CHCO2CH3), 52.9
(CO2CH3), 168.9 (CH3C(O)), 180.6 (COOCH3); (R)-14a was not de-
tected by HRMS.
suspension was stirred at room temperature (3–12 h). In those cases
where a salt did not precipitate, DMTMM was added after 15 min to
the solution. The salts were removed by filtration, washed with THF,
and the solvent was removed in vacuo. The obtained residue was
purified by flash column chromatography to afford the benzyla-
mide, and then recrystallized with EtOAc and hexanes.
4.8. Synthesis of (R)-methyl 2-acetamido-3-methoxypropionate
((R)-15a) and (R)-ethyl 2-acetamido-3-methoxypropionate ((R)-
15b)
Using Method A, a ꢂ 9:1 mixture of (R)-14a and (R)-14b (5.46 g,
40.6 mmol), and BF3ꢀEt2O (5.1 mL, 40.6 mmol) in MeOH (50 mL)
gave 3.95 g (56%) of (R)-15a and (R)-15b as a pale yellow residue that
solidified under high vacuum and was used without further purifica-
tion: Rf = 0.40 ((R)-15a), 0.42 ((R)-15b) (5:95 hexanes/EtOAc); IR
(CH2Cl2 film) 3300, 3062, 2996, 2940, 1743, 1656, 1547, 1444,
1380, 1214, 1119 cmꢁ1. Spectral data for (R)-15a (ꢂ90 mol percent
based on 1H NMR integrations): 1H NMR (CDCl3) d 2.06 (s,
CH3C(O)NH), 3.34 (s, OCH3), 3.61 (dd, J = 4.0, 9.3 Hz, CHCHH0OCH3),
3.77 (s, C(O)OCH3), 3.81 (dd, J = 4.0, 9.3 Hz, CHCHH0OCH3), 4.75
(app dt, J = 4.0, 7.8 Hz, CHCH2OCH3), 6.74 (br d, J = 7.8 Hz,
CH3C(O)NH); 13C NMR (CDCl3) d 22.9 (CH3C(O)), 52.4 (CHCH2OCH3
or C(O)OCH3), 52.5 (C(O)OCH3 or CHCH2OCH3), 59.1 (CH2OCH3),
72.2 (CHCH2OCH3), 170.1, 170.8 (CH3C(O)NH, C(O)OCH3); Mr (+ESI)
[M+Na]+ (calcd for C7H13NO4Na+ 198.0742) 198.0740.
Spectral data for (R)-14b (ꢂ10 mol percent based on 1H NMR
integrations): 1H NMR (CDCl3) d 1.31 (t, J = 6.9 Hz, C(O)OCH2CH3),
4.24 (q, J = 6.9 Hz, C(O)OCHH0CH3), 4.25 (q, J = 6.9 Hz,
C(O)OCHH0CH3), the remaining signals were not detected and are
believed to overlap with the 1H signals for (R)-14a; 13C NMR
(CDCl3) no 13C signals were detected for (R)-14b; Mr (+ESI)
[M+Na]+ (calcd for C7H11NO3Na+ 180.0637) 180.0631.
Spectral data for (R)-15b (ꢂ10 mol percent based on 1H NMR
integrations): 1H NMR (CDCl3) d 1.29 (t, J = 7.2 Hz, C(O)OCH2CH3)
1.99 (s, CH3C(O)NH), 3.44 (s, OCH3), 3.92 (dd, J = 4.0, 9.3 Hz,
CHCHH0OCH3), 4.19–4.28 (m, C(O)OCH2CH3), 6.40–6.50 (br d,
CH3C(O)NH), the remaining peaks were not detected and are be-
lieved to overlap with (R)-15a signals; 13C NMR signals were not
detected for (R)-15b; Mr (+ESI) 212.0896 [M+Na]+ (calcd for
C8H15NO4Na+ 212.0899 [M+Na]+).
4.5. General procedure for the aziridine ring opening of (R)-
14a/(R)-14b with alcohols. Method A
To a cooled solution (ice bath) of a binary mixture of (R)-14a
and (R)-14b in the appropriate alcohol or in CH2Cl2 ([C] ꢂ 0.5–
1 M) was added BF3ꢀEt2O (1 equiv) dropwise while stirring. Upon
addition, the mixture was warmed to room temperature and stir-
red for an additional 90 min. An equal volume of saturated aqueous
NaHCO3 was added to the solution and after 15 min of vigorous
stirring, the organic layer separated. The aqueous layer was ex-
tracted with CH2Cl2 until no more product was detected (TLC anal-
ysis). The combined organic layers were combined, dried (Na2SO4),
and removed in vacuo to yield a mixture of methyl and ethyl esters
that was either used without further purification or, when needed,
purified by flash column chromatography.
4.9. Synthesis of (R)-methyl 2-acetamido-3-ethoxypropionate
((R)-16a) and (R)-ethyl 2-acetamido-3-ethoxypropionate ((R)-
16b)
Using Method A, a mixture of (R)-14a and (R)-14b (ꢂ90% (R)-
14a and ꢂ10% (R)-14b) (1.88 g, 13.0 mmol), and BF3ꢀEt2O
(1.63 mL, 13.0 mmol) in EtOH (25 mL) gave 1.34 g (54%) of (R)-
16a and (R)-16b as a pale yellow oil that was used without further
purification: Rf = 0.43 ((R)-16a), 0.45 ((R)-16b) (5:95 hexanes/
EtOAc); IR (neat) 3287, 3064, 2977, 2876, 1745, 1661, 1542,
1442, 1375, 1212, 1119 cmꢁ1. Spectral data for (R)-16a (ꢂ90 mol
percent based on 1H NMR integrations): 1H NMR (CDCl3) d 1.16
(t, J = 7.2 Hz, CH2OCH2CH3), 2.06 (s, CH3C(O)NH), 3.50 (q,
J = 7.2 Hz, CH2OCHH0CH3), 3.51 (q, J = 7.2 Hz, CH2OCHH0CH3), 3.65
(dd, J = 4.0, 8.7 Hz, CHCHH0OCH2CH3), 3.76 (s, C(O)OCH3), 3.84
(dd, J = 4.0, 8.7 Hz, CHCHH0OCH2CH3), 4.75 (app dt, J = 4.0, 7.5 Hz,
CHCH2OCH2CH3), 6.54 (br d, J = 7.5 Hz, CH3C(O)NH); 13C NMR
(CDCl3) d 15.0 (OCH2CH3), 23.3 (CH3C(O)), 52.7 (CHCH2OCH3 or
4.6. General procedure for the methyl/ethyl ester hydrolysis of
(R)-15a/(R)-15b-(R)-20a/(R)-20b with LiOH. Method B
To a solution of methyl and ethyl esters in 2 volumes of THF
([C] ꢂ 0.1 M) was added LiOH (1 equiv) in 1 volume of H2O. The
reaction was stirred at room temperature (90 min), after which
time the aqueous layer was washed with Et2O (2 volumes). The
aqueous layer was acidified (pH 1) by the dropwise addition of
aqueous concentrated HCl at 0 °C, saturated with NaCl, and ex-
tracted with EtOAc until no further product was detected (TLC
analysis). The combined organic layers were combined, dried
(Na2SO4), and evaporated to an oily residue that was used directly
in the next step, or recrystallized when needed from EtOAc and
hexanes to provide an analytical sample.
C(O)OCH3),
(CHCH2OCH2CH3),
52.8
(C(O)OCH3
70.2 (CHCH2OCH2CH3),
or
CHCH2OCH2H3),
170.1,
67.1
171.1
(CH3C(O)NH, C(O)OCH3); Mr (+ESI) 212.0897 [M+Na]+ (calcd for
C8H15NO4Na+ 212.0899 [M+Na]+).
Spectral data for (R)-16b (ꢂ10 mol percent based on 1H NMR
integrations): 1H NMR (CDCl3) d 1.24 (t, J = 7.2 Hz, CH2OCH2CH3
or C(O)OCH2CH3), 1.29 (t, J = 7.2 Hz, C(O)OCH2CH3 or
CH2OCH2CH3), 1.99 (s, CH3C(O)NH), 3.96–4.04 (m, CH2OCHH0CH3),
4.19–4.30 (m, C(O)OCH2CH3), 6.10–6.22 (br d, J = 6.8 Hz,
CH3C(O)NH), the remaining peaks were not detected and are be-
lieved to overlap with (R)-16a signals; 13C NMR signals were not
detected for (R)-16b; Mr (+ESI) 226.1054 [M+Na]+ (calcd for
C9H17NO4Na+ 226.1055 [M+Na]+).
4.7. General procedure for the DMTMM amide coupling
reaction. Method C
To a THF solution of acid ([C] ꢂ 0.1 M) at room temperature was
added benzylamine (1.2 equiv). The solution was stirred for 5–
10 min until the benzylammonium carboxylate precipitated. While
stirring, DMTMM (1.2 equiv) was added at once, and the resulting

8972
P. Morieux et al. / Bioorg. Med. Chem. 16 (2008) 8968–8975
4.10. Synthesis of (R)-methyl 2-acetamido-3-(2-(2-methoxye-
thoxy)ethoxy)propionate ((R)-17a) and (R)-ethyl 2-acetamido-
3-(2-(2-methoxyethoxy)ethoxy)propionate ((R)-17b)
(30 mL) gave 2.75 g (52%) of (R)-19a and (R)-19b as a pale yellow
oil: Rf = 0.52 ((R)-19a), 0.54 ((R)-19b) (5:95 hexanes/EtOAc); IR
(neat) 3298, 3062, 2974, 1749, 1663, 1537, 1370, 1204,
1098 cmꢁ1. Spectral data for (R)-19a (ꢂ90 mol percent based on
1H NMR integrations): 1H NMR (CDCl3) d 1.14 (s, CH2OC(CH3)3),
2.06 (s, CH3C(O)NH), 3.56 (dd, J = 3.0, 9.0 Hz, CHCHH0OC(CH3)3),
3.76 (s, C(O)OCH3), 3.81 (dd, J = 3.0, 9.0 Hz, CHCHH0OC(CH3)3),
4.72 (app dt, J = 3.0, 7.2 Hz, CHCH2OC(CH3)3), 6.41 (br d,
J = 7.2 Hz, CH3C(O)NH); 13C NMR (CDCl3) d 22.9 (CH3C(O)), 27.7
(OC(CH3)3), 52.1 (CHCH2OC(CH3)3 or C(O)OCH3), 53.3 (C(O)OCH3
Using Method A, a ꢂ1:1 mixture of (R)-14a and (R)-14b (4.50 g,
30.0 mmol), DEGME (11.3 g, 94.5 mmol), and BF3ꢀEt2O (3.8 mL,
30.0 mmol) in CH2Cl2 (30 mL) gave 2.84 g (35%) of (R)-17a and
(R)-17b as a colorless viscous oil after purification by flash chroma-
tography column (2:1 hexanes/EtOAc to EtOAc): Rf = 0.31 ((R)-17a),
0.33 ((R)-17b) (EtOAc); IR (neat) 3300, 3063, 2940, 2940, 1744,
1659, 1553, 1446, 1216, 1120 cmꢁ1. Spectral data for (R)-17a and
(R)-17b (1:1): 1H NMR (CDCl3) d 1.28 ((R)-17b, t, J = 7.2 Hz,
C(O)OCH2CH3), 2.06 ((R)-17a,b, s, CH3C(O)NH), 3.39 ((R)-17a,b, s,
CH2CH2OCH3), 3.52–3.58 ((R)-17a,b, m, CH2CH2OCH3), 3.60–3.64
((R)-17a,b, m, OCH2CH2OCH2), 3.68–3.74 ((R)-17a,b, m,
CHCHH0OCH2), 3.76 ((R)-17a, s, C(O)OCH3), 3.94, 3.97 ((R)-17a,b,
app t, J = 4.2 Hz CHCHH0OCH2), 4.22 ((R)-17b, t, J = 7.2 Hz,
C(O)OCH2CH3), 4.68–4.76 ((R)-17a,b, m, CHCH2OCH2), 6.52–6.70
((R)-17a,b, m, CH3C(O)NH); 13C NMR (CDCl3) d 14.3 ((R)-17a,b,
C(O)OCH2CH3), 23.1 ((R)-17a,b, CH3C(O)), 52.6, 52.9, 53.0 ((R)-
17a,b, CHCH2OCH2, (R)-17a, C(O)OCH3), 61.7 ((R)-17b,
C(O)OCH2CH3), 70.5, 70.6, 71.1, 71.2, 71.3 ((R)-17a,b, OCH2-
CH2OCH2CH2OCH3), 170.1, 170.4, 170.9 ((R)-17a,b, CH3C(O)NH,
C(O)OCH3), the remaining resonances were not detected and are
believed to overlap with nearby signals; Compound (R)-17a was
not detected by HRMS; (R)-17b: Mr (+ESI) 300.1421 [M+Na]+ (calcd
for C12H23NO6Na+ 300.1423 [M+Na]+).
or
CHCH2OCH(CH3)2),
62.4
(CHCH2OC(CH3)3),
73.8
(CHCH2OC(CH3)3), 170.3, 171.5 (CH3C(O)NH, C(O)OCH3); Mr (+ESI)
240.1211 [M+Na]+ (calcd for C10H19NO4Na+ 240.1212 [M+Na]+).
Spectral data for (R)-19b (ꢂ10 mol percent based on 1H NMR
integrations): 1H NMR (CDCl3) d 1.21 (s, CH2OC(CH3)3), 1.99 (s,
CH3C(O)NH), 4.18–4.24 (m, C(O)OCH2CH3), 5.95–6.15 (br m,
CH3C(O)NH), the remaining signals were not detected and are be-
lieved to overlap with (R)-19a signals or are too small to be de-
tected; 13C NMR signals were not detected for (R)-19b; Mr (+ESI)
254.1368 [M+Na]+ (calcd for C11H21NO4Na+ 254.1368 [M+Na]+).
4.13. Synthesis of (R)-methyl 2-acetamido-3-phenoxypropio-
nate ((R)-20a) and (R)-ethyl 2-acetamido-3-phenoxypropionate
((R)-20b)
Using Method A, a ꢂ3:7 mixture of (R)-14a and (R)-14b (2.00 g,
13.1 mmol), phenol (3.95 g, 42.0 mmol), and BF3ꢀEt2O (1.6 mL,
13.1 mmol) in CH2Cl2 (20 mL) gave 1.40 g (43%) of (R)-20a and
(R)-20b as a slight yellow residue: Rf = 0.50 ((R)-20a), 0.52 ((R)-
20b) (5:95 hexanes/EtOAc); IR (neat) 3067, 2984, 1743, 1660,
1596, 1541, 1498, 1379, 1296, 1238, 1159 cmꢁ1; Spectral data for
(R)-20a and (R)-20b (ꢂ3:7): 1H NMR (CDCl3) d 1.25 ((R)-20b, t,
J = 7.2 Hz, C(O)OCH2CH3), 2.06 ((R)-20a,b, s, CH3C(O)NH), 3.76
((R)-20a, s, C(O)OCH3), 4.20–4.23 ((R)-20a,b, m, CHCHH0OPh),
4.24 ((R)-20b, q, J = 7.2 Hz, C(O)OCH2CH3), 4.36–4.43 ((R)-20a,b,
m, CHCHH0OPh), 4.68–5.06 ((R)-20a,b, m, CHCH2OPh), 6.52 ((R)-
20a,b, d, J = 7.2 Hz, CH3C(O)NH), 6.84–6.90 ((R)-20a,b, m, 2 ArH
(o)), 6.95–7.00 ((R)-20a,b, m, ArH (p)), 7.24–7.32 ((R)-20a,b, m, 2
ArH (m)); 13C NMR (CDCl3) d 14.3 ((R)-20b, C(O)OCH2CH3), 23.1
((R)-20a,b, CH3C(O)), 52.4, 52.5, 52.9 ((R)-20a,b, CHCH2OPh, (R)-
20a, C(O)OCH3), 62.1 ((R)-20b, C(O)OCH2CH3), 68.1, 68.2 ((R)-
20a,b, CHCH2OPh), 114.8, 121.7, 129.7, 158.3, 158.4 ((R)-20a,b,
CH2OPh), 170.0, 170.1, 170.5 ((R)-20a,b, CH3C(O)NH, (R)-20a
C(O)OCH3), the remaining signals were not detected and are be-
lieved to overlap with nearby peaks; Compound (R)-20a, Mr
(+ESI) 268.0895 [M+Na]+ (calcd for C12H15NO4Na+ 260.0899
[M+Na]+); Compound (R)-20b, Mr (+ESI) [M+Na]+ (calcd for
4.11. Synthesis of (R)-methyl 2-acetamido-3-isopropoxypro-
pionate ((R)-18a) and (R)-ethyl 2-acetamido-3-isopropoxypro-
pionate ((R)-18b)
Using Method A, a ꢂ9:1 mixture of (R)-14a and (R)-14b (3.40 g,
23.5 mmol), and BF3ꢀEt2O (2.95 mL, 23.5 mmol) in iPrOH (30 mL)
gave 2.98 g (62%) of (R)-18a and (R)-18b as a pale yellow oil:
Rf = 0.46 ((R)-18a), 0.48 ((R)-18b) (5:95 hexanes/EtOAc); IR (neat)
3295, 3062, 2972, 2877, 1748, 1663, 1538, 1442, 1375, 1212,
1147 cmꢁ1. Spectral data for (R)-18a (ꢂ90 mol percent based on
1H NMR integrations): 1H NMR (CDCl3) d 1.10 (d, J = 6.0 Hz,
CH2OCHCH3(C0H3)), 1.12 (d, J = 6.0 Hz, CH2OCHCH3(C0H3)), 2.06 (s,
CH3C(O)NH), 3.55 (hept, J = 6.0 Hz, CH2OCH(CH3)2), 3.64 (dd,
J = 3.7, 9.3 Hz, CHCHH0OCH(CH3)2), 3.76 (s, C(O)OCH3), 3.84 (dd,
J = 3.7, 9.3 Hz, CHCHH0OCH(CH3)2), 4.72 (app dt, J = 3.7, 7.2 Hz,
CHCH2OCH(CH3)2), 6.41 (br d, J = 7.2 Hz, CH3C(O)NH); 13C NMR
(CDCl3)
(CH3C(O)), 52.1 (CHCH2OCH(CH3)2 or C(O)OCH3), 52.6 (C(O)OCH3
or CHCH2OCH(CH3)2), 67.5 (CHCH2OCH(CH3)2), 70.2
d
21.5 (OCHCH3(C0H3)), 21.6 (OCHCH3(C0H3)), 22.9
(CHCH2OCH(CH3)2), 169.6, 170.4 (CH3C(O)NH, C(O)OCH3); Mr
(+ESI) 226.1054 [M+Na]+ (calcd for C9H17NO4Na+ 226.1055
[M+Na]+).
C
12H15NO4Na+ 274.1055 [M+Na]+) 274.1052.
4.14. Synthesis of (R)-2-acetamido-3-methoxypropionic acid
((R)-21)
Spectral data for (R)-18b (ꢂ10 mol percent based on 1H NMR
integrations): 1H NMR (CDCl3)
d
1.16 (d, J = 6.0 Hz,
CH2OCHCH3(C0H3)), 1.21 (d, J = 6.0 Hz, CH2OCHCH3(C0H3)), 1.28 (t,
J = 6.0 Hz, C(O)OCH2CH3), 1.99 (s, CH3C(O)NH), 4.06–4.12 (m,
CHCHH0OCH(CH3)2), 4.18–4.26 (m, C(O)OCH2CH3), 5.95–6.10 (br
m, CH3C(O)NH), the remaining signals were not detected and are
believed to overlap with (R)-18a signals; 13C NMR signals were
not detected for (R)-18b; Mr (+ESI) 240.1211 [M+Na]+ (calcd for
Using Method B, a mixture of (R)-15a and (R)-15b (3.79 g,
21.5 mmol) in THF (210 mL), and LiOH (515 mg, 21.5 mmol) in
H2O (100 mL) gave 1.31 g (38%) of (R)-21 as a white solid after
work-up and recrystallization from EtOAc: mp 108–109 °C; ½a D25
ꢄ
ꢁ20.9°(c0.65, MeOH)(lit.17
½ ꢄ ꢁ16.9°(c1.2;MeOH))forapartially
a 2D5
racemized sample (ꢂ4:1, (R) to (S))); Rf = 0–0.1 (EtOAc); IR (nujol
C
10H19NO4Na+ 240.1212 [M+Na]+).
mull) 3352, 3100–2200, 1746, 1631, 1549, 1459, 1375 cmꢁ1 1H
;
NMR (DMSO-d6) d 1.86 (s, CH3C(O)), 3.25 (s, CH2OCH3), 3.49 (dd,
J = 3.9, 10.0 Hz, CHH0OCH3), 3.63 (dd, J = 6.0, 10.0 Hz, CHH0OCH3),
4.36–4.45 (m, CHCH2O), 8.20 (d, J = 7.2 Hz, CH3C(O)NH), 12.7 (s,
CO2H); 13C NMR (DMSO-d6) d 22.3 (CH3C(O)), 52.1 (CHCH2OCH3),
58.3(OCH3), 71.8 (CHCH2OCH3), 169.4, 171.7(CHCO2H, CH3C(O)NH).
(R)-21 was not detected by HRMS. Anal. Calcd for C6H11NO4: C,
44.72; H, 6.88; N, 8.69. Found: C, 44.75; H, 6.82; N, 8.77.
4.12. Synthesis of (R)-methyl 2-acetamido-3-tert-
butoxypropionate ((R)-19a) and (R)-ethyl 2-acetamido-3-tert-
butoxypropionate ((R)-19b)
Using Method A, a ꢂ9:1 mixture of (R)-14a and (R)-14b (3.50 g,
24.2 mmol), and BF3ꢀEt2O (3.05 mL, 24.2 mmol) in tert-BuOH

P. Morieux et al. / Bioorg. Med. Chem. 16 (2008) 8968–8975
8973
4.15. Synthesis of (R)-2-acetamido-3-ethoxypropionic acid ((R)-
H2O (50 mL) gave 1.10 g (55%) of (R)-25 as a white solid after
22)
work-up. Recrystallization from EtOAc and hexanes afforded an
analytical sample: mp 154–156 °C; ½a D25
ꢁ46.7° (c 0.8, MeOH);
ꢄ
Using Method B, a mixture of (R)-16a and (R)-16b (2.48 g,
13.0 mmol) in THF (130 mL), and LiOH (312 mg, 13.0 mmol) in
H2O (65 mL) gave 1.57 g (69%) of (R)-22 as a white solid after
work-up and recrystallization from EtOAc: mp 149–151 °C;
Rf = 0.48 (5:95 hexanes/EtOAc); IR (nujol mull) 3370, 3300–2100
(br), 1875, 1708, 1613, 1542, 1459, 1371, 1229, 1103 cmꢁ1 1H
;
NMR (DMSO-d6) d 1.11 (s, OC(CH3)3), 1.87 (s, CH3C(O)), 3.47 (dd,
J = 4.2, 9.3 Hz, CHH0OC(CH3)3), 3.60 (dd, J = 5.1, 9.3 Hz,
CHH0OC(CH3)3), 4.30–4.38 (m, CHCH2O), 8.01 (d, J = 7.2 Hz,
CH3C(O)NH), 12.6 (CO2H); 13C NMR (DMSO-d6) d 22.4 (s, CH3C(O)),
27.2 (OC(CH3)3), 52.8 (CHCH2OC(CH3)3), 61.7 (CH2OC(CH3)3), 72.8
(CHCH2OC(CH3)3), 169.4, 171.9 (CH3C(O)NH, CO2H); Mr (+ESI)
242.0794 [M+K]+ (calcd for C9H17NO4K+ 242.0795 [M+K]+). Anal.
Calcd for C9H17NO4: C, 53.19; H, 8.43; N, 6.89. Found: C, 53.04;
H, 8.49; N, 6.84.
½
a 2D5
ꢄ
ꢁ31.5° (c 0.70, MeOH); Rf = 0–0.15 (5:95 hexanes/EtOAc);
IR (nujol mull) 3355, 3300–2100 (br), 1951, 1747, 1630, 1545,
1457, 1374, 1204, 1107 cmꢁ1 1H NMR (DMSO-d6) d 1.09 (t,
;
J = 6.9 Hz, OCH2CH3), 1.86 (s, CH3C(O)), 3.39–3.49 (m,
CH2OCH2CH3), 3.53 (dd, J = 4.2, 10.0 Hz, CHH0OCH2CH3), 3.63
(dd, J = 6.0, 10.0 Hz, CHH0OCH2CH3), 4.36–4.42 (m, CHCH2O),
8.15 (d, J = 7.2 Hz, CH3C(O)NH), the carboxylic acid proton could
not be detected; 13C NMR (DMSO-d6) d 14.9 (OCH2CH3), 22.3
(CH3C(O)),
52.4
(CHCH2OCH3),
65.8
(OCH2CH3),
69.6
4.19. Synthesis of (R)-2-acetamido-3-phenoxypropionic acid
((R)-26)
(CHCH2OCH2CH3), 169.4, 171.7 (CHCO2H, CH3C(O)NH); Mr (+ESI)
214.0480 [M+K]+ (calcd for C7H13NO4K+ 214.0482 [M+K]+). Anal.
Calcd for C7H13NO4: C, 47.99; H, 7.48; N, 8.00. Found: C, 48.21;
H, 7.56; N, 7.95.
Using Method B, a mixture of (R)-20a and (R)-20b (1.4 g,
5.7 mmol) in THF (60 mL), LiOH (142 mg, 5.9 mmol) in H2O
(30 mL) gave 950 mg (74%) of (R)-26 after recrystallization: mp
4.16. Synthesis of (R)-2-acetamido-3-(2-(2-
methoxyethoxy)ethoxy)propionic acid ((R)-23)
168–169.5 °C; ½a D25
ꢁ91.2° (c 0.5, MeOH); Rf = 0–0.15 (10:90
ꢄ
MeOH/CHCl3); IR (nujol mull) 3362, 2300–2800 (br), 1950, 1746,
1607, 1551, 1461 cmꢁ1 1H NMR (DMSO-d6) d 1.90 (s, CH3C(O)),
;
Using Method B, a mixture of (R)-17a and (R)-17b (3.85 g,
14.2 mmol) in THF (160 mL), and LiOH (376 mg, 15.6 mmol) in
H2O (80 mL) gave 2.44 g (68%) of (R)-23 as a colorless viscous oil
4.13 (dd, J = 3.9, 9.6 Hz, CHH0OPh), 4.37 (dd J = 5.1, 9.6 Hz,
CHH0OPh), 4.60–4.68 (m, CHCH2O), 6.88–6.98 (m, OC6H5, (o) and
(p)), 7.24–7.32 (m, OC6H5, (m)), 8.42 (d, J = 7.5 Hz, NHCHCH2),
12.50–13.00 (br, C(O)OH); 13C NMR (DMSO-d6) d 22.3 (CH3C(O)),
51.8 (CHCH2OPh), 67.6 (CH2OPh), 114.6 (OC6H5, (o)), 121.0
(OC6H5, (p)), 129.8 (OC6H5, (m)), 158.1 (OC6H5, (i)), 169.5, 171.3
(CH3C(O)NH, CH3C(O)OH); Mr (+ESI) 246.0739 [M+Na]+ (calcd for
after work-up: ½a D25
ꢁ38.5° (c 1.15, CHCl3); Rf = 0–0.11 (10:90
ꢄ
MeOH/CHCl3); IR (neat) 3500–2500 (br), 1974, 1731, 1654, 1547,
1103 cmꢁ1 1H NMR (CDCl3) d 2.08 (s, CH3C(O)), 3.40 (s, OCH3),
;
3.54–3.70 (m, OCH2CH2OCH2CH2OCH3), 3.75 (dd, J = 3.3, 9.7 Hz,
CHH0OCH2), 3.98 (dd J = 3.3, 9.7 Hz, CHH0OCH2), 4.68–4.78 (m,
CHCH2O), 6.98 (d, J = 7.8 Hz, C(O)NHCH), 9.10–9.50 (br s,
C
C
11H13NO4Na+
246.0742
[M+Na]+).
Anal.
Calcd
for
11H13NO4ꢀ0.25H2O: C, 58.02; H, 5.98; N, 6.15. Found: C, 58.00;
C(O)OH); 13C NMR (CDCl3)
d
22.9 (CH3C(O)), 53.0
H, 5.98; N, 5.91.
(CHCH2OCH2CH2), 59.0 (OCH3), 70.3, 70.4, 70.7, 70.8, 72.1
(CH2OCH2CH2OCH2CH2O), 171.4, 172.3 (C(O)OH, CH3C(O)NH); Mr
(+ESI) 272.1107 [M+Na]+ (calcd for C18H20N2O3Na+ 272.1110
[M+Na]+). Anal. Calcd for C10H9NO6ꢀ0.33H2O: C, 46.50; H, 7.81; N,
5.42. Found: C, 46.34; H, 7.74; N, 5.46.
4.20. Synthesis of (R)-2-acetamido-N-benzyl-3-
methoxypropionamide ((R)-1)
Using Method C, (R)-21 (100 mg, 0.62 mmol), benzylamine
(81 lL, 0.74 mmol), and DMTMM (205 mg, 0.74 mmol) in anhy-
4.17. Synthesis of (R)-2-acetamido-3-isopropoxypropionic acid
((R)-24)
drous THF (10 mL) gave 95 mg (61%) of (R)-1 after flash column
chromatography (10:90 MeOH/CHCl3) and recrystallization from
EtOAc: mp 142–143 °C (lit.17 mp 142–143 °C); ½a 2D5
ꢄ
+16.1° (c 0.9,
Using Method B, a mixture of (R)-18a and (R)-18b (2.47 g,
12.0 mmol) in THF (120 mL), and LiOH (288 mg, 12.0 mmol) in
H2O (60 mL) gave 2.15 g (95%) of (R)-24 as a white solid after
work-up. Recrystallization from EtOAc and hexanes afforded an
MeOH) (lit.17
½
a 2D5
+16.0° (c 1.0; MeOH)); Rf = 0.47 (10:90 MeOH/
ꢄ
CHCl3); 1H NMR (CDCl3) d 2.03 (s, CH3C(O)), 3.37 (s, CH2OCH3),
3.46 (dd, J = 7.2, 8.4 Hz, CHH0OCH3), 3.79 (dd J = 4.2, 8.4 Hz,
CHH0OCH3), 4.40–4.52 (m, NHCH2C6H5), 4.52–4.60 (m, CHCH2O),
6.40–6.60 (br m, CH3C(O)NH), 6.78–6.92 (br m, C(O)NHCH2Ph),
7.18–7.38 (m, NHCH2C6H5), addition of excess (R)-(ꢁ)-mandelic
acid to a CDCl3 solution of (R)-1 gave only one signal for the acetyl
methyl protons and the methoxy protons, addition of excess (R)-
(ꢁ)-mandelic acid to a CDCl3 solution of authentic (S)-1 and (R)-1
(1:2 ratio) gave two signals for the acetyl methyl protons (d
analytical sample: mp 128–130 °C; ½a D25
ꢁ36.5° (c 0.60, MeOH);
ꢄ
Rf = 0.05–0.18 (5:95 hexanes/EtOAc); IR (nujol mull) 3366, 3300–
2100 (br), 1751, 1636, 1548, 1457, 1376, 1328 cmꢁ1 1H NMR
;
(DMSO-d6) d 1.06 (d, J = 6.0 Hz, OCHCH3(C0H3)), 1.07 (d, J = 6.0 Hz,
OCHCH3(C0H3), 1.87 (s, CH3C(O)), 3.49–3.50 (m, CHH0OCH(CH3)2),
3.64 (dd, J = 5.7, 9.9 Hz, CHH0OCH(CH3)2), 4.33–4.40 (m, CHCH2O),
8.10 (d, J = 7.2 Hz, CH3C(O)NH), 12.70 (CO2H); 13C NMR (DMSO-
d6) d 21.8 (OCHCH3(C0H3)), 21.9 (OCHCH3(C0H3), 22.4 (s, CH3C(O)),
2.023 (S) and 2.010 (R) (
oxy protons (d 3.311 (S) and 3.350 (R) (
D
ppm = 0.013)), and two signals the meth-
D
ppm = 0.039)); 13C NMR
52.6
(CHCH2OCH(CH3)2),
67.4
(CH2OCH(CH3)2),
71.3
(CDCl3) d 23.4 (CH3C(O)), 43.7 (NHCH2Ph), 52.6 (CHCH2OCH3),
59.3 (CH2OCH3), 71.9 (CH2OCH3), 127.6, 127.7, 138.1 (NHCH2C6H5),
170.2, 170.5 (CHC(O)NH, CH3C(O)NH), the remaining aromatic res-
onance was not detected and is believed to overlap with nearby
signals.
(CH2OCH(CH3)2), 169.4, 171.8 (CH3C(O)NH, CO2H); Mr (+ESI)
212.0897 [M+Na]+ (calcd for C8H15NO4Na+ 212.0899 [M+Na]+).
Anal. Calcd for C8H15NO4: C, 50.78; H, 7.99; N, 7.40. Found: C,
50.87; H, 8.02; N, 7.34.
4.18. Synthesis of (R)-2-acetamido-3-tert-butoxypropionic acid
((R)-25)
4.21. Synthesis of (R)-2-acetamido-N-benzyl-3-
ethoxypropionamide ((R)-27)
Using Method B, a mixture of (R)-19a and (R)-19b (2.17 g,
Using Method C, (R)-22 (1.34 g, 7.7 mmol), benzylamine
9.90 mmol) in THF (100 mL), and LiOH (237 mg, 9.90 mmol) in
(1.00 mL, 9.2 mmol), and DMTMM (2.54 g, 9.2 mmol) in anhydrous

8974
P. Morieux et al. / Bioorg. Med. Chem. 16 (2008) 8968–8975
THF (80 mL) gave 1.11 g (46%) of (R)-27 as a white solid after flash
not detected and is believed to overlap with nearby signals, the
second C(O) peak was not observed; Mr (+ESI) 301.1530 [M+Na]+
(calcd for C15H22N2O3Na+ 301.1528 [M+Na]+). Anal. Calcd for
C15H22N2O3: C, 64.73; H, 7.97; N, 10.06. Found: C, 64.56; H, 8.00;
N, 10.12.
column chromatography (8:92 MeOH/CHCl3) and two recrystalli-
zations from EtOAc: mp 129–130 °C; ½a D25
ꢁ34.1° (c 0.64, CHCl3);
ꢄ
Rf = 0.35 (5:95 MeOH/CHCl3); IR (nujol mull) 3283, 1634, 1555,
1456, 1375, 1114 cmꢁ1
;
1H NMR (CDCl3) d 1.15 (t, J = 7.2 Hz,
OCH2CH3), 2.04 (s, CH3C(O)), 3.44 (dd, J = 8.4, 9.3 Hz,
CHH0OCH2CH3), 3.48–3.62 (m, OCH2CH3), 3.85 (dd J = 4.2, 9.3 Hz,
CHH0OCH2CH3), 4.40–4.58 (m, CHCH2OCH2, NHCH2C6H5), 6.40–
6.50 (br d, CH3C(O)NH), 6.78–6.90 (br t, C(O)NHCH2Ph), 7.22–
7.38 (m, NHCH2C6H5), addition of excess (R)-(ꢁ)-mandelic acid to
a CDCl3 solution of (R)-27 gave only one signal for the acetyl
methyl protons (d 2.017); 13C NMR (CDCl3) d 15.1 (OCH2CH3),
23.3 (CH3C(O)), 43.6 (NHCH2Ph), 52.7 (CHCH2OCH2CH3), 67.0
(CHCH2OCH2CH3), 69.9 (CHCH2OCH2CH3), 127.6, 127.7, 128.7,
138.1 (NHCH2C6H5), 170.3, 170.5 (CHC(O)NH, CH3C(O)NH); Mr
(+ESI) 287.1374 [M+Na]+ (calcd for C14H20N2O3Na+ 287.1372
[M+Na]+). Anal. Calcd for C14H20N2O3: C, 63.62; H, 7.63; N, 10.60.
Found: C, 63.62; H, 7.56; N, 10.47.
4.24. Synthesis of (R)-2-acetamido-N-benzyl-3-tert-
butoxypropionamide ((R)-30)
Using Method C, (R)-25 (1.10 g, 5.4 mmol), benzylamine
(0.71 mL, 6.5 mmol), and DMTMM (1.80 g, 6.5 mmol) in anhydrous
THF (50 mL) gave 730 mg (46%) of (R)-30 as a white solid after flash
column chromatography (5:95 MeOH/CHCl3) and recrystallization
from EtOAc: mp 126–127 °C; ½a D25
ꢁ22.9° (c 0.85, CHCl3); Rf = 0.39
ꢄ
(5/95 MeOH/CHCl3); IR (nujol mull) 3280, 3091, 1641, 1550, 1459,
1372, 1246, 1194, 1090 cmꢁ1; 1H NMR (CDCl3) d 1.14 (s, OC(CH3)3),
2.04 (s, CH3C(O)), 3.40 (app t, J = 8.5 Hz, CHH0OC(CH3)3), 3.84 (dd,
J = 4.2, 8.5 Hz, CHH0OC(CH3)3), 4.38–4.57 (m, CHCH2O,
NHCH2C6H5), 6.40–6.50 (br d, CH3C(O)NH), 6.80–6.92 (br t,
C(O)NHCH2Ph), 7.23–7.40 (m, NHCH2C6H5), addition of excess
(R)-(ꢁ)-mandelic acid to a CDCl3 solution of (R)-30 gave only one
signal for the acetyl methyl protons (d 2.009) and the tert-butoxy
methyl protons (d 1.112); 13C NMR (CDCl3) d 23.4 (CH3C(O)), 27.6
(OC(CH3)3), 43.8 (NHCH2Ph), 53.2 (CHCH2OC(CH3)3), 61.7
(CH2OC(CH3)3), 74.5 (CH2OC(CH3)3), 127.7, 127.8, 128.8, 138.1
(NHCH2C6H5), 170.3, 170.5 (CHC(O)NH, CH3C(O)NH); Mr (+ESI)
315.1687 [M+Na]+ (calcd for C16H24N2O3Na+ 315.1685 [M+Na]+).
Anal. Calcd for C16H24N2O3: C, 65.73; H, 8.27; N, 9.58; Found: C,
65.64; H, 8.08; N, 9.57.
4.22. Synthesis of (R)-2-acetamido-N-benzyl-3-(2-(2-
methoxyethoxy)ethoxy)propionamide ((R)-28)
Using Method C, (R)-23 (1.67 g, 6.70 mmol), benzylamine
(876 lL, 8.04 mmol), and DMTMM (2.22 g, 8.04 mmol) in THF
(70 mL) gave a residue that was purified twice by flash chromatog-
raphy (5:95 MeOH/CHCl3) to yield (R)-28 (1.20 g, 53%) as a yellow
oil that progressively turned to an amorphous solid after 3 d under
high vacuum: mp 48–52 °C; ½a D25
ꢄ
+7.7° (c 1.18, MeOH); Rf = 0.51
(10:90 MeOH/CHCl3); IR (neat) 3313, 3072, 2921, 2358, 2245,
1657, 1538, 1103 cmꢁ1 1H NMR (CDCl3) d 2.02 (s, CH3C(O)), 3.26
;
(s, OCH3), 3.39–3.80 (m, CHH0OCH2CH2OCH2CH2OCH3), 4.05 (dd,
J = 3.9 Hz, 9.9 Hz, CHH0OCH2CH2O), 4.48 (d, J = 6.0 Hz, NHCH2C6H5),
4.54–4.62 (m, CHCH2O), 6.77 (d, J = 6.0 Hz, NHCH2C6H5), 7.20–7.39
(m, C6H5), addition of excess (R)-(ꢁ)-mandelic acid to a CDCl3 solu-
4.25. Synthesis of (R)-2-acetamido-N-benzyl-3-
phenoxypropionamide ((R)-31)
Using Method C, (R)-26 (376 mg, 1.68 mmol), benzylamine
(219 lL, 2.02 mmol), and DMTMM (557 mg, 2.02 mmol) in THF
tion of (R)-28 gave only one signal for the acetyl peak protons; 13
C
NMR (CDCl3)
d
23.4 (CH3C(O)), 43.7 (NH2CH2C6H5), 52.5
(20 mL) gave a residue that was purified by flash column chroma-
tography (5:95 MeOH/CHCl3) and further recrystallized from
EtOAc to yield (R)-31 (305 mg, 58%) as a white solid: mp 169–
(CHCH2OCH2CH2), 59.0 (OCH3), 70.4, 70.5, 70.6, 71.9 (OCH2-
CH2OCH2CH2O), 127.5, 127.7, 128.8, 137.8 (C6H5), 170.3, 170.4
(CHC(O)NH, CH3C(O)), the remaining signal was not detected and
is believed to overlap with nearby peaks; Mr (+ESI) 361.1743
[M+Na]+ (calcd for C17H26N2O5Na+ 361.1739 [M+Na]+). Anal. Calcd
for C17H26N2O5ꢀ0.33H2O: C, 58.77; H, 7.83; N, 8.06. Found: C, 58.59;
H, 7.88; N, 8.10.
170 °C; ½a 2D5
ꢄ
ꢁ18.0° (c 0.4, MeOH); Rf = 0.52 (5/95 MeOH/CHCl3);
1H
2.03 (s, CH3C(O)), 4.05 (dd, J = 7.5, 9.6 Hz,
IR (nujol mull) 3288, 3073, 1687, 1551, 1458, 1375 cmꢁ1
;
NMR (CDCl3)
d
CHH0OCH3), 4.37 (dd J = 4.2, 9.6 Hz, CHH0OCH3), 4.40–4.56 (m,
NHCH2C6H5), 4.78–4.86 (m, CHCH2O), 6.66 (d, J = 6.0 Hz,
CH3C(O)NH), 6.87 (d, J = 7.8 Hz, OC6H5 (o)), 6.98 (t, J = 7.8 Hz,
OC6H5 (p)), 7.16–7.35 (m, CH2C6H5 (m) and NHCH2C6H5), addition
of excess (R)-(ꢁ)-mandelic acid to a CDCl3 solution of (R)-31 gave
only one signal for the acetyl peak protons; 13C NMR (CDCl3) d
23.4 (CH3C(O)), 43.9 (NH2CH2Ph), 52.6 (CHCH2OPh), 67.4 (CH2OPh),
114.8 (OC6H5, (o)), 121.9 (OC6H5, (p)), 127.7, 127.8, 128.9
(CH2C6H5), 129.8 (OC6H5, (m)), 137.8 (CH2C6H5), 157.9 (OC6H5,
(i)), 169.5, 170.6 (CHC(O)NH, CH3C(O)); Mr (+ESI) 335.1366
[M+Na]+ (calcd for C18H20N2O3Na+ 335.1372 [M+Na]+). Anal. Calcd
for C18H20N2O3: C, 69.21; H, 6.45; N, 8.97; Found: C, 69.29; H, 6.52;
N, 9.05.
4.23. Synthesis of (R)-2-acetamido-N-benzyl-3-
isopropoxypropionamide ((R)-29)
Using Method C, (R)-24 (1.90 g, 10.0 mmol), benzylamine
(1.31 mL, 12.0 mmol), and DMTMM (3.32 g, 12.0 mmol) in anhy-
drous THF (100 mL) gave 2.01 g (72%) of (R)-29 as a white solid
after flash column chromatography (5:95 MeOH/CHCl3) and
recrystallization from EtOAc: mp 151–153 °C; ½a D25
ꢁ23.4° (c
ꢄ
0.50, CHCl3); Rf = 0.37 (5:95 MeOH/CHCl3); IR (nujol mull) 3280,
3098, 1642, 1555, 1458, 1377, 1298, 1258, 1147 cmꢁ1 1H NMR
;
(CDCl3) d 1.09 (d, J = 6.0 Hz, OCHCH3(C0H3)), 1.13 (d, J = 6.0 Hz,
OCHCH3(C0H3)), 2.04 (s, CH3C(O)), 3.40 (app t, J = 8.7 Hz,
CHH0OCH(CH3)2), 3.63 (hept, J = 6.0 Hz, OCH(CH3)2), 3.84 (dd
J = 3.9, 8.7 Hz, CHH0OCH(CH3)2), 4.38–4.57 (m, CHCH2OCH,
NHCH2C6H5), 6.42–6.50 (br d, CH3C(O)NH), 6.82–6.94 (br t,
C(O)NHCH2Ph), 7.24–7.38 (m, NHCH2C6H5), addition of excess
(R)-(ꢁ)-mandelic acid to a CDCl3 solution of (R)-29 gave only one
signal for the acetyl methyl protons (d 2.014); 13C NMR (CDCl3) d
22.0 (OCHCH3(C0H3)), 22.2 (OCHCH3(C0H3)), 23.4 (CH3C(O)), 43.7
(NHCH2Ph), 52.9 (CHCH2OCH(CH3)2), 67.5 (CH2OCH(CH3)2), 72.7
(CH2OCH(CH3)2), 127.7, 128.8, 138.1 (NHCH2C6H5), 170.5
(CHC(O)NH or CH3C(O)NH), the remaining aromatic signal was
4.26. Pharmacology
Compounds were screened under the auspices of the National
Institutes of Health’s Anticonvulsant Screening Program. Experi-
ments were performed in male rodents [albino Carworth Farms
No. 1 mice (intraperitoneal route, ip), albino Sprague–Dawley rats
(oral route, po)]. Housing, handling, and feeding were in accor-
dance with recommendations contained in the ‘Guide for the Care
and Use of Laboratory Animals’. Anticonvulsant activity was estab-
lished using the MES test14,18 and the scMet test,14 using previ-
ously reported methods.19,20

P. Morieux et al. / Bioorg. Med. Chem. 16 (2008) 8968–8975
8975
3. Choi, D.; Stables, J. P.; Kohn, H. J. Med. Chem. 1996, 39, 1907–1916.
4. Choi, D.; Kohn, H. unpublished results.
Acknowledgments
5. Nakajima, K.; Neya, M.; Yamada, S.; Okawa, K. Bull. Chem. Soc. Jpn. 1982, 55,
The authors thank the NINDS and the Anticonvulsant Screening
Program (ASP) at the National Institutes of Health for supporting
the pharmacological studies via the ASP’s contract site at the
University of Utah with Drs. H. Wolfe, S. White, M. Franklin, and
K. Wilcox. The project described was supported by Grants
RO1NS054112 (H.K.), and F31NS060358 (P.M.) from the National
Institute of Neurological Disorders and Stroke. The content is solely
the responsibility of the authors and does not necessarily represent
the official views of the National Institute of Neurological Disorders
and Stroke or the National Institutes of Health.
3049–3050.
6. Nakajima, K.; Oda, H.; Okawa, K. Bull. Chem. Soc. Jpn. 1983, 56,
520–522.
7. Larsson, U.; Carlson, R. Acta Chem. Scand. 1994, 48, 511–516.
ˇ
´
8. Belohradsky, M.; Ridvan, L.; Závada, J. Collect. Czech Chem. Commun. 2003, 68,
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9. Kuyl-Yeheskiely, E.; Dreef-Tromp, C.; van der Marel, G.; van Boom, J. Recl. Trav.
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10. Mathieu-Pelta, I.; Evans, S. A. J. Org. Chem. 1994, 59, 2234–2237.
11. Salomé, C.; Kohn, H. unpublished results.
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1999, 55, 13159–13170.
13. Morrison, J.; Weisman, G.. In Asymmetric Synthesis—Analytical Methods;
Academic Press: New York, 1983; Vol. 1, pp 153–171.
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Drugs; Avanzini, G., Tanganelli, P., Avoli, M., Eds.; John Libbey: London, 1977;
pp 191–198.
Supplementary data
15. Porter, R. J.; Cereghino, J. J.; Gladding, G. D.; Hessie, B. J.; Kupferberg, H. J.;
Scoville, B.; White, B. G. Cleve. Clin. Q. 1984, 51, 293–305.
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Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmc.2008.08.055.
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