Functionalized amido ketones: New anticonvulsant agents

Article abstract of DOI:10.1016/S0968-0896(03)00434-6

We have reported that functionalized amino acids (FAA) are potent anticonvulsants. Replacing the N-terminal amide group in FAA with phenethyl, styryl, and phenylethynyl units provided a series of functionalized amido ketones (FAK). We show that select FAK

Full text of DOI:10.1016/S0968-0896(03)00434-6

Bioorganic & Medicinal Chemistry 11 (2003) 4275–4285
Functionalized Amido Ketones: New Anticonvulsant Agents
Cecile Beguin,a Shridhar V. Andurkar,a,b Albert Y. Jin,c James P. Stables,d
Donald F. Weavere and Harold Kohnf,*
aDepartment of Chemistry, University of Houston, Houston, TX 77204-5641, USA
bSchool of Pharmacy, Midwestern University, 555 31st Street, Downers Grove, IL 60515, USA
cDepartment of Chemistry, Queen’s University, Kingston, Ontario, Canada K7L 3N6
dEpilepsy Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health,
6001 Executive Boulevard, Suite 2106, Rockville, MD 20852, USA
eDepartment of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J3
fDivision of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North Carolina,
Chapel Hill, NC 27599-7360, USA
Received 22 January 2003; accepted 15 April 2003
Abstract—We have reported that functionalized amino acids (FAA) are potent anticonvulsants. Replacing the N-terminal amide
group in FAA with phenethyl, styryl, and phenylethynyl units provided a series of functionalized amido ketones (FAK). We show
that select FAK exhibit significant anticonvulsant activities thereby providing information about the structural requirements for
FAA and FAK bioactivity.
# 2003 Elsevier Ltd. All rights reserved.
Introduction
We, and others, have shown that functionalized amino
acids (FAA, 1) are potent anticonvulsants.1ꢀ3 Eval-
uation of more than 250 FAA have provided 12 com-
pounds with anticonvulsant activity in rodents that is
equal to or greater than phenytoin4 according to the
MES-seizure test.1eꢀh,j The MES test is a proven method
of generalized tonic-clonic seizures and identifies clinical
candidates that prevent seizure spread.5,6 FAA provided
excellent protection against MES-induced seizures when
R1 was an N-acetyl unit, R2 was either a small aromatic,
a small heteroaromatic, or a substituted heteroatom one
carbon removed from the asymmetric center, and R3
was a benzylamide group. Distinguishing this class of
compounds was our demonstration that the principal
anticonvulsant activity resided in the (R)-stereo-
isomer.1cꢀe,g,j,k Preclinical studies have identified (R)-N-
benzyl-2-acetamido-3-methoxypropionamide [(R)-2]1j as
the lead FAA, and (R)-2 has entered Phase II clinical
trials for the treatment of epilepsy and neuropathic pain
under Schwarz Pharma sponsorship.
We have recently studied whether or not con-
formationally restricted7 and peptidomimetic8 FAA
derivatives can provide analogues with improved phar-
macological properties. We tested whether altering the
N-terminus9 and the central a-carbon1b,8 within FAA
would provide compounds with efficacy in the MES-
seizure test. We learned that both sites can be modified
in select cases without appreciable losses in activities.
Now, we examine whether functionalized amidoketones
(FAK, 3) display anticonvulsant activity when the C-
terminal amide in the FAA has been replaced with a
ketone unit. In our study, we chose to retain in the FAK
other FAA structural components that provided MES-
seizure protection.1 The ketone for amide substitution
eliminated a potential hydrogen bond donor interaction
of the anticonvulsant with its receptor, altered the con-
formationally mobility of the test compound, and
reduced the number of sites for amidase metabolism.
We show herein that FAK exhibit significant anti-
convulsant activities.
*Corresponding author. Tel.: +1-919-966-2680; fax: +1-919-843-
7835; e-mail: harold_kohn@unc.edu
0968-0896/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0968-0896(03)00434-6

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4276
Results and Discussion
Choice of compounds and method of evaluation
FAA 4–6 served as our reference compounds. In this
study, we systematically modified two structural sites to
provide the FAK 7–14. The first was the R3 group in
which we successively replaced the terminal benzyl-
amino (N(H)CH2Ph) group in FAA with a phenethyl
(CH2CH2Ph), a styryl (C(H)C(H)Ph), and a phenyl-
ethynyl (CCPh) unit. Next, we prepared FAK deriva-
tives in which the R2 moiety was either a methyl (CH3),
phenyl (C6H5), or methoxymethyl (CH2OCH3) unit.
For FAA we found a significant improvement in anti-
convulsant activities in the MES-induced seizure test in
mice as we progressed from 41b to 51b to 6.1j We elected
to prepare the racemic FAK since we did not know if
either isomer would exhibit preferential activity. This
choice obviated the need to prepare optically pure
FAK. For 7, however, we synthesized both (R)-7 and
(S)-7 to learn if the pharmacological properties of FAK,
like FAA,1cꢀe,g,j,k was stereoselective.
Scheme 1. Synthesis of saturated functionalized amido ketones.
(S)-15, 16 and 17 with n-BuLi (1 equiv) followed by
phenethylmagnesium chloride (2–3 equiv) gave ketones
7, (R)-7, (S)-7, 8, and 18, respectively, in 22–43% yields.
Methylation of 18 with MeI and Ag2O gave 19, which
was then converted to 9 by catalytic hydrogenation (H2,
Pd/C) followed by acetylation (Ac2O, Et3N).
Two of the three vinylogous ketones (10, 12) were pre-
pared using a Horner–Emmons reaction (Scheme 2).
Treatment of either N-tert-Boc-alanine methyl ester (20)
or N-acetyl-O-methylserine methyl ester (25) with the
lithium anion of dimethylmethanephosphonate13,14 gave
the corresponding dimethyl phosphonate esters 22 and
26. Phosphonates 22 and 26 were readily converted to
the trans vinylogous ketones 24 and 12, respectively,
upon reaction with benzaldehyde (23) and base.15 Con-
version of 24 to 10 was straightforward. Acid (TFA)
removal of the tert-Boc protecting group in 24 followed
by acetylation (Ac2O, Et3N) gave 10 in 78% yield. We
utilized the thiazolium-catalyzed cross-coupling of
aldehydes with acylimines described by Murry and
Frantz16 to prepare 11 (Scheme 2). Accordingly, benz-
aldehyde (23) and acetamide (27) were treated with
toluenesulfinic acid sodium salt (28) and TMSCl to give
29.17 Subsequent addition of cinnamaldehyde (30) to a
tosyl amide 29 and 3-benzyl-5-(2-hydroxyethyl)-4-
methylthiazolium chloride (31) suspension provided
trans-11 in 59% yield. Inspection of the 1H NMR
spectra18 for vinylic FAK 10–12 documented that the
predominant product was the trans-isomer. We deter-
mined that 10 existed as a 97:3 trans:cis mixture, 11 to
be solely trans, and 12 to be a 98:2 trans:cis mixture.
The FAK were evaluated in rodents at the NIH Epilepsy
Branch. In one test, the compound was administered to
mice intraperitoneally (ip) and then the anticonvulsant
properties determined using MES- and scMet-induced
seizure models.5,6 In the second test, the compound was
administered to rats orally (po) and then evaluated in
the MES-seizure model. The neurological toxicity (Tox)
of the compound was evaluated in mice using the
rotorod model10 and in rats by the observation of motor
impairment.
Synthesis
It was necessary to use different methods to prepare
compounds 7–14. For saturated compounds 7–9, the
method of Rapoport11,12 was employed to introduce the
ketone unit starting from either the N-acetyl or the N-
Cbz-amino acid (Scheme 1). Treatment of 15, (R)-15,
Lithium phenylacetylide19 (34) served as the organome-
tallic reagent for a,b-acetylenic ketones 13 and 14
(Scheme 3). For 13, we coupled 34 with N-acetylalanine-
N-methoxy-N0-methylamide20 (33), which was prepared
from N-acetylalanine (15) and N,O-dimethylhydroxylamine

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4277
Scheme 2. Synthesis of (E)-vinylic amido ketones.
(32), using the mixed anhydride coupling method.
Synthesis of 14 began with N-Cbz-serine (17). Conver-
sion of 17 to 35 with CH3I and Ag2O followed by
removal of the Cbz-protecting group (H2, Pd/C) and
acetylation (Ac2O, pyridine) gave 25.21 Treatment of 25
with 34 provided 14 in 36% yield.
1
FAK 7–14 gave satisfactory spectroscopic (IR, H and
13C NMR, MS) and elemental analyses in accordance
with their proposed structures. We observed a diag-
nostic upfield shift in the 13C NMR spectra for the
terminal carbonyl carbon as it proceeded from the
saturated FAK 7–9 (d205.3–208.6) to the vinylic FAK
10–12 (d194.4–198.0) and then to the acetylenic FAK 13
and 14 (d184.1–186.3).24
We wanted to compare the pharmacological properties
of the trans-vinylogous ketone 10 with its cis-isomer 36.
Several reductive methods beginning with 13 were
examined, but none proved satisfactory. We observed
that catalytic reduction of 13 to 36 was accompanied by
production of the trans-isomer 10 and the saturated
ketone 7. The use of Pd/CaCO3/Pb(OAc)2 and quino-
line22 (5 equiv) provided the highest amount of cis-36
(73%) (Scheme 4). Attempts to separate the ternary
mixture (PTLC, column chromatography) were unsatis-
factory. Moreover, cis-36 slowly isomerized to trans-10
at room temperature (data not shown).23
Pharmacological evaluation
The FAK (Table 1) were tested for anticonvulsant
activity using the procedure described by Stables and
Kupferberg.5 We wished to learn if their in vivo phar-
macological profile followed the general profile pre-
viously observed for FAA.1 Table 1 lists the results
obtained from qualitative (MES, scMet) testing in mice
(ip) along with quantitative (MES ED50) mice (ip) and
rat (po) evaluations. We include in this table the median
neurologically impairing dose (TD50) values using the
rotorod test in mice10 and motor impairment in rats.
Finally, protective indices (PI=TD50/MES ED50) for
these adducts, when appropriate, are shown.
Scheme 3. Synthesis of acetylenic amido ketones.
Scheme 4. Synthesis of (Z)-vinylic amido ketones.

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4278
Table 1. Selected physical and pharmacological data for amidoketones
Compd
Mpc
Mice (ip)a
scMet, ED50
Rat (po)b
MES, ED50
Tox, TD50
PId
MES, ED50
Tox, TD50
PId
Section A: FAA
4
138–139
202–203
121–122
76 [1]
(67–89)
20 [0.5]
(17–25)
8.3 [0.5]
(7.9–9.8)
>600
>120
>25
450 [0.5]
(420–500)
97 [0.5]
(80–120)
43 [0.25]
(38–47)
5.9
4.8
5.2
48 [1]
(32–72)
48 [4]
(31–68)
3.8 [2]
(2.9–5.5)
>1000
>1000
>21
>21
102
5
6
390 [1]
(320–520)
Section B: Saturated FAK
7
64–66
82–84
49 [0.25]
(43–53)
62 [0.25]
(54–65)
>30, <100
>100, <300
>100, <300
>300
94 [0.25]
(84–120)
160 [0.25]
(130–180)
>100, <300
1.9
2.5
—
47 [0.25]
(37–61)
26 [0.25]
(18–37)
>30
120 [0.25]
(100–140)
>500
2.5
>19
—
(R)-7
(S)-7
8
79–81
>30
>500
>250
106–107
66–68
>30, <100
>100, <300
>150, <300
ꢁ100
—
23 [0.25]
(18–26)
18 [0.25]
(12–24)
>22
>14
9
47 [0.25]
(37–61)
120 [0.25]
(100–140)
2.5
Section C: Vinylic FAK
10
109–110
96 [0.25]
(83–110)
>100, <300
120 [0.25]
(100–150)
>350
190 [0.25]
(140–240)
>100, <300
120 [0.25]
(72–150)
2.0
ꢁ30 [2]
>30
>30
—
11
12
119–121
127–128
>100, <300
>300
—
1.0
>30
>130
—
—
e
—
Section D: Acetylenic FAK
13
14
f
f
oil
96–99
>300
>300
>300
>300
>30, <100
>30, <100
—
—
—
—
—
—
—
—
f
f
Section E: Antiepileptic agents
Phenytoing
h
i
—
—
—
9.5 [2]
(8.1–10)
22 [1]
(15–23)
270 [0.25]
(250–340)
—
66 [2]
(53–72)
69 [0.5]
(63–73)
430 [0.25]
(370–450)
6.9
3.2
1.6
30 [4]
(22–39)
9.1 [5]
(7.6–12)
490 [0.5]
(350–730)
—
>100
Phenobarbitalg
Valproateg
13 [1]
(5.9–16)
61 [0.5]
(44–96)
280 [0.5]
(190–350)
6.7
0.6
MES, maximal electroshock seizure test; scMet, subcutaneous metrazol; Tox, neurologic toxicity determined from rotorod test in mice and motor
impairment in rats.
aThe compounds were administered intraperitoneally. ED50 and TD50 values are in mg/kg. Numbers in parentheses are 95% confidence intervals.
The dose effect data was obtained at the ‘time of peak effect’ (indicated in h in the square brackets).
bThe compounds were administered orally.
cMelting points (ꢂC) are uncorrected.
dPI, protective index (TD50/ED50).
e2/2 animals protected at 15 mg/kg after 2 h. The ED50 could not be determined because the response was not linear.
fNot determined.
gRef 26.
hNot effective.
iNo ataxia observed up to 3000 mg/kg.
Table 1A lists the prototypical FAA 4–6, B gives the
saturated FAK 7–9, C are the vinylic FAK 10–12, D are
acetylenic FAK 13 and 14, and E contains the anti-
epileptic agents, phenytoin, phenobarbital, and valpo-
rate.25,26 For FAA 4–6 where R3 is a benzylamino
group (N(H)CH2Ph), we observed an increase in anti-
convulsant activity (MES-seizure test) in mice (ip) as we
progressed from R2 equal to methyl1b (4) to phenyl1b (5)
to methoxymethyl1j (6). In rats, 4 and 5 show similar
activity but 6 displayed increased activity. The ED50
values for 4 and 6 were lower in rats than in mice. We
saw on the rotorod test that 4–6 exhibited low toxicity,
which led to high PI values. None of the three FAA
showed noticeable activity in the scMet test in mice.
The saturated FAK 7–9 displayed a comparable activity
pattern when administered to rats (po). The ED50 values
for 7, 8, and 9 were 47, 23, and 18 mg/kg, respectively.
The ED50 values for 8 and 9 compared favorably with
phenytoin (ED50=30 mg/kg) and phenobarbital
(ED50=9.1 mg/kg),26 and both 8 and 9 exhibited PI
values that exceeded 14. When the (R)- and (S)-enan-
tiomers of 7 were evaluated, (R)-7 (ED50=26 mg/kg)
was found to be nearly 50% more potent than (R,S)-7

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4279
(ED50=47 mg/kg) and more active than the (S)-isomer
(ED50 >30 mg/kg). This trend mirrors the findings for
FAA 4 in rats [ED50 values (mg/kg): (R,S)-4, 48; (R)-4,
28; (S)-4, 55].1c,d These patterns of activity were not
evident when FAK 7–9 were administered to mice. Little
difference in activity was observed as we modified the
R2 group (ED50 values (mg/kg): 7, 49; 8, 30–100; 9, 47).
Moreover, the ED50 value for (R)-7 (62 mg/kg) exceeded
that of the racemate (R,S)-7 (49 mg/kg). It is unclear
why the mouse data differed from rat data. For FAA,
we generally observed increased anticonvulsant activity
in the rat compared with the mice, but SAR trends were
similar in both mice and rats. FAK 7–9 showed no
appreciable scMet activity when administered to mice.
analyses (CDCl3) showed that both 37 and 38 existed as
a 65:35 mixture of conformational isomers. Our finding
that the activities of FAK 7–9 and 10–12 approached
that of FAA 4–6 indicated that the C-terminal amide
hydrogen within FAA 1 is not essential for anti-
convulsant activity and that the conformation of this
structural unit may be critical for drug function.
The rise in neurological toxicity for 13 and 14 was
striking. This finding was reminiscent of an earlier
structure–toxicity relationship study of alkanones, a,b-
unsaturated alkenones and ynones in a static Tetra-
hymena pyriformis population growth assay.27 Schultz
and co-workers observed toxicity to increase in pro-
ceeding from the alkanones, to alkenones, to ynones27
and discussed the proclivity of alkenones and ynones to
undergo Michael addition.28 Accordingly we asked if
vinylic and acetylenic FAK readily underwent chemical
modification. Both vinylic and acetylenic FAK contain
an unsaturated unit in conjugation with a carbonyl
group, and may undergo Michael addition with nucleo-
philes. Accordingly, we treated 12 and 14 with both
EtSH (16 equiv) and EtNH2 (16 equiv) in THF under
Ar at room temperature for 18 h. We observed no
reaction for 12 with either EtSH or EtNH2. We further
tested whether 12 underwent reversible conjugate addi-
tion with EtSH by repeating the experiment in a 1:2
CD3OD–THF mixture. Isolation of 12 after 18 h
showed no deuterium incorporation at the vinylic site
(data not shown). When we treated acetylenic FAK 14
with EtSH we again observed no reaction. Correspond-
ingly, reaction of 14 with EtNH2 led to the full con-
sumption of 14 (room temperature, 18 h) and the
appearance of a single, major product (TLC analysis)
that has been tentatively identified as 39. We assigned
39 as the trans-product on the basis of NOESY analysis
The profile for vinylic FAK 10–12 was similar to FAA
4–6 and FAK 7–9. We observed that the ED50 values in
the rat for 10–12 (ED50 values (mg/kg): 10, ꢁ30; 11,
>30; 12 est. 15) were comparable with 7–9 (ED50 mg/kg
values: 7, 47; 8, 23; 9, 18). When 10–12 were tested in
mice we found that the anticonvulsant activities were
less than those in rats, that the activities did not
improve in proceeding from 10 to 12, and that none of
the compounds exhibited noticeable anticonvulsant
activities in the scMet seizure test.
The remaining compounds were acetylenic FAK 13 and
14. These amidoynones were only evaluated in mice
because of their toxicity (>30, <100 mg/kg). We
observed that both compounds exhibited low activity in
the MES-seizure test (ED50 >300 mg/kg).
The saturated FAK 7–9 and vinylic FAK 10–12 showed
anticonvulsant activities in rats that matched FAA 4–6.
Inspection of activity in each of the three active sets of
compounds (Table 1, Sections A–C) suggested that they
all functioned by similar pathways. For the FAA, satu-
rated FAK, and vinylic FAK series we observed a gen-
eral increase in anticonvulsant activity in the MES-
seizure test (rat) as we changed the R2 group from
methyl to methoxymethyl. For 4 and 7 we found that
the (R)-enantiomer was more active than either the
(R,S)-racemate or the (S)-isomer.
1
and a comparison of the H NMR chemical shift (d
10.69) for the N(H) enaminone proton with related
compounds.29
The near equal anticonvulsant activities of FAA 4–6,
saturated FAK 7–9 and the trans-vinylic FAK 10–12
suggested that the terminal substituent in the three
active series (N(H)CH2Ph, CH2CH2Ph, trans-
C(H)C(H)Ph) adopted a similar conformation when
eliciting drug function. Accordingly, the diminished
anticonvulsant activities for the acetylenes 13 and 14
may be explained by the placement of a linear terminal
group within the FAK. The pattern observed for FAK
may explain an earlier finding.7 We reported that pla-
cement of a N-methyl unit within 4 and 6 to give 37 and
38, respectively, led to a loss in activity.7 The MES ED50
values for 37 and 38 in mice were between 100 and 300
mg/kg, and in rats they exceeded 30 mg/kg. We were
unsure whether the diminished activities for 37 and 38
resulted from the loss of a N(H) hydrogen bond inter-
action, the increased size of the FAA, or the adoption of
an FAA conformation for the terminal unit that was
unfavorable for seizure protection. Indeed, 1H NMR
Table 2. Vinylic aminoketones with anticonvulsant activitiesa
Compd
MES ED50 (mg/kg)b
Inactive
87.9
53.9
36.2
aAll compounds were tested in mice.30
bMES, maximal electroshock seizure test, the compounds were
administered intraperitoneally (ip).

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4280
combined and washed successively with saturated aqu-
eous NaHCO3 (200–300 mL), and brine (200–300 mL),
dried (Na2SO4), filtered and evaporated in vacuo. The
resulting oily residue was triturated with Et2O (100–200
mL) to obtain a white solid which upon filtration and
drying afforded the desired product. Using this general
procedure, the following compounds were prepared.
Vinylic aminoketones have been previously evaluated in
seizure models.30 Most ketones showed activity (Table
2). The compounds in our series differ from those in
Table 2 in the nature of the R1 and R2 groups and the
incorporation of a central a-amino acid moiety. None-
theless, the anticonvulsant activities for our FAK with
those previously reported document that this class of
compounds deserve further investigation.
Synthesis of (R,S)-2-acetamido-5-phenyl-3-pentanone
(7). Compound 7 (3.00 g, 40%) was prepared as a
white crystalline solid from 15 (5.00 g, 38 mmol), n-
BuLi (24 mL, 38 mmol), phenethylmagnesium chloride
(96 mL, 96 mmol), THF (150 mL): mp 64–66 ꢂC; Rf 0.42
(EtOAc); IR (KBr) 3313, 3074, 3030, 2936, 1717, 1634,
1
1546, 1442, 1374, 1296, 1073, 996, 750, 697 cmꢀ1; H
NMR (CDCl3) d 1.28 (d, J=7.2 Hz, CHCH3), 1.99 (s,
CH3C(O)), 2.70–3.01 (m, CH2CH2Ph), 4.50–4.65 (m,
CHCH3), 6.30–6.35 (m, NH), 7.15–7.40 (m, PhH),
addition of (R)-(ꢀ)-mandelic acid to a CDCl3 solution
of 7 did not lead to a separation of the NMR signals;
13C NMR (CDCl3) d 17.7 (CHCH3), 23.4 (CH3C(O)),
29.7 (CH02CH2Ph), 41.1 (CH2CH2Ph), 54.3 (CHCH3),
Conclusions
We have determined that FAK exhibit excellent anti-
convulsant activities that approach those observed for
their FAA counterparts in rats. The favorable activities
for FAK have been attributed to the incorporation of
key R2 structural units within the FAK backbone and
the conformation of the terminal ketone unit. The neuro-
logical toxicities of select FAK in rats exceeded that
found for the corresponding FAA.
0
0
0
0
126.5 (C4 ), 128.5 (2C2 or 2C3 ), 128.8 (2C2 or 2C3 ),
0
140.7 (C1 ), 169.8 (C(O)NH), 208.6 (C(O)); MS (+CI)
(rel intensity) 220 (M++1, 100), 178 (22); Mr (+CI)
220.133 93 [M++1] (calcd for C13H18NO2 220.133 75).
Anal. calcd for C13H17NO2: C, 71.23%; H, 7.76%; N,
6.39%. Found C, 71.31%; H, 7.86%; N, 6.34%.
Synthesis of (S)-2-acetamido-5-phenyl-3-pentanone [(S)-
7]. Compound (S)-7 (1.10 g, 22%) was prepared as a
white crystalline solid from (S)-15 (3.00 g, 22.9 mmol),
n-BuLi (14.3 mL, 22.9 mmol), phenethylmagnesium
chloride (46 mL, 46 mmol), THF (100 mL): mp 79–
81 ꢂC; [a]2D4=ꢀ57.3ꢂ (c 0.8, MeOH); Rf 0.42 (EtOAc);
IR (KBr) 3324, 3067, 3038, 2941, 1721, 1642, 1541,
Experimental
General methods
Melting points were determined with a Thomas–Hoover
melting point apparatus and are uncorrected. Infrared
spectra (IR) were run on a ATI Mattson Genesis Series
TM
1
FTIR spectrometer. Absorption values are expressed in
1438, 1362, 1301, 1077, 989, 749, 695 cmꢀ1; H NMR
wave-numbers (cmꢀ1). Optical rotations were obtained on
a Jasco P-1030 polarimeter. Proton (1H NMR) and carbon
(13C NMR) nuclear magnetic resonance spectra were
taken on a General Electric QE-300 NMR instrument.
Chemical shifts (d) are in parts per million (ppm) rela-
tive to tetramethylsilane and coupling constants (J
values) are in Hertz. Low resolution mass spectra (CI+)
were obtained with a Varian MAT CH-5 spectrometer
by Dr. M. Moini at the University of Texas-Austin. The
high-resolution chemical ionization mass spectrum was
performed on a Finnigan MAT TSQ-70 by Dr. M.
Moini at the University of Texas-Austin. Microanalysis
were provided by Atlantic Microlab, Inc. (Norcross,
GA). Thin layer chromatography was performed on a
precoated silica gel GHLF microscope slides (2.5ꢃ10
cm; Analtech No. 21521).
(CDCl3) d 1.27 (d, J=7.5 Hz, CHCH3), 1.98 (s,
CH3C(O)), 2.70–3.00 (m, CH2CH2Ph), 4.50–4.62 (m,
CHCH3), 6.40–6.50 (m, NH), 7.15–7.40 (m, PhH); 13C
NMR (CDCl3) d 17.3 (CHCH3), 23.3 (CH3C(O)), 28.6
(CH2CH2Ph), 41.0 (CH2CH2Ph), 54.2 0(CHCH3), 126.4
0
0
0
0
0
(C4 ), 128.4 (2C2 or 2C3 ), 128.7 (2C2 or 2C3 ), 140.7
(C1 ), 169.8 (C(O)NH), 208.6 (C(O)); MS (+CI) (rel
intensity) 220 (M++1, 100); Mr (+CI) 220.133 34
[M++1] (calcd for C13H18NO2 220.133 75). Anal. calcd
for C13H17NO2: C, 71.23%; H, 7.76%; N, 6.39%.
Found C, 71.46%; H, 7.85%; N, 6.21%.
Synthesis of (R)-2-acetamido-5-phenyl-3-pentanone [(R)-
7]. Compound (R)-7 (1.80 g, 36%) was prepared as a
white crystalline solid from (R)-15 (3.00 g, 22.9 mmol),
n-BuLi (14.3 mL, 22.9 mmol), phenethylmagnesium
chloride (46 mL, 46 mmol), THF (100 mL): mp 82–
84 ꢂC; [a]D24=+58.7ꢂ (c 0.95, MeOH); Rf 0.42 (EtOAc);
IR (KBr) 3328, 3072, 3033, 2945, 1718, 1650, 1544,
Synthesis of saturated ꢀ-amidoketones. General proce-
dure. n-BuLi (1 equiv) was added to a stirred N2-blan-
keted solution of the N-acylamino acid (1 equiv) in dry
THF at ꢀ78 ꢂC. To the resulting suspension was slowly
added phenethylmagnesium chloride (2–3 equiv) and
the reaction was stirred at ꢀ78 ꢂC (30 min) and then at
room temperature (18 h). The mixture was poured into
an equal volume of aqueous 1 N HCl and extracted with
EtOAc (3ꢃ100–200 mL). The organic extracts were
1
1435, 1366, 1296, 1079, 992, 752, 690 cmꢀ1; H NMR
(CDCl3) d 1.28 (d, J=7.2 Hz, CHCH3), 1.99 (s,
CH3C(O)), 2.65–3.00 (m, CH2CH2Ph), 4.50–4.65 (m,
CHCH3), 6.30–6.40 (m, NH), 7.15–7.40 (m, PhH); 13C
NMR (CDCl3) d 17.7 (CHCH3), 23.4 (CH3C(O)), 29.7
(CH2CH2Ph), 41.1 (CH2CH2Ph), 54.3 0(CHCH3), 126.5
0
0
0
0
(C4 ), 128.5 (2C2 or 2C3 ), 128.7 (2C2 or 2C3 ), 140.7

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4281
0
(C1 ), 169.8 (C(O)NH), 208.6 (C(O)); MS (+CI) (rel
OCH2Ph), 5.76 (d, J=7.2 Hz, NH), 7.15–7.46 (m, 10
PhH); 13C NMR (CDCl3) d 29.5 (CH2CH2Ph), 41.6
(CH2CH2Ph), 59.4 (CH2OCH3 or CHCH2OCH3), 60.5
(CH2OCH3 or CHCH2OCH3), 67.2 (OCH2Ph), 72.2
(CH2OCH3), 126.4, 128.3, 128.5, 128.6, 128.7, 128.8,
136.4, 140.9 (2 C6H5), 156.2 (OC(O)NH), 206.5 (C(O));
MS (+CI) (rel intensity) 342 (M++1, 100), 298 (17);
Mr (+CI) 342.169 72 [M++1] (calcd for C20H24NO4
342.170 53). Anal. calcd for C20H23NO4: C, 70.38%; H,
6.74%; N, 4.11%. Found C, 70.20%; H, 6.83%; N,
4.16%.
intensity) 220 (M++1); Mr (+CI) 220.133 11 [M++1]
(calcd for C13H18NO2 220.133 75). Anal. calcd for
C13H17NO2: C, 71.23%; H, 7.76%; N, 6.39%. Found C,
71.47%; H, 7.94%; N, 6.22%.
Synthesis of (R,S)-1-acetamido-1,4-diphenyl-2-butanone
(8). Compound 8 (2.00 g, 35%) was prepared as a
white crystalline solid from 16 (4.00 g, 21 mmol), n-
BuLi (13.2 mL, 21 mmol), phenethylmagnesium chlo-
ride (42 mL, 42 mmol), THF (100 mL): mp 106–107 ꢂC;
Rf 0.33 (EtOAc); IR (KBr) 3283, 3061, 3024, 1717, 1649,
1540, 1452, 1371, 1297, 1073, 1020, 751, 699 cmꢀ1; H
Synthesis of (R,S)-2-acetamido-1-methoxy-5-phenyl-3-
pentanone (9). A MeOH (250 mL) solution of 19 (4.04
g, 11.8 mmol) and aqueous 12 N HCl (1.1 mL, 13.2
mmol) was hydrogenated in the presence of 10% Pd/C
(0.5 g) at room temperature (2 h). The catalyst was
removed by filtration through Celite and the filtrate was
evaporated in vacuo to obtain a solid residue. To a vig-
orously stirred CH2Cl2 (50 mL) suspension of the resi-
due was added Ac2O (1.13 mL, 12 mmol) followed by
the slow addition of Et3N (3.35 mL, 24 mmol). The
mixture was stirred (1 h) and then concentrated in
vacuo to obtain an oil, which was purified first by col-
umn chromatography (SiO2, EtOAc), and then by
recrystallization from Et2O–hexanes to afford 9 (1.80 g,
61%): mp 66–68 ꢂC; Rf 0.50 (EtOAc); IR (KBr) 3315,
1
NMR (CDCl3) d 1.98 (s, CH3C(O)), 2.62–2.93 (m,
CH2CH2Ph), 5.54 (d, J=6.0 Hz, CHPh), 6.83 (d, J=6.0
Hz, NH), 7.00–7.35 (m, 10 PhH); 13C NMR (CDCl3)
d 23.3 (CH3C(O)), 29.8 (CH2CH2Ph), 41.5 (CH2CH2Ph),
63.3 (CHPh), 126.4, 128.2, 128.4, 128.7, 128.8, 129.4,
136.4, 140.4 (2 C6H5), 169.5 (C(O)NH), 205.3 (C(O));
MS (+CI) (rel intensity) 282 (M++1); Mr (+CI)
282.148 62 [M++1] (calcd for C18H20NO2 282.149 40).
Anal. calcd for C18H19NO2: C, 76.87%; H, 6.76%; N,
4.98%. Found C, 76.99%; H, 6.87%; N, 4.95%.
Synthesis of (R,S)-2-(carbobenzyloxy)amino-1-hydroxy-
5-phenyl-3-pentanone (18). Compound 18 (4.22 g, 43%)
was prepared as a white crystalline solid from 17 (7.10 g,
29.7 mmol), n-BuLi (18.6 mL, 29.7 mmol), phen-
ethylmagnesium chloride (90 mL, 90 mmol), THF (150
mL): mp 88–90 ꢂC; Rf 0.39 (1:1, EtOAc/hexanes); IR
(KBr) 3417, 3383, 2949, 1714, 1684, 1454, 1262, 1059,
742, 697 cmꢀ1; 1H NMR (CDCl3) d 2.10–2.20 (m, OH),
2.80–3.00 (m, CH2CH2Ph), 3.80–4.00 (m, CH2OH),
4.30–4.40 (m, CH), 5.12 (s, OCH2Ph), 5.79–5.90 (m,
NH), 7.10–7.40 (m, 10 PhH); 13C NMR (CDCl3) d 29.6
(CH2CH2Ph), 41.7 (CH2CH2Ph), 62.2 (CH or
OCH2Ph), 62.9 (CH or OCH2Ph), 67.4 (CH2O), 126.5,
128.3, 128.5, 128.8, 136.2, 140.7 (2 C6H5), 156.5
(OC(O)NH), 206.8 (C(O)), the remaining aromatic sig-
nals were not detected and are believed to overlap with
nearby signals; MS (+CI) (rel intensity) 328 (M++1,
100), 310 (73), 298 (77), 284 (56), 266 (36), 254 (62); Mr
(+CI) 328.154 02 [M++1] (calcd for C19H22NO4
328.154 88). Anal. calcd for C19H21NO4: C, 69.72%; H,
6.42%; N, 4.28%. Found C, 70.10%; H, 6.71%; N,
3.98%.
1
2923, 1719, 1646, 1529, 1375, 1115, 748, 700 cmꢀ1; H
NMR (CDCl3) d 2.04 (s, CH3C(O)), 2.65–3.11 (m,
CH2CH2Ph), 3.27 (s, OCH3), 3.58 (dd, J=3.9, 9.6 Hz,
CHH0OCH3), 3.80 (dd, J=3.3, 9.6 Hz, CHH0OCH3),
4.60–4.70 (m, CH), 6.52 (d, J=6.0 Hz, NH), 7.10–7.40
(m, PhH); 13C NMR (CDCl3) d 23.3 (CH3C(O)), 29.5
(CH2CH2Ph), 41.6 (CH2CH2Ph), 59.0 (OCH3 or CH),
0
59.4 (OCH3 or C0H), 72.0 (CH2OCH3), 126.4 (C4 ),
0
0
0
0
128.5 (2C2 or 2C3 ), 128.7 (2C2 or 2C3 ), 140.8 (C1 ),
170.2 (C(O)NH), 206.5 (C(O)); MS (+CI) (rel intensity)
250 (M++1, 100), 129 (18); Mr (+CI) 250.144 17
[M++1] (calcd for C14H20NO3 250.144 32). Anal. calcd
for C14H19NO3: C, 67.47%; H, 7.63%; N, 5.62%.
Found C, 67.55%; H, 7.73%; N, 5.59%.
Synthesis of (R,S)-(3-tert-butoxycarbonylamino-2-oxo-
butyl)phosphonic acid dimethyl ester (22). To a THF
(150 mL) solution of 21 (3.65 mL, 34.12 mmol) was
added n-BuLi (2.5 M in hexanes, 13.6 mL) at ꢀ78 ꢂC
and the mixture was stirred (1 h). A THF (80 mL)
solution of 20 (3.00 g, 14.8 mmol) was added dropwise
to the lithium salt of 21 and the mixture was stirred at
ꢀ78 ꢂC (2 h) and then at ꢀ23 ꢂC (1 h). Glacial acetic
acid (0.5 mL) was added and the reaction mixture was
poured into saturated aqueous NaHCO3 (150 mL). The
solution was extracted with EtOAc (2ꢃ100 mL) and the
combined organic layers were dried (Na2SO4) and eva-
porated. The crude was purified by flash column chro-
matography (SiO2; 2:23, MeOH/CHCl3) to obtain 22
(3.58 g, 83%) as a colorless oil: Rf 0.40 (1:9, MeOH/
CHCl3); IR (KBr) 3289 (br), 2974, 1710, 1521, 1455,
Synthesis of (R,S)-2-(carbobenzyloxy)amino-1-methoxy-
5-phenyl-3-pentanone (19). To an acetonitrile (150 mL)
solution of 18 (3.19 g, 9.8 mmol) was added successively
Ag2O (9.28 g, 40 mmol) and MeI (3.25 mL, 50 mmol)
and the mixture was stirred at room temperature (4
days). The insoluble salts were removed by filtration
and the filtrate was concentrated under reduced pres-
sure to obtain an oily residue, which was purified by
column chromatography (SiO2, 1:4, EtOAc/hexanes) to
afford pure 19 (2.05 g, 62%) as a viscous oil, which
solidified upon standing: mp 47–49 ꢂC; Rf 0.31 (1:4,
EtOAc/hexanes); IR (KBr) 3420, 3372, 2956, 1722,
1369, 1253, 1172, 1036, 865, 814 cmꢀ1 1H NMR
;
1687, 1551, 1456, 1270, 1059, 745, 687 cmꢀ1; H NMR
(CDCl3) d 2.75–3.00 (m, CH2CH2Ph), 3.27 (s, OCH3),
3.57 (dd, J=3.9, 9.6 Hz, CHH0OCH3), 3.80 (dd, J=3.2,
9.6 Hz, CHH0OCH3), 4.35–4.45 (m, CH), 5.11 (s,
(CDCl3) d 1.36 (d, J=7.2 Hz, CH3CH), 1.45 (s,
(CH3)3C), 3.14 (dd, J=22.2 Hz, JPH=14.1 Hz,
CHH0P(O)), 3.32 (dd, J=22.2 Hz, JPH=14.1 Hz,
CHH0P(O)), 3.79 (d, JPH=11.1 Hz, P(O)(OCH3)), 3.80
1

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4282
(d, JPH=11.4 Hz, P(O)(OCH03)), 4.36 (dq, J=7.2, 7.2
Hz, CH), 5.46 (d, J=7.2 Hz, NH); 13C NMR (CDCl3)
d 16.4 (CH3CH), 28.0 ((CH3)3C), 37.7 (d, JPC=131.1
Hz, CH2P(O)), 52.7 (d, JPC=2.3 Hz, P(O)(OCH3)), 52.8
(d, JPC=2.9 Hz, P(O)(OC0H3)), 55.8 (CH), 79.6
((CH3)3C), 155.1 (OC(O)NH), 201.6 (C(O)); MS (+CI)
(rel intensity) 296 (18), 268 (10), 257 (17), 240 (100), 222
(21), 196 (76); Mr (+CI) 296.125 59 [M++1] (calcd for
C11H23NO6P 296.126 30).
C13H16NO2 218.118 10). Anal. calcd for C13H15NO2: C,
71.87%; H, 6.96%; N, 6.45%. Found C, 71.71%; H,
6.93%; N, 6.45%.
Synthesis of (R,S)-(3-acetamido-2-oxo-butyl-4-methoxy)-
phosphonic acid dimethyl ester (26). To a THF (65 mL)
solution of 21 (7.95 mL, 74.32 mmol) was added n-BuLi
(1.6 M in hexanes, 46.1 mL) at ꢀ78 ꢂC, and the mixture
was stirred (1 h). A THF (45 mL) solution of 25 (1.98 g,
11.31 mmol) was added dropwise to the lithium salt of
21 and the mixture was stirred at ꢀ78 ꢂC (1 h) and then
at 0 ꢂC (3 h). Glacial acetic acid (0.5 mL) was added and
the reaction mixture was poured into saturated aqueous
NaHCO3 (70 mL). The solution was extracted with
CH2Cl2 (4ꢃ70 mL) and the combined organic layers
were dried (Na2SO4) and evaporated. The crude was
purified by flash column chromatography (SiO2; 1:49,
MeOH/CHCl3) to obtain 26 (1.81 g, 60%) as a colorless
Synthesis of (R,S)-(1-methyl-2-oxo-4-phenyl-but-3-enyl)-
carbamic acid tert-butyl ester31 (24). Using the proce-
dure of Koskinen and co-workers15 compound 24 was
prepared. To a MeCN (100 mL) solution of 22 (3.58 g,
14.14 mmol) was added dried (140 ꢂC, 18 h) K2CO3
(3.35 g, 24.27 mmol) and 23 (1.67 mL, 24.17 mmol). The
suspension was stirred at room temperature (24 h) and
then the insoluble solids were filtered and the reaction
solvent evaporated. The oily crude residue was purified
by flash column chromatography (SiO2; 1:9, EtOAc/
hexanes) to obtain 24 (2.30 g, 69%) as an off-white
solid: mp 71–72 ꢂC; Rf 0.44 (1:4, EtOAc/hexanes); IR
(KBr) 3352 (br), 2979, 2935, 1701, 1612, 1502, 1451,
1
oil: Rf 0.37 (1:49, MeOH/CHCl3); H NMR (CDCl3) d
2.07 (s, CH3C(O)), 3.13 (dd, J=22.2 Hz, JPH=14.1 Hz,
CHH0P(O)), 3.34 (s, OCH3), 3.39 (dd, J=22.2 Hz,
JPH=14.1 Hz, CHH0P(O)), 3.60 (dd, J=4.2, 9.6 Hz,
CHH0OCH3), 3.79 (d, JPH=11.1 Hz, P(O)(OCH3)),
3.80 (d, JPH=11.4 Hz, P(O)(OCH03)), 3.89 (dd, J=3.9,
9.6 Hz, CHH0OCH3), 4.80–4.85 (m, CH), 6.67 (br s,
NH); 13C NMR (CDCl3) d 23.0 (CH3C(O)), 38.6 (d,
JPC=131.1 Hz, CH2P(O)), 53.1 (d, JPC=6.3 Hz,
P(O)(OCH3)), 53.2 (d, JPC=6.9 Hz, P(O)(OC0H3)), 59.0
(OCH3 or CH), 59.1 (OCH3 or CH), 71.2 (CH2OCH3),
170.0 (C(O)NH), 199.0 (d, JPC=6.9 Hz, C(O)).
1
1364, 1249, 1168, 1051, 864, 764, 698 cmꢀ1; H NMR
(CDCl3) d 1.37 (d, J=7.2 Hz, CH3CH), 1.43 (s,
(CH3)3C), 4.66 (dq, J=7.2, 7.2 Hz, CH), 5.48 (d, J=7.2
Hz, NH), 6.80 (d, J=16.2 Hz, CHC(O)), 7.33–7.38 (m,
PhH, 3H), 7.52–7.55 (m, PhH, 2H), 7.69 (d, J=16.2 Hz,
CHPh); 13C NMR (CDCl3) d 18.5 (CH3CH), 28.3
((CH3)3C),0 53.7 (CH), 79.6 ((CH3)3C), 1202.3 (CHC(O)),
0
0
0
128.4 (2C2 or 2C3 ), 128.9 (2C2 or 2C3 ), 130.7 (C4 ),
0
134.2 (C1 ), 144.3 (CHPh), 155.1 (OC(O)NH), 198.2
Synthesis
of
trans-(R,S)-2-acetamido-1-methoxy-5-
(C(O)); MS (+CI) (rel intensity) 276 (M++1, 14), 248
(13), 221 (14), 220 (100), 176 (43); Mr (+CI) 276.159 26
[M++1] (calcd for C16H22NO3 276.159 97). Anal. calcd
for C16H21NO3: C, 69.79%; H, 7.69%; N, 5.09%.
Found C, 69.85%; H, 7.75%; N, 5.05%.
phenyl-4-penten-3-one (12). To a MeCN (50 mL) solu-
tion of 26 (1.75 g, 6.55 mmol) was added dried (140 ꢂC,
18 h) K2CO3 (1.81 g, 13.10 mmol) and 23 (0.9 mL, 13.10
mmol). The suspension was stirred at room temperature
(24 h) and the insoluble solids were filtered and the
reaction solvent evaporated. The oily crude residue was
purified by flash column chromatography (SiO2; 1:49,
MeOH/CHCl3 to 1:24, MeOH/CHCl3) and then crys-
tallized (EtOAc) to obtain 12 (920 mg, 57%) as an off-
white solid: mp 127–128 ꢂC; Rf 0.47 (1:49, MeOH/
CHCl3); IR (KBr) 3362, 3056, 2901, 2822, 1654, 1616,
Synthesis of trans-(R,S)-2-acetamido-5-phenyl-4-penten-
3-one (10).32 To a cold (0 ꢂC) CH2Cl2 (35 mL) solution
of 24 (1.36 g, 4.95 mmol) was added TFA (7.6 mL,
98.65 mmol) dropwise and the mixture was stirred at
0 ꢂC (1 h). The reaction solvent was evaporated in vacuo
and the residue dissolved in THF and Ac2O (4.7 mL,
49.81 mmol) and Et3N (3.4 mL, 24.39 mmol) were suc-
cessively added. The solution was stirred at room tem-
perature (75 min), and then the solvent evaporated. The
crude product was purified by flash column chromato-
graphy (SiO2; 1:49, MeOH/CHCl3) to obtain a yellow
solid, which was further purified by crystallization
(EtOAc) to give 10 (835 mg, 78%) as a crystalline solid:
mp 109–110 ꢂC; Rf 0.31 (1:49, MeOH/CHCl3); IR (KBr)
3285 (br), 3061, 2983, 2935, 1745, 1653, 1611, 1540,
1
1508, 1378, 1117, 1072, 987, 748, 662, 589 cmꢀ1; H
NMR (CDCl3) d 2.09 (s, CH3C(O)), 3.33 (s, OCH3),
3.72 (dd, J=4.2, 9.9 Hz, CHH0OCH3), 3.87 (dd, J=3.6,
9.9 Hz, CHH0OCH3), 5.03–5.08 (m, CH), 6.65 (d,
J=6.9 Hz, NH), 6.90 (d, J=15.9 Hz, CHC(O)), 7.39–
7.60 (m, PhH), 7.75 (d, J=15.9 Hz, CHPh); 13C NMR
(CDCl3) d 23.2 (CH3C(O)), 57.4 (OCH3 or CH), 59.4
(OCH3 or0 CH), 72.1 (CH2OCH3), 122.1 (CHC(O)),
0
0
0
0
128.6 (2C2 or 2C3 ), 129.0 (2C2 or 2C3 ), 131.0 (C4 ),
0
134.1 (C1 ), 144.7 (CHPh), 169.9 (C(O)NH), 195.4
1
1450, 1375, 1304, 1205, 1152, 1071, 985, 763 cmꢀ1; H
(C(O)); MS (+CI) (rel intensity) 249 (27), 248 (M++1,
100), 236 (41), 129 (11), 111 (13); Mr (+CI) 248.128 15
[M++1] (calcd for C14H18NO3 248.128 67). Anal. calcd
for C14H17NO3: C, 68.00%; H, 6.93%; N, 5.66%.
Found C, 67.95%; H, 6.86%; N, 5.65%.
NMR (CDCl3) d 1.44 (d, J=6.9 Hz, CH3CH), 2.05 (s,
CH3C(O)), 4.94–5.03 (m, CH), 6.54 (br s, NH), 6.80 (d,
J=15.9 Hz, CHC(O)), 7.38–7.59 (m, PhH), 7.74 (d,
J=15.9 Hz, CHPh); 13C NMR (CDCl3) d 18.6
(CH3CH), 023.3 (CH3C(O)), 52.5 (CH), 1202.2 (CHC(O)),
0
0
0
128.5 (2C2 or 2C3 ), 129.0 (2C2 or 2C3 ), 131.0 (C4 ),
Synthesis of (R,S)-N-(toluylsulfonylphenylmethyl)acet-
amide17 (29). Using the procedure of Murry and co-
workers,16 compound 29 was prepared. To a MeCN
(250 mL) solution of 27 (710 mg, 12.02 mmol) and 28
0
134.0 (C1 ), 144.9 (CHPh), 169.5 (C(O)NH), 198.0
(C(O)); MS (+CI) (rel intensity) 219 (15), 218 (M++1,
100); Mr (+CI) 218.117 96 [M++1] (calcd for

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4283
(2.14 g, 12.01 mmol) was added 23 (813 mL, 8.00 mmol).
The mixture was cooled to 0 ꢂC and TMSCl (2.0 mL,
15.21 mmol) was added dropwise. The reaction mixture
was warmed to room temperature and stirred (24 h).
The reaction solvent was evaporated and the crude
residue was triturated (1:9, MeOH/H2O). The remain-
ing white solid was purified by crystallization (2:1,
EtOAc/hexanes) to give 29 (1.28 g, 35%) as a white
solid: mp 140–141 ꢂC; Rf 0.65 (1:9, MeOH/CHCl3); IR
(KBr) 3345, 2979, 1663, 1519, 1316, 1146, 1084, 703,
citric acid (30 mL), saturated aqueous NaHCO3 (2ꢃ30
mL), and then dried (Na2SO4) and evaporated to yield
33 (940 mg, 36%) as a white solid: mp 81–82 ꢂC; Rf 0.18
(1:49, MeOH/CHCl3); IR (KBr) 3300, 1645, 1551, 1457,
1
1377, 1298, 1184, 984, 621 cmꢀ1; H NMR (CDCl3) d
1.34 (d, J=6.9 Hz, CH3CH), 2.00 (s, CH3C(O)), 3.22 (s,
NCH3), 3.78 (s, OCH3), 4.93–5.02 (m, CH), 6.50 (br s,
NH); 13C NMR (CDCl3) d 18.4 (CH3CH), 23.2
(CH3C(O)), 32.0 (NCH3), 45.4 (CH), 61.6 (OCH3),
169.4 (C(O)N), 173.2 (C(O)NH); MS (+CI) (rel inten-
sity) 175 (M++1, 13), 114 (100); Mr (+CI) 175.107 97
[M++1] (calcd for C7H15N2O3 175.108 27). Anal. calcd
for C7H14N2O3: C, 48.26%; H, 8.10%; N, 16.08%.
Found C, 48.29%; H, 8.00%; N, 16.06%.
1
673, 584 cmꢀ1; H NMR (CDCl3) d 1.92 (s, CH3C(O)),
2.44 (s, CH3Ph), 6.31 (d, J=10.5 Hz, CH), 7.11 (d,
J=10.5 Hz, NH), 7.26–7.44 (m, PhH, 7H), 7.72–7.75
(m, PhH, 2H); 13C NMR (CDCl3) d 21.7 (CH3C(O) or
CH3Ph), 22.9 (CH3C(O) or CH3Ph), 72.2 (CH), 128.7,
129.0, 129.3, 129.7, 129.8, 130.3, 133.5, 145.4 (2 C6H5),
168.9 (C(O)NH); MS (+CI) (rel intensity) 304 (M++1,
5), 157 (16), 149 (12), 148 (100), 106 (55); Mr (+CI)
304.100 02 [M++1] (calcd for C16H18NO3S 304.100
74). Anal. calcd for C16H17NO3S: C, 63.34%; H, 5.65%;
N, 4.62%. Found C, 63.05%; H, 5.65%; N, 4.57%.
Synthesis of (R,S)-2-acetamido-5-phenyl-4-pentyn-3-one
(13). To a cold (ꢀ78 ꢂC) THF (50 mL) solution of 33
(920 mg, 5.29 mmol) was added 34 (1.0 M in THF, 18.5
mL) dropwise. The solution was warmed to ꢀ30 ꢂC and
then stirred (2 h). The reaction was then quenched with
aqueous 1.0 M NaH2PO4 (30 mL) and extracted with
EtOAc (2ꢃ50 mL). The combined organic layers were
successively washed with aqueous 1.0 M NaH2PO4 (30
mL), H2O (30 mL) and brine (30 mL) and then dried
(Na2SO4) and evaporated. The oily crude was purified
by PTLC (thick plates, 1:49, MeOH/CHCl3) to yield 13
(509 mg, 45%) as a yellow oil: Rf 0.45 (1:49, MeOH/
CHCl3); IR (neat) 3286, 3062, 2985, 2198, 1678, 1539,
Synthesis of trans-(R,S)-1-acetamido-1,4-diphenyl-3-pen-
ten-2-one (11). To a ClCH2CH2Cl (100 mL) suspension
of tosyl amide 29 (2.00 g, 6.60 mmol) and 31 (550 mg,
1.98 mmol) was added 30 (920 mL, 7.26 mmol). The
mixture was warmed to 35 ꢂC and then Et3N (13.8 mL,
99.01 mmol) was added in one portion and the mixture
was stirred at 35 ꢂC (24 h). The solvent was evaporated
and the crude residue was purified by flash column
chromatography (SiO2; 1:49, MeOH/CHCl3), followed
by crystallization (EtOH/iPr2O, 1:9) to give 11 (1.08 g,
59%) as a pale yellow solid: mp 119–121 ꢂC; Rf 0.41
(1:49, MeOH/CHCl3); IR (KBr) 3351, 3058, 2914, 1656,
1
1446, 1373, 1296, 1146, 1072, 1041, 760, 690 cmꢀ1; H
NMR (CDCl3) d 1.52 (d, J=6.6 Hz, CH3CH), 2.05 (s,
CH3C(O)), 4.82 (dq, J=6.6, 6.6 Hz, CH), 6.52 (d,
J=6.6 Hz, NH), 7.27–7.59 (m, PhH); 13C NMR
(CDCl3) d 17.6 (CH3CH), 23.0 (CH3C(O)), 55.9 (CH),
0
0
85.8 (CCPh), 94.6 (CCPh), 119.3 (C1 ), 128.6 (2C3 ),
1
0
0
1607, 1516, 1448, 1336, 1076, 993, 730, 693 cmꢀ1; H
131.1 (C4 ), 133.1 (2C2 ), 169.8 (C(O)NH), 186.3 (C(O));
MS (+CI) (rel intensity) 216 (M++1, 51), 174 (100),
114 (21); Mr (+CI) 216.102 58 [M++1] (calcd for
C13H14NO2 216.102 45). Anal. calcd for C13H13NO2: C,
71.35%; H, 6.17%; N, 6.40%. Found C, 71.48%; H,
6.19%; N, 6.39%.
NMR (CDCl3) d 2.04 (s, CH3C(O)), 5.88 (d, J=6.5 Hz,
CH), 6.69 (d, J=15.9 Hz, CHC(O)), 6.99 (d, J=6.5 Hz,
NH), 7.26–7.44 (m, 10 PhH), 7.72 (d, J=15.9 Hz,
CHPh); 13C NMR (CDCl3) d 23.2 (CH3C(O)), 61.8
(CH), 122.4 (CHCHPh), 128.3, 128.5, 128.6, 128.9,
129.2, 131.0, 134.0, 136.7 (2 C6H5), 144.8 (CHCHPh),
169.2 (C(O)NH), 194.4 (C(O)); MS (+CI) (rel intensity)
281 (18), 280 (M++1, 100); Mr (+CI) 280.134 25
[M++1] (calcd for C18H18NO2 280.134 75). Anal. calcd
for C18H17NO2: C, 77.40%; H, 6.13%; N, 5.01%.
Found C, 77.27%; H, 6.23%; N, 5.10%.
Synthesis of (R,S)-2-acetamido-1-methoxy-5-phenyl-4-
pentyn-3-one (14). (R,S)-2-Acetylamino-3-methoxy-
propionic acid methyl ester31 (25) was prepared using
the procedure of Andurkar and co-workers.21 To a cold
(ꢀ78 ꢂC) THF (25 mL) solution of 25 (1.00 g, 5.71
mmol) was added 34 (1.0 M in THF, 11.4 mL) dropwise
and the mixture was stirred at ꢀ78 ꢂC (2 h). The reac-
tion mixture was then quenched with a saturated aqu-
eous NH4Cl solution (20 mL) and extracted with EtOAc
(2ꢃ25 mL). The combined organic layers were washed
with brine (30 mL) and then dried (Na2SO4) and eva-
porated. The crude residue was crystallized in Et2O (20
mL) to yield 14 (500 mg, 36%) as a yellow solid: mp 96–
99 ꢂC; Rf 0.62 (1:32, MeOH/CHCl3); IR (KBr) 3356,
2997, 2935, 2198, 1678, 1520, 1446, 1369, 1284, 1250,
Synthesis of (R,S)-N-acetylalanine-N-methoxy-N-methyl-
amide (33). Hydroxylamine 32 (1.79 g, 18.35 mmol)
was dissolved in THF (20 mL) and H2O (1 mL) and
then anhydrous K2CO3 (5.04 g, 36.47 mmol) was added,
and the mixture stirred at room temperature (2 h). In a
separate flask 15 (2.00 g, 15.26 mmol) was dissolved in
THF (70 mL) and the solution was cooled to ꢀ15 ꢂC
under Ar, and then N-methylmorpholine (1.7 mL, 15.26
mmol) was added, followed by isobutyl chloroformate
(2.0 mL, 15.26 mmol). After 1 min, the 32 solution was
added in one portion through a cannula. The mixture
was stirred at ꢀ15 ꢂC (1.5 h) and then H2O (10 mL) was
added. The solvents were evaporated leaving a clear oil
and then aqueous 5% citric acid (30 mL) was added and
the mixture was extracted with EtOAc (2ꢃ50 mL). The
combined organic layers were washed with aqueous 5%
1
1165, 1057, 995, 760, 690, 606 cmꢀ1; H NMR (CDCl3)
d 2.11 (s, CH3C(O)), 3.37 (s, OCH3), 3.76 (dd, J=2.8,
9.9 Hz, CHH0OCH3), 4.15 (dd, J=3.2, 9.9 Hz,
CHH0OCH3), 4.90–4.95 (m, CH), 6.60 (d, J=7.8 Hz,
NH), 7.38–7.60 (m, PhH); 13C NMR (CDCl3) d 23.4
(CH3C(O)), 59.7 (OCH3 or CH), 60.5 (OCH3 or CH),
71.8 (CH2OCH3), 86.1 (CCPh), 94.5 (CCPh), 119.7

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4284
0
0
0
0
(C1 ), 128.9 (2C3 ), 131.4 (C4 ), 133.4 (2C2 ), 170.2
(C(O)NH), 184.1 (C(O)); MS (+CI) (rel intensity) 246
(M++1, 38), 214 (11), 199 (16), 198 (100), 197 (15); Mr
(+CI) 246.113 41 [M++1] (calcd for C14H16NO3
J=7.2 Hz, CH2CH3), 2.04 (s, CH3C(O)), 3.13–3.22 (m,
CH2CH3), 3.33 (s, OCH3), 3.63 (dd, J=4.2, 9.6 Hz,
CHH0OCH3), 3.69 (dd, J=3.9, 9.6 Hz, CHH0OCH3),
4.62–4.67 (m, CH), 5.10 (s, CHCPh), 6.61 (d, J=6.6 Hz,
NHC(O)), 7.31–7.43 (m, 5 PhH), 10.69 (br s, N(H)); 13C
NMR (CDCl3) d 15.8 (CH3CH2), 23.3 (CH3C(O)), 39.7
(N(H)CH2CH3), 56.5 (OCH3 or CH), 59.4 (OCH3 or
CH), 73.5 (CH2OCH3), 93.5 (C(H)C(O)), 127.4, 128.4,
.
246.113 02). Anal. calcd for C14H15NO3 0.2H2O: C,
67.56%; H, 6.24%; N, 5.63%. Found C, 67.54%; H,
6.24%; N, 5.67%.
0
0
0
0
Synthesis of cis-(36) and trans-(10)-2-acetamido-5-
phenyl-4-penten-3-one. An EtOH (50 mL) solution 13
(440 mg, 2.05 mmol) was hydrogenated in the presence
of Lindlar catalyst (30 mg) and quinoline (1.2 mL, 10.15
mmol) at room temperature (4 h). The catalyst was
removed by filtration through a Celite pad and the
reaction solvent was evaporated. The crude product was
treated with an 1:1 Et2O (30 mL) and aqueous 0.1 N
HCl (30 mL) mixture. The aqueous layer was separated
and extracted with Et2O (3ꢃ30 mL) and the combined
organic layers were successively washed with aqueous
0.1 N HCl (20 mL) and brine (20 mL), and dried
(Na2SO4). The solution was concentrated in vacuo to
give an oil (649 mg, 73%) that contained 36, 10 and 7 in
an approximate 11:3:1 ratio, respectively: Rf 0.31 (1:49,
MeOH/CHCl3); 1H NMR (CDCl3) d 1.24 (d, J=7.2 Hz,
CH3CH (7)), 1.35 (d, J=7.2 Hz, CH3CH (36)), 1.40 (d,
J=7.2 Hz, CH3CH (10)), 1.96 (s, CH3C(O) (7)), 1.98 (s,
CH3C(O) (36)), 2.01 (s, CH3C(O) (10)), 2.75–2.93 (m,
CH2CH2Ph (7)), 4.50–4.60 (m, CH (7)), 4.66–4.76 (m,
CH (36)), 4.92–5.02 (m, CH (10)), 6.26 (d, J=12.6 Hz,
CHC(O) (36)), 6.77 (br s, NH (36)), 6.82 (d, J=16.2 Hz,
CHC(O) (10)), 6.88 (br s, NH (10)), 6.92 (d, J=12.6 Hz,
CHPh (36)), 7.31–7.64 (m, PhH (36, 10, 7)), 7.72 (d,
J=16.2 Hz, CHPh (10)); 13C NMR d (CDCl3) 18.0
(CH3CH (36)), 18.5 (CH3CH (10)), 23.2 (CH3C(O)
(36)), 52.5 (CH (10)), 54.4 (CH (36)), 122.20 (CHC(O)
129.9 (2C2 , 2C3 , C4 ), 135.0 (C1 ), 166.7 (C(O)NH or
C(Ph)(N(H)CH2CH3), 169.6 (C(O)NH or
C(Ph)(N(H)CH2CH3), 191.5 (C(O)C(H)).
Pharmacology
Compounds were screened under the auspices of the
National Institutes of Health’s Anticonvulsant Screen-
ing Project. Experiments were performed in male
rodents [albino Carworth Farms No. 1 mice (intraperi-
toneal route, ip), albino Sprague–Dawley rats (oral
route, po)]. The mice weighed between 18 and 25 g while
rats were between 100 and 150 g. All animals had free
access to feed and water except during actual testing
period. Housing, handling and feeding were all in
accordance with recommendations contained in the
‘Guide for the Care and Use of Laboratory Animals’.
All of the test compounds were administrated in sus-
pensions of 0.5% (w/v) of methylcellulose in water. The
volumes administered were 0.01 mL/g of body weight
for mice and 0.2 mL/10 g for rats. Anticonvulsant
activity was established using the maximal electroshock
(MES) test.5,26 For the MES test, a drop of electrolyte
solution with an anesthetic (0.5% butacaine hemisulfate
in 0.9% sodium chloride) was placed in the eyes of the
animals prior to positioning the corneal electrodes and
delivery of a non-lethal current. A 60-cycle alternating
current was administered for 0.2 s in both species, uti-
lizing 50 mA in mice and 150 mA in rats. Protection
endpoints were defined as the abolition of the hind limb
tonic extensor component of the induced seizure.6 The
subcutaneous pentylenetetrazole (Metrazol1) seizure
threshold test (scMet) entailed administration of either
85 mg/kg of pentylenetetrazole in mice (Carworth
Farms No. 1) or 70 mg/kg in rats (Sprague–Dawley) as
a 0.5% solution subcutaneously in the posterior mid-
line. This amount of pentylenetetrazole produces clonic
seizures in 97% (CD97) of animals tested. The animal is
observed for 30 min. Protection is defined as the failure
to observe even a threshold seizure (a single episode of
clonic spasms of at least 5-s duration). In mice, effects of
compounds on forced spontaneous motor activity were
determined using the rotorod test.10,33 The inability of
experimental mice to maintain their balance for 1 min
on a 1-inch diameter knurled rod rotating at 6 rpm in
three successive trials was interpreted as a demonstra-
tion of motor impairment or toxicity. Under these con-
ditions, mice can normally maintain their balance
indefinitely. Endpoints for motor impairment in rats
also referred to as toxicity or neurological deficit was
assessed by observing any overt evidence of ataxia,
problems with the righting reflex, abnormal gait and
stance, and/or loss of placing response and muscle tone.
In the mouse identification screens all compounds were
administered at three dose levels (30, 100, 300 mg/kg)
0
(10)), 123.7, 128.1, 128.9 (CHC(O) and 2C2 and 2C3
0
0
0
0
(36)), 128.5 (2C2 or 2C3 (10)), 129.0 (2C2 or 2C3 (10)),
0
0
0
131.0 (C4 (10)), 134.0 (C1 (10)), 134.6, 136.0, 144.4 (C1
0
and C4 and CHPh (36)), 144.9 (CHPh (10)), 169.4
(C(O)NH (36)), 198.0 (C(O) (10)), 199.0 (C(O) (36));
MS (+CI) (rel intensity) 220 (17), 219 (15), 218
(M++1, 100), 114 (16); Mr (+CI) 218.118 15 [M++1]
(calcd for C13H16NO2 218.118 10).
Chemical evaluation of 12 and 14. EtSH (46–54 mL,
0.63–0.73 mmol) or EtNH2 (2.0 M in THF, 310–350 mL,
0.62–0.70 mmol) was added to a solution of either 12 or
14 (9.5–11.3 mg, 37–46 mmol) in THF (0.7–1.0 mL) and
the reaction was stirred at room temperature (18 h) and
then analyzed by TLC. For 12 no reaction was observed
with EtSH and EtNH2. For 14 no reaction was
observed for EtSH and with EtNH2 the starting mate-
rial was consumed and a new product [Rf 0.23 (1:49,
MeOH/CHCl3)] was observed.
Chemical evaluation of 14 withEtNH . EtNH2 (2.0 M in
2
THF, 166 mL, 0.33 mmol) was added to a solution of 14
(10.2 mg, 42 mmol) in THF-d8 (0.7 mL) and the reaction
was stirred at room temperature (18 h) and then was
analyzed by H NMR and TLC. The reaction was con-
centrated to dryness, purified by PTLC (1:49, MeOH/
1
CHCl3) to give 39 (5.4 mg, 45%) as a pale yellow oil: Rf
1
0.23 (1:49, MeOH/CHCl3); H NMR (CDCl3) d 1.16 (t,

´
C. Beguin et al. / Bioorg. Med. Chem. 11 (2003) 4275–4285
4285
using two time periods (0.5 and 4 h). Typically, in the
MES seizure test two animals were used at each of two
time periods for doses of 30 and 300 mg/kg, and a total
of six animals at 100 mg/kg (three per time period). In
the rotorod toxicity test four animals were used at 30
and 300 mg/kg, and eight animals at 100 mg/kg (Table
1). Oral rat identification screening was performed using
four animals per time point over five time points (1/4, 1/
2, 1, 2, 4 h) at a fixed dose of 30 mg/kg for the MES
tests. The quantitative determination of the median
effective (ED50) and toxic doses (TD50) were conducted
at previously calculated time of peak effect using ip
route in mice and oral route in rats. Groups of at least
eight animals were tested using different doses of test
compound until at least two points were determined
between 100 and 0% protection and minimal motor
impairment. The dose of the candidate substance
required to produce the desired endpoint (abolition of
hindlimb tonic extensor component) in 50% of the animals
in each test, and 95% confidence interval were calculated
by a computer program based on methods described by
Finney.34
4. Levy, R. H.; Mattson, R.; Meldrum, B. Antiepileptic Drugs,
4th ed; Raven: New York, 1995; Chapter 6.
5. Stables, J. P.; Kupferberg, H. J. In Molecular and Cellular
Targets for Antiepileptic Drugs; Avanzini, G., Tanganelli, P.,
Avoli, M., Eds.; John Libbey: London, 1997; p 191.
6. White, H. S.; Woodhead, J. H.; Franklin, M. R. In Anti-
epileptic Drugs, 4rd ed.; Levy, R. H., Mattson, R. H., Mel-
drum, B. S., Eds.; Raven: New York, 1995; p 99.
7. LeTiran, A.; Stables, J. P.; Kohn, H. Bioorg. Med. Chem.
2001, 9, 2693.
8. Andurkar, S. V.; Beguin, C.; Stables, J. P.; Kohn, H. J.
Med. Chem. 2001, 44, 1475.
9. Shen, M.; LeTiran, A.; Xiao, Y.; Golbraikh, A.; Kohn, H.;
Tropsha, A. J. Med. Chem. 2002, 45, 2811.
10. Dunham, M. S.; Miya, T. A. J. Am. Pharm. Assoc. Sci.
Edit. 1957, 46, 208.
11. Knudsen, C. G.; Rapoport, H. J. Org. Chem. 1983, 48, 2260.
12. Maurer, P. J.; Takahata, H.; Rapoport, H. J. Am. Chem.
Soc. 1984, 106, 1095.
13. Chakravarty, P. K.; Greenlee, W. J.; Parsons, W. H.;
Patchett, A. A.; Combs, P.; Roth, A.; Busch, R. D.; Mellin,
T. N. J. Med. Chem. 1989, 32, 1886.
14. Deziel, R.; Plante, R.; Caron, V.; Grenier, L.; Llinas-
Burnet, M.; Duceppe, J. S.; Malenfant, E.; Moss, N. J. Org.
Chem. 1996, 61, 2901.
15. Koskinen, A. M. P.; Koskinen, P. J. Synlett 1993, 501.
16. Murry, J. A.; Frantz, D. E.; Soheili, A.; Tillyer, R.; Gra-
bowski, E. J.; Reider, P. J. J. Am. Chem. Soc. 2001, 123, 9696.
17. Sisko, J.; Mellinger, M.; Sheldrake, P. W.; Baine, N. H.
Tetrahedron Lett. 1996, 37, 8113.
18. Jackman, L. M.; Sternhell, S. In Applications of Nuclear
Magnetic Resonance Spectroscopy in Organic Chemistry, 2nd
ed.; Pergamon: New York, 1969; p 278.
Acknowledgements
The authors thank the NINDS and the Anticonvulsant
Screening Project (ASP) at the National Institutes of
Health, for kindly performing the pharmacological
studies via the ASP’s contract site at the University of
Utah with Drs. H. Wolf, S. White, and Karen Wilcox.
19. Cupps, T. L.; Boutin, R. H.; Rapoport, H. J. Org. Chem.
1985, 50, 3972.
20. Boutin, R. H.; Rapoport, H. J. Org. Chem. 1986, 51, 5320.
21. Andurkar, S. V.; Stables, J. P.; Kohn, H. Tetrahedron:
Asymmetry 1998, 9, 3841.
References and Notes
1. (a) Cortes, S.; Liao, Z.-K.; Watson, D.; Kohn, H. J. Med.
Chem. 1985, 28, 601. (b) Conley, J. D.; Kohn, H. J. Med.
Chem. 1987, 30, 567. (c) Kohn, H.; Conley, J. D. Chem. Br.
1988, 24, 231. (d) Kohn, H.; Conley, J. D.; Leander, J. D.
Brain Res. 1988, 457, 371. (e) Kohn, H.; Sawhney, K. N.;
LeGall, P.; Conley, J. D.; Robertson, D. W.; Leander, J. D. J.
Med. Chem. 1990, 33, 919. (f) Kohn, H.; Sawhney, K. N.;
LeGall, P.; Robertson, D. W.; Leander, J. D. J. Med. Chem.
1991, 34, 2444. (g) Kohn, H.; Sawhney, K. N.; Bardel, P.;
Robertson, D. W.; Leander, J. D. J. Med. Chem. 1993, 36,
3350. (h) Bardel, P.; Bolanos, A.; Kohn, H. J. Med. Chem.
1994, 37, 4567. (i) Kohn, H.; Sawhney, K. N.; Robertson,
D. W.; Leander, J. D. J. Pharm. Sci. 1994, 83, 689. (j) Choi,
D.; Stables, J. P.; Kohn, H. J. Med. Chem. 1996, 39, 1907. (k)
LeTiran, A.; Stables, J. P.; Kohn, H. J. Med. Chem. 2002, 45,
4762.
22. (a) Marvell, E. N.; Li, T. Synthesis 1973, 457. (b) Lindlar,
H.; Dubuis, R. John Wiley: New York, 1973 Org. Synth.,
Collective Vol. 5, p 880.
23. 1H NMR analysis showed that the ratio of cis-36 to trans-
10 changed from 3.7:1 to approximately 1:1 upon standing at
room temperature for 3 months.
24. Pretsch, E.; Simon, W.; Seibl, J.; Clerc, T., In Tables of
Spectral Data for Structure Determination of Organic Com-
pounds. 2nd ed.; 1989: Springer: New York; p C188.
25. Porter, R. J.; Cereghino, J. J.; Gladding, G. D.; Hessie,
B. J.; Kupferberg, H. J.; Scoville, B.; White, B. G. Cleveland
Clin. Q. 1984, 51, 293.
26. Krall, R. L.; Perry, J. K.; White, B. G.; Kupferberg, H. J.;
Swinyard, E. A. Epilepsia 1978, 19, 409.
27. Schultz, T. W.; Sinks, G. D.; Hunter, R. S. SAR QSAR
Env. Res. 1995, 3, 27.
2. (a) Paruszewski, R.; Rostafinska-Suchar, G.; Strupinska,
M.; Jaworski, P.; Stables, J. P. Pharmazie 1996, 3, 145. (b)
Paruszewski, R.; Rostafinska-Suchar, G.; Strupinska, M.;
Jaworski, P.; Winiecka, I.; Stables, J. P. Pharmazie 1996, 51,
212. (c) Paruszewski, R.; Rostafinska-Suchar, G.; Strupinska,
M.; Winiecka, I.; Stables, J. P. Pharmazie 2000, 55, 27. (d)
Paruszewski, R.; Strupinska, M.; Stables, J. P.; Swiader, M.;
Czuczwar, S.; Kleinrock, Z.; Turski, W. Chem. Pharm. Bull.
2001, 49, 629.
28. Hermens, J. L. M. Environ. Health Perspect. 1990, 87, 219.
29. Zhuo, J.-C. Mag. Reson. Chem. 1997, 35, 21.
30. Balsamo, A.; Crotti, P.; Lapucci, A.; Macchia, B.; Mac-
chia, F.; Cuttica, A.; Passerini, N. J. Med. Chem. 1981, 24, 525.
31. Synge, R. L. M. Biochem. J. 1939, 33, 1913.
32. The (S)-isomer of 10 corresponds to the N-acetyl deriva-
tive of the natural product merucathione, see: Brenneisen, R.;
Geisshusler, S. J. Nat. Prod. 1987, 50, 1188.
¨
33. Woodbury, D. M.; Penry, J. K.; Pippenger, C. E. Anti-
epileptic Drugs, 2nd ed; Raven: New York, 1982.
34. Finney, D. J. Probit Analysis, 3rd ed; Cambridge Uni-
versity: London, 1971.
3. Ho, B.; Venkatarangan, P. M.; Cruse, S. F.; Hinko, C. N.;
Andersen, P. H.; Crider, A. M.; Adloo, A. A.; Roane, D. S.;
Stables, J. P. Eur. J. Med. Chem. 1998, 33, 23.