Synthesis of N-substituted Clausenamide analogues

Article abstract of DOI:10.1016/j.ejmech.2010.08.041

A practical synthesis of N-substituted Clausenamide analogues, including (-) and (+) CM1, Piracetam analogue 1 and Nefiracetam analogue 2, have been developed.

Full text of DOI:10.1016/j.ejmech.2010.08.041

European Journal of Medicinal Chemistry 45 (2010) 5531e5538
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journal homepage: http://www.elsevier.com/locate/ejmech
Laboratory note
Synthesis of N-substituted Clausenamide analogues
,
b
,
a
a
a
a
a,
*
XingZhou Li a , ChuangJiang Zhu , ChangHui Li , KeMei Wu , DaoFei Huang , Liang Huang
*
a Beijing Institute of Pharmacology and Toxicology, 27 Taiping Rd., Beijing 100850, China
b Institute of Materia Medica, Chinese Academy of Medical Sciences.1 Xian Nong Tan St., Beijing, 100050, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A practical synthesis of N-substituted Clausenamide analogues, including (ꢀ) and (þ) CM1, Piracetam
analogue 1 and Nefiracetam analogue 2, have been developed.
Received 24 February 2010
Received in revised form
14 August 2010
Ó 2010 Elsevier Masson SAS. All rights reserved.
Accepted 16 August 2010
Available online 24 August 2010
Keywords:
Nootropic agents
N-substituted Clausenamide
Metabolites
Pyrrolidin-2-one
1. Introduction
(þ)-Clausenamide. The synthesis of (ꢀ)-CM1 is required to support
the preclinical studies of (ꢀ)-Clausenamide. In vivo and in vitro
The pyrrolidin-2-one family of cognition-enhancers, often
referred to as nootropics and exemplified by Piracetam and Nefir-
acetam (Fig. 1), has been the subject of studies for almost four
decades. Several members are in use in several countries to control
cognition impairment, to afford neuroprotection after stroke and to
treat epilepsy [1]. Racemic Clausenamide (Fig. 1) is a pyrrolidin-2-
one derivative isolated from Clausena lansium (lour.), a Chinese folk
medicine [2]. Its two optical isomers, namely (þ) and (ꢀ) Clause-
namide, had been synthesized by our group [3,4]. (ꢀ)-Clausena-
mide showed potent nootropic activity in many behavioral
experiments, and is developed as a promising antidementia drug
now. While, (þ)-Clausenamide does not possess such effects [5].
The structure of Clausenamide is quite different from that of
Piracetam and Nefiracetam. In Clausenamide, there are four ster-
eogenic centers resulted from three substituents at 3, 4, 5 positions
of the central pyrrolidin-2-one. While, in Piracetam or Nefiracetam,
there is only one, but larger, substituent. These substituents are
suggested to be closely related to their respectively nootropic
activities. Therefore, demethyl-Clausenamide derivatives with the
side chain of Piracetam and Nefiracetam (Compounds 1 and 2,
Fig. 1) are designed with the aim of finding novel nootropic agents.
CM1 (Fig. 1), the hydroxylation product of Clausenamide, is one
of the major metabolites of both (ꢀ)-Clausenamide and
metabolic studies also revealed that the content of CM1 in the
metabolites of (ꢀ)-Clausenamide is significantly higher than that of
(þ)-Clausenamide [6]. It seems that there may be some correlation
between the different physiological roles of (þ) and (ꢀ) Clausena-
mide and their different metabolic behavior. If so, (ꢀ)-CM1 may
also be a nootropic agent and may enhance and prolong the noo-
tropic effect of (ꢀ)-CM1 in vivo.
To acquire novel compounds with nootropic activities and to
support the preclinical studies of (ꢀ)-Clausenamide, the synthesis
of Piracetam analogue 1, Nefiracetam analogue 2 and CM1 as well
as its optical isomers, has been conducted. An elegant method was
devised to construct the g-lactam skeleton and establish the rela-
tive configuration of the substituents, especially the 4/5 syn-
configuration, which is essential to keep the nootropic activities [7].
The present report describes our efforts in this field.
1.1. Synthesis of racemic demethyl-Clausenamide
In our strategy, 4/5 syn-demethyl-Clausenamidone 9a was
chosen as the key intermediate for the synthesis of desired
compounds. Our group has successfully fulfilled the total syntheses
of Clausenamidone 9d by an elegant base induced cyclization of
compound 8d (Scheme 1) [8]. Thus, the synthetic route of demethyl-
Clausenamidone 9a was designed following the same strategy. The
key to the success of this strategy is conversion of 8a to g-lactam 9a
through intramolecular cyclization, Cyclization to 5-numbered ring
from such structural type as 8a is against Baldwin’s rule [9]. But
* Corresponding author. Beijing Institute of Pharmacology and Toxicology, 27
Taiping Rd., Beijing 100850, China. Tel.: þ86 10 63165250.
E-mail address: xingzhouli@yahoo.cn (XingZhou Li).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.08.041

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XingZhou Li et al. / European Journal of Medicinal Chemistry 45 (2010) 5531e5538
Fig. 1. The structure of Clausenamide, CM1, Piracetam and Nefiracetam, Piracetam analogue 1 and Nefiracetam analogue 2.
previous study had showed that the intramolecular cyclization of
compound 8d under the catalyst of LiOH worked nice to give
a mixture of 9d and 10d. The electronic effect induced by phenyl
copper sulfate furnished amide 8a in good yield. However the
cyclization of compound 8a did not take place under catalytic
amount or stoichiometric amount of base (LiOH) at room temper-
ature. It proceeded when the reaction mixture was heated to 60 ꢁC,
but produced a complex mixture of products. Only a small quantity
of 9a (5% yield) and 10a (36% yield) was obtained through careful
separation. We proposed that it is the amide hydrogen atom of 8a,
which can also dissociate to generate anion other than the proton at
group at
nucleophilic attack at
The -phenyl-ethanol amine 5a was prepared from styrene
oxide 3 and aqueous ammonia. 5a took place amine-ester exchange
reaction with methyl -phenyl-glycidate 6 giving the straight-chain
amide 7a. Oxidation of 7a with potassium permanganate and
b
-carbon of the epoxy group may be favorable factor for the
b
-carbon to form the -lactam.
g
b
b
the
a
position of carbonyl group (10 position) under the alkaline
Scheme 1. Reagents and conditions: a: room temperature, 10days; b: sodium methoxide/methanol, a week; c: KMnO4/CuSO4, CH2Cl2, d: LiOH/MeOH, H2O; e: (NH4)2Ce(NO3)6/
CH3CN, H2O; f: NaBH4/CH3OH.

XingZhou Li et al. / European Journal of Medicinal Chemistry 45 (2010) 5531e5538
5533
reaction condition, handicap and complicate the reaction, and
changing the amide hydrogen atom to an inert group, for example
benzyl, may facilitate the reaction. Thus N-Bn amide 8b was
prepared following the method for the preparation of 8a from
benzylamine 4b and styrene oxide 3. 8b underwent cyclization
smoothly to give 9b and 10b as the main components of the reac-
tion products. Unfortunately, the debenzylation of 9b failed with
various methods, such as catalytic hydrogenolysis, acidic solvolysis
[10], Li/NH3 reduction [11] and t-BuLi/O2 oxidation [12]. N-p-
methoxybenzyl (PMB) substituted amide 8c was thus prepared,
considering the p-methoxybenzyl group was easier to be stripped
off than benzyl group. The intramolecular cyclization of compound
easily separated by SiO2 column chromatography. Reduction of the
ketone of 15a or 15b with NaBH4 followed by hydrolysis with aq. NaOH
in one pot gave the enantiomerically pure demethyl-Clausenamidone
(ꢀ)-11 or (þ)-11 respectively. Hydroxymethylation of (ꢀ)-11 and
18
(þ)-11 yielded the corresponding (ꢀ)-CM1{[
a
]
¼ ꢀ119ꢁ (c,0.261,
D
18
CH3OH)} and (þ)-CM1 {[
a
]
¼ þ117ꢁ (c, 0.394, CH3OH)} with ee >99%
D
(determined by HPLC with chiral column). The retention time of
(ꢀ)-CM1 is in line with that of CM1 obtained from the metabolism of
(ꢀ)-Clausenamide. This result indicated that (ꢀ)-CM1 was the
metabolite of (ꢀ)-Clausenamide and the absolute configuration of
(ꢀ)-CM1 must be 3S,4R,5R,6S. Then the absolute configuration of
(þ)-CM1 must be 3R,4S,5S,6R.
8c gave a mixture of
g-lactam 9c and 10c. The desired 4/5-cis
compound 9c was separated by silica gel column chromatography.
The debenzylation of 9c by CAN oxidation [13] worked well to give
the key intermediate demethyl-Clausenamidone 9a, which yielded
racemic demethyl-Clausenamide 11 by subsequent reduction of the
ketone group with sodium borohydride.
1.4. Pharmacology
Long-term potentiation (LTP) is the long-lasting improvement in
communication between two neurons that results from stimulating
them simultaneously. Since neurons communicate via chemical
synapses, and because memories are believed to be stored within
these synapses, LTP is widely considered to be one of the major
cellular mechanisms that underlie learning and memory.
1.2. Synthesis of Piracetam analogue 1, Nefiracetam analogue 2
The synthesis of compounds 1 and 2 is illustrated in Scheme 2.
The two hydroxyl groups of demethyl-Clausenamide 11 were pro-
tected with 3,4-2H-dihydropyran to give 3,6-di-O-tetrahydropyran-
demethyl-Clausenamide 12. Condensation of compound 12 with
ethyl bromoacetate or 2-bromo-N-(2,6-dimethylphenyl) acetamide
in the presence of sodium hydride [14] and subsequent deprotection
yielded N-(ethoxycarbonyl-methyl)-demethyl-Clausenamide 13 or
Nefiracetam analogue 2 respectively. Incubation of compound 13 in
NH3/CH3OH overnight gave the Piracetam analogue 1.
Herein, the nootropic activity of (ꢀ) and (þ) CM1, Piracetam
analogue 1 and Nefiracetam analogue 2, were evaluated herein in
LTP assays compared with (ꢀ)-Clausenamide and (þ)-Clausena-
mide [16,17]. As shown in Table 1, at an estimated final brain
concentration of 1
m
M, (ꢀ)-CM1 caused over 30% increase of PS
amplitude relative to basal level, and 27%e41% increase relative to
the vehicle control, while (þ)-CM1 exhibited 18%e25% and 11%e
20% of decrease in the PS amplitude when compared with basal and
vehicle control, respectively. These results implied that the activity
of (ꢀ)-Clausenamide could be partly contributed from its active
metabolite (ꢀ)-CM1. The completely different behaviors of (ꢀ) and
(þ) CM1 further demonstrated that the stereochemistry around the
pyrrolidin-2-one was a very important determinant for the activi-
ties of this type of cognition-enhancers.
1.3. Synthesis of racemic and optical active CM1
Hydroxymethylation [15] of 11 in acetone in the presence of
K2CO3 using formaldehyde afforded the desired racemic CM1,
which showed identical 1H NMR, 13C NMR and MS spectra to the
sample obtained from metabolites of Clausenamide (Scheme 3).
Enantiomers of CM1 were prepared by resolution of the interme-
Results in Table 1 also showed that 60 min after compounds
administration, Nefiracetam analogue 2 increased PS amplitude by
37% and 22% relative to basal PS amplitude and vehicle control
respectively. While no significant effect was observed for Piracetam
analogue 1. These results indicated that the structure of the side
chain on the N atom of amide has a great impact on the nootropic
activity of N-substituted Clausenamide analogues. But the relatively
low activity of compounds 1 and 2 might be due to the antagonism
diate (ꢂ) 9c using phthalyl-
L
-alanine as the resolving agent (Scheme 3).
Condensation of (ꢂ) 9c with phthalyl-
L-alanine gave a mixture of dia-
stereoisomers 14a and 14b, which was difficult to be separated by
chromatography. Therefore debenzylation of the mixture of 14a and
14b with CAN was carried out first, the mixture of 15a and 15b was
Scheme 2. Reagents and conditions: a: 3,4-2H-dihydropyran, PPTS/THF; b: (1) bromoacetate or 2-bromo-N-(2,6-dimethylphenyl) acetamide, NaH/benzene, reflux, (2) Hþ/EtOH,
reflux; c: NH3/MeOH.

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XingZhou Li et al. / European Journal of Medicinal Chemistry 45 (2010) 5531e5538
Scheme 3. Reagents and conditions: a: formaldehyde, K2CO3/acetone, water; b: (1) SOCl2/toluene, (2) pyridine/CH2Cl2; c: (NH4)2Ce(NO3)6/CH3CN, H2O; d: (1) NaBH4/CH3OH,
(2) NaOH.
effect of their (þ)-isomer. Additional N-substituted Clausenamide
analogues and their enantiomers should be synthesized and eval-
uated to provide a better understanding of their SAR.
activities of N-substituted Clausenamide analogues. These hints will be
helpful in the design of more efficient pyrrolidin-2-one type of
cognition-enhancers.
2. Conclusion
3. Experiment
In summary, a practical synthesis of N-substituted Clausenamide
analogues, including (ꢀ) and (þ) CM1, Piracetam analogue 1 and
Nefiracetam analogue 2, have been developed. The nootropic activities
of these targets compounds were evaluated by LTP assay. The result
indicated that the stereochemistry around the pyrrolidin-2-one and
the structure of the N-side chain have a great impact on the nootropic
All the reagents for synthesis were commercially available and
used without further purification or purified by standard methods
prior to use. Melting points were determined using an RY-1 appa-
ratus and the thermometer is uncorrected. 1H NMR spectra were
recorded using a multinuclear FT NMR spectrometer YS-300 or
Table 1
Activity data in enhancing LTP of synthesized compounds at a concentration of 1 mM.
Compound
Animal number
Relative PS (PSA %)a,b
P.A.
15 min A A.
30 min A A.
60 min A A.
DMSO
6
6
6
5
5
3
5
100
100
100
100
100
100
100
110.0 ꢂ 7.0
131.8 ꢂ 0.4
90.6 ꢂ 0.3
108.4 ꢂ 6.4
138.5 ꢂ 8.9*
110.2 ꢂ 13.1
133.5 ꢂ 24.2*
74.5 ꢂ 21.8*
79.8 ꢂ 22.3
97.4 ꢂ 32.2
112.5 ꢂ 4.2
(ꢀ)-Clausenamide
(þ)-Clausenamidec
(ꢀ)-CM1
158.1 ꢂ 4.2**
106.4 ꢂ 4.1
134.5 ꢂ 7.2*
81.7 ꢂ 14.9*
85.2 ꢂ 17.4
87.5 ꢂ 19.6
133.0 ꢂ 16.2*
76.6 ꢂ 19.3*
117.4 ꢂ 13.5
137.2 ꢂ 37.2*
(þ)-CM1
(ꢂ)-1
(ꢂ)-2
a
Test *p < 0.05, **p < 0.01, vs Control.
P.A.: Prior Administration, A.A., After Administration.
b

XingZhou Li et al. / European Journal of Medicinal Chemistry 45 (2010) 5531e5538
5535
Bruker-500. Mass spectra were obtained from Micromass ZAD-2F
and VG300 instruments.
Compound 9a: mp: 138e142 ꢁC, 1H NMR (300 MHz, CDCl3)
3.94 (1H, dd, J ¼ 9.3, 8.4 Hz), 4.74 (1H, d, J ¼ 9.3 Hz), 5.76 (1H, d,
d
J ¼ 8.4 Hz), 6.96e7.66 (10H, m). FAB-MS (m/e,%): 282 (MHþ, 75), 176
(75), 148(40), 120 (85), 77(85), 91(55), 105(100); IR (KBr, cmꢀ1):
3372, 3213, 1701 1598, 1499,1452, 758, 698, 1231. 13C NMR
3.1. Synthesis of racemic CM1
3.1.1. (ꢂ)-2-Amino-1-phenylethanol (5a)
(100 MHz, CDCl3) d 197.4, 177.2, 135.6, 134.7, 133.4, 128.5, 128.4,
To a cold solution of 25% aqueous ammonia (750 mL, 11.3 mol) in
methanol (200 mL), styrene oxide 3(12 mL, 0.11 mol) was added. The
mixture was sealed and kept at 4 ꢁC for 15 days. The solution was
concentrated to give a yellow oily residue (24.5 g). It was acidified to
pH z 1 with aqueous hydrochloric acid (100 mL, 2 mol/L) and
extracted with CH2Cl2. The water layer was alkalized with aqueous
NaOH solution (50 mL, 4 mol/L) to pH z 12 and extracted with CH2Cl2
(50 mL ꢃ 6). The combined organic layer was washed with brine
(50 mL), dried over sodium sulfate and concentrated to give pale
yellow oil (12.2 g). The residue was purified with flash chromatog-
raphy on silica gel eluted with EtOAc/methanol/aqueous ammonia
(200/6/7.5) to afford the title compound as pale yellow solid (3.52 g),
128.1, 128.0, 127.8, 72.7, 59.7, 52.8. HRMS (QFT-ESI): calculated for
C19H16N1O3 (MHþ) 282.1125, found 282.1129.
Compound 10a: mp: 211e215 ꢁC, 1H NMR (300 MHz, CDCl3) 3.36
(1H, dd, J ¼ 8.4, 8.1 Hz), 4.65 (1H,d, J ¼ 8.4 Hz), 5.16 (1H, d,
J ¼ 8.1 Hz), 7.01e7.57(10H, m). ESI-MS (m/e,%): 563(2MHþ, 23), 282
(55), 158(100).
3.1.5. (ꢂ)-N-Benzyl-2-hydroxy-2-phenyl-ethylamine (5b)
The mixture of benzylamine 4b (50 mL, 0.45 mol) and styrene
oxide 3 (12 mL, 0.102 mol) was sealed and kept at room temperature
for 7 days. The precipitated solid was collected by suction, washed
with cold ether, and dried to afford title compound as a white solid
yield: 66.5%, mp: 60e63 ꢁC,1H NMR (300 MHz, CDCl3)
d
2.81, 2.97(2H,
(2.97 g), yield: 41%, mp 97e97 ꢁC, 1H NMR (300 MHz, CDCl3)
d 2.70,
ddd (AB part of an ABX system), J ¼ 12.9, 7.8, 4.2 Hz, C2H), 4.64(1H, dd
2.98 (2H, ddd (AB part of an ABX system), J ¼ 12.6, 7.8, 4.2 Hz), 4.64
(1H, dd (X part of an ABX system), J ¼ 7.8, 4.2 Hz), 7.24e7.37 (5H, m).
ESI-MS (m/e, 100): 250(MNaþ, 17), 228(MHþ, 100), 210(82).
(XpartofanABXsystem),J¼ 7.8, 4.2Hz, C1H),7.23e7.37(5H, m, Ph-H).
3.1.2. (ꢂ)-N-(2-Hydroxy-2-phenylethyl)-3-phenyl-glycidyl amide
(7a)
3.1.6. (ꢂ)-N-Benzyl-N-(2-hydroxy-2-phenylethyl)-3-phenyl-
glycidyl amide (7b)
To a cold solution of 5a (5.0 g, 34.6 mol) in methanol (18 mL),
methyl 3-phenyl-glycidate 6 (12 mL, 0.11 mol) was added. After the
reactants were dissolved, a solution of sodium methoxide in
methanol (3 mol/L, 3 mL) was introduced. The mixture was sealed
and kept at ꢀ20 ꢁC for 7 days. The precipitate was filtered off by
suction, washed with cold methanol, and recrystallized from
ethanol to yield the title compound (6.44 g) as a white solid, yield:
To a suspension of 5b (7.45g, 32.8 mmol) and methyl 3-phenyl-
glycidate 6 (6.42 g, 36.0 mol) in absolute methanol (18 mL),
a solution of sodium methoxide in methanol (1.6 mol/L 12 mL) was
added. The mixture was sealed and kept at ꢀ20 ꢁC for 7 days. The
precipitate was collected and washed with cold methanol to yield
title compound as a white solid (31.21 g), yield: 66%. A sample was
recrystallized from alcohol for analysis, mp: 158e159 ꢁC, 1H NMR
62%, mp: 143e146 ꢁC, 1H NMR (300 MHz, CDCl3)
J ¼ 1.8 Hz), 3.37e3.47(1H, m), 3.67e3.80 (1H, m), 3.78,3.81(1H,
d þ d, J ¼ 1.8 Hz), 4.89(1H, dd, J ¼ 3.0,5.1 Hz), 7.22e7.42(10H, m, Ph-
H). ESI-MS (m/e, %): 306(MNaþ, 80), 284 (MHþ, 30), 266(100).
d
3.53 (1H, d þ d,
(300 MHz, CDCl3),
d
3.63, 3.95 (1H, d þ d, J ¼ 1.8 Hz), 4.07, 4.10 (1H,
d þ d, J ¼ 1.8 Hz), 3.37e3.79 [2H, m (two AB part of ABX system)],
4.83e5.04 (1H, d þ d (two X part of ABX system), J ¼ 8.1, 3.0 Hz)
4.48e4.83 (2H, two AB system, J ¼ 16.2 Hz, J ¼ 14.1 Hz), 7.11e7.38
(15H, m). ESI-MS (m/e,%): 769 (2MNaþ, 45), 396 (MNaþ, 100), 374
(MHþ, 14).
3.1.3. (ꢂ)-N-(2-Oxo-2-phenylethyl)-3-phenyl-glycidyl amide (8a)
To a solution of 7a (1.4 g, 5.0 mmol) in methylene chloride
(52 mL), potassium permanganate powder (200 mesh, 2.34 g,
14.8 mmol) and copper sulfate powder (200 mesh, 1.18 g, 7.4 mmol)
were added. The mixture was stirred at room temperature for 24 h
and then filtrated with the aid of Celite. The filtrate was concen-
trated to give a pale yellow oil (900 mg). The oil was recrystallized
from ethanol to give the title compound as a white solid (464 mg),
3.1.7. (ꢂ)-N-Benzyl-N-(2-oxo-2-phenylethyl)-3-phenyl-glycidyl
amide (8b)
To a solution of 7b (18.2 g, 64.1 mmol) in methylene chloride
(750 mL), potassium permanganate powder (30.3 g, 0.192 mol) and
copper sulfate powder (15.4 g, 0.096 mol) were added. The mixture
was stirred at room temperature for 12 h and then filtrated with the
aid of Celite. The filtrate was concentrated to give a pale yellow oily
residue (21.5 g), which was precipitated from ether, mp: 141e143 ꢁC,
yield: 34%, mp:140e143 ꢁC, 1H NMR (300 MHz, CDCl3)
d 3.60(1H, d,
J ¼ 2.1 Hz), 4.04 (1H, d, J ¼ 2.1 Hz), 4.83, 4.81(2H, AB part of an ABX
system, J ¼ 19.8, 5.1, 4.5 Hz), 7.23e8.01(11H, m, Ph-H and NeH). ESI-
MS (m/e,%): 304(MNaþ, 100), 282(45).
yield:88%.1HNMR(300 MHz, CDCl3)
d
4.09, 4.14(1H,dþ d, J¼ 1.2 Hz),
3.53, 3.79(1H, d þ d, J ¼ 1.2 Hz), 4.70, 4.77 and 4.78, 4.80 (2H, two AB
system, J¼ 15.0,18.6Hz), 4.70, 4.97 and4.70, 4.83(2H, twoABsystem,
J ¼ 17.4 Hz, J ¼ 17.1 Hz), 7.01(15H, m). ESI-MS (m/e,%): 394 (MNaþ, 46),
372(MHþ, 100).
3.1.4. Intramolecular cyclization of (ꢂ)-N-(2-oxo-2-phenylethyl)-3-
phenyl-glycidyl amide (8a)
To a solution of 8a (154 mg, 0.614 mmol) in methanol (4 mL) and
water (2 mL), LiOH$H2O (26 mg, 0.60 mmol) was added. The
mixture was heated to 60 ꢁC for 40 min. TLC analysis showed that
the reactant had been consumed and complicated products formed.
The mixture was cooled to room temperature, neutralized with
diluted hydrochloric acid (2 mol/L), and concentrated under
vacuum to remove methanol. The oily residue was dissolved in
methylene dichloride (30 mL), washed with water and brine, dried
over sodium sulfate, and concentrated to afford a pale yellow oil
3.1.8. (ꢂ)-(3S*,4R*,5R*)-5-Benzoyl-3-hydroxy-1-benzyl-4-
phenylpyrrolidin-2-one (N-benzyl-demethyl-Clausenamidone, 9b)
and (ꢂ)-(3S*,4R*,5S*)-5-benzoyl-3-hydroxy-1-benzyl-4-
phenylpyrrolidin-2-one (N-benzyl-demethyl-neoclausenamide, 10b)
To a suspension of 8b (7.00 g, 18.8 mmol) in methanol (250 mL)
and water (170 mL), LiOH$H2O (160 mg, 3.8 mmol) was added. The
mixture was stirred at room temperature for 48 h. It was neutral-
ized with diluted hydrochloric acid (2 mol/L), and concentrated
under vacuum to remove methanol. The solid was collected by
filtration, washed with water, and dried to give a white solid
(6.88 g), which was separated by chromatography on silica gel
(ethyl acetate/petroleum ether/methylene dichloride, 2/2/1) to give
(142
mg).
(ꢂ)-(3S*,4R*,5R*)-5-benzoyl-3-hydroxy-4-phenyl-
pyrrolidin-2-one (demethyl-Clausenamidone, 9a) (8 mg, yield: 5%)
and (ꢂ)-(3S*,4R*,5S*)-5-benzoyl-3-hydroxy-4-phenylpyrrolidin-2-
one (demethyl-Clausenamidone, 10a) (56 mg, 36%) were finally
separated by preparative thin-layer chromatography.

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XingZhou Li et al. / European Journal of Medicinal Chemistry 45 (2010) 5531e5538
compounds 9b (2.66 g, 38% yield) and 10b (2.52 g, 36% yield). 1.4 g
of unseparated 9b and 10b was recovered.
128.3, 128.1, 127.9, 127.7, 114.2, 71.8, 61.2, 55.2, 51.2, 54.7. ESI-MS
(m/z, 100) 475 (MNaþ, 30), 402 (MHþ, 100). HRMS (QFT-ESI):
calculated for C25H23Na1N1O4 (MNaþ) 424.1519, found 424.1525.
Compound 10c: mp: 155e157 ꢁC, 1H NMR (300 MHz, CDCl3)
Compound 9b: mp: 182e185 ꢁC, 1H NMR (300 MHz, CDCl3)
d
3.75 (1H, dd,
J
¼
9.9, 5.7 Hz), 3.78, 5.19 (AB system,
J ¼ 15.0 Hz),5.06 (1H, d, J ¼ 9.9 Hz), 5.20 (1H, d, J ¼ 5.7 Hz),
6.99e7.46 (10H, m). FAB-MS (m/e, %): 372 (MHþ, 100) 266 (5), 105
(40), 91(50), 77(5). HRMS (QFT-ESI): calculated for C24H22N1O3
(MHþ) 372.1594, found 372.1598.
d
3.25(1H, dd, J ¼ 6.3, 6.3 Hz) 3.75 (3H, s) 3.81, 5.25 (2H, AB system,
J ¼ 14.4 Hz), 4.49 (1H, d, J ¼ 6.3 Hz) 4.83 (1H, d, J ¼ 6.3 Hz) 6.73e7.51
(10H, m, Ph-H). ESI-MS (m/z,100) 475(MNaþ,22), 402(MHþ,100).13
NMR (100 MHz, CDCl3) 198.1,175.4,159.5,136.5,134.1,133.5,130.4,
C
d
Compound 10b: mp: 154e156 ꢁC, 1H NMR (300 MHz, CDCl3)
128.5, 128.3, 128.0, 127.8, 126.9, 72.0, 61.4, 53.4, 55.4, 51.3, 45.8. ESI-
MS (m/z,100) 475 (MNaþ, 24), 402(MHþ, 100). HRMS (QFT-ESI):
Calculated for C25H23Na1N1O4 (MNaþ) 424.1519, found 424.1524.
d
3.27(1H, dd, J ¼ 6.6 Hz, 6.3 Hz), 3.94, 5.33 (2H, AB system,
J ¼ 14.4 Hz), 4.52 (1H, d, J ¼ 6.6 Hz), 4.84 (1H, d, J ¼ 6.3 Hz),
7.01e7.50 (10H, m). FAB-MS (m/e,%): 372(MHþ, 100) 266 (10), 105
(30), 91(60), 77(5).
3.1.13. (ꢂ)-(3S*,4R*,5R*)-5-Benzoyl-3-hydroxy-4-phenylpyrrolidin-
2-one (demethyl-Clausenamidone, 9a)
3.1.9. (ꢂ)-N-(4-Methoxybenzyl)-2-hydroxy-2-phenyl-ethylamine (5c)
Compound 5c was obtained by a similar procedure used for the
preparation of 5b except using 4c instead of 4b as reactant. Yield
To a solution of 9c (515 mg,1.33 mmol) in acetonitrile (18 mL) and
water (6 mL), cerium ammonium nitrate (2.90 g, 5.29 mmol) was
added. After stirringat room temperature for 25min, the mixturewas
poured into water (150 mL) and extracted with ethyl acetate
(40 mL ꢃ 4). The organic phase was washed with sat. aq. sodium
bicarbonate (20 mL ꢃ 2), dried over sodium sulfate, and concentrated
to give a filemot oil (422 mg). The crude oil was purified by chroma-
tography on silica gel (methylene dichloride/methanol, 100/1) to
afford a white solid (287 mg, 77%), mp: 149e152 ꢁC. The 1H NMR and
MS data were identical with that of compound 9a prepared from 8a.
66%, mp: 107e109 ꢁC 1H NMR (300 MHz, CDCl3):
d 2.74, 2.91 (2H,
AB part of ABX system, J ¼ 12.0, 8.7 Hz), 4.72(1H, X part of ABX
system, J ¼ 8.7H), 3.80 (5H, m), 6.85e7.32 (9H, m). ESI-MS
(m/e,100): 280 (MNaþ, 8), 258(MHþ,90), 121(100). HRMS (QFT-ESI):
calculated for C16H20N1O2 (MHþ) 258.1488, found 258.1490.
3.1.10. (ꢂ)-N-(4-Methoxybenzyl)-N-(2-hydroxy-2-phenylethyl)-3-
phenyl-glycidyl amide (7c)
Compound 7c was obtained by a similar procedure used for the
preparation of 7b except using 5c instead of 5b as reactant. Yield:
86%. A sample was recrystallized from alcohol for analysis. mp:
3.1.14. (ꢂ)-(3S*,4R*,5R*)-3-Hydroxy-5-((S*)-hydroxy(phenyl)
methyl)-4-phenylpyrrolidin-2-one (demethyl-Clausenamide, 11)
To a solution of 9a (120 mg, 0.427 mmol) in methanol (10 mL),
sodium borohydride (48 mg, 1.28 mol) was added. The reaction
mixture was stirred at room temperature for 30 min, and then
acidified with dilute hydrochloric acid to pH 3e4. The mixture was
concentrated in vacuum to remove methanol. The residue was dis-
solved with methylene dichloride (40 mL), washed with water, dried
over sodium sulfate, and concentrated for chromatography on silica
gel (methylene dichloride/methanol, 100/2.5) to afford the title
compound (117 mg), yield 96%, mp: 199e201 ꢁC, 1H NMR (300 MHz,
142e146 ꢁC 1H NMR(300 MHz, CDCl3),
d
3.41, 3.54 (1H, d þ d,
J ¼ 1.8 Hz), 3.92, 4.07(1H, d þ d, J ¼ 1.8 Hz), 3.37e4.09(2H, two AB
part of ABX system) 5.10, 4.81(1H, two X part of ABX system) 4.51,
4.67 (2H, two ABX system, J ¼ 16.2 Hz, J ¼ 14.1 Hz), 3.77, 3.80(3H,
s þ s). 6.80e7.36(15H, m), ESI-MS (m/e,100): 426(MNaþ,100), 404
(MHþ,50), 386(15). HRMS (QFT-ESI): calculated for C25H26N1O4
(MHþ) 404.1856, found 404.1859.
3.1.11. (ꢂ)-N-(4-Methoxybenzyl)-N-(2-oxo-2-phenylethyl)-3-
phenyl-glycidyl amide (8c)
Compound 8c was obtained by a similar procedure used for the
preparation of 8b except using 7c instead of 7b as reactant. Yield:
CDCl3):
d
3.72 (1H, dd, J ¼ 9.9, 8.1 Hz), 3.78(1H, d, J ¼ 9.9 Hz), 4.42(1H,
dd, J ¼ 8.1, 3.3 Hz), 4.62(1H, d, J ¼ 3.3 Hz), 6.78e7.33(10H, m); CI-MS
(m/e,%): 284 (MHþ, 68), 266(12), 177(15), 109(74). IR (KBr, cmꢀ1):
3393, 3052, 1703, 1602, 1495,1456, 1264, 1136, 1042, 754, 700. 13C
93%. 1H NMR (300 MHz, CDCl3)
d
2.50, 3.88 (1H, d þ d, J ¼ 1.8 Hz),
NMR (100 MHz, DMSO-d6) d 176.2, 140.8, 136.8, 128.5, 127.8, 127.6,
4.00, 4.08 (1H, d þ d, J ¼ 1.8 Hz), 4.77, 4.62 and 5.68, 4.64 (2H, two
AB system, J ¼ 16.5 Hz, J ¼ 15.0 Hz), 4.95, 5.68 and 5.57, 5.64(2H,
two AB system, J ¼ 18.0 Hz, J ¼ 22.5 Hz), 3.79 (3H, s), 6.80e7.31(14H,
m). ESI-MS (m/e,100): 424(MNaþ,18), 402(MHþ,100). HRMS (QFT-
ESI): calculated for C25H24N1O4 (MHþ) 402.1700, found 404.702.
127.1, 127.0, 126.3, 72.4, 68.6, 59.0, 49.4. HRMS (QFT-ESI): calculated
for C17H18N1O3 (MHþ) 284.1281.1700, found 284.1286.
3.2. Synthesis of Piracetam analogue 1, Nefiracetam analogue 2
3.2.1. (ꢂ)-(3S*,4R*,5R*)-4-Phenyl-5-((1S*)-phenyl(tetrahydro-2H-
pyran-2-yloxy)methyl)-3-(tetrahydro-2H-pyran-2-yloxy)
pyrrolidin-2-one (3,6-di-O-tetrahydropyranyl-demethyl-
Clausenamide, 12)
A mixture of demethyl-Clausenamide 11 (443 mg, 1.5 mmol),
3,4-dihydropyran (280 mg, 4.5 mmol) and pyridinium p-toluene-
sulonate (38 mg, 0.15 mmol) in methylene dichloride (10 mL) was
stirred at room temperature overnight. The mixture was then
diluted with methylene dichloride (10 mL), washed with aqueous
sodium chloride, dried over anhydrous sodium sulfate, and
concentrated to give the title compound as a mixture of diaste-
reomers (0.51 g,), yield: 90%, mp: 181e187 ꢁC. ESI-MS (m/e,%): 474
(MNaþ, 100), 452 (MHþ, 33).
3.1.12. (ꢂ)-(3S*,4R*,5R*)-5-Benzoyl-3-hydroxy-1-(4-
methoxybenzyl)-4-phenylpyrrolidin-2-one (N-(4-methoxybenzyl)-
demethyl-Clausenamidone, 9c) and (ꢂ)-(3S*,4R*,5S*)-5-benzoyl-3-
hydroxy-1-(4-methoxybenzyl)-4-phenylpyrrolidin-2-one (N-(4-
methoxybenzyl)-demethyl-neoclausenamide, 10c)
To a solution of 8c (2.48 g, 6.17 mmol) in methanol (40 mL) and
water (5 mL), LiOH$H2O (52 mg,1.24 mmol) was added. The mixture
was stirred at room temperature for 25 min, and then neutralized
with diluted hydrochloric acid (2 mol/L), concentrated under
vacuum to remove methanol. The residue was dissolved in methy-
lene dichloride (60 mL), washed with water, dried over sodium
sulfate, and concentrated for chromatography on silica gel (ethyl
acetate/petroleum ether/methylene dichloride, 2/2/1). Compounds
9c (1.05 g, 42% yield) and 10c (1.10 g, 45% yield) were obtained.
3.2.2. (ꢂ)-Ethyl 2-((3S*,4R*,5R*)-3-hydroxy-5-((S*)-hydroxy
(phenyl)methyl)-2-oxo-4-phenyl pyrrolidin-1-yl)acetate (N-
ethoxycarbonyl-methyl-demethyl-Clausenamide, 13)
To a solution of 12 (120 mg, 0.266 mol) in anhydrous benzene
(5 mL), sodium hydride (21 mg) was added. The mixture was
Compound 9c: mp: 152e154 ꢁC,1H NMR (300 MHz, CDCl3)
d 3.71
(1H, dd, J ¼ 10.8, 8.7 Hz) 3.76, 5.19 (2H, AB system, J ¼ 14.4 Hz) 5.04
(1H, d, J ¼ 10.8 Hz) 5.16 (1H, d, J ¼ 8.7 Hz) 6.80e7.39 (10H, m). 13C
NMR (100 MHz, CDCl3) d197.9, 174.9, 174.7, 159.4, 133.3, 130.2, 128.4,

XingZhou Li et al. / European Journal of Medicinal Chemistry 45 (2010) 5531e5538
5537
refluxed for half an hour. After cooling to room temperature,
a solution of ethyl bromoacetate (66 mg) in dried benzene (5 mL)
was added. The mixture was heated at 60 ꢁC for 20 min and then
cooled to room temperature, followed by the addition of water
(3 mL) and neutralization with hydrochloric acid (2 N). The resulted
mixture was extracted with methylene chloride. The organic layer
was separated, washed with brine, dried over anhydrous sodium
sulfate, and concentrated to an oily product.
To the alcoholic solution (5 mL) of the oily product, p-toluene-
sulfonic acid (10 mg) was added. The mixture was heated at 60 ꢁC
overnight. It was then concentrated for column chromatography
(methylene dichloride/methanol, 100/1) to obtain the oily title
compound (79 mg, 82%). 1H NMR (300 MHz, CDCl3) 1.27(3H, t,
J ¼ 7.2 Hz), 3.85 (1H, dd, J ¼ 11.1, 8.4 Hz), 4.03, 4.39 (2H, AB system,
J ¼ 18.0 Hz), 4.24 (1H, d, J ¼ 11.1 Hz), 4.22 (2H, q, J ¼ 7.2 Hz), 4.43(1H,
dd, J ¼ 8.4, 3.6 Hz), 4.78 (1H, d, J ¼ 3.6 Hz), 6.76e7.31 (10H, m). 13C
NMR (100 MHz, CDCl3) 175.6, 169.26, 138.6, 134.5, 128.5, 128.4,
128.1, 128.0, 127.3, 126.9, 73.5, 69.2, 64.5, 61.7, 50.0, 44.8, 14.1. FAB-
MS (m/e, %) 370(MHþ, 52), 352(83), 334(12), 324(17), 278 (35), 105
(64), 91(100), 77(25). HRMS (QFT-ESI): calculated for C21H24N1O5
(MHþ) 370.1649, found 370.1650.
the title compound as a white solid (54 mg). Yield 73%, mp:
199e201 ꢁC, 1H NMR (300 MHz, CD3COCD3)
d
3.58(1H dd J ¼ 11.7,
8.4 Hz), 3.82(1H, d, J ¼ 11.7), 4.58 (1H, dd, J ¼ 8.4, 2.7 Hz), 4.69 (1H,
d, J ¼ 2.7 Hz), 5.10, 5.15(2H, AB system), 6.67e7.25(10H, m). 13C
NMR (100 MHz, Acetone-d6) d 176.8, 141.7, 137.9, 129.5, 128.9, 128.6,
128.4, 128.2, 127.5, 73.9, 70.5, 60.5, 51.0. FAB-MS (m/e,%): 314 (MHþ,
98), 296(100), 284(20), 266(20). IR (KBr, cmꢀ1): 3456, 3348, 3028,
1703, 1475, 1447, 1265, 1151, 1061, 1016, 756, 747, 693. Element
Analysis: C18H19N1O4 Found C: 68.81, 68.75, H: 5.81, 6.01 N: 4.66,
4.52 for C: 68.88, H: 6.11, N: 4.47. HRMS (QFT-ESI): calculated for
C18H20N1O4 (MHþ) 314.1399, found 314.1387.
3.3.2. (ꢀ)-(3S,4R,5R)-5-Benzoyl-3-(phthalyl-
methoxybenzyl)-4-phenylpyrrolidin-2-one (14a) and
(þ)-(3R,4S,5S)-5-benzoyl-3-(phthalyl- -alanyloxy)-1-(4-
methoxybenzyl)-4-phenylpyrrolidin-2-one (14b)
L-alanyloxy)-1-(4-
L
(1) To
a stirred solution of the phthalyl-L-alanine (1.71 g,
7.78 mmol) in toluene (20 mL) was added thionyl chloride
(3.71g, 31.2 mmol) at room temperature. The mixture was
heated to reflux for 2 h and then cooled to room temperature. It
was concentrated in vacuo to afford the phthalyl-L-alanyl
chloride as pale-yellow oil.
3.2.3. (ꢂ)-N-(2,6-Dimethylphenyl)-2-((3S*,4R*,5R*)-3-hydroxy-5-
((S*)-hydroxy(phenyl)methyl)-2-oxo-4-phenylpyrrolidin-1-yl)
acetamide {N-[N-(2,6-dimethylphenyl)-aminocarbonyl-methyl]-
demethyl-Clausenamide, 2}
(2) To a stirred solution of 9c (2.60 g, 6.49 mmol) in methylene
chloride (20 mL) was added a solution of phthalyl- -alanyl
L
chloride in methylene chloride (20 mL) in one portion. The
mixture was cooled to 0 ꢁC, a solution of dried pyridine (0.77 g,
9.47 mmol) in methylene chloride (20 mL) was added drop-
wise. The resultant mixture was allowed to warm to room
temperature and stirred for 3 h. Water (40 mL) was added to
quench the reaction. The aqueous layer was separated and
extracted with dichloromethane (10 mL). The combined
organic extracts were washed with dilute hydrochloric acid
(2 mol/L), sat. aq. sodium bicarbonate and brine, dried over
anhydrous sodium sulfate, and concentrated in vacuo to afford
the title compounds mixture as a pale yellow oily residue
(4.35 g), crude yield 96%. It was recrystallized from ethyl
Compound 2 was prepared as described for compound 13, with
2-bromo-N-(2,6-dimethylphenyl)acetamide instead of ethyl bro-
moacetate as the alkylating agent. mp: 242e245 ꢁC, yield:51%, 1H
NMR(500 MHz, DMSO-d6): 3.64 (1H, dd, J ¼ 11.5, 8.5 Hz), 3.92 (1H,
d, J ¼ 11.5 Hz), 4.47 (1H, dd, J ¼ 8.4, 2.5 Hz) 4.69(1H, d, J ¼ 2.5 Hz),
4.32, 4.62(2H, AB system, J ¼ 16.5 Hz) 6.67e7.25(13H, m) 9.44(1H, s,
exchangeable), 2.20 (6H, s). 13C NMR (100 MHz, CD3COOD)
d 177.3,
169.0, 140.5, 136.4, 136.1, 134.6, 129.3, 128.7, 128.6, 128.3, 128.1,
128.0, 127.5, 73.9, 70.1, 65.4, 50.5, 46.5. FAB-MS (m/e,%) 445 (MHþ,
93), 427 (26), 91(100). HRMS (QFT-ESI): calculated for C27H29N2O4
(MHþ) 445.2122, found 445.2125.
acetate twice to provide 789 mg (18%) of (3S,4R,5R)-14a, mp:
25
3.2.4. (ꢂ)-2-((3S*,4R*,5R*)-3-Hydroxy-5-((S*)-hydroxy(phenyl)
methyl)-2-oxo-4-phenyl pyrrolidin-1-yl) acetamide [N-
(aminocarbonyl-methyl)-demethyl-Clausenamide, 1]
173e175 ꢁC,[
CDCl3)
a
]
D
¼ ꢀ175 (c, 0.460,CHCl3), 1H NMR (300 MHz,
d
1.65(3H, d, J ¼ 7.2 Hz), 3.73 (3H, s), 3.81(1H, dd, J ¼ 8.7,
8.7 Hz), 3.84, 5.09 (2H, AB system, J ¼ 16.2 Hz), 5.07 (1H, d,
Compound 13 (100 mg, 0.252 mmol) was treated with NH3/
CH3OH (10 mL) overnight, then the mixture was concentrated for
column chromatography (methylene dichloride/methanol, 100/2)
to obtain the title compound as a white solid (40 mg). mp:
146e148 ꢁC, yield 72%. 1H NMR (300 MHz, DMSO-d6) 4.07, 4.32
(2H, AB system, J ¼ 5 Hz), 3.61 (1H, dd, J ¼ 11.0, 8.5 Hz), 3.89 (1H,
dd, J ¼ 11.0, 6.5 Hz), 4.01 (1H, dd, J ¼ 8.5, 2.0 Hz), 4.63 (1H, s) 5.45
(1H, d, J ¼ 6.5 Hz, exchangeable), 5.60 (1H, d, J ¼ 4.0 Hz,
exchangeable), 6.62e7.24 (10H, m), 7.47, 7.49(2H, 2ꢃ d, J ¼ 2.0 Hz,
exchangeable). FAB-MS (m/e, %) 341 (MHþ, 8), 284(20). 13C NMR
J ¼ 8.7 Hz), 5.01e5.12(1H, m), 6.06 (1H, d, J ¼ 8.7 Hz), 6.67e7.76
(18H, m). 13C NMR(100 MHz, CDCl3)
d 197.0, 169.9, 168.7, 166.9,
159.2, 136.0, 134.0, 133.4, 132.8, 131.7, 130.2, 128.3, 128.2, 127.8,
126.6, 123.4, 114.0, 74.4, 61.3, 55.1, 48.3, 47.3, 45.7, 15.5. ESI-MS
(m/e, %): 603(MHþ, 100). HRMS (QFT-ESI): calculated for
C36H31N2O7 (MHþ) 603.2126, found 603.2129.
3.3.3. (ꢀ)-(3S,4R,5R)-5-Benzoyl-3-(phthalyl-
phenylpyrrolidin-2-one (15a) and (þ)-(3R,4S,5S)-5-benzoyl-3-
(phthalyl- -alanyloxy)-4-phenylpyrrolidin-2-one (15b)
L-alanyloxy)-4-
(100 MHz, CD3COOD)
d
177.3, 172.6, 140.4, 136.1, 129.3, 128.7, 128.2,
L
128.1,127.9,127.4, 73.8, 70.0, 65.2, 50.5, 46.0. HRMS (QFT-ESI):
The crude mixture of 15a and 15b was obtained by a similar
procedure used for the preparation of 9a except using the mixture
of 14a and 14b instead of 9c as reactant. Crude yield: 86%, the crude
products were purified by chromatography on silica gel (methylene
dichloride/ethyl acetate, 4/1). Compounds 15a (30% yield) and 15b
(30% yield) were obtained, respectively. 20% was recovered as
a mixture of 15a and 15b.
calculated for C19H21N2O4 (MHþ) 341.1496, found 341.1500.
3.3. Synthesis of racemic and optical active CM1
3.3.1. (ꢂ)-(3S*,4R*,5R*)-3-Hydroxy-5-((S*)-hydroxy(phenyl)
methyl)-1-(hydroxymethyl)-4-phenyl-pyrrolidin-2-one (CM1)
To a solution of demethyl-Clausenamide 11 (67 mg, 0.24 mmol)
in acetone (2.5 mL) and a drop of water, formaldehyde (11 mg,
0.37 mmol) and K2CO3 (3 mg, 0.09 mmol) were added. The mixture
was heated at 60 ꢁC for 25 min and then quickly cooled to room
temperature with ice and water. Then the mixture was concen-
trated for column chromatography (CH2Cl2/CH3OH 100/2) to obtain
Compound 15a: mp: 186e188 ꢁC, 1H NMR(300 MHz, CDCl3)
d
1.69 (3H, d, J ¼ 7.2 Hz), 4.15(1H, dd, J ¼ 6.6, 2.1 Hz), 5.08(1H, q,
J ¼ 7.2 Hz), 5.27(1H, d, J ¼ 2.1 Hz), 5.41(1H, d, J ¼ 6.6 Hz), 6.39(1H, s),
6.88e7.88(14H, m). 13C NMR (100 MHz, CDCl3)
196.5, 171.9, 168.9,
d
167.0, 135.3, 134.3, 134.1, 133.4, 131.7, 128.3, 128.3, 127.9, 127.8, 127.7,
123.5, 76.5, 60.6, 49.8, 47.4, 15.2. ESI-MS (m/e,%): 505 (MNaþ, 60),

5538
XingZhou Li et al. / European Journal of Medicinal Chemistry 45 (2010) 5531e5538
483 (MHþ, 100). HRMS (QFT-ESI): calculated for C28H22N2Na1O6
(MNaþ) 505.1370, found 505.1376.
0.12 mmol) gave compound (ꢀ)-CM1 (54 mg, 64% yield) as a white
solid, which showed the same Rf value and 1H NMR as racemic
18
Compound 15b: mp: 213e216 ꢁC, 1H NMR (300 MHz, CDCl3)
CM1. mp: 191e193 ꢁC, [
a
]
¼ ꢀ119ꢁ (c ¼ 0.261,CH3OH).
D
d
1.69 (3H, dd, J ¼ 7.2 Hz), 3.57(1H, dd, J ¼ 6.6, 6.3 Hz), 5.00(1H, q,
J ¼ 7.2 Hz), 5.15(1H, d, J ¼ 6.3 Hz), 5.51(1H, d, J ¼ 6.6 Hz), 6.89e7.82
(14H, m). 13C NMR (100 MHz, CDCl3)
195.3, 171.0, 169.2, 167.2,
3.3.7. (þ)-(3R,4S,5S)-3-hydroxy-5-((R)-hydroxy(phenyl)methyl)-1-
(hydroxymethyl)-4-phenylpyrrolidin-2-one ((þ)-CM1)
d
134.9, 134.5, 133.8, 131.8, 128.7, 128.6, 127.9, 127.8, 123.6, 78.3, 62.1,
50.4, 47.4, 15.8. ESI-MS (m/e,%): 505(MNaþ, 63), 483 (MHþ, 100).
HRMS (QFT-ESI): calculated for C28H22N2Na1O6 (MNaþ) 505.1370,
found 505.1376.
Compound (þ)-CM1 was obtained by a similar procedure to that
used for racemic CM1. Treatment of (þ)-11 (78 mg, 0.50 mmol) with
formaldehyde (23 mg, 0.77 mmol) and K2CO3 (7 mg, 0.21 mmol)
gave compound (þ)-CM1 (90 mg, 58% yield) as a white solid, which
showed the same Rf value and 1H NMR as racemic CM1. mp:
18
3.3.4. (þ)-(3S,4R,5R)-3-Hydroxy-5-((S)-hydroxy(phenyl)methyl)-
4-phenylpyrrolidin-2-one (demethyl-Clausenamide, (þ)-11)
189e191 ꢁC, [
a
]
¼ þ117ꢁ (c ¼ 0.394, CH3OH).
D
To a solution of 15b (565 mg, 1.17 mmol) in methanol (6 mL) and
methylene chloride (4 mL), sodium borohydride (67 mg, 1.757 mol)
was added. The reaction mixture was stirred at room temperature
for 30 min. Sodium hydroxide (187 mg, 4.684 mmol) was added. The
mixture was stirred overnight, neutralized with diluted hydro-
chloric acid (2 mol/L), concentrated in vacuum to remove methanol
and methylene chloride. The residue was dissolved with methylene
dichloride (60 mL), washed with water and brine, dried over sodium
sulfate, and concentrated for chromatography on silica gel (methy-
lene dichloride/methanol, 100/2.5) to afford the title compound
Acknowledgments
We are grateful to the National Natural Science Foundation of
China for financial supports and to professor Jun-Tian Zhang and
the group of the neouropharmacological laboratory for affording
LTP assay data.
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D
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3.3.5. (ꢀ)-(3R,4S,5S)-3-Hydroxy-5-((R)-hydroxy(phenyl)methyl)-
4-phenylpyrrolidin-2-one (demethyl-Clausenamide, (ꢀ)-11)
Compound (ꢀ)-11 was obtained by a similar procedure used for
the preparation of (þ)-11. Treatment of compound 15a (250 mg,
0.52 mmol) with sodium borohydride (30 mg, 0.78 mmol), and
sodium borohydride (83 mg, 2.08 mol) gave compound (ꢀ)-11
(87 mg, 60% yield) as a white solid, which showed the same Rf value
15
and 1H NMR as racemic 11. mp: 203e205 ꢁC, [
(c ¼ 0.497, methanol).
a]
¼ ꢀ144ꢁ
D
3.3.6. (ꢀ)-(3S,4R,5R)-3-Hydroxy-5-((S)-hydroxy(phenyl)methyl)-
1-(hydroxymethyl)-4-phenylpyrrolidin-2-one [(ꢀ)-CM1]
Compound (ꢀ)-CM1 was obtained with the same procedure as
described for racemic CM1. Treatment of (ꢀ)-11 (78 mg, 0.28 mmol)
with formaldehyde (13 mg, 0.43 mmol) and K2CO3 (4 mg,