Design and synthesis of novel chloramphenicol amine derivatives as potent aminopeptidase N (APN/CD13) inhibitors

Article abstract of DOI:10.1016/j.bmc.2009.04.038

Herein we report a series of novel chloramphenicol amine derivatives as aminopeptidase N (APN)/CD13 inhibitors. All compounds were synthesized starting from commercially available (1S,2S)-2-amino-1-(4-nitrophenyl) propane-1,3-diol. The preliminary biologi

Full text of DOI:10.1016/j.bmc.2009.04.038

Bioorganic & Medicinal Chemistry 17 (2009) 3810–3817
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Design and synthesis of novel chloramphenicol amine derivatives
as potent aminopeptidase N (APN/CD13) inhibitors
a
a
b
Kanghui Yang a, Qiang Wang a, Li Su a, Hao Fang a, , Xuejian Wang , Jianzhi Gong , Binghe Wang , Wenfang
*
Xu a,
*
a Department of Medicinal Chemistry, School of Pharmacy, Shandong University, 44 West Culture Road, Ji’nan, Shandong 250012, China
b Department of Chemistry, Georgia State University, Atlanta, 30303, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein we report a series of novel chloramphenicol amine derivatives as aminopeptidase N (APN)/CD13
inhibitors. All compounds were synthesized starting from commercially available (1S,2S)-2-amino-1-(4-
nitrophenyl) propane-1,3-diol. The preliminary biological screening showed that some compounds
exhibited potent inhibitory activity against APN. It should be noted that one compound, 13b
Received 16 March 2009
Revised 17 April 2009
Accepted 18 April 2009
Available online 24 April 2009
(IC50 = 7.1 lM), possess similar APN inhibitory activity compared with Bestatin (IC50 = 3.0 lM).
Ó 2009 Published by Elsevier Ltd.
Keywords:
Synthesis
Aminopeptidase N
Chloramphenicol amine
Inhibitor
QSAR
1. Introduction
xyl-4-phenylbutanoic acid) is a common scaffold in many natural
APN inhibitors. The co-crystal complex of APN and Bestatin
(AHPA-Leu) from Escherichia coli indicated that the hydroxyl and
carbonyl belong to zinc binding group (ZBG). The phenyl ring in
AHPA fragment can insert into S1 pocket and amino group in AHPA
can interact with Glu 350 (Fig. 1).
Aminopeptidase N (APN/CD13) is a Zn2+-dependent metalloec-
topeptidase existing in a wide variety of human tissues and cell
lines (endothelial, epithelial, fibroblast, leukocyte, etc.).1 APN
expression is dysregulated in inflammatory diseases and in cancers
(solid and hematologic tumors). APN is also a receptor for coronav-
iruses, the pathogenesis of upper respiratory infection. In recent
years, the identification of activities of anti-APN/CD13 monoclonal
antibody and natural/synthetic APN inhibitors suggests that APN
plays a crucial role in modulating bioactive peptide responses
(pain management, vasopressin release) and in influencing im-
mune functions and major biological events (cell proliferation,
secretion, invasion, angiogenesis).2 Therefore, the development of
APN inhibitors may be of clinically significance for the discovery
of anti-cancer and anti-inflammatory agents.
For most APN inhibitors reported in literatures, so far there are
four possible binding sites, including a zinc binding group (ZBG),
two hydrophobic groups interacting with the S1 and S01 subsites
in APN, and one appropriate group interacting with the S02 subsite
surrounded by several Arg residues.3–5 It should be emphasized
that among these four sites, at least three ones are necessary for
a potent inhibitor. For example, AHPA ((2S,3R)-3-amino-2-hydro-
Our group has previously reported several kinds of new APN
inhibitors, such as
tuted 2,6-piperidinedione-N-acetamide
L
-lysine derivates6, 3-galloylamido-N0-substi-
peptidomimetics7,
1,3,4-thiadiazole derivates8, and AHPA (b-amino-
a-hydroxyl-phe-
nylbutanoic acid) derivates.9 In our recent screening, compound
(2R,3S)-2-amino-3-hydroxy-3-(4-nitrophenyl)propanoic acid (1,
His
387
His
S2'
Glu
406
383
S1
Zn2+
O
Glu 350
COOH
H3N
N
H
OH
S1'
Figure 1. The binding mode of bestatin to the active sites of APN.
* Corresponding authors. Tel./fax: +86 531 88382264 (W.X.).
E-mail addresses: haofangcn@sdu.edu.cn (H. Fang), xuwenf@yahoo.cn, wfxu@
yahoo.cn (W. Xu).
0968-0896/$ - see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.bmc.2009.04.038

K. Yang et al. / Bioorg. Med. Chem. 17 (2009) 3810–3817
3811
AHNPA) developed from commercially available chloramphenicol
amine 2, exhibited a moderate APN inhibition (IC50 = 140.2 M).
by NaOH/H2O in methanol, and then converted into target com-
pounds 8a–8b, 10a–10e, and 13a–13b by deprotecting Boc group.
Compounds 11a–11b containing hydroximic acid groups were ob-
tained from 9a–9b by reacting with NH2OK and then cleaving Boc.
l
Considering the structural similarity between compound 1 and
AHPA, this molecule could act as a new lead compound for further
chemical modification and optimization. Therefore, different amino
acids and other functional groups can be coupled with compound 1
to generate diverse dipeptide and tripetide derivatives. In this arti-
cle, we would like to describe the synthesis, enzymatic evaluation
and possible binding mode of the chloramphenicol amine derivates.
3. Results and discussion
All the target compounds were tested for their inhibition
against APN as listed in Table 1. As a result, the structural addition
of different alkylamine, simple benzylamine and phenethylamine
can not significantly enhance the inhibitory activity compared
2. Chemistry
with parent compound AHNPA (IC50 = 140.2 lM). It seems that
The synthetic route of target compounds is shown in Schemes 1
and 2. Chloramphenicol amine (1S,2R)-2-amino-1-(4-nitro-
phenyl)propane-1,3-diol, 2) was firstly protected by (Boc)2O, then
was selectively oxidized at the terminal hydroxyl group to give the
N-Boc-protected acid 4.10 The compound 4 was easily deprotected
with 3 N HCl in EtOAc to provide product 1. The key intermediate 4
can be coupled with different substituted amine by classical EDCI/
HOBt method, and then converted into compound 6a–6m after
deprotection. Using the same procedure, different moieties, such
the substitution of phenyl ring in phenethyl group of R position
can slightly contribute to the affinity. For example, para-hydroxy
substitution shows up to 50 lM IC50 value.
On the other hand, the incorporation of natural amino acids
would generate compounds with similar or better inhibitory activ-
ities compared with parent compound AHNPA, while
x amino acid
derivative showed very poor inhibition (Table 2). These results
suggest that the introduction of natural amino acids to AHNPA
scaffold would be better than of simple nonpeptide fragment. As
a zinc binding group (ZBG), hydroximate group has been used in
many enzyme inhibitors especially Zn2+-dependent enzyme to im-
prove affinity.11 In our case, the AHNPA-amino acid derivatives can
as
x-amino acids, natural a-amino acids and dipeptides, were cou-
pled with intermediate 4 to obtain AHNPA derivatives 7a–7b, 9a–
9e, 12a–12b. Finally, the esters were hydrolyzed to carboxylic acid
O2N
O2N
Boc
O2N
Boc
O2N
NH2
NH
NH
NH2
c
b
a
OH
OH
OH OH
OH OH
OH
O
OH
O
2
3
4
1
Scheme 1. Reagents and conditions: (a) (Boc)2O/THF; (b) 13% w/w NaOCl, 5% NaHCO3,TEMPO/CH3COCH3, H2O, 0 °C; (c) HCl/anhydrous EtOAc, Na2CO3.
O2N
NH2
O2N
Boc
H
N
NH
b
H
N
R1
R1
OH
O
OH
O
6a-m
5a-m
R1
-
H 2
N
a
O2N
Boc
O2N
O2N
NH
O
n
NH2
O
n
H
N
c
H
N
H
3
C
O
OCH3
O
C
(
OH
OH
n-
a
)
H2
4)
,
C
(
-
3
=
n
OH
O
H
N
2
OH
O
8a-b
O2N
Boc
NH
7a-b
OH
a
OH
O
c
NH2
O
R2
H
HCl
O2N
Boc
4
N
NH
O
OCH3
H
N
H2N
NH2
OH
O
R2
O
HCl
R4
OCH3
O
10a-e
OH
O
R2
a
d
HN
O
O2N
9a-e
R3
NH2
O
H
N
OH
N
OCH3
O2N
H
OH
11a-b
R3
O
R2
Boc
O
HN
O
R3
O2N
H
N
NH2
O
OCH3
H
N
N
H
c
OH
N
H
OH
R4
O
OH
O
R4
13a-b
O
12a-b
Scheme 2. Reagents and conditions: (a) EDCI, HOBt/anhydrous THF, 0 °C to room temperature; (b) HCl/anhydrous EtOAc, Na2CO3; (c) (i) 4% NaOH/CH3OH; (ii) HCl/anhydrous
EtOAc, Na2CO3; (d) (i) NH2OKa/anhydrous CH3OH; (ii) HCl/anhydrous EtOAc, Na2CO3.

3812
K. Yang et al. / Bioorg. Med. Chem. 17 (2009) 3810–3817
Table 1
Table 2
The structure and inhibitory activities of compounds 6a–6m, 8a–8b against APN
The structure and inhibitory activities of AHNPA-amino acid and AHPNPA-dipeptide
derivatives against APN
O2N
NH2
H
O2N
NH2
O
N
R
H
N
R2
OH
O
OH
O
R1
Compound
R
APN/IC50 (lM)
Compound
R1
R2
APN/IC50
85.6
(lM)
6a
6b
6c
6d
–CH2CH2CH3
–CH2(CH3)2
–CH2CH2CH3
–CH2CH2CH3
183.2
250.7
232.6
521.7
10a
–OH
–OH
–OH
–OH
–OH
6e
251.3
169.9
302.5
144.7
106.3
136.8
51.4
10b
10c
10d
10e
11a
11b
60.4
6f
159.9
102.8
162.2
54.0
6g
6h
6i
F
OCH3
HN
–NHOH
–NHOH
6j
31.3
Cl
6k
6l
O2N
NH2
O
OH
H
N
13a
34.6
7.10
3.00
OH
N
H
116.3
90.3
OH
O
O
O
OH
O
O
6m
8a
8b
O2N
NH2
O
H
N
OH
13b
O
N
H
2891.2
1388.6
OH
O
OH
O
OH
NH2
O
Bestatin
also enhance their activity after converting terminal carboxylate to
hydroximate group. For instance, compounds 11a and 11b shows
more potent inhibition than compounds 10a and 10b.
OH
N
H
OH
O
The enzyme inhibitory results unveiled that AHNPA-dipeptide
derivative 13b shows the best inhibition among all target com-
pounds. This phenomenon suggests that the dipeptide side chain
would be helpful to increase the interaction with APN binding
sites. Furthermore, compounds 13a and 13b were further assessed
on their inhibition against HL-60 cell proliferation by using MTT
method. The IC50 values of these two compounds (13a
2.02 0.13 mM and 13b 2.21 0.11 mM) confirmed again that
their inhibitory activities are similar with Bestatin (1.65
0.09 mM) (Fig. 2).
another phenyl group closed to the AHNPA scaffold could have
interaction with the pocket S01 (Fig. 3). His297, Glu298 and His301
are the essential amino acids of the conserved sequence (HEX-
XHX18E) in the catalytic domain of peptidase M1 family.13 Com-
pound 13b could form hydrogen bonds with these three residues
at the distance of 2.40 Å, 3.06 Å, 2.79 Å, respectively. In addition,
the carboxylate group of 13b could interact with Arg825 and
Tyr381 residue in the S02 pocket by hydrogen bond for stabilizing
the reaction intermediate with the zinc ion14 (Fig. 4).
In order to determine the interaction between AHNPA deriva-
tives and APN, compound 13b was docked into the active sites of
APN (PDB entry: 2DQM) using SYBYL 7.0.12 The docking results
showed that the carbonyl group and amine group of compound
13b could chelate with the zinc ion in APN. The nitrophenyl group
of the 13b could insert to the pocket S1 by forming hydrophobic
interactions with this subsite. The phenyl ring in the terminal ami-
no acid residue could also insert to the pocket S02, in the meantime
4. Conclusions
In summary, we reported the synthesis and biological evalua-
tion of a series of novel chloramphenicol amine derivatives as po-
tent APN inhibitors. Compound 13b is the most active. Among
these compounds, compound 13b not only exhibited similar enzy-
matic inhibition compared with natural APN inhibitor Bestatin, but

K. Yang et al. / Bioorg. Med. Chem. 17 (2009) 3810–3817
3813
determined by the MTT (3-[4,5-dimethyl-2-thiazolyl]-2.5-diphe-
nyl-2H-tetrazolium bromide) assay. Briefly, cells were plated in a
96-well plate at 10,000 cells per well, cultured for 4 h in complete
3
2
1
0
growth medium, then treated with 2000, 1000, 500, 250, 125 lg/
mL of compounds for 48 h. 0.5% MTT solution was added to each
well. After further incubation for 4hr, formazan formed from
MTT was extracted by adding DMSO and mixing for 15 min. Optical
density was read with an ELISA reader at 570 nm.
5.3. Chemistry: general procedures
The starting material 2 is a white powder (mp = 159–162 °C,
½
a 2D5
ꢀ
¼ þ28:3 (c 1, MeOH)), purchased from Wuhan Kaitong Fine
Chemical Co., Ltd, China. Unless otherwise specified, other materi-
als were purchased from commercial suppliers and used without
further purification. Solvents were distilled prior to use and flash
chromatography was performed using silica gel (60 Å, 200 300
mesh).Melting points are uncorrected. Proton nuclear magnetic
resonance (1H NMR) spectra were recorded at either 300 MHz.
Chemical shifts are reported in delta (d) units, parts per million
(ppm) downfield from trimethylsilane. High-resolution mass spec-
tral (HRMS) data are reported as m/e (relative intensity). Elemental
analyses for compounds were performed using an elementar vario
EL III CN analyzer (Germany).
Bes
13a
Compound
13b
Figure 2. Effects of bestatin and compound 13a–13b on the HL-60 cell line
proliferation. Each column represents the mean values with S.E values for five
independent experiments.
5.3.1. N-Protected (1S,2S)(+)-2-amino-1-(4-nitrophenyl)-1,3-
propanediol (3)
To a solution of compound 2 (2.12 g, 10 mmol) in THF (10 mL)
was added dropwise
a solution of di-tert-butyl dicarbonate
(2.93 g, 11 mmol) in THF (5 mL). After 24 h stirring at room tem-
perature the solvent was concentrated under vacuum to leave a
residue. The crude product was recrystallized with EtOAc to give
white solid (2.80 g), yield: 90%, mp = 115–116 °C, ½a D25
¼ þ22:5 (c
ꢀ
1, MeOH). ESI-MS m/z: 313.3 (M+H); 1H NMR (DMSO-d6) d 1.214
(s, 9H), 3.478–3.704 (m, 2H), 4.771–4.790 (m, 1H), 5.607 (d,
J = 5.40, 1H), 6.194 (d, J = 9.00, 1H), 7.564 (d, J = 8.40, 2H), 8.181
(d, J = 8.40, 2H). Anal. Calcd for C14H20N2O6: C, 53.84; H, 6.45; N,
8.97. Found: C, 53.79; H, 6.31; N, 8.77.
Figure 3. The docking result of 13b is showed by SYBYL7.0 (Bestatin in the X-ray
crystal is showed in red).
5.3.2. (2R,3S)-2-(tert-Butoxycarbonylamino)-3-hydroxy-3-(4-
nitrophenyl) propanoic acid (4)
also showed good cell-based inhibitory activity. Therefore, 13b
could be a lead compound to search new chloramphenicol amine
derivatives as APN inhibitors.
To a solution of compound 3 (3.12 g, 10 mmol) in acetone
(50 mL) containing TEMPO (0.16 g, 1 mmol) was added a 5% aque-
ous NaHCO3 solution (50 ml). The mixture was cooled to 0 °C and
NaOCl (20.5 mL, ca. 10% w/w) was added dropwise over 15 min
while following the reaction by TLC. The solution was concentrated
under vacuum to remove acetone. The remaining mixture was
washed with EtOAc (2 ꢁ 10 mL), acidified to pH 1–2 by a 1 N citric
acid solution, extracted with EtOAc (3 ꢁ 20 mL), dried over Na2SO4
and concentrated under reduced pressure. The crude product was
purified by flash column chromatography(DCM/MeOH, 20:1 (V/
V)) to give the desired compound 4 as a white solid (0.97 g), yield:
5. Experimental
5.1. APN inhibition assay
IC50 values against APN were determined by using L-Leu-p-
nitroanilide as substrate and Microsomal aminopeptidase from
Porcine Kidney Microsomes (Sigma) as the enzyme in 50 mM
PBS, pH 7.2, at 37 °C. The hydrolysis of the substrate was moni-
tored by following the change in the absorbance measured at
405 nm with the UV–vis spectrophotometer Pharmacia LKB, Bio-
chrom 4060. All solutions of inhibitors were prepared in the assay
buffer, and pH was neutralized to 7.5 by the addition of 0.1 M HCl
or 0.1 M NaOH. All inhibitors were pre-incubated with APN for
30 min at room temperature. The assay mixture, which contained
the inhibitor solution (concentration dependent on the inhibitor),
30%, mp = 80–82 °C, ½a D25
¼ þ29:1 (c 1, MeOH). ESI-MS m/z: 327.5
ꢀ
(M+H); 1H NMR (DMSO-d6) d 1.224 (s, 9H), 4.344 (dd, J = 9.60,
J = 3.00, 1H), 5.265 (d, J = 3.00, 1H), 6.483 (d, J = 9.60, 1H), 7.658
(d, J = 8.40, 2H), 8.190 (d, J = 8.40, 2H). Anal. Calcd for
C14H18N2O7: C, 51.53; H, 5.56; N, 8.59. Found: C, 51.49; H, 5.62;
N, 8.37.
the enzyme solution (4 lg/mL final concentration), and the assay
buffer, was adjusted to 200 lL.
5.3.3. (2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)propanoic
acid (1)
To a solution of compound 4 (3.26 g, 10 mmol) in dry EtOAc at
0 °C was added dropwise a solution of EtOAc (10 mL) saturated
with dry HCl gas. The reaction solution was stirred at 0 °C for
2 h, and then the temperature is raised to room temperature and
the reaction proceeds for 5 h before being concentrated in vacuo.
5.2. MTT assay
HL-60 Cell was grown in RPMI1640 medium containing 10% FBS
at 37 °C in 5% CO2 humidified incubator. Cell proliferation was

3814
K. Yang et al. / Bioorg. Med. Chem. 17 (2009) 3810–3817
Figure 4. The docking result of 13b is showed by Ligplot.
The residue was dissolved in water (5 mL), and then washed with
EtOAc (2 ꢁ 5 mL). 1 N NaOH was added to the mixture until pH
6–7, and the solid was crystallized out. The solution was removed
by filtration, and the remaining solid was sequentially washed
with water and dried overnight, then recrystallized with MeOH
5.009 (d, J = 3.90, 1H), 7.895 (m, 2H), 7.621 (d, J = 8.70, 2H), 8.187 (d,
J = 8.70, 2H). Anal. Calcd for C17H25N3O6: C, 55.58; H, 6.86; N, 11.44.
Found: C, 55.67; H, 6.59; N, 11.83.
To a solution of compound 5a (1.83 g, 5 mmol) in dry EtOAc at
0 °C was added dropwise a solution of EtOAc (10 mL) saturated by
dry HCl gas. The reaction solution was stirred at 0 °C for 2 h, and
then the temperature is raised to room temperature and the reac-
tion proceeds for 5 h before being concentrated in vacuo. The res-
idue was dissolved by saturated Na2CO3 (10 mL), the aqueous
solution was extracted with ethyl ether (3 ꢁ 30 mL). The extrac-
tions were combined, washed with brine, dried over Na2SO4, and
evaporated in vacuo. The residue was purified by flash column
chromatography(DCM/MeOH, 6/1) to give the desired compound
to give
a yellow crystals, yield: 74.2%, mp = 187–189 °C,
½
a 2D5
ꢀ
¼ þ20:8 (c 1, MeOH). ESI-MS m/z: 227.3 (M+H); 1H NMR
(DMSO-d6) d 3.425 (d, J = 3.90, 1H), 5.193 (d, J = 3.90, 1H), 7.659
(d, J = 8.70, 2H), 8.194 (d, J = 8.70, 2H). Anal. Calcd for C9H10N2O5:
C, 47.79; H, 4.46; N, 12.39. Found: C, 47.58; H, 4.31; N, 12.27.
5.3.3.1. (2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)-N-propyl-
propanamide (6a). To a 150 mL solution of Compound 4 (3.26 g,
10 mmol), 1-propylamine (0.71 g, 12 mmol), and HOBt (1.62 g,
12 mmol) in dry THF, was added TEA (1.11 g, 11 mmol). The reaction
mixture was gently cooled to 0 °C in ice bath. To the reaction mixture
was added dropwise a solution of EDCI (3.82 g, 20 mmol) in THF for
1 h. After removal of the ice bath, the reaction mixture was stirred
at room temperature for 12 h and filtered to remove the precipitate.
The filtrate was washed with 1 N citric acid solution, saturated NaH-
CO3 and brine, dried over Na2SO4, and evaporated in vacuo to give the
crude product compound 5a (3.15 g, yield 86%). This product was
used for the following reaction without further purification, yield
6a as
a white solid (1.12 g), yield 84%, mp = 118–120 °C,
½
a 2D5
ꢀ
¼ þ24:3 (c 1, MeOH). ESI-MS m/z: 268.3 (M+H); 1H NMR
(DMSO-d6) d 0.738–0.787 (m, 3H), 1.290–1.407 (m, 2H), 2.898–
3.104 (m, 2H), 3.234 (d, J = 3.90, 1H), 5.018 (d, J = 3.90, 1H), 7.894
(t, J = 6.00, 1H), 7.613 (d, J = 8.70, 2H), 8.187 (d, J = 8.70, 2H). Anal.
Calcd for C12H17N3O4: C, 53.92; H, 6.41; N, 15.72. Found: C, 78.67;
H, 7.70; N, 4.12.
The other compounds of 6 series were synthesized following
the general procedure as described above.
84%, mp = 104–106 °C, ½a D25
ꢀ
¼ þ27:9 (c 1, MeOH). ESI-MS m/z: 368.2
5.3.3.2. (2R,3S)-2-Amino-3-hydroxy-N-isopropyl-3-(4-nitrophenyl)-
propanamide (6b). White solid, yield 79%, mp = 132–134 °C,
(M+H); 1H NMR (DMSO-d6) d 0.828–0.835 (m, 3H), 1.251 (s, 9H),
1.301–1.405 (m, 2H), 2.843–2.904 (m, 2H), 3.203 (d, J = 3.90, 1H),
½
a 2D5
ꢀ
¼ þ16:5 (c 1, MeOH). ESI-MS m/z: 268.3 (M+H);1H NMR (DMSO-

K. Yang et al. / Bioorg. Med. Chem. 17 (2009) 3810–3817
3815
d6) d 0.926 (d, J = 6.60, 3H), 1.033 (d, J = 6.60, 3H), 3.193 (d, J = 4.20, 1H),
3.748–3.862 (m, 1H), 4.963 (d, J = 4.20, 1H), 7.591 (d, J = 8.70, 2H),
7.651 (d, J = 7.80, 1H), 8.182 (d, J = 8.70, 2H). Anal. Calcd for
C12H17N3O4: C, 53.92; H, 6.41; N, 15.72. Found: C, 53.89; H, 6.48; N, 15.91.
8.182 (d, J = 8.70, 2H). Anal. Calcd for C17H19N3O4: C, 62.00; H,
5.81; N, 12.76. Found: C, 62.13; H, 5.80; N, 12.65.
5.3.3.10. (2R,3S)-2-Amino-N-(2-chlorophenethyl)-3-hydroxy-3-
(4-nitrophenyl) propanamide (6j). White solid, yield 72.3%,
5.3.3.3. (2R,3S)-2-Amino-N-butyl-3-hydroxy-3-(4-nitrophenyl)-
propanamide (6c). White solid, yield 83%, mp = 88–89 °C,
mp = 140–142 °C, ½a D25
¼ þ25:2 (c 1, MeOH). ESI-MS m/z: 364.2
ꢀ
(M+H); 1H NMR (DMSO-d6) d 2.730 (t, J = 6.30, 1H), 3.220–3.391
(m, 2H), 3.398 (d, J = 3.9, 1H), 5.041 (d, J = 3.90, 1H), 7.226–7.260
(m, 3H), 7.400–7.432 (m, 1H), 7.601 (d, J = 8.70, 2H), 8.184 (t,
J = 5.70, 1H), 8.213 (d, J = 8.70,2H). Anal. Calcd for C17H18ClN3O4:
C, 56.13; H, 4.99; N, 11.55. Found: C, 56.52; H, 5.01; N, 11.54.
½
a 2D5
ꢀ
¼ þ24:2 (c 1, MeOH). ESI-MS m/z: 282.4 (M+H); 1H NMR
(DMSO-d6) d 0.786–0.835 (m, 3H), 1.082–1.204 (m, 2H), 1.242–
1.333 (m, 2H), 2.908–3.233 (m, 2H), 3.234 (d, J = 3.90, 1H), 4.982
(d, J = 3.90, 1H), 7.591 (d, J = 8.70, 2H), 7.854 (t, J = 6.00, 1H),
8.188 (d, J = 8.70, 2H). Anal. Calcd for C13H19N3O4: C, 55.50; H,
6.81; N, 14.94. Found: C, 55.31; H, 6.76; N, 14.83.
5.3.3.11. (2R,3S)-2-Amino-3-hydroxy-N-(4-hydroxyphenethyl)-
3-(4-nitrophenyl) propanamide (6k). White solid, yield 83%,
5.3.3.4. (2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)-N-pentyl-
propanamide (6d). White solid, yield 83%, mp = 112–144 °C,
mp = 99–100 °C, ½a D25
¼ þ21:0 (c 1, MeOH). ESI-MS m/z: 346.3
ꢀ
(M+H); 1H NMR (DMSO-d6) d 2.538–2.563 (m, 2H), 3.145–3.164
(m, 2H), 3.188 (d, J = 3.90, 1H), 5.067 (d, J = 3.90, 1H), 6.657 (d,
J = 8.70, 2H), 6.953 (d, J = 8.70, 2H), 7.591 (d, J = 8.70, 2H), 7.988
(t, J = 6.00, 1H), 8.187 (d, J = 8.70, 2H). Anal. Calcd for
C17H19N3O5: C, 59.12; H, 5.55; N, 12.17. Found: C, 59.08; H, 5.57;
N, 12.46.
½
a 2D5
ꢀ
¼ þ26:8 (c 1, MeOH). ESI-MS m/z: 296.4 (M+H); 1H NMR
(DMSO-d6) d 0.795–0.842 (m, 3H), 1.098–1.319 (m, 6H), 2.908–
2.970 (m, 1H), 3.044–3.108 (m, 1H), 3.228 (d, J = 3.60, 1H), 4.968 (d,
J = 3.60, 1H), 7.597 (d, J = 8.70, 2H) 7.849 (t, J = 6.00, 1H.), 8.176 (d,
J = 8.70,2H). Anal. Calcd for C14H21N3O4: C, 56.94; H, 7.17; N, 14.23.
Found: C, 56.92; H, 7.07; N, 14.29.
5.3.3.12. (2R,3S)-2-Amino-3-hydroxy-N-((S)-1-hydroxy-3-phe-
nylpropan-2-yl)-3-(4-nitrophenyl)propanamide (6l). White so-
5.3.3.5. (2R,3S)-2-Amino-N-cyclohexyl-3-hydroxy-3-(4-nitrophenyl)
propanamide (6e). White solid, yield 83%, mp = 127–129 °C,
lid, yield 80.3%, mp = 133–134 °C, ½a D25
¼ þ22:3 (c 1, MeOH). ESI-
ꢀ
½
a 2D5
ꢀ
¼ þ13:2 (c 1, MeOH). ESI-MS m/z: 308.5 (M+H); 1H NMR (DMSO-
MS m/z: 360.3 (M+H); 1H NMR (DMSO-d6) d 3.259–2.809 (m,
2H), 3.176–3.343 (m, 2H), 3.882 (d, J = 3.30, 1H), 5.047 (d,
J = 3.30, 1H), 7.151–7.176 (m, 3H), 7.223–7.272 (m, 2H), 7.593 (d,
J = 8.70, 2H), 7.901 (d, J = 8.70, 1H), 8.164 (d, J = 8.70, 2H). Anal.
Calcd for C18H21N3O5: C, 60.16; H, 5.89; N, 11.69. Found: C,
60.19; H, 5.88; N, 11.48.
d6) d 0.679–1.312 (m, 6H), 1.437–1.990 (m, 4H), 3.417 (d, J = 4.50, 1H),
3.393–4.064 (m, 1H), 4.988 (d, J = 4.50, 1H), 7.659 (d, J = 9.00, 1H),
8.238 (d, J = 9.00, 2H), 8.283 (d, J = 7.80, 1H). Anal. Calcd for
C15H21N3O4: C, 58.62; H, 6.89; N, 13.67. Found: C, 58.42; H, 6.40; N, 13.99.
5.3.3.6.
(2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)-N-pro-
pylpropanamide (6f). White solid, yield 88%, mp = 125–127 °C,
5.3.3.13. (2R,3S)-2-Amino-N-(2-(benzo[d][1,3]dioxol-5-yl)ethyl)-
3-hydroxy-3-(4-nitrophenyl) propanamide (6m). White solid,
½
a 2D5
ꢀ
¼ þ26:4 (c 1, MeOH). ESI-MS m/z: 316.3 [M+H]; 1H NMR
(DMSO-d6) d 3.355 (d, J = 3.90, 1H). 4.217 (dd, J = 5.70, J = 15.70,
1H), 4.326 (dd, J = 5.70, J = 15.70, 1H), 5.040 (d, J = 3.90, 1H),
7.181–7.285 (m, 5H), 7.618 (d, J = 8.70, 2H), 8.157 (d, J = 8.70,
2H), 8.442 (t, J = 5.70, 1H). Anal. Calcd for C16H17N3O4: C, 60.94;
H, 5.43; N, 13.33. Found: C, 60.44; H, 5.73; N, 12.97.
yield 85.9%, mp = 136–137 °C, ½a D25
¼ þ18:7 (c 1, MeOH). ESI-MS
ꢀ
m/z: 374.4 (M+H); 1H NMR (DMSO-d6) d 2.581 (t, J = 7.20, 2H),
3.171–3.214 (m, 2H), 3.236 (d, J = 3.30, 1H), 5.060 (d, J = 3.30,
1H), 5.961 (s, 2H), 6.622 (d, J = 7.80, 1H), 6.756–6.819 (m, 2H),
7.696 (d, J = 8.70, 2H), 7.998 (t, J = 5.40, 1H), 8.183 (d, J = 8.70 Hz,
2H). Anal. Calcd for C18H19N3O6: C, 57.90; H, 5.13; N, 11.25. Found:
C, 57.84; H, 5.11; N, 11.20.
5.3.3.7.
(2R,3S)-2-Amino-N-(4-fluorobenzyl)-3-hydroxy-3-(4-
nitrophenyl) propanamide (6g). White solid, yield 81.5%,
Compounds 8a and 8b were synthesized following the general
procedure as described bellow (preparation of 12a).
mp = 115–118 °C, ½a D25
¼ þ24:5 (c 1, MeOH). ESI-MS m/z: 334.3
ꢀ
(M+H); 1H NMR (DMSO-d6) d 3.327 (d, J = 3.60, 1H), 4.193 (dd,
J = 6.00, J = 15.00, 1H), 4.294 (dd, J = 6.00, J = 15.00, 1H), 5.053 (d,
J = 3.60, 1H), 7.052–7.111 (m, 2H), 7.187–7.235 (m, 2H) 7.593 (d,
J = 8.70, 2H), 8.155 (d, J = 8.70, 2H), 8.458 (t, J = 6.30,1H). Anal.
Calcd for C16H16FN3O4: C, 57.56; H, 4.84; N, 12.61. Found: C,
57.09; H, 4.82; N, 12.30.
5.3.3.14. 4-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)prop-
anamido)butanoic acid (8a). White solid, yield 43.3%, mp = 141–
143 °C, ½a 2D5
ꢀ
¼ þ20:5 (c 1, MeOH). ESI-MS m/z: 312.3 (M+H); 1H
NMR (DMSO-d6) d 1.186–1.210 (m, 2H), 2.137 (t, J = 7.50, 2H),
2.996–3.020 (m, 2H), 3.581 (d, J = 5.10, 1H), 5.024 (d, J = 5.10,
1H), 7.649 (d, J = 8.70, 2H), 8.204 (d, J = 8.70, 2H), 8.292 (d,
J = 7.80, 1H). Anal. Calcd for C13H17N3O6: C, 50.16; H, 5.50; N,
13.50. Found: C, 50.12; H, 5.53; N, 13.60.
5.3.3.8. (2R,3S)-2-Amino-3-hydroxy-N-(4-methoxybenzyl)-3-(4-
nitrophenyl) propanamide (6h). White solid, yield 66.7%,
mp = 141–143 °C, ½a D25
¼ þ21:3 (c 1, MeOH). ESI-MS m/z: 346.3
ꢀ
(M+H); 1H NMR (DMSO-d6) d 3.330 (d, J = 3.30, 1H), 3.717 (s, 3H),
4.114 (dd, J = 6.30, J = 15.70, 1H), 4.225 (dd, J = 6.30, J = 15.70,
1H), 5.014 (d, J = 3.30, 1H), 7.061 (d, J = 8.70, 2H), 7.592 (d,
J = 8.70, 2H), 7.907 (d, J = 8.70, 2H), 8.147 (d, J = 8.70,2H), 8.325
(t, J = 6.30, 1H). Anal. Calcd for C17H19N3O5: C, 59.12; H, 5.55; N,
12.17. Found: C, 59.15; H, 5.61; N, 12.48.
5.3.3.15. 6-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)prop-
anamido)hexanoic acid (8b). White solid, yield 43.3%, mp = 150–
153 °C, ½a 2D5
ꢀ
¼ þ25:6 (c 1, MeOH). ESI-MS m/z: 340.3 (M+H); 1H
NMR (DMSO-d6) d 1.066–1.165 (m, 2H), 1.214–1.430 (m, 4H),
2.134 (t, J = 7.50, 2H), 3.006–3.055 (m, 2H), 3.583 (d, J = 4.80, 1H),
5.028 (d, J = 4.80, 1H), 7.633 (d, J = 8.70, 2H), 8.204 (d,
J = 8.70,2H), 8.259 (d, J = 7.00,1H). Anal. Calcd for C15H21N3O6: C,
53.09; H, 6.24; N, 12.38. Found: C, 53.04; H, 6.28; N, 12.36.
5.3.3.9. (2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)-N-phen-
ethylpropanamide (6i). White solid, yield 76%, mp = 126–128 °C,
½
a 2D5
ꢀ
¼ þ27:4 (c 1, MeOH). ESI-MS m/z: 330.3 (M+H); 1H NMR
5.3.3.16. (S)-2-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)
propanamido)-4-methylpentanoic acid (10a). To a 150 mL solu-
(DMSO-d6) d 2.664 (t, J = 7.50, 2H), 3.246 (d, J = 3.60, 1H), 3.286–
3.349 (m, 2H), 5.059 (d, J = 3.60, 1H), 7.167–7.213 (m, 3H),
7.225–7.306 (m, 2H), 7.593 (d, J = 8.70, 2H), 8.037 (t, J = 5.70, 1H),
tion of compound 4 (3.26 g, 10 mmol),
L-leucine methyl ester
hydrochloride (1.81 g, 10 mmol), and HOBt (1.62 g, 12 mmol) in

3816
K. Yang et al. / Bioorg. Med. Chem. 17 (2009) 3810–3817
dry THF, was added TEA (2.22 g, 22 mmol). The reaction mixture
was gently cooled to 0 °C in ice bath, to the reaction mixture was
added dropwise a solution of EDCI (3.82 g, 20 mmol) in THF for
1 h. After removal of the ice bath, the reaction mixture was stirred
at room temperature for 12 h. and filtered to remove the precipi-
tate. The filtrate was washed with 1 M citric acid solution, satu-
rated NaHCO3 and brine, dried over Na2SO4, and evaporated in
vacuo. The residue was purified by flash column chromatography
(EtOAc/PE, 1:4(V/V)) to give the desired compound 9a as a white
1.591–1.594 (m, 1H), 3.504 (d, J = 3.00, 1H), 4.095–4.098 (m, 1H),
4.964 (d, J = 3.00, 1H), 7.632 (d, J = 8.70, 2H), 8.081 (d, J = 6.00,
1H), 8.195 (d, J = 8.70, 2H). Anal. Calcd for C15H21N3O6: C, 53.09;
H, 6.24; N, 12.38. Found: C, 53.51; H, 6.19; N, 12.40.
5.3.3.20. (S)-2-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)-
propanamido)-3-(1H-indol-2-yl) propanoic acid (10e). White so-
lid, yield 85.9%, mp = 179–180 °C, ½a D25
¼ þ26:1 (c 1, MeOH). ESI-MS
ꢀ
m/z: 413.4 (M+H); 1H NMR (DMSO-d6) d 3.064–3.113 (m, 2H), 3.163
(d, J = 3.00, 1H), 4.487–4.490 (m, 1H), 5.106 (d, J = 3.00, 1H), 6.965–
7.030 (m, 1H), 7.054–7.078 (m, 2H), 7.327 (d, J = 8.10, 1H), 7.504
(d, J = 7.50, 1H), 7.599 (d, J = 8.70, 2H), 8.132 (d, J = 8.70, 2H), 8.275
(d, J = 6.50, 1H). Anal. Calcd for C20H20N4O6: C, 58.25; H, 4.89; N,
13.59. Found: C, 58.60; H, 4.73; N, 13.54.
solid (4.08 g), yield 88.7%, mp = 141–143 °C, ½a D25
¼ þ29:1 (c 1,
ꢀ
MeOH). ESI-MS m/z: 454.3 (M+H); 1H NMR (DMSO-d6) d 0.789 (d,
J = 20.40, 6H), 1.235 (s, 9H), 1397–1.423 (m, 1H), 1.442–1.529 (m,
2H), 3.628 (s, 3H), 4.234 (d, J = 4.50, 1H), 4.313–4.359 (m, 1H),
5.033 (d, J = 4.50, 1H), 6.423 (s, J = 9.60, 1H), 7.625 (d, J = 8.40,
2H), 8.194 (d, J = 8.40, 2H), 8.472 (d, J = 7.80 Hz, 1H). Anal. Calcd
for C21H31N3O8: C, 55.62; H, 6.89; N, 9.27. Found: C, 55.42; H,
6.83; N, 9.23.
5.3.3.21. (S)-2-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)-
propanamido)-N-hydroxy-4-methylpentanamide (11a). To
a
To a solution of compound 9a (4.53 g, 10 mmol) in MeOH at 5 °C
was added dropwise a solution of 1 N NaOH (12 mL). The reaction
was warmedslowly to room temperature and stirred for 5 h. The sol-
vent was concentrated under vacuum to remove the MeOH. The
remaining mixture was added water (10 ml) and acidified to pH 1–
2 by a 1 N citric acid solution. The precipitate was collected, washed
withwater(20 mL), anddriedovernight. Thecrudeproductwasthen
recrystallized with EtOAc to give the desired compound as white so-
solution of compound 10a (4.53 g, 10 mmol) in MeOH at room tem-
perature was added dropwise a solution of 1.5 N H2N–OK (12 mL),
The reaction mixture was stirred for 1 h, and then acidified to pH 7
by acetic acid. The solvent was evaporated in vacuo to give the yel-
low solid. The crude product was purified by flash column chroma-
tography (DCM/MeOH, 40:1 (V/V)) to give the desired compound
as
a
white solid (3.15 g), yield 70.7%, mp = 153–155 °C,
½
a 2D5
ꢀ
¼ þ20:1 (c 1, MeOH). ESI-MS m/z: 455.3 (M+H); 1H NMR
lid (4.39 g), yield 93.1%, mp = 128–130 °C, ½a D25
ꢀ
¼ þ27:2 (c 1, MeOH).
(DMSO-d6) d 0.545–0.610 (m, 6H), 0.703–0.801 (m, 1H), 0.934–
1.187 (m, 2H), 3.954 (d, J = 3.50, 1H), 4.062–4.082 (m, 1H), 4.903
(d, J = 3.50, 1H), 7.652 (d, J = 8.70, 2H), 8.246 (d, J = 8.70, 2H), 8.746
(m, 2H).
ESI-MS m/z: 440.7 (M+H); 1H NMR (DMSO-d6) d 0.809 (d, J = 18.60,
6H), 1.231 (s, 9H), 1.330–1.420 (m, 1H), 1.421–1.439 (m, 2H),
4.165 (d, J = 4.50, 1H), 4.318–4.363 (m, 1H), 5.054 (d, J = 4.50, 1H),
6.398 (d, J = 9.60, 1H), 7.633 (d, J = 8.40, 2H), 8.197 (d, J = 8.40, 2H),
8.332 (d, J = 8.10, 1H). Anal. Calcd for C20H29N3O8: C, 54.66; H,
6.65; N, 9.56. Found: C, 54.51; H, 6.62; N, 9.57.
The compound 11a was synthesized following the general pro-
cedure as described above (preparation of 1), yield 74.2%,
mp = 212–213 °C. ½a D25
¼ þ27:7 (c 1, MeOH). ESI-MS m/z: 355.6
ꢀ
The compound 10a was synthesized from following the general
procedure as described above (preparation of 1), white solid, yield
(M+H); 1H NMR (DMSO-d6) d 0.548–0.609 (m, 6H), 0.701–0.811
(m, 1H), 0.911–1.198 (m, 2H), 3.967 (d, J = 3.50, 1H), 4.063–4.081
(m, 1H), 4.968 (d, J = 3.50, 1H), 7.651 (d, J = 8.70, 2H), 8.244 (d,
J = 8.70, 2H), 8.746 (d, J = 8.10, 2H). Anal. Calcd for C15H22N4O6: C,
50.84; H, 6.26; N, 15.81. Found: C, 50.90; H, 6.06; N, 16.17.
60%, mp = 203–205 °C, ½a D25
¼ þ36:2 (c 1, MeOH). ESI-MS m/z:
ꢀ
340.4 (M+H); 1H NMR (DMSO-d6) d 0.731 (d, J = 12.10, 6H), 1.121–
1.142 (m, 1H), 1.336–1.354 (m, 2H), 3.417 (d, J = 4.50, 1H), 4.094–
4.113 (m, 1H), 4.882 (d, J = 4.50, 1H), 7.631 (d, J = 8.70, 2H), 8.092
(d, J = 7.50, 1H), 8.180 (d, J = 8.70, 2H). Anal. Calcd for C15H21N3O6:
C, 53.09; H, 6.24; N, 12.38. Found: C, 53.50; H, 6.43; N, 12.30.
The other compounds of 10 series were synthesized following
the general procedure as described above (preparation of 10a).
5.3.3.22. (2R,3S)-2-Amino-3-hydroxy-N-((S)-1-(hydroxyamino)-
1-oxo-3-phenylpropan-2-yl)-3-(4-nitrophenyl)propanamide
(11b). The compound 11b was synthesized following the general
procedure as described above, yield 74.2%, mp = 215–217 °C,
½
a 2D5
ꢀ
¼ þ26:7 (c 1, MeOH). ESI-MS m/z: 389.5 (M+H); 1H NMR
5.3.3.17. (S)-2-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)-
propanamido)-3-phenylpropanoic acid (10b). White solid, yield
(DMSO-d6) d 2.553–2.763 (m, 2H), 4.071 (d, J = 3.30, 1H), 4.317–
4.366 (m, 1H), 5.063 (d, J = 3.30, 1H), 7.043–7.065 (m, 2H),
7.118–7.268 (m, 3H), 7.636 (d, J = 8.70, 2H), 8.199 (d, J = 8.70,
2H), 8.958 (d, J = 8.10, 2H). Anal. Calcd for C18H20N4O6: C, 55.67;
H, 5.19; N, 14.43. Found: C, 55.34; H, 5.16; N, 14.30.
85.9%, mp = 215–218 °C, ½a D25
¼ þ28:4 (c 1, MeOH). ESI-MS m/z:
ꢀ
374.4 (M+H); 1H NMR (DMSO-d6) d 2.854–3.013 (m, 2H), 3.462 (d,
J = 3.90, 1H), 4.375–4.442 (m, 1H), 5.061 (d, J = 3.90, 1H), 7.079–
7.105 (m, 2H), 7.132–7.243 (m, 3H), 7.606 (d, J = 8.70, 2H), 8.165
(d, J = 8.70, 2H), 8.272 (d, J = 7.20, 1H). Anal. Calcd for C18H19N3O6:
C, 57.90; H, 5.13; N, 11.25. Found: C, 57.85; H, 5.16; N, 11.23.
5.3.3.23.
(S)-2-((S)-2-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitro-
phenyl)propanamido)-4-methylpentanamido)-3-phenylpropa-
noic acid (13a). Compounds 13a, 13b were synthesized following
the general procedure as described above (preparation of 10a).
5.3.3.18. (S)-2-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)-
propanamido)-3-methylbutanoic acid (10c). White solid, yield
White solid, yield 85.9%, mp = 115–116 °C, ½a D25
¼ þ27:2 (c 1,
ꢀ
85.9%, mp = 179–180 °C, ½a D25
ꢀ
¼ þ21:6 (c 1, MeOH). ESI-MS m/z:
MeOH). ESI-MS m/z: 487.4 (M+H); 1H NMR (DMSO-d6) d 0.692 (d,
J = 12.10, 6H), 1.023–1.110 (m, 1H), 1.218–1.287 (m, 2H), 2.849–
3.053 (m, 2H), 3.742 (d, J = 4.80, 1H), 4.114–4.225 (m, 1H),
4.252–4.295 (m, 1H), 4.919 (d, J = 4.80, 1H), 7.179–7.279 (d,
J = 8.70, 5H), 7604 (d, J = 8.70, 2H), 8.021 (t, J = 7.50, 1H), 8.150 (t,
J = 7.30, 1H), 8.185 (d, J = 8.70, 2H). Anal. Calcd for C24H30N4O7: C,
59.25; H, 6.22; N, 11.52. Found: C, 59.19; H, 6.34; N, 11.28.
326.3 (M+H); 1H NMR (DMSO-d6) d 0.688–0.731 (m, 6H), 1.912–
1.919 (m, 1H), 3.493 (d, J = 3.00, 1H), 4.055–4.059 (m, 1H),
5.001–5.003 (d, J = 3.00, 1H), 7.632 (d, J = 8.70, 2H), 8.087 (d,
J = 6.00, 1H), 8.177 (d, J = 8.70, 2H). Anal. Calcd for C18H19N3O6: C,
51.69; H, 5.89; N, 12.92. Found: C, 51.67; H, 5.49; N, 12.61.
5.3.3.19. (S)-2-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitrophenyl)-
propanamido)-3-methylbutanoic acid (10d). White solid, yield
5.3.3.24.
(S)-2-((S)-2-((2R,3S)-2-Amino-3-hydroxy-3-(4-nitro-
85.9%, mp = 178–179 °C, ½a D25
ꢀ
¼ þ24:8 (c 1, MeOH). ESI-MS m/z:
phenyl)propanamido)-3-phenylpropanamido)-3-phenylpropa-
340.3 (M+H); 1H NMR (DMSO-d6) d 0.685 (d, J = 6.60, 3H), 0.752
(t, J = 7.50, 3H), 0.939–0.940 (m, 1H), 1.210–1.213 (m, 1H),
noic acid (13b). White solid, yield 85.9%, mp = 169–170 °C,
½
a 2D5
ꢀ
¼ þ22:1 (c 1, MeOH). ESI-MS m/z: 521.3 (M+H); 1H NMR

K. Yang et al. / Bioorg. Med. Chem. 17 (2009) 3810–3817
2. Bauvois, B.; Dauzonne, D. Med. Res. Rev. 2006, 26, 88.
3817
(DMSO-d6) d 2.722–2.933 (m, 2H), 2.941–3.097 (m, 2H), 3.427 (d,
J = 3.60, 1H), 4.322–4.441 (m, 1H), 4.457–4.511 (m, 1H), 5.004 (d,
J = 3.60, 1H), 7.088–7.563 (m, 10H), 7.498 (d, J = 8.70, 2H). 8.139 (d,
J = 8.70, 2H), 8.281 (t, J = 7.30, 2H). Anal. Calcd for C27H28N4O7: C,
62.30; H, 5.42; N, 10.76. Found: C, 62.28; H, 5.37; N, 11.12.
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Acknowledgments
This work was supported by National Natural Foundation Re-
search Grant (Grant Nos. 9071304 and 30772654) and National
High Technology Research and Development Program of China
(863 Project; Grant No. 2007AA02Z314) and Doctoral Foundation
of Ministry of Education of the People’s Republic of China (Grant
No. 20060422029).
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References and notes
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