Synthesis of 2-aminoxazole-5-carbamides and 2-aminothiazole-5-carbamides as potent inhibitors of CML

Article abstract of DOI:10.1007/s00706-014-1403-6

Abstract 2-Aminoxazole-5-carbamide was discovered as novel potent inhibitor against human chronic myeloid leukemia K562 cells; several new corresponding 2-aminothiazole-5-carbamides were also prepared and evaluated the biological activity. The results dem

Full text of DOI:10.1007/s00706-014-1403-6

Monatsh Chem
DOI 10.1007/s00706-014-1403-6
ORIGINAL PAPER
Synthesis of 2-aminoxazole-5-carbamides and 2-aminothiazole-5-
carbamides as potent inhibitors of CML
•
Ying Zhou XiaoBing He YuanZhen Xiong
•
•
•
XingXing Chai HongPing Chen
Received: 23 September 2014 / Accepted: 28 December 2014
Ó Springer-Verlag Wien 2015
Abstract 2-Aminoxazole-5-carbamide was discovered as
novel potent inhibitor against human chronic myeloid
leukemia K562 cells; several new corresponding 2-ami-
nothiazole-5-carbamides were also prepared and evaluated
the biological activity. The results demonstrated that all of
the new compounds exhibited antiproliferative potency on
human K562 leukemia cells.
Treatment of CML generally relies on Bcr-Abl tyrosine
kinase inhibitors. This recognition of the Bcr-Abl gene and
corresponding proteins led to the synthesis of small-mol-
ecule drugs, which were used to interfere with Bcr-Abl
tyrosine kinase activated by competitive binding at the
ATP-binding site [3]. Five Bcr-Abl tyrosine kinase inhib-
itors (TKIs) (imatinib, nilotinib, dasatinib, bosutinib, and
ponatinib) are currently approved for the treatment of CML
[4]. Within these CML inhibitory categories, imatinib is
one of the most well-known molecular drugs for all newly
diagnosed CML patients [5, 6]. Dasatinib (Scheme 1), a
potent dual inhibitor of Src and Abl kinase, was approved
for the oral treatment of CML and Philadelphia chromo-
some-positive acute lymphoblastic leukemia [2, 7–11]. As
a second-generation Bcr-Abl inhibitor, dasatinib has shown
significant activity after imatinib failure in clinical trials,
but still faces obstacles similar to imatinib, including
negligible activity against the frequent Bcr-Abl T315I
mutation and modest effects in advanced phases of CML
[9]. The emergence of mutations in the Bcr-Abl kinase
domain is a common mechanism of TKI resistance; there is
a continued interest in developing new agents that have
highly potent kinase inhibition profile. A survey of the
literature revealed that there had been extensive progress
on the preparation of 2-aminothiazole-5-carboxylic acid
phenyl amide derivatives [2, 7–11] including dasatinib. To
investigate whether the pyrimidin-4-ylamino moiety is
critical for activity in this series compounds, acetyl and
phenyl acetyl substitution were adopted as alternate scaf-
folds at the 2-amino group, and some derivatives with the
absence of the chloro atom at the phenyl ring moiety were
reported as TKIs [2, 8–10]. However, modification on
replacement of the thiazole core has not been reported so
far. Considering oxazole and thiazole are bioisosteres, we
made an effort to design a series of 2-aminoxazole-5-
Graphical abstract
Keywords 2-Aminoxazole-5-carbamides Á
2-Aminothiazole-5-carbamides Á CML Á Inhibitor
Introduction
Chronic myeloid leukemia (CML) is a myeloproliferative
disorder that is characterized by the presence of a consti-
tutively active tyrosine kinase, Bcr-Abl, which drives the
malignant phenotype of leukemic stem cells [1, 2].
Y. Zhou and X. He contributed equally to this work.
X. He Á Y. Xiong (&) Á X. Chai
Department of Pharmacy, Nanchang University, Nanchang
330006, People’s Republic of China
e-mail: xyz16262@163.com
Y. Zhou Á H. Chen
Department of Histology and Embryology, Nanchang
University, Nanchang 330006, People’s Republic of China
123

Y. Zhou et al.
carbamide compounds, aimed to observe whether these
different heterocyclic compounds favor greater inhibition
of cell proliferation and higher induction of cell death in
treatment of CML. Herein, a new and efficient method has
been developed for the synthesis of 2-aminoxazole-5-car-
bamides and 2-aminothiazole-5-carbamides, with their
in vitro cytostatic effect screened on human chronic mye-
loid leukemia cell line K562.
marketed drug dasatinib and imatinib used as references,
and the assays are summarized in Table 1. They are
expressed as IC50, a concentration at which the compounds
inhibit the cell proliferation for 50 %. The results displayed
an encouraging spectrum of cell inhibitory activity, espe-
cially five compounds 4b, 6c, 7a, 7f, 7h, which were more
potent than the other analogs including imatinib.
In a direct comparison of 2-aminoxazole-5-carbamides
(6a, 6c, 6d, 6e, 6g) with their counterparts 2-aminothiazole-
5-carbamides (7a, 7c, 7d, 7e, 7f), similar potent and broad
spectrum cellular activity were observed; it might be
explained that whether thiazole or oxazole scaffold in the
heterocyclic compounds is crucial for the potency; its elec-
trostatic field effect in the interaction of molecular with Bcr-
Abl has no significant role on the whole set of the interac-
tions. As part of a systematic preliminary structure–activity
relationship (SAR) approach, we first investigated the
importance of the carboxanilide side chain on the 5-position
of oxazole and thiazole ring, and found that inhibitory
activity was weakly affected by substitution at this position.
Our next effort focused on developing the SAR with
respect to the substitution pattern on the 2-aminooxazole
skeleton. To our surprise, when benzamide or para-methyl-
benzamide attended to 5-position of the oxazole ring,
improvement in the cellular activity profile was observed
when 2-NH2 group was N-acylated by benzoyl substituent
(6d, 6c) prior to acetyl group (6b, 6g, and 6a, 6f, respec-
tively), it is hypothesized that the specific interaction of
aromatic ring with Abl is responsible for favorable activity
of this series compounds. To evaluate electron withdrawing
effect on the potency, compound 7h was synthesized and
identified as the most potent inhibitor versus the K562 cell
line in this series, almost the equivalent inhibition per-
centage compared with dasatinib, this result implied that an
Results and discussion
Synthesis
Preparation of the two series compounds is outlined in
Scheme 1.
(E)-3-Ethoxy-N-arylpropenamides
3a–3c
served as advanced intermediates, synthesized by nucleo-
philic substitution of appropriate aniline onto (E)-3-
ethoxyacryloyl chloride (2), which was obtained in one pot
from ethyl vinyl ether (1) and oxalyl chloride by Effen-
berger addition followed by thermal decarbonylation
according to the literature [12]. Reaction of the advanced
enones 3a–3c with N-bromosuccinimide (NBS) followed
by a coupling of urea or thiourea installs the oxazole
skeleton in 4a–4c or thiazole ring in 5a–5c [9, 10]. The
final step was a nucleophilic displacement of acetic anhy-
dride or different benzoyl chloride onto 4a–4c or 5a–5c to
yield the corresponding target 6a–6g and 7a–7h,
respectively.
Anti-CML activity
All newly synthesized compounds were evaluated on K562
cell in vitro for anti-CML activity, in comparison with
Scheme 1
123

Synthesis of 2-aminoxazole-5-carbamides and 2-aminothiazole-5-carbamides
Table 1 The inhibitory activity against K562 cell of novel compounds
R1
R2
R3
IC50/lM
4a
CH3
H
H
0.174 0.046
0.090 0.002
0.185 0.033
0.172 0.027
0.159 0.034
0.087 0.003
0.125 0.016
0.109 0.035
0.149 0.028
0.134 0.037
0.080 0.004
0.166 0.051
0.222 0.062
0.121 0.033
0.129 0.041
0.093 0.006
0.111 0.016
0.060 0.003
0.050 0.002
0.112 0.045
4b
CH3
H
4c
H
6a
CH3
H
H
CH3
CH3
Ph
6b
H
6c
CH3
H
H
6d
H
Ph
6e
H
CH3
H
Ph
6f
CH3
H
PhCH2
PhCH2
CH3
CH3
CH3
Ph
6g
H
7a
CH3
H
H
7b
CH3
H
7c
H
7d
CH3
H
H
7e
H
Ph
7f
H
CH3
H
Ph
7g
H
PhCH2
3-NO2–Ph
7h
H
CH3
Dasatinib
Imatinib
improvement of the biological profile could be obtained by
the introduction of electron withdrawing substituent group
(e.g., NO2) to the benzoyl ring.
254 nm under a UV lamp. All chemicals and solvents were
reagent grade purified by standard methods prior to use.
In summary, we identified a novel oxazole lead as a
CML inhibitor; further development of the SAR, and
optimization of the cell and in vivo activity of this series
will be reported in due course.
(E)-3-Ethoxy-N-arylpropenamides 3a–3c
The preparation of (E)-3-ethoxyacryloyl chloride (2) was
according to the literature [13]. To a solution of aniline
(28 mmol) and 3.2 cm3 pyrimidine (40 mmol) in 40 cm3
THF was added 3.6 cm3 (E)-3-ethoxyacryloyl chloride
(30 mmol) dropwise at 0 °C, after stirred for another 2 h at
room temperature, 7.0 cm3 HCl (1 mol/cm3) was added
slowly, the resultant was concentrated in vacuo, the crude
product was crystallized from toluene to afford 3a–3c.
Experimental
1H NMR and 13C NMR spectra were measured on a Bruker
AV 600 MHz spectrometer. Chemical shifts were expres-
sed in ppm downfield from TMS, which was used as an
internal standard. Mass spectra were obtained on an Agi-
lent MS/5975 mass spectrometer. IR spectra (KBr) were
recorded on a JASCO FT/IR-8400 instrument. Elemental
analysis was performed on a Carloerba 1106 instrument
and the results of elemental analysis for C, H, N, S were
within 0.4 % of the theoretical values. All the reactions
were monitored by TLC on pre-coated silica gel G plates at
(E)-3-Ethoxy-N-(4-methylphenyl)acryamide
(3a, C12H15NO2)
White powder, yield 5.0 g (87.0 %); m.p.: 148–150 °C; 1H
NMR (600 MHz, DMSO-d6): d = 9.29 (s, 1H, –NH–CO–
), 7.40–7.46 (m, 2H, Ar–H), 7.32 (d, J = 12.4 Hz, 1H, –
CO–CH=), 7.18–7.23 (m, 2H, Ar–H), 5.58 (d,
J = 12.4 Hz, 1H, –O–CH=), 3.94 (q, J = 7.0 Hz, 2H, –
CH2–), 2.16 (s, 3H, –CH3), 1.27 (t, J = 7.0 Hz, 3H, –CH3)
123

Y. Zhou et al.
ppm; 13C NMR (125 MHz, DMSO-d6): d = 19.11 (CH3),
19.34 (CH3), 41.44 (CH2), 66.76 (O–CH=), 75.87 (=CH),
119.23 (2), 124.58, 129.50 (2), 135.66, 152.36 (C=O,
carboxamide) ppm; IR (KBr): mꢀ = 3,257, 1,662, 1,508,
1,292, 1,161 cm-1; MS (70 eV): m/z = 205 (M?).
DMSO-d6): d = 20.86 (CH3), 120.49, 120.56, 129.50,
129.60, 132.11, 133.35, 136.19, 138.65, 155.87 (C=O,
carboxamide), 163.45 (O–C=N, oxazole) ppm; IR (KBr):
mꢀ = 3,404, 3,304, 3,067, 2,978, 1,641, 1,614, 1,483, 1,290,
1,178 cm-1; MS (70 eV): m/z = 217 (M1).
2-Amino-N-phenyl-5-oxazolecarboxamide
(E)-3-Ethoxy-N-phenylacrylamide (3b, C11H13NO2)
1
(4c, C10H9N3O2)
Yellow powder, yield 4.8 g (89.4 %); m.p.: 79–81 °C; H
Yellow powder, yield 3.5 g (68.7 %); m.p.: 244–245 °C;
1H NMR (600 MHz, DMSO-d6): d = 9.76 (s, 1H, –NH–
CO–), 7.66 (d, J = 7.2 Hz, 1H, Ar–H), 7.64 (m, 2H, Ar–
H), 7.31 (t, J = 7.8 Hz, 2H, Ar–H), 7.30 (s, 2H, NH2), 7.05
(t, J = 7.2 Hz, 1H, Ar–H) ppm; 13C NMR (125 MHz,
DMSO-d6): d = 120.47 (2), 129.55 (2), 132.10, 133.36,
136.18, 138.55, 155.74 (C=O, carboxamide), 163.21 (O–
NMR (600 MHz, DMSO-d6): d = 9.00 (s, 1H, –NH–CO–
), 7.50 (m, 1H, Ar–H), 7.32–7.29 (m, 2H), 7.18–7.23 (m,
2H, Ar–H), 5.58 (d, J = 12.4 Hz, 1H, –O–CH=), 4.00 (q,
J = 7.0 Hz, 2H, –CH2–), 1.22 (t, J = 7.0 Hz, 3H, –CH3)
ppm; 13C NMR (125 MHz, DMSO-d6): d = 19.35 (CH3),
41.46 (CH2), 66.78 (O–CH=), 73.56 (=CH), 119.59 (2),
129.36 (2), 135.67, 137.82, 150.56 (C=O, carboxamide)
ꢀ
C=N, oxazole) ppm; IR (KBr): m = 3,306, 3,105, 1,662,
ꢀ
ppm; IR (KBr): m = 3,261, 1,660, 1,621, 1,509, 1,408,
1,634, 1,612, 1,574, 1,489, 1,283, 1,173 cm-1; MS
1,357, 1,292, 1,244, 1,161 cm-1; MS (70 eV): m/z = 191
(70 eV): m/z = 203 (M1).
(M1).
(E)-3-Ethoxy-N-(2-methylphenyl)acrylamide (3c)
Yellow powder, yield 4.9 g (85.4 %); m.p.: 92–94 °C (Ref.
[9, 10] 92–96 °C)
General procedure for preparation of 6a–6g
To a solution of 4a–4c (2.15 mmol) and 0.5 cm3 Et3N in
10 cm3 THF was added benzoyl chloride or acetic anhy-
dride (2.46 mmol) dropwise at 0 °C and stirred for 1 h,
then the mixture was warmed to room temperature and
stirred for another 2 h, the resultant was concentrated in
vacuo. The resulting mixture was partitioned between ethyl
acetate and water, and the organic layer was washed with
1 N HCI, 5 % NaHCO3, and brine, and dried over MgSO4.
After removal of the solvent under reduced pressure, the
residue was purified by silica gel chromatography and then
recrystallized from toluene, affording the counterparts 6a–
6g.
2-Amino-N-aryloxazole-5-carboxamides 4a–4c
To a solution of 3a–3c (25 mmol) in 40 cm3 H2O and
40 cm3 1,4-dioxane was added 4.4 g NBS (25 mmol) at
0 °C while kept stirring for 1 h, after warmed to room
temperature and stirred for another 2 h, 4.4 g urea
(25 mmol) was added, the mixture was allowed to 70 °C
and stirred for 2 h, the pH of the resultant was adjusted to
8–9 by ammonia and then concentrated in vacuo. The
crude product was crystallized from toluene, affording the
counterparts 4a–4c.
2-Amino-N-(4-methylphenyl)-5-oxazolecarboxamide
(4a, C11H11N3O2)
2-Acetylamino-N-(4-methylphenyl)-5-oxazolecarboxamide
(6a, C13H13N3O3)
1
Yellow solid, yield 2.5 g (45.7 %); m.p.: 271–272 °C; H
NMR (600 MHz, DMSO-d6): d = 9.70 (s, 1H, –NH–CO–
), 7.61 (s, 1H, –C=CH–N=), 7.53 (d, J = 8.4 Hz, 2H, Ar–
H), 7.30 (s, 2H, –NH2), 7.12 (d, J = 8.4 Hz, 2H, Ar–H),
2.26 (s, –CH3) ppm; 13C NMR (125 MHz, DMSO-d6):
d = 20.96 (CH3), 120.46 (2), 129.53 (2), 132.10, 133.30,
136.18, 138.55, 155.85 (C=O, carboxamide), 163.45 (O–
White powder, yield 0.34 g (61.5 %); m.p.: 278–280 °C;
1H NMR (600 MHz, DMSO-d6): d = 11.56 (s, 1H, –NH–
CO–), 10.10 (s, 1H, –NH–CO–), 7.88 (s, 1H, –C=CH–N=),
7.56 (d, J = 7.2 Hz, 2H, Ar–H), 7.16 (d, J = 6.6 Hz, 2H,
Ar–H), 2.27 (s, 3H, –CH3), 2.14 (s, 3H, –CH3) ppm; 13C
NMR (125 MHz, DMSO-d6): d = 20.97 (CH3), 23.01
(CH3), 120.79 (2), 128.19, 129.58 (2), 133.20, 136.20,
140.75, 159.84 (C=O, carboxamide), 163.51 (O–C=N,
oxazole), 169.45 (C=O, acetamido) ppm; IR (KBr):
ꢀ
C=N, oxazole) ppm; IR (KBr): m = 3,304, 3,103, 1,663,
1,633, 1,607, 1,574, 1,529, 1,173 cm-1; MS (70 eV): m/
z = 217 (M1).
m = 3,330, 3,169, 1,688, 1,651, 1,590, 1,288 cm-1; MS
ꢀ
2-Amino-N-(2-methylphenyl)-5-oxazolecarboxamide
(4b, C11H11N3O2)
(70 eV): m/z = 259 (M1).
Yellow powder, yield 2.4 g (43.7 %); m.p.: 230–232 °C;
1H NMR (600 MHz, DMSO-d6): d = 9.31 (s, 1H, –NH–
CO–), 7.56 (s, 1H, –C=CH–N=), 7.32 (d, J = 7.8 Hz, 1H,
Ar–H), 7.26 (s, 2H, NH2), 7.24 (d, J = 7.8 Hz, 1H, Ar–H),
7.19 (t, J = 7.2 Hz, 1H, Ar–H), 7.13 (t, J = 7.2 Hz, 1H,
Ar–H), 2.20 (s, 3H, –CH3) ppm; 13C NMR (125 MHz,
2-Acetylamino-N-phenyl-5-oxazolecarboxamide
(6b, C12H11N3O3)
White powder, yield 0.40 g (75.4 %); m.p.: 244–246 °C;
1H NMR (600 MHz, DMSO-d6): d = 11.58 (s, 1H, –NH–
CO–), 10.17 (s, 1H, –NH–CO–), 7.91 (s, 1H, –C=CH–N=),
7.67 (d, J = 7.2 Hz, 2H, Ar–H), 7.36 (t, J = 7.8 Hz, 2H,
123

Synthesis of 2-aminoxazole-5-carbamides and 2-aminothiazole-5-carbamides
Ar–H), 7.11 (t, J = 7.2 Hz, 1H, Ar–H), 2.15 (s, 3H, –CH3)
ppm; 13C NMR (125 MHz, DMSO-d6): d = 23.80 (CH3),
120.74 (2), 128.22, 129.59 (2), 133.26, 136.24, 140.75,
159.89 (C=O, carboxamide), 163.50 (O–C=N, oxazole),
2-Phenylacetamino-N-(4-methylphenyl)-5-oxazolecarbox-
amide (6f, C19H17N3O3)
White powder, yield 0.29 g (39.6 %); m.p.: 245–247 °C;
1H NMR (600 MHz, DMSO-d6): d = 11.83 (s, 1H, –NH–
CO–), 10.10 (s, 1H, –NH–CO–), 7.88 (s, 1H, –C=CH–N=),
7.56 (d, J = 7.8 Hz, 2H, Ar–H), 7.34–7.40 (m, 2H, Ar–H),
7.28–7.33 (m, 3H, Ar–H), 7.12 (d, J = 8.4 Hz, 2H, Ar–H),
3.75 (s, 2H, –CO–CH2–), 2.50 (s, 3H, –CH3) ppm; 13C
NMR (125 MHz, DMSO-d6): d = 20.99 (CH3), 42.91
(CH2), 120.77 (2), 127.33, 128.89 (2), 129.53 (2), 129.85
(2), 131.15, 133.30, 136.78, 138.55, 141.52, 155.20 (C=O,
carboxamide), 155.85 (C=O, carboxamide), 163.46 (O–
ꢀ
169.40 (C=O, acetamido) ppm; IR (KBr): m = 3,328,
3,149, 1,668, 1,650, 1,589, 1,330 cm-1; MS (70 eV):
m/z = 245 (M?).
2-Benzoylamino-N-(4-methylphenyl)-5-
oxazolecarboxamide (6c, C18H15N3O3)
White powder, yield 0.45 g (65.5 %); m.p.: 261–263 °C; 1H
NMR (600 MHz, DMSO-d6): d = 11.94 (s, 1H, –NH–CO–
), 10.17 (s, 1H, –NH–CO–), 8.01 (s, 2H, Ar–H), 7.97 (s, 1H, –
C=CH–N=), 7.65 (s, 1H, Ar–H), 7.56 (m, 4H, Ar–H), 7.17 (d,
J = 5.4 Hz, 2H, Ar–H), 2.28 (s, 3H, –CH3) ppm; 13C NMR
(125 MHz, DMSO-d6): d = 23.40 (CH3), 120.16 (2),
124.41, 127.30, 128.91 (2), 129.39 (2), 129.89 (2), 131.41,
135.21, 138.89, 141.46, 155.12 (C=O, carboxamide), 155.35
(C=O, carboxamide), 163.87 (O–C=N, oxazole) ppm; IR
ꢀ
C=N, oxazole) ppm; IR (KBr): m = 3,340, 3,137, 3,059,
2,922, 1,688, 1,645, 1,600, 1,487, 1,300, 1,193 cm-1; MS
(70 eV): m/z = 335 (M1).
2-Phenylacetamino-N-phenyl-5-oxazolecarboxamide
(6g, C18H15N3O3)
White powder, yield 0.35 g (50.2 %); m.p.: 239–241 °C;
1H NMR (600 MHz, DMSO-d6) : d = 11.85 (s, 1H, –NH–
CO–), 10.18 (s, 1H, –NH–CO–), 7.93 (s, 1H, –C=CH–N=),
7.60–7.67 (m, J = 7.8 Hz, 3H, Ar–H), 7.34–7.44 (m, 4H,
Ar–H), 7.25–7.29 (m, 2H, Ar–H), 7.11 (t, J = 7.2 Hz, 1H,
Ar–H), 3.76 (s, 2H, –CO–CH2–) ppm; 13C NMR
(125 MHz, DMSO-d6): d = 42.91 (CH2), 120.79 (2),
127.33, 128.88 (2), 129.43 (2), 129.85 (2), 131.15,
133.30, 136.78, 138.55, 141.52, 155.20 (C=O, carboxam-
ide), 155.85 (C=O, carboxamide), 163.46 (O–C=N,
ꢀ
(KBr): m = 3,373, 3,007, 1,690, 1,612, 1,539, 1,493, 1,259,
1,151 cm-1; MS (70 eV): m/z = 321 (M1).
2-Benzoylamino-N-phenyl-5-oxazolecarboxamide
(6d, C17H13N3O3)
White powder, yield 0.34 g (51.2 %); m.p.: 250–252 °C;
1H NMR (600 MHz, DMSO-d6): d = 11.96 (s, 1H, –NH–
CO–), 10.25 (s, 1H, –NH–CO–), 8.05 (s, 1H, Ar–H), 8.00
(s, 1H, –C=CH–N=), 7.71–7.22 (m, 3H, Ar–H), 7.66 (t, 1H,
J = 7.2 Hz, Ar–H), 7.56 (t, J = 7.2 Hz, 2H, Ar–H), 7.37
(t, J = 7.2 Hz, 2H, Ar–H), 7.12 (t, J = 7.8 Hz, 1H, Ar–H)
ppm; 13C NMR (125 MHz, DMSO-d6): d = 120.09 (2),
124.42, 127.37, 128.90 (2), 129.27 (2), 129.88 (2), 131.41,
135.21, 138.79, 141.40, 155.11 (C=O, carboxamide),
155.30 (C=O, carboxamide), 163.96 (O–C=N, oxazole)
ꢀ
oxazole) ppm; IR (KBr): m = 3,322, 3,060, 2,917, 1,681,
1,632, 1,600, 1,487, 1,304, 1,188 cm-1; MS (70 eV):
m/z = 321 (M1).
2-Amino-N-arylthiazole-5-carboxamides 5a–5c
To a solution of 3a–3c (25 mmol) in 40 cm3 H2O and
40 cm3 1,4-dioxane was added 4.4 g NBS (25 mmol) at
0 °C, while kept stirring for 1 h, after warmed to room
temperature and stirred for another 2 h, 4.4 g thiourea
(25 mmol) was added, the mixture was allowed to 70 °C
and stirred for 2 h, the pH of the resultant was adjusted to
8–9 by ammonia and then concentrated in vacuo. The
crude product was crystallized from toluene, affording the
counterparts 5a–5c.
ꢀ
ppm; IR (KBr): m = 3,387, 1,709, 1,676, 1,622, 1,499,
1,267, 1,148 cm-1; MS (70 eV): m/z = 307 (M1).
2-Benzoylamino-N-(2-methylphenyl)-5-oxazolecarbox-
amide (6e, C18H15N3O3)
White powder, yield 0.42 g (61.5 %); m.p.: 227–229 °C;
1H NMR (600 MHz, DMSO-d6): d = 12.93 (s, 1H, –NH–
CO–), 9.90 (s, 1H, –NH–CO–), 8.01 (d, J = 7.2 Hz, 2H,
Ar–H), 7.94 (s, 1H, –C=CH–N=), 7.65 (t, J = 7.2 Hz, 1H,
Ar–H), 7.55 (t, J = 7.2 Hz, 2H, Ar–H), 7.34 (d,
J = 7.2 Hz, 1H, Ar–H), 7.28 (d, J = 7.2 Hz, 1H, Ar–H),
7.23 (t, J = 7.2 Hz, 1H, Ar–H), 7.19 (t, J = 7.2 Hz, 1H,
Ar–H), 2.26 (s, 3H, –CH3) ppm; 13C NMR (125 MHz,
DMSO-d6): d = 23.34 (CH3), 120.16, 124.42, 127.24,
128.90 (2), 129.36 (2), 129.86, 129.89, 131.41, 132.10,
135.22, 138.79, 141.46, 155.10 (C=O, carboxamide),
155.35 (C=O, carboxamide), 163.82 (O–C=N, oxazole)
2-Amino-N-(4-methylphenyl)-5-thiazolecarboxamide
(5a, C11H11N2OS)
Yellow powder, yield 5.1 g (87.6 %); m.p.: 240–241 °C;
1H NMR (600 MHz, DMSO-d6): d = 9.77 (s, 1H, –NH–
CO–), 7.87 (s, 1H, –C=CH–N=), 7.60 (s, 2H, –NH2), 7.52
(d, J = 8.4 Hz, 2H, Ar–H), 7.11 (d, J = 7.8 Hz, 2H, Ar–
H), 2.25 (s, 3H, –CH3) ppm; 13C NMR (125 MHz, DMSO-
d6): d = 21.16 (CH3), 120.55 (2), 129.63 (2), 132.10,
133.30, 136.18, 138.55, 155.75 (C=O, carboxamide),
ꢀ
ppm; IR (KBr): m = 3,423, 3,124, 1,713, 1,684, 1,624,
1,456, 1,271, 1,153 cm-1; MS (70 eV): m/z = 321 (M1).
161.26 (S–C=N, thiazole) ppm; IR (KBr): m = 3,429,
ꢀ
123

Y. Zhou et al.
3,271, 3,063, 2,866, 1,626, 1,603, 1,531, 1,485,
1,302 cm-1; MS (70 eV): m/z = 233 (M1).
CO–), 10.17 (s, 1H, –NH–CO–), 7.99 (s, 1H, –C=CH–N=),
7.67 (d, J = 7.2 Hz, 2H, Ar–H), 7.36 (t, J = 7.8 Hz, 2H,
Ar–H), 7.11 (t, J = 7.3 Hz, 1H, Ar–H), 2.15 (s, 3H, –CH3)
ppm; 13C NMR (125 MHz, DMSO-d6): d = 23.08 (CH3),
120.77 (2), 128.19, 129.59 (2), 133.20, 136.21, 140.72,
159.85 (C=O, carboxamide), 161.52 (S–C=N, thiazole),
169.39 (C=O, acetamido) ppm; IR (KBr): mꢀ = 3,269,
1,679, 1,656, 1,589, 1,283 cm-1; MS (70 eV): m/z = 261
(M1).
2-Amino-N-(2-methylphenyl)-5-thiazolecarboxamide
(5b)
Yellow powder, yield 3.7 g (63.5 %); m.p.: 226–228 °C
(Ref. [9, 10] 226–230 °C).
2-Amino-N-phenyl-5-thiazolecarboxamide
(5c, C10H9N3OS)
Yellow powder, yield 4.4 g (79.5 %); m.p.: 238–240 °C;
1H NMR (600 MHz, DMSO-d6): d = 9.83 (s, 1H, –NH–
CO–), 7.89 (s, 1H, –C=CH–N=), 7.64 (d, J = 7.8 Hz, 2H,
Ar–H), 7.62 (s, 2H, –NH2), 7.31 (t, J = 7.8 Hz, 2H, Ar–
H), 7.05 (t, J = 7.2 Hz, 1H, Ar–H) ppm; 13C NMR
(125 MHz, DMSO-d6): d = 120.42 (2), 129.53 (2), 132.10,
133.30, 136.18, 138.50, 155.55 (C=O, carboxamide),
2-Acetylamino-N-(2-methylphenyl)-5-thiazolecarboxamide
(7c, C13H13N3O2S)
White powder, yield 0.33 g (56.7 %); m.p.: 205–207 °C;
1H NMR (600 MHz, DMSO-d6): d = 11.58 (s, 1H, –NH–
CO–), 10.17 (s, 1H, –NH–CO–), 7.91 (s, 1H, –C=CH–N=),
7.68 (d, J = 7.2 Hz, 1H, Ar–H), 7.36 (t, J = 7.8 Hz, 2H,
Ar–H), 7.13 (t, J = 7.2 Hz, 1H, Ar–H), 2.28 (s, 3H, –CH3),
2.15 (s, 3H, –CH3) ppm; 13C NMR (125 MHz, DMSO-d6):
d = 20.92 (CH3), 23.01 (CH3), 120.79, 121.80, 128.19,
129.48 129.61, 133.26, 136.20, 140.76, 159.85 (C=O,
carboxamide), 161.49 (S–C=N, thiazole), 169.33 (C=O,
ꢀ
161.16 (S–C=N, thiazole) ppm; IR (KBr): m = 3,275,
3,092, 1,628, 1,600, 1,549, 1,531, 1,483, 1,273 cm-1; MS
(70 eV): m/z = 219 (M?).
General procedure for preparation of 7a–7 h
ꢀ
acetamido) ppm; IR (KBr): m = 3,155, 1,668, 1,597,
1,281 cm-1; MS (70 eV): m/z = 275 (M1).
To a solution of 5a–5c (2.15 mmol) and 0.5 cm3 Et3N in
THF was added benzoyl chloride or acetic anhydride
(2.46 mmol) dropwise at 0 °C and stirred for 1 h, then the
mixture was warmed to room temperature and stirred for
another 2 h, the resultant was concentrated in vacuo. The
resulting mixture was partitioned between ethylacetate and
water, and the organic layer was washed with 1 N HCI,
5 % NaHCO3, and brine, and dried over MgSO4. After
removal of the solvent under reduced pressure, the residue
was purified by silica gel chromatography, and then re-
crystallized from toluene, affording the desired products
7a–7h.
2-Benzoylamino-N-(4-methylphenyl)-5-thiazolecarbox-
amide (7d, C18H15N3O2S)
White powder, yield 0.47 g (66.1 %); m.p.: 283–285 °C;
1H NMR (600 MHz, DMSO-d6): d = 12.93 (s, 1H, –NH–
CO–), 10.17 (s, 1H, –NH–CO–), 8.01 (s, 1H, –C=CH–N=),
8.13 (d, J = 7.2 Hz, 2H, Ar–H), 7.67 (t, J = 7.2 Hz, 1H,
Ar–H), 7.61 (d, J = 8.4 Hz, 2H, Ar–H), 7.57 (t,
J = 7.8 Hz, 2H, Ar–H), 7.17 (d, J = 8.4 Hz, 2H, Ar–H),
2.29 (s, 3H, –CH3) ppm; 13C NMR (125 MHz, DMSO-d6):
d = 23.44 (CH3), 120.15 (2), 124.42, 127.34, 128.90 (2),
129.30 (2), 129.88 (2), 131.40, 135.22, 138.79, 141.43,
155.12 (C=O, carboxamide), 155.35 (C=O, carboxamide),
2-Acetylamino-N-(4-methylphenyl)-5-thiazolecarboxamide
(7a, C13H13N3O2S)
ꢀ
161.51 (S–C=N, thiazole) ppm; IR (KBr): m = 3,136,
1,676, 1,634, 1,514, 1,298, 1,182 cm-1; MS (70 eV):
White powder, yield 0.27 g (45.4 %); m.p.: 287–288 °C;
1H NMR (600 MHz, DMSO-d6): d = 12.27 (s, 1H, –NH–
CO–), 10.10 (s, 1H, –NH–CO–), 8.28 (s, 1H, –C=CH–N=),
7.57 (d, J = 4.2 Hz, 2H, Ar–H), 7.15 (d, J = 4.2 Hz, 2H,
Ar–H), 2.28 (s, 3H, –CH3), 2.19 (s, 3H, –CH3) ppm; 13C
NMR (125 MHz, DMSO-d6): d = 21.07 (CH3), 23.0
(CH3), 120.81 (2), 128.19, 129.61 (2), 133.20, 136.21,
140.75, 159.84 (C=O, carboxamide), 161.51 (S–C=N,
thiazole), 169.44 (C=O, acetamido) ppm; IR (KBr):
m/z = 337 (M1).
2-Benzoylamino-N-phenyl-5-thiazolecarboxamide
(7e, C17H13N3O2S)
White powder, yield 0.39 g (53.6 %); m.p.: 232–235 °C;
1H NMR (600 MHz, DMSO-d6): d = 11.96 (s, 1H, –NH–
CO–), 10.25 (s, 1H, –NH–CO–), 8.02 (s, 1H, –C=CH–N=),
7.97–8.00 (m, 2H, Ar–H), 7.71 (d, J = 7.8 Hz, 1H, Ar–H),
7.66–7.69 (m, J = 6.6 Hz, 2H, Ar–H), 7.56 (t, J = 7.8 Hz,
2H, Ar–H), 7.37 (t, J = 7.8 Hz, 2H, Ar–H), 7.12 (t,
J = 7.2 Hz, 1H, Ar–H) ppm; 13C NMR (125 MHz,
DMSO-d6): d = 120.10 (2), 124.42, 127.34, 128.96 (2),
129.27 (2), 129.79 (2), 131.41, 135.23, 138.79, 141.43,
155.12 (C=O, carboxamide), 155.35 (C=O, carboxamide),
m = 3,329, 1,674, 1,657, 1,593, 1,279 cm-1; MS (70 eV):
ꢀ
m/z = 275 (M1).
2-Acetylamino-N-phenyl-5-thiazolecarboxamide
(7b, C12H11N3O2S)
White powder, yield 0.40 g (70.4 %); m.p.: 273–275 °C;
1H NMR (600 MHz, DMSO-d6): d = 11.58 (s, 1H, –NH–
ꢀ
161.01 (S–C=N, thiazole) ppm; IR (KBr): m = 3,238,
123

Synthesis of 2-aminoxazole-5-carbamides and 2-aminothiazole-5-carbamides
3,062, 2,930, 1,682, 1,634, 1,595, 1,515, 1,489, 1,267,
1,184 cm-1; MS (70 eV): m/z = 323 (M1).
Biologic activity
The human erythroleukemia K562 cell line maintained in
suspension culture in Iscove’s medium supplemented with
10 % iron-supplemented calf serum, 100 IU/cm3 penicillin
and 0.1 mg/cm3 streptomycin was added at 37 °C in a 7 %
CO2 incubator. Cells were seeded in triplicate in 96-well
plates, at a density of 104 cells/well, in the presence of
various concentrations of drugs (10-5 to 10-10 lM) dis-
solved in dimethyl sulfoxide (DMSO), the concentration of
DMSO did not exceed 0.5 % to avoid the effect of DMSO
on K562 cells. The cell proliferation assay was determined
by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoli-
um bromide (MTT) colorimetric method after 2 days of
incubation; the percentage of growth inhibition IC50 was
calculated by a comparison with DMSO-treated control
cells, which provided the drug.
2-Benzoylamino-N-(2-methylphenyl)-5-
thiazolecarboxamide (7f, C18H15N3O2S)
White powder, yield 0.47 g (62.4 %); m.p.: 237–239 °C;
1H NMR (600 MHz, DMSO-d6): d = 12.93 (s, 1H, –NH–
CO–), 9.90 (s, 1H, –NH–CO–), 8.13 (d, J = 7.8 Hz, 2H,
Ar–H), 8.06 (s, 1H, –C=CH–N=), 7.67 (t, J = 7.8 Hz, 1H,
Ar–H), 7.57 (t, J = 7.8 Hz, 2H, Ar–H), 7.34 (d,
J = 7.8 Hz, 1H, Ar–H), 7.29 (d, J = 7.2 Hz, 1H, Ar–
H), 7.23 (t, J = 7.2 Hz, 1H, Ar–H), 7.18 (t, J = 7.2 Hz,
1H, Ar–H), 2.26 (s, 3H, –CH3) ppm; 13C NMR
(125 MHz, DMSO-d6): d = 23.49 (CH3), 120.13,
120.27, 124.42, 127.34, 128.90 (2), 129.27, 129.30,
129.80 (2), 131.40, 135.22, 138.79, 141.43, 155.36
(C=O, carboxamide), 155.35 (C=O, carboxamide),
ꢀ
161.40 (S–C=N, thiazole) ppm; IR (KBr): m = 3,158,
3,061, 2,916, 1,680, 1,636, 1,605, 1,490, 1,267 cm-1; MS
Acknowledgments This work is supported by National Basic
Research Program of China (No.81260470) and Technology Sup-
porting Program of Jiangxi province (BE2009639).
(70 eV): m/z = 337 (M?).
2-Phenylacetamino-N-(4-methylphenyl)-5–thiazolecarbox-
amide (7g, C19H17N3O2S)
White powder, yield 0.50 g (70.1 %); m.p.: 224–226 °C;
1H NMR (600 MHz, DMSO-d6): d = 12.63 (s, 1H,
–NH–CO–), 10.11 (s, 1H, –NH–CO–), 8.09 (s, 1H,
–C=CH–N=), 7.56 (d, J = 7.8 Hz, 2H, Ar–H), 7.34 (m,
4H, Ar–H), 7.27 (m, 1H, Ar–H), 7.14 (d, J = 7.8 Hz,
2H, Ar–H), 3.82 (s, 2H, –CO–CH2), 2.35 (s, 3H, –CH3)
ppm; 13C NMR (125 MHz, DMSO-d6): d = 20.96 (CH3),
42.91 (CH2), 120.77 (2), 127.33, 128.88 (2), 129.53 (2),
129.87 (2), 131.15, 133.30, 136.78, 138.55, 141.52,
155.20 (C=O, carboxamide), 155.85 (C=O, carboxamide),
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ꢀ
161.46 (S–C=N, thiazole) ppm; IR (KBr): m = 3,223,
2,957, 1,665, 1,630, 1,603, 1,441 cm-1; MS (70 eV):
m/z = 351 (M ?).
2-(3-Nitrobenzoyl)amino-N-(4-methylphenyl)-5-
thiazolecarboxamide (7h, C18H14N4O4S)
White powder, yield 0.32 g (40.1 %); m.p.: 274–276 °C;
1H NMR (600 MHz, DMSO-d6): d = 12.63 (s, 1H, –NH–
CO–), 10.11 (s, 1H, –NH–CO–), 7.59 (s, 1H, –C=CH–N=),
7.56 (d, J = 7.8 Hz, 1H, Ar–H), 7.34–7.44 (m, 3H, Ar–H),
7.27 (d, J = 4.2 Hz, 2H, Ar–H), 7.14 (d, J = 7.8 Hz, 2H,
Ar–H), 2.27 (s, 3H, –CH3) ppm; 13C NMR (125 MHz,
DMSO-d6): d = 25.44 (CH2), 120.23, 124.26, 126.48,
127.39, 128.95 (2), 129.31, 129.32, 129.80 (2), 131.42,
135.27, 138.79, 141.48, 155.17 (C=O, carboxamide),
155.38 (C=O, carboxamide), 161.11 (S–C=N, thiazole)
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ꢀ
ppm; IR (KBr): m = 3,277, 2,957, 1,661, 1,632, 1,600,
1,500,1,488 cm-1. MS (70 eV): m/z = 382 (M1).
123