Design, synthesis, and biological evaluation of novel 4-alkylamino-1- hydroxymethylimidazo[1,2-a]quinoxalines as adenosine A1 receptor antagonists

Article abstract of DOI:10.1016/j.bmc.2004.06.026

The preparation and biological evaluation of a series of 4-alkylamino-1-hydroxymethylimidazo[1,2-a]quinoxalines as adenosine A ₁ receptor antagonists are described. 4-Cyclopentylamino-7,8- dichloro-1-hydroxymethylimidazo[1,2-a]quinoxaline shows potent adenosine A ₁ receptor inhibitory activity, having K_i = 7 nM. A series of 4-alkylamino-1-hydroxymethylimidazo[1,2-a]quinoxalines have been synthesized and evaluated for their adenosine A₁ receptor inhibitory activity in the radioligand binding assays. The compounds were tested for the inhibition percent (IP) and the affinity toward A₁AR (K_i) that IP were more than 90% in the nanomolar range. 4-Cyclopentylamino-7,8-dichloro-1- hydroxymethylimidazo[1,2-a]quinoxaline 18 is the most potent compound in this series, having K_i = 7 nM, which is remarkably higher than that of IRFI-165 (K_i = 48). 1-Hydroxymethyl groups of the tricyclic heteroarmatic compounds displayed the potent affinities toward A₁AR.

Full text of DOI:10.1016/j.bmc.2004.06.026

Bioorganic & Medicinal Chemistry 12 (2004) 4701–4707
Design, synthesis, and biological evaluation of novel
-alkylamino-1-hydroxymethylimidazo[1,2-a]quinoxalines as
4
adenosine A receptor antagonists
1
*
Chun-He Liu, Bo Wang, Wei-Zhang Li, Liu-Hong Yun, Ying Liu, Rui-Bing Su,
*
Jin Li and He Liu
No. 7 Department, Beijing Institute of Pharmacology and Toxicology Academy, 27 Taiping Road, Beijing 100850, PR China
Received 16 May 2004;revised 20 June 2004;accepted 21 June 2004
Available online 20 July 2004
Abstract—A series of 4-alkylamino-1-hydroxymethylimidazo[1,2-a]quinoxalines have been synthesized and evaluated for their adeno-
sine A
1
receptor inhibitory activity in the radioligand binding assays. The compounds were tested for the inhibition percent (IP) and
AR (K ) that IP were more than 90% in the nanomolar range. 4-Cyclopentylamino-7,8-dichloro-1-hydroxy-
methylimidazo[1,2-a]quinoxaline 18 is the most potent compound in this series, having K =7nM, which is remarkably higher than
the affinity toward A
1
i
i
that of IRFI-165 (K =48). 1-Hydroxymethyl groups of the tricyclic heteroarmatic compounds displayed the potent affinities toward
i
A
ꢀ
1
AR.
2004 Elsevier Ltd. All rights reserved.
1
. Introduction
overlap
N
OH
ribose
N
Adenosine is a neurotransmitter and neuromodulator in
the central nervous system. It is now well established
that the multiple effects of the nucleoside are mediated
by activation of adenosine receptors, which have been
classified into four subtypes A , A , A , and A , based
N
N
R1
R1
N
R2
N
N
N
N
1
2a
2b
3
H
H
on biochemical, pharmacological, and molecular clon-
ing properties. The main potential therapeutic indica-
tions of adenosine A receptor antagonists are for the
Figure 1. Putative binding mode of 1-hydroxmethyl-4-alkylaminoim-
6
idazo[1,2-a]quinoxaline: overlap with the agonist N -cyclopentylade-
1
treatment of cognitive deficits, renal failure, acute respi-
ratory distress syndrome, cardiac arrhythmias, and asys-
tolic arrest.
nosine.
1
,2
1
amino acids, for example, N , N , N , and the three ribo-
se-hydroxyl groups. Therefore we designed 4-alkylam-
ino-1-hydroxymethyl imidazo[1,2-a]quinoxalines, these
6
9
The various types of adenosine A1 receptor (A AR)
1
10
3
–7
antagonists have described by other groups and were
reported to display A AR antagonistic structure–activ-
1
compounds bind to A AR by mimicking adenosine
1
8
,9
ity requirement. Lots of tricyclic heteroaromatic com-
pounds have been synthesized to develop new centrally
active A AR antagonists. The six–six–five ring system
derivatives as shown in Figure 1. From this overlap it
appears that hydroxymethyl group is overlapped with
the ribose-hydroxyl group, which may be an optimal
interaction with the binding site of the receptor to in-
crease the affinity. We recently synthesized 19 com-
pounds. All of them were evaluated for IP toward
radioligand, and the compounds whose IP were more
than 90% were tested for their affinity toward adenosine
1
can overlap with endogenous adenosine, which has
several sites that can potentially interact with receptor
1
Keywords: Adenosine A receptor;Imidazo[1,2- a]quinoxaline;Tricy-
clic heteroaromatic compounds.
*
0
Corresponding authors. Tel.: +86-10-66874612;fax: +86-10-
8211626;e-mail: liuhe@nic.bmi.ac.cn
A receptor, and structure–activity relationship (SAR)
1
studies were reported here.
6
968-0896/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.06.026

4702
C.-H. Liu et al. / Bioorg. Med. Chem. 12 (2004) 4701–4707
2
. Chemistry
determined using standard radioligand binding assay
2
procedures.
,17–20
3
Competitive displacement of [ H]-
3
Compounds 5–23 were synthesized as outlined in
Scheme 1. In detail, the hydroxy group of glycidol was
protected with 3,4-2H-pyran, then treated with NH3Æ-
H O to afford 1-amino-3-(tetrahydropyran-2-yloxy)pro-
pan-2-ol 1. Next, a mixture of the intermediate 1 and
substituted 2,3-dichloroquinoxalines was refluxed for
1,3-dipropyl-8-cyclopentyxanthine ([ H]-DPCPX) in
rat brain membranes was used to determine a full con-
centration-inhibition curve for each compound. The
binding potencies of the tested compounds, expressed
as their inhibited percent. The compounds whose IP
were more than 90% were tested for their affinity toward
A AR, expressed as their K values. The data of IP and
1
1
2
2
intermediates 2a–c.
0h in trichloromethane and Et N to transform into
3
1
i
1
2,13
2a–c were oxidated with CrO -
1
K values were listed in Table 1.
i
3
4,15
pyridine or Swernꢀs oxidant to intermediates 3a–c.
Intermediates 4a–c were prepared from 3a–c in trifluo-
roacetic acid and trifluoroacetic anhydride. Com-
pounds 5–23 were obtained from 4a–c with substituted
1
2
4. Results and discussion
1
6
amine in hexamethyldisilazane.
Based on the results of the site-directed mutagenesis
studies, the ribose-hydroxy groups of adenosine
interacts with Val87, Ser94, Ile274, Leu276, Thr277,
Compounds 5–23 were purified with up-dry column
UDC). The manipulation of UDC was ruled out. (i) Sil-
(
and His278 of adenosine A receptor, which were the
1
ica gel (GF254, U<38lm) was added into a 250·20mm
glass tube under reduced pressure. The sample was added
to about 20mm from the mouth of tube. The tube was
sealed with absorbent cotton. (ii) The tube was reversed
and immerged into solvent. (iii) After completely evolved,
the gel was pushed out, irradiated with ultraviolet lamp,
and cut down the region-adsorbed product, which was
washed with suitable solvent. The solvent was evaporated
under reduced pressure to give pure compounds.
1
0
amino acids shown to influence ligand binding. There-
fore, hydroxymethyl group in the compounds was intro-
duced in order to improve the affinities of the
compounds for A AR. As a result, the affinities of 4-al-
1
kylamino-1-hydroxymethyl imidazo[1,2-a]quinoxalines
(7, 12, 17, and 18) is higher than that of IRFI-165, which
was considered the most potent antagonist in the litera-
1
0
ture.
Affinity data reported in Table 1 clearly showed that all
the new compounds were characterized by a biological
profile. The affinities of compounds 7, 12, 17, 18, and
3. Biology
The adenosine A AR binding affinities of the 4-alkylam-
1
19 toward A AR were in the nanomolar range. On the
1
ino-1-hydroxymethylimidazo[1,2-a]quinoxalines
were
basis of both A AR affinity data and structural proper-
1
OH
(a)
OH
2
H N
O
+
O
O
O
1
OH
R
R
1
1
N
N
Cl
Cl
NH
R
1
1
N
N
O
(b)
+
1
O
R
Cl
2a-c
O
R
R
1
N
NH
Cl
O
(d)
(c)
O
1
N
3a-c
HO
HO
N
R
R
1
1
N
N
N
O
(e)
R
1
1
N
R
2
N
R
N
H
H
4a-c
5-23
Scheme 1. Reagents and conditions: (a) pyridinium p-toluenesulfonate, CH
2
Cl
2
, NH
4
3 3 3
OH/EtOH;(b) Et N, CH CN;(c) CrO –2Py or DMSO–
(
COCl) ;(d) (CF CO) O–CF COOH;(e) R NH , hexamethyldisilazane.
3
2
3
2
2
2

C.-H. Liu et al. / Bioorg. Med. Chem. 12 (2004) 4701–4707
4703
Table 1. Inhibition of adenosine A
1
receptor, IP± SEM (%) and K
i
(nM)
HO
N
R
R
1
1
N
N
R
2
N
H
Compd
R
1
R
2
i
IP± SEM (K , nM)
a
IRFI-165
92.0± 4.0% (48)
68.5± 4.5%
5
6
H
H
3 2 2
(CH ) –CH–CH –
CH
3
–(CH
2
)
2
–CH
2
–
75.5± 0.5%
7
8
9
H
H
H
94.0± 6.0% (19)
82.5± 3.5%
O
N
CH CH -
21.7± 11.3%
2
2
1
0
1
CH
CH
3
–
–
(CH
CH
3
)
2
–CH–CH
2
–
–(CH –CH –
47.0± 8.0%
73.5± 5.5%
1
3
3
2
)
3
2
12
CH
3
–
92.5± 0.5% (13)
1
3
4
CH
CH
3
–
–
C
(CH
6
H
5
–CH
2
–
44.0± 9.0%
32.5± 5.5%
1
3
3
)
2
2 3 2 2
N–CH –C(CH ) CH –
15
CH
3
–
O
N
CH CH -
24.0± 11.0%
2
2
1
6
7
Cl–
Cl–
CH
(CH
3
–(CH
2
)
2
–CH
2
–
76.5± 9.7%
94.5± 2.5% (23)
1
3
)
2
–CH–CH
2
–
1
8
9
Cl–
Cl–
93.0± 7.0% (7)
93.0± 1.0% (87)
1
2
0
1
Cl–
Cl–
C
6
H
5
–CH
2
–
60.5± 3.5%
2
N
CH CH -
77.0± 11.4%
2
2
2
2
3
Cl–
Cl–
(CH
3
)
2
N–CH –C(CH
2
3
)
2
CH
2
–
65.0± 20.6%
72.0± 3.0%
2
O
N
CH CH -
2 2
a
IRFI-165: N-Cyclopentyl-1-methylimidazo[1,2-a]quinoxalin-4-amine.
ties of the studied compounds, some suggestions can be
ruled out. (i) A common feature of these compounds
was the increase in A potency seen with the N-cyclopen-
site with strict steric requirements. A hydrophobic re-
gion having a limited degree of lipophilicity accommo-
dating ability has also been suggested.
1
tyl substitution at the exocyclic amine. (ii) Comparison
between the dichloride substitution class and the
remaining series suggested that the chloride was benefi-
5. Conclusion
cial to A AR affinities, for example, the affinity of 17
1
were higher than those of 5 and 10. (iii) The size of sub-
stitution at the exocyclic amine was very important for
In the present paper, we described the synthesis of
4-alkylamino-1-hydroxymethylimidazo[1,2-a]quinoxalines
defining toward A AR affinity. The affinities of com-
1
and their affinity toward A AR. The synthesis was based
1
pounds (9, 15, and 23), which were substituted with 2-
on intramolecular cyclization of quinoxaline substituted
by an aminoketone group. The affinities toward A AR
were determined using standard radioligand binding
assay procedures. Hydroxymethyl group in position 1
was beneficial to interaction with the binding site of
(
morpholin-4-yl)ethyl group at the exocyclic amine were
remarkably lower than those of compounds (6, 11, and
7) substituted with isobutyl group at the exocyclic
amine, which suggested the presence of an alkyl binding
1
1

4704
C.-H. Liu et al. / Bioorg. Med. Chem. 12 (2004) 4701–4707
the receptor. Substitution at the exocyclic amine was
previously shown to be essential.
6.1.6. 1-(3,6,7-Trichloroquinoxalin-2-amino)-3-(tetrahyd-
ropyran-2-yloxy)propan-2-one (3c). Chromium trioxide
(9.9g, 99mmol) was added to a magnetically stirred
solution of pyridine (16mL, 198mmol) in 150mL of
dry CH Cl . The deep burgundy solution was stirred
6. Experimental
2
2
for 15min at ambient temperature. At the end of this
period, a solution of the 2c (5g, 12.3mmol) in 30mL
of CH Cl was added in one portion. A tarry, black de-
posit separated immediately. After stirring an additional
1h at ambient temperature, the solution was decanted
from the residue, which was washed with 200mL of
6
6
.1. Chemistry
.1.1. General procedure. Melting points were deter-
2
2
mined using a RY-1 apparatus and are uncorrected.
H NMR spectra were recorded on Varian UNITY
1
INOVA 600MHz and JNM-ECA-400 400MHz instru-
ment in the solvent indicated below. Chemical shift val-
ues are reported in parts per million (ppm) relative to
that for tetramethylsilane used as an internal reference
standard. Spectral splitting patterns are designated as
follows: s, singlet;br, broad;d, doublet;t, triplet;m,
multiplet. Mass spectra were obtained from Micromass
ZabSpec and API3000 instruments. Elemental analysis
was carried at the CarloErba-1106.
CHCl . The combined organic solution was washed with
3
three 100mL portion of 5% aqueous sodium hydroxide
and three 100mL portion of saturated brine, and dried
over anhydrous magnesium sulfate. The solution was
evaporated under reduced pressure and purified by
chromatography on silica gel column, eluting with a
petroleum ether/EtOAc mixture (4:1) to give 59.3% yield
of white solid. MS (ESI): 404.1 (M+1).
6
.1.7. 1-(3-Chloroquinoxalin-2-amino)-3-(tetrahydropy-
All reactions were monitored by TLC on 25·75mm
glass sheets precoated with silica gel (GF254) to a thick-
ness of 0.25mm and viewed at 254nm UV-light.
ran-2-yloxy)propan-2-one (3a). 3a was prepared
from 2a following the protocol described for 3c. The
product was yellow oil (Yield: 50.2%). MS (ESI): 336.4
(M+1).
6
(
.1.2. 1-Amino-3-(tetrahydropyran-2-yloxy)propan-2-ol
1). A mixture of glycidol (29g, 0.392mol), 3,4-dihydro-
6.1.8. 1-(6,7-Dimethyl-3-chloroquinoxalin-2-amino)-3-(tet-
rahydropyran-2-yloxy)propan-2-one (3b). A solution of
oxalyl chloride (5.4g, 50mmol) in dry dichloromethane
(20mL) was cooled to ꢀ60ꢁC, which was added drop-
wise to a solution of DMSO (7.4g, 100mmol) in dry
dichloromethane (30mL) with the temperature
maintained below ꢀ50ꢁC. After being stirred at the
same temperature for 10min, to mixture was added
dropwise a solution of 2b (3.7g, 10mmol) in dry dichlo-
romethane (10mL), the mixture was stirred for 1h, and
then triethylamine (10.9g, 108mmol) was added drop-
wise to the mixture with the temperature maintained be-
low ꢀ50ꢁC. After 10min the reaction mixture was
allowed to warm to room temperature and then poured
into ice-water (200mL). The solution was extracted with
chloroform, and the organic layers were collected,
washed with saturated aqueous NaCl, dried over anhy-
drous magnesium sulfate. The solution was evaporated
under reduced pressure and purified by chromatography
on silica gel column, eluting with a petroleum ether/
EtOAc mixture (4:1) to give 40.3% yield of yellow oil.
MS (ESI): 364.0 (M+1).
pyran (61g, 0.726mol), and pyridinium p-toluenesulfo-
nate (10g, 0.04mol) in dry dichloromethane was
stirred for 40h at ambient temperature. Then the solu-
tion was diluted with ether and washed once with half
saturated brine to remove the catalyst. After evapora-
tion of the solvent, 35g of the oil was obtained. The
oil was added to a solution of 500mL of 25–28% NH3Æ-
H O and 500mL of ethanol. The solution was stirred for
2
40h at 40ꢁC. The mixture evaporated under reduced
pressure and purified by chromatography on silica gel
column, eluting with a CHCl /MeOH/NH ÆH O mixture
3
3
2
(
1
3:1:0.01) to give 50.4% yield of colorless oil. MS (ESI):
76.2 (M+1).
6.1.3. 1-(3,6,7-Trichloroquinoxalin-2-amino)-3-(tetrahyd-
ropyran-2-yloxy)propan-2-ol (2c). A solution of 1 (16g,
9
6
1.4mmol),
2,3,6,7-tetrachloroquinxaline
6mmol), and Et N (15mL, 100mmol) in 120mL of
(15g,
3
CHCl was refluxed under stirring for 30h. The mixture
3
evaporated under reduced pressure and purified by
chromatography on silica gel column, eluting with a
petroleum ether/EtOAc mixture (3:1) to give yellow
solid (Yield: 74.5%). Mp 114–116ꢁC. MS (ESI): 406.4
6.1.9. 7,8-Dichloro-1-hydroxymethylimidazo[1,2-a]quino-
xalin-4-one (4c). A mixture of 3c (2.95g, 7.3mmol),
(
M+1).
0
.5mL of trifluoroacetic acid, and 15mL of trifluoroace-
tic anhydride in 25mL of CHCl was refluxed for 40h.
6
2
.1.4. 1-(3-Chloroquinoxalin-2-amino)-3-(tetrahydropyran-
-yloxy)propan-2-ol (2a). 2a was prepared from 2,3-di-
3
The mixture was evaporated under reduced pressure.
The residue was stirred in 30mL of CH Cl and filtered
chloroquinxaline following the protocol described for
c. The product was yellow oil (Yield: 85.2%). MS
ESI): 338.2 (M+1).
2
2
2
(
to give 97.0% yield of yellow solid. Mp >300ꢁC. MS
1
(ESI): 283.9 (M+1). H NMR (DMSO-d ) (d): 12.18
6
(1H, s, H–N), 8.03 (1H, s, 2-ArH), 7.79 (1H, s, 9-
ArH), 7.58 (1H, s, 6-ArH), 6.08 (2H, s, CH ), 4.90
(1H, s, –OH).
6
.1.5. 1-(6,7-Dimethyl-3-chloroquinoxalin-2-amino)-3-(tet-
2
rahydropyran-2-yloxy)propan-2-ol (2b). 2b was prepa-
red from 2,3-dichloro-6,7-dimethylquinxaline following
the protocol described for 2c. The product was yellow
oil (Yield: 68.4%). MS (ESI): 366.1 (M+1).
6.1.10. 1-Hydroxymethylimidazo[1,2-a]quinoxalin-4-one
(4a). 4a was prepared from 3a following the protocol

C.-H. Liu et al. / Bioorg. Med. Chem. 12 (2004) 4701–4707
4705
1
described for 4c. The product was yellow solid (Yield:
8
60.3%). Mp 146–148ꢁC. MS (ESI): 328.3 (M+1). H
0.2%). MS (ESI): 216.3 (M+1).
NMR (DMSO-d ) (d): 8.39 (1H, s, ArH), 8.06 (1H, m,
6
ArH), 7.58 (1H, m, ArH), 7.40 (1H, m, ArH), 7.29
(1H, m, ArH), 4.63 (2H, s, CH ), 3.67 (2H, t, CH ),
6
.1.11. 7,8-Dimethyl-1-hydroxymethylimidazo[1,2-a]qui-
2
2
noxalin-4-one (4b). 4b was prepared from 3b following
the protocol described for 4c. The product was yellow
solid (Yield: 64.6%). MS (FAB): 244.1 (M+1).
3.58 (4H, t, 2CH ), 2.62 (2H, t, CH ), 2.50 (4H, t,
2 2
2CH ). Anal. Calcd for C H N O : C, 62.37;H,
2
17 21
5
2
6.47;N, 21.39. Found: C, 62.46;H, 6.35;N, 21.45.
6
.1.12. 1-Hydroxymethyl-4-isobutylaminoimidazo[1,2-a]-
6.1.17. 7,8-Dimethyl-1-hydroxymethyl-4-isobutylamino-
imidazo[1,2-a]quinoxaline (10). 10 was prepared from
4b and isobutylamine following the protocol described
quinoxaline (5). A mixture of 4a (0.5g, 2.3mmol), hexa-
methyldisilazane (5mL, 21.7mmol), p-toluenesulfonic
acid (0.06g, 032mmol), and isobutylamine (6mL,
for 5. The product was white solid (Yield: 36.2%). Mp
246–248ꢁC. MS (ESI): 299.1 (M+1).
1
6
0.6mmol) was stirred under stirring for 40h. The mix-
H NMR
(DMSO-d ) (d): 7.17 (1H, s, ArH), 7.10 (1H, s, NH),
ture was filtered, and the filtrate was evaporated under
reduced pressure and purified by UDC to give 38.2 yield
6
7.07 (1H, s, ArH), 6.90 (1H, s, ArH), 3.24 (2H, m,
CH ), 3.16 (2H, s, CH ), 2.25 (3H, s, CH ), 2.21 (3H,
of white solid. Mp 162–164ꢁC. MS (ESI): 271.4 (M+1).
2
2
3
1
H NMR (DMSO-d ) (d): 8.45 (1H, s, ArH), 8.08 (1H,
s, CH ), 2.25–221 (1H, br, OH), 1.98 (1H, m, CH),
3
6
dd, J=8Hz, ArH), 7.66 (1H, t, J=8Hz, NH),7.56
(
0.95 (6H, d, J=6.8Hz, 2CH ). Anal. Calcd for
3
1H, m, ArH), 7.37 (1H, m, ArH), 7.26 (1H, m, ArH),
.34 (1H, br, OH), 4.65 (2H, s, CH ), 3.66 (2H, t,
CH ), 2.09 (1H, m, CH), 0.93 (6H, d, J=8Hz, 2CH ).
C H N O: C, 68.43;H, 7.43;N, 18.78. Found: C,
1
7
22
4
5
68.55;H, 7.35;N, 18.81.
2
2
3
Anal. Calcd for C H N O: C, 65.61;H, 6.29;N,
1
6.1.18. 4-n-Amylamino-7,8-dimethyl-1-hydroxymethylim-
idazo[1,2-a]quinoxaline (11). 11 was prepared from 4b
and n-amylamine following the protocol described for
5
18
4
2
1.86. Found: C, 65.42;H, 6.35;N, 21.97.
6
.1.13. 4-Butylamino-1-hydroxymethylimidazo[1,2-a]qui-
5. The product was white solid (Yield: 27.2%). Mp
164–166ꢁC. MS (ESI): 313.5 (M+1).
1
noxaline (6). 6 was prepared from 4a and butylamine fol-
lowing the protocol described for 5. The product is
H NMR
(DMSO-d ) (d): 8.04 (1H, s, ArH), 7.46 (1H, s, ArH),
6
white solid (Yield: 33.6%). Mp 146–148ꢁC. MS (ESI):
7.41 (1H, s, ArH), 7.16 (1H, d, NH), 4.95 (2H, s,
CH ), 3.50 (2H, m, CH ), 2.34 (3H, s, CH ), 2.31 (3H,
1
2
70.9 (M+1). H NMR (DMSO-d ) (d): 8.40 (1H, s,
6
2
2
3
ArH), 8.05 (1H, d, ArH), 7.56 (2H, m, ArH, NH),
.50 (1H, m, ArH), 7.26 (1H, m, ArH), 5.20 (1H, t,
OH), 4.65 (2H, d, J=4Hz, CH ), 3.60 (2H, m, CH ),
s, CH ), 1.65 (2H, m, CH ), 1.34 (4H, m, 2CH ) 0.88
3 2 2
(3H, t, CH ). Anal. Calcd for C H N O: C, 69.20;
3 17 22 4
H, 7.74;N, 17.93. Found: C, 69.35;H, 7.55;N, 18.19.
7
2
2
1
CH ). Anal. Calcd for C H N O: C, 65.61;H, 6.29;
N, 21.86. Found: C, 65.73;H, 6.16;N, 21.66.
.70 (2H, m, CH ), 1.40 (2H, m, CH ), 0.95 (3H, t,
2 2
6.1.19. 4-Cyclopentylamino-7,8-dimethyl-1-hydroxyme-
thylimidazo[1,2-a]quinoxaline (12). 12 was prepared from
3
15 18
4
4b and cyclopentylamine following the protocol de-
scribed for 5. The product was white solid (Yield:
6
.1.14. 4-Cyclopentylamino-1-hydroxymethylimidazo[1,2-
1
a]quinoxaline (7). 7 was prepared from 4a and cyclopen-
tylamine following the protocol described for 5. The
product was white solid (Yield: 40.5%). Mp 170–
37.2%). Mp 240–242ꢁC. MS (ESI): 311.3 (M+1). H
NMR (DMSO-d ) (d): 8.04 (1H, s, ArH), 7.46 (1H, s,
6
ArH), 7.41 (1H, s, ArH), 7.16 (1H, m, NH), 5.66 (1H,
t, OH), 4.96 (2H, m, CH ), 4.51 (1H, m, CH), 2.34
1
1
72ꢁC. MS (ESI): 283.1 (M+1). H NMR (DMSO-d )
6
2
(
d): 8.44 (1H, s, ArH), 8.08 (1H, m, ArH), 7.58 (1H,
m, NH), 7.42 (1H, m, ArH), 7.38 (1H, m, ArH), 7.26
1H, m, ArH), 5.34 (1H, t, OH), 4.65 (2H, d, J=4Hz,
(3H, s, CH ), 2.31 (3H, s, CH ), 2.09–1.58 (8H, m,
3
3
4CH ). Anal. Calcd for C H N O: C, 69.65;H, 7.14;
2
18 22
4
(
N, 18.05. Found: C, 69.30;H, 7.32;N, 18.12.
CH ), 4.58 (1H, m, CH), 1.58–2.03 (8H, m, 4CH ).
2
2
Anal. Calcd for C H N O: C, 68.06;H, 6.43;N,
4
6.1.20. 4-Benzylamino-7,8-dimethyl-1-hydroxymethylimi-
dazo[1,2-a]quinoxaline (13). 13 was prepared from 4b
and benzylamine following the protocol described for
1
6
18
1
9.84. Found: C, 68.33;H, 6.16;N, 20.06.
6
.1.15. 4-Cyclohexylamino-1-hydroxymethylimidazo[1,2-
5. The product was white solid (Yield: 51.4%). Mp
144–146ꢁC. MS (ESI): 333.0 (M+1).
1
a]quinoxaline (8). 8 was prepared from 4a and cyclohex-
ylamine following the protocol described for 5. The
product was white solid (Yield: 21.5%). Mp 190–
H NMR
(DMSO-d ) (d): 8.05 (1H, s, ArH), 7.87 (1H, m, NH),
6
7.20–7.51 (7H, m, 7ArH), 4.97 (2H, s, CH ), 4.74 (2H,
2
1
1
92ꢁC. MS (ESI): 297.2 (M+1). H NMR (DMSO-d )
s, CH ), 2.34 (3H, s, CH ), 2.29 (3H, s, CH ). Anal.
3
6
2
3
(
d): 8.27 (1H, m, ArH), 7.60 (1H, m, ArH), 7.51 (1H,
s, ArH), 7.40 (1H, m, ArH), 7.29 (1H, m, ArH), 4.96
2H, s, CH ), 4.14 (1H, m, CH), 1.15–1.96 (10H, m,
Calcd for C H N O: C, 72.27;H, 6.06;N, 16.85.
20 20 4
Found: C, 72.42;H, 5.98;N, 16.78.
(
2
5
N, 18.90. Found: C, 68.78;H, 6.91;N, 18.98.
CH ). Anal. Calcd for C H N O: C, 68.90;H, 6.80;
6.1.21. 7,8-Dimethyl-4-(3-dimethylamino-2,2-dimethyl-
propyl)amino-1-hydroxymethylimidazo[1,2-a]quinoxaline
2
17 20
4
(14). 14 was prepared from 4b and N,N,2,2-tetramethyl-
3-aminopropylamine following the protocol described
6
.1.16. 1-Hydroxymethyl-4-[2-(morpholino-4-yl)ethyl]am-
inoimidazo[1,2-a]quinoxaline (9). 9 was prepared from 4a
and 2-(morpholino-4-yl)ethylamine following the proto-
col described for 5. The product was white solid (Yield:
for 5. The product was white solid (Yield: 51.4%). Mp
136–138ꢁC. MS (ESI): 356.4 (M+1).
1
H NMR
(DMSO-d ) (d): 8.04 (1H, s, ArH), 7.48 (1H, s, ArH),
6

4706
C.-H. Liu et al. / Bioorg. Med. Chem. 12 (2004) 4701–4707
7
2
2
.41 (1H, s, ArH), 4.95 (2H, s, CH ), 3.46 (2H, s, CH ),
2
C H Cl N O: C, 55.90;H, 4.97;N, 15.34. Found: C,
17 18 2 4
55.67;H, 5.05;N, 15.52.
2
.34 (3H, s, CH ), 2.31 (3H, s, CH ), 2.29 (6H, s, 2CH ),
3
3
3
.27 (2H, s, CH ), 0.96 (6H, s, 2CH ). Anal. Calcd for
2
3
C H N O: C, 67.58;H, 8.22;N, 19.70. Found: C,
2
0
29
5
6.1.27. 4-Benzylamino-7,8-dichloro-1-hydroxymethylimi-
dazo[1,2-a]quinoxaline (20). 20 was prepared from 4c
and benzylamine following the protocol described for
6
8.66;H, 8.05;N, 19.81.
6
4
.1.22. 7,8-Dimethyl-1-hydroxymethyl-4-[2-(morpholino-
-yl)ethyl]aminoimidazo[1,2-a]quinoxaline (15). 15 was
5
2
. The product is white solid (Yield: 56.9%). Mp 212–
1
14ꢁC. MS (ESI): 373.0 (M+1). H NMR (DMSO-d )
6
prepared from 4b and 2-(morpholino-4-yl)ethylamine
following the protocol described for 5. The product
(d): 8.52 (1H, s, ArH), 7.75 (1H, s, ArH), 7.59 (1H, s,
ArH), 7.43–7.19 (5H, m, 5ArH), 4.94 (2H, s, CH2),
4
57.92;H, 3.78;N, 15.01. Found: C, 57.73;H, 3.82;N,
1
was white solid (Yield: 61.0%). Mp 128–130ꢁC. MS
.75 (2H, s, CH ). Anal. Calcd for C H Cl N O: C,
2
18 14
2
4
1
(
ESI): 356.2 (M+1). H NMR (DMSO-d ) (d): 8.04
6
(
4
1H, s, ArH), 7.48 (1H, s, ArH), 7.40 (1H, s, ArH),
.96 (2H, s, CH ), 3.63 (2H, t, CH ), 3.58 (4H, t,
2 2
5.18.
2
CH ), 2.60 (2H, t, CH ), 2.50 (4H, t, 2CH ), 2.34
2
2
2
6
.1.28. 7,8-Dichloro-1-hydroxymethyl-4-[2-(pyrrolidin-1-
(3H, s, CH ), 2.30 (3H, s, CH ). Anal. Calcd for
3 3
C H N O : C, 64.20;H, 7.09;N, 19.70. Found: C,
6
yl)ethyl]aminoimidazo[1,2-a]quinoxaline (21). 21 was pre-
pared from 4c and 2-(pyrrolidin-1-yl)ethylamine follow-
ing the protocol described for 5. The product was white
1
9
25
5
2
3.95;H, 7.12;N, 19.81.
solid (Yield: 52.9%). Mp 194–196ꢁC. MS (ESI): 380.2
6.1.23. 4-Butylamino-7,8-dichloro-1-hydroxymethylimi-
dazo[1,2-a]quinoxaline (16). 16 was prepared from 4c
1
(
M+1). H NMR (DMSO-d ) (d): 8.50 (1H, s, ArH),
6
7
.74 (1H, s, ArH), 7.56 (1H, s, ArH), 4.92 (2H, s,
CH ), 3.65 (2H, t, CH ), 2.60 (2H, t, CH ), 1.69 (4H,
and isobutylamine following the protocol described for
5
2
2
2
. The product was white solid (Yield: 32.4%). Mp
10–212ꢁC. MS (ESI): 339.1 (M+1).
1
m, 2CH
H, 5.04;N, 18.42. Found: C, 53.91;H, 4.75;N, 18.55.
2
). Anal. Calcd for C17
H
19Cl
2
N
5
O: C, 53.69;
2
(
H NMR
DMSO-d ) (d): 8.51 (1H, s, ArH), 7.74 (1H, s, ArH),
6
7
CH ), 1.65 (2H, m, CH ), 1.37 (2H, m, CH ), 0.93
.56 (1H, s, ArH), 4.93 (2H, s, CH ), 3.54 (2H, t,
2
6.1.29. 7,8-Dichloro-4-(3-dimethylamino-2,2-dimethyl-
propyl)amino-1-hydroxymethylimidazo[1,2-a]quinoxaline
(22). 22 was prepared from 4c and N,N,2,2-tetramethyl-
3-aminopropylamine following the protocol described
2
2
2
(
3H, t, CH ). Anal. Calcd for C H Cl N O: C,
3 15 16 2 4
5
1
3.11;H, 4.75;N, 16.52. Found: C, 53.33;H, 4.65;N,
6.35.
for 5. The product was white solid (Yield: 61.0%). Mp
154–156ꢁC. MS (ESI): 396.1 (M+1).
1
6
.1.24. 7,8-Dichloro-1-hydroxymethyl-4-isobutylamino-
H NMR
(DMSO-d ) (d): 8.50 (1H, s, ArH), 7.75 (1H, s, ArH),
imidazo[1,2-a]quinoxaline (17). 17 was prepared from
c and isobutylamine following the protocol described
for 5. The product was white solid (Yield: 32.4%). Mp
6
4
7.57 (1H, s, ArH), 4.92 (2H, s, CH ), 3.49 (2H, s,
2
CH ), 2.30 (8H, s, 2CH ,CH ), 0.96 (6H, s, 2CH ). Anal.
2
3
2
3
1
2
10–212ꢁC. MS (ESI): 339.1 (M+1).
H
NMR
Calcd for C H Cl N O: C, 54.55;H, 5.85;N, 17.67.
18 23 2 5
Found: C, 54.66;H, 5.74;N, 17.81.
(
DMSO-d ) (d): 8.52 (1H, s, ArH), 8.03 {1H, t, NH},
6
7
OH), 4.93 (2H, m, CH ), 3.38 (2H, m, CH ), 2.08 (1H,
m, CH), 0.92 (6H, m, 2CH ). Anal. Calcd for
3
.75 (1H, s, ArH), 7.56 (1H, s, ArH), 5.84 (1H, t,
6.1.30. 7,8-Dichloro-1-hydroxymethyl-4-[2-(morpholino-
4-yl)ethyl]aminoimidazo[1,2-a]quinoxaline (23). 23 was
prepared from 4c and 2-(morpholino-4-yl)ethylamine
following the protocol described for 5. The product
2
2
C H Cl N O: C, 53.11;H, 4.75;N, 16.52. Found: C,
1
5
16
2
4
5
3.48;H, 4.55;N, 16.55.
was white solid (Yield: 63.8%). Mp 184–186ꢁC. MS
1
6
.1.25. 4-Cyclopentylamino-7,8-dichloro-1-hydroxymeth-
(ESI): 396.4 (M+1). H NMR (DMSO-d ) (d): 8.52
6
ylimidazo[1,2-a]quinoxaline (18). 18 was prepared from
c and cyclopentylamine following the protocol de-
scribed for 5. The product was white solid (Yield:
(1H, s, ArH), 7.76 (1H, s, ArH), 7.58 (1H, s, ArH),
4.93 (2H, s, CH ), 3.65 (2H, t, CH ), 3.57 (4H, t,
4
2
2
2CH ), 2.60 (2H, t, CH ), 2.50 (4H, t, 2CH ). Anal.
2
2
2
1
3
4.4%). Mp 240–242ꢁC. MS (ESI): 351.2 (M+1). H
Calcd for C H Cl N O : C, 51.53;H, 4.83;N, 17.67.
17 19 2 5 2
Found: C, 51.26;H, 5.01;N, 17.58.
NMR (DMSO-d ) (d): 8.52 (1H, s, ArH), 7.83 {1H, t,
6
NH}, 7.75 (1H, s, ArH), 7.56 (1H, s, ArH), 5.87 (1H,
t, OH), 4.93 (2H, m, CH ), 4.56 (1H, m, CH), 2.09–
2
6
affinities
.2. Biochemistry: measurement of A AR binding
1
1
.57 (8H, m, 4CH ). Anal. Calcd for C H Cl N O:
2 16 16 2 4
C, 54.71;H, 4.59;N, 15.95. Found: C, 54.48;H, 4.75;
N, 15.78.
6.2.1. Materials. Adenosine deaminase from calf intesti-
nal mucosa (ADA) was supplied by Fluka Chemie
6.1.26. 4-Cyclohexylamino-7,8-dichloro-1-hydroxymethyl-
imidazo[1,2-a]quinoxaline (19). 19 was prepared from 4c
6
GmbH. N -(phenylisopropyl)adenosine (R-PIA) was
3
provided by Sigma-Aldrich. [ H]-DPCPX (9.25MBq,
and cyclohexylamine following the protocol described
for 5. The product was white solid (Yield: 34.4%). Mp
2
50lCi) was from Amersham Biosciences.
1
2
(
58–260ꢁC. MS (ESI): 365.3 (M+1).
H NMR
DMSO-d ) (d): 8.51 (1H, s, ArH), 7.76 (1H, s, ArH),
6.2.2. Compounds radioligand binding assay. Com-
pounds were assessed for their ability to inhibit binding
6
7
CH), 1.98–1.15 (10H, m, 5CH ). Anal. Calcd for
.56 (1H, s, ArH), 4.93 (2H, s, CH ), 4.13 (1H, m,
2
3
of the A AR selective antagonist radioligand [ H]-
2
1

C.-H. Liu et al. / Bioorg. Med. Chem. 12 (2004) 4701–4707
4707
DPCPX to synaptosomal membranes from rat brain.
Briefly, membrane protein (30lM, 100lL) were incu-
bated with test compound solution (10lM, 100lL)
and [ H]-DPCPX (100lL) for 30min at 37ꢁC. Nonspe-
cific binding was determined in the presence of R-PIA
5. Colotta, V.;Catarzi, D.;Varano, F.;Cecchi, L.;Filacchi-
oni, G.;Martini, C.;Trincavellim, L.;Lucacchini, A.
Med. Chem. 2000, 43, 3118.
6. Chebib, M.;McKeveney, D.;Quinn, R. J. Bioorg. Med.
Chem. 2000, 8, 2581.
J.
3
7
. Settimo, F. D.;Primofiore, G.;Primofiore, G.;Paliani, S.;
Marini, A. M.;Matta, C. L.;Novelline, E.;Grecom, G.;
(
10lM, 100lL). The incubations were blocked by filtra-
tion using a cell harvester and the radioactivity contents
were measured by liquid scintillation. All the assays
were performed in triplicate or in quadruplicate.
The inhibition percent were calculated according to an
equation. Here, TCPM is total rate of binding, PCMP is
rate of test compounds binding, and NCMP is rate of
nonspecific binding.
Lucacchinim, A.;Trincavelli, L.;Martini, C.
Chem. 2001, 44, 316.
8. Bondavalli, F.;Botta, M.;Bruno, O.;Ciacci, A.;Corelli,
F.;Fassa, P.;Lucacchini, A.;Manetti, F.;Martini, C.;
Menozzi, G.;Mosti, L.;Ranise, A.;Schenone, S.;Tafi, A.;
Trincavelli, M. L. J. Med. Chem. 2002, 45, 4875.
J. Med.
9
. Doytchinova, I. J. Comp.-Aided Mol. Des. 2001, 15, 29.
J. Bio.
1
1
1
0. Rivkees, S. A.;Barbhaiya, H.;Ijzerman, A. P.
Chem. 1999, 274, 3617.
T
CPM ꢀ PCPM
CPM ꢀ NCPM
IP ¼ T
ꢁ 100%
1. Parham, W. E.;Anderson, E. L. J. Am. Chem. Soc. 1948,
0, 4187.
2. Ohmori, J.;Shimizu-Sasamata, M.;Okada, M.;Saka-
7
The compounds whose IP were more than 90% were
tested for their affinity toward A AR according to a
1
moto, S. J. Med. Chem. 1997, 40, 2053.
13. Lumma, W. C., Jr.;Randall, W. C.;Cresson, E. L.;Hoff,
J. R.;Hartman, R. D.;Lyon, T. F. J. Med. Chem. 1983,
1
9
published procedure and K values were obtain from
i
2
0
the Cheng–Prusoff equation.
2
6, 357.
4. Ratccliffe, R.;Rodehorst, R. J. Org. Chem. 1970, 35, 4000.
15. Mancuso, A. J.;Swern, D. Synthesis, 1981, 165.
1
References and notes
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6. Vorbruggen, H.;Krolikiewicz, K. Chem. Ber. 1984, 117,
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1
2
3
. Poulsen, S. A.;Quinn, R. J. Bioorg. Med. Chem. 1998, 6,
6
19–641.
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. Baraldi, P. G.;Cacciari, B.;Borea, P. A.;Varani, K.;
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19. Lohse, M. J.;Klotz, K. N.;Lindenborn-Fotinos, J.;
Reddington, M.;Schwabe, U.;Olsson, R. A.
Pharmacol. 1987, 336, 204.
4
. Novellino, E.;Abignente, E.;Cosimelli, B.;Greco, G.;
Iadanza, M.;Laneri, S.;Lavecchia, A.;Rimoli, M. G.;Da
Settimo, F.;Primofiore, G.;Tuscano, D.;Trincavelli, L.;
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Arch.
20. Cheng, Y. C.;Prusoff, W. H. Biochem. Pharmacol. 1973,
22, 3099.