Chromeno[3,4-c]pyridin-5-ones: Selective human dopamine D4 receptor antagonists as potential antipsychotic agents

Article abstract of DOI:10.1021/jm970170v

The discovery of a series of chromeno[3,4-c]pyridin-5-ones with selective affinity for the dopamine D₄ receptor is described. Target compounds were tested for binding to cloned human dopamine D₂, D₃ and D₄ receptor subtypes expressed in Chinese hamster ovary (CHO) K-1 cells. Several compounds demonstrated single digit nanomolar K(i) values for binding to the D₄ receptor with several hundred-fold selectivities toward the D₂ and D₃ receptors. A limited SAR study of this series is discussed. In a mitogenesis assay measuring [³H]thymidine uptake, the target compounds showed antagonist to weak, partial agonist activity at the D₄ receptor, with intrinsic activities ranging from 0 to 35%. Compound 6, 3-benzyl-8-methyl-1,2,3,4- tetrahydrochromeno[3,4-c]pyridin-5-one, increased DOPA (L-3 4- dihydroxyphenylalanine) synthesis 84% in the hippocampus and 10% in the striatum of rat brain when dosed orally at 10 mg/kg.

Full text of DOI:10.1021/jm970170v

2688
J . Med. Chem. 1997, 40, 2688-2693
Ch r om en o[3,4-c]p yr id in -5-on es: Selective Hu m a n Dop a m in e D4 Recep tor
An ta gon ists a s P oten tia l An tip sych otic Agen ts
Paul C. Unangst,* Thomas Capiris, David T. Connor, Thomas G. Heffner, Robert G. MacKenzie,
Steven R. Miller, Thomas A. Pugsley, and Lawrence D. Wise
Departments of Chemistry and Therapeutics, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert Company,
2800 Plymouth Road, Ann Arbor, Michigan 48105
Received March 14, 1997X
The discovery of a series of chromeno[3,4-c]pyridin-5-ones with selective affinity for the
dopamine D4 receptor is described. Target compounds were tested for binding to cloned human
dopamine D2, D3, and D4 receptor subtypes expressed in Chinese hamster ovary (CHO) K-1
cells. Several compounds demonstrated single digit nanomolar Ki values for binding to the D4
receptor with several hundred-fold selectivities toward the D2 and D3 receptors. A limited
SAR study of this series is discussed. In a mitogenesis assay measuring [3H]thymidine uptake,
the target compounds showed antagonist to weak partial agonist activity at the D4 receptor,
with intrinsic activities ranging from 0 to 35%. Compound 6, 3-benzyl-8-methyl-1,2,3,4-
tetrahydrochromeno[3,4-c]pyridin-5-one, increased DOPA (L-3,4-dihydroxyphenylalanine) syn-
thesis 84% in the hippocampus and 10% in the striatum of rat brain when dosed orally at 10
mg/kg.
In tr od u ction
Schizophrenia is a complex disorder affecting ap-
proximately 1% of the population.1 The etiology of the
disease is unknown, but classical antipsychotics such
as haloperidol (1) are thought to act by blockade of
dopamine D2-like receptors in the brain.2 Molecular
biology techniques have now shown that these receptors
are subdivided into D2, D3, and D4 subtypes.3 D4
receptors are preferentially located in cortical and other
areas of the brain believed to control emotional and
cognitive functions.4 Some studies5,6 also suggest that
the concentration of D4 receptors in the brain is elevated
in schizophrenia, although this assertion is controver-
sial.7
Existing antipsychotic drugs, while generally ef-
fectively treating the positive symptoms of schizophre-
nia, can also induce the onset of Parkinson-like extrapy-
ramidal side effects. The atypical antipsychotic clozapine
(2) alleviates both positive and negative symptoms while
inducing a very low incidence of undesirable motor side
effects. Clozapine exhibits an approximately 10-fold
selectivity for D4 versus D2 receptors, and this may be
one possible mechanism contributing to the therapeutic
value of the drug.4,8 However, clozapine also has a high
affinity for a variety of other brain receptors, which may
explain in part its unique clinical profile.9
The recent cloning of the different dopamine (DA)
receptor subtypes allows the identification of ligands
selective for a single specific receptor subtype. Thus,
there is a need for selective ligands to elucidate the
pharmacological role of the D4 receptor. A selective D4
receptor antagonist may show antipsychotic activity
devoid of undesirable side effects.
receptor antagonist. This chemical series is structurally
quite different in comparison to the pyrrolo[2,3-b]-
pyridines and other previously reported selective D4
receptor antagonists. In this report we describe the
synthesis and receptor binding activity of the chromeno-
[3,4-c]pyridines.
Selective D4 receptor antagonists have recently been
reported in several chemical series. These include the
benzenesulfonamide U-101,387(3)10 and the pyrrolo[2,3-
b]pyridine L-745,870 (4),11 as well as several others.12-14
Screening of the Parke-Davis compound library identi-
fied a chromeno[3,4-c]pyridine 5 as a selective D4
Ch em istr y
Preparation of an initial group of chromeno[3,4-c]-
pyridine target compounds is shown in Scheme 1.
Condensation of an appropriate phenol with an N-
benzylpiperidone ester under strongly acidic conditions
(method A) gave the N-benzyl derivatives 5-8 (Table
1). Catalytic removal of the benzyl group of 5 and 6
X Abstract published in Advance ACS Abstracts, August 1, 1997.
S0022-2623(97)00170-2 CCC: $14.00 © 1997 American Chemical Society

Chromeno[3,4-c]pyridin-5-ones
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 17 2689
Sch em e 1a
a
Reagents: (a) methyl 1-benzyl-4-oxo-3-piperidinecarboxylate hydrochloride, H2SO4; (b) methyl 4-oxo-3-piperidinecarboxylate hydro-
chloride, H2SO4; (c) 20% Pd/C, H2, THF, MeOH; (d) R3R4PhCHO, NaBH(OAc)3, THF, 1,3-dimethyl-2-imidazolidinone.
Sch em e 2a
Ta ble 1. Receptor Binding Data for
N-Benzylchromeno[3,4-c]pyridines
a
Reagents: (a) 4-pyridinecarboxaldehyde, NaBH(OAc)3, THF,
Ki (nM)a
D2 D3
60
1,3-dimethyl-2-imidazolidinone.
Sch em e 3a
compd R1
R2
R3
R4 D4
D2/D4
5
6
7
OMe
Me
OMe 7-OMe
Me
OMe
OMe 9-OMe 4-Cl
Me
OH
OMe
Me
OMe
OMe
OMe
OMe
OMe
OMe
OMe
H
H
H
H
H
H
H
1.5
3.6
16
436
774
659
291
216
41
H
H
H
H
H
H
H
H
H
H
H
338
1300
8
10-OH
H
145
13
14
15
16
17
18
19
20
21
22
23
24
31
4-Cl
8.7 >5800
2780
667
682
106
8.5 >5800 >3000
H
H
H
H
H
H
H
H
H
H
H
4-Cl
4-Cl
4-F
4-F
2-Cl
3-Cl
3-Cl
4-Me
4-OMe
4-CF3
4-NO2
11
2.4
1170
2780
317 1160
548 1350
2210
2620
2630
4.3 >5800
7.5 >5800
34 >5800
773
171
324
95
450
69
17
5500
4-Cl 61 >5800
H
H
H
H
2.6
84 >5800
8.2 3700
1170
491
966
451
773
7.5 >5800 >3000
a
Affinities for cloned human dopamine receptors; Ki values are
means of one to four separate experiments obtained from six
concentrations of each compound, run in triplicate. Variation
between experiments was less than 15%.
a
Reagents: (a) ethyl 4-oxo-1-phenyl-3-piperidinecarboxylate
(method B) yielded the intermediates 9 and 10. Inter-
mediates 9-12 were also accessible by condensation of
phenols with an unsubstituted piperidone ester.15 Re-
action of 9-12 with substituted benzaldehydes in the
presence of sodium triacetoxyborohydride16 (method C)
gave a series of substituted benzyl analogs 13-24. A
similar reaction with 4-pyridinecarboxaldehyde gave the
pyridine derivative 25 (Scheme 2). Condensation of
phenol 26 with the appropriate piperidone ester (Scheme
3) permitted preparation of an N-phenyl analog 27 and
an isomeric pyridine ring derivative 28. Acylation of 9
hydrochloride, H2SO4; (b) ethyl 1-benzyl-3-oxo-4-piperidinecar-
boxylate hydrochloride, H2SO4.
with benzoyl chloride in pyridine gave the amide 29
(Scheme 4). Alkylation of 9 in DMF with alkyl bromides
gave derivatives 30 and 31. Physical data for the target
compounds are shown in Table 3.
Resu lts a n d Discu ssion
The affinities of the target compounds for the DA D2,
D3, and D4 receptors were determined in vitro by

2690 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 17
Unangst et al.
Ta ble 3. Physical Data for Chromeno[3,4-c]pyridin-5-ones
Sch em e 4a
compd
% yield
mp (°C)
formulaa
5
6
47
60
35
5
118-120
109-111
138-140
225-228b
140-142
173-175
147-149
C20H19NO3
C20H19NO2
7
C21H21NO4
C20H19NO3
8
13
14
15
16
17
18
19
20
21
22
23
24
25
27
28
29
30
31
70
48
65
52c
36
57
65
65
65
72
54
70
53
26
5
C20H18ClNO3
C21H20ClNO4
C20H18ClNO2
C19H16ClNO3‚HCl
>250
110-112
130-131
137-139
112-115
144-146
147-149
101-103
203-206
119-122
145-147
120-122
173-174
135-136
176-178
C20H18FNO3
C20H18FNO2
C20H18ClNO3
C20H18ClNO3
C20H17Cl2NO3
C21H21NO3
C21H21NO4
C21H18F3NO3
C19H18N2O3
C19H17NO3
C20H19NO3
C20H17NO4
C21H21NO3
C20H18N2O5
24
27
47
a
Compounds were analyzed for C, H, N. and are within (0.4%
b
of the theoretical values. Literature mp 222-224 °C (ref 22).
c Yield of the free base.
Ta ble 4. Antagonism of Quinpirole-Induced Mitogenesis
a
Reagents: (a) benzoyl chloride, pyridine; (b) R5Br, K2CO3,
intrinsic activitya
compd
intrinsic activitya
DMF.
compd
5
6
13
14
16
17
23.2 ( 3.4
12.4 ( 2.0
26.8 ( 7.4
21.2 ( 7.8
23.2 ( 0.85
35.2 ( 5.5
18
20
22
24
30
31
0
Ta ble 2. Receptor Binding Data for Compounds 25 and 27-30
30.7 ( 5.8
10.0 ( 1.4
0
and Standards
Ki (nM)a
23.6 ( 8.9
25.2 ( 5.2
compdb
D4
74
>3300
>3300
420
D2
D3
D2/D4
78
25
27
28
29
30
1
>5800
a
Percent stimulation of mitogenesis in transfected CHO 10001
cells in comparison to the full agonist quinpirole. Values are
means of four experiments ( SEM.
7.9
2.2
16
>5800
1.6
591
2.2
222
734
0.73
5.7
and 8-hydroxy, 4-chloro (16) derivatives were the most
selective compounds prepared. Substitution at the
7-position of the fused benzene ring (7) or at the 10-
position (8) was detrimental, while substitution at the
9-position (14) was well tolerated.
2
91
a
Affinities for cloned human dopamine receptors; Ki values are
means of one to four separate experiments obtained from six
concentrations of each compound, run in triplicate. Variation
b
between experiments was less than 15%. Compound structures
In general, substitution at the benzyl 4-position (13,
17, 22, 24, and 31) improved selectivity of D4 versus D2
binding in comparison to 5. The sole exception was the
4-methoxy derivative (23), which exhibited weak D4
binding. Other benzyl aromatic ring substitution pat-
terns (19, 21) gave inferior compounds. Similarly,
replacement of pyridine for benzene (25) or removal of
the side chain methylene (27) decreased activity. Chain
extension by one carbon (30) improved selectivity in
comparison to 5. The intermediates 9-12 (lacking a
tertiary amine moiety) were without substantial activ-
ity, as were the amide 29 and isomeric piperidine
derivative 28.
The intrinsic activities of the more selective com-
pounds were determined by measuring their ability to
block stimulation of mitogenesis, specifically [3H]thy-
midine uptake, caused by the full DA agonist quinpirole
in CHO 10001 cells transfected with DA D4 recep-
tors.17,18 The results are presented in Table 4 as percent
intrinsic activity relative to the full agonist quinpirole.
By definition, all compounds with 20% or less intrinsic
activity in this model (6, 18, 22, and 24) are antagonists,
while those exhibiting >20% intrinsic activity (5, 13,
14, 16, 17, 20, 30, and 31) are considered as partial
agonists.
are shown in Schemes 2-4.
measuring their ability to displace the DA ligand [3H]-
spiperone from cloned human DA receptor subtypes
expressed in Chinese hamster ovary (CHO) K-1 cells.17
Receptor affinities are presented as Ki values in Tables
1 and 2. Structure-activity relationships in the
chromeno[3,4-c]pyridine system were explored with
variation of the R1 and R2 phenyl substituents, the R3
and R4 benzyl side chain substituents, and the side
chain itself.
The 8-methoxy compound (5) initially identified in the
mass screening assay exhibited potent binding at the
D4 receptor as well as moderate selectivity. The cy-
clization reaction employed in the synthesis of the
chromeno[3,4-c]pyridine ring system (method A of
Scheme 1) requires an electron-donating function meta
to the hydroxy group. On a practical basis, this re-
quirement restricts SAR investigation of the fused
aromatic ring substituents (especially R1). Replace-
ments of the R1 methoxy group of 5 with methyl (6)
resulted in a compound with slightly lower D4 potency
and less selectivity toward the D2 receptor in compari-
son to 5. A similar relationship between the 8-methoxy
and 8-methyl derivatives was observed when the benzyl
side chain contained a 4-chloro (13 and 15) or 4-fluoro
(17 and 18) substituent. The 8-methoxy, 4-fluoro (17)
On the basis of its overall pharmacological profile,
compound 6 was chosen for additional evaluation. In

Chromeno[3,4-c]pyridin-5-ones
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 17 2691
Met h od A. 3-Ben zyl-8-m et h oxy-1,2,3,4-t et r a h yd r o-
ch r om en o[3,4-c]p yr id in -5-on e (5). A mixture of 26 (28.3
g, 227 mmol) and methyl 1-benzyl-4-oxo-3-piperidinecarboxy-
late hydrochloride (46.1 g, 162 mmol) was cooled in ice and
treated dropwise with a solution of 38 mL of H2O and 142 mL
of concentrated H2SO4. The mixture was stirred at room
temperature for 48 h and then added slowly to 500 g of ice
and 100 mL of NH4OH. Additional ice and NH4OH were
added until the pH of the resulting mixture was 10-11.
Stirring was continued until the initial gummy precipitate
became granular. The solid was filtered and washed with 3%
aqueous NaOH solution, followed by 10% MeOH in H2O.
Recrystallization from 2-propanol gave 24.5 g (47%) of 5: mp
118-120 °C; IR 1704, 1615, 1280, 1156 cm-1; 1H NMR (DMSO-
d6) δ 2.73 (t, J ) 5.6 Hz, 2H, CH2), 2.86 (m, 2H, CH2), 3.25 (s,
2H, CH2), 3.70 (s, 2H, CH2Ph), 3.84 (s, 3H, OCH3), 6.94-6.98
(m, 2H, 7,9-H), 7.26-7.36 (m, 5H, CH2Ph), 7.60 (d, J ) 8.7
Hz, 1H, 10-H); EIMS m/z 322 (MH+). Anal. (C20H19NO3)
C,H,N.
agreement with its affinities for DA receptors, 6 inhib-
ited the ability of the DA agonist quinpirole to stimulate
[3H]thymidine uptake in D4 cells with an IC50 of 3.7 nM,
but lacked significant activity in a similar DA D2 assay.
The functional role of brain D4 receptors is still unclear.
Thus, it is difficult to associate a given effect with a
specific antagonism of D4 receptors in the brain. In vivo,
DA antagonists are known to increase the rate of brain
DA synthesis in rodents. Pugsley et al.19 recently
reported that the Merck D4 antagonist (4) increased
catecholamine synthesis in striatal and hippocampal
regions of rat brain in wildtype mice but not in D4
knockout mice (that is, mice lacking functional D4
receptors). These results suggested that D4 receptors
may play a role in modulating brain catecholamine
synthesis in rodents. The effect of compound 6 on brain
catecholamine synthesis in rats was evaluated by
measuring the ability of 6 to increase the accumulation
of the catecholamine precursor DOPA (L-3,4-dihydrox-
yphenylalanine) after inhibition of L-aromatic amino
acid decarboxylase with NSD 1015.17 When dosed orally
at 10 mg/kg, 6 increased DOPA accumulation by 84%
in the D4-enriched hippocampus20,21 (DOPA levels were
141 ( 13 ng/g for control versus 259 ( 4.4 ng/g for
compound 6 treated animals). In contrast, DOPA levels
in the predominantly D2-expressing striatum were only
increased by a nonsignificant 10% (control 1236 ( 60
ng/g versus 1358 ( 160 ng/g for 6). In an additional
study, compound 6 when dosed at 3-30 mg/kg ip also
caused dose-dependent increases in hippocampal DOPA
accumulation without increasing DOPA levels in the
striatum. Thus, the large increase in catecholamine
synthesis in the hippocampus compared to the lack of
effect in the striatum may indicate a modulatory role
for 6 mediated by interaction with D4 receptors. Other
possible mechanisms to explain the increase in cat-
echolamine synthesis, such as antagonism of adrenergic
or serotonergic receptors seem unlikely, as compound
6 had no appreciable affinity (Ki > 700 nm) for rat brain
R1, R2, adrenergic, serotonin1A, or serotonin2A receptors.
Although not conclusive, since receptor occupancy has
not been measured, these findings, together with previ-
ous data involving D4 knockout mice, suggest the action
of 6 in the hippocampus may be related to D4 receptor
antagonism. Thus, in both in vitro assays and in vivo
in rats, compound 6 appears to have the profile of a
selective DA D4 antagonist.
Meth od B. 8-Meth oxy-1,2,3,4-tetr a h yd r och r om en o-
[3,4-c]p yr id in -5-on e (9). A solution of 5 (8.2 g, 26 mmol) in
150 mL of MeOH and 100 mL of THF was hydrogenated at
room temperature over a 20% palladium on carbon catalyst
(0.85 g) for 18 h. The catalyst was filtered and the filtrate
evaporated. Recrystallization of the residue from MeCN with
a small amount of added H2O gave 2.9 g (49%) of 9: mp 179-
181 °C (lit.15 mp 179-183 °C); IR 3324, 1691, 1614, 1279 cm-1
;
1H NMR (DMSO-d6) δ 2.71 (m, 2H, CH2), 2.97 (t, J ) 5.7 Hz,
2H, CH2), 3.53 (s, 2H, CH2), 3.85 (s, 3H, OCH3), 6.94-6.99 (m,
2H, 7,9-H), 7.61 (d, J ) 8.6 Hz, 1H, 10-H); EIMS m/z 232
(MH+). Anal. (C13H13NO3) C, H, N.
Meth od C. 8-Meth oxy-3-(4-m eth ylben zyl)-1,2,3,4-tet-
r a h yd r och r om en o[3,4-c]p yr id in -5-on e (22). A solution of
9 (1.2 g, 5.2 mmol) and 4-methylbenzaldehyde (0.68 g, 5.7
mmol) in 20 mL of THF and 7 mL of 1,3-dimethyl-2-imidazo-
lidinone was treated with acetic acid (0.29 mL, 5.2 mmol). The
mixture was stirred for 10 min, and sodium triacetoxyboro-
hydride (1.6 g, 7.5 mmol) was added over 30 min. The mixture
was stirred for 18 h and added to 300 mL of ice and H2O. The
precipitated solid was filtered, washed with H2O, and recrys-
tallized from EtOAc to yield 1.2 g (70%) of 22: mp 147-149
°C; IR 1706, 1611, 1237, 1085 cm-1; 1H NMR (DMSO-d6) δ 2.30
(s, 3H, CH3), 2.73 (t, J ) 5.6 Hz, 2H, CH2), 2.88 (m, 2H, CH2),
3.23 (s, 2H, CH2), 3.65 (s, 2H, CH2Ph), 3.85 (s, 3H, OCH3),
6.95-6.99 (m, 2H, 7,9-H), 7.15 (d, J ) 7.7 Hz, CH2Ph), 7.23
(d, J ) 8.0 Hz, 2H, CH2Ph), 7.62 (d, J ) 8.7 Hz, 1H, 10-H);
EIMS m/z 336 (MH+). Anal. (C21H21NO3) C, H, N.
3-(4-C h lo r o b e n zy l)-8-h y d r o x y -1,2,3,4-t e t r a h y d r o -
ch r om en o[3,4-c]p yr id in -5-on e Hyd r och lor id e (16). A so-
lution of 1215 (1.1 g, 5.0 mmol) and 4-chlorobenzaldehyde (0.71
g, 5.1 mmol) was reacted with sodium triacetoxyborohydride
(1.6 g, 7.5 mmol) as described in method C. The solid product
was recrystallized from EtOH to give 0.89 g (52%) of the free
base of 16. A solution of this material (0.45 g, 1.3 mmol) in
100 mL of Et2O was treated with HCl gas. The precipitated
product was filtered and triturated in EtOH to yield 0.48 g
(96%) of 16: mp >250 °C; IR 2586, 1726, 1617, 1416 cm-1; 1H
NMR (DMSO-d6) δ 3.24 (m, 3H, CH2), 3.70 (br s, 1H, CH2),
3.95 (br s, 2H, CH2), 4.51 (br s, 2H, CH2), 6.79 (d, J ) 2.2 Hz,
1H, 7-H), 6.88 (dd, J ) 2.4, 8.7 Hz, 1H, 9-H), 7.57-7.72 (m,
5H, Ph), 10.75 (s, 1H, OH), 11.54 (br s, 1H, NH+); EIMS m/z
342 (MH+). Anal. (C19H16ClNO3‚HCl) C, H, N.
We have described the synthesis and preliminary
dopamine receptor binding SAR for a novel series of
chromeno[3,4-c]pyridin-5-ones. These compounds will
be useful tools in exploring the significance of the role
of the D4 receptor in schizophrenia.
Exp er im en ta l Section
8-Met h oxy-3-p h en yl-1,2,3,4-t et r a h yd r och r om en o[3,4-
c]p yr id in -5-on e (27). Prepared from 26 (2.7 g, 22 mmol) as
described in method A, except that the piperidone used was
ethyl 4-oxo-1-phenyl-3-piperidinecarboxylate hydrochloride23
(2.7 g, 9.7 mmol). Recrystallization of the product from EtOH
gave 0.78 g (26%) of 27: mp 145-147 °C; IR 1711, 1614, 1408,
Melting points were determined on a Thomas-Hoover or
Electrothermal capillary apparatus and are uncorrected.
Elemental analyses were performed by the Analytical Chem-
istry staff at Parke-Davis (Ann Arbor, MI). The IR spectra
were recorded as potassium bromide disks on a Mattson
Cygnus 100 FTIR spectrometer. The 1H NMR spectra were
recorded on a Varian Unity 400 spectrometer with chemical
shifts reported in ppm relative to internal tetramethylsilane.
Mass spectra were recorded on a VG Masslab Trio-2A mass
spectrometer. Reactions were usually run under a nitrogen
atmosphere, and organic solutions were concentrated at
aspirator pressure on a rotary evaporator. Flash chromatog-
raphy was performed with E. Merck silica gel 60, 230-400
mesh ASTM.
1
1157 cm-1; H NMR (DMSO-d6) δ 2.99 (m, 2H, CH2), 3.58 (t,
J ) 5.7 Hz, 2H, CH2), 3.86 (s, 3H, OCH3), 4.04 (s, 2H, CH2),
6.97-7.28 (m, 7H, Ph), 7.67 (d, J ) 8.7 Hz, 1H, 10-H); EIMS
m/z 308 (MH+). Anal. (C19H17NO3) C, H, N.
3-Be n zyl-7-m e t h oxy-1,2,3,4-t e t r a h yd r o-9-oxa -3-a za -
p h en a n th r en -10-on e (28). Prepared from 26 (12.0 g, 97
mmol) as described in method A, except that the piperidone
used was ethyl 1-benzyl-3-oxo-4-piperidinecarboxylate hydro-

2692 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 17
Unangst et al.
chloride (29.8 g, 100 mmol). The crude product after treatment
with NH4OH was extracted with EtOAc. The organic layer
was washed with 2 N NaOH solution and brine, dried (Na2-
SO4), and evaporated. The residue was purified by chroma-
tography (30% EtOAc in hexane elution) and recrystallized
from EtOAc/hexane to yield 1.7 g (5%) of 28: mp 120-122 °C;
crease of DA synthesis (as indicated by DOPA levels) relative
to control animals.
Ack n ow led gm en t. We thank Dr. Gary McClusky
and staff for microanalytical and spectral data and Lynn
Georgic, Yu-Hsin Shih, Steven Whetzel, and Kim Zoski
for performing the biological assays. Compounds 14 and
29 were prepared by Robert Doubleday.
Su p p or tin g In for m a tion Ava ila ble: IR and 1H NMR
spectral data for compounds 6-8, 13-15, 17-21, and 23-25
(3 pages). Ordering information is given on any current
masthead page.
1
IR 1708, 1609, 1281, 1021 cm-1; H NMR (DMSO-d6) δ 2.51
(m, 2H, CH2), 2.66 (t, J ) 5.7 Hz, 2H, CH2), 3.71 (s, 2H, CH2),
3.75 (s, 2H, CH2), 3.84 (s, 3H, OCH3), 6.91 (dd, J ) 2.5, 8.8
Hz, 1H, 6-H), 6.97 (d, J ) 2.7 Hz, 1H, 8-H), 7.26-7.41 (m, 5H,
Ph), 7.44 (d, J ) 8.7 Hz, 1H, 5-H); EIMS m/z 322 (MH+). Anal.
(C20H19NO3) C, H, N.
3-Ben zoyl-8-m eth oxy-1,2,3,4-tetr a h yd r och r om en o[3,4-
c]p yr id in -5-on e (29). A suspension of 9 (0.50 g, 2.2 mmol)
in 5.0 mL of pyridine was cooled in a cold H2O bath while
benzoyl chloride (0.40 mL, 0.48 g, 3.4 mmol) was slowly added.
The mixture was stirred at room temperature for 18 h and
then added to 150 mL of ice cold 4 N HCl. The solid was
filtered, stirred in 150 mL of 5% aqueous Na2CO3, and filtered
again. Recrystallization from aqueous MeCN gave 0.17 g
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(24%) of 29: mp 173-174 °C; IR 1708, 1613, 1278, 1156 cm-1
;
1H NMR (DMSO-d6), run at 95 °C, δ 2.94 (m, 2H, CH2), 3.77
(m, 2H, CH2), 3.86 (s, 3H, OCH3), 4.39 (s, 2H, CH2), 6.94-
6.98 (m, 2H, 7,9-H), 7.44-7.49 (m, 5H, Ph), 7.62 (d, J ) 8.4
Hz, 1H, 10-H); EIMS m/z 336 (MH+). Anal. (C20H17NO4) C,
H, N.
8-Met h oxy-3-p h en et h yl-1,2,3,4-t et r a h yd r och r om en o-
[3,4-c]p yr id in -5-on e (30). A mixture of 9 (1.5 g, 6.5 mmol),
anhydrous K2CO3 (0.50 g, 4.7 mmol), and (2-bromoethyl)-
benzene (1.0 mL, 1.4 g, 7.3 mmol) in 10 mL of DMF was heated
at 90 °C for 18 h. The cooled reaction mixture was added to
300 mL of H2O and 150 mL of Et2O. The insoluble material
was filtered and washed with fresh Et2O. Recrystallization
from aqueous 2-propanol gave 0.60 g (27%) of 30: mp 135-
1
136 °C; IR 1704, 1621, 1295, 1160 cm-1; H NMR (DMSO-d6)
δ 2.71 (m, 2H, CH2), 2.97 (t, J ) 5.7 Hz, 2H, CH2), 3.53 (s, 2H,
CH2), 3.85 (s, 2H, OCH3), 6.94-6.99 (m, 2H, 7,9-H), 7.61 (d, J
) 8.6 Hz, 1H, 10-H); EIMS m/z 336 (MH+). Anal. (C21H21
NO3) C, H, N.
-
8-M e t h o x y -3-(4-n i t r o b e n z y l)-1,2,3,4-t e t r a h y d r o -
ch r om en o[3,4-c]p yr id in -5-on e (31). A mixture of 9 (1.2 g,
5.2 mmol), anhydrous K2CO3 (0.69 g, 5.0 mmol), and 4-ni-
trobenzyl bromide (1.1 g, 5.1 mmol) in 15 mL of DMF was
heated at 90 °C for 4 h. The cooled reaction mixture was
evaporated, and the residue was partitioned between EtOAc
and brine. The organic layer was dried (MgSO4) and evapo-
rated. Recrystallization of the residue from EtOAc yielded
0.87 g (47%) of 31: mp 176-178 °C; IR 1697, 1515, 1343, 1152
cm-1 1H NMR (DMSO-d6) δ 2.77 (t, J ) 5.5 Hz, 2H, CH2),
;
2.91 (m, 2H, CH2), 3.30 (s, 2H, CH2), 3.85 (s, 3H, OCH3), 3.86
(s, 2H, CH2Ph), 6.96-7.00 (m, 2H, 7,9-H), 7.62-7.67 (m, 3H,
Ph), 8.22 (d, J ) 8.7 Hz, 2H, Ph); EIMS m/z 367 (MH+). Anal.
(C20H18N2O5) C, H, N.
P h a r m a cology. Recep tor Bin d in g. The in vitro affini-
ties of compounds for cloned human DA receptors versus [3H]-
spiperone in CHO K1 cells were determined as previously
described.17
Mitogen esis Assa y. The effects of test compounds on [3H]-
thymidine uptake were determined essentially as described
by Chio.18 In brief, CHO 10001 cells transfected with human
D4 receptors were plated on 96-well plates in a minimum
essential medium (R MEM, Gibco) with 10% fetal calf serum
containing penicillin (100 units/mL) and streptomycin (100 µg/
mL). Forty-eight hours later, cells were washed with serum-
free media and maintained thereafter in serum-free media.
After 24 h, test compounds were added. Eighteen hours later,
[3H]thymidine (0.25 µCi/well) was added for 2 h, trypsin (100
µL of 0.25%) was added for 1 h, and the assay was terminated
by filtration using a Brandel 96-well harvester. The filters
were counted for radioactivity using the LKB â-plate counting
system.
Effects on DA Syn th esis.17 Striatal and hippocampal DA
synthesis were measured by HPLC with electrochemical
detection in rats given drug (60 min) and the L-aromatic amino
acid decarboxylase inhibitor NSD 1015 30 min prior to sacrifice
by decapitation. Data are expressed as the percentage in-

Chromeno[3,4-c]pyridin-5-ones
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J M970170V