1,2,3,4,5,6-Hexahydrobenzo[h][1,6]naphthyridin-5-ones: 5-HT7 receptor affinity

Article abstract of DOI:10.1211/146080800128735656

Synthesis of new analogues of DR 4004, derived from 1,2,3,4,5,6,- hexahydrobenzo[h][1,6]naphthyridin-5-ones is described. Their central pharmacological effects on the 5-HT₇ receptor have been studied in-vitro.

Full text of DOI:10.1211/146080800128735656

Pharm. Pharmacol. Commun. 2000, 6: 67±71
Received December 9, 1999
Accepted December 22, 1999
# 2000 Pharm. Pharmacol. Commun.
1,2,3,4,5,6-Hexahydrobenzo[h][1,6]naphthyridin-5-ones:
5-HT7 Receptor Af®nity
A. HINSCHBERGER, A. C. GILLARD, F. DAUPHIN* AND S. RAULT
Â
Centre d'Etudes et de Recherche sur le Medicament de Normandie, Laboratoire de Pharmacochimie, UFR
des Sciences Pharmaceutiques, 5 Rue Vaubenard, 14032 Caen Cedex and *UMR 6551 CNRS, Centre
Â
Â
Cyceron, boulevard Henri Becquerel, BP 5229, 14074 Caen, Cedex France
Abstract
Synthesis of new analogues of DR 4004, derived from 1,2,3,4,5,6,-hexahydrobenzo-
[h][1,6]naphthyridin-5-ones is described. Their central pharmacological effects on the 5-
HT7 receptor have been studied in-vitro.
A research programme has been developed to
design and synthesize new compounds with thera-
peutic potential via the 5-HTergic system against
CNS disorders, and to evaluate their biological
properties. In particular, we have recently used the
novel techniques of drug design and scaffolding in
association with studies of quantitative structure-
activity relationships (QSAR). Biological results
(binding with subtypes of 5-hydroxytryptamine (5-
HT) receptors) are obtained rapidly because of the
development of an appropriate structure (ATBI)
that contains the chemical structures and chemical
and pharmacological properties of more than 400
compounds with 5-HTergic activity.
meter (400 MHz) employing d6-DMSO as solvent.
Chemical shifts (d ppm) refer to tetramethylsilane,
which was used as internal reference. NH signals
appeared as broad singlets exchangeable with D2O.
In the data below, s ˆ singlet, d ˆ doublet, dd ˆ
double doublet, t ˆ triplet, q ˆ quartet, m ˆ
multiplet. Mass spectra were recorded on a Jeol
JMS GCmate spectrometer. Elemental analysis (C,
H, N) was performed by INSA, Rouen, France and
agreed with the proposed structures within Æ 0Á3%
of the theoretical values.
Representative preparative procedures
In this paper we describe the synthesis and
reactivity of 1,2,3,4,5,6-hexahydrobenzo[h][1,6]-
naphthyridines that have been recently reported
(Rault et al 1995; Gillard et al 1997a, b; Bureau
et al 1999). The structures of these compounds
were similar to that of DR 4004 (pKi 8Á67; Kikuchi
et al 1999; Figure 1), which has high af®nity
and selectivity for the 5-HT7 receptor.
5-Methoxy-1,2,3,4-tetrahydrobenzo[h][1,6]naphthy-
ridine(2a). Sodium methoxide (2 g, 36Á6 mmol) was
added to a solution of 5-chloro-1,2,3,4-tetrahydro-
benzo[h][1,6]naphthyridine 1a (2 g, 9Á2 mmol) in dry
N, N-dimethylformamide (15 mL) and the solution
was heated under re¯ux for 3h. The solvent was
removed under reduced pressure and the oily
residue dissolved in water (60 mL) and extracted
with diethyl ether (2 6 70 mL). The organic layer
was washed with water (2 6 90 mL), dried with
magnesium sulphate, treated with charcoal and
evaporated to dryness to give an oil that crystal-
lized from petroleum ether to give 2a as a yellow
powder (1Á3g, 72%); mp 147 ꢀC. IR (KBr) n: 3250,
1600, 1540, 1370, 1130 cmÀ1; 1H NMR (d6-
DMSO) d: 7Á91 (1H, d, H10), 7Á55 (1H, d, H7),
7Á46 (1H, t, H8), 7Á23(1H, t, H 9), 7Á06 (1H, s, NH),
3Á90 (3H, s, CH3), 3Á34 (2H, t, H2), 2Á61 (2H, t,
H4), 1Á85 (2H, m, H3); 13C NMR (d6-DMSO) d:
169Á7, 148Á9, 136Á3, 131Á9, 129Á6, 122Á1, 116Á7,
113Á8, 112Á9, 47Á8, 37Á1, 36Á6, 13Á3. Calculated
Materials and Methods
Chemical procedures
Melting points were determined on a Ko¯er block
È
and are uncorrected. IR spectra were recorded on a
1
Genesis Series FTIR spectrometer. H NMR spec-
tra were recorded on a Jeol JNM-LA 400 spectro-
Correspondence: S. Rault, Centre d'Etudes et de Recherche
Â
sur le Medicament de Normandie, UFR des Sciences Pharma-
ceutiques, 5 Rue Vaubenard, 14032 Caen Cedex, France.
Â

68
A. HINSCHBERGER ET AL
(1 g, 60%); mp 80ꢀC. IR (KBr) n: 3447, 2942, 1609,
1578, 1535, 1400, 1333, 1211, 1146, 1018, 903,
1
755 cmÀ1; H NMR (d6-DMSO) d: 8Á12 (1H, d,
H10), 8Á06 (1H, s, NH), 7Á66 (2H, m, H7 and H8),
7Á49 (1H, m, H9), 3Á44 (2H, m, H2), 2Á72 (2H, t, H4),
‡
1Á91 (2H, m, H3); MS m=z 3 3 2 (M), 199, 183, 171.
Calculated for C13H11N2O3SF3: C, 46Á99; H, 3Á34; N,
8Á43; found: C, 46Á95; H, 3Á48; N, 8Á45%.
Figure 1. The structure of DR 4004.
5-N-Benzylpiperazino-1,2,3,4-tetrahydrobenzo[h]-
[1,6]naphthyridine difumarate (7a). N-Benzyl-
piperazine (0Á18 mL, 1Á08 mmol) was added to a
solution of 5- tri¯uoromethylsulphonyl- 1,2,3,4-
tetrahydrobenzo[h][1,6]naphthyridine 5a (0Á3g,
0Á9 mmol) and potassium carbonate (0Á25 g,
1Á8 mmol) in N,N-dimethylformamide (5 mL).
After stirring for 3h under re¯ux, the solvent was
removed. The residue was dissolved in ether
(100 mL) and washed with water (2 6 70 mL).
The organic layer was dried over magnesium sul-
phate, treated with charcoal and evaporated to
dryness to give an oil that was dissolved in iso-
propanol (3mL). This solution was heated under
re¯ux with fumaric acid (1Á17 mmol) for 3min.
After cooling, the precipitate was ®ltered and
dried to give 7a as a yellow powder (0Á1 g, 20%);
mp 210ꢀC. IR (KBr) n: 3258, 2995, 2862, 1702,
1640, 1591, 1556, 1349, 1279, 1184, 1165, 983,
for C13H14N2O: C, 72Á82; H, 6Á54; N, 13Á07;
found: C, 73Á08; H, 6Á25; N, 12Á82%.
1,2,3,4,5,6-Hexahydrobenzo[h][1,6]naphthyridin-
5-one (4a). Potassium iodide (0Á90 g, 5Á60 mmol)
was added to a solution of 5-methoxy-1,2,3,4-
tetrahydrobenzo[h][1,6]naphthyridine 2a (1 g,
4Á67 mmol) in glacial acetic acid (35 mL) and the
mixture was heated at 110ꢀC for 3h. After evapora-
tion of the solvent the residue was dissolved in
water and extracted with chloroform (2 6 60 mL).
The organic layer was washed with aqueous
sodium hydrogen carbonate (2 6 100 mL) and
iodine was removed with an aqueous solution of
sodium thiosulphate (3 6 100 mL). The organic
layer was then evaporated in-vacuo and the solid
residue was recrystallized from ether to give 4a as a
white powder (0Á75 g, 80Á3%); mp > 260ꢀC. IR
(KBr) n: 3285, 2953, 1640, 1600, 1541, 1472, 1413,
1
965 cmÀ1; H NMR (d6-DMSO) d: 7Á93(1H, d,
H10), 7Á58 (1H, d, H7), 7Á48 (1H, t, H8), 7Á35 (5H,
m, Hphenyl), 7Á26 (2H, m, NH and H9), 3Á59 (2H, s,
1
1207 cmÀ1; H NMR (d6-DMSO) d: 10Á80 (1H, s,
0
CH2benzyl), 3Á39 (2H, t, H2), 3Á18 (4H, m, H2 and
H6, NH), 7Á78 (1H, d, H10), 7Á37 (1H, t, H8), 7Á19
(1H, d, H7), 7Á07 (1H, t, H9), 6Á92 (1H, s, H1, NH),
3Á40 (2H, t, H2), 2Á45 (2H, t, H4), 1Á79 (2H, m, H3);
13C NMR (d6-DMSO) d: 164Á6, 147Á4, 132Á5,
128Á0, 118Á2, 117Á6, 113Á8, 112Á9, 107Á2, 37Á0,
0
0
0
H6 ), 2Á67 (2H, t, H4), 2Á57 (4H, m, H3 and H5 ),
‡
1Á76 (2H, m, H3); MS m=z 358 (M ), 212, 199,
183, 146. Calculated for C31H35N4O8Á5: C, 62Á04;
H, 5Á83; N, 9Á33; found: C, 62Á07; H, 5Á78; N,
9Á46%.
‡
36Á8, 13Á2; MS m=z 200 (M ), 181, 162. Calculated
for C12H12N2O: C, 71Á98; H, 6Á04; N, 13Á99; found:
C, 72Á13; H, 5Á76; N, 13Á96%.
6-(4-Bromobutyl)-2,3,4,5-tetrahydro-1H-benzo[h]-
[1,6]naphthyridin-5-one (6a). Sodium hydride
(0Á45 g, 15 mmol) was added to a suspension of
1,2,3,4,5,6-hexahydrobenzo[h][1,6]naphthyridin-5-
one 4a (2 g, 10 mmol) in dry N,N-dimethylforma-
mide (40 mL). The mixture was stirred for 15 min
(approx.) at room temperature before addition of
1,4-dibromobutane (1Á3mL, 11 mmol). Stirring
was then continued for 19 h at room temperature.
This mixture was poured into water (150 mL)
and extracted with diethyl ether (2 6 150 mL).
The organic layer was washed with water
(2 6 100 mL), dried over magnesium sulphate and
evaporated under reduced pressure to give 6a as an
oily residue which was puri®ed by chromatography
on silica gel with ethyl acetate±cyclohexane
(50 : 50 v=v) as eluent to give solid 6a (0Á73g,
22%); mp 122ꢀC. IR (KBr) n: 3308, 2929, 2844,
5-Tri¯uoromethylsulphonyl-1,2,3,4-tetrahydrobenzo-
[h][1,6]naphthyridine (5a). Tri¯uoromethanesul-
phonyl anhydride (1Á5 mL, 9 mmol) was added
dropwise to a suspension of 1,2,3,4,5,6-hexahydro-
benzo[h][1,6]naphthyridin-5-one 4a (1 g, 5 mmol)
cooled to 0ꢀC in dry pyridine (12 mL). The mixture
was stirred at room temperature overnight under
argon. Water (50 mL) was added and the solution
was extracted with dichloromethane (3 6 40 mL),
washed with water (3 6 50 mL), and the organic
layer was dried over magnesium sulphate, treated
with charcoal and ®ltered through celite. Evapora-
tion of the solvents furnished 5a as an oil that was
triturated in petroleum ether until crystallization

1,2,3,4,5,6-HEXAHYDROBENZO[H][1,6]NAPHTHYRIDIN-5-ONES
69
1624, 1599, 1534, 1453, 1325, 1260, 1190,
C30H36N4O5Á5: C, 66Á46; H, 6Á83; N, 10Á34;
found: C, 66Á59; H, 6Á78; N, 10Á32%.
1
749 cmÀ1; H NMR (d6-DMSO) d: 7Á87 (1H, d,
H10), 7Á52 (1H, t, H8), 7Á45 (1H, d, H7), 7Á17 (1H, t,
0
H9), 6Á95 (1H, s, NH), 4Á20 (2H, t, H4 ), 3Á59 (2H, t,
0
H1 ), 3Á30 (2H, t, H2), 2Á48 (2H, t, H4), 1Á80 (6H, m,
‡
Results and Discussion
0
0
H2 =3 and H3); MS m=z 3 3 5 (M), 255, 200, 174.
Calculated for C16H19N2OBr: C, 57Á32; H, 5Á71; N,
8Á36; found: C, 57Á67; H, 5Á89; N, 8Á68%.
Chemistry
5-Chloro-1,2,3,4-tetrahydrobenzo[h][1,6]naphthyri-
dine 1a and 6-chloro-2,3,4,5-tetrahydro-1H-aze-
pino[3,2-c]quinoline 1b, respectively, were
obtained by rearrangement of pyrrolo[2,1-c]-
[1,4]benzodiazepine-5,11-dione and pyrido[2,1-c]-
[1,4]benzodiazepin-6,12-dione by treatment with
phosphorus oxychloride under microwave heating
conditions (Rault et al 1995; Bureau et al 1999).
1,2,3,4,5,6 - Hexahydrobenzo [h][1,6] naphthyrid-
in-5-one 4a and its homologue 2,3,4,5,6,7-hexa-
hydro-1H-azepino[3,2-c]quinoline 4b were easily
obtained by treating the chloroimidates 1a and 1b
with sodium methoxide or ethoxide in N,N-dime-
thylformamide to give the corresponding alkyl-
iminoethers 2a, 2b and 3a, 3b (Figure 2) which
were then converted to the lactams 4a, 4b in good
yield, by the action of potassium iodide (1Á5 eq) in
acetic acid at 100ꢀC (Hoffman et al 1993). The
tautomeric equilibrium lactam±lactim enabled
reactivity of the N6 amine group (lactam) or
hydroxyl group (lactim). On the other hand, the
lack of reactivity of nitrogen N1 was because of the
tautomeric equilibrium encountered in the 4-amino-
quinoline series (Renault & Cartron 1966). Thus,
the tri¯uoromethanesulfonate (tri¯ate) 5a was
obtained by treatment of the chloroimidate 4a with
tri¯uoromethanesulphonyl anhydride (1Á8 eq) in dry
pyridine at room temperature for 12 h. This tri¯ate
reacted with N-benzylpiperazine (1Á2 eq) in N,N-
dimethylformamide under re¯ux for 3h to give the
amidine 7a (Figure 3).
6-[4-(4-Phenylpiperazin-1-yl)-butyl]-2,3,4,5-tetra-
hydro-1H-benzo[h][1,6]naphthyridin-5-one fuma-
rate (8a). 6-(4-Bromobutyl)-2,3,4,5-tetrahydro-1H-
benzo[h][1,6]naphthyridin-5-one 6a (0.6 g, 1.79
mmol) was dissolved in N,N-dimethylformamide
(10 mL) in the presence of potassium carbonate
(0Á29 g, 2Á15 mmol) and N-phenylpiperazine
(0Á3mL, 1Á79 mmol) and the mixture was main-
tained under re¯ux for 45 min. After cooling, water
(100 mL) was added and the mixture was extracted
with chloroform (150 mL). The organic layer was
washed with water (3 6 100 mL), dried over mag-
nesium sulphate and calcium chloride, treated with
charcoal, and concentrated to dryness to give an
oily residue that was triturated in diethyl ether until
crystallization. The resulting solid was dissolved in
isopropanol (11 mL). Fumaric acid (2Á76 mmol)
was added and the mixture was warmed under
re¯ux for 1 h. After cooling, a white powder was
obtained; this was collected by ®ltration to give 8a
(0Á5 g, 52%); mp 188ꢀC. IR (KBr) n: 3308, 2932,
2842, 1702, 1625, 1599, 1542, 1455, 1362, 1213,
1
748 cmÀ1; H NMR (d6-DMSO) d: 7Á86 (1H, d,
H10), 7Á50 (2H, m, H7 and Hphenyl), 7Á18 (3H, m,
H8 and Hphenyl), 6Á93(3H, m, NH, and H phenyl),
0
6Á78 (1H, t, H9), 4Á19 (2H, t, H1 ), 3Á29 (2H, t, H2),
0
0
0
3Á16 (4H, m, H7 and H9 ), 2Á61 (4H, m, H6 and
0
0
H10 ), 2Á50 (4H, m, H4 and H4 ), 1Á80 (2H, m, H3),
‡
0
0
1Á59 (4H, m, H2 and H3 ); MS m=z 416 (M ), 284,
255, 207, 161, 111, 84. Calculated for
Figure 2. Preparation of 1,2,3,4,5,6-hexahydrobenzo[h][1,6]naphthyridin-5-one (4a) and 2,3,4,5,6,7-hexahydro-1H-azepino[3,2-
c]quinoline (4b). Reagents: i. RONa, dimethylformamide; ii. KI, CH3COOH.

70
A. HINSCHBERGER ET AL
Figure 3. Preparation of 5-N-benzylpiperazino-1,2,3,4-tetrahydrobenzo[h][1,6]naphthyridine difumarate (7a). Reagents: i. Tf2O
(tri¯uoromethane sulphonic acid anhydride), pyridine; ii. N-benzylpiperazine, K2CO3, dimethylformamide.
Figure 4. Preparation of 6-[4-(4-Phenyl-piperazin-1-yl)-butyl]-2,3,4,5-tetrahydro-1H-benzo[h][1,6]naphthyridin-5-one fumarate.
Reagents: i. Br(CH2)4Br, HNa, dimethylformamide; ii. N-phenylpiperazine, K2CO3, dimethylformamide.
Table 1. Percentage inhibition of [3H]LSD binding by 10À6
The direct substitution of chloroimidate 1a was
and 10À8 M 5-N-benzylpiperazino-1,2,3,4-tetrahydrobenzo[h]-
dif®cultandrequiredhightemperatureandpressureÐ
[1,6]naphthyridine difumarate (7a) and 6-[4-(4-phenylpipera-
zin-1-yl)-butyl]-2,3,4,5-tetrahydro-1H-benzo[h][1,6]naphthyri-
din-5-one fumarate (8a).
reaction in a sealed tube with microwave-heating.
The N-bromobutyllactam 6a was prepared by the
action of 1,4-dibromobutane in the presence of
sodium hydride (1Á5 eq) in N,N-dimethylformamide
for 19 h at room temperature. Treatment of this
lactam 6a with N-phenylpiperazine in boiling N,N-
dimethylformamide, in the presence of potassium
carbonate, gave, after 45 min, the N-phenylpiper-
azinobutyllactam 8a in good yield (Figure 4).
Inhibition (%)
Compound
10À6
M
10À8
M
7a
8a
58
88
27
12
Compounds 7a and 8a were tested for their
capacity to displace [3H]LSD (2 nM) from its
binding site in the guinea-pig. The percentage in-
hibition (I%) was determined at 10À6 or 10À8 M and
values of Ki (inhibition constants) or IC50 (dose
resulting in inhibition) were evaluated (Table 1).
These preliminary results are encouraging
because the compound 8a has an af®nity of 0Á1 mM
(approx.) for the 5-HT7 receptor from man.
Biological results
To assess the central pharmacological action of
compounds 7a and 8a on the 5-HT7 receptor, samples
of cloned subtype 7 5-HTergic receptor from man
(Nen, CRM-047; 38 mg mLÀ1) were incubated in
buffer (Tris-HCl 50 nM, MgSO4 10 nM, EDTA
0Á5 nM, pH 7Á4) for 60 min with different amounts
(0Á5±8 nM) of [3H]LSD (Shen et al 1993). Protein-
radioligand binding was terminatedbyrapid ®ltration
through Whatman GF=A ®bre ®lters. The ®lters were
washed with Tris-HCl buffer (50 mM, pH 7Á4;
5 6 1 mL). Non-speci®c binding of [3H]LSD was
quanti®ed in the presence of 10 mM clozapine.
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