Novel N-[1-(1-substituted 4-piperidinylmethyl)-4-piperidinyl]benzamides as potent colonic prokinetic agents.

Article abstract of DOI:10.1016/S0960-894X(02)00060-4

A series of novel N-[1-(1-substituted 4-piperidinylmethyl)-4-piperidinyl]benzamides was prepared and its compounds were evaluated for their binding to 5-HT(4) receptors and effects on gastrointestinal motility in conscious dogs. 4-Amino-N-[1-[1-(4-aminobu

Full text of DOI:10.1016/S0960-894X(02)00060-4

Bioorganic & Medicinal Chemistry Letters 12 (2002) 967–970
Novel N-[1-(1-Substituted 4-Piperidinylmethyl)-4-
piperidinyl]benzamides as Potent Colonic Prokinetic Agents
Hiroshi Harada,a Hiroshi Yamazaki,a Yoshihito Toyotomi,a Hirotaka Tateishi,a
Yukiko Mine,b Naoyuki Yoshidab and Shiro Katoa,*
aMedicinal Chemistry Group, Chemistry Research Laboratories, Dainippon Pharmaceutical Co., Ltd.,
Enoki 33-94, Suita, Osaka 564-0053, Japan
bDiscovery Pharmacological II Group, Pharmacology & Microbiology Research Laboratories, Dainippon Pharmaceutical Co., Ltd.,
Enoki 33-94, Suita, Osaka 564-0053, Japan
Received 10 December 2001; accepted 19 January 2002
Abstract—A series of novel N-[1-(1-substituted 4-piperidinylmethyl)-4-piperidinyl]benzamides was prepared and its compounds
were evaluated for their binding to 5-HT4 receptors and effects on gastrointestinal motility in conscious dogs. 4-Amino-N-[1-[1-(4-
aminobutyl)-4-piperidinylmethyl]-4-piperidinyl]-5-chloro-2-methoxybenzamide (15) was found to have a potent binding affinity for
5-HT4 receptors (IC50: 6.47 nM) and showed excellent colonic prokinetic activity. # 2002 Published by Elsevier Science Ltd.
Introduction
associated with mass movement.14,15 We designed the
structurally novel 4-amino-1-[1-(3-amino-2-hydroxy-
propyl)-4-piperidinylmethyl]piperidine (2) from 2 -amino-
methyl-4-(4-fluorobenzyl)morpholine, which is the amine
moiety of mosapride, via 1-(3-amino-2-hydroxypropyl)-
4-benzylpiperidine (1, Scheme 1). On the basis of the
results of structure–activity relationships (SARs), we
found that 4-amino-N-[1-[1-(4-aminobutyl)-4-piperidinyl-
methyl]-4-piperidinyl]-5-chloro-2-methoxybenzamide (15)
is a potent colonic motility enhancer. Here, the synthesis
and SARs concerning the binding affinity for 5-HT4
receptors and gastric antral and colonic motility in dogs
of a series of N-[1-(1-substituted 4-piperidinylmethyl)-
4-piperidinyl]benzamides are described.
The serotonin 4 (5-HT4) receptors are located in the
gastrointestinal tract,1À3 heart,4 urinary bladder,5 and
brain.6 In the gastrointestinal system, in particular,
5-HT4 receptors are distributed from the esophagus to
the colon and are especially involved in the regulation of
gastrointestinal motility.7,8 Mosapride,9 a 5-HT4 recep-
tor partial agonist developed in our laboratories, is used
clinically as a gastroprokinetic agent in Japan. Other
novel and potent 5-HT4 receptor agonists such as the
indole carbazimidamide tegaserod10,11 and the 2,3-
dihydrobenzo[b]furan-7-carboxamide
prucalopride12
are currently advanced in clinical development for the
treatment of various forms of constipation. As the
colonic motility enhancement of mosapride is weaker
than the gastric antral motility in conscious dogs
implanted with force transducers,13 we were interested
in identifying a potent and selective 5-HT4 receptor
agonist which enhances lower gastrointestinal motility.
Colonic motility in dogs consists of rhythmically occur-
ring contractile states that have migrating and non-
migrating motor complexes. The main propulsive force
in the canine colon appears to be a function of large-
amplitude giant migrating contractions (GMCs). It is
well known that GMCs occur during defecation and are
*Corresponding author. Tel.: +81-6-6337-5904; fax: +81-6-6338-
7656; e-mail: shiro-kato@dainippon-pharm.co.jp
0960-894X/02/$ - see front matter # 2002 Published by Elsevier Science Ltd.
PII: S0960-894X(02)00060-4

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H. Harada et al. / Bioorg. Med. Chem. Lett. 12 (2002) 967–970
Chemistry
group of 10a,b by hydrogenolysis, the other deprotec-
tion of the Cbz group was carried out. Thus, reaction of
10a,b with MeSO3H in the presence of anisole in
refluxing CHCl3 afforded the deprotected piperidines
11a,b, which were treated with N-protected amino acid
derivatives, followed by deprotection to give 19–28.
Reduction of the several N-protected amides with bor-
ane and reaction of 11a with EPP, following by depro-
tection afforded 12–17. Methanesulfonylation of 14 in
the presence of Et3N gave 18 in ca. 50% yield (Scheme
3).
Isonipecotic acid was treated with benzyl chloroformate
in aqueous NaOH–CH2Cl2 mixture to give 1-benzyloxy-
carbonyl (Cbz) piperidine-4-carboxylic acid (3) in 94%
yield. Treatment of 3 with SOCl2, followed by reaction
of the resulting 4-piperidinecarbonyl chloride with
commercially available 4-[tert-butoxycarbonyl (Boc)]-
aminopiperidine (4) in the presence of Et3N in CH2Cl2
afforded the piperidinylamide 5 in 83% yield. Reduction
of the amide moiety of 5 with borane–THF complex
gave the corresponding 1-(4-piperidinylmethyl)piperi-
dine 6 in 96% yield. After deprotection of the Cbz group
using hydrogenolysis, the resulting 4-(tert-butoxy-
carbonyl)amino-1-(4-piperidinylmethyl)piperidine was
treated with N-(2,3-epoxypropyl)phthalimide (EPP) to
produce the epoxy ring opened product 7. Reaction of 7
with hydrazine monohydrate, followed by condensation
of the aminoethanol 8 with 4-amino-5-chloro-2-meth-
oxybenzoic acid (ACMB) using 1-ethyl-3-[3-(dimethyl-
amino)propyl]carbodiimide hydrochloride (EDC) as a
coupling agent and successive deprotection of the Boc
group gave the benzamide 9 in 67% overall yield
(Scheme 2).
Results and Discussion
Gastric and colonic motility enhancing activities in
conscious dogs implanted with force transducers were
measured as follows. The compounds prepared (1.0 mg/
kg, iv) were administered to dogs in a postprandial state
(2–3 h after feeding). The signals from the force trans-
ducers implanted in the gastric antrum and ascending
colon were analyzed using our own system controlled by
a computer. The motor index given by the processing
system corresponded to the measurements of the area
surrounded by the contraction wave and base line, that
is, the product of the amplitude (voltage) and the time
in min over a fixed period. The motor index for the
30 min period after administration of each compound is
expressed as a percentage of that for the 30 min period
before administration. The colonic motility was expres-
sed by the induction number of GMCs. Mosapride at
1.0 mg/kg, iv did not induce any GMCs associated with
defecation and all other compounds except 16 produced
a less potent gastric motility enhancement than mosa-
pride. The binding affinity for 5-HT4 receptors was
assayed using [3H]GR1138038, a specific 5-HT4 receptor
ligand in guinea-pig striatum. All compounds exhibited
much more potent affinity for 5-HT4 receptors than
mosapride. The pharmacological results are given in
Table 1.
Treatment of the key intermediates 5 and 6 with
aqueous HCl, following by condensation of the result-
ing 4-aminopiperidines with ACMB provided 10a,b in
good yield. In order to avoid the elimination of 5-chloro
Scheme 1.
Scheme 2. Reagents andꢀconditions: (i) (1) ClCO2Bn, rt, 15 h; (ii) (1) SOCl2, CH2Cl2, reflux, 1 h; (2) 4, Et3N, rt, 4 h; (iii) BH3, THF, rt, 13 h; (iv) (1)
HCl–EtOH, rt, 2h.
.
5% Pd/C, H2, EtOH, 30 C; (2) EPP, MeCN, reflux, 15 h; (v) NH2NH2 H2O, EtOH, reflux, 0.5 h; (vi) (1) ACMB, EDC, CH2Cl2, rt, 3 h; (2) 30% aq
Scheme 3. Reagent and conditions: (i) (1) 30% aq HCl–EtOH, rt, 1 h; (2) ACMB, EDC, CH2Cl2, rt, 3 h; (ii) MeSO3H, PhOMe, 3 h; (iii) HOOC-Y-
.
NHP, EDC; (iv) deprotection; (v) (1) BH3, THF, rt, 15 h; (2) deprotection; (vi) (1) EPP, MeCN, reflux, 15 h; (2) NH2NH2 H2O, EtOH, reflux, 0.5 h;
(vii) MeSO2Cl, Et3N, rt, 3 h.

H. Harada et al. / Bioorg. Med. Chem. Lett. 12 (2002) 967–970
969
The binding affinity for 5-HT4 receptors of the N-[1-(4-
piperidinylmethyl)-4-piperidinyl]benzamide 12 was
more potent than that of the N-[3-(1-piperidinyl)-2-
hydroxypropyl]benzamide 9 (IC50: 14.4 nM vs IC50:
40.6 nM). In addition, 9 showed a moderate toxi-
city. Thus, 12 was selected and we examined a
series of N-[1-(1-substituted 4-piperidinylmethyl)-4-
piperidinyl]benzamides. The benzamide 13 with a 2-
aminoethyl substituent showed the same binding affinity
for 5-HT4 receptors as 12. Compounds 12 and 13 as well
as mosapride did not produce any GMCs. On the other
hand, elongation of the methylene chain of 13 (yielding
14–16) led to an increase in colonic motility enhance-
ment as GMCs were observed several times. The bind-
ing affinity for 5-HT4 receptors of 15 was ca. 2times
more potent than that of 14 and 16. Compound 15
having a straight alkylene group showed more potent
colonic motility enhancement and 5-HT4 receptor affin-
ity than 17 having the corresponding branched alkylene
group. Introduction of methanesufonyl group (giving
18) into the amino group of 14 produced a moderate
colonic motility enhancement independent of the
potency of affinity for 5-HT4 receptors. This result sug-
gested that the binding affinity for 5-HT4 receptors and
the induction number of GMCs are not remarkably
influenced by the basicity of amine moiety. Next, we
addressed compounds with a carbonyl group. Exchange
of a methylene group of 13 into a carbonyl group (giv-
ing 19) was found to cause an increase in gastro-
intestinal motility and affinity for 5-HT4 receptors.
Introduction of methylene and ethylene groups (giving
20 and 21, respectively) in 19 yielded a colonic motility
enhancement identical to that of 19. Compound 21
showed a much potent affinity for 5-HT4 receptors
(IC50; 3.99 nM). Replacement of a methylene group
between two piperidine rings of 21 by a carbonyl group
(yielding 22) caused a drastic decrease in 5-HT4 receptor
affinity, indicating that the basic nitrogen atom in the
piperidine ring would be an important factor for a
potent 5-HT4 receptor affinity. Compound 23, which is
the n-butylene analogue of 19, did not induce GMCs
although it showed a potent affinity for 5-HT4 recep-
tors. Introduction of methyl and propyl groups (giving
24–28) in 19 or 20 led to a decrease in colonic motility
enhancement. These compounds exhibited a potent affi-
nity for 5-HT4 receptors. As a whole, the clear relation-
ship between the binding affinity for 5-HT4 receptors
Table 1. Pharmacological results of benzamide derivatives 12–28
Compd
R
X
Gastrointestinal
motility
(1.0 mg/kg, iv)
5-HT4
binding
IC50 (nM)
Stomach GMCs
(number)
(%)
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
CH2CH(OH)CH2NH2 H2
121
127
151
148
194
177
151 1.1
165
107
130
5.4132242
112—
127
121
—
—
7
6
4
1
22
5
3
5
14.4
14.3
13.4
6.47
11.2
14.3
(CH2)2NH2
(CH2)3NH2
(CH2)4NH2
(CH2)5NH2
H2
H2
H2
H2
CH2CH(Me)CH2NH2 H2
(CH2)3NHSO2Me
COCH2NH2
H2
H2
H2
H2
O
9.30
9.50
3.99
CO(CH2)2NH2
CO(CH2)3NH2
CO(CH2)3NH2
CO(CH2)4NH2
COCH(Me)NH2
H2
H2
3.91
—
—
1
5.06
5.08
2.57
2.53
COCH(Me)CH2NH2 H2
COCH(Pr)NH2
COCH(isoPr)NH2
COCMe2NH2
H2
H2
H2
117
147
112— .60
—
2
Mosapride
188
—
113.0
— no GMCs.
Figure 1. Effects of 15 on gastrointestinal motility in postprandial state in a conscious dog.

970
H. Harada et al. / Bioorg. Med. Chem. Lett. 12 (2002) 967–970
and the induction number of GMCs was not observed;
it was considered that other mechanisms contributed to
the colonic motility enhancement. On the basis of the
above screening results, 15 with a 4-aminobutyl sub-
stituent was found to be optimal as novel colonic pro-
kinetic agent. Finally, we examined the effects of 15 on
the gastrointestinal motility in postprandial state in a
conscious dog. When 15 was given as an intravenous
bolus dose of 1.0 mg/kg, the motility of the gastric
antrum, duodenum, and colons 1–5 (4, 8, 16, 24, and
32cm from the ileocolonic junction, respectively) was
rapidly enhanced as shown in Figure 1. Compound 15
induced several times GMCs associated with defecation
without causing diarrhea and vomit in comparison with
mosapride. Furthermore, 15 was effective in fecal
excretion in unfasted mice at doses >1 mg/kg, sc.
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