Synthesis and structure-activity relationships of N-propyl-N-(4- pyridinyl)-1H-indol-1-amine (besipirdine) and related analogs as potential therapeutic agents for Alzheimer's disease

Article abstract of DOI:10.1021/jm9506433

A series of novel N-(4-pyridinyl)-1H-indol-1-amines and other heteroaryl analogs was synthesized and evaluated in tests to determine potential utility for the treatment of Alzheimer's disease. From these compounds, N-propyl-N- (4-pyridinyl)-1H-indol-1-amine (besipirdine, 4c) was selected for clinical development based on in-depth biological evaluation. In addition to cholinomimetic properties based initially on in vitro inhibition of [³H]quinuclidinyl benzilate binding, in vivo reversal of scopolamine- induced behavioral deficits, and subsequently on other results, 4c also displayed enhancement of adrenergic mechanisms as evidenced in vitro by inhibition of [³H]clonidine binding and synaptosomal biogenic amine uptake, and in vivo by reversal of tetrabenazine-induced ptosis. The synthesis, structure-activity relationships for this series, and the biological profile of 4c are reported.

Full text of DOI:10.1021/jm9506433

570
J . Med. Chem. 1996, 39, 570-581
Syn th esis a n d Str u ctu r e-Activity Rela tion sh ip s of
N-P r op yl-N-(4-p yr id in yl)-1H-in d ol-1-a m in e (Besip ir d in e) a n d Rela ted
An a logs a s P oten tia l Th er a p eu tic Agen ts for Alzh eim er ’s Disea se1
J oseph T. Klein,* Larry Davis, Gordon E. Olsen, George S. Wong, Francis P. Huger, Craig P. Smith,
Wayne W. Petko, Michael Cornfeldt, J effrey C. Wilker, R. D. Blitzer, E. Landau, V. Haroutunian,
Lawrence L. Martin, and Richard C. Effland
Hoechst-Roussel Pharmaceuticals Inc., Neuroscience Therapeutic Domain, Somerville, New J ersey 08876
Received August 30, 1995X
A series of novel N-(4-pyridinyl)-1H-indol-1-amines and other heteroaryl analogs was synthe-
sized and evaluated in tests to determine potential utility for the treatment of Alzheimer’s
disease. From these compounds, N-propyl-N-(4-pyridinyl)-1H-indol-1-amine (besipirdine, 4c)
was selected for clinical development based on in-depth biological evaluation. In addition to
cholinomimetic properties based initially on in vitro inhibition of [3H]quinuclidinyl benzilate
binding, in vivo reversal of scopolamine-induced behavioral deficits, and subsequently on other
results, 4c also displayed enhancement of adrenergic mechanisms as evidenced in vitro by
inhibition of [3H]clonidine binding and synaptosomal biogenic amine uptake, and in vivo by
reversal of tetrabenazine-induced ptosis. The synthesis, structure-activity relationships for
this series, and the biological profile of 4c are reported.
In tr od u ction
systems are affected in the disease process, including
somatostatinergic,8,9 glutamatergic,10-12 and noradren-
ergic systems.13-15 In addition to enhancement of
central cholinergic mechanisms, a program was initiated
to discover compounds which would mitigate multiple
biochemical deficits associated with AD. As a class, the
aminopyridines were known to enhance release of
both acetylcholine and norepinephrine.16 Since more
lipophilic aminopyridine analogs had not been exten-
sively investigated, synthesis of a series of (arylamino)-
pyridines was initiated. The novel N-(4-pyridinyl)-
1H-indol-1-amine 4c emerged from this program, and
the biological profile of 4c shows a unique combination
of adrenergic and cholinomimetic properties.1 The
synthesis, structure-activity relationships, and biologi-
cal profile of 4c constitute the subject of this paper.
Various heteroaryl and pyrrole analogs of 4c were
reported in preliminary form,17,18 and results for the
heteroaryl compounds are included in this paper. Pyr-
role analogs of 4c constitute the subject of a companion
paper.19
Alzheimer’s disease (AD) is an age-related, chronic
neurodegenerative disorder occurring in middle or late
life. The disease is characterized by a progressive de-
mentia, which is associated with both severe disability
in performing the activities of everyday life and a re-
duced life expectancy after onset of the disease. The
disease is estimated to currently affect three to four mil-
lion persons in the United States, and its prevalence is
increasing as a greater proportion of the population
reaches a longer life expectancy.2 The well-known choli-
nergic hypothesis3-5 of AD was based on accumulated
evidence suggesting that enzymes involved in the syn-
thesis and/or hydrolysis of acetylcholine were deficient
in brains of AD patients versus age-matched controls.
This breakdown of central cholinergic transmission
resulted in efforts to treat AD with cholinomimetic
agents which either augment the synthesis or inhibit
the hydrolysis of acetylcholine,4 or act directly at cho-
linergic receptors (first generation agents). On the basis
of this approach, the potent acetylcholinesterase inhibi-
tors velnacrine6 (HP 029) and HP 290,7 discovered in
our laboratories, were advanced for clinical evaluation.
Ch em istr y
Treatment of appropriately substituted indoles 1a -
g, pyrazole (5a ), carbazole (5b), and indazole (5c) with
hydroxylamine O-sulfonic acid and potassium or sodium
hydroxide, utilizing the conditions reported by Somei
and Natsume,20 afforded substituted 1H-indol-1-amines
2a -g and heteroaryl analogs 6a ,21 6b,22 6c,23 and 6d 23
(Tables 1 and 2, Schemes 1 and 2). Condensation of
2a -g with 4-chloropyridine hydrochloride in 2-propanol
or N-methyl-2-pyrrolidinone (NMP) provided the sec-
ondary pyridinylaminoindoles 3a -g, which were alky-
lated to give tertiary (pyridinylamino)indoles 4a -n
(Table 3, Scheme 1). Deaza compounds 3h and 4s were
prepared by alkylation of 1a with 4-(chloromethyl)-
pyridinium chloride and subsequent alkylation of the
active methylene group with n-butyllithium and bro-
mopropane.
Neuropathological studies of brains from Alzheimer’s
patients also demonstrated that other neurotransmitter
Compounds 4p -r were prepared from aldehyde 4o,
which was synthesized from 4c under Vilsmeier condi-
X Abstract published in Advance ACS Abstracts, December 15, 1995.
0022-2623/96/1839-0570$12.00/0 © 1996 American Chemical Society

Potential Therapeutic Agents for Alzheimer’s Disease
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2 571
Sch em e 1a
Ta ble 1. Substituted 1H-Indol-1-amines
starting
mat.
yield,
%
compd
R1
R2
R3
R4
mp, °C
2a
2b
2c
2d
2e
2f
H
H
H
H
H
H
H
H
H
H
Br
Cl
NO2
OCH3
H
H
CH3
H
H
H
H
H
H
H
H
CH3
H
H
H
H
H
1a
1b
1c
1d
1e
1f
46-47a
53-55b
108-109c
oil
32
40
17
48
55
18
18
68
oil
166-167
115-117
oil
2g
1g
2a
2h d
n-C3H7
a
b
Literature20 mp 41-41.5 °C. Literature20 mp 59.5-60.5 °C.
c Literature20 mp 114-115 °C. C: calcd, 75.82; found, 75.41.
d
Ta ble 2. Heteroarylamines
a
(a) H2NOSO3H, KOH, DMF; (b) 4-chloropyridine hydrochlo-
ride, NMP; (c) R1X or (R1O)2SO2, NaH, DMF; (d) 4-(chlorometh-
yl)pyridinium chloride; (e) n-BuLi, n-C3H7Br.
Sch em e 2a
a
The amination product was a 1:1 mixture of 5a and 6a , which
was used directly for the preparation of 7a without further
b
purification. The amination product was a 1:1 mixture of 5b and
6b, which was used directly for the preparation of 7b without
further purification. c The amination afforded a 2:1 mixture of 6c
and 6d which was separated by HPLC (silica, 10% ethyl acetate
in DCM). The identity of each compound was determined by
comparison of UV spectra to the literature.23
tions (Scheme 3, Table 3). Conversion of 4o to the oxime
and subsequent dehydration with benzenesulfonyl chlo-
ride afforded nitrile 4p . Treatment of 4o with methyl-
magnesium bromide under Grignard conditions and
oxidation of the intermediate carbinol with pyridinium
dichromate provided ketone 4q. Wittig olefination of
4o with methyltriphenylphosphonium bromide and
subsequent hydrogenation afforded the 3-ethyl analog
4r . Using similar synthetic methodology as previously
described, various heteroaryl analogs related to 4c were
also prepared (7a -d , 8a -d , 9a -d ; Schemes 2 and 4;
Table 4).
a
(a) H2NOSO3H, KOH, DMF; (b) 4-chloropyridine hydrochlo-
ride, NMP; (c) NaH, DMF; n-C3H7Br.
of assays, including assessment of potential cholinergic
properties based on in vitro inhibition of acetylcho-
linesterase (CHEI), affinity for central muscarinic cho-
linergic receptors by in vitro inhibition of [3H]quinu-
clidinyl benzilate binding (QNB, a potent muscarinic
antagonist), and in vivo reversal of the amnestic-like
effects of the muscarinic receptor antagonist scopola-
mine in the scopolamine dementia dark avoidance
(SDDA, mice) paradigm. Potential enhancement of
adrenergic mechanisms was also assessed by in vitro
inhibition of synaptosomal biogenic amine (norepineph-
rine) uptake and by in vivo prevention of tetrabenazine-
Discu ssion
Investigation of the pyrroloaminopyridines afforded
a vinyl-substituted pyrrole analog as an initial lead
compound with combined adrenergic and cholinomi-
metic-like properties.19 Extension of this lead provided
a series of (pyridinylamino)indoles with enhanced ad-
renergic properties, and 4c emerged as the most prom-
ising compound. With respect to evaluation of prelimi-
nary mechanistic information and structure-activity
relationships, all compounds were screened in a battery

572 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2
Ta ble 3. N-(4-Pyridinyl)-1H-indol-1-amines and Analogs
Klein et al.
compd
R1
R2
R3
R4
starting mat.
mp, °C
yield, %a recrystn solventb
formulac
3a
3b
3c
3d
3e
3f
3g
3h
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
H
H
H
H
H
H
H
H
H
H
H
Br
Cl
NO2
OCH3
H
H
H
H
H
H
H
H
H
Br
Br
Cl
NO2
OCH3
H
H
CH3
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
H
H
H
H
H
H
H
H
H
H
H
H
CH3
H
H
H
H
H
H
H
H
H
H
2a
2b
2c
2d
2e
2f
2g
1a
3a
3a
3a
3a
3a
3a
3a
3c
3d
3d
3e
3f
145-146
137
75-78
161-162
150-152
300-302
oil
50
72
31
49
33
47
27
83
18
60
65
22
39
24
16
34
31
63
63
30
52
51
66
58
32
40
56
A
B
C13H11N3‚C4H4O4
C14H13N3‚C2H2O4
C14H13N3
C13H10BrN3‚C4H4O4
C13H10ClN3‚C4H4O4
C13H10N4O2‚HCl
C14H13N3O
d
A
A
A
65-68
C14H12N2
CH3
CH2CH3
103-104
119-120
115-116
108-110
121-123
111-112
107-109
155-156
110-111
157-158
130
A
A
A
B
A
A
B
B
B
A
A
A
B
A
A
A
C
A
C14H13N3‚C4H4O4
C15H15N3‚C4H4O4
C16H17N3‚C4H4O4
C17H19N3‚C4H4O4
C16H17N3‚C4H4O4
C16H15N3‚C4H4O4
C16H13N3‚C4H4O4
C17H19N3‚C4H4O4
C14H12BrN3‚C4H4O4
C16H16BrN3‚C4H4O4
C16H16ClN3‚C4H4O4
C14H12N4O2‚C4H4O4
C17H19N3O‚C4H4O4
C17H19N3‚C4H4O4
C17H17N3O‚C4H4O4
C17H16N4‚C4H4O4
C18H19N3O
CH2CH2CH3
CH2CH2CH2CH3
CH(CH3)2
CH2CHdCH2
CH2CtCH
CH2CH2CH3
CH3
CH2CH2CH3
CH2CH2CH3
CH3
CH2CH2CH3
CH2CH2CH3
CH2CH2CH3
CH2CH2CH3
CH2CH2CH3
CH2CH2CH3
CH2CH2CH3
H
H
H
H
174-175
138-139
148-149
169-171
163-164
103-105
133-134
91-94
4m
4n
4o
4p
4q
4r
H
3g
3b
4c
4o
4o
4o
3h
CH3
CHO
CN
COCH3
CH2CH3
H
H
H
H
H
C18H21N3‚C4H4O4
C17H18N2
4s
H
H
a
b
Yield from immediate precursor. A ) methanol-ether; B ) ethanol-ether; C ) methanol. c Elemental analysis agrees within (0.4%
of the theoretical values for C, H, N, except for 3g, which was not analyzed and used directly for the preparation of 4m . C4H4O4 represents
maleate salt unless otherwise noted. Oxalate salt.
d
Sch em e 3a
Sch em e 4a
a
(a) POCl3-DMF, DCE; (b) H2NOH‚HCl, pyridine; C6H5SO2Cl,
pyridine; (c) CH3MgBr, ether; pyridinium dichromate, DMF; (d)
CH3P(C6H5)3Br, ether; (e) H2/Pd-C.
induced ptosis (TBZ, mice). The data are summarized
in Tables 5 and 6, including reference standard data in
Table 6.
a
(a) ClCO2C2H5, pyridine, toluene; (b) KOtBu, THF; n-C3H7Br;
(c) CH2(OH)CH2OH, NaOH, H2O; (d) Cl-aryl, HCl, NMP; (e) H2,
10% Pd/C, MgO, C2H5OH.
In contrast to our previous experience with ami-
noacridine and carbamate type acetylcholinesterase
inhibitors, most of these compounds (3a -f; 4a -o,q,r ;
7a -d ; 8a -d ; 9c,d ) were, at best, weak in vitro acetyl-
cholinesterase inhibitors with the exception of 4p which

Potential Therapeutic Agents for Alzheimer’s Disease
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2 573
Ta ble 4. Heteroaryl Analogs of 4c
a
Yield from immediate precursor. b A ) methanol-ether; B ) ethanol-ether. c Elemental analysis agrees within (0.4% of the theoretical
d
values for C, H, N, and C4H4O4 represents maleate salt unless otherwise noted. N: calcd, 28.75; found, 28.20.
exhibited moderate inhibitory activity. With respect to
in vitro affinity for muscarinic binding sites, secondary
(pyridinylamino)indoles 3a -f only weakly inhibited [3H]-
QNB binding24 in comparison with the muscarinic
agonist reference standard oxotremorine (-Zn column
in Tables 5 and 6). N-Alkylation of 3a provided tertia-
ryamines 4a -g which displayed significantly enhanced
affinity for [3H]QNB-labeled muscarinic binding sites,
with the N-propyl (4c) and N-butyl (4d ) analogs being
approximately equipotent to oxotremorine. Introduction
of indole C-2, C-3, and C-5 aromatic substituents did
not provide any further enhancement in binding affinity
(4h -r vs 4c). However, the indole N-amino nitrogen
is apparently required for more optimal binding affinity
(3a vs 3h ; 4c vs 4s). With the exception of 8b,c, various
heteroaryl analogs (7a -d , 8a ,d , 9a -d ) of 3a and 4c also
only weakly inhibited [3H]QNB binding.
Inhibition of [3H]QNB binding cannot, however, dis-
tinguish between muscarinic agonists (e.g. oxotremo-
rine) and antagonists (e.g. scopolamine). Aronstam et
al.25 demonstrated that zinc and other heavy metals or
sulfhydryl reagents increase the affinity of QNB binding
sites for cholinergic agonists in rat forebrain mem-
branes, and this selective agonist-enhancing effect of
zinc was purported to provide a useful in vitro procedure
to identify agonist activity. In our laboratory,26
a
muscarinic agonist-like profile for a compound is as-
sociated with a ratio of [3H]QNB IC50 values equal to
or greater than 3 obtained in the absence (-Zn) and
presence (+Zn) of zinc. As shown in Tables 5 and 6,
many of these compounds (3d -f; 4b ,c,e-h ,l,n ,q -s;
7a ,c,d ; 8a -d ; 9a ,d ) are characterized by -Zn/+Zn
ratios greater than 3.0, suggesting that these com-
pounds may be muscarinic receptor agonists.

574 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2
Klein et al.
Ta ble 5. Biological Data for 3a -h , 4a -sa
QNBc
uptake inhibitiond
rat, IC50 (µM)
[3H]NE
SDDAf
A, NA, or NT,
mg/kg, sc (% response)
IC50 (µM)
AChEIb
ratio
-Zn/+Zn
TBZe
ED50 (mg/kg, ip)
compd
IC50, µM
-Zn
+Zn
3a
>100
>100
>100
>100
>100
>100
40
(33-49)
82
(48-140)
60
(32-114)
44
(25-75)
42
(34-52)
146
(76-278)
NT
223
(134-372)
9.0
16
(12-22)
35
(22-55)
29
(15-56)
7.5
(5.5-10)
5.9
(3.0-11)
12
(9.6-16)
NT
84
(63-111)
5.1
2.5
2.3
2.1
5.9
7.1
12
2.5
(1.9-3.4)
12.8
(5.8-28.1)
3.6
(2.0-6.5)
>20
3.0
(2.6-3.3)
1.0
(0.9-1.1)
<10
A (3/9)
0.02 (27), 0.08 (20), 0.16 (23)
A (1/6)
0.31 (33)
NA (0/3)
3b
3c
3d
3e
3f
>20
>20
>20
NT
>20
NA (0/3)
NT
9.9
(3.6-27)
NT
3g
3h
NT
NT
-
2.7
NT
NT
NT
A (2/3)
>20
0.3 (33), 1.0 (20)
A (3/9)
0.02 (33), 0.04 (53), 0.08 (33)
A (1/6)
0.63 (33)
A (5/6)
0.02 (24), 0.04 (30), 0.08 (33),
0.16 (27), 0.63 (40)
A (1/6)
0.04 (23)
A (5/6)
4a
4b
4c
>100
>100
>100
1.8
4.2
3.2
1.0
(0.56-1.7)
0.25
(0.15-0.44)
0.43
(0.29-1.7)
3.5
(3.3-3.6)
3.3
(3.0-3.6)
3.1
(2.9-3.4)
(7.3-11)
10
(3.5-21)
3.0
(3.9-6.8)
2.4
(1.3-4.7)
0.94
(1.9-4.6)
(0.56-1.6)
4d
4e
62
(45-84)
>100
4.0
(2.4-6.6)
6.0
1.5
(1.1-1.9)
0.63
2.7
9.5
0.43
(0.32-0.50)
2.3
5.4
(5.0-5.9)
2.9
(4.5-8.0)
(0.25-1.6)
(1.1-4.9)
(2.7-3.1)
0.16 (33), 0.31 (60), 1.25 (36),
2.5 (20), 5.0 (20)
NA (0/6)
4f
4g
4h
4i
>100
>100
>100
>100
>100
>100
>100
7.3
(5.6-9.4)
11
(9.1-14)
7.2
(3.9-13)
4.6
(2.6-7.9)
4.4
(3.4-5.6)
5.8
(4.5-7.6)
29
(18-47)
1.0
(0.57-1.9)
2.5
(1.4-4.4)
1.4
(1.1-1.7)
2.5
(1.3-4.8)
1.6
(1.2-2.1)
2.4
(1.9-3.2)
7.6
(4.4-13)
7.3
4.4
5.1
1.8
2.7
2.4
3.8
6.2
(1.4-28)
0.68
(0.18-2.6)
1.1
(0.9-1.4)
13
(9.8-17)
2.6
(2.0-3.5)
1.9
(1.5-2.5)
>30
4.2
(4.1-4.5)
3.9
(3.6-4.2)
3.2
(2.9-3.5)
>20
A (3/11)
2.5 (21), 10 (21), 20 (27)
A (3/9)
0.02 (20), 2.5 (20), 5.0 (23)
A (1/3)
1.0 (44)
A (2/6)
0.63 (33), 5.0 (33)
A (1/6)
1.25 (20)
A (4/6)
4j
>20
>20
>20
4k
4l
0.16 (20), 0.63 (20), 1.25 (20),
5.0 (20)
4m
>100
14
(7.3-26)
4.8
(2.8-8.4)
2.9
0.57
(0.31-1.0)
>20
A (4/6)
0.16 (20), 0.31 (20), 0.63 (26),
5.0 (36)
4n
4o
4p
29
(22-37)
20
(15-26)
6.8
19
(12-33)
3.3
(2.2-4.8)
8.6
4.5
(1.7-12)
1.8
(0.90-3.3)
3.5
4.2
1.8
2.5
1.3
(0.63-2.6)
2.2
(0.55-8.6)
0.75
1.8
(1.6-2.1)
18
(15-21)
9.2
A (2/10)
0.04 (22), 0.31 (20)
NA (0/6)
A (5/6)
(5.1-9.1)
(5.1-15)
(2.8-4.4)
(0.53-1.1)
(8.5-10)
0.16 (40), 0.31 (53), 0.63 (36),
1.25 (29), 5.0 (27)
A (1/10)
4q
4r
4s
58
29
2.7
11
3.3
5.0
(44-77)
(19-44)
(1.7-4.3)
(1.6-6.8)
(4.7-5.3)
0.16 (20)
NA (0/9)
20
2.7
0.71
3.8
4.9
2.1
0.44
(16-25)
NT
(2.1-3.4)
142
(0.55-0.92)
29
(1.2-3.5)
0.67
(0.41-0.47)
NT
A (1/3)
(93-215)
(17-51)
(0.34-1.3)
0.30 (20)
a
IC50 and ED50 values are corrected for the percentage of base compound in the case of salts. Numbers in parentheses are 95% confidence
b
limits unless otherwise noted. Inhibition of acetylcholinesterase (AChEI) in a rat striatal preparation using acetylthiocholine (5 mM) as
substrate. c Inhibition of [3H]quinuclidinyl benzilate (QNB) binding from rat forebrain membranes in the absence (-Zn) and presence
(+Zn) of zinc. Inhibition of [3H]norepinephrine (NE) uptake in rat whole brain synaptosome preparations. e Prevention of tetrabenazine-
d
induced (TBZ) ptosis by intraperitoneal compound administration in mice. f Antagonism of scopolamine-induced behavioral deficits in
mice in the scopolamine dementia dark avoidance (SDDA) paradigm. A cutoff was defined for the scopolamine-vehicle group as the
value for the animal with the second longest latency time. Results are reported as active (A), not active (NA), or not tested (NT) with the
number of active (g20% response) dosages versus the total number of dosages evaluated in parentheses. For active compounds, the
second line of data represents the active doses (mg/kg, sc) with the percent response (i.e. the percent of animals in the scopolamine-drug
group with latencies greater than the cutoff time) in parentheses.
With respect to adrenergic properties, most secondary
and tertiary amines were assessed in vitro for inhibition
of synaptosomal norepinephrine uptake and in vivo for
prevention of TBZ-induced ptosis (Table 5). Compounds
3a ,c inhibited in vitro norepinephrine uptake at micro-
molar concentrations, while compounds 3b,d -f were
much weaker. Secondary amine 3a and the 2-methyl
analog 3b significantly antagonized TBZ-induced ptosis,

Potential Therapeutic Agents for Alzheimer’s Disease
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2 575
Ta ble 6. Biological Data for 7a -d , 8a -d , and 9a -d a
QNBc
uptake inhibitiond
rat, IC50 (µM)
[3H]NE
TBZe
ED50
(mg/kg, ip)
SDDAf
A, NA, or NT,
mg/kg, sc (% response)
IC50 (µM)
AChEIb
ratio
-Zn/+Zn
compd
IC50, µM
-Zn
>1000
+Zn
7a
7b
7c
7d
8a
8b
8c
8d
9a
9b
9c
>100
247
(137-444)
8.2
(6.7-10)
29
(15-54)
128
(77-211)
31
(23-41)
0.5
(0.12-1.9)
4
(3.7-5.2)
15
(11-19)
58
(32-105)
180
(94-344)
>1000
>4
>20
>20
NT
>100
>100
>100
>100
>100
>100
>100
NT
20
(11-36)
128
(66-248)
409
(238-702)
127
(66-247)
5.5
(3.0-10)
13
(10-17)
91
(53-154)
>300
2.4
4.4
3.2
4.1
11
1.4
(0.57-3.4)
17
(7.5-37)
>20
2.3
(2.0-2.6)
3.8
NA (0/6)
NA (0/6)
NT
(3.5-4.2)
>20
>20
1.5
>20
NT
2.4
(1.3-4.4)
1.4
(0.8-2.3)
4.7
(2.4-9.2)
12
(6.1-24)
6.9
(4.0-12)
2.6
A (2/8)
1.25 (20), 10 (24)
NA (0/6)
(1.2-1.9)
11
(9.5-13)
>20
3.3
6.1
>5.2
>1.7
NT
>20
>20
>20
A (2/6)
0.16 (20), 0.63 (20)
A (1/6)
2.5 (29)
A (3/6)
NT
>300
>100
>1000
(0.9-7.6)
0.63 (33), 2.5 (33),
5.0 (20)
9d
>100
391
(82-1860)
2.7
(2.2-3.7)
0.004
(0.0031-0.0051) (0.0021-0.0075)
NT
11
(8-14)
0.66
(0.43-1.0)
0.004
35
4.2
1
1.4
(0.6-3.4)
NT
>20
A (1/6)
5.0 (23)
NT
Oxotremorine NT
NT
Scopolamine
Clonidine
NT
NT
NT
NT
NT
>20
0.36
(0.31-0.42)
>8
>10
NA (0/6)
Yohimbine
THAg
NT
0.32
NT
7.3
NT
5.9
(3.5-9.8)
>20
11
(6.3-19)
NT
A (3/6)
0.63 (33), 2.5 (31),
5.0 (33)
1.2
(0.25-0.42) (5.9-9.0)
idazoxan
NT NT
NT
>20
NT
A (5/6)
0.31 (60), 0.63 (43),
1.25 (47), 2.5 (53),
5.0 (33)
g
a-f See corresponding footnotes to Table 5. Tetrahydroaminoacridine (tacrine, THA).
while other nuclear-substituted secondary amines 3c-f
were much less potent in this in vivo assay. Tertiary
amines 4a -g inhibited in vitro norepinephrine uptake
at micromolar and submicromolar concentrations, and
also significantly antagonized TBZ-induced ptosis in
vivo. Interestingly, the nature of the nitrogen alkyl
substituent appeared to have little influence on the
level of anti-TBZ activity of 4a -g. Introduction of
indole C-3 alkyl substituents (4n ,r ) resulted in a pos-
sible slight enhancement of in vivo antagonism of
TBZ-induced ptosis versus 4c, while C-3 electron-
withdrawing substituents diminished activity (4o-q).
Substitution at C-5 led to a significant loss of anti-TBZ
activity (4i-m ) regardless of the nature of the aromatic
substituent.
Although the SDDA paradigm is a passive avoidance
model used by many laboratories to assess compound
effects on learning and memory, it was noted some time
ago that research in the Alzheimer’s disease area
presents formidable challenges due to the unavailability
of proven efficacious drugs (with exception of the cho-
linesterase inhibitor tacrine which recently received
FDA approval) and the lack of definitive biological
models.27 In this respect, the SDDA paradigm is not
highly specific for cholinomimetics and gives positive
results with other compounds including analgesics,
motor stimulants, and nootropics.28 Evidence has also
accumulated associating R2 adrenergic mechanisms with
the cognitive decline in aged nonhuman primates,29 and
the R2 antagonist idazoxan was reported to facilitate
memory retrieval in rats.30 Idazoxan was also active
in the SDDA paradigm (Table 6). Thus, it is highly
desirable to have biochemical or other data to mecha-
nistically support the observed activity of a compound
in SDDA.
In the SDDA assay, an animal (mouse) is placed on
the lighted side of a divided chamber. The normal
behavior is to escape into the adjacent dark compart-
ment, and when this occurs a foot shock is received
through a floor grid. After 24 h an animal is assessed
for its ability to remember the experience by determin-
ing the increased time interval (latency) before the
animal reenters the dark compartment. Scopolamine
is an anticholinergic agent known to cause memory
impairment in humans. If scopolamine is administered
before an animal’s initial exposure to the test apparatus,
the animal is observed to reenter the dark compartment
just shortly after being placed in the test chamber 24 h
later, as do naive animals. Experience with a number
of reference standards in SDDA led to the development
of an empirical level of positive activity at 20% of the
animals with latencies greater than a cutoff value. Due
to the numerous dosages (ranging from 0.01 to 20 mg/
kg, sc) utilized to evaluate the compounds in this study,

576 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2
Klein et al.
Ta ble 7. Adrenergic Biochemical Properties and SDDA Comparisona
inhibition of
inhibition of binding, IC50 (µM)
[3H]NE uptakeb
compd
IC50 (µM)
[3H]clonidinec
[3H]WB4101d
SDDA,e mg/kg, sc (% response)
3a
2.5
0.008
0.51
A (3/9)
(1.9-3.4)
(0.004-0.015)
(0.38-0.69)
0.02 (27), 0.08 (20), 0.16 (23)
A (3/9)
0.02 (33), 0.044 (53), 0.08 (33)
A (1/6)
0.63 (33)
A (5/6)
4a
4b
4c
1.0
0.024
1.2
(0.60-1.7)
0.25
(0.15-0.44)
0.43
(0.017-0.033)
0.11
(0.08-0.14)
0.33
(0.91-1.5)
3.3
(2.5-4.2)
10
(0.29-1.7)
(0.22-0.51)
(6.4-17)
0.02 (24), 0.04 (30), 0.08 (33),
0.16 (27), 0.63 (40)
A (1/6)
0.04 (23)
A (5/6)
0.16 (33), 0.31 (60), 1.25 (36),
2.5 (20), 5.0 (20)
A (3/11)
2.5 (21), 10 (21), 20 (27)
A (3/9)
0.02 (20), 2.5 (20), 5.0 (23)
A (2/10)
0.04 (22), 0.31 (20)
NA (0/9)
4d
4e
0.43
(0.32-0.50)
2.3
0.63
(0.55-1.6)
>10
NT
NT
(1.1-4.9)
4g
4h
4n
4r
0.68
(0.18-2.6)
1.1
(0.9-1.4)
1.3
(0.63-2.6)
2.1
0.50
(0.28-0.91)
2.3
(1.7-3.0)
2.5
(0.98-6.4)
3.6
NT
NT
NT
NT
(1.2-3.5)
2.4
(1.7-7.6)
0.54
8b
3.2
A (2/8)
(1.3-4.4)
(0.24-1.2)
(1.6-6.4)
1.25 (20), 10 (24)
a
IC50 values are corrected for the percentage of base compound in the case of salts. Numbers in parentheses are 95% confidence limits
unless otherwise noted. Inhibition of [3H]norepinephrine (NE) uptake in rat whole brain synaptosome preparations. c Rat cortical
b
membranes. Rat whole brain minus cerebella. e Scopolamine dementia dark avoidance (SDDA) paradigm in mice. See Footnote f of
d
Table 5.
SDDA results are reported as active (A) or not active
(NA) in Tables 5 and 6. To provide an index of activity,
the number of active versus the total number of doses
evaluated is given in parentheses, and the active doses
with the percent response in parentheses are presented
in the second line of SDDA data for each compound. On
the basis of positive activity in SDDA, compounds of
interest were arbitrarily selected as those with choli-
nomimetic mechanistic support as provided by a QNB
IC50 e10 µM and a -Zn/+Zn ratio greater than 3, in
combination with potential enhancement of adrenergic
mechanisms as supported by in vitro inhibition of
norepinephrine uptake and in vivo low dose (<5 mg/
kg, ip) antagonism of TBZ-induced ptosis (4b,c,e,g,h ,n ;
8b). Of these compounds, 4c and 4e produced the most
robust reversal of scopolamine-induced behavioral defi-
cits in SDDA, with activity at low doses (4c) and over a
broad dosage range (4c,e).
Previous investigation of the (pyrroloamino)pyridines
also revealed significant affinity for R adrenergic bind-
ing sites was associated with some compounds.18 As will
be discussed below, in vitro evaluation of 4c indicated
that R2 antagonist properties are associated with the
compound and raised the possibility of enhancing ad-
renergic neurotransmission by multiple mechanisms.
Compounds 3a , 4a -e,g,h ,n ,r , and 8b were additionally
assessed for R2 adrenoceptor affinity by inhibition of [3H]-
clonidine binding and compounds 3a , 4a -c, 8b for R1
adrenoceptor affinity by inhibition of [3H]WB4101 bind-
ing (to assess potential R1 mediated cardiovascular side
effect liability). These data are presented in Table 7,
and inhibition of NE uptake and SDDA are included
for ease of comparison. Secondary amine 3a exhibited
nanomolar affinity for R2 adrenoceptors, with a 64-fold
lower affinity for R1 adrenoceptors. Introduction of
linear N-alkyl substituents resulted in a significant
enhancement of norepinephrine uptake inhibitory prop-
erties, but affinity for R1 and R2 binding sites progres-
sively decreased (3a vs 4a -c). Of the compounds
mentioned above (4b,c,e,g,h ,n ; 8b), 4c again appeared
to offer the most promising combination of biochemical
properties including submicromolar inhibition of nore-
pinephrine uptake, submicromolar affinity for R2 adreno-
ceptors, and a 32-fold separation in IC50 values for R2
versus R1 adrenoceptors. Although 4e,g,h ,n appeared
interesting based on activity in QNB and TBZ, 4e,h ,n
exhibited much weaker affinity for R2 adrenoceptors
than 4c, and 4g was not as robustly active in SDDA as
4c. Carbazole 8b displayed only a 6-fold separation in
R1/R2 binding affinities and also was not robustly active
in SDDA.
On the basis of this assessment, 4c was advanced for
further study, and the overall profile of the compound
is summarized in Table 8. With respect to in vitro R2
adrenergic properties, 4c also inhibited R2 antagonist
binding ([3H]yohimbine, [3H]idazoxan) in the same
concentration range as observed for the inhibition of R2
agonist ([3H]clonidine) binding. Rodbell et al.31 reported
that in the presence of the nonhydrolyzable guanine
nucleotide 5′-guanylimidodiphosphate [GPP(NH)P] the
apparent affinities of R2 adrenoceptor agonists for [3H]-
idazoxan-labeled receptors are reduced while the bind-
ing affinity of R2 adrenoceptor antagonists are largely
unaffected. The observation that the inhibition of [3H]-
idazoxan binding by 4c in the presence of GPP(NH)P
was not reduced suggested that the compound is not
an R2 agonist. Subsequent investigation demonstrated
that 4c increases electrically-stimulated norepinephrine
release from cortical tissue slices, which is consistent
with R2 antagonist activity.32 In addition, 4c signifi-
cantly inhibits norepinephrine (in both whole brain and
hypothalamic synaptosomes) and dopamine reuptake,
and the compound antagonizes TBZ-induced ptosis in
vivo. More recently, 4c at low concentrations was
shown to enhance [3H]norepinephrine release due to a
combination of R-adrenergic blockade and norepineph-

Potential Therapeutic Agents for Alzheimer’s Disease
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2 577
Ta ble 9. Additional Receptor Binding Assays for 4c
Ta ble 8. Biological Profile of 4c
in vitro assay
IC50 (µM)a
receptor
[3H] ligand
tissuea
IC50 (µM)
Receptor Binding: Adrenergic
dopamine-D1
dopamine-D2
5HT1A
5HT1B
5HT2
opiate-µ
opiate-Κ
NMDA
SCH 23390
spiroperidol
DPAT
striatum
striatum
hippocampus
striatum
cortex
whole brain
cerebellumc
cortex
>20
>20
e20
>20
>20
>1
>10
>20
>20
>100
[3H]clonidineb (R2, cortex)
[3H]yohimbineb (R2, cortex)
[3H]idazoxanb (R2, cortex)
+GPP(NH)Pc
0.33 (0.22-0.51)
0.25 (0.18-0.33)
0.47 (0.24-0.91)
0.14 (0.07-0.29)
10 (6.4-17)
5HT
spiroperidol
[3H]WB4101d (R1, whole brain)
DHMb
bremazocine
CPPd
Biogenic Amine Uptakee
[3H]norepinephrine
whole brain
PCP
TCPe
cortex
heart
0.43 (0.29-1.7)
0.27 (0.11-0.67)
0.41 (0.23-0.73)
2.6 (1.4-5.0)
Ca2+ channel
nitrendipine
hypothalamus
[3H]dopamine (striatum)
[3H]serotonin (whole brain)
a
Rat, unless otherwise specified. b [3H]Dihydromorphine. c Guin-
ea pig. [3H]-(()-[3-(2-Carboxypiperazin-4-yl)propyl]phosphonate.
d
e [3H]-N-[1-(2-Thienyl)cyclohexyl]piperidine.
Receptor Binding: Cholinergic
[3H]QNBf (muscarinic, forebrain)
+Zn2+
3.0 (1.9-4.6)
0.94 (0.56-1.6)
1.3 (1.0-1.8)
1.0 (0.81-1.2)
affinity of 4c was not reduced in the presence of GPP-
(NH)P. The compound also inhibited binding of the full
muscarinic agonist oxotremorine-M, but was less potent
than the partial agonist oxotremorine in this assay. In
contrast to the -Zn/+Zn [3H]QNB data, the lack of a
guanine nucleotide induced decrease in binding affinity
and data from subsequent studies32 suggest that 4c is
not a muscarinic agonist. The disparity between the
QNB data and these studies is unclear, given the fact
that various compounds from different therapeutic
classes with anticholinergic properties (scopolamine,
atropine, clozapine, thioridazine, amitriptyline, imi-
pramine) failed to produce significant zinc shifts.26 In
addition, the weak inhibition of binding of the nicotinic
agonist N-methylcarbamylcholine (NMCC) to frontal
cortex preparations by 4c suggests the compound has
little affinity for nicotinic binding sites, nor is the
compound an acetylcholinesterase inhibitor (AChE in-
hibition, Table 8). It can also be seen from Table 9 that
4c shows little affinity for dopaminergic, serotonergic,
opiate, NMDA, and PCP binding sites, nor for nitren-
dipine-labeled calcium channels.
Subsequent studies demonstrated in vivo cholinomi-
metic-like effects of 4c with respect to modulation of
brainstem auditory-evoked potentials (BAEP) in rats.
Wave VI of the BAEP is modulated by cholinergic
neuronal pathways.36 Cholinomimetics (e.g. oxotremo-
rine, physostigmine) increase the amplitude of wave VI,
and 4c was observed to produce the same effect over a
broad dosage range (0.01-0.08 mg/kg, sc). Hemicho-
linium blocks high-affinity choline uptake, which results
in depletion of acetylcholine and reduction of cholinergic
neurotransmission. Compound 4c was shown to reverse
the reduction in wave VI induced by pretreatment with
hemicholinium.37 The R2 antagonist yohimbine was not
active in BAEP, an observation which provides support
for the association of cholinomimetic properties with 4c.
In addition to the above studies, 4c was independently
evaluated in a combined cholinergic-noradrenergic
lesion model designed to assess whether or not noncho-
linergic deficits in Alzheimer’s brain may contribute to
the cognitive impairments associated with the disease.38
The results indicated that a nucleus basalis of Meynert
(nbM, cholinergic) lesion combined with a lesion of the
ascending noradrenergic bundle (ANB) did not exacer-
bate 72-h passive avoidance retention deficits beyond
the degree of impairment produced by nbM lesions
alone. However, the addition of an ANB lesion did block
the efficacy of the cholinomimetics physostigmine and
oxotremorine to reverse the lesion-induced memory
impairment. Memory in combined lesioned rats was
[3H]pirenzepineb (M1, cortex)
[3H]-N-methylscopolamineg
(M2, cerebellum)
oxotremorine
0.016 (0.011-0.024)
0.65 (0.53-0.80)
0.053 (0.035-0.082)
0.46 (0.33-0.64)
+GPP(NH)Pc
oxotremorine
[3H]oxotremorine-Mh (muscarinic,
forebrain)
oxotremorine
0.008 (0.0043-0.0148)
>20
[3H]NMCCi (nicotinic, cortex)
AChE Inhibitionj
acetylthiocholine (striatum)
>100
in vivo assay
SDDAk
active at 0.02, 0.04, 0.08, 0.16,
0.63 mg/kg, sc
ED50 3.1 (2.9-3.4) mg/kg, ip;
5.1 (4.5-5.8) mg/kg, po
TBZl
a
IC50 and ED50 values are corrected for the percentage of base
compound in the case of salts. Numbers in parentheses are 95%
b
confidence limits. Rat cortical membranes. c 5′-Guanylimido-
diphosphate. Rat whole brain minus cerebella. e Rat brain syn-
d
aptosomes. f Inhibition of [3H]quinuclidinyl benzilate binding, rat
g
h
i
forebrain membranes. Rat cerebellum. Rat forebrain. Inhibi-
tion of [3H]-N-methylcarbamylcholine (NMCC) binding, rat cortical
membranes. j Acetylcholinesterase inhibition (rat striatum) using
acetylthiocholine as substrate. k Scopolamine dementia dark avoid-
ance paradigm (mice). l Prevention of tetrabenazine-induced ptosis
(mice).
rine uptake inhibition,33 and at higher concentrations
4c further enhances [3H]norepinephrine release via a
calcium-independent mechanism (purportedly from a
cytoplasmic origin).34 These combined properties dis-
tinguish 4c from pure biogenic amine uptake inhibitors
and R2 antagonists and strongly suggest that 4c would
significantly enhance adrenergic mechanisms in the
clinic.
Confirmation of the cholinomimetic properties of 4c
has been more challenging. As previously discussed, 4c
significantly inhibited [3H]QNB binding with an in-
creased affinity in the presence of zinc, suggesting that
the compound may be a muscarinic agonist. With
respect to muscarinic receptor selectivity and affinity,
4c displayed equal affinity for M1- and M2-muscarinic
receptors as determined by inhibition of binding of the
selective muscarinic antagonists [3H]pirenzepine and
[3H]-N-methylscopolamine from cortical and cerebellar
preparations, respectively (Table 8). Aronstam et al.35
have shown that guanine nucleotides, including GPP-
(NH)P, induce conversion of muscarinic binding sites
from high- to low-affinity states. Thus the muscarinic
agonist oxotremorine showed a 3-fold decrease in bind-
ing affinity for [3H]-N-methylscopolamine-labeled sites
in the presence of GPP(NH)P, whereas the binding

578 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2
Klein et al.
toluene layer under reduced pressure afforded a residue which
was purified by chromatography (silica gel, eluted with toluene
followed by 3% 2-propanol in toluene). Concentration of the
appropriate fractions provided a solid (49 g) which was
recrystallized from 3% 2-propanol in hexanes to give 34 g (27%)
of N-(ethoxycarbonyl)-1H-indol-1-amine as a pale yellow solid,
mp 89-90 °C. To a cold (5 °C) stirred solution of the ethoxy
carbamate (15 g, 0.074 mol) and tetrahydrofuran (THF, 100
mL) was added potassium tert-butoxide (9 g, 0.08 mol). After
stirring for 1 h, the cold solution was treated with 1-bromopro-
pane (7.3 mL, 0.08 mol) which was followed by stirring for 5
h at room temperature. The mixture was poured into ice-
water (300 mL) and extracted with ethyl acetate. The organic
phase was washed with water, dried, filtered, and concentrated
to afford N-(1H-indol-1-yl)-N-propylcarbamic acid ethyl ester
as a brown oil (16 g). A solution of the oil, sodium hydroxide
(10 g, 0.25 mol), water (20 mL), and ethylene glycol (35 mL)
was stirred at 120 °C for 4 h. The mixture was poured into
ice-water (300 mL), stirred for 5 min, and extracted with ethyl
acetate. The organic phase was washed with water, dried,
filtered, and concentrated to give a brown oil (9 g). Purification
of the oil by Kugelrohr distillation provided 2h (8 g, 68%) as
a light yellow oil: bp 145 °C (1 mmHg). IR (CHCl3) 3060, 3018,
2970, 2940, 2880, 1512, 1470, 1458, 1330, 1135, 1090, 1040,
restored when cholinomimetic therapy was adminis-
tered in combination with the R2 agonist clonidine,
suggesting that pharmacological enhancement of both
neurotransmitter systems was necessary for improving
retention of the passive avoidance response. Compound
4c produced memory-enhancing effects in these com-
bined lesion animals without the need for clonidine.
In summary, 4c appears to be a unique compound
which displays combined adrenergic and cholinomimetic
properties. Although the cholinomimetic properties of
4c are supported by activity in a number of in vivo
models, its mechanism of action via a cholinergic target
is unclear. Further investigation of non-receptor-medi-
ated cholinomimetic effects of 4c, possibly through
interaction with ion channels, is the subject of another
paper.39 Given the fact that multiple biochemical
deficits are associated with Alzheimer’s disease, com-
pounds which exhibit facilitatory modulation of neu-
rotransmission by multiple biochemical mechanisms
may find utility in a broader patient population than
pure cholinesterase inhibitors. Compound 4c indeed
may be the first example of a “second generation” agent
to provide such therapeutic benefit to Alzheimer’s
disease patients, and the compound40 is presently in
advanced clinical trials.
1010 cm-1 1H NMR (CDCl3) δ 0.96 (t, 3H, J ) 8 Hz), 1.48
;
(sextet, 2H, J ) 8 Hz), 3.15 (t, 2H, J ) 8 Hz), 4.58 (br s, 1H),
6.40 (d, 1H, J ) 4 Hz), 7.10 (q, 1H, J ) 8 Hz), 7.17 (m, 2H),
7.46 (d, 1H, J ) 8 Hz), 7.58 (d, 1H, J ) 7 Hz); MS m/ e 174.
Properties of 2h are included in Table 1.
N-(4-P yr id in yl)-1H-in d ol-1-a m in e Ma lea te (3a ). A solu-
tion of 2a (0.22 mol) and 4-chloropyridine hydrochloride (0.22
mol) in 150 mL of 2-propanol was stirred at 80 °C for 2 h. After
cooling, the mixture was poured into 500 mL of ice-water and
made basic by slow addition of sodium carbonate. The product,
which separated, was extracted into DCM (3 × 200 mL). The
organic layer was washed with water and brine, dried, and
filtered, and the solvent was removed in vacuo. Elution of the
residue with ethyl acetate via preparative HPLC afforded 24
g of 3a free base as a yellow oil which solidified, mp 140 °C.
An analytical sample of 3a was obtained by converting 3.5 g
of the free base to the maleate salt: mp 145-146 °C; IR (KBr)
3440, 3260, 3100, 1645, 1460 cm-1; 1H NMR (DMSO-d6) δ 6.13
(s, 2H), 6.55-6.75 (m, 3H), 7.10-7.33 (m, 3H), 7.56 (d, 1H, J
) 4 Hz), 7.70 (d, 1H, J ) 10 Hz), 8.42 (d, 2H, J ) 10 Hz),
12-15 (br s, 3H, exchangeable with deuterium oxide); MS m/ e
209. Properties of 3a , and of 3b-g and 7a -d prepared in a
similar manner, are included in Tables 3 and 4.
Exp er im en ta l Section
Melting points were determined on a Thomas-Hoover capil-
lary melting point apparatus and are uncorrected. The
structures of all compounds are supported by their IR (Perkin-
Elmer 1420 ratio recording infrared spectrophotometer or
1
Nicolet 205 FT-IR), H-NMR (Varian XL 200, chemical shifts
are reported in δ units downfield relative to tetramethylsilane
as internal standard), and mass (Finnigan 4023) spectra.
Reactions were generally conducted under a dry nitrogen
atmosphere with exclusion of moisture. Organic product
solutions were dried over anhydrous magnesium sulfate.
Preparative HPLC separations were performed on silica gel
with a Waters Associates Prep LC/System 500 equipped with
a Gow Mac Model 80-800 UV detector. Product yields were
not maximized. Elemental analyses were performed by either
Micro-Tech Laboratories, Inc., Skokie, IL, Midwest Microlab,
Indianapolis, IN, or Oneida Research Services, Inc., Whites-
boro, NY.
Gen er a l P r oced u r e for P r ep a r in g Com p ou n d s 2 a n d
6. Aminoindoles 2a -g (Table 1) and heteroaryl analogs 6a -d
(Table 2) were prepared by modification of the procedure
previously described by Somei and Natsume.20 A typical
procedure is reported for the synthesis of 2a . A cooled solution
of indole (1a , 0.1 mol) in DMF (100 mL) was treated with
powdered potassium hydroxide (1 mol) and then slowly with
hydroxylamine O-sulfonic acid (0.2 mol) such that the internal
temperature remained below 20 °C. After stirring an ad-
ditional hour at room temperature, the mixture was poured
into ice-water and extracted with ethyl acetate. The extract
was washed with water and brine, then dried, and concen-
trated in vacuo. Separation from unreacted 1a was achieved
by preparative HPLC using dichloromethane (DCM)-hexanes
(1:1) as eluent. Product N-amino compounds 2a -g and 6a -d
were used directly in condensations with 4-chloropyridine
hydrochloride or other chloroheterocyclics. Starting materials
1a -g, pyrazole (5a ), carbazole (5b), and indazole (5c) were
purchased from Aldrich Chemical Co.
N-P r opyl-N-(4-pyr idin yl)-1H-in dol-1-am in e Maleate (4c).
A solution of 3a (0.03 mol) in 25 mL of DMF was added
dropwise to an ice-cooled suspension of sodium hydride (60%
oil dispersion, 0.03 mole, washed with hexanes) in 5 mL of
DMF. After 1 h a solution of 1-bromopropane (0.03 mol) in 5
mL of DMF was added. After stirring 1 h at ambient
temperature, the reaction mixture was poured into 500 mL of
ice-water and extracted with DCM. The organic layer was
washed with water and brine, dried, and filtered. After
concentration in vacuo, the residue was purified eluting with
ethyl acetate via preparative HPLC, followed by elution with
ether through alumina via column chromatography, to afford
6.4 g of a yellow oil. Conversion to the maleate salt provided
6.8 g of 4c as pale yellow crystals: mp 115-116 °C; IR (CHCl3)
3010, 1710, 1643, 1515, 1470, 1450, 1350, 880, 820, 645 cm-1
;
1H NMR (CDCl3) δ 1.05 (t, 3H, J ) 8 Hz), 1.82 (sextet, 2H, J
) 8 Hz), 3.95 (m, 2H), 6.32 (s, 2H), 6.50-6.70 (br s, 2H), 6.72
(d, 1H, J ) 4 Hz), 7.05-7.16 (m, 2H), 7.20-7.33 (m, 2H), 7.75
(d, 1H, J ) 8 Hz), 8.35 (d, 2H, J ) 8 Hz), 15.3-16.5 (br s, 2H,
exchangeable with deuterium oxide); MS m/ e 251. Properties
of 4c, and of 4a ,b,d -n and 8a -d prepared in a similar
manner, are included in Tables 3 and 4.
N-P r op yl-1H-in d ol-1-a m in e (2h ). A stirred solution of 2a
(80.7 g, 0.61 mol), pyridine (54 mL, 0.67 mol), and toluene (620
mL) was treated over 1.25 h with a solution of ethyl chloro-
formate (59 mL, 0.61 mol) and toluene (59 mL). After the
reaction was complete, 3 N hydrochloric acid solution (500 mL)
was added and the resultant mixture was filtered through
Celite, the Celite pad being washed with toluene (100 mL).
Separation of the filtrate layers and concentration of the
N-P r op yl-N-(4-p yr id in yl)-1H-in d ol-1-a m in e-3-ca r box-
a ld eh yd e Ma lea te (4o). A Vilsmeier formylating complex
was prepared by slow addition of phosphorous oxychloride (0.1
mol) to ice-cooled DMF (0.1 mol). A solution of 4c (0.05 mol)
in 200 mL of dichloroethane was added, and the resultant
solution was stirred at 80-85 °C for 5 h. The solution was
then cooled and hydrolyzed with sodium acetate trihydrate

Potential Therapeutic Agents for Alzheimer’s Disease
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2 579
(0.15 mol) in 200 mL of water. After 1 h, the reaction mixture
was made basic by slow addition of sodium carbonate, the
phases were separated, and the aqueous phase was extracted
with DCM (3 × 100 mL). The combined organics were washed
with water and brine and dried. After filtering, the solvent
was removed in vacuo and elution of the residual oil through
silica with ethyl acetate via flash column chromatography gave
14 g of an oil. Repeated elution of a 3 g aliquot provided 2.2
g of 4o free base as an oil. Conversion to the maleate salt
afforded 2.8 g of 4o as white crystals: mp 169-171 °C; IR
(KBr) 3110, 2960, 2575, 1675, 1640, 1520, 1470, 1375, 1350,
1210, 1125, 870, 820, 740, 640 cm-1; 1H NMR (CDCl3/DMSO-
d6 (10:1)) δ 1.06 (t, 3H, J ) 8 Hz), 1.80 (sextet, 2H, J ) 8 Hz),
4.03 (m, 2H), 6.30 (s, 2H), 6.75 (d, 2H, J ) 10 Hz), 7.20 (m,
1H), 7.33-7.48 (m, 2H), 8.12 (s, 1H), 8.35-8.50 (m, 3H), 10.12
(s, 1H), 10.5-12.0 (br s, 2H, exchangeable with deuterium
oxide); MS m/ e 279. Properties of 4o are included in
Table 3.
7.25-7.40 (m, 2H), 7.80 (s, 1H), 8.30 (d, 2H, J ) 6 Hz), 8.48
(d, 1H, J ) 10 Hz); MS m/ e 293. Properties of 4q are included
in Table 3.
3-E t h yl-N -p r op yl-N -(4-p yr id in yl)-1H -in d ol-1-a m in e
Ma lea te (4r ). Potassium tert-butoxide (0.031 mol) was added
to a suspension of methyltriphenylphosphonium bromide
(0.031 mol) in 200 mL of anhydrous ether. A solution of 4o
(0.021 mol) in 200 mL of anhydrous ether was then added to
the freshly prepared phosphorane. After stirring for 2 h at
ambient temperature, the mixture was poured into water and
separated. The aqueous layer was extracted with ether, and
the combined organic layers were washed with water and
brine, dried, and filtered. After concentration in vacuo, the
residue was eluted through silica with ethyl acetate-DCM (1:
1) via flash column chromatography to provide 13 g of the
product contaminated with triphenylphosphine oxide. Separa-
tion was achieved by conversion of the product to the hydro-
chloride salt in ether, filtration, and basification of the filter
cake to afford the intermediate olefin as an oil.
3-Cya n o-N-p r op yl-N-(4-p yr id in yl)-1H -in d ol-1-a m in e
Ma lea te (4p ). Hydroxylamine hydrochloride (0.07 mol) was
added to a solution of 4o (0.04 mol) in 100 mL of pyridine.
After stirring for 1 h at ambient temperature, the mixture was
concentrated in vacuo. The residue was stirred with water,
made basic by slow addition of sodium carbonate, and ex-
tracted with ethyl acetate. The organic layer was washed with
water and brine, dried, and filtered. The solvent was removed
in vacuo and the residue eluted through silica with ethyl
acetate via flash column chromatography to give 10 g (98%)
of the intermediate oxime as an oil.
A solution of the olefin (0.014 mol) in 250 mL of 95% ethanol
containing 0.25 g of PtO2 was hydrogenated at 60 psi on a Parr
hydrogenation apparatus for 6 h. The catalyst was removed
by filtration through Celite, the filtrate was concentrated in
vacuo, and the residue was eluted through silica with 30%
ethyl acetate in DCM via flash column chromatography to yield
an oil. Conversion to the maleate salt and recrystallization
afforded 2.3 g of 4r as white crystals: mp 133-134 °C; IR
(CHCl3) 3020, 1710, 1645, 1520, 1460, 1350, 1200, 870, 820,
1
640 cm-1; H NMR (CDCl3) δ 1.05 (t, 3H, J ) 8 Hz), 1.38 (t,
3H, J ) 8 Hz), 1.82 (sextet, 2H, J ) 8 Hz), 2.85 (q, 2H, J ) 8
Hz), 3.92 (m, 2H), 6.32 (s, 2H), 6.60 (br s, 2H), 6.88 (s, 1H),
7.08 (m, 1H), 7.27 (m, 2H), 7.70 (m, 1H), 8.33 (d, 2H, J ) 10
Hz); MS m/ e 279. Properties of 4r are included in
Table 3.
Benzenesulfonyl chloride (0.03 mol) was added to a solution
of the oxime (0.03 mol) in 125 mL of ether and pyridine (0.06
mol). The mixture was warmed gently on a steam bath to near
dryness, and was then cooled, poured into water, and made
basic by slow addition of sodium carbonate. The product was
extracted into ethyl acetate, washed with water and brine,
dried, and filtered. The solvent was removed in vacuo and
the residue eluted through silica with ethyl acetate-DCM (1:
1) via flash column chromatography to give 5.5 g of 4p free
base as an oil. An analytical sample was obtained by convert-
ing 2.5 g of the free base to the maleate salt, which was
recrystallized to afford 2.8 g of 4p as pale yellow crystals: mp
163-164 °C; IR (CHCl3) 3030, 2250, 1720, 1650, 1525, 1465,
1360, 1240, 880, 825, 655 cm-1; 1H NMR (CDCl3/DMSO-d6 (10:
1)) δ 1.05 (t, 3H, J ) 8 Hz), 1.77 (sextet, 2H, J ) 8 Hz), 3.98
(m, 2H), 6.33 (s, 2H), 6.65 (d, 2H, J ) 10 Hz), 7.20 (m, 1H),
7.45 (m, 2H), 7.90 (m, 2H), 8.45 (d, 2H, J ) 10 Hz), 10.6-12.8
(br s, 2H, exchangeable with deuterium oxide); MS m/ e 276.
Properties of 4p are included in Table 3.
N-(1H-in dol-1-yl)-N-pr opyl-6-pu r in am in e (9a). A stirred
solution of 6-chloropurine (5.0 g, 0.032 mol) and 1-methyl-2-
pyrrolidinone (50 mL) was acidified with ethereal hydrogen
chloride solution, and then a solution of 2h (5.2 g, 0.030 mol)
and N-methyl-2-pyrrolidinone (50 mL) was added. After
stirring at 120 °C for 6 h, the mixture was cooled and decanted
into water (500 mL). After adjusting to pH 10 with Na2CO3,
the mixture was extracted with ethyl acetate and the organic
phase was dried, filtered, and concentrated to an oil. The
crude oil was purified by HPLC eluting with ethyl acetate and
the desired fractions were combined and concentrated to afford
9a (2.2 g, 25%) as a tan solid: mp 90-95 °C; IR (CHCl3) 3450,
1
3020, 1580, 1470, 1420, 1265, 1095 cm-1; H NMR (CDCl3) δ
0.98 (t, 3H, J ) 8 Hz), 1.73 (sextet, 2H, J ) 8 Hz), 4.12 (m,
1H), 4.68 (m, 1H), 6.62 (d, 1H, J ) 6 Hz), 7.15 (m, 3H), 7.25
(d, 1H, J ) 6 Hz), 7.63 (m, 1H), 7.70 (s, 1H), 8.45 (s, 1H), 11.30
(br s, 1H); MS m/ e 292. Properties of 9a , and of 9b,c prepared
in a similar manner, are included in Table 4.
3-Acet yl-N-p r op yl-N-(4-p yr id in yl)-1H -in d ol-1-a m in e
(4q). Methylmagnesium bromide (3.2 M in ether, 0.048 mol)
was added slowly to a solution of 4o (0.014 mol) in 300 mL of
anhydrous ether. After stirring for 1 h at ambient tempera-
ture, the mixture was hydrolyzed by slow addition of am-
monium chloride (20 g) in 400 mL of water. The mixture was
then made basic by slow addition of sodium carbonate and
extracted with ether. The organic layer was washed with
water and brine, dried, filtered, and concentrated in vacuo to
an oil. Elution through silica with ethyl acetate via flash
column chromatography afforded 3.8 g (90%) of the intermedi-
ate carbinol as a white solid, mp 114-116 °C.
Pyridinium dichromate (0.035 mol) was added to a solution
of the carbinol (0.027 mol) in 80 mL of DMF. After stirring
for 1 h at ambient temperature, the mixture was poured into
water, made basic by slow addition of sodium carbonate, and
extracted with ether. After filtering, the organic layer was
washed with water and brine, dried, filtered, and concentrated
in vacuo to an oil. Elution through silica with ethyl acetate
via flash column chromatography afforded 6.5 g of an oil, which
was crystallized from methanol to provide 5.5 g of 4q as a
white solid. Recrystallization afforded 2.5 g of white crys-
tals: mp 103-105 °C; IR (CHCl3) 3020, 2980, 1660, 1595, 1535,
1510, 1380, 1200, 990, 940, 810 cm-1; 1H NMR (CDCl3) δ 1.03
(t, 3H, J ) 8 Hz), 1.70 (sextet, 2H, J ) 8 Hz), 2.55 (s, 3H),
3.80 (m, 2H), 6.30 (d, 2H, J ) 6 Hz), 7.12 (d, 1H, J ) 10 Hz),
N-(1H-In d ol-1-yl)-N-p r op yl-4-p yr im id in a m in e (9d ). A
mixture of 9c (4.2 g, 0.014 mol), 10% Pd/C (1.2 g), MgO (1.0
g), and ethanol (100 mL) was stirred at atmospheric pressure
under hydrogen for 3 h. The mixture was filtered, and the
filtrate was concentrated to afford a yellow oil which was
purified by HPLC eluting with 10% ethyl acetate in DCM.
Concentration of the desired fractions provided 9d (2.4 g, 64%)
as a viscous yellow oil: IR (CHCl3) 2980, 1590, 1490, 1400,
1340, 1225, 1130, 990, 830 cm-1 1H NMR (CDCl3) δ 1.0 (t,
;
3H, J ) 8 Hz), 1.70 (sextet, 2H, J ) 8 Hz), 3.96 (m, 1H), 4.28
(m, 1H), 5.64 (d, 1H, J ) 8 Hz), 6.67 (d, 1H, J ) 6 Hz), 7.12 (d,
1H, J ) 6 Hz), 7.23 (m, 3H), 7.72 (d, 1H, J ) 8 Hz), 8.12 (d,
1H, J ) 10 Hz), 8.80 (s, 1H); MS m/ e 252. Properties of 9d
are included in Table 4.
Biologica l Meth od s. Procedural details for the in vivo
prevention of tetrabenazine-induced (TBZ) ptosis41,42 and
reversal of scopolamine dementia dark avoidance (SDDA),6,43
and in vitro inhibition of synaptosomal biogenic amine (nore-
pinephrine, serotonin, dopamine) uptake6,44 and inhibition of
[3H]quinuclidinyl benzilate (QNB),24, 26,44 [3H]-N-methylscopo-
lamine,35 [3H]SCH23390,44 [3H]spiroperidol,44 [3H]WB4101,44,45
[3H]clonidine,46 [3H]yohimbine,47 [3H]idazoxan,31,48 [3H]-(()-[3-
(2-carboxypiperazin-4-yl)propyl]phosphonate (CPP),49 [3H]-N-
[1-(2-thienyl)cyclohexyl]piperidine (TCP),49 [3H]nitrendipine,50

580 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2
Klein et al.
[3H]-8-hydroxy-2-(di-n-propylamino)tetralin (DPAT),51 [3H]di-
hydromorphine (DHM),52 [3H]bremazocine,53 [3H]pirenzepine,54
[3H]oxotremorine-M55 and [3H]-N-methylcarbamylcholine56
binding were previously reported. In vitro inhibition of
acetylcholinesterase was determined by the method of Ell-
man.57
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Substituted (pyrroloamino)pyridines: Potential agents for the
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Ack n ow led gm en t. The authors express their ap-
preciation to Anastasia R. Linville and Sandra H.
Anselmo for spectral data and to Dianne M. Saumsiegle
for typing the manuscript.
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