Nonpeptide somatostatin agonists with sst4 selectivity: Synthesis and structure-activity relationships of thioureas

Article abstract of DOI:10.1021/jm980118e

Utilizing NNC 26-9100 (11) as a structural lead, a variety of nonpeptide derivatives of somatostatin were synthesized and evaluated for sst₂ and sst₄ receptor binding affinity. A novel thiourea scaffold was utilized to attach (1) a h

Full text of DOI:10.1021/jm980118e

J . Med. Chem. 1998, 41, 4693-4705
4693
Non p ep tid e Som a tosta tin Agon ists w ith sst4 Selectivity: Syn th esis a n d
Str u ctu r e-Activity Rela tion sh ip s of Th iou r ea s
Shenquan Liu,† Cheng Tang,† Bin Ho,† Michael Ankersen,‡ Carsten E. Stidsen,§ and A. Michael Crider*,†
Division of Basic Pharmaceutical Sciences, School of Pharmacy, Northeast Louisiana University,
Monroe, Louisiana 71209-0470, and MedChem Research and Molecular Pharmacology, Novo Nordisk A/ S,
Novo Nordisk Park, DK-2760 Ma˚løv, Denmark
Received February 20, 1998
Utilizing NNC 26-9100 (11) as a structural lead, a variety of nonpeptide derivatives of
somatostatin were synthesized and evaluated for sst2 and sst4 receptor binding affinity. A
novel thiourea scaffold was utilized to attach (1) a heteroaromatic nucleus to mimic the Trp8
residue, (2) a nonheteroaromatic nucleus to mimic Phe7, and (3) a primary amine or other
basic group to mimic the Lys9 residue of somatostatin. Displacement studies were carried out
using membranes from cell lines expressing ssts [BHK cells (sst4) and HEK 293 cells (sst2)]
utilizing [125I]Tyr11-SRIF as the radioligand. Several thioureas (11, 38, 39, 41, and 42) and
the urea 66 exhibited Ki values of less than 100 nM. The thioureas 11 (Ki ) 6 nM) and 41 (Ki
) 16 nM) and the urea 66 (Ki ) 14 nM) are believed to be the most potent nonpeptide sst4
agonists known. Since the thiourea 11 and the urea 66 exhibit high sst4 selectivity, these
novel nonpeptide derivatives may be useful tools for studying the sst4 receptor. Studies are
currently in progress to evaluate the therapeutic potential of NNC 26-9100 (11) in the treatment
of glaucoma.
In tr od u ction
Somatostatin [somatotropin release-inhibiting factor
(SRIF)] is a cyclic tetradecapeptide containing one
internal disulfide bond between residues 3 and 14, was
isolated initially from bovine hypothalamus, and is
characterized as a potent inhibitor of growth hormone
(GH) secretion from the anterior pituitary.1 SRIF-14
(1; Figure 1) and SRIF-28, a 28-amino acid form of
SRIF-14 extended from the N-terminal end, display
similar biological activities with a different pattern of
potency depending on the tissue.2 In addition to the
inhibitory effects on GH release, both peptides inhibit
the release of a variety of other peptides including
glucagon, insulin, and gastrin,3 and they act as neu-
rotransmitters and neuromodulators in the central
nervous system and the periphery.4
F igu r e 1. Chemical structures of SRIF-14 (1), MK 678 (2),
octreotide (3), and 4.
basis of structural and pharmacological properties, sst2,
sst3, and sst5 belong to the SRIF1 receptor subclass (65-
75% sequence homology). The sst1 and sst4 subtypes
comprise the SRIF2 subclass8-10 (71% sequence homol-
ogy). The major difference between these two subclasses
is that SRIF1 receptors bind octapeptide and hexapep-
tide SRIF-14 analogues with high affinity, while SRIF2
receptors bind these analogues with drastically reduced
affinity.11
Due to its poor bioavailability and rapid degradation
by proteases, the therapeutic utility of SRIF-14 is
limited. As a result, considerable efforts have focused
on the development of peptidomimetics of SRIF-14.
Systematic replacement12 of all amino acids in SRIF-
14 by L-Ala revealed that Trp8 and Lys9 are essential
for biological activity, whereas Phe7 and Thr10 can
undergo minor modifications. These studies showed
that SRIF-14 contains a â-turn composed of the tet-
rapeptide Phe7-Trp8-Lys9-Thr10. Additional work dem-
onstrated that the first two amino acids, Ala-Gly, are
SRIF exerts its potent inhibitory effects following
binding to high-affinity SRIF receptors (ssts) that have
been identified on target tissues. The existence of
multiple receptor subtypes was first demonstrated by
Reubi5 in radioligand binding studies using rat brain
cortex. The recent cloning of five sst subtypes has
confirmed that the effects of SRIF are mediated by a
family of G protein-coupled receptors (sst1-5),6 formerly
designated SSTR 1-5.7 These five sst isoforms have
seven hydrophobic transmembrane domains (20-30-
amino acid-forming helices) which are separated by
stretches of hydrophilic residues. The transmembrane
regions show a higher degree of homology, whereas
extensive differences are seen in the amino acid se-
quences and the sizes of the N- and C-termini. On the
* To whom correspondence should be addressed. Phone: (318) 342-
1707. Fax: (318) 342-1606. E-mail: pycrider@alpha.nlu.edu.
† Northeast Louisiana University.
‡ MedChem Research, Novo Nordisk A/S.
§ Molecular Pharmacology, Novo Nordisk A/S.
10.1021/jm980118e CCC: $15.00 © 1998 American Chemical Society
Published on Web 10/30/1998

4694 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Liu et al.
F igu r e 2. Chemical structures of 5-8.
F igu r e 3. Chemical structures of 9, 10, and NNC 26-9100 (11).
not necessary for full biological activity.13 Using this
information and structure-activity relationship (SAR)
studies on hexapeptides led to the development of the
hexapeptide MK 678 (2; Figure 1).14 This peptide was
50-100 times more potent that SRIF-14 in the in vitro
inhibition of GH release and in the in vivo release of
insulin and glucagon. Due to bioavailability problems
and side effects associated with a malfunction in ab-
sorption of fats, clinical trials with MK 678 were
terminated. Additional studies15 led to the discovery
of octreotide (3; Figure 1). This octapeptide is a potent
SRIF1 receptor subclass agonist that has been the
subject of extensive SAR studies. Long-acting prepara-
tions of octreotide are available for use in the treatment
of acromegaly, neuroendocrine tumors, and gastrointes-
tinal disorders.16 Until recently, no full antagonist of
SRIF-14 had been reported. The octapeptide 4 (Figure
1) which incorporates a D-Cys at position 2 and an
4-NO2-L-Phe at position 1 was shown to be a full sst2
antagonist.17
A number of nonpeptide derivatives (Figure 2) of SRIF
have recently been reported.18-21 In these analogues a
D-sugar or heterocyclic scaffold was utilized to mimic
the â-turn of SRIF. Molecular modeling studies sug-
gested that the substituents at C2, C1, and C6 of the
sugar may mimic the critical Phe7-Trp8-Lys9 side chains
found in SRIF. Additionally, the benzyl group at C4
may mimic the Phe11 residue in SRIF. Compound 5 was
superimposed on the solution structure of the hexapep-
tide L-363,301, a sst2 agonist, and a local minimum of
the sugar derivative was found to overlap quite well
with the bioactive conformation of L-363,301. The
nonpeptide 5 was found to be the most potent derivative
in this series, with an in vitro IC50 of 1.9 µM in
membranes from a subclone of the AtT-20 cell line;
however, this derivative also binds to â2-adrenergic and
NK-1 receptors.19 Several tetrasubstituted xylofuranose
derivatives were synthesized by Papageorgiou et al.,20
and compound 6 exhibited an IC50 of 23 µM in displace-
ment of [125I]Tyr11-SRIF-14 from rat whole brain homo-
genates. Using molecular modeling, five- to seven-
membered nitrogen heterocycles were used as scaffolds
to synthesize SRIF agonists. The azepine 7 was the
most potent derivative with an IC50 of 10 µM in
displacement of 3-[125I]Tyr11-SRIF-14 in rat brain ho-
mogenates.21 Using the benzodiazepine skeleton as a
â-turn mimetic scaffold led to the synthesis of compound
8. This nonpeptide analogue of SRIF exhibited an IC50
of 7 µM in displacement of [125I]Tyr3-octreotide in rat
brain homogenates.22
Since a nonpeptide SRIF ligand may offer therapeutic
advantages23 over peptides, a screening program was
initiated to identify a lead nonpeptide with affinity for
sst1-5 receptors. The search focused on a scaffold with
the following attachments: (1) a heteroaromatic nucleus
to mimic the Trp8 residue, (2) a nonheteroaromatic
nucleus to mimic Phe7, and (3) a primary amine or other
basic groups to mimic the Lys9 residue of SRIF-14.
Using these search criteria, the thiourea 9 (Figure 3)
was identified as a structural lead. The key fragments
in this compound are a heteroaromatic moiety (pyri-
dine), an aromatic group, and a basic imidazole group
connected through a thiourea scaffold. This compound
showed moderate affinity for sst2 with a 20-fold selectiv-
ity of sst4 over sst2. The S-methylisothiourea 10 (Figure
3) had a slightly greater affinity for sst2 than 9; however,
this analogue exhibited about a 100-fold sst2/sst4 selec-
tivity. Evaluation of additional compounds in this series
led to the discovery of the thiourea 11 (NNC 26-9100)
(Figure 3). To our knowledge this was the first report
of the evaluation of nonpeptides at cloned ssts. Com-
pound 11 exhibited high affinity (Ki ) 6 nM) for sst4
and sst2/sst4 selectivity of about 100-fold. In a func-
tional assay based on inhibition of forskolin-induced
accumulation of adenosine cyclic 3′,5′-monophosphate
(cAMP) in BHK cells expressing human ssts, the
thiourea 11, like SRIF-14, potently inhibited cAMP
accumulation.24
Using in situ hybridization techniques, Mori et al.25
showed that the predominant expression of sst4 is in

Somatostatin Agonists with sst4 Selectivity
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4695
Sch em e 1
the posterior iris epithelium and ciliary body. Since sst4
activation induces inhibition of cAMP accumulation in
BHK cells expressing this receptor, a similar effect may
also occur in the iris/ciliary body. The fact that a
decrease in cAMP levels leads to reduction in aqueous
humor production suggests that an sst4 agonist would
likely lower intraocular pressure. Recently, a combina-
tion of SRIF-14 (0.1 µM) and acetylcholine (10 µM) was
shown to induce an increase in Ca2+ levels in the
nonpigmented cells of the rabbit ciliary body by over
25-fold. The effect was attributed to the interaction of
SRIF-14 with a novel sst.26 Thus, selective sst4 agonists
may have potential therapeutic utility in the treatment
of glaucoma.
In an effort to increase the affinity and selectivity at
sst4 receptors, an extensive SAR study of the lead
compound 11 was initiated. This investigation involved
the following modifications of the thiourea 11: (1)
replacement of the benzyl group by an R-naphthylm-
ethyl group, (2) replacement of the 5-bromo substituent
on the pyridine ring with a 5-nitro group or a hydrogen,
(3) varying the distance between the thiourea group and
the two aromatic rings, (4) replacement of the thiourea
group by a urea group, (5) varying the distance between
the thiourea group and the imidazole ring, (6) incorpo-
rating the spacer group between the thiourea moiety
and the imidazole ring into a heterocycle or an aromatic
ring, and (7) replacement of the imidazole ring by other
basic functionalities (Figure 3).
thylmethyl bromide in dimethyl sulfoxide using sodium
hydride as the base gave the N-(1,1-disubstituted)-
diamines 21-29. The key N-(1,1-disubstituted)ami-
noalkyl isothiocyanates 30-36 were prepared by reac-
tion of N-(1,1-disubstituted)diamines 21-29 with 1
equiv of DCC in the presence of carbon disulfide in
tetrahydrofuran.28 The 2-(aminoalkylamino)pyridines
14-20 and the N-(1,1-disubstituted)diamines 21-29
were generally purified by column chromatography to
yield nonanalytically pure oils which were utilized in
the subsequent reaction without further purification.
Reaction of the isothiocyanates 30-36 with an amine
or a trityl-protected amine afforded the desired thio-
ureas 11 and 37-64 after removal of the trityl protect-
ing group with refluxing 1 N hydrochloric acid (Scheme
2, Tables 1-3). Most of the thioureas were isolated as
solid foams which could not be crystallized; however,
in most cases analytically pure samples could be ob-
tained by column chromatography. Numerous attempts
to prepare salts with a variety of organic and inorganic
acids gave very hygroscopic oils or solids. The urea 66
was readily prepared29 by reaction of the diamine 21
with triphosgene and 3-[1-(triphenylmethyl)-1H-imida-
zol-4-yl]propylamine24 (65) in the presence of triethy-
lamine followed by removal of the trityl protecting group
(Scheme 2).
P h a r m a cology
Displacement studies were carried out using mem-
branes from cell lines expressing ssts [BHK cells (sst4)
and HEK 293 cells (sst2)] utilizing [125I]Tyr11-SRIF-14
as the radioligand.24 Several of the thioureas (11, 38,
39, 41, and 42) and the urea 66 exhibited Ki values of
less than 100 nM at sst4 (Table 1).
With the exception of the aminopropyl (59) and the
aminobutyl (63 and 64) derivatives, all thioureas and
the urea 66 demonstrated greater affinity for sst4 than
for sst2. Replacement of the 4-bromobenzyl group (9)
Ch em istr y
Thioureas are conveniently prepared by coupling an
amine with an isothiocyanate under mild reaction
conditions.27 Reaction of the 2-bromopyridines 12 and
13 with an excess of a diaminoalkane in the presence
of a catalytic amount of pyridine readily afforded the
2-(aminoalkylamino)pyridines 14-20 (Scheme 1). Alky-
lation of 14-20 with either a benzyl halide or R-naph-

4696 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Liu et al.
Sch em e 2a
a
(a) Amine/THF; (b) i. amine/THF, ii. refluxing 1 N HCl; (c) i. triphosgene/Et3N/THF, ii. refluxing 1 N HCl.
Ta ble 1. In Vitro Binding at sst2 and sst4 Receptors by Thioureas 11 and 37-50 and the Urea 66
b
c
compd
Y
X
Ara
n
m
sst2
894
sst4
37
38
39
66
40
9d
Br
S
S
S
O
S
S
S
S
S
S
S
S
S
S
S
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
4-BrC6H4
3,4-Cl2C6H3
10H7
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
4-BrC6H4
2
4
2
2
2
3
3
3
4
5
3
3
4
4
4
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
476
96
70
Br
Br
Br
NO2
H
Br
Br
Br
Br
Br
H
2000
310
4200
500
2500
621
14
176
118
6
16
53
11d
41
42
43
44
45
46
47
48
C
778
565
777
132
1700
7000
7000
4000
1400
520
413
50
2200
33000
12000
8000
2000
1700
1000
4600
0.2
H
H
Br
4-BrC6H4
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
49
50
10d
SRIFd
octreotided,e
MK 678d
1.4
0.3
0.3
1904
3200
a
b
Ar groups: 3,4-Cl2C6H3 (3,4-dichlorophenyl), C10H7 (1-naphthyl), 4-BrC6H4 (4-bromobenzyl). Ki (nM) in transfected HEK 293 cells.
c Ki (nM) in transfected BHK cells. Reference 24. e SMS 201-995.
d
by 3,4-dichlorobenzyl (11) or R-methylnaphthyl (41)
groups resulted in enhanced sst4 affinity of 7- and 20-
fold, respectively. Introduction of a 5-Br substituent on
the pyridine ring enhances binding affinity at sst4 by
about 3-fold (compare compounds 47 and 48). Decreas-
ing the distance between the thiourea group and the
5-bromopyridyl moiety of 11 by one methylene group
(compound 39) led to a decrease in sst4 affinity of 12-
fold. Similarly, increasing the distance (n ) 4 and 5,
Table 1) between the 5-bromopyridyl moiety and the
thiourea group of compound 11 (compounds 42 and 43)
resulted in a decrease in sst4 affinity by 9- and 22-fold,
respectively. Replacement of the thiourea group of 39
by a urea group (compound 66) results in a compound
with essentially the same sst4 binding affinity but
dramatically decreased sst2 affinity. The urea 66
exhibited the greatest sst2/sst4 selectivity of any com-
pound evaluated in this investigation.
Compounds having the 3-(imidazol-4-yl)propyl group
demonstrated the greatest sst4 affinity (compounds 11,
38, 39, 41, 42, and 66). These compounds all exhibited
Ki values less than 100 nM at sst4 receptors. Replace-

Somatostatin Agonists with sst4 Selectivity
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4697
Ta ble 2. In Vitro Binding at sst2 and sst4 Receptors by Thioureas 54-58
X
X
X
X
b
c
compd
X
Ara
n
Y
Z
sst2
sst4
51
52
53
54
55
56
57
58
Br
Br
Br
Br
Br
H
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
4-BrC6H3
>300000
3000
1200
1000
15000
71000
1700
113
185
71000
1.4
2
3
3
3
3
4
>300000
>300000
74000
114000
>300000
>300000
0.2
(CH2)2
N
N
N
C
(CH2)3NH
(CH2)3NH
(CH2)3
Br
H
3,4-Cl2C6H3
4-BrC6H4
SRIFd
octreotided,e
MK 678
0.3
0.3
1904
3200
a
-eSee corresponding footnotes in Table 1.
Ta ble 3. In Vitro Binding at sst2 and sst4 Receptors by
Thioureas 59-64
Ta ble 4. Inhibition by Selected Thioureas of
Forskolin-Induced cAMP Accumulation in BHK Cells
Expressing the Human sst4 Receptor
inhibition of cAMP accumulation,
EC50 (nM)a
compd
11
37
41
50
57
61
26 ( 6
2350 ( 30
24 ( 16
990 ( 340
154 ( 46
4000 ( 145
b
c
compd
Ara
n
m
R
sst2
sst4
59
60
61
62
63
64
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
3,4-Cl2C6H3
2
2
2
3
3
3
3
3
3
3
4
4
NH2
N(CH3)2
2300 4200
2000 803
1-pyrrolidinyl 1700 477
1-pyrrolidinyl 1600 514
a
EC50, mean ( SEM; n ) 3 or 4.
NH2
NH2
830
1000
C
10H7
1000 2000
SRIFd
0.2
0.3
0.3
1.4
octreotided,e
MK 678d
1904
3200
a
-eSee corresponding footnotes in Table 1.
ment of the 3-(imidazol-4-yl)propyl group by a 2-(imi-
dazol-4-yl)ethyl group led to decreased sst4 affinity by
2-7-fold (compare compounds 37, 39 and 38-42).
Introduction of conformational constraints between the
thiourea group and the imidazole ring, using either a
heterocyclic system (compare compounds 39 and 50) or
a phenyl ring (compare compounds 38 and 49), de-
creased sst4 affinity by 6- and 10-fold, respectively.
F igu r e 4. Inhibition by thiourea derivatives of forskolin-
induced cyclic AMP accumulation in BHK cells expressing the
human sst4 receptor subtype. The data are from representative
experiments performed in triplicate for compound 11 (+),
compound 37 ([), compound 41 (9), and compound 57 (×).
Thioureas with high (11 and 41), moderate (57), and
low (37, 50, and 61) sst4 binding affinity were evaluated
in a functional assay to assess inhibition of forskolin-
induced adenosine cyclic 3′,5′-monophosphate (cAMP)
in BHK cells expressing the human sst4 receptor (Table
4 and Figure 4). The thioureas with the highest affinity
for sst4 receptors (compounds 11 and 41) potently
inhibited forskolin-induced cAMP accumulation with
EC50 values of 26 and 24 nM, respectively. These data
demonstrate that the thioureas act as full agonists at
the human sst4 receptor.

4698 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Liu et al.
NH), 6.31 (d, J ) 9 Hz, 1 H, pyridine H-3), 7.44 (dd, J ) 2.7
Hz, J ) 9 Hz, 1 H, pyridine H-4), 8.09 (d, J ) 2.5 Hz, 1 H,
pyridine H-6); 13C NMR (CDCl3) δ 41.22, 44.74, 106.72, 108.67,
139.55, 148.54, 148.70.
Con clu sion s
The amino acid sequence Phe7-Trp8-Lys9-Thr10 is
thought to comprise the â-turn of SRIF, and these
residues appear to play an important role in the binding
at ssts.30 Additionally, the proximity of the Trp8-Lys9
residues is considered essential for sst binding. Based
on the results of the in vitro binding studies of the target
thioureas at ssts, several conclusions can be made. The
pyridine ring may mimic the Trp8 of SRIF, and the
nonheteroaromatic benzyl or naphthyl groups may
mimic Phe7 in the natural peptide. Although less basic
that the ꢀ-NH2 group of Lys, the imidazoyl group, found
in the most potent thioureas, may mimic the Lys9
residue of SRIF. Hirschmann et al.19 have shown that
the Phe8 of SRIF can be replaced by a His residue. This
leads to the speculation that the imidazoyl group of the
thiourea derivatives could mimic the Phe7 of SRIF. The
role of the thiourea moiety is uncertain. Perhaps, this
group serves as a scaffold to properly orient the het-
eroaromatic, aromatic, and basic groups at ssts. The
thioureas 11 (Ki ) 6 nM) and 41 (Ki ) 16 nM) and the
urea 66 (Ki ) 14 nM) are, to our knowledge, the most
potent nonpeptide sst4 agonists known. Since the
thiourea 11 and the urea 66 exhibit high selectivity for
sst4 over sst2, these compounds may be useful tools for
studying the pharmacological effects of the sst4 receptor.
Selective sst4 agonists may lead to a decrease of aqueous
humor production in the iris/ciliary body.25 This opens
the possibility that these nonpeptide sst4 agonists may
represent novel therapeutic agents for the treatment of
glaucoma. Studies are currently in progress to evaluate
the potential utility of NNC 26-9100 (11) in this
disorder.
N-1-(P yr id -2-yl)p r op a n e-1,3-d ia m in e (16). 2-Bromopy-
ridine (12; 20.0 g, 126.7 mmol), pyridine (12.7 g, 160.8 mmol),
and 1,3-diaminopropane (47.4 g, 639 mmol) afforded a dark-
brown oil. Vacuum distillation gave 9.19 g (48%) of 16 as a
light-yellow oil: bp 111-114 °C (0.65 mmHg); 1H NMR
(CDCl3) δ 1.28 (br s, 2 H, NH2), 1.75 (m, 2 H), 2.84 (t, 2 H),
3.35 (m, 2 H), 5.00 (br s, 2 H, NH), 6.50 (m, 2 H), 7.40 (ddd, 1
H), 8.07 (m, 1 H); 13C NMR (CDCl3) δ 32.93, 39.92 (2×), 106.77,
112.30, 137.17, 148.00, 159.00.
N-1-(5-Br om op yr id -2-yl)p r op a n e-1,3-d ia m in e (17). 2,5-
Dibromopyridine (13; 4.40 g, 18.6 mmol), pyridine (1.86 g, 23.6
mmol), and 1,3-diaminopropane (25 mL) yielded an oil. Vacuum
distillation afforded 2.69 g (63%) of 17 as an oil: bp 135-139
°C (0.1 mmHg); 1H NMR (CDCl3) δ 1.52 (br s, 2 H, NH2), 1.72
(m, 2 H), 2.89 (t, 2 H), 3.36 (m, 2 H), 5.30 (br s, 1 H, NH), 6.29
(d, J ) 9 Hz, 1 H, pyridine H-3), 7.44 (dd, J ) 2.4 Hz, J ) 9
Hz, 1 H, pyridine H-4), 8.09 (d, J ) 2.4 Hz, 1 H, pyridine H-6);
13C NMR (CDCl3) δ 32.61, 39.98, 40.25, 106.45, 108.29, 139.50,
148.49, 157.48.
N-1-(P yr id -2-yl)bu ta n e-1,4-d ia m in e (18). 2-Bromopyri-
dine (12; 20.0 g, 126.7 mmol), pyridine (12.7 g, 160.8 mmol),
and 1,4-diaminobutane (56.3 g, 639 mmol) gave 11.5 g (55%)
of 18 as a light-yellow oil: bp 103-105 °C (0.05 mmHg) [lit.32
bp 136-138 °C (2 mmHg)]; 1H NMR (CDCl3) δ 1.56 (br s, 2 H,
NH2), 1.61 (m, 4 H), 2.73 (t, 2 H), 3.25 (m, 2 H), 4.73 (br s, 1
H, NH), 6.43 (m, 2 H), 7.40 (ddd, 1 H), 8.08 (m, 1 H); 13C NMR
δ 27.03, 31.25, 41.98, 42.09, 106.56, 112.57, 137.27, 148.22,
159.00.
N-1-(5-Br om op yr id -2-yl)b u t a n e-1,4-d ia m in e (19). 13
(10.0 g, 42.2 mmol), 1,4-diaminobutane (52.6 g, 597 mmol),
and pyridine (10.0 g, 42.2 mmol) gave a brown oil. Vacuum
distillation afforded 7.87 g (76%) of 19 as a colorless oil: bp
1
165-170 °C (0.8 mmHg); H NMR (CDCl3) δ 1.15-1.75 (m, 6
H), 2.72 (t, 2 H), 3.25 (br s, 2 H, NH2), 4.75 (br s, 1 H, NH),
6.30 (d, J ) 9 Hz, pyridine H-3), 7.47 (dd, J ) 2.7 Hz, J ) 9
Hz, 1 H, pyridine H-4), 8.10 (d, J ) 2.4 Hz, pyridine H-6); 13
C
Exp er im en ta l Section
NMR (CDCl3) δ 26.87, 31.09, 41.87, 42.20, 108.07, 139.66,
148.71.
Ch em istr y. Melting points were determined on a Thomas-
Hoover melting point apparatus and are not corrected. The
IR spectra were recorded as liquid films or as potassium
bromide pellets on a Nicolet Impact 400D spectrometer. The
NMR spectra were recorded on a J EOL FX 90Q 90-MHz
spectrometer or a J EOL Eclipse 400-MHz spectrometer, and
chemical shifts are recorded in parts per million (δ) relative
to tetramethylsilane. Analytical data were obtained from
Oneida Research Services, Inc., Whitesboro, NY, and Desert
Analytics, Tucson, AZ. Precoated plastic TLC (5- × 20-cm)
0.2-mm aluminum oxide M/UV254 and silica gel 0.25-mm with
fluorescent indicator UV254 plates were purchased from the
Brinkmann Instrument Co. or EM Industries, Inc. Flash
chromatography was performed on Ace glass columns (i.d. )
5 cm, length ) 45 cm) with 150-200 g of silica gel (40 µm)
purchased from the J . R. Baker Chemical Co. All solvents
which were used for recrystallizations and column chroma-
tography were of analytical grade, and 2-(2-aminoethylamino)-
5-nitropyridine (15) was obtained from the Aldrich Chemical
Co.
Repr esen ta tive P r oced u r e for th e Syn th esis of 2-(Am i-
n oa lk yla m in o)p yr id in es. P r ep a r a t ion of N-1-(5-Br o-
m op yr id -2-yl)eth a n e-1,2-d ia m in e (14). A mixture of 2,5-
dibromopyridine (13; 10.0 g, 42.2 mmol) and pyridine (4.24 g,
53.6 mmol) in 1,2-diaminoethane (43 mL) was refluxed under
nitrogen for 18 h. The reaction mixture was evaporated under
reduced pressure and cooled, and the resulting residue was
treated with THF (150 mL) to yield a white precipitate. The
precipitate was filtered and washed with additional THF (100
mL). Evaporation of the filtrate afforded a brown oil which
was vacuum distilled to give 6.48 g (71%) of 14 as a light-
N-1-(5-Br om op yr id -2-yl)p en ta n e-1,5-d ia m in e (20). 13
(8.42 g, 35.5 mmol), pyridine (3.54 g, 44.8 mmol), and 1,5-
diaminopentane (25.0 g, 244.7 mmol) gave an oil. Flash
chromatography on silica gel using CH2Cl2/MeOH/concen-
trated NH4OH (50:50:1) as the solvent afforded 5.50 g (60%)
of 20 as an oil: 1H NMR (CDCl3) δ 1.50 (m, 6 H), 1.85 (br s,
2 H, NH2), 2.72 (m, 2 H), 3.25 (m, 4 H), 4.70 (br s, 1 H, NH),
6.30 (d, J ) 9 Hz, 1 H, pyridine H-3), 7.47 (dd, 1 H, H-4), 8.09
(d, 1 H, pyridine H-6); 13C NMR (CDCl3) δ 24.38, 29.40, 33.75,
41.88, 42.50, 106.88, 107.19, 140.00, 149.06, 157.50.
Repr esen tative P r ocedu r e for th e Alkylation of 2-(Am i-
n oa lk yla m in o)p yr id in es Usin g Sod iu m Hyd r id e in Dim -
et h yl Su lfoxid e. P r ep a r a t ion of N-1-(5-Br om op yr id -2-
yl)-1-(3,4-d ich lor oben zyl)eth a n e-1,2-d ia m in e (21). A 60%
mineral oil dispersion of NaH (0.584 g, 14.6 mmol) and 14 (3.00
g, 13.9 mmol) in DMSO (30 mL) was stirred for 2 h under
nitrogen. The suspension was cooled to 0-5 °C and treated
dropwise with 3,4-dichlorobenzyl chloride (2.71 g, 13.9 mmol)
in DMSO (15 mL). After stirring overnight at room temper-
ature, the reaction mixture was poured into 200 mL of an ice-
water mixture. The mixture was extracted with ethyl acetate
(3 × 75 mL), and the combined ethyl acetate extracts were
washed with water (2 × 50 mL), dried (Na2SO4), filtered, and
evaporated to yield an oil. Flash chromatography on silica gel
using CH2Cl2/MeOH/Et3N (90:5:5) as the solvent system gave
3.5 g (67%) of 21 as a yellow oil: 1H NMR (CDCl3) δ 1.45 (s,
2 H, NH2), 2.92 (t, 2 H, NCH2), 3.57 (m, 2 H, CH2), 4.72 (s, 2
H, ArCH2), 6.39 (d, J ) 9 Hz, 1 H, pyridine H-3), 7.32 (m, 4 H,
ArH), 8.16 (d, J ) 2 Hz, 1 H, pyridine H-6); 13C NMR (CDCl3)
δ 39.82, 51.47, 51.95, 107.00, 107.27, 126.23, 128.77, 130.62,
131.04, 132.73, 138.85, 139.77, 148.66, 156.62.
1
yellow oil: bp 134-142 °C (0.6 mmHg); H NMR (CDCl3) δ
1.33 (s, 2 H, NH2), 2.92 (t, 2 H), 3.29 (m, 2 H), 5.22 (br s, 1 H,

Somatostatin Agonists with sst4 Selectivity
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4699
N-1-(5-Nit r op yr id -2-yl)-1-(3,4-d ich lor ob en zyl)et h a n e-
1,2-d ia m in e (22). 15 (3.00 g, 16.5 mmol), NaH (0.692 g, 17.3
mmol), and 3,4-dichlorobenzyl chloride (3.22 g, 16.5 mmol) in
DMSO (25 mL) gave an oil. Flash chromatography on silica
gel using EtOAc/MeOH/concentrated NH4OH (60:40:1) as the
solvent yielded 2.84 g (51%) of 22 as an oil: 1H NMR (CDCl3)
δ 1.35 (br s, 2 H, NH2), 3.68 (t, 2 H), 4.88 (s, 2 H), 6.55 (d, J )
9.6 Hz, 1 H, pyridine H-3), 7.30 (m, 3 H), 8.23 (dd, J ) 2.7 Hz,
J ) 9.3 Hz, 1 H, pyridine H-4), 9.08 (d, 2.9 Hz, 1 H, pyridine
H-6); 13C NMR (CDCl3) δ 39.82, 51.47, 52.12, 104.61, 126.23,
130.83, 137.33, 146.49.
N-[1-(5-Br om op yr id -2-yl)-1-(n a p h t h -1-yl)m et h yl]p r o-
p a n e-1,3-d ia m in e (25). 17 (8.71 g, 37.9 mmol), a 60%
mineral oil dispersion of NaH (1.67 g, 41.6 mmol), and
1-(bromomethyl)naphthalene33 (9.21 g, 41.6 mmol) in DMSO
(60 mL) gave an oil. Flash chromatography on silica gel using
CH2Cl2/MeOH/concentrated NH4OH (50:50:1) afforded 5.10 g
(35%) of 25 as an oil: 1H NMR (CDCl3) δ 1.43 (br s, 2 H, NH2),
1.75 (m, 2 H), 3.67 (t, 2 H), 5.12 (s, 2 H, ArCH2), 6.31 (d, J )
9 Hz, 1 H, pyridine H-3), 7.15-8.05 (m, 8 H, ArH), 8.20 (d, J
) 2.4 Hz, 1 H, pyridine H-6); 13C NMR (CDCl3) δ 31.31, 39.55,
45.72, 106.29, 107.54, 122.76, 123.84, 125.47, 125.85, 126.23,
127.74, 128.94,131.32, 132.24, 133.92, 139.55, 148.55, 156.94.
N -1-(4-B r o m o b e n zy l)-1-(p y r id -2-y l)b u t a n e -1,4-d i-
a m in e (26). 18 (10.1 g, 30.3 mmol), a 60% mineral oil
dispersion of NaH (1.27 g, 31.8 mmol), and 4-bromobenzyl
bromide (7.57 g, 30.3 mmol) in DMSO (60 mL) gave an oil.
Flash chromatography on silica gel using CH2Cl2/MeOH/Et3N
(90:5:5) yielded 4.29 g (57%) of 26 as a thick oil: 1H NMR
(CDCl3) δ 1.45 (m, 4 H, CH2 and NH2), 2.65 (t, 2 H), 3.45 (t, 2
H), 4.70 (s, 2 H, ArCH2), 6.95 (m, 2 H), 7.25 (m, 5 H), 8.15 (m,
1 H); 13C NMR (CDCl3) δ 24.66, 31.05, 41.94, 48.39, 50.99,
105.65, 111.88, 113.01, 120.49, 128.67, 130.73, 137.23, 148.07,
157.93.
N-1-(3,4-Dich lor ob en zyl)-1-(p yr id -2-yl)b u t a n e-1,4-d i-
a m in e (27). 18 (2.41 g, 14.6 mmol), a 60% mineral oil
dispersion of NaH (613 mg, 15.3 mmol), and 3,4-dichlorobenzyl
bromide (3.50 g, 14.6 mmol) gave an oil. Purification by flash
chromatography on silica gel using a solvent system of CH2-
Cl2/MeOH/concentrated NH4OH (50:50:1) afforded 0.95 g (20%)
of a light-green oil: 1H NMR (CDCl3) δ 1.52 (m, 4 H), 2.02 (br
s, 2 H, NH2), 2.70 (t, 2 H), 3.43 (t, 2 H), 4.71 (s, 2 H, ArCH2),
6.50 (m, 2 H), 7.00-7.52 (m, 4 H), 8.16 (m, 1 H).
N-1-(5-Br om op yr id -2-yl)-1-(3,4-d ich lor oben zyl)bu ta n e-
1,4-d ia m in e (28). 19 (7.00 g, 28.7 mmol), a 60% mineral oil
dispersion of NaH (1.20 g, 30.1 mmol), and 3,4-dichlorobenzyl
chloride (5.62 g, 28.7 mmol) in DMSO (75 mL) gave an oil.
Flash chromatography on silica gel using a solvent system of
CH2Cl2/MeOH/concentrated NH4OH (50:50:1) yielded 2.32 g
(20%) of 28 as an oil: 1H NMR (CDCl3) δ 1.50 (m, 4 H, CH2
and NH2), 2.72 (t, 2 H), 3.45 (t, 2 H, NCH2), 4.68 (s, 2 H,
ArCH2), 6.35 (d, J ) 9 Hz, pyridine H-3), 7.00-7.55 (m, 4 H,
ArH), 8.15 (d, J ) 2.4 Hz, 1 H, pyridine H-6); 13C NMR (CDCl3)
δ 24.48, 30.93, 41.87, 48.81, 59.76, 106.61, 107.10, 126.28,
128.77, 130.45, 139.12, 148.60, 156.29. Anal. (C16H18BrCl2N3)
C, H, N.
N-1-(5-Br om opyr id-2-yl)-1-(3,4-dich lor oben zyl)pen tan e-
1,5-d ia m in e (29). 20 (5.50 g, 21.3 mmol), a 60% mineral oil
dispersion of NaH (940 mg, 23.4 mmol), and 3,4-dichlorobenzyl
chloride (4.60 g, 23.4 mmol) in DMSO (75 mL) afforded an oil.
Purification by flash chromatography on silica gel using CH2-
Cl2/MeOH/concentrated NH4OH (50:50:1) as the solvent gave
1.46 g (16%) of 29 as an oil: 1H NMR (CDCl3) δ 1.35 (m, 6 H),
2.70 (m, 2 H), 3.40 (t, 2 H), 4.68 (s, 2 H, ArCH2), 6.35 (d, J )
9 Hz, 1 H, pyridine H-3), 7.35 (m, 4 H, ArH), 8.15 (d, 1 H,
pyridine H-6); 13C NMR (CDCl3) δ 24.38, 27.19, 33.75, 42.20,
49.06, 50.63, 106.25, 107.50, 126.25, 127.81, 130.94, 131.25,
131.90, 140.00, 149.06, 156.56.
mmol) in THF (20 mL). The reaction mixture was allowed to
warm to room temperature and was stirred overnight under
nitrogen. Removal of the solvent under reduced pressure
afforded a white solid. The solid was triturated with diethyl
ether (200 mL), and the dicyclohexylthiourea was removed by
filtration. The filtrate was evaporated, and acetonitrile (100
mL) was added to the resulting residue. The remaining
dicyclohexylthiourea was filtered, and the filtrate was evapo-
rated under vacuum to afford an oil. Flash chromatography
on silica gel using CH2Cl2/hexane/Et3N (50:50:1) gave 4.31 g
(78%) of a white solid. Recrystallization from Et2O/hexane
gave an analytical sample: mp 83-85 °C; 1H NMR (CDCl3) δ
3.84 (m, 4 H), 4.69 (s, 2 H, ArCH2), 6.33 (d, J ) 8.3 Hz, 1 H,
pyridine H-3), 7.40 (m, 4 H), 8.20 (d, J ) 2 Hz, 1 H, pyridine
H-6); 13C NMR (CDCl3) δ 43.34, 49.19, 52.71, 107.70, 108.19,
125.74, 128.34, 130.83, 140.10, 148.71, 155.65. Anal. (C15H12
BrCl2N3S) C, H, N.
-
2-[N-(3,4-Dich lor oben zyl)-N-(5-n itr op yr id -2-yl)a m in o-
]eth yl Isoth iocya n a te (31). 22 (2.80 g, 8.21 mmol), CS2 (6.70
g, 88.0 mmol), and DCC (1.70 g, 8.21 mmol) in THF (60 mL)
gave a dark-yellow solid. Flash chromatography on silica gel
using CH2Cl2/hexane/Et3N (50:50:1) as the solvent system gave
2.20 g (71%) of a yellow solid: mp 104-106 °C; 1H NMR
(CDCl3) δ 3.94 (m, 4 H), 4.85 (s, 2 H, ArCH2), 6.49 (d, J ) 10
Hz, 1 H, pyridine H-3), 7.29 (m, 3 H, ArH), 8.23 (dd, J ) 2.7
Hz, J ) 9.3 Hz, 1 H, pyridine H-4), 9.08 (d, J ) 2 Hz, 1 H,
pyridine H-6).
3-[N-(4-Br om oben zyl)-N-(p yr id -2-yl)a m in o]p r op yl Iso-
th iocya n a te (32). 2324 (2.00 g, 6.24 mmol), CS2 (5.08 g, 66.7
mmol), and DCC (1.29 g, 6.24 mmol) in THF (45 mL) yielded
an oil. Flash chromatography on silica gel using hexane/
EtOAc/Et3N (70:30:1) as the solvent gave 1.35 g (60%) of 32
as an oil: 1H NMR (CDCl3) δ 2.04 (m, 4 H), 3.55 (m, 2 H),
4.67 (s, 2 H, ArCH2), 6.50 (m, 2 H), 7.25 (m, 5 H), 8.15 (m, 1
H); 13C NMR (CDCl3) δ 28.28, 43.01, 45.72, 51.68, 105.86,
112.57, 120.86, 128.61, 131.75, 137.49, 148.11, 157.81.
3-[N-(5-Br om op yr id -2-yl)-N-(3,4-d ich lor ob en zyl)a m i-
n o]p r op yl Isoth iocya n a te (33). 24 (3.64 g, 9.35 mmol), CS2
(7.62 g, 100 mmol), and DCC (1.94 g, 9.35 mmol) in THF (45
mL) gave an oil. Purification by flash chromatography on
silica gel using hexane/EtOAc/Et3N (70:30:1) as the solvent
afforded 3.19 g (79%) of 33 as an oil: 1H NMR (CDCl3) δ 2.06
(m, 2 H), 3.62 (m, 4 H), 4.66 (s, 2 H, ArCH2), 6.40 (m, 1 H),
7.35 (m, 4 H), 8.22 (m, 1 H); 13C NMR (CDCl3) δ 28.06, 42.91,
46.10, 51.41, 107.21, 107.43, 126.17, 128.72, 130.72, 131.26,
138.31, 139.93, 148.76, 156.13; MS (CI, CH4) 432 M+. Anal.
(C16H14BrClN3S) C, H, N.
3-[N-(5-Br om op yr id -2-yl)-N-(n a p h t h -1-ylm et h yl)a m i-
n o]p r op yl Isoth iocya n a te (34). 25 (4.00 g, 10.8 mmol), CS2
(8.80 g, 115 mmol), and DCC (2.32 g, 10.8 mmol) in THF (140
mL) afforded an oil. Flash chromatography on silica gel using
a solvent system of CH2Cl2/hexane/Et3N (50:50:1) gave 2.70 g
(84%) of 34 as a colorless oil: 1H NMR (CDCl3) δ 2.00 (m, 2
H), 3.54 (t, 2 H), 3.74 (t, 2 H), 5.11 (s, 2 H, ArCH2), 6.30 (d, J
) 9 Hz, 1 H, pyridine H-3), 7.15-8.02 (m, 8 H, ArH), 8.25 (d,
J ) 2.4 Hz, 1 H, pyridine H-6); 13C NMR (CDCl3) δ 28.28,
43.01, 45.77, 50.32, 106.99, 107.59, 122.65, 123.89, 125.41,
125.90, 126.39, 128.93, 139.71, 148.60, 156.62. Anal. (C20H18
BrN3S) C, H, N.
-
4-[N-(5-Br om op yr id -2-yl)-N-(3,4-d ich lor ob en zyl)a m i-
n o]bu tyl Isoth iocya n a te (35). 28 (1.68 g, 4.16 mmol), CS2
(1.85 g, 44.2 mmol), and DCC (858 mg, 4.16 mmol) in THF
(45 mL) afforded an oil. Purification by flash chromatography
on silica gel using a solvent system of hexane/EtOAc/Et3N (80:
20:1) gave 1.53 g (83%) of 35 as an oil: 1H NMR (CDCl3) δ
1.72 (m, 4 H), 3.54 (m, 4 H), 4.65 (s, 2 H, ArCH2), 6.32 (d, J )
9 Hz, 1 H, pyridine H-3), 6.97-7.50 (m, 4 H), 8.16 (d, J ) 2.4
Hz, 1 H, pyridine H-6); 13C NMR (CDCl3) δ 24.32, 27.36, 44.80,
47.90, 51.62, 107.10, 126.18, 128.66, 130.56, 130.99, 132.67,
138.63, 139.71, 148.60, 156.18. Anal. (C17H16BrCl2N3S) H, N;
C: calcd, 45.86; found, 46.50.
Gen er al Meth od for th e Syn th esis of 2-P yr idyl Isoth io-
cya n a tes. P r ep a r a tion of 2-[N-(5-Br om op yr id -2-yl)-N-
(3,4-d ich lor oben zyl)a m in o]eth yl Isoth iocya n a te (30). A
mixture of DCC (2.74 g, 13.2 mmol) and CS2 (10.1 g, 132.6
mmol) in THF (30 mL) was cooled to -10 °C in an ice-salt
bath and treated dropwise with a solution of 21 (5.00 g, 13.2
5-[N-(5-Br om op yr id -2-yl)-N-(3,4-d ich lor ob en zyl)a m i-
n o]p en tyl Isoth iocya n a te (36). 29 (1.46 g, 3.50 mmol), CS2
(2.84 g, 37.3 mmol), and DCC (722 mg, 3.50 mmol) in THF

4700 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Liu et al.
(45 mL) gave an oil. Flash chromatography using hexane/
EtOAc/Et3N (80:20:1) afforded 1.38 g (86%) of 36 as an oil: 1H
NMR (CDCl3) δ 1.60 (m, 6 H), 3.47 (m, 4 H), 4.69 (s, 2 H,
ArCH2), 6.35 (d, J ) 9 Hz, 1 H, pyridine H-3), 7.33 (m, 4 H),
8.17 (d, 1 H, pyridine H-6); 13C NMR (CDCl3) δ 23.99, 26.44,
29.63, 44.86, 48.65, 50.92, 106.72, 107.05, 126.33, 128.72,
130.51, 132.62, 138.90, 139.66, 148.60, 156.24.
3-[2-(1H-Im id a zol-4-yl)eth yl]-1-[2-[N-(5-br om op yr id -2-
yl)-N-(3,4-d ich lor oben zyl)a m in o]eth yl]th iou r ea (37). A
suspension of histamine (320 mg, 2.88 mmol) in THF (40 mL)
was treated with a solution of 30 (1.20 g, 2.88 mmol) in THF
(15 mL). The reaction mixture was stirred for 48 h under a
nitrogen atmosphere, and the solvent was removed under
reduced pressure to afford a foam. Flash chromatography on
silica gel using a solvent system of EtOAc/MeOH/concentrated
NH4OH (90:5:5) gave 987 mg (67%) of a white foam: mp 72-
78 °C; 1H NMR (CDCl3) δ 2.85 (m, 2 H), 3.68 (m, 6 H), 4.59 (s,
2 H, ArCH2), 6.40 (d, 1 H, pyridine H-3), 6.80-7.50 (m, 9 H,
NHCdSNH and ArH), 8.02 (d, 1 H, pyridine H-6); 13C NMR
(CDCl3) δ 27.66, 42.81, 47.74, 51.80, 107.49, 108.19, 116.16,
125.96, 130.84, 131.33, 132.95, 134.90, 135.55, 137.82, 140.32,
148.12, 156.63, 181.71. Anal. H, N; C: calcd, 45.46; found,
44.90.
3-[2-(1H-Im id a zol-4-yl)eth yl]-1-[4-[N-(5-br om op yr id -2-
yl)-N-(3,4-d ich lor oben zyl)a m in o]bu tyl]th iou r ea (38). A
suspension of histamine (352 mg, 3.17 mmol) in THF (10 mL)
was cooled to 0-5 °C and treated dropwise with 35 (1.41 g,
3.17 mmol) in THF (20 mL). After stirring overnight, the
solvent was removed under reduced pressure to yield an oil
which was purified by flash chromatography using a solvent
system of EtOAc/MeOH/concentrated NH4OH (85:15:1). Frac-
tions homogeneous by TLC were combined and evaporated
under reduced pressure to afford 1.59 g (90%) of a white foam:
1H NMR (CDCl3) δ 1.60 (m, 4 H), 2.80 (m, 2 H), 3.60 (m, 8 H),
4.63 (s, 2 H, ArCH2), 6.37 (s, 1 H), 6.79-7.55 (m, 7 H), 8.16 (d,
J ) 2.2 Hz, 1 H); 13C NMR (CDCl3) δ 24.65, 26.27, 26.65, 43.94,
44.21, 48.49, 50.87, 106.72, 107.37, 115.34, 126.17, 128.61,
130.56, 130.94, 132.62, 134.68, 139.82, 148.44, 156.29, 181.59.
Anal. (C24H25BrCl2N6S) C, H, N.
3-[3-(1H-Im id a zol-4-yl)p r op yl]-1-[2-[N-(5-br om op yr id -
2-yl)-N-(3,4-d ich lor oben zyl)a m in o]eth yl]th iou r ea (39). A
suspension of 3-[1-(triphenylmethyl)imidazol-4-yl]propylamine
(65; 0.87 g, 2.64 mmol) in THF (40 mL) was stirred under a
nitrogen atmosphere at 0-5 °C and treated dropwise with a
solution of 30 (1.10 g, 2.64 mmol) in THF (15 mL). The
reaction mixture was allowed to warm to room temperature
and was stirred overnight. TLC on silica gel using EtOAc/
MeOH /Et3N (90:5:5) indicated that considerable starting
material remained. The reaction mixture was stirred for an
additional 24 h, and the solvent was removed under reduced
pressure to yield a white foam. Flash chromatography on
silica gel using EtOAc/MeOH/Et3N (90:5:5) as the solvent
afforded 1.72 g (87%) of the trityl-protected thiourea as a
colorless oil. The oil was suspended in 2 N HCl (40 mL) and
was refluxed for 8 h under nitrogen. The precipitated triph-
enylmethanol was filtered, and the filtrate was evaporated
under reduced pressure to yield a foam. The foam was
suspended in 1 N NaOH (60 mL) and extracted with EtOAc
(3 × 75 mL). The combined EtOAc extracts were washed with
water (2 × 50 mL), dried (Na2SO4), filtered, and evaporated
to yield upon trituration with hexane 765 mg (57%) of a white
hygroscopic foam: 1H NMR (CDCl3) δ 1.90 (m, 2 H), 2.64 (m,
6 H), 3.55 (m, 6 H), 4.62 (s, 2 H, ArCH2), 6.44 (d, J ) 9 Hz, 1
H, pyridine H-3), 7.20-7.55 (m, 8 H, NHCdSNH and ArH),
8.09 (d, J ) 2.5 Hz, 1 H, pyridine H-6); 13C NMR (CDCl3) δ
23.49, 28.87, 42.42, 43.50, 47.84, 51.79, 107.51, 108.19, 115.99,
126.01, 128.50, 130.78, 131.31, 132.89, 134.35, 137.22, 137.98,
140.26, 148.04, 156.62, 181.75. Anal. (C21H23BrClN6S) C:
calcd, 46.50; found, 45.13. H: calcd, 4.28; found, 5.00. N:
calcd, 15.50; found, 16.22.
overnight at room temperature under a nitrogen atmosphere,
the solvent was removed under reduced pressure to yield 2.1
g of a yellow foam. The intermediate trityl-protected thiourea
was suspended in 1 N HCl (35 mL) and refluxed for 1.5 h.
The solution was filtered, extracted with diethyl ether (2 ×
200 mL), basified with 6 N NaOH, and extracted with EtOAc
(3 × 100 mL). The combined EtOAc extracts were washed
with water (3 × 100 mL), dried (Na2SO4), and evaporated
under vacuum to yield a foam. Flash chromatography on silica
gel using a solvent system of CH2Cl2/MeOH/concentrated NH4-
OH (90:10:1) yielded 500 mg (38%) of 40 as a yellow foam: 1H
NMR (DMSO-d6) δ 1.72 (m, 2 H), 3.50 (m, 8 H), 4.93 (s, 2 H,
ArCH2), 6.75 (s, 1 H), 7.35 (m, 7 H), 8.22 (dd, 1 H, pyridine
H-4), 8.97 (d, J ) 2.7 Hz, pyridine H-6); 13C NMR (CDCl3) δ
23.14, 28.99, 42.05, 42.40, 48.01, 51.58, 105.27, 126.45, 128.89,
130.89, 133.17, 133.98, 146.28, 160.58, 181.46. Anal. (C21H23
Cl2N7O2S) C, H; N: calcd, 19.29; found, 18.86.
-
3-[3-(1H-Im id a zol-4-yl)p r op yl]-1-[3-[N-(5-br om op yr id -
2-yl)-N-(n a p h th -1-ylm eth yl)a m in o]p r op yl]th iou r ea (41).
A solution of 65 (1.24 g, 3.38 mmol) was dissolved in THF (20
mL) and treated dropwise with a solution of 34 (1.40 g, 3.38
mmol) in THF (20 mL) at 0-5 °C under a nitrogen atmosphere.
The reaction mixture was allowed to warm to room temper-
ature and was stirred overnight. The solvent was evaporated
under reduced pressure to yield an oil which was purified by
flash chromatography on silica gel using a solvent system of
EtOAc/MeOH/Et3N (92:4:4). Fractions homogeneous on TLC
were combined and evaporated to give 2.63 g of the trityl-
protected thiourea. The oil was suspended in 1 N HCl (60 mL)
and refluxed for 1.5 h. The precipitate was filtered, and the
filtrate was extracted with Et2O (2 × 100 mL). The aqueous
layer was basified with 6 N NaOH and extracted with EtOAc
(3 × 100 mL). The combined EtOAc extracts were washed
with water (2 × 50 mL), dried (Na2SO4), filtered, and evapo-
rated to yield an oil. Flash chromatography on silica gel using
an eluent of CH2Cl2/MeOH/concentrated NH4OH (90:10:1)
afforded 1.10 g (61%) of 41 as a foam: 1H NMR (CDCl3) δ 1.88
(m, 4 H), 2.65 (m, 2 H), 3.30-3.80 (m, 6 H), 5.02 (s, 2 H,
ArCH2), 6.18-8.11 (m, 14 H); 13C NMR (CDCl3) δ 24.06, 27.19,
29.38, 42.20, 43.75, 50.94, 108.44, 115.63, 122.50, 123.44,
125.31, 125.94, 126.56, 128.13, 129.38, 131.56, 134.75, 135.00,
138.75, 140.63, 148.44, 157.81, 181.56. Anal. (C26H29BrN6S)
C, H, N.
3-[3-(1H-Im id a zol-4-yl)p r op yl]-1-[4-[N-(5-br om op yr id -
2-yl)-N-(3,4-d ich lor oben zyl)a m in o]bu tyl]th iou r ea (42). A
suspension of 65 (0.50 g, 1.51 mmol) in THF (20 mL) was
treated dropwise with a solution of 35 (0.67 g, 1.51 mmol) in
THF (10 mL) under a nitrogen atmosphere. After stirring
overnight at room temperature, the solvent was removed under
reduced pressure to afford an oil. Flash chromatography on
silica gel using CH2Cl2/MeOH/Et3N (100:2.5:2.5) afforded 0.62
g (71%) of a colorless oil. The oil was suspended in a mixture
of 2 N HCl (50 mL) and EtOH (10 mL) and refluxed for 10 h.
The precipitated triphenylmethanol was filtered, and the
filtrate was evaporated. The residue was suspended in 2 N
NaOH (40 mL), and the aqueous phase was extracted with
CH2Cl2 (3 × 50 mL). The combined CH2Cl2 extracts were
washed with water (3 × 50 mL), dried (Na2SO4), filtered, and
evaporated to give 107 mg (18%) of a hygroscopic solid: mp
1
63-67 °C; H NMR (CDCl3) δ 1.50-2.00 (m, 6 H), 2.60 (m, 2
H), 3.45 (br m, 6 H), 4.63 (s, 2 H, ArCH2), 5.95-7.50 (m, 9 H),
8.13 (d, J ) 2.4 Hz, 1 H, pyridine H-6); 13C NMR (CDCl3) δ
23.51, 24.65, 28.88, 43.39, 44.37, 48.59, 50.87, 106.72, 107.37,
115.12, 126.23, 128.66, 130.56, 130.89, 132.62, 134.14, 138.20,
148.49, 156.29, 181.65. Anal. (C23H27BrCl2N6S) N; C: calcd,
48.43; found, 46.41. H: calcd, 4.78; found, 4.33.
3-[3-(1H-Im id a zol-4-yl)p r op yl]-1-[5-[N-(5-br om op yr id -
2-yl)-N-(3,4-d ich lor oben zyl)a m in o]p en tyl]th iou r ea (43).
A solution of 65 (1.02 g, 2.77 mmol) was dissolved in THF (20
mL) and treated dropwise with a solution of 36 (1.27 g, 2.77
mmol) in THF (40 mL) at 0-5 °C under a nitrogen atmosphere.
The reaction was allowed to warm to room temperature and
was stirred overnight. The mixture was treated with ad-
ditional amine 65 (0.182 g, 0.495 mmol) and was refluxed for
3-[3-(1H-Im id a zol-4-yl)p r op yl]-1-[2-[N-(5-n itr op yr id -2-
yl)-N-(3,4-d ich lor oben zyl)a m in o]eth yl]th iou r ea (40). A
suspension of 65 (959 mg, 2.61 mmol) in THF (20 mL) was
cooled to 0-5 °C in an ice-water bath and treated dropwise
with 31 (1.00 g, 2.61 mmol) in THF (40 mL). After stirring

Somatostatin Agonists with sst4 Selectivity
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4701
24 h. Removal of the solvent afforded an oil which was purified
by flash chromatography on silica gel using a solvent system
of EtOAc/MeOH/Et3N (92:4:4). Fractions homogeneous by
TLC were combined and evaporated to yield 2.20 g of a foam.
The trityl-protected thiourea was refluxed in 1 N HCl (50 mL)
for 1.5 h, and the precipitated triphenylmethanol was removed
by filtration. The filtrate was extracted with Et2O (2 × 100
mL), and the Et2O phase was washed with water (100 mL)
and evaporated under reduced pressure. The residue was
dissolved in EtOAc (300 mL), and the EtOAc phase was
washed with water (2 × 50 mL), dried (Na2SO4), filtered, and
evaporated. The resulting residue was flash chromatographed
on silica gel using EtOAc/MeOH/concentrated NH4OH (85:15:
1) as the solvent. Fractions homogeneous by TLC were
combined and evaporated to yield 500 mg (31%) of 43 as a solid
foam: 1H NMR (CDCl3) δ 1.15-2.00 (m, 8 H), 2.25 (m, 2 H),
3.45 (m, 6 H), 4.64 (s, 2 H, ArCH2), 6.25-8.13 (m, 10 H); 13C
NMR (CDCl3) δ 23.86, 24.43, 26.98, 29.04, 43.61, 44.64, 48.97,
50.98, 106.78, 107.48, 126.44, 128.88, 130.67, 134.35, 139.17,
139.93, 148.65, 156.51, 181.70. Anal. (C24H29BrCl2N6S) C, H,
N.
afforded 691 mg (41%) of 46: mp 122-124 °C; 1H NMR
(CDCl3) δ 1.63 (m, 4 H), 2.07 (m, 2 H), 3.55 (m, 6 H), 4.01 (t,
J ) 7.4 Hz, 2 H), 4.66 (s, 2 H, ArCH2), 6.36-8.18 (m, 13 H);
13C NMR (CDCl3) δ 25.02, 26.16, 30.16, 41.28, 44.09, 44.16,
48.05, 51.19, 106.02, 112.14, 119.23, 120.64, 128.50, 129.09,
131.64, 136.95, 137.49, 147.84, 157.97, 182.89. Anal. (C23H29
BrN6S) H, N; C: calcd, 54.48; found, 55.04.
-
3-[3-(Im idazol-1-yl)pr opyl]-1-[4-[N-(3,4-dich lor oben zyl)-
N-(p yr id -2-yl)a m in o]bu tyl]th iou r ea (47). A solution of 27
(900 mg, 2.79 mmol) in THF (20 mL) was treated dropwise
with 3-(imidazol-1-yl)propyl isothiocyanate (470 mg, 2.79
mmol) in THF (15 mL). After stirring overnight under
nitrogen, the solvent was removed under reduced pressure.
The resulting residue was flash chromatographed on silica gel
using a solvent system of CH2Cl2/MeOH/concentrated NH4OH
(100:10:1) to yield a yellow foam. The foam was triturated
with MeOH/water to yield a white solid. Recrystallization
from CH2Cl2/Et2O afforded 659 mg (48%) of 47 as a white,
1
crystalline solid: mp 112-113.5 °C; H NMR (CDCl3) δ 1.60
(m, 4 H), 2.08 (m, 2 H), 3.50 (m, 6 H), 4.00 (t, 2 H), 4.63 (s, 2
H, ArCH2), 7.20 (m, 12 H); 13C NMR (CDCl3) δ 24.97, 26.17,
30.61, 41.39, 44.10, 44.69, 48.22, 50.87, 106.02, 112.47, 126.23,
128.66, 129.21, 130.61, 137.71, 139.23, 147.95, 182.95. Anal.
(C23H28Cl2N6S) C, H, N.
3-[3-(Im id a zol-1-yl)p r op yl]-1-[3-[N-(5-b r om op yr id -2-
yl)-N-(3,4-d ich lor oben zyl)a m in o]p r op yl]th iou r ea (44). A
solution of 24 (1.00 g, 2.57 mmol) in THF (15 mL) was cooled
to 0-5 °C under a nitrogen atmosphere and treated dropwise
with 3-(imidazol-1-yl)propyl isothiocyanate (432 mg, 2.57
mmol) in THF (15 mL). The reaction mixture was allowed to
warm to room temperature and was stirred overnight. Re-
moval of the solvent under reduced pressure afforded a
semisolid. Trituration with Et2O/petroleum ether gave a solid
which was recrystallized from EtOAc/Et2O to yield 450 mg
(31%) of 44: mp 94-97 °C; 1H NMR (CDCl3) δ 1.60-2.35 (m,
4 H), 3.54 (m, 5 H), 4.05 (t, 2 H), 4.57 (s, 2 H, ArCH2), 6.28 (d,
J ) 9 Hz, 1 H), 6.99 (d, J ) 4.4 Hz, 1 H), 7.19 (m, 9 H); 13C
NMR (CDCl3) δ 27.03, 30.91, 41.01, 41.50, 44.59, 51.03, 107.05,
107.64, 119.18, 125.90, 128.39, 129.21, 130.78, 131.21, 132.89,
3-[3-(Im id a zol-1-yl)p r op yl]-1-[4-[N-(5-b r om op yr id -2-
yl)-N-(3,4-d ich lor oben zyl)a m in o]bu tyl]th iou r ea (48). A
solution of 28 (1.01 g, 2.48 mmol) in THF (20 mL) was treated
dropwise with 3-(imidazol-1-yl)propyl isothiocyanate (431 mg,
2.48 mmol) in THF (15 mmol). After stirring overnight at room
temperature under nitrogen, the solvent was removed under
reduced pressure. The resulting residue was triturated with
Et2O/hexane to afford a solid. Recrystallization from CH2Cl2/
Et2O gave 1.00 g (71%) of 48 as white crystals: mp 139-141
°C; 1H NMR (CDCl3) δ 1.61 (m, 4 H), 2.07 (m, 2 H), 3.50 (m, 6
H), 4.00 (t, 2 H), 4.62 (s, 2 H, ArCH2), 6.30 (d, J ) 9 Hz, 1 H,
pyridine H-3), 7.15 (m, 9 H), 8.12 (d, 1 H, pyridine H-6); 13C
NMR (CDCl3) δ 24.70, 26.33, 30.44, 41.28, 43.87, 44.64, 48.43,
50.97, 106.77, 107.32, 119.23, 126.17, 128.61, 130.62, 130.99,
136.89, 138.74, 139.77, 148.54, 182.94. Anal. (C23H27BrCl2N6S)
C, H, N.
3-[3-(1H-Im id a zol-4-yl)p h en yl]-1-[4-[N-(5-br om op yr id -
2-yl)-N-(3,4-d ich lor oben zyl)a m in o]bu tyl]th iou r ea (49). A
suspension of 4-(3-aminophenyl)-1H-imidazole dihydrochlo-
ride34 (521 mg, 2.25 mmol) and Et3N (455 mg, 4.49 mmol) in
THF (30 mL) was stirred under nitrogen for 2 h, and the
reaction mixture was treated dropwise with 35 (1.00 g, 2.25
mmol) in THF (15 mL). The reaction mixture was heated at
45 °C for 48 h and filtered, and the solvent was evaporated
under reduced pressure. The residue was flash chromato-
graphed on silica gel using CH2Cl2/MeOH/concentrated NH4-
OH (100:10:1) to give a solid. Recrystallization from Et2O/
hexane afforded 300 mg (22%) of 49: mp 140-160 °C; 1H
NMR (CDCl3) δ 1.49 (m, 4 H), 3.47 (m, 4 H), 4.51 (s, 2 H,
ArCH2), 6.22 (d, 1 H, pyridine H-3), 7.30 (m, 10 H), 8.00 (d, 1
H, pyridine H-6), 8.53 (br s, 1 H); 13C NMR (CDCl3) δ 24.43,
26.38, 44.85, 48.48, 50.92, 106.67, 107.32, 121.51, 123.41,
126.17, 126.61, 130.18, 130.56, 130.88, 132.56, 135.11, 135.97,
137.11, 138.79, 148.43, 156.18, 180.56. Anal. (C26H25BrCl2N6S)
C, H, N.
N-1-(5-Br om op yr id -2-yl)-N-1-(3,4-d ich lor oben zyl)-N-2-
[4-(1H-im id a zol-4-yl)p ip er id -1-yl]th ioxom eth yl]eth a n e-
1,2-d ia m in e (50). A suspension of 4-(piperidin-4-yl)-1H-
imidazoledihydrochloride35 (387mg,1.73mmol)and triethylamine
(350 mg, 3.50 mmol) in THF (30 mL) was stirred for 2 h at
room temperature under nitrogen and treated dropwise with
30 (662 mg, 1.73 mmol) in THF (15 mL). After the mixture
had stirred overnight, considerable starting material re-
mained. The reaction mixture was heated at 60 °C for 24 h,
cooled to room temperature, filtered, and evaporated to yield
an oil. Flash chromatography on silica gel using a solvent
system of EtOAc/MeOH/concentrated NH4OH (85:15:1) af-
forded 700 mg (71%) of 50 as a white foam: 1H NMR (CDCl3)
δ 1.58 (m, 2 H), 2.03 (m, 2 H), 2.89 (m, 1 H), 3.09 (m, 2 H),
3.85 (t, 4 H), 4.62 (d, 4 H), 6.32-8.11 (m, 15 H); 13C NMR
136.95, 137.98, 140.04, 148.33, 156.62, 182.62. Anal. (C22H25
BrCl2N6S) C, H, N.
-
3-[3-(Im id a zol-1-yl)p r op yl]-1-[3-[N-(4-br om oben zyl)-N-
(p yr id -2-yl)a m in o]p r op yl]th iou r ea Dih yd r obr om id e (45).
A solution of 23 (616 mg, 1.92 mmol) in THF (15 mL) was
treated dropwise with 3-(imidazol-1-yl)propyl isothiocyanate
(323 mg, 1.92 mmol) in THF (10 mL) under a nitrogen
atmosphere. The reaction mixture was stirred overnight at
room temperature, filtered, and evaporated under reduced
pressure to afford a yellow oil. The oil was dissolved in MeOH
and acidified with methanolic hydrogen bromide. Addition of
Et2O afforded a cloudy solution which produced a light-tan
solid upon standing in the refrigerator. The solid was filtered
and dried to yield 0.94 g (75%) of 45. Recrystallization from
absolute EtOH/Et2O afforded an analytical sample: mp 199-
201 °C; 1H NMR (DMSO-d6) δ 1.55-2.25 (m, 4 H, CH2), 3.20-
3.90 (m, 6 H, CH2), 4.26 (t, 2 H), 7.00 (t, 1 H), 7.26 (d, J ) 8.3
Hz, 2 H), 7.57 (d, J ) 8.3 Hz, 2 H), 7.86 (m, 9 H); 13C NMR
(CDCl3) δ 25.57, 29.09, 37.87, 39.98, 46.10, 47.40, 51.57, 111.76,
112.20, 121.78, 131.37, 134.73, 135.11, 137.44, 143.40, 151.27,
181.66. Anal. (C22H29Br3N6S) H, N; C: calcd, 40.69; found,
39.96.
3-[3-(Im id a zol-1-yl)p r op yl]-1-[4-[N-(4-br om oben zyl)-N-
(p yr id -2-yl)a m in o]b u t yl]t h iou r ea (46). A solution of 26
(1.11 g, 3.34 mmol) in THF (30 mL) was treated dropwise with
a solution of 3-(imidazol-1-yl)propyl isothiocyanate (559 mg,
3.34 mmol) in THF (10 mL). After stirring overnight at room
temperature under nitrogen, the solvent was removed under
reduced pressure to afford an oil. The oil was dissolved in
absolute EtOH and acidified with ethanolic hydrogen chloride.
Addition of Et2O afforded a very hygroscopic solid. The
solvents were removed under reduced pressure, and the
residue was partitioned between 10% NaOH (100 mL) and
CH2Cl2 (50 mL). The basic layer was extracted with CH2Cl2
(2 × 50 mL), and the combined organic extracts were washed
with water (2 × 50 mL), dried (Na2SO4), filtered, and evapo-
rated. The resulting oil was triturated with Et2O to yield 950
mg (57%) of a tan solid. Recrystallization from EtOAc/Et2O

4702 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Liu et al.
(CDCl3) δ 31.42, 34.78, 46.31, 47.67, 47.89, 51.46, 107.59,
134.67, 137.38, 140.47, 157.26, 180.99. Anal. (C23H25BrCl2N6S)
H, N; C: calcd, 48.61; found, 49.09.
123.63, 125.91, 128.40, 130.67, 131.11, 132.79, 136.96, 137.99,
139.99, 148.50, 148.93, 156.57, 159.06, 181.11. Anal. (C23H24
BrCl2N5S) C, H, N.
-
3-[(1H-Ben zim id a zol-2-yl)m eth yl]-1-[2-[N-(5-br om op y-
r id-2-yl)-N-(3,4-dich lor oben zyl)am in o]eth yl]th iou r ea (51).
A mixture of 2-(aminomethyl)benzimidazole dihydrochloride
hydrate (600 mg, 2.73 mmol), Et3N (552 mg, 5.46 mmol), and
30 (1.14 g, 2.73 mmol) in THF (45 mL) was stirred overnight
under nitrogen. The mixture was filtered, and the filtrate was
evaporated under reduced pressure. Flash chromatography
of the residue on silica gel using CH2Cl2/EtOH/NH4OH (100:
3-[3-[N-(P yr id-2-yl)am in o]pr opyl]-1-[3-[N-(4-br om oben -
zyl)-N-(p yr id -2-yl)a m in o]p r op yl]th iou r ea (56). A solution
of 16 (419 mg, 2.76 mmol) in THF (25 mL) was cooled to 0-5
°C under a nitrogen atmosphere and treated dropwise with
32 (1.00 g, 2.76 mmol) in THF (25 mL). After stirring
overnight at room temperature, the solvent was removed under
reduced pressure to afford an oil. The oil was flash chromato-
graphed on silica gel using a solvent system of CH2Cl2/MeOH/
Et3N (90:5:5) to yield 9 50-mL fractions. Fractions 3-9 were
combined and evaporated under reduced pressure to give 1.31
g (92%) of 56 as an oil: 1H NMR (CDCl3) δ 1.82-2.40 (m, 7
H), 3.58 (m, 5 H), 4.57 (s, 2 H, ArCH2), 4.75 (br m, NH), 6.35-
8.14 (m, 14 H); 13C NMR (CDCl3) δ 27.14, 29.53, 38.63, 41.17,
45.34, 51.30, 106.40, 108.29, 112.52, 112.85, 120.86, 128.18,
131.81, 136.68, 137.39, 137.77, 147.63, 158.73, 181.05; MS (CI,
CH4) m/z 513 (M+). Anal. (C24H29BrN6S) C, H, N.
3-[3-[N-(P yr id -2-yl)a m in o]p r op yl]-1-[3-[N-(3,4-d ich lo-
r ob e n zyl)-N -(5-b r om op yr id -2-yl)a m in o]p r op yl]t h io-
u r ea (57). A solution of 24 (352 mg, 2.32 mmol) in THF (30
mL) was cooled to 0-5 °C under nitrogen and treated dropwise
with 33 (1.00 g, 2.32 mmol) in THF (20 mL). After stirring
overnight at room temperature, the solvent was removed under
reduced pressure to afford an oil. Flash chromatography on
silica gel using a solvent system of CH2Cl2/MeOH/Et3N (98:
1:1) gave an oil which solidified upon trituration with hexane.
Recrystallization from EtOAc/hexane gave a hygroscopic
solid: mp 88 °C; 1H NMR (CDCl3) δ 0.90-2.10 (m, 4 H), 3.50
(m, 8 H), 4.57 (s, 2 H, ArCH2), 4.90 (br s, 1 H, NH), 6.30 (d, J
) 9.3 Hz, 1 H, pyridine H-3), 6.45-8.18 (m, 11 H); 13C NMR
(CDCl3) δ 27.09, 29.64, 38.63, 41.34, 41.45, 46.05, 51.14, 107.16,
107.65, 108.57, 112.90, 125.99, 128.51, 130.78, 131.21, 132.89,
137.55, 138.15, 140.10, 147.30, 148.50, 156.62, 158.79, 181.43;
MS (CI, CH4) m/z 583 (M+). Anal. (C24H27BrCl2N6S) C, H, N.
5:0.5) afforded 1.00 g (66%) of a solid foam. Anal. (C23H21
BrCl2N6S) H, N; C: calcd, 48.94; found, 48.27.
-
3-(1H-Ben zotr ia zol-5-yl)-1-[2-[N-(5-br om op yr id -2-yl)-N-
(3,4-d ich lor oben zyl)a m in o]eth yl]th iou r ea (52). A solu-
tion of 5-aminobenzotriazole (312 mg, 2.28 mmol) in THF (40
mL) was stirred under nitrogen and treated with a solution of
30 (950 mg, 2.28 mmol) in THF (25 mL). After the mixture
stirred overnight, a TLC [silica gel, EtOAc/MeOH/concentrated
NH4OH (9:1:0.5)] of the reaction mixture indicated that only
starting material was present. The mixture was refluxed for
48 h, cooled to room temperature, and evaporated under
reduced pressure to afford a brown foam. Trituration of the
foam with hexane afforded a solid which was recrystallized
from EtOAc/hexane to give 1.08 g (86%) of 52: mp 189.5-
1
191.5 °C; H NMR (DMSO-d6) δ 3.67 (m, 4 H), 4.78 (s, 2 H,
ArCH2), 6.78-8.06 (m, 11 H), 9.86 (s, 1 H, NdN-NH); 13C
NMR (DMSO-d6) δ 46.84, 50.01, 106.02, 108.08, 115.99, 122.92,
127.04,128.67, 129.21, 130.56, 131.00, 136.47, 139.94, 147.63,
156.24, 180.72. Anal. (C21H19BrCl2N7S) C, H, N.
3-[4-(P ip er id -1-yl)p h en yl]-1-[2-[N-(5-br om op yr id -2-yl)-
N-(3,4-d ich lor oben zyl)a m in o]eth yl]th iou r ea (53). A solu-
tion of N-(4-aminophenyl)piperidine (388 mg, 2.16 mmol) in
THF (40 mL) was stirred under nitrogen and treated dropwise
with 30 (0.90 g, 2.16 mmol) in THF (15 mL). The reaction
mixture was stirred at 40 °C for an additional 24 h. Evapora-
tion of the solvent afforded a dark-brown oil. Trituration with
hexane gave a solid which was recrystallized from Et2O/hexane
to yield 930 mg (73%) of a light-brown solid: mp 146-147.5
°C; 1H NMR (CDCl3) δ 1.66 (m, 6 H), 3.21 (m, 4 H), 3.80 (br s,
4 H), 4.85 (s, 2 H, ArCH2), 6.32 (d, 1 H, pyridine H-3), 7.30
(m, 11 H, ArH and NHCdSNH); 13C NMR (CDCl3) δ 24.16,
25.67, 45.07, 47.07, 49.84, 51.30, 107.59, 116.52, 125.73,
127.36, 128.23, 130.83, 137.60, 140.04, 148.11, 151.36, 156.56,
181.37. Anal. (C26H28BrClN5S) C, H, N.
3-(3-P h en ylp r op yl)-1-[4-[N-(4-br om oben zyl)-N-(p yr id -
2-yl)a m in o]bu tyl]th iou r ea (58). A solution of 26 (1.00 g,
2.99 mmol) in THF (25 mL) was treated dropwise with
3-phenylpropyl isothiocyanate (530 mg, 2.99 mmol) in THF
(10 mL). After stirring overnight under nitrogen at room
temperature, the solvent was evaporated under reduced pres-
sure to afford an oil. Flash chromatography using a mobile
phase of CH2Cl2/MeOH/Et3N (95:2.5:2.5) afforded 817 mg
(55%) of 58 as a light-yellow oil. Upon standing, a tan solid
1
formed: mp 105-108 °C; H NMR (CDCl3) δ 1.72 (m, 6 H),
3-[4-(P ip er id in -1-yl)p h en yl]-1-[3-[N-(5-b r om op yr id -2-
yl)-N-(3,4-d ich lor oben zyl)a m in o]p r op yl]th iou r ea (54). A
solution of N-(4-aminophenyl)piperidine (0.78 g, 4.40 mmol)
in THF (50 mL) was stirred under nitrogen and treated
dropwise with 33 (1.90 g, 4.40 mmol) in THF (20 mL). After
stirring overnight at room temperature, the solvent was
removed under reduced pressure to afford an oil. Trituration
of the oil with EtOAc/hexane gave a dark-brown solid which
was recrystallized from EtOAc/hexane to give 1.74 g (65%) of
54. An analytical sample was obtained by a second recrys-
tallization from EtOAc/hexane to give a tan solid: mp 125-
2.67 (m, 2 H), 3.50 (m, 6 H), 4.63 (s, 2 H, ArCH2), 7.22 (m, 15
H); 13C NMR (CDCl3) δ 25.03, 25.78, 30.50, 33.21, 43.88, 44.15,
47.94, 51.35, 106.07, 112.25, 120.70, 126.17, 128.34, 128.44,
131.64, 137.55, 141.07, 147.84, 158.02, 181.75. Anal. (C26H31
BrN4S) C, H, N.
-
3-(3-Am in op r op yl)-1-[3-[N-(5-br om op yr id -2-yl)-N-(3,4-
d ich lor oben zyl)a m in o]eth yl]th iou r ea (59). A suspension
of N-(3-aminopropyl)phthalimide hydrochloride36 (1.11 g, 4.6
mmol) and Et3N (1.2 g, 12 mmol) in THF (50 mL) was stirred
under nitrogen for 3 h. The reaction mixture was treated
dropwise with the isothiocyanate 30 (1.92 g, 4.6 mmol), stirred
overnight at room temperature, filtered, and evaporated under
reduced pressure. The resulting mixture was purified by flash
chromatography on silica gel using EtOAc/hexane/Et3N (60:
40:1) to yield 2.44 g (85%) of the phthalimide. A portion of
this compound (1.92 g, 3.09 mmol) and hydrazine hydrate (1.24
g, 25.4 mmol) in absolute EtOH (100 mL) were refluxed for 8
h, cooled, and filtered. The residue was dissolved in EtOAc
(60 mL) and washed with water (10 mL). The organic layer
was dried (Na2SO4), filtered, and evaporated. The resulting
oil was purified by flash chromatography on silica gel using
EtOAc/MeOH/concentrated NH4OH (50:50:1) to yield 1.06 g
(70%) of a solid foam: 1H NMR (CDCl3) δ 1.85 (m, 6 H), 2.17
(s, 2 H, NH2), 3.50 (m, 6 H), 4.65 (s, 2 H, ArCH2), 7.03 (d, J )
6 Hz, 1 H), 7.33 (m, 6 H), 8.15 (d, J ) 2.2 Hz, 1 H, pyridine
H-6). Anal. (C18H22BrCl2N5S) C, H, N.
1
127 °C; H NMR (CDCl3) δ 1.69 (m, 8 H), 3.22 (m, 4 H), 3.63
(m, 4 H), 4.49 (s, 2 H, ArCH2), 6.15 (d, J ) 9 Hz, 1 H, pyridine
H-3), 6.90-7.56 (m, 11 H). Anal. (C27H30BrCl2N5S) C, H, N.
3-[2-(P yr id -2-yl)et h yl]-1-[3-[N-(5-b r om op yr id -2-yl)-N-
(3,4-d ich lor oben zyl)a m in o]p r op yl]th iou r ea (55). A solu-
tion of 2-(2-aminoethyl)pyridine (0.33 g, 2.71) in THF (50 mL)
was cooled to 0-5 °C under a nitrogen atmosphere and treated
with a solution of 33 (1.17 g, 2.71 mmol) in THF (25 mL). The
reaction mixture was allowed to warm to room temperature
and was stirred overnight. Removal of the solvent under
reduced pressure afforded an oil which was purified by flash
chromatography on silica gel using EtOAc/MeOH/concentrated
NH4OH (96:4:1) as the solvent system. Fractions homoge-
neous by TLC were combined and evaporated to yield 1.11 g
(74%) of a foam: 1H NMR (CDCl3) δ 1.78 (m, 2 H), 3.00 (t, 2
H), 3.69 (m, 6 H), 4.59 (s, 2 H, ArCH2), 6.30 (d, J ) 9 Hz, 1 H,
pyridine H-3), 6.88-8.49 (m, 11 H); 13C NMR (CDCl3) δ 26.82,
36.30, 41.34, 43.34, 45.89, 50.93, 107.05, 107.59, 121.84,
3-[3-(Dim eth yla m in o)p r op yl]-1-[2-[N-(5-br om op yr id -2-
yl)-N-(3,4-d ich lor oben zyl)a m in o]eth yl]th iou r ea (60). A

Somatostatin Agonists with sst4 Selectivity
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4703
solution of 21 (1.00 g, 2.67 mmol) in THF (25 mL) was cooled
to 0-5 °C under a nitrogen atmosphere and treated dropwise
with a solution of 3-(dimethylamino)propyl isothiocyanate (385
mg, 2.67 mmol) in THF (15 mL). After stirring overnight at
room temperature, the solvent was removed under reduced
pressure to afford an oil. Flash chromatography on silica gel
using a solvent system of EtOAc/MeOH/concentrated NH4OH
(85:15:1) gave 900 mg (65%) of 60 as a white foam: 1H NMR
(CDCl3) δ 1.70 (m, 2 H), 1.95-2.45 (m, including s at 2.23
N(CH3)2, 8 H), 2.50-3.95 (m, 6 H), 4.68 (s, 2 H, ArCH2), 6.47
(d, J ) 9 Hz, 1 H), 7.20 (m, 6 H), 7.55 (d, J ) 2.2 Hz, 1 H),
8.18 (d, J ) 2.5 Hz, 1 H); 13C NMR (CDCl3) δ 26.32, 43.11,
44.85, 47.67, 51.52, 57.28, 107.97, 126.06, 128.55, 130.77,
131.26, 132.89, 138.09, 140.15, 148.33, 156.72, 182.46. Anal.
(C20H26BrClN5S) C, H, N.
125.90, 128.39, 130.78, 137.87, 140.15, 148.28, 156.78, 181.11.
Anal. (C20
H26BrCl2N5S) C, H; N: calcd, 13.49; found, 12.90.
3-(4-Am in obu tyl)-1-[3-[N-(5-br om opyr id-2-yl)-N-(n aph th -
1-ylm eth yl)a m in o]p r op yl]th iou r ea (64). A solution of
N-(4-aminobutyl)phthalimide hydrochloride (688 mg, 2.7 mmol)
and Et3N (547 mg, 5.4 mmol) in THF (25 mL) was stirred for
2 h at room temperature. The reaction mixture was treated
dropwise with a solution of 34 (1.11 g, 2.7 mmol) in THF (20
mL), and the mixture was stirred overnight under nitrogen.
The precipitated Et3N‚HCl was filtered, and the filtrate was
evaporated under reduced pressure to afford an oil. Purifica-
tion by flash chromatography on silica gel using a solvent
system of CH2Cl2/MeOH/concentrated NH4OH (100:2:1) gave
1.08 g of a yellow foam. The foam was suspended in a mixture
of EtOH (20 mL) and 85% hydrazine hydrate (641 mg, 12.7
mmol), and the mixture was refluxed for 5 h. The mixture
was filtered to remove the precipitated phthalhydrazide, and
the solvent was removed under reduced pressure to yield an
oily residue. The oil was dissolved in CH2Cl2 (75 mL), washed
with water (3 × 50 mL), separated, dried (Na2SO4), filtered,
and evaporated to yield 700 mg of the amine as a light-yellow
foam. Flash chromatography on silica gel using EtOAc/MeOH/
concentrated NH4OH (50:50:1) as the solvent yielded 650 mg
(48%) of 64 as a white foam: 1H NMR (CDCl3) δ 1.70 (m, 10
H), 2.79 (m, 2 H), 3.70 (m, 6 H), 5.06 (s, 2 H, ArCH2), 6.29 (d,
J ) 9 Hz, 1 H), 6.70-8.20 (m, 11 H); 13C NMR (CDCl3) δ 26.32,
27.18, 30.27, 41.43, 41.59, 43.71, 45.39, 49.83, 106.66, 108.34,
122.37, 123.07, 125.45, 126.00, 126.43, 127.95, 129.03, 130.82,
3-[3-(P yr r olid in -1-yl)p r op yl]-1-[2-[N-(5-br om op yr id -2-
yl)-N-(3,4-d ich lor oben zyl)a m in o]eth yl]th iou r ea (61). A
solution of N-(3-aminopropyl)pyrrolidine (354 mg, 2.76 mmol)
in THF (50 mL) was cooled to 0-5 °C in an ice-water bath
under a nitrogen atmosphere and treated with 30 (1.19 g, 2.76
mmol) in THF (25 mL). The reaction mixture was allowed to
warm to room temperature and was stirred overnight. Re-
moval of the solvent under reduced pressure afforded an oil
which solidified upon trituration with hexane/EtOAc. Recrys-
tallization from EtOAc/hexane afforded 1.03 g (66%) of 61 as
a white solid: mp 123-125 °C; 1H NMR (CDCl3) δ 1.77 (m, 6
H), 2.45 (m, 6 H), 3.50 (m, 6 H), 4.68 (s, 2 H, ArH), 6.50 (d, 1
H), 7.00-7.55 (m, 6 H), 8.16 (d, J ) 2.2 Hz, 1 H); 13C NMR
(CDCl3) δ 23.62, 28.17, 43.07, 47.89, 51.74, 107.59, 108.08,
126.33, 128.83, 130.94, 138.47, 140.26, 148.55, 156.84, 183.0.
Anal. (C22H28BrCl2N5S) C, H, N.
131.03, 133.86, 140.08, 147.99, 157.47, 181.03. Anal. (C24H30
-
BrN5S) H; C: calcd, 57.59; found, 56.80. N: calcd, 14.00;
found, 13.58.
3-[3-(1H-Im id a zol-4-yl)p r op yl]-1-[2-[N-(5-br om op yr id -
2-yl)-N-(3,4-d ich lor oben zyl)a m in o]eth yl]u r ea (66). The
amine 21 (1.5 g, 4.0 mmol) in THF (50 mL) was cooled to 0 °C
in an ice bath. Triphosgene (392 mg, 1.3 mmol) was added in
one portion and stirred for 5 min. A solution of Et3N (1.22 g,
12.0 mmol) in THF (5 mL) was added dropwise, and a white
precipitate formed upon stirring. The mixture was allowed
to warm to 17 °C over 15 min and cooled to 0 °C. The reaction
mixture was treated dropwise with a suspension of 65 (915
mg, 2.8 mmol) in THF (20 mL) over 5 min. After stirring
overnight at room temperature under a nitrogen atmosphere,
the solvent was removed under reduced pressure to yield a
yellow foam. The intermediate trityl-protected urea was
suspended in 1 N HCl (35 mL) and refluxed for 1.5 h. The
solution was filtered, extracted with Et2O (2 × 200 mL),
basified with 6 N NaOH, and extracted with EtOAc (3 × 100
mL). The combined EtOAc extracts were washed with water
(3 × 100 mL), dried (Na2SO4), and evaporated under vacuum
to yield a foam. Flash chromatography on silica gel using a
solvent system of CH2Cl2/MeOH/concentrated NH4OH (90:10:
1) yielded 300 mg of 66 as a yellow foam which was recrystal-
lized from CHCl3/hexane to afford 200 mg (10%) of an
analytical sample: mp 143-146 °C; 1H NMR δ 1.60 (m, 2 H),
2.50 (m, 2 H), 3.15 (m, 4 H), 3.49 (d, 2 H), 4.75 (s, 2 H, ArCH2),
6.04-7.78 (m, 10 H), 8.12 (d, J ) 2.4 Hz, 1 H, pyridine H-6);
1C NMR (CDCl3) δ 23.84, 30.12, 38.19, 39.93, 48.60, 50.27,
106.07, 108.19, 116.90, 127.25, 128.94, 129.50, 130.72, 131.16,
134.90, 136.00, 139.77, 140.37, 147.90, 156.51, 158.41. Anal.
(C21H23BrCl2N6O) C, H, N.
Biologica l Assa y. Cell Lin es Exp r essin g sst Recep tor
Su btyp es. BHK cells (tk-ts13, ATCC CRL# 1573) were grown
to 20-40% confluency in a tissue dish in DMEM containing
1% penicillin/streptomycin, 10% fetal bovine serum, and 1%
Glutamax. Prior to transfection, the cells were washed twice
with calcium-free PBS after which 20 mL of serum-free DMEM
was added to the cells.
Transfection was carried out as described previously (prod-
uct description: Lipofectamin, Gibco BRL catalog no. 18324-
012). Briefly, 10 µg of cDNA encoding an sst receptor subtype
inserted into the mammalian vector pcDNA3 (Invitrogen) was
diluted with 300 µL of sterile water. Lipofectamin (30 µg) was
diluted in 300 µL of sterile water, and the cDNA and lipo-
fectamin/cDNA mixture was added dropwise to the cells (HEK
3-[3-(P yr r olid in -1-yl)p r op yl]-1-[3-[N-(5-br om op yr id -2-
yl)-N-(3,4-d ich lor oben zyl)a m in o]p r op yl]th iou r ea (62). A
solution of N-(3-aminopropyl)pyrrolidine (354 mg, 2.76 mmol)
in THF (50 mL) was cooled to 0-5 °C under a nitrogen
atmosphere and treated dropwise with a solution of 33 (1.19
g, 2.76 mmol) in THF (25 mL). The reaction mixture was
allowed to warm to room temperature and was stirred over-
night. The solvent was removed under reduced pressure to
afford an oil which solidified upon trituration with EtOAc/
hexane. Recrystallization from EtOAc/hexane gave 1.03 g
(66%) of 62 as a white solid: mp 122-124 °C; 1H NMR (CDCl3)
δ 1.73 (m, 8 H), 2.57 (m, 6 H), 3.60 (m, 6 H), 4.63 (s, 2 H,
ArCH2), 6.33 (d, J ) 9 Hz, 1 H, pyridine H-3), 7.00-7.53 (m,
6 H), 8.18 (d, J ) 2.4 Hz, 1 H, pyridine H-6); 13C NMR (CDCl3)
δ 23.46, 27.14, 41.99, 46.16, 51.09, 53.36, 53.69, 107.05, 107.48,
126.12, 128.61, 130.72, 132.72, 132.84, 138.31, 139.99, 148.55,
156.51, 182.13. Anal. (C23H30BrCl2N5S) C, H, N.
3-(4-Am in ob u t yl)-1-[3-[N-(5-b r om op yr id -2-yl)-N-(3,4-
d ich lor oben zyl)a m in o]p r op yl]th iou r ea (63). A suspen-
sion of N-(4-aminobutyl)phthalimide hydrochloride37 (1.50 g,
5.89 mmol) and Et3N (1.49 g, 14.7 mmol) was stirred under
nitrogen for 3 h at room temperature, and a solution of 33
(2.54 g, 5.89 mmol) in THF (50 mL) was added dropwise. After
stirring overnight, the precipitate was filtered, and the filtrate
was evaporated under reduced pressure to yield an oil. Flash
chromatography on silica gel using CH2Cl2/MeOH/concen-
trated NH4OH (100:1:1.5) as the solvent afforded 2.06 g of the
intermediate phthalimide as an oil. The oil was dissolved in
a mixture of 85% hydrazine hydrate (635 mg, 12.7 mmol) and
absolute EtOH (75 mL) and refluxed for 8 h. The reaction
mixture was cooled, filtered, and evaporated to yield an oil.
Absolute EtOH (25 mL) was added, and the solution was
concentrated under reduced pressure. The resulting residue
was partitioned between Et2O (200 mL) and water (50 mL),
and the Et2O phase was separated, dried (Na2SO4), filtered,
and evaporated under reduced pressure. Flash chromatogra-
phy on silica gel using EtOAc/MeOH/concentrated NH4OH (50:
50:1.2) afforded 1.15 g (70%) of 63 as a colorless oil: 1H NMR
(CDCl3) δ 1.66 (m, 6 H), 2.80 (t, 2 H), 3.59 (m, 6 H), 4.62 (s, 2
H, ArCH2), 6.35 (d, J ) 9 Hz, 1 H, pyridine H-3), 6.99-7.56
(m, 6 H), 8.18 (d, J ) 2.4 Hz, 1 H, pyridine H-6); 13C NMR
(CDCl3) δ 26.33, 27.09, 30.28, 41.44, 41.61, 43.83, 50.98, 107.75,

4704 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Liu et al.
(13) Rivier, J .; Rivier, C.; Koerber, S. C.; Kornreich, W. D.; deMir-
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293 cells for sst2 and BHK cells for sst4) while the plates were
gently swirled. The cells were then incubated for 16-24 h,
after which the medium was replaced with standard medium
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Bin d in g Assa y. Cells expressing individual sst receptor
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centrifugation. Final membrane pellets were resuspended at
a protein concentration of 125 µg/mL in buffer. Binding assays
using 75 pM [125I]Tyr-SRIF (Amersham, IM-161) were done
in duplicates in minisorb polypropylene tubes in a volume of
250 µL. The assays were incubated at 30-37 °C for 30-90
min depending on the receptor subtype. Binding was termi-
nated by filtration through Whatman GF/B glass fiber filters
presoaked for 4 h in 0.5% poly(ethylenimine) and 0.1% BSA.
Filters were washed three times with 5 mL of ice-cold 0.9%
saline and counted in a Packard Cobra II gamma counter.
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F u n ction a l Assa y. Baby hamster kidney (BHK) cells
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a â-D-
Glucose Scaffolding. A Partial Somatostatin Agonist Bearing a
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Ack n ow led gm en t. The financial support of Novo
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