Human beta3 adrenergic receptor agonists containing cyanoguanidine and nitroethylenediamine moieties.

Article abstract of DOI:10.1016/S0960-894X(00)00669-7

Pyridineethanolamine derivatives containing cyanoguanidine or nitroethylenediamine moieties were examined as human beta3 adrenergic receptor (AR) agonists. Notably, indoline derivatives 6a and 11 were potent beta3 AR agonists (beta3 EC50 = 13 and 19 nM, respectively), which showed good selectivity over binding to and minimal activation of the beta1 and beta2 ARs.

Full text of DOI:10.1016/S0960-894X(00)00669-7

Bioorganic & Medicinal Chemistry Letters 11 (2001) 379±382
Human ꢀ3 Adrenergic Receptor Agonists Containing
Cyanoguanidine and Nitroethylenediamine Moieties
Linda L. Brockunier, Mari R. Candelore, Margaret A. Cascieri, Yong Liu, Laurie Tota,
Matthew J. Wyvratt, Michael H. Fisher, Ann E. Weber and Emma R. Parmee*
Departments of Medicinal Chemistry, Biochemistry and Physiology, Merck Research Laboratories, Rahway, NJ 07065, USA
Received 7 September 2000; accepted 21 November 2000
AbstractÐPyridineethanolamine derivatives containing cyanoguanidine or nitroethylenediamine moieties were examined as human
b3 adrenergic receptor (AR) agonists. Notably, indoline derivatives 6a and 11 were potent b3 AR agonists (b3 EC50=13 and 19 nM,
respectively), which showed good selectivity over binding to and minimal activation of the b1 and b2 ARs. # 2001 Elsevier Science
Ltd. All rights reserved.
Elevation of metabolic rate by activation of the human
b3 adrenergic receptor (AR) may be an e€ective
approach toward the treatment of obesity.1 Heretofore,
our e€orts have largely focused on the preparation of
analogues containing a benzenesulfonamide functionality,
exempli®ed by indoline 1 (Fig. 1).2 This compound is a
potent b3 AR agonist (EC50=0.93 nM), which shows
>1000-fold selectivity over binding to the b1 and b2
ARs. This excellent in vitro pro®le is due in part to the
presence of the benzenesulfonamide moiety.
indolines related to analogues 1 and 2. Both the 4-octyl
thiazole and a 4-(4-tri¯uoromethoxy)phenyl thiazole
indoline were included. Three positions of attachment
of the cyanoguanidine to the indoline ring were also
investigated. This work resulted in the discovery of a
novel series of potent, selective human b3 AR agonists
containing a cyanoguanidine moiety. Preliminary data
of simple nitroethylenediamine analogues will also be
reported.5
Cyanoguanidines 3±6 and nitroethylenediamines 7 were
prepared from aniline 86 by reaction with either diphenyl
cyanocarbonimidate in acetonitrile or 1,1-bis(methyl-
thio)-2-nitroethylene in isopropanol (Scheme 1).7 This
was followed by displacement with the amine and
deprotection to yield the desired compounds 3±7. The
requisite indoline derived amines 9 were prepared from
the corresponding nitroindoline8 by reaction with
potassium thiocyanate to yield thiourea 10. Condensa-
tion with a chloroketone and reduction with stannous
chloride yielded anilines 9.
While examining potential replacements of the benzene-
sulfonamide in an attempt to improve the overall in
vivo properties of these compounds, we investigated a
series of thiourea derivatives. Interestingly, the compounds
were potent agonists of the b3 AR (data not shown).
Indoline 2, for example, showed only a 6-fold loss in
potency at the b3 AR compared to sulfonamide 1 and
was somewhat selective over binding to the b1 and b2
ARs (20- and 50-fold, respectively).3
The thiourea moiety is prone to in vivo metabolism that
can result in signi®cant toxicity.4 We decided, therefore, to
focus our investigation on the bioisosteric cyanoguanidine
and nitroethylenediamine moieties. Herein we would
like to report the results of this study that not only
included the preparation of simple aryl cyanoguani-
dines, but was extended to more fully explore a series of
Cyanoguanidines 3 were tested at the human b ARs
and the results are shown in Table 1. The compounds
3a±h were partial agonists of the b3 AR and were gen-
erally only moderately potent (b3 EC50=26±150 nM).
Comparison of iodo derivatives 3a and 3b showed a
slight preference for meta substitution. The selectivity
for the b3 AR, however, was generally very low. Only
the 1-naphthyl derivative 3h showed >10-fold selectivity
over binding to both the b1 and b2 ARs. Agonist activity
at the b1 and b2 ARs was not measured.
*Corresponding author. Tel.: +1-732-594-6626; fax: +1-732-594-7877;
e-mail: emma_parmee@merck.com
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00669-7

380
L. L. Brockunier et al. / Bioorg. Med. Chem. Lett. 11 (2001) 379±382
Table 1. Activity of cyanoguanidines 3 at the cloned human b adre-
nergic receptors
Compd
Ar
b3 EC50 nM
b1 binding
IC50 nM
b2 binding
IC50 nM
b
b
(%act)a
3a
3b
3c
3d
3e
3f
4-I-Ph
3-I-Ph
3,5-DichloroPh
3-F-Ph
3-CONH2Ph
3-PhOPh
2-Naphthyl
1-Naphthyl
100 (38)
59 (51)
89 (72)
100 (69)
150 (76)
26 (70)
130 (41)
42 (64)
730
230
290
590
980
240
740
480
170
67
140
200
400
40
3g
3h
50
570
aAdenylyl cyclase activation given as % of the maximal stimulation
with isoproterenol.
bReceptor binding assays were carried out with membranes prepared
from CHO cells expressing the cloned human receptor in the presence
of 125I-iodocyanopindolol.
Figure 1.
b2 ARs. The 4-tri¯uoromethoxyphenyl compound 6b was
slightly less potent but displayed improved selectivity over
binding to the b1 and b2 ARs (>140- and >175-fold,
respectively).
In an e€ort to improve the in vitro pro®le of the cyano-
guanidine b3 AR agonists, we investigated indoline
derivatives 4±6 (Table 2). The in vitro results showed
that activity and selectivity of these compounds were
highly dependent on the position of the cyanoguanidine
moiety on the indoline ring. The 5-substituted com-
pounds 4, which had traditionally been preferred in the
sulfonamide series,9 were potent human b3 AR agonists
(b3 EC50=11 and 13 nM). Both these derivatives, how-
ever, lacked any selectivity over binding to the b1 and b2
ARs. Additionally, compound 4b was a full agonist of
the b1 AR. Substitution at the 6-position was not pre-
ferred, as octyl derivative 5a showed a 5-fold loss in
potency when compared to its isomer 4a, and the aryl
analogue 5b did not activate the b3 AR at 1 mM.
An impressive improvement in selectivity could also be
achieved in the 5-substituted series by modi®cation of
the central portion of the molecule. Replacement of the
phenyl ring with a naphthyl group had been explored in
the benzenesulfonamide series but yielded less potent b3
AR agonists.10 This modi®cation was incorporated into
cyanoguanidine 4b to give compound 11 (Fig. 2, Table
2), and in this case there was no signi®cant loss in
potency at the b3 AR (EC50=19 nM). Naphthalene 11
did not activate the b1 and b2 ARs to any extent at 10
mM. This was a major improvement over phenyl deri-
vative 4b, which had signi®cant agonist activity at the b1
AR. Selectivity over binding to the b1 and b2 ARs also
increased dramatically from 5- and 13-fold, respectively,
for compound 4b, to 120- and 350-fold, respectively, for
the naphthyl analogue.
The 4-substituted indolines 6 proved to have a much
more interesting overall in vitro pro®le. These com-
pounds were partial agonists of the b3 AR (62 and 72%
of the maximal response of isoproterenol), with only
minimal activation of the b1 or b2 AR at 10 mM. Octyl
analogue 6a was a 13 nM b3 AR agonist which exhib-
ited >70-fold selectivity over binding to both the b1 and
Simple aryl analogues were also prepared in the nitro-
ethylenediamine series 7 and the initial results were very
promising (Table 3). Unlike cyanoguanidines 3, these
Scheme 1. (a) NCNˆC(OC6H5)2, CH3CN, 81 ꢀC; (b) ArNH2 or 9, 2-PrOH, 100 ꢀC, sealed tube; (c) HCl(g)/Et2O; (d) O2NCHˆC(SCH3)2, 2-PrOH,
95 ꢀC, sealed tube; (e) TFA, CH2Cl2; (f) RCOCH2Cl, EtOH, 78 ꢀC; (g) SnCl2, EtOH, 70 ꢀC.

L. L. Brockunier et al. / Bioorg. Med. Chem. Lett. 11 (2001) 379±382
381
Table 2. Activity of indoline derived cyanoguanidines 4±6 and 11 at the cloned human b adrenergic receptors
Compd
Position of subn
on indoline ring
R
b3 EC50 nM
b1 EC50 nM
b1 binding
b2 EC50 nM
b2 binding
IC50 nM
b
(% act)a
(% act)a
IC50b nM
(% act)a
4a
4b
5a
5b
6a
6b
11
5
5
6
6
4
4
5
n-Oct
4-CF3OPh
n-Oct
4-CF3OPh
n-Oct
11 (39)
13 (82)
59 (38)
(11@1000)
13 (62)
57 (72)
ndc
41 (73)
16
65
74
620
1200
8400
2300
ndc
(51@10,000)
ndc
(20@10,000)
(25@10,000)
(20@10,000)
(11@10,000)
50
180
66
710
ndc
(27@10,000)
(11@10,000)
(6@10,000)
(2@10,000)
930
>10,000
7100
4-CF3OPh
4-CF3OPh
19 (62)
aAdenylyl cyclase activation given as % of the maximal stimulation with isoproterenol. Single point data are reported in parentheses as (% activa-
tion@concentration in nM).
bReceptor binding assays were carried out with membranes prepared from CHO cells expressing the cloned human receptor in the presence of 125I-
iodocyanopindolol.
cnd, not determined.
AR agonists. In particular, the 4-substituted indolines 6
exhibit very little activation of the b1 and b2 ARs and
>70-fold selectivity for the b3 AR over binding to the b1
and b2 ARs. Replacement of the central phenyl ring
with a naphthyl group gave compound 11, which shows a
greatly improved in vitro pro®le over its phenyl analogue
4b. Finally, preliminary data has shown that a series of
simple nitroethylenediamines 7 are potent, full agonists
of the b1 AR, which exhibit up to 100-fold selectivity
Figure 2.
over binding to the b1 and b2 ARs. Both these series repre-
sent an important development in the discovery of non-
sulfonamide pyridineethanolamine human b3 AR agonists.
Table 3. Activity of nitroethylenediamines 7 at the cloned human b
adrenergic receptors
Acknowledgements
Compd
Ar
b3 EC nM
b1 binding
b2 binding
IC50 nM
(% act)a
IC50b nM
b
The authors thank Professor James G. Grannemann
(Wayne State University) for supplying the cloned human
b3 AR.
7a
7b
7c
7d
7e
7f
3-I-Ph
3,5-DichloroPh
3-F-Ph
3-CONH2Ph
3-PhOPh
22 (97)
35 (85)
1100
3800
3000
790
830
820
1200
5600
2400
1200
220
300 (79)
10 (101)
120 (93)
180 (74)
140 (79)
2-Naphthyl
1-Naphthyl
3400
370
References and Notes
7g
1800
aAdenylyl cyclase activation given as % of the maximal stimulation
with isoproterenol.
bReceptor binding assays were carried out with membranes prepared
from CHO cells expressing the cloned human receptor in the presence
of 125I-iodocyanopindolol.
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the maximal response of isoproterenol) and those com-
pounds tested had minimal agonist activity at the b1 and
b2 ARs (e.g., 7a and 7b caused only 11±21% of the
maximal response of isopretorenol, data not shown).
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potency at the b3 AR and a much greater degree of
selectivity over the b1 and b2 ARs than had been seen
with the analogous cyanoguanidines (cf Table 1). For
example, carboxamide 7d and 3,5-dichlorophenyl deri-
vative 7b were >70- and >100-fold selective for the b3
AR, respectively.
In this paper we have described a novel series of b3 AR
agonists in which the sulfonamide moiety has been
replaced with a cyanoguanidine. SAR studies high-
lighted the di€erent structural preferences in this series
which resulted in the discovery of potent, selective b3

382
L. L. Brockunier et al. / Bioorg. Med. Chem. Lett. 11 (2001) 379±382
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