Tetrahydroisoquinoline derivatives containing a benzenesulfonamide moiety as potent, selective human β3 adrenergic receptor agonists

Article abstract of DOI:10.1016/S0960-894X(00)00459-5

Tetrahydroisoquinoline derivatives containing a 4-(hexylureido)benzenesulfonamide were examined as human β₃ adrenergic receptor (AR) agonists. Notably, 4,4-biphenyl derivative 9 was a 6 nM full agonist of the β₃ AR. Naphthyloxy compound 18 (β₃ EC₅₀ = 78 nM) did not activate the β₁ and β₂ ARs at 10 μM, and showed >1000-fold selectivity over binding to the β₁ and β₂ ARs. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0960-894X(00)00459-5

Bioorganic & Medicinal Chemistry Letters 10 (2000) 2283±2286
Tetrahydroisoquinoline Derivatives Containing a
Benzenesulfonamide Moiety as Potent, Selective Human ꢀ3
Adrenergic Receptor Agonists
Emma R. Parmee,* Linda L. Brockunier, Jiafang He, Suresh B. Singh,
Mari R. Candelore, Margaret A. Cascieri, Liping Deng, Yong Liu, Laurie Tota,
Matthew J. Wyvratt, Michael H. Fisher and Ann E. Weber
Departments of Medicinal Chemistry, Molecular Systems, and Biochemistry and Molecular Pharmacology,
Merck Research Laboratories, Rahway, NJ 07065, USA
Received 21 June 2000; accepted 1 August 2000
AbstractÐTetrahydroisoquinoline derivatives containing a 4-(hexylureido)benzenesulfonamide were examined as human b3 adre-
nergic receptor (AR) agonists. Notably, 4,4-biphenyl derivative 9 was a 6 nM full agonist of the b3 AR. Naphthyloxy compound 18
(b3 EC50=78 nM) did not activate the b1 and b2 ARs at 10 mM, and showed >1000-fold selectivity over binding to the b1 and b2
ARs. # 2000 Elsevier Science Ltd. All rights reserved.
In recent years, elevation of metabolic rate by activation
of the human b3 adrenergic receptor (AR) has attracted
much attention as a potential approach toward the
treatment of obesity.1 Selectivity over both binding to
and activation of b1 and b2 ARs has always been an
important issue in developing b3 AR agonists free of the
side e€ects seen with early drug candidates.2 Design of
potent, selective human b3 AR agonists has traditionally
focused on compounds with an aryloxypropanolamine
or arylethanolamine pharmacophore. These two groups
are exempli®ed by phenoxypropanolamine 1 and pyr-
idineethanolamine 2, which have been recently reported
from our laboratories (Fig. 1).3,4 Both of these derivatives
are very potent b3 AR agonists (b3 EC50=0.43 and
6.3 nM, respectively), which show excellent selectivity
over binding to the b1 and b2 ARs (>440- and >1400-
fold, respectively).
an e€ort to improve the selectivity of TMQ.7 This led to
the discovery of aminothiazole 4, which in our assays
was a weak partial agonist of the b3 AR and did not
activate the b1 and b2 ARs. It did not, however, show
any selectivity for activation of the b3 AR over binding
to the b1 and b2 ARs (Table 1).
In a search for novel structural classes of b3 AR agonists,
we turned our attention to trimetoquinol 3 (TMQ), a
human b AR agonist containing a tetrahydroisoquino-
line core.5 TMQ is a potent agonist of the human b3 AR
(EC50=1.7 nM, 92% activation), which exhibits only
marginal selectivity over the b1 and b2 ARs (Table 1).6
Other workers have investigated catechol bioisosteres in
Figure 1.
The excellent in vitro pro®les of analogues 1 and 2 are
due in part to the presence of the benzenesulfonamide
moiety,3,4 and it was postulated that the selectivity of
*Corresponding author. Tel.: +1-732-594-6626; fax: +1-732-594-
7877; e-mail: emma_parmee@merck.com
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00459-5

2284
E. R. Parmee et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2283±2286
TMQ might be enhanced by incorporation of the 4-
(hexylureido)benzenesulfonamide into the potent tetra-
hydroisoquinoline backbone. Hence, amine 5 was pre-
pared and tested at the human b ARs.8,9 Despite a
considerable drop in potency compared to TMQ, sulfo-
namide 5 retained all of its agonist ecacy at the b3 AR
with only minimal agonist activity at the b1 and b2 ARs.
Selectivity over binding to the b1 AR was also slightly
improved (18- vs 4-fold).
Superimposition of low energy conformations of pyr-
idineethanolamine 2 (pink) with tetrahydroisoquinoline
5 (green) revealed that when the b agonist pharmaco-
phores are aligned, overlay of the benzenesulfonamide
and hexyl urea moieties is not possible (Fig. 2).10 In this
paper we would like to describe our e€orts to improve
the potency and selectivity of benzyl derivative 5 by
designing compounds in which all the hydrogen bond-
ing regions of the molecule could be aligned with the
corresponding groups in pyridineethanolamine 2. Thus,
the phenyl ring of the benzyl linker was replaced with
either a biphenyl, naphthyl, or aryloxy unit (Schemes 1
and 2).
Figure 2. Superimposition of low energy conformations of pyridine-
ethanolamine 2 (pink) and tetrahydroisoquinoline 5 (green).
coupled with 3,4-dibenzyloxyphenethylamine hydro-
chloride, followed by sulfonamide formation to yield
amides 21. Cyclization and deprotection gave the
desired compounds 17 and 18.
Compounds 6±12, 17, and 18 were tested at the cloned
human b ARs and the results are shown in Table 1. Of
the biphenyl derivatives 6±9, the 4,4-substitution pattern
was obviously preferred as compound 9 was >20-fold
more potent than the other biphenyl derivatives (b3
EC50=6 nM). Derivative 9 had an IC50 at the b3
AR=9.4 nM and hence showed >300-fold selectivity
for both activation of and binding to the b3 AR over
binding to the b1 and b2 ARs. The compound exhibited
only weak partial agonist activity at the b1 and b2 ARs
(EC50=1800 and 340 nM, respectively). Additionally,
several 4,4-biphenyl derivatives lacking the benzene-
sulfonamide were prepared and shown to be non-
selective b AR agonists (b3 EC50=8±230 nM, data not
shown). The exception was 3,4,5-trimethoxy compound
22 (Scheme 1), which was prepared as a comparison to
TMQ. The longer compound 22 was nearly 16-fold less
potent than TMQ (b3 EC50=27 nM), but showed
improved selectivity over the b1 and b2 ARs.
Biphenyl analogues 6±11 were prepared from bromides
13±15 by Suzuki coupling using either 3-aminophenyl
boronic acid or the pinacol ester of 4-nitrophenyl boro-
nic acid (Scheme 1).11,12 In the latter case, the nitro
group was then reduced with palladium hydroxide and
hydrogen (which resulted in concomitant loss of the
benzyl ethers) or Raney nickel and hydrazine. Reaction
of the biphenyl anilines with 4-(hexylureido) benzene-
sulfonyl chloride3 and deprotection yielded the desired
compounds. Phenoxy derivative 12 was prepared directly
from the nitro compound 16 in an analogous manner.
The synthesis of both naphthalene compounds 17 and 18
originated from BOC protected 2-amino-6-hydro-
xynaphthalene 19 (Scheme 2).13 Alkylation, saponi®ca-
tion and treatment with oxalyl chloride gave acid chloride
20 (n=1). Tri¯ate formation, palladium coupling with
TMS acetylene, and oxidative hydroboration yielded
the acid precursor to 20 (n=0). The acid chlorides were
Of the oxygen linked derivatives 10±12, only the 4,4-
biphenyl 11 showed any agonist activity at <100 nM. It
Table 1. Activity of tetrahydroisoquinoline derivatives 3±12, 17, 18 and 22, at the cloned human b adrenergic receptors
Compound
b3 EC50 nM
b1 EC50 nM
b1 binding
IC50 nM
b2 EC50 nM
b2 binding
(%act)a
(%act)a
(%act)a
IC50b nM
b
3
4
5
6
7
8
9
10
11
12
17
18
22
1.7 (92)
800 (36)
66 (82)
360 (62)
600 (64)
140 (100)
6 (91)
(10 @ 100)
16 (72)
(4 @ 100)
(7 @ 100)
78 (72)
14 (50)
(2 @ 10,000)
(19 @ 10,000)
>10,000 (22)
>1000 (12)
970 (69)
6.1
780
1200
3.5 (77)
(1 @ 10,000)
(36 @ 10,000)
2700 (36)
>1000 (33)
1300 (71)
340 (67)
6.1
56
200
530
710
100,000
10,000
3000
6500
2000
1000
1000
80,000
1800
100,000
32,000
3400
1800 (44)
ndc
ndc
990
160
300
300
2400 (23)
ndc
580 (29)
ndc
ndc
ndc
(3 @ 10,000)
6100 (45)
(37 @ 10,000)
1500 (85)
>100,000
760
27 (77)
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.

E. R. Parmee et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2283±2286
2285
ꢀ
.
Scheme 1. (a) 3-NH2PhB(OH)2 0.5 H2SO4, toluene, EtOH, 2 M Na2CO3, Pd(PPh3)4, 80 C; (b) pinacol ester of 4-NO2PhB(OH)2, Pd(dppf)Cl2, tol-
uene, EtOH, 2 M Cs2CO3, 80 ꢀC; (c) Raney Ni, NH2NH2, MeOH, 60 ꢀC; (d) 4-(hexylureido)benzenesulfonyl chloride, py, CH2Cl2; (e) concd HCl,
MeOH; (f) H2, Pd(OH)2, MeOH; (g) TFA, CH2Cl2; (h) 3,4,5-trimethoxyphenylboronic acid, Pd(OAc)2, EtOH, Ba(OH)2.
Scheme 2. (a) BrCH2CO2Et, Cs2CO3, DMF; (b) 5 N NaOH, MeOH; (c) (COCl)2, CH2Cl2; (d) PhNTf2, Et3N, THF; (e) TMSCCH, Et3N,
Pd(PPh)2Cl2, DMF, 70 ꢀC; (f) BH3.THF, C6H10, THF then 2 N NaOH, H2O2, MeOH; (g) 3,4-dibenzyloxyphenethylamine hydrochloride, Et3N,
CH2Cl2; (h) TFA, CH2Cl2; (i) 4-(hexylureido)benzenesulfonyl chloride, py, CH2Cl2; (j) POCl3, CH3CN then NaBH4, EtOH; (k) concd HCl, MeOH.
was a potent b3 AR agonist (EC50=16 nM), however,
the selectivity over binding to the b2 AR was only 10-
fold. A much greater degree of selectivity was seen with
naphthyloxy derivative 18. A moderately potent b3 AR
agonist (EC50 78 nM, 72% activation), this derivative
was >1000-fold selective for agonist activity at the b3
AR over binding to the b1 and b2 ARs. Compound 18
exhibited only minimal agonist activity at the b1 and b2
ARs. Interestingly, naphthyl derivative 17, lacking the
oxygen linker, was devoid of agonist activity at the b3
AR at <100 nM.
Low energy conformations of tetrahydroisoquinolines 9
and 18 were superimposed on pyridineethanolamine 2 in
order to see if there was indeed superior alignment of the
hydrogen bonding regions of the molecules (Figs. 3 and
Figure 3. Superimposition of low energy conformations of pyridine-
ethanolamine 2 (pink) and tetrahydroisoquinoline 9 (yellow).
4). As predicted the biphenyl derivative 9 showed
improved overlap of the urea moiety, while the naph-
thyloxy compound 18 demonstrated excellent alignment
of all parts of the molecule with pyridineethanolamine 2.
4,4-biphenyl derivative 9 is a very potent compound (b3
EC50=6 nM), which is a full agonist of the b3 AR and
exhibits good selectivity over binding to the b1 and b2
ARs. Also noteworthy is naphthyloxy derivative 18,
which shows excellent selectivity for the b3 AR, with
minimal binding to or activity at the b1 and b2 ARs. The
improvements in selectivity for the b3 AR seen in this
In this paper we have described a novel series of b3 AR
agonists derived from trimetoquinol. In particular, the

2286
E. R. Parmee et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2283±2286
human b1 and b2 ARs were cloned as described in Frielle, T.;
Collins, S.; Daniel, K. W.; Caron, M. G.; Lefkowitz, R. J.;
Kobilka, B. K. Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 7920
and Kobilka, B. K.; Dixon, R. A.; Frielle, T.; Dohlman, H. G.;
Bolanoski, M. A.; Sigal, I. S.; Yan-Feng, T. L.; Francke, U.;
Caron, M. G.; Lefkowitz, R. J. Proc. Natl. Acad. Sci. U.S.A.
1987, 84, 46. The receptors were expressed in CHO cells at
receptor densities of 46±88 fmol/mg (b3 receptors) or 300±
500 fmol/mg (b1 and b2 ARs). Agonist activity and binding
anity were assessed by measurement of cellular cAMP levels
relative to isoproterenol and inhibition of 125I-cyanopindolol
binding, respectively.
7. (a) Zheng, W.; Nikulin, V. I.; Konkar, A. A.; Vansal, S. S.;
Shams, G.; Feller, D. R.; Miller, D. D. J. Med. Chem. 1999,
42, 2287. (b) He, Y.; Nikulin, V. I.; Vansal, S. S.; Feller, D. R.;
Miller, D. D. J. Med. Chem. 2000, 43, 591.
Figure 4. Superimposition of low energy conformations of pyridine-
ethanolamine 2 (pink) and tetrahydroisoquinoline 18 (yellow).
8. Prepared from the aniline described in Christo€, J. J.;
Bradley, L.; Miller, D. D.; Lei, L.; Rodriguez, F.; Fraundor-
fer, P.; Romstedt, K.; Shams, G.; Feller, D. R. J. Med. Chem.
1997, 40, 85.
class of compounds represent an important break-
through in the design of structurally distinct human b3
AR agonists as potential therapeutics for the treatment
of obesity.
9. For experimental details, see Brockunier, L. L.; Parmee, E.
R.; Weber, A. E. U. S. Patent 6 043 253, 2000. All compounds
were puri®ed by reverse-phase HPLC (eluent MeOH/H2O/
0.1% TFA) and characterized as their TFA salts by 1H NMR,
and mass spectrometry prior to submission for biological eva-
luation. The compounds prepared in this paper are racemic,
however, it is known that all of the b AR activity resides in the
(S) isomer of the tetrahydroisoquinoline series (see Fraundor-
fer, P. F.; Lezama, E. J.; Salazar-Bookman, M. M.; Fertel, R.
H.; Miller, D. D.; Feller, D. R. Chirality 1994, 6, 76).
10. Twenty-six structurally diverse conformations of com-
pounds 2, 5, 9, and 18 were generated with the program Enu-
merate Torsions (ET) (Feuston, B. P.; Miller, M. D.;
Culberson, J. C.; Nachbar, R. B.; Kearsley, S. K. manuscript
in preparation), and each structure was energy minimized with
MMFFS force ®eld (Halgren, T. A.; J. Comput. Chem. 1999,
20, 720) and the Newton-Raphson method until the gradient
converged (<0.001). Each of the 26 conformations for tetra-
hydroisoquinolines 5, 9, and 18 were then superimposed with
the lowest energy conformation of pyridineethanolamine 2
with exhaustive enumeration of all possible superimposition's
using the program SQ (Miller, M. D.; Sheridan, R. P.; Kears-
ley, S. K.; J. Med. Chem. 1999, 42, 1505). The highest scoring
superimposition in each case was then further manually mod-
eled to achieve best possible overlay with pyridineethanolamine
2. The ®nal model was then energy minimized to obtain a fully
re®ned superimposed model that is consistent with the experi-
mental data.
Acknowledgements
We thank Professor James G. Grannemann (Wayne
State University) for supplying the cloned human b3 AR
and Ms. Amy Bernick for mass spectrometric analyses.
References and Notes
1. For recent reviews see: (a) Weyer, C.; Gautier, J. F.; Dan-
forth, J. Diab. Metab. 1999, 25, 1. (b) Weber, A. E. Annu. Rep.
Med. Chem. 1998, 33, 193. (c) Dow, R. L. Exp. Opin. Invest.
Drugs, 1997, 6, 1811. (d) Lowell, B. B.; Flier, J. S. Annu. Rev.
Med. 1997, 48, 307. (e) Arch, J. R. S.; Wilson, S. Int. J. Obe-
sity 1996, 20, 191.
2. (a) Connacher, A. A.; Jung, R. T.; Mitchell, P. E. G. Br.
Med. J. Clin. Res. Ed. 1988, 296, 1217. (b) Wheeldon, N. M.;
McDevitt, D. G.; Lipworth, B. J. Br. J. Clin. Pharmacol. 1994,
37, 363.
3. Parmee, E. R.; Ok, H. O.; Candelore, M. R.; Tota, L.;
Deng, L.; Strader, C. D.; Wyvratt, M. J.; Fisher, M. H.;
Weber, A. E. Bioorg. Med. Chem. Lett. 1998, 8, 1107.
4. Naylor, E. M.; Colandrea, V. J.; Candelore, M. R.; Cas-
cieri, M. A.; Colwell, L. F., Jr.; Deng, L.; Feeney, W. P.;
Forrest, M. J.; Hom, G. J.; MacIntyre, D. E.; Strader, C. D.;
Tota, L.; Wang, P-R.; Wyvratt, M. J.; Fisher, M. H.; Weber,
A. E. Bioorg. Med. Chem. Lett. 1998, 8, 3087.
11. Compounds 13±16 were prepared from the appropriate
phenyl or phenoxy acetic acid as described in ref 8.
12. Ishiyama, T.; Murata, M.; Miyaura, N. J. Org. Chem.
1995, 60, 7508.
5. Iwasawa, Y.; Kiyomot, A. Jpn. J. Pharmacol. 1967, 18, 85.
6. The human b3 AR was obtained from Professor J. Gran-
nemann (Wayne State Universtiy), Grannemann, J. G.; Lah-
ners, K. N.; Rao, D. D. Mol. Pharmacol. 1992, 42, 964. The
13. Prepared by BOC protection of 6-amino-2-naphthol,
which was synthesized from 6-bromo-2-naphthol as described
by Wisansky, W. A.; Ansbacher, S. In Org. Synth., Collective
Vol. 3; Horning, E. C., Ed.; Wiley: New York, 1955; p 307.