Potent oxindole based human β3 adrenergic receptor agonists

Article abstract of DOI:10.1016/j.bmcl.2007.09.011

The synthesis and biological evaluation of a series of oxindole β₃ adrenergic receptor agonists is described. A modulation of rat atrial tachycardia was observed with substitution at the 3-position of the oxindole moiety.

Full text of DOI:10.1016/j.bmcl.2007.09.011

Bioorganic & Medicinal Chemistry Letters 17 (2007) 6270–6273
Potent oxindole based human b3 adrenergic receptor agonists
F. Craig Stevens, William E. Bloomquist, Anthony G. Borel, Marlene L. Cohen,
Christine A. Droste, Mark L. Heiman, Aidas Kriauciunas, Daniel J. Sall,
Frank C. Tinsley and Cynthia D. Jesudason*
Lilly Research Laboratories, Eli Lilly & Company, Lilly Corporate Center, Indianapolis, IN 46285, USA
Received 1 August 2007; revised 30 August 2007; accepted 4 September 2007
Available online 7 September 2007
Abstract—The synthesis and biological evaluation of a series of oxindole b3 adrenergic receptor agonists is described. A modulation
of rat atrial tachycardia was observed with substitution at the 3-position of the oxindole moiety.
Ó 2007 Elsevier Ltd. All rights reserved.
The b3 adrenoceptor is expressed predominantly in the
adipose tissue and is known to be involved in mediating
lipolysis in white adipose tissue1 and thermogenesis in
brown adipose tissue.2 It has been reported that stimula-
tion of this receptor induces a variety of pharmacologi-
cal effects such as an increase in fat oxidation,
enhancement of energy expenditure and improvement
of glucose uptake in rodent models of obesity and diabe-
tes3; however, there have only been mixed reports of
clinical efficacy in humans.4 This receptor is also ex-
pressed in the gastrointestinal tract5 and bladder6 where
it mediates relaxation and may be of therapeutic value
for gastrointestinal7 and urinary disease.8
As described earlier, we identified a compound containing
a benzimidazolone moiety (1, Fig. 1) which exhibited po-
tent b3 agonist activity (EC50 = 7.1 nM, Emax = 80%).13
Our previous SAR studies also indicated that one of the
NHs of the benzimidazolone was more critical for b3
activity. We thus considered the replacement of the benz-
imidazolone moiety with an oxindole and also further ex-
plored the role of steric bulk in the 3-position of this
moiety in modulating rat atrial tachycardia in vitro.
4-Methoxyoxindole (2, Scheme 1)14 was demethylated to
yield the corresponding phenol (3a, R1, R2 = H). This
phenol was reacted with (2S)-glycidyl 3-nitrobenzene-
sulfonate to provide the epoxide (4a, R1, R2 = H) which
was opened using 2 equivalents of the amine (5)13 to
yield the desired propanolamine (6a, R1, R2 = H).
Although activation of b1 receptors is known to increase
heart rate, evidence has accumulated to suggest that
some b3 agonists may produce a chronotropic effect in
rat atria,9 and there has been considerable debate in
the literature as to the underlying mechanism of the ef-
fect.10 Reports suggesting the existence of a fourth b
adrenoceptor11 observed in cardiac and white adipose
tissue have now been modified since this phenotype dis-
appears in b1 and b1/b2 adrenoceptor knockout mice.12
This unique pharmacology observed is probably due
to the interaction of these compounds with a low affinity
state of the b1 receptor. One of the goals of this SAR
was to minimize this in vitro atrial tachycardia.
In order to introduce substituents at the 3-position of
the oxindole, 4-methoxyoxindole (2, Scheme 1) was trea-
ted with two equivalents of n-butyl lithium in the pres-
ence of TMEDA15 followed by alkyl iodides to give
the desired monoalkylated product (7b–d). These prod-
ucts could be resubjected to the same alkylation condi-
tions to yield the desired dialkylated oxindoles (8e–g).
Alternatively, the dilakylated compounds could be
Keywords: b3 adrenergic receptors; Tacyhcardia; b3 agonists.
*
Corresponding author. Tel.: +1 317 276 7984; fax: +1 317 277
7287; e-mail: jesudason_cynthia_d@lilly.com
Figure 1. Initial compound.
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.09.011

F. C. Stevens et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6270–6273
6271
Scheme 1. Reagents and conditions: (a) pyridine hydrochloride, 180 °C (40–90%); (b) (2S)-glycidyl 3-nitrobenzenesulfonate, K2CO3, acetone, reflux,
18 h; (c) EtOH, reflux, 18 h; (d) 2 equiv n-BuLi, TMEDA, RI, THF, À78 °C to rt (30–70%).
obtained in one step by adding excess alkylating agent.
These intermediates (7b–d) and (8e–g) could be further
elaborated as described for compound 6a to provide
the final compounds (6b–g).16
The synthesis of the cyclopropyl analog is outlined in
Scheme 4. 4-Hydroxyoxindole (3a) was treated with
acetic anhydride to give the diacetate (13).18 Milder
alkylating conditions using potassium carbonate pro-
vided the cyclopropyl analog (14), which was depro-
tected under acidic conditions to provide the
necessary phenol (15) for further elaboration to com-
pound (16).
The 3-isopropyloxindole derivative (6h) was prepared as
described in Scheme 2. 4-Methoxyoxindole (2) was con-
verted to the 3-isopropylidine substituted compound (9)
by reaction with acetone.17 The resulting double bond
was hydrogenated to yield the desired branched alkyl
oxindole (10) which can be converted to the desired pro-
panolamine (6h) as detailed in Scheme 1.
The replacement of the benzimidazolone with the oxin-
dole moiety resulted in a compound (6a) which was
slightly less potent than compound 1. We then explored
substitution at the 3-position of the oxindole, and found
that the 3-methyl and 3,3-dimethyl substitution resulted
in compounds (6b and 6e) that were more active than the
unsubstituted compound (6a). However, larger substitu-
ents led to a decrease in the efficacy of these compounds
as agonists at the b3 adrenergic receptor as shown in Ta-
ble 1. We further investigated forming 3,3-fused spirocy-
cles instead of the dialkylated compounds.
The 4-methoxyoxindole (2) was also alkylated with
alkyl diiodides in a similar manner to form spirofused
oxindole intermediates (11a–c, Scheme 3) which were
further elaborated to yield the desired final com-
pounds (12).
A marked difference in both b3 adrenergic activity and
rat atrial tachycardia was seen between the 3,3-diethyl
compound (6f; Table 1) and the cyclopentyl fused spiro-
cyclic compound (12b; Table 2), alluding to the spatial
requirements of this site. We have demonstrated in our
earlier publication that the differences in potency at
the rat b3 receptor do not account for the differences
we see in rat atrial tachycardia.13 The b adrenergic ago-
nist data of these compounds are shown in Table 2.
These compounds are also agonists of the b3 receptor
with little or no agonist activity at the b1 or b2 receptors,
Scheme 2. Reagents and conditions: (a) acetone, piperidine, reflux,
17%; (b) H2, 50 psi, PtO2, EtOH, 38%.
Scheme 3. Reagents and conditions: (a) 2 equiv n-BuLi, TMEDA, I–(CH2)n–I, THF, À78 °C to rt (33–45%).

6272
F. C. Stevens et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6270–6273
Scheme 4. Reagents and conditions: (a) Ac2O, AcOH, reflux; (b) Ac2O, Na2CO3, THF, 16% two steps; (c) 1,2-dibromoethane, K2CO3, DMSO, rt,
79%; (d) 3 N H2SO4, THF, reflux, 2 h, 50%.
Table 1. In vitro agonist activitya at human b adrenergic receptors for variations in R
Compound R1, R2
Human b3
Human b2
Human b1
Rat atrial
tachycardiab
% increase in
heart rate (n)
EC50 (nM) (n)
Emax (%) (n)
EC50 (nM) (n) Emax (%)
(n)
EC50 (nM) (n) Emax (%)
(n)
6a
6b
6h
6c
6d
6e
6f
H, H
24.4 5.6 (n = 6)
50.5 4.4 (n = 6) >10,000 (n = 4) <10 (n = 4) >10,000 (n = 4) <10 (n = 4) 19.5 4.1 (n = 4)
72.6 5.4 (n = 3) >10,000 (n = 4) <10 (n = 4) >10,000 (n = 4) <10 (n = 4) 10.4 2.1 (n = 3)
41.7 8.4 (n = 3) >10,000 (n = 3) <10 (n = 3) >10,000 (n = 3) <10 (n = 3) NTc
49.4 5.7 (n = 4) >10,000 (n = 5) <10 (n = 5) >10,000 (n = 5) <10 (n = 5) NTc
15.6 0.6 (n = 2) >10,000 (n = 2) <10 (n = 2) >10,000 (n = 2) <10 (n = 2) NTc
67.9 2.0 (n = 6) >10,000 (n = 5) <10 (n = 5) >10,000 (n = 6) <10 (n = 6) 9.7 1.7 (n = 7)
Me, H 12.0 3.5 (n = 5)
i-Pr, H 13.9 7.2 (n = 3)
i-Bu, H 14.0 2.8 (n = 4)
Bn, H
Me, Me 5.2 2.1 (n = 6)
Et, Et 2.7 (n = 1)
Bn, Bn 268.1 21.3 (n = 2) 48.5 2.3 (n = 2) >10,000 (n = 2) <10 (n = 2) >10,000 (n = 2) <10 (n = 2) NTc
12.3 4.4 (n = 2)
14.2 (n = 1)
>10,000 (n = 1) <10 (n = 1) >10,000 (n = 1) <10 (n = 1) 2.0 0.6 (n = 3)
6g
a b agonist activities are expressed by a measurement of cAMP levels in CHO cells expressing the human b adrenergic receptors. Intrinsic activity was
determined as the maximal response of the compound as a percentage of the maximal response of isoproterenol at 10 mM.
b Maximal rat atrial tachycardia or response to 0.1 mM agonist if maximal response was not obtained.
c Not tested.
Table 2. In vitro agonist activitya at human b adrenergic receptors for variations in ring size
Compound n
Human b3
Human b2
Human b1
Rat atrial
tachycardiab
% increase in
heart rate (n)
EC50 (nM) (n) Emax (%) (n)
EC50 (nM) (n) Emax (%) (n)
EC50 (nM) (n) Emax (%) (n)
16
0 6.6 0.2 (n = 3) 76.8 3.2 (n = 3) 35.2 30.6 (n = 3) 13.5 0.4 (n = 3) 58.3 35.5 (n = 3) 21.4 4.2 (n = 3) 13.2 2.8 (n = 3)
12a
12b
12c
1 17.6 4.6 (n = 3) 71.2 3.9 (n = 3) >10,000 (n = 3)
2 10.6 1.2 (n = 9) 66.3 2.8 (n = 9) >10,000 (n = 9)
<10 (n = 3)
<10 (n = 9)
<10 (n = 3)
>10,000 (n = 3)
>10,000 (n = 9)
>10,000 (n = 3)
<10 (n = 3)
<10 (n = 9)
<10 (n = 3)
14.8 5.1 (n = 3)
8.6 1.4 (n = 9)
16.0 2.3 (n = 3)
3
8.3 0.8 (n = 3) 41.0 5.8 (n = 3) >10,000 (n = 3)
a b agonist activities are expressed by a measurement of cAMP levels in CHO cells expressing the human b adrenergic receptors. Intrinsic activity was
determined as the maximal response of the compound as a percentage of the maximal response of isoproterenol at 10 mM.
b Maximal rat atrial tachycardia or response to 0.1 mM agonist if maximal response was not obtained.
Table 3. Acute in vivo studies in diet-induced obese Long Evans rats
Compound
Dose
(mg/kg) pob
Respiratory quotient
% reduction over vehicle (20 h)
Energy expenditure %
increase over vehicle (20 h)
Food
consumption (g)
6e
6e
10
1
45%a
31%a
—
14%a
8%
11.8 1.7a
13.7 1.8
19.9 2.1
Vehicle
0
—
a p < 0.05.
b Rat oral bioavailability (F344 rats) was found to be 10%.
though the efficacy appears to fall off with increasing
ring size. Interestingly, we found that introducing bulk
at the 3-position did appear to modulate the in vitro
rat atrial tachycardia exhibited by these compounds.19
The pharmacological profile of compound 6e (rat b3
EC50 = 6.5 2.5 nM, Emax = 67.8 4.2%) was further
assessed by measuring carbohydrate and fat utilization
in diet-induced obese Long Evans rats by indirect calo-

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6273
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Acknowledgments
The authors thank Mr. Jack Fisher and Mr. William
Trankle for the large-scale preparation of amine 5.
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