Design and synthesis of cyclic sulfonamides and sulfamates as new calcium sensing receptor agonists

Article abstract of DOI:10.1016/j.bmcl.2010.10.006

The design, synthesis and calcimimetic properties of various cyclic sulfonamides and sulfamates are described. The latter were prepared from the corresponding o-alkenylarenesulfonamides via copper- or rhodium-catalyzed intramolecular aziridination. The si

Full text of DOI:10.1016/j.bmcl.2010.10.006

Bioorganic & Medicinal Chemistry Letters 20 (2010) 7483–7487
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and synthesis of cyclic sulfonamides and sulfamates
as new calcium sensing receptor agonists
Lionel Kiefer a, Tatiana Gorojankina b, Philippe Dauban a, Hélène Faure b, Martial Ruat b, Robert H. Dodd a,
⇑
a Institut de Chimie des Substances Naturelles, UPR 2301, Centre National de la Recherche Scientifique, bât. 27, 1 av. de la Terrasse, F-91198 Gif-sur-Yvette, France
b Signal Transduction and Developmental Neuropharmacology Team, Laboratoire de Neurobiologie et Développement, Centre National de la Recherche Scientifique, Institut
de Neurobiologie Alfred Fessard-IFR 2118, UPR 3294, F-91198 Gif-sur-Yvette, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The design, synthesis and calcimimetic properties of various cyclic sulfonamides and sulfamates are
described. The latter were prepared from the corresponding o-alkenylarenesulfonamides via copper- or
rhodium-catalyzed intramolecular aziridination. The size of the cyclic sulfonamide rings as well as the posi-
tion of the crucial (R)-naphthylethylamine substituent significantly affected calcimimetic activity. The
most active compounds were the six- and seven-membered sulfonamides 30a and 31a and sulfamate 34a.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 29 July 2010
Revised 1 October 2010
Accepted 2 October 2010
Available online 30 October 2010
Keywords:
Calcium sensing receptor
Calcimimetics
Hyperparathyroidism
Parathyroid hormone
Calindol
Aziridine
The extracellular calcium sensing receptor (CaSR), identifieda lit-
tle over a decade ago, is a G-protein coupled receptor (GPCR) which
responds to small variations in extracellular calcium levels thereby
maintaining calcium homeostasis in the organism.1,2 Failure to
H
N
H
N
OMe
F3C
Cl
2 NPS-568
1 Cinacalcet
maintain constant levels of extracellular ionized calcium [Ca2+
] ,
ex
generally in the 1.1–1.3 mM range, has been associated with several
disorders such as hyperparathyroidism and osteoporosis.
Figure 1. Positive allosteric modulators (calcimimetics) of the CaSR.
In addition to the parathyroid glands, the CaSR has been identi-
fied in a wide range of tissues including kidney, intestine, and bone
which are major contributors to systemic Ca2+ homeostasis as well
as in cells not directly involved in this regulation process such as
neurons and glial cells.3,4 With respect to the parathyroid glands,
pound, a structural analogue of NPS-568 (2) one of the first synthetic
small molecule ligand of the CaSR,7,8 thus presents an alternative to
parathyroidectomy for these disorders. The new treatment options
offered by calcimimetics9 are a strong motivation for the pursuit
of new clinically useful drugs of this type.10,11
low [Ca2+
]
levels result in low activation of the CaSR inducing
ex
2
parathyroid hormone (PTH) secretion which then raises [Ca2+
] .
ex
We have recently developed calindol (3, R = H) as a potent
positive allosteric modulator of the CaSR.12 Structurally, calindol
is a rigid analog of the arenesulfonamide 4, a novel calcimimetic
family also first reported by us (Fig. 2).13 Compound 4 can, in turn,
be seen as an arenesulfonamide analogue of cinacalcet (1). While
the in vivo activity of calindol is currently under investigation, this
compound has already proven to be a valuable tool for the study of
the mode of function of the CaSR14 as well as of the GPRC6A recep-
tor, another member of family 3 GPCRs related to the CaSR.15
Calindol has also been used to demonstrate the presence of the
CaSR in arterial endothelial cells and its possible role in the vascu-
lar complications associated with type 2 diabetes.16–18 As part of
an exploratory program aimed at the development of new poten-
tially more active or selective calcimimetics, we decided to prepare
Inversely, in response to high levels of [Ca2+
]ex, the activated CaSR
diminishes the secretion of PTH. Such an action can be mimicked
by positive allosteric modulators of the CaSR, referred to as type II
calcimimetics, useful for the treatment of primary and secondary
hyperparathyroidism (HPT).5 Only one such compound, cinacalcet
1 (SensiparÒ in the USA, MimparaÒ in Europe, Fig. 1) is presently
commercialized for the treatment of secondary hyperparathyroid-
ism in patients with end-stage renal disease (ESRD) and on mainte-
nance dialysis therapy as well as for the reduction of hypercalcaemia
in patients with primary HPT and parathyroid carcinoma.6 This com-
⇑
Corresponding author. Tel.: +33 1 69 82 45 94; fax: +33 1 69 07 72 47.
E-mail address: dodd@icsn.cnrs-gif.fr (R.H. Dodd).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.10.006

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L. Kiefer et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7483–7487
O O
R
S
NH
H
N
A
R
R
O
S
HN
5
O
H
N
H
B
N
N
H
O
O
4
S
3 (R = H, calindol)
NH
H
N
6
Figure 2. Calcimimetics developed by our groups (3, 4) and targeted in this study (5, 6).
alternative rigid analogs of 4 in which the sulfur atom of the
sulfonamide group (instead of the nitrogen atom as in calindol)
is now bound to phenyl ring B as in compound 5. Alternatively,
linking of the two A and B phenyl rings to give the biphenyl deriv-
atives of type 6 was also studied. In this Letter, we describe the
synthesis and in vitro calcimimetic activity of the prototypic cyclic
sulfonamides 5 and 6 and of cyclic sulfamate analogs together with
preliminary optimization studies in which, among other structural
elements, the size of the sulfonamide (or sulfamate) ring and the
position of the naphthylethylamine group were varied.
The key compounds were prepared by way of the one-pot
copper(I) catalyzed intramolecular aziridination of unsaturated
sulfonamides developed in our laboratory.19 Thus, using this strat-
egy, iodosylbenzene treatment of an arenesulfonamide bearing an
olefinic side-chain of varying length at C2 (7) affords, in the
presence of a copper(I) salt catalyst, the product of intramolecular
aziridination (8). The latter should then be subject to nucleophilic
attack by (R)-1-(1-naphthyl)ethylamine to give the desired cyclic
sulfonamides (9) (Fig. 3).20
We first set out to prepare the different olefinic arenesulfona-
mide precursors (Scheme 1). Thus, starting from N-(t-butyl)ben-
zenesulfonamide 10, prepared by reaction of benzenesulfonyl
chloride with t-butylamine, the o-vinyl derivative 11 was obtained
using the modified Schlosser procedure involving sequential addi-
tions of n-BuLi, DMF, Ph3PCH3Br, and t-BuONa.21 The homolog of
11 was efficiently prepared by ortho-lithiation using n-butyllith-
ium in the presence of TMEDA followed by reaction with allylbro-
mide to give 13. Further homologation was accomplished by
subjecting propene derivative 13 to hydroboration followed by
oxidation of the resulting primary alcohol 15 using TPAP to give
aldehyde 16. Wittig reaction between 16 and methyltriphenyl-
phosphonium bromide in the presence of n-butyllithium then
afforded the 3-butene derivative 17 though in moderate yield.22
Two alternative structures were also employed for this study, the
first being the biphenylsulfonamide 21. This compound was
prepared by treating N-t-butylphenylsulfonamide 10 with
n-butyllithium and trimethylborate to give, after acid hydrolysis,
the 2-boronic acid derivative 19. Suzuki coupling between 19
and bromostyrene then furnished the 2-vinylbiphenyl derivative
20. Trifluoroacetic acid—promoted deprotection of these unsatu-
rated arenesulfonamides in the presence of anisole gave respec-
tively 12, 14, 18, and 21.23 Finally, the sulfonamide group of allyl
O
O
NH2
O O
O
O
N
Nu
R
R
R
Cu(I), PhIO
solvent,T
S
S
S
NH
Nu
n
n
n
n = 0,1,2
n = 0,1,2
n = 0,1,2
7
8
9
Figure 3. General procedure for the aziridination and ring-opening reaction to give
cyclic sulfonamides.
O
O
NH2
O
O
S
S
O
O
Cl
O
O
O
O
NHt-Bu
a
j
S
k
l
S
S
NHt-Bu
NHt-Bu
t-BuNH2
B(OH)2
10
19
20
21
b
d
O
O
NH2
O O
O
O
O O
S
S
c
S
S
e
NHt-Bu
NHt-Bu
NH2
12
11
13
14
f
O
O
O
O
O
NH2
O
O
O
O
O
O
NH2
S
S
S
S
g
i
h
S
NHt-Bu
NHt-Bu
OH
NHt-Bu
OH
m
O
17
16
18
15
23
22
Scheme 1. Reagents and conditions: (a) (1) CHCl3, 0 °C; (2) HCl, rt (quantitative); (b) (1) n-BuLi, THF, 0 °C; (2) DMF, 0 °C; (3) Ph3PCH3Br, 0 °C; (4) t-BuONa, rt (79%);21 (c) TFA,
anisole, 0 °C to rt (91%); (d) (1) n-BuLi, TMEDA, THF, 0 °C; (2) allylbromide, À60 °C to rt (70%); (e) TFA, anisole, 0 °C to rt (89%); (f) (1) 9-BBN, THF, reflux; (2) NaOH, HOOH,
50 °C (85%); (g) TPAP, NMO, MS, CH3CN, rt (65%); (h) Ph3PCH3Br, n-BuLi, THF, À20 °C (19%);22 (i) TFA, anisole, 0 °C to rt (85%); (j) (1) n-BuLi, TMEDA, THF, 0 °C; (2)
trimethylborate, 0 °C; (3) HCl, rt; (k) Pd(PPh3)4, NaHCO3, DME/H2O, 2-bromostyrene, reflux (70% for two steps); (l) TFA, anisole, 0 °C to rt (20%);23 (m) (1) HCO2H, ClSO2NCO,
DMA, 0 °C; (2) H2O, rt (80%).25

L. Kiefer et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7483–7487
7485
derivative 14 was replaced by a sulfamate group (i.e., compound
23)24 by treating 2-allylphenol 22 with chlorosulfonylisocyanate.25
Transformation of the olefinic arenesulfonamides 12, 14, 18, 21
and of sulfamate 23 to their corresponding aziridines was then ef-
fected (Table 1). Using our one-pot procedure (iodosylbenzene and
catalytic Cu(CH3CN)4PF6 in acetonitrile), compounds 14, 18 and 21
gave the expected aziridines 25, 26 and 27 in 65%, 31% and 70%
yields, respectively. The relatively low yield of compound 26 is
due to competitive formation of the product of allylic insertion.20,26
Application of these reaction conditions to the vinyl derivative 12
proved unsuccessful. However, use of dirhodium tetraacetate as
the catalyst together with iodosylbenzene diacetate afforded the
desired aziridine 24 in 90% yield.27 These same reaction conditions
were used to promote aziridination of the sulfamate substrate 23,
affording compound 33 in 83% yield.
Previous SAR studies have shown that the biological activity of
NPS-568 and of calindol is intimately related to the configuration
of their methyl-bearing chiral centers. Thus, both (R)-NPS-568
and calindol are approximately 100 times more potent than their
(S) counterparts.12,8 The aziridines 24–27 and 33 were thus opened
using (R)-naphthylethylamine as the nucleophile.
These ring-opening reactions, conducted in THF at 50 °C, were
completely regioselective in the case of 25, 26, and 27: the nucle-
ophile attacks the less hindered carbon of the aziridine affording
the corresponding ring-opened products 30, 31, and 32, respec-
tively, in good yields (Table 1). In the case of compound 24,
Table 1
Intramolecular aziridination and nucleophilic ring-opening reactions
NH2
O
O
O
O
O
NH
O
S
O
S
n
O
M, I(III)
O
S
NH2
n
N
n
H
N
THF, 50ºC
solvent, T
n = 0,1
n = 0,1
n = 0,1
Sulfonamide
Aziridine
Yielda (%)
90c
Product
Yielda,b (%)
O
O
O
S
O
O
O
S
S
NH
NH2
H
N
N
50
24
12
28
O
S NH
O
26
85
68
HN
29
O
O
NH2
O
O
N
O
O
NH
S
S
S
S
65d
31d
H
N
25
14
30
O
O
NH2
O
N
O
O
O
S
S
NH
HN
18
26
31
O
O
NH2
O
O
S
O
S
O
S
NH
N
70d
86f
NH
27
21
23
32
O
O
O
NH2
O
S
O
S
S
O
O
N
O
O
NH
83e
35g
33
HN
34
O
O S
O
NH
35g
NH
35
a
b
c
d
e
f
Isolated yield after flash chromatography based on starting sulfonamides.
1:1 mixture of two diastereoisomers.
Rhodium-catalyzed aziridination using Rh2(OAc)4, PhI(OAc)2, Al2O3, CH2Cl2, 40 °C.27
Copper-catalyzed aziridination using Cu(CH3CN)4PF6, PhIO, CH3CN, MS, rt.16
Rhodium-catalyzed aziridination using Rh2(OAc)4, PhI(OAc)2, MgO, CH2Cl2, À28 °C.24
Reaction performed at 80 °C.
g
Reaction performed at rt.

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L. Kiefer et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7483–7487
opening of the aziridine at the more substituted site was also ob-
served to a minor degree, leading to a 2:1 mixture of five- and six-
membered ring products 28 and 29, respectively. While the two
diastereomers of products 28, 30, and 31, formed in equimolar
amounts, could be easily separated by chromatography on silica
gel, HPLC was required to separate the diastereomers of products
29 and 32.
O
O
O
O
S
S NH
NH
NH
HN
29a
32a
Reaction of the tricyclic N-sulfamate 33 with (R)-naphthylethyl-
amine was also non-regioselective though in contrast to the reac-
tion of the same nucleophile with 24, a 1:1 ratio of regioisomers,
that is, 34 and 35, was obtained, HPLC being required to separate
the diastereomers of 35.
Figure 4. Absolute configurations of 29a and 32a as determined by X-ray
crystallography.29
the sulfonamide ring, both showed diminished activities (30%
and 13% accumulation) compared to 28a,b and 30a,b in which
the amine function is now linked to the sulfonamide ring via a
methylene group. Finally, in this series, the seven-membered sul-
fonamide 31a displayed almost identically high agonist activity
(75% accumulation) as the six-membered sulfonamide 30a (71%
accumulation), its diastereomer 31b being again significantly less
active (37% accumulation). While the biphenyl cyclic sulfonamide
derivatives 32a,b were revealed to be among the least active CaSR
agonists prepared (29% and 19% accumulation), the seven-mem-
bered sulfamate derivatives 34a and 34b were the most active,
the former stimulating IP accumulation by 85% which compares
favorably with the agonist effect of calindol (95% accumulation)
at the same concentration. Finally, the eight-membered sulfamate
derivative 35a was also observed to be very active (67% accumula-
tion) while its diastereomer 35b was considerably less active (17%
accumulation). Compound 35 thus displays the largest stereo-
chemically determined activity difference of all the compounds
studied.
All the synthesized compounds except the less active ones 29
and 32 were also assayed for agonist activity on human CaSR
(hCaSR) expressed in HEK293 cells.30 As shown in Table 2 (column
2), the measured activities were in all cases remarkably similar to
those determined in rat CaSR (rCaSR).
We have previously shown using point mutations of the hCaSR
expressed in HEK293 cells that glutamate residue 837 (E837) was
essential for efficient stimulation of IP accumulation by positive
allosteric ligands such as NPS-568 and calindol.31,32 Thus, as shown
in Table 2 (column 3), mutation of this glutamate residue to
alanine (E836A) results in only 41% IP accumulation produced by
The hydrochloride salts of compounds 28a,b–32a,b, 34a,b and
35a,b (where ‘a’ and ‘b’ designate the more and less lipophilic
diastereomers, respectively) were then evaluated for agonist activ-
ity in Chinese hamster ovarian (CHO) cells stably expressing cloned
calcium sensing receptor from rat brain (CHO(CaSR)) as previously
described.28 In these cells, Ca2+ as well as positive allosteric mod-
ulators (agonists) stimulate PLC activity resulting in accumulation
of inositol phosphates (IP). The IP accumulation produced by the
test compounds (10 l
M) in the presence of 3 mM [Ca2+]e was mea-
sured and compared to the effect produced by calindol.
As shown in Table 2, all arenesulfonamide and arenesulfamate
derivatives demonstrated calcimimetic activity at 10 lM ranging
from weak (29, 32) to strong (30, 34). The more lipophilic ‘a’ iso-
mers were consistently more active than their less lipophilic ‘b’
counterparts and in some cases (e.g., 31a vs 31b; 35a vs 35b), this
difference in activity was quite large. Since the absolute configura-
tions of only compounds 29 and 32 have been determined,29 no
correlations can be made at this point regarding activity and ste-
reochemistry. However, it may be noted that for compounds 29
and 32, the ring substituents of the more active ‘a’ isomers both
show the same spatial arrangement (Fig. 4).
Both diastereomers of the six-membered sulfonamide 30 were
more active than those of the five-membered sulfonamide 28
(71% and 69% IP accumulation for 30a and 30b vs 57% and 39%
for 28a and 28b) though less active than calindol (95% accumula-
tion). Interestingly, the six-membered sulfonamides 29a,b, in
which the amine function of the side-chain is directly attached to
calindol (10 lM) compared to 95% accumulation in the WT recep-
Table 2
Accumulation of IP induced by the test compounds in CHO cells expressing wild-type
(WT) rat CaSR (rCaSR) and in HEK293 cells expressing WT human CaSR (hCaSR) or
mutant (E837A) hCaSR
tor. Again, except for the less potent compounds 29 and 32, the sul-
fonamides and sulfamates were evaluated for agonist activity on
E837A mutated human CaSR. Interestingly, all tested compounds
showed a major loss of activity as a result of its interaction with
the mutated receptor. This suggests that the activity of all of the
compounds studied depends on E837 and bind to the CaSR in a
similar manner.
In conclusion, this report describes exploratory studies aimed at
the discovery of new calcimimetic lead structures. The strategy
used was based on imposing conformational restrictions to the first
calcimimetic family discovered in our groups, the sulfonamides 4,
an approach previously used successfully by us for the develop-
ment of calindol.12 Among the cyclic sulfonamides prepared, the
six- and seven-membered derivatives 30a and 31a, respectively,
were shown to be the most potent calcimimetics. Conservation of
the seven-membered ring of the latter but replacement of the
sulfonamide function by a sulfamate led to an even more active
compound, 34a. Although the calcimimetic activities of 30a, 31a
and 34a are less robust than that of calindol, a wide variety of eas-
ily accessible structural modifications of these lead candidates can
be envisioned which can be expected to result in higher activities.
This study is currently underway. It has been recently proposed
that NPS-568 is also a positive allosteric modulator of the GPRC6A,
Compounda (10
l
M)
IP accumulationb (% of Ca2+ 10 mM) Mean S.E.M.
rCaSR (WT) hCaSR (WT) hCaSR (E837A)
10 mM [Ca2+
Calindol
28a
28b
29a
29b
30a
30b
31a
31b
32a
32b
34a
34b
35a
35b
]
e
100
95
57
39
30
13
71
69
75
37
29
19
85
76
67
17
4
5
5
4
4
3
4
4
2
1
4
4
3
5
3
5
100
94
58
51
ND
ND
73
64
70
3
100
41
11
4
4
3
4
4
1
3
11
ND
ND
22
3
2
3
3
2
3
10
3
2
40
1
4
ND
ND
75
65
67
ND
ND
51
27
1
3
3
3
2
3
4
3
2
2
1
a
‘a’ and ‘b’ refer to the more and less lipophilic diastereomers, respectively.
The IP accumulation produced by the test compounds in the presence of 3 mM
] was measured and compared to the effect produced by calindol and by
e
b
[Ca2+
10 mM [Ca2+
] (a concentration resulting in maximal CaSR activation). Results are
e
expressed as % of stimulation by Ca2+ 10 mM taken as 100%. See Ref. 30 for
experimental details.
a receptor closely related to the CaSR, stimulated by L-a-amino

L. Kiefer et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7483–7487
7487
acids and modulated by calcium.33 These data might suggest that
other CaSR ligands could also modulate GPRC6A activation. Further
work is needed for evaluating the specificity of new calcimimetics
towards the CaSR and the GPRC6A, including those described in the
present work.
22. Under the strongly basic conditions of the Wittig reaction, compound 16 led to
40% yield of the product of aldol condensation which, isolated and
characterized, was shown to have the following structure:
a
O
O
NH
S
O
O
S
NH
O
Acknowledgments
We thank the Institut de Chimie des Substances Naturelles for
financial support and for a fellowship (L.K.). This work was
supported by an ANR (ANR-07-PHYSIO-027-02) grant to M.R. and
R.H.D.
23. The strongly acidic conditions required to cleave the t-butyl group of 20 also
generated a vinyl cation which was trapped by the excess anisole in the
reaction mixture to give the following adduct, isolated in 65% yield:
MeO
NH2
O
S
References and notes
O
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Eagle’s medium supplemented with 10% fetal calf serum (Invitrogen) and 107
cells were transiently transfected with plasmid containing WT or mutant
hCaSR by electroporation as described.31 After electroporation, the cells were
resuspended in 13 ml of culture medium, then distributed (200
ll) on 96-well
white plates (VWR) coated with poly- -lysine (0.05 mg/ml) and used to
D
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Alternatively Chinese hamster ovary (CHO) cells stably expressing rat cloned
calcium sensing receptor (CHO(CaSR)) were cultured in basal Ham’s F-12
medium (0.3 mM Ca2+, 0.6 mM Mg2+) as previously described,28 seeded at
4 Â 104 cells/well in 96-well white plates and used for IP-One HTRF assay 24 h
later. Test compounds were dissolved at 10 mM in DMSO and then diluted in
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following IP-One bulk kit (Cisbio, France) instructions. Briefly, cells were
washed and pre-incubated for 10 min at 37 °C in 100
l
l
of provided
stimulation buffer. The buffer was then replaced with 70
ll of stimulation
buffer containing the indicated drug concentrations and 3 mM Ca2+. After
30 min incubation at 37 °C, the reaction was stopped as recommended. Assay
plates were then incubated for 1 h at room temperature and FRET and
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fluorescence signals were measured 50
at 337 nm using a Genios Pro apparatus (TECAN, Austria GmbH). The assay
fluorescence ratio and the percentage of basal signal inhibition were
ls at 620 and 665 nm after excitation
D
F
calculated as described in IP-One bulk kit protocol.
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