Synthesis and pharmacological evaluation of aryl aminosulfonamide derivatives as potent 5-HT6 receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2010.06.060

A series of novel aryl aminosulfonamides was designed and synthesized as 5-HT₆ receptor ligands. Many compounds screened in a functional reporter gene based assay displayed potent antagonistic activity with Kb values in the range of 0.02-10 nM. The lead compound 11m exemplified in this series showed good ADME surrogate properties, acceptable pharmacokinetic profile and is active in animal models of cognition like novel object recognition test and Morris water maze. The compound was selected for detailed profiling.

Full text of DOI:10.1016/j.bmcl.2010.06.060

Bioorganic & Medicinal Chemistry Letters 20 (2010) 4440–4443
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and pharmacological evaluation of aryl aminosulfonamide
derivatives as potent 5-HT6 receptor antagonists
a
a
a
a
Ramakrishna V. S. Nirogi a, , Anand V. Daulatabad , G. Parandhama , Shaikh Mohammad , K. R. Sastri ,
*
Anil K. Shinde a, P. K. Dubey b
a Discovery Research, Suven Life Sciences Ltd, Serene Chambers, Road-5, Avenue-7, Banjara Hills, Hyderabad 500 034, India
b Department of Chemistry, Jawaharlal Nehru Technological University Hyderabad, Kukatpally, Hyderabad 500 072, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel aryl aminosulfonamides was designed and synthesized as 5-HT6 receptor ligands. Many
compounds screened in a functional reporter gene based assay displayed potent antagonistic activity
with Kb values in the range of 0.02–10 nM. The lead compound 11m exemplified in this series showed
good ADME surrogate properties, acceptable pharmacokinetic profile and is active in animal models of
cognition like novel object recognition test and Morris water maze. The compound was selected for
detailed profiling.
Received 20 January 2010
Revised 20 May 2010
Accepted 9 June 2010
Available online 12 June 2010
Keywords:
5-HT6R
Ó 2010 Elsevier Ltd. All rights reserved.
NORT
Morris water maze
Cognition
Identification of ligands for the 5-hydroxytryptamine6 receptor
(5-HT6R) has been the focus of several reports in the last decade.1–9
Ligands for the 5-HT6R may be useful in the treatment of CNS
disorders such as schizophrenia, depression, Alzheimer’s disease
(AD)10–14 and metabolic disorders like obesity. Research efforts from
several groups, worldwide, have led to the discovery of several clas-
ses of serotonin 5-HT6 receptor ligands5,15–18 with high affinity and
selectivity. Several lead molecules like SB-742457 and SUVN-502 for
cognition, PRX-07034 for obesity and LY-483518 (SGS-518) for
schizophrenia are in advanced stages of clinical studies. For all these
compounds positive clinical study data have been reported in liter-
ature.19–22 A common feature in many of these compound classes is
the presence of basic amine functionality, which imparts potent
binding site to the 5-HT6 receptor and a second aryl moiety, which
maintains the selectivity over other receptors.
chain. There was measurable impact on brain penetrations with
these attempts. As can be seen in 2, these analogues were closely
related to SB-399885.
LY-483518, which was developed at Lilly for the treatment of
cognitive impairment associated with schizophrenia, contains 3-
piperadinyl indole as essential pharmacophore, confirming the
importance of tertiary nitrogen on piperidine for receptor binding
and affinity.
Cl
F
F
O
NH
O2
S
O
S
NH
H
N
O2
N
O
N
O
Cl
N
H
1 (SB-399885)
Kb = 0.25 nM
2 (Abbott)
Ki < 10 nM
All the reported compounds by Glaxo Smithkline contain char-
acteristic monocyclic aryl piperazine SB-399885 (compound 1) or
herteroaryl piperazine SB-742457 moiety as essential part of their
structure. SB-399885 was active in animal model of cognition and
SB-742457 is advanced into clinical studies.
N
Cl
O
F
O2
H
N
A
O
S
Most recently4 scientists at Abbott disclosed their various
efforts to modulate the brain penetration by changing the overall
lipophilicity of the molecule (compound 2). There was an attempt
to decrease the electron density around sulfonamide moiety by
incorporating a difluoromethylene unit in aryl sulfonamide side
S
N
Cl
O2
F
B
H
N
N
O
11m Kb = 0.02 nM
3 LY-483518
Based on the above observations, we hypothesized that a basic
amine function, like the terminal nitrogen of piperazine (as in
* Corresponding author. Tel.: +91 40 23556038/23541142; fax: +91 40 23541152.
E-mail address: ramakrishna_nirogi@yahoo.co.in (R.V.S. Nirogi).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.06.060

R. V. S. Nirogi et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4440–4443
4441
Table 1
SB-399885), is essential for binding to the receptor and the nitrogen
5-HT6R binding affinitiesa
attached directly to the aromatic ring presumably help to impart the
appropriate orientation for binding to 5-HT6R. Based upon the struc-
tural features of Lilly and SKB compounds, we proposed that a 4-ami-
no piperidine group could allow the appropriate spacing of the basic
amine and the distal aryl group for binding to 5-HT6R, as shown in
11m. Thus, it is hypothesized that the NH group attached to ring B
will impart the appropriate orientation for binding and the terminal
nitrogen is expected to bind to the receptor. The results of these mod-
ifications constitute the subject matter of this report.
Synthesis of the proposed compounds was achieved as shown
in Scheme 1. In general, sulfonamide compounds 2 were prepared
by reacting appropriately substituted 3-nitrobenzene sulfonyl
chlorides 1 with substituted amines. Compound 2 was reduced
with Fe–HCl to obtain intermediate amines 3. Reaction of these
amines with appropriately substituted piperidones under reduc-
tive amination conditions afforded compound 4. In situ deprotec-
tion and salt formation with IPAÁHCl gave compounds 5a–5d
with good yields. Compound 7 was prepared from 4 using standard
alkylation conditions. This intermediate 7 was further treated with
isopropanolic hydrogen chloride to obtain compounds 8a–8c. Fur-
ther alkylation on piperidine nucleus yielded compound 9a. The
derivatives 11a–11p were obtained from 3 by reductive amination
of the appropriate sulfonamide with 1-methyl-4-piperidone. Few
of the appropriately substituted 3-nitrobenzenesulfonyl chlorides
were not readily available. Hence, the synthesis of compound 3
was achieved by reacting substituted 3-acetamido benzenesulfo-
nyl chloride 10 with various substituted amines to obtain N-acetyl
intermediate 6, which on deacetylation with aqueous HCl yielded
compound 3.
R3
R1
N
B
C
O
N
S
O
N
R2
R4
n
A
H
Compound
R1
R2
R3
R4
n
Kb (nM)
5a
5b
5c
5d
8a
8b
8c
9a
OCH3
OCH3
OCH3
C2H5
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
H
H
H
H
H
OCH3
CH3
H
H
H
H
CH3
CH3
CH3
CH3
C2H5
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
2-Br
2-Cl
H
2-Br
2-Br
2-Cl
H
H
H
H
H
0
0
1
0
0
0
1
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
2
2
0
0.6
0.48
4.26
0.1
0.2
0.86
2.65
3.9
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
9b
18.6
3.36
1.23
0.584
10.0
>10,000
16.0
12.2
>10,000
0.296
1.31
0.19
0.02
0.02
38.0
26.0
1.65
0.25
11a
11b
11c
11d
11e
11f
11g
11h
11i
11j
11k
11l
11m
11n
11o
11p
SB399885
2-Cl
2,4-Di-OCH3
2,4-Di-CH3
2,5-Di-OCH3
4-Br, 2-F
2-Br, 4,6-Di-F
2-Br
H
H
H
H
H
H
H
2-Br
2-Br
C2H5
OCH3
OCH3
OCH3
OCH3
C2H5
2-OCH3, 5-CH3
3,5-Di-Cl, 2-OCH3
2-Br
2-Cl
3,5-Di-Cl, 2-OCH3
The compounds were tested in a functional reporter gene based
assay23,24 for their functional effect on 5-HT6R. In-short the assay
uses a stable CHO cell line expressing recombinant human 5-
HT6R and pCRE-Luc reporter system which refers a non-radioactive
based approach to determine binding of a compound to GPCRs. The
Kb values of Aryl aminosulfonamides obtained from the cell-based
assay of 5-HT6R are given in Table 1.
a
The compounds were tested in vitro with non-radioactive based approach for
determination of Kb values with cell-based assay for 5-HT6R. The values reported
here are a mean of two experiments. All the compounds were characterized by 1H
NMR and Mass and the purities were determined by HPLC.
As part of SAR various substitutions were tried on ring B, like
alkoxy, alkyl and halo. All of these substitutions gave potent
NH2
NO2
R2
NO2
R2
a
b
R2
+
SO2NHR1
R1-NH2
SO2NHR1
50-75%
30-60%
3
SO2Cl
2
1
65-85%
j
c
50-70%
40-60%
e
CH3
H3C
CH3
SO2NHR1
N
d
NH
O
Boc
O
NH
NH
R1-NH2
R2
N
R2
R2
+
20-40%
SO2Cl
N
H
SO2NHR1
R2
SO2NHR1
10
6
4
11
f
75-95%
g
15-50%
HN
R2
Boc
HN
R2
H3C
N
N
i
h
80-85%
SO2NHR1
NH
CH3
CH3
CH3
N
N
N
R2
R2
65-80%
SO2NHR1
SO2NHR1
SO2NHR1
5
9
8
7
Scheme 1. Synthesis of aryl aminosulfonamide derivatives. Reagents and conditions: (a) TEA, DCM, 0–5 °C, 2–4 h or KOH/THF, rt, 24–48 h; (b) Fe/HCl, ethanol, reflux, 2–4 h;
(c) NaBH(OAc)3, AcOH, Na2SO4, 25–30 °C, 5–10 h, 1-boc-4-piperidone; (d) DCM, TEA; (e) ethanol, concd HCl, reflux; (f) IPAÁHCl, IPA, heat; (g) HCHO, NaBH3CN, MeOH; (h)
IPAÁHCl, IPA, heat; (i) HCHO, NaBH3CN, MeOH; (j) 1-methyl-4-piperidone, NaBH(OAc)3, AcOH, Na2SO4, 25–30 °C, 5–10 h.

4442
R. V. S. Nirogi et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4440–4443
Table 2
Pharmacokinetic profile of compound 11m in male Wister ratsa
Compound 11m
AUCt (ng h/mL)
Route
n
Dose (mg/kg)
Cmax (ng/mL)
t1/2 (h)
Vz (mL/kg)
Cl (mL/hr/kg)
F (%)
Oral
iv
3
3
10
10
536 416
1915 130
941 533
2533 129
1.72 1.22
2.96 2.38
34,332
16,935
12,399
3929
38 22
a
Fasted male Wistar rats, vehicle used: water for injection for both oral and iv routes. Dosing volumes: 10 mL/kg for oral and 2 mL/kg for iv.
Table 3
Human cytochrome P450 inhibitory data and %surrogate metabolism for compounds
11k and 11m
Compound
IC50
(
lM)
Surrogate% metabolism
2D6
>45
3A4
Human
Wister rat
11k
11m
9.62
8.44
26
21
99
77
41.75
The cytochrome P450 inhibitory potential was determined using isoform-selective
assays and heterologously expressed human CYP2D6 and CYP3A4. These values are
the mean of duplicate determinations. Microsomal metabolic stability in Wistar Rat
and Human at 0.5 h, Concn 2.5 lM.
Figure 2. Effect of acute treatment of compound 11m in Morris water maze for
*
latency to target in rats. Data represents mean SEM of latency to target, p < 0.05,
(one way ANOVA, Dunnett’s post hoc analysis).
the compound, in addition to the substitution pattern on ring B. The
compound with 2,4-dimethoxy substitution in ring A was very
potent (11d, Kb = 10 nM) compared to its 2,4-dimethyl analogue
(11e, Kb = >10,000 nM). Introduction of spacer between sulfonamide
NH and ring A was not tolerated (11n, Kb = 38 nM and 11o,
Kb = 26 nM).
Furthermore, majority of these compounds were profiled for
their selectivity against a panel of receptors including several 5-
HT receptor subtypes like 5-HT4, 5-HT2A and 5-HT2C, Adrenergic
a1b, Dopamine D2, Histamine H1, and the transporters like SERT,
NET and DAT. The compounds were found to have >100-fold selec-
tivity over these panel of CNS receptors (data not shown).
The most potent and selective 5-HT6R antagonist 11m was fur-
ther evaluated for its pharmacokinetic profile (Table 2), CYP liabil-
ity and metabolic stability (Table 3). The effect of 11m on
cytochrome P450 (CYP) enzyme was determined in human liver
Figure 1. Data represents mean SEM of exploration time (Paired ‘t’ test), *p <0.05).
Vehicle-PEG 400 50% v/v; 1 mL/kg, po n = 6–9 /group, po, dosing vehicle/
drug:60 min prior to test (po).
in vitro compounds. There was sevenfold increase in potency when
we introduced ethyl group instead of methyl group in ring B (11j,
Kb = 1.31 nM; 11k, Kb = 0.19 nM). N-Alkylation on the spacer NH
group between ring B and C is tolerated and maintains the potent
binding affinity as that of its unalkylated analogues (5b,
Kb = 0.48 nM and 8b, Kb = 0.86 nM). However, moving from methyl
to ethyl on this spacer nitrogen generally reduces affinity by more
than 10-fold compared to unsubstituted or methyl analogues (11b,
Kb = 1.23 nM and 9b, Kb = 18.6 nM). With the optimum substitu-
tion in ring B, we focused our SAR effort on ring A. In ring A,
halogen and alkoxy are among the most tolerated groups (11c,
Kb = 0.584 nM; 11i, Kb = 0.296 nM and 11m, Kb = 0.02 nM). Multiple
halo substitutions on ring A were found to deteriorate the activities
when the ring B was not substituted (11h, Kb = >10,000 nM), while
these multiple substitutions were tolerated when the alkoxy was
present in ring B (11m, Kb = 0.02 nM) confirming the importance
of alkoxy group on ring B for activity. The compound 11p, where
in R1 is ethyl has a Kb value of 1.65 nM. It was found that 5d (R1 is
ethyl) was sixfold more potent than 5a (R1 is methoxy), where as
in the case of 11p (R1 is ethyl) the molecule was almost eighty fold
less potent compared to 11m (R1 is methoxy). Obviously the substi-
tution pattern on ring A was playing a role in the in vitro potency of
microsomes. The IC50 values were found to be >40
lM and
8.44 M for CYP2D6 and CYP3A4, respectively. The pharmacoki-
l
netics profile of compound 11m was investigated in rats. The com-
pound 11m was found to be rapidly metabolized in rat (77%
metabolized) and minimally metabolized (22% metabolized) in hu-
man liver microsomes. The low oral bioavailability of 11m in rats
was in consistence with its high metabolic instability in rat liver
microsomes. The dose of 10 mg/kg was rapidly absorbed in rats
with t1/2 of 1.72 1.22 h, when it was administered orally. The per-
cent bioavailability (%F) was found to be 38 22. The observed
Cmax value was 536 416 ng/mL and occurred at 0.33 0.14 h.
The clearance (12,399 ml/h/kg) value was found to be very high.
The volume of distribution (Vz) was found to be 34,332 mL/kg for
10 mg/kg, po dose and 16,935 mL/kg for 10 mg/kg, iv dose. In stea-
dy state brain penetration study in Male Wistar Rat (water for
injection) Cb/Cp was found to be 0.08 indicating low brain penetra-
tion properties of the lead compound.
Compound 11m was further profiled in animal models of cogni-
tion like novel object recognition test (NORT) and Morris water
maze.25,26 Oral administration of compound 11m has shown
improvement in cognitive performance of rats in NORT (Fig. 1)

R. V. S. Nirogi et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4440–4443
4443
6. Sikazwe, D.; Bondarev, M. L.; Dukat, M.; Rangisetty, J. B.; Roth, B. L.; Glennon, R.
A. J. Med. Chem. 2003, 46, 2795.
and significantly reversed scopolamine induced special memory
deficits (Fig. 2) in Morris water maze test indicating cognitive
improvement potential of the compound.
7. Ahmed, M.; Briggs, M. A.; Bromidge, S. M.; Buck, T.; Campbell, L.; Deeks, N. J.;
Garner, A.; Gordon, L.; Hamprecht, D. W.; Holland, V.; Johnson, C. N.; Medhurst,
A. D.; Mitchell, D. J.; Moss, S. F.; Powles, J.; Seal, J. T.; Stean, T. O.; Stemp, G.;
Thompson, M.; Trail, B.; Upton, N.; Winborn, K.; Witty, D. R. Bioorg. Med. Chem.
Lett. 2005, 15, 4867.
8. Holenz, J.; Pauwels, P. J.; Diaz, J. L.; Merce, R.; Codony, X.; Buschmann, H. Drug
Dis. Today 2006, 11, 283.
9. Lee, M.; Rangisetty, J. B.; Pullagurla, M. R.; Dukat, M.; Setola, V.; Roth, B. L.;
Glennon, R. A. Bioorg. Med. Chem. Lett. 2005, 15, 1707.
10. Pullagurla, M.; Bondareva, T.; Young, R.; Glennon, R. A. Pharmacol. Biochem.
Behav. 2004, 78, 263.
11. Minabe, Y.; Shirayama, Y.; Hashimoto, K.; Routledge, C.; Hagan, J. J.; Ashby, C.
R., Jr. Synapse 2004, 52, 20.
12. Lacroix, L. P.; Dawson, L. A.; Hagan, J. J.; Heidbreder, C. A. Synapse 2004, 51, 158.
13. King, M. V.; Sleight, A. J.; Woolley, M. L.; Topham, I. A.; Marsden, C. A.; Fone, K.
C. Neuropharmacology 2004, 47, 195.
14. Woolley, M. L.; Marsden, C. A.; Sleight, A. J.; Fone, K. C. Psychopharmacology
2003, 170, 358.
In summary, a novel series of 5-HT6 receptor antagonists have
been identified. In vitro functional data confirms the antagonistic
nature of this series. This series also confirms our hypothesis about
the importance of terminal nitrogen for binding to 5-HT6R. Com-
pound 11m was active in animal models of cognition like NORT
and Water maze confirming the cognitive enhancing properties of
the series. Further development and SAR modifications to improve
the brain penetration and overall pharmacokinetics behavior are in
progress and will the subject matter of subsequent publication.
Acknowledgement
The authors wish to acknowledge the support and encourage-
ment given by the CEO, Venkateswarlu Jasti throughout the re-
search work.
15. Lindner, M. D.; Hodges, D. B., Jr.; Hogan, J. B.; Orie, A. F.; Corsa, J. A.; Barten, D.
M.; Polson, C.; Robertson, B. J.; Guss, V. L.; Gillman, K. W.; Starrett, J. E., Jr.;
Gribkoff, V. K. J. Pharmacol. Exp. Ther. 2003, 307, 682.
16. Glennon, R. A. J. Med. Chem. 2003, 46, 2795.
17. Slassi, A.; Isaac, M.; O’Brien, A. Expert Opin. Ther. Pat. 2002, 12, 513.
18. Wesolowska, A. Pol. J. Pharmacol. 2002, 54, 327.
19. Zvartau-Hind. Abstract of papers, 11th Int. Conf. Alzheimer’s. Dis. Relat. Disord:
Chicago, US, 2008; Abstract 03-04-06.
20. Mather-Edwards, G. et al. Abstract of papers, 11th Int. Conf. Alzheimer’s. Dis.
Relat. Disord: Chicago, US, 2008, Abstract P4-341.
21. Lesem, M. Abstract of papers, 11th Int. Congr. Schizophr. Res: Colorado Springs,
2007 (Abst).
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.06.060.
References and notes
22. Nirogi, Ramakrishna; Ramasastri, K.; Anil, S.; Vishwottam, K.; Koteshwara, M.;
Gopinadh, B.; Pradeep, J.; Renny, A.; Mohmad, S. M.; Venkat, J. Alzheimer’s
Dement. 2009, 5, P250.
1. Liu, K. G.; Robichaud, A. J. Drug Dev. Res. 2009, 70, 145.
2. Maher-Edwards, G.; Zvartau-Hind, M.; Hunter, A. J.; Gold, M.; Hopton, G.;
Jacobs, G.; Davy, M.; Williams, P. Curr. Alzheimer Res. 2009, 7, 1.
3. Geldenhuys, Werner J.; Cornelis, J.; der schyf, Van Exp. Rev. Neurother. 2009, 9,
1073.
4. Witty, David; Ahmed, Mahmood; Chuang, Tsu Tshen Prog. Med. Chem. 2009, 48,
163.
5. Russell, M. G. N.; Dias, R. Curr. Top. Med. Chem. 2002, 2, 643.
23. Ruth, K.; Lucy, A. F.; Doris, E. A. H.; Chris, R. G.; Mark, W. H. Mol. Brain Res. 2001,
90, 110.
}
24. Gonzalo, R.; Elisabeth, S.; Marta, P.; Pilar, P.; Xavier, C.; Jorg, H.; Helmut, B.;
Petrus, J. P. Br. J. Pharmacol. 2006, 148, 1133.
25. Morris, R. J. Neurosci. Methods 1984, 11, 47.
26. Woolley, M. L.; Bentley, J. C.; Sleight, A. J.; Marsden, C. A. Neuropharmacology
2001, 41, 210.