Potent inhibition of Norwalk virus by cyclic sulfamide derivatives

Article abstract of DOI:10.1016/j.bmc.2011.08.054

A new class of compounds that exhibit anti-norovirus activity in a cell-based system and embody in their structure a cyclosulfamide scaffold has been identified. The structure of the initial hit (compound 2a, ED₅₀ 4 μM, TD₅₀ 50 μM) has been prospected by exploiting multiple points of diversity and generating appropriate structure-activity relationships.

Full text of DOI:10.1016/j.bmc.2011.08.054

Bioorganic & Medicinal Chemistry 19 (2011) 5975–5983
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Potent inhibition of Norwalk virus by cyclic sulfamide derivatives
Dengfeng Dou a, Kok-Chuan Tiew a, Guijia He a, Sivakoteswara Rao Mandadapu a, Sridhar Aravapalli a,
Kevin R. Alliston a, Yunjeong Kim b, Kyeong-Ok Chang b, William C. Groutas a,
⇑
a Department of Chemistry, Wichita State University, Wichita, KS 67260, United States
b Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 July 2011
Revised 16 August 2011
Accepted 24 August 2011
Available online 27 August 2011
A new class of compounds that exhibit anti-norovirus activity in a cell-based system and embody in their
structure a cyclosulfamide scaffold has been identified. The structure of the initial hit (compound 2a, ED50
4
l
M, TD50 50
lM) has been prospected by exploiting multiple points of diversity and generating appro-
priate structure–activity relationships.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Norwalk virus
Inhibitor
1. Introduction
N
O
R
N
S
O
Noroviruses are the most common cause of acute viral gastro-
enteritis outbreaks in the U.S. and worldwide.1–3 These outbreaks,
which occur primarily in hospitals, cruise ships, army barracks, and
schools, are the cause of significant morbidity and mortality,
particularly in children, the elderly, and immunocompromised
patients. There is currently an urgent and unmet need for the
discovery and development of effective therapeutics for the
treatment of norovirus infections.
As part of an ongoing program aimed at discovering novel
norovirus inhibitors, a subset of compounds from a pharmacologi-
cally-rich in-house library of compounds (ꢀ2000 compounds)
encompassing an array of peptidomimetics characterized by high
structural diversity, drug-like characteristics, and high synthetic
tractability was screened using a cell-based replicon system
(HG23 cells containing Norwalk virus [NV] replication unit),4–7 lead-
ing to the identification of several hits8 whose structures shared in
common the cyclosulfamide scaffold (I), a robust and versatile core
structure that embodies multiple points of diversity (Fig. 1). The
structural motif embodied in the sulfamide moiety is known to
promote enhanced binding, increased aqueous solubility, and better
bioavailability.9 The sulfamide moiety (–NHSO2NH–) can also
serve as a bioisosteric replacement of the sulfonamide moiety
(–SO2NH–)10 and is well-suited to the design of therapeutic agents.9
Consequently, a hit-to-lead optimization campaign was launched by
initiating structure–activity relationships (SARs) aimed at increas-
ing the potency of the identified hit and to understand the SAR
O
(I) (R=H, ED50: 4
M
µ
TD50: 50 µM)
Figure 1. General structure of cyclosulfamide inhibitors (I) and structure of initial
hit 2a (R = H).
landscape around the cyclosulfamide scaffold.11 We report herein
the results of studies related to the optimization of this series of
compounds.
2. Chemistry
The general strategy undergirding the hit-to-lead optimization
campaign entailed probing the effect of making sequential changes
in structure (I) (Fig. 1) on anti-norovirus activity. Specifically, the
(m-phenoxy)phenyl moiety in (I) was probed via the initial synthe-
sis of derivatives 2b–t (Scheme 1). These compounds were readily
synthesized by reductive amination of an appropriate aldehyde
with excess ethylediamine in the presence of sodium borohydride
in methanol12,13 to yield the corresponding N-substituted ethylene
diamine which, without isolation, was refluxed with sulfamide in
pyridine to form the corresponding N-substituted cyclosulfamide
⇑
Corresponding author. Tel.: +1 316 978 7374; fax: +1 316 978 3431.
E-mail address: bill.groutas@wichita.edu (W.C. Groutas).
0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2011.08.054

5976
D. Dou et al. / Bioorg. Med. Chem. 19 (2011) 5975–5983
O
H
i
ii
NH
O
NH2
N
NH
+
NH2
excess
S
H2N
R
O
R
R
2
1
R=
O
OH
O
F
O
O
O
O
a
b
c
d
e
f
g
O
O
O
SCH3
h
i
j
k
r
l
m
n
O
CF3
OCH3
Cl
OCH3
Cl
O
CF3
o
p
q
s
t
Scheme 1. Reagents and condition: (i) NaBH4/MeOH; (ii) NH2SO2NH2/pyridine/reflux 16 h.
Cl
i
ii
iii
Cl
NH2
NBoc
O
HN
NHBoc
O
HN
S
S
O
O
3
N
N
O
NH
NBoc
R=
S
S
O
NBoc
O
N
N
N
iv
N
N
v
O
S
O
O
N
N
R
R
6
5
4
OCH3
a
b
Scheme 2. Reagents and condition: (i) ClSO2NCO/t-BuOH/TEA/CH2Cl2; (ii) K2CO3/DMSO; (iii) NaH/propargyl bromide/DMF; (iv) RCH2N3/sodium ascorbate/CuSO4/t-BuOH/
H2O; (v) 4 M HCl in 1,4-dioxane.
2. Further structural variations in this segment of (I) included the
synthesis of derivatives 6a–b (Scheme 2) and 10–12 (Scheme 3).
In the case of compounds 6a–b, this involved the synthesis of
Boc-protected cyclosulfamide 313 followed by N-alkylation with
propargyl bromide. Subsequent Click chemistry14–16 with an array
of azides and deprotection of the resulting compounds with TFA,
yielded the desired compounds. Compounds 10–12 were readily
synthesized starting with the commercially available 3-(hydroxy-
methyl)piperidine. Treatment with benzylchlorofomate afforded
the protected alcohol 7 which was oxidized to the corresponding
aldehyde 8 with pyridinium chlorochromate.17 Reductive amina-
tion using excess ethylene diamine and sodium borohydride
yielded 9 which was cyclized to form 10 by refluxing with sulfam-
ide in pyridine. Subsequent catalytic hydrogenation gave com-
pound 11 which was alkylated with benzyl bromide by refluxing
in ethanol in the presence of sodium bicarbonate. The effect of
the nature of R (Fig. 1) was probed by generating a series of deriv-
atives of (I), as illustrated in Scheme 4. Thus, treatment of 2a with
sodium hydride in acetonitrile, followed by the addition of
Br(CH2)nCOOCH3 yielded esters 13a–f which were hydrolyzed with
LiOH/aqueous dioxane to yield the corresponding acids 14a–f.
Derivatives 13g–m were readily obtained by alkylating compound
2a (Scheme 4). Treatment of cyclosulfamide derivative 13a with
lithium borohydride yielded the corresponding alcohol which

D. Dou et al. / Bioorg. Med. Chem. 19 (2011) 5975–5983
5977
O
OH
OH
H
NH
NH2
i
iii
ii
NCbz
NH
NCbz
NCbz
9
7
8
N
NH
S
N
NH
N
NH
v
iv
S
vi
S
O
O
O
O
O
O
N
NCbz
NH
10
11
12
Scheme 3. Reagents and condition: (i) Benzyl chloroformate/TEA/THF; (ii) PCC/CH2CI2; (iii) excess ethylenediamine/NaBH4/MeOH; (iv) NH2SO2NH2/pyridine/reflux 16 h; (v)
H2/Pd-C; (vi) benzyl bromide/NaHCO3/EtOH, reflux.
O
O
OCH3
NH
O
N
O
X
N
O
OH
N
X
N
N
S
S
S
O
O
O
i
ii
O
O
O
13a-f
2a
14a-f
X = CH2
14a
X = CH2
13a
(CH2)2
14b
14c
14d
14e
14f
(CH2)2
13b
13c
13d
13e
13f
iii
(CH2)3
(CH2)3
(CH2)4
(CH2)6
(CH2)4
(CH2)6
N
O
R
N
CH2-p-C6H4
CH2-p-C6H4
S
O
R = methyl
ethyl
13g
13h
O
13i
13j
13k
cyanomethyl
benzyl
4-fluorobenzyl
3-pyridinemethyl 13l
13g-m
-CH2CONH2
13m
Scheme 4. Reagents: (i) NaH/ACN/BrXCOOCH3; (ii) LiOH/1,4-dioxane; (iii) NaH/ACN/RBr or RI.
N
N
N
OMs
iii
OH
ii
N
O
N
O
S
N
N
X
S
O
S
O
O
O
i
13a
O
O
O
X=O
17a
16
15
X=CH2 17b
Scheme 5. Reagents and condition: (i) LiBH4/THF/EtOH; (ii) MsCl/TEA/CH2CI2; (iii) RH/NaHCO3/95% EtOH/reflux.
was treated with CH3SO2Cl/TEA to yield the mesylate. Subsequent
refluxing of the mesylate with morpholine or piperidine in the
presence of sodium bicarbonate in 95% ethanol, gave compounds
17a–b (Scheme 5).

5978
D. Dou et al. / Bioorg. Med. Chem. 19 (2011) 5975–5983
Table 1
to optimizing pharmacological activity, a secondary but important
goal was to increase the aqueous solubility of the generated com-
pounds. Inspection of the data shown in Table 1 indicates that the
methyl esters were inactive, however, the corresponding carbox-
ylic acids were either active or inactive depending on the length
of the methylene chain (compare compounds 14a and 14d vs com-
pounds 14b–c and 14e–f, Table 1). With the exception of com-
pound 13l, the rest of the alkyl or arylalkyl-substituted
compounds (Table 1 compounds 13g–k and 13m) also lacked
activity. The morpholine and piperidine derivatives (Table 1 com-
pounds 17a–b) were active, however, their therapeutic indices
were lower than that of compound 2a ( Fig. 1, structure (I),
R = H). Taken together, the SAR studies indicate that structural
variations in multiple segments of structure (I) impact pharmaco-
logical activity and toxicity. The optimization process was gravely
hampered by the lack of information about the target of this class
of compounds. It should be noted that the anti-norovirus activity of
compound 2a does not arise from the inhibition of Norwalk virus
3C protease (unpublished data).18 Ongoing studies aimed at iden-
tifying the viral or cellular target of this class of compounds are
currently in progress.
Compound ED50
(
l
M) TD50
(
l
M) Compound ED50
(
l
M) TD50 (lM)
2a
2b
2c
2d
2e
2f
2g
2h
2i
4.1 1.2a
>10
5.2 1.5
> 10
5.8 2.1
5.2 1.7
9.8 3.2
>10
50 9.2
98 6.4
18 3.6
N/Db
57 4.2
96 4.9
12
>10
>10
>10
>10
9.7 2.2
>10
N/D
N/D
N/D
N/D
46 7.9
N/D
N/D
48 6.2
N/D
N/D
100
N/D
N/D
N/D
N/D
N/D
N/D
N/D
53 6.7
N/D
51 3.2
49 7.7
9.8 4.1
13a
13b
13c
13d
13e
159 11.6 13f
>10
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D
14a
14b
14c
14d
14e
14f
7.8 2.2
>10
>10
6.1 1.7
>10
>10
>10
2j
2k
2l
9.5 1.5
>10
>10
2m
2n
2o
2p
2q
2r
2s
2t
9.7 1.9
> 10
>10
>10
>10
> 10
>10
>10
13g
13h
13i
>10
>10
>10
13j
>10
13k
13l
13m
17a
17a
17b
>10
8.1 2.1
>10
4.2 1.8
5.4 1.7
4.3 1.3
5a
5b
6a
6b
>10
9.8 3.2
>10
In summary, a new class of anti-norovirus agents based on the
cyclosulfamide scaffold has been reported. The salient features
responsible for the pharmacological activity of these compounds
have been delineated via SAR studies.
>10
a
Mean value standard deviation with at least two independent experiments.
N/D: not determined due to high ED50 value.
b
5. Experimental section
3. Biochemical studies
5.1. General
The antiviral effects of the synthesized compounds were deter-
mined following previously described procedures using NV
replicon-harboring cells (HG23 cells)4–7 and the results are
summarized in Table 1. Detailed procedures for studying the anti-
viral effects using HG23 cells have been reported elsewhere4–7 (see
also Section 5).
The 1H spectra were recorded on a Varian XL-300 or XL-400
NMR spectrometer. Melting points were determined on
a
Mel-Temp apparatus and are uncorrected. High resolution mass
spectra (HRMS) were performed at University of Kansas Mass
Spectrometry Lab. Reagents and solvents were purchased from
various chemical suppliers (Aldrich, Acros Organics, TCI America,
and Bachem). Silica gel (230–450 mesh) used for flash chromatog-
raphy was purchased from Sorbent Technologies (Atlanta, GA).
Thin layer chromatography was performed using Analtech silica
gel plates to determine the compound purity. The TLC plates for
all the compounds were eluted using two different solvent systems
and visualized using iodine and/or UV light. Each individual
compound was identified as a single spot on TLC plate (purity
greater than 95%).
4. Results and discussion
4.1. General strategy and structure–activity relationships
The structure of the initial hit (Fig. 1, structure (I), R = H) was
used as a launching pad for the design and synthesis of structural
variants displaying improved pharmacological activity. We envi-
sioned accomplishing this goal by exploiting the multiple points
of diversity present in structure (I). Thus, structure (I) was system-
atically probed via the construction of focused libraries, an endea-
vor that was greatly facilitated by the synthetic tractability of this
series of compounds. Furthermore, a minimal number of chemical
modifications were initially carried out to prospect the entire
structure. Overall, an iterative approach involving the use of
medicinal chemistry and cell-based screening was utilized to at-
tain our objectives.
The import of the (m-phenoxy)phenyl moiety was probed by
using an array of structurally-diverse aldehydes to construct com-
pounds 2a–t (Scheme 1). It is clearly evident from Table 1 that
replacement of the m-phenoxy substituent has a profound and,
mostly, adverse effect on anti-norovirus activity. While there was
a modest improvement in the therapeutic index (TI) of some of
the compounds (e.g., compound 2f vs 2a, Table 1), in the majority
of cases activity was reduced or completely abolished. Replace-
ment of one of the aromatic rings in (I) by either a 1,2,3-triazole
ring or a piperidine ring yielded compounds that were devoid of
anti-norovirus activity (Table 1, compounds 6a–b, 12). The nature
of the R group in structure (I) was then investigated (Schemes 4
and 5). With respect to compounds 14a–f and 17a–b, in addition
5.1.1. Synthesis of compounds 2a–t
5.1.1.1. Representative synthesis. 2-(3-Phenoxybenzyl)-1,2,5-
thiadiazolidine 1,1-dioxide (2a). To a solution of ethylenediamine
(6.0 g; 100 mmol) in 65 mL methanol was added 3-(phenoxy)benz-
aldehyde (4.95 g; 25 mmol) in small portions under an ice-bath.
After the addition, sodium borohydride (0.94 g; 25 mmol) was
added slowly in small portions at 0 °C. The reaction was allowed
to warm to room temperature overnight. The solvent was removed
and the residue was taken up in ethyl acetate (100 mL) and water
(40 mL). The layers were separated and the organic layer was
washed with water (40 mL). The organic layer was dried over
anhydrous sodium sulfate. The drying agent was filtered and the
solvent was removed using a rotary evaporator to give pure com-
pound 1a as a colorless oil (6.0 g; 24.8 mmol; 99% yield). To a
refluxing solution of sulfamide (2.38 g; 24.8 mmol) in anhydrous
pyridine (60 mL) was slowly added compound 1a (6.0 g;
24.8 mmol) over 1 h. The resulting reaction mixture was refluxed
for an additional 16 h. Pyridine was removed under vacuum and
the residue was taken up in ethyl acetate (100 mL). The organic
layer was washed with 5% HCl (3 Â 50 mL), brine (50 mL) and then
dried over anhydrous sodium sulfate. The drying agent was filtered

D. Dou et al. / Bioorg. Med. Chem. 19 (2011) 5975–5983
5979
off and the solvent was evaporated, leaving a crude product which
was purified using flash chromatography (silica gel/ethyl acetate/
hexanes) to give pure compound 2a as a yellow oil (6.3 g; 83%
5.1.1.10. 2-(4-Butoxybenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2j). Yellow solid (75% yield), mp 49–50 °C. 1H NMR (CDCl3): d
0.97 (t, J = 7.3 Hz, 3H), 1.43–1.56 (m, 2H), 1.72–1.81 (m, 2H), 3.25
(t, J = 6.2 Hz, 2H), 3.46 (q, J = 6.7 Hz, 2H), 3.95 (t, J = 5.5 Hz, 2H),
4.12 (s, 2H), 4.29 (s, 1H), 6.87 (d, J = 9.1 Hz, 2H), 7.27 (d,
yield). 1H NMR (CDCl3):
d 3.29 (t, J = 6.2 Hz, 2H), 3.47 (q,
J = 7.2 Hz, 2H), 4.16 (s, 2H), 4.44 (s, 1H), 6.90–7.40 (m, 9H). HRMS
(ESI): calculated m/z for C15H16N2O3S [M+Na]+ 327.0779; found
327.0779.
J = 9.1 Hz, 2H). HRMS (ESI) calculated m/z for
C13H20N2O3S
[M+Na]+ 307.1092; found 307.1094.
5.1.1.2.
2-[3-(4-Fluorophenoxy)benzyl]-1,2,5-thiadiazolidine
5.1.1.11. 2-(4-Propylbenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2k). White solid (60% yield), mp 52–53 °C. 1H NMR (CDCl3): d
0.94 (t, J = 6.7 Hz, 3H), 1.57–1.70 (m, 2H), 2.58 (t, J = 7.8 Hz, 2H),
3.38 (t, J = 6.1 Hz, 2H), 3.49 (q, J = 6.7 Hz, 2H), 4.15 (s, 2H), 4.36
(s, 1H), 7.17 (d, J = 7.4 Hz, 2H), 7.28 (d, J = 7.4 Hz, 2H). HRMS (ESI)
1,1-dioxide (2b). Yellow oil (74% yield). 1H NMR (CDCl3): d 3.29
(t, J = 6.3 Hz, 2H), 3.50 (q, J = 6.0 Hz, 2H), 4.15 (s, 2H), 4.37
(t, J = 5.7 Hz, 1H), 6.87–7.13 (m, 6H), 7.25–7.34 (m, 2H). HRMS
(ESI): calculated m/z for C15H15FN2O3S [M+Na]+ 345.3444; found
345.0685.
calculated m/z for
C
12H18N2O2S [M+Na]+ 277.0987; found
277.0991.
5.1.1.3. 2-[3-(Benzyloxy)benzyl]-1,2,5-thiadiazolidine 1,1-diox-
ide (2c). Colorless oil (85% yield). 1H NMR (CDCl3): d 3.23 (t,
J = 7.0 Hz, 2H), 3.44 (q, J = 7.0 Hz, 2H), 4.13 (s, 2H), 4.42 (t,
J = 6.0 Hz, 1H), 6.82–7.03 (m, 3H), 7.20–7.44 (m, 6H). HRMS (ESI):
calculated m/z for
341.0936.
5.1.1.12. 2-(4-Butylbenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2l). White solid (67% yield), mp 40–41 °C. 1H NMR (CDCl3): d
0.92 (t, J = 7.1 Hz, 3H), 1.25–1.42 (m, 2H), 1.52–1.65 (m, 2H), 2.62
(t, J = 6.8 Hz, 2H), 3.27 (t, J = 6.0 Hz, 2H), 3.48 (q, J = 6.9 Hz, 2H),
4.15 (s, 2H), 4.39 (s, 1H), 7.16 (d, J = 7.1 Hz, 2H), 7.27 (d.
C
16H18N2O3S [M+Na]+ 341.3805; found
J = 7.1 Hz, 2H). HRMS (ESI) calculated m/z for
C13H20N2O2S
5.1.1.4. 2-[3-(Hydroxy)benzyl]-1,2,5-thiadiazolidine 1,1-dioxide
(2d). To a solution of compound 2c (0.23 g; 0.72 mmol) in metha-
nol (20 mL) was added Pd-C (10% w/w; 0.05 g) and applied 20
psi hydrogen gas on a Parr hydrogenator for 12 h. The catalyst
was filtered off and the solvent was removed, leaving pure com-
pound 2d as a colorless oil (100% yield). 1H NMR (CDCl3): d 3.29
(t, J = 6.6 Hz, 2H), 3.50 (q, J = 6.5 Hz, 2H), 4.13 (s, 2H), 4.42
(s, 1H), 5.27 (s, 1H), 6.77–6.94 (m, 3H), 7.20–7.26 (m, 1H). HRMS
(ESI): calculated m/z for C9H12N2O3S [M+Na]+ 251.2579; found
251.0466.
[M+Na]+ 291.1143; found 291.1152.
5.1.1.13.
1,1-dioxide (2m). White solid (66% yield), mp 62–63 °C. 1H NMR
(CDCl3): 0.91 (d, J = 7.5 Hz, 6H), 1.80–1.92 (m, 1H), 2.48
2-[4-(2-Methylpropyl)benzyl]-1,2,5-thiadiazolidine
d
(d, J = 6.7 Hz, 2H), 3.26 (t, J = 5.9 Hz, 2H), 3.44 (q, J = 6.8 Hz, 2H),
4.15 (s, 2H), 4.26 (s, 1H), 7.16 (d, J = 8.6 Hz, 2H), 7.26
(d, J = 8.6 Hz, 2H). HRMS (ESI) calculated m/z for C13H20N2O2S
[M+Na]+ 291.1143; found 291.1143.
5.1.1.14. 2-[4-(Methylsulfanyl)benzyl]-1,2,5-thiadiazolidine 1,1-
5.1.1.5. 2-(4-Phenoxybenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2e). White solid (59% yield), mp 110–112 °C. 1H NMR (CDCl3): d
3.30 (t, J = 7.2 Hz, 2H), 3.49 (q, J = 7.8 Hz, 2H), 4.15 (s, 2H), 4.34
(s, 1H), 6.94–7.41 (m, 9H). HRMS (ESI) calculated m/z for
dioxide (2n). Yellow solid (78% yield), mp 133–135 °C, 1H NMR
(CDCl3):
d 2.48 (s, 3H), 3.26 (t, J = 18.8 Hz, 2H), 3.45 (q,
J = 28.1 Hz, 2H), 4.16 (s, 2H), 4.29 (t, J = 28.1 Hz, 1H), 7.21–7.34
(m, 4H). HRMS (ESI) calculated m/z for C10H14N2O2S2 [M+Na]+
281.0394; found 281.0396.
C
15H16N2O3S [M+Na]+ 327.0779; found 327.0764.
5.1.1.6. 2-(4-Propoxybenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2f). Yellow oil (22% yield). 1H NMR (CDCl3): d 1.02 (t, J = 18.2 Hz,
3H), 1.72–1.88 (m, 2H), 3.25 (t, J = 18.2 Hz, 2H), 3.34 (q,
J = 27.3 Hz, 2H), 3.91 (t, J = 18.2 Hz, 2H), 4.10 (s, 2H), 4.41 (t,
J = 27.3 Hz, 1H), 6.87 (d, 2H), 7.26 (d, 2H). HRMS (ESI) calculated
m/z for C12H18N2O3S [M+Na]+ 293.0936; found 293.0935.
5.1.1.15. 2-[4-(Trifluoromethoxy)benzyl]-1,2,5-thiadiazolidine
1,1-dioxide (2o). Colorless oil (92% yield). 1H NMR (CDCl3): d
3.30 (t, J = 6.6 Hz, 2H), 3.52 (s, 2H), 4.20 (s, 2H), 4.55 (s, 2H), 7.22
(d, J = 8.2 Hz, 2H), 7.42 (d, J = 8.2 Hz, 2H).
5.1.1.16. 2-[3-(Trifluoromethoxy)benzyl]-1,2,5-thiadiazolidine
1,1-dioxide (2p). Yellow oil (22% yield). 1H NMR (CDCl3): d 3.30
(t, J = 5.9 Hz, 2H), 3.51 (q, J = 6.8 Hz, 2H), 4.20 (s, 2H), 4.63 (s,
1H), 7.17–7.43 (m, 4H). HRMS (ESI) calculated m/z for
5.1.1.7. 2-[4-(Benzyloxy)benzyl]-1,2,5-thiadiazolidine 1,1-diox-
ide (2g). Brown solid (52% yield), mp 85–87 °C. 1H NMR (CDCl3): d
3.25(t, J = 18.2 Hz, 2H), 3.44 (q, J = 27.3 Hz, 2H), 4.10 (s, 2H), 5.05 (s,
2H), 6.95 (d, 2H), 7.28–7.48 (m, 7H). HRMS (ESI) calculated m/z for
C
10H11F3N2O3S [M+Na]+ 319.0340; found 319.0344.
C
16H18N2O3S [M+Na]+ 341.0936; found 341.0924.
5.1.1.17. 2-(3-Chlorobenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2q). Yellow oil (83% yield). 1H NMR (CDCl3): d 3.29 (t, J = 6.4 Hz,
2H), 3.52 (q, J = 6.9 Hz, 2H), 4.16 (s, 2H), 4.43 (s, 1H), 7.23–7.41
(m, 4H). HRMS (ESI) calculated m/z for C9H11ClN2O2S [M+Na]+
269.0127; found 269.0143.
5.1.1.8. 2-(4-Ethoxybenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2h). Yellow oil (89% yield). 1H NMR (CDCl3): d 1.43 (t, J = 6.8 Hz,
3H), 3.29 (t, J = 6.2 Hz, 2H), 3.48 (q, J = 6.8 Hz, 2H), 4.05 (q,
J = 7.2 Hz, 2H), 4.14 (s, 2H), 4.40 (s, 1H), 6.80–6.94 (m, 3H), 7.22–
7.28 (m, 1H). HRMS (ESI) calculated m/z for
C11H16N2O3S
[M+Na]+ 279.0779; found 279.0804.
5.1.1.18. 2-(3-Methoxybenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2r). Yellow oil (36% yield), 1H NMR (CDCl3): d 3.28 (t, J = 18.2 Hz,
2H), 3.48 (q, J = 27.3 Hz, 2H), 3.81 (s, 3H), 4.15 (s, 3H), 6.82–6.97
(m, 3H), 7.29–7.32 (m, 1H). HRMS (ESI) calculated m/z for
5.1.1.9. 2-[4-(Propan-2-yloxy)benzyl]-1,2,5-thiadiazolidine 1,1-
dioxide (2i). Yellow oil (76% yield). 1H NMR (CDCl3): d 1.33 (d,
J = 5.9 Hz, 6H), 3.26 (t, J = 6.4 Hz, 2H), 3.45 (q, J = 6.7 Hz, 2H), 4.11
(s, 2H), 4.37 (s, 1H), 4.51–4.60 (m, 1H), 6.86 (d, J = 9.0 Hz, 2H),
7.24 (d, J = 9.0 Hz, 2H). HRMS (ESI) calculated m/z for C12H18N2O3S
[M+Na]+ 293.0936; found 293.0926.
C
10H14N2O3S [M+H]+ 243.0803; found 243.0811.
5.1.1.19. 2-(4-Methoxybenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2s). Colorless oil (87% yield). 1H NMR (CDCl3): d 3.25 (t, J = 5.7 Hz,

5980
D. Dou et al. / Bioorg. Med. Chem. 19 (2011) 5975–5983
2H), 3.45 (q, J = 6.5 Hz, 2H), 3.80 (s, 3H), 4.12 (s, 2H), 4.36 (s, 1H),
6.88 (d, J = 9.7 Hz, 2H), 7.37 (d, J = 9.7 Hz, 2H). HRMS (ESI) calcu-
lated m/z for C10H14N2O3S [M+Na]+ 265.0623; found 265.0615.
2H), 7.23–7.40 (m, 5H), 7.62 (s, 1H). HRMS (ESI) calculated m/z
for C17H23N5O4S [M+Na]+ 416.1368; found 416.1353.
5.1.2.2. tert-Butyl 5-[(1-(4-methoxybenzyl)-1H-1,2,3-triazol-4-
5.1.1.20. 2-(4-Chlorobenzyl)-1,2,5-thiadiazolidine 1,1-dioxide
(2t). White solid (52% yield), mp 90–91 °C. 1H NMR (CDCl3): d
3.28 (t, J = 5.7 Hz, 2H), 3.50 (q, J = 6.9 Hz, 2H), 4.17 (s, 2H), 3.55
(s, 1H), 7.23–7.40 (m, 4H). HRMS (ESI) calculated m/z for
C9H11ClN2O2S [M+Na]+ 269.0127; found 269.0147.
yl)methyl]-1,2,5-thiadiazoli-dine-2-carboxylate
1,1-dioxide
(5b)
.
White solid (23% yield), mp 129–131 °C. 1H NMR (CDCl3): d
1.55 (s, 9H), 3.43 (t, J = 11.8 Hz, 2H), 3.71 (t, J = 11.8 Hz, 2H), 4.40
(s, 2H), 5.58 (s, 2H), 7.26–7.38 (m, 1H), 7.60 (d, J = 8.2 Hz, 1H),
7.69 (s, 1H), 8.60 (s, 2H). HRMS (ESI) calculated m/z for
C
18H25N5O5S [M+Na]+ 446.1474; found 446.1458.
5.1.1.21. tert-Butyl 1,2,5-thiadiazolidine-2-carboxylate 1,1-diox-
ide (3)
.
To
a
stirred solution of N-chlorosulfonyl isocyanate
5.1.2.3. 2-[(1-Benzyl-1H-1,2,3-triazol-4-yl)methyl]-1,2,5-thiadia
zolidine 1,1-dioxide (6a). Compound 5a (0.16 g; 0.4 mmol) was
added 10 ml 4 M HCl in 1,4-dioxane, and the reaction was at room
temperature for 30 min. Solvent was removed, leaving a colorless
oil, which was purified by flash chromatography (silica gel/ethyl
acetate/hexanes) to give compound 6a as white solid (100% yield)
mp 88–90 °C 1H NMR (CDCl3): d 3.38–3.52 (m, 4H), 4.3 (s, 2H), 4.8
(t, J = 10.2 Hz, 1H), 5.54 (s, 2H), 7.22–7.41 (m, 5H), 7.6 (s, 1H).
HRMS (ESI) calculated m/z for C12H15N5O2S [M+Na]+ 316.0844;
found 316.0829.
(10.00 g; 70 mmol) in 200 mL dry methylene chloride was added
dropwise a solution of t-butanol (6.11 g; 82.5 mmol) in 20 mL
methylene chloride at 0 °C. The resulting reaction mixture was stir-
red for an additional 30 min. The above solution and triethylamine
(35.46 g; 350 mmol) were added dropwise to a suspension of 2-
chloroethylamine hydrochloride (9.57 g; 82.5 mmol) in 75 mL dry
methylene chloride at 0 °C. The reaction mixture was allowed to
warm to room temperature and stirred overnight. Methylene chlo-
ride (250 mL) was added to the reaction mixture and the resulting
mixture was washed with 5% HCl until pH neutral, and then
washed with brine (150 ml). The organic layer was dried over
anhydrous sodium sulfate. The drying agent was filtered off and
the solvent was removed under vacuum, leaving a colorless oil
(17.0 g). The oil was dissolved in dry DMSO (80 mL) and anhydrous
K2CO3 (55.20 g; 400 mmol) was added. The mixture was stirred at
room temperature overnight. Water (400 mL) was added and the
product was extracted with ethyl acetate (3 Â 200 mL). The com-
bined organic layers were washed with brine (100 mL) and dried
over anhydrous sodium sulfate. The drying agent was filtered off
and the solvent was removed to give compound 3 as a white solid
(6.5 g; 42% yield), mp 140–141 °C. 1H NMR (CDCl3): d 1.53 (s, 9H),
3.46 (t, J = 7.1 Hz, 2H), 3.83 (t, J = 7.1 Hz, 2H).
Compound 6b was prepared using the same procedure as that
used in the synthesis of compound 6a.
5.1.2.4. 2-{[1-(4-Methoxybenzyl)-1H-1,2,3-triazol-4-yl]methyl}-
1,2,5-thiadiazolidine 1,1-dioxide (6b). White solid (0.21 g; 100%
yield), mp 126–128 °C 1H NMR (CDCl3): d 3.4 (s, 4H), 3.82 (s, 3H),
4.3 (d, J = 8.6 Hz, 2H), 5.45 (s, 2H), 6.92 (d, J = 9.0 Hz, 2H), 7.26 (d,
J = 9.0 Hz, 2H), 7.68 (s, 1H). HRMS (ESI) calculated m/z for
C
13H17N5O3S [M+Na]+ 346.0950; found 346.0934.
5.1.2.5. Benzyl 3-(hydroxymethyl)piperidine-1-carboxylate (7).
To a chilled solution of 3-(hydroxymethyl)piperidine (0.61 g;
5 mmol) in methylene chloride (10 mL) was added triethylamine
(0.51 g; 5 mmol), followed by the dropwise addition of benzyl
chloroformate (0.88 g; 5 mmol). The resulting reaction mixture
was allowed to warm to room temperature and stirred overnight.
Methylene chloride (50 mL) was added to the reaction and the or-
ganic layer was washed with 5% HCl (2 Â 20 mL), saturated NaH-
CO3 (20 mL) and brine (20 mL). The organic layer was dried over
anhydrous sodium sulfate. The drying agent was filtered off and
the solvent was removed. The crude product was purified using
flash chromatography (silica gel/ethyl acetate/hexanes) to give
compound 7 as a colorless oil (1.21 g; 96% yield). 1H NMR (CDCl3):
d 1.20–1.83 (m, 5H), 2.78–3.20 (m, 2H), 3.50 (s, 2H), 3.69–4.05 (m,
2H), 5.14 (s, 2H), 7.25–7.40 (m, 5H).
5.1.1.22. tert-Butyl 5-(prop-2-yn-1-yl)-1,2,5-thiadiazolidine-2-
carboxylate 1,1-dioxide (4).To a chilled solution of compound 3
(2.22 g; 10 mmol) in dry DMF (10 mL) was added NaH (60% w/w;
0.4 g; 10 mmol) portion wise. The reaction mixture was stirred
for 0.5 h before adding propargyl bromide (1.18 g; 10 mmol). The
reaction mixture was stirred at room temperature overnight. The
solvent was removed and the residue was taken up in ethyl acetate
(30 mL). The ethyl acetate solution was washed with 5% HCl
(3 Â 20 mL), saturated NaHCO3 (20 mL) and brine (20 mL). The or-
ganic layer was dried over anhydrous sodium sulfate. The drying
agent was filtered and the solvent was removed, yielding com-
pound 4 as a brown oil (2.46 g; 95% yield). 1H NMR (CDCl3): d
1.55 (s, 9H), 2.40 (t, J = 2.7 Hz, 1H), 3.45–3.56 (m, 2H), 3.83–3.94
(m, 4H).
5.1.2.6. Benzyl 3-formylpiperidine-1-carboxylate (8). To a sus-
pension of pyridinium chlorochromate (0.65 g; 3 mmol) in 10 ml
methylene chloride was added compound 7 (0.50 g; 2 mmol) in
methylene chloride (5 mL). The reaction was stirred at room tem-
perature for 2 h and filtered. The filtrate was evaporated and the
residue was treated with diethyl ether (25 mL). The precipitate
was filtered off again and the filtrate was evaporated, leaving pure
product 8 as a pink oil (0.50 g; 90% yield). 1H NMR (CDCl3): d 1.42–
1.78 (m, 3H), 2.00 (br s, 1H), 2.43 (br s, 1H), 3.08–3.20 (m, 1H),
3.33–3.41 (m, 1H), 3.71–3.82 (m, 1H), 3.92–4.10 (m, 1H), 5.13 (s,
2H), 7.27–7.42 (m, 5H), 9.68 (s, 1H).
5.1.2. Synthesis of compounds 5a–b
5.1.2.1. Representative synthesis. tert-Butyl 5-[(1-benzyl-1H-
1,2,3-triazol-4-yl)methyl]-1,2,5-thiadiazolidine-2-carboxylate
1,1-dioxide (5a). To a solution of compound 4 (0.52 g; 2 mmol)
and benzyl azide (0.27 g; 2 mmol) in 6 mL 1:1 t-butanol and water
was added sodium ascorbate (0.10 g; 1 mmol) and a catalytic
amount of CuSO4. The reaction was stirred at room temperature
overnight. The solvent was removed and the residue was taken
up in ethyl acetate (30 mL). The organic layer was washed with
brine (2 Â 20 mL) and dried over anhydrous sodium sulfate. The
drying agent was filtered off and the solvent was removed. The
crude product was purified using flash chromatography (silica
gel/ethyl acetate/hexanes) to give compound 5a as a white solid
(41% yield), mp 149–151 °C. 1H NMR (CDCl3): d 1.53 (s, 9H), 3.44
(t, J = 11.9 Hz, 2H), 3.69 (t, J = 11.9 Hz, 2H), 4.38 (s, 2H), 5.53 (s,
Compounds 9 and 10 were prepared using the same procedure
as that used in the synthesis of compounds 1a and 2a.
5.1.2.7. Benzyl 3-{[(2-aminoethyl)amino]methyl}piperidine-1-
carboxylate (9). Colorless oil (52% yield). 1H NMR (CDCl3): d 1.40–
1.90 (m, 5H), 2.42–2.80 (m, 7H), 2.87–2.98 (m, 1H), 3.90–4.10 (m,
2H), 5.14 (s, 2H), 7.28–7.39 (m, 5H).

D. Dou et al. / Bioorg. Med. Chem. 19 (2011) 5975–5983
5981
5.1.2.8. Benzyl 3-[(1,1-dioxido-1,2,5-thiadiazolidin-2-yl)methyl]
piperidine-1-carboxylate (10). Brown oil (70% yield). 1H NMR
(CDCl3): d 1.12–1.33 (m, 1H), 1.36–1.57 (m, 1H), 1.60–1.92 (m,
3H), 2.58–3.02 (m, 4H), 3.18–3.54 (m, 4H), 3.88–4.20 (2H), 5.12
(s, 2H), 7.36 (s, 5H).
6.92–7.40 (m, 9H). HRMS (ESI) calculated m/z for C21H26N2O5S
[M+H]+ 419.1641; found 419.1658.
5.1.3.5. Methyl 7-[5-(3-phenoxybenzyl)-1,1-dioxido-1,2,5-thi-
adiazolidin-2-yl]heptanoate (13e). Colorless oil (36% yield). 1H
NMR (CDOD): d 1.24 (t, J = 6.7 Hz, 3H), 1.31–1.46 (m, 4H), 1.55–
1.67 (m, 4H), 2.30 (t, J = 7.7 Hz, 2H), 3.04 (t, J = 7.7 Hz, 2H), 3.17–
3.28 (m, 4H), 4.07–4.18 (m, 4H), 6.89–7.37 (m, 9H). HRMS (ESI)
calculated m/z for C23H30N2O5S [M+H]+ 447.1954; found 447.1964.
5.1.2.9. 3-[(1,1-Dioxido-1,2,5-thiadiazolidin-2-yl)methyl]piperi-
dine (11). To a stirred solution of compound 10 (0.71 g; 2 mmol) in
methanol (20 mL) was added Pd-C (10% w/w; 0.13 g) and applied
20 psi hydrogen gas on a Parr hydrogenator overnight. The reaction
mixture was filtered through a pad of Celite and the filtrate was
evaporated to give pure compound 11 as a colorless oil (0.45 g;
100% yield). 1H NMR (CDCl3): d 1.04–1.18 (m, 1H), 1.40–1.56 (m,
1H), 1.66–1.90 (m, 3H), 2.28–2.37 (m, 1H), 2.52–2.62 (m, 1H),
2.78–2.95 (m, 2H), 2.97–3.06 (m, 1H), 3.26–3.33 (m, 1H), 3.30–
3.53 (m, 4H).
5.1.3.6. Methyl 4-[(5-(3-phenoxybenzyl)-1,1-dioxido-1,2,5-thi-
adiazolidin-2-yl)methyl]-benzoate 13f. White solid (63% yield),
mp 72–73 °C. 1H NMR (CDCl3): d 3.18 (s, 4H), 3.90 (s, 3H), 4.20
(s, 2H), 4.25 (s, 2H), 6.89–7.37 (m, 9H), 7.43 (d, J = 8.7 Hz, 2H),
8.02 (d, J = 8.7 Hz, 2H). HRMS (ESI) calculated m/z for C24H24N2O5S
[M+Na]+ 475.1304; found 475.1305.
5.1.2.10. 1-Benzyl-3-[(1,1-dioxido-1,2,5-thiadiazolidin-2-yl)me
thyl]piperidine (12). A mixture of compound 11 (0.33 g; 1.5 mmol),
benzyl bromide (0.26 g; 1.5 mmol) and NaHCO3 (0.38 g; 4.5 mmol)
in dry DMF (5 mL) was stirred for 2 days. DMF was removed in vacuo
and the residue was treated with 5% HCl (20 mL). The solution was
extracted with ethyl acetate (2 Â 20 mL) to remove impurities. The
aqueous layer was adjusted to pH 9 with 1 N NaOH, whereupon a
precipitate formed. The precipitate was collected by vacuum filtra-
tion and air dried to give compound 12 as a white solid (0.47 g;
49% yield), mp 100–101 °C. 1H NMR (CDCl3): d 0.49–2.07 (m, 5H),
2.64–2.75 (m, 1H), 2.83 (d, J = 8.7 Hz, 1H), 2.92 (d, J = 7.6 Hz, 2H),
3.29–3.58 (m, 8H), 4.23 (s, 1H), 7.20–7.34 (m, 5H). HRMS (ESI) calcu-
lated m/z for C15H23N3O2S [M+Na]+ 332.1409; found 332.1408.
5.1.3.7.
2-Methyl-5-(3-phenoxybenzyl)-1,2,5-thiadiazolidine
1,1-dioxide (13g). Colorless oil (80% yield). 1H NMR (CDCl3): d
2.77 (s, 3H), 3.17–3.30 (m, 4H), 4.19 (s, 2H), 6.90–7.40 (m, 9H).
HRMS (ESI) calculated m/z for C16H18N2O3S [M+Na]+ 341.0936;
found 341.0937.
5.1.3.8. 2-Ethyl-5-(3-phenoxybenzyl)-1,2,5-thiadiazolidine 1,1-
dioxide (13h). Colorless oil (51% yield). 1H NMR (CDCl3): d 1.26 (t,
J = 6.4 Hz, 3H), 3.08–3.29 (m, 6H), 4.17 (s, 2H), 6.89–7.39 (m, 9H).
HRMS (ESI) calculated m/z for C17H20N2O3S [M+Na]+ 355.1092;
found 355.1085.
5.1.3.9. [5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazolidin-
2-yl]acetonitrile (13i). White solid (85% yield), mp 80–81 °C. 1H
NMR (CDCl3): d 3.30 (t, J = 6.3 Hz, 2H), 3.49 (t, J = 6.3 Hz, 2H),
4.04 (s, 2H), 4.19 (s, 2H), 6.92–7.40 (m, 9H). HRMS (ESI) calculated
m/z for C17H17N3O3S [M+H]+ 344.1069; found 344.1072.
5.1.3. Synthesis of compounds 13a–m
5.1.3.1. Representative synthesis. Methyl [5-(3-phenoxybenzyl)-
1,1-dioxido-1,2,5-thiadiazolidin-2-yl]acetate (13a). To a solution
of compound 2a (7.3 g; 24 mmol) in dry DMF (50 mL) was added
sodium hydride (1.28 g; 60% w/w; 31.2 mmol) at 0 °C. After stirring
the reaction mixture for 0.5 h, methyl bromoacetate (4.03 g;
326.4 mmol) was added and the reaction mixture was stirred at
room temperature overnight. DMF was removed under vacuum
and the residue was taken up in ethyl acetate (200 mL). The organ-
ic layer was washed with 5% HCl (2 Â 100 mL), brine (100 mL) and
then dried over anhydrous sodium sulfate. The drying agent was
filtered off and the solvent was removed to give product 13a as a
light yellow solid (8.3 g; 92% yield), mp 69–71 °C. 1H NMR (CDCl3):
d 3.26 (t, J = 5.4 Hz, 2H), 3.54 (t, J = 5.4 Hz, 2H), 3.78 (s, 3H), 3.89 (s,
2H), 4.19 (s, 2H), 6.92–7.40 (m, 9H). HRMS (ESI) calculated m/z for
5.1.3.10.
2-Benzyl-5-(3-phenoxybenzyl)-1,2,5-thiadiazolidine
1,1-dioxide (13j). Yellow oil (79% yield). 1H NMR (CDCl3): d 3.17
(s, 4H), 4.20 (s, 2H), 4.21 (s, 2H), 6.91–7.40 (m, 14H). HRMS (ESI)
calculated m/z for C22H22N2O3S [M+Na]+ 417.1249; 417.1231.
5.1.3.11.
2-(4-Fluorobenzyl)-5-(3-phenoxybenzyl)-1,2,5-thi-
adiazolidine 1,1-dioxide (13k). Yellow oil (61% yield). 1H NMR
(CDCl3): d 3.17 (s, 4H), 4.18 (s, 2H), 4.19 (s, 2H), 6.89–7.38 (m,
13H). HRMS (ESI) calculated m/z for
413.1335; found 413.1338.
C
22H21FN2O3S [M+H]+
C
18H20N2O5S [M+Na]+ 399.0991; found 399.0984.
5.1.3.12. 3-{[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazoli-
din-2-yl]methyl}pyridine (13l). White solid (75% yield), mp 60–
61 °C. 1H NMR (CDCl3): d 3.09 (s, 4H), 4.20 (s, 2H), 4.24 (s, 2H),
6.93–7.40 (m, 10H), 7.76–7.80 (m, 1H), 8.58–8.62 (m, 2H). HRMS
(ESI) calculated m/z for C21H21N3O3S [M+H]+ 396.1382; found
396.1378.
5.1.3.2. Methyl 3-[5-(3-phenoxybenzyl)-1,1-dioxido-1,2,5-thi-
adiazolidin-2-yl]propanoate (13b). Yellow oil (80% yield). 1H
NMR (CDCl3): d 2.71 (t, J = 5.7 Hz, 2H), 3.18 (t, J = 5.7 Hz, 2H),
2.23–3.53 (m, 4H), 3.72 (s, 3H), 4.17 (s, 2H), 6.92–7.40 (m, 9H).
HRMS (ESI) calculated m/z for C19H22N2O5S [M+H]+ 391.1328;
found 391.1338.
5.1.3.13. 2-[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazoli-
din-2-yl]acetamide (13m). White solid (80% yield), mp 122–
5.1.3.3. Methyl 4-[5-(3-phenoxybenzyl)-1,1-dioxido-1,2,5-thi-
adiazolidin-2-yl]butyrate (13c). Yellow oil (76% yield). 1H NMR
(CDCl3): d 1.95 (t, J = 6.5 Hz, 2H), 2.44 (t, J = 7.0 Hz, 2H), 3.07–
3.32 (m, 6H), 3.68 (s, 2H), 4.15 (s, 2H), 6.88–7.38 (m, 9H). HRMS
(ESI) calculated m/z for C20H24N2O5S [M+H]+ 405.1484; found
405.1469.
123 °C. 1H NMR (CDCl3):
d 3.26 (t, J = 6.3 Hz, 2H), 3.44 (t,
J = 6.3 Hz, 2H), 3.80 (s, 2H), 4.18 (s, 2H), 5.60 (s, 1H), 6.60 (s, 1H),
6.94–7.40 (m, 9H). HRMS (ESI) calculated m/z for C17H19N3O4S
[M+H]+ 362.1175; found 362.1179.
5.1.4. Synthesis of compounds 14a–f
5.1.4.1. Representative synthesis. [5-(3-Phenoxybenzyl)-1,1-
dioxido-1,2,5-thiadiazolidin-2-yl]acetic acid (14a). Compound
13a (0.30 g; 0.8 mmol) was dissolved in dry 1,4-dioxane (8 mL)
and 6 mL 1 M LiOH and the reaction was stirred at room tempera-
ture for 1 h. TLC indicated the completion of hydrolysis. The
5.1.3.4. Methyl 5-[5-(3-phenoxybenzyl)-1,1-dioxido-1,2,5-thi-
adiazolidin-2-yl]pentanoate (13d). Yellow oil (100% yield). 1H
NMR (CDCl3): d 1.64–1.78 (m, 4H), 2.38 (t, J = 6.2 Hz, 2H), 3.07
(t, J = 6.2 Hz, 2H), 3.17–3.32 (m, 4H), 3.67 (s, 3H), 4.18 (s, 2H),

5982
D. Dou et al. / Bioorg. Med. Chem. 19 (2011) 5975–5983
solvent was removed and the residue was taken up in water
(20 mL). The aqueous solution was extracted with ethyl acetate
(2 Â 15 mL) to remove any remaining starting material. The aque-
ous layer was adjusted to pH 1 and extracted with ethyl acetate
(2 Â 20 mL). The combined organic extracts were dried over anhy-
drous sodium sulfate. The drying agent was filtered off and the sol-
vent was removed to give pure compound 14a as a colorless oil
(0.19 g; 63% yield). 1H NMR (CDCl3): d 3.26 (t, J = 6.1 Hz, 2H),
3.52 (t, J = 6.1 Hz, 2H), 3.96 (s, 2H), 4.17 (s, 2H), 6.89–7.38 (m,
9H), 9.75 (br s, 1H). HRMS (ESI) calculated m/z for C17H18N2O5S
[MÀH]+ 361.0858; found 361.0871.
temperature and stirred overnight. Additional methylene chloride
(10 mL) was added to the reaction and the solution was washed
with saturated sodium bicarbonate (2 Â 20 mL). The organic layer
was separated and dried over anhydrous sodium sulfate. The dry-
ing agent was filtered off and the solvent was removed to give
compound 16 as a colorless oil (1.58 g; 100% yield). 1H NMR
(CDCl3): d 3.07 (s, 3H), 3.23 (t, J = 6.0 Hz, 2H), 3.40–3.46 (m, 4H),
4.17 (s, 2H), 4.44 (t, J = 4.5 Hz, 2H), 6.92–7.39 (m, 9H).
5.1.4.9. 4-{2-[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazoli
din-2-yl]ethyl}morpholine (17a). A mixture of compound 16
(0.92 g; 2.2 mmol), morpholine (0.19 g; 2.2 mmol) and anhydrous
sodium bicarbonate (1.0 g; 12 mmol) in 95% ethanol (10 mL) was
refluxed overnight. The solvent was removed and the residue
was taken up with ethyl acetate (30 mL) and water (30 mL). The or-
ganic layer was separated and washed with brine (30 mL). The or-
ganic layer was dried over anhydrous sodium sulfate. The drying
agent was filtered off and the solvent was removed to give pure
compound 17a as a colorless oil (0.92 g; 100% yield). 1H NMR
(CDCl3): d 2.51 (t, J = 5.0 Hz, 4H), 2.63 (t, J = 5.8 Hz, 2H), 3.20 (q,
J = 6.5 Hz, 4H), 3.39 (t, J = 6.3 Hz, 2H), 3.71 (t, J = 4.3 Hz, 2H), 4.19
(s, 2H), 6.92–7.39 (m, 9H). HRMS (ESI) calculated m/z for
5.1.4.2. 3-[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazolidi
n-2-yl]propionic acid (14b). Colorless oil (82% yield). 1H NMR
(CDCl3): d 2.77 (t, J = 6.8 Hz, 2H), 3.20 (t, J = 6.8 Hz, 2H), 3.32–
3.45 (m, 4H), 4.16 (s, 2H), 6.92–7.38 (m, 9H). HRMS (ESI) calculated
m/z for C18H20N2O5S [M+Na]+ 399.0991; found 399.0977.
5.1.4.3. 4-[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazolidi
n-2-yl]butyric acid (14c). Colorless oil (100% yield). 1H NMR
(CDCl3):
d
1.92–2.01 (m, 2H), 2.52 (t, J = 7.3 Hz, 2H), 3.15
(t, J = 7.3 Hz, 2H), 3.19–3.34 (m, 4H), 4.17 (s, 2H), 6.90–7.40 (m,
9H). HRMS (ESI) calculated m/z for
C
19H22N2O5S [M+H]+
C
21H27N3O4S [M+Na]+ 440.1620; found 440.1631.
391.1328; found 391.1332.
5.1.4.10. 2-[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazolid
5.1.4.4. 5-[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazolidi
in-2-yl]ethylpiperidine (17b). Yellow oil (75% yield). 1H NMR
n-2-yl]pentanoic acid (14d). Yellow oil (70% yield). 1H NMR
(CDCl3):
d
1.39–1.60 (m, 6H), 2.35–2.50 (m, 4H), 2.58
(CDCl3):
d
1.65–1.80 (m, 4H), 2.42 (t, J = 5.9 Hz, 2H), 3.07
(t, J = 7.0 Hz, 2H), 3.20 (q, J = 6.7 Hz, 4H), 3.39 (t, J = 5.5 Hz, 2H),
4.16 (s, 2H), 6.89–7.38 (m, 9H). HRMS (ESI) calculated m/z for
(t, J = 5.9 Hz, 2H), 3.17–3.30 (m, 4H), 4.17 (s, 2H), 6.91–7.40 (m,
9H). HRMS (ESI) calculated m/z for
C
20H24N2O5S [M+Na]+
C
22H29N3O3S [M+Na]+ 438.1827; found 438.1815.
427.1304; found 427.1283.
5.2. Biochemical studies
5.1.4.5. 7-[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazolidi
n-2-yl]heptanoic acid (14e). Colorless oil (99% yield). 1H NMR
The antiviral effects of compounds were determined following
previously described procedures using NV replicon-harboring
cells.4–7 Briefly, one-day old, 80–90% confluent HG23 cells were
treated with varying concentrations of each compound (0 [mock-
(CDCl3):
d
1.32–1.49 (m, 4H), 1.53–1.72 (m, 4H), 2.36 (t,
J = 6.7 Hz, 2H), 3.04 (t, J = 6.7 Hz, 2H), 3.16–3.30 (m, 4H), 4.17 (s,
2H), 6.90–7.39 (m, 9H). HRMS (ESI) calculated m/z for C22H28N2O5S
[M+H]+ C22H28N2O5S [M+H]+ 433.1797; found 433.1790.
DMSO]-10 lM) to examine its effects on the replication of NV. At
24 or 48 h of treatment, the NV genome was analyzed with qRT-
PCR. The ED50s of the compounds for NV genome levels were deter-
mined at 24 h post-treatment. The ED50s of the compounds listed
in Table are the average of at least two independent experiments.
The cytotoxic effects of the compounds on HG23 cells were
determined with varying concentrations of each compound
5.1.4.6. 4-[(5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazolidi
n-2-yl)methyl]benzoic acid (14f). White solid (51% yield), mp
144–145 °C. 1H NMR (DMSO-d6): d 3.23 (s, 4H), 4.17 (s, 2H), 4.23
(s, 2H), 6.92–7.43 (m, 9H), 7.49 (d, J = 8.7 Hz, 2H), 7.95 (d,
J = 8.7 Hz, 2H). HRMS (ESI) calculated m/z for
C23H22N2O5S
[M+Na]+ 461.1147; found 461.1159.
(0 [mock-DMSO]-320 lM) using a cell cytotoxicity assay kit
(Promega, Madison, WI) to calculate the median toxic dose
5.1.4.7. 2-[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazolidi
n-2-yl]ethanol (15). To a solution of compound 13a (1.88 g;
5 mmol) in dry THF (8 mL) was added dropwise a solution of 2 M
LiBH4 (2.5 ml; 5 mmol), followed by the dropwise addition of abso-
lute ethanol (15 mL). The reaction mixture was stirred at room
temperature overnight and then acidified with cold 5% HCl to pH
4. The solvent was removed under vacuum and the residue was ta-
ken up in ethyl acetate (85 mL) and washed with brine (25 mL).
The organic layer was dried over anhydrous sodium sulfate. The
drying agent was filtered off and the solvent was removed under
vacuum to give compound 15 as a colorless oil (1.62 g; 89.6%
yield). 1H NMR (CDCl3): d 2.48 (t, J = 5.0 Hz, 1H), 3.20–3.29 (m,
4H), 3.40 (t, J = 3.40 Hz, 2H), 3.83 (q, J = 6.0 Hz, 2H), 4.18 (s, 2H),
6.92–7.38 (m, 9H).
(TD50) at 48 h of treatment.
Acknowledgments
The generous financial support of this work by the National
Institutes of Health (AI081891) is gratefully acknowledged.
References and notes
1. Bergmann, R. J.; Gebhardt, J.; Gould, E.; Tucker, P.; Unge, T.; Hilgenfeld, R.;
Neyts, J. Antiviral Res. 2010, 87, 162.
2. Koo, H. L.; Ajami, N.; Atmar, R. L.; DuPont, H. L. Discov. Med. 2010, 10, 61.
3. Atmar, R. L. Food Environ. Virol. 2011, 2, 117.
4. Chang, K. O.; Sosnovtsev, S. V.; Belliot, G.; King, A. D.; Green, K. Y. Virology 2006,
2, 463.
5. Chang, K. O.; George, D. W. J. Virol. 2007, 22, 12111.
6. Chang, K. O. J. Virol. 2009, 83, 8587.
7. Kim, Y.; Thapa, M.; Hua, D. H.; Chang, K.-O. Antiviral Res. 2011, 89, 165.
8. Compounds were screened using a 10 lM inhibitor concentration. Those that
significantly reduced NV RNA replication (>50% relative to control) at 24 h were
classified as hits.
9. Winum, J.-Y.; Scozzafava, A.; Montero, J.-L.; Supuran, C. T. Med. Res. Rev. 2006,
26, 767.
5.1.4.8. 2-[5-(3-Phenoxybenzyl)-1,1-dioxido-1,2,5-thiadiazolidi
n-2-yl]ethyl methanesulfonate (16). To a solution of compound
15 (1.36 g; 4 mmol) and triethylamine (0.41 g; 4 mmol) in methy-
lene chloride (10 mL) was added methanesulfonyl chloride (0.50 g;
4.3 mmol) at 0 °C. The reaction was allowed to warm to room

D. Dou et al. / Bioorg. Med. Chem. 19 (2011) 5975–5983
5983
10. Reitz, A. B.; Smith, G. R.; Parker, M. H. Expert Opin. Ther. Patents 2009, 19, 1449.
11. Gillespie, P.; Goodnow, R. Annu. Rep. Med. Chem. 2004, 39, 289.
12. Kruse, L. I.; Kaiser, C.; DeWolf, W. E.; Finkelstein, J. A.; Frazee, J. S.; Hilbert, E. L.;
Ross, S. T.; Flaim, K. E.; Sawyer, J. L. J. Med. Chem. 1990, 33, 781.
13. Kim, S. J.; Park, H. B.; Lee, J. S.; Jo, N. H.; Yoo, K. H.; Baek, D.; Kang, B.; Cho, J.-H.;
Oh, C.-H. Eur. J. Med. Chem. 2007, 42, 1176.
15. Moses, J. E.; Moorhouse, A. D. Chem. Soc. Rev. 2007, 36, 1249.
16. Shen, J.; Woodward, R.; Kedenburg, J. P.; Liu, X.; Chen, M.; Fang, L.; Sun, D.;
Wang, P. G. J. Med. Chem. 2008, 51, 7417.
17. Corey, E. J.; Suggs, J. W. Tetrahedron Lett. 1975, 16, 2647.
18. Tiew, K.-C.; He, G.; Aravapalli, S.; Mandadapu, S. R.; Gunnam, M. R.; Alliston, K.
R.; Lushington, G. H.; Kim, Y.; Chang, K.-O.; Groutas, W. C. Bioorg. Med. Chem.
Lett. 2011. doi:10.1016/j.bmcl.2011.07.016.
14. Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004.