The first synthesis of natural disulfide bruguiesulfurol and biological evaluation of its derivatives as a novel scaffold for PTP1B inhibitors

Article abstract of DOI:10.1016/j.bmcl.2013.07.039

Bruguiesulfurol (1), a cyclic 4-hydroxy-dithiosulfonate isolated from mangrove plant Bruguiera gymnorrhiza, was concisely synthesized for the first time in four steps, and a series of its synthetic derivatives were evaluated for in vitro inhibitory effects on PTP1B and related PTPs. Some derivatives were found to have improved pharmacological profile compared with hit 1. Among them, 5a showed the potent selectivity towards PTP1B over other PTPs, including TCPTP, and 7j exhibited the strongest PTP1B inhibitory activity with an IC ₅₀ value of 4.54 μM.

Full text of DOI:10.1016/j.bmcl.2013.07.039

Bioorganic & Medicinal Chemistry Letters 23 (2013) 5061–5065
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
The first synthesis of natural disulfide bruguiesulfurol and biological
evaluation of its derivatives as a novel scaffold for PTP1B inhibitors
Jing Chen a, , Cheng-Shi Jiang a, , Wen-Quan Ma b, Li-Xin Gao a, Jing-Xu Gong a, Jing-Ya Li a, Jia Li a,
Yue-Wei Guo a,
⇑
a State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zi Road, Zhangjiang Hi-Tech Park,
Shanghai 201203, PR China
b Biomedical Science Park of Weifang, Weifang National High-Tech Industrial Development Zone, Weifang, Shandong 261205, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Bruguiesulfurol (1), a cyclic 4-hydroxy-dithiosulfonate isolated from mangrove plant Bruguiera gymno-
rrhiza, was concisely synthesized for the first time in four steps, and a series of its synthetic derivatives
were evaluated for in vitro inhibitory effects on PTP1B and related PTPs. Some derivatives were found to
have improved pharmacological profile compared with hit 1. Among them, 5a showed the potent selec-
tivity towards PTP1B over other PTPs, including TCPTP, and 7j exhibited the strongest PTP1B inhibitory
Received 7 May 2013
Revised 8 June 2013
Accepted 17 July 2013
Available online 25 July 2013
activity with an IC50 value of 4.54 lM.
Keywords:
Ó 2013 Elsevier Ltd. All rights reserved.
Bruguiesulfurol
Derivative
PTP1B inhibitor
Type 2 diabetes
Selectivity
According to the World Health Organization (WHO), about 346
million people worldwide suffer from diabetes and its prevalence
is projected to roughly double by 2030.1 Type 2 diabetes, resulting
from the body’s ineffective use of insulin, makes up 90% of diabetes
cases.2 Protein tyrosine phosphatase 1B (PTP1B), the first mamma-
lian PTP to be purified and characterized, has been demonstrated
to play a key role in the insulin-dependent signaling cascade.3 Tre-
mendous experimental data have validated PTP1B as one of the
best therapeutical targets for the treatment of type 2 diabetes
and obesity.4 For example, PTP1B-deficient mice have remarkably
low adiposity, and are protected from diet-induced obesity by
increasing basal metabolic rate and total energy expenditure. This
result is consistent with the inference that PTP1B is a major regu-
lator of energy balance insulin sensitivity and body fat stores
in vivo.5 In addition, accumulating evidence also indicates that
PTP1B is involved in cancer.6 The positive physiological role of
PTP1B attracts great interest of medicinal chemists, and in the past
decades numerous drug-like PTP1B inhibitors, mostly involving
phosphotyroine (pTyr) mimetics, have been developed.7,8 How-
ever, discovery of anti-type 2 diabetes drugs targeting PTP1B is still
a big challenging task because of the fundamental nature of highly
conserved and positively charged active-site pocket.9 The current
pTyr mimetics usually have undesirable cell permeability and oral
bioavailability due to the presence of highly negative charged polar
residues in their structures, or show poor PTP1B selectivity versus
TCPTP (T-cell protein tyrosine phosphatase) due to their highly
homologous catalytic domain and identical active sites.10 There-
fore, there is an urgent need to develop novel potential drug scaf-
folds targeting PTP1B.
Marine natural products are a prolific source of lead molecules
for discovering clinically drugs for human diseases.11 As a special
and important member, marine disulfide- and multisulfide-con-
taining metabolites possess varying bioactivities and fantastic
molecular skeletons, which have been paid more and more
attentions by pharmacologists and chemists recently.12–16 Our
group has focused on this field for many years, and in our research
project for finding promising anti-type 2 diabetes drug candidates
a series of unique marine cyclic disulfides and multisulfides with
PTP1B inhibitory activity had been isolated and synthesized.17 Bru-
guiesulfurol (1, Fig. 1), a cyclic 4-hydroxy-dithiosulfonate isolated
for the first time from the flowers of mangrove plant Bruguiera
gymnorrhiza,18 was found to exhibit PTP1B inhibitory activity
(IC50 = 17.5
icant bioactivity, and low natural yield of 1 stimulated our interest
to synthesize and perform more-in-depth pharmacological
l
M) by our group.17b The uncommon structure, signif-
a
evaluation. Herein, the present letter describes the first concise
synthesis of 1 and biological evaluation of its synthetic derivatives
as selective PTP1B inhibitors.
⇑
Corresponding author. Tel.: +86 21 50805813; fax: +86 21 50807088.
E-mail address: ywguo@mail.shcnc.ac.cn (Y.-W. Guo).
These authors contributed equally to the study.
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.07.039

5062
J. Chen et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5061–5065
bond. In addition, it is also vital to select a suitable and practical
hydroxyl protecting group. 4-Bromobenzoyl as a common hydro-
xyl protecting group was used since it makes small-molecule com-
pound easy to crystallize, which is helpful for purification and
structural identification. The initial approach to synthesize 1
(shown in Scheme 1) started from commercially available epi-
bromohydrin (2). Treatment of 2 with 40% aqueous HBr gave 1,3-
dibromo-2-propano (3). The esterification between bromide 3
and 4-bromobenzene carboxylic acid yielded ester 4a. Then, ester
4a was reacted with Na2S2 (prepared from Na2S and S)22 to form
the key intermediate 5a with the assistance of tetrabutyl ammo-
nium bromide (TBAB) as phase transfer catalyst, following oxidiza-
tion by treatment with oxone to give oxidative product 6a. The
structures of 5a and 6a were confirmed through X-ray diffraction
analysis (Fig. 2).23 Disappointingly, no expected compound 1 was
Figure 1. Structure of bruguiesulfurol (1).
The construction of sulfur–sulfur bond is the decisive step for
the synthesis of 1. Many methods for the formation of disulfides
have been reported, such as oxidative coupling of thiols or Bunte
salts,19 reductive formation from sulfenyl, sulfinyl, sulfonyl or thio-
cyanate derivatives,20 or the reaction of alkyl halide with sodium
disulfide (Na2S2).21 Based on our previous study and analysis of
structural features of 1, the last method was used to form disulfide
Scheme 1. Reagents and conditions: (a) 40% aqueous HBr, CH2Cl2, 0 °C, 5 h, 85%; (b) 4-bromobenzene carboxylic acid, EDCI, DMAP, CH2Cl2, rt, 12 h, 88%; (c) Na2S2, cat. TBAB,
CHCl3, rt, 5 h, 60%; (d) Oxone, NaHCO3, acetone, 2 h, 81%.
Figure 2. Single-crystal X-ray structures of 5a and 6a.
Scheme 2. Reagents and conditions: (a) pyridinium-p-toluene sulfonate, 2,3-dihydropyran, THF, rt, 2 h, 85%; (b) Na2S2, cat. TBAB, CHCl3, rt, 5 h, 58%; (c) mCPBA, CH2Cl2, rt,
4 h, 30%.
Scheme 3. Reagents and conditions: (a) RCO2H, EDCI, DMAP, CH2Cl2, rt, 12 h; (b) Na2S2, cat. TBAB, CHCl3, rt, 5 h; (c) mCPBA, CH2Cl2, rt, 4 h.

J. Chen et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5061–5065
5063
Table 1
Inhibitory activity of 5a–t against PTP1B and other PTPs presented as IC50
(lM)
Compd
R
PTP1B
17.5
TCPTP
ND
SHP-1
ND
SHP-2
ND
LAR
ND
1
H
5a
5b
11.01 1.31
NAa
33.97 3.47
NDb
NA
ND
NA
ND
34.57 4.55
ND
Br
Br
5c
NA
ND
ND
ND
ND
Br
5d
5e
5f
NA
ND
ND
ND
ND
NA
NA
NA
ND
F
Cl
I
NA
ND
ND
ND
33.42 2.02
48.18 4.91
25.62 4.53
34.10 3.63
42.08 7.86
20.43 3.15
NA
NA
5g
5h
NA
20.36 4.12
NA
I
Br
10.91 2.47
Br
O
O
5i
24.88 2.68
40.67 0.46
14.05 3.63
13.36 2.98
NA
S
NH2
5j
22.56 2.95
37.37 5.86
NA
ND
ND
NA
ND
ND
NA
ND
ND
O2N
Br
5k
5l
NA
NA
ND
ND
Br
O2N
5m
5n
5o
14.83 2.31
27.28 7.43
24.37 7.74
13.81 2.72
NA
ND
ND
NO2
NA
NA
ND
ND
ND
ND
ND
ND
OCH3
H3CO
H3C
5p
5q
NA
ND
NA
ND
ND
ND
NA
78.19 6.98
17.94 1.71
21.45 2.13
O
O
5r
5s
35.23 2.82
NA
75.41 4.21
ND
15.77 0.79
ND
22.29 3.01
ND
NA
ND
H
N
H
N
5t
24.08 4.48
3.02 0.20
35.84 4.29
ND
NA
ND
NA
ND
NA
ND
Oleanolic acid
a
NA, not active.
ND, not determined.
b
obtained upon subjection of 6a to a variety of deprotection condi-
tions.24 Furthermore, 6a is very stable in acidic conditions resulting
in no reaction occurring. However, it rapidly decomposed in basic
conditions, which suggested the disulfide bond might be unstable
in basic condition, but stably exist in acidic condition.
Based on the experimental results above, using hydroxyl pro-
tection group that can be deprotected in acidic conditions seems
available for access to 1. Therefore, the 2-tetrahydropyranyl group
was used as protecting group. The synthetic route to 1 was carried
out as shown in Scheme 2. The hydroxyl group of 3 was protected

5064
J. Chen et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5061–5065
Table 2
Inhibitory activity of series of 6 and 7 against PTP1B and other PTPs presented as IC50 (lM)
Compd
R
X
Y
PTP1B
NAa
TCPTP
NDb
SHP-1
ND
SHP-2
ND
LAR
ND
6a
O
O
Br
6b
6c
O
O
O
O
NA
ND
NA
ND
NA
ND
NA
ND
NA
Br
29.00 3.38
Br
6d
6f
O
O
O
O
O
O
O
O
NA
NA
NA
NA
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
F
I
6g
6j
I
Br
Br
H
N
6n
O
O
NA
ND
ND
ND
ND
6t
O
O
O
O
NA
NA
NA
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
Br
Br
7a
7b
Lone pair
Lone pair
Br
7c
O
Lone pair
27.96 3.83
NA
NA
NA
NA
Br
7d
7f
O
O
O
O
Lone pair
Lone pair
Lone pair
Lone pair
NA
ND
ND
NA
NA
NA
ND
NA
NA
NA
ND
NA
NA
NA
F
I
22.38 1.85
29.68 2.66
4.54 0.47
32.97 2.33
36.80 0.89
11.12 1.14
7g
7j
I
Br
Br
H
N
7n
O
O
Lone pair
Lone pair
31.42 2.42
44.98 5.10
52.64 2.87
NA
NA
NA
NA
NA
NA
NA
7t
Br
a
NA, not active.
ND, not determined.
b
by 2,3-dihydropyran to yield 3a, which was reacted smoothly with
Na2S2 to give the desired disulfide 3b in 49% overall yield over two
steps. In order to oxidize the disulfide bond in 3b, several oxidants
were tried.25 Finally, 3-chloroperoxybenzoic acid (mCPBA) was
found to be an efficient oxidant, and target compound 1 was pro-
duced by oxidation and deprotection in one pot with an overall
yield of 30%. The physical and spectral data of 1 were in agreement
with the literature data.17b,18
original natural product 1, with an IC50 value of 11.01
l
M, and also
showed significant selectivity toward PTP1B versus other PTPs,
especially the most homologous PTPCP by threefold. These positive
results encouraged us to prepare a series of derivatives of 1, and to
conduct a preliminary structure–activity relationship (SAR) study
on these compounds.
The syntheses of three series of 5, 6 and 7 were carried out as
shown in Scheme 3. Esterification of bromide 3 with various car-
boxylic acids, and following nucleophilic substitution reaction be-
tween ester 4 and Na2S2 provided disulfide 5. Compounds 6 and 7
During the process for synthesizing 1, the key intermediate 5a
was found to exhibit stronger PTP1B inhibitory activity than the

J. Chen et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5061–5065
5065
were finished by oxidative reaction of 5 with mCPBA. The synthetic
derivatives were evaluated in the enzyme inhibition assay against
PTP1B and other four PTPs (TCPTP, SHP-1, SHP-2 and LAR).
Foundation Grant (No. 2012M520956), and was partially funded
by the EU 7th Framework Programme-IRSES Project (No. 246987).
The results of the first series of analogs (5a–t) are shown in Ta-
ble 1. Among 5a–h with halo-substituted group in benzene ring,
para-bromo substituted compound 5a was the most active towards
PTP1B, and showed highest selectivity over other PTPs (about
threefold selectivity over TCPTP and LAR; inactive toward to SHP-
1 and SHP-2). Compounds 5f–h were active towards PTP1B with
A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.
07.039.
IC50 values ranging from 25.62 4.53 to 48.18 4.91
did not showed selectivity towards TCPTP with IC50 values ranging
from 20.43 3.15 to 42.08 2.77 M. Compounds 5i and 5j, also
lM, but they
References and notes
1. Sarah, W.; Gojka, R.; Anders, G.; Richard, S.; Hilary, K. Diabetes Care 2004, 35,
1047.
l
bearing para-substitutions (sulfonamide and nitro groups, respec-
tively), showed significant improved PTP1B inhibitory activity com-
pared with 5b–g, however, these two compounds still did not show
noticeable selectivity towards TCPTP as 5a. The results above indi-
cated that the para-bromo substitution might play a key role in the
PTP1B inhibitory activity and selectivity for 5a. Further, another
two analogs (5k and 5l) with para-bromo substitution in benzene
ring were prepared, but it is disappointing that their PTP1B inhibi-
tory activity were lost with increase in the amount of carbon atoms
between benzene ring and carbonyl group. It is worth noting that
2. For latest information, please visit the website of World Health Organization at
http://www.who.int/mediacentre/factsheets/fs312/en/.
3. (a) Kennerm, K. A.; Anyanwu, E.; Olefsky, J. M.; Kusari, J. J. Biol. Chem. 1996, 271,
19810; (b) Ahmad, F.; Li, P. M.; Meyerovitch, J.; Goldstein, B. J. J. Biol. Chem.
1995, 270, 20503.
4. (a) You-Ten, L. D.; Muise, E. S.; Itie, A.; Michaliszyn, E.; Wagner, J.; Jothy, S.;
Lapp, W. S.; Tremblay, M. L. J. Exp. Med. 1997, 186, 683; (b) Trauring, M.; Janson,
R. L.; Kobes, S.; Bogardus, C.; Baier, L. J. Diabetologia 2007, 50, 985; (c) Cheyssac,
C.; Lecoeur, C.; Dechaume, A.; Bibi, A.; Charpentier, G.; Baulkau, B.; Marre, M.;
Froguel, P.; Gibson, F.; Vaxillaire, M. BMC Med. Genet. 2006, 7, 44.
5. Klaman, L. D.; Boss, O.; Peroni, O. D.; Kim, J. K.; Martino, J. L.; Zabolotny, J. M.;
Moghal, N.; Lubkin, M.; Kim, Y. B.; Sharpe, A. H.; Stricker-Krongrad, A.;
Shulman, G. I.; Neel, B. G.; Kahn, B. B. Mol. Cell. Biol. 2000, 20, 5479.
6. Lessard, L.; Stuible, M.; Tremblay, M. L. Biochim. Biophys. Acta 2010, 1804, 613.
7. Combs, A. P. J. Med. Chem. 2010, 53, 2333.
8. Xu, J.-Q.; Shen, Q.; Li, J.; Hu, L.-H. Bioorg. Med. Chem. 2010, 18, 3934.
9. Zhang, S.; Zhang, Z.-Y. Drug Discovery Today 2007, 12, 373.
10. Iverson, L. F.; Moller, K. B.; Pedersen, A. K.; Peters, G. H.; Petersen, A. S.;
Andersen, H. S.; Branner, S.; Mortensen, S. B.; Møller, N. P. H. J. Biol. Chem. 2002,
277, 19982.
11. Blunt, J. W.; Copp, B. R.; Keyzers, R. A.; Munro, M. H. G.; Prinsep, M. R. Nat. Prod.
Rep. 2012, 29, 144 [references cited therein and previous reviews in this series].
12. Lee, S. H. Arch. Pharm. Res. 2009, 32, 299.
13. Jiang, C.-S.; Müller, W. E. G.; Schröder, H. C.; Guo, Y.-W. Chem. Rev. 2012, 112,
2179.
14. Nicolaou, K. C.; Lu, M.; Totokotsopoulos, S.; Heretsch, P.; Giguère, D.; Sun, Y.-P.;
Sarlah, D.; Nguyen, T.-H.; Wolf, I.-C.; Smee, D.-F.; Day, C.-W.; Bopp, S.;
Winzeler, E.-A. J. Am. Chem. Soc. 2012, 134, 17320.
15. Kim, J.; Ashenhurst, A.; Movassaghi, M. Science 2009, 324, 238.
16. Boyer, N.; Movassaghi, M. Chem. Sci. 2012, 3, 1798.
17. (a) Sun, Y.-Q.; Guo, Y.-W. Tetrahedron Lett. 2004, 45, 5533; (b) Huang, X.-Y.;
Wang, Q.; Liu, H.-L.; Zhang, Y.; Xin, G.-R.; Shen, X.; Dong, M.-L.; Guo, Y.-W.
Phytochemistry 2009, 70, 2096; (c) Gong, J.-X.; Shen, X.; Yao, L.-G.; Jiang, H.-L.;
Krohn, K.; Guo, Y.-W. Org. Lett. 2007, 9, 1715; (d) Liu, H.-L.; Shen, X.; Jiang, H.-
L.; Guo, Y.-W. Chin. J. Org. Chem. 2008, 28, 246; (e) Gong, J.-X.; Sun, Y.-Q.; Wang,
J.-D.; Guo, Y.-W. Chin. J. Org. Chem. 2008, 28, 252.
18. Homhual, S.; Zhang, H.-J.; Bunyapraphatsara, N.; Kondratyuk, T. P.; Santarsiero,
B. D.; Mesecar, A. D.; Herunsalee, A.; Chaukul, W.; Pezzuto, J.; Fong, H. H. S.
Planta Med. 2006, 72, 255.
19. (a) Akdag, A.; Webb, T.; Worley, S. D. Tetrahedron Lett. 2006, 47, 3509; (b) Alam,
A.; Takaguchi, Y.; Tsuboi, S. Synth. Commun. 2005, 35, 1329; (c) Ali, M. H.;
McDermott, M. Tetrahedron Lett. 2002, 43, 6271; (d) Hirano, M.; Yakabe, S.;
Fukami, M.; Morimoto, T. Synth. Commun. 1997, 27, 2783; (e) Jia, X.; Zhang, Y.;
Zhou, X. Synth. Commun. 1994, 24, 2893.
20. (a) Liu, Y.; Zhang, Y. Tetrahedron Lett. 2003, 44, 4291; (b) Sheppard, W. A. In
Organic Syntheses; Wiley: New York, 1973; Collect. Vol. 5,; p 843; (c) Chan, T H.;
Montillier, J. P.; Horn, W. F.; Harpp, D. N. J. Am. Chem. Soc. 1970, 92, 7224; (d)
Alper, H. Angew. Chem., Int. Ed. Engl. 1969, 8, 677; (e) Chattopadhyay, S. K.;
Srivastava, S.; Sashidhara, K. V.; Tripathi, A. K.; Bhattacharya, A. K.; Negi, A. S.
Bioorg. Med. Chem. Lett. 2004, 14, 1729.
21. Sonavane, S. U.; Chidambaram, M.; Almog, J.; Sasson, Y. Tetrahedron Lett. 2007,
48, 6048.
22. Sonavane, S. U.; Chidambaram, M.; Khalil, S.; Almog, J.; Sasson, Y. Tetrahedron
Lett. 2008, 49, 520.
23. Crystallographic data for the structures of 5a and 6a in this Letter have been
deposited with the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC 934510 and 934511 respectively. Copies of the data
can be obtained, free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: +44 (0) 1223 336033 or E-mail:
deposit@ccdc.cam.ac.uk].
24. Among these attempts were reactions with concd hydrochloric acid, acetic
acid, concd sulfuric acid, sodium bicarbonate, sodium carbonate, and
potassium carbonate in MeOH, respectively.
compound 5m (IC50 = 14.83 2.31 lM), bearing two electron-with-
drawing nitro groups at ortho- and meta-position, almost shows
similar level of PTP1B inhibitory activity to that of 5a, however,
5m did not show good PTP1B selectivity as 5a. Among compounds
5q–t with heteroaromatic substitutions, 5q, 5r and 5t showed weak
or moderate PTP1B inhibitory activity, but they also did not have
PTP1B selectivity as good as 5a.
The results of series of oxidative products 6 and 7 are shown in
Table 2. Surprisingly, most of sulfoxides 7 showed higher PTP1B
inhibitory than their precursor 5. Among all the tested sulfoxides,
compound 7j showed the highest PTP1B inhibitory activity with
an IC50 value of 4.54 lM (about 2.4-fold selectivity over TCPTP),
and no effect against other PTPs. Interestingly, the PTP1B inhibitory
activity of 7a was lost compared with 5a, so that there seems to be
ambiguous effect about the formation of sulfoxide. Compared with
sulfoxides 7, sulfones 6 nearly did not have PTP1B inhibitory activ-
ity except compound 6c. It was speculated that the introduction of
another oxygen atom change the configuration of 1,2-dithiolane
and/or increase steric hindrance, which might make these sulfones
can not bind to the active site of PTP1B resulting in the loss of
PTP1B inhibitory activity.
In summary, the first concise synthesis of bruguiesulfurol (1)
has been achieved in only four steps in 12.6% overall yield, and a
series of its derivatives were developed and evaluated for in vitro
inhibitory activity against a panel of PTPs. Some derivatives were
found to have improved PTP1B inhibitory activity compared with
hit 1, such as 5a and 7j showing high PTP1B inhibitory activity
and relatively good selectivity. The preliminary SAR study provides
a novel potential scaffolds for designing novel class of PTP1B inhib-
itors. Further studies to improve pharmacological profile and clar-
ify action mechanism for this class of disulfide PTP1B inhibitors are
in progress and will be reported in due time.
Acknowledgments
This research work was financially supported by the
National Marine ‘863’ Projects (Nos. 2011AA09070102 and
2013AA092902), the Natural Science Foundation of China (Nos.
21021063, 81273430, 21072204, and 81072572), the SKLDR/SIMM
Projects (No. SIMM1203ZZ-03), China Postdoctoral Science
25. The oxidants are mCPBA, oxone, and tert-butyl hydroperoxide, respectively.