Synthesis of functionalized acetophenones as protein tyrosine phosphatase 1B inhibitors

Article abstract of DOI:10.1016/j.bmcl.2005.05.024

Protein tyrosine phosphatase 1B (PTP1B) is an enzyme that plays a critical role in down-regulating insulin signaling through dephosphorylation of the insulin receptor. Studies have shown that PTP1B knock-out mice showed increased insulin sensitivity in mu

Full text of DOI:10.1016/j.bmcl.2005.05.024

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3394–3397
Synthesis of functionalized acetophenones as protein
tyrosine phosphatase 1B inhibitorsq
Manish Dixit,a Brajendra K. Tripathi,b Arvind K. Srivastavab and Atul Goela,*
aDivision of Medicinal and Process Chemistry, Central Drug Research Institute, Lucknow 226001, India
bDivision of Biochemistry, Central Drug Research Institute, Lucknow 226001, India
Received 11 March 2005; revised 4 May 2005; accepted 9 May 2005
Abstract—Protein tyrosine phosphatase 1B (PTP1B) is an enzyme that plays a critical role in down-regulating insulin signaling
through dephosphorylation of the insulin receptor. Studies have shown that PTP1B knock-out mice showed increased insulin sen-
sitivity in muscle and liver as well as resistance to obesity. A series of functionalized acetophenones were synthesized and evaluated
for their PTP1B inhibitory activity. Some of the screened compounds displayed good inhibitory activity.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
tin, isolated from the culture filtrate of Streptomyces
sp. MJ742-NF5. Later on, they prepared alkyl 3,4-dep-
hostatin (I) as a stable, selective inhibitor of PTP1B
(Fig. 1). Recently, Pei and co-workers10 have reported
several a-haloacetophenone (II) derivatives as potent
neutral protein tyrosine phosphatase inhibitors, which
covalently alkylate the conserved catalytic cysteine resi-
due in the PTP active site. Several formyl chromone (III)
derivatives were reported as human PTP1B possessing
inhibitory activity in the micromolar range.11 Recently,
Hu and co-workers12 have shown that the ethanolic ex-
tract of the roots of Broussonetia papyrifera (L.) Vent,
which are composed of several flavonoids including a
flavonol IV, showed potent inhibitory activity against
PTP1B enzyme. Based on the reported PTP1B
Protein kinases and phosphatases are a large family of
enzymes that control several fundamental cellular func-
tions via phosphorylation and de-phosphorylation reac-
tions. In recent years, studies on protein tyrosine
phosphatases (PTPs) as drug targets for controlling
intracellular signaling have been rapidly increasing.1
Among PTPs, PTP-1B has received much attention due
to its pivotal role in type 2 diabetes and obesity as a neg-
ative regulator of the insulin and leptin-signaling path-
way.2 Clinical studies have demonstrated that PTP-1B
is primarily responsible for dephosphorylation of the
insulin receptor and thus down regulates insulin signal-
ing.3 Therefore, the search for potent small molecule pro-
tein tyrosine phosphatase 1B inhibitors is a major thrust
area in the management of type 2 diabetes mellitus.4
Several synthetic and naturally occurring PTP inhibitors
reported in the literature have shown efficacy in in vitro
and in vivo models. The majority of them possess tyro-
sine mimetic structures functionalized with negatively
charged moieties such as phosphonates,5 malonates,6
carboxylates,7 or cinnamates.8 Umezawa et al.9 discov-
ered a naturally occurring PTPase inhibitor, dephosta-
Keywords: Diabetes; Protein tyrosine phosphatase 1B; Acetophenone;
Insulin signaling.
q CDRI Communication No. 6740.
*
Corresponding author. Tel.: +91 522 2612411; fax: +91 522
2623405; e-mail: agoel13@yahoo.com
Figure 1. Structures of PTP1B inhibitors.
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.05.024

M. Dixit et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3394–3397
3395
Scheme 1. Reagents and conditions: (i) RBr, K2CO3, acetone; (ii) ArCOCl, pyridine, rt; (iii) t-BuOK, pyridine, rt; (iv) BrCH2CH(OC2H5)2, DMF,
140 ꢁC; (v) Amberlyst 15, toluene, 120 ꢁC.
Table 1. In vitro PTP1B enzyme inhibitory activity for the compounds
2a–e, 3a–c, 4a–c, 6, 7, 8a–c, 9a–e, and 10
inhibitors, we have synthesized various small molecule
acetophenones functionalized with alkoxy and aroyloxy
moieties as potential PTP1B inhibitors.
Entry
R
Ar
Inhibitiona(%)
2a
2b
2c
2d
CH2CN
—
—
—
—
22.4
NI
The precursor used for the synthesis of various hydroxy
chalcones and functionalized acetophenones was 2,4-
dihydroxyacetophenone 1, which on reaction with alkyl
halide in the presence of a base afforded 2 in 60–70%
yield as depicted in Scheme 1. The reaction of 2 with ar-
oyl chloride in pyridine gave products 3a–c in good
yields. The benzoylated acetophenone 3 was stirred with
potassium tertiary butoxide in pyridine to yield hydroxy
chalcone derivatives 4 in 70–80% yield. The 2,4-dihydr-
oxyacetophenone was further exploited to prepare ben-
zofuran-based hydroxy ketone compounds, which are
useful precursors for several naturally occurring fur-
anoflavonoids that possess diverse biological activities.
Compound 1 was alkylated with bromoacetaldehyde
diethyl acetal in the presence of potassium carbonate
to yield corresponding alkylated product 5, which was
cyclized with Amberlyst 15 by refluxing in toluene as de-
scribed earlier by us.13 Both the products 6 and 7 were
benzoylated separately to the corresponding derivative
8 and 9, respectively. Compound 8c was further trans-
formed to corresponding chalcones in the presence of
potassium tertiary butoxide as shown in Scheme 1. All
the synthesized compounds were characterized by spec-
troscopic data and elemental analysis.14
CH2CH@CH2
CH2CH2C6H5
CH2CH2OH
38.6
NI
H2C
2e
—
C6H5
22.4
12.8
NI
O
3a
3b
3c
CH2CN
CH2CN
4-FC6H4
4-FC6H4
C6H5
CH2CH2C6H5
CH2CN
NI
NI
4a
4b
4c
CH2CN
CH2CH2C6H5
4-FC6H4
4-FC6H4
—
NI
NI
6
—
—
NI
7
—
C6H5
19.1
43.2
54.1
32.4
NI
8a
8b
8c
—
—
3,4-Cl2C6H3
4-CF3C6H4
C6H5
—
—
9a
9b
9c
—
—
4-OCH3C6H4
3,4-(OMe)2C6H3
3-OCH3C6H4
3,4-CH2O2C6H3
—
13.5
NI
9d
9e
—
—
8.1
34
10
Na3VO4
—
(Control)
NI
56.2
—
a Values are means from three independent sets of experiments tested
at 100 lM concentration; NI means no inhibition.
pounds demonstrated moderate to good PTP1B inhib-
itory activity at 100 lM concentration. Compounds 8a
and b displayed 43.2% and 54.1% inhibition against
PTP1B enzyme.
2. Result and discussion
Vanadate is a non-selective inhibitor of PTPs, and
studies have shown that treatment with vanadate can
normalize blood glucose level in diabetics.2b,15 Taking
sodium vanadate as a control, we have evaluated
PTP1B inhibitory activity of functionalized acetophe-
nones at 100 lM concentration and their results are
summarized in Table 1. Some of the screened com-
2.1. Protein tyrosine phosphatase inhibitory activity16
The effect of test compounds on protein tyrosine phos-
phatase was studied by pre-incubating 100 lM of the
test chemicals in the reaction system for 10 min and
the residual protein tyrosine phosphatase activity deter-

3396
M. Dixit et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3394–3397
mined according to the method of Goldstein et al.16
Activity of PTPase (LAR) was evaluated using p-nitro-
phenylphosphate (PNPP) as the substrate. Assay mix-
ture was made up to 1 mL containing 10 mM PNPP in
50 mM HEPES buffer (pH 7), with 1 mM EDTA and
DTT. The reaction was stopped by the addition of
500 lL of 0.1 N NaOH and absorbance was determined
Curchod, M. L.; Gobert, R. P.; Arkinstall, S.; Hooft van
Huijsduijnen, R. J. Biol. Chem. 2000, 275, 9792.
4. (a) Szczepankiewicz, B. G.; Liu, G.; Hajduk, P. J.; Abad-
Zapatero, C.; Pei, Z.; Xin, Z.; Lubben, T. H.; Trevillyan,
J. M.; Stashko, M. A.; Ballaron, S. J.; Liang, H.; Huang,
F.; Hutchins, C. W.; Fesik, S. W.; Jirousek, M. R. J. Am.
Chem. Soc. 2003, 125, 4087; (b) Liu, G.; Xin, Z.; Pei, Z.;
Hajduk, P. J.; Abad-Zapatero, C.; Hutchins, C. W.; Zhao,
H.; Lubben, T. H.; Ballaron, S. J.; Haasch, D. L.;
Kaszubska, W.; Rondinone, C. M.; Trevillyan, J. M.;
Jirousek, M. R. J. Med. Chem. 2003, 46, 4232.
5. (a) Burke, T. R., Jr.; Kole, H. K.; Roller, P. P. Biochem.
Biophys. Res. Commun. 1994, 204, 129; (b) Taylor, W. P.;
Zhang, Z.-Y.; Widlanski, T. S. Bioorg. Med. Chem. 1996,
4, 1515; (c) Taylor, S. D.; Kotoris, C. C.; Dinaut, A. N.;
Wang, Q.; Ramachandran, C.; Huang, Z. Bioorg. Med.
Chem. 1998, 6, 1457; (d) Taing, M.; Keng, Y.-F.; Shen, K.;
Wu, L.; Lawrence, D. S.; Zhang, Z.-Y. Biochemistry 1999,
38, 3793; (e) Shen, K.; Keng, Y.-F.; Wu, L.; Guo, X.-L.;
Lawrence, D. S.; Zhang, Z.-Y. J. Biol. Chem. 2001, 276,
47311.
6. (a) Ye, B.; Akamatsu, M.; Shoelson, S. E.; Wolf, G.;
Giogetti-Peraldi, S.; Yan, X.; Roller, P. P.; Burke, T. R.,
Jr. J. Med. Chem. 1995, 38, 4270; (b) Burke, T. R., Jr.;
Ye, B.; Akamatsu, M.; Ford, H.; Yan, X. J.; Kole, H.
K.; Wolf, G.; Shoelson, S. E.; Roller, P. P. J. Med.
Chem. 1996, 39, 1021; (c) Akamatsu, M.; Roller, P. P.;
Chen, L.; Zhang, Z.-Y.; Ye, B.; Burke, T. R., Jr. Bioorg.
Med. Chem. 1997, 5, 157; (d) Roller, P. P.; Wu, L.;
Zhang, Z.-Y.; Burke, T. R., Jr. Bioorg. Med. Chem. Lett.
1998, 8, 2149.
7. (a) Sarmiento, M.; Wu, L.; Keng, Y.-Y.; Song, L.; Luo,
Z.; Huang, Z.; Wu, G.-Z.; Yuan, A. K.; Zhang, Z.-Y. J.
Med. Chem. 2000, 43, 146; (b) Iversen, L. F.; Andersen, H.
S.; Branner, S.; Mortensen, S. B.; Peters, G. H.; Norris,
K.; Olsen, O. H.; Jeppesen, C. B.; Lundt, B. F.; Ripka, W.;
Møller, K. B.; Møller, N. P. H. J. Biol. Chem. 2000, 275,
10300; (c) Wrobel, J.; Li, Z.; Sredy, J.; Sawicki, D. R.;
Seestaller, L.; Sullivan, D. Bioorg. Med. Chem. Lett. 2000,
10, 1535; (d) Chen, Y. T.; Onaran, M. B.; Doss, C. J.;
Seto, C. T. Bioorg. Med. Chem. Lett. 2001, 11, 1935; (e)
Malamas, M. S.; Sredy, J.; Moxham, C.; Katz, A.; Xu, W.
X.; McDevitt, R.; Adebayo, F. O.; Sawicki, D. R.;
Seestaller, L.; Sullivan, D.; Taylor, J. R. J. Med. Chem.
2000, 43, 1293.
at 410 nm.
A
molar extinction coefficient of
1.78 · 104 MÀ1 cmÀ1 was used to calculate the concen-
tration of p-nitrophenolate ions produced in the reac-
tion mixture.
The structure–activity relationship of the screened 4-alk-
oxy-2-hydroxyacetophenones revealed that bulky non-
polar moiety at the terminus of alkyl group possesses
good inhibitory activity (38.6%). None of the benzoyl-
ated acetophenones (3a–c) and their corresponding
chalcones (4a–c) showed inhibition except 3a, which
showed little activity. Various benzofuran derivatives
have shown to possess PTP1B inhibitory activity in the
low micromolar range.17 Thus, various hydroxy benzo-
furan methyl ketones and their benzoylated derivatives
have been evaluated as PTP1B inhibitors. It is evident
from the activity profile that 4-aroyloxy-5-acetyl-
benzofuran (8a–c), showed good inhibitory activity
comparable to reference compound sodium vanadate.
One of these compounds, 4-(3,4-dichlorobenzoyloxy)-
5-acetyl-benzofuran (8b), showed 54% inhibition against
PTP1B at 100 lM concentration. The rest of the com-
pounds were either inactive or possessed a low range
activity.
In conclusion, we have identified a series of functional-
ized acetophenones as protein tyrosine phosphatase
inhibitors. This is an initial report and optimization of
these compounds is in progress.
Acknowledgments
We thank Sophisticated Analytical Instrumentation
Facility (SAIF) for providing spectral data of synthe-
sized compounds. The financial support from CSIR,
New Delhi is gratefully acknowledged.
8. (a) Moran, E. J.; Sarshr, S.; Cargill, J. E.; Shahbaz, M. M.;
Lio, A.; Mjalli, A. M. M.; Armstrong, R. W. J. Am. Chem.
Soc. 1995, 117, 10787; (b) Cao, X.; Moran, E. J.; Siev, D.;
Lio, A.; Ohashi, C.; Mjalli, A. M. M. Bioorg. Med. Chem.
Lett. 1995, 5, 2953.
9. Umezawa, K.; Kawakami, M.; Watanabe, T. Pharmacol.
Ther. 2003, 99, 15.
References and notes
10. Arabaci, G.; Guo, X.-C.; Beebe, K. D.; Coggeshall, K. M.;
Pei, D. J. Am. Chem. Soc. 1999, 121, 5085.
11. Shim, Y. S.; Kim, K. C.; Chi, D. Y.; Lee, K.-H.; Cho, H.
Bioorg. Med. Chem. Lett. 2003, 13, 2561.
12. Chen, R. M.; Hu, L. H.; An, T. Y.; Li, J.; Shen, Q. Bioorg.
Med. Chem. Lett. 2002, 12, 3387.
13. Goel, A.; Dixit, M. Synlett 2004, 1990.
1. (a) Ostman, A.; Bohmer, F. D. Trends Cell Biol. 2001, 11,
258; (b) Denu, J. M.; Dixon, J. E. Curr. Biol. 1998, 2, 633;
(c) Zhan, X.-L.; Wishart, M. J.; Guan, K.-L. Chem. Rev.
2001, 101, 2477; (d) Zhang, Z.-Y. Curr. Opin. Chem. Biol.
2001, 5, 416; (e) Neel, B. G.; Tonks, N. K. Curr. Opin. Cell
Biol. 1997, 9, 193.
2. (a) Elchelby, M.; Payette, P.; Michaliszyn, E.; Cromlish,
W.; Collins, S.; Lee Loy, A.; Normandin, D.; Cheng, A.;
Himms-Hagen, J.; Chan, C.-C.; Ramanchandran, C.;
Gresser, M. J.; Tremblay, M. L.; Kennedy, B. P. Science
1999, 283, 1544; (b) Kennedy, B. P. Biomed. Pharma-
cother. 1999, 53, 466.
3. (a) Kenner, K. A.; Anyanwu, E.; Olefsky, J. M.; Kusari, J.
J. Biol. Chem. 1996, 271, 19810; (b) Chen, H.; Wertheimer,
S. J.; Lin, C. H.; Katz, S. L.; Amrein, K. E.; Burn, P.;
Quon, M. J. J. Biol. Chem. 1997, 272, 8026; (c) Walchli, S.;
14. General procedure for the synthesis of compounds 2, 3
and 4: A mixture of 2,4-dihydroxy-acetophenone (1,
6 mmol, 912 mg) with alkyl halide (6 mmol) and potas-
sium carbonate (2 equiv) was refluxed in acetone for 8–
10 h. The resulting mixture was filtered to remove the
potassium carbonate. The filtrate was concentrated to
dryness to get the pure compound (2) in 60–70% yield. An
acetophenone derivative (2, 6 mmol) and aroyl chloride
(6 mmol) in dry pyridine (5 mL) was stirred at room
temperature for an hour before heating at 100 ꢁC for

M. Dixit et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3394–3397
3397
10 min under anhydrous condition. The resulting solution
was poured into 1 M HCl containing crushed ice, which
yielded a solid benzoate (3) in 80–85% yield. The potas-
sium tertiary butoxide was slowly added to magnetically
stirred solution of the benzoate (3) for 4–5 h in dry
pyridine. The resulting solution mixture was added to 10%
acetic acid solution. The yellow solid thus obtained was
filtered, dried, and crystallized in hexane–ethyl acetate to
give yellow needle-like crystals in good yield. Compound
4a: Yield 73%; mp: 119–120 ꢁC; MS (FAB): m/z 296
(M++1); IR (KBr): 1605 (CO), 2218 (CN), 3422 cmÀ1
1H, J = 2.0 Hz, CH), 7.48 (d, 1H, J = 6.0 Hz, ArH), 7.54–
7.59 (m, 2H, ArH), 7.66 (d, 1H, J = 2.0 Hz, CH), 7.67–
7.72 (m, 1H, ArH), 7.89 (d, 1H, J = 6.0 Hz, ArH), 8.27–
8.30 (m, 2H, ArH). Compound 8b: Yield 85%; mp: 109–
110 ꢁC; MS (FAB): m/z 349 (M++1); IR (KBr): 1685 (CO),
1
1748 cmÀ1 (CO); H NMR (200 MHz, CDCl3): d 2.60 (s,
3H, CH3), 6.75 (d, 1H, J = 2.0 Hz, CH), 7.51 (d, 1H,
J = 8.6 Hz, ArH), 7.62–7.68 (m, 2H, ArH), 7.88 (d, 1H,
J = 8.6 Hz, ArH), 8.10 (d, 1H, J = 8.4 Hz, ArH), 8.35 (d,
1H, J = 2.0 Hz, CH).
15. Sekar, N.; Li, J.; Shechter, Y. Crit. Rev. Biochem. Mol.
Biol. 1996, 31, 339.
1
(OH); H NMR (200 MHz, CDCl3): d 4.81 (s, 2H, CH2),
6.53–6.59 (m, 2H, ArH), 6.74 (s, 1H, CH), 7.49–7.57 (m,
3H, ArH), 7.78 (d, 1H, J = 8.9 Hz, ArH), 7.93 (d, 2H,
J = 8.1 Hz, ArH), 12.56 (s, 1H, OH), 15.36 (s, 1H, OH).
Compound 8a: Yield 80%; mp: 79–81 ꢁC; MS (FAB): m/z
16. Goldstein, B. J.; Bittner-Kowalezyk, A.; White, M. F.;
Harbeck, M. J. Biol. Chem. 2000, 275, 4283.
17. Malamas, M. S.; Sredy, J.; Moxham, C.; Katz, A.; Xu,
W.; Devitt, R. M.; Adibayao, F. O.; Sawicki, D. R.;
Seestaller, L.; Sullivan, D.; Taylor, X., Jr. J. Med. Chem.
2000, 43, 1293.
1
281 (M++1); IR (KBr): 1683 (CO), 1742 cmÀ1 (CO); H
NMR (200 MHz, CDCl3): d 2.60 (s, 3H, CH3), 6.74 (d,