Novel 2-aryl-naphtho[1,2-d]oxazole derivatives as potential PTP-1B inhibitors showing antihyperglycemic activities

Article abstract of DOI:10.1016/j.ejmech.2008.03.009

A series of 2-aryl-naphtho[1,2-d]oxazole derivatives have been synthesized and evaluated for PTP-1B inhibitory activity. The compounds have been screened in vivo for antidiabetic activity under sucrose loaded model (SLM), sucrose-challenged streptozotocin

Full text of DOI:10.1016/j.ejmech.2008.03.009

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 44 (2009) 109e116
http://www.elsevier.com/locate/ejmech
Original article
Novel 2-aryl-naphtho[1,2-d]oxazole derivatives as potential PTP-1B
inhibitors showing antihyperglycemic activities
a
a
Atul Kumar a, , Pervez Ahmad , Ram Awatar Maurya ,
*
A.B. Singh b, Arvind K. Srivastava b
a Medicinal and Process Chemistry Division, Central Drug Research Institute, P.O. Box 172, Lucknow 226001, Uttar Pradesh, India
b Biochemistry Division, Central Drug Research Institute, Lucknow 226001, Uttar Pradesh, India
Received 3 December 2007; received in revised form 10 March 2008; accepted 13 March 2008
Available online 27 March 2008
Abstract
A series of 2-aryl-naphtho[1,2-d]oxazole derivatives have been synthesized and evaluated for PTP-1B inhibitory activity. The compounds
have been screened in vivo for antidiabetic activity under sucrose loaded model (SLM), sucrose-challenged streptozotocin-induced diabetic
rat model (STZ-S) and db/db mice model. Compounds 8 and 12 have shown promising PTP-1B inhibitory activity, significant antidiabetic ac-
tivity, moderate lipid and triglyceride lowering activity.
Ó 2008 Elsevier Masson SAS. All rights reserved.
Keywords: 2-Aryl-naphtho[1,2-d]oxazole; Protein tyrosine phoshatase-1B inhibitors; Antidiabetic activity; Lipid and triglyceride lowering activity
1. Introduction
for potent small molecules as protein tyrosine phosphatase-
1B inhibitors is a major thrust area in the management of di-
abetes and obesity.
Protein tyrosine phosphatase-1B (PTP-1B) has emerged
as new target for the treatment of diabetes and obesity
[1e7]. These enzymes belong to a family of tyrosine phos-
phatase, which have about 90 members. The insulin recep-
tor is activated via autophosphorylation on tyrosine residue,
so a tyrosine phosphatase is required to shut off the recep-
tor. PTP-1B knockout mice have shown increased insulin
sensitivity and also exhibited decreased tendency of obesity
[8,9].
Enhanced IR as well as IRS-1 phosphorylation have been
observed in liver and skeleton muscles of PTP-1B knockout
mice. The results suggest that the target have potential to ad-
dress the defects in hepatic glucose output as well as defects in
hepatic glucose uptake. PTP-1B inhibitors are negative in in-
sulin and leptin signaling cascades. Thus, they play a critical
role in diabetes and obesity [10,11]. Therefore, the search
Recently, the interest in the development of small mole-
cules such as PTP-1B inhibitors has dramatically increased
[12]. Majority of PTP-1B inhibitors are peptidomimics or
tyrosine-mimicking structures with negatively charged mo-
tifs such as phosphonate and carboxylates [13,14]. Wrobel
and coworkers have reported Ertiprotafib (I) as potent
PTP-1B inhibitor [15]. These compounds have PPARg ago-
nistic activity also, which could contribute to their in vivo
efficacy. Recently, Broussonetia papyrifera root extract hav-
ing flavonides and flavones (II) were reported as potent
PTP-1B inhibitors [16]. Malamas et al. have reported
[17,18] benzofuran, benzothiophene and oxazole derivatives
(III, IV, V) as potent PTP-1B inhibitors (Fig. 1). Based on
reported PTP-1B inhibitors, we have designed and synthe-
sized 2-aryl-naphtho[1,2-d]oxazole derivatives as potential
PTP-1B inhibitors.
In this paper we wish to report synthesis, PTP-1B inhibitory
activity and in vivo antidiabetic activity of 2-aryl-naphtho
[1,2-d]oxazole derivatives.
* Corresponding author. Tel.: þ91 522 2612411; fax: þ91 522 2623405.
E-mail address: dratulsax@gmail.com (A. Kumar).
0223-5234/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.03.009

110
A. Kumar et al. / European Journal of Medicinal Chemistry 44 (2009) 109e116
COOH
F3C
O
O
HO
O
O
OH
O
HO
X
OH
N
O
OH
S
OR1
OH O
O
R2
OR1
Br
R2
I
II
III
IV
V
Ertiprota fib
Fig. 1. Structures of some Potent PTP-1B inhibitors
2. Results and discussion
presence of BF3$Et2O at 100 ꢀC gave corresponding naphtho-
phenone (3) in good yields. Naphthophenone (3) on reaction
with hydroxylamine hydrochloride and sodium acetate in reflux-
ing ethanol gave naphthophenone oxime (4) in very good yield.
Compound (4) on reaction with neat acetic anhydride at
room temperature gave naphthophenone oxime acetate (5).
Naphthophenone oxime acetate on reaction with neat pyridine
at 110 ꢀC under goes Beckmann type rearrangement to give
exclusively 2-aryl-naphtho [1,2-d]oxazole (6). Compound 6
on Williamson type O-alkylation reaction with different 1-
(2-chloro-ethyl)-substituted amine hydrochloride in presence
of potassium carbonate/potassium iodide in acetone/DMF
gave 2-[4-(2-substituted amino ethoxy) phenyl]-naphtho[1,2-d]
oxazoles. All the synthesized compounds are characterized by
spectroscopic analysis.
2.1. Chemistry
It seems from the structure of potent PTP-1B inhibitors
(Fig. 1) that a 6/6 fused bicyclic system (I, II, III, IV) along
with a five member heterocyclic ring (I, III, IV, V) are keys
for their activity. Based on these we have designed a 6/6/5
fused heterocylic system 6. We provided a phenolic group
(OH) in 6 for the addition of amine side chains and thus giving
additional amine binding site.
Synthesis of key intermediate of the series 4-naphtho[1,2-d]-
oxazole-2-yl-phenol (6) was achieved via a multi-step synthetic
route starting from b-naphthol (Scheme 1). Friedel Crafts ben-
zoylation of b-naphthol (1) with 4-hydroxybenzoic acid (2) in
OR
HO
OH
(a)
AcO
O
OH
HO
OH
NOCOCH3
OH
N
(b)
(c)
(d)
NOH
OH
O
1
COOH
3
6:R=H,
7:R=Ac
4
5
R1
O
R1 = N(CH3)2, 8, N(C2H5)2, 9,
(e)
Pyrrolidine, 10, piperidine, 11, N(CH3)nC H ,
12
4 9
N
O
O
x
8-12
(h)
OH
O
Cl
X H = Toludine, 14, Anisidine,
15, Methyl n-butyl
amine, 16,
(f)
N
O
N
N
O
O
n-Octylamine, 17,
Piperidine, 18
Pyrrolidine, 19,
Dimethylamine, 20,
Diethyl amine, 21
14-21
13
O(CH2)nCOOR1
6
n = 1, R1 = C2H5, 22
n = 3, R1 = C2H5, 23
(g)
N
O
n = 1, R1 = H, 24
n = 3, R1 = H, 25
22-25
Scheme 1. Reagents and condition: (a) BF3$Et2O, 100 ꢀC, (b) hydroxylamine hydrochloride, sodium acetate. Ethanol, reflux, (c) acetic anhydride, RT, (d) pyridine,
reflux, (e) K2CO3, acetone, ClCH2CH2R1$HCl, (f) BrCH2CH2CH2Cl, K2CO3, acetone, (g) K2CO3, acetone, bromoalkyl esters, (h) DMF, KI, XH (amines).

A. Kumar et al. / European Journal of Medicinal Chemistry 44 (2009) 109e116
111
2.2. Biological activity
dissociation constant Ki of the active compounds are given
in Table 1.
The synthesized compounds were tested for protein tyro-
sine phosphatase-1B (PTP-1B) inhibition study by pre-incu-
bating 100 mM of compounds in the test system for 10 min
and the residual PTPase activity was determined according
to the method of Goldstein et al. [19]. Vanadate (sodium ortho
vanadate) a non-selective PTP’s inhibitor was taken as a con-
trol. All 2-aryl-naphtho[1,2-d]oxazole derivatives were evalu-
ated as PTP-1B inhibitors. The structureeactivity relationship
of 2-aryl-naphtho[1,2-d]oxazoles reveals that although the par-
ent compound 6 has exhibited moderate activity, compounds
having side chains at phenolic OH of 6 have shown promising
PTP-1B inhibitory activity.
All the compounds were screened for their in vivo antidia-
betic activity in sucrose loaded model (SLM) male albino rats.
Compounds 8 (35.9%), 9 (21.7%), 11 (26.9%), 12 (35.3%), 18
(25.0%), 20 (25.2%), and 21 (20.5%) have shown significant
blood glucose lowering activity. Compounds showing good
blood glucose lowering activity were further tested for antidi-
abetic activity in sucrose-challenged streptozotocin (STZ-S)
induced diabetic rat model and in db/db mice model. Com-
pounds 8, 12 and 20 have shown significant antidiabetic activ-
ity in STZ-S model as well as in db/db mice model (Table 1).
Two compounds (8, 18.9% and 12, 22.3%) have shown better
blood glucose lowering profiles than standard drugs (metfor-
min, 11.2%; glybenclamide, 13.6%; glyclazide, 17.4%) in
db/db mice model.
Two compounds (8 and 12) were further tested for their an-
tidiabetic as well as antidyslipidemic activity in db/db mice
model under 6 days’ and 10 days’ protocol (Table 2). Interest-
ingly, these compounds (8 and 12) have shown promising in
vivo antidiabetic, lipid, triglyceride and cholesterol lowering
activity.
Compounds 8e12 having the two carbon chain along with
amines showed better activity than corresponding three carbon
chain compounds 14e21.
Activity data suggest that side chain having open chain al-
iphatic amines (8, 9, 12, 20 and 21) were more active than
compounds containing cyclic/aromatic amines (14, 15). Sur-
prisingly, compounds having ester and acid functionality did
not exhibit good inhibition. To rule out the possibility of pro-
miscuous inhibition in our results, we selected compounds 8e
12, 20 and 21 in the presence and absence of Triton X-100 (de-
tergent). The values of PTP-1B inhibitory activity revealed
that there is no significant variation in activity by addition of
Triton X-100 due to promiscuous inhibition. The IC50 and
3. Conclusion
In conclusion, we have synthesized 2-aryl-naphtho[1,2-
d]oxazoles and evaluated these compounds for their protein
Table 1
In vitro PTP-1B inhibitory activity as well as in vivo antidiabetic activity of 2-aryl-naphtho[1,2-d]oxazole derivatives in SLM, STZ-S and db/db mice model
Entry
Compound
PTP-1B inhibitory activity
% Antihyperglycemic activity
Inhibitiona (%)
ꢁTriton 100a,b
IC50 (mM)
þTriton 100a,b
IC50 (mM)
SLM
STZ-S
5 h
db/db micec
Ki (mM)
Ki (mM)
24 h
1
6
23.6
31.1
89.4
86.8
84.2
98.2
95.0
ND
e
e
e
e
10.8
16.8
35.9
21.7
8.7
ND
ND
27.9
11.4
ND
16.4
17.4
ND
14.6
ND
7.8
ND
ND
25.7
9.7
e
2
7
e
e
e
e
e
3
8
3.51
4.60
5.71
1.90
2.50
e
25.1
35.0
34.2
27.5
44.4
e
3.56
4.55
5.70
1.86
2.52
e
28.7
355
37.0
27.1
41.0
e
18.9
e
4
9
10
5
ND
15.7
18.7
ND
15.2
ND
9.2
e
6
11
12
26.9
35.3
7.4
10.4
22.3
e
7
8
13
14
9
44.2
43.6
44.5
39.7
34.2
46.7
87.8
88.4
30.7
ND
e
e
e
e
17.2
11.8
14.7
15.0
25.0
17.2
25.2
20.5
11.4
9.5
e
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
15
16
e
e
e
e
e
e
e
e
e
e
17
18
e
e
e
e
ND
13.4
12.6
15.6
11.5
ND
ND
ND
ND
ND
11.2
12.9
20.3
13.6
ND
ND
ND
ND
e
e
e
e
e
e
19
20
e
e
3.50
3.40
e
34.1
40.5
e
3.52
3.36
e
36.3
41.0
e
16.7
10.8
e
21
22
23
24
e
e
e
e
e
e
e
e
e
e
21.3
25.4
80.5
4.6
5.8
25
e
7.70
e
e
e
e
Na2VO3
Metformin
Glybenclamide
Glyclazide
12.9
33.9
44.8
19.1
32.8
27.7
20.2
11.2
13.6
17.4
ND ¼ not done.
a
Values are mean from three independent sets of experiments screened at 100 mM concentration.
Compounds were tested in the presence of 0.01% Triton X-100.
a 3 day protocol experiment.
b
c

112
A. Kumar et al. / European Journal of Medicinal Chemistry 44 (2009) 109e116
Table 2
Antihyperglycemic and antidyslipidemic activity in db/db mice model
Entry (compound
number)
Antihyperglycemic and antidyslipidemic activity in db/db mice (% efficacy, 6 and 10 days) (100 mg/kg)
Antihyperglycemic
Antidyslipidemic activity
6 Days
21.4
22.4
10 Days
23.6
24.1
TG
CHOL
ꢁ17.6
ꢁ12.2
HDL
þ3.0
þ1.3
8
12
ꢁ10.5
ꢁ7.5
tyrosine phosphatase-1B inhibitory activity. Several com-
pounds of this series have shown significant PTP-1B inhibitory
activity. The compounds were also screened for in vivo antidi-
abetic activity in SLM, STZ-S and db/db mice models. Com-
pounds 8 and 12 have exhibited most promising activity. The
compounds 8 and 12 were also tested for their dyslipidemic
activity and compound 8 has shown slightly better triglyceride
as well as lipid lowering profile.
4.1.2. Typical experimental procedure for the synthesis of 2-
hydroxy-41-hydroxy naphthophenone oxime (4)
2-Hydroxy-41-hydroxy naphthophenone 3 (2.64 g, 10 mmol)
was taken in 20 ml of ethyl alcohol. To it hydroxylamine
hydrochloride (3.0 g) and sodium acetate (3.0 g) were added.
Reaction mixture was then refluxed at water bath for 2 h. After
completion (TLC), ethyl alcohol was removed and reaction
mixture was extracted with ethyl acetate. The organic layer
was concentrated, dried over anhydrous sodium sulphate and
chromatographed on silica gel using a gradient mixture of hex-
ane/ethyl acetate to yield compound 4. Yieldþ(2.62 g, 93.90%);
mp 199e202 ꢀC; FABMS (m/z) 280 (M þ 1); IR (KBr,
4. Experimental
1
cmꢁ1), 3364, 1602, 1247; H NMR (DMSO-d6, 200 MHz) d:
4.1. Chemistry
7.05 (d, J ¼ 8.4 Hz, 2H), 7.36 (m, 4H), 7.78 (d, J ¼ 8.6 Hz,
2H), 7.90 (m, 1H), 10.1 (bs, 1H). Anal. calcd for
C17H13NO3, C, 73.11; H, 4.69; N, 5.02; Found: C, 72.97; H,
4.61; N, 4.83.
All the chemical reagents were purchased from SigmaeAl-
drich chemical company and were used directly without any
further purification. NMR spectra were obtained using the
Brucker DRX 200 MHz spectrometer. Chemical shifts (d)
are given in parts per million relative to TMS, coupling con-
stants (J ) in hertz. Mass spectra were obtained by using
a JEOL SX-102 (FAB) instrument. IR spectra were taken on
a VARIAN FT-IR spectrometer as KBr pellets. Elemental
analysis was preformed at a Perkin Elmer Autosystem XL An-
alyzer. Melting points were measured on a COMPLAB melt-
ing point apparatus. Reactions were monitored by thin-layer
chromatography (TLC) carried out on 0.25 mm silica gel
plates visualized with UV light.
4.1.3. Typical experimental procedure for the synthesis of
acetate of naphthophenone oximes (5)
2-Hydroxy-41-hydroxy-naphthophenone oxime 4 (2.79 g,
10 mmol) was taken in 10 ml of acetic anhydride and stirred
for 30 min. The reaction mixture was then poured in ice water
and extracted with ethyl acetate. The organic layer was dried
over anhydrous sodium sulphate and concentrated to remove
ethyl acetate yielding compound 5. Yield (2.84 g); physical
1
state (oil); FABMS (m/z) 364 (Mþ þ 1); H NMR (CDCl3,
200 MHz) d: 2.27 (s, 3H); 2.06 (s, 3H); 7.21 (d, J ¼ 8.8 Hz,
2H); 7.59 (m, 4H); 7.90 (d, J ¼ 8.4 Hz, 1H); 8.27 (d,
J ¼ 8.8 Hz); 8.50 (d, J ¼ 8.2 Hz, 1H). Anal. calcd for
C21H17NO5, C, 59.41; H, 4.72; N, 3.85; Found: C, 59.39; H,
4.61; N, 3.73.
4.1.1. Typical experimental procedure for the synthesis of 2-
hydroxy-41-hydroxy naphthophenone (3)
To a stirred solution of b-naphthol 1 (1.44 g, 10 mmol) in
10 ml of boron trifluoride etherate, 4-hydroxybenzoic acid 2
(1.51 g, 11 mmol) was added and the reaction mixture was
heated at 100 ꢀC for 6 h. Then, the reaction mixture was
poured in water and extracted with ethyl acetate. The organic
layer was separated, dried over anhydrous sodium sulphate
and concentrated to give a crude oil. The oil was then chroma-
tographed on silica gel using a gradient mixture of hexane/
ethyl acetate to yield 3. Yield (1.2 g, 49.9%); mp 178e
179 ꢀC; FABMS (m/z) 265 (M þ 1)þ; IR (KBr, cmꢁ1) 3364,
1573, 1508; 1H NMR (CDCl3, 200 MHz) d: 6.80 (d,
J ¼ 8.4 Hz, 2H), 7.26 (m, 3H), 7.40 (d, J ¼ 7.8 Hz, 1H), 7.69
(d, J ¼ 8.7 Hz, 2H), 7.76 (d, J ¼ 8.4 Hz, 2H); 13C NMR
(CDCl3, 50 MHz) d: 195.4, 161.6, 151.4, 131.2, 131.1,
129.5, 128.9, 127.0, 126.9, 125.7, 122.9, 122.0, 119.0,
117.4, 114.4. Anal. calcd for C21H12O3, C, 77.26; H, 4.58;
Found: C, 77.39; H, 4.61.
4.1.4. Typical experimental procedure for the synthesis of
naphtho[1,2-d]oxazole-2-yl-phenol (6)
(a) Naphthophenone oxime acetate 5 (2.79 g, 10 mmol) was
dissolved in10 ml of pyridine and heated at 80 ꢀC for
18 h. The reaction was quenched with ice water and ex-
tracted with ethyl acetate. The organic layer was dried
on sodium sulphate and evaporated under vacuum yielding
naphtho[1,2-d]oxazole-2-yl-phenol 6 and acetic acid-4-
naphtho[1,2-d]oxazole-2-yl-phenyl ester 7 (70:30).
(b) Naphthophenone oxime acetate 5 (2.79 g, 10 mmol) was
dissolved in 10 ml of pyridine and refluxed for 14 h. The
reaction was quenched with ice water and extracted with
ethyl acetate. The organic layer was dried on sodium

A. Kumar et al. / European Journal of Medicinal Chemistry 44 (2009) 109e116
113
sulphate and evaporated under vacuum yielding exclu-
sively naphtho[1,2-d]oxazole-2-yl-phenol 6. Yield
(2.07 g, 79%); mp 278 ꢀC; FABMS (m/z) 262 (M)þ; IR
(KBr, cmꢁ1), 3450, 1610, 1437; 1H NMR (DMSO-d6,
200 MHz) d: 6.98 (d, J ¼ 8.7 Hz, 2H); 7.46 (m, 1H);
7.58 (m, 2H); 7.92 (m, 2H); 8.09 (m, 3H); 8.41 (d,
J ¼ 8.1 Hz, 1H); 9.6 (bs, IH). Anal. calcd for
C17H11NO2, C, 78.12; H, 4.25; N, 5.36; Found: C,
78.22; H, 4.26; N, 5.48.
(M þ 1)þ; IR (KBr, cmꢁ1), 3446, 1607, 1245; 1H NMR
(CDCl3, 200 MHz) d: 1.84 (m, 4H); 2.64 (m, 4H); 2.95 (t,
J ¼ 5.8 Hz, 2H); 4.2 (t, J ¼ 5.9 Hz, 2H); 7.06(d, J ¼ 8.4 Hz,
2H); 7.68 (m, 4H); 7.95 (d, J ¼ 8.2 Hz, 1H); 8.25(d,
J ¼ 8.8 Hz, 2H); 8.57 (d, J ¼ 8.2 Hz, 1H); Anal. calcd for
C23H22N2O2, C, 77.07; H, 6.19; N, 7.82; Found: C, 77.22;
H, 6.26; N, 7.68.
4.1.6.4. 2-[4-(2-Piperidine-1-yl-ethoxy)-phenyl]-naphtho[1,2-
d]oxazole (11). Yield (92.6%); mp 118e120 ꢀC; FABMS
1
4.1.5. Typical experimental procedure for the synthesis of
acetic acid-4-naphtho[1,2-d]oxazole-2-yl-phenyl ester (7)
2-Hydroxy-41-hydroxy naphthophenone oxime 4 (2.79 g,
10 mmol) was dissolved in 14 ml of acetic anhydride and
cooled. Then 18 ml of pyridine was added to it. The reaction
mixture was heated at 80 ꢀC for 13 h to afford exclusively ace-
tic acid-4-naphtho[1,2-d]oxazole-2-yl-phenyl ester 7. Yield
(2.87 g, 94.91%), mp 185e187 ꢀC FABMS (m/z) 304
(M þ 1)þ IR (KBr cmꢁ1), 3416, 1748, 1605 1H NMR
(CDCl3, 200 MHz) d: 2.27 (s, 3H); 7.22 (m, 2H); 7.68 (m,
4H); 7.90 (d, J ¼ 8.06, 1H); 8.28 (m, 2H); 8.51(d, J ¼ 8.1,
1H) Anal. calcd for C19H13NO3, C, 75.24; H, 4.32; N, 4.62.
Found: C, 75.34; H, 4.42; N, 4.83.
(m/z) 373 (M þ 1)þ; IR (KBr, cmꢁ1), 3436, 1612, 1256; H
NMR (CDCl3, 200 MHz) d: 1.47 (m, 2H); 1.62 (m, 4H);
2.52 (m, 4H); 2.80 (t, J ¼ 5.8 Hz, 2H); 4.18 (t, J ¼ 5.9 Hz,
2H); 7.04 (d, J ¼ 7.4, 2H); 7.68 (m, 4H); 7.95 (d,
J ¼ 8.2 Hz, 1H); 8.25 (d, J ¼ 8.8 Hz, 2H); 8.57 (d, J ¼ 8.2,
1H); Anal. calcd for C24H24N2O2, C, 77.39; H, 6.49; N,
7.52; Found: C, 77.32; H, 6.36; N, 7.63.
4.1.6.5.
Butyl-methyl-[2-(4-naphtho[1,2-d]oxazol-2-yl-phe-
noxy)-ethyl]-amine (12). Yield (80%); mp 125e128 ꢀC (HCl
salt); FABMS (m/z) 375 (M þ 1)þ; 1H NMR (CDCl3,
200 MHz) d: 1.09 (t, J ¼ 5.4 Hz, 3H); 1.35 (m, 4H); 2.23 (s,
3H); 2.36 (t, J ¼ 5.2 Hz, 2H); 2.53 (J ¼ 4.6 Hz, 2H); 4.08 (t,
J ¼ 2.6 Hz, 2H); 7.02 (d, J ¼ 6 Hz, 2H); 7.68 (m, 4H); 7.93
(m, 1H); 8.25 (m, 2H); 8.57 (d, J ¼ 5.2 Hz, 1H); Anal. calcd
for C24H26N2O2, C, 76.98; H, 7.00; N, 7.48; Found: C,
77.14; H, 7.27; N, 7.63.
4.1.6. General synthetic procedure for synthesis of 8e12
To a solution of 6 (2 mmol) in 35 ml of dry acetone, 1-(2-
chloro-ethyl)-alkyllamino hydrochloride (2.5 mmol) and po-
tassium carbonate (6.9 g, 50 mmol) was added. The reaction
mixture was then refluxed for 8 h. After completion (TLC),
the reaction was filtered and concentrated to remove acetone.
Then, the reaction mixture was extracted with ethyl acetate
(100 ml) and dried over sodium sulphate to give a crude oil.
The crude oil was purified by column chromatography using
ethyl acetate/hexane as an eluent on basic alumina to yield
compounds 8e12.
4.1.7. Typical experimental procedure for the synthesis of 4-
(3-chloro-propoxy)-phenyl]-naphtho[1,2-d]oxazole (13)
Compound 6 (1.32 g, 5 mmol) was taken in 35 ml of dry
acetone. To it 1-bromo-3-chloropropane (1.22 ml, 11 mmol)
and potassium carbonate (13.8 g) were added. The reaction
mixture was refluxed for 8 h. After completion (TLC), the re-
action mixture was filtered and concentrated to remove ace-
tone. Then it was dissolved in ethyl acetate and washed with
water. Compound 13 was obtained by crystallization of ethyl
acetate layer with hexane. Yield (3.21 g, 95%); mp 108e
110 ꢀC; FABMS (m/z) 338 (M þ 1)þ; 1H NMR (CDCl3,
200 MHz) d: 4.20 (t, J ¼ 5.8 Hz, 2H,); 3.77 (t, J ¼ 6.40 Hz,
2H); 2.28 (m, 2H); 7.04 (d, J ¼ 8.7 Hz, 2H); 7.68 (m, 4H);
7.86 (d, J ¼ 8.2 Hz, 1H); 8.25 (d, J ¼ 8.8 Hz, 2H); 8.57 (d,
J ¼ 8.0 Hz, 1H). Anal. calcd for C20H16ClNO2, C, 71.11; H,
4.77; N, 4.15; Found: C, 71.23; H, 4.87; N, 4.02.
4.1.6.1. Dimethyl-[2-(4-naphtho[1,2-d]oxazol-2-yl-phenoxy)-
ethyl]-amine (8). Yield (92.%); mp 102e104 ꢀC; FABMS
1
(m/z) 333 (M þ 1)þ; IR (KBr, cmꢁ1), 3417, 1609, 1210; H
NMR (CDCl3, 200 MHz) d: 2.3 (s, 6H); 2.78 (t, J ¼ 5.6 Hz);
4.16 (t, J ¼ 5.6 Hz, 2H); 7.07 (d, J ¼ 8.2 Hz, 2H); 7.68 (m,
4H); 7.74 (d, J ¼ 5.4 Hz, 1H); 7.76 (m, 2H); 8.26 (d,
J ¼ 9.8 Hz, 1H); Anal. calcd for C21H20N2O2, C, 75.58; H,
5.65; N, 8.26; Found: C, 75.68; H, 5.86; N, 8.33.
4.1.6.2.
Diethyl-[2-(4-naphtho[1,2-d]oxazol-2-yl-phenoxy)-
4.1.8. General synthetic procedure for synthesis of 14e21
Compound 13 (675 mg, 2 mmol) was taken in 15 ml of dry
DMF. To it amines (2.5 mmol) and potassium iodide (830 mg,
5 mmol) were added. The reaction mixture was stirred at
100 ꢀC for 4 h and then extracted with ethyl acetate. Organic
layer was dried over sodium sulphate and chromatographed
on basic alumina. Elution with a gradient mixture of hexane/
ethyl acetate yielded compounds 14e21, respectively.
ethyl]-amine (9). Yield (93%); mp 98e100 ꢀC; FABMS (m/z)
361 (M þ 1)þ; IR (KBr, cmꢁ1), 3437, 1608, 1246; H NMR
1
(CDCl3, 200 MHz) d: 1.06 (m, 6H); 2.60 (m, 4H); 2.91
(t, J ¼ 5.4 Hz, 2H); 4.13 (t, J ¼ 5.6 Hz, 2H); 7.04 (d,
J ¼ 9.2 Hz, 2H); 7.68 (m, 4H); 7.96 (d, J ¼ 8.2 Hz, 1H);
8.25 (d, J ¼ 8.8 Hz, 2H); 8.56 (d, J ¼ 8.2, 1H); Anal. calcd
for C23H24N2O2, C, 76.58; H, 6.85; N, 8.26; Found: C,
76.64; H, 6.71; N, 8.07.
4.1.8.1. [3-(4-Naphtho[1,2-d]oxazol-2-yl-phenoxy)-propyl]-p-
4.1.6.3. 2-[4-(2-Pyrrolidin-1-yl-ethoxy)-phenyl]-naphtho[1,2-d]
oxazole (10). Yield (89%); mp 98e100 ꢀC; FABMS (m/z) 359
tolyl-amine (14). Yield (92%); mp 118e120 ꢀC; FABMS (m/
1
z) 409 (M þ 1)þ; H NMR (CDCl3, 200 MHz) d: 2.11 (m,

114
A. Kumar et al. / European Journal of Medicinal Chemistry 44 (2009) 109e116
2H); 2.23 (s, 3H); 3.34 (t, J ¼ 4.4 Hz, 2H); 4.14 (t, J ¼ 3.8 Hz,
2H); 5.27 (s, 1H); 6.57 (d, J ¼ 5.6 Hz, 2H); 6.99 (t, J ¼ 6.0 Hz,
4H); 7.52 (m, 1H); 7.68 (m, 3H); 7.95 (d, J ¼ 5.4 Hz, 1H);
8.25 (m, 2H); 8.57 (d, J ¼ 5.2 Hz, 1H); Anal. calcd for
C27H24N2O2, C, 79.39; H, 5.92; N, 6.86; Found: C, 79.44;
H, 5.74; N, 6.86.
1H); Anal. calcd for C24H24N2O2, C, 77.39; H 6.49, N, 7.52;
Found: C, 77.30; H, 6.66; N, 7.68.
4.1.8.7. Dimethyl-[3-(4-naphtho[1,2-d]oxazol-2-yl-phenoxy)-
propyl]-amine (20). Yield (75%); mp 128e134 ꢀC; FABMS
1
(m/z) 347 (M þ 1)þ; H NMR (CDCl3, 200 MHz) d: 2.3 (s,
6H); 1.72 (m, 2H); 2.78 (t, J ¼ 5.6 Hz, 2H); 4.16 (t,
J ¼ 5.6 Hz, 2H); 7.07 (m, 2H); 7.68 (m, 4H); 7.74 (m, 1H);
7.76 (m, 2H); 8.26 (m, 1H); Anal. calcd for C22H22N2O2, C,
76.28; H, 6.40; N, 8.09; Found: C, 76.11; H, 6.26; N, 8.23.
4.1.8.2. 4-(Methoxy-phenyl)-[3-(4-naphtho[1,2-d] oxazol-2-yl-
phenoxy)-propyl]-amine (15). Yield þ (84%); mp 136e
140 ꢀC; FABMS (m/z) 425 (M þ 1) ; 1H NMR (CDCl3,
200 MHz) d: 2.11 (m, 2H); 3.37 (t, J ¼ 6.4 Hz, 2H); 3.77
(s, 3H); 4.14 (t, J ¼ 4.0 Hz, 2H); 6.67 (d, J ¼ 6.6 Hz, 2H);
6.82 (d, J ¼ 6.6 Hz, 2H); 7.07 (d, J ¼ 5.8 Hz, 2H); 7.77
(m, 4H); 7.99 (d, J ¼ 5.4 Hz, 1H); 8.28 (d, J ¼ 6.6 Hz,
2H); 8.59 (d, J ¼ 5.8 Hz, 1H); Anal. calcd for
C27H24N2O3, C, 76.39; H, 5.70; N, 6.60; Found: C, 76.54;
H, 5.55; N, 6.74.
4.1.8.8.
Diethyl-[3-(4-naphtho[1,2-d]oxazol-2-yl-phenoxy)-
propyl]-amine (21). Yield (72%); mp 136e140 ꢀC; FABMS
(m/z) 375 (M þ 1)þ; H NMR (CDCl3, 200 MHz) d: 1.03 (s,
1
6H); 1.72 (m, 2H); 2.28 (m, 2H); 2.68 (m, 2H); 4.16 (t,
J ¼ 5.6 Hz, 2H); 7.07 (m, 2H); 7.68 (m, 4H); 7.74 (m, 1H);
7.76 (m, 2H); 8.26 (m, 1H); Anal. calcd for C24H26N2O2, C,
76.98; H, 7.00; N, 8.54; Found: C, 76.82; H, 7.16; N, 8.39.
4.1.8.3.
Butyl-methyl-[2-(4-naphtho[1,2-d]oxazol-2-yl-phe-
noxy)-propyl]-amine (16). Yield (90%); mp 115e118 ꢀC
(HCl salt); FABMS (m/z) 389 (M þ 1)þ; IR (KBr, cmꢁ1),
4.1.9. Typical experimental procedure for the synthesis of 4-
(4-naphtho[1,2-d]oxazole-2yl-phenoxy)-acetic acid ethyl
ester (22)
1
3443, 1611, 1246; H NMR (CDCl3, 200 MHz) d: 0.99 (t,
J ¼ 5.4 Hz, 3H); 1.35 (m, 4H); 1.97 (t, J ¼ 4.8 Hz, 2H);
2.24 (s, 3H); 2.36 (t, J ¼ 5.2 Hz, 2H); 2.53 (J ¼ 4.6 Hz,
2H); 4.08 (t, J ¼ 2.6 Hz, 2H); 7.02 (d, J ¼ 6 Hz, 2H); 7.68
(m, 4H); 7.94 (d, J ¼ 5.6 Hz, 1H); 8.25 (d, J ¼ 5.8 Hz,
2H); 8.57 (d, J ¼ 5.2 Hz, 1H); Anal. calcd for
C25H28N2O2, C, 77.29; H, 7.26; N, 7.28; Found: C, 77.34;
H, 7.37; N, 7.43.
Naphtho[1,2-d]oxazole-2-yl-phenol 6 (1.31 g, 5 mmol) was
taken in 30 ml of dry acetone. To it bromoethyl acetate
(0.66 ml, 6 mmol) and potassium carbonate (13.8 g,
100 mmol) were added. The reaction mixture was refluxed
for 8 h. After completion (TLC), the reaction mixture was fil-
tered and concentrated to remove acetone. The reaction mix-
ture was extracted with ethyl acetate and dried over sodium
sulphate to give a crude oil. The crude oil was purified by col-
umn chromatography using silica gel as adsorbent and hexane/
ethyl acetate as an eluent to yield compound 22. Yield (1.51 g,
87%); mp 138 ꢀC; FABMS (m/z) 348 (M þ 1)þ; 1H NMR
(CDCl3, 200 MHz) d: 1.30 (t, J ¼ 7.0 Hz, 3H); 4.29 (q,
J ¼ 7.2 Hz, 2H); 4.69 (s, 2H); 7.04 (d, J ¼ 5.2 Hz, 2H); 7.72
(m, 4H); 7.95 (d, J ¼ 8.0 Hz, 1H); 8.25 (d, J ¼ 7.0 Hz, 2H);
8.56 (d, J ¼ 8.2 Hz, 1H). Analysis calcd for C21H17NO4: C,
72.61; H, 4.93; N, 4.03; Found C, 72.49; H, 4.80; N, 3.91.
4.1.8.4. [3-(4-Naphtho[1,2-dloxazol-2-yl-phenoxy)-propyl]-oc-
tyl-amine (17). Yield (82.5%); mp 67e69 ꢀC; FABMS (m/z)
1
431 (M þ 1)þ; IR (KBr, cmꢁ1), 3463, 1659, 1250; H NMR
(CDCl3, 200 MHz) d: 0.88 (t, J ¼ 4.2 Hz, 3H); 1.20 (m, 8H);
1.52 (m, 4H); 2.01 (m, 2H); 2.63 (J ¼ 4.0 Hz, 2H); 2.83 (t,
J ¼ 5.4 Hz, 2H); 4.13 (t, J ¼ 6.4 Hz, 2H); 7.04 (d,
J ¼ 6.0 Hz, 2H); 7.68 (m, 4H); 7.96 (d, J ¼ 4.2 Hz, 1H);
8.25 (d, J ¼ 6.0 Hz, 2H); 8.57 (d, J ¼ 8.2 Hz, 1H); Anal. calcd
for C28H34N2O2, C, 78.10; H, 7.96; N, 6.51; Found: C, 78.24;
H, 7.83; N, 6.63.
4.1.10. Typical experimental procedure for the synthesis of
4-(4-naphtho[1,2-d]oxazole-2yl-phenoxy)-butyric acid ethyl
ester (23)
4.1.8.5. 2-[-4-(Piperidin-1-yl-propoxy)-phenyl]-naptho[1,2-d]
oxazole (18). Yield (87%); mp 119 ꢀC; FABMS (m/z) 387
(M þ 1)þ; IR (KBr, cmꢁ1), 3432, 1604, 1250; 1H NMR
(CDCl3, 200 MHz) d: 1.65 (m, 2H); 1.70 (m, 4H); 2.05 (m,
2H); 2.48 (m, 4H); 2.56 (t, J ¼ 8.0 Hz, 2H); 4.09 (t,
J ¼ 6.2 Hz, 2H); 7.02 (d, J ¼ 6.9 Hz, 2H); 7.72 (m, 4H);
7.95 (d, J ¼ 7.2 Hz, 1H); 8.23 (d, J ¼ 7.2 Hz, 2H); 8.57 (d,
J ¼ 7.6 Hz, 1H); Anal. calcd for C25H26N2O2, C, 77.69; H,
6.75; N, 7.25; Found: C, 77.42; H, 6.56; N, 7.38.
4-Naphtho[1,2-d]oxazole-2-yl-phenol 6 (1.31 g, 5 mmol)
was taken in 30 ml of dry acetone. To it ethyl-4-bromobutyrate
(0.90 ml, 6 mmol) and potassium carbonate (13.8 g) were
added. The reaction mixture was refluxed for 8 h. After com-
pletion (TLC), the reaction mixture was filtered and concen-
trated to remove acetone. The reaction mixture was
extracted with ethyl acetate and dried over sodium sulphate
to give a crude oil. The crude oil was purified by column chro-
matography using silica gel as adsorbent and hexane/ethyl ac-
etate as a eluent to yield compound 23. Yield (þ1.51 g, 87%);
mp 83e85 ꢀC; FABMS (m/z) 376 (M þ 1) ; 1H NMR
(CDCl3, 200 MHz) d: 1.27 (t, J ¼ 7.0 Hz, 3H), 2.16 (m, 2H),
2.53 (m, 2H), 4.13 (m, 4H), 7.02 (d, J ¼ 8.8 Hz, 2H), 7.27
(m, 4H), 7.74 (d, J ¼ 5.4 Hz, 2H), 8.25 (d, J ¼ 5.4 Hz, 2H);
4.1.8.6.
2-[4-(3-Pyrrolidin-1-yl-propoxy)-phenyl]-naphtho
[1,2-d]oxazole (19). Yield (80%); mp 127e130 ꢀC; FABMS
(m/z) 373 (M þ 1)þ; 1H NMR (CDCl3, 200 MHz) d: 1.47
(m, 2H); 1.67 (m, 4H); 2.48 (m, 4H); 2.56 (t, J ¼ 8.0 Hz,
2H); 4.09 (t, J ¼ 6.2 Hz, 2H); 7.02 (m, 2H); 7.72 (m, 4H);
7.95 (m, 1H); 8.23 (d, J ¼ 7.2 Hz, 2H); 8.57 (d, J ¼ 7.6 Hz,

A. Kumar et al. / European Journal of Medicinal Chemistry 44 (2009) 109e116
115
Analysis calcd for C23H21NO4: C, 73.58; H, 5.64; N, 3.73;
Found C, 73.47; H, 5.60; N, 3.61.
a dose of 100 mg/kg body weight. Animals of control group
were given an equal amount of 1.0% gum acacia. A sucrose
load of 2.5 g/kg body weight was given after 30 min of com-
pound administration. After 30 min of post-sucrose load blood
glucose level was again checked by glucostrips at 30, 60, 90,
120, 180, 240, 300 min and at 24 h, respectively. Animals not
found diabetic after 24 h post-treatment of the test sample
were not considered and omitted from the calculations and
termed as non-responders. The animals, which did not show
any fall in blood glucose profile in a group while the others
in that group, showed fall in blood glucose profile were also
considered as non-responders. Food but not water was with-
held from the cages during the experimentation. Comparing
the AUC of experimental and control groups determined the
percent antihyperglycemic activity.
4.2. Pharmacology
4.2.1. Protein tyrosine phosphatase-1B inhibitory assay
Protein tyrosine phosphatase inhibitory activity of com-
pounds was determined by modified method of Goldstein
et al. [19]. The test compounds were pre-incubated for
10 min with the enzyme in the absence and presence of
0.01% Triton X-100. Assay was performed in final volume
of 1.0 ml in test mixture containing 10 mM of pNPP in
50 mM HEPES buffer (pH 7.0) with 1 mM DTT and 2 mM
EDTA. The reaction was stopped after 30 min of incubation
at 37 ꢀC by addition of 500 ml of 0.1 N NaOH and the absor-
bance was determined at 410 nm. A molar extinction coeffi-
cient of 1.78 ꢂ 104 Mꢁ1 cmꢁ1 was utilized to calculate the
concentration of p-nitrophenolate ion generated in the reaction
mixture. Sodium orthovanadate was taken as standard in en-
zyme assay.
4.2.4. Antihyperglycemic activity in db/db mice
The db/db mouse is a well-characterized model of type 2
diabetes. The background for the db/db mouse is the
C57BL/Ks strain. The optimal age of db/db mice used for ex-
periments is from week 12e18 when they have developed
NIDDM with diabetic dyslipidemia but still have functional
b-cells in the pancreas. C57BL/KsBom-db mice 12e18
weeks, 40e50 g bred in the animal house of CDRI, Lucknow.
Ten mice (five males and five females) were used in the exper-
iments. The mice were housed in groups of five (same sex) in
a room controlled for temperature (23 ꢃ 2.0 ꢀC) and 12/12 h
light/dark cycle (lights on at 6.00 a.m.). Body weight was
measured daily from day 1 to day 10. All animals had free ac-
cess to fresh water and to normal chow except on the days of
the postprandial protocol day 6 and during the overnight fast
before the OGTT on day 10. The animals always had access
to water during experimental periods. Blood glucose was
checked every morning up till day 5. On day 6 postprandial
protocol was employed, in this method blood glucose was
checked at e0.5 and 0 h. Test drugs were given to the treat-
ment group whereas vehicle received only gum acacia
(1.0%); the blood glucose was again checked at 1, 2, 3, 4
and 6 h post-test drug treatment. On day 8, blood was col-
lected for serum insulin measurements and finally on day 10
an oral glucose tolerance test (OGTT) was performed after
an overnight fasting. Blood glucose was measured at e
30.0 min and test drugs were administered. The blood glucose
was again measured at 0.0 min post-treatment and at this junc-
ture glucose solution was given at a dose of 3 g/kg to all the
groups including vehicle. The blood glucose levels were
checked at 30, 60, 90 and 120 min post-glucose administra-
tion. Compound 8 showed blood glucose lowering effect on
postprandial protocol on days 3, 6 and 10 in db/db (Tables 1
and 2).
4.2.2. Sucrose loaded rat model (SLM)
Male albino rats of Charles Foster/Wistar strain of average
body weight 160 ꢃ 20 g were selected for this study. The
blood glucose level of each animal was checked by glucometer
using glucostrips (Boehringer Mannheim) after 16 h starva-
tion. Animals showing blood glucose levels between 3.33
and 4.44 mM (60e80 mg/dl) were divided into groups of
five to six animals in each. Animals of experimental group
were administered suspension of the desired synthetic com-
pound orally (made in 1.0% gum acacia) at a dose of
100 mg/kg body weight. Animals of control group were given
an equal amount of 1.0% gum acacia. A sucrose load (10.0 g/
kg) was given to each animal orally exactly after 30 min post-
administration of the test sample/vehicle. Blood glucose pro-
file of each rat was again determined at 30, 60, 90 and
120 min post-administration of sucrose by glucometer. Food
but not water was withheld from the cages during the course
of experimentation. Quantitative glucose tolerance of each an-
imal was calculated by area under curve (AUC) method (Prism
Software). Comparing the AUC of experimental and control
groups determined the percentage antihyperglycemic activity.
4.2.3. Sucrose-challenged streptozotocin-induced diabetic
rat model (STZ-S)
Male albino rats of Sprague Dawley strain of body weight
160 ꢃ 20 g were selected for this study. Streptozotocin 13
(Sigma, USA) was dissolved in 100 mM citrate buffer pH
4.5 and calculated amount of the fresh solution was injected
to overnight fasted rats (45 mg/kg) intraperitoneally. Blood
glucose level was checked 48 h later by glucostrips and ani-
mals showing blood glucose values between 144 and
270 mg/dl (8e15 mM) were included in the experiment and
termed diabetic. The diabetic animals were divided into
groups consisting of five to six animals in each group. Animals
of experimental groups were administered suspension of the
desired test samples orally (made in 1.0% gum acacia) at
Acknowledgements
Pervez Ahmad, Ram Awatar Maurya and Amar Bahadur
Singh are thankful to CSIR New Delhi for financial support
in the form of SRF. Authors also acknowledge SAIFeCDRI
for providing spectral and analytical data.

116
A. Kumar et al. / European Journal of Medicinal Chemistry 44 (2009) 109e116
[9] L.D. Klaman, O. Boss, O.D. Peroni, J.K. Kim, Z. Martino, J.M. Abolotny,
References
N. Moghal, M. Lubkin, Y.B. Kim, A.H. Sharpe, K.A. Strricker,
G.I. Shulman, B.G. Neel, B.B. Kahan, Mol. Cell. Biol. 20 (2000) 5479.
[10] C.R. Kahan, Diabetes 43 (1994) 1066.
[1] W.C. Ripka, in: A.M. Doherty (Ed.), Annual Reports in Medicinal Chem-
istry, vol. 35, Academic, San Diego, CA, 2000, p. 231.
[2] T.O. Johnson, J. Ermolieff, M. Jirousek, Nat. Rev. Drug Discov. 1 (2000)
696.
[11] M.A. Balskovich, H.O. Kim, Expert Opin. Ther. Pat. 12 (2002) 871.
[12] S. Lee, Q. Wang, Med. Res. Rev. 27 (2007) 553.
[13] D.L. Scott, B. Tjeerd, L. Charlotta, D.M. Paul, O. Derek, J.O. Theresa,
J.P. Barbara, J.S. Heinrich, F.C. Stevens, E.B. John, J. Med. Chem. 45
(2002) 598e622.
[3] Z.-J. Yao, B. Ye, X.-W. Wu, S. Wang, L. Wu, Z.-Y. Zhang, T.R. Burke Jr.,
Bioorg. Med. Chem. 6 (1998) 1799.
[4] H.G. Cheon, S.-M. Kim, S.-D. Yang, J.D. Ha, J.-K. Choi, Eur. J. Pharma-
col. 485 (2004) 333.
[14] C. Liljebris, S.D. Larsen, D. Ogg, B.J. Palazuk, J.E. Beasdale, J. Med.
Chem. 42 (2002) 3199.
[5] C. Dufresne, P. Roy, Z. Wang, E. Asante-Appiah, W. Cromlish, Y. Boie,
F. Forghani, S. Desmarais, Q. Wang, K. Skorey, D. Waddleton,
C. Ramachandran, B.P. Kennedy, L. Xu, R. Gordon, C.C. Chan,
Y. Leblanc, Bioorg. Med. Chem. Lett. 14 (2004) 1039.
[6] R.H. van Huijsduijnen, W.H.B. Sauer, A. Bombrun, D. Swinnen, J. Med.
Chem. 47 (2004) 4142e4146.
[15] J. Wrobel, J. Sredy, C. Moxham, A. Dietrich, Z. Li, D.R. Sawicik,
L. Festaller, L. Wu, A. Katz, D. Sullivan, C. Tio, Z. Zhong-Yin, J.
Med. Chem. 45 (1999) 1785.
[16] R.M. Chen, L.H. Hu, T.Y. An, J. Li, Q. Shen, Bioorg. Med. Chem. Lett.
12 (2002) 3387.
[17] M.S. Malamas, J. Sredy, I. Gunavan, B. Mihan, D.R. Sawichi,
L. Seestaller, D. Sullivan, B.R. Flam, J. Med. Chem. 43 (2000) 995.
[18] M.S. Malamas, J. Sredy, A. Katz Moxham, W.X. Xu, R. Mcdevitt,
F.O. Adedayo, D.R. Sawiciki, L. Seetaller, L. Sullivan, J.R. Taylor, J.
Med. Chem. 43 (2000) 1293.
[7] S.Y. Cho, J.Y. Baek, S.S. Han, S.K. Kang, J.D. Ha, J.H. Ahn, J.D. Lee,
K.R. Kim, H.G. Cheon, S.D. Rhee, S.D. Yang, G.H. Yon, C.S. Pak, J.-
K. Choi, Bioorg. Med. Chem. Lett. 16 (2006) 499.
[8] M. Elchebly, P. Payette, E. Michaliszyn, W. Cromlish, S. Collins,
A.L. Loy, D. Normandin, A. Cheng, J. Himms-Hagen, C.C. Chen,
C. Ramchandran, M.J. Gresser, M.L. Treblay, B.P. Kennedy, Science
183 (1999) 1544.
[19] B.J. Goldstein, A. Bittner-Kowalezyk, M.F. White, M. Harbeck, J. Biol.
Chem. 275 (2000) 4283.