Synthesis, resolution, and antiplatelet activity of 3-substituted 1(3H)-isobenzofuranone

Article abstract of DOI:10.1016/j.bmcl.2007.06.082

A series of 3-substituted-1(3H)-isobenzofuranone 6a-g and 7a-g were synthesized from phthalic anhydride. The compound 6a-g was resolved. The antiplatelet activities of these compounds were evaluated using in vitro experiment of platelet aggregation. The levels of antiplatelet activity were displayed as following sequence: l-isomer > dl-isomer > d-isomer, respectively. The alkylphthalide is more active than the corresponding alkenephthalide. All these compounds were less active than n-butylphthalide (NBP, 6c) and Aspirin (Asp).

Full text of DOI:10.1016/j.bmcl.2007.06.082

Bioorganic & Medicinal Chemistry Letters 17 (2007) 5210–5213
Synthesis, resolution, and antiplatelet activity
of 3-substituted 1(3H)-isobenzofuranone
Hua Yang, Gao-Yun Hu,* Jun Chen, Yi Wang and Zhong-Hua Wang
Research Institute of Medicinal Chemistry, School of Pharmaceutical Sciences, Central South University, Changsha 410013, PR China
Received 4 December 2006; revised 27 June 2007; accepted 28 June 2007
Available online 1 July 2007
Abstract—A series of 3-substituted-1(3H)-isobenzofuranone 6a–g and 7a–g were synthesized from phthalic anhydride. The com-
pound 6a–g was resolved. The antiplatelet activities of these compounds were evaluated using in vitro experiment of platelet aggre-
gation. The levels of antiplatelet activity were displayed as following sequence: l-isomer > dl-isomer > d-isomer, respectively. The
alkylphthalide is more active than the corresponding alkenephthalide. All these compounds were less active than n-butylphthalide
(NBP, 6c) and Aspirin (Asp).
Ó 2007 Elsevier Ltd. All rights reserved.
Cardiovascular and cerebrovascular disorders are the
main cause of deformity and death in recent years. As
a result, seeking ideal medicine for the treatment of cer-
ebralapoplexy with good effectiveness and low toxicity
has become the interest of many investigators. It was
found out that 1(3H)-isobenzofuranone had the anti-
platelet activity. n-Butylphthalide (NBP) is a represen-
tive compound from such group, represent which has
already been in the market as antiplatelet drug for ische-
mia-cerebralapoplexy. There was significant difference
in the antiplatelet effect of NBP stereo isomers, which
is known as l NBP > dl-NBP > d-NBP.1–4 Structure
modification of NBP has not been investigated yet. In
addition, butylidenephthalide also has the activity of
antiplatelet.5 In this study, 3-alkyl-1(3H)-isobenzofura-
none derivatives 6a–g and 3-alkene-1(3H)-isobenzofura-
none derivatives 7a–g were designed and synthesized
with the different substituent on the 3-position. Further-
more, the stereo isomers of 3-alkyl-1(3H)-isobenzofura-
none were resolved using chemical method.
The compounds 6a–g and 7a–g were synthesized by five-
step reaction as outlined in Scheme 1.7 The 3-substi-
tuted-1(3H)-isobenzofuranone derivatives 6a–g and
7a–h were synthesized (Scheme 1) from RBr. The key
intermediates 5a–g were synthesized by the formation
of RMgBr, followed by transforming to 3a–g with the
treatment of CdCl2. 3-alkyl-1(3H)-isobenzo-furanone
6a–g were prepared by the reduction of 5a–g with
NaBH4, eluted by column chromatography (light petro-
leum/acetone = 100:1),11 Z-3-alkene-1(3H)-isobenzof-
uranone 7a–g were obtained by dehydration of 5a–g
with p-TsOH (Scheme 1 and Table 1).13
The resolution route of the compounds 6a–g is outlined
in Scheme 2.
The compounds 8a–g was synthesized by hydrolysis in
the presence of NaOH, followed by acidification with
HCl to pH 3–4 at ꢀ20–0 °C. The compounds 9a–g were
obtained from the compounds 8a–g and (ꢀ) a-phenyl-
ethylamine.12 Similarly, the compounds 10a–g were pre-
pared using (+) a-phenylethylamine. Cyclization of the
compounds 9a–g/10a–g gave the corresponding com-
pounds 11a–g/12a–g under acid condition in good yield
(Scheme 2 and Table 2).13
The antiplatelet effect of the target-compounds was
screened by Borns’ method6 using Adenosine 50-di-
phos-phate (ADP) and Arachidonic Acid (AA) as the
inducers.
All compounds reported here were fully characterized
on the basis of their H NMR, 13C NMR, IR and MS
spectroscopic and analytical data. The purity of all com-
pounds were examined by High Performance Liquid
Chromatography.
1
Keywords: 1(3H)-Isobenzofuranone; Synthesize; Specific rotation;
Antiplatelet.
*
Corresponding author. Tel./fax: +86 731 2650371; e-mail: hugaoyun@
yahoo.com.cn
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.06.082

H. Yang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5210–5213
5211
O
O
O
a
c
b
e
d
RBr
RMgBr
R2Cd
O
O
O
1a-g
2a-g
3a-g
R
R
5a-g
OCd1/2
4a-g
OH
R
6a-g
f
O
O
R1
H
7a-g
Scheme 1. Reagents and conditions: (a) Mg, ether, 40 °C, reflux, 3 h; (b) CdCl2, ether, 40 °C, reflux, 1 h; (c) phthalic anhydride, ether, 40 °C, 3 h; (d)
3 M HCl; (e) NaBH4, 2–3 h; (f) p-TsOH, benzene, rt, 1.5 h.
Table 1. IE50 (lmol Lꢀ1) of compounds 6a–g and 7a–g against platelet
aggregation
Table 2. [a]D and IE50 (lmol Lꢀ1) against platelet aggregation of
compounds 11a–g and 12a–g
Compound
R
R1
IE50 (lmol Lꢀ1
)
Compound
[a]D/°C
Measured
IE50 (lmol Lꢀ1
)
Induced
by ADP
Induced
by AA
Reported
+77.38
Induced
by ADP
Induced
by AA
6a
6b
6c
6d
6e
6f
C2H5
C3H7
C4H9
164.09
133.26
169.96
180.4
15.16
14.94
14.49
16.37
15.39
15.85
16.06
15.98
16.05
16.11
17.61
17.88
17.13
18.04
12.3
11a
11b
11c
11d
11e
11f
+73.3
+69.7
+69.7
+59.7
+63.7
+62.5
+68.4
ꢀ64.5
ꢀ63.7
ꢀ64.6
ꢀ59.7
ꢀ61.4
ꢀ60.3
ꢀ65.1
209.17
142.43
193.06
203.24
207.01
217.34
175.86
113.85
111.51
94.72
16.95
16.92
16.12
17.91
17.22
18.54
18.66
14.13
13.81
13.25
15.14
14.32
14.36
14.69
12.3
C5H11
i-C5H11
C6H13
C7H15
201.34
220.34
153.13
170.12
171.21
204.22
201.21
204.34
242.99
289.47
117.94
6g
7a
7b
7c
7d
7e
7f
11g
12a
12b
12c
12d
12e
12f
CH3
ꢀ76.09
C2H5
C3H7
C4H9
i-C4H9
C5H11
C6H13
ꢀ61.310
178.3
115.65
138.72
142.86
117.94
7g
Asp
12g
Asp
OH
R
O
R
OH
R
*
COOH[B]*
*
R
a
b
c
parted
d
e
O
9a-g
O
11a-g
R
COOH
COOH[B]*
O
8a-g
O
R
6a-g
OH
O
12a-g
10a-g
Scheme 2. Reagents and conditions: (a) 10 M NaOH, reflux, 1 h; (b) 3 M HCl, ꢀ20–0 °C; (c) (ꢀ)/(+) a-phenylethylamine, ꢀ20–0 °C; filtering after
10 h; (d) 2 M NaOH; (e) 3 M HCl.
The antiplatelet activities of the compounds 6a–g, 7a–g,
11a–g, 12a–g were evaluated in vitro by antiplatelet
aggregation induced by ADP and AA. At first, plate-
let-rich plasma (PRP) was prepared from the whole
blood of healthy volunteers. The target-compounds
6a–g, 7a–g, 11a–g, 12a–g and Asp were added to PRP
(The concentrations of the target-compounds were 10,
20, 50 and 100 lmol Lꢀ1. The concentration of Asp
was 5 lmol Lꢀ1). PEG-400 was also added to PRP as
the control. Then, the mixtures were pre-heated at
37 °C for 5 min. ADP (5lmol Lꢀ1
)
and AA
(0.5 lmol Lꢀ1) were added subsequently. The most

5212
H. Yang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5210–5213
(99.8%), yield: 46.7%. 1H NMR:
d 7.90 (1H, d,
platelet aggregation rate was determined after 5 min.
The compounds 6c (NBP) and Asp were used for com-
parison. All the compounds’ inhibit-rates of platelet
aggregation were calculated. IE50 is shown in Tables 1
and 2.
J = 8.0 Hz), 7.68 (1H, t, J = 7.2, 8.0 Hz), 7.53 (1H, t,
J = 7.2, 8.0 Hz), 7.45 (1H, d, J = 8.0 Hz), 5.46 (1H, q,
J=4.8 Hz), 2.13 (1H, m), 1.83 (1H, m), 1.01 (3H, t). 13C
NMR: d 170.62, 149.70, 133.88, 129.00, 126.34, 125.62,
121.69, 82.25, 27.61, 8.75. MS: m/z 162 (M+).
Compound 6b: yellow oil (99.2%), yield: 43.9%. 1H NMR:
d 7.89 (1H, d, J = 7.6 Hz), 7.67 (1H, t, J = 7.6, 7.6 Hz),
7.52 (1H, t, J = 7.6, 7.6 Hz), 7.44 (1H, d, J = 7.6 Hz), 5.48
(1H, q, J = 4.0 Hz), 2.02 (1H, m), 1.76 (1H, m), 1.53 (2H,
m), 0.98 (3H, t). 13C NMR: d 170.55, 150.10, 133.85,
128.94, 126.13, 125.62, 121.67, 81.18, 36.78, 18.17, 13.72.
MS: m/z 176 (M+).
All these compounds showed activity against platelet
aggregation when tested at the range between 10 and
100 lmol Lꢀ1. The compound 12c (1-NBP) exhibited
the highest activity. The inhibition of platelet aggrega-
tion by all the compounds exhibited dose dependence.
The magnitude of antiplatelet activity was displayed as
following sequence, l-isomer > dl-isomer > d-isomer,
respectively. The alkylphthalide is more active than the
corresponding alkenephthalide. It appears that, with
the increase of substituting-group magnitude, the effects
became weaker. All these compounds were less active
than NBP and Asp.
Compound 6c: yellow oil (99.5%), yield: 42.7%. 1H NMR:
d 7.89 (1H, d, J = 7.6 Hz), 7.68 (1H, t, J = 7.6, 7.6 Hz),
7.51 (1H, t, J = 7.6, 7.6 Hz), 7.44 (1H, d, J = 7.6 Hz), 5.48
(1 H, q, J = 4.0 Hz), 2.04 (1H, m), 1.75 (1H, m), 1.42 (4H,
m), 0.91 (3H, t). 13C NMR: d 170.62, 150.10, 133.86,
128.96, 126.21, 125.64, 121.68, 81.38, 34.41, 26.83, 22.38,
13.78. MS: m/z 190 (M+).
Compound 6d: yellow oil (98.1%), yield: 42.5%. 1H NMR:
d 7.89 (1H, d, J = 7.6 Hz), 7.68 (1H, t, J = 7.6, 7.6 Hz),
7.52 (1H, t, J = 7.6, 7.6 Hz), 7.44 (1H, d, J = 7.6 Hz), 5.48
(1H, q, J = 4.0 Hz), 2.04 (1H, m), 1.76 (1H, m), 1.50 (2H,
m), 1.34 (4H, m), 0.89 (3H, t). 13C NMR: d 170.59, 150.13,
133.87, 128.98, 126.21, 125.67, 121.68, 81.41, 34.72, 31.47,
24.45, 22.39, 13.90. MS: m/z 204(M+).
In conclusion, a series of chiral 3-alkyl-1(3H)-isobenzo-
furanone and Z-3-alkene-1(3H)-isobenzofuranone were
designed and synthesized systematically. The antiplate-
let activities of all compounds were screened. These
results suggest that the antiplatelet activities of 1(3H)-
isobenzofuranone maybe associated with the substituent
and configuration of the group on the 3-position.
Compound 6e: yellow oil (92.3%), yield: 38.9%. 1H NMR:
d 7.90 (1H, d, J = 7.6 Hz), 7.68 (1H, m, J = 0.8, 7.6, 7.6
Hz), 7.53 (1H, t, J = 7.6, 7.6 Hz), 7.44 (1H, m, J = 0.8,
7.6 Hz), 5.47 (1H, q, J = 4.0 Hz), 2.06 (1H, m), 1.76 (1H,
m), 1.60 (1H, m), 1.35 (2H, m), 0.89 (6H, m). 13C NMR: d
170.68, 150.06, 133.92, 129.00, 126.18, 125.68, 121.68,
81.62, 33.56, 32.61,27.84, 22.45, 22.29. MS: m/z 204 (M+).
Compound 6f: yellow oil (99.6%), yield: 42.8%. 1H NMR:
d 7.89 (1H, d, J = 7.2 Hz), 7.68 (1H, t, J = 0.8, 7.2, 7.2 Hz),
7.52 (1H, t, J = 7.2, 7.6 Hz), 7.44 (1H, d, J = 0.8, 7.6 Hz),
5.48 (1H, q, J = 4.0 Hz), 2.04 (1H, m), 1.76 (1H, m),
1.48(2H, m), 1.33 (6H, m), 0.88 (3H, t). 13C NMR: d
170.56, 150.11, 133.85, 128.94, 126.16, 125.62, 121.67,
81.37, 34.72, 31.52, 28.92, 24.71, 22.45, 13.94. MS: m/z 218
(M+).
We wish to express our thanks to the State Key Labora-
tory of Chemo/Biosensing and Chemometrics of Hunan
1
University for H NMR, 13C NMR and MS of all the
compounds synthesized.
References and notes
1. Gorman, R. R.; Wierenga, W.; Miller, O. V. Biochim.
Biophys. Acta 1979, 572, 95.
2. Xu, H. L.; Feng, Y. P. Acta Pharmacol. Sin. 1999, 34, 172.
3. Xu, H. L.; Feng, Y. P. Acta Pharmacol. Sin. 1999, 20, 929.
4. Chong, Z. Z.; Feng, Y. P. Acta Pharmacol. Sin. 1997, 18,
505.
5. Teng, C. M.; Chen, W. Y.; Ko, W. C. Biochim. Biophys.
Acta 1987, 924, 375.
6. Herbert, J. M.; Bernar, A.; Samama, M. Thromb.
Haemost. 1996, 76, 94.
7. Aziz, A. D.; John, H. P. T. J. Chem. Soc., Perkin Trans. 1,
1979, 2069.
8. Hiroto, N.; Noriyuki, K. Tetrahedron: Asymmetry, 8,
1391.
9. Takashi, K. Tetrahedron: Asymmetry, 8, 3765.
10. Veeraraghavan, P. R.; Guang, M. C.; Herbert, C.;
Tetrahedron Lett., 37, 2205.
11. The reaction is high stereoselectivity, Z-isom is the most
production.
Compound 6g: yellow oil (99.8%), yield: 41.6%. 1H NMR:
d 7.90 (1H, d, J = 7.6 Hz), 7.68 (1H, t, J = 0.8, 7.6, 7.6 Hz),
7.53 (1H, t, J = 7.6, 8.0 Hz), 7.43 (1H, d, J = 0.8, 8.0 Hz),
5.48 (1H, q, J = 4.0 Hz), 2.04 (1H, m), 1.77 (1H, m), 1.37
(10H, m), 0.88 (3H, t). 13C NMR: d 170.68, 150.12, 133.90,
128.98, 126.13, 125.67, 121.68, 81.44, 34.73, 31.68, 29.27,
29.03, 24.79, 22.58, 14.04. MS: m/z 232 (M+).
Compound 7a: yellow oil (93.3%), yield: 39.8%. 1H NMR:
d 7.48–7.90 (4H, m), 5.68 (1H, q, J = 7.6 Hz), 2.03 (3H,
m).
Compound 7b: yellow oil (74.8%), yield: 40.8%. 1H NMR: d
7.48–7.90 (4H, m), 5.68 (1H, q, J = 8.0 Hz), 2.03 (3H, m).
Compound 7c: yellow oil (90.8%), yield: 39.5%. 1H NMR: d
7.49–7.90 (4H, m), d 5.65 (1H, t, J = 8.0 Hz), 2.46 (2 H, dt),
1.56 (2H, m), 0.99 (3H, t).
Compound 7d: yellow oil (81.2%), yield: 36.1%. 1H NMR: d
7.49–7.90 (4H, m), 5.64 (1H, t, J = 8.0 Hz), 2.48 (2H, dt),
1.52 (2H, m), 1.42 (2H, m), 0.94 (3H, t).
12. When (ꢀ) a-phenylethylamine was added, compounds
9a–g were separated as solid, while compounds 10a–g were
dissolved in the solution; when (+) a-phenylethylamine
was added, compounds 10a–g were separated as solid,
while compounds 9a–g were dissolved in the solution.
Compound 7e: yellow oil (81.5%), yield: 38.7%. 1H NMR: d
7.49–7.90 (4H, m), 5.66 (1H, t, J = 8.0 Hz), 2.38 (2H, q), 1.82
(1H, m), 0.83–1.00 (2H, m).
1
13. Analytical data for compounds 6a–g and 7a–g H NMR
Compound 7f: yellow oil (88.3%), yield: 38.4%. 1H NMR: d
7.49–7.90 (4H, m), 5.65 (1H, t, J = 8.0 Hz), 2.47 (2H, q),
1.38 (2H, m), 1.34–1.38 (4H, m), 0.90 (3H, t).
spectra were recorded on a Varian INOVA 400 MHz
instrument as solutions (CDCl3) using TMS as internal
reference, and chemical shift values are express in d units.
Mass spectra were run on an Applied Biosystems QStar
instrument using a direct inlet system under positive ion
electrospray ionization source. Compound 6a: yellow oil
Compound 7g: yellow oil (92.8%), yield: 36.9%. 1H NMR: d
7.50–7.90 (4H, m), 5.65 (1H, t, J = 8.0 Hz), 2.47 (2H, q), 1.52
(2H, m), 1.26–1.41 (6H, m), 0.88 (3H, m).

H. Yang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5210–5213
5213
Compound 11a: yellow oil (99.8%), yield: 32.5%.
Compound 12a: yellow oil (99.8%), yield: 31.9%.
Compound 12b: yellow oil (99.1%), yield: 32.8%.
Compound 12c: yellow oil (99.8%), yield: 49.4%.
Compound 12d: yellow oil (99.8%), yield: 49.1%.
Compound 12e: yellow oil (92.1%), yield: 48.3%.
Compound 12f: yellow oil (99.3%), yield: 48.7%.
Compound 12g: yellow oil (99.7%), yield: 48.5%.
Compound 11b: yellow oil (96.7%), yield: 33.5%.
Compound 11c: yellow oil (99.8%), yield: 48.9%.
Compound 11d: yellow oil (99.3%), yield:47.9%.
Compound 11e: yellow oil (90.5%), yield: 48.7%.
Compound 11f: yellow oil (99.7%), yield: 49.6%.
Compound 11g: yellow oil (99.8%), yield: 48.2%.