Synthesis and antibacterial evaluation of typharin analog: 6,8-dihydroxy-7-methyl-3-styryl-3,4-dihydroisocoumarin

Article abstract of DOI:10.1080/10286020.2012.751978

Synthesis of the 6-hydroxy-7-methyl analog of typharin (8-dihydroxy-3- styryl-3,4-dihydroisocoumarin) isolated from the rhizomes of Typha capensis has been described. Direct condensation of 3,5-dimethoxy-4-methylhomophthalic acid (1) with cinnamoyl chlori

Full text of DOI:10.1080/10286020.2012.751978

This article was downloaded by: [Yale University Library]
On: 11 March 2013, At: 06:23
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Asian Natural Products
Research
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/ganp20
Synthesis and antibacterial evaluation
of typharin analog: 6,8-dihydroxy-7-
methyl-3-styryl-3,4-dihydroisocoumarin
Aamer Saeed a , Hummera Rafique a & Zaman Ashraf b
a Department of Chemistry, Quaid-I-Azam University, 45320,
Islamabad, Pakistan
b Department of Chemistry, Allama Iqbal Open University,
Islamabad, Pakistan
Version of record first published: 17 Jan 2013.
To cite this article: Aamer Saeed , Hummera Rafique & Zaman Ashraf (2013): Synthesis
and antibacterial evaluation of typharin analog: 6,8-dihydroxy-7-methyl-3-styryl-3,4-
dihydroisocoumarin, Journal of Asian Natural Products Research, 15:2, 130-135
To link to this article: http://dx.doi.org/10.1080/10286020.2012.751978
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Journal of Asian Natural Products Research, 2013
Vol. 15, No. 2, 130–135, http://dx.doi.org/10.1080/10286020.2012.751978
Synthesis and antibacterial evaluation of typharin analog:
6,8-dihydroxy-7-methyl-3-styryl-3,4-dihydroisocoumarin
Aamer Saeeda*, Hummera Rafiquea and Zaman Ashrafb
b
aDepartment of Chemistry, Quaid-I-Azam University, 45320 Islamabad, Pakistan; Department of
Chemistry, Allama Iqbal Open University, Islamabad, Pakistan
(Received 3 August 2012; final version received 18 November 2012)
Synthesis of the 6-hydroxy-7-methyl analog of typharin (8-dihydroxy-3-styryl-
3,4-dihydroisocoumarin) isolated from the rhizomes of Typha capensis has been
described. Direct condensation of 3,5-dimethoxy-4-methylhomophthalic acid (1) with
cinnamoyl chloride at elevated temperature under inert conditions afforded
6,8-dihydroxy-7-methyl-3-styrylisocoumarin (2). Hydrolysis of isocoumarin to keto
acid (3) followed by reduction and cyclodehydration of hydroxy acid analog (4)
afforded (^)-6,8-dimethoxy-3-(4-methoxyphenyl)-3,4-dihydroisocoumarin (5).
Demethylation of the latter using anhydrous aluminum chloride/ethane thiol furnished
the title isocoumarin (6). Compounds (1–6) were screened for in vitro antibacterial
activity against a representative panel of Gram-positive and Gram-negative bacteria
using levofloxacin as the reference drug.
Keywords: dihydroisocoumarin; Typha capensis; typharin; antibacterial
1. Introduction
easy delivery, for venereal diseases,
dysmenorrhea, diarrhea, and dysentery,
and to increase male potency and libido.
Shode et al. [8] during chemical investi-
gations of T. capensis isolated two new
phenolics, named typharin (an 3,4-dihy-
droisocoumarin) and typhaphthalide (a
benzyl phthalide) from the hexane extract
of the rhizomes. The structure of the new
3,4-dihydroisocoumarin was established
unambiguously as (E)-8-hydroxy-3-
styryl-3,4-dihydroisocoumarin (6a) by the
analysis of spectroscopic data [8] (Figure
1).
3,4-Dihydroisocoumarins (3,4-dihydro-
1H-2-benzopyran-1-ones) are natural lac-
tones, isolated from a wide range of natural
sources (microbes, plant, and insects), and
possess an array of biological activities
including nephroatoxic, hepatotoxic, cyto-
toxic, immunomodulatory, antiallergic,
algicidal, gastroprotective, protease inhibi-
tory, antifungal, and antimalarial activities
[1–6]. Structurally, isocoumarins are iso-
meric to coumarins with an inverted
lactone ring, and most of the natural iso-
coumarins possess a 3-alkyl (C1–C17) or a
substituted 3-phenyl ring and 8-oxygen-
ation due to their typical biosynthetic
origin [7].
Simple (S)-3-[(E)-styryl]-3,4-dihy-
droisocoumarin, with no substitution on
benzene ring, has already been synthesized
by lateral lithiation of (S)-4-isopropyl-
2-(o-tolyl)oxazoline in diethyl ether
followed by the reaction with cinnamalde-
hyde in the presence of tetramethylethyle-
Typha capensis commonly known as
bulrush is a common plant of South Africa.
Its rhizomes are used in traditional
medicine during pregnancy to ensure
*Corresponding author. Email: aamersaeed@yahoo.com
q 2013 Taylor & Francis

Journal of Asian Natural Products Research
131
Cinnamoyl chloride was freshly pre-
pared from cinnamic acid on reaction with
thionyl chloride. Direct condensation of
cinnamoyl chloride with 3,5-dimethoxy-4-
methylhomophthalic acid (1) at 2008C
afforded 6,8-dimethoxy-7-methyl-3-styryl
isocoumarin (2). The latter was purified by
preparative thin layer chromatography
using petroleum ether and ethyl acetate
(7:3) as eluent. It showed lactonic carbonyl
absorption at 1723 cm21 and a trans-
olefinic group at 986 cm21 in the IR
spectrum, as well as a characteristic singlet
for H-4 at d 6.24 and doublets for vinylic
protons with trans configuration at d 6.82
(J ¼ 16.2 Hz) in its 1H NMR spectrum.
The isocoumarin (2) was then subjected to
alkaline hydrolysis to afford 2,4-
dimethoxy-3-methyl-6-(2-oxo-4-phenyl-
but-3-enyl)benzoic acid (3) in 72% yield.
The keto acid showed characteristic singlet
at d 4.31 for (Ar–CH2) and another singlet
R1
O
R2
(6a) R1=R2=H
(6) R1=OH, R2=CH3
OH
O
Figure 1. Natural typharin (6a) and its 6-
hydroxy-7-methyl anaolg (6).
nediamine in high stereoselectivity [9,10],
and synthesis of racemic 3,4-dihydro-
3-styrylisocoumarin has been reported by
reaction of ethyl 2-bromomethyl benzoate
and benzaldehyde using titanocene (III)
chloride as the radical initiator [11]. In fact,
this compound is easily accessible from
3-styrylisocoumarin prepared by us, by the
condensation of commercial homophthalic
acid with cinnamoyl chloride during
model studies for the synthesis of typharin
skeleton.
1
at d 10.21 for ZCOOH in its H NMR
spectrum. The ketonic and carboxylic
carbonyl absorptions were observed in
Herein, a simple and efficient synthesis
of the title compound (6) as a structural
analog of typharin is described in pro-
longation of our focusing on the synthesis,
characterization, crystal structure, and
bioevaluation of this important class of
secondary metabolites [12–17]. The struc-
tural simplicity and the bioactivity associ-
ated with these molecules make them an
attractive target for synthesis.
the IR spectrum at 1736 and 1712 cm21
respectively.
,
Sodium borohydride reduction of the
keto acid (3) afforded the 6-(2-hydroxy-4-
phenyl-but-3-enyl)-2,4-dimethoxy-3-
methyl benzoic acid (4). The absorption at
3454 cm21 was observed due to ZOH
functionality in the IR spectrum. The
hydroxyl proton showed a singlet at d 2.47
in the 1H NMR spectrum and the
methylene protons at C-4 showed the
diastereotopic effect as the newly gener-
ated chiral center is contiguous to them.
Both the methylene protons give the
signals at d 3.92 and d 3.12 with double
doublet multiplicity in the 1H NMR
spectrum. The hydroxy acid (4) upon
treatment with acetic anhydride endured
cyclodehydration to give 6,8-dimethoxy-
7-methyl-3-styryl-3,4-dihydroisocoumarin
(5). It showed the lactonic carbonyl
absorption at 1714 cm21 and the disap-
pearance of the absorption for ZOH in the
IR spectrum. 3,4-Dihydroisocoumarin (5)
2. Results and discussion
We now unveil a squat efficient synthesis
of
6,8-dihydroxy-7-methyl-3-styryl-
3,4-dihydroisocoumarin (6) as a typharin
analog. The 6-(carboxymethyl)-2,4-
dimethoxy-3-methylbenzoic acid (1) was
obtained from methyl 3,5-dimethoxy-4-
methyl phenylacetate prepared earlier
during our synthesis of stellatin [18] by
successive Vilsmeier–Haack formylation,
sulfamic acid–sodium chlorite oxidation,
and alkaline hydrolysis, identical in
physical and spectroscopic data to that
reported in the literature [19].

132
A. Saeed et al.
O
H3CO
H3C
COOH
COOH
200˚C
Cl
5h
OCH3
(1)
H3CO
H3C
H3CO
H3C
NaBH4 / EtOH
5% KOH / EtOH
O
O
COOH
(2)
(3)
OCH
3O
OCH3
H3CO
H3C
H3CO
H3C
Ac2O
EtSH / anhy.AlCl3
(6)
OH
COOH
O
(4)
(5)
O
OCH3
OCH3
Scheme 1. Synthetic pathway to 6,8-dihydroxy-7-methyl-3-styryl-3,4-dihyroisocoumarin (6).
showed a characteristic H-3 double doub-
let at d 5.24 due to coupling with H-4
methylene hydrogens in the 1H NMR
spectrum. The final demethylation of the
dihydroisocoumarin was carried out in the
presence of ethane thiol [20] to furnish the
3,4-dihydroisocoumarin (6). The presence
of singlet at d 4.81 for hydroxyl protons
and the absence of methoxy signals in the
1H NMR spectrum confirmed the for-
mation of title dihydroisocoumarin (6)
(Scheme 1).
negative bacteria, viz. Pseudomonas aero-
ginosa, Escherichia coli, Salmonella typhi,
Shigella species, Salmonella paratyphi,
and Proteus mirabilis and four were
Gram-positive bacteria, viz. Bacillus sub-
tilus, Micrococcus aureus, Staphylococcus
aureus, and Streptococcus species [21].
Antibacterial activity was determined by
using the Mueller Hinton Agar. The fresh
inoculums of these bacteria were prepared
and diluted by sterilized normal saline. The
turbidity of these cultures was adjusted by
using 0.5 Mc-Farland. A homogeneous
bacterial lawn was developed by sterile
cotton swabs. The inoculated plates were
bored using a borer of 6 mm to make the
wells. The solutions were prepared by
dissolving each sample (1.0 mg) in 1.0 ml
In vitro evaluation of antibacterial
activity of the isocoumarin, dihydroiso-
coumarins, and their precursors (1–6) was
carried out by agar well diffusion assay [21]
against 10 different Gram-positive and
Gram-negative bacteria. Six were Gram-
Table 1. Antibacterial activity of compounds 1–6.
Compounds
P. a.
E. c.
S. t.
P. m.
B. s.
M. l.
S. a.
S. S.
S. para.
S. s.
1
2
3
4
–
11
–
–
–
–
–
6
–
4
20
15
11
–
9
15
24
16
12
14
13
14
12
29
12
9
–
9
12
9
20
12
21
10
20
12
38
14
12
16
–
09
12
32
–
–
–
–
–
4
–
24
–
–
–
21
9
6
14
2
–
6
24
5
6
Standard
11
25
–
33
–
14
34
Notes: Gram-positive bacteria: Bacillus subtilus (B. s.), Micrococcus aureus (M. l.), Staphylococcus aureus (S. a.),
Streptococcus species (S. S.). Gram-negative bacteria: Pseudomonas aeroginosa (P. a.), Escherichia coli (E. c.),
Salmonella typhi (S. t.), Shigella species (S. s.), Salmonella paratyphi (S. para.), and Proteus mirabilis (P. m.).

Journal of Asian Natural Products Research
133
of DMSO used as a negative control in this
bioassay. The equimolar concentration of
levofloxacin (1.0 mg/ml), a broad spectrum
antibiotic (positive control), was prepared.
These plates were incubated at 378C for
24 h. Antibacterial activity of the syn-
thesized compounds (1–6) was determined
by measuring the diameter of zone of
inhibition (mm, ^SD) and presented by
subtracting the activity of the negative
control in Table 1.
by thin layer chromatography using silica
gel from Merck (Darmstadt, Germany).
3.2 6,8-Dimethoxy-7-methyl-3-
styrylisocoumarin (2)
A mixture of cinnamic acid (0.5 g,
3.38 mmol) and thionyl chloride (0.44 ml,
5.1 mmol) was refluxed for 1 h in the
presence of a drop of DMF. The completion
of reaction was determined by the stoppage
of evolution of gas. Excess of the thionyl
chloride was rotary evaporated to afford
acid chloride. A solution of 6-(carboxy-
methyl)-2,4-dimethoxy-3-methylbenzoic
acid (1) (0.5 g, 1.97 mmol) and cinnamoyl
chloride (0.56 g, 0.327 mmol) was heated
under reflux at an internal temperature of
2008C for 5 h. After the completion of
reaction, the cooling bath was removed and
the reaction was allowed to cool. The
reaction mixture was concentrated and then
extracted with ethyl acetate. The two
phases were separated, and the organic
layer was washed with saturated sodium
chloride solution and then dried over
anhydrous Na2SO4. 6,8-Dimethoxy-
7-methyl-3-styrylisocoumarin (2) was pur-
ified by the preparative thin layer chroma-
tography using petroleum ether and ethyl
acetate (7:3) as eluent; yield 78%; Rf 0.6;
mp 123–1248C; IR (KBr) nmax: 3023,
3,5-Dimethoxy-4-methylhomophthalic
acid (1) exhibited moderate to good
activity against most of the bacterial
strains tested. 6,8-Dimethoxy-7-methyl-3-
styrylisocoumarin (2) showed significantly
greater antibacterial activity against
various strains of Gram-negative and
Gram-positive bacteria as compared to its
3,4-dihydroisocoumarin derivative (5).
The keto acid (3) was much potent
than hydroxyl acid (4) and in case of
S. paratyphi it showed activity greater than
levofloxacin, the standard antibiotic drug.
Title compound, dihydroxydihydroisocou-
marin (6), displayed comparatively lesser
activity than its dimethoxy analog (5).
3. Experimental
3.1 General experimental procedures
Melting points were recorded using a
digital Gallenkamp (SANYO, Loughbor-
ough, UK) model MPD BM 3.5 apparatus
and are uncorrected. 1H and 13C NMR
spectra were determined in CDCl3 at 300
and 75 MHz, respectively, using Bruker
AM-300 spectrophotometer (Billerica,
Middlesex, MA, USA). FT-IR spectra
were recorded using Bio-Rad Excalibur
FTS 3000 MX spectrophotometer (Madi-
son, WI, USA).
2914, 1723, 1567, 986 cm21 1H NMR
;
(CDCl3, d ppm): 7.76–7.21 (5H, m, Ar),
6.82 (1H, d, J ¼ 16.2 Hz, Ha), 6.63 (1H, d,
J ¼ 16.2 Hz, Hb), 6.47 (1H, s, H-5), 6.24
(1H, s, H-4), 3.83 (6H, s, OCH3), 2.36 (1H,
s, CH3); 13C NMR (CDCl3, d ppm): 168.4
(C-1), 150.5 (C-3), 146.7 (C-6, C-8), 138.6
(C-10), 137.7 (C-10), 135.4 (C-1a), 134.8
(C-1b), 127.8 (C-9), 127.4 (C-20, C-60),
126.7 (C-30, C-50), 123.3 (C-40), 118.5
(C-7), 109.3 (C-4), 104.6 (C-5), 56.4
(2 £ OCH3), 28.6 (Ar-CH3); MS (70 eV)
m/z (%): 322 [M]þz (24), 245 (32), 192
(100%), 132 (53), 103 (41), 77 (13);
elemental analysis: found: C, 73.14%, H,
5.26%; calcd for C20H18O4: C, 73.05%, H,
5.19%.
Mass spectra (EI, 70 eV) were
recorded on a GC–MS instrument (Agi-
lent Technologies 1200 series, Santa
Clara, CA, USA), and elemental analyses
were carried out with a LECO-183 CHNS
analyzer (LECO Corporation, St Joseph,
MI, USA). All compounds were purified

134
A. Saeed et al.
3.3 2,4-Dimethoxy-3-methyl-6-(2-oxo-
4-phenyl-but-3-enyl)benzoic acid (3)
nesium sulfate and concentrated to afford
hydroxyl acid (4); yield 70%; Rf 0.2; mp
87–888C; IR (KBr) nmax: 3454, 3063,
A stirred solution of isocoumarin (2)
(0.45 g, 1.4 mmol) in ethanol (10 ml) was
treated with 5% KOH (20 ml) and the
mixture refluxed for 4 h. After cooling the
reaction mixture, most of the ethanol was
evaporated under reduced pressure. Cold
water (20 ml) was added and the mixture
acidified with dilute hydrochloric acid
when solid was precipitated. Filtration
followed by drying under vacuum afforded
keto acid (3); yield 72%; Rf 0.3; mp 158–
1598C; IR (KBr) nmax: 3444, 3013, 2934,
1736 (carboxylic CvO), 1712 (ketonic
2962,
1564 cm21
1725
;
(carboxylic
CvO),
1H NMR (CDCl3, d ppm):
10.83 (1H, s, COOH), 7.63–7.36 (5H, m,
Ar), 6.85 (1H, d, J ¼ 16.2 Hz, Ha), 6.76
(1H, d, J ¼ 16.2 Hz, Hb), 6.34 (1H, s, H-
5), 4.35 (1H, dd, Jtrans ¼ 14.3, Jcis ¼ 6.2,
H-3), 3.92 (6H, s, OCH3), 3.12 (1H, dd,
Jgem ¼ 11.8 Hz, Jtrans ¼ 14.3 Hz, H-4),
2.86 (1H, dd, Jgem ¼ 11.8 Hz, Jcis ¼ 6.2
Hz, H-40), 2.47 (1H, s, OH), 2.36 (3H, s,
Ar-CH3); 13C NMR (CDCl3, d ppm):
168.6 (COOH), 147.2 (C-2), 142.4 (C-4),
140.1 (C-1), 138.7 (C-a), 137.8 (C-b),
136.5 (C-10), 132.4 (C-5), 130.3 (C-6),
129.4 (C-20, C-60), 128.5 (C-30, C-50),
125.4 (C-40), 121.6 (C-3), 82.8 (C-OH),
64.6 (2-OCH3), 62.1 (4-OCH3), 48.7
(CH2), 29.6 (Ar-CH3); MS (70 eV) m/z
(%): 342 [M]þz (27), 279 (56), 219 (100%),
189 (46), 119 (36), 91 (32); elemental
analysis: found: C, 70.24%, H, 6.23%;
calcd for C20H20O5: C, 70.17%, H, 6.43%.
1
CvO), 1597 cm21; H NMR (CDCl3, d
ppm): 10.21 (1H, s, COOH), 8.11–7.86
(5H, m, Ar), 7.74 (2H, d, J ¼ 16.2 Hz, H-
a), 7.41 (1H, d, J ¼ 16.2 Hz, Hb), 7.23
(1H, s, H-5), 4.31 (2H, s, ZCH2), 3.93
(3H, s, 2-OCH3), 3.87 (3H, s, 4-OCH3),
2.35 (3H, s, Ar-CH3) ppm; 13C NMR d
(CDCl3): 196.8 (CvO), 167.6 (COOH),
146.2 (C-2), 141.5 (C-4), 138.8 (C-1),
138.1 (C-1a), 137.5 (C-1b), 136.7 (C-10),
131.3 (C-5), 129.4 (C-6), 128.7 (C-20, C-
60), 127.6 (C-30, C-50), 124.6 (C-40), 120.4
(C-3), 64.3 (2-OCH3), 61.6 (4-OCH3),
48.7 (C-10), 29.6 (Ar-CH3); MS (70 eV)
m/z (%): 340 [M]þz (31), 237 (16), 219
(100%), 193 (62), 131 (43), 77 (22);
elemental analysis: found: C, 70.31%, H,
5.59%; calcd for C20H20O5: C, 70.25%, H,
5.48%.
3.5 6,8-Dimethoxy-7-methyl-3-styryl-
3,4-dihydroisocoumarin (5)
Hydroxy acid (4) (0.25 g, 0.73 mmol) was
dissolved in acetic anhydride (5 ml) and
refluxed for 2 h. The reaction mixture was
poured into chilled water, and then
extracted with ethyl acetate (2 £ 25 ml).
Organic layer was washed with 1%
NaHCO3 and water. The organic layer
was dried with Na2SO4 and concentrated to
get 6,8-dimethoxy-7-methyl-3-styryl-3,4-
dihydroisocoumarin (5); yield 68%; Rf 0.5;
mp 134–1358C; IR (KBr) nmax: 3045,
2940, 1714, 1583 cm21; 1H NMR (CDCl3,
d ppm): 7.83–7.28 (5H, m, Ar), 7.11 (1H, s,
H-5), 6.81 (1H, d, J ¼ 16.2 Hz, Ha), 6.54
(1H, d, J ¼ 16.2 Hz, Hb), 5.24 (1H, dd,
Jtrans ¼ 14.2 Hz, Jcis ¼ 6.1 Hz, H-3), 3.78
(6H, s, OCH3), 3.38 (1H, dd, Jgem ¼ 11.8
Hz, Jtrans ¼ 14.2 Hz, H-4), 3.13 (1H, dd,
Jgem ¼ 11.8 Hz, Jcis ¼ 6.1 Hz, H-40), 2.47
(1H, s, CH3); 13C NMR (CDCl3, d ppm):
3.4 6-(2-Hydroxy-4-phenyl-but-3-enyl)-
2,4-dimethoxy-3-methyl benzoic acid (4)
Sodium borohydride (0.28 g, 0.87 mmol)
was added portionwise to a stirred solution
of keto acid (3) (0.3 g, 0.88 mmol) in
ethanol (25 ml) and water (75 ml). The
reaction mixture was stirred for 2 h at room
temperature, diluted with water (100 ml),
acidified with concentrated HCl, and
stirred for further 2 h. It was then saturated
with ammonium sulfate and extracted with
ethyl acetate (3 £ 100 ml). The organic
layer was dried over anhydrous mag-

Journal of Asian Natural Products Research
135
168.4 (C-1), 144.5 (C-6, C-8), 141.7 (C-
10), 138.6 (C-10), 137.2 (C-a), 136.4 (C-b),
134.3 (C-9), 131.8 (C-7), 130.5 (C-5),
128.5 (C-20, C-60), 127.3 (C-30, C-50), 123.6
(C-40), 84.5 (C-3), 56.7 (OCH3), 41.3
(C-4), 28.7 (Ar-CH3); MS (70 eV) m/z
(%): 324 [M]þ(31), 263 (17), 249 (26), 192
(100%), 103 (14), 77 (21); elemental
analysis: found: C, 73.96%, H, 6.04%;
calcd for C20H20O4: C, 74.07%, H, 6.17%.
29.4 (Ar-CH3); MS (70 eV) m/z (%): 296
[M]þz (37), 263 (23), 219 (61), 164 (100%),
151 (43), 77 (31); elemental analysis:
found: C, 73.12%, H, 5.24%; calcd for
C18H16O4: C, 72.97%, H, 5.41%.
References
[1] W. Zhang, K. Krohn, S. Draeger, and
B. Schulz, J. Nat. Prod. 71, 1078 (2008).
[2] K.F. Devienne, G. Raddi, R.G. Coelho,
and W. Vilegas, J. Phytother. Phytopharm.
12, 378 (2005).
[3] L.C. Di Stasi, D. Camuesco, A. Nieto, W.
Vilegas, A. Zarzuelo, and J. Galvez,
Planta Med. 70, 315 (2004).
3.6 6,8-Dihydroxy-7-methyl-3-styryl-
3,4-dihydroisocoumarin (6)
Dihydroisocoumarin
(5)
(0.2 g,
0.617 mmol) was dissolved in ethane thiol
(2.5 ml) and solution was cooled on ice.
Aluminum chloride (0.23 g, 0.187 mmol)
was added as three portions with an interval
of 30 min. After the addition of all the
aluminum chloride was complete, the
reaction mixture was stirred on ice for 1 h.
The reaction was quenched with 10%
NaHCO3 and extracted with ethyl acetate;
then sodium chloride was added to enhance
layer separation. The combined organic
layers were washed once with brine, dried
over sodium sulfate, and concentrated to
give 6,8-dihydroxy-7-methyl-3-styryl-
3,4-dihydroisocoumarin (6); yield 73%;
[4] I. Kostova, Curr. Med. 5, 29 (2005).
[5] K. Krohn, U. Florke, M.S. Rao, K.
Steingrover, H.J. Aust, S. Draeger, and
B. Schulz, Nat. Prod. Lett. 15, 353 (2001).
[6] Y.F. Huang, L.H. Li, L. Tian, L. Qiao,
H.M. Hua, and Y.H. Pei, J. Antibiot. 59,
355 (2006).
[7] R.A. Hill, Naturst. Fortschr. 49, 1 (1986).
[8] F.O. Shode, A.S. Mahomed, and C.B.
Rogers, Phytochemistry 61, 955 (2002).
[9] Y. Kurosaki, T. Fukuda, and M. Iwao,
Tetrahedron 61, 3289 (2005).
[10] N. Tahara, T. Fukuda, and M. Iwao,
Tetrahedron Lett. 45, 5117 (2004).
[11] S.K. Mandal and S.C. Roy, Tetrahedron
64, 11050 (2008).
[12] A. Saeed, Helv. Chim. Acta 86, 377
(2003).
Rf 0.3; mp 168–1698C; IR (KBr) nmax
3425 (OZH), 3065, 2925, 1712,
1567 cm21 1H NMR (CDCl3, d ppm):
:
[13] A. Saeed, Nat. Prod. Res. 18, 373 (2004).
[14] A. Saeed and S. Ehsan, J. Braz. Chem.
Soc. 16, 739 (2005).
;
8.13–7.39 (5H, m, Ar), 7.21 (1H, s, H-5),
6.78 (1H, d, J ¼ 16.2 Hz, Ha), 6.43 (1H, d,
J ¼ 16.2 Hz, Hb), 5.31 (1H, dd,
Jtrans ¼ 14.2 Hz, Jcis ¼ 6.1 Hz, H-3), 3.59
(1H, dd, Jgem ¼ 11.8 Hz, Jtrans ¼ 14.2 Hz,
H-4), 3.26 (1H, dd, Jgem ¼ 11.8 Hz,
Jcis ¼ 6.1 Hz, H-40), 4.81 (2H, s, OH),
2.51 (1H, s, CH3); 13C NMR (CDCl3, d
ppm): 169.5 (C-1), 146.3 (C-6, C-8), 141.6
(C-10), 139.5 (C-10), 138.6 (C-a), 137.4
(C-1b), 135.2 (C-9), 132.3 (C-7), 131.5
(C-5), 129.4 (C-20, C-60), 126.4 (C-30,
C-50), 125.3 (C-40), 85.4 (C-3), 42.6 (C-4);
[15] A. Saeed, J. Asian Nat. Prod. Res. 8, 417
(2006).
[16] A. Saeed, Synth Commun. 37, 1485
(2007).
[17] A. Saeed, J. Asian Nat. Prod. Res. 12, 88
(2010).
[18] A. Saeed, Z. Ashraf, and H. Rafique,
J. Asian Nat. Prod. Res. 13, 92 (2011).
[19] C.N. Lewis, J. Staunton, and D.C. Sunter,
J. Chem. Soc. Perkin Trans. 1, 747 (1988).
[20] M. Node, K. Nishide, K. Fuji, and
E. Fujita, J. Org. Chem. 45, 4275 (1980).
[21] M.I. Okeke, C.U. Iroegbu, E.N. Eze, A.S.
Okoli, andC.O. Esimone, J.Ethnopharma-
col. 78, 119 (2001).