Synthesis of DNA-Intercalating 6H-Benzo[c]chromen-6-one Derivatives through a Strategic Combination of Garratt-Braverman and Minisci Acyloxylation Reactions

Article abstract of DOI:10.1002/ejoc.201501529

A new strategy for the synthesis of 6H-benzo[c]chromen-6-ones through judicious use of Garratt-Braverman (GB) Cyclization and Minisci acyloxylation reactions in moderate to good yield is reported. The uniqueness of the GB reaction is exemplified in providing the required biaryl esters, which could be successfully converted into the target skeleton by means of Minisci reaction on the free carboxylates. Ethidium bromide displacement and UV-based assay on the final molecules established them as DNA intercalators with binding constants in the range of about 10⁴. Synthesis of DNA-intercalating benzochromenones through a combination of Garratt-Braverman and Minisci acyloxylation reactions is described.

Full text of DOI:10.1002/ejoc.201501529

DOI: 10.1002/ejoc.201501529
Full Paper
6
H-Benzo[c]chromen-6-one
Synthesis of DNA-Intercalating 6H-Benzo[c]chromen-6-one
Derivatives through a Strategic Combination of Garratt–
Braverman and Minisci Acyloxylation Reactions
[a]
[b]
[a]
Prabuddha Bhattacharya, Santi M. Mandal, and Amit Basak*
Abstract: A new strategy for the synthesis of 6H- ters, which could be successfully converted into the target skel-
benzo[c]chromen-6-ones through judicious use of Garratt– eton by means of Minisci reaction on the free carboxylates.
Braverman (GB) Cyclization and Minisci acyloxylation reactions Ethidium bromide displacement and UV-based assay on the fi-
in moderate to good yield is reported. The uniqueness of the nal molecules established them as DNA intercalators with bind-
4
GB reaction is exemplified in providing the required biaryl es- ing constants in the range of about 10 .
Introduction
as anticancer and antiviral agents. Small molecules may bind
DNA is the pharmacological target of many of the drugs that noncovalently to DNA through intercalation between nucleo-
[
1]
are currently in clinical use or in advanced clinical trials. Over base pairs, major or minor groove binding and electrostatic in-
[
3]
the last four decades, extensive research has focused on the teractions. Thus, the study of interaction of drug with DNA
effects of small organic compounds that noncovalently bind to is crucial to understand the mechanism of interaction and for
[
2]
nucleic acids. These interactions are known to disrupt replica- designing of new drugs. Recently during the course of our work
[
4]
tion and/or transcription that culminates in cellular death. Ac- to synthesize ortho-condensed polynuclear heterocycles by
[
5]
cordingly, DNA-binding compounds have potential applications using the Garratt–Braverman (GB) cyclization reaction, we
Figure 1. Some of the well-known natural products with the benzochromenone moiety.
found that 6H-benzo[c]chromene derivatives have low DNA in-
[
[
a] Department of Chemistry, Indian Institute of Technology,
Kharagpur 721302, India
http://www.iitkgp.ac.in
b] Department of Microbiology, Vidyasagar University,
Midnapore 721102, India
tercalating affinities (binding constant of the order of about
3
1
0 ), which probably results from their in-built helicity (as con-
firmed by their crystal structures). It was at this point that our
attention was drawn towards a special class of highly bioactive
molecules that contain a core structure of 6H-benzo[c]chromen-
E mail: absk@chem.iitkgp.ernet.in
http://www.chemistry.iitkgp.ac.in/~absk/
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201501529.
6
-one (Z). These compounds form an important group of hep-
taketide coumarin derivatives that have an angularly fused tri-
Eur. J. Org. Chem. 2016, 1439–1448
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cyclic nucleus (Figure 1). It was expected that the change of oxylation reaction. Acid F should be obtainable from corre-
3
2
hybridization from sp to sp for the benzylic C atom would sponding biaryl ester G, which in turn may be obtained through
make it more planar, and thereby impart higher intercalating GB cyclization reaction of a suitable bis-propargyl ether H
ability to these classes of molecules (Figure 2). We realized that (Scheme 1).
same core skeleton Z and a fused dihydroisofuran moiety may
be accessed from the corresponding bis-propargyl ether by a
strategic combination of GB cyclization and acyloxylation reac-
[
6]
tion (a specific variant of Minisci reaction). The isofuran part
acts as an additional handle for functionalization and may help
in further modification and lead to other bioactive motifs (e.g.
[
7]
oxidation to butyrolactone). In addition, there are only a few
literature reports on DNA intercalation studies for this class of
[
8]
heterocycle-fused coumarin derivatives. Driven by the afore-
said objectives, we pursued the synthesis of dihydroisofuran-
fused benzochromenones and carried out basic spectroscopic
studies to probe their DNA binding affinities. The synthetic pro-
tocol developed here offers easy access to the desired skeletal
[
9]
motif and the molecules also show higher DNA intercalation.
The results of our study are reported in this paper.
Scheme 1. Retrosynthetic pathway.
The precursors for the GB reaction were ethoxycarbonyl bis-
propargyl ethers 1a–1g, which were synthesized by following a
multistep synthetic protocol that starts from various suitably
substituted halo arenes in accordance with our previously pub-
[
4]
lished procedure (details are included in the Supporting Infor-
mation). Precursors 1a–1g were subjected to GB cyclization re-
action conditions for ethers (DBU, benzene, reflux tempera-
tures). Likewise to our earlier report, we found that for sub-
strates 1a–1f that have a substituted benzene ring tethered to
the alkyne terminus, the vinylic double bond exclusively partici-
pated in the GB cyclization reaction to furnish products 2a–2f
(Scheme 2). However, for 1g, which has a naphthyl ring teth-
Figure 2. The benzochromene and benzochromenone skeletons.
ered to the alkyne, the major product was 3g, in which the
naphthyl ring preferentially participated in the cyclization proc-
ess. Desired product 2g, which was produced by the participa-
tion of the vinylic double bond, was formed as a minor product
Results and Discussion
(
major/minor = 2:1) and could be isolated pure by HPLC. The
H NMR spectra of the mixture of 2g and 3g and of pure 2g
To validate our choice of target skeleton, energy-minimized
structures of dihydroisofuran-fused benzochromene and benzo-
chromenone were obtained by means of MM2 calculations. A
dihedral angle of 20.08° and 8.54° (between the two benzene
units) for representative molecules A and B, respectively, were
obtained that suggest greater planarity of the benzochrome-
none systems (Figure 3).
1
are shown in Figure 4. The lower sacrifice of resonance energy
in the case of participation of naphthalene (ca. 30.5 kcal/mol)
relative to benzene derivatives (ca. 36 kcal/mol), may be the
possible reason behind this interesting observation.
esters 2a–2g thus obtained were subjected to alkaline hydroly-
sis to obtain acids 4a–4g.
[
10]
Biaryl
With biaryl acids 4a–4g in hand, we proceeded with the final
lactonization step by Minisci acyloxylation reaction. We
screened several reagent systems and conditions by following
[
11]
literature reports
with substrate 4a to optimize the reaction
conditions. Along with desired benzochromenone 5a, in some
cases, further oxidized products like lactols and lactones were
obtained, which lowered the overall yield of desired acyloxyl-
ation product (Scheme 3). The results of the various reagents
and reaction conditions are listed in Table 1.
Use of K S O as the oxidant in CH CN/H O at 50 °C gave a
complex mixture of lactols and lactone (functionalization of the
benzylic methylene groups of the dihydroisofuran part and ring
2
2
8
3
2
Figure 3. Energy-minimized structure for dihydroisofuran-fused benzo-
chromene (A) and benzochromenone (B).
Retrosynthetic analysis revealed that biaryl acid F should act closure). The generation of a new chiral center in 6a (which has
as a precursor to target molecule benzochromenone E. The inherent axial chirality due to a slight molecular twist) results
former can be directly converted into E through a Minisci acyl- in a mixture of diastereomeric lactols. This mixture of diastereo-
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Scheme 2. Synthetic route to the synthesis of biaryl acid derivatives.
Table 1. Various reaction conditions screened for their effectiveness in the
final ring-closure reaction. The reaction conditions were optimized with com-
pound 4a as the model substrate. For NMR spectra of the lactols and lactone,
see the Supporting Information.
Figure 4. (A) 1H NMR spectrum of the mixture of compounds 3g and 2g.
1
(
B) H NMR spectrum of pure 2g, which was isolated by HPLC.
meric lactols 6a was isolated and subjected to IBX-mediated
[
12]
oxidation
to afford single regioisomeric lactone 7a (which
demonstrated that 6a is a diastereomeric mixture of lactols
Scheme 3. Various products obtained through attempted ring closure by oxidative lactonization.
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rather than regioisomeric mixture of exo and endo lactols). The tioned synthetic protocol, seven new benzochromenone deriva-
site of over oxidation was confirmed from the comparative anal- tives 5a–5g were synthesized (Table 2).
ysis of NMR spectroscopic data of lactone 7a with that of native
Table 2. Results of Minisci reaction.[a]
dihydro-isofuran 5a. The downfield shift of the aryl hydrogen
H ) was only observed if the oxidation happened at the exo
(
b
position (owing to –R effect of the newly generated keto func-
tionality ortho to H ). The chemical shift values of the aromatic
b
1
protons were assigned by using the H COSY spectrum for com-
pound 7a (Figure 5).
Figure 5. Top: Stacked 1H NMR spectra of compound 5a and 7a (aromatic
region expanded). Bottom: 1H COSY spectrum of compound 7a (aromatic
region expanded) that shows the various through-bond interactions (for the
complete COSY spectrum see the Supporting Information).
[
4 2 2 8 2 2 2 3
a] Reaction conditions: (NH ) S O , CH Cl /H O, AgNO (50 mol-%), KOAc.
The final benzochromenones were characterized by NMR
Thus, chemoselectivity emerged as a vital issue that needed and HRMS spectroscopic studies. For 5b, as a representative
to be resolved. As evident from the data given in Table 1, example, the appearance of a new singlet at δ = 7.21 ppm in
1
(
NH ) S O as oxidant, AgNO (50 mol-%) as catalyst, KOAc to the H NMR spectrum and the downfield shift of the benzylic
4
2
2
8
3
maintain pH, and stirring at room temp. for 15 h resulted in a methylene protons (as a result of extended conjugation with
much cleaner product profile in which the desired benzo- the lactone carbonyl) confirmed the formation of the lactone.
1
3
chromenone was obtained as the exclusive product in excellent In the C NMR spectra, disappearance of the peak at δ =
yield and establishes the chemoselectivity of the reagent sys- 172.6 ppm (for the carboxylic acid C atom) and appearance of
tem chosen. The use of a larger amount of AgNO (50 mol-%) a new peak at δ = 161.5 ppm (which corresponds to the carb-
3
[
11a]
relative to reported quantities
(20 mol-%) sped up the aryl onyl C, included in the lactone) confirms the formation of the
C–H activation thereby reducing the reaction time and sup- desired compound (Figure 6). The IR spectra also showed char-
pressing the formation of side products, which result from over acteristic absorption for a δ-lactone at 1717 cm– (see the Sup-
oxidation to lactols and lactones. By using the above-men- porting Information).
1
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Figure 6. Stacked 1H and 13C NMR spectra of compound 5b and 4b.
DNA Binding Studies
in which A and A are the absorbances of the compound in the
0
presence and absence of DNA, respectively, ε and ε are the
molar extinction coefficients of compound-DNA complex and
free compound, respectively, at the titration wavelength, [com-
b
f
The synthesized benzochromenones were screened for their
[
13]
DNA-binding activity. For this study, UV/Visible spectroscopy
[
14]
and fluorescence emission spectroscopy
were performed to
pound] is the concentration of compound, and [DNA] is the
0
study their relative strength and possible mode of binding to
DNA. UV absorption titrations were carried out with Tris-HCl
buffer (pH 7.2). The concentration of compounds 5a–5g (dis-
solved in acetonitrile buffer) were fixed and known concentra-
tions of CT DNA solution were added into both the cuvettes
in increasing amounts until saturation in hypochromism was
observed. Absorbance values were recorded after each succes-
sive addition of DNA solution and equilibration. The data were
fitted to Equation (1) to obtain the binding constant (Fig-
concentration of DNA added.
The hypochromism observed in the UV absorption titration
[
16]
is indicative of DNA intercalative mode of binding. Hence, to
ascertain the mode of compound–DNA interaction, Ethidium
bromide (EB) displacement assay was carried out by using fluo-
rescence emission spectroscopy. Quenching of fluorescence in-
tensity was observed for compounds 5a–5g, of which 5g
showed maximum quenching as evident from the plot of F/F0
versus the concentration of compound added, in which F and
F0 are the fluorescence intensities of EB–DNA complex in the
presence and absence of compounds, respectively (Figure 8).
The observed quenching supports the DNA intercalating prop-
erty of these compounds. Furthermore, the relative florescence
1) quenching obtained for the seven compounds are in agree-
[
15]
ure 7).
(
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Figure 7. Absorption titration spectra of the compounds (denoted on their respective spectra) in the presence of CT DNA. In all cases, the uppermost spectrum
represents the compound alone in the absence of DNA. The lower spectra were obtained by the gradual increase in the concentration of DNA for a fixed
–
5
–5
–5
–5
concentration of compound. Concentration of compounds: [5a] = 6.67 × 10
M, [5b] = 3.33 × 10
M
, [5c] = 6.67 × 10
M
, [5d] = 3.33 × 10
M, [5e] =
.33 × 10–5
M, [5f] = 3.33 × 10
–5
M
, and [5g] = 3.33 × 10 M. Double reciprocal plots are shown for the binding of different compounds with CT DNA. The
– A) versus 1/[DNA]. The binding constants were found to be 3.15 × 10 , 5.0 × 10 , 1.82 × 10 , 3.25 × 10 , 1.99 × 10 ,
, for compounds 5a–5g, respectively (each experiment was performed three times and the mean value of the binding constant
–5
3
4
4
4
4
4
linear fits were obtained by plotting 1/(A
0
4
4
–1
4
.28 × 10 , and 5.71 × 10
M
was reported).
ment with the trends observed in the binding constants ob-
tained from UV absorption titration.
The EB-DNA binding assay indicates an intercalative mode of
binding. The binding constants obtained are in the order of
4
3
1
0 relative to 10 obtained for the saturated analogues (6H-
[
4]
benzo[c]chromene). This difference can be attributed to the
expected increase in planarity for these molecules relative to
the latter. Compound 5g, with naphthyl substitution, induced
maximum fluorescence quenching, which was also supported
by the UV absorption titration.
Figure 8. (A) Fluorescence spectral overlay of DNA-EB complex in the presence
of compound 5a. Relative fluorescence intensity reduced after EB replacement
induced by compound 5a. A fixed concentration of DNA (6 μL of 1 mg/mL)
and EB (3 μL of 0.5 mg/mL) was used to make a final sample volume of 3 mL. Conclusions
Fluorescence emission spectra (λmax = 600 nm, excitation wavelength 546 nm)
were recorded. (B) Relative fluorescence intensity decrease of EB induced by
the competitive binding of compounds 5a–5g to CT DNA.
We have developed a simple, moderate to high yielding syn-
thetic protocol for the synthesis of 6H-benzo[c]chromen-6-one
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derivatives that makes use of a Garratt–Braverman cyclization Ethyl
(E)-6-[3-(4-Chlorophenyl)prop-2-ynyloxy]hex-2-ene-4-
ynoate (1c): Gummy solid, 730 mg, 78 %. R = 0.7 (hexane/EtOAc,
and Minisci acyloxylation reaction as the key steps in the multi-
step synthetic route. The method avoids the use of costly transi-
tion metal based catalysts required for conventional synthetic
alternatives. Preliminary DNA binding studies through UV/Vis
absorption titration and ethidium bromide displacement assay
reveal moderately good DNA intercalative activity of the benzo-
chromenone class of molecules. Exploration of the potency of
f
1
0:1). The reaction product was purified by column chromatogra-
1
phy (230–400 mesh, hexane/EtOAc = 15:1). H NMR (600 MHz,
D]chloroform): δ = 7.32 (d, J = 6.8 Hz, 2 H), 7.23 (d, J = 6.5 Hz, 2
H), 6.74 (d, J = 15.9 Hz, 1 H), 6.20 (d, 1 H), 4.43 (s, 2 H), 4.42 (s, 2 H),
[
13
4
[
9
.16 (q, J = 7.3 Hz, 2 H), 1.23 (t, 3 H) ppm. C NMR (150 MHz,
D]chloroform): δ = 165.4, 134.6, 132.9, 131.1, 128.6, 124.1, 120.8,
3.5, 85.8, 85.1, 83.6, 60.8, 57.4, 57.2, 14.1 ppm. HRMS: m/z calcd.
+
GB cyclization to synthesize broader libraries of bioactive ortho- for C H ClO [M + H] 303.0788; found 303.0785.
1
7
15
3
condensed polynuclear heterocycles is ongoing in our labora-
tory.
Ethyl
(E)-6-[3-(4-Bromophenyl)prop-2-ynyloxy]hex-2-ene-4-
ynoate (1d): Gummy solid, 816 mg, 76 %. R = 0.7 (hexane/EtOAc,
f
1
0:1). The reaction product was purified by column chromatogra-
1
phy (230–400 mesh, hexane/EtOAc = 15:1). H NMR (400 MHz,
[D]chloroform): δ = 7.43 (d, J = 8.5 Hz, 1 H), 7.29 (d, J = 8.5 Hz, 1
H), 6.77 (dt, J = 15.9, 2.0 Hz, 1 H), 6.23 (d, J = 15.9 Hz, 1 H), 4.46 (d,
Experimental Section
General Information: All dry reactions were conducted with oven-
dried glassware under an atmosphere of nitrogen. All common rea-
gents were commercial grade and used without further purification.
Silica gel (60–120 and 230–400 mesh) was used for column chroma-
tography. TLC was performed with aluminum-backed plates coated
with Silica gel 60 with F254 indicator. A locally available UV-lamp
J = 1.9 Hz, 2 H), 4.44 (s, 2 H), 4.20 (q, J = 7.2 Hz, 2 H), 1.28 (t, J =
13
7
1
5
3
.1 Hz, 3 H) ppm. C NMR (100 MHz, [D]chloroform): δ = 165.7,
33.4, 131.8, 131.3, 124.3, 123.1, 121.4, 93.6, 86.1, 85.4, 83.8, 61.0,
7.7, 57.5, 14.3 ppm. HRMS: m/z calcd. for C H BrO [M + H]+
17
15
3
47.0283; found 347.0283.
chamber and I -blower were used to visualize compounds. HRMS Ethyl (E)-6-[3-(4-Methoxyphenyl)prop-2-ynyloxy]hex-2-ene-4-
2
1
were obtained with an ESI-TOF mass spectrometer. H NMR spectra
were recorded at 600 and 400 MHz and C NMR spectra were
ynoate (1e): Gummy solid, 711 mg, 77 %. R = 0.6 (hexane/EtOAc,
f
1
3
10:1). The reaction product was purified by column chromatogra-
phy (230–400 mesh, hexane/EtOAc = 15:1). 1H NMR (400 MHz,
[D]chloroform): δ = 7.36 (d, J = 8.7 Hz, 2 H), 6.81 (d, J = 8.6 Hz, 2
H), 6.76 (dt, J = 16.1, 1.8 Hz, 1 H), 6.23 (d, J = 15.9 Hz, 1 H), 4.46 (s,
measured at 150 and 100 MHz in CDCl . Residual solvent signals
3
1
were used as internal standards; δ = 7.26 ppm for H NMR spectra
and δ = 77.2 ppm for C NMR spectra (middle peak) in CDCl , and
1
3
3
the following abbreviations are used to describe peak patterns: s 2 H), 4.44 (s, 2 H), 4.19 (q, J = 7.1 Hz, 2 H), 3.77 (s, 3 H), 1.26 (t, J =
singlet, d doublet, t triplet, q quartet, m multiplet, br. s broad sin- 7.2 Hz, 3 H) ppm. 13C NMR (100 MHz, [D]chloroform): δ = 165.7,
glet.
159.9, 133.4, 131.2, 124.4, 114.4, 114.0, 93.9, 87.2, 83.6, 82.6, 60.9,
+
5
2
7.8, 57.2, 55.3, 14.3 ppm. HRMS: m/z calcd. for C H O [M + H]
99.1283; found 299.1280.
18 18 4
General Method for the Preparation of α,ꢀ-Unsaturated Esters
1
a–1f: Aldehyde (3.1 mmol) dissolved in dry benzene (15 mL) was
treated with (ethoxycarbonymethylene)triphenylphosphorane
1.2 equiv.) and stirred and heated to reflux for 3–4 h under a nitro- ynoate (1f): Gummy solid, 716 mg, 78 %. R
gen atmosphere. The benzene was removed under reduced pres- 12:1). The reaction product was purified by column chromatogra-
phy (230–400 mesh, hexane/EtOAc = 20:1). 1H NMR (600 MHz,
sure. The reaction mixture was partitioned between EtOAc
30 × 2 mL) and water (50 mL). The organic layer was dried with [D]chloroform): δ = 7.08 (s, 2 H), 6.95 (s, 1 H), 6.79 (dt, J = 15.9,
anhydrous Na SO . The solvent was evaporated under reduced 2.0 Hz, 1 H), 6.25 (d, J = 15.9 Hz, 1 H), 4.48 (d, J = 2.2 Hz, 2 H), 4.46
Ethyl (E)-6-[3-(3,5-Dimethylphenyl)prop-2-ynyloxy]hex-2-ene-4-
= 0.7 (hexane/EtOAc =
(
f
(
2
4
pressure and the product was purified by flash silica gel column (s, 2 H), 4.21 (q, J = 7.1 Hz, 2 H), 2.27 (s, 6 H), 1.29 (t, J = 7.2 Hz, 3
H) ppm. 13C NMR (150 MHz, [D]chloroform): δ = 165.7, 137.9, 131.2,
chromatography with hexane/ethyl acetate as eluent.
1
1
2
30.7, 129.6, 124.4, 122.1, 93.9, 87.6, 83.6, 83.3, 60.9, 57.8, 57.2, 21.2,
Ethyl (E)-6-(3-Phenylprop-2-ynyloxy)hex-2-ene-4-ynoate (1a):
+
4.3 ppm. HRMS: m/z calcd. for C H O [M + H] 297.1491; found
19 20 3
Gummy solid, 665 mg, 80 %. R = 0.7 (hexane/EtOAc = 12:1). The
f
97.1486.
reaction product was purified by column chromatography (230–
1
4
00 mesh, hexane/EtOAc = 20:1). H NMR (600 MHz, [D]chloroform):
Ethyl
(E)-6-[3-(Naphthalen-2-yl)prop-2-ynyloxy]hex-2-ene-4-
= 0.6 (hexane/EtOAc =
δ = 7.43 (dd, J = 7.5, 2.4 Hz, 2 H), 7.32–7.27 (m, 3 H), 6.78 (dt, J = ynoate (1g): Gummy solid, 690 mg, 70 %. R
f
1
5.9, 2.0 Hz, 1 H), 6.24 (d, J = 15.9 Hz, 1 H), 4.46 (s, 2 H), 4.46 (s, 2
12:1). The reaction product was purified by column chromatogra-
phy (230–400 mesh, hexane/EtOAc = 20:1). 1H NMR (600 MHz,
[D]chloroform): δ = 7.98 (s, 1 H), 7.80–7.78 (m, 3 H), 7.50–7.49 (m, 3
13
H), 4.19 (q, J = 7.1 Hz, 2 H), 1.26 (t, J = 7.2 Hz, 3 H) ppm. C NMR
(150 MHz, [D]chloroform): δ = 165.6, 131.8, 131.2, 128.7, 128.4,
1
24.3, 93.7, 87.1, 84.1, 83.6, 60.9, 57.6, 57.2, 14.2 ppm. HRMS: calcd. H), 6.80 (d, J = 15.9 Hz, 1 H), 6.27 (d, J = 15.9 Hz, 1 H), 4.54 (s, 4 H),
+
13
for C H O [M + H] 269.1178; found 269.1173.
4.22 (q, J = 7.2 Hz, 2 H), 1.30 (t, J = 7.2 Hz, 3 H) ppm. C NMR
17 16 3
(
150 MHz, [D]chloroform): δ = ppm. 13C NMR (150 MHz, CDCl ): δ =
3
Ethyl (E)-6-(3-p-Tolylprop-2-ynyloxy)hex-2-ene-4-ynoate (1b):
1
1
65.6, 132.9, 132.9, 131.9, 131.2, 128.4, 128.1, 127.8, 126.9, 126.6,
Gummy solid, 682 mg, 78 %. R = 0.7 (hexane/EtOAc = 12:1). The
f
24.3, 119.7, 93.8, 87.5, 84.4, 83.7, 60.9, 57.7, 57.3, 14.1 ppm. HRMS:
reaction product was purified by column chromatography (230–
+
m/z calcd. for C H O [M + H] 319.1334; found 319.1336.
1
21 18 3
4
00 mesh, hexane/EtOAc = 20:1). H NMR (600 MHz, [D]chloroform):
δ = 7.32 (d, J = 8.0 Hz, 2 H), 7.09 (d, J = 7.6 Hz, 2 H), 6.77 (dt, J =
5.8, 2.1 Hz, 1 H), 6.23 (d, J = 16.1 Hz, 1 H), 4.46 (s, 2 H), 4.45 (s, 2
General Method for the Preparation of Biaryl Esters 2a–2g by
Using the Garratt–Braverman Reaction: Bis-propargyl ether
1
H), 4.19 (q, J = 7.1 Hz, 2 H), 2.31 (s, 3 H), 1.27 (t, J = 7.2 Hz, 3 H) ppm.
C NMR (150 MHz, [D]chloroform): δ = 165.6, 138.8, 131.7, 131.1, (2.0 equiv.) and stirred and heated at reflux for 6–8 h under a nitro-
(2.0 mmol) dissolved in dry benzene (50 mL) was treated with DBU
13
1
1
2
29.1, 124.3, 119.3, 93.8, 87.3, 83.5, 83.3, 60.8, 57.7, 57.1, 21.5, gen atmosphere. The benzene was removed under reduced pres-
+
4.2 ppm. HRMS: m/z calcd. for C H O [M + H] 283.1334; found sure. The reaction mixture was partitioned between EtOAc
1
8 18 3
83.1340.
(30 × 2 mL) and water (50 mL). The organic layer was dried with
Eur. J. Org. Chem. 2016, 1439–1448
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1445
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
anhydrous Na SO . The solvent was evaporated under reduced [D]chloroform): δ = 7.80 (d, J = 7.9 Hz, 1 H), 7.23 (d, J = 7.9 Hz, 1
2
4
pressure and the product was purified by silica gel column chroma-
tography with hexane/ethyl acetate as eluent.
H), 6.98 (s, 1 H), 6.83 (s, 2 H), 5.17 (s, 2 H), 4.93 (s, 2 H), 4.06 (q, J =
1
3
7.1 Hz, 2 H), 2.32 (s, 6 H), 0.98 (t, J = 7.2 Hz, 3 H) ppm. C NMR
150 MHz, [D]chloroform): δ = 168.2, 142.6, 139.4, 139.1, 137.6,
(
Ethyl 4-Phenyl-1,3-dihydroisobenzofuran-5-carboxylate (2a):
1
1
2
36.9, 130.5, 129.7, 129.0, 125.6, 119.6, 74.0, 73.5, 60.8, 21.3,
Viscous liquid, 391 mg, 73 %. R = 0.6 (hexane/EtOAc = 12:1). The
f
+
3.7 ppm. HRMS: m/z calcd. for C H O [M + H] 297.1491; found
19 20 3
reaction product was purified by column chromatography (60–
97.1493.
1
1
20 mesh, hexane/EtOAc = 12:1). H NMR (600 MHz, [D]chloroform):
δ = 7.87 (d, J = 7.9 Hz, 1 H), 7.42–7.39 (m, 2 H), 7.38–7.37 (m, 1 H),
.29 (d, J = 7.9 Hz, 1 H), 7.23 (d, J = 6.9 Hz, 2 H), 5.21 (s, 2 H), 4.93 oxylate (2g): Viscous liquid, 477 mg, 75 % (combined yield for
s, 2 H), 4.06 (q, J = 7.1 Hz, 2 H), 0.96 (t, J = 7.2 Hz, 3 H) ppm. 13
products 4 and 2g). R = 0.5 (hexane/EtOAc = 12:1). Products 4 and
NMR (150 MHz, [D]chloroform): δ = 168.1, 142.8, 139.6, 139.4, 136.8, 2g were purified by HPLC with MeOH as eluent (flow rate 0.4 mL/
Ethyl
4-(Naphthalen-2-yl)-1,3-dihydroisobenzofuran-5-carb-
7
(
C
f
1
1
30.5, 130.0, 128.3, 127.9, 127.5, 119.9, 74.1, 73.5, 60.9, 13.7 ppm.
min). Minor isomer 4g: 159 mg, 25 %. H NMR (600 MHz, [D]chloro-
form): δ = 7.90 (d, J = 7.9 Hz, 1 H), 7.87 (dd, J = 9.0, 3.8 Hz, 2 H),
+
HRMS: m/z calcd. for C H O [M + H] 269.1178; found 269.1175.
1
7 16 3
7
2
2
.81 (dd, J = 6.2, 3.3 Hz, 1 H), 7.67 (s, 1 H), 7.51 (dt, J = 6.2, 3.4 Hz,
H), 7.35 (dd, J = 8.4, 1.7 Hz, 1 H), 7.31 (d, J = 7.9 Hz, 1 H), 5.22 (s,
H), 4.93 (s, 2 H), 3.99 (q, J = 7.1 Hz, 2 H), 0.81 (t, J = 7.1 Hz, 3
Ethyl 4-p-Tolyl-1,3-dihydroisobenzofuran-5-carboxylate (2b):
Gummy solid, 418 mg, 74 %. R = 0.6 (hexane/EtOAc = 12:1). The
f
reaction product was purified by column chromatography (60–
13
H) ppm. C NMR (150 MHz, CDCl ): δ = 168.1, 143.1, 139.9, 137.0,
1
3
1
20 mesh, hexane/EtOAc = 12:1). H NMR (600 MHz, [D]chloroform):
1
1
36.9, 133.4, 132.7, 130.6, 130.2, 128.2, 127.9, 126.60, 126.55, 126.52,
26.3, 120.1, 74.3, 73.7, 61.1, 13.8 ppm. HRMS: m/z calcd. for
δ = 7.84 (d, J = 7.9 Hz, 1 H), 7.26 (d, J = 8.0 Hz, 1 H), 7.21 (d, J =
.9 Hz, 2 H), 7.12 (d, J = 7.8 Hz, 2 H), 5.20 (s, 2 H), 4.94 (s, 2 H), 4.09
q, J = 7.2 Hz, 2 H), 2.41 (s, 3 H), 1.01 (t, J = 7.3 Hz, 3 H) ppm. 13
7
+
C H O [M + H] 319.1334; found 319.1333.
21
18 3
(
C
NMR (150 MHz, [D]chloroform): δ = 168.1, 142.7, 139.6, 137.1, 136.8, General Method for the Preparation of Carboxylic Acids 4a–4g:
1
1
2
36.3, 130.5, 129.8, 128.9, 127.8, 119.7, 74.1, 73.5, 60.9, 21.3, Biaryl ester (1.3 mmol) dissolved in MeOH (10 mL) was treated with
+
3.8 ppm. HRMS: m/z calcd. for C H O [M + H] 283.1334; found aqueous NaOH (3eq; 2 mL) and stirred and heated at reflux for 8 h.
1
8 18 3
83.1330.
The MeOH was removed at reduced pressure. The excess base was
neutralized by HCl solution (10 ) at 0 °C (ice) and monitored with
N
Ethyl 4-(4-Chlorophenyl)-1,3-dihydroisobenzofuran-5-carboxyl-
ate (2c): Viscous liquid, 429 mg, 71 %. R = 0.6 (hexane/EtOAc =
pH paper. Then the reaction mixture was partitioned between
EtOAc (30 × 2 mL) and water (50 mL). The organic layer was dried
with anhydrous Na SO . The solvent was evaporated under reduced
f
1
0:1). The reaction product was purified by column chromatogra-
1
2
4
phy (60–120 mesh, hexane/EtOAc = 10:1). H NMR (600 MHz,
D]chloroform): δ = 7.89 (d, J = 7.9 Hz, 1 H), 7.38 (d, J = 8.2 Hz, 2
H), 7.29 (d, J = 8.1 Hz, 1 H), 7.15 (d, J = 8.1 Hz, 2 H), 5.19 (s, 2 H),
pressure to furnish the acid, which was used for the next step with-
out further purification.
[
4
.88 (s, 2 H), 4.08 (q, J = 7.2 Hz, 2 H), 1.03 (t, J = 7.3 Hz, 3 H) ppm.
C NMR (150 MHz, [D]chloroform): δ = 167.5, 143.1, 139.6, 137.9, Solid, 306 mg, 98 %. R = 0.4 (hexane/EtOAc, 1:1). H NMR (600 MHz,
4-Phenyl-1,3-dihydroisobenzofuran-5-carboxylic Acid (4a):
1
3
1
f
1
1
35.6, 133.5, 130.2, 130.1, 129.3, 128.5, 120.3, 74.1, 73.3, 61.0, [D]chloroform): δ = 7.94 (d, J = 7.9 Hz, 1 H), 7.39–7.19 (m, 3 H), 7.27
3.8 ppm. HRMS: m/z calcd. for C H ClO [M + H]+ 303.0788; (d, J = 7.9 Hz, 1 H), 7.20 (d, J = 6.8 Hz, 2 H), 5.20 (s, 2 H), 4.88 (s, 2
1
7
15
3
found 303.0780.
H) ppm. 13C NMR (150 MHz, [D]chloroform): δ = 172.5, 143.8, 139.9,
1
38.9, 137.8, 131.0, 128.6, 128.4, 127.9, 127.7, 120.0, 74.2, 73.5 ppm.
Ethyl 4-(4-Bromophenyl)-1,3-dihydroisobenzofuran-5-carboxyl-
+
HRMS: m/z calcd. for [M + H] C H O 241.0865; found 241.0869.
15 12 3
ate (2d): Viscous liquid, 484 mg, 70 %. R = 0.6 (hexane/EtOAc =
f
1
0:1). The reaction product was purified by column chromatogra- 4-p-Tolyl-1,3-dihydroisobenzofuran-5-carboxylic Acid (4b):
1
1
phy (60–120 mesh, hexane/EtOAc = 10:1). H NMR (600 MHz,
D]chloroform): δ = 7.88 (d, J = 7.9 Hz, 1 H), 7.52 (d, J = 8.4 Hz, 2
H), 7.28 (d, J = 7.9 Hz, 1 H), 7.08 (d, J = 8.4 Hz, 2 H), 5.18 (s, 2 H),
Solid, 317 mg, 96 %. R = 0.4 (hexane/EtOAc, 1:1). H NMR (600 MHz,
f
[
[D]chloroform): δ = 7.95 (d, J = 8.0 Hz, 1 H), 7.28 (d, J = 7.9 Hz, 1
H), 7.21 (d, J = 7.8 Hz, 2 H), 7.13 (d, J = 7.8 Hz, 2 H), 5.22 (s, 2 H),
4.93 (s, 2 H), 2.41 (s, 3 H) ppm. 13C NMR (150 MHz, [D]chloroform):
4
.86 (s, 2 H), 4.07 (q, J = 7.1 Hz, 2 H), 1.02 (t, J = 7.2 Hz, 3 H) ppm.
13
C NMR (150 MHz, [D]chloroform): δ = 167.6, 143.2, 139.6, 138.4, δ = 172.6, 143.6, 139.9, 137.7, 137.3, 135.8, 130.9, 129.1, 128.8, 127.8,
+
1
1
35.7, 131.5, 130.3, 130.0, 129.7, 121.7, 120.3, 74.1, 73.4, 61.1, 119.8, 74.1, 73.6, 21.4 ppm. HRMS: m/z calcd. for C H O [M + H]
16 14 3
3.8 ppm. HRMS: m/z calcd. for C H BrO [M + H]+ 347.0283;
255.1021; found 255.1016.
1
7
15
3
found 347.0287.
4
-(4-Chlorophenyl)-1,3-dihydroisobenzofuran-5-carboxylic Acid
1
Ethyl 4-(4-Methoxyphenyl)-1,3-dihydroisobenzofuran-5-carb-
(4c): Solid, 346 mg, 97 %. R = 0.3 (hexane/EtOAc, 1:1). H NMR
f
oxylate (2e): Viscous liquid, 447 mg, 75 %. R = 0.5 (hexane/EtOAc =
(600 MHz, [D]chloroform): δ = 7.97 (d, J = 8.0 Hz, 1 H), 7.35 (d, J =
f
1
0:1). The reaction product was purified by column chromatogra- 8.0 Hz, 2 H), 7.29 (d, J = 8.0 Hz, 1 H), 7.13 (d, J = 8.4 Hz, 2 H), 5.19
1
13
phy (60–120 mesh, hexane/EtOAc = 10:1). H NMR (600 MHz,
D]chloroform): δ = 7.79 (d, J = 7.9 Hz, 1 H), 7.22 (d, J = 7.9 Hz, 1
H), 7.12 (d, J = 8.7 Hz, 2 H), 6.91 (d, J = 8.7 Hz, 2 H), 5.16 (s, 2 H),
(s, 2 H), 4.85 (s, 2 H) ppm. C NMR (150 MHz, [D]chloroform): δ =
[
172.1, 144.1, 139.9, 137.4, 136.7, 133.7, 131.3, 129.3, 128.7, 128.4,
+
120.4, 74.2, 73.4 ppm. HRMS: m/z calcd. for C H ClO [M + H]
15
11
3
4
3
1
6
2
.91 (s, 2 H), 4.06 (q, J = 7.1 Hz, 2 H), 3.82 (s, 3 H), 1.01 (t, J = 7.2 Hz,
H) ppm. 13C NMR (150 MHz, [D]chloroform): δ = 168.2, 159.0,
42.6, 139.7, 136.4, 131.5, 130.6, 129.8, 129.1, 119.6, 113.7, 74.1, 73.5,
275.0475; found 275.0478.
4-(4-Bromophenyl)-1,3-dihydroisobenzofuran-5-carboxylic Acid
1
(4d): Solid, 393 mg, 95 %. R = 0.3 (hexane/EtOAc, 1:1). H NMR
+
f
0.9, 55.3, 13.9 ppm. HRMS: m/z calcd. for C H O [M + H]
1
8 18 4
(600 MHz, [D]chloroform): δ = 7.98 (d, J = 7.8 Hz, 1 H), 7.51 (d, J =
99.1283; found 299.1281.
7.9 Hz, 2 H), 7.30 (d, J = 7.9 Hz, 1 H), 7.08 (d, J = 8.0 Hz, 2 H), 5.20
13
Ethyl 4-(3,5-Dimethylphenyl)-1,3-dihydroisobenzofuran-5-carb-
(s, 2 H), 4.85 (s, 2 H) ppm. C NMR (150 MHz, [D]chloroform): δ =
oxylate (2f): Viscous liquid, 438 mg, 74 %. R = 0.6 (hexane/EtOAc =
172.0, 144.2, 139.9, 137.9, 136.7, 131.7, 131.3, 129.6, 128.2, 121.9,
f
+
1
2:1). The reaction product was purified by column chromatogra- 120.5, 74.2, 73.4 ppm. HRMS: m/z calcd. for C H BrO [M + H]
15 11 3
1
phy (60–120 mesh, hexane/EtOAc = 12:1). H NMR (600 MHz,
318.9970; found 318.9975.
Eur. J. Org. Chem. 2016, 1439–1448
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1446
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
4
-(4-Methoxyphenyl)-1,3-dihydroisobenzofuran-5-carboxylic δ = 8.41 (d, J = 7.6 Hz, 1 H), 7.48 (d, J = 7.6 Hz, 1 H), 7.41 (br. s, 2
1
13
Acid (4e): Solid, 337 mg, 96 %. R = 0.2 (hexane/EtOAc, 1:1). H NMR H), 7.33 (d, J = 8.4 Hz, 1 H), 5.58 (s, 2 H), 5.26 (s, 2 H) ppm. C NMR
f
(600 MHz, [D]chloroform): δ = 7.91 (d, J = 8.0 Hz, 1 H), 7.24 (d, J =
(150 MHz, [D]chloroform): δ = 160.6, 152.1, 148.0, 136.3, 134.9,
7
.9 Hz, 1 H), 7.13 (d, J = 8.6 Hz, 2 H), 6.91 (d, J = 8.6 Hz, 2 H), 5.19
131.4, 129.8, 126.8, 125.3, 121.9, 121.0, 118.4, 117.2, 74.7, 73.5 ppm.
1
3
+
(
s, 2 H), 4.91 (s, 2 H), 3.82 (s, 3 H) ppm. C NMR (150 MHz, [D]chloro-
form): δ = 172.6, 159.1, 143.5, 140.1, 137.3, 131.1, 130.9, 129.1, 128.9,
HRMS: m/z calcd. for C H ClO [M + H] 273.0318; found 273.0327.
15
9
3
9
-Bromo-1,3-dihydro-2,7-dioxacyclopenta[c]phenanthren-6-
1
+
19.7, 113.9, 74.1, 73.6, 55.3 ppm. HRMS: m/z calcd. for C H O [M
16 14 4
one (5d): Solid, 57 mg, 85 %. R = 0.7 (hexane/EtOAc = 10:1). The
f
+
H] 271.0970; found 271.0966.
reaction product was purified by column chromatography (60–
1
4
-(3,5-Dimethylphenyl)-1,3-dihydroisobenzofuran-5-carboxylic 120 mesh, hexane/EtOAc = 12:1). H NMR (600 MHz, [D]chloroform):
1
Acid (4f): Solid, 338 mg, 97 %. R = 0.4 (hexane/EtOAc, 1:1). H NMR δ = 8.42 (d, J = 8.0 Hz, 1 H), 7.58 (d, J = 2.0 Hz, 1 H), 7.52–7.47 (m,
f
1
3
(600 MHz, [D]chloroform): δ = 7.94 (d, J = 7.9 Hz, 1 H), 7.27 (d, J =
2 H), 7.36 (d, J = 8.5 Hz, 1 H), 5.58 (s, 2 H), 5.27 (s, 2 H) ppm.
NMR (150 MHz, [D]chloroform): δ = 160.5, 152.0, 148.1, 134.9, 131.4,
.34 (s, 6 H) ppm. C NMR (150 MHz, [D]chloroform): δ = 172.6, 129.9, 128.2, 126.9, 124.1, 122.0, 121.4, 121.1, 117.6, 74.7, 73.5 ppm.
C
7
2
1
7
2
.9 Hz, 1 H), 6.99 (s, 1 H), 6.85 (s, 2 H), 5.21 (s, 2 H), 4.92 (s, 2 H),
13
+
43.6, 139.9, 138.7, 137.9, 137.8, 130.9, 129.4, 128.7, 125.7, 119.8, HRMS: m/z calcd. for C15
H
BrO
9
[M + H] 316.9813; found 316.9814.
3
+
4.2, 73.7, 21.5 ppm. HRMS: m/z calcd. for C17H16O [M + H]
3
9
-Methoxy-1,3-dihydro-2,7-dioxacyclopenta[c]phenanthren-6-
69.1178; found 269.1184.
one (5e): Solid, 35 mg, 63 %. R = 0.6 (hexane/EtOAc = 10:1). The
f
4
-(Naphthalen-2-yl)-1,3-dihydroisobenzofuran-5-carboxylic reaction product was purified by column chromatography (60–
1
1
Acid (4g): Solid, 370 mg, 98 %. R = 0.3 (hexane/EtOAc, 1:1). H NMR
600 MHz, [D]chloroform): δ = 7.98 (d, J = 7.9 Hz, 1 H), 7.86 (d, J =
120 mesh, hexane/EtOAc = 12:1). H NMR (600 MHz, [D]chloroform):
f
(
7
δ = 8.35 (d, J = 8.0 Hz, 1 H), 7.37 (d, J = 8.4 Hz, 2 H), 6.92–6.89 (m,
2 H), 5.53 (s, 2 H), 5.23 (s, 2 H), 3.89 (s, 3 H) ppm. 13C NMR (100 MHz,
.5 Hz, 1 H), 7.83–7.80 (m, 2 H), 7.66 (s, 1 H), 7.50 (d, J = 3.6 Hz, 1
13
H), 7.33–7.28 (m, 3 H), 5.21 (s, 2 H), 4.88 (s, 2 H) ppm. C NMR [D]chloroform): δ = 161.5, 161.4, 153.2, 147.6, 133.8, 131.2, 130.9,
126.9, 120.5, 119.9, 112.5, 111.6, 102.3, 74.8, 73.5, 55.9 ppm. HRMS:
(
150 MHz, [D]chloroform): δ = 172.0, 144.0, 140.4, 137.8, 136.6,
+
1
1
2
33.3, 132.8, 131.2, 128.6, 128.2, 128.0, 127.9, 126.5, 126.4, 126.3, m/z calcd. for C16
H O
12
4
[M + Na ] 291.0633; found 291.0633.
+
20.2, 74.2, 73.6 ppm. HRMS: m/z calcd. for C19H14O [M + H]
3
8,10-Dimethyl-1,3-dihydro-2,7-dioxacyclopenta[c]phenanthren-
-one (5f): Solid, 43 mg, 80 %. R = 0.6 (hexane/EtOAc = 12:1).
91.1021; found 291.1025.
6
f
The reaction product was purified by column chromatography (60–
General Method for the Preparation of Dihydro-isofuran Fused
Benzochromenones 5a–5g by Using the Minisci Acyloxylation
1
120 mesh, hexane/EtOAc = 15:1). H NMR (600 MHz, [D]chloroform):
δ = 8.39 (d, J = 8.0 Hz, 1 H), 7.42 (d, J = 8.0 Hz, 1 H), 7.17 (s, 1 H),
Reaction: To biarylcarboxylic acid (0.2 mmol), AgNO (0.5 equiv.),
3
7
.03 (s, 1 H), 5.52 (s, 2 H), 5.23 (s, 2 H), 2.45 (s, 3 H), 2.41 (s, 3 H) ppm.
C NMR (150 MHz, [D]chloroform): δ = 161.4, 148.0, 147.4, 134.8,
(
NH ) S O (3 equiv.), KOAc (3 equiv.), distilled CH Cl (2 mL), and
4 2 2 8 2 2
1
3
deionized water (2 mL) were added. The reaction mixture was
stirred at room temperature until complete disappearance of the
starting material (monitored by TLC; 10–15 h). Then the reaction
mixture was partitioned between CH Cl (30 × 3 mL) and water
1
1
2
33.7, 133.0, 131.1, 130.9, 126.9, 123.5, 121.2, 117.8, 74.9, 73.4, 21.5,
+
6.3 ppm. HRMS: m/z calcd. for C H O [M + Na ] 289.0841; found
17 14
3
89.0841.
2
2
(
50 mL). The organic layer was dried with anhydrous Na SO . The
2 4
3,5-Dihydro-4,12-dioxacyclopenta[c]chrysen-13-one (5g): Solid,
9 mg, 65 %. R = 0.6 (hexane/EtOAc = 10:1). The reaction product
solvent was evaporated under reduced pressure and product was
purified by silica gel column chromatography with hexane/ethyl
acetate as eluent.
3
f
was purified by column chromatography (60–120 mesh, hexane/
1
EtOAc = 12:1). H NMR (600 MHz, [D]chloroform): δ = 8.63 (d, J =
7
.8 Hz, 1 H), 8.49 (d, J = 7.9 Hz, 1 H), 7.89 (d, J = 7.2 Hz, 1 H), 7.78
1
,3-Dihydro-2,7-dioxacyclopenta[c]phenanthren-6-one (5a):
(d, J = 8.8 Hz, 1 H), 7.65 (qt, J = 7.0, 3.4 Hz, 1 H), 7.57 (d, J = 8.8 Hz,
Solid, 46 mg, 95 %. R = 0.7 (hexane/EtOAc = 10:1). The reaction
product was purified by column chromatography (60–120 mesh,
hexane/EtOAc = 12:1). H NMR (600 MHz, [D]chloroform): δ = 8.39
f
1
3
1
H), 7.48 (d, J = 8.0 Hz, 1 H), 5.72 (s, 2 H), 5.28 (s, 2 H) ppm.
C
1
NMR (150 MHz, [D]chloroform): δ = 161.3, 147.96, 147.87, 134.8,
1
1
34.1, 131.4, 131.3, 128.5, 127.7, 127.5, 124.8, 123.9, 122.7, 121.8,
(d, J = 8.0 Hz, 1 H), 7.52–7.48 (m, 1 H), 7.47–7.44 (m, 2 H), 7.39 (d,
21.5, 121.3, 113.5, 74.9, 73.5 ppm. HRMS: m/z calcd. for C H O
J = 8.2 Hz, 1 H), 7.36–7.33 (m, 1 H), 5.56 (s, 2 H), 5.24 (s, 2 H) ppm.
19 12
3
+
13
[M + Na ] 311.0684; found 311.0684.
C NMR (150 MHz, [D]chloroform): δ = 161.2, 151.7, 147.7, 134.8,
1
7
2
31.2, 130.6, 130.5, 125.8, 124.9, 121.6, 121.3, 118.4, 118.2, 74.8,
Method Used for DNA Binding Studies
+
3.4 ppm. HRMS: m/z calcd. for C H O [M + H] 239.0708; found
1
5 10 3
UV-Based Assay: A Jasco V 730 spectrophotometer was used for
absorption spectral studies. Solutions of Calf Thymus DNA (CT DNA)
39.0708.
-Methyl-1,3-dihydro-2,7-dioxacyclopenta[c]phenanthren-6-
one (5b): Solid, 36 mg, 72 %. R = 0.7 (hexane/EtOAc = 10:1). The
9
were prepared in Tris-HCl buffer (1 m
absorbances at 260 and 280 nm (A260/A280) was found to be 1.84.
reaction product was purified by column chromatography (60– The DNA concentrations were determined by using an extinction
M; pH = 7.2). The ratio of UV
f
1
–1
1
20 mesh, hexane/EtOAc = 12:1). H NMR (600 MHz, [D]chloroform):
δ = 8.40 (d, J = 8.0 Hz, 1 H), 7.43 (d, J = 8.0 Hz, 1 H), 7.37 (d, J =
.2 Hz, 1 H), 7.21 (s, 1 H), 7.16 (dd, J = 7.9, 1.9 Hz, 1 H), 5.58 (s, 2
coefficient of 6600
M
at 260 nm and were expressed in terms of
base molarity. UV absorption titrations were carried out by keeping
the concentration of compounds 5a–5g (dissolved in acetonitrile
buffer) fixed, and by adding a known concentration of CT DNA
solution into both the cuvettes in increasing amounts until hypo-
8
1
3
H), 5.25 (s, 2 H), 2.46 (s, 3 H) ppm. C NMR (150 MHz, [D]chloro-
form): δ = 161.5, 151.7, 147.6, 141.6, 134.5, 131.2, 130.8, 126.0, 125.6,
1
21.1, 121.0, 118.3, 115.9, 74.8, 73.5, 21.6 ppm. HRMS: m/z calcd. for chromism saturation was observed. Absorbance values were re-
+
C H O [M + Na ] 275.0684; found 275.0688.
corded after each successive addition of DNA solution and equili-
bration.
1
6 12 3
9
-Chloro-1,3-dihydro-2,7-dioxacyclopenta[c]phenanthren-6-
one (5c): Solid, 42 mg, 78 %. R = 0.7 (hexane/EtOAc = 10:1). The
Ethidium Bromide Displacement Assay: DNA (6 μL of 1 mg/mL
f
reaction product was purified by column chromatography (60– solution), EB (3 μL of 0.5 mg/mL), and Tris-HCl buffer (pH 7.2) that
1
1
20 mesh, hexane/EtOAc = 12:1). H NMR (600 MHz, [D]chloroform):
contained NaCl (40 mM) was used to make a total volume of 3 mL.
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Full Paper
EB displacement fluorescence assay was employed to verify DNA
intercalation. Fluorescence emission spectra (λmax = 600 nm, excita-
tion wavelength 546 nm; slit width 10 nm; 1 cm path length) were
obtained at 30 °C on a Beckman fluorescence spectrophotometer.
The assays were performed by using different concentrations (0–
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Acknowledgments
A. B. is grateful to the Department of Science and Technology
1651; d) A. W. Wood, M.-T. Huang, R. L. Chang, H. L. Newmark, R. E. Lehr,
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fellowship. P. B. thanks Council of Scientific and Industrial Re-
search (CSIR), New Delhi, for a research fellowship (NET). The
authors are also grateful to DST for the funds for an 400 MHz
NMR spectroscopic facility under the IRPHA program and IIT
Kharagpur for the 600 MHz NMR spectroscopic facility.
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Keywords: Synthetic methods · Oxygen heterocycles ·
Cyclization · Chemoselectivity · Medicinal chemistry · DNA ·
Intercalations
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Received: December 4, 2015
2014, 79, 3789.
Published Online: February 4, 2016
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1448
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim