A solvent- And catalyst-free tandem reaction: Synthesis, and photophysical and biological applications of isoindoloquinazolinones

Article abstract of DOI:10.1039/c9nj05808g

An easy green synthetic approach for fused isoindoloquinazolinones has been developed under neat reaction (yields up to 91%) conditions. This new one-pot tandem methodology involves condensation of readily available anthranilamide with 3-(2-formylcycloalk

Full text of DOI:10.1039/c9nj05808g

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A solvent- and catalyst-free tandem reaction:
synthesis, and photophysical and biological
Cite this:DOI: 10.1039/c9nj05808g
applications of isoindoloquinazolinones†
a
Anirban Bera,ab Sk Asraf Ali,
Susanta Kumar Manna,a Mohammed Ikbal,c
Sandip Misra,d Amit Saha *b and Shubhankar Samanta
*
a
An easy green synthetic approach for fused isoindoloquinazolinones has been developed under neat reaction
(yields up to 91%) conditions. This new one-pot tandem methodology involves condensation of readily available
anthranilamide with 3-(2-formylcycloalkenyl)-acrylic ester under solvent- and catalyst-free conditions. This
strategy avoids the use of oxidant, and heavy metal catalysts and also is free from work-up and generation of
toxic by-products. A dramatic change of photophysical properties of dihydroisoindoloquinazolinones in basic
and aqueous media has also been documented in our study. Moreover, our model synthetic compound shows
cytotoxic activity towards metastatic HepG2 and PC3 cancer cell lines.
Received 21st November 2019,
Accepted 13th February 2020
DOI: 10.1039/c9nj05808g
rsc.li/njc
synthetic strategy for fused quinazolinones and their applications
Introduction
in in vitro and in vivo bio-systems are highly needed.7
In recent years, one-pot tandem chemical transformations
Different approaches have been reported in the literature to
under metal- and solvent-free conditions have widely been used synthesize highly condensed quinazolinone derivatives.8 Suzuki
for complex organic molecule syntheses with reduced reaction coupling followed by Pd/Cu catalysed oxidative C–H amination,9
time period and minimum energy requirement. A variety of and tandem Sonogashira coupling and hydroamination
chemical conversions, like oxidation, reduction, substitution, cyclization10 are the two independent approaches towards fused
condensation, etc. have been developed using this principle.1 quinazolinone, where 2-bromobenzaldeyde and anthranilamide
Hence, heterocyclic ring formation using this green technique were taken as the starting materials. Another recent report involves
has been an active and attractive field in the recent era.2
ruthenium(II)-catalyzed one-pot oxidative C–H/N–H functionalization
Among the heterocyclic molecular architectures, N-fused of substituted dihydroquinazolinones with alkynes.11 Radical
heterocycles are ubiquitous in nature and a common structural cyclization of N-(2-iodobenzyl)-N-acylcyanamides is another reported
motif for bioactive molecules and drug candidates. In particular, strategy to access fused pyrroloquinazoline.12 Li-Jiang Xuan and his
substituted quinazolinones have a wide range of biological and group synthesized the same scaffolds via ruthenium-catalyzed oxida-
pharmacological activities, such as diuretic, anti-inflammatory, tive coupling of 2-arylquinazolinones followed by an intramolecular
antidiabetic, anti-hepatitis C, anticonvulsant, antileshmanial, aza-Michael reaction.13 However, to the best of our knowledge, no
anticancer and so forth.3 Two major types of fused quinazolinones attention has been devoted towards the synthesis of fused quinazo-
available in nature are carbocycle fused quinazolinones, such as linones under metal- and solvent-free conditions. For eco-friendly
phaitanthrin, tryptanthrin, vasicione etc. (Fig. 1)4 and heterocycle reaction conditions, the chemical community always searches for
fused quinazolinones, like luotonin A and wuzhuyurutine A.5 green reactions under metal-free and solvent-free conditions. It is
Quinazolinone molecular frameworks are also popular as efficient always better to perform the reaction in a non-hazardous solvent
organic fluorescence materials.6 Hence, development of a modern medium such as water, but it is also far better to run a reaction
without any solvent, which reduces the steps in a multistep proce-
dure e.g. work up and purification. As a part of our ongoing studies
devoted towards the development of new heterocycles,14 we have
disclosed here an operatively simple, catalyst- and solvent-free
synthesis of pyrrolo/isoindolo quinazolinone derivatives from
3-(2-formylcycloalkenyl)-acrylic ester derivatives 1 and anthranil-
amide 2 under heating conditions (120 1C) with moderate to
good yields (Scheme 1). In addition, their photophysical properties
have been studied, which are limited in the literature.
a Department of Chemistry, Bidhannagar College, Kolkata 700064, India.
E-mail: chemshubha@gmail.com; Fax: (9133) 2337 4782; Tel: +919775550193
b Department of Chemistry, Jadavpur University, Kolkata 700032, India.
E-mail: amit.saha@jadavpuruniversity.in
c Department of Chemistry Berhampore Girls’ College, Berhampore 742101, India
d Department of Microbiology, Bidhannagar College, Kolkata 700064, India
† Electronic supplementary information (ESI) available. CCDC 1945935. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c9nj05808g
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Fig. 1 Naturally occurring bioactive fused quinazolinone scaffolds.
Scheme 1 Previous approaches vs. the present approach towards polycyclic fused quinazolinone.
Results and discussion
and dioxane (entries 7–9). In order to increase the efficacy of our
developed methodology, studies without any solvent were car-
At the outset of this investigation to synthesize highly condensed ried out and the desired fused quinazolinone 3a was obtained in
fused quinazolinone derivatives 3, the reaction was commenced very good yield (91%), (entry 10).
with (E)-methyl 3-(2-formylphenyl)acrylate 1a and anthranilamide
With the optimal conditions in hand, the scope of the new
2a in DMSO at room temperature, but no reaction occurred two-component neat reaction was evaluated with a variety
(Table 1; entry 1). However, the intermolecular condensation of substrates as shown in Table 2. Methyl/ethyl/tertiary butyl
reaction followed by intramolecular aza-cyclization in one-pot (E)-3-(2-formylphenyl)acrylates were smoothly converted to the
succeeded by increasing the temperature up to 120 1C in DMSO corresponding isoindoloquinazolines 3a–3c in moderate to
(entry 4). It was found that cyclization was inefficient below high yields. The cyclised product 3b was unambiguously confirmed
120 1C (entries 2 and 3). The two component coupling reaction by X-ray crystal structure as shown in Table 2.15 With this
proceeds satisfactorily in toluene and ethanol (entries 5 and 6). encouraging result in hand, the scope of the neat reaction was
However, no fruitful product was isolated in acetonitrile, THF examined with different cycloalkenyl derivatives. Formation of
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fruitful condensed derivatives 3a–3h and 3q–3r.13 The product
formation of 3i–3p could be elucidated via a competitive
intramolecular aza-Michael reaction of more nucleophilic
amide N-atoms.
Table 1 Optimization of the reaction conditions towards a highly con-
densed quinazolinonea
The formation of 3s and 3t could be explained via a two-step
1,5-H shift of intermediate I (Scheme 3).
Interestingly, it is noticed that the substrate 3j possesses
high fluorescent properties and hence investigation of the
photophysical properties has also been discussed. The tolerance
of these valuable functional groups would offer an opportunity
for further transformations.
Entry
Solvent
T (1C)
Time (h)
Yield of 3a (%)
1
2
3
4
5
6
7
8
9
10
DMSO
DMSO
DMSO
DMSO
Ethanol
Toluene
Acetonitrile
THF
25
60
80
120
78
110
82
66
101
120
8
8
8
2
2.5
3
6
6
6
0
0
0
82
73
85
0
Photophysical studies
0
Dioxane
—
0
2
91b
After successful synthetic studies, attention was drawn towards
photophysical studies of the synthesized dihydroquinazolinone
molecule 3j. The UV/Vis absorption spectra of degassed 2 Â
10À6 M solution of 3j in different solvents have been recorded
(ESI;† Fig. S1), and the results are tabulated in Table 3.
Excited state properties of quinazolinone derivative 3j were
a
Conditions: (E)-methyl 3-(2-formylphenyl)acrylate 1a (1 mmol),
b
anthranilamide 2a (1 mmol), and solvent (2 ml). Reaction performed
without solvent.
the oxidized and reduced forms of the cyclized product depends on
the nature of the ring. Aromatic moieties of ester derivatives were investigated by fluorescence emission spectroscopy. Like those
prone to air oxidation and lead to 3a–3f, whereas the corresponding of other quinazolinone derivatives, the fluorescence properties
cycloalkenyl ester derivatives 3i–3p (7 and 8 membered rings) are of 3j were also found to be strongly dependent on solvent
reluctant to undergo air oxidation. On the contrary, methyl/ polarity.17 The heterocyclic compound 3j showed negative
ethyl (E)-3-(2-formylcyclohexenyl)acrylates 3g and 3h smoothly solvatochromatic emission (Fig. 2) as a function of solvent
transformed to their corresponding oxidized quinazolinones.
polarity.18 As the solvent polarity increases (from non-polar
The two component coupling reactions of 2-aminothiophene- e.g. toluene to polar e.g. acetonitrile (MeCN)), a hypsochromic
3-carboxamide 2d with (E)-3-(2-formylphenyl)acrylates under shift for 3j was noticed and the emission maximum was found
neat conditions were well tolerated and deliver 3f, 3m and 3n. to shift from 431 to 416 nm. The above solvent effect observed
We further extended the scope of the novel methodology to is due to the close lying (1p–p*) and (1n–p*) singlet excited
pentacyclic quinazolinones 3o but the yield of the desired states.19 The higher dissolving ability of a solvent with lower
product was reduced to 55% due to the high steric constancy of dielectric constant (non-polar solvent) favours the p–p* interaction
the starting material. Notably, chloride and bromide substituted in the quinazolinone unit and produces greater emission.20
anthranilamides (2b–2c) were unable to produce cyclized products Conversely, in polar protic solvent (e.g. MeOH) due to the inter-
3d and 3e at 120 1C under neat conditions and the condensations molecular H-bonding effect with the quinazolinone unit, the p–p*
were performed at 140 1C under solvent-free conditions, which transition dominates, which results in shifting of the emission
resulted in the formation of the desired products (3d and 3e) in band towards longer wave length.
good yields. The neat reaction of 1a furnished a very low yield of 3r
The fluorescence properties of dihydroquinazolinone derivative
for an electron withdrawing substituted anthranilamide (–NO2), 3j were also investigated in an aqueous binary solvent system
but the same reaction gave satisfactory yield of two isomeric to understand the effect of hydrogen bonding interaction. The
quinazolinones 3r and 3s in DMSO at 120 1C. Nevertheless, only emission spectra (Fig. 3) of 3j in MeCN–H2O binary mixtures were
one isomer 3p was generated for the cycloheptenyl system under recorded and it was observed that with an increasing amount of
equivalent conditions. Our green protocol was equally adequate water in the MeCN–H2O mixture, there is a bit of a bathochromic
compared to another acrylonitrile-substituted aza-Michael accep- shift with a gradual decrease in fluorescence intensity. The above
tor and furnished a good yield of quinazolinone derivative 3q. fact can be attributed to solute–solvent interactions through the
Furthermore, we have extended the scope of the reaction to the formation of hydrogen bonds between the solvent and the hetero-
substrate (2E,4E)-methyl 6-oxo-4-phenylhexa-2,4-dienoate, which cyclic part of the quinazolinone moiety (Scheme 4).21
furnished cyclised product 3t with a good yield of 72%.
As the quinazolinone derivative contains a basic labile
The mechanism of the reaction could be ascertained via a proton (NH), it is quite interesting to check the emission
four-step sequential process in one-pot (Scheme 2). The step- spectral behaviour with increase of pH (Fig. 4). The fluores-
atom economical mechanistic pathway involves Schiff base (A) cence maximum of 3j in neutral MeCN is around 412 nm,
formation followed by intramolecular aza-cyclisation to pro- which is red shifted to E437 nm by the successive addition of
duce intermediate B, which affords the quinazolinone deriva- different concentrations of NaOH (micromolar). This is because
tive after air oxidation.16 The quinazolinone intermediate C in pure MeCN, protonated 3j is the predominant species. Thus
undergoes intramolecular aza-Michael reaction and provided the fluorescence spectrum in pure MeCN is mainly due to
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Table 2 Substrate scope for tandem one-pot neat reactionb
a
c
b
Reactions were performed in DMSO. Conditions: (E)-methyl 3-(2-formylcycloalkenyl)acrylate 1a (1 mmol), and anthranilamide 2 (1 mmol).
Reactions were performed at 140 1C.
protonated 3j in the excited state. At higher pH, a bathochromic
shift was obtained due to the deprotonation of 3j followed by
Biological study
extended conjugation and the decrease of fluorescence inten- After successful investigation of the photophysical properties,
sity may be explained by the lower solubility of the molecule in our research turned towards biological application of our
an alkaline solution (Scheme 5).
model compound 3j using two different metastatic cancer cell
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Scheme 2 Plausible mechanism for the synthesis of fused quinazolinones.
Scheme 3 Synthetic route of isomerised quinazolinone.
Table 3 UV-Vis absorption and fluorescence data of 3j in different
solvents
ea
(25 1C) bondingb
dH hydrogen lmax
lemi Stokes’
c
e
(nm) shift f (nm)
d
Solvent
(nm) emax
Toluene
Chloroform 4.81
DCM
MeOH
CAN
2.38
2.0
7.1
7.1
330 132 000 431 101
329 159 000 431 101
9.10
33.00 19.4
37.50
46.70
331 133 000 429
333 120 500 430
331 119 000 416
329 87 500 416
98
97
82
87
6.1
7.8
DMSO
a
b
c
Dielectric constant at 25 1C. Hydrogen bonding capability. Max-
d
imum absorption wavelength. Molar absorption coefficient at max-
e
imum absorption wavelength. Maximum emission wavelength.
f
Fig. 2 Fluorescence spectra of quinazolinone derivatives 3j in different
Difference between maximum absorption wavelength and maximum
solvents.
emission.
lines; hepatocellular carcinoma (HepG2) and prostate cancer widely in research and drug development.23 To examine the
(PC3). HepG2 is a human liver cancer cell line, obtained from anticancer activity of the compound 3j, HepG2 and PC3 were
the liver tissue of a 15-year-old American adolescent boy of seeded in 48-well plates at 1 Â 104 cells per well in DMEM and
European ancestry.22 The human prostate cancer cell line (PC3) RPMI (10% FBS) medium, respectively, and exposed to 3j at
is derived from bone metastasis of a grade IV prostatic adeno- different concentrations for 24 h (Fig. 5). After incubation, the
carcinoma from a 62-year-old male Caucasian, which is used cells were washed twice with PBS and incubated with MTT
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Fig. 4 Fluorescence spectral change of 3j by stepwise addition of NaOH
in MeCN (lmax shifted from 408 nm in pure MeCN to 438 nm in MeCN-
206 mM NaOH).
Fig. 3 Fluorescence quenching of 3j vs. water % in MeCN–H2O mixtures.
solution (450 mg mlÀ1) for 3 h at 37 1C. The resulting formazan
crystals were dissolved in an MTT solubilising buffer and the
absorbances were measured at 570 nm by using a microplate
reader (Biotek, USA). Each point was assessed in triplicate.
Untreated cells were considered as 100% viable. We found
that this compound has significant anticancer activity against
both of the cell lines. The IC-50 values of this compound were
found to be 134 mg mlÀ1 for HepG2 cells and 112 mg mlÀ1 for
PC3 cells.
Cells were incubated with increasing concentrations of the
compound for 24 h and their percentage of survivability was
assessed by the MTT assay. Data represented are means Æ SD of
three identical experiments made in three replicates.
Scheme 4 Solvent–solute H-bonding interactions.
Fig. 5 Cytotoxic effects of the compound 3j on PC3 and HepG2 cells.
Scheme 5 Solute–alkali interaction in the excited state.
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Conclusion
To conclude, an environmentally benign catalyst and solvent-
free tandem approach for the synthesis of highly functionalized
fused quinazolinones with good to excellent yields has been
demonstrated. The designed substrates, 3-(2-formylcycloalkenyl)-
acrylic ester derivatives, are effective coupling partners for anthra-
nilamide compounds to synthesize highly fused quinazolinones
under neat conditions with wide substrate scope, step-atom
economy and minimal work-up procedure. The synthesized
compounds show good fluorescence properties and hence
photophysical properties in different solvents and solvent–solute
interactions in the excited state of the synthesized fluorophore are
also documented. Since our study compound chemosensitized
HepG2 and PC3 cell lines, we will use this compound in an
in vivo mouse model for future research.
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We thank the Department of Science, Technology and Biotech-
nology under the Government of West Bengal (212 (sanc.)/ST/P/
S&T/15G-44/2017) for financial support.
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