Photocaging of Single and Dual (Similar or Different) Carboxylic and Amino Acids by Acetyl Carbazole and its Application as Dual Drug Delivery in Cancer Therapy

Article abstract of DOI:10.1021/acs.joc.6b02152

A new fluorescent photoremovable protecting group (FPRPG) based on acetylcarbazole framework has been explored for the first time release of single and dual (similar or different) substrates from single chromophore. Mechanistic studies of the photorelease process revealed that photorelease of two (similar or different) substrates from acetyl carbazole proceeds via a stepwise pathway. Further, we constructed photoresponsive dual drug delivery system (DDS) to release two different anticancer drugs (caffeic acid and chlorambucil, 1 equiv each). In vitro study reveals that our DDS exhibit excellent properties like biocompatibility, cellular uptake, and photoregulated dual drug release.

Full text of DOI:10.1021/acs.joc.6b02152

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Article
Photocaging of Single and Dual (similar or different)
Carboxylic and Amino Acids by Acetyl Carbazole and
its Application as Dual Drug Delivery in Cancer Therapy
Yarra Venkatesh, Yetirajam Rajesh, Sambath Karthik, Chetan
Anabur C., Mahitosh Mandal, Avijit Jana, and N. D. Pradeep Singh
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b02152 • Publication Date (Web): 18 Oct 2016
Downloaded from http://pubs.acs.org on October 18, 2016
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Photocaging of Single and Dual (similar or different) Carboxylic and
Amino Acids by Acetyl Carbazole and its Application as Dual Drug
Delivery in Cancer Therapy
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,
Yarra Venkatesh,† Y. Rajesh,‡ S. Karthik,† Chetan A C,‡ Mahitosh Mandal,‡ Avijit Jana,*§ ┴ and
N. D. Pradeep Singh*†
‡
†Department of Chemistry, School of Medical Science and Technology, Indian Institute of Technology Kharagpur,
┴
§
721302, West Bengal, India. Biomaterials Group, Division of Natural Products Chemistry, CSIR-Indian Institute of
Chemical Technology, Hyderabad, 500007, India.
ABSTRACT: A new fluorescent photoremovable protecting group (FPRPG) based on acetylcarbazole
framework has been explored for the first time release of single and dual (similar or different) substrates
from single chromophore. Mechanistic studies of the photorelease process revealed that photorelease of
two (similar or different) substrates from acetyl carbazole proceeds via a stepwise pathway. Further, we
constructed photoresponsive dual drug delivery system (DDS) to release of two different anticancer
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drugs (Caffeic acid and Chlorambucil 1 equivalent each). In vitro study reveals that our DDS exhibit
excellent properties like biocompatibility, cellular uptake and photoregulated dual drug release.
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INTRODUCTION:
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In recent times, photoremovable protecting groups (PRPGs) have gained considerable importance
particularly in the area of photoresponsive drug delivery systems (DDSs),1ꢀ3 because of their ability to
offer high spatiotemporal control over the release of biologically active molecules on exposure to light.
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Several PRPGs have been successfully utilized for the construction of photoresponsive DDSs which
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includes oꢀnitrobenzyl,4 coumarinylꢀ4ꢀylmethyl,5 acridinꢀ9ꢀylmethyl,6,
peryleneꢀ3ꢀylmethyl,8,9
peryleneꢀ3,4,9,10ꢀtetrayltetramethyl, pyreneꢀ1ꢀylmethyl10 and quinolinꢀ2ꢀylmethyl11ꢀ13 derivatives.
DDSs constructed so far by the means of the aforementioned PRPGs, can deliver only one active
molecule at a given time. Recently, dual DDSs have become a promising strategy particularly in cancer
treatment.14 Hence there is a real need to develop single chromophoric photoresponsive dual DDSs
which will release two different drugs simultaneously on exposure to light. On account of this issue here
we designed a fluorescent photoremovable protecting group (FPRPG) based on carbazole chromophore
with two arms so that two different active molecules can be photocaged and followed by exposure to
light will release them simultaneously.
Carbazoles are gaining considerable importance among nitrogen containing heterocyclic compounds,
mainly because of their interesting properties like (i) wide band gap and high luminescence efficiency15
(ii) exhibit diverse biological activities16 (iii) flexible functionalization on the parent skeleton etc. The
above said unique properties of carbazoles prompted us to design carbazole derived FPRPGs for the
photocaging and subsequent release of either one or two equivalent of caged substrate.
Herein, we demonstrated for the first time Acetyl carbazole (ACꢀCBZ) as a FPRPG for the release of
single and dual (similar or different) carboxylic acids including amino acids on exposure to UV light (λ
≥ 365 nm). Further, we synthesized a dual drug delivery system using ACꢀCBZ and demonstrated its
ability to perform as a fluorescent imaging agent and phototrigger for delivery of caffeic acid (CA) and
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chlorambucil (CBL) simultaneously. Primarily CA is reported for possessing antitumor activity and antiꢀ
metastatic activity.17 Secondly CBL, an alkylating agent is mainly used in chronic lymphocytic
leukemia.18 By employing a natural compound like CA in the system, the anticancer activity of CBL
gets potentiated in comparison to CBL individually.
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RESULTS AND DISCUSSION:
Single and dual arm carbazole FPRPGs (2 & 6) and their caged esters were synthesized following a
sequence of chemical reactions as shown in Scheme 1. Firstly, Single arm FPRPG 2 was readily
prepared from the commercially available 9Hꢀcarbazole (1) by reacting with ethyl bromide followed by
FriedelꢀCrafts (FC) acylation with one equiv of bromoacetyl bromide. The corresponding caged esters
4(a-e) of FPRPG 2 were synthesized by carrying out esterification reaction with corresponding
carboxylic acids and amino acids 3(a-e) in presence of K2CO3. Next, the dual arm FPRPG 6 was
prepared by FC acylation of 5 with two equiv of bromoacetyl bromide. Now, the corresponding dual
arm caged esters 8(a-c) of similar acids were obtained by treating 6 with two equiv of carboxylic acids
and amino acids 7(a-c) respectively.
Scheme 1. Synthesis of single, dual (similar or different) arm caged esters of Acetyl Carbazole
O
O
R1
1. EtBr,TBAB
Toluene, 60 oC, 12 h
Br
O
R1CO2H (3a-e)
O
2. AlCl3
O
R1 = p-CH3OC6H4(3a)
K2CO3
N
H
1
N
N
= C6H5(3b)
DMF, 30 min
2
= o-CH3OCH2C6H5(3c)
= p- FC6H4(3d)
Br
Br
4a-e
Dry DCM, 0 oC,4 h
= CH2CH2CH2(NHBoc)(3e)
R2
R2
O
O
O
O
Br
Br
O
O
O
O
R2CO2H (7a-c)
AlCl3
O
N
K2CO3
Br
R2 = p-CH2=CHC6H4(7a)
= p-IC6H4(7b)
N
N
Br
DMF, 1 h
Dry DCM, 0 oC, 16 h
8a-c
6
5
= CH2(NHBoc)(7c)
R4
R3
O
R3
O
O
R3
O
O
Br
O
O
O
O
O
O
O
O
AlCl3
R4CO2H (10)
O
N
N
N
K2CO3
R4 = p-CH3C6H4(10)
Br
Br
DMF, 30 min, rt
9
Dry DCM, 1 hr, 0 o
C
11
4a
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Finally, the dual arm caged ester 11 with two different caged acids (pꢀToluic acid and 3a respectively)
was synthesized by the means of second FC acylation on 4a and subsequent esterification reaction with
pꢀToluic acid as shown in Scheme 1. All the synthesized caged esters were characterized by 1H, 13C and
mass spectral analysis (See Fig S1-S11 in SI).
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UV absorption and emission spectra of 1×10–5 M solution of caged esters (4a-e, 8a-c and 11) in
absolute ethanol were recorded. Figure1a & b shows the normalized absorption and emission spectra of
4c and 11 respectively in absolute ethanol. The absorption spectrum of 4c and 11 shows intense peak
centered at 328 nm and 338 nm respectively, while in the emission spectrum the emission maximum of
4c and 11 were centered at about 488 nm and 456 nm respectively. The absorption, emission maxima,
Stoke’s shifts and fluorescence quantum yield of all the caged esters are summarized in Table 1. The
fluorescence quantum yields (Φf) of 4a-e and 8a-c, 11 in absolute ethanol (EtOH) at room temperature
were in the range of 0.091<Φf<0.097 and 0.27<Φf<0.28 respectively (Table 1). Fluorescence quantum
yields were calculated using 9, 10ꢀDiphenylanthracene as the standard (Φf = 0.95 in ethanol).
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Figure 1. UV absorption and emission spectra of (a) single arm caged ester 4c (b) dual arm caged ester
11.
Considering our main interest to study the application of acetyl Carbazole as a FPRPG, we irradiated
degassed solution of caged esters 4a–e, 8a-c and 11 (1.0×10–4 M) individually in acetonitrile/H2O
(ACN/H2O) (7:3 v/v) using 125 W medium pressure Hg lamp as the UV light source (λ ≥ 365 nm) and
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1M CuSO4 solution as the UV cut–off filter. Irradiation of single arm caged esters 4a-e in ACN/H2O
(7:3 v/v) for 60 min results in release of the corresponding carboxylic and amino acids 3a-e in high
chemical (93–97%) and quantum (0.100–0.104) yields as shown in Table 1.
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Table 1. Synthetic yield, photophysical and photochemical data for caged esters (4a–e, 8a-c & 11)
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b
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aBased on isolated yield, Maximum absorption wavelength. Maximum emission wavelength.
dDifference between maximum absorption wavelength and maximum emission wavelength.
eFluorescence quantum yield (error limit within ± 5%). % of the acid released as determined by H
f
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NMR, gPhotochemical quantum yield for the acid release (error limit within ± 5%).
As a representative example, we have shown the course of the photorelease of 4c at regular intervals of
irradiation time by reverse phase (RP) HPLC (Figure 2). The HPLC chart shows gradual depletion of
the peak at tR 5.76 min with an increase in irradiation time, indicating the photodecomposition of 4c. On
the other hand, we also noted a gradual increase of two new major peaks at tR 4.42 min and tR 2.64 min,
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corresponding to the photoproducts 3ꢀ(hydroxyacetyl) 9ꢀethyl 9H carbazole and 2ꢀmethoxyphenylacetic
acid (3c), respectively. The corresponding photoproducts were confirmed by injecting authentic sample
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and also by isolation followed by H NMR spectroscopy (See Fig S12 in SI) which depicts clean
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photocleavage of the ester linkage.
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Figure 2. HPLC profile for the photolysis of the caged ester 4c (1 x 10ꢀ4 M) in ACN/H2O (70:30 v/v) at
regular interval of time (0ꢀ60 min, time interval = 20 min).
To understand whether the photorelease proceeds through a triplet or singlet excited state, the Sternꢀ
Volmer quenching experiment on the carbazole caged ester 4c (see Fig S15 in SI) was performed by
using triplet quencher potassium sorbate (PS). Photolysis of 1×10ꢀ4 M solution of 4c was irradiated
without addition and with addition of different (0.5×10ꢀ4, and 1×10ꢀ4 M respectively) concentration of a
triplet quencher, potassium sorbate (PS) and the course of photolysis was monitored by reverse phase
HPLC and the normalized HPLC peak area was plotted against irradiation time (min). From the Fig S15
in SI, it can be seen that on addition of increasing amount of PS, rate of photorelease decreases
drastically, indicating photocleavage of 4c proceeds via the triplet excited state.
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Scheme 2. Possible photorelease mechanism
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Based on the SternꢀVolmer quenching experiment, solvent effect studies on photorelease along with the
literature12 precedence we suggested a possible mechanism for the photolysis of 4a–e, 8a-c and 11 as
shown in Scheme 2. Irradiation of 4c in aqueous ACN leads to a singlet excited state, which then
undergoes intersystem crossing to the triplet state. Cleavage of the ester CꢀO linkage in carbazole caged
esters proceeds from the triplet excited state either by heterolytic or homolytic fashion followed by
single electron transfer, to form an ionꢀpair intermediate. Trapping of the ionꢀpair intermediate by polar
solvent yields 3ꢀ(hydroxyacetyl) 9ꢀethyl 9H carbazole along with the free carboxylic acid “2ꢀ
methoxyphenylacetic acid”.
Formation of the 1ꢀ(9ꢀethylꢀ9Hꢀcarbazolꢀ3ꢀyl) ethanoyl carbocation intermediate was supported by the
means of trapping of the intermediate by performing photolysis of 4c in MeOH system for 60 min.
Formation of the photoproduct 3ꢀ(methoxyacetyl) 9ꢀethyl 9H carbazole (See Fig S14 in SI) confirms the
trapping of 1ꢀ(9ꢀethylꢀ9Hꢀcarbazolꢀ3ꢀyl) ethanoyl carbocation by the nucleophilic attack of methanol.
In case of dual arm caged esters 8a-c it was observed that photoirradiation results in release of two
equivalent of caged carboxylic acids 7a-c simultaneously (Scheme 3) in high chemical (92–95%) and
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quantum (0.099–0.102) yields (Table 1). The photoproducts were isolated and analyzed by spectroscopy
and in every case we found the released carboxylic and amino acids were the only significant
photoproduct in addition to the FPRPGs (See Fig S13 in SI). The photochemical quantum yield (Φp)
was calculated using potassium ferrioxalate as an actinometer8 (see pages 23, 24 in the SI).
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Scheme 3. Stepwise photorelease of dual arm caged esters 8a-c
After successful demonstration of Acetyl Carbazole as a FPRPG for two similar carboxylic and amino
acids. Further, we intended to explore the same FPRPG for the release of two different carboxylic acids
simultaneously. We irradiated dual arm caged ester 11 in ACN/H2O (7:3 v/v) for 60 min and recorded 1H
NMR (see Fig S16 in SI) and we found that it releases carboxylic acids 3a in 94% (Φp=0.05) and 10 in
92% (Φp=0.049).
A stepwise photocleavage of ester linkage for the release of two different carboxylic acids from 11 was
proposed. Photoirradiation of 11 results in release of two different carboxylic acids 3a and 10 along with
the production of the photoproduct 3, 6ꢀbis (hydroxyacetyl) 9ꢀethyl 9H carbazole through the two
probable intermediates as shown in Scheme 4. The above proposed mechanism was further validating
by analyzing the photolysate of 11 by the means of high resolution mass spectrometry (HRMS). After
30 min of photoirradiation of the caged ester 11, the reaction mixture was subjected to HRMS analysis,
and it was found that all the possible intermediates (see Scheme S1 in SI) for the stepwise mechanism
were present in the reaction mixture along with released carboxylic acids (see Fig S17 in SI).
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Scheme 4. Stepwise photorelease of dual arm caged ester 11
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After successful demonstration of bisꢀacetyl Carbazole as a FPRPG for the simultaneous release two
different carboxylic acids, we were interested to explore its ability as a phototrigger for the construction
of a DDS with the potency of simultaneous delivery of two different antiꢀcancer drugs. For this purpose,
we synthesized singly protected CBZꢀCA, CBZꢀCBL, and dual CBZꢀCAꢀCBL conjugate 14 by caging
CA on one arm and CBL on another arm of the FPRPG ACꢀCBZ as depicted in Scheme 5. The
conjugates were characterized by 1H, 13C and mass spectral analysis (See Fig S18-S20 in SI).
Scheme 5. Synthesis of photoresponsive CBZ-CA, CBZ-CBL and CBZ-CA-CBL conjugates
Photorelease of the corresponding drug molecule from the dual caged CBZꢀCAꢀCBL conjugate was
performed by photoirradiation of CBZꢀCAꢀCBL conjugate (14) in ACN/H2O (7:3 v/v). After photolysis
the aliquot was evaporated under vacuum and the photolysate was redissolved in CDCl3 with mesitylene
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as the internal standard and the H NMR was recorded (see Fig S21 in SI). The % of CA (91% and
Φp=0.046) and CBL (94% and Φp=0.051) released was calculated by 1H NMR spectroscopy.
To investigate the cellular uptake property of the designed dual DDS CBZꢀCAꢀCBL conjugate (14), the
cell imaging studies were performed by treating the glial cancer cells (U87MG) with 10 µM of DDS 14.
Confocal microscopy study confirms the cellular internalization of DDS 14 into U87MG cells within 3
h of treatment (Green coloration, Figure. 3ib and ic).
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Figure 3. Confocal fluorescence and brightfield images of U87MG cells after 3 h of incubation with
DDS 14 exhibited green fluorescence indicating successful internalization (ib and ic) (Scale bar = 20
ꢁm).
The in vitro cytotoxicity assay of CBZꢀCAꢀCBL conjugate (14) in normal (HaCaT) cells reveals 80%
cell viability before photolysis and 40% cell viability after photolysis at higher concentration (80 µM) of
DDS 14 (See Figure 4). Henceforth, it could be said that our DDS 14 is biocompatible in nature.
Figure 4. Cell viability assay of DDS 14 in HaCaT cells with and without UV. Values are presented as
mean ± SD.
In order to assess the anticancer activity, MTT assay was performed for CBZꢀCA, CBZꢀCBL, and CBZꢀ
CAꢀCBL in the cancer cells (U87MG). It was observed that before photolysis cell viability remains
more than 70% at highest concentration (25 µM) of CBZꢀCA, CBZꢀCBL, and CBZꢀCAꢀCBL (Figure
5a). After photolysis, CBZꢀCA exhibited above 75% viability (IC50 at 15 µM) and CBZꢀCBL 60%
viability (IC50 at 15 µM) individually. But our CBZꢀCAꢀCBL expressed appreciably lower cell viability
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of 45% (IC50 at 9 µM) of CBZꢀCAꢀCBL (Figure 5b). Thus, the efficient anticancer activity of the CBZꢀ
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CAꢀCBL could be attributed to dual effect of released CA and CBL from the CBZꢀCAꢀCBL.
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Figure 5. (a−b) Cell viability assay of CBZꢀCA, CBZꢀCBL, and CBZꢀCAꢀCBL in U87MG cell line: (a)
before photolysis, (b) after photolysis. Values are presented as mean ± SD.
CONCLUSION:
We have developed single and dual arm fluorescent PRPGs based on Acetyl carbazole for the
photocontrolled release of carboxylic and amino acids. Acetyl carbazole showed unique ability to
release two (similar or different) carboxylic acids simultaneously in high chemical and quantum yield
on exposure to UV light. Further, the photoresponsive dual CBZꢀCAꢀCBL conjugate has been explored
for the in vitro cellular imaging and showed good biocompatibility as well as precise drug release of
both CBL and CA, simultaneously and exhibited enhanced anticancer activity in comparison to singly
protected CBZꢀCA, CBZꢀCBL conjugates. In future, using our newly developed FPRPG we will try to
cage two different functional groups like carboxylic acids and alcohols which will open up a new area in
the design of photoresponsive DDSs.
EXPERIMENTAL SECTION:
General Information: All commercially available anhydrous solvents dimethylformamide (DMF),
dichloromethane (DCM), petroleum ether (PE) and ethyl acetate (EA) and other chemicals were used
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without further purification. Acetonitrile and dichloromethane were distilled from CaH2 before use.
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NMR spectra were recorded on a 600 and 400 MHz instrument. H NMR chemical shifts were
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referenced to the tetramethylsilane signal (0 ppm), C NMR chemical shifts were referenced to the
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solvent resonance (77.23 ppm, CDCl3). Chemical shifts (δ) are reported in ppm, and spin−spin coupling
constants (J) are given in Hz. The following abbreviations were used to explain multiplicities: s =
singlet, d = doublet, t = triplet, q = quadruplet, m = multiplet. UV/vis absorption spectra were recorded
on UV/vis spectrophotometer and fluorescence spectra were recorded on fluorescence
spectrophotometer. Highꢀresolution mass spectra (HRMS) were recorded on ESIꢀTOF (electrospray
ionizationꢀtimeꢀofꢀflight). Photolysis of all the ester conjugates was carried out using a 125 W medium
pressure mercury lamp. Chromatographic purification was done with 60–120 mesh silica gel. For
reaction monitoring, precoated silica gel 60 F254 TLC sheets were used.
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9-ethyl-9H-carbazole (5): According to a previously reported procedure,19 a mixture of carbazole (0.21
g, 1.25 mmol), bromoethane (0.54 g, 5.02 mmol), NaOH (aq., 12.5 mol Lꢀ1, 5 mL, 62.5 mmol) and a
catalytic amount of tetrabutyl ammonium bromide (0.05 g, 0.14 mmol) were charged in a flask. The
flask was heated at 70 ºC continuously for 12 h. After the completion of the reaction monitored by thinꢀ
layer chromatography, the reaction mixture was cooled to room temperature, and extracted with
dichloromethane. The organic layer was washed with water and dried over anhydrous sodium sulfate
(Na2SO4). The solvent was removed under reduced pressure and the crude product was
chromatographed on a silica gel column with 20% EtOAc in pet ether as an eluent. White solid (0.20 g,
83%). mp: 68–69 ºC (Lit.20 mp 67–68 ºC). 1H NMR (400 MHz, CDCl3): δ 8.15 (d, J = 8.0 Hz, 2H), 7.52
(t, J = 15.2 Hz, 2H), 7.44 (d, J = 8 Hz, 2H), 7.28 (t, J = 14.8 Hz, 2H), 4.43–4.37 (m, 2H), 1.47 (t, J =
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14.4 Hz, 3H). C NMR (100 MHz, CDCl3): δ 140.0, 125.6, 122.9, 120.4, 118.8, 108.4, 37.5, 13.8.
MALDIꢀTOF, m/z calcd for C14H13N, 196.0; found, 196.7. Physical and NMR spectral data are in
accordance with those previously reported.19
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2-bromo-1-(9-ethyl-9H-carbazol-3-yl)ethanone (2): 9ꢀethyl carbazole ( 0.300 g , 1.53 mmol ) was
dissolved in DCM (20 mL), followed by aluminium chloride (AlCl3) (0.205 g, 1.53 mmol) was added
and the solution of bromoacetyl bromide (0.310 g, 1.53 mmol) in DCM (10 mL) was added over 30
minutes while stirring at 0 °C. After completion of addition, stirring was done at 25 °C for additional 4
h. The reaction mixture was poured in 800 g of ice water and extracted with DCM (100 mL). The
organic layer was dried over magnesium sulfate (MgSO4), the solvent was evaporated by rotary
evaporator, the residue was purified by column chromatography (eluting agent: chloroform),
recrystallized from ethyl acetateꢀhexane to obtain the product 2. Light green crystals (0.349 g, 72%).
mp: 99ꢀ100 ºC. 1H NMR (600 MHz, Chloroformꢀd) δ 8.74 (s, 1H), 8.23 – 8.02 (m, 2H), 7.53 (q, J = 6.2,
4.6 Hz, 1H), 7.44 (dd, J = 8.9, 3.6 Hz, 1H), 7.41 – 7.36 (m, 1H), 7.32 (t, J = 7.4 Hz, 1H), 4.57 (s, 2H),
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4.36 (q, J = 7.1 Hz, 2H), 1.45 (t, J = 7.2 Hz, 3H). C NMR (151 MHz, CDCl3) δ 190.9, 143.2, 140.9,
127.1, 126.9, 125.4, 123.3, 123.1, 122.8, 120.9, 120.5, 109.3, 108.5, 38.1, 31.4, 14.0. HRMS (ESI+)
calcd for C16H14BrNO [M + Na]+, 338.0156; found: 338.0160.
1, 1'-(9-ethyl-9H-carbazole-3, 6-diyl) bis (2-bromoethanone) (6): A sample of 9ꢀethyl carbazole (0.3
g, 1.53 mmol) was taken in 10 mL of dry DCM. To this solution, AlCl3 (0.43 g, 3.22 mmol) was added
and the suspension was stirred for 5 min at room temperature. The reaction mixture was cooled to 0 °C,
and bromoacetyl bromide (0.28 mL, 3.22 mmol), in 10 mL of dry DCM, was added drop wise through
dropping funnel over a period of 1 h. After addition, the reaction mixture was stirred at room
temperature for 16 h followed by the mixture was poured on crushed ice. After melting of ice, the
mixture was extracted with DCM (2 x 25 mL), washed with water (20 mL), sat. NaHCO3 (20 mL) then
the organic layer was dried over anhydrous MgSO4. The solvent was removed in vacuo and the crude
was purified by column chromatography to obtain the product. Yellowish green crystal (0.604 g, 90%).
mp: 184ꢀ186 ºC (lit.21 mp 186ꢀ190 ºC). 1H NMR (600 MHz, ) δ 8.81 (s, 2H), 8.21 (d, J = 8.8 Hz, 2H),
7.50 (d, J = 8.6 Hz, 2H), 4.59 (s, 4H), 4.43 (q, J = 7.4 Hz, 2H), 1.50 (t, J = 7.2 Hz, 3H). 13C NMR (151
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MHz, CDCl3) δ 190.9, 144.1, 128.1, 126.7, 123.3, 123.0, 109.4, 38.6, 31.1, 14.1. HRMS (ESI+) calcd
for C18H15Br2NO2 [M + Na]+, 457.9367; found: 457.9368.
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General procedure for the synthesis of the ester conjugates (4a-e):
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2ꢀbromoꢀ1ꢀ(9ꢀethylꢀ9Hꢀcarbazolꢀ3ꢀyl)ethanone(1 equiv) was dissolved in dry N, N Dimethylformamide
(DMF) (2 mL), potassium carbonate (1 equiv), and the corresponding carboxylic and amino acids 3a-e
(1 equiv) were added. The reaction mixture was stirred at room temperature for 30 min. After
completion of the reaction it was extracted with ethylacetate and washed with saturated NaCl solution
and dried over Na2SO4. The solvent was removed by rotary evaporation under reduced pressure and the
crude residue was purified by column chromatography using ethylacetate (EtOAC) in pet ether.
2-(9-ethyl-9H-carbazol-3-yl)-2-oxoethyl benzoate (4a): Treatment of 2 (0.100 g, 0.31 mmol) with
Benzoic acid (0.038 g, 0.31 mmol) in the presence of potassium carbonate (K2CO3) (0.052 g, 0.37
mmol) in dry N,NꢀDimethylformamide (DMF) at room temperature for a period of 30 min. The crude
conjugate was purified by column chromatography using 20% EtOAc in pet ether to give the product.
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White solid (0.099 g, 88%). mp: 142ꢀ143 ºC. H NMR (600 MHz, Chloroformꢀd) δ 8.79 (s, 1H), 8.21
(d, J = 7.5 Hz, 2H), 8.17 (dd, J = 19.8, 8.2 Hz, 2H), 7.65 – 7.60 (m, 1H), 7.56 (t, J = 7.6 Hz, 1H), 7.52 –
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7.48 (m, 3H), 7.35 (t, J = 7.4 Hz, 1H), 5.76 (s, 2H), 4.43 (m, 2H), 1.50 (t, J = 7.3 Hz, 3H). C NMR
(101 MHz, CDCl3) δ 191.5, 166.5, 143.3, 140.9, 133.5, 130.2, 129.9, 128.6, 126.9, 126.0, 123.3, 123.1,
121.6, 121.0, 120.4, 109.3, 108.7, 66.7, 38.1, 14.0. HRMS (ESI+) calcd for C23H19NO3 [M + H]+,
358.1443; found: 358.1452.
2-(9-ethyl-9H-carbazol-3-yl)-2-oxoethyl 4-methoxybenzoate (4b): Treatment of 2 (0.100 g, 0.31
mmol) with pꢀAnisic acid (0.048 g, 0.31 mmol) in the presence of K2CO3 (0.052 g, 0.37 mmol) in dry
DMF at room temperature for a period of 30 min. The crude conjugate was purified by column
chromatography using 20% EtOAc in pet ether to give the product. Pale yellow solid (0.112 g, 92%).
mp: 150ꢀ151 ºC. 1H NMR (600 MHz, Chloroformꢀd) δ 8.76 (s, 1H), 8.21 – 8.08 (m, 4H), 7.54 (t, J = 7.7
Hz, 1H), 7.45 (t, J = 8.7 Hz, 2H), 7.32 (t, J = 7.5 Hz, 1H), 6.96 (d, J = 8.5 Hz, 2H), 5.70 (s, 2H), 4.40 (q,
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J = 7.3 Hz, 2H), 3.88 (s, 3H), 1.47 (t, J = 7.3 Hz, 3H). C NMR (151 MHz, CDCl3) δ 191.8, 166.2,
163.8, 143.2, 140.9, 132.3, 126.9, 126.1, 126.0, 123.3, 123.1, 122.3, 121.6, 121.0, 120.4, 113.9, 109.3,
108.6, 66.5, 55.7, 38.1, 14.0. HRMS (ESI+) calcd for C24H21NO4 [M + H]+, 388.1549; found: 388.1544.
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2-(9-ethyl-9H-carbazol-3-yl)-2-oxoethyl 2-(2-methoxyphenyl)acetate (4c): Treatment of 2 (0.100 g,
0.31 mmol) with oꢀMethoxyphenylacetic acid ( 0.052 g, 0.31 mmol) in the presence of K2CO3 (0.052 g,
0.37 mmol) in dry DMF at room temperature for a period of 30 min. The crude conjugate was purified
by column chromatography using 20% EtOAc in pet ether to give the product. White solid (0.120 g,
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95%). mp: 116ꢀ117 ºC. H NMR (600 MHz, Chloroformꢀd) δ 8.63 (s, 1H), 8.08 (d, J = 7.8 Hz, 1H),
8.01 (dd, J = 8.5, 1.9 Hz, 1H), 7.48 (t, J = 7.8 Hz, 1H), 7.40 (d, J = 8.3 Hz, 1H), 7.36 (d, J = 8.7 Hz,
1H), 7.28 – 7.24 (m, 2H), 7.23 – 7.20 (m, 1H), 6.89 (t, J = 7.4 Hz, 1H), 6.83 (d, J = 8.3 Hz, 1H), 5.45 (s,
2H), 4.34 (q, J = 7.4 Hz, 2H), 3.82 (s, 2H), 3.79 (s, 3H), 1.40 (t, J = 7.3 Hz, 3H). 13C NMR (151 MHz,
CDCl3) δ 191.7, 171.7, 157.8, 143.2, 140.8, 131.3, 128.8, 126.9, 126.0, 125.9, 123.3, 123.0, 123.0,
121.6, 121.0, 120.8, 120.4, 110.7, 109.3, 108.6, 66.5, 55.7, 38.1, 35.7, 14.0. HRMS (ESI+) calcd for
C25H23NO4 [M + H]+, 402.1705; found: 402.1710.
2-(9-ethyl-9H-carbazol-3-yl)-2-oxoethyl 4-fluorobenzoate (4d): Treatment of 2 (0.100 g, 0.31 mmol)
with 4ꢀFluorobenzoic acid (0.048 g, 0.31 mmol) in the presence of K2CO3 (0.052 g, 0.37 mmol) in dry
DMF at room temperature for a period of 30 min. The crude conjugate was purified by column
chromatography using 20% EtOAc in pet ether to give the product. White solid (0.105 g, 89%). mp:
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149ꢀ150 ºC. H NMR (600 MHz, Chloroformꢀd) δ 8.75 (s, 1H), 8.21 (dd, J = 8.9, 5.4 Hz, 2H), 8.17 –
8.10 (m, 2H), 7.54 (t, J = 7.1 Hz, 1H), 7.49 – 7.43 (m, 2H), 7.33 (t, J = 7.4 Hz, 1H), 7.15 (t, J = 8.7 Hz,
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2H), 5.73 (s, 2H), 4.41 (q, J = 7.3 Hz, 2H), 1.47 (t, J = 7.3 Hz, 3H). C NMR (151 MHz, CDCl3) δ
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123.3, 123.1, 121.6, 121.0, 120.5, 115.6 (d, JCꢀF = 21.9 Hz), 109.3, 108.7, 66.8, 38.1, 14.0. HRMS
(ESI+) calcd for C23H18FNO3 [M + H]+, 376.1349; found: 376.1374.
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2-(9-ethyl-9H-carbazol-3-yl)-2-oxoethyl 4-((tert-butoxycarbonyl)amino)butanoate (4e): Treatment
of 2 (0.100 g, 0.31 mmol) with 4ꢀ((tertꢀbutoxycarbonyl) amino) butanoic acid (0.048 g, 0.31 mmol) in
the presence of K2CO3 (0.052 g, 0.37 mmol) in dry DMF at room temperature for a period of 30 min.
The crude conjugate was purified by column chromatography using 20% EtOAc in pet ether to give the
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product. White solid (0.110 g, 80%). mp: 128ꢀ129 ºC. H NMR (400 MHz, Chloroformꢀd) δ 8.70 (s,
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1H), 8.15 (d, J = 7.7 Hz, 1H), 8.08 (s, 1H), 7.54 (t, J = 7.6 Hz, 1H), 7.49 – 7.41 (m, 2H), 7.32 (t, J = 7.4
Hz, 1H), 5.52 (s, 2H), 4.82 (s, 1H), 4.37 (s, 2H), 3.26 (t, J = 6.6 Hz, 2H), 2.59 (t, J = 7.2 Hz, 2H), 1.95
(m, J = 7.0 Hz, 2H), 1.48 (t, J = 7.2 Hz, 3H), 1.45 (s, 9H). 13C NMR (151 MHz, CDCl3) δ 191.6, 173.1,
156.3, 143.3, 140.9, 126.9, 125.9, 125.7, 123.3, 123.1, 121.5, 121.0, 120.5, 109.3, 108.6, 66.2, 38.1,
31.5, 28.6, 25.5, 14.0. HRMS (ESI+) calcd for C25H30N2O5 [M + H]+, 439.2233; found: 439.2224.
General procedure for the synthesis of the ester conjugates (8a-c):
1, 1'ꢀ(9ꢀethylꢀ9Hꢀcarbazoleꢀ3, 6ꢀdiyl) bis (2ꢀbromoethanone) (1 equiv) was dissolved in dry N, N
Dimethylformamide (DMF) (2 mL), potassium carbonate (2 equiv), and the corresponding carboxylic
and amino acids 7a-c (2 equiv) were added. The reaction mixture was stirred at room temperature for 1
h. After completion of the reaction it was extracted with ethylacetate and washed with saturated NaCl
solution and dried over Na2SO4. The solvent was removed by rotary evaporation under reduced pressure
and the crude residue was purified by column chromatography using ethylacetate (EtOAC) in pet ether.
(9-ethyl-9H-carbazole-3,6-diyl)bis(2-oxoethane-2,1-diyl) bis(4-vinylbenzoate) (8a): Treatment of 6
(0.100 g, 0.22 mmol) with 4ꢀVinylbenzoic acid (0.067 g, 0.44 mmol) in the presence of K2CO3 (0.052 g,
0.44 mmol) in dry DMF at room temperature for a period of 1 h. The crude conjugate was purified by
column chromatography using 40% EtOAc in pet ether to give the product. Pale yellow solid (0.108 g,
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83%). mp: 178ꢀ179 ºC. H NMR (600 MHz, ) δ 8.73 (s, 2H), 8.16 (d, J = 8.5 Hz, 2H), 8.12 (d, J = 8.0
Hz, 4H), 7.47 (t, J = 9.0 Hz, 6H), 6.76 (dd, J = 17.6, 10.9 Hz, 2H), 5.88 (d, J = 17.6 Hz, 2H), 5.72 (s,
4H), 5.39 (d, J = 10.9 Hz, 2H), 4.38 (q, J = 7.2 Hz, 2H), 1.47 (t, J = 7.2 Hz, 3H). 13C NMR (151 MHz,
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CDCl3) δ 191.5, 166.1, 143.9, 142.5, 136.2, 130.5, 128.8, 127.0, 126.9, 126.4, 123.1, 121.7, 116.9,
109.4, 66.7, 38.4, 29.9, 14.1. HRMS (ESI+) calcd for C36H29NO6 [M + H]+, 572.2073; found: 572.2073.
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(9-ethyl-9H-carbazole-3,6-diyl)bis(2-oxoethane-2,1-diyl) bis(4-iodobenzoate) (8b): Treatment of 6
(0.100 g, 0.22 mmol) with 4ꢀIodobenzoic acid (0.113 g, 0.44 mmol) in the presence of K2CO3 (0.052 g,
0.44 mmol) in dry DMF at room temperature for a period of 1 h. The crude conjugate was purified by
column chromatography using 40% EtOAc in pet ether to give the product. Pale yellow solid (0.155 g,
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88%). mp: 183ꢀ184 ºC. H NMR (600 MHz, ) δ 8.74 (s, 2H), 8.16 (d, J = 8.5 Hz, 2H), 7.86 (d, J = 7.9
Hz, 4H), 7.82 (d, J = 8.2 Hz, 4H), 7.49 (d, J = 8.5 Hz, 2H), 5.72 (s, 4H), 4.41 (q, J = 7.2 Hz, 2H), 1.48
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(t, J = 7.2 Hz, 3H). C NMR (151 MHz, CDCl3) δ 191.1, 165.9, 144.0, 138.0, 131.6, 129.2, 126.9,
126.9, 123.2, 121.7, 109.5, 101.5, 66.8, 38.5, 14.1. HRMS (ESI+) calcd for C32H23I2NO6 [M + H]+,
771.9693; found: 771.9679.
(9-ethyl-9H-carbazole-3,6-diyl)bis(2-oxoethane-2,1-diyl)
bis(2-((tert-
butoxycarbonyl)amino)acetate) (8c): Treatment of 6 (0.100 g, 0.22 mmol) with 2ꢀ((tertꢀ
butoxycarbonyl) amino) acetic acid (0.080g, 0.44 mmol) in the presence of K2CO3 (0.052 g, 0.44 mmol)
in dry DMF at room temperature for a period of 1 h. The crude conjugate was purified by column
chromatography using 40% EtOAc in pet ether to give the product. Dark yellow solid (0.108 g, 76%).
mp: 148ꢀ149 ºC. 1H NMR (600 MHz) δ 8.64 (s, 2H), 8.10 (s, 2H), 7.46 (d, J = 8.7 Hz, 2H), 5.57 (s, 4H),
5.19 (s, 2H), 4.39 (q, J = 7.0 Hz, 2H), 4.20 (d, J = 5.3 Hz, 4H), 1.48 (t, 3H)1.48 (s, 18H). 13C NMR (151
MHz, CDCl3) δ 190.9, 170.5, 156.0, 144.0, 126.8, 123.1, 121.6, 109.5, 80.3, 66.8, 42.6, 38.5, 28.6, 14.1.
HRMS (ESI+) calcd for C32H39N3O10 [M + H]+, 626.2714; found: 626.2663.
2-(9-ethyl-6-(2-((4-methoxybenzoyl)oxy)acetyl)-9H-carbazol-3-yl)-2-oxoethyl
4-methylbenzoate
(11): Compound 4a (0.100 g , 0.25 mmol) was dissolved in DCM (20 mL), followed by AlCl3 (0.041 g,
0.25 mmol) was added and the solution of bromoacetyl bromide (0.057 g, 0.25mmol) in DCM (10 mL)
was added over 30 minutes while stirring at 0 °C. After the completion of addition, stirring was done at
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25 °C for 1 h. The reaction mixture was poured in 100 g of ice water and extracted with DCM (100
mL). The organic layer was dried over MgSO4, the solvent was evaporated to give the product 9. White
solid (0.111 g, 85%). and in situ reaction of 9 (0.100 g, 0.19 mmol) with pꢀToluic acid (10) (0.040 g,
0.19 mmol) in the presence of K2CO3 (0.052 g, 0.39 mmol) in dry DMF at room temperature for a
period of 30 min. The crude conjugate was purified by column chromatography using 40% EtOAc in
pet ether to give the product. White solid (0.095 g, 86%). mp: 185ꢀ186 ºC. 1H NMR (600 MHz,
Chloroformꢀd) δ 8.79 (s, 2H), 8.23 – 8.18 (m, 2H), 8.18 – 8.13 (m, 2H), 8.09 (d, J = 7.9 Hz, 2H), 7.52
(d, J = 8.7 Hz, 2H), 7.30 (d, J = 8.0 Hz, 2H), 7.03 – 6.94 (m, 2H), 5.73 (s, 2H), 5.72 (s, 2H), 4.44 (q, J
= 7.3 Hz, 2H), 3.89 (s, 3H), 2.45 (s, 3H), 1.51 (t, J = 7.2 Hz, 3H). 13C NMR (151 MHz, CDCl3) δ 191.6,
191.4, 166.3, 165.9, 163.7, 144.1, 143.7, 132.1, 130.1, 129.2, 126.9, 126.9, 126.8, 126.7, 123.0, 121.9,
121.5, 113.7, 109.2, 66.4, 66.3, 55.5, 38.3, 21.7, 13.9. HRMS (ESI+) calcd for C34H29NO7 [M + H]+,
564.2022; found: 564.2014.
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(E)-2-(9-ethyl-9H-carbazol-3-yl)-2-oxoethyl 3-(3,4-dihydroxyphenyl)acrylate (12): Treatment of 2
(0.100 g, 0.31 mmol) with caffeic acid (0.096 g, 0.31 mmol) in the presence of K2CO3 (0.052 g, 0.37
mmol) in dry DMF at room temperature for a period of 30 min. The crude conjugate was purified by
column chromatography using 20% EtOAc in pet ether to give the product 12. Dark yellow solid (0.105
g, 80%). mp: 157ꢀ158 °C. 1H NMR (600 MHz, DMSOꢀd6) δ 8.92 (s, 1H), 8.32 (d, J = 7.7 Hz, 1H), 8.09
(d, J = 8.4 Hz, 1H), 7.75 (d, J = 8.6 Hz, 1H), 7.70 (d, J = 8.3 Hz, 1H), 7.57 – 7.52 (m, 2H), 7.30 (t, J =
7.5 Hz, 1H), 7.09 (s, 1H), 7.01 (d, J = 7.5 Hz, 1H), 6.72 (d, J = 7.6 Hz, 1H), 6.38 (d, J = 15.8 Hz, 1H),
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5.69 (s, 2H), 4.52 (q, J = 7.2 Hz, 2H), 1.34 (t, J = 7.2 Hz, 3H). C NMR (151 MHz, DMSO) δ 192.4,
166.7, 146.7, 145.0, 142.9, 140.7, 127.1, 126.6, 126.0, 125.8, 123.2, 122.9, 122.4, 122.2, 122.0, 121.4,
120.4, 116.4, 115.1, 113.0, 110.3, 109.7, 66.6, 37.8, 14.2. HRMS (ESI+) calcd for C25H21NO5 [M + H]+,
416.1498; found: 416.1520.
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2-(9-ethyl-9H-carbazol-3-yl)-2-oxoethyl 4-(4-(bis(2-chloroethyl)amino)phenyl)butanoate (13):
Treatment of 2 (0.100 g, 0.31 mmol) with chlorambucil (0.096 g, 0.31 mmol) in the presence of K2CO3
(0.052 g, 0.37 mmol) in dry N, Nꢀdimethylformamide (DMF) at room temperature for a period of 30
min. The crude conjugate was purified by column chromatography using 20% EtOAc in pet ether to
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give the product 12. Light yellow solid (0.150 g, 88%). mp: 150−152 °C. H NMR (600 MHz,
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Chloroformꢀd) δ 8.70 (s, 1H), 8.16 (d, J = 7.7 Hz, 1H), 8.08 (dd, J = 8.8, 1.7 Hz, 1H), 7.62 – 7.44 (m,
2H), 7.42 (d, J = 8.6 Hz, 1H), 7.35 (t, J = 7.3 Hz, 1H), 7.21 – 7.10 (m, 2H), 6.71 – 6.63 (m, 2H), 5.52 (s,
2H), 4.37 (q, J = 7.3 Hz, 2H), 3.72 (t, J = 7.4 Hz, 4H), 3.65 (t, J = 6.7 Hz, 4H), 2.69 (t, J = 7.6 Hz, 2H),
2.58 (t, J = 7.4 Hz, 2H), 2.07 (p, J = 7.5 Hz, 2H), 1.46 (t, J = 7.3 Hz, 3H). 13C NMR (151 MHz, CDCl3)
δ 191.5, 173.2, 144.3, 143.0, 140.6, 130.8, 129.8, 126.7, 125.7, 125.6, 123.1, 122.8, 121.3, 120.8, 120.2,
112.2, 109.1, 108.4, 66.0, 53.6, 40.6, 37.9, 33.9, 33.3, 26.9, 13.8. HRMS (ESI+) calcd for
C30H32Cl2N2O3 [M + Na]+, 561.1688; found: 561.1688.
(E)-2-(6-(2-((3-(3,4-dihydroxyphenyl)acryloyl)oxy)acetyl)-9-ethyl-9H-carbazol-3-yl)-2-oxoethyl 4-
(4-(bis(2-chloroethyl)amino)phenyl)butanoate (14): Compound 12 (0.100 g, 0.18 mmol) was
dissolved in DCM (20 mL), followed by AlCl3 (0.29 g, 0.18 mmol) was added and the solution of
bromoacetyl bromide (0.037 g, 0.18 mmol) was dissolved in dichloromethane 10 mL was added over 30
minutes while stirring at 0 °C. After the completion of reaction, stirring was done at 25 °C for 1 h. The
reaction solution was poured in 400 g of ice water and extracted with dichloromethane 100 mL. The
organic layer was dried over MgSO4, the solvent was evaporated to give the product (0.105 g, 86%) and
in situ reaction of 13 (0.100 g, 0.15 mmol) with caffeic acid (0.027 g, 0.15 mmol) in the presence of
K2CO3 (0.020 g, 0.18 mmol) in dry DMF at room temperature for a period of 30 min afforded the
conjugate 14. The crude conjugate was purified by column chromatography using 40% EtOAc in pet
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ether to give the product. Dark yellow solid (0.089 g, 78%). mp: 180−182 °C. H NMR (600 MHz, ) δ
8.86 (s, 1H), 8.77 (s, 1H), 8.20 (d, J = 8.6 Hz, 1H), 8.13 (d, J = 8.2 Hz, 1H), 7.69 (d, J = 16.0 Hz, 1H),
7.50 (d, J = 8.4 Hz, 2H), 7.19 (s, 1H) 7.15 (d, J = 8.5 Hz, 2H), 6.97 (d, J = 7.6 Hz, 1H), 6.88 (d, J = 8.0
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Hz, 1H), 6.71 (d, J = 7.4 Hz, 2H), 6.40 (d, J = 15.8 Hz, 1H), 5.57 (s, 2H), 5.54 (s, 2H), 4.44 (q, J = 7.2
Hz, 2H), 3.70 (t, J = 7.4 Hz, 4H), 3.63 (t, J = 6.8 Hz, 4H), 2.66 (t, J = 7.5 Hz, 2H), 2.55 (t, J = 7.4 Hz,
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2H), 2.04 (q, J = 7.5 Hz, 2H), 1.49 (t, J = 7.3 Hz, 3H). C NMR (151 MHz, CDCl3) δ 191.6, 191.0,
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173.3, 167.9, 148.5, 146.1, 145.9, 144.02, 144.0, 134.4, 132.4, 130.1, 127.1, 127.0, 126.9, 126.9, 126.3,
123.2, 123.2, 121.7, 115.7, 114.7, 114.3, 112.9, 109.5, 66.7, 66.1, 54.1, 40.5, 38.5, 34.1, 33.5, 27.0,
14.1. HRMS (ESI+) calcd for C41H40Cl2N2O8 [M + H]+, 759.2240; found: 759.2220.
Characterisation of Photoproducts:
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3-(hydroxyacetyl) 9-ethyl 9H carbazole: 1H NMR (400 MHz, Chloroformꢀd) δ 8.65 (s, 1H), 8.13 (d, J
= 7.7 Hz, 1H), 8.03 (d, J = 8.6 Hz, 1H), 7.59 – 7.50 (m, 1H), 7.44 (d, J = 8.2 Hz, 1H), 7.39 (d, J = 8.7
Hz, 1H), 7.32 (t, J = 7.5 Hz, 1H), 4.99 (s, 2H), 4.35 (t, J = 7.2 Hz, 2H), 3.45 (s, 1H), 1.44 (t, J = 7.3 Hz,
3H).13C NMR (101 MHz, CDCl3) δ 197.5, 143.4, 140.8, 126.9, 125.7, 124.7, 123.1, 123.1, 121.4, 120.9,
120.4, 109.3, 108.6, 77.5, 77.2, 76.9, 65.3, 38.0, 14.0. HRMS (ESI+) calcd for C16H15NO2 [M + H]+,
254.1181; found: 254.1169.
3-(methoxyacetyl) 9-ethyl 9H carbazole: 1H NMR (400 MHz, Chloroformꢀd) δ 8.73 (s, 1H), 8.16 (d, J
= 7.7 Hz, 1H), 8.10 (d, J = 8.6 Hz, 1H), 7.52 (t, 1H), 7.44 (d, J = 8.2 Hz, 1H), 7.40 (d, J = 8.7 Hz, 1H),
7.31 (t, J = 7.5 Hz, 1H), 4.85 (s, 2H), 4.38 (t, J = 7.2 Hz, 2H), 3.57 (s, 1H), 1.45 (t, J = 7.3 Hz, 3H).13C
NMR (101 MHz, CDCl3) δ 197.5, 143.4, 140.8, 126.9, 125.7, 124.7, 123.1, 123.1, 121.4, 120.9, 120.4,
109.3, 108.6, 75.6, 59.6, 38.0, 14.0. HRMS (ESI+) calcd for C17H17NO2 [M + H]+, 268.1338; found:
268.1324.
3,6-bis(hydroxyacetyl) 9-ethyl 9H carbazole: 1H NMR (400 MHz, Chloroformꢀd) δ 8.74 (s, 2H), 8.14
(d, J = 8.6 Hz, 2H), 7.52 (d, J = 8.6 Hz, 2H), 5.03 (s, 4H), 4.45 (q, J = 7.2 Hz, 2H), 2.75 (s, 1H), 1.49 (d,
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J = 7.2 Hz, 3H). C NMR (101 MHz, CDCl3) δ 197.6, 144.3, 126.8, 126.2, 123.3, 121.6, 109.5, 65.5,
38.6, 14.0. HRMS (ESI+) calcd for C18H17NO4 [M + H]+, 312.1236; found: 312.1245.
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ASSOCIATED CONTENT
Supporting Information
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Synthesis details, characterization data, and other experimental details.
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AUTHOR INFORMATION
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Corresponding Author
ndpradeep@chem.iitkgp.ernet.in
janaavijit2@gmail.com, avijit@iict.res.in
Notes. The authors declare no competing financial interests.
ACKNOWLEDGMENT
We thank DST (SERB) for financial support. DSTꢀFIST for 600 and 400 MHz NMR. Yarra Venkatesh is
thankful to IIT KGP for the fellowship. Avijit Jana is thankful to Department of Science & Technology
(DST), India for DSTꢀINSPIRE Faculty Research project grant (GAP 0546) at CSIRꢀIICT, Hyderabad.
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