An efficient synthesis and biological evaluation of novel analogues of natural product Cephalandole A: A new class of antimicrobial and antiplatelet agents

Article abstract of DOI:10.1016/j.fitote.2018.06.003

Cephalandole A 2, a small indole alkaloid isolated from the Taiwanese orchid Cephalanceropsis gracilis (Orchidaceae), exhibits anticancer activity. Surprisingly, this natural product has not been evaluated for any other biological activity so far. To discover other novel potential of Cephalandole A 2, an efficient and economic synthetic protocol for novel Cephalandole A analogues 21a-o has been developed, in only 3 steps from using indole, and applied for their biological activity. Biological testing showed that Cephalandole A 2 and its novel analogues 21a-o exhibited potential antimicrobial and antiplatelet activity in preliminary assay. To the best of our knowledge, this is the first report of Cephalandole A 2 and its novel synthetic analogues 21a-o as a new class of antimicrobial and antiplatelet agents. In this study, 2 and other analogues i.e., 21b, 21d, 21i and 21o showed promising antimicrobial activity against the phytopathogenic bacteria and fungi. Cephalandole A 2, 21c, 21f and 21i, also showed potent antiplatelet activity.

Full text of DOI:10.1016/j.fitote.2018.06.003

Fitoterapia129(2018)13–19
Contents lists available at ScienceDirect
Fitoterapia
journal homepage: www.elsevier.com/locate/fitote
An efficient synthesis and biological evaluation of novel analogues of
natural product Cephalandole A: A new class of antimicrobial and
antiplatelet agents
Vashundhra Sharmaa,1, Pradeep K. Jaiswala,1, Krishan Kumara, Mukesh Saranb, Manas Mathurb,
Ajit K. Swamib, Sandeep Chaudharya,⁎
a
Laboratory of Organic & Medicinal Chemistry, Department of Chemistry, Malaviya National Institute of Technology, Jawaharlal Nehru Marg, Jaipur 302017, India
Department of Advance Molecular Microbiology, Seminal Applied Sciences Pvt. Ltd., Jaipur 302015, India
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Cephalandole A
Antimicrobial
Antibacterial
Antifungal
Cephalandole A 2, a small indole alkaloid isolated from the Taiwanese orchid Cephalanceropsis gracilis
(Orchidaceae), exhibits anticancer activity. Surprisingly, this natural product has not been evaluated for any
other biological activity so far. To discover other novel potential of Cephalandole A 2, an efficient and economic
synthetic protocol for novel Cephalandole A analogues 21a-o has been developed, in only 3 steps from using
indole, and applied for their biological activity. Biological testing showed that Cephalandole A 2 and its novel
analogues 21a-o exhibited potential antimicrobial and antiplatelet activity in preliminary assay. To the best of
our knowledge, this is the first report of Cephalandole A 2 and its novel synthetic analogues 21a-o as a new class
of antimicrobial and antiplatelet agents. In this study, 2 and other analogues i.e., 21b, 21d, 21i and 21o showed
promising antimicrobial activity against the phytopathogenic bacteria and fungi. Cephalandole A 2, 21c, 21f and
21i, also showed potent antiplatelet activity.
Antiplatelet activity
Structure–activity relationship
1. Introduction
leukotriene B4, tyrosinase inhibitors, immunomodulator, etc. [4a–g].
Several reports are available in the literature [5a–e], including our
Natural products have been extensively proven to be the rich source
of bioactive lead compounds and in medicinal chemistry for a long
time, according to their potential biological activity, good chemically
structural diversity, and compatibility with the environment.
Cephalandole A, a small hybrid molecule consisting of benzo[1,4]ox-
azine and indole scaffolds, is a naturally occurring molecule which was
isolated from the Taiwanese orchid Cephalanceropsis gracilis
(Orchidaceae) in 2006 [1]. Its initial proposed structure 1 was cor-
rected to 2 in 2008 [2] [Fig. 1].
So far, only anticancer activity has been reported in this molecule.
Its crude extract exhibited excellent activity against lung (NCI-H460;
IC50 = 7.8 μM), breast (MCF-7; IC50 = 7.57 μM) and CNS (SF-268;
IC50 = 12.2 μM) carcinoma cell lines [2, 3].
work [5f], which reveals that benzo[1,4]oxazines 3–7 exhibited ex-
cellent antimicrobial activity. In addition, several similar bioactive class
of compounds are also reported in the literature such as substituted
benz[1,4]oxazine-3-ones
8 [6a–b], functionalized quinolinones 9
[6c–d], coumarin analogues 10 [6e] and 2-morpholino substituted
benzoxazines 11 [6f] etc., which exhibits promising platelet aggrega-
tion inhibitory activity. Also, functionalized indoles 12–16 possess
promising antimicrobial [7] as well as platelet aggregation inhibitory
activities [8] (Fig. 2). Since, the constituting scaffolds of Cephalandole
A 2 possesses promising antimicrobial as well as antiplatelet activities;
it can be anticipated that this molecule will show antimicrobial and
platelet aggregation inhibitory activities. Moreover, since its discovery,
no other biological activity in 2 has been reported yet.
It has been reported that molecules, having either benzo[1,4]ox-
azines or indole moieties as a part or as a whole of molecular archi-
tecture, are endowed with a wide range of biological activities, such as
antibacterial, antiplatelet, antimalarial, anticancer, antiviral, anti-
oxidant, antiulcer, antileishmanial, antitubercular, inhibitor of
In our endeavour to search for novel bioactive heterocycles as a new
antimicrobial as well as antiplatelet agents, herein, we report the ul-
trasound-assisted synthesis, antimicrobial as well as arachidonic acid
(AA)-induced platelet aggregation inhibitory activities of a series of
novel functionalized Cephalandole A analogues 21a-o. To the best of
⁎
Corresponding author.
E-mail address: schaudhary.chy@mnit.ac.in (S. Chaudhary).
Both authors have equal contribution.
1
https://doi.org/10.1016/j.fitote.2018.06.003
Received 24 April 2018; Received in revised form 29 May 2018; Accepted 3 June 2018
Availableonline09June2018
0367-326X/©2018PublishedbyElsevierB.V.

V. Sharma et al.
Fitoterapia129(2018)13–19
are presented uncorrected. Ultrasonic irradiation was performed in an
Elmasonic S 30 (H) ultrasonic water bath cleaner and the reaction
vessel was positioned in the maximum energy area in the cleaner and
the removal or addition of water was used to control the temperature of
the water bath. Infrared spectra were recorded on a Perkin-Elmer FT-IR
Spectrum 2 spectrophotometer 1H NMR and 13C NMR spectra were
recorded on ECS 400 MHz (JEOL) NMR spectrometer using CDCl3,
CD3OD and CD3SOCD3 as solvent and tetramethylsilane as internal
reference. Electrospray ionization mass spectrometry (ESI-MS) and
HRMS were recorded on Xevo G2-S Q Tof (Waters, USA) Spectrometer.
Column chromatography was performed over Merck silica gel (particle
size: 60–120 mesh) procured from Qualigens™ (India), flash silica gel
(particle size: 230–400 mesh). All chemicals and reagents were ob-
tained from Sigma Aldrich (USA), Merck (India) or Spectrochem (India)
and were used without further purification.
Fig. 1. Structures of natural product Cephalandole A (1) First proposed struc-
ture (2) Revised correceted.
our knowledge, for the first time, Cephalandole A 2 and its analogues
21a-o, have been identified as new class of antimicrobial agents as well
as AA-induced platelet aggregation inhibitors.
Few methods were reported in the literature for the synthesis of
Cephalandole A 2 [2, 9]. In addition to the method we had developed in
our previous study for the synthesis of Cephalandole A (upto 81%) [10]
was unsuccessful in getting higher yields of the synthesis of the novel
analogues of Cephalandole A 21a-o. Therefore, a modified protocol was
developed for the synthesis of Cephalandole A analogues 21a-o.
2.1.1. General procedure for the synthesis of functionalized 2-(1H-indol-3-
yl)-2-oxoacetic acid 19a–c
To a CH2Cl2 solution (15 mL) of indole 17a–c (0.2 mmol, 1 eq) was
added anhyd. AlCl3 (0.3 mmol, 1.5 eq) at 0 °C. The mixture was stirred
at 0 °C for 30 min. Then, to this solution was added drop wise acetyl
chloride (0.22 mmol, 1.1 eq) dissolved in CH2Cl2 solution (2 mL) at 0 °C.
The resulting solution was stirred at 0 °C for 4 h. After completion of the
reaction, maintained at around pH 7, aqueous buffer was added to
quench the reaction. After usual workup, the crude product was pur-
ified by silica gel using ethyl acetate: hexane as an eluant to furnish
substituted 3-acetylindole 18a-c in 72–87% yields.
2. Material and methods
2.1. Chemistry
In the next step; substituted 3-acetylindole 18a–c (0.2 mmol, 1 eq)
and selenium dioxide (0.3 mmol, 1.5 eq.) in pyridine (15 mL) were
heated to 100 °C for 10 h. The selenium salt was filtered through celite
All glass apparatus were oven dried prior to use. Melting points
were taken in open capillaries on complab melting point apparatus and
Fig. 2. Structures of selected functionalized benzoxazines and indole incorporated scaffolds as antibacterial and antiplatelet agents.
14

V. Sharma et al.
Fitoterapia129(2018)13–19
pad and the orange solution was concentrated in vacuo to approxi-
mately 5 mL in volume. The residue was dissolved in 100 mL of 5%
NaOH aq. solution and extracted with ethyl acetate (3 × 15 mL). The
aqueous layer was acidified with 2 N HCl solution (1–2 mL) and ex-
tracted with ethyl acetate (3 × 15 mL). The combined organic layers
were washed with water (25 mL), then with brine (2 × 15 mL), dried
over anhydrous Na2SO4 and solvent removed under reduced pressure.
The crude products were then purified either by recrystalization
method or by flash column chromatography method over silica gel
using MeOH/CHCl3 (2.5:7.5, v/v) as an eluant which afforded the pure
2-(1H-indol-3-yl)-2-oxoacetic acid analogues 19a-c in 62–82% yields.
128.6, 127.5125.9, 125.2, 122.9, 122.5, 121.3, 115.6, 111.9, 110.6;
HRMS (ESI) calcd. for
308.0667.
C : 308.0666; found
16H9N3O4 [M+H]+
2.2.5. 3-(1H-indol-3-yl)-6-nitro-2H-benzo[b][1,4]oxazin-2-one (21d)
Yellowish solid; yield: 62%, m.p. > 200 °C; FT-IR (KBr, νmax/
cm−1) 3414, 2922, 1753, 1619, 1524, 1424, 1109, 877; 1H NMR
(400 MHz, DMSO-d6) δ 11.89 (s, 1H), 8.76–8.70 (m, 2H), 8.56 (d,
J = 2.8 Hz, 1H), 8.23 (dd, J = 2.0, 8.4 Hz, 1H), 7.57–7.53 (m, 2H),
7.29–7.26 (m, 2H); 13C NMR (100 MHz, DMSO-d6) δ 150.6, 148.9,
144.4, 136.5, 134.5, 131.7, 125.7, 122.9, 122.6, 122.5, 122.1, 122.0,
121.7, 116.7, 111.9, 110.3; HRMS (ESI) calcd. for C16H9N3O4 [M
+H]+: 308.0666; found 308.0663.
2.1.2. General procedure for the synthesis of Cephalandole A 2 and
analogues 21a-o
To a solution of 19a-c (0.2 mmol, 1 eq) in diethylene glycol and
glacial acetic acid (2.0 mL, 1:1, v/v) was added 20a-g (0.2 mmol, 1 eq)
and the reaction mixture was irradiated under ultrasonic Sonicator at
80 °C temperature for about 180–300 min. (depending upon the sub-
strate employed). The progress of reaction was monitored by TLC. After
completion of reaction, the reaction mixture was filtered off by passing
through the celite pad, washed with distilled water (3 × 50 mL), and
then with brine (2 × 30 mL), dried over anhyd. Na2SO4 and con-
centrated under reduced pressure. The crude product were purified
either by recrystalization using EtOAc/hexane; or by flash column
chromatography method over silica gel using hexane/ethyl acetate as
an eluent which afforded the pure Cephalandole A 2 and its analogues
21a-o in good yields (58–79%).
2.2.6. 8-bromo-3-(1H-indol-3-yl)-6-methyl-2H-benzo[b] [1,4]oxazin-2-
one (21e)
Yellowish solid; yield: 73%, m.p. > 200 °C; FT-IR (KBr, νmax/
cm−1) 3429, 2922, 1717, 1617, 1572, 1494, 1113, 751; 1H NMR
(400 MHz, DMSO-d6 + CDCl3) δ: 11.51 (s, 1H), 8.66–8.63 (m, 2H), 7.50
(s, 1H), 7.41–7.40 (m, 1H), 7.32 (s, 1H), 7.18 (s, 2H), 2.35 (s, 3H); 13C
NMR (100 MHz, DMSO-d6 + CDCl3) δ: 151.1, 147.1, 139.2, 136.1,
135.1, 133.5, 132.1, 131.5, 126.7, 125.4, 122.5, 122.3, 121.1, 111.4,
110.0, 107.2, 19.8; HRMS (ESI) calcd. for C17H11BrN2O2 [M+2]+
356.0004; found 356.0006.
:
2.2.7. 3-(5-nitro-1H-indol-3-yl)-2H-benzo[b][1,4]oxazin-2-one (21f)
Yellowish solid; yield: 67%, m.p. > 300 °C; FT-IR (KBr, νmax/
cm−1) 3408, 2921, 1731, 1606, 1517, 1463, 1331, 1099, 780; 1H NMR
(400 MHz, DMSO-d6 + CDCl3) δ: 12.09 (s, 1H), 9.41 (s, 1H), 8.61 (s,
1H), 7.97–7.94 (m, 1H), 7.72–7.69 (m, 1H), 7.41–7.33 (m, 3H),
7.17–7.15 (m, 1H); 13C NMR (100 MHz, DMSO-d6 + CDCl3) δ: 151.3,
146.4, 144.5, 142.2, 139.4, 135.7, 131.1, 128.9, 127.7, 124.9 (2C),
119.3, 117.8, 115.4, 111.9, 111.7; HRMS (ESI) calcd. for C17H10BrN3O4
[M+H]+: 308.0666; found 308.0669.
2.2. Characterization data of Cephalandole analogues 2 and 21a-o
2.2.1. 3-(1H-indol-3-yl)-2H-benzo[b][1,4]oxazin-2-one (2)1
Yellowish solid; yield: 255 mg (81) %, m.p. 230–232 °C; FT-IR (KBr,
νmax/cm-1) 3292, 3053, 2921, 2852, 1713, 1604, 1428, 1151; 1H NMR
(400 MHz) δ 11.99 (s, 1H), 8.77–8.75 (m, 1H), 8.70 (s, 1H), 7.84 (d,
J = 6.4 Hz, 1H), 7.55–7.53 (m, 1H), 7.48–7.38 (m, 3H), 7.29–7.24 (m,
2H); 13C NMR (100 MHz) δ 152.1, 147.9, 144.9, 136.6, 133.8, 131.9,
128.7, 127.7, 126.0, 125.3, 123.1, 122.9, 121.6, 115.9, 112.2, 110.6;
2.2.8. 6-methyl-3-(5-nitro-1H-indol-3-yl)-2H-benzo[b] [1,4]oxazin-2-one
(21 g)
HRMS (ESI) calcd. for
263.0815.
C
16H10N2O2 [M+H]+
:
263.0815; found
Yellowish solid; yield: 64%, m.p. > 300 °C; FT-IR (KBr, νmax/
cm−1) 3426, 2920, 2852, 1725, 1621, 1589, 1437, 1114, 808; 1H NMR
(400 MHz, DMSO-d6 + CDCl3) δ: 12.4 (s, 1H), 9.33 (s, 1H) 8.58 (s, 1H),
7.98 (d, J = 10.8 Hz, 1H), 7.51 (d, J = 8.8 Hz, 1H), 7.40 (s, 1H), 2.35
(s, 3H); 13C NMR (100 MHz, DMSO-d6 + CDCl3) δ: 151.8, 146.8, 142.8,
139.7, 136.1, 135.9, 135.2, 131.1, 130.4, 127.6, 125.2, 119.2, 118.2,
2.2.2. 3-(1H-indol-3-yl)-6-methyl-2H-benzo[b][1,4]oxazin-2-one (21a)
Yellowish solid; yield: 77%, m.p. > 200 °C; FT-IR (KBr, νmax/
cm−1) 3411, 2923, 1714, 1629, 1529, 1444, 1063, 880; 1H NMR
(400 MHz, DMSO-d6 + CDCl3) δ: 11.03 (s, 1H), 8.60–8.48 (m, 2H), 7.41
(s, 1H), 7.24 (s, 1H), 7.04–7.03 (m, 2H), 6.97–6.91 (m, 2H), 2.22 (s,
3H); 13C NMR (100 MHz, DMSO-d6 + CDCl3) δ: 152.3, 147.2, 142.5,
136.4, 134.6, 133.2, 131.6, 129.1, 127.6, 125.8, 122.7, 122.7, 121.3,
114.9, 115.5, 110.8, 20.5; HRMS (ESI) calcd. For C17H12N2O2 [M
+H]+: 277.0972; found 277.0974.
115.6, 112.5, 112.2, 20.2; HRMS (ESI) calcd. for C18H11N3O4 [M+H]+
322.0823; found 322.0825.
:
2.2.9. 6-nitro-3-(5-nitro-1H-indol-3-yl)-2H-benzo[b] [1, 4] oxazin-2-one
(21h)
Yellowish solid; yield: 58%, m.p. > 300 °C; FT-IR (KBr, νmax/
cm−1) 3376, 1759, 1631, 1574, 1419, 1308, 1229, 1112; 1H NMR
(400 MHz, DMSO-d6) δ: 9.02 (s, 1H), 8.73 (s, 1H), 8.34 (s, 1H), 8.04 (d,
J = 8.8 Hz, 1H), 7.69–7.63 (m, 2H), 7.38–7.36 (m, 1H); HRMS (ESI)
calcd. For C16H8N4O6 [M+H]+: 353.0517; found 353.0515.
2.2.3. 6-chloro-3-(1H-indol-3-yl)-2H-benzo[b][1,4]oxazin-2-one (21b)
Yellowish solid; yield: 67%, m.p. > 200 °C; FT-IR (KBr, νmax/
cm−1) 3365, 2927, 1723, 1599, 1473, 1101, 799; 1H NMR (400 MHz,
DMSO-d6) δ: 11.74 (s, 1H), 8.67–8.63 (m, 2H), 7.78 (s, 1H), 7.52–7.50
(m, 1H), 7.42–7.39 (m, 1H), 7.33–7.31 (m, 1H), 7.27–7.21(m, 2H); 13
C
2.2.10. 7-nitro-3-(5-nitro-1H-indol-3-yl)-2H-benzo[b] [1, 4] oxazin-2-one
(21i)
NMR (100 MHz, DMSO-d6) δ: 151.5, 148.4, 143.6, 136.6, 134.1, 132.7,
128.9, 127.8, 126.5, 125.9, 123.0, 122.8, 121.6, 117.2, 112.0, 110.6;
Yellowish solid; yield: 63%, m.p. > 300 °C; FT-IR (KBr, νmax/
cm−1) 3376, 1760, 1630, 1576, 1422, 1303, 1233, 1116; 1H NMR
(400 MHz, DMSO-d6) δ: 9.06 (s, 1H), 8.39 (s, 1H), 8.05–8.02 (m, 1H),
7.68–7.51 (m, 3H), 6.63 (d, J = 8.8 Hz, 1H); HRMS (ESI) calcd. For
HRMS (ESI) calcd. For
298.0357.
C : 298.0353; found
16H9ClN2O2 [M+2]+
2.2.4. 3-(1H-indol-3-yl)-7-nitro-2H-benzo[b][1,4]oxazin-2-one (21c)
Yellowish solid; yield: 65%, m.p. > 300 °C; FT-IR (KBr, νmax/
cm−1) 3373, 2921, 1718, 1605, 1531, 1477, 1244, 1105, 941; 1H NMR
(400 MHz, DMSO-d6) δ 11.67 (s, 1H), 8.70 (d, J = 8.4 Hz, 1H), 8.63 (s,
C
16H8N4O6 [M+H]+: 353.0517; found 353.0519.
2.2.11. 8-bromo-6-methyl-3-(5-nitro-1H-indol-3-yl)-2H-benzo[b][1,4]
oxazin-2-one (21j)
1H), 7.81 (d, J = 8 Hz, 1H), 7.53–7.33 (m, 3H), 7.28–7.22 (m, 2H); 13
C
Yellowish solid; yield: 61%, m.p. > 200 °C; FT-IR (KBr, νmax/
NMR (100 MHz, DMSO-d6) δ: 151.9, 147.6, 144.7, 136.6, 133.5, 131.8,
cm−1) 3414, 2922, 1734, 1684, 1575, 1466, 1010, 830; 1H NMR
15

V. Sharma et al.
Fitoterapia129(2018)13–19
(400 MHz, DMSO-d6 + CDCl3) δ: 9.37 (s, 1H), 8.66 (s, 1H), 8.03 (s, 2H),
7.59 (d, J = 8.8 Hz 1H), 7.46 (s, 1H), 2.34 (s, 3H); 13C NMR (100 MHz,
DMSO-d6 + CDCl3) 151.0, 147.3, 142.6, 139.8, 139.5, 136.5, 135.9,
132.6, 132.0, 127.0, 124.9, 118.7, 118.0, 112.5, 111.6, 107.3, 19.63;
HRMS (ESI) calcd. for C17H10BrN3O4 [M + 2]+: 400.9855; found
400.9859.
2.3. Biological assay.
2.3.1. Determination of antimicrobial MIC value using serial dilution
method [13].
Concentration of analogues and positive control drugs at 100 μg/mL
were prepared in an appropriate solvent. Inoculums of the bacterial and
fungal cultures were also prepared. Inoculum (0.2 mL) and sterile water
(3.8 mL) were added to a series of tubes each containing 1 mL of test
compound solution at the six different concentrations. The tubes were
incubated for 24 h and carefully observed for the presence of turbidity.
The minimum concentration at which no growth was observed was
taken as the MIC. The MIC for all the analogues examined ranged from
3.12–100 μg/mL.
2.2.12. 3-(5-methoxy-1H-indol-3-yl)-2H-benzo[b] [1, 4] oxazin-2-one
(21k)
Yellowish solid; yield: 75%, m.p. > 200 °C; FT-IR (KBr, νmax/
cm−1) 3441, 2935, 1722, 1535, 1428, 1122, 588; 1H NMR (400 MHz,
DMSO-d6) δ: 11.63 (s, 1H), 8.60 (s, 1H), 8.29 (s, 1H), 7.81 (d,
J = 7.6 MHz, 1H), 7.43–7.34 (m, 3H), 6.95–6.86 (m, 2H), 3.87 (s, 3H);
13C NMR (100 MHz, DMSO-d6) δ: 155.3, 151.8, 147.5, 144.6, 133.6,
131.7, 131.4, 128.2, 127.3, 126.6, 125.0, 118.9, 115.5, 112.3, 110.2,
105.5, 55.4; HRMS (ESI) calcd. For C17H12N2O3 [M+H]+:293.0921;
found 293.0923.
2.3.1.1. Platelet aggregation inhibitory activity evaluation [15a, b]. The
synthesized Cephalandole A 2 and its novel analogues 21a-o were
dissolved in DMSO before testing. In order to eliminate the effects of the
solvent on aggregation, the final concentration of DMSO was fixed at
0.5%. Arachidonic acid (AA), EDTA (disodium salt), bovine serum
albumin and dimethyl sulfoxide (DMSO) were purchased from Sigma
Chemical Co.
2.2.13. 3-(5-methoxy-1H-indol-3-yl)-6-methyl-2H-benzo[b] [1,4]oxazin-
2-one (21l)
Yellowish solid; yield: 79%, m.p. > 200 °C; FT-IR (KBr, νmax/
cm−1) 3310, 2926, 2852, 1709, 1619, 1590, 1435, 1035, 874; 1H NMR
(400 MHz, DMSO-d6 + CDCl3) δ: 11.39 (s, 1H), 8.58 (s, 1H), 8.27 (s,
1H), 7.50 (s, 1H), 7.30 (d, J = 8.8 Hz, 1H), 7.13–7.07 (m, 2H), 6.81 (d,
J = 8.0 Hz, 1H), 3.86 (s, 3H), 2.38 (s, 3H); 13C NMR (100 MHz, DMSO-
d6 + CDCl3) δ: 155.2, 152.2, 147.2, 142.4, 134.6, 133.6, 131.5, 131.4,
128.9, 127.4, 126.6, 115.0, 112.3, 112.2, 110.4, 104.9, 55.2, 20.4;
2.3.1.2. Platelet aggregation inhibitory bioassay [15c]. Blood was
collected from the rabbit marginal ear vein (several studies
established that rabbit platelets are surrogate to human platelets both
in vitro as well as in vivo) [16] and was mixed with EDTA to a final
concentration of 6 mM. It was centrifuged for 10 min at 90g at room
temperature, and the supernatant was obtained as platelet-rich plasma.
The latter was further centrifuged at 500g for 10 min. The platelet
pellets were washed with Tyrode's solution (Ca+2-free) containing
2 mM EDTA, 0.1 mg/mL and 3.5 mg/mL bovine serum albumin, and
centrifuged at 500g for 10 min. Then, the pellets were washed with
Tyrode's solution without EDTA. After centrifugation under the same
conditions, the platelet pellets were finally suspended in Tyrode's
solution of the following composition (mM): NaCl (136.8), KCl (2.8),
NaHCO3 (11.9), MgCl2 (2.1), NaH2PO4 (0.33), CaCl2 (1.0), and glucose
(11.2) containing bovine serum albumin (0.35%).
HRMS (ESI) calcd. for
307.1078.
C : 307.1077; found
18H14N2O3 [M + H]+
2.2.14. 6-chloro-3-(5-methoxy-1H-indol-3-yl)-2H-benzo[b] [1,4]oxazin-
2-one (21 m)
Yellowish solid; yield: 68%, m.p. > 200 °C; FT-IR (KBr, νmax/
cm−1) 3404, 2926, 1730, 1609, 1527, 1483, 1111, 801; 1H NMR
(400 MHz, DMSO-d6) δ: 11.73 (s, 1H), 8.62 (s, 1H), 8.23 (s, 1H), 7.81 (s,
1H), 7.44–7.35 (m, 3H), 6.93–6.90 (m, 1H), 3.87 (s, 3H); 13C NMR
(100 MHz, DMSO-d6) δ: 156.3, 152.1, 149.2, 144.2, 135.3, 135.1,
133.5, 132.2, 129.6, 128.3, 127.4, 127.0, 117.9, 113.3, 110.9, 106.3,
56.3; HRMS (ESI) calcd. For C17H11ClN2O3 [M+2]+: 328.0458; found
328.0459.
Aggregation was measured by a turbidimetric method using a Lumi-
aggregometer (Chrono-Log Corp., Havertown, PA). All glassware was
siliconized. Three minutes before the addition of the aggregation in-
ducer, the platelet suspension was stirred at 1200 rpm. The percentage
of aggregation was calculated as follows (abs. = absorbance):
(Abs. of platelet suspension‐Finalabs.after aggregation)
%Aggregation =
Percentage aggregation was expressed assuming the absorbance of
platelet suspension as 0% aggregation and the absorbance of platelet-
free Tyrode's solution as 100% aggregation. For each compound IC50
values were calculated by Sigma Plot.
(Abs. of platelet suspension‐Abs. of Tyrode solution)
2.2.15. 8-bromo-3-(5-methoxy-1H-indol-3-yl)-6-methyl-2H-benzo[b][1,4]
oxazin-2-one (21n)
× 100
Yellowish solid; yield: 74%, m.p. > 200 °C; FT-IR (KBr, νmax/
cm−1) 3411, 2933, 1729, 1615, 1587, 1477, 1105, 846; 1H NMR
(400 MHz, DMSO-d6) δ: 11.68 (s, 1H), 8.59 (s, 1H), 8.24 (s, 1H), 7.60 (s,
1H), 7.50 (s, 1H), 7.42 (d, J = 8.4 Hz, 1H), 6.93–6.90 (m, 1H), 3.87 (s,
3H), 2.39 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ: 155.3, 151.2,
147.7, 142.5, 139.6, 135.6, 134.1, 132.5, 131.6, 131.4, 130.4, 126.7,
126.5, 121.0, 112.3, 109.9, 55.4, 19.6; HRMS (ESI) calcd. For
3. Results and discussion
C
18H13BrN2O3 [M + 2]+: 386.0110; found 386.0112.
3.1. Synthetic chemistry
The commercially available substituted indole 17a-c were subjected
to Friedel-Crafts acetylation reaction using reported protocol [11],
which furnished substituted 3-acetyl indoles 18a-c in excellent yields,
as shown in Scheme 1. Substituted 3-acetyl indoles 18a-c were then
converted into substituted 2-(1H-indol-3-yl)-2-oxoacetic acids 19a-c by
subsequent oxidation with SeO2 [12]. 2-(1H-indol-3-yl)-2-oxoacetic
acids 19a and 2-amino-4-methylphenol 20b were chosen as starting
materials for the optimization of last condensation step in which dif-
ferent solvents (DMF, DMSO, CH3CN, Glacial acetic acid, EtOH, MeOH,
Diethylene glycol) or their combinations were examined. After several
2.2.16. 3-(1H-indol-3-yl)quinoxalin-2(1H)-one (21o)
Yellowish solid; yield: 71%, m.p. > 300 °C; FT-IR (KBr, νmax/
cm−1) 3421, 2921, 1713, 1660, 1580, 1420, 1018, 741; 1H NMR
(400 MHz, DMSO-d6) δ: 8.89–8.84 (m, 2H), 7.85 (d, J = 8.8 Hz, 1H),
7.51 (d, J = 4.8 Hz, 1H), 7.44–7.30 (m, 3H), 7.25–7.23 (m, 2H); 13C
NMR (100 MHz, DMSO-d6) δ: 173.4, 154.4, 151.9, 136.4, 132.7, 130.1,
127.8, 127.4, 126.2, 123.2, 122.7, 122.4, 120.9, 114.9, 117.7, 111.4;
HRMS (ESI) calcd. for
262.0978.
C : 262.0975; found
16H11N3O [M+H]+
16

V. Sharma et al.
Fitoterapia129(2018)13–19
Scheme 1. aReagents and Conditions: (i) Compound 17a-c (0.2 mmol, 1 eq.) in CH2Cl2 (15 mL), AlCl3 (0.3 mmol, 1.5 eq.), CH3COCl (0.22 mmol, 1.1 eq.), 0 °C, 4 h; (ii)
Compound 18a-c (0.2 mmol, 1 eq.) in pyridine (15 mL), SeO2 (0.3 mmol, 1.5 eq.), 100 °C for 10 h; (iii) Compound 19a-c (0.2 mmol, 1 eq.) and 20a-g (0.2 mmol, 1 eq.)
in diethylene glycol and glacial acetic acid (2.0 mL; 1:1, v/v) at 80 °C temperature for 180–300 min under ultrasound irradiation. bIsolated yield.
permutations and combinations of solvents at different reaction time
under ultrasonic irradiation condition; the diethylene glycol and glacial
acetic acid (1:1, v/v) was found to be the best solvent system for the
synthesis of 21a upto 77% yield in 180 min (see Supporting information
for detail optimization study).
Compounds 19a-c were finally reacted with substituted o-amino-
phenols 20a-f and 1,2-diaminobenzene 20 g under optimized condi-
tions which furnished Cephalandole A analogues 21b-o in 58–79%
yield range in 180–300 min (Scheme 1). The purification of the target
compounds were done either by flash column chromatography method
or by recrystalization method. All the synthesized compounds were well
characterized by 1H NMR, 13C NMR, HRMS and IR spectroscopy ana-
lysis.
(MTCC 10619), and gram-negative bacterial strains Escherichia coli [EC]
(MTCC 443) taking ampicillin as positive control. Antibacterial
screening of all the compounds, 2 and 21a-o as well as positive controls
were performed at a concentration of 6.25–100 μg/mL. Additionally, 2
and its analogues 21a-o were also initially screened, for the first time,
for their in vitro antifungal activity against fungal species (i.e. A. niger,
P. funiculosum and C. albicans) taking ketoconazole as positive control
listed in Table 1.
The minimum inhibitory concentration (MIC) values for all the as-
sessed compounds (2 and 21a-o) and ampicillin were determined by
the serial dilution method [13a–f]. In this study, several analogues
exhibited promising antimicrobial activity compared to ampicillin and
ketoconazole.
It has been observed that nitro-based analogues 21c-d and 21f-j
were obtained in comparatively lower yields due to the poor solubility
in ethyl acetate, which makes the purification of these compounds via
column chromatography tedious and cumbersome. A broad range of
functional groups, like Cl, Br, OMe and NO2 were found to be compa-
tible under optimized conditions, which can be utilized for further
functionalization.
As it can be seen from Table 1; Compounds 21o, the first aza ana-
logues of Cephalandole A, was identified as the most potent anti-
bacterial agents of the series showing MIC value of 12.5 μg/mL against
[BS] as well as [SG] strains, respectively; as it showed two times more
activity than ampicillin against [BS] strain and equal potency than
ampicillin against [SG] strains (Entry 16; Table 1). The next potent
compound was 21b (MIC = 12.5 μg/mL) which showed two times
greater potency than ampicillin (MIC = 25 μg/mL) against [BS] strain.
Further, the next potent compounds found in this assay were 21 h, 21j,
21 k and 21 l having MIC values of 12.5 μg/mL against [SG] and [SA]
strains which showed equal potency than ampicillin. Compounds 21a,
21d and 21i (MIC = 25 μg/mL) showed two times lesser potency than
ampicillin against [SG] and [SA] strains. Finally, compounds 21a, 21c,
21e-g, and 21 k which have shown MIC = ≥25 μg/mL in all strains
3.2. Antibacterial activity and the structure-activity relationships (SAR)
Cephalandole A 2 and its analogues 21a-o were initially screened,
for the first time, for their in vitro antibacterial activity against gram-
positive bacterial strains, Streptomyces griseus [SG] (MTCC 4734),
Staphylococcus aureus [SA] (MTCC 3381) and Bacillus subtilis [BS]
17

V. Sharma et al.
Fitoterapia129(2018)13–19
Table 1
Table 2
MIC values for Cephalandole A (2) and its novel analogues (21a-o) and positive
AA-induced platelet aggregation inhibitory activity for novel Cephalandole A
control drugs against pathogenic bacterial and fungal strains.a.
(2) and its analogues (21a-o).a,b
S·No. Comp. No. Minimum inhibitory concentration (MIC)a
Bacterial strainsb,c
Fungal strainsd
SGb
SAb
BSb
ECc
AN
PF
CA
1
2
3
4
5
6
7
8
2
NA
25
NA
NA
NA
NA
25
NA
50
NA
NA
NA
100
NA
NA
NA
NA
NA
NA
NA
50
NA
NA
NA
NA
12.5
–
100
12.5
NA
12.5
12.5
NA
100
12.5
25
12.5
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
100
–
12.5
50
12.5
NA
12.5
100
NA
21a
21b
21c
21d
21e
21f
21g
21h
21i
NA
NA
NA
NA
NA
NA
12.5
25
12.5
NA
NA
NA
NA
12.5
12.5
–
12.5
NA
NA
100
100
100
NA
NA
NA
NA
NA
NA
NA
12.5
25
S·No. Comp. no. R1
R2 R3
R4
R5
X
Antiplatelet activitya,b
NA
NA
NA
NA
NA
NA
12.5
12.5
NA
NA
NA
12.5
–
(IC50 in μg/mL)
NA
25
1
2
3
4
5
6
7
8
2
H
H
H
H
H
H
NO2
NO2
NO2
NO2
NO2
OCH3
OCH3
OCH3
H
H
H
H
H
Br
H
H
H
H
Br
H
H
H
H
H
H
H
NO2
H
H
H
H
NO2
H
H
H
H
H
H
–
H
CH3
Cl
NO2
H
CH3
H
CH3
NO2
H
CH3
H
CH3
Cl
CH3
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
–
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
19.34
31.56
71.56
20.21
45.67
44.32
18.99
111.83
30.18
21.59
27.33
52.46
56.81
60.77
54.54
0.27
0.88
1.09
0.28
1.02
0.98
0.21
1.87
0.72
0.31
0.74
1.06
1.11
1.23
1.08
1.63
0.51
9
21a
21b
21c
21d
21e
21f
21g
21h
21i
21j
21k
21l
21m
21n
21o
Aspirin
10
11
12
13
14
15
16
17
18
12.5
100
100
NA
100
NA
NA
–
25
21j
21 k
21 l
21 m
21n
21o
AMPe
KETf
NA
12.5
12.5
12.5
12.5
–
9
10
11
12
13
14
15
16
17
–
12.5
25
NA = Compounds which were found Not Active.
a
MIC of all compounds was measured at the range from 6.25 to 100 μg/mL.
Gram-positive bacteria: SG, Streptomyces griseus; SA, Staphylococcus aureus;
b
OCH3 Br
H
–
H
–
NH 104.45
22.17
BS, Bacillus subtilis.
–
–
c
Gram-negative bacteria: EC, Escherichia coli.
Fungi: AN, Aspergillus niger; PF, Penicillium funiculosum; CA, Candida albi-
d
a
Platelets were incubated along with either a tested compound or 0.5%
cans.
DMSO at 37 °C for 60 s, then AA (100 μM) was added to accelerate the ag-
gregation. Aspirin was taken as positive control. Values are expressed as
mean_SE from three to six separations.
e
AMP: Ampicillin.
f
KET: Ketoconazole.
b
The data represent mean of three independent determinations.
were found to be either less active or no activity as compared to am-
picillin. Overall, SAR study shows that introduction of nitrogen atom in
Cephalandole A i.e. 21o increases its antibacterial potency.
It can be further interpreted that substitution of electron-with-
drawing group (EWG) i.e. NO2 as well as halo group (eCl, Br) at 2-oxo-
benzo[1,4]oxazines moieties of Cephalandole A have significant bene-
ficial effects on antibacterial activity than ampicillin except compound
21c.
Compounds 21d and 21i, the most potent antifungal compounds
(MIC = 12.5 μg/mL) of the series, have shown equal potency than ke-
toconazole (MIC = 12.5 μg/mL) in [AN] fungal strain and showed two
times potency than ketoconazole (MIC = 25 μg/mL) in [CA] fungal
strain, respectively. In this study, it was observed that Cephalandole A
analogues have shown antifungal potency, particularly to [AN] and
[CA] strains. While compounds 21a, 21c-d, 21g, 21i, 21l-o showed
equal potency than ketoconazole (MIC = 12.5 μg/mL) in [AN] strain;
compounds 2, 21b, and 21i showed two times greater potency than
ketoconazole (MIC = 25 μg/mL) in [CA] strain. Compound 21 h,
having nitro group at both indole and 2-oxo-benzo[1,4]oxazines moi-
eties of Cephalandole A, showed equal potency in [CA] strain but
showed less potency than ketoconazole in [AN] strain. Finally, all those
compounds which have shown (MIC = ≥50 μg/mL) in [AN], [PF], and
[CA] strains were found to be either less active or no activity as com-
pared to ketoconazole.
aggregation inhibitory activities taking aspirin as the standard re-
ference drug (IC50 = 22.17
[15] and the results are shown in Table 2.
0.51 μg/mL) using reported protocol
The structure of Cephalandole A 2, can be visualized as a 2-oxo-
benzo[1,4]oxazine containing bicyclic rings A and B linked at C-3 po-
sition of substituted indole rings C and D (Table 2).
As depicted from Table 2, Cephalandole A 2 which has no sub-
stitutions at ring A or D; displayed greater AA-induced platelet ag-
gregation inhibitory activity (IC50 = 19.34
ison to the standard reference drug aspirin (IC50 = 22.17
mL; entry 1; Table 2). Compound 21c having electron-withdrawing
0.27 μg/mL) in compar-
0.51 μg/
groups (EWG) i.e. NO2 at C-6 position on ring A showed greater anti-
platelet activity (IC50 = 20.21
Table 2). Changing the position of NO2 group diminishes the activity as
in compound 21d (IC50 = 45.67 μg/mL, entry 5; Table 2).
0.28 μg/mL) than aspirin (entry 4;
Further, putting electron-donating groups (EDG) in ring A do not
have substantial improvement in the antiplatelet activity which lead us
to infer that electron-donating group do not have profound effect on
antiplatelet activity whereas, EWG increases AA-inducted platelet ag-
gregation inhibitory activity (entry 2–3 and 6; Table 2).
Since EWG increases antiplatelet activity of Cephalandole A analo-
gues; we were interested to study the effect of EWG on indole ring.
Thus, we prepared 21f and further substituted analogues at ring D i.e.,
21 g-j and assessed for their antiplatelet activities. Compound 21f
showed high order of AA-induced platelet aggregation activity having
3.3. Antiplatelet activity and the structure-activity relationships (SAR)
IC50 value of 18.99
0.21 μg/mL and was found to be the active
compound of the series (entry 7; Table 2). Then, electron-donating
group i.e. CH3 was introduced at C-4 position of ring A which lead to
complete loss of antiplatelet activity (entry 8; Table 2). However, we
were delighted when we observe the restoration of activity by the in-
troduction of NO2 group at C-3/4 position of ring A (entry 9–10;
Recently, we have identified a new class of non-peptide based
functionalized 2-oxo-benzo[1,4]oxazines as arachidonic acid (AA)-in-
duced platelet aggregation inhibitors [14]. Since Cephalandole A also
possesses 2-oxo-benzo[1,4]oxazines; we have screened all the synthe-
sized compounds (2 and 21a-o) for their AA-induced platelet
18

V. Sharma et al.
Fitoterapia129(2018)13–19
Table
(IC50 = 21.59
exhibited comparable activity to aspirin (entry 10; Table 2). Similarly,
21h (IC50 = 30.18 0.72 μg/mL, entry 9; Table 2), having NO2 group
2).
The
antiplatelet
activity
of
compound
21i
Supplementary data to this article can be found online at doi: https://
doi.org/10.1016/j.fitote.2018.06.003.
0.31 μg/mL), was found slightly lesser than 21f and
References
at C-6 position of ring D, also displayed lower activity than 21i.
We were further interested to study the effect of EDG i.e., OMe
group in ring D of indole moiety of Cephalandole A. Thus, we prepared
Cephalandole A analogues 21k-n and evaluated for their antiplatelet
activity. Thus, no substitution in 2-oxo-benzo[1,4]oxazine moiety leads
[1] P.-L. Wu, Y.-L. Hsu, C.-W. Jao, J. Nat. Prod. 69 (2006) 1467.
[2] J. Mason, J. Bergman, T. Janosik, J. Nat. Prod. 71 (2008) 1447.
[3] (a) R.B. Moffett, J. Med. Chem. 9 (1966) 475–478;
(b) Moffett, R.B. U.S. Patent 3, 255,187, 1966.
[4] (a) M. Liu, P. Wilairat, L.M.J. Go, Med. Chem. 44 (2001) 4443–4452;
(b) C.L. Miranda, G.L.M. Aponso, J.F. Stevens, M.L. Deinzer, D.R. Buhler, J. Agric.
Food Chem. 48 (2000) 3876–3884;
to substantial decrease in activity as in 21k (IC50 = 52.46
1.06 μg/
mL, entry 12; Table 2), Similarly, no further improvement in anti-
platelet activity was observed by substituting halo (Cl, Br) or CH3 group
of ring A (Compound 21m-n; entry 14–15; Table 2). In addition to the
above study; we were also interested to study the effect of nitrogen or
oxygen atom in 2-oxo-benzo[1,4]oxazine moiety of Cephalandole A.
Thus, azacephalandole A 21o, which was prepared by replacing O-atom
with N-atom, displayed lower platelet aggregation inhibitory activity
(c) R.K. Zee-Cheng, C.C. Cheng, J. Pharm. Sci. 71 (1982) 708–709;
(d) H.H. Ko, L.T. Tsao, K.L. Yu, C.T. Liu, J.P. Wang, C.N. Lin, Bioorg. Med. Chem.
11 (2003) 105–111;
(e) A.M. Deshpande, N.P. Argade, A.A. Natu, Eckman, J. Bioorg. Med. Chem. 7
(1999) 1237–1240;
(f) S. Khatib, O. Nerya, R. Musa, M. Shmnel, S. Tamir, J. Vay, J. Bioorg. Med.
Chem. 13 (2005) 433–441;
(g) R.R. Kumar, S. Perumal, P. Senthilkumar, P. Yogeeswari, D. Sriram, J. Med.
Chem. 51 (2008) 5731–5735.
[5] (a) Beach, M.; Frechette, R. WO Patent Appl. 9728167, 1997;
(b) M. Pamerla, D.R.S. Reddy, B.S. Rao, N. Bodipati, Y.L.N. Murthy, Med. Chem.
Res. 24 (2015) 611–615;
(IC50 = 104.45
as Cephalandole A 2.
1.63 μg/mL; entry 16; Table 2) than aspirin as well
(c) A. Macchiarulo, G. Costantino, D. Fringuelli, A. Vecchiarelli, F. Schiaffella, R.
Fringuelli, Bioorg. Med. Chem. 10 (11) (2002) 3415–3423;
(d) R. Fringuelli, N. Giacchè, L. Milanese, E. Cenci, A. Macchiarulo, A. Vecchiarelli,
G. Costantino, F. Schiaffella, Bioorg. Med. Chem. 17 (2009) 3838–3846;
(e) R. Fringuelli, D. Pietrella, F. Schiaffella, A. Guarraci, S. Perito, F. Bistoni, A.
Vecchiarelli, Bioorg. Med. Chem. 10 (2002) 1681–1686;
(f) R. Sharma, L. Yadav, J. Lal, P.K. Jaiswal, M. Mathur, A.K. Swami, S. Chaudhary,
Bioorg. Med. Chem. Lett. 27 (2017) 4393–4398
Based on the above antiplatelet SAR study; it can be concluded that
introduction of EWG or EDG have significant effect on antiplatelet ac-
tivity. While EWG increases AA-induced platelet aggregation inhibitory
activity, EDG leads to either decreases or complete loss of activity. We
also interpret the positional effect of EWG i.e., NO2 group. We observed
that placing two nitro group, one at indole ring and another at C-6 or C-
7 position of 2-oxobenzo[1,4]oxazine moiety i.e., in compound 21 h
and 21i, respectively, leads to significant change in AA-induced platelet
aggregation inhibitory activity.
[6] (a) X. Tian, L.-Y. Wang, S. Xia, Z.-B. Li, X.-H. Liu, Y. Yuan, L. Fang, H. Zuo, Bioorg.
Med. Chem. Lett. 22 (2012) 204–206;
(b) S. Xia, J.-Q. Liu, X.-H. Wang, Y. Tian, Y. Wang, J.-H. Wang, L. Fang, H. Zuo,
Bioorg. Med. Chem. Lett. 24 (2014) 1479–1483 (and references cited therein);
(c) G. Roma, M.D. Braccio, G. Grossi, D. Piras, G. Leoncini, D. Bruzzese,
M.G. Signorello, P. Fossa, L. Mosti, J. Med. Chem. 50 (2007) 2886–2895;
(d) T.-C. Ko, M.-J. Hour, J.-C. Lien, C.-M. Teng, K.-H. Lee, S.-C. Kuo, L.-J. Huang,
Bioorg. Med. Chem. Lett. 11 (2001) 279–282;
4. Conclusions
(e) C. Kontogiorgis, O. Nicolotti, G.F. Mangiatordi, M. Tognolini, F. Karalaki,
C. Giorgio, A. Patsilinakos, A. Carotti, D. Hadjipavlou-Litina, E. Barocelli, J. Enzyme
Inhib. Med. Chem. 30 (6) (2015) 925–933;
(f) K.M. Pritchard, J.M.A. Al-Rawi, C.J. Bradley, Eur. J. Med. Chem. 42 (2007)
1200–1210.
In conclusion, we have synthesized natural product Cephalandole A
2 and its novel analogues 21a-n along with the first synthesis of aza-
cephalandole A 21o using our modified protocol, for the first time,
under ultrasound irradiation conditions in good yields from readily
available starting substrates, which were analyzed for their in vitro
antimicrobial as well as AA-induced platelet aggregation inhibitory
activities. In our study, Cephalandole A 2 and its novel analogues 21a-o
were identified as a new class of antimicrobial and antiplatelet agents.
The promising biological activity of Cephalandole A analogues com-
bined with ease of preparation found it as a promising scaffold worthy
of further structural optimization to develop potent antimicrobial as
well as antiplatelet agents.
[7] (a) A.S. Salman, N.A. Mahmoud, A. Abdel-Aziem, M.A. Mohamed, D.M. Elsisi,
Inter. J. Org. Chem. 5 (2015) 81–99;
(b) D. Yuksek, O. Algul, A. Dogen, O. Tari, E. Kucuk, Z.F. Otag, M.S. Serin, Afri. J.
Microbio. Res. 7 (2013) 1708–1715;
(c) B.P. Yadav, I. Ahmad, M. Thakur, IOSR J. Pharm. 6 (2016) 27–33.
[8] (a) M.S. Estevão, L.C.R. Carvalho, M. Freitas, A. Gomes, A. Viegas, J. Manso,
S. Erhardt, E. Fernandes, M. Cabrita, E.J. MMB, Eur. J. Med. Chem. 54 (2012)
823–833;
(b) H.S. Chen, S.C. Kuo, C.M. Teng, F.Y. Lee, J.P. Wang, Y.C. Lee, C.W. Kuo,
C.C. Huang, C.C. Wu, L.J. Huang, Bioorg. Med. Chem. 16 (2008) 1262–1278;
(c) K.H.M.E. Tehrani, M.E. Zadeh, V. Mashayekhi, M. Hashemi, F. Kobarfard,
F. Gharebaghi, S. Mohebbi, Iran. J. Pharm. Res. 14 (2015) 1077–1086;
(d) F.-Y. Lee, J.-C. Lien, Li-J Huang, T.-M. Huang, S.-C. Tsai, C.-M. Teng, C.-C. Wu,
F.-C. Cheng, S.-C. Ku, J. Med. Chem. 44 (2001) 3746–3749;
(e) S.S. Mirfazli, F. Kobarfard, L. Firoozpour, A. Asadipour, M. Esfahanizadeh,
K. Tabib, A. Shafiee, A. Foroumadi, DARU, J. Pharm. Sci. 22 (2014) 6.
[9] (a) S. Yan, L. Ye, M. Liu, J. Chen, J. Ding, W. Gao, X. Huangam, H. Wu, RSC Adv. 4
(2014) 16705–16709;
Conflict of interest
The authors declare no conflicts of interest.
Acknowledgements
(b) C. Huo, J. Dong, Y. Su, J. Tang, F. Chen, Chem. Commun. 52 (2016)
13341–13344.
[10] P.K. Jaiswal, V. Sharma, J. Prikhodko, I.V. Mashevskaya, S. Chaudhary,
Tetrahedron Lett. 58 (22) (2017) 2077–2083.
[11] O.V. Ottoni, A.V.F. Neder, A.K.B. Dias, R.P.A. Cruz, L.B. Aquino, Org. Lett. 3
(2001) 7.
[12] M.J. Taylor, T.Z. Hoffman, J.T. Yli-Kauhaluoma, R.A. Lerner, K.D. Janda, J. Am.
Chem. Soc. 120 (1998) 12783–12790.
S. C. acknowledges SERB, New Delhi for fast track scheme for young
scientist (CS-037/2013); DST, New Delhi for DST-RFBR Indo-Russian
Joint Research Project (INT/RUS/RFBR/P-169) and CSIR-New Delhi
EMR Grant [02 (0189)/14/EMR-II]. V. S.; P. K. J. and K. K. thanks
MNIT, Jaipur and CSIR, New Delhi for providing financial assistance in
the form of institute fellowship and RA fellowship, respectively.
Materials Research Centre, MNIT, Jaipur is gratefully acknowledged for
providing analytical facilities.
[13] (a) S. Alam, J. Chem. Sci. 166 (2004) 325–331;
(b) P.M. Reddy, Y.P. Ho, K. Shanker, R. Rohini, V. Ravinder, Eur. J. Med. Chem. 44
(2009) 2621;
(c) B. Shadidi, S. Aghighi, N.A. Karimi, Iran. J. Biol. Sci. 4 (2005) 405–412;
(d) R. Cruickshank, J.P. Duguid, B.P. Marmion, R.H.A. Swain, Medical
Microbiology, 12th Ed., Vol. II (1975);
(e) U. Omrum, S. Arikan, S. Kocago, B. Semeak, S. Unala, Diagn. Microbiol. Infect.
Dis. 38 (2000) 101–107;
(f) M. Malue, J.M. Bastide, A. Biancard, Int. J. Antimicrob. Agents 25 (2005)
321–328.
Appendix A. Supplementary data
[14] P.K. Jaiswal, V. Sharma, Saloni, M. Mathur, A.K. Swami, D.K. Yadav, S. Chaudhary,
Arch. Pharm. 351 (3–4) (2018) 1–17, http://dx.doi.org/10.1002/ardp.201700349.
[15] (a) K.-S. Chen, F.-N. Ko, Che-M Teng, Y.-C. Wu, J. Nat. Prod. 59 (1996) 531–534;
(b) C.M. Teng, W.Y. Chen, W.C. Ko, C. Ouyang, Biochim. Biophys. Acta 924 (1987)
375–382;
The supporting information related to this article includes, general
experimental procedure, characterization data of all synthesized com-
pounds (2 and 21a-o) and copies of 1H and 13C spectral data of some
representative compounds (21a, 21c, 21e, 21f, 21l and 21o).
(c) J.R. O'Brien, J. Clin. Pathol. 15 (1962) 452–455.
19