Application of Cu (II)-Guanine Complexes Anchored on SBA-15 and MCM-41 as Efficient Nanocatalysts for One-Pot, Four-Component Domino Synthesis of Phenazine Derivatives and Investigation of Their Antimicrobial Behavior

Article abstract of DOI:10.1007/s10562-020-03185-0

Abstract: A one-pot, two-step, four-component synthesis of benzo[c]pyrano[3,2-a]phenazine and bis-benzo[c]pyrano[3,2-a]phenazine derivatives was carried out by the reaction of 2-hydroxy-1,4-naphthoquinone, benzene-1,2-diamine, carbonyl compounds and alkyl

Full text of DOI:10.1007/s10562-020-03185-0

Catalysis Letters
https://doi.org/10.1007/s10562-020-03185-0
Application of Cu (II)‑Guanine Complexes Anchored on SBA‑15
and MCM‑41 as Eꢀcient Nanocatalysts for One‑Pot, Four‑Component
Domino Synthesis of Phenazine Derivatives and Investigation of Their
Antimicrobial Behavior
Mohsen Nikoorazm · Maryam Khanmoradi1
1
Received: 1 December 2019 / Accepted: 15 March 2020
©
Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
A one-pot, two-step, four-component synthesis of benzo[c]pyrano[3,2-a]phenazine and bis-benzo[c]pyrano[3,2-a]phenazine
derivatives was carried out by the reaction of 2-hydroxy-1,4-naphthoquinone, benzene-1,2-diamine, carbonyl compounds and
alkylmalonates using new copper (II) ions complexes of guanine (2-amino-1H-purin-6(9H)-one) supported into MCM-41
(
Cu-guanine-MCM-41) and SBA-15 (Cu-guanine-SBA-15) channels as eꢀcient and heterogeneous catalysts in PEG. The
desired products were obtained in good to excellent yields. The prepared catalysts have been extensively characterized by
diꢁerent methods and can be reused for several times without any signiꢂcant loss of their catalytic activities. The phenazine
derivatives were also tested for their antimicrobial activities.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-020-03185-0) contains
supplementary material, which is available to authorized users.
*
Mohsen Nikoorazm
e_nikoorazm@yahoo.com
1
Department of Chemistry, Faculty of Science, Ilam
University, P. O. Box 69315516, Ilam, Iran
Vol.:(0
1
123456789)
3

M. Nikoorazm, M. Khanmoradi
Graphic Abstract
Keywords MCM-41 · SBA-15 · Guanine · Multi-component reactions (MCRs) · Phenazine · Heterogeneous catalyst ·
Antimicrobial · Copper (II)
1
Introduction
catalysts which have many unique properties and advan-
tages such as low cost, stability, non-toxicity, and reus-
ability can overcome most of the disadvantages of homog-
enous catalysts. They can also play an important role in
organic synthesis [7–10]. Although there are many meth-
ods for the preparation of the catalysts, rational design and
synthesis of the highly eꢀcient catalysts have become the
ultimate goals of the catalysis research [11]. Among diꢁer-
During recent years, nanotechnology has been focused on
the opportunity to develop catalysts that exhibit the reduc-
tion of the number of stages in a given chemical process
and hence, reduce the environmental impact. This type of
selective process is often called green chemistry or green
technology. Stability, desirable activity, selectivity, reus-
ability and minimizing collateral toxicity etc., in catalysis
behaviour, are the other aims of nanotech [1–6]. Besides,
catalysts may be gases, liquids, or solids. Nanohetrogenous
ent solid supports, silica (SiO2
)
materials play a signiꢂcant
role in the synthesis of heterogeneous catalyst [12–19]. In
particular, there have been extensive researches focused on
1
3

Application of Cu (II)‑Guanine Complexes Anchored on SBA‑15 and MCM‑41 as Eꢀcient…
the synthesis and applications of the modiꢂed mesoporous
EtO
O
OH
EtO Si
EtO
Cl
MCM-41 and SBA-15 [8, 20–23]. In this sense, MCM-41
and SBA-15 mesoporous silica with nano-sized channels,
high surface area and unique properties, such as great
diversity in surface functionalization, and thermal and
mechanical stability have been widely studied by vari-
ous groups [19, 24–30]. It is worth mentioning that the
channel surface of the MCM-41 and SBA-15 is covered
by hydroxyl groups which make it a suitable support for
anchoring metal complexes to form the heterogeneous
catalyst in the nanotechnology ꢂeld [21, 30]. These desir-
able properties led researchers to extensively apply them
in heterogeneous catalysts [31–34]. Recently, the develop-
ment of multi-component reactions, in which more than
two components are combined to form a product, is an
excellent tool in generating products in a single synthetic
operation [35–40] and these types of reactions are popu-
lar area of research in drug discovery, total synthesis and
bioconjugation [41–43]. During the past decade, synthesis
of nitrogen-containing heterocyclics phenazine derivatives
has become a popular ꢂeld for research and development.
Because they are one group of antibiotic agents which
have a broad spectrum of biological and pharmaceutical
activities, such as fungicidal, antimalarial, antiplatet, tryp-
anocidal, antiphrastic and antitumor, they can also act as
the main core of many natural and synthetic organic mate-
rials [44–46]. Accordingly, in the present work, we will
synthesize a number of these useful compounds. Guanine
O Si
O
Cl
OH
OH
n-hexane, 24 h, reflux
MCM-41
Or SBA-15
O
nPrCl-MCM-41
Or nPrCl-SBA-15
O
N
NH
NH2
N
HN
N
H
N
O
N
H
O Si
O
N
H
N
Toluene, 24 h, reflux
N , atmospher
guanine-MCM-41
Or guanine-SBA-15
2
Cu(NO
Ethanol, 20 h reflux
)
.6H
O
Cu
3
2
2
O
N
O
O
HN
O Si
N
N
N
Cu
Cu-guanine-MCM-41
Or Cu-guanine-SBA-15
Scheme 1 Synthesis of Cu-guanine-MCM-41 and Cu-guanine-
MCM-41 nanostructure
environmentally-friendly guanine supported into MCM-
41 and SBA-15 mesoporous nanoparticles (Cu-guanine-
MCM-41 and Cu-guanine-SBA-15). Besides, their anti-
microbial behaviors were investigated.
(
2-amino-1H-purin-6(9H)-one), which is a fused pyrimi-
dine-imidazole ring system with conjugated double bonds,
is one of the ꢂve main nucleobases found in DNA and
RNA. Several models of metal complexes in which the
metal ions binding to the guanine ring through carbonyl
oxygen O (6) or imidazolyl nitrogen, and N (7) position
of guanine have been reported (Fig. 1) [47–51]. In the
present work, an approach using solid-state chemistry was
used for a one-pot, two-steps, four-component reaction to
synthesize various functionalized benzo[c]pyrano[3,2-a]
phenazine and bis-benzo[c]pyrano[3,2-a]phenazine deriv-
atives via multi-component reaction catalyzed by new and
2 Experimental
2.1 Materials
Tetraethylorthosilicate (TEOS, 98%), cationic surfactant
cetyltrimethylammonium bromide (CTAB, 98%), guanine
(2-amino-1H-purin-6(9H)-one), Cu(II) nitrate hexahydrate
(Cu(NO ) ·6H O), solvents and other reagents that were
3
2
2
employed in this work were purchased from Aldrich, Merck
or Fluka chemical companies and used as received.
2.2 Preparation of Cu‑Guanine‑MCM‑41
MCM-41 mesoporous material was prepared via sol–gel
method [13]. For this purpose, 1 g of cationic surfactant,
hexadecyl-trimethylammonium bromide (CTAB), was added
to an aqueous solution containing 3.5 mL of NaOH (2 M)
and deionized water (480 mL) and then, stirred at 80 °C.
After dissolution of the surfactant, 5 mL tetraethylorthosili-
cate (TEOS) was slowly added into the mixture and reꢃuxed
Fig. 1 Guanine structure
1
3

M. Nikoorazm, M. Khanmoradi
Fig. 2 Small-angle XRD patterns of Cu-guanine-MCM-41
Fig. 4 TEM image of Cu-guanine-MCM-41 (a) and Cu-guanine-
SBA-15 (b)
reꢃuxed for 20 h. After completion of the reaction, the
product was ꢂltered and washed with ethanol several times.
The obtained solid catalyst was dried at room temperature
Fig. 3 Small-angle XRD patterns of Cu-guanine-SBA-15
(
Scheme 1).
2
.3 Synthesis of Cu‑Guanine‑SBA‑15
for 2 h. When the reaction was completed, the obtained
white solid was recovered by ꢂltration, washed with deion-
ized water and calcined at 823 K for 5 h with the rate of
In a typical experiment, Pluronic P123 (4 g) (surfactant tem-
plate) was dissolved in a solution of deionized water (30 mL)
containing 90 mL of HCl (2 M). The reaction mixture was
stirred at 35 °C for 5 h. Afterwards, 9.04 mL of the silica
precursor and tetraethylorthosilicate (TEOS) were added to
the mixture and stirring continued for another 20 h. Finally,
the white solid product was recovered by ꢂltration, washed
several times with deionized water and dried overnight at
−
1
2
°C min to remove the residual surfactant.
Continuously, 4.8 mL 3-chloropropyltriethoxysilane
(
4.8 g) was slowly added to a round-bottomed ꢃask contain-
ing the mixture of 4.8 g of MCM-41 and n-hexane (100 mL).
The reaction mixture was reꢃuxed for 24 h. After completion
of the reaction, the resulting mixture was ꢂltered, washed
with n-hexane and dried under vacuum [13].
1
00 °C. The white powder was calcinated at 823 K for 5 h
The obtained nPrcl-MCM-41 (0.5 g) and guanine
−
1
at a rate of 2 °C min to remove the template and produce
the pure siliceous SBA-15 material [21]. In order to func-
tionalize mesoporous SBA-15, the obtained pure SBA-15
(
2-amino-1H-purin-6(9H)-one) (1.2 mmol, 0.181 g) were
dispersed in Toluene (25 mL) and the reaction mixture was
reꢃuxed at 120 °C under nitrogen atmosphere for 24 h. After
cooling the solution to room temperature, the ꢂnal white
product was ꢂltered, washed with ethanol and dried in a
desiccator under vacuum to obtain the pure guanine-func-
tionalized mesoporous MCM-41.
(
1 g) with 3-chloropropyltriethoxysilane (nPrCl) (1.5 mL)
was reꢃuxed in n-hexane (20 mL) for 24 h. After the com-
pletion of the reaction, the resulting mixture was ꢂltered,
washed with n-hexane, dried under vacuum and denoted as
nPrCl-SBA-15 [21].
Finally, to prepare the catalyst, the mixture containing
the obtained guanine-MCM-41 (0.5 g) and Cu (NO ) ·6H O
Guanine-SBA-15 was prepared by the reaction of nPrcl-
SBA-15 (0.5 g) and guanine (2-amino-1H-purin-6(9H)-
one) (1.2 mmol, 0.181 g) in toluene (25 mL) under reꢃux
3
2
2
(
1.4 mmol, 0.34 g) was added to ethanol (25 mL) and
1
3

Application of Cu (II)‑Guanine Complexes Anchored on SBA‑15 and MCM‑41 as Eꢀcient…
Fig. 5 SEM images of Cu-guanine-MCM-41 (a) and Cu-guanine-SBA-15 (b)
Fig. 6 Adsorption/desorption isotherm Cu-guanine-MCM-41
Fig. 7 Adsorption/desorption isotherm Cu-guanine-SBA-15
condition at 120 °C under nitrogen atmosphere for 24 h. The
resulting sample was named as guanine-SBA-15.
2
5 mL of round-bottom ꢃask containing PEG (4 mL) and
resulting mixture was heated to 120 °C under stirring as long
as compound (a) was formed (about 10 min). Subsequently,
diꢁerent aromatic aldehydes (1 mmol) and alkylmalonates
The guanine-SBA-15 (0.5 g) in ethanol with Cu
(
NO ) ·6H O (1.4 mmol, 0.34 g) under the reꢃux condi-
3 2 2
tions for 20 h, led to the formation of Cu-guanine-SBA-15
Scheme 1).
(
1.5 mmol) (1:1.5 ratios) were added to the reaction mixture
(
and heated further for the times illustrated in Tables 2 and
. After completion of the reaction (monitored by TLC),
3
2
.4 General Procedure for the Synthesis of Benzo[c]
pyrano[3,2‑a]phenazine and bis‑benzo[c]
pyrano[3,2‑a]phenazine Derivatives
the organic layer was separated from the reaction mixture
using the separating funnel. After the evaporation of ethyl
acetate, the product was obtained and recrystallized from
hot ethanol.
To synthesize phenazines, 2-hydroxy-1,4-naphthoquinone
1 mmol) and 1,2-diamines (1 mmol) were charged into a
(
1
3

M. Nikoorazm, M. Khanmoradi
Table 1 Surface properties
of Cu-guanine-MCM-41 and
Cu-guanine-SBA-15
SBET (m2 g−1)
Pore vol. (cm3 g−1)
Sample
Pore diam. (nm)
Cu-guanine-MCM-41
Cu-guanine-SBA-15
739.68
164.99
2.654
5.667
0.4908
0.2338
exhibited three well-resolved peaks which were indexed to
(
d
) along with two additional peaks (d and d ), indi-
100 110 200
cating the characteristic of typical regular hexagonal sym-
metry mesostructure [21, 26]. In the low-angle XRD pattern
of Cu-guanine-MCM-41 (Fig. 2) and Cu-guanine-SBA-15
(
Fig. 3). These peaks became weaker and shifted to lower
angle and only a weaker XRD peak appeared at 2θ ≈ 2.48°
and 2θ ≈ 1.225° in Cu-guanine-MCM-41 and Cu-guanine-
SBA-15 XRD patterns respectively. Moreover, the other two
peaks which were not observed indicated the functionaliza-
tion of MCM-41 and SBA-15 hexagonal channels and the
successful formation of Cu complexes supported on these
silica nanoparticles.
3
.2 Scanning Electron Microscopy, Atomic
Absorption Spectroscopy and Transmission
Electron Microscopy
Fig. 8 TGA thermograms of Cu-guanine-MCM-41 and Cu-guanine-
SBA-15
The TEM (transmission electronic microscopy) micrograph
of Cu-guanine-MCM-41 (Fig. 4a) and Cu-guanine-SBA-15
3
Result and Discussion
(
Fig. 4b) clearly shows typical shapes of these materials
Scheme 1 illustrates the synthesis of Cu-guanine-MCM-41
and Cu-guanine-MCM-41 nanostructures. The X-ray
powder diꢁraction patterns of these catalysts were meas-
ured on a Philips diꢁractometer with Cu Kα radiation at
with nano size and a regular hexagonal array of mesoporous
channels.
Figure 5 shows the SEM images of Cu-guanine-MCM-41
(a) and Cu-guanine-SBA-15 (b) catalysts. Morphology of
Cu-guanine-MCM-41 and Cu-guanine-SBA-15 samples
consists of uniform spherical and cylindrical particles,
respectively [21, 26]. Besides, the particle sizes of both
catalysts were nanometer size. The Cu content in Cu-gua-
nine-MCM-41 and Cu-guanine-SBA-15 was determined by
atomic absorption spectroscopy (AAS) (in a NovAA 400p
Analyticaljena-Germany device). Based on these analyses,
the copper content in Cu (II)-guanine-MCM-41 and Cu-
4
0 kV and 30 mA. Fourier transform infrared (FT-IR)
spectra were examined by KBr pellets utilizing a VRTEX
0 model Bruker FT-IR spectrometer. Thermogravimetric
7
analyses (TGA) of the samples were carried out between
3
1
0 and 900 °C in air atmosphere with the heating rate of
−
1
0 °C min using Shimadzu DTG-60 automatic ther-
mal analyzer. Scanning electron microscopy (SEM) was
used to confirm the particle size and morphology by a
JEOLJEM-2010, on an accelerating voltage of 200 kV. Spe-
ciꢂc surface area of samples was examined by BET method
using BET instrument (NOVA 1000). The Cu content in the
catalysts was determined by atomic absorption spectroscopy
−
1
−1
guanine-SBA-15 was 0.27 mmol g and 0.22 mmol g ,
respectively.
3.3 N Adsorption–Desorption Isotherms
2
(
AAS) (in a NovAA 400p Analyticaljena-Germany device).
The transmission electron microscopy (TEM) images were
taken by a Philips CM10 microscope with operating voltage
at 200 kV.
N adsorption–desorption isotherms of Cu-guanine-
2
MCM-41 and Cu-guanine-SBA-15 which are illustrated in
Fig. 6 and 7 respectively, exhibit the type IV isotherms as
deꢂned by IUPAC for mesoporous material [30]. Pore vol-
ume, surface areas, and average pore size distribution of both
catalysts were calculated via the Brunauer–Emmett–Teller
(BET) and Barrett–Joyner–Halenda (BJH) models. The
obtained results are shown in Table 1. It was seen that when
the complex is loaded in MCM-41 and SBA-15, pore size,
3.1 X‑ray Diꢀraction
The XRD diffraction pattern of Cu-guanine-MCM-41
and Cu-guanine-SBA-15 are illustrated in Figs. 2 and 3
respectively. In the previous works, MCM-41 and SBA-15
1
3

Application of Cu (II)‑Guanine Complexes Anchored on SBA‑15 and MCM‑41 as Eꢀcient…
Fig. 9 The FT-IR spectra for
MCM-41 (a), nPrCl-MCM-41
(
b), guanine-MCM-41 (c) and
Cu-guanine-MCM-41 (d)
pore volume and surface areas of the supporting materials
are reduced [21, 26]. The reduction of these parameters in
Cu-guanine-MCM-41 and Cu-guanine-SBA-15 in compar-
ison to their substrates (MCM-41 and SBA-15) is due to
the incorporation of Cu nanoparticles in the framework of
MCM-41 and SBA-15 which indicates that the surface area,
pore size and pore volume values are closely related to the
loading of the complex. The cell parameter corresponding to
the distance between two-pore centers (a) and the wall thick-
ness (b) of Cu-guanine-MCM-41 and Cu-guanine-SBA-15
was estimated by the following equations, respectively.
Cu-guanine-MCM-41 shows three weight losses. The
ꢂrst mass loss in the range of 100–150 °C is attributed to
the removal of physically adsorbed water and the solvent
present inside the pores channels [52]. The second and the
third mass losses have about 23% and 11% weight losses
which occurred between 300 °C-400°C and 400–500 °C
can be typically attributed to the thermal decomposition
of the organically modiꢂed framework and silanol groups,
respectively.
As shown in Fig. 8, the TGA curve of Cu-guanine-
SBA-15 which shows the 3% weight loss below 200 °C, is
due to the removal of the physically adsorbed solvent and
surface hydroxyl groups, and the second and the third weight
losses (25% and 10%) which occurred between 200 and
600 °C, respectively, can be related to the decomposition of
functional groups chemisorbed onto the surface of SBA-15
nanoparticles [21].
3.4 Thermogravimetric Analysis
Figure 8 shows the TGA curve of Cu-guanine-MCM-41
and Cu-guanine-SBA-15. It is worth mentioning that
from room temperature to 800 °C, The TGA curve of
1
3

M. Nikoorazm, M. Khanmoradi
Fig. 10 The FT-IR spectra for
SBA-15 (a), nPrCl-SBA-15 (b),
guanine-SBA-15 (c) and Cu-
guanine-SBA-15 (d)
3
.5 FT‑IR Spectroscopy
the (C=N) present in the ligand to the lower frequency area
(
Fig. 9d [53–55].
The FT-IR spectra for MCM-41 (a) nPrCl-MCM-41 (b),
guanine-MCM-41 (c) and Cu-guanine-MCM-41 (d) are
shown in Fig. 9. MCM-41 spectrum shows a lot of bands.
The main absorbances of MCM-41 formation are asymmet-
ric stretching, symmetric stretching and bending Si–O–Si
The FT-IR spectra for SBA-15 (a) nPrCl-SBA-15 (b),
guanine-SBA-15 (c) and Cu-guanine-SBA-15 (d) are shown
in Fig. 10. Figure 10a which is related to SBA-15 shows
−
1
−1
the typical adsorption bands at 1082 cm , 807 cm , and
−
1
462 cm , which are attributed to the asymmetric Si–O–Si
stretch, symmetric Si–O–Si stretch and Si–O–Si bending
mode, respectively [52]. The hydrated silane group and
the bending vibration of surface hydroxide bands appear at
−
1
−1
vibrations at 1059, 962 cm and 454 cm , respectively
21, 52]. Moreover, the OH stretching band of silanol groups
[
−
1
appears at 3443 cm (Fig. 9a) [43]. In Fig. 9b, the appear-
−
1
−1
−1
ance of a peak at around 2928 cm (CH vibrations cor-
3439 cm and 1634 cm , respectively. In the Fig. 10b, the
functionalized SBA-15 with 3-chloropropyltriethoxysilane
was identiꢂed via the presence of the characteristic bands for
2
responding to the C–H stretching) indicated the function-
alization of MCM-41 with 3-chloropropyltriethoxysilane.
–
1
−1
In Fig. 9c, ν(C=N) 1673 and ν(aromatic C–C) 1588 cm
aliphatic C–H stretching vibrations at around 2935 cm . In
–
1
can be attributed to guanine ring. The Cu–ligand bond for-
mation is observed by shifting the absorption frequency of
Fig. 10c, ν(C=N) 1678 and ν(aromatic C–C) 1588 cm can
be attributed to the guanine ring (Fig. 10c). In Fig. 10d, it
was observed that the band corresponding to N–H stretching
1
3

Application of Cu (II)‑Guanine Complexes Anchored on SBA‑15 and MCM‑41 as Eꢀcient…
O
N
OHC
+
X
CN
CHO
X
+
CN
N
Ar
H
(a)
OH
N
N
N
H N
X
N
N
2
O
Ar
X
O
NH2
NH2
X
NH
2
O
N
(
c)
+
NH2
(b)
O
OH
X= CN, CO Et
2
O
Scheme 2 One-pot, domino, multicomponent synthesis of benzo[c]pyrano[3,2-a]phenazine (b), and bis-benzo[c]pyrano[3,2-a]phenazine (c)
derivatives in the presence of Cu-guanine-MCM-41 and Cu-guanine-SBA-15
Table 2 Optimization of
reaction conditions for the
preparation of 3-amino-1-(4-
bromo-phenyl)-1H-benzo[a]
pyrano [2,3-c]phenazine-2-
carbonitrile in the presence of
Cu-guanine-MCM-41
Yield (%)a
Entry
Catalyst
Amount of
Temperature (°C)
Solvent
Time (h)
catalyst (mg)
1
2
3
4
5
6
7
8
9
Guanine-MCM-41
30
30
40
50
40
40
40
40
40
40
40
0
120
120
120
120
Reꢃux
Reꢃux
100
120
120
PEG
PEG
PEG
PEG
10
5
5
Trace
54
89
90
NR
47
71
80
34
62
Cu-guanine-MCM-41
Cu-guanine-MCM-41
Cu-guanine-MCM-41
Cu-guanine-MCM-41
Cu-guanine-MCM-41
Cu-guanine-MCM-41
Cu-guanine-MCM-41
Cu-guanine-MCM-41
Cu-guanine-MCM-41
Cu-guanine-MCM-41
Cu-guanine-MCM-41
5
H O
10
10
5
5
5
5
5
24
2
EtOH
DMF
DMF
DMSO
PEG
PEG
PEG
1
1
1
0
1
2
100
80
120
41
Trace
aIsolated yield
−
1
vibrations (3102 cm ) is shifted to the higher frequency
3.6 Catalytic Study
−
1
(
3138 cm ) which can be due to the coordination of N
group of the guanine ring to the Cu metal [53–55].
The catalytic activity of Cu-guanine-MCM-41 for
the synthesis of benzo[c]pyrano[3,2-a]phenazine,
and bis-benzo[c]pyrano[3,2-a]phenazine derivatives
was examined by the condensation reaction between
1
3

M. Nikoorazm, M. Khanmoradi
Table 3 Optimization of
reaction conditions for the
preparation of 3-amino-1-(4-
bromo-phenyl)-1H-benzo[a]
pyrano [2,3-c] phenazine-2-
carbonitrile in the presence of
Cu-guanine-SBA-15
Yield (%)a
Entry
Catalyst
Solvent
Temperature (°C)
Amount of
Time (h)
catalyst (mg)
1
2
3
4
5
6
7
8
9
guanine-SBA-15
PEG
PEG
DMF
DMSO
120
120
120
120
Reꢃux
Reꢃux
110
100
130
40
40
40
40
40
40
40
40
40
45
50
35
14
5
5
Trace
80
63
40
NR
56
71
74
80
83
Cu-guanine-SBA-15
Cu-guanine-SBA-15
Cu-guanine-SBA-15
Cu-guanine-SBA-15
Cu-guanine-SBA-15
Cu-guanine-SBA-15
Cu-guanine-SBA-15
Cu-guanine-SBA-15
Cu-guanine-SBA-15
Cu-guanine-SBA-15
Cu-guanine-SBA-15
5
H O
10
10
5
5
5
5
5
5
2
EtOH
PEG
PEG
PEG
PEG
PEG
PEG
1
1
1
0
1
2
120
120
120
83
78
aIsolated yield
2
4
-hydroxynaphthalene-1,4-dione, benzene-1,2-diamine,
Moreover, to evaluate the role of Cu-guanine-SBA-15
for the synthesis of these products, the reaction between
2-hydroxynaphthalene-1, 4-dione (1 mmol), benzene-1,
2-diamine (1 mmol), 4-bromorobenzaldehyde (1 mmol) and
malononitrile (1.5 mmol) in the presence of Cu-guanine-
SBA-15 was selected as the model reaction. Thus, the opti-
mal conditions have been determined as seen in Table 3.
First, the reaction was examined in the presence of diꢁerent
-bromorobenzaldehyde and malononitrile (Scheme 2).
In this regard, the model reaction was examined in two
steps. First, 2-hydroxynaphthalene-1,4-dione (1 mmol) and
benzene-1,2-diamine (1 mmol) were simultaneously stirred
and heated until the orange solid was formed (after 10 min).
In the second step, 4-bromorobenzaldehyde (1 mmol) and
malononitrile (1.5 mmol) were added to the mixture under
the same conditions.
solvents (Table 3, entries 2–6). It was found that H O gave a
2
The above reaction was tested in various solvents, tem-
perature and amounts of the catalyst. The results are shown
in Table 2. It can be seen from the table that the reaction
did not proceed in water as solvent (Table 2, entry 5) and
among the other solvents, the best yields were obtained in
PEG (Table 2, entries 3, 4).
low yield of the product (Table 3, entry 5), whereas the best
results were obtained in PEG as the solvent (Table 3, entry
2). In the next step, the inꢃuence of the reaction tempera-
ture (Table 3, entries 7–9) and the amounts of Cu-guanine-
SBA-15 (Table 3, entries 10–12) were examined. As shown
in Table 3, the product yield increased at higher tempera-
tures and the catalyst concentration. But raising the amount
of the catalyst from 45 to 50 mg did not lead to a pronounced
increase in the conversion. The eꢁect of guanine-SBA-15
on the reaction progression was investigated and the results
in Table 3, entry 1 showed that in the presence of guanine-
SBA-15 no desirable product was detected even at higher
times (Table 3, entry 1). Therefore, the best reaction condi-
tions were obtained at 120 °C in the presence of 45 mg of
the catalyst (Table 3, entry 10).
In a further attempt to optimize the reaction condition, we
found that in the absence of the catalyst no desirable product
was detected in the second step of the reaction (Table 2,
entry 12). Besides, the eꢁect of guanine-MCM-41 on reac-
tion progression was investigated. The results in Table 2,
entry 1 showed that in the presence of guanine-MCM-41 no
desirable product was detected even at higher times (Table 2,
entry 1). In this sense, when 30 mg of the catalyst was added
into the reaction mixture, only 54% yield of the product was
achieved (Table 2, entry 2), while in the presence of 40 mg
Cu-guanine-MCM-41 or more, 89% or 90% yield of the
product was achieved (Table 2, entries 3, 4). Moreover, the
temperature had a great inꢃuence on the yield of the product
so that the reaction at lower temperature did not show much
progress(Table 2, entries 10, 11) and the reaction at 120 °C
had high conversion (Table 2, entry 3). Based on the above
observations, it was found that 40 mg Cu-guanine-MCM-41
in PEG as solvent at 120 °C is the best combination (Table 2,
entry 3).
After optimization, to explore the scope and eꢀciency of
the reaction, these catalytic systems were used for the syn-
thesis of various benzo[c]pyrano[3,2-a]phenazine (Table 4,
entries 1–11), and bis-benzo[c]pyrano[3,2-a]phenazine
derivatives in the presence of Cu-guanine-MCM-41 and Cu-
guanine-SBA-15 catalysts (Table 4, entries 12–14). Accord-
ingly, a wide range of substituted aldehydes with electron-
donating and electron-withdrawing groups were successfully
applied and, then, the corresponding products were obtained
in good to excellent yields. The obtained results are sum-
marized in Table 4. The yield of the reactions for aldehydes
1
3

Application of Cu (II)‑Guanine Complexes Anchored on SBA‑15 and MCM‑41 as Eꢀcient…
Table 4 One pot, domino, multi component synthesis of benzo[c]pyrano[3,2-a]phenazine (entries 1–11) and bis-benzo[c]pyrano[3,2-a]phena-
zine (entries 11–14) derivatives using Cu-guanine-MCM-41 (40 mg) and Cu-guanine-SBA-15 (45 mg) in PEG at 120 °C for 5 h
Entry
Product
Yield (%) (in the presence of Cu- Yield (%) (in the presence of
M.p. (°C) [Ref.]
285–286 [56]
guanine-MCM-41)a
89
Cu-guanine-SBA-15)
83
a
1
N
Br
N
O
CN
NH2
N
2
82
78
297–299 [56]
N
O
CN
NH2
N
3
4
84
79
80
76
281–284 [56]
283–285 [56]
N
NO2
O
CN
NH2
N
N
NO2
O
CN
NH2
5
6
75
80
78
70
293–295 [56]
287–289 [56]
N
CH3
N
O
CN
NH2
N
Cl
N
O
CN
NH2
1
3

M. Nikoorazm, M. Khanmoradi
Table 4 (continued)
Entry
Product
Yield (%) (in the presence of Cu- Yield (%) (in the presence of
M.p. (°C) [Ref.]
275–277 [57]
guanine-MCM-41)a
73
Cu-guanine-SBA-15)
69
a
7
N
OCH3
OCH3
N
O
CN
NH2
8
9
76
87
75
75
80
68
276–278 [57]
281–284 [57]
289–292 [57]
N
F
N
O
CN
NH2
N
N
NO2
O
CO Et
2
NH2
1
1
1
0
1
2
N
Cl
N
O
CO Et
2
NH2
89
75
85
63
>300 [58]
>300 [59]
N
CN
N
O
CN
NH2
N
H N
CO Et
N
2
2
O
O
N
N
EtO C
2
NH
2
c
1
3

Application of Cu (II)‑Guanine Complexes Anchored on SBA‑15 and MCM‑41 as Eꢀcient…
Table 4 (continued)
Entry
Product
Yield (%) (in the presence of Cu- Yield (%) (in the presence of
M.p. (°C) [Ref.]
>300 [59]
guanine-MCM-41)a
82
Cu-guanine-SBA-15)
71
a
1
3
N
H N
CN
N
2
O
O
N
NC
NH2
N
c
1
4
74
70
>300 [59]
N
N
N
O
NC
H N
NC
NH2
2
O
N
c
aIsolated yield
with electron-donating groups is higher than aldehydes with
electron-withdrawing groups. The use of malononitrile leads
to higher yield as compared to ethyl cyanoacetate. Besides,
the catalytic activity of Cu-guanine-MCM-41 was slightly
higher than the Cu-guanine-SBA-15.
bacteria (Klebsiella pneumonia and Escherichia coli) were
selected. Accordingly, the bacteria were cultured on Mueller
Hinton agar medium for 24 h. From these cultured bacteria,
a suspension with dilution 0.5 McFarland (MHA) surface
of 7 cm diameter Petri dishes in Hinton broth medium was
prepared. A ꢂlter paper disk which is loaded with the sample
was placed on the surface of the MHA (incubated at room
temperature for 24 h) and, then, the inhibition zone was
measured in mm. The antimicrobial eꢁects of 3-amino-1-(4-
boromophenyl)-1H-benzo[a]pyrano[2,3-c]phenazine-2-car-
bonitrile (Table 4, entry 1) in comparison to tetracycline and
gentamicin antibiotic discs were tested and, then, the aver-
age antimicrobial activity of 3-amino-1-(4-boromophenyl)-
1H-benzo[a]pyrano[2,3-c]phenazine-2-carbonitrile was
determined in triplicates. It was observed that 3-amino-1-
(4-boromophenyl)-1H-benzo[a]pyrano[2,3-c]phenazine-
2-carbonitrile showed better eꢀcacy against the growth of
Staphylococcus aureus white 14 mm inhibition zone (this
parameter for tetracycline is 15 mm).
Scheme 3 depicts the possible reaction mechanism for the
synthesis of benzo[c]pyrano[3, 2-a]phenazines that is based
on the previously-reported reaction pathway [56, 57, 60, 61].
Initially, the intermediate A was formed from the Schiꢁ-base
condensation of benzene-1,2-diamine and 2-hydroxynaph-
thalene 1,4-dione in the presence of the catalyst. Sequen-
tially, a possible intermediate C was formed via Michael
addition of B with Benzo[a]phenazin-5-ol (intermediate B is
formed via the Knoevenagel condensation of aldehyde with
malononitrile in the presence of Cu-guanine-MCM-41 and
Cu-guanine-SBA-15 catalysts). In the next step, intermo-
lecular cyclization of intermediate C produced intermediate
D. Ultimately, a tautomeric proton shift produced the ꢂnal
benzo[c]pyrano[3, 2-a]phenazines product (Scheme 3).
Disc diꢁusion agar method was selected to investigate the
antimicrobial activity of 3-amino-1-(4-boromophenyl)-1H-
benzo[a]pyrano[2,3-c]phenazine-2-carbonitrile (1.00 µL). In
this sense, several types of microorganisms; including, two
types of gram-positive bacteria (Streptococcus agalactiae
and Staphylococcus aureus) and two types of gram-negative
AAS of the supernatant solution of the reaction mixture
and hot ꢂltration were performed to test if metal was leach-
ing out from the solid catalysts during the reactions. After
doing AAS experiment, we saw the absence of copper ions
in the liquid phase.
1
3

M. Nikoorazm, M. Khanmoradi
Cu
O
O
O
OH
OH
Ar
O
Tatomerization
(1)
O
Cu
O
H
CN
CN
+
Ar
H
NH2
Knoevenagel
condensation
OH
H
NH2
CN
(2)
Cu
Ar
CN
N
Ar
Schiff-base
condensation
N
CN
-
H O
2
O
NH2
CN
Ar
B
CN
3-amino-1H- benzo[c]pyrano[3, 2-a]phenazine
Tautomeric
proton shift
N
N
Cu
N
Ar
O
N
Ar
Michael
addition
HO
N
CN
NH
N
CN
N
A
Cu
OH
Benzo[a]phenazin-5-ol
Cu
D
C
Cyclization
Cu : Cu-guanine-MCM-41 Or Cu-guanine-SBA-15
Scheme 3 The proposed mechanism for the synthesis of benzo[c]pyrano[3, 2-a]phenazine derivatives in the presence of Cu-guanine-MCM-41
and Cu-guanine-SBA-15
Moreover, hot ꢂltration test was studied to know the het-
erogeneity and copper leaching from the catalysts. For this
purpose, we carried out a reaction (Table 4, entry 5) whose
optimum time was 5 h for each catalyst. At half the reac-
tion time (2.5 h), we stopped the reaction and separated the
catalysts (in this step, 50% and 54% of the products were
obtained for Cu-guanine-MCM-41 and Cu-guanine-SBA-15)
respectively and then the ꢂltrated solution was then permit-
ted to continue the reaction without a catalyst for another
2
.5 h. When the reactions completed, no improvement was
revealed in conversion. These results conꢂrmed that the pre-
pared catalysts were truly heterogeneous.
The recyclability of Cu-guanine-MCM-41 and Cu-gua-
nine-SBA-15 was examined by the reaction of 2-hydrox-
ynaphthalene-1,4-dione (2 mmol) and benzene-1,2-diamine
Fig. 11 Reusability of Cu-guanine-MCM-41 (column a) and Cu-gua-
nine-SBA-15 (column b) nanocatalyst for the preparation of 3-amino-
1
-(4-bromophenyl)-1H-benzo[a]pyrano[2,3-c]phenazine-2-carboni-
(
(
2 mmol) in the first step and 4-bromorobenzaldehyde
2 mmol) and malononitrile (3 mmol) in the second step in
trile under optimized conditions
1
3

Application of Cu (II)‑Guanine Complexes Anchored on SBA‑15 and MCM‑41 as Eꢀcient…
Table 5 Comparison of Cu-guanine-MCM-41 and Cu-guanine-SBA-15 in the synthesis of 3-Amino-1-(4-chloro-phenyl)-1H-benzo[a]pyrano
[
2,3-c]phenazine-2-carbonitrile with previously reported procedures
Entry Catalyst
Nature
Amount
Conditions
TON
Yield (%)
TOF (h−1
)
Ref
of catalyst
(
mol%)
1
2
3
4
5
6
Caꢁeine
DABCO
DABCO
HOAC
Homogenous 30
Homogenous 30
Homogenous 20
Homogenous 3500
Microwave heating (180 w)
EtOH, Reꢃux
Microwave irradiation
Microwave heating (120 °C)
PEG, 120 °C
3.00
3.03
4.55
0.025 89
74.04 80
70.707 70
90
91
91
3.00
0.606
13.65
0.152
14.81
14.14
[59]
[58]
[58]
[56]
This work
This work
Cu-guanine-MCM-41 Heterogenous 1.08
Cu-guanine-SBA-15 Heterogenous 0.99
PEG, 120 °C
Fig. 12 Small angle XRD patterns of recovered Cu-guanine-MCM-41
Fig. 14 TEM image of recovered Cu-guanine-MCM-41 (a) and
reused Cu-guanine-SBA-15 (b)
shown in Fig. 11, the boss catalysts have been reused up to
4
runs without any signiꢂcant loss of their catalytic activity.
To demonstrate the superiority of our catalysts to other
Fig. 13 Small angle XRD patterns of recovered Cu-guanine-SBA-15
reported catalysts for the synthesis of phenazine derivatives
(
Table 5), using para-chlorobenzaldehyde as the representa-
order to prepare 3-amino-1-(4-bromophenyl)-1H-benzo[a]
pyrano[2,3-c]phenazine-2-carbonitrile in the presence of
tive example, they were compared to the best of the well-
known data from the literature as outlined in Table 5. As it
can be seen in this Table, this new method was better than
the other methods in terms of the amount of catalyst, TOF,
TON and green condition for the synthesis of phenazine
compounds (A number of these catalysts have been synthe-
sized in microwave condition). Also, homogeneous catalysts
8
0 mg Cu-guanine-MCM-41 or 90 mg Cu-guanine-SBA-15
under the described conditions. After the completion of the
reaction, the reaction mixture was decanted in water and
ethyl acetate then, the catalyst was separated from the reac-
tion mixture by ꢂltration, washed with hot ethanol, dried in
air and, ꢂnally, reused for a subsequent similar reaction. As
1
3

M. Nikoorazm, M. Khanmoradi
Fig. 15 SEM images of recovered Cu-guanine-MCM-41 (a) and recovered Cu-guanine-SBA-15 (b)
Fig. 16 The FT-IR spectrum for
recovered Cu-guanine-SBA-15
were used in many reported methods which cannot be recov-
ered and reused.
and FT-IR analysis for characterization of recovered cata-
lysts were applied.
The XRD diꢁraction patterns of the recycled catalysts are
illustrated in Figs. 12 and 13, respectively. In this sense, it
was clariꢂed that the structure of the catalysts has not been
changed after recycling.
3.7 Characterization of the recycled catalysts
In order to examine the stability of Cu-guanine-MCM-41
and Cu-guanine-SBA-15 catalysts after recycling, the recy-
cled catalysts have been characterized by XRD, TEM, SEM,
Also, The TEM micrograph of recovered Cu-guanine-
MCM-41 and recovered Cu-guanine-SBA-15 are shown in
1
3

Application of Cu (II)‑Guanine Complexes Anchored on SBA‑15 and MCM‑41 as Eꢀcient…
Fig. 17 The FT-IR spectrum for
recovered Cu-guanine-SBA-15
Fig. 14a and b, respectively. nano size and a regular hexago-
nal array of mesoporous channels of the recovered catalysts
are conꢂrmed by TEM micrograph. This characterization
illustrated that the recovered catalysts are in good agreement
with the fresh catalysts.
4 Conclusions
The use of the environmentally-friendly, more active,
reusable and selective catalysts to produce compounds
that exhibit interesting pharmacological activities such
as phenazine motifs, is becoming increasingly more com-
mon. In the present work, a one-pot, two-step, four-com-
ponent synthesis of pyrano[3,2-a]phenazine derivatives as
antimicrobial compounds by the reaction of 2-hydroxy-
1,4-naphthoquinone, 1,2-diamines, different aromatic
aldehydes and alkylmalonates in the presence of Cu-gua-
nine-MCM-41 and Cu-guanine-SBA-15 was established.
The new catalysts are characterized by TGA, FT-IR spec-
troscopy, XRD, SEM, TEM, AAS and BET analyses. And
also, the recovered catalysts are characterized by FT-IR,
XRD, SEM and TEM analyses. Moreover, antimicrobial
activity of the product was investigated in which 3-amino-
1-(4-chlorophenyl)-1H-benzo[a]pyrano[2,3-c]phenazine-
2-carbonitrile showed efficient antimicrobial activity
against the growth of Staphylococcus aureus. The advan-
tages of this two-step protocol are: allowing the one-pot
four-component reaction to be controlled and avoiding the
separation of the intermediates. Using low loading of non-
toxic and reusable catalysts, high yields and easy puriꢂca-
tion are the other advantages of this procedure.
Also, to examine the stability of these catalysts after recy-
cling, the recycled Cu-guanine-MCM-41 and Cu-guanine-
SBA-15 catalysts have been characterized by SEM technique
as showed in Fig. 15a and b, respectively, in which the par-
ticles of the recovered catalysts were observed in homogene-
ous nano size and spherical morphology. SEM image of the
recycled catalyst is in good agreement with SEM image of the
fresh catalyst (Fig. 5a, b). Therefore, the size and shape of the
catalyst have not been changed after recycling.
FT-IR spectrums of the recycled catalyst are shown in
Figs. 16 and 17. The results which showed that a good agree-
ment can be observed for FT-IR of the fresh catalysts (Figs. 9d
and Fig. 10d) and the recycled catalysts illustrated high sta-
bility of Cu-guanine-MCM-41 and Cu-guanine-SBA-15 after
recycling.
These characterizations conꢂrmed that the recovered cata-
lysts are in good agreement with the fresh catalysts. These
characterizations are strong evidences for the high stabil-
ity of Cu-guanine-MCM-41 and Cu-guanine-SBA-15 after
recycling.
Acknowledgements This work was supported by the Iran National Sci-
ence Foundation and research facilities of Ilam University, Ilam, Iran.
1
3

M. Nikoorazm, M. Khanmoradi
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