Utility of Suzuki-Miyaura cross-coupling reaction in synthesis of benzo[a]phenothiazine and benzo[a]phenoxazine derivatives and their antimicrobial screening

Article abstract of DOI:10.14233/ajchem.2015.19182

Palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of 6-chloro-5H-benzo[a]phenothiazin-5-one (1), 11-amino-6-chloro-9-thio-5H-naphtho[2,1-b]pyrimido[5,4-e][1,4]oxazin-5-one (2) and 6-chloro-5H-naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-5-one (3) with phenylboronic acid and 3-nitrophenylboronic acid were thoroughly investigated. The above intermediates were prepared by the reactions of 2-aminothiophenol, 4,5-diamino-6-hydroxylpyrimidine-2-thiol and 2-aminopyridin-3-ol each with 2,3-dichloronaphthalene-1,4-dione in a basic medium using benzene/DMF as the solvent. Thereafter, each was subjected to the Suzuki-Miyaura coupling reaction with phenylboronic acid and 3-nitrophenyl boronic acid, refluxing for 7-8 h at 110 °C using tris(dibenzylideneacetone)palladium(0), dicyclohexylphosphino-2',6'-dimethoxybiphenyl (SPhos), potassium phosphate and toluene as the catalyst, ligand, base and solvent correspondingly to yield the derivatives (1a-b), (2a-b) and (3a-b), respectively. Structures of the compounds were characterized using UV/visible spectrophotometry, FT-IR, ¹H NMR and ¹³C NMR spectroscopy and elemental analysis. The compounds were screened against six microorganisms, viz: Bacillus subtitis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Candida albicans and Aspergillus niger and were shown to have significant activity against some Gram-positive micro-organisms.

Full text of DOI:10.14233/ajchem.2015.19182

Asian Journal of Chemistry; Vol. 27, No. 12 (2015), 4467-4473
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.19182
Utility of Suzuki-Miyaura Cross-Coupling Reaction in Synthesis of Benzo[a]phenothiazine
and Benzo[a]phenoxazine Derivatives and their Antimicrobial Screening
1,*
1
2
JUDE I. AYOGU , BENJAMIN E. EZEMA and CHIDIMMA G. EZEMA
1Department of Pure and Industrial Chemistry, Faculty of Physical Sciences, Synthetic Organic Chemistry Unit, University of Nigeria, Nsukka
410002, Nigeria
2National Centre for Energy Research and Development, University of Nigeria, Nsukka, Nigeria
*Corresponding author: Tel: +234 8060542419; E-mail: jude.ayogu@unn.edu.ng
Received: 19 March 2015;
Accepted: 11 May 2015;
Published online: 29 August 2015;
AJC-17492
Palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of 6-chloro-5H-benzo[a]phenothiazin-5-one (1), 11-amino-6-chloro-9-
thio-5H-naphtho[2,1-b]pyrimido[5,4-e][1,4]oxazin-5-one (2) and 6-chloro-5H-naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-5-one (3) with
phenylboronic acid and 3-nitrophenylboronic acid were thoroughly investigated. The above intermediates were prepared by the reactions
of 2-aminothiophenol, 4,5-diamino-6-hydroxylpyrimidine-2-thiol and 2-aminopyridin-3-ol each with 2,3-dichloronaphthalene-1,4-dione
in a basic medium using benzene/DMF as the solvent. Thereafter, each was subjected to the Suzuki-Miyaura coupling reaction with
phenylboronic acid and 3-nitrophenyl boronic acid, refluxing for 7-8 h at 110 °C using tris(dibenzylideneacetone)palladium(0), dicyclohexyl-
phosphino-2',6'-dimethoxybiphenyl (SPhos), potassium phosphate and toluene as the catalyst, ligand, base and solvent correspondingly
to yield the derivatives (1a-b), (2a-b) and (3a-b), respectively. Structures of the compounds were characterized using UV/visible
spectrophotometry, FT-IR, 1H NMR and 13C NMR spectroscopy and elemental analysis. The compounds were screened against six micro-
organisms, viz: Bacillus subtitis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Candida albicans and Aspergillus
niger and were shown to have significant activity against some Gram-positive micro-organisms.
Keywords: Suzuki-Miyaura cross-coupling reaction, Benzo[a]phenothiazine, Benzo[a]phenoxazine, Antimicrobial screening.
Phenothiazine, one of the most frequently encountered
bioactive heterocycles in compounds of biological interest2
and its derivatives have been found to show tremendous bio-
logical activities such as antiparkinsonian3, anticonversant4,
INTRODUCTION
The emergence of new catalytic systems, utilizing pallad-
acyclic complexes, electron-rich trialkylphosphine ligands and
the bulky biphenyl-based phosphines developed by Buchwald
and co-workers1, has virtually transformed the trend in organic
synthesis. This has led to the development of some novel
compounds from unreactive aryl and heteroaryl chlorides that
exhibit strong actions against drug-resistant microbes and other
potentials. However, the applications of phenothiazine (1) and
phenoxazine (2) compounds and their derivatives in drug,
textile, agriculture and other related industries have long been
recognized.
antidepressant5, neuroleptic6, anti-inflamatory7-9, antimalarial10-12
,
antipsychotic13-15, antimicrobial16,17, anti-tubercular18-21, anti-
tumor22,23, antihistaminic24,25, analgesic26,prion disease drug27.
In textile, paint and plastic industries, they are used as dyes
and pigments28 and in agricultural industries as insecticides29.
In petroleum industries, they are used as antioxidants in
lubricants and fuels30. It has been observed that some
phenothiazines inhibit intracellular replication of viruses
including human immunodeficiency viruses (HIV)31. On the
other hand, some have been reported to exhibit significant
anticancer activity32,33
.
H
N
H
N
Similarly, phenoxazine and related compound have been
reported to possess various biological activities such as anti-
parkinsonian34,35, anticonvulsant36, antihistamic37, antihel-
matic38, antiviral36, antitumor39, anticancer40, antiparasitic41,
antibacterial41,42 and CNS depressant31. Other applications
include their use as antioxidants and biological stains, laser
j
j
a
a
c
i
i
b
b
c
h
S
O
h
2
1

4468 Ayogu et al.
Asian J. Chem.
dyes, indicators and especially as chromophoric compound43-49
in host guest artificial protonic antenna system.
to the crude product, stirred and filtered. The pure product
was obtained as dark orange solid upon recrystallization with
benzene-toluene after treatment with activated charcoal. yield
Although several synthetic routes to linear and angular
phenoxazines and phenothiazines have been reported, methods
are often not applicable for the preparation of a wide variety
of derivatives with excellent yields and good biological activity.
Therefore, it becomes imperative to investigate elegant and
facile reaction procedures to synthesize possible derivatives
with variety of functionalities.
= 7.18 g (86 %); m.p: dec. 290 °C; UV-visible (MeOH) λmax
:
220, 317, 414, 451,731; 13C NMR (DMSO, 700 MHz) δ: 178.0
(carbonyl carbon), 170.1, 168.0, 150.4, 147.1, 141.3, 134.6,
131.7, 131.5, 131.1, 130.8, 126.4, 125.9, 124.7 (sp2 hybridized
carbon atoms); IR (KBr, νmax, cm-1): 627, 569 (C-S-C str), 749
(C-Cl str), 1159 (C-N str, oxazine ring), 1266 (C-N str, aromatic
primary amine), 1454 (ArC=C str), 1553 (C=N str, pyrimidine
ring), 1647 (C=O str), 2354 (S-H str, thiol), 3395 cm-1 (N-H
str, amine). Anal. cald. for C14H7N4O2SCl:C 50.79, H 2.12, Cl
10.73, N 16.93, O 9.68, S 9.68; Found: C 51.02, H 2.01, Cl
10.79, N 16.70, S 9.68.
EXPERIMENTAL
All chemicals used were of laboratory grade (Sigma-
Aldrich). The melting points were determined with a Fischer
John’s apparatus and were uncorrected. UV/visible spectra
were recorded on UV-2500PC series spectrophotometer using
matched 1 cm quartz cells. The IR spectra (cm-1) were recorded
on 8400S FT-IR spectrometer using KBr discs (at NARICT,
ZARIA). The 1H NMR and 13C NMR were scanned at University
of Newcastle, United Kingdom on a Jeol FX 90Q spectrometer
using TMS as internal standard (chemical shift in δ). Elemental
analysis was carried on CHN rapid analyzer and the antimicrobial
screening was done at the Faculty of Pharmaceutical Sciences,
University of Nigeria, Nsukka, Nigeria.
6-Chloro-5H-benzo[a]phenothiazin-5-one (1): To a
mixture of 2-aminothiophenol (4 g, 32 mmol) and anhydrous
sodium trioxocarbonate (IV) (3.3 g, 31 mmol) in a 250 mL
two-necked flask equipped with magnetic stirrer, thermometer
and reflux condenser, was added a solution of benzene (100
mL) and DMF (10 mL). The mixture was boiled for 1 h and
thereafter, 2,3-dichloro-1,4-naphthoquinone (7.26 g, 32 mmol)
was added and the entire solution refluxed with continuous
stirring for more 7 h at 78-80 °C. Then, the solvent was distilled
off and the slurry poured into water and stirred for 20 min to
dissolve the inorganic materials. It was left overnight, filtered
and recrystallized from methanol-acetone mixture to obtain a
purple microcrystalline powder of 1 (8.5 g, 85 % yield). m.p.
234 °C; UV-V (MeOH) λmax (nm) log(ε): 210 (1.978), 221
(1.4779), 228 (1.2517), 234 (1.3543), 247 (0.2255), 255
(0.5149), 261 (1.4326), 266 (1.2138), 289 (2.3308), 314
(2.3640), 379 (2.3041), 491 (2.2271); 13C NMR (DMSO, 700
MHz) δ: 178.0 (carbonyl carbon), 164.6, 149.0, 138.0, 136.3,
134.6, 131.1, 131.5, 130.2, 129.5, 127.5, 126.4, 124.7, 121.1,
116.5; IR (KBr, νmax, cm-1): 582, 651(C-S str), 752 (C-Cl str),
880 (C-H out-of-plane bend), 1141, 1084 (arom. in-plane C-H
bend), 1297 (C-O str), 1472 (C=C str, aromatic), 1628 (C=N
str), 1732 (C=O str), 3390, 3623 cm-1 (>NH str); Anal. calcd.
for C16H8NOSCl: C 64.45, H 2.69, Cl 11.92, N 4.70, S 10.75;
Found: C 65.59, H 3.77, Cl 11.71, N 5.40, S 10.99.
6-Chloro-5H-naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-
5-one (3): By similar method, 6-chloro-5H-naphtho[2,1-
b]pyrido[2,3-e][1,4]oxazin-5-one was afforded as yellowish
brown solid using 2-aminopyridin-3-ol (2 g, 18 mmol) and
2,3-dichloro-1,4-naphthoquinone(3.45 g, 15 mmol) and after
recrystallization from acetone and treatment with activated
carbon. Yield = 4.47 g (81 %); m.p. 208-209 °C; UV-visible
(MeOH) λmax: 207, 219, 346, 443, 732; 13C NMR (DMSO,
700 MHz) δ: 177.2(carbonyl carbon), 150.2, 147.2, 146.0,
144.3, 140.6, 133.1, 132.9, 131.3, 129.8, 126.8, 126.2, 125.9,
124.5, 115.9; IR (KBr, νmax, cm-1): 780 (C-Cl str), 940 (C-H
out-of-plane bend) 1125, 1055 (arom. in-plane C-H bend),
1220, 1261 (C-O str), 1467 (C=C str, aromatic), 1555 (C=N
str, pyridine), 1645(C=N str, oxazine ring), 1703 (C=O str),
3101 cm-1 (C-H str, arom.); Anal. cald for C15H7N2O2Cl: C
63.68, H 2.48, Cl 12.56, N 9.91; Found: C 63.23, H 3.16, Cl
12.47, N 9.84.
General procedure for derivatives synthesis using
Suzuki Cross-coupling reaction: Dried and degassed toluene
(2 mL) was charged to a mixture of RX (1 mmol), RB(OH)2
(1.5 mmol), K3PO4 (0.58 g, 4 mmol), Pd2(dba)3 (1 mol % Pd)
and SPhos (Pd/L = 1:2) in round bottom flask (100 mL). The
mixture was flushed with nitrogen three times and stirred at
110 °C under nitrogen for 6-8 h. It was then cooled to room
temperature and partitioned with water (10 mL) and chloroform
(10 mL). The organic layer was separated, dried over sodium
tetraoxosulphate (VI), concentrated and purified by column
chromatography (10 % EtOAc/90 % petroleum ether eluent)
to provide the analytical pure title product.
Synthesis of derivatives of 6-chloro-5H-benzo[a]phenothiazin-
5-one (1)
6-Phenyl-5H-benzo[a]phenothiazin-5-one (1a):The above
method was employed using 6-chlorobenzo-5H-phenoxazin-
5-one (0.30 g, 1 mmol), boronic acid (1.5 mmol), Pd2(dba)3
(0.03 g, 1 mol %), S-Phos (0.06 g, 2 mol %), K3PO4 (0.64 g, 3
mmol) and product was afforded as crystalline reddish brown
solid.Yield = 146 mg (43 %); m.p. 220 °C. UV-visible (MeOH)
11-Amino-6-chloro-9-mercapto-5H-naphtho[2,1-
b]pyrimido[5,4-e][1,4]oxazin-5-one (2): To a mixture of 4,5-
diamino-5-hydroxyl-2-mercaptopyrimidine (2.00 g, 13 mmol)
and Na2CO3 (1.34 g, 13 mmol) in benzene (120 mL) and DMF
(10 mL) stirred at room temperature for 0.5 h in a 250 mL
two-necked flask equipped with magnetic stirrer, thermometer
and reflux condenser, was added 2,3-dichloro-1,4-naphtho-
quinone (2.87 g, 13 mmol). The entire reaction mixture was
refluxed in a water bath at 75-80 °C for about 6 h. Thereafter,
solvent was distilled off in vacuum and water (50 mL) added
λ
max: 206, 219, 318, 358, 371, 484, 737; 1H NMR (DMSO,
700 MHz) δ: 8.90-8.89 (1H, d), 8.21 -8.20 (2H, d), 7.94-7.80
(2H, t), 8.99-8.98 (2H,d), 7.67-7.65(2H, dd), 7.58- 7.56 (2H,
t), 7.52-7.49 (2H, m, aromatic protons), 7.36-7.35 (2H,d); 13C
NMR (DMSO, 700 MHz) δ (ppm): 178.1 (carbonyl carbon),
144.6, 137.9, 135.8, 134.9, 134.4, 133.0, 132.5, 132.2, 132.1,
131.9, 130.9, 129.7, 129.6, 129.1, 128.6, 126.0, 125.9, 125.7,

Vol. 27, No. 12 (2015) Suzuki-Miyaura Cross-Coupling Reaction in Synthesis of Benzo[a]phenothiazine and Benzo[a]phenoxazine Derivatives 4469
123.6; IR (KBr, νmax, cm-1): 582 (C-S str.), 741 (C-H def.),
1078 (aromatic C-H in-plane bend), 1338 (C-N str.), 1511,
1621 (C=N str., thiazine ring), 1728 cm-1 (C=O str.); Anal.
cald for C22H13NOS: C 77.78, H 3.83, N 4.12, S 9.43; Found:
C 78.02, H 4.25, N 4.24, S 9.56.
6-chloro-5H-naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-5-one
(0.28 g, 1 mmol), boronic acid (1.5 mmol), Pd2(dba)3 (0.03 g,
1 mol %), SPhos (0.06 g, 2 mol %), K3PO4 (0.64 g, 3 mmol)
and the product was afforded as black solid. Yield = 143 mg
1
(44 %); m.p: dec. 237 °C. H NMR (DMSO, 700 MHz) δ:
6-(3-Nitrophenyl)-5H-benzo[a]phenothiazin-5-one
(1b): The product was obtained as yellowish red solid. Yield
8.88-8.85 (1H, m); 8.53-8.51 (1H, dd,); 8.31-8.29 (1H, m);
7.78-7.75 (2H, m); 7.47-7.44 (5H, m); 7.40-7.37 (1H, m), 7.32-
7.29(1H, dd); 13C NMR (DMSO, 700 MHz) δ: 182.4 (Carbonyl
carbon), 151.7, 146.4, 144.6, 140.9, 135.6, 132.9, 132.5, 131.9,
130.6, 130.5, 130.3, 129.5, 128.4, 128.3, 128.0, 127.5, 127.2,
126.6, 125.5, 124.4, 120.6, 115.4,; IR (KBr, νmax, cm-1): 748
(C-H def. benzene ring with 4 adjacent H atoms), 877, 1076
(aromatic C-H out-of-plane bend), 1237 (C-O-C str.), 1386
(C-N str.), 1457 (C=C str., aromatic), 1714 cm-1 (C=O str.);Anal.
cald for C21H12N2O2: C 77.70, H 3.70, N 8.63; Found: C 78.20,
H 3.62, N 8.58.
= 173 mg (45 %); m.p 230-231 °C; UV-visible (MeOH) λmax
:
314, 370, 495; 1H NMR (DMSO, 700 MHz) δ: 8.99-8.97 (1H,
d); 8.90-8.89 (1H, d); 8.21-8.20 (1H, d); 7.99-7.98 (2H, d);
7.94-7.93 (2H, m); 7.90-7.89 (2H, d); 7.67-7.65 (2H, dd); 7.36-
7.35 (1H, d). 13C NMR (DMSO, 700 MHz) δ: 178.1 (carbonyl
carbon), 147.8, 146.8, 137.9, 135.8, 134.9, 134.4, 133.0, 132.5,
132.2, 132.1, 131.9, 130.9, 129.7, 129.6, 129.1, 126.0, 125.9,
123.1, 121.0; IR (KBr, νmax, cm-1): 755 (C-H bend), 1080
(aromatic ring str.), 1319 (C-N str.), 1504 (-NO2 str., aromatic),
1610 (C=N str., thiazine ring), 1722 (C=O str.), 3071 cm-1
(aromatics C-H str.); Anal. cald. for C22H12N2O3S: C 68.68, H
3.12, N 7.28, S 8.32; Found: C 68.92, H 3.55, N 7.40, S 8.45.
6-(3-Nitrophenyl)-5H-naphtho[2,1-b]pyrido[2,3-
e][1,4]oxazin-5-one (3b): As yellowish red solid;Yield = 143
mg (44 %); m.p: dec. above 270 °C; UV-visible (MeOH) λmax
:
342, 448, 738, 758; 1H NMR (DMSO, 700 MHz) δ: 8.88-8.85
(1H, m); 8.53-8.51 (1H, dd,); 8.31-8.29 (1H, m); 7.78-7.75
(2H, m); 7.47-7.44 (4H, m); 7.40-7.37(1H, m), 7.32-7.29(1H,
dd); 13C NMR (DMSO, 700 MHz) δ: 182.4 (carbonyl carbon),
151.7, 148.4, 145.9, 144.6, 140.9, 135.6, 132.9, 132.5, 131.9,
130.6, 130.5, 130.3, 129.5, 128.4, 128.3, 128.0, 127.5, 127.2,
126.6, 125.7, 125.5, 124.4, 120.6, 115.4; IR (KBr, νmax, cm-1):
751, 886 (aromatic C-H out-of-plane bend), 1123 (C-O str),
1264 (C-N str), 1443 (C=C str, aromatic), 1545 (-NO2 str,
aromatic), 1646 cm-1 (C=C str); Anal. cald for C21H11N3O4: C
68.23, H 2.98, N 11.37; Found: C 68.56, H 3.00, N 11.31.
Synthesis of derivatives of 11-amino-6-chloro-9-mercapto-
5H-naphtho[2,1-b]pyrimido[5,4-e][1,4]oxazin-5-one (2)
11-Amino-9-mercapto-6-phenyl-5H-naphtho[2,1-
b]pyrimido[5,4-e][1,4]oxazin-5-one (2a): 11-Amino-6-chloro-
9-mercapto-5H-naphtho[2,1-b]pyrimido[5,4-e][1,4]oxazin-5-
one (0.33 g, 1 mmol), boronic acid (1.5 mmol), Pd2(dba)3 (0.03
g, 1 mol %), SPhos (0.06 g, 2 mol %), K3PO4 (0.64 g, 3 mmol)
was uses and the product obtained as dark purple solid;Yields
= 190 mg (51 %); m.p: dec. 290 °C; UV-visible (MeOH) λmax
:
207, 223, 737, 764, 780; 1H NMR (DMSO, 700 MHz) δ: 12.15
(IH, s); 8.53 (2H, s); 8.03-8.00 (2H, d); 7.78- 7.69 (2H, m);
7.35-7.17 (5H, m); 13C NMR (DMSO, 700 MHz) δ: 170.1
(carbonyl carbon), 165.7, 150.4, 147.3, 136.4, 134.5, 132.5,
131.5, 131.1, 130.6, 128.9, 128.6, 126.4, 125.9, 124.7, 123.2;
IR (KBr, νmax, cm-1): 580 (C-S str), 618, 883 (C-H out-of-plane
bending), 919, 1076 (in-plane C-H bending vibr. of arom.
compd), 1275 (C-N str, aromatic amine), 1239 (C-O-C str),
1644 (C=N str), 1714 (C=O str), 2346 cm-1 (S-H str, thiol);
Anal. cald. for C20H12N4O2S: C 64.45, H 3.22, N 15.04, S 8.59;
Found: C 65.00, H 3.31, N 15.10, S 8.55.
RESULTS AND DISCUSSION
The intermediates, 1-3 were prepared by the condensation
of 2-aminothiophenol, 4,5-diamino-6-hydroxylpyrimidine-2-
thiol and 2-aminopyridin-3-ol each with 2,3-dichloronaph-
thalene-1,4-dione in a basic medium using benzene/DMF
as the solvent (Scheme-I). They were obtained as shiny red,
dark orange and yellowish brown solids respectively after re-
crystallization from toluene-benzene. The structures assigned
to the intermediates were consistent with their spectra and these
were confirmed by the microanalysis.
Synthesis of coupled products via SMC: The bulky
biphenyl-based phosphine developed by Buchwald and co-
workers was applied in successful synthesis of phenothiazine
and phenoxazine derivatives (1a-a, 2a-b and 3a-b). Like
Buchwald, we applied Pd2(dba)3 and SPhos (Pd/L = 1:2) to
form our catalytic system in combination with either of the
bases, Na2CO3 and K3PO4 and non-polar solvents (toluene).
We started our preliminary experiment by coupling 6-chloro-
benzo[a]phenothiazine 600 mg (1 mmol) with phenyl- and
3-nitrophenyl boronic acid 180 mg (1.5 mmol), 2 mol % of
Pd2(dba)3 (3 mg), 4 mol % of SPhos (6 mg) and 637 mg (3
mmol) K3PO4 and run the reaction in toluene at temperature
of 110 °C while the progress of reaction monitored on 1 h
bases by TLC. We observed product formation after 1 h with
trace conversion which increases with time. However, after
7 h there was no change in TLC spot of product even after the
reaction was left to run overnight. We obtained an isolated
11-Amino-9-mercapto-6-(3-nitrophenyl)-5H-naphtho-
[2,1-b]pyrimido[5,4-e][1,4]oxazin-5-one (2b): As yellowish
purple solid. Yields = 232 mg (60 %); m.p.: dec. above 300
°C; UV-visible (MeOH) λmax: 219, 285, 734; 1H NMR (DMSO,
700 MHz) δ: 12.15 (IH, s); 8.53 (2H, s); 8.14 (1H, d); 8.03-
8.00 (2H, d); 7.91 (1H,s); 7.78- 7.69 (2H, m); 7.66-7.56 (2H,
m) 7.35-7.17 (5H, m); 13C NMR (DMSO, 700 MHz) δ: 168.7,
158.0, 141.2 few peaks because of insolubility; IR (KBr, νmax
,
cm-1): 617 (C-S str), 747, 880 (aromatic out-of-plane bend),
1192 (aromatic C-H in-plane bend), 1267 (C-O-C str), 1375
(-NO2 str), 1460 (C=C str, aromatic) 1558 (C=C + C=N str), 3398
cm-1 (NH str, arom. prim. amine);Anal. cald for C20H11N5O4S:
C 57.50, H 2.64, N 16.77, S 7.67; Found: C 58.00, H 2.52, N
16.87, S 7.72.
Synthesis of derivatives of 6-chloro-5H-naphtho[2,1-
b]pyrido[2,3-e][1,4]oxazin-5-one (3)
6-Phenyl-5H-naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-
5-one (3a): The above general protocol was employed using

4470 Ayogu et al.
Asian J. Chem.
NH
2
N
O
N
HS
N
O
(2)
Cl
Na2CO3
C6H6/DMF, 6 h
NH
N
2
O
O
NH
2
N
Cl
Na2CO3
C6H6/DMF, 6 h
N
HS
OH
Cl
NH
2
S
(
O
Cl
SH
NH
N
2
1
)
Anhydrous Na2CO3
C6H6/DMF, 6 h
OH
N
O
N
O
Cl
(3)
Scheme-I
product yield of 53 % with a conversion of over 70 % after
work-up and purification by column chromatography on silica
gel using 5 % EtOAc/95 % petroleum ether solvent mixture
(Scheme-II).
The spectra and elemental analysis confirmed the identity
of the isolated product of each of the coupling reaction of
6-chloro-5H-phenothiazin-5-one (1) with phenyl- and 3-nitro-
phenyl boronic acids as 6-phenyl-5H-phenothiazin-5-one (1a)
and 6-(3-nitrophenyl)-5H-phenothiazin-5-one (1b) with mole-
cular formula C22H13NOS and C22H12N2O3S, respectively.
The structure assigned to the 6-phenyl-5H-benzo[a]pheno-
thiazine was consistent with the UV-visible, IR, 1H NMR and
13C NMR spectra. The structural assignment was confirmed by
the micro-analytical result of compound. Likewise, the struc-
tural assignment of the 6-(3-ntrophenyl)-5H-benzo[a]pheno-
thiazine was consistent with spectroscopic data.
The reaction ran without addition of the ligand practically
gave no conversion even when it was left over night (24 h).
Equally, the use of triphenylphosphine (PPh3) instead of SPhos
gave no conversion within the reaction time of 8 h and conver-
B(OH)2
N
N
S
Pd2(dba)3 (1 mol %),
SPhos (2 mol %)
+
R
K3PO4 (3 mmol),
toluene, 110 °C, 4 h
S
O
O
Cl
(a)
R
R
(a)
(
1a
H-benzo[a]phenothiazin-5-one
)
6-Phenyl-5
H
NO2
(
1b)
6-(3-Nitrophenyl)-5
H-benzo[a]phenothiazin-5-one
Scheme-II

Vol. 27, No. 12 (2015) Suzuki-Miyaura Cross-Coupling Reaction in Synthesis of Benzo[a]phenothiazine and Benzo[a]phenoxazine Derivatives 4471
sion of > 10 % when reaction was left over night (24 h).
Consquently, the ligand plays a crucial role in Suzuki-Miyaura
cross-coupling reactions. Besides the bulkiness which has been
corroborated to assist in generation of monoligated complex
ion (L1Pd) that was believed to undergo oxidative reaction more
readily than [PdL2] complex, the strong σ-electron donating
character of SPhos equally contributes to the ease with which
chloro-phenothiazine and phenoxazines were coupled to
boronic acids. We believed that the electron richness of SPhos
minimized the rate of potential binding of the heteroatoms in
the reactants and/or product to metal center thereby increasing
the rate of the reaction as well as yield of expected product.
We used slight excess of boronic acids to compensate for the
fractions that may be converted to side products such as
homocoupled products. While the use of Na2CO3 in place
K3PO4 gave lower product yields (24 %), K2CO3 gave compa-
rable yield to K3PO4 under the same conditions.It is also noticed
that the reactions performed without prior solvent degassing
gave comparable yield of products under these conditions.
Although we used only Pd2(dba)3 as palladium source. It is
also believed that other palladium species such as PdCl2,
Pd(NO)2 and Pd(OAc)2 together with SPhos will effect similar
transformations.
Each completed reaction was work-up by first extracting
the crude product from water with chloroform followed by
purification by column chromatography on silica gel.
The numbers of aromatic protons were accounted for in
the 1H NMR of the compounds prepared by Suzuki-Miyaura
cross-coupling and were found at 8.919-6.003 ppm. The
carbon nuclei were nicely represented in the carbon nuclear
magnetic spectra for 1a with the carbonyl carbon signals found
in a far distance low field from the others sp2 hybridized carbon
peaks except in 2a, 3a and 3b. The IR absorption maxima for
carbonyl functional groups in synthesized compounds were
in the range of 1725-1610 cm-1.
Furthermore the UV-visible spectra data of compounds
revealed bathochromic shifts as a result of increase in conjuga-
tion with compound 2a exhibiting the highest shifts. However,
results from elemental analysis of compounds undoubtedly
confirmed their molecular and structural formulae assignment.
Antimicrobial activity: All the synthesized compounds
were screened for their antimicrobial activity at concentration
10 mg/disc in agar media following the method of Bauer
et al.50. Using ciprofloxacin, an antibacterial and ketoconazole,
an antifungal activity as reference drugs, the compounds were
screened against six micro-organisms, viz: Bacillus subtitis,
Staphylococcus aureus, Pseudomonas aeruginosa, Escheri-
chia coli, Candida albicans and Aspergillus niger. This was
carried under sensitivity test and minimum inhibitory concen-
tration (MIC).
Consequently, the procedure was applied in coupling other
intermediates (2 and 3) to phenyl and 3-nitrophenyl boronic
acids, running the reaction for a maximum of 8 h under refux
(Schemes III and IV).
NH2
NH2
B(OH)2
N
Pd2(dba) (1 mol %),
SPhos (2 mol %)
N
O
N
N
+
R
K3PO4 (3 mmol),
Dioxane, 100 °C, 4 h
HS
N
O
O
HS
N
O
Cl
(b)
11-Amino-9-thio-6-phenyl-5
R
H
R
H
-naphtho[2,1-b]pyrimido[5,4-e][1,4]oxazin-5-one (2a)
NO2
11-Amino-9-thio-6-(3-nitrophenyl)-5
H
-naphtho[2,1-b]pyrimido[5,4-e][1,4]oxazin-5-one (2b)
Scheme-III
B(OH)
2
N
N
Pd2(dba)3 (1 mol %),
SPhos (2 mol %)
N
O
N
+
R
Na2CO3 (3 mmol),
Toluene, 110 °C, 6 h
O
R
O
O
Cl
(c)
-naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-5-one (3a)
R
6-Phenyl-5
H
H
6-(3-Ntrophenyl)-5
H
-naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-5-one (3b
Scheme-IV
)
NO
2

4472 Ayogu et al.
Asian J. Chem.
TABLE-1
ANTIMICROBIAL SENSITIVITY RESULTS OF SYNTHESIZED COMPOUNDS AND
THE VALUES ARE GIVEN IN INHIBITION ZONES DIAMETER (mm)
Gram-positive bacteria
B. subtilis S. aureus
10
Gram-negative bacteria
P. aeruginosa E. coli
11
Fungi Organism
Compound
C. albicans
A. niger
1
2
3
1a
1b
2a
2b
3a
3b
9
4
–
15
11
–
–
–
–
–
–
–
10
12
8
–
–
–
–
–
–
–
–
–
–
6
9
9
5
25
23
–
–
–
–
–
–
–
–
–
–
17
21
25
17
–
–
–
–
20
–
–
–
–
–
13
–
16
13
8
Ciprofloxacin
Ketoconazole
(–) Resistance
–
21
–
16
TABLE-2
MINIMUM INHIBITORY CONCENTRATION OF THE COMPOUNDS (mg/mL)
Gram-positive bacteria Gram-negative bacteria
Fungi Organism
Compound
B. subtilis
S. aureus
P. aeruginosa
E. coli
0.41635
0.13200
0.20200
–
C. albicans
A. niger
1
2
3
1a
1b
2a
0.17380
–
0.12020
0.15140
0.69960
0.46320
–
0.09120
–
–
–
0.08500
0.13000
–
0.06500
0.15000
0.01442
0.01567
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2b
3a
3b
0.02121
0.01716
0.01442
0.02120
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0.08385
0.10320
0.16770
–
–
0.02130
–
–
0.0323
–
Ciprofloxacin
Ketoconazole
0.06220
0.13560
Sensitivity test: The assay was carried out by applying
agar-well diffusion method51 using a concentration of 10 mg/
mL of each of the compounds as described in the experimental.
From the results (Table-1), the synthesized derivatives showed
substantial activity against Bacillus subtilis and E. coli only,
except compound 2a which is inactive against B. subtilis as
well as E. coli and compound 1a, 1b, 2a and 2b which are
inactive against E. coli. All the derivatives were found to be
insensitive to S. aureus, P. aeruginosa, C. albicans and A. niger.
In the same vein, the intermediates (1-3) are all sensitive to
the test organisms except 1 which is inactive to C. albicans;
and compound 2 and 3 that are insensitive to the Gram-positive
bacteria (Table-1).
Minimum inhibitory concentration (MIC) determination
result: Here, serial dilutionsof 5, 2.5, 1.25 and 0.625 mg/mL
of each of the sensitive compounds obtained from the sensi-
tivity test were used following the procedure outlined by Chemical
Laboratory Standards Institute (CLSI)52. Almost all the sensi-
tive synthesized phenothiazine and phenoxazine derivatives
were active against the microorganisms even at very low
concentrations following from the fact that the lower the MIC
values, the higher the activity. Compound 1a and 3b have the
lowest MIC value (0.01442 mg/mL) and hence, most activity
against B. subtilis (Table-2) when compared to the referent
drug. Similarly, activity against E. coli was much pronounced
in compound 3a followed by compound 3b and then the
intermediates. Intermediate 1 has no MIC values for C. albicans
since it is insensitive to the test organism. All the synthesized
compounds were insensitive to fungal organisms except the
intermediates. The intermediate, 1 has the stongest activity
against A. niger consequent on its lowest MIC value. However,
it has no activity against C. albicans. From the forgoing, it could
be inferred that the synthesized compounds can be used as
antibacteria against E. coli and B. subtilis since they have better
activity compared to the standard reference drugs (Table-2).
Conclusion
This study introduced new reactions for derivatization of
benzophenothiazine and benzophenoxazine rings. Palladium-
SPhos mediated Suzuki-Miyaura cross-coupling reaction was
developed as a facile and mild reaction procedure for functionali-
zation of the phenothiazines and phenoxazines in good to
excellent yields. The prepared compounds exhibited high
activities against Gram-positive bacteria (B. subtilis and E.
coli) and the activity was much pronounced for 6-phenyl-5H-
benzo[a]phenothiazin-5-one and 6-(3-nitrophenyl)-5H-
naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-5-one than the others.
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