Synthesis of some novel fluoro-substituted benzo[a]phenothiazines and their nucleosides as possible antimicrobial agents

Article abstract of DOI:10.1016/s0022-1139(99)00077-9

6-(2-Methoxy-5-methyl/2-methoxy-4-chloro-5-methyl anilino)-9-fluoro-5H-benzo-[a]phenothiazine-5-ones/thiones, 12H-benzo[a]phenothiazine-5-ols, 5-acetoxy-12H-benzo[a]phenothiazines, 5-methoxy-12H-benzo[a]phenothiazines and nucleosides viz; N-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-6-(2-methoxy-5-methyl/2-methoxy-4-chloro-5-methyl anilino)-9-fluoro-5-acetoxy benzo[a]phenothiazines and 9-fluoro-5-methoxy benzo[a]phenothiazines have been synthesized. All the synthesized compounds were tested for their antimicrobial activity. Structural elucidation has been made on the basis of elemental analysis IR, ¹H and ¹⁹F NMR studies.

Full text of DOI:10.1016/s0022-1139(99)00077-9

Journal of Fluorine Chemistry 98 (1999) 37±40
Synthesis of some novel ¯uoro-substituted benzo[a]phenothiazines
and their nucleosides as possible antimicrobial agents
Gajendra Singh Swati, A.K. Mishra, L. Prakash*
Department of Chemistry, University of Rajasthan, Jaipur 302004, India
Received 24 April 1998; accepted 1 April 1999
Abstract
6-(2-Methoxy-5-methyl/2-methoxy-4-chloro-5-methyl anilino)-9-¯uoro-5H-benzo-[a]phenothiazine-5-ones/thiones, 12H-benzo[a]pheno-
thiazine-5-ols, 5-acetoxy-12H-benzo[a]phenothiazines, 5-methoxy-12H-benzo[a]phenothiazines and nucleosides viz; N-(2,3,5-tri-O-
benzoyl-b-D-ribofuranosyl)-6-(2-methoxy-5-methyl/2-methoxy-4-chloro-5-methyl anilino)-9-¯uoro-5-acetoxy benzo[a]phenothiazines
and 9-¯uoro-5-methoxy benzo[a]phenothiazines have been synthesized. All the synthesized compounds were tested for their antimicrobial
1
activity. Structural elucidation has been made on the basis of elemental analysis IR, H and 19F NMR studies. # 1999 Elsevier Science
S.A. All rights reserved.
Keywords: Benzo[a]phenothiazines; Nucleosides; IR; 1H NMR; 19F NMR; Antimicrobial activity
1. Introduction
and on reduction by sodium dithionite in acetone±water
mixture gave corresponding 5-ols (V). Reductive acetylation
of III and acetylation of V in pyridine gave 5-acetoxy-12H-
benzo[a]phenothiazines (VI). Von treatment with dimethyl-
sulphate in alkaline media gave 5-methoxy-12H-benzo[a]-
phenothiazines (VII). A pasty mixture of VI/VII in toluene
on stirring with 2,3,5-tri-O-benzoyl-1-acetate-b-D-ribofura-
nose at 155±1608C for 10 h gave corresponding nucleosides
VIII and IX. (Scheme 1).
A thorough survey of literature reveals that the benzo[a]-
phenothiazine nucleus is an integral part of compounds used
as antibacterial [1], antifungal [2], antitumour [3], antic-
ancer [4] and antileukemic [5] agents. Although N-alkyl and
N-acyl derivatives of benzo[a]phenothiazines have been
reported as anticancer drugs [6], their nucleosides have
not been reported so far, therefore it was thought worthwhile
to undertake the synthesis of some new ¯uoro substituted
benzo[a]phenothiazines and their nucleosides viz; N-(2,3,5-
tri-O-benzoyl-b-D-ribofuranosyl)-6-(2-methoxy-5-methyl/
2-methoxy-4-chloro-5-methyl anilino)-9-¯uoro-5-acetoxy
benzo[a]phenothiazines (VIII) and 9-¯uoro-5-methoxy ben-
zo[a]phenothiazines (IX).
2,3-Dichloro-1,4-naphthoquinone on treatment with
2-methoxy-5-methyl/2-methoxy-4-chloro-5-methyl aniline
produces 2-(2-methoxy-5-methyl/2-methoxy-4-chloro-5-
methyl anilino)-3-chloro-1,4-naphthoquinone (II). II on
reaction with ¯uoro substituted zinc mercaptide (I) in dry
pyridine gave 6-(2-methoxy-5-methyl/2-methoxy-4-chloro-
5-methyl anilino)-9-¯uoro-5H-benzo[a]phenothiazines-5-
ones (III). III on treatment with P2S5 in pyridine afforded
6-(2-methoxy-5-methyl/2-methoxy-4-chloro-5-methyl ani-
lino)-9-¯uoro-5H benzo[a]phenothiazine-5-thiones (IV)
2. Spectroscopic analysis
All the synthesized compounds were characterized by IR,
1H NMR and 19F NMR spectral studies (see Table 1).
The IR spectra of compound III showed a >NH stretching
vibration in the region of 3110±3075 cm 1 as a weak band
and the carbonyl stretching band was observed at 1680±
1660 cm 1. Bands due to C=N and C±N stretching vibra-
1
tions were observed at 1570±1540 and 1335±1325 cm
respectively. Absence of bands for >C=O and appearance of
,
1
a new band in the region 1195±1160 cm due to >C=S
con®rm the thionation of III. Reduction of compound III into
V was con®rmed by the absence of carbonyl group fre-
quency and shifting of >NH absorption from 3110±3075 to
3345±3305 cm 1. The >NH stretching vibrations were
1
observed in the region of 3340±3265 cm in compounds
VI and VII. The carbonyl group was found to absorb
*Corresponding author. Tel.: +91-141-510-306.
0022-1139/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 9 9 ) 0 0 0 7 7 - 9

38
G.S. Swati et al. / Journal of Fluorine Chemistry 98 (1999) 37±40
3. Antimicrobial activity
All the synthesized compounds were screened for their
antimicrobial activity at conc. 100 mg/disc in agar media
following the method of Varma and Nobles [7] (see
Table 2). A sterile ®lter disc (5 mm diameter) saturated
with the solution of test compounds in CHCl3/DMSO, was
placed on media. Streptomycin and Mycostatin were used as
reference compounds while testing antibacterial and anti-
fungal activity, respectively.
All the compounds were found to be moderately active
against tested microorganisms E. coli, S. aureus (bacteria)
and A. niger, A. ¯avus, C. lunata (fungi) but 5-acetyl
derivatives and the nucleosides were found to be signi®-
cantly active.
4. Experimental
Melting points were determined in sealed, evacuated
capillary tubes and are uncorrected. IR spectra were
recorded on a NICOLET MEGNA FT-IR 550 spectrometer
1
in KBr discs and H NMR in CDCl3 on a Jeol FX 90Q
(90 MHz) spectrometer using TMS as an internal standard
(chemical shift in ꢀ ppm). The purities of the compounds
were checked by TLC using silica gel ``G'' as adsorbent,
visualization was accomplished by UV light or iodine.
4.1. Synthesis of 2-(2-methoxy-5-methyl/2-methoxy-4-
chloro-5-methyl anilino)-3-chloro-1,4-
naphthoquinone (II)
Compound II was synthesized by reported methods
[8].
Scheme 1.
4.2. Synthesis of 6-(2-methoxy-5-methyl/2-methoxy-4-
chloro-5-methyl anilino)-9-fluoro-5H-
benzo[a]phenothiazine-5-ones (III)
strongly at 1740±1690 cm 1 in compounds VI, VIII and IX.
The C±F absorption was observed in the region 1245±
1
1215 cm
.
A
mixture of 2-(2-methoxy-5-methyl/2-methoxy-4-
In 1H NMR a complex multiplet of aromatic protons was
observed in the region of ꢀ 6.65±8.29 ppm. The protons of ±
OCH3 and ±CH3 groups appeared as sharp singlets at ꢀ
3.92±4.06 and ꢀ 1.96±2.32 ppm, respectively. The >NH
proton of the anilino group was observed at ꢀ 5.90±
6.40 ppm (in most of the cases it was found to be merged
with aromatic protons) whereas the >NH proton of phe-
nothiazine ring was observed at ꢀ 8.9±9.20 ppm. The
absence of a peak of >NH proton of phenothiazine ring
in compounds VIII and IX con®rm the ribosylation at this
position. Aromatic protons and the protons of sugar moiety
in nucleosides were found to be shifted slightly down®eld as
compared to protons of VI, VII and the free sugar.
chloro-5-methyl anilino)-3-chloro-1,4-naphthoquinone II
(0.01 mol), zinc mercaptide of 5-¯uoro-2-amino benze-
nethiol I (0.005 mol) and dry pyridine (50 ml) was re¯uxed
for 3 h. An equal volume (50 ml) of methanol was added
and the mixture was chilled. The solid thus obtained was
®ltered, washed with ethanol, 5% hydrochloric acid, dried
and then recrystallized from benzene±petroleum ether (60±
808C).
4.3. Synthesis of 6-(2-methoxy-5-methyl/2-methoxy-4-
chloro-5-methyl anilino)-9-fluoro-5H-
benzo[a]phenothiazine-5-thiones (IV)
In the 19F NMR spectra, a characteristic signal was
observed in the region of ꢀ 109.43 to 113.78 ppm
assigned to the ¯uorine atom on the phenyl ring.
A mixture of III (0.01 mol) and P2S5 (0.01 mol) in 25 ml
of dry pyridine was stirred at 1308C under a nitrogen

G.S. Swati et al. / Journal of Fluorine Chemistry 98 (1999) 37±40
39
Table 1
Characterization and analytical data of the compounds synthesized
Compounds
R
Molecular
formula
Melting
point (8C)
Yield (%)
Elemental analysis percent found (calculated)
C
H
N
S
IIIa
H
C
C
C
C
C
C
C
C
C
C
C
C
C
C
24H17N2O2SF
24H16N2O2SFCl
24H17N2OS2F
24H16N2OS2FCl
24H19N2O2SF
24H18N2O2SFCl
26H21N2O3SF
26H20N2O3SFCl
25H21O2N2SF
25H20O2N2SFCl
52H41O10N2SF
52H40O10N2SFCl
51H41O9N2SF
51H40O9N2SFCl
178
160
148
156
145
158
125
115
135
139
105
118
138
147
78
72
67
69
72
76
62
67
69
71
66
72
63
65
69.27
(69.23)
63.95
4.13
6.71
7.65
(4.09)
3.38
(6.73)
6.17
(7.69)
7.08
IIIb
IVa
Cl
H
(63.93)
66.73
(3.55)
3.98
(6.21)
6.42
(7.10)
14.75
(14.81)
13.67
(13.71)
7.61
(66.67)
61.78
(3.93)
3.45
(6.48)
5.96
IVb
Va
Cl
H
(61.73)
68.93
(3.43)
4.57
(6.00)
6.68
(68.90)
63.68
(4.54)
3.99
(6.70)
6.18
(7.65)
7.01
Vb
Cl
H
(63.65)
63.85
(3.98)
4.59
(6.19)
6.03
(7.07)
6.92
VIa
VIb
VIIa
VIIb
VIIIa
VIIIb
IXa
IXb
(63.83)
63.39
(4.56)
4.10
(6.09)
5.63
(6.96)
6.49
Cl
H
(63.35)
72.25
(4.06)
4.89
(5.68)
6.41
(6.50)
7.36
(72.22)
64.35
(4.86)
4.37
(6.48)
5.95
(7.41)
6.82
Cl
H
(64.31)
69.09
(4.29)
4.58
(6.00)
3.07
(6.86)
3.51
(69.03)
69.91
(4.53)
4.73
(3.10)
3.17
(3.54)
3.63
Cl
H
(69.86)
66.65
(4.68)
4.29
(3.20)
2.95
(3.65)
3.39
(66.63)
67.27
(4.27)
4.42
(2.99)
3.01
(3.42)
3.47
Cl
(67.21)
(4.39)
(3.07)
(3.51)
atmosphere for 12 h. After completion of reaction, the
solution was cooled and poured into a solution of NaCl
(15 gm) in water (60 ml) at below 58C. The suspension was
stirred for a further 1 h. The precipitate thus obtained was
®ltered, washed with H2O and 5% HCl, dried and recrys-
tallized from benzene.
4.4. Synthesis of 6-(2-methoxy-5-methyl/2-methoxy-4-
chloro-5-methyl anilino)-9-fluoro-12H-
benzo[a]phenothiazine-5-ols (V)
A mixture of III (0.003 mol) and sodium dithionite
(0.006 mol) in water (4 ml) and acetone (40 ml) was
Table 2
Antimicrobial activity of synthesized compounds, zone of growth inhibition (mm) (activity index)a
Compounds
Escherichia coli
(Gram ‡ve)
Staphylococcus aureus
(Gram ve)
Aspergillus
flavus
Aspergillus
niger
Curvularia
lunata
IIIa
9.1 (1.04)
8.7 (1.00)
9.6 (1.10)
10.0 (1.15)
7.2 (0.84)
8.2 (0.94)
10.2 (1.17)
10.5 (1.21)
8.9 (1.02)
8.1 (0.93)
10.3 (1.18)
10.1 (1.16)
10.7 (1.23)
10.4 (1.20)
8.3 (1.04)
7.0 (0.88)
7.8 (0.98)
8.4 (1.05)
7.9 (0.99)
7.3 (0.91)
9.7 (1.21)
10.1 (1.26)
8.0 (1.00)
8.6 (1.08)
10.1 (1.26)
10.6 (1.32)
10.2 (1.27)
9.9 (1.24)
7.5 (0.81)
8.1 (0.88)
8.8 (0.96)
7.6 (0.82)
8.2 (0.89)
9.2 (1.00)
9.8 (1.06)
10.1 (1.09)
8.1 (0.88)
8.6 (0.93)
10.8 (1.17)
9.6 (1.04)
9.9 (1.08)
10.5 (1.14)
7.8 (0.82)
9.5 (1.00)
9.0 (0.95)
9.2 (0.97)
7.8 (0.82)
7.2 (0.76)
10.2 (1.07)
9.9 (1.04)
7.6 (0.80)
7.3 (0.77)
10.7 (1.13)
10.3 (1.08)
10.1 (1.06)
10.0 (1.05)
8.7 (0.97)
8.2 (0.91)
9.0 (1.00)
9.2 (1.02)
7.8 (0.87)
7.6 (0.84)
9.7 (1.07)
9.5 (1.05)
8.1 (0.90)
8.3 (0.92)
10.1 (1.12)
10.5 (1.16)
10.3 (1.14)
10.8 (1.20)
IIIb
IVa
IVb
Va
Vb
VIa
VIb
VIIa
VIIb
VIIIa
VIIIb
IXa
IXb
a Activity indexˆZone of growth inhibition of sample/Zone of growth inhibition of standard.

40
G.S. Swati et al. / Journal of Fluorine Chemistry 98 (1999) 37±40
re¯uxed for 2 h. The colourless solution thus obtained was
allowed to cool and poured into a very dilute solution of
sodium dithionite in ice cold water. The precipitate so
obtained was extracted by ether, dried and recrystallized
from benzene.
4.7. Synthesis of N-(2,3,5-tri-O-benzoyl-b-D-
ribofuranosyl-6-(2-methoxy-5-methyl/2-methoxy-4-
chloro-5-methyl anilino)-9-fluoro-5-methoxy/9-fluoro-
5-acetoxy-12H-benzo[a]phenothiazine (VIII) and
(IX)[9]
To a concentrated solution of VI/VII (0.002 mol)
in toluene, 2,3,5-tri-O-benzoyl-1-acetate-b-D-ribofuranose
(0.002 mol) was added and stirred in vacuo in an oil bath
(155±1608C) for 15 min.
4.5. Synthesis of 6-(2-methoxy-5-methyl/2-methoxy-4-
chloro-5-methyl anilino)-9-fluoro-5-acetoxy-12H-
benzo[a]phenothiazines (VI)
The vacuum was broken and the reaction was protected
from moisture using a guard tube. Stirring was further
continued for 10 h with application of vacuum for 5 min
at every hour. The melt was dissolved in methanol, boiled
for 10 min and cooled to room temperature. The precipitate
was ®ltered and the ®ltrate was evaporated to dryness. The
viscous residue was dissolved in ether, ®ltered, concentrated
and kept in a refrigerator overnight to get crystalline nucleo-
side.
4.5.1. Method a: by reductive acetylation of (III)
A mixture of III (0.001 mol), acetic anhydride (1.5 ml),
pyridine (0.2 ml) and Zn dust (0.001 mol), was stirred for
15 min at room temperature and then warmed on a water
bath for 15 min. The excess of zinc dust was removed by
®ltration and the ®ltrate was poured onto crushed ice. The
precipitate thus obtained was extracted from chloroform and
the solution was washed with saturated aqueous sodium
hydrogen carbonate and water. The desired product was
obtained by evaporation of solvent and was recrystallized
from benzene±petroleum ether (b.p. 60±808C).
Acknowledgements
The authors are thankful to the Head, Chemistry Depart-
ment, University of Rajasthan, Jaipur for providing labora-
tory facilities.
4.5.2. Method b: by acetylation of (V)
A mixture of V (0.001 mol), acetic anhydride (1.5 ml)
and pyridine (0.2 ml) was heated under re¯ux for 6 h. The
reaction mixture was cooled, ®ltered, dried and recrystal-
lized from benzene±petroleum ether (b.p. 60±808C).
References
[1] Merck Frosst Canada, Inc., Jpn Kokkai Tokkyo Koho JP 59 144 774
[84 144 774] (Cl. CO 7D 265/38) 18 August 1984, US Appl.
459 924, 21 January 1983; 49 pp; Chem. Abstr. 102 (1985) 6515.
[2] R. Sharma, R.D. Goyal, L. Prakash, Phosphorus, Sulfur and Silicon
80 (1993) 23±29.
4.6. Synthesis of 6-(2-methoxy-5-methyl/2-methoxy-4-
chloro-5-methyl anilino)-9-fluoro-5-methoxy-12H-
benzo[a]phenothiazines (VII)
[3] J.W. Foley, L. Cincotta, US 4 962 197 (Cl. 544-31; CO 7D 265/30) 9
October (1990) Appl. 157 214, 12 February (1988); 10 pp; Chem.
Abstr. 114 (1991) 185524.
A
mixture of V (0.001 mol), sodium dithionite
[4] D.C. Thang, E.H. Kossoff, P. Jacquignon, M. Dufour, Collect. Gzech.
Chem. Commun. 41 (4) (1976) 1212; Chem. Abstr. 85 (1976) 63007.
[5] N. Motohashi, H. Sakagami, K. Kamata, Y. Yamamoto, Anticancer
Res. 11 (5) (1991) 1933±1937; Chem. Abstr. 116 (1992) 165862.
[6] D.A. Shirley, T.G. Jackson, J. Med. Chem. 11 (1968) 622.
[7] R.S. Varma, W.L. Nobles, J. Pharm. Sci. 61 (1972) 112.
[8] J.P. Tiwari, R.L. Mital, Indian J. Chem. 17B (1979) 408±409.
[9] S. Shukla, L. Prakash, Indian J. Heterocyclic Chem. 5 (1995) 41.
(0.002 mol), 10% ethanolic potassium hydroxide solution
(12 ml) and dimethylsulphate (0.0015 mol) was re¯uxed
over a steam bath for 5 h and then the reaction contents
were poured onto crushed ice. The brown precipitate so
obtained was ®ltered, washed well with ethanol, dried and
recrystallized from benzene.