Syntheses of 1,5-benzothiazepines-part XXXI: Syntheses and antimicrobial studies of 10-substituted-7-(monochlorophenyl/dichlorophenyl)-6H-6a,7-dihydro-6- phenyl[1]benzopyrano[3,4-c]-[1,5]benzothiazepines

Article abstract of DOI:10.1080/104265090517325

Two flavindogenides, 3-(2-chlorobenzylidene)-flavanone and 3-(2,4-dichlorobenzylidene)-flavanone reacted with six 5-substituted-2- aminobenzenethiols, the substituents being fluoro, chloro, bromo, methyl, methoxyl, and ethoxyl, to give respective 12 new compounds, 10-substituted-7-(2- chlorophenyl/2,4-dichlorophenyl)-6H-6a, 7-dihydro-6-phenyl[1]benzopyrano[3,4-c] [1,5]benzothiazepines (5a-l) in 60-70% yields. The products were characterized on the basis of microanalytical data for elements and IR, ¹H, and ¹³C NMR and mass spectral studies. All the synthesized compounds were evaluated for their antimicrobial activity against the bacteria, Escherichia coli and GFC, and the fungi, Aspergillus niger, Aspergillus flavus, and Curvularia lunata. Copyright Taylor & Francis Inc.

Full text of DOI:10.1080/104265090517325

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Phosphorus, Sulfur, and Silicon
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Syntheses of 1,5-
Benzothiazepines-Part XXXI:
Syntheses and Antimicrobial
Studies of 10-Substituted-7-
(monochlorophenyl/
dichlorophenyl)-6H-6a,7-
dihydro-6-
phenyl[1]benzopyrano[3,4-c]-
[1,5]benzothiazepines
Umesh C. Pant a , A. Dandia a , Hem Chandra a ,
Shweta Goyal a & Seema Pant b
a Department of Chemistry , University of Rajasthan
b L.B.S. Government P.G. College, Kotputli , Jaipur,
Rajasthan, 303108
Published online: 21 Dec 2010.
To cite this article: Umesh C. Pant , A. Dandia , Hem Chandra , Shweta
Goyal & Seema Pant (2005) Syntheses of 1,5-Benzothiazepines-Part XXXI:
Syntheses and Antimicrobial Studies of 10-Substituted-7- (monochlorophenyl/
dichlorophenyl)-6H-6a,7-dihydro-6-phenyl[1]benzopyrano[3,4-c]-
[1,5]benzothiazepines, Phosphorus, Sulfur, and Silicon and the Related Elements,
180:2, 559-571, DOI: 10.1080/104265090517325
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Phosphorus, Sulfur, and Silicon, 180:559–571, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/104265090517325
Syntheses of 1,5-Benzothiazepines-Part XXXI: Syntheses
and Antimicrobial Studies of 10-Substituted-7-
(monochlorophenyl/dichlorophenyl)-6H-6a,7-dihydro-6-
phenyl[1]benzopyrano[3,4-c]-[1,5]benzothiazepines
Umesh C. Pant
A. Dandia
Hem Chandra
Shweta Goyal
Department of Chemistry, University of Rajasthan
Seema Pant
L.B.S. Government P.G. College, Kotputli, 303108, Jaipur, Rajasthan
Two flavindogenides, 3-(2-chlorobenzylidene)-flavanone and 3-(2,4-dichloro-
benzylidene)-flavanone reacted with six 5-substituted-2-aminobenzenethiols, the
substituents being fluoro, chloro, bromo, methyl, methoxyl, and ethoxyl, to give re-
spective 12 new compounds, 10-substituted-7-(2-chlorophenyl/2,4-dichlorophenyl)-
6H-6a,7-dihydro-6-phenyl[1]benzopyrano[3,4−c][1,5]benzothiazepines (5a–l) in
60–70% yields. The products were characterized on the basis of microanalytical data
1
13
for elements and IR, H, and C NMR and mass spectral studies. All the synthe-
sized compounds were evaluated for their antimicrobial activity against the bacte-
ria, Escherichia coli and GFC, and the fungi, Aspergillus niger, Aspergillus flavus,
and Curvularia lunata.
Keywords α,β-unsaturated carbonyl; acidic; aminobenzene thiols; basic
INTRODUCTION
In continuation of our studies on the reactions of aminobenzenethi-
ols with α,β-unsaturated carbonyl compounds (i) in acidic medium-
ethanol/methanol containing glacial acetic acid;1,2 ethanol saturated
Received March 18, 2004; in final form December 17, 2004.
The paper was presented in Indian Science Congress at Chandigarh. Proc. 91st Ind.
Sc. Cong. Part III (Advance Abstracts) pp. 58, No. 73 (2004).
The authors gratefully acknowledge the financial assistance granted by the University
Grants Commission, New Delhi, and the Head of the Department of Chemistry for the
facility to work and the Central Drug Research Institute for providing Microanalysis and
Spectral data.
Address correspondence to Umesh C. Pant, Department of Chemistry, University of
Rajasthan, Jaipur 302004, India. E-mail: ucp212001@yahoo.co.in
559

560
U. C. Pant et al.
with hydrogen chloride gas;3 toluene containing trifluoroacetic acid4
(ii) in basic medium-pyridine;5 toluene containing piperidine6 and
(iii) in neutral medium-anhydrous toluene;7,8 o-xylene,9,10 we have car-
ried out the reactions of 5-substituted-2-aminobenzenethils with aryli-
dene flavanones in both acidic and basic media, i.e., (i) dry toluene
containing trifluoroacetic acid and (ii) dry toluene containing piperi-
dine. Toluene was chosen as a higher boiling solvent and trifluoroacetic
acid and piperidine were used to provide stronger acidic3 and basic6
medium, respectively. To study the effect of the acidic or basic catalyst
on the yields of the final products, the reactions of 5-substituted-2-
aminobenzenethiols(4a–f) with 3-(2-chlorophenyl/2,4-dichlorophenyl)
benzylidene flavanones (3a, b) have been studied in the presence of
acidic and basic catalyst. Chlorobenzylidene-flavanones, having one
and two chlorine atoms, have been specifically chosen for the reaction
with the expectation that they may exhibit antibacterial and/or antifun-
gal activity and to evaluate as to what extent the presence of chlorine
imparts antimicrobial activity and also to evaluate whether the change
in percentage of chlorine in the molecule would affect the antimicrobial
activity.
All the synthesised compounds 10 substituted-7-(monochlorophenyl/
dichlorophenyl)-6H-6a,7-dihydro-6-phenyl[1]benzopyrano[3,4-c]-[1,5]
benzothiazepines (5a–l) were, therefore, screened for their antimicro-
bial activity against bacteria Escherichia coli and GFC and fungus
Aspergillus flavus, Aspergillus niger, and C. lunata.
RESULTS AND DISCUSSION
Six 5-substituted-2-aminobenzenethiols11–15(4a–f), the substituents
being, F, Cl, Br, CH3, OCH3, and OC2H5, and arylidene flavanone16,17 (3)
were prepared in the laboratory by literature methods. The flavanone
(1) was reacted with two aldehydes, 2-chlorobenzaldehyde (2a) and 2,4-
dichlorobenzaldehyde (2b) by dissolving these in ethanol and passing
dry hydrogen chloride gas till the color of the reaction mixture turned
blackish red and kept overnight to afford the crude product. The solid
obtained was crystallized from dry ethanol to give flavindogenides, 3-(2-
chlorobenzylidene)-flavanone,16 (3a) and 3-(2,4-dichlorobenzylidene)-
flavanone17 (3b), respectively (Scheme 1).
Two flavindogenides, 3-(2-chlorobenzylidene)-flavanone (3a) and
3-(2,4-dichlorobenzylidene)-flavanone (3b) reacted with six 5-sub-
stituted-2-aminobenzenethiols (4a–f) in toluene with trifluoroacetic
acid as acidic and piperidine as basic catalyst to give the final prod-
ucts, 5a–l (Tables I & II) in 60–70% yields.

Syntheses of 1,5-Benzothiazepines
561
SCHEME 1

562
U. C. Pant et al.
TABLE I Physical Constants of 10-Substituted-7-(2-chlorophenyl)-
6H-6a,7-dihydro-6-phenyl[1]benzopyrano[3,4-c][1,5]benzothiazepines
(5a–f)
Elemental analysis
Yield (%)
Found (Calcd.) (%)
Compd.
no.
Mol. Formula
(Mol. Weight)
X
R M.P. (◦C) Rf
A
B
C
H
N
5a
5b
5c
5d
5e
5f
F
Cl 111–112 0.78 68 62
Cl 112–115 0.82 64 60
Cl 118–119 0.70 67 60
Cl 117–118 0.81 62 58
C28H19ClFNOS 71.32
4.15
2.95
(471.5)
28H19Cl2NOS
(488)
(71.26) (4.02) (2.96)
68.91 3.90 2.78
(68.85) (3.89) (2.86)
Cl
Br
C
C
28H19BrClNOS
(532.5)
—
—
2.55
(2.62)
2.82
(2.99)
2.98
CH3
C29H22ClNOS
(467.5)
—
—
OCH3 Cl 111–112 0.72 64 62
OC2H5 Cl 111–113 0.70 70 66
C29H22ClNO2S
(483.5)
72.10
4.68
(71.97) (4.55) (2.89)
C30H24ClO2S
(497.5)
—
—
2.90
(2.81)
Benzylidene flavanones have exocyclic α,β-unsaturation in conju-
gation with cyclic carbonyl group and would thus behave as α, β-
unsaturated carbonyl system. The compounds having α,β-unsaturated
carbonyl system have been reported to react with 2-aminobenzenethiols
in two steps, depending upon the reaction conditions.3,8,12–14,18–22
TABLE II Physical Constants of 10-Substituted-7-(2,4-
dichlorophenyl)-6H-6a,7-dihydro-6-phenyl[1]benzopyrano[3,4-c][1,5]
benzothiazepines(5g–l)
Yield
(%)
Elemental analysis
Found (Calcd.) (%)
Compd.
no.
M.P.
(◦C)
Mol. Formula
(Mol. Weight)
X
R
Rf
A
B
C
H
N
5g
5h
5i
F
2,4-Cl2 99–101 0.68 68 60 C28H18Cl2FNOS
—
—
2.68
(2.77)
2.50
(2.68)
2.34
(506)
Cl
Br
2,4-Cl2 109–110 0.71 66 61 C28H18Cl3NOS
—
—
—
—
(522.5)
2,4-Cl2 105–107 0.70 65 63 C28H18BrCl2NOS
(567)
2,4-Cl2 98–102 0.73 69 60 C29H21Cl2NOS
(501)
(2.47)
2.62
5j
CH3
69.43
4.36
(69.32) (4.21) (2.79)
67.26 4.21 2.58
(67.18) (4.08) (2.70)
67.84 4.44 2.53
(67.67) (4.35) (2.63)
5k
5l
OCH3 2,4-Cl2 108–110 0.72 66 58 C29H21Cl2NO2S
(517)
OC2H5 2,4-Cl2 102–103 0.74 68 60 C30H23Cl2NO2S
(532)
A = Acidic medium; B = Basic medium.

Syntheses of 1,5-Benzothiazepines
563
Studies by Stephens and Field20 show that when such reactions are
carried out in methanol containing a basic catalyst, a Michael adduct is
obtained as an intermediate which undergoes cyclization on boiling in
acidic medium, using glacial acetic acid, to give the final products. The
reactions, when carried out by Levai and Bognar,22,23 in high boiling sol-
vent like toluene without any catalyst yielded the intermediate which
cyclized on reacting further in acidic medium using glacial acetic acid.
They obtained22,23 the final products in a single step when the reactions
of chalcone and aminobenzenethiols were carried out in methanol con-
taining glacial acetic acid. Reid and Marx21 also obtained the products
in a single step when the reactions were carried out using methanol con-
taining hydrochloric acid. The spectral evidences are reported3,8,18–28 to
support the formation of the intermediate.
These observations indicate that at first, the intermediate, a Michael
adduct, is formed by the nucleophilic attack24–28 of the sulfhydryl
electrons1 of the thiol on the β-carbon of the α,β-unsaturated car-
bonyl system. Benzylidene flavanones, behaving as α,β-unsaturated
carbonyl systems, have electrophilic β-carbon atom, making it sus-
ceptible to nucleophilic attack by the sulfhydryl electrons of the
benzenethiol. In the basic medium, the abstraction of a proton by
the base increases the nucleophilicity of the sulfhyhydryl group,
resulting in its attack on the β-carbon atom of the arylidene
flavanone. We have carried out the reactions of 5-substituted-2-
aminobenzenethiols (4a–f) with substituted benzylidene flavanones
(3a, b) in toluene containing piperidine to obtain the final products, 10-
substituted-7-(monochlorophenyl/dichlorophenyl)-6H-6a, 7-dihydro-6-
phenyl[1]benzopyrano[3,4-c][1,5]benzothiazepines (5a–l) without the
isolation of the intermediate. From the study of analogous reactions, as
referred above,3,8,18–28 it is evident that the intermediates (Scheme 2),
are formed prior to the cyclized product.
In acidic medium, the protonation of the carbonyl group of the aryli-
dene flavanone renders β-carbon atom electrophilic, making it suscepti-
ble to nucleophilic attack by the sulfhydryl electrons of the thiol. Thus,
the reaction proceeds via the formation of Michael type adduct, lead-
ing to the formation of cyclized products (5a–l) by dehydrative cycliza-
tion. It is, thus, observed that the aminobenzenethiols react with α,β-
unsaturated carbonyl systems to give the final products in one step, by
concerted mechanism, in nearly equal yields (Tables I and II).
SPECTRAL STUDIES
In the IR spectra of the compounds, 5a–l, the absence of characteristic
carbonyl and amino group absorption signals around 1650–1685 cm1

564
U. C. Pant et al.
SCHEME 2
and 3400–3100 cm−1 respectively, show that the carbonyl and amino
groups are absent in the final products (5a–l). The presence of a strong
absorption signal in the range 1612–1602 cm−1 which is characteristic
for carbon nitrogen double bond indicate that the amino group of the
thiols and carbonyl group of 3-arylidine flavanones have reacted to form
carbon nitrogen double bond.

Syntheses of 1,5-Benzothiazepines
565
1
In the H NMR spectrum of 5l, absorption signals as a quartet at
δ4.10 (J = 6 Hz) and a triplet at δ1.42 (J = 6 Hz) may be assigned
to two methylene protons and three methyl protons of ethoxyl group
(CH3CH2O ). Besides, other three protons attached to the sp3 hy-
bridized carbons, i.e., C-6-H, C-6a-H, and C-7-H, were expected to show
absorption in the upfield region of the 1H NMR spectra. In the spectra
recorded at 90 MHz, these three protons showed very weak absorption
signals. In 1H NMR spectra recorded at 300 MHz, the signals were ob-
served as two doublets and a double-doublet in the slightly downfield re-
gion, each integrating for one proton. Two doublets at δ4.92 (J = 1.1 Hz)
and δ4.98 (J = 12.2Hz) may be assigned to C-6-H and C-7-H, because
these protons are attached to sp3 carbons which are attached with elec-
tronegative oxygen and sulphur atom, respectively. A double-doublet
at δ3.68 (J1 = 12.3, J2 = 1.1) may be assigned to C-6a-H. Other pro-
tons of the molecule were found to show downfield absorption signals
in the spectra in the region δ6.40–δ8.24 integrating for 15/16 aromatic
protons (Tables III, IV). For the assignments of 13C NMR signals in
benzopyranobenzothiazepines, extensive studies of the 13C NMR spec-
tra of the reactants and products were made by G. Toth, A. Szollosy,
A. Levai and H. Duddeck. For example, in order to assign the signals
of ring D carbon atoms (Figure 1), the chemical shift data of the ref-
erence compounds, indanones29–31 tetralones,31,32 thiochromanones,33
chromanone33 and flavanone34 were used. Similarly, to support the as-
signment of the ring carbons, different derivatives having different sub-
stituents were studied35 including steric environments and the assign-
ments of 13C NMR signals of the structure. They have measured the
spectra of compounds at 100, 200, and 250 MHz. Based on these data,
the 13C NMR signals of carbon atoms of substituted benzopyranoben-
zothiazepines may be summarized to appear around the values given
as under.
FIGURE 1 6,7,10-substituted benzopyranobenzothiazepine.

566

567

568
U. C. Pant et al.
13C NMR spectrum of 5f at 100 MHz shows signals in this pat-
tern. Upfield absorption signals at δ21.1 and δ56.4 may be assigned to
methyl (CH3 ) carbon and methylene ( CH2 ) carbon of ethoxyl group
(CH3CH2O ). Three characteristic absorption signals in the relatively
downfield region at δ76.4, δ45.3, and δ66.5 may be assigned to three
sp3 carbons, C-6, C-6a, and C-7 respectively. All the other carbons of
the molecule showed absorption signals at δ118.5, 120.1, 121.8, 124.4,
125.1, 126.8, 127.2, 127.4, 127.7, 128.7, 129.4, 131.1, 131.8, 133.7, 136.2,
137.4, 137.7, 138.2, 142.7, 150.3, 155.8, 159.8, and 161.7.
In the mass spectra of the final products (5a–l), molecular ion peaks
[M]+ and [M+2]+ corresponded to the calculated molecular weights of
the compounds.
ANTIMICROBIAL ACTIVITY
All the synthesised compounds, 5a–l were evaluated for their relative
antibacterial and antifungal activity against the bacteria, Escherichia
coli and GFC and fungi, Aspergillus niger, Aspergillus flavus and Curvu-
laria lunata following the Plate Disc Method.36,37 To evaluate the rel-
ative activity in the form of activity index, Bacitracin and Mycostatin
were used as reference compounds in case of bacteria and fungi, re-
spectively. Zones of inhibition, exhibited by the reference and test com-
pounds, were measured and relative activities of the test compounds
(5a–l) were calculated as activity index (Table V).
Zone of Inhibition exhibited by test compound
Activity Index =
Zone of Inhibition exhibited by the reference compound
All the synthesised compounds, 5a–l, showed moderate to good activity
(activity index = 0.8–1.28) against bacteria Escherichia coli and GFC on in-
cubation for a duration of 40 hr. Monochloro derivatives showed greater bacte-
ricidal activity than the dichloro derivatives whereas increase in the percent-
age of chlorine showed enhancement of antifungal activity, especially against
C. lunata (Table V).
EXPERIMENTAL
All the recorded melting points are uncorrected. Thin layer chromatography
(TLC) on silica gel G coated glass plates using benzene:methanol:aq. ammonia
(7:2:1) as eluent was used for monitoring the progress of the reaction and for
checking the purity of the compounds (5a–l). The IR spectra were taken in
KBr pellets on a Perkin-Elmer Infracord 577 spectrometer. 13C NMR spectra
were recorded on Jeol 90 MHz FT NMR and Bruker DRX300 spectrometer using
CDCl3 as solvent and TMS as internal standard and mass spectra were recorded
on a Jeol D-300 (EI/Cl) instrument at 70 eV. Elemental analyses were carried
out at the Regional Sophisticated Instrumentation Centre, CDRI, Lucknow.

569

570
U. C. Pant et al.
I. Preparation of 5-Substituted-2-aminobenzenethiols (4a–f)
Six 5-substituted-2-aminobenzenethiols (4a–f) were synthesised by following
reported methods.11−15
II. Preparation of 3-(4-Substituted Arylidine)-flavanones
(3a & 3b)
Equimolar quantities of flavanone38,39(1) in ethanol and 2-chlorobenzaldehyde
(2a) or 2,4-dichlorobenzaldehyde (2b) were mixed. Dry hydrogenchloride gas
was passed while heating the reaction mixture gently with stirring. The color
of the reaction mixture changed from yellow to black-blackish red. On keeping
it overnight, the crude-substituted arylidene flavanones were obtained which
were crystallized from dry methanol. (3a, m.p. 137◦C, reported16 137–138◦C,
yield 1.45g ,42%; 3b, m.p. 126◦C reported16 127–128◦C, yield 1.44g, 38%).
General Procedure for the Preparation of 10-Substituted-6H-
6a,7-dihydro-7-(monochlorophenyl/dichlorophenyl)-6-phenyl-
[1]benzopyrano[3,4-c][1,5]benzothiazepines (5a–l)
5-Substituted-2-aminobenzenethiol (4,0.001 mol) and substituted benzylidene
flavanone (3, 0.001 mol) were dissolved in dry toluene (15 mL) and mixed.
Trifluoroacetic acid (5 drops) as acidic catalyst, or piperidine (10 drops) as a
basic catalyst, was then added to the reaction mixtures and refluxed until color
change occurred from light yellow to deep red over 6 h. The solvent was removed
under reduced pressure to get a crude solid. The crude solid thus obtained, was
crystallized from dry methanol to give the title compounds (5a–l).
The microanalytical, spectral, and antimirobial activity data of 5a–l are
given in Tables I–V.
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Syntheses of 1,5-Benzothiazepines
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