Synthesis and antibacterial activity of isochromene and isoquinoline derivative

Article abstract of DOI:10.1002/jhet.245

Synthesis of 4-thioureidobenzoic acid (2), which on cyclization with ethyl chloroacetate gave 4-(2-imino-5-oxothiazolidin-3-yl)-benzoic acid (3), which on further reacting with benzoin (4) in the presence of polyphosphoric acid afforded the synthesis of 2-imino-3-(-1-oxo-3,4-diphenyl-1H-isochromen-6-yl) thiazolidin-5-one (5). Compound 5 was then reacted with substituted anilines to give 6-(2-imino-5-oxothiazolidin-3-yl)-3,4-diphenyl-2-(substituted)-isoquinolin- 1(2H)-one (6). The structures of the compounds have been elucidated on the basis of IR 1HNMR, 13C NMR, and elemental analysis. Representative samples were screened for their antimicrobial activity against gram-negative bacteria, E. coli and P. aeruginosa and gram-positive bacteria, S. aureus, and C. diphtheriae using disc diffusion method.

Full text of DOI:10.1002/jhet.245

May 2011
Synthesis and Antibacterial Activity of Isochromene and
Isoquinoline Derivative
529
Vijay V. Dabholkar and Dilip R. Tripathi*
Organic Research Laboratory, Department of Chemistry, K. C. College, Churchgate,
Mumbai-400 020, India
*E-mail: diliptripathi1@yahoo.co.in
Received March 6, 2009
DOI 10.1002/jhet.245
Published online 8 February 2011 in Wiley Online Library (wileyonlinelibrary.com).
Synthesis of 4-thioureidobenzoic acid (2), which on cyclization with ethyl chloroacetate gave 4-(2-im-
ino-5-oxothiazolidin-3-yl)-benzoic acid (3), which on further reacting with benzoin (4) in the presence
of polyphosphoric acid afforded the synthesis of 2-imino-3-(-1-oxo-3,4-diphenyl-1H-isochromen-6-yl)
thiazolidin-5-one (5). Compound 5 was then reacted with substituted anilines to give 6-(2-imino-5-oxo-
thiazolidin-3-yl)-3,4-diphenyl-2-(substituted)-isoquinolin-1(2H)-one (6). The structures of the compounds
have been elucidated on the basis of IR 1HNMR, 13C NMR, and elemental analysis. Representative
samples were screened for their antimicrobial activity against gram-negative bacteria, E. coli and P.
aeruginosa and gram-positive bacteria, S. aureus, and C. diphtheriae using disc diffusion method.
J. Heterocyclic Chem., 48, 529 (2011).
INTRODUCTION
ment in their structure [8]. Hence, there is a continuing
interest in the elaboration of new routes to the isochro-
mene ring as well as to new interesting derivatives of
this heterocyclic system.
Para-aminobenzoic acid (PABA) is a B complex vita-
min that is synthesized in the body. PABA is used in
the formation of folic acid and the metabolism of pro-
tein. It is an antioxidant that helps to protect skin from
sunburn and cancer [1]. PABA supplementation appears
to increase the ability of some infertile women to
become pregnant [2]. PABA is also used in the treat-
ment of rheumatoid arthritis [3].
The vast pharmacological activity of simple 4-substi-
tuted tetrahydroisoquinolines has generated much inter-
est in their synthesis and in the last years several new
naturally occurring compounds of this type have been
isolated [9]. For example, the antidepressant drug Nomi-
fensine [10] has a close relationship to the alkaloid
Cherylline. Some of the isoquinoline derivatives have
proved to be an agonist of dopamine receptors [11].
The pharmacophoric activity of thiazoles, isochro-
mene, and isoquinoline with the PABA as the starting
material prompted the design and synthesis of 2-imino-
3-(-1-oxo-3,4-diphenyl-1H-isochromen-6-yl)thiazolidin-
5-one (5) and 6-(2-imino-5-oxothiazolidin-3-yl)-3,4-di-
phenyl-2-(substituted)-isoquinolin-1(2H)-one (6).
Thiazoles are amongst the most frequently encoun-
tered heterocyclic compounds of biological interest,
along with many other applications. Thiazoles have
received attention in a range of applications from antibi-
otics [4] to photosensitizers [5].
The isochromene framework is a frequent structural
motif in naturally occurring molecules. For example,
flaccidin isolated from the orchids Dendrobium amoe-
num and Coelogyne flaccida includes an isochromene
framework [6]. A number of compounds isolated from
Cannabis sativa also can be viewed as isochromene
derivatives [7]. The roots and the stem of a tree Ulmus
davidiana (widespread in Korea) are used in oriental
medicines for the treatment of inflammations, edema,
and stomach cancer. Natural sesquiterpenoids isolated
from U. davidiana also incorporate an isochromene frag-
RESULTS AND DISCUSSION
PABA was treated with ammonium thiocynate in the
presence of concentrated hydrochloric acid to form the
thiocarbamide, 4-thioureidobenzoic acid (2), which on
cyclization in the presence of pyridine with chloroacetyl
C
V
2011 HeteroCorporation

530
V. V. Dabholkar and D. R. Tripathi
Vol 48
Scheme 1
Scheme 2
chloride forms 4-(2-imino-5-oxothiazolidin-3-yl)-benzoic
acid (3). Compound 3 on condensation with benzoin (4),
in the presence of a dehydrating agent like polyphos-
phoric acid yielded 2-imino-3-(-1-oxo-3,4-diphenyl-1H-
isochromen-6-yl)thiazolidin-5-one (5). Compound 5 on
further reaction with substituted anilines in the presence
of anhydrous pyridine gives 6-(2-imino-5-oxothiazoli-
din-3-yl)-3,4-diphenyl-2-(substituted)-isoquinolin-1(2H)-
one (6).
Antimicrobial and antifungal activities. Representa-
tive compounds were evaluated for their antibacterial
activity against gram-negative bacteria, E. coli and
P. aeruginosa and gram-positive bacteria, S. aureus and
C. diphtheriae using disc diffusion method [12,13]. The
zone of inhibition was measured in mm and the activity
was compared with standard drug ampicillin trihydrate.
about 2 h monitored the reaction progress by TLC. After com-
pletion of the reaction it was poured onto crushed ice and neu-
tralized with dilute NaOH solution. The precipitate separated
was filtered and washed with excess water (Scheme 1). The
solid was recrystallized from alcohol, yield 78%, m.p. 242ꢀC.
IR (KBr): 3160 (¼¼NH), 1710 (AC¼¼O), 1680 (AC¼¼O), 1415
(AC¼¼S), 875 (ACASACA).
2-Imino-3-(-1-oxo-3,4-diphenyl-1H-isochromen-6-yl)thia-
zolidin-5-one (5). A mixture of 4-(2-imino-5-oxothiazolidin-3-
yl)-benzoic acid (3) (0.01 mol, 2.36 g) and benzoin (desyl
alcohol) (4) (0.01 mol, 2.12 g) in polyphosphoric acid (10 mL)
[18 parts by weight of P2O5 and 10 parts by weight of H3PO4]
was heated at 100ꢀC for 5 h. During heating the contents were
occasionally stirred. Subsequently, the reaction mixture was
poured into ice cold water (100 mL) and left as such for 1 h.
A solid separated out, which was filtered off and washed ini-
tially with 10% aqueous sodium bicarbonate solution (50 mL)
and finally with excess water (checked with litmus paper for
the completed removal of acid) (Scheme 2). The solid thus
obtained was dried under vacuum and recrystallized from ace-
tonitrile:methanol (1:1), yield 68%, m.p. 85ꢀC. IR (KBr): 3090
(¼¼NH), 1710 (AC¼¼O), 1680 (AC¼¼O), 1430 (AC¼¼S), 850
(ACASACA). 1H NMR; 3.62 (s, 1H, NH), 4.11 (s, 1H, CH2),
6.5–8.2 (m, 13H, Ar-C). 13C NMR; 68.2 (CH2), 96.5–140.1
(C¼¼C & Ar-C), 155.3 (C¼¼N), 161.5 & 166.1 (2x C¼¼O). Ele-
mental Analysis: Actual, C; 69.90, H; 3.88, N; 3.40. Observed,
C; 69.97, H; 3.92, N; 3.46
EXPERIMENTAL
Melting points of all synthesized compounds were deter-
mined in open capillary tubes on an electro thermal apparatus
and are uncorrected. The purity of the compounds was moni-
tored by thin layer chromatography on silica gel coated alumi-
num plates (Merck) as adsorbent and UV light as visualizing
agent. 1H NMR spectra were recorded on Varian 500 MHz
NMR spectrophotometer using DMSO-d6 as solvent and TMS
as an internal standard (chemical shifts in d ppm). C, H, N
estimation was recorded on Carlo Erba 1108 (CHN) Elemental
Analyzer.
General procedure for the synthesis of thiocarbamide
(2). Thiocarbamides required for the reaction was prepared by
the method as described by Joshua [14]. Aromatic amine (0.1
mol), ammonium thiocyanate (0.1 mol) and conc. hydrochloric
acid (15 cm3) were taken in 10 cm3 water in a conical flask
and heated on a wire gauze till turbidity appeared. It was then
poured onto crushed ice and the solid obtained was recrystal-
lized from hot water (Scheme 1).
General procedure for the synthesis of 6-(2-imino-5-oxo-
thiazolidin-3-yl)-3,4-diphenyl-2-(substituted)-isoquinolin-1(2H)-
one (6). The synthesis was reported by Pandey [15]. Com-
pound 6 was synthesized by heating under reflux a mixture of
2-imino-3-(-1-oxo-3,4-diphenyl-1H-isochromen-6-yl)thiazoli-
din-5-one (5) (0.001 mol) and substituted aromatic amine
(0.001 mol) in anhydrous pyridine (20 mL) for 6 h. The solu-
tion was cooled to RT and acidified with dil. HCl (50 mL).
A solid separated out, which was filtered off and washed
with water successively (4 ꢁ 25 mL) (Scheme 3).
Preparation of thiocarbamide (4-thioureidobenzoic acid)
(2). PABA (0.1 mol, 13.7 g), ammonium thiocynate (0.1 mol,
7.6 g) and conc. hydrochloric acid (15 cm3) and 10 cm3 of
water was taken in a conical flask and heated on wire gauze
till turbidity appeared. It was then poured onto crushed ice and
the solid separated out was recrystallized from alcohol to give
4-thioureidobenzoic acid, yield 75%, m.p. > 300ꢀC. IR (KBr):
3310 (ANH2), 3100 (ANH), 1710 (AC¼¼O), 1410 (AC¼¼S).
Scheme 3
4-(2-Imino-5-oxothiazolidin-3-yl)-benzoic acid (3). In
a
100 cm3 round bottom flask 4-thioureidobenzoic acid (2)
(0.01 mol, 1.96 g) was weighed and added (0.01 mol, 0.80
mL) of chloroacetyl chloride. This mixture was refluxed for
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

May 2011
Synthesis and Antibacterial Activity of Isochromene and Isoquinoline Derivative
531
Table 1
6-(2-Imino-5-oxothiazolidin-3-yl)-3,4-diphenyl-2-(m-tolyl)-iso-
quinolin-1(2H)-one (6a). Compound 6a was synthesized by
heating under reflux, a mixture of 2-imino-3-(-1-oxo-3,4-di-
phenyl-1H-isochromen-6-yl)thiazolidin-5-one (5) (0.001 mol,
0.41 g) and substituted aromatic amine (0.001 mol) in anhy-
drous pyridine (20 mL) for 6 h. The solution was cooled to
RT and acidified with dil. HCl (50 mL). The solid separated
out was filtered off and washed with water successively (4 ꢁ
25 mL). The solid thus obtained was dried under vacuum and
recrystallized from absolute alcohol, yield 72%, m.p. 210ꢀC.
IR (KBr): 3060 (¼¼NH), 1690 (AC¼¼O), 1610 (AC¼¼O), 1450
(AC¼¼S), 860 (ACASACA). 1H NMR; 2.37 (s, 3H, CH3),
3.78 (s, 1H, NH), 4.30 (s, 2H, CH2), 6.5–8.0 (m, 17H, Ar-H).
13C NMR; 17.7 (CH3), 68.2 (CH2), 96.5–140.1 (C¼¼C & Ar-
C), 155.3 (C¼¼N), 161.5 & 166.1 (2x C¼¼O). Elemental Analy-
sis: Actual, C; 74.25, H; 4.59, N; 8.38. Observed, C; 74.19, H;
4.50, N; 8.44.
Antibacterial activity.
Gram positive
Gram negative
Compounds S. aureus C. diphtheria P. aeruginosa E. coli
5
6a
6b
6c
6d
6e
15
21
16
23
22
21
26
17
23
17
25
23
22
28
14
19
13
20
21
18
22
11
20
11
19
19
20
21
Ampicillin
trihydrate
(standard)
DMSO
0
0
0
0
Concentration selected was 100 lg/mL and DMSO was used as the
solvent.
6-(2-Imino-5-oxothiazolidin-3-yl)-2,3,4-triphenylisoquino-
lin-1(2H)-one (6b). IR (KBr): 3060 (¼¼NH), 1710 (AC¼¼O),
1630 (AC¼¼O), 1460 (AC¼¼S), 850 (ACASACA). 1H NMR;
3.62 (s, 1H, NH), 4.31 (s, 1H, CH2), 6.8–7.8 (m, 18H, Ar-H).
13C NMR; 65.2 (CH2), 111.9–144.1 (C¼¼C & Ar-C), 158.1
(C¼¼N), 163.4 & 169.1 (2x C¼¼O). Elemental Analysis: Actual,
C; 73.92, H; 4.31, N; 8.62. Observed, C; 73.85, H; 4.39, N; 8.68.
6-(2-Imino-5-oxothiazolidin-3-yl)-3,4-diphenyl-2-(2-chloro-
phenyl)-isoquinolin-1(2H)-one (6c). IR (KBr): 3060 (¼¼NH),
1690 (AC¼¼O), 1610 (AC¼¼O), 1480 (AC¼¼S), 850
(ACASACA), 750 (CACl). 1H NMR; 3.71 (s, 1H, NH), 4.40
(s, 1H, CH2), 7.0–8.2 (m, 17H, Ar-H). 13C NMR; 69.7 (CH2),
104.2–147.3 (C¼¼C & Ar-C), 151.5 (C¼¼N), 161.7 & 168.3 (2x
C¼¼O). Elemental Analysis: Actual, C; 69.03, H; 3.84, N;
8.05. Observed, C; 69.11, H; 3.91, N; 8.11
6-(2-Imino-5-oxothiazolidin-3-yl)-3,4-diphenyl-2-(2-carbox-
ilic acid)-isoquinolin-1(2H)-one (6d). IR (KBr): 3080 (¼¼NH),
1690 (AC¼¼O), 1610 (AC¼¼O), 1460 (AC¼¼S), 850
(ACASACA). 1H NMR; 3.69 (s, 1H, NH), 4.40 (s, 1H, CH2),
7.15–7.89 (m, 17H, Ar-H), 8.85 (s, 1H, OH). 13C NMR; 69.1
(CH2), 96.1–147.3 (C¼¼C & Ar-C), 157.7 (C¼¼N), 168.1 &
170.1 (2x C¼¼O), 175.2 (C¼¼O). Elemental Analysis: Actual, C;
70.06, H; 3.95, N; 7.91. Observed, C; 70.11, H; 3.87, N; 7.83.
6-(2-Imino-5-oxothiazolidin-3-yl)-3,4-diphenyl-2-(4-methoxy-
phenyl)-isoquinolin-1(2H)-one (6e). IR (KBr): 3050 (¼¼NH),
2850 (OCH3), 1690 (AC¼¼O), 1610 (AC¼¼O), 1460 (AC¼¼S),
850 (ACASACA). 1H NMR; 3.71 (s, 1H, NH), 3.89 (s, 3H,
OCH3), 4.24 (s, 2H, CH2), 6.72–8.34 (m, 17H, Ar-H). 13C
NMR; 55.6 (OCH3), 69.4 (CH2), 112.2–144.1 (C¼¼C & Ar-C),
151.2 (CAOCH3), 161.3 & 168.4 (2x C¼¼O), 179.3 (C¼¼N).
Elemental Analysis: Actual, C; 71.95, H; 4.45, N; 8.12.
Observed, C; 71.88, H; 4.38, N; 8.08.
absorbed before applying the antibiotic disc. There should be a
confluent lawn of growth when done properly. If only isolated
colonies grow, the inoculums were too light and the test
should be repeated.
Disc (4 mm diameter) were prepared from Wattmann filter
paper no.41 and were used after autoclaving them at 121 psi
then for 15 min. It was then dried in hot air oven. The com-
pounds were tested at the concentration of 100 lg/mL using
dimethylsulphoxide (DMSO) as the diluent. Now dip the disc
in the appropriate dilution and place them evenly on the sur-
face of agar plate either by using sterile forceps or the dispens-
ing apparatus, no more than five disc on a 100 mm plate. A
blank DMSO disc should also be placed on the plate to see if
DMSO is interfering with the zone of inhibition. The disc
should not be moved, once it has come in contact with the agar
surface as some of the compound diffuses almost instantaneously.
Invert the plate and place them in an incubator at 35ꢀC with in
15 min after the disc are applied. Plates should be incubated
aerobically. After 16–18 h of incubation examine each plate. The
zone of inhibition was measured in mm and was compared with
the reference standard antibiotics namely Ampicilline trihydrate
drugs 100 lg/mL. Zone of inhibition were determined and the
results of such studies are summarized in Table 1.
Compound 6a and 6e with a methyl and methoxy substitu-
ent, respectively showed moderate activity against gram posi-
tive and gram negative organisms, whereas compound 6b with
no substituent showed very low activity.
Highest degree of activity against gram negative micro
organisms, S. aureus and C. diphtheria was shown by 6c with
a chloro substituent, and 6d with a carboxylic acid substituent
showed good activity against gram positive microorganisms,
P. aeruginosa and E. coli.
Experimental procedure for antibacterial testing. Make
suspension of the desired cultures in saline with the help of
nichrome loop. The turbidity achieved should be 0.5 macfar-
land standard. Within 15 min after adjusting the turbidity of
the inoculum suspension, dip a sterile nontoxic swab into the
adjusting suspension. Rotate the swab several times, pressing
firmly on the inside wall of the tube above the flute level to
remove excess inoculums from the swab.
Inoculate the dried surface of MH plate by streaking the
swab over the entire sterile agar surface. Repeat this two more
times. Place the plate top and allow standing for 3–5 min, but
not longer than 15 min, for any excess surface moisture to be
The substituted, carboxylic and chloro derivatives of the title
compound were found to be the lead antimicrobial agents.
Acknowledgments. The authors are grateful to the Principal Ms.
Manju J. Nichani and Management of K.C. College, Mumbai for
providing necessary facilities and to the Head, Department of Mi-
crobiology for antimicrobial studies. Authors are also thankful to
the Director, Institute of Science, Mumbai (India) for providing
spectral analyses.
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V. V. Dabholkar and D. R. Tripathi
Vol 48
[8] Kim, J. P.; Kim, W. G.; Koshino, H.; Jung, J.; Yoo, I. D.
Phytochemistry 1996, 43, 425.
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