Synthesis of halogenated derivatives of thymol and their antimicrobial activities

Article abstract of DOI:10.1007/s00044-013-0809-8

In order to test the antibacterial and antifungal activities of different halogenated thymol derivatives, thymol has been converted into chlorothymol, dichlorothymol with N-chlorosuccinimide; monobromothymol, dibromothymol with N-bromosuccinimide; O-methylated iodothymol with ceric ammonium nitrate and iodine from methylated thymol. Among the different derivatives tested, 4-chlorothymol was found to be most active against Staphylococcus aureus and Staphylococcus epidermis at a concentration of 12.5 and 25 ppm, respectively. Also it was tested to be active against Candida albicans (AI). Springer Science+Business Media 2013.

Full text of DOI:10.1007/s00044-013-0809-8

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2014) 23:2212–2217
DOI 10.1007/s00044-013-0809-8
ORIGINAL RESEARCH
Synthesis of halogenated derivatives of thymol and their
antimicrobial activities
•
Ranjeet Kaur Mahendra P. Darokar
•
•
•
Sunil Kumar Chattopadhyay Vinay Krishna
Ateeque Ahmad
Received: 28 June 2013 / Accepted: 24 September 2013 / Published online: 15 October 2013
Ó Springer Science+Business Media New York 2013
Abstract In order to test the antibacterial and antifungal
activities of different halogenated thymol derivatives,
thymol has been converted into chlorothymol, dichloroth-
ymol with N-chlorosuccinimide; monobromothymol, di-
bromothymol with N-bromosuccinimide; O-methylated
iodothymol with ceric ammonium nitrate and iodine from
methylated thymol. Among the different derivatives tested,
4-chlorothymol was found to be most active against
Staphylococcus aureus and Staphylococcus epidermis at a
concentration of 12.5 and 25 ppm, respectively. Also it was
tested to be active against Candida albicans (AI).
essential oil (Rahimifard et al., 2008). It has been dem-
onstrated that the biological effects of T. vulgaris are
mainly due to the presence of phenolic compounds, espe-
cially thymol and carvacrol (Blumenthal, 2000; Cherallier,
1996).Thymol content in thyme essential oil is much higher
than carvacrol content (Fig. 1). This compound shows 30
times higher antiseptic effect and four times lower toxicity
than phenol (Zekovic et al., 2000; Hajimehdipoor et al.,
2009). In India major source of thymol is an essential oil
from Ajowain, botanically known as Trachyspermum ammi
(Linn.) sprague (Family; Umbelliferae). The plant is a
native of Mediterranean region and is cultivated and found
growing wild in South West Asia. In India it is grown in
north-western states of Gujarat, Maharashtra, Rajasthan,
Madhya Pradesh, Uttar Pradesh, and Bihar (Husain et al.,
1988; Anonymous, 1976). The oil of Ajowain contains
about 53.8 % thymol. Thymol has been known and isolated
since 1853. Expensive synthetic thymol has been in the
market since 1960 and is commonly used for its antiseptic
effect in toothpaste and flavour in cough drops, mouth
washes, gargles, and chewing gum. It is often used partly in
such products (Arctander, 1969). Recent medical applica-
tion of thymol extract on rats established that it had
relaxing effects on organs possessing b2-receptors of uterus
and trachea (Weinkotter et al., 2007). Recently, two new
natural thymol derivatives together with five known thymol
derivatives were isolated from Centipeda minima and their
antimicrobial activities have been tested (Liang et al.,
2007). Various derivatives of thymol were also reported in
literature (Ahmad et al., 2002). In this paper, we are going
to report thymol derivatives i.e. the reaction of thymol and
N-halosuccinimide under different reaction conditions as
outlined in Scheme 1. All the products formed from the
above reactions were evaluated for their antimicrobial
activities.
Keywords Thymol derivatives Á N-Halosuccinimide Á
Antibacterial activity Á Antifungal activity
Introduction
The genus of Thymus comprises 300–400 species, some of
which are used in folk medicine. The main medicinal
Thymus is Thymus vulgaris (common thyme) which is used
for dry coughs, bronchitis, laryngitis, indigestion, and
gastritis (Rustaiyan et al., 1997; Blumenthal, 2000). There
are also some reports about antimicrobial effects of Thymus
R. Kaur Á S. K. Chattopadhyay Á A. Ahmad (&)
Process Chemistry and Chemical Engineering Department,
Central Institute of Medicinal and Aromatic Plants (CSIR),
Lucknow 226015, India
e-mail: ateeque97@gmail.com
M. P. Darokar Á V. Krishna
Genetic Resource Biotechnology Department, Central Institute
of Medicinal and Aromatic Plants (CSIR), Lucknow 226015,
India
123

Med Chem Res (2014) 23:2212–2217
2213
Chromatographic purifications were performed using silica
gel (60–120-mesh size, Merck chemicals). FT-IR spectra
were recorded in KBr or neat on Perkin Elmer AC-1
CH3
CH3
OH
1
spectrophotometer. H and 13C NMR spectra were recor-
OH
ded at 300 and 75 MHz, respectively, on a Brucker Avance
DRX-300 spectrometer. Chemical shift are given in d
values, downfield from TMS as internal standard. Coupling
constant (J) values are given in Hz. ESI mass spectra were
recorded on a API-3000, LC–MS/MS (Applied Biosystem/
MDS SCIEX, Toranto, Canada) mass spectrometer using a
standard ESI source coupled with LC separation system.
All the solvents and reagents were of LR/AR grade. Dry
solvents were prepared as per standard methods. Elemental
analysis (C, H, N) was performed on a Elementar Vario EL
III (Carlo Erbe 1108). The 1H and 13C NMR data of known
compounds are in agreement with those reported in liter-
ature (Ahmad et al., 2002).
H3C
CH3
H3C
CH3
Thymol
Carvacrol
Fig. 1 Structure of thymol and carvacrol
Materials and methods
Experimental
Melting points were determined in open capillary tube on a
JSGW melting point apparatus and are uncorrected.
Scheme 1 Synthesis and
structures of thymol derivatives
CH3
CH3
I
DMSO4/K2CO3
acetone, 700C,24 hr
CAN, I2
acetonitrile
OMe
OMe
CH3
H3C
Cl
CH3
H3C
Cl
8
7
7CH3
CH3
CH3
5
4
3
Br
6
1
CHCl3/NBS
60-700C
CCl4/NCS
OH
2
8
OH
OH
10
9
H3C
CH3
H3C
CH3
H3C
CH3
6
1
2
CH3
Cl
Cl
CCl4/NCS
60-700C
OH
H3C
CH3
3
CH3
CH3
Br
Br
DMSO4/K2CO3
CHCl3/NBS
40-450C
acetone
OH
CH3
OMe
700C, 24 hr
H3C
Br
H3C
CH3
9
4
CH3
Br
CHCl3/NBS
at 70-750C
OH
CH3
H3C
5
123

2214
Med Chem Res (2014) 23:2212–2217
1
1213, 1172, 1035, 879, 812, 766 cm-1; H NMR (CDCl3;
Isolation of thymol (1)
300 MHz): d 7.07 (s, 1H, C3–H), 5.65 (s, 1H, Ar–OH), 3.22
(m, 1H, C8–H), 2.22 (s, 3H, C7–H), 1.12 (d, 6H, J = 6.3 Hz,
C9–H and C10–H); 13C NMR (CDCl3; 75 MHz): d 147.9 (C-
1), 134.7 (C-5), 131.5 (C-6), 126.2 (C-2), 125.7 (C-3), 121.5
(C-4), 28.2 (C-8), 22.1 (C-9, 10) 17.9 (C-7); ESI–MS
(positive mode) m/z 219 [M ? H]?, MS m/z 218 [M]? (on
the basis of GC–MS). Elemental analysis (% found) C 54.82
(54.98), H 5.52 (5.68).
Ajowain oil was kept in a freezer and crystals were
obtained by filtering the crystallized portion through sin-
tered funnel and obtained as colourless pure crystals of
thymol, 98 % purity (on the basis of GC analysis); m.p.
51–52 °C; IR (KBr) mmax: 3464, 3361, 2963, 2872, 2367,
1719, 1582, 1513, 1420, 1299, 1225, 1154, 1099, 1060,
1
730 cm-1; H NMR (CDCl3; 300 MHz): d 7.07 (d, 1H,
J = 7.8 Hz, C3–H), 6.71 (d, 1H, J = 7.8 Hz, C4–H), 6.50
(br s, 1H, C6–H), 5.09 (s, 1H, Ar–OH), 3.16 (m, 1H, C8–
H), 2.30 (br s, 3H, C7–H), 1.22 (d, 6H, J = 6.9 Hz, C9–H
and C10–H); 13C NMR (CDCl3; 75 MHz): d 152.5 (C-1),
136.6 (C-5), 131.7 (C-2), 126.3 (C-3), 121.9 (C-4), 116.3
(C-6), 26.7 (C-8), 22.7 (C-9), 22.7 (C-10), 20.8 (C-7); EI-
MS: m/z 150 [M]?. Elemental analysis (% found) C 80.00
(80.40); H 9.33 (10.08).
6-Bromothymol (4)
To a solution of thymol (5 g, 33.33 mmol) in chloroform
(25 ml), (5 g, 28.08 mmol) N-bromosuccinimide was
added and refluxed over water bath for 5–6 h at tempera-
ture of 40–50 °C. To this distilled water was added and
extracted with chloroform (3 9 25 ml). Organic layer was
washed with water dried over sodium sulphate and evap-
orated to dryness. The reaction product was purified by
silica gel column and eluted with hexane/EtOAc as col-
ourless oil (97.6 %). Yield: 65 %; light yellow viscous; IR
(neat) mmax: 3506, 2962, 2870, 1465, 1373, 1398, 1208,
4-Chlorothymol (2)
To a solution of thymol 2 g (13.33 mmol) in carbon tetra-
chloride (20 ml), N-chlorosuccinimide (2.5 g, 18.605 mmol)
was added and refluxed over water bath 60–70 °C tempera-
ture. The reaction mixture was cooled to room temperature,
diluted with water and extracted with chloroform
(3 9 25 ml). Organic layer was washed with water, dried
over sodium sulphate and evaporated to dryness. The crude
reaction product was purified by silica gel column and eluted
with hexane/ethyl acetate. It crystallized from hexane as
colourless needles (purity 97–98 %). Yield: 65 %; m.p.
57–61 °C; IR (KBr) mmax: 3320, 2966, 1504, 1452, 1337,
1254, 1164, 880, 757 cm-1; 1H NMR (CDCl3; 300 MHz): d
7.12 (s, 1H, C3–H), 6.60 (s, 1H, C6–H), 4.76 (s, 1H, Ar–OH)
3.12 (m, 1H, C8–H), 2.26 (s, 3H, C7–H), 1.22 (d, 6H,
J = 6.9 Hz, C9–H and C10–H); 13C NMR (CDCl3; 75 MHz):
d 151.4 (C-1), 134.4 (C-5), 134.3 (C-6), 127.3 (C-2), 126.4 (C-
3), 118.2 (C-4), 19.9 (C-7), 27.2 (C-8), 22.1 (C-9, 10); ESI–
MS (Negative mode) m/z 183 [M-H]?; MS m/z 184 [M]? (on
the basis of GC–MS). Elemental analysis (% found) C 65.04
(65.52), H 7.10 (7.58).
1169, 1123, 1028, 879, 789, 735, 651 cm-1 1H NMR
;
(CDCl3; 300 MHz): d 7.02 (d, 1H, J = 7.8 Hz, C3–H),
6.76 (d, 1H, J = 7.8 Hz, C4–H), 5.68 (Ar–OH), 3.22
(m,1H, C8–H), 2.31 (s, 3H, C7–H), 1.27 (d, 6H,
J = 6.9 Hz, C9–H and C10–H); 13C NMR (CDCl3;
75 MHz): d 149.8 (C-1), 135.8 (C-6), 134.7 (C-5), 125.4
(C-2), 122.5 (C-3), 114.1 (C-4), 28.5 (C-8), 23.3 (C-7),
22.7 (C-9, 10); MS m/z 228 [M]?; Elemental analysis (%
found) C 52.42 (51.93), H 5.72 (5.78).
4,6-Dibromothymol (5)
To a solution of thymol 5 g (33.33 mmol) in chloroform
(25 ml), (12 g, 67.41 mmol) N-bromosuccinimide was
added and refluxed over water bath for 5–6 h at tempera-
ture of 60–70 °C. To this distilled water was added and
extracted with chloroform (3 9 25 ml). Organic layer was
washed with water dried over sodium sulphate and evap-
orated to dryness. The reaction product was purified by
silica gel column and eluted with hexane/ethyl acetate. It
was obtained as yellow viscous oil (98 %). Yield: 56 %; IR
(neat) mmax: 3506, 2962, 2870, 1596,1465, 1343, 1306,
1208, 1169, 1123, 1028, 879, 607 cm-1; 1H NMR (CDCl3;
300 MHz): d 7.29 (s, 1H, C3–H), 5.66 (s, 1H, Ar–OH),
3.28 (m, 1H, C8–H), 2.43 (s, 3H, C7–H), 1.20 (d, 6H,
J = 6.9 Hz, C9–H and C10–H); 13C NMR (CDCl3;
75 MHz): d 149.3 (C-1), 135.2 (C-6), 134.6 (C-4), 129.6
(C-5), 115.50 (C-2), 114.4 (C-3), 28.5 (C-7), 24.3 (C-8),
22.9 (C-9, 10); ESI–MS (negative mode) m/z 307 [M–H]?;
MS m/z 308 [M]? (on the basis of GC–MS). Elemental
analysis (% found) C 38.99 (39.25), H 3.93 (4.07).
4,6-Dichlorothymol (3)
To a solution of thymol 2 g (13.33 mmol) in carbon tetra-
chloride (20 ml), N-chlorosuccinimide (5 g, 37.31 mmol)
was added and refluxed over water bath 60–70 °C temper-
ature. The reaction mixture was cooled to room temperature,
diluted with water, and extracted with chloroform
(3 9 25 ml). Organic layer was washed with water, dried
over sodium sulphate, and evaporated to dryness. The reac-
tion product was purified by silica gel column and eluted with
hexane/ethyl acetate as colourless oil (purity, 97.5 %).
Yield: 55 %; IR (neat) mmax: 3527, 2964, 1470, 1402, 1313,
123

Med Chem Res (2014) 23:2212–2217
2215
6-Bromo, 4-chlorothymol (6)
obtained was purified by column chromatography using
hexane/EtOAc as eluant to give 20 mg of product as col-
ourless oil (97.8 %). Yield: 64 %, IR (neat) mmax: 2927,
To a solution of chlorothymol (5 g, 27.17 mmol) in chlo-
roform (25 ml), N-bromosuccinimide (10 g, 56.17 mmol)
was added and the mixture was refluxed over water bath for
5–6 h at temperature 60–70 °C. To this distilled water was
added and extracted with chloroform (3 9 25 ml). Organic
layer was washed with water dried over sodium sulphate and
evaporated to dryness. The reaction product was purified by
silica gel column and eluted with hexane/chloroform as light
yellow oil (97.6 %). Yield: 50 %; IR (neat) mmax: 3416, 2890,
2780, 1620, 1560, 1430, 1303, 1210, 1110, 1026, 816,
676 cm-1. 1H NMR (CDCl3; 300 MHz): d 7.13 (s, 1H, C3–
H), 5.64 (s, 1H, Ar–OH), 3.26 (m, 1H, C8–H), 2.44 (s, 3H,
C7–H), 1.22 (d, 6H, J = 6.9 Hz, C9–H and C10–H); 13C
NMR (CDCl3; 75 MHz): d 149.3 (C-1), 135.2 (C-6), 134.6
(C-4), 129.6 (C-5), 115.5 (C-2), 114.4 (C-3), 28.54 (C-7),
24.3 (C-8), 22.9 (C-9, 10); MS m/z 264 [M]? (on the basis of
GC–MS). Elemental analysis (% found) C 45.57 (45.33), H
4.59 (4.56).
1
2343, 1489, 1461, 1242, 1192, 1068, 949, 763 cm-1; H
NMR (CDCl3; 300 MHz): d 7.44 (s, 1H, C3–H), 6.64 (s,
1H, C6–H), 3.60 (s, 3H, OMe), 2.299 (s, 3H, C7–H), 1.10
(d, 6H, J = 6.9, C9–H and C10–H); 13C NMR (CDCl3;
75 MHz): d 157.5 (C-1), 139.6 (C-5), 137.4 (C-3), 136.1
(C-2), 112.8 (C-6), 90.4 (C-4), 28.3 (C-8), 26.8 (C-7), 23.6
(C-9, 10), 58.9 (O-Me); ESI–MS (positive mode) m/z 313
[M?Na]?; m/z 291 [M?H]?. Elemental analysis (%
found) C 45.54 (45.21), H 5.21 (5.35).
Methyl ether of mono bromo thymol (9)
Hundred mg of mono bromo thymol was taken in 5 ml
acetone, to this solution, 500 mg of K2CO3 and 0.5 ml of
dimethyl sulphate was added. After refluxing for about
24 h the reaction was worked up by removal of solvent.
The residue was fractionated between chloroform and
water. Organic layer was dried over Na2SO4. The residue
obtained was purified by column chromatography on silica
gel to give 124 mg of product as yellow colourless oil
(96.8 %). IR (neat) mmax: 2962, 2920, 1490, 1462, 1369,
Thymol methyl ether (7)
To a solution of 150 mg thymol (1 mmol) in acetone
(10 ml), 550 mg of K2CO3 (3.9 mmol), and 0.5 ml of
dimethyl sulphate was added. After stirring at 70 °C under
reflux for about for 24 h the reaction was worked up by
removal of solvent. The residue was partitioned between
chloroform and water. Organic layer was washed with
water and dried over Na2SO4. The residue obtained was
purified by column chromatography on silica gel column
with petroleum ether-ethyl acetate as elutant to give
135 mg of methyl ether of thymol as colourless oil (98 %).
Yield: 80 %, IR (neat) mmax: 2962, 2928, 1490, 1462, 1369,
1244,1172, 1046, 885, 670 cm-1
;
1H NMR (CDCl3;
300 MHz): d 7.02 (d, 1H, J = 7.8, C3–H), 6.928 (d, 1H,
J = 7.8, C4–H), 3.71 (s, 3H, O-Me), 3.19 (m, 1H, C8–H),
2.30 (s, 3H, C7–H), 1.11 (d, 6H, J = 6.9, C9–H and C10–
H), 13C NMR (CDCl3; 75 MHz): d 157.1 (C-1), 135.8 (C-
5), 134.3 (C-2), 126.1 (C-3), 125.4 (C-4), 113.8 (C-6), 21.6
(C-7), 26.8 (C-8), 23.1 (C-9, 10), 58.9 (O–Me); ESI–MS
(positive mode) m/z 242.7 [M?H]?. Elemental analysis (%
found) C 54.34 (54.58), H 6.22 (6.08).
1260, 1244, 1194, 1172, 1046, 959 cm-1 1H NMR
;
Microbial strains and media
(CDCl3; 300 MHz): d 7.00 (d, 1H, J = 7.8, C3–H), 6.65 (d,
1H, J = 7.8, C4–H), 6.58 (s, 1H, C6–H), 3.71 (s, 3H,
OMe), 3.16 (m, 1H, C8–H), 2.23 (s, 3H, C7–H) 1.11 (d, 6H,
J = 6.9, C9–H and C10–H); 13C NMR (CDCl3; 75 MHz): d
157.1 (C-1), 136.6 (C-5), 134.3 (C-2), 126.1 (C-3), 121.4
(C-4), 111.8 (C-6), 26.8 (C-8), 23.1 (C-9,10), 21.6 (C-7),
58.9 (O–Me); ESI–MS (positive mode) m/z 165 [M?H]?;
Elemental analysis (% found) C 80.44 (80.38), H 9.82
(9.97).
The bacterial and fungal cultures were grown on the Muel-
ler–Hinton agar (Hi-Media) and Sabouraud dextrose agar
(Hi-Media) media by incubation at the strain wise optimum
temperatures. Streptomycin was used as control antibiotic in
the bioactivity assays in case of bacteria whereas ampho-
tericin B was used as the standard antifungal compound.
Bacterial strains
Mono iodo methyl ether of thymol (8)
Staphylococcus aureus, Staphylococcus epidermidis,
Enterococcus faecalis, Enterobacter aerogenes, Strepto-
coccus mutans, Escherichia coli, Klebsiella pneumoniae.
To a solution of 50 mg of methyl ether of thymol in ace-
tonitrile (5 ml) was added 16.4 mg ceric ammonium nitrate
and 38 mg of Iodine. After stirring at room temperature for
about 8 h the reaction was worked up adding 5 % Na2SO4
solution and extracted with EtOAc. Organic layer was
washed with water and dried over Na2SO4. Residue
Fungal Strains
Candida albicans (AI), C. albicans (MTCC), C. albicans
(CN).
123

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Med Chem Res (2014) 23:2212–2217
Disc diffusion assay
in that reaction (Ahmad et al., 2002; Daniel et al., 1950).
Reaction of thymol with N-chlorosuccinimide (NCS), N-
bromosuccinimide (NBS) and iodination with iodine have
not been studied thoroughly. Reaction of thymol with N-
chlorosuccinimide at mild temperature (40–45 °C) in car-
bon tetra chloride-afforded 4-chlorothymol (2) and at
higher temperature formed 4,6-dichlorothymol (3). Treat-
ment of thymol with N-bromosuccinimde at mild temper-
ature (40–45 °C) in chloroform afforded 6-bromothymol
(4) and at higher temperature (70–75 °C)-afforded 4,6-di-
bromothymol (5). Reaction of 4-chlorothymol (2) with N-
bromosuccinimide at temperature 60–70 °C afforded to
6-bromo, 4-chlorothymol (6). Reaction of thymol with N-
iodo succinimide did not occur. Iodination of thymol with
I2 in the presence of ceric ammonium nitrate also failed.
However, when the same reaction was carried out with
methyl ether of thymol (7) it gave mono iodo derivative
(8).
Antibacterial activity testing was done as per Bauer et al.,
(1996). All bacteria were subcultured from -80 °C stock
cultures into 5 mL of Mueller–Hinton broth and incubated
for 24 h at desired temperatures. For use as an inoculum,
the turbidity of the bacterial suspension was adjusted to the
McFarland standard 0.5 (ca. 2–4 9 106 cfu/ml). About
100 lL amount of bacterial culture was spread plated on
solid medium and discs (5-mm diameter) containing test
compound were placed on the pre-inoculated agar surface.
Observations were recorded after 48 h of incubation of
plates at desired temperatures.
Antifungal activity testing was done as per Wannisorn
et al., (1966). Fungal cultures were grown on SDA at 28 °C
for 7 days except C. albicans. Suspension of each fungus
was prepared in 0.85 % normal saline containing 0.1 %
Tween 80. For use as inoculum, the turbidity of the fungal
suspensions was also adjusted to the McFarland standard 0.5.
A seeded agar plate was prepared by pouring (a) 20 mL of
SDA into a sterile plate and, (b) uniformly overlaying of
solid medium with 5 mL of soft agar, pre-inoculated with
0.1 mL of fungal suspension. Each of the essential oil or
fractions was diluted/dissolved in DMSO to the required
concentration and applied into filter paper discs (diameter
5 mm) @ 5 lL/disc. The discs were transferred into the
surface of seeded agar plate (1 disc/plate) and gently pressed
down to ensure contact. The plates were incubated at 28 °C
for 7–10 days when inhibition zone was measured.
The antibacterial activities of different thymol deriva-
tives were studied as per Bauer et al., (1996) and the results
are presented in Table 1. Thymol 1 was found to be most
active against S. epidermidis, E. faecalis, and S. mutans at a
concentration of 32.2, 62.5, and 62.5 ppm, respectively. It
was also found to be active against S. aureus, Enterobacter
aerogenes at a concentration of 125 ppm and against K.
pneumoniae at a concentration of 250 ppm. Among the
halogenated derivatives of thymol 1, 4-chlorothymol 2 was
found to be most active against S. aureus and S. epide-
rmidis at a concentration of 12.5 and 25 ppm and 4,6-
dibromothymol 5 was found to be more active against S.
aureus followed by S. epidermidis, respectively. 6-Bro-
mothymol 4 was found to be marginally effective against S.
mutans at a concentration of 125 ppm and at a high con-
centration of 1,000 ppm slightly active against E. aeroge-
nes. The other thymol derivatives 3, 6, 7, 8, and 9 did not
show any antibacterial activity.
Broth-dilution assay
Two-fold serial dilution technique was employed to assess
the minimum inhibitory concentration (MIC) of a given
compound using 96-well microplate. The MIC was taken
as the lowest concentration of the test compound, which
inhibited the appearance of visible growth.
Thymol and its different derivatives were also tested for
their antifungal activities as shown in Table 2. Antifungal
activity testing was done as per Wannisorn et al., (1966).
4-Chlorothymol 2 was found to be the most active com-
pound. Thymol 1 at a concentration 100 ppm showed
marginal activity against C. albicans (AI), C. albicans
(MTCC), and C. albicans (CN). 4-Chlorothymol 2 at the
Results and discussion
Previously, the reaction of thymol with sulfuryl chloride
was studied and dichloro and trichloro thymol were formed
Table 1 Antibacterial activities of thymol and its derivatives (zone of inhibition in mm, MIC in lg/mL given in parenthesis
Compounds
S. aureus
S. epidermis
E. faecalis
E. aerogenes
S. mutans
E. coli
K. pneumoniae
Thymol (1)
12 (125)
–
18 (32.25)
–
10 (62.5)
8 (125)
2 (100)
–
11 (62.5)
3 (100)
6 (250)
Monobromothymol (4)
Dibromothymol (5)
Chlorothymol (2)
Streptomycin
–
3 (125)
–
–
13 (250)
5 (12.5)
9 (12.5)
16 (1000)
6 (250)
9 (6.35)
–
–
–
–
–
–
–
–
–
10 (0.36)
10 (2.71)
13 (6.35)
9 (1.35)
9 (2.71)
123

Med Chem Res (2014) 23:2212–2217
2217
Fig. 2 Antifungal activity of
different thymol derivatives
30
25
20
15
10
5
C. albicans AI
C. albicans (MTCC)
C. albicans (CN)
0
Thymol
4-
Amphotericin
B
chlorothymol
Table 2 Antifungal activities of thymol and its derivatives (zone of
inhibition in mm, MIC in lg/ml given in parenthesis
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Conclusion
Different halogenated derivatives of thymol have been pre-
pared and they were tested for antimicrobial and antifungal
activities. 4-Chlorothymol (2) was tested to be most active
against S. aureus, S. epidermis at a concentration of 12.5 and
25 ppm, respectively. Also the same compound 4-chloro-
thymol (2) was found to be six times, 2.5 times and over two
times more active than thymol against C. albicans (AI),
C. albicans (MTCC), and C. albicans (CN), respectively.
Acknowledgments The authors are thanks to Prof. Ram Raja-
sekhran, Ex-Director and Shri Sudeep Tandon, Head, Process
Chemistry and Technology Department, Central Institute of Medici-
nal and Aromatic Plants, for his keen interest in the work.
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