Upload
others
View
6
Download
0
Embed Size (px)
Citation preview
51
Chapter 3
Synthesis and antibacterial activity of
phenolic monoterpene derivatives
Estelar
52
3.1. Introduction
Natural products have been the mainstay in providing novel chemical
scaffolds for many drugs1 as well as leads that were chemically modified and
developed as antibacterial agents. Herbs and higher plants containing terpenoids and
their oxygenated derivatives have been used as fragrance and flavours for centuries.
Terpenes have been drawn increasing commercial attention because of their role in
prevention and therapy of several diseases including natural insecticides and
antimicrobial agents. The large terpene family has provided numerous examples of
antibacterial compounds including monoterpenoids, sesquiterpenoids, diterpenoids
and triterpenoids.2-5 Monoterpenes are abundant natural C-10 compounds that meet
the non-toxicity and ecological role for new drug candidates. Antiparasitic activities
have already been reported for pure monoterpenes.6
The phenolic monoterpenes are well represented in the family Asteraceae,7
particularly within the genus Senecio, Eupatorium and Inula.8,9 Monoterpenoid
phenol derivatives, like zingerone and vanillin are potent vanilloid receptor agonists.
Guaiacol is used as an expectorant.10 Eugenol, the principal chemical component of
clove oil from Eugenia aromatica and Cinnamon11 has been reported to inhibit the
growth of several microbes viz. Listeria monocytogenes, Bacillus cereus,
Campylobacter jejuni, Escherichia coli, Salmonella enterica and fungi viz.
Microsporum gypseum and Aspergillus sp. by interaction with the cell membrane.12,13
The monoterpenes thymol, carvacrol, menthol and carveol exhibited marked potency
in the snail vector of schistosomiasis and showed molluscicidal activity.14 Thymol and
carvacrol are biologically active monoterpene phenols that have been isolated from
Thymus vulgaris, Origanum vulgare, Satureja thymbra and Thymbra capitata15-18
and
are widely used as general antiseptic in medicine, cosmetics and food industry due to
their potent fungicide, bactericide and antioxidants properties.19-21
As component of
volatile oils in many plants they have been proved to possess antimicrobial and
antioxidant activities.22
The essential oils of Satureja cuneifolia, Origanum dictamnus and Thymus
caramanicus having thymol and carvacrol as major constituents showed significant
antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Salmonella
enterica, Escherichia coli and Campylobacter jijuni and human pathogenic fungus.23-
26 Several hydroxyl derivatives of thymol, isolated from Centipida minima and 10-
Estelar
53
isobutyryloxy-8,9-epoxythymol isobutyrate from Inula helenium root showed good to
moderate antimicrobial activity against Gram-positive bacteria.27,28
Semi-synthetic
studies of natural products have been a reliable method for the generation of more
active and less toxic derivatives. Chemical modification of natural monoterpenoids to
various ether and ester derivatives have been reported to result in modification of
biological activity.29,30
Keeping the diverse therapeutic activities of phenolic monoterpenes in view, it
was contemplated to synthesize a novel series of thymol and carvacrol derivatives to
improve the antibacterial activity of title compounds. Literature search revealed
limited reports on the ester and ether derivatives of thymol and carvacrol. The
synthesis and antibacterial evaluation of fourteen esters and six ether analogues of
thymol and carvacrol have been given here.
3.2. Experimental
3.2.1. Scheme for the synthesis of ester derivatives
OH
O
OHR O R
O+
i. SOCl2
ii. TEA, DCM
O
OHR+
i. SOCl2
ii. TEA, DCM
OH
Th 1 - Th 7thymol acid derivatives
Ca 1 - Ca 7carvacrol acid derivatives
CH3 CH2CH3 CH
CH3
CH3
H2C CH
CH3
CH3
HCCH
CH3 H2C
where R =
Scheme 3.1. Reagents and conditions: i. SOCl2, reflux, 2 h; ii. TEA, anhydrous DCM,
0 oC, 10 h
O R
O
Estelar
54
3.2.2. Scheme for the synthesis of ether derivatives
OH
Br
O
R
O
O
R
+
i
Br
O
R+
i
thymol p-substituted
phenacyl bromide derivativesTh 8 - Th 10
OH O
O
R
carvacrol p-substituted
phenacyl bromide derivativesCa 8 - Ca 10
where R =Br CH3 OCH3
Scheme 3.2. Reagent and condition: i. K2CO3, MeCN, 0 oC - rt, 8 -10 h
3.2.3. General experimental procedure for the synthesis of ester derivatives
(Th 1 to Th 7) and (Ca 1 to Ca 7)
To the acid derivatives (1.0 mequiv) was added thionyl chloride (3.0 mequiv)
drop wise at 0 oC then the resulting reaction mixture was refluxed for 2 h with
constant stirring. After completion of reaction, excess of thionyl chloride was
evaporated under reduced pressure to obtain acid chloride derivatives. To a solution
of thymol or carvacrol (1.0 equiv) and triethylamine (1.1 equiv) in anhydrous
dichloromethane (20 ml) at 0 oC were added corresponding acid chlorides (1.1 equiv).
The reaction mixture was stirred at 0 oC for about 1 h and the stirring was continued
at room temperature for about 10 h (progress of reaction was monitored by TLC and
GC). After completion of reaction, reaction mixture was diluted with 50 ml of
distilled water and extracted with DCM (3×50 ml). The combined organic layer was
washed with distilled water (3×50 ml), brine solution (3×50 ml) and dried over
anhydrous sodium sulphate, concentrated it under reduced pressure to get crude
product. The crude product was purified by column chromatography using silica gel
(60-120 mesh) column with 3-4% diethyl ether: hexane as an eluting solvent to get
pure corresponding ester derivatives (Th 1 to Th 7) and (Ca 1 to Ca 7) with 75 - 85%
Estelar
55
yield. All the ester derivatives were characterized with the help of their IR, MS, and
NMR (1H &
13C NMR) spectroscopic data.
3.2.4. General experimental procedure for the synthesis of ether
derivatives (Th 8 to Th 10) and (Ca 8 to Ca 10)
To a solution of thymol or carvacrol (1.0 equiv) in dry acetonitrile, were added
powdered potassium carbonate (5.0 equiv) and corresponding p-substituted phenacyl
bromide derivatives (1.1 equiv) at 0 oC. The reaction mixture was stirred at 0
oC for
about 15 min and the stirring was continued at room temperature for about 8-10 h
(progress of reaction was monitored by TLC). After completion of reaction, the
reaction mixture was quenched with distilled water and extracted with
dichloromethane (3×50 ml), combined organic layer was washed with aqueous
solution of sodium bicarbonate (3×50 ml), distilled water (3×50 ml), brine solution
(3×50 ml) and dried over anhydrous sodium sulphate. After removal of solvent in
vacuo, the residue obtained was purified by column chromatography using silica gel
(60-120 mesh) column with Hexane/Et2O (1:20 to 2:20) as eluent to afford the pure
ether derivatives (Th 8 to Th 10) and (Ca 8 to Ca 10) in 61– 78% yields. All the ether
derivatives were characterized with the help of their IR, MS, and NMR (1H &
13C
NMR) spectroscopic data.
3.3. Synthesis of derivatives
3.3.1. Synthesis of ester derivatives of Thymol (Th 1 to Th 7)
3.3.1.1. Synthesis of 2-isopropyl-5-methylphenyl acetate (Th 1)
The general synthetic method described earlier, afforded compound Th 1 from
thymol (1.0 g, 6.6 mmol, 1.0 mequiv) with acetyl chloride (0.5 g, 7.3 mmol. 1.1
mequiv) and triethyl amine (0.7 g, 7.3 mmol, 1.1 mequiv) in anhydrous DCM (20 ml)
as reaction solvent.
O
O
2-isopropyl-5-methylphenyl acetate
Molecular Formula: C12H16O2 (M.W. 192.0); Physical state: colourless liquid;
Yield: 80%; Purity: 97%; GC-MS (EI, 70 eV): m/z (%)= 192 ([M+], 5), 150 (36),
135 (100), 115 (6), 107 (10), 91 (8); IR υmax: 3028, 2962, 2872, 1760, 1622, 1368,
Estelar
56
1207, 1149, 1089, 899, 671 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.18 (d, J = 8.0 Hz,
1H, Ar-H), 7.01 (d, J = 7.5 Hz, 1H, Ar-H), 6.80 (s, 1H, Ar-H), 2.93-3.00 (m, 1H, CH),
2.30 (s, 6H, CH3), 1.18 (d, J = 7.0 Hz, 6H, CH3); 13
C NMR (CDCl3, 125 MHz): δ
169.7 (C=O), 147.8 (CAr), 136.9 (CAr), 136.3 (CAr), 127.0 (CHAr), 126.4 (CHAr), 122.6
(CHAr), 27.0 (CH), 25.4 (COCH3), 22.9 (2 × CH3), 20.8 (CH3).
3.3.1.2. Synthesis of 2-isopropyl-5-methylphenyl propionate (Th 2)
The general synthetic method described earlier, afforded compound Th 2 from
thymol (1.0 g, 6.6 mmol, 1.0 mequiv) with propionyl chloride (0.6 g, 7.3 mmol. 1.1
mequiv) and triethyl amine (0.7 g, 7.3 mmol, 1.1 mequiv) in anhydrous DCM (20 ml)
as reaction solvent.
O
O
2-isopropyl-5-methylphenyl propionate
Molecular Formula: C13H18O2 (M.W. 206.0); Physical state: colourless liquid;
Yield: 80%; Purity: 96%; GC-MS (EI, 70 eV): m/z (%)= 206 ([M+], 6), 150 (36),
135 (100), 115 (4), 107 (6), 91 (8); IR υmax: 3028, 2964, 2872, 1759, 1621, 1461,
1344, 1194, 1151, 897 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.17 (d, J = 8.0 Hz, 1H,
Ar-H), 6.99 (d, J = 7.5 Hz, 1H, Ar-H), 6.80 (s, 1H, Ar-H), 2.95-2.97 (m, 1H, CH),
2.58 (q, J = 7.5 Hz, 2H, CH2), 2.29 (s, 3H, CH3), 1.27 (t, J = 7.5 Hz, 3H, CH3), 1.18
(d, J = 7.0 Hz, 6H, CH3); 13
C NMR: (CDCl3, 125 MHz): δ 172.5 (C=O), 147.8 (CAr),
136.8 (CAr), 136.3 (CAr), 126.9 (CHAr), 124.0 (CHAr), 122.6 (CHAr), 34.9 (CH2), 27.0
(CH), 22.8 (2 × CH3), 20.6 (CH3), 12.0 (CH3).
3.3.1.3. Synthesis of 2-isopropyl-5-methylphenyl isobutyrate (Th 3)
The general synthetic method described earlier, afforded compound Th 3 from
thymol (1.0 g, 6.6 mmol, 1.0 mequiv) with isobutyryl chloride (0.7 g, 7.3 mmol. 1.1
mequiv) and triethyl amine (0.7 g, 7.3 mmol, 1.1 mequiv) in anhydrous DCM (20 ml)
as reaction solvent.
O
O
2-isopropyl-5-methylphenyl isobutyrate
Estelar
57
Molecular Formula: C14H20O2 (M.W. 220.0); Physical state: colourless liquid;
Yield: 76%; Purity: 98%; GC-MS (EI, 70 eV): m/z (%)= 220 ([M+], 8), 150 (46),
135 (100), 107 (6), 91 (8); IR υmax: 3029, 2964, 2871, 1756, 1618, 1461, 1344, 1224,
1149, 878 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.20 (d, J = 8.0 Hz, 1H, Ar-H), 7.04
(d, J = 8.0 Hz, 1H, Ar-H), 6.78 (s, 1H, Ar-H), 3.24 (hept, J = 7.0 Hz, 1H, CH), 2.83
(hept, J = 7.0 Hz, 1H, CH), 2.30 (s, 3H, CH3), 1.32 (d, J = 6.5 Hz, 6H, CH3), 1.18 (d,
J = 6.5 Hz, 6H, CH3); 13
C NMR (CDCl3, 125 MHz): δ 175.3 (C=O), 148.1 (CAr),
137.1 (CAr), 136.1 (CAr), 126.5 (CHAr), 126.2 (CHAr), 122.5 (CHAr), 33.4 (CH), 26.9
(CH), 22.6 (2 × CH3), 20.5 (CH3), 18.7 (2 × CH3).
3.3.1.4. Synthesis of 2-isopropyl-5-methylphenyl 3-methylbutanoate (Th 4)
The general synthetic method described earlier, afforded compound Th 4 from thymol
(1.0 g, 6.6 mmol, 1.0 mequiv) with isovaleryl chloride (0.8 g, 7.3 mmol. 1.1 mequiv)
and triethyl amine (0.7 g, 7.3 mmol, 1.1 mequiv) in anhydrous DCM (20 ml) as
reaction solvent.
O
O
2-isopropyl-5-methylphenyl 3-methylbutanoate
Molecular Formula: C15H22O2 (M.W. 234.0); Physical state: colourless liquid;
Yield: 80%; Purity: 92%; GC-MS (EI, 70 eV): m/z (%)= 234 ([M+], 4), 150 (48),
135 (100), 107 (4), 91 (8); IR υmax: 3028, 2931, 2872, 1757, 1621, 1463, 1364, 1238,
1150, 816 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.19 (d, J = 8.0 Hz, 1H, Ar-H), 7.01
(d, J = 8.0 Hz, 1H, Ar-H), 6.79 (s, 1H, Ar-H), 2.96-2.99 (m, 1H, CH), 2.46 (d, J = 7.0
Hz, 2H, CH2), 2.31 (s, 3H, CH3), 2.25-2.29 (m, 1H, CH), 1.18 (d, J = 7.0 Hz, 6H,
CH3), 1.07 (d, J = 7.0 Hz, 6H, CH3); 13
C NMR (CDCl3, 125 MHz): δ 171.6 (C=O),
147.7 (CAr), 136.8 (CAr), 136.3 (CAr), 126.8 (CHAr), 126.2 (CHAr), 122.5 (CHAr), 43.2
(CH2), 26.8 (CH), 25.6 (CH), 22.9 (2 × CH3), 22.3 (2 × CH3), 20.7 (CH3).
3.3.1.5. Synthesis of (E)-2-isopropyl-5-methylphenyl but-2-enoate (Th 5)
The general synthetic method described earlier, afforded compound Th 5 from
thymol (1.0 g, 6.6 mmol, 1.0 mequiv) with crotonyl chloride (0.7 g, 7.3 mmol, 1.1
mequiv) and triethyl amine (0.7 g, 7.33 mmol, 1.1 mequiv) in anhydrous DCM (20
ml) as reaction solvent.
Estelar
58
O
O
(E)-2-isopropyl-5-methylphenyl but-2-enoate
Molecular Formula: C14H18O2 (M.W. 218.0); Physical state: colourless liquid;
Yield: 84%; Purity: 87%; GC-MS (EI, 70 eV): m/z (%)= 218 ([M+], 4), 150 (46),
135 (100), 107 (6), 91 (8); IR υmax: 3025, 2927, 2871, 1761, 1657, 1621, 1458, 1363,
1231, 1154, 816 cm-1;
1H NMR (CDCl3, 500 MHz,): δ 7.16 (d, J = 8.0 Hz, 1H, Ar-
H), 7.00 (d, J = 8.0 Hz, 1H, Ar-H), 6.80 (s, 1H, Ar-H), 6.00-6.08 (m, 1H, CH), 5.25
(d, J = 11.0 Hz, 1H, CH-), 2.88-3.01 (m, 1H, CH), 2.29 (s, 3H, CH3), 1.94 (d, J = 6.0
Hz, 3H, CH3), 1.17 (d, J = 7.0 Hz, 6H, CH3); 13
C NMR: (CDCl3, 125 MHz): δ 169.0
(C=O), 146.8 (CAr), 145.5 (CH), 135.8 (CAr), 135.4 (CAr), 126.0 (CHAr), 125.2 (CHAr),
121.7 (CHAr), 118.0 (CH), 25.9 (CH), 21.8 (2 × CH3), 19.7 (CH3), 17.0 (CH3).
3.3.1.6. Synthesis of 2-isopropyl-5-methylphenyl benzoate (Th 6)
The general synthetic method described earlier, afforded compound Th 6 from
thymol (1.0 g, 6.6 mmol, 1.0 mequiv) with benzoyl chloride (1.0 g, 7.3 mmol. 1.1
mequiv) and triethyl amine (7.4 g, 7.3 mmol, 1.1 mequiv.) in anhydrous DCM (20 ml)
as reaction solvent.
O
O
2-isopropyl-5-methylphenyl benzoate
Molecular Formula: C17H18O2 (M.W. 254.0); Physical state: colourless liquid;
Yield: 85%; Purity: 98%; GC-MS (EI, 70 eV): m/z (%)= 254 ([M+], 10), 150 (10),
149 (82), 105 (100), 91 (4), 77 (48), 51 (8); IR υmax: 3032, 2926, 2870, 1736, 1621,
1451, 1363, 1236, 1150, 816 cm-1;
1H NMR (CDCl3, 500 MHz): δ 8.27 (d, J = 7.5
Hz, 2H, Ar-H), 7.69 (t, J = 7.5 Hz, 1H, Ar-H), 7.57 (t, J = 8.0 Hz, 2H, Ar-H), 7.29 (d,
J = 8.0 Hz, 1H, Ar-H), 7.12 (d, J = 7.5 Hz, 1H, Ar-H), 6.99 (s, 1H, Ar-H), 3.07-3.15
(m, 1H, CH), 2.39 (s, 3H, CH3), 1.26 (d, J = 6.5 Hz, 6H, CH3); 13
C NMR (CDCl3, 125
MHz): δ 165.4(C=O), 148.1 (CAr), 137.2 (CAr), 136.7 (CAr), 133.5 (CAr), 130.1 (2 ×
CHAr), 129.6 (CHAr), 128.6 (2 × CHAr), 127.2 (CHAr), 126.5 (CHAr), 122.9 (CHAr),
27.3 (CH), 23.1 (2 × CH3), 20.9 (CH3).
Estelar
59
3.3.1.7. Synthesis of 2-isopropyl-5-methylphenyl-2-phenylacetate (Th 7)
The general synthetic method described earlier, afforded compound Th 7 from
thymol (1.0 g, 6.6 mmol, 1.0 mequiv) with 2-phenyl acetyl chloride (1.1 g, 7.3 mmol.
1.1 mequiv) and triethyl amine (7.4 g, 7.3 mmol, 1.1 mequiv.) in anhydrous DCM (20
ml) as reaction solvent.
O
O
2-isopropyl-5-methylphenyl-2-phenylacetate
Molecular Formula: C18H20O2 (M.W. 268.0); Physical state: colourless liquid;
Yield: 85%; Purity: 98%; GC-MS (EI, 70 eV): m/z (%)= 268 ([M+], 2), 150 (68),
135 (100), 118 (26), 91 (34), 65 (6); IR υmax: 3031, 2927, 2870, 1753, 1621, 1454,
1363, 1230, 1149, 817 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.35 (d, J = 7.5 Hz, 2H,
Ar-H), 7.30 (t, J = 7.5 Hz, 2H, Ar-H), 7.24 (t, J = 7.5 Hz, 1H, Ar-H), 7.10 (d, J = 8.0
Hz, 1H, Ar-H), 6.94 (d, J = 7.5 Hz, 1H, Ar-H), 6.74 (s, 1H, Ar-H), 3.80 (s, 2H, CH2),
2.69-2.75 (m, 1H, CH), 2.23 (s, 3H, CH3), 1.02 (d, J = 8.0 Hz, 6H, CH3); 13
C NMR:
(CDCl3, 125 MHz): δ 170.2 (C=O), 148.0 (CAr), 137.1 (CAr), 136.5 (CAr), 133.7 (CAr),
129.4 (2 × CHAr), 128.8 (2 × CHAr), 127.4 (CHAr), 127.2 (CHAr), 126.4 (CHAr), 122.7
(CHAr), 41.7 (CH2), 27.0 (CH), 23.0 (2 × CH3), 19.7 (CH3).
3.3.2. Synthesis of ester derivatives of Carvacrol (Ca 1 to Ca 7)
3.3.2.1. Synthesis of 5-isopropyl-2-methylphenyl acetate (Ca 1)
The general synthetic method described earlier, afforded compound Ca 1 from
carvacrol (1.0 g, 6.66 mmol, 1.0 mequiv) with acetyl chloride (0.5g, 7.3 mmol. 1.1
mequiv) and triethyl amine (0.7 g, 7.3 mmol, 1.1 mequiv) in anhydrous DCM (20 ml)
as reaction solvent.
O
O
5-isopropyl-2-methylphenyl acetate
Molecular Formula: C12H16O2 (M.W. 192.0); Physical state: colourless liquid;
Yield: 78%; Purity: 97%; GC-MS (EI, 70 eV): m/z (%)= 192 ([M+], 4), 150 (66),
135 (100), 107 (12), 91 (10); IR υmax: 3025, 2961, 2928, 2871, 1766, 1623, 1460,
Estelar
60
1369, 1215, 1169, 819 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.13 (d, J = 8.0 Hz, 1H,
Ar-H), 7.00 (dd, J = 1.5 Hz & 7.5 Hz, 1H, Ar-H), 6.85 (d, J = 1.5 Hz, 1H, Ar-H),
2.85-2.87 (m, 1H, CH), 2.29 (s, 3H, CH3), 2.12 (s, 3H, CH3), 1.21 (d, J = 7.0 Hz, 6H,
CH3); 13
C NMR (125 MHz, CDCl3): δ 167.8 (C=O), 147.8 (CAr), 146.6 (CAr), 129.4
(CAr), 125.7 (CHAr), 122.7 (CHAr), 118.3 (CHAr), 32.1 (CH), 22.4 (2 × CH3), 19.3
(CH3),14.3 (CH3).
3.3.2.2. Synthesis of 5-isopropyl-2-methylphenyl propionate (Ca 2)
The general synthetic method described earlier, afforded compound Ca 2 from
carvacrol (1.0 g, 6.6 mmol, 1.0 mequiv) with propionyl chloride (0.6 g, 7.3 mmol. 1.1
mequiv) and triethyl amine (0.7 g, 7.3 mmol, 1.1 mequiv) in anhydrous DCM (20 ml)
as reaction solvent.
O
O
5-isopropyl-2-methylphenyl propionate
Molecular Formula: C13H18O2 (M.W. 206.0); Physical state: colourless liquid;
Yield: 75%; Purity: 98%; GC-MS (EI, 70 eV): m/z (%)= 206 ([M+], 4), 150 (66),
135 (100), 107 (8), 91 (6); IR υmax: 3028, 2961, 2871, 1761, 1622, 1460, 1351, 1236,
1148, 898 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.13 (d, J = 7.5 Hz, 1H, Ar-H), 7.01
(d, J = 7.5 Hz, 1H, Ar-H), 6.86 (s, 1H, Ar-H), 2.84-2.88 (m, 1H, CH), 2.60 (q, J = 7.5
Hz, 2H, CH2), 2.12 (s, 3H, CH3), 1.28 (t, J = 7.5 Hz, 3H, CH3), 1.22 (d, J = 7.0 Hz,
6H, CH3); 13
C NMR (CDCl3, 125 MHz): δ 172.5 (C=O), 149.1 (CAr), 147.9 (CAr),
130.7 (CAr), 127.0 (CHAr), 123.9 (CHAr), 119.6 (CHAr), 33.4 (CH), 27.5 (CH2), 23.8 (2
× CH3), 15.6 (CH3), 9.1 (CH3).
3.3.2.3. Synthesis of 5-isopropyl-2-methylphenyl isobutyrate (Ca 3)
The general synthetic method described earlier, afforded compound Ca 3 from
carvacrol (1.0 g, 6.66 mmol, 1.0 mequiv) with isobutyryl chloride (0.7 g, 7.3 mmol.
1.1 mequiv) and triethyl amine (0.7 g, 7.3 mmol, 1.1 mequiv) in anhydrous DCM (20
ml) as reaction solvent.
Estelar
61
O
O
5-isopropyl-2-methylphenyl isobutyrate
Molecular Formula: C14H20O2 (M.W. 220.0); Physical state: colourless liquid;
Yield: 85%; Purity: 98%; GC-MS (EI, 70 eV): m/z (%)= 220 ([M+], 10), 150 (92),
135 (100), 107 (8), 91 (8); IR υmax: 3024, 2963, 2931, 2874, 1757, 1622, 1469, 1343,
1232, 1132, 818 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.13 (d, J = 7.0 Hz, 1H, Ar-H),
7.01 (d, J = 5.0 Hz, 1H, Ar-H), 6.85 (s, 1H, Ar-H), 2.81-2.88 (m, 2H, CH), 2.13 (s,
3H, CH3), 1.35 (d, J = 6.5Hz, 6H, CH3), 1.23 (d, J = 7.0 Hz, 6H, CH3); 13
C NMR
(CDCl3, 125 MHz): δ 175.0 (C=O), 149.1 (CAr), 147.8 (CAr), 130.6 (CAr), 126.9
(CHAr), 123.7 (CHAr), 119.5 (CHAr), 34.0 (CH), 33.0 (CH), 23.7 (2 × CH3), 18.9 (2 ×
CH3), 15.5 (CH3).
3.3.2.4. Synthesis of 5-isopropyl-2-methylphenyl 3-methylbutanoate (Ca 4)
The general synthetic method described earlier, afforded compound Ca 4 from
carvacrol (1.0 g, 6.6 mmol, 1.0 mequiv) with isovaleryl chloride (0.8 g, 7.3 mmol. 1.1
mequiv) and triethyl amine (0.7 g, 7.3 mmol, 1.1 mequiv) in anhydrous DCM (20 ml)
as reaction solvent.
O
O
5-isopropyl-2-methylphenyl 3-methylbutanoate
Molecular Formula: C15H22O2 (M.W. 234.0); Physical state: colourless liquid;
Yield: 75%; Purity: 97%; GC-MS (EI, 70 eV): m/z (%)= 234 ([M+], 6), 150 (88),
135 (100), 107 (4), 91 (8); IR υmax: 3024, 2961, 2930, 2872, 1759, 1622, 1462, 1364,
1233, 1115, 818 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.14 (d, J = 8.0 Hz, 1H, Ar-H),
7.00 (dd, J = 1.5 Hz & 6.5 Hz, 1H, Ar-H), 6.84 (d, J = 1.5 Hz, 1H, Ar-H), 2.84-2.91
(m, 1H, CH), 2.46 (d, J = 7.00 Hz, 2H, CH2), 2.22-2.30 (m, 1H, CH), 2.13 (s, 3H,
CH3), 1.22 (d, J = 7.0 Hz, 6H, CH3), 1.07 (d, J = 6.5 Hz, 6H, CH3); 13
C NMR
(CDCl3, 125 MHz): δ 171.1 (C=O), 149.0 (CAr), 147.8 (CAr), 130.6 (CAr), 126.9
(CHAr), 123.7 (CHAr), 119.6 (CHAr), 43.0 (CH2), 33.3 (CH), 25.6 (CH), 23.7 (2 ×
CH3), 22.3 (2 × CH3), 15.6 (CH3).
Estelar
62
3.3.2.5. Synthesis of (E)-5-isopropyl-2-methylphenyl but-2-enoate (Ca 5)
The general synthetic method described earlier, afforded compound Ca 5 from
carvacrol (1.0 g, 6.6 mmol, 1.0 mequiv) with crotonyl chloride (0.7 g, 7.3 mmol, 1.1
mequiv) and triethyl amine (0.7 g, 7.3 mmol, 1.1 mequiv) in anhydrous DCM (20 ml)
as reaction solvent.
O
O
(E)-5-isopropyl-2-methylphenyl but-2-enoate
Molecular Formula: C14H18O2 (M.W. 218.0); Physical state: colourless liquid;
Yield: 78%; Purity: 91%; GC-MS (EI, 70 eV): m/z (%)= 218 ([M+], 20), 150 (100),
135 (52), 107 (5), 91 (10), 69 (25); IR υmax: 3024, 2961, 2928, 2871, 1738, 1657,
1622, 1459, 1363, 1232, 1157, 819 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.16-7.19
(m, 1H, CH), 7.13 (d, J = 8.0 Hz, 1H, Ar-H), 7.00 (dd, J = 1.5 Hz & 6.5 Hz, 1H, Ar-
H), 6.88 (s, 1H, Ar-H), 6.06 (dd, J = 1.5Hz & 14 Hz, 1H, CH), 2.86 (m, 1H, CH), 2.12
(s, 3H, CH3), 1.94 (dd, J = 1.5 Hz & 7.0Hz, 3H, CH3), 1.22 (d, J = 7.0 Hz, 6H, CH3);
13C NMR (CDCl3, 125 MHz): δ 164.5 (C=O), 149.1 (CAr), 147.8 (CH), 146.5 (CAr),
130.7 (CAr), 127.2 (CHAr), 123.8 (CHAr), 121.9 (CH), 119.7 (CHAr), 33.4 (CH), 23.7
(2 × CH3), 18.0 (CH3), 14.0 (CH3).
3.3.2.6. Synthesis of 5-isopropyl-2-methylphenyl benzoate (Ca 6)
The general synthetic method described earlier, afforded compound Ca 6 from
carvacrol (1.0 g, 6.6 mmol, 1.0 mequiv) with benzoyl chloride (1.0 g, 7.3 mmol. 1.1
mequiv) and triethyl amine (7.4 g, 7.3 mmol, 1.1 mequiv.) in anhydrous DCM (20 ml)
as reaction solvent.
O
O
5-isopropyl-2-methylphenyl benzoate
Molecular Formula: C17H18O2 (M.W. 254.0); Physical state: colourless liquid;
Yield: 82%; Purity: 97%; GC-MS (EI, 70 eV): m/z (%)= 254 ([M+], 12), 105 (100),
77 (26), 51 (4); IR υmax: 3062, 2960, 2927, 2870, 1737, 1621, 1451, 1341, 1238,
Estelar
63
1116, 819 cm-1;
1H NMR (CDCl3, 500 MHz): δ 8.23 (d, J = 8.0 Hz, 2H, Ar-H), 7.65
(t, J = 7.5 Hz, 1H, Ar-H), 7.52 (t, J = 7.5 Hz, 2H, Ar-H), 7.20 (d, J = 8.0 Hz, 1H, Ar-
H), 7.06 (d, J = 8.0 Hz, 1H, Ar-H), 7.00 (s, 1H, Ar-H), 2.89-2.92 (m, 1H, CH), 2.19
(s, 3H, CH3), 1.25 (d, J = 7.0 Hz, 6H, CH3); 13
C NMR (CDCl3, 125 MHz): δ 164.7
(C=O), 149.2 (CAr), 148.0 (CAr), 133.3 (CHAr), 130.7 (CHAr), 130.0 (2 × CHAr), 129.4
(CAr), 128.4 (2 × CHAr), 127.2 (CAr), 124.0 (CHAr), 119.7 (CHAr), 33.4 (CH), 23.8 (2 ×
CH3), 15.7 (CH3).
3.3.2.7. Synthesis of 5-isopropyl-2-methylphenyl 2-phenylacetate (Ca 7)
The general synthetic method described earlier, afforded compound Ca 7 from
carvacrol (1.0 g, 6.6 mmol, 1.0 mequiv) with 2-phenyl acetyl chloride (1.1 g, 7.3
mmol. 1.1 mequiv) and triethyl amine (7.4 g, 7.3 mmol, 1.1 mequiv.) in anhydrous
DCM (20 ml) as reaction solvent.
O
O
5-isopropyl-2-methylphenyl 2-phenylacetate
Molecular Formula: C18H20O2 (M.W. 268.0); Physical state: colourless liquid;
Yield: 78%; Purity: 88%; GC-MS (EI, 70 eV): m/z (%)= 268 ([M+], 2), 150 (100),
135 (96), 118 (35), 91 (42), 65 (8); IR υmax: 3088, 3064, 3031, 2960, 2926, 2870,
1747, 1622, 1454, 1234, 1119, 820 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.41 (d, J =
7.0 Hz, 2H, Ar-H), 7.37 (t, J = 7.0 Hz, 1H, Ar-H), 7.30 (t, J = 6.0 Hz, 2H, Ar-H), 7.09
(d, J = 8.0 Hz, 1H, Ar-H), 6.99 (dd, J = 1.5 Hz & 7.5 Hz, 1H, Ar-H), 6.83 (d, J = 1.5
Hz, 1H, Ar-H), 3.87 (s, 2H, CH2), 2.83-2.86 (m, 1H, CH), 1.97 (s, 3H, CH3), 1. 20 (d,
J = 6.5 Hz, 6H, CH3); 13
C NMR (CDCl3, 125 MHz): δ 169.7 (C=O), 149.24 (CAr),
148.0 (CAr), 133.6 (CAr), 130.9 (CHAr), 129.4 (2 × CHAr), 128.7 (2 × CHAr), 127.3
(CAr), 127.1 (CHAr), 124.1 (CHAr), 119.7 (CHAr), 41.5 (CH2), 33.6 (CH), 23.9 (2 ×
CH3), 15.6 (CH3).
Estelar
64
Figure 3.1. 1H NMR spectrum of Th 1
Figure 3.2. 13
C NMR spectrum of Th 1
O
O
O
O
Estelar
65
Figure 3.3. 1H NMR spectrum of Th 2
Figure 3.4. 13
C NMR spectrum of Th 2
O
O
O
O
Estelar
66
Figure 3.5. 1H NMR spectrum of Th 3
Figure 3.6. 13
C NMR spectrum of Th 3
O
O
O
O
Estelar
67
Figure 3.7. 1H NMR spectrum of Th 4
Figure 3.8. 13
C NMR spectrum of Th 4
O
O
O
O
Este
lar
68
Figure 3.9. 1H NMR spectrum of Th 5
Figure 3.10. 13
C NMR spectrum of Th 5
O
O
O
O
Estelar
69
Figure 3.11. 1H NMR spectrum of Th 6
Figure 3.12. 13
C NMR spectrum of Th 6
O
O
O
O
Estelar
70
Figure 3.13. 1H NMR spectrum of Th 7
Figure 3.14. 13
C NMR spectrum of Th 7
O
O
O
O
Estelar
71
Figure 3.15. 1H NMR spectrum of Ca 1
Figure 3.16. 13
C NMR spectrum of Ca 1
O
O
O
O
Estelar
72
Figure 3.17. 1H NMR spectrum of Ca 2
Figure 3.18. 13
C NMR spectrum of Ca 2
O
O
O
O
Estelar
73
Figure 3.19. 1H NMR spectrum of Ca 3
Figure 3.20. 13
C NMR spectrum of Ca 3
O
O
O
O
Estelar
74
Figure 3.21. 1H NMR spectrum of Ca 4
Figure 3.22. 13
C NMR spectrum of Ca 4
O
O
O
O
Estelar
75
Figure 3.23. 1H NMR spectrum of Ca 5
Figure 3.24. 13
C NMR spectrum of Ca 5
O
O
O
O
Estelar
76
Figure 3.25. 1H NMR spectrum of Ca 6
Figure 3.26. 13
C NMR spectrum of Ca 6
O
O
O
O
Estelar
77
Figure 3.27. 1H NMR spectrum of Ca 7
Figure 3.28. 13
C NMR spectrum of Ca 7
O
O
O
O
Estelar
78
3.3.3. Synthesis of ether derivatives of thymol (Th 8 to Th 10) and
carvacrol (Ca 8 to Ca 10)
3.3.3.1. Synthesis of 2-(2-isopropyl-5-methylphenoxy)-1-(4-bromophenyl)
ethanone (Th 8)
The general synthetic method described earlier, afforded compounds 15 from
thymol (1.0 g, 6.6 mmol, 1.0 mequiv) with 4-bromophenacyl bromide (2.0 g, 7.3
mmol, 1.1 mequiv) and potassium carbonate (4.6 g, 33.3 mmol, 5.0 mequiv.) in
acetonitrile (20 ml) as reaction solvent.
O
O
Br
2-(2-isopropyl-5-methylphenoxy)-1-(4-bromophenyl)ethanone
Molecular Formula: C18H19BrO2 (M.W. 346.0); Physical state: off white solid;
Yield: 64.6%; Purity: 97%; mp: 54-56 oC; MS: [M
+1]: m/z 347; IR υmax: 3075,
3060, 2942, 2924, 2865, 1690, 1609, 1356, 1177, 1145, 806 cm-1;
1H NMR (CDCl3,
500 MHz): δ 7.88 (d, 2H, J = 6.5 Hz, Ar-H), 7.63 (d, 2H, J = 7.0 Hz, Ar-H), 7.12 (d,
1H, J = 8.0 Hz, Ar-H), 6.79 (d, 1H, J = 8.0 Hz, Ar-H), 6.57 (s, 1H, Ar-H), 5.16 (s, 2H,
CH2), 3.29- 3.36 (m, 1H, CH), 2.29 (s, 3H, CH3), 1.20 (d, 6H, J = 7.0 Hz, CH3); 13
C
NMR (CDCl3, 125 MHz): δ 194.1 (C=O), 154.7 (CAr), 136.2 (CAr), 134.3 (CAr),
133.3 (CAr), 131.8 (2 × CHAr), 129.7 (2 × CHAr), 128.8 (CAr), 126.1 (CHAr), 122.2
(CHAr), 112.2 (CHAr), 71.1 (CH2), 26.2 (CH), 22.7 (2 × CH3), 21.1 (CH).
3.3.3.2. Synthesis of 2-(2-isopropyl-5-methylphenoxy)-1-p-tolylethanone
(Th 9)
The general synthetic method described earlier, afforded compounds Th 9 from
thymol (1.0 g, 6.6 mmol, 1.0 mequiv) with 4-methylphenacyl bromide (1.5 g, 7.3
mmol, 1.1 mequiv) and potassium carbonate (4.6 g, 33.3 mmol, 5.0 mequiv.) in
acetonitrile (20 ml) as reaction solvent.
O
O
CH3
2-(2-isopropyl-5-methylphenoxy)-1-p-tolylethanone
Estelar
79
Molecular Formula: C19H22O2 (M.W. 282.0); Physical state: off white solid; Yield:
69.9%; Purity: 98%; mp: 56- 58 oC; MS: [M
+1], m/z 283; IR υmax: 3070, 3027, 2940,
2904, 2864, 1695, 1606, 1453, 1356, 1146, 807 cm-1;
1H NMR (CDCl3, 500 MHz): δ
7.92 (d, 2H, J = 6.5 Hz, Ar-H), 7.26 (d, 2H, J = 7.5 Hz, Ar-H), 7.12 (d, 1H, J = 7.5
Hz, Ar-H), 6.78 (d, 1H, J = 7.5 Hz, Ar-H), 6.58 (s, 1H, Ar-H), 5.21 (s, 2H, CH2),
3.35- 3.40 (m, 1H, CH), 2.42 (s, 3H, CH3), 2.28 (s, 3H, CH3), 1.20 (d, 6H, J = 7.0 Hz,
CH3); 13
C NMR (CDCl3, 125 MHz): δ 194.4 (C=O), 155.0 (CAr), 144.5 (CAr), 136.2
(CAr), 134.4 (CAr), 132.1 (CAr), 129.2 (2 × CHAr), 128.2 (2 × CHAr), 126.1 (CHAr),
122.0 (CHAr), 112.4 (CHAr), 71.1 (CH2), 26.3 (CH), 22.7 (2 × CH3), 21.6 (CH3), 21.1
(CH3).
3.3.3.3. Synthesis of 2-(2-isopropyl-5-methylphenoxy)-1-(4-methoxyphenyl)
ethanone (Th 10)
The general synthetic method described earlier, afforded compounds Th 10
from thymol (1.0 g, 6.6 mmol, 1.0 mequiv) with 4-methoxyphenacyl bromide (1.6 g,
7.3 mmol, 1.1 mequiv) and potassium carbonate (4.6 g, 33.3 mmol, 5.0 mequiv) in
acetonitrile (20 ml) as reaction solvent.
O
O
OCH3
2-(2-isopropyl-5-methylphenoxy)-1-(4-methoxyphenyl)ethanone
Molecular Formula: C19H22O3 (M.W. 298.0); Physical state: off white solid; Yield:
61.2%; Purity: 98%; mp: 88- 90 oC; MS: [M
+1], m/z 299; IR υmax: 3054, 3020, 2960,
2904, 2866, 1689, 1603, 1364, 1179, 1114, 807 cm-1;
1H NMR (CDCl3, 500 MHz): δ
8.01 (dd, 2H, J = 2.0 Hz & 7.0 Hz, Ar-H), 6.95 (dd, 2H, J = 2.0 & 7.0 Hz, Ar-H), 7.11
(d, 1H, J = 8.0 Hz, Ar-H), 6.77 (d, 1H, J = 8.0 Hz, Ar-H), 6.59 (s, 1H, Ar-H), 5.17 (s,
2H, CH2), 3.87 (s, 3H, OCH3), 3.34- 3.40 (m, 1H, CH), 2.28 (s, 3H, CH3), 1.21 (d,
6H, J = 7.0 Hz, CH3); 13
C NMR (CDCl3, 125 MHz): δ 193.3 (C-12), 163.7 (CAr),
155.0 (CAr), 136.1 (CAr), 134.3 (CAr), 130.5 (2 × CHAr), 127.7 (CAr), 126.0 (CHAr),
121.9 (CHAr), 113.7 (2 × CHAr), 112.3 (CHAr), 71.0 (CH2), 55.3 (OCH3), 26.2 (CH),
22.7 (2 × CH3), 21.1 (CH3).
3.3.3.4. Synthesis of 2-(5-isopropyl-2-methylphenoxy)-1-(4-bromophenyl)
ethanone (Ca 8)
Estelar
80
The general synthetic method described earlier, afforded compounds Ca 8
from carvacrol (1.0 g, 6.6 mmol, 1.0 mequiv) with 4-bromophenacyl bromide (2.0 g,
7.3 mmol, 1.1 mequiv) and potassium carbonate (4.6 g, 33.3 mmol, 5.0 mequiv.) in
acetonitrile (20 ml) as reaction solvent.
O
O
Br
2-(5-isopropyl-2-methylphenoxy)-1-(4-bromophenyl) ethanone
Molecular Formula: C18H19BrO2 (M.W. 346.0); Physical state: off white solid;
Yield: 77.3%; Purity: 97%; mp: 70- 72 oC; MS: [M
+1], m/z 347; IR υmax: 3053,
2956, 2926, 2866, 1690, 1585, 1360, 1174, 1132, 822 cm-1;
1H NMR (CDCl3, 500
MHz): δ 7.90 (d, 2H, J = 6.5 Hz, Ar-H), 7.64 (d, 2H, J = 6.5 Hz, Ar-H), 7.07 (d, 1H,
J = 7.5 Hz, Ar-H), 6.78 (dd, 1H, J = 1.5 Hz & 7.5 Hz, Ar-H), 6.62 (d, 1H, J = 1.5 Hz,
Ar-H), 5.16 (s, 2H, CH2), 2.81- 2.86 (m, 1H, CH), 2.22 (s, 3H, CH3), 1.21 (d, 6H, J =
7.0 Hz, CH3); 13
C NMR (CDCl3, 125 MHz): δ 194.5 (C=O), 155.7 (CAr), 147.9
(CAr), 133.3 (CAr), 131.8 (2 × CHAr), 130.7 (CHAr), 129.8 (2 × CHAr), 128.8 (CAr),
124.2 (CAr), 119.1 (CHAr), 109.7 (CHAr), 71.2 (CH2), 33.8 (CH), 23.9 (2 × CH3), 15.7
(CH3).
3.3.3.5. Synthesis of 2-(5-isopropyl-2-methylphenoxy)-1-p-tolylethanone
(Ca 9)
The general synthetic method described earlier, afforded compounds Ca 9
from carvacrol (1.0 g, 6.6 mmol, 1.0 mequiv) with 4-methylphenacyl bromide (1.5 g,
7.3 mmol, 1.1 mequiv) and potassium carbonate (4.6 g, 33.3 mmol, 5.0 mequiv.) in
acetonitrile (20 ml) as reaction solvent.
O
O
CH3
2-(5-isopropyl-2-methylphenoxy)-1-p-tolylethanone
Molecular Formula: C19H22O2 (M.W. 282.0); Physical state: off white solid; Yield:
71.6%; Purity: 96%; mp: 45- 48 oC; MS: [M
+1], m/z 283; IR υmax: 3065, 3030, 2960,
2925, 2868, 1703, 1606, 1341, 1180, 819 cm-1;
1H NMR (CDCl3, 500 MHz): δ 7.92
(d, 2H, J = 8.0 Hz, Ar-H), 7.27 (d, 2H, J = 7.5 Hz, Ar-H), 7.06 (d, 1H, J = 7.5 Hz, Ar-
Estelar
81
H), 6.76 (dd, 1H, J = 1.5 & 7.5 Hz, Ar-H), 6.63 (s, 1H, Ar-H), 5.19 (s, 2H, CH2),
2.79- 2.86 (m, 1H, CH), 2.45 (s, 3H, CH3), 2.24 (s, 3H, CH3), 1.20 (d, 6H, J = 7.0 Hz,
CH3); 13
C NMR (CDCl3, 125 MHz): δ 194.8 (C=O), 156.2 (CAr), 147.9 (CAr), 144.6
(CAr), 132.3 (CAr), 130.8 (CHAr), 129.4 (2 × CH3), 128.4 (2 × CH3), 124.5 (CAr), 119.0
(CHAr), 110.0 (CHAr), 71.3 (CH2), 34.0 (CH), 24.1 (2 × CH3), 21.7 (CH3), 15.9 (CH3).
3.3.3.6. Synthesis of 2-(5-isopropyl-2-methylphenoxy)-1-(4-methoxyphenyl)
ethanone (Ca 10)
The general synthetic method described earlier, afforded compounds Ca 10
from carvacrol (1.0 g, 6.6 mmol, 1.0 mequiv) with 4-methoxyphenacyl bromide (1.6
g, 7.3 mmol, 1.1 mequiv) and potassium carbonate (4.6 g, 33.3 mmol, 5.0 mequiv) in
acetonitrile (20 ml) as reaction solvent.
O
O
OCH3
2-(5-isopropyl-2-methylphenoxy)-1-(4-methoxyphenyl)ethanone
Molecular Formula: C19H22O3 (M.W. 298.0); Physical state: off white solid; Yield:
62.3%; Purity: 95%; mp: 50-52 oC; MS: [M
+1], m/z 299; IR υmax: 3058, 3033, 2963,
2905, 2865, 2844, 1694, 1603, 1177, 813 cm-1;
1H NMR (CDCl3, 500 MHz): δ 8.02
(d, 2H, J = 7.0 Hz, Ar-H), 6.95 (d, 2H, J = 6.5 Hz, Ar-H), 6.87 (d, 1H, J = 7.5 Hz, Ar-
H), 6.76 (dd, 1H, J = 1.5 & 8.0 Hz, Ar-H), 6.64 (s, 1H, Ar-H), 5.16 (s, 2H, CH2), 3.88
(s, 3H, OCH3), 2.80-2.85 (m, 1H, CH), 2.24 (s, 3H, CH3), 1.21 (d, 6H, J = 6.5 Hz,
CH3); 13
C NMR (CDCl3, 125 MHz): δ 194.6 (C=O), 163.7 (CAr), 156.0 (CAr), 147.8
(CAr), 130.6 (3 × CHAr), 127.7 (CAr), 124.2 (CAr), 118.8 (CHAr), 113.7 (2 × CHAr),
109.8 (CHAr), 71.2 (CH2), 55.3 (OCH3), 33.8 (CH), 23.9 (2 × CH3), 15.8 (CH3).
Estelar
82
Figure 3.29. 1H NMR spectrum of Th 8
Figure 3.30. 13
C NMR spectrum of Th 8
O
O
Br
O
O
Br
Estelar
83
Figure 3.31. 1H NMR spectrum of Th 9
Figure 3.32. 13
C NMR spectrum of Th 9
O
O
CH3
O
O
CH3
Estelar
84
Figure 3.33. 1H NMR spectrum of Th 10
Figure 3.34. 13
C NMR spectrum of Th 10
O
O
OCH3
O
O
OCH3
Estelar
85
Figure 3.35. 1H NMR spectrum of Ca 8
Figure 3.36. 13
C NMR spectrum of Ca 8
O
O
Br
O
O
Br
Estelar
86
Figure 3.37. 1H NMR spectrum of Ca 9
Figure 3.38. 13
C NMR spectrum of Ca 9
O
O
CH3
O
O
CH3
Estelar
87
Figure 3.39. 1H NMR spectrum of Ca 10
Figure 3.40. 13
C NMR spectrum of Ca 10
O
O
OCH3
O
O
OCH3
Estelar
88
3.4. Results and discussion
The esters of thymol (Th 1 to Th 7) and carvacrol (Ca 1 to Ca 7) have been
prepared by the conventional esterification reaction with corresponding acid chloride
in the presence of triethyl amine. The condensation of 1.0 mequiv of thymol or
carvacrol with the 1.1 mequiv of acetyl chloride, propionyl chloride, isobutyryl
chloride, 3-methylbutanoyl chloride, (E)-but-2-enoyl chloride, benzoyl chloride, 2-
phenylacetyl chloride and 1.1 mequiv of triethylamine in dry DCM at 250 C for 10 h
gave thymyl acetate (2-isopropyl-5-methylphenyl acetate) Th 1, thymyl propionate
(2-isopropyl-5-methylphenylpropio-nate) Th 2, thymyl isobutyrate (2-isopropyl-5-
methylphenylisobutyrate) Th 3, thymyl isovalerate (2-isopropyl-5-methylphenyl-3-
methylbutanoate) Th 4, thymyl crotonate ((E)-2-isopropyl-5-methylphenyl-but-2-
enoate) Th 5, thymyl benzoate (2-isopropyl-5-methylphenylbenzoate) Th 6, thymyl
phenylacetate (2-isopropyl-5-methylphenyl-2-phenylacetate) Th 7, carvacryl acetate
(5-isopropyl-2-methylphenylacetate) Ca 1, carvacryl propionate (5-isopropyl-2-
methylphenylpropionate) Ca 2, carvacryl isobutyrate(5-isopropyl-2-methylphenyl-
isobutyrate) Ca 3, carvacryl isovalerate (5-isoprop-yl-2-methylphenyl-3-methyl-
butanoate) Ca 4, carvacryl crotonate ((E)-5-isopropyl-2-methylphenylbut-2-enoate)
Ca 5, carvacryl benzoate (5-isopropyl-2-methyl phenylbenzoate) Ca 6, carvacryl
phenyl acetate (5-isopropyl-2-methylphenyl-2-phenylacetate) Ca 7 respectively in 75-
85 % yields as colourless liquids. The reaction conditions and physicochemical
properties of ester analogues of thymol and carvacrol have been summarized in Table
3.1.
The ether derivatives of thymol (Th 8 to Th 10) and carvacrol (Ca 8 to Ca
10) have been synthesized by the nucleophilic substitution of thymol and carvacrol
with different p-substituted phenacyl bromide derivatives.31-33
The nucleophilic
substitution reaction of 1.0 mequiv of thymol or carvacrol with 1.1 mequiv of 2-
bromo-1-(4-bromophenyl)ethanone, 2-bromo-1-p-tolylethanone, 2-bromo-1-(4-
methoxyphenyl)ethanone and 5.0 mequiv of potassium carbonate in acetonitrile at 0
oC to 25
oC for 8-10 h gave 2-(2-isopropyl-5-methylphenoxy)-1-(4-bromophenyl)-
ethanone Th 8, 2-(2-isopropyl-5-methylphenoxy)-1-p-tolylethanone Th 9, 2-(2-
isopropyl-5-methylphenoxy)-1-(4-methoxyphenyl)ethanone Th 10, 2-(5-isopropyl-2-
methylphenoxy)-1-(4-bromophenyl)ethanone Ca 8, 2-(5-isopropyl-2-methylphen-
oxy)-1-p-tolylethanone Ca 9, 2-(5-isopropyl-2-methylphenoxy)-1-(4-methoxyphenyl)
Estelar
89
ethanone Ca 10 respectively in 61-77% yields as off white solids. The reaction
conditions and physicochemical properties of ether analogues of thymol and carvacrol
have been summarized in Table 3.2.
Table 3.1. Reaction conditions and physicochemical properties of
ester analogues
Comp. Structures Reaction conditions Yield
(%)
Physical state Purity
(%)
Th 1
O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt.
80%
colourless liquid
97%
Th 2
O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
80%
colourless liquid
96%
Th 3
O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
76%
colourless liquid
98%
Th 4
O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
80%
colourless liquid
92%
Th 5
O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
84%
colourless liquid
87%
Th 6
O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
85%
colourless liquid
98%
Th 7
O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
85%
colourless liquid
98%
Ca 1 O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
78%
colourless liquid
97%
Estelar
90
Ca 2 O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
75%
colourless liquid
98%
Ca 3 O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
85%
colourless liquid
98%
Ca 4 O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
75%
colourless liquid
97%
Ca 5 O
O
i. SOCl2, 2h, ∆.
ii. phenol, TEA, dry.
DCM, 16h, rt
78%
colourless liquid
91%
Ca 6
O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
82%
colourless liquid
97%
Ca 7 O
O
i. SOCl2, 2h, ∆.
ii. TEA, dry. DCM,
16h, rt
78%
colourless liquid
88%
Estelar
91
Table 3.2. Reaction conditions and physicochemical properties of
ether analogues
Comp. Structures Reaction conditions Yield
(%)
Physical state M.p. Purity
(%)
Th 8
O
O
Br
K2CO3, CH3CN, rt,
15h
64.6%
off white solid
54-56oC
97%
Th 9
O
O
CH3
K2CO3, CH3CN, rt,
15h
69.9%
off white solid
56-58 oC
98%
Th 10
O
O
OCH3
K2CO3, CH3CN, rt,
15h
61.2%
off white solid
88-90 oC
98%
Ca 8 O
O
Br
K2CO3, CH3CN, rt,
15h
77.3%
off white solid
70-72 oC
97%
Ca 9 O
O
CH3
K2CO3, CH3CN, rt,
15h
71.6%
off white solid
45-48 oC
96%
Ca 10 O
O
OCH3
K2CO3, CH3CN, rt,
15h
70%
off white solid
50-52 oC
95%
The EI-MS of compounds Th 1-Th 7 and Ca 1-Ca 7 showed their
corresponding m/z values related to their molecular weight. Formation of ester
derivatives were confirmed by their IR spectral data which revealed the disappearance
of –OH str. and appearance of >C=O str. at 1736- 1766 cm-1, which was further
supported by the 1H &
13C NMR data. Presence of doublet at δ 7.0 (d, 1H, J = 7.0
Hz), 7.13 (d, 1H, J = 8.0 Hz), 1.22 (d, 6H, J = 7.0 Hz) and singlet at δ 6.85 (s, 1H) &
2.12 (s, 3H), showed the presence of thymol and carvacrol skeleton in all the ester and
ether derivatives, which was further confirmed by 13C-NMR data. The
1H NMR
spectra of compound Th 1 and Ca 1 showed a sharp singlet at δ 2.30 & 2.29 (3H for
Estelar
92
each) revealed the presence of acetyl group. A quartet at δ 2.58 & 2.60 (2H for each, J
= 7.5 Hz) and triplet at δ 1.27 & 1.28 (3H for each, J = 7.5 Hz) in the 1H NMR of
compound Th 2 & Ca 2 showed the presence of –CH2CH3 group in parent skeleton.
The presence of –CH(CH3)2 group was confirmed by the presence of a doublet at δ
1.32 & 1.35 (6H for each, J = 6.5 Hz) and multiplet at δ 2.81-2.99 & 2.82- 2.88 (1H
for each) in the 1H NMR of compound Th 3 & Ca 3 respectively, approximately
similar pattern was noticed for compounds Th 4 & Ca 4 except a doublet at δ 2.46 for
CH2 group. The presence of doublet at δ 5.25 and δ 6.06 with coupling constant (J)
11.0 Hz and 14.0 Hz showed the trans- arrangement in compounds Th 5 & Ca 5
respectively. Compounds Th 6, Th 7, Ca 6 and Ca 7 have similar pattern with phenyl
and benzyl group in compounds Th 6, Ca 6 and Th 7, Ca 7, respectively.
Formation of ether derivatives Th 8 to Th 10 and Ca 8 to Ca 10 was
confirmed by presence of C-O-C stretching vibrational absorption at 1150- 1180 cm-1
in IR spectra of ethers derivatives. The mass spectra of compounds Th 8 - Th 10 and
Ca 8 - Ca 10 showed their corresponding [M+] values related to their molecular
formula. All the ether analogues where characterized by their NMR (1H &
13C NMR)
data.
3.5. Antibacterial activity of phenolic monoterpene derivatives
Antibacterial activity of all the synthesized derivatives were performed against
four Gram positive bacterial strains viz. Streptococcus mutans (MTCC- 890),
Staphylococcus aureus (MTCC- 96), Bacillus subtilis (MTCC- 121), Staphylococcus
epidermidis (MTCC- 435) and one Gram negative bacterial strain Escherichia coli
(MTCC- 723) using disc diffusion34 and microbroth dilution methods.
35 Ampicillin
was used as a standard drug. The zone of inhibition (in mm) and minimum inhibitory
concentration (in µg/ml) of tested compounds are shown in Table 3.3 and Table 3.4.
The antibacterial activity of the synthesized analogues were lower in
comparison with the standard antibiotic ampicillin but some of the synthetic
analogues showed better activity than the parent compound. Most of the compounds
showed significant to moderate activity excepting Ca 6 to Ca 8 and Th 8 to Th 10
which were found to be inactive against all the tested strains. Among the thymyl ester
derivatives (Th 1 to Th 7) and carvacryl ester derivatives (Ca 1 to Ca 7), Th 1 to
Th 3, Ca 1, Ca 2, Ca 4 and Ca 5 showed significant activity against all the tested
Gram-positive bacterial strains. Compounds Th 1 to Th 3, Ca 4 and Ca 5 showed
Estelar
93
lower activity against E. coli whereas Ca 1 and Ca 2 were found to be inactive. The
thymyl isovalerate and thymyl benzoate esters showed moderate activity against
B. subtilis and S. epidermidis. The most notable enhancement in the activity was
noticed for thymyl ester derivatives Th 1 to Th 3 for Gram-positive bacterial strains.
Thymyl acetate Th 1 and thymyl isobutyrate Th 3 were found to be more effective
than thymol (IZ= 17mm; MIC= 125µg/ml) and all other esters against S. mutans (IZ=
30mm and 18mm; MIC= 11.7 and 93.7µg/ml respectively), B. subtilis (IZ= 30mm
and 21mm; MIC= 11.7 and 46.8µg/ml respectively) and S. epidermidis (IZ= 32mm
and 20mm; MIC= 11.7 and 46.8µg/ml respectively) whereas Th 2 was found to be
more active for B. subtilis (IZ= 25mm; MIC= 46.8µg/ml) and S. epidermidis (IZ=
28mm; MIC= 46.8µg/ml) as compared to thymol. All other derivatives possessed
much less activity as compared to thymol itself and generally showed decrease in
their activity with increase in the size of substituent (R). Carvacrol was much more
active than its isomer thymol against all the test bacteria even at lower concentration.
Nikumbh et al., (2003), have also synthesized carvacryl esters namely carvacryl
acetate and carvacryl phenyl acetate and evaluated their antibacterial activity against
B. japonicum, B. megaterium, B. substilits, and B. polymyx.36 In the present study,
carvacryl phenyl acetate was not active against the tested strains. All the thymyl ether
derivatives (Th 8 to Th 10) were found to be inactive against all the bacterial strains
whereas carvacrol ether derivatives (Ca 8 to Ca 10) showed moderate activity against
Gram positive bacterial strains.
Estelar
94
Tab
le 3
.3. A
nti
bacte
rial acti
vit
y o
f th
ym
ol der
ivati
ves
(Th
1 t
o T
h 1
0)
In-vitro activity – zone of inhibition (in mm)a and MIC (in µg ml-1)
Streptococcus mutans
Staphylococcus aureus
Bacillus subtilis
Staphylococcus epidermidis
Escherichia coli
Compounds
zone of
inhibition
MIC
zone of
inhibition
MIC
zone of
inhibition
MIC
zone of
inhibition
MIC
zone of
inhibition
MIC
Thym
ol
17 ± 0.79
125
25 ± 0.98
62.5
15 ± 0.68
125
14 ± 0.57
125
13 ± 0.51
250
Th 1
30 ±
1.3
1
11.7
18 ± 0.81
93.7
30 ±
1.2
8
11.7
32 ±
1.3
7
11.7
12 ± 0.53
375
Th 2
12 ± 0.53
187.5
10 ± 0.41
187.5
25 ±
1.0
7
46.8
28 ±
1.2
1
46.8
7 ± 0.27
>1000
Th 3
18 ±
0.8
6
93.7
17 ± 0.78
93.7
21 ±
0.9
6
46.8
20 ±
0.8
7
46.8
7 ± 0.26
>1000
Th 4
NI
ND
NI
ND
8 ± 0.29
ND
7 ± 0.27
ND
NI
ND
Th 5
12 ± 0.53
750
9 ± 0.37
750
10 ± 0.46
750
9 ± 0.35
ND
7 ± 0.28
>1000
Th 6
NI
ND
NI
ND
7 ± 0.29
ND
10 ± 0.39
ND
NI
ND
Th 7
8 ± 0.31
187.5
15 ± 0.66
93.7
8 ± 0.33
750
12 ± 0.49
187.5
7 ± 0.28
>1000
Th 8
NI
ND
NI
ND
NI
ND
NI
ND
NI
ND
Th 9
NI
ND
NI
ND
NI
ND
NI
ND
NI
ND
Th 1
0
NI
ND
NI
ND
NI
ND
NI
ND
NI
ND
Am
pic
illin
27 ± 1.21
4
22 ± 0.94
8
25 ± 1.12
4
25 ± 1.07
2
12 ± 0.49
12
a values are mean of three determinations, the ranges of which are less than 5% of the mean in all cases.
ampicillin (20µg/disc) was used as positive reference; compounds (100µg/disc) were used for experiments.
NI = no inhibition. ND = not determined. Este
lar
95
Tab
le 3
.4. A
nti
bact
eria
l act
ivit
y o
f carvacro
l d
eriv
ati
ves
(C
a 1
to C
a 1
0)
In-vitro activity – zone of inhibition (in mm)a and MIC (in µg ml-1)
Streptococcus mutans
Staphylococcus aureus
Bacillus subtilis
Staphylococcus epidermidis
Escherichia coli
Compounds
zone of
inhibition
MIC
zone of
inhibition
MIC
zone of
inhibition
MIC
zone of
inhibition
MIC
zone of
inhibition
MIC
Carvacr
ol
30 ± 1.29
23.4
25 ± 1.07
23.4
35 ± 1.41
11.7
32 ± 1.39
11.7
35 ± 1.49
11.7
Ca 1
17 ± 0.78
93.7
15 ± 0.66
93.7
25 ± 0.98
46.8
20 ± 0.89
93.7
NI
ND
Ca 2
12 ± 0.46
187.5
15 ± 0.74
187.5
20 ± 0.87
46.8
18 ± 0.72
93.7
NI
ND
Ca 3
7 ± 0.29
>1000
9 ± 0.37
375
9 ± 0.38
375
12 ± 0.56
187.5
NI
ND
Ca 4
22 ± 1.03
46.8
21 ± 0.91
46.8
25 ± 1.12
23.4
21 ± 0.96
46.8
10 ± 0.42
375
Ca 5
17 ± 0.82
187.5
20 ± 0.89
93.7
20 ± 0.88
93.7
18 ± 0.86
93.7
10 ± 0.46
375
Ca 6
NI
ND
NI
ND
NI
ND
NI
ND
NI
ND
Ca 7
NI
ND
NI
ND
NI
ND
NI
ND
NI
ND
Ca 8
NI
ND
NI
ND
NI
ND
NI
ND
NI
ND
Ca 9
22 ± 1.03
46.8
NI
ND
15 ± 0.74
187.5
11 ± 0.46
375
10 ± 0.42
375
Ca 1
0
10 ± 0.46
375
9 ± 0.37
750
12 ± 0.56
375
11 ± 0.46
375
NI
ND
Am
pic
illi
n
27 ± 1.21
4
22 ± 0.94
8
25 ± 1.12
4
25 ± 1.07
2
12 ± 0.49
12
a values are mean of three determinations, the ranges of which are less than 5% of the mean in all cases.
ampicillin (20µg/disc) was used as positive reference; compounds (100µg/disc) were used for experiments.
NI = no inhibition. ND = not determined. Este
lar
96
3.6. Structures of active compounds
O
O
Th 1
O
O
Th 2
O
O
Th 3
O
O
O
O
Ca 2 Ca 3
3.7. Conclusion
In conclusion, fourteen ester and six ether derivatives of thymol and carvacrol
have been synthesized and evaluated as antibacterial agents. These modifications
resulted in change in the antibacterial activity of thymol and carvacrol analogues. The
enhancement in activity was noticed in the thymyl ester derivatives Th 1 to Th 3
against S. mutans, B. subtilis and S. epidermidis whereas it diminished in case of
carvacryl esters derivatives. Based on the present results, compounds Th 1, Th 2 and
Th 3 possess potential for developing as antibacterial agents.
Estelar
97
3.8. References:
1. Newmann, D. J., Cragg, G. M., Snader, K. M., Journal of Natural Products,
2003, 66, 1022.
2. Aggarwal, K. K., Khanuja, S. P. S., Ahmad, A., Santakumar, T. R., Gupta, V.
K., Kumar. S., Flavour & Fragrance Journal, 2002, 17, 59.
3. Medeiros, J. R., Medeiros, N., Medeiros H., Davin, L. B., Lewis, N. G., Journal
of Essential Oil Research, 2003, 15, 293.
4. Zgoda-Pols, J. R., Freyer, A. J., Killmer, L. B., Porter, J. R., Fitoterapia, 2002,
73, 434.
5. Akbar, E., Malik, A., Natural Products Letters, 2002, 16, 339.
6. Moura, I. C., Wunderlich, G., Uhrig, M. L., Couto, A. S., Peres, V. J., Katzin,
A. M., Kimura, E. A., Antimicrobial Agent Chemotherapy, 2001, 45, 2553.
7. David, J. R. (1977). The Biology and Chemistry of The Compositae, vol II,
Heywood VH, Harborne JB, Turner Bl (eds). Academic Press: London, New
York, 831.
8. Flamini, G., Cioni, P. L., Morelli, I., Journal of Essential Oil Research, 2003,
15 (2), 127.
9. Mathela, C. S., Tiwari, A., Padalia, R. C., Chanotia C. S., Indian Journal of
Chemistry, 2008, 47 B, 1249.
10. Sterner, O., Szallasi, A., Trends in Pharmacological Sciences, 1999, 20, 459.
11. Davidson, P.M. (1997). Chemical preservatives and natural antimicrobial
compounds, In M.P. Dayle, L. R. Beuchat, T. J. Montville. Food Microbiology
Fundamentals and Frontiers. Washington DC. ASM Press, pp. 520-556.
12. Walsh S. E., Maillard J. Y., Russell A. D., Catrenich C. E., Charbonneau D. L.,
Bartolo R. G., Journal of Applied Microbiology, 2003, 94, 240.
13. Lee, S. J., Han, Je-Ik, Lee, G. S., Park, M. J., Choi, I. G., Ki-Jeong N. A., Jeung,
E. B., Chemical & Pharmaceutical Bulletin, 2007, 30 (1) 184.
14. Radwan, M. A., El-Zemity, S. R., Mohamed, S. A., Sherby, S. M.,
Ecotoxicology and Environmental Safety, 2008, 71 (3), 889.
15. Puertas-Mejia, M., Hillebrand, S., Stashenko, E., Winterhalter, P., Flavour &
Fragrance Journal, 2002, 17, 380.
16. Mirza, M., Baher, Z. F., Journal of Essential Oil Research, 2003, 15, 404.
Estelar
98
17. Goren, A. C., Topcu, G., Bilsel, G., Bilsel, M., Wilkinson, J. M., Cavanagh, H.
M. A., Natural Product Research, 2004, 18, 189.
18. Salgueiro, L. R., Pinto, E., Goncalves, M. J., Pina-Vag, C., Cavaleiro, C.,
Rodrigies, A. G., Palmeria, A., Tavares, C., Costa-de-Oliveira, S., De-Olivera,
J. M., Planta Medica, 2004, 70, 572.
19. Manou, L., Bouillard, L., Devleeschouwer, M. J., Barel, A. O., Journal of
Applied Microbiology, 1998, 84, 368.
20. Ogaard, B., Larsson, E., Glans, R., Henriksson, T., Birkhed, D., Journal of
Orofactary and Orthopathology, 1997, 58, 206.
21. Aeschbach, R., Loliger, J., Scott, B. C., Murcia, A., Butler, J., Halliwell, B.,
Aruoma, O. I., Food & Chemical Toxicology, 1994, 32, 31.
22. Kordali, S., Cakir, A., Ozer, H., Cakmakei, R., Kesdek, M., Mete, E.,
Bioresource Technology, 2008, 99, 8788.
23. Oke, F., Aslim, B., Oztirk, S., Altundag, S., Food Chemistry, 2009, 112, 874.
24. Liolios, C. C., Gortzi, O., Lalas, S., Tsaknis, J., Chinou, I., Food Chemistry,
2009, 112, 77.
25. Ebrahimi, S. N., Hadian, J., Mirjalili, M. H., Sonboli, A., Yousefzadi, M., Food
Chemistry, 2008, 110, 927.
26. Tippayatum, P., Chonhenchob, V., Journal of Natural Sciences, 2007, 41, 319.
27. Liang, H., Bao, F., Dong, X., Tan, R., Zhang, C., Lu, Q., Cheng, Y., Molecules,
2007, 12, 1606.
28. Stojakowska, A., Kedzia, B., Kisiel, W., Fitoterapia, 2005, 76, 687.
29. Kumbhar (alias Mahulikar), P. P., Dewang, P. M., Pestology, 1999, 23 (1), 27.
30. Kumbhar (alias Mahulikar), P. P., Dewang, P. M., Journal of Scientific &
Industrial Research, 2001, 60, 645.
31. Joshi, M. C., Bisht, G. S., Rawat, D. S., Bioorganic & Medicinal Chemistry
Letters, 2007, 17, 3226.
32. Lienard, B. M. R., Horsfall, L. E., Galleni, M., Frere, J. M., Schofield, C. J.,
Bioorganic & Medicinal Chemistry Letters, 2007, 17, 964.
33. Yamato, T., Saruwatari, Y., Yasumatsu, M., Journal of Chemical Society Perkin
Trans, 1997, 1, 1731.
34. Bauer, A. W., Kirby, W. M. M., Sherries, J. C., Turk, M., American Journal of
Clinical Pathology, 1996, 45 (4), 493.
Estelar
99
35. Gupta, V. K., Fatima, A., Faridi, U., Negi, A. S., Shankar, K., Kumar, J. K.,
Rahuja, N., Luqman, S., Sisodia, B. S., Saikia, D., Darokar, M. P., Khanuja, S.
P. S., Journal of Ethnopharmacology, 2008, 116, 377.
36. Nikumbh V. P., Tare V. S., Mahulikar P. P., Journal of Scientific & Industrial
Research, 2003, 62, 1086.
Estelar