Vol. 28, No. 3 (2016)
Synthesis and Antibacterial Activity of New Lauroyl Thiourea Amino Acid Derivatives 597
sulfoxide (DMSO) as the solvents and chemical shift values
were given in parts per million (ppm) relative to solvent
resonances as internal standard.
17.70 (CH3), 19.02-36.64 (10 × CH2), 25.77 (CH-(CH3)2),
57.21 (CH-NH), 174.19 (C=O-NH), 176.44 (C=O-OH),
179.94 (C=S).
(3-Dodecanoyl-thioureido)acetic acid (R3): R3 was
obtained as pale yellow solid. Yield: 2.61 g (55.07 %); m.p.
81-83 ºC; FT-IR (KBr pellets, νmax, cm-1): 3320 (NH), 3197
(OH), 1705 (C=O carboxylic), 1643 (C=O amide), 1406 (C-N),
General methods
Syntheses of lauroyl thiourea derivatives: Lauroyl
chloride (3.5 g, 0.015 mol) and ammonium thiocyanate (1.142
g, 0.015 mol) in acetone (25 mL) was stirred for 1 h to give
white precipitate which indicates the formation of lauroyl
isothiocyanate. β-Alanine (1.337 g, 0.015 mol) was added
dropwise to the mixture and further heated at refluxed for
another 5 h. After the reaction was completed, the mixture
was filtered into a beaker of ice, collected by filtration, washed
with acetone and dried under vacuum to give R1. β-Alanine
was then replaced with valine, glycine and phenylalanine and
reacted with lauroyl isothiocyanate to produce compounds R2,
R3 and R4 in the similar manner describes for R1.
Antibacterial assay: The antibacterial activities of
compounds R1-R4 were screened against test strains of Gram-
positive (Bacillus subtilis ATCC 11774, Staphylococcus
epidermidis ATCC 13518 and Staphylococcus aureus ATCC
25923) and Gram-negative (Escherichia coliATCC 11775 and
Salmonella typhimurium ATCC 14128) strains using common
well diffusion method. Mueller-Hinton media were seeded with
bacterial inoculum using cotton swab. Wells of 6 mm diameter
were bored into the media using sterile cork borer and 90 µL
of the diluted compounds at a dose range of 10-0.01 mg/mL
were added in each well. Streptomycin (Abtek Biologicals Ltd)
was used as the positive control while methanol served as
negative control.All plates were incubated overnight at 37 °C.
The antibacterial activities were evaluated by measuring
the zones of inhibition (mm) and minimum inhibitory concen-
trations (MIC).
1
720 (C=S). H NMR (DMSO-d6, ppm): 0.85 (3H, t, J = 6.8
Hz, CH3), 1.24 (18H, s, 9×CH2), 1.47 (2H, s, CH2), 2.17 (2H,
t, J = 7.4 Hz, CH2), 3.71 (1H, s, NH), 8.08 (1H, t, J = 5.8 Hz,
NH), 11.25 (1H, s, OH); 13C NMR (DMSO-d6, ppm): 14.40
(CH3), 22.57-34.13 (10×CH2), 41.05 (CH2-NH), 171.96
(C=O-NH), 172.98 (C=O-OH), 174.79 (C=S).
2-(3-Dodecanoyl-thioureido)-3-phenyl-propionic acid
(R4): R4 was obtained as yellow solid.Yield: 3.14 g (51.66 %);
m.p. 134-136 ºC; FT-IR (KBr pellets, νmax, cm-1): 3316 (NH,
OH), 1722 (C=O carboxylic), 1712 (C=O amide), 1463 (C-N),
720 (C=S). 1H NMR (DMSO-d6, ppm): 0.84-0.87 (7H, m, J =
4.2 Hz, CH3 + 2×CH2), 1.07-1.11 (2H, m, J = 7.0 Hz, CH2),
1.35-1.39 (2H, m, J = 6.3 Hz, CH2), 1.47-1.51 (2H, m, J = 7.0
Hz, CH2), 2.00-2.03 (2H, m, J = 6.0 Hz, CH2), 2.32-2.36 (2H,
m, J = 6.6 Hz, CH2), 2.81-2.84 (2H, m, J = 7.9 Hz, CH2),
3.03-3.06 (2H, m, J = 6.3 Hz, CH2), 3.10 (2H, t, J = 7.0 Hz,
CH2), 4.42 (2H, d, J = 3.5 Hz, CH2), 5.05 (1H, t, J = 6.3 Hz,
CH), 7.14-7.28 (5H, m, J = 7.7 Hz, Ar-H), 8.09 (1H, s, NH),
10.97 (1H, d, J = 7.7 Hz, NH), 11.28 (1H, s, OH); 13C NMR
(DMSO-d6, ppm): 14.37 (CH3), 22.60-34.12 (10×CH2), 37.22
(CH2-Ph), 53.69 (CH-NH), 126.69-138.25 (C6H5), 172.58
(C=O-NH), 173.70 (C=O-OH), 174.89 (C=S).
RESULTS AND DISCUSSION
The synthesis of four new thiourea compounds was
described. Compounds 3-(3-dodecanoyl-thioureido)propionic
acid (R1), 2-(3-dodecanoyl-thioureido)-3-methyl butyric acid
(R2), (3-dodecanoyl-thioureido)acetic acid (R3) and 2-(3-
dodecanoyl-thioureido)-3-phenyl propionic acid (R4) were
prepared by combination of equimolar amounts of lauroyl
chloride, ammonium thiocyanate and amino acid in acetone.
The first stage of the synthesis requires preparation of lauroyl
isothiocyanate from reaction between lauroyl chloride and
ammonium thiocyanate. The obtaining lauroyl isothiocyanate
was then combined with respective amino acids to give the
products as clear solution. This solution was poured into a
beaker containing ice cubes for rapid precipitation where white
solid was immediately formed in the water solution. Compounds
R1-R4 were collected and further characterized by elemental
analysis, FTIR, UV-visible and NMR spectroscopy techniques.
The general schematic diagram on the synthesis of the compounds
is outlined in Scheme-I.
Thioamide band (NH–C=S) are commonly indicated at
1500, 1300, 1100 and 750 cm-1 in the IR spectra. The charac-
teristic band in 1600-1500 cm-1 region is originated from the
deformation of NH and the stretching mode of C=C. The C-N
stretching is commonly indicated in region 1300-1400 cm-1
while the C=S stretching coupled with S-C-N bending normally
appeared at range 800-700 cm-1. In the IR spectra of these four
compounds, several distinctive peaks that assigned to ν(N-H),
ν(O-H), ν(C=O carboxylic acid), ν(C=O amide), ν(C-N) and
Spectral data
3-(3-Dodecanoyl-thioureido)propionic acid (R1):
Compound R1 was obtained as white solid.Yield: 4.25 g (85.84
%); m.p. 83-84 ºC; FT-IR (KBr pellets, νmax, cm-1): 3292 (NH),
3200 (OH), 1694 (C=O carboxylic), 1634 (C=O amide), 1443
1
(C-N), 720 (C=S). H NMR (CDCl3, ppm): 0.89 (3H, t, J =
6.8 Hz, CH3), 1.27 (16H, s, 8×CH2), 1.61-1.68 (2H, m, J = 7.3
Hz, CH2), 2.17-2.52 (2H, m, J = 8.1 Hz, CH2), 2.36 (2H, t, J =
7.6 Hz, CH2), 2.61 (2H, t, J = 5.8 Hz, CH2), 3.55 (1H, t, 6.0
Hz, NH), 6.25 (1H, s, NH), 10.85 (1H, s, OH); 13C NMR
(CDCl3, ppm): 14.12 (CH3), 22.69-31.91 (9×CH2), 33.98 (CH2-
CO), 34.04 (CH2-COOH), 36.75 (CH2-NH), 177.31 (C=O-NH,
C=O-OH), 179.47 (C=S).
2-(3-Dodecanoyl-thioureido)-3-methyl-butyric acid
(R2): Compound R2 was obtained as white solid.Yield: 3.08
g (57.44 %); m.p. 87-88 ºC; FT-IR (KBr pellets, νmax, cm-1):
3332 (NH), 2922-3332 (OH, broad), 1712 (C=O carboxylic),
1650 (C=O amide), 1415 (C-N), 723 (C=S). 1H NMR (CDCl3,
ppm): 0.89 (3H, t, J = 7.0 Hz, CH3), 0.97 (3H, d, J = 7.0 Hz,
CH3), 1.00 (3H, d, J = 7.0 Hz, CH3), 1.06-1.09 (6H, m, J = 5.8
Hz, CH2), 1.64-1.69 (2H, m, J = 7.9 Hz, CH2), 2.24-2.30 (8H,
m, J = 5.2 Hz, CH2), 2.36-2.38 (4H, m, J = 3.4 Hz, CH2),
4.60-4.62 (1H, m, J = 4.4 Hz, CH), 4.99 (1H, d, J = 4.2 Hz,
CH), 6.13 (1H, d, J = 8.4 Hz, NH), 9.16 (1H, s, OH), 11.03
(1H, s, NH); 13C NMR (CDCl3, ppm): 14.17 ((2 × CH3)-CH),