176
Hülya Çelik Onar and Begüm Alevli Vardar
EXPERIMENTAL
Chemicals. All applied chemicals and reagents were purchased from the Merck Chemical
Company.
Syntheses of coumarin derivatives. A mixture of phenol (10 mmol), β-keto esters (10 mmol) and
o
oxalic acid (10 mol%) was heated to 80 C till completion of the reaction (monitored using
TLC). Then, the reaction mixture was cooled to room temperature, and it was poured in ice-
water mixture and stirred for 10 min. The precipitated product was collected by filtration,
washed with water and dried. The product obtained was recrystallized from appropriate solvent
(
like ethanol) to afford corresponding pure coumarin product [12]. All synthesized coumarin
derivatives were characterized using IR (Mattson-1000 FTIR spectrometer), NMR (Varian
Unity INOVA 500 spectrometer), Mass (Thermo Finnigan LCQ Advantage Max LC/MS/MS
Spectrometer), elemental analysis (Thermo Finnigan Flash EA 1112 Series Elemental Analyser)
and melting point (Buchi B-540).
Sample preparation. Stock solutions of synthesized coumarins were prepared in ethanol in
concentration 0.1 mol/L. Ascorbic acid, BHA (butylated hydroxy anisole), BHT (butylated
hydroxy toluene) and NDGA (nordihydroguairetic acid) were used as standard controls for
antioxidant testing and they were prepared in same concentration as tested coumarins.
1
,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. 1,1-Diphenyl-2-
picrylhydrazyl radical was used for determination of free radical scavenging activity of the
synthesized compounds by modified method of Brand-Williams [13]. The concentrations of the
tested samples ranged from 0.10 to 0.0001 mol/L. A portion of the sample solution (200 µL)
-
5
was mixed with 3.0 mL of 5.25 x 10 mol/L DPPH in absolute ethanol. After 30 min at room
temperature the absorbance was recorded at 517 nm using a Jenway 6105 UV/Vis
spectrophotometer. All experiments were carried out in triplicate.
The radical-scavenging activity of the tested samples, exhibited as percentage inhibition of
DPPH, was calculated according to the formula IC (%) = [(A -A)/A ] [14]. A is the absorbance
0
0
0
value of the tested sample and A is the absorbance value of blank sample. Percent inhibition
was plotted against concentration, and the equation for the line was used to obtain the IC value.
5
0
A lower IC50 value indicates greater antioxidant activity.
o
4
1
2
-Methyl-8-formyl coumarin (7). White solid; yield 45%; m.p.: 91.1-91.8 C; IR (KBr): ν 1746,
684, 1615, 1215; H-NMR (500 MHz, DMSO): δ 2.4-2.5 (s, -CH
1
3
, 3H), 7.36-7.46 (m, Ar-H,
H), 7.69-7.75 (t, Ar-H, J = 8.7 Hz, 1H), 7.85-7.88 (d, Ar-H, J = 7.8 Hz, 1H), 8.6-8.65 (s,
CHO, 1H); C-NMR (125.66 MHz, DMSO): δ 196.7 (1C, Ar-CHO), 159.2 (1C, coumarin
C=O), 155.01, 148.07, 135.44, 131.32 (4C, Ar-C), 125.76, 124.66, 118.49, 116.64 (4C, vinyl-
CH and Ar-CH), 30.42(1C, CH ); MS (EI) m/z: 89, 101, 118, 131, 145, 160, 173, 188; anal.
calcd. for C H O : C, 70.20; H, 4.30; found C, 70.09; H, 4.59.
1
3
-
3
1
1
8
3
o
4
1
-Phenyl-8-formyl coumarin (8). White solid; yield 52%; m.p.: 133.8-134.7 C, IR (KBr): ν
1
3
715, 1661, 1615, 1246; H-NMR (500 MHz, CDCl ): δ 7.3 (t, Ar-H, 1H. J = 7.3 Hz), 7.42 (t,
Ar-H, 3H, J = 7.8 Hz), 7.5-7.6 (m, Ar-H, 3H), 7.82 (d, Ar-H, 1H, J = 8.3 Hz), 7.88 (d, Ar-H, 1H,
J = 8.3 Hz), 8.0 (s, -CHO, 1H); APT (125.66 MHz, CDCI ) : δ 191.8, 145.57, 145.55, 134.04,
33.82, 129.82, 129.41, 128.83, 125.2, 117.21 (10C, -CHO, vinyl-CH and Ar-CH), 156.6,
55.4, 146.3, 136.5, 127.36, 118.44 (6C, coumarin C=O ve Ar-C); MS (EI) m/z: 77, 105, 145,
73, 178, 194, 207, 221, 250; anal. calcd. for C11 : C,76.80; H,4.00; found C,76.76; H, 4.49.
3
1
1
1
8 3
H O
Bull. Chem. Soc. Ethiop. 2018, 32(1)