Synthesis and antidepressant evaluation of three para-benzoquinone mono-oximes and their oxy derivatives

Article abstract of DOI:10.3390/11020148

A series of three para-benzoquinone mono-oximes and four oxy-derivatives were prepared and tested for their antidepressant properties. The (4E) oxime of 2-isopropyl-5-methyl-para-benzoquinone (4) and the corresponding 2-diethylamino-ethyl derivative (10)

Full text of DOI:10.3390/11020148

Molecules 2006, 11, 148-155
molecules
ISSN 1420-3049
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Full Paper
Synthesis and Antidepressant Evaluation of Three
para-Benzoquinone Mono-oximes and Their Oxy Derivatives
Damião Pergentino de Sousa*, Renata Rabelo Schefer, Ursula Brocksom and Timothy John
Brocksom*
Laboratório de Química Bio-Orgânica, Departamento de Química, Universidade Federal de São Carlos,
Caixa Postal 676, 13565-905 São Carlos, SP, Brazil
*Authors to whom correspondence should be addressed. E-mail: brocksom@terra.com.br or
damiao50@yahoo.com.br
Received: 18 January 2006 / Accepted: 7 March 2006 / Published: 10 March 2006
Abstract: A series of three para-benzoquinone mono-oximes and four oxy-derivatives were
prepared and tested for their antidepressant properties. The (4E) oxime of 2-isopropyl-5-
methyl-para-benzoquinone (4) and the corresponding 2-diethylamino-ethyl derivative (10)
present antidepressant activities and were slightly more potent than the reference standard.
Keywords: Oximes, para-benzoquinones, antidepressant activity.
1. Introduction
Depression is a syndrome or collection of symptoms which occur together with sufficient frequency
to constitute a recognizable clinical condition. The most common symptoms are apathy, fatigue,
depressed mood, depressive thought content and diminished concentration. Theoretical approaches to
depression tend to be either strongly biological or strongly psychological in nature. It is now clear that
a variety of different factors are implicated in the etiology of depression. There is no doubt that new
antidepressants are needed. Existing drugs have undesirable side-effects which reduce compliance
with therapy and significant numbers of depressives do not make a satisfactory response [1].
In recent years much work has been published on oxime derivatives with different
pharmacological properties: for example: anti-tumor [2], anti-microbial, anticonvulsant [3,4], anti-
arrhythmic, analgesic and anesthetic properties [5,6]. Many oximes also have been studied to
investigate their antidepressant activity [7-9]. Since some oxime derivatives have therapeutic potential
as antidepressant drugs, the main aim of the present work was to synthesize several structurally-related

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149
oximes and to submit them to a preliminary screening to determine the relationship between the
structures and their antidepressant activity.
2. Results and Discussion
The mono-oximes 4-6 were synthesized in 80, 90 and 82 % yields, respectively, (Scheme 1) by
oximation of the corresponding para-benzoquinones 1-3 under standard conditions [10,11].
Scheme 1.
OH
OH
O
N
N
O
6
5
NH2OH . HCl,
NaOAc, EtOH,
reflux, 1.5h.
R
O
O
O
N
HO
6 (82%)
1 R = 5- i-Pr
2 R = 5- Me
3 R = 6- Me
5 (90%)
4 (80%)
Scheme 2.
O
C
OH
OCH3
N
O
CH3
N
N
O
Ac2O, py
DMAP, CH2Cl2
NaH
CH3I
O
O
7 (84%)
4
8 (71%)
NaH
BrCH2CH2Br
OCH2CH2Br
OCH2CH2N(CH2CH3)2
N
N
O
diethylamine
EtOH
O
9 (70%)
10 (49%)

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The mono-oxime derivatives 7-9 (Scheme 2) were obtained by standard alkylation and acylation
reactions of compound 4. The ether 7 was synthesized in 84% yield with methyl iodide whereas
reaction of 4 with acetic anhydride resulted in 8 in 71% yield. Treatment of 4 with dibromoethane gave
the bromide 9 in 70% yield, which was further converted with diethylamine into the amine 10 in 49%
yield.
Antidepressant activity
None of the compounds tested caused mortality up to a dose of 100 mg/kg i.p. in mice. The
antidepressant evaluation of the compounds is presented in Table 1.
Table 1. Antidepressant activity of compounds 4-10.
Dose
Duration of immobility
(sec + S.E.M.)
205.5 + 4.4
Compound
(mg/kg i.p.)
Control
---
15
10
10
10
10
10
10
10
Imipramine
178.3 + 7.8*
174.8 + 8.9*
188.8 + 12.7
183.8 + 14.6
207.1 + 6.0
4
5
6
7
8
212.5 + 4.3
9
189.5 + 5.8
10
175.1 + 7.8*
*p < 0.05
The forced swimming test showed a relationship between structure and antidepressant activity.
Compounds 4 and 10 were shown to be nearly equipotent and slightly more potent than imipramine,
the drug used as reference standard.
Of the three mono-oximes studied only 4 was active, indicating the relevance of the isopropyl group
for the antidepressant activity in this series. The oxime ethers 7 and 9, as well as the acetyl mono-
oxime 8, present no statistical difference from the control group in reducing the immobility time of
mice. The amine derivative 10 significantly shortened this immobility period, which is perhaps not
surprising considering that its structure is similar to the second-generation antidepressant drug
fluvoxamine [8].
The behavioural despair test is a classic model very well known for screening of new antidepressant
drugs. The onset of immobility is delayed by pretreatment with a wide variety of antidepressants.
Effective agents include tricyclics, MAOIs, most atypical antidepressants, deprivation of rapid eye
movement sleep and electroconvulsive shock [1]. Indeed, there is a significant correlation between the
potency of antidepressants in the behavioural despair test and their clinical potency, which has not
been demonstrated with any other animal model of depression [12].
The preliminary screening results reported in this paper show that compounds 4 and 10 are
psychoactive, evidencing a pharmacological profile of an antidepressant drug. Our results also

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suggested that by appropriate structural modification of para-benzoquinone mono-oximes, it may be
possible to develop novel therapeutic agents against depression.
Acknowledgements
We thank FAPESP, CNPq and CAPES for financial support and Cristalia Produtos Químicos
Farmacêuticos Ltda for a donation of imipramine.
3. Experimental Section
Chemistry
GLC analyses were conducted on a Shimadzu GC-17A instrument equipped with a flame-ionization
detector, using a DB-1 (30 m x 0.25 mm) glass column. Column chromatography was performed on
silica gel 60 (70-230 mesh ASTM Merck). Radial thin-layer chromatography was carried out on a
Chromatotron model 8924 (silica gel 60PF274 Merck). Melting points were determined on a
Microquímica MQWAPF-301 apparatus and are uncorrected. Infrared spectra were recorded with a
Bomen Hartman & Braun MB-Series spectrometer. 1H- and 13C- NMR spectra were recorded at 200 or
50 MHz, respectively, either on a Bruker ARX-200 or a Bruker DRX-400 spectrometer in CDCl3 with
TMS as internal standard. The mass spectra were recorded on a Micromass mass spectrometer Quattro
LC, coupled with a chemical ionization source (reagent MeOH) under atmospheric pressure (APCI).
Microanalyses were performed on a Fisons EA 1108 CHNS-O analyzer, at the Chemistry Department,
Universidade Federal de São Carlos. Solvents were purified prior to use: dichloromethane and hexane
were refluxed over P2O5, distilled and stored over molecular sieves; pyridine was stirred and refluxed
over KOH, distilled and stored over KOH; acetic anhydride was stirred over P2O5 and K2CO3, distilled
and stored over molecular sieves.
General procedure for the syntheses of the oximes 4, 5 and 6:
A solution of the hydroxylamine hydrochloride (0.221 g, 3.18 mmol) and sodium acetate (0.169 g,
2.08 mmol) were added to para-benzoquinone (1.22 mmol) in EtOH (11.70 ml), and the resulting
mixture was stirred and refluxed for 1.5 hours. After the solvent was evaporated under reduced
pressure, the solid residue was diluted in water (50 mL) and extracted with a mixture of ethyl acetate
and ethyl ether (1:1, 3 × 20 mL). The organic layer was washed with aqueous NaHCO3 (3 × 20 mL)
and NaCl (3 × 20 mL), dried over anhydrous Na2SO4 and the solvent was evaporated under reduced
pressure. The solid residue was washed with hexane (4 × 20 mL) to eliminate soluble impurities.
(4E)-2-isopropyl-5-methylbenzo-1,4-quinone 4-oxime (4)
o
o
Yield: 80%; Mp 142.6-143.2 C; lit. 140 C [13], IR (ν
, KBr, cm–1): 3180, 2964, 1639, 1605,
max.
1439, 1241, 1056; 1H-NMR δ: 1.13 (6H, d, J=6.8 Hz), 2.20 (3H, d, J=1.3 Hz), 3.07 (1H, d hept, J=1.1
and 6.8 Hz), 6.27 (1H, q, J=1.3 Hz), 7.56 (1H, d, J=1.1 Hz); 13C-NMR δ: 16.8, 21.5, 26.3, 118.2, 128.4,

Molecules 2006, 11
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146.0, 147.9, 150.1, 186.8; MS m/z (%): 180 [M+1]+ (100), 163 (4), 109 (28); Anal. Calcd. for
C10H13NO2: 7.82 (N), 67.02 (C), 7.31 (H); Found: 7.56 (N), 67.11 (C), 7.55 (H).
(1E)-2,5-dimethylbenzo-1,4-quinone oxime (5)
Yield: 90%; Mp 126.5-127.4 oC; IR (ν
, KBr, cm–1): 3232, 2889, 1642, 1611, 1353, 1187, 1025;
max.
1H-NMR δ: 2.03 (3H, d, J=1.4 Hz), 2.19 (3H, d, J=1.3 Hz), 6.31 (1H, q, J=1.3 Hz), 7.63 (1H, q, J=1.4
13
Hz); C-NMR δ: 15.8, 16.8, 121.5, 128.2, 138.9, 146.9, 150.2, 187.9; MS (m/z (%): 152 [M+1]+
(100), 124 (5), 109 (7); Anal. Calcd. for C8H9NO2: 9.27 (N), 63.56 (C), 6.00 (H). Found: 9.13 (N),
63.13 (C), 5.88 (H).
(4E)-2,6-dimethylbenzo-1,4-quinone oxime (6)
Yield: 82%; Mp 138.4-139.0 oC; IR (ν
, KBr, cm–1): 3216, 2853, 1632, 1604, 1423, 1199, 1058;
max.
1H-NMR δ: 2.01 (3H, d, J=1.1 Hz), 2.04 (3H, d, J=1.2 Hz), 7.02 (1H, q, J=1.1 Hz), 7.58 (1H, q, J=1.2
Hz); 13C-NMR δ: 15.7, 16.3, 120.5, 133.8, 136.4, 139.0, 149.2, 187.8; MS m/z (%): 152 [M+1]+ (100),
138 (5), 122 (14); Anal. Calcd. for C8H9NO2: 9.27 (N), 63.56 (C), 6.00 (H). Found: 9.28 (N), 63.23 (C),
5.98 (H).
(4E)-2-isopropyl-5-methylbenzo-1,4-quinone 4-(O-methyloxime) (7)
A solution of 4 (0.100 g; 0.56 mmol) in dichloromethane (2.5 mL) and THF (0.1 mL), was added to
sodium hydride (60%, 0.020 g, 0.83 mmol, previously washed several times with dry hexane) and the
resulting mixture was stirred for 1 hour at room temperature. Methyl iodide (0.16 mL, 2.57 mmol) was
added and the reaction was allowed to stand at room temperature for 18 hours. The mixture was
diluted with water (20 mL) and the layers were separated. The aqueous layer was extracted with ethyl
acetate (3 × 20 mL). The combined organic layers were washed with aqueous NH4Cl (3 × 20 mL),
dried over anhydrous Na2SO4 and the solvents were evaporated under reduced pressure. The oily
residue was purified by radial thin-layer chromatography (9:1 hexane-ethyl acetate as eluent) to
provide a pure sample of 7: (0.091 g, 0.470 mmol, 84% yield). IR (ν
, KBr, cm–1): 2972, 1637,
max.
1613, 1518, 1372, 1240; 1H-NMR δ: 1.12 (6H, d, J=6.8 Hz), 2.16 (3H, d, J=0.8 Hz), 3.06 (1H, d hept,
13
J=6.8, 0.8 Hz), 3.46 (3H, s), 6.26 (1H, d, J=0.8 Hz), 7.38 (1H, d, J=0.8 Hz); C-NMR δ: 16.8, 22.1,
26.6, 63.7, 118.4, 129.1, 145.6, 149.0, 149.6, 186.7; MS m/z (%): 194 [M+1]+ (100), 179 (26), 164
(30), 152 (5); Anal. Calcd. for C11H15NO2: 7.25 (N), 68.37 (C), 7.82 (H). Found: 6.98 (N), 67.99 (C),
7.72 (H).
(4E)-2-isopropyl-5-methylbenzo-1,4-quinone 4-(O-acetyloxime) (8)
Pyridine (0.34 mL) was added to a mixture of 4 (0.100 g, 0.56 mmol), DMAP (catalytic amount)
and acetic anhydride (0.13 mL, 1.36 mmol). The resulting mixture was stirred for 20 hours at room
temperature. The mixture was diluted with ethyl ether (20 mL) and washed successively with 10%
aqueous CuSO4 (3 × 20 mL), 5% aqueous NaHCO3 (2 × 20 mL) and distilled water (20 mL), dried

Molecules 2006, 11
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over Na2SO4 and the solvent was evaporated under reduced pressure. The solid residue was purified by
radial thin-layer chromatography (9:1 hexane-ethyl acetate as eluent) to provide a pure sample of 8:
(0.088 g, 0.40 mmol, 71% yield). Mp 68.4 – 70.4 oC; IR (ν
, KBr, cm–1): 2965, 1785, 1650, 1630,
max.
1601, 1522, 1249, 1150; 1H-NMR δ: 1.13 (6H, d, J=6.9 Hz), 2.26 (3H, d, J=1.4 Hz), 2,37 (3H, s), 3.09
(1H, d hept, J1=1.1 Hz and J2=6.9 Hz), 6.39 (1H, d, J=1.4 Hz), 7.39 (1H, d, J=1.1 Hz); C-NMR δ:
13
17.3, 19.8, 21.7, 34.1, 118.4, 131.1, 145.5, 151.9, 154.1, 168.9, 186.7; MS m/z (%): 222 [M+1]+ (45),
180 (100), 164 (24), 152 (18), 138 (30), 110 (90); Anal. Calcd. for C12H15NO3: 6.33 (N), 65.14 (C),
6.79 (H). Found: 6.00 (N), 64.89 (C), 6.56 (H).
(4E)-2-isopropyl-5-methylbenzo-1,4-quinone 4-[O-(2-bromoethyl)-oxime] (9)
A solution of 4 (0.118 g, 0.66 mmol) in dichloromethane (2.5 mL) and THF (0.1 mL) was added to
sodium hydride (60%, 0.020 g, 0.83 mmol, previously washed several times with dry hexane) and the
resulting mixture was stirred for 1 hour at room temperature. Dibromoethane (0.11 mL, 1.32 mmol)
was added and the reaction was allowed to stand at room temperature for 6 hours. The mixture was
diluted with water (20 mL) and the layers were separated. The aqueous layer was extracted with ethyl
acetate (3 × 20 mL). The organic layers were combined, washed with aqueous NH4Cl (3 × 20 mL),
dried over anhydrous Na2SO4 and the solvent was evaporated under reduced pressure. The oily residue
was purified by radial thin-layer chromatography (9:1 hexane-ethyl acetate as eluent) to provide a pure
sample of 9: (0.132 g, 0.46 mmol, 70% yield). IR (ν
, KBr, cm–1): 2963, 1630, 1623, 1424, 1239,
max.
1
1077, 1010; H-NMR δ: 1.11 (6H, d, J=6.7 Hz), 2.14 (3H, s), 3.05 (1H, m), 3.62 (2H, t, J=6.3 Hz),
13
4.59 (2H, t, J=6.3 Hz), 7.39 and 6.28 (2H,s); C-NMR δ: 16.8, 21.6, 26.7, 28.9, 75.0, 118.5, 129.5,
133.3, 145.4, 149.6, 186.7; MS m/z (%): 287 [M+1]+ (100), 268 (10), 235 (15), 179 (45), 163 (18);
Anal. Calcd. for C12H16NO2Br: 4.89 (N), 50.37 (C), 5.64 (H). Found: 4.76 (N), 50.24 (C), 5.54 (H).
(4E)-2-isopropyl-5-methylbenzo-1,4-quinone-(O-[2-(diethylamino)-ethyl]-oxime) (10)
A solution of (9) (0.40 g; 1.39 mmol) in EtOH (15 ml) was added to diethylamine (0.43 ml, 0.307 g;
4.2 mmol) and the resulting mixture was stirred for 6 hours at room temperature. The solvent and
excess diethylamine were evaporated under reduced pressure. The oily residue was purified by radial
thin-layer chromatography (9:1 hexane-ethyl acetate as eluent) to provide a pure sample of 10: (0.192
1
g, 0.69 mmol, 49% yield). IR (ν
max.
, KBr, cm–1): 2966, 1640, 1626, 1466, 1306, 1240, 1044; H-
NMR δ: 1.10 (6H, t, J=7.2 Hz), 1.15 (6H, d, J= 6.9 Hz), 2.15 (3H, d, J=1.3 Hz), 2.7 (4H, q, J=7.2 Hz),
2.95 (2H, t, J=5.9 Hz), 3.08 (1H, d hept, J1=1.1, J2=6.9 Hz), 4.5 (2H, t, J= 5.9 Hz), 6.28 (1H, q, J= 1.3
Hz), 7.39 (1H, d, J= 1.1 Hz); 13C-NMR δ: 11.2, 16.8, 21.7, 26.7, 47.5, 50.8, 74.2, 118.6, 129.2, 145.5,
149.3, 149.9, 186.7; MS m/z (%): 279 [M+1]+ (100), 164 (13), 116 (11); Anal. Calcd. for C16H24N2O2:
10.06 (N), 69.03 (C), 9.41 (H). Found: 9.80 (N), 68.65 (C), 9.12 (H).
Acute toxicity
The toxicity study was performed with different doses of compounds to groups of mice (n = 10)
administered intraperitoneally (i.p.), and mortality was recorded for 48 h [14].

Molecules 2006, 11
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Pharmacology
The forced swimming (behavioural despair) test was employed on 6-8 week old male Swiss
albino mice (weighing 28-36 g). The animals were maintained at constant room temperature (23 ± 1oC)
and on a 12/12 hour light-dark cycle (light from 07:00 to 19:00 hours) with free access to food and
water. They were acclimatized for a minimum of 7 days.
The synthesized compounds (10 mg/kg) and imipramine (15 mg/kg) were dissolved in 5% Tween
80 and saline (0.9%), respectively. They were injected i.p. into mice (n = 6) in dose/volume of 1
mL/100 g, one hour prior to testing. Saline was used as control. One hour after injection the mice were
placed one at a time into a plexi-glass cylinder (22 cm height, 10 cm diameter) containing 8 cm height
of water at 24 oC and the immobility time of each mouse was measured between 2 and 6 min [15].
Statistical analysis
Analysis of variance and Student’s “t” test were made and the results were considered significant
when p < 0.05.
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Sample availability: Available from the authors.
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