118 N. Salewska et al.
spectra were recorded on the Varian Gemini 200 and
500 MHz spectrometers. UV–vis spectra were recorded
in an UV–vis Lambda 45, Perkin Elmer spectrophotom-
eter. in layer chromatography (TLC) was performed
on silica gel (Merck) in a solvent system benzene:ethyl
acetate:ethanol (50:15:5). Elementary analysis (EA) was
run on the Carlo Erba, type EA 1108 analyser.
N-(2-tert-butylphenyl)maleimide (7)
Yield 85% and m.p. 90°C. 1H NMR (CDCl3) δ [ppm]:
7.2 (d, 1H, J= 8 Hz, C6H5); 7.1 (t, 1H, J= 7 Hz, C6H5); 7.9
(s, 1H, = CH); 6.93 (d, 1H, C6H5); 6.2 (s,1H, CH=); 1.1 (s,
9H, (CH3)3C). Anal. found: C 73.11, H 6.54, N 6.07%.
Calculated for C14H15NO2: C 73.34, H 6.59, N 6.11%.
N-(4-bromophenyl)maleimide (8)
Yield 53% and m.p. 118–119°C. 1H NMR (CDCl3) δ [ppm]:
7.73 (m, 2H, C6H5); 7.71 (m, 2H, C6H5); 6.7 (s, 2H, CH=CH).
Anal. found: C 47.66, H 2.51, N 5.32%. Calculated for
C10H6NO2Br: C 47.65, H 2.40, N 5.36%.
General procedure for the synthesis of
maleimides 3–10
Maleic anhydride (20 mmol) was dissolved in 20 ml of
CH2Cl2. e stirred solution was cooled to 0–5°C and
equimolar amount of an appropriate amine dissolved
in 15 ml of CH2Cl2 was added to the mixture. e result-
ing suspension was refluxed for 2 h and then cooled to
room temperature. e precipitated solids were filtered
off and washed twice with ethyl ether. e maleamic
acids formed in the first step (15 mmol) were dissolved in
24 ml of acetic anhydride and anhydrous sodium acetate
(10 mmol) was added to the mixture. e resulting sus-
pension was refluxed and reaction progress was followed
by TLC. When the reaction was completed, the mixture
was cooled and 100 ml of water was added. e result-
ing solution of maleimide in water was extracted with
ethyl acetate (3 × 50 ml), extracts were combined, dried
with MgSO4, filtered and the solvent was evaporated.
Crude products were re-crystallised from the solvent or
distilled.
N-(4-methoxyphenyl)maleimide (9)
Yield 58% and m.p. 150–151°C. 1H NMR (CDCl3) δ [ppm]:
7.5 (d, 2H, J= 8.8 Hz, C6H5); 7.2 (d, 2H, J= 8.8 Hz, C6H5); 6.5
(s, 2H, CH=CH); 3.4 (s, 3H,−OCH3). Anal. found: C 64.98,
H 4.48, N 6.79%. Calculated for C11H9NO3: C 65.02, H 4.46,
N 6.89%.
N-(4-nitrophenyl)maleimide (10)
Yield 70% and m.p. 161°C. 1H NMR (CDCl3) δ [ppm]: 8.33
(d, 2H, J= 2 Hz, C6H5); 7,.8 (d, 2H, J= 2 Hz, C6H5); 6.3 (s,
2H, CH=CH). Anal. found: C 55.04, H 2.75, N 12.77%.
Calculated for C10H6N2O4: C 55.05, H 2.77, N 12.84%.
N-[2-(N,N-dimethylamino)ethyl]maleimide (11)
Yield 52% and m.p. 175–176°C. 1H NMR (CDCl3): δ [ppm]:
6.67 (s, 2H, CH=CH), 3.61 (t, J= 6.3 Hz, 2H, CH2), 2.47 (t,
J= 6.4 Hz, 2H, CH2), 2.23 (s, 6H, CH3). Anal. found: C 56.99,
H 7.09, N 16.51%. Calculated for C8H12N2O2: C 57.14, H,
7.14, N 16.67%.
Basic maleimides 11 and 12 were synthesised accord-
ing to the described procedures10,11
.
N-cyclohexylmaleimide (3)
Yield 70% and m.p. 84°C. 1H NMR (CDCl3): δ [ppm]:
7.29 (s, 1H, = CH); 6.65 (s, 1H, HC=); 3.93 (t, 1H, J= 3.9
Hz, CH); 2.08 (qd, 2H, J= 12.9 Hz and 3.9 Hz, CH2); 1.86
(d, 2H, J= 13.2 Hz, CH2); 1.68 (m, 3H, CH2), 1.3 (m, 3H,
CH2). Analytically found (Anal. Found): C 66.93, H 7.27,
N 7.78%. Calculated for C10H13NO2: C 67.02, H 7.31, N
7.82%.
N-[2-(N-morpholinoethyl]maleimide (12)
Yield 33% and m.p. 132°C. 1H NMR (CDCl3): δ [ppm]: 6.65
(s, 2H, CH=CH), 3.55 (t, J= 6.8 Hz, 2H, CH2), 2.49 (t, J= 6.8
Hz, 2 H, CH2), 2.42 (m, 8H, CH2). Anal. found: C 56.99,
H, 6.48, N 13.17%. Calculated for C10H14N2O3: C 57.14, H
6.67, N 13.33%.
Determination of the model reaction rate
N-benzylmaleimide (4)
Yield 58% and m.p. 69°C. H NMR (CDCl3) δ [ppm]: 7.35
(m, 5H, C6H5); 6.72 (s, 2H, CH=CH); 4.69 (s, 2H, CH2).
Anal. found: C 71.48, H 5.01, N 7.42%. Calculated for
C11H9NO2: C 71.48, H 4.85, N 7.48%.
Progress of the reaction between maleimides and
N-acetyl methyl cysteinate (ACME) was determined
spectrophotometrically, measuring decrease in the
absorption at 300 nm (A300). Stock solutions of maleim-
ides (50 µmol ml−1 in dimethyl sulfoxide) and ACME
(50 µmol ml−1 in water) were prepared. Sample of the
maleimide solution (50 µl) was added to 1400 µl of the
sodium phosphate buffer (pH 5.0 or 7.0) and A300 of the
resulting solution was recorded. Reaction was initiated
by addition of 50 µl of the ACME solution and mea-
surement of A300 was continued at room temperature.
Concentration of a particular maleimide in the reac-
tion mixture at the given moment was calculated from
the standard curves A300 = f(c) determined separately
for each compound from the 1–12 series. Data were
plotted as 1/c versus time, to give the second order rate
constants k as slopes of the linear plots.
1
N-(2,6-dimethylphenyl)maleimide (5)
Yield 51% and m.p. 105–107°C. 1H NMR (CDCl3) δ [ppm]:
7.1 (m, 3H, C6H5); 6.8 (s, 2H, CH=CH); 2.2 (s, 6H, CH3).
Anal. found: C 69.34, H 5.58, N 6.83%. Calculated for
C12H11NO2: C 69.63, H 5.51, N 6.95%.
N-(2,4,6-trimethylphenyl)maleimide (6)
Yield 64% and m.p. 99–100°C. H NMR (CDCl3) δ [ppm]:
6.7 (m, 5H, C6H5); 6.6 (s, 2H, CH=CH); 2.1 (s, 3H, CH3);
2.7 (s, 6H, CH3). Anal. found: C 72.21, H 6.11, N 6.45%.
Calculated for C13H13NO2: C 72.54, H 6.09, N 6.51%.
1
Journal of Enzyme Inhibition and Medicinal Chemistry