stirred for 3 hours. Finally, the solvent was removed and the crude
product was purified by column chromatography to give the 14
vinyl-sulfone product (128 mg, 14%) 1H NMR (500 MHz, DMSO-
d6): δ 8.34 (s, 2H), 8.13 (s, 1H), 6.74 – 6.61 (m, 2H), 6.24 (d, J =
8.7 Hz, 1H) ppm.
1H), 3.58 (q, J = 6.2 Hz, 2H), 2.73 (dt, J = 8.4, 6.4 Hz, 2H), 1.34
(t, J = 8.5 Hz, 1H) ppm.
4.3.9. 2-benzamido-3-mercaptopropanoic acid (N-benzoyl-
cysteine) (26)
Reduced L-cysteine (0.5 g; 4.13 mmol) was dissolved in 10 mL
N,N-dimethylformamide, and 575 μl triethylamine was added
(4.13 mmol). The reaction mixture was cooled on ice and half-
equivalent of benzoyl-chloride (240 μL, 2.06 mmol) was added
dropwise, the the mixture was stirred overnight. Then the solvent
was removed under reduced pressure, then the residue was
dissolved in 15 mL brine and washed with 3×15 mL ethyl acetate.
The organic phase was dried, filtered and evaporated. Then the
crude product was purified on reversed phase column
chromatography, applying acetonitrile-water gradient to yield 211
mg (46%) of 26 product. 1H NMR (500 MHz, CDCl3): δ 11.06 (s,
1H), 7.87 (d, J = 7.2 Hz, 2H), 7.55 (t, J = 7.4 Hz), 7.48 (t, J = 7.5
Hz, 2H), 7.14 (d, J = 5.4 Hz, 1H), 5.07 – 5.03 (m, 1H), 3.23 – 3.19
(m, 2H), 1.50 (t, J = 9.0 Hz, 1H) ppm.
4.3.4. 1-(3,5-Bis(trifluoromethyl)phenyl)-1H-pyrrole-2,5-dione
(15)40
To a solution of maleic anhydride (214 mg, 2.18 mmol) in
dichloromethane (20 mL) 3,5-bis(trifluoromethyl)aniline (0.34
mL, 2.2 mmol) was added dropwise at 40 °C, and the mixture was
allowed to stir for 2 h. The intermediate was obtained as white
crystals (705 mg, 98 %) and collected by filtration. The
intermediate was dissolved in toluene (30 mL), then catalytic
sulfuric acid was added (1-2 drops). The reaction flask was
equipped with a Dean-Stark apparatus and the mixture was
refluxed at 130 °C for 3 h. The solvent was removed under vacuum
and the residue was purified by flash column chromatography with
a mixture of hexane and ethyl acetate as eluent. The product was
1
obtained as brown solid (272 mg, 40 %). H NMR (500 MHz,
4.3.10. 2-benzamido-5-((1-((carboxymethyl)amino)-3-mercapto-
1-oxopropan-2-yl)amino)-5-oxopentanoic acid (N-benzoyl-
glutathione) (27)
DMSO-d6): δ 8.15 (s, 1H), 8.12 (s, 2H), 7.27 (s, 2H) ppm.
4.3.5. N-(3,5-Bis-trifluoromethyl-phenyl)-2-chloro-acetamide
(20)41
First oxidized L-glutathione (1000 mg, 1.63 mmol) was
acylated with benzoyl-chlorid (378 μL, 3.26 mmol) in N,N-
dimethylformamide, in the presence of triethylamine (453 μL, 3.26
mmol). After, the reaction was completed, the solvent was
removed under reduced pressure, then the residue was dissolved in
50 mL ethyl acetate and washed with 50 mL brine. The organic
phase was dried, filtered and evaporated. Then the crude product
was dissolved in 30 mL water : tetrahydrofuran 1 : 100 solvent
mixture, then triphenylphosphine (427 mg, 1.63 mmol) was added
and the reaction mixture was stirred at 50 °C overnight. After the
reduction was completed the solvent was evaporated and the
residue was directly purified by reversed phase column
cromatography, applying acetonitrile-water gradient elution to
give the 27 product (160 mg, 24%). 1H NMR (500 MHz, CDCl3):
δ 7.87 (d, J = 7.3 Hz, 2H), 7.56 – 7.49 (m, 1H), 7.49 – 7.42 (m,
2H), 4.46 – 4.26 (m, 2H), 3.77 – 3.64 (m, 2H), 2.88 – 2.71 (m, 1H),
2.71 – 2.55 (m, 1H), 2.37 – 2.21 (m, 2H), 2.12 – 2.08 (m, 1H), 1.99
– 1.93 (m, 1H) ppm.
The same procedure as for 12 except using chloroacetyl
chloride (0.80 mL, 10 mmol). Pure 21 was obtained as a white
1
powder (2.31 g, 75%). H NMR (500 MHz, DMSO-d6): δ 10.90
(s, 1H), 8.24 (s, 2H), 7.80 (s, 1H), 4.32 (s, 2H) ppm.
4.3.6. 1-(3,5-Bis(trifluoromethyl)phenyl)-2-bromoethanone (21)42
To
a
stirred
solution
of
0.18
mL
3’,5’-
bis(trifluoromethyl)acetophenone (1 mmol) in 10 mL
tetrahydrofuran 0.32 pyridinium-tribromide (1 mmol) was added
dropwise in 10 mL tetrahydrofuran. The reaction mixture was
stirred for 4 h. Water (20 mL) was added, and the mixture was
separated. The aqueous phase was extracted with 2 x 20 mL ethyl
acetate. The organic phase was dried over magnesium sulfate, and
evaporated to silica. Flash column chromatography using hexane
– ethyl acetate 95:5 as the eluent afforded the 22 product (190 mg,
57%) as a yellow oil that solidified overnight. 1H NMR (500 MHz,
DMSO-d6): δ 8.55 (s, 2H), 8.44 (s, 1H), 5.12 (s, 2H) ppm.
4.3.7. 2-(3,5-Bis(trifluoromethyl)phenyl)oxirane (22)43
Declaration of Competing Interest
The authors declare that they have no conflict of interest.
Acknowledgements
3,5-Bistrifluoromethylphenyl-styrene (0.36 mL, 2 mmol) was
dissolved in 20 mL chloroform, and 1.38 g 3-chloroperbenzoic
acid (4 mmol) was added at 0 °C. The reaction mixture was stirred
overnight, followed by washing with 10 mL saturated aqueous
solution of sodium bicarbonate. The organic phase was dried over
magnesium sulfate and evaporated to silica. The crude product was
purified with flash chromatography using hexane – ethyl acetate
Financial support of H2020 MSCA FRAGNET (project
675899), National Research Development and Innovation Office
(grant number SNN_17 125496) and by the Slovenian Research
Agency (grant number N1-0068 (B) and research core funding No.
P1-0208) and OTKA PD124598 is gratefully acknowledged.
1
93:7 as the eluent. H NMR (500 MHz, CDCl3): δ 7.82 (s, 1H),
7.74 (s, 2H), 3.99 (dd, J = 3.8, 2.6 Hz, 1H), 3.23 (dd, J = 5.3, 4.1
Hz, 1H), 2.79 (dd, J = 5.4, 2.4 Hz, 1H) ppm.
References and notes
4.3.8. N-(2-mercaptoethyl)benzamide (25)44
Cysteamine hydrochloride (341 mg, 3 mmol) was dissolved in
15 mL dichloromethane and benzoyl-chloride (280 μL, 3 mmol)
and triethylamine (835 μL, 6 mmol) was added at 0 °C, under Ar
atmosphere. After addition the reaction mixture was stirred at
room temperature overnight. The reaction was extracted with 25
mL saturated aqueous solution of sodium bicarbonate, then the
aqueous layer was washed with 2×15 mL dichloromethane. The
organic layer was dried and concentrated, then purified by
reversed phase column chromatography applying acetonitrile :
water gradient elution. The 26 product was obtained as white solid
(203 mg, 37%). 1H NMR (500 MHz, DMSO-d6): δ 7.72 (d, J = 7.2
Hz, 2H), 7.45 (t, J = 7.4 Hz, 1H), 7.38 (t, J = 7.5 Hz, 2H), 6.56 (s,
1.
Bauer RA. Covalent inhibitors in drug discovery: from accidental
discoveries to avoided liabilities and designed therapies. Drug
Discov Today. 2015;20(9):1061-1073.
doi:10.1016/j.drudis.2015.05.005
2.
3.
4.
5.
De Cesco S, Kurian J, Dufresne C, Mittermaier AK, Moitessier N.
Covalent inhibitors design and discovery. Eur J Med Chem.
2017;138:96-114. doi:10.1016/j.ejmech.2017.06.019
Singh J, Petter RC, Baillie TA, Whitty A. The resurgence of
covalent drugs. Nat Rev Drug Discov. 2011;10(4):307-317.
doi:10.1038/nrd3410
González-Bello C. Designing Irreversible Inhibitors-Worth the
Effort? ChemMedChem. 2016;11(1):22-30.
doi:10.1002/cmdc.201500469
Smith AJT, Zhang X, Leach AG, Houk KN. Beyond Picomolar
Affinities: Quantitative Aspects of Noncovalent and Covalent