2
W. Bai et al. / Tetrahedron Letters 61 (2020) 152366
10a-h were synthesized by the addition reaction of 3,5-bis(trifluo-
romethyl)phenyl isothiocyanate with compounds 9a-h.
Biological evaluation
In vitro antiproliferative activity analysis
The newly synthesized compounds were evaluated for their
antiproliferative activities against human endothelial cells (Human
umbilical vein endothelial cells, HUVEC) and cancer cells including
human large cell lung cancer cell line (NCI-H460), human colorec-
tal adenocarcinoma cell line (Colo-205), human colon carcinoma
cell line (HCT116), human breast adenocarcinoma cell line (MDA-
MB-231), human breast adenocarcinoma cell line (MCF-7), human
hepatoma cell line (HepG2) and human hepatoma cell line (PLC/
PRF/5). All of them were tested by CCK-8 assay using Sorafenib
and Regorafenib as positive control. As presented in Table 1 and
Table 2, antiproliferative activities were shown as the percent of
Figure 1. Structure of synthesized potent compound 10e.
were firstly synthesized by the reaction of 4-(4-aminophenoxy)-N-
methylpicolinamide or 4-(4-amino-3-fluorophenoxy)-N-
1
methylpicolinamide 2 with various isothiocyanates 3a-p (phenyl
isothiocyanate, 4-fluorophenyl isothiocyanate, 2,4-difluorophenyl
isothiocyanate,
4-bromophenyl
isothiocyanate,
4-(trifluo-
romethyl)phenyl isothiocyanate, 4-chloro-3-(trifluoromethyl)phe-
nyl isothiocyanate, 3,5-bis(trifluoromethyl)phenyl isothiocyanate,
3-nitrophenyl isothiocyanate, 4-carboxyphenyl isothiocyanate, 3-
ethoxycarbonylphenyl isothiocyanate, 4-(trifluoromethoxy)phenyl
isothiocyanate, 4-(methylthio)phenyl isothiocyanate, 4-tert-butyl-
phenyl isothiocyanate, 4-fluoro-2-methylphenyl isothiocyanate,
4-(benzyloxy)phenyl isothiocyanate, 3,4-methylenedioxyphenyl
isothiocyanate) in the presence of THF, DMF or ACN (Scheme 1)
[26,27].
inhibition values at 10 lM.
Initially, we evaluated the effects of substituents (R1) attached
to the thiourea moiety on the antiproliferative activity against
the tested cell lines. As shown in Table 1, compound 4a with a phe-
nyl ring in the absence of any substituent failed to exhibit antipro-
liferative effects at the concentration of 10
lM, which indicated
Furthermore, to assess the effects of R2 groups on the antiprolif-
erative activity, compounds 10a-h were synthesized as described
in Scheme 2 [26,28,29]. Firstly, 4-chloro-pyridine-2-carbonyl chlo-
ride 7 was prepared from 2-Picolinic acid 6 and SOCl2 in the pres-
ence of DMF. Subsequently, various substituted amines (i.e.
cyclopentylamine, cyclopropylamine, N,N-dimethylethylenedi-
amine, benzylamine, aniline, pyrrolidine, piperidine, 4-aminote-
trahydropyran) were treated with 7 to generate compounds 8a-
h. Then, the key intermediates 9a-h were obtained by coupling
of compounds 8a-h with 4-aminophenol in the presence of
K2CO3 with potassium tert-butoxide. Finally, the target compounds
that the important role of substituent on the aromatic ring. Then,
various thiourea derivatives with electron-withdrawing or elec-
tron-donating groups on aromatic ring were examined. Generally,
the compounds 4d-4j bearing electron withdrawing group on the
phenyl ring showed good antiproliferative activities. Moreover,
compound 4 g with the 3,5-bis(trifluoromethyl)phenyl exhibited
the best antiproliferative activities against cancer cell lines and
HUVECs, which indicated that trifluoromethyl moiety increased
the antiproliferative activity. Compounds 4 k-4p containing elec-
tron-donating groups showed relative weaker activity against cell
lines, which suggested that the electron-donating group on the
Scheme 1. Reagents and conditions: (a) THF, DMF, ACN, 25℃, 2 h.
Scheme 2. Reagents and conditions: (a) SOCl2, DMF, 70℃, 16 h; (b) RNH2 / Pyrrolidine / Piperidine, DCM, Et3N, 0℃, 6 h; (c) 4-aminophenol, DMF, tBuOK, K2CO3, 100℃, 12 h;
(d) 3,5-bis(trifluoromethyl)phenyl isothiocyanate, THF, DMF, ACN 25℃, 2 h.