M. Djukic et al.
Chemico-Biological Interactions 286 (2018) 119–131
antioxidant defense systems to mediate the concentration of free radi-
cals within the body results in oxidative, nitrosative, thilyl or carbonyl
stress. Free radicals indiscriminately oxidize any substance within
range, causing injury to endogenous as well as exogenous substances,
including all classes of biomolecules (proteins, lipids, DNA), disrupting
normal cell signaling mechanisms, devastating cellular energy supplies,
depleting reducing equivalents (reduced nicotinamide adenine dinu-
cleotide and glutathione) and causing cell death by eventually inducing
apoptosis [3–6].
Compounds with 1,3-thiazole or thiazolidinone structures impose a
broad spectrum of biological activities including the neutralization/
sequestration of ROS and RNS [7–12]. The antioxidant activity (AOA)
of thiazole derivatives has been acknowledged recently [13]. Kavitha
et al. synthesized some novel 4-(4-chlorophenyl)-2-aryl substituted
metheniminothiazoles as possible antioxidant agents [14]. Kachroo
et al. reported the antibacterial and AOA of newly synthesized N-[(4E)-
arylidene-5-oxo-2-phenyl-4,5-dihydro-1H-imidazol-1-yl]-2-(2-methyl-
(Center of Instrumental Analysis of the University of Thessaloniki). The
reactions were monitored by thin layer chromatography (TLC) plates on
F254 silica-gel coated sheets (Merck, Darmstadt, Germany) and each of
the purified compounds showed a single spot. Solvents, unless other-
wise specified, were of analytical reagent grade or of the highest quality
commercially available. Synthetic starting materials, reagents and sol-
vents were purchased from Aldrich Chemie (Steinheimm, Germany).
1,1-Diphenyl 2-picryl hydrazyl (DPPH), 2,4,6-tripyridyl-s-triazine
(TPTZ), Vitamin C (L-ascorbic acid), Vitamin E (α-tocopherol) and α-
lipoic acid (α-LA) were obtained from Sigma Chemical Co. (St. Louis,
USA); thiobarbituric acid (TBA), ferric chloride, ferrous chloride, tri-
chloroacetic acid (TCA) and ethylenediaminetetraacetic acid (EDTA)
were purchased from Merck (Darmstadt, Germany). All reagents were
of analytical grade.
2.2. Chemistry
1,3-thiazol-4-yl) acetamide [15]. Gull et al. synthesized 2- amino-6-
Compounds 5–8 were synthesized and described in our previous
arylbenzothiazoles and investigated, inter alia, their RNS scavenging
activities [16]. Sarkanj et al. synthesized 4-methyl-7-hydroxycoumarin
derivatives (substituting at positions 7 - thiosemicarbazide and 4 -
thiazolidinone) and evaluated their potential AOA [14,17]. Another
interesting core is thiazolidinone with a wide spectrum of biological
activities, including antioxidant [18–20].
In view of the considerable importance of thiazoles and thiazolidi-
nones, which are the core structures in a variety of pharmaceuticals
with a broad spectrum of biological activity, specifically referencing
their ability to prevent ROS formation, the present work is intended to
synthesize new heterocyclic compounds bearing the thiazole moiety
paper [21]. The mechanisms used to synthesize compounds 1–4 are as
portrayed in the generic synthetic Scheme 1, while compound 9 was
synthesized as illustrated in Scheme 2.
2.2.1. Synthesis
of
N-((5-adamantan-1-yl)-1,3,4-thiadiazol-2-yl)-2-
chloroacetamide (Cb)
Anhydrous sodium carbonate (0.0302 mol, 3.2 g) was added with
stirring into a solution of (2-amino-4-adamantane) - 1,3,4-thiadiazole
(
(
Ab) (0.0266 mol, 6.251 g) in anhydrous dimethylformamide (DMF)
64 mL). Afterwards, chloroacetyl chloride (B) (0.0798 mol, 9.02 g) in
anhydrous DMF (34.9 mL) was added dropwise into the mixture. The
reaction was stirred at room temperature for 3 h. The course of the
reaction was controlled by TLC. After the reaction was complete, ice
was added and the precipitate was filtered and washed thoroughly with
water. The solid product (Cb) was recrystallized from ethanol (yield:
[
8]. The substitutions in the chosen derivatives were intended to sta-
bilize the radicals formed from compounds via resonance (as shown in
Figs. 4–8), or to donate labile hydrogens from the 1,3-thiazolidinone
system. These hydrogens could be donated to the DPPH radical to form
stable DPPH molecules. In vivo confirmation of the in vitro documented
AOA for derivatives of thiazole, thiadiazole, or thiazolidinone is the
next step in the preclinical phase of drug development research [9].
The goal of our study was to evaluate the AOA of newly synthesized
compounds (1–4 and 9) as well as that of compounds 5–8 which were
previously synthesized by three in vitro tests [21]. The compounds that
were tested in this study were categorized as follows: group I: 1,3-
thiazole based thiazolidinones (compounds 1 and 2); group II: thia-
diazole-based thiazolidinone (compounds 3 and 4); group III: thiazo-
lidinone derivatives fused to a 1,2,4-triazol heterocyclic system (com-
pounds 5–8); and group IV: an ethylaminothiazole-based chalcone
9
3.4%), m.p.179–180 °C. IR: 1562 (aromatic), 1712 (C=O), 3087 (NH).
1
H NMR: (δ ppm, DMSO-d6, 300 MHz): 1.26 (s, 6H, adamantane),
1.52–1.57 (d, 9H, adamantane), 3.91 (s, 2H, CH2), 7.46 (s, 1H, NHCO).
2.2.2. Synthesis of N-((5-adamantan-1-yl)-1,3,4-thiadiazol-2-yl-imino)-
thiazolidin-4-one (Eb)
While stirring, ammonium thiocyanate (D) (0.1 mol, 7.5 g) was
added into the N-[(5-adamantan-1-yl) -1,3,4-thiadiazol-2-yl] chlor-
oacetamide (Cb) (0.05 mol/16.7 g in 50 mL of 95% ethanol). The mix-
ture was boiled in a water bath and refluxed under stirring for 1 h. The
course of the reaction was controlled by TLC. The product (Eb) re-
mained unchanged overnight and was then filtered, washed with water
and recrystallized from ethanol (yield 61%), m.p. 258–259 °C. IR: 1602
(
compound 9) [21,22] (Fig. 1).
We used three in vitro tests that make use of different principles of
red-ox reactions: a) 1,1-diphenyl-2-picrylhydrazyl scavenging capacity
test, i.e. DPPH radical scavenging capacity (or DPPH) assay [23]; b)
ferric reducing antioxidant power (FRAP) assay [24]; and c) thiobarbituric
acid reactive substances (TBARS) assay [25,26].
(
3
4
aromatic), 1740 (C=O), 3360 (NH). 1H NMR: (δ ppm, DMSO-d6,
00 MHz): 1.75 (s, 6H, adamantane), 1.99–2.06 (d, 9H, adamantane),
.07 (s, 2H, CH2 thiazolidinone), 12.20 (s, 1H, NHCO) [27].
Synthesis: Aryl aldehyde (6 mmol) was added into a well-stirred
solution of 0.8 g of 4/5-substituted (thiazol-2-ylimino) thiazolidin-4-
one (4 mmol) in acetic acid (35 mL) previously buffered with sodium
acetate (8 mmol). The solution was refluxed for 4 h and then poured
into ice-cold water. The precipitate was filtered and washed with water.
The crude product was purified by recrystallization from dioxane [27].
2
. Material and methods
2.1. Chemicals
Melting points were determined with a MELTEMP II capillary ap-
paratus (LAB Devices, Holliston, MA, USA) without correction.
Elemental analyses were performed on a Perkin–Elmer 2400 CHN ele-
mental analyzer. All compounds synthesized were documented to be
within 0.4% of theoretical values. IR spectra were recorded as Nujol
mulls on a Perkin Elmer Spectrum BX. Wave numbers collected from IR
2.2.2.1. Synthesis of (2E,5Z)-((5-adamatane-1-yl)-1,3,4-thiadiazol-2-yl)-
imino)-5-(4-hydroxybenzylidene)-thiazolidin-4-one (3). Yield: 48.9%,
−
1
m.p. 258–259 °C. Rf = 0.71 (toluene-EtOH 7:3). IR (cm , Nujol):
1570 (aromatic), 1708 (C=O), 3089 (NH). 1H NMR (δ ppm, DMSO-
d6, 300 MHz): 1.77 (s, 6H, adamantane), 2.03–2.07 (d, 9H,
adamantane), 6.95–6.98 (d, 2H, C3′-C5′), 7.51–7.53 (d, 2H,C2′- C6′),
7.67 (s, 1H, C=C), 10.22 (s, 1H, -OH), 12.690 (s, 1H, NHCO). Anal.
Calc. for C22H22N4O2S2 (MW 438): C: 60.25%; H: 5.06%; N: 12.78%.
Found: C: 60.13%; H: 5.11%; N: 12.75%.
−1
1
13
spectra are given in cm
synthesized compounds in DMSO-d6 or CDCl
.
H NMR. C NMR spectra of the newly
solution were recorded
3
on a Bruker AC 300 instrument (Bruker, Karlsruhe, Germany) at 298 K.
Chemical shifts are reported as δ (ppm) relative to TMS which was used
as an internal standard. Coupling constants (J) are expressed in Hertz
120