Synthesis, Antioxidant Activity and Cytotoxicity of N-Functionalized Organotellurides

Article abstract of DOI:10.1016/j.bmc.2018.12.017

The use of antioxidants is the most effective means to protect the organism against cellular damage caused by oxidative stress. In this context, organotellurides have been described as promising antioxidant agents for decades. Herein, a series of N-functionalized organotellurium compounds has been tested as antioxidant and presented remarkable activities by three different in vitro chemical assays. They were able to reduce DPPH^[rad] radical with IC₅₀ values ranging from 5.08 to 19.20 μg mL^?1, and some of them also reduced ABTS^[rad]+ radical and TPTZ-Fe³⁺ complex in ABTS^[rad]+ and FRAP assays, respectively. Initial structure-activity relationship discloses that the nature of N-substituent strongly influenced both activity and cytotoxicity of the studied compounds. Furthermore, radical scavenging activities of N-functionalized organotellurides have been compared with those of their selenilated congeners, demonstrating that the presence of tellurium atom has an essential role in antioxidant activity.

Full text of DOI:10.1016/j.bmc.2018.12.017

Bioorganic&MedicinalChemistryxxx(xxxx)xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis, Antioxidant Activity and Cytotoxicity of N-Functionalized
Organotellurides
Pamela T. Bandeiraa, Mara C. Dalmolina, Mariana M. de Oliveirab, Karine C. Nunesb,
Francielle P. Garciab, Celso V. Nakamurab, Alfredo R.M. de Oliveiraa, Leandro Piovana,
⁎
a Departamento de Química, Universidade Federal do Paraná, Curitiba 4106902, Brazil
b Centro de Ciências da Saúde, Universidade Estadual de Maringá, Maringá 4115200, Brazil
A R T I C L E I N F O
A B S T R A C T
Keywords:
The use of antioxidants is the most effective means to protect the organism against cellular damage caused by
oxidative stress. In this context, organotellurides have been described as promising antioxidant agents for
decades. Herein, a series of N-functionalized organotellurium compounds has been tested as antioxidant and
Organotellurium chemistry
Nitrogenated tellurides
Antioxidant agents
Radical scavengers
%
presented remarkable activities by three different in vitro chemical assays. They were able to reduce DPPH
%
+
radical with IC50 values ranging from 5.08 to 19.20 µg mL−1, and some of them also reduced ABTS
radical
%+
and TPTZ-Fe3+ complex in ABTS
and FRAP assays, respectively. Initial structure-activity relationship dis-
closes that the nature of N-substituent strongly influenced both activity and cytotoxicity of the studied com-
pounds. Furthermore, radical scavenging activities of N-functionalized organotellurides have been compared
with those of their selenilated congeners, demonstrating that the presence of tellurium atom has an essential role
in antioxidant activity.
1. Introduction
tetravalent state, which often makes tellurides excellent scavengers for
reactive oxygen or nitrogen species.18 Antioxidants can protect the
For many years, tellurium was among the few elements in the
Periodic Table virtually ignored in biology and medicinal chemistry
fields.1 Tellurium’s low abundance (about 0.027 ppm) is an important
point to be considered, which could instantiate the scarcity of tellurium
species in nature and, consequently, the absence of natural biological
functions.2,3 Furthermore, pharmacological and toxicological proper-
ties of tellurium-containing substances still remain uncertain, demon-
strating the need for more in-depth studies about these compounds.4
Syntheses and applications of organotellurium compounds have
steadily increased in the last decades. These substances have shown
promising and advantageous alternatives for numerous synthetic ap-
organism against cellular damage caused by oxidative stress, avoiding
or retarding the progress of many chronic diseases as well as lipid
peroxidation.19 Moreover, among the methods employed to prevent the
oxidative damage, the use of antioxidants is the most effective and
convenient means, clearly justifying the efforts to find new substances
with high antioxidant performances.
In this context, this work describes in vitro antioxidant activity and
cytotoxicity of N-functionalized tellurides. The combination of ni-
trogenated organic functions (amines, oximes and hydrazones) with
alkyl-aryl tellurides moieties afforded a new class of prominent anti-
oxidants, which performances were strongly influenced by the nature of
N-substituent.
proaches, including carbon-carbon bond-forming reactions and
a
variety of functional group interconversions.5–7 Additionally, organo-
tellurium compounds have been described as promising pharmacolo-
gical agents that possess anti-cancer, anti-inflammatory, antibacterial,
antifungal, antiprotozoal and antioxidant activities.8–13Among these,
the antioxidant potential is, certainly, the best studied pharmacological
property.14–17
2. Results and discussion
2.1. Synthesis of organotellurium compounds
A series of N-substituted organotellurides was designed in order to
investigate some preliminary structure-activity relationships: a) sub-
stitution pattern on aromatic ring (meta or para); b) nitrogenated
Organotellurium compounds are very attractive as antioxidant
agents due to their ability of readily oxidizing from the divalent to
⁎ Corresponding author.
E-mail address: lpiovan@quimica.ufpr.br (L. Piovan).
https://doi.org/10.1016/j.bmc.2018.12.017
Received 2 October 2018; Received in revised form 28 November 2018; Accepted 10 December 2018
0968-0896/©2018ElsevierLtd.Allrightsreserved.
Pleasecitethisarticleas:Bandeira,P.T.,Bioorganic&MedicinalChemistry,https://doi.org/10.1016/j.bmc.2018.12.017

P.T. Bandeira et al.
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Table 1
%
Antioxidant activity of N-functionalized organotellurides by DPPH scavenging
assay.
Entry
Substance
IC50
SD (µg mL−1
)
1
LQ9
19.22
12.07
5.12
2.17
1.68
0.71
0.33
2
LQ10
LQ11
LQ12
LQ26
LQ27
LQ28
LQ29
LQ37
LQ47
Quercetin
3
4
7.79
5
> 100
8.63
6
0.06
0.17
0.09
0.87
1.84
0.05
7
12.49
11.41
5.08
Fig. 1. Structural design of organotellurides for structure-activity insights.
8
9
10
11
13.06
2.54
functional group (primary and secondary amines, oximes and hy-
drazones); c) the nature of N-substituents; d) the nature of Te-sub-
stituents (Fig. 1).
N-Functionalized alkyl-aryl tellurides LQ9-12, LQ26-29, LQ37 and
LQ47 and some selenium-containing analogues (LQ17, LQ18 and
LQ20) were synthesized as showed in Scheme 1.
The majority of screened organotellurium compounds exhibited
high antioxidant activity, presenting exciting results as radical sca-
vengers (Table 1). The most active substances were tellurium-con-
taining oximes LQ11 and LQ12 (Table 1, entries 3 and 4, respectively)
and hydrazone LQ37 (Table 1, entry 9), with relatively close perfor-
mance to standard quercetin (Table 1, entry 11). Primary telluro-
amines LQ9 and LQ10, although less active than oximes, also exhibit
prominent antioxidant performances (Table 1, entries 1 and 2, respec-
tively). It was not possible to establish a direct relationship between
tellurium atom position on aromatic ring – meta or para – and ni-
trogenated functional group – primary amine or oxime – since p-Te-
substituted amine (LQ10) and m-Te-substituted oxime (LQ12) were the
most active substances in each class.
The key starting materials arylchalcogen ketones (Y = Te, Se) were
previously synthesized according to literature (See Supporting
Information for details).20,21 Primary and secondary Te/Se-amines
(LQ9-10, LQ17-18, LQ20 and LQ26-29) were conveniently prepared
through microwave-assisted synthesis, in just 5 min and yields up to
89%.17 Te-oximes LQ10-11, LQ47 and Te-hydrazone LQ37 were pre-
pared in 63%–82% yields after 4 h, by refluxing an alcoholic solution of
corresponding carbonyl compound with hydroxylamine hydrochloride
or hydrazine dihydrochloride (Scheme 1). Whereas chalcogen amines
LQ9-10, LQ17-18, LQ20 and LQ26-29 and oximes LQ10-11 were ob-
tained as bad smelling yellow liquids, telluro-hydrazone LQ37 was
obtained as an odorless yellow powder. Spectroscopic data (1H, 13C and
125Te NMR, FTIR and GC–MS) of all synthesized compounds are
available in Supporting Information.
p-Substituted primary amine LQ10 presented remarkable anti-
oxidant activity, thus encouraging the investigation of the influence of
N-substitution using alkyl groups with varying bulk and flexibility. For
this purpose, secondary telluro-amines LQ26-29 were conveniently
achieved through microwave-assisted synthesis.17 Surprisingly, bran-
ched aliphatic chain (i-butyl) or benzyl group in N-position (LQ28 and
LQ29, Table 1, entries 7 and 8, respectively) did not result in any ac-
tivity improvements when compared to the unsubstituted co-partner
LQ10 (Table 1, entry 2). In fact, the insertion of N-allyl group in LQ26
led to total loss of activity (IC50 > 100 µg mL−1, Table 1, entry 5). On
the other hand, N-substitution with a straight aliphatic chain (n-butyl)
furnished LQ27, a telluro-amine endowed with high antioxidant ac-
tivity (Table 1, entry 6). Based on these findings, it is possible to reason
that the nature of N-substituent strongly influenced the antioxidant
2.2. Antioxidant activity
In vitro antioxidant activity of organotellurated substances LQ9-12,
%
LQ26-29, LQ37 and LQ47 were preliminarily studied by the DPPH
(2,2-diphenyl-1-picryl-hydrazyl radical) scavenging assay (Table 1).
This method is based on an electron transfer reaction and hydrogen
atom abstraction, reflecting the capacity of tested substance to reduce
%
DPPH to corresponding DPPH2. The results were expressed in con-
%
centration of antioxidant required to scavenge 50% of DPPH radical
(IC50, Table 1). Quercetin was used as standard antioxidant.22,23
Scheme 1. Reagents and conditions: i. NH2OH·HCl, NaOH/H2O, EtOH, reflux, N2, 3 h; ii. AcONH4, NaBH3CN, EtOH, microwaves, 80 °C, 5 min. iii. RNH2, NaBH3CN,
AcOH, EtOH, microwaves, 80 °C, 5 min. iv. NH2NH2.2HCl, AcONa/H2O, EtOH, 4 h.
2

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%+
Fig. 2. Antioxidant activity of N-functionalized organotellurides by ABTS
and FRAP assays. Results are expressed in trolox equivalent antioxidant capacity
(TEAC).
profile of the studied compounds.
For Te-amines and oximes LQ9-12, weak cytotoxic effects were
observed only at the lowest concentration tested (1.9 µg mL−1, Fig. 3).
The cell viability drastically decreased after treatment with higher
concentrations (3.9 µg mL−1, 7.8 µg mL−1 and 15.6 µg mL−1, Fig. 3),
indicating that, despite the great antioxidant potential, organotellu-
rated substances LQ9-12 displayed strong cytotoxic effects leading to
cellular damage.
%
Despite the highly satisfactory results obtained in DPPH assay,
organotellurium compounds were also investigated about their radical
%
+
scavenging activity according to ABTS
(2,2-azinobis-3-ethylben-
zothiazoline-6-sulfonic acid, Fig. 2a) and FRAP (ferric reducing anti-
oxidant power) assays (Fig. 2b).
The most active substances were primary Te-amines LQ9-10 and Te-
oximes LQ11-12, with activities similar to quercetin (Fig. 2). The in-
sertion of substituents at N-position led to a strong decrease of activity
Unlike observed in antioxidant activity evaluation, the N-substitu-
tion pattern had a positive effect in cytotoxicity assays, being secondary
Te-amines LQ27-29 less cytotoxic at higher concentrations than un-
substituted co-partner LQ10 (Fig. 3).
%
+
in both ABTS
stances LQ27-29.
and FRAP assays, as it was clearly observed for sub-
p-Substituted Te-oxime LQ12 exhibited remarkable reducing anti-
oxidant capacity in FRAP assay, with better performance than quercetin
(Fig. 2b). The replacement of Te-substituent (n-Bu with n-PrOH group)
led to a decrease in antioxidant power, evidenced by profile of the
congener oxime LQ47.
The nature of Te-substituents also influenced the cytotoxicity of
synthesized substances. Unlike Te-oxime LQ12 (R = p-TeBu) that dis-
played accentuated toxicity, the congener LQ47 (R = p-TePrOH)
showed weak cell damage effects in all tested concentrations (Fig. 3).
The least cytotoxic substance was Te-hydrazone LQ37, with low
cytotoxicity on fibroblasts cell lines in all concentrations (Fig. 3). Since
In general, TEAC values of screened substances in FRAP assay
%+
%
(Fig. 2b) were higher than those obtained by ABTS
assay (Fig. 2a).
LQ37 has presented high antioxidant activity in DPPH assay
Thus, it could be estimated that the mechanism of antioxidant activity
of these organotellurium compounds is probably based on hydrogen-
transfer, since reactions in FRAP assay generally involve donation of a
(IC50 = 5.08
0.87 µg mL−1), these findings indicate that this sub-
stance is a promising antioxidant agent for further biological studies.
%+
hydrogen atom, whereas the reactions with ABTS
involve an elec-
tron transfer process.24 Furthermore, these results are in agreement
3. Conclusions
%
with the high performance observed in DPPH assay, which mechanism
also involve a hydrogen radical transfer. However, additional studies
are needed to elucidate the detailed mechanism of action of these
substances.
In summary, a series of N-functionalized organotellurides has been
synthesized and evaluated as novel antioxidants. The results showed
that the nature of nitrogenated organic functions, as well as the kind of
the tellurium moiety, are important factors that influenced both anti-
oxidant activity and cytotoxicity of studied compounds. Furthermore,
the selenium-containing analogues showed no significant activity,
proving that the presence of tellurium atom is essential to the anti-
oxidant character.
In order to verify the influence of chalcogen atom in biological ac-
tivity, the antioxidant properties of some selenium-containing analo-
%
gues (LQ17, LQ18 and LQ20, Scheme 1) were evaluated by DPPH
scavenging assay (data not shown). Curiously, no activity was observed
for selenium-containing analogues under our assay’s conditions.
Whereas Te-substituted compounds presented high antioxidant poten-
tial, the selenium analogues had no significant activity
(IC50 > 100 µg mL−1). As reported for other classes of chalcogen-
containing compounds,25,26 the replacement of tellurium with selenium
led to a dramatic decrease in antioxidant activity. These outcomes in-
dicated that antioxidant activity is remarkably influenced by the pre-
sence of tellurium atom on the chemical structure.
Although all screened substances had displayed remarkable in vitro
activities, most of them presented accentuated toxicity on L929 fibro-
blasts cell lines. Nevertheless, the combination of hydrazone organic
function with butyltellurium moiety provided the substance LQ37,
which presented high activity and low cytotoxicity. These results in-
dicate that this organotelluride is a promising antioxidant agent for
further pharmacological studies and provides useful criteria for design
of good synthetic tellurium-containing antioxidants. Furthermore, this
work can contribute with cytotoxicity data for organotellurium com-
pounds as antioxidant agents, as this is not an usual analysis available
in the current literature.
Considering potential therapeutic applications, additional studies
about toxicity were necessary. Thus, having confirmed the great anti-
oxidant potential of the studied organotellurium compounds, these
substances were tested for cytotoxicity on L929 normal fibroblast cell
lines (Fig. 3).
3

P.T. Bandeira et al.
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Fig. 3. Mean values of cell viability obtained on L929 fibroblast cell lines after 24 h of treatment with different concentrations of organotellurium compounds by
neutral red assay. NC: negative control. Results are expressed as mean
significant difference from NC according to the Tukey's test.
S.E.M. for three independent experiments. *(p < 0.05) and ***(p < 0.001) indicate
4. Experimental section
N-(1-(4-(Butyltellanyl)phenyl)ethyl)prop-2-en-1-amine (LQ26). Yellow
oil. Yield: 54%. 1H NMR (200 MHz, CDCl3, TMS): 0.89 (t, J = 7.2 Hz,
3H), 1.35 (d, J = 6.6 Hz, 3H), 1.25–1.48 (m, 1H), 1.78 (quint,
J = 7.7 Hz, 3H), 2.90 (t, J = 7.7 Hz, 2H), 3.09 (d, J = 6.0 Hz, 2H),
3.78 (q, J = 6.6 Hz, 1H), 5.05–5.16 (m, 2H), 5.78–5.98 (m, 1H),
7.13–7.17 (dd, JA = 8.2 Hz and JB = 2.0 Hz, 2H), 7.64–7.68 (dd,
4.1. Chemical
General procedure for synthesis of telluroamines LQ9-10 and LQ26-2917
To a microwave reactor flask equipped with magnetic stirring bar,
the appropriate amine source (6 equiv.), AcOH (15 equiv.), NaBH3CN
(1.2 equiv.) were added to a solution of chalcogen-acetophenone of
interest (100 mg) in ethanol (1 mL). The reaction medium was assisted
by microwave irradiation at 80° C for 5 min. Then, the solvent was
removed under reduced pressure, the crude residue dissolved in dis-
tilled water (5 mL) and the pH adjusted to 10 with NaOH (1 mol L−1).
The product was extracted with dichloromethane (3 × 10 mL), the
combined organic layers dried over with anhydrous MgSO4 and con-
centrated under reduced pressure. The products were purified via
chromatographic column using ethyl acetate:ethanol (9:1) as solvent
system.
J
A = 8.2 Hz e JB = 2.0 Hz, 2H), 7.70 (sl, NH). 13C NMR (50 MHz,
CDCl3): 8.4, 13.4, 24.1, 25.0, 33.9, 50.1, 57.2, 116.0, 127.6, 128.5,
136.6, 138.4, 144.8. FTIR (cm−1): 3391, 3074, 2936, 2798, 1638,
1176, 989, 929. GC–MS (70 eV), m/z (relative abundance): 347 (M+
,
26), 330 (100), 289 (11), 275 (86), 271 (58), 232 (22), 205 (6), 146
(60), 117 (34), 104 (90), 77 (36), 56 (20), 51 (10).
N-(1-(4-(Butyltellanyl)phenyl)ethyl)butan-1-amine (LQ27). Pale orange
oil. Yield: 70%. 1H NMR (200 MHz, CDCl3, TMS), δ (ppm): 0.91 (m,
6H), 1.35 (d, J = 6.6 Hz, 3H), 1.41 (m, 6H), 1.81 (quint, J = 7.6 Hz,
2H), 2.47 (m, 2H), 2.92 (t, J = 7.5 Hz, 2H), 3.74 (q, J = 6.6 Hz, 1H),
7.17 (dd, JA = 8.1 Hz and JB = 1.7 Hz, 2H), 7.69 (dd, JA = 8.1 Hz and
JB = 1.7 Hz, 2H). 13C NMR (50 MHz, CDCl3): 8.4, 13.4, 14.0, 20.5, 24.3,
25.0, 32.4, 33.9, 47.6, 58.1, 109.5, 127.5, 138.4, 145.5. FTIR (cm−1):
3315, 3191, 2950, 2929, 2860, 1466, 1121, 1003, 817. GC–MS (70 eV),
m/z (relative abundance): 363 (M+, 21), 348 (96), 291 (100), 243 (13),
162 (7), 104 (42), 78 (10), 57 (8), 41 (8).
1-(3-(Butyltellanyl)phenyl)ethanamine (LQ9). Pale yellow oil. Yield:
89%. 1H NMR (200 MHz, CDCl3, TMS): 0.93 (t, J = 7.4 Hz, 3H),
1.25–1.53 (m, 2H), 1.40 (d, J = 6.5 Hz, 3H), 1.72–1.90 (m, 2H), 2.95
(t, J = 7.5 Hz, 2H), 4.08 (q, J = 6.5 Hz, 1H), 7.08–7.26 (m, 2H), 7.56
(d, J = 7.3 Hz, 1H), 7.68 (s, 1H), 9.50 (sl, NH2). 13C NMR (50 MHz,
CDCl3), δ (ppm): 8.4, 13.4, 25.0, 25.5, 33.9, 51.1, 112.1, 124.9, 129.1,
136.5, 148.4.
N-(1-(4-(Butyltellanyl)phenyl)ethyl)-2-methylpropan-1-amine
1-(4-(Butyltellanyl)phenyl)ethanamine (LQ10). Pale orange oil. Yield:
73%. 1H NMR (200 MHz, CDCl3, TMS): 0.90 (t, J = 7.3 Hz, 3H),
1.23–1.49 (m, 3H), 1.36 (d, J = 6.6 Hz, 3H), 1.67 (sl, NH2), 1.77 (m,
3H), 2.88 (t, J = 7.8 Hz, 2H), 4.08 (q, J = 6.6 Hz, 1H), 7.15–7.19 (dd,
(LQ28). Pale yellow oil. Yield: 86%. 1H NMR (200 MHz, CDCl3, TMS):
0.88 (d, J = 6.6 Hz, 6H), 0.89 (t, J = 7.2 Hz, 3H), 1.37 (m, 2H), 1.44 (d,
J = 6.7 Hz, 3H), 1.78 (quint, J = 7.5 Hz, 3H), 2.32 (m, 2H), 2.90 (t,
J = 7.5 Hz, 2H), 3.84 (q, J = 6.7 Hz, 1H), 4.85 (sl, NH), 7.20 (dd,
J
A = 8.2 Hz and JB = 1.9 Hz, 2H), 7.65–7.69 (dd, JA = 8.2 Hz
e
JA = 8.1 Hz and JB = 1.6 Hz, 2H), 7.67 (dd, JA = 8.1 Hz and
JB = 1.9 Hz, 2H). 13C NMR (50 MHz, CDCl3): 8.4, 13.4, 25.0, 25.6,
33.9, 51.0, 109.5, 126.6, 128.5, 147.2. FTIR (cm−1): 3343, 3280, 2963,
2915, 2874, 1569, 1481, 1003, 817. GC–MS (70 eV), m/z (relative
abudance): 307 (M+, 84), 292 (82), 249 (8), 235 (63), 206 (2), 120
(51), 104 (100), 91 (14), 77 (44), 65 (4), 44 (78), 41 (39).
JB = 1.6 Hz, 2H). 13C NMR (50 MHz, CDCl3): 8.4, 13.4, 20.5, 20.7,
23.1, 25.0, 27.7, 33.9, 55.1, 58.5, 110.8, 127.8, 138.3, 142.5. FTIR
(cm−1): 3315, 2963, 2915, 2874, 1459, 1121, 1010, 824. GC–MS
(70 eV), m/z (relative abundance): 363 (M+, 12), 346 (28), 291 (100),
234 (18), 207 (7), 105 (81), 78 (22), 41 (21).
4

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N-Benzyl-1-(4-(butyltellanyl)phenyl)ethanamine (LQ29). Pale orange oil.
Yield: 44%. 1H NMR (200 MHz, CDCl3, TMS): 0.89 (t, J = 7.2 Hz, 3H),
1.34 (d, J = 6.6 Hz, 3H), 1.37–1.48 (m, 2H), 1.61 (sl, NH), 1.79 (quint,
J = 7.2 Hz, 2H), 2.90 (t, J = 7.2 Hz, 2H), 3.61 (d, J = 4.8 Hz, 2H), 3.77
(q, J = 6.6 Hz, 1H), 7.06–7.22 (dd, JA = 8.1 Hz and JB = 1.9 Hz, 2H),
7.24–7.40 (m, 5H), 7.58–7.78 (dd, JA = 8.1 Hz and JB = 1.9 Hz, 2H).
13C NMR (50 MHz, CDCl3): 8.4, 13.4, 24.4, 25.0, 33.9, 51.6, 57.2,
109.7, 126.9, 127.6, 128.1, 128.3, 138.4, 140.5, 145.1. FTIR (cm−1):
3032, 2963, 2922, 2839, 1622, 1452, 996, 707. GC–MS (70 eV), m/z
(relative abundance): 397 (M+, 21), 382 (40), 325 (13), 291 (3), 234
(2), 196 (5), 104 (11), 91 (100), 65 (5), 41 (3).
4.2. Antioxidant activity assays
The antioxidant activities of organotellurium compounds LQ9-12,
LQ26-29, LQ37 and LQ47 (Scheme 1) were evaluated by the following
%
in vitro chemical assays: radical scavenging activity (DPPH and
%
+
ABTS ) and FRAP. The standard antioxidant quercetin was used as
reference.
%
DPPH assay
The methanolic solution of DPPH (100 μL, 130 μmol L−1) were
%
added to the methanolic solution of samples (100 μL) at different con-
centrations. After 30 min at room temperature, protected from the
light, the absorbance was measured in a microplate spectrophotometer
(Bio Tek, PowerWave XS microplate spectrophotometer) at 517 nm.
General procedure for synthesis of telluro-oximes LQ11-12, LQ47 and
telluro-hydrazone LQ37
%
The percentage of inhibition of DPPH was calculated using the fol-
In a round-bottom flask equipped with magnetic stirring bar and
reflux condenser were added the telluro-acetophenone of interest
(0.4 mmol, 113 mg) and ethanol (1 mL). Then, for the synthesis of
oximes, hydroxylamine hydrochloride (1.2 mmol, 83 mg) and sodium
hydroxide (8.2 mmol, 325 mg) dissolved in distilled water (0.2 mL)
were subsequently added. For the synthesis of tellurohydrazone, hy-
drazine dihydrochloride (1.2 mmol, 126 mg) and sodium acetate
(8.2 mmol, 627 mg) dissolved in distilled water (0.4 mL) were em-
ployed. The reaction was maintained under reflux and inert atmosphere
until total consumption of the starting material (ca. 2 h). The solvent
was removed under reduced pressure, the crude mixture dissolved in
distilled water (10 mL), extracted with dichloromethane (3 × 5 mL),
washed with saturated NaCl solution (5 mL), dried over with anhydrous
MgSO4 and concentrated.
lowing equation:
Absnc Abss
DPPH·scavenging ability(%) =
× 100
Absnc
Absnc is the absorbance of the negative control (100 µL of methanol
%
mixed in 100 µL of DPPH and maintained under the same conditions as
samples) at 517 nm and Abss is the absorbance of the samples at
517 nm. IC50 values were estimated by linear regression.27 The assays
were performed in triplicate.
%
+
ABTS
assay
%+
The ABTS
was generated with ABTS (5 mL, 7 mmol L−1) and
potassium persulfate (0.88 mL, 140 mmol L−1) solutions. After 16 h, at
%
+
room temperature and protected from the light, the ABTS
solution
0.05
was dissolved in ethanol until obtained the absorbance of 0.70
at 734 nm. Then, the sample solution (7 μL) in different concentrations
(E)-1-(3-(Butyltellanyl)phenyl)ethanone oxime (LQ11). Pale yellow oil.
Yield: 82%. 1H NMR (200 MHz, CDCl3, TMS): 0.89 (t, J = 7.2 Hz, 3H),
1.40 (sext, J = 7.3 Hz, 2H), 1.79 (quint, J = 7.6 Hz, 2H), 2.28 (s, 3H),
2.93 (t, J = 7.7 Hz, 2H), 7.20 (t, J = 7.5 Hz, 1H), 7.50 (d, J = 8.0 Hz,
1H), 7.70 (d, J = 7.7 Hz, 1H), 7.95 (s, 1H), 9.24 (sl, NOH). 13C NMR
(50 MHz, CDCl3), δ (ppm): 8.7, 12.3, 13.4, 25.0, 33.9, 112.1, 125.2,
129.0, 135.6, 137.3, 138.8, 155.5.
%+
was added to ABTS
solution (200 μL). After 6 min, the absorbance
was measured in a microplate spectrophotometer (Bio Tek, PowerWave
XS microplate spectrophotometer) at 734 nm. Ethanol solutions of
Trolox (20–600 μmol L−1) were used for the calibration curve and the
results were expressed as mmol TE g−1. All assays were performed in
triplicate.28
Ferric reducing antioxidant power (FRAP)
(E)-1-(4-(Butyltellanyl)phenyl)ethanone oxime (LQ12). Orange oil.
Yield: 77%. 1H NMR (200 MHz, CDCl3, TMS): 0.90 (t, J = 7.4 Hz,
3H), 1.39 (sext, J = 7.7 Hz, 2H), 1.79 (quint, J = 7.6 Hz, 2H), 2.27 (s,
3H), 2.92 (t, J = 7.6 Hz, 2H), 7.43 (dd, JA = 8.3 Hz and JB = 1.7 Hz,
2H), 7.69 (dd, JA = 8.3 Hz and JB = 1.7 Hz, 2H), 9.50 (sl, NOH). 13C
NMR (50 MHz, CDCl3), δ (ppm): 8.6, 12.2, 13.4, 25.0, 33.8, 113.7,
126.5, 128.5, 137.7, 155.6. FTIR (cm−1): 3275, 3059, 2957, 2870,
1582, 1464, 1404, 1366, 1292, 1246, 1181, 1163, 995, 926, 787, 692,
646, 496. GC–MS (70 eV), m/z (relative abundance): 321 (M+, 39), 305
(25), 301 (15), 265 (21), 247 (47), 233 (6), 206 (10), 175 (3), 146 (8),
130 (5), 118 (100), 104 (36), 91 (15), 77 (68), 57 (30), 41 (38).
FRAP reagent solution was prepared by mixing 0.3 mM sodium
acetate buffer pH 3.6, 20 mM FeCl3 and 10 mM tripyridyltriazine 10:1:1
(v/v/v). An aliquot of 30 µL of different samples concentrations was
added to 180 µL of FRAP reagent. The mixture was incubated at 37 °C
for 40 min protected from light. The absorbance of the resulting solu-
tions was measured at 593 nm in a microplate spectrophotometer (Bio
Tek, PowerWave XS microplate spectrophotometer). Ethanol trolox
solutions (100–1000 μmol L−1) were used for the calibration curve and
the results were expressed as mmol TE g−1. All assays were performed
in triplicate.29
4.3. Cytotoxicity assay
(E)-1-(4-((3-Hydroxypropyl)tellanyl)phenyl)ethanone oxime (LQ47). Yellow
solid. Yield: 82%. 1H NMR (200 MHz, CDCl3, TMS): 2.04–2.08 (m, 2H),
2.26 (s, 3H), 2.98 (t, J = 7.6 Hz, 2H), 3.70 (t, J = 6.1 Hz, 2H), 7.44–7.45
(dd, JA = 1.8 Hz and JB = 8.3 Hz, 2H), 7.70–7.72 (dd, JA = 1.8 Hz and
JB = 8.3 Hz, 2H). 13C NMR (50 MHz, CDCl3): 4.3, 11.9, 34.2, 63.9, 113.4,
126.6, 135.8, 138.0, 155.7.
The cytotoxicity of N-functionalized organotellurium compounds on
L929 cell lines (NCTC clone 929 [L cell, L929, derivative of Strain L]
(ATCC® CCL1™, Manassas, USA) was evaluated by neutral red assay.24
L929 cell lines were maintained and cultured in Dulbecco's modified
Eagle's medium (DMEM, Life Technologies/Gibco Laboratories, Grand
Island, NY, USA) supplemented with 2 mM ʟ-glutamine, 10% fetal bo-
vine serum (FBS, Life Technologies/Gibco Laboratories, Grand Island,
NY, USA), penicillin (50 U/mL) and streptomycin (50 µg/mL) at 37 °C
in a 5% CO2 atmosphere.
(E)-(1-(4-(Butyltellanyl)phenyl)ethylidene)hydrazine
(LQ37). Yellow
solid. Yield: 63%. 1H NMR (200 MHz, CDCl3, TMS): 0.91 (t,
J = 7.2 Hz, 3H), 1.41 (sext, J = 7.4 Hz, 2H), 1.81 (quint, J = 7.4 Hz,
2H), 2.29 (s, 3H), 2.94 (t, J = 7.8 Hz, 2H), 7.73 (s, 4H). 13C NMR
(50 MHz, CDCl3), δ (ppm): 8.6, 13.4, 14.8, 25.1, 33.9, 114.6, 127.1,
137.4, 137.6, 157.7. FTIR (cm−1): 3047, 2957, 2924, 2870, 2854,
1601, 1583, 1489, 1391, 1360, 1192, 1167, 1080, 1005, 820, 593.
A suspension of L929 fibroblasts (2.5 × 105 cells ml−1) was plated
on 96-well sterile microplates and maintained at 37 °C in a 5% CO2
atmosphere. After 24 h, the cells were treated with different samples
concentrations (1.95–15.625 μg mL−1) for 24 h, under the same con-
ditions previously mentioned. After the treatment, the plate was
5

P.T. Bandeira et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxx–xxx
washed twice with phosphate buffered saline (PBS, 100 μL), and neutral
red (Interlab, São Paulo, Br) in DMEM (200 μL, 40 μg mL−1) was added.
After 3 h, the plate was washed with fixative solution (200 μL, 1%
calcium chloride and 2% formaldehyde in PBS). Then, the supernatant
was discarded and 200 μL of a solution of 50% ethanol and 1% acetic
acid were added. Absorbance was measured after 15 min at 540 nm on
a microplate spectrophotometer (Bio Tek, PowerWave XS microplate
spectrophotometer). The samples were aseptically dissolved in DMSO
and diluted in DMEM, with a final maximum DMSO concentration of
1.5%. The percentage of viable cells was calculated in relation to the
negative control.30
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Acknowledgements
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