Synthesis of methyl 2-[2-(4-phenyl[1,2,4]triazolo-[4,3-a]quinoxalin-1-ylsulfanyl)acetamido]alkanoates and their N-regioisomeric analogs

Article abstract of DOI:10.1007/s10593-015-1662-0

[Figure not available: see fulltext.] Methyl 2-[2-(4-phenyl[1,2,4]triazolo[4,3-a]quinoxalin-1-ylsulfanyl)acetamido]alkanoates were formed by the reaction of 2-(4-phenyl-1,2-dihydro[1,2,4]triazolo[4,3-a]quinoxalin-1-ylsulfanyl)acetic acid with a variety of amino acid esters via DCC coupling method in the presence of N-hydroxybenzotriazole in good yields. These amino acid derivatives linked to triazoloquinoxaline moiety were also obtained by the reaction of 2-(4-phenyl[1,2,4]triazolo[4,3-a]quinoxalin-1-ylsulfanyl)acetohydrazide with amino acid ester derivatives via azide coupling method in poor yields due to the competing decomposition of the corresponding azide resulting in the starting 4-phenyl-[1,2,4]triazolo[4,3-a]quinoxaline-1(2H)-thione. The N-regioisomeric methyl 2-[3-(4-phenyl-1-thioxo[1,2,4]triazolo[4,3-a]quinoxalin-2(1H)-yl)propanamido]alkanoates were efficiently produced from the 3-(4-phenyl-1-thioxo[1,2,4]triazolo[4,3-a]quinoxalin-2(1H)-yl)-propanohydrazide and amino acid esters via azide coupling method in good to moderate yields.

Full text of DOI:10.1007/s10593-015-1662-0

DOI 10.1007/s10593-015-1662-0
Chemistry of Heterocyclic Compounds 2015, 51(1), 73–79
Synthesis of methyl 2-[2-(4-phenyl[1,2,4]triazolo-
[4,3-a]quinoxalin-1-ylsulfanyl)acetamido]alkanoates
and their N-regioisomeric analogs
Walid Fathalla1*
1 Department of Mathematics and Physics, Faculty of Engineering, Port-Said University,
Port-Said, 41200, Egypt; e-mail: walid3369@yahoo.com
Submitted October 15, 2014
Accepted November 28, 2014
Published in Khimiya Geterotsiklicheskikh Soedinenii,
2015, 51(1), 73–79
Methyl 2-[2-(4-phenyl[1,2,4]triazolo[4,3-a]quinoxalin-1-ylsulfanyl)acetamido]alkanoates were formed by the reaction of 2-(4-phenyl-
1,2-dihydro[1,2,4]triazolo[4,3-a]quinoxalin-1-ylsulfanyl)acetic acid with a variety of amino acid esters via DCC coupling method in the
presence of N-hydroxybenzotriazole in good yields. These amino acid derivatives linked to triazoloquinoxaline moiety were also ob-
tained by the reaction of 2-(4-phenyl[1,2,4]triazolo[4,3-a]quinoxalin-1-ylsulfanyl)acetohydrazide with amino acid ester derivatives via
azide coupling method in poor yields due to the competing decomposition of the corresponding azide resulting in the starting 4-phenyl-
[1,2,4]triazolo[4,3-a]quinoxaline-1(2H)-thione. The N-regioisomeric methyl 2-[3-(4-phenyl-1-thioxo[1,2,4]triazolo[4,3-a]quinoxalin-
2(1H)-yl)propanamido]alkanoates were efficiently produced from the 3-(4-phenyl-1-thioxo[1,2,4]triazolo[4,3-a]quinoxalin-2(1H)-yl)-
propanohydrazide and amino acid esters via azide coupling method in good to moderate yields.
Keywords: amino acids, N,N'-dicyclohexylcarbodiimide, azide coupling, chemoselective alkylation, Michael addition, tautomerism.
These results motivated the development of a series of
N- and S-substituted amino acid esters of biologically
promising triazoloquinoxaline ring system. In the present
article, we report the preparation of methyl 2-[2-(4-phenyl-
[1,2,4]triazolo[4,3-a]quinoxalin-1-ylsulfanyl)acetamido]
alkanoates and their isomers methyl 2-[3-(4-phenyl-
1-thioxo[1,2,4]triazolo[4,3-a]quinoxalin-2(1H)-yl)propan-
amido]alkanoates. Triazoloquinoxaline 1 displays an inte-
resting tautomeric equilibrium between thiol (structure 1a)
and thione (structure 1b) forms.23–26 Triazoloquinoxaline 1,
therefore, is amenable to structure modification by simple
chemoselective alkylation reactions at the sulfur and
nitrogen atoms. Thus, the reaction of triazoloquinoxaline 1
with methyl chloroacetate or methyl acrylate in the pre-
sence of a base afforded the S-alkylation product 2 and
N-alkylation product 3, respectively (Scheme 1).25,26 The
esters 2 and 3 were refluxed with hydrazine hydrate in
ethyl alcohol to afford the corresponding hydrazides 4 and 5,
respectively. Hydrazides 4 and 5 are excellent precursors
for the structure modification of triazoloquinoxaline with
amino acids via azide coupling method at sulfur and
nitrogen atoms, respectively.
Quinoxaline and triazoloquinoxaline derivatives are
important components of several pharmacologically active
compounds.1 Among [1,2,4]triazolo[4,3-a]quinoxalines,
many compounds had been found with pronounced anti-
microbial,2 antiallergic,3 antihypertensive,4 antidepressant,5
antiischemic activity,6 excellent binding affinity at both the
A1 and A2 adenosine receptor sites,7 as well as compounds
used in the treatment of indications caused by hyperactivity
of the excitatory neurotransmitters.8
Non-proteinogenic amino acids are major components in
a number of drugs including β-lactam antibiotics,9 glutamate
antagonists,10 antiviral11 and cytotoxic agents.12 The attach-
ment of a heterocyclic moiety to non-proteinogenic amino
acid esters might provide structures with interesting confor-
mation and biological activity.
The chemoslective reactions of thioamides have always
attracted the attention of our research group. Earlier we
reported13–15 the chemoselective S- and N-alkylation of the
model compound 4-methyl-1-thioxo-1,2,4,5-tetrahydro[1,2,4]-
triazolo[4,3-a]quinazolin-5-one with different electro-
philes. These results were supported by quantum-chemical
calculations.13–15 We also applied these findings to the synthe-
sis of interesting heterocycles via domino reactions,16–18
rearrangement reactions,19–20 and the preparation of hetero-
cycle-coupled amino acid esters.21,22
Azide coupling method is considered as one of the
important methods to couple amino acid derivatives starting
from hydrazides. It was also reported that this method
0009-3122/15/5101-0073©2015 Springer Science+Business Media New York
73

Chemistry of Heterocyclic Compounds 2015, 51(1), 73–79
Scheme 1
N
N
N
N
N
ClCH2CO2Me
NH2NH2
N
N
N
N
N
Et3N
EtOH , 4 h
N
N
EtOH, , 6 h
S
S
HS
MeO2C
H2NHNOC
1a
2
4
N
N
N
N
CH2=CHCO2Me
NH2NH2
N
S
N
N
N
N
N
N
NH
EtOH , 4 h
Et3N
EtOH, , 4 h
S
S
CONHNH2
CO2Me
1b
5
3
decreases the degree of racemization in the amino acid
coupling.27,28 Carbohydrazide 4 was converted to the cor-
responding carbonyl azide 6 by treatment with NaNO2 and
HCl mixture in an ice bath along with the precipitation of
triazoloquinoxaline 1 as a side product. Azide 6 solution
reacted with amino acid methyl ester hydrochlorides in the
presence of triethylamine to afford a series of S-substituted
[1,2,4]triazolo[4,3-a]quinoxaline derivatives 7a–d in poor
yields (Scheme 2, see Experimental, Method A).
Proposed mechanistic rationalization for the formation of
triazoloquinoxaline 1 from azide 6 through Smiles rearrange-
ment29 is shown in Scheme 3. The first step is acid-catalyzed
tautomerization of the azide derivative 6 giving rise to enol I.
The next step is nucleophilic substitution by oxygen at
position 1 of the triazoloquinoxaline system to give the five-
membered spiro intermediate II leaving a negative charge on
the nitrogen atom. The final step is the regaining of the
aromaticity at the triazoloquinoxaline ring with the subsequent
cleavage of the OC(N3)CH fragment (its final molecular form
was not established) to finally give tricycle 1. Several examp-
les were reported in literature showing similar results.20,30 The
earlier examples show the formation of amides from carbonyl
azides with the elimination of thiirane ring residue30. A similar
result was obtained by our group. Applying the azide coupling
method to 2-(3-aryl-4-oxo-3,4-dihydroquinazolin-2-ylsulfanyl)-
acetohydrazide gave an interesting rearrangement with the
formation of 3-phenylarylquinazoline-2,4-dione, with the
thiirane ring elimination20. This latter reaction appears to
confirm the formation of intermediates I and II, but differs in
the cleavage of the spiro system probably due to the differen-
ces in the properties of quinazoline and triazoloquinoxaline
ring systems.
An alternative effort to introduce a peptide chain at the S
atom connected to the triazoloquinoxaline tricycle was
efficiently carried out with the key substrate carboxylic
acid derivative 8 via N,N'-dicyclohexylcarbodiimide (DCC)
Scheme 2
Scheme 3
74

Chemistry of Heterocyclic Compounds 2015, 51(1), 73–79
Scheme 4
coupling method. The carboxylic acid 8 was formed by
saponification of ester 2 in the presence of NaOH at room
temperature for 4 h. The DCC coupling is one of the major
tools employed to introduce peptide bonds by the reaction
of carboxylic acid with amino acid methyl ester.31 Hydroxy-
benzotriazole (HOBt) is widely used as an additive to de-
crease racemization in the carbodiimide peptide coupling.32,33
Treatment of carboxylic acid 8 with amino acid ester
hydrochlorides in the presence of coupling reagents DCC
and HOBt afforded S-hetaryl acyclic amino acid esters 7a–f
and the analogous hydroxyproline derivative 9 in good yield
(Scheme 4, see Experimental, Method B).
Our attempt to connect a peptide chain to position 2 of
triazoloquinoxaline tricycle was carried out starting from
hydrazide 5 obtained from N-alkylated triazoloquinoxaline
derivative 3 (Scheme 1). Hydrazide 5 was converted into
azide 10 by treatment with NaNO2 and HCl. The obtained
azide 10 dissolved in ethyl acetate reacted with amino acid
methyl ester hydrochlorides in the presence of triethyl-
amine to afford N-substituted acyclic amino acid deriva-
tives 11a–f and analogous hydroxyproline derivative 12
(Scheme 5). The azide 10 as ethyl acetate solution reacted
also with morpholine to give N-substituted amide 13.
The structure assignment of both the S-substituted amino
acid derivatives and their N-regioisomeric analogs is based
1
on H, 13C NMR spectroscopy, as well as physicochemical
analysis (Fig. 1). The 1H NMR clearly confirms the alkylation
site for all the isolated S- and N-substituted derivatives. Thus
1
the the H NMR spectrum of compound 7a exhibits two
singlet signals at 3.88 and 3.73 ppm corresponding to NCH2
and OCH3 groups, respectively. The 1H NMR spectrum also
shows an interesting singlet signal at 4.28 ppm in the region
typically associated with the SCH2CO group,13 which is
common to all S-substituted amino acid derivatives 7a–f
and 9. The 13C NMR spectrum of compound 7a shows also
a signal at 37.66 ppm, i.e., in the region characteristic of
SCH2 group carbon signals, along with signals at 170.37,
167.44, 52.19, and 41.43 ppm assigned to ester C=O,
amide C=O, OCH3, and NHCH2 groups, respectively.
1
On the other hand, the H NMR spectrum of compound
11a exhibits a triplet signal at 4.87 ppm typically associated
with the NCH2CH2CO group,14 which is common for all other
Ar
Scheme 5
NH2(CH2)nCHRCO2Me·HCl
NH
R
Et3N, EtOAc
O
0°C, 24 h; rt 24 h
n
CO2Me
11a–f
HO
NH·HCl
Ar
OH
Ar
NaNO2, HCl
CO2Me
Et3N, EtOAc
0°C, 24 h; rt, 24 h
N
5
AcOH, H2O
–5 0°C, 1 h
CON3
O
MeO2C
10
12
Ar
O
NH
N
N
O
EtOAc
0°C, 24 h; rt, 24 h
Ar =
O
N
S
N
N
13
11 a–c,e,f n = 0, d n = 1,
a,d R = H, b R = Me, c R = CH2OH, e R = CH2CHMe2, f R = CMeOH
75

Chemistry of Heterocyclic Compounds 2015, 51(1), 73–79
crystallized from aqueous ethanol to yield corresponding
hydrazide.
2-(4-Phenyl[1,2,4]triazolo[4,3-a]quinoxalin-1-ylsulfanyl)-
acetohydrazide (4). Yield 0.31 g (91%), white crystals, mp
235–236°C. 1H NMR spectrum, δ, ppm: 1.84–1.97 (2H, m,
NH2); 4.21 (2H, s, SCH2CO); 7.61–7.79 (5H, m, H Ar);
8.11–8.15 (1H, m, H Ar); 8.53–8.56 (1H, m, H Ar); 8.69–
8.73 (2H, m, H Ar); 9.14 (1H, s, NH). Found, %: C 57.67;
H 3.89; N 23.88. C17H14N6OS. Calculated, %: C 58.27; H
4.03; N 23.98.
3-(4-Phenyl-1-thioxo[1,2,4]triazolo[4,3-a]quinoxalin-
2(1H)-yl)propanohydrazide (5). Yield 0.3 g (82%), white
crystals, mp 255–256°C. 1H NMR spectrum, δ, ppm (J, Hz):
1.86–1.98 (2H, m, NH2); 3.08 (2H, t, J = 7.1, CH2); 4.83
(2H, t, J = 7.1, CH2); 7.57–7.67 (5H, m, H Ar); 8.06–8.10
(1H, m, H Ar); 8.52–8.56 (2H, m, H Ar); 10.46–10.55 (1H,
m, H Ar). Found, %: C 59.21; H 4.34; N 23.01. C18H16N6OS.
Calculated, %: C 59.32; H 4.43; N 23.06.
1
Figure 1. Selected H and 13C NMR chemical shifts of S- and
N-substituted triazoloquinoxalines 7a and 11a.
1
N-substituted derivatives 11a–f, 12, and 13. The H NMR
spectrum of compound 11a shows also three signals at 4.06,
3.62 and 2.99 ppm assigned to NCH2, OCH3, and CH2CO,
1
respectively. The H NMR spectrum also showed a very
2-(4-Phenyl[1,2,4]triazolo[4,3-a]quinoxalin-1-ylsulfanyl)-
acetic acid (8). A solution of sodium hydroxide (0.11 g,
2.8 mmol) in H2O (10 ml) was added to a solution of ester
2 (0.35 g, 1.0 mmol) in methanol (30 ml). The reaction
mixture was stirred for 4 h till complete consumption of the
ester 2 (monitored by TLC). The reaction mixture was
evaporated under reduced pressure, diluted with water, and
acidified by 1 N HCl to pH 3. The yellowish precipitate
formed was filtered off and washed several times with water,
dried, and crystallized from DMF–H2O, 7:3. Yield 0.27 g
(80%), white crystals, mp 263–264°C (mp 260–261°C26).
1H NMR spectrum, δ, ppm: 4.23 (2H, s, SCH2CO); 7.61–
7.68 (3H, m, H Ar); 7.69–7.81 (2H, m, H Ar); 8.17–8.22
(1H, m, H Ar); 8.48–8.57 (1H, m, H Ar); 8.72–8.78 (2H,
m, H Ar). Found, %: C 60.63; H 3.59; N 16.64. C17H12N4O2S.
Calculated, %: C 60.70; H 3.60; N 16.66.
Preparation of methyl 2-[2-(4-phenyl[1,2,4]triazolo-
[4,3-a]quinoxalin-1-ylsulfanyl)acetamido]alkanoates
7a–f and 9 (General Method). A (for compounds 7a–d only).
A solution of NaNO2 (0.34 g, 5.0 mmol) in cold water (3 ml)
was added to a cold solution (–5°C) of hydrazide 4 (0.35 g,
1.0 mmol) in AcOH (6 ml), 1 N HCl (3 ml), and water
(25 ml). After stirring at –5°C for 15 min, a thick precipitate
started to form. The reaction mixture was stirred in ice bath
for further 1 h. The reaction mixture was filtered, and the
precipitate, identified as 4-phenyl[1,2,4]triazolo[4,3-a]-
quinoxaline-1(2H)-thione (1), was washed several times
with ethyl acetate and air-dried. The filtrate was extracted
twice with ethyl acetate (30 ml). The combined organic
layer was washed with 0.5 N HCl (30 ml), 3% NaHCO3
(30 ml), H2O (30 ml) and finally dried over Na2SO4 (10 g)
to give an ethyl acetate solution of azide 6. A solution of an
appropriate amino acid ester hydrochloride (1.0 mmol) in
ethyl acetate (20 ml) containing triethylamine (0.2 ml,
2 mmol) was added to the solution of azide 6. The mixture
was kept at –5°C for 24 h, then at 25°C for another 24 h,
followed by washing with 0.5 N HCl (30 ml), 3% NaHCO3
(30 ml), H2O (30 ml) and finally dried over Na2SO4 (10 g).
The solution was evaporated to dryness, and the residue
was recrystallized from petroleum ether–ethyl acetate, 1:3,
to give the desired S-coupled product 7a–d.
interesting doublet signal at 10.52 ppm corresponding to an
aromatic proton. This strongly downfielded shift is likely
due to an interesting anisotropy caused by the adjacent
thiocarbonyl group (Fig. 1). This aromatic proton shift is
common for all N-substituted derivatives 11a–f, 12, 13 and
can be used as an indicator for N-substitution. Thus
13C NMR spectrum can be used to discriminate between
alternative chemoselective alkylation products coupled to
amino acid chain. The 13C NMR spectrum of compound 11a
also shows characteristic signals at 172.9, 169.5, 161.3,
52.1, and 41.0 ppm assigned to ester C=O, C=S, amide
C=O, OCH3, and NHCH2 groups, respectively.
To conclude, a series of S- and N-substituted triazolo-
quinoxaline attached to amino acid esters by a spacer have
been prepared via azide and DCC coupling methods.
Although both methods were applied to the preparation of
S-alkylated triazoloquinoxalines, due to instability of the
intermediate 2-(hetarylsulfanyl)acetyl azide better yields
were obtained with the DCC method. On the other hand,
the azide coupling method gave excellent results for the
N-substituted derivatives.
Experimental
1H and 13C NMR spectra were recorded on a Bruker AC
250 instrument (250 and 63 MHz, respectively) in DMSO-
d6 with TMS as internal standard. Elemental analyses were
performed on a Flash EA-1112 instrument at the Micro-
analytical laboratory, Faculty of Science, Suez Canal
University, Ismailia, Egypt. Melting points were deter-
mined on a Buchi 510 apparatus and are uncorrected. For
TLC, silica gel 60 F254 plastic plates (E. Merck, layer
thickness 0.2 mm) were used. Solvents were purified by
standard procedures. Compounds 1, 2, and 3 were prepared
as reported.25
Preparation of hydrazides 4 and 5 (General Method).
Hydrazine hydrate (80%) (2.4 ml, 5 mmol) was added to a
solution of ester 2 (0.35 g, 1.0 mmol) or 3 (0.36 g, 1.0 mmol)
in absolute ethanol (30 ml). The reaction mixture was
refluxed for 4 h and cooled. The resultant precipitate was
filtered off, washed with ethanol and diethyl ether, then
76

Chemistry of Heterocyclic Compounds 2015, 51(1), 73–79
1
B. 2-(4-Phenyl-1,2-dihydro[1,2,4]triazolo[4,3-a]quin-
149°C. H NMR spectrum, δ, ppm: 3.61 (3H, s, OCH3);
3.65–3.73 (2H, m, OCH2); 4.24–4.29 (1H, m, CH); 4.34
(2H, s, SCH2); 5.08 (1H, br. s, OH, D2O exchangeable);
7.62–7.65 (3H, m, H Ar); 7.73–7.83 (2H, m, H Ar); 7.94
(1H, br. s, NH); 8.43–8.59 (1H, m, H Ar); 8.71–8.81 (2H,
m, H Ar); 8.85–8.94 (1H, m, H Ar). 13C NMR spectrum, δ,
ppm: 37.9 (SCH2); 52.3 (OCH3); 57.6 (CH); 61.6 (OCH2);
116.4 (C Ar); 126.1 (C Ar); 128.2 (C Ar); 128.8 (C Ar);
129.7 (C Ar); 129.8 (C Ar); 130.5 (C Ar); 131.7 (C Ar);
134.9 (C Ar); 136.2 (C Ar); 145.2 (C Ar); 146.4 (C Ar);
148.8 (C Ar); 167.1 (C=O amide); 171.1 (C=O ester).
Found, %: C 57.45; H 4.21; N 15.72. C21H19N5O4S.
Calculated, %: C 57.66; H 4.38; N 16.01.
oxalin-1-ylsulfanyl)acetic acid (8) (0.340 g, 1.0 mmol),
N,N'-dicyclohexylcarbodiimide (0.207 g, 1.0 mmol), and
N-hydroxybenzotriazole (0.135 g, 1.0 mmol) were succes-
sively added to a cold solution (–5°C) of the appropriate
amino acid methyl ester hydrochloride (1.0 mmol) in aceto-
nitrile (6 ml) containing triethylamine (0.14 ml, 1.0 mmol).
The reaction mixture was stirred at 0°C for 1 h, then at 5°C
for 1 h, then at room temperature for 8 h. The reaction
mixture was set aside overnight. The precipitated N,N'-di-
cyclohexylurea was filtered off and the filtrate was eva-
porated under reduced pressure. The residue was dissolved
in ethyl acetate, filtered, and the filtrate was washed with
0.5 N HCl (30 ml), 3% NaHCO3 (30 ml), H2O (30 ml) and
finally dried over Na2SO4 (10 g). After evaporation of the
solvent, the remaining oily residue was triturated with
petroleum ether (bp 40–60°C) at 0°C, and the formed solid
was filtered off and crystallized from petroleum ether–ethyl
acetate, 1:3.
Methyl 3-[2-(4-phenyl[1,2,4]triazolo[4,3-a]quinoxalin-
1-ylsulfanyl)acetamido]propanoate (7d). Yield 16%
(Method A), 64% (Method B), white crystals, mp 111–
1
112°C. H NMR spectrum, δ, ppm (J, Hz): 2.54 (2H, t,
J = 6.4, CH2); 3.54 (2H, q, J = 6.6, NCH2); 3.59 (3H, s,
OCH3); 4.22 (2H, s, SCH2); 7.59–7.68 (3H, m, H Ar);
7.69–7.71 (3H, m, H Ar); 7.84 (1H, br. s, NH); 8.17–8.23
(1H, m, H Ar); 8.48–8.55 (1H, m, H Ar); 8.77–8.79 (1H,
m, H Ar). 13C NMR spectrum, δ, ppm: 33.8 (CH2CO); 35.6
(NHCH2); 37.9 (SCH2); 51.8 (OCH3); 116.4 (C Ar); 126.1
(C Ar); 128.2 (C Ar); 128.8 (C Ar); 129.7 (C Ar); 129.8
(C Ar); 130.5 (C Ar); 131.7 (C Ar); 135.0 (C Ar); 136.1
(C Ar); 145.2 (C Ar); 146.4 (C Ar); 148.9 (C Ar); 166.8
(C=O amide); 172.0 (C=O ester). Found, %: C 59.80;
H 4.55; N 16.58. C21H19N5O3S. Calculated, %: C 59.84;
H 4.54; N 16.62.
4-Phenyl[1,2,4]triazolo[4,3-a]quinoxaline-1(2H)-thi-
one (1). Yield 0.17 g (63%) (Method A), white crystals, mp
1
265–266°C (DMF–H2O, 7:3) (mp 272–274°C25). H NMR
spectrum, δ, ppm: 7.57–7.68 (5H, m, H Ar); 8.04–8.10
(1H, m, H Ar); 8.44–8.56 (2H, m, H Ar); 10.49–10.56 (1H,
m, H Ar). Found, %: C 64.68; H 3.45; N 20.12. C15H10N4S.
Calculated, %: C 64.73; H 3.62; N 20.13.
Methyl 2-[2-(4-phenyl[1,2,4]triazolo[4,3-a]quinoxalin-
1-ylsulfanyl)acetamido]acetate (7a). Yield 16% (Method A),
1
71% (Method B), white crystals, mp 164–165°C. H NMR
spectrum, δ, ppm (J, Hz): 3.73 (3H, s, OCH3); 3.88 (2H, d,
J = 5.7, NCH2); 4.28 (2H, s, SCH2); 7.55–7.64 (3H, m,
H Ar); 7.78–7.85 (3H, m, H Ar); 8.14–8.17 (1H, m, H Ar);
8.68–8.79 (2H, m, H Ar); 8.81 (1H, t, J = 5.7, NH). 13C NMR
spectrum, δ, ppm: 37.6 (SCH2); 41.4 (NCH2); 52.2 (OCH3);
116.3 (C Ar); 125.9 (C Ar); 128.1 (C Ar); 128.8 (C Ar);
129.6 (C Ar); 129.8 (C Ar); 131.7 (C Ar); 134.9 (C Ar);
136.1 (C Ar); 145.1 (C Ar); 146.2 (C Ar); 148.7 (C Ar);
167.4 (C=O amide); 170.3 (C=O ester). Found, %:
C 58.84; H 4.18; N 17.11.C20H17N5O3S. Calculated, %:
C 58.96; H 4.21; N 17.19.
Methyl 2-[2-(4-phenyl[1,2,4]triazolo[4,3-a]quinoxalin-
1-ylsulfanyl)acetamido]propanoate (7b). Yield 22%
(Method A), 56% (Method B), white crystals, mp 133–134°C.
1H NMR spectrum, δ, ppm (J, Hz): 1.42 (3H, d, J = 7.2,
CH3); 3.69 (3H, s, OCH3); 4.04 (1H, d, J = 14.4) and 4.12
(1H, d, J = 14.4, SCH2); 4.48–4.63 (1H, m, CH); 7.58–7.61
(3H, m, H Ar); 7.68–7.71 (2H, m, H Ar); 7.93 (1H, d,
J = 8.1, NH); 8.27–8.18 (1H, m, H Ar); 8.43–8.59 (1H, m,
H Ar); 8.77–8.80 (2H, m, H Ar). 13C NMR spectrum,
δ, ppm: 18.4 (CH3); 37.8 (SCH2); 51.6 (CH); 52.6 (OCH3);
116.4 (C Ar); 126.1 (C Ar); 128.1 (C Ar); 128.8 (C Ar);
129.4 (C Ar); 129.9 (C Ar); 130.5 (C Ar); 131.7 (C Ar);
135.0 (C Ar); 136.1 (C Ar); 145.2 (C Ar); 146.4 (C Ar);
148.6 (C Ar); 166.4 (C=O amide); 172.3 (C=O ester).
Found , %: C 59.76; H 4.51; N 16.60. C21H19N5O3S.
Calculated, %: C 59.84; H 4.54; N 16.62.
Methyl 4-methyl-2-[2-(4-phenyl[1,2,4]triazolo[4,3-a]-
quinoxalin-1-ylsulfanyl)acetamido]pentanoate (7e). Yield
51% (Method B), white crystals, mp 145–146°C. H NMR
1
spectrum, δ, ppm (J, Hz): 0.87 (6H, d, J = 6.0, 2CH3) 0.95–
0.97 (1H, m, CH); 1.45–1.63 (2H, m, CH2); 3.81 (3H, s,
OCH3); 4.28 (2H, d, J = 5.1, SCH2); 4.48–4.61 (1H, m,
CH); 7.60–7.67 (3H, m, H Ar); 7.68–7.85 (2H, m, H Ar);
7.95 (1H, d, J = 8.1, NH); 8.20–8.24 (1H, m, H Ar); 8.50–
8.54 (1H, m, H Ar); 8.71–8.86 (2H, m, H Ar). 13C NMR
spectrum, δ, ppm: 10.1 (CH3); 22.7 (CH); 25.1 (CH2); 37.7
(SCH2); 52.7 (OCH3); 55.4 (CH); 116.4 (C Ar); 126.1
(C Ar); 128.2 (C Ar); 128.8 (C Ar); 129.6 (C Ar); 129.7
(C Ar); 130.5 (C Ar); 131.7 (C Ar); 135.1 (C Ar); 136.1
(C Ar); 145.2 (C Ar); 146.2 (C Ar); 148.4 (C Ar); 166.4
(C=O amide); 172.3 (C=O ester). Found, %: C 62.14;
H 5.42; N 15.03. C24H25N5O3S. Calculated, %: C 62.18;
H 5.44; N 15.11.
Methyl 3-hydroxy-2-[2-(4-phenyl[1,2,4]triazolo[4,3-a]-
quinoxalin-1-ylsulfanyl)acetamido]butanoate (7f). Yield
1
75% (Method B), white crystals, mp 134–135°C. H NMR
spectrum, δ, ppm (J, Hz): 1.42 (3H, d, J = 7.2, CH3); 3.71
(3H, s, OCH3); 4.13–4.34 (3H, m, SCH2, CH); 4.65 (1H, d,
J = 6.0, CH); 7.55–7.58 (3H, m, H Ar); 7.59–7.69 (2H, m,
H Ar); 7.94 (1H, d, J = 6.0, NH); 8.16–8.20 (1H, m, H Ar);
8.42–8.60 (2H, m, H Ar, OH); 8.71–8.74 (2H, m, H Ar).
13C NMR spectrum, δ, ppm: 22.1 (CH3); 37.8 (SCH2); 52.6
(OCH3); 58.4 (CH); 65.3 (OCH); 116.4 (C Ar); 126.1
(C Ar); 128.2 (C Ar); 128.8 (C Ar); 129.6 (C Ar); 130.5
(C Ar); 131.7 (C Ar); 135.1 (C Ar); 136.2 (C Ar); 145.2
(C Ar); 146.3 (C Ar); 148.7 (C Ar); 166.8 (C=O amide);
Methyl 3-hydroxy-2-[2-(4-phenyl[1,2,4]triazolo[4,3-a]-
quinoxalin-1-ylsulfanyl)acetamido]propanoate (7c). Yield
25% (Method A), 48% (Method B), white crystals, mp 148–
77

Chemistry of Heterocyclic Compounds 2015, 51(1), 73–79
172.4 (C=O ester). Found, %: C 58.36; H 4.52; N 15.34.
(1H, m, H Ar). Found, %: C 60.63; H 4.85; N 16.02.
C22H21N5O3S. Calculated, %: C 60.67; H 4.86; N 16.08.
Methyl 3-hydroxy-2-[3-(4-phenyl-1-thioxo[1,2,4]triazolo-
[4,3-a]quinoxalin-2(1H)-yl)propanamido]propanoate
(11c). Yield 68%, yellow crystals, mp 154–155°C. 1H NMR
spectrum, δ, ppm (J, Hz): 2.89 (2H, t, J = 7.1, CH2); 3.18
(1H, br. s, OH, D2O-exchangeable); 3.58–3.85 (5H, m,
OCH2, OCH3); 4.19–4.26 (1H, m, CH); 4.61 (2H, t, J = 7.1,
NCH2); 7.03 (1H, br. s, NH); 7.60–7.69 (3H, m, H Ar);
7.70–7.73 (2H, m, H Ar); 8.02–8.06 (1H, m, H Ar); 8.44–
8.49 (2H, m, H Ar); 10.41–10.45 (1H, m, H Ar). 13C NMR
spectrum, δ, ppm: 33.2 (CH2CO); 45.9 (NCH2); 52.2
(OCH3); 55.2 (CH); 61.6 (OCH2); 115.6 (C Ar); 127.6
(C Ar); 128.1 (C Ar); 128.8 (C Ar); 129.1 (C Ar); 129.4
(C Ar); 130.1 (C Ar); 131.8 (C Ar); 134.3 (C Ar); 135.9
(C Ar); 138.3 (C Ar); 148.6 (C Ar); 161.1 (C=O amide);
169.7 (C=S); 172.4 (C=O ester). Found, %: C 58.48;
H 4.64; N 15.36. C22H21N5O4S (451.5). Calculated, %: C 58.52;
H 4.69; N 15.51.
C22H21N5O4S. Calculated, %: C 58.52; H 4.69; N 15.51.
Methyl 4-hydroxy-1-[2-(4-phenyl[1,2,4]triazolo[4,3-a]-
quinoxalin-1-ylsulfanyl)acetyl]pyrrolidine-2-carb-
oxylate (9). Yield 63% (Method B), white crystals, mp 103–
1
104°C. H NMR spectrum, δ, ppm (J, Hz): 1.95–2.18 (2H,
m, CH2); 3.58 (3H, s, OCH3); 3.73–3.83 (2H, m, CH2);
4.29 (1H, d, J = 6.0, CH); 4.35 (1H, br. s, OH, D2O-
exchangeable); 4.44 (1H, d, J = 14.6) and 4.63 (1H, d,
J = 14.4, SCH2); 5.26 (1H, d, J = 6.0, CH); 7.63–7.64 (3H,
m, H Ar); 7.65–7.87 (2H, m, H Ar); 8.16–8.23 (1H, m,
H Ar): 8.71–8.79 (3H, m, H Ar). Found, %: C 59.60;
H 4.32; N 14.59. C23H21N5O4S. Calculated, %: C 59.60;
H 4.57; N 15.11.
Preparation of 2-[3-(4-phenyl-1-thioxo[1,2,4]triazolo-
[4,3-a]quinoxalin-2(1H)-yl)propanamido]alkanoates
11a–f, 12, and 13 (General Method). A solution of NaNO2
(0.340 g, 5.0 mmol) in cold water (3 ml) was added to a
cold solution (–5°C) of hydrazide 5 (0.300 g, 1.0 mmol) in
a mixture of AcOH (6 ml), 1 N HCl (3 ml), and water (25
ml). After stirring at –5°C for 15 min, a thick precipitate
started to form. The reaction mixture was stirred for further
1 h and extracted by cold ethyl acetate (30 ml). The organic
layer was washed with 3% NaHCO3 (30 ml), H2O (30 ml)
and finally dried over Na2SO4 (10 g) to give an ethyl
acetate solution of the azide 10. A solution of the
appropriate amino acid ester hydrochloride (1.0 mmol) or
morpholine (0.174 g, 2.0 mmol) in ethyl acetate (20 ml),
containing, in the case of amino acid ester hydrochlorides,
triethylamine (0.2 ml), was added to the azide 10 solution.
The mixture was kept at –5°C for 24 h, then at 25°C for
another 24 h. The reaction mixture was washed with 0.5 N
HCl, water, 3% solution of NaHCO3 and finally dried over
Na2SO4. The solution was evaporated to dryness and the
residue was recrystallized from petroleum ether–ethyl acetate,
3:1, to give the desired N-coupled product 11a–f, 12, or 13.
Methyl 2-[3-(4-phenyl-1-thioxo[1,2,4]triazolo[4,3-a]-
quinoxalin-2(1H)-yl]propanamido]acetate (11a). Yield
Methyl 3-[3-(4-phenyl-1-thioxo[1,2,4]triazolo[4,3-a]-
quinoxalin-2(1H)-yl)propanamido]propanoate (11d). Yield
1
74%, yellow crystals, mp 191–192°C. H NMR spectrum,
δ, ppm (J, Hz): 2.51 (2H, t, J = 7.1, CH2CO2CH3); 2.92 (2H,
t, J = 7.1, CH2); 3.50 (2H, q, J = 7.1, NHCH2); 3.61 (3H,
s, OCH3); 4.84 (2H, t, J = 7.1, NCH2); 6.34 (1H, br. s,
NH), 7.57–7.64 (3H, m, H Ar); 7.66–7.68 (2H, m, H Ar);
8.07–8.15 (1H, m, H Ar), 8.50–8.53 (2H, m, H Ar), 10.43–
10.51 (1H, m, H Ar). Found, %: C 60.49; H 4.74; N 16.03.
C22H21N5O3S. Calculated, %: C 60.67; H 4.86; N 16.08.
Methyl 4-methyl-2-[(3-(4-phenyl-1-thioxo[1,2,4]triazolo-
[4,3-a]quinoxalin-2(1H)-yl)propanamido]pentanoate (11e).
Yield 59%, yellow crystals, mp 174–175°C. 1H NMR
spectrum, δ, ppm (J, Hz): 0.83–0.88 (6H, m, 2CH3); 0.95–
0.97 (1H, m, CH); 1.48–1.68 (2H, m, CHCH2CH); 2.92
(2H, t, J = 7.1, CH2); 3.62 (3H, s, OCH3); 4.59–4.68 (1H,
m, CH); 4.64 (2H, t, J = 7.1, NCH2); 6.18 (1H, d, J = 7.2,
NH), 7.58–7.63 (3H, m, H Ar), 7.64–7.67 (2H, m, H Ar),
8.06–8.11 (1H, m, H Ar), 8.49–8.54 (2H, m, H Ar), 10.52–
10.56 (1H, m, H Ar). 13C NMR spectrum, δ, ppm: 8.9
(CH3); 23.0 (CH); 24.6 (CH2); 33.2 (CH2CO); 45.8
(NCH2); 50.7 (CH); 52.2 (OCH3); 115.6 (C Ar); 127.6
(C Ar); 128.2 (C Ar); 128.9 (C Ar); 129.1 (C Ar); 129.4
(C Ar); 130.1 (C Ar); 131.9 (C Ar); 134.3 (C Ar); 135.9
(C Ar); 138.2 (C Ar); 148.6 (C Ar); 161.2 (C=O amide);
169.5 (C=S); 173.3 (C=O ester). Found, %: C 62.78;
H 5.69; N 14.56. C25H27N5O3S. Calculated, %: C 62.87;
H 5.70; N 14.66.
Methyl 3-hydroxy-2-[3-(4-phenyl-1-thioxo[1,2,4]triazolo-
[4,3-a]quinoxalin-2(1H)-yl)propanamido]butanoate (11f).
Yield 47%, yellow crystals, mp 161–162°C. 1H NMR
spectrum, δ, ppm (J, Hz): 1.03 (3H, d, J = 7.2, CH3); 2.89
(2H, t, J = 7.1, CH2); 3.57 (3H, s, OCH3); 4.02–4.09 (1H,
m, CH); 4.32 (1H, d, J = 6.0, CH); 4.63 (2H, t, J = 7.1,
NCH2); 7.60–7.75 (5H, m, H Ar); 8.04–8.08 (1H, m,
H Ar); 8.26 (1H, d, J = 8.1, NH); 8.45–8.50 (2H, m, H Ar);
10.43–10.47 (1H, m, H Ar). 13C NMR spectrum, δ, ppm.:
20.5 (CH3); 33.2 (CH2CO); 45.9 (NCH2); 52.2 (OCH3);
58.4 (CH); 66.7 (OCH); 115.6 (C Ar); 127.5 (C Ar); 128.1
(C Ar); 128.8 (C Ar); 129.0 (C Ar); 129.4 (C Ar); 130.0
1
66%, yellow crystals, mp 191–192°C. H NMR spectrum,
δ, ppm (J, Hz): 2.99 (2H, t, J = 7.1, CH2); 3.62 (3H, s,
OCH3); 4.06 (2H, d, J = 6.4, NHCH2); 4.87 (2H, t, J = 7.1,
NCH2); 6.27 (1H, br. s, NH); 7.54–7.62 (3H, m, H Ar);
7.64–7.69 (2H, m, H Ar); 8.07–8.10 (1H, m, H Ar); 8.49–
8.53 (2H, m, H Ar); 10.50–10.53 (1H, m, H Ar). 13C NMR
spectrum, δ, ppm: 33.2 (CH2CO); 41.0 (NHCH2); 45.8
(NCH2); 52.1 (OCH3); 115.7 (C Ar); 127.4 (C Ar); 128.2
(C Ar); 128.9 (C Ar); 129.1 (C Ar); 129.5 (C Ar); 130.2
(C Ar); 131.9 (C Ar); 134.4 (C Ar); 135.8 (C Ar); 138.1
(C Ar); 148.7 (C Ar); 161.3 (C=O amide); 169.5 (C=S); 172.9
(C=O ester). Found, %: C 59.82; H 4.45; N 16.57.
C21H19N5O3S. Calculated, %: C 59.84; H 4.54; N 16.62.
Methyl 2-[3-(4-phenyl-1-thioxo[1,2,4]triazolo[4,3-a]-
quinoxalin-2(1H)-yl)propanamido]propanoate (11b).
Yield 48%, yellow crystals, mp 173–174°C. 1H NMR
spectrum, δ, ppm (J, Hz): 1.17 (3H, d, J = 7.2, CH3); 2.83
(2H, t, J = 7.1, CH2); 3.57 (3H, s, OCH3); 4.21–4.33 (1H,
m, CH), 4.61 (2H, t, J = 7.1, NCH2); 7.01 (1H, br. s, NH);
7.52–7.71 (3H, m, H Ar); 7.73–7.77 (2H, m, H Ar); 8.04–
8.07 (1H, m, H Ar); 8.45–8.51 (2H, m, H Ar); 10.42–10.46
78

Chemistry of Heterocyclic Compounds 2015, 51(1), 73–79
5. Saul, B.; Sarges, K. R. US Patent 4623725.
(C Ar); 131.8 (C Ar); 134.2 (C Ar); 135.9 (C Ar); 138.2
(C Ar); 148.5 (C Ar); 161.1 (C=O amide); 170.1 (C=S);
172.4 (C=O ester). Found, %: C 59.22; H 4.87; N 15.02.
C23H23N5O4S. Calculated, %: C 59.34; H 4.98; N 15.04.
Methyl 4-hydroxy-1-[3-(4-phenyl-1-thioxo[1,2,4]tri-
azolo[4,3-a]quinoxalin-2(1H)-yl)propanoyl]pyrrolidine-
2-carboxylate (12). Yield 38%, yellow crystals, mp 142–
6. Sakamoto, S.; Ohmori, J.-Y.; Sasamata, M.; Okada, M.;
Hidaka, K. WO Patent 1993020077.
7. Trivedi, B. K. US Patent 4780464.
8. Jacobsen, P.; Nielsen, F. E. US Patent 5504085.
9. Townsend, C. A.; Brown, A. M. J. Am. Chem. Soc. 1983,
105, 913.
10. Maloney, M. G. Nat. Prod. Rep. 1999, 16, 485.
11. Bhide, R.; Mortezaei, R.; Scilimati, A.; Sih, C. J. Tetrahedron
Lett. 1990, 31, 4827.
12. Kawasaki, T.; Enoki, H.; Matsumura, K.; Ohyama, M.;
Inagawa, M.; Sakamoto, M. Org. Lett. 2000, 2, 3027.
13. Fathalla, W.; Čajan, M.; Pazdera, P. Molecules 2001, 6, 557.
14. Fathalla, W.; Čajan, M.; Pazdera, P. Molecules 2000, 5,
1210.
15. Fathalla, W.; Pazdera, P.; Čajan, M.; Marek, J. J. Heterocycl.
Chem. 2002, 39, 1145.
16. Fathalla, W.; Pazdera, P.; Marek, J. J. Heterocycl. Chem.
2002, 39, 1139.
17. Fathalla, W.; Marek, J.; Pazdera, P. Heterocycl. Commun.
2002, 8, 157.
18. Fathalla, W.; Marek, J.; Pazdera, P. J. Sulfur Chem. 2008, 29, 31.
19. Fathalla, W.; Ali, I. A. I.; Marek, J.; Pazdera, P. J. Sulfur
Chem. 2012, 33, 49.
20. Elfekki, I.; Fathalla, W.; Abd El Hamid, H.; Ali, I. A. I.;
Eltamany, S. Chem. Pharm. Bull. 2014, 62, 675.
21. Fathalla, W.; Ali, I. A. I. Heteroat. Chem. 2007, 18, 637.
22. Fathalla, W.; El Rayes, S. M.; Ali, I. A. I. ARKIVOC 2007,
(xvi), 173.
23. El-Hawash, S. A. M.; Habib, N. S.; Kassem, M. A. Arch
Pharm. (Weinheim) 2006, 339, 564.
24. Stöesser, R.; Siegmund, M.; Westphal, G. Tetrahedron 1978,
34, 2701.
25. Westphal, G.; Wasicki, H.; Esser, A.; Zielinski, U.; Weber,
F. G.; Tonew, M.; Tonew, E. Pharmazie 1977, 32, 687.
26. Westphal, G.; Zielinski, U.; Esser, A.; Wasicki, H.; Tonev,
E.; Tonev, M. DD Patent 126390.
1
143°C. H NMR spectrum, δ, ppm (J, Hz): 1.94–2.13 (2H,
m, CH2); 3.00 (2H, t, J = 7.1, CH2); 3.63 (3H, s, OCH3);
3.64–3.76 (2H, m, CH2); 4.10 (1H, br. s, OH, D2O-
exchangeable); 4.34 (1H, t, J = 7.1, CH); 4.60 (2H, t,
J = 7.1, NCH2); 5.11 (1H, d, J = 6.0, CH); 7.58–7.63 (3H,
m, H Ar); 7.69–7.73 (2H, m, H Ar); 8.02–8.05 (1H, m, H Ar);
8.44–8.47 (2H, m, H Ar); 10.40–10.43 (1H, m, H Ar).
Found, %: C 60.24; H 4.81; N 14.55. C24H23N5O4S. Calcu-
lated, %: C 60.36; H 4.85; N 14.67.
1-Morpholino-3-(4-phenyl-1-thioxo[1,2,4]triazolo-
[4,3-a]quinoxalin-2(1H)-yl)propan-1-one (13). Yield 72%,
yellow crystals, mp 220–221°C. 1H NMR spectrum, δ, ppm
(J, Hz): 2.99 (2H, t, J = 7.1, CH2); 3.45 (4H, t, J = 7.1,
2NCH2); 3.65 (4H, t, J = 7.1, 2OCH2); 4.62 (2H, t, J = 7.1,
NCH2); 7.63–7.70 (3H, m, H Ar); 7.72–7.76 (2H, m, H Ar);
8.04–8.08 (1H, m, H Ar); 8.42–8.46 (2H, m, H Ar); 10.41–
10.45 (1H, m, H Ar). Found, %: C 62.74; H 5.01; N 16.53.
C22H21N5O2S. Calculated, %: C 62.99; H 5.05; N 16.69.
The author would like to thank Faculty of Engineering,
Port-Said University, Egypt for financial support, Assoc.
Professor Pavel Pazdera, Head of the Centre for the
Syntheses at Sustainable Conditions and their
Management, Faculty of Science of Masaryk University for
technical support, and, finally, Ministry of Higher
Education, Arab Republic of Egypt, for financial support.
27. Han, S.-Y.; Kim, Y.-A. Tetrahedron 2004, 60, 2447.
28. Ali, I. A. I.; Al-Masoudi, I. A.; Saeed, B.; Al-Masoudi, N. A.;
La Colla P. Heteroat. Chem. 2005, 16, 148.
29. Warren, L. A.; Smiles, S. J. Chem. Soc. 1930, 956.
30. Plesniak, K.; Zarecki, A.; Wicha, J. In Sulfur-Mediated
Rearrangements II, Schaumann, E., Ed.; Springer: Berlin,
2007, p. 163.
References
1. Brown, D. J. In Quinoxalines, Taylor, E. C.; Wipf, P.;
Weissberger, A., Eds.; John Wiley & Sons, Inc.: Hoboken,
2004, suppl. II, vol. 61, p. 1.
2. Badran, M. M.; Abouzid, K. A. M.; Hussein, M. H. M. Arch.
Pharm. Res. 2003, 26, 107.
31. Davis, J. S.; Mohammed, A. K. J. Chem. Soc., Perkin Trans.
1 1981, 2982.
3. Loev, B.; Musser, J. H.; Brown, R. E.; Jones, H.; Robert, K. R.;
Huang, F-C.; Khandwala, A.; Sonnino-Goldman,
P.;
32. König, W.; Geiger, R. Chem. Ber. 1970, 103, 788.
33. Pennigton, R. M.; Fischer, R. R. J. Biol. Chem. 1981, 256,
8963.
Leibowitz, M. J. J. Med. Chem. 1985, 28, 363.
4. Loev, B.; Suh, J. T.; Williams, B. E.; Georgiev, V. US Patent
4354027.
79