SAR studies on 1,2,4-triazolo[3,4-b][1,3,4]thiadiazoles as inhibitors of Mtb shikimate dehydrogenase for the development of novel antitubercular agents

Article abstract of DOI:10.1039/c5ra19334f

Shikimate dehydrogenase, an essential protein for the biosynthesis of the chorismate end product, is a highly promising therapeutic target, especially for the discovery and development of new-generation anti-TB agents. Following up the identification of one lead 3,6-disubstituted 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole (1), targeting Mt SD in our previous study, an extensive SAR study for optimization of the lead compound was performed through systematic modification of the 3 and 6 positions. This study has successfully led to the discovery of two highly potent advanced leads 6d-4, 6c-4 and several other compounds with comparable potencies (6d-4, MIC-H37Rv = 0.5 μg mL^-1; MIC-MDRTB = 4.0 μg mL^-1; MIC-RDRTB = 0.5 μg mL^-1; Mt SD-IC50 = 14.20 μg mL^-1; and 6c-4, MIC-H37Rv = 0.5 μg mL^-1; MIC-MDRTB = 4.0 μg mL^-1; MIC-RDRTB = 1.0 μg mL^-1; Mt SD-IC50 = 6.82 μg mL^-1). These advanced lead compounds possess a para-halogen phenyl at the 3 position. In vitro Mt SD inhibitory assay indicates that Mt SD is the target for their antitubercular activity. Moreover, the BacT/ALERT 3D liquid culture technology and in vitro Mt SD inhibitory assay were initially applied.

Full text of DOI:10.1039/c5ra19334f

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: Z. li, Y. liu, X. bai,
Q. deng, J. wang, G. zhang, C. Xiao, Y. Mei and Y. wang, RSC Adv., 2015, DOI: 10.1039/C5RA19334F.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
SAR Studies on 1,2,4-Triazolo[3,4-b][1,3,4]thiadiazoles as Inhibitors
of Mtb Shikimate Dehydrogenase for the Development of Novel
Antitubercular Agents
a
Ziqiang Li, Yishuang Liu, Xiaoguang Bai, Qi Deng, Juxian Wang, Guoning Zhang,
a
a
a
a
a
a
Chunling Xiao, Yaning Mei and Yucheng Wang
∗,b
*,a
*
,a
Institute of Medicinal Biotechnology, Chinese Academy of Medical Science & Peking Union Medical
College, Beijing 100050, China. E-mail address: wyc9999@gmail.com; Tel: +86-10-63165263.
∗
,b
Department of Laboratory Medicine, the First Affiliated Hospital of Nanjing Medical University, Nanjing
10029, China. E-mail address: myn303@163.com; Tel: +86-25-68136287.
2
†
Electronic supplementary information (ESI) available: Antibacterial activity of triazolothiadiazoles 6 against
Mtb H37Rv strain and NMR spectra of synthesized compounds. See DOI:
1

RSC Advances
Page 2 of 52
View Article Online
DOI: 10.1039/C5RA19334F
ABSTRACT:
Shikimate dehydrogenase, an essential protein for the biosynthesis of the chorismate end
product, is a highly promising therapeutic target, especially for the discovery and development of
new-generation anti-TB agents. Following up the identification of one lead 3,6-disubstituted
1,2,4-triazolo[3,4-b][1,3,4]thiadiazole (1), targeting Mt SD in our previous study, an extensive
SAR study for optimization of the lead compound was performed through systematic
modification of the 3 and 6 positions. This study has successfully led to the discovery of two
highly potent advanced leads 6d-4, 6c-4 and several other compounds with comparable potencies
(6d-4, MIC-H37Rv = 0.5 ꢀg/mL; MIC-MDRTB = 4.0 ꢀg/mL; MIC-RDRTB = 0.5 ꢀg/mL; Mt
SD-IC50 = 14.20 ꢀg/mL; and 6c-4, MIC-H37Rv = 0.5 ꢀg/mL; MIC-MDRTB = 4.0 ꢀg/mL;
MIC-RDRTB = 1.0 ꢀg/mL; Mt SD-IC50 = 6.82 ꢀg/mL). These advanced lead compounds
possess a para-halogen phenyl at the 3 position. In vitro Mt SD inhibitory assay indicates that Mt
SD is the target for their antitubercular activity. Moreover, the BacT/ALERT 3D liquid culture
technology and in vitro Mt SD inhibitory assay were initially applied.
Keywords:
Shikimate dehydrogenase
Antitubercular agent
3,6-Disubstituted triazolothiadiazole
SAR
BacT/ALERT 3D
2

Page 3 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
1．Introduction
Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) remains a leading cause of
morbidity and mortality. Worldwide, there were approximately 9 million cases in 2013, of which
1
00,000 were multidrug-resistant (MDR). The only FDA-approved TB drug, Bedaquiline, has
5
2
been recently announced for the treatment of MDR-TB since the 1960s. It specifically inhibits
mycobacterial ATP (adenosine 5’-triphosphate) synthase which is essential for the final step in
3
ATP production by oxidative phosphorylation. Its associated risk of potentially lethal heart
problems has emphasized the unmet and urgent need for the development of safer antitubercular
drugs with novel targets and mechanisms of action to treat resistant forms of the disease.
The shikimate pathway is used in a variety of bacteria, including Mycobacterium tuberculosis,
for the production of chorismate, a precursor for aromatic amino acids and other aromatic
compounds. Mammals do not need the shikimate pathway enzymes necessary for de novo
synthesis of these amino acids but rather obtain them from the diet, making these potential
4
targets considerably less toxic in humans. Shikimate pathway enzymes may offer attractive
5
targets for new TB drug and vaccine development. One favorable mechanism for antitubercular
agents is the inhibition of shikimate dehydrogenase (SD) in the shikimate pathway.
Consequently, inhibitors of SD are anticipated to be selective antitubercular drugs. SD is the
fourth of seven enzymes involved in the shikimate pathway. SD is responsible for catalyzing the
+
NADPH-dependent reduction of 3-dehydroshikimate to form shikimate and NADP . M.
4
tuberculosis shikimate dehydrogenase (Mt SD) is encoded by aroE and is essential for the
6
survival of M. tuberculosis. Recently, we have established a high-throughput screening (HTS)
model targeting Mycobacterium tuberculosis shikimate dehydrogenase (Mt SD) for the discovery
of novel antituberculosis drugs. 80, 000 compounds have been screened by using this model and
3

RSC Advances
Page 4 of 52
View Article Online
DOI: 10.1039/C5RA19334F
evaluated for their activity against Mtb H37Rv, MDRTB (Isoniazid and Rifampin resistant
strains) and RDRTB (Rifampin resistant strains) initially using the BacT/ALERT 3D (MB/BacT)
7
liquid culture technology . One 3,6-disubstituted triazolothiadiazole (1, MIC-H37Rv = 8.0
ꢀ
g/mL; MIC-MDRTB = 8.0 ꢀg/mL; MIC-RDRTB = 8.0 ꢀg/mL; Mt SD-IC = 23.00 ꢀg/mL) has
50
been identified as a promising lead for antitubercular drug development.
Triazolothiadiazoles have been attracting increasing interest over the past decade because of
8-16
their utility in various applications such as antibacterial , anti-inflammatory
8,11,112
, analgesic
8
,11,12,13
11-15
16
, urease inhibitory , antitubercular
13,14,17
13,18-21
,
antifungal
, antitumor
, antioxidant
1
6,19
21
acetylcholinesterase inhibitory , PDE4 inhibitory and anticonvul activity . Among
22
23
,
these, interesting observations on the antitubercular activity of triazolothiadiazole derivatives
were made. At present, several triazole bearing compounds, like Flutrox, Nefazodone,
Trazodone, Triazoledione, etc., are used in modern medicine. Fluorine incorporated heterocycles,
triazoles and thiadiazoles displayed varied pharmacological properties. Since there have been
few reports on dichlorofluorophenyl containing triazolothiadiazoles, it was contemplated to
1
synthesize them and to pursue antitubercular screening so as to obtain a promising lead 2 (Fig.
3
1). Isopropylthiazole moiety has already been identified for its antimicrobial activity and its
24
coupling with other heterocyclic rings furnishes novel biologically active compounds . It was
contemplated to synthesize a series of clubbed isopropylthiazole derivatives triazolothiadiazoles,
study their antitubercular activity against H37Rv strain to get two potent and low-toxicity lead
1
4
14
and 4 (Fig. 1). Literature survey revealed that the pyrazine ring is important for
3
2
antimycobacterial activity . Some novel fused heterocycles incorporation of the pyrazine in
5
triazolothiadiazoles have been synthesized and evaluated for their antimycobacterial activity to
1
obtain two promising leads 5 and 6 (Fig. 1). However, against Mt SD, no compound has
7
17
4

Page 5 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
emerged as a promising lead in the past years. Since the early lead compounds 1 (MIC-H37Rv =
.0 ꢀg/mL), 5 (MIC-H37Rv = 0.4 ꢀg/mL) and 6 (MIC-H37Rv = 1.0 ꢀg/mL) possess a
8
methyleneoxo group at the 6 or 3 position, we consider the effect of unsubstituted and substituted
aryloxymethylene groups at the 6 position as well as unsubstitution and different substitution of
aromatic and hetero-aromatic groups at the 3 position on the potency against Mtb. Considering
above facts and the principles of group replacement, scaffold hopping, bioisosterism, we set out
for the structure–activity relationships (SAR) study and optimization of the lead through
systematic structural modifications at the 3 and 6 positions, keeping the methyleneoxo group at
the 6 position intact as shown in Fig. 2. We describe here our SAR study and successful
optimization of the early lead compound, which has led to the identification of two highly potent
lead compounds 6d-4, 6c-4 (MIC-H37Rv = 0.5 ꢀg/mL) and others with comparable potencies.
5

RSC Advances
Page 6 of 52
View Article Online
DOI: 10.1039/C5RA19334F
2
. Chemical synthesis
Synthesis of compounds for the optimization library of 3,6-disubstituted triazolothiadiazoles (72
compounds in total) is outlined in Scheme 1. The commercially available aromatic and hetero-
aromatic acid was firstly activated by 1,1'-carbonyldiimidazole and then hydrazinolysized to give
corresponding aroyl hydrazides 3a−h in 79−95% yields in one-pot, which reacted with carbon
disulfide and potassium hydroxide in ethanol to yield potassium dithiocarbazinate 4a−h, which
later cyclized to 4-amino-3-mercapto-1,2,4-triazole 5a−h by reacting with hydrazine hydrate
(80%) in 60−70% yields. The resulting triazoles 5a−h were further converted to triazolo
thiadiazoles 6 in one pot-reaction by condensation with unsubstituted and substituted
aryloxyacetic acids in the presence of phosphorous oxychloride under microwave irradiation
(MWI) in 91−98% yields.
6

Page 7 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
3
. Results and discussions
.1. Evaluation of antitubercular activity and SAR study
3
The 3,6-disubstituted triazolothiadiazoles 6a-h (72 compounds) were evaluated for their activity
against Mtb H37Rv, MDRTB and RDRTB using the BacT/ALERT 3D liquid culture
7
technology . The antitubercular activities of the compounds are indicated by MIC values. Results
are summarized in Table 1. Compounds were tested in 8.0 ꢀg/mL (MIC) for the preliminary
assessment of the activity against Mtb H37Rv. 54 compounds result inactive at 8.0 ꢀg/mL
concentration, whereas 17 compounds are found to inhibit the growth of Mtb H37Rv, MDRTB
and RDRTB at variable concentrations (Table 1). Some of the most representative compounds
are also tested toward Vero and HepG2 cells to ascertain the cytotoxicity profile. To further
analyze the biological profile of these compounds, in vitro Mt SD inhibitory assay has been
carried out as well. These modifications lead to a variable range of activities and allow us to
construct a plausible SAR as will be described below.
Selected 17 derivatives were tested for their ability to inhibit the growth of the acquired
clinical MDRTB and RDRTB strains from Jiangsu province hospital, China (Table 1). To our
delight, although these triazolothiadiazoles are less potent than positive control medicine INH
and RFP against H37Rv, maintain similar excellent activities against the susceptible M.
tuberculosis strain H37Rv in two tested drug-resistant strains.
As Table 1 shows, the substituents at both 3 and 6 positions have substantial effects on
antibacterial activity, but it is very clear that electron-donating group (the 4-methoxy group)
attached at para position and unsubstituted of the phenyl ring at the 3 position are detrimental to
the potency of compounds (6a-1−9, 6e-1−9). On the contrary, different electron-withdrawing
groups, i.e., fluoro, chloro and bromo groups, attached at para position of the phenyl ring at the 3
7

RSC Advances
Page 8 of 52
View Article Online
DOI: 10.1039/C5RA19334F
position exert a remarkable enhancement in potency (6b-5, 6b-7, 6c-2, 6c-4, 6c-7, 6c-8, d-2−6,
d-8, 6d-9), leading to the discovery of two highly active lead compounds 6d-4 and 6c-4 (MIC-
6
H37Rv = 0.5 ꢀg/mL), which are 16-fold more potent than 1. The nature of phenoxymethyl group
at the 6 position exhibits substantial effects on the potency. Bromo, chloro, fluoro, nitro and
methoxy groups in the para position of the benzene ring at the 6 position are well tolerated, and
6c-4 and 6d-4 bearing a bromo moiety possess high potency.
In the 3-(4-fluorophenyl) series of compounds (6b-1−9), the potency is very sensitive to the
substitution pattern of the 6-phenoxymethyl moiety. Thus, the compounds with 4-fluoro-, 4-
chloro-, 4-bromo-, 2,4-dichloro-, 3,4-butenyl-, 4-nitro- and 2-methyl-4-chlorophenoxymethyl
moieties at the 6 position do not show appreciable antitubercular activity (MIC > 8.0 ꢀg/mL).
3,4-butenylphenoxymethyl moiety shows only modest activities. Compound 6b-5 shows better
potency than the parent compound 1 (MIC-H37Rv = 0.5 ꢀg/mL; MIC- RDRTB = 0.5 ꢀg/mL),
which is approximately 2-fold more active than INH (MIC-RDRTB = 1.0 ꢀg/mL), the standard
first-line drug used against RDRTB.
In the 3-(4-chlorophenyl) series of compounds (6c-1−9), the potency of the compounds is also
sensitive to the substitution pattern of the 6-phenoxymethyl moiety. Nevertheless, 4-chloro-, 4-
methoxy-, 2,4-dichloro-, 2-methyl-4-chloro- and phenoxymethyl moieties decrease the potency.
Two compounds bearing 4-fluorophenoxymethyl and 3,4-butenylphenoxymethyl moieties
possess better activity than compound 1. Meanwhile, Two compounds bearing 4-
bromophenoxymethyl and 4-nitrophenoxymethyl moieties, 6c-4 (MIC-MDRTB = 4.0 ꢀg/mL)
and 6c-8 (MIC-MDRTB= 2.0 ꢀg/mL) exhibit good activity, which are approximately 4-fold and
8-fold more potent than RFP (MIC-MDRTB ≥ 16.0 ꢀg/mL), the standard first-line drug used
against MDRTB, respectively.
8

Page 9 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
In the 3-(4-bromophenyl) series of compounds (6d-1−9), almost all compounds (except 6d-1
and 6d-7) examined possess good to excellent antitubercular activities, wherein five compounds
have MIC less than 4.0 ꢀg/mL. The results clearly indicate that the introduction of the 4-
bromophenyl group to the 3 position is a breakthrough in this SAR study. Also, 4-bromo, 4-
chloro, 4-fluoro, 4-nitro, 4-methoxy, 2,4-dichloro and 2-methyl-4-chloro groups of the benzene
ring at the 6 position are found to be beneficial to increase the potency. The most potent
compounds in this series, at present, are 6d-3 and 6d-4 (MIC-MDRTB = 4.0 ꢀg/mL; MIC-
RDRTB = 0.5 ꢀg/mL), which are approximately 2-fold and 32-fold more potent than INH (MIC-
RDRTB = 1.0 ꢀg/mL) and RFP (MIC-RDRTB = 16.0 ꢀg/mL) against RDRTB, and 4-fold in
activity to RFP (MIC-MDRTB ≥ 16.0 ꢀg/mL) against MDRTB.
On the basis of these data, the next investigation is to introduce a methylene spacer between
carbon atom at the 3 position and the β-naphthalene ring. Quite surprisingly, small electron-
donating groups such as methoxy, or electron-withdrawing groups such as the chloro, bromo and
2
,4-dichloro of the benzene ring at the 6 position, fail to show any activity (MIC-H37Rv > 8.0
g/mL). However, compound 6f-8, bearing 4-nitrophenoxymethyl moiety at the 6 position, is
found to be the most active compound of the series (MIC-H37Rv = 0.5 ꢀg/mL; MIC-MDRTB =
.0 ꢀg/mL; MIC-RDRTB = 1.0 ꢀg/mL), which is comparable in activity to INH. Besides, 4-
ꢀ
4
fluorophenoxymethyl moiety is also tolerated.
Aiming to improve the water solubility by introduction of ionizable nitrogen groups, 6g-1−9
have been synthesized whereby the benzene ring at the 3 position is replaced with a pyridine
ring. Unfortunately, these modifications result in a dramatic attenuation of activity, compared to
the MIC value of compound 1. Further attempts to introduce fluoro attached at meta position of
the pyridine ring (6h-1−9). Fortunately, the modifications lead to the identification of two active
9

RSC Advances
Page 10 of 52
View Article Online
DOI: 10.1039/C5RA19334F
compounds in the series, 6h-1 (MIC-MDRTB = 2.0 ꢀg/mL; MIC-RDRTB = 2.0 ꢀg/mL) and 6h-
(MIC-MDRTB = 2.0 ꢀg/mL; MIC-RDRTB = 2.0 ꢀg/mL), which are approximately 2- to 16-
6
fold more than INH and RFP against MDRTB and RDRTB.
Assessment of the collocation of these data within the SAR is difficult, but we might speculate
that antitubercular activity of the newly synthesized heterocyclic compounds, containing 1,2,4-
triazole moiety fused with 1,3,4-thiadiazole ring depends on the substituents rather the basic
skeleton of the molecule.
3.2. In vitro Mt SD inhibitory activity
To confirm that this series of compounds actually target Mt SD, the 17 potent compounds were
selected for further evaluation of their in vitro Mt SD inhibitory activity (Table 1). As Table 1
shows, the potent derivatives, 6c-4, 6c-8 and 6d-4 display potential inhibitory activity on Mt SD
(
6c-4, Mt SD-IC = 6.82 ꢀg/mL; 6c-8, Mt SD-IC = 9.37 ꢀg/mL; 6d-4, Mt SD-IC = 14.42
5
0
50
50
ꢀ
g/mL), which demonstrates the extent of inhibitory effect on Mt SD correlates to the extent of
antitubercular activity.
.3. Cytotoxicity
3
Some of the potent derivatives synthesized were tested to assess their apparent cytotoxicity
toward Vero and HepG2 cells (Table 2). In general, the selectivity index (SI), that in this case is
the ratio between IC toward Vero or HepG2 cells and the MIC toward Mtb H37Rv, for a
5
0
compound to be considered a valuable lead has usually to be > 10. As Table 2 displays, we are
pleased to notice that most compounds are apparently not toxic (SI>10), while maintaining good
activity compared with the hit compound 1. Unfortunately, modifications of 6c-8 and 6d-9
leading to an enhancement of activity, also result in a counterproductive improvement of
cytotoxicity. Summarizing, the extended investigation around the SAR for these antitubercular
10

Page 11 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
triazolothiadiazoles, leads to the synthesis of more active compounds, moreover devoid of
apparent cytotoxicity. Thus, 6c-4 and 6d-4 have emerged as advanced lead compounds for
further preclinical drug development.
11

RSC Advances
Page 12 of 52
View Article Online
DOI: 10.1039/C5RA19334F
4. Conclusions
The extensive SAR study on triazolothiadiazoles for their antitubercular activities against Mtb
H37Rv strain was performed, building upon the identification of promising early lead
compounds 1 obtained from an high-throughput screening campaign. The purpose of this SAR
study was to optimize the aromatic or hetero-aromatic substituents at the 3 and 6 positions of the
lead compound 1 through systematic modifications. It has been found that the nature of the
substitute group on the para site of 3-phenyl exerts remarkable effects on the antitubercular
activity. For example, electron-donating (4-methoxy) and unsubstituted groups are detrimental to
the activity. On the contrary, halogen group at this position dramatically increases the potency.
This breakthrough finding in this SAR study has led to the discovery of 6c-4 and 6d-4 with
exceptional potency (MIC-H37Rv = 0.5 ꢀg/mL), which bear a p-bromophenoxymethyl group at
the 6 position and a p-chlorophenyl or a p-bromophenyl at the 3 position. Also, 15 other
compounds were found to possess comparable potencies (MIC-H37Rv ≤ 4.0 ꢀg/mL), including
6d-3 (MIC-H37Rv = 0.25 ꢀg/mL), bearing a p-chlorophenoxymethyl group at the 6 position and
a p-bromophenyl group at the 3 position. These advanced lead compounds do not show
appreciable cytotoxicity against Vero and HepG2 cells (SI > 10). The advanced leads 6c-4 and
6d-4 exhibit the similar potencies against drug-resistant Mtb clinical isolates, as anticipated.
Other important findings in this SAR study include the fact that unsubstituted pyridyl group at
the 3 position is detrimental to the antitubercular activity of this series of triazolothiadiazoles,
while 3-fluoropyridyl group is tolerated, although only unsubstituted and 2,4-
dichlorophenoxymethyl moieties at the 6 position are favorable. In vitro Mt SD inhibitory
activity by the most potent compounds, shows effective inhibition, which validates that Mt SD is
the target of these compounds. The observation strongly suggests that the advanced lead
12

Page 13 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
triazolothiadiazoles have a novel mechanism of action on the inhibition of Mt SD. Extensive
preclinical evaluations for the pharmacological properties of these advanced lead compounds as
well as in vivo efficacy evaluations are actively underway, and the results will be reported in due
course.
13

RSC Advances
Page 14 of 52
View Article Online
DOI: 10.1039/C5RA19334F
5. Experimental section
5.1. Methods and materials
1
13
Methods. H and C NMR spectra were measured on a Bruker or Varian 400 or 500 MHz NMR
spectrometer. Melting points were measured on a Mettler Toledo capillary melting point
apparatus and are uncorrected. TLC experiments were carried out on pre-coated silica gel plates
(F 254 Merck). APCI high-resolution mass spectra (HRMS) was recorded on an Autospec
Ultima-TOF spectrometer. MB/BacT ALERT 3D system, which includes a computerized
database management system. Carbon dioxide released into the medium by actively growing
mycobacteria is detected through a gas-permeable sensor containing a colorimetric indicator
TM
embedded at the bottom of culture vials. Ensprire enzyme-labelling measuring instrument
(Perkin Elmer) was used in vitro Mt SD inhibitory activity and cell cytotoxicity experiments.
Materials. Modified Middlebrook 7H9 broth, MB reconstituting fluid, and the buffers were
purchased from Biomerieux. RFP and INH were purchased from National Institute for Food and
Drug Control.
5.2. Synthetic procedure and analytical data of aryl or hetero-aryl acid hydrazides(3a-h)
Isonicotinohydrazide (3g). In 250 mL reaction flask, 1,1'-carbonyldiimidazole (10.27 g, 63.36
mmol) was added to a solution of isonicotinic acid (6.0 g, 48.74 mmol) in tetrahydrofuran (THF)
(60 mL). After stirring at room temperature for 3 h, upon completion of the reaction, the reaction
mixture was added dropwise to the hydrazine hydrate 80% (v/v) (9.15 g, 146.22 mmol) in 40 mL
THF over 3 h. The reaction mixture was stirred at room temperature overnight. After completion
of the reaction, solvent was evaporated in vacuum to give a pale yellow precipitate. The crude
product was recrystallized in ethanol to give isonicotinohydrazide (3g, 5.25 g, 79% yield) as a
14

Page 15 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
1
colorless solid: mp 173-174 ℃; H NMR (400 MHz, DMSO-d ) δ 10.11 (s, 1H), 8.71 (dd, J =
6
+
.4, 1.6 Hz, 2H), 7.74 (dd, J = 4.4, 1.6 Hz, 2H), 4.64 (s, 2H); MS (ESI) m/z 137 (M+1) .
4
The same procedure was followed for the synthesis of 3a−h.
1
White solid (95% yield); mp 128 – 129 °C; H NMR (400 MHz,
Benzohydrazide (3a)
.
DMSO-d ) δ 9.77 (s, 1H), 7.82 (d, J = 8.0 Hz, 2H), 7.50 (dd, J = 7.2, 2.0 Hz, 1H), 7.45 (m, 2H),
6
+
.44 (s, 2H); MS (ESI) m/z 137.2 (M+1) .
4
1
-Fluorobenzohydrazide (3b). White solid (93% yield); mp 157 – 158 °C; H NMR (500
4
MHz, DMSO-d ) δ 9.82 (s, 1H), 7.91 – 7.88 (m, 2H), 7.27 (m, 2H), 4.46 (s, 2H); MS (ESI) m/z
6
+
55.2 (M+1) .
1
1
-Chlorobenzohydrazide (3c). White solid (86% yield); mp 167 – 168 °C; H NMR (400
4
MHz, DMSO-d ) δ 9.85 (s, 1H), 7.84 (dd, J = 8.4, 1.2 Hz, 2H), 7.53 – 7.51 (m, 2H), 4.51 (s, 2H);
6
+
MS (ESI) m/z 171.1 (M+1) .
1
-Bromobenzohydrazide (3d). White solid (85% yield); mp 166 – 167 °C; H NMR (400
4
MHz, DMSO-d ) δ 9.86 (s, 1H), 7.77 (d, J = 8.8 Hz, 2H), 7.67 – 7.65 (m, 2H), 4.52 (s, 2H); MS
6
+
ESI) m/z 215.1 (M+1) .
(
1
-Methoxybenzohydrazide (3e). White solid (92% yield); mp 135 – 136 °C; H NMR (400
4
MHz, DMSO-d ) δ 9.61 (s, 1H), 7.80 (d, J = 8.0 Hz, 2H), 6.97 (d, J = 7.2 Hz, 2H), 4.38 (s, 2H),
6
+
.80 (s, 3H); MS (ESI) m/z 167.2 (M+1) .
3
1
-(Naphthalen-2-yl)acetohydrazide (3f). White solid (89% yield); mp 167 – 168 °C; H
2
NMR (400 MHz, DMSO-d ) δ 9.33 (s, 1H), 8.12 (d, J = 7.6 Hz, 1H), 7.96 – 7.86 (m, 1H), 7.81
6
15

RSC Advances
Page 16 of 52
View Article Online
DOI: 10.1039/C5RA19334F
(dd, J = 5.6, 2.8 Hz, 1H), 7.52 (m, 2H), 7.44 (dd, J = 6.4, 3.2 Hz, 2H), 4.23 (s, 2H), 3.84 (s, 2H);
+
MS (ESI) m/z 201.2 (M+1) .
1
-Fluoroisonicotinohydrazide (3h). White solid (91% yield); mp 152 – 153 °C; H NMR
3
(
400 MHz, DMSO-d ) δ 9.82 (s, 1H), 8.68 (s, 1H), 8.52 (d, J = 4.8 Hz, 1H), 7.55 (t, J = 5.2 Hz,
6
+
H), 4.64 (s, 2H); MS (ESI) m/z 156.2 (M+1) .
1
1
1
5.3. General method for the synthesis of potassium dithiocarbazinate 4a-g
Potassium hydroxide (0.15 mol) was dissolved in absolute ethanol (200 mL). To the above
solution, aryl or hetero-aryl acid hydrazide (0.1 mol) was added. To this, carbon disulfide (0.15
mol) was added in small portions with constant stirring. The reaction mixture was agitated
continuously for a period of 9-10 h. Then, it was diluted with anhydrous ether. The precipitated
potassium dithiocarbazinate was collected by filtration. The precipitate was further washed with
anhydrous ether (100 mL) and dried under vacuum. The potassiumsalt thus obtained was in
quantitative yield and was used in the next step without further purification.
5.4. Synthetic procedure and analytical data of 4-amino-5-substituted -3-mercapto-1,2,4-
triazoles (5a-h)
1
-Amino-5-phenyl-3-mercapto-1,2,4-triazole (5a) . A suspension of potassium
1
4
dithiocarbazinate of the aromatic esters 4a, (11.10 g, 44.33 mmol) in water (50 mL) and
hydrazine hydrate 80% (v/v) (5.55 g, 88.66 mmol) was refluxed for 6-7 h with constant stirring.
The color of the reaction mixture changed to green with the production of hydrogen sulfide gas
(lead acetate paper and odor). A homogenous reaction mixture was obtained during the reaction
process. The reaction mixture was cooled to room temperature and diluted with water. On
acidification with concentrated hydrochloric acid, the required triazole was precipitated. It was
16

Page 17 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
filtered, washed thoroughly with cold water, and recrystallized from ethanol to give 5a (5.25 g,
1
6
1
1
1% yield) as a colorless solid: mp 219 – 220 °C; H NMR (400 MHz, DMSO-d ) δ 13.93 (s,
6
H), 8.03 (dd, J = 5.2, 1.6 Hz, 2H), 7.54 (dd, J = 5.2, 1.6 Hz, 3H), 5.80 (s, 2H). MS (ESI) m/z
+
93.14 (M+1) .
The same procedure was followed for the synthesis of 5b−h.
4
-Amino-5-(4-fluorophenyl)-3-mercapto-1,2,4-triazole (5b). White solid (68% yield); mp
1
2
00 – 201 °C; H NMR (400 MHz, DMSO-d ) δ 9.79 (s, 1H), 7.89 (m, 2H), 7.28 (m, 2H), 4.57
6
+
s, 2H); MS (ESI) m/z 212.1 (M+1) .
(
4
-Amino-5-(4-chlorophenyl)-3-mercapto-1,2,4-triazole (5c). White solid (65% yield); mp
1
2
01 – 202 °C; H NMR (400 MHz, DMSO-d ) δ 14.00 (s, 1H), 8.08 (d, J = 8.4 Hz, 2H), 7.62 (d,
6
+
J = 8.4 Hz, 2H), 5.81 (s, 2H); MS (ESI) m/z 227.1 (M+1) .
4
-Amino-5-(4-bromophenyl)-3-mercapto-1,2,4-triazole (5d). White solid (60% yield); mp
1
2
04 – 205 °C; H NMR (400 MHz, DMSO-d ) δ 13.99 (s, 1H), 8.00 (d, J = 8.0 Hz, 2H), 7.76 (d,
6
+
J = 8.0 Hz, 2H), 5.79 (s, 2H); MS (ESI) m/z 271.1 (M+1) .
4
-Amino-5-(4-methoxyphenyl)-3-mercapto-1,2,4-triazole (5e). White solid (70% yield);
1
mp 185 – 186 °C; H NMR (400 MHz, DMSO-d ) δ 13.82 (s, 1H), 7.99 (d, J = 8.8 Hz, 2H), 7.08
6
+
d, J = 8.8 Hz, 2H), 5.77 (s, 2H), 3.83 (s, 3H); MS (ESI) m/z 223.13 (M+1) .
(
4
-Amino-5-(naphthalen-2-ylmethyl)-3-mercapto-1,2,4-triazole (5f). White solid (68%
1
yield); mp 206 – 207 °C; H NMR (400 MHz, DMSO-d ) δ 13.48 (s, 1H), 8.09 – 8.04 (m, 1H),
6
7.97 – 7.93 (m, 1H), 7.86 (d, J = 8.0 Hz, 1H), 7.57 – 7.51 (m, 2H), 7.46 (t, J = 7.2 Hz, 1H), 7.40
+
d, J = 6.4 Hz, 1H), 5.55 (s, 2H), 4.47 (s, 2H); MS (ESI) m/z 257.2 (M+1) .
(
17

RSC Advances
Page 18 of 52
View Article Online
DOI: 10.1039/C5RA19334F
4
-Amino-5-(pyridin-4-yl)-3-mercapto-1,2,4-triazole (5g). White solid (67% yield); mp 217
1
–
218 °C; H NMR (500 MHz, DMSO-d ) δ 14.17 (s, 1H), 8.76 (dd, J = 4.0, 1.5 Hz, 2H), 8.03
6
+
dd, J = 3.6, 1.2 Hz, 2H), 5.86 (s, 2H); MS (ESI) m/z 194.11 (M+1) .
(
4
-Amino-5-(3-fluoropyridin-4-yl)-3-mercapto-1,2,4-triazole (5h). White solid (61%
1
yield); mp 211 – 212 °C; H NMR (500 MHz, DMSO-d ) δ 14.23 (s, 1H), 8.82 (d, J = 2.0 Hz,
6
+
H), 8.64 (d, J = 5.0 Hz, 1H), 7.89 (t, J = 5.5 Hz, 1H), 5.70 (s, 2H); MS (ESI) m/z 212.1 (M+1) .
1
5
6
.5. Synthetic procedure and analytical data of 3,6-disubstituted triazolothiadiazoles (6a-h)
-(Phenoxymethyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6a-1). A mixture of 5a
(
0.10 g, 0.52 mmol), phenoxyacetic acid (0.10 g, 0.62 mmol), 4-dimethylaminopyridine (0.006 g,
.052 mmol), tetrabutyl ammonium bromide (0.05 g, 0.156 mmol) in phosphorus oxychloride
2.5 mL) was heated at 95℃ in the microwave for 25 min. After cooling, the mixture was
0
(
gradually poured onto crushed ice with stirring. The mixture was allowed to stand overnight,
separated solid was filtered, washed thoroughly with cold water, and dried. The crude product
was stirred in 5 mL ether for 2 h , filtered, washed thoroughly with ether, and dried to obtain 6a-
1
1
–
7
(0.15 g, 94% yield) as a white solid: mp 157 – 158 °C; H NMR (500 MHz, DMSO-d ) δ 8.25
6
8.20 (m, 2H), 7.62 (t, J = 7.0 Hz, 2H), 7.57 (t, J = 7.0 Hz, 1H), 7.37 (dd, J = 8.5, 7.5 Hz, 2H),
1
3
.14 (d, J = 8.0 Hz, 2H), 7.05 (t, J = 7.5 Hz, 1H), 5.64 (s, 2H); C NMR (101 MHz, DMSO-d )
6
δ 168.26, 157.06, 154.40, 145.29, 130.43, 129.81, 129.21, 125.84, 125.39, 122.16, 115.08, 64.85.
+
HRMS (APCI) m/z calcd. for C H N OSH : 309.0805. Found: 309.0811.
1
6
12
4
The same procedure was followed for the synthesis of 6a-2−9, 6b-1−9, 6c-1−9, 6d-1−9, 6e-1−9,
f-1−9, 6g-1−9, 6h-1−9.
6
18

Page 19 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
6
-((4-Fluorophenoxy)methyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6a-2).
1
White solid (96% yield); mp 176 – 177 °C; H NMR (500 MHz, DMSO-d ) δ 8.22 (d, J = 7.0
6
1
3
Hz, 2H), 7.62 (t, J = 7.0 Hz, 2H), 7.57 (m, J = 7.0 Hz, 1H), 7.23 – 7.15 (m, 4H), 5.62 (s, 2H); C
NMR (101 MHz, DMSO-d ) δ 168.00, 156.19, 154.41, 153.38, 145.29, 130.43, 129.21, 125.83,
6
+
25.38, 116.76, 116.67, 116.31, 116.08, 65.51. HRMS (APCI) m/z calcd. for C H FN OSH :
1
1
6
11
4
327.0710. Found: 327.0722.
6
-((4-Chlorophenoxy)methyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6a-3).
1
White solid (98% yield); mp 182 – 183 °C; H NMR (500 MHz, DMSO-d ) δ 8.24 – 8.19 (m,
6
2
2
1
H), 7.64 – 7.60 (m, 2H), 7.59 – 7.55 (m, 1H), 7.41 (dd, J = 7.0, 2.5 Hz, 2H), 7.18 (dd, J = 7.0,
1
3
.5 Hz, 2H), 5.65 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 167.71, 155.93, 154.42, 145.29,
6
30.43, 129.55, 129.20, 125.91, 125.83, 125.37, 116.97, 65.18. HRMS (APCI) m/z calcd. for
+
C H Cl N OSH : 343.0415. Found: 343.0413.
16
11
4
6
-((4-Bromophenoxy)methyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6a-4).
1
White solid (95% yield); mp 190 – 191 °C; H NMR (400 MHz, DMSO-d ) δ 8.22 (dd, J = 8.4,
6
1
5
1
3
.6 Hz, 2H), 7.65 – 7.56 (m, 3H), 7.54 (dd, J = 6.8, 2.4 Hz, 2H), 7.13 (dd, J = 6.8, 2.4 Hz, 2H),
1
3
.65 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 167.67, 156.38, 154.41, 145.29, 132.44, 130.43,
6
+
29.20, 125.83, 125.37, 117.46, 113.69, 65.11. HRMS (APCI) m/z calcd. for C H BrN OSH :
1
6
11
4
88.9890. Found: 388.9886.
6
-((4-Methoxyphenoxy)methyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6a-5).
1
White solid (92% yield); mp 170 – 171 °C; H NMR (500 MHz, DMSO-d ) δ 8.22 (dd, J = 8.5,
6
1.5 Hz, 2H), 7.64 – 7.60 (m, 2H), 7.59 – 7.55 (m, 1H), 7.08 (dd, J = 6.5, 2.0 Hz, 2H), 6.91 (dd, J
1
3
=
6.5, 2.0 Hz, 2H), 5.56 (s, 2H), 3.71 (s, 3H); C NMR (101 MHz, DMSO-d ) δ 169.03, 154.93,
6
19

RSC Advances
Page 20 of 52
View Article Online
DOI: 10.1039/C5RA19334F
154.84, 151.44, 145.73, 130.89, 129.67, 126.29, 125.84 , 116.78, 115.24, 66.02, 55.85. HRMS
+
APCI) m/z calcd. for C H N O SH : 339.0910. Found: 339.0907.
(
1
7
14
4
2
6
-((2,4-Dichlorophenoxy)methyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6a-6).
1
White solid (91% yield); mp 202 – 203 °C; H NMR (400 MHz, DMSO-d ) δ 8.22 (d, J = 6.8
6
1
3
Hz, 2H), 7.70 (d, J = 2.4 Hz, 1H), 7.64-7.55 (m, 3H), 7.458-7.40 (m, 2H), 5.76 (s, 2H); C NMR
(
101 MHz, DMSO-d ) δ 167.21, 154.42, 151.62, 145.29, 130.44, 129.63, 129.19, 128.35, 126.23,
6
+
25.82, 125.36, 122.83, 116.23, 66.02. HRMS (APCI) m/z calcd. for C H Cl N OSH :
1
1
6
10
2
4
377.0025. Found: 377.0025.
6
-((2-Naphthyloxy)methyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6a-7).
1
White solid (95% yield); mp 215 – 216 °C; H NMR (400 MHz, DMSO-d ) δ 8.24 (dd, J = 8.4,
6
1
7
1
1
.6 Hz, 2H), 7.95 – 7.83 (m, 3H), 7.66 – 7.57 (m, 4H), 7.53 – 7.48 (m, 1H), 7.44 – 7.39 (m, 1H),
1
3
.35 (dd, J = 8.8, 2.4 Hz, 2H), 5.77 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 168.01, 154.91,
6
45.30, 133.93, 130.44, 129.82, 129.22, 129.12, 127.65, 126.96, 126.75, 125.85, 125.41, 118.24,
+
08.32, 64.95. HRMS (APCI) m/z calcd. for C H N OSH : 359.0961. Found: 359.0956.
2
0
14
4
6
-((4-Nitrophenoxy)methyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6a-8).
1
White solid (95% yield); mp 216 – 217 °C; H NMR (500 MHz, DMSO-d ) δ 8.28 (dd, J = 7.0,
6
2.5 Hz, 2H), 8.24 – 8.19 (m, 2H), 7.64 – 7.60 (m, 2H), 7.59– 7.56 (m, 1H), 7.37 (dd, J = 7.0, 2.0
1
3
Hz, 2H), 5.81 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 166.69, 162.12, 154.53, 145.34,
6
141.95, 130.47, 129.21, 126.01, 125.85, 125.35, 115.75, 65.46. HRMS (APCI) m/z calcd. for
+
C H N O SH : 354.0655. Found: 354.0654.
16
11
5
3
6
-((2-Methyl-4-chlorophenoxy)methyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6a-9). White solid (93% yield); mp 197 – 198 °C; H NMR (500 MHz, DMSO-d ) δ 8.25 – 8.20
6
20

Page 21 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
(m, 2H), 7.64 – 7.60 (m, 2H), 7.59 – 7.55 (m, 1H), 7.32 (d, J = 2.5 Hz, 1H), 7.26 (dd, J = 9.0, 2.5
1
3
Hz, 1H), 7.17 (d, J = 9.0 Hz, 1H), 5.65 (s, 2H), 2.26 (s, 3H); C NMR (101 MHz, DMSO-d ) δ
6
1
1
3
68.20, 154.35, 154.07, 145.29, 130.45, 130.34, 129.22, 128.73, 126.68, 125.84, 125.44, 125.39,
+
13.96, 65.28, 15.73. HRMS (APCI) m/z calcd. for C H ClN OSH : 357.0571. Found:
1
7
13
4
57.0561.
3
-(4-Fluorophenyl)-6-(phenoxymethyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6b-1).
1
White solid (97% yield); mp 183 – 184 °C; H NMR (400 MHz, DMSO-d ) δ 8.26 (dd, J = 8.8,
6
5
7
1
.6 Hz, 2H), 7.48 (t, J = 8.8 Hz, 2H), 7.36 (dd, J = 8.8, 7.6 Hz, 2H), 7.14 (d, J = 8.0 Hz, 2H),
1
3
.05 (t, J = 7.2 Hz, 1H), 5.63 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 168.34, 164.35, 161.88,
6
57.03, 154.34, 144.53, 129.78, 128.32, 128.23, 122.15, 116.49, 116.27, 115.07, 64.83. HRMS
+
APCI) m/z calcd. for C H FN OSH : 327.0710. Found: 327.0696.
(
1
6
11
4
6
-((4-Fluorophenoxy)methyl)-3-(4-fluorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6b-2). White solid (95% yield); mp 188 – 189 °C; H NMR (400 MHz, DMSO-d ) δ 8.26 (dd, J
6
=
8.8, 5.2 Hz, 2H), 7.48 (t, J = 9.2 Hz, 2H), 7.20-7.17(m, 4H), 5.62 (s, 2H). HRMS (APCI) m/z
+
calcd. for C H F N OSH : 345.0616. Found: 345.0630.
1
6
10
2
4
6
-((4-Chlorophenoxy)methyl)-3-(4-fluorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6b-3). White solid (97% yield); mp 183 – 184 °C; H NMR (500 MHz, DMSO-d ) δ 8.25 (dd, J
6
=
9.0, 5.5 Hz, 2H), 7.50-7.44 (m, 2H), 7.41 (dd, J = 6.5, 2.0 Hz, 2H), 7.17 (dd, J = 7.0, 2.5 Hz,
1
3
2
H), 5.64 (s, 2H); C NMR (126 MHz, DMSO-d ) δ 167.83, 155.90, 154.37, 144.53, 129.54,
6
128.26, 125.92, 122.03, 116.95, 116.47, 116.29, 65.17. HRMS (APCI) m/z calcd. for
+
C H ClFN OSH : 361.0321. Found: 361.0322.
16
10
4
21

RSC Advances
Page 22 of 52
View Article Online
DOI: 10.1039/C5RA19334F
6
-((4-Bromophenoxy)methyl)-3-(4-fluorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6b-4). White solid (96% yield); mp 179 – 180 °C; H NMR (500 MHz, DMSO-d ) δ 8.26 (dd, J
6
=
8.5, 5.5 Hz, 2H), 7.53 (d, J = 9.0 Hz, 2H), 7.48 (t, J = 8.5 Hz, 2H), 7.12 (d, J = 9.0 Hz, 2H),
1
3
5
.64 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 167.80, 161.88, 156.37, 140.81, 132.45, 128.30,
6
122.05, 117.47, 116.51, 116.29, 113.71, 65.10. HRMS (APCI) m/z calcd. for
+
C H BrFN OSH : 406.9796. Found: 406.9791.
16
10
4
3
-(4-Fluorophenyl)-6-((4-methoxyphenoxy)methyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6b-5). White solid (95% yield); mp 201 – 202 °C; H NMR (400 MHz,
DMSO-d ) δ 8.26 (dd, J = 8.8,5.6 Hz, 2H), 7.48 (d, J = 8.8 Hz, 2H), 7.08 (d, J = 8.8 Hz, 2H),
6
6.91 (d, J = 9.2 Hz, 2H), 5.56 (s, 2H), 3.71 (s, 3H). HRMS (APCI) m/z calcd. for C H FN O S
17 13 4 2
+
H : 357.0816. Found: 357.0823.
6
-((2,4-Dichlorophenoxy)methyl)-3-(4-fluorophenyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6b-6). White solid (93% yield); mp 186 – 187 °C; H NMR (500 MHz,
DMSO-d ) δ 8.25 (dd, J = 9.0, 5.5 Hz, 2H), 7.69 (d, J = 2.5 Hz, 1H), 7.50 – 7.44 (m, 3H), 7.41
6
+
d, J = 8.5 Hz, 1H), 5.75 (s, 2H). HRMS (APCI) m/z calcd. for C H Cl FN OSH : 394.9931.
(
1
6
9
2
4
Found: 394.9933.
3
-(4-Fluorophenyl)-6-((2-naphthyloxy)methyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6b-7). White solid (96% yield); mp 226 – 227 °C; H NMR (400 MHz, DMSO-d ) δ 8.31 – 8.25
6
(m, 2H), 7.94 – 7.82 (m, 3H), 7.59 (d, J = 2.4 Hz, 1H), 7.53 – 7.46 (m, 3H), 7.43 – 7.38 (m, 1H),
+
.35 (dd, J = 9.2, 2.8 Hz, 1H), 5.76 (s, 2H). HRMS (APCI) m/z calcd. for C H FN OSH :
7
20
13
4
377.0867. Found: 377.0863.
22

Page 23 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
3
-(4-Fluorophenyl)-6-((4-nitrophenoxy)methyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6b-8). White solid (94% yield); mp 212 – 213 °C; H NMR (400 MHz, DMSO-d ) δ 8.30 – 8.24
6
1
m, 4H), 7.51 – 7.45 (m, 2H), 7.36 (dd, J = 7.2, 2.4 Hz, 2H), 5.81 (s, 2H); C NMR (101 MHz,
3
(
DMSO-d ) δ 166.80, 162.09, 154.49, 144.60, 141.96, 128.31, 126.00, 122.04, 116.52, 116.30,
6
+
15.75, 65.44. HRMS (APCI) m/z calcd. for C H FN O SH : 372.0561. Found: 372.0548.
1
1
6
10
5
3
3
-(4-Fluorophenyl)-6-((2-methyl-4-chlorophenoxy)methyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6b-9). White solid (95% yield); mp 178 – 179 °C; H NMR (400 MHz,
DMSO-d ) δ 8.26 (dd, J = 8.8, 5.2 Hz, 2H), 7.49 (t, J = 8.8 Hz, 2H), 7.32 (d, J = 2.0 Hz, 1H),
6
1
.26 (dd, J = 8.8, 2.4 Hz, 1H), 7.17 (d, J = 8.8 Hz, 1H), 5.64 (s, 2H), 2.26 (s, 3H); C NMR (101
3
7
MHz, DMSO-d ) δ 168.30, 154.05, 144.55, 130.33, 128.72, 128.32, 128.24, 126.65, 125.45,
6
+
1
22.06, 116.51, 116.28, 113.96, 65.26, 15.70 . HRMS (APCI) m/z calcd. for C H ClFN OSH :
17 12 4
375.0477. Found: 375.0465.
3
-(4-Chlorophenyl)-6-(phenoxymethyl)-1,2,4-triazolo[3,4-b][1,3,4]thiadiazole (6c-1).
1
White solid (96% yield); mp 191 – 192 °C; H NMR (500 MHz, DMSO-d ) δ 8.23 (dd, J = 7.0,
6
2
7
1
.0 Hz, 2H), 7.71 (dd, J = 6.5, 2.0 Hz, 2H), 7.39 – 7.34 (m, 2H), 7.14 (dd, J = 8.5, 0.5 Hz, 2H),
1
3
.05 (t, J = 2.0 Hz, 1H), 5.63 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 168.55, 157.04, 154.62,
6
44.41, 135.03, 129.80, 129.38, 127.47, 124.27, 122.17, 115.07, 64.82. HRMS (APCI) m/z
+
calcd. for C H Cl N OSH : 343.0415. Found: 343.0422.
1
6
11
4
3
-(4-Chlorophenyl)-6-((4-fluorophenoxy)methyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6c-2). White solid (96% yield); mp 227 – 228 °C; H NMR (400 MHz, DMSO-d ) δ 8.23 (d, J =
6
1
.4 Hz, 2H), 7.71 (d, J = 8.8 Hz, 2H), 7.23 – 7.13 (m, 4H), 5.62 (s, 2H); C NMR (101 MHz,
3
8
23

RSC Advances
Page 24 of 52
View Article Online
DOI: 10.1039/C5RA19334F
DMSO-d ) δ 168.28, 154.63, 153.38, 144.42, 135.03, 129.38, 127.47, 124.26, 116.72, 116.30,
6
+
16.07, 65.50. HRMS (APCI) m/z calcd. for C H ClFN OSH : 361.0321. Found: 361.0326.
1
1
6
10
4
6
-((4-Chlorophenoxy)methyl)-3-(4-chlorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6c-3). White solid (97% yield); mp 181 – 182 °C; H NMR (500 MHz, DMSO-d ) δ 8.22 (dd, J
6
=
6.5, 2.0 Hz, 2H), 7.71 (dd, J = 6.5, 2.0 Hz, 2H), 7.41 (dd, J = 7.0, 2.5 Hz, 2H), 7.17 (dd, J =
1
3
6
.5, 2.0 Hz, 2H), 5.64 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 168.02, 155.92, 154.66,
6
144.44, 135.05, 129.56, 129.39, 127.49, 125.93, 124.26, 116.98, 65.18. HRMS (APCI) m/z
+
calcd. for C H Cl N OSH : 377.0025. Found: 377.0018.
1
6
10
2
4
6
-((4-Bromophenoxy)methyl)-3-(4-chlorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6c-4). White solid (98% yield); mp 181 – 182 °C; H NMR (400 MHz, DMSO-d ) δ 8.23 (d, J =
6
8
6
1
.4 Hz, 2H), 7.71 (d, J = 8.4 Hz, 2H), 7.57 – 7.50 (dd, J = 7.2, 2.0 Hz, 2H), 7.15 – 7.10 (dd, J =
1
3
.8, 2.0 Hz, 2H), 5.64 (s, 2H); C NMR (126 MHz, DMSO-d ) δ 167.98, 156.36, 154.64,
6
44.40, 135.04, 132.45, 129.37, 127.44, 124.23, 117.44, 113.73, 65.08. HRMS (APCI) m/z
+
calcd. for C H BrClN OSH : 422.9498. Found: 422.9480.
1
6
10
4
3
-(4-Chlorophenyl)-6-((4-methoxyphenoxy)methyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6c-5). White solid (96% yield); mp 146 – 147 °C; H NMR (400 MHz,
DMSO-d ) δ 8.23 (dd, J = 6.4, 1.6 Hz, 2H), 7.70 (dd, J = 8.4, 1.6 Hz, 2H), 7.08 (dd, J = 6.8, 2.4
6
1
Hz, 2H), 6.91 (dd, J = 7.2, 2.4 Hz, 2H), 5.56 (s, 2H), 3.71 (s, 3H); C NMR (101 MHz, DMSO-
3
d6) δ 168.84, 154.59, 154.48, 150.98, 144.39, 135.01, 129.36, 127.46, 124.25, 116.32, 114.78,
+
5.56, 55.39. HRMS (APCI) m/z calcd. for C H ClN O SH : 373.0521. Found: 373.0527.
6
1
7
13
4
2
3
-(4-Chlorophenyl)-6-((2,4-dichlorophenoxy)methyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6c-6). White solid (95% yield); mp 208 – 209 °C; H NMR (400 MHz,
24

Page 25 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
DMSO-d ) δ 8.22 (dd, J = 6.4, 1.6 Hz, 2H), 7.72 – 7.69 (m, 3H), 7.46 (dd, J = 8.8, 2.4 Hz, 1H),
6
1
3
7
.41 (d, J = 8.8 Hz, 1H), 5.75 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 167.49, 154.63, 151.60,
6
144.42, 135.04, 129.61, 129.36, 128.33, 127.45, 126.24, 124.23, 122.82, 116.23, 66.00. HRMS
+
APCI) m/z calcd. for C H Cl N OSH : 412.9607. Found: 412.9589.
(
1
6
9
3
4
3
-(4-Chlorophenyl)-6-((2-naphthyloxy)methyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6c-7). White solid (96% yield); mp 190 – 191 °C; H NMR (400 MHz, DMSO-d ) δ 8.25 (dd, J
6
=
6.8, 2.0 Hz, 2H), 7.94 – 7.82 (m, 3H), 7.71 (dd, J = 6.8, 2.0 Hz, 2H), 7.59 (d, J = 2.8 Hz, 1H),
1
.53 – 7.48 (m, 1H), 7.44 – 7.39 (m, 1H), 7.35 (dd, J = 9.2, 2.8 Hz, 1H), 5.77 (s, 2H); C NMR
3
7
(
101 MHz, DMSO-d ) δ 168.26, 154.88, 154.63, 144.41, 135.02, 133.91, 129.79, 129.35, 129.11,
6
127.62, 127.46, 126.94, 126.71, 124.34, 124.26, 118.19, 108.32, 64.93. HRMS (APCI) m/z
+
calcd. for C H ClN OSH : 393.0571. Found: 393.0556.
2
0
13
4
3
-(4-Chlorophenyl)-6-((4-nitrophenoxy)methyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6c-8). White solid (95% yield); mp 201 – 202 °C; H NMR (400 MHz, DMSO-d ) δ 8.28 (dd, J
6
=
7.2, 2.4 Hz, 2H), 8.23 (dd, J = 6.8, 2.0 Hz, 2H), 7.71 (dd, J = 6.8, 2.0 Hz, 2H), 7.36 (dd, J =
1
3
6
.8, 2.0 Hz, 2H), 5.81 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 166.97, 162.09, 154.75,
6
144.48, 141.96, 135.07, 129.40, 127.50, 126.00, 124.24, 115.75, 65.44. HRMS (APCI) m/z
+
calcd. for C H ClN O SH : 388.0265. Found: 388.0266.
1
6
10
5
3
3
-(4-Chlorophenyl)-6-((2-methyl-4-chlorophenoxy)methyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6c-9). White solid (93% yield); mp 202 – 203 °C; H NMR (400 MHz,
DMSO-d ) δ 8.23 (d, J = 8.8 Hz, 2H), 7.71 (d, J = 8.4 Hz, 2H), 7.32 (d, J = 2.0 Hz, 1H), 7.26
6
1
dd, J = 8.8, 2.8 Hz, 1H), 7.17 (d, J = 8.8 Hz, 1H), 5.65 (s, 2H), 2.26 (s, 3H); C NMR (101
3
(
MHz, DMSO-d ) δ 168.47, 154.55, 154.04, 144.41, 135.03, 130.32, 129.37, 128.71, 127.46,
6
25

RSC Advances
Page 26 of 52
View Article Online
DOI: 10.1039/C5RA19334F
+
26.65, 125.45, 124.25, 113.96, 65.25, 15.69. HRMS (APCI) m/z calcd. for C H Cl N OSH :
1
1
7
12
2
4
391.0182. Found: 391.0173.
3
-(4-Bromophenyl)-6-(phenoxymethyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6d-1).
1
White solid (96% yield); mp 191 – 192 °C; H NMR (400 MHz, DMSO-d ) δ 8.16 (dd, J = 6.8,
6
2
7
1
.0 Hz, 2H), 7.85 (dd, J = 6.8, 2.0 Hz, 2H), 7.37 (dd, J = 8.8, 7.6 Hz, 2H), 7.15 – 7.13 (m, 2H),
1
3
.08 – 7.03 (m, 1H), 5.64 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 168.58, 157.05, 154.67,
6
44.51, 132.30, 129.81, 127.65, 124.62, 123.82, 122.17, 115.08, 64.83. HRMS (APCI) m/z
+
calcd. for C H BrN OSH : 388.9890. Found: 388.9899.
1
6
11
4
3
-(4-Bromophenyl)-6-((4-fluorophenoxy)methyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6d-2). White solid (95% yield); mp 222 – 223 °C; H NMR (400 MHz, DMSO-d ) δ 8.16 (d, J
6
1
3
8.8 Hz, 2H), 7.84 (d, J = 8.4 Hz, 2H), 7.22 – 7.15 (m, 4H), 5.62 (s, 2H); C NMR (101 MHz,
=
DMSO-d ) δ 168.77, 155.13, 153.83, 144.96, 132.75, 128.09, 125.05, 124.27, 117.16, 116.76,
6
+
16.53, 65.95. HRMS (APCI) m/z calcd. for C H BrFN OSH : 406.9796. Found: 406.9788.
1
1
6
10
4
3
-(4-Bromophenyl)-6-((4-chlorophenoxy)methyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6d-3). White solid (97% yield); mp 204 – 205 °C; H NMR (400 MHz, DMSO-d ) δ 8.15 (dd, J
6
=
6.8, 1.6 Hz, 2H), 7.84 (dd, J = 6.8, 1.6 Hz, 2H), 7.41 (dd, J = 6.8, 2.0 Hz, 2H), 7.17 (dd, J =
1
3
6
.8, 2.4 Hz, 2H), 5.65 (s, 2H); C NMR (101 MHz, DMSO-d ) δ 168.03, 155.92, 154.68,
6
144.52, 132.30, 129.55, 127.65, 125.93, 124.60, 123.83, 116.98, 65.17. HRMS (APCI) m/z
+
calcd. for C H BrClN OSH : 422.9498. Found: 422.9494.
1
6
10
4
6
-((4-Bromophenoxy)methyl)-3-(4-bromophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6d-4). White solid (98% yield); mp 176 – 177 °C; H NMR (400 MHz, DMSO-d ) δ 8.15 (dd, J
6
=
6.4, 1.6 Hz, 2H), 7.84 (dd, J = 6.8, 2.0 Hz, 2H), 7.53 (dd, J = 6.8, 2.4 Hz, 2H), 7.13 (dd, J =
26

Page 27 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
1
3
6
.8, 2.0 Hz, 2H), 5.64 (s, 2H); C NMR (126 MHz, DMSO-d )) δ 168.00, 156.35, 154.68,
6
144.48, 132.45, 132.27, 127.59, 124.56, 123.83, 117.44, 113.73, 65.08. HRMS (APCI) m/z
+
calcd. for C H Br N OSH : 466.8995. Found: 466.8998.
1
6
10
2
4
3
-(4-Bromophenyl)-6-((4-methoxyphenoxy)methyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6d-5). White solid (96% yield); mp 162 – 163 °C; H NMR (400 MHz,
DMSO-d ) δ 8.16 (dd, J = 6.8, 2.0 Hz, 2H), 7.84 (dd, J = 6.8, 2.0 Hz, 2H), 7.08 (dd, J = 6.8, 2.0
6
1
Hz, 2H), 6.91 (dd, J = 6.8, 2.4 Hz, 2H), 5.56 (s, 2H), 3.71 (s, 3H); C NMR (101 MHz, DMSO-
3
d6) δ 168.90, 154.66, 154.48, 150.98, 144.49, 132.30, 127.64, 124.61, 123.82, 116.33, 114.79,
+
5.56, 55.41. HRMS (APCI) m/z calcd. for C H BrN O SH : 418.9996. Found: 418.9980.
6
1
7
13
4
2
3
-(4-Bromophenyl)-6-((2,4-dichlorophenoxy)methyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6d-6). White solid (95% yield); mp 208 – 209 °C; H NMR (400 MHz,
DMSO-d ) δ 8.15 (d, J = 8.8 Hz, 2H), 7.84 (d, J = 8.8 Hz, 2H), 7.69 (d, J = 2.4 Hz, 1H), 7.46
6
1
dd, J = 8.8, 2.4 Hz, 1H), 7.41 (d, J = 8.8 Hz, 1H), 5.75 (s, 2H); C NMR (101 MHz, DMSO-d )
3
(
6
δ 167.51, 154.67, 151.60, 144.51, 132.27, 129.62, 128.33, 127.61, 126.24, 124.57, 123.82,
+
22.82, 116.23, 66.00. HRMS (APCI) m/z calcd. for C H BrCl N OSH : 456.9101. Found:
1
1
6
9
2
4
456.9108.
3
-(4-Bromophenyl)-6-((2-naphthyloxy)methyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6d-7). White solid (97% yield); mp 185 – 186 °C; H NMR (400 MHz, DMSO-d ) δ 8.18 (dd, J
6
=
6.8, 2.0 Hz, 2H), 7.91 (dd, J = 15.6, 8.8 Hz, 2H), 7.87 – 7.82 (m, 3H), 7.59 (d, J = 2.8 Hz, 1H),
7.53 – 7.48 (m, 1H), 7.43 – 7.39 (m, 1H), 7.35 (dd, J = 8.8, 2.4 Hz, 1H), 5.77 (s, 2H). HRMS
+
APCI) m/z calcd. for C H BrN OSH : 439.0047. Found: 439.0044.
(
2
0
13
4
27

RSC Advances
Page 28 of 52
View Article Online
DOI: 10.1039/C5RA19334F
3
-(4-Bromophenyl)-6-((4-nitrophenoxy)methyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
1
(
6d-8). White solid (93% yield); mp 210 – 211 °C; H NMR (400 MHz, DMSO-d ) δ 8.28 (d, J
6
=
9.2 Hz, 2H), 8.15 (d, J = 8.4 Hz, 2H), 7.84 (d, J = 8.4 Hz, 2H), 7.36 (d, J = 9.2 Hz, 2H), 5.81
1
3
(
s, 2H); C NMR (101 MHz, DMSO-d ) δ 166.98, 162.08, 154.78, 144.55, 141.95, 132.30,
6
+
1
27.65, 125.99, 124.57, 123.85, 115.74, 65.43. HRMS (APCI) m/z calcd. for C H BrN O SH :
16 10 5 3
433.9741. Found: 433.9736.
3
-(4-Bromophenyl)-6-((2-methyl-4-chlorophenoxy)methyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6d-9). White solid (95% yield); mp 202 – 203 °C; H NMR (400 MHz,
DMSO-d ) δ 8.16 (dd, J = 6.8, 2.0 Hz, 2H), 7.85 (dd, J = 6.8, 2.0 Hz, 2H), 7.32 (d, J = 2.8 Hz,
6
1
3
H), 7.26 (dd, J = 8.8, 2.4 Hz, 1H), 7.17 (d, J = 8.8 Hz, 1H), 5.65 (s, 2H), 2.26 (s, 3H); C NMR
1
(
101 MHz, DMSO-d ) δ 168.52, 154.61, 154.05, 132.30, 130.34, 128.72, 127.64, 126.66, 125.45,
6
+
24.61, 123.83, 113.96, 65.26, 15.72. HRMS (APCI) m/z calcd. for C H BrClN OSH :
1
1
7
12
4
436.9654. Found: 436.9647.
3
-(4-Methoxyphenyl)-6-(phenoxymethyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole (6e-1).
1
White solid (95% yield); mp 127 – 128 °C; H NMR (400 MHz, DMSO-d ) δ 8.15 (d, J = 8.8
6
Hz, 2H), 7.37 (t, J = 8.4 Hz, 2H), 7.16 (dd, J = 14, 8.8 Hz, 4H), 7.05 (t, J = 7.6 Hz, 1H), 5.62 (s,
1
3
2
H), 3.85 (s, 3H); C NMR (126 MHz, DMSO-d ) δ 167.96, 160.83, 157.05, 153.78, 145.22,
6
129.81, 127.50, 122.15, 117.74, 115.06, 114.60, 64.84, 55.43. HRMS (APCI) m/z calcd. for
+
C H N O SH : 339.0910. Found: 339.0894.
17
14
4
2
6
-((4-Fluorophenoxy)methyl)-3-(4-methoxyphenyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6e-2). White solid (96% yield); mp 151 – 152 °C; H NMR (400 MHz,
1
3
DMSO-d ) δ 8.15 (dd, J = 6.8, 2.0 Hz, 2H), 7.23 – 7.14 (m, 6H), 5.61 (s, 2H), 3.85 (s, 3H); C
6
28

Page 29 of 52
RSC Advances
View Article Online
DOI: 10.1039/C5RA19334F
NMR (126 MHz, DMSO-d ) δ 167.65, 160.80, 158.32, 156.43, 153.77, 153.39, 145.22, 127.47,
6
117.77, 116.66, 116.28, 116.10, 114.58, 65.50, 55.40. HRMS (APCI) m/z calcd. for
+
C H FN O SH : 357.0816. Found: 357.0811.
17
13
4
2
6
-((4-Chlorophenoxy)methyl)-3-(4-methoxyphenyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6e-3). White solid (94% yield); mp 149 – 150 °C; H NMR (500 MHz,
DMSO-d ) δ 8.14 (dd, J = 7.0, 2.5 Hz, 2H), 7.41 (dd, J = 6.5, 2.0 Hz, 2H), 7.17 (dd, J = 7.0, 5.0
6
1
3
Hz, 4H), 5.63 (s, 2H), 3.85 (s, 3H). C NMR (101 MHz, DMSO-d ) δ 167.40, 160.84, 155.93,
6
153.80, 145.25, 129.55, 127.52, 125.90, 117.78, 116.97, 114.64, 65.20, 55.43. HRMS (APCI)
+
m/z calcd. for C H Cl N O SH : 373.0521. Found: 373.0520.
1
7
13
4
2
6
-((4-Bromophenoxy)methyl)-3-(4-methoxyphenyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6e-4). White solid (96% yield); mp 150 – 151 °C; H NMR (400 MHz,
DMSO-d ) δ 8.15 (dd, J = 7.2, 2.4 Hz, 2H), 7.54 (dd, J = 6.8, 2.4 Hz, 2H), 7.18 (dd, J = 7.2, 2.4
6
1
Hz, 2H), 7.12 (dd, J = 6.8, 2.0 Hz, 2H), 5.64 (s, 2H), 3.85 (s, 3H); C NMR (101 MHz, DMSO-
3
d6) δ 167.38, 160.85, 156.40, 147.70, 145.25, 132.45, 127.53, 117.78, 117.47, 114.65, 113.70,
+
5.12 , 55.44. HRMS (APCI) m/z calcd. for C H BrN O SH : 418.9996. Found: 418.9994.
6
1
7
13
4
2
6
-((4-Methoxyphenoxy)methyl)-3-(4-methoxyphenyl)-[1,2,4]triazolo[3,4-
1
b][1,3,4]thiadiazole (6e-5). White solid (93% yield); mp 141 – 142 °C; H NMR (500 MHz,
DMSO-d ) δ 8.15 (dd, J = 7.0, 2.0 Hz, 2H), 7.17 (dd, J = 7.0, 2.0 Hz, 2H), 7.08 (dd, J = 6.5, 2.0
6
1
Hz, 2H), 6.91 (dd, J = 6.5, 2.5 Hz, 2H), 5.55 (s, 2H), 3.85 (s, 3H), 3.71 (s, 3H); C NMR (101
3
MHz, DMSO-d ) δ 168.24, 160.83, 154.47, 153.77, 150.99, 145.23, 127.51, 117.83, 116.33,
6
+
14.79, 114.65, 65.58, 55.43, 55.40. HRMS (APCI) m/z calcd. for C H N O SH : 369.1016.
1
1
8
16
4
3
Found: 369.1003.
29