Safe and easy route for the synthesis of 1,3-dimethyl-1,2,3-triazolium salt and investigation of its anticancer activities

Article abstract of DOI:10.1016/j.bmcl.2013.08.078

We have developed a new safe and easy route for the synthesis of 1,3-dimethyl-1,2,3-triazolium derivatives. We have reported the synthesis of 4,9-dioxo-1,3-dimethylnaphtho[2,3-d][1,2,3]triazol-3-ium chloride from methylation of 1-methyl-1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione. The synthesis of 1-methyl-1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione is inefficient as a significant amount of by-product is formed that is difficult to separate and also unsafe as it requires the use of hazardous methylazide as a starting material. It is, however, important to develop an improved method for the synthesis of 4,9-dioxo-1,3-dimethylnaphtho[2,3-d][1,2,3]triazol-3-ium salt due to its significant anticancer activities. Herein, we report a safe and convenient route for the synthesis of this compound, which lead to more detailed exploration of its profound anticancer activities. The improved method can be applicable for the synthesis of other 1,3-dimethyl-1,2,3-triazolium salts of interest without the use of potentially explosive methylazide. The compound synthesized in this new method shows significant anticancer activities against melanoma, colon cancer, non-small cell lung cancer and central nervous system (CNS) cancer with GI50 values ranging from low μM to nM.

Full text of DOI:10.1016/j.bmcl.2013.08.078

Bioorganic & Medicinal Chemistry Letters 23 (2013) 5909–5911
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Safe and easy route for the synthesis of 1,3-dimethyl-1,2,3-triazolium
salt and investigation of its anticancer activities
⇑
Jaya P. Shrestha, Cheng-Wei Tom Chang
Department of Chemistry and Biochemistry, Utah State University, 0300 Old Main Hill, Logan, UT 84322-0300, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
We have developed a new safe and easy route for the synthesis of 1,3-dimethyl-1,2,3-triazolium deriva-
tives. We have reported the synthesis of 4,9-dioxo-1,3-dimethylnaphtho[2,3-d][1,2,3]triazol-3-ium chlo-
ride from methylation of 1-methyl-1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione. The synthesis of
1-methyl-1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione is inefficient as a significant amount of by-product
is formed that is difficult to separate and also unsafe as it requires the use of hazardous methylazide as a
starting material. It is, however, important to develop an improved method for the synthesis of 4,9-dioxo-
1,3-dimethylnaphtho[2,3-d][1,2,3]triazol-3-ium salt due to its significant anticancer activities. Herein,
we report a safe and convenient route for the synthesis of this compound, which lead to more detailed
exploration of its profound anticancer activities. The improved method can be applicable for the synthesis
of other 1,3-dimethyl-1,2,3-triazolium salts of interest without the use of potentially explosive methylaz-
ide. The compound synthesized in this new method shows significant anticancer activities against mel-
anoma, colon cancer, non-small cell lung cancer and central nervous system (CNS) cancer with GI50
Received 25 July 2013
Revised 16 August 2013
Accepted 19 August 2013
Available online 26 August 2013
Keywords:
Cancers
Chemotherapeutics
Cationic anthraquinones
Triazoles
Methylazide
values ranging from low lM to nM.
Ó 2013 Elsevier Ltd. All rights reserved.
1,3-Dipolar cycloaddition of azides, for example in the case of
‘Click’ chemistry, has attracted great interest due to its potential
X
R
R = Alkyl Chain
X = Cl, Br
2
applications in various areas.1 This reaction is typically carried
out by reacting alkynes with azides leading to the formation of
1,2,3-triazoles.2 In a similar fashion, we have reported the synthe-
sis of 1-alkyl-1H-naphtho[2,3-d][1,2,3]triazole-4,9-diones, 4 via a
tandem cycloaddition/oxidation of 1,4-naphthoquinone, 1 and al-
kyl azides, 3 (Scheme 1).3,4 Further alkylation of the cycloaddi-
tion/oxidation adducts using alkyl triflate, 5 forms the 4,9-dioxo-
1,3-dialkylnaphtho[2,3-d][1,2,3]triazol-3-ium salts, 6 which can
be viewed as cationic anthraquinone analogs.5,6 Several of the cat-
ionic anthraquinone analogs exert interesting biological activities
ranging from antibacterial, antifungal to anticancer. With the
exception of methylazide and ethylazide, the alkyl azides em-
ployed for this synthesis were prepared from a nucleophilic substi-
tution of sodium azide and the corresponding alkyl halides, 2. Since
small organic azides are known to be explosive, we used methyl
and ethyl 1-bromoacetate as the surrogate of methyl or ethyl
halides.4 This method is, however, inefficient which offers only
modest yields and hard to scale-up.
NaN3, DMSO
O
O
O
O
3
1
N
N
N3
3
R
N
DMF, 120oC
24 h
R
1
4
R = Alkyl Chain
O
O
R'
OTf-
3
R'OTf
N
5
N
Toluene
100°C
N
1
R
6
In an attempt to resolve this problem, we have previously
developed an alternative one-pot approach for the synthesis of
the same cationic compounds by generating alkylazides in situ
R, R' = Alkyl Chain
Scheme 1. Two-step synthesis of compound 4.
⇑
Corresponding author.
E-mail address: tom.chang@usu.edu (C.-W.T. Chang).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.08.078

5910
J. P. Shrestha, C.-W.T. Chang / Bioorg. Med. Chem. Lett. 23 (2013) 5909–5911
O
O
O
O
N
OTf-
N
N
N
MeOTf, toluele
100oC
N
R
N
N
O
O
N
N
R
X
2
7
O
O
O
NaN3, DMF
4a
DMF, 120oC
24h
1
MeO
MeO
R = Alkyl Chain
X = Cl, Br
N
N
N
R
4
O
O
O
O
Me
3
Me
3
N
MeOTf, toluele
100oC
N
R'OTf, Toluene
100oC
N
N
OTf-
Me
N
N
1
1
O
R'
10
O
8
OTf-
3
N
N
N
1
6
R
O
R, R' = Alkyl Chain
Scheme 2. One-pot synthesis of compound 4.
O
Me
Scheme 4. Proposed mechanism for the formation of compound 8 from compound
4a.
2a,
2b,
2c,
R = p-methoxybenzyl
R = benzyl
Cl
R
R = 2-methoxyethoxy
O
NaN3, DMSO
O
OTf-
N
N3
MeOTf, Toluene
100oC
N
N
N
N
N
R
O
O
3a,
3b,
3c,
R = p-methoxybenzyl
R = benzyl
O
O
O
O
3
1
O
R = 2-methoxyethoxy
N
N
4c
N
O
O
DMF, 80oC
2 days
1
O
R
4a,
4b,
4c,
R = p-methoxybenzyl, 81%
R = benzyl
O
O
O
R = 2-methoxyethoxy, 59%
Me
Me
3
3
1
N
N
MeOTf (4 equiv.)
Toluene, 100oC
MeOTf (4 equiv.)
Toluene, 100oC
MeOTf
N
N
OTf-
N
N
R = p-methoxybenzyl
R = benzyl
1
or 2-methoxyethoxy
Me
O
8
10
O
O
Me
Me
OTf-
3
3
OTf-
N
N
O
N
N
N
1
N
1
8
9
Me
O
O
O
4a
99% from
81% from 4c
Scheme 5. Proposed mechanism for the formation of compound 8 from compound
4c.
Scheme 3. Synthesis of compound 8.
(Scheme 2).4,5 This method has the shortcoming of generating by-
product, 7, which is difficult to be separated from the desired prod-
uct, 4. Also from this study, a particular cationic anthraquinone
analog, 4,9-dioxo-1,3-dimethylnaphtho[2,3-d][1,2,3]triazol-3-ium
(R@R0@Me, 8) was noted to manifest strong anticancer activities,
especially against melanoma, colon cancer, non-small cell lung

J. P. Shrestha, C.-W.T. Chang / Bioorg. Med. Chem. Lett. 23 (2013) 5909–5911
5911
Table 1
b
Anticancer activities of 8a,
Melanoma
GI50
Colon cancer
GI50
Non-small cell lung cancers
GI50
0.32 SF-268(Astrocytoma)
1.21 SF-295(Gliolastoma-Multiforme) 1.05
CNS cancer
GI50
LOX IMVI (Malignant)
MALME-3M (Malignant)
M14
0.50 COLO 205(Adenocarcinoma) 1.01 A549/ATCC(Adenocarcinoma)
0.15 HCC-2998(Carcinoma)
0.68 HCT-116(Carcinoma)
0.95
1.24 EKVX (Adenocarcinoma)
0.68 HOP-62 (Adenocarcinoma)
1.61 NCI-H226 (Squamous)
1.14 NCI-H23(Adenocarcinoma)
0.79 NCI-H322M(Carcinoma)
1.54 SF-539
1.35
1.59
1.68
1.27
MDA-MB-435 (Adenocarcinoma) 0.20 HCT-15 (Adenocarcinoma)
0.51 SNB-19(Gliblastoma)
0.62 SNB-75 (Astrocytoma)
0.28 U251 (Gliblastoma)
SK-MEL-2 (Malignant)
SK-MEL-28 (Malignant)
SK-MEL-5 (Malignant)
UACC-257
1.57 HT29(Adenocarcinoma)
1.61 KM12(Adenocarcinoma)
0.38 SW-620(Adenocaracinoma)
1.79
1.15 NCI-H460 (Large cell carcinoma) 0.30
NCI-H522(Adenocarcinoma) 1.41
a
Unit:
l
M.
b
The anticancer activities were tested through the Developmental Therapeutic Program (DTP) of National Cancer Institute (NCI) (Ref. 11).
cancer and central nervous system (CNS) cancer. Thus, there is an
imminent need for an efficient and safer synthetic approach for the
synthesis of this particular compound.
In summary, we have successfully developed a convenient and
safe route for the large scale synthesis of 4,9-dioxo-1,3-dimethyl-
naphtho[2,3-d][1,2,3]triazol-3-ium triflate with significant anti-
cancer activities. This new method is essential for providing
sufficient amount of material for ongoing anticancer investigations
in vivo which could lead to the development of new chemothera-
peutic agents. This protocol can also be applicable for the synthesis
of other 1,3-dimethyl-1,2,3-triazolium salts of various applications
without the use of potentially explosive methylazide. Finally, this
discovery can also augment the application of ‘Click’ chemistry that
involves the use of small molecules of organic azides.
Alkyl azides that have the ratio of the sum of carbon and oxy-
gen atoms to nitrogen atoms lower than three are considered
too reactive or explosive and cannot be safely isolated.7–9 There-
fore, 1,2,3-triazole substituted with shorter alkyl chains, such as
methyl or ethyl, cannot be safely synthesized by using methylaz-
ide or ethylazide. In an effort to expand the library of cationic
anthraquinone analogs, we were surprised to find out that, upon
methylation of a triazole adduct, 1-p-methoxybenzyl-1H-naph-
tho[2,3-d][1,2,3]triazole-4,9-dione, 4a, an unexpected product, 8
was obtained in good yield (Scheme 3). However, same methyl-
ation of 1-benzyl-1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione, 4b,4
yielded the expected product, 9 rather than compound 8. There-
fore, we proposed that the electron-donating effect of p-methoxy
renders the p-methoxybenzyl group a good leaving group during
methylation (Scheme 4). The resulted 1-methyl-1H-naphtho[2,3-
d][1,2,3]triazole-4,9-dione, 10,4 can then be further methylated
in the presence of excess MeOTf to form compound 8. Although
no attempt has been made to isolate compound 10 during this
process, we have previously demonstrated that compound 8
can be synthesized from methylation of compound 10 using
MeOTf.5
Acknowledgments
We thank the NCI for conducting the single- and five-dose as-
says. We thank the support from Utah State University and Depart-
ment of Chemistry and Biochemistry, Utah State University.
Supplementary data
Supplementary data (Experimental procedures and spectro-
scopic information for the synthesized compounds.) associated
with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.bmcl.2013.08.078.
The relationship between electron-donating effect and leav-
ing group capability was re-exemplified in another compound
4c containing a 2-methoxyethoxymethyl group at the N-1 posi-
tion (Scheme 5). Upon methylation using methyl triflate, com-
References and notes
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Singh, S. K. Heterocycles 2003, 60, 1225; (c) Abu-Orabi, S. T.; Atfah, M. A.; Jibril,
I.; Mari’i, F. M.; Ali, A. A.-S. J. Heterocycl. Chem. 1989, 26, 1461; (d) Krivopalov, V.
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4. Zhang, J.; Chang, C.-W. T. J. Org. Chem. 2009, 74, 4414–4417.
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pound
8 was also obtained in good yield. This reaction
proceeded, presumably, via similar mechanism and intermedi-
ate. In both syntheses, the initial cycloaddition/oxidation starts
by using p-methoxybenzyl azide or 2-methoxyethoxymethyl
azide rather than hazardous methylazide and, thus, is superior
in providing compound 8. In fact, both of these syntheses can
provide 1–2 g of compound 8 in one batch. When necessary,
the counterion, triflate can be exchanged into chloride using
Dowex 1X (Clꢀ) resin.
Following the success in safe and scale-up synthesis of com-
pound 8, more detailed investigation on the anticancer activities
of 8 was conducted through the Developmental Therapeutic Pro-
gram (DTP) of National Cancer Institute (NCI). Compound 8 is par-
ticularly active against melanoma, colon cancer, non-small cell
lung cancer and central nervous system (CNS) cancer with GI50
10. For more information on the cell-lines, please see: http://cancer.sanger.ac.uk/
cell_lines/cbrowse/nci.
11. For more information on the anticancer activities testing protocol, please see:
http://dtp.nci.nih.gov/branches/btb/ivclsp.html.
(50% growth inhibition) values ranging from low
lM to nM
(Table 1).10 Continuing investigation of the anticancer activity of
compound 8 is currently being carried out also by NCI.