Design, synthesis and cytotoxicity of nitrogen-containing tanshinone derivatives

Article abstract of DOI:10.1016/j.tetlet.2017.11.046

Tanshinones were used as starting material to synthesize a small library of nitrogen heterocyclic derivatives featured with oxazole, imidazole, and pyrazine ring between C-11/C-12 by simple methods. Except for salviamine A and isosalviamine A, 22 new derivatives were synthesized. Their structures were confirmed by spectroscopic analysis. Moreover, 11 derivatives exhibited moderate cytotoxic activities against five human cancer lines in vitro.

Full text of DOI:10.1016/j.tetlet.2017.11.046

Accepted Manuscript
Design, synthesis and cytotoxicity of Nitrogen-containing Tanshinone deriva-
tives
Ming-Ming Li, Fan Xia, Cheng-Ji Li, Gang Xu, Hong-Bo Qin
PII:
S0040-4039(17)31461-2
https://doi.org/10.1016/j.tetlet.2017.11.046
TETL 49489
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
24 October 2017
15 November 2017
21 November 2017
Please cite this article as: Li, M-M., Xia, F., Li, C-J., Xu, G., Qin, H-B., Design, synthesis and cytotoxicity of
Nitrogen-containing Tanshinone derivatives, Tetrahedron Letters (2017), doi: https://doi.org/10.1016/j.tetlet.
2017.11.046
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Design, synthesis and cytotoxicity of Nitrogen-containing Tanshinone derivatives
†
†
Ming-Ming Lia, , Fan Xiaa,b, , Cheng-Ji Lia,b, Gang Xua,∗, and Hong-Bo Qina,∗
a State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, and Yunnan Key
Laboratory of Natural Medicinal Chemistry, Kunming 650201, P. R. China
b University of Chinese Academy of Sciences, Beijing 100049, P. R. China
ARTICLE INFO
ABSTRACT
Article history:
Received
Tanshinones were used as starting material to synthesize a small library of nitrogen heterocyclic
derivatives featured with oxazole, imidazole, and pyrazine ring between C-11/C-12 by simple
methods. Except for salviamine A and isosalviamine A, 22 new derivatives were synthesized.
Their structures were confirmed by spectroscopic analysis. Moreover, 11 derivatives exhibited
moderate cytotoxic activities against five human cancer lines in vitro.
Received in revised form
Accepted
Available online
Keywords:Tanshinones Heterocyclic compounds,
Cytotoxicity
ole7 and pyrazine8 derivatives demonstrated the utilities in On-
cology. Therefore, we planned to synthesize oxazole, imidazole,
and pyrazine derivatives by treating Tanshinones (1-4) with var-
ious amines. As a result, 22 new derivatives were synthesized. In
addion, salviamine A and isosalviamine A, two known natural
products reported from Salvia famliy, were synthesized
biomimetically for the first time.3a, 3d Subsequently, these synthe-
sized compounds were tested against five human cancer cell lines
(i.e., HeLa: Henrietta Lacks strain of cancer cells, K562: leuke-
mia cell, MCF-7: human breast cancer, PC 3: Prostate cancer-3,
and CNE: nasopharyngeal carcinoma cells) by MTT method.
Tanshinones, possessing a characteristic 11,12-orthoquinone
abietane skeleton, were first isolated by Nakao in 1930 from the
roots of Salvia miltiorrhiza (‘tanshen’), a well-known traditional
Chinese medicine (TCM).1 Extensive studies have demonstrated
that tanshinones and their analogs exhibit various pharmacologi-
cal activities, including antibacterial, antioxidant, anti-
inflammatory, and antineoplastic. These diterpenoids attracted
widespread attention in terms of organic synthesis, structural
modification and biological evaluation.1, 2
Since 2005, a series of abietane diterpenoid alkaloids were
characterized from the genus Salvia, which causing our attention
for its special structure of the oxazole ring between C-11/C-12 as
well as its cytotoxic activity.3 Although series of structural modi-
fication products about tanshinone IIA and cryptotanshinone
have been reported from 2001 to 2003, these N-containing deriv-
atives were still an interesting concern from the chemical and
pharmaceutical point of view. Furthermore, studies on the activi-
ty of these compounds are rare.4 Therefore, studies on the 11,12-
orthoquinone of tanshinones (tanshinone IIA, cryptotanshinone,
tanshinone I, and dihydrotanshinone I, Fig. 1) will reveal more
potent analogues with better biological activity.
Some N-containg natural products are collected in Fig. 2.
Oxazolines from tanshinone IIA showed cytotoxicity with a
CD50 range of 32-63 µM against HeLa cell lines.
Izumiphenazines A−C exhibited activity in overcoming TRAIL
(TNF-related apoptosis-inducing ligand) resistance in human
gastric adenocarcinoma cells.5 Meanwhile, Oxazoline6, imidaz-
Fig. 1. Structures of tanshinone IIA, cryptotanshinone, tanshinone I,
and deyhrotanshinone I.
Current address of M.M.Li, Yunnan Baiyao group corporation limited, Kunming, 650032, China.
∗Corresponding authors. Tel.: +86-871-65217971; e-mails: qinhongbo@mail.kib.ac.cn; xugang008@mail.kib.ac.cn.
†Both authors contributed equally to this work.

2
Tetrahedron Letters
F
HO
F
HO
N
N
N
N
N
N
HN
N
HN
N
HN
HN
O
O
O
O
O
O
1d 50%
40%
N
1f
3e
75%
1e 75%
3d 60%
3f
80%
N
O
N
N
N
O
HN
N
HN
N
HN
O
O
O
O
O
O
1a 55%
3a 40%
40%
3c 62%
60%
3b
1b
1c 55%
O
O
O
O
O
O
O
O
O
O
O
O
4
2
3
1
N
N
N
N
N
N
Fig. 2. Structures of N-containing natural products.
O
HN
HN
N
HN
N
O
O
O
O
O
O
Three types of hetero atom containing derivatives were syn-
thesized (Scheme 1 and Fig. 3).
4c
61%
4b
47%
76%
4a 66%
2a
2b
65%
2c
45%
F
HO
F
HO
1) Oxazoline formation: tanshinones were treated with me-
thyl amine or ethyl amine in EtOH. Salviamine A (3a)
and isosalviamine A (3b), two known natural products
reported from Salvia family, were synthesized
biomimetically for the first time. The structures of 3a and
N
N
N
N
N
N
N
HN
HN
HN
HN
N
O
O
O
O
O
O
1
3b were determined by comparing the H NMR and 13C
2d
4f
75%
52%
4d
4e
70%
2e
53%
74%
2f 70%
NMR date with salviamine A and isosalviamine A.3a, 3d
Yields varied between 50%-76% when tanshinones 1-4
were used. Particularly, when methyl amine was used, no
formation of N-Me imidazole was observed.4a
Fig. 3 synthesized tanshinone derivatives and isolated yield.
Next, these compounds were tested for in vitro inhibitory ac-
tivities against HeLa, K562, MCF-7, PC3, and CNE human tu-
mor cell lines using the MTT method described previously.9 The
results indicated that 11 tanshinone derivatives exhibited some
cytotoxic activities against five human cancer lines in vitro (Ta-
ble 1).
2) Imidazole formation: tanshinones were reacted with am-
monium acetate, aldehyde in refluxing EtOH (y. 55-80%).
3) Pyrazine formation: tanshinones and diamine were react-
ed in refluxing EtOH (y. 40-60%).
Table 1. Cytotoxicities of compounds against five cancer cell lines
(IC50 µM)
Compoundsa
HeLa
7.11
9.39
16.66
5.29
17.1
>100
>100
7.4
K562
6.94
7.16
6.12
3.92
3.9
MCF-7
6.05
3.28
21.82
3.05
13.6
10.0
10.0
8.7
PC 3
21.09
9.62
5.15
2.80
20.6
>100
>100
14.8
>100
>100
46.6
15.3
21.2
>100
15.4
0.007
CNE
5.75
6.69
11.36
3.09
23.8
>100
>100
24.6
44.8
6.1
1
2
3
4
1b
1f
2b
>100
>100
3.2
2e
2f
3b
>100
19.3
5.6
>100
41.4
10.7
2.6
10.0
14.7
7.8
3c
3e
8.5
6.8
8.4
15.7
22.9
13.9
28.0
0.009
3f
4c
11.6
8.3
3.8
10.8
9.1
21.4
6.2
4e
paclitaxelb
10.4
0.01
10.2
0.21
0.005
a Other derivatives with IC50 > 40 µM for all the cell lines are not
listed.
Scheme 1. Representative synthetic route to oxazoline, imidazole
and pyrazine.
b Positive control.
Our experiments revealed that, for the first time, modification
of C11-C12 quinone have shown some antitumor activity. Espe-
cially, introduction of imidazole ring at C11-C12 (2e) maintained
the activity to cell line (Hela, K562, MCF-7). All derivatives are
not active towards PC 3 cell line and 3b, 3c showed activity to
CNE. Therefore, imidazole derivatives showed higher activity
when compared with oxazoline and pyrazine alternatives. Among
imidazole derivatives, aryl substitution (1f, 2f, 3f, 2e, 3e, 4e) on
oxazoline ring is proved to be effective. The bioactivity of 2e and

3
3e, compared with 2 and 3, demonstrated that our modification
strategy is promising.
9. Alley, M. C.; Scudiero, D. A.; Monks, A.; Hursey, M. L.;
Czerwinski, M. J.; Fine, D. L.; Abbott, B. J.; Mayo, J. G.;
Shoemaker, R. H.; Boyd, M. R. Cancer Res. 1988, 48, 589-
601.
Acknowledgments
The work was financially supported by the foundations from
NSFC (81373291) to Dr. G. Xu, NSFC (21372229) to Dr. H. B.
Qin, and from Foundation of Kunming Institute of Botany
(KIB2017007) to Dr. G. Xu.
Supplementary data
The details of chemical transformation, and biological exper-
imental procedures, MS and NMR spectra of the synthesized
compounds associated with this article can be found in the online
version at http://dx.doi.org/XXX.
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4
Tetrahedron Letters
Highlights
ꢀ
ꢀ
Nitro-containing tanshinone derivatives have been
investigated.
22 derivatives, including oxazole, imidazole and
pyrazine have been subjected to antitumor activity
test.
ꢀ
SAR of these heterocyclic compounds has been
figured out and our modification strategy is prom-
ising.

5