Synthesis and antitumor activity of camptothecin- 4β-triazolopodophyllotoxin conjugates

Article abstract of DOI:10.1080/14786419.2018.1538223

Two new compounds (9 and 10) having a camptothecin (CPT) analog conjugated to the 4β-azido-4-deoxypodophyllotixin analog by untilizing the copper-catalyzed azide-alkyne cycloadditon (CuAAC) reaction, and were evaluated for their cytotoxicity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7 and SW480) using the MTT (3-(4,5-dimethyl-thiahiazo-2-yl)-2,5-diphenyltetrazolium bromide) assay. Two novel conjugates shown weak cytotoxicity, compound 10 showed highly potent against HL-60 cell line tested, with IC₅₀ value 17.69 ± 0.19 μM. This compound suggested its potential as anticancer agents for further development. (Figure presented.).

Full text of DOI:10.1080/14786419.2018.1538223

Natural Product Research
Formerly Natural Product Letters
ISSN: 1478-6419 (Print) 1478-6427 (Online) Journal homepage: http://www.tandfonline.com/loi/gnpl20
Synthesis and antitumor activity of
camptothecin-4β-triazolopodophyllotoxin
conjugates
Cheng-Ting Zi, Liu Yang, Fa-Wu Dong, Qing-Hua Kong, Zhong-Tao Ding, Jun
Zhou, Zi-Hua Jiang & Jiang-Miao Hu
To cite this article: Cheng-Ting Zi, Liu Yang, Fa-Wu Dong, Qing-Hua Kong, Zhong-Tao
Ding, Jun Zhou, Zi-Hua Jiang & Jiang-Miao Hu (2019): Synthesis and antitumor activity
of camptothecin-4β-triazolopodophyllotoxin conjugates, Natural Product Research, DOI:
10.1080/14786419.2018.1538223
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NATURAL PRODUCT RESEARCH
https://doi.org/10.1080/14786419.2018.1538223
Synthesis and antitumor activity of camptothecin-
4β-triazolopodophyllotoxin conjugates
Cheng-Ting Zia,b,c, Liu Yangb, Fa-Wu Dongb, Qing-Hua Kongb, Zhong-Tao Dingc,
Jun Zhoub, Zi-Hua Jiangd and Jiang-Miao Hub
aKey Laboratory of Pu-er Tea Science, Ministry of Education, College of Science, Yunnan Agricultural
b
University, Kunming, China; State Key Laboratory of Phytochemistry and Plant Resources in West
c
China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, China; Key Laboratory
of Medicinal Chemistry for Nature Resource, Ministry of Education, School of Chemical Science and
d
Technology, Yunnan University, Kunming, China; Department of Chemistry, Lakehead University,
Thunder Bay, ON, Canada
ABSTRACT
ARTICLE HISTORY
Received 8 August 2018
Accepted 15 October 2018
Two new compounds (9 and 10) having a camptothecin (CPT)
analog conjugated to the 4b-azido-4-deoxypodophyllotixin analog
by untilizing the copper-catalyzed azide-alkyne cycloadditon
(CuAAC) reaction, and were evaluated for their cytotoxicity
against a panel of five human cancer cell lines (HL-60, SMMC-
7721, A-549, MCF-7 and SW480) using the MTT (3-(4,5-dimethyl-
thiahiazo-2-yl)-2,5-diphenyltetrazolium bromide) assay. Two novel
conjugates shown weak cytotoxicity, compound 10 showed
highly potent against HL-60 cell line tested, with IC50 value
17.69 0.19 lM. This compound suggested its potential as anti-
cancer agents for further development.
KEYWORDS
antitumor activity; CuAAC
reaction; camptothecin;
podophyllotixin
CONTACT Cheng-Ting Zi
zichengting@126.com
Cheng-Ting Zi and Liu Yang contributed equally to this work.
Supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2018.1538223.
ß 2018 Informa UK Limited, trading as Taylor & Francis Group

2
C.-T. ZI ET AL.
Figure 1. Structures of camptothecin (1) and camptothecin conjugates (2 and 3), podophyllotixin
(4) and etoposide (5).
1. Introduction
DNA topoisomerases (Tops) anzymes relax helical supercoiling renerated during
transcription, replication, recombination and chromatin remodeling (Wang 2002).
Topoisomerases I (Top I) cuts one strand of DNA, relaxes the strands, and then
re-annels the strands (Wang 1971), whereas topoisomerases II (Top II) incises double-
stranded DNA to facilitate the passae of an intact duples through the gap before
rejoining the cut DNA (Gellert et al. 1976). Many evidences suggests that Tops are
the targets of important anticancer drugs (Delgado et al. 2018; Reddy et al. 2018;
Bielawski et al. 2006).
Camptothecin (CPT, Figure 1), an alkaloid isolated from Camptotheca acuminate by
Wall and co-workers in 1966, was identified specific inhibitor of Top I (Wall et al.
1966). Historically, several CPT-derivatives, including topotecan and irinotecan
(Figure 1) (Johnson et al. 1989; Fukuoka et al. 1992; Sriram et al. 2005), have good
water solubility and have been used clinically for the treatment of ovarian, colorecral
and small cell lung cancers. Etoposide (VP-16, Figure 1), a semisynthetic derivative
of podophyllotoxin, is another widely used anticancer drug by inhibiting Top II
isoenzymes (Ye et al. 2012). Previously, numberous podophyllotoxin derivatives were
synthesized and used in the chemotherapy for a variety of cancers (Terada et al. 1993;
Xiao et al. 2002; Tawa et al. 1997; Chattopadhyay et al. 2004). However, drug
resistance is still a critical clinical problem.
It has been demonstrated the inhibitory mechanism of all the above-mentioned
Topos inhibitors, inhibitors act by stabilizint the Tops-DNA-drug ternaty comples,
ultimately leads to cell death (Tsao et al. 1993; Hsiang et al. 1989; Chen et al. 1984;
Ross et al. 1984). The mechanisms of CPT-derivatives resistance characterized to date
include (a) reduced drug accumulation, (b) reduced Top I content, (c) altered Top I
resulting in decreased formation of protein-linked DNA breaks (PLDBs). The mecha-
nisms of podophyllotoxin-derivatives resistance have been proposed to be involved (a)
decreased cellular uptake of drug, (b) quantitative change of Top II, (c) qualitative
change of Top II (Chang et al. 2000).
Dual target inhibitors would likely retain cytotoxic activity when resistance was
acquired due to alteration of only one drug target, which could possibly overcome

NATURAL PRODUCT RESEARCH
3
Scheme 1. Synthesis of camptothecin-4?-triazolopodophyllotoxin conjugates
9
and 10.
Reagentsand conditions: (a) NaH, DMF, 0 oC, propargyl bromide, then, reflux, overnight, 65%; (b)
MeSO3H, NaI, CH2Cl2, then, H2O-Acetone, BaCO3, rt.; (c) NaN3, CHCl3, 40–60%; (d) CuSO4ꢁ5H2O,
sodium ascorbate, THF, t-BuOH: H2O (1: 1), 4 h, rt, 76–80%.
drug resistance. The aim of this paper was interested in the development of com-
pounds that can act on both Top I and Top II by conjugating derivatives of the proto-
typical CPT, with an analogue of podophyllotoxin. The (S)-a-hrdroxy-d-lactone moiety
contained in CPT-derivatives is a crucial structural feature required for biological activ-
ity, and structure activity relationship (SAR) analysis of podophyllotoxin analogues indi-
cated that the conpounds with substitutions in the glycosidic moiety of etoposide
can’t have significant effect on their anticancer activity.
In recent years, we have been working on the chemical modification of podophyllo-
toxin and focused on carbohydrate based 1,2,3-triazole derivatives have been gener-
ated, some of which exhibited significant anticancer activity (Zi et al. 2013; Zi et al.
2015; Zi et al. 2015; Zi et al. 2017). In this paper, we have synthesized two camptothe-
cin-4b-triazolopodophyllotoxin conjugates and tested for their cytotoxic activity
against a panel of five human cancer cell lines HL-60 (leukemia), SMMC-7721
(hepatoma), A-549 (lung cancer), MCF-7 (breast cancer) and SW480 (colon cancer)
using MTT (3-(4,5-dimethyl-thiahiazo-2-yl)-2,5-diphenyltetrazolium bromide) assay.
2. Results and discussion
The novel camptothecin-4b-triazolopodophyllotoxin conjugates 9 and 10 were
synthesised according to the synthetic route shown in Scheme 1. Camptothecin-
20(S)-1-propyne (6) was prepared by the treatment of camptothecin (1) with sodium
hydride (NaH) and propargyl bromide with 65% yield. The preparation of 4b-azido-
4-deoxypodophyllotoxin (7) and 4b-azido-4-deoxy-40-demethypodophyllotoxin (8)
using a similar method have been reported in the literatures (Hansen et al. 1993;
Kamal et al. 2000). Then, the azides 7 and 8 were allowed to react with the abole ter-
minal alkyne (6) in the presence of copper(II) sulfate pentahydrate (CuSO4ꢀ5H2O),
sodium ascorbate in t-butyl alcohol (t-BuOH) and water (1:1) at room temperature

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C.-T. ZI ET AL.
Table 1. In vitro anticancer activity (IC50, lM) of camptothecin-4b-triazolopodophyllotoxin
conjugates 9 and 10.
IC50 (lM)
Compounds
HL-60
SMMC-7721
A-549
MCF-7
SW480
9
10
>40
17.69 0.19
<0.064
0.31 0.24
1.67 0.44
>40
>40
0.45 0.11
8.12 0.72
6.93 0.28
>40
>40
0.09 0.32
11.92 0.12
7.42 0.12
>40
>40
0.68 0.47
32.82 0.44
10.85 0.51
>40
>40
0.29 0.15
17.11 0.67
9.89 0.53
Camptothecin (1)
Etoposide (5)
Cisplatin
for 4 h to give camptothecin-4b-triazolopodophyllotoxin conjugates 9 and 10 in
76–80% yield (Rostovtsev et al. 2002). All of synthesized compounds were character-
ized by 1H-NMR, 13C-NMR, electrospray ionization mass spectrometry (ESI-MS) and
high-resolution mass spectrometry (HRESI-MS).
Compound 9 was obtained as yellow amorphous powder with a specific rotation of
-17.00 (c 0.10, MeOH). Its molecular formula, C45H39N5O11, was established by HRESIMS
(m/z 848.2524 [M þ Na]þ, calcd 848.2538). Its IR spectrum showed the presence of
a lcactone carbonyl group (1636 cmꢂ1). The UV absorption bands at 363.00 and
0
207.50 nm were characteristic of a lignin. The 1H-NMR data showed that the C4 -H
chemical shifts of 4b-triazole-substituted compounds appears as a doublet at 5.38 ppm,
with a coupling constant J3,4 ¼ 4.8 Hz (<5.0 Hz), indacaating a cis-relationship between
0
0
C3 -H and C4 -H. The C-25 chemical shifts of the triazole ring was supported by two
characteristic carbon signals at around 146 ppm and 122 ppm in the 13C-NMR spectra.
Compound 10 was obtained as yellow amorphous powder with a specific rotation of
ꢂ92.86 (c 0.10, MeOH). Its molecular formula, C45H39N5O11, was established by HRESIMS
(m/z 834.2384 [M þ Na]þ, calcd 834.2382). Its IR spectrum showed the presence of
a lcactone carbonyl group (1777, 1747 cmꢂ1). The UV absorption bands at 360.00
0
and 207.00 nm were characteristic of a lignin. The C4 -H chemical shifts of 4b-triazole-
substituted compounds appears as a doublet at 5.57 ppm, with a coupling constant J3,4
¼
0
0
1
4.8 Hz (<5.0 Hz), indacaating a cis-relationship between C3 -H and C4 -H in the H-NMR
spectra. The C-25 chemical shifts of the triazole ring was supported by two characteristic
carbon signals at around 146 ppm and 122 ppm in the 13C-NMR spectra.
Camptothecin, etoposide, and cisplatin were used as positive controls. Their
activities were expressed by the IC50 value (concentration of drug inhibiting 50%
cell growth), which was presented in Table 1. The compounds having IC50 value more
than 40 lM were considered inactive. As shown in Table 1, compound 9 displayed weak
anticancer activity to the five cancer cells (IC50 > 40 lM). However, compound 10 showed
highly potent against HL-60 cell line tested, with IC50 value 17.69 0.19 lM.
As compunds 9 and 10 does not show eddicacy, logP and the topological polar
surface area (tPSA) may reflect the topoisomerases modulating activity. Here, we have
calculated the PSA and ClogP values of compounds 9 and 10 by SyBYL-X 2.0 (data
shown in Table 2). For the potent Tops inhibitors, the PSA value fall 100 Å2, while
LogP value fall 5 (Onawolea et al. 2017; Pajouhesh and Lenz 2005; van de
Waterbeemd and Rose 2008). The two compounds have cLogP values of 1.79 and
2.13, PSA values of 160.7 Å2 and 230.4 Å2, both are expected to have less cell
permeability.

NATURAL PRODUCT RESEARCH
5
Table 2. The CogP values and PBA of camptothecin-4b-triazolopodophyllotoxin conjugates 9
and 10.
Compounds
Molecular formula
m.p. (ꢃC)
Yield (%)
cLogP
PSA (Å2)
9
10
C45H39N5O11
C44H37N5O11
195–197
201–203
76
80
–
2.13
1.79
0.90
0.03
230.4
160.7
113.8
236.1
Camptothecin (1)
Etoposide (5)
C20H16N2O4
–
–
C29H32O13
–
3. Experimental
3.1. Genetal information
Melting points were measured by an X-4 melting point apparatus and were uncor-
rected. MS data were obtained in the ESI mode on API Qstar Pulsar instrument; HRMS
data were obtained in the ESI mode on LCMS-IT-TOF (Shimadzu, Kyoto, Japan); NMR
spectra were acquired on Bruker AV-400 (Bruker BioSpin GmbH, Rheinstetten,
Germany) instruments, using tetramethylsilane (TMS) as an internal standard: chemical
shifts (d) are given in ppm, coupling constants (J) in Hz, the solvent signals were used
as references (CDCl3: dC ¼ 77.2 ppm; residual CHCl3 in CDCl3: dH ¼ 7.26 ppm; CD3OD:
dC ¼ 49.0 ppm). Column chromatography (CC): silica gel (200–300 mesh; Qingdao
Makall Group CO., LTD; Qingdao; China). All reaction was monitored using thin-layer
chromatography (TLC) on silica gel plates.
3.2. Synthesis of camptothecin-20(S)-1-propyne (6)
To a solution of camptothecin (348.4 mg, 1.0 mmol) was added at 0 ꢃC to a suspension
of sodium hydride (NaH) (60.0 mg, 1.5 mmol) in dry N,N-Dimethylformamide (DMF)
(5 mL) under nitrogen. The mixture was stirred at room temperature for 0.5 h, then the
propargyl bromide (0.1 mL, 1.2 mmol) was quickly added and the reaction was refluxed
overnight. The solvent was evaporated and the residue was purified on a silica gel
chromatography (petroleum ether: acetic ether ¼ 1:1) to afford the product 6
1
(250.9 mg, 65%). H-NMR (CDCl3, 400 MHz) d 8.43 (d, 1H, J ¼ 6.4 Hz, C9-CH), 8.21 (d, 1H,
J ¼ 8.4 Hz, C12-CH), 7.96 (s, 1H, C14-CH), 7.88 (t, 1H, J ¼ 7.2 Hz, C10-CH), 7.77 (t, 1H,
J ¼ 7.2 Hz, C11-CH), 7.60 (t, 1H, J ¼ 6.8 Hz), 5.75–5.73 (m, 1H), 5.63 (d, 1H, J ¼ 16.4 Hz),
5.22 (d, 1H, J ¼ 16.4 Hz), 3.40 (t, 1H, J ¼ 9.6 Hz, CꢄCH), 2.82 (s, 2H, CH2CꢄC), 1.89–1.83
(m, 2H, C18-CH2), 0.98 (t, 3H, J ¼ 7.6 Hz, C19-CH3); 13C-NMR (CDCl3, 100 MHz) d 173.6,
162.5, 157.8, 151.9, 150.4, 149.0, 146.0, 131.8, 131.2, 130.7, 129.6, 128.4, 127.9, 119.6,
98.1, 72.7, 72.4 (CꢄCH), 66.2 (CꢄCH), 60.3, 36.5 (CH2-CꢄC), 31.4, 21.5, 7.8; MS-ESI m/z
409 [M þ Na]þ.
3.3. General procedure for the synthesis of camptothecin-4b-
triazolopodophyllotoxin conjugates (9 and 10)
To a solution of camptothecin-20(S)-1-propyne (6) (0.1 mmol) and 4b-azido-4-deoxypo-
dophyllotoxin (7)/4b-azido-4-deoxy-4’-demethypodophyllotoxin (8) (0.1 mmol) in tetra-
hydrofuran (THF) (1.0 mL) and t-BtOH-H2O (1.0 mL, 1:1) at room temperature were
added copper (II) acetate (0.01 mmol) and sodium ascorbate (1.0 M in H2O, 0.1 M). The

6
C.-T. ZI ET AL.
reaction mixture was stirred at room temperature for 4 h until the starting material
disappeared as indicated by TLC. The solvent was evaporated and the residue was
chromatographed on silica gel (dichloromethane: methyl alcohol ¼15:1) to afford
the product.
3.3.1. Camptothecin-20(S)-[4b-(1,2,3-trizaol-1-yl-4-deoxypodophyllotoxin)] ether (9)
Yellow amorphous powder; yield 76%; m.p. 195–197 ꢃC (CH2Cl2); [a]D 24.6 -17.00
(c 0.10, CH3OH); UV (CH3OH) kmax (log e) 363.00 (0.13), 207 (0.93); IR (KBr) mmax 3444,
1
2920, 1635, 1399, 1202, 1144, 1053 cmꢂ1; H-NMR (CDCl3, 400 MHz) d 7.79–7.78 (m, 2H,
C9, C10-H), 7.42–7.40 (m, 1H), 7.28–7.25 (m, 1H), 7.10–7.08 (m, 1H), 7.00 (s, 1H), 6.00
0
(s, 1H), 5.91–5.90 (m, 2H), 5.79 (s, 1H), 5.60–5.56 (m, 2H), 5.38 (d, 1H, J ¼ 4.8 Hz, C4 -H),
5.25–5.20 (m, 1H), 4.80–4.76 (m, 1H), 4.00–3.98 (m, 1H), 3.79–3.76 (m, 2H), 3.50–3.42
00
00
(m, 1H), 3.35 (s, 3H, C4’’-OCH3), 3.30 (s, 6H, C3 , C5 -OCH3), 2.50–2.45 (m, 1H), 2.20–2.18
(m 1H), 1.73–1.38 (m, 2H, C19-CH2), 1.00 (t, 3H, J ¼ 7.0 Hz, C18-CH3); 13C-NMR (CD3Cl,
100 MHz) d 173.7 (C-120), 172.7 (C-21), 157.7 (C-17), 152.7 (C-300, 500), 152.7 (C-2), 151.2
(C-15), 150.0 (C-13), 149.3 (C-70), 148.9 (C-60), 142.8 (C-3), 141.2 (C-24), 134.0 (C-400),
133.0 (C-100), 132.1 (C-90), 132.0 (C-100), 131.0 (C-7), 130.9 (C-6), 129.9 (C-11), 128.3
(C-12), 128.1 (C-8), 127.8 (C-9), 124.2 (C-10), 122.4 (C-25), 119.7 (C-16), 110.2 (C-50),
108.3 (C-8’), 108.0 (C-20’, 600), 102.0 (OCH2O), 102.0 (C-14), 97.5 (C-20), 72.6 (C-40), 68.1
(C-110), 67.1 (C-22), 66.2 (C-23), 60.7 (C-400), 56.3 (C-300, 500), 53.7 (C-5), 43.4 (C-10), 41.3
(C-20), 31.4 (C-19), 29.2 (C-20), 7.8 (C-18); ESIMS: m/z 848 [M þ Na]þ, HRESIMS: calcd for
C45H39N5O11Na [M þ Na]þ 848.2538, found 848.2524.
3.3.2. Camptothecin-20(S)-[4b-(1,2,3-trizaol-1-yl)-4-deoxy-4’-demethylpodophyllotoxin]
ether (10)
Yellow amorphous powder; yield 80%; m.p. 201–203 ꢃC (CH2Cl2); [a]D 24.3 -92.86ꢃ
(c 0.14, CH3OH); UV (CH3OH) kmax (log e) 364.00 (1.30), 290.00 (1.07), 245.50 (1.54),
207.00 (1.95); IR (KBr) mmax 3439, 2935, 1747, 1660, 1485, 1236, 1108, 1041, 1002 cmꢂ1
;
1H-NMR (CDCl3, 400 MHz) d 8.28 (s, 1H, C9-H), 8.13–8.12 (m, 1H, C10-H), 7.87–7.85
(m, 1H), 7.76–7.75 (m, 1H), 7.61–7.52 (m, 2H), 6.51 (s, 1H), 6.39–6.36 (m, 2H), 6.05–5.90
0
(m, 3H), 5.72–5.60 (m, 2H), 5.57 (d, 1H, J ¼ 4.8 Hz, C4 -H), 5.29–5.26 (m, 1H), 4.59–4.58
00
00
(m, 1H), 4.01–3.83 (m, 3H), 3.84 (s, 6H, C3 , C5 -OCH3), 3.10–2.90 (m, 2H), 1.89–1.85
(m, 2H, C19-CH2), 1.00 (t, 3H, J ¼ 7.0 Hz, C18-CH3); 13C-NMR (CDCl3, 100 MHz) d 173.6
(C-120), 173.3 (C-21), 157.8 (C-17), 151.6 (C-2), 150.3 (C-15), 149.0 (C-13), 148.4 (C-70),
148.0 (C-60), 147.7 (C-3), 146.5 (C-300, 500), 146.3 (C-24), 133.9 (C-100), 132.4 (C-400), 132.0
(C-90), 131.9 (C-100), 131.4 (C-7), 129.9 (C-6), 129.6 (C-11), 128.3 (C-12), 128.1 (C-8), 128.0
(C-9), 126.7 (C-10), 126.5 (C-25), 119.5 (C-16), 110.1 (C-50), 107.4 (C-8’), 105.8 (C-20’, 600),
101.8 (OCH2O), 101.8 (C-14), 97.6 (C-20), 72.6 (C-40), 69.8 (C-110), 66.3 (C-22), 62.8
(C-23), 56.3 (C-300, 500), 53.7 (C-5), 43.7 (C-10), 43.6 (C-20), 31.7 (C-19), 29.2 (C-20), 7.8
(C-18); ESIMS: m/z 834 [M þ Na]þ, HRESIMS: calcd for C44H37N5O11Na [M þ Na]þ
834.2382, found 834.2384.

NATURAL PRODUCT RESEARCH
7
3.4. Cell culture and cytotoxicity assay
The following human tumor cell lines were used: HL-60, SMMC-7721, A-549, MCF-7,
and SW480. All the cells were cultured in RMPI-1640 or DMEM medium (Hyclone,
Logan, UT, USA), supplemented with 10% fetal bovine serum (Hyclone) at 37 ꢃC in a
humidified atmosphere with 5% CO2. Cell viability was assessed by conducting colori-
metric measurements of the amount of insoluble formazan formed in living cells
based on the reduction of 3-(4,5-dimethyl- thiazol-2-yl)-2,5-diphenyltetrazolium brom-
ide (MTT) (Sigma, St. Louis, MO, USA). Briefly, adherent cells (100 lL) were seeded into
each well of a 96-well cell culture plate and allowed to adhere for 12 h before drug
addition, while suspended cells were seeded just before drug addition, both with an
initial density of 1 ꢅ 105 cells/mL in 100 lL of medium. Each tumor cell line was
exposed to the test compound at various concentrations in triplicate for 48 h. After
the incubation, MTT (100 lg) was added to each well, and the incubation continued
for 4 h at 37 ꢃC. The cells lysed with SDS (200 lL) after removal of 100 lL of medium.
The optical density of lysate was measured at 595 nm in a 96-well microtiter plate
reader (Bio-Rad 680) to determine the concentration that killed 50% of cells (IC50).
Data represent the means of at least three separate experiments. The IC50 value was
defined as the concentration that caused 50% inhibition of cell proliferation.
3.5. Calculated molecular descriptors
Calculated descriptors such as CLogP and PSA were determined by SyBYL-X 2.0. The
structures of compounds 9 and 10 were built and energy minimized under the Tripos
force dield with 0.05 kcal/(mol Å). The Gasteiger-Huchel method was used to calcu-
lated charges. Energy minimization was performed by the Powell method with 2000
iterations. Then, the distance of linkers was calculated.
4. Conclusions
In summary, the two new camptothecin-4b-triazolopodophyllotoxin conjugates have
been synthesized by untilizing the copper-catalyzed azide-alkyne cycloadditon
(CuAAC) reaction, and screened for anticancer activity against five human cancer cell
lines. Compound 10 showed highly potent against HL-60 cell line tested, with IC50
value 17.69 0.19 lM. This compound suggested its potential as anticancer agents for
further development.
Disclosure statement
The authors declare no conflict of interest.
Funding
This work was financially supported by Yunnan provincial science and technology department
(2015HB093 and 2015FB168) and the National Key Research and Development Program of
China (2017YFD0201402).

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C.-T. ZI ET AL.
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