Synthesis and in vitro biological evaluation of novel dendrocandin analogue as potential anti-tumor agent

Article abstract of DOI:10.1080/14786419.2021.1901698

Dendrocandins are characteristic chemical structures of D. officinale and have strong physiological bioactivities. In this study, a dendrocandin analogue (1) has been prepared by total synthesis (9 steps, 12.6% overall yield) in which coupling reaction and Wittig reaction as the key steps. Compound 1 was also evaluated for its anticancer activity in vitro against six human cancer cells (MCF-7, A549, A431, SW480, HepG-2 and HL-60) using MTT assays. Compound 1 showed potent cytotoxicity, with the IC50 value 16.27 ± 0.26 μM. The expression levels of apoptotic proteins indicated that compound 1 can up-regulate the expression of apoptotic proteins, leading to apoptosis. This compound suggested that it’s potential as anticancer agent for further development.

Full text of DOI:10.1080/14786419.2021.1901698

Natural Product Research
Formerly Natural Product Letters
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gnpl20
Synthesis and in vitro biological evaluation of
novel dendrocandin analogue as potential anti-
tumor agent
Jing-Yun Yan, Hao-Nan Yang, Ning Yang, Yin-Rong Xie, Xiu-Li Sun, Ye-Wei
Huang, Cheng-Ting Zi, Xuan-Jun Wang & Jun Sheng
To cite this article: Jing-Yun Yan, Hao-Nan Yang, Ning Yang, Yin-Rong Xie, Xiu-Li Sun, Ye-Wei
Huang, Cheng-Ting Zi, Xuan-Jun Wang & Jun Sheng (2021): Synthesis and in vitro biological
evaluation of novel dendrocandin analogue as potential anti-tumor agent, Natural Product
Research, DOI: 10.1080/14786419.2021.1901698
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NATURAL PRODUCT RESEARCH
https://doi.org/10.1080/14786419.2021.1901698
Synthesis and in vitro biological evaluation of novel
dendrocandin analogue as potential anti-tumor agent
a,b
a
ꢀ
a,b
ꢀ
a,b
a,b
a,b
Jing-Yun Yan
, Hao-Nan Yang
, Ning Yang , Yin-Rong Xie a,,bXiu-Li Sun
,
a
a
Ye-Wei Huang , Cheng-Ting Zi , Xuan-Jun Wang and Jun Sheng
a
Key Laboratory of Pu-er Tea Science, Ministry of Education, Yunnan Agricultural University,
b
Kunming, China; College of Food Science and Technology, Yunnan Agricultural University,
Kunming, China
ABSTRACT
ARTICLE HISTORY
Dendrocandins are characteristic chemical structures of D. offici-
nale and have strong physiological bioactivities. In this study, a
dendrocandin analogue (1) has been prepared by total synthesis
Received 23 October 2020
Accepted 7 March 2021
KEYWORDS
(
9 steps, 12.6% overall yield) in which coupling reaction and
Dendrocandin analogue;
synthesis; anticancer
activity; apoptosis
Wittig reaction as the key steps. Compound 1 was also evaluated
for its anticancer activity in vitro against six human cancer cells
(
MCF-7, A549, A431, SW480, HepG-2 and HL-60) using MTT assays.
Compound 1 showed potent cytotoxicity, with the IC50 value
6.27 ± 0.26 mM. The expression levels of apoptotic proteins indi-
1
cated that compound 1 can up-regulate the expression of apop-
totic proteins, leading to apoptosis. This compound suggested
that it’s potential as anticancer agent for further development.
Graphical Abstract
1. Introduction
Dendrobium officinale Kimura et Migo (D. officinale, Tiepi Shihu) is one of the most
popular and valuable Dendrobium species and has been widely used as health supple-
ments and traditional Chinese medicine (TCM) for antipyretic, eyes-benefiting, and
tonic purposes et al. (China Pharmacopoeia Committee 2010). The main chemical com-
ponents of D. officinale are polysaccharides, sesquiterpenoids, alkaloids, and phenolic
compounds had the bioactivities of antioxidantion, antitumor, hypoglycemic and
CONTACT Cheng-Ting Zi
zichengting@126.com; Xuan-Jun Wang
wangxuanjun@gmail.com; Jun Sheng
shengj@ynau.edu.cn
These authors contributed equally to this work
ꢀ
Supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2021.1901698.
ß 2021 Informa UK Limited, trading as Taylor & Francis Group

2
J.-Y. YAN ET AL.
Figure 1. Structures of aiphanol and dendrocandin analogues (Dendrocandins V and compound 1).
enhancing immune ability (Ma et al. 1994; Wu et al. 2004; Zha et al. 2007; Hsieh
et al. 2008).
The natural dendrocandins were extracted from the stem of the Dendrobium spe-
cies (Li et al. 2008, 2014; Yang et al. 2015; Zhang et al. 2017; Yang et al. 2018; Li et al.
2020). The structure of dendrocandin was elucidated as an unprecedented stilbenoli-
gnan skeleton in which a bibenzyl moiety is linked to a phenylpropane unit through a
dioxane bridge. It has a wide range of biological activities, such as antioxidantive, anti-
cancer, and anti-inflammatory activities (Kuboki et al. 2003; Li et al. 2008, 2014; Yang
et al. 2015; Zhang et al. 2017; Yang et al. 2018; Li et al. 2020). Among the dendrocan-
din family, aiphanol (Figure 1) exerts a potent anticancer activity (Shou et al. 2017).
Zhang et al. (2017) reported that Dendrocandin V (Figure 1) showed cytotoxic activ-
ities against five human cancer cell lines (HL-60, A-549, SMMC-7721, MCF-7 and SW-
480). Thus, those compounds may serve as a new anticancer drug that utilized starva-
tion tactics to attack solid tumors.
However, dendrocandins are found in the stem of the Dendrobium species have
very low levels, and also isolated very difficult because they have very similar chemical
structures. So, very little information regarded dendrocandins from D. officinale has
been reported. To study the relationship between the structure of dendrocandins and
the anti-proliferati effects in human cancer cells, we synthesized a novel dendrocandin
(1) using the starting materials 4-hydroxy-3,5-dimethoxybenzaldehyde and 3,4-
dihydroxybenzaldehyde.
Aiphanol has been synthesized through a [4 þ 2]-cycloaddition reaction and Witing
reaction (Wang et al. 2004; Banwell et al. 2005). Compound 1 was prepared by total
synthesis using a similar method of aiphanol, except the oxidative coupling reaction
was promoted by an Ag(I) species (Guz et al. 2001). In the retrosynthetic analysis
(Figure 2), the stibene moiety of compound 1 would be obtained from aldehyde 2
and phosphonium salt 3 by Wittig reaction. The 1,4-benzodioxane skeleton might be
available through a silver oxide promoted oxidative coupling of a benzylallylic alcohol
4
and 3,4-dihydroxybenzaldehyde 5. Compound 4 would be prepared from 4-hydroxy-
,5-dimethoxybenzaldehyde 6 by Wittig olefination and reduction reaction with
DIBAL-H.
Furthermore, we have evaluated cytotoxicity of compound 1 against human cancer
3
cells in vitro using the MTT assay, and analysed cell apoptosis in SW480 cells by flow
cytometry. The synthetic procedures and the biological assay results are also pro-
vided herein.

NATURAL PRODUCT RESEARCH
3
Figure 2. A retrosythetic analysis of compound 1.
2. Results and discussion
2.1. Chemical synthesis
As shown in Scheme 1, the first half of the convergent synthesis required preparation
of compound 4 Synthesis of compound 4 began from 4-hydroxy-3,5-dimethoxybenzal-
dehyde 6. By following the reported method (Banwell et al. 2005), the phenolic unit of
commercially available syringealdehyde 6 was protected as the corresponding MOM-
ehter 7 in 95% yield. Aldehyde 7 was reacted with triethyl phosphonoacetate and
sodium hydride (NaH) to afford the E-configured a,b-unsaturated ester 8 in 80% yield,
which was reduced with diisobutyl aluminium hydride (DIBAL-H) in toluene to corre-
sponding the cinnamyl alcohol 9 in 80% yield (Toshio et al. 1996).
Following the procedure of Merlini et al. (1980) the hetero-Diels–Alder reaction
between the cinnamyl alcohol 9 and 3,4-dihydroxybenzaldehyde 5 gave the cyclo-
adduct 2 in 56% yield (Scheme 2). The next step was construction of a stibene skel-
eton by Witting reaction using phosphonium salt 3 (Townsend et al. 1981), which was

4
J.-Y. YAN ET AL.
prepared from benzyl alcohol in the 2 steps using a similar method has been reported
Scheme 1. Synthesis of compound 4. Reagents and reaction conditions: (a) MOM-Cl, DIPEA, DCM,
ꢁ ꢁ
–18 C, 6 h, 95%; (b) EtOCOCH P(O)(OEt) , NaH, THF, 0–18 C, 4 h, 80%; (c) DIBAL-H, toluene,
2 2
ꢂ10 C, 1 h, 78%.
0
ꢁ
in the literature. Aldehyde 2 was treated with 3 in the presence of cesium fluoride
CsF) in toluene under reflux conditions to give protected the E/Z diastereomeric mix-
ture in 60% yield, which was hydrogenated under hydrogen balloon conditions using
% palladium-carbon (Pd-C) as a catalyst to afford protected dendrocandin 9 in 96%
(
5
yield. Finally, the MOM group 9 was removed under acidic conditions to give com-
pound 1 in 83% yield, which was further confirmed by the conducting of sets of 2D
NMR experiments (1H-1H COSY, HSQC, HMBC, and ROESY spectra) (Supplementary
material Figure S1). To determine the absolute configuration of compound 1, the com-
parison between the experimental and calculated electronic circular dichroism (ECD)
spectra of 1 was performed using the time dependent density functional theory
(
TDDFT) method with B3LYP/6-311þþG(d, p)//B3LYP/6-31 G(d, p) level. The calculated
ECD spectrum was comparable with the measured for compound 1 (Supplementary
material Figure S2). From the above evidence, the structure of compound 1 was eluci-
dated with 7 R, 8 S configurations.
0
0
2.2. In vitro antiproliferative activities
Combretastatin A-4P (CA-4P) was used as positive control. The activity of compound 1
was expressed by the IC50 value was presented in Table 1. As shown in Table S1
(Supplementary material), compound 1 displayed weak cytotoxicity to the A549, MCF-
7
and HL-60 cell lines (IC50 > 40 mM). However, compound 1 showed potent against
SW480 cell line tested at IC50 value with 16.27 ± 0.26 mM. Thus, we decided to study
the effect of compound 1 on SW480 cells. Moreover, colony formation assays were
performed to further validate the anti-proliferating effect of compound 1 when the
concentration of 1 reached 15 mM (Supplementary material Figure S3).
2.3. Compound 1 induced apoptosis in the SW480 cells
Considering that compound 1 exhibits antiproliferative activity in vitro, we further
studied the capacity of 1 to induce cell death through apoptosis. The apoptotic effect
of compound 1 on SW480 cells was detected by using CA-4P as the reference com-
pound. As shown in the Figure S4A (Supplementary material), the percentages of
apoptotic cells were determined to be greater than those under control conditions,
indicating that compound 1 induced apoptosis in SW480 cells. Caspase-3 and PARP
(poy ADP ribose polymerase) are considered to be an important indicator of apoptosis

NATURAL PRODUCT RESEARCH
5
Scheme 2. Synthesis of compound 1. Reagents and reaction conditions: (a) Ag O, benzene-acetone
2
ꢁ
(
2:1), reflux, 24 h, 56%; (b) CsF, toluene, 110 C, 24 h, 60%; (c) H , Pd-C (5%), CH Cl , 8 h, 96%; (d)
2
2 2
ꢁ
AcOH, CH OH, 18 C, 20 h, 83%.
3
(
Hensley et al. 2013). SW480 cell lines were treated with compound 1 at different con-
centrations (3.75, 7.5 and 15 lM) for 24 h and the expression level of cleaved caspase-
and PARP was monitored using western blot. As shown in the Figure S4B
Supplementary material), the expression levels of apoptotic proteins (cl-PARP) were
3
(
significantly up-regulated, indicating that compound 1 can up-regulate the expression
of apoptotic proteins, leading to apoptosis.
3. Conclusions
In summary, the total synthesis of a dendrocandin analogue (1) was achieved using a
convergent strategy (9 steps, 12.6% overall yield) using the starting materials 4-
hydroxy-3,5-dimethoxybenzaldehyde and 3,4-dihydroxybenzaldehyde which included a
silver oxide promoted oxidative coupling and Wittig reaction as the key steps, and
screened for anticancer activity against six human cancer cells (MCF-7, A549, A431,
SW480, HepG-2 and HL-60). Compound 1 showed potent cytotoxicity against SW480
cells, with the IC50 value 16.27 ± 0.26 mM. The colony formation assays were performed
to further validate the anti-proliferating effect of compound 1. Compound 1 also can
up-regulate the expression of apoptotic proteins (cl-PARP). Zhang et al. (2017)
reported the anti-cancer mechanism of Aiphanol. There were many autophagosomes
appeared in the cytoplasm treated with Aiphanol. However, after the addition of
autophagy inhibitors, autophagosomes were significantly reduced. The structure of
Compound 1 is similar to Aiphanol. We speculate that 1 may induce cell death
through autophagy.Thus, this compound suggested that its potential as anticancer
agent for further development. Further refinement of the synthetic scheme and struc-
ture-function relationships (SARs) of dendrocandins will be reported in due course.
Disclosure statement
No potential conflict of interest was reported by the authors.

6
J.-Y. YAN ET AL.
Funding
This work was financially supported by grants from National Nature Science Foundation of
China (grant numbers 21602196, 31960075); the Science and Technology Project of Yunnan
province (grant numbers 2017ZF003, 2017FG001-046, 2018FG001-035 and 2019ZG00904).
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