Bioactive tigliane diterpenoids from the latex of Euphorbia fischeriana

Article abstract of DOI:10.1080/14786419.2019.1616728

Latex is a type of sticky endogenous fluids derived from diverse plants including Euphorbia fischeriana, and is of great scientific and commercial values. In the current study, it was demonstrated that the latex extracted from E. fischeriana strongly respelled the growth of cotton bollworm, Helicoverpa armigera. Using spectroscopic methods, HPLC, and GC-MS analyses, six aliphatic tigliane diterpenoids were isolated from the latex of E. fischeriana, among which three compounds (2, 3, and 5) were new. Two major compounds (1 and 4) exhibited remarkable antifeedant activity against H. armigera, with EC₅₀ values at 2.59 and 15.32 μg/cm², respectively. In addition, the quantification analysis of diterpenoids in different organs indicated that 4 was the most abundant constituent and was highly accumulated in the latex. Collectively, the current study highlighted that the diterpenoids in latex of E. fischeriana had a considerable antifeedant function against H. armigera, which might be employed for the future development of natural insecticides for organic farming.

Full text of DOI:10.1080/14786419.2019.1616728

Natural Product Research
Formerly Natural Product Letters
ISSN: 1478-6419 (Print) 1478-6427 (Online) Journal homepage: https://www.tandfonline.com/loi/gnpl20
Bioactive tigliane diterpenoids from the latex of
Euphorbia fischeriana
Yan-Yan Deng, Bo Qu, Zhong-Lang Zhan, An-Qi Wang, Wei Zhou, Ming-Yue
Jia, Juan Hua & Shi-Hong Luo
To cite this article: Yan-Yan Deng, Bo Qu, Zhong-Lang Zhan, An-Qi Wang, Wei Zhou, Ming-Yue
Jia, Juan Hua & Shi-Hong Luo (2019): Bioactive tigliane diterpenoids from the latex of Euphorbia
fischeriana, Natural Product Research, DOI: 10.1080/14786419.2019.1616728
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NATURAL PRODUCT RESEARCH
https://doi.org/10.1080/14786419.2019.1616728
Bioactive tigliane diterpenoids from the latex of
Euphorbia fischeriana
Yan-Yan Deng, Bo Qu, Zhong-Lang Zhan, An-Qi Wang, Wei Zhou, Ming-Yue Jia,
Juan Hua and Shi-Hong Luo
College of Bioscience and Biotechnology, Shenyang Agricultural University, Shenyang, Liaoning
Province, 110866, China
ABSTRACT
ARTICLE HISTORY
Received 15 March 2019
Accepted 6 May 2019
Latex is a type of sticky endogenous fluids derived from diverse
plants including Euphorbia fischeriana, and is of great scientific
and commercial values. In the current study, it was demonstrated
that the latex extracted from E. fischeriana strongly respelled the
growth of cotton bollworm, Helicoverpa armigera. Using spectro-
scopic methods, HPLC, and GC-MS analyses, six aliphatic tigliane
diterpenoids were isolated from the latex of E. fischeriana, among
which three compounds (2, 3, and 5) were new. Two major com-
pounds (1 and 4) exhibited remarkable antifeedant activity against
H. armigera, with EC50 values at 2.59 and 15.32 lg/cm2, respect-
ively. In addition, the quantification analysis of diterpenoids in dif-
ferent organs indicated that 4 was the most abundant constituent
and was highly accumulated in the latex. Collectively, the current
study highlighted that the diterpenoids in latex of E. fischeriana
had a considerable antifeedant function against H. armigera, which
might be employed for the future development of natural insecti-
cides for organic farming.
KEYWORDS
Euphorbia fischeriana; latex;
tigliane diterpenoids;
antifeedant activity; insect
growth inhibition
CONTACT Shi-Hong Luo
luoshihong@syau.edu.cnJuan Hua
huajuan@syau.edu.cn
College of Bioscience
and Biotechnology, Shenyang Agricultural University, Shenyang, Liaoning Province, 110866, China.
Supplemental data for this article is available online at https://doi.org/10.1080/14786419.2019.1616728.
ß 2019 Informa UK Limited, trading as Taylor & Francis Group

2
Y.-Y. DENG ET AL.
1. Introduction
The laticifer cells of plant were composed of long tubular or branched structures that
permeated the plant roots, leaves, stems and fruits (Konno 2011). Plant latex, a sticky
endogenous fluid, is flowed inside laticifers and secreted immediately after plant tissue
being injured (Agrawal and Konno 2009). It has been found that more than 20,000
species from over 40 families can exude latex, such as Euphorbiaceae, Asteraceae,
Apocynaceae, and Moracea (Agrawal and Konno 2009, Konno 2011). Latex was an
important natural material of scientific and commercial value because of containing
wide diversity and high concentrations of secondary metabolites, which possessed a
broad range of biological activities, including pharmacological and insecticidal activ-
ities (Konno 2011). Latex of mulberry leaves was rich in sugar-mimic alkaloids that
were the effective inhibitors of sugar-metabolizing enzymes and deleterious to herbiv-
orous insects (Konno et al. 2006).
Euphorbia is the largest genus of the family Euphorbiaceae, with more than 2000 spe-
cies. The character of this genus is the production of irritant latex that is rich in kinds of
biologically active terpenoids (Hua et al. 2017; Hua et al. 2015; Rozimamat et al. 2018; Xu
et al. 2015). The latex of several species of this genus was vital role in indigenous medicine
and poisons to kill the fish and large animals (Betancur-Galvis et al. 2003). Euphorbia
fischeriana, is a perennial herbaceous plant with white latex, which distributed mainly in
northeast mainland China (Jian et al. 2018). The dried roots called “lang-du” had long been
used as a famous traditional Chinese medicine for the treatment of cancer, psoriasis, tuber-
culosis, and ascites (Shi et al. 2017). In addition, the plant could be developed as a new bio-
logical pesticide because of the obvious toxicity of E. fischeriana (Sun and Liu 2011).
Numerous investigations have mostly focused on the secondary metabolites of the roots
of E. fischeriana and their pharmacological activities (He et al. 2019; Huang et al. 2017; Shi,
et al. 2017; Wang et al. 2017; Wang et al. 2006; Wei et al. 2018). However, the detailed
investigation about the specific constituents in the plentiful latex of E. fischeriana is still
lacking. Furthermore, biological activities of the latex remain unclear. To exploit E. fischeri-
ana latex on the economic value and potential application, bioactive-guided isolation of
methanolic extract of latex was carried out and six tigliane diterpenoids, including three
new compounds (2, 3, and 5), were identified as shown in Figure 1. Two dominant
Figure 1. Chemical structures of compounds 1–6 from the latex of Euphorbia fischeriana.

NATURAL PRODUCT RESEARCH
3
compounds (1 and 4) were performed the antifeedant activity against a generalist herbi-
vore Helicoverpa armigera and quantified in the latex and different organs by
HPLC analyses.
2. Results and discussion
2.1. Antifeedant activity and growth inhibition against H. armigera
The antifeedant activity of fresh latex collected from the roots of E. fischeriana against
a generalist insect herbivore, Helicoverpa armigera was investigated. The larvae fed
almost solely upon the control leaf discs, but scarcely touched the latex treated leaf
discs, which indicated that the latex was power antifeedant activity against insect
(Supplementary material Figure S1). Through detection of the detrimental effect on
the weight gain of H. armigera, the growth inhibitory activity of latex methanol extract
against the larvae of H. armigera was investigated. From the results in the Figure S2,
the tested samples showed obvious inhibitory activity in a dose-dependent manner
after 96 h. Larvae weighed significantly less when fed latex extracts in concentrations
both 500 and 1000 lg/g in diets. At the maximum concentration of 1000 lg/g in diet,
larvae weight reduced approximately 50% comparing with those of the control team,
indicating that the latex methanol extracts may be a growth inhibition substance
for insect.
2.2. Secondary metabolites analyses by HPLC
For analyzing the major active lactic metabolites, 200 mg roots latex of E. fischeriana
was suspended with 2 mL of methanol by ultrasonication for 45 min to remove the
macromolecular substances including proteins and polysaccharides. After centrifuga-
tion, the supernatant was directly analyzed with reversed-phase HPLC, equipped with
a diode array detector recorded at 254 nm. Six major peaks (1–6) with retention times
at 23.46, 24.03, 25.56, 28.60, 29.15, and 30.30 min, respectively, were detected in the
chromatogram.
2.3. Structural elucidation and identification of latex secondary metabolites
Using column chromatography and reversed-phase semi-preparative HPLC, six com-
pounds were successfully purified and identified as three new aliphatic tigliane diter-
penoids (2, 3, and 5) and three known ones (1, 4, and 6) from the latex methanol
extract of E. fischeriana.
Compound 2 was obtained as colorless oil and had a molecular formula of
C36H56O6, as established by 13C NMR spectroscopic data and HR-ESI-MS molecular ion
at m/z 609.3963 [M þ Na]þ (calcd 609.3969), deducing the presence of nine degrees
1
of unsaturation. In the H NMR spectrum (Supplementary material Table S1), two ole-
finic protons at dH 5.59 (d, J ¼ 4.7 Hz) and 7.54 (s), together with four methyl protons
at dH 0.90 (3H, overlap), 1.06, 1.16, and 1.74 (d, J ¼ 1.5 Hz) were observed. The 13C
and DEPT spectra showed 36 carbon resonances, including five methyls, fifteen meth-
ylenes, eight methines and eight quaternary carbons. Several typical carbon signals

4
Y.-Y. DENG ET AL.
were clear visible, consisting of one carbonyl at dC 210.6, two trisubstituted double
bonds at dC 160.9, 134.8, 142.0 and 130.4, three oxygenated quaternary carbons at dC
77.6, 74.8, and 65.0, and one oxygenated methylene carbon at dC 68.3. Taking into
account above observations, 2 was confirmed to have tigliane-type diterpenoid skel-
eton (Wang et al. 2015). Besides the resonances for the diterpenoid skeleton, the
remaining 13C NMR data demonstrated the presence of the long chain fatty acid with
C16H30O ester moiety. The 1D NMR spectra of 2 resembled those of 12-deoxyphor-
bol-13-hexadecanoate (4) (Ma et al. 1997), which was a known tigliane diterpenoid
with one ester chain of C16H32O also isolated in this study. Comparing the NMR data
of 2 with those of 4, one more unsaturated unit should be assigned in the 2. The
NMR data at dH 5.34 (2H, m), 2.33 (2H, d, J ¼ 7.3 Hz), 1.24-1.38 (m), and dC 130.8 (d),
130.9 (d), and 30.1-30.8 also confirmed that a long-chain aliphatic group with one cis
1
double bond attaching to the skeleton. In the HMBC spectrum of 2, the H-13C long-
range correlation of protons at dH 3.91 and 3.95 (H2-20) with C-5 (dC 38.6), C-6 (dC
142.0), and C-7 (dC 130.4) disclosed that the hydroxyl group of C-20 was free. The
ester moiety could be assigned to C-13 because no HMBC correlation was observed
between carbonyl carbon dC 177.5 and any protons from the tigliane skeleton, which
was further supported by the similar chemical shift of C-13 (dC 65.0) comparing with
those of 12-deoxyphorbol-13-hexadecanoate (4) (dC 63.3). 2 was hydrolyzed by etha-
nolic KOH (Teixeira et al. 1997), and gave the resultant fatty acid that was analyzed
as 7Z-hexadecenoic acid by GC-MS analysis. The ROESY spectrum of 2 indicated that
the relative configurations of the stereogenic centers in 2 were same as those in 4.
Accordingly, the structure of compound 2 was determined as 12-deoxyphorbol-13-
(7Z)-hexadecenoate.
Compound 3, colorless oil, was assigned as a molecular formula of C38H58O6 according
to the 13C NMR and HR-ESI-MS data at m/z 633.4124 ([M þ Na]þ, calcd. 633.4126), implying
the presence of ten degrees of unsaturation. The 1D and 2D NMR spectra of 3 showed sim-
ilarities to those of 2 except for two more olefinic methines for the ester residue, suggest-
ing 3 was also a tigliane diterpenoid. The 1D NMR data at dH 5.59 (2H, m), 5.34 (2H, m),
1.28-1.39 (m), and dC 129.1 (d), 129.1 (d), 130.8 (d), 130.9 (d), and 30.1–30.8 also confirmed
that 3 contains a long-chain aliphatic group with two cis double bond. The chain of length
and location of double bond of ester moiety was deduced by hydrolysis and GC-MS ana-
lysis, which was identified as 9Z,12Z-octadecadienoic acid. Consequently, compound 3
was isolated as 12-deoxyphorbol-13-(9Z,12Z)-octadecadienoate.
Compound 5 was isolated as colorless oil, with the molecular formula of C38H60O6
from the 13C NMR and HR-ESI-MS data at m/z 635.4279 ([M þ Na]þ, calcd. 635.4282),
indicating nine degrees of unsaturation. The characteristic resonances were unambigu-
1
ously assigned to tigliane diterpenoid, as observed in the H and 13C NMR spectra.
Careful comparison of the 1D NMR spectra of 5 with those of 3 revealed that two ole-
finic methines were absent in 5, while two methylenes were present in the aliphatic
acid chain. Those differences were confirmed by the degrees of unsaturation and the
1
1Hꢀ H COSY, HSQC, and HMBC correlations. The same general approach as described
above was used to elucidate the structure of aliphatic chain as 6Z-octadecenoic acid.
Therefore, the structure of compound 5 was elucidated as 12-deoxyphorbol-13-(6Z)-
octadecenoate.

NATURAL PRODUCT RESEARCH
5
Three known compounds were identified as 12-deoxyphorbol-13-tetradecanoate (1)
(Seip et al. 1983), 12-deoxyphorbol-13-hexadecanoate (4) (Ma et al. 1997), and 12-
deoxyphorbaldehy-13-hexadecanoate (6) (Wang et al. 2006), respectively, by compari-
son of their spectrum data with those previously reported in the literatures. Through
comparison of their retention times and UV spectra of HPLC analyses, the identities of
peaks 1–6 in the latex of E. fischeriana were further validated to be compounds 1–6
(Supplementary material Figure S3).
2.4. Antifeedant activities of 1 and 4
To determine whether these major latex metabolites are the responsible active com-
pounds, the antifeedant activity of the major compounds 1 and 4 against H. armigera
were investigated. From the results in the Table S2, both diterpenoids were potential
deterrents to H. armigera. Notably, 1 and 4 showed obvious antifeedant activity with EC50
values of 2.59 0.35 and 15.32 1.61 lg/cm2, respectively. The antifeedant activity of 1
was approximately closed with commercial neem oil containing 1% azadirachtin (EC50 ¼ 4.
07 0.30lg/cm2), while 4 was less active. The results strongly suggested that 1 and 4
could effective constitutes acting as antifeedant against insect herbivores.
2.5. Quantification of compounds 1 and 4
Since compounds 1 and 4 are the main latex metabolites of E. fischeriana, the exact
contents of the two compounds in latex, root, stem, and leaves were carried out.
Quantitative analyses were performed by HPLC-DAD with the above isolated samples
as external standards. The latex contained the highest concentrations of two diterpe-
noids, especially compound 4 that was the most abundant single metabolite with con-
centration of up to 4319.07 143.26 lg/g (Figure 2). In addition, the content of 4 in
the root was 2459.82 262.79 lg/g, while the concentration of 4 was a few in the
leaves and stem. In contrast, the content of 1 in the root was equal with in the stem
and leaves, which were approximately 232.31 35.96 lg/g. These findings suggested
that the tigliane diterpenoids 1 and 4 were mainly accumulated in the latex.
Through comparison of the content of diterpenoids 1 and 4 in latex with the bio-
assay results, including antifeedant and growth inhibition of latex and EC50 values of
the diterpenoids, it found that the content of both diterpenoids was exactly in
Figure 2. Quantification of compounds 1 and 4 in latex and different organs of Euphorbia
ꢁꢁꢁ
fischeriana ( p < 0.001, student’s test).

6
Y.-Y. DENG ET AL.
agreement with antifeedant activity, which suggested that diterpenoids might be bio-
active components in latex of E. fischeriana against insect.
3. Experimental
3.1. Plant material
The root latex and whole plant of Euphorbia fischeriana (Euphorbiaceae) were col-
lected from Tieling city (E: 124ꢂ040, N: 42ꢂ270) of Liaoning province in China in May
2018 and identified by Professor Bo Qu. The voucher specimens
(SYNUB015929–SYNUB015935) were deposited at College of Bioscience and
Biotechnology, Shenyang Agricultural University.
3.2. Metabolite analysis of latex by HPLC
200 mg root latex of E. fischeriana was suspended with 2 mL methanol under ultra-
sonic bath for 45 min and then centrifuged at 12,000 rpm for 5 min. After centrifuga-
tion, the supernatant was directly analyzed by HPLC. At a flow rate of 1 mL/min, 20 mL
of the sample was injected into an Eclipse XDB-C18 column (5 lm, 4.6 ꢃ 250 mm), and
the column temperature was maintained at 30 ꢂC. The eluent was monitored at
200–400 nm. The mobile phase composed of (A) water and (B) methanol were used
(0–15 min: linear 30–90% of B, 15–43 min, isocratic 92% of B, 43–48 min, isocratic 95%
of B).
3.3. Extraction and isolation of latex metabolites
The root latex of E. fischeriana was collected in the methanol (3 ꢃ 0.5 L). The methanol
solution was concentrated and evaporated to dryness in vacuo. The crude extract
(11.7 g) was subjected to MCI gel column chromatography eluting with methanol/
water (70–100%) to give 5 fractions (fractions 1–5). Fraction 3 (80 mg, 80% methanol/
water) was purified on a Sephadex LH-20 column (dichloromethane/methanol, 1:1, v/v)
to yield 2 (3.5 mg). Fraction 4 (1.3 g, 90% methanol/water) was further separated by a
silica gel column (dichloromethane/acetone, 25:1, v/v) to afford 2 subfractions (4a and
4 b). Subfraction 4a (900 mg) was chromatographed on a Sephadex LH-20 column
(dichloromethane/methanol, 1:1, v/v) and was finally purified by reversed-phase semi-
preparative HPLC (90% methanol in water; 3 mL/min; Eclipse XDB-C18 column, 5 lm,
9.4 ꢃ 250 mm) to yield 1 (67 mg, tR 15.5 min), 3 (3.3 mg, tR 19.6 min), and 4 (81 mg, tR
25.3 min). Subfraction 4 b (400 mg) was further subjected to column chromatography
on silica gel (petroleum ether/acetone, 4:1, v/v) and Sephadex LH-20 (acetone) to yield
5 (2.2 mg) and 6 (1.5 mg).
3.4. Antifeedant activity
The insect cotton bollworm (H. armigera) was purchased from the Pilot-Scale Base of
Bio-Pesticides, Institute of Zoology, Chinese Academy of Sciences. A dual-choice bio-
assay was performed for antifeedant test as previously described (Shan et al. 2018).

NATURAL PRODUCT RESEARCH
7
The larvae were reared on an artificial diet in our laboratory under controlled photo-
period (light: dark, 12: 8 h) and temperature (25 2 ꢂC). For the antifeedant assay of
the latex, treated leaf discs were painted with 1, 2, 5, and 10 lL of the freshly collected
latex, while control leaf discs were added the same amount of water. For the antifeed-
ant assay of isolated pure compounds, treated leaf discs were painted with 10 lL of
acetone solution containing the test compound, and control leaf discs with the same
amount of acetone. The insect antifeedant potency of the tested compound was eval-
uated in terms of the EC50 value (the effective dosage for 50% feeding reduction)
which was determined by Probit analysis for each insect species. Commercial neem oil
was used as positive control.
3.5. Larval growth inhibition assay
The effect of latex of E. fischeriana on larval growth of H. armigera was evaluated as
previously described (Zalucki and Malcolm 1999) with briefly modifications. Latex
methanol extract was incorporated into insect artificial diet to obtain a concentration
of 0, 100, 500, and 1000 lg/g. After diet mixture stirred evenly and divided into the
24-well plates, each 3rd larva being weighed was placed into each well. Individual larva
weight was recorded every 24 h until 75% of larvae in the control team reached the
pupal stage. Seven replicates were set for each treatment.
4. Conclusion
Plant latex possessed significant biological activities, including antimicrobial, anti-prolif-
erative, anti-inflammatory, anti-parasitic and insecticidal activities, and so on. In this
study, the root latex of E. fischeriana was screened for their antifeedant and growth
inhibitory effects on a generalist plant-feeding insect, H. armigera (cotton bollworm),
which showed potent antifeedant and growth inhibitory activities. Six tigliane diterpe-
noids, including three new diterpenoids were isolated and identified from the root latex
of E. fischeriana. Compounds 1 and 4 showed significant antifeedant activity and
detected high content in the latex, suggesting that the two compounds, especially 4 as
the most abundant and also most bioactive diterpenoid, should be responsible for anti-
feedant and growth inhibition effect of the latex against insect. Our findings not only
provided a scientific basis for further development and sustainable utilization of E.
fischeriana latex, but also indicated the potential application of plant latex compounds
as novel insecticide or antifeedant based on natural product.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This research was financially supported by the National Key Research & Development (R&D)
Program of China (2017YFD0201400, 2017YFD0201403) and the Talent Program of Shenyang
Agricultural University (awarded to Shi-Hong Luo).

8
Y.-Y. DENG ET AL.
ORCID
Shi-Hong Luo
http://orcid.org/0000-0003-3500-3466
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