Nematicidal activity of oleanolic acid derivatives on Meloidogyne incognita

Article abstract of DOI:10.1080/14786419.2020.1786826

In this study, oleanolic acid and its derivatives were studied for their invivo nematicidal activity against root-knot nematode (RKN) Meloidogyne incognita. A series of C-28-oleanolates including five new (5, 7–10) and seven known (1–4, 6, 11, 12) compounds were synthesised and their nematicidal activity was determined and compared with the standard nematicide furadan for the first time. The structures of the compounds were elucidated through ¹H NMR, ¹³C NMR and EIMS. Compounds 4, 5, 7, 8 and 10 showed ～ 90percent inhibition of RKN at 0.125percent concentration after 72 h showing their potential use in nematicidal control.

Full text of DOI:10.1080/14786419.2020.1786826

Natural Product Research
Formerly Natural Product Letters
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gnpl20
Nematicidal activity of oleanolic acid derivatives
on Meloidogyne incognita
Zareena Kiran , Nabila Hassan , Anjum Ayub , Sara Sara , Zarina Bano ,
Sabira Begum , Bina S. Siddiqui , Shahina Fayyaz & Erum Iqbal
To cite this article: Zareena Kiran , Nabila Hassan , Anjum Ayub , Sara Sara , Zarina Bano ,
Sabira Begum , Bina S. Siddiqui , Shahina Fayyaz & Erum Iqbal (2020): Nematicidal activity
of oleanolic acid derivatives on Meloidogyneꢀincognita , Natural Product Research, DOI:
10.1080/14786419.2020.1786826
To link to this article: https://doi.org/10.1080/14786419.2020.1786826
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NATURAL PRODUCT RESEARCH
https://doi.org/10.1080/14786419.2020.1786826
Nematicidal activity of oleanolic acid derivatives on
Meloidogyne incognita
a
b
b
a
a
Zareena Kiran , Nabila Hassan , Anjum Ayub , Sara Sara , Zarina Bano , Sabira
a
a
c
c
Begum , Bina S. Siddiqui , Shahina Fayyaz and Erum Iqbal
a
H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences,
b
University of Karachi, Karachi, Pakistan; Department of Chemistry, NED University of Engineering &
Technology, Karachi, Pakistan; National Nematological Research Center, University of Karachi,
c
Karachi, Pakistan
ABSTRACT
ARTICLE HISTORY
In this study, oleanolic acid and its derivatives were studied for
their invivo nematicidal activity against root-knot nematode (RKN)
Meloidogyne incognita. A series of C-28-oleanolates including five
new (5, 7–10) and seven known (1–4, 6, 11, 12) compounds
were synthesised and their nematicidal activity was determined
and compared with the standard nematicide furadan for the first
time. The structures of the compounds were elucidated through
Received 12 December 2019
Accepted 10 June 2020
KEYWORDS
Oleanolic acid; Meloidogyne
incognita; nematicidal
activity; 28-oleanolates
1
13
H NMR, C NMR and EIMS. Compounds 4, 5, 7, 8 and 10
showed ꢀ 90% inhibition of RKN at 0.125% concentration after
2 h showing their potential use in nematicidal control.
7
1. Introduction
Oleanolic acid (OA) is a naturally occurring pentacyclic triterpenoid (C H O ) (Xia et al.
30 48 3
2
012) which biosynthetically comes from cyclisation of squalene. It is found in stem, leaves
and fruits of different edible and medicinal plants (Fai and Tao 2009). Lantana camara
Vyas and Argal 2013), Lisgustrum lucidum (Xia et al. 2012) and olive oil (Guinda et al. 2010)
(
are rich sources of OA. Apple, grape, sage, elderberry and loquat are also good sources of
oleanolic acid (J €a ger et al. 2009). In China, it has been used as a drug against hepatitis for
several years (Liu et al. 1995). It also has several other biological activities including
CONTACT Sabira Begum
dr.sabirabegum@yahoo.com
Supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2020.1786826.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
Z. KIRAN ET AL.
antioxidant (Yin and Chan 2007), antimicrobial (Kim et al. 2015), antinociceptive, anti-
inflammatory (Rali et al. 2016), anti-HIV (Zhu et al. 2001), anti-diabetic (Treadway et al.
2001), anti-tumour (Liese et al. 2015) and anticancer (Shanmugam et al. 2014).
Due to its natural abundance and high biological potential, researchers are trying to
modify its structure by various chemical changes to increase the stability and water solu-
bility. Chemical structure of OA clearly shows three ‘active sites’ at C-3, double bond
between C-12 and C-13, and C-28 (Pollier and Goossens 2012; Zhang et al. 2012).These
sites can be transformed to achieve increased pharmaceutical properties and enhanced
bioactivity. C-28 of oleanolic acid can be converted into amides, alcohols, nitriles, tria-
zoles and esters analogues (Gupta et al. 2010). Keeping this view in mind, a series
(1–12) of 28-esters of oleanolic acid including five new (5, 7–10) and seven known
derivatives (1–4, 6, 11, 12) was prepared, in which carboxlic group of oleanolic acid was
converted into ester with a target of enhancing the biological activity.
Root-knot nematodes (RKN; Meloidogyne spp.) are pathogenic sedentary endoparasites
of the plant root system. They occur worldwide, and their host range includes many import-
ant agricultural crops. Hence, a search for the management plant-parasitic nematodes is
being undertaken worldwide. Two compounds, acibenzolar-S-methyl, a derivative of salicylic
acid and a plant hormone methyl jasmonate which can elicit the plant’s defence system
against RKN, were recently reported for their direct nematicidal effect on Meloidogyne incog-
nita (Schouteden et al. 2017). Considering the background and need for potential nemati-
cides, the nematicidal effect of oleanolic acid and its C-28-oleanolates was studied against
root-knot nematode, Meloidogyne incognita for the first time in the present work.
2. Results and discussion
2.1. Chemistry
Oleanolic acid was isolated from the dried flower buds of Syzygium aromaticum (clove). In
this study, a series of 28-oleanolates (1–12) of oleanolic acid was prepared (Figure 1) in
quantitative yield. Among them, five compounds (5, 7–10) are new, while seven (1–4, 6,
1
1, 12) have been synthesised earlier (Chen et al. 2016). EIMS showed the absence of car-
boxylic group of oleanolic acid in all ester derivatives (1–12) as the characteristic r.D.A
fragment m/z of 248 was missing and replaced with methyl, ethyl, propyl, butyl, pentyl,
hexyl, heptyl, octyl, nonyl, decyl, benzyl and 4-nitro benzyl esters, respectively. In com-
pounds 1–10, a signal for CH adjacent to oxygen function of ester moiety was observed
2
at d ꢀ3.91 as multiplet. In the benzyl derivatives (11–12), the aromatic protons were
H
observed at d 7.31 in benzyl oleanolate and 7.49–8.19 in case of 4-nitro benzyl oleanolate
H
1
in the H NMR. The structures of new compounds (5, 7–10) were further confirmed by
1
3
C NMR. Ester carbonyl carbon was appeared at d ꢀ177.8, while oxygenated methylene
C
was observed at d ꢀ64.1 that indicated the conversion of carboxylic group into ester
C
moiety (Experimental section). Their structures are illustrated in Figure 1.
2.2. Nematicidal activity
In the present investigation, nematicidal activity of 28-oleanolates (1–12) against root-
knot nematode Meloidogyne incognita at three different concentrations (1.0%, 0.5%

NATURAL PRODUCT RESEARCH
3
Figure 1. Synthetic route of ester formation.
and 0.125%) after 24, 48 and 72 h of exposure were determined (Table S1). The tested
alkyl derivatives (1–10) showed good toxicity (70 to 90%) against Meloidogyne incog-
nita at 0.125% concentration after 72 h. It was observed that mortality increased with
increasing concentration and time duration. After 48 h, all these esters displayed mod-
erate-to-good inhibition 60%–80% at 0.125% concentration. Butyl to decyl oleanolates
(
7
(
4–10) showed comparable activity as oleanolic acid at 0.125% concentration after
2 h. Among benzyl derivatives (11–12), 4-nitrobenzyl oleanolate was more active
68%) than benzyl oleanolate (58%) at same concentration and same time duration
indicating that nitro group enhanced the activity. Nematicidal activity of 28-easters of
oleanolic acid was determined for the first time in the present investigation.
3. Experimental
3.1. Chemistry
3
.1.1. General
1
13
Mass spectrometry was carried out on JEOL JMS600H-1. H NMR and C NMR spectra
were obtained on AVANCE NEO 500 MHz and 125 MHz, respectively. Spectra were
taken in deuterated chloroform (CDCl ), and chemical shifts were recorded in d (ppm).
3

4
Z. KIRAN ET AL.
Residual solvent was used as the internal standard. Reaction was monitored by thin-
layer chromatography and visualised by UV lamp (254 nm), iodine spray and 5% H SO4
2
solution in MeOH. Oleanolic acid was isolated from the flower buds of Syzygium aro-
maticum (clove) according to the method described earlier (Ghulam and Ahmad 2014).
Acetone and potassium carbonate were purchased from Sigma-Aldrich (Steinheim,
Germany) and Fluka Chemie (Buchs, Switzerland), respectively. All the alkyl halides
were purchased from Sigma-Aldrich (Steinheim, Germany). Silica gel (Merck 9385) was
used for column chromatography. Thin-layer chromatography was performed on silica
gel 60 F254 (Merck) (Damstadt, Germany)..
3.1.2. General procedure for the synthesis of 28-Oleanolates and characterisation
To a solution of oleanolic acid (100 mg, 0.23 mmol) in acetonitrile (10 mL), K CO3
2
(66 mg, 0.46 mmol) was added. After 10 minutes of stirring at room temperature, differ-
ent alkyl halides were added. The reaction mixture was kept overnight at room tem-
perature, freed of the solvent by keeping in fuming hood overnight. The solid mass
left was partitioned between ethyl acetate and water. The organic layer was dried
with anhydrous Na SO , filtered and freed of the solvent through rotary evaporator.
2
4
The residue thus obtained was purified by silica gel column chromatography using
petroleum ether-ethyl acetate (9:1) system to obtain compounds 1–12.
Methyl oleanolate (1). Yield 71%. White amorphous solid. EIMS m/z (rel. int. %): 470
þ
1
[
(
4
M ] (6), 455 (3), 411 (5), 262 (52), 203 (100), 189 (19), 133 (12). H NMR (CDCl ) d: 3.21
3
1H, dd, J ¼ 10.8, 4.4 Hz, H-3a), 5.29 (1H, t, J ¼ 3.6 Hz, H-12), 2.84 (1H, dd, J ¼ 14.0,
.0 Hz, H-18b), 1.13, 0.99, 0.93, 0.91, 0.90, 0.78, 0.73 (each 3H, s, 7XCH ), 3.63 (3H, s,
3
0
H-1 ).
Ethyl oleanolate (2). Yield 70%. White amorphous solid. EIMS m/z (rel. int. %): 484
þ
[
M ] (17), 465 (5), 411 (16), 293 (79), 276 (61), 203 (72), 189 (41), 166 (38), 148 (100).
1
H NMR (CDCl ) d: 3.20 (1H, dd, J ¼ 10.1, 3.0 Hz, H-3a), 5.26 (1H, t, J ¼ 3.6 Hz, H-12),
3
2
7
.84 (1H, dd, J ¼ 13.5, 3.9 Hz, H-18b), 1.11, 0.97, 0.90, 0.88, 0.87, 0.76, 0.72 (each 3H, s,
0
0
XCH ), 4.06 (2H, m, H-1 ), 1.20 (3H, t, J ¼ 7.2 Hz, H-2 ).
3
Propyl oleanolate (3). Yield 65%. White amorphous solid. EIMS m/z (rel. int. %): 498
þ
1
[M ] (18), 480 (5), 411 (29), 290 (87), 203 (100), 189 (73), 133 (26). H NMR (CDCl ) d:
3
3
3
1
.19 (1H, dd, J ¼ 10.8, 5.4 Hz, H-3a), 5.26 (1H, t, J ¼ 3.3 Hz, H-12), 2.85 (1H, dd, J ¼ 13.5,
.6 Hz, H-18b), 1.11, 0.96, 0.90, 0.88, 0.88, 0.76, 0.71 (each 3H, s, 7XCH ), 3.95 (2H, m, H-
3
0
0
), 0.92 (3H, t, J ¼ 7.2 Hz, H-3 ).
Butyl oleanolate (4). Yield 71%. White amorphous solid. EIMS m/z (rel. int. %): 512
þ
1
[
(
(
(
M ] (27), 494 (23), 411 (37), 393 (23), 304 (77), 291 (26), 203 (100), 189 (78). H NMR
CDCl ) d: 3.20 (1H, dd, J ¼ 10.0, 3.1 Hz, H-3a), 2.85 (1H, dd, J ¼ 14.0, 4.0 Hz, H-18b), 5.26
3
1H, t, J ¼ 3.6 Hz, H-12), 1.11, 0.97, 0.90, 0.89, 0.88, 0.76, 0.72 (each 3H, s, 7XCH ), 3.99
3
0
0
2H, m, H-1 ), 0.90 (3H, t, J ¼ 7.0 Hz, H-4 ).
Pentyl oleanolate (5). Yield 68%. White amorphous solid. EIMS m/z (rel. int. %): 526
þ
1
[M ] (6), 411 (14), 393 (5), 318 (51), 203 (100), 189 (64). H NMR (CDCl ) d: 3.19 (1H,
3
dd, J ¼ 9.9, 3.9 Hz, H-3a), 5.25 (1H, t, J ¼ 3.0 Hz, H-12), 2.85 (1H, dd, J ¼ 14.1, 3.6 Hz, H-
1
1
8b), 1.11, 0.97, 0.90, 0.88, 0.87, 0.76, 0.71 (each 3H, s, 7XCH ), 3.99 (2H, t, J ¼ 6.6 Hz, H-
3
0
0
13
), 0.88 (3H, t, J ¼ 7.1 Hz, H-5 ). C NMR (CDCl , 75 MHz): d 38.4 (C-1), 27.2 (C-2), 79.0
3
(C-3), 38.4 (C-4), 55.2 (C-5), 17.0 (C-6), 33.0 (C-7), 39.3 (C-8), 47.6 (C-9), 38.4 (C-10), 23.4

NATURAL PRODUCT RESEARCH
5
(C-11), 122.3 (C-12), 143.9 (C-13), 43.9 (C-14), 29.7 (C-15), 22.2 (C-16), 46.6 (C-17), 41.3
(
2
2
C-18), 45.9 (C-19), 30.7 (C-20), 33.4 (C-21), 33.8 (C-22), 28.1 (C-23), 15.3 (C-24), 15.6 (C-
0
ꢁ
5), 18.3 (C-26), 23.0 (C-27), 177.8 (C-28), 33.0 (C-29), 23.6 (C-30), 64.3 (C-1 ), 28.2 (C-
0
ꢁ
0
0
0
ꢁ
), 28.3 (C-3 ), 25.9 (C-4 ), 14.0 (C-5 ). Values may be interchanged.
Hexyl oleanolate (6). Yield 67%. White amorphous solid. EIMS m/z (rel. int. %): 540
þ
1
[
(
M ] (5), 411 (8), 332 (15), 293 (34), 203 (30), 189 (10), 167 (20), 149 (100). H NMR
CDCl3) d: 3.19 (1H, dd, J ¼ 11.0, 4.0 Hz, H-3a), 5.26 (1H, t, J ¼ 4.0 Hz, H-12), 2.85 (1H,
dd, J ¼ 14.0, 4.5 Hz, H-18b), 1.11, 0.97, 0.90, 0.88, 0.87, 0.76, 0.71 (each 3H, s, 7XCH ),
3
0
0
3
.98 (2H, m, H-1 ), 0.88 (3H, t, J ¼ 6.9 Hz, H-6 ).
Heptyl oleanolate (7). Yield 68%. White amorphous solid. EIMS m/z (rel. int. %): 554
8), 537 (5), 410 (15), 393 (10), 346 (31), 333 (12), 203 (100), 189 (33). H NMR (CDCl )
1
(
3
d: 3.19 (1H, dd, J ¼ 9.9, 4.2 Hz, H-3a), 5.25 (1H, t, J ¼ 3.3 Hz, H-12), 2.85 (1H, dd, J ¼ 14.1,
4
1
.5 Hz, H-18b), 1.11, 0.97, 0.90, 0.88, 0.88, 0.76, 0.71 (each 3H, s, 7XCH ), 3.98 (2H, m, H-
3
0
0
13
), 0.87 (3H, t, J ¼ 6.8 Hz, H-7 ). C NMR (CDCl , 75 MHz): d 38.4 (C-1), 27.2 (C-2), 79.0
3
(
(
(
C-3), 38.4 (C-4), 55.2 (C-5), 17.0 (C-6), 33.0 (C-7), 39.3 (C-8), 47.6 (C-9), 38.4 (C-10), 23.4
C-11), 122.6 (C-12), 143.9 (C-13), 43.9 (C-14), 29.7 (C-15), 23.5 (C-16), 46.6 (C-17), 41.3
C-18), 45.9 (C-19), 30.7 (C-20), 33.4 (C-21), 33.8 (C-22), 28.1 (C-23), 15.3 (C-24), 15.6 (C-
0
ꢁ
2
2
5), 18.3 (C-26), 23.0 (C-27), 177.8 (C-28), 33.0 (C-29), 23.6 (C-30), 64.3 (C-1 ), 28.8 (C-
0
0
ꢁ
0
0
0
0
ꢁ
), 26.0 (C-3 ), 28.6 (C-4 ), 31.8 (C-5 ), 25.9 (C-6 ), 14.1(C-7 ). Values may be
interchanged.
Octyl oleanolate (8). Yield 73%. White amorphous solid. EIMS m/z (rel. int. %): 568
þ
1
[
M ] (10), 550 (5), 410 (29), 393 (8), 360 (81), 347 (17), 203 (100), 189 (60), 133 (20). H
NMR (CDCl ) d: 3.19 (1H, dd, J ¼ 10.2, 4.5 Hz, H-3a), 5.26 (1H, t, J ¼ 3.0 Hz, H-12), 2.83
3
(
7
(
(
(
1H, dd, J ¼ 14.1, 4.2 Hz, H-18b), 1.11, 0.96, 0.90, 0.88, 0.88, 0.76, 0.71 (each 3H, s,
0
0
13
XCH ), 3.98 (2H, m, H-1 ), 0.86 (3H, t, J ¼ 7.0 Hz, H-8 ). C NMR (CDCl , 75 MHz): d 38.4
3
3
C-1), 28.1 (C-2), 79.0 (C-3), 38.7 (C-4), 55.2 (C-5), 17.0 (C-6), 33.1 (C-7), 39.3 (C-8), 47.7
C-9), 37.0 (C-10), 23.6 (C-11), 122.3 (C-12), 143.9 (C-13), 41.3 (C-14), 29.2 (C-15), 22.7
C-16), 46.7 (C-17), 41.3 (C-18), 45.6 (C-19), 30.7 (C-20), 33.9 (C-21), 32.8 (C-22), 27.7 (C-
2
3
1
3), 15.3 (C-24), 15.6 (C-25), 18.0 (C-26), 23.4 (C-27), 177.8 (C-28), 32.5 (C-29), 23.4 (C-
0
0
0
ꢁ
0
ꢁ
0
0
0
0), 64.2 (C-1 ), 28.2 (C-2 ), 26.0 (C-3 ), 29.2 (C-4 ), 29.1 (C-5 ), 31.7 (C-6 ), 25.9 (C-7 ),
0
ꢁ
4.1 (C-8 ). Values may be interchanged.
Nonayl oleanolate (9). Yield 77%. White amorphous solid. EIMS m/z (rel. int. %): 582
[
Mþ] (25), 408 (49), 393 (11), 374 (81), 361 (28), 203 (100), 189 (78), 173 14), 133 (23).
1
H NMR (CDCl ) d: 3.19 (1H, dd, J ¼ 10.8, 4.0 Hz, H-3a), 5.26 (1H, t, J ¼ 3.2 Hz, H-12),
3
2
7
3
4
2
2
2
3
.83 (1H, dd, J ¼ 14.0, 4.4 Hz, H-18b), 1.11, 0.97, 0.90, 0.88, 0.88, 0.76, 0.72 (each 3H, s,
0
0
13
XCH ), 3.98 (2H, m, H-1 ), 0.84 (3H, t, J ¼ 6.8 Hz, H-9 ). C NMR (CDCl , 125 MHz): d
3
3
8.2 (C-1), 27.7 (C-2), 78.5 (C-3), 38.8 (C-4), 55.7 (C-5), 17.0 (C-6), 33.4 (C-7), 38.9 (C-8),
7.1 (C-9), 36.5 (C-10), 23.1 (C-11), 121.8 (C-12), 142.9 (C-13), 41.2 (C-14), 28.1 (C-15),
2.6 (C-16), 46.1 (C-17), 40.0 (C-18), 45.4 (C-19), 31.3 (C-20), 33.4 (C-21), 32.6 (C-22),
7.2 (C-23), 14.8 (C-24), 15.0 (C-25), 18.3 (C-26), 22.5 (C-27), 177.8 (C-28), 32.2 (C-29),
0
ꢁ
0
ꢁꢁ
0
ꢁ
0
0
0
2.9 (C-30), 63.8 (C-1 ), 28.8 (C-2 ), 25.6 (C-3 ), 28.7 (C-4 ), 30.2 (C-5 ), 29.0 (C-6 ),
0
ꢁꢁ ꢁ ꢁꢁ
0
0
1.9 (C-7 ), 25.4 (C-8 ), 13.6 (C-9 ). ,
Values may be interchanged.
Decyl oleanolate (10). Yield 75%. White amorphous solid. EIMS m/z (rel. int. %): 596
1
[
Mþ] (8), 578 (5), 410 (15), 388 (34), 203 (100), 188 (26). H NMR (CDCl ) d: 3.20 (1H,
3
dd, J ¼ 9.3, 3.3 Hz, H-3a), 5.26 (1H, t, J ¼ 3.3 Hz, H-12), 2.84 (1H, dd, J ¼ 14.4, 4.5 Hz, H-

6
Z. KIRAN ET AL.
0
8b), 1.11, 0.96, 0.90, 0.88, 0.88, 0.76, 0.71 (each 3H, s, 7XCH ), 3.98 (2H, m, H-1 ), 0.85
3
1
(
0
13
3H, t, J ¼ 7.2 Hz, H-10 ). C NMR (CDCl , 125 MHz): d 38.4 (C-1), 27.2 (C-2), 79.0 (C-3),
3
3
1
1
1
2
1
8.7 (C-4), 55.4 (C-5), 17.0 (C-6), 33.1 (C-7), 39.3 (C-8), 47.7 (C-9), 37.0 (C-10), 23.6 (C-
1), 122.3 (C-12), 143.9 (C-13), 41.7 (C-14), 29.2 (C-15), 22.7 (C-16), 46.7 (C-17), 41.3 (C-
8), 45.6 (C-19), 30.7 (C-20), 33.9 (C-21), 32.8 (C-22), 27.7 (C-23), 15.3 (C-24), 15.6 (C-25),
0
ꢁ
0
0
8.0 (C-26), 23.0 (C-27), 177.8 (C-28), 32.5 (C-29), 23.4 (C-30), 64.2 (C-1 ), 28.1 (C-2 ),
6.0ꢁ
0
0
0
ꢁꢁ
0
ꢁꢁ
0
0
0
(C-3 ), 28.6 (C-4 ), 29.5 (C-5 ), 29.6 (C-6 ), 29.3 (C-7 ), 31.9 (C-8 ), 25.9 (C-9 ),
ꢁ ꢁꢁ
4.1 (C-10 ). , Values may be interchanged.
Benzyl oleanolate (11). Yield 65%. White amorphous solid. EIMS m/z (rel. int. %): 546
1
[
(
Mþ] (7), 455 (10), 437 (100), 411 (21), 338 (22), 247 (82), 203 (92), 189 (37). H NMR
CDCl ) d: 3.18 (1H, dd, J ¼ 11.2, 4.4 Hz, H-3a), 5.27 (1H, t, J ¼ 3.6 Hz, H-12), 2.88 (1H, dd,
3
J ¼ 14.0, 4.4 Hz, H-18b), 1.10, 0.96, 0.89, 0.87, 0.86, 0.75, 0.59 (each 3H, s, 7XCH ), 5.07
3
(
1H, d, J ¼ 12.4Hz, OCH ), 5.02 (1H, d, J ¼ 12.4 Hz, OCH ), 7.31 (5H, s, H-Ar).
a
b
4
-Nitrobenzyl oleanolate (12). Yield 67%. White amorphous solid. EIMS m/z (rel. int.
%
): 591 [Mþ] (5), 558 (6), 453 (7), 437 (10), 410 (15), 383 (45), 248 (20), 203 (100), 189
(
1
25). 1H NMR (CDCl3) d: 3.18 (1H, dd, J ¼ 11.0, 4.3 Hz, H-3a), 5.27 (1H, t, J ¼ 3.6 Hz, H-
2), 2.88 (1H, dd, J ¼ 14.0, 4.4 Hz, H-18b), 1.11, 0.96, 0.90, 0.89, 0.84, 0.75, 0.54 (each
H, s, 7XCH ), 5.18 (1H, d, J ¼ 13.5 Hz, OCH ), 5.08 (1H, d, J ¼ 13.5 Hz, OCH ), 7.49 (2H,
3
3
a
b
0
0
0
0
d, J ¼ 8.7 Hz, H-2 , H-6 ), 8.19 (2H, d, J ¼ 8.7 Hz, H-3 , H-5 ).
3.2. Nematicidal activity
Activity was determined under laboratory conditions. M. incongita culture was devel-
oped according to the method previously described (Ravichandra 2010) and inocu-
lated on locally available brinjal plants and kept under net conditions. 5% aqueous
DMSO was used for preparing the stock solutions of compounds using distilled water
in order to obtain the required concentration. Commonly used nematicide furadan
was used as positive control, while 5% aqueous DMSO as negative control. A total of
100 second-stage juveniles (freshly hatched) were introduced on different compounds
for checking the nematicidal effect. Movement of nematodes was checked with the
help of needle under different time durations. The larvae were counted with the help
of stereoscopic microscopic. Larvae that showed mortality after 72 h was transferred
into another cavity containing distilled water, and their mortality was confirmed after
24 h. The experiment was repeated three times. The results are listed in the Table S1.
4
. Conclusion
In conclusion, a series of oleanolic esters (1–12) was synthesised including five new
5, 7–10) and seven known derivatives (1–4, 6, 11, 12). Their nematicidal toxicity was
(
examined against root-knot nematode, Meloidogyne incognita for the first time.
Among these compounds, butyl to decyloleanolates (4–10) displayed comparable tox-
icity with that of OA at 0.125% concentration after 72 h. It has been noted that with
the increase of carbon chain, activity increases. Hence, oleanolic acid and its ester
derivatives can be studied further for their safe and novel nematode control.

NATURAL PRODUCT RESEARCH
7
Disclosure statement
No potential conflict of interest was reported by the authors.
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