Heterocyclic pyrrolizinone and indolizinones derived from natural lactam as potential antifungal agents

Article abstract of DOI:10.1016/j.fitote.2018.07.013

With the aim to develop highly potential active heterocyclic compounds, two series of multi-substituted pyrrolizinone and indolizinones derived from lactam were designed, synthesized and evaluated for their potential antifungal activities against six species of the plant pathogen fungi (Fusarium graminearum, Sclerotinia sclerotiorum, Phomopsis adianticola, Gloeosporium theae-sinensis, Alternaria tenuis Nees, Magnaporthe oryzae). The structure of all the newly molecules were confirmed by analytical spectroscopic data, including ¹H NMR, ¹³C NMR and ESI-MS. According to the preliminary studies on bio-evaluation assay, some of the obtained compounds exhibited moderate and broad-spectrum activities against six fungi compared to the intermediates 6a, 6f and the hymexazol. Particularly, the inhibition rate of compounds 7l, 7m and 7t reached 69.25%, 74.76%, 65.38% against Phomopsis adianticola and Magnaporthe oryzae in vitro activity. Furthermore, compounds 7l and 7t displayed obviously inhibition activities against Phomopsis adianticola compared to the hymexazol. Consequently, compounds 7l and 7t with six-membered alkane ring could be used as new motifs for further investigation.

Full text of DOI:10.1016/j.fitote.2018.07.013

Fitoterapia129(2018)257–266
Contents lists available at ScienceDirect
Fitoterapia
journal homepage: www.elsevier.com/locate/fitote
Heterocyclic pyrrolizinone and indolizinones derived from natural lactam as
potential antifungal agents
Shuangshuang Wang, Longzhu Bao, Wenda Wang, Di Song, Jingjing Wang, Xiufang Cao⁎
College of Science, Huazhong Agricultural University, Wuhan, 430070, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Pyrrolizinone
Indolizinone
Synthesis
Plant pathogen fungi
Antifungal activities
Structure-activity relationships
With the aim to develop highly potential active heterocyclic compounds, two series of multi-substituted pyr-
rolizinone and indolizinones derived from lactam were designed, synthesized and evaluated for their potential
antifungal activities against six species of the plant pathogen fungi (Fusarium graminearum, Sclerotinia scler-
otiorum, Phomopsis adianticola, Gloeosporium theae-sinensis, Alternaria tenuis Nees, Magnaporthe oryzae). The
structure of all the newly molecules were confirmed by analytical spectroscopic data, including 1H NMR, 13C
NMR and ESI-MS. According to the preliminary studies on bio-evaluation assay, some of the obtained com-
pounds exhibited moderate and broad-spectrum activities against six fungi compared to the intermediates 6a, 6f
and the hymexazol. Particularly, the inhibition rate of compounds 7l, 7m and 7t reached 69.25%, 74.76%,
65.38% against Phomopsis adianticola and Magnaporthe oryzae in vitro activity. Furthermore, compounds 7l and
7t displayed obviously inhibition activities against Phomopsis adianticola compared to the hymexazol.
Consequently, compounds 7l and 7t with six-membered alkane ring could be used as new motifs for further
investigation.
1. Introduction
have been explored and isolated. What's more, many natural lactam
derivatives (Fig. 1) presented extensively remarkable pharmacological
In view of the increasing environmental safety issues, the creation of
friendly and low toxicity pesticides has become a vital research project
in recent years, which is closely related to the development of agri-
cultural production, the stable national economy and the sustainable
environment [1–3]. Moreover, leading optimization based on natural
products with excellent biological properties has been a useful way to
discovery and synthesize better performance agrochemicals more ra-
pidly and effectively [4, 5].
In addition, nitrogen-containing heterocyclic compounds are a very
important branch of heterocyclic chemistry in the field of modern
pesticide synthesis, and due to the similarity of the chemical structure
of alkaloids in organisms, they have some characteristics such as high
target specificity and good environmental compatibility [6–8]. There-
fore, the molecular design, synthesis and biological activity of nitrogen-
containing heterocyclic compounds have been one of the hot fields in
the new pesticides creation.
and biological activities, including antibacterial [12, 17], antifungal
[18, 19], antiviral [20], herbicidal [21], antitumor activities [22], and
cytogenetic toxicity [23] etc. Hence, it can be further confirmed that
lactam units can be used as a class of important pharmacophores in
searching for novel active compounds, which will help us to explore the
highly active molecules as soon as possible.
Recently, in the process of studying active compounds, we have
synthesized and evaluated a series of novel functionalized multi-sub-
stituted heterocyclic compounds containing lactam segments (Fig. 2),
and the antifungal activities against plant pathogenic fungi have been
estimated. So, in order to explore the potential applications for these
heterocyclic compounds, we report herein the synthesis and char-
acterization of twenty pyrrolizinone and indolizinone derivatives via
mild cyclization reaction, and their antifungal activities against the
phytopathogenic fungi including Fusarium graminearum, Sclerotinia
sclerotiorum, Phomopsis adianticola, Gloeosporium theae-sinensis, Alter-
naria tenuis Nees, Magnaporthe oryzae have also been fully investigated.
It is hoped that these pyrrolizinone and indolizinone derivatives con-
taining lactam unit will provide a certain theoretical basis and useful
information for the creation and innovation of novel antifungal agents.
It is well known that lactams [9–11] are natural product fragments
that are widely found in terrestrial and marine organisms in nature
(including bacteria, fungi, cyanobacteria, sponges, etc.), whose mother
nucleus structure is pyrrolidine-2,4-dione [12–16]. According to nu-
merous reports, many lactam fragments-containing natural products
⁎
Corresponding author.
E-mail address: caoxiufang@mail.hzau.edu.cn (X. Cao).
https://doi.org/10.1016/j.fitote.2018.07.013
Received 14 June 2018; Received in revised form 24 July 2018; Accepted 25 July 2018
Availableonline26July2018
0367-326X/©2018ElsevierB.V.Allrightsreserved.

S. Wang et al.
Fitoterapia129(2018)257–266
Fig. 1. Representative structure of naturally occurring lactam derivatives.
Fig. 2. Design strategy of pyrrolizinone and indolizinone derivatives containing lactam unit.
2. Materials and methods
heated to reflux at 65–70 °C for 12 h, which was detected by TLC. After
the completion of reaction, the solvent was removed in vacuo and the
residue was washed with CH2Cl2. The above procedure was repeated
twice to obtain the crude intermediates 4, which were used for the next
reaction without further purification.
2.1. Instrumentation and chemicals
All chemicals or reagents used for syntheses were of AR grand, were
commercially available and used directly without purification.
Anhydrous CH2Cl2 and MeOH were obtained under standard methods.
1H NMR spectra were recorded on a Brucker spectrometer at 600 MHz
with the CDCl3 as the solvent and TMS as the internal standard. 13C
NMR spectra were recorded on a Brucker spectrometer at 150 MHz with
CDCl3 as the solvent. Chemical shifts were reported in δ (parts per
million) values. Coupling constants nJ was reported in Hz. Mass spectra
were performed on a Waters ACQUITY UPLC® H-CLASS PDA (Waters®)
instrument. Analytical thin-layer chromatography (TLC) was carried
out on precoated plates, and spots were visualized with ultraviolet
light. Column chromatography was carried out on silica gel (Qingdao
Haiyang Chemical, Qingdao, China).
2.4. General synthetic procedures for intermediates 5
To a solution of methyl piperidinecarboxylate hydrochloride 2
(0.02 mol) in methylene chloride (20 ml) was added in a dried round-
bottom flask, to which triethylamine (0.05 mol) and solution of phe-
nylacetyl chloride in methylene chloride (0.024 mol) was added drop-
wise separately in an ice bath for over 20 min, next the cold bath was
removed. The reaction was stirred at room temperature for 12 h, and
TLC traced the reaction to completion. After the completion of the re-
action, the solution was dissolved in water (20 ml), and the aqueous
solution was extracted with methylene chloride (30 ml × 2) twice. The
combined organic phases were washed with 5% Na2CO3 solution
(30 ml × 2) and water to neutrality and dried over anhydrous Na2SO4.
After filtration and concentration, the corresponding compound 5 were
received through the above methods.
2.2. General synthetic procedures for intermediates 2
To a solution of α-amino acid 1 (0.134 mmol) in methanol (50 ml)
was slowly added dropwise thionyl chloride (0.200 mmol), which was
stired at ice bath (0 °C) for 30 min, and then the mixture was heated to
80 °C for 12 h reaction,and monitored by TLC. After the completion of
reaction, the reaction solution was concentrated, filtered and washed
twice with CH2Cl2 to obtain the crude amino-acid ester hydrochlorides
2, which were used for the next reaction without further purification.
2.5. General synthetic procedures for intermediates 6a-j
A freshly prepared intermediates 5 (17.5 mmol) and the tetra-
hydrofuran solution (30 ml) were dissolved under stirring and then
potassium tert-butoxide (30 mmol) was added. A 12 h reflux reaction
under heating in a 70 °C oil bath, and TLC monitored the reaction to
completion. Then added water to the system and stirred for 10 min,
adjusted the pH to 2–3 with 10% dilute hydrochloric acid. The aqueous
phase was extracted twice with ethyl acetate (30 ml × 2). The organic
phases were combined and washed by water once, and dried over
2.3. General synthetic procedures for intermediates 4
The substituted phenylacetic acid (3 mmol) and thionyl chloride
(10 ml) were placed in a dry round-bottomed flask, and the mixture was
258

S. Wang et al.
Fitoterapia129(2018)257–266
anhydrous Na2SO4. Finally, after filtration and concentration, inter-
mediates 6a-j was obtained, their physico-chemical properties and ESI-
MS spectra data are as follows:
1-hydroxy-2-(4-methoxyphenyl)-6,7,8,8a-tetrahydroindolizin-3(5H)-
one 6j
This compound was obtained following the above method as brown
powder, MS (ESI) m/z 260.4 (M + H)+, calcd. for C19H23NO3 m/
z = 259.1.
1-hydroxy-2-phenyl-5,6,7,7a-tetrahydro-3H-pyrrolizin-3-one 6a
This compound was obtained following the above method as white
powder, MS (ESI) m/z 216.6 (M + H)+, calcd. for C19H23NO3m/
z = 215.1.
2.6. General synthetic procedures for target compounds 7a-t
Intermediate 6 (0.93 mmol), 20 ml of dichloromethane, triethyla-
mine (1.39 mmol) were added into a round bottom flask, and stirred for
0.5 h after isobutyl chloride or 2,2-dimethylbutyryl chloride
(1.12 mmol) was added dropwise in an ice bath (0 °C), and then the
temperature rose to room temperature for 12 h, which was detected by
TLC. After the reaction completed, it was extracted twice with water
and CH2Cl2 (30 ml × 3). The organic phases were combined and wa-
shed to neutrality by saturated brine and water respectively. Finally,
they were dried with anhydrous Na2SO4 and concentrated under re-
duced pressure to obtain the target compounds 7a-t, the physico-che-
mical properties and analytical spectra data of the all newly compounds
7a-t are as follows:
1-hydroxy-2-(o-tolyl)-5,6,7,7a-tetrahydro-3H-pyrrolizin-3-one 2-Me 6b
This compound was obtained following the above method as white
powder, MS (ESI) m/z 230.3 (M + H)+, calcd. for C19H23NO3m/
z = 229.11.
2-(2,4-dichlorophenyl)-1-hydroxy-5,6,7,7a-tetrahydro-3H-pyrrolizin-3-
one 6c
This compound was obtained following the above method as white
powder, MS (ESI) m/z 284.4 (M + H)+, calcd. for C19H23NO3m/
z = 283.0.
5-oxo-6-phenyl-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl isobutyrate 7a
2-(4-fluorophenyl)-1-hydroxy-5,6,7,7a-tetrahydro-3H-pyrrolizin-3-one
6d
Yellowish semisolid, yield 97%. 1H NMR (600 MHz, CDCl3):
δ = 7.72 (d, J = 6 Hz, 2H), 7.39 (t, J = 6 Hz, 2H), 7.32 (t, J = 6 Hz,
1H), 4.67 (q, J = 6 Hz, 1H), 3.66–3.61 (m, 1H), 3.35–3.31 (m, 1H),
2.80–2.76 (m, 1H), 2.33–2.28 (m, 1H), 2.25–2.17 (m, 2H), 1.55–1.48
(m, 1H), 1.28–1.25 (m, 6H); 13C NMR (150 MHz, CDCl3): δ = 181.48,
173.29, 172.90, 161.98, 129.29, 128.57, 128.22, 119.54, 63.87, 42.71,
34.28, 29.39, 28.70, 18.71; MS (ESI) m/z 308.3 (M + Na)+, calcd. for
This compound was obtained following the above method as white
powder, MS (ESI) m/z 234.6 (M + H)+, calcd. for C19H23NO3m/
z = 233.1.
1-hydroxy-2-(4-methoxyphenyl)-5,6,7,7a-tetrahydro-3H-pyrrolizin-3-
one 6e
C
17H19O3 m/z = 285.1.
This compound was obtained following the above method as white
powder, MS (ESI) m/z 246.6 (M + H)+, calcd. for C19H23NO3m/
z = 245.1.
5-oxo-6-phenyl-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl 2,2-dimethylbu-
tanoate 7b
Orange-yellow semisolid, yield 91%. 1H NMR (600 MHz, CDCl3):
1-hydroxy-2-phenyl-6,7,8,8a-tetrahydroindolizin-3(5H)-one 6f
δ = 7.71 (d, J = 6 Hz, 2H), 7.38 (t, J = 6 Hz, 2H), 7.31 (t, J = 6 Hz,
1H), 4.68 (q, J = 6 Hz, 1H), 3.66–3.61 (m, 1H), 3.35–3.31 (m, 1H),
2.34–2.28 (m, 1H), 2.25–2.17 (m, 2H), 1.67 (q, J = 6 Hz, 2H),
1.55–1.48 (m, 1H), 1.26 (s, 6H), 0.88 (t, J = 6 Hz, 3H); 13C NMR
(150 MHz, CDCl3): δ = 174.03, 173.28, 162.22, 129.26, 128.61,
128.19, 128.15, 119.77, 63.78, 43.45, 42.69, 33.13, 29.38, 28.71,
24.04, 9.28; MS (ESI) m/z 336.3 (M + Na)+, calcd. for C19H23NO3 m/
z = 313.2.
This compound was obtained following the above method as white
powder, MS (ESI) m/z 230.4 (M + H)+, calcd. for C19H23NO3m/
z = 229.1.
1-hydroxy-2-(o-tolyl)-6,7,8,8a-tetrahydroindolizin-3(5H)-one 6g
This compound was obtained following the above method as white
powder, MS (ESI) m/z 244.5 (M + H)+, calcd. for C19H23NO3m/
z = 243.1.
5-oxo-6-(o-tolyl)-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl isobutyrate 7c
Orange-yellow semisolid, yield 95%. 1H NMR (600 MHz, CDCl3):
δ = 7.23 (q, J = 6 Hz, 2H), 7.19–7.12 (m, 2H), 4.61 (dd, J1 = 12 Hz,
J2 = 6 Hz, 1H), 3.64 (dd, J1 = 18 Hz, J2 = 6 Hz, 1H), 3.33 (t, J = 6 Hz,
1H), 2.67–2.58 (m, 1H), 2.39–2.30 (m, 1H), 2.27 (s, 3H), 2.26–2.17 (m,
2H), 1.21 (dd, J1 = 6 Hz, J2 = 2 Hz, 1H), 1.12 (dd, J1 = 12 Hz,
J2 = 6 Hz, 6H); 13C NMR (150 MHz, CDCl3): δ = 182.18, 173.59,
172.97, 162.73, 137.27, 130.18, 129.88, 128.54, 128.34, 125.43,
64.42, 42.76, 33.99, 29.43, 28.91, 19.88, 18.81; MS (ESI) m/z 322.3
(M + Na)+, calcd. for C18H21NO3 m/z = 299.2.
2-(2,4-dichlorophenyl)-1-hydroxy-6,7,8,8a-tetrahydroindolizin-3(5H)-
one 6h
This compound was obtained following the above method as white
powder, MS (ESI) m/z 298.3 (M + H)+, calcd. for C19H23NO3m/
z = 297.0.
2-(4-fluorophenyl)-1-hydroxy-6,7,8,8a-tetrahydroindolizin-3(5H)-one
6i
5-oxo-6-(o-tolyl)-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl 2,2-dimethylbu-
This compound was obtained following the above method as white
powder, MS (ESI) m/z 248.4 (M + H)+, calcd. for C19H23NO3m/
z = 247.1.
tanoate 7d
Orange-yellow semisolid, yield 69%. 1H NMR (600 MHz, CDCl3):
δ = 7.28–7.20 (m, 2H), 7.19–7.08 (m, 2H), 4.59 (dd, J1 = 12 Hz,
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Fitoterapia129(2018)257–266
J2 = 6 Hz, 1H), 3.70–3.59 (m, 1H), 3.41–3.30 (m, 1H), 2.34–2.27 (m,
3H), 2.24–2.18 (m, 1H), 1.65–1.56 (m, 3H), 1.57–1.46 (m, 2H), 1.14 (d,
J = 6 Hz, 6H), 0.70 (t, J = 6 Hz, 3H); 13C NMR (150 MHz, CDCl3):
δ = 183.85, 174.00, 173.64, 163.07, 137.25, 130.10, 129.91, 128.53,
128.28, 125.37, 64.42, 43.25, 42.76, 33.16, 29.32, 28.95, 24.47, 19.84,
9.21; MS (ESI) m/z 350.4 (M + Na)+, calcd. for C20H25NO3 m/
z = 327.2.
(M + Na)+, calcd. for C18H21NO4 m/z = 315.1.
6-(4-methoxyphenyl)-5-oxo-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl
2,2-dimethylbutanoate 7j
Brownish yellow semisolide, yield 95%. 1H NMR (600 MHz, CDCl3):
δ = 7.69 (d, J = 12 Hz, 2H), 6.92 (d, J = 6 Hz, 2H), 4.65 (q, J = 6 Hz,
1H), 3.82 (s, 3H), 3.64–3.60 (m, 1H), 3.34–3.30 (m, 1H), 3.12–3.08 (m,
1H), 2.32–2.27 (m, 1H), 2.24–2.16 (m, 2H), 1.68 (q, J = 6 Hz, 2H),
1.26 (d, J = 6 Hz, 6H), 0.92 (t, J = 6 Hz, 3H); 13C NMR (150 MHz,
CDCl3): δ = 174.12, 173.54, 160.91, 159.39, 129.92, 121.85, 119.30,
113.63, 63.70, 55.25, 42.65, 33.20, 29.71, 28.69, 24.52, 24.03, 9.31;
MS (ESI) m/z 366.4 (M + Na)+, calcd. for C20H25NO4 m/z = 343.2.
6-(2,4-dichlorophenyl)-5-oxo-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl
isobutyrate 7e
Orange-yellow semisolid, yield 69%. 1H NMR (600 MHz, CDCl3):
δ = 7.44 (s, 1H), 7.29 (s, 2H), 4.68 (q, J = 6 Hz, 1H), 3.64 (m, 1H),
3.40–3.29 (m, 1H), 2.73–2.63 (m, 1H), 2.40–2.29 (m, 1H), 2.30–2.19
(m, 2H), 1.59–1.50 (m, 1H), 1.18 (d, J = 6 Hz, 6H); 13C NMR
(150 MHz, CDCl3): δ = 182.17, 172.57, 172.29, 163.80, 134.92,
134.57, 132.30, 129.44, 127.00, 117.64, 64.48, 42.84, 34.13, 33.73,
28.79, 18.81; MS (ESI) m/z 376.2 (M + Na)+, calcd. for C17H17Cl2NO3
m/z = 353.1.
3-oxo-2-phenyl-3,5,6,7,8,8a-hexahydroindolizin-1-yl isobutyrate 7k
Brownish yellow semisolid, yield 84%. 1H NMR (600 MHz, CDCl3):
δ = 7.74–7.72 (m, 2H), 7.38 (t, J = 6 Hz, 2H), 7.31 (t, J = 6 Hz, 1H),
4.42 (dd, J1 = 12 Hz, J2 = 6 Hz, 1H), 4.35 (dd, J1 = 12 Hz, J2 = 6 Hz,
1H), 2.88–2.83 (m, 1H), 2.80–2.75 (m, 1H), 2.07–2.04 (m, 1H),
1.98–1.95 (m, 1H), 1.98–1.95 (m, 1H), 1.83–1.76 (m, 1H), 1.57–1.50
(m, 1H), 1.43–1.35 (m, 1H), 1.27 (t, J = 6 Hz, 6H); 13C NMR (150 MHz,
CDCl3): δ = 181.82, 173.51, 166.41, 160.50, 129.37, 129.02, 128.54,
128.19, 127.95, 119.47, 57.13, 39.00, 34.19, 33.67, 29.70, 25.57,
23.25, 18.81; MS (ESI) m/z 322.3 (M + Na)+, calcd. for C18H21NO3 m/
z = 299.2.
6-(2,4-dichlorophenyl)-5-oxo-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl
2,2-dimethylbutanoate 7f
Orange-yellow semisolid, yield 96%. 1H NMR (600 MHz, CDCl3):
δ = 7.44–7.41 (m, 1H), 7.30–7.27 (m, 2H), 4.71 (q, J = 12 Hz, 1H),
3.66–3.61 (m, 1H), 3.35–3.32 (m, 1H), 2.36–2.31 (m, 1H), 2.30–2.17
(m, 2H), 2.17–2.06 (m, 1H), 1.62 (q, J = 6 Hz, 2H), 1.21 (s, 6H), 0.92
(t, J = 6 Hz, 3H); 13C NMR (150 MHz, CDCl3): δ = 183.24, 173.54,
164.14, 134.92, 134.61, 132.41, 132.31, 129.41, 129.27, 126.96,
64.42, 43.41, 42.83, 33.17, 33.04, 32.92, 24.03, 9.12; MS (ESI) m/z
404.2 (M + Na)+, calcd. for C19H21Cl2NO3 m/z = 381.1.
3-oxo-2-phenyl-3,5,6,7,8,8a-hexahydroindolizin-1-yl 2,2-dimethylbu-
tanoate 7l
Brownish yellow semisolid, yield 98%. 1H NMR (600 MHz, CDCl3):
δ = 7.71 (d, J = 12 Hz, 2H), 7.37 (t, J = 6 Hz, 2H), 7.30 (t, J = 6 Hz,
1H), 4.43 (dd, J1 = 12 Hz, J2 = 6 Hz, 1H), 2.88–2.83 (m, 1H),
2.80–2.75 (m, 1H), 2.07–2.04 (m, 1H), 1.98–1.95 (m, 1H), 1.79–1.76
(m, 1H), 1.72–1.63 (m, 2H), 1.63–1.56 (m, 2H), 1.55–1.50 (m, 1H),
1.26 (d, J = 6 Hz, 6H), 0.87 (t, J = 6 Hz, 3H); 13C NMR (150 MHz,
CDCl3): δ = 174.62, 166.30, 160.67, 129.97, 129.37, 128.62, 128.09,
119.66, 57.06, 43.36, 38.93, 32.99, 29.63, 25.58, 24.51, 23.35, 9.22;
MS (ESI) m/z 350.3 (M + Na)+, calcd. for C20H25NO3m/z = 327.2.
6-(4-fluorophenyl)-5-oxo-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl
butyrate 7g
iso-
Yellowish semisolid, yield 97%. 1H NMR (600 MHz, CDCl3):
δ = 7.75–7.72 (m, 2H), 7.08 (t, J = 6 Hz, 2H), 4.67 (dd, J1 = 12 Hz,
J2 = 6 Hz, 1H), 3.65–3.60 (m, 1H), 3.35–3.31 (m, 1H), 2.81–2.74 (m,
1H), 2.32–2.28 (m, 1H), 2.26–2.17 (m, 2H), 1.54–1.47 (m, 1H), 1.28
(dd, J1 = 6 Hz, J2 = 2 Hz, 6H); 13C NMR (150 MHz, CDCl3):
δ = 173.11, 172.79, 163.24, 161.76, 161.60, 130.45, 130.40, 125.41,
118.47, 115.33, 115.19, 63.86, 42.69, 34.28, 29.37, 28.69, 18.83; MS
(ESI) m/z 326.3 (M + Na)+, calcd. for C17H18FNO3 m/z = 303.1.
3-oxo-2-(o-tolyl)-3,5,6,7,8,8a-hexahydroindolizin-1-yl isobutyrate 7m
Yellow semisolid, yield 98%. 1H NMR (600 MHz, CDCl3):
δ = 7.25–7.21 (m, 2H), 7.20–7.12 (m, 2H), 4.40 (dd, J1 = 12 Hz,
J2 = 6 Hz, 1H), 4.28 (dd, J1 = 12 Hz, J2 = 6 Hz, 1H), 2.90–2.85 (m,
1H), 2.64–2.61 (m, 1H), 2.27–2.24 (m, 3H), 2.12–2.09 (m, 1H),
2.00–1.95 (m, 1H), 1.80–1.77 (m, 1H), 1.58–1.51 (m, 1H), 1.46–1.38
(m, 1H), 1.28–1.24 (m, 1H), 1.11 (dd, J1 = 12 Hz, J2 = 6 Hz, 6H); 13C
NMR (150 MHz, CDCl3): δ = 173.49, 166.43, 161.08, 137.26, 130.09,
129.92, 128.52, 128.40, 125.40, 122.34, 57.55, 39.12, 33.94, 25.64,
23.27, 19.88, 18.81, 18.56; MS (ESI) m/z 336.3 (M + Na)+, calcd. for
6-(4-fluorophenyl)-5-oxo-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl 2,2-
dimethylbutanoate 7h
Orange-yellow semisolid, yield 86%. 1H NMR (600 MHz, CDCl3):
δ = 7.72 (q, J = 6 Hz, 2H), 7.08 (t, J = 6 Hz, 2H), 4.67 (dd, J1 = 12 Hz,
J2 = 6 Hz, 1H), 3.65–3.60 (m, 1H), 3.35–3.31(m, 1H), 2.34–2.28 (m,
1H), 2.25–2.18 (m, 2H), 1.68 (q, J = 6 Hz, 2H), 1.53–1.49 (m, 1H),
1.26 (s, 6H), 0.88 (t, J = 6 Hz, 3H); 13C NMR (150 MHz, CDCl3):
δ = 173.11, 172.79, 163.24, 161.76, 161.75, 161.60, 130.45, 130.40,
118.47, 115.33, 115.19, 63.86, 42.69, 34.28, 29.37, 28.69, 18.83; MS
(ESI) m/z 354.3 (M + Na)+, calcd. for C19H22FNO3 m/z = 331.2.
C
19H23NO3m/z = 313.2.
3-oxo-2-(o-tolyl)-3,5,6,7,8,8a-hexahydroindolizin-1-yl 2,2-dimethylbu-
tanoate 7n
6-(4-methoxyphenyl)-5-oxo-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl iso-
Brownish yellow semisolid, yield 89%. 1H NMR (600 MHz, CDCl3):
butyrate 7i
δ = 7.23–7.19 (m, 2H), 7.16–7.11 (m, 2H), 4.40 (dd, J1 = 12 Hz,
J2 = 6 Hz, 1H), 4.24 (dd, J1 = 12 Hz, J2 = 6 Hz, 1H), 2.90–2.85 (m,
1H), 2.26 (s, 3H), 2.10–2.08 (m, 1H), 2.00–1.97 (m, 1H), 1.79–1.77 (m,
1H), 1.62–1.58 (m, 2H), 1.49 (q, J = 6 Hz, 2H), 1.44–1.39 (m, 1H),
1.09 (d, J = 18 Hz, 6H), 0.66 (t, J = 6 Hz, 3H); 13C NMR (150 MHz,
CDCl3): δ = 174.44, 166.47, 161.36, 137.26, 130.00, 128.52, 128.39,
125.34, 122.96, 99.98, 57.69, 43.21, 39.10, 32.99, 25.64, 24.51, 23.29,
Yellowish semisolid, yield 78%. 1H NMR (600 MHz, CDCl3):
δ = 7.71 (d, J = 6 Hz, 2H), 6.92 (d, J = 12 Hz, 2H), 4.64 (q, J = 6 Hz,
1H), 3.82 (s, 3H), 3.65–3.60 (m, 1H), 3.33 (t, J = 6 Hz, 1H), 2.81–2.76
(m, 1H), 2.32–2.28 (m, 1H), 2.24–2.16 (m, 2H), 1.53–1.46 (m, 1H),
1.28 (dd, J1 = 6 Hz, J2 = 2 Hz, 6H); 13C NMR (150 MHz, CDCl3):
δ = 173.49, 172.92, 160.59, 159.32, 129.80, 121.81, 119.02, 113.63,
63.71, 55.19, 42.64, 34.22, 29.40, 28.63, 18.68; MS (ESI) m/z 338.3
19.84, 9.21, 8.92; MS (ESI) m/z 364.4 (M + Na)+
21H27NO3m/z = 341.2.
, calcd. for
C
260

S. Wang et al.
Fitoterapia129(2018)257–266
2-(2,4-dichlorophenyl)-3-oxo-3,5,6,7,8,8a-hexahydroindolizin-1-yl iso-
2-(4-methoxyphenyl)-3-oxo-3,5,6,7,8,8a-hexahydroindolizin-1-yl 2,2-
butyrate 7o
dimethylbutanoate 7t
Brownish yellow semisolid, yield 70%. 1H NMR (600 MHz, CDCl3):
δ = 7.43 (d, J = 6 Hz, 1H), 7.33 (d, J = 6 Hz, 1H), 7.29 (dd, J1 = 6 Hz,
J2 = 2 Hz, 1H), 4.39 (dd, J1 = 12 Hz, J2 = 6 Hz, 1H), 2.90–2.85 (m,
1H), 2.72–2.67 (m, 1H), 2.62–2.56 (m, 1H), 2.12–2.08 (m, 1H),
2.01–1.95 (m, 1H), 1.81–1.76 (m, 1H), 1.60–1.51 (m, 1H), 1.45–1.39
(m, 1H), 1.25–1.23 (m, 1H), 1.19 (dd, J1 = 6 Hz, J2 = 2 Hz, 6H); 13C
NMR (150 MHz, CDCl3): δ = 172.82, 165.62, 162.16, 134.80, 134.49,
132.38, 129.35, 127.30, 126.98, 117.45, 57.63, 39.21, 34.10, 29.62,
25.54, 23.23, 18.63; MS (ESI) m/z 390.4 (M + Na)+, calcd. for
Brownish yellow semisolid, yield 89%. 1H NMR (600 MHz, CDCl3):
δ = 7.70 (d, J = 12 Hz, 2H), 6.91 (d, J = 12 Hz, 2H), 4.41 (dd,
J1 = 12 Hz, J2 = 6 Hz, 1H), 4.32 (dd, J1 = 12 Hz, J2 = 6 Hz, 1H), 3.82
(s, 3H), 2.87–2.81 (m, 1H), 2.06–2.02 (m, 1H), 1.99–1.92 (m, 1H),
1.78–1.75 (m, 1H), 1.72–1.65 (m, 2H), 1.63–1.60 (m, 1H), 1.54–1.47
(m, 1H), 1.43–1.34 (m, 1H), 1.26 (s, 6H), 0.89 (t, J = 6 Hz, 3H); 13C
NMR (150 MHz, CDCl3): δ = 174.70, 166.55, 159.38, 159.33, 129.90,
121.98, 113.58, 99.98, 56.96, 55.24, 43.35, 38.89, 33.01, 29.71, 29.67,
25.60, 24.61, 24.55, 23.35, 9.29; MS (ESI) m/z 380.4 (M + Na)+
calcd. for C21H27NO4 m/z = 357.2.
,
C
18H19Cl2NO3 m/z = 367.1.
2-(2,4-dichlorophenyl)-3-oxo-3,5,6,7,8,8a-hexahydroindolizin-1-yl
2.7. In vitro biological assays
2,2-dimethylbutanoate 7p
Drug solution of the required concentration was prepared in ad-
vance, added to a certain amount of PDA culture medium (9 mm dia-
meter) to make the poisonous petri plates, and the same amount of
acetone solution (< 2%, v/v) added to the culture medium as the blank
control. The pre-activated strains (Φ = 0.50 cm) was punched at the
edges subsequently, and inoculated at drug concentrations of 6.25,
12.5, 25, 50, 100, 200 μg/ml respectively, drug-free PDA culture
medium containing acetone solution served as a control. The dish was
Brownish yellow semisolid, yield 89%. 1H NMR (600 MHz, CDCl3):
δ = 7.43 (d, J = 6 Hz, 1H), 7.31–7.27 (m, 2H), 4.39 (dd, J1 = 12 Hz,
J2 = 6 Hz, 1H), 4.36–4.31 (m, 1H), 2.90–2.85 (m, 1H), 2.10–2.07 (m,
1H), 2.01–1.95 (m, 1H), 1.81–1.75 (m, 1H), 1.65–1.59 (m, 2H), 1.57 (q,
J = 6 Hz, 2H), 1.45–1.38 (m, 1H), 1.16 (d, J = 12 Hz, 6H), 0.77 (t,
J = 6 Hz, 3H); 13C NMR (150 MHz, CDCl3): δ = 173.90, 173.54,
165.60, 162.45, 134.80, 134.55, 132.38, 129.30, 127.30, 126.94,
57.72, 43.36, 39.20, 32.96, 29.70, 25.53, 24.03, 23.26, 9.12; MS (ESI)
m/z 418.4 (M + Na)+, calcd. for C20H23Cl2NO3 m/z = 395.1.
sealed and incubated at 28
1 °C for two to ten days. The colony
diameter (unit mm) was measured by the cross-cross method to cal-
culate the relative bacteriostatic rate of each compound at this con-
centration. The formula is as follows:
2-(4-fluorophenyl)-3-oxo-3,5,6,7,8,8a-hexahydroindolizin-1-yl
butyrate 7q
iso-
I = (d0 − dt)/d0× 100
Brownish yellow semisolid, yield 82%. 1H NMR (600 MHz, CDCl3):
δ = 7.76–7.73 (m, 2H), 7.11–7.04 (m, 2H), 4.41 (dd, J1 = 12 Hz,
J2 = 6 Hz, 1H), 4.33 (dd, J1 = 12 Hz, J2 = 6 Hz, 1H), 2.89–2.82 (m,
1H), 2.82–2.75 (m, 1H), 2.09–2.03 (m, 1H), 2.00–1.93 (m, 1H),
1.80–1.76 (m, 1H), 1.55–1.50 (m, 2H), 1.40–1.37 (m, 1H), 1.27 (q,
J = 6 Hz, 6H); 13C NMR (150 MHz, CDCl3): δ = 173.42, 166.16,
163.24, 160.21, 130.40, 130.35, 125.54, 118.46, 115.30, 115.16,
57.04, 38.94, 34.20, 29.56, 25.56, 23.28, 18.85, 18.83, 18.73; MS (ESI)
m/z 340.3 (M + Na)+, calcd. for C18H20FNO3 m/z = 317.1.
where I is the growth inhibition rate of mycelia (100%), d0 is the dia-
meter of the blank control colony, and dt is the diameter of the colony
treated with the medicine. IC50 values (compound concentration re-
quired to inhibit colony growth by 50%) could be calculated by IBM
SPSS Statistics 22.0 software.
3. Results and discussion
3.1. Synthesis
In this research project, we designed and synthesized a series of
multi-substituted pyrrolizinone and indolizinone derivatives containing
lactam unit 7a-t by simple, convenient and mild methods. In Scheme 1,
the general synthetic routes and methods of all target compounds were
summarized.
2-(4-fluorophenyl)-3-oxo-3,5,6,7,8,8a-hexahydroindolizin-1-yl 2,2-di-
methylbutanoate 7r
Brownish yellow semisolid, yield 90%. 1H NMR(600 MHz, CDCl3):
δ = 7.73–7.69 (m, 2H), 7.09–7.05 (m, 2H), 4.41 (dd, J1 = 12 Hz,
J2 = 6 Hz, 1H), 4.34 (dd, J1 = 12 Hz, J2 = 6 Hz, 1H), 3.72 (q, J = 6 Hz,
2H), 2.88–2.83 (m, 1H), 2.07–2.04 (m, 1H), 1.98–1.94 (m, 1H),
1.70–1.65 (m, 2H), 1.43–1.36 (m, 2H), 1.26–1.25 (d, J = 6 Hz, 6H),
0.88 (t, J = 6 Hz, 3H); 13C NMR (150 MHz, CDCl3): δ = 174.53, 166.17,
164.12, 163.43, 130.49, 130.43, 128.74, 118.69, 115.22, 115.08,
57.07, 43.38, 38.95, 33.00, 29.61, 25.56, 23.32, 18.44, 9.26; MS (ESI)
m/z 368.4 (M + Na)+, calcd. for C20H24FNO3 m/z = 345.2.
From Scheme 1, we can see that two kinds of easily obtained α-
amino acids 1, proline and pipecolinic acid, were selected as the
starting materials. Firstly, 1 were methylated to give the corresponding
amino acid methyl ester hydrochloride. Then, in order to investigate the
structural diversity, we took the intermediate 2 and five different types
of phenylacetyl chlorides 4 to construct 5 by N-acylation, and followed
the intermediates 5 undergone an intramolecular heterocyclization to
obtain 6a-j under basic conditions. Finally, under mild conditions,
isobutyryl chloride and 2,2-dimethylbutyryl chloride were reacted with
6a-j respectively to produce the target compounds 7a-t. The structure
of intermediates 6a-j were confirmed by ESI-MS, and all newly target
heterocycles 7a-t were analyzed by chemical spectroscopy, including
1H NMR, 13C NMR and ESI-MS spectra.
2-(4-methoxyphenyl)-3-oxo-3,5,6,7,8,8a-hexahydroindolizin-1-yl iso-
butyrate 7s
Brownish yellow semisolid, yield 96%. 1H NMR (600 MHz, CDCl3):
δ = 7.72 (d, J = 12 Hz, 2H), 6.92 (d, J = 6 Hz, 2H), 4.41 (dd,
J1 = 12 Hz, J2 = 6 Hz, 1H), 4.31 (dd, J1 = 12 Hz, J2 = 6 Hz, 1H), 3.82
(s, 3H), 2.87–2.82 (m, 1H), 2.81–2.76 (m, 1H), 2.06–2.04 (m, 1H),
1.97–1.94 (m, 1H), 1.78–1.75 (m, 1H), 1.54–1.51 (m, 1H), 1.42–1.32
(m, 2H), 1.28 (dd, J1 = 7 Hz, J2 = 6 Hz, 6H); 13C NMR (150 MHz,
CDCl3): δ = 173.60, 166.53, 159.34, 159.12, 129.81, 122.01, 118.88,
113.67, 56.94, 55.24, 38.89, 34.21, 29.71, 29.62, 25.60, 23.31, 18.89,
18.76; MS (ESI) m/z 352.3 (M + Na)+, calcd. for C19H23NO4 m/
z = 329.2.
3.2. Spectrum analyses
The structures of all target compounds 7a-t were confirmed by 1H
NMR, 13C NMR and mass spectrometry, and their structures were well
consistent with all the spectral data. The 1H NMR of compounds 7a-t
exhibited different proton signal peaks through different chemical shifts
and peak intensities. A representative 1H NMR spectrum of 7 h shown
261

S. Wang et al.
Fitoterapia129(2018)257–266
Scheme 1. General synthetic route for target compounds. Reagents and conditions: I. SOCl2, MeOH, 0 °C to reflux; II. SOCl2, 65–70 °C; III. Et3N, CH2Cl2, 0 °C to rt.; IV.
t-BuOK, THF, rt. to 70–75 °C; V. Et3N, CH2Cl2, 0 °C to rt.
in Fig. 3 illustrated all 1H NMR spectra characteristic peak of com-
pounds 7a-t, which displayed a unique signal of CeH proton linked the
lactam ring with the alkyl heterocycle, which appeared as a quadruple
peak in the range of 4.62–4.65 ppm. Generally speaking, the signal
peaks in higher chemical shift belonged to aromatic ring protons, and
lower chemical shift were designated as alkyl or cycloalkyl heterocyclic
protons. Hence, the shift values of benzene ring CH protons were at
6.91–7.71 ppm, and CH2 protons assigned to the cycloalkyl hetero-
cycles were in the range of 3.82–1.48 ppm, which were a type of mul-
tiple peak. For the 13C NMR spectrum, the chemical shift values of the
C]O bond in the lactam ring and the enol structure C]C bond were
160–185 ppm respectively. The other peaks appearing in the higher
part were the aromatic and heterocyclic protons between δ 110–135
and 8–64 ppm. The ESI-MS spectrum measured the molecular ion peak
Fig. 3. Representative 1H NMR spectra for compound 7 h.
262

S. Wang et al.
Fitoterapia129(2018)257–266
Table 1
The in vitro fungicidal activity of novel lactam derivatives 7a-t.
Entry
Compd.No.
Substituents
R1
In vitro Fungicidal activity (%)/100 μg/ml
R2
n
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
P.Aa
F.G
A.T
M.O
G.T
S.S
1
7a
7b
7c
7d
7e
7f
H
19.35
51.74
31.17
40.74
33.00
46.85
33.61
54.34
23.02
48.68
24.45
69.25
29.13
56.01
43.79
56.62
53.57
61.71
38.91
65.38
6.77
4.44
7.29
13.26
33.56
10.01
20.42
11.99
11.00
15.21
17.94
18.68
16.20
4.55
-34.71
37.04
14.20
4.94
2
H
31.27
14.33
15.56
13.15
20.38
28.96
28.96
8.59
15.52
19.10
19.10
3.83
63.19
21.53
41.10
31.21
61.29
61.71
37.31
47.62
41.94
49.09
42.15
74.76
40.89
52.67
40.05
39.62
50.35
54.35
46.57
3
2-Me
2-Me
2,4-Cl2
2,4-Cl2
4-F
4
5
0.00
6
10.99
4.07
32.10
56.17
-5.56
12.96
40.12
12.96
28.40
14.81
50.62
43.21
29.63
14.81
40.12
14.81
-13.58
7
7g
7h
7i
8
4-F
21.25
8.60
9
4-MeO
4-MeO
H
10
11
12
13
14
15
16
17
18
19
20
7j
15.29
4.03
23.63
21.49
46.31
22.68
48.21
23.40
31.75
21.49
37.71
29.84
39.86
7k
7l
H
38.61
18.78
37.27
38.08
42.10
11.27
25.21
8.32
37.28
3.56
7m
7n
7o
7p
7q
7r
7s
7t
2-Me
2-Me
2,4-Cl2
2,4-Cl2
4-F
21.66
13.23
23.15
7.77
4-F
27.36
3.81
4-MeO
4-MeO
23.33
36.04
21
22
23
6a
6f
H
H
-
H
H
-
1
2
-
16.30
11.82
51.12
6.18
-1.06
71.58
3.59
15.28
98.33
18.17
43.62
92.22
-3.38
0.09
21.16
-56.79
2.47
100.00
Hymexazolb
a
P.A - Phomopsis adianticola; F.G - Fusarium graminearum; A.T - Alternaria tenuis Nees; M.O - Magnaporthe oryzae; G.T - Gloeosporium theae-sinensis; S·S - Sclerotinia
sclerotiorum.
b
Hymexazol, used as positive control.
of the compounds 7a-t as well as [M + H]+ or [M + Na]+ in the po-
sitive ion mode ions. From the results, all compound 7a-t displayed a
distinct [M + H]+ addition ion fragmentation peak.
results of the preliminary activity screening at the concentration of
100 μg/ml were summarized in Table 1 and Fig. 4, and the IC50 values
indicated the linear relationship between drug concentration and the
inhibition rate, the data were summarized in Table 2.
Generally, viewing the initial screening data in Fig. 4, it could be
learned that most of the compounds 7a-t showed more significant and
broad-spectrum antifungal activities against six plant pathogenic fungi
at 100 μg/ml than the intermediates 6a and 6 f. In addition, most target
compounds had moderate-to-good activity, especially against for pho-
mopsis adianticola and Magnaporthe oryzae, including that compounds
7b, 7f, 7g, 7m for Magnaporthe oryzae and compounds 7l, 7r, 7t for
Phomopsis adianticola showed the inhibition rate are 60–75%, from that
the most significant ones were 7 l, 7 m and 7 t, whose excellent anti-
bacterial activities were 69.25%, 74.76%, 65.38% respectively. Above
all, it was suggested that compounds bearing the lactam structural may
3.3. Bioassay
In this study, we carried out screening on the in vitro antifungal
activity of obtained compounds 7a-t and representative intermediates
6a, 6 f. The petri plate test for determining fungicide inhibition of
mycelial growth method (fungicide inhibition of mycelial growth
method) was specifically adopted, and the six common types of phy-
topathogenic fungi in agriculture were evaluated respectively, in-
cluding Fusarium graminearum, Sclerotinia sclerotiorum, Phomopsis
adianticola, Gloeosporium theae-sinensis, Alternaria tenuis Nees,
Magnaporthe oryzae, and hymexazol was used as a positive control. The
263

S. Wang et al.
Fitoterapia129(2018)257–266
Fig. 4. Antifungal activities of compounds 6a, 6f and 7a-t at 100 μg/ml.
Table 2
The IC50 and logP values of some target compounds against the plant pathogen fungi.
a
Entry
Compd.No.
Substituents
R1
IC50 (μg/ml)
F.Gb
logPc
R2
n
1
1
1
2
2
2
2
2
2
2
-
S.S
P.A
G.T
A.T
M.O
2.85
3.96
1
2
7b
H
> 200
> 200
> 200
7f
2,4-Cl2
4-F
3
7g
-
> 200
> 100
1.88
3.26
3.75
4.38
2.30
3.42
2.01
3.14
-
4
7l
H
73.41
47.51
80.65
86.26
> 100
72.23
96.44
> 100
> 200
5
7n
2-Me
2,4-Cl2
4-F
97.13
6
7p
> 200
7
7q
8
7r
4-F
> 200
> 200
9
7s
4-MeO
4-MeO
-
10
7t
34.86
86.61
> 200
19.82
11
Hymexazold
-
27.6
22.97
> 100
> 200
45.27
a
IC50 - compound concentration required to inhibit colony growth by 50%.
F.G - Fusarium graminearum, S·S - Sclerotinia sclerotiorum, P.A - Phomopsis adianticola, G.T - Gloeosporium theae-sinensis, A.T - Alternaria tenuis Nees, M.O -
b
Magnaporthe oryzae.
c
logP - lipid/water partition coefficients.
Hymexazol, used as positive control.
d
possess certain control effects on Phomopsis adianticola and Magnaporthe
oryzae, and it might be a novel pesticide with small molecule precursor
structure. Moreover, compared with the positive control hymexazol, the
inhibition rate of most derivatives (10%–69.5%) against Phomopsis
adianticola was higher than it (51.12%), compounds 7l and 7t against
Gloeosporium theae-sinensis was also better than the positive control
(21.16%) (Fig. 5).
According to the above preliminary activities, a variety of the target
compounds had good inhibitory effects. To further pursue their highly
potential inhibitory effects, we thus selected some compounds like 7b,
7f, 7g, 7l, 7n, 7p, 7q, 7r, 7s, 7t to have further exploration in such a
situation, and compared the values of IC50 with hymexazol at different
concentrations (6.25, 12.5, 25, 50, 100, 200 μg/ml). Besides, we also
conducted statistical studies on the lipid-water partition coefficient
(logP) of the target compounds, and the IC50 values and logP values for
all lactam derivatives as well as the positive control hymexazol were
showed in Table 2.
80.65, 86.26, 72.23, 34.86 μg/ml) all displayed good inhibitory effects
on phomopsis adianticola compared with the positive control hymexazol
(IC50 > 100 μg/ml). Among these compounds, the IC50 values of sig-
nificant compounds 7l and 7t were 47.51 and 34.86 μg/ml. At the same
time, the data further confirmed that the structure containing lactam
unit also had a good control effect against phomopsis adianticola, com-
pounds 7l and 7t can be used as potential pilot skeleton for further
studies on pharmaceutical molecular discovery.
What's more, the lipid-water partition coefficient (logP) played an
important role in the study of structure-activity relationship (QSAR/
SAR) as a necessary physicochemical property in the drug molecules
design, which was a measure of the hydrophobicity of organic com-
pounds and widely used in pharmacy, biochemistry and environmental
chemistry. The specific logP values also can provide a certain theore-
tical support in medicine structure design. As shown in Table 2, the logP
values of the compounds were calculated and displayed in the range of
1.88–4.38. Generally, the molecules with higher logP values always had
the stronger the lipophilicity, and vice versa. In summary, compounds
As shown in Table 2, compounds 7l, 7n, 7p, 7r, 7t (IC50 = 47.51,
264

S. Wang et al.
Fitoterapia129(2018)257–266
Fig. 5. Inhibitory effect of Compounds 7 l, 7 t and hymexazol on Phomopsis adianticola.
Fig. 6. General structure-activity relationships for target compounds.
7l and 7t revealed an average lipophilicity with logP values of 3.26 and
3.14, while compounds 7g (logP 1.88) and 7s (logP 2.01) have the
lowest logP values, and thus another biological research of these
compounds was expected to further branch out other aspects.
former activity was significantly better than the latter. Through the
above preliminary activity-structure-activity relationship analysis, it
might be helpful to discover more promising novel fungicidal deriva-
tives based on lactam cores. Moreover, it also might have a further
optimization value for the SARs currently acquired and integrated, and
be in progress in our laboratory.
In this system, the structural evolution was achieved through the
functionalization of amino acids, and the heterocyclic derivatives 7a-t
had been constructed by combining five or six-membered alkane het-
erocycle, polysubstituted benzene ring, and an alkanoyl group together
with a lactam ring. According to the in vitro tests (Fig. 4 and Table 2),
we could obtain the possible structure-activity profiles of the novel
lactam derivatives. As shown in Fig. 6, the target compounds 7k-t
containing six-membered heterocycle had better fungicidal activity
than 7a-j bearing five-membered heterocycle, which proved the im-
portance of multiple heterocycle attached to the lactam ring. More
importantly, when the structure of these derivatives had a variety of
substituent R1 connected with benzene rings as well as substituent R2
connected with ester groups, it would result in the varying degrees of
effect in the antibacterial activity. For the aryl substituents attached to
the phenyl ring, it could be seen that the structure of compounds with
4-F-substitute group exhibited more better activity than the electron-
donating substituted compounds, Therefore, the type of substituents on
the benzene ring, electrical and spatial positions will have an important
impact on the antibacterial activity of the compounds. For the short
alkyl groups attached to the oligoacyl groups, we discussed the differ-
ence between 2,2-dimethylbutyryl and isobutyryl groups, which the
4. Conclusions
Based on the natural cyclic ketone-enol structure, two series of
multi-substituted pyrrolizinone and indolizinone derivatives were de-
signed and synthesized, and the systematic biological activity evalua-
tion was also performed. From the current data, most compounds have
broad-spectrum inhibitory effects on six pathogenic fungi. In particular,
it could be found that this type of derivatives had expressive preventive
effect against three pathogens such as phomopsis adianticola,
Magnaporthe oryzae and Gloeosporium theae-sinensis. In a word, the
compounds with more significant activity are 7l and 7t, which can be
used as prospective molecules for further structural exploration and
possible study on mechanism, and the structure-activity relationships
with research value has also been initially obtained, which can lay a
foundation for the subsequent design synthesis and structural optimi-
zation of novel lactam derivatives.
265

S. Wang et al.
Fitoterapia129(2018)257–266
Conflict of interest
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Acknowledgements
We gratefully acknowledge the support of this work by the
Fundamental Research Funds for the Central Universities
(2662016PY112).
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