Synthesis and insecticidal evaluation of chiral neonicotinoids analogs: The laurel wilt case

Article abstract of DOI:10.3390/molecules26144225

Xyleborus sp beetles are types of ambrosia beetles invasive to the United States and recently also to Mexico. The beetle can carry a fungus responsible for the Laurel Wilt, a vascular lethal disease that can host over 300 tree species, including redbay and avocado. This problem has a great economic and environmental impact. Indeed, synthetic chemists have recently attempted to develop new neonicotinoids. This is also due to severe drug resistance to “classic” insecticides. In this research, a series of neonicotinoids analogs were synthesized, characterized, and evaluated against Xyleborus sp. Most of the target compounds showed good to excellent insecticidal activity. Generally, the cyclic compounds also showed better activity in comparison with open-chain compounds. Compounds R-13, 23, S-29, and 43 showed a mortality percent of up to 73% after 12 h of exposure. These results highlight the enantioenriched compounds with absolute R configuration. The docking results correlated with experimental data which showed both cation-π interactions in relation to the aromatic ring and hydrogen bonds between the search cavity 3C79 and the novel molecules. The results suggest that these sorts of interactions are responsible for high insecticidal activity.

Full text of DOI:10.3390/molecules26144225

molecules
Article
Synthesis and Insecticidal Evaluation of Chiral Neonicotinoids
Analogs: The Laurel Wilt Case
Saúl A. Luna-Hernández 1 , Israel Bonilla-Landa 1, Alfonso Reyes-Luna 1 , Alfredo Rodríguez-Hernández 1,
Ulises Cuapio-Muñoz 1, Luis A. Ibarra-Juárez 1, Gabriel Suarez-Mendez 1, Felipe Barrera-Méndez 1,2
Irving D. Pérez-Landa 1 , Francisco J. Enríquez-Medrano 3 , Ramón E. Díaz de León-Gómez 3
,
and José L. Olivares-Romero 1,
*
1
Instituto de Ecología, A.C., Red de Estudios Moleculares Avanzados, Clúster Científico y Tecnológico
BioMimic®, Campus III, Carretera Antigua a Coatepec No. 351, Xalapa 91073, Mexico;
c7h5n3o6.lh@gmail.com (S.A.L.-H.); israel.bonilla@inecol.mx (I.B.-L.);
alfonsoreyeslunauv@gmail.com (A.R.-L.); fredor2236@gmail.com (A.R.-H.);
ulisescuapio@gmail.com (U.C.-M.); luis.ibarra@inecol.mx (L.A.I.-J.);
investigacion.suarez@hotmail.com (G.S.-M.); felipe.barrera@inecol.mx (F.B.-M.);
david.perez@posgrado.ecologia.edu.mx (I.D.P.-L.)
Cátedra CONACyT en el Instituto de Ecología, A.C. Carretera Antigua a Coatepec No. 351,
Xalapa 91073, Mexico
Centro de Investigación en Química Aplicada, Blvd. Enrique Reyna, No. 140, Saltillo 25294, Mexico;
javier.enriquez@ciqa.edu.mx (F.J.E.-M.); ramon.diazdeleon@ciqa.edu.mx (R.E.D.d.L.-G.)
Correspondence: jose.olivares@inecol.mx
2
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
3
ꢀꢁꢂꢃꢄꢅꢆ
Citation: Luna-Hernández, S.A.;
Bonilla-Landa, I.; Reyes-Luna, A.;
Rodríguez-Hernández, A.;
*
Abstract: Xyleborus sp beetles are types of ambrosia beetles invasive to the United States and recently
also to Mexico. The beetle can carry a fungus responsible for the Laurel Wilt, a vascular lethal disease
that can host over 300 tree species, including redbay and avocado. This problem has a great economic
and environmental impact. Indeed, synthetic chemists have recently attempted to develop new
neonicotinoids. This is also due to severe drug resistance to “classic” insecticides. In this research,
a series of neonicotinoids analogs were synthesized, characterized, and evaluated against Xyleborus
sp. Most of the target compounds showed good to excellent insecticidal activity. Generally, the cyclic
compounds also showed better activity in comparison with open-chain compounds. Compounds
Cuapio-Muñoz, U.; Ibarra-Juárez,
L.A.; Suarez-Mendez, G.;
Barrera-Méndez, F.; Pérez-Landa, I.D.;
Enríquez-Medrano, F.J.; et al.
Synthesis and Insecticidal Evaluation
of Chiral Neonicotinoids Analogs:
The Laurel Wilt Case. Molecules 2021,
26, 4225. https://doi.org/10.3390/
molecules26144225
R-13
results highlight the enantioenriched compounds with absolute R configuration. The docking results
correlated with experimental data which showed both cation- interactions in relation to the aromatic
, 23, S-29, and 43 showed a mortality percent of up to 73% after 12 h of exposure. These
Academic Editors: Carlotta Granchi
and Valeria Patricia Sülsen
π
ring and hydrogen bonds between the search cavity 3C79 and the novel molecules. The results
suggest that these sorts of interactions are responsible for high insecticidal activity.
Received: 1 June 2021
Accepted: 5 July 2021
Published: 12 July 2021
Keywords: neonicotinoids; nitroguanidines; chiral; enantiopure compound; insecticidal activity
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
1. Introduction
The redbay ambrosia beetle, Xyleborus glabratus, is the vector of the laurel wilt disease
fungal pathogen, Raffaellea lauricola. Since the vector’s initial detection in the USA in the
early 2000s, laurel wilt has killed millions of redbay, Persea borbonia, trees, and other mem-
bers of the plant family Lauraceae [1]. In this context, avocado (Persea Americana Mill.) is
the most important agricultural crop susceptible to laurel wilt [
2]. As the disease continues
Copyright:
© 2021 by the authors.
to move south and west from its original focus, it has caused significant concern in Florida,
California, and other avocado-producing areas such as western Mexico. In the absence of
effective control measures, monetary losses caused by laurel wilt could eventually range
up to USD 54 million in the USA, and greater losses might occur if the disease moves
elsewhere [3].
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
To the best of our knowledge, management is currently focused on monitoring, sanita-
tion and direct control using contact or systemic insecticides [4], and these are still subject
Molecules 2021, 26, 4225. https://doi.org/10.3390/molecules26144225
https://www.mdpi.com/journal/molecules

Molecules 2021, 26, 4225
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to ongoing investigations [5]. Indeed, efficacious and cost-effective measures are urgently
needed to protect avocado from laurel wilt. In this context, neonicotinoids are an important
type of compound with potent insecticidal activity. Since their introduction in the 1980s,
these compounds have been established as the insecticides of choice for agricultural, animal
health, and public health usages [
the central nervous system of the insect and can be efficient ligands for the nicotinic acetyl-
choline receptors (nAChRs) of insects [ ]. However, with the increase in neonicotinoids
used for crop protection over a long time period, the problems of cross-resistance [ ], and
6,7]. They are a type of insecticide that act selectively on
8
9
bee toxicity [10] have received more attention, and this calls for a new strategy of molecular
design to find new leading compounds. Neonicotinoids act selectively on the insect central
nervous system (CNS) as an agonist of the postsynaptic nicotinic acetylcholine receptors
(nAChRs) [11–13]. The great attributes of neonicotinoids are their novel mode of action, low
mammalian toxicity, broad insecticidal spectrum, and good systemic properties [14]. An-
other important property of neonicotinoids is their environmental footprint, which allows
for the replacement of the more toxic and non-selective organophosphorus, pyrethroid,
and carbamate insecticides. The reported neonicotinoids can be classified according to
the pharmacophore as N-nitroguanidines, (imidacloprid, thiamethoxam, clothianidin, and
dinotefuran), nitromethylenes (nitenpyram), and N-cyano-amidines (acetamiprid and
thiacloprid) (Figure 1).
Cyclic neonicotinoids
CN
S
NO2
NH
NO2
N
N
N
O
CH3
N
N
N
N
N
S
N
N
Cl
Cl
Cl
Imidacloprid
Bayer CropScience
1991
Thiacloprid
Bayer CropScience
2000
Thiamethoxam
Syngenta
1998
Non-cyclic neonicotinoids
NO2
CN
N
NO2
HC
NO2
N
N
CH3
N
N
N
CH3
N
N
H
CH3
N
N
H
H
H
H
N
CH3
S
O
N
N
Cl
Cl
Cl
Clothianidin
Sumitake
Bayer CropScience
2001
Dinotefuran
Mitsui Chemicals
2002
Acetamiprid
Nippon Soda
1995
Nitempyram
Sumitake
1995
Figure 1. Neonicotinoids.
All these compounds are characterized by their high insecticidal activities against
insects and relative safety toward mammals and aquatic life [15]. Encouraged by these re-
ports, we envisaged that incorporating different substituents into dinotefuran by switching
the heterocyclic ring with different chiral enantioenriched and non-chiral amines could
improve their insecticidal activity. Therefore, in a search for improvement, neonicotinoids
with enantiomers of chiral amines were designed, synthesized, and evaluated.
2. Results and Discussion
2.1. Synthesis
The starting material one was prepared using 1 equivalent of S-methylisothiourea
◦
hemisulfate salt in the presence of nitric (10 mL) and sulfuric acids (10 mL) at 0 C for

Molecules 2021, 26, 4225
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6 h (Scheme 1). Then, compound one was used to prepare the non-cyclic nitroguani-
dines 2–17. After dissolving the corresponding amine in chloroform, compound one was
added in one portion. Most of the target compounds were purified through flash column
chromatography in yields of up to 95%.
Scheme 1. Preparation of starting material 1.
Sixteen non-cyclic nitroguanidines were prepared and these produced different substi-
tution patterns. For instance, nitroguanidines 2 and 3 had heterocyclic rings while 4 to 10
had an aromatic moiety with electron-donating and withdrawing substituents. Enantiop-
ure non-cyclic nitroguanidines were also prepared using different sorts of chiral amines
such as R- and S-phenylethylamine, and napthylethylamine, S-cyclopropylethylamine, and
R-cyclohexylethylamine (Scheme 2). All these reactions proceeded through nucleophilic
substitution: the lone pair of electrons on the amine attacked the sp2 carbon of compound
one, then the -SCH3 moiety was displaced to obtain the desired nitroguanidine.
NO2
NO2
NH2
R2
R2
N
N
+
NH2
R1
R1
H3CS
NH2
N
CHCl3
24 h, rt
H
1
NO2
NH2
NO2
NO2
NO2
NH2
N
N
N
N
N
N
H
N
NH2
N
NH2
N
H
H
H
S
O
2
5
3
4
NO2
NH2
NO2
NH2
NO2
NH2
NO2
NH2
NO2
NH2
N
N
N
N
N
N
N
N
N
H
8
N
H
H
H
H
O
6
7
10
9
F3C
Cl
NO2
NO2
NH2
NO2
N
N
N
N
NH2
N
H
N
H
NH2
H
S -1 1
R -1 3
S -1 2
NO2
NO2
NH2
NO2
NO2
N
N
N
N
N
NH2
S -1 7
N
N
N
NH2
R -1 4
NH2
H
H
H
H
R -1 6
S -1 5
Scheme 2. Synthesis of non-cyclic nitroguanidines.
Scheme 3 shows that cyclic nitroguanidines were prepared using 6 mL of the solution
of formaldehyde and formic acid (1:1) and the corresponding nitroguanidine. The mixture
◦
was heated at 90 C for 6 h. Most of the compounds were obtained from moderate to
good yields.

Molecules 2021, 26, 4225
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NO2
NH
NO2
NH2
CH2O
R2
R2
N
O
N
HCOOH
6 h, 90 °C
R1
R1
N
N
H
NO2
NH
NO2
NH
NO2
NH
N
N
O
N
O
N
N
N
O
19
Cl
20
18
88%
9%
87%
NO2
NO2
NO2
N
N
N
N
NH
N
NH
N
NH
O
O
22
17%
F3C
O
21
67%
O
N
O
23
36%
NO2
NH
NO2
NH
NO2
NH
NO2
NH
N
N
N
N
O
N
N
N
O
O
O
S-25
54 %
R-26
37 %
S-27
44 %
R-24
57 %
NO2
NO2
NO2
NO2
N
N
N
N
N
NH
N
NH
N
NH
N
NH
O
S-30
19 %
O
31
35 %
O
R-28
38 %
O
S-29
64 %
Scheme 3. Synthesis of cyclic compounds.
The reaction proceeded through the Mannich-type reaction; here, the acid was used as
a catalyst to promote the reaction where the key intermediate was the diol, which was then
cyclized to obtain the corresponding cyclic nitroguanidine (Scheme 4) [16].
Scheme 4. Plausible mechanism reaction.
To obtain the N-methylated compounds 33–42, compound 32 was synthesized using
phthaloyl chloride, pyridine, and a solution of HCl/H2O. The resulting precipitate was
filtered and recrystallized from EtOH to obtain the heterocyclic compound (Scheme 5).
Afterwards, a stirred solution of 32 in acetonitrile was added dropwise to a solution of
the corresponding amine at 0 ◦C. Then, the reaction was stirred for 30 min at the same
temperature and a 2.0 M solution of methylamine in MeOH was immediately added. Most
of the compounds were obtained with good yields (Scheme 6). It is important to point out
that the reactions were carried out in one-pot. The addition of the amine and the addition
of the methylamine were nucleophilic substitutions that took place at the sp2 carbon.

Molecules 2021, 26, 4225
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O2N
S
O
O
N
O
O2N
S
Pyridine
N
Cl
Cl
N
+
HCl/H2O
40 min, 0 °C
NH2
O
32
1
Scheme 5. Synthesis of compound 32.
NO2
N
O
R-NH2
CH3NH2
O2N
N
N
S
R
N
H
N
CH3CN, 24 h,
O
H
0 ˚C
32
NO2
N
NO2
NO2
N
N
N
N
N
N
H
N
N
H
H
H
H
H
Cl
34
38%
33
85%
35
77%
NO2
NO2
N
NO2
N
N
N
N
H
N
N
H
N
N
H
H
H
H
O
F3C
O
38
82%
36
74%
37
74%
NO2
NO2
N
N
NO2
NO2
N
N
N
N
H
N
N
H
H
N
N
H
H
N
N
H
S
H
H
S-39
13 %
41
57 %
S-40
29 %
42
55 %
Scheme 6. Synthesis of N-methylated compounds.
To synthesize compounds 43 to 47, the same procedure described for compounds 18
to R-31 was followed. Again, these reactions proceeded through a Mannich-type reaction.
The five products were obtained in yields of up to 71% (Scheme 7).
NO2
NO2
N
CH2O
HCOOH
N
CH3
CH3
R
N
N
R
N
N
H
H
6 h, 90˚C.
O
NO2
NO2
NO2
N
O
N
O
N
O
CH3
CH3
CH3
N
N
N
N
N
N
Cl
H3C
45
63%
44
71%
43
68%
NO2
NO2
N
O
N
O
CH3
CH3
N
N
N
N
H3C
F3C
O
47
46
45%
58%
Scheme 7. N-methylated cyclic nitroguanidines.

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2.2. Biological Activities
The insecticidal assays of the title compounds against Xyleborus affinis were tested us-
ing the filter paper contact toxicity method. The results were graphed for comparison. Most
of the non-cyclic compounds showed a lower insecticidal activity than dinotefuran and
the chiral and enantiopure compounds such as (R,E)-1-(cyclohexylethyl)-2-nitroguanidine
R-13, which showed up to 67% mortality (Figure 2).
80
70
67
60
50
40
30
20
10
0
53
53
40
40
40
33
27
27
27
27
20
20
13
13
13 13
Compound
NO2
N
N
NH2
R -1 3
H
Figure 2. Analysis of non-cyclic nitroguanidines.
The cyclic nitroguanidines 21, 23, R-24, R-28, and R-29 showed insecticidal activities
of up to 73%. The comparison between nitroguanidines 21 and 23 suggest that compounds
with an electron-donating group in the para position could have a higher mortality percent
than compounds that have electron-withdrawing groups. It was also observed that enan-
tiopure aliphatic nitroguanidines, R-28 and S-29, have a good insecticidal activity up to
73% (Figure 3).
80
70
73
73
60
50
40
30
20
10
0
67
67
67
60
60
60 60
40 40
27
20 20
13
Compound
NO2
NO2
NH
NO2
NH
NO2
NO2
NH
N
O
N
N
N
N
N
O
N
NH
N
N
NH
N
F3C
O
O
O
O
R-24
S-29
21
23
R-28
Figure 3. Analysis of cyclic nitroguanidines.

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The analysis of non-cyclic and cyclic N-methylated nitroguanidines allows us to
highlight the compounds 36, 43, and 47. The structure–activity relationship suggests
again that compounds with electron-donating or electron-withdrawing groups at the para
position of the aromatic ring have higher insecticidal activities (Figure 4).
(a)
(b)
80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
73
67
67
60
53
53
53
47
47
40
40
40
33
27
20
13
7
Compound
Compound
NO2
NO2
NO2
N
N
N
CH3
CH3
CH3
N
N
N
N
N
H
N
H
H3C
H3C
O
O
O
F3C
36
43
47
Figure 4. Analysis of (a) non-cyclic nitroguanidines; (b) cyclic and N-methylated nitroguanidines.
2.3. Structure–Activity Relationship (SAR) of the Para Halogenated Aromatic Derivatives
The SAR analysis showed that non-cyclic and N-methylated compounds had a higher
insecticidal activity. On the other hand, compounds that incorporated the para electron-
withdrawing group attached to the aromatic ring, such as CF3 or Cl, had the same tendency
in terms of insecticidal activity. As a matter of fact, the presence of a halogen at a specific
position in the molecule can influence its biological activity [17]. The N-methylated com-
pounds have a better insecticidal activity than non-methylated compounds (compound 21
and
8 vs. compound 9 and 20). In contrast to our results with neonicotinoids, Xu, et al. [18]
designed and synthesized a series of 1,5-diphenyl-2-penten-1-one analogues with piper-
azine and evaluated their bioactivities. The SAR analysis showed that the R ring plays
a crucial role, and that the antifungal activities and larvicide against mosquitoes of the
compounds with N’-unsubstituted piperazine were better than those of the compounds
with N’-methyl piperazine. Likewise, its larvicidal activity was severely decreased when
the substituent on the benzene ring was changed from position four to position two or
three. However, the improved biopotential of the N-methylated compounds studied in our
work is in agreement with Dahiya et al. [19], who synthesized an N-methylated analog of
a proline-rich cyclic tetracyclopeptide from marine bacteria with enhanced anthelmintic
and antifungal activity, compared to the non-methylated tetracyclopeptide. Cyclic com-
pounds showed up to 67% mortality for compound 36 and 47% mortality for compound 35
(Figure 5).

Molecules 2021, 26, 4225
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Figure 5. Structure–activity analysis of new neonicotinoids.
It is well known that chirality plays an important role when bioactive enantiopure
compounds are administered to living organisms [20]. As a part of our research pro-
gram in relation to biologically active and enantioenriched compounds, we prepared
both the enantiomers of nitroguanidines derivatives that had the phenylethylamine or
the naphtyletylamine in enantiopure form. Those compounds were bioassayed and they
showed interesting differences in their insecticidal activity. For instance, the non-cyclic
R enantiomers showed a higher insecticidal activity. Moreover, the cyclic enantiomers
with an absolute R configuration showed a higher insecticidal activity when compared
with the S enantiomers (Figure 6). The favored insecticidal activity of the R enantiomers
has previously been reported, for instance, in limonene against Tribolium confusum [21], in
cycloprothrins against the larvae of Tetranychus cinnabarnus, Nilaparvatalegen, Mythimasepa-
rata, and Aphismedicagini [22], and also in pyridine methanesulfonates against Diabrotica
undecimpunctata howardi and Nephotettix cincticeps [23].
Non-cyclic
S-enantiomers R-enantiomers
Cyclic
S-enantiomers
R-enantiomers
Figure 6. Absolute configuration–activity relationship (ACAR) of chiral nitroguanidines.
2.4. Docking Analysis
To perform the docking analysis, the highly bioactive compounds 47, R-13, 43, 23,
36, and S-29 were selected. First, the score of dinotefuran was obtained since this was
our model insecticide. The score was 5.64 kcal/mol. The lower the score, the better the
−
affinity with the receptor in the search cavity of 3C79. The compound with an outstanding
affinity was the cyclic N-methylated compound 47 which has a p-methoxy-substituted
aromatic ring. This compound was followed by the enantiopure compound R-13 that
possessed an absolute R configuration. The results suggest that the non-methylated 23
and non-cyclic 36 compounds presented a diminished affinity. The compound with an
absolute R configuration had a better affinity when compared with the S compound. All the
docking calculations agreed with the experimental results. Another interesting observation

Molecules 2021, 26, 4225
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derived from docking was that the inhibitions constants (Ki) were lower for compounds 47
,
R-13, and 43. For instance, the comparison between dinotefuran, R-13, and S-29, showed
that these values were 24.23, 73.06, 263.75 µM, respectively. These results suggest again
that compounds with absolute R configurations are more potent and improved inhibitors
since the concentration to produce the half-maximum inhibition could be reduced by up
to 33% in comparison with dinotefuran. The comparison of the Ki between compounds
with opposite absolute configurations of R-13 and S-29 showed a huge difference since
these values were 24.23 and 263.75, respectively (Table 1). The experimental results and the
docking results suggest again that compounds with an R configuration could have a highly
insecticidal activity at lesser doses. Additionally, the in-silico calculations suggest that cyclic
N-methylated compounds 47 and 43 are highly active insecticides against Xyleborus affinis.
Table 1. Affinity and inhibition constants of highly bioactive compounds a.
Free Energy
(kcal/mol) “Score”
Inhibition Constant
Compound
(Ki, µM)
−6.53
−6.3
16.29
24.23
−6.08
−5.64
35.22
73.06
−5.47
−5.19
−4.88
98.40
157.1
NO2
N
O
N
NH
263.75
S-29
a
To perform the simulations, the parameters of 100 runs with 5 million evaluations were used for each molecular
coupling experiment using a Lamarckian genetic algorithm.

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The 2D and 3D representations of the molecular recognition with the residues of
the search cavity of the binding protein 3C79 (AChBP) with dinotefuran and the com-
pounds selected to perform the docking showed different types of interactions among them
(Figure 7). For instance, dinotefuran showed interactions between the nitrogen attached
to a heterocyclic moiety and the receptor in Glu153 and Asp77. An interaction between
the oxygen of the heterocyclic ring and the Thr24 of the receptor was also observed. On
the other hand, a cation-π interaction between the aromatic ring of compounds 47 and 43
and Phe78 was found. These sorts of interactions play an important role in neonicotinoid
insecticidal activity [24]. The enantiopure compound 13 showed interactions with Glu153
and As77; in comparison with dinotefuran, these interactions appear to be due to hydrogen
bonds and the results suggest that these sorts of interactions are responsible for the higher
insecticidal activity. These results also suggest that this strategy could result in a useful tool
to fight cross-resistance, since the nature of the interactions between the novel molecules
and the receptor are quite different. Examples of intragroup cross-resistance are well
documented for most major insecticide groups, including pyrethroids, organophosphate,
and neonicotinoids [25–27]. However, cross-resistance can also be unpredictable, affecting
compounds with diverse structures and those that are considered to have different modes
of action.
Dinotefuran
47
R-13
43
Figure 7. The 2D and 3D representations of the interaction of dinotefuran and compounds 47, R-13
,
and 43, with the residues of the search cavity in 3C79.

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3. Materials and Methods
3.1. Instrumentation and Chemicals
All reactions were carried out in flame-dried glassware with a nitrogen atmosphere
and magnetic stirring unless otherwise noted. Analytical thin-layer chromatography (TLC)
was performed on Merck pre-coated TLC plates (silica gel 60 GF254, 0.25 mm). Flash
chromatography was performed on silica gel E. Merck 9385 or silica gel 60 extra pure (for
final products). Dichloromethane (CH2Cl2) and toluene (PhCH3) were purchased from
Sigma-Aldrich and were purified by distillation. Most of the chemicals were purchased
from Aldrich, Stream, or Alfa Aesar and handled and stored in a desiccator. Molecular
sieves were purchased from Sigma-Aldrich and activated with a microwave oven. All other
reagents and starting materials, unless otherwise noted, were purchased from commercial
vendors and used without further purification. Infrared (IR) spectra were recorded on an
Agilent Technologies Cary 600 Series FTIR. 1H, 13C, DEPTQ 135, and bidimensional NMR
spectra were recorded on a Bruker Avance III HD 500 spectrometer (Billerica, MA, USA).
Chemical shift values (δ) are expressed in ppm downfield relative to an internal standard
(tetramethylsilane at 0 ppm). Multiplicities are indicated as s (single), d (doublet), t (triplet),
q (quartet), m (multiplet), and br s (broad signal). The solvent CDCl3 at 77.16, DMSO-d6 at
39.52, and CD3OD at 49 ppm were used as internal standards for 13C NMR spectra. Spectra
were processed using TopSpin 4.0.7 from Bruker BioSpin
©
(Billerica, MA, USA). The 1H
and 13C NMR spectra for all compounds can be found in the Supplementary Materials.
Optical rotations were measured on a Bellingham + Stanley ADP 440 + polarimeter (Kent,
UK). High-resolution mass spectra (HRMS) were obtained in a Q-TOF mass spectrometer
equipped with electrospray ionization (ESI) interface Synapt G2-Si, Waters Inc. (Milford,
MA, USA). Melting points were not corrected and determined on a Stuart SMP10 apparatus
(Staffordshire, UK) using open glass capillaries.
3.2. Synthetic Procedures
Unless otherwise noted, reagents and solvents were used as received from commer-
cial suppliers. Yields were not optimized. The synthetic procedures have already been
described in the literature and were followed to prepare the novel neonicotinoids.
3.2.1. Synthetic Procedure to Obtain the Methyl N-Carbamimidothioate 1
Concentrated sulfuric acid (10 mL) was placed in a balloon flask equipped with a
stirring bar and a thermometer and it was cooled with an ice bath to 0 ◦C. When this tem-
perature was reached, 70% nitric acid was added (10 mL). The cooling was maintained until
the initial temperature of 0 ◦C was reached, and then 1 equivale◦nt of S-methylisothiourea
hemisulfate was added. The mixture was stirred for 6 h at 0 C and once the reaction
time had elapsed, the contents of the flask were poured over a beaker with ice to obtain
a precipitate. This mixture was kept under refrigeration for 24 h to melt the remaining
ice. The isolation of the product was achieved by filtration under reduced pressure and
washing of the solid with cold distilled water. Finally, the solid was dried under a high
vacuum to obtain 1 [28].
3.2.2. General Synthetic Procedure for Non-Cyclic Compounds 2–17
To a stirred solution of the corresponding amine (1.1 mmol) in chloroform (1 mL)
compound 1 was added (1.0 mmol) in one portion, after that the reaction was stirred for
24 h at room temperature. The solvent was evaporated under reduced pressure and the
crude was purified using flash column chromatography [29]. See Data Compounds in
Appendix A.
3.2.3. General Synthetic Procedure for Cyclic Compounds 18–31
In a solution of formaldehyde (37%) and formic acid (1:1, 6 mL) the corresponding
nitroguanidine (1 mmol) was suspended. The mixture was heated at 90 ◦C for 6 h. The
reaction was extracted using AcOEt (3
×
10 mL). The organic phases were collected, filtered

Molecules 2021, 26, 4225
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over Na2SO4, and evaporated. The crude was purified using flash column chromatogra-
phy [16]. See Data Compounds in Appendix B.
3.2.4. Synthetic Procedure to Obtain the Intermediate 32
In a flask equipped with a stir bar, compound
1
(1 mmol) was dissolved in pyridine
◦
(1 mL) and cooled in an ice-water bath to 0 C. Subsequently, 90% phthaloyl chloride
solution (2 mmol) was added dropwise for 30 min. After the addition was completed, the
reaction was stirred for an additional 10 min and at the end of that time, the mixture was
poured over a 1:5 HCl/H2O solution (20 mL). The resulting precipitate was filtered under
reduced pressure, recrystallized in EtOH, and dried under a high vacuum to obtain 32.
3.2.5. General Synthetic Procedure to Obtain N-Methylated Compounds
To a stirred solution of 32 (1 mmol) in acetonitrile (2 mL) a solution of the correspond-
ing amine (1.1 mmol) in acetonitrile (1.0 mL) was added over 20 min at 0 ◦C. The reaction
was stirred for 30 min at the same temperature and a 2.0 M solution of methylamine in
MeOH (3.0 mmol) was added immediately. The mixture was stirred for 3 h at room tem-
perature. The solvent was evaporated under reduced pressure and the crude was purified
using flash column chromatography [29]. See Data Compounds in Appendix C.
3.3. Biological Assay
The insecticidal activities of the title compounds against Xyleborus affinis were tested
according to the previously reported procedure of the contact toxicity on filter paper [30]:
A WhatmanTM (Buckinghamshire, UK) grade 42, ashless filter paper (5 cm diameter)
was placed in a glass Petri dish (50
×
17 mm diameter). An aliquot of 0.25 mL of the
solution 0.05 M of the compound in dimethylsulfoxide:water (1:1) was applied uniformly
to the filter paper disc. The mixture of solvents was used as the negative control and the
solution of dinotefuran at the same concentration was used as the positive control. The
solvent was allowed to distribute evenly for 5 min prior to the introduction of 5 adult
insects into each dish. Since the boiling point of dimethyl sulfoxide and water are high
enough to be volatilized at room temperature, it was not necessary to replenish the solvent
mixture. According to statistical requirements, each treatment was replicated 3 times at
25 ◦C
±
1 ◦C with the organism grown in the laboratory. Xyleborus affinis were reared in
an artificial media according to Biedermann et al. [31], with some modification. Rearing
media were maintained in a climatic chamber at 26 ◦C and 60% of RH in complete dark.
Adults were obtained at 30 days after female inoculation by dissecting the media culture.
Insect mortalities were recorded after 12 h. Insects were presumed dead if they remained
immobile and did not respond to three probings with a blunt dissecting probe after a 5-min
recovery period.
4. Conclusions
A series of novel neonicotinoid analogs were designed and synthesized by introducing
aliphatic and aromatic amines. Interestingly, enantiopure amines with opposite absolute
configurations were prepared and analyzed as insecticides against Xyleborus affinis. The re-
sults showed us that the amines with an absolute R configuration have a superior biological
activity when compared to the opposite enantiomer S. Four lead compounds that had
percent mortalities up to 73% were derived from this study, while dinotefuran had only a
40% mortality.
The docking studies suggested some interesting interactions between the molecules
and the search cavity 3C79 of the receptor, which were cation-π interactions between the
aromatic ring moiety of the molecules and hydrogen bonds. These interactions are likely to
be the reason for the high insecticidal activity. Hence, this technology has emerged as a
strategic tool to develop new chiral and enantiopure neonicotinoids with high insecticidal
activity to fight against cross-resistance and protect important economical crops while
reducing the ecotoxicity of pollinators [32].

Molecules 2021, 26, 4225
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Supplementary Materials: The followings are available online. 1H and 13C NMR data for
all compounds.
Author Contributions: Conceptualization, J.L.O.-R.; methodology, S.A.L.-H., I.B.-L., A.R.-L., A.R.-H.
U.C.-M., L.A.I.-J., F.J.E.-M. and R.E.D.d.L.-G.; software, G.S.-M.; validation, I.B.-L., F.B.-M. and
G.S.-M.; formal analysis, J.L.O.-R., L.A.I.-J., F.J.E.-M. and R.E.D.d.L.-G.; investigation, S.A.L.-H.,
I.B.-L., A.R.-L., A.R.-H. and U.C.-M.; writing—original draft preparation, J.L.O.-R. and I.D.P.-L.;
writing—review and editing, J.L.O.-R. and I.D.P.-L.; supervision, J.L.O.-R.; project administration,
J.L.O.-R.; funding acquisition, J.L.O.-R. All authors have read and agreed to the published version of
the manuscript.
,
Funding: This work was supported by Consejo Nacional de Ciencia y Tecnología (CONACyT)
through the Fondo Institucional de Fomento Regional para el Desarrollo Científico, Tecnológico y de
Innovación (FORDECyT), Grant 292399.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Data are available from the authors on request.
Acknowledgments: We thank to Juan Luis Monribot Villanueva for technical assistance in the
acquisition of the HRMS-QTOF analysis.
Conflicts of Interest: The authors declare no conflict of interest.
Appendix A
Data for 2-nitro-1-(pyridin-2-ylmethyl)guanidine
poses); TLC Rf 0.78 (MeOH); 1H NMR (500 MHz, DMSO-d6, 50 C):
1.0 Hz, 1H), 7.93 (br s, 2H), 7.81 (td, J = 7.6, 1.8 Hz, 1H), 7.36–7.33 (m, 2H), 7.33–7.31 (m,
2
. Gray solid, 82%, m.p. 175–177 ◦C (decom-
◦
δ
8.56 (ddd, J = 4.9, 1.8,
1H), 4.54 (s, 2H), 13C NMR (125 MHz, DMSO-d6, 50 ◦C):
δ 149.4, 137.5, 123.0, 121.8, 46.0.
HRMS (ESI): [M + Na]+ calculated for C7H9N5NaO2 [M + Na]+ 218.0648, found 218.0647
(5.0 ppm). IR (ATR) νmax: 3378, 3145, 3301, 1652.
Data for 2-nitro-1-(thiophen-2-ylmethyl)guanidine
3
. White solid, 74% yield, m◦ .p. 129–131 ◦C;
1
TLC Rf 0.21 (AcOEt/Hexane, 1:1); H NMR (500 MHz, DMSO-d6, 50 C):
δ 7.93 (br s,
2H), 7.43–7.42 (m, 1H), ◦7.07–7.05 (m, 1H), 7.01–6.98 (m, 1H), 4.58 (br s, 2H), 13C NMR
(125 MHz, DMSO-d6, 50 C):
δ 159.0, 127.0, 126.8, 126.1, 125.6, 38.4. HRMS (ESI): calculated
for C6H9N4O2S [M + H]+ 201.0441, found 201.0441 (5.0 ppm). IR (ATR)
3312, 1644.
νmax: 3371, 3160,
Data for 2-nitro-1-phenethylguanidine
4
. Yellow solid, 89% yield, m.p. 128–130 ◦C; TLC Rf
1
◦
0.46 (AcOEt/Hexane, 6:4); H NMR (500 MHz, DMSO-d6, 50 C):
δ 7.35–7.29 (m, 2H),
7.29–7.20 (m, 3H), 3.48–3.40 (m, 2H), 2.83 (t, J = 7.4 Hz, 2H), 13C NMR (125 MHz, DMSO-d6,
◦
50 C):
δ 159.7, 139.0, 129.2, 128.8, 126.8, 42.5, 34.4. HRMS (ESI): calculated for C9H13N4O2
[M + H]+ 209.1033, found 209.1030 (5.0 ppm). IR (ATR) νmax: 3367, 3170, 3302, 1644.
◦
Data for (E)-1-(4-methoxybenzyl)-2-nitroguanidine 5. White solid, 91% yield, m.p. 192–194 C;
TLC Rf 0.19 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6, 50 ◦C): δ 7.86 (br s, 2H),
7.26 (d, J = 8.6 Hz, 1H), 6.93 (d, J = 8.6 Hz, 1H), 4.34 (s, 2H), 3.75 (s, 3H), 13C NMR (125 MHz,
DMSO-d6, 50 ◦C):
δ 159.0, 129.1, 114.3, 55.5, 43.7. HRMS (ESI): calculated for C9H13N403
[M + H]+ 225.0982, found 225.0988 (−2.2 ppm). IR (ATR) νmax: 3382, 3322, 3166.522, 1648.
Data for (E)-1-(4-methylbenzyl)-2-nitroguanidine 6
. White solid, 86% yield, m.p. 188–191 ◦C;
TLC Rf 0.28 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6, 50 ◦C): δ 7.87 (br s, 3H),
7.21 (d, J = 8.1 Hz, 2H), 7.17 (d, J = 8.1 Hz, 2H), 4.37 (br s, 2H), 2.30 (s, 3H), 13C NMR
(125 MHz, DMSO-d6, 50 ◦C): 159.8, 136.9, 129.4, 127.7, 44.1, 21.0. HRMS (ESI): [M + H]+
δ
calculated for C9H13N4O2 [M + H]+ 209.1033, found 209.1039 (
3374, 3305, 3155, 1648.
−
3.8 ppm). IR (ATR)
ν
:
max

Molecules 2021, 26, 4225
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Data for ◦(E)-1-(naphthalen-1-ylmethyl)-2-nitroguanidine
7
. White solid, 73% yield, m.p.
1
◦
189–192 C; TLC Rf 0.34 (AcOEt/Hexane, 6:4); H NMR (500 MHz, DMSO-d6, 50 C):
δ
8.05 (d, J = 8.2 Hz, 1H), 7.97 (d, J = 8.0 Hz, 1H), 7.89 (d, J = 8.0 Hz, 1H), 7.63–7.54 (m,
2H), 7.54–7.45 (m, 2H), 4.89 (s, 2H), 13C NMR (125 MHz, DMSO-d6, 50 ◦C):
δ
160.0, 133.8,
131.1, 129.0, 128.3, 126.8, 126.3, 125.8, 123.6, 42.6. HRMS (ESI): calculated for C12H13N4O2
[M + H]+ 245.1033 found 245.1039, (−2.9 ppm). IR (ATR) νmax: 3381, 3311, 3180, 1644.
Data for (E)-1-(4-chlorobenzyl)-2-nitroguanidine
8
. White solid, 72% yield, m.p. 190–192 ◦C;
TLC Rf 0.22 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6):
δ
7.95 (s, 2H), 7.46–7.38
159.9, 132.3,
(m, 3H), 7.33 (d, J = 8.5 Hz, 2H), 4.40 (s, 2H), 13C NMR (125 MHz, DMSO-d6):
δ
129.5, 128.8, 43.6. HRMS (ESI): calculated for C8H10ClN4O2 [M + H]+ 229.0487, found
229.0492 (−3.9 ppm). IR (ATR) νmax: 3370, 3312, 3180, 1645.
Data for◦(E)-2-nitro-1-(4-(trifluoromethyl)benzyl)guanidine
9. White solid, 83% yield, m.p.
◦
161–164 C; TLC Rf 0.19 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6, 50 C):
δ 7.97
(br s, 2H), 7.72 (d, J = 8.0 Hz, 2H), 7.52 (d, J = 7.9 Hz, 2H), 4.52 (s, 2H), 13C NMR (125 MHz,
DMSO-d6, 50 ◦C):
δ
159.8, 128.3, 128.1, 125.7 (q, J = 3.75 Hz), 125.3 (q, J = 270 Hz), 43.72;
19F NMR (470 MHz, DMSO-d6, 50 C): δ −60.86. HRMS (ESI): calculated for C9H10F3N4O2
◦
[M + H]+ 263.0750, found 263.0756 (−3.8 ppm). IR (ATR) νmax: 3378, 3305, 3178, 1648.
Data for (E)-1-(2-methoxybenzyl)-2-nitroguanidine 10. White solid, 85% yield, m.p. 203–205 ◦C
;
1
TLC Rf 0.25 (AcOEt/Hexane, 6:4); H NMR (500 MHz, DMSO-d6):
δ 7.82 (br s, 2H),
7.33–7.28 (m, 1H), 7.23 (dd, J = 1.0, 7.4 Hz, 1H), 7.04 (d, J = 8.2 Hz, 1H), 7.04 (d, J = 8.2 Hz,
1H), 6.95 (t, J = 7.4 Hz, 1H), 4.37 (br s, 2H), 3.84 (s, 3H), 13C NMR (125 MHz, DMSO-d6):
δ
157.2, 129.3, 128.3, 120.7, 111.2, 55.8. HRMS (ESI): calculated for C9H12N4O3Na [M + Na]+
247.0802, found 247.0807 (−1.6 ppm). IR (ATR) νmax: 3382, 3322, 3166, 1648.
Data for (S)-1-(1-cyclopropylethyl)-2-nitroguanidine S-11. White solid, 72%, m.p. 109–111 ◦C;
26
1
TLC Rf 0.37 (AcOEt/Hexane, 7:3); [
α
]
= +18.81 (c = 1.0, acetone); H NMR (500 MHz,
CDCl3): 7.78 (br s, 1H), 6.85 (br s, 2H), 3.10–3.06 (m, 1H), 1.38 (d, J = 6.5 Hz, 3H),
δ
1.04–0.97 (m, 1H), 0.68–0.61 (m, 2H), 0.40–0.27 (m, 2H), 13C NMR (125 MHz, CDCl3):
δ
158.6, 52.3, 20.0, 16.8, 3.8, 3.1. HRMS (ESI): calculated for C6H13N4O2 [M + H]+ 173.1033,
found 173.1035 (5.0 ppm). IR (ATR) νmax: 3310, 3159, 3373, 1634.
Data for (S)-2-nitro-1-(1,2,3,4-tetrahydronaphthalen-1-yl)guanidine S-12. White solid, 59% yield,
◦
26
m.p. 180–182 C; TLC Rf 0.40 (AcOEt/Hexane, 1:1); [
α
]
=
−
49.29 (c = 0.1, isopropyl
◦
alcohol); 1H NMR (500 MHz, CD3OD, 50 C):
δ 7.29–7.11 (m, 4H), 5.00 (s, 1H), 2.91–2.74 (m,
2H), 2.13–2.05 (m, 1H), 1.97–1.81 (m, 3H). 13C NMR (126 MHz, CD3OD, 50 ◦C):
δ 159.05,
137.35, 128.89, 128.02, 127.30, 125.94, 49.53, 29.62, 28.58, 19.48. HRMS (ESI): [M + Na]+
calculated for C11H14N4NaO2 [M + Na]+ 257.1009 found 257.1014 (5.0 ppm). IR (ATR)
ν
max: 3380, 3191, 3322, 1643.
Data for ◦(R)-1-(1-cyclohexylethyl)-2-nitroguanidine R-13
.
White solid, 61% yield, m.p.
26.3
1
139–140 C; TLC Rf 0.38 (AcOEt/Hexane, 6:4); [
α
]
=
−
30.71 (c = 0.5, acetone); H
NMR (500 MHz, CDCl3):
δ 8.45 (br s, 1H), 6.63 (br s, 2H), 3.32 (br s, 1H), 1.82–1.68 (m, 6H),
1.48 (br s, 1H), 1.29–0.95 (m, 9H), 13C NMR (125 MHz, CDCl3):
δ 158.6, 53.3, 42.9, 28.9,
26.1, 25.9, 17.6. HRMS (ESI): calculated for C9H19N4O2 [M + H]+ 215.1503, found 215.1508
(5.0 ppm). IR (ATR) νmax: 3355, 3310, 3170, 1644.
Data for (R)-1-(1-(naphthalen-1-yl)ethyl)-2-nitroguanidine R-14. Yellow solid, 30% yield, m.p.
26.5
175 ◦C (decomposes); TLC Rf 0.38 (AcOEt/Hexane, 6:4); [
α
]
=
−
67.5 (c = 0.5, acetone,);
1H NMR (500 MHz, CDCl3):
1H), 7.87 (d, J = 8.2 Hz, 1H), 7.65–7.60 (m, 1H), 7.60–7.56 (m, 3H), 7.54–7.50 (m, 1H), 6.15
(br s, 2H), 5.42 (s, 1H), 1.78 (d, J = 6.8 Hz, 3H), 13C NMR (125 MHz, CDCl3):
158.9, 135.4,
δ 8.30 (br s, 1H), 8.02 (d, J = 8.4 Hz, 1H), 7.95 (d, J = 7.5 Hz,
δ
134.1, 129.6, 129.6, 129.3, 127.2, 126.3, 125.8, 122.8, 121.5, 49.2, 22.9. HRMS (ESI): calculated
for C13H14N4NaO2 [M + Na]+ 281.1009, found 281.1014 (5.0 ppm). IR (ATR)
3222, 3283, 1637.
νmax: 3415,

Molecules 2021, 26, 4225
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Data for (S)-1-(1-(naphthalen-1-yl)ethyl)-2-nitroguanidine S-15. Yellow solid, 46% yield, m.p
◦
26.6
1
178 C; TLC Rf 0.38 (AcOEt/Hexane, 6:4); [
(500 MHz, CDCl3): 8.35 (s, 1H), 8.02 (d, J = 8.4 Hz, 1H), 7.97–7.93 (m, 1H), 7.87 (d,
J = 8.1 Hz, 1H), 7.62 (ddd, J = 8.5, 6.8, 1.5 Hz, 1H), 7.60–7.56 (m, 2H), 7.52 (dd, J = 8.2, 7.2 Hz,
1H), 6.19 (s, 2H), 5.42 (s, 1H), 1.78 (d, J = 6.7 Hz, 3H), 13C NMR (125 MHz, CDCl3):
158.9,
α
]
= +74.77 (c = 0.5, acetone), H NMR
δ
δ
135.3, 134.1, 129.6, 129.5, 129.3, 127.2, 126.3, 125.8, 122.8, 121.5, 49.1, 22.9. HRMS (ESI):
[M + Na]+ calculated for C13H14N4NaO2 [M + Na]+ 281.1009, found 281.1014 (5.0 ppm).
IR (ATR) νmax: 3415, 3222, 3283, 1636.
◦
Data for (R)-2-nitro-1-(1-phenylethyl)guanidine R-16. Yellow solid, 79% yield, m.p. 126–127 C;
24.4
1
TLC Rf 0.29 (AcOEt/Hexane, 6:4) [
α
]
= +37.4 (c = 0.5, acetone), H NMR (500 MHz,
CDCl3): 8.36 (br s, 1H), 7.43–7.40 (m, 2H), 7.37–7.33 (m, 3H), 6.46 (br s, 2H), 4.62 (br s, 1H),
δ
1.64 (d, J = 6.8 Hz, 3H), 13C NMR (125 MHz, CDCl3):
δ 159.0, 140.6, 129.6, 128.7, 125.5, 52.7,
24.0. HRMS (ESI): calculated for C9H13N4O2 [M + H]+ 209.1033, found 209.1039 (5.0 ppm).
IR (ATR) νmax: 3392, 3210.
◦
Data for (S)-2-nitro-1-(1-phenylethyl)guanidine S-17. Yellow solid, 95% yield, m.p. 127–128 C;
23.9
TLC Rf 0.29 (AcOEt/Hexane, 6:4) [
CDCl3):
α
]
=
−
40.32 (c = 0.5, acetone,), 1H NMR (500 MHz,
δ
8.41 (br s, 1H), 7.43–7.40 (m, 2H), 7.36–7.33 (m, 3H), 6.52 (br s, 2H), 4.62 (br s, 1H),
1.63 (3H, d, J = 6.8 Hz), 13C NMR (125 MHz, CDCl3):
δ 159.0, 140.6, 129.6, 128.6, 125.5, 52.6,
23.9. HRMS (ESI): calculated for C9H13N4O2 [M + H]+ 209.1033, found 209.1039 (2.86 ppm).
IR (ATR) νmax: 3392, 3211.
Appendix B
Data for (E)-N-(3-(4-methylbenzyl)-1,3,5-oxadiazinan-4-ylidene)nitramide 18. White solid, 87%
yie◦ld, m.p. 110–113 ◦C; TLC Rf 0.44 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6,
50 C):
δ 9.73 (br s, 1H), 7.21 (d, J = 8.2 Hz, 2H), 7.18 (d, J = 8.1 Hz, 2H), 4.97 (s, 2H), 4.93 (s,
2H), 4.56 (s, 2H), 2.30 (s, 3H), 13C NMR (125 MHz, DMSO-d6, 50 ◦C):
δ 154.6, 137.2, 133.6,
129.6, 127.8, 77.3, 73.8, 48.5, 21.0. HRMS (ESI): calculated for C11H14N4O3Na [M + Na]+
273.0958, found 273.0964 (−3.7 ppm). IR (ATR) νmax: 3275, 1545.
Data for (E)-N-(3-(naphthalen-2-ylmethyl)-1,3,5-oxadiazinan-4-ylidene)nitramide 19. White solid,
◦
88% yield, m.p. 170–174 C; TLC Rf 0.47 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-
d6, 50 C):
◦
δ 9.85 (s, 1H), 8.12–8.07 (m, 1H), 8.01–7.95 (m, 1H), 7.90 (d, J = 8.2 Hz, 1H),
7.63–7.56 (m, 2H), 7.52 (dd, J = 8.2, 7.1 Hz, 1H), 7.43–7.39 (m, 1H), 5.13 (s, 2H), 5.04 (s,
2H), 4.97 (s, 2H), 13C NMR (125 MHz, DMSO-d6, 50 ◦C):
154.7, 133.9, 131.8, 131.1, 129.1,
128.4, 126.9, 126.5, 125.9, 124.6, 123.4, 78.1, 73.9, 47.1 ppm. HRMS (ESI): calculated for
C14H14N4O3Na [M + Na]+ 309.0958, found 309.0964 (
2.6 ppm). IR (ATR) max: 3297, 1546.
δ
−
ν
Data for (E)-N-(3-(4-chlorobenzyl)-1,3,5-oxadiazinan-4-ylidene)nitramide 20. White solid, 9%
yield, m.p. 123–127 ◦C; TLC Rf 0.34 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6):
δ
9.82 (s, 1H), 7.44 (d, J = 8.1 Hz, 3H), 7.33 (d, J = 8.1 Hz, 3H), 5.00–4.94 (m, 4H), 4.59 (s, 2H),
13C NMR (125 MHz, DMSO-d6):
δ 154.4, 135.9, 132.5, 129.6, 129.1, 78.1, 73.86, 48.1. HRMS
(ESI): calculated for C10H11CIN4O3Na [M + Na]+ 293.0412, found 293.0417 (
3.4 ppm). IR
−
(ATR) νmax: 3308, 1589.
Data for (E)-N-(3-(4-(trifluoromethyl)benzyl)-1,3,5-oxadiazinan-4-ylidene)nitramide 21. White
solid, 67% yield, m.p. 176–178 ◦C; TLC Rf 0.31 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz,
DMSO-d6): δ 9.86 (s, 1H), 7.75 (d, J = 8.1 Hz, 2H), 7.51 (d, J = 8.0 Hz, 2H), 5.00 (s, 2H), 4.99
(s, 2H), 4.69 (s, 2H), 13C NMR (125 MHz, DMSO-d6):
δ 154.9, 138.9, 130.6 (q, J = 36.25 Hz),
128.0, 126.02 (q, J = 3.75 Hz), 123.8 (q, J = 270 Hz), 77.6, 73.5, 48.8, 19F NMR (470 MHz,
DMSO-d6): δ −60.86. HRMS (ESI): calculated for C11H12F3N4O3+ [M + H]+ 305.0856, found
305.0861 (−4.9 ppm). IR (ATR) νmax: 3316, 1550.
Data for (E)-N-(3-(2-methoxybenzyl)-1,3,5-oxadiazinan-4-ylidene)nitramide 22. White solid, 17%
yield, m.p. 143–145 ◦C; TLC Rf 0.44 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6,
50 ◦C):
δ 9.71 (s, 1H), 7.29 (td, J = 8.3, 7.4, 1.7 Hz, 1H), 7.21 (dd, J = 7.5, 1.7 Hz, 1H), 7.03

Molecules 2021, 26, 4225
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(dd, J = 8.2, 1.1 Hz, 1H), 6.95 (td, J = 7.5, 1.1 Hz, 1H), 4.98 (s, 2H), 4.96 (s, 2H), 4.54 (s, 2H),
3.83 (s, 3H), 13C NMR (125 MHz, DMSO-d6, 50 ◦C):
δ 157.3, 154.7, 129.2, 128.3, 124.4, 120.8,
111.4, 78.5, 73.9, 55.9, 44.7. HRMS (ESI): calculated for C11H14N404Na [M + Na]+ 289.0907,
found 289.0913 (−2.4 ppm). IR (ATR) νmax: 3284, 1551.
Data for (E)-N-(3-(4-methoxybenzyl)-1,3,5-oxadiazinan-4-ylidene)nitramide 23. White solid, 36%
yie◦ld, m.p. 162–167 ◦C; TLC Rf 0.34 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6,
50 C):
δ 9.72 (s, 1H), 7.29–7.23 (m, 2H), 6.93 (d, J = 8.7 Hz, 2H), 4.96 (d, J = 2.4 Hz, 2H), 4.93
◦
(s, 2H), 4.54 (s, 2H), 3.76 (s, 3H), 13C NMR (125 MHz, DMSO-d6, 50 C):
δ 159.3, 154.5, 129.3,
128.6, 114.6, 77.8, 73.8, 55.6, 48.2. HRMS (ESI): calculated for C11H14N4O4Na [M + Na]+
289.0907, found 289.0913 (−3.5 ppm). IR (ATR) νmax: 3266, 1547.
Data for (R)-N-(3-(1-phenylethyl)-1,3,5-oxadiazinan-4-ylidene)nitramide R-24. White solid, 57%
◦
yield, m.p. 108–109 C; TLC Rf 0.44 (AcOEt/Hexane, 6:4) [
1H NMR (500 MHz, CDCl3):
10.00 (s, 1H), 7.41–7.36 (m, 3H), 7.35–7.30 (m, 4H), 6.06 (q,
J = 7.1 Hz, 1H), 5.00 (dd, J = 8.6, 2.4 Hz, 1H), 4.95 (dd, J = 8.6, 2.2 Hz, 1H), 4.76 (d, J = 9.4 Hz,
α]
25.5 = +169.78 (c = 0.5, acetone),
δ
1H), 4.51 (d, J = 9.4 Hz, 1H), 13C NMR (125 MHz, CDCl3):
δ
154.4, 137.8, 128.9, 128.2, 127.2,
73.8, 73.7, 52.2, 16.1. HRMS (ESI): calculated for C11H14N4NaO3 [M + Na]+ 273.0958,
+
found 273.0964 (5.0 ppm). IR (ATR) νmax: 3280.
Data for (S)-N-(3-(1-◦phenylethyl)-1,3,5-oxadiazinan-4-ylidene)nitramide S-25. White solid, 54%
25.9
yield, m.p. 104–105 C; TLC Rf 0.44 (AcOEt/Hexane, 6:4) [
α
]
=
−
165.12 (c = 0.5, acetone,),
1H NMR (500 MHz, CDCl3):
δ
9.98 (s, 1H), 7.41–7.35 (m, 2H), 7.35–7.30 (m, 3H), 6.05 (q,
J = 7.1 Hz, 1H), 5.01 (dd, J = 8.6, 2.6 Hz, 1H), 4.95 (dd, J = 8.6, 2.5 Hz, 1H), 4.76 (d, J = 9.4 Hz,
1H), 4.51 (d, J = 9.4 Hz, 1H), 1.59 (d, J = 7.2 Hz, 3H), 13C NMR (125 MHz, CDCl3):
154.4,
δ
137.8, 128.9, 128.2, 127.2, 73.8, 73.7, 52.1, 16.1. HRMS (ESI): calculated for C11H14N4NaO3
[M + Na]+ 273.0958, found 273.0964 (5.0 ppm). IR (ATR) νmax: 3282, 1578.
Data for (R)-N-(3-(1-(naphthalen-1-yl)ethyl)-1,3,5-oxadiazinan-4-ylidene)nitramide R-26. White
26.7
solid, 37% yield, m.p. 211–214 ◦C (decomposes); TLC Rf 0.55 (AcOEt/Hexane, 6:4) [
α]
= +174.44 (c = 0.5, acetone), 1H NMR (500 MHz, CDCl3):
δ 10.00 (s, 1H), 8.06 (dd, J = 8.4,
1.1 Hz, 1H), 7.93–7.87 (m, 2H), 7.64–7.60 (m, 1H), 7.59–7.55 (m, 2H), 7.52–7.48 (m, 1H), 6.58
(q, J = 6.8 Hz, 1H), 4.98 (ddd, J = 8.7, 3.5, 1.2 Hz, 1H), 4.72 (ddd, J = 9.6, 7.7, 1.6 Hz, 2H),
3.97 (d, J = 9.6 Hz, 1H), 1.79 (d, J = 6.8 Hz, 3H), 13C NMR (125 MHz, CDCl3):
δ 153.9, 133.8,
132.4, 131.5, 129.8, 128.9, 127.5, 126.4, 125.0, 124.8, 123.2, 73.7, 73.4, 49.9, 16.3. HRMS (ESI):
[M + Na]+ calculated for C15H16N4NaO3 [M + Na]+ 323.1115, found 323.1120 (5.0 ppm). IR
(ATR) νmax: 3269, 1572.
Data for (S)-N-(3-(1-◦(naphthalen-1-yl)ethyl)-1,3,5-oxadiazinan-4-ylidene)nitramide S-27. White
26.6
solid, m.p. 210–213 C; TLC Rf 0.55 (AcOEt/Hexane, 6:4) [
α
]
=
−
198.29 (c = 0.5, acetone),
1H NMR (500 MHz, CDCl3):
δ 9.98 (s, 1H), 8.04 (d, J = 8.3 Hz, 1H), 7.89 (t, J = 7.8 Hz, 2H),
7.60 (t, J = 6.9 Hz, 1H), 7.55 (dd, J = 7.0, 3.0 Hz, 2H), 7.50–7.46 (m, 1H), 6.56 (q, J = 6.8 Hz,
1H), 4.96 (ddd, J = 8.6, 3.5, 1.0 Hz, 1H), 4.73–4.66 (m, 2H), 3.95 (d, J = 9.6 Hz, 1H), 1.77 (d,
J = 6.8 Hz, 3H), 13C NMR (125 MHz, CDCl3):
δ
153.9, 133.8, 132.5, 131.5, 129.8, 128.9, 127.5,
+
126.4, 125.0, 124.8, 123.2, 73.7, 73.4, 49.9, 16.3. HRMS (ESI): calculated for C15H16N4NaO3
[M + Na]+ 323.1115, found 323.1120 (5.0 ppm). IR (ATR) νmax: 3269, 1573.
Data for (R)-N-(3-(1-cyclohexylethyl)-1,3,5-oxadiazinan-4-ylidene)nitramide R-28. White solid,
◦
26.3
38% yield, m.p. 139–140 C; TLC Rf 0.51 (AcOEt/Hexane, 6:4) [
α
]
=
−
22.39 (c = 0.5,
1
acetone), H NMR (500 MHz, CDCl3):
δ 9.99 (br s, 1H), 5.01-5.00 (d, J = 2.4 Hz, 2H),
4.88–4.86 (d, J = 9.5 Hz, 1H), 4.82–4.80 (d, J = 9.4 Hz, 1H), 4.48–4.43 (m, 1H), 1.78–1.66 (m,
5H), 1.37–1.30 (m, 1H), 1.25–0.95 (m, 9H), 13C NMR (125 MHz, CDCl3):
δ
154.90, 73.72,
73.31, 55.50, 40.82, 29.81, 29.73, 25.93, 25.80, 16.06. HRMS (ESI): calculated for C11H21N4O3
[M + H]+ 257.1608, found 257.1614 (5.0 ppm). IR (ATR) νmax: 3729, 1567.
Data for (S)-N-(3-(1-cyclo◦propylethyl)-1,3,5-oxadiazinan-4-ylidene)nitramide S-29. White solid,
64% yield, m.p. 111–113 C; TLC Rf 0.63 (AcOEt/Hexane, 7:3) [α]
26 = +12.15 (c = 1, acetone),
◦
1H NMR (500 MHz, DMSO-d6, 50 C):
δ 9.67 (s, 1H), 5.09 (s, 2H), 4.93 (s, 2H), 3.71 (dq,

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J = 9.3, 6.9 Hz, 1H), 1.21 (d, J = 6.9 Hz, 3H), 1.10–1.01 (m, 1H), 0.61–0.53 (m, 1H), 0.49–0.42
◦
(m, 1H), 0.36–0.30 (m, 1H), 0.29–0.23 (m, 1H), 13C NMR (125 MHz, DMSO-d6, 50 C):
δ 153.3,
73.5, 73.1, 55.2, 16.8, 13.7, 4.2, 3.0. HRMS (ESI): calculated for C8H14N4NaO3 [M + Na]+
237.0958 found 237.0954 (5.0 ppm). IR (ATR) νmax: 3295, 1578.
Data for (S)-N-(3-(1,2,3,4-tetrahydronaphthalen-1-yl)-1,3,5-oxadiazinan-4-ylidene)nitramide S-30
.
24
White solid, 19% yield, m.p. 167–169 ◦C; TLC Rf 0.25 (AcOEt/Hexane, 6:4) [
α
]
=
−
47.14
1
(c = 1, acetone). H NMR (500 MHz, CDCl3):
δ 10.05 (s, 1H), 7.21–7.11 (m, 4H), 5.94 (dd,
J = 10.2, 6.1 Hz, 1H), 5.04 (d, J = 2.4 Hz, 2H), 4.69 (d, J = 9.6 Hz, 1H), 4.60 (d, J = 9.5 Hz,
1H), 2.86–2.73 (m, 2H), 2.24–2.17 (m, 1H), 1.99–1.91 (m, 1H), 1.89–1.79 (m, 1H), 1.72 (tdd,
J = 12.2, 10.0, 2.9 Hz, 1H). 13C NMR (125 MHz, CDCl3):
δ
155.19, 138.67, 132.49, 129.64,
127.76, 127.36, 126.59, 74.76, 74.03, 54.17, 29.19, 28.21, 21.43. HRMS (ESI): calculated for
C13H16N4NaO3 [M + Na]+ 299.1115, found 299.1111 (5.0 ppm). IR (ATR)
max: 3303, 1557.
ν
Data for N-(3-phenethyl-1,3,5-oxadiazinan-4-ylidene)nitramide R-31. White solid, 35% yield,
m.p. 134–136 ◦C; TLC Rf 0.45 (AcOEt/Hexane, 6:4) 1H NMR (500 MHz, CDCl3):
9.77
(br s, 1H), 7.35–7.31 (m, 2H), 7.28–7.25 (m, 1H), 7.23–7.19 (m, 2H), 4.89 (d, J = 2.7 Hz, 2H),
4.46 (s, 2H), 3.67 (t, J = 6.8 Hz, 2H), 2.96 (t, J = 6.8 Hz, 2H), 13C NMR (125 MHz, CDCl3):
δ
δ
154.5, 138.1, 128.9, 128.8, 126.9, 78.8, 73.2, 48.9, 34.4. HRMS (ESI): [M + Na]+ calculated for
C11H14N4NaO3 [M + Na]+ 273.0958, found 273.0956. (5.0 ppm). IR (ATR)
νmax: 3324, 1587.
Appendix C
Data for◦ (E)-1-methyl-3-(4-methylbenzyl)-2-nitroguanidine 33. White solid, 85%, m.p.
1
166–168 C; TLC Rf 0.33 (AcOEt/Hexane, 6:4); H NMR (500 MHz, DMSO-d6):
δ 9.17
(br s, 1H), 7.79 (br s, 1H), 7.19 (d, J = 7.8 Hz, 2H), 7.15 (d, J = 7.8 Hz, 2H), 4.38 (s, 2H), 2.84
(br s, 3H), 2.28 (s, 3H), 13C NMR (125 MHz, DMSO-d6):
δ 158.3, 136.6, 129.4, 127.4, 44.2,
28.7, 21.1. HRMS (ESI): calculated for C10H14N4O2Na [M + Na]+ 245.1009, found 245.1014
(−2.9 ppm). IR (ATR) νmax: 3285, 1627.
Data for (E)-1-◦methyl-3-(naphthalen-2-ylmethyl)-2-nitroguanidine 34. White solid, 38% yi◦eld,
m.p. 159–162 C; TLC Rf 0.37 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6, 50 C):
δ
8.11 (d, J = 8.2 Hz, 1H), 7.99–7.95 (m, 1H), 7.87 (d, J = 8.1 Hz, 1H), 7.62–7.54 (m, 2H),
7.50 (dd, J = 8.1, 7.1 Hz, 1H), 7.46 (dd, J = 7.0, 1.3 Hz, 1H), 7.33 (s, 2H), 4.93 (d, J = 4.7 Hz,
2H), 2.88 (s, 3H), 13C NMR (125 MHz, DMSO-d6, 50 ◦C):
δ 158.5, 133.7, 130.9, 128.1, 124.6,
42.8, 28.8. HRMS (ESI): calculated for C13H14N4O2Na [M + Na]+ 281.1009, found 281.1014
(−1.8 ppm). IR (ATR) νmax: 3352, 1623.
Data for ◦(E)-1-(4-chlorobenzyl)-3-methyl-2-nitroguanidine 35. White solid, 77% yield, m.p.
191–194 C; TLC Rf 0.23 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6):
δ 9.19 (br s,
1H), 7.85 (br s, 1H), 7.41 (d, J = 8.1 Hz, 2H), 7.32 (d, J = 8.0 Hz, 2H), 4.41 (s, 2H), 2.85 (br s,
3H), 13C NMR (125 MHz, DMSO-d6):
158.3, 132.0, 129.3, 128.7, 43.8, 28.8. HRMS (ESI):
calculated for C9H11CIN4O2Na [M + Na]+ 265.0463, found 265.0468 (
4.2 ppm). IR (ATR)
max: 3282, 1625.
δ
−
ν
Data for (E)-1-methyl-2-nitro-3-(4-(trifluoromethyl)benzyl)guanidine 36. White solid, 74% yield,
◦
m.p. 170–173 C; TLC Rf 0.20 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6):
δ 9.22
(br s, 1H), 7.88 (br s, 1H), 7.72 (d, J = 8.0 Hz, 2H), 7.51 (d, J = 8.0 Hz, 2H), 4.51 (s, 2H), 2.88
(br s, 3H), 13C NMR (125 MHz, DMSO-d6): δ 158.4, 131.2, 128.0, 125.7 (q, J = 3.5 Hz), 124.7
(q, J = 261.25 Hz), 123.7, 44.1, 28.8, 19F NMR (470 MHz, DMSO-d6): δ −60.77. HRMS (ESI):
calculated for C10H12F3N4O2 [M + H]+ 277.0907, found 277.0912 (
2.2 ppm). IR (ATR)
−
ν
max: 3235, 1625.
Data for (E)-1-(2-methoxybenzyl)-3-methyl-2-nitroguanidine 37. White solid, 74% yield, m.p.
◦
◦
148–152 C; TLC Rf 0.33 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6, 50 C):
δ 8.20
(d, J = 164.9 Hz, 2H), 7.29 (td, J = 7.9, 1.7 Hz, 1H), 7.20 (d, J = 7.4 Hz, 1H), 7.03 (d, J = 8.2 Hz,
1H), 6.95 (td, J = 7.4, 1.0 Hz, 1H), 4.42 (d, J = 5.5 Hz, 2H), 3.84 (s, 3H), 2.85 (s, 3H), 13C NMR
(125 MHz, DMSO-d6):
δ 169.0, 136.8, 129.6, 127.9, 120.7, 111.0, 55.8, 28.7, 26.5. HRMS (ESI):

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[M + Na]+ calculated for C10H14N4O3Na [M + Na]+ 261.0958, found 261.0964 (
IR (ATR) νmax: 3328, 1621.
−
1.9 ppm).
Data for (E)-1-(4-methoxybenzyl)-3-methyl-2-nitroguanidine 38. White solid, 82% yield, m.p.
189–192 ◦C; TLC Rf 0.23 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6):
9.16 (s,
1H), 7.77 (s, 1H), 7.24 (d, J = 8.1 Hz, 2H), 6.91 (d, J = 8.2 Hz, 2H), 4.35 (d, J = 5.2 Hz, 2H),
δ
3.73 (s, 3H), 2.83 (s, 3H), 13C NMR (125 MHz, DMSO-d6):
δ 158.9, 158.2, 131.0, 129.0, 114.2,
55.5, 43.9, 28.7. HRMS (ESI): calculated for C10H14N4O3Na+ [M + Na]+ 261.0958, found
261.0964 (−1.5 ppm). IR (ATR) νmax: 3264, 1627.
Data for (S)-1-(1-cyclopropylethyl)-3-methyl-2-nitroguanidine S-39. White solid, 13% yield, m.p.
◦
25
1
148–150 C; TLC Rf 0.31 (AcOEt/Hexane, 6:4) [
(500 MHz, DMSO-d6, 50 ◦C):
8.27 (s, 2H), 3.36–3.26 (m, 1H), 2.81 (d, J = 4.9 Hz, 3H), 1.21
(d, J = 6.6 Hz, 3H), 1.08–0.99 (m, 1H), 0.53–0.46 (m, 1H), 0.46–0.39 (m, 1H), 0.34–0.28 (m,
α
]
= +31.89 (c = 1, acetone), H NMR
δ
1H), 0.24–0.17 (m, 1H), 13C NMR (125 MHz, DMSO-d6, 50 ◦C):
δ 157.25, 51.01, 28.01, 19.89,
16.68, 2.91, 2.70. HRMS (ESI): calculated for C7H14N4NaO2 [M + Na]+ 209.1009, found
209.1006 (5.0 ppm). IR (ATR) νmax: 3334, 3290, 1622.
Data for (S)-1-methyl-2-ni◦tro-3-(1,2,3,4-tetrahydronaphthalen-1-yl)guanidine S-40. White solid,
26
29% yield, m.p. 192–194 C; TLC Rf 0.43 (AcOEt/Hexane, 6:4) [
α
]
=
−
2.98 (c = 1, acetone),
◦
1H NMR (500 MHz, DMSO-d6, 50 C):
δ 8.28 (br s, 2H), 7.28–7.09 (m, 4H), 5.05 (s, 1H), 2.86
(s, 3H), 2.83–2.68 (m, 2H), 2.06–1.97 (m, 1H), 1.91 (d, J = 6.8 Hz, 1H), 1.86-1.80 (m, 1H),
1.79–1.70 (m, 1H), 13C NMR (125 MHz, DMSO-d6, 50◦C): δ 157.6, 137.1, 128.6, 127.4, 126.9,
125.8, 49.3, 29.5, 28.4, 28.1, 19.9. HRMS (ESI): calculated for C12H17N4O2 [M + H]+ 249.1346,
found 249.1340 (5.0 ppm) IR (ATR) νmax: 3337, 3302, 1623.
Data for 1-methyl-2-nitro-3-(thiophen-2-ylmethyl)guanidine 41. Yellow solid, 57%, m.p. 100–102
1
◦C; TLC Rf 0.29 (AcOEt/Hexane, 65:35) H NMR (500 MHz, DMSO-d6):
δ 9.18 (s, 1H),
8.10–7.82 (m, 1H), 7.42 (d, J = 5.1 Hz, 1H), 7.03 (s, 1H), 7.00–6.95 (m, 1H), 4.57 (s, 2H), 2.81
(s, 3H), 13C NMR (125 MHz, DMSO-d6):
δ 157.78, 126.86, 126.10, 125.68, 39.48, 28.51. HRMS
(ESI): calculated for C7H10N4NaO2S [M + Na]+ 237.0417, found 237.0413 (5.0 ppm). IR
(ATR) νmax: 3286, 3210.
Data for 1-methyl-2-nitro-3-phenethylguanidine 42. White solid, 55% yield, m.p. 151–153 ◦C;
1
TLC Rf 0.18 (AcOEt/Hexane, 6:4) H NMR (500 MHz, DMSO-d6):
δ 7.31 (t, J = 7.5 Hz,
2H), 7.27–7.19 (m, 3H), 3.49–3.41 (m, 2H), 2.86 (t, J = 7.4 Hz, 2H), 2.78 (d, J = 2.8 Hz, 3H),
13C NMR (125 MHz, DMSO-d6):
δ 157.83, 138.53, 128.51, 128.20, 126.13, 42.22, 34.59, 27.97.
HRMS (ESI): calculated for C10H14N4NaO2 [M + Na]+ 245.1009, found 245.1009 (5.0 ppm).
IR (ATR) νmax: 3336, 3284, 1619.
These compounds were prepared following the same procedure used for the cycliza-
tion of non-methylated nitroguanidines.
N-(3-methyl-5-(4-methylbenzyl)-1,3,5-oxadiazinan-4-ylidene)nitramide 43. White solid, 68%
yield, m.p. 146–151 ◦C; TLC Rf 0.06 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-d6):
δ
7.22–7.15 (m, 4H), 5.00 (s, 2H), 4.95 (s, 2H), 4.57 (s, 2H), 2.87 (s, 3H), 2.29 (s, 3H), 13C NMR
(125 MHz, DMSO-d6):
(ESI): calculated for C12H17N4O3 [M + H]+ 265.1295, found 265.1301 (
max: 1601.
δ
156.8, 137.5, 132.9, 129.6, 128.1, 79.6, 77.4, 50.7, 33.9, 21.1. HRMS
−
0.8 ppm). IR (ATR)
ν
Data for N-(3-methyl-5-(naphthalen-2-ylmethyl)-1,3,5-oxadiazinan-4-ylidene)nitramide 44. White
solid, 71% yield, m.p. 151–153 ◦C; TLC Rf 0.06 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz,
CDCl3):
δ 7.99 (dd, J = 8.4, 1.1 Hz, 1H), 7.92–7.85 (m, 2H), 7.62–7.57 (m, 1H), 7.56–7.51
(m, 1H), 7.48–7.41 (m, 2H), 5.19 (s, 2H), 4.81 (s, 2H), 4.65 (s, 2H), 3.12 (s, 3H), 13C NMR
(125 MHz, CDCl3):
δ 157.8, 133.9, 131.2, 129.8, 129.0, 128.9, 127.7, 127.3, 126.4, 125.2, 123.0,
79.6, 50.0, 34.8. HRMS (ESI): calculated for C15H17N4O3 [M + H]+ 301.1295, found 301.1301
(0.3 ppm). IR (ATR) νmax: 1609.

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Data for (E)-N-(3-(4-chlorobenzyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene)nitramide 45. White
solid, 63% yield, m.p. 163–166 ◦C; TLC Rf 0.03 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz,
DMSO-d6):
δ 7.50–7.40 (m, 2H), 7.36–7.29 (m, 2H), 5.02 (s, 2H), 5.0 (s, 2H), 4.62 (s, 2H),
2.87 (s, 3H), 13C NMR (125 MHz, DMSO-d6):
δ 156.9, 135.3, 132.8, 129.9, 129.0, 79.6, 77.6,
50.3, 34.0. HRMS (ESI): calculated for C11H14ClN4O3 [M + H]+ 285.0749, found 285.0754
(0.7 ppm). IR (ATR) νmax: 1608.
Data for N-(3-methyl-5-(4-(trifluoromethyl)benzyl)-1,3,5-oxadiazinan-4-ylidene)nitramide 46
.
◦
1
White solid, 58% yield, m.p. 126–129 C; TLC Rf 0.03 (AcOEt/Hexane, 6:4); H NMR
(500 MHz, DMSO-d6): 7.72 (d, J = 7.9 Hz, 2H), 7.50 (d, J = 8.0 Hz, 2H), 5.02 (s, 4H), 4.71
δ
(s, 2H), 2.87 (s, 3H), 13C NMR (125 MHz, DMSO-d6):
δ 157.0, 141.1, 128.7 (q, J= 31.25 Hz),
128.5, 125.9 (q, J = 3.75 Hz), 124.6 (q, J = 271.25 Hz), 79.6, 77.9, 50.6, 33.9, 19F (470 MHz,
DMSO-d6): δ −60.77. HRMS (ESI): calculated for C12H13F3N4O3Na [M + Na]+ 341.0837,
found 341.0837 (0.9 ppm). IR (ATR) νmax: 1609.
Data for N-(3-(4-methoxybenzyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene)nitramide 47. White solid,
◦
45% yield, m.p. 139–142 C; TLC Rf 0.03 (AcOEt/Hexane, 6:4); 1H NMR (500 MHz, DMSO-
d6):
δ 7.24 (d, J = 8.4 Hz, 2H), 6.92 (d, J = 8.6 Hz, 1H), 4.99 (s, 2H), 4.94 (s, 2H), 4.54 (s, 2H),
3.74 (s, 2H), 2.88 (s, 3H), 13C NMR (125 MHz, DMSO-d6):
δ
159.4, 156.8, 129.7, 127.7, 114.5,
79.5, 77.3, 55.5, 50.4, 33.9. HRMS (ESI): calculated for C12H17N4O4 [M + H]+ 281.1244,
+
found 281.1250 (−1.4 ppm). IR (ATR) νmax: 1587.
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