Azine-Hydrazone Tautomerism of Guanylhydrazones: Evidence for the Preference Toward the Azine Tautomer

Article abstract of DOI:10.1021/acs.joc.6b01258

Guanylhydrazones have been known for a long time and have wide applications in organic synthesis, medicinal chemistry, and material science; however, little attention has been paid toward their electronic and structural properties. Quantum chemical analysis on several therapeutically important guanylhydrazones indicated that all of them prefer the azine tautomeric state (by about 3-12 kcal/mol). A set of simple and conjugated azines were designed using quantum chemical methods, whose tautomeric preference toward the azine tautomer is in the range of 3-8 kcal/mol. Twenty new azines were synthesized and isolated in their neutral state. Variable temperature NMR study suggests existence of the azine tautomer even at higher temperatures with no traces of the hydrazone tautomer. The crystal structures of two representative compounds confirmed that the title compounds prefer to exist in their azine tautomeric form.

Full text of DOI:10.1021/acs.joc.6b01258

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Article
On the Azine-Hydrazone Tautomerism of Guanylhydrazones:
Evidence for the Preference Towards the Azine Tautomer
Sumit Sunil Chourasiya, Deepika Kathuria, Sampada Sunil Nikam, Ashok Ramakrishnan,
Sadhika Khullar, Sanjay K. Mandal, Asit K Chakraborti, and Prasad V. Bharatam
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b01258 • Publication Date (Web): 05 Aug 2016
Downloaded from http://pubs.acs.org on August 5, 2016
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On the AzineꢀHydrazone Tautomerism of Guanylhydrazones:
Evidence for the Preference Towards the Azine Tautomer
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Sumit S. Chourasiya,† Deepika Kathuria,† Sampada S. Nikam,† Ashok Ramakrishnan,† Sadhika Khullar‡
Sanjay K. Mandal,*‡ Asit K. Chakraborti*† and Prasad V. Bharatam*†
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† Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER),
Sector 67, S.A.S. Nagar – 160 062, Punjab, India
‡ Department of Chemical Sciences, Indian Institute of Science Education and Research, Mohali
Sector 81, S.A.S. Nagar – 140 306, Punjab, India
Eꢀmail: pvbharatam@niper.ac.in, akchakraborti@niper.ac.in, sanjaymandal@iisermohali.ac.in
Table of content graphics
Abstract: Guanylhydrazones have been known for a long time and have wide applications in
organic synthesis, medicinal chemistry and material science; however, little attention has been
paid towards their electronic and structural properties. Quantum chemical analysis on several
therapeutically important guanylhydrazones indicated that all of them prefer the azine tautomeric
state (by about 3ꢀ12 kcal/mol). A set of simple and conjugated azines were designed using
quantum chemical methods, whose tautomeric preference towards the azine tautomer is in the
range of 3ꢀ8 kcal/mol. Twenty new azines were synthesized and isolated in their neutral state.
Variable temperature NMR study suggests existence of the azine tautomer even at higher
temperatures with no traces of the hydrazone tautomer. The crystal structures of two
representative compounds confirmed that the title compounds prefer to exist in their azine
tautomeric form.
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Introduction
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Guanylhydrazones also known as amidinohydrazones are a class of compounds obtained by
the condensation of oxo compounds (aldehyde/ketone) with aminoguanidine, known in the
literature for more than 50 years.1 Guanylhydrazones have been reported to possess
antiprotozoal,2,3 antibacterial,4 antimalarial,3,5 trypanocidal,6 antisecretory,7 antidiarrheal,7
anticoagulant,8,9 antihypertensive,10–13 antiviral,14 antileukemic,15 cardiotonic16 and anticancer17–
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activities. Recently, guanylhydrazones have been reported to inhibit Chk, a novel target for
cancer.22–26 Apart from their medicinal importance, guanylhydrazones are also useful as building
blocks for the synthesis of heterocycles27,28 and recently furoxan derivatives of
guanylhydrazones have been reported as thermally stable energetic material.29
Surprisingly, in spite of their use in organic synthesis and potential biological applications,
very little is known about their structure and tautomeric preferences. These compounds can
undergo 1,3ꢀH shift to exhibit the azine⇋hydrazone tautomerism.30 Only a few studies have paid
attention to the structure and tautomeric preferences of guanylhydrazones. These studies includes
(i) the crystal and molecular structure of the free base of the antileukemic agent glyoxal bis
(amidinohydrazones),31 (ii) the crystal and conformational analysis of guanabenz (GBZ) free
base,32 (iii) the structure of guanylhydrazones derived from aromatic aldehydes (NMR,33,34 Xꢀ
ray34), and (iv) the crystal structure of 2ꢀ(1ꢀphenylethylideneamino)guanidine.35 All these studies
reported the presence of azine (2,3ꢀdiazaꢀ1,3ꢀbutadiene) tautomer (A) in solution as well as in the
solid state. These crystal structures indicate that guanylhydrazones should be represented as
azines. However, they are mostly being represented in their ‘classical’ hydrazone form (B)
(Figure 1). The most probable reason for this misrepresentation could be that in many cases the
salts (hydrochloride or bicarbonate) of guanylhydrazones were synthesized and used for their
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biological activity. Protonation of the azine and hydrazone tautomers leads to the same structure
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(C).30
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Figure 1. Two possible tautomeric forms (A and B) of guanylhydrazones along with their
protonated form (C).
The free base of guanylhydrazones cannot be ignored since the available literature on the
biological activity of guanylhydrazone hydrochloride suggested the existence of considerable
proportion (~16%) of free base at physiological temperature (37 °C) and pH (7.4).31,32 Moreover,
in many reports, wherein the enzymatic activity of the guanylhydrazones is reported, the
inhibitory action of these compounds was interpreted with the help of molecular modeling
studies.22,36 For example, Qian et al. reported guanylhydrazones as anticancer agents targeting
tubulin, and during molecular docking studies, they have used hydrazone tautomer instead of
azine tautomer as a neutral ligand.36 Recently, NSC109555, the sole lead chemotype from HTS
of 100,000 compounds has been reported as Chk2 inhibitor.22–26 Molecular modeling studies
were carried out to predict the binding pose, in which case the hydrazone tautomer as a neutral
ligand was considered rather than the azine tautomer.22 This can potentially mislead the
interpretation of interactions with the target enzymes. Similarly, it may lead to a mistaken
information about the Structure Activity Relationship (SAR) by considering the wrong
pharmacophoric feature, i.e., hydrazone instead of azine.
Consideration of the energetically preferred azine tautomer of guanylhydrazone under neutral
condition will open many new opportunities for exploring these compounds as substrates for the
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various crisscross cycloaddition reactions and/or in the synthesis of heterocyclic rings such as
1,2,4ꢀtriazoles,27,37 oxadiazoles,38 isoquinolines,39–41 etc. It is also worth noting that azines can be
involved in NꢀN cleavage chemistry39–42 and in exchange reactions of the =NꢀN= group with an
azo group.43 Similarly, conjugation in such azines can be studied since previous studies
identified conjugation stopper44 and conjugation switch properties45 as characteristics of azines.
The pushꢀpull effect,46,47 liquid crystals,48,49 nonꢀlinear optics,50 optoꢀelectronics,51 etc., are
properties which are exhibited by azines but not by hydrazones. Hence, it is very important to
consider both the tautomers separately. In this article, we report the quantum chemical studies,
synthesis and structural analysis of two series of neutral guanylhydrazones (Figure 2). The
structures of two such examples were established as azines through quantum chemical and
spectral studies and confirmed by single crystal Xꢀray diffraction studies.
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Figure 2. Guanylhydrazones considered in this study in their preferred azine form. E/Z isomers
are expected for compounds in series 2. Based on the known literature E/Z isomers are not
generally expected for compounds in series 1.
Results and Discussion
A. Quantum Chemical Studies
This work was initiated by calculating the azine⇋hydrazone tautomeric energy difference in a
few important guanylhydrazones listed in Figure 3. In all these cases it was found that the global
minimum tautomer is in the azine form (A). In literature, they were reported in the salt form but
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Figure 3. 2D structures of several important azine derivatives. In the literature all of these
compounds were represented as guanylhydrazone derivatives. In this figure, they are given in
their energetically preferred azine tautomeric representation (values in parenthesis indicate the
azine⇋hydrazone tautomeric energy difference, ꢁGT in kcal/mol, where T represents tautomer,
calculated at B3LYP/6ꢀ311++G(d,p) level). Absolute Gibbs free energy and the optimized 3D
structures are given in supporting information (Table SIꢀ1).
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are represented (e.g. in ZINC database)52 in the form of hydrazone tautomer (B) in the neutral
state.
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Due to the presence of C4=N3 double bond in these guanylhydrazones (Figure 3), all these
compounds may exhibit E/Z isomerism and hence the energy differences between the E and Z
isomers of global minimum tautomer (Azine) were also estimated (Table SIꢀ2). In most of these
cases, the E isomer was found to be more stable than the Z isomer (0.49 – 6.35 kcal/mol) except
in the case of compounds VIII and X where the Z isomer was found to be marginally more stable
(0.43 – 1.90 kcal/mol). Hence, the azines IꢀXIV in Figure 3 have been represented in the
energetically most stable geometrical isomeric state.
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In order to explore the effect of substitutions and extended conjugation on tautomeric energy
differences in the designed molecules (series 1 and 2), ꢁGT was calculated using quantum
chemical method (Table 1). In all cases, the azine tautomers are more stable than the
corresponding hydrazone tautomers by 3ꢀ8 kcal/mol. Compounds containing an electron
donating methoxy groups on the phenyl ring showed relatively lower ꢁGT (19 and 20) whereas
compounds containing electron withdrawing groups such as chloro, fluoro and nitro showed
relatively higher ꢁGT (11, 16 and 17). Even under implicit solvent conditions (DMSO and H2O),
the preference is for the azine tautomers (Table SIꢀ3). For compounds in series 1 and series 2,
two geometrical isomers (E/Z) are possible with reference to the newly formed C4=N3 double
bond. The crystal structure data of compounds 4 and 14 showed E geometry across C4=N3
double bond (vide infra). The ꢁGT values given in Table 1 are after employing the E geometrical
isomer in all cases. The ꢀGEZ values (the difference between the E and Z isomers) were estimated
using quantum chemical methods, the results are provided in Table SIꢀ4.
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Table 1. Influence of Substituents on the Energy Difference (∆GT in kcal/mol) Between the
Azine and the Hydrazone Tautomers (1ꢀ20) with Azine Structure Taken as a Base.
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∆GT
Compd
V
Ar
R
∆GT
Compd
11
Ar
Ar'
H
5.96
H
5.40
6.25
1
H
H
5.00
5.50
5.51
5.65
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3
12
13
H
5.69
5.62
4
14
H
H
5.90
4.84
6.04
6.21
5.72
8.43
6.35
6.43
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H
CH3
H
H
5.74
5.55
3.72
4.04
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B. Synthesis and Spectral Analysis
The conventional method for the synthesis of guanylhydrazones involves the condensation of
the carbonyl compounds (aldehyde/ketone) with aminoguanidine hydrochloride in ethanol
under reflux to give the desired hydrochloride salt.7,53 The neutralization of the salts can be
carried out to afford the guanylhydrazone free bases;34 however, many workers did not report
this neutralization step. In this work, the same reaction is carried out in the presence of
aqueous NaOH to produce the compounds 1ꢀ10 directly in their neutral form, as precipitates
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(Scheme 1). Several advantages were noticed, though the modification is very nominal – (i)
the green reaction conditions (aqueous solvent instead of organic solvent), (ii) the reaction is
completed within an hour, whereas the conventional method required more than 6 h, (iii) the
reaction can be carried out at room temperature, instead of reflux (~80 °C), (iv) in the
conventional method, during neutralization, some loss of the product was noticed, which is
avoided during the single step procedure. The neutral compounds (11ꢀ20) in series 2 (Scheme
2) were obtained by the neutralization of 11ꢀ20.HCl. The salts (11ꢀ20.HCl) were synthesized
using conventional method from chalcones which were obtained employing reported
methods.36,54ꢀ57 The direct synthesis of 11ꢀ20 using the above defined method (as in
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compounds of Series 1) is not applicable because the reaction of
under basic conditions, is known to yield cyclised products.58,59
Scheme 1. Synthesis of Azines 1ꢀ20.
α,βꢀunsaturated ketones,
During neutralization, two geometrical isomers (E and Z) across the newly formed ꢀC=N bond
have been observed in two of the compounds, i.e., 12 and 18 in the ratio of 2:1 (E:Z) (calculated
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from integration of proton signals). It is important to note that the compounds 2, 7, 8 and 11 were
previously reported in their hydrochloride salt.36,60ꢀ62
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All the synthesized compounds were characterised by NMR, IR and mass spectroscopy
techniques. The most convincing evidence for the presence of the azine tautomer in the
synthesized compounds is obtained from the 1H NMR in solution.63 In dimethyl sulfoxideꢀd6, the
1H NMR spectrum of the synthesized free bases 1ꢀ20 exhibited two slightly broadened singlets
(at ~5.4ꢀ6.5 ppm). The broad peaks were due to the protons bound to the nitrogen atoms and
were confirmed by deuterium exchange study (Figure SIꢀ1). The consistent pattern and the
intensity ratio (1:1) of the broad peaks in 1ꢀ20 can be explained by assuming that the compounds
carry two terminal NH2 groups which are chemically nonequivalent and thus would be expected
to have different chemical shifts. They are chemically nonequivalent because of the presence of
hydrogenꢀbond interactions between the hydrogen atoms of guanidinyl group and an imino N3
atom (Figure 2). In the case of hydrazone and its salt, the ꢀNH proton appears in the range of 11ꢀ
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1
14 ppm in H NMR.64–67 This was found to be true in all the salts (Scheme 2) prepared during
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this work. After neutralization, disappearance of ꢀNH proton in the region 11ꢀ14 ppm in H
NMR and an existence of two broad singlets of ꢀNH2 at 5.5ꢀ6.5 ppm confirms the formation of
the azine at room temperature.
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Variable temperature H NMR of compound 14 was recorded and it was found that at higher
temperature (70 °C), (because of the breaking of hydrogen bond interactions between hydrogen
atom of guanidinyl group and an imino N3) the two –NH2 peaks become equivalent and thus
give rise to broad singlet of four protons. Even at 70 °C, the characteristic –NH peak of the
hydrazone tautomer in the range of 11ꢀ14 ppm did not appear (Figure 4). This indicates that no
traces of hydrazone tautomer can be identified even at higher temperature and hence confirm that
under experimental condition only the azine tautomer exists. The quantum chemical studies were
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carried out for further exploration. Though azine⇋hydrazone tautomerism was not observed
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even at higher temperature, thermal isomerization may be possible in compound 14 due to the
presence of two imine groups. Three different mechanisms of E/Z isomerization i.e. pure
inversion, pure rotation or intermediate mechanism were proposed earlier in the literature.68ꢀ71 In
order to explore the mechanism of thermal isomerization in the case of azine 14, we calculated
the Nꢀinversion barriers for N2 and N3 imine nitrogen centres in the gas phase. The inversion
barrier for N2 and N3 nitrogen centres were found to be 22.7 kcal/mol and 38.7 kcal/mol
respectively. Based on the angle α (CꢀNꢀN) in the ground (αG) and in the transition (αT) states,
the percentage of inversion and rotation mechanism associated with thermal isomerization were
estimated using the following Equation 172
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ꢀ
ꢅ
ꢁꢂꢃꢁꢄ ×ꢆꢇꢇ
βI =
(1)
ꢆꢈꢇꢃꢁꢄ
where βI is percent of inversion mechanism, αG = CNN bond angle in the ground state, αG =
112°. ꢉT = CNN bond angle in the transition state, αGN2 = 146.3°, αGN3 = 160.6°. The percentage
of rotation mechanism, βR can be obtained by subtracting βI from 100.
rt
Figure 4. Variable temperature 1H NMR of compound 14.
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The βI for N2 nitrogen was found to be 50% indicating that the N2 nitrogen is associated with
mixed inversion and C=N rotation. The βI for N3 was found to be ~ 70% (A table comparing
energy barriers and structural parameters in ground state and transition state of azine 14 is given
in Table SIꢀ5). Thus at 70 °C, it is possible that the compound 14 may undergo two fold nitrogen
inversion across the N2 and N3 nitrogen centres.
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The C NMR chemical shift were estimated using the GIAO method for both the azine and
the hydrazone tautomers of compounds 1ꢀ20. The characteristic signal to distinguish the
tautomers is due to C1 carbon which was observed in the range of 159ꢀ162 ppm in all of the
synthesized compounds. The NMR simulation study of compounds in series 1 revealed that in
case of the hydrazone tautomer, the calculated chemical shift for the C1 carbon is appearing in
the range of 154ꢀ157 which is far from the experimentally observed C1 chemical shift. However,
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in case of the azine tautomer, the calculated C NMR of azine tautomer, the chemical shift for
C1 carbon is appearing in the range of 159ꢀ164 which is very close to the experimental values
(Table 2). A similar clear distinction was not observed for compounds in series 2 (Table SIꢀ6).
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Table 2. Comparision of Experimental and Theoretical C NMR Chemical Shift Values
(ppm) for the Azine and the Hydrazone Tautomers of Compounds 1ꢀ10.
13C NMR, C1
(Calculated, Gas phase)
13C NMR, C1
(Observed)
Compd
Experimental
Hydrazone
Azine
156.9
153.9
157.4
156.6
157.0
154.2
157.7
156.5
156.3
154.5
163.1
159.3
164.0
162.2
163.0
159.0
161.3
162.8
162.7
164.0
161.0
162.2
161.7
161.5
161.7
161.7
160.1
160.5
161.9
162.4
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C. Crystal Structure Analysis
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In order to confirm the structural features of the synthesized compounds, single crystals of
compounds 4 and 14, obtained by slow evaporation of their methanol solutions, were studied by
Xꢀray diffractometry.73ꢀ74 The analysis of single crystal structures reveals that 4 and 14 contain
free terminal NH2 groups and exist in sꢀtrans form across the NꢀN single bond (Figure SIꢀ3 and
SIꢀ4). The geometrical parameters from the crystal structures of 4 and 14 indicate that the
synthesized compounds are in the azine tautomeric state (Figure 5). The important geometrical
parameters of 4 and 14 are given in Table 3. The molecular geometries of compounds 4 and 14
are also consistent with the 1H NMR spectrum, which shows a characteristic azine ꢀNH2 signal at
5.5ꢀ6.5 ppm. The geometrical parameters obtained from quantum chemical analysis and Xꢀray
diffraction are quite comparable (Table 3), the small differences are due to the packing forces
(which are governed by intermolecular interaction) in the solid state.
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Figure 5. 3D solid state structures of 4 (left) and 14 (right) determined by the single crystal Xꢀ
ray diffraction method
.
According the quantum chemical data, compound 4 prefers a Z geometrical isomer in gas
phase condition by a marginal ꢀGEZ value (0.75 kcal/mol, see supporting information, Table SIꢀ
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4). But in the crystal structure, the intermolecular hydrogen bonds ensure that the E isomer is the
preferred geometrical isomer. The crystal structure of the corresponding hydrochloride salt of
compound 1475 is provided in the supporting information (FigureꢀSIꢀ5).
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The crystal structure of 14·HCl (Figure SIꢀ5) indicates E geometry across N3ꢀC4 bond, which
is different from the crystal structure of guanidine derivative reported earlier as Z isomer.36 The
∆GEZ in 14 is 1.20 kcal/mol (in favour of E isomer) and ∆GEZ in 14.HCl is 2.72 kcal/mol (in
favour of Z isomer) calculated using B3LYP with 6ꢀ311++G(d,p) basis set (Scheme 2, Table SIꢀ
7). The observed structural differences and the small energy differences indicate that 11ꢀ20 can
possibly show polymorphism originating from geometrical isomerism.
Scheme 2. The ∆GEZ Values Across N3ꢀC4 Bond in Compounds 14 and 14H+ Calculated at
B3LYP/6ꢀ311++G(d,p) Level of Theory.
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Table 3. Important Geometrical Parameters of 4 and 14. Comparison Between the XRD
data and DFT (B3LYP/6ꢀ311++G(d,p)) Data is Listed. Distances are in Å and Angles are in
Degree (°).
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14
Parameters
DFT
Xꢀray
DFT
Xꢀray
Bond lengths
C1ꢀN2
1.301
1.327
1.302
1.330
C4ꢀN3
N2ꢀN3
1.285
1.381
1.278
1.385
1.302
1.380
1.306
1.386
Bond angles
C1ꢀN2ꢀN3
112.89
114.07
110.37
116.68
111.58
116.98
111.22
116.08
C4ꢀN3ꢀN2
Dihedral angles
C1ꢀN2ꢀN3ꢀC4
C5ꢀC4ꢀN3ꢀN2
175.67
179.32
179.74
178.77
174.125
2.84
161.86
6.40
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Conclusions
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Several guanylhydrazones have been reported in literature. Recent quantum chemical studies
reported that these compounds should be considered as azines rather than hydrazones. To verify
this dichotomy, two series of azines (with and without extended conjugation) were synthesized.
The quantum chemical calculations, NMR and XRD data clearly suggest that the azine tautomer
is the preferred tautomeric state of this class of compounds. Although, the tautomeric energy
difference is small (3ꢀ8 kcal/mol), the NMR data up to 70 °C showed only the azine tautomer
without any traces of hydrazone tautomer. Thus, in the case of guanylhydrazones, we should
consider only the azine tautomer in all future studies. In the organic and medicinal chemistry
literature, these compounds are generally represented in their hydrazone form, but this study
shed light on its structural features and suggests that the correct tautomer (azine) should be
considered in medicinal chemistry as well as in organic chemistry. The modified synthetic
strategy adopted in this work carry the additional advantage of direct access of the preparation of
neutral azines.
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Experimental Section
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Computational Methods
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9
The quantum chemical calculations were performed using the Gaussian 0976 suite of
programs. Geometry optimization of compounds IꢀXIV and 1ꢀ20 was performed by DFT77 using
B3LYP78 method. The basis set used was 6ꢀ311++G(d,p). To estimate the effect of the solvent,
we employed the selfꢀconsistent reaction field theory (SCRF) polarizable continuum model
(IEFPCM),79 as implemented in Gaussian09, at the B3LYP/6ꢀ311++G(d,p) level of theory.
Frequency calculations were carried out on all the structures to verify stationary point with zero
negative frequency. NMR calculations were performed by using the GIAO method.80,81
Chemistry
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The reagents and chemicals required for the study were procured and were used as such without
further purification unless otherwise mentioned. The progress of the reaction was monitored by
Thin Layer Chromatography (TLC) performed on silica gel aluminium plates and visualization
was done by UV light. 1H NMR and 13C NMR spectra were recorded at 400 MHz and 100 MHz
spectrometer respectively, with TMS as an internal standard. The 1H NMR and 13C NMR spectra
were recorded for DMSOꢀd6 at 2.50 ppm and 39.51 ppm respectively. Chemical shift (δ) are
reported in part per million (ppm). Coupling constants (J) were reported in hertz (Hz). The
abbreviations used to characterize the signals are as follows: s = singlet, m = multiplet, d =
doublet, br s = broad singlet, dd = doublet of doublet, t = triplet. High resolution mass spectra
were taken using ESIꢀTOF method. Mass spectra were recorded using ESI mode. Melting points
were determined by using melting point apparatus.
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General Procedure for the Synthesis of Azines (1ꢀ10)
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8
To the substituted carboxaldehyde and aminoguanidine hydrochloride in H2O was added 1N
NaOH (2 mL) and the reaction mixture was stirred for 5 minꢀ1 h, until precipitate is formed. The
resultant precipitate was filtered and dried to afford the desired azines 1ꢀ10 in 63 to 96 % yields.
(E)ꢀ4ꢀ([1,1'ꢀbiphenyl]ꢀ4ꢀyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazabutaꢀ1,3ꢀdiene (1)
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1
White solid (420 mg, 81%). mp 235ꢀ237 °C; IR (KBr, cmꢀ1): 3358, 1663, 1538, 1148; H NMR
(400 MHz, DMSOꢀd6)
δ 8.03 (s, 1H), 7.76 (d, J = 8.2 Hz, 2H), 7.69 (d, J = 7.2 Hz, 2H), 7.64 (d,
J = 8.2 Hz, 2H), 7.47 (t, J = 7.6 Hz, 2H), 7.36 (s, 1H), 5.95 (br s, 2H), 5.53 (br s, 2H); 13C NMR
(100 MHz, DMSOꢀd6)
δ 161.0, 143.2, 140.2, 139.6, 136.6, 129.4, 127.8, 127.2, 127.0, 126.9;
HRMS (ESIꢀTOF) m/z: [M + H]+ Calcd for C14H15N4 239.1296; Found 239.1283.
(E)ꢀ4ꢀ(2ꢀchloroquinolinꢀ3ꢀyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazabutaꢀ1,3ꢀdiene (2)
Yellow solid (440 mg, 82%). mp 217ꢀ220 °C; IR (KBr, cmꢀ1): 3477, 1616, 1519, 1137; 1H NMR
(400 MHz, DMSOꢀd6)
δ 9.09 (s, 1H), 8.30 (s, 1H), 7.99 (d, J = 7.5 Hz, 1H), 7.91 (d, J = 8.2 Hz,
1H), 7.76 (t, J = 8.0 Hz, 1H), 7.65 (d, J = 8.0 Hz, 1H), 6.29 (br s, 2H), 5.81 (br s, 2H); 13C NMR
(100 MHz, DMSOꢀd6)
δ 162.2, 146.5, 137.0, 134.2, 130.7, 129.1, 128.5, 128.1, 127.9, 127.8;
HRMS (ESIꢀTOF) m/z: [M + H]+ Calcd for C11H11ClN5 248.0703; Found 248.0699.
(E)ꢀ4ꢀ(4ꢀ(dimethylamino)ꢀ2ꢀnitrophenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazabutaꢀ1,3ꢀdiene (3)
1
Brown solid (472 mg, 87%). mp 170ꢀ173 °C; IR (KBr, cmꢀ1): 3361, 1602, 1519, 1371; H NMR
(400 MHz, DMSOꢀd6)
δ 8.13 (s, 1H), 8.04 (d, J = 12 Hz, 1H), 7.05 (d, J = 4 Hz, 1H), 6.98 (dd, J
= 8.8, 2.5 Hz, 1H), 6.49 (br s, 4H), 2.99 (s, 6H); 13C NMR (100 MHz, DMSOꢀd6)
δ
159.6, 150.5,
149.5, 139.5, 129.2, 116.6, 116.3, 105.8, 23.7; HRMS (ESIꢀTOF) m/z: [M + H]+ Calcd for
C10H15N6O2 251.1256; Found 251.1250.
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(E)ꢀ4ꢀ(1Hꢀimidazolꢀ2ꢀyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazabutaꢀ1,3ꢀdiene (4)
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6
Yellow solid (315 mg, 96%). mp 200ꢀ203 °C; IR (KBr, cmꢀ1): 3378, 1621, 1538, 1144; 1H NMR
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8
9
13
(400 MHz, DMSOꢀd6)
(100 MHz, DMSOꢀd6)
δ
7.81 (s, 1H), 7.06 (s, 2H), 6.49 (br s, 2H), 6.02 (br s, 2H); C NMR
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δ
175.8, 161.6, 146.2, 133.4; HRMS (ESIꢀTOF) m/z: [M + Na]+ Calcd for
C5H8N6Na 175.0708; Found 175.0708.
4ꢀ(1,2,3ꢀthiadiazolꢀ4ꢀyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazabutaꢀ1,3ꢀdiene (5)
White solid (174 mg, 96%). mp 180ꢀ183 °C; IR (KBr, cmꢀ1): 3407, 1634, 1541, 1159; H NMR
1
13
(400 MHz, DMSOꢀd6)
(100 MHz, DMSOꢀd6)
δ
9.64 (s, 1H), 8.68 (s, 1H), 5.97 (br s, 2H), 5.90 (br s, 2H); C NMR
δ
161.7, 161.5, 133.8, 131.8; HRMS (ESIꢀTOF) m/z: [M + H]+ Calcd for
C4H7N6S 171.0452; Found 171.0450.
(E)ꢀ4ꢀ(benzofuranꢀ2ꢀyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazabutaꢀ1,3ꢀdiene (6)
Yellow solid (120 mg, 86%). mp 205ꢀ207 °C; IR (KBr, cmꢀ1): 3410, 1599, 1525, 1158; 1H NMR
(400 MHz, DMSOꢀd6)
δ
7.99 (s, 1H), 7.60 (d, J = 7.2 Hz, 1H), 7.53 (d, J = 7.7 Hz, 1H), 7.16ꢀ
13
7.32 (m, 2H), 7.02 (s, 1H), 6.02 (br s, 2H), 5.81 (br s, 2H); C NMR (100 MHz, DMSOꢀd6)
δ
161.7, 154.6, 154.7, 133.2, 129.0, 124.9, 123.5, 121.4, 111.3, 104.8; HRMS (ESIꢀTOF) m/z:
[M]+ Calcd for C10H11N4O 203.0932; Found 203.0929.
(E)ꢀ4ꢀ(1Hꢀpyrrolꢀ2ꢀyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazabutaꢀ1,3ꢀdiene (7)
Yellow solid (120 mg, 77 %). mp 195ꢀ197 °C; IR (KBr, cmꢀ1): 3402, 1622, 1440, 1278; 1H NMR
(400 MHz, DMSOꢀd6)
δ
12.32 (br s, 1H), 7.02 (s, 1H), 6.85 (s, 1H), 6.24 (s, 1H), 6.08 (s, 1H),
13
5.89 (br s, 2H), 5.57 (br s, 2H); C NMR (100 MHz, DMSOꢀd6)
δ 160.2, 133.9, 130.2, 118.9,
111.1, 108.4; HRMS (ESIꢀTOF) m/z: [M]+ Calcd for C6H9N5 151.0858; Found 151.0880.
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(E)ꢀ4ꢀ(4ꢀ(1Hꢀimidazolꢀ1ꢀyl)phenyl)ꢀ1,1ꢀdiamineꢀ2,3ꢀdiazaꢀ1,3ꢀpentadiene (8)
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6
Yellow solid (330 mg, 63%). mp 208ꢀ210 °C; IR (KBr, cmꢀ1): 3439, 1651, 1520, 1166; 1H NMR
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8
9
(400 MHz, DMSOꢀd6)
δ
8.28 (s, 1H), 7.91 (d, J = 8.7 Hz, 2H), 7.77 (t, J = 4, 1H), 7.58 (d, J =
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8.7 Hz, 2H), 7.11 (s, 1H), 5.94 (br s, 2H), 5.54 (br s, 2H), 2.24 (s, 3H); C NMR (100 MHz,
DMSOꢀd6)
δ 176.8, 159.6, 146.9, 139.2, 135.8, 130.1, 127.1, 120.4, 118.0, 13.5; HRMS (ESIꢀ
TOF) m/z: [M+H]+ Calcd for C12H15N6 243.1358; Found 243.1347.
(E)ꢀ4ꢀ(thiazolꢀ2ꢀyl)1,1ꢀdiaminoꢀ2,3ꢀdiazabutaꢀ1,3ꢀdiene (9)
Yellow solid (138 mg, 76%). mp 190ꢀ193 °C; IR (KBr, cmꢀ1): 3435, 1618, 1532, 1145; 1H NMR
(400 MHz, DMSOꢀd6)
δ 8.07 (s., 1H), 7.84 (s, 1H), 7.45 (s 1H), 6.00 (br s, 2H), 5.93 (br s, 2H);
13C NMR (100 MHz, DMSOꢀd6). 13C NMR (100 MHz, DMSOꢀd6)
δ
167.9, 161.9, 143.5, 137.3,
119.1; HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C5H8N5S 170.0500; Found 170.0500.
(E)ꢀ4ꢀ(benzo[d]thiazolꢀ2ꢀyl) 1,1ꢀdiaminoꢀ2,3ꢀdiazabutaꢀ1,3ꢀdiene (10)
Yellow solid (120 mg, 86%). mp 215ꢀ218 °C; IR (KBr, cmꢀ1): 3413, 1618, 1490, 1141; 1H NMR
(400 MHz, DMSOꢀd6)
8 Hz, 1H), 7.37 (t, J = 8 Hz, 1H) 6.20 (br s, 4H). 13C NMR (100 MHz, DMSOꢀd6)
168.6, 162.5, 153.9, 136.7, 133.9, 126.6, 125.6, 122.6, 122.3; HRMS (ESIꢀTOF) m/z: [M+H]+
δ 8.15 (s, 1H), 7.97 (d, J = 8 Hz, 2H), 7.88 (d, J = 8 Hz, 2H), 7.45 (t, J =
δ
Calcd for C9H10N5S 220.0656; Found 220.0647.
General Procedure for the Synthesis of Conjugated Azines (11ꢀ20):
Conjugated azines 11ꢀ20 were synthesized from substituted chalcones and aminoguanidine
hydrochloride by adopting conventional synthesis. The substituted chalcones were in turn
prepared by treating substituted acetophenone with substituted aldehydes using 10% NaOH in
ethanol at room temperature for 2ꢀ72 h. These chalcones (1 mmole) and aminoguanidine HCl (1
mmole) in ethanol (2 mL) were refluxed in presence of conc. HCl (0.2 mL). The completion of
reaction was monitored by TLC (1ꢀ4 h). The reaction mixture was subjected to rota evaporation
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and recrystallized using ethyl acetate/acetone/hexane to obtain 11ꢀ20·HCl in the yield of 63ꢀ95
%. The recrystallized salts were neutralized by treating with 1N NaOH in methanol at 50 °C for
4 h. The reaction mixture was concentrated by evaporation under reduced pressure, and the
aqueous residue was extracted with EtOAc. The combined organic extracts were dried over
Na2SO4, filtered and evaporated to obtain neutral conjugated azines 11ꢀ20 in the yield of 73ꢀ95
%.
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(3E,5E)ꢀ6ꢀ(4ꢀchlorophenyl)ꢀ4ꢀ(phenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀhexatriene (11)
Yellow solid (65 mg, 73 %). mp 170ꢀ173 °C; IR (KBr, cmꢀ1): 3468, 1617, 1530, 1255; 1H NMR
(400 MHz, DMSOꢀd6)
δ 7.88 (d, J = 16 Hz, 1H), 7.56 (d, J = 8 Hz, 2H), 7.51 (d, J = 8 Hz, 2H),
7.33ꢀ7.42 (m, 5H), 6.75 (d, J = 16 Hz, 1H), 5.96 (br s, 2H), 5.80 (br s, 2H); 13C NMR (100 MHz,
DMSOꢀd6) 162.8, 160.7, 149.4, 139.5, 136.7, 132.7, 131.6, 129.2, 128.9, 128.7,128.4, 127.9,
122.1; ΗRΜS (ESIꢀTOF) m/z: [M+H]+ Calcd for C16H16ClN4 299.1063; Found 299.1058.
(E)ꢀ2ꢀ((E)ꢀ1,3ꢀbis(4ꢀmethoxyphenyl)allylidene)hydrazinecarboximidamide hydrochloride
(12. HCl)
Cream solid (280 mg, 70 %). mp 180ꢀ183 °C; IR (KBr, cmꢀ1): 3445, 1687, 1593, 1235; 1H NMR
(400 MHz, CDCl3) δ 11.74 (br s, 2H), 7.97 (br s, 2H), 7.68 (d, J = 8 Hz, 2H), 7.54 (d, J = 16 Hz,
1H), 7.47 (d, J = 12 Hz, 2H), 6.94 (d, J = 8 Hz, 2H), 6.88 (d, J = 8 Hz, 2H), 6.87 (d, J = 16 Hz,
13C
CDCl3)
1H),
3.86
(s,
3H),
3.79
(s,
3H);
NMR
(100
MHz,
δ
160.9, 156.4, 154.6, 142.6, 130.7,
130.0, 128.9, 128.2, 115.8, 114.2, 113.7, 55.4, 55.3; HRMS (ESIꢀTOF) m/z: [M]+ Calcd for
C18H21N4O2 325.1659; Found 325.1653.
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(3E,5E)ꢀ6ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀ(4ꢀmethoxyphenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀhexatriene
(12); mixture of E and Z isomers (2:1)
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9
Yellow solid (88 mg, 89 %). mp 153ꢀ155 °C; IR (KBr, cmꢀ1): 3448, 1607, 1503, 1245; 1H NMR
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(400 MHz, DMSOꢀd6)
δ 7.80 (d, J = 16 Hz, 1H), 7.53 (d, J = 8 Hz, 2H), 7.48 (d, J = 12 Hz, 2H),
7.39 (d, J = 8 Hz, 1H), 7.19 (d, J = 8 Hz, 1H), 7.06 (d, J = 16 Hz, 1H), 7.01ꢀ6.98 (m, 5H), 6.93
(d, J = 8 Hz, 1H), 6.71 (d, J = 16 Hz, 1H), 6.21 (d, J = 16 Hz, 0.5H), 5.98 (br s, 1H), 5.89 (br s,
2H), 5.69 (br s, 2H), 5.50 (br s, 1H), 3.85 (s, 5 H), 3.83 (s, 3H), 3.80 (s, 1Η); 13C NMR (400
MHz, DMSOꢀd6) 160.1, 159.7, 159.3, 159.1, 158.6, 150.4, 133.1, 132.0, 130.8, 130.5, 130.2,
128.5, 127.9, 119.7, 114.6, 114.7, 113.8, 113.7, 55.6, 55.5, 55.4; HRMS (ESIꢀTOF) m/z: [M+H]+
Calcd for C18H21N4O2 325.1664; Found 325.1659.
(E)ꢀ2ꢀ((E)ꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ3ꢀ(3,4,5ꢀtrimethoxyphenyl)allylidene)hydrazine
carboximidamide hydrochloride (13.HCl)
Cream solid (400 mg, 95 %). mp 172ꢀ175 °C; IR (KBr, cmꢀ1): 3460, 1570, 1413, 1254; 1H NMR
(400 MHz, DMSOꢀd6)
δ 11.91 (br s, 1H), 7.75 (br s, 3H), 7.66 (d, J = 12 Hz, 1H), 7.64 (d, J = 16
Hz, 2H), 7.16 (s, 2H), 7.04 (d, J = 8.8 Hz, 2H), 6.83 (d, J = 16 Hz, 1H), 3.84 (s, 6H), 3.82 (s,
13
3H), 3.69 (s, 3H); C NMR (100 MHz DMSOꢀd6)
δ 160.3, 155.8, 152.9, 152.6, 141.1, 138.7,
130.8, 130.5, 128.3, 117.5, 113.7, 105.6, 60.0, 56.2, 55.2; HRMS (ESIꢀTOF) m/z: [M]+ Calcd
for C20H25N4O4 385.1870; Found 385.1868.
(3E,5E)ꢀ4ꢀ(4ꢀmethoxyphenyl)ꢀ6ꢀ(3,4,5ꢀtrimethoxyphenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀ
hexatriene (13)
Yellow solid (80 mg, 89 %). mp 148ꢀ151 °C; IR (KBr, cmꢀ1): 3434, 1634, 1463, 1125; 1H NMR
(400 MHz, DMSOꢀd6)
δ 7.81 (d, J = 16 Hz, 1H), 7.54 (d, J = 9.56 Hz, 2H), 7.01 (d, J = 8 Hz,
2H), 6.86 (s, 2H), 6.73 (d, J = 16.7 Hz, 1H), 5.93 (br s, 2H), 5.71 (br s, 2H), 3.86 (s, 6H), 3.85 (s,
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3H), 3.72 (s, 3H); 13C NMR (400 MHz, DMSOꢀd6)
δ 160.2, 159.3, 153.5, 149.8, 138.1,
5
6
7
8
133.5, 132.2, 130.2, 121.3, 113.8, 104.5, 60.6, 60.2, 56.4, 55.6 ; HRMS (ESIꢀTOF) m/z: [M+H]+
Calcd for C20H25N4O4 385.1875; Found 385.1861.
9
10
11
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17
18
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(E)ꢀ2ꢀ((E)ꢀ3ꢀ(2,5ꢀdimethoxyphenyl)ꢀ1ꢀ(4ꢀmethoxyphenyl)allylidene)hydrazinecarboximid
amide hydrochloride (14.HCl)
Yellow solid (234 mg, 66 %). mp 168ꢀ170 °C; IR (KBr, cmꢀ1): 3469, 1682, 1513, 1249; 1H NMR
(400 MHz, DMSOꢀd6)
δ 11.97 (s, 1H), 7.78 (br s, 3H), 7.69 (d, 1H), 7.64 (d, J = 16 Hz,
1H), 7.60 (d, J = 8 Hz, 2H), 7.18 (d, J = 16 Hz, 1H), 7.03 (d, J = 8 Hz, 2H), 6.96−6.97 (m,
2H), 3.84 (s, 3H), 3.83 (s, 3H), 3.71 (s, 3H); 13C NMR (100 MHz, DMSOꢀd6)
δ
160.8, 156.4,
153.9, 152.0,135.3, 131.1, 128.9, 124.7, 118.7, 118.1, 114.1, 113.5, 56.6, 56.4, 55.7; LCꢀMS
(ESI) m/z: [M]+ Calcd for C19H23N4O3 355.1770; Found 355.14.
(3E,5E)ꢀ6ꢀ(2,5ꢀdimethoxyphenyl)ꢀ4ꢀ(4ꢀmethoxyphenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀ
hexatriene (14)
Yellow solid (80 mg, 88 %). mp 155ꢀ158 °C; IR (KBr, cmꢀ1): 3436, 1626, 1509, 1246; 1H NMR
(400 MHz, DMSOꢀd6)
δ 7.82 (d, J = 16 Hz, 1H), 7.48 (d, J = 8 Hz, 2H), 7.13 (d, J = 2.8 Hz,
1H), 6.96ꢀ6.84 (m, 5H), 5.89 (br s, 2H), 5.71 (br s, 2H), 3.79 (s, 3H), 3.75 (s, 3H), 3.69 (s, 3H);
13C NMR (400 MHz, DMSOꢀd6)
δ
160.2, 159.4, 153.8, 151.4, 150.9, 131.8, 130.3, 127.9, 126.7,
121.7, 115.3, 13.9, 113.2, 111.3, 60.5, 56.5, 55.9, 55.6; HRMS (ESIꢀTOF) m/z: [M]+ Calcd for
C19H23N4O3 355.1770; Found 355.1757.
(E)ꢀ2ꢀ((E)ꢀ3ꢀ(4ꢀ(benzyloxy)phenyl)ꢀ1ꢀ(4ꢀmethoxyphenyl)allylidene)hydrazine
carboximidamide hydrochloride (15.HCl)
White solid (280 mg, 71 %). mp 180ꢀ182 °C; IR (KBr, cmꢀ1): 3246, 3158, 1604, 1509, 1244; H
1
NMR (400 MHz, DMSOꢀd6)
δ
11.61 (s, 1H), 7.74 (d, J = 8.8 Hz, 5H), 7.61 (d, J = 9.0 Hz, 2H),
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7.45 (d, J = 8 Hz, 2H), 7.41 (d, J = 8 Hz, 3H), 7.40 (d, J = 16 Hz, 1H), 7.05 (d, J = 8.8 Hz, 2H),
7.02 (d, J = 9.0 Hz, 2H), 6.85 (d, J = 16 Hz, 1H), 5.17 (s, 2H), 3.81 (s, 3H); 13C NMR (100 MHz,
7
8
9
DMSOꢀd6)
δ 160.9, 160.0, 156.3, 153.5, 141.2, 137.2, 131.0, 128.9, 128.7, 128.3, 128.1, 116.5,
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115.6, 114.2, 69.8, 55.8; LCꢀMS (ESI) m/z: [M]+ Calcd for C24H25N4O2 401.1977; Found
401.24.
(3E,5E)ꢀ6ꢀ(4ꢀ(benzyloxy)phenyl)ꢀ4ꢀ(4ꢀmethoxyphenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀ
hexatriene (15)
Yellow solid (82 mg, 90 %). mp 160ꢀ162 °C ; IR (KBr, cmꢀ1): 3435, 1633, 1508, 1247; 1H NMR
(400 MHz, DMSOꢀd6) δ 7.74 (d, J = 16 Hz, 1H), 7.48ꢀ7.31 (m, 9H), 7.01 (d, J = 8 Hz, 2H), 6.94
(d, J = 8 Hz, 2H), 6.65 (d, J = 16 Hz, 1H), 5.84 (br s, 2H), 5.65 (br s, 2H), 5.12 (s, 2H), 3.78 (s,
3H); 13C NMR (400 MHz, DMSOꢀd6)
δ
160.1, 159.3, 158.8, 137.4, 132.9, 130.5, 130.2, 128.9,
128.5, 128.3, 119.9, 115.6, 113.8, 69.7, 55.6; HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for
C24H25N4O2 401.1977; Found 401.1960.
(E)ꢀ2ꢀ((E)ꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ3ꢀ(3ꢀnitrophenyl)allylidene)hydrazinecarboximidamide
hydrochloride (16.HCl)
1
Yellow solid (250 mg, 86 %). mp 163ꢀ165 °C ; IR (KBr, cmꢀ1): 3507, 1610, 1509, 1251; H
NMR (400 MHz, DMSOꢀd6) δ 11.58 (br s, 1H), 8.58 (s, 1H), 8.30 (d, J = 7.84 Hz, 1H), 8.23 (dd,
J = 4, 8.24 Hz, 1H), 7.74 (br s, 3H), 7.73 (d, J = 8 Hz, 1H), 7.69 (d. J = 8.88 Hz, 2H), 7.66 (d, J
= 16 Hz, 1H), 7.08 (d, J = 16.36 Hz, 1H), 7.02 (d, J = 9.76 Hz, 2H), 3.82 (s, 3Η); 13C NMR (100
MHz,
DMSOꢀd6)
δ 161.1, 156.2, 152.3, 148.7, 138.7, 137.7, 134.7, 130.9, 130.7,
128.4, 124.2, 122.9,
121.7, 114.3, 55.8; LCꢀMS (ESI) m/z: [M]+ Calcd for C17H18N5O3 340.1409; Found 340.16.
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(3E,5E)ꢀ4ꢀ(4ꢀmethoxyphenyl)ꢀ6ꢀ(3ꢀnitrophenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀhexatriene (16)
5
6
Brown solid (77 mg, 86 %). mp 142ꢀ143 °C; IR (KBr, cmꢀ1): 3434, 1626, 1414, 1254; 1H NMR
7
8
9
(400 MHz, DMSOꢀd6)
δ 8.35 (s, 1H), 8.12 (dd, J = 8 Hz, 2 Hz, 1H), 8.01 (d, J = 8 Hz, 1H), 7.97
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(d, J = 16 Hz, 1H), 7.65 (t, J = 8 Hz, 1H), 7.53 (d, J = 16 Hz, 2H), 6.96 (d, J = 8 Hz, 2H), 6.92
(d, J = 16 Hz, 1H), 6.07 (br s, 4H), 3.79 (s, 3H); 13C NMR (100 MHz, DMSOꢀd6)
δ
159.9, 159.6, 149.1, 148.7, 139.5, 133.7, 132.0, 131.2, 130.6, 130.3, 123.8, 122.9, 121.3, 113.9,
55.3; HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C17H18N5O3 340.1409; Found 340.1396.
(E)ꢀ2ꢀ((E)ꢀ3ꢀ(4ꢀfluorophenyl)ꢀ1ꢀ(4ꢀmethoxyphenyl)allylidene)hydrazinecarboximidamide
hydrochloride (17.HCl)
Cream solid (278 mg, 89 %). mp 133ꢀ135 °C; IR (KBr, cmꢀ1): 3449, 1624, 1508, 1256; 1H NMR
(400 MHz, DMSOꢀd6)
δ 11.78 (s, 1Η), 7.86ꢀ7.89 (m, 2H), 7.82 (br s, 3H), 7.63 (d, J = 8.8 Hz,
2H), 7.56 (d, J = 16.4 Hz, 1Η), 7.24 (t, J = 8.8 Hz, 2H), 7.02 (d, J = 8.8 Hz, 2H), 6.89 (d, J =
16.4 Hz, 1H), 3.82 (s, 3Η); 13C NMR (100 MHz, DMSOꢀd6)
δ
159.4, 159.2, 158.0, 154.9 (d,
1JCꢀF
=
274.5
Hz), 141.7, 137.9, 131.0, 130.2,
127.1,119.5, 118.5, 117.3, 115.6, 114.9, 55.7; LCꢀMS
(ESI) m/z: [M]+ Calcd for C17H18FN4O 313.1464; Found 313.09.
(3E,5E)ꢀ6ꢀ(4ꢀfluorophenyl)ꢀ4ꢀ(4ꢀmethoxyphenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀhexatriene
(17)
1
Brown solid ( 89 mg, 89 %). mp 118ꢀ120 °C; IR (KBr, cmꢀ1): 3466, 1604, 1508, 1249; H NMR
(400 MHz, DMSOꢀd6)
δ
7.71 (d, J = 16 Hz, 1H), 7.47ꢀ7.39 (m, 4H), 7.10 (t, J = 8 Hz, 2H), 6.85
13
(d, J = 8, 2H), 6.63 (d, J = 16 Hz, 1H), 5.81 (s, 2H), 5.64 (s, 2H), 3.79 (s, 3H); C NMR (100
MHz, DMSOꢀd6)
δ
162.3 (d, 1JCꢀF = 244 Hz), 160.3, 159.3, 149.4, 134.2 (JCꢀCꢀCꢀCꢀF = 3
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Hz), 132.0, 131.8, 130.1, 129.0, 128.9, 121.9, 116.2, 115.9, 113.8, 55.5; HRMS (ESIꢀTOF)
m/z: [M+H]+ Calcd for C17H18FN4O, 313.1464; Found 313.1450.
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(E)ꢀ2ꢀ((E)ꢀ3ꢀ(1Hꢀimidazolꢀ2ꢀyl)ꢀ1ꢀ(4ꢀmethoxyphenyl)allylidene)hydrazinecarboximidamide
hydrochloride (18.HCl)
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Cream solid (290 mg, 74 %). mp 198ꢀ201 °C; IR (KBr, cmꢀ1): 3504, 1610, 1509, 1251; 1H NMR
(400 MHz, DMSOꢀd6)
δ 11.56 (br s, 1H), 7.91 (br s, 3H), 7.75ꢀ7.82 (m, 5Η), 7.02 (d, J = 8 Hz,
2H), 6.89 (d, J = 16 Hz, 1H), 3.88 (s, 3Η); 13C NMR (100 MHz, DMSOꢀd6)
δ
161.5, 156.2,
150.3, 141.7, 130.5, 128.2, 127.3, 121.6, 121.3, 114.4, 55.8;LCꢀMS (ESI) m/z: [M]+ Calcd for
C14H17N6O 285.1463; Found 285.05.
(3E,5E)ꢀ6ꢀ(1Hꢀimidazolꢀ2ꢀyl)ꢀ4ꢀ(4ꢀmethoxyphenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀhexatriene
(18); mixture of E and Z isomers (2:1)
Brown solid (88 mg, 95 %). mp 180ꢀ183 °C; IR (KBr, cmꢀ1): 3362, 1608, 1509, 1246; 1H NMR
(400 MHz, DMSOꢀd6)
δ 12.14 (s, 2H), 7.90 (d, J = 16 Hz, 1H), 7.46 (d, J = 8Hz, 2H), 7.23 (d, J
= 16Hz, 1H), 7.21ꢀ6.94 (m, 6H), 6.56 (d, J = 16 Hz, 1H), 6.03 (d, J = 16 Hz, 1H), 5.92 (br s,
13C
DMSOꢀ
2H),
5.64
(br
s,
3H),
3.77 (s, 5Η);
NMR
(100
MHz,
d6); 160.3, 159.3, 158.6, 158.1,151.4,
149.5, 147.7, 145.9, 131.8,130.8, 130.1,122.4, 122.0, 113.9, 113.8, 55.6, 55.5. HRMS (ESIꢀTOF)
m/z: [M+H]+ Calcd for C14H16N6O 285.1463; Found 285.1477.
(E)ꢀ2ꢀ((E)ꢀ3ꢀ(2,4,6ꢀtrimethoxyphenyl)ꢀ1ꢀ(phenyl)allylidene)hydrazinecarboximidamide
hydrochloride (19.HCl)
Orange solid (136 mg, 66 %). mp 175ꢀ178 °C; IR (KBr, cmꢀ1): 3401, 1616, 1446, 1249; 1H NMR
(400 MHz, DMSOꢀd6)
δ 11.17 (br s, 1H), 7.77 (br s, 3H), 7.60 (d, J = 8 Hz, 2Η), 7.55 (d, J = 16
Hz, 1Η), 7.45ꢀ7.48 (m, 3H), 7.07 (d, J = 16 Hz, 1H), 6.28 (s, 2H), 3.83 (s, 3H), 3.82 (s, 6Η); 13C
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NMR (100 MHz, DMSOꢀd6) 162.8, 160.6, 156.5, 156.3, 137.1, 133.7, 129.8, 128.7, 117.8,
105.7, 91.3, 56.5, 55.9; LCꢀMS (ESI) m/z: [M]+ Calcd for C19H23N4O3 355.1770; Found 355.21.
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(3E,5E)ꢀ6ꢀ(2,4,6ꢀtrimethoxyphenyl)ꢀ4ꢀ(phenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀhexatriene (19)
5
6
1
Yellow solid (80 mg, 88 %). mp 153ꢀ155 °C; IR (KBr, cmꢀ1): 3421, 1626, 1436, 1219; H NMR
7
8
9
(400 MHz, DMSOꢀd6)
δ
8.00 (d, J = 16 Hz, 1Η), 7.60 (d, J = 8 Hz, 2H), 7.37ꢀ7.45 (m, 3H), 6.87
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(d, J = 16 Hz, 1H), 6.30 (s, 2H), 5.92 (br s, 2H), 5.70 (br s, 2H), 3.86 (s, 3H), 3.79 (s, 6Η); C
NMR (100 MHz, DMSOꢀd6)
δ 160.9, 159.8, 159.5, 152.8, 139.9, 129.2, 128.2, 127.8, 125.2,
123.1, 107.4, 91.3, 60.2, 56.2, 55.7; HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C19H23N4O3
355.1770; Found 355.1754.
(E)ꢀ2ꢀ((E)ꢀ1ꢀ(4ꢀchlorophenyl)ꢀ3ꢀ(2,4,6ꢀtrimethoxyphenyl)allylidene)hydrazine
carboximidamide hydrochloride (20.HCl)
Cream solid (136 mg, 63 %). mp 180ꢀ183 °C ; IR (KBr, cmꢀ1): 3459, 1545, 1487, 1135; 1H NMR
(400 MHz, DMSOꢀd6) 11.04 (s, 1H), 7.77 (br s, 3H), 7.67 (d, J = 8 Hz, 3Η), 7.53 (d, J = 8 Hz,
13
2Η), 7.48 (d, J = 16 Hz, 1H), 7.05 (d, J = 16 Hz, 1H), 6.29 (s, 2H), 3.83 (s, 9Η); C NMR
(100MHz, DMSOꢀd6) δ 162.4, 160.1, 155.8, 154.4, 135.4, 134.2, 133.0, 131.0, 128.2, 116.9
105.0, 90.8, 56.0, 55.4; LCꢀMS (ESI) m/z: [M]+ Calcd for C19H22ClN4O3 389.1380; Found
389.87.
(3E,5E)ꢀ6ꢀ(2,4,6ꢀtrimethoxyphenyl)ꢀ4ꢀ(4ꢀchlorophenyl)ꢀ1,1ꢀdiaminoꢀ2,3ꢀdiazaꢀ1,3,5ꢀ
hexatriene (20)
Yellow solid ( 69 mg, 75 %). mp 168ꢀ170 °C ; IR (KBr, cmꢀ1): 3450, 1575, 1457, 1125; 1H NMR
(400 MHz, DMSOꢀd6) 7.96 (d, J = 16 Hz, 1H), 7.62 (d, J = 8 Hz, 2H), 7.46 (d, J = 8 Hz, 2H),
6.85 (d, J = 16 Hz, 1H), 6.30 (s, 2H), 5.90 (br s, 2H), 5.66 (br s, 2H), 3.86 (s, 3H), 3.83 (s, 6Η);
13C NMR (100 MHz, DMSOꢀd6)
δ 161.0, 160.1, 159.6, 138.9, 132.2, 130.8, 128.3, 125.0, 122.9,
107.3, 91.3, 56.2, 55.7; HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C19H22ClN4O3 389.1380;
Found 389.1367.
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Acknowledgements
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S.S.C. acknowledges the Physical Chemistry division and D. K. acknowledges the
INSPIRE division of Department of Science and Technology (DST), New Delhi, India for
financial support. The Xꢀray facility at IISER Mohali is gratefully acknowledged. Authors
are thankful to the reviewers of this article for their valuable suggestions.
Supporting Information
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The 1H NMR and 13C NMR for the synthesized azines (1ꢀ20) are provided. VTꢀ1H NMR spectra
of compound 4 is provided (Figure SIꢀ2). Deuterated NMR of compounds 4 and 14 is provided.
Complete crystallographic data of 4, 14.CH3OH and 14.HCl for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre, CCDC No. 1473843, 1473844 and
1473846 respectively, and a combined cif file is provided in the supporting information.
Cartesian coordinates and absolute energies of the optimized geometry of all synthesized azines
and reported biologically active molecules are provided in SI. This material is available free of
charge via the Internet at http://pubs.acs.org
AUTHORS INFORMATION
Corresponding Authors
*Email: pvbharatam@niper.ac.in, akchakraborti@niper.ac.in
Telephone:+91ꢀ172ꢀ2214682
, sanjaymandal@iisermohali.ac.in
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