Highly diastereoselective synthesis of rigid 3-enamino-1, 5-benzodiazepines

Article abstract of DOI:10.24820/ark.5550190.p010.426

A variety of new (3-Z)-3-((alkyl/aryl)aminomethylene)-4-(2-hydroxyphenyl)-1, 3-dihydro-2H-1, 5-benzodiazepin-2-ones were synthesized via addition of primary amines on the benzopyrano[4, 3-c]-1H-1, 5-benzodizepin-2-one. High yields with excellent diastereoselectivity were obtained. The structure of cis-?-enamino-1, 5-benzodiazepine derivatives was characterized by 1D and 2D NMR and confirmed by an X-Ray diffraction analysis. All prepared compounds were evaluated for their in vitro antibacterial activities and promising results were given.

Full text of DOI:10.24820/ark.5550190.p010.426

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Organic Chemistry
Arkivoc 2018, part v, 0‐0
Highly diastereoselective synthesis of rigid 3‐enamino‐1,5‐benzodiazepines
Sami Chnitia, Asma Nsira a, Sadok Khouaja b, Ali Mechria a, Rafik Gharbi a, Moncef Msaddek a,
and Marc Lecouvey c *
a Laboratory of Heterocyclic Chemistry, Natural Products and Reactivity/CHPNR, Department of Chemistry,
Faculty of Science of Monastir, University of Monastir, Avenue of Environment, 5019 Monastir, Tunisia
bDepartment of Clinical biology, Laboratory of Analysis, Treatment and valorization of Pollutants of the
Environment and Products, Faculty of Pharmacy of Monastir, University of Monastir, 5019 Monastir, Tunisia
c Université Paris 13, Sorbonne Paris Cité, Laboratoire CSPBAT, CNRS UMR 7244, F‐93017, Bobigny, France
E‐mail: marc.lecouvey@univ‐paris13.fr
Received 12‐08‐2017
Accepted 03‐01‐2018
Published on line 07‐03‐2018
Abstract
A variety of new (3‐Z)‐3‐((alkyl/aryl)aminomethylene)‐4‐(2‐hydroxyphenyl)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐
2‐ones were synthesized via addition of primary amines on the benzopyrano[4,3‐c]‐1H‐1,5‐benzodizepin‐2‐
one. High yields with excellent diastereoselectivity were obtained. The structure of cis‐β‐enamino‐1,5‐
benzodiazepine derivatives was characterized by 1D and 2D NMR and confirmed by an X‐Ray diffraction
analysis. All prepared compounds were evaluated for their in vitro antibacterial activities and promising results
were given.
Methylidenation
(DMFDMA)
H
H
O
Aza-Michael
Addition
N
O
N
N
O
NH
O
NH
O
N
O
NH
O
in situ
R-NH2
O
H
Intramolecular
Cyclisation
-[NH(CH3)2]
N
Active
R
Rigid
enamino-1,5-benzodiazepines
methylene
Group
Keywords: 1, 5‐Benzodiazepin‐2‐one, cis‐β‐enaminone, intramolecular hydrogen bond
DOI: https://doi.org/10.24820/ark.5550190.p010.426
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Introduction
Benzodiazepines are an important class of seven membered N‐heterocyclic compounds reported for
psychotherapeutic activities.1 Among this family, 1,5‐benzodiazepine scaffolds are extremely versatile. They
have been repeatedly reported to possess different clinical uses as anticonvulsant, anxiolytic and sedative
agents.2
More recently, different studies have shown new important biological properties of these compounds
such as anti‐HIV, anti‐neuroinflammatory,3 antioxidant,4 antimicrobial,5 and antitumor,6 which have led to
considerable interest in their synthesis and biological study. These biological properties are correlated with
the benzodiazepine structural changes in particular by introduction of a stereogenic unit at C‐3 of the
benzodiazepine core.7 This modification leads to conformational restraints necessary to increase the selectivity
for a particular receptor. 8
In order to increase this selectivity, we are interested in the introduction of β‐enaminone moiety at the C3
position. β‐Enaminones are chemical compounds which can exist in different fixed conformations owing to
restricted rotations around the C=C double bonds and the C–C=O and C–N single bonds.9 They have synthetic
utility as building blocks in preparation of many pharmaceuticals including anticonvulsant, antimalarial and
antibacterial agents.10,11
The introduction of enaminone moiety at the C‐3 position may reduce the flexibility of the diazepine ring,
and commonly enhance its selective recognition by receptors inducing novel pharmacological activities.11,12
Herein, we propose the synthesis of novel biologically effective 1,5‐benzodiazepine scaffolds from 4‐(2‐
hydroxyphenyl)‐1H‐1,5‐benzodiazepin‐2‐one 1.13 To the best of our knowledge, there is only one route to
access to enaminone‐1,5‐benzodiazepine derivatives via a transamination reaction between 3‐
dimethylaminomethylene‐1,5‐benzodiazepine, and a corresponding amine.12, 14
Here, we developed a new strategy from benzopyrano[4,3‐c]‐1,5‐benzodiazepin‐2‐one 2 as a suitable and
easily accessible starting material. In present work, the preparation of the desired derivatives and their
evaluation as antibacterial and antifungal agents were described.
Results and Discussion
In our strategy, the first key intermediate was benzopyrano[4,3‐c]‐1,5‐benzodiazepine‐2‐one 2 which was
prepared according to literature method (scheme 1).15 Based on the recent results of the literature, the
reactivity of 2 towards amines was tested.
Previously, it was shown that the N, N‐bisnucleophiles are able to react on the ethylenic carbon of pyrane
ring.16,17,18 We have thus studied these reaction conditions with a model amine, the n‐butylamine in THF
(Table 1). The color‐change of the reaction mixture from yellow to orange was observed by the naked‐eye and
the progress of the reaction which was monitored by TLC showed the formation of a new only compound.
After evaporation of the solvent and recrystallization in ethanol a new product was isolated albeit in low yield.
On the basis of its spectral data, the isolated product, was identified as the 3‐((butylamino)methylene)‐4‐(2‐
hydroxyphenyl)‐1H‐1,5‐benzodiazepin‐2‐one 3d (Table 1). In order to optimize the reaction conditions, we
carried out the above reaction in different solvents such as: acetone, DMF and DMSO. The desired compound
was isolated in good to excellent yields and we have found that DMSO was an efficient reaction medium in
terms of reaction time as well as yields (90%).
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Scheme 1. Synthetic route to new 3‐((alkyl/aryl)aminomethylene)‐1,5‐benzodiazepin‐2‐ones.
1
The H NMR spectrum analysis of a model compound 3d showed characteristic signal of deshielded
phenolic hydrogen singlet observed around 15 ppm. The presence of this proton confirmed a nucleophilic
attack of the amino group at the C‐2 of the benzopyrane moiety and the consequent ring‐opening. The upfield
chemical displacement indicates the presence of an intramolecular hydrogen bonding between the phenolic
hydrogen and the nitrogen of the imine function.19
A careful review of the literature revealed that NMR spectroscopic techniques have been widely applied
to enaminones.20 Accordingly, The configurational E‐ and Z‐ isomers can be easily distinguished by the 1H NMR
chemical shifts of the NHenaminone protons: the E‐form at high field (δ= 4.1‐6.5 ppm) and the hydrogen bonded
Z‐form at lower field (δ= 9.5‐12 ppm). The Z‐s‐E conformation of enaminone‐benzodiazepine 3d can be clearly
deduced from the set of both doublet (6.91 ppm, 1H) and the broadened multiplet (8.80 ppm, 1H) assigned to
H‐1' and H‐2' (NHenaminone) respectively, due to restricted rotation around the C‐N single bond (Table 1).
Additionally, single crystals suitable for an X‐Ray diffraction study were grown for 3d by crystallization in
CH2Cl2/n‐Hexane. The crystal structure of the enaminone‐1,5‐benzodiazepines 3d shown in Figure 5 allowed
to establish that the solid state structure contains only the Z‐isomer found in solution.
As it can be observed from the ORTEP view of derivative 3d, the benzodiazepine skeleton is not planar
with the folding of the seven membered ring which adopts a boat‐like conformation.21 It is important to note
also, that the molecular structure reveals two strong intramolecular hydrogen bonds. The first one, between
the phenolic hydrogen and the nitrogen N of the imine function [d (O1–H1∙∙∙N2) of 1.81 Å] and the second one
is along the heterodienic O=C–C=C–NH moiety, which adopts the form of six membered ring [d (N3–H3∙∙∙O2)
of 2.12 Å] conferring to the structure more rigidity. The dihedral angle of 169.76°, between the protons in the
=CH‐NH moiety, is in accordance with the one estimated by ¹H NMR in solution using the coupling constant
and the Karplus type equation.22
In the light of these findings, the proposed reaction mechanism is a simple Michael/retro‐Michael
sequence involving primary amines. The starting material 2 has the same reactivity as an α,β‐unsaturated
ketone as well as an α,β‐unsaturated imine system. This compound is able to undergo two different
nucleophilic attacks of amines on the most electrophilic position (carbon C6) (pathway I or pathway II, Scheme
2). In the initial step, 1,4‐conjugate addition (aza‐Michael addition) can lead to β‐aminoenol intermediate (i1)
or to β‐amino enamine intermediate (i2).
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Table 1. Study of the reaction conditions.
OH
N
NH
O
3d (E)
H
HN
N
NH
O
NH2
7
6
8
9
Solvent
Time
5a
N
9a
H
O
5
NH
O
1
2
1"
3
6"
3d (Z)
2
4
5"
2"
3"
O
H
H
1'
N
4"
2'
5'
3'
4'
6'
Entry
Solvent
Time (h)
Yield (%)
1
2
3
THF
Acetone
DMF
24
10
6
30
60
84
4
DMSO
4
90
As a second step, these two potential intermediates can be converted, respectively by enol‐ketone and
enamine‐imine tautomerisms, into an unstable intermediate (i3). A retro‐oxa‐Michael addition, with a
subsequent carbon‐oxygen bond cleavage of the benzopyrane moiety, gives the desired compound stabilized
by intramolecular hydrogen bonding.
To study the efficiency of this method various substituted amines were used. In all cases, the desired new
compounds 3a‐m were obtained in yields ranging from 50% to 90% (Table 2).
Aliphatic amines such as ethylamine, isopropylamine, n‐butylamine and isobutylamine reacted with 2 in
DMSO giving the desired products in good yields. However, the reaction was sluggish with the substrates: tert‐
butylamine 2,4,4‐trimethylpentan‐2‐amine and sec‐butylamine, this may be due to the steric hindrance of
methyl groups in the proximity of the amino group. In aromatic series, the reaction is less efficient and
reaction times are longer because of the weak nucleophilicity of the amine.
The structure of the prepared compounds 3a‐m was completely characterized by NMR. High Resolution
Mass Spectrometry (HRMS) data of all the formed derivatives were also in agreement with the proposed
structures.
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Figure 5. ORTEP representation of the molecular structure of 3d with atom labeling scheme and anisotropic
displacement ellipsoid depicted at 50% probability (293 °K).
N
H
N
Aza-Michael
Addition
enol/ketone
tautomerism
H
O
Pathway I
O
NH
R
(i1)
H
13N
13a
O
N
H
Retro-Oxa-Michael
N
N
H
N
H
N
7
H
Addition
6a
O
O
O
+
6
R-NH2
H
H
O
NH
R
N
R
O
2
(i3)
3a-m
H
N
H
N
Aza-Michael
Addition
enamine/imine
tautomerism
O
O
NH
R
Pathway II
(i2)
Scheme 2. Proposed mechanism of enaminone‐1,5‐benzodiazepines 3a‐m formation.
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1
The H NMR and 13C NMR data of 3a‐m confirmed the existence of the same conformer for each
1
compound. In fact, the H NMR spectrum showed only one doublet between 6.5 ppm and 7.5ppm
characteristic of Holefinic and one NHenaminone signal between 8.5 ppm and 10.5 ppm with a multiplicity
depending on the amine structure (Table 3).
For all enaminones 3a‐m, the chemical shift of the NHenaminone proton was found at lower field due to the
deshielded effect of the C=O∙∙∙HN type of intramolecular hydrogen bonding. These spectral data proved that
3
the reaction led exclusively to the Z‐form. Furthermore, the vicinal coupling constants J=CH‐NHenaminone (12.1‐
14.1Hz) for the =CH‐NHenaminone moiety of each derivative indicated a dihedral angle of 180° which was in
agreement with the s‐trans conformation. We concluded also that the reaction was conducted with complete
diastereoselectivity for both aromatic and aliphatic amines.
Table 2. Preparation of cis‐β‐enaminone‐1,5‐benzodiazepines 3a‐m in DMSO
Entry
R
Compound
Time (h)
3
Yields
(%)a
52
1
Me
3a
2
3
Et
iPr
3b
3c
2
2
78
85
4
5
n‐Bu
3d
3e
4
3
90
80
2,4,4‐
trimethylpentan‐2‐yl
tert‐Bu
6
7
3f
3g
3
3
77
85
iBu
8
9
sec‐Bu
n‐Hex
3h
3i
3
5
85
65
10
11
Cyhex
C6H5
3j
5
84
55
3k
12
12
4‐MeOC6H4
3l
10
12
60
50
13
4‐ClC6H4
3m
a Isolated Yield
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1
Table 3. H NMR data for 3a‐m
Compounds
Ha
H‐Nb
olefinic
enaminone
(ppm)
3J=CH‐NHenaminone (Hz)
(ppm)
3J=CH‐NHenaminone (Hz)
3a
3b
3c
3d
3e
3f
3g
3h
3i
6.88 (d)
6.93( d)
6.98 (d)
6.91 (d)
7.05 (d)
7.06(d)
6.89 (d)
6.96 (d)
6.93 (d)
6.99 (d)
7.34 (d)
7.20 (d)
6.90 (d)
13.8
13.8
14.1
13.8
14.1
14.4
13.8
13.8
13.8
13.8
13.2
12.0
12.1
8.56‐8.73 (m)
8.68‐8.78 (m)
8.69‐8.76 (m)
8.64‐8.76 (m)
9.27 (d)
/
/
/
/
14.1Hz
14.4Hz
/
9.05 (d)
8.38‐8.88(m)
8.7‐8.81(m)
8.71‐8.90(m)
8.82 (d)
10.17 (d)
10.24 (d)
/
/
3j
3k
3l
13.8
13.2
12.0
12.1
3m
10.20 (d)
All of the benzodiazepines derivatives 3a˗m were tested for antibacterial activities against both standard
Gram‐positive and Gram‐negative bacterial strains. Their minimum inhibitory concentrations (MICs g/ml) are
shown in Table 4. Streptomycin was used as reference compound. It has been observed that some of the
compounds exhibited interesting antibacterial activity against both Gram‐positive and Gram‐negative bacteria
(Table 4) showing moderate to excellent activities against the used microorganisms. Indeed, compounds 3a‐c,
3f‐i and 3m showed effective activity against M. luteus (Table 4, entries 1‐3; 6‐9 and 13, MIC= 0.125‐0.5
µg/mL) compared to that of Streptomycin (MIC= 2 µg/mL). Moreover, compounds 3f‐k and 3m showed
effective activity against E.feacalis (Table 4, entries 6‐11 and 13, MIC= 0.125‐0.5 µg/mL) compared to that of
antibacterial standard (MIC= 0.5 µg /mL). The obtained data revealed also, that compounds 3e‐f and 3j‐k
might be the major active compounds against E. coli and exhibited a similar activity (Table 4, entries 5‐6; 10‐11
, MIC = 0.25 µg/mL). Compound 3m was significantly the most potent derivative against all used bacteria
(Table 4, entry 13, MIC= 0.125‐2 µg/mL). This effect may be explained by the importance of the 4‐
chlorophenylamino system for the antibacterial activity of the enaminone‐benzodiazepinic analogs. Most of
the tested compounds displayed poor activity against P. aeruginosa known by its resistance against many
antibiotic agents. This was very clear from the higher amounts of these compounds (MIC = 4‐8 µg/mL) that
were required for the inhibition of this bacteria.
Table 4. Antibacterial activity of compounds 3a–m, expressed in MIC (µg /mL)
Entry and
Gram‐positive bacteria
Gram‐negative bacteria
M.L.1 B.C. 2 S.A.3 S.E. 4 E.F. 5
E.C. 6 P.A.7 S.T. 8 L.M9
Compound
1
2
3
4
3a
3b
3c
3d
0.25
0.25
0.5
2
1
1
1
1
0.5
1
0.5
1
0.5
8
2
2
1
8
8
8
8
2
4
2
8
4
0.25 0.25 0.5
0.25
0.25 0.5
4
1
1
4
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Table 4 (continued)
Entry and
Gram‐positive bacteria
Gram‐negative bacteria
M.L.1 B.C. 2 S.A.3 S.E. 4 E.F. 5
E.C. 6 P.A.7 S.T. 8 L.M9
Compound
5
6
7
8
9
10
11
12
13
3e
3f
3g
2
0.25
2
2
1
1
4
0.5
1
1
2
2
2
1
1
1
1
2
8
0.25
0.25
0.5
0.5
2
0.25
0.25
0.5
2
8
4
8
8
2
8
4
2
4
4
4
4
2
4
0.25
4
0.5
4
4
8
2
1
4
8
1
0.125
0.25
0.5 0.125
0.5
0.5
2
2
2
0.25
0.25
0.25
0.25
0.25
1
3h 0.125
3i
3j
3k
3l
3m
0.5
2
2
2
0.5
2
0.125 0.5
0.5 0.125
0.125
0.25
Streptomycin
2
0.5
2
0.5 0.5
0.5
2
0.5
2
1Micrococcus luteus; 2Bacillus cereus; 3Staphylococcus aureus; 4Staphylococcus epidermidis ; 5Enterococcus
faecalis ; 6Escherichia coli ;7Pseudomonas aeruginosa ;8Salmonella typhimurium ;9Listeria monocytogenes ;
MIC (µg/mL), minimum inhibitory concentration, i.e., the lowest concentration of the compound to inhibit the
growth of bacteria completely.
Conclusions
In summary, we have disclosed an efficient access to new (3Z)‐3‐((alkyl/aryl)aminomethylene)‐4‐(2‐
hydroxyphenyl)‐1,3‐dihydro‐2H‐1‐benzodiazepin‐2‐ones. Simple workup, easy isolation, good yields and high
diastereoselectivity for the desired products under mild conditions are the best features of the present
methodology. These novel cis‐β‐enaminone‐1,5‐benzodiazepines present a new class of benzodiazepine
derivatives which are promising systems to exhibit new pharmacological activities. Their evaluation as
antimicrobial agents showed that most of the compounds exhibited moderate to good action on bacterial
species.
Experimental section
General. Reagents were prepared in laboratory or were commercial products of analytical purity (Merck,
Fluka, and Aldrich) and used as received. The Mueller‐Hinton agar which was used in antibacterial
susceptibility testing, was purchased from Merck. Melting points were taken on a Buchi‐510 capillary
apparatus and are uncorrected. 1H, 13C and two‐dimensional NMR spectra were recorded with AC‐300 Bruker
spectrometer at room temperature (rt) in CDCl3 at 300 MHz and at 75 MHz, using residual non deuterated
solvent peaks as internal reference. Coupling constants are given in Hz. IR spectra were recorded on a Perkine
Elmer Spectrum two FT‐IR instrument with the Universal ATR Sampling Accessory. HRMS spectra were
acquired with an electrospray‐ time‐of‐flight (ESI‐TOF, LCT Premier XE, Waters) mass spectrometer in the
positive ion mode. All reactions were followed by TLC using aluminium sheets of Merck silica gel 60 F254, 0.2
mm. The starting materials 1 and 2 were prepared according to the literature. 13, 15
General procedure for the synthesis of the enaminone‐1,5‐benzodiazepinones 3(a‐m).
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To a stirred suspension of compound 2 (262 mg, 1 mmol) in DMSO (10 mL) was added the aliphatic amines
(1,5 eq). The solution was allowed to react for 2 to 12 hours and its progress was monitored by a TLC control
(cyclohexane‐ethyl acetate 80:20). After the completion of the reaction, the reaction mixture was extracted
with dichloromethane (15 mL). The organic layer was dried over MgSO4 and solvents were removed in
vacuum. Diethyl ether was added to the resulted yellow crude oil, the so‐formed yellow precipitate was
collected and recrystallized from ethanol to afford the corresponding pure 3a‐m in 50–90% yields.
(3Z)‐4‐(2‐hydroxyphenyl)‐3‐((methylamino)methylene)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one (3a)
Yellow solid; yield 52%, mp 180‐183 °C; 1H NMR (300 MHz, CDCl3) δH : 3.01 (d, 3H, CH3, J 5.1 Hz), 6.47 (s, 1H,
NHbzd), 6.77‐6.83 (m, 2Harom), 6.88 (d, 1H, Holefinic, J 13.8 Hz) 6.99‐7.46 (m, 6Harom), 8.56‐8.73 (m, 1H,
NHenaminone), 15.12 (bd‐s, 1H, OH). 13C NMR (75.47 MHz, CDCl3) δC : 29.7, 95.1, 117.7, 118.2, 120.7, 121.5,
124.6, 126.7, 127.6, 130.8, 132.7, 132.9, 137.0, 157.8, 163.2, 167.6, 178.3; IR (ATR) νmax/cm-1: 3280‐3170 (NH),
3027 (OH) 1640 (C=O), 1577 (C=N); HRMS (ESI‐TOF) for C17H15N3O2 [M + H]+: calcd, 294.1164 found 294.1155.
(3Z)‐3‐((ethylamino)methylene)‐4‐(2‐hydroxyphenyl)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one (3b) Yellow
solid, yield 78%; mp: 188‐191 °C; 1H NMR (300 MHz, CDCl3) δH : 1.22 (t, 3H, CH3, J 7.2 Hz), 3.25 (qt, 2H, CH2,3J1
3
7.2 Hz, J2 6.6 Hz), 6.49 (s, 1H, NHbzd), 6.79‐6.86 (m, 2Harom), 6.93 (d, 1H, Holefinic, J 13.8 Hz), 6.99‐7.44 (m,
6Harom), 8.67 (m, 1H, NHenaminone), 15.12 (bd‐s, 1H, OH). 13C NMR (75.47 MHz, CDCl3) δC : 16.2, 43.9, 95.2, 117.6,
118.2, 120.7, 121.6, 124.5, 126.8, 127.7, 130.8, 131.9, 133.5, 137.0, 157.5, 163.2, 168.0, 178.3; IR (ATR)
νmax/cm-1: 3287‐3174 (NH), 3047 (OH) 1644 (C=O), 1576 (C=N); HRMS (ESI‐TOF) for C18H18N3O2 [M + H]+: calcd
308.1321 found 307.1315.
(3Z)‐4‐(2‐hydroxyphenyl)‐3‐((isopropylamino)methylene)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one (3c)
Yellow solid, yield 85%, mp: 150‐153 °C; 1H NMR (300 MHz, CDCl3) δH : 1.24 (d, 6H, 2xCH3, J 6.6 Hz), 3.43 (m,
1H), 6.62 (s, 1H, NHbzd), 6.77‐6.82 (m, 2Harom), 6.95‐6.99 (d, 1H, Holefinic, J 14.1 Hz), 6.98‐7.00 (d, 1Harom, J 7.5Hz),
13
6.99‐7.43 (m, 5Harom), 8.75 (m, 1H, NHenaminone), 15.12, (bd‐s, 1H, OH). C NMR (75.47 MHz, CDCl3) δC : 23.5,
50.5, 94.7, 117.5, 118.3, 120.7, 121.5, 124.5, 126.7, 127.5, 130.7, 132.7, 133.1, 136.9, 155.0, 163.2, 168.1,
178.3; IR (ATR) νmax/cm-1: 3254‐3192 (NH), 3045 (OH) 1646 (C=O), 1561 (C=N); HRMS (ESI‐TOF) for C19H20N3O2
[M + H]+: calcd 322.1480 found 322.1461.
(3Z)‐3‐((butylamino)methylene)‐4‐(2‐hydroxyphenyl)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one (3d)
Yellow solid, yield 90%, mp: 193‐195 °C; 1H NMR (300 MHz, CDCl3) δH : 0.91 (t, 3H, CH3, J 7.5Hz), 1.34 (m, 2H,
3
3
CH2), 1.54 (m, 2H, CH2), 3.19 (qd, 2H, CH2, J1 8 Hz, J2 6 Hz ), 6.57 (s, 1H, NHbzd), 6.77‐6.85 (m, 2Harom), 6.91 (d,
1H, Holefinic, J 13.8Hz), 6.98‐7.44 (m, 6Harom), 8.8 (m, 1H, NHenaminone), 15.2 (bd‐s, 1H, OH). 13C NMR (75.47 MHz,
CDCl3) δC : 13.5, 19.6, 32.8, 49.1, 95.1, 117.5, 118.1, 120.7, 121.6, 124.5, 126.7, 127.6, 130.7, 132.7, 133.1,
137.1, 157.1, 163.2, 167.9, 178.4; IR (ATR) νmax/cm-1: 3283‐3179 (NH), 3056 (OH) 1641 (C=O), 1578 (C=N);
Crystal suitable for single‐crystal X‐ray diffraction analysis were grown from a mixture of CH2Cl2/n‐hexane
solution (3:1 v/v) upon standing at ambient temperature. Crystal data for 3d C20H21N3O2: Mr = 335.39,
monoclinic, C2/c', a = 26.0905(14), b = 9.0775(4), c = 15.1426(7) Å, βᵒ = 97.260(3), V = 3557.6(3) ų, Z = 8, δcalcd
= 1.249 g/cm3; F(000) 1416; 3979 reflections collected, 1937 independent reflections. Final agreement factors:
R1 = 0.1456 (all observed) and 0.1418 with I >2s(I), wR2 = 0.0632 (all observed) and 0.1144 with I >2r(I). GOF =
1.012. CCDC 1035304.HRMS (ESI‐TOF) for C20H22N3O2 [M + H]+: calcd, 336.1634 found 336.1610.
(3Z)‐4‐(2‐hydroxyphenyl)‐3‐((2,4,4‐trimethylpentan‐2‐yl‐amino)methylene)‐1,3‐dihydro‐2H‐1,5‐benzodiaze‐
‐pin‐2‐one (3e). Yellow solid, yield 80%, mp 195‐198°C; 1H NMR (300 MHz, CDCl3) δH : 0.95 (s, 9H, 3xCH3), 1.20
(s, 6H, 2xCH3), 1.46 (s, 2H, CH2), 6.55 (s, 1H, NHbzd), 6.76‐6.83 ( m,2Harom), 6.76‐6.83 ( d, Harom ,J 8.1Hz) 7.03‐
7.07 (d, 1H, Holefinic, J 14.1 Hz), 7.13‐7.43 (m, 5Harom), 9.27 (d, 1H, NHenaminone, J 13.8 Hz), 15.35 (bd‐s, 1H, OH).
13C NMR (75.47 MHz, CDCl3) δC : 7.7, 36.5, 38.1, 61.9, 63.2, 94.7, 117.3, 118.2, 120.6, 121.6, 124.4, 126.7,
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127.5, 130.7, 132.7, 133.3, 137.1, 152.9, 163.3, 168.3, 178.3; IR (ATR) νmax/cm-1: 3224‐3202 (NH), 3056 (OH)
1644 (C=O), 1557 (C=N); HRMS (ESI‐TOF) for C24H29N3O2 [M + H]+: calcd, 391.2260 found 391.2254.
(3Z)‐3‐((tert‐butylamino)methylene)‐4‐(2‐hydroxyphenyl)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one (3f)
1
Orange solid, yield 77%, mp 189‐192 °C; H NMR (300 MHz , CDCl3) δH : 1.14 (s, 9H, 3xCH3), 6.77‐6.83 (m,
2Harom), 6.85 (s, 1H, NHbzd), 6.99 (d, 1Harom, J 8.1Hz), 7.06 (d, 1H, Holefinic, J 14.4Hz), 7.08‐7.44 (m, 5Harom), 9.05
13
(d, 1H, NHenaminone, J 14.1 Hz), 15.45 (bd‐s, 1H, OH). C NMR (75.47 MHz, CDCl3) δC : 16.1, 43.8, 94.9, 117.6,
118.2, 120.7, 121.6, 124.5, 126.8, 127.7, 130.8, 131.9, 133.5, 137.0, 153.7, 163.3, 168.8, 178.0; IR (ATR)
νmax/cm-1: 3287‐3147 (NH), 3060 (OH) 1650 (C=O), 1567 (C=N); HRMS (ESI‐TOF) for C20H22N3O2 [M + H]+: calcd
336.1634 found 336.1625.
(3Z)‐4‐(2‐hydroxyphenyl)‐3‐((isobutylamino)methylene)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one
(3g).
Orange solid, yield 85 %; mp 160‐163 °C; 1H NMR (300 MHz, CDCl3) δH : 0.93 (d, 6H, 2xCH3, J 6.6Hz), 1.78 (m,
1H), 3.72 (t, 2H, CH2, J 6.3Hz), 6.72 (s, 1H, NHbzd), 6.76‐6.85 (m, 2Harom), 6.89 (d, 1H, Holefinic, J 13.8 Hz), 6.99‐
7.45 (m, 6Harom), 8.77 (m, 1H, NHenaminone]), 15.27, (bd‐s, 1H, OH). 13C NMR (75.47 MHz, CDCl3) δC : 19.7, 29.7,
57.1, 94.9, 117.5, 118.1, 120.8, 121.5, 124.4, 126.7, 127.1, 130.8, 132.7, 133.2, 136.9, 157.4, 163.1, 167.9,
178.6; IR (ATR) νmax/cm-1: 3289‐3147 (NH), 3064 (OH) 1652 (C=O), 1567 (C=N); HRMS (ESI‐TOF) for C20H22N3O2
[M + H]+: calcd, 336.1634 found 336.1623.
(3Z)‐3‐((sec‐butylamino)methylene)‐4‐(2‐hydroxyphenyl)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one
Orange solid, yield 85 %; mp 156‐158 °C; 1H NMR (300 MHz, CDCl3) δH : 0.94 (t, 3H, CH3, J 7.2Hz), 1.21 (d, 3H,
CH3, J 6.6Hz), 1.54 (m, 2H, CH2), 3.14 (m, 1H, CH), 6.71 (s, 1H, NHbzd), 6.74‐6.80 (m, 2Harom), 6.96 (d, 1H, Holefinic
(3h).
,
J 13.8 Hz), 6.97‐7.00 (d, 1Harom, J 8.4 Hz), 7.02‐7.45 (m, 5Harom), 8.76 (m, 1H, NHenaminone]), 15.00, (bd‐s, 1H, OH).
13C NMR (75.47 MHz, CDCl3) δC : 9.8, 20.7, 29.9, 56.2, 94.4, 117.7, 118.7, 120.2, 120.3, 123.9, 126.2, 127.0,
130.2, 132.1, 132.7, 136.6, 155.0, 162.8, 167.6, 177.9; IR (ATR) νmax/cm-1: 3286‐3168 (NH), 3043 (OH) 1640
(C=O), 1576 (C=N); HRMS (ESI‐TOF) for C20H22N3O2 [M + H]+: calcd, 336.1636 found 335.1621.
(3Z)‐3‐((hexylamino)methylene)‐4‐(2‐hydroxyphenyl)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one (3i). Yellow
solid, yield 65%, m.p 198‐195 °C; 1H NMR (300 MHz, CDCl3) δH : 0.90 (t, 3H, CH3, J 6.6 Hz), 1.31 (m, 6H, 3xCH2),
1.57 (m, 2H, CH2), 3.20 (qd, 2H, CH2, 3J1=3J2 6.6 Hz ), 6.69 (s, 1H, NHbzd), 6.79‐6.88 (m, 2Harom), 6.93 (d, 1H,
Holefinic ,J 13.8 Hz), 7.01‐7.46 (m, 6Harom), 8.85 (m, 1H, NHenaminone), 15.2 (bd‐s, 1H, OH). 13C NMR (75.47 MHz,
CDCl3) δC : 13.4, 21.9, 25.6, 30.8, 31.3, 49.4, 94.5, 117.5, 118.3, 120.7, 121.5, 124.5, 126.8, 127.5, 130.8, 132.3,
132.8, 137.1, 156.5, 162.8, 167.5, 177.8; IR (ATR) νmax/cm-1: 3302‐3191 (NH), 3057 (OH) 1648 (C=O), 1580
(C=N); HRMS (ESI‐TOF) for C22H26N3O2 [M + H]+: calcd, 364.1947 found 364.1940.
(3Z)‐3‐((cyclohexylamino)methylene)‐4‐(2‐hydroxyphenyl)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one
(3j).
Yellow solid, yield 84%, m.p 191‐194 °C; 1H NMR (300 MHz, CDCl3) δH : 1.019‐1.91 (m, 10H‐cyclohexyl), 3.03 (m,
1H‐cyclohexyl) 6.58 (s, 1H, NHbzd), 6.77‐ 6.85 (m, 2Harom), 6.99 (d, 1H, Holefinic, J 13.8 Hz), 7.00‐7.43 (m, 6Harom),
8.82 (dd, 1H, NHenaminone, J1 5.7Hz, J2 11.4 Hz), 15.41 (bd‐s, 1H, OH). 13C NMR (75.47 MHz, CDCl3) δC : 24.5, 25.0,
33.8, 57.5, 94.7, 117.5, 118.1, 120.7, 121.5, 124.5, 126.7, 127.5, 130.7, 132.7, 133.1, 136.9, 155.1, 163.2,
168.1, 178.3; IR (ATR) νmax/cm-1: 3317‐3197 (NH), 3072 (OH) 1649 (C=O), 1588 (C=N); HRMS (ESI‐TOF) for
C22H24N3O2 [M + H]+: calcd, 362.1790 found 362.1780.
(3Z)‐4‐(2‐hydroxyphenyl)‐3‐((phenylamino)methylene)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one (3k). Yellow
1
solid 55%; mp 232‐235 °C; H NMR (300 MHz, CDCl3) δH : 6.70‐6.90 (m, 1Harom), 6.76 (s, 1H, NHbzd), 6.96‐7.29
(m, 11Harom), 7.34 (d, 1H, Holefinic, J 13.2 Hz), 7.50 (m, 1Harom), 10.17 (d, 1H, NHenaminone, J 13.2 Hz), 15.07 (bd‐s,
1H, OH). 13C NMR (75.47 MHz, CDCl3) δC : 98.8, 116.1, 117.6, 117.8, 121.0, 123.8, 124.4, 126.6, 127.4, 129.3,
130.3, 131.5, 132.7, 136.3, 138.9, 146.6, 156.8, 162.6, 166.3, 176.8; IR (ATR) νmax/cm-1: 3240‐3184 (NH), 3107
(OH) 1651 (C=O), 1576 (C=N); HRMS (ESI‐TOF) C22H18N3O2 [M + H]+: calcd, 356.1321 found 356.1317.
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(3Z)‐4‐(2‐hydroxyphenyl)‐3‐((4‐methoxyphenylamino)methylene)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one
1
(3l). Yellow solid, yield 60%, mp 200‐198 °C; H NMR (300 MHz, CDCl3) δH : 3.68 (s, 3H, CH3), 6.70‐6.82 (m,
4Harom), 6.90 (s, 1H, NHbzd), 6.94‐7.09 (m, 3Harom), 7.20 (d, 1H, Holefinic, J 12.0 Hz), 7.24‐7.47 (m, 5Harom), 10.24
(d, 1H, NHenaminone, J= 12.9 Hz), 14.93 (bd‐s, 1H, OH). 13C NMR (75.47 MHz, CDCl3) δC : 55.5, 98.1, 115.0, 118.0,
118.2, 118.3, 120.8, 121.2, 124.8, 127.0, 127.8, 130.7, 132.3, 133.0, 133.1, 137.1, 148.38, 158.2, 163.0, 167.1,
178.0; IR (ATR) νmax/cm-1: 3237‐3212 (NH), 3101 (OH) 1654 (C=O), 1591 (C=N); HRMS (ESI‐TOF) C23H20N3O3 [M
+ H]+: calcd 386.1426 found 386.1435.
(3Z)‐3‐((4‐chlorophenylamino)methylene)‐4‐(2‐hydroxyphenyl)‐1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one
(3m). Yellow solid, yield 50%, mp: 220‐224 °C; 1H NMR (300 MHz, CDCl3) δH : 6.87‐6.91 (d, 1H, Holefinic, J 12.0
Hz), 6.86‐6.92 (m, 1Harom), 7.04 (s, 1H, NHbzd), 7.07‐7.58 (m, 11Harom), 10.20 (d, 1H, NHenaminone, J 12.1 Hz), 15.00
13
(bd‐s, 1H, OH). C NMR (75.47 MHz, CDCl3) δC : 99.1, 115.1, 117.4, 118.2, 118.3, 120.7, 121.2, 124.3, 127.0,
127.9, 130.7, 132.1, 133.0, 133.9, 137.1, 146.2, 156.1, 162.2, 166.1, 176.0; IR (ATR) νmax/cm-1: 3207‐3154 (NH),
3047 (OH) 1654 (C=O), 1566 (C=N); HRMS (ESI‐TOF) C22H17ClN3O2 [M + H]+: calcd, 390.0931 found 390.0927.
Single‐crystal X‐ray diffraction analysis. A yellow prism of crystals of 3d, was chosen by size, habit, and
polarized light microscopy and mounted on a glass fiber. Intensity data were collected at ambient temperature
on an Enraf‐Nonius CAD‐4 diffractometer equipped with graphite monochromated Mo Ka radiation (λMoK
=
α
0.71073 Å). Reflection data were corrected for Lorentz‐polarization effects but not for absorption. The
structure was solved by direct methods and subsequent difference Fourier techniques (SIR‐92) 23 and refined
with SHELXL‐2013.24 Non‐hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms
were placed in idealized positions on parent atoms in the final refinement.
Further crystallographic data can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: (+44)1223‐336‐033; e‐mail: deposit@ccdc.cam.ac.uk, website
http://www.ccdc.cam.ac.uk).CCDC 1035304.
Antibacterial test of cis‐β‐enaminone‐1,5‐benzodiazepines 3(a‐m)
The antibacterial activity of compounds 3a–m was tested against different microorganisms, including
reference strains consisting of Gram‐negative rods: Escherichia coli (ATCC35218), Pseudomonas aeruginosa
(ATCC 27853), Salmonella typhimurium (LT2 DT104), Listeria monocytogenes (ATCC 19115), and Gram‐positive
cocci: Staphylococcus aureus (ATCC 25923) and Enterococcus faecalis (ATCC 29212), Micrococcus luteus
(NCIMB8166), Bacillus cereus (ATCC11778), and Staphylococcus epidermidis (CIP106510). Strains were
cultured over night at 37 °C in Muller Hinton agar. The minimal inhibition concentration (MIC) was determined
by micro‐titer plate dilution method using sterile 10% H2O solution to dissolve samples.25 Streptomycin
obtained from commercial sources was used as reference antibacterial agent.
Acknowledgements
The authors acknowledge Dr Basma Hamdi (Faculty of Sciences of Sfax) for the X‐ray crystallographic analysis,
and Miss Amna Benzarti, NMR service at the Faculty of Monastir, University of Monastir for the 1D and 2D
NMR analysis and to the Ministry of Higher Education and Scientific Research of Tunisia for financial support
(LR11ES39).
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