Diastereoselective synthesis and cytotoxic evaluation of new isoxazoles and pyrazoles with monoterpenic skeleton

Article abstract of DOI:10.1016/j.molstruc.2019.126924

New series of chiral isoxazoles and pyrazoles with monoterpenic skeleton, have been efficiently synthesized from naturally occurring (R)-Carvone, using 1,3-dipolar cycloaddition reaction with arylonitrile oxides and diarylnitrilimines. The reaction showed

Full text of DOI:10.1016/j.molstruc.2019.126924

Journal of Molecular Structure 1198 (2019) 126924
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Diastereoselective synthesis and cytotoxic evaluation of new
isoxazoles and pyrazoles with monoterpenic skeleton
,
Ali Oubella a, My Youssef Ait Itto a *, Aziz Auhmani a, Abdelkhalek Riahi b,
Anthony Robert b, Jean-Claude Daran c, Hamid Morjani d, Carol A. Parish e,
M'hamed Esseffar a
a
ꢀ
ꢁ
ꢁ
ꢁ
Laboratoire de Synthese Organique et Physico-Chimie Moleculaire, Departement de Chimie, Faculte des Sciences, Semlalia, B.P 2390, Marrakech, 40001,
Morocco
b
ꢁ
ꢁ
^
Equipe MSO, CNRS UMR 7312 Institut de Chimie Moleculaire Universite de Reims Champagne-Ardenne, Bat. Europol'Agro - Moulin de La Housse UFR
ꢁ
Sciences B.P., 1039, 51687 REIMS Cedex 2, France
c UPR-CNRS 8241 Laboratoire de Chimie de Coordination, 205, Route de Narbonne, 31077, Toulouse Cedex 04, France
d
ꢁ
BioSpectroscopie Translationnelle, BioSpecT - EA7506, UFR de Pharmacie, Universite de Reims Champagne-Ardenne, 51 Rue Cognacq Jay, 51096, Reims
Cedex, France
e C-210 Gottwald Center for the Sciences, University of Richmond, 28 Westhampton Way Richmond, VA, 23173, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
New series of chiral isoxazoles and pyrazoles with monoterpenic skeleton, have been efficiently syn-
thesized from naturally occurring (R)-Carvone, using 1,3-dipolar cycloaddition reaction with arylonitrile
oxides and diarylnitrilimines. The reaction showed high peri-, and regioselectivity. In the case of dia-
rylnitrilimines, the reaction revealed to be highly diastereoselective. The structure of the newly syn-
thesized adducts were fully established via spectroscopic analysis and X-ray crystallography. A succinct
theoretical study was used to explain the diastereoselectivity experimentally observed. All the newly
synthesized monoterpenic isoxazole and pyrazole derivatives were evaluated for their cytotoxic activity
against human HT1080, MCF-7 and A-549 cancer cells.
Received 9 May 2019
Received in revised form
22 July 2019
Accepted 12 August 2019
Available online 13 August 2019
Keywords:
Isoxazoles
Pyrazoles
© 2019 Published by Elsevier B.V.
Cycloaddition
Diastereoselectivity
DFT
Cytotoxicity
1. Introduction
Consequently, various methods for the preparation of these
interesting heterocyclic rings were reported in the literature
Nowadays, there is no denying that five-membered heterocycles
are of great interest in chemical and pharmaceutical industries.
Indeed, many bioactive natural product, pharmaceuticals and ag-
rochemicals bear at least one heterocyclic unit. In addition, het-
erocyclic systems are important building-blocks for new materials
possessing interesting physical or biological properties.
The five membered heterocyclic compounds, particularly with
pyrazole and isoxazole nuclei, are components of a diverse array of
compounds with a broad spectrum of bioactivities such as analgesic
[1e3], anti-inflammatory [3e5], antibacterial [3,6,7], antifungal
[3,8,9], antitumoral [3,10,11] and antiviral [3,12,13] activities.
[3,14e16]. Among synthetic routes most often employed, 1,3-
dipolar cycloaddition reaction of suitable 1,3-dipole with appro-
priate dipolarophile is the main approach to access these valuable
nucleous, because of its simplicity, efficiency and high selectivity
[17e21]. As part of our ongoing research project aiming at the
preparation of heterocyclic systems with monoterpenic skeleton
[22e28], we report in this work the hemisynthesis of new iso-
xazoles and pyrazoles, through 1,3-dipolar cycloaddition reaction
of naturally occurred (R)-Carvone (1), with nitrile oxides and
nitrilimines respectively.
Both spectroscopic and theoretical studies had been undertaken
to account for the peri-, regio- and diastereo-selectivity of these
[3 þ 2] cycloaddition reactions. The evaluation of the cytotoxic
activity of the newly prepared isoxazole and pyrazole derivatives is
also reported here.
* Correponding author.
E-mail address: aititto@uca.ac.ma (M.Y. Ait Itto).
https://doi.org/10.1016/j.molstruc.2019.126924
0022-2860/© 2019 Published by Elsevier B.V.

2
A. Oubella et al. / Journal of Molecular Structure 1198 (2019) 126924
Table 1
2. Results and discussion
Effect of NaOCl concentration on the reaction yield of benzonitrile oxide and (R)-
Carvone.
(R)-Carvone (1) is a ketonic monoterpene containing two un-
symmetrical C]C double bonds. A trisubstituted endocyclic one,
activated a withdrawing effect of the carbonyl group in alpha po-
sition, while the other is a disubstituted exocylic double bond far
from the electronic attractive effect of the carbonyl group. Thus,
involvement of these two different dipolarophiles in a 1,3-dipolar
cycloaddition will result in regio- and peri-selectivity outcomes
(Scheme 1).
Aqueous [NaOCl]
3a yield (%)
2.5%
71.5
5.0%
78
7.5%
72.5
10.0%
70.5%
methylene group H2C4’. These spectral data clearly show that 1,3-
dipolar cycloaddition reaction of arylnitrile oxides with (R)-Car-
vone is highly periselective as only the external double bond was
reactive. This cycloaddition reaction was revealed to be also highly
regioselective as we noticed in the 13C NMR spectra, a quaternary
carbon (C50) resonance between 87.74 and 89.73 ppm, which makes
evidence that the direction of the cycloaddition was unique (the
oxygen of the dipoles is linked to the more sterically hindered
carbon of the external double bond). However, a splitting of H2C40,
CH3eC5’ signals in 1H NMR spectroscopy and most of the signals in
13C NMR spectra shows the presence of a diastereoisomeric mixture
for all the isoxazoles (3a-e).
To ascertain all these structural evidences, X-ray analyses were
carried out on single crystals of (3b) (Fig. 1), which provide
noticeable proofs of the assigned structures and allow us to state
with certainty that 1,3-dipolar cycloaddition of arylonitrile oxides
(2a-e) on (R)-Carvone (1) is highly peri- and regioselective.
The structure is built up by the association of three rings, a
cyclohexene, an oxazole and a phenyl ring. The cyclohexene ring
has an envelope conformation with puckering parameters
An additional diastereoselectivity problem will be encountered,
as one or two new stereogenic centers will be generated during the
cycloaddition reaction.
2.1. Synthesis of isoxazoles
(R)-Carvone (1) was treated, with half stoechiometric amounts
of arylonitriles (2a-e), generated from the corresponding oximes
using commercial bleaching agent [29]. Different concentrations of
aqueous NaOCl were tested; the best results were obtained with 5%
of NaOCl (Table 1).
The reaction was performed at 0 ꢀC, in dichloromethane as
solvent to yield the corresponding isoxazoles (3a-e) in a high peri-
and regioselevtive manner with good yields (3a: 78%, 3b: 74%, 3c:
80%, 3d: 60% and 3e: 73%) (Scheme 2). All isoxazoles (3a-e) were
isolated as inseparable (R,R)/(R,S) diastereoisomeric mixtures. It is
worth noting here that when using stoechiometric quantities of 2a-
e, other products were formed leading to a significant decrease of
the desired cycloadducts yield. Furthermore, our approach leads to
an improvement in yields compared to the methodology developed
by Clapp et al. [30] and subsequently adopted by Ilidirissi et al. [31].
All the prepared isoxazoles (3a-e) were fully characterized from
their HRMS and NMR (1D & 2D) spectral data. Indeed, their HRMS
spectra show the corresponding pseudo-molecular ion MNa˥þ at m/
z ¼ 292.1323, m/z ¼ 306.1466, m/z ¼ 326.0932, m/z ¼ 337.1173 and
m/z ¼ 334.1790 respectively, consistent with monocycloadduct
molecular formula (3a: C17H19NO2, 3b: C18H21NO2, 3c: C17H18ClNO2,
3d: C17H18N2O4, 3e: C20H25NO2).
q
¼ 126.4ꢀ and 4 ¼ 70.2ꢀ [32], the oxazole ring is nearly planar with
the largest deviation being ꢁ0.091(1) Å at C5’ but it could be also
regarded as having an envelope conformation with the puckering
parameter 4 ¼ 139.5ꢀ. The dihedral angle between the phenyl and
the oxazole rings is 9.3(1)ꢀ whereas the dihedral angle between the
phenyl and the (C1,C2,C3) and C4 plane is 66.12(8)ꢀ.
There are (CeH/N) interactions (See Table 2) which stabilize
the packing building layer parallel to the (0 0 1) plane. The O1 atom
plays acceptor role for four (CeH/O) interactions: C40-H42,
C6eH602, C6eH6B, C3eH3 and C5eH5 whereas there is one
CeH/N interaction.
Besides phenyl group resonances
123e152 ppm), the salient features of their NMR spectra is the
persistence of signals (
1H 6.75 ppm; 13C 144.10e144.58 ppm) due
to its internal double bond methine group (¼C3eH) and the
disappearance of resonances 4.76 ppm;
1H 4.81 13C
(d d
1H 7.1e8.4 ppm; 13C
2.2. Synthesis of pyrazoles
d
d
Aiming at the synthesis of new pyrazoles with monoterpenic
skeleton, we have examined the 1,3-dipolar cycloaddition reaction
of (R)-Carvone (1) with stoechiometric quantities of diary-
lnitrilimines (4a-d), generated in situ, from their hydrazonoyl
precursors and triethylamine [33]. The reaction was performed, at
room temperature, in dichloromethane as solvent to produce the
corresponding pyrazoles (5a-d) in good yields (5a: 84%; 5b: 84%;
(d
&
d
110.45 ppm), characterizing the methylene group of the external
double bond of starting material. These latters are replaced in 1H
NMR spectra, by a two shielded and split doublets (J ¼ 17 Hz) be-
tween 2.97 and 3.28 ppm while in 13C NMR spectra we note a
shielded and split signal at (39.19e44.35) ppm ascribed to isoxazole
Scheme 1. The two double bonds involved in the reaction.

A. Oubella et al. / Journal of Molecular Structure 1198 (2019) 126924
3
Scheme 2. The different isoxazoles synthesized in this work.
4.67 and 4.63 ppm; Csp2 carbons
d
13C 110.16 and 147.06 ppm)
characterizing the external vinylic double bond. Whereas, the in-
ternal double bond is not revealed and instead we note C3a (one
hydrogen doublet of doublet
carbon
d
1H 3.69 ppm J ¼ 1.1 & 6.8 Hz; HCsp3
d
13C 56.89 ppm) and C7a ( 13C 73.28 ppm) resonances. This
d
proves that the 1,3-dipolar cycloaddition has occurred solely on the
internal double bond.
If well examined, 2D NMR NOESY spectrum of (5a) (Fig. 2),
shows correlations between C7a-CH3 methyl group (
and shielded aromatic hydrogens (two hydrogen doublets
J ¼ 7.9 Hz at
1H 7.12 ppm). This shielding is likely due to the
d
1H 1.35 ppm)
d
mesomeric donor effect of the sp3 nitrogen bearing the corre-
sponding phenyl. So, we can clearly state that pyrazole (5a) (and
the other pyrazoles) is formed as a unique regioisomer where the
sp3 nitrogen of the nitrilimine is attached to the more substituted
carbon of the C]C internal dipolarophile of the (R)-Carvone (1).
No split signals were observed in its NMR spectra, therefore,
(5a), and all the other pyrazoles (5b-d) were isolated as single di-
astereoisomers. However, the absolute configuration of the two
newly formed asymmetric carbons C3a and C7a remained un-
known. This prompted us to carry out X-ray crystal structural
analysis which allowed an unambiguous assignment of the abso-
lute configuration (R) to both new stereogenic centers (Fig. 3).
Compound (5a) is built up from two fused rings a pyrazole and a
cyclohexene. The pyrazole ring is roughly planar with the largest
deviation being 0.131(1) Å at C3. However as for compound (3b) it
could also be considered as having an envelope conformation with
the puckering parameter 4 ¼ 257ꢀ. The cyclohexene ring has a twist
boat conformation as suggested by the puckering parameters:
Fig. 1. Molecular view of compound (3b) with the atom labeling scheme. Ellipsoids are
drawn at the 50% probability level. H atoms are represented as small circle of arbitrary
radii.
Table 2
Hydrogen bonds for (3b) [Å and ꢀ].
D-H … A
d(D-H)
d(H … A)
d(D … A)
<(DHA)
C(40)-H(402) … O(1)i
C(60)-H(602) … N(20)ii
C(6)-H(6B)/O(1)i
C(3)eH(3) … O(1)ii
C(5)eH(5) … O(1)iii
0.97
0.96
0.97
0.93
0.98
2.66
2.64
2.57
2.60
2.66
3.615(3)
3.592(3)
3.522(3)
3.510(3)
3.567(3)
168.1
172.5
167.1
167.6
153.6
q
¼ 84.8ꢀ and 4 ¼ 275ꢀ. The two phenyl rings attached to the pyr-
azole display dihedral angles with the pyrazole of 5.3(1)ꢀ and
0.7(1)ꢀ respectively for the C11 > C16 and C211 > C216 phenyl rings.
There is no (CeH/O) or (CeH/N) intermolecular interactions
Symmetry code: (i) -xþ1,yþ1/2,-zþ3/2; (ii) x-1,y,z; (iii) -xþ1, y-1/2, -zþ3/2.
but there is one (CeH …
p) interaction involving C2eH2 and the
C211 > C216 phenyl ring (H … Cgi ¼ 2.97 Å, C … Cgi ¼ 3.97 and CeH
… Cgi ¼ 174ꢀ; symetry code (i) 1-x, ꢁ1/2 þ y, 3/2-z) (Fig. 4).
Thus, we have been able to prepare efficiently new isoxazoles
(3a-e) and pyrazoles (5a-d), through 1,3-dipolar cycloaddition re-
action of (R)-Carvone (1) with the corresponding 1,3-dipoles. Dur-
ing the synthesis, 1,3-dipolar cycloaddition reaction was revealed to
be highly peri- and regio-selective and even diastereoselective in
the case of nitrilimines.
5c: 88%; 5d: 46%) (Scheme 3).
All pyrazoles (5a-d) were isolated as monocycloadducts since
they show in their HRMS spectra, pseudo-molecular ion MH˥þ at,
m/z ¼ 345.1972,
m/z ¼ 359.2116,
m/z ¼ 379.1569
and
m/
z ¼ 390.1826 respectively, consistent with the corresponding mo-
lecular formula (5a: C23H24N2O, 5b: C24H26N2O, 5c: C23H23ClN2O,
5d: C23H23N3O3). Furthermore, their NMR spectral analysis show
evidences that the reaction is highly peri-, regio- and diaster-
eoselective. It should be specified here that (5a-d) NMR spectra are
closely similar.
3. Computational section
A representative example is the pyrazole (5a) which mainly
Hoping to explain the diastereoselectivity of the [3 þ 2] cyclo-
addition reaction of (1) with, both nitrile oxides (2a-e) and
reveals in its NMR spectra, signals (two one-hydrogen singlets: d
1H

4
A. Oubella et al. / Journal of Molecular Structure 1198 (2019) 126924
Scheme 3. The different pyrazoles synthesized in this work.
Fig. 2. The NOESY correlations of (5a).
diarylnitrilimines (4a-d), theoretical calculations were carried out
using the density functional theory (DFT) [34]. The structures of the
experimentally obtained isoxazoles (3a-e) and pyrazoles (5a-d)
were optimized using the hybrid exchange functional B3LYP [35]
and 6-31G* basis set [36] (Fig. 5).
The calculations were performed with the Gaussian 09 set of
programs [37]. The investigated structures were fully optimized.
Frequencies were calculated to ensure that the optimized struc-
tures correspond to the equilibrium geometries of the minima and
to obtain the zero-point vibrational energies (ZPE) and thermal
correction to enthalpy (TCH). The reported energies including ZPE
correction are scaled by the empirical factor 0.9806 [38]. The
calculated energies, ZPE and TCH of the relevant species are sum-
marized in Table 1S of the Supporting Information. Enthalpies are
calculated as H ¼ E (corrected with ZPE)þTCH. The total and rela-
tive energies between (5R,50R) and (5R,50S) in the case of isoxazole
derivatives and between (3aR,5R,7aR) and (3aS,5R,7aS) in the case
of pyrazole derivatives are gathered in Table 3.
In terms of
DE and DH, the values of Table 3 show that the
stability difference between the (5R,50R) and the (5R,50S) di-
astereoisomers is relatively weak in the case of isoxazoles (3a-e).
This result agrees relatively well with the experimental one where
we obtain a mixture of the two diastereoisomers. In the case of
pyrazoles (5a-d), this difference between the (3aR,5R,7aR) and the
(3aS,5R,7aS) diastereoisomers is more accentuated. In term of DH it
is approximately three times larger than that in the case of iso-
xazoles (about 9.2 kJ/mol) confirming the experimental result
where the (3aR,5R,7aR) diastereoisomer was only isolated.
4. Cytotoxic activity evaluation
The synthesized compounds were evaluated for cytotoxic

A. Oubella et al. / Journal of Molecular Structure 1198 (2019) 126924
5
cells. In MCF-7 cells, only the IC50 values of (3c) and (5c) were
moderate. Finally, both compounds (5a) and (5b) were the less
active in these cells with IC50 values over 100 mM.
5. Conclusion
In summary, we have reported an efficient synthesis of new
chiral isoxazoles and pyrazoles having monoterpenic skeleton, via
1,3-dipolar cycloaddition reaction of (R)-Carvone (1) with the cor-
responding nitrile oxides and nitrilimines. All these pentagonal
heterocyclic systems were fully identified using spectroscopic and
crystallographic data. The cycloaddition reaction was revealed to be
highly peri-, regio- and diastereoselective. This diastereoselectivity
was rationalized by a brief computational study. Among mono-
adducts molecules (3a-e) and (5a-d), evaluated for their general
cytotoxicity against human HT-1080, MCF-7 and A-549 cancer cells,
only isoxazoline derivatives (3a), (3b) and (3d) presented an anti-
proliferative activity in HT-1080 cells. IC50 of the compounds (3a),
(3b), (3d), (3e) and (5d) were the most lower in MCF-7 and A-
549 cells. The cytotoxic activity of compounds (3c), (5a) and (5c)
was moderate in A-549 cells, whereas only the IC50 values of (3c)
and (5c) were moderate in MCF-7 cells.
6. Experimental section
Fig. 3. Molecular view of compound (5a) with the atom labeling scheme. Ellipsoids are
drawn at the 50% probability level. H atoms are represented as small circle of arbitrary
radii.
All chemicals were used as obtained from commercial sources
(Aldrich and Acros). Melting points (m.p.) were determined using a
capillary apparatus and are inaccurate. Analytical thin-layer chro-
matography (TLC) was performed on plates precoated with E.
Merck silica gel 60 F254 to a thickness of 0.25 mm. HRMS were
obtained on a Q-TOF micromass spectrometer. 1H and 13C NMR
spectra were recorded in CDCl3 with 500 MHz Bruker Avance III
spectrometer with a BBFO þ probe. Chemical shifts (
d) are
expressed in parts per million (ppm). They were recorded relative
to solvent CDCl3 signal (7.26 ppm and 77.16 ppm). Arylonitrile ox-
ides (2a-e) and diarylnitrilimines (4a-d) were generated in situ
from the corresponding precursors according to the reported pro-
cedures [24,29e33].
Cell culture: The human fibrosarcoma cell line HT-1080 (CCL
121) was purchased from Sigma Aldrich (ECACC collection, Saint-
Quentin Fallavier, France). The human breast adenocarcinoma
MCF-7 (HTB-22) and lung carcinoma A-549 (CCL-185) cell lines
were purchased from the American Type Culture Collection (ATCC).
Cells were cultured in MEM with Earle salts and Glutamax I (Invi-
trogen, Cergy-pontoise, France) supplemented with 10% fetal
bovine serum, (Invitrogen) and 1% penicillin-streptomycin (Invi-
trogen). Cultures were maintained at 37 ꢀC in a humidified atmo-
sphere containing 5% CO2 (v/v). Cells were routinely passaged at
preconfluency using 0.05% trypsin, 0.53 mM EDTA (Invitrogen) and
screened for the absence of mycoplasma using PCR methods.
General procedure for the preparation of Isoxazoles (3a-e): To
a stirred solution of (R)-Carvone (1) (6.57 mmol) and p-substituted
benzaldoximes (3.28 mmol) in CH2Cl2 (15 mL) was added dropwise
(during 30min) at 0 ꢀC 20 mL of aqueous NaOCl (5.2%; 15,65 mmol).
After 10 min stirring (the reaction was monitored by TLC) at room
temperature, the layers were separated and the aqueous layer was
extracted with CH2Cl2 (3 ꢂ 10 mL). The combined organic extracts
were dried over anhydrous Na2SO4 and evaporated in vacuo. The
residue was purified by column chromatography using hexane/
Ethylacetate mixture (88:12) as eluent.
Fig. 4. Partial packing view showing intermolecular CeH …
pound (5a).
p interaction for com-
activity in vitro against HT-1080, MCF-7 and A-549 cancer cell lines
using doxorubicin as a positive control. The IC50 are presented in
Table 4.
For compounds (3a), (3b) and (3d), the anticancer activities
were the highest ones in HT-1080 cells, with IC50 values less than
20
mM. However, for the same isoxazoline family the group of
molecules including (3c) and (3e), IC50 was over 100
last group of pyrazole family compounds (5a, 5b, 5c and 5d) has
been identified as the less cytotoxic among all molecules with an
IC50 over 100 mM. In MCF-7 and A-549 cells, several evaluated
compounds were more active. In fact, the IC50 of the compounds
mM. Finally, a
(3a), (3b), (3d), (3e) and (5d) were the most lower in both cell lines
6.1. (R)-2-Methyl-5-((R/S)-5-methyl-3-phenyl-4,5-
dihydroisoxazol-5-yl)cyclohex-2-enone (3a)
(IC50 values less than 30
compounds (3c), (5a) and (5c) was moderate in A-549 cells. The
IC50 value of (5b) compound was however over 100 M in these
mM), whereas the cytotoxic activity of
Yield 78%; white solid: mp ¼ 107 ꢀC (Ethanol); HRMS (TOF-MS
m

6
A. Oubella et al. / Journal of Molecular Structure 1198 (2019) 126924
Fig. 5. Optimized structures of the two diastereoisomers of isoxazole 3a and pyrazole 5a, at the B3LYP/6-31G* level.
Table 3
B3LYP/6-31G* total (E and H, in au) and relative (DE, D
H, in kJ/mol) energies and enthalpies, of (5R,50R) and (5R,50S) diastereoisomers in the case of isoxazole derivatives and
(3aR,5R,7aR) and (3aS,5R,7aS) in the case of pyrazole derivatives.
Isoxazoles
Ea
DE
H
DH
(5R,50R)
(5R,50S)
(5R,50R)
(5R,50S)
3a
3b
3c
3d
3e
Pyrazoles
ꢁ864.081795
ꢁ903.3731931
ꢁ1323.687004
ꢁ1068.580239
ꢁ1212.906444
ꢁ864.080499
ꢁ903.3718655
ꢁ1323.685738
ꢁ1068.578974
ꢁ1212.906013
ꢁ3.40
ꢁ3.48
ꢁ3.32
ꢁ3.32
ꢁ1.13
ꢁ864.062872
ꢁ903.352378
ꢁ1323.66689
ꢁ1068.55879
ꢁ1212.87877
ꢁ864.061571
ꢁ903.351045
ꢁ1323.66556
ꢁ1068.55749
ꢁ1212.87852
ꢁ3.42
ꢁ3.50
ꢁ3.47
ꢁ3.42
ꢁ0.66
(3aR.5R,7aR)
ꢁ1075.172352
ꢁ1114.46314
ꢁ1534.778142
ꢁ1279.675813
(3aS,5R,7aS)
ꢁ1075.169115
ꢁ1114.4599
(3aR,5R,7aR)
ꢁ1075.14901
ꢁ1114.43779
ꢁ1534.75356
ꢁ1279.64996
(3aS,5R,7aS)
ꢁ1075.14534
ꢁ1114.43416
ꢁ1534.75027
ꢁ1279.64655
5a
5b
5c
5d
ꢁ8.50
ꢁ8.51
ꢁ7.36
ꢁ7.76
ꢁ9.64
ꢁ9.54
ꢁ8.64
ꢁ8.94
ꢁ1534.775342
ꢁ1279.672859
a
: Total energies are corrected by ZPE which is scaled by the empirical factor of 0.9806.
Table 4
6.2. (R)-2-Methyl-5-((R/S)-5-methyl-3-p-tolyl-4,5-
dihydroisoxazol-5-yl)cyclohex-2-enone (3b)
Cytotoxic activities of the synthesized (3a-e) and (5a-d) compounds against human
HT-1080, MCF-7 and A-549 cells.
Yield 74%; white solid: mp ¼ 96 ꢀC (Ethanol); HRMS (TOF-MS
ESþ) (m/z): found 306.1466 [MþH]þ, calculated 306.1470. 1H NMR
Compound
IC50 (mM)
HT-1080
MCF-7
A-549
d
(ppm): 1.43 & 1.46 (3H, 2s); 1.78 (3H, s); 2.38 (3H, s); 2.52 (1H, m);
3a
3b
3c
3d
3e
5a
5b
5c
5d
16.10
10.72
>100
9.02
>100
>100
>100
>100
>100
23.84
19.52
48.24
20.24
22.14
>100
>100
49.33
24.19
27.87
15.24
61.31
18.14
28.01
52.17
>100
51.66
27.18
2.25e2.37 (2H, m); 2.55e2.63 (2H, m); 2.95e3.30 (2H, 2d
J ¼ 16.62 MHz); 6.76 (1H, m); 7.20 (2H, d J ¼ 7.98 Hz); 7.53 (2H,dd
J ¼ 8.28 & 2.04 Hz). 13C NMR
d (ppm):15.76 (CH3); 21.57 (CH3);
23.08 & 24.46 (CH3); 27.16&27.26 (CH2); 39.42&39.81 (CH2);
43.48&43.94 (CH); 44.00 & 44.35 (CH2); 87.77 & 87.83 (C5’); 126.90
& 126.67 (CAr); 126.53 (HCAr); 129.56 (HCAr); 135.55 & 135.61
(¼C); 140.45 (CAr); 144.50 & 144.58 (HC ¼ ); 155.71 &155.89 (C]
N); 199.04 & 199.16 ppm (-C]O). Single crystals of 3b suitable for
X-ray analysis were obtained by slow crystallization from Chloro-
form solution.
ESþ) (m/z): found 292.1323 [MþH]þ, calculated 292.1313. 1H NMR
d
(ppm): 1.43 &1.47 (3H, 2s); 1.77 (3H, s); 2.36 (1H, m); 2.26e2.33
6.3. (R)-2-Methyl-5-((R/S)-5-methyl-3-p-chlorophenyl-4,5-
dihydroisoxazol-5-yl)cyclohex-2-enone (3c)
(2H, m); 2.45e2.64 (2H, m); 3.00e3.30 (2H, 2d J ¼ 16.73 Hz); 6.75
(1H, m); 7.38 (3H, m); 7.62 (2H, m). 13C NMR
d
(ppm):15.74 (CH3);
23.11 & 24.42 (CH3); 27.13 &27.23 (CH2); 39.37 & 39.74 (CH2); 43.91
& 44.16 (CH); 43.95 & 43.37 (CH2); 88.08 & 88.00 (C5’); 126.56
(HCAr); 128.84 (HCAr); 129.77&129.70 (CAr); 130.18 (HCAr); 135.60 &
135.54 (¼C); 144.43 &144.50 (HC ¼ ); 155.74 & 155.89 (C]N);
199.08 & 198.95 ppm (C]O).
Yield 80%; white solid: mp ¼ 104 ꢀC (Ethanol); HRMS (TOF-MS
ESþ) (m/z): found 326.0932 [MþH]þ, calculated 326.0924. 1H NMR
d
(ppm):1.42 & 1.47 (3H, 2s); 1.77 (3H, s); 2.37 (1H, m); 2.22e2.30
(2H, m); 2.42e2.63 (2H, m); 2.95e3.30 (2H, 2d J ¼ 16.74 Hz); 6.75
(1H, m); 7.36 (2H, d J ¼ 7.88 Hz); 7.5 (2H,dd J ¼ 8.15 & 1.75 Hz). 13
C

A. Oubella et al. / Journal of Molecular Structure 1198 (2019) 126924
7
NMR
d
(ppm): 15.74 (CH3); 23.07&24.38 (CH3); 27.11&27.21 (CH2);
[MþH]þ, calculated 359.2123. 1H NMR
d
(ppm): 1.34 (3H, s); 1.60
39.31 & 39.71 (CH2); 43.26 &43.91 (CH2); 43.98 & 43.88 (CH); 88.40
& 88.50 (C5’); 127.79 (HCAr); 128.29 (CAr); 129.12 (HCAr); 135.59 &
135.65 (¼C); 136.11 (CAr); 144.31 &144.39 (HC ¼ ); 154.82 & 154.97
(C]N); 198.80 & 199.95 ppm (C]O).
(3H, s); 1.64 (1H, m); 1.87e2.35 (2H, m); 2.40 (3H, s); 2.76e3.00
(2H, m); 3.67 (1H, dd J ¼ 6.75 & 1.2 Hz); 4.63 (1H, s); 4.70 (1H, s);
6.90 (1H, t J ¼ 7.30 Hz); 7.11 (2H, d J ¼ 7.8 Hz); 7.25 (4H, m); 7.68 (2H,
d J ¼ 8.15 Hz). 13C NMR
d (ppm):17.56 (CH3); 20.60 (CH3); 20.60
(CH3); 29.47 (CH2); 37.76 (CH); 44.20 (CH2); 57.00 (HC3a); 73.14
(C7a); 110.11 (H2C ¼ ); 114.95 (HCAr); 120.66 (HCAr); 126.28
(HCAr); 128.33 (CAr); 129.36 (HCAr); 129.68 (HCAr); 139.29 (CAr);
144.04 (N-CAr); 147.08 (¼C); 150.06 (¼C3); 212.39 (C]O).
6.4. (R)-2-Methyl-5-((R/S)-5-methyl-3-p-nitrorophenyl-4,5-
dihydroisoxazol-5-yl)cyclohex-2-enone (3d)
Yield 60%; white solid: mp ¼ 121 ꢀC (Ethanol); HRMS (TOF-MS
ESþ) (m/z): found 337.1173 [MþH]þ, calculated 337.1164. 1H NMR
6.8. (3aR,5R,7aR)-3-p-chlorophenyl-7a-methyl-7-oxo-1-phenyl-5-
(prop-1-en-2-yl)-3a,4,5,6,7,7a-hexahydrobenzopyrazole (5c)
d
(ppm): 1.46 &1.46 (3H, 2s); 1.77 (3H, s); 2.40 (1H, m); 2.22e2.33
(2H, m); 2.46e2.63 (2H, m); from 3.02 to 3.33 (2H, 2d J ¼ 16.75 Hz);
6.75 (1H, m); 7.80 (2H, d J ¼ 7.45 Hz); 8.25 (2H,d J ¼ 8.80 Hz). 13C
Yield 88%; oil. HRMS (TOF-MS ESþ) (m/z): found 379.1569
NMR d (ppm):15.71 (CH3); 23.14 & 24.33 (CH3); 27.05 & 27.15 (CH2);
[MþH]þ, calculated 379.1577. 1H NMR
d (ppm): 1.35 (3H, s); 1.61
39.19 & 39.57 (CH2); 43.83 (CH); 42.90 & 43.43 (CH2); 89.59 & 89.7
(C5’); 124.12 (HCAr); 127.26 (HCAr); 135.80 & 135.87 (¼C); 135.67
(CAr); 144.10 & 144.15 (HC ¼ ); 148.49 (CAr); 154.32 (C]N); 198.68
& 198.50 (C]O).
(3H, s); 1.65 (1H, m); 1.80e2.40 (2H, m); 2.70e3.00 (2H, m); 3.65
(1H, dd J ¼ 6.70 & 1.25 Hz); 4.60 (1H, s); 4.68 (1H, s); 6.92 (1H, t
J ¼ 7.30 Hz); 7.12 (2H, d J ¼ 8.30 Hz); 7.27 (2H, t J ¼ 8.50 Hz); 7.40
(2H, d J ¼ 8.70 Hz); 7.72 (2H, d J ¼ 8.60 Hz). 13C NMR
d (ppm):17.67
(CH3); 20.56 (CH3); 29.37 (CH2); 37.72 (CH); 44.08 (CH2); 56.71
(HC3a); 73.36 (C7a); 110.25 (H2C ¼ ); 114.97 (HCAr); 121.02 (HCAr);
127.44 (HCAr); 129.20 (HCAr); 129.42 (HCAr); 129.64 (CAr); 134.87
(CAr); 143.63 (N-CAr); 146.84 (¼C); 148.72 (¼C3); 211.78 (-C]O).
6.5. (R)-2-Methyl-5-((R/S)-5-methyl-3-p-isopropylphenyl-4,5-
dihydroisoxazol-5-yl)cyclohex-2-enone (3e)
Yield 73%; white solid: mp ¼ 111 ꢀC (Ethanol); HRMS (TOF-MS
ESþ) (m/z): found 334.1790 [MþH]þ, calculated 334.1783. 1H NMR
6.9. (3aR,5R,7aR)-7a-methyl-3-p-nitrophenyl-7-oxo-1-phenyl-5-
(prop-1-en-2-yl)-3a,4,5,6,7,7a-hexahydrobenzopyrazole (5d)
d
(ppm):1.22 & 1.27 (6H, 2s); 1.42 &1.46 (3H, 2s); 1.77 (3H, s); 2.30
(1H, m); 2.22e2.34 (2H, m); 2.46e2.63 (2H, m); 2.90 (1H, m);
2.90e3.40 (2H, 2d J ¼ 16.75 Hz); 6.75 (1H, m); 7.25 (2H,
1.70 Hz).13
C
NMR
Yield 46%; brown solid mp ¼ 70 ꢀC (Ethanol). HRMS (TOF-MS
ESþ) (m/z): found 390.1826 [MþH]þ, calculated 390.1818. 1H NMR
d
d
J ¼ 8.55 Hz); 7.57 (2H,dd J ¼ 8.30
&
(ppm):15.73 (CH3); 23.10 & 24.40 (CH3); 23.89 (CH3); 27.13 &
d
(ppm): 1.40 (3H, s); 1.60 (3H, s); 1.67 (1H, m); 1.80e2.40 (2H, m);
27.24 (CH2); 39.39 & 39.57 (CH2); 34.17 (CH); 43.96 & 44.30 (CH);
43.45 & 43.90 (CH2); 87.74 & 87.80 (C5’); 126.64 (HCAr); 126.92
(HCAr); 127.24 & 127.31 (CAr); 135.51 & 135.56 (¼C); 144.46 &
144.54 (HC ¼ ); 151.33 (CAr); 155.69 (C]N); 199.10 & 198.99 (C]O).
General procedure for the preparation of Pyrazoles (5a-d): To a
solution of (R)-Carvone (1) (0.23 g, 1.37 mmol) and hydrazonoyl
chlorides, precursors of diarylnitrilimines (4a-d) (1.37 mmol) in
dichloromethane (20 mL), triethylamine (0.3 mL) in dichloro-
methane (2 mL) was added slowly at room temperature. The re-
action mixture was then, stirred at room temperature for three days
(monitoring by tlc), filtered and concentrated under reduced
pressure. The resulting residue was purified by column chroma-
tography using hexane/ethyl acetate 96:4.
2.70e2.93 (2H, m); 3.71 (1H, dd J ¼ 6.55 & 1.10 Hz); 4.30 (1H, s);
4.69 (1H, s); 6.97 (1H, t J ¼ 7.35 Hz); 7.42 (2H, d J ¼ 7.85 Hz); 7.28
(2H, dd J ¼ 8.60 & J ¼ 7.40 Hz); 7.91 (2H, d J ¼ 8.95 Hz); 8.28 (2H,
d J ¼ 8.95 Hz). 13C NMR
d (ppm):17.99 (CH3); 20.48 (CH3); 29.34
(CH2); 37.70 (CH); 43.95 (CH2); 56.19 (HC3a); 73.92 (C7a); 110.47
(H2C ¼ ); 115.11 (HCAr); 121.83 (HCAr); 124.36 (HCAr); 126.45 (HCAr);
129.56 (HCAr); 137.40 (CAr); 142.82 (N-CAr); 146.53 (¼C); 147.19
(¼C3); 147.41 (CAr); 210.86 (-C]O).
X-ray structural analyses: Single crystal of each compound was
mounted under inert perfluoropolyether at the tip of glass fiber and
cooled in the cryostream of either a Rigaku Oxford Diffraction
GEMINI EOS diffractometerfor (3b) or a Bruker Nonius APEXII for
(5a). The structures were solved by direct methods SHELXT-2015
[39] and refined by least-squares procedures on F2 using SHELXL-
2014 [40]. All H atoms attached to carbon were introduced in
calculation in idealised positions and treated as riding models.
Owing to the absence of atoms heavier than Si, the absolute
configuration could not be reliably established by refinement of the
Flack's parameter [41] but it is confirmed by the synthetic pro-
cedure. The drawing of the molecules was realised with the help of
ORTEP32 [42]. Crystal data and refinement parameters are shown
in Tables (2Se4S).
6.6. (3aR,5R,7aR)-7a-methyl-7-oxo-1,3-diphenyl-5-(prop-1-en-2-
yl)-3a,4,5,6,7,7a-hexahydrobenzopyrazole (5a)
Yield 84%; brown solid: mp ¼ 99 ꢀC (Ethanol); HRMS (TOF-MS
ESþ) (m/z): found 345.1972 [MþH]þ, calculated 345.1967. 1H NMR
d
(ppm):1.35 (3H, s); 1.61 (3H, s); 1.65 (1H, m); 1.80e2.50 (2H, m);
2.60e3.00 (2H, m); 3.69 (1H, ddJ ¼ 6.80 & 1.10 Hz); 4.63 (1H, s);
4.68 (1H, s); 6.90 (1H, t J ¼ 7.30 Hz); 7.12 (2H, dd J ¼ 8.7 & 1.0 Hz);
7.25 (2H, t J ¼ 8.1 Hz); 7.36 (1H, m); 7.42 (2H, m); 7.79 (2H, dd
J ¼ 7.15 & 1.5 Hz). 13C NMR
d (ppm):17.62 (CH3); 20.60 (CH3); 29.42
CCDC 1910555e1910556 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Cytotoxicity Assay: Cytotoxicity of the synthesized compounds
was assessed by the CellTiter 96® Non-Radioactive Cell Prolifera-
(CH2); 37.77 (CH); 44.20 (CH2); 56.88 (HC3a); 73.27 (C7a); 110.16
(H2C ¼ ); 114.99 (HCAr); 120.82 (HCAr); 126.31 (HCAr); 128.98
(HCAr); 129.11 (HCAr); 129.40 (HCAr); 131.16 (CAr); 143.92 (N-CAr);
147.08 (¼C); 149.89 (¼C3); 212.22 (C]O). Single crystals of 5a
suitable for X-ray analysis were obtained by slow crystallization
from Chloroform solution.
ꢀ
tion Assay (MTT) (Promega, Charbonnieres les Bain, France). Briefly,
the cells were plated at a density of 2500 cells/well in a 96-well
6.7. (3aR,5R,7aR)-7a-methyl-3-p-methylphenyl-7-oxo-1-phenyl-5-
(prop-1-en-2-yl)-3a,4,5,6,7,7a-hexahydrobenzopyrazole (5b)
plate with 100
concentrations of the previously cited molecules (6.25, 12.5, 25, 50
and 100 M). After 24 h, 15 L of MTT dye solution was added in
each well. The plates were further incubated for 4 h. Then, 100 L of
mL culture medium per well, containing different
m
m
Yield 85%; oil. HRMS (TOF-MS ESþ) (m/z): found 359.2116
m

8
A. Oubella et al. / Journal of Molecular Structure 1198 (2019) 126924
43 (2008) 1715.
the solubilization/stop solution was added into each well and the
plate was incubated 1h at room temperature. The optical density of
each well was measured at 570 nm using a microplatereader
Revelation 96-well multiscanner (Dynex Technologies, Chantilly,
VA). Results were represented as a percentage of cell survival with
respect to untreated controls. The IC50 was defined as the drug
concentration required for inhibition of cell growth by 50%, relative
to untreated controls. IC50 values were estimated from the dose
response curve.
[19] P. Conti, A. Pinto, L. Tamborini, V. Rizzo, C. De Micheli, Tetrahedron 63 (2007)
5554.
[20] K.A. Franzen, J. William, J.K.-H.P. Marshall, Tetrahedron Lett. 57 (2016) 3194.
[21] C. Sun, M.J. O'Connor, D. Lee, D.J. Wink, R.D. Milligan, Angew. Chem. Int. Ed. 53
(2014) 3197e3200.
[22] A. Feddouli, My Y. Ait Itto, A. Hasnaoui, D. Villemin, P.-A. Jaffres, J.S. De Oliveira
Santos, A. Riahi, F. Huet, J.-C. Daran, J. Heter. Chem. 41 (2004) 731.
[23] A. Feddouli, My Y. Ait Itto, M. Ait Ali, A. Hasnaoui, A. Riahi, Synth. Commun. 36
(2006) 3617.
[24] My Y. Ait Itto, A. Feddouli, A. Boutalib, A. Riahi, J.-C. Daran, J. Sulfur Chem. 34
(2013) 250.
[25] A. N'Ait Ousidi, My Y. Ait Itto, Az Auhmani, A. Riahi, J.-C. Daran, Aw Auhmani,
Acta Crystallogr. E72 (2016) 334.
[26] A. N'Ait Ousidi, My Y. Ait Itto, Az Auhmani, M. Barakate, A. Riahi, H. Ben El
Ayouchia, H. Anane, N. El Aouad, M. De LaCruz, C. Díaz, F. Vicente, IOSR J. Appl.
Chem. 9 (2016) 52.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molstruc.2019.126924.
[27] A. N'Ait Ousidi, My Y. AitItto, Az Auhmani, A. Riahi, Aw Auhmani, J.-C. Daran,
Acta Crystallogr. E73 (2017) 296.
[28] A. N’ait Ousidi, My Y. AitItto, Az Auhmani, A. Riahi, A. Robert, Aw Auhmani, J.-
C. Daran, Acta Crystallogr. C74 (2018) 1629.
References
[29] Y.-S. Lee, S.M. Park, B.H. Kim, Bioorg. Med. Chem. Lett 19 (2009) 1126.
[30] C.-Y. Shiue, R.G. Lawler, L.B., Clapp J. Org. Chem. 41 (1976) 2210e2212.
[31] A. El Mebtoul, M. Rouani, M. Chammache, H. Bouidida, A. Ilidrissi, Helv. Chim.
Acta 94 (2001) 433e437.
[32] D. Cremer, J.A. Pople, J. Am. Chem. Soc. 97 (1975) 1354.
[33] R. Huisgen, M. Seidel, G. Wallbillich, H. Knupfer, Tetrahedron 17 (1962) 3.
[34] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[35] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B37 (1988) 785.
[36] W.J. Here, L. Radom, P.v.R. Schleyer, J.A. Pople, Ab Initio Molecular Orbital
Theory, Wiley, New York, 1986.
[1] A.G. El-Sehemi, S. Bondock, Y.A. Ammar, Med. Chem. Res. 23 (2014) 827.
[2] V.A. Airody, T. Karabasanagouda, M. Girisha, Indian J. Chem. 48B (2009) 430.
[3] V.C. KRISHNA, S. RAJA, Int. J. Pharm. Pharm. Sci. 9 (7) (2017) 13.
[4] S.G. Alegaon, K.R. Alagawadi, M.K. Garg, K. Dushyant, D. Vinod, Bioorg. Chem.
54 (2014) 51.
[5] J. Lincy, G. Mathew, Eur. Int. J. Sci. Tech. 5 (2016) 35.
[6] B. Umesha, Y.B. Basavaraju, Med. Chem. Res. 23 (2014) 3744.
[7] P. Sagar, K. Vilasrao, B. Ramesh, S.M. Sachin, P. Vijay, Int. J. Comp. Adv.
Pharmacol. 2 (2017) 19.
[37] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino,
G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J.A. Montgomery, J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers,
K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam,
M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski,
R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador,
J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz,
J. Cioslowski, D.J. Fox, Gaussian 09, Revision A.02, Gaussian, Inc., Wallingford,
CT, 2009.
[8] R. Nagamallu, B. Srinivasan, M.B. Ningappa, A.K. Kariyappa, Bioorg. Med.
Chem. Lett 26 (2016) 690.
[9] A. Aiman, A. Anis, V. Himani, R. Abdul, R. Mohd, S. Naidu, Eur. J. Med. Chem. 70
(2013) 887.
[10] J. Ren, S. Wang, H. Ni, R. Yao, C. Liao, B. Ruan, J. Inorg. Organomet. Polym. 25
(2015) 419.
[11] W.S. Hamama, M.E. Ibrahim, H.H. Zoorob, J. Heterocycl. Chem. 54 (2017) 341.
[12] R. Fioravanti, N. Desideri, M. BiavaP. Droghini, E.M. Atzori, C. Ibba, G. Collu,
G. Sanna, I. Delogu, R. Loddo, Bioorg. Med. Chem. Lett 25 (2015) 2401.
[13] F. Li, Y. Hu, Y. Wang, C. Ma, J. Wang, J. Med. Chem. 60 (2017) 1580.
[14] G.S. Singh, T.H. Tabane, Green Synthetic Approaches for Biologically Relevant
Heterocycles, Elsevier Inc., 2015, pp. 163e184. Chap. 7.
[15] A.F. da Silva, A.A.G. Fernandes, S. Thurow, M.L. Stivanin, I.D. Jurberg, Synthesis
50 (2018) 2473.
[38] A.P. Scott, L. Radom, J. Phys. Chem. 100 (1996) 16502.
[39] G.M. Sheldrick, Acta Crystallogr. A71 (2015) 3.
[40] G.M. Sheldrick, Acta Crystallogr. C71 (2015) 3.
[41] H.D. Flack, G. Bernardinelli, Chirality 20 (2008) 681.
[42] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[16]
.
a
H.G. Bonacorso, G.M. Dal Forno, C. Wiethan, A. Ketzer, N. Zanatta,
C.P. Frizzo, M.A.P. Martins, M. Stradiotto, RSC Adv. 7 (2017) 43957;
H.G. Bonacorso, A. Ketzer, W.C. Rosa, T.P. Calheiro, M.B. Rodrigues,
N. Zanatta, M.A.P. Martins, C.P. Frizzo, J. Fluorine Chem. 210 (2018) 142.
b
[17] K.N. Houk, J. Sims, C.R. Watts, L.J. Luskus, A. Am. Chem. Soc. 95 (1973) 7301.
[18] N.S. Rai, B. Kalluraya, B. Lingappa, S. Shenoy, V.G. Puranic, Eur. J. Med. Chem.