Design, synthesis and analgesic properties of novel conformationally-restricted N-acylhydrazones (NAH)

Article abstract of DOI:10.1016/j.bmcl.2009.07.075

A set of six azaheterocycles were designed as conformationnaly-constrained N-acylhydrazones and tested as analgesics.

Full text of DOI:10.1016/j.bmcl.2009.07.075

Bioorganic & Medicinal Chemistry Letters 19 (2009) 4963–4966
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis and analgesic properties of novel conformationally-restricted
N-acylhydrazones (NAH)
Arthur E. Kümmerle a,b,c, Marina M. Vieira a,d, Martine Schmitt c, Ana L. P. Miranda a,d, Carlos A. M. Fraga a,b,d
,
a,b,d,
Jean-Jacques Bourguignon c, , Eliezer J. Barreiro
*
*
a Laboratório de Avaliação e Síntese de Substâncias Bioativas (LASSBio), Faculdade de Farmácia, Universidade Federal do Rio de Janeiro, RJ 21944-971, Brazil
b Programa de Pós-Graduação em Química, Instituto de Química, Universidade Federal do Rio de Janeiro, RJ 21949-900, Brazil
c Laboratoire de Innovation Thérapeutique UMR 7200 du CNRS, Faculté de Pharmacie, Université Louis Pasteur, 67401 Illkirch Cedex, France
d Programa de Pós-Graduação em Farmacologia e Química Medicinal, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, RJ 21941-590, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
A set of six azaheterocycles were designed as conformationnaly-constrained N-acylhydrazones and
Received 11 May 2009
Revised 9 July 2009
Accepted 14 July 2009
Available online 18 July 2009
tested as analgesics.
Ó 2009 Elsevier Ltd. All rights reserved.
Key words:
N-Acylhydrazones
Conformational restriction
Analgesic
Among the class of N-acylhydrazones (NAH) developed at our
laboratory, some of them presented various pharmacological prop-
erties, specially analgesic and anti-inflammatory.1 It is well known
that medicinal chemistry tools including molecular hybridization,2
bioisosterism,3 molecular simplification,4 homologation or confor-
mational restriction5 may dramatically change the pharmacologi-
cal profile of a given molecule and were utilized on the first
series of bioactive NAH’s. As a prototypical example given in
Scheme 1, NAH’s 1 may be considered as seco derivatives of 6-aryl
pyridazinones 2.
We recently identified two compounds (cpds 3 and 4) as anal-
gesics with about the same potency (inhibition of AcOH-induced
constriction in mice, ED50 about 2 mg/kg, see Table 1).
The aim of this work was the design and synthesis of a set of
NAH structurally-related compounds, as depicted in Chart 1.
Among the various conformational possibilities provided by the
N-acylhydrazone chemotype, we selected the most favorable con-
formations highlighting:
Finally three different main prototypical geometries could be
easily identified, as depicted in Chart 1.
We focused our interest on these conformers (I–III) for building
semi-constrained NAH structural analogues. As illustrated in Chart
1, the full extended semi-folded conformation I provided the qui-
nazoline 5 by bridging the N-acyl nitrogen onto the ortho position
of the benzamide (mode a), whereas bridging the oxygen amide of
3 in a similar fashion through an amidine isosteres (mode b) gave
an hydrazinoquinazoline (6). Through another type of rigidification
(modes c and d) starting from the conformer II, two other hetero-
cycles were identified. The first one results from the incorporation
of the hydrazine into a ring system, a pyridazine (7), or a pyrazole
ring (8) (mode d).
In the first compound (7), another constraint was introduced by
means of a triazole ring (mode c) leading to a rigid core (triazolo
[4,3-b] pyridazine) bearing two aromatics.
(i) E or Z relative configuration for the phenyl imine function.
(ii) E or Z for the benzamide group.
(iii) s-cis or s-trans junction between both functions.
* Corresponding authors. Tel./fax: +55 21 25626644 (E.J.B.).
E-mail address: ejbarreiro@ccsdecania.ufrj.br (E.J. Barreiro).
Scheme 1. Structural pattern of NAHs framework included in the piridazinone ring.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.07.075

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A. E. Kümmerle et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4963–4966
Table 1
Antinociceptive activity for derivatives 3–10, paracetamol and indomethacin in the inhibition of AcOH-induced constrictions (0.1 N) in mice
Compounds
Molecular formula
Mw
Dose
mol/Kg
Number of constrictionsa
Analgesic activityb
ED50
l
mg/Kg
lmol/Kg
mg/Kg
Vehicle (arabic gum)
Paracetamol
Indomethacin
3
4
5
6
7
—
—
—
—
60.6 1.2
38.8 0.9
35.1 1.3
28.2 1.5
30.4 0.7
43.0 2.4
31.8 2.5
47.2 3.1
30.4 2.7
40.6 2.0
38.6 1.4
—
—
—
—
—
C8H9NO2
151
358
254
268
278
279
302
292
252
266
100
100
100
100
100
100
100
100
100
100
15
36
25
27
28
28
30
29
25
27
36c
42c
54c
50c
28c
48c
22c
50c
33c
36c
C19H16ClNO4
C15H14N2O2
C16H16N2O2
C16H14N4O
C16H13N3O2
C18H14N4O
56.2
9.2
5.9
—
4.2
—
5.1
—
—
20.1
2.3
1.6
—
1.2
—
1.5
—
—
8
C
18H16N2O2
9a + 9b
10
C15H12N2O2
C16H14N2O2
All compounds were administered orally; N = 7–10 animals.
a
Results expressed in terms of mean SEM.
Percentage of inhibition obtained by comparison with the vehicle control group.
p <0.05 (ANOVA one way followed by Dunnet test).
b
c
By another hand, considering the semi-folded conformer III,
two other heterocycles were designed. The phtalazinone 9 (direct
bridging the imine carbon onto ortho position of benzamide, mode
e) and its homologous 2,3 benzodiazepinone 10 (bridging the
imine carbon onto ortho position of benzamide through a methy-
lene group) were also selected.
The successive chemical methodologies yielding the com-
pounds 5–10 are described, as following.
Quinazoline 5 was prepared according to Scheme 2 starting
from the anthranilic acid 11 by a cyclization with formamidine
acetate under microwaves heat followed by chlorination of the
intermediate quinazolinone with POCl3 to furnish the chloroqui-
nazoline 12.6 Reaction of 12 with hydrazine hydrate followed by
acid catalyzed condensation of 13 with benzaldehyde generated
the desired quinazolinyl-hydrazone derivative.7 The careful analy-
sis of 1H NMR spectra of 5 demonstrated the presence of only one
imino hydrogen signal at d 8.4 ppm, similar to the shift observed
for the lead compound 3 (see Supplementary data), which was
Scheme 2. Reaction conditions: (a) formamidine acetate, EtOH, lW 120 °C, 40 min,
87%; (b) POCl3, 90 °C, 1 h, 97%; (c) NH2NH2ÁH2O, 90 °C, 6 h, 88%; (d) benzaldehyde,
EtOH, HClcat, 1 h, 92%.
Chart 1. Design of conformationally-restricted derivatives of NAH’s 3 and 4.

A. E. Kümmerle et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4963–4966
4965
obtained from the cyclization of butane-1,3-dione 20 with hydra-
zine hydrate.
Phtalazinones 9 were prepared as shown in Scheme 6. Conden-
sation of phthalic acid 23 with acetic anhydride followed by addi-
tion of hydrazine sulfate led to phtalazine-1,4-dione 22. Tosylation
of 22 produced two regioisomers 24a and 24b (ratio 6:4) which
were involved in a Suzuki reaction in presence of phenylboronic
acid14 to produce the phthalazin-1(2H)-one 9 as a mixture of
regioisomers 9a, 9b (ratio 6:4 identified by 1H NMR signal
integration).11
The synthesis of homologous derivative benzo[1,2-d]-diazepin-
1-one 10 is described in scheme 7. Starting from the commercially
available phenol 25, reaction with triflic anhydride followed by a
Sonogashira cross-coupling reaction15 with phenylacetylene under
microwaves irradiation provided the acetylene 26. Cyclization of
26 in acidic conditions produced the isochromen-1-one 27 which
was subsequently reacted with hydrazine hydrate to furnish the fi-
nal product benzo[1,2-d]diazepin-1-one 10.16
Scheme 3. Reaction conditions: (a) BOC–NH2NH2, CH3CN, 90 °C, 12 h, 92%; (b)
ethyl orthoformate, 90 °C, 4 h, 73%; (c) TFA, CH2Cl2, 1 h, 89%; (d) benzaldehyde,
EtOH, HClcat, 1 h, 87%.
Scheme 4. Reaction conditions: (a) POCl3, 100 °C, 2 h, 99%; (b) NH2NH2ÁH2O, EtOH,
90 °C, 2 h, 90%; (c) benzaldehyde, MeOH, HClcat 50 °C, 2 h, 80%; (d) DIAD, n-BuOH,
120 °C, 4 h, 64%.
Scheme 6. Reaction conditions: (a) acetic anhydride, 120 °C, 1 h; (b) NH2NH2ÁH2SO4,
DME:H2O, 90 °C, 20 h, 82% two steps; (c) tosyl chloride, pyridine, 80 °C, 6 h, 74%; (d)
phenylboronic acid, Pd(Ph3)4, Na2CO3, DME:H2O, lW 155 °C, 20 min, 77%.
attributed to the (E)-diastereomer on the basis of several previous
reports.1,8,9
The synthesis of quinazolin-4(3H)-one 6 shown in Scheme 3
started from the reaction of t-butyl carbazate with isatoic anhy-
dride (14)10 followed by a cyclization with ethyl orthoformate pro-
ducing the protected quinazolinyl derivative 15. Deprotection of 15
with TFA followed by acid catalyzed condensation of 16 with benz-
aldehyde7 furnished only the desired (E)-diastereomer derivative
6, characterized by the presence of only one imino hydrogen signal
in 1H NMR (d 8.7 ppm).8
The 1,2,4-triazolo[4,3-b]pyridazine 7 was obtained from the
pyridazinone 17 by initial treatment with POCl3, to give the 3-chlo-
ropyridazine 18,11 followed by a reaction with hydrazine hydrate
to yield the hydrazinopyridazine 19 (Scheme 4). This compound
(19) was then condensed with benzaldehyde in the presence of
catalytic amount of acid leading to the corresponding hydrazone.
Finally cyclization with DIAD produced the compound 7 in good
yield.12
The pyrazole compound 8 was obtained employing the de-
scribed regioselective N-acylation of 5-methyl-pyrazole 21 with
4-methoxybenzoyl chloride (Scheme 5).13 This intermediate was
Scheme 7. Reaction conditions: (a) triflic anhydride, CH2Cl2, Et3N, 0 °C, 1 h, 93%; (b)
phenylacetylene, CH3CN, Et3N, PdCl2(PPh3)2, PPh3, W 120 °C, 20 min, 89%; (c) TFA,
6 h, 89%. (d) NH2NH2ÁH2O, n-BuOH, 90 °C, 6 h, 79%.
l
Scheme 5. Reaction conditions: (a) NH2NH2ÁH2O, EtOH, 4 h, 92%; (b) 4-methoxybenzoyl chloride, pyridine, 3 h, 74%.

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A. E. Kümmerle et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4963–4966
Figure 1. Structure–activity relationship between the NAH and cyclic compounds 3, 4, 6 and 8. HI—hydrophobic interactions, HBA—hydrogen bond acceptor, HBD—hydrogen
bond donor. (A) Putative pharmacophore model for the NAH 3 and N-methyl-NAH 4. (B) Compounds 6 and 8 fitted in putative pharmacophore model of original NAHs 3 and
4. (C) Superposition of NAHs 3 (yellow) and 4 (green) and cyclic compounds 6 and 8.
Among the 6 synthesized heterocycles, that is, 5, 6, 7, 8, 9a/9b
and 10, considered as putative 3 and 4 NAH biomimetics, two of
them (6, 8) presented similar analgesic properties, in vivo, com-
pared to the NAH lead compounds in the AcOH-induced abdominal
constrictions test using oral administrations in mice (Table 1).17
They were around two times more potent than 3 showing that
for these two new derivatives, we were able to improve their bio-
activity despite the conformational difference between both clas-
ses of compounds. The others four tested compounds (5, 7, 9a/9b
(as a mixture of regioisomers) and 10) did not present significant
activity compared to 3 and 4 in this assay.
Acknowledgments
Thanks are due to CAPES-COFECUB (2260/06-9), CNPq (INCT-
INOFAR, BR.), PRONEX (BR.) and FAPERJ (BR.) for financial support
and fellowships.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2009.07.075.
To evaluate the similarity of the two new heterocyclic scaffolds
(6, 8) with the original lead compounds (3, 4), these compounds
were first sketched in the BioMedCAche 6.0 software.18 Then, the
local and global energy minimizations were obtained with semi-
empirical AM1 method using dihedral angle search in a 24 steps
of 15 degrees by dihedral angle (Fig. 1). The results demonstrated
the typically difference between the NAH and the N-methyl-
NAH,19 as described for aromatic methyl amides:20 the N-methyl-
ation leads to an amide bond rotation generating a synperiplanar
conformation, as seen for LASSBio-1385 (4).19 After we have done
a putative pharmacophore model for 3 and 4 (Fig. 1A) and we were
able to identify that LASSBio-1418 (8) and LASSBio-1419 (6) fit per-
fectly in the models made from LASSBio-575 (3) and LASSBio-1385
(4), respectively. This result validated the initial structural design
strategy to exploit the conformational differences between the
NAH and N-methyl-NAH derivatives (Fig. 1B). In addition, the
alignment of the central NAH framework of the lead compounds
3 and 4 with the corresponding heterocyclic scaffolds in 8 and 6
confirmed the correlation between the NAH and the mimic com-
pounds with a RMS ranging from 0.0956 (4 and 6) to 0.0161 (3
and 8) (Fig. 1C).
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The use of conformational restriction in optimization of NAH
compounds produced two original analgesic compounds (6, 8)
which present scaffolds that have never been reported for this
pharmacological activity, and now it can be applied to different
NAH derivatives, a structure easily accessed that may present
numerous pharmacological profiles.
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