Novel ring systems: Spiro[cycloalkane] derivatives of triazolo-and tetrazolo-pyridazines

Article abstract of DOI:10.3390/molecules26082140

In orderto synthesize new pyridazine derivatives anellated with different nitrogen hetero-cyclic moieties, spiro[cycloalkane]pyridazinones were transformed into the corresponding thioxo derivatives via a reaction with phosphorus pentasulfide. The reaction of the formed 2,3-diazaspiro[5.5] undec-3-ene-1-thiones with hydrazine provided the corresponding 1-hydrazono-2,3-diazaspiro[5.5] undec-3-ene, whose diazotization led to the desired spiro[cyclohexane-1,8^′-tetrazolo[1,5-b]pyridazines. The reaction of dihydropyridazinethiones with benzhydrazide afforded the corresponding 7H-spiro[[1,2,4]triazolo[4,3-b]pyridazin-8,1^′-cyclohexanes]. As a result of our work, seven new pyri-dazinethione intermediates were prepared, which served as starting materials for the synthesis of two kinds of new ring systems: tetrazolo-pyridazines and triazolo-pyridazines. The six new annulated derivatives were characterized by physicochemical parameters. The new N-heterocycles are valuable members of the large family of pyridazines.

Full text of DOI:10.3390/molecules26082140

molecules
Article
Novel Ring Systems: Spiro[Cycloalkane] Derivatives of
Triazolo- and Tetrazolo-Pyridazines
Csilla Sepsey Für 1, Gergo˝ Riszter 1, Áron SzigetvárI 2, Miklós Dékány 2, György Keglevich 1 , László HazaI 1
and Hedvig BölcskeI 1,
*
1
Department of Organic Chemistry and Technology, Budapest University of Technology and Economics,
H-1111 Budapest, Hungary; sepsey.fur.csilla@vbk.bme.hu (C.S.F.); riszter93@gmail.com (G.R.);
keglevich.gyorgy@vbk.bme.hu (G.K.); hazai.laszlo@vbk.bme.hu (L.H.)
Gedeon Richter Plc. Budapest X, Gyömro˝i út 19-21, 10 P.O. Box 27, H-1475 Budapest, Hungary;
szigetvaria@richter.hu (Á.S.); m.dekany@richter.hu (M.D.)
2
*
Correspondence: bolcskei.hedvig@vbk.bme.hu; Tel.: +36-1-463-2229
Abstract: In orderto synthesize new pyridazine derivatives anellated with different nitrogen hetero-
cyclic moieties, spiro[cycloalkane]pyridazinones were transformed into the corresponding thioxo
derivatives via a reaction with phosphorus pentasulfide. The reaction of the formed 2,3-diazaspiro[5.5]
undec-3-ene-1-thiones with hydrazine provided the corresponding 1-hydrazono-2,3-diazaspiro[5.5]
0
undec-3-ene, whose diazotization led to the desired spiro[cyclohexane-1,8 -tetrazolo[1,5-b]pyridazines.
The reaction of dihydropyridazinethiones with benzhydrazide afforded the corresponding 7H-
spiro[[1,2,4]triazolo[4,3-b]pyridazin-8,10-cyclohexanes]. As a result of our work, seven new pyri-
dazinethione intermediates were prepared, which served as starting materials for the synthesis of two
kinds of new ring systems: tetrazolo-pyridazines and triazolo-pyridazines. The six new annulated
derivatives were characterized by physicochemical parameters. The new N-heterocycles are valuable
members of the large family of pyridazines.
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Citation: Sepsey Für, C.; Riszter, G.;
SzigetvárI, Á.; Dékány, M.; Keglevich,
G.; HazaI, L.; BölcskeI, H. Novel Ring
Systems: Spiro[Cycloalkane]
Keywords: N-heterocycles; pyridazine derivatives; thionation; diazotization; triazolo-pyridazines;
Derivatives of Triazolo- and
tetrazolo-pyridazines
Tetrazolo-Pyridazines. Molecules 2021,
26, 2140. https://doi.org/10.3390/
molecules26082140
Academic Editor: María
Ángeles Castro
1. Introduction
Pyridazine derivatives are representative members of N-heterocycles [
number of pyridazines show various types of bioactivity [ ]. For example,
sulfamethoxypyridazine is an old sulfonamide antibacterial drug [ ], while hydralazine
(Apresoline) is a well-known antihypertensive agent [ ]. The calcium sensitizer levosimen-
dan is useful in congestive heart failure [10]. The monoamine oxidase (MAO) inhibitor is
induced by minaprine [11 12] and the tricyclic pipofezine (Azaphen) [13] are well-known
antidepressants. The aldose-reductase inhibitor zopolrestat was developed for treating
diabetic neuropathy [14]. The pyridazines under development are also noteworthy. The
anaplastic lymphoma kinase (ALK) inhibitor ensartinib is in Phase II clinical trials [15].
The gonadotropin releasing hormone (GnRH) receptor antagonist relugolix (Relumina)
was approved for the treatment of uterine fibroids [16]. Talazoparib (Talzenna) is a poly
adenosine diphosphate (ADP) ribose polymerase (PARP) inhibitor, which was developed
for treating advanced breast cancer [17]. Talazoparib has a similar phthalazin-1(2H)-one
motif with that found in the other PARP inhibitor olaparib (Lynparza) [18] (Figure 1).
The spirocycles have recently gained more attention, as they usually have a high Fsp3
character, and the three-dimensionality is better in the case of flat aromatic rings. The use
of spiro building blocks better optimizes physicochemical parameters, structural novelty,
and higher patentability. There are well-known examples among the spiro compounds, e.g.,
the anxiolytic agent buspirone, the angiotensin receptor blocker irbesartan, the antifungal
natural product griseofulvin, or the spironolactone with sterane skeleton. The кopioid
1,2]. A large
3–7
8
Received: 10 March 2021
Accepted: 5 April 2021
Published: 8 April 2021
9
,
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright:
© 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Molecules 2021, 26, 2140. https://doi.org/10.3390/molecules26082140
https://www.mdpi.com/journal/molecules

Molecules 2021, 26, 2140
2 of 12
agonist enadoline seemed to be the most potent кselective analgesic. Most of the recently
published spiro compounds contain five and six membered rings, but there are examples
for 4-membered or 7-membered spirocyclic systems too [19–23].
Figure 1. Pyridazine derivatives under clinical development: ensartinib, relugolix, talazoparib, and olaparib.
Realizing that the use of the nitrogen containing heterocycles and the spiro motif
may be advantageous, a few spiro[cycloalkane]pyridazinone derivatives were synthe-
sized by us (Scheme 1) [24
(2-oxaspiro[4.4]nonane-1,3-dione (1a) and 2-oxaspiro[4.5]-1,3-dione (1b)) were converted
to the desired keto-carboxylic acids ( and ) either by the Friedel–Crafts reaction or the
Grignard reaction. This was followed by the ring closure with hydrazine hydrate in reflux-
,25]. Depending on the substituents, the starting anhydrides
2
3
ing ethanol to give the corresponding pyridazinone derivatives (4a–d, 4e and 5a,b) in high
yields [24,25].
Scheme 1. Synthesis of spiro[cycloalkane]pyridazinones (4a–d and 5a,b) [24
,
25]; (a) 1a,b (1.0 mmol), Friedel–Crafts reaction:
◦
AlCl3 (3.0 mmol), ArH derivative (3.0 mmol), 0 C (30 min) -> room temperature (RT) (24 h); Grignardreaction: Grignard
reagent (1.0 mmol), 0 ◦C (30 min) -> RT (24 h); (b) 2,3 (0.80 mmol), hydrazine hydrate (2.40 mmol), EtOH, reflux, (4 h);
(c) 4a–d, 5a,b isolated yields after thin layer chromatography (TLC) purification: 35–97% [24,25].
In this work, we described the use of spiro[cycloalkane]pyridazinone derivatives (4a–
d,
5a,b) in the synthesis of new triazolo-pyridazine and tetrazolo-pyridazine derivatives
via the corresponding thioxo intermediates.

Molecules 2021, 26, 2140
3 of 12
2. Results and Discussion
Our plan was to synthesize derivatives, where the pyridazine ring was fused with
another N-heterocyclic moiety (9 and 10).
2.1. Synthesis of Pyridazinethiones
Phosphorus pentasulfide or the Lawesson reagent may be used for the thionation of an
amide function [26]. The earlier described spiro[cycloalkane]pyridazinones (4a–d and 5a,b
reacted with phosphorus pentasulfide in the refluxing toluene. According to thin layer
chromatography (TLC), the starting material was consumed after 6–8 h. After the workup
comprising extraction, concentration, and preparative TLC purification, the products (6a–d
and 7a,b) were isolated in yields of 40–89% (Scheme 2). The new compounds (6a–d and
7a,b) were characterized by 1H and 13C nuclear magnetic resonance spectroscopy (NMR),
as well as high resolution mass spectrometry (HRMS).
)
Scheme 2. Thionation reaction of the spiro[cycloalkane]pyridazinones (4a–d and 5a,b); (a) 4a–d, 5a,b (1.0 mmol), P2S5 (3.0
mmol), PhMe, reflux, (6–8 h); (b) 6a–d, 7a,b isolated yields after TLC purification: 40–89%.
During the preparation of the p-methoxyphenyl[spirocyclohexane]pyridazinone (4a),
the isomeric pyridazinone derivative (4e) was isolated as a byproduct. The formation
of the two isomers was explained earlier [24]. The thionation reaction with phosphorus
pentasulfide led to the corresponding pyridazinethione (6e) in a yield of 14% (Scheme 3).
Scheme 3. Preparation of 1-(4-methoxyphenyl)-2,3-diazaspiro[5.5]undec-1-ene-4-thione (6e): (a) 1a (1.0 mmol), Friedel–
Crafts reaction: AlCl3 (3.0 mmol), anizole (3.0 mmol), 0 ◦C (30 min) -> RT (24 h); (b) 2a,e (0.80 mmol), hydrazine hydrate
(2.40 mmol), EtOH, reflux, (4 h); (c) 2a,e (1.0 mmol), P2S5 (3.0 mmol), PhMe, reflux, (6–8 h); (d) 2e isolated yield after TLC
purification: 14%.

Molecules 2021, 26, 2140
4 of 12
2.2. Preparing the Tetrazole Derivatives through Hydrazones
After reacting the thioxo derivatives 6a–c with hydrazine hydrate, the corresponding
hydrazones 8a–c were isolated in 48–61% yields. The 4-(phenyl)-2,3-diazaspiro[5.5]undec-
3-ene-1-thiones (6a–c) and hydrazine hydrate in THF had to be stirred at reflux for 5 h. It
was observed that compounds (8a–c) were unstable when standing at room temperature.
After a week, they began decomposing. However, after preparation, intermediates 8a–c
were immediately reacted further in a diazotization reaction. The tetrazolo-pyridazinones
(
9a–c) were obtained in 45–77% yields (Scheme 4) after a preparative TLC purification.
Compounds 8a–c and 9a–c were new and were characterized by 1H and 13C NMR, as well
as HRMS. A similar method was applied in the sphere of benzodiazepines, where the
extended conjugation helped the transformation [27]. In the case of spiro compounds 8a–c
,
the reaction was new.
Scheme 4. Synthesis of the hydrazono-pyridazinone (8a–c) and tetrazole derivatives (9a–c) (a) 6a–c (0.40 mmol), hydrazine
◦
monohydrate (1.20 mmol), tetrahydrofuran (THF), reflux, (5 h); (b) 8a–c (0.34 mmol), NaNO2 (0.51 mmol), 0.5 N HCl, 5 C,
(2 h); (c) 8a–c isolated yields after TLC purification: 48–61%; (d) 9a–c isolated yields after TLC purification: 45–77%.
Table 1 summarizes the most important physicochemical parameters of the tetrazolo-
pyridazinones (9a–c). All compounds revealed excellent Fsp3 character values: 0.5 ± 0.05
.
The logP (3.1–3.7) and topological polar surface area (TPSA) values (52.7–61.9) were sat-
isfactory according to the Lipinski rules and Lovering studies [28–32]. For comparison,
the launched pyridazinone derivatives sometimes have lower Fsp3 characters (e.g., hy-
dralazine: 0, zopolrestate: 0.16, levosimendan: 0.21), while pipofezine and minaprine have
higher Fsp3 characters (e.g., 0.38 and 0.41, respectively). The drugs under development
showed similar Fsp3 values (i.e., talazoparib: 0.16, relugolix: 0.21, ensartinib: 0.27, olaparib:
0.34 (Table 2)).
Table 1. The physicochemical parameters of the hydrazone derivatives (8a–c and 9a–c).
Starting Material
R
Product
Fsp3
LogP
ClogP
TPSA
8a
8b
8c
OMe
Me
Cl
9a
9b
9c
0.50
0.50
0.47
3.08 *
3.47 *
3.70 *
3.55
4.13
4.34
61.91
52.68
52.68
The physicochemical parameters were calculated using ChemDraw, but only Molinspiration software was suitable
for calculating logP values *.

Molecules 2021, 26, 2140
5 of 12
Table 2. The physicochemical parameters of drugs and drugs under development a.
Drug
Fsp3
LogP
ClogP
TPSA
Hydralazine
Zopolrestate
Levosimendan
Pipofezin
0
0.73
4.37
1.23
1.98
2.70
2.58
4.98
4.04
2.02
1.17
2.55
1.91
3.33
3.19
0.35
4.58
5.22
1.24
62.77
82.33
113.43
43.67
49.22
81.45
128.17
121.41
82.08
0.16
0.21
0.38
0.41
0.16
0.21
0.27
0.34
Minaprine
Talazoparib a
Relugolix a
Ensartinib a
Olaparib a
The physicochemical parameters were calculated using ChemDraw, a drugs under development.
2.3. Preparing the Triazole Derivatives from Thioxo Compounds with Acid Hydrazides
Our next purpose was to synthesize triazole derivatives starting from the thioxo
compounds (6a–c). The thioxo compounds (6a–c) were refluxed with benzoic acid hy-
drazide (11) in n-butanol. After evaporation and chromatographic purification, the triazole-
pyridazinone derivatives (10a–c) were isolated in yields of 14–42% (Scheme 5). This annula-
tion technique was also applied in the sphere of benzodiazepines [33], where the extended
aromatic conjugation may be advantageous for the reaction. Similarly to the preparation of
tetrazoles, this reaction is new in case of spiro derivatives 10a–c. After the preparative TLC
chromatographic separation, the three new products (10a–c) were characterized by 1H and
13C NMR, as well as HRMS. Table 3 summarizes the physicochemical parameters of the
triazolo-pyridazinones (10a–c). The introduction of an additional aromatic ring increased
the log P and clogP values, and decreased the Fsp3 character.
Scheme 5. Reaction of thioxo-derivatives (6a–c) with benzoic acid hydrazide (11) (a) 6a–c (0.73 mmol),
11 (2.20 mmol), n-BuOH, reflux, (84 h); (b) (c) 10a–c isolated yields after TLC purification: 14–42%.
Table 3. The physicochemical parameters of the triazole derivatives (10a–c).
Starting Material
R
Product
Fsp3
logP
ClogP
TPSA
6a
6b
6c
OMe
Me
Cl
10a *
10b *
10c *
0.35
0.35
0.32
5.33
5.72
5.95
4.36
4.94
5.16
49.55
40.32
40.32
The physicochemical parameters were calculated using ChemDraw, but only Molinspiration software was suitable
for calculating logP values *.

Molecules 2021, 26, 2140
6 of 12
3. Materials and Method
3.1. LC-MS Analysis, TLC, and Preparative TLC
Liquid chromatography-mass spectrometry (LC-MS) spectra were recorded on an
Agilent 1100/ZQMSD (Santa Clara, CA, USA) instrument equipped with UV (220 nm
and 254 nm) and MSAP+ and PL-ELS detectors. TLC was carried out using Kieselgel 60
F254 (Merck 1.05554.0001, Merck KGaA, Darmstadt, Germany). The analytical samples for
NMR and HRMS studies were purified by preparative TLC using Kieselgel 60 F254 (Merck
1.07748.1000, Merck KGaA, Darmstadt, Germany) coated glass plates.
3.2. NMR Spectroscopy
NMR measurements were performed on a Varian VNMRS 400 MHz (Varian, Palo
Alto, CA, USA) NMR spectrometer equipped with a 15N-31P(1H-19F) 5 mm one NMR
room temperature probe, a Varian VNMRS 500 MHz NMR spectrometer equipped with
a 1H (13C/15N) 5 mm pulsed field gradient (PFG) Triple Resonance 13C Enhanced Cold
Probe, a Varian VNMRS 800 MHz NMR spectrometer equipped with a 1H(13C/15N) Triple
Resonance 13C Enhanced Salt Tolerant Cold Probe (Varian, Inc., Palo Alto, CA, USA), a
Bruker Avance III HDX 500 MHz NMR spectrometer equipped with a 1H (13C/15N) 5 mm
TCI CryoProbe, and a Bruker Avance III HDX 800 MHz NMR spectrometer equipped
with a 1H-19F(13C/15N) 5 mm TCI CryoProbe (Bruker Corporation, Billerica, MA, USA).
1H and 13C chemical shifts are given on the delta scale as parts per million (ppm) with
tetramethylsilane (TMS) (1H, 13C) or dimethylsulfoxide-d6(13C) as the internal standard
1
(0.00 ppm and 39.4 ppm, respectively). H-1H, direct 1H-13C, and long-range 1H-13C scalar
spin-spin connectivity were established from 2D. correlation spectroscopy, total correla-
tion spectroscopy, heteronuclear single quantum coherence and heteronuclear multiple
1
bond correlation (COSY, TOCSY, HSQC, and HMBC) experiments. H-1H spatial prox-
imities were determined using two-dimensional nuclear Overhauser effect spectroscopy
or rotating-frame Overhauser effect spectroscopy (NOESY or ROESY) experiments. 15N
Chemical shifts were referenced to nitromethane (0.0 ppm) and were obtained from 1H-15N
HMBC measurements. All pulse sequences were applied using the standard spectrometer
software package. All experiments were performed at 298 K. NMR spectra were processed
using VnmrJ 2.2 Revision C (Varian, Inc., Palo Alto, CA, USA), Bruker TopSpin 3.5 pl 6
(Bruker Corporation, Billerica, MA, USA) and ACD/Spectrus Processor version 2017.1.3
(Advanced Chemistry Development, Inc., Toronto, ON, Canada).
3.3. Mass Spectrometry
HRMS and MS-MS analyses were performed on a Thermo Velos Pro Orbitrap Elite
(Thermo Fisher Scientific, Bremen, Germany) system. The ionization method was ESI
operated in a positive ion mode. The protonated molecular ion peaks were fragmented
by collisison-induced dissociation (CID) at a normalized collision energy of 35%. For the
CID experiment helium was used as the collision gas. The samples were dissolved in
methanol. Data acquisition and analysis were accomplished with Xcalibur software version
2.0 (Thermo Fisher Scientific, Bremen, Germany).
3.4. Synthesis of the Starting Materials
The preparation of the starting pyridazinone derivatives (4a–e and 5a,b) was described
earlier [24,25].
3.5. General Procedure for the Synthesis of the Pyridazine-Thiones (6a–e and 7a,b)
The pyridazinone derivatives (4a–e and 5a,b) (1.0 mmol) were dissolved in toluene
(60 mL) and phosphorus pentasulfide (0.67 g, 3.0 mmol) was added. The reaction mixture
was stirred at reflux for 6–8 h. After the completion of the reaction, the mixture was washed
with 5% NaHCO3 solution (80 mL), and then with distilled water (80 mL). The organic
layer was dried over MgSO4 and then concentrated. The crude product was purified by

Molecules 2021, 26, 2140
7 of 12
preparative thin layer chromatography (eluent: heptane:dichloromethane:methanol/5:5:1)
to give the thioxo derivatives as a yellow solids (6a–e and 7a,b).
4-(4-Methoxyphenyl)-2,3-diazaspiro[5.5]undec-3-ene-1-thione
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.60, 1H-NMR (499.9 MHz; CDCl3)
= 1.33–2.04 (m, 10H, cyclohexyl); 2.79 (s, 2H; H2-5); 3.86 (s, 3H; C(40)-OCH3); 6.97
(m, 2H; H-30, H-50); 7.78 (m, 2H; H-20, H-60); 10.28 (br s, 1H; NH-2) ppm; 13C-NMR (125.7
(6a). Yield
=
74%,
δ
MHz; CDCl3)
δ
= 20.2 (C-8, C-10); 025.4 (C-9); 27.6 (C-5); 33.44 (C-7, C-11); 41.14 (C-6);
0
0
0
0
0
55.45 (C(4 )-O
C
H3); 114.22 (C-3 , C-5 ); 127.74 (C-2 , C-6 ); 127.97 (C-1 ); 154.54 (C-4), 161.61
(C-40); 204.34 (C-1) ppm; HRMS: M + H = 289.13657 (delta =
−
1.2 ppm; C16H21ON2S).
HR-ESI-MS-MS (CID = 35%; rel. int. %): 272(4); 255(100); 255(46); 241(4); 166(8); 156(10);
134(6); 121(6).
1-(4-Metoxyphenyl)-2,3-diazaspiro[5.5]undec-1-ene-4-thione
(
6e). Yield
=
14%,
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.40, 1H NMR (399.8 MHz; CDCl3)
δ
= 1.10–1.24 (m; 1H; Hax-9); 1.45–1.60 (m; 4H; H2-8, H2-10); (br s; 1H; NH-3); 1.61–1.68
(m; 4H; H2-7, H2-11);01.69–1.75 (m; 1H; Heq-9); 3.08 (s; 2H; H2-5); 3.84 (s; 3H; C(40)-OCH3);
6.90–6.95 (m; 2H; H-3 , H-5 ); 7.30–7.35 (m; 2H; H-2 , H-6 ); 10.05 (br s; 1H; NH-3) ppm; 13
C
0
0
0
NMR (100.5 MHz; CDCl3)
δ
= 20.20(C-8, C-10); 25.4 (C-9); 31.4 (C-7, C0-11); 36.8 (C-6); 42.7
0
0
0
0
0
(C-5); 55.4 (C(4 )-O
C
H3); 113.7 (C-3 , C-5 ); 127.5 (C-1 ); 129.5 (C-2 , C-6 ); 160.4 (C-4 ); 165.8
(C-1); 193.9 (C-4) ppm; HRMS: M + H = 289.13769 (delta = 2.7 ppm; C16H21ON2S). MS-MS
(CID = 45%; rel. int. %): 272(6); 257(6); 255(11); 189(38); 181(39); 121(100); 113(12).
4-(p-Tolyl)-2,3-diazaspiro[5.5]undec-3-ene-1-thione
(
6b).
Yield
=
41%,
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.60, LC-MS: UV (220 nm) (M + H = 273):
100%, UV (254 nm) (M + H = 273): 100%, 1H NMR (499.9 MHz; DMSO-d6)
δ = 1.16–1.84
(m, 10H, cyclohexyl); 2.35 (s, 3H; C(40)-CH3); 2.83 (s, 2H; H2-5); 7.29 (m, 2H; H-30, H-50);
7.82 (m, 2H; H-20, H-60); 12.69 (br s, 1H; NH-2) ppm; 13C-NMR (125.7 MHz; DMSO-d6)
δ = 20.35 (C-8, C-10); 20.86 (C(40)-
(C-6); 125.93 (C-2 , C-6 ); 129.28 (C-3 , C-5 ); 132.68 (C-1 ); 140.12 (C-4 ); 154.26 (C-4); 202.78
C
H3); 025.26 (C-9); 206.39 (C-5); 32.75 (C-7, C-11); 40.05
0
0
0
0
(C-1) ppm; HRMS: M + H = 273.14235 (delta =
rel. int. %): 256(5); 241(53); 240(100); 239(75); 225(4); 186(4); 171(5); 166(11); 159(18); 156(12);
133(6); 118(5).
−
1.6 ppm; C16H21N2S). MS-MS (CID = 45%;
4-(4-Chlorophenyl)-2,3-diazaspiro[5.5]undec-3-ene-1-thione
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.66, LC-MS: UV (220 nm) (M + H = 293):
100%, UV (254 nm) (M + H = 293): 100%, 1H NMR (499.9 MHz; DMSO-d6)
= 1.16–1.84 (m,
10H, cyclohexyl); 2.86 (s, 2H; H2-5); 7.54 (m, 2H; H-30, H-50); 7.95 (m, 2H; H-20, H-60); 12.78
(brbr s, 1H; NH-2) ppm; 13C-NMR (125.7 MHz; DMSO-d6)
= 20.28 (C-8, C-10); 25.23 (C-9);
(6c). Yield
=
55%,
δ
δ
0
0
0
0
0
26.33 (C-5); 32.85 (C-7, C-11); 40.05 (C-6) 127.76 (C-2 , C-6 ); 128.72 (C-3 , C-5 ); 134.31 (C-1 );
134.87 (C-40); 153.11 (C-4); 203.20 (C-1) ppm; HRMS: M + H = 293.08752 (delta = 0.5 ppm;
C15H18N2ClS). HR-ESI-MS-MS (CID = 45%; rel. int. %): 276(5); 259(100); 191(23); 179(28);
166(6); 154(5).
4-(3,4-Dimethoxyphenyl)-2,3-diazaspiro[5.5]undec-3-ene-1-thione (6d). Yield = 40%,
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.40, 1H NMR (499.9 MHz; CDCl3)
δ
= 1.27–1.35 (m; 1H; Hax-9); 1.35–1.45 (m; 2H; Hax-8, Hax-10); 1.50–1.56 (m; 2H; Heq-7,
Heq-11); 1.67–1.75 (m; 3H; Heq-8, Heq-10, Heq-9); 2.01–2.08 (m; 2H; Hax-7, Hax-11); 2.79
(s; 2H; H2-5); 3.94 (s; 3H; C(40)-OCH3); 3.95 (s; 3H; C(30)-OCH3); 6.91 (d, J = 8,4 Hz; 1H;
H-50); 7.29 (dd, J = 8.4, 2.1 Hz; 1H; H-60); 7.50 (d, J = 2.1 Hz; 1H; H-20); 10.11 (br s; 1H;
NH-2) ppm; 13C-NMR (125.7 MHz; CDCl3) δ = 21.2 (C-8, C-10); 25.4 (C-9); 27.4 (C-5); 33.5
(C-7, C-11); 41.2 (C-6); 55.99, 56.02 (C(30)- CH3, C(40)-O H3); 108.1 (C-20); 110.5 (C-50);
O C
119.8 (C-60); 128.2 (C-10); 149.4 (C-30); 151.5 (C-40); 154.4 (C-4); 204.6 (C-1) ppm; HRMS:
M + H = 319.14735 (delta = 0.39 ppm; C17H23O2N2S). MS-MS (CID = 65%; rel. int. %):
−
304(5); 302(5); 287(100); 286(75); 285(45); 271(10).
9-(4-Methoxyphenyl)-7,8-diazaspiro[4.5]dec-8-ene-6-thione
(7a). Yield
=
71%,
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.40, 1H NMR (499.9 MHz; CDCl3)

Molecules 2021, 26, 2140
8 of 12
δ
= 1.56–1.62 (m; 2H; Hx-1, Hx-4); 1.68–1.77 (m; 2H; Hx-2, Hx-3); 1.87–1.96 (m; 2H; Hy-2,
0
Hy-3); 2.28–2.35 (m; 2H; Hy-1, Hy-4); 2.68 (s; 2H; H2-10); 3.86 (s; 3H; C(4 )-OCH3); 6.93–6.97
(m; 2H; H-30, H-50); 7.71–7.75 (m; 2H; H-20, H-60); 10.13 (br s; 1H; NH-7) ppm; 13C-NMR
(125.7 MHz; CDC0l3)
δ
= 25.5 (C-2, C-3); 32.9 (C-10); 38.8 (C-1, C-4); 48.9 (C-50); 55.5 (C(40)-
0
0
0
0
O
C
H3); 114.2 (C-3 , C-5 ); 127.7 (C-2 , C-6 ); 128.0 (C-1 ); 155.2 (C-9); 161.6 (C-4 ); 204.2 (C-6)
ppm; HRMS: M + H = 275.12072 (delta =
int. %): 259(3); 242(100); 227(5); 201(6); 152(7); 142(7); 134(3).
−
1.9 ppm; C15H19ON2S). MS-MS (CID = 45%; rel.
9-(3,4-Dimethoxyphenyl)-7,8-diazaspiro[4.5]dec-8-ene-6-thione
(
7b). Yield = 89%,
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.40, 1H-NMR (499.9 MHz; CDCl3)
δ
= 1.57–1.63 (m; 2H; Hx-1, Hx-4); 1.69–1.78 (m; 2H; Hx-2, Hx-3); 1.87–1.96 (m; 2H; Hy-2,
Hy-3); 2.29–2.36 (m; 2H; Hy-1, Hy-4); 2.69 (s; 2H; H2-10); 3.93 (s; 3H), 3.95 (s; 3H): C(30)-
OCH3, C(40)-OCH3; 6.89 (d, J = 8.4 Hz; 1H; H- 50); 7.23 (dd, J = 8.4, 2.0 Hz; 1H; H-60); 7.47
(d, J = 2.0 Hz; 1H; H-2 ); 10.23 (br s; 1H; NH-7) ppm; 13C-NMR (125.7 MHz; CDCl3)
δ
= 25.5
H3, C(40)-O
H3);
108.1 (C-20); 110.5 (C-50); 119.8 (C- 60); 128.2 (C-10); 149.3 (C-30); 151.4 (C-40); 155.1 (C-9);
204.2 (C-6) ppm; HRMS:M + H = 305.13149 (delta = 1.10 ppm; C16H21O2N2S). MS-MS
0
(C-2, C-3); 32.8 (C-10); 38.8 (C-1, C-4); 49.0 (C-5); 55.98, 56.02 (C(30)-O
C
C
−
(CID = 35%; rel. int. %): 288(5); 273(100); 272(80); 271(38); 257(12); 231(18); 164(8); 138(7).
3.6. General Procedure for the Preparation of Hydrazones (8a–c)
A solution of hydrazine monohydrate (0.10 mL, 1.2 mmol) in THF (5 mL) was added
to the corresponding pyridazinone derivatives (6a–c) (0.40 mmol) in THF (15 mL) drop-
wise. The reaction mixture was stirred at reflux for 5 h, then the solvent was evapo-
rated. The residue was dissolved in dichloromethane (20 mL) and washed with distilled
water (2
×
10 mL). The organic layer was dried over MgSO4, filtered and evaporated.
The crude product was purified by preparative thin layer chromatography (eluent: hep-
tane:dichloromethane:methanol/5:5:1) to give the hydrazones (8a–c).
1-Hydrazono-4-(4-Methoxyphenyl)-2,3-diazaspiro[5.5]undec-3-ene (8a). Yield: 48%,
1
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.30, H NMR (499.9 MHz; DMSO-d6)
δ
= 1.20–1.64 (m, 10H, cyclohexyl); 2.62 (s, 2H, H-5); 3.78 (s, 3H, C(40)-OCH3); 5.01 (br
s, 2H, NH2-2”); 6.95 (m, 2H, H-30, H-50); 7.69 (m, 2H, H-20, H-60); 9.32 (br s, 1H, NH-2)
ppm; 13C-NMR (125.7 MHz; DMSO-d6)
δ
= 20.7 (C(40)-CH3); 21.1 (C-8, C-10); 25.7(C-9);
31.0 (C-5); 32.6 (C-6); 33.0 (C-7, C-11); 55.1 (C(40)-OCH3); 113.7 (C-30, C-50); 126.0 (C-20,
C-60);130.2 (C-10); 142.8 (C-4); 144.8 (C-1); 159.2 (C-40) ppm; HRMS: M + H = 287.18646
(
delta = −0.6 ppm; C16H23ON4). HR-ESI-MS-MS (CID = 35%; rel. int. %): 270(99); 255(21);
242(47); 228(22); 216(13); 186(21); 164(100); 148(10); 133(19); 121(23).
1-Hydrazono-4-(p-tolyl)-2,3-diazaspiro[5.5]undec-3-ene 8b).
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.27. 1H-NMR (499.9 MHz; DMSO-d6)
= 1.18–1.72 (m, 10H, cyclohexyl); 2.31 (s, 3H, C(40)-CH3); 2.62 (s, 2H, H-5); 5.07 (br s, 2H,
NH2-2”); 7.19 (m, 2H, H-30, H-50); 7.64 (m, 2H, H-20, H-60); 9.39 (br s, 1H, NH-2) ppm; 13
NMR (125.7 MHz; DMSO-d6) = 21.1 (C-8, C-10); 25.7(C-9); 31.1 (C-5); 32.5 (C-6); 33.0
(C-7, C-11); 124.6 (C-20, C-60); 128.9 (C-30, C-50); 134.9 (C-10); 137.3 (C-40); 142.8 (C-4); 144.6
(C-1) ppm; HRMS: M + H = 271.19165 (delta = 0.3 ppm; C16H23N4). HR-ESI-MS-MS
CID = 35%; rel. int. %): 254(70); 239(45); 226(54); 212(40); 181(29); 164(100); 147(67); 131(27);
117(59); 105(24).
(
Yield:
59%,
δ
C
δ
−
(
4-(4-Chlorophenyl)-1-hydrazono-2,3-diazaspiro[5.5]undec-3-ene (8c). Yield = 61%,
1
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.50, H-NMR (499.9 MHz; DMSO-d6)
δ
= 1.25–1.58 (m, 10H, cyclohexyl); 2.64 (s, 2H, H-5); 5.12 (br s, 2H, NH2-2”); 7.43 (m, 2H,
H-30, H-50); 7.77 (m, 2H, H-20, H-60); 9.57 (br s, 1H, NH-2) ppm; 13C-NMR (125.7 MHz;
DMSO-d6)
= 21.1 (C-8, C-10); 25.7(C-9); 31.0 (C-5); 32.4 (C-6); 33.0 (C-7, C-11); 126.3 (C-20,
C-60); 128.3 (C-30, C-50); 132.4 (C-40); 136.5 (C-10); 141.4 (C-4); 144.0 (C-1) ppm; HRMS:
M + H = 291.13630 (delta = 2.8 ppm; C15H20N4Cl). HR-ESI-MS-MS (CID = 45%; rel. int.
δ
−
%): 274(38); 261(42); 259(46); 246(26); 232(35); 220(21); 204(24); 201(22); 190(100); 167(26);
164(52); 152(22); 137(82); 125(29).

Molecules 2021, 26, 2140
9 of 12
3.7. Preparation of Tetrazolo-Pyridazines (9a–c)
A solution of sodium nitrite (35.2 mg, 0.51 mmol) in water (3.8 mL) was added
dropwise to a suspension of (8a–c) (100 mg, 0.34 mmol) in 0.5 N HCI (1.22 mL) at 5 ◦C.
After stirring for 2 h, the reaction mixture was neutralized with a saturated solution of
NaHCO3 (0.40 mL) and the precipitate was filteredand it was purified by preparative
thin layer chromatography (eluent: heptane:dichloromethane:methanol/5:5:1) to give the
tetrazolo-pyridazines (9a–c).
60-(4-Methoxyphenyl)-70H-spiro[cyclohexane-1,80-tetrazolo[1,5-b]pyridazine]
(9a).
Yield = 66%, LC-MS: UV (220 nm) (M + H = 298): 100%, UV (254 nm) (M + H = 298):
100%, Rf(heptane:dichloromethane:methanol/5:5:1) = 0.42, 1H NMR (499.9 MHz; DMSO-
d6)
δ
= 1.36–1.85 (m, 10H, cyclohexyl); 3.27 (s, 2H, H-70); 3.87 (s, 3H, C(4”)-OCH3); 7.12 (m,
2H, H-3”, H-5”); 8.08 (m, 2H, H-2”, H-6”) ppm; 13C NMR (125.7 MHz; DMSO-d6)
δ = 20.98
(C-2, C-5); 24.85 (C-4); 32.28 (C-1 = C-80); 33.44 (C-2, C-6); 34.98 (C-70); 114.34 (C-3”, C-5”);
125.73 (C-1”); 129.44 (C-2”, C-6”); 149.62 (C-90);162.59 (C-4”); 164.16 (C-60) ppm; HRMS: M
+ H = 298.16613 (delta = −0.4 ppm; C16H20ON5). HR-ESI-MS-MS (CID = 40%; rel. int. %):
270(100); 242(73); 227(6); 215(8); 200(4); 174(19); 162(27); 160(18); 133(5); 121(4).
60-(p-Tolyl)-70H-spiro[cyclohexane-1,80-tetrazolo[1,5-b]pyridazine] (9b). Yield = 45%, LC-
MS: UV (220 nm) (M + H = 282): 100%, UV (254 nm) (M + H = 282): 100%
1
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.42, H-NMR (499.9 MHz; DMSO-d6)
δ
= 1.36–1.86 (m, 10H, cyclohexyl); 2.41 (s, 3H, C(4”)-CH3); 3.29 (s, 2H, H-70); 7.40 (m, 2H,
H-3”, H-5”); 8.00 (m, 2H, H-2”, H-6”) ppm; 13C-NMR (125.7 MHz; DMSO-d6)
δ = 20.97 (C-2,
C-5, C(4”)-CH3); 24.83 (C-4); 32.28 (C-1 = C-80); 33.48 (C-2, C-6); 35.13 (C-70); 129.51 (C-3”,
C-5”); 127.44 (C-2”, C-6”); 130.80 (C-1”); 142.69 (C-4”); 149.73 (C-90); 164.72 (C-60) ppm;
HRMS: M + H = 282.17121 (delta =
int. %): 254(100); 226(64); 209(7); 184(4); 170(12); 158(9); 146(17); 144(14); 117(6).
−
0.4 ppm; C16H20N5). HR-ESI-MS-MS (CID = 40%; rel.
60-(4-Chlorophenyl)-70H-spiro[cyclohexane-1,80-tetrazolo[1,5-b]pyridazine]
(9c).
Yield = 77%, LC-MS: UV (220 nm) (M + H = 302): 97%, UV (254 nm) (M + H = 302):
98% Rf(heptane:dichloromethane:methanol/5:5:1) = 0.42, 1H NMR (499.9 MHz; DMSO-d6)
δ
= 1.40–1.82 (m, 10H, cyclohexyl); 3.22 (s, 2H, H-70); 7.60 (m, 2H, H-3”, H-5”); 8.12 (m,
2H, H-2”, H-6”) ppm; 13C NMR (125.7 MHz; DMSO-d6)
δ = 20.91 (C-2, C-5); 24.80 (C-4);
32.29 (C-1 = C-80); 33.56 (C-2, C-6); 35.13 (C-70); 129.01 (C-3”, C-5”); 129.29 (C-2”, C-6”);
132.40 (C-1”); 137.19 (C-4”); 149.70 (C-90); 163.95 (C-60) ppm; HRMS: M + H = 302.11716
(
delta = 1.5 ppm; C15H17N5Cl). MS-MS (CID = 40%; rel. int. %): 274(100); 246(44); 229(6);
211(13); 190(23); 178(8); 166(13); 164(21); 137(6).
3.8. General Procedure for the Preparation of
6-(4-Substituted-phenyl)-3-phenyl-7H-spiro[[1,2,4]triazolo[4,3-b]pyridazin-8,10-cyclohexanes]
(10a–c)
Benzhydrazide (11) (300 mg, 2.2 mmol) was added to the appropriate thioxo derivative
(
6a
material disappeared (84 h). The solvent was evaporated, then the residue was taken up in
dichloromethane (15 mL). It was washed with 1% (w/w) aqueous HCl solution (2 10 mL),
–c) (0.73 mmol) in n-BuOH (25 mL). The reaction mixture was refluxed until the starting
×
and then with water (10 mL). The organic layer was dried over MgSO4, then filtered and
evaporated. The crude product was purified by preparative thin layer chromatography
(eluent: heptane:dichloromethane:methanol/5:5:1) to give the triazole derivatives (10a–c).
0
6-(4-Methoxyphenyl)-3-phenyl-7H-spiro[[1,2,4]triazolo[4,3-b]pyridazin-8,1 -cyclohexane] (10a).
Yield = 29%, LC-MS: UV (220 nm) (M + H = 373): 93%, UV (254 nm) (M + H = 373):
98%, Rf(heptane:dichloromethane:methanol/5:5:1) = 0.32, 1H-NMR (799.7 MHz; DMSO-d6)
δ = 1.45–1.85 (m, 10H, cyclohexyl); 3.14 (s, 2H, H-7); 3.85 (s, 3H, C(4”)-CH3); 7.10 (m, 2H,
H-3”, H-5”); 7.53 (m, 1H, H-4000); 7.57 (m, 2H, H-3000, H-5000); 8.01 (m, 2H, H-2”, H-6”);
8.12 (m, 2H, H-2000, H-6000) ppm; 13C-NMR (201.1 MHz; DMSO-d6)
δ
= 21.14 (C-30, C-50);
25.17 (C-40); 32.65 (C-10 = C-8); 33.63 (C-20, C-60); 34.07 (C-7); 55.39 (C(4”)-CH3); 114.25

Molecules 2021, 26, 2140
10 of 12
(C-3”, C-5”); 126.59 (C-1000); 127.03 (C-1”); 127.79 (C-2000, C-6000); 128.58 (C-3000, C-5000); 128.80
(C-2”, C-6”); 129.70 (C-4000); 148.97 (C-3); 151.18 (C-9); 161.23 (C-6); 161.86 (C-4”) ppm;
HRMS: M + H = 373.20153 (delta =
rel. int. %): 226(100); 148(11).
−
2.0 ppm; C23H25ON4). HR-ESI-MS-MS (CID = 40%;
3-Phenyl-6-(p-tolyl)-7H-spiro[[1,2,4]triazolo[4,3-b]pyridazin-8,10-cyclohexane]
(10b).
Yield = 14%, LC-MS: UV (220 nm) (M + H = 357): 87%, UV (254 nm) (M + H = 357):
85%, Rf(heptane:dichloromethane:methanol/5:5:1) = 0.32, 1H-NMR (499.9 MHz; DMSO-d6)
δ
= 1.41–1.89 (m, 10H, cyclohexyl); 2.39 (s, 3H, C(4”)-CH3); 3.16 (s, 2H, H-7); 7.37 (m, 2H,
H-3”, H-5”); 7.54 (m, 1H, H-4000); 7.58 (m, 2H, H-3000, H-5000); 7.93 (m, 2H, H-2”, H-6”); 8.12
= 20.95 (C(4”)- H3); 21.14
(m, 2H, H-2000, H-6000) ppm; 13C NMR (125.7 MHz; DMSO-d6)
δ
C
(C-30, C-50); 25.18 (C-40); 32.65 (C-10 = C-8); 33.67 (C-20, C-60); 34.21 (C-7); 126.52 (C-1000);
126.98 (C-2”, C-6”); 127.85 (C-2000, C-6000); 128.60 (C-3000, C-5000); 129.44 (C-3”, C-5”); 129.75
(C-4000); 132.09 (C-1”); 141.58 (C-4”); 149.09 (C-3); 151.21 (C-9); 161.73 (C-6) ppm; HRMS:
M + H = 357.20934 (delta = 5.5 ppm; C23H25N4). HR-ESI-MS-MS (CID = 35%; rel. int. %):
226(100); 132(8).
0
6-(4-Chlorophenyl)-3-phenyl-7H-spiro[[1,2,4]triazolo[4,3-b]pyridazin-8,1 -cyclohexane] (10c).
Yield = 42%, LC-MS: UV (220 nm) (M + H = 377): 100%, UV (254 nm) (M + H = 377): 99%,
1
Rf(heptane:dichloromethane:methanol/5:5:1) = 0.36, H NMR (499.9 MHz; DMSO-d6)
δ = 1.41–1.90 (m, 10H, cyclohexyl); 3.18 (s, 2H, H-7); 7.51–7.59 (m, 3H, H-3000, H-4000, H-5000);
7.63 (m, 2H, H-3”, H-5”); 8.05 (m, 2H, H-2”, H-6”); 8.09 (m, 2H, H-2000, H-6000) ppm; 13C-
NMR (125.7 MHz; DMSO-d6)
δ
= 21.10 (C-30, C-50); 25.15 (C-40); 32.65 (C-10 = C-8); 33.71
(C-20, C-60); 34.20 (C-7); 126.38 (C-1000); 127.90 (C-2000, C-6000); 128.64 (C-3000, C-5000); 128.83
(C-2”, C-6”); 128.94 (C-3000, C-5000); 129.83 (C-4000); 133.65 (C-1”); 136.25 (C-4”); 149.24 (C-3);
151.04 (C-9); 160.90 (C-6) ppm; HRMS: M + H = 377.15255 (delta =
HR-ESI-MS-MS (CID = 35%; rel. int. %): 226(100).
−
0.5 ppm; C22H22N4Cl).
4. Conclusions
Herein, we soughtto expand the family of spiro[cycloalkane]pyridazinones with fur-
ther derivatives by anellating the spiro[cyclohexane]pyridazinones and spiro[cyclopentane]
pyridazinones with tetrazole or triazole rings. To this end, seven new 4-substituted phenyl-
2,3-diazaspiro[5.5]undec-3-ene-1-thiones and nine substituted phenyl-7,8-diazaspiro[4.5]
dec-8-ene-6-thiones were prepared by the reaction of the spiro[cycloalkane]pyridazinones
with phosphorus pentasulfide. By treating the p-substituted 4-phenyl-2,3-diazaspiro[5.5]
undec-3-ene-1-thiones (6a–c) with hydrazine hydrate, the desired hydrazones were ob-
tained (8a–c) to give the tetrazolo-pyridazine after diazotization (9a–c). The reaction of the
p-substituted phenyldiazaspiroundecene-thiones (6a–c) with benzhydrazide (11) yielded
the triazolo-pyridazines (10a–c). Eventually two kinds of new ring systems were prepared:
a tetrazolo-pyridazine and triazolo-pyridazines.
Supplementary Materials: The followings are available, Figure: NMR and HRMS spectrum.
Author Contributions: C.S.F. and H.B. planned the experiments. C.S.F. and G.R. carried out the
experimental work. H.B. managed the project and wrote the paper. Á.S. measured the NMR spectra,
M.D. performed the HRMS measurements. L.H. was the consultant. G.K. refined the manuscript. All
authors have read and agreed to the published version of the manuscript.
Funding: C.S.F. is grateful for the support of the Gedeon Richter’s Centenárium Foundation.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available in Supplementary
information.
Acknowledgments: The authors are grateful to Zoltán Urbán and Klára Szlifka-Petho˝ for the LC-
MS studies.

Molecules 2021, 26, 2140
11 of 12
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds prepared are available from the authors.
References
1.
2.
Wermuth, C.G. Are pyridazines privileged structures? Med. Chem. Comm. 2011, 2, 935–941. [CrossRef]
Castle, R.N. (Ed.) The Chemistry of Heterocyclic Compounds Pyridazines; Wiley: Hoboken, NJ, USA, 2009; Volume 28, ISBN 978-0-
470-18849-1.
3.
Heinisch, G.; Holzer, W.; Kunz, F.; Langer, T.; Lukavsky, P.; Pechlaner, C.; Weissenberger, H. On the Bioisosteric Potential of
Diazines: Diazine Analogues of the Combined Thromboxane A2 Receptor Antagonist and Synthetase Inhibitor Ridogrel. J. Med.
Chem. 1996, 39, 4058–4064. [CrossRef] [PubMed]
4.
5.
6.
7.
8.
9.
Asif, M. The Pharmacological Importance of Some Diazine Containing Drug Molecules. Sci. Online Pub. Trans. Org. Chem. 2014
1, 1–17.
Akhtar, W.; Shaquiquzzaman, M.; Akhter, M.; Verma, G.; Khan, M.F.; Alam, M.M. The therapeutic journey of pyridazinone. Eur. J.
Med. Chem. 2016, 123, 256–281. [CrossRef]
Seth, S.; Sharma, A.; Raj, D. Pyridazinones: A wonder nucleus with scaffold of pharmacological activities. Am. J. Biol. Pharm. Res.
2014, 1, 105–116.
Dubey, S.; Bhosle, P.A. Pyridazinone: An important element of pharmacophore possessing broad spectrum of activity. Med. Chem.
Res. 2015, 24, 3579–3598. [CrossRef]
Bartlett, M.S.; Shaw, M.M.; Smith, J.W.; Meshnick, S.R. Efficacy of Sulfamethoxypyridazine in a Murine Model of Pneumocystis-
carinii Pneumonia. Antimic. Agents Chemother. 1998, 42, 934–935. [CrossRef]
Vigil-De Gracia, P.; Lasso, M.; Ruiz, E.; Vega-Malek, J.C.; De Mena, F.T.; Lopez, J.C. Severe hypertension in pregnancy: Hydralazine
or labetalol: A randomized clinical trial. Eur. J. Obstet. Gynecol. Reproduc. Biol. 2006, 128, 157–162. [CrossRef]
,
10. Papp, Z.; Édes, I.; Fruhwald, S.; De Hert, S.G.; Salmenperä, M.; Leppikangas, H.; Mebazaa, A.; Landoni, G.; Grossini, E.; Caimmi,
P.; et al. Levosimendan: Molecular Mechanisms and Clinical Implications: Consensus of Experts on the Mechanisms of Action of
Levosimendan. Int. J. Cardiol. 2012, 159, 82–87. [CrossRef] [PubMed]
11. Kan, J.P.; Mouget-Goniot, C.; Worms, P.; Biziere, K. Effect of the antidepressant minaprine on both forms of monoamine oxidase
in the rat. Biochem. Pharm. 1986, 35, 973–978. [CrossRef]
12. Contreras, J.M.; Rival, Y.M.; Chayer, S.; Bourguignon, J.J.; Wermuth, C.G. Aminopyridazines as acetylcholinesterase inhibitors. J.
Med. Chem. 1999, 42, 730–741. [CrossRef]
13. Aleeva, G.N.; Molodavkin, G.M.; Voronina, T.A. Comparison of antidepressant effects of azafan, tianeptine, and paroxetine. Bul.
Exp. Biol. Med. 2009, 148, 54–56. [CrossRef] [PubMed]
14. Inskeep, P.B.; Reed, A.E.; Ronfeld, R.A. Pharmacokinetics of zopolrestat, a carboxylicacid aldose reductase inhibitor in normal
and diabetic rats. Pharm. Res. 1991, 8, 1511–1515. [CrossRef] [PubMed]
15. Horn, L.; Infante, J.R.; Reckamp, K.L.; Blumenschein, G.R.; Leal, T.A.; Waqar, S.N.; Gitlitz, B.J.; Sanborn, R.E.; Whisenant, J.G.; Du,
L.; et al. Ensartinib (X-396) in ALK-Positive Non-Small Cell Lung Cancer: Results from a First-in-Human PhaseI/II, Multicenter
Study. Clin. Cancer Res. 2018, 24, 2771–2779. [CrossRef] [PubMed]
16. Barra, F.; Seca, M.; Della Corte, L.; Giampaolino, P.; Ferrero, S. Relugolix for the treatment of uterine fibroids. Drugs Today 2019
,
55, 503–512. [CrossRef] [PubMed]
17. Brown, J.S.; Kaye, S.B.; Yap, T.A. PARP inhibitors: The race is on. Br. J. Cancer 2016, 114, 713–715. [CrossRef]
18. Robson, M.; Im, S.A.; Senkus, E.; Xu, B.; Domchek, S.M.; Masuda, N.; Delaloge, S.; Li, W.; Tung, N.; Armstrong, A.; et al. Olaparib
for Metastatic Breast Cancer in Patients with a Germline BRCA Mutation. N. Eng. J. Med. 2017, 377, 523–533. [CrossRef]
19. Li, D.B.; Rogers-Evans, M.; Carreira, E.M. Synthesis of novel azaspiro[3.4]octanes as multifunctional modules in drug discovery.
Org. Lett. 2011, 13, 6134–6136. [CrossRef]
20. Burkhard, J.A.; Guérot, C.; Knust, H.; Carreira, E.M. Expanding the Azaspiro[3.3]heptanes Family: Synthesis of Novel Highly-
Functionalized Building Blocks. Org. Lett. 2012, 14, 66–69. [CrossRef]
21. Li, D.B.; Rogers-Evans, M.; Carreira, E.M. Construction of multifunctional modules for drug discovery: Synthesis of novelthia/oxa-
azaspiro [3.4] octanes. Org. Lett. 2013, 15, 4766–4769. [CrossRef]
22. Carreira, E.M.; Fessard, T.C. Four-membered ring-containing spirocycles: Synthetic strategies and opportunities. Chem. Rev. 2014
,
144, 8257–8322. [CrossRef]
23. Zheng, Y.; Tice, C.M.; Singh, S.B. The use of spirocyclic scaffolds in drug discovery. Bioorg. Med. Chem. Lett. 2014, 24, 3673–3682.
[CrossRef]
24. Sepsey Für, C.; Riszter, G.; Gerencsér, J.; Szigetvári, A.; Dékány, M.; Hazai, L.; Keglevich, G.; Bölcskei, H. Synthesis of
Spiro[Cycloalkane-pyridazinones] with High Fsp3 Character. Lett. Drug Des. Discov. 2020, 17, 731–744.
25. Sepsey Für, C.; Horvát, E.J.; Szigetvári, A.; Dékány, M.; Hazai, L.; Keglevich, G.; Bölcskei, H. Synthesis of Spiro[Cycloalkane-
pyridazinones] with High Fsp3 Character Part 2. Lett. Org. Chem. 2021, 18, 373–381.
26. Ozturk, T.; Ertas, E.; Mert, O. A Berzelius Reagent, Phosphorus Decasulfide (P4S10), in Organic Syntheses. Chem. Rev. 2010, 110,
3419–3478. [CrossRef]
27. Chimirri, A.; Zappala, M.; Gitto, R.; Quartarone, S.; Bevacqua, F. Synthesis and structural features of 11H-Tetrazolo[1,5-
c][2,3]benzodiazepines. Heterocycles 1999, 51, 1303–1309. [CrossRef]

Molecules 2021, 26, 2140
12 of 12
28. Lipinski, C.A.; Lombardo, F.; Dominy, B.W.; Feeney, P.J. Experimental and Computational Approaches to Estimate Solubility and
Permeability in Drug Discovery and Development Settings. Adv. Drug Deliv. Rev. 1997, 23, 3–25. [CrossRef]
29. Lipinski, C.A. Lead- and drug-like compounds: The rule-of five revolution. Drug Discov. Today Tech. 2004, 1, 337–341. [CrossRef]
30. Veber, D.F.; Johnson, S.R.; Cheng, H.Y.; Smith, B.R.; Ward, K.W.; Kopple, K.D. Molecular Properties That Influence the Oral-
Bioavailability of Drug Candidates. J. Med. Chem. 2002, 45, 2615–2623. [CrossRef] [PubMed]
31. Lovering, F.; Bikker, J.; Humblet, C. Escape from Flatland: Increasing Saturation as an Approach to Improving Clinical Success. J.
Med. Chem. 2009, 52, 6752–6756. [CrossRef]
32. Lovering, F. Escape from Flatland 2: Complexity and promiscuity. Med. Chem. Commun. 2013, 4, 515–519. [CrossRef]
33. Chimirri, A.; Bevacqua, F.; Gitto, R.; Quartarone, S.; Zappala, M.; De Sarro, A.; Maciocco, L.; Biggio, G.; De Sarro, G. Synthesis
and anticonvulsant activity of new 11H-triazolo[4,5-c][2,3]benzodiazepines. Med. Chem. Res. 1999, 9, 203–212.