One-pot synthesis of dihydropyridine carboxylic acids via functionalization of 3-((trimethylsilyl)ethynyl)pyridines and an unusual hydration of alkynes: Molecular docking and antifungal activity

Article abstract of DOI:10.1016/j.tet.2021.132086

Activation of 3-((trimethylsilyl)ethynyl)pyridine with triflic anhydride followed by nucleophilic addition of bis(trimethylsili) ketene acetals and a unusual alkyne hydration allowed to obtain new series of 3-acetylated dihydropyridine acids 3a-h in a sin

Full text of DOI:10.1016/j.tet.2021.132086

Tetrahedron 86 (2021) 132086
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
One-pot synthesis of dihydropyridine carboxylic acids via
functionalization of 3-((trimethylsilyl)ethynyl)pyridines and an
unusual hydration of alkynes: Molecular docking and antifungal
activity
a
b
a
ꢀ
~
Ricardo Ballinas-Indilí , Omar Gomez-García , Eric Trevino-Crespo ,
c
,
Dulce Andrade-Pavon d, Lourdes Villa-Tanaca d, Ruben A. Toscano a,
ꢀ
a, *
ꢀ
Cecilio Alvarez-Toledano
Instituto de Química, Universidad Nacional Autonoma de Mexico (UNAM), Circuito Exterior s/n, Ciudad Universitaria, 04510, Ciudad de Mexico, Mexico
a
ꢀ
ꢀ
ꢀ
b
ꢀ
ꢀ
ꢀ
Departamento de Química Organica, Escuela Nacional de Ciencias Biologicas, Instituto Politecnico Nacional, Prol., de Carpio y Plan de Ayala. Col. Sto.
ꢀ
ꢀ
Tomas, 11340, Ciudad de Mexico, Mexico
c
ꢀ
ꢀ
Departamento de Fisiología, Escuela Nacional de Ciencias Biologicas, Instituto Politecnico Nacional, Av. Wilfrido Massieu S/N Unidad Profesional “Adolfo
ꢀ
ꢀ
Lopez Mateos”, Zacatenco. Col. Lindavista, CP 07700, Ciudad de Mexico, Mexico
d
ꢀ
ꢀ
ꢀ
Departamento de Microbiología, Escuela Nacional de Ciencias Biologicas, Instituto Politecnico Nacional, Prol. de Carpio y Plan de Ayala. Col. Sto. Tomas,
ꢀ
11340, Ciudad de Mexico, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Activation of 3-((trimethylsilyl)ethynyl)pyridine with triflic anhydride followed by nucleophilic addition
of bis(trimethylsili) ketene acetals and a unusual alkyne hydration allowed to obtain new series of 3-
acetylated dihydropyridine acids 3a-h in a single step. Secondly, docking studies were conducted on
four of the test compounds (3b, 3e, 17a and 17b) and a reference drug (fluconazole) at the active site of
Received 1 February 2021
Received in revised form
11 March 2021
Accepted 12 March 2021
Available online 18 March 2021
lanosterol 14a-demethylase enzymes (CYP51) from Candida spp., in vitro inhibition assays were per-
formed with the same compounds and yeast species. Compounds 3b, 3e, 17a and 17b interacted with key
amino acids of the active site of CYP51 enzymes in a similar manner as fluconazole. Compared to flu-
conazole, the test compounds showed better binding energy values (ꢀ4.84 to ꢀ9.1 vs. ꢀ1.51 to 5.68 kcal/
mol) and in vitro antifungal activity (lower MIC values) on different Candida species. Hence, the dihy-
dropyridine derivatives can be considered candidates for the development of new antifungal drugs.
© 2021 Elsevier Ltd. All rights reserved.
Keywords:
Dihydropyridines
Hydration of alkynes
Molecular docking
Antifungal activity
Candida spp
1. Introduction
Our group has used such compounds to obtain diverse substituted
g
and
d-lactones [6e8].
The pyridine nucleus is a versatile building block in Organic
Synthesis [1,2]. It is intrinsically reactive and susceptible to acti-
vation by different agents. For example, the reaction of pyridines
with triflic anhydride (Tf2O) [3], ethyl chloroformate (ClCO2Et) [4],
alkyl halides and other electrophiles affords pyridinium salts. The
latter display an enhanced electrophilic character in the 4 or 2
position, thus allowing them to react with a variety of nucleophiles
[5]. Bis(trimethylsilyl) ketene acetals are nucleophiles that react
with pyridinium salts to generate functionalized dihydropyridines.
The common method of preparing 3,4-disubstituted dihy-
dropyridine carboxylic acids involves pyridines with certain sub-
stituents (e.g., CO2Et, CN or CHO) in position 3, which lacks
ꢀhydrogens.5 In the presence of an acetyl group, however, the
a
nucleophilic addition of bis(trimethylsilyl) ketene acetals is not
favored. The enolization of the carbonyl group and its subsequent
triflation not only activates the aromatic ring, but also sterically
hampers the approach of the silylated nucleophile. Consequently,
the nucleophilic addition at C-4 is not successful. Therefore, the
development of direct methodologies for the preparation of 1,3,4-
trisubstituted dihydropyridine carboxylic acids with an enolizable
group at C-3 represents a synthetic challenge. Such compounds
may be instrumental in the elaboration of more sophisticated
* Corresponding author.
ꢀ
E-mail address: cecilio@unam.mx (C. Alvarez-Toledano).
https://doi.org/10.1016/j.tet.2021.132086
0040-4020/© 2021 Elsevier Ltd. All rights reserved.

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R. Ballinas-Indilí, O. Gomez-García, E. Trevino-Crespo et al.
Tetrahedron 86 (2021) 132086
structures.
2. Results and discussion
On the other hand, fungal infections are a serious and increas-
ingly common problem, especially in hospitals, being the principle
cause of morbidity and mortality in immunocompromised patients
[9]. Among the particularly problematic fungi are candidiasis,
aspergillosis, cryptococcosis and mucormycosis [10,11].
Invasive candidiasis is a serious infection induced by any type of
Candida yeast. Although C. albicans is most frequently responsible
for this disease, other species such as C. glabrata, C. dubliniensis,
C. kefyr, C. krusei, C. lusitaniae and C. parapsilosis have emerged as
important causative agents in recent years [12]. Consequently, a
variety of antifungal agents have been developed and classified
according to their mechanism of action: inhibitors of ergosterol,
nucleic acid, cell wall and microtubule biosynthesis, as well as
fungal membrane disruptors [13].
Azole derivatives are the most commonly used antifungal
agents [14], but are becoming less effective for treating certain drug
resistant Candida species [15]. Moreover, the administration of
azole derivatives against fungal infections can lead to severe
adverse effects, including hepatotoxicity and nephrotoxicity.
Hence, it is necessary to design, synthesize and test new antifungal
agents that have different structures than those of azoles and other
antifungal drugs of choice in clinical practice.
In this sense, recent studies have provided evidence of the
antifungal potential of dihydropyridine derivatives in relation to
C. albicans, Aspergillus niger and A. clavatus. [16,17] Pyridine de-
rivatives are present in several natural and synthetic compounds
with antioxidant, anti-inflammatory, anticancer, antiviral, antihy-
pertensive, antiamoebic, antimalarial and antimicrobial activities
[18e20].
2.1. Chemistry
Dihydropyridine carboxylic acid 3a was synthesized by the
activation of 3-((trimethylsilyl)ethynyl)pyridine 1 with a slight
excess (1.2 equiv) of triflic anhydride followed by the nucleophilic
addition of 1.2 equiv of the corresponding bis(trimethylsilyl) ketene
acetal of structure 2a. With these conditions, bis(trimethylsilyl)
ketene acetal 2a underwent nucleophilic addition to the C4 posi-
tion of the pyridinium salt. The subsequent aqueous workup
induced the hydration of the alkyne moiety to yield the final
product 3a (Scheme 1). It is remarkable that this one-pot reaction
activated the pyridine ring, promoted the nucleophilic addition of
the ketene acetal, and favored the hydration of the alkyne in a
single step, generating a ketone functionality in position 3.
In order to generalize the method, a series of acids was syn-
thesized by using different bis(trimethylsilyl) ketene acetals,
obtaining compounds 3a-h (Table 1).
The preparation of compounds 3 involved the initial activation
of the pyridine ring with triflic anhydride to give a pyridinium salt
[2,3]. The latter underwent the nucleophilic addition of bis(-
trimethyl) ketene acetal to furnish the dihydropyridine system 6a.
Deprotection of the alkyne by TfOe afforded the acetylide 7a, which
Table 1
Synthesized dihydropyridine carboxylic acids 3a-h.
The aim of the current study was to synthesize a series of de-
rivatives of trisubstituted dihydropyridines (3a-h, 17a and 17b),
evaluate their antifungal activity against six Candida species
(C. glabrata, C. dubliniensis, C. kefyr, C. krusei, C. lusitaniae and
C. parapsilosis), and perform molecular docking of the derivatives
on the active site of the Lanosterol 14a-demethylase (CYP51)
enzyme of Candida spp. The compounds were synthesized with a
novel one-pot methodology, involving the activation of 3-((trime-
thylsilyl)ethynyl) pyridine, the nucleophilic addition of a series of
bis(trimethylsilyl) ketene acetals at the C-4 position, and an un-
usual hydration of the alkyne moiety. Based on the inhibitory ac-
tivity against Candida species and the docking results, we herein
propose the test derivatives as a possible alternative for the treat-
ment of mycosis.
Compound
R1
R2
R3
R4
Yield (%)
3a
3b
3c
3d
3e
3f
Me
Me
Me
Me
Me
Me
Me
Me
Me
H
CN
OMe
F
H
H
H
H
95
48
62
58
78
59
47
80
Me
-(CH)4-
-(CH2)3-
-(CH2)4-
-(CH2)5-
e
e
e
e
e
e
3g
3h
Scheme 1. Synthesis of dihydropyridine carboxylic acid 3a.
2

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R. Ballinas-Indilí, O. Gomez-García, E. Trevino-Crespo et al.
Tetrahedron 86 (2021) 132086
was protonated in the presence of TfOH generated in situ during the
aqueous workup to provide an alkyne intermediate. Then a reaction
with triflic acid through a Markovnikov electrophilic addition led to
the carbocation 8a. The attack of the nucleophilic water molecule
on the electrophilic carbocation created an oxonium ion 9a. This
was deprotonated by a triflate to produce the enol 10a, which was
tautomerized to the keto form to obtain compound 3a (Scheme 2).
It is not possible to attain dihydropyridine derivatives 3 from 3-
acetyl pyridine because the carbonyl group becomes enolized and
enol triflation occurs. Hence, the presence of the bulky trimethyl
silane group blocks the nucleophilic addition of ketene acetal at
position 4 of the pyridine ring.
thus indicating the loss of aromaticity of the pyridine ring as a
consequence of the nucleophilic addition of bis(trimethylsilyl)
ketene acetal. The signal at 2.10e2.46 ppm was assigned to the
acetyl group in position 3, corroborating the hydration of the
alkyne group. The 13C NMR spectra display
a signal at
179.6e181.9 ppm, ascribed to a carboxylic acid functionality, and a
signal at 36.2e5.03 ppm corresponding to C4. The carbonyl signals
of the acetyl group between 195.3 and 200.1 ppm and the methyl
signals between 24.0 and 25.5 ppm were identified as well,
evidencing the conversion of the alkyne to an acyl group. The high
resolution mass spectra confirm the presence of the molecular ion
in all cases, while the low resolution mass spectra reveal the typical
loss of important fragments such as eOH and the carboxylic acid
fraction. Finally, the molecular structure of 3a was fully established
through an X-ray diffraction analysis (Fig. 1).
The next focus of investigation was the unusual hydration of the
alkyne functionality. Reaction of 3-ethynylpyridine 11 under the
aforementioned protocol gave 3a in low yield (23%), demonstrating
the importance of the trimethylsilyl group to favor this process
(Scheme 3).
The alkyne hydration that takes place to deliver 3a is carried out
in the absence of Hg reagents, which if utilized are not only highly
toxic but also imply a potential risk for escalation, resulting in quite
long reaction times [21]. Moreover, the successful route to achieve
3a does not require the use of expensive transition metals such as
Au, Ag, Rh and Ru [22e26].
In the 1H NMR spectra of compounds 3, the signal at around
3.93e4.62 ppm corresponds to H4 of a dihydropyridine moiety,
Scheme 2. Proposed mechanism for the formation of compounds 3a-h.
3

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R. Ballinas-Indilí, O. Gomez-García, E. Trevino-Crespo et al.
Tetrahedron 86 (2021) 132086
the steric hindrance of the tert-butyldimethylsilyl group, which
limits the approach of the acetal to the pyridinium salt (Scheme 4).
Further experiments were conducted with alkynes linked to
aromatic rings 13 and 14, resulting in the lack of hydration of the
alkyne. Nevertheless, these experiments revealed that Tf2O is
capable of removing the SiMe3 fragment and thereby leaving the
alkyne unprotected (Scheme 5).
In another synthetic approach, alkynes with aliphatic or aro-
matic moieties linked to the triple bond, such as 16a and 16b, were
reacted under the established protocol. The products were dihy-
dropyridines 17a and 17b, with an intact alkyne group. This
outcome clearly demonstrates that the SiMe3 group is responsible
for the hydration of the alkyne moiety (Scheme 6).
The viability of the isotopic exchange process was also examined
in several ways. Firstly, deuterated water was added after the total
consumption of the raw material, a process monitored by thin layer
chromatography (TLC). The result was a mixture, the mass spec-
trometry of which exhibited molecular ions with m/z ¼ 342, m/
z ¼ 343 and m/z ¼ 344, corresponding to 18, 19 and 20 of mono-, di-
and trideuteration, respectively. The compounds were separated by
column chromatography and characterized individually.
When the reaction conditions were varied, using CD2Cl2 in the
first stage instead of CH2Cl2 but with the aqueous workup (as
previously described), the same results were obtained. It was
possible to identify 3a and compounds 18, 19 and 20. Moreover, the
synthetic route was carried out by first employing CDCl2 and then
D2O in a second stage to generate 3a, 18, 19 and 20 (see Scheme 7).
In a mechanistic approach to the study, H128O was used instead of
water in order to corroborate the nucleophilic addition of water on
the carbocation 8a during the hydration of the alkyne. Mass spec-
trometry showed a molecular ion with m/z ¼ 344, confirming the
Fig. 1. ORTEP view of compound 3a. Thermal ellipsoids are shown at the 40% proba-
bility level.
The reaction of bis(tert-butyldimethylsilyl) ketene acetal 12 also
provides 3a in low yield (28%). This outcome may be attributed to
Scheme 3. Synthesis of 2-(3-acetyl-1-((trifluoromethyl)sulfonyl)-1,4-dihydropyridin-4-yl)-2-methylpropanoic acid 3a from 3-etynil pyridine 11.
Scheme 4. Synthesis of 2-(3-acetyl-1-((trifluoromethyl)sulfonyl)-1,4-dihydropyridin-4-yl)-2-methylpropanoic acid 3a using the bis(tert-butyldimethylsilyl) ketene acetal 12.
4

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Tetrahedron 86 (2021) 132086
Scheme 5. Reactivity of different alkynes.
Scheme 6. Synthesis of the dihydropyridine carboxylic acids 17a and 17b.
presence of 21 (see Scheme 8).
and 17b showed the best values and were selected for docking
simulations and an in vitro evaluation of biological activity. The
CYP51 enzymes used for docking were those of C. albicans, C.
dubliniensis, C. glabrata, C. krusei, C. lusitaniae and C. parapsilosis.
The compounds were selected for their capacity to inhibit Candida
spp. growth together with their interaction at the active site of the
CYP51 enzymes (Fig. 2 and Figs. S1-S5). According to the results, the
corresponding derivatives could have a mechanism of action
similar to that of azoles (e.g., fluconazole).
The binding energy (Kcal/mol) found for 3b, 3e, 17a, 17b and
fluconazole at the active site of the CYP51 enzymes of Candida are
listed in Table 2. The four test compounds showed better binding
energies (ꢀ4.84 to ꢀ9.1 kcal/mol) than fluconazole (ꢀ1.51 to
5.68 kcal/mol). For four of the CYP51 enzymes, the best binding
energies were displayed by 3e (with a quinoline ring) and 17a,
which may be due to the aromatic benzene ring favoring the
interaction with the amino acid side chain at the active site of the
enzymes.
2.2. Molecular docking of the dihydropyridine derivatives on CYP51
from Candida spp.
To predict the antifungal activity of the dihydropyridine de-
rivatives 3a-h herein synthesized, a molecular docking study was
conducted between some of these compounds and the active site of
the CYP51 enzyme from Candida. The parameters used to analyze
plausible antifungal activity were the binding mode and binding
energy of the series of compounds 3 on the CYP51 enzyme. Diverse
docking studies have examined potential anti-candidiasis agents in
relation to their binding to the CYP51 enzyme, since it is the main
target of most antifungal compounds [27e29]. To our knowledge,
however, there are no reports of docking studies of dihydropyridine
derivatives on this enzyme.
Initially, screening was carried out in order to select the com-
pounds with the best binding energy of the series of dihydropyr-
idine carboxylic acids 3a-h, 17a and 17b. Compounds 3b, 3e, 17a
The amino acid residues and interactions that participate in
5

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Tetrahedron 86 (2021) 132086
Scheme 7. Deuteration experiments of 3a.
Scheme 8. Hydration of the alkyne with H218O.
Fig. 2. Binding mode of the selected dihydropyridine derivatives 3b, 3e, 17a and 17b as well as fluconazole at the active site of CYP51 of C. albicans. The protein is portrayed in flat
ribbon representation, and the heme group with the stick model (purple). The compounds are illustrated with the ball and stick denotation: fluconazole (red), 3b (yellow), 3e (hot
pink), 17a (green) and 17b (blue).
6

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Tetrahedron 86 (2021) 132086
Table 2
Binding energy from docking simulations of the dihydropyridines 3b, 3e, 17a, 17b and fluconazole at the active site of CYP51 enzymes of Candida spp.
Compounds
Binding Energy (Kcal/mol)
C. albicans
C. dubliniensis
C.glabrata
C.krusei
C.lusitaniae
C.parapsilosis
Fluconazole
3b
3e
17a
17b
ꢀ4.44
ꢀ8.66
ꢀ9.83
ꢀ7.6
ꢀ4.56
ꢀ7.46
ꢀ8.32
ꢀ8.06
ꢀ8.98
ꢀ4.38
ꢀ8.23
ꢀ8.28
ꢀ7.52
ꢀ7.96
ꢀ5.68
ꢀ7.82
ꢀ9.1
ꢀ5.16
ꢀ8.18
ꢀ9.44
ꢀ8.75
ꢀ9.05
ꢀ1.51
ꢀ0.29
ꢀ1.19
ꢀ4.84
2.79
ꢀ9.0
2.53
ꢀ8.72
Table 3
Data from the docking of the dihydropyridines on CYP51 enzymes of Candida spp.
Compounds amino acid residues
hydrophilic
interactions
hydrophobic
interactions
CYP51 C. albicans
Fluconazole Tyr94, Leu97, Thr98, Phe102, Ile107, Tyr108, Phe204, Met282, Gly283, Gly284, Thr287, Leu352, Ile355, Met484, CeH ….O (Tyr108)
p
-p
T-shaped
Val485
CeH ….O (Gly283)
N ….HeO (Thr287)
Tyr94
p
p
p
-alkyl Leu352
-alkyVal485
-sigma Tyr94
3e
Tyr94, Leu97, Thr98, Phe102, Tyr108, Phe204, Met282, Gly283, Gly284, Thr287, Leu352, Met484, Val485
OeH ….O (Tyr108)
O ….HeN (Thr287)
Halogen Met282
p
-alkyl Leu352
CYP51 C. dubliniensis
Fluconazole Tyr94, Thr98, Phe102, Tyr108, Phe204, Gly279, Met282, Gly283, Gly284, Thr287, Leu352, Val485
CeH ….O (Tyr108)
CeH ….O (Met282)
N ….HeC (Gly283)
OeH ….O (Gly283)
p
Tyr94
Halogen Gly279
Halogen Gly283
-p T-shaped
p
p
p
p
-alkyl Val485
-anion Tyr94
-alkyl Tyr94
17b
Tyr94, Thr98, Phe102, Val106, Ile107, Tyr108, Phe204, Gly279, Ile280, Gly283, Thr287, Leu352, Met484, Val485 OeH ….O (Tyr108)
-p T-shaped
Phe102
-alkyl Ile107
Halogen Met484
p
p
p
-alkyl Leu352
CYP51 C. glabrata
Fluconazole Tyr108, Phe116, Ile121, Tyr122, Phe218, Phe223, Gly296, Thr300, Leu362, Leu365, Met493
CeH ….O (Tyr122)
-p T-shaped
Tyr108
-alkyl Ile121
Halogen Gly296
p
p
p
-alkyl Leu362
-p T-shaped
3e
Tyr108, Phe116, Ile121, Tyr122, Phe218, Met295, Gly296, Gly297, Thr300, Pro361, Leu362, Leu365, Met493, OeH ….O (Met295)
Val494 O ….HeO (Thr300)
Tyr108
p
-alkyl Leu362
CYP51 C. krusei
Fluconazole Tyr94, Leu97, Phe102, Tyr108, Phe199, Ile207, Gly273, Val274, Gly277, Gly278, Thr281, Leu344, Ile347, Met478 CeH ….O (Tyr108)
p
-p T-shaped
N ….HeN (Gly277)
N ….HeO (Gly281)
Tyr94
T-shaped
Phe102
p-p
p
p
-alkyl Leu344
-sigma Tyr94
3e
Tyr94, Leu97, Phe102, Ile207, Tyr108, Phe199, Gly273, Val274, Met276, 8Gly277, Gly278, Thr281, Leu344,
Ile347, Met478
F ….HeN (Gly277)
F ….HeN (Gly278)
Halogen Gly273
T-shaped
Gly277
p-p
CYP51 C. lusitaniae
Fluconazole Tyr94, Thr98, Ile107, Tyr108, Leu115, Gly283, Gly284, Thr287, Leu352, Ile355, Met481
OeH ….O (Tyr108)
F ….HeO (Thr287)
p
Tyr94
-
p
T-shaped
p
-sigma Ile107
Halogen Gly283
p
-alkyl Leu352
3e
Tyr94, Leu97, Thr98, Ile107, Tyr108, Gly279, Val280, Gly283, Thr287, Leu352, Met481
CYP51 C. parapsilosis
Fluconazole Tyr94, Tyr108, Phe204, Arg274, Phe333, Gly336, Pro382, Met428, Arg337
Halogen Arg274
Halogen Arg337
17a
Phe102, Phe204, Arg274, Gly275, Val278, Phe333, Arg337, Met428, Val429
O ….HeN (Arg337)
p
p
p
-sigma Phe204
-alkyl Val278
-alkyl Phe333
Halogen Phe333
binding are summarized in Table 3. The following residues of the
active site of the CYP51 enzymes are involved in the majority of
interactions with fluconazole and the four test compounds (3b, 3e,
17a and 17b): Tyr94, Thr98, Phe102, Tyr108, Phe204, Gly283,
Gly284 and Thr287 (see Table 4).
The 3D and 2D portrayal of the interactions of the test com-
pounds and reference drug with the CYP51 enzymes of the Candida
species herein evaluated are shown in Fig. 3 and S6-11. In the 3D
7

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Tetrahedron 86 (2021) 132086
Table 4
MIC for the dihydropyridine derivatives and the reference drug, calculated from in vitro antifungal assays against Candida spp.
Compounds
MIC mg/mL
C. albicans
C. dubliniensis
C. glabrata
C. krusei
C. lusitaniae
C. parapsilosis
Fluconazole
3b
3e
17a
17b
16
10
10
10
10
8
16
10
10
10
10
32
10
20
10
10
>64
10
10
5
4
10
10
10
5
10
10
2.5
10
10
diagrams, the surface involved in the interaction and the corre-
sponding amino acids can be appreciated. On the other hand, the
2D illustration reveals the type of interactions between the com-
pounds and CYP51.
further testing as alternative antifungal treatments. Their likely
mechanism of action is the inhibition of yeast growth by binding to
the active site of CYP51 of Candida species.
Several hydrophilic interactions were identified, such as
hydrogen bonds formed between fluconazole and the Tyr108 res-
idue in C. albicans, C. dubliniensis and C. krusei. Conventional
hydrogen bonds were found between Tyr108 of C. albicans and the
dihydroquinoline derivative 3e. This same amino acid residue in
C. lusitaniae interacts with fluconazole. In C. albicans and
C. dubliniensis, Gly283 is an important fragment that interacts with
fluconazole. Interestingly, both 3e and fluconazole share a con-
ventional hydrogen bond interaction with Thr287 from C. albicans
and with Gly277 from C. krusei. Similar interactions have been re-
ported between CYP51 and other pyrimidine derivatives [27].
Meanwhile, the analysis of hydrophobic interactions revealed
3. Conclusions
A new series of dihydropyridine carboxylic acids were synthe-
sized through a one-pot process involving the activation of 3-
((trimethylsilyl)ethynyl)pyridine with triflic anhydride, followed by
the nucleophilic addition of bis(trimethylsilyl) ketene acetals, and
finally an unusual alkyne hydration. The advantage of this method
over current methodologies for the hydration of alkynes is that it
does not require Hg reagents or expensive transition metals. Ac-
cording to the docking results, the dihydropyridine derivatives 3b,
3e, 17a and 17b interact with key amino acid residues at the active
site of CYP51 enzymes of Candida species, evidencing a mechanism
of action similar to the reference drug (fluconazole). Compared to
fluconazole, 3b, 3e, 17a and 17b showed better binding energy
values and therefore greater affinity for the active site of CYP51 of
C. albicans, C. dubliniensis, C. glabrata, C. krusei, C. lusitaniae and
C. parapsilosis. The in vitro assays carried out to evaluate the inhi-
bition of the Candida species revealed lower MIC values for the
dihydropyridines than fluconazole. As can be appreciated, 3b, 3e,
17a and 17b are promising compounds for the treatment of mycosis
and should certainly be of value as lead compounds for the
development of new antifungal drugs.
which amino acids participate in type
teractions: Tyr94, Phe333, Leu344, Leu352, Val485,
(Tyr94, Phe102 and Thr108), -sigma (Tyr94, Ile107 and Phe204)
p-alkyl non-polar in-
p-p
T-shaped
p
and halogen (Gly273, Arg274, Gly279, Met282, Gly283, Gly296,
Phe333, Arg337 and Met484). Moreover, the heme group of the
CYP51 enzymes of the Candida species herein considered interacts
with fluconazole and 3e through their aromatic fraction, presenting
p-p stacked and p-p T-shaped interactions. Finally, the CF3 group of
some derivatives formed halogen bonds with amino acid residues
such as Gly273, Met282, Gly296 and Met484.
The interaction between the aforementioned residues and
various compounds has been described in previous reports
[27e29]. Thus, the current findings of the interaction of 3b and 3e
with the same residues indicates that their probable mechanism of
action is the inhibition of the CYP51 enzyme in each species of
Candida yeast herein examined.
4. Experimental section
4.1. General information
All reagents and solvents were of analytical grade, acquired from
commercial suppliers and used without further purification.
Melting points were measured on a Melt Temp II apparatus. The IR
spectra were recorded on a Bruker TENSOR 27 spectrophotometer,
and the 1H and 13C NMR spectra on a Bruker Advance III apparatus
at 300 MHz and 75 MHz, respectively, in chloroform-d. Chemical
shifts are given in ppm with reference to TMS. MS-DART spectra
were obtained with a JEOL JMS-T100LC spectrometer.
Suitable crystals of 3a were grown in a hexane/acetone system
for a more detailed scrutiny of its molecular structure with X-ray
diffraction. The crystal was placed on fiberglass at 25 ꢁC and then
put in a Bruker Smart Apex CC diffractometer equipped with Mo
2.3. Antifungal Activity
The compounds were tested in vitro for antifungal activity on
the presently considered Candida species, determining the mini-
mum inhibitory concentration (MIC). The results corroborate the
data on binding energy from the docking simulations. As was found
with the binding energy values, the MIC values were better for the
dihydropyridine derivatives than fluconazole. Each of the com-
pounds had a MIC of 10
mg/mL for most Candida spp., with the best
MIC (2.5 g/mL) corresponding to 17a applied to C. parapsilosis. The
m
MIC values are lower than those obtained in other studies with
similar derivatives [30e36], revealing a greater inhibitory effect of
the proposed compounds on the Candida species herein evaluated.
Compound 3e showed the lowest MIC for C. albicans and the
lowest binding energy for C. dubliniensis. Derivative 17a displayed
the lowest MIC for C. parapsilosis and 17b for C. dubliniensis. These
results suggest that the dihydropyridine derivatives probably all
have a similar mechanism of inhibition of the CYP51 enzyme.
Based on their MIC values and affinity for the CYP51 enzyme,
compounds 3b and 3e proved to be promising candidates for
radiation (lMoK ¼ 0.71073 Å). The decay was negligible in all cases.
a
Systematic absences and intensity statistics were employed for
space group determination. The structure was established with
direct methods on the SHELXS-2013 program. The solution and
refinement of structures were performed with SHELXL-2013.The
refinements of the anisotropic structure were made with the
least squares technique for all non-hydrogen atoms. The hydrogens
were placed in idealized positions based on their hybridization
with isotropic thermal parameters fixed at 1.2 times the value of the
attached atom. The different acetals of bis(trimethyl) silyl ketene
8

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Tetrahedron 86 (2021) 132086
Fig. 3. Molecular interactions of selected dihydropyridine derivatives (3b and 3e) and fluconazole with the active site of CYP51 of C. albicans. The surface and slab are illustrated in
the 3D structure. The heme group is shown in stick representation (purple), while the compounds are portrayed in ball and stick representation: fluconazole (red), 3b (yellow) and
3e (hot pink). The 2D structure depicts the participating interactions on the right side of the figure.
9

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Tetrahedron 86 (2021) 132086
2a-e were prepared according to methods reported in the literature
[37].
4.3.1. 2-(3-acetyl-1-((trifluoromethyl)sulfonyl)-1,4-dihydropyridin-
4-yl)-2-methylpropanoic acid (3a)
4.2. General procedure for the synthesis of ((trimethylsilyl)ethynyl)
pyridine derivatives
The starting materials pyridine and quinoline derivatives were
prepared following the reported procedure [38]. A sealed 10 mL
glass tube containing bromopyridine derivative 0.24 g (1.5 mmol),
trimethylsilylacetylene (1.5 mmol), triethylamine (7.5 mmol),
Pd(PPh3)2Cl2 (5 mol %), CuI (10 mol %), and acetonitrile (2 mL) was
placed in the cavity of a microwave reactor and irradiated for 5 min,
at 120 ꢁC and power 150 W. After cooling to room temperature by
an airflow, the tube was removed of the reactor. The reaction
mixture was extracted with dichloromethane (30 mL) and water
(30 mL). The organic layer was separated and washed with water
(2 ꢂ 30 mL), dried over anhydrous sodium sulfate, and concen-
trated under vacuum. Purification by column chromatography,
using hexane: ethyl acetate as elution system gave ((trimethylsilyl)
ethynyl)pyridine derivatives as colored oils or solids. All the prod-
ucts were characterized.
4.3. General procedure for the synthesis of dihydropyridine
carboxylic acids 3a-h
The compound was obtained as a white solid. mp. 92e94 ꢁC,
To a solution with 0.3g (1.76 mmol) 3-((trimethylsilyl)ethynyl)
pyridine dissolved in 15 mL of anhydrous CH2Cl2 (under inert at-
mosphere and cooled to ꢀ78 ꢁC), 0.36 mL (2.12 mmol, 1.2 equiv) of
triflic anhydride were added with a syringe, and the mixture was
stirred constantly for 3 h. Subsequently, 2.12 mmol (1.2 equiv) of
the corresponding ketene acetal were added and stirring continued
at ꢀ78 ꢁC for 2 h. The reaction was then allowed to reach 25 ꢁC
before being transferred to a separatory funnel and washed with
water (3 ꢂ 30 mL). The organic phases were combined and dried
with anhydrous Na2SO4, and the solvent was removed by vacuum
evaporation. The reaction crude was purified by column chroma-
tography using silica gel with hexane/AcOEt mixtures as eluents to
obtain the title compounds 3a-h.
(0.49 g, 85%). IR vmax (KBr): 3512, 3123, 2982, 1707, 1676, 1233 cmꢀ1
.
1H NMR (CDCl3, 300 MHz);
d
¼ 12.2 (s, H-9), 7.59 (s, 1H, H-2), 6.73
(d, J ¼ 7.5 Hz, 1H, H-6), 5.45 (dd, J ¼ 7.5, 6.0 Hz, 1H, H-5), 4.1 (d,
J ¼ 6.0 Hz, 1H, H-4), 2.39 (s, 3H, H-12), 1.14 (s, H-10), 1.06 (s, H-100)
ppm. 13C NMR (CDCl3, 75 MHz);
d
¼ 196.8, 182.1, 132.5, 122.7, 122.5,
119.1 (J ¼ 321.0 Hz, CF3), 111.8, 47.4, 37.8, 25.2, 21.6, 20.4 ppm;
MHRMS: calcd for C12H15F3NO5S 342.0623, found 342.0500.
10

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Tetrahedron 86 (2021) 132086
4.3.2. 2-(3-acetyl-5-cyano-1-((trifluoromethyl)sulfonyl)-1,4-
dihydropyridin-4-yl)-2-methylpropanoic acid (3b)
4.3.4. 2-(3-acetyl-5-fluoro-1-((trifluoromethyl)sulfonyl)-1,4-
dihydropyridin-4-yl)-2-methylpropanoic acid (3d)
The compound was obtained as a white solid. mp. 110e112 ꢁC,
(0.30 g, 48%). IR vmax (KBr): 3431, 3105, 2965, 1705, 1651, 1424, 1242,
The compound was obtained as a white solid. mp. 122e124 ꢁC,
1127 cmꢀ1. 1H NMR (Acetone-d6, 300 MHz):
d
¼ 7.88 (d, J ¼ 2.1 Hz,
(0.37 g, 58%). IR vmax KBr): 3097, 2978, 1705, 1661, 1203 cmꢀ1 1H
.
1H, H-2), 7.28 (t, J ¼ 1.2 Hz,1H, H-6), 4.03 (s, 1H, H-4), 2.06 (s, 3H, H-
NMR (CDCl3, 300 MHz):
H-6), 4.31 (d, J ¼ 8.4 Hz, 1H, H-4), 2.31 (s, H12, 3H, H-12), 1.18 (s, 3H,
H-10), 1.00 (s, 3H, H-100) ppm. 13C NMR (CDCl3, 75 MHz);
d
¼ 7.49 (s, 1H, H-2), 6.78 (d, J ¼ 4.8 Hz, 1H,
12), 1.35 (s, 3H, H-10), 1.27 (s, 3H, H-100) ppm. 13C NMR (Acetone-d6,
75 MHz);
d
¼
185.6, 175.4, 151.4, 145.0, 136.1, 123.7, 119.1
d
¼ 195.1,
(J ¼ 321.0 Hz, CF3), 116.6, 106.0, 48.7, 22.5, 20.4 ppm. HRMS: calcd
179.6, 152.0, 149.4, 131.9, 122.6 (C6), 122.4 (C3), 119.1 (J ¼ 321.0 Hz,
for C13H14F3N2O5S; calculated 367.0575, found 367.0724.
CF3), 117.4, 109.21, 46.3, 41.8, 25.4, 21.9, 21.3 ppm. HRMS: calcd for
C
12H14F4NO5S; calculated 360.0528, found 360.0532.
4.3.3. 2-(3-acetyl-5-methoxy-1-((trifluoromethyl)sulfonyl)-1,4-
dihydropyridin-4-yl)-2-methylpropanoic acid (3c)
4.3.5. 2-(3-acetyl-1-((trifluoromethyl)sulfonyl)-1,4-
dihydroquinolin-4-yl)-2-methylpropanoic acid (3e)
The compound was obtained as a white solid. mp. 100e102 ꢁC,
(0.38 g, 62%). IR vmax (KBr): 3458, 3111, 2958, 1762, 1637, 1418,
The compound was obtained as a white solid. mp. 140e144 ꢁC,
(0.21 g, 78%). IR vmax (KBr): 2983, 1700, 1645, 1210 cmꢀ1. 1H NMR
1203 cmꢀ1. 1H NMR (CDCl3, 300 MHz):
d
¼ 12.35 (s,1H, H-9), 6.99 (s,
(CDCl3, 300 MHz):
H-7), 7.37-7.31 (m, 3H, H-5, H-6, H-8), 4.62 (d, J ¼ 0.9 Hz, 1H, H-4),
d
¼ 7.75 (s, 1H, H-2), 7.62 (dd, J ¼ 8.5, 1.5 Hz, 1H,
1H, H-2), 6.10 (s, 1H, H-6), 3.83 (s, 1H, H-4), 3.36 (s, 3H, OCH3), 2.31
(s, 3H, H-12), 0.93 (s, 3H, H-10), 0.84 (s, H-100) ppm. 13C NMR
2.45 (s, 1H, H-12), 1.10 (s, 3H, H-16) 1.09 (H-160) ppm. 13C NMR
(CDCl3, 75 MHz);
d
¼ 191.9, 177.2, 145.6, 132.0, 129.1, 124.6, 120.9
(CDCl3, 75 MHz):
d
¼ 195.3, 181.6, 135.8, 134.5, 131.1, 128.0, 127.4,
(J ¼ 321.0 Hz, CF3), 105.7, 100.55, 56.8, 51.7, 46.1, 23.0, 22.3 ppm.
127.0, 126.2, 119.1 (J ¼ 321.0 Hz, CF3), 119.0, 49.1, 42.2, 25.2, 22.3,
20.9 ppm. HRMS: calcd for C16H17F3NO5S; calculated 392.0779,
found 392.0711.
HRMS: calcd for
372.0781.
C13H17F3NO6S; calculated 372.0728, found
11

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Tetrahedron 86 (2021) 132086
4.3.6. 1-(3-acetyl-1-((trifluoromethyl)sulfonyl)-1,4-dihydropyridin-
4-yl)cyclobutanecarboxylic acid (3f)
J ¼ 6.0 Hz, H6), 5.22-5.18 (m, H5), 3.84 (d, J ¼ 6.0 Hz, H4), 2.10 (s,
H13), 1.83-1.81 (m, H10’), 1.79-1.77 (m, H10), 1.34-1.30 (m, H11,
H11’) ppm. 13C NMR (CDCl3, 75 MHz):
d
¼ 196.7, 181.8, 132.1, 123.1,
122.1, 119.2 (J ¼ 321.0 Hz, CF3), 112.6, 60.5, 50.3, 32.4, 31.9, 25.3,
23.8 ppm. DARTþ-MS: 368 [Mþ1]þ, 350 [M ꢀ 18]þ, 254 [M ꢀ 113]þ
m/z. HRMS: calcd for C14H17F3NO5S 368.0779, found 368.0802.
4.3.8. 1-(3-acetyl-1-((trifluoromethyl)sulfonyl)-1,4-dihydropyridin-
4-yl)cyclohexanecarboxylic acid (3h)
The compound was obtained as a white solid. mp. 78e80 ꢁC,
(0.37 g, 59%). IR vmax (KBr): 3437, 2959, 1681, 1621, 1415, 1231 cmꢀ1
.
1H NMR (CDCl3, 300 MHz):
d
¼ 10.21 (s, 1H, H-9), 7.36 (s, 1H, H-2),
6.45 (d, J ¼ 6.0 Hz, 1H, H-6), 5.25-5.20 (m, 1H, H-5), 3.83 (d,
J ¼ 6.0 Hz, 1H, H-4), 2.47 (s, 3H, H-12), 2.07-1.95 (m, 2H, H-10, H-
100), 1.73-1.68 (m, 2H, H-100, H-10), 1.52-1.49 (m, 2H, H-13) ppm. 13C
NMR (CDCl3, 75 MHz):
d
¼ 196.5, 181.1, 132.3, 123.0, 122.3, 119.2
(J ¼ 321.0 Hz, CF3), 111.6, 53.5, 50.2, 28.4, 25.4, 23.0, 15.8 ppm.
The compound was obtained as a white solid. mp. 162e164 ꢁC,
HRMS: calcd for C13H15F3NO5S 354.0623, found 354.0650.
(0.48 g, 80%). IR vmax (KBr): 3451, 2931, 1677, 1617, 1417, 1232 cmꢀ1
.
1H NMR (CDCl3, 300 MHz):
d
¼ 9.43 (s, 1H, H-9), 7.56 (s, 1H, H-2),
4.3.7. 1-(3-acetyl-1-((trifluoromethyl)sulfonyl)-1,4-dihydropyridin-
4-yl)cyclopentanecarboxylic acid (3g)
6.73 (d, J ¼ 9.0 Hz, 1H, H-6), 5.47-5.43 (m, 1H, H-5), 3.94 (d,
J ¼ 6.0 Hz, 1H, H-4), 2.37 (s, 3H, H-13), 2.05-1.95 (t, J ¼ 7.0 Hz, 2H, H-
10, H-100),1.63 (t, J ¼ 7.0 Hz, 2H, H-100, H-10),1.40-1.22 (m, 4H, H-11,
H-110), 1.09-0.92 (m, 2H, H-14) ppm. 13C NMR (CDCl3, 75 MHz):
d
¼ 197.4, 180.4, 131.9, 122.6, 121.3, 119.1 (J ¼ 321.0 Hz, CF3), 111.8,
53.1, 38.8, 29.9, 29.7, 25.6, 25.3, 23.4, 23.3 ppm. HRMS: calcd for
15H19F3NO5S 382.0936, found 382.0904.
C
4.4. General procedure for the synthesis of dihydropyridine
carboxylic acids 17a and 17b
To
a solution of the corresponding alkyne 16a or 16b
(1.76 mmol) dissolved in 15 mL of anhydrous CH2Cl2 (under an inert
atmosphere and cooled to ꢀ78 ꢁC), 0.36 mL (2.12 mmol, 1.2 equiv)
triflic anhydride were added with a syringe and the mixture was
stirred constantly for 3 h. Subsequently, 2.12 mmol (1.2 equiv) of
the corresponding ketene acetal was added, followed by stirring
at ꢀ78 ꢁC for 2 h. The reaction was allowed to reach 25 ꢁC, at which
point it was transferred to a separatory funnel and washed with
water (3 ꢂ 30 mL). The organic phases were combined and dried
with anhydrous Na2SO4, and the solvent was removed by vacuum
evaporation. The reaction crude was purified by column chroma-
tography using silica gel with hexane/AcOEt mixtures as eluents to
obtain 17a and 17b.
The compound was obtained as a white solid. mp. 58e60 ꢁC,
(0.31 g, 47%). IR vmax (KBr). 3537, 2960, 1675, 1614, 1418, 1232 cmꢀ1
.
1H NMR (CDCl3, 300 MHz):
d
¼ 10.9 (s, H9), 7.26 (s, H2), 6.40 (d,
12

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R. Ballinas-Indilí, O. Gomez-García, E. Trevino-Crespo et al.
Tetrahedron 86 (2021) 132086
4.4.1. 2-(3-(hex-1-yn-1-yl)-1-((trifluoromethyl)sulfonyl)-1,4-
dihydropyridin-4-yl)-2-methylpropanoic acid (17a)
The compound was obtained as a white solid. mp. 136e138 ꢁC,
(0.36 g, 82%). IR vmax (KBr): 3096, 2992, 2073, 1696, 1670,
1202 cmꢀ1. 1H NMR (CDCl3, 300 MHz):
d
¼ 7.44-7.40 (m, 2H, H-14,
H-140), 7.36-7.32 (m, 3H, H-15, H-150, H-16), 7.03 (s, 1H, H-2), 6.63
(d, J ¼ 8.1 Hz, 1H, H-6), 5.14 (dd, J ¼ 8.1, 5.1 Hz, 1H, H-5), 3.63 (d,
J ¼ 5.1 Hz, H4), 1.31 (s, 3H, H-10), 1.15 (s, 3H, H-100) ppm. 13C NMR
(CDCl3, 75 MHz)
d
¼ 183.1, 131.4, 128.6, 128.4, 128.1, 122.7, 122.5,
119.4 (J ¼ 324.3 Hz, CF3), 109.6, 105.3, 90.8, 86.9, 47.4, 42.8, 21.7,
21.3 ppm. HRMS: calcd for C18H17F3NO5S; calculated 400.0830,
found 400.0842.
4.5. General procedure for the synthesis of 2-(3-acetyl-1-
((trifluoromethyl)sulfonyl)-1,4-dihydropyridin-4-yl)-2-
methylpropanoic acid using D2O
The compound was obtained as a white solid. mp. 124e126 ꢁC,
(0.31 g, 65%). IR vmax (KBr): 3106, 2937, 2226, 1699, 1620 cmꢀ1. 1H
To a solution with 0.3g (1.76 mmol) 3-((trimethylsilyl)ethynyl)
pyridine dissolved in 15 mL of anhydrous CH2Cl2 (under inert at-
mosphere and cooled to ꢀ78 ꢁC), 0.36 mL (2.12 mmol, 1.2 equiv) of
triflic anhydride were added with a syringe, and the mixture was
stirred constantly for 3 h. Subsequently, 2.12 mmol (1.2 equiv) of
the corresponding ketene acetal were added and stirring continued
at ꢀ78 ꢁC for 2 h. The reaction was then allowed to reach 25 ꢁC. To
this solution were added deuterium oxide 99.9 atom % D (D2O).
Then the reaction mixture was stirred (500 rpm) for 1h. The crude
was transferred to a separating funnel and washed with water
(3 ꢂ 30 mL). The organic phases were combined and dried with
anhydrous Na2SO4, and the solvent was removed by vacuum
evaporation. The reaction crude was purified by column chroma-
tography using silica gel with hexane/AcOEt mixtures as eluents to
obtain the title compounds.
NMR (CDCl3, 300 MHz):
d
¼ 6.61 (s, 1H, H-2), 6.38 (dd. J ¼ 8.2,
1.7 Hz,1H, H-6), 4.93 (dd, J ¼ 8.2, 5.0 Hz,1H, H-5), 3.30 (d, J ¼ 5.0 Hz,
1H, H-4), 2.02 (d, J ¼ 6.9 Hz, 2H, H-13),1.32-1.11 (m, 4H, H-14, H-15),
1.08 (s, 3H, H-100), 0.95 (s, 3H, H-10), 0.69 (t, J ¼ 6.9 Hz, 3H, H-16)
ppm. 13C NMR (CDCl3, 75 MHz):
d
¼ 183.0, 127.1, 122.7, 119.34
(J ¼ 321.0 Hz, CF3), 109.5, 105.9, 92.5, 78.0, 47.3, 42.9, 30.4, 22.1, 21.9,
21.3, 19.0, 13.6 ppm. HRMS: calcd for C16H21F3NO4S; calculated
380.1143, found 380.1101.
4.4.2. 2-methyl-2-(3-(phenylethynyl)-1-((trifluoromethyl)
sulfonyl)-1,4-dihydropyridin-4-yl)propanoic acid (17b)
The compound was obtained as a white solid. 1H NMR (CDCl3,
300 MHz);
d
¼ 7.37 (s, 1H, H-2), 6.51 (q, J ¼ 6.0 Hz, J ¼ 1.2 Hz, 1H, H-
6), 5.22 (q, J ¼ 6.0 Hz, J ¼ 4.5 Hz, 1H, H-5), 3.85 (d, J ¼ 4.5 Hz, 1H, H-
4), 2.16-2.12 (m, 1H, H-12), 0.92 (s, 3H, H-100), 0.83 (s, 3H, H-100)
ppm. 13C NMR (CDCl3, 75 MHz);
d
¼ 196.6, 181.7, 132.5, 122.8, 122.4,
119.1 (C, J ¼ 321.0 Hz, CF3), 111.6, 47.2, 37.7, 29.7, 20.9, 20.4 ppm;
MHRMS: calcd for C12H15F3NO5S 344.0622, found 344.0560.
13

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Tetrahedron 86 (2021) 132086
4.6. General procedure for the synthesis of 2-(3-acetyl-1-
((trifluoromethyl)sulfonyl)-1,4-dihydropyridin-4-yl)-2-
methylpropanoic acid using CD2Cl2
were added with a syringe, and the mixture was stirred constantly
for 3 h. Subsequently, 1.06 mmol (1.2 equiv) of the corresponding
ketene acetal were added and stirring continued at ꢀ78 ꢁC for 2 h.
The reaction was then allowed to reach 25 ꢁC. To this solution were
added water-18O 97 atom % 18O (0.25 mL, H128O). Then the reaction
mixture was stirred (500 rpm) for 1h. The crude was transferred to
a separating funnel and washed with water (3 ꢂ 30 mL). The
organic phases were combined and dried with anhydrous Na2SO4,
and the solvent was removed by vacuum evaporation. The reaction
crude was purified by column chromatography using silica gel with
hexane/AcOEt mixtures as eluents to obtain the title compounds.
The compound was obtained as a white solid. 1H NMR (CDCl3,
To a solution with 0.15 g (0.88 mmol) 3-((trimethylsilyl)ethynyl)
pyridine dissolved in 7.5 mL of dichloromethane-d2 99.9 atom % D
(under inert atmosphere and cooled to ꢀ78 ꢁC), 0.18 mL
(1.06 mmol, 1.2 equiv) of triflic anhydride were added with a sy-
ringe, and the mixture was stirred constantly for 3 h. Subsequently,
1.06 mmol (1.2 equiv) of the corresponding ketene acetal were
added and stirring continued at ꢀ78 ꢁC for 2 h. The reaction was
then allowed to reach 25 ꢁC before being transferred to a separatory
funnel and washed with water (3 ꢂ 15 mL). The organic phases
were combined and dried with anhydrous Na2SO4, and the solvent
was removed by vacuum evaporation. The reaction crude was pu-
rified by column chromatography using silica gel with hexane/
AcOEt mixtures as eluents to obtain the title compound.
300 MHz);
d
¼ 7.39 (s, 1H, H-2), 6.53 (d, J ¼ 6.0 Hz, 1H, H-5), 5.24 (q,
J ¼ 5.7 Hz, J ¼ 4.2 Hz, 1H, H-5), 3.87 (d, J ¼ 4.2 Hz, 1H, H-4), 2.18 (s,
3H, H-12), 0.93 (s, 3H, H-10), 0.85 (s, 3H, H-100) ppm. 13C NMR
(CDCl3, 75 MHz);
d
¼ 196.5, 181.5, 132.5, 122.8, 122.3, 119.2
(J ¼ 321.0 Hz, CF3), 111.6, 47.2, 37.8, 29.7, 21.5, 20.4 ppm; MHRMS:
calcd for C12H12D3F3NO5S 344.06655, found 344.06546.
4.8. Analysis of the X-ray crystal structure of 3a
The compound was obtained as a white solid. 1H NMR (CDCl3,
300 MHz);
d
¼ 7.39 (s, 1H, H-2), 6.53 (q, J ¼ 6.0 Hz, J ¼ 1.2 Hz, 1H, H-
Suitable X-ray quality crystals of 3a were grown by slow evap-
oration from n-hexane/acetone solution at 4 ꢁC. Details of the data
collected and structure refinement parameters employed are
summarized in Table 5.
6), 5.24 (q, J ¼ 6.0 Hz, J ¼ 4.5 Hz, 1H, H-5), 3.87 (d, J ¼ 6.0 Hz, 1H, H-
4), 1.09-1.06 (m, 1H-12), 0.94 (s, 3H, 10), 0.85 (s, 3H, H-100) ppm. 13C
NMR (CDCl3, 75 MHz);
d
¼ 196.5, 181.0, 132.5, 122.8, 122.4, 119.1 (C,
J ¼ 321.0 Hz, CF3), 111.6, 47.2, 37.7, 31.6, 21.6, 20.4 ppm.; MHRMS:
calcd for C12H12D3F3NO5S 345.0811, found 345.0560.
4.9. Molecular docking
The dihydropyridine derivatives 3b, 3e, 17a and 17b as well as
fluconazole were docked at the active site of the CYP51 enzymes of
C. albicans, C. dubliniensis, C. glabrata, C. krusei, C. lusitaniae and
C. parapsilosis on the AutoDock4 program [39]. The CYP51 enzymes
4.7. General procedure for the synthesis of 2-(3-acetyl-1-
((trifluoromethyl)sulfonyl)-1,4-dihydropyridin-4-yl)-2-
methylpropanoic acid using H2O [18]
of Candida spp. were previously modeled based on the crystallized
CYP51 proteins of C. glabrata (PDB: 5JLC) and C. albicans (PDB:
5V5Z), deposited in the protein data bank (PDB) [40] as a template.
To prepare the proteins, hydrogen atoms were added and water
To a solution with 0.15 g (0.88 mmol) 3-((trimethylsilyl)ethynyl)
pyridine dissolved in 7.5 mL of CH2Cl2 (under inert atmosphere and
cooled to ꢀ78 ꢁC), 0.18 mL (1.06 mmol,1.2 equiv) of triflic anhydride
14

ꢀ
~
R. Ballinas-Indilí, O. Gomez-García, E. Trevino-Crespo et al.
Tetrahedron 86 (2021) 132086
Table 5
Funding
Crystal data and structure refinement for 3a.
The authors wish to thank Maria del Rocio Patineo-Maya for
technical support. The authors gratefully acknowledge the financial
and the DGAPA-PAPIIT Project Number IN203120. JOGG and DMAP
acknowledges financial support from the SIP-IPN, Project Number
20200950.
Empirical formula
Formula wt (g$molꢀ1):
Crystal size (mm)
Color
Crystal system
Space group
a (Å)
C12H14F3NO5S
341.30
0.35 ꢂ 0.35 x 0.34
Colourless
Monoclinic
P21/c
12.021(2)
9.911(2)
13.838(3)
90
106.59
90
1580.2(6)
4
1.435
ꢀ
support of CONACYT-Mexico, under the Project Number 252020,
b (Å)
c (Å)
Declaration of competing interest
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
The authors declare that they have no known competing
financial interests or personal relationships that could appear to
influence the work reported in this paper.
V (Å3)
Z
Dcalcd(g/cm3)
No. of reflections collected
No. of independent reflections (Rint)
Maximum and minimum transmission
Data/parameters
3419
3419
0.746 and 0.611
3419/207
1.019
Acknowledgments
The authors would like to thank Miguel A. Sierra Rodriguez and
Bruce Allan Larsen for proofreading the manuscript.
Goodness-of-fit on F
Appendix A. Supplementary data
molecules around the proteins removed before optimization on the
Nanoscale Molecular Dynamics (NAMD) program [41].
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2021.132086.
The test compounds and reference drug were drawn on
ChemBioDraw Ultra 12.0 software [42], converted to 3D with the
Open Babel GUI program [43] and optimized with GaussView 6.0
software, involving the addition of hydrogen atoms and a check of
the bond lengths and angles. The docking parameters were
examined with AutoDock Tools (ADT), adopting a grid box of
48 ꢂ 42 ꢂ 40 Å3 and points separated by 0.375 Å. The grid center
values were established for each CYP51 enzyme: X ¼ ꢀ47,731,
Y ¼ ꢀ13,422 and Z ¼ 22,982 for the CYP51 of C. albicans;
X ¼ ꢀ43,598, Y ¼ ꢀ13,588 and Z ¼ 25,836 for the CYP51 of
C. dubliniensis; X ¼ ꢀ31,107, Y ¼ 68,515 and Z ¼ ꢀ21,415 for the
CYP51 of C. glabrata; X ¼ ꢀ43,311, Y ¼ ꢀ9941 and Z ¼ 25,384 for the
CYP51 of C. krusei and C. lusitaniae; X ¼ ꢀ45,446, Y ¼ ꢀ10.26 1 and
Z ¼ 22,645 for the CYP51 of C. parapsilosis. The Lamarckian genetic
algorithm was employed, performing a total of 100 docking runs.
The docked model with the lowest binding energy was considered.
The docking results were edited with Discovery Studio client [44].
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