Synthesis and Antimicrobial Activity of (3-Formyl-4-hydroxybenzyl)triphenylphosphonium Chloride Acylhydrazones

Article abstract of DOI:10.1134/S1070363220090194

Abstract: In this study, four novel quaternary phosphonium acylhydrazones, derivatives of (3-formyl-4-hydroxybenzyl)triphenylphosphonium chloride, have been synthesized and their structures elucidated from IR and NMR spectra, and elemental analysis. All synthesized compounds have been tested for their antimicrobial activity, and acylhydrazones have demonstrated selective activity against Gram-positive bacteria strains.

Full text of DOI:10.1134/S1070363220090194

ISSN 1070-3632, Russian Journal of General Chemistry, 2020, Vol. 90, No. 9, pp. 1716–1720. © Pleiades Publishing, Ltd., 2020.
Synthesis and Antimicrobial Activity
of (3-Formyl-4-hydroxybenzyl)triphenylphosphonium Chloride
Acylhydrazones
M. R. Milenkovića, V. Živković-Radovanovića, and L. Andjelkovićb,*
a Faculty of Chemistry, University of Belgrade, Belgrade, 11000 Serbia
b University of Belgrade, Institute of Chemistry, Technology and Metallurgy, Department of Chemistry, Belgrade, 11000 Serbia
*e-mail: ljubica@chem.bg.ac.rs
Received July 7, 2020; revised August 18, 2020; accepted August 21, 2020
Abstract—In this study, four novel quaternary phosphonium acylhydrazones, derivatives of (3-formyl-4-hydroxy-
benzyl)triphenylphosphonium chloride, have been synthesized and their structures elucidated from IR and NMR
spectra, and elemental analysis. All synthesized compounds have been tested for their antimicrobial activity, and
acylhydrazones have demonstrated selective activity against Gram-positive bacteria strains.
Keywords: delocalized lipophilic cations, hydrazones, antimicrobial activity, triphenylphosphonium ions
DOI: 10.1134/S1070363220090194
INTRODUCTION
their conjugates with acylhydrazones could lead to new
efficient antimicrobial drugs.
Rapidly developed microbial resistance to different
commonly used antimicrobial drugs became an increasing
public health threat [1–3]. For instance, Gram-positive
bacterial pathogen, Staphylococcus aureus, responsible
for community-acquired and hospital-associated infec-
tions, has an extraordinary ability to develop resistance
to the antibiotics it has been exposed [4, 5]. Therefore,
due to occurrence of new pathogens and growing
antibiotic resistance, intensive search for new therapeutic
antibiotics’ alternatives is of high priority.
Herein, we present triphenylphosphonium-containing
acylhydrazone derivatives that could act as alternative
antibacterial agents. No reports on antimicrobial activity of
such compounds have been found in literature. Therefore,
this paper presents the preliminary study of synthesis,
characterization and antimicrobial activity of cationic
triphenylphosphonium-containing acylhydrazones.
RESULTS AND DISCUSSION
(3-Formyl-4-hydroxybenzyl)triphenylphosphonium
chloride was obtained in the reaction of triphenylphosphine
with 5-chloromethyl salicylaldehyde according to the
previously reported procedure (Scheme 1) [20].
Compounds containing delocalized lipophilic cations,
such as quaternary ammonium and phosphonium ions,
have been widely used as antiseptics and disinfectants
[6–13]. Recently developed mitochondria-targeted
antioxidants, conjugates of ubiquinone (MitoQ) and
plastoquinone (SkQ1) with triphenylphosphonium
moiety, exhibited the pronounced antimicrobial activity
against strains of Bacillus subtilis [14–17]. So far Gram-
positive bacteria have not developed resistance to SkQ1
and alkyl-triphenylphosphonium compounds.
Acylhydrazones of (3-formyl-4-hydroxybenzyl)-
triphenylphosphonium chloride were synthesized in
the reaction of (3-formyl-4-hydroxybenzyl)triphenyl-
phosphonium chloride with semicarbazide hydrochloride,
4-phenylsemicarbazide hydrochloride, ethyl carbazate,
and oxamic acid hydrazide (Scheme 2).
In IR spectra of the products 1–4 (Table 1) the
characteristic bands assigned to vibrations of the
carbonyl, azomethine, phenol groups, and C‒P bond
Hydrazones make an important class of compounds
used in development of new drugs due to their wide
range of biological activities such as antimicrobial,
anticonvulsant, analgesic, anti-inflammatory, antiplatelet,
antitubercular, and antitumor [18, 19]. Due to excellent
antimicrobial activity of delocalized lipophilic cations,
1
of triphenylphosphonium were recorded. In H NMR
spectra of the products 1–4 the signal of aldehyde proton
at 10.14 ppm was not recorded [20]. Instead, signal of
the azomethine group proton was observed in the spectra
1716

SYNTHESIS AND ANTIMICROBIAL ACTIVITY
1717
Scheme 1. Synthesis of (3-formyl-4-hydroxybenzyl)triphenylphosphonium chloride.
Scheme 2. Synthesis of (3-formyl-4-hydroxybenzyl)triphenylphosphonium chloride acylhydrazones 1–4.
of compounds 1–4. 13C NMR spectra of compounds 1–4
also confirmed their structures.
highest antimicrobial activity probably due to more
active hydrolysis of the ester functional group under
physiological conditions.
Antimicrobial activity. In applied concentration of
1×10–3 mol/L, the tested compounds were not active
against Candida albicans and Gram-negative Escherichia
coli. Sensitivity of tested bacterial strains was different
(Table 2) and depended mostly on the bacterial wall
structure. All investigated compounds were active
against Gram-positive bacteria, particularly Micrococcus
lysodeikticus. The compound 3 demonstrated the
EXPERIMENTAL
The reagents were obtained from Sigma-Aldrich
and Acros Organics. Melting points were determined
on an Electrothermal Melting Point Apparatus and are
uncorrected. IR spectra were recorded on a Nicolet 6700
1
FT-IR spectrophotometer using the ATR technique. H
Table 1. Characteristic IR spectral bands recorded for acylhydrazones 1–4
ν, cm–1
Band
1
1677
1590
1273
1438
3569
3400, 3185
3297
–
2
3
4
C=O
C=N
C‒O(phenol)
C‒P
1709
1616
1279
1440
3433
3195
3249
–
1718
1617
1284
1439
3565
–
1680 and 1719
1608
1278
1441
O‒H
3190 [overlapped with ν(N‒H)amide]
N‒H(amide)
N‒H(hydrazide)
C‒O(ester)
3372, 3190
3260
1251
3228
–
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MILENKOVIĆ et al.
Table 2. Antimicrobial activity of compounds 1–4
Zone of inhibition, mm
Compound
no.
1
2
3
4
Staphylococcus aureus
Bacillus subtilis
Micrococcus lysodeikticus
12.0
21.0
25.0
19.0
11.0
22.0
20.5
16.5
20.0
21.0
35.0
24.0
and 13C, and 2D NMR (COSY, HSQC) spectra were
measured on a Bruker Avance 500 spectrometer at room
temperature using DMSO-d6 as a solvent and TMS as an
internal standard. Elemental analyses were performed on
an ELEMENTARVario ELIII CHNSO analyzer.
chloride (2). Light brown crystals, yield 75%, mp
224–226°C. H NMR spectrum, δ, ppm: 4.86–4.89 d
1
(2H, J = 15.00 Hz, C5H), 6.61–6.62 d (1H, J = 5.00 Hz,
C10H), 6.67–6.70 d (1H, J = 15.00 Hz, C11H), 6.92–6.95 t
(1H, J = 5.00 Hz, C17H), 7.20–7.23 t (2H, J = 5.00 Hz,
C16H), 7.29 s (1H, C7H), 7.43–7.44 d (2H, J = 5.00 Hz,
C15H), 7.53–7.60 m (12H, C2H, C3H), 7.69–7.72 m (3H,
C4H), 7.96 s (1H, NH), 8.40 s (1H, C12H), 10.47 s (1H,
OH), 10.59 s (1H, NHhydrazide). 13C NMR spectrum, δС,
ppm: 27.92–28.30 d (JPC = 47.50 Hz, C5), 116.97 s (C10),
117.95–118.63 d (JPC = 85.00 Hz, C1), 118.19–118.25 d
(JPC = 7.50 Hz, C6), 119.97 s (C8), 121.03 s (C17), 123.38 s
(C16), 129.35 s (C15), 129.96 s (C7), 130.57–130.66 d
(JPC = 11.25 Hz, C3), 133.33 s (C11), 134.47–134.55 d
(JPC = 10.00 Hz, C2), 135.63 s (C4), 138.33 s (C12), 139.17 s
(C14), 153.24 s (C9), 156.49 s (C13). Found, %: С 70.11;
Н 5.32; N 7.40. С33Н29ClN3О2P. Calculated, %: С 70.02;
Н 5.16; N 7.42. M 566.
General procedure for synthesis of (3-formyl-
4-hydroxybenzyl)triphenylphosphonium chloride
acylhydrazones 1–4. (3-Formyl-4-hydroxybenzyl)-
triphenylphosphonium chloride (0.5 mmol) and the
appropriate acylhydrazide (semicarbazide hydrochloride,
4-phenylsemicarbazide hydrochloride, ethyl carbazate,
or oxamic acid hydrazide) (0.5 mmol) were dissolved in
25 mL of ethanol. In case of oxamic acid hydrazide and
ethyl carbazate the reaction mixtures were acidified by
adding one drop of conc. HCl. The reaction mixture
was refluxed for 3 h then stored for few days at room
temperature to allow the solvent to evaporate. Thus
obtained precipitate of the corresponding product was
filtered off. NMR spectra of compounds 1–4 were
measured without further purification.
(E)-(3-{[2-(Ethoxycarbonyl)hydrazono]methyl}-4-
hydroxybenzyl)triphenylphosphonium chloride (3).
(E)-{3-[(2-Carbamoylhydrazono)methyl]-4-
1
White crystals, yield 62%, mp 252–254°C. H NMR
hydroxybenzyl}triphenylphosphonium chloride
spectrum, δ, ppm: 1.19–1.22 t (3H, J = 10.00 Hz, C15H),
4.10–4.14 q (2H, J = 10.00 Hz, C14H), 4.97–4.99 d (2H,
J = 10.00 Hz, C5H), 6.70–6.72 d (1H, J = 10.00 Hz, C10H),
6.78–6.80 d (1H, J = 10.00 Hz, C11H), 7.04 s (1H, C7H),
7.60–7.65 m (6H, C2H), 7.69–7.73 m (6H, C3H),7.85–
7.88 m (3H, C4H), 7.98 s (1H, C12H), 10.94 s (1H, OH),
11.23 br. s (1H, NHhydrazide). 13C NMR spectrum, δС,
ppm: 14.85 s (C15), 27.65–28.03 d (JPC = 47.50 Hz, C5),
1
(1). White solid, yield 71%, mp 252–254°C. H NMR
spectrum, δ, ppm (numbering of atoms according to
Scheme 2): 4.95–4.98 d (2H, J = 15.00 Hz, C5H),
6.14 br. s (2H, NH2), 6.71–6.73 d (1H, J = 10.00 Hz,
C10H), 6.79–6.81 d (1H, J = 10.00 Hz, C11H), 7.24 s
(1H, C7H), 7.63–7.67 m (6H, C2H), 7.69–7.73 m (6H,
C3H), 7.85–7.88 m (3H, C4H), 7.97 s (1H, C12H), 10.26 s
(1H, OH), 10.40 s (1H, NHhydrazide). 13C NMR spectrum,
δС, ppm (numbering of atoms according to Scheme 2):
26.97–27.34 d (JPC = 46.25 Hz, C5), 116.01 s (C10),
117.08–117.76 d (JPC = 85.00 Hz, C1), 117.31–117.38 d
(JPC = 8.75 Hz, C6), 120.56 s (C8), 127.85 s (C7),
129.63–129.73 d (JPC = 12.50 Hz, C3), 132.25 s (C11),
133.54–133.62 d (JPC = 10.00 Hz, C2), 134.72 s (C4),
135.75 s (C12), 155.33 s (C9), 156.10 s (C13). Found, %:
С 66.21; Н 5.23; N 8.56. С27Н25ClN3О2P. Calculated, %:
С 66.19; Н 5.14; N 8.58. M 490.
61.39 s (C14), 117.04 s (C10), 117.74–118.41 d (JPC
=
83.75 Hz, C1), 118.29–118.37 d (JPC = 10.00 Hz, C6),
119.90 s (C8), 130.49–130.59 d (JPC = 12.50 Hz, C3),
131.04 s (C7), 133.25 s (C11), 134.26–134.34 d (JPC
=
10.00 Hz, C2), 135.55 s (C4), 143.15 s (C12), 153.78 s
(C9), 156.87 s (C13). Found, %: С 67.13; Н 5.47; N 5.41.
С29Н28ClN2О3P. Calculated, %: С 67.12; Н 5.44; N 5.40.
M 519.
(E)-(3-{[2-(2-Amino-2-oxoacetyl)hydrazono]-
methyl}-4-hydroxybenzyl)triphenylphosphonium
chloride (4). White solid, yield 69%, mp 258–260°C. 1H
(E)-(4-Hydroxy-3-{[2-(phenylcarbamoyl)hyd-
razono]methyl}benzyl)triphenylphosphonium
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SYNTHESIS AND ANTIMICROBIAL ACTIVITY
1719
NMR spectrum, δ, ppm: 5.13–5.17 d (2H, J = 20.00 Hz,
C5H), 6.86 s (2H, C10H, C11H), 7.17 s (1H, C7H), 7.63–
7.68 m (6H, C3H), 7.68–7.73 m (6H, C2H), 7.84–7.88 m
(3H, C4H), 7.97 s (1H, NH2), 8.25 s (1H, NH2), 8.54 s (1H,
hydrazones in high yields. All synthesized compounds
have been characterized by supporting each other
1
IR, and H and 13C NMR spectra. The products have
demonstrated selective activity against Gram-positive
bacteria, especially on Micrococcus lysodeikticus,
and (E)-{3-[{2-(ethoxycarbonyl)hydrazono}methyl]-
4-hydroxybenzyl}triphenylphosphonium chloride
containing ester functional group in hydrazide fragment
of the molecule has been determined as the most
active one. The present study is the first report of
antimicrobial activity of (3-formyl-4-hydroxybenzyl)tri-
phenylphosphonium hydrazones which provides useful
information for design of new triphenylphosphonium
derivatives with the desired biological properties. The
studied triphenylphosphonium acylhydrazones can be
considered as the promising ligands for synthesis of
potential biologically active metal complexes.
C12H), 11.12 s (1H, OH), 12.24 s (1H, NHhydrazide). 13
C
NMR spectrum, δС, ppm: 27.66–28.12 d (JPC = 57.50 Hz,
C5), 117.87–118.72 d (J = 106.25 Hz, C1), 118.46–118.55 d
(J = 11.25 Hz, C6), 131.31–131.37 d (JPC = 7.50 Hz, C7),
119.79–119.82 d (JPC = 3.75 Hz, C8), 117.33–117.35 d
(JPC = 2.50 Hz, C10), 130.44–130.57 d (J = 16.25 Hz, C3),
134.03–134.08 d (JPC = 6.25 Hz, C11), 134.45–134.55 d
(J = 12.50 Hz, C2), 135.48 s (C4),149.03 s (C12), 157.01 s
(C9), 157.80 s (C14), 162.02 s (C13). Found, %: С 65.02;
Н 4.95; N 8.10. С28Н25ClN3О3P. Calculated, %: С 64.93;
Н 4.87; N 8.11. M 518.
Antimicrobial activity. Antimicrobial tests were
performed against one standard fungal and four bacterial
strains using agar well diffusion assay. Bacteria, Gram-
negative Escherichia coliATCC 25922 and Gram-positive
Staphylococcus aureus ATCC 6853, Bacillus subtilis
ATCC 6633, and Micrococcus lysodeikticus ATCC
4698, were cultivated on nutrient agar slants of LAB 8
and yeast Candida albicans ATCC 24433 on a maltose
agar slant of LAB 37 (Lab M, Bury, United Kingdom),
respectively. The bacteria were thermostated at 37°C for
24 h, while Candida albicans was thermostated at 28°C
for 48 h. Each grown culture was suspended in 5 mL of
sterile physiological solution (8 g NaCl/L) and 0.5 mL
of the suspension was carefully mixed with 10 mL of
the cooled molten agar medium in a Petri dish. In the
solidified inoculated agar plates, the diameter 10 mm
holes were made with a sterile cork borer and 100 μL
aliquots of the investigated solutions were introduced
therein. After three hours at room temperature (to permit
diffusion before intensive microbial growth), the agar
plates were thermostated as described. The obtained
zones of inhibition (bactericidal and bacteriostatic) were
measured. Equimolar stock solutions of the investigated
compounds (1×10–2 mol/L) were prepared in DMSO and
before the application were diluted 10 times with sterile
deionized water.
FUNDING
This work was financially supported by the Serbian Ministry
of Education, Science and Technological Development (grant
no. 451-03-68/2020-14/200026).
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
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