Synthesis, characterization and antibacterial applications of pyrazolyl-sulfonamides and their palladium complexes

Article abstract of DOI:10.1039/d0nj05143h

A series of pyrazolyl sulfonamide compounds were prepared by a multi-step procedure involving preparation of phenyl pyrazolyl compounds (C1, C2) and their chlorosulfonated derivatives (C3-C5), which were then converted to sulfonamides (L1-L6). Complexes of L1-L6 with palladium(ii) show the standard trans square-planar coordination environment for the six complexes (1-6). All products were prepared in moderate to high yield (61-81%). All compounds were successfully characterized by NMR spectroscopy, IR spectroscopy, mass spectrometry and in one case single X-ray crystallography. Conversion of C1 and C2 to C3-C5 is governed by steric hindrance on the pyrazolyl group as sulfonation of the phenyl only is observed for tBu groups (C4), whereas for Me groups sulfonation of the pyrazolyl is observed C3 as well as phenyl ring for C5. Antimicrobial screening was carried out on the compounds using the agar-well diffusion method at varying concentrations of (62.5, 125, 250, 500 and 1000 μg mL-1) on ten (10) bacteria strains. The zone of inhibition for all the compounds are within the ranges of 9.5 mm to 25 mm compared to the control antibiotic, gentamicin that was between 16.5 mm to 36 mm. The compounds L1-L6 generally showed mild to strong antibacterial activity in the zones of inhibition against most Gram negative bacteria strains tested, but no activity against Gram positive bacteria strains Staphylococcus aureus and Enterococcus faecalis, except L4 which showed activity towards Staphylococcus. The palladium(ii) complexes generally showed improved activities for all the bacteria strains studied with 4 exhibiting the most potent in vitro anti-bacterial activity with MICs of 1.046 μg mL-1 and 0.237 μg mL-1 against Staphylococcus epidermidis and Proteus mirabilis respectively. Theoretical Log P calculation show values between 3.06 and 5.95 for the ligands and between 6.67 and 12.36 for complexes. Suggesting high affinity of these compounds to the lipophilic medium. However, the experimental Log P value gave a different trend, which shows that compounds with sulfonation only on the phenyl ring (L3 (-0.83), L4 (-0.53), 3 (-0.96) and 4 (-0.72)) have high affinity for the hydrophilic medium. This journal is

Full text of DOI:10.1039/d0nj05143h

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Synthesis, characterization and antibacterial
applications of pyrazolyl-sulfonamides and their
Cite this: New J. Chem., 2021,
45, 3716
palladium complexes†
ab
ab
Cephas Amoah,
Collins Obuah,
*
Michael Kojo Ainooson,ab
bc
Christian Kwaku Adokoh
and Alfred Mullerb
A series of pyrazolyl sulfonamide compounds were prepared by a multi-step procedure involving
preparation of phenyl pyrazolyl compounds (C1, C2) and their chlorosulfonated derivatives (C3–C5),
which were then converted to sulfonamides (L1–L6). Complexes of L1–L6 with palladium(II) show the
standard trans square-planar coordination environment for the six complexes (1–6). All products were
prepared in moderate to high yield (61–81%). All compounds were successfully characterized by NMR
spectroscopy, IR spectroscopy, mass spectrometry and in one case single X-ray crystallography.
Conversion of C1 and C2 to C3–C5 is governed by steric hindrance on the pyrazolyl group as sulfo-
nation of the phenyl only is observed for tBu groups (C4), whereas for Me groups sulfonation of the
pyrazolyl is observed C3 as well as phenyl ring for C5. Antimicrobial screening was carried out on the
compounds using the agar-well diffusion method at varying concentrations of (62.5, 125, 250, 500 and
1000 mg mLꢀ1) on ten (10) bacteria strains. The zone of inhibition for all the compounds are within the
ranges of 9.5 mm to 25 mm compared to the control antibiotic, gentamicin that was between 16.5 mm
to 36 mm. The compounds L1–L6 generally showed mild to strong antibacterial activity in the zones of
inhibition against most Gram negative bacteria strains tested, but no activity against Gram positive
bacteria strains Staphylococcus aureus and Enterococcus faecalis, except L4 which showed activity towards
Staphylococcus. The palladium(II) complexes generally showed improved activities for all the bacteria strains
studied with 4 exhibiting the most potent in vitro anti-bacterial activity with MICs of 1.046 mg mLꢀ1 and
0.237 mg mLꢀ1 against Staphylococcus epidermidis and Proteus mirabilis respectively. Theoretical Log
P calculation show values between 3.06 and 5.95 for the ligands and between 6.67 and 12.36 for
complexes. Suggesting high affinity of these compounds to the lipophilic medium. However, the
experimental Log P value gave a different trend, which shows that compounds with sulfonation only on the
phenyl ring (L3 (ꢀ0.83), L4 (ꢀ0.53), 3 (ꢀ0.96) and 4 (ꢀ0.72)) have high affinity for the hydrophilic medium.
Received 19th October 2020,
Accepted 1st February 2021
DOI: 10.1039/d0nj05143h
rsc.li/njc
mortality, higher treatment costs and increased illness recovery
time.1 The use of heterocyclic moieties have attracted significant
1. Introduction
Antibacterial resistance has become a threat to global health, interest and attention in the development of pharmacologically
food security and human development. In recent years, the active molecules.2,3 Pyrazole, a five membered aromatic com-
rapid emergence of multidrug resistant bacteria caused by the pound as well as its derivatives have gained popularity in drug
wide application of antibiotics in clinical practices has cause development due to its manifold use in agents such as anti-
great difficulties in medical treatment leading to increased bacterial,4 anti-microbial,5 anticonvulsant,6,7 anti-cancer8,9 and
anti-tubercular.10 Sulfonamides, on the other hand are structural
analogues of para-aminobenzoic acid (PABA) (the precursor for
making folic acid), which shows varying solubility, absorption
and excretion characteristics. The significance of the sulfon-
amide moiety in medicinal chemistry cannot be ignored as they
exhibit diverse biological properties including anti-bacterial and
anti-diabetic properties. According to Jain et al.11 sulfonamides
play an important role in the transition state mimetic of peptide
hydrolysis, as a potent irreversible inhibitor of cysteine proteases
a Department of Chemistry, University of Ghana, Legon, Ghana.
E-mail: cobuah@ug.edu.gh
b Department of Chemical Sciences, University of Johannesburg,
Auckland Park 2006, Johannesburg, South Africa
c Department of Forensic Sciences, School of Biological Sciences,
University of Cape Coast, Cape Coast, Ghana
† Electronic supplementary information (ESI) available. CCDC 2039260. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
d0nj05143h
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during anti-microbial activities. More recently, they have also employed were based on the standard operating procedure (SOP)
found use as anti-cancer, antiviral agents and in the treatment of adapted from Clinical and Laboratory Standards Institute (CLSI)
Alzheimer’s disease.12 Experimental analysis has also shown that of the United States of America (CLSI, 2017).23 Bacteria strains
anti-microbial activities of organic ligands and their metal used are: Gram-positive Staphylococcus aureus, Enterococcus fae-
complexes are strongly dependent on the central metal ion.13 calis, Staphylococcus epidermidis and Gram negative Citrobacter
Hence the emergence of some metal complexes of palladium freundii, Salmonella typhi, Pseudomonas aeruginosa, Vibro cholera
and platinum complexes have shown appreciable activities as O1E1 Tor, Proteus mirabilis, Escherichia coli and Klebsiella
anti-tumor agents. This is attributed to the labile nature of these pnemoniae.
complexes compared to known compounds such as cisplatin
Infrared (IR) spectra of ligands and complexes were recorded
and carboplatin.14 Palladium, due to its similar coordination on a PerkinElmer Spectrum Two equipped with a diamond
chemistry to platinum and some advantages like higher ATR. Elemental analyses were performed on a Vario Elementar
solubility of its complexes when compared to platinum, has III microcube CHNS. The mass spectrometry unit at the
attracted attentions as
a
potential candidate in drug Chemistry Department, University of Cape Coast performed
discovery.15–18 It has been reported that palladium(II) complexes the ESI-MS spectra on a Waters API Qualtro micro spectro-
show high cytotoxicity activity against head and neck squamous photometer. NMR spectra were recorded on a Bruker 500 MHz
cancer, ovarian cancer, breast cancer, malignant melanoma, instrument (1H at 500 MHz and 13C{1H} at 125 MHz) at the
glioma, human colorectal adenocarcinoma, osteogenic sarcoma, Department of Chemistry, University of Ghana. The chemical
human chronic myelogenous leukemia, prostate cancer, lung shifts are reported in d (ppm) and referenced to the residual
cancer and human cervical epithelial cancer.19 However, the proton and carbon signals 7.24 ppm and 77.0 ppm respectively
evolution of resistant strains of bacteria, viruses and fungi to of CDCl3 NMR solvent.
commonly known biologically active agents have become a great
2.1.1 Preparations of test compounds (pyrazolyl sulfonamides)
concern in clinical medicine. For these reasons, synthesis of new for anti-microbial screening. Test ligands and complexes were
chemical products are on the rise to fight these diseases and prepared through a serial dilution (1000, 500, 250, 125 and
infections. A number of combinatory synthesis of very active 62.5 mg mLꢀ1) of approximately 0.01 g of individual compounds
compounds have been employed to provide a sure inhibition of dissolved in 10 mL DMSO to obtain a stock concentration of
resistant breeds. It is therefore well known that combination of 1000 mg mLꢀ1
multiple biologically active moieties in a single pharmacophore
improves the bioactivity of the compound and associated resis- cultured on nutrient agar with each bacterial cell smeared on
tance to the microbes.20
a slide and heat fixed. Crystal violet (primary stain) was added
.
2.1.2 Gram staining. Individual organisms were sub
As such, this study report the synthesis of biological active onto the slide for a minute and gently rinse with running tap
scaffold comprising of the combination of sulfonamide and water to remove excess crystal violet. Subsequently, iodine
pyrazolyl moieties into a single pharmacophore, complexed (mordant) was added for a minute and rinse with acetone for
with palladium(II) metal. The anti-bacterial activities of the 30 seconds. Then, Safranin was added for a minute and rinse
ligands and palladium complexes are also reported here in.
with running tap water. The slide was viewed under an electron
microscope to establish the virility of the bacteria strains.
2.1.3 Preparations of sub-cultures from control strains.
The control strains; Staphylococcus aureus (ATCC 25923), Klebsiella
pnuemoniae (ATCC 43816), Citrobacter freundii (ATCC43864),
Escherichia coli (ATCC 25922), Salmonella typhi (ATCC 19430),
2. Experimental section
2.1 Materials and methods
Unless otherwise stated, all manipulations were carried out under Staphylococcus epidermidis (ATCC 12228), Pseudomonas aeruginosa
nitrogen atmosphere using standard Schlenck techniques. All (ATCC 15442), Proteus mirabilis (ATCC 25933), Vibro cholerae
organic solvents were dried and purified by distillation over (ATCC 39451) and Enterococcus faecalis (ATCC 9790) were kept at
standard reagents under nitrogen prior to use. Compound ꢀ80 1C and thawed before use. Nutrient agar plates were prepared
[PdCl2(NCMe)2] was synthesized according to literature and a loop full of control bacteria strains spread over the surface
procedure.21 Compounds chlorosulfonic acid, phenyl hydrazine, of the agar-based nutrient medium in quadrants so that bacterial
pentane-2,4-dione, tert-butylamine, propylamine and 2,2,6,6- cells are deposited at widely separated points on the surface of
tetramethyl-3,5-heptadione, octanol were purchased from Sigma- the medium. All the procedures were aseptically performed, by
Aldrich. All chemicals were used as received.
flaming both the loop and rim of the bottle or tube, before and
Antimicrobial activity was carried out using the well diffusion after removing the inoculum. The plates were then incubated
method.22 The standard bacteria strains used for the anti- upside-down for 24 h.23
microbial activity were obtained from Noguchi Memorial
2.1.4 Preparation of inoculum and media. The sub cultured
Institute for Medical Research, Accra, Ghana. The compounds test organisms were transferred into 0.1% sterile peptone water
were screened for their antimicrobial activity in triplicate, via a sterile inoculating loop and emulsified to 0.5 MacFarland
against the selected bacteria at varying concentrations of 1000, standard. Prior to antibiotic susceptibility testing, the bacterial
500, 250, 125 and 62.5 mg mL .
ꢀ1 22 Gentamicin, used as positive suspensions were incubated at 37 1C for 10 to 15 mins in a
control, was purchased from the pharmacy stores. All procedures bacteriological incubator.
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A Mueller-Hinton (MH) agar, for Antibiotic Susceptibility Test- as the log of the ratio of the concentration of the compound in
ing (AST) was prepared according to the manufacturer’s instruc- the octanol phase to the concentration in the aqueous phase at
tions (Microgen, Central Drug 40 House LTD, New Delhi – India). pH 7.4.
2.1.5 Test procedure. The well diffusion technique was
2.1.9 Statistical analysis. All data were entered into a
used according to National Committee for Clinical Laboratory spreadsheet of Microsoft Excel and transferred to a graph pad
Standards (NCCLS) for AST using Muller Hinton medium prism. This was done to present the results in tables and graph
plates. Inoculum containing 106 cfu per mL of each bacterium charts for the analysis of the inhibition zones and to compute
to be tested was spread on the plates with a sterile swab the minimum inhibition concentration of the drugs.
moistened with the bacterial suspension.24 Subsequently, wells
2.2 Synthesis of ligands
of 6 mm diameter were punched into the agar medium and
filled with two drops of each test compounds with different
2.2.1 Synthesis of 3,5-dimethyl-1-phenyl-1H-pyrazole (C1).
concentrations. Wells containing the same volume of two An ethanol solution (20 mL) of pentane-2,4-dione (5.45 g, 0.05
percent concentrated DMSO and distilled water served as mol) was added to a stirring ethanol solution (30 mL) of phenyl
negative controls while standard gentamycin drug was used hydrazine (5.05 g, 0.05 mol). The resultant mixture was refluxed
as the positive control. Three replicates were carried out for at 80 1C for 12 h to give an orange solution. This solution was
each drug against each of the test organisms. Plates were then evaporated to afford analytically pure dark orange oil. Yield =
incubated at 37 1C for 18–24 h in a bacteriological incubator. 6.98 g (81%). 1H NMR (CDCl3): d 2.27 (s, 3H, CH3); 2.28 (s, 3H,
Zones of inhibition of the various compounds were measured CH3); 5.97 (s, 1H, pz-H); 7.33 (m, 1H, Ph); 7.42 (m, 4H, Ph).
to the nearest millimeters (mm).
13C{1H} NMR (CDCl3): d 12.2; 13.41; 106.8; 124.6; 127.1; 128.8;
2.1.6 Determination of the minimum inhibition concen- 139.2; 139.8. GCMS (EI) m/z [M]+ calcd 172.100: found: 172.152
tration. The zones of inhibition, X, was measured for each (100%).
concentration of gentamicin and the novel compounds as
shown in the eqn (1).24
Compound C2 was prepared in a similar manner as
described for C1, using appropriate reagents.
2.2.2 Synthesis of 3,5-di-tert-butyl-1-phenyl-1H-pyrazole
(C2). The compound 2,2,6,6-tetramethylheptane-3,5-dione
X = (a ꢀ b)/2
(1)
where X = zone of inhibition, a = inhibition zone diameter and (0.92 g, 5.0 mmol) was reacted with phenyl hydrazine (0.54 g,
b = diameter of wells. 5.0 mmol) to give light brown solid. Yield = 0.83 g (65%).
t
t
The diameter of inhibition zone was determined to be 1H NMR, (CDCl3): d 1.14 (s, 9H, Bu); 1.31 (s, 9H, Bu); 5.98 (s,
directly proportional to concentration of drugs. A graph 1H, pz-H); 7.37 (m, 1H, Ph); 7.40 (m, 4H, Ph). 13C{1H} NMR
relation of X2 against the log of concentration was plotted to (CDCl3): d 30.6; 30.8; 100.2; 128.5; 128.7; 129.0. GCMS (EI) m/z
obtain the intercept of the various drug action. Anti-log of the [M]+ calcd 256.190: found: 256.182 (100%).
x intercept was then calculated to obtain the MIC of the drug
2.2.3 Synthesis of 3,5-dimethyl-1-phenyl-1H-pyrazole-4-
sulfonyl chloride (C3). Solution of compound C1 (1.85 g,
compounds as reported in literature.25
2.1.7 Theoretical calculation of the lipophilicity or hydro- 11.0 mmol) was added slowly to an excess chlorosulfonic acid
philicity of the compounds using their relative solubility while stirring under ice bath. This dark solution was stirred
Log P values. The solubility profile of all tested compounds were under ice bath for 30 min and further refluxed for 2 h. The
estimated using atom/fragment contribution method that pre- resulting mixture was poured into ice and the product extracted
26
dicts log Pcalc
.
The solubility contributions (groups and substi- with chloroform. The extract was evaporated to obtain a brown
1
tuents) are expressed as hydrophilic negative value or lipophilic oil. Yield = 2.23 g (77%). H NMR (CDCl3): d 2.53 (s, 3H, CH3);
(positive value) fragment constants as shown in eqn (2).26
2.54 (s, 3H, CH3); 7.39 (d, 2H, JHH = 8.5 Hz, Ph); 7.53 (m, 3H,
Ph); 13C{1H} NMR (CDCl3): d 12.0;13.1; 122.8; 125.7; 129.5; 137.6.
GCMS (EI) m/z [M]+ calcd: 270.020; found; 270.150 (100%).
Compounds C4 and C5 were prepared in a similar manner
as described for C3, using the appropriate reagents.
3
P
Log Pcalc. =
w
(2)
P
where Log Pcalc = log of partition coefficient and w = sum of
hydrophilic or lipophilic constants.
2.1.8 Experimental Log P estimation. In determining the
2.2.4 Synthesis of 4-(3,5-di-tert-butyl-1H-pyrazol-1-yl)benzene-
Log P of the ligands (L1–L6) and metal complexes (1–6), the 1-sulfonyl chloride (C4). Compound C2 (0.73 g, 2.8 mmol) was
traditional shake-flask method was employed at a temperature added to chlorosulfonic acid to obtain a light brown oil. Yield =
of 298 K. An aqueous phase adjusted with phosphate buffer at 0.82 g (81%). 1H NMR, (CDCl3): d 1.15 (s, 9H, tBu); 1.52 (s, 9H, tBu);
3
pH 7.4 was used whilst 1-octanol was used as the organic phase. 6.25 (s, 1H, pz-H); 7.43 (m, 1H, JHH = 8.0 Hz, Ph); 7.65 (d, 2H,
Equal amounts of the both phases were combined and kept for 3JHH = 7.0 Hz, Ph); 7.73 (s, 1H, Ph). 13C{1H} NMR (CDCl3): d 29.65;
saturation for 24 hours. Known amounts of the compounds 29.73; 29.91; 32.25; 32.72; 102.73; 126.18; 126.78; 128.61; 128.88;
were dissolved in equal amounts of the aqueous and octanol 130.30; 133.92; 146.38; 158.99. GCMS (EI) m/z [M]+ calcd: 354.120;
phases, shaken and left for separation for 24 h. The concen- found: 354.250 (100%).
tration of the compounds in the aqueous and octanol phase
2.2.5 Synthesis of 1-(4-(chlorosulfonyl)phenyl)-3,5-dimethyl-
were determined using analytical UV method from developed 1H-pyrazole-4-sulfonyl chloride (C5). Compound C1 (0.7 g,
calibration curves (Fig. S31–S35, ESI†). The Log P was calculated 4.1 mmol) was added to chlorosulfonic acid to obtain a brown
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oil which solidifies after 3 days. Yield = 1.06 g (71%). H NMR
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1
2.2.9 Synthesis of 4-(3,5-di-tert-butyl-1H-pyrazol-1-yl)-N-
(CDCl3): d 2.55 (s, 3H, CH3); 2.64 (s, 3H, CH3); 2.67 (s, 3H, CH3); propylbenzenesulfonamide (L4). A 20 mL CH2Cl2 solution of
3
3
7.73 (d, 1H, JHH = 8.5 Hz, Ph); 7.83 (d, 1H, JHH = 5.0 Hz, Ph); 4-(3,5-di-tert-butyl-1H-pyrazol-1-yl)benzene-1-sulfonyl chloride
8.16 (s, 1H, Ph); 8.22 (d, 1H, JHH = 8.5 Hz, Ph). 13C{1H} NMR (C4) (0.22 g, 0.6 mmol) was added to propylamine to afford a
3
(CDCl3): d 12.1; 12.3; 13.0; 13.1; 123.9; 126.2; 127.4; 128.5; 131.1; dark brown oil, which solidifies after few hours. Yield = 0.177 g
131.6; 138.7. GCMS (EI) m/z = [M]+ calcd 367.950; found: 368.012 (76%). 1H NMR (CDCl3): d 0.87 (t, 3H, 3JHH = 7.5 Hz, CH3); 1.13
(100%).
(s, 9H, CH3); 1.22 (s, 6H, CH3); 1.26 (d, 7H, CH3); 1.35 (s, 5H,
2.2.6 Synthesis of N-(tert-butyl)-3,5-dimethyl-1-phenyl-1H- CH3); 1.61 (m, 2H, CH2); 2.83 (m, 2H, 3JHH = 7.5 Hz, CH2); 5.99
pyrazole-4-sulfonamide (L1). To a 10 mL CH2Cl2 solution of 3,5- (s, 1H, pz-H); 7.76 (d, 1H, Ph); 7.83 (d, 1H, Ph); 7.92 (m, 2H, Ph).
dimethyl-1-phenyl-1H-pyrazole-4-sulfonyl chloride (C3) (0.41 g, 13C{1H} NMR (CDCl3): 10.74; 20.72; 30.35; 30.37; 30.46; 30.79;
1.5 mmol) was added tert butylamine in a 1 : 1 mole ratio and 31.82; 31.86; 32.79; 33.48; 41.53; 100.63; 106.88; 126.44; 128.8;
the resulting solution stirred at 50 1C for 3 h. The solvent was 130.28; 130.77; 144.72; 153.51; 155.83. IR (Diamond ATR,
evaporated to afford analytically pure dark brown oil. The cmꢀ1): 3428 n(N–H). GCMS (EI) m/z[M]+ calcd: 377.210; found:
compound was purified by column chromatography, using 377.257 (100%). Anal. calcd for C20H31N3O2S: C, 63.63; H, 8.28;
a solvent system of a mixture of ethyl acetate–hexane in a N, 11.13; S, 8.49%. Found C, 63.71; H, 8.44; N, 11.40; S, 8.80%.
10 : 1 ratio. The purified product was oily but solidifies after a Calculated log Po/w: 5.77; experimental Log Po/w: ꢀ0.53.
few hours. Yield = 0.36 g (77%). 1H NMR (CDCl3): d 1.26 (s, 9H,
2.2.10 Synthesis of N-(tert-butyl)-1-(4-(N-(tert-butyl)sulfamoyl)
phenyl)-3,5-dimethyl-1H-pyrazole-4-sulfonamide (L5). A CH2Cl2
3
tBu); 2.44 (s, 3H, CH3); 2.45 (s, 3H, CH3); 7.34 (d, 2H, JHH
=
8.5 Hz, Ph); 7.42 (t, 1H, 3JHH = 5.0 Hz, Ph); 7.46 (t, 2H, 3JHH = 8.5 solution of 1-(4-(chlorosulfonyl)phenyl)-3,5-dimethyl-1H-pyrazole-
Hz, Ph). 13C{1H} NMR (CDCl3): d 11.8; 13.0; 27.3; 29.9; 54.4; 4-sulfonyl chloride (C5) (0.34 g, 0.9 mmol) was added to tert-
120.17; 125.7; 128.7; 129.2; 138.3; 141.6. IR (Diamond ATR, butylamine in a ratio of 1 : 2 to afford a bright brown oil, which
cmꢀ1): 3254 n(N–H) amine. GCMS (EI) m/z [M]+ calcd 307.140; solidifies after few hours. Yield = 0.28 g (71%). 1H NMR (CDCl3):
found: 307.135 (100%). Anal. calcd for C15H21N3O2S: C, 58.61; d 1.22 (s, 9H, CH3); 1.26 (s, 9H, CH3); 2.45 (s, 3H, CH3); 2.50 (s,
H, 6.89; N, 13.67; S, 10.43%. Found: C, 58.82; H, 7.01; N, 13.41; 3H, CH3); 4.86 (d, 1H, NH); 5.03 (d, 1H, NH); 7.51 (d, 1H, 3JHH
=
S, 10.72%. Calculated log Po/w: 3.44; experimental Log Po/w: 1.01. 9.0 Hz, Ph); 7.58 (m, 1H, Ph); 7.91 (t, 1H, Ph); 8.04 (d, 1H, Ph).
Compounds L2–L6 were prepared in a similar manner as 13C{1H} NMR (CDCl3): d 11.90; 12.06; 13.10; 14.13; 20.98; 29.69;
described for L1, using the appropriate reagents.
30.11; 30.13; 54.59; 54.97; 55.08; 60.35; 121.41; 123.85; 125.64;
2.2.7 Synthesis of N-(propyl)-3,5-dimethyl-1-phenyl-1H- 126.77; 128.13; 129.07; 130.05; 138.92; 141.30; 141.72; 141.75.
pyrazole-4-sulfonamide (L2). A CH2Cl2 solution of 3,5-dimethyl- IR (Diamond ATR, cmꢀ1): 3276 n(N–H) amine. GCMS (EI) m/z
1-phenyl-1H-pyrazole-4-sulfonyl chloride (C3) (0.55 g, 2.0 mmol) [M]+ calcd:442.170; found: 442.544 (100%). Anal. calcd for
was added to propylamine to afford a light brown oil, which
C19H30N4O4S2: C, 51.56; H, 6.83; N, 12.66; S, 14.49%. Found
solidifies after few hours. Yield = 0.47 g (79%). 1H NMR (CDCl3): C, 51.76; H, 6.99; N, 12.78; S, 14.61%. Calculated log Po/w: 3.41;
3
3
d 0.91 (t, 3H, JHH = 7.5 Hz, CH3); 1.54 (m, 2H, JHH = 7.0 Hz, experimental Log Po/w: 0.94.
CH2); 2.45 (s, 3H, CH3); 2.46 (s, 3H, CH3); 2.94 (m, 2H, 3JHH = 7.0
2.2.11 Synthesis of
Hz, CH2); 4.41 (s, 1H, NH); 7.36 (d, 2H, 3JHH = 7.0 Hz, Ph); 7.43 propylsulfamoyl)phenyl)-1H-pyrazole-4-sulfonamide (L6).
3,5-dimethyl-N-propyl-1-(4-(N-
A
(t, 1H, Ph); 7.48 (t, 2H, Ph). 13C{1H} NMR (CDCl3): d 11.18; CH2Cl2 solution of 1-(4-(chlorosulfonyl)phenyl)-3,5-dimethyl-
11.86; 13.13; 22.87; 44.48; 116.87; 125.70; 128.86; 129.31; 1H-pyrazole-4-sulfonyl chloride (C5) (0.37g, 1.0 mmol) was
138.38; 142.60. IR (Diamond ATR, cmꢀ1): 3278 n(N–H) amine. added to propylamine in a ratio of 1 : 2 mole to afford a bright
GCMS (EI) m/z [M]+ calcd: 293.120; found: 293.119 (100%). Anal. brown oil, which solidifies after few hours. Yield = 0.34 g (83%).
calcd for C14H19N3O2S: C, 57.31; H, 6.53; N, 14.32; S, 10.93%. 1H NMR (CDCl3): d 0.89 (m, 6H, CH3); 1.51 (m, 4H, CH2); 2.45
Found C, 57.52; H, 6.80; N, 14.91; S, 10.62%. Calculated logPo/w
3.16; experimental Log Po/w: 2.96.
:
(s, 3H, CH3); 2.51 (s, 3H, CH3); 2.94 (m, 4H, CH2); 4.71 (t, 1H,
3
NH); 4.77 (t, 1H, NH); 7.55 (d, 1H, JHH = 6.5 Hz, Ph); 7.62 (m,
3
3
2.2.8 Synthesis of N-(tert-butyl)-4-(3,5-di-tert-butyl-1H- 1H, Ph); 7.91 (t, 1H, JHH = 5.0 Hz, Ph); 7.98 (d, 1H, JHH
=
pyrazol-1-yl)benzenesulfonamide (L3). A 20 mL CH2Cl2 solution 6.5 Hz, Ph). 13C{1H} NMR (CDCl3): d 10.96; 11.10; 11.87; 12.02;
of 4-(3,5-di-tert-butyl-1H-pyrazol-1-yl)benzene-1-sulfonyl chloride 13.06; 13.08; 22.85; 22.93; 22.95; 44.44; 44.95; 45.00; 124.08;
(C4) (0.51 g, 1.4 mmol) was added to tert-butylamine to afford a 125.75; 126.91; 128.23; 129.25; 130.15; 140.19. IR (Diamond
dark brown oil, which solidifies after few hours. Yield = 0.498 g ATR, cmꢀ1): 3292 n(N–H) amine. GCMS (EI) m/z [M]+ calcd:
1
(81%). H NMR (CDCl3): d 1.12 (s, 9H, CH3); 1.21 (s, 9H, CH3); 414.140; found: 414.141 (100%). Anal. Calcd for C17H26N4O4S2:
1.27 (s, 9H, CH3); 4.08 (s, 1H, NH); 5.98 (s, 1H, pz-H); 7.75 (d, 1H, C, 49.25; H, 6.32; N, 13.52; S, 15.47%. Found: C, 49.51; H, 6.71;
Ph); 7.82 (s, 1H, Ph); 7.89 (m, 2H, Ph). 13C{1H} NMR (CDCl3): d N, 13.80; S, 15.54%. Calculated log Po/w: 3.06; experimental
27.59; 28.66; 30.44; 32.86; 33.53; 52.49; 100.64; 106.92; 126.4; Log Po/w: 0.67.
128.8; 129.03; 130.33; 130.89; 142.2. IR (Diamond ATR, cmꢀ1):
3415 n(N–H) amine. GCMS (EI) m/z [M ꢀ Me]+ calcd: 377.210;
2.3 Synthesis of complexes
found: 377.250 (100%). Anal. calcd for C21H33N3O2S: C, 64.41; H,
2.3.1 Synthesis of dichloro-bis-N-(tert-butyl)-3,5-dimethyl-
8.49; N, 10.73; S, 8.19%. Found C, 64.60; H, 8.54; N, 10.86; S, 1-phenyl-1H-pyrazole-4-sulfonamide pallidum(II) complex (1).
8.33%. Calculated logPo/w: 5.95; experimental Log Po/w: ꢀ0.83. To a 10 mL MeOH solution of (0.46 g, 1.5 mmol) N-(tert-
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butyl)-3,5-dimethyl-1-phenyl-1H-pyrazole-4-sulfonamide
(L1) 129.9; 132.0; 142.4; 144.8. IR (Diamond ATR, cmꢀ1): 3459 n(N–H).
was added to (0.19 g, 0.7 mmol) [Pd(MeCN)2Cl2] precursor as GCMS (EI) m/z [M]+ 930.270; found: 930.280 (80%). Anal. calcd for
prepared in literature21 and the resulting solution stirred at C40H62Cl2N6O4PdS2: C, 51.53; H, 6.70; N, 9.01; S, 6.88%. Found C,
room temperature for 5 h. The solvent was evaporated and the 51.79; H, 6.66; N, 9.25; S, 6.96%. Calculated log Po/w: 12.00;
complex formed precipitated after a CH2Cl2 solution was experimental Log Po/w: ꢀ0.72.
layered with hexane. Further recrystallization were done to
2.3.5 Synthesis of dichloro-bis-N-(tert-butyl)-1-(4-(N-(tert-
1
afford a pure complex. Yield = 0.49 g (83%). H NMR (CDCl3): butyl)sulfamoyl)phenyl)-3,5-dimethyl-1H-pyrazole-4-sulfonamide
d 1.56 (s, 18H, CH3); 2.30 (s, 6H, CH3); 2.36 (s, 6H, CH3); 4.42 (s, palladium(II) complex (5). To a 10 mL MeOH solution of (0.37 g,
3
2H, NH); 7.36 (d, 2H, JHH = 8.5 Hz, Ph); 7.67 (m, 10H, Ph). 0.8 mmol) N-(tert-butyl)-1-(4-(N-(tert-butyl)sulfamoyl)phenyl)-3,5-
13C{1H} NMR (CDCl3): d 11.9; 13.5; 29.86; 55.0; 121.5; 129.4; dimethyl-1H-pyrazole-4-sulfonamide (L5) was added to (0.11 g,
129.9; 130.8; 136.3; 145.4; 150.5. IR (Diamond ATR, cmꢀ1): 3280 0.4 mmol) [Pd(MeCN)2Cl2]. Yield = 0.35 g (78%). 1H NMR (CDCl3):
n(N–H) amine. GCMS (EI) m/z [M]+ calcd: 790.110; found: d 1.25 (d, 18H, CH3); 1.34 (s, 9H, CH3); 1.35 (s, 9H, CH3); 2.32 (m,
790.148 (80%). Anal. calcd for C30H42Cl2N6O4PdS2: C, 45.49; 6H, CH3); 2.40 (m, 6H, CH3); 4.60 (s, 1H, NH); 4.83 (m, 3H, NH);
H, 5.34; N, 10.61; S, 8.10%. Found: C, 45.67; H, 5.51; N, 10.70; S, 7.82 (d, 2H, 3JHH = 7.0 Hz, Ph); 7.88 (t, 1H, 3JHH = 8.0 Hz, Ph); 7.97
8.42%. Calculated log Po/w: 7.05; experimental Log Po/w: 1.20.
Compounds 2–6 were prepared in a similar manner as (CDCl3): d 11.92; 29.88; 30.14; 30.22; 50.75; 128.11; 130.44. IR
described for 1, using the appropriate reagents.
(Diamond ATR, cmꢀ1): 3296 n(N–H). GCMS (EI) m/z [M]+
(d, 1H, Ph); 8.05 (d, 1H, Ph); 8.25 (t, 3H, Ph). 13C{1H} NMR
2.3.2 Synthesis of dichloro-bis-N-(propyl)-3,5-dimethyl-1- 1060.180; found: 1060.181 (55%). Anal. calcd for C38H60Cl2
phenyl-1H-pyrazole-4-sulfonamide pallidum(II) complex (2). To N8O8PdS4: C, 42.96; H, 5.69; N, 10.55; S, 12.07%. Found C,
a MeOH solution of (0.44 g, 1.50 mmol) N-(propyl)-3,5-dimethyl- 43.05; H, 5.73; N, 10.68; S, 12.11%. Calculated log Po/w: 7.38;
1-phenyl-1H-pyrazole-4-sulfonamide (L2) was added to (0.19 g, experimental LogPo/w: 1.10.
0. 7 mmol) [Pd(MeCN)2Cl2]. Yield = 0.46 g (81%). 1H NMR
2.3.6 Synthesis of dichloro-bis-3,5-dimethyl-N-propyl-1-(4-(N-
propylsulfamoyl)phenyl)-1H-pyrazole-4-sulfonamide palladium(II)
3
3
(CDCl3): d 0.88 (t, 6H, JHH = 7.5 Hz, CH3); 1.49 (m, 4H, JHH
=
7.0 Hz, CH2); 2.30 (s, 6H, CH3); 2.36 (s, 6H, CH3); 2.88 (m, 4H, complex (6). To a 10 mL MeOH solution of (0.38 g, 0.9 mmol) 3,5-
3JHH = 7.0 Hz, CH2); 4.35 (t, 2H, NH); 7.69 (s, 10H, Ph). 13C{1H} dimethyl-N-propyl-1-(4-(N-propylsulfamoyl)phenyl)-1H-pyrazole-4-
NMR (CDCl3): d 11.0; 12.0; 13.6; 22.81; 44.4; 118.8; 129.5; 129.8; sulfonamide (L6) was added to (0.12 g, 0.5 mmol)
1
130.9; 146.0; 150.8. IR (Diamond ATR, cmꢀ1): 3265 n(N–H) [Pd(MeCN)2Cl2]. Yield = 0.37 g (81%). H NMR (CDCl3): d 0.90
amine. GCMS (EI) m/z [M + H]+ calcd: 762.080; found: 762.148 (m, 12H, 3JHH = 6.0 Hz, CH3); 0.95 (m, 4H, CH2); 1.23 (s, 4H, CH2);
(65%). Anal. calcd for C17H26N4O4S2: C, 49.25; H, 6.32; N, 13.52; 2.36 (m, 12H, CH3); 2.95 (m, 4H, 3JHH = 7.0 Hz, CH2); 3.09 (m, 4H,
S, 15.47%. Found C, 49.51; H, 6.71; N, 13.80; S, 15.54%. 3JHH = 8.0 Hz, CH2); 4.70 (t, 2H, NH); 4.93 (m, 2H, NH); 7.88 (m,
Calculated log Po/w: 6.69; experimental Log Po/w: 3.23.
3H, 3JHH = 8.5 Hz, Ph); 8.00 (t, 2H, 3JHH = 7.5 Hz, Ph); 8.20 (t, 3H,
2.3.3 Synthesis of dichloro-bis-N-(tert-butyl)-4-(3,5-di-tert- 3JHH = 8.5 Hz, Ph). 13C{1H} NMR (CDCl3): d 11.1; 12.1; 12.3; 22.8;
butyl-1H-pyrazol-1-yl)benzenesulfonamide palladium(II) complex 23.0; 23.1; 29.6; 44.4; 44.5; 45.2; 128.18; 130.5. IR (Diamond
(3). To a 10 mL MeOH solution of (0.25 g, 0.6 mmol) N-(tert- ATR, cmꢀ1): 3283 n(N–H) amine. GCMS (EI) m/z [M + H]+ calcd:
butyl)-4-(3,5-di-tert-butyl-1H-pyrazol-1-yl)benzenesulfonamide (L3) 1004.120 found; 1004.125 (60%). Anal. calcd for C34H52Cl2N8
was added to (0.08 g, 0.3 mmol) [Pd(MeCN)2Cl2]. Yield = 0.19 g O8PdS4: C, 40.58; H, 5.21; N, 11.13; S, 12.74%. Found: C, 40.66;
(62%). 1H NMR (CDCl3): d 1.15 (d, 18H, CH3); 1.22 (d, 18H, CH3); H, 5.49; N, 11.32; S, 12.89%. Calculated log Po/w: 6.67; Experi-
1.78 (m, 9H, CH3); 1.99 (m, 9H, CH3); 4.12 (m, 1H, NH); (m, 1H, mental Log Po/w: 0.91.
NH); 6.10 (s, 2H, Pz); 7.77 (m, 2H, Ph); 7.89 (m, 2H, Ph); 8.59 (m,
4H, Ph). 13C{1H} NMR (CDCl3): d 27.79; 29.68; 29.98; 30.13; 31.3;
32.6; 33.6; 53.5; 108.1; 127.3; 129.9; 132.0; 142.4; 144.8. IR
3. Results and discussion
3.1 Synthesis of ligands
(Diamond ATR, cmꢀ1): 3445 n(N–H) amine. GCMS (EI) m/z [M]+
calcd: 958.300; found: 958.311 (75%). Anal. calcd for
C42H66Cl2N6O4PdS2: C, 52.52; H, 6.93; N, 8.75; S, 6.68%. Found Compounds C1 and C2 were prepared from the condensation
C, 52.70; H, 7.01; N, 8.65; S, 6.81%. Calculated log Po/w: 12.36; reaction of phenyl hydrazine with appropriate diketones;
experimental Log Po/w: ꢀ0.96.
pentane-2,4-dione in C1 and 2,2,6,6-tetramethylheptane-3,5-
2.3.4 Synthesis of dichloro-bis-4-(3,5-di-tert-butyl-1H-pyrazol- dione in C2 as reported in Scheme S1 (ESI†). They afforded a
1-yl)-N-propylbenzenesulfonamide palladium(II) complex (4). To a viscous dark brown oil which solidifies after some time for C2.
1
10 mL MeOH solution of (0.22 g, 0.6 mmol) 4-(3,5-di-tert-butyl- The structure of these compounds were confirmed by H NMR
1H-pyrazol-1-yl)-N-propyl benzenesulfonamide (L4) was added to spectroscopy (Fig. S1 and S2, ESI†). Compounds C3–C5
(0.08 g, 0.3 mmol) [Pd(MeCN)2Cl2]. Yield = 0.17 g (61%). 1H NMR (Scheme S1, ESI†) were synthesized from the sulfonation of
(CDCl3): d 0.86 (t, 12H, CH3); 1.19 (m, 9H, CH3); 1.23 (m, 9H, CH3); C1 and C2 with excess chlorosulfonic acid followed by extraction
3
1.65 (d, 4H, JHH = 7.5 Hz, CH2); 1.80 (m, 9H, CH3); 2.02 (m, 9H, of the compounds from aqueous-dichloromethane solvent
CH3); 2.93 (s, 4H, CH2); 6.07 (m, 2H, Pz); 7.63 (m, 2H, Ph); 7.91 (m, mixture to yield tacky brown solids which solidified after few
2H, Ph); 7.91 (s, 2H, Ph); 8.33 (m, 2H, Ph). 13C{1H} NMR (CDCl3): hours. These compounds were purified by column chromatogra-
d 10.88; 13.98; 20.74; 22.53; 29.86; 30.05; 31.46; 41.89; 108.1; 127.3; phy, using a solvent system of a mixture of ethyl acetate-hexane
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in a 10 : 1 ratio. The compounds were characterized by IR and under ambient temperature after a long time of storage signify-
NMR spectroscopies. The IR spectra revealed the absence of the ing a possible longer shelf life. However, ligands L5 and L6 were
pyrazolyl proton, which was not observed in the pyrazole sulfo- found to be hygroscopic and required to be stored under inert
nated products but present in the phenyl sulfonated products. conditions.
This is evident in the corresponding IR spectra of the ligands
Ligands L1–L6 were characterized using 1H-NMR, 13C{1H}-
(Fig. S6–S8, ESI†) around 3051 cmꢀ1. In addition, the spectra of NMR, IR and GC-MS. IR spectra of compounds L1–L6 (Fig. S6–
the corresponding ligands C4 and C5 showed C–H bending S8, ESI†) suggest the formation of the proposed sulfonamides
vibrations in the fingerprint region and is characteristic of di- from the presence of characteristic secondary amine (N–H)
substituted phenyls (Fig. S7 and S8, ESI†).
peaks around B3200–3450 cmꢀ1
As expected, the 1H NMR spectra of L1–L6 (Fig. S9–S11, ESI†)
.
The 1H-NMR analysis of the sulfonated products C3–C5
showed a shift to higher frequencies compared to the starting showed the upfield shift of the proton peaks compared to their
compounds C1 and C2. For example, methyl and tert-butyl precursor compounds C3–C5 due to the presence of an amine
proton peaks for C1 and C2 is observed at 2.26 ppm, and group. For example, methyl and tert-butyl proton peaks for
1.14–1.31 ppm respectively, whiles in the sulfonated products precursors C3 and C4 are observed at 2.54 ppm, and 1.16–1.55
were observed at 2.54 ppm, and 1.17–1.55 ppm (Fig. S3 and S4, ppm. On the other hand, for compounds L1 and L3 they are
ESI†) for C3 and C4 respectively. These observations are observed at 2.49 ppm and 1.13–1.27 ppm (Fig. S9 and S10,
expected as the sulfonyl group is an electron withdrawing ESI†). One characteristic peak which confirmed the formation
group. Further 1H-NMR analysis on C3–C5 (Fig. S3–S5, ESI†) of all the expected compounds is the presence of the amine
confirmed the absence of the pyrazolyl proton in C3 and C5 and proton peak which is between 4.49 ppm and 4.78 ppm. The
in addition substituted phenyl ring for C4 and C5 as predicted 1H-NMR data of ligands L5 and L6 showed a peculiar peak
by the IR spectroscopy. The 1H-NMR of C3 in Fig. S3 (ESI†) splitting of the pyrazolyl methyl protons. Three distinct peaks
showed a doublet and a triplet between 7.37 ppm and for the methyl protons was observed instead of the expected
7.52 ppm, both integrating for five protons for the phenyl two, in a 2 : 1 ratio. (Fig. S11, ESI†). Also, 13C{1H}-NMR
group. In the case of C4 and C5, four protons were observed spectrum confirmed that the carbon bearing these protons
in the spectra in the same region (Fig. S4 and S5, ESI†). From showed three peaks instead of two peaks (Fig. S14, ESI†). HSQC
experimental observations, the sulfonation first occurs on the experiment carried on L6 demonstrated three carbons to
pyrazolyl ring before the phenyl ring if the 3,5-positions of the proton correlation from the F1 and F2 axis indeed existed in
pyrazolyl ring has less bulky substituents. Similar observations the compound (Fig. S30, ESI†). The same observation was
have been made by Attaryan et al.27 in which the substitution obtained for C5 (Fig. S5, ESI†). This could be due to poly-
was a first to the pyrazolyl ring before the phenyl ring, thus morphic behavior of the sulphonyl group. Similar observations
establishing that the pyrazolyl proton is the more acidic have been reported by Koike et al.29 and Nangia et al.30 in which
compared to the phenyl protons in the system.
the presence of co-crystals polymorphic forms were observed in
This observation differ from the known chemistry of sulfathiazole-oxalic acid complex and sulfonamide with carbox-
pyrazole compounds in which the simplest route of attack is amide compounds respectively. Thus, the sulfonamide point of
always to the substituent attached to the pyrazole but will later attachment to the pyrazole in L6 provides free movement for
attack the pyrazole upon further harsh conditions such as the sulfonamide group to flip between two forms (that is one in
increased temperature.28 However, due to steric hindrance, this plane and the other out of plane), hence observed in the NMR
observation could not be made for C4 (Fig. S4, ESI†). The spectrum when the pyrazolyl methyl group show 3 peaks.
1H NMR spectrum of C4 shows distinct splitting pattern of Therefore, it could be concluded that the presence of possible
doublets and triplets for the phenyl ring between 7.40 ppm and polymorphic forms of the double substituted phenylpyrazolyl
7.67 ppm suggesting an aromatic substitution at the para sulfonamide existed in C5 and its analogs.
1
position. Interestingly, H NMR spectrum of C5 (Fig. S5, ESI†)
GC-MS analysis on the compounds provided a further con-
also showed a distinct splitting of all the phenyl protons into firmation of the formation of the proposed compounds from
doublets and multiplets which suggest an para substitution, In the GC-trace and mass spectra of each compound as shown
all, C3 and C4 are mono sulfonated compounds while C5 is a in Fig. S24–S29 (ESI†). For example, L1 showed m/z of the
di-sulfonated compound.
molecular ion as [M+] = 307.135 which corresponds to the
Further reactions were carried on C3–C5 with tert-
butylamine and propylamine, in 1 : 1 mole ratio to yield
L1–L4 (Schemes 1 and 2) and 1 : 2 mole ratio to yield L5 and
L6 (Scheme 3). The methyl substituted pyrazolyl derivatives
gave oily product which solidified after few hours while the
tert-butyl substituted pyrazolyl derivative yielded a solid product.
The compounds L1, L2, L5 and L6 were purified by column
chromatography with a solvent system of ethyl acetate-hexane in
a 10: 1 ratio while L3 and L4 was ethyl acetate-methanol in a 7 : 3
ratio. All synthesized ligands were observed to be very stable
Scheme 1 Synthesis of single sulfonated phenylpyrazolyl sulfonamides.
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Scheme 2 Synthesis of phenyl-sulfonated pyrazolyl sulfonamides.
Scheme 4 Synthesis of single sulfonated phenylpyrazolyl sulfonamides
palladium(II) complexes.
Scheme 3 Synthesis of double sulfonated phenylpyrazolyl sulfonamides.
molecular mass of the proposed compound. Compound L3 also
showed a m/z of 377.250 which correspond [M ꢀ CH3]+ while L5
had a m/z of 442.544 which also agrees with the proposed
structure. Elemental analysis was used to confirm the purity
and proposed structures.
Scheme 5 Synthesis of single sulfonated phenylpyrazolyl sulfonamides
palladium(II) complexes.
3.2 Synthesis of palladium(II) complexes
Palladium(II) precursor, [Pd(MeCN)2Cl2] was reacted with L1–L6
in a 2 : 1 mole ratio at room temperature to yield complexes 1–6
as depicted in Schemes 4–6. Through recrystallization in dichlor-
omethane and hexane, complexes 1–6 were isolated as solids
with a characteristic pale yellow to brown. The solubility of the
complexes were found to decrease with decreasing polarity of the
complexes. For example, 1 and 2 easily precipitated from metha-
nol during the reaction while the rest were soluble.
Scheme 6 Synthesis of double sulfonated phenylpyrazolyl sulfonamides
palladium(II) complexes.
All complexes were characterized using IR, 1H NMR and
13C{1H} NMR spectroscopy. IR spectroscopy revealed a general
shift of all the bands to higher wave numbers in all the
complexes synthesized compared to their corresponding made for all the complexes suggesting the absence of a bridging
ligands (Fig. S9–12 and S15–S17, ESI†). center within them. In addition, a careful study of the pyrazolyl
1
The H-NMR and 13C{1H} NMR spectra showed a downfield methyl substituent in both spectrum showed a clear splitting of
shift in frequency for the various groups depending on their what was previously observed as a singlet peak at around
relative electron densities and distance from the metal center. 2.46 ppm in L1 with a peak integration of 6 protons, separated
For example, for the 1H NMR of L1 and 1, it was observed that into two peaks (2.36 ppm and 2.29 ppm) in 1 with an integra-
the addition of a metal resulted in a further shifting of the tion of 3 protons for each ligand (Fig. S9 and S15, ESI†),
aromatic protons downfield from about 7.44 ppm to 7.66 ppm confirming that an attachment to the nitrogen atom could
and while there was an upfield shift for the tert-butyl protons possibly account for the unequal or dissimilar chemical
from 1.28 ppm to 1.21 ppm (Fig. S9 and S15, ESI†), owing to the environment for the methyl substituents. This again provides
nature of the group and point of attachment in the complex first-hand information on which nitrogen atom is involved in
(attached to an electron rich nitrogen atom). Also, integration the metal binding. A similar observation is made for L2 and 2
of the peaks of the compounds indicate there are two ligands and the splitting of the 3,5-pyrazolyl substituent is well noticed
complexes to a palladium metal. This observation could be in the complexes of L5 and L6.
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3.3 Molecular structure of 2
Single crystals suitable for X-ray analysis of 2 were obtained by
slow evaporation of their CH2Cl2 solutions at 25 1C. Crystal-
lographic data are tabulated in Table 1, whereas the molecular
geometries and selected bond lengths and angles are presented
in Fig. 1. Complex 2 crystallizes as one independent molecule
in the asymmetric unit, in a monoclinic crystal system and
P21/c space group.
The crystal structures of 2 showed slightly distorted square
planar geometries about the palladium centre with bond angles
between 88.74(9)–91.26(9)1. The smallest N–Pd–Cl angles are
88.74(9)1, whereas the largest N–Pd–Cl angles are 91.26(9)1. The
Fig. 1 A molecular drawing of 2 with 50% probability ellipsoids. Selected
bond lenght [Å] and angles [1]: Pd1–Cl1, 2.2936(9); Pd1–N1, 1.999(3); N1–
Pd–N bond lengths of 2 (1.999(3) Å), is somewhat shorter than N2, 1.369(4); C3–S1, 1.744(3); S1–O2, 1.429(3); S1–O1, 1.427(3); S1–N3,
1.625(3); Cl11–Pd1–Cl1, 180.0; N1–Pd1–Cl1, 88.74(9);N11–Pd1–Cl1,
the Pd–N bond lengths found in pyrazolyl palladium complexes
91.26(9); S1–N3–C15, 116.9(3).
that have Pd–N(pz) bonds where they range from 2.034(3) to
2.060(3) Å,31,32 and the Pd–Cl bond lengths of 2 (2.2936(9) Å),
is in the normal range (2.242–2.516 Å) as 1776 palladium
or antimicrobial agent34 and expulsion of antimicrobial agents
complexes to which two nitrogen atoms and two chloride ions
from the bacterial cell to survive within the host.35 It has
become imperative for new formulation be made to overcome
are ligated to the palladium that are reported in the Cambridge
Structural Database (CSD).33
their resistance. For this study, gentamicin, the standard anti-
biotic, was used as a positive control with DMSO as solvent. The
well diffusion method was employed for the antimicrobial
sensitivity test, which provides accurate and reproducible
results as well as good aseptic methods as prescribed by the
WHO.36 The growth inhibitions as well as the minimum
inhibition concentration (MIC) values were determined for
concentrations of 62.5, 125, 250, 500 and 1000 mg mLꢀ1. Table
S1 (ESI†) presents the zones of inhibition of the test com-
pounds for these concentrations. The compounds generally
exhibited mild to strong antibacterial activities as shown in
zones of inhibition against mostly Gram negative bacteria
strains tested. The zone of inhibition for all the compounds
fell within the ranges of 9.5 mm to 25 mm and that of the
control antibiotic gentamicin was between 16.5 mm to 36 mm
3.4 Antimicrobial activity
3.4.1 Anti-microbial activities of sulfonamide pyrazolyl
compounds against both Gram-negative & positive bacteria.
The pyrazolyl sulfonamide ligands (L1–L6) and their palladium
complexes (1–6) were dissolved in DMSO and the resulting
solutions screened for their antimicrobial activity against seven
Gram negative bacteria; Citrobacter freundii (ATCC43864),
Escherichia coli (ATCC 25922), Salmonella typhi (ATCC 19430),
Proteus mirabilis (ATCC 25933), Vibro cholerae (ATCC 39451),
Klebsiella pnuemoniae (ATCC 43816) and three Gram positives;
Staphylococcus aureus (ATCC 25923), Enterococcus faecalis (ATCC
9790) and Staphylococcus epidermidis (ATCC 12228). These
microbes are human pathogenic bacteria that tend to cause
wide range of infections including urinary tract infections,
intestinal infections and respiratory tract infections. Also, they
can develop certain resistant strategies such as inactivation of
antimicrobial agents and modification of microbial target
within the host organism, which impedes the activity of drug
for low dosage of 62.5 mg mLꢀ1 to high dosage of 1000 mg mLꢀ1
.
The highest concentration (1000 mg mLꢀ1) recorded the highest
zone of inhibition of all the tested compounds. The control
antibiotic gentamicin showed maximum activity against all
selected microbes with zones of inhibition ranging between
16.5-36 mm at 1000 mg mLꢀ1. However, all the ligands showed
no activity against Gram positive bacteria strains Staphylococcus
aureus and Enterococcus faecalis, except L4 which showed
activity for Staphylococcus aureus within the zone inhibition
comparable to the standard test drug Gentamicin (Table S1:
entries 4 and 13, ESI†). Also, trends similar to the observed
activity for the ligands could be made for their palladium
complexes except for 1 and 4 (Table S1: entries 7 and 10, ESI†).
The most significant observation made is that the addition of
palladium to the ligands improved the activities of some
compounds. For example, compound L1 was not active against
Staphylococcus aureus but its palladium adduct showed good
activity comparable to the standard drug (Table S1 entries 1, 7
and 13, ESI†). Complex 4 showed improved zone inhibition
activity compared to it ligand L4 (Table S1: entries 4 and 10,
Table 1 Crystal data and structure refinement for complex 2
2
Empirical formula
Formula weight
Temperature/K
Wavelength/Å
Crystal system
Space group
a/Å
b/Å
C14H19ClN3O2Pd0.5
382.03
100.01
S
0.71073
Monoclinic
P21/c
11.6678(17)
8.0747(12)
17.753(3)
90
93.372(4)
90
1669.7(4)
4
c/Å
a/(1)
b/(1)
g/(1)
Volume (Å3)
Z
Density (Mg mꢀ3
)
1.520
Final R indices [I 4 2sigma(I)]
R1 = 0.0507, wR2 = 0.1121
ESI†). Complexes
1 and 4 showing activities towards
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Table 2 Minimum inhibition concentrations (mg mLꢀ1) of tested compounds for both Gram positive and Gram negative bacteria
Entry Compound S. aureus S. epidermidis E. faecalis E. coli P. aeruginosa V. cholerae S. typhii C. freundiii K. pneumoniae P. mirabilis
1
2
3
4
5
6
7
8
L1
L2
L3
L4
L5
L6
1
2
3
4
5
—
—
—
—
—
—
—
—
—
—
—
—
32.58
7.24
—
23.01
60.67
—
3.36
1.61
—
1.05
40.23
—
—
—
—
—
—
—
—
—
—
—
—
—
10.79 9.55
42.46
13.06
15.92
—
55.59
—
7.98
8.46
9.31
32.30
32.56
—
7.64
4.92
14.50
—
—
10.19
—
3.26
12.01
—
—
8.64
6.90
3.83
21.23
14.43
—
—
8.51
—
10.25
11.23
—-
—
7.01
36.00
47.86
34.83
46.88
46.70
—
41000
9.05
10.69
—
—
—
41000
—
3.64
—
—
0.237
41000
—
5.23
27.35
—
7.12
—
—
—
41000
64.41 6.40
5.12
3.66
10.55
6.52
4.88
—
4.30
9
31.21
21.35
—
41000
10.70
10
11
12
13
41.59 33.73
41000
—
6
20.58 4.69
0.031 33.73
Gentamicin 11.75
7.01
23.40
2.04
0.00027
Staphylococcus aureus could be due to the fact that metal as drugs. The Log P of each molecule was compared to the
complexes penetrate more easily through the bacteria cell wall Lipinski Rule which states that molecules or compounds with
and destroying it.37
Log P values of less than five are more likely to show high
3.4.2 Sensitivity patterns of isolates to the tested com- absorption with less lipophilicity.38
pounds. The minimum inhibition concentration (MIC) and
The ligands showed moderate to very good log P values
the diameter of inhibition zone has been determined to be hence suggest to have a better absorption; a quality which will
directly proportional to concentration of test compounds. A affect their ability to stand as variable therapeutics. A close
graph relation of X2 against the log of concentration was observation showed that, the compounds with sulfonation on
plotted to obtain the intercept of the various drug action. the pyrazolyl moiety have better Log P values (L1 (3.44), L2
Anti-log of intercept was used to calculate MIC of the tested (3.16), L5 (3.41) and L6 (3.06)) compared to L3 and L4 with LogP
compounds. Based on this, All the compounds show some form of 5.95 and 5.77 respectively. These suggest that compounds L1,
of inhibition for at least two (2) of the bacterial strains studied L2, L5 and L6 are highly absorbable with optimum lipophilicity
(Table 2). Compound L1 shows inhibition of eight (8) bacterial and could reach their desired targets easily.
strain out of ten (10) strain studied (Table 2: entry 1).
The palladium complexes on the other hand showed higher
Compound 4 was found to exhibit the most potent in vitro Log P values of 7.05, 6.69, 7.38 and 6.67 for 1, 2, 5 and 6
anti-bacterial activity with MICs of 1.046 mg mLꢀ1 and 0.237 mg respectively as well as 12.36 for 3 and 12.00 for 4. These value
mLꢀ1 against Staphylococcus epidermidis and Proteus mirabilis are higher compared to the Lipinski rule for their lipophilicity.
respectively (Table 2: entry 10), while the standard control The Log P of the complexes were found to be about twice that of
gentamycin was observed to have MICs ranging from 0.0003 their respective ligands, a feature that could makes them very
to 33.73 mg mLꢀ1 for the ten (10) strains. For the same bacterial good prodrugs capable of delivering double activity during the
strain (S. epidermidis), compound 4 performed better compared decomposition of the complexes. From this calculated
to gentamicin, MIC of 1.046 mg mLꢀ1 and 7.006 mg mLꢀ1 Log P values suggest that these complexes will show higher
respectively (Table 2: entries 10 and 13). The promising anti- activities during in vivo studies.
microbial effect of 4 may be associated to the palladium metal
Experimental Log P values were obtained for the com-
present since its corresponding ligand L4 (Table 2: entries 4 pounds. The experimental values confirmed the calculated
and 10) did not perform that well against most of the strains. observation that L1, L2, L5 and L6 (Table S2, ESI†) have more
Interestingly, all the compound were not activity against affinity to the lipophilic medium. However, a deviation was
S. aureus.
observed for the L3 and L4 which showed to have high affinity
Generally, the incorporation of palladium metal improve the to hydrophilic medium. For example, L3 was observed to be
MIC of the corresponding ligand. For example, Compound L2 more hydrophilic with a Log P of ꢀ0.83 (Table S2, ESI†)
recorded MIC between 4.92 mg mLꢀ1 and 34.83 mg mLꢀ1 while compared to the calculated Log P value of 5.95. A similar trend
the corresponding complex 2 recorded MIC between 1.61 mg Lꢀ1 was observed for the metal complexes where the experimental
and 8.46 mg mLꢀ1 (Table 2: entries 2 and 8). These trend suggest Log P values for 3 (ꢀ0.96) and 4 (ꢀ0.72) show affinity for
that the electrophilicity brought about by the dative covalent hydrophilic medium while the rest had affinity for the lipophi-
bonding between the ligands and palladium metal may be lic medium.
responsible for the increase in the inhibition activities at low
concentrations of the complexes.
3.4.3 Relative solubility (Log Pcalc and Experimental Log P)
Profile of the tested compounds. Log P values of all the ligands
4. Conclusion
L1–L6 and complexes 1–6 were calculated to predict their Six pyrazolyl sulfonamide ligands as well as their monometallic
lipophilicity or hydrophilicity. This is one way of determining palladium complexes were synthesized and used as antibacter-
the extent of their absorption in the human body if formulated ial agent against 10 bacterial strains. The bacterial strains were
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NJC
based 1,3-thiazoles and 1,3,4-thiadiazoles as anticancer
agents, Eur. J. Med. Chem., 2013, 70, 740–749.
made of Gram positive and Gram negative strain. The MIC
values show that the compounds were more active against
Gram negative bacteria strain compared to Gram positive
strain. The palladium complexes gave improved antibacterial
activities compared to their corresponding ligands. Theoretical
Log P calculations show that the ligands and complexes
could exhibit higher antibacterial activities in vivo. However,
the experimental Log P value gave a different trend, which
shows that compounds with sulfonation only on the phenyl
ring make the compounds have high affinity for the hydrophilic
medium.
10 R. C. Khunt, V. M. Khedar, R. S. Chawda, N. A. Chauhan,
A. R. Parikh and E. C. Coutinho, Synthesis, antitubercular
evaluation and 3D-QSAR study of N-phenyl-3-(4- fluorophe-
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11 P. Jain, C. Saravanan and S. K. Singh, Sulfonamides: Deser-
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12 CHEMIK. Biological activity and synthesis of sulfonamide
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Conflicts of interest
There are no conflicts to declare.
14 E. Budzisz, M. Krajewska and M. Rozalski, Cytotoxic and
proapoptotic effects of new Pd(II) and Pt(II)- 489 -complexes
with 3-ethanimidoyl-2-methoxy-2H-1,2-benzoxaphosphinin-
4-ol-2-oxide, Pol. 490, J. Pharmacol., 2004, 56, 473–478.
15 M. Eslami-Moghadam, A. Divsalar, A. Abolhosseini-
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ment, and interaction and docking of novel palladium(II)
complexes of imidazole derivatives with human serum
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17 T. T. H. Fong, C. N. Lok, C. Y. S. Chung, Y. M. E. Fung,
P. K. Chow and P. K. Wan, Cyclometalated palladium(II)
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Acknowledgements
We acknowledge the Building A New Generation Of Academics
In Africa (BANGA-Africa - Carnegie Corporation of New York),
the University of Ghana and the University of Johannesburg for
financial support for this project.
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