Synthesis and Bioactivity of Reduced Chalcones Containing Sulfonamide Side Chains

Article abstract of DOI:10.1021/acs.jnatprod.7b00570

The effect on the bioactivity of antibacterial sulfonamide drugs against malaria and tuberculosis via an increase of the lipid solubility groups by condensation with a reduced chalcone was investigated. Sulfonamide derivatives (8a-8d) were obtained via a

Full text of DOI:10.1021/acs.jnatprod.7b00570

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Cite This: J. Nat. Prod. XXXX, XXX, XXX−XXX
Synthesis and Bioactivity of Reduced Chalcones Containing
Sulfonamide Side Chains
Anwar E. M. Noreljaleel,†,§ A. Wilhelm,*,† S. L. Bonnet,† and J. H. van der Westhuizen‡,⊥
‡
†Department of Chemistry and Directorate: Research Development, University of the Free State, 205 Nelson Mandela Drive,
Bloemfontein 9301, South Africa
§Chemistry Department, Faculty of Science and Technology, Omdurman Islamic University, PO Box 382, Omdurman, Sudan
S
* Supporting Information
ABSTRACT: The effect on the bioactivity of antibacterial sulfonamide drugs against malaria and tuberculosis via an increase of
the lipid solubility groups by condensation with a reduced chalcone was investigated. Sulfonamide derivatives (8a−8d) were
obtained via a 1,3-diarylpropane scaffold, prepared by reduction of the relevant chalcones, followed by the addition of a
sulfonamide moiety via the Mannich and the Mannich exchange reactions. The ClogP values indicated that the lipophilicities of
8a−8d and intermediate reduced chalcones and N-alkylated reduced chalcones (5a−7a) were much higher than those of the
sulfonamides (1a−1c). The N-alkylated reduced chalcone derivatives 6 and 7 exhibited the highest antimalarial (Plasmodium
falciparum (NF54 strain)) activity. Addition of the sulfonamide group weakened the activity, even though some ClogP values
were higher, while 1a−1c showed no activity. The reduced chalcones 5a and 5 showed potent growth inhibition of
Mycobacterium tuberculosis (H37Rv strain), but the sulfonamide derivatives 8a and 8d showed no or insignificant activity (0 and
14%, respectively) against M. tuberculosis, despite high ClogP values. Thus, the possible increase in bioactivity expected from an
increase in ClogP values (lipophilicity) might be counteracted by the higher molecular weight of the studied analogues.
Chalcones are precursors in the biosynthesis of flavonoids
and occur widely in medicinal plants. Chemically, their C6·C3·
C6 architecture comprised two aromatic rings linked via a three-
carbon α,β-unsaturated carbonyl system.6 A number of
chalcones having hydroxy and alkoxy groups in different
positions on the aromatic rings have been reported to possess
antibacterial,7 antifungal,8 antioxidant,9 and antimalarial10
activities. Wilhelm et al. reported good antimalarial activity of
N-alkylated 1,3-diarylpropanes, synthesized via reduction of
chalcones with subsequent amino-alkylation via the Mannich
reaction.11 Mannich bases are furthermore known for their
biological potential including anticonvulsant activity.12,13
Antibacterial sulfonamides such as sulfanilamide (1a) and
derivatives 1b and 1c target a bacterial metabolic pathway as
competitive inhibitors of the enzyme dihydropteroate synthe-
tase (DHPS).14 DHPS activity is vital in the synthesis of folate,
needed by cells to synthesize nucleic acids such as DNA or
RNA. Thus, inhibition of DNA replication and cell division
leads to a bacteriostatic effect. The sulfonamide group is
present in a number of biologically active molecules, e.g.,
alaria is a serious problem in the tropical and subtropical
Mparts of Asia, Africa, Central and South America, and
parts of the Middle East, where it affects millions of people.1
The disease is caused by Plasmodium, a parasitic species carried
by the female of the anopheles mosquito, and it is introduced
into the bloodstream of humans by an infected mosquito. The
costs involved in the treatment and management of malaria are
exorbitant, taking into account not only the cost of medical
treatment but also the cost of lost production.2 One of the
major obstacles to control malaria is the growing resistance of
the malaria parasite to most of the commonly used antimalaria
drugs.3 Parallel to malaria, Mycobacterium tuberculosis remains a
serious health problem in many regions of the world, especially
in developing countries.4 Tuberculosis is a transferable disease
that can reach epidemic proportions. In South Africa the
disease is exacerbated by the high incidence of HIV/AIDS
infections that compromise the patients’ immune systems. The
added complication of the emergence of multidrug-resistant
tuberculosis (MDR) and extensively drug resistant tuberculosis
(XDR), as in the case of malaria, has complicated the treatment
of TB considerably.5 The world’s future ability to treat these
drug-resistant diseases depends on continued investigations
into new, better performing drugs, including the exploration of
the potential bioactivity of natural-product-derived compounds.
Received: July 4, 2017
© XXXX American Chemical Society and
American Society of Pharmacognosy
A
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antibacterial,15,16 antifungal,15−17 antimalarial,16−18 anti-
molecular mass smaller than 500, calculated octanol/water
partition coefficient (CLogP) smaller than 5, number of
hydrogen bond donors (HBD) smaller than 5, number of
hydrogen bond acceptors (HBA) smaller than 10. The polar
surface area (PSA) is a descriptor that shows good correlation
with passive molecular membrane transport and thus is an
indication of the transport properties of drugs. The PSA value
should be no more than 140. However, the increased
absorption of compounds with low molecular mass (Mr) and
a suitable ClogP appear to be the two physicochemical
parameters that best determine oral absorption potential.11
Chemistry. In this report, the influence on the antibacterial
activity against Plasmodium falciparum and Mycobacterium
tuberculosis when a sulfonamide group is added to an N-
alkylated 1,3-diarylpropane scaffold was investigated.
The syntheses of 4-{[2-hydroxy-4-(3-phenylpropyl)benzyl]-
amino}benzenesulfonamide (8a), N-(5,6-dimethoxypyrimidin-
4-yl)-4-{[2-hydroxy-4-(3-phenylpropyl)benzyl]amino}-
benzenesulfonamide (8b), and 4-{[2-hydroxy-4-(3-
phenylpropyl)benzyl]amino}-N-(5-methylisoxazol-3-yl)-
benzenesulfonamide (8c) were achieved through the Mannich
exchange reaction by replacement of the dimethylamine
hydrochloride moiety of the reduced chalcone with different
sulfonamide functionalities. The reaction is illustrated in
Scheme 1. The amino functionality was introduced via the
Mannich reaction into a series of chalcones available via the
aldol reaction (Scheme 1). The Mannich reaction can be
applied to aromatic systems provided that it possesses a vacant
location ortho to the phenolic group (Scheme 2).
cancer,18 and anti-inflammatory agents.19
Chemically modified sulfanilamide may lead to a wider
spectrum of bioactivities with more prolonged action. There-
fore, the aim of this study was to investigate if condensation of a
sulfanilamide side chain with a reduced chalcone via the
Mannich or Mannich exchange reaction, where a tertiary amine
hydrochloride group is substituted with a primary amine,20
could potentially increase the antimalaria and antituberculosis
bioactivity by slightly increasing the lipophilicity.
RESULTS AND DISCUSSION
■
Membrane permeability is one of the key determinants in
pharmacokinetic behavior and plays a role in absorption and
distribution of drugs in the human body. The structure of cell
membranes is a fluid-like bilayer arrangement of phospholipids,
with the outer leaflet consisting of electrically neutral lipids,
such as phosphatidylcholine (PC) and phosphatidylethanol-
amine (PE), while the negatively charged lipids, such as
phosphatidylserine, are located in the inner layer. Most drugs
are delivered via passive diffusion across a biomembrane, and it
may occur through its lipid structure.21 It is generally accepted
that more lipophilic molecules will interact more readily with
the fatty acid tails of the lipid bilayer, thus allowing the
molecule to cross cell membranes.22 However, the optimal
lipophilicity of a molecule needs to be determined, because if
the solute is too lipophilic, it will remain trapped in the
membrane. The best indication of lipophilicity is the logarithm
of the octanol/water partition coefficient (ClogP). Compounds
with a high ClogP (>6) display low absorption due to their
poor aqueous solubility, whereas compounds with suboptimal
lipophilicity (ClogP ← 3) are unable to penetrate membrane
barriers.23 The ClogP value forms part of the “rule of five”
criteria for drug-likeness formulated by Lipinski in 1997,24 i.e., a
Structure Elucidation. The 1H NMR spectra of the
sulfonamides 8a, 8b, and 8c displayed the following character-
istics (ppm values given as a range to include values for 8a, 8b,
and 8c): a propyl group represented by two triplet resonances
in the range δH 2.54−2.49 (t, J = 7.4−7.8 Hz) and δH 2.62−
2.55 (t, J = 7.4−7.8 Hz) corresponding to H-1 and H-3,
respectively, and a multiplet in the range δH 1.93−1.79 assigned
to H-2, respectively; an aromatic ABX system comprising H-3′
(δH 6.65−6.60, d, J = 1.4−1.6 Hz), H-5′ (δH 6.60−6.56, dd, J =
1.4−1.6 Hz, 7.6−7.8 Hz), and H-6′ (δH 7.10−7.03, d, J = 7.6−
7.8 Hz); an aromatic AA′BB′C system at δH 7.19−7.09 (H-2″/
a
Scheme 1. Synthesis of Sulfonamides 8a, 8b, and 8c via Pathways A and B
a
(i) 50% KOH, EtOH, rt; (ii) H2/Pd(OH)2/C, EtOAc/H2O; (iii) CH2O/Me2NH, CH3CN, reflux; (iv) HCl (g)/n-hexane; (v) 1a or b or c, EtOH,
reflux; (vi) CH2O.
B
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a
Scheme 2. Synthesis of 8d via Pathway A (Direct Mannich Reaction) and Pathway B (Mannich Exchange Reaction)
a
(i) H2/Pd(OH)2/C, EtOAc/H2O; (ii) CH2O/Me2NH, CH3CN, reflux; (iii) EtOH; (iv) HCl (g)/n-hexane; (v) EtOH/H2O, reflux.
H-6″ and H-4″, overlapped) and δH 7.26−7.21 (H-3″/H-5″, t, J
= 7.4−7.8 Hz); an aromatic AA′BB′ system representing H-2‴/
H-6‴ (δH 7.73−7.52, d, J = 8.5−8.9 Hz) and H-3‴/H-5‴ (δH
6.67−6.58, d, J = 8.5−8.9 Hz); and the aminomethylene
protons (−NH-CH2) as broadened singlets in the range δH
4.32−4.25. Compound 8d showed the same spin systems as 8a,
8b, and 8c, except for the ABX system that is replaced by a two-
proton singlet at δH 7.10 corresponding to H-4′/H-6′,
indicating disubstitution during the Mannich reaction. This
was confirmed by the observation that the H-2‴/H-6‴ and H-
3‴/H-5‴ resonances integrated for four protons, respectively.
Compounds 8b and 8c further displayed singlets at δH 8.01 and
5.99, respectively, corresponding to H-2⁗ and H-4⁗,
respectively. The 13C NMR spectra of compounds 8a, 8b, 8c,
and 8d displayed the expected number of carbons, respectively,
and all methine carbons were assigned via 2D HSQC
experiments. Salient in the 13C NMR spectra of 8a, 8b, 8c,
and 8d are an oxygenated tertiary carbon at δC 156.3−151.7, a
nitrogenated tertiary carbon at δC 154.1−151.7, and a
sulfonylated tertiary carbon at δC 131.5−125.4. These tertiary
carbon assignments were confirmed via long-range 2D HMBC
correlations between the aminomethylene protons for 8a, 8b,
and 8c and C-2′ and C-1‴, respectively, and correlations
between H-3‴, H-5‴, and the sulfonylated C-4‴ carbon
(Figure 1). Assignments of three (four for 8d) quaternary
carbons at δC 125.2−122.1 (C-1′ for 8a, 8b, and 8c, C-1′, C-3′
for 8d, respectively), δC 143.9−142.3 (C-4′ for 8a, 8b, and 8c),
δC 143.6−142.2 for 8a−8d (C-1″), and δC 133.5 for 8d (C-5′)
were confirmed via 2D HMBC correlations between H-1 and
C-4′, H-3 and C-1″, and the aminomethylene protons and C-1′,
respectively. Four (five for 8d) aliphatic methylene carbons
were assigned to the propyl groups (C-1, C-2, and C-3) and
one resonance (two for 8d) to the aminomethylene carbons.
The long-range coupling data of compounds 8a, 8b, and 8c
observed between the aminomethylene protons and C-1′, C-2′,
and C-6′ served as evidence for the presence of the Mannich
functional group.
Bioactivity. The results of the bioactivity tests are
summarized in Tables 1 and 2. Testing against M. tuberculosis
(5, 5a, 6, 6a, 7, 7a, 1a, 8a, and 8d) revealed that the reduced
chalcones 5 and 5a showed potent growth inhibition (94% and
96%, respectively), while the N-alkylated 1,3-diarylpropane 6
showed a moderate 74% inhibition. In the case of the
sulfanilamide Mannich bases with substituted reduced
chalcones, inhibition of M. tuberculosis of 14% (8a) compared
to the zero activity of 1a was observed (Table 1).
The synthesized compounds 5, 6, 7, 8a, 8b, and 8c were
tested against P. falciparum, and the results are collated in Table
2. Compounds 6 and 7 showed moderate activity against P.
falciparum of 58.3 and 117.7 nM, respectively. In the case of the
sulfanilamide Mannich bases 8b and 8c, weak activity against
P. falciparum of 497.5 and 324.5 nM was observed, respectively.
Other compounds such as the reduced chalcone (5) and
sulfonamide Mannich base (8a) showed no activity.
It is clear from the ClogP values that the lipophilicities of
8a−8c and 5a−7a are much higher than those of the
sulfonamides 1a−1c. The antimycobacterial tests showed a
small increase in activity from 1a (0%, ClogP 0.0035) to the
derivative 8a (14%, ClogP 3.888), supporting our hypothesis.
However, the increased bulk of derivative 8d based on the
increase in molecular weight may account for the lack of
activity. Compounds 5a and 5 have relatively high ClogP values
(4.450 for both), but much lower molecular weights and
therefore show the highest inhibition. The same trends were
observed in the antiplasmodium tests: the most potent
compounds 6 and 7 have high lipophilicity and low molecular
weights, sulfanilamide (1a) and derivatives 1b and 1c have very
low lipophilicity and showed no activity, but the sulfonamide
derivatives 8b and 8c, with the highest ClogP values of 5.691
Figure 1. Long-Range HMBC correlations for compounds 8a−8c.
C
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Table 1. Bioactivity Screening against Mycobacterium tuberculosis (H37Rv Strain) (All Compounds Were Tested at 10 μM)
and 5.023, respectively, showed only slight activity, probably
due to their high molecular weights.
EXPERIMENTAL SECTION
■
General Experimental Procedures. A 600 MHz Bruker Avance
spectrometer was used to record the H NMR, COSY, HMBC, and
1
In conclusion, it was established that reduced chalcones 5
and 5a displayed potent inhibition against the growth of M.
tuberculosis of 96% and 94%, respectively. However, derivatiza-
tion of the reduced chalcones into sulfonamide Mannich bases
reduced activity significantly, probably due to the increased
molecular weight of the sulfonamide derivatives. Bioassays
against P. falciparum revealed once more that activity is
decreased when the reduced chalcone is derivatized to
sulfanilamide Mannich bases, but 8b and 8c did indicate low
antimalarial activity. Sulfanilamide and derivatives 1a−c were
inactive against P. falciparum. These results demonstrated that
the lipophilicity of the tested compounds was not the sole
parameter affecting antimycobacterial and antiplasmodium
activity, but molecular weight and electrostatic effects caused
by hydrogen bond donors and acceptors also play a role.
HMQC (600 MHz) and 13C, APT (150 MHz) experiments in either
CDCl3 (δH = 7.24; δC = 77.2), acetone-d6 (δH = 2.04; δC = 29.8), or
methanol-d4 (δH = 4.87 and 3.31; δC = 49.2) with tetramethylsilane as
internal standard. Chemical shifts were expressed as parts per million
(ppm) on the delta (δ) scale, and coupling constants (J) are accurate
to 0.01 Hz. Low-resolution mass spectrometry was performed on a
Sciex instrument model API 4000 LC/MS/MS System (QTRAP triple
quadrupole ion trap mass spectrometer). All samples were dissolved
and diluted to ∼2 ng/μL and infused without additives. Thin-layer
chromatography (TLC) was performed on Merck aluminum sheets
(silica gel 60 F254, 0.25 mm). Reactions were monitored by TLC on
silica gel, with detection by UV light (254 nm). Thin-layer
chromatograms were sprayed with a 2% (v/v) solution of form-
aldehyde (40% solution in H2O) in concentrated H2SO4 and
subsequently heated to 110 °C to effect maximum development of
D
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Table 2. Antiplasmodial Activity of Compounds against NF54 (Chloroquine-Sensitive P. falciparum Strain)
color. Chemicals purchased from commercial vendors were used
without purification.
EtOAc (2 × 50 mL). The organic layer was washed with H2O (1 × 50
mL) and dried over Na2SO4, and the solvent evaporated under
reduced pressure. Recrystallization from EtOH yielded the title
compound. This is demonstrated for the synthesis of (E)-3-(3-
hydroxyphenyl)-1-phenylprop-2-en-1-one (4) using 3-hydroxybenzal-
dehyde (3).
General Procedure for the Synthesis of the Chalcones via
the Aldol Condensation. A mixture of acetophenone (2.974 g; 24.7
mmol) and 3-hydroxybenzaldehyde (2.963 g; 24.3 mmol) was stirred
in EtOH (50 mL) at room temperature. KOH solution (50%, 25 mL)
was added after 10 min, which turned the reaction mixture bright
yellow. The mixture was left to stir overnight, after which it was
quenched with ice-cold 1 N HCl (100 mL) solution and extracted with
(E)-3-(3-Hydroxyphenyl)-1-phenylprop-2-en-1-one (4) was ob-
tained as yellow crystals25 (1.260 g, 23%): H NMR δ (600 MHz,
1
acetone-d6, Me4Si) 8.60 (s, 1 × OH), 8.17−8.13 (2H, m, H-2″, H-6″),
E
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7.81 (1H, d, J = 15.6 Hz, H-3), 7.73 (1H, d, J = 15.6 Hz, H-2), 7.66
(1H, tt, J = 6.9, 1.2 Hz, H-4″), 7.60−7.55 (2H, m, H-3″, H-5″), 7.33
(1H, dt, J = 7.6, 1.2 Hz, H-6′), 7.31 (1H, d, J = 7.6 Hz, H-5′), 7.29
(1H, t, J = 1.9 Hz, H-2′), 6.96 (1H, ddd, J = 7.6, 2.4, 1.3 Hz, H-4′);
13C NMR δ (150 MHz, acetone-d6, Me4Si) 189.1 (C-1), 157.8 (C-3′),
144.1 (C-2), 138.2 (C-1″), 136.5 (C-1′), 132.8 (C-4″), 130.0 (C-5′),
128.7 (C-3″/ C-5″), 128.4 (C-2″/C-6″), 122.0 (C-3), 120.1 (C-6′),
117.6 (C-4′), 115.0 (C-2′).
dissolved in aqueous EtOH (2 mL), and paraformaldehyde solution
(37% v/v, 0.25 mL) was added slowly with constant stirring. The pH
of the mixture was adjusted to 3.5 by adding a 1 mol/L HCl solution
(0.05 mL). The mixture was stirred on ice for 30 min followed by
overnight reflux. The reaction mixture was purified by TLC
chromatography (n-hexane/EtOAc/MeOH, 5:2:3). which yielded
the title compound (8a) as pale yellow crystals, mp 108−110 °C
(Rf 0.7, 0.039 g, 10%).
Pathway B. A mixture of 2-[(dimethylamino)methyl]-5-(3-
phenylpropyl)phenol hydrochloride (7) (0.080 g, 262 mmol) and
sulfanilamide (0.052 g, 291 mmol) in 50% aqueous EtOH (6 mL) was
refluxed for 24 min. The solvent was removed at reduced pressure, and
the mixture was separated by TLC chromatography (n-hexane/
EtOAc/MeOH, 5:2:3) to afford the title compound (8a) as pale
yellow crystals, mp 108−110 °C (Rf 0.7, 0.050 g, 50%).
General Procedure for the Synthesis of the Diarylpropanes.
To a solution of the appropriate chalcone (1.000 g, 0.04 mol) in
EtOAc (3 mL) and H2O (9 mL) was added 20% Pd(OH)2/C (600
mg, 60 wt %). The flask was sealed, and hydrogen gas was passed
through the reaction mixture. After stirring overnight at room
temperature, the reaction mixture was filtered through silica gel. The
filtrate was dissolved in EtOAc followed by extraction with EtOAc (2
× 50 mL). The organic layer was washed with H2O (2 × 30 mL) and
dried over anhydrous MgSO4, and the solvent evaporated under
reduced pressure. Column chromatography (n-hexane/EtOAc, 7:3)
afforded the pure diarylpropanes. This is demonstrated for the
synthesis of 3-(3-phenylpropyl)phenol (5) using (E)-3-(3-hydrox-
yphenyl)-1-phenylprop-2-en-1-one.
3-(3-Phenylpropyl)phenol (5) was obtained as a brown oil (215
mg, 23%): 1H NMR δ (600 MHz, CDCl3, Me4Si) 7.39 (2H, t, J = 7.6
Hz, H-2″, H-6″), 7.32−7.27 (3H, m, H-3″, H-4″, H-5″), 7.24 (1H, t, J
= 6.6 Hz, H-5′), 6.86 (1H, d, J = 7.7 Hz, H-6′), 6.79−6.74 (2H, m, H-
2′, H-4′), 2.74 (2H, m, H-3), 2.69 (2H, m, H-1), 2.07−1.99 (2H, m,
H-2); 13C NMR δ (150 MHz, CDCl3, Me4Si) 155.5 (C-3′), 144.4 (C-
1′), 142.4 (C-1″), 129.6 (C-5′), 128.6 (C-2″/C-6″), 128.5 (C-3″/C-
5″), 125.9 (C-5′), 121.1 (C-6′), 115.6 (C-2′), 112.9 (C-4′), 35.5 (C-
3), 35.4 (C-1), 32.8 (C-2).
1
LREIMS m/z 395.3 (calcd for C22H24N2O3S, 396.5); H NMR δ
(600 MHz, methanol-d4, Me4Si) 7.59 (2H, d, J = 8.9 Hz, H-2‴, H-6‴),
7.26 (2H, t, J = 7.2, H-3″, H-5″), 7.19−7.13 (3H, m, H-2″, H-4″, H-
6″), 7.10 (1H, d, J = 7.7, H-6′), 6.67 (2H, d, J = 8.9 Hz, H-3‴, H-5‴),
6.65 (1H, d, J = 1.6 Hz, H-3′), 6.61 (1H, dd, J = 7.8, 1.6 Hz, H-5′),
4.32 (2H, s, N-CH2), 2.62 (2H, t, J = 7.8 Hz, H-3), 2.54 (2H, t, J = 7.8
Hz, H-1), 1.93−1.86 (2H, m, H-2); 13C NMR δ (150 MHz, methanol-
d4, Me4Si) 154.9 (C-2′), 152.2 (C-1‴), 142.4 (C-4′), 142.2 (C-1″),
129.0 (C-4‴), 128.1 (C-6′), 128.0 (C-2″/C-6″), 127.9 (C-3″/C-5″),
127.4 (C-2‴/C-6‴), 125.3 (C-4″), 122.1 (C-1′), 119.2 (C-5′), 114.6
(C-3′), 111.2 (C-3‴/C-5‴), 41.3 (N-CH2), 35.0 (C-3), 34.7 (C-1),
33.1 (C-2).
N-(5,6-Dimethoxypyrimidin-4-yl)-4-{[2-hydroxy-4-(3-
phenylpropyl)benzyl]amino}benzenesulfonamide (8b). A mixture of
2-[(dimethylamino)methyl]-5-(3-phenylpropyl)phenol hydrochloride
(7) (0.1 g, 0.47 mmol) and sulfadoxine (0.1 g, 0.32 mmol) in 50%
aqueous EtOH (6 mL) was refluxed for 48 h. The solvent was
removed under reduced pressure, and the mixture was purified by
TLC chromatography (n-hexane/acetone, 6:4), to yield the title
compound (8b) as a pale yellow oil (Rf 0.7, 0.04 g, 23%): LREIMS m/
General Procedure for the Synthesis of Aminoalkylated
Diarylpropanes. A mixture of the appropriate diarylpropane (0.212
g, 0.001 mol), paraformaldehyde (0.040 g, 0.01 mol), and Me2NH
(0.045 g, 1 mL, 0.01 mol) in dry MeCN (10 mL) was refluxed
overnight. The mixture was purified by TLC chromatography (n-
hexane/EtOAc, 7:3). This is demonstrated for the synthesis of 2-
[(dimethylamino)methyl]-5-(3-phenylpropyl)phenol (6).
1
z 535.0 and [M + Na] 557.3 (calcd for C28H30N4O5S, 534.2); H
NMR δ (600 MHz, methanol-d4, Me4Si) 8.01 (1H, s, H-2⁗), 7.73
(2H, d, J = 8.5 Hz, H-2‴, H-6‴), 7.23 (2H, t, J = 7.5 Hz, H-3″, H-5″),
7.18−7.11 (3H, m, H-2″, H-4″, H-6″), 7.04 (1H, d, J = 7.7 Hz, H-6′),
6.64 (1H, d, J = 1.6 Hz, H-3′), 6.61 (2H, d, J = 8.6 Hz, H-3‴, H-5‴),
6.56 (1H, dd, J = 7.8, 1.7 Hz, H-5′), 4.28 (2H, s, N-CH2), 3.91 (3H, s,
OCH3), 3.72 (3H, s, OCH3), 2.59−2.55 (2H, m, H-3), 2.51 (2H, t, J =
7.7 Hz, H-1), 1.92−1.83 (2H, m, H-2); 13C NMR δ (150 MHz,
methanol-d4, Me4Si) 161.6 (C-6⁗), 154.9 (C-2′), 152.8 (C-1‴), 151.7
(C-4⁗), 150.6 (C-2⁗), 142.5 (C-4′), 142.2 (C-1″), 129.5 (C-2‴/C-
6‴), 128.2 (C-6′), 128.1 (C-2″/C-6″), 128.0 (C-3″/C-5″), 127.9 (C-
5⁗), 125.4 (C-4‴), 125.3 (C-4″), 122.0 (C-1′), 119.3 (C-5′), 114.7
(C-3′), 110.8 (C-3‴/C-5‴), 59.3 (OCH3), 53.1 (OCH3), 41.3 (N-
CH2), 35.0 (C-3), 34.7 (C-1), 33.0 (C-2).
The title compound was obtained as a brown oil (0.242 g, 90%):
1
LREIMS m/z 269.0 (calcd for C18H23NO, 269.4); H NMR δ (600
MHz, CDCl3, Me4Si) 7.34 (2H, t, J = 7.6 Hz, H-2″, H-6″), 7.28−7.21
(3H, m, H-3″, H-4″, H-5″), 6.93 (1H, d, J = 7.6 Hz, H-5′), 6.77 (1H,
d, J = 1.7 Hz, H-2′), 6.67 (1H, dd, J = 7.7, 1.7 Hz, H-6′), 3.66 (2H s,
CH2), 2.74−2.69 (2H, m, H-3), 2.68−2.63 (2H, m, H-1), 2.37 (6H, s,
2 × N-CH3), 2.06−1.97 (2H, m, H-2).; 13C NMR δ (150 MHz,
CDCl3, Me4Si) 158.0 (C-3′), 143.3 (C-1″), 142.4 (C-1′), 128.5(C-2″/
C-6″), 128.4 (C-3″/C-5″), 128.2 (C-5′), 125.8 (C-4″), 119.4 (C-4′),
119.2 (C-6′), 116.1 (C-2′), 62.7 (CH2), 44.5 (2 × N-CH3), 35.5 (C-
3), 35.3 (C-1), 32.9 (C-2).
General Synthesis of HCl Salts of the Aminoalkylated
Diarylpropanes 2-[(Dimethylamino)methyl]-5-(3-
phenylpropyl)phenol Hydrochloride (7). The appropriate amino-
alkylated diarylpropane (0.242 g, 0.9 mmol) was dissolved in n-hexane
(5 mL) at 0 °C. HCl gas was bubbled through the mixture for 60 min
to obtain the HCl salt as white crystals. This is demonstrated for the
synthesis of 2-[(dimethylamino)methyl]-5-(3-phenylpropyl)phenol
hydrochloride (7).
The title compound was obtained as an amorphous, white powder
(0.30 g, 98%): LREIMS m/z 306.4 (calcd for C18H24ClNO, 305.2); 1H
NMR δ (600 MHz, CDCl3, Me4Si) 9.30 (1H, bs, OH), 7.24 (2H, d, J
= 7.6 Hz, H-2″, H-6″), 7.18−7.08 (5H, m, H-2′, H-5′, H-3″, H-4″, H-
5″), 6.65 (1H, dd, J = 7.7, 1.6 Hz, H-6′), 4.19 (2H, d, J = 3.3 Hz,
CH2), 2.72 (6H, d, J = 4.1 Hz, 2 × N-CH3), 2.61−2.56 (2H, m, H-3),
2.55−2.48 (2H, m, H-1), 1.89−1.81 (2H, m, H-2); 13C NMR δ (150
MHz, CDCl3, Me4Si) 156.8 (C-3′), 147.2 (C-1″), 142.2 (C-1′), 132.8
(C-5′), 128.6 (C-2″/C-6″), 128.5 (C-3″/C-5″), 126.0 (C-4″), 120.6
(C-6′), 117.5 (C-2′), 112.0 (C-4′), 55.6 (CH2), 42.0 (2 × N-CH3),
35.7 (C-3), 35.4 (C-1), 32.8 (C-2).
4-{[2-Hydroxy-4-(3-phenylpropyl)benzyl]amino}-N-(5-methyli-
soxazol-3-yl)benzenesulfonamide (8c).
A mixture of 2-
[(dimethylamino)methyl]-5-(3-phenylpropyl)phenol hydrochloride
(7) (101 mg, 332 mmol) and sulfamethoxazole (84 mg, 332 mmol)
in 50% aqueous EtOH (12 mL) was refluxed for 48 h. The solvent was
removed under reduced pressure, and the reaction mixture was
purified by TLC chromatography (n-hexane/EtOAc/MeOH, 6:2:2),
which yielded the title compound as an amorphous, white powder (Rf
0.7, 0.06 g, 40%). LREIMS m/z 476.2 (calcd for C28H30N4O5S, 477.2);
1H NMR δ (600 MHz, methanol-d4, Me4Si) 7.52 (2H, d, J = 8.9 Hz,
H-2‴, H-6‴), 7.21 (2H, t, J = 7.6 Hz, H-3″, H-5″), 7.14−7.09 (3H, m,
H-2″, H-4″, H-6″), 7.03 (1H, d, J = 7.8 Hz, H-6′), 6.60 (1H, d, J = 1.4
Hz, H-3′), 6.58 (2H, d, J = 9.0 Hz, H-3‴, H-5‴), 6.56 (1H, dd, J = 7.7,
1.5 Hz, H-5′), 5.99 (1H, s, H-4⁗), 4.25 (2H, s, N-CH2), 2.57 (2H, t, J
= 7.4 Hz, H-3), 2.49 (2H, t, J = 7.4 Hz, H-1), 2.23 (3H, s, CH3), 1.88−
1.83 (2H, m, H-2); 13C NMR δ (150 MHz, methanol-d4, Me4Si) 171.2
(C-5⁗), 161.0 (C-3⁗), 156.3 (C-2′), 154.1 (C-1‴), 143.9 (C-4′),
143.6 (C-1″), 129.9 (C-2‴/C-6‴), 129.6 (C-6′), 129.5 (C-2″/C-6″),
129.3 (C-3″/C-5″), 127.0 (C-4‴), 126.7 (C-4″), 123.4 (C-1′), 120.7
(C-5′), 116.0 (C-3′), 112.5 (C-3‴/C-5‴), 96.7 (C-4⁗), 42.7 (N-
CH2), 36.4 (C-3), 36.1 (C-1), 34.4 (C-2), 12.3 (CH3).
4-[(2-Hydroxy-4-(3-phenylpropyl)benzyl)amino]benzene-
sulfonamide (8a). Pathway A. 3-(3-Phenylpropyl)phenol (5) (0.212
g, 0.001 mol) and sulfanilamide (1a) (0.172 g, 0.001 mol) were
F
DOI: 10.1021/acs.jnatprod.7b00570
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4,4′-{[(2-Hydroxy-5-(3-phenylpropyl)-1,3-phenylene)bis-
(methylene)]bis(azanediyl)}dibenzenesulfonamide (8d). A mixture
of 7a (100 mg, 327 mmol) and 1a (130 mg, 582 mmol) in 50%
aqueous EtOH (6 mL) was refluxed for 48 h. The solvent was
removed under reduced pressure, and the mixture was separated by
TCL chromatography (n-hexane/acetone, 5:5), which yielded the title
compound (8d) as brown crystals: mp 125−128 °C (Rf 0.4, 0.054 g,
20%); LREIMS m/z 579.5 (calcd for C29H32N4O5S2, 580.2); 1H NMR
δ (600 MHz, acetone-d6, Me4Si) 7.62 (4H, d, J = 8.8 Hz, H-2‴, H-6‴),
7.26 (2H, t, J = 7.6 Hz, H-3″, H-5″), 7.18−7.14 (3H, m, H-2″, H-4″,
H-6″), 7.10 (2H, s, H-4′, H-6′), 6.79 (4H, d, J = 8.8 Hz, H-3‴, H-5‴),
6.19 (4H, s, 2 × −SO2NH2), 4.45 (4H, d, J = 5.4, 2 × −NHCH2−),
2.58 (2H, t, J = 7.7 Hz, H-3), 2.52 (2H, t, J = 7.7 Hz, H-1), 1.89−1.81
(2H, m, H-2); 13C NMR δ (150 MHz, acetone-d6, Me4Si) 151.7 (C-
1‴), 151.5 (C-2′), 142.3 (C-1″), 133.6 (C-5′), 131.5 (C-4‴), 128.4
(C-3″/C-5″), 128.3 (C-2″/C-6″), 127.8 (C-4′/C-6′), 127.7 (C-2‴/C-
6‴), 125.6 (C-4″), 125.2 (C-1′/C-3′) 112.0 (C-3‴/C-5‴), 43.1 (N-
CH2), 35.0 (C-3), 34.4 (C-1), 33.4 (C-2).
Synthesis of 4-{[2-hydroxy-4-(3-phenylpropyl)benzyl]amino}-
benzenesulfonamide (8a) and 4,4′-{[(2-hydroxy-5-(3-phenylpropyl)-
1,3-phenylene)bis(methylene)]bis(azanediyl)}dibenzenesulfonamide
(8d) was achieved via two pathways (Schemes 1 and 2); first, via direct
Mannich reaction by reacting a reduced chalcone with sulfanilamide
and paraformaldehyde, and second via a Mannich exchange reaction
by replacing the Me2NH.HCL moiety of a reduced chalcone with
sulfonamides (Scheme 1).
Bioassays. Antiplasmodial Assay. Continuous in vitro cultures of
asexual erythrocyte stages of P. falciparum were maintained using the
modified method of Trager and Jensen.26 Quantitative assessment of
antiplasmodial activity in vitro was determined via the parasite lactate
dehydrogenase assay using a modified method described by Makler.27
The test samples were tested in triplicate on one or two separate
occasions. Compounds were initially screened for antiplasmodial
activity against the chloroquine-sensitive (CQS) D10 or NF54 strains.
The most promising compounds were subsequently tested against the
chloroquine-resistant (CQR) strains, Dd2 and K1.
CQ was used as an internal standard to monitor the experimental
conditions and showed IC50 values within an acceptable range of
0.018−0.060 μM for the CQS strains and 0.470−0.780 μM for the
CQR strains. The 50% inhibitory concentration (IC50) values were
obtained from full dose−response curves (Supporting Information),
using a nonlinear dose−response curve fitting analysis via GraphPad
Prism v.4 software.
Anti-Tuberculosis Assay. BACTEC 460 TB system: The work was
carried out in the BSL3 laboratory of the Division of Molecular
Biology of the University of Stellenbosch. M. tuberculosis H37Rv
reference strain (atcc 25618) was used to evaluate compounds against
a well-characterized M. tuberculosis strain. Bacterial colonies were
cultured and selected from Loewenstein-Jensen slant cultures followed
by culture in 7H9 mycobacterial medium. Cultures were stained by
acid-fast staining (ZN staining) to control for contamination. The
H37Rv was subsequently cultured in 7H9 mycobacterial medium
(Difco) enriched with ADC (Biolab art. C70) until it reached a density
of approximately 0.16 at A600 nm (one McFarland), and then 0.1 mL
was inoculated into a 4 mL Bactec vial (primary culture).28
Compounds were dissolved in H2O or 100% DMSO. Subsequent
dilutions were made in 100% DMSO. A final volume of 0.1 mL of
DMSO was added to each 4 mL BACTEC vial, giving a final
concentration of the required drug and also a final DMSO
concentration of 2.5%. This final concentration did not have an effect
on the growth rate of M. tuberculosis as compared to a non-DMSO-
treated culture. All DMSO solvent and drug preparations were
sterilized through a syringe filter with 0.22 μm pore size (Millex-LG,
organic solvent resistant).
culture and 0.1 mL of drug compound were added to a BACTEC vial,
the vials were incubated at 37 °C, and the growth (GI) was monitored
every 24 h. Appropriate controls were included.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jnat-
prod.7b00570.
Experimental details and 1D and 2D NMR data (PDF)
AUTHOR INFORMATION
Corresponding Author
*Tel: +27 (0)51 401 9305. Fax: +27 (0)51 401 7295. E-mail:
wilhelma@ufs.ac.za.
■
ORCID
A. Wilhelm: 0000-0003-4561-5589
Notes
The authors declare no competing financial interest.
⊥Deceased October 25, 2015.
ACKNOWLEDGMENTS
■
Financial support by the University of the Free State and the
National Research Foundation (NRF) of South Africa is
acknowledged.
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