Multicomponent Petasis-borono Mannich Preparation of Alkylaminophenols and Antimicrobial Activity Studies

Article abstract of DOI:10.1002/cmdc.201600244

In this work we report the antibacterial activity of alkylaminophenols. A series of such compounds was prepared by a multicomponent Petasis-borono Mannich reaction starting from salicylaldehyde and its derivatives. The obtained compounds were tested again

Full text of DOI:10.1002/cmdc.201600244

DOI: 10.1002/cmdc.201600244
Full Papers
Multicomponent Petasis-borono Mannich Preparation of
Alkylaminophenols and Antimicrobial Activity Studies
ꢀris Neto,[a] Joana Andrade,[a] A. S. Fernandes,[a] Catarina Pinto Reis,[a] Jagadish K. Salunke,[b]
Arri Priimagi,[b] Nuno R. Candeias,*[b] and Patrꢁcia Rijo*[a, c]
In this work we report the antibacterial activity of alkylamino-
phenols. A series of such compounds was prepared by a multi-
component Petasis-borono Mannich reaction starting from sali-
cylaldehyde and its derivatives. The obtained compounds were
tested against a large panel of microorganisms, Gram-positive
and Gram-negative bacteria, and a yeast. Among the several
tertiary amine derivatives tested, indoline-derived aminophe-
nols containing a nitro group at the para-phenol position
showed considerable activity against bacteria tested with mini-
mal inhibitory concentrations as low as 1.36 mm against Staphy-
loccocus aureus and Mycobacterium smegmatis. Cytotoxicity of
the new para-nitrophenol derivatives was observed only at
concentrations much higher than those required for antibacte-
rial activity.
Introduction
Antimicrobial drugs have been successful therapeutics in treat-
ing many life-threatening bacterial infections since the begin-
ning of the 20th century. However, in the last 50 years, the un-
restrained use of antibacterial drugs has been cited as the
main cause for the emergence of multidrug-resistant bacteria.
In some instances, bacteria resistant to more than one antibi-
otic have been reported. As microorganisms are becoming re-
sistant to antibiotics, the development of new antibacterial
agents is of pivotal importance for global health. Enterococcus
faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acineto-
bacter baumanii, Pseudomonas aeruginosa, and Enterobacteria-
ceae are some examples of pathogens known to be multidrug-
resistant organisms.[1]
bacterial cells are still obscure, making the process of finding
novel penetrating compounds difficult. Despite many efforts in
finding new antibacterial agents, there are some hurdles that
hamper the process of finding new antibiotics, such as: the
narrow selection of chemical compounds and their limited
range of mechanisms, the complex mechanisms of action of
antibiotics in current use, and the incompatibility of existing
antibiotics regarding their physical and chemical properties
with conventional medicinal chemistry approaches.[5] Maybe
for these reasons most synthetic antibiotics have been discov-
ered outside antibiotics discovery programs.[6]
Many phenolic compounds, either natural products or syn-
thetic molecules, have been reported to have antibacterial ac-
tivity. Natural phenol derivative arzanol has been identified as
a lead structure in the development of new antibacterials,[7]
and carvacrol has been reported to act as a biocidal agent by
causing disruption of the bacterial membrane and to have an-
tioxidant activities improved by modification into its Schiff
bases.[8] Phenolic triterpenoids were reported to have bacterio-
static action against Staphylococcus epidermidis,[9] while simple
3-alkylphenols have shown moderate in vitro antibacterial ac-
tivity.[10] Bromophenols have been shown to be inhibitors of
Candida albicans isocitrate lyase.[11]
Despite the technologies used in the development of new
antibacterial drugs, specifically challenging network pharma-
cology[2] and functional genomics profiling,[3] drugs from natu-
ral origin encompass around 75% of all the antibacterial
agents discovered between 1981 and 2010,[4] while considera-
bly fewer examples of synthetic antimicrobials have been re-
ported. Despite the many thousands of natural antibiotics dis-
covered, our knowledge about their targets remains very limit-
ed. The structural requirements for a compound to penetrate
While salicylaldehydes,[12] as well as their Schiff bases,[13]
have been reported to have antimicrobial activity, reports on
the antibacterial activity of tertiary amines derived from addi-
tion to the sp2 carbon of the iminium are scarce. Jameel et al.
reported that the antibacterial activity of N-[(5-amino-2-hydrox-
yphenyl)(phenyl)methyl]-N-phenyl amides increased after for-
mation of metal chelates.[14]
[a] ꢀ. Neto, J. Andrade, Prof. A. S. Fernandes, C. Pinto Reis, Prof. P. Rijo
Center for Research in Biosciences & Health Technologies (CBIOS), Universi-
dade Lusꢁfona de Humanidades e Tecnologias, 1749-024 Lisboa (Portugal)
E-mail: patricia.rijo@ulusofona.pt
[b] J. K. Salunke, Prof. A. Priimagi, Prof. N. R. Candeias
Department of Chemistry and Bioengineering, Tampere University of Tech-
nology, Korkeakoulunkatu 8, 33101 Tampere (Finland)
E-mail: nuno.rafaelcandeias@tut.fi
[c] Prof. P. Rijo
As a continuation of our work on the preparation of alkyla-
minophenols derived from the Petasis-borono Mannich reac-
tion,[15] and considering the aforementioned antibacterial activ-
ity of salicylaldehyde derivatives, we envisioned such com-
pounds to also have antibacterial properties. To identify the
Instituto de Investigażo do Medicamento (iMed.ULisboa), Faculdade de
Farmꢂcia, Universidade de Lisboa, 1649-003 Lisboa (Portugal)
Supporting information and the ORCID identification number(s) for the
author(s) of this article can be found under http://dx.doi.org/10.1002/
cmdc.201600244.
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structural elements needed for antibacterial activity, various
secondary amines were initially considered, and the substitu-
ents of the aromatic rings further tuned. Herein we present
the results of our study of the antibacterial activity of alkylami-
nophenols derived from eight different secondary amines.
viding a small library of alkylaminophenols for the antimicrobi-
al assays (Scheme 2, Table 1).
Although the PBM reaction is known to proceed in a variety
of solvents, glycerol was used as solvent in the preparation of
most alkylaminophenols.[15a] Reaction of indoline with 5-nitro-
salicylaldehyde in glycerol resulted in several instances in for-
mation of side products that hampered the purification of the
desired tertiary amine. Replacing glycerol by ethanol and dilut-
ing the reaction conditions, it was possible to isolate the de-
sired compounds 25–28 in reasonably good yields at 508C,
namely when employing para-substituted aryl boronic acids
(Table 1). An attempt to increase the reaction yield by increas-
ing the reaction temperature to reflux ethanol led to consider-
able formation of the N-alkylindoline resultant from the inter-
molecular hydride transfer as reported by Sun, Pan, and col-
leagues.[18] All desired compounds were purified by column
chromatography in silica gel, and their chemical structures
were confirmed by NMR and mass spectrometry.
Results and Discussion
Synthesis
Compounds 1–43 were prepared by a Petasis-borono Mannich
(PBM) reaction (Scheme 1),[16] according to previously reported
Scheme 1. General method for the preparation of alkyalminophenols.
Antimicrobial activity
procedures. The multicomponent character of such methodol-
ogy allows the rapid preparation of large libraries of com-
pounds by replacement of a single component of the reac-
tion.[17] Furthermore, this method allowed us to rapidly obtain
several alkylaminophenols starting from different secondary
amines. Cyclic amines such as pyrrolidine, piperidine, morpho-
line, and indoline, as well as acyclic amines such as diallyla-
mine, methylbenzyl amine, and dibenzyl amine are known to
be efficient partners for the PBM reaction. Such amines and
tetrahydroquinoline were condensed with different salicylalde-
hyde derivatives in the presence of various boronic acids, pro-
All prepared compounds were screened for their antimicrobial
activity by the well diffusion assay. This preliminary test aimed
to identify the antimicrobial compounds comparing with the
corresponding positive controls. The antimicrobial activity was
evaluated against a large panel of microorganisms: Gram-posi-
tive and Gram-negative bacteria and a yeast (data not shown).
The synthesized compounds did not reveal antimicrobial activi-
ty against Gram-negative bacteria and the yeast; however,
compounds 22–29 were active against Gram-positive bacteria.
Thus, this primary test allowed us to select compounds 22–29
Scheme 2. Structures of prepared alkyalminophenols 1–43.
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trol exhibit higher activity, with MIC values ranging from 23.93
to 154.55 mm; compounds 22–27 were more active and
showed MIC values of <1.36 to 147.93 mm. Considering all the
strains tested, compound 23 was the most active (MIC values
ranging from <1.36 to 2.72 mm). Higher antibacterial activity of
the indoline derivatives than salicylaldehydes was observed
against S. aureus.[12b,c]
Table 1. Preparation and isolated yields of alkylaminophenols.
Compd
Method[a]
Yield [%]
Compd
Method[a]
Yield [%]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
A[b]
A
A
A
A
A
A[b]
A[b]
A
A
A
A
A
A
A
A
A
44
70
49
69
77
77
34
72
26
76
75
70
11
17
58
55
94
92
90
97
95
51
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
A
A
B
B
B[c]
B
57
58
81
80
50
65
13
64
44
62
42
60
70
60
70
66
54
74
75
76
60
Considering the cyclic amines pyrrolidine, piperidine, mor-
pholine and indoline, as well as the acyclic amines such as dia-
llylamine, methylbenzyl amine, and dibenzyl amine used in the
alkylaminophenol derivative synthesis, the more potent deriva-
tives were those with the indoline group, 22–28. This could be
considered an essential group for the antimicrobial activity of
these new alkylaminophenols. The presence of this aromatic
heterocyclic group confers to the antimicrobial compounds
higher lipophilicity than the other derivatives (Table 3), an ap-
parent requirement to inhibit the growth of the tested bacte-
ria.
A
A[d]
A
A
A
A[b]
A
A
A
A
A
A
A
A
A
A
A
A
A
Table 3. Predicted logP, dipole moment, and frontier molecular orbital
B
energies of selected compounds.
[a] Method A: aldehyde (0.41 mmol), 1.5 equiv amine and boronic acid in
glycerol (1 mL), 508C, 24–48 h; Method B: aldehyde (0.5 mmol), 1.0 equiv
amine and boronic acid in ethanol (5 mL), 508C, 48 h. [b] Reaction con-
ducted at 808C. [c] Reaction conducted in ethanol (8 mL) at reflux for
24 h. [d] Reaction conducted at 808C for 3 h.
Compd logP[a] Dipole [D][b] EHOMO [eV][b] ELUMO [eV][b] DEHOMOÀLUMO [eV][b]
1
3
5
3.56
3.95
2.76
2.66
4.80
4.61
4.96
4.50
5.18
6.13
4.52
4.31
5.44
3.87
2.97
2.19
6.20
3.21
7.27
7.31
7.10
7.26
7.23
7.96
7.36
7.10
À5.61
À5.76
À5.90
À6.63
À5.79
À6.20
À6.17
À6.15
À6.19
À6.18
À6.27
À6.08
À6.03
À0.23
À0.16
À0.27
À1.82
À0.28
À1.78
À1.75
À1.74
À1.78
À1.77
À1.84
À1.71
À1.78
5.38
5.60
5.63
4.81
5.50
4.42
4.42
4.41
4.41
4.41
4.43
4.38
4.25
16
17
22
23
24
25
26
27
28
29
for further evaluation of their minimum inhibitory concentra-
tion (MIC) values by the microdilution method. The MIC values
were tested against a reference MSSA Staphyloccocus aureus
and selected resistant microorganisms (MRSA and VRE) as well
as a non-pathogenic strain Mycobacterium smegmatis, from the
common genus of the Mycobacterium tuberculosis, the most
significant mycobacterium that causes human tuberculosis.
The obtained results listed in Table 2 were compared with cor-
responding positive controls (vancomycin for Gram-positive
bacteria, and rifampicin for the mycobacteria). Only in the case
of compounds 28 and 29 did the corresponding positive con-
[a] Predicted logP.[21] [b] Calculated using DFT at the PBE1PBE/6-31G(d,p)
level of theory using polarizable continuum model as water solvation
model.
Considering these indoline compounds 22–28, the para-
nitro group in the phenol ring is another essential structural
feature for antimicrobial activity. A similar feature was ob-
served for salicylaldehyde derivatives in which the 5-nitro
group conferred some antibacterial activity.[12b] However, the
nitro group on other derivatives (e.g., 7 and 16) did not confer
antimicrobial activity. It is also notable that 23, the derivative
with a para-methylphenyl group was the most active com-
pound. This structural relationship is verified on compound 29,
which, although not having an indoline moiety, still presents
antimicrobial activity probably due to the structural similarities
with compound 23.
To test for a correlation between the antimicrobial activity
and the electronic properties of alkylaminophenols, the struc-
tures of the series of 5-nitro-substituted derivatives 23–29 and
selected unsubstituted alkylaminophenols were geometrically
optimized by density functional theory (DFT) calculations[19]
(Table 3). Further analysis of dipole moments and natural bond
Table 2. Antimicrobial activity of the synthesized alkylaminophenol deriv-
atives.
Compd
MIC [mm][a]
S. aureus E. faecalis M. smegmatis
S. aureus
ATCC25923
(MSSA)
CIP106760
(MRSA)
ATCC51299
(VRE)
ATCC607
22
23
24
25
26
27
28
29
2.83
<1.36
10.39
2.63
36.92
2.42
38.58
47.79
5.40
2.83
<1.36
2.60
2.63
2.32
9.67
77.27
23.93
2.70
–
11.29
2.72
2.60
5.24
9.25
9.67
154.55
23.93
2.70
–
11.29
<1.36
5.18
10.50
147.93
19.31
77.27
11.98
–
vancomycin
rifampicin
–
<0.60
[a] Data are the median values of at least three replicates.
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orbitals suggest a relation between the antibacterial activity of
the compounds and their electronic properties, as only more
polar compounds with smaller frontier molecular orbital gaps
are active.
Cytotoxicity
The most active compound 23 and two other compounds, 24
and 29, selected based on their antimicrobial properties, were
evaluated for their cytotoxicity in a human keratinocyte
(HaCaT) cell line. The results are depicted in Figure 2. Under
The results obtained also suggest a relationship between an-
timicrobial activity and the unsubstituted meta position of the
phenyl group as in all active compounds 22–28. In this series,
compound 28, with an ethylenedioxy moiety, proved to be the
less active amongst the para-nitro derivatives. For all this, it is
possible to identify important structural relationships in the
new alkylaminophenols and the antimicrobial activity tested,
namely the indoline group, the para-nitrophenol, and the
para-methyl group in the phenyl ring. These structural features
conferred to these derivatives potent antimicrobial activity that
should be further explored to study and identify their mode of
action.
Figure 2. Effect of compounds 23 (A), 24 (B), and 29 (C) on the viability of
human keratinocytes, as evaluated by MTT assay. Cells were incubated with
increasing concentrations of the compounds for 24 h. Results are average
values ÆSD from two independent experiments, each comprising four repli-
cate cultures.
The analysis of the effect of compound 23 (Figure 1) on bac-
terial growth over time was performed for an S. aureus strain,
the conditions tested, the three compounds did not show rele-
vant cytotoxicity at 0.3 and 2.7–3.0 mm. However, the viability
of HaCaT cells exposed to the highest concentration tested
(27.8–30.4 mm) decreased considerably, especially for com-
pounds 23 and 24. It is important to note that the concentra-
tions at which the compounds exhibited antibacterial proper-
ties were generally lower than those presenting cytotoxicity.
The obtained results, although preliminary, suggest that these
compounds should be safe for cutaneous application.
Conclusions
The objective of this study was to synthesize novel alkylamino-
phenol derivatives, to screen their antimicrobial and cytotoxic
activities, and to obtain new antimicrobial structural entities. A
series of new alkylaminophenol analogues was synthesized
through convenient and efficient synthetic procedures.
The antimicrobial activity of the synthesized compounds
was evaluated against a large panel of microorganisms, Gram-
positive and Gram-negative bacteria, and a yeast. The struc-
ture–activity relationship of the synthesized compounds re-
vealed that the compounds 22–28 bearing an indoline group
were the most potent derivatives. The influence of the indoline
moiety in antimicrobial activity of these compounds may be
explained by the hydrophobicity. In addition to the indoline
group, it was also possible to identify other important structur-
al relationships on the new alkylaminophenols and the antimi-
crobial activity tested. The para-nitrophenol group, the para-
methyl substituent, and meta-unsubstitution of the phenyl
group were identified as beneficial for higher antibacterial ac-
tivity.
Figure 1. Growth curves of bacterial strains S. aureus ATCC 25923 independ-
ently challenged with compound 23. Bacterial growth was assessed in the
absence of compound (S. aureus) or in the presence of 23 at various concen-
trations as indicated. The optical density was monitored at 620 nm.
as a model of Gram-positive bacteria. For compound 23 at
1.36 mm (MIC <1.36 mm), no inhibitory effect was observed. At
2.72 and 4.08 mm, compound 23 was responsible for a strong
delay and decrease in the growth rate of the Gram-positive
strain. At these concentrations, the growth profiles of S. aureus
differed from the control (cells grown in the absence of com-
pound). This behavior could be explained by the adaptation of
the bacterial cells to the presence of the compound, decreas-
ing its antimicrobial activity.
To address the bacteriostatic and bactericidal properties of
compound 23 against S. aureus, the MBC value was also evalu-
ated. The MBC value (130.56 mm) was much higher than the
MIC value (<1.36 mm) of the compound tested. A compound
is usually regarded as bactericidal if the MBC is no more than
four times the MIC value,[20] so there is evidence of bacterio-
static properties for compound 23 against S. aureus.
The compounds that showed highest activity against Gram-
positive bacteria were not cytotoxic to human keratinocytes at
MIC values. Considering the obtained results from the growth
inhibition and MBC values, there is a suggestion of bacterio-
static properties for compound 23 against S. aureus.
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3H), 6.98 (dd, J=7.47, 1.61 Hz, 1H), 6.88 (dd, J=8.2, 0.9 Hz, 1H),
6.72 (td, J=7.3, 1.2 Hz, 1H), 4.39 (s, 1H), 2.66–2.51 (m, 4H), 2.31 (s,
3H), 1.90–1.81 ppm (m, 4H).
The data obtained herein support further studies toward the
potential use of these compounds in the topical treatment of
skin infections. The preparation of derivatives of 23, their anti-
bacterial activity, and mode of action as well as the identifica-
tion of specific targets of bacterial cell will be reported in due
course.
2-(phenyl(piperidin-1-yl)methyl)phenol (3): 1H NMR (300 MHz,
CDCl3): d=13.02–11.99 (m, 1H), 7.40 (d, J=6.4 Hz, 2H), 7.36–7.19
(m, 3H), 7.18–7.04 (m, 1H), 6.94–6.82 (m, 2H), 6.69 (t, J=7.4 Hz,
1H), 4.48 (s, 1H), 2.42 (brs, 4H), 1.75–1.55 (m, 4H), 1.55–1.20 ppm
(m, 2H).
2-(piperidin-1-yl(p-tolyl)methyl)phenol (4): 1H NMR (300 MHz,
CDCl3): d=12.63 (brs, 1H), 7.39–7.20 (m, 2H), 7.20–7.05 (m, 3H),
6.88 (t, J=8.2 Hz, 2H), 6.69 (t, J=7.6 Hz, 1H), 4.47 (s, 1H), 2.43
(brs, 4H), 2.33 (s, 3H), 1.67–1.56 (m, 4H), 1.57–1.38 ppm (m, 2H).
Experimental Section
Synthesis
General: All reactions using glycerol as solvent were performed in
air atmosphere in long, capped test tubes. The reagents and sol-
vents were used as obtained from the suppliers (Sigma–Aldrich,
Fluka and TCI). Bi-distilled glycerol (99.5% w/v) was used as ob-
tained from VWR (0.5% maximum water content). The reactions
were monitored by thin-layer chromatography (TLC) carried out on
pre-coated (Merck TLC silica gel 60 F254) aluminum plates by using
UV light as visualizing agent and cerium molybdate solution as de-
veloping agent. Flash column chromatography was performed on
silica gel 60 (Merck, 0.040–0.063 mm). NMR spectra were recorded
with Varian Mercury 300 MHz instrument using CDCl3 as solvent
and calibrated using tetramethylsilane as internal standard. Chemi-
cal shifts are reported in ppm relative to TMS, and coupling con-
stants are reported in Hz. High-resolution mass analysis (ES, posi-
tive) was determined on a WatersSynapt G1 instrument.
2-(morpholino(phenyl)methyl)phenol
(5):
1H NMR
(CDCl3,
300 MHz): d=11.74 (brs, 1H), 7.45–7.42 (m, 2H), 7.37–7.21 (m, 3H),
7.16–7.10 (m, 1H), 6.97–6.86 (m, 2H), 6.73 (td, J=7.5, 1.2 Hz, 1H),
4.41 (s, 1H), 3.78–3.71 (m, 4H), 2.61–2.43 ppm (m, 4H).
2-((4-methoxyphenyl)(morpholino)methyl)phenol (6): 1H NMR
(CDCl3, 300 MHz): d=11.81 (brs, 1H), 7.34 (d, J=8.5 Hz, 2H), 7.15–
7.09 (m, 1H), 6.93 (dd, J=7.6, 1.6 Hz, 1H), 6.87–6.82 (m, 3H), 6.73
(td, J=7.6, 1.2 Hz, 1H), 4.38 (s, 1H), 3.76–3.74 (brs, 7H), 2–59–
2.41 ppm (m, 4H).
2-(morpholino(4-nitrophenyl)methyl)phenol (7): 1H NMR (CDCl3,
300 MHz): d=11.29 (brs, 1H), 8.16 (d, J=9.1 Hz, 2H), 7.66 (d, J=
8.5 Hz, 2H), 7.19–7.13 (m, 1H), 6.96–6.87 (m, 2H), 6.76 (t, J=7.5 Hz,
1H), 4.50 (s, 1H), 3.77–3.83 (m, 4H), 2.63 (brs, 2H), 2.49–2.42 ppm
(m, 2H).
Compounds 1, 4, 6, 15, 31, 33, 36, and 40 were obtained with the
same spectral characterization as reported elsewhere.[15c] The char-
acterization of compounds 2, 7, 10, 13, 16–21, 32, 35, 37, and 42
has been previously described.[15a] Compounds 3, 34, and 39 have
been described elsewhere.[22] Other compounds such as 5,[23] 8,[24]
11,[25] 12,[26] 23,[27] and 41[28] have been obtained with the same
spectral characterization as previously described.
2-((4-chlorophenyl)(morpholino)methyl)phenol
(8):
1H NMR
(CDCl3, 300 MHz): d=11.58 (brs, 1H), 7.38 (d, J=8.2 Hz, 2H), 7.29
(d, J=8.5 Hz, 2H), 7.18–7.12 (m, 1H), 6.94–6.86 (m, 2H), 6.75 (t, J=
7.6 Hz, 1H), 4.39 (s, 1H), 3.83–3.72 (m, 4H), 2.60–2.41 ppm (m, 4H).
1-(4-((2-hydroxyphenyl)(morpholino)methyl)phenyl)ethan-1-one
(9): 1H NMR (CDCl3, 300 MHz): d=11.50 (brs, 1H), 7.89 (d, J=
6.0 Hz, 2H), 7.55 (d, J=8.2 Hz, 2H), 7.19–7.07 (m, 1H), 6.99–6.81
(m, 2H), 6.76–6.71 (m, 1H), 4.45 (s, 1H), 3.87–3.60 (m, 4H), 2.79–
2.52 (m, 5H), 2.51–2.36 ppm (m, 2H); 13C NMR (CDCl3, 75 MHz): d=
197.7, 156.1, 144.9, 137.0, 129.4, 129.3, 128.8, 124.2, 120.1, 117.4,
76.7, 67.0, 52.5, 26.9 ppm; HRMS (ESI+): calcd for C19H22NO3 [M+
H+]: 312.1600, found: 312.1628.
Method A: A long, capped test tube containing a magnetic stirrer
was charged with boronic acid (1.5 equiv) and pure glycerol
(1.0 mL). The boronic acid was left to dissolve for 5 min at 50 or
808C, after which the aldehyde (0.41 mmol) was added and left
stirring for 2 min at the same temperature, followed by addition of
amine (1.5 equiv). The reactions were left stirring at that tempera-
ture, at the longest, for 48 h or until complete consumption of the
aldehyde, as monitored by TLC. After cooling at room temperature,
the reaction was quenched with addition of 1.0 mL of water and
1.0 mL of saturated NaHCO3 solution and then extracted diethyl
ether (3 to 5ꢃ5 mL) until no product was visible on TLC. Solvent
was removed under reduced pressure, and the product further pu-
rified by flash chromatography on silica gel using a mixture of
ethyl acetate/hexane as solvent.
2-(morpholino(4-vinylphenyl)methyl)phenol (10): 1H NMR (CDCl3,
300 MHz): d=11.71 (brs, 1H), 7.41–7.33 (m, 4H), 7.16–7.11 (m, 1H),
6.96–6.86 (m, 2H), 6.76–6.62 (m, 2H), 5.72 (d, J=17.6 Hz, 1H), 5.24
(d, J=10.8 Hz, 1H), 4.41 (s, 1H), 3.82–3.71 (m, 4H), 2.60–2.43 ppm
(m, 4H).
2-(morpholino(o-tolyl)methyl)phenol
(11):
1H NMR
(CDCl3,
300 MHz): d=11.92 (brs, 1H), 7.63–7.60 (m, 1H), 7.10–7.19 (m, 4H),
6.95–6.87 (m, 2H), 6.72 (t, J=7.5 Hz, 1H), 4.90 (s, 1H), 3.78–3.75 (m,
4H), 2.59–2.48 ppm (m, 7H).
Method B: Aryl boronic acid (0.5 mmol) was dissolved in ethanol
(5 mL), followed by addition of the aldehyde (1.0 equiv). After stir-
ring at 508C for 5 min, the amine (1.0 equiv) was added and the
mixture left stirring at that temperature for 48 h. The solvent was
evaporated under reduced pressure and the desired compound
isolated by flash chromatography in toluene.
2-((3-methoxyphenyl)(morpholino)methyl)phenol (12): 1H NMR
(CDCl3, 300 MHz): d=11.68 (brs, 1H), 7.22 (t, J=7.5 Hz, 1H), 7.15–
7.10 (m, 1H), 7.05–6.94 (m, 3H), 6.87 (d, J=8.2, 1H), 6.81–6.70 (m,
2H), 4.36 (s, 1H), 3.76 (brs, 7H), 2.60–2.45 ppm (m, 4H).
2-(phenyl(pyrrolidin-1-yl)methyl)phenol (1): 1H NMR (300 MHz,
CDCl3): d=12.27 (brs, 1H), 7.47 (d, J=7.3 Hz, 2H), 7.37–7.17 (m,
3H), 7.17–7.05 (m, 1H), 6.96 (d, J=7.6 Hz, 1H), 6.86 (d, J=8.2 Hz,
1H), 6.71 (t, J=7.3 Hz, 1H), 4.38 (s, 1H), 2.65 (brs, 2H), 2.51 (brs,
2H), 1.89–1.80 ppm (m, 4H).
2-((2,6-dimethylphenyl)(morpholino)methyl)phenol (13): 1H NMR
(CDCl3, 300 MHz): d=12.30 (brs, 1H), 7.10–7.05 (m, 3H), 7.02–6.89
(m, 1H), 6.76 (d, J=9.0 Hz, 1H), 6.72–6.64 (m, 2H), 5.41 (s, 1H),
3.90–3.63 (m, 4H), 3.19 (brs, 1H), 2.57–2.20 ppm (m, 9H).
2-(mesityl(morpholino)methyl)phenol (14): 1H NMR (300 MHz,
CDCl3): d=12.35 (s, 1H), 7.10–7.05 (m, 1H), 6.92 (brs, 1H), 6.78–
2-(pyrrolidin-1-yl(p-tolyl)methyl)phenol (2): 1H NMR (CDCl3,
300 MHz): d=12.27 (brs, 1H), 7.39 (d, J=7.9 Hz, 2H), 7.15–7.09 (m,
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6.65 (m, 5H), 5.37 (s, 1H), 3.94–3.62 (m, 4H), 3.18 (brs, 1H), 2.55–
2.45 (m, 5H), 2.32–2.16 ppm (m, 6H); 13C NMR (75 MHz, CDCl3): d=
156.9, 137.7, 137.7, 134.2, 131.3, 129.6, 128.0, 122.6, 119.4, 117.0,
105.0, 69.8, 21.0 ppm; HRMS (ESI+): calcd for C20H26NO2 [M+H+]:
312.1964, found: 312.1934
(m, 2H); 13C NMR (CDCl3, 75 MHz): d=162.7, 159.7, 150.1, 140.7,
132.4, 130.0, 130.0, 127.4, 127.0, 125.0, 124.9, 124.7, 122.3, 117.5,
114.3, 112.2, 69.8, 55.2, 53.3, 28.4 ppm; HRMS (ESI+): calcd for
C22H21N2O4 [M+H+]: 377.1501, found: 377.1498.
2-(indolin-1-yl(4-vinylphenyl)methyl)-4-nitrophenol (25): 1H NMR
(CDCl3, 300 MHz): d=11.80 (brs, 1H), 8.12 (dd, J=8.9, 2.8 Hz, 1H),
8.02 (d, J=2.6 Hz, 1H), 7.42 (s, 4H), 7.20 (d, J=7.3 Hz, 1H), 7.07–
6.92 (m, 3H), 6.72 (dd, J=17.7, 11.0 Hz, 1H), 6.55 (d, J=7.9 Hz, 1H),
5.79 (d, J=17.6 Hz, 1H), 5.38 (s, 1H), 5.31 (d, J=10.8 Hz, 1H), 3.31–
3.24 (m, 1H), 3.13–3.01 (m, 1H), 2.99–2.92 ppm (m, 2H); 13C NMR
(CDCl3, 75 MHz): d=163.0, 150.5, 141.1, 138.4, 137.7, 136.2, 132.7,
129.2, 127.8, 127.2, 127.0, 125.4, 125.3, 125.0, 122.7, 117.9, 115.3,
112.6, 70.6, 53.9, 28.7 ppm; HRMS (ESI+): calcd for C23H21N2O3 [M+
H+]: 373.1552, found: 373.1559.
5-methoxy-2-(morpholino(phenyl)methyl)phenol (15): 1H NMR
(CDCl3, 300 MHz): d=11.85 (brs, 1H), 7.47–7.39 (m, 2H), 7.33–7.25
(m, 3H), 6.82 (d, J=8.5 Hz, 1H), 6.43 (d, J=2.6 Hz, 1H), 6.30 (dd,
J=8.3, 2.5 Hz, 1H), 4.38 (s, 1H), 3.74 (brs, 7H), 2.60–2.40 ppm (m,
4H)
1
2-(morpholino(phenyl)methyl)-4-nitrophenol (16): H NMR (CDCl3,
300 MHz): d=13.24 (brs, 1H), 8.04 (dd, J=8.9, 2.8 Hz, 1H), 7.90 (d,
J=2.6 Hz, 1H), 7.39–7.31 (m, 5H), 6.91 (d, J=8.8 Hz, 1H), 4.55 (s,
1H), 3.77 (brs, 4H), 2.61–2.46 ppm (m, 4H).
2-([1,1’-biphenyl]-4-yl(indolin-1-yl)methyl)-4-nitrophenol
(26):
2-(indolin-1-yl(phenyl)methyl)phenol (17): 1H NMR (CDCl3,
300 MHz): d=10.12 (brs, 1H), 7.48–7.44 (m, 2H), 7.37–7.25 (m, 3H),
7.23–7.14 (m, 2H), 7.02–6.79 (m, 5H), 6.50 (d, J=7.9 Hz, 1H), 5.33
(s, 1H), 3.25–3.17 (m, 1H), 3.09 (q, J=9.2 Hz, 1H), 2.96–2.89 ppm
(m, 2H).
1H NMR (CDCl3, 300 MHz): d=11.87 (brs, 1H), 8.15 (dd, J=8.8,
2.6 Hz, 1H), 8.09 (d, J=2.3 Hz, 1H), 7.65–7.61 (m, 4H), 7.56–7.46
(m, 4H), 7.41 (d, J=7.0 Hz, 1H), 7.23 (d, J=5.9 Hz, 1H), 7.11–6.95
(m, 3H), 6.60 (d, J=7.6 Hz, 1H), 5.44 (s, 1H), 3.37–3.30 (m, 1H),
3.18–3.08 (m, 1H), 3.02–2.96 ppm (m, 2H); 13C NMR (CDCl3,
75 MHz): d=163.0, 150.6, 142.0, 141.1, 140.3, 137.3, 132.7, 129.4,
129.2, 128.1, 128.0, 127.9, 127.4, 127.1, 125.5, 125.3, 125.1, 122.8,
118.0, 112.6, 70.7, 54.0, 28.8 ppm; HRMS (ESI+): calcd for C27H23N2O3
[M+H+]: 423.1709, found: 423.1692.
2-(indolin-1-yl(p-tolyl)methyl)phenol
(18):
1H NMR
(CDCl3,
300 MHz): d=10.24 (brs, 1H), 7.43 (d, J=8.0 Hz, 2H), 7.28–7.20 (m,
4H), 7.10–6.87 (m, 5H), 6.59 (d, J=7.9 Hz, 1H), 5.38 (s, 1H), 3.32–
3.27 (m, 1H), 3.15 (q, J=9.2 Hz, 1H), 3.00–2.94 (m, 2H), 2.40 ppm
(s, 3H).
methyl
4-((2-hydroxy-5-nitrophenyl)(indolin-1-yl)methyl)ben-
1
2-(indolin-1-yl(4-methoxyphenyl)methyl)phenol (19): 1H NMR
(CDCl3, 300 MHz): d=10.18 (brs, 1H), 7.41 (d, J=8.8 Hz, 2H), 7.25–
7.17 (m, 2H), 7.06–6.84 (m, 7H), 6.54 (d, J=7.9 Hz, 1H), 5.34 (s,
1H), 3.81 (s, 3H), 3.28–3.21 (m, 1H), 3.12 (q, J=9.2 Hz, 1H), 2.97–
2.91 ppm (m, 2H).
zoate (27): H NMR (CDCl3, 300 MHz): d=11.52 (brs, 1H), 8.12 (dd,
J=9.1, 2.6 Hz, 1H), 8.04 (d, J=8.2 Hz, 2H), 7.94 (d, J=2.6 Hz, 1H),
7.52 (d, J=8.2 Hz, 2H), 7.18 (d, J=7.0 Hz, 1H), 7.04–6.91 (m, 3H),
6.48 (d, J=7.9 Hz, 1H), 5.41 (s, 1H), 3.91 (s, 3H), 3.27–3.18 (m, 1H),
3.06–3.92 ppm (m, 3H); 13C NMR (CDCl3, 75 MHz): d=166.6, 162.8,
150.2, 143.0, 141.1, 132.5, 130.8, 130.7, 129.0, 127.9, 126.2, 125.7,
125.3, 124.9, 122.9, 118.1, 112.5, 70.4, 53.9, 52.6, 28.7 ppm; HRMS
(ESI+): calcd for C23H21N2O5 [M+H+]: 405.1450, found: 405.1442.
2-(indolin-1-yl(4-vinylphenyl)methyl)phenol (20): 1H NMR (CDCl3,
300 MHz): d=10.13 (brs, 1H), 7.50–7.41 (m, 4H), 7.28–7.19 (m, 2H),
7.08–6.85 (m, 5H), 6.75 (dd, J=17.7, 11.0 Hz, 1H), 6.57 (d, J=
7.6 Hz, 1H), 5.80 (d, J=17.6 Hz, 1H), 5.39 (s, 1H), 5.31 (d, J=
10.8 Hz, 1H), 3.32–3.25 (m, 1H), 3.14 (q, J=9.5 Hz, 1H), 2.99–
2.93 ppm (m, 2H).
2-((2,3-dihydrobenzo[b][1,4]dioxin-6-yl)(indolin-1-yl)methyl)-4-ni-
1
trophenol (28): H NMR (CDCl3, 300 MHz): d=11.80 (brs, 1H), 8.10
(dd, J=8.9, 2.8 Hz, 1H), 7.99 (d, J=2.6 Hz, 1H), 7.30–7.15 (m, 1H),
7.05–7.00 (m, 1H), 7.05–6.83 (m, 5H), 6.51 (d, J=7.6 Hz, 1H), 5.25
(s, 1H), 4.25 (s, 4H), 3.32–3.25 (m, 1H), 3.12–2.91 ppm (m, 3H);
13C NMR (CDCl3, 75 MHz): d=163.0, 150.4, 144.2, 144.0, 141.0,
132.7, 131.5, 127.8, 127.2, 125.3, 125.2, 125.0, 122.6, 122.1, 118.1,
117.9, 117.9, 112.5, 70.3, 64.5, 53.7, 28.7 ppm; HRMS (ESI+): calcd
for C23H21N2O5 [M+H+]: 405.1450, found: 405.1440.
2-((2,3-dihydrobenzo[b][1,4]dioxin-6-yl)(indolin-1-yl)methyl)phe-
nol (21): 1H NMR (CDCl3, 300 MHz): d=10.08 (brs, 1H), 7.24–7.15
(m, 2H), 7.07–6.83 (m, 8H), 6.52 (d, J=7.9 Hz, 1H), 5.25 (s, 1H),
4.23 (s, 4H), 3.32–3.25 (m, 1H), 3.12 (q, J=9.4 Hz, 1H), 2.97–
2.91 ppm (m, 2H).
1
2-(indolin-1-yl(phenyl)methyl)-4-nitrophenol (22): H NMR (CDCl3,
2-((3,4-dihydroquinolin-1(2H)-yl)(p-tolyl)methyl)phenol
(29):
300 MHz): d=11.83 (brs, 1H), 8.11 (dd, J=9.1, 2.9 Hz, 1H), 7.98 (d,
J=2.6 Hz, 1H), 7.51–7.31 (m, 5H), 7.19 (d, J=7.3 Hz, 1H), 6.83–7.09
(m, 3H), 6.51 (d, J=7.6 Hz, 1H), 5.34 (s, 1H), 3.29–3.14 (m, 1H),
3.11–2.80 ppm (m, 3H); 13C NMR (CDCl3, 75 MHz): d=163.0, 150.4,
141.0, 138.4, 132.7, 129.4, 129.1, 129.0, 127.8, 127.0, 125.4, 125.2,
125.0, 122.7, 117.9, 112.6, 71.1, 53.9, 28.7 ppm; HRMS (ESI+): calcd
for C21H19N2O3 [M+H+]: 347.1342, found: 347.1385.
1H NMR (CDCl3, 300 MHz) d=7.16–7.11 (m, 4H), 7.16–7.03 (m, 2H),
6.92 (t, J=4.4 Hz, 1H), 6.87–6.82 (m, 3H), 6.59 (d, J=5.0 Hz, 2H),
5.46 (s, 1H), 3.20–3.17 (m, 2H), 2.80 (t, J=6.3 Hz, 2H), 2.35 (s, 3H),
1.90–1.82 ppm (m, 2H); 13C NMR (CDCl3, 75 MHz): d=154.1, 142.0,
138.1, 136.5, 130.1, 129.4, 129.2, 129.1, 128.4, 128.1, 127.3, 126.6,
122.8, 120.8, 117.2, 116.4, 46.0, 42.4, 27.5, 21.9, 21.1 ppm; HRMS
(ESI+): calcd for C23H24NO [M+H+]: 330.1858, found: 330.1848.
2-(indolin-1-yl(p-tolyl)methyl)-4-nitrophenol (23): 1H NMR (CDCl3,
300 MHz): d=11.81 (brs, 1H), 8.10 (dd, J=9.1, 2.6 Hz, 1H), 7.99 (d,
J=2.6 Hz, 1H), 7.33 (d, J=7.9 Hz, 2H), 7.17–7.09 (m, 3H), 7.09–6.85
(m, 3H), 6.53 (d, J=7.9 Hz, 1H), 5.34 (s, 1H), 3.33–3.18 (m, 1H),
3.00–3.13 (m, 1H), 3.00–2.82 (m, 2H), 2.35 ppm (s, 3H).
2-((3,4-dihydroquinolin-1(2H)-yl)(4-methoxyphenyl)methyl)phe-
nol (30): H NMR (CDCl3, 300 MHz): d=7.16–7.11 (m, 1H), 7.09–7.04
1
(m, 2H), 6.86–6.81 (m, 5H), 6.72–6.69 (m, 2H), 6.41 (d, J=7.9 Hz,
1H), 5.43 (s, 1H), 3.79 (s, 3H), 3.30–3.26 (m, 2H), 2.68 (t, J=6.4 Hz,
2H), 1.95–1.87 ppm (m, 2H); 13C NMR (CDCl3, 75 MHz): d=158.3,
154.0, 143.7, 135.4, 131.5, 130.9, 130.5, 130.5, 127.9, 127.8, 122.1,
120.7, 116.5, 114.8, 114.1, 55.4, 50.0, 42.3, 27.2, 22.4 ppm; HRMS
(ESI+): calcd for C23H24NO2 [M+H+]: 346.1807, found: 346.1795.
2-(indolin-1-yl(4-methoxyphenyl)methyl)-4-nitrophenol
(24):
1H NMR (CDCl3, 300 MHz): d=11.89 (brs, 1H), 8.10 (dd, J=8.9,
2.8 Hz, 1H), 7.96 (d, J=3.5 Hz, 1H), 7.38–7.28 (m, 2H), 7.17 (d, J=
6.4 Hz, 1H), 7.08–6.82 (m, 5H), 6.50 (d, J=7.9 Hz, 1H), 5.31 (s, 1H),
3.80 (s, 3H), 3.28–3.12 (m, 1H), 3.12–2.98 (m, 1H), 2.98–2.81 ppm
2-((diallylamino)(phenyl)methyl)phenol (31): 1H NMR (300 MHz,
CDCl3): d=12.13 (s, 1H), 7.53–7.21 (m, 5H), 7.20–7.04 (m, 1H),
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6.97–6.75 (m, 2H), 6.75–6.57 (m, 1H), 6.09–5.72 (m, 2H), 5.32–5.09
(m, 4H), 5.06 (s, 1H), 3.42–3.34 (m, 2H), 3.07–3.00 ppm (m, 2H).
2-((dibenzylamino)(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)methyl)-
phenol (43): H NMR (CDCl3, 300 MHz) d=12.16 (s, 1H), 7.40–7.29
1
(m, 10H), 7.20 (t, J=7.6 Hz, 1H), 6.98–6.89 (m, 5H), 6.78–6.73 (m,
1H), 5.06 (s, 1H), 4.29 (s, 4H), 3.96 (d, J=13.5 Hz, 2H), 3.47 ppm (d,
J=13.2 Hz, 2H); 13C NMR (CDCl3, 75 MHz): d=157.7, 143.8, 143.7,
137.3, 130.0, 129.9, 129.1, 128.9, 127.8, 124.9, 124.0, 119.6, 119.3,
117.4, 116.9, 68.0, 64.6, 64.6, 54.0 ppm; HRMS (ESI+): calcd for
C29H28NO3 [M+H+]: 438.2069, found: 438.2045.
2-((diallylamino)(p-tolyl)methyl)phenol (32): 1H NMR (CDCl3,
300 MHz): d=12.23 (s, 1H), 7.35–7.32 (m, 2H), 7.26–7.13 (m, 3H),
6.92–6.84 (m, 2H), 6.73–6.68 (m, 1H), 6.01–5.87 (m, 2H), 5.28–5.98
(m, 5H), 3.42 (dd, J=14.1, 5.9 Hz, 2H), 3.06 (dd, J=13.8, 7.6 Hz,
2H), 2.38 ppm (s, 3H).
2-((diallylamino)(thiophen-3-yl)methyl)phenol
(33):
1H NMR
(CDCl3, 300 MHz): d=12.00 (brs, 1H), 7.35 (dd, J=5.1, 3.1 Hz, 1H),
7.25 (dd, J=3.1, 1.3 Hz, 1H), 7.18–7.12 (m, 2H), 6.87 (dd, J=8.2,
1.2 Hz, 1H), 6.82–6.79 (m, 1H), 6.73–6.67 (m, 1H), 5.91 (m, 2H),
5.31 (s, 1H), 5.26–5.14 (m, 4H), 3.44–3.37 (m, 2H), 2.95 ppm (dd,
J=13.9, 8.1 Hz, 2H).
Computational details
All calculations were performed using the Gaussian 09 software
package,[29] without symmetry constraints. The PBE1PBE functional
was employed in the geometry optimizations. That functional uses
a hybrid generalized gradient approximation (GGA), including 25%
mixture of Hartree–Fock[30] exchange with DFT[19] exchange-correla-
tion, given by Perdew, Burke and Ernzerhof functional (PBE).[31] The
optimized geometries were obtained with a standard 6-31G(d,p)[32]
basis set and solvent effects (water) were considered using the Po-
larizable Continuum Model (PCM) initially devised by Tomasi and
co-workers[33] as implemented on Gaussian 09, with radii and non-
electrostatic terms for Truhlar and co-workers’ SMD solvation
model.[34] A Natural Population Analysis (NPA)[35] was used to study
the electronic structure of the optimized species as implemented
on Gaussian 09. Atomic coordinates for all the optimized species
can be found in the Supporting Information.
2-((benzyl(methyl)amino)(phenyl)methyl)phenol (34): 1H NMR
(300 MHz, CDCl3): d=12.38 (brs, 1H), 7.50 (d, J=7.3 Hz, 2H), 7.42–
7.28 (m, 8H), 7.16 (t, J=7.8 Hz, 1H), 7.00–6.89 (m, 2H), 6.74 (t, J=
7.3 Hz, 1H), 4.73 (s, 1H), 3.58 (brs, 2H), 2.19 ppm (s, 3H).
2-((benzyl(methyl)amino)(p-tolyl)methyl)phenol (35): 1H NMR
(CDCl3, 300 MHz): d=12.46 (brs, 1H) 7.43–7.31 (m, 7H), 7.16–7.22
(m, 3H), 6.99–6.95 (m, 2H), 6.77 (t, J=7.0 Hz, 1H), 4.75 (s, 1H), 3.60
(brs, 2H), 2.38 (s, 3H), 2.21 ppm (s, 3H).
2-((benzyl(methyl)amino)(4-methoxyphenyl)methyl)phenol (36):
1H NMR (CDCl3, 300 MHz): d=12.48 (brs, 1H), 7.43–7.29 (m, 7H),
7.20–7.14 (m, 1H), 6.96–6.90 (m, 4H), 6.78–6.72 (m, 1H), 4.73 (s,
1H), 3.81 (s, 3H), 3.58 (brs, 2H), 2.18 ppm (s, 3H).
2-((benzyl(methyl)amino)(4-vinylphenyl)methyl)phenol
(37):
Biological assays
1H NMR (CDCl3, 300 MHz): d=12.39 (brs, 1H), 7.31–7.51 (m, 9H),
7.22–7.17 (m, 1H), 6.96–6.99 (m, 2H), 6.80–6.69 (m, 2H), 5.79 (d,
J=17.6 Hz, 1H), 5.29 (d, J=11.7 Hz, 1H), 4.75 (s, 1H), 3.61 (s, 2H),
2.22 ppm (s, 3H).
Dimethyl sulfoxide (DMSO) was purchased from Merck, (Darmstadt,
Germany). Trypsin, Dulbecco’s modified Eagle’s medium (DMEM),
penicillin–streptomycin solution, fetal bovine serum and thiazolyl
blue tetrazolium bromide (MTT) were obtained from Sigma–Al-
drich, (Saint Louis, MO, USA).
2-((benzyl(methyl)amino)(thiophen-3-yl)methyl)phenol
(38):
1H NMR (CDCl3, 300 MHz): d=12.27 (brs, 1H), 7.41–7.26 (m, 8H),
7.22–7.17 (m, 1H), 6.95 (m, 2H), 6.79–6.74 (m, 1H), 4.97 (s, 1H),
3.59 (brs, 2H), 2.20 ppm (s, 3H); 13C NMR (CDCl3, 75 MHz): d=
157.4, 138.9, 137.4, 129.6, 129.2, 129.1, 128.9, 128.1, 127.9, 126.7,
125.3, 124.6, 119.4, 117.1, 69.4, 59.5, 38.9 ppm; HRMS (ESI+): calcd
for C19H20NOS [M+H+]: 310.1266, found: 310.1302.
Microbial strains: The in vitro antimicrobial study was carried out
using Gram-positive bacteria (Staphylococcus aureus ATCC 25923,
S. aureus CIP106760 (MRSA), Enterococcus faecalis ATCC 51299,
E. faecalis ATCC 29212 and Mycobacterium smegmatis ATCC 607),
Gram-negative bacteria (Escherichia coli ATCC 25922 and Pseudo-
monas aeruginosa ATCC 27853), and a yeast (Candida albicans
ATCC 10231).
1
2-((dibenzylamino)(phenyl)methyl)phenol (39): H NMR (300 MHz,
CDCl3): d=12.12 (s, 1H), 7.49–7.28 (m, 15H), 7.19 (t, J=7.3 Hz, 1H),
6.96 (d, J=7.9 Hz, 1H), 6.83 (d, J=7.0 Hz, 1H), 6.72 (t, J=7.6 Hz,
1H), 5.16 (s, 1H), 3.97 (d, J=13.2 Hz, 2H), 3.42 ppm (d, J=13.5 Hz,
2H).
Well diffusion assay: The well diffusion assay was used to deter-
mine and screen the antimicrobial activity of all compounds. Petri
dishes containing 20 mL Mueller-Hinton culture medium were ino-
culated with 0.1 mL of a bacterial cell suspension matching
a 0.5 McFarland standard solution. The suspension was uniformly
spread using a sterile swab over the surface of the medium. Wells
of 5 mm in diameter were made in the agar plates with a sterile
glass Pasteur pipette and 50 mL of each compound (1 mgmLÀ1),
previously reconstituted by dissolving in DMSO, was added into
wells. DMSO was used as a negative control, while vancomycin
(1 mgmLÀ1) and norfloxacin (1 mgmLÀ1) were used as positive con-
trols for Gram-positive and Gram-negative bacteria, respectively
and nystatin for the yeast. The plates were then incubated at 378C
for 24 h. The antimicrobial activity was assayed by measuring the
diameter of the inhibition zone formed around the wells in mm.
Each assay was performed at least in duplicate.
2-((dibenzylamino)(p-tolyl)methyl)phenol (40): 1H NMR (CDCl3,
300 MHz): d=12.19 (s, 1H), 7.39–7.24 (m, 14H), 7.21–7.15 (m, 1H),
6.95 (d, J=8.1 Hz, 1H), 6.83 (d, J=7.6 Hz, 1H), 6.71 (t, J=7.6 Hz,
1H), 5.13 (s, 1H), 3.96 (d, J=13.2 Hz, 2H), 3.40 (d, J=13.2 Hz, 2H),
2.42 ppm (s, 3H).
2-((dibenzylamino)(4-methoxyphenyl)methyl)phenol
(41):
1H NMR (CDCl3, 300 MHz): d=12.27 (s, 1H), 7.41–7.18 (m, 13H),
7.02–6.98 (m, 3H), 6.86 (d, J=7.3 Hz, 1H), 6.75 (t, J=7.5 Hz, 1H),
5.16 (s, 1H), 3.98 (d, J=13.2 Hz, 2H), 3.88 (s, 3H), 3.43 ppm (d, J=
13.2, 2H).
2-((dibenzylamino)(4-vinylphenyl)methyl)phenol (42): 1H NMR
(CDCl3, 300 MHz): d=12.18 (brs, 1H), 7.54 (d, J=8.8 Hz, 2H), 7.45–
7.31 (m, 12H), 7.24 (t, J=7.9 Hz, 1H), 7.02 (d, J=7.9 Hz, 1H), 6.90–
6.75 (m, 3H), 5.87 (d, J=17.6 Hz, 1H), 5.37 (d, J=11.1 Hz, 1H), 5.20
(s, 1H), 4.02 (d, J=13.2 Hz, 2H), 3.46 ppm (d, J=13.2 Hz, 2H).
Microdilution method: The minimum inhibitory concentrations
(MICs) of antimicrobial compounds evaluated previously by the
well diffusion assay, was determined by means of the twofold
serial broth microdilution assay.[36] The compounds, dissolved in
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The Academy of Finland is acknowledged for financial support,
provided by the Academy Research Fellowship Program to N.R.C.
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Keywords: alkylaminophenols
multicomponent reactions · structure–activity relationships
·
antibacterial activity
·
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Received: May 10, 2016
Revised: June 30, 2016
Published online on && &&, 0000
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ꢀ. Neto, J. Andrade, A. S. Fernandes,
C. Pinto Reis, J. K. Salunke, A. Priimagi,
N. R. Candeias,* P. Rijo*
&& – &&
Multicomponent Petasis-borono
Mannich Preparation of
Alkylaminophenols and Antimicrobial
Activity Studies
Antibiotics by MCR: We disclose a new
family of antibacterial agents derived
from para-nitrophenols and indoline,
prepared by a multicomponent reaction
(MCR). The new alkylaminophenols
show minimum inhibitory concentra-
tions lower than 1.4 mm against selected
resistant microorganisms. Cytotoxicity
assays demonstrated that such com-
pounds are viable candidates as anti-
bacterials, as no cytotoxicity was ob-
served at these concentrations.
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