Synthesis, Characterization and Antibacterial Properties of Dihydroxy Quaternary Ammonium Salts with Long Chain Alkyl Bromides

Article abstract of DOI:10.1111/cbdd.12427

Five N-methyl-N-R-N,N-bis(2-hydroxyethyl) ammonium bromides (R = -benzyl (chloride, BNQAS), -dodecyl (C12QAS), -tetradecyl (C14QAS), -hexadecyl (C16QAS), -octadecyl (C18QAS)) were prepared based on N-methyldiethanolamine (MDEA) and halohydrocarbon. Five QAS were characterized by FTIR, NMR, and MS. BNQAS, C12QAS, C14QAS, and C16QAS were confirmed by X-ray single-crystal diffraction. Their antibacterial properties indicated good antibacterial abilities against E. coli, S. aureus, B. subtilis, especially C12QAS with the best antibacterial ability (100% to E. coli, 95.65% to S. aureus, and 91.41% to B. subtilis). In addition, C12QAS also displayed the best antifungal activities than BNQAS and C18QAS against Cytospora mandshurica, Botryosphaeria ribis, Physalospora piricola, and Glomerella cingulata with the ratio of full marks. The strategy provides a facile way to design and develop new types of antibacterial drugs for application in preventing the fruit rot, especially apple. Five dihydroxy quaternary ammonium salts (QAS) with long chain alkyl bromides were prepared, and their structures of four QAS were confirmed by X-ray single-crystal diffraction. Their antibacterial property and cytotoxicity were evaluated.

Full text of DOI:10.1111/cbdd.12427

Chem Biol Drug Des 2015; 85: 91–97
Research Article
Synthesis, Characterization and Antibacterial
Properties of Dihydroxy Quaternary Ammonium Salts
with Long Chain Alkyl Bromides
Wen-Shuai Liu1, Chun-Hua Wang1,*, Ju-Feng
antibacterial activity. Drug toxicity of shorter chain alkyl-
QAS is weak than that of comparatively longer chain alkyl-
QAS; benzyl-QAS has high drug toxicity than methyl-QAS;
More importantly, the antibacterial activities are influenced
Sun1, Gui-Ge Hou1,*, Yu-Peng Wang2 and
Rong-Jun Qu2
1School of Pharmacy, Binzhou Medical University, Yantai
by the alkyl chain length. As the growth of the alkyl chain,
264003, China
the antibacterial activities gradually increase, until they
reach a reasonable limit (11,12). Many discrete QAS were
reported with good antibacterial activities in the literature
and wildly used because they were cheap and could disin-
fect quickly and exhaustively (13). In this study, N-methyld-
iethanolamine (MDEA) has been selected as activity
donors to construct novel QAS because MDEA contains
two flexible hydroxyl groups. It is expected that novel QAS
with two flexible hydroxyl groups can more easily pass
through cell membrane into the cell to passivate enzyme
and damage bacteria (14,15).
2School of Chemistry & Materials Science, Ludong
University, Yantai 264025, China
*Corresponding authors: Chun-Hua Wang,
chunhuawang508@126.com, Gui-Ge Hou,
guigehou@163.com
Five N-methyl-N-R-N,N-bis(2-hydroxyethyl) ammonium
bromides (R = -benzyl (chloride, BNQAS), -dodecyl
(C12QAS), -tetradecyl (C14QAS), -hexadecyl (C16QAS),
-octadecyl (C18QAS)) were prepared based on N-meth-
yldiethanolamine (MDEA) and halohydrocarbon. Five
QAS were characterized by FTIR, NMR, and MS.
BNQAS, C12QAS, C14QAS, and C16QAS were con-
firmed by X-ray single-crystal diffraction. Their antibac-
terial properties indicated good antibacterial abilities
against E. coli, S. aureus, B. subtilis, especially
C12QAS with the best antibacterial ability (100% to
E. coli, 95.65% to S. aureus, and 91.41% to B. subtilis).
In addition, C12QAS also displayed the best antifungal
activities than BNQAS and C18QAS against Cytospora
mandshurica, Botryosphaeria ribis, Physalospora piri-
cola, and Glomerella cingulata with the ratio of full
marks. The strategy provides a facile way to design
and develop new types of antibacterial drugs for appli-
cation in preventing the fruit rot, especially apple.
Motivated by our interest in the antibacterial material
based on dihydroxy QAS with long chain alkyl bromides,
an effective strategy for getting novel QAS by designing
and synthesizing novel dihydroxy QAS with long chain alkyl
bromides is carried out and we report five N-methyl-N-R-
N,N-bis(2-hydroxyethyl) ammonium bromides (R = -benzyl
(BNQAS), -dodecyl (C12QAS), -tetradecyl (C14QAS), -hex-
adecyl (C16QAS), -octadecyl (C18QAS)) based on MDEA
and halohydrocarbon (Scheme 1), respectively. And their
antibacterial properties and antifungal properties were
tested by the methods of qualitative test (inhibition zone
method) and quantitative test (oscillation method).
Key words: antibacterial, antifungal, quaternary ammonium salt
Experimental
Received 30 January 2014, revised 14 August 2014 and
accepted for publication 26 August 2014
Materials
N-methyldiethanolamine (MDEA), dodecyl bromide, te-
tradecyl bromide, hexadecyl bromide, octadecyl bromide,
Over the past decades, many quaternary ammonium salts
(QAS) due to the antibacterial activities were used for anti-
septics, disinfectants, and a variety of clinical purposes,
such as preoperative disinfection of unbroken skin, appli-
cation to mucous membranes, and disinfection of non-crit-
ical surfaces (1–6). For example, alkyl-QAS, dialkyl-QAS,
QAS-iodine, and BQAC [Bisquaternary ammonium com-
pounds, such as dequalinium chloride (7)] have received
increasing attentions due to their vital antibacterial activities
(8–10). Therein, long chain alkyl-QAS shows unsurpassed
Scheme 1: The synthesis and structures of five QAS.
ª 2014 John Wiley & Sons A/S. doi: 10.1111/cbdd.12427
91

Liu et al.
benzyl bromide, and chlorhexidine acetate were pur-
chased from Sinopharm Chemical Reagent Co Ltd.
(Shanghai, China) and were used as obtained without fur-
ther purification. E. coli, S. aureus, B. subtilis, and fungus
(Cytospora mandshuria, Botryosphaeria ribis, Physalospora
piricola, and Glomerella cingulata) were purchased from
American Type Culture Collection, Manassas, VA, USA.
Cytotoxicity testing with MTT method
3-(4,5-Dimethythiazol-2-yl)-2,5-diphenyl-tetrazolium
bro-
mide (MTT) assay was used to determine cellular mitochon-
drial dehydrogenase activity reflecting initial cell death (17).
Mouse alveolar epithelial type II (AT2) cell line were cultured
in Dulbecco‘s modified Eagle‘s medium containing 10%
fetal bovine serum, 1% penicillin, and 1% streptomycin at
37 °C in a 5% CO2/95% air incubator MCO-15AC (SANYO).
AT2 cells in 96-well plate were adjusted to 1.0 9 105
cells mL, cells were passed, and cell supernatant was pour
out before plating on glass slide at 37 °C, 5% CO2 for 24 h.
Cells were pretreated with 100 lL QAS for 24 h, and cell
supernatant with QAS was pour out and washed with PBS
buffer system. Then, the cells were treated with the MTT
solution (20 lL, 5 mg/mL) for 4 h. The dark blue formazan
crystal formed in the intact cells was solubilized with
dimethyl sulfoxide, and absorbance at 570 nm was mea-
sured with a microplate reader (Multiskan MK3-Thermo
Labsystems, Marietta, GA, USA). The results were
expressed as percentage of the control value from the nor-
mal cells without treatments of QAS.
Methods
Infrared (IR) samples were prepared as KBr pellets, and
spectra were obtained in the 400–4000 cmÀ1 range using a
Nicolet MAGNA-IR 550 FTIR spectrometer. Elemental analy-
ses were performed on a Perkin-Elmer Model 2400 analyzer
1
(Waltham, MA, USA). H NMR data were collected using a
Bruker Avance 400 spectrometer. All 13C NMR data were
collected at 100 MHz using Bruker Avance-400 spectrome-
ter. Chemical shifts are reported in d relative to TMS. MS
data were collected using an Agilent GC-MS 7890A-5975C.
Single-crystal structure determination
Suitable single crystals of BNQAS, C12QAS, C14QAS,
and C16QAS were selected and mounted in air onto thin
glass fibers. X-ray intensity data were measured at 293 K
on a Bruker SMART APEX CCD-based diffractometer (Mo
Results and Discussion
Structural analysis
ꢀ
Ka radiation, k = 0.71073 A). The raw frame data were
In this study, five N-methyl-N-R-N,N-bis(2-hydroxyethyl)
ammonium bromides (R = -benzyl (chloride, BNQAS),
-dodecyl (C12QAS), -tetradecyl (C14QAS), -hexadecyl
(C16QAS), -octadecyl (C18QAS)), respectively) were pre-
pared from MDEA and halohydrocarbon. The reaction con-
ditions including temperatures and times of reactions were
optimized to get pure products in high yields (Table 2).
integrated into SHELX-format reflection files and corrected
for Lorentz and polarization effects using SAINT (16). None
of the crystals showed evidence of crystal decay during
data collection. All structures were solved by a combina-
tion of direct methods and difference Fourier syntheses
and refined against F2 by the full-matrix least-squares
technique. Crystal data, data collection parameters, and
refinement statistics for BNQAS, C12QAS, C14QAS, and
C16QAS are listed in Table 1. Relevant bond lengths,
bond angles, and torsion angles are shown in Table S1.
1
Their structures were characterized by FTIR, H NMR, MS,
1
and elemental analysis. The FTIR and H NMR spectra are
shown in Figure S1–S25. From the FTIR spectra, strong
Table 1: Crystallographic data for BNQAS, C12QAS, C14QAS, and C16QAS
C
12H20ClNO2
C17H38BrNO2
C12QAS
C19H42BrNO2
C14QAS
C21H46BrNO2
C16QAS
Formula
BNQAS
CCDC
fw
983 195
245.74
1 007 475
368.39
983 196
396.45
1 007 476
424.50
crystal size (mm)
crystal system
0.20 9 0.14 9 0.10
Orthorhombic
9.595 (4)
9.894 (4)
27.420 (10)
90
0.14 9 0.10 9 0.10
Monoclinic
19.217 (6)
7.305 (2)
14.552 (5)
95.084 (6)
2034.9 (11)
P2 (1)/c
0.17 9 0.12 9 0.12
Monoclinic
20.952 (10)
7.322 (4)
14.465 (7)
90.413 (8)
2219.2 (19)
P2 (1)/c
0.15 9 0.10 9 0.08
Monoclinic
22.767 (7)
7.331 (2)
14.479 (5)
94.796 (5)
2408.2 (13)
P2 (1)/c
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
b (°)
ꢀ3
V (A )
2603.1 (17)
Pbca
Space group
Z value
q calc. (g/cm3)
l (Mo Ka) (mmÀ1
Temp (K)
8
4
4
4
1.254
0.281
296 (2)
1.203
2.025
296 (2)
1.187
1.862
296 (2)
1.171
1.720
296 (2)
)
No. of observations (I > 3r)
2413
0.0387, 0.0968
3778
0.0503, 0.1173
4115
0.0497, 0.1115
4466
0.0399, 0.0908
Final R indices [I > 2sigma (I)]: R1a; wR2a
aR1 = Σ ||Fo| – |Fc||/Σ |Fo|. wR2 = {Σ [w(Fo – Fc2)2]/Σ [w(Fo2)2]}1/2
.
2
92
Chem Biol Drug Des 2015; 85: 91–97

Quaternary Ammonium Salt; Antibacterial; Antifungal
Table 2: The optimum conditions and yields for synthesis of QAS
graphically independent molecule, respectively. The central
N atoms of QAS bond one methyl, two 2-hydroxyethyl
groups, and one benzyl group in BNQAS or a linear paraf-
fin in other QAS, respectively. The C2-N1-C4 angels are
QAS
Temperature/°C
Time/h
Yield/%
BNQAS
60
80
80
70
80
6
6
8
10
12
93.2
91.6
74.5
66.7
81.2
ꢀ
ꢀ
107.39(13) A in BNQAS, 111.8(2) A in C12QAS, 109.7(2)
C12QAS
C14QAS
C16QAS
C18QAS
ꢀ
ꢀ
A in C14QAS, and 111.72(18) A in C16QAS, respectively.
In the four QAS, the directions of two 2-hydroxyethyl com-
pared to the central N atom in BNQAS are obviously differ-
ent from that of C12QAS, C14QAS, and C16QAS, which
can be proved by the torsion angles of N1-C2-C3-O1
characteristic absorption band of hydroxy and stretching
vibration band of C-O can be found, which demonstrates
the existence of -OH of QAS. For example in FTIR spectra of
BNQAS, the two bands lie in 3346 and 1076 cmÀ1, respec-
tively. In addition, the distinct band in 772 cmÀ1 belongs to
the stretching vibration band of linear paraffin in FTIR spec-
tra of BNQAS. In other QAS, the stretching vibration bands
of linear paraffin are 722 cmÀ1 (C12QAS), 723 cmÀ1
(C14QAS), 721 cmÀ1 (C16QAS), and 721 cmÀ1 (C18QAS),
respectively. In 1H NMR spectra, the single bands of
hydroxy of BNQAS can be found at d 5.53–5.51 ppm, but
the hydroxyl bands disappeared in 1H NMR spectra by D2O
exchange (Figures S3, S8, S13, S18 and S23). This further
proved the presence of hydroxyl in BNQAS.
ꢀ
ꢀ
ꢀ
(94.6(2) A in BNQAS, 68.2(4) A in C12QAS, 67.4(3) A in
ꢀ
C14QAS, and 68.0(3) A in C16QAS) and N1-C4-C5-O2
ꢀ
(À79.7(2) A in BNQAS, À175.8(3) in C12QAS, À174.5
ꢀ
ꢀ
(3) A in C14QAS, and À175.8(2) A in C16QAS). Another
data also can help explain that point by the O1-N1-O2
ꢀ
ꢀ
angles (87.2(2) A in BNQAS, 101.9(1) A in C12QAS, 101.3
ꢀ
ꢀ
(2) A in C14QAS, and 101.7(1) A in C16QAS, respectively).
In addition, in C12QAS, C14QAS, and C16QAS, there are
long alkyl chains of C12H25, C14H29, and C16H33. In these
ꢀ
long alkyl chains, the C-C-C angel (109.8(3)ÁÁÁ117.5(3) A)
are similarly as well as the C-C-C-C torsion angles (175.4
ꢀ
(4)ÁÁÁ180.0(3) A), which well confirm the linear-type confor-
mation of long alkyl chains in the solid state. Relevant
bond lengths, bond angles, and torsion angles in BNQAS,
C12QAS, C14QAS, and C16QAS are shown in Table S1.
Two flexible hydroxyl groups and the linear-type alkyl chain
of C14QAS could easily pass through cell membrane into
the cell. It can be a structural advantage of five QAS to
display their unsurpassed antibacterial activity.
X-Ray single-crystal analysis indicates that BNQAS crystal-
lizes in an orthorhombic space group Pbca and C12QAS,
C14QAS, C16QAS in monoclinic space group P2(1)/c. As
shown in Figure 1, the asymmetric unit of BNQAS,
C12QAS, C14QAS, and C16QAS contains one crystallo-
Antibacterial properties
In this study, antibacterial activities of five QAS were
detected through qualitative test and quantitative test. The
data of diameter of inhibition zone for five QAS against
S. aureus, B. subtilis, and E. coli were obtained. Chlorhex-
idine acetate was selected as positive controls. In qualita-
tive test, the inhibition zone could be found during the
concentration of 100, 500, 2500 ppm in Table 3. The
diameters of inhibition zone of QAS were gradually
increasing following the concentration gradient. The results
demonstrate that all five QAS have good antibacterial
activities against S. aureus, B. subtilis, and E. coli.
Therein, BNQAS and C12QAS are the most sensitive to
E. coli, C14QAS and C16QAS are the most powerful to
B. subtilis, and C18QAS are the most potent to S. aureus.
In quantitative test, the curves of antibacterial activity of five
QAS at different concentrations and at the same contact
times were tested, respectively. Chlorhexidine acetate was
selected as positive controls. We could see from Figure 2,
the antibacterial ratios of five QAS went up along with the
increasing of the concentration. It is interesting that the anti-
bacterial ratios of BNQAS and C12QAS against E. coli were
always greater than against S. aureus and B. subtilis at the
same concentration (2500 ppm, Table 4 and Figure 2).
Specifically, the ratios against E. coli could reach 90.52%
and 100%, against S. aureus were 84.78% and 95.65%,
Figure 1: The ORTEP figures of BNQAS, C12QAS, C14QAS,
and C16QAS (displacement ellipsoids with 30% probability).
Chem Biol Drug Des 2015; 85: 91–97
93

Liu et al.
Table 3: Diameter of inhibition zone (mm) of five QAS
S. aureus
B. subtilis
E. coli
Concentration/ppm
100
500
2500
100
500
2500
100
500
2500
BNQAS
C12QAS
C14QAS
C16QAS
C18QAS
Chlorhexidine Acetate
10.3
10.2
14
13
11.2
16.1
16.5
22.4
15.2
13.8
11.5
25.2
24.6
34.2
16.7
14.6
12.1
37.5
10.1
10.5
13.3
13.5
10.5
12.8
14.7
17
18
14.3
11
21.2
19.2
31.1
21.1
15.5
11.4
35.4
11.6
11.2
10.1
0
0
13.4
19.2
24.1
10.5
10.2
0
28
36.3
11.2
10.6
0
27.5
41.3
Figure 2: Antimicrobial activities of five QAS at different concentrations at the same contact times.
Table 4: Antibacterial ratios of five QAS against S. aureus,
B. subtilis, and E. coli under the concentration of 2500 ppm,
respectively
those of C14QAS and C16QAS against S. aureus and
E. coli at the same concentration. The ratios against B. sub-
tilis could reach 89.57% and 84.66%, against S. aureus
were 77.54% and 80.43%, and against E. coli were 70.69%
and 68.97% at the concentration of 2500 ppm for C14QAS
and C16QAS. Lastly, the antibacterial ratios of C18QAS
against S. aureus were always more than those of C18QAS
against B. subtilis and E. coli at the same concentration.
The ratio against S. aureus could reach 74.64%, against
B. subtilis was 63.19%, and against E. coli was 54.31% at
the concentration of 2500 ppm for C18QAS. The results
showed the antibacterial ratios of C12QAS against
S. aureus, B. subtilis, and E. coli were all bigger than those
of the other four QAS. In other words, C12QAS displayed
the best antibacterial abilities against E. coli, S. aureus, and
B. subtilis under the concentration of 2500 ppm. The
results suggest that the antibacterial activities of five QAS
are influenced by the alkyl chain length (18).
Antibacterial
ratios against
S. aureus
Antibacterial
ratios against
B. subtilis
Antibacterial
ratios against
E. coli
QAS
BNQAS
84.78
95.65
77.54
80.43
74.64
97.52
79.14
91.41
70.69
84.66
63.19
96.8
90.52
100
89.57
68.97
54.31
100
C12QAS
C14QAS
C16QAS
C18QAS
Chlorhexidine
acetate
and against B. subtilis were 79.14% and 91.41% at the
concentration of 2500 ppm for BNQAS and C12QAS. The
antibacterial ratios of C12QAS against E. coli, S. aureus,
and B. subtilis can approach chlorhexidine acetate at the
most extent. Additionally, the antibacterial ratios of C14QAS
and C16QAS against B. subtilis were always more than
Moreover, as shown in Figure 3, the antibacterial ratios of
five QAS synthesized increased rapidly during the short
94
Chem Biol Drug Des 2015; 85: 91–97

Quaternary Ammonium Salt; Antibacterial; Antifungal
Figure 3: Antibacterial activities of five QAS under the concentration of 2500 ppm at different contact times.
time (1–2 h), but the ratios reached a maximum after
touching for 3 h, which displayed that five QAS played
potent antibacterial activity further.
mandshuria, Botryosphaeria ribis, and Physalospora piri-
cola, but not fit for Glomerella cingulata because of the
bad antifungal activity. However, the best antifungal drug
should display the highest antifungal activity against sev-
eral funguses of apple, such as Cytospora mandshuria,
Botryosphaeria ribis, Physalospora piricola, and Glome-
rella cingulata. Only then like this, application as antifun-
gal drug for apple will only be possible. Fortunately,
C12QAS displays the highest antifungal activity than
BNQAS and C18QAS, which can be proved by the ratio
of full marks against the four kinds of fungus. Moreover,
good antifungal activity can be found under the concen-
tration of 500 ppm and 100 ppm, except against Cytos-
pora mandshuria.
Antifungal properties
To study the possibility as antifungal drugs of BNQAS,
C12QAS, and C18QAS, four funguses, such as Cytospora
mandshuria, Botryosphaeria ribis, Physalospora piricola,
and Glomerella cingulata were selected to detect antifun-
gal activity of BNQAS, C12QAS, and C18QAS. And the
examination of antifungal activity of three QAS is per-
formed by placing fungus with 5 mm diameter in contact
with growth medium mixed QAS solution of 2500 ppm.
The antifungal activity of QAS is judged based on the
growth diameter of inhibition zone to fungus compared
with the growth diameter of fungus without any QAS.
The shorter diameter of inhibition zone to fungus proves
the better antifungal activity of QAS. In other method, it
is judged also based on the ratio between the growth
diameter of fungus mixed QAS solution and that of fun-
gus without any QAS. The bigger ratio proves the better
antifungal activity of QAS. As shown in Figure 4, BNQAS
displays barely antifungal activity, except against Cytos-
pora mandshuria with the ratios of 77%. For C18QAS,
the better antifungal activities can be found. The ratios
of 84% against Cytospora mandshuria, 89% aganist
Botryosphaeria ribis, and 100% against Physalospora pir-
icola are higher than that of BNQAS. It happens that
there is a special case that the ratio against Glomerella
cingulata is only 56%, which demonstrates C18QAS can
Cytotoxicity
The cytotoxicity of QAS was evaluated for mouse alveolar
epithelial type II (AT2) cell line using MTT assay. The
results are showed in Figure 5 summarizing the corre-
sponding cell viability (%) under the different concentra-
tions of QAS. And IC50 values can be estimated. For
example, IC50 values of C14QAS and C16QAS are about
4–8 ppm, while IC50 value of C12QAS is under the con-
centration of 2–4 ppm; however, the value of C18QAS
can reach the concentration of 8–16 ppm. Through com-
parative analysis, all QAS except BNQAS were potent
inhibitors of the growth of AT2 cell line, and the IC50 value
of C12QAS is smallest compared with other QAS, demon-
strating the biggest cytotoxicity for AT2 cell, which is cor-
responding to the highest antibacterial activity of C12QAS.
In addition, BNQAS displays weaker cytotoxicity, which
be as
a
good antifungal drug aganist Cytospora
Chem Biol Drug Des 2015; 85: 91–97
95

Liu et al.
Figure 4: Antifungal activities of five QAS under different concentrations at the same contact time.
Figure 5: Cell viability of five QAS under different concentrations for AT2 cell.
can be proved by the IC50 value of 1000–10 000 ppm.
The results display that the cytotoxicity of QAS of dodecyl
QAS is stronger than that of comparatively longer chain
alkyl-QAS and benzyl-QAS have very weak drug cytotoxic-
ity than long chain alkyl-QAS.
on MDEA and halohydrocarbon, and their structures were
characterized by FTIR and NMR. BNQAS and C14QAS
were confirmed by X-ray single-crystal diffraction. Their
antibacterial properties were tested. The result displays
that the antibacterial activity and antifungal activity of QAS
are basically related to the introduction of the long chain
alkyl group in MDEA. The long chain alkyl group in QAS
can change the geometric arrangement of QAS, which
can help two flexible hydroxyl groups of QAS to pass
through cell membrane into the cell to passivate enzyme
and damage bacteria. All the long chain alkyl-QAS show
unsurpassed antibacterial activities, especially C12QAS
Conclusions
In this study, five N-methyl-N-R-N,N-bis(2-hydroxyethyl)
ammonium bromides (BNQAS (chloride), C12QAS,
C14QAS, C16QAS, and C18QAS) were prepared based
96
Chem Biol Drug Des 2015; 85: 91–97

Quaternary Ammonium Salt; Antibacterial; Antifungal
against E. coli, S. aureus, B. subtilis, and four funguses
with the ratio of full marks. In addition, the cytotoxicity of
QAS was evaluated for AT2 cell line using MTT assay. The
results display that the cytotoxicity of QAS is influenced by
the alkyl chain length, and the cytotoxicity and the antibac-
terial activity of C12QAS are stronger than other QAS. The
strategy provides a facile way to design and develop new
types of antibacterial and antifungal drugs for application
in preventing the fruit rot, especially apple.
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We are grateful for financial support from the National Nat-
ural Science Foundation of China (No. 21402010), the
Foundation of Shandong province (Nos. ZR2013BM022,
J11LF27), and the Foundation of Yantai (Nos. 2013ZH095,
2011076).
Conflict of Interest
All authors declare no conflict of interests.
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Data S1. 1H NMR, 13C NMR, GC-MS, IR data for five
QAS and relevant bond lengths, bond angles and torsion
angles of BNQAS, C12QAS, C14QAS and C16QAS.
Chem Biol Drug Des 2015; 85: 91–97
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