Efficient synthesis and antibacterial evaluation of (±)-Yanglingmycin and its analogues

Article abstract of DOI:10.3390/molecules21010096

An efficient synthetic route was developed for the large-scale preparation of (±)-Yanglingmycin and its analogues. Three series of derivatives of (±)-Yanglingmycin were synthesized and the structures of all compounds were elucidated by analyses of NMR and ESI-MS spectra data. Moreover, their antibacterial activities against seven species of bacteria were systematically evaluated by the micro-broth dilution method, most of which displayed considerable activity. It was worth noting that compounds 5b, 5c, 5d, 6g, and 7 were found to be the most promising leading candidates, with peak MIC values of 0.98 μg.mL^-1 for Bacillus subtilis, which is superior to positive controls (MIC = 3.91 μg.mL^-1). The above results might lay the firm foundation for the design and synthesis of novel antibacterial drugs based on (±)-Yanglingmycin.

Full text of DOI:10.3390/molecules21010096

molecules
Article
Efficient Synthesis and Antibacterial Evaluation of
(˘)-Yanglingmycin and Its Analogues
Wenjia Dan 1,2,†, Huiling Geng 1,†, Jianwen Qiao 1, Rui Guo 1,2, Shaopeng Wei 2, Longbo Li 1,2
,
Wenjun Wu 2 and Jiwen Zhang 1,2,
*
Received: 12 November 2015 ; Accepted: 12 January 2016 ; Published: 15 January 2016
Academic Editor: Derek J. McPhee
1
College of Science, Northwest A & F University, Yangling 712100, Shaanxi, China; dwj586@gmail.com (W.D.);
genghuiling5@163.com (H.G.); 18700427513@163.com (J.Q.); 18740456637@163.com (R.G.);
lilongbo528@126.com (L.L.)
Key Laboratory of Botanical Pesticide R & D in Shaanxi Province, Northwest A & F University,
Yangling 712100, Shaanxi, China; weishaopeng@nwsuaf.edu.cn (S.W.); wuwenjun@nwsuaf.edu.cn (W.W.)
Correspondence: nwzjw@nwsuaf.edu.cn; Tel.: +86-29-87092191
2
*
†
These authors contributed equally to this work.
Abstract: An efficient synthetic route was developed for the large-scale preparation of
)-Yanglingmycin and its analogues. Three series of derivatives of ( )-Yanglingmycin were
(
˘
˘
synthesized and the structures of all compounds were elucidated by analyses of NMR and
ESI-MS spectra data. Moreover, their antibacterial activities against seven species of bacteria were
systematically evaluated by the micro-broth dilution method, most of which displayed considerable
activity. It was worth noting that compounds 5b
promising leading candidates, with peak MIC values of 0.98
superior to positive controls (MIC = 3.91
mL´1). The above results might lay the firm foundation
,
5c,
5d
,
6g, and
7 were found to be the most
µg
¨
mL´1 for Bacillus subtilis, which is
µg
¨
for the design and synthesis of novel antibacterial drugs based on (˘)-Yanglingmycin.
Keywords: synthesis; Yanglingmycin; antibacterial activity; analogues
1. Introduction
Since the 1940s, antibiotics have been widely used in daily life mainly due to their key
role in prevention and control of human, animal, and plant diseases, etc. [
1]. Since the effective
targets of the antibiotics are still rather limited [ ], the abuse of antibiotics resulted in the target
2
sites becoming less sensitive. This context has led to the emergence of antibiotic resistance, for
higher doses of antibiotics required to successfully cure certain bacterial infections, with some
antibiotics losing their antibiotic activity completely [
)-Yanglingmycin (Figure 1) was carefully isolated from the fermentation broth of Streptomyces
djakartensis by our group [ ]. As a 2-aryl-substituted 4,5-dihydrooxazol derivative, ( )-Yanglingmycin
3,4]. In 2013, biologically-active natural product
(´
5
´
has been found to possess wide-range functionality and exhibited a variety of biological activities
useful for applications, such as pharmaceutical drugs, polymeric materials, insecticides, and so
on [
satisfying antibacterial activity for Pseudomonas syringae pv. Actinidiae and Ralstonia solanacearum
with peak MIC values 7.81 and 15.62 ]. As far as the antibacterial data
mL´1, respectively [
6
,7]. As reported by us recently, both (
´)-Yanglingmycin and (+)-Yanglingmycin exhibited
µ
g
¨
8
of Yanglingmycin was concerned, we postulated that this compound has the potential to act as
the lead compound for the development of new antibacterial drugs. Unfortunately, the content of
)-Yanglingmycin in Streptomyces djakartensis fermentation broth was less than 2
which could not provide enough pure target compound for our further study. In the last decades,
the total synthesis of oxazole compounds has attracted more and more attention of researchers
(´
µg
mL´1, obviously,
¨
Molecules 2016, 21, 96; doi:10.3390/molecules21010096
www.mdpi.com/journal/molecules

Molecules 2016, 21, 96
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all over the world [
9–
13]. In order to obtain more substrates for drug development, an efficient,
low-cost, and convenient route was developed to synthesize (
˘
)-Yanglingmycin, based on our previous
studies [ 14]. To our delight, ( )-Yanglingmycin showed considerable MIC values against all tested
5,
8,
´
bacteria. Herein, a series of hydroxyl ester and hydroxyl ether derivatives of the racemic compound
and its phenyl different-substituted analogues were designed and synthesized to further explore
the antibacterial potency. Moreover, all compounds were successively screened against several
Gram-negative and Gram-positive bacteria species, which consisted of Bacillus cereus, Bacillus subtilis,
Staphylococcus aureus, Escherichia coli, Pseudomonas syringae pv. Actinidiae, Pseudomonas solanacearum,
and Ralstonia solanacearum.
Figure 1. The structure of (´)-Yanglingmycin.
2. Results and Discussion
2.1. Preparation of 2-Arylthiazoline Analogues
Large scale synthesis of (
pathway outlined in Scheme 1 [13]. In addition, series of derivatives of (
prepared as well as assayed the antibacterial activities. Twenty-six derivatives 5a
59%–86% yields by esterification reactions using catalytic amount of 4-N,N-dimethylaminepyridine
and EDC HCl (Scheme 2) [15]. Simultaneously, etherification of the alcoholic hydroxyl groups of
compound 4a provided fifteen derivatives 6a 6o with yields 63%–88% (Scheme 3) [16 17]. Only one
phenolic hydroxyl group usually reacted with an alkylating agent more easily than the alcoholic
hydroxyl group under the base conditions. However, ( )-Yanglingmycin took a prior reaction on the
˘
)-Yanglingmycin and its analogues have been executed via an efficient
)-Yanglingmycin were
5z were afforded in
˘
–
¨
–
,
˘
alcoholic hydroxyl. From its molecular structure, we could infer that the activation energy of phenolic
hydroxyl may be increased because of the presence of intramolecular hydrogen bonds. A fluorinated
compound was afforded via (˘)-Yanglingmycin reacted with DAST (Scheme 4) [18,19].
The preliminary results proved that compounds 5a, 5b, 5c, 5d, 5e, 5f, 5g, 6f, 6g, and 7 were
found to possess superior activity than (
MIC values, compounds 5b 5c 5d 6g, and
for further medicine-relevant studies, compared to none of the 4b
Taking a comprehensive view of the relationship between the compounds structure and its antibacterial
data, most compounds lost their activity after the alcoholic hydroxyl derivatized or the 2-hydroxy
substitution of the phenyl ring disappeared. However, short-chain ester group and electron-deficient
ether moiety contribute significantly to the potency of antibacterial activity. Meanwhile, alcoholic
hydroxyl fluorinate increased the antibacterial activity greatly.
˘
)-Yanglingmycin. According to the evaluation results of
have more potential to be the leading compounds
MICs within 31.25 .
mL´1
,
,
,
7
–
h
µg
¨
Scheme 1. The synthetic route of (˘)-Yanglingmycin and its analogues.

Molecules 2016, 21, 96
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Scheme 2. The synthetic route of esterified derivatives of (˘)-Yanglingmycin.
Scheme 3. The synthetic route etherified derivatives of (˘)-Yanglingmycin.
Scheme 4. The synthetic route fluorinated derivatives of (˘)-Yanglingmycin.
2.2. Antibacterial Activities Assay
All the synthesized compounds were evaluated for their in vitro antibacterial activities against
four Gram-negative (Escherichia coli, Pseudomonas syringae pv. Actinidiae, Pseudomonas solanacearum,
Ralstonia solanacearum) and three Gram-positive bacteria (Bacillus cereus, Bacillus subtilis,
Staphylococcus aureus). The minimum inhibitory concentrations (MICs) were determined by the
double-dilution method using ampicillin sodium and fosfomycin sodium as the positive controls. All
data of MIC values were summarized in Tables 1 and 2.

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Table 1. The MICs of (˘)-Yanglingmycin and its derivatives.
Bacillus
cereus
Bacillus
subtilis
Staphylococcus
aureus
Escherichia
coli
Pseudomonas syringae
Pseudomonas
solanacearum
Ralstonia
solanacearum
Compound
pv. actinidiae
(˘)-Yanglingmycin
15.62 (˘2.25)
62.50 (˘5.96)
15.62 (˘0)
15.62 (˘2.25)
7.81 (˘1.13)
7.81 (˘1.13)
0.98 (˘0)
31.25 (˘2.98)
7.81 (˘0.56)
7.81 (˘0)
7.81 (˘1.13)
>125 (˘0)
125 (˘0)
7.81 (˘0.56)
31.25 (˘1.13)
31.25 (˘0)
31.25 (˘1.13)
125 (˘0)
15.62 (˘2.25)
31.25 (˘0)
62.50 (˘0.40)
31.25 (˘1.13)
125 (˘2.25)
125 (˘2.25)
125 (˘0)
15.62 (˘2.25)
7.81 (˘1.13)
0.98 (˘0)
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
5q
5r
5s
5t
5u
5v
5w
5x
5y
3.91 (˘0.56)
7.81 (˘1.13)
15.62 (˘0)
3.91 (˘0)
125 (˘0)
1.95 (˘0)
7.81 (˘0)
15.62 (˘1.13)
15.62 (˘0)
31.25 (˘1.13)
31.25 (˘0)
62.50 (˘0)
62.50 (˘1.13)
62.50 (˘2.25)
62.50 (˘0)
62.50 (˘0)
62.50 (˘0)
62.50 (˘2.25)
62.50 (˘0)
62.50 (˘0)
125 (˘2.25)
62.50 (˘0)
31.25 (˘1.13)
62.50 (˘0)
125 (˘0)
>125 (˘0)
>125 (˘0)
>125 (˘0)
>125 (˘0)
>125 (˘0)
>125 (˘0)
15.62 (˘0.56)
>125 (˘0)
125 (˘1.13)
125 (˘0)
3.91 (˘0.40)
31.25 (˘1.13)
3.91 (˘0.56)
15.62 (˘0)
15.62 (˘0)
7.81 (˘1.13)
7.81 (˘0)
125 (˘1.13)
>125 (˘0)
>125 (˘0)
>125 (˘0)
>125 (˘0)
125 (˘1.13)
>125 (˘0)
>125 (˘0)
>125 (˘0)
>125 (˘0)
>125 (˘0)
125 (˘0)
31.25 (˘2.25)
62.50 (˘1.13)
62.50 (˘0)
125 (˘0)
31.25 (˘2.25)
62.50 (˘2.25)
62.50 (˘9.02)
62.50 (˘1.13)
31.25 (˘0)
31.25 (˘0)
31.25 (˘0)
62.50 (˘0)
31.25 (˘1.13)
62.50 (˘0)
15.62 (˘0)
31.25 (˘0)
62.50 (˘0)
62.50 (˘0)
62.50 (˘2.25)
62.50 (˘1.13)
31.25 (˘1.13)
31.25 (˘0)
62.50 (˘0)
7.81 (˘1.13)
15.62 (˘0)
125 (˘2.25)
15.62 (˘0)
125 (˘0)
31.25 (˘0)
125 (˘1.13)
15.62 (˘2.25)
62.50 (˘0)
62.50 (˘1.13)
31.25 (˘2.98)
62.50 (˘0)
125 (˘2.25)
62.50 (˘0.53)
62.50 (˘0)
62.50 (˘0.56)
125 (˘2.25)
125 (˘0)
62.50 (˘0)
62.50 (˘1.13)
62.50 (˘0)
62.50 (˘0)
62.50 (˘5.96)
62.50 (˘0)
125 (˘5.96)
>125 (˘0)
125 (˘0)
62.50 (˘1.13)
62.50 (˘0)
62.50 (˘0)
31.25 (˘0.56)
15.62 (˘0)
31.25 (˘0)
>125 (˘0)
125 (˘0)
>125 (˘0)
125 (˘1.13)
125 (˘0)
125 (˘1.13)
15.62 (˘0)
62.50 (˘2.25)
125 (˘1.13)
125 (˘2.25)
125 (˘0)
31.25 (˘2.25)
62.50 (˘9.02)
62.50 (˘0)
31.25 (˘0)
62.50 (˘1.13)
125 (˘0)
62.50 (˘1.13)
62.50 (˘0)
125 (˘1.13)
125 (˘0)
125 (˘0)
>125 (˘0)
>125 (˘0)
62.50 (˘1.13)
62.50 (˘0)
125 (˘0)
125 (˘0)
62.50 (˘5.96)
125 (˘0)
125 (˘0)
125 (˘0)
62.50 (˘0)
62.50 (˘2.25)
62.50 (˘0)
62.50 (˘0)
125 (˘2.25)
3.91 (˘0.53)
3.91 (˘0.53)
125 (˘5.96)
125 (˘0)
62.50 (˘1.13)
62.50 (˘2.25)
62.50 (˘0)
62.50 (˘1.13)
7.81 (˘0)
62.50 (˘2.25)
31.25 (˘1.13)
31.25 (˘0)
62.50 (˘0)
31.25 (˘2.25)
62.50 (˘2.25)
3.91 (˘0)
125 (˘2.25)
>125 (˘0)
0.98 (˘0)
5z
>125 (˘0)
1.95 (˘0.40)
0.98 (˘0)
62.50 (˘2.25)
7.81 (˘0.56)
1.95 (˘0.40)
Ampicillin Sodium
Fosfomycin Sodium
3.91 (˘0.53)
>125 (˘0)
125 (˘0)

Molecules 2016, 21, 96
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Table 2. The MICs of (˘)-Yanglingmycin and its derivatives.
Bacillus
cereus
Bacillus
subtilis
Staphylococcus
aureus
Escherichia
coli
Pseudomonas syringae
Pseudomonas
solanacearum
Ralstonia
solanacearum
Compound
pv. actinidiae
(˘)-Yanglingmycin
15.62 (˘2.25)
62.50 (˘5.96)
31.25 (˘0)
15.62 (˘2.25)
31.25 (˘4.06)
15.62 (˘2.25)
31.25 (˘0)
31.25 (˘2.98)
125 (˘0)
7.81 (˘1.13)
125 (˘0)
7.81 (˘0.56)
31.25 (˘0)
1.95 (˘0)
15.62 (˘2.25)
31.25 (˘4.51)
15.62 (˘2.25)
31.25 (˘0)
15.62 (˘0)
31.25 (˘0)
7.81 (˘0)
15.62 (˘2.25)
125 (˘0)
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
7
62.50 (˘5.96)
62.50 (˘1.13)
62.50 (˘0)
62.50 (˘0)
15.62 (˘0.40)
7.81 (˘0)
31.25 (˘0)
125 (˘0)
62.50 (˘0)
62.50 (˘0)
31.25 (˘1.13)
31.25 (˘0)
15.62 (˘1.13)
7.81 (˘0)
62.50 (˘4.06)
62.50 (˘0)
31.25 (˘0.56)
62.50 (˘2.25)
62.50 (˘0)
3.91 (˘0)
31.25 (˘2.25)
62.50 (˘0)
62.50 (˘1.13)
62.50 (˘1.13)
125 (˘0)
31.25 (˘0)
15.62 (˘1.13)
15.62 (˘0)
7.81 (˘0.53)
15.62 (˘0)
125 (˘0)
0.98 (˘0)
0.98 (˘0)
125 (˘0)
62.50 (˘0)
62.50 (˘0)
62.50 (˘1.13)
31.25 (˘0)
62.50 (˘0)
31.25 (˘0.56)
62.50 (˘0)
31.25 (˘0)
62.50 (˘0)
7.81 (˘0)
>125 (˘0)
125 (˘0)
125 (˘0)
125 (˘4.06)
62.50 (˘0)
62.50 (˘1.13)
125 (˘2.98)
15.62 (˘0)
62.50 (˘0.53)
31.25 (˘0.40)
62.50 (˘2.25)
0.98 (˘0)
125 (˘4.51)
125 (˘0)
62.50 (˘0.53)
31.25 (˘0.40)
62.50 (˘0)
62.50 (˘4.51)
31.25 (˘0)
62.50 (˘2.25)
62.50 (˘0)
125 (˘0)
125 (˘0)
62.50 (˘0)
125 (˘0)
62.50 (˘0.53)
31.25 (˘0.40)
31.25 (˘0)
>125 (˘0)
125 (˘0)
31.25 (˘0)
31.25 (˘0)
62.50 (˘1.13)
31.25 (˘1.13)
62.50 (˘2.25)
0.98 (˘0)
31.25 (˘0)
62.50 (˘1.13)
31.25 (˘0)
31.25 (˘0)
15.62 (˘0.40)
7.81 (˘0.56)
1.95 (˘0.40)
62.50 (˘1.13)
31.25 (˘0)
125 (˘0)
31.25 (˘0)
125 (˘0)
62.50 (˘0)
31.25 (˘0.53)
15.62 (˘0)
>125 (˘0)
31.25 (˘0.56)
1.95 (˘0.40)
0.98 (˘0)
31.25 (˘1.13)
3.91 (˘0)
Ampicillin Sodium
Fosfomycin Sodium
7.81 (˘1.13)
15.62 (˘0)
3.91 (˘0.53)
3.91 (˘0.53)
0.98 (˘0)
7.81 (˘0)
3.91 (˘0.53)
>125 (˘0)
125 (˘0)

Molecules 2016, 21, 96
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3. Experimental Section
3.1. Chemistry
General unless otherwise noted, all reagents and solvents were purchased from commercial
suppliers and used without further purification, which were of analytical reagent (AR) grade. TLC was
performed on GF254 silica gel plates (Qingdao Haiyang Co., Ltd., Qingdao, Shandong, China).
Column chromatography was carried out with silica gel (Qingdao Haiyang Co., Ltd.); all compounds
were eluted with petroleum ether and ethyl acetate in sequence. Melting point (m.p.) was determined
on a Yanagimoto apparatus (uncorrected). 1H-NMR and 13C-NMR spectra were performed on
a Bruker-Avance-500 spectrometer (Bruker Daltonics Inc., Bremen, Germany) with DMSO-d6 or CDCl3
as solvent and SiMe4 (tetramethylsilane) as the internal standard. MS were recorded on an electrospray
ionization (ESI) conditions by using a Thermo LCQ Fleet instrument (Thermo Fisher Scientific Co.,
Waltham, MA, USA). HR-MS were recorded on an Agilent 1290-6224 instrument (Agilent, Santa Clara,
CA, USA).
3.1.1. Synthesis of 4a–4h
The solution of substituted benzonitrile (100 mmol), serinol (54.660 g, 600 mmol), and Na2CO3
(10.599 g, 100 mmol) in anhydrous methanol (100 mL) was heated to reflux for 10 h. After the reaction
solution was cooled to room temperature, the solvent was removed under vacuum, the resulting
residue was then diluted with anhydrous CH2Cl2 (30 mL). The organic fractions were successively
washed with an aqueous saturated solution of NH4Cl (30 mL
anhydrous Na2SO4. The solvent was got rid of under vacuum to afford a scarlet residue which was
ˆ
2), brine (30 mL
ˆ
3), and dried over
purified by flash column chromatography using petroleum ether/ethyl acetate (8:1, v/v) as the eluent.
2-(4-(Hydroxymethyl)-4,5-dihydrooxazol-2-yl)phenol (4a) Yield: 68%–78%; white solids; m.p. 78–80 ˝C;
ESI-MS m/z 194.07 [M + H]+; HR-MS m/z: Calcd for C10H12NO3: 194.0817 [M + H]+; found 194.0803
[M + H]+; 1H-NMR (CDCl3, 500 MHz)
δ 7.66 (dd, J = 1.5, 7.5 Hz, 1H), 7.39 (m, 1H), 7.01 (d, J = 8.0 Hz,
1H), 6.89 (m, 1H), 4.50 (m, 2H), 4.36 (t, J = 6.0 Hz, 1H), 3.89 (dd, J = 3.5, 11.5 Hz, 1H), 3.71 (dd, J = 3.5,
11.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
66.87, 63.95.
δ 166.93, 159.78, 133.68, 128.22, 118.81, 116.75, 110.40, 68.58,
˝
3-(4-(Hydroxymethyl)-4,5-dihydrooxazol-2-yl)phenol (4b) Yield: 67%; white solids; m.p. 91–93 C; ESI-MS
m/z 194.17 [M + H]+; 1H-NMR (500 MHz, CDCl3)
7.48 (m, 1H), 7.44 (m, 1H), 7.28 (m, 1H), 7.03 (m,
δ
1H), 4.52 (dd, J = 3.5, 9.5 Hz, 1H), 4.42 (m, 1H), 4.36 (t, J = 7.5 Hz, 1H), 3.95 (dd, J = 3.5, 11.5 Hz, 1H),
3.67 (m, 1H); 13C-NMR (125 MHz, CDCl3)
68.11, 64.58.
δ 165.41, 159.86, 128.98, 127.49, 120.81, 118.42, 113.19, 69.27,
˝
4-(4-(Hydroxymethyl)-4,5-dihydrooxazol-2-yl)phenol (4c) Yield: 65%; white solids; m.p. 192–194 C;
ESI-MS m/z 194.02 [M + H]+; 1H-NMR (500 MHz, DMSO-d6)
10.03 (br.s., 1H), 7.69 (d, J = 8.8 Hz, 2H),
δ
6.81 (d, J = 8.5 Hz, 2H), 4.79 (t, J = 5.5 Hz, 1H), 4.37 (t, J = 8.2 Hz, 1H), 4.19 (t, J = 6.0 Hz, 1H), 3.62
(m, 1H), 3.41 (td, J = 5.5, 10.8 Hz, 1H); 13C-NMR (125 MHz, DMSO-d6)
δ 163.25, 160.66, 130.17, 118.3,
115.65, 69.95, 68.43, 63.74.
˝
(2-Phenyl-4,5-dihydrooxazol-4-yl)methanol (4d) Yield: 69%; white solids; m.p. 82–84 C; ESI-MS m/z
178.12 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.98 (m, 2H), 7.47 (m, 1H), 7.38 (m, 2H), 4.43 (m, 1H),
4.34 (m, 1H), 4.49 (m, 1H), 3.98 (dd, J = 3.5, 11.5 Hz, 1H), 3.67 (dd, J = 4.0, 11.5 Hz, 1H); 13C-NMR
(125 MHz, CDCl3) δ 165.61, 131.57, 128.37, 128.31, 127.21, 69.29, 68.08, 63.94.
(2-(2-Fluorophenyl)-4,5-dihydrooxazol-4-yl)methanol (4e) Yield: 46%; yellow oil; ESI-MS m/z 196.16
1
[M + H]+; H-NMR (500 MHz, CDCl3)
δ 7.88 (td, J = 1.5, 7.5 Hz, 1H), 7.47 (m, 1H), 7.19 (m, 2H),
4.50 (m, 2H), 4.34 (m, 1H), 3.85 (dd, J = 3.0, 11.5 Hz, 1H), 3.71 (dd, J = 4.0, 11.5 Hz, 1H); 13C-NMR
(125 MHz, CDCl3)
69.06, 68.42, 64.16.
δ 162.28, 162.21, 162.17, 160.22, 133.16, 133.09, 131.19, 124.01, 123.98, 116.80, 116.63,

Molecules 2016, 21, 96
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(2-(m-Tolyl)-4,5-dihydrooxazol-4-yl)methanol (4f) Yield: 71%; white solids; m.p. 146–148 ˝C; ESI-MS m/z
192.12 [M + H]+; 1H-NMR (500 MHz, CDCl3)
7.71 (s, 1H), 7.68 (m, 2H), 7.28 (m, 2H), 4.49 (dd, J = 7.5,
δ
9.5 Hz, 1H), 4.44 (m, 1H), 4.34 (m, 1H), 3.96 (dd, J = 3.5, 11.5 Hz, 1H), 3.68 (dd, J = 4.0, 11.5 Hz, 1H),
2.36 (s, 3H); 13C-NMR (125 MHz, CDCl3)
68.07, 64.06, 21.23.
δ 165.73, 138.05, 132.31, 128.92, 128.23, 127.16, 125.44, 69.26,
(2-(3-Methoxyphenyl)-4,5-dihydrooxazol-4-yl)methanol (4g) Yield: 67%; white solids; m.p. 123–125 ˝C;
ESI-MS m/z 208.03 [M + H]+; 1H-NMR (500 MHz, CDCl3)
7.49 (m, 1H), 7.42 (m, 1H), 7.29 (m, 1H),
δ
7.02 (m, 1H), 4.50 (dd, J = 3.5, 9.5 Hz, 1H), 4.44 (m, 1H), 4.35 (t, J = 7.5 Hz, 1H), 3.97 (dd, J = 3.5, 11.5 Hz,
1H), 3.83 (s, 3H), 3.68 (m, 1H); 13C-NMR (125 MHz, CDCl3)
118.34, 112.69, 69.34, 68.12, 64.03, 55.40.
δ 165.47, 159.46, 129.38, 128.53, 120.83,
(2-(4-Bromophenyl)-4,5-dihydrooxazol-4-yl)methanol (4h) Yield: 80%; yellow oil; ESI-MS m/z 255.01:257.13
(1:1), [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.74 (m, 2H), 7.51 (m, 2H), 4.51 (dd, J = 7.5, 9.5 Hz, 1H),
4.41 (m, 1H), 4.36 (m, 1H), 3.98 (dd, J = 3.5, 11.5 Hz, 1H), 3.68 (dd, J = 4.0, 11.5 Hz, 1H); 13C-NMR
(125 MHz, CDCl3) δ 175.12, 164.74, 131.59, 129.85, 126.30, 126.21, 69.44, 68.19, 63.85.
3.1.2. Synthesis of 5a–5z
A solution of compound 4a (193 mg, 1.0 mmol), carboxylic acid (1.2 mmol), EDC HCl (288 mg,
¨
1.5 mmol), and DMAP (6 mg, 5%) in anhydrous CH2Cl2 (8 mL) is stirred at room temperature for 6 h.
Then, the reaction solution was quenched with saturated aqueous NaHCO3 (50 mL), concentrated
under reduced pressure until approximately 30 mL remained. The organic layer was separated with
CH2Cl2 (30 mL
ˆ
3) and washed sequentially with water (30 mL
ˆ
2), brine (30 mL
ˆ
3), and dried
over anhydrous Na2SO4. The solvent is concentrated under reduced pressure, and purified by flash
column chromatography using petroleum ether/ethyl acetate (10:1, v/v) as the eluent.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl acetate (5a) Yield: 72%; yellow oil; ESI-MS m/z 236.12
[M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.66 (dd, J = 2.0, 9.0 Hz, 1H), 7.41 (m, 1H), 7.02 (dd, J = 1.0,
8.5 Hz, 1H), 6.90 (m, 1H), 4.65 (m, 1H), 4.51 (dd, J = 8.5, 9.5 Hz, 1H), 4.31 (m, 2H), 4.21 (dd, J = 5.5,
21.5 Hz, 1H), 2.07 (s, 3H); 13C-NMR (125 MHz, CDCl3)
116.88, 110.29, 69.14, 65.43, 64.21, 20.78.
δ 170.83, 166.74, 159.95, 133.75, 128.18, 118.72,
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl propionate (5b) Yield: 75%; orange oil; ESI-MS m/z
1
250.17 [M + H]+; H-NMR (500 MHz, CDCl3)
δ 7.66 (dd, J = 1.5, 8.0 Hz, 1H), 7.40(m, 1H), 7.02(dd,
J = 1.0, 7.5 Hz, 1H), 6.89 (m, 1H), 4.65 (m, 1H), 4.51 (dd, J = 1.5, 8.0 Hz, 1H), 4.32 (m, 2H), 4.23 (dd,
J = 5.5, 11.0 Hz, 1H), 2.34 (q, J = 7.5 Hz, 2H), 1.12 (m, 3H); 13C-NMR (125 MHz, CDCl3)
δ 174.25, 166.71,
159.95, 133.72, 128.16, 118.71, 116.87, 110.31, 69.13, 65.25, 64.27, 27.44, 9.05.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl butyrate (5c) Yield: 82%; yellow oil; ESI-MS m/z 264.09
[M + H]+; 1H-NMR (500 MHz, CDCl3)
11.88 (s, 1H, Ar-OH), 7.66 (dd, J = 2.0, 8.0 Hz, 1H), 7.40 (m,
δ
1H), 7.02 (dd, J = 1.0, 8.5 Hz, 1H), 6.89 (m, 1H), 4.65 (m, 1H), 4.50 (dd, J = 9.0, 10.0 Hz, 1H), 4.31 (m,
2H), 4.24 (dd, J = 4.5, 9.5 Hz, 1H), 2.29 (t, J = 7.0 Hz, 2H), 1.66 (m, 2H), 0.91 (t, J = 7.5 Hz, 3H); 13C-NMR
(125 MHz, CDCl3)
36.13, 18.45, 13.60.
δ 173.47, 166.71, 159.96, 133.74, 128.17, 118.73, 116.87, 110.32, 69.13, 65.25, 64.27,
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl isobutyrate (5d) Yield: 84%; yellow oil; ESI-MS m/z
264.13 [M + H]+; 1H-NMR (500 MHz, CDCl3)
7.65 (dd, J = 2.0, 8.0 Hz, 1H), 7.40 (m, 1H), 7.01(dd,
J = 0.5, 8.5 Hz, 1H), 6.89 (m, 1H), 4.65 (m, 1H), 4.50 (m, 1H), 4.30 (m, 1H), 4.27 (m, 1H), 2.59 (m, 1H),
1.13 (t, J = 8.0 Hz, 6H); 13C-NMR (125 MHz, CDCl3)
176.85, 166.70, 159.95, 133.71, 128.14, 118.70,
116.86, 110.30, 69.06, 65.08, 64.32, 33.93, 18.91, 18.87, 1.03.
δ
δ
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl pentanoate (5e) Yield: 79%; orange oil; ESI-MS m/z
278.09 [M + H]+; 1H-NMR (500 MHz, CDCl3)
11.60 (br. s, 1H, Ar-OH), 7.65 (d, J = 7.5 Hz, 1H), 7.39 (t,
J = 7.5 Hz, 1H), 7.02 (d, J = 8.0 Hz, 1H), 6.88 (t, J = 7.0 Hz, 1H), 4.62 (m, 1H), 4.48 (t, J = 9.0 Hz, 1H),
δ

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4.27 (m, 3H), 2.32 (m, 2H), 1.57 (m, 2H), 1.32 (m, 2H), 0.86 (t, J = 6.5 Hz, 3H); 13C-NMR (125 MHz,
CDCl3) 173.66, 166.70, 159.94, 133.71, 128.15, 118.71, 116.86, 110.30, 69.09, 65.14, 64.27, 33.88, 26.98,
δ
22.19, 13.63.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl hexanoate (5f) Yield: 67%; orange oil; ESI-MS m/z
292.17 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 11.88(br. s, 1H, Ar-OH), 7.66 (dd, J = 2.0, 8.0 Hz, 1H),
7.40 (m, 1H), 7.02 (dd, J = 1.0, 8.5 Hz, 1H), 6.89 (m, 1H), 4.63 (m, 1H), 4.50 (dd, J = 9.0, 10.0 Hz, 1H), 4.30
(m, 3H), 2.30 (t, J = 7.5 Hz, 2H), 1.61 (m, 2H), 1.29(m, 4H), 0.85 (t, J = 7.0 Hz, 3H); 13C-NMR (125 MHz,
CDCl3) δ 173.67, 166.70, 159.94, 133.70, 128.15, 118.71, 116.86, 110.32, 69.10, 65.14, 64.29, 34.14, 31.22,
24.60, 22.25, 13.84.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl heptanoate (5g) Yield: 77%; pale yellow oil; ESI-MS
m/z 306.13 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 11.87 (br. s, 1H, Ar-OH), 7.66 (d, J = 7.0 Hz, 1H),
7.38 (t, J = 6.5 Hz, 1H), 7.02 (d, J = 9.0 Hz, 1H), 6.88 (t, J = 6.5 Hz, 1H), 4.61 (m, 1H), 4.48 (t, J = 8.0 Hz,
1H), 4.28 (m, 3H), 2.30 (t, J = 6.5 Hz, 2H), 1.57 (t, J = 6.5 Hz, 2H), 1.25 (m, 6H), 0.86 (t, J = 6.5 Hz, 3H);
13C-NMR (125 MHz, CDCl3)
δ 173.65, 166.70, 159.95, 133.71, 128.15, 118.70, 116.86, 110.30, 69.10, 65.12,
64.28, 34.18, 31.39, 28.75, 24.88, 22.42, 14.01.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl octanoate (5h) Yield: 72%; yellow oil; ESI-MS m/z
320.17 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 11.84 (br. s, 1H, Ar-OH), 7.66 (dd, J = 1.5, 9.0 Hz, 1H),
7.40 (m, 1H), 7.02 (dd, J = 1.0, 8.5 Hz, 1H), 6.89 (m, 1H), 4.64 (m, 1H), 4.50 (dd, J = 8.5, 9.5 Hz, 1H), 4.30
(m, 3H), 2.30 (t, J = 6.5 Hz, 2H), 1.60 (m, 2H), 1.29 (m, 8H), 0.87 (t, J = 7.0 Hz, 3H); 13C-NMR (125 MHz,
CDCl3) δ 173.65, 166.69, 159.94, 133.71, 128.15, 118.70, 116.86, 110.31, 69.10, 65.12, 64.28, 34.18, 31.60,
29.04, 28.87, 24.92, 22.59, 14.06.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl dodecanoate (5i) Yield: 83%; pale yellow oil; ESI-MS
m/z 376.22 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.66 (dd, J = 1.5, 9.0 Hz, 1H), 7.40 (m, 1H), 7.02
(dd, J = 0.5, 8.5 Hz, 1H), 6.89 (m, 1H), 4.64 (m, 1H), 4.50 (dd, J = 8.5, 9.5 Hz, 1H), 4.30 (m, 3H), 2.30
(t, J = 6.5 Hz, 2H), 1.60 (m, 2H), 1.31 (m, 16H), 0.88 (t, J = 7.0 Hz, 3H); 13C-NMR (125 MHz, CDCl3)
δ
173.64, 166.71, 159.97, 133.71, 128.16, 118.70, 116.88, 110.31, 69.11, 65.12, 64.29, 34.18, 31.92, 29.60,
29.42, 29.34, 29.22, 29.09, 24.93, 22.69, 14.12.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl isonicotinate (5j) Yield: 76%; white solid; m.p. 111
1
˝C; ESI-MS m/z 299.12 [M + H]+; H-NMR (500 MHz, CDCl3)
δ 11.83 (br. s, 1H, Ar-OH), 8.76 (dd,
J = 1.5, 5.0 Hz, 2H), 7.79 (dd, J = 1.5, 4.5 Hz, 2H), 7.69 (dd, J = 1.5, 8.0 Hz, 1H), 7.42 (m, 1H), 7.02 (dd,
J = 0.5, 8.5 Hz, 1H), 6.91 (m, 1H), 4.80 (m, 1H), 4.59 (m, 3H), 4.39 (dd, J = 6.5, 8.5 Hz, 1H); 13C-NMR
(125 MHz, CDCl3)
68.98, 66.59, 64.18.
δ 167.02, 164.89, 159.95, 150.68, 136.79, 133.93, 128.18, 122.83, 118.85, 116.93, 110.12,
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 2-(4-methoxyphenyl)acetate (5k) Yield: 63%; colorless
solid; m.p. 105–106 ˝C; ESI-MS m/z 342.21 [M + H]+; 1H-NMR (500 MHz, CDCl3)
7.64 (dd, J = 1.5,
δ
8.0 Hz, 1H), 7.41 (m, 1H), 7.14 (m, 2H), 7.03 (dd, J = 1.0, 8.5 Hz, 1H), 6.90 (m, 1H), 6.78 (m, 2H), 4.61 (m,
1H), 4.43 (dd, J = 8.5, 9.5 Hz, 1H), 4.27 (dd, J = 3.0, 4.5 Hz, 2H), 4.19 (dd, J = 7.5, 8.5 Hz, 1H), 3.76 (s,
3H), 3.55 (s, 2H); 13C-NMR (125 MHz, CDCl3)
δ 171.63, 166.70, 159.95, 158.72, 133.70, 130.17, 128.18,
125.62, 118.69, 116.85, 114.00, 110.30, 68.87, 65.43, 64.20, 55.22, 40.39.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 4-chlorobenzoate (5l) Yield: 71%; white solid; m.p.
˝
106 C; ESI-MS m/z 332.06:334.11 (3:1), [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ
7.93 (m, 2H), 7.68 (dd,
J = 1.5, 7.5 Hz, 1H), 7.42 (m, 3H), 7.02 (dd, J = 0.5, 8.0 Hz, 1H), 6.91 (m, 1H), 4.78 (m, 1H), 4.57 (m, 2H),
4.47 (dd, J = 4.5, 9.5 Hz, 1H), 4.39 (dd, J = 7.0, 8.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
166.90, 165.48,
δ
159.96, 139.78, 133.84, 131.05, 128.84, 128.16, 128.04, 118.80, 116.91, 110.21, 69.12, 66.11, 64.29.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 4-fluorobenzoate (5m) Yield: 59%; white solid; m.p.
85–87 ˝C; ESI-MS m/z 316.12 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ
8.02 (m, 2H), 7.68 (dd, J = 1.5,
8.0 Hz, 1H), 7.41 (m, 1H), 7.10 (m, 2H), 7.03 (dd, J = 1.0, 8.5 Hz, 1H), 6.91 (m, 1H), 4.78 (m, 1H), 4.57 (m,

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2H), 4.47 (dd, J = 4.5, 9.5 Hz, 1H), 4.39 (dd, J = 7.0, 9.0 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ
166.95,
166.88, 165.36, 164.93, 159.98, 133.82, 132.29, 132.21, 128.17, 125.85, 118.78, 116.91, 115.75, 115.58, 110.24,
69.14, 66.02, 64.33.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 3-chlorobenzoate (5n) Yield: 72%; white solid; m.p.
87–89 ˝C; ESI-MS m/z 332.11:333.06 (3:1), [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ
7.79 (m, 2H), 7.70
(dd, J = 2.0, 8.0 Hz, 1H), 7.40 (m, 1H), 7.36 (m, 1H), 7.30 (m, 1H), 7.01 (dd, J = 0.5, 8.5 Hz, 1H), 6.90
(m, 1H), 4.78 (m, 1H), 4.56 (m, 2H), 4.44 (m, 2H); 13C-NMR (125 MHz, CDCl3)
166.81, 166.45, 160.29,
δ
138.20, 134.10, 133.72, 130.22, 129.45, 128.37, 128.27, 126.86, 118.83, 116.39, 110.38, 69.27, 65.69, 64.54.
The structure of 5n was also confirmed by 2D NMR data and can be seen in Table 3 and Figure 2.
Figure 2. The main HMBC of compound 5n.
Table 3. HMBC data of compound 5n.
13C-NMR
1H-NMR
C No.
δC
HMBC Correlations
H No.
δ
H
HMBC Correlations
1-C
2-C
3-C
4-C
5-C
6-C
7-C
159.94, C
116.89, CH
133.83, CH
118.81, CH
128.20, CH
110.21, C
2-H, 3-H, 5-H
3-H, 4-H
4-H, 5-H
2-H
3-H, 4-H
Ar-OH
2-H
3-H
4-H
5-H
-
-
7.02, dd, J = 0.5, 9.0 Hz, 1H
1-C, 4-C, 6-C, 7-C
1-C, 2-C, 5-C
2-C, 3-C, 5-C, 6-C
1-C, 3-C, 7-C
-
7.41–7.38, m, 1H
6.90–6.87, m, 1H
7.69, dd, J = 1.5, 8.0 Hz, 1H
2-H, 4-H
2-H, 4-H, 5-H, 8-H, 9-H
6-H
7-H
-
-
166.95, C
-
4.57–4.54, m, 1H; 4.39, dd,
J = 7.0, 9.0 Hz, 1H
4.78–4.73, m, 1H;
4.54–4.52, m, 1H; 4.47, dd,
J = 5.5, 11.5 Hz, 1H
-
8-C
9-C
66.33, CH2
64.26, CH
69.19, CH2
9-H, 10-H
8-H, 10-H
8-H
8-H
9-H
7-C, 9-C, 10-C
7-C, 8-C
10-C
10-H
8-C, 9-C, 11-C
11-C
12-C
165.13, C
134.64, C
10-H, 13-H, 16-H, 17-H
13-H, 16-H, 17-H
11-H
12-H
-
-
-
11-C, 12-C, 14-C,
15-C, 17-C
-
13-C
14-C
15-C
129.74, CH
131.33, C
15-H, 16-H, 17-H
13-H, 15-H, 16-H
13-H, 16-H, 17-H
13-H
14-H
15-H
7.95, t, J = 1.5 Hz, 1H
-
13-C, 14-C, 16-C,
133.29, CH
7.53, dq, J = 1.5, 8.5 Hz, 1H
17-C
11-C, 12-C, 14-C,
15-C, 17-C
11-C, 12-C, 13-C,
15-C, 16-C
16-C
17-C
129.80, CH
127.77, CH
15-H, 17-H
16-H
17-H
7.37, t, J = 8.0 Hz, 1H
13-H, 15-H, 16-H
7.87, dt, J = 1.5, 7.5 Hz, 1H
(E)-(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl but-2-enoate (5o) Yield: 69%; pale yellow solid;
˝
m.p. 106 C; ESI-MS m/z 262.08 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 11.89 (br. s, 1H, Ar-OH), 7.66
(dd, J = 1.5, 7.5 Hz, 1H), 7.40 (m, 1H), 7.02 (m, 2H), 6.89 (m, 1H), 5.86 (dq, J = 1.5, 15.5 Hz, 1H), 4.67 (m,
1H), 4.51 (dd, J = 9.0, 10.0 Hz, 1H), 4.38 (dd, J = 4.5, 11.0 Hz, 1H), 4.30 (dd, J = 7.0, 8.5 Hz, 1H), 4.26 (dd,
J = 4.5, 9.5 Hz, 1H), 1.87 (dd, J = 2.0, 7.0 Hz, 3H). 13C-NMR (125 MHz, CDCl3)
δ 166.69, 166.22, 159.95,
145.77, 133.69, 128.16, 122.02, 118.70, 116.86, 110.34, 69.18, 65.14, 64.32, 18.04.

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(2E,4E)-(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl hexa-2,4-dienoate (5p) Yield: 77%; dark green
˝
1
solid; m.p. 67–69 C; ESI-MS m/z 288.10 [M + H]+; H-NMR (500 MHz, CDCl3)
δ 11.90 (br. s, 1H,
Ar-OH), 7.67 (dd, J = 1.5, 8.0 Hz, 1H), 7.40 (m, 1H), 7.26 (dd, J = 10.5, 15.5 Hz, 1H), 7.02 (dd, J = 1.0,
8.5 Hz, 1H), 6.89 (m, 1H), 6.20 (m, 2H), 5.77 (d, J = 15.5 Hz, 1H), 4.68 (m, 1H), 4.52 (m, 1H), 4.40 (m, 1H),
4.30 (dd, J = 7.0, 8.5 Hz, 1H), 4.26 (dd, J = 4.5, 9.5 Hz, 1H), 1.85 (m, 3H). 13C-NMR (125 MHz, CDCl3)
δ
166.99, 166.70, 159.97, 145.97, 140.13, 133.68, 129.65, 128.16, 118.68, 118.03, 116.87, 110.35, 69.25, 65.24,
64.35, 18.67.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 3-bromopropanoate (5q) Yield: 70%; pale yellow solid;
m.p. 113–114 ˝C; ESI-MS m/z 328.17:330.21 (1:1), [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.65 (dd,
J = 1.5, 8.0 Hz, 1H), 7.39 (m, 1H), 7.00 (dd, J = 1.0, 7.5 Hz, 1H), 6.89 (m, 1H), 4.67 (m, 1H), 4.56 (dd,
J = 1.5, 8.0 Hz, 1H), 4.32 (m, 2H), 4.20 (dd, J = 5.5, 11.0 Hz, 1H), 3.66 (t, 2H), 2.38 (q, J = 7.5 Hz, 2H);
13C-NMR (125 MHz, CDCl3)
64.37, 37.49, 27.01.
δ 174.31, 166.60, 159.88, 133.71, 128.16, 118.71, 116.57, 110.19, 69.03, 65.77,
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 2-fluorobenzoate (5r) Yield: 85%; white solid; m.p.
˝
83–84 C; ESI-MS m/z 316.07 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.79 (dd, J = 1.5, 8.0 Hz, 1H), 7.67
(dd, J = 1.5, 8.0 Hz, 1H), 7.42 (m, 3H), 7.29 (m, 1H), 7.02 (dd, J = 0.5, 8.0 Hz, 1H), 6.90 (m, 1H), 4.79
(m, 1H), 4.57 (m, 2H), 4.49 (dd, J = 4.5, 9.5 Hz, 1H), 4.42 (dd, J = 7.0, 8.5 Hz, 1H); 13C-NMR (125 MHz,
CDCl3)
δ 166.92, 165.59, 159.94, 133.79, 133.77, 132.86, 131.67, 131.16, 129.57, 128.18, 126.67, 118.75,
116.88, 110.32, 69.17, 66.37, 64.20.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 2-(naphthalen-2-yl)acetate (5s) Yield: 66%; white solid;
m.p. 80 ˝C; ESI-MS m/z 362.17 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.94 (m, 1H), 7.83 (dd, J = 2.5,
7.5 Hz, 1H), 7.75 (m, 1H), 7.57 (dd, J = 2.0, 8.0 Hz, 1H), 7.48 (m, 2H), 7.39 (m, 1H), 7.34 (m, 2H), 7.01
(dd, J = 0.5, 8.0 Hz, 1H), 6.89 (m, 1H), 4.53 (m, 1H), 4.29 (dd, J = 4.0, 11.0 Hz, 1H), 4.24 (m, 2H), 4.06 (s,
2H), 3.98 (dd, J = 7.5, 9.0 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ 171.30, 166.63, 159.91, 133.75, 133.67,
131.91, 130.09, 128.75, 128.23, 128.16, 127.99, 126.40, 125.79, 125.42, 123.51, 118.64, 116.83, 110.22, 68.68,
65.46, 64.07, 39.05.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 2-phenylacetate (5t) Yield: 71%; white solid; m.p.
˝
106 C; ESI-MS m/z 312.07 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ
7.64 (dd, J = 1.5, 7.5 Hz, 1H), 7.41 (m,
1H), 7.25 (m, 5H), 7.02 (dd, J = 0.5, 8.0 Hz, 1H), 6.90 (m, 1H), 4.61 (m, 1H), 4.42 (dd, J = 8.5, 9.5 Hz, 1H),
4.30 (m, 2H), 4.18 (dd, J = 7.5, 9.0 Hz, 1H), 3.61 (s, 2H); 13C-NMR (125 MHz, CDCl3)
171.31, 166.70,
δ
159.95, 133.72, 133.57, 129.13, 128.57, 128.21, 127.17, 118.69, 116.86, 110.29, 68.84, 65.50, 64.17, 41.30.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 3-phenylpropanoate (5u) Yield: 78%; pale yellow oil;
ESI-MS m/z 326.07 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.64 (dd, J = 1.5, 7.5 Hz, 1H), 7.41 (m, 1H),
7.24 (m, 5H), 7.02 (dd, J = 0.5, 8.0 Hz, 1H), 6.92 (m, 1H), 4.60 (m, 1H), 4.42 (dd, J = 8.5, 9.5 Hz, 1H),
4.30 (m, 2H), 4.04 (dd, J = 7.5, 9.0 Hz, 1H), 3.61 (t, J = 7.5 Hz, 2H), 2.83 (t, J = 7.5 Hz, 2H); 13C-NMR
(125 MHz, CDCl3)
δ 171.31, 166.70, 159.95, 133.72, 133.57, 129.13, 128.57, 128.21, 127.17, 118.69, 116.86,
110.29, 68.84, 65.50, 64.17, 41.30, 34.12.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl cinnamate (5v) Yield: 69%; white solid; m.p. 85 ˝C;
ESI-MS m/z 324.22 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.65 (dd, J = 1.5, 7.5 Hz, 1H), 7.40 (m, 1H),
7.28 (m, 2H), 7.21 (m, 3H), 7.02 (dd, J = 0.5, 8.0 Hz, 1H), 6.89 (m, 1H), 4.58 (m, 1H), 4.41 (dd, J = 9.0,
10.0 Hz, 1H), 4.30 (dd, J = 4.5, 11.5 Hz, 1H), 4.20 (dd, J = 4.5, 9.5 Hz, 1H), 4.16 (dd, J = 7.0, 8.5 Hz, 1H),
2.92 (t, J = 7.5 Hz, 2H), 2.65 (t, J = 7.5 Hz, 2H); 13C-NMR (125 MHz, CDCl3)
δ 172.65, 166.73, 159.95,
140.19, 133.74, 128.52, 128.23, 128.17, 126.35, 118.72, 116.88, 110.28, 69.08, 65.35, 64.17, 35.62, 30.86.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl benzoate (5w) Yield: 81%; white solid; m.p. 88 ˝C;
ESI-MS m/z 298.21 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 11.86 (br. s, 1H, Ar-OH), 7.99 (dd, J = 1.0,
8.0 Hz, 2H), 7.69 (dd, J = 1.5, 8.0 Hz, 1H), 7.57 (m, 1H), 7.43 (m, 3H), 7.02 (dd, J = 0.5, 8.0 Hz, 1H), 6.90
(m, 1H), 4.79 (m, 1H), 4.57 (m, 2H), 4.46 (dd, J = 4.5, 9.5 Hz, 1H), 4.40 (dd, J = 7.0, 8.5 Hz, 1H); 13C-NMR

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(125 MHz, CDCl3)
δ
166.87, 166.32, 159.99, 133.77, 133.25, 129.68, 129.64, 128.46, 128.18, 118.74, 116.89,
110.30, 99.98, 69.23, 65.92, 64.37.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 2-methylbenzoate (5x) Yield: 86%; white solid; m.p.
63 ˝C; ESI-MS m/z 312.10 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.86 (dd, J = 1.5, 7.5 Hz, 1H), 7.67
(dd, J = 1.5, 8.0 Hz, 1H), 7.40 (m, 2H), 7.22 (m, 2H), 7.02 (dd, J = 1.0, 7.5 Hz, 1H), 6.90 (m, 1H), 4.78 (m,
1H), 4.56 (m, 2H), 4.46 (dd, J = 4.5, 9.5 Hz, 1H), 4.38 (dd, J = 7.0, 8.5 Hz, 1H), 2.55 (s, 3H); 13C-NMR
(125 MHz, CDCl3)
δ 167.33, 166.81, 159.98, 140.36, 133.74, 132.29, 131.77, 130.76, 129.03, 128.17, 125.80,
118.73, 116.87, 110.34, 69.15, 65.76, 64.39, 21.78.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 2-nitrobenzoate (5y) Yield: 74%; pale yellow crystal;
˝
m.p. 108–109 C; ESI-MS m/z 343.12 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 11.80 (br. s, 1H, Ar-OH),
7.91 (dd, J = 1.5, 7.5 Hz, 1H), 7.73 (dd, J = 2.0, 7.5 Hz, 1H), 7.67 (m, 3H), 7.40 (m, 1H), 7.02 (dd, J = 1.0,
8.5 Hz, 1H), 6.89 (m, 1H), 4.75 (m, 1H), 4.58 (m, 2H), 4.44 (dd, J = 6.5, 11.0 Hz, 1H), 4.34 (dd, J = 6.5,
9.0 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ 167.07, 165.17, 159.95, 133.79, 133.02, 132.02, 130.07, 128.28,
127.12, 123.94, 118.74, 116.87, 110.30, 69.31, 67.12, 63.91.
(2-(2-Hydroxyphenyl)-4,5-dihydrooxazol-4-yl)methyl 2-chlorobenzoate (5z) Yield: 69%; white needle crystal;
m.p. 91 ˝C; ESI-MS m/z 332.12: 333.10 (1:1), [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 11.85 (br. s, 1H,
Ar-OH), 7.79 (dd, J = 1.0, 7.5 Hz, 1H), 7.67 (dd, J = 2.0, 8.0 Hz, 1H), 7.42 (m, 3H), 7.29 (m, 1H), 7.02 (dd,
J = 0.5, 8.5 Hz, 1H), 6.89 (m, 1H), 4.79 (m, 1H), 4.57 (m, 2H), 4.49 (dd, J = 4.5, 9.5 Hz, 1H), 4.42 (dd,
J = 7.5, 9.0 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ 166.92, 165.57, 159.97, 133.79, 133.77, 132.84, 131.66,
131.15, 129.60, 128.19, 126.67, 118.74, 116.88, 110.33, 69.19, 66.37, 64.21.
3.1.3. Synthesis of 6a–6o
A solution of compound 4a (193 mg, 1.0 mmol) and halides (1.1 mmol), NaH (192 mg, 8.0 mmol)
in anhydrous THF (8 mL) is heated to reflux for 6 h. After cooling, the solution is quenched with water
(95.0
diluted with CH2Cl2 (50 mL). Then the mixture is separated with CH2Cl2 (30 mL
washed with an aqueous saturated solution of NH4Cl (30 mL 2), brine (30 mL
µ
L, 8.0 mmol), concentrated under reduced pressure until approximately 5 mL remained, and
3) and subsequently
3), and dried over
ˆ
ˆ
ˆ
anhydrous Na2SO4. The solvent is concentrated under reduced pressure, and purified by flash column
chromatography using petroleum ether/ethyl acetate (12:1, v/v) as the eluent.
2-(4-(Methoxymethyl)-4,5-dihydrooxazol-2-yl)phenol (6a) Yield: 77%; pale yellow oil; ESI-MS m/z 208.09
[M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.66 (dd, J = 1.5, 8.0 Hz, 1H), 7.39 (m, 1H), 7.01 (dd, J = 1.0,
8.5 Hz, 1H), 6.88 (m, 1H), 4.56 (m, 1H), 4.48 (dd, J = 8.0, 9.0 Hz, 1H), 4.33 (dd, J = 7.5, 8.5 Hz, 1H),
3.67 (dd, J = 4.0, 9.5 Hz, 1H), 3.46 (dd, J = 6.5, 9.5 Hz, 1H), 3.40 (s, 3H); 13C-NMR (125 MHz, CDCl3)
δ 166.36, 159.92, 137.59, 134.79, 133.46, 129.16, 128.13, 127.90, 118.61, 116.75, 110.60, 73.41, 71.71, 69.98,
65.25, 21.16.
2-(4-(Ethoxymethyl)-4,5-dihydrooxazol-2-yl)phenol (6b) Yield: 72%; pale yellow oil; ESI-MS m/z 222.10
[M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.71 (dd, J = 2.0, 9.0 Hz, 1H), 7.43 (m, 1H), 7.06(dd, J = 0.5,
9.0 Hz, 1H), 6.93 (m, 1H), 4.60 (m, 1H), 4.53 (m, 1H), 4.37 (dd, J = 7.0, 9.0 Hz, 1H), 3.78 (dd, J = 4.5,
9.5 Hz, 1H), 3.64 (m, 2H), 3.51 (dd, J = 7.0, 9.5 Hz, 1H), 1.24 (t, J = 3.0 Hz, 3H); 13C-NMR (125 MHz,
CDCl3) δ 166.33, 159.93, 133.46, 128.14, 118.63, 116.76, 110.65, 72.45, 70.07, 67.04, 65.29, 15.10.
2-(4-(Propoxymethyl)-4,5-dihydrooxazol-2-yl)phenol (6c) Yield: 83%; brown oil; ESI-MS m/z 236.17
[M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.66 (dd, J = 1.5, 9.0 Hz, 1H), 7.38 (m, 1H), 7.01 (dd, J = 0.5,
9.0 Hz, 1H), 6.88 (m, 1H), 4.56 (m, 1H), 4.48 (m, 1H), 4.33 (dd, J = 7.0, 8.0 Hz, 1H), 3.72 (dd, J = 4.5,
10.0 Hz, 1H), 3.49 (m, 3H), 1.16 (m, 2H), 0.90 (t, J = 7.5 Hz, 3H); 13C-NMR (125 MHz, CDCl3)
δ 166.33,
159.94, 133.44, 128.12, 118.61, 116.75, 110.65, 73.39, 72.60, 70.04, 65.30, 22.79, 10.48.
2-(4-(Butoxymethyl)-4,5-dihydrooxazol-2-yl)phenol (6d) Yield: 79%; yellow oil; ESI-MS m/z 250.10
[M + H]+; 1H-NMR (500 MHz, CDCl3)
7.66 (dd, J = 1.5, 7.5 Hz, 1H), 7.38 (m, 1H), 7.01 (dd, J = 0.5
δ
,

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8.5 Hz, 1H), 6.88 (m, 1H), 4.55 (m, 1H), 4.48 (m, 1H), 4.33 (dd, J = 7.0, 8.0 Hz, 1H), 3.72 (dd, J = 4.0,
9.5 Hz, 1H), 3.53 (m, 3H), 1.57 (m, 2H), 1.38 (m, 2H), 0.90 (t, J = 7.5 Hz, 3H); 13C-NMR (125 MHz, CDCl3)
δ 166.32, 159.94, 133.44, 128.12, 118.61, 116.75, 110.66, 72.65, 71.53, 70.05, 65.30, 31.67, 19.26, 13.86.
2-(4-((Pentyloxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6e) Yield: 83%; yellow oil; ESI-MS m/z 264.17
[M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.66 (dd, J = 2.0, 9.0 Hz, 1H), 7.38 (m, 1H), 7.01(dd, J = 1.0,
8.5 Hz, 1H), 6.88 (m, 1H), 4.55 (m, 1H), 4.48 (m, 1H), 4.33 (dd, J = 6.5, 8.0 Hz, 1H), 3.72 (dd, J = 4.5,
9.5 Hz, 1H), 3.52 (m, 3H), 1.58 (m, 2H), 1.32 (m, 4H), 0.87 (t, J = 7.0 Hz, 3H); 13C-NMR (125 MHz,
CDCl3)
δ 166.33, 159.94, 133.44, 128.12, 118.61, 116.75, 110.66, 72.63, 71.86, 70.04, 65.30, 29.28, 28.27,
22.48, 14.00.
2-(4-((Allyloxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6f) Yield: 87%; yellow oil; ESI-MS m/z 234.12
[M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 11.99 (br. s, 1H, Ar-OH), 7.66 (dd, J = 1.5, 6.5 Hz, 1H), 7.38 (m,
1H), 7.01 (dd, J = 1.0, 8.5 Hz, 1H), 6.88 (m, 1H), 5.92 (m, 1H), 5.29 (dq, J = 1.5, 17.0 Hz, 1H), 5.21 (dq,
J = 1.5, 10.5 Hz, 1H), 4.57 (m, 1H), 4.49 (m, 1H), 4.35 (dd, J = 7.0, 9.0 Hz, 1H), 4.04 (dq, J = 1.5, 5.5 Hz,
2H), 3.73 (dd, J = 4.5, 9.5 Hz, 1H), 3.49 (dd, J = 7.0, 9.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ 166.39,
159.92, 134.37, 133.48, 128.14, 118.63, 117.42, 116.75, 110.61, 72.46, 71.92, 69.94, 65.25. The structure of 6f
was also confirmed by 2D-NMR data and can be seen in Table 4 and Figure 3.
Figure 3. The main HMBC of compound 6f.
Table 4. HMBC data of compound 6f.
13C-NMR
1H-NMR
C No.
δC
HMBC Correlations
H No.
δ
H
HMBC Correlations
1-C
2-C
3-C
4-C
5-C
6-C
7-C
8-C
9-C
10-C
11-C
12-C
159.67, C
116.93, CH
134.23, CH
119.41, CH
128.28, CH
110.57, C
Ar-OH, 2-H, 3-H, 5-H
Ar-OH, 4-H
2-H, 4-H
5-H
3-H, 4-H
Ar-OH, 4-H, 5-H
2-H, 5-H, 8-H, 9-H
9-H
Ar-OH
2-H
3-H
4-H
5-H
6-H
7-H
8-H
9-H
12.22, s, 1H
7.65, dd, J = 1.5, 80 Hz, 1H
7.49–7.46, m, 1H
6.97–6.94, m, 1H
7.02, dd, J = 0.5, 8.5 Hz, 1H
1-C, 2-C, 6-C
1-C, 3-C, 7-C
1-C, 5-C, 6-C
1-C, 2-C, 3-C, 5-C, 6-C
1-C, 4-C, 6-C, 7-C
-
-
-
165.84, C
-
71.56, CH2
65.19, CH
71.80, CH2
69.71, CH2
135.49, CH
4.57–4.54, m, 1H; 4.32–4.30, m, 1H
4.62–4.58, m, 1H
7-C, 9-C, 10-C
7-C, 10-C
9-C, 11-C
10-C, 12-C, 13-C
10-C
8-H, 10-H
8-H, 11-H
10-H
10-H
11-H
12-H
3.64–3.57, m, 2H
4.03–4.02, m, 2H
5.93–5.86, m, 1H
11-H, 13-H
5.28–5.24, ddd, J = 1.5, 3.5, 17.5
13-C
117.06, CH2
11-H
13-H
10-C, 12-C
Hz, 1H; 5.17–5.15, m, 1H
2-(4-((Prop-2-yn-1-yloxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6g) Yield: 69%; yellow oil; ESI-MS m/z
232.10; [M + H]+; 1H-NMR (500 MHz, CDCl3)
11.98 (br. s, 1H, Ar-OH), 7.66 (dd, J = 1.5, 6.5 Hz, 1H),
δ
7.37 (m, 1H), 7.03 (dd, J = 1.0, 8.5 Hz, 1H), 6.88 (m, 1H), 4.51 (d, J = 4.5 Hz, 2H), 4.49 (m, 1H), 4.11
(s, 2H), 3.73 (dd, J = 4.5, 9.5 Hz, 1H), 3.49 (dd, J = 7.0, 9.5 Hz, 1H), 3.35 (s, 1H); 13C-NMR (125 MHz,
CDCl3) δ 166.39, 159.92, 134.37, 133.48, 128.14, 118.63, 117.42, 116.75, 110.61, 72.46, 71.92, 69.94, 65.25.

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2-(4-(((4-Chlorobenzyl)oxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6h) Yield: 77%; pale pink oil; ESI-MS
m/z 318.09: 320.02 (3:1), [M + H]+; 1H-NMR (500 MHz, CDCl3)
7.65 (dd, J = 1.5, 8.0 Hz, 1H), 7.39 (m,
δ
1H), 7.31 (dt, J = 2.0, 7.5 Hz, 2H), 7.24 (m, 2H), 7.01 (dd, J = 0.5, 9.0 Hz, 1H), 6.88 (m, 1H), 4.57(m, 1H),
4.52 (d, J = 4.0 Hz, 2H), 4.49 (m, 1H), 4.33 (dd, J = 7.0, 8.0 Hz, 1H), 3.73 (dd, J = 4.0, 9.5 Hz, 1H), 3.53
(dd, J = 6.5, 9.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ 166.45, 159.91, 136.38, 133.58, 133.54, 128.98,
128.64, 128.15, 118.67, 116.77, 110.53, 72.73, 71.93, 69.73, 65.24.
2-(4-(((2-Methylbenzyl)oxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6i) Yield: 88%; pale yellow oil; ESI-MS
m/z 298.10 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 7.65 (dd, J = 2.0, 9.0 Hz, 1H), 7.38 (m, 1H), 7.29
(m, 1H), 7.21 (m, 3H), 7.01 (dd, J = 0.5, 8.0 Hz, 1H), 6.88 (m, 1H), 4.58 (m, 3H), 4.48 (dd, J = 8.5, 9.5 Hz,
1H), 4.32 (dd, J = 7.0, 8.0 Hz, 1H), 3.77 (dd, J = 4.0, 9.5 Hz, 1H), 3.53 (dd, J = 6.5, 9.5 Hz, 1H), 2.32 (s,
3H); 13C-NMR (125 MHz, CDCl3)
δ 166.39, 159.93, 136.85, 135.67, 133.47, 130.36, 128.78, 128.13, 128.08,
125.81, 118.62, 116.75, 110.59, 72.07, 72.01, 69.93, 65.25, 18.79.
2-(4-(((2-Fluorobenzyl)oxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6j) Yield: 63%; pale yellow oil; ESI-MS
m/z 302.11 [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ 11.98 (br. s, 1H, Ar-OH), 7.65 (dd, J = 1.5, 6.5 Hz,
1H), 7.38 (m, 2H), 7.29 (m, 1H), 7.14 (m, 1H), 7.06 (m, 1H), 7.01 (dd, J = 0.5, 8.0 Hz, 1H), 6.88 (m, 1H),
4.66 (m, 2H), 4.59 (m, 1H), 4.48 (m, 1H), 4.35 (dd, J = 7.0, 8.0Hz, 1H), 3.79 (dd, J = 4.0, 9.5 Hz, 1H), 3.55
(dd, J = 7.0, 9.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ 166.46, 161.80, 159.94, 133.50, 130.12, 129.65,
128.15, 124.18, 118.63, 116.77, 115.41, 115.24, 110.58, 72.15, 69.89, 67.04, 65.17. The structure of 6j was
also confirmed by 2D NMR data and can be seen in Table 5 and Figure 4.
Figure 4. The main HMBC of compound 6j.
Table 5. HMBC data of compound 6j.
13C-NMR
1H-NMR
C No.
δC
HMBC Correlations
H No.
δ
H
HMBC Correlations
1-C
2-C
3-C
4-C
5-C
159.64, C
116.93, CH
134.27, CH
119.42, CH
128.30, CH
110.52, C
2-H, 3-H, 5-H
4-H
2-H, 4-H
5-H
3-H, 4-H
5-H
Ar-OH
2-H
3-H
4-H
5-H
12.17, s, 1H
7.65, dd, J = 1.5, 8.0 Hz, 1H
7.49–7.46, m, 1H
6.98–6.95, m, 1H
7.02–7.01, m, 1H
-
-
1-C, 3-C, 7-C
1-C, 5-C
1-C, 2-C, 3-C, 5-C, 6-C
1-C, 4-C, 6-C, 7-C
6-C
6-H
-
7-C
8-C
9-C
10-C
11-C
12-C
13-C
165.90, C
2-H, 5-H, 8-H, 9-H
10-H
8-H, 10-H
8-H, 9-H, 11-H
10-H, 13-H
11-H
7-H
8-H
9-H
10-H
11-H
12-H
13-H
-
-
69.59, CH2
64.91, CH
71.12, CH2
58.38, CH2
80.55, C
4.58–4.55, m, 1H; 4.31–4.28, m, 1H
4.63–4.59, m, 1H
3.67–3.66, m, 2H
4.23–4.22, m, 2H
-
7-C, 9-C, 10-C
7-C, 10-C
8-C, 9-C, 11-C
10-C, 12-C, 13-C
-
77.95, CH
11-H
3.49–3.48, m, 1H
11-C
2-(4-(((4-Fluorobenzyl)oxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6k) Yield: 67%; yellow oil; ESI-MS m/z
302.18 [M + H]+; 1H-NMR (500 MHz, CDCl3)
7.65 (dd, J = 1.5, 8.0 Hz, 1H), 7.38 (m, 1H), 7.28 (m, 2H),
7.04 (m, 3H), 6.88 (m, 1H), 4.57 (m, 1H), 4.52 (m, 2H), 4.47 (m, 1H), 4.33 (dd, J = 7.5, 8.5 Hz, 1H), 3.73
(dd, J = 4.5, 5.0 Hz, 1H), 3.52 (dd, J = 7.0, 9.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
166.44, 163.41,
δ
δ
161.46, 159.92, 133.64, 133.62, 133.53, 129.49, 129.43, 128.15, 118.67, 116.77, 115.43, 115.26, 110.56, 72.82,
71.85, 69.80, 65.24.

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2-(4-(((2,6-Difluorobenzyl)oxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6l) Yield: 79%; pale yellow oil;
ESI-MS m/z 320.08 [M + H]+; 1H-NMR (500 MHz, CDCl3)
11.96(br. s, 1H, Ar-OH), 7.64 (dd, J = 1.5
δ
,
8.0 Hz, 1H), 7.38 (m, 1H), 7.31 (m, 1H), 7.00 (dd, J = 0.5, 8.0 Hz, 1H), 6.92 (m, 2H), 6.87 (m, 1H), 4.69 (m,
2H), 4.56 (m, 1H), 4.46 (m, 1H), 4.30 (dd, J = 7.5, 8.5 Hz, 1H), 3.81 (dd, J = 4.0, 9.0 Hz, 1H), 3.51 (dd,
J = 7.5, 9.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ 166.47, 162.92, 160.93, 159.91, 133.48, 130.40, 128.14,
118.62, 116.75, 111.45, 111.25, 110.59, 72.09, 70.02, 65.06, 60.60.
2-(4-(((2,4-Dichlorobenzyl)oxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6m) Yield: 75%; colourless oil;
1
ESI-MS m/z 352.14:354.23:353.12 (9:6:1), [M + H]+; H-NMR (500 MHz, CDCl3)
δ 7.65 (dd, J = 1.5,
8.0 Hz, 1H), 7.39 (m, 1H), 7.35 (m, 1H), 7.01 (m, 1H), 6.88 (m, 2H), 6.82 (m, 1H), 4.61 (m, 2H), 4.56 (m,
1H), 4.48 (m, 1H), 4.33 (dd, J = 7.0, 8.0 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ
166.49, 159.92, 133.55,
131.11, 131.07, 131.04, 130.99, 128.15, 118.67, 116.78, 111.41, 111.25, 111.22, 110.53, 104.01, 103.81, 103.60,
72.10, 69.76, 66.58, 66.55, 65.16.
2-(4-(((4-(Trifluoromethyl)benzyl)oxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6n) Yield: 72%; yellow oil;
1
ESI-MS m/z 352.10 [M + H]+; H-NMR (500 MHz, CDCl3)
δ 7.66 (dd, J = 1.5, 9.0 Hz, 1H), 7.60 (d,
J = 9.0 Hz, 2H), 7.42 (d, J = 9.0 Hz, 2H), 7.40 (m, 1H), 7.02 (d, J = 8.5 Hz, 1H), 4.65 (dd, J = 7.5, 12.5 Hz,
2H), 4.59 (m, 1H), 4.50 (m, 1H), 4.37 (dd, J = 7.0, 8.0 Hz, 1H), 3.77 (dd, J = 4.5, 9.0 Hz, 1H), 3.59 (dd,
J = 6.5, 9.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
δ 166.53, 159.92, 141.99, 133.59, 128.16, 127.56, 125.44,
125.41, 118.71, 116.79, 110.50, 72.72, 72.19, 69.64, 65.24.
2-(4-(((4-(Benzyloxy)benzyl)oxy)methyl)-4,5-dihydrooxazol-2-yl)phenol (6o) Yield: 87%; brown oil; ESI-MS
m/z 390.19; [M + H]+; 1H-NMR (500 MHz, CDCl3)
δ
7.65 (dd, J = 1.5, 8.0 Hz, 1H), 7.39 (m, 1H), 7.31 (dt,
J = 2.0, 7.5 Hz, 2H), 7.24 (m, 2H), 7.10 (m, 7H), 5.22 (s, 2H), 4.52 (s, 2H), 4.49 (m, 1H), 4.13 (d, J = 6.5 Hz,
2H), 3.73 (dd, J = 4.0, 9.5 Hz, 1H), 3.56 (dd, J = 6.5, 9.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
166.45,
δ
159.91, 136.38, 133.58, 133.54, 128.98, 128.64, 128.15, 126.07, 126.01, 125.34, 123.44, 118.67, 116.77, 110.53,
72.73, 71.93, 70.88, 69.73, 65.24.
3.1.4. Synthesis of 7
Compound 4a (193 mg, 1.0 mmol) is dissolved in anhydrous CH2Cl2 (12 mL), and the system was
cooled to
for 12 h. Then the reaction was quenched with K2CO3. After returning to r.t., organic fractions were
washed successively with saturated aqueous NaHCO3 (30 mL 2), brine (30 mL 3), and dried over
´
80 ˝C. DAST (345 mg, 2.0 mmol) was added, and the solution was then stirred at
´
80 ˝C
ˆ
ˆ
anhydrous Na2SO4. Then the solution is concentrated under reduced pressure, and purified by flash
column chromatography using ether/ethyl acetate (15:1, v/v) as the eluent to afford compound 7.
2-(4-(Fluoromethyl)-4,5-dihydrooxazol-2-yl)phenol (
7) Yield: 68%; white needle crystal; ESI-MS m/z 196.10
[M + H]+; 1H-NMR (500 MHz, CDCl3)
δ
11.79 (br. s, 1H, Ar-OH), 7.67 (dd, J = 2.0, 9.0 Hz, 1H), 7.40 (m,
1H), 7.02 (dd, J= 0.5, 9.5 Hz, 1H), 6.89 (m, 1H), 4.66 (m, 1H), 4.60 (m, 1H), 4.53 (m, 2H), 4.41 (dd, J = 7.0,
8.5 Hz, 1H); 13C-NMR (125 MHz, CDCl3)
82.85, 68.38, 65.22.
δ 167.12, 159.94, 133.81, 128.26, 118.78, 116.87, 110.30, 84.23,
3.2. Biology
Minimal Inhibitory Concentration (MIC)
The three kinds of Gram-positive bacteria (Staphylococcus aureus 1.89, Bacillus subtilis 1.88,
Bacillus cereus 1.1846) and Escherichia coli 1.1636, were purchased from the China General
Microbiological Culture Collection Center (CGMCC). Ralstonia solanacearum (Gram-negative bacteria)
was provided by the College of Plant Protection, Southwest University. Pseudomonas syringae pv.
Actinidiae, Pseudomonas solanacearum E. F. Smith (Gram-negative bacteria) were provided by the Plant
Pathology Laboratory of Northwest A and F University.

Molecules 2016, 21, 96
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Antibacterial activities were evaluated by the micro-broth dilution method in 96-well culture
plates using the Mueller-Hinton broth, according to the National Committee for Clinic˝al Laboratory
Standards [20,21]. The tested bacteria were incubated in the Mueller–Hinton broth at 30 C at 190 rpm
for 12 h and the spore concentration was diluted to approximately 1
ˆ
105–1
ˆ
106 CFU/mL with
Mueller-Hinton broth. After incubation at 30 ˝C for 24 h, the MICs were examined. Briefly, bacteria
were grown to mid-log phase, diluted with fresh Luria-Bertani culture broth to an optical density of
0.08–0.1 at 600 nm (OD600) and diluted again 1:100. This suspension (50
a 96 well microtiter plate (Sarstedt) and 50 L of compound dissolved in DMSO-water was added to
give a final concentration of from 125 to 0.245 DMSO by volume. A DMSO
mL´1 and at most 1
negative control and standard antibiotic positive controls (Ampicillin Sodium, 10
mL´1) were
µL) was added to wells in
µ
µg
¨
‰
µg
¨
included in each plate. All compounds we˝re tested in triplicate for each concentration. Plates were
sealed with parafilm and incubated at 37 C (Pseudomonas syringae pv. actinidiae and Pseudomonas
solanacearum E. F. Smith at 28 ˝C) for 12–16 h. The OD600 values for each well were determined with
a plate reader (Shimadzu, UV1800, Kyoto, Japan) and the data were standardized to the Luria-Bertani
culture broth control wells.
4. Conclusions
A novel, efficient, synthetic method was developed for the large-scale preparation of
(˘
)-Yanglingmycin and its analogues. In this way, arylnitriles reacted with serinol under the condition
of sodium carbonate in dry methanol to obtain 2-aryl substituent of 4,5-dihydrooxazol analogues
with good yields. Series of ( )-Yanglingmycin derivatives were designed and synthesized as potent
antibacterial compounds, among which 5b 5c 5d 6g, and were identified as the most promising
˘
,
,
,
7
candidates with good antibacterial activity, but 4b–h did not possess antibacterial activity at all. This
result indicated that the alternation in antibacterial activity of these compounds was dominated
by unsaturated bond, electronic interaction, intramolecular hydrogen bond, and stereoscopic effect.
Neither electron-drawing nor electron-donating groups could perish the antibacterial activities unless
introduction 2-hydroxy to the 2-aryl substituent of 4,5-dihydrooxazol analogues. Further research on
the mechanism and toxicology for their bioactivity is ongoing and will be reported in due time.
Acknowledgments: This work was supported by the National Natural Science Foundation of China
(Nos, 21372185 & 31572038).
Author Contributions: Wenjia Dan and Jiwen Zhang were responsible for designed research. Wenjia Dan,
Jianwen Qiao, Rui Guo performed all experiment. Huiling Geng, Shaopeng Wei and Wenjun Wu were performed
all statistical analysi. Wenjia Dan, Huiling Geng and Jiwen Zhang wrote down the paper. Longbo Li helped to
review the manuscript.
Conflicts of Interest: The authors declare no conflict of interest
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2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
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(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).