Improved synthesis of YT-14, a potent antibiotic to multidrug-resistant strains

Article abstract of DOI:10.3184/174751918X15314830456124

A new practical synthetic approach produced clinical drug candidate YT-14, improving the overall yield from 1.3% to 13.8%. Compared with the previous route, the new route is two steps shorter and all of the steps involve purifications without column chrom

Full text of DOI:10.3184/174751918X15314830456124

354 RESEARCH PAPER
VOL. 42 JULY, 354–360
JOURNAL OF CHEMICAL RESEARCH 2018
Improved synthesis of YT-14, a potent antibiotic to multidrug-resistant strains
Jianhai Weia, Deyu Konga, Lei Wangb, Yinyong Zhangb, Wenhao Hua and Yushe Yangb*
aShanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Molecular Engineering, East China
Normal University, 3663 North Zhongshan Road, Shanghai, 200062, P.R. China
bState Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, University of Chinese Academy of Sciences, Shanghai 201203, P.R. China
A new practical synthetic approach produced clinical drug candidate YT-14, improving the overall yield from 1.3% to 13.8%. Compared
with the previous route, the new route is two steps shorter and all of the steps involve purifications without column chromatography. The
advantages of this procedure include simple operating conditions and higher yields.
Keywords: drug candidate, YT-14, multidrug resistant, Gram-negative bacteria
The development and spread of bacterial resistance has evolved
into a major public health crisis that endangers human health.1
Especially for multidrug-resistant Gram-negative bacteria with
high lethality, there is almost no completely effective therapeutic
drug in the world.2 Even worse, effective drugs against Gram-
negative bacteria in phase II and III clinical trials are also rare.
Hence, the development of a Gram-negative antibacterial drug
is of great clinical significance and likely social value.3
is as good as that of S-649266 against Kpn and Pae and is
slightly better than S-649266 against Aba, which is recognised
as a increasing class of aggressively pathogenic Gram-negative
bacteria (Table 1).11,12 Moreover, YT-14 exhibits a favourable
pharmacokinetic profile and has no hERG inhibition. For a
preclinical study, considerable material is needed. Considering
this, we have developed a novel synthetic route for the potent
antibiotic YT-14.
Table 1 Antibacterial activity of YT-14, BAL30072 and S-649266a
Recently, a new siderophore conjugated antibiotic YT-
14 (Fig. 1) has been reported.4 With the Trojan strategy,5–7
YT-14 shows excellent in vitro and in vivo activity against
multidrug-resistant bacteria, including Escherichia coli (Eco),
Klebsiella pneumoniae (Kpn), Acinetobacter baumannii (Aba)
and Pseudomonas aeruginosa (Pae), which are resistant to
meropenem and aztreonam (Table 1). Compared with the phase
I clinical drug BAL30072 (Fig. 1),8 YT-14 displays a potent in
vitro activity against Kpn, whereas BAL30072 has very weak
activity (Table 1). For the antibacterial activity against Eco,
Aba, and Pae, YT-14 is significantly better than BAL30072.
Meanwhile, compared with the current most promising phase
III clinical drug S-649266 (Fig. 1),9,10 the activity of YT-14
−1
MIC (μg mL )
Compound
Ecob
<0.03–0.5
0.125–1
Abac
1–4
Kpnd
0.125–4
0.5–>64
0.125–4
>64
Paee
0.5–4
1–8
0.5–4
32–64
16–64
YT-14
BAL30072
S-649266 <0.03–0.125
Meropenem
Aztreonam
1–>64
1–8
64–>64
64–>64
0.25–8
0.03–32
>64
aActivity of YT-14, BAL30072 and S-649266 were tested under iron limitation.
bEco, E. coli, five strains.
cAba, multidrug-resistant A. baumannii.
dKpn, multidrug-resistant K. pneumoniae, five strains.
ePae, multidrug-resistant P. aeruginosa, five strains.
O
OH
COOH
N
O
N
H
O
O
OH
N
N
S
N
S
H
O
Cl
H2N
N
N
S
N
N
O
OH
OH
H2N
N
O
N
H
COO
H
OSO3
O
BAL30072
S-649266
O
OH
N
O
OH
N
H
N
N
S
H2N
N
O
H
OSO3
O
YT-14
Fig. 1 Chemical structures of siderophore cephalosporin antibiotics.
* Correspondent. E-mail: ysyang@simm.ac.cn

JOURNAL OF CHEMICAL RESEARCH 2018 355
Results and discussion
a less-hindered benzyl group for a series of reactions first,
followed by deprotection of alcohol 6 to give compound 7 and
protection with a benzhydryl group to obtain the intermediate
8. Finally, YT-14 was synthesised through a series of reactions
using the intermediate 8 as a starting material. However, this
route had three major problems that hampered its scale-up
(Scheme 1): (1) the step of compound 6 to 8 was low yielding
(total yield 38%), and the purification of compound 9 was
difficult (purification by column chromatography) and hence
not suitable for industrial amplification; (2) the synthetic route
We hoped to design a synthetic route for YT-14 based on
the synthetic route for BAL30072. Mitsunobu reaction of
compound 1 and N-hydroxyphthalimide gives key intermediate
2, and BAL30072 is obtained through a series of reactions using
compound 2 as a starting material. Therefore, compound 1 was
oxidised first to provide aldehyde 3, and alcohol 4 was obtained
by Grignard reaction. Unfortunately, however, the Mitsunobu
reaction from alcohol 4 to phthalimide 5 could not be carried
out under any conditions (Fig. 2). Thus, we considered using
O
O
OH
OCHPh2
O
N
OCHPh2
N
N
O
O
OH
O
N
OCHPh2
N
H
N
N
S
O
O
OH OCHPh2
H2N
N
1
2
H
OSO3
O
BAL30072
O
OCHPh2
O
O
OCHPh2
OCHPh2
N
O
N
OCHPh2
O
N
N
steric
effect
O
O
OH OCHPh2
OCHPh2
3
5
4
Fig. 2 Original proposed synthetic route of the key intermediate 5 towards YT-14.
O
O
O
O
OBn
N
OBn
OBn
OH
a
c
b
OBn
d
HO
HO
HO
HO
O
N
H
OBn
OCHPh2
OCHPh2
OBn
O
OBn
OBn
OBn
OH
e
OBn
f
g
h
O
N
N
O
N
O
N
N
OH
OH
OH
OH OH
7
6
8
OCHPh2
O
OCHPh2
OCHPh2
OCHPh2
OH
OCHPh2
OCHPh2
l,m
i
k
j
N
O
N
N
O
O
N
N
O
O
OH
O
O
N
N
H
O
O
O
N
OH
N
S
N
S
NH2
H2N
Ph
3CHN
N
O
H
O
OSO3
YT-14
9
21
22
Scheme 1 Initial medicinal chemistry route to YT-14. Reagents and conditions: (a) BnCl, NaOH, MeOH, 60 °C, 91%; (b) NH4OH, MeOH, 55 °C, 90%; (c)
BnCl, K CO3, DMSO, 50 °C, 43%; (d) pyridine-SO , DMSO, NEt3, CH2Cl , 95%; (e) i-PrMgBr, THF, 68%; (f) m-CPBA, CH2Cl2, r.t., 81%; (g) BCl3, CH2Cl2,
−10 °C;2(h) diphenyldiazomethane, MeOH/CH2Cl , 3r.t., 38% for two steps2; (i) N-hydroxyphthalimide, PPh3, DIAD, THF, 56%; (j) N2H4, MeOH, r.t., 79%; (k)
MeOH/CH2Cl2, r.t., 65%; (l) HATU, NaHCO3, DMS2O, 94%; (m) TFA, Et3SiH, CH2Cl2, −15 °C, 69%.

356 JOURNAL OF CHEMICAL RESEARCH 2018
was long, while column chromatographic purification was
required following most of the reactions; and (3) phthalimide 9
was difficult to obtain from the Mitsunobu reaction in the post-
processing because of the polarity of triphenylphosphine oxide,
and the reduction products DIAD and phthalimide 9 had very
similar characteristics. These problems prompted us to seek a
better synthesis of YT-14, which in turn meant that an efficient
synthesis of the precursor 9 was needed.
As shown in Scheme 2, retrosynthetic analysis suggests that
phthalimide 9 could be obtained by m-CPBA oxidation of
compound 10. Meanwhile, compound 10 is easily separated
from triphenylphosphine and the reduction products of DEAD.
With less steric hindrance, alcohol 11, which is obtained by
Grignard reaction of compound 12 and isopropylmagnesium
bromide, can promote the Mitsunobu reaction. Furthermore,
direct protection using the benzhydryl group can reduce the
number of reaction steps. However, in the reaction of 14 to 13,
a large amount of the byproduct alcohol 15 was produced. This
may be due to the equilibrium of 14 and 16 and steric effects
in the reaction. Therefore, we considered whether it might be
better to oxidise compound 14 first, giving compounds 17 and
18. Owing to the conjugation effect of the aldehyde groups
and aromatic rings, it might form the more stable intermediate
18 (Scheme 3). At the same time, the decrease in pKa of the
phenolic hydroxyl group also facilitates the Sn2 reaction of 18 to
12 (calculated by ACDLABS) (Scheme 4). Finally, aldehyde 12
was obtained in a very high yield (Scheme 3).
The final synthetic route to YT-14 is illustrated in Scheme 5.
Selectively protecting the hydroxyl group of kojic acid 19 with
diphenyldiazomethane provides intermediate 20. By heating
with ammonia, alcohol 14 was obtained, which was oxidised
to give compound 18 by heating with manganese dioxide in
Scheme 2 Initial retrosynthetic analysis of compound 9.
OH
OCHPh2
OCHPh2
OCHPh2
N
N
OH
OH
OH
14
13
OCHPh2
N
OH
O
O
N
OCHPh2
OCHPh2
14
N
H
OH
OH CHPh2
15
16
O
OCHPh2
OCHPh2
OH
OH
OCHPh2
OCHPh2
OCHPh2
N
H
N
N
N
O
O
O
OH
14
17
18
12
Scheme 3 Synthetic route changes of the key intermediate 13.

JOURNAL OF CHEMICAL RESEARCH 2018 357
OH
OH
OCHPh2
OCHPh2
N
N
OH
O
14
18
pKa=7.33±0.48
pKa=6.83±0.48
Scheme 4 pKa prediction of phenolic hydroxyl group.
O
OH
O
OH
N
OCHPh2
OCHPh2
c
OH
a
b
OCHPh2
d
HO
HO
HO
O
O
N
O
19
20
14
18
OCHPh2
OCHPh2
OCHPh2
OCHPh2
OCHPh2
OCHPh2
OCHPh2
OCHPh2
f
e
N
O
g
N
h
O
O
N
O
N
N
N
O
O
OH
O
O
10
11
12
9
O
OCHPh2
OCHPh2
OCHPh2
OCHPh2
OCHPh2
OH
OCHPh2
k
i
j
N
N
O
N
O
H2N
N
O
O
O
OH
O
O
O
N
O
N
N
H
N
H
N
N
S
NH2
OH
H
N
O
OSO3
3CHN
23
N
N
H2N
Ph
Ph
3CHN
N
N
O
S
S
H
O
OSO3
H
OSO3
O
21
22
24
YT-14
Scheme 5 Final synthetic route to YT-14. Reagents and conditions: (a) diphenyldiazomethane, MeOH/CH2Cl2, r.t., 82.7%; (b) NH4OH, MeOH, 55 °C,
90.6%; (c) MnO2, C2H5OH, 60 °C, 53.1%; (d) diphenylbromomethane, DMF, K2CO3, 78%; (e) i-PrMgBr, THF; (f) N-hydroxyphthalimide, PPh3, DEAD, THF;
(g) m-CPBA, CH2Cl2, r.t., 73.2% for three steps; (h) N2H4, MeOH, r.t.; (i) MeOH/CH2Cl2, r.t., 86% for two steps; (j) HATU, NaHCO3, DMSO, 93%; (k) TFA,
Et3SiH, CH2Cl2, −15°C, 83%.
ethanol, and then reacting with bromodiphenylmethane, to give
aldehyde 12. Nucleophilic addition of isopropylmagnesium
bromide afforded alcohol 11. Mitsunobu reaction with
N-hydroxyphthalimide provided compound 10, which was
converted to phthalimide 9 with m-CPBA. By reaction with
hydrazine hydrate and removal of the phthaloyl groups,
the alkoxyamine 21 was obtained. The key intermediate
oxime acid 22 was prepared via condensation of 2-oxo-2-(2-
(tritylamino)thiazol-4-yl) acetic acid and alkoxyamine 21. With
condensation of the oxime acid 22 with compound 23, the acid
24 was provided. The final product YT-14 was obtained by
deprotection of acid 24.
Finally, the YT-14 that we obtained and the YT-14 obtained by
the previous method were compared.4 YT-14 has two isomers in
the isopropyl position. In the previous route, YT-14 in the S and
R configurations were synthesised by asymmetric synthesis.
Furthermore, the crystal structure of compound 8 in the S
configuration was resolved. However, the antibacterial activity
of an isomeric mixture of YT-14 was better than either of the
single R or S configurations of YT-14.4 Therefore, a racemic
form of YT-14 was chosen for further study. We synthesised YT-
14 with a R/S ratio of 46:54 without column chromatography
purification whereas the previous method obtained YT-14 with
a R/S of 48:52 but column chromatography was required in
many post-treatments.4 Moreover, the relationship between the
R/S ratio and the antibacterial activity of YT-14 needs further
study in the future. However, it is undeniable that our new route
greatly simplifies the synthesis of YT-14, and we were able to
obtain key intermediate phthalimide 9 (R/S 50:50) in an overall
yield of 20.8% without purification by column chromatography,
while the yield obtained via the previous route was only 3.9%
with complicated post-processing.
Conclusion
A novel synthetic route to drug candidate YT-14 has been
developed. By changing the materials in the Mitsunobu
reaction, the key alkoxyamine 10 could be easily separated from
triphenylphosphine oxide and the reduction products of DEAD

358 JOURNAL OF CHEMICAL RESEARCH 2018
the desired product 14 was obtained without further purification.
The product was dried at 40 °C under reduced pressure to provide
compound 14 as a light brown solid; yield 115.0 g (90.6%); m.p.
by a silicone sand core funnel. Compared with the previous
route, this new route is shorter by two steps. All of these
reactions did not need to be purified by column chromatography
and could be amplified. Using this new process, we were able
to obtain key intermediate phthalimide 9 in an overall yield of
20.8% in seven steps while the previous route was only 3.9%
in nine steps and the scale has been increased to more than 50
g. The final product YT-14 was obtained in an overall yield of
13.8%, which was better than the previous route with a yield
of 1.3%. Furthermore, the key intermediate 9 was increased by
more than 500 g by Xi’an Manareco through this route.
1
191–193 °C; HPLC purity (condition A): 93%; H NMR (400 MHz,
DMSO-d6): δ 7.79 (s, 1H), 7.63–7.18 (m, 10H), 6.68 (s, 1H), 6.57 (s,
1H), 5.05 (s, 0H), 4.24 (s, 2H); 13C NMR (101 MHz, DMSO-d6): δ
149.82, 145.36, 142.04 (3C), 128.88, 128.78 (4C), 127.91 (2C), 127.23
(4C), 112.63, 80.88, 60.39. MS (ESI) m/z: 306 [M − H]–. HRMS (ESI)
m/z calcd for C19H16NO3 [M − H]–: 306.1136; found: 306.1139.
Synthesis of 5-(benzhydryloxy)-4-hydroxypicolinaldehyde (18)
A solution of 14 (100 g, 325.2 mmol) in ethanol (800 mL) was treated
with MnO2 (428 g, 4.922 mol). The reaction mixture was heated to
65 °C and stirred 5 h. The resulting mixture was filtered and the filter
residue was washed by ethanol. Then the filtrate was concentrated in
vacuo. The resulting residue was taken up in ethyl acetate (EA) and
filtered with a silicone core funnel. Then the filtrate was concentrated
in vacuo to a final volume (150 to 250 mL). The solid was filtered off
and the desired product 18 was obtained without further purification.
The product was dried at 40 °C under reduced pressure to provide
compound 18 as a white solid; yield 52.8 g (53.1%); m.p. 196–198 °C;
Experimental
Unless otherwise mentioned, all reagents were purchased from
commercial suppliers and used without further purification. All
reactions were monitored by TLC, using silica gel plates with
fluorescence GF254 (Yu Cheng Chemical, Shanghai) and UV light
visualisation. Analytical HPLC was conducted using UV detection
and the following conditions: (A) Platisil ODS column (250 × 4.6 mm,
5 μm) using a gradient of 10% v/v MeCN in H2O to 90% v/v MeCN in
H2O with detection at 254 nm; (B) Platisil ODS column (250 × 4.6 mm,
5 μm) using a gradient of 30% v/v MeCN in buffer solution (0.1%
CF3COOH and 0.1% NH4OH in water, PH 3.5) to 70% v/v MeCN in
H2O with detection at 254 nm. Melting points were determined on
1
HPLC purity (condition A): 93%; H NMR (400 MHz, DMSO-d6): δ
11.14 (s, 1H), 9.70 (s, 1H), 8.34 (s, 1H), 7.64–7.19 (m, 11H), 6.86 (s,
1H); 13C NMR (101 MHz, DMSO-d6): δ 193.00, 154.86, 147.99,
146.56, 141.19 (2C), 138.22, 129.09 (4C), 128.34 (2C), 127.09 (4C),
109.45, 81.24; MS (ESI) m/z: 304 [M − H]–. HRMS (ESI) m/z calcd for
C19H14NO3 [M − H]–: 304.0979; found: 304.0983.
1
an X-4 melting point apparatus without further correction. H NMR
and 13C NMR spectra were provided on a Bruker ARX-400 or ARX-
500 spectrometer using TMS as an internal standard. Chemical
shifts (δ) are given in parts per million (ppm) relative to the internal
residual solvent peak. Coupling constants (J) are recorded in Hertz
(Hz). ESI-MS spectra were obtained on an Agilent G6520 Q-TOF
mass spectrometer. All pure solid compounds, such as 10, 11 and 21,
were obtained by column chromatography to test the melting point,
1H NMR, 13C NMR and ESI-MS spectra. Diphenyldiazomethane
should be used and prepared carefully.
Synthesis of 4,5-bis(benzhydryloxy)picolinaldehyde (12)
A
solution of 18 (41.8 g, 136.9 mmol) in anhydrous N,N-
dimethylformamide (DMF) (300 mL) was treated with MgSO4 (41.8 g,
347.2 mmol), K2CO3 (37.8 g, 273.8 mmol) and bromodiphenylmethane
(40.6 g, 164.3 mmol) under argon. The resulting mixture was heated
to 55 °C and stirred for 12 h. The resulting mixture was extracted with
EA and the organic phase was washed with water and brine, dried over
anhydrous Na2SO4 and filtered, and the filtrate was concentrated in
vacuo. Purification by recrystallisation from a 4:1 (v/v) mixture of PE
and EA (50 °C, 750 mL) afforded compound 12. The product was dried
at 40 °C under reduced pressure to provide compound 12 as a white
solid; yield 50.3 g (78%); m.p. 99–101 °C. HPLC purity (condition
Synthesis of 5-(benzhydryloxy)-2-(hydroxymethyl)-4H-pyran-4-one
(20)
A solution of benzophenone hydrazone (276 g, 1.406 mol) in petroleum
ether (PE) (600 mL) was treated with MnO2 (293.6 g, 3.377 mol).
The reaction mixture was stirred at room temperature for 1 h. The
resulting mixture was filtered and then the filtrate was concentrated
in vacuo to give diphenyldiazomethane. Then diphenyldiazomethane
was dissolved in dichloromethane (DCM) (300 mL), which was
used in the next step without further purification. A suspension of
kojic acid 19 (80 g, 562.9 mmol) in methanol (300 mL) was treated
with the dichloromethane solution of diphenyldiazomethane. The
mixture was stirred at room temperature for 20 h and concentrated in
vacuo to remove methanol and DCM. The resulting residue was taken
up in PE (500 mL) to give a precipitate. The solids were filtered off
and the product was washed with a mixture 1:1 (v/v) of PE and water
(25 °C, 300 mL) to obtain the desired product 20 without further
purification. The product was dried at 40 °C under reduced pressure
to provide compound 20 as a white solid; yield 143.6 g (82.7%); m.p.
1
A): 99%; H NMR (400 MHz, CDCl3): δ 9.76 (s, 1H), 8.23 (s, 1H),
7.52–7.26 (m, 21H), 6.43 (s, 1H), 6.42 (s, 1H); 13C NMR (126 MHz,
CDCl3): δ 192.22, 155.03, 148.23, 148.04, 140.37(2C), 139.98 (2C),
138.82, 128.87 (4C), 128.78 (4C), 128.28 (2C), 128.23 (2C), 126.76
(4C), 126.60 (4C), 107.75, 83.72, 82.43; MS (ESI) m/z: 472 [M + H]+.
HRMS (ESI) m/z calcd for C32H26NO3 [M + H]+: 472.1907; found:
472.1915.
Synthesis of 1-(4,5-bis(benzhydryloxy)pyridin-2-yl)-2-methylpropan-
1-ol (11)
A solution of isopropylmagnesium bromide (3 M) in tetrahydrofuran
(THF) (127.4 mL, 382.2 mmol) under argon atmosphere was cooled
to 0 °C, and then a solution of 12 (60.1 g, 127.4 mmol) in dry THF
(400 mL) was added dropwise to keep the reaction mixture below
10 °C. After addition, the resulting mixture was allowed to warm to
room temperature and stirred for 5 h. After the reaction was completed,
it was quenched by slow addition of saturated aqueous NH4Cl. The
resulting mixture was filtered and filter residue was washed with EA.
Then the solution was extracted with EA, washed with brine, dried
over anhydrous Na2SO4 and filtered, and the filtrate was concentrated
in vacuo to obtain the crude racemic compound 11 as a light yellow
oil (without further purification); yield 56.7 g. Pure racemic form
compound 11 as a white waxy solid; m.p. 103–105 °C; 1H NMR
(400 MHz, CDCl3): δ 7.97 (s, 1H), 7.51–7.18 (m, 20H), 6.63 (s, 1H),
6.33 (s, 1H), 6.24 (s, 1H), 4.23 (d, J = 4.6 Hz, 1H), 1.71 (pd, J = 6.8, 4.7
Hz, 1H), 0.76 (d, J = 6.8 Hz, 3H), 0.57 (d, J = 6.7 Hz, 3H); 13C NMR
(101 MHz, CDCl3): δ 156.32, 155.37, 143.92, 141.08, 141.07, 140.26,
140.22, 138.51, 128.82 (4C), 128.60 (4C), 128.16, 128.12, 127.98,
127.96, 127.08 (2C), 127.01 (2C), 126.65 (2C), 126.63 (2C), 107.85,
1
126–128 °C; HPLC purity (condition A): 98%; H NMR (400 MHz,
CDCl3): δ 7.45 (s, 1H), 7.41–7.28 (m, 10H), 6.48 (s, 1H), 6.34 (s, 1H),
4.39 (d, J = 6.5 Hz, 2H), 2.88 (t, J = 6.6 Hz, 1H); 13C NMR (101 MHz,
DMSO-d6): δ 174.25, 168.51, 145.51, 145.07, 140.99 (2C), 129.02 (2C),
128.33 (4C), 127.18 (4C), 112.13, 81.37, 59.70; MS (ESI) m/z: 331 [M
+ Na]+. HRMS (ESI) m/z calcd for C19H16NaO4 [M + Na]+: 331.0941;
found: 331.0937.
Synthesis of 5-(benzhydryloxy)-1-hydroxy-2-(hydroxymethyl)pyridin-
4(1H)-one (14)
A suspension of 20 (127.3 g, 412.9 mmol) in methanol (500 mL) was
treated with NH4OH (500 mL, 6.6 mol). The resulting mixture was
heated to 55 °C and stirred for 20 h. The reaction mixture was cooled
to room temperature and filtered off. The solids were washed with a
2:1 (v/v) mixture of water and dichloromethane (25 °C, 300 mL) and

JOURNAL OF CHEMICAL RESEARCH 2018 359
84.45, 82.26,77.11, 34.98, 19.04, 16.34. MS (ESI) m/z: 516 [M + H]+.
HRMS (ESI) m/z calcd for C35H34NO3 [M + H]+: 516.2533; found:
516.2542.
128.31 (2C), 128.25 (2C), 126.73 (4C), 126.68 (4C), 110.29, 84.58,
84.48, 83.14, 30.41, 19.00, 16.59; MS (ESI) m/z: 547 [M + H]+. HRMS
(ESI) m/z calcd for C35H35N2O4 [M + H]+: 547.2591; found: 547.2600.
Synthesis of 2-(1-(4,5-bis(benzhydryloxy)pyridin-2-yl)-2-methyl-
propoxy)isoindoline-1,3-dione (10)
Synthesis of (Z)-4,5-bis(benzhydryloxy)-2-(1-(((carboxy(2-(trityl-
amino)thiazol-4-yl)methylene)amino) oxy)-2-methylpropyl)pyridine
1-oxide (22)
A solution of 11 (56.7 g) in dry THF (300 mL) was treated with
N-hydroxyphthalimide (24.6 g, 152.9 mmol) and PPh3 (40.1 g,
152.9 mmol) under an argon atmosphere and the mixture was cooled to
0 °C. A solution of DEAD (24.0 mL, 152.9 mmol) in dry THF (80 mL)
was added dropwise. After addition, the resulting mixture was allowed
to warm to room temperature and stirred for 3 h. The solution was
concentrated in vacuo. The resulting residue was taken up in PE (1.2 L)
and EA (240.0 mL) and filtered with a silicone core funnel. Then the
filtrate was concentrated in vacuo to afford the crude racemic form
compound 10 as a colourless oil (without further purification); yield
93.5 g. Pure racemic form compound 10: Colourless waxy solid; m.p.
128–130 °C; 1H NMR (400 MHz, CDCl3): δ 7.89 (s, 1H), 7.74–7.64 (m,
4H), 7.57–7.50 (m, 4H), 7.47–7.38 (m, 5H), 7.37–7.20 (m, 12H), 6.62 (s,
1H), 6.21 (s, 1H), 5.01 (d, J = 6.5 Hz, 1H), 2.00 (dq, J = 13.6, 7.4, 6.8
Hz, 1H), 0.88 (d, J = 6.7 Hz, 3H), 0.65 (d, J = 6.9 Hz, 3H); 13C NMR
(101 MHz, CDCl3): δ 163.70 (2C), 154.92, 152.70, 144.43, 141.17,
141.14, 140.94, 140.50, 138.96, 134.28 (2C), 128.99, 128.85 (2C),
128.54 (4C), 128.49 (3C), 127.96, 127.89, 127.86, 127.80, 127.07 (2C),
126.88 (2C), 126.84 (2C), 126.67 (2C), 123.36 (2C), 109.68, 94.09,
84.21, 82.05, 32.72, 18.41, 17.82; MS (ESI) m/z: 661 [M + H]+. HRMS
(ESI) m/z calcd for C43H37N2O5 [M + H]+: 661.2697; found: 661.2690.
A solution of 21 (9.3 g) in anhydrous methanol and DCM (3:8,
110 mL) was treated with 2-oxo-2-(2-(tritylamino)thiazol-4-yl)acetic
acid (5.8 g, 14.0 mmol) and the resulting mixture was stirred at room
temperature for 4 h. 2-Oxo-2-(2-(tritylamino)thiazol-4-yl)acetic acid
was synthesised according to a previous method.13 When the reaction
was complete, the mixture was filtered and the filter cake was washed
with EA. After purification by recrystallisation from a 1:1 (v/v)
mixture of PE and DCM (40 °C, 200 mL), the mixture was cooled to
15 °C for 12 h and filtered off. The product was dried at 40 °C under
reduced pressure to provide compound 22 as a white solid; yield 12.0
g (86%) for two steps; m.p. 160–162 °C; HPLC purity (condition A):
1
98%; H NMR (400 MHz, DMSO-d6): δ 8.88 (s, 1H), 7.99 (s, 1H),
7.61–7.14 (m, 35H), 6.96 (s, 1H), 6.90 (s, 1H), 6.69 (s, 1H), 6.55 (s, 1H),
5.29 (d, J = 3.2 Hz, 1H), 2.06 (pt, J = 6.7, 2.9 Hz, 1H), 0.91 (d, J = 6.8
Hz, 3H), 0.44 (d, J = 6.9 Hz, 3H); 13C NMR (126 MHz, DMSO-d6): δ
167.84, 164.35, 145.66, 145.08, 144.14, 143.87, 141.10, 140.86, 140.62,
140.60, 140.52, 129.40, 129.25, 129.21, 129.17, 129.00, 128.48, 128.40,
128.33, 128.16, 127.28, 126.80, 126.74, 126.69, 111.61, 111.39, 83.21,
81.78, 81.62, 71.85, 29.15, 19.62, 16.05; MS (ESI) m/z: 941 [M − H]–.
HRMS (ESI) m/z calcd for C59H49N4O6S [M − H]–: 941.3378; found:
941.3379.
Synthesis of 4,5-bis(benzhydryloxy)-2-(1-((1,3-dioxoisoindolin-2-yl)
oxy)-2-methylpropyl)pyridine 1-oxide (9)
Synthesis of 4,5-bis(benzhydryloxy)-2-(1-((((Z)-2-(((S)-2,2-dimethyl-4-
oxo-1-(sulfooxy)azetidin-3-yl)amino)-2-oxo-1-(2-(tritylamino)thiazol-4-
yl)ethylidene)amino)oxy)-2-methylpropyl) pyridine 1-oxide (24)
A solution of 10 (93.5 g) in DCM (450 mL) was treated with m-CPBA
(65.9 g, 382.2 mmol). The resulting mixture was stirred for 1 h before
being quenched by addition of saturated Na2S2O3 solution. Then the
resulting mixture was extracted with DCM, washed with saturated
aqueous NaHCO3 and brine, dried over anhydrous Na2SO4 and
filtered, and the filtrate was concentrated in vacuo. After purification
by recrystallisation from a 3:1 (v/v) mixture of PE and EA (60 °C,
400 mL), the mixture was cooled to 15 °C for 12 h and filtered off.
The product was dried at 40 °C under reduced pressure to provide
compound 9 as a white solid; yield 58.0 g (67.2%) for three steps; m.p.
A solution of 22 (6.6 g, 7.0 mmol) in DMSO (100 mL) was treated
with HATU (3.5g, 9.1 mmol), NaHCO3 (1.8 g, 21.0mmol) and 23
(1.9 g, 9.1 mmol), and then the reaction mixture was stirred at room
temperature for 5 h. After completion of the reaction, water (300 mL),
EA (30 mL) and saturated ammonium chloride solution (100 mL) were
added and the mixture was stirred for 10 min. The mixture was filtered
and the filter cake was taken up in a 1:1 (v/v) mixture of PE and EA
(25 °C, 30 mL) to obtain compound 24 without further purification.
The product was dried at 40 °C under reduced pressure to provide
compound 24 as a white solid: yield 7.4 g (93%); m.p. 186 °C decomp.;
1
191–193 °C; HPLC purity (condition A): 98%, R/S 50:50; H NMR
(400 MHz, CDCl3): δ 7.75 (dd, J = 5.6, 3.1 Hz, 2H), 7.73 (s, 1H), 7.70
(dd, J = 5.6, 3.1Hz, 2H), 7.59 (s, 1H), 7.59–7.55 (m, 4H), 7.46–7.27 (m,
16H), 6.72 (s, 1H), 6.15 (s, 1H), 5.88 (d, J = 6.8 Hz, 1H), 2.11 (h, J = 6.9
Hz, 1H), 1.08 (d, J = 6.9 Hz, 3H), 0.64 (d, J = 6.9 Hz, 3H); 13C NMR
(126 MHz, CDCl3): δ 163.64 (2C), 147.46, 145.49, 142.83, 140.66,
140.11 (2C), 140.04, 134.48 (2C), 130.34 (2C), 128.99 (2C), 128.94,
128.80 (2C), 128.72 (2C), 128.53 (2C), 128.29, 128.20, 128.17, 127.95,
126.79 (2C), 126.77 (2C), 126.73 (2C), 126.61 (2C), 123.49 (2C),
111.50, 85.90, 84.39, 82.83, 31.02, 18.95, 15.66; MS (ESI) m/z: 677
[M + H]+. HRMS (ESI) m/z calcd for C43H37N2O6 [M + H]+: 677.2646;
found: 677.2662.
1
HPLC purity (condition B): 96%; H NMR (400 MHz, DMSO-d6):
δ 9.77 (d, J = 7.7 Hz, 1/2H), 9.68 (d, J = 7.0 Hz, 1/2H), 8.90 (s, 1H),
8.02 (s, 1/2H), 7.99 (s, 1/2H), 7.63–7.16 (m, 35H), 7.04 (s, 1/2H), 6.87
(s, 1/2H), 6.79 (s, 1/2H), 6.77 (s, 1/2H), 6.74 (s, 1/2H), 6.73 (s, 1/2H),
6.72 (s, 1/2H), 6.70 (s, 1/2H), 5.32 (d, J = 3.2 Hz, 1/2H), 5.26 (d,
J = 3.7 Hz, 1/2H), 4.81 (d, J = 7.8 Hz, 1/2H), 4.65 (d, J = 7.1 Hz, 1/2H),
2.05–1.93 (m, 1H), 1.57 (s, 3/2H), 1.52 (s, 3/2H), 1.37 (s, 3/2H), 1.34
(s, 3/2H), 0.87 (d, J = 6.9 Hz, 3/2H), 0.82 (d, J = 7.0 Hz, 3/2H), 0.36
(d, J = 7.0 Hz, 3/2H), 0.32 (d, J = 7.1 Hz, 3/2H); 13C NMR (126 MHz,
DMSO-d6) (most carbons show two peaks because of diastereomers):
δ 168.23 and 168.17, 163.68 and 163.63, 162.07 and 161.88, 151.28
and 150.93, 145.72 and 145.67, 144.94 and 144.87, 144.30 and 144.10,
143.93, 141.75 and 141.71, 141.21, 141.10, 140.98, 140.80 and 140.54,
129.40, 129.26, 129.23, 129.05, 129.02, 128.48, 128.44, 128.26, 128.19,
127.44, 126.85, 126.75, 126.72, 126.64, 112.97 and 112.72, 111.75 and
111.65, 83.27 and 83.09, 81.60 and 81.57, 81.44 and 81.26, 71.62, 68.01
and 67.89, 61.58 and 61.22, 29.57 and 29.12, 24.02 and 23.97, 21.17 and
21.07, 19.46 and 19.37, 16.22 and 15.99. HRMS (ESI) m/z calcd for
C64H57N6O10S2 [M − H]–: 1133.3583; found: 1133.3608.
Synthesis of 4,5-bis(benzhydryloxy)-2-(1-((1,3-dioxoisoindolin-2-yl)
oxy)-2-methylpropyl)pyridine 1-oxide (21)
A solution of 9 (10 g, 14.8 mmol) in methanol (150 mL) was treated
with 85% hydrazine hydrate (1.69 ml, 29.6 mmol). The resulting
mixture was stirred at room temperature for 60 min. Then the filtrate
was concentrated in vacuo. Then EA (100 mL) and PE (200 mL) were
added to the residue. The mixture was filtered and the filter residue
was washed by a 2:1 (v/v) mixture of PE and EA (25 °C, 90 mL).
The filtrate was concentrated in vacuo to afford crude compound 21
as: Colourless oil (without further purification); yield 9.3 g. Pure
compound 21 as a colourless colloidal solid; m.p. 71–73 °C; 1H NMR
(400 MHz, DMSO-d6): δ 7.96 (s, 1H), 7.61–7.21 (m, 20H), 6.87 (s, 1H),
6.81 (s, 1H), 6.68 (s, 1H), 4.67 (d, J = 3.7 Hz, 1H), 1.82 (td, J = 7.0,
3.8 Hz, 1H), 0.81 (d, J = 6.9 Hz, 3H), 0.35 (d, J = 7.0 Hz, 3H); 13C NMR
(126 MHz, CDCl3): δ 147.74, 145.70, 145.41, 140.04, 140.02, 139.96,
139.80, 130.87, 128.89 (2C), 128.81 (2C), 128.79 (2C), 128.77 (2C),
Synthesis of (3S)-3-((Z)-2-(2-Aminothiazol-4-yl)-2-((1-(1,5-dihydroxy-
4-oxo-1,4-dihydropyridin-2-yl)-2-methylpropoxy)imino)acetamido)-2,2-
dimethyl-4-oxoazetidin-1-yl hydrogen sulfate (YT-14)
A solution of 24 (2 g, 1.76 mmol) in anhydrous DCM (24 mL) was
treated with triethylsilane (0.84 mL, 5.29 mmol) and cooled to −15 °C.
Then trifluoroacetic acid (5.89 mL, 52.9 mmol) was added dropwise.
The reaction mixture was stirred at −15 °C for 5 h. After completion

360 JOURNAL OF CHEMICAL RESEARCH 2018
of the reaction, the reaction mixture was slowly warmed to 0 °C. Then, a
mixture of 4:1 (v/v) EA and hexane (25 °C, 50 mL) was added dropwise,
the resulting precipitate was further stirred for 20 min and collected
by filtration, and then the cake was washed with EA without further
purification. The product was dried at 25 °C under reduced pressure to
provide compound YT-14 as a white solid; yield 820 mg (83%); m.p. 151 °C
decomp. (lit.4 151 °C decomp.); HPLC purity (condition B): 97%, R/S in
isopropyl position 46:54; IR (KBr) (υ cm−1): 3390, 3306, 3235, 3103,
2976, 2939, 2879, 1776, 1672, 1639, 1541, 1456, 1390, 1263, 1200, 1142,
1051, 1016, 721, 600; 1H NMR (500 MHz, DMSO-d6): δ 9.69 (d, J = 8.0
Hz, 1/2H), 9.65 (d, J = 7.5 Hz, 1/2H), 8.24 (s, 1/2H), 8.23 (s, 1/2H), 7.02
(s, 1/2H), 7.00 (s, 1/2H), 6.83 (s, 1/2H), 6.81 (s, 1/2H), 5.44 (d, J = 4.8 Hz,
1/2H), 5.37 (d, J = 5.4 Hz, 1/2H), 4.71 (d, J = 7.9 Hz, 1/2H), 4.68 (d, J = 7.6
Hz, 1/2H), 2.23–2.09 (m, 1H), 1.48 (s, 3/2H), 1.47 (s, 3/2H), 1.35 (s, 3/2H),
1.34 (s, 3/2H), 1.00–0.96 (m, 3H), 0.92–0.85 (m, 3H); 13C NMR (126 MHz,
DMSO-d6) (most carbons show two peaks because of diastereomers): δ
169.35, 162.58, 162.02 and 161.98, 157.35 and 157.31, 150.93 and 150.90,
145.72 and 145.54, 145.13, 140.55 and 140.39, 127.97, 111.87 and 111.60,
110.97 and 110.88, 83.04 and 82.90, 68.17 and 68.05, 61.33 and 61.29, 31.90
and 31.67, 23.88 and 23.86, 21.13 and 21.06, 19.15 and 19.06, 17.32 and
17.08. HRMS (ESI) m/z calcd for C19H23N6O10S2 [M – H]−: 559.0917; found:
559.0923.
Received 25 April 2018; accepted 26 June 2018
Paper 1805400
https://doi.org/10.3184/174751918X15314830456124
Published online: 18 July 2018
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No. 81573284). Jianhai Weia and Deyu
Kong contributed equally to this work.