New procedure for the preparation of (Z)-2-(5-amino-1,2,4-thiadiazole-3-yl) -2-trityloxyiminoacetic acid

Article abstract of DOI:10.1021/op100323b

A novel and efficient procedure has been developed for the preparation of the C-7 side chain of ceftobiprole, (Z)-2-(5-amino-1,2,4-thiadiazole-3-yl)-2- trityloxyiminoacetic acid (2) from malononitrile (9) in a total yield of 19%. The key intermediate N-(3

Full text of DOI:10.1021/op100323b

TECHNICAL NOTE
pubs.acs.org/OPRD
New Procedure for the Preparation
of (Z)-2-(5-Amino-1,2,4-thiadiazole-3-yl)-2-trityloxyiminoacetic Acid
Weihui Zhong,* Wendong Zhang, Yanhui Chen, Yanbin Liu, and Yi Yao
Key Laboratory of Pharmaceutical Engineering of Ministry of Education, College of Pharmaceutical Sciences,
Zhejiang University of Technology, Hangzhou 310014, P.R. China
S Supporting Information
b
ABSTRACT: A novel and efficient procedure has been developed for the preparation of the C-7 side chain of ceftobiprole, (Z)-
2-(5-amino-1,2,4-thiadiazole-3-yl)-2-trityloxyiminoacetic acid (2) from malononitrile (9) in a total yield of 19%. The key
intermediate N-(3-(2-acetamido-2-oxoethyl)-1,2,4-thiadiazol-5-yl)benzamide (15b) was synthesized for the first time in 76% yield
by treatment of N-(3-aminoisoxazol-5-yl)acetamide (13) with benzoyl isothiocyanate. More importantly, (Z)-N-(3-(2-acetamido-
2-oxo-1-(trityloxyimino)ethyl)-1,2,4-thiadiazol-5-yl)benzamide (16b) was prepared from 15b with high stereoselectivity and good
yield via successive oximation and protection of oxime hydroxy group. The process has a good prospect for industrial synthesis.
’ INTRODUCTION
The C-7 side chain of ceftobiprole, (Z)-2-(5-amino-1,2,4-thia-
diazole-3-yl)-2-trityloxyiminoacetic acid 2, was proved to having a
broad antibacterial spectrum. The original medicinal chemistry-
based route of 2 is outlined in Scheme 1.7 Commercially available
3-aminoisoxazole 3 was treated with methoxycarbonyl isothiocya-
nate in acetonitrile to give the thiourea derivative 4, following by
warming in methanol at 60 °C to afford the thiadiazolyl acetalde-
hyde 5. Oxidation of 5 with peracetic acid provided the correspond-
ing acetic acid, which was esterified with thionyl chloride and
methanol to give methyl ester 6. The hydroxyimino compound 7
was prepared from 6 through the corresponding keto ester in 60%
yield via three-reaction sequence. Stereoselective protection of 7
with trityl chloride at 0 °C in the presence of triethylamine to give
the Z-configuration of trityloxyimino methyl ester 8, which was
finally led to 2 by a base hydrolysis. However, there were the two
following problems regarding Scheme 1 in the reported method,
namely: (1) the overall yield of 2 was low (11% yield); (2) toxic and
hazardous agents such as bromine and peracetic acid were used.
Alternatively, the key intermediate 6 could be prepared from the
3-amino-5-methoxyisoxaole (11) directly through the skeletal re-
arrangement in several routes.8,9 As shown in Scheme 2, the starting
compound 11 was prepared from the malononitrile (9) through
3,3-dimethoxyacrylonitrile (10). Reaction of 11 with methoxycar-
bonyl isothiocyanate afforded 6 in 86% yield. Unfortunately, this
route was impractical on a large scale due to its shortcomings such as
low yield (38%) and harsh reaction conditions.
Ceftobiprole (Zeftera/Zevtera, 1) is regarded as a new broad-
spectrum fifth-generation cephalosporin antibiotic with high activity
against a wide range of Gram-positive and Gram-negative patho-
gens, including several resistant species such as methicillin-resistant
Staphylococcus aureus (MRSA),1,2 penicillin-resistant Streptococcus
pneumoniae (PRSP),1,2 Enterococcus faecalis,2 and Pseudomonas
aeruginosa.2,3 It was discovered and commercial produced by Basilea
Pharmaceutical Company and developed by Johnson & Johnson
Pharmaceutical Research and Development. Ceftobiprole (1) was
approved in Canada in 2008 for the treatment of complicated skin
and skin-structure infections under the trade name Zeftera.4,5 The
therapeutic activity of ceftobiprole medocaril, the water-soluble
prodrug of ceftobiprole, was compared to that of vancomycin in a
rat tissue cage model of chronic MRSA foreign-body infection.2,6
To improve the quality and the yield of product 2, as well as to
reduce the cost and make the process more environmentally suitable
for a commercial production, we developed a new and efficient
procedure for the preparation of 2 outlined in Scheme 3. Initially, an
efficient one-pot synthesis of N-(3-aminoisoxazol-5-yl)acetamide (13)
from malononitrile under mild conditions was described.10,11 Impor-
tant intermediates N-(3-(2-acetamido-2-oxoethyl)-1,2,4-thiadiazol-5-yl)-
benzamide (15b) were prepared from compound 13 and benzoyl iso-
thiocyanate through the skeletal rearrangement of thiourea intermediate
Received: December 6, 2010
Published: March 28, 2011
r
2011 American Chemical Society
698
dx.doi.org/10.1021/op100323b Org. Process Res. Dev. 2011, 15, 698–703
|

Organic Process Research & Development
TECHNICAL NOTE
Scheme 1
Scheme 2
Scheme 3
14 with good yield and purity.8,9,12 The target compound 2 was
formed and isolated as a white solid, and a purity of 98.5% was
obtained by HPLC analysis after being recrystallized with
ethanol. In this new procedure, up to 19% overall isolated yield
was achieved from malononitrile.9
with 71% yield through chemoselective acetylation of amino with
1.1 equiv of acetyl chloride at 5 °C.1
’ RESULTS AND DISCUSSION
Then, how to efficiently convert compound 13 into 1,2,4-
thiadiazoles 15 via a skeleton rearrangement of the thiourea
intermediate 14 was one of our main tasks. Initially, treatment of
compound 13 with ethoxycarbonyl isothiocyanate under various
condition to afford ethyl 3-(2-acetamido-2-oxoethyl)-1,2,4-thia-
diazol-5-ylcarbamate (15a) was investigated.8,9 The results in
Table 1 reveal that Lewis acids (zinc chloride) or bases (pyridine,
The starting N-(3-aminoisoxazol-5-yl)acetamide (13) was pre-
pared from commercially available malononitrile (9) via two-reaction
sequence in one pot. Thus, malononitrile was treated with hydro-
xylamine hydrochloride in the presence of sodium methoxide in
methanol to afford 3,5-diamine-isoxazole (12),10 which was subse-
quently converted into N-(3-aminoisoxazol-5-yl)acetamide (13)
699
dx.doi.org/10.1021/op100323b |Org. Process Res. Dev. 2011, 15, 698–703

Organic Process Research & Development
TECHNICAL NOTE
Table 1. Preparation of 15 from 13 under various conditions
entry
R
solvents
CH3CN
bases (equiv)
temp (°C)
time (h)
product 15 and yielda (%)
1
EtO
EtO
EtO
EtO
EtO
EtO
EtO
EtO
EtO
EtO
EtO
Ph
/
0
0
4
5
15a (55)
15a (34)
15a (50)
15a (39)
15a (64)
15a (50)
15a (42)
15a (40)
15a (39)
15a (41)
15a (30)
15b (76)
15b (70)
15b (63)
15c (66)
15d (60)
15e (50)
15f (68)
15g (70)
2
MeOH
/
3
CH3COCH3
EtOAc
/
0
5
4
/
0
4
5
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
/
25
40
70
25
25
25
25
25
40
70
25
25
25
25
25
3
6
/
3
7
/
2
8
pyridine (1.0)
4
9
Et3N (1.0)
TEMEDb (1.0)
4
10
11
12
13
14
15
16
17
18
19
4
ZnCl2 (1.0)
4
/
/
/
/
/
/
/
/
6
Ph
4
Ph
3
MeO
BnO
6
8
Me
8
n-Pr
10
6
o-ClC6H4
a Isolated yields of 15 based on 13 (1.27 mol). b TEMED: N,N,N0,N0-tetramethylethylenediamine.
triethyl amine, and N,N,N0,N0-tetramethylethylenediamine)
could not increase the yields of 15a, and the highest yield was
64% under acid- or base-free condition (Table 1, entry 5). HPLC
analysis revealed that the main byproduct was the unrearranged
thiourea 14a, and the crude product was purified by recrystalliza-
tion from acetone to yield a white crystalline. To improve the yield
and product quality, other isothiocyanates instead of ethoxycarbo-
nyl isothiocyanate were investigated for this reaction, and the
results are summarized in Table 1. To our delight, when compound
13 was reacted with benzoyl isothiocyanate in acetonitrile at
ambient temperature, the thiourea intermediate was nearly rear-
ranged to the corresponding 1,2,4-thiadiazole 15b, and the product
was isolated as yellow crystals with 76% yield (Table 1, entry 12).
With compounds 15 in hand, we then converted 15 into the
corresponding trityloxyimino product 16. Treatment of 15a with
isopropyl nitrite in THF containing conc. HCl to give the
corresponding oxime compound, followed by addition of trityl
chloride in the presences of triethylamine to give (Z)-config-
uration of trityloxyimino product 16. However, under various
reaction conditions, the substrate 15a always brought out a
mixture of the desired product 16a and its E-isomer 17a,
which was isolated by silca gel chromatography (Table 2,
entries 1-4). Low yield and cumbersome purification proce-
dure of 16a led us to use other 1,2,4-thiadiazole to synthesize
the Z-configuration of trityloxyimino product. Fortunately, it
was found that N-(3-(2-acetamido-2-oxoethyl)-1,2,4-thiadiazol-5-
yl)benzamide (15b) could be converted into the corresponding
product 16b with the yield of 74% at room temperature under the
similar condition, and only trace amount of E-isomer 17b was
detected (less than 1%) by HPLC.
Finally, hydrolysis of the trityloxyimino product 16b to afford
the target product 2 in a NaOH solution was investigated. Initially,
the hydrolysis was carried out by using 20% NaOH (6 equiv) at
100 °C for 8 h; after acidification to pH = 3 with 10% HCl and
filtration, the crude product was purified by recrystallization from
ethanol to afford the desired product 2in 29% yield (Table 3, entry 1).
With respect to improving the yield of 2, various factors including
the amount and concentration of NaOH and reaction tempera-
ture were carefully screened. Experimental results revealed that a
higher concentration of NaOH (Table 3, entries 1-3) or a lower
concentration of NaOH but longer reaction time (Table 3, entry 7)
at high temperature easily led to the ring-opening of 1,2,4-
thiadiazole to give some unknown side products, so that lower
yields of 2 were obtained. The optimal condition was to carry out
16b with 5% NaOH (6 equiv) at 100 °C for 8 h (Table 3, entry 4)
to give 2 with the isolated yield of 48% and a HPLC purity of 98.5%.
In summary, we have developed a new practical, efficient, and
environmentally friendly process for the preparation of (Z)-2-(5-
amino-1,2,4-thiadiazole-3-yl)-2-trityloxyiminoacetic acid 2 with
a total yield of 19% from malononitrile. Several key intermediates
700
dx.doi.org/10.1021/op100323b |Org. Process Res. Dev. 2011, 15, 698–703

Organic Process Research & Development
TECHNICAL NOTE
Table 2. Preparation of 16 from 15 under different
conditions
Table 3. Preparation of 2 from 16b under different
conditions
entry
base (equiv)
temp (°C) time (h) yielda of product 2 (%)
1
2
3
4
5
6
7
20% NaOH (6)
10% NaOH (6)
8% NaOH (6)
5% NaOH (6)
5% NaOH (6)
5% NaOH (4)
2% NaOH (6)
100
100
100
100
80
8
8
29
34
36
48
40
30
28
8
8
12
12
12
100
product 16/17 and yieldsa (%)
100
a Isolated yields of 2 based on 16b.
entry
R
solvent temp (°C) time (h)
Z-isomer
E-isomer
1
2
3
4
5
6
7
EtO THF
EtO THF
EtO THF
EtO THF
EtO THF
Ph THF
Ph THF
-20
-10
0
7
6
5
4
4
5
4
16a (40)
16a (39)
16a (40)
16a (34)
16a (30)
16b (68)
16b (74)
17a (18)
17a (20)
17a (21)
17a (35)
17a (47)
-
afford 13 (226.6 g, 71% from 9) as a pale-yellow solid. Mp
208.3-209.0 °C dec. IR (KBr): 3430, 3215, 1674, 1565,
1
1255 cm-1. H NMR (400 MHz, DMSO-d6): δ 2.04 (s, 3H,
25
40
0
CH3), 5.50 (s, 2H, -NH2), 5.68 (s, 1H, Ar-H), 11.15 (s, 1H, -
NHCO-). 13C NMR (100 MHz, DMSO-d6): δ = 23.0, 80.4,
159.0, 164.2, 166.3. MS (ESI): m/z (%) 140.3 [M - 1]-. HRMS
(ESI) m/z calcd for C5H7N3O2: 141.0538; found: 141.0546. The
HPLC analysis was performed on Agilent 1200 HPLC
(Chromatographic column: Alltima C18 250 mm ꢀ 4.6 mm 5
μm) with DAD UV detector. Mobile phase was water/acetoni-
trile/40% Et3N solution = 94:4:1with a flow rate of 1.0 mL/min.
Detection wavelength was 230 nm, and injection volume was 20 μL.
Preparation of Ethyl 3-(2-acetamido-2-oxoethyl)-1,2,4-
thiadiazol-5-yl Carbamate (15a). To a solution of potassium
thiocyanate (135.8 g, 1.4 mol) in acetonitrile (350 mL) was
dropwise added ethyl chloroformate (151.9 g 1.4 mol) at 5 °C
over a period of 4 h. The mixture was stirred for 1 h further at
room temperature. Then a solution of 13 (179.0 g, 1.27 mol) in
acetonitrile (350 mL) was added, and the mixture was stirred at
25 °C for 3 h. Then the reaction mixture was cooled, and the
formed solid was filtered. The crude product was recrystallized
from acetone to give 15a (221.8 g, 64% from 13) as a white
crystalline solid. Mp 167.4-168.5 °C dec. IR (KBr): 3453, 3302,
1710, 1566, 1242 cm-1. 1H NMR (400 MHz, DMSO-d6): δ 1.27
(t, J = 7.2 Hz, 3H, CH3), 2.16 (s, 3H, CH3), 3.98 (s, 2H, -CH2-),
4.28 (q, J = 7.2 Hz, 2H, -CH2-), 10.91 (s, 1H, -NHCOO-),
12.54 (s, 1H, -NHCOCH3). 13C NMR (100 MHz, DMSO-d6):
14.2, 24.8, 41.2, 62.7, 154.5, 165.2, 168.9, 171.1, 177.5. MS (ESI):
m/z (%) 271.2 [M - 1]-. HRMS (ESI) m/z calcd for
C9H12N4O4S: 272.0579 found: 272.0585.
25
-
a Isolated yields based on 15.
such as N-(3-aminoisoxazol-5-yl)acetamide 13, N-(3-(2-aceta-
mido-2-oxoethyl)-1,2,4-thiadiazol-5-yl)benzamide (15b), and
(Z)-N-(3-(2-acetamido-2-oxo-1-(trityloxyimino)ethyl)-1,2,4-
thiadiazol-5-yl)benzamide (16b) were prepared with good yield
and quality under mild conditions. For the well-controlled
impurities, good yield, and no use of toxic and environmentally
unfriendly reagents and solvents, this procedure is amenable to
large-scale production.
’ EXPERIMENTAL SECTION
Materials and Instrument. All solvents and reagents were
purchased from commercial sources and were used without
additional purification. Melting points were determined with a
B€uchi B-540 capillary melting point apparatus and are uncor-
rected. IR spectra were recorded on a Nicolet Avatar 370
instrument. 1H and 13C NMR spectra were recorded on a Varian
(400 MHz) instruments in DMSO-d6 with TMS as internal
standard. Mass spectra were measured with a Finnigan Trace
DSQ instrument. The HPLC analysis was performed on Agilent
1200 HPLC with DAD UV detector.
N-(3-(2-Acetamido-2-oxoethyl)-1,2,4-thiadiazol-5-yl)benza-
mide (15b). To a solution of potassium thiocyanate (160.5 g,
1.65 mol) in acetonitrile (420 mL) was dropwise added benzoyl
chloride (231.8 g 1.65 mol) at 5 °C over a period of 5 h. The
mixture was stirred for 3 h further at room temperature. Then a
solution of 13 (179.0 g, 1.27 mol) in acetonitrile (350 mL) was
added, and the mixture was stirred at 25 °C for 6 h. Then the
reaction mixture was cooled, and the formed crystals were
filtered, washed with ethanol, and dried to constant weight at
40 °C under high vacuum to give 15b (293.42 g, 76% from 13) as
yellow crystals. Mp 178.2-178.9 °C dec. Chromatographic
Preparation of N-(3-Aminoisoxazol-5-yl)acetamide (13).
To a mixture of malononitrile (150 g, 2.27 mol) and hydro-
xylamine hydrochloride (156.6 g, 2.27 mol) in methanol
(400 mL) was dropwise added a solution of sodium methoxide
(240.3 g, 4.45 mol) in methanol (300 mL) at 5 °C over a period
of 4 h. After stirring at the same temperature for 8 h, acetyl
chloride (196.3 g, 2.50 mol) was dropwise added within 3 h. The
reaction was stirred for 4 h further at the same temperature and
condensed to one-third of the volume under vacuum. Then cold
water (800 mL) was dropwise added, and the formed precipitates
were filtered off, washed successively with water, and dried to
701
dx.doi.org/10.1021/op100323b |Org. Process Res. Dev. 2011, 15, 698–703

Organic Process Research & Development
TECHNICAL NOTE
purity by HPLC was shown to be 98%. IR (KBr): 3270, 3207,
1698, 1544, 1293 cm-1. 1H NMR (400 MHz, DMSO-d6): δ 2.18
(s, 3H, CH3), 4.09 (s, 2H, -CH2-), 7.57 (t, J = 7.2 Hz, 2H,
ArH), 7.68 (t, J = 6.8 Hz, 1H, ArH), 8.14 (d, J = 7.6 Hz, 2H, ArH),
10.94 (s, 1H, -NHCOPh), 13.49 (s, 1H, -NHCOCH3).
13CNMR (100 MHz, DMSO-d6): 24.9, 41.3, 128.5 (2C),
128.8 (2C), 130.5, 133.4, 164.7, 166.5, 169.0, 171.2, 176.0. MS
(ESI): m/z (%) 305.1 [M þ 1]þ. HRMS (ESI) m/z calcd for
C13H12N4O3S: 304.0552; found: 304.0560. The HPLC analysis
was performed on Agilent 1200 HPLC (Chromatographic
column: XDB C18 150 mm ꢀ 4.6 mm 5 μm) with DAD UV
detector. Mobile phase was 0.02 mol/L ammonium acetate water
solution/acetonitrile = 20:80 with a flow rate of 1.0 mL/min.
Detection wavelength was 226 nm, and injection volume was
20 μL.
Similarly, compounds 15c-g could be prepared from the
corresponding isothiocyanates with satisfactory yield (Table 1)
Methyl 3-(2-acetamido-2-oxoethyl)-1,2,4-thiadiazol-5-
ylcarbamate(15c): 66% from 13, yellow crystals. Mp 203.3-
205.2 °C dec. IR (KBr): 3465, 3146, 1681, 1564, 1274 cm-1. 1H
NMR (400 MHz, DMSO-d6): δ 2.16 (s, 3H, CH3), 3.82 (s, 3H,
CH3), 3.99 (s, 2H, -CH2-), 10.92 (s, 1H, -NHCOO-), 12.61
(s, 1H, -NHCOCH3). 13C NMR (100 MHz, DMSO-d6): δ
24.9, 41.2, 53.7, 155.1, 165.3, 168.9, 171.2, 177.6. MS (ESI): m/z
(%) 257.3 [M - 1]-. HRMS (ESI) m/z calcd for C8H10N4O4S:
258.0423; found: 258.0426.
NMR (100 MHz, DMSO-d6): δ 25.0, 41.3, 127.2, 129.6, 129.9,
130.4, 132.5, 132.6, 164.7, 166.2, 168.8, 170.9, 174.8. MS (ESI):
m/z (%) 337.1 [M - 1]-. HRMS (ESI) m/z calcd for
C13H11ClN4O3S: 338.0240; found: 338.0233.
Preparation of (Z)-Ethyl 3-(2-acetamido-2-oxo-1-(trity-
loxyimino)ethyl)-1,2,4-thiadiazol-5-yl Carbamate (16a). To
a solution of 15a (54.4 g, 0.2 mol) and conc. HCl (4 mL, 0.04
mol) in THF (200 mL) was dropwise added isopropyl nitrite
(21.4 g, 0.24 mol) at 0 °C within 1.5 h. The reaction mixture was
stirred for further 3 h at the same temperature. Then the pH value
of this mixture was adjusted to 10 with Et3N (30.3 g, 0.3 mol),
followed by addition of trityl chloride (78.0 g, 0.28 mol). After
stirring at the same temperature for 2 h, the formed precipitate
was filtered off and purified by column chromatography on silica
gel with hexane/AcOEt (8:1) afford 16a (43.7 g, 40%) as
colorless crystals. Mp 260.7-262.5 °C dec. IR (KBr): 3458,
3301, 1685, 1524, 1242. 1H NMR (400 MHz, DMSO-d6): δ 1.29
(m, 3H, CH3), 2.05 (s, 3H, CH3), 4.32 (q, J = 7.2 Hz, 2H, -
CH2-), 7.28-7.35 (m, 15H, ArH), 10.70 (s, 1H, -NHCOO-),
12.90 (s, 1H, -NHCOCH3). 13C NMR (100 MHz, DMSO-d6):
14.2, 24.3, 63.1, 92.7 127.4 (3C), 127.8 (6C), 128.6 (6C),
143.3 (3C), 145.3, 154.9, 157.7, 162.3, 170.2, 177.5. MS (ESI):
m/z (%) 566.2 [M þ Na]þ. HRMS (ESI) m/z calcd for
C28H25N5O5S: 543.1576; found: 543.1581.
(E)-Ethyl 3-(2-Acetamido-2-oxo-1-(trityloxyimino)ethyl)-
1,2,4-thiadiazol-5-yl carbamate (17a): 21% from 15a, colorless
crystal Mp 214.9-215.6 °C dec. IR (KBr): 3456, 3230, 1664,
1516, 1279 cm-1. 1H NMR (400 MHz, DMSO-d6): δ 1.23 (m,
3H, CH3), 2.06 (s, 3H, CH3), 4.25 (q, J = 7.2 Hz, 2H, -CH2-),
7.21-7.36 (m, 15H, ArH), 11.83 (s, 1H, -NHCOO-), 12.83
(s, 1H, -NHCOCH3). 13C NMR (100 MHz, DMSO-d6):
δ14.2, 24.3, 63.1, 92.7 127.4 (3C), 127.8 (6C), 128.6 (6C),
143.3 (3C), 145.3, 154.9, 157.7, 162.3, 170.2, 177.5. MS (ESI):
m/z (%) 566.2 [M þ Na]þ. HRMS (ESI) m/z calcd for
C28H25N5O5S: 543.1576; found: 543.1584.
Benzyl 3-(2-acetamido-2-oxoethyl)-1,2,4-thiadiazol-5-yl-
carbamate (15d): 60% from 13, yellow crystals. Mp 178.5-
179.0 °C dec. IR (KBr): 3445, 3270, 1756, 1526, 1230 cm-1. 1H
NMR (400 MHz, DMSO-d6): δ 2.16 (s, 3H, CH3), 4.00 (s, 2H,
-CH2-), 5.30 (s, 2H, -CH2-), 7.37-7.46 (m, 5H, ArH),
10.92 (s, 1H, -NHCOO-), 12.69 (s, 1H, -NHCOCH3). 13
C
NMR (100 MHz, DMSO-d6): 24.8, 41.2, 67.9, 128.3 (2C),
128.4, 128.5 (2C), 135.3, 154.5, 165.3, 168.8, 171.1, 177.4. MS
(ESI): m/z (%) 333.1 [M - 1]-. HRMS (ESI) m/z calcd for
C14H14N4O4S: 334.0736; found: 334.0742.
Preparation of (Z)-N-(3-(2-Acetamido-2-oxo-1-(trityloxy-
imino)ethyl)-1,2,4-thiadiazol-5-yl)benzamide (16b). To a so-
lution of 15b (208 g, 0.68 mol) and conc. HCl(14mL, 0.13mol) in
THF (800 mL) was dropwise added isopropyl nitrite (72.9 g, 0.82
mol) at 25 °C within 2 h. The reaction mixture was stirred for 3 h
further at the same temperature. Then the pH value of this mixture
was adjusted to 10 with Et3N (103.0 g, 1.02 mol), followed by
addition of trityl chloride (265.5 g, 0.95 mol). After stirring at the
same temperature for 2.5 h, the formed precipitate was filtered off,
washed with acetone, and dried to constant weight at 30 °C under
high vacuum to afford 16b as colorless crystals (290.2 g, 74%). Mp
2-(5-Acetamido-1,2,4-thiadiazol-3-yl)-N-acetylacetamide
(15e): 50% from 13, yellow solid. Mp 205.6-207.1 °C dec. IR
(KBr): 3155, 3007, 1704, 1540, 1295 cm-1. 1H NMR (400 MHz,
DMSO-d6): δ 2.17 (s, 3H, CH3), 2.24 (s, 3H, CH3), 4.01 (s, 2H,
-CH2-), 10.93 (s, 1H, -NHCOCH3-), 12.89 (br, 1H, -
NHCOCH3). 13C NMR (100 MHz, DMSO-d6): 22.1, 24.8, 41.3,
164.5, 168.9, 170.5, 171.1, 175.1. MS (ESI): m/z (%) 243.0 [M þ
1]þ. HRMS (ESI) m/z calcd for C8H10N4O3S: 242.0474; found:
242.0479.
N-(3-(2-Acetamido-2-oxoethyl)-1,2,4-thiadiazol-5-yl)butyra-
mide (15f): 68% from 13, yellow solid. Mp 134.9-135.8 °C dec.
IR (KBr): 3217, 3157, 1679, 1282 cm-1. 1H NMR (400 MHz,
DMSO-d6): δ 0.91(t, J = 7.4 Hz, 3H, CH3), 1.65 (m, 2H, -
CH2-), 2.17 (s, 3H, CH3), 2.51 (t, J = 7.2 Hz, 2H, -CH2), 4.01
(s, 2H, -CH2-), 10.92 (s, 1H, -NHCOCH2-), 12.92 (s, 1H,
-NHCOCH3). 13C NMR (100 MHz, DMSO-d6): 13.4, 17.9,
24.8, 36.4, 41.2, 164.5, 169.0, 171.1, 173.2, 175.0. MS (ESI): m/z
(%) 269.1 [M - 1]-. HRMS (ESI) m/z calcd for C10H14N4O3S:
270.0787; found: 270.0781.
227.4-228.6 °C dec. IR (KBr): 3458, 3228, 1688, 1539, 1289 cm-1
.
H NMR (400 MHz, DMSO-d6): δ 2.08 (s, 3H, CH3), 7.26-7.37
(m, 15H, ArH), 7.59 (dd, J = 7.6, 7.6, 2H, ArH), 7.70 (dd, J = 7.6,
7.6, 1H, ArH), 8.17-8.20 (m, 2H, ArH), 10.73 (s, 1H, -
NHCOPh), 13.78 (s, 1H, -NHCOCH3). 13C NMR (100
MHz, DMSO-d6): 24.4, 92.6, 127.2 (3C), 127.6 (6C), 128.4
(6C), 128.5 (4C), 130.1, 133.3, 143.0 (3C), 145.2, 156.8, 161.9,
166.7, 169.9, 175.4. MS (ESI): m/z (%) 574.1 [M - 1]-. HRMS
(ESI) m/z calcd for C32H25N5O4S: 575.1627; found: 574.1635.
The HPLC analysis was performed on Agilent 1200 HPLC
(Chromatographic column: C18 150 mm ꢀ 4.6 mm 5 μm) with
DAD UV detector. Mobile phase was water/methanol/acetoni-
trile = 60:20:20 with a flow rate of 1.0 mL/min. Detection
wavelength was 234 nm, and injection volume was 10 μL.
Preparation of (Z)-2-(5-Amino-1,2,4-thiadiazole-3-yl)-2-
trityloxyiminoacetic Acid (2). A mixture of compound 16b
N-(3-(2-Acetamido-2-oxoethyl)-1,2,4-thiadiazol-5-yl)-2-
chlorobenzamide (15g): 70% from 13, colorless crystals. Mp
93.8-95.0 °C dec. IR (KBr): 3540, 3214, 1687, 1550, 1295 cm-1
.
1H NMR (400 MHz, DMSO-d6): δ 2.15 (s, 3H, CH3), 4.05 (s,
2H, -CH2-), 7.44 (td, J1 = 7.2 Hz, J2 = 1.6 Hz, 1H, ArH), 7.51-
7.57 (m, 2H, ArH), 7.66 (dd, J1 = 7.2 Hz, J2 = 1.2 Hz, 1H, ArH),
10.86 (s, 1H, -NHCO-), 13.46 (s, 1H, -NHCOCH3). 13C
702
dx.doi.org/10.1021/op100323b |Org. Process Res. Dev. 2011, 15, 698–703

Organic Process Research & Development
TECHNICAL NOTE
(150 g, 0.26 mol) with NaOH (62.6 g, 1.57 mol) in water (1.25
L) was stirred for 8 h at 100 °C. After completion, the mixture
was cooled to room temperature and acidified with 10% HCl to
pH = 3. The formed crystals were filtered off and washed with
water. Recrystallization from ethanol gave 2 as a white, cotton-
wool-like solid (54.1 g, 48%). Mp 172.8-174.2 °C dec. IR
(12) (a) Carroll, W. A.; Meyer, M. D. PCT Int. Appl. WO/2008/
130953 A2, 2008. (b) Lydie, P.; Valerie, B.; Carole, S.; Roubert, P.;
Pascale, P. U. S. Patent U.S. 7,816,539, 2010.
1
(KBr): 3460, 3348, 1626, 1519 cm-1. H NMR (400 MHz,
DMSO-d6): δ7.19-7.21 (m, 6H, ArH), 7.25-7.34 (m, 9H,
ArH), 8.17 (s, 2H, -NH2). 13C NMR (100 MHz, DMSO-d6):
91.7, 127.3 (3C), 127.7 (6C), 128.3 (6C), 143.1 (3C), 146.1,
162.0, 162.5, 183.1 MS (ESI): m/z (%) 453.1 [M þ Naþ]þ.
HRMS (ESI) m/z calcd for C23H18N4O3S: 430.1100 found:
430.1105. The HPLC analysis was performed on Agilent 1200
HPLC (Chromatographic column: Allima C18 150 mm ꢀ 4.6
mm 5 μm) with DAD UV detector. Mobile phase was water/
acetonitrile/40% Et3N solution = 60:38:2 with a flow rate of
1.0 mL/min. Detection wavelength was 234 nm, and injection
volume was 20 μL.
’ ASSOCIATED CONTENT
S
Supporting Information. Proton NMR and mass spectra
b
of compounds 13, 15a-15 g, 16a, 16b, 17a, and 2. This material
is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
pharmlab@zjut.edu.cn.
’ ACKNOWLEDGMENT
We thank the National Key Technology R&D Program [No:
2007BAI34B00] and National Natural Science Foundation of
China [21076194] for financial support.
’ REFERENCES
(1) Fritsche, T. R.; Sader, H. S.; Jones, R. N. Diagn. Microbiol. Infect.
Dis. 2008, 61, 85–95.
(2) Deresinski, S. C. Diagn. Microbiol. Infect. Dis. 2008, 61, 82–85.
(3) Marti, S.; Sꢀanchez-Cꢀespedes, J.; Espinal, P.; Vila, J. Int. J.
Antimicrob. Agents 2009, 34, 265–267.
(4) Lodise, T. P.; Patel, N.; Renaud-Mutart, A.; Gorodecky, E.;
Fritsche, T. R.; Jones, R. N. Diagn. Microbiol. Infect. Dis. 2008,
61, 96–102.
(5) Barbour, A.; Schmidt, S.; Rand, K. H.; Derendorf, H. Int. J.
Antimicrob. Agents 2009, 34, 1–7.
(6) Vaudaux, P.; Gjinovci, A.; Bento, M.; Li, D. M.; Schrenzel, J.;
Lew, D. P. Antimicrob. Agents Chemother. 2005, 49, 3789–3793.
(7) (a) Glinka, T.; Huie, K.; Cho, A.; Ludwikow, M.; Blais, J.;
Griffith, D.; Hecker, S.; Dudley, M. Bioorg. Med. Chem. 2003,
11, 591–600.(b) Wagman, A. S.; Moser, H. E. PCT Int. Appl. WO/
2010/030810, A1, 2010.
(8) Tatsuta, K.; Kurita, Y.; Inagaki, T.; Yoshida, R. Eur. Pat. Appl.
0536900 A2, 1992.
(9) Tatsuta, K.; Miura, S.; Gunji, H.; Tamai, T.; Yoshida, R.; Inagaki,
T.; Kurita, Y. Bull. Chem. Soc. Jpn. 1994, 67, 1701–1707.
(10) Fanshawe, W. J.; Bauer, V. J.; Safir, S. R. J. Org. Chem. 1965,
30, 2862–2864.
(11) (a) Zvilichovsky, G.; David, M. J. Org. Chem. 1983,
48, 575–579. (b) Tochiro, T.; Kazuhisa, N.; Shuji, K.; Shinji, I.; Hiroshi,
M.; Hiroshi, Y.; Michinao, M.; Takao, S.; Hideomi, F. Chem. Pharm. Bull.
1986, 34, 1643–1655. (c) Liu, T.; Dong, X. W.; Xue, N.; Wu, R.; He,
Q. J.; Yang, B.; Hu, Y. Z. Bioorg. Med. Chem. 2009, 17, 6279–6285.
703
dx.doi.org/10.1021/op100323b |Org. Process Res. Dev. 2011, 15, 698–703