Synthesis and preliminary antibacterial evaluation of 2-butyl succinate-based hydroxamate derivatives containing isoxazole rings

Article abstract of DOI:10.1007/s12272-010-0605-7

Two series of novel 2-butyl succinate-based Hydroxamate derivatives containing isoxazole rings were synthesized, characterized and evaluated for antibacterial activity. The synthesized compounds were found to exhibit weak to moderate inhibitory activity against Staphytlococcus aureu and Klebsiellar pneumonia in vitro. All the compounds synthesized were found to be more effective against Klebsiellar pneumonia compared to Staphytlococcus aureu.

Full text of DOI:10.1007/s12272-010-0605-7

Arch Pharm Res Vol 33, No 6, 831-842, 2010
DOI 10.1007/s12272-010-0605-7
Synthesis and Preliminary Antibacterial Evaluation of 2-Butyl Succi-
nate-based Hydroxamate Derivatives Containing Isoxazole Rings
Datong Zhang1,2, Jiong Jia1, Lijuan Meng1, Weiren Xu3, Lida Tang3, and Jianwu Wang1
1School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China, 2School of
3
Chemical Engineering, Shandong Institute of Light Industry, Jinan, Shandong 250353, China, and Tianjin Key Labora-
tory of Molecular Design and Drug Discovery, Tianjin Institute of Pharmaceutical Research, Tianjin 300193, China
(Received October 19, 2009/Revised March 22, 2010/Accepted March 24, 2010)
Two series of novel 2-butyl succinate-based Hydroxamate derivatives containing isoxazole
rings were synthesized, characterized and evaluated for antibacterial activity. The synthe-
sized compounds were found to exhibit weak to moderate inhibitory activity against Staphyt-
lococcus aureu and Klebsiellar pneumonia in vitro. All the compounds synthesized were found
to be more effective against Klebsiellar pneumonia compared to Staphytlococcus aureu.
Key words: 2-Butyl succinate-based hydroxamate derivatives, Isoxazole, Synthesis, Antibac-
terial activity
step in bacterial protein synthesis is essential for
bacterial proliferation (Giglione et al., 2000). The PDF
INTRODUCTION
Emergence of bacterial resistance to all known inhibitors mentioned above share a common scaffold
classes of antibiotics is a serious threat to humans, of -alkyl substituted succinate and the hydroxamate
δ
and continued discovery of new antibiotics with novel or the carboxylic group can complex the metal ion in
modes of action is urgent to overcoming resistant the active pocket of the peptide deformylase, which is
bacteria (Davies, 1994; Spratt, 1994; Aarons et al., necessary to maintain the enzyme's activity (Clements
1997). Some
δ
-alkyl substituted succinate derivatives et al., 2001; Madison et al., 2002).
have been found to show inhibitory activity against
Recent studies from several research groups have
Gram positive or Gram negative bacteria, such as shown that PDF inhibitors may act as broad-spectrum
actinonin, Sch 382582, VRC3375, macrocyclic inhibitor, antibacterial agents (Lofland et al., 2004; Jain et al.,
etc (Chen et al., 2000, 2004; Chu et al., 2001; Shen et 2005). However, these compounds often suffer from
al., 2008) (Fig. 1). The action mechanism of these com- weak in vivo activity, poor pharmacokinetic properties
pounds is believed to inhibit the peptide deformylase. or selectivity for their apparent peptidic characteri-
Peptide deformylase (PDF) is a ferrous-containing stics (Broughton et al., 1975; Clements et al., 2001;
metalloprotease, which catalyzes the removal of a Lee et al., 2004; Shen et al., 2008). Electron-rich hetero-
formyl group from the N-termini of polypeptides bio- cyclics play an important role in diverse biological
synthesized in prokaryotes (Yuan et al., 2001). This activities. To remove the influence of the hydrolyzable
peptidic structures, we designed two series of confor-
mationally restricted compounds in which isoxazole
Correspondence to: Jianwu Wang, School of Chemistry and
heterocycle was incorporated to replace the amide
Chemical Engineering, Shandong University, No 27, Shandan-
fragment of PDF inhibitors to work as an amide iso-
anlu, Jinan City, Shandong Province 250100, China
stere (Fig. 2). Such peptidomimetic modification has
led to the discovery of potent and selective αvβ3 receptor
antagonist with good pharmacokinetic properties
(Penning et al., 2006). This strategy has also been
employed to develop potent HIV protease inhibitors
(Chung et al., 1995). The hydroxamate group was
Tel: 86-531-88362708, Fax: 86-531-88564464
E-mail: jwwang@sdu.edu.cn
Datong Zhang, School of Chemical Engineering, Shandong
Institute of Light Industry, Western University Science Park,
Jinan City, Shandong Province 250353, China
Tel: 86-531-89631208, Fax: 86-531-89631207
E-mail: dt_zhang@yahoo.com.cn
831

832
D. Zhang et al.
Fig. 1. Natural and synthetic δ-alkyl substituted succinate derivatives
Fig. 2. Design strategy
retained to fulfill the demand of a common structural analyses were conducted on a Perkin-Elmer 2400
feature of a “chelator + peptidomimetic” scaffold of analyzer. Optical rotations were measured with a WZZ-
PDF inhibitors (Guilloteau et al., 2002; Smith et al., 2 polarimeter. All reagents were used as purchased
2002). For type 2 compounds, the second chiral center from commercial suppliers without further purification.
was constructed to model the actual steric orientation
The synthetic chemical routes employed for the
of the corresponding moiety of PDF inhibitors. In this synthesis of 6a-e, 12a, 12b and 12f is outlined in
paper, we describe the synthesis and preliminary anti- Scheme 1 and Scheme 2. 3-arylisoxazole was chosen
bacterial activity evaluation of some new isoxazole- to be incorporated into the target compounds. The
containing 2-alkyl substituted succinate hydroxamate commercially available compounds 1a-f was treated
derivatives.
with hydroxylamine hydrochloride to give the aromatic
oximes, which underwent a 3+2 dipolar cycloaddition
with propargyl alcohol, in the presence of N-chlorosuc-
cinimide and triethylamine, to provide the 3-aryl-5-
hydroxy- methylisoxazoles 2a-f. The hydroxy group of
MATERIALS AND METHODS
Chemistry
Melting points were determined by using an XT-4 the primary alcohols was transformed into amine
microscopic apparatus and are uncorrected. Thin- group via methylsulfonylation, azidation and reduc-
layer chromatography (TLC) was performed on Silica tion in turn. The chiral intermediate (R)-2-butylbuta-
Gel F254 plates with visualization by UV or iodine nedioic acid 4-tert-butyl ester was prepared in high ee
1
vapor. H NMR spectra of CDCl3/DMSO-d6 solutions value according to the literature method (Zhang et al.,
(TMS as internal standard) were recorded at Bruker 2006). 5-aminomethyl-3-arylisoxazoles 3a-e was coupled
DPX300 and DPX400 spectrometers, respectively. The with the chiral succinate with the acceleration of 1-
IR spectra were measured on a Bruker Vector FT-IR chloro-3, 5-dimethoxy-2, 4, 6-triazine (CDMT) and N-
spectrophotometer as KBr pellets or film. Mass spectra methyl morpholine (NMM) (Kamiski, 1987). After de-
were obtained with an API4000 spectrometer. Elemental protection and esterification, the methyl esters 5a-e

Synthesis of 2-Butyl Succinate Hydroxamates Containing Isoxazole Rings
833
Scheme 1. Synthetic route of type 1 compounds. (i) Na2CO3, CH3OH/H2O; propargyl alcohol, NCS/Et3N/CH2Cl2 (ii) MsCl/
NEt3; NaN3/DMF; Zn/NH4Cl (iii) (R)-2-butylbutanedioic acid 4-tert-butyl ester, CDMT/NMM/CH2Cl2 (iv) HCOOH; CH3OH/
DCC/DMAP (v) NH2OH, NaCN, CH3OH/THF
Scheme 2. Synthetic route of type 2 compounds. (i) PCC, CH2Cl2 (ii) R2MgBr, THF (iii) MsCl/NEt3; NaN3/DMF; Zn/NH4Cl
(iv) (R)-2-butylbutanedioic acid 4-tert-butyl ester, CDMT, NMM, CH2Cl2 (v) HCOOH; CH3OH/DCC/DMAP (vi) NH2OH,
NaCN, CH3OH/THF
were transformed into hydroxamates via a cyanide- to afford the secondary alcohols. The hydroxyl group
catalyzed hydroxylamination procedure (Ho et al., of compounds 8a
2005). amine via the three-step reaction sequence. The
Oxidation of 3-aryl-5-hydroxymethylisoxazoles 3a synthesis of target compounds 12a 12b and 12f was
, 8b and 8f was transformed into
,
,
3b and 3f with PCC produced 3-arylisoxazole-5- achieved using procedures similar to that depicted in
carbaldehyde, which reacted with the Grignard reagents Scheme 1.

834
D. Zhang et al.
5-Hydroxymethyl-3-phenylisoxazole (2f)
Slightly yellow solid, yield 61.7%, mp 52-53.5oC. 1H
: 4.75 (s, 2H), 6.40 (s, 1H),
General procedure for the synthesis of com-
pounds (2a-f)
A mixture of NH2OH·HCl (8.34 g, 0.12 mol), aroma- NMR (CDCl3, 400 MHz)
δ
tic aldehyde (0.1 mol), methanol (50 mL) and water 7.32-7.35 (m, 3H), 7.72-7.75 (m, 2H).
(150 mL) was stirred at room temperature until the
solution turned clear. Sodium carbonate (6.36 g, 0.06
mol) was added slowly to the solution and then the
mixture was stirred for additional 4 h. 200 mL of
General procedure for the synthesis of com-
pounds (3a-e)
To a solution of substituted 5-hydroxymethyl-3-
water was added and the resulting aqueous solution phenylisoxazole (17.18 mmol) and triethylamine (2.08
was extracted with dichloromethane. The combined g, 20.57 mmol) in dichloromethane (30 mL) was added
organic phase was washed with water, brine and a solution of mesyl chloride (2.36 g, 20.57 mmol) in
dried over sodium sulfate. The solvent was removed to dichloromethane (10 mL) at 0oC. The mixture was
afford the desired aromatic oximes.
stirred under 5oC for 1 h and then stirred at room
N-chlorosuccinimide (3.2 g, 24.06 mmol) was added temperature for 10 h. The resulting mixture was
portionwise to a solution of substituted benzaldoxime washed with 20% sodium carbonate solution (10 mL),
(20 mmol) in dry dichloromethane (30 mL). After stirred brine (10 mL) and dried over sodium sulfate. The
at room temperature for 40 min, propargyl alcohol solvent was removed to afford the mesylate intermedi-
(1.12 g, 20.00 mmol) was added to the solution followed ates as white solid
.
by triethylamine (2.20 g, 21.78 mmol). The mixture The white solid obtained was dissolved in dry DMF
was heated to reflux for 4 h and then cooled to room (20 mL) and sodium azide (1.98 g, 30.47 mmol) was
temperature. The reaction mixture was washed with added slowly to the solution. The reaction mixture
brine (10 mL), dried over sodium sulfate and concen- was stirred at 55oC for 8 h. 250 mL of water was added
trated. The residue was purified on silica gel column, and the resulting aqueous solution was extracted with
eluting with petroleum ether/EtOAc (3:1) to provide ethyl ether (4 × 60 mL). The combined organic phase
compounds 2a-f
.
was washed with water (60 mL), brine (60 mL) and
dried over sodium sulfate. The organic solvent was
removed to afford the azide intermediates as yellow
3-
Slightly yellow solid, yield 75%, mp 73.5-74oC. H solid.
NMR (CDCl3, 400 MHz) : 4.82 (s, 2H), 6.72 (s, 1H),
7.37 (m, 2H), 7.49 (m, 1H), 7.72 (m, 1H).
o-Chlorophenyl-5-hydroxymethylisoxazole (2a)
1
δ
To a solution of azide intermediates obtained above
in ethyl alcohol (30 mL) and water (7 mL) was added
Zinc powder (1.44 g, 22.18 mmol) and ammonium
5-Hydroxymethyl-3-
p-methylphenylisoxazole (2b) chloride (1.58 g, 29.56 mmol). The mixture was stirred
Slightly yellow solid, yield 71%, mp 73-74oC. 1H NMR at reflux for 0.5 h and then cooled to room temper-
(CDCl3, 90 MHz)
= 7.8 Hz, 2H), 7.63 (d,
δ
: 4.75 (s, 2H), 6.49 (s, 1H), 7.21 (d,
J
ature. Ethyl acetate (100 mL) and 15% sodium
hydroxide aqueous solution (100 mL) was introduced
to the reaction mixture. The organic phase was
separated, washed with brine (20 mL) and dried with
J
= 7.8 Hz, 2H).
3-p-Chlorophenyl-5-hydroxymethylisoxazole (2c)
Slightly yellow solid, yield 75%, mp 99.5-100oC. H sodium sulfate. Removal of the solvent provide
1
NMR (CDCl3, 90 MHz)
δ
: 4.79 (s, 2H), 6.51 (s, 1H), compound 3a-e
.
7.39 (d, = 9 Hz, 2H), 7.69 (d,
J
J = 9 Hz, 2H).
5-Aminomethyl-3-o-chlorophenylisoxazole (3a)
1
5-Hydroxymethyl-3-
m
-trifluoromethylphenylisoxa- Slightly yellow liquid, yield 55.6%. H NMR (CDCl3,
zole (2d)
400 MHz) : 3.60 (s, 2H), 6.24 (s, 1H), 6.89-6.96 (m,
δ
Slightly yellow liquid, yield 70%. 1H NMR (CDCl3, 90 2H), 7.05-7.07 (m, 1H), 7.32-7.34 (m, 1H); IR (KBr,
ν/
MHz) δ
: 4.85 (s, 2H), 6.59 (s, 1H), 7.45-7.71 (m, 2H), cm-1) 3311, 3374, 3065; ESI-MS m/z 209 [M+H]+.
7.89-8.01 (m, 2H).
5-Aminomethyl-3-
White solid, yield 75%, mp 63.3-64.5oC. 1H NMR
(CDCl3, 400 MHz) : 4.00 (s, 2H), 6.41 (s, 1H), 7.25 (d,
= 8 Hz, 2H), 7.68 (d, = 8 Hz, 2H); IR (KBr,
/cm-1)
p-methylphenylisoxazole (3b)
3-(3,4-Dichlorophenyl)-5-hydroxymethylisoxazole
(2e)
δ
1
Slightly yellow solid, yield 73%, mp 106-108oC. H
J
J
ν
NMR (CDCl3, 90 MHz)
7.42-7.65 (m, 2H), 7.82 (d,
δ
: 4.81 (s, 2H), 6.51 (s, 1H), 3359, 3385, 3017; ESI-MS m/z 189 [M+H]+, 211
J
= 1.5 Hz, 1H).
[M+Na]+.

Synthesis of 2-Butyl Succinate Hydroxamates Containing Isoxazole Rings
835
5-Aminomethyl-3-
White solid, yield 75%, mp 78.8-79.4oC. 1H NMR 35.5 (
(CDCl3, 400 MHz) : 4.02 (s, 2H), 6.42 (s, 1H), 7.42 (d, 0.82 (t,
= 8 Hz, 2H), 7.72 (d, = 8 Hz, 2H); IR (KBr,
/cm-1) 2.26 (dd,
3356, 3484, 3044; ESI-MS m/z 209 [M+H]+.
= 8.4, 16 Hz, 1H), 2.58-2.71 (m, 1H), 4.42 (t,
Hz, 2H), 6.75 (s, 1H), 7.31 (d,
= 8 Hz, 2H); IR (KBr,
/cm-1) 3303, 3055, 2958, 5931,
2861, 1727, 1654, 1545, 1154; ESI-MS m/z 401 [M+H]+.
p
-chlorophenylisoxazole (3c)
White solid, yield 85%, mp 101.5-103.5oC, [δ D
]
= +
δ:
20
1
c
1, CHCl3). H NMR (DMSO-d6, 400 MHz)
δ
J = 7.1 Hz, 3H), 1.19-1.60 (m, 6H), 1.35 (s, 9H),
J
J
ν
J
= 5.4, 16 Hz, 1H), 2.35 (s, 3H), 2.46 (dd,
J
= 5.7
J
J
= 8 Hz, 2H), 7.70 (d, J
5-Aminomethyl-3-
m
-trifluoromethylphenylisoxa-
ν
zole (3d)
White solid, yield 70%, mp 43.5-44.5oC. 1H NMR
(CDCl3, 400 MHz)
δ
: 4.03 (s, 2H), 6.49 (s, 1H), 7.46- N-[(3-
J = 8.3 Hz, 2H); IR (KBr, ν
p
-chlorophenylisoxazol-5-yl)-methyl]-(R)-2-
7.74 (m, 2H), 7.93 (d,
/cm-1) tert-butoxycarbonylmethylhexanamide (4c)
3330, 1327; ESI-MS m/z 243 [M+H]+, 265 [M+Na]+.
White solid, yield 81%, mp 115-117oC, [δ D
1, CHCl3). 1H NMR (DMSO-d6, 400 MHz)
= 7.1 Hz, 3H), 1.19-1.60 (m, 6H), 1.35 (s, 9H), 2.26 (dd,
= 5.5, 16 Hz, 1H), 2.46 (dd, = 8.9, 16 Hz, 1H), 2.56-
= 5.7 Hz, 2H), 6.83 (s, 1H), 7.58
= 6.8 Hz, 2H), 7.83 (d, = 6.8 Hz, 2H); IR (KBr,
/cm-1) 3319, 3090, 2976, 2931, 2862, 1732, 1655,
ν
/cm-1) 3321, 3384, 3082; ESI-MS 1552, 1155; ESI-MS m/z 421[M+H]+.
]
20 = + 43.5 (
c
δ: 0.82 (t,
J
5-Aminomethyl-3-(3,4-dichlorophenyl)isoxazole
(3e)
J
J
White solid, yield 73%, mp 96.1-96.6oC. 1H NMR 2.71 (m, 1H), 4.42 (t,
J
(CDCl3, 400 MHz)
δ
: 4.03 (s, 2H), 6.43 (s, 1H), 7.51 (d, (d,
J
J
J
= 8 Hz, 1H), 7.62 (dd,
J
= 2, 8 Hz, 1H), 7.88 (d,
J
=
ν
2 Hz, 1H); IR (KBr,
m/z 243 [M+H]+.
N-[(3-m-trifluoromethylphenylisoxazol-5-yl)-me-
thyl]-(R)-2-tert-butoxycarbonylmethylhexanamide
(4d)
General procedure for the synthesis of com-
pounds (4a-e)
4, 6-Dimethoxy-2-chloro-1, 3, 5-triazine (CDMT) (424 White solid, yield 90%, mp 51-53oC, [δ D
]
20 = + 44.0 (
c
1,
=
J
1
mg, 2.42 mmol) and (R)-(+)-2- butylbutanedioic acid-4- CHCl3). H NMR (DMSO-d6, 400 MHz)
δ: 0.83 (t,
J
tert-butyl monoester (506 mg, 2.2 mmol) were dis- 7.1 Hz, 3H), 1.19-1.60 (m, 6H), 1.35 (s, 9H), 2.26 (dd,
solved in dry methylene dichloride (15 mL). N-methyl- = 5.4, 16 Hz, 1H), 2.50 (dd,
morpholine (267 mg, 2.64 mmol) was added at -5-0oC. 2.65 (m, 1H), 4.43 (dd,
= 5.6, 16 Hz, 1H), 4.50 (dd,
After 4 h, substituted 5-aminomethyl-3-phenylisoxa- = 5.9, 16 Hz, 1H), 6.97 (s, 1H), 7.77 (t, = 7.8 Hz, 1H),
zole (3a-e) (2.31 mmol) was added to the reaction mix- 7.88 (d, = 7.9Hz, 1H), 8.10 (s, 1H), 8.15 (d, = 7.8 Hz,
/cm-1) 3296, 3075, 2960, 2932, 2862,
J
= 9.1, 16 Hz, 1H), 2.58-
J
J
J
J
J
ture. The mixture was stirred at the same temperature 1H); IR (KBr,
ν
for 2 h, then overnight at room temperature. The 1725, 1655, 1543, 1156; ESI-MS m/z 455 [M+H]+.
precipitate produced was removed by suction filtration
and washed with a small amount of methylene N-[[[3-(3,4-dichlorophenyl)isoxazol]-5-yl]methyl]-
dichloride. The filtrate was washed with water, 0.5 N (R)-2-tert-butoxycarbonylmethylhexanemide (4e)
HCl, saturated NaHCO3, brine successively and dried White solid, yield 92%, mp 99-101oC, [δ D
= + 49.5 (c
20
]
with sodium sulfate. The solvent was concentrated, 1, CHCl3). 1H NMR (DMSO-d6, 400 MHz)
and the residue was purified on silica gel with petro- = 6.8 Hz, 3H), 1.19-1.60 (m, 6H), 1.35 (s, 9H), 2.26 (dd,
leum ether/EtOAc (1:1). = 5.5, 16 Hz, 1H), 2.49 (dd, = 8.8, 16 Hz, 1H), 2.58-
2.65 (m, 1H), 4.42 (m, 2H), 6.92 (s, 1H), 7.78 (d,
Hz, 1H), 7.83 (dd, = 1.9, 8.4 Hz, 1H), 8.06 (d,
δ: 0.83 (t, J
J
J
J
J
= 8.4
= 1.9
N-[(3-
o
-chlorophenyisoxazol-5-yl)-methyl]-(R)-2-
J
tert-butoxycarbonylmethylhexanamide (4a)
Hz, 1H); IR (KBr,
ν
/cm-1) 3300, 3086, 2931, 2860,
Colorless liquid, yield 80%, [δ D
1H NMR (DMSO-d6, 400 MHz)
]
20 = + 18.5 (
c
1, CHCl3). 1731, 1653, 1556, 1155; ESI-MS m/z 455 [M+H]+.
δ: 0.82 (t,
J
= 7.1 Hz,
J = 5.3,
3H), 1.19-1.60 (m, 6H), 1.33 (s, 9H), 2.26 (dd,
16 Hz, 1H), 2.46 (dd, = 9.2, 16 Hz, 1H), 2.58-2.71 (m,
1H), 4.48 (d, = 5.8 Hz, 2H), 6.68 (s, 1H), 7.47-7.55
(m, 2H), 7.61-7.67 (m, 2H); IR (KBr,
3065, 2958, 2931, 2861, 1727, 1655, 1546, 1154; ESI- 7 h. Removal of the solvent under vacuum gave a
General procedure for the synthesis of com-
pounds (5a-e)
J
J
A solution of compound 4a-e (1.66 mmol) in formic
ν
/cm-1) 3300, acid (98%, 8 mL) was stirred at room temperature for
MS m/z 421 [M+H]+.
white solid. The white solid was added to CH2Cl2 (12
mL), followed by methanol (3 mL) and 4-dimethyl-
aminopyridine (0.158 mmol). After cooled to 0oC, DCC
(342 mg, 1.66 mmol) was added and the solution was
N-[(3-p-methylphenylisoxazol-5-yl)-methyl]-(R)-
2-tert-butoxycarbonylmethylhexanamide (4b)

836
D. Zhang et al.
stirred at the same temperature for 0.5 h. Then the N-[[[3-(3,4-dichlorophenyl)isoxazol]-5-yl]-methyl]-
reaction was continued at room temperature for 8 h. (R)-2-methoxycarbonylmethylhexanamide (5e)
The precipitate produced was removed by suction White solid, yield 82%, mp 136-138oC, [δ D
]
20 = + 45.0 (
: 0.82 (t,
= 5.2, 16
c
J
filtration. The solvent was concentrated, and the 1, CHCl3). 1H NMR (DMSO-d6, 400 MHz)
residue was purified on silica gel with petroleum = 7.2 Hz, 3H), 1.18-1.51 (m, 6H), 2.38 (dd,
δ
J
ether/EtOAc (3:1).
Hz, 1H), 2.59 (dd,
1H), 3.56 (s, 3H), 4.45 (d,
J
= 8.9, 16 Hz, 1H), 2.65-2.69 (m,
= 5.7 Hz, 2H), 6.93 (s, 1H),
J
N-[(3-
methoxycarbonylmethylhexanamide (5a)
White solid, yield 78.9%, mp 80.5-82.5oC, [δ D
1, CHCl3). 1H NMR (DMSO-d6, 400 MHz)
= 7.2 Hz, 3H), 1.18-1.50 (m, 6H), 2.38 (dd,
Hz, 1H), 2.58 (dd, = 9.2, 16 Hz, 1H), 2.65-2.69 (m,
1H), 3.54 (s, 3H), 4.48 (d, = 5.8 Hz, 2H), 6.67 (s, 1H),
7.78-7.54 (m, 2H), 7.62-7.68 (m, 2H); IR (KBr,
/cm-1)
o
-chlorophenyisoxazol-5-yl)-methyl]-(R)-2-
7.79 (d,
8.08 (d,
J
J
= 8.4 Hz, 1H), 7.84 (dd,
= 1.9 Hz, 1H), 8.67 (t,
J
J
=1.9, 8.4 Hz, 1H),
= 5.7 Hz, 1H); IR
]
20 = + 32.5 (KBr,
: 0.82 (t, MS m/z 414 [M+H]+.
J = 5.1, 16
ν
/cm-1) 3269, 3051, 1733, 1640, 1541, 1179; ESI-
(
J
c
δ
J
General procedure for the synthesis of com-
pounds (6a-e)
To a methanol/tetrahydrofuran (4 mL, 1:1) solution
J
ν
3302, 3067, 2955, 2930, 2859, 1737, 1654, 1603, 1542, of compound 5a-e (1.06 mmol) was added 50% aqueous
1171; ESI-MS m/z 380 [M+H]+.
hydroxylamine (10.6 mmol), followed by NaCN (40
mg). After 5 h, several drops of acetic acid were added
to adjust the pH of the reaction mixture to 6. The solu-
tion was concentrated and the residue was purified on
= + silica gel with methylene dichloride/methanol (20:1).
N-[(3-
2-methoxycarbonylmethylhexanamide (5b)
White solid, yield 75%, mp 109.5-111.5oC, [δ D
p-methylphenylisoxazol-5-yl)-methyl]-(R)-
]
20
1
43.5 (
0.82 (t,
2.38 (dd,
1H), 2.65-2.69 (m, 1H), 3.56 (s, 3H), 4.42 (d,
Hz, 2H), 6.73 (s, 1H), 7.31 (d, = 8 Hz, 2H), 7.70 (d,
= 8 Hz, 2H); IR (KBr,
/cm-1) 3277, 3076, 2955, 2928, 0.79 (t,
2859, 1730, 1645, 1550, 1171; ESI-MS m/z 360 [M+H]+. 2H), 2.45-2.68 (m, 1H), 4.36-4.52 (m, 2H), 6.69 (s, 1H),
7.47 (t, = 7.4 Hz, 1H), 7.53 (t, = 7.5 Hz, 1H), 7.63 (d,
= 7.8 Hz, 1H), 7.67 (d, = 7.5 Hz, 1H); IR (KBr,
/cm-1)
c
1, CHCl3). H NMR (DMSO-d6, 400 MHz)
= 7.2 Hz, 3H), 1.18-1.50 (m, 6H), 2.35 (s, 3H), (R)-2-Butyl-N4-hydroxy-N1-[(3-
= 5.2, 16 Hz, 1H), 2.59 (dd, = 9, 16 Hz, xazol-5-yl)-methyl]succinamide (6a)
= 5.8 White solid, yield 66.8%, mp 132-134.5oC, [δ D
δ:
J
o-chlorophenyiso-
J
J
J
]
= +
20
1
J
J
18.5 (
c
0.5, MeOH). H NMR (DMSO-d6, 400 MHz)
δ:
ν
J = 7.1 Hz, 3H), 1.15-1.46 (m, 6H), 2.01-2.29 (m,
J
J
N-[(3-
methoxycarbonylmethylhexanamide (5c)
White solid, yield 88%, mp 105.5-107.5oC, [δ D
p-chlorophenylisoxazol-5-yl)-methyl]-(R)-2-
J
J
ν
3296, 3062, 2958, 2923, 2855, 1624, 1543; ESI-MS m/z
]
= + 380 [M+H]+; Anal. Calcd for C18H22ClN3O4: C, 56.92; H,
20
1
45.5 (
0.82 (t,
= 5.2, 16 Hz, 1H), 2.59 (dd,
(m, 1H), 3.56 (s, 3H), 4.44 (d,
1H), 7.58 (d, = 8.5 Hz, 2H), 7.70 (d,
IR (KBr,
/cm-1) 3277, 3068, 2959, 2928, 2857, 1731,
1641, 1541, 1174; ESI-MS m/z 380 [M+H]+.
c
1, CHCl3). H NMR (DMSO-d6, 400 MHz)
= 7.2 Hz, 3H), 1.18-1.51 (m, 6H), 2.39 (dd,
= 9, 16 Hz, 1H), 2.65-2.69 (R)-2-Butyl-N4-hydroxy-N1-[(3-
= 5.8 Hz, 2H), 6.81 (s, xazol-5-yl)-methyl]succinamide
= 8.5 Hz, 2H); White solid, yield 51.5%, mp 143-145oC, [δ D
δ
:
5.84; N, 11.06; found C, 57.04; H, 5.90; N, 10.93.
J
J
J
p
-methylphenyiso-
(
J
6b)
J
J
]
20 = + 20.0
0.5, MeOH). H NMR (DMSO-d6, 400 MHz) : 0.82
= 7.2 Hz, 3H), 1.15-1.51 (m, 6H), 2.01-2.41 (m,
2H), 2.36 (s, 3H), 2.47-2.68 (m, 1H), 4.41 (d, = 5.6
Hz, 2H), 6.76 (s, 1H), 7.30 (d, = 8 Hz, 2H), 7.73 (d,
= 8 Hz, 2H); IR (KBr,
/cm-1) 3276, 3070, 2960, 2926,
2855, 1628, 1542; ESI-MS m/z 360 [M+H]+; Anal.
1
ν
(c
δ
(t,
J
J
N-[(3-m-trifluoromethylphenylisoxazol-5-yl)me-
J
J
thyl]-(R)-2-methoxycarbonylmethylhexanemide
(5d)
ν
White solid, yield 78.5%, mp 104-106oC, [δ D
]
20 = + 50.5 Calcd for C19H25N3O4: C, 63.49; H, 7.01; N, 11.69; found
1, CHCl3). 1H NMR (DMSO-d6, 400 MHz)
: 0.82 (t, C, 63.58; H, 6.95; N, 11.71.
= 7.2 Hz, 3H), 1.18-1.51 (m, 6H), 2.38 (dd, = 5.2, 16
Hz, 1H), 2.59 (dd,
= 9, 16 Hz, 1H), 2.65-2.69 (m, 1H), (R)-2-Butyl-N4-hydroxy-N1-[(3-
3.56 (s, 3H), 4.46 (d, = 5.7 Hz, 2H), 6.96 (s, 1H), 7.71 xazol-5-yl)-methyl]succinamide (6c)
(t, = 7.8 Hz, 1H), 7.88 (d,
= 7.8 Hz, 1H), 8.12 (s, White solid, yield 45%, mp 146-148oC, [δ D
1H), 8.16 (d, = 7.8 Hz, 1H); IR (KBr,
/cm-1) 3296, 0.6, MeOH). 1H NMR (DMSO-d6, 400 MHz)
(c
δ
J
J
J
p-chlorophenyiso-
J
J
J
]
20 = + 21.0 (
: 0.82 (t,
= 6.9,
= 7.1, 14.4 Hz, 1H), 2.65-2.72
(m, 1H), 4.37-4.49 (m, 2H), 6.84 (s, 1H), 7.57 (d,
c
J
ν
δ
3068, 2960, 2928, 2856, 1739, 1645, 1546, 1327, 1124;
J
= 7.1 Hz, 3H), 1.17-1.51 (m, 6H), 2.06 (dd,
J
ESI-MS m/z 414[M+H]+.
14.4 Hz, 1H), 2.24 (dd,
J
J
=

Synthesis of 2-Butyl Succinate Hydroxamates Containing Isoxazole Rings
837
8.4 Hz, 2H), 7.87 (d,
3298, 3216, 3068, 2958, 2927, 2857, 1649, 1555; ESI- Slightly yellow solid, yield 65%, mp 67-69oC. 1H NMR
MS m/z 380 [M+H]+; Anal. Calcd for C18H22ClN3O4: C, (CDCl3, 400 MHz)
: 7.28 (s, 1H), 7.49-7.51 (m, 3H),
56.92; H, 5.84; N, 11.06; found C, 56.84; H, 5.87; N, 7.83-7.86 (m, 2H), 10.03 (s, 1H); IR (KBr,
/cm-1) 3048,
J = 8.4 Hz, 2H); IR (KBr, ν
/cm-1) 3-Phenylisoxazole-5-carbaldehyde (7f)
δ
ν
11.12.
2857, 1704; ESI-MS m/z 174 [M+H]+.
(R)-2-Butyl-N4-hydroxy-N1-[(3-
m-trifluoromethyl-
phenyisoxazol-5-yl)-methyl]succinamide (6d)
General procedure for the synthesis of com-
pounds (8a, 8b, and 8f)
White solid, yield 55%, mp 140.5-142.5oC, [δ D
]
= + 0.23 g of magnesium powder was covered with 5 mL of
δ:
20
28.1 (
0.82 (t,
(m, 2H), 2.50-2.70 (m, 1H), 4.44-4.47 (m, 2H), 6.97 (s, tetrahydrofuran was added dropwise under N2 to keep
1H), 7.76 (t, = 7.7 Hz, 1H), 7.86 (d, = 7.7 Hz, 1H), the reaction mixture boiling slightly. When the addi-
c
0.82, MeOH). 1H NMR (DMSO-d6, 400 MHz)
tetrahydrofuran, and an iodine crystal was added. A
J
= 7.2 Hz, 3H), 1.19-1.48 (m, 6H), 2.01-2.45 solution of n-bromobutane (1.0 g, 7.3 mmol) in 2 mL of
J
J
8.15-8.19 (m, 1H); IR (KBr, ν
/cm-1) 3310, 3224, 3076, tion was complete, the mixture was refluxed for further
2952, 2930, 2861, 1628, 1555; ESI-MS m/z 414 [M+H]+; 1 h and then cooled to room temperature. The Grignard
Anal. Calcd for C19H22F3N3O4: C, 55.20; H, 5.36; N, reagent obtained was introduced slowly to a solution
10.16; found C, 55.30; H, 5.29; N, 10.18.
of substituted 3-phenylisoxazole-5-carbaldehyde (2.6
mmol) in 20 mL of tetrahydrofuran in an ice bath.
(R)-2-Butyl-N4-hydroxy-N1-[[[3-(3,4-dichlorophenyl) After the addition, the stirring was continued for 3 h
isoxazol]-5-yl]-methyl]succinamide (6e)
and then for additional 10 h at room temperature. 20
White solid, yield 85%, mp 145-147.5oC, [δ D
]
20 = + 13.6 mL of 10% aqueous ammonium chloride was added
(
(t,
c
0.85, MeOH). 1H NMR (DMSO-d6, 400 MHz)
J
δ
: 0.82 and the mixture was extracted by CH2Cl2 (20 mL × 3).
= 7.1 Hz, 3H), 1.15-1.45 (m, 6H), 2.01-2.42 (m, The organic phase was dried over Na2SO4 and concen-
2H), 2.45-2.69 (m, 1H), 4.37-4.48 (m, 2H), 6.91 (s, 1H), trated at reduced pressure. The residue was purified
7.77 (d, = 8 Hz, 1H), 7.86 (d, = 8 Hz, 1H), 8.11 (s, on silica gel with petroleum ether/EtOAc (9:1)
1H); IR (KBr,
/cm-1) 3290, 3179, 3029, 2957, 2930,
2859, 1649, 1558; ESI-MS m/z 414 [M+H]+; Anal. 1-[3-(
Calcd for C18H21Cl2N3O4: C, 52.19; H, 5.11; N, 10.14; 1-ol (8a)
J
J
ν
o-Chlorophenyl)isoxazol-5-yl]-3-methylbutan-
found C, 52.17; H, 5.05; N, 10.21.
Light yellow sticky liquid, yield 75%. 1H NMR (CDCl3,
400 MHz) : 0.97 (d, = 8 Hz, 3H), 0.99 (d, = 8 Hz,
3H), 1.77-1.90 (m, 3H), 4.98-5.01 (m, 1H), 6.66 (s, 1H),
7.35 (dt, = 7.2, 1.6 Hz, 1H), 7.38 (dt, = 7.6, 2 Hz,
= 7.6, 2 Hz, 1H), 7.72 (dd, = 7.2, 2
/cm-1) 3364, 3036, 1605; ESI-MS
δ
J
J
General procedure for the synthesis of com-
pounds (7a, 7b, and 7f)
J
J
To a solution of PCC (3.23 g, 15 mmol) in CH2Cl2 (20 1H), 7.48 (dd,
J
J
mL) was added substituted 5-Hydroxymethyl-3-pheny- Hz, 1H); IR (KBr,
lisoxazole (10 mmol). The mixture was stirred at room m/z 265 [M+H]+.
temperature for 3 h and monitored by TLC. After the
ν
end of reaction, the reaction mixture was filtered 1-[3-(p-Methylphenyl)isoxazol-5-yl]-3-methylbutan-
through a pad of silica gel and washed with petroleum 1-ol (8b)
ether/EtOAc(9:1). The solvent was concentrated, and Light yellow sticky liquid, yield 70%. 1H NMR (CDCl3,
the residue was purified on silica gel with petroleum 400 MHz)
ether/EtOAc (9:1). 3H), 1.72-1.76 (m, 3H), 2.40 (s, 3H), 4.95-4.98 (m, 1H),
6.49 (s, 1H), 7.26 (d, = 8 Hz, 2H), 7.69 (d, = 8 Hz,
2H); IR (KBr,
/cm-1) 3367, 3065, 1607; ESI-MS m/z
Slightly yellow liquid, yield 60%. 1H NMR (CDCl3, 300 246 [M+H]+.
δ: 0.96 (d, J = 8 Hz, 3H), 0.98 (d, J = 8 Hz,
J
J
3-o-Chlorophenylisoxazole-5-carbaldehyde (7a)
ν
MHz)
δ
: 7.36-7.47 (m, 2H), 7.49 (s, 1H), 7.50-7.53 (m,
1H), 7.77-7.80 (m, 1H), 10.03 (s, 1H); IR (KBr,
ν
/cm-1) 1-(3-Phenylisoxazol-5-yl)pentan-1-ol (8f)
3051, 2856, 1703; ESI-MS m/z 208 [M+H]+.
Light yellow sticky liquid, yield 72%. 1H NMR (CDCl3,
400 MHz)
1.88-1.96 (m, 2H), 4.88-4.91 (m, 1H), 6.51 (s, 1H), 7.43-
White solid, yield 55%, mp 77-79oC. H NMR (CDCl3, 7.47 (m, 3H), 7.79-7.81 (m, 2H); IR (KBr, /cm-1) 3353,
400 MHz) : 2.44 (s, 3H), 7.28 (s, 1H), 7.33 (d,
= 7.8 3045, 1608; ESI-MS m/z 232 [M+H]+.
Hz, 2H), 7.77 (d, = 7.8 Hz, 2H), 10.04 (s, 1H); IR (KBr,
/cm-1) 3045, 2857, 1704; ESI-MS m/z 188 [M+H]+.
δ: 0.93 (t, J = 5.2 Hz, 3H), 1.35-1.50 (m, 4H),
3-p-Methylphenylisoxazole-5-carbaldehyde (7b)
1
ν
δ
J
J
ν

838
D. Zhang et al.
3371, 3035,1607; ESI-MS m/z 231 [M+H]+.
General procedure for the synthesis of com-
pounds (9a, 9b, and 9f)
To an ice-cooled mixture of compounds
and triethylamine (0.25 g, 2.5 mmol) in CH2Cl2 (25
mL) was added Mesyl chloride (0.26 g, 2.3 mmol) in
8 (2 mmol)
General procedure for the synthesis of com-
pounds (10a, 10b, and 10f)
4, 6-Dimethoxy-2-chloro-1, 3, 5-triazine (CDMT) (193
CH2Cl2 (5 mL). The reaction mixture was stirred at 0 mg, 1.1 mmol) and (R)-(+)-2- butylbutanedioic acid-4-
to 5oC for 1 h and then for additional 5 h at room tem- tert-butyl monoester (230 mg, 1 mmol) were dissolved
perature. The mixture was washed with 20% aqueous in dry methylene dichloride (7 mL). N-methylmor-
Na2CO3 solution and water, dried over Na2SO4, and pholine (1.98 mmol) was added at -5-0oC. After 4 h,
evaporated under vacuum to afford a light yellow compound
9 (1.05 mmol) was added to the reaction
sticky liquid. mixture. The mixture was stirred at the same tem-
DMF (15 mL) was added to dissolve the syrupy perature for 2 h, then overnight at room temperature.
residue, followed by NaN3 (0.13 g, 1.94 mmol) and the The precipitate produced was removed by suction
reaction mixture was stirred at room temperature for filtration and washed with a small amount of methy-
5 h. Upon completion of the reaction, as monitored by lene dichloride. The combined washing and filtrate
TLC, 50 mL of water was added and the mixture was were washed with water, 0.5 N HCl, saturated NaHCO3,
extracted with diethyl ether (30 mL × 3). The combined saturated saline successively and dried with sodium
organic phase was washed with water, dried over sulfate. The solvent was concentrated, and the residue
Na2SO4, and evaporated under vacuum. The obtained was purified on silica gel with methylene dichloride/
light-yellow syrup was dissolved in a mixture of methanol (3:1).
ethanol (25 mL) and water (8 mL), Zinc powder (0.13g,
1.95 mmol) and NH4Cl (0.17 g, 3.14 mmol) were added, N-[1-[3-(o-chlorophenyl)isoxazol-5-yl]-3-methyl]
and the mixture was heated to reflux for 0.5 h. After butyl-(R)-2-tert-butoxycarbonylmethylhexan-
cooling to room temperature, 70 mL of ethyl acetate amide (R, R/S, R mixture) (10a)
and 10 mL of 15% aqueous NaOH solution were added White solid, yield 93%, mp 92-94oC, [δ D
]
20 = + 13.0 (
to the mixture. The organic phase was separated, CHCl3). H NMR (DMSO-d6, 400 MHz) : 0.76-0.95
dried and evaporated. The residue was purified on (m, 9H), 1.11-1.48 (m, 15H), 1.63-1.82 (m, 3H), 2.25-
c 1,
1
δ
silica gel with petroleum ether/EtOAc (2:1)
2.27 (m, 1H), 2.46-2.51 (m, 1H), 2.60-2.69 (m, 1H),
5.12-5.20 (m, 1H), 6.68/6.74 (s/s, 1H), 7.45-7.55 (m,
1-[3-(
1-amine (9a)
o
-Chlorophenyl)isoxazol-5-yl]-3-methylbutan- 2H), 7.61-7.67 (m, 2H); IR (KBr, ν
/cm-1) 3291, 3057,
2959, 2932, 2870, 1730, 1645, 1550,1154; ESI-MS m/
Light yellow sticky liquid, yield 57.5%. 1H NMR
z
477 [M+H]+.
(CDCl3, 400 MHz)
= 8 Hz, 3H), 1.65-1.80 (m, 3H), 1.87 (brs, 2H), 4.18- N-[1-[3-(
4.21 (m, 1H), 6.57 (s, 1H), 7.34 (dt, = 7.2, 1.6 Hz, butyl-(R)-2-tert-butoxycarbonylmethylhexan-
1H), 7.37 (dt, = 7.6, 2 Hz, 1H), 7.47 (dd, = 7.6, 2 amide (R, R/S, R mixture) (10b)
Hz, 1H), 7.72 (dd, = 7.2, 2 Hz, 1H); IR (KBr,
/cm-1) White solid, yield 85%, mp 102-104oC, [δ D
3304, 3377, 3063, 1605; ESI-MS m/z 265 [M+H]+. 1, CHCl3). 1H NMR (DMSO-d6, 400 MHz)
(m, 9H), 1.13-1.48 (m, 15H), 1.65-1.82 (m, 3H), 2.25
(dd, = 5.4, 16 Hz, 1H), 2.35 (s, 3H), 2.46 (dd, = 9,
16 Hz, 1H), 2.60-2.69 (m, 1H), 5.06-5.17 (m, 1H), 6.73/
= 1.8, 8 Hz, 2H), 7.70 (dd,
= 8 Hz, =3.7, 8 Hz, 2H); IR (KBr,
/cm-1) 3297, 3059, 1730,
3H), 1.62-1.76 (m, 3H), 1.81 (brs, 2H), 2.39 (s, 3H), 4.14- 1645, 1547, 1154; ESI-MS m/z 457 [M+H]+.
4.18 (m, 1H), 6.39 (s, 1H), 7.25 (d, = 8 Hz, 2H), 7.68
/cm-1) 3304, 3374, 3021, N-[1-(3-phenylisoxazol-5-yl)]pentyl-(R)-2-tert-but-
δ: 0.96 (d, J = 8 Hz, 3H), 0.98 (d, J
p-methylphenyl)isoxazol-5-yl]-3-methyl]
J
J
J
J
ν
]
20 = + 22.5 (
c
δ: 0.76-0.95
3-Methyl-1-[3-(p-methylphenyl)isoxazol-5-yl)butan-
J
J
1-amine (9b)
Light yellow sticky liquid, yield 55%. 1H NMR (CDCl3, 6.76 (s/s, 1H), 7.30 (dd,
J
J
400 MHz)
δ: 0.95 (d,
J
= 8 Hz, 3H), 0.97 (d,
J
ν
J
(d,
J = 8 Hz, 2H); IR (KBr, ν
1606; ESI-MS m/z 245 [M+H]+.
oxycarbonylmethylhexanamide (R, R/S, R mixture)
(10f)
1-(3-Phenylisoxazol-5-yl)pentan-1-amine (9f)
White solid, yield 85%, mp 91-93oC, [δ D
]
20 = + 21.5 (
: 0.76-0.89
= 5.2 Hz, 3H), 1.35-1.42 (m, 4H), (m, 9H), 1.13-1.48 (m, 17H), 1.65-1.82 (m, 2H), 2.25
1.75-1.89 (m, 4H), 4.08-4.11 (m, 1H), 6.42 (s, 1H), 7.42- (dd, = 5.2, 16 Hz, 1H), 2.46 (dd, = 6.5, 16 Hz, 1H),
7.45 (m, 3H), 7.78-7.80 (m, 2H); IR (KBr,
/cm-1) 3305, 2.60-2.69 (m, 1H), 5.03-5.07 (m, 1H), 6.80/6.87 (s/s,
c 1,
1
Light yellow sticky liquid, yield 53%. 1H NMR (CDCl3, CHCl3). H NMR (DMSO-d6, 400 MHz)
δ
400 MHz) δ: 0.91 (t, J
J
J
ν

Synthesis of 2-Butyl Succinate Hydroxamates Containing Isoxazole Rings
839
1H), 7.48-7.52 (m, 3H), 7.80-7.83 (m, 2H); IR (KBr,
ν
/
=5, 16 Hz, 1H), 2.54-2.62 (m, 1H), 2.64-2.72 (m, 1H),
cm-1) 3278, 3068, 2958, 2931, 2861, 1728, 1646, 1548, 3.53/3.57 (s/s, 3H), 5.01-5.07 (m, 1H), 6.80/6.84 (s/s,
1154; ESI-MS m/z 443 [M+H]+.
1H), 7.47-7.54 (m, 3H), 7.82-7.84 (m, 2H); IR (KBr, ν/
cm-1) 3286, 3066, 2955, 2931, 2860, 1737, 1648, 1543,
1173; ESI-MS m/z 401 [M+H]+.
General procedure for the synthesis of com-
pounds (11a, 11b, and 11f)
A solution of compound 10 (0.66 mmol) in formic
acid (98%, 4 mL) was stirred at room temperature for
7 h. Removal of the solvent under vacuum gave a
General procedure for the synthesis of com-
pounds (12a, 12b, and 12f)
To a methanol/tetrahydrofuran (2 mL, 1:1) solution
white solid. The white solid was added to CH2Cl2 (5 of compound 11 (0.449 mmol) was added 50% aqueous
mL), followed by methanol (1 mL) and 4, 4’-dimethyl- hydroxylamine (0.27 mL, 4.49 mmol), followed by
aminopyridine (8 mg, 0.0656 mmol). After cooled to NaCN (20 mg). After 5 h, several drops of acetic acid
0oC, DCC (142 mg, 0.689 mmol) was added and the were added to adjust the pH of the reaction mixture to
solution was stirred at the same temperature for 0.5 6. The solution was concentrated and the residue was
h. Then the reaction was continued at room tempera- purified on silica gel with methylene dichloride/
ture for 12 h. The precipitate produced was removed methanol (20:1).
by suction filtration. The solvent was concentrated, and
the residue was purified on silica gel with petroleum (R)-2-Butyl-N4-hydroxy-N1-[1-[3-(
o-chlorophenyl)
ether/EtOAc (3:1).
isoxazol-5-yl]-3-methyl]butylsuccinamide (R, S/
R, R mixture) (12a)
N-[1-[3-(
o
-chlorophenyl)isoxazol-5-yl]-3-methyl] White solid, yield 61%, mp 97-99oC, [δ D
]
20 = + 11.0 (
c
1
butyl-(R)-2-methoxycarbonylmethylhexanamide
0.68, MeOH). H NMR (DMSO-d6, 400 MHz)
δ: 0.75-
(R, R/S, R mixture) (11a)
0.94 (m, 9H), 1.18-1.50 (m, 6H), 1.68-1.78 (m, 3H),
White solid, yield 80%, mp 83.5- 85.5oC, [δ D
]
20 = + 17.0 2.01-2.06 (m, 1H), 2.15-2.21 (m, 1H), 2.65-2.72 (m,
1, CHCl3). H NMR (DMSO-d6, 400 MHz) : 0.76- 1H), 5.11-5.18 (m, 1H), 6.67/6.76 (s/s, 1H), 7.45-7.55
0.94 (m, 9H), 1.18-1.50 (m, 6H), 1.68-1.77 (m, 3H), (m, 1H), 7.61-7.69 (m, 1H); IR (KBr,
/cm-1) 3268,
2.37 (dd, = 5, 16 Hz, 1H), 2.56 (dd, = 9.3, 16Hz, 3062, 2957, 2930, 2870, 1645, 1616, 1540; ESI-MS m/
1H), 2.63-2.72 (m, 1H), 3.50/3.56 (s/s, 3H), 5.12-5.16
436 [M+H]+; Anal. Calcd for C22H30ClN3O4: C, 60.61;
(m, 1H), 6.67/6.72 (s/s, 1H), 7.47 (dt, = 1.2, 7.4 Hz, H, 6.94; N, 9.64; found C, 60.51; H, 6.85; N, 9.87.
1H), 7.53 (dt, = 1.8, 8 Hz, 1H), 7.63 (dd, = 1.1, 8
Hz, 1H), 7.67 (dd, = 1.5, 8 Hz, 1H); IR (KBr,
/cm-1) (R)-2-Butyl-N4-hydroxy-N1-[1-[3-(
3288, 3065, 2958, 2930, 2870,1739, 1647, 1545, 1173; isoxazol-5-yl]-3-methyl]butylsuccinamide (R, S/
1
(c
δ
ν
J
J
z
J
J
J
J
ν
p-methylphenyl)
ESI-MS m/z 435 [M+H]+.
R, R mixture) (12b)
White solid, yield 68%, mp 135-137oC, [δ D
]
20 = + 20.3 (
c
N-[1-[3-( -methylphenyl)isoxazol-5-yl]-3-methyl]
p
0.91, CHCl3). 1H NMR (DMSO-d6, 400 MHz)
δ: 0.74-
butyl-(R)-2-methoxycarbonylmethylhexanamide
0.93 (m, 9H), 1.13-1.48 (m, 6H), 1.65-1.82 (m, 3H),
2.02-2.10 (m, 1H), 2.18-2.26 (m, 1H), 2.35 (s, 3H), 2.62-
2.70 (m, 1H), 5.05-5.16 (m, 1H), 6.75/6.84 (s/s, 1H),
(R, R/S, R mixture) (11b)
White solid, yield 83%, mp 123-125oC, [δ D
]
20 = + 25.0 (
1, CHCl3). 1H NMR (DMSO-d6, 400 MHz)
(m, 9H), 1.13-1.48 (m, 6H), 1.65-1.82 (m, 3H), 2.35 (s, 3073, 2956, 2929, 2870, 1644, 1616, 1543; ESI-MS m/
3H), 2.38-2.40 (m, 1H), 2.52-2.60 (m, 1H), 2.60-2.69
416 [M+H]+; Anal. Calcd for C23H33N3O4: C, 66.48;
(m, 1H), 3.52/3.56 (s/s, 3H), 5.05-5.16 (m, 1H), 6.76/ H, 8.00; N, 10.11; found C, 66.28; H, 7.90; N, 10.32.
6.80 (s/s, 1H), 7.31 (dd, = 2.8, 8.1 Hz, 2H), 7.71 (dd,
= 2.2, 8.1 Hz, 2H); IR (KBr,
/cm-1) 3304, 3108, 2955, (R)-2-Butyl-N4-hydroxy-N1-[1-(3-phenylisoxazol-5-
c
δ
: 0.75-0.94 7.30 (m, 2H), 7.72 (m, 2H); IR (KBr, ν
/cm-1) 3276,
z
J
J
ν
2932, 2870, 1736, 1652, 1540, 1172; ESI-MS m/z 415 yl)]pentylsuccinamide (R, S/R, R mixture) (12f)
[M+H]+.
White solid, yield 62%, mp 153.5-155.5oC, [δ D
] = +
20
1
15.5 (
c 0.5, MeOH). H NMR (DMSO-d6, 400 MHz) δ:
N-[1-(3-phenylisoxazol-5-yl)]pentyl-(R)-2-methoxy-
0.75-0.89 (m, 6H), 1.15-1.45 (m, 10H), 1.75-1.88 (m,
carbonylmethylhexanamide (R, R/S, R mixture) 2H), 2.01-2.07 (m, 1H), 2.18-2.23 (m, 1H), 2.65-2.74
(11f) (m, 1H), 5.01-5.06 (m, 1H), 6.80/6.88 (s/s, 1H), 7.48-
White solid, yield 95%, mp 61-63oC, [δ D /cm-1) 3270,
1, 7.54 (m, 3H), 7.81-7.88 (m, 2H); IR (KBr,
CHCl3). 1H NMR (DMSO-d6, 400 MHz)
: 0.76-0.89 (m, 3079, 2957, 2929, 2870, 1646, 1619, 1543; ESI-MS m/
6H), 1.23-1.50 (m, 10H), 1.75-1.89 (m, 2H), 2.38 (dd,
402 [M+H]+; Anal. Calcd for C22H31N3O4: C, 65.81;
]
20 = + 24.0 (
δ
c
ν
J
z

840
D. Zhang et al.
H, 7.78; N, 10.47; found C, 65.92; H, 7.85; N, 10.35.
amide carbonyl stretching frequency was observed at
about 1640 cm-1. The other prominent absorption
bands observed in the IR spectrum are 3060 (Ar-H)
In vitro antibacterial activity evaluation
Microdilution broth susceptibility assay was used and 1550 (C=N) cm-1.
for the antibacterial evaluation of the new compounds
1H NMR spectrum of 6a showed a triplet at
δ 0.79
(Koneman et al., 1997; NCCLS documents, 2003). due to the CH3 protons at the terminal of the butyl
Muller-Hinton broth was used as the test medium. group. The six methylene protons of the butyl group
Each compound was tested over a range of doubling resonated as complex multiplets at
dilution concentrations. Tested microorganism strains two methylene protons of the succinate moiety ap-
were Staphylococcus aureus (CMCC26112) and peared as multiplets at 2.01-2.29 with a total integral
Klebsiellar pneumonia (CMCC46117). The minimum of two. The chiral proton of succinate was observed as
inhibitory concentratio ns (MIC) was determined multiplet between 2.45-2.68. A multiplet at 4.36-
δ 1.15-1.46. The
δ
δ
δ
according to the lowest concentration that prevented 4.52 integrating for two protons was attributable to
visible growth of bacteria after incubation at 37°C for the methylene protons adjacent to the isoxazole ring.
24 h. Cefoperazone was used as a standard drug (posi- The proton on the isoxazole resonated as singlet at
δ
1
tive control). Bacterial strains and broth were bought 6.69. H NMR spectrum of 12a showed nine more
from National Institute for the Control of Pharma- protons at 0.75-1.78 than that of 6a. The tertiary
proton adjacent to the isoxazole ring appeared as
multiplet at 5.14. The two singlets at 6.67 and 6.76
δ
ceutical and Biological Products.
RESULTS AND DISCUSSION
Chemistry
δ
δ
having a total integral of one were assigned as the
proton on the isoxazole. The integration values of the
two singlets were approximately 1:1, which meant that
Eight novel 2-butyl succinate-based hydroxamate the compound was composed of a pair of diastereoiso-
derivatives containing isoxazole rings were synthesiz- mers in equal quantities.
ed. 3, 5-disubstituted isoxazoles 2a-f were obtained
utilizing a 3+2 dipolar cycloaddition reaction. To
create the second chiral center in type 2 compounds,
Biological activity
All target compounds (6a-e
,
12a, 12b and 12f) were
3,5-disubstituted isoxazoles 3a, 3b and 3f were oxi- evaluated for their antibacterial activities against
dized with PCC to form 3-arylisoxazole-5-carbaldehyde, Staphylococcus aureus and Klebsiella pneumoniae
which reacted with Grignard reagents to afford the using microbroth dilution method (Koneman et al.,
secondary alcohols 8a, 8b and 8f. The hydroxy group 1997; NCCLS documents, 2003). MICs were recorded
of these 3-aryl-5-(hydroxymethyl)isoxazoles derivatives as the minimum concentration of a compound that
were transformed to amino group via a convenient inhibits the growth of tested microorganisms. The
three-step reaction procedure in modest yield. The MIC values of all the new compounds are generally
condensation of the chiral succinate with the eight 5- within the range of 8-64
aminomethyl-3-arylisoxazoles derivatives (3a-e 9a strains. The observed data on the antimicrobial acti-
9b and 9f) was accelerated by 1-chloro-3, 5-dimethoxy- vity of the compounds and control drug are given in
2, 4, 6-triazine and -methyl morpholine. With the Table I.
combination of the two reagents, high-yield target com- The antibacterial screening data revealed that all
µg/mL against the evaluated
,
,
N
pounds were obtained and the work-up procedures the tested compounds showed weak to moderate
were simple. The free acids, obtained after removal of bacterial inhibition. Compounds 6b and 6e exhibited
the tert-butyl group in 98% formic acid, were trans- moderate activity against the two bacteria. Compound
formed to methyl esters. The reaction of the methyl 6c was effective against K. pneumoniae (MIC value of
esters with 50% aqueous hydroxylamine solution cata-
lyzed by cyanide led to the target hydroxamates in (MIC > 64
8
µ
g/mL), whereas it was less active against S. aureus
µ
g/mL). Compounds 12a 12b and 12f
,
better yield and purity compared with these reported showed weak activity against both S. aureus and K.
methods (Levy et al., 1998; Reddy et al., 2000). Struc- pneumoniae. To the two tested bacteria, all the com-
tures of all the newly synthesized compounds were pounds were found to exhibit better activity against K.
supported by IR, MS, NMR spectral data analysis and pneumoniae.
elemental analysis.
The SAR investigation of the synthesized compounds
In the IR spectrum of these compounds, a broad revealed that variation of the substituents on the
absorption band around 3270 cm-1 indicates the pre- benzene attached at position 3 of isoxazole affected
sence of active hydrogen group in the compounds. The the activity significantly. As can be seen that com-

Synthesis of 2-Butyl Succinate Hydroxamates Containing Isoxazole Rings
841
Table I. Antimicrobial activities of compounds 6a-e, 12a,
12b and 12f (MICa,
g/mL)
vity. It seems the steric changes at this region have a
slight influence on the activity. These preliminary
results are beneficial for further lead optimization.
µ
Compound Staphylococcus aureus Klebsiella pneumoniae
6a
6b
32
16
16
8
ACKNOWLEDGEMENTS
6c
6d
6e
12a
>64
64
16
>64
>64
>64
0.25
8
32
8
32
64
64
0.25
This research was supported by National key Re-
search Priority Program of Science and Technology
Ministry, China (2003CCA027), the Special Project of
Science and Technology of Shandong Province, China
(032090104), and the Key Science and Technology
Project of Shandong Province (No. 2009GG20002027).
12b
12f
Standardb
aThe MIC (
µg/mL) values of reported compounds against
Staphylococcus aureus were: 8-16 (Actinonin) and 1-4
(VRC3375) (Chen et al., 2000, 2004).
bStandard: Cefoperazone
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