â-Lactams and Analogous
â
-Sultams
A R T I C L E S
3.94 (2H, t, J 7.4, CH2sNH); 13C NMR δ (CDCl3) 167.45 (CdO),
133.64 (quaternary carbon), 128.95 (CH (Ph)), 128.44 (CH (Ph)), 56.88
(CH2sSO2), 30.91 (CH2sNH). High-resolution electrospray ionization
mass spectrometry (HREI-MS) [M + H]+ for C9H9NO3S calcd
212.0376, measured 212.0376.
UV-visible spectrophotometer (Varian, Australia) equipped with a
twelve-compartment cell block. The instrument was used in double-
beam mode, allowing six reaction cells to be followed in a single run.
The cell block was thermostated using a peltier system. Stopped-flow
experiments used an SX.18 MV Spectrakinetic monochromator (Ap-
plied Photophysics, Leatherhead, England) equipped with an absorbance
photomultiplier. The reagent syringes were thermostated with a Grant
thermostated water circulator. pH stat experiments were performed on
a ABU 91 Autoburet (Radiometer, Copenhagen, Denmark), controlled
by a VIT 90 video titrator. The SAM 90 sample station incorporated
an aluminum E2000 sample block rotor thermostated by a MGW Lauda
M3 water circulator. pH was measured by a pHG200-8 Glass pH
electrode and a REF200 “Red Rod” reference electrode (Radiometer).
The temperature was monitored by a T101 temperature sensor.
pH measurements were made with either a φ40 (Beckman, Fullerton,
USA) or 3020 (Jenway, Dunmow, England) pH meters. Electrodes were
semi-micro Ag/AgCl and Calomel (Russel, Fife, Scotland, and Beck-
man, respectively). A calibration of the pH meter was carried out at
30 °C using pH 6.99 ( 0.01, pH 4.01 ( 0.02, or pH 10.00 ( 0.02
calibration buffers.
2-(4′-Chlorobenzoyl)-1,2-thiazetidine-1,1-dioxide. Yield 0.89 g
(39%); mp 84-86 °C; IR υmax (cm-1, neat) 1676, 1593, 1404, 1357, 1323,
1159, 1092, 1016; 1H NMR δ (CDCl3) 7.96 (2H, d, J 8.64,), 7.51 (2H,
d, J 8.69,), 4.33 (2H, t, J 7.10, CH2SO2), 3.93 (2H, t, J 7.07, CH2N);
13C NMR 166.2 (CdO), 140.2 (quaternary carbon), 134.5 (quaternary
carbon), 129.85 (ArCH), 129.34 (ArCH), 57.0 (CH2SO2), 30.9 (CH2N);
HREI-MS (EI) C9H8ClNO3S calcd 244.9908, measured 244.9905.
2-(4′-Nitrobenzoyl)-1,2-thiazetidine-1,1-dioxide. Yield 0.82 g (34%);
mp 90-92 °C; IR υmax (cm-1) 3114, 3057, 1664, 1604, 1521, 1347,
1
1324, 1284, 1215, 1164; H NMR δ (CDCl3) 8.27 (2H, d, J 8.86),
8.06 (2H, d, J 8.83), 4.37 (2H, t, J 7.15, CH2SO2), 3.88 (2H, t, J 7.22,
CH2N); 13C NMR 165.88 (CdO), 149.98 (quaternary carbon), 137.14
(quaternary carbon), 129.02 (ArCH), 123.45 (ArCH), 57.34 (CH2SO2),
30.86 CH2N); HREI-MS (EI) C9H8N2O5S calcd 256.0148, measured
256.0151
AnalaR-grade reagents and deionized water were used throughout.
Organic solvents were glass distilled prior to use and stored under
nitrogen. Sodium hydroxide solutions were titrated prior to use against
a 1.00 M ( 0.1% hydrochloric acid volumetric reagent (D. H. Scientific,
Huddersfield, England) using phenolphthalein as an indicator. For
solution pHs g 3 and e 11, the pH was controlled by the use of e0.2
M buffer solutions of formate (pKa 3.75), ethanoate (pKa 4.72), MES
(pKa 6.1), MOPS (pKa 7.2), TAPS (pKa 8.4), CAPSO (pKa 9.6), and
CAPS (pKa 10.4). Buffers were prepared by partial neutralization of
solutions of their sodium salts to the required pH. In all experiments,
temperatures were maintained at 30 °C and ionic strength at 1.0 M
with AnalaR-grade KCl unless otherwise stated. Reaction concentrations
were generally within the range g2 × 10-5 M e 2 × 10-4 M to ensure
pseudo-first-order conditions.
2-(4-Methoxybenzoyl)-1,2-thiazetidine-1,1-dioxide. Yield 1.2 g
(53%); mp 98-99 °C; IR υmax (cm-1, Neat) 3035, 2977, 2841, 1662,
1606, 1513, 1327, 1262. 1201, 1156, 1031; H NMR δ (CDCl3) 8.01
(2H, d, J 8.95, Ha/Hc), 7.01 (2H, d, J 8.87, Hb/Hd), 4.27 (2H, t, J
7.35, CH2SO2), 3.98 (2H, t, J 7.22, CH2N), 3.88 (3H, s, CH3); 13C NMR
163.95 (CdO), 132.25 (quaternary carbon), 130.67 (ArCH), 124.26
(quaternary carbon), 114.22 (ArCH), 55.56 (CH2SO2), 55.45 (CH3),
30.72 (CH2N).
1
General Method for N-Aroyl â-Lactams. To a -78 °C stirred
solution of 2-azetidinone (0.5 g, 7.03 mmol) in dry dichloromethane
(DCM) (20 mL) was added 4,4-(dimethylamino)pyridine (0.1 g, 0.82
mmol) and a solution of aroyl chloride (1.57 g, 8.46 mmol) in
dichloromethane (10 mL) dropwise over 5 min. Triethylamine (0.98
mL, 7.02 mmol) was added dropwise over 10 min forming a white
precipitate. The reaction mixture was stirred at -78 °C for 1 h and for
a further 24 h at ambient temperature. DCM (10 mL) was added to the
reaction mixture, and the mixture was washed with water (15 mL) and
saturated brine (2 × 15 mL). The organic extract was dried over Na2-
SO4, and the solvent was removed by reduced pressure rotary
evaporation at 30 °C to yield a pale-yellow oil, which was purified by
column chromatography.
1-(4′-Methoxybenzoyl)-1-azetidin-2-one. Yield 0.6 g (42%); mp
125-127 °C; IR υmax (cm-1) (CHCl3): 3020, 3009, 2975, 2912, 2842,
1784, 1668, 1606, 1325, 1259, 1195, 1108, 1028; 1H NMR δ (CDCl3)
7.99 (2H, d, J 8.88,), 6.92 (2H, d, J 8.97), 3.85 (3H, s, CH3), 3.77 (2H,
t, J 5.44, CH2N), 3.02 (2H, t, J 5.45, CH2CO); 13C NMR δ (CDCl3)
165.23 (CdO), 163.92 (CdO), 132.57 (quaternary carbon), 131.92
(ArCH), 123.76 (quaternary carbon), 113.948 (ArCH), 55.21 (CH3)
36.45 (CH2N), 34.44 (CH2CO); HREI-MS [M + H]+ for C11H11NO3
calcd 206.0812, measured 206.0812.
Hydroxide ion concentrations were calculated using pKw (H2O) )
13.83 at 30 °C.
Reactions studied by UV spectrophotometry were usually com-
menced by injections of acetonitrile or dioxan stock solutions of the
substrate (5-50 µL) into the cells containing preincubated buffer (2.5
mL). Final reaction cells contained e5% acetonitrile or dioxan v/v.
The pH of the reaction cells was measured before and after each kinetic
run at 30 °C; kinetic runs experiencing a change >0.05 units were
rejected. Reactant disappearance or product appearance were followed
at absorbance change maxima for individual compounds. The solubility
of compounds was ensured by working within the linear range of
absorbance in corresponding Beer-Lambert plots. Pseudo-first-order
rate constants from exponential plots of absorbance against time or
gradients of initial slopes were obtained using the Enzfitter package
(Elsevier Biosoft, Cambridge, England) or the CaryBio software
(Varian). PH rate profiles were modeled to theoretical equations using
the Scientist program (V2.02, Micromath Software Ltd, USA).
Reactions studied by stopped-flow UV spectrophotometry used stock
solutions prepared at twice the standard UV concentration in 1 M KCl.
Hydroxide solutions, buffer solutions, or solutions of nucleophilic
reagents were prepared at twice the required concentration. The substrate
solution and the reaction mixture were placed in separate syringes and
thermostated at 30 °C before pneumatic injection into the reaction cell.
Where applicable, the pH of solutions was measured prior to use. The
photomultplier voltage was set to a maximum on deionized water and
absorbance wavelengths common to the standard UV experiments were
used. Pseudo-first-order rate constants from exponential plots of
absorbance against time were obtained using the supplied fitting
software (Applied Photophysics).
1-(4′-Chlorobenzoyl)-1-azetidin-2-one. Yield 0.85 g (58%); IR υmax
(cm-1) (CHCl3) 3020, 1788, 1673, 1593, 1404, 1324, 1284, 1217, 1093;
1H NMR δ (CDCl3) 7.95 (2H, d, J 6.68,), 7.44 (2H, d, J 8.66), 3.77
(2H, t, J 5.5, CH2N), 3.12 (2H, t, J 5.61, CH2CO); 13C NMR δ (CDCl3)
165.01 (CdO), 163.84 (CdO), 139.51 (quaternary carbon), 131.14 (CH
a/c), 130.1 (quaternary carbon), 128.44 (ArCH), 36.73 CH2N), 34.99
(CH2CO); HREI-MS [M + H]+ for C10H8NO2Cl calcd 210.0316,
measured 210.0316.
1-(4′-Nitrobenzoyl)-1-azetidin-2-one. Yield 1.23 g (80%); mp 130-
131 °C; IR υmax (cm-1) (CHCl3) 3020, 1787, 1686, 1599, 1523, 1397,
1
1309, 1252, 1204, 992; H NMR δ (CDCl3) 8.33 (2H, d, J 8.75, Hb/
Hd), 8.14 (2H, d, J 8.74, Ha/Hc), 3.85 (2H, t, J 5.58, CH2N), 3.2 (2H,
t, J 5.57, CH2CO); 13C NMR δ (CDCl3) 164.16 (CdO), 163.79 (Cd
O), 150.29 (quaternary carbon), 137.32 (quaternary carbon), 130.76
(CH b/d), 123.28 (CH a/c), 37.0 CH2N), 35.5 (CH2CO).
Enzyme Inhibition Studies. Enterobacter cloacae P99 â-lactamase
was obtained from the Centre of Applied Microbiology and Research
(Porton Down, UK).
Kinetics. Standard UV spectroscopy was carried out on a Cary 1E
9
J. AM. CHEM. SOC. VOL. 127, NO. 49, 2005 17563