C. Antczak et al. / Bioorg. Med. Chem. 9 (2001) 2843–2848
2847
added ditertbutoxycarbonylanhydride (1.1 equiv, 7.86
g). After stirring for 0.5 h at room temperature, the
mixture was extracted with EtOAc. The organic layer
was washed with water and brine, dried over MgSO4
and the solvent was removed under reduced pressure.
Flash chromatography [cyclohexane/ethyl acetate (1:1
v/v)] led to compound 3 isolated as a yellow oil (4.2 g,
80%), nmax (CHCl3) 1170 (C–O), 1707 (C¼O ester),
3455 (NH), 3626 (OH); dH (90 MHz, solvent CDCl3)
1.50 (9H, s, tBu), 2.10 (1H, s, OH), 3.3 (2H, t, J=5 Hz,
CH2–NH), 3.70 (2H, t, J=5 Hz, CH2–OH), 4.95 (1H,
sl, NH); m/z 162 [M+H]+, 179 [M+NH4]+.
Jcb=8.4 Hz, Hc), 7.45 (1H, dd, Jbc=8.4 Hz, Jba=1.9
Hz, Hb), 7.65 (1H, d, Jab=1.9 Hz); m/z (DCI/NH3) 375
(M+H)+, 392 (M+NH4)+; anal. calcd for
C19H22N2O6: C, 60.95; H, 5.92; N, 7.48; found: C,
61.13; H, 5.85; N, 7.42.
2,2-Dimethyl-propionic acid 2-[2-(2,5-dioxo-2,5-dihydro-
pyrrol-1-yl)-ethylcarbamoyl]-4-(4-nitro-phenoxycarbony-
loxymethyl)-phenyl ester (7). To a solution of p-nitro-
phenyle chloroformate (270 mg, 1,36 mmol) and
anhydrous pyridine (120 mL, 1,52 mmol) in anhydrous
dichloromethane (5 mL) was added a solution of 6 in
dichloromethane (5 mL). The reaction mixture was
stirred for 3 h at room temperature and extracted with
dichloromethane. Purification by chromatography on
silica gel gave 7 (190 mg, 88%), nmax (CHCl3) 1669
(C¼O amide), 1713 (C¼O ester), 1767 (C¼O carbonate)
2940 (C¼O); dH (300 MHz, solvent CDCl3) 1.37 (9H, s,
tBu), 3.61(2H, dd, J=6 Hz, CH2–NH), 3.79 (2H, t,
J=6 Hz, CH2–N), 5.29 (2H, s, CH2–O), 6.54 (1H, t,
J=6 Hz, NH), 6.71(2H, s, CH ¼CH), 7.08 (1H, d,
[2-(2,5-Dioxo-2,5-dihydro-pyrrol-1-yl)-ethyl]-carbamic
acid tert - butyl ester (4). A solution of triphenylpho-
sphine (8.6 g, 32.9 mmol) in anhydrous THF (100 mL)
was cooled at ꢁ78 ꢀC prior successive additions of
DEAD (5.2 mL, 32.9 mmol), a solution of 3 (5.3 g, 32.9
mmol) in THF (20 mL), and maleimide (3.19 g, 32.9
mmol). The mixture was stirred for 5 min at ꢁ78 ꢀC,
and then at room temperature, overnight. After removal
of the solvent, diethyl oxide was added. The mixture
was then filtered and the filtrate was purified, after con-
centration, by flash chromatography [cyclohexane/ethyl
acetate (3:1v/v)]. This gave white crystals of 4 (6.3 g,
80%), mp 116 ꢀC; nmax (CHCl3) 1719 (C¼O), 3459
(NH); dH (90 MHz, solvent CDCl3+DMSO) 1.45 (9H,
s, tBu), 3.3 (2H, m, CH2–NH), 3.75 (2H, m, CH2–N),
4.8 (1H, sl, NH), 6.7 (2H, s, CH¼CH); m/z (DCI/NH3)
258 (M+NH4)+.
0
0
Jcb=8.3 Hz, Hc), 7.40 (2H, d, Ja b =7.6 Hz), 7.51(1H,
dd, Jbc=8.3 Hz, Jba=2 Hz, Hb), 7.76 (1H, d, Jab=2 Hz,
0
Ha), 8.28 (2H, d, Jb a =7.6 Hz, Hb )
0
0
2,2-Dimethyl-propionic acid 4-[carboxy-(3-chloro-4,5-di-
hydro-isoxazol-5-yl)-methylcarbamoyloxymethyl]-2-[2-
(2,5-dioxo-2,5-dihydro-pyrrol-1-yl)-ethylcarbamoyl]-
phenyl ester (8). To a solution of acivicin (16 mg, 91
mmol) and triethylamine (182 mmol, 25 mL) in anhy-
drous DMF (5 mL), was added a solution of 7 (49 mg,
91mmol) in DMF (5 mL). The reaction mixture was
stirred at room temperature for 48 h. The solvent was
removed under reduced pressure and the residue was
purified by flash chromatography on silica gel (di-
chloromethane, methanol 6%, acetic acid 0.5%) afford-
ing 8 as a colorless oil (50 mg, 95%). RMN 1H
(300 MHz, CDCl3): d (ppm) 1.33 (9H, s, tBu), 3.26 (2H,
lm, CH2NH), 3.56 (2H, ls, H4), 3.72 (2H, ls, CH2N),
4.53 (1H, ls, H1), 5.06 (3H, ls, CH2O, H3), 6.42 (1H, ls,
HN-acivicin), 6.70 (1H, ls, Mal), 6.97 (1H, d, Jcb=8.1
Hz, Hc), 7.33 (1H, d, Jbc=8.1Hz, H b), 7.62 (1H, s, Ha);
RMN 13C (300 MHz, solvent CDCl3): d (ppm) 26.99
(tBu); 37.29 (CH2N); 38.94 (CH2NH); 39.12 (C4); 65.81
(CH2O, C3); 123.10 (Cc); 128.20 (Ca); 130.80 (Cb);
134.30 (Mal); mass spectra (ESI positive) 579.2
[M+H]+, 601.2 [M+Na]+, 617.1 [M+K]+, (ESI
negative) 577.1[M ꢁH]+, 493 [M–(tBu–C¼O)]+.
2-(2,5-Dioxo-2,5-dihydro-pyrrol-1-yl)-ethylamine trifluor-
oacetate (5). Trifluoroacetic acid (2.5 mL) was added to
a cooled solution (0 ꢀC) of 4 (279 mg) in anhydrous di-
chloromethane (6 mL). After evaporation of dichloro-
methane, excess of trifluoroacetic acid was removed by
coevaporation with toluene. The residue was dissolved
in hot methanol and the trifluoroacetate 5 was pre-
cipitated with ethyl dioxide. After filtration, white nee-
dles crystals of 5 were collected (247 mg, 78%), mp
127 ꢀC; nmax (KBr) 1676 (C¼O), 1714 (C¼O); dH
(90 MHz, solvent CD3OD) 3.1(2H, t, C H2–NH+3 ), 3.8
(2H, t, CH2–N), 6.8 (2H, s, CH¼CH); m/z (DCI/NH3)
141 (M+H)+, 158 (M+NH4)+.
2,2-Dimethyl-propionic acid 2-[2-(2,5-dioxo-2,5-dihydro-
pyrrol-1-yl)-ethylcarbamoyl]-4-hydroxymethyl-phenyl es-
ter (6). A solution of the acid 2 (760 mg, 3 mmol), the
trifluoroacetate 5 (1equiv, 760 mg) and triethylamine (1
equiv, 410 mL) in anhydrous dichloromethane (100 mL)
was stirred at 0 ꢀC. DCC (1.1 equiv) was added and the
mixture was cooled at 0 ꢀC for 0.5 h. The reaction mix-
ture was then stirred at room temperature for 36 h. The
urea formed was removed by filtration and the filtrate
was evaporated under reduced pressure. The residue
obtained was purified by flash chromatography [cyclo-
hexane/ethyl acetate (1:1 v/v)] and crystallization from
EtOAc to afford 6 as a white solid (560 mg, 50%), mp
142 ꢀC; nmax (CHCl3) 1715 (C¼O), 2928 (CH¼CH),
3606 (OH); dH (90 MHz, solvent CDCl3) 1.36 (9H, s,
tBu), 3.60 (2H, dd, JCH NH=JCH N=5.5 Hz, CH2NH),
2,2-Dimethyl-propionic acid 4-[carboxy-(3-chloro-4,5-di-
hydro-isoxazol-5-yl)-methylcarbamoyloxymethyl]-2-[2-(3
-carboxymethylsulfanyl-2,5-dioxo-pyrrolidin-1-yl)-ethyl-
carbamoyl] - phenyl ester (9). To a solution of 8 (16.8
mg, 29 mmol) and triethylamine (35 mmol, 4.9 mL) in
anhydrous dichloromethane was added mercaptoacetic
acid (35 mmol, 2.5 mL). The mixture was stirred at room
temperature for 30 min, and the solvent was evaporated
before purification by flash chromatography on silica
gel (acetonitrile, water 8%). The final product 9 was
isolated after lyophilisation as a white powder (15.5 mg,
80%). dH (300 MHz, solvent CDCl3+CD3OD) 1.31
2
2
0
3.77 (2H, t, J=5.5 Hz, CH2N), 4.70 (2H, s, CH2O), 6.50
(1H, sl, NH), 6.72 (2H, s, CH¼CH), 7.02 (1H, d,
(9H, s, tBu), 3.53 (2H, dd, J12=2Hz, J1 2=6.1Hz, H ),
1
0
3.72 (2H, dd, J21=2.0 Hz, J2 1=6.1Hz, H ), 5.19 (2H,
2