F. Felluga et al. / Tetrahedron: Asymmetry 12 (2001) 3241–3249
3245
Porcine pancreatic lipase type II (PPL), esterase from
pig liver in 3.2 M (NH4)2SO4 suspension (PLE), and
porcine liver acetone powder (PLAP) were supplied by
Sigma, while a-chymotrypsin (a-CT; 53.1 U/mg) was
purchased from Fluka.
2.80–2.60 (3H, m), 2.60 (1H, dd), 1.55 (1H, br, NH),
1.02 (6H, d, J 7.7, CH(CH3)2); 13C NMR, l, ppm: 174.3
(s), 172.3 (s), 51.8 (q), 51.6 (q), 48.3 (d), 48.(t), 42.0 (d),
34.05 (t), 22.8 (q). Treatment of the crude reaction
mixture in refluxing toluene in the presence of p-tolue-
nesulphonic acid allowed compound 8c to be obtained
in 81% yield as an oil, bp 85–87°C (0.05 torr); IR, cm−1
4.2. Synthesis of substrate 8a
1
(film): 1738 (COO), 1690 (CON); H NMR, l, ppm:
4.2.1. Methyl 5-oxo-3-pyrrolidinecarboxylate 8a12. A
suspension of ammonium chloride (10.7 g, 0.2 mol) at
room temperature was treated by dropwise addition of
a solution of dimethyl itaconate (4.0 g, 25 mmol) in
methanol (100 mL) and triethylamine (3.3 mL, 0.2
mol). The mixture was stirred overnight, then further
ammonium chloride (0.2 mol) and triethylamine (0.2
mol) was added. Stirring was continued for further 24
h, then the solid was filtered off, the solution evapo-
rated and the residue distilled (bp 135–138°C) (1.0 torr)
to give pure 8a as a solid (2.2 g, 60%), mp 61–62°C
(lit.12 61–3°C); IR, cm−1 (Nujol): 3360, 3242 (NH), 1735
4.37 (1H, septet, J 7.0, CH(CH3)2), 3.75 (3H, s, OCH3),
3.51 (2H, d, H-2), 3.22 (1H, m, H-3), 2.66, 2.62 (2H,
part AB of an ABX system, J 17.1, 8.3, 7.3, H-4), 1.15
(6 H, d, J 7.0, CH(CH3)2); 13C NMR, l, ppm: 173.2 (s),
171.3 (s), 52.3 (q), 43.7 (t), 42.5 (d), 35.9 (d), 34.5 (t),
+
19.6 (q), 19.4 (q); EI-MS, m/z: 185 (9, M ), 171 (9),
170 (100), 127 (14), 110 (7), 99 (8), 84 (16), 82 (8), 56
(67), 55 (15).
4.3.3. Methyl 1-(1-butyl)-5-oxo-3-pyrrolidinecarboxylate
8d. The title compound was obtained in 88% yield as an
oil, bp 132–134°C (3.0 torr); IR, cm−1 (film): 1733
1
1
(COO), 1685 (CON); H NMR, l, ppm: 6.57 (1H, bs,
(COO), 1689 (CON); H NMR, l, ppm: 3.74 (3H, s,
NH), 3.75 (3H, s, OCH3), 3.63 (2H, m, H-4), 3.36 (1H,
m, H-3), 2.57, 2.65 (2H, part AB of an ABX system, J
17.1, 9.8, 7.8, H-2); 13C NMR, l, ppm: 176.5 (s), 172.9
OCH3), 3.59 (2H, m, H-2), 3.34–3.21 (3H, m, H-3,
NCH2), 2.68 (2H, m, H-4), 1.51 (2H, m,
NCH2CH2CH2CH3), 1.32 (2H, m, N(CH2)2CH2CH3),
0.93 (3H, t, N(CH2)3CH3); 13C NMR, l, ppm: 173.2 (s),
(s), 52.1 (q), 44.1 (t), 38.2 (d), 32.8 (t); EI–MS, m/z: 143
+
(3, M ), 115 (57), 112 (21), 101 (84), 87 (13), 83 (40), 70
172.0 (s), 52.3 (q), 48.8 (t), 42.1 (t), 35.9 (d), 34.2 (t),
+
(21), 59 (19), 56 (53), 55 (100).
29.1 (t), 19.9 (t), 13.6 (q); EI–MS, m/z: 199 (18, M ),
170 (14), 157 (45), 156 (100), 140 (13), 127 (48), 96 (16),
68 (27), 55 (21).
4.3. Synthesis of lactams 8b–f
To a solution of dimethyl itaconate (0.16 g, 1 mmol) in
methanol, an equimolar amount of the appropriate
primary amine was added dropwise under stirring at
room temperature (0°C in the case of EtNH2). After
stirring the mixture for 12 h at room temperature, the
solvent was removed in vacuo and the residue was
distilled under reduced pressure. When the amine was
iso-propylamine, the residue was stirred under reflux in
toluene for 1 h in the presence of a catalytic amount of
p-toluenesulphonic acid before distillation. When the
amine was benzylamine, the product was obtained by
trituration of the crude reaction mixture with light
petroleum.
4.3.4. Methyl 1-(2-hydroxyethyl)-5-oxo-3-pyrrolidinecar-
boxylate 8e. The title compound was obtained in 72%
yield as an oil, bp 157–159°C (0.1 torr). IR, cm−1 (film):
3379 (OH), 1737 (COO), 1678 (CON); 1H NMR l,
ppm: 3.74 (1H, s, OH), 3.20 (1H, m, H-3), 3.65 (7H, m
and s, N(CH2)2OH, OCH3), 3.33 (2H, m, H-2), 2.60
(2H, m, H-4); 13C NMR l, ppm: 173.4 (s), 173.3 (s),
60.0 (t), 52.3 (q), 50.1 (t), 45.5 (t), 36.1 (d), 34.1 (t);
+
EI–MS, m/z: 187 (5, M ), 169 (8), 157 (16), 156 (100),
144 (29), 128 (18), 127 (43), 96 (9), 68 (20), 42 (30).
4.3.5. Methyl 1-(phenylmethyl)-5-oxo-3-pyrrolidinecar-
boxylate 8f. The title compound was obtained in 85%
yield as an oil, bp 144–147°C (0.06 torr), which crys-
tallised by treatment with petroleum ether, mp 65–
4.3.1. Methyl 1-ethyl-5-oxo-3-pyrrolidinecarboxylate 8b.
The title compound was obtained in 85% yield as an
oil, bp 89–92°C (0.05 torr); IR, cm−1 (film): 1735
1
67°C; IR, cm−1 (film): 1733 (COO), 1689 (CON); H
NMR l, ppm: 7.28–7.35 (3H, m, Ar-H), 7.23 (2H, d,
Ar-H), 4.45 (2H, AB system, J 14.7, NCH2Ph), 3.70
(3H, s, OCH3), 3.48–3.43 (2H, m, H-2), 3.20 (1H, m,
H-3), 2.76, 2.73 (2H, part AB of an ABX system, J
17.2, 9.8, 7.3, H-4); 13C NMR l, ppm: 173.0 (s), 172.2
(s), 133.7 (s), 128.6 (d), 128.0 (d), 127.6 (d), 52.3 (q),
48.3 (t), 46.4 (t), 35.7 (d), 33.9 (t); EI–MS, m/z: 213 (24,
M+), 198 (10), 170 (100), 142 (14), 141 (19), 113 (14), 86
(9), 68 (7).
1
(COO), 1688 (CON); H NMR, l, ppm: 3.69 (3H, s,
OCH3), 3.54 (2H, m, H-2), 3.32–3.17 (3H, m, H-3 and
NCH2CH3), 2.62 (2H, m, 2 H-4), 1.07 (3H, t, J 8.0,
NCH2CH3); 13C NMR, l, ppm: 173.2 (s), 171.7 (s), 52.3
(q), 48.2 (t), 36.9 (t), 35.7 (d), 34.1 (t), 12.2 (q); EI-MS,
+
m/z: 171 (41, M ), 156 (71), 143 (54), 140 (18), 128
(26), 127 (58), 112 (56), 96 (25), 84 (75), 68 (42), 58 (55),
56 (46), 55 (52), 42 (87), 41 (100).
4.3.2. Methyl 1-(methylethyl)-5-oxo-3-pyrrolidinecar-
boxylate 8c. The title compound was formed in admix-
ture (1:1) with the open chain adduct dimethyl
[(methylethyl)aminomethyl]-butanedioate 7c which was
detected in the NMR spectrum of the crude reaction
mixture: H NMR, l, ppm: 3.71 (3H, s, OCH3), 3.68
(3H, s, OCH3), 2.99 (1H, m, CH(CH3)2), 2.90 (1H, dd),
4.4. General procedure for the enzymatic hydrolysis of
lactams 8a–f
The lactamic esters were reacted with the enzyme in a
0.1 M KH2PO4/Na2PO4 buffer, at pH 7.4, under vigor-
ous stirring. The pH was continuously adjusted to pH
7.4 with 1N aqueous NaOH using a pH-stat. At the
1