Cordero et al.
2.31 (ddd, J ) 12.7, 7.3, 2.6 Hz, 1H), 2.16 (dd, J ) 13.9, 2.2
Hz, 1H), 2.10-1.96 (m, 2H), 2.03 (dd, 13.9, 7.9 Hz, 1H), 1.85
(br s, 1H), 1.49 (ddd, J ) 12.7, 10.6, 8.8 Hz, 1H), 1.31 (d, J )
6.6 Hz, 3H); 13C NMR (50 MHz) δ 175.2 (s), 174.6 (s), 145.0
(s), 128.3 (d, 2C), 127.0 (d, 2C), 126.9 (d), 71.9 (s), 60.9 (d),
56.4 (d), 52.6 (q), 41.6 (t), 39.0 (t), 36.0 (t), 25.6 (t), 24.2 (q);
MS (EI) m/z (%) 303 (MH+, 1), 287 (10), 124 (49), 120 (100),
105 (87), 77 (11); IR (CDCl3) 3331, 2955, 1735, 1688, 1451,
1209 cm-1. Anal. calcd for C17H22N2O3: C, 67.53; H, 7.33; N,
9.26. Found: C, 67.64; H, 7.28; N, 9.70.
9H); 13C NMR (50 MHz) δ 173.9 (s), 172.1 (s), 170.7 (s), 170.4
(s), 156.1 (s), 143.7 (s, 2C), 141.2 (s, 2C), 127.6 (d, 2C), 127.0
(d, 2C), 125.1 (d, 2C), 119.9 (d, 2C), 81.7 (s), 72.0 (s), 67.4 (t),
54.4 (d), 53.0 (q), 51.5 (d), 47.1 (d), 42.1 (t), 37.7 (t), 36.9 (t),
35.1 (t), 28.0 (q, 3C), 25.7 (t); MS (EI) m/z (%) 458 (<1), 333
(1), 236 (55), 178 (100), 176 (48), 165 (11), 152 (23), 122 (60),
88 (14); IR (CDCl3) 3417, 3068, 2982, 1721, 1498, 1247 cm-1
.
Anal. calcd for C32H37N3O8: C, 64.96; H, 6.30; N, 7.10. Found:
C, 64.61; H, 5.96; N, 7.11.
(2R,7aR)-2-[((2S)-4-tert-Butoxy-2-{[(9H-fluoren-9-
ylmethoxy)carbonyl]amino}-4-oxobutanoyl)amino]-3-
oxotetrahydro-1H-pyrrolizine-7a(5H)-carboxylic Acid
[(2R,7aR)-25a]. The tripeptide (2R,7aR)-24a (296 mg, 0.50
mmol) and NaOH (24, mg, 0.6 mmol) were added to a 0.8 M
solution of CaCl2 in iPrOH/H2O 7:3 (11.2 mL). The reaction
mixture was stirred for 6 h at room temperature and then was
neutralized with 1 M AcOH and concentrated. The residue was
dissolved in CH2Cl2, and the solution was dried over Na2SO4,
filtered, and concentrated. The crude compound was purified
by column chromatography on silica gel (eluent: CHCl3/MeOH/
AcOH, 200:10:0.1) to afford the compound (2R,7aR)-25a (108
mg, 37%) as a white solid.
(2S,7aS)-23b: Rf ) 0.25 (Et2O); [R]26 ) -72.9 (c ) 0.48,
D
1
CHCl3); H NMR (500 MHz) δ 7.35-7.28 (m, 2H), 7.27-7.25
(m, 2H), 7.24-7.20 (m, 1H), 3.85 (q, J ) 6.6 Hz, 1H), 3.74 (s,
3H), 3.65 (dt, J ) 11.6, 7.8 Hz, 1H), 3.34 (dd, J ) 7.5, 2.8 Hz,
1H), 3.24 (ddd, J ) 11.6, 8.6, 5.0 Hz, 1H), 2.49 (dd, J ) 13.6,
2.8 Hz, 1H), 2.26 (ddd, J ) 12.7, 6.8, 3.3 Hz, 1H), 2.09 (dd, J
) 13.6, 7.5 Hz, 1H), 2.07-1.98 (m, 2H), 1.82 (br s, 1H), 1.56
(dt, J ) 12.7, 9.7 Hz, 1H), 1.37 (d, J ) 6.6 Hz, 3H); 13C NMR
(50 MHz) δ 175.0 (s), 174.6 (s), 144.4 (s), 128.6 (d, 2C), 127.1
(d), 126.5 (d, 2C), 72.0 (s), 60.0 (d), 55.67 (d), 52.6 (q), 42.1 (t),
37.2 (t), 35.7 (t), 25.6 (t), 24.0 (q); MS (EI) m/z (%) 303 (MH+,
1), 287 (8), 124 (44), 120 (100), 105 (67), 77 (7); IR (CDCl3)
3330; 2955; 1734; 1690; 1450; 1214 cm-1. Anal. calcd for
C17H22N2O3: C, 67.53; H, 7.33; N, 9.26. Found: C, 67.51; H,
7.37; N, 9.48.
(2R,7aR)-25a: Rf ) 0.22 (CHCl3/MeOH/AcOH ) 20:1:0.1);
mp ) 108-110 °C; [R]27D ) -0.56 (c ) 1.25, CHCl3); 1H NMR
(400 MHz) δ 7.79-7.72 (m, 2H), 7.61-7.66 (m, 2H), 7.44-7.29
(m, 4H + NH), 5.96-5.88 (m, 1H), 4.60-4.30 (m, 2H), 4.46 (d,
J ) 6.8 Hz, 2H), 4.23 (t, J ) 6.8 Hz, 1H), 3.69 (dt, J ) 11.8,
8.0 Hz, 1H), 3.26-3.17 (m, 1H) 2.90 (br d, J ) 17.1 Hz, 1H),
2.69 (dt, J ) 11.9, 4.4 Hz, 1H), 2.59 (br dd, J ) 17.1, 3.8 Hz,
1H), 2.50 (dd, J ) 14.6, 9.5 Hz, 1H), 2.37-2.26 (m, 1H), 2.13-
2.03 (m, 2H), 1.58-1.42 (m, 1H), 1.44 (s, 9H); 13C NMR (50
MHz, CD3OD) δ 176.8 (s), 174.7 (s), 173.0 (s), 171.3 (s), 159.1
(s), 145.2 (s, 2C), 142.6 (s, 2C), 128.8 (d, 2C), 128.2 (d, 2C),
126.3 (d, 2C), 120.9 (d, 2C), 82.4 (s), 73.3 (s), 68.2 (t), 55.4 (d),
53.1 (d), 48.3 (d), 44.5 (t), 38.7 (t), 36.8 (t), 35.9 (t), 28.3 (q,
3C), 26.3 (t); MS (EI) m/z (%) 178 (100), 176 (24), 165 (4), 152
(17), 150 (10), 111 (2), 89 (5), 86 (9), 84 (10), 76 (11); IR (CDCl3)
Methyl (2R,7aR)-2-Amino-3-oxotetrahydro-1H-pyrroli-
zine-7a(5H)-carboxylate ((2R,7aR)-15a). A solution of
(2R,7aR)-23a (181 mg, 060 mmol) in MeOH (5 mL) was
hydrogenated in an autoclave in the presence of 20%
Pd(OH)2/C (50 mg) at room temperature and a pressure of 35
atm for 20 h. The catalyst was removed by filtration through
a short pad of Celite, and then the solution was concentrated
to give the crude amine (2R,7aR)-15a (116 mg, 97%), suf-
ficiently pure to be used in the next step without further
purification.
(2R,7aR)-15a: spectral properties are identical with those
of cis-15.
3688, 3519, 3404, 2928, 1705, 1602, 1506, 1369, 1216 cm-1
.
Methyl (2S,7aS)-2-Amino-3-oxotetrahydro-1H-pyrroli-
zine-7a(5H)-carboxylate [(2S,7aS)-15b)]. The amine
(2S,7aS)-23b (295 mg, 0.98 mmol) was hydrogenated under
the same conditions as its diastereomers (2R,7aR)-23a. The
purification of the crude amine (200 mg) by column chroma-
tography on silica gel (eluent: CH2Cl2/MeOH 50:1 then 25:1
and 20:1) afforded the pure compound (2S,7aS)-15b (166 mg,
86%).
Anal. calcd for C31H35N3O8: C, 64.46; H, 6.11; N, 7.27. Found:
C, 64.96; H, 6.20; N, 6.99.
Methyl (2S,7aS)-2-[((2S)-4-tert-Butoxy-2-{[(9H-fluor-
en-9-ylmethoxy)carbonyl]amino}-4-oxobutanoyl)ami-
no]-3-oxotetrahydro-1H-pyrrolizine-7a(5H)-carboxy-
late [(2S,7aS)-24b]. The amine (2S,7aS)-15b (166 mg, 0.84
mmol) was coupled with Fmoc-L-Asp(OtBu)-OH (345 mg, 0.84
mmol) to afford (2S,7aS)-24b (422 mg, 85%) by the same
procedure as described for the synthesis of (2R,7aR)-24a.
(2S,7aS)-15b: [R]25 ) +28.1 (c ) 0.66, CHCl3); spectral
D
properties are identical with those of cis-15.
(2S,7aS)-24b: white solid, Rf ) 0.38 (AcOEt/Et2O, 1:1); mp
) 82-83 °C; [R]27D ) +43.30 (c ) 1.03, CHCl3); 1H NMR (500
MHz) δ 7.78-7.76 (m, 2H), 7.63-7.60 (m, 2H), 7.43-7.39 (m,
2H), 7.37.34-7.30 (m, 2H), 7.27-7.24 (m, 1H), 5.94-5.91 (m,
1H), 4.69 (dt, J ) 2.2, 8.3 Hz, 1H), 4.56-4.50 (m, 1H), 4.46-
4.40 (m, 2H), 4.25 (t, J ) 7.0 Hz, 1H), 3.78 (s, 3H), 3.66 (dt, J
) 11.7, 8.1 Hz, 1H), 3.24 (ddd, J ) 11.7, 9.6, 3.7 Hz, 1H), 2.97
(dd, J ) 17.1, 4.0 Hz, 1H), 2.59 (dd, J ) 17.1, 5.3 Hz, 1H),
2.53 (dd, J ) 12.2, 7.0 Hz, 1H), 2.41 (dd, J ) 14.3, 8.5 Hz,
1H), 2.30 (dd, J ) 14.3, 2.2 Hz, 1H), 2.20-2.12 (m, 1H), 2.11-
2.01 (m, 1H), 1.60 (ddd, J ) 12.5, 11.1, 8.8 Hz, 1H), 1.45 (s,
9H); 13C NMR (50 MHz) δ 174.0 (s), 171.6 (s), 171.2 (s), 170.5
(s), 155.8 (s), 143.6 (s, 2C), 141.2 (s, 2C), 127.7 (d, 2C), 127.0
(d, 2C), 125.0 (d, 2C), 119.9 (d, 2C), 81.8 (s), 72.1 (s), 67.2 (t),
54.8 (d), 53.0 (q), 51.1 (d), 47.0 (d), 41.8 (t), 37.7 (t), 37.4 (t),
35.2 (t), 27.9 (q, 3C), 25.7 (t); MS (EI) m/z (%) 333 (1), 236
(55), 178 (100), 176 (26), 165 (6), 152 (26), 122 (36), 88 (82), 76
(50); IR (CDCl3) 3417, 3068, 2976, 1712, 1496, 1215 cm-1. Anal.
calcd for C32H37N3O8: C, 64.96; H, 6.30; N, 7.10. Found: C,
64.63; H, 6.29; N, 7.14
Methyl (2R,7aR)-2-[((2S)-4-tert-Butoxy-2-{[(9H-fluor-
en-9-ylmethoxy)carbonyl]amino}-4-oxobutanoyl)ami-
no]-3-oxotetrahydro-1H-pyrrolizine-7a(5H)-carboxy-
late [(2R,7aR)-24a]. DIPEA (200 µL, 1.15 mmol) was added
to a solution of amine (2R,7aR)-15a (116 mg, ∼0.58 mmol),
Fmoc-L-Asp(OtBu)-OH (238 mg, 0.58 mmol), and PyBroP (270
mg, 0.58 mmol) in CHCl3 (6 mL) with cooling in an ice/water
bath. The mixture was allowed to stand at room temperature
overnight and then concentrated. The crude compound was
diluted with AcOEt, then filtered and washed sequentially
with 5% KHSO4, 5% NaHCO3, and brine. The organic solution
was dried over Na2SO4, filtered, and concentrated. The crude
product was purified by column chromatography on silica gel
(eluent: AcOEt/Et2O, 1:1) to afford (2R,7aR)-24a (334 mg,
97%) as a white solid.
(2R,7aR)-24a: Rf ) 0.21; mp ) 85-86 °C; [R]27D ) -3.26 (c
) 0.49, CHCl3); 1H NMR (500 MHz) δ 7.78-7.75 (m, 2H),
7.63-7.58 (m, 2H), 7.42-7.38 (m, 2H), 7.35-7.30 (m, 2H),
7.29-7.25 (m, 1H), 5.99-5.94 (m, 1H), 4.68 (dt, J ) 2.5, 8.4
Hz, 1H), 4.58-4.51 (m, 1H), 4.41 (d, J ) 7.1 Hz, 2H), 4.24 (t,
J ) 7.1 Hz, 1H), 3.72 (s, 3H), 3.65 (dt, J ) 11.6, 8.1 Hz, 1H),
3.23 (ddd, J ) 11.6, 9.7, 3.7 Hz, 1H), 2.86 (dm, J ) 16.5 Hz,
1H), 2.69 (dd, J ) 16.5, 5.6 Hz, 1H), 2.50-2.42 (m, 1H), 2.46
(dd, J ) 14.3, 9.0 Hz, 1H), 2.30 (br d, J ) 14.3 Hz, 1H), 2.18-
2.00 (m, 2H), 1.59 (ddd, J ) 12.5, 10.9, 8.8 Hz, 1H), 1.45 (s,
(2S,7aS)-2-[((2S)-4-tert-Butoxy-2-{[(9H-fluoren-9-
ylmethoxy)carbonyl]amino}-4-oxobutanoyl)amino]-3-
oxotetrahydro-1H-pyrrolizine-7a(5H)-carboxylic acid
[(2S,7aS)-25b]. The tripeptide (2S,7aS)-24b (170 mg, 0.29
mmol) was hydrolyzed to (2S,7aS)-25b by the same pro-
866 J. Org. Chem., Vol. 70, No. 3, 2005