A Potent Analogue of clasto-Lactacystin â-Lactone
J. Am. Chem. Soc., Vol. 121, No. 43, 1999 9975
layer was extracted with AcOEt (2 × 200 mL), and the combined
organic layers were washed successively with H2O (2 × 200 mL),
saturated aqueous NaHCO3 (2 × 200 mL), and brine (2 × 300 mL)
and then dried over Na2SO4/MgSO4 and concentrated in vacuo,
affording 41.55 g (>100%) of crude aldol 31 as a pale and thick yellow
oil, which used as such in the subsequent step. A sample was purified
by flash chromatography (hexanes/AcOEt 2:1), followed by recrystal-
lization from hexanes to afford pure aldol adduct 31 as white needles:
mp 55-57 °C; [R]25D ) -124.0° (c 0.50, CHCl3); 1H NMR (300 MHz,
CDCl3) δ 8.02-7.97 and 7.53-7.39 (m, 5H), 6.58 (d, J ) 9.9 Hz,
1H), 4.82 (d, J ) 2.4 Hz, 1H), 3.73 (s, 3H), 3.69-3.61 (m, 2H), 3.49-
3.39 (m, 2H), 3.24-3.16 (m, 1H), 3.05 (m, 1H), 2.89 (m, 1H), 2.28-
2.23 (m, 1H), 1.98-1.91 (m, 1H), 1.37-1.20 (m, 6H), 1.19-1.06 (m,
6H), 0.87 (t, J ) 7.1 Hz, 3H), 0.70 (d, J ) 6.7 Hz, 3H); 13C NMR (75
MHz, CDCl3) δ 175.9, 170.5, 164.2, 131.6, 128.4, 128.2, 127.2, 89.5,
82.8, 78.6, 51.8, 42.4, 40.0, 37.2, 33.8, 29.6, 20.7, 20.3, 15.0, 13.9,
13.7, 12.8; FAB-MS, m/z (relative intensity) 433 [(M + H)+, 100].
Anal. Calcd for C24H36N2O5: C, 66.64; H, 8.39; N, 6.48. Found: C,
66.76; H, 8.60; N, 6.40.
solution of dihydroxy acid 32 (19.20 g, 74.0 mmol) in anhydrous THF
(250 mL) containing triethylamine (15.9 mL, 114.1 mmol) was treated
dropwise with isopropenyl chloroformate (8.65 mL, 79.2 mmol). After
being stirred for 30 min at 0-5 °C, the mixture was allowed to reach
ambient temperature, stirred for another 30 min, and diluted with diethyl
ether (375 mL). The mixture was stirred for 10 min, filtered, and
concentrated in vacuo. Purification on a SiO2 pad, eluting with 2:3
AcOEt/hexane, afforded 15.71 g (86%) of desired â-lactone 4 as a white
solid. It was further purified by dissolving it in 2:1 boiling THF/CH2-
Cl2 (145 mL) and slowly adding hot hexane (500 mL) to the solution.
After the mixture was allowed to cool to ambient temperature, the solid
formed was filtered and washed with 20% CH2Cl2/hexane (100 mL),
and the last traces of solvent were removed under high vacuum. This
afforded 13.7 g of pure â-lactone 4 (75% yield, 98.7% pure by reverse-
phase HPLC) as a fluffy white solid: mp ) 181-183 °C; [R]23
)
D
-130.8° (c 0.25, MeCN); FTIR (KBr pellet) 1834, 1689 cm-1; 1H NMR
(300 MHz, CDCl3) δ 6.07 (br s, 1H), 5.26 (d, J ) 6.1 Hz, 1H), 3.97
(dd, J ) 6.4, 4.4 Hz, 1H), 2.70-2.63 (m, 1H), 2.03 (d, J ) 6.4 Hz,
3H), 1.93-1.44 (m, 5H), 1.07 (d, J ) 7.0 Hz, 3H), 0.99 (d, J ) 7.3
1
Hz, 3H), 0.91 (d, J ) 6.7 Hz, 3H); H NMR (300 MHz, pyridine-d5)
When some unreacted aldehyde 26 contaminates the aldol adduct
31, it is conveniently removed by dissolving the material in hexanes
and washing the solution successively with 0.35 M aqueous NaHSO3
(made by dissolving 31 g of Na2SO3 in 380 mL of H2O and 220 mL
of 1 M aqueous HCl), H2O, saturated aqueous NaHCO3, and brine.
The solution is then dried over Na2SO4, filtered, and concentrated in
vacuo.
δ 10.46 (br s, 1H), 7.86 (d, J ) 6.8 Hz, 1H), 5.82 (d, J ) 6.1 Hz, 1H),
4.98 (s, 1H), 4.37 (dd, J ) 6.7, 3.8 Hz, 1H), 3.06-3.00 (m, 1H), 2.17-
2.09 (m, 2H), 1.99-1.82 (m, 1H), 1.61-1.52 (m, 2H), 1.14 (d, J )
6.9 Hz, 3H), 1.04 (d, J ) 6.7 Hz, 3H), 0.88 (t, J ) 7.3 Hz, 3H); 13C
NMR (75 MHz, pyridine-d5) δ 177.03, 172.37, 80.60, 76.53, 70.74,
44.15, 29.91, 27.41, 21.45, 20.41, 16.64, 14.21; FAB LRMS, m/z 242
(M + H+). Anal. Calcd for C12H19NO4: C, 59.73; H, 7.94; N, 5.80.
Found: C, 59.72; H, 8.00; N, 5.66.
3S-Hydroxy-2R-(1S-hydroxy-2-methylpropyl)-4R-n-propyl-5-oxo-
pyrrolidine-2-carboxylic Acid Methyl Ester (8). A solution of crude
aldol adduct 31 (17.5 g, 40.5 mmol) in 100 mL of 1:9 AcOH/MeOH,
to which was added 17.5 g of 20% Pd(OH)2/C, was vigorously shaken
under 55 psi H2 for 75 h at ambient temperature. The mixture was
then filtered and concentrated in vacuo. The solid obtained was taken
up in a mixture of AcOEt (600 mL), CH2Cl2 (100 mL), and THF (100
mL), and the obtained solution was treated with a 4.5 M aqueous
solution of K2CO3 (20 mL) and brine (30 mL). The layers were then
separated, and the organic layer was washed with brine (50 mL), dried
over MgSO4, filtered, and concentrated in vacuo. The crude solid (11.84
g) was then dissolved in 150 mL of boiling THF and slowly diluted
with boiling hexane (300 mL). The cloudy solution was allowed to
cool to ambient temperature for 2 h and was then placed in a 4 °C
cold room for another 2 h. The crystals that had formed were then
filtered and washed with 10% THF/hexane. This afforded 8.75 g of
pure desired γ-lactam 8 (79%) as a white solid: mp 195-197 °C dec;
[R]23D ) -12.6° (c 0.54, MeCN); FTIR (KBr pellet) 3241, 2958, 1726,
1689 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.89 (br s, 1H), 4.77 (br d,
J ) 11.5 Hz, 1H), 4.47 (dd, J ) 11.5, 5.6 Hz, 1H), 4.08 (dd, J ) 9.4,
5.0 Hz, 1H), 3.83 (s, 3H), 2.93 (m, 1H), 1.78-1.39 (m, 6H), 1.02-
0.88 (m, 9H); 13C NMR (75 MHz, pyridine-d5) δ 179.7, 173.1, 79.9,
76.7, 75.9, 51.7, 47.1, 32.2, 27.0, 21.8, 20.3, 19.7, 14.6; FAB-MS, m/z
(relative intensity) 274 (M + H+, 100). Anal. Calcd for C13H23NO5:
C, 57.13; H, 8.48; N, 5.12. Found: C, 56.85; H, 8.58; N, 5.04.
3S-Hydroxy-2R-(1S-hydroxy-2-methylpropyl)-4R-n-propyl-5-oxo-
pyrrolidine-2-carboxylic Acid (32). To a cold (0-5 °C) suspension
of γ-lactam 8 (17.42 g, 63.7 mmol) in H2O (100 mL) was added cold
(0-5 °C) 0.6 N aqueous NaOH (213 mL, 127.8 mmol). The mixture
was stirred at 4 °C for 34 h, acidified with 2 N aqueous HCl (75 mL),
washed with CH2Cl2 (2 × 50 mL), frozen, and lyophilized for 4 days.
The obtained solid was transferred into a desiccator containing P2O5
and dried under high vacuum for 30 h. It was then suspended in THF
containing 6.0 g of Celite, and the suspension was filtered to get rid of
sodium chloride. Concentration in vacuo afforded 16.68 g (100%) of
3-(5S-Isopropyl-4S-methoxycarbonyl-2-phenyl-4,5-dihydro-oxazol-
4-yl)-3S-hydroxy-2R-methyl-N,N-diethylpropionamide (33). To a
cold (-78.8 °C, internal temperature) solution of oxazolidine 10 (2.00
g, 8.10 mmol) in anhydrous THF (40 mL) was added lithium
bis(trimethylsilyl)amide (8.9 mL of a 1 M solution in hexane, 8.90
mmol) over 50 min. After 45 min, the orange solution was treated over
40 min with a 1 M solution of dimethylaluminum chloride in hexanes
(19.4 mL, 19.4 mmol), and the mixture was stirred for another 60 min
before being cooled to -85 °C (internal temperature, liquid N2 was
added to the dry ice/acetone bath). A solution of aldehyde 30 (1.61 g,
10.2 mmol) in THF (8 mL) was then added over 30 min, after which
time the mixture was allowed to warm slowly to -20 °C and then
cooled again to ca. -60 °C and cautiously quenched by addition of
saturated aqueous NH4Cl (2.0 mL). The mixture was cannulated into
a mixture of saturated aqueous NH4Cl (70 mL) and 1:1 AcOEt/hexanes
(50 mL), and 6 N aqueous HCl (12 mL) was then added slowly. After
the layers were separated, the aqueous layer was extracted with AcOEt/
hexanes (2 × 30 mL), and the combined organic layers were washed
successively with 0.5 N aqueous HCl (2 × 30 mL), H2O (30 mL), 0.4
M NaHSO3 (2 × 30 mL), saturated aqueous NaHCO3 (2 × 30 mL),
and brine (35 mL) and then dried over Na2SO4/MgSO4 and concentrated
in vacuo, affording 3.22 g of an off-white solid that was used as such
in the following step. A pure sample was obtained by recrystallization
and afforded pure aldol adduct 33 as white crystals: mp 91-92 °C;
1
[R]23 ) -151.8° (c 0.50, CHCl3); H NMR (300 MHz, CDCl3) δ
D
8.02-7.99 (m, 2H), 7.54-7.39 (m, 3H), 6.51 (d, J ) 9.9 Hz, 1H),
4.84 (d, J ) 2.2 Hz, 1H), 3.74 (s, 3H), 3.67-3.54 (m, 2H), 3.47-3.35
(m, 1H), 3.26-3.12 (m, 2H), 2.97-2.85 (m, 1H), 2.34-2.24 (m, 1H),
1.36-1.29 (m, 6H), 1.12 (d, J ) 7.0 Hz, 3H), 1.07 (t, J ) 7.4 Hz,
3H), 0.68 (d, J ) 6.6 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 176.3,
170.4, 164.2, 131.7, 128.5, 128.2, 127.2, 89.4, 82.9, 81.8, 51.9, 42.3,
40.0, 32.4, 29.5, 20.7, 18.3, 14.9, 14.0, 12.8; FAB-MS, m/z (relative
intensity) 405 [(M + H)+, 100]. Anal. Calcd for C22H32N2O5: C, 65.32;
H, 7.97; N, 6.93. Found: C, 65.53; H, 8.10; N, 6.83.
the desired dihydroxy acid 32 as a white solid: [R]23 ) +20.8° (c
D
1
0.50, MeCN); H NMR (300 MHz, CD3OD) δ 4.42 (d, J ) 5.8 Hz,
3S-Hydroxy-2R-(1S-hydroxy-2-methyl-propyl)-4R-methyl-5-oxo-
pyrrolidine-2-carboxylic Acid Methyl Ester (34). A solution of crude
aldol adduct 33 (3.12 g, 7.72 mmol) in 40 mL of 1:9 AcOH/MeOH, to
which was added 3.10 g 20% Pd(OH)2/C, was vigorously shaken under
50 psi H2 for 75 h at ambient temperature. The mixture was then filtered
and concentrated in vacuo. The solid obtained was taken up in 10:6:
6:1 CH2Cl2/THF/AcOEt/MeOH and treated successively with brine (10
mL) and 6 N aqueous HCl (2 mL). The separated aqueous layer was
then extracted with 2:2:1 CH2Cl2/THF/AcOEt (3 × 15 mL), and the
1H), 3.90 (d, J ) 6.5 Hz, 1H), 2.84 (m, 1H), 1.70-1.24 (m, 6H), 0.95-
0.84 (m, 9H); 13C NMR (75 MHz, pyridine-d5) δ 179.9, 175.2, 79.3,
77.0, 76.4, 47.2, 32.2, 26.8, 21.6, 21.1, 18.7, 14.4; FAB-MS, m/z
(relative intensity) 260 [(M + H)+, 100], 282 {(M + Na)+, 19]. Anal.
Calcd for C12H21NO5: C, 55.58; H, 8.16; N, 5.40. Found: C, 55.12.72;
H, 8.39; N, 5.21.
[1R-[1S,4R,5S]]-1-(1-Hydroxy-2-methylpropyl)-4-n-propyl-6-oxa-
2-azabicyclo[3.2.0]heptane-3,7-dione (4) [PS-519]. A cold (0-5 °C)