5548 J . Org. Chem., Vol. 62, No. 16, 1997
Andrus et al.
10.6, 5.0 Hz, 1H, other rotamer), 4.80 (t, J )9.4 Hz, 1H, one
rotamer), 4.78 (t, J )9.4 Hz, 1H, other rotamer), 4.26 (d, J )
11.1 Hz, 1H, one rotamer), 4.19 (d, J ) 11.1 Hz, 1H, other
rotamer), 3.67 (m, 1H), 3.12 (s, 3H, one rotamer), 3.00 (s, 3H,
one rotamer), 2.97 (s, 3H, other rotamer), 2.88 (s, 3H, other
rotamer), 2.80 (m, 1H), 2.26 (m, 1H), 1.70 (m, 3H), 1.39 (m,
1H), 1.25 (m, 6H), 1.15 (d, J ) 7.0 Hz, 3H), 1.12 (d, J ) 6.5
Hz, 3H), 1.08 (m, 1H), 1.05 (d, J ) 6.2 Hz, 3H), 1.00 (m, 1H),
0.94 (d, J ) 7.0 Hz, 3H), 0.90 (d, J ) 6.5 Hz, 3H), 0.88 (t, J )
6.5 Hz, 3H), 0.84 (d, J ) 6.4 Hz, 3H), 0.81 (d, J ) 6.0 Hz, 3H);
MS (CI) m/ e 514 (M + H)+.
Desa cetylm icr ocolin B. 23 (10.8 mg, 0.0195 mmol) and
imide 2 were dissolved in CH2Cl2 (0.5 mL). This solution was
treated with BROP (Aldrich, 7.6 mg, 0.0195 mmol) and
diisopropylethylamine (DIEA, 10 µL, 0.058 mmol). After being
stirred at rt for 12 h, the reaction mixture was diluted with
CH2Cl2 (5 mL), washed with saturated NH4Cl (5 mL), satu-
rated NaHCO3 (5 mL), and brine (5 mL), dried (MgSO4), and
concentrated. The crude was purified by flash chromatography
eluting with EtOAc:hexanes (7:3) to give 7.43 mg (55%) of pure
desacetylmicrocolin B as a colorless oil: [R]23D -156° (c 0.001,
EtOH); 1H NMR (500 MHz, CDCl3) δ 7.24 (dd, J ) 6.5, 2.0
Hz, 1H), 6.96 (d, J ) 9.5 Hz, 1H), 6.06 (dd, J ) 6.0, 1.5 Hz,
1H), 5.46 (dd, J ) 8.5, 5.0 Hz, 1H), 5.22 (dd, J ) 8.5, 7.0 Hz,
1H), 5.02 (d, J ) 11.5 Hz, 1H), 4.77 (q, J ) 7.0 Hz, 1H), 4.76
(d, J ) 8.0 Hz, 1H), 4.09 (dq, J ) 6.0, 1.5 Hz, 1H), 3.80 (m,
2H), 3.09 (s, 3H), 2.97 (s, 3H), 2.83 (m, 1H), 2.38 (ddd, J )
15.0, 12.5, 7.0 Hz, 1H), 2.28 (m, 1H), 2.04 (m, 1H), 1.95 (m,
1H), 1.88 (m, 1H), 1.85 (m, 1H), 1.73 (ddd, J ) 14.5, 10.5, 4.5
Hz, 1H), 1.57 (ddd, J ) 14.5, 10.0, 5.0 Hz, 1H), 1.46 (d, J )
6.5 Hz, 3H), 1.41 (m, 2H), 1.25 (m, 6H), 1.12 (d, J ) 6.5 Hz,
3H), 1.09 (m, 1H), 1.06 (d, J ) 6.0 Hz, 3H), 1.01 (d, J ) 6.5
Hz, 3H), 0.94 (d, J ) 6.5 Hz, 3H), 0.87 (t, J ) 6.5 Hz, 3H),
0.86 (d, J ) 7.0 Hz, 3H), 0.83 (d, J ) 6.5 Hz, 3H), 0.81 (d, J )
6.5 Hz, 3H); FABMS 690.5 (M + H)+, HR-FABMS calcd for
C37H64N5O7 690.4806, found 690.4791.
67.1, 57.8, 57.6, 55.1, 54.5, 52.3, 52.0, 38.0, 38.2; MS (CI) m/ e
280 (M + H)+.
Meth yl (2S,4S)-N-Cbz-4-h yd r oxyp r olin a te (25). To a
stirring solution of the ester 24 (5.26 g, 18.9 mmol) in THF
(150 mL) was added p-nitrobenzoic acid (PNBA, 12.6 g, 75.8
mmol) followed by Ph3P (19.8 g, 75.4 mmol). The solution was
then cooled to 0 °C, and diethyl azodicarboxylate (DEAD, 13.2
g, 75.6 mmol) was added dropwise over ca. 10 min. After being
stirred at rt for 18 h, the reaction mixture was concentrated
to give a thick yellow oil. Et2O and a small amount of hexane
was added, and the reaction mixture was stirred until a
precipitate formed. The precipitate was removed by vacuum
filtration, and the filter cake was washed with Et2O/hexane
(1:1). The filtrates were concentrated to give crude PNBA
ester. Flash chromatography eluting with a gradient between
EtOAc:hexanes (1:9) and EtOAc:hexanes (1:1) gave 7.13 g
(88%) of pure PNBA ester as a white solid: mp 112 °C; [R]25
D
1
-19.5° (c 0.062, CHCl3); H NMR (200 MHz, CDCl3) mixture
of two rotamers in a ratio of ca. 1:1 δ 8.30 (d, J ) 8.5 Hz, 2H),
8.15 (d, J ) 8.5 Hz, 2H), 7.36 (m, 5H), 5.61 (m, 1H), 5.21 (m,
2H), 4.64 (m, 1H), 3.89 (m, 2H), 3.72 (s, 3H, one rotamer), 3.58
(s, 3H, other rotamer), 2.55 (m, 2H).
The above PNBA ester (2.5 g, 5.84 mmol) was treated with
1 N NaOH (5.2 mL) in MeOH (30 mL) at 0 °C for 15 min.
Saturated NaHSO4 (25 mL) was added, and the mixture was
extracted with EtOAc (3 × 40 mL). The combined extracts
were washed with H2O (2 × 50 mL) and brine (1 × 50 mL),
dried (MgSO4), and concentrated. The crude was purified by
flash chromatography eluting with a gradient between EtOAc:
hexanes (1:9) and EtOAc/hexanes (1:1) to give 1.54 g (94.4%)
1
of pure 25 as a colorless oil: [R]25 -22° (c 0.035, CHCl3); H
D
NMR (200 MHz, CDCl3) mixture of two rotamers in a ratio of
ca. 1:1 δ 7.34 (m, 5H), 5.13 (m, 2H), 4.40 (m, 2H), 3.80 (s, 3H,
one rotamer), 3.68 (m, 2H), 3.61 (s, 3H, other rotamer), 2.86
(bs, 1H), 2.32 (m, 1H), 2.13 (d, J ) 13.6 Hz, 1H); 13C NMR (50
MHz, CDCl3) mixture of two rotamers δ 175.6, 175.4, 155.5,
154.7, 136.8, 136.7, 129.0, 128.7, 128.6, 128.5, 128.3, 71.6, 70.6,
67.8, 58.6, 58.2, 56.5, 56.2, 53.4, 53.1, 39.2, 38.3; MS (CI) m/ e
280 (M + H)+.
Micr ocolin B. Desacetylmicrocolin B (6.1 mg, 0.0085
mmol) was dissolved in CH2Cl2 (0.5 mL). This solution was
treated with 4-pyrrolidinopyridine (2.7 mg, 0.0257 mmol)
followed by acetic anhydride (2.5 µL, 0.0266 mmol). After
being stirred at rt for 6 h, the reaction mixture was concen-
trated, and the residue was purified by flash chromatography
eluting with EtOAc:hexanes (7:3) to give 6.1 mg (96%) of pure
P en t a flu or op h en yl
(2S,4S)-N-Cb z-4-[(ter t-b u t yld i-
m eth ylsilyl)oxy]p r olin a te (26). A solution of the hydroxy-
proline 25 (1.5 g, 5.37 mmol), imidazole (0.768 g, 11.28 mmol),
and tert-butyldimethylsilyl chloride (0.89 g, 5.91 mmol) in DMF
(14 mL) was stirred at room temperature for 36 h. The
reaction then was quenched by adding 25 mL of water. This
solution was extracted with EtOAc (3 × 50 mL). The combined
extracts were washed with H2O (5 × 50 mL) and brine (2 ×
50 mL), dried (MgSO4), and concentrated to give 2.00 g (95%)
of TBS protected product, which was used directly in the next
step without further purification. 1H NMR (200 MHz, CDCl3)
mixture of two rotamers in a ratio of ca. 1:1 δ 7.34 (m, 5H),
5.22 (d, J ) 12.2 Hz, 1H, one rotamer), 5.21 (d, J ) 12.2 Hz,
1H, one rotamer), 5.12 (d, J ) 12.2 Hz, 1H, other rotamer),
5.08 (d, J ) 12.2 Hz, 1H, other rotamer), 4.43 (m, 2H), 3.73 (s,
3H, one rotamer), 3.66 (m, 1H), 3.61 (s, 3H, other rotamer),
3.43 (m, 1H), 2.22 (m, 2H), 0.86 (s, 9H), 0.05 (s, 6H); 13C NMR
(50 MHz, CDCl3) mixture of two rotamers δ 172.9, 172.5, 155.4,
155.0, 137.2, 137.1, 128.9, 128.4, 128.3, 71.1, 70.3, 67.6, 67.5,
58.4, 58.2, 55.6, 55.3, 52.6, 52.5, 39.3, 26.1, 18.4, -4.48, -4.57;
microcolin B as a clear glass: [R]25 -168.3° (c 0.001, EtOH)
D
(lit.3 [R]25D -174° (c 0.005, EtOH)); 1H NMR (500 MHz, CDCl3)
δ 7.23 (dd, J ) 6.0, 1.5 Hz, 1H), 6.99 (d, J ) 9.0 Hz, 1H), 6.06
(dd, J ) 6.0, 1.5 Hz, 1H), 5.46 (dd, J ) 8.5, 5.0 Hz, 1H), 5.28
(dd, J ) 10.5, 5.5 Hz, 1H), 5.26 (q, J ) 6.5 Hz, 1H), 5.05 (d, J
) 11.0 Hz, 1H), 4.97 (dd, J ) 9.0, 3.5 Hz, 1H), 4.76 (q, J ) 6.5
Hz, 1H), 3.79 (ddd, J ) 16.5, 10.0, 6.5 Hz, 1H), 3.71 (ddd, J )
16.5, 10.0, 6.5 Hz, 1H), 3.12 (s, 3H), 2.96 (s, 3H), 2.84 (m, 1H),
2.42 (m, 1H), 2.26 (m, 1H), 2.01 (m, 2H), 2.00 (s, 3H), 1.87 (m,
1H), 1.85 (m, 1H), 1.73 (ddd, J ) 14.5, 10.5, 4.5 Hz, 1H), 1.57
(ddd, J ) 15.0, 9.5, 5.5 Hz, 1H), 1.46 (d, J ) 6.5 Hz, 3H), 1.41
(m, 1H), 1.27 (m, 1H), 1.26 (m, 1H), 1.25 (m, 4H), 1.18 (m,
1H), 1.16 (d, J ) 6.5 Hz, 3H), 1.13 (d, J ) 6.5 Hz, 3H), 1.09
(m, 1H), 1.00 (d, J ) 6.5 Hz, 3H), 0.94 (d, J ) 7.0 Hz, 3H),
0.88 (t, J ) 6.5 Hz, 3H), 0.86 (d, J ) 6.5 Hz, 3H), 0.84 (d, J )
6.5 Hz, 3H), 0.80 (d, J ) 6.5 Hz, 3H); 13C NMR (75 MHz,
CDCl3) δ 178.0, 172.1, 171.3, 169.9, 169.84, 169.79, 168.4,
153.8, 125.6, 68.8, 60.1, 59.4, 58.2, 53.9, 52.1, 48.1, 42.0, 37.2,
36.0, 33.9, 30.9, 30.6, 30.5, 29.2, 29.0, 27.4, 24.9, 24.7, 23.5,
23.0, 21.7, 21.1, 19.7, 18.9, 18.5, 18.3, 17.3 (2), 14.2; FABMS
732.5 (M + H)+; HR-FABMS calcd for C39H66N5O8 732.4911,
found 732.4896.
MS (CI) m/ e 394 (M + H)+; FTIR (CDCl3) 1760, 1716 cm-1
.
A solution of the above TBS-protected compound (1.5 g, 3.81
mmol) and LiOH‚H2O (0.48 g, 11.43 mmol) in THF/MeOH/
H2O (150 mL, 3:1:1) was stirred at 0 °C for 24 h. Then
saturated citric acid (90 mL) was added, and the reaction
mixture was extracted with EtOAc (3 × 100 mL). The
combined extracts were washed with H2O (1 × 100 mL) and
brine (1 × 100 mL), dried (MgSO4), and concentrated. The
crude was purified by flash chromatography eluting with
EtOAc:hexanes (2:3) to give 1.20 g (83%) of TBS-protected cis-
hydroxyproline: 1H NMR (200 MHz, CDCl3) δ 10.78 (s, 1H),
7.30 (m, 5H), 5.14 (m, 2H), 4.40 (m, 2H), 3.64 (m, 1H), 3.42
(m, 1H), 2.21 (m, 2H), 0.84 (s, 9H), 0.04 (s, 6H); 13C NMR (50
MHz, CDCl3) mixture of two rotamers δ 177.3, 176.8, 155.7,
155.2, 136.9, 128.9, 128.7, 128.4, 128.2, 71.0, 70.3, 67.7, 58.3,
58.0, 55.6, 55.2, 40.0, 39.0, 26.1, 18.3, -4.4; MS (CI) m/ e 380
(M + H)+.
Meth yl (2S,4R)-N-Cbz-4-h yd r oxyp r olin a te (24). Using
the DIAZALD procedure outlined for 18, (2S,4R)-N-Cbz-4-
hydroxyproline (5.0 g, 18.9 mmol) was converted to its corre-
sponding methyl ester 24 to yield 5.26 g (100%) as a colorless
oil: 1H NMR (200 MHz, CDCl3) mixture of two rotamers in a
ratio of ca. 3:2 δ 7.32 (m, 5H), 5.11 (m, 2H), 4.46 (m, 2H), 3.73
(s, 3H, minor rotamer), 3.62 (m, 2H), 3.53 (s, 3H, major
rotamer), 2.86 (bs, 1H), 2.30 (m, 1H), 2.03 (m, 1H); 13C NMR
(50 MHz, CDCl3) mixture of two rotamers δ 173.1, 173.0, 155.0,
154.5, 136.2, 136.0, 128.3,128.2, 127.9, 127.7, 127.6, 69.8, 69.1,