Y. Shiro et al. / Tetrahedron 62 (2006) 8687–8695
8693
(5.05 g, 46.7 mmol), and Ti(O-i-Pr)4 (0.332 g, 1.17 mmol)
in benzene (40 ml) was stirred for 12 h at reflux. The reac-
tion mixture was diluted with 7% aqueous NaHCO3 and ex-
tracted with AcOEt. The organic layer was washed with
brine and dried over MgSO4. Evaporation of the organic sol-
vent provided a crude oily product, which was chromato-
graphed on silica gel (50 g, n-hexane/EtOAc¼20:1) to give
an oily product. To a solution of the above oily product in
THF (10 ml) was added 1 M Bu4N+Fꢁ/THF solution
(5 ml) and the whole mixture was stirred for 12 h at room
temperature. The reaction mixture was diluted with H2O
and extracted with AcOEt. The organic layer was washed
with brine and dried over MgSO4. Evaporation of the or-
ganic solvent provided a crude oily product, which was
chromatographed on silica gel (50 g, n-hexane/AcOEt¼2:1)
to give 21 (0.706 g, 86%) as colorless oil. (4S,6R)-21: [a]D25
for C12H20N2O7: C, 47.36; H, 6.62; N, 9.21%. Found: C,
47.21; H, 6.84; N, 9.11%.
4.1.14. Coupling reaction of (4S,6R)-23 and uracil
polyoxcin C (3). A mixture of 23 (0.077 g, 0.25 mmol),
N-hydroxysuccinimide (0.032 g, 0.28 mmol), and N,N-dicy-
clohexylcarbodiimide (DCC, 0.058 g, 0.28 mmol) in AcOEt
(5 ml) was stirred for 1 h at room temperature. The reaction
mixture was evaporated to give a crude residue 24. To a
solution of the above residue in DMSO (3 ml) was added
a mixture of uracil polyoxin C (3, 0.088 g, 0.28 mmol) and
i-Pr2NEt (0.13 ml, 0.506 mmol) in DMSO (1 ml) and the
whole mixture was stirred for 12 h at room temperature.
The reaction mixture was directly subjected to column chro-
matography (silica gel, 10 g, CHCl3/MeOH¼1:1) to afford
25 (0.107 g, 74%) as amorphous solid. 25: mp 207–
210 ꢀC (dec); [a]2D5 ꢁ4.3 (c 0.6, MeOH); IR (KBr): 3401,
ꢁ29.88 (c 1.23, CHCl3); IR (KBr): 3425, 1748, 1703 cmꢁ1
.
NMR (pyridine-d5, 90 ꢀC): d 1.43 (9H, s), 2.22–2.37 (2H,
m), 3.75 (1H, dd, J¼4.4, 11.6 Hz), 3.81 (1H, dd, J¼5.2,
11.6 Hz), 3.89–3.96 (1H, m), 4.58 (1H, dd, J¼6.0, 9.6 Hz),
5.04 (1H, d, J¼9.6 Hz), 5.10 (1H, br s), 5.24–5.31 (3H,
m), 7.24–7.32 (3H, m), 7.42 (2H, d, J¼7.2 Hz). Anal. Calcd
for C18H25NO6: C, 61.52; H, 7.17; N, 3.99%. Found: C,
61.26; H, 7.41; N, 4.06%.
1685, 1670, 1637, 1625 cmꢁ1 1H NMR (pyridine-d5,
.
90 ꢀC): d 1.45 (9H, s), 2.34–2.37 (2H, m), 4.08–4.12 (1H,
m), 4.27 (1H, dd, J¼4.8, 11.2 Hz), 4.40 (1H, dd, J¼6.4,
11.2 Hz), 4.70–4.78 (2H, m), 4.91–4.94 (1H, m),
5.04–5.07 (1H, m), 5.17 (1H, d, J¼9.8 Hz), 5.22 (1H, d,
J¼9.8 Hz), 5.29–5.32 (1H, m), 5.79 (1H, d, J¼7.8 Hz),
6.39 (1H, d, J¼3.6 Hz), 6.66 (2H, br s), 7.94 (1H, d,
13
J¼7.8 Hz). C NMR (pyridine-d5, 90 ꢀC): d 27.9, 28.4,
4.1.12. (4S,6R)-4-Benzyloxycarbonyl-3-tert-butoxycar-
bonylamino-6-carbamoyloxymethyl-tetrahydro-2H-1,3-
oxazine 22. To a solution of 21 (0.646 g, 1.84 mmol) in THF
(15 ml) was added pyridine (0.945 g, 12 mmol), Et3N
(0.372 g, 3.7 mmol), and 4-nitrophenyl chloroformate
(1.112 g, 5.52 mmol) at ꢁ20 ꢀC and the reaction mixture
was stirred for 30 min at the same temperature. To the above
reaction mixture was added saturated NH3/MeOH (5 ml)
and the whole mixture was stirred for 1 h at 0 ꢀC. The reac-
tion mixture was evaporated and the resulting residue was di-
luted with H2O and extracted with AcOEt. The organic layer
was washed with brine and dried over MgSO4. Evaporation
of the organic solvent provided a crude oily product, which
was chromatographed on silica gel (10 g, n-hexane/
AcOEt¼2:1) to give 22 (0.58 g, 80%) as colorless oil.
(4S,6R)-22: [a]2D3 ꢁ33.12 (c 0.77, CHCl3); IR (KBr): 3444,
1734, 1716, 1701 cmꢁ1. NMR (pyridine-d5, 90 ꢀC): d 1.42
(9H, s), 2.18–2.22 (2H, m), 4.00–4.08 (1H, m), 4.22 (1H,
dd, J¼4.8, 11.6 Hz), 4.32 (1H, dd, J¼6.0, 11.6 Hz), 4.56
(1H, t, J¼7.2 Hz), 5.01 (1H, d, J¼9.6 Hz), 5.22 (1H, d,
J¼9.6 Hz), 5.26 (1H, d, J¼12.4 Hz), 5.30 (1H, d,
J¼12.4 Hz), 6.67 (2H, br s), 7.24–7.33 (3H, m), 7.41–7.43
(2H, m). Anal. Calcd for C19H26N2O7$1/4H2O: C, 57.20;
H, 6.70; N, 7.02%. Found: C, 56.91; H, 6.88; N, 6.98%.
55.6, 56.6, 66.5, 71.3, 71.8, 71.8, 74.8, 81.3, 86.0, 90.9,
103.2, 141.5, 150.3, 152.3, 155.3, 158.0, 164.2, 172.2.
HRMS (FAB) Calcd for C22H32N5O13 (M++H; m/z)
574.1997. Found 574.1932.
4.1.15. Polyoxin M (1). To a solution of 25 (0.107 g,
0.187 mmol) in a mixed solvent [MeOH (2 ml)/H2O
(2 ml)] was added CF3COOH (2 ml) at 0 ꢀC and the reaction
mixture was stirred for 12 h at room temperature. The reac-
tion mixture was evaporated to give a crude residue, which
was directly subjected to column chromatography (ODS,
10 g, H2O) to afford 1 (0.040 g, 47%) as amorphous solid.
1: mp 215–220 ꢀC (dec); [a]D25 +46.9 (c 0.29, H2O); IR
(KBr): 3423, 1677, 1655, 1648, 1637, 1631 cmꢁ1 1H
.
NMR (D2O): d 1.76–1.86 (1H, m), 1.94–1.99 (1H, m),
3.79 (1H, dd, J¼6.0, 11.2 Hz), 3.89 (1H, dd, J¼3.6,
11.2 Hz), 3.92–3.97 (1H, m), 4.04–4.12 (2H, m), 4.21–
4.28 (1H, m), 4.33 (1H, t, J¼6.0 Hz), 4.62–4.66 (1H, m),
5.60 (1H, d, J¼4.0 Hz), 5.70 (1H, d, J¼8.0 Hz), 7.38 (1H,
d, J¼8.0 Hz). 13C NMR (D2O): d 33.0, 51.3, 53.7, 66.4,
67.6, 69.4, 71.8, 81.9, 90.5, 102.1, 142.0, 151.0, 158.6,
165.4, 168.9, 170.7. HRMS (FAB) Calcd for C16H24N5O11
(M++H; m/z) 462.1472. Found 462.1495.
4.1.16. (4S,6R)-3-tert-Butoxycarbonylamino-6-hydroxy-
methyl-4-methoxycarbonyl-tetrahydro-2H-1,3-oxazine
25. A mixture of 20 (0.35 g, 0.68 mmol), HF$pyridine com-
plex (0.135 g, 1.36 mmol) in a mixed solvent [THF (5 ml)/
pyridine (5 ml)] was stirred for two days at room tempera-
ture. The reaction mixture was diluted with H2O and ex-
tracted with AcOEt. The organic layer was washed with
brine and dried over MgSO4. Evaporation of the organic sol-
vent provided a crude oily product, which was chromato-
graphed on silica gel (10 g, n-hexane/AcOEt¼3:2) to give
25 (0.182 g, 97%) as colorless oil. (4S,6R)-25: NMR (pyri-
dine-d5): d 1.44 (9H, s), 2.18–2.31 (2H, m), 3.69 (3H, s),
3.75 (1H, dd, J¼4.8, 11.2 Hz), 3.82 (1H, dd, J¼5.4,
11.2 Hz), 3.89–3.95 (1H, m), 4.51 (1H, dd, J¼6.4, 9.6 Hz),
4.1.13. (4S,6R)-3-tert-Butoxycarbonylamino-6-carba-
moyloxymethyl-tetrahydro-2H-1,3-oxazin-3-carboxylic
acid 23. A mixture of 22 (0.54 g, 1.37 mmol) and 10% Pd–C
(0.1 g) in MeOH (10 ml) was subjected to a catalytic hydro-
genation for 1 h at ordinary temperature. The reaction mix-
ture was filtered with the aid of Celite and the filtrate was
evaporated to give 23 (0.409 g, 98%) as amorphous solid.
(4S,6R)-23: [a]2D0 ꢁ40.98 (c 0.82, CHCl3); IR (KBr): 3443,
3367, 1733, 1715, 1703 cmꢁ1. NMR (pyridine-d5, 90 ꢀC):
d 1.48 (9H, s), 2.31–2.38 (2H, m), 4.08–4.14 (1H, m), 4.29
(1H, dd, J¼4.4, 11.6 Hz), 4.44 (1H, dd, J¼6.4, 11.6 Hz),
4.70 (1H, d, J¼7.6 Hz), 5.20 (1H, d, J¼9.6 Hz), 5.31 (1H,
d, J¼9.6 Hz), 6.66 (2H, br s), 7.77 (1H, br s). Anal. Calcd