Synthesis of Cytoxazone
147
was stirred at room temperature. A conventional workup
afforded (ꢁ)-6 (143.2 mg, quantitative from 4), whose
purity was good enough as judged from its TLC
analysis. This compound was recrystallized from a
mixture of hexane (0.5 ml) and ethyl acetate (1.0 ml) to
afford colorless fine needles (91.4 mg, 67%), mp 151.4–
151.5 ꢀC. NMR ꢁH (270 MHz, CDCl3): 1.41 (9H, s),
2.37 (1H, d, J ¼ 6:9 Hz), 3.05 (1H, s), 3.65–3.75 (2H,
m), 3.75–3.85 (1H, m), 3.79 (3H, s), 4.61 (1H, t,
J ¼ 7:7 Hz), 5.07 (1H, m), 6.89 (2H, d, J ¼ 8:6 Hz),
7.24 (2H, d, J ¼ 8:6 Hz). Anal. Found: C, 60.61; H,
7.74; N, 4.61%. Calcd. for C15H23NO5: C, 60.59; H,
7.80; N, 4.71%. Its NMR spectrum was identical with
that reported previously.6) Any attempts at in situ
cyclization by either applying refluxing temperature, or
adding DBU (1.5 eq.) or DMAP (1.0 eq.) had no further
effect on the desired reaction.
mp 143–144 ꢀC]. IR ꢀmax cmꢃ1: 3371, 3265, 2960, 1734,
1616, 1520, 1429, 1311, 1254, 1223, 1036, 980, 850,
814; NMR ꢁH (400 MHz, DMSO-d6): 2.90–3.00 (2H,
m), 3.74 (3H, s), 4.69 (1H, ddd, J ¼ 4:4, 7.3, 8.3 Hz),
4.82 (1H, t, J ¼ 5:1 Hz), 4.90 (1H, d, J ¼ 8:3 Hz), 6.92
(2H, d, J ¼ 8:6 Hz), 7.14 (2H, d, J ¼ 8:6 Hz), 8.06 (1H,
s); NMR ꢁC (100 MHz, DMSO-d6): 55.01, 56.18, 61.03,
80.01, 113.56, 127.90, 129.14, 158.61, 158.84. Anal.
Found: C, 59.02; H, 5.91; N, 6.26%. Calcd. for
C11H13NO4: C, 59.19; H, 5.87; N, 6.27%. The spectral
data were identical with those reported previously.1,2,7)
The mother liquor from the final recrystallization was
concentrated in vacuo, and the residue was dissolved in
Ac2O (5.8 ml) and pyridine (5.8 ml). The mixture was
stirred overnight at room temperature. After a conven-
tional workup, the resulting oily residue (605.9 mg) was
loaded into a silica gel column (30 g). Elution with
hexane–EtOAc (2:3) afforded (ꢁ)-8a. The residue was
recrystallized from a mixture of hexane (1.5 m) and
EtOAc (1.4 ml) to afford colorless fine needles
(277.4 mg). The mother liquor was further purified by
preparative thin-layer chromatography [developed twice
with hexane–EtOAc (2:3)] to give 34.3 mg of (ꢁ)-8a,
mp 114.5–114.7 ꢀC. IR ꢀmax cmꢃ1: 3452, 3263, 1776,
1734, 1612, 1514, 1250, 1068, 1047; NMR ꢁH
(270 MHz, CDCl3): 1.98 (3H, s), 3.70–3.90 (2H, m),
3.80 (3H, s), 4.97 (2H, m), 5.37 (1H, s), 6.89 (2H, d,
J ¼ 8:6 Hz), 7.18 (2H, d, J ¼ 8:6 Hz); NMR ꢁC
(100 MHz, CDCl3): 20.64, 55.34, 57.35, 63.04, 77.50,
114.35, 126.96, 127.80, 158.70, 160.04, 170.17. Anal.
Found: C, 58.67; H, 5.70; N, 5.17%. Calcd. for
C13H15NO5: C, 58.86; H, 5.70; N, 5.28%.
(2Rꢂ,3Rꢂ)-3-Carbamylamino-3-(4-methoxyphenyl)pro-
pane-1,2-diol (7). Crude aminoalcohol HCl salt 5 (2.276
g; 6.75 mmol was expected) was dissolved in aq. HCl
(2 M, 0.7 ml) and H2O (3.4 ml), before KCNO (822 mg,
10.1 mmol) was added portionwise at room temperature.
The mixture was stirred overnight and concentrated in
vacuo. The residual solid was extracted with EtOH, and
the extract was concentrated in vacuo again to give
carbamylamino alcohol (ꢁ)-7 (1.996 g, quantitative) as a
viscous oil. NMR ꢁH (270 MHz, CD3OD): 3.20–3.40
(2H, m), 3.67 (3H, s), 3.67–3.72 (1H, m), 4.64 (1H, d,
J ¼ 5:2 Hz), 6.77 (2H, d, J ¼ 8:6 Hz), 7.17 (2H, d,
J ¼ 8:6 Hz). This was employed for the next step
without further purification.
Epimeric (ꢁ)-8b was isolated in the course of
preparative TLC separation (1.8 mg, 0.2% from 4).
NMR ꢁH (270 MHz, CDCl3): 2.05 (3H, s), 3.75 (3H, s),
4.22 (1H, dd, J ¼ 5:1, 12.3 Hz), 4.28 (1H, dd, J ¼ 3:7,
12.3 Hz), 4.43–4.47 (1H, m), 4.57 (1H, d, J ¼ 6:8 Hz),
5.25 (1H, s), 6.87 (2H, d, J ¼ 8:5 Hz), 7.20 (2H, d,
J ¼ 8:5 Hz).
(4Rꢂ,5Rꢂ)-5-Hydroxymethyl-4-(4-methoxyphenyl)-2-
oxazolidinone (1). Carbamylaminoalcohol 7 was dis-
solved in aq. HCl (3 M, 9.0 ml), the reaction vessel being
briefly evacuated under ultrasonic vibration and then
purged with Ar. To this mixture NaNO2 (465.6 mg,
6.75 mmol) was added. Effervescence of N2 gas was
observed and a white solid precipitated. The mixture
was stirred at room temperature for 2 hr, before NaNO2
(95.5 mg, 1.38 mmol) was added and the reaction
continued for a further 20 min. After being neutralized
by adding aq. NaOH (1 M), the mixture was concentrated
in vacuo. The residual solid was extracted with THF,
and the extract was concentrated in vacuo again. The
resulting solid residue was dissolved in THF (2 ml).
After standing in a refrigerator, a solid (405.4 mg) of
(ꢁ)-1 was precipitated and then recovered by decant-
ation. The supernatant was concentrated in vacuo, the
resulting residue (1.20 g) being loaded into a silica gel
column (120 g). Elution with THF–EtOAc (1:5) afforded
partially purified (ꢁ)-1 (1.13 g). The combined material
was dissolved in THF (9.0 ml) and hexane (3 ml) while
heating. The solution was left to stand in a refrigerator,
and the precipitated crystals were collected by filtration.
Racemic cytoxazone (ꢁ)-1 (794.2 mg, 53% from 4) was
obtained as colorless prisms, mp 143.9–144.1 ꢀC [lit.7)
The combined amount of (ꢁ)-8a was 311.7 mg, and
this was converted into (ꢁ)-1 in a quantitative manner
by treating with triethylamine in refluxing methanol.
The total yield of (ꢁ)-1 then reached 70% from (ꢁ)-4.
Acknowledgment
This work formed part of the 21st century COE
program (Keio LCC) from the Ministry of Education,
Culture, Sports, Science, and Technology of Japan. Keio
Gijuku Funding for the advancement of education and
research is also acknowledged with thanks.
References
1) Kakeya, H., Morishita, M., Kobinata, K., Osono, M.,
Ishizuka, M., and Osada, H., Isolation and biological
activity of a novel cytokine modulator, cytoxazone. J.
Antibioics, 51, 1126–1128 (1998).