6
SATO ET AL.
the mixture that was then stirred at 25ꢀC for 16 hours.
The reaction mixture was extracted twice with AcOEt.
The organic layer was washed with 0.1 M HCl and brine,
and dried with anhydrous Na2CO3. After evaporation,
the residue was purified using silica gel column chroma-
tography (1:1 1-hexane:AcOEt) to afford 10 (42 mg, 64%
yield) as an ivory colored powder.
Ivory prism (EtOH). Mp > 300ꢀC. Rf 0.41 (5:2:0.5 tolu-
ene: AcOEt: AcOH). IR (KBr) ν: 3588, 3470, 3338, 1822,
1617, 1587, 1428, 1406, 1365, 1328, 1296, 1226,
1
1177 cm−1. H NMR (DMSO-d6): δ 13.43, 13.43, 13.10,
11.19, 9.93 (total 5H, each s, OH x 5), 5.38 and 5.35 (total
1H, each s, >CH-), 2.68 and 2.64 (total 6H, s, Ac × 2),
1.883 and 1.877 (total 6H, each s, CH3 × 2). 13C NMR
(DMSO-d6): δ 7.72, 8.64, 30.64, 32.22, 32.76, 100.36,
102.78, 102.90, 103.12, 105.67, 105.71, 105.78, 105.81,
105.89, 106.02, 153.40, 153.44, 157.54, 157.67, 159.81,
159.99, 160.89, 161.19, 175.78, 175.93, 200.75, 200.93,
203.51, 203.69. HRESIMS: (m/z) Calcd for C20H17O9 [M-
H]−: 401.0878. Found: 401.0889.
Ivory powder. Rf 0.42 (20:1 CHCl3:MeOH). IR (KBr)
ν: 3021, 2940, 2858, 1784, 1754, 1706, 1623, 1594, 1435,
1371, 1229, 1192, 1140, 1112 cm−1.1H NMR (DMSO-d6): δ
1.617, 1.766, 1.896, 2.011, 2.036, 2.046, and 2.067 (each
3H, s, OAc × 7), 2.290 (6H, s, ArOAc×2), 2.283 and 2.367
(each 3H, s, ArOAc×2), 2.379 and 2.397 (each 3H, s, C-
Ac × 2), 3.712 (3H, s, CO2Me), 3.92 (each 1H, dd, J = 1.6
and 12.5 Hz, H-6'a) and 3.99 (each 1H, dd, J = 1.7 and
13.3 Hz, H-600a), 4.12 (m, 2H, H50, 500), 4.55 (dd, 1H,
J = 4.1 and 13.3 Hz, H6'b), 4.68 (dd, 1H, J = 5.0 and
12.5 Hz, H600b), 5.42 and 5.47 (each t, 1H, J = 9.2 Hz, H30,
300), 5.48 and 5.49 (each d, 1H, J = 9.2 Hz, H10, 100), 5.52
and 5.57 (each t, J = 9.2 Hz, H20, 200). 13C NMR (CDCl3):
δ (xanthene moiety) 53.92, 70.79, 114.63, 114.90, 126.52,
127.14, 145.57, 146.32, 148.3, 148.7, 149.3, 149.4, 166.4,
196.34, 196.65, (glucose moiety) 61.94, 62.02, 67.66, 67.72,
71.35, 71.47, 72.56, 72.90, 74.52, 74.61, 77.00, 77.26, (ace-
tyl group) 19.98, 20.24, 20.44, 20.53, 20.56, 20.59, 20.71,
21.08, 21.14, 30.25, 30.58, 167.71, 167.93, 168.02, 168.55,
168.58, 168.79, 169.54, 169.57, 169.78, 169.92, 170.30,
170.37, 196.34, 196.65. HRESIMS: (m/z) Calcd for
C57H62NaO33: 1297.3071. Found: 1297.3061.
4.7 | Synthesis of methyl 2,5-diacetyl-
1,3,8-trihydroxy-4,7-dimethyl-3-oxo-3H-
xanthene-9-carboxylate (6) and methyl
2,7-diacetyl-1,6,8-trihydroxy-4,5-dimethyl-
3-oxo-3H-xanthene-9-carboxylate (7)
Dimer-lactone 5 (197 mg, 0.49 mmol) was dissolved in
MeOH (1.0 mL), followed by the addition of the pyridine
mixture (11 Equation 436 μL). The resulting solution was
stirred vigorously at 25ꢀC under air or O2 atmosphere
(cooler or balloon) for 18 hours. After confirmation of the
completion of reaction and the production of two red
dyes, the organic solvent was removed by evaporation.
The residue was dissolved in AcOEt, washed with a
0.1 M HCl aqueous solution, water, and brine, and then
dried with Na2SO4. After evaporating the organic solvent,
the residue was separated using silica-gel column chro-
matography (toluene:AcOEt:AcOH with ranging from
6:1:0.2 to 6:3:1 ratio) to afford 6 (102 mg, 50% yield) as a
reddish-purple dye and 7 (73 mg, 36% yield) as a fluores-
cent red dye.
4.6 | Synthesis of 7-acetyl-3-(3-acetyl-
2,4,6-trihydroxy-5-methylphenyl)-
4,6-dihydroxy-5-methylbenzofuran-2(3H)-
one and 5-acetyl-3-(3-acetyl-
2,4,6-trihydroxy-5-methylphenyl)-
4,6-dihydroxy-7-methylbenzofuran-2(3H)-
one (5)
4.8 | Methyl 2,5-diacetyl-1,3,8-trihydroxy-
4,7-dimethyl-3-oxo-3H-xanthene-
9-carboxylate (6)
3-Methylphloroacetophenone (4) (119 mg, 0.705 mmol)
and 0.5 eq. of glyoxylic acid monohydrate (30 mg,
0.352 mmol) were dissolved in 5% aq. Na2CO3 (0.5 mL)
and MeOH (1.5 mL); the resulting mixture was stirred at
25ꢀC under Ar atmosphere for 6 hours. After confirming
the completion of reaction by means of TLC (toluene:
AcOEt:AcOH in 5:2:0.5 ratio), 1 M HCl (3 mL) was added
to the mixture, and then extracted twice with AcOEt. The
organic layer was washed with water and brine, and then
dried with Na2SO4. After removing the organic solvent,
the residue was purified using silica gel column chroma-
tography (toluene:AcOEt:AcOH with ranging from 6:1:0.2
to 6:3:1) to afford dimer-lactone 5 (266 mg, 94% yield) as a
pale-red powder, that was crystallized from EtOH.
Dark purple prism (from acetone). Mp > 300ꢀC. Rf 0.79
(6:3:1 toluene:AcOEt:AcOH). IR (KBr) ν: 3254, 2951,
1754, 1647, 1581, 1508, 1448, 1429, 1404, 1274, 1217,
1161 cm−1. UV-Vis (MeOH) (log ε) 284 (4.16), 338 (4.25),
528 (3.98) nm. 1H NMR (DMSO-d6, 50ꢀC): δ 2.00 and 2.04
(each s, 3H, CH3 × 2), 2.49 and 2.56 (each s, 3H, Ac × 2),
3.89 (s, 3H, CO2CH3), 8.29, 14.6, and 18.02 (each s, 1H,
OH × 3). 13C NMR (DMSO-d6, 50ꢀC): δ 8.03, 13.92, 29.44,
33.20, 52.11, 103.77, 108.41, 108.60, 108.76, 108.81,
115.22, 141.40, 155.51, 156.00, 159.36, 166.70, 167.85,
175.36, 181.15, 202.27, 202.45.