filtered through Celite and the filtrate, after neutralisation with
sodium hydrogen carbonate, was concentrated in vacuo. The oil
recovered by extraction with ethyl acetate was chromato-
graphed (hexane–ethyl acetate, 7:3 v/v) to give the anthra-
quinone 8a (0.823 g, 85%) as a glass, [α]D20 ϩ33 (c 1, CHCl3);
νmax(CHCl3)/cmϪ1 1727, 1672, 1584 and 1465; λmax(EtOH)/nm
(log ε) 269 (4.472) and 375 (3.77); δH(500 MHz; CDCl3) 1.396 (3
H, t, J 7, OCH2CH3), 2.638 (3 H, s, 1-Me), 3.626 (1 H, ddd, J5Ј,4Ј
9.5, J5Ј,6Јa 4, J5Ј,6Јb 2, 5Ј-H), 3.718 (1 H, dd, J6Јb,6Јa 11, J6Јb,5Ј 2, 6Ј-
Hb), 3.75–4.00 (4 H, overlapping, 1Ј-, 2Ј-, 3Ј- and 4Ј-H), 3.776
(1 H, dd, J6Јa,6Јb 11, J 4.0, 6Ј-Ha), 3.832 (3 H, s, OMe), 3.842
(3 H, s, OMe), 3.996 (3 H, s, OMe), 4.178 (1 H, d, J 11,
OCHAr), 4.438 (2 H, q, J 7, OCH2CH3), 4.504 (1 H, d, J 12,
OCHAr), 4.566 (1 H, d, J 11, OCHAr), 4.572 (1 H, d, J 12,
OCHAr), 4.660 (1 H, d, J 10.5, OCHAr), 4.881 (1 H, d, J 10.5,
OCHAr), 4.937 (1 H, part B of an AB system, J 11, OCHAr),
4.962 (1 H, part A of an AB system, J 11, OCHAr), 7.136 (1 H,
s, 6-H), 6.80–7.35 (20 H, ArH) and 7.572 (1 H, s, 4-H).
chromatography on silica gel (chloroform–ethanol) and the
tetraol acid 1d was obtained as a light yellow glass (0.551 g,
83%), which was directly acetylated.
1-Methyl-3,5,8-trimethoxy-9,10-dioxo-7-(2Ј,3Ј,4Ј,6Ј-tetra-O-
acetyl-â-D-glucopyranosyl)-9,10-dihydroanthracene-2-carboxylic
acid 1e
(i) The tetraol acid 1d (0.497 g, 0.959 mmol), pyridine (3.82 g,
3.90 cm3, 48.2 mmol) and acetic anhydride (0.97 g, 0.90 cm3,
9.53 mmol) in dry, stirred dichloromethane (50 cm3) containing
4-(dimethylamino)pyridine (DMAP) (0.012 g, 0.10 mmol) were
allowed to react together at ambient temperature until TLC
showed absence of 1d. After work-up [acidification, extraction,
and column chromatography on silica gel (gradient elution
with chloroform–ethanol)], title acid 1e was obtained as a pale
yellow glass (0.270 g, 41%), Rf 0.45 (CHCl3–MeOH, 4:1)
(Found: [M ϩ H]ϩ, 687.1925. C33H35O16 requires m/z,
687.1925); δH(400 MHz; CDCl3) 1.779 (3 H, s, 2Ј-Ac), 1.963,
1.995 and 2.014 (3 × 3 H, 3 s, 3Ј-, 4Ј- and 6Ј-OAc), 2.658 (3 H, s,
1-Me), 3.845, 3.931 and 3.962 (3 × 3 H, 3 s, 3-, 5- and 8-OMe),
3.86–3.90 (1 H, m, 5Ј-H), 4.07–4.12 (1 H, m, 6Ј-Ha), 4.17–4.21
(1 H, m, 6Ј-Hb), 5.00 (1 H, d, J 9.7, 1Ј-H), 5.15–5.20 (1 H, m, 4Ј-
H), 5.35–5.38 (2 H, m, 2Ј- and 3Ј-H), 7.275 (1 H, s, 6-H) and
7.499 (1 H, s, 4-H); δC(400 MHz; CDCl3) 18.37, 20.38, 20.52
and 20.63 (4 × OAc), 29.57 (1-Me), 56.30, 56.62, 62.28, 63.63,
68.55, 70.86, 74.19, 76.49 and 77.10 (3 × OMe, glucose-H),
106.36, 116.46, 122.22, 126.72, 129.57, 138.57, 139.00, 151.56,
155.61 and 158.80 (C-aryl), 169.25, 169.55, 170.13 and 170.54
Ethyl 7-â-D-glucopyranosyl-3,5,8-trimethoxy-1-methyl-9,10-
dioxo-9,10-dihydroanthracene-2-carboxylate 8b
A solution of the ethyl ester 8a (1 g, 1.2 mmol) in methanol (400
cm3) containing 10% Pd–C (0.200 g) and acetic acid (1 cm3) was
hydrogenolysed at ambient temperature and pressure during
a period of 6 h. Filtration, and evaporation of the solvent,
gave the product 8b (0.510 g, 85%) as a yellow solid (from diiso-
propyl ether), mp 142–145 ЊC (decomp.); [α]D20 Ϫ23 (c 1, CHCl3);
νmax(KBr)/cmϪ1 3600, 3420, 1725, 1670, 1585 and 1468;
λmax(EtOH)/nm (log ε), 269 (4.39) and 383 (3.72); δH(500 MHz,
CDCl3) 1.386 (3 H, t, J 7, OCH2CH3), 2.586 (3 H, s, 1-Me),
3.5–4.0 (6 H, overlapping, 2Ј-, 3Ј-, 4Ј- and 5Ј-H and 6Ј-H2),
3.982 (3 H, s, OMe), 3.941 (3 H, s, OMe), 3.982 (3 H, s, OMe),
4.417 (2 H, q, J 7, OCH2CH3), 4.779 (1 H, d, J 9, 1Ј-H), 7.352
(1 H, s, 6-H) and 7.535 (1 H, s, 4-H).
(4 × OCOCH ) and 187.50 and 184.34 (quinone C᎐O); m/z
᎐
3
(FAB) (709 [M ϩ Na]ϩ, 57%) and 687 ([M ϩ H]ϩ, 100).
Other fractions separated were partially acetylated material
(0.170 g) and an impurity (0.157 g), Rf 0.98 (CHCl3–MeOH,
4:1), 0.54 (CHCl3–EtOAc, 1:1).
(ii) A solution of the ethyl ester 8b (1 g, 1.83 mmol) in
methanol (25 cm3) was refluxed with 20% aq. sodium hydroxide
(25 cm3) for 6 h. After cooling, the mixture was acidified with
conc. HCl, concentrated, extracted with butan-1-ol, and the
extracts were evaporated. The residue (crude acid 1d) was
acetylated with acetic anhydride (3 cm3) in pyridine (6 cm3)
containing DMAP (0.200 g) during 12 h. Work-up afforded
the crude acetate, which was crystallised (diisopropyl ether) to
give the title acid 1e (0.815 g, 65%) as a yellow solid, mp 146–
148 ЊC (decomp.); [α]D Ϫ33.3 (c 1, CHCl3); νmax(KBr)/cmϪ1
1750, 1675, 1583, 1465, 1370 and 1332; δH(500 MHz; CDCl3)
1.818 (3 H, s, OAc), 2.003 (3 H, s, OAc), 2.034 (3 H, s, OAc),
2.054 (3 H, s, OAc), 2.699 (3 H, s, 1-Me), 3.888 (3 H, s, OMe),
3.921 (1 H, ddd, J5Ј,4Ј 9.5, J5Ј,6Јa 5.5, J5Ј,6Јb 2.5, 5Ј-H), 3.970 (3 H,
s, OMe), 4.003 (3 H, s, OMe), 4.140 (1 H, dd, J6Јb,6Јa 12.5, J6Јb,5Ј
2.5, 6Ј-Hb), 4.234 (1 H, dd, J6Јa,6Јb 12.5, J6Јa,5Ј 5.5, 6Ј-Ha), 5.044 (1
H, d, J1Ј,2Ј 9.5, 1Ј-H), 5.218 (1 H, dd, J4Ј,5Ј 9.5, J4Ј,3Ј 9.5, 4Ј-H),
5.378 (1 H, dd, J3Ј,2Ј 9.5, J3Ј,4Ј 9.5, 3Ј-H), 5.412 (1 H, dd, J2Ј,3Ј 9.5,
J2Ј,1Ј 9.5, 2Ј-H), 7.319 (1 H, s, 6-H) and 7.544 (1 H, s, 4-H).
Benzyl 3,5,8-trimethoxy-1-methyl-9,10-dioxo-7-(2Ј,3Ј,4Ј,6Ј-
tetra-O-benzyl-â-D-glucopyranosyl)-9,10-dihydroanthracene-2-
carboxylate 8c
2,3,4,6-Tetra-O-benzyl--glucopyranose (1.00 g, 1.85 mmol)
and TFAA (1.0 cm3, 1.49 g, 7.1 mmol) were allowed to react in
dichloromethane (10 cm3) to form the trifluoroacetate as
described for compound 6. After removal of excess of reactant
in vacuo, a solution of the anthracene 5c (1.76 g, 3.70 mmol) in
dichloromethane (5.0 cm3) was added. The solution was cooled
to Ϫ40 ЊC and cold boron trifluoride–diethyl ether (3.55 mmol)
added slowly, after which the temperature was allowed to rise to
ambient and the reaction mixture was then stirred for 24 h
(under N2). Following monitoring by TLC and work-up (acid-
ification and dichloromethane extraction), the brown viscous
syrup (containing C-glycoside 7b) obtained by evaporation of
the mixture was dissolved in dichloromethane (50 cm3) and the
solution stirred with PCC (0.80 g, 3.7 mmol) for 15 min. Ether-
eal extraction, filtration, evaporation and column chroma-
tography on silica gel (diethyl ether–light petroleum) afforded
the title anthraquinone 8c as a brown syrup (1.400 g, 78%)
(Found: [M ϩ H]ϩ, 969.3850. C60H57O12 requires m/z,
969.3850); δH(200 MHz; CDCl3) 2.56 (3 H, s, 1-Me), 3.78, 3.86
and 3.92 (9 H, 3 s, 3-, 5- and 8-OMe), 3.50–5.00 (15 H, m, 1Ј-,
2Ј, 3Ј-, 4Ј- and 5Ј-H, 6Ј-H2 and 4 × OCH2Ph), 5.37 (2 H, s,
CO2CH2Ph), 6.70–7.50 (26 H, m, 6-H and 5 × Ph) and 7.59
(1 H, s, 4-H); m/z (FAB) 969 ([M ϩ H]ϩ, 24%).
3,5,8-Trihydroxy-1-methyl-9,10-dioxo-7-(2Ј,3Ј,4Ј,6Ј-tetra-O-
acetyl-â-D-glucopyranosyl)-9,10-dihydroanthracene-2-
carboxylic acid (6-deoxycarminic acid tetraacetate) 1f
To a solution of compound 1e (0.157 g, 0.058 mmol) in dry
dichloromethane (10 cm3) at Ϫ80 ЊC was added boron tri-
bromide as a solution in dichloromethane (0.60 cm3, 0.60
mmol) cooled to Ϫ80 ЊC. The temperature of the mixture was
allowed to rise slowly to 0 ЊC and was kept at that value for 24 h.
Work-up with 1 hydrochloric acid, extraction with dichloro-
methane, drying, filtration and recovery followed by TLC on
silica gel (CHCl3–MeOH, 5:1) gave the trihydroxy product
1f, isolated as an orange-red glass (0.106 g, 72%), Rf 0.26
(CHCl3–MeOH, 5:1) (Found: [M ϩ H]ϩ, 645.1456. C30H29O16
requires m/z, 645.1455); νmax(KBr)/cmϪ1 3400br (O᎐H), 2960w
7-â-D-Glucopyranosyl-1-methyl-3,5,8-trimethoxy-9,10-dioxo-
9,10-dihydroanthracene-2-carboxylic acid 1d
The quinone 8c (1.240 g, 1.28 mmol) with 10% Pd–C (0.130 g) in
THF containing conc. hydrochloric acid (0.65 cm3) was hydro-
genolysed at atmospheric pressure until no further absorption
of hydrogen occurred. After filtration, and aerial oxidation of
the filtrate, the recovered material was purified by column
and 2840w (C᎐H, aliph), 1740 and 1630 (C᎐O), 1570 (aryl),
᎐
1430, 1370, 1220 and 1030; δH(200 MHz; CDCl3) 1.90 (3 H, s,
2Ј-OAc), 2.01, 2.02 and 2.12 (3 × 3 H, 3Ј, 4Ј and 6Ј- OAc), 2.88
580
J. Chem. Soc., Perkin Trans. 1, 1998