I. Ibnusaud et al. / Tetrahedron 58 ꢀ2002) 4887±4892
4891
2
7
requires C, 64ꢀ86; H, 4ꢀ89%]; [a]D 134ꢀ7 .c 1ꢀ0, CHCl );
dC .400 MHz, DMSO-d ) 172ꢀ7, 170ꢀ8, 166ꢀ1, 81ꢀ96,
6
77ꢀ90, 53ꢀ12, 53ꢀ03, 40ꢀ14; FABMS m/z 219 .66, M11),
191 .2), 159 .100), 141 .10), 130 .38), 99 .100), 74 .25%)ꢀ
3
2
nmax .KBr) 3500, 3100, 1820, 1700 cm ; d .400 MHz,
1
H
CDCl ) 7ꢀ25±7ꢀ34 .10H, m, CH Ar); 5ꢀ09±4ꢀ92 .4H, m,
3
2
CH Ar); 4ꢀ87 .1H, s, CH±COOCH Ar); 3ꢀ07 .1H, d,
2
2
J13ꢀ5Hz, C H H COHCOOCH Ar); 2ꢀ80 .1H, d,
2.1.11. Dimethyl !2S,3R)-tetrahydro-3-oxo-[!methyl-
thio)methoxy]-5-oxo-2,3-furandicarboxylate !2c). The
procedure adopted for 1c was followed using acetic acid
.1ꢀ5mL), acetic anhydride .10 mL), 2b .1 g, 4ꢀ6 mmol)
and anhydrous DMSO .14 mL)ꢀ After work-up and puri®ca-
tion of the crude product by column chromatography .18%
hexne/chloroform), gave the title compound 2c 0ꢀ50 g
19ꢀ3% as a yellow oilꢀ [Found: C, 42ꢀ43; H, 5ꢀ04ꢀ
a
b
2
J13ꢀ5Hz, CH H COHCOOCH Ar); dC .400 MHz,
a
b
2
CDCl ) 171ꢀ8, 170, 166ꢀ2, 134ꢀ3, 133ꢀ8, 129ꢀ1, 128ꢀ8,
3
1
28ꢀ7, 128ꢀ6, 84ꢀ1, 78ꢀ9, 69ꢀ0, 67ꢀ9, 39ꢀ7; m/z .EIMS) 370
7ꢀ0, M1), 280 .6ꢀ6), 251 .3ꢀ9), 180 .9ꢀ4), 107 .86ꢀ4), 91
.
.
100), 65.20ꢀ8), 43 .4ꢀ4%)ꢀ
2
2
.1.8. Isolation of !2S,3R)-tetrahydro-3-hydroxy-5-oxo-
,3,furandicarboxylic acid !Hibiscus acid, 2). A: To
1
1
19
C H O S requires C, 43ꢀ32; H, 5ꢀ05%]; [a] 2147ꢀ7
1
0
14
7
D
2
1
the hexane washed, concentrated water extract .250 mL)
of fresh leaves of Hibiscus furcatus/Hibiscus sabdariffa
.c 0ꢀ98, CHCl ); n
3
.liquid ®lm) 1800, 1745cm ; d
max H
.400 MHz, CDCl ) 5ꢀ10 .1H, s, CH±COOMe); 4ꢀ74 .2H,
3
.
1 kg), acetone .1 L) was added to precipitate insoluble
s, SCH ); 3ꢀ77 .3H, s, CH±COOMe); 3ꢀ76 .3H, s, COCH S
2
2
materialsꢀ After evaporating the acetone, suf®cient NaOH
solution .8 M) was added to adjust the pH to 12ꢀ0ꢀ Addition
of alcohol .ca 1 L) resulted in the precipitation of trisodium
salt of 2ꢀ The pH was readjusted to 2ꢀ0 by the addition of
HCl .2 M) and which was concentrated to a syrup followed
by extraction with acetone .2£250 mL)ꢀ The crude acid .2)
resulted, upon concentration, was recrystallised .ether±
chloroform) to yield 10 g of 2 .1%) as colourless crystalsꢀ
CH COOMe); 3ꢀ23 .1H, d, J1ꢀ9 Hz, CH H COCH SCH -
a b 2 3
3
a
b
2
3
COOMe); 2ꢀ97 .1H, d, J17ꢀ9 Hz, CH H COCH SCH -
COOMe); 2ꢀ14 .3H, s, SMe); d .400 MHz, CDCl ) 172ꢀ0,
C
3
168ꢀ0, 167ꢀ1, 85ꢀ0, 81ꢀ7, 71ꢀ4, 53ꢀ3, 53ꢀ1, 40ꢀ1, 14ꢀ5; m/z
.EIMS) 278 .11ꢀ6, M1), 262 .13ꢀ3), 259 .24ꢀ3), 220 .8ꢀ7),
219 .64ꢀ9), 191 .29ꢀ9), 159 .100), 141 .14ꢀ6), 131 .11ꢀ9), 113
.5ꢀ2), 99 .40ꢀ3), 90 .4ꢀ5), 69 .2ꢀ98), 59 .17ꢀ1), 44 .25ꢀ3%)ꢀ
2.1.12. Diethyl !2S,3R)-tetrahydro-3-hydroxy-5-oxo-2,3-
B: Fresh calyxes .1 kg) of Hibiscus sabdariffa were
extracted following the procedure described above yielding
furandicarboxylate !2d). The procedure adopted for 1d
was followed with 2a .1ꢀ0 g, 4ꢀ4 mmol), ethanol .10 mL)
and thionyl chloride .0ꢀ7 mL, 10 mmol)ꢀ After work-up and
puri®cation gave the title compound 2d .0ꢀ8 g, 68%) as a
pale yellow liquid; [Found: C, 48ꢀ65; H, 5ꢀ70ꢀ C H O
8
6 g of 2 .1ꢀ6%)ꢀ Mp 1828C requires 182±1838C; [Found:
1
C, 37ꢀ72; H, 3ꢀ15ꢀ C H O requires C, 37ꢀ89; H, 3ꢀ16%];
6
6
7
2
7
8
25
[
H O); n
a]D 1111 .c 1ꢀ0, H O), litꢀ [a] 1110 .c 1ꢀ37,
2
D
10 14
7
2
1
.KBr) 3400, 1790, 1735cm ; d .400 MHz,
27
requires C, 48ꢀ98; H, 5ꢀ71%]; [a]D 151ꢀ4 .c 1ꢀ0,
2
max
H
2
.liquid ®lm) 3450, 1800, 1740 cm ; d
3 max H
1
acetone-d ) 5ꢀ38 .1H, s, CH±COOH); 3ꢀ30 .1H, d,
6
CHCl ); n
J17ꢀ1 Hz, CH H COHCOOH); 2ꢀ80 .1H, d, J17ꢀ1 Hz,
.400 MHz, CDCl ) 5ꢀ10 .1H, s, CH±COOEt); 4ꢀ20 .4H,
3
a
b
CH H COHCOOH); d .400 MHz, acetone-d ) 173ꢀ2,
C
m, OCH CH £2); 3ꢀ90 .1H, d, J19ꢀ6 Hz, CH H COH-
a
b
6
2
3
a
b
1
72ꢀ3, 167ꢀ1, 82ꢀ9, 78ꢀ4, 42ꢀ2; m/z .EIMS) 191 .2, M11),
COOEt); 3ꢀ10 .1H, d, J19ꢀ6 Hz, CH H COHCOOEt);
a
b
1
.
72 .1), 162 .5), 145 .60), 127 .12), 116 .38), 99 .84), 88
100), 60 .48), 55 .28%)ꢀ
1ꢀ18±1ꢀ32 .6H, m, CH CH £2); d .400 MHz, CDCl )
2 3 C 3
173ꢀ0, 170ꢀ5, 170ꢀ0, 82ꢀ0, 74ꢀ0, 62ꢀ5, 62ꢀ0, 44ꢀ0, 15ꢀ0; m/z
EIMS) 246 .14ꢀ7 M11), 218 .30ꢀ80), 188 .27ꢀ9), 144
.
2
.1.9. Disodium!2S,3R)-tetrahydro-3-hydroxy-5-oxo-2,3-
.100), 114 .27ꢀ9), 103 .28), 98ꢀ .57ꢀ3), 82 .52ꢀ9), 75
.55ꢀ8) 57 .5ꢀ88), 46 .26ꢀ4), 42 .44ꢀ1%)ꢀ
furandicarboxylate !2a). The procedure adopted for 1a
was followed with 2 and obtained as a colourless solid
.
2ꢀ0 g, 82%); [Found: C, 30ꢀ74; H, 1ꢀ70ꢀ C H O Na
2
2.1.13. Diisopropyl !2S,3R)-tetrahydro-3-hydroxy-5-oxo-
2,3-furandicarboxylate !2e). The procedure adopted for 1e
was followed with 2a .1ꢀ0 g, 4ꢀ4 mmol), isopropyl alcohol
.10 mL) and thionyl chloride .0ꢀ7 mL, 10 mmol)ꢀ 2e was
isolated as a pale yellow oil .0ꢀ5g, 41%); [Found: C,
52ꢀ47; H, 6ꢀ58, C H O requires C, 52ꢀ55; H, 6ꢀ57%];
6
4
7
2
9
requires C, 30ꢀ76; H, 1ꢀ71%]; [a]D 156ꢀ5 .c 1ꢀ02,
2
1
H O); n
2
.KBr) 3400, 1800, 1600 cm ; d .400 MHz,
H
max
D O) 5ꢀ17 .1H, s, CH±COONa), 3ꢀ21 .1H, d, J17ꢀ8 Hz,
2
CH H COHCOONa); 2ꢀ24 .1H, d, J17ꢀ8 Hz, CH H COH-
a
b
a
b
COONa); 2ꢀ27 .1H, s, COHCOONa); d .400 MHz, D O)
2
C
12 18
7
2
7
1
79ꢀ9, 178ꢀ1, 173ꢀ9, 88ꢀ5, 80ꢀ5, 43ꢀ7; m/z .ESI) 257 .100,
M123), 238 .41ꢀ23), 195.43 ꢀ95 ), 168 .39ꢀ9), 142ꢀ1
15ꢀ96%)ꢀ
[a]D 141ꢀ2 .c 1ꢀ0, CHCl ); n
.liquid ®lm) 3500,
max
3
2
1800, 1740 cm ; d .400 MHz, CDCl ) 5ꢀ10 .1H, m,
1
H
3
.
CH±COOCHMe ); 4ꢀ90 .1H, m, COH±COOCHMe );
2 2
4
ꢀ27 .1H, s, CH±COOCHMe ); 3ꢀ10 .1H, d, J17ꢀ3 Hz,
2
2.1.10. Dimethyl !2S,3R)-tetrahydro-3-hydroxy-5-oxo-
2,3-furandicarboxylate !2b). A solution of 2 .1ꢀ0 g,
5ꢀ25 mmol in 25 mL ether) was treated with excess diazo-
CH H COHCOOCHMe ); 2ꢀ80 .1H, d, J17ꢀ3 Hz, CH H
a
b
2
a
b-
C
COHCOOCHMe ); 1ꢀ10±1ꢀ30 .12H, m, CH.CH ) £2); d
2 3 2
.400 MHz, CDCl ) 171ꢀ7, 170ꢀ21, 169ꢀ5, 82ꢀ0, 74ꢀ6, 70ꢀ0,
3
methane in etherꢀ The reaction mixture on concentration
gave the title compound 2b .1ꢀ13 g; 98%) as colourless
crystalsꢀ Mp 128±1298C; [Found: C, 44ꢀ07; H, 4ꢀ61ꢀ
68ꢀ4, 40ꢀ6, 21ꢀ5, 20ꢀ6; m/z .EIMS) 274 .2ꢀ9, M1), 246 .5ꢀ9),
232 .4ꢀ9), 216 .5ꢀ9), 204 .13ꢀ4), 190 .11ꢀ9), 174 .20ꢀ8), 162
.35ꢀ8), 144 .52ꢀ2), 132 .47ꢀ7), 117 .10ꢀ4), 98 .14ꢀ9), 86
.4ꢀ4), 76 .41ꢀ7), 42 .100%)ꢀ
2
2
C H O requires C, 44ꢀ04; H, 4ꢀ59%]; [a] 1116 .c
8
10
7
D
8
25
0
.
ꢀ49, MeOH), litꢀ [a]D 1112 .c 0ꢀ49, MeOH); n
H 3
max
2
KBr) 3500, 1795, 1745 cm ; d .400 MHz, CDCl ) 5ꢀ31
1
2.1.14. Dibenzyl !2S,3R)-tetrahydro-3-hydroxy-5-oxo-
2,3-furandicarboxylate !2f). The procedure adopted for
1f was followed with 2 .4ꢀ0 g, 20ꢀ8 mmol), benzyl alcohol
.6ꢀ4 mL), p-toluene sulphonic acid monohydrate .50ꢀ0 mg,
.
1H, s, CH±COOMe); 3ꢀ95.3H, s, CH±COO Me); 3ꢀ84 .3H,
s, COH±COOMe); 3ꢀ10 .1H, d, J20ꢀ3 Hz, CH H COH-
a
b
COOMe); 2ꢀ87 .1H, d, J20ꢀ3 Hz, CH H COHCOOMe);
a
b