A new chemical synthesis of Ascopyrone P from 1,5-anhydro-d-fructose

Article abstract of DOI:10.1016/j.carres.2006.03.037

The naturally occurring antioxidant Ascopyrone P (1,5-anhydro-4-deoxy-d-glycero-hex-1-en-3-ulose, 1) was prepared from the rare sugar 1,5-anhydro-d-fructose (AF, 3) in three steps in an overall yield of 36%. Thus, acetylation of 3 afforded the enolone 3,6-di-O-acetyl-1,5-anhydro-4-deoxy-d-glycero-hex-3-en-2-ulopyranose (4), which could be isomerised to 2,6-di-O-acetyl-1,5-anhydro-4-deoxy-d-glycero-hex-1-ene-3-ulose (6). Deacetylation of 6 under mild conditions gave crystalline Ascopyrone P (1).

Full text of DOI:10.1016/j.carres.2006.03.037

Carbohydrate Research 341 (2006) 1692–1696
Note
A new chemical synthesis of Ascopyrone P from
1,5-anhydro-D-fructose
Mikkel Andreassen and Inge Lundt*
Department of Chemistry, Technical University of Denmark, Building 201, DK-2800 Kgs. Lyngby, Denmark
Received 20 February 2006; received in revised form 21 March 2006; accepted 27 March 2006
Available online 21 April 2006
Abstract—The naturally occurring antioxidant Ascopyrone P (1,5-anhydro-4-deoxy-D-glycero-hex-1-en-3-ulose, 1) was prepared
from the rare sugar 1,5-anhydro-D-fructose (AF, 3) in three steps in an overall yield of 36%. Thus, acetylation of 3 afforded the
enolone 3,6-di-O-acetyl-1,5-anhydro-4-deoxy-D-glycero-hex-3-en-2-ulopyranose (4), which could be isomerised to 2,6-di-O-acetyl-
1,5-anhydro-4-deoxy-D-glycero-hex-1-ene-3-ulose (6). Deacetylation of 6 under mild conditions gave crystalline Ascopyrone P (1).
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Ascopyrone P; 1,5-Anhydro-D-fructose; Antioxidant; Synthesis
1,5-Anhydro-4-deoxy-D-glycero-hex-1-en-3-ulose
(1),
three steps8,9 (Fig. 1). Likewise, an enzymatic prepara-
tion of APP from starch has recently been patented.10
In view of the interesting properties of APP and the
lack of efficient synthetic procedures for its preparation,
we undertook the investigation of synthesis of APP from
1,5-anhydro-D-fructose (3). This rare sugar is formed by
degradation of starch by a-1,4-glucan lyase (EC
4.2.1.13)11,12 and can now be produced enzymatically
from starch13 but has not lead to AF as a commercial
product. The chemistry and biochemistry of AF has
recently been reviewed,14 and we have now developed
and improved chemical synthesis of 1,5-anhydro-
D-fructose.15
Ascopyrone P (APP), is a metabolite from fungi1,2 with
antioxidant and antibacterial activities2,3 as well as
antibrowning properties.4 APP (1) can only be found
in sparse amounts in nature where it is formed predom-
inantly from breakdown of 1,5-anhydro-D-fructose
(AF).5 It has previously been prepared by pyrolysis of
cellulose and other natural occurring polysaccharides
in about 1.5% yield.6 A chemical synthesis of 1 was
reported recently, which started from 2,3,4,6-tetra-O-
acetyl-1,5-anhydro-D-arabino-hex-1-enitol (tetra-O-acet-
yl-2-hydroxy-D-glucal, 2) and gave 1 in an overall yield
of 15%.7 Compound 2 was prepared from D-glucose in
AcO
AcO
HO
O
O
5 steps
15 % 7
Pyrolysis
1.5 % 6
Cellulose
AcO
OAc
O
OH
2
1
APP
Figure 1.
*
Corresponding author. Tel.: +45 4525 2133; fax: +45 4593 3968; e-mail: il@kemi.dtu.dk
0008-6215/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2006.03.037

M. Andreassen, I. Lundt / Carbohydrate Research 341 (2006) 1692–1696
1693
3-keto derivative, which during the acidic work-up
reacts with the solvent.
HO
HO
AcO
AcO
iii
O
O
O
i
Other amines like piperidine and triethylamine were
investigated and they gave similar results. In dichloro-
methane, piperidine afforded the fastest conversion but
triethylamine gave the relative best yield with a ratio
of 4:6 being about 1:4. The rearrangement proved to
be faster when using a secondary amine but the amount
of decomposed material was also greater as 6 is sensitive
to base.
HO
O
AcO
O
O
OAc
3
4
6
AF
ii
AcO
O
Using a tertiary amine gave a slower reaction but an
improved yield. The equilibrium between 4 and 6 was
shifted continuously towards 6 but the product was also
degraded under the reaction conditions. Allowing the
reaction to stir overnight gave a higher ratio of the
desired product but also a lower overall yield of both
substrates. The reaction conditions were optimised to
quench the mixture even if some starting material still
was left. The driving force for the rearrangement is for-
mation of a more stable conjugate system in 6 (–C3(O)–
C2(OAc)@C1–O–) than in 4 (–C4@C3(OAc)–C2(O)–C1)
(Scheme 2). The acetylated APP (6) could be purified
by flash chromatography of the mixture and was iso-
lated in 59% yield.
Finally, deacetylation of 6 to give Ascopyrone P was
performed under acidic conditions because the com-
pound is base sensitive; however, too strongly acidic con-
ditions resulted in an almost quantitative formation of 2-
hydroxy-1-(2-furyl)ethanone (8)20 (Scheme 3). Dry meth-
anol containing 0.01–0.05% dry HCl resulted in a clean
deacetylation to give the crystalline Acopyrone P (1) in
77% yield after column chromatography (Scheme 5).
The contrast in stability between 4 and 6 towards acid
is striking. The enolone 4 could be deacetylated using
strong aqueous acid (4 M HCl) giving the Ascopyrone
M (9) and corresponding isomers thereof,7 whereas
treatment of 6 with 1% HCl in methanol exclusively
gave the furan 8 in 68% yield (Scheme 3). The formation
of 8 probably involves, the addition of water to the
conjugated system in 6 leading to a free sugar, which
EtO
EtO
O
5
Scheme 1. Reagents and conditions: (i) H2O, 30 equiv, 2 h, then Ac2O,
pyridine;19 (ii) DIPEA, EtOH; (iii) Et3N, CH2Cl2.
In our ongoing investigations of using AF as a starting
material for new organic compounds,14,16,17 we envi-
sioned that acetylated APP (6) might be obtained by rear-
rangement of the acetylated enolone 4, which can be
obtained directly from AF (3) by acetylation (Scheme 1).
1,5-Anhydro-D-fructose exists as a mixture of a mono-
mer, the hydrated ketone and two stereoisomeric dimeric
forms14 and acetylation under normal conditions (Ac2O,
pyridine) gave, in addition to the enolone 4, a mixture of
acetylated dimers.14,18 The method was improved by pre-
treating 3 with an excess of water to convert all forms of
AF into the hydrated form before acetylation in pyridine
to give 4 as the only compound.16,19
To perform the rearrangement of 4 into the acetylated
APP (6) secondary and tertiary amines were tested both
in a polar as well as in a non-polar solvent. In ethanol,
N,N-diisopropyl-N-ethyl amine (DIPEA) surprisingly
gave 5, a diethyl ketal of a 3-oxo-compound, as a mix-
ture with starting material (4:1), whereas the same amine
in dichloromethane gave the rearranged product 6 to-
gether with starting material (3.5:1). Formation of the
ketal 5 in ethanol might be explained by a faster selective
deacetylation of the enolic acetate to give formally the
AcO
AcO
+ H+
AcO
AcO
- H+
O
O
O
O
O
O
-
O
-
O
O
O
O
O
O
O
O
O
AcO
O
6
4
O
O
-
O
7
Scheme 2. Mechanism of the rearrangement of enolone 4 to acetylated APP (6).

1694
M. Andreassen, I. Lundt / Carbohydrate Research 341 (2006) 1692–1696
HO
AcO
O
O
O
HCl
O
OH
or
MeOH
O
OH
O
OAc
8
6
1
Ascopyrone P
AcO
HO
HO
O
HCl
O
O
hydrates
+
+
MeOH
AcO
O
HO
O
O
O
9
10
4
Ascopyrone T
Ascopyrone M
Scheme 3. Deacetylation of 6 compared to 4.7
HO
HO
+ H+
HO
+
O
HO
H+
H
O
O
OH2
O
+
- H+
OH2
OH
O
OH
HO
+
OH
HO
OH
HO
OH
1
HO
HO
O
OH
OH
HO
OH
H+
O
- 2 H2O
O
OH
O
HO
O
HO
O
O
HO
OH
8
HO
HO
HO
H2O
O
O
+
H2O
O
+ H+
no ring opening
is possible
HO
O
HO
OH
HO
OH
+
9
Scheme 4. Degradation pathways of 1 and 9 under acidic conditions.
after opening to the aldehyde can be transformed into
the furan as suggested in Scheme 4. A similar conjugate
addition of water to the deacetylated enolone 9 will not
lead to further transformations. It is well known that
sugars are degraded under acidic conditions leading to
formation of aromatic compounds among which are
furan derivatives.21 The 20-furyl hydroxymethyl ketone
(8) has previously been identified in acid degradation
of hexoses21,22 via unsaturated keto sugars.23
one considers D-glucose to be the starting material.
In addition, the overall yield has been improved almost
threefold from approximately 13% (from D-glucose) to
36%.
1. Experimental
1.1. General methods
In conclusion, we have shown that 1,5-anhydro-D-
fructose (3) can be transformed into Ascopyrone P in
three steps in an overall yield of 36% (Scheme 5). Com-
pared to the previous published synthesis, consisting of
five steps and starting from the advanced intermediate
2,3,4,6-tetra-O-acetyl-1,5-anhydro-D-arabino-hex-1-eni-
tol (2)7 or eight steps counting from D-glucose, the
existing synthesis has been shortened by five steps if
TLC was performed on Merck 60 F254 pre-coated sil-
ica plates. Spots were detected by spraying with a solu-
tion of Cemol: 1.5% NH4Mo2O2, 1% Ce(IV)SO4 and
10% H2SO4, followed by heating. For flash chromato-
graphy Silica Gel 60, particle size 40–63 l (Merck) was
used. The following solvent systems were used: (A)
EtOAc/heptane 1:1, (B) EtOAc/hexane 4:1, (C)

M. Andreassen, I. Lundt / Carbohydrate Research 341 (2006) 1692–1696
1695
HO
AcO
AcO
HO
HO
O
O
O
O
iii
ii
i
O
OH
AcO
O
HO
O
O
OAc
1
6
4
3
Scheme 5. Reagents and conditions: (i) H2O, 30 equiv, 2 h, then Ac2O 15 equiv, pyridine, 80%; (ii) Et3N (1.5 equiv), CH2Cl2, 59%; (iii) CH3OH/dry
HCl (0.01%), rt, 20 h, 77%.
EtOAc/heptane/CH2Cl2 1:3:3, (D) CH2Cl2/CH3OH
12:1. Optical rotations were measured on a Perkin–
Elmer 241 polarimeter, and the concentrations are
given in units of g 100 mLꢀ1. [a]D values are given in
units of 10ꢀ1 deg cm2 gꢀ1. NMR spectra were recorded
on Varian Mercury 300. Chemical shifts (d) are
reported in ppm using the solvent residues as internal
standards: CDCl3 7.26 (1H), 77.16 (13C); CD3OD
3.31 (1H); 49.0 (13C).24 Peak multiplicity is reported
as s (singlet), d (doublet), t (triplet), m (multiplet)
and b (broad). Melting points are uncorrected. CH3OH
1.3. 6-O-Acetyl-1,5-anhydro-4-deoxy-D-glycero-hexo-2,3-
diulo-pyranose 3,3-di-ethyl acetal (5)
Acetylated enolone 4 (0.612 g, 2.7 mmol, 1 equiv) was
dissolved in EtOH (15 mL) and DIPEA (0.693 g/ca.
0.77 mL, 2.0 equiv) and the solution was stirred over-
night at rt. The solution was concentrated in vacuo to
a residue to which CH2Cl2 was added together with aq
HCl (1 M). The aqueous phase was extracted with
CH2Cl2 (2 · 10 mL) and the combined organic phases
were washed with aq HCl (1 M), satd aq NaHCO3,
water and dried (MgSO4), filtered and concentrated
in vacuo to yield a brown syrup, which consisted of
starting material and 5 in about 1:1 ratio. Flash chroma-
tography (1:3:3, EtOAc/heptane/CH2Cl2) gave 5 as a
colourless syrup (0.330 g, 47% yield); Rf = 0.26 (solvent
˚
was dried over 3 A molecular sieves, Et3N was dried
over solid KOH, pyridine was dried over solid KOH,
˚
CH2Cl2 was dried over 4 A molecular sieves and
N,N-diisopropyl-N-ethyl-amine (DIPEA) was dried
˚
over 4 A molecular sieves.
1
C); H NMR (CDCl3): d 4.14 (d, 1H, J1a,1b 16.0 Hz,
1.2. 3,6-Di-O-acetyl-1,5-anhydro-4-deoxy-D-glycero-hex-
3-en-2-ulopyranose (4)19
H-1a), 4.06 (dd, 1H, J6a,6b 13.8, J6a,5 7.2 Hz, H-6a),
3.99 (1H, d, J6b–5 3.8 Hz, H-6b), 3.98–3.90 (m, 4H,
2 · CH2O), 3.74 (d, 1H, H-1b), 3.68 (dddd, 1H, J5–4ax
14.1, J5–4eq 4.5 Hz, H-5), 2.82 (dd, 1H, J4ax–4eq
16.7 Hz, H-4ax), 2.59 (dd, 1H, H-4eq), 2.03 (3H, s,
CH3CO), 1.13–1.06 (6H, m, 2 · CH3CH2); 13C NMR
(CDCl3): d 196.1 (C-2), 169.8 (CH3CO), 102.4 (C-3),
78.2 (C-5), 72.7 (C-1), 65.2 (C-6), 59.5, 59.2 (CH2O),
40.4 (C-4), 20.8 (CH3CO), 12.2, 11.9 (CH3CH2).
1,5-Anhydro-D-fructose (1.04 g, 6.2 mmol, 1 equiv) was
mixed with H2O (3.4 mL, 30 equiv) and the suspension
was stirred for 2 h at 25 ꢁC. Pyridine (50 mL) was then
added and the solution was cooled to 0 ꢁC. Ac2O
(26.24 mL, 45 equiv) was added and the mixture was
stirred for 2 h at rt followed by addition of H2O
(100 mL) and CH2Cl2 (100 mL). The phases were sepa-
rated and the aqueous phase was extracted with CH2Cl2
(25 mL). The combined organic phases were washed
with aq HCl (1 M), satd aq NaHCO3 and H2O
(50 mL), dried (MgSO4), filtered and concentrated
in vacuo to give a brown syrup. The residue was co-con-
centrated with toluene (3 · 10 mL), to give a coloured
syrup (1.26 g, 90%), which contained a trace of pyridine.
The residue was purified by flash chromatography (1:1,
EtOAc/heptane) to yield 4 as a colourless syrup (1.09 g,
1.4. 2,6-Di-O-acetyl-1,5-anhydro-4-deoxy-D-glycero-
hex-1-en-3-ulose (6)
To a solution of the enolone 4 (0.672 g, 2.9 mmol, 1 equiv)
in CH2Cl2 (20 mL) was added Et3N (0.38 mL, 1.0 equiv)
at 0 ꢁC. The mixture was warmed to rt and stirred for
0.5 h, followed by addition of an additional amount of
Et3N (0.19 mL, 0.5 equiv). After stirring for 16 h at ambi-
ent temperature aq HCl (10 mL) was added and the
phases were separated and the aqueous phase was ex-
tracted with CH2Cl2. The combined organic phases were
washed with aq HCl (1 M) and satd aq NaHCO3, water,
dried (MgSO4), filtered and concentrated in vacuo to a
brown syrup (0.484 g, 72%), which consisted of a mixture
of 4 and 6. The isomers were separated by flash chroma-
tography (1:3:3, EtOAc/heptane/CH2Cl2) and 6 was iso-
20
78%); ½aꢁD ꢀ42.8 (c 1.7, CHCl3); Rf = 0.42 (solvent B);
1H NMR (CDCl3): d 6.58 (d, 1H, J4,5 2.9 Hz, H-4),
4.77 (m, 1H, H-5), 4.39 (d, 1H, J1a,1b 15.6 Hz, H-1a),
4.37 (dd, 1H, J6a,6b 13.9, J6a,5 7.8 Hz, H-6a), 4.20 (dd,
1H, J6b–5 3.9 Hz, H-6b), 4.19 (d, 1H, H-1b), 2.18 (s,
3H, CH3CO), 2.02 (s, 3H, CH3CO); 13C NMR (CDCl3):
d 187.8 (C-2), 170.6, 168.1 (CH3CO), 143.9 (C-3), 133.1
(C-4), 72.8 (C-5), 71.5 (C-1), 64.5 (C-6), 20.5, 20.4
(CH3CO). Anal Calcd for C10H12O6: C, 52.63; H,
5.30. Found: C, 52.12; H, 5.40.
20
lated as a clear syrup (0.397 g, 59%); ½aꢁD 48.5 (c 1,
CHCl3); Rf = 0.27 (solvent C); 1H NMR (CDCl3): d
7.36 (s, 1H, H-1), 4.71 (m, 1H, H-5), 4.33 (dd, 1H, J6a,6b

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M. Andreassen, I. Lundt / Carbohydrate Research 341 (2006) 1692–1696
13.3, J6a–5 7.2 Hz, H-6a), 4.27 (dd, 1H, J6b–5 4.6 Hz, H-
6b), 2.78 (dd, 1H, J4ax,4eq 17.0, J4ax–5 14.1 Hz, H-4ax),
2.52 (dd, 1H, J4eq–5 3.7 Hz, H-4eq), 2.10 (s, 3H, CH3CO),
2.04 (s, 3H, CH03CO); 13C NMR (CDCl3): d 183.9 (C-3),
170.3, 168.6 (CH3CO), 155.1 (C-1), 131.8 (C-2), 77.4 (C-
5), 63.9 (C-6), 37.3 (C-4), 20.6, 20.1. Anal Calcd for
C10H12O6: C, 52.63; H, 5.30. Found: C, 52.28; H, 5.42.
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(Ascopyrone P) (1)
To acetylated APP (6, 0.215 g, 0.94 mmol) was added
CH3OH (10 mL) containing 0.01% dry HCl (made by
addition of 0.12 mL AcCl to 100 mL CH3OH) at ambient
temperature and the mixture was left overnight. Then,
basic ion-exchange resin (Amberlite IR-400) was added
and the mixture was stirred briefly, filtered and concen-
trated in vacuo. Flash chromatography (12:1, CH2Cl2/
CH3OH; Rf = 0.32) gave 1 as a colourless crystalline com-
pound (0.104 g, 77%); Mp 92–94 ꢁC (lit.6 90–95 ꢁC; lit.7
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20
98.5–99 ꢁC); ½aꢁD +143.0 (c 1.0, H2O) (lit.7 +139.5 (c
1
1.0, H2O), lit.6 +155 (c 1.1 H2O)); Rf = 0.32 (D); H
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3.82–3.79 (m, 2H, H-6a+b), 2.82 (dd, 1H, J4ax,4eq 14.7,
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4eq); 13C NMR (D2O): d 190.1 (C-3), 150.1 (C-1), 133.6
(C-2), 78.4 (C-5), 61.3 (C-6), 35.1 (C-4). Anal Calcd for
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´
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1.6. 2-Hydroxy-1-(2-furyl)ethanone (8)
To the acetylated APP (6) (0.302 g, 1.3 mmol, 1 equiv)
was added CH3OH (10 mL) containing 1.0% of dry
HCl (made by addition of 1.2 mL AcCl to 10 mL
CH3OH) and stirred at ambient temperature for 16 h.
Then basic ion-exchange resin (Amberlite IR-400) was
added and the mixture was stirred briefly, filtered and
concentrated in vacuo. The residue was purified by flash
chromatography (16:1, CH2Cl2/CH3OH; Rf = 0.50) to
give 8 as a crystalline compound (0.113 g, 68%); Mp
83–85 ꢁC (lit.20 87–88 ꢁC). The NMR data were consis-
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Acknowledgements
The supply of 1,5-anhydro-D-fructose from Shukun Yu,
Danisco A/S Copenhagen, is greatly acknowledged as
well as the support from the European Union under
the Cell Factory of 5th Framework program QLK3-
2001-02400.