Chemical syntheses of inulin and levan structures.

Article abstract of DOI:10.1021/jo020341q

A fructofuranosyl thiglycoside donor, ethyl 6-O-acetyl-3-O-benzyl-1,4-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)-2-thio-beta-D-fructofuranoside (11), designed to yield stereospecifically beta-linkages and also to allow subsequent elongation in the 6- and/or 1-positions, was prepared and used in syntheses of levan and inulin structures. DMTST-promoted glycosylation between 11 (1.3 mol equiv) and methyl beta-D-fructofuranoside 6-OH and 1-OH acceptors (3 and 6) gave stereospecifically the protected methyl levanobioside 12 and inulinobioside 17 in excellent yields (80 and 86%), respectively. Protecting group manipulations on these afforded new disaccharide 6'-OH and 1'-OH acceptors (13 and 19), which were coupled again with donor 11 (1.0 mol equiv) to yield methyl levanotrioside 14 and inulinotrioside 20 in high yields, 65 and 67%, respectively. These were transformed into new acceptors and also fully deprotected to afford the methyl glycosides of levanotriose and inulinotriose, all structures that have earlier not been accessible by chemical synthesis.

Full text of DOI:10.1021/jo020341q

Ch em ica l Syn th eses of In u lin a n d Leva n Str u ctu r es
Stefan Oscarson* and Fernando W. Sehgelmeble
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University,
S-106 91 Stockholm, Sweden
s.oscarson@organ.su.se
Received May 21, 2002
A fructofuranosyl thiglycoside donor, ethyl 6-O-acetyl-3-O-benzyl-1,4-O-(1,1,3,3-tetraisopropyldisi-
loxane-1,3-diyl)-2-thio-â-D-fructofuranoside (11), designed to yield stereospecifically â-linkages and
also to allow subsequent elongation in the 6- and/or 1-positions, was prepared and used in syntheses
of levan and inulin structures. DMTST-promoted glycosylation between 11 (1.3 mol equiv) and
methyl â-D-fructofuranoside 6-OH and 1-OH acceptors (3 and 6) gave stereospecifically the protected
methyl levanobioside 12 and inulinobioside 17 in excellent yields (80 and 86%), respectively.
Protecting group manipulations on these afforded new disaccharide 6′-OH and 1′-OH acceptors
(13 and 19), which were coupled again with donor 11 (1.0 mol equiv) to yield methyl levanotrioside
14 and inulinotrioside 20 in high yields, 65 and 67%, respectively. These were transformed into
new acceptors and also fully deprotected to afford the methyl glycosides of levanotriose and
inulinotriose, all structures that have earlier not been accessible by chemical synthesis.
In tr od u ction
To be able to synthesize levan and inulin structures,
the protecting group pattern in the earlier used4 donor
(Figure 1) had to be changed, since a differentiation
between positions 1 and 6 is necessary, and thus, these
position require orthogonal protecting groups. Investiga-
tions had shown that the disiloxane group as a bridge is
almost a necessity, considering efficiency both in the
formation and function as a donor.7 Diacyl bridges, e.g.,
are formed in low yields and are not stable during the
glycosylation conditions. It was therefore decided to
change the 6-O-protecting group, from a silyl group to
an acetate (Scheme 2). The TBDMS group in 74 was
cleaved off and the resulting diol 8 regioselectively
acetylated8 in the primary position (f9). Detritylation
(f10) and treatment with 1,3-dichloro-1,1,3,3-tetraiso-
propyldisiloxane (TIPS chloride) then afforded the desired
donor 11.
Fructofurans built up from â-linked D-fructofuranoside
units are common in plants and also bacteria.1-3 Two
major types are found, 2f1-linked (inulin-type) and 2f6-
linked (levan-type) (Figure 1). Although there are several
reports on enzymatic syntheses of part structures of these
fructans,3 chemical syntheses have never been reported,
since the methodology to synthesize â-fructofuranosides
in a stereospecific way has not been available. Recently,
we developed a new concept for a â-directing fructofura-
nosyl donor (Figure 1) and used this successfully in the
first stereospecific coupling to yield sucrose.4 In this paper
this concept is further investigated and utilized for the
synthesis of inulin and levan structures.
Resu lts a n d Discu ssion
Earlier we found that the 6-O-TBDMS donor deriv-
ative was more efficient as a donor than the correspond-
ing 6-O-TBDPS analogue regarding the yields.4 Both
donors were, however, stereospecific for â-fructofurano-
side formation. The 6-O-acetyl analogue 11 also proved
to be a most efficient and stereoselective donor. Coupling
between acceptor 3 and donor 11 (1.3 mol equiv) yielded
the levanobiose derivative 12 in 80% yield using di-
methyl(methylthio)sulfonium trifluoromethanesulfonate
(DMTST)9 as promoter. In this coupling also two other
commonly used thiophilic promoters, MeOTf10 and NIS/
TfOH,11were tried. The results (Table 1) showed that all
Methyl â-D-fructofuranosides were chosen as model
acceptors, the 6-OH acceptor 3 for levan structures and
the 1-OH acceptor 6 for inulin structures, and synthe-
sized according to Scheme 1. Methyl â-D-fructofuranoside5
(1) was regioselectively tritylated (f2) or silylated (f4)
at the 6-position. Benzylation of 2 and consecutive
detritylation6 yielded acceptor 3, whereas regioselective
tritylation of 4 followed by desilylation, benzylation, and
detritylation afforded acceptor 6.
(1) Stephen, A. M. In The Polysaccharides; Aspinall, G. O., Ed.;
Academic Press: New York, 1983; Vol. 2, p 97.
(2) Kenne, L.; Lindberg, B. In The Polysaccharides; Aspinall, G. O.,
Ed.; Academic Press: New York, 1983; Vol. 2, p 287.
(3) Matheson, N. K.; McCleary B. V. In The Polysaccharides;
Aspinall, G. O., Ed.; Academic Press: New York, 1983; Vol. 3, p 1.
(4) Oscarson, S.; Sehgelmeble, F. W. J . Am. Chem. Soc. 2000, 122,
8869.
(5) Duker, J . M.; Serianni, A. S. Carbohydr. Res. 1993, 249, 281.
(6) Ravikumar, V. T.; Krotz, A. H.; Cole, D. L. Tetrahedron Lett.
1995, 36, 6587
(7) Sehgelmeble, F. W., Licentiate Thesis, Stockholm University,
2000.
(8) Ishihara, K.; Hideki, K.; Yamamoto, H. J . Org. Chem. 1993, 58,
3791.
(9) Fu¨gedi, P.; Garegg, P. J . Carbohydr. Res. 1986, 149, C9.
(10) Lo¨nn, H. Carbohydr. Res. 1985, 139, 105.
(11) Veeneman, G. H.; van Leeuwen, S. H.; van Boom, J . H.
Tetrahedron Lett. 1990, 31, 1331.
10.1021/jo020341q CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/02/2002
J . Org. Chem. 2002, 67, 8457-8462
8457

Oscarson and Sehgelmeble
F IGURE 1. Structures of inulin and levan and the â-directing fructofuranosyl donor.
SCHEME 1. Syn th esis of th e F r u ctofu r a n osyl
Accep tor sa
SCHEME 2. Syn th esis of th e F r u ctofu r a n osyl
Don or a
a
Key: (i) TBAF, THF; (ii) AcCl, 2,4,6-collidine, CH2Cl2, -70
°C; (iii) 1% TFA in CH2Cl2, TES; (iv) TIPSCl2, imidazole, DMF.
TABLE 1. Testin g of Differ en t P r om oter s in th e
Cou p lin g of Accep tor 3 a n d Don or 11 To Give
Disa cch a r id e 12
a
Key: (i) MeOH, H2SO4; (ii) DMTrCl, pyridine; (iii) BnBr, NaH,
promoter
base
solvent
temp
% yield
DMF; (iv) 1% TFA in CH2Cl2, TES; (v) TBDMSCl, pyridine; (vi) 1
M TBAF in THF.
MeOTf
NIS/TfOH
DMTST
DTBMP
CH2Cl2
CH2Cl2
CH2Cl2
rt
rt
rt
75
63
80
DTBMP
three promoters gave high yields and stereospecificity,
but that the first tried promoter, DMTST, was the best
one.
shifts of â-fructofuranosides, i.e., between 103 and 105
ppm as opposed to 107-109 ppm for R-linked fructofura-
nosides.13 Also the rest of the NMR spectra was in
accordance with literature data on levan structures.14 The
change in chemical shift of the anomeric carbon due to
the introduction of the TIPS bridge is also noticed in the
formation of the thioglycoside donor. C-2 of compound
11 gives a signal at 98 ppm as compared to 94 ppm in
10.
For the synthesis of inulin structures acceptor 6 was
coupled with donor 11 (1.3 mol equiv) to yield the
inulinobiose derivative 17 in 86% yield (Scheme 4).
Removal of the disiloxane bridge gave the 1′,4′-diol 18,
which was tried as acceptor in an attempted regioselec-
tive glycosylation to give inulinotriose. However, the
selectivity of donor 11 for the primary hydroxyl group
Built into the synthetic pathway is the possibility to
do an iterative repetition of these reactions to obtain
levanoligomers with increasing and exact chain length.
Deacetylation of compound 12 afforded a new acceptor
13, which could be glycosylated again with donor 11 (1
mol equiv) to give the levanotrioside 14 in 65% yield
(Scheme 3). Due to some hydrolysis of the donor, not all
acceptor is consumed; therefore, the coupling yield can
probably be raised by using an excess of the donor.
Removal of the acetate in 14 would afford a new 6-OH
acceptor. Complete deprotection of 14 gave the â-methyl
glycoside 16 of levanotriose. As was found in the earlier
paper,4 â-fructofuranosides containing the 1,4-TIPS group
show “abnormal” anomeric 13C NMR chemical shifts,
around 110 ppm. However, after removal of the TIPS
group (e.g. with TASF12), they all show the characteristic
(13) Angyal, S. J .; Bethell, G. S. Austr. J . Chem. 1976, 29, 1249.
(14) Timmermans, J . W.; Slaghek, T. M.; Iizuka, M.; van den Ende,
W.; de Roover, J .; van Laere, A. J . Carbohydr. Chem. 2001, 20, 375.
(12) Scheidt, K. A.; Chen, H.; Fellows, B. C.; Chemler, S. R.; Coffey,
D. S.; Roush, W. R. J . Org. Chem. 1998, 63, 6436.
8458 J . Org. Chem., Vol. 67, No. 24, 2002

Chemical Syntheses of Inulin and Levan Structures
SCHEME 3. Syn th esis of Leva n Der iva tivesa
cerium(IV) sulfate-10% sulfuric acid 100 g:2 g:2 L]. Organic
solutions were dried over MgSO4 before concentrations, which
were performed under reduced pressure at 40°C (water bath).
Silica gel (Si 60A, 35-70 µm, Amicon) was used for column
chromatography. NMR spectra were recorded in CDCl3 at 25
°C (internal standard Me4Si, δ ) 0.00) unless otherwise stated,
using a 270 MHz or a 400 MHz instrument. MALDI-TOF
spectra were recorded using 2′,4′,6′-trihydroxyacetophenone
monohydrate (THAP) as matrix.
Meth yl 1,3,4-Tr i-O-ben zyl-â-D-fr u ctofu r a n osid e (3). A
solution of 4,4’-dimethoxytrityl chloride (1.02 g, 4.47 mmol)
in pyridine (6 mL) was added, under Ar, to a cooled (0 °C)
solution of methyl â-D-fructofuranoside5 (1,789 mg, 4.06 mmol)
in pyridine (15 mL). The mixture was stirred for 24 h at 6 °C.
MeOH (2 mL) was then added and the mixture concentrated.
Column chromatography (CHCl3-MeOH 14:1 + 1% Et3N) of
the residue afforded methyl 6-O-(4,4’-dimethoxytriphenyl)-
methyl-â-D-fructofuranoside (2) (1.35 g, 2.64 mmol, 65%). 13C
NMR: δ 49.2, 55.2, 61.1, 64.2, 79.9, 78.8, 80.7, 86.0, 103.3,
113.1-158.4. Compound 2 (0.4 g, 0.78 mmol) in DMF (3 mL)
was added dropwise, under N2, to a suspension of NaH-60%
oil dispersion (0.37 g, 9.25 mmol) in DMF (0.5 mL). The
mixture was stirred for 1 h and benzyl bromide (1 mL, 8.44
mmol) was then added. After stirring for 2 h, the reaction was
quenched by the addition of MeOH (3 mL). The mixture was
diluted with toluene (40 mL), washed twice with water (15
mL), dried, concentrated, and dried in a vacuum overnight.
Triethylsilane (0.124 mL, 0.78 mmol), followed by TFA (15 mL,
1% solution in CH2Cl2), was added to the concentrate. The
reaction mixture was stirred for 1 h and then diluted with CH2-
Cl2 (30 mL), washed with aqueous saturated NaHCO3 and
water, dried, and concentrated. The crude product was sub-
jected to flash chromatography (toluene-EtOAc 1.5:1) to yield
3 (0.24 g, 0.52 mmol, 67%). [R]D -8 (c 1.06, CHCl3). NMR
(CDCl3): 1H, δ 3.37 (s, 3H), 3.57 (d, 2H), 3.60-3.76 (m, 2H),
3.96 (m, 1H), 4.15 (t, 1H), 4.31 (d, 1H, J ) 6.87 Hz), 4.46 (d,
1H, J ) 11.81 Hz), 4.52-4.63 (m, 4H), 4.71 (d, 1H, J ) 11.81
Hz); 13C, δ 50.12, 64.13, 70.28, 72.86, 73.00, 73.87, 80.87, 82.99,
84.98, 104.50, 127.96-138.36. Anal. Calcd for C28H32O6: C,
72.39; H, 6.94. Found: C, 72.21; H, 7.03.
Meth yl 3,4,6-Tr i-O-ben zyl-â-D-fr u ctofu r a n osid e (6). A
solution of tert-butyldimethylsilyl chloride (93 mg, 0.62 mmol)
in pyridine (0.7 mL) was added, at -10 °C and under Ar, to 1
(100 mg, 0.515 mmol) in pyridine (1 mL). The reaction was
allowed to attain room temperature and stirring was continued
for an additional 3 h. MeOH (2 mL) was added and the reaction
mixture was concentrated. Column chromatography (CHCl3-
MeOH 7:1) of the residue gave methyl 6-O-tert-butyldimeth-
ylsilyl-â-D-fructofuranoside (4) (86 mg, 0.28 mmol, 55%).
NMR: 1H, δ 0.09 (s, 6H), 0.91 (s, 9H), 3.31 (s, 3H), 3.61 (m,
5H), 4.01 (m, 2H); 13C, δ -5.37, -5.32, 18.44, 25.96, 49.10, 61.24,
64.17, 76.23, 78.75, 81.78, 103.39. Compound 4 (77 mg, 0.25
mmol) was dissolved in pyridine (0.5 mL) and 4,4’-dimethoxy-
trityl chloride (93 mg, 0.27 mmol) in pyridine (0.5 mL) was
added. The reaction mixture was stirred overnight and then
concentrated and the residue was applied to a silica gel
column. Elution (toluene-EtOAc 4:1 + 1% Et3N) gave methyl
6-O-tert-butyldimethylsilyl-1-O-(4,4’-dimethoxytriphenyl)methyl-
â-D-fructofuranoside (5) (94 mg, 0.15 mmol, 60%). NMR:1H, δ
0.09 (d, 6H), 0.91 (s, 9H), 3.18 (s, 3H), 3.19 (m, 2H), 3.7 (s,
6H), 3.82 (m, 3H), 4.12 (m, 2); 13C, δ -5.41, -5.37, 18.33, 25.90,
49.01, 55.13, 62.71, 64.16, 77.37, 80.42, 81.49, 86.18, 102.99,
113.06-135.72. To a solution of compound 5 (145 mg, 0.23
mmol) in THF (2 mL) was added tetrabutylammonium fluoride
(TBAF) (0.46 mL, 1 M in THF). The mixture was stirred for 1
h and then diluted with CH2Cl2 (20 mL), washed with brine,
dried, and concentrated. The product was purified by flash
chromatography (CHCl3-MeOH 9:1 + 1% Et3N) and dried
a
Key: (i) DMTST, DTBMP, CH2Cl2, 4 Å MS; (ii) 1 M MeONa
in MeOH; (iii) 11, DMTST, DTBMP, CH2Cl2, 4 Å MS; (iv) TASF,
DMF; (v) H2, Pd/C, Amberlite IR-45 (OH-) resin, MeOH-EtOAc.
was low and only a ratio of 1.3:1 between the 1′-O-linked
and the 4′-O-linked trisaccharides was obtained in an
inefficient glycosylation reaction (40% total yield). Hence,
the 1′-OH acceptor 19 was prepared by dimethoxytrity-
lation, benzoylation, and detritylation of diol 18 in an
overall yield of 60%. DMTST-promoted glycosylation of
19 with donor 11 (1 mol equiv) then gave the inulino-
trioside 20 in good yield (67%), proving a working
iterative approach also to inulin oligomers. Removal of
the protecting groups gave 22, which also had NMR data
in accordance with the literature.15,16
In conclusion, thiofructofuranoside donors containing
the 1,4-TIPS group seem to be a general solution to the
stereospecific formation of â-fructofuranoside-containing
oligosaccharides, making possible the formation of struc-
tures earlier not available by chemical synthesis.
Exp er im en ta l Section
Gen er a l Meth od s. CH2Cl2 and pyridine were distilled from
calcium hydride. Thin-layer chromatography was performed
using silica gel 60 F-254 (Merck) plates with detection by UV
and charring with 8% H2SO4 or AMC [ammonium molybdate-
(15) Timmermans, J . W.; de Waard, P.; Tournois, H.; Leeflang, B.
R.; Vliegenhart, J . F. G. Carbohydr. Res. 1993, 243, 379.
(16) Timmermans, J . W.; de Wit, D.; Tournois, H.; Leeflang, B. R.;
Vliegenhart, J . F. G. J . Carbohydr. Chem. 1993, 12, 969.
J . Org. Chem, Vol. 67, No. 24, 2002 8459

Oscarson and Sehgelmeble
SCHEME 4. Syn th esis of In u lin Der iva tivesa
a
Key: (i) DMTST, DTBMP, CH2Cl2, 4 Å MS; (ii) TASF, DMF; (iii) (a) DMTrCl, pyridine, (b) BzCl, pyridine-CH2Cl2 (1:1), 4-DMAP, (c)
1%TFA in CH2Cl2, Et3SiH, CH2Cl2; (iv) 11, DMTST, DTBMP, CH2Cl2, 4 Å MS; (v) (a) TBAF, THF, (b) NaOMe, MeOH:CH2Cl2, (c) H2,
Pd/C, Amberlite IR-45 (OH-) resin, MeOH-EtOAc-H2O.
overnight on the oil pump. The residue was dissolved in DMF
(1 mL) and this solution was added to a suspension of sodium
NaH-60% oil dispersion (111 mg, 2.77 mmol) in DMF (3 mL).
After 1 h, benzyl bromide (0.35 mL, 2.08 mmol) was added
and the stirring was continued for an additional 1 h. MeOH
(2 mL) was added dropwise followed by addition of toluene
(40 mL). The reaction mixture was washed with water (15 mL),
dried, concentrated, and dried under reduced pressure. Tri-
ethylsilane (37 µL, 0.23 mmol), followed by TFA (10 mL, 1%
solution in CH2Cl2), was added to the concentrate. After
stirring for 1 h, CH2Cl2 (30 mL) was added and the mixture
was washed with aqueous saturated NaHCO3, water, dried,
and concentrated. Flash chromatography (toluene-EtOAc 3:1)
yielded 6 (47 mg, 0.102 mmol, 68%). [R]D +6 (c 0.43, CHCl3).
NMR (CDCl3): 1H, δ 3.30 (s, 3H), 3.53 (m, 3H), 3.69 (d, 1H, J
) 11.72 Hz), 4.06 (m, 1H), 4.13 (t, 1H), 4.26 (d, 1H, J ) 6.96
Hz), 4.50 (m, 4H), 4.65 (d, 1H, J ) 11.72 Hz), 4.76 (d, 1H,
J ) 11.71 Hz); 13C, δ 49.61, 62.65, 71.33, 72.55, 72.98, 73.41,
79.69, 83.71, 84.33, 104.38, 127.53-137.94. Anal. Calcd for
) 12.09 Hz), 4.02 (m, 1H), 4.27-4.46 (m, 4H), 4.62 (d, 1H, J
) 11.81 Hz), 4.78 (d, 1H, J ) 11.82 Hz), 7.28-7.39 (m, 5H);
13C, δ 14.96, 20.78, 20.88, 64.75, 65.34, 73.15, 76.64, 80.57,
85.19, 94.31, 127.81-137.82, 171.25. 1,3-Dichloro-1,1,3,3-
tetraisopropyldisiloxane-TIPSCl2 (66 µL in 0.1 mL DMF) was
added, at -30 °C and under argon, to a solution of compound
10 (58 mg, 0.16 mmol) and imidazole (44 mg, 0.65 mmol) in
DMF (2 mL). The cooling bath was removed after 30 min and
the mixture was allowed to attain room temperature and to
stir for 6 h. MeOH (1 mL) was then added and the mixture
concentrated and coconcentrated three times with toluene (2
mL). The residue was applied to a silica gel column and eluted
(toluene-EtOAc 4:1) to give 11 (76 mg, 0.13 mmol, 81%). [R]D
-4 (c 0.81, CHCl3). NMR: 1H, δ 0.89-1.03 (m, 28H), 1.23 (t,
3H), 2.06 (s, 3H), 2.72 (q, 2H), 3.90 (d, 1H, J ) 11.72 Hz), 4.16
(d, 1H, J ) 11.72 Hz), 4.26-4.36 (m, 5H), 4.64 (d, 1H, J )
12.09 Hz), 4.76 (d, 1H, J ) 12.08 Hz), 7.26-7.37 (m, 5H); 13C,
δ 12.67, 13.33, 13.61, 13.91, 14.86, 17.19, 17.23, 17.29, 17.35,
17.45, 20.88, 22.18, 64.82, 65.07, 73.15, 79.82, 85.92, 86.57,
98.14, 127.52-137.66, 170.81. Anal. Calcd for C29H50O7SSi2:
C, 58.15; H, 8.41. Found: C, 58.15; H, 8.53.
C
28H32O6: C, 72.39; H, 6.94. Found: C, 72.25; H, 7.05.
Eth yl 6-O-Acetyl-3-O-ben zyl-1,4-O-(1,1,3,3-tetr a isop r o-
p yld isiloxa n e-1,3-d iyl)-2-th io-â-D-fr u ctofu r a n osid e (11).
To a solution of 74 (351 mg, 0.47 mmol) in THF (2 mL) was
added TBAF (0.7 mL, 1M in THF). The reaction mixture was
stirred for 30 min and then diluted with CH2Cl2 (20 mL),
washed with brine, dried, and concentrated. Column chroma-
tography of the residue (toluene-EtOAc 1:1) gave ethyl 3-O-
benzyl-1-O-(4,4’-dimethoxytriphenyl)methyl-2-thio-â-D-fructo-
furanoside (8, 263 mg, 0.43 mmol, 90%). NMR: 1H, δ 1.12 (t,
3H), 2.42 (m, 2H), 3.24 (d, 1H, J ) 10.25 Hz), 3.62 (d, 1H, J )
10.26 Hz), 3.76 (s, 6H), 3.79 (m, 3H), 4.11 (m, 1H), 4.34 (d,
1H, J ) 11.72 Hz), 4.48 (m, 1H), 4.56 (d, 1H, J ) 11.9 Hz),
6.76-7.46 (m, 18H); 13C, δ 14.89, 21.20, 55.20, 62.44, 66.61,
72.83, 75.36, 82.63, 85.83, 86.43, 93.98, 113.17-130.15. Acetyl
chloride (23 µL, 0.32 mmol) in CH2Cl2 (0.1 mL) was added
dropwise, at -70 °C, to a solution of 8 (183 mg, 0.29 mmol)
and 2,4,6-collidine (0.19 mL, 1.45 mmol) in CH2Cl2 (5 mL). The
reaction was stirred for 2 h and then quenched with MeOH (2
mL) and concentrated. The residue was applied to a silica gel
column and eluted with (toluene-EtOAc 4:1) to give ethyl 6-O-
acetyl-3-O-benzyl-1-O-(4,4’-dimethoxytriphenyl)methyl-2-thio-
â-D-fructofuranoside (9) (187 mg, 0.28 mmol, 97%). NMR: 1H,
δ 1.11 (t, 3H), 2.09 (s, 3H), 2.42 (m, 2H), 3.20 (d, 1H, J ) 10.17
Hz), 3.60 (d, 1H, J ) 10.17 Hz), 3.74 (s, 6H), 4.16 (m, 1H),
4.33 (m, 4H), 4.34 (d, 1H, J ) 11.81 Hz), 4.53 (d, 1H, J ) 11.81
Hz), 6.78-7.47 (m, 13H); 13C, δ 14.76, 20.87, 21.25, 55.16,
64.19, 66.93, 72.83, 76.14, 79.92, 85.28, 86.36, 93.47, 113.14-
158.49, 171.17. TFA (2 mL, 1% solution in CH2Cl2) was added
to a mixture of compound 9 (136 mg, 0.20 mmol) and trieth-
ylsilane (38 µL, 0.24 mmol). The reaction mixture was stirred
for 30 min and then diluted with CH2Cl2 (25 mL), washed with
aqueous saturated NaHCO3 and water, dried, and concen-
trated. Chromatography (toluene-EtOAc 1:1) of the residue
gave ethyl 6-O-acetyl-3-O-benzyl-2-thio-â-D-fructofuranoside
(10) (62 mg, 0.173 mmol, 86%). NMR: 1H, δ 1.2 (t, 3H), 2.07
(s, 3H), 2.5 (m, 3H), 3.60 (d, 1H, J ) 12.09 Hz), 3.77 (d, 1H, J
Met h yl â-D-F r u ct ofu r a n osyl-(2f6)-â-D-fr u ct ofu r a n o-
syl-(2f6)-â-D-fr u ctofu r a n osid e (16). The acceptor 3 (40 mg,
67 µmol), the donor 11 (40 mg, 86 µmol) and 2,6-di-tert-butyl-
4-methylpyridine (31 mg, 67 µmol) were dissolved in CH2Cl2
(2 mL) containing crushed molecular sieves (4 Å, 0.3 g). The
mixture was stirred at room temperature and under an argon
atmosphere. After 10 min, dimethyl(methylthio)sulfonium
triflate (DMTST) (52 mg, 0.2 mmol) was added and the
stirring was continued another 30 min, after which Et3N (0.1
mL) was added. The mixture was diluted with CH2Cl2, filtered
through Celite, and concentrated, and the residue was puri-
fied on silica gel (toluene-EtOAc 10:1) to yield methyl 6-O-
acetyl-3-O-benzyl-1,4-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-
diyl)-â-D-fructofuranosyl-(2f6)-1,3,4-tri-O-benzyl-â-D-fructo-
furanoside (12) (54 mg, 53 µmol, 80%). NMR: 1H, δ 0.96-1.05
(m, 28H), 2.00 (s, 3H), 3.34 (s, 3H), 3.55 (s, 2H), 3.91-4.03
(m, 2H), 3.95 (s, 2H), 4.06-4.15 (m, 2H), 4.24-4.29 (m, 5H),
4.31(d, 1H, J ) 6.96 Hz), 4.44 (d, 1H, J ) 12.09 Hz), 4.53-
4.67 (m, 5H), 4.71 (d, 1H, J ) 12.08 Hz), 4.83 (d, 1H, J ) 12.09
Hz), 7.23-7.30 (m, 20H); 13C, δ 13.64, 13.23, 13.58, 13.70,
17.12, 17.14, 17.16, 17.28, 17.39, 20.82, 49.60, 64.44, 64.55,
64.76, 69.92, 72.45, 72.62, 73.15, 73.53, 79.22, 79.74, 82.65,
84.22, 84.63 (2C), 103.99, 109.59, 127.48-138.42, 170.81.
Compound 12 (40 mg, 39 µmol) was dissolved in CH2Cl2-
MeOH (1:1, 2 mL) and treated with methanolic sodium
methoxide (3 drops, 1 M in MeOH). After stirring for 1 h, the
reaction was diluted with CH2Cl2 (25 mL), washed with brine,
dried, and concentrated. Purification of the residue on silica
gel (toluene-EtOAc 6:1) yielded methyl 3-O-benzyl-1,4-O-
(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)-â-D-fructofuranosyl-
(2f6)-1,3,4-tri-O-benzyl-â-D-fructofuranoside (13) (34 mg, 36
µmol, 90%). NMR: 1H, δ 0.8-1.05 (m, 28H), 3.35 (s, 3H), 3.52-
3.58(s, 2H), 3.66-3.81 (m, 2H), 3.92-3.98 (m, 6H), 4.07 (m,
2H), 4.24-4.32 (m, 4H), 4.46 (d, 1H, J ) 12.09 Hz), 4.55-4.61
(m, 4H), 4.72 (d, 1H, J ) 12.09 Hz), 4.83 (d, 1H, J ) 12.08
8460 J . Org. Chem., Vol. 67, No. 24, 2002

Chemical Syntheses of Inulin and Levan Structures
Hz); 13C, δ 12.7, 13.3, 13.6, 13.8, 17.2, 17.3, 17.4, 49.8, 63.3,
63.5, 64.4, 70.4, 72.3, 72.6, 73.2, 73.6, 78.9, 79.7, 82.6, 84.1,
84.7, 87.7, 104.2, 109.2, 127.5-138.4. The acceptor 13 (32 mg,
33 µmol), the donor 11 (20 mg, 34 µmol), and 2,6-di-tert-butyl-
4-methylpyridine (6 mg, 34 µmol) were dissolved in CH2Cl2 (2
mL) at room temperature and under argon atmosphere.
Crushed molecular sieves (4 Å, 0.3 g) were added, and the
mixture was stirred for 10 min before DMTST (35 mg, 0.136
mmol) was added. The stirring was continued for 1 h, where-
after Et3N (0.1 mL) was added. The mixture was diluted with
CH2Cl2, filtered through Celite, and concentrated, and the
residue was purified on silica gel (toluene-EtOAc 12:1) to yield
methyl 6-O-acetyl-3-O-benzyl-1,4-O-(1,1,3,3-tetraisopropyld-
isiloxane-1,3-diyl)-â-D-fructofuranosyl-(2f6)-3-O-benzyl-1,4-O-
(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)-â-D-fructofuranosyl-
(2f6)-1,3,4-tri-O-benzyl-â-D-fructofuranoside (14) (32 mg, 22
µmol, 65%). NMR: 1H, δ 0.75-0.99 (m, 56H), 1.95 (s, 3H), 3.32
(s, 3H), 3.54 (s, 2H), 3.86-3.98 (s, 7H), 4.02-4.31 (m, 11H),
4.44 (d, 1H, J ) 12.08 Hz), 4.51-4.68 (m, 7H), 4.71 (d, 1H, J
) 12.09 Hz), 4.76 (d, 1H, J ) 12.08 Hz), 4.86 (d, 1H, J ) 12.81
Hz), 7.19-7.33 (m, 25H); 13C, δ 12.6, 12.7, 13.1, 13.3, 13.6,
13.67, 13.71, 17.14, 17.17, 17.22, 17.26, 17.32, 17.39, 20.79,
49.68, 62.89, 63.31, 64.27, 65,02, 70.24, 72.52, 72.61, 72.73,
73.14, 73.56, 78.65, 79.69, 79.73, 81.99, 82.64, 84.19, 84.69,
84.85, 86.18, 103.87, 109.53, 109.79, 127.39-138.59, 170.71.
Tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF)
(0.123 mL, 1.3 M in DMF) was added to a solution of compound
14 (40 mg, 27 µmol) in DMF (1.5 mL). After stirring for 1 h
the reaction was diluted with EtOAc (50 mL) and washed with
water buffer solution (pH ) 7, 30 mL). The aqueous layer was
extracted with EtOAc (3 × 10 mL), and the combined organic
layers were dried and concentrated, and the residue was
purified by silica gel chromatography (CHCl3-MeOH 18:1) to
afford methyl 6-O-acetyl-3-O-benzyl-â-D-fructofuranosyl-(2f6)-
3-O-benzyl-â-D-fructofuranosyl-(2f6)-1,3,4-tri-O-benzyl-â-D-
fructofuranoside (15) (22 mg, 24 µmol, 81%. NMR: 1H, δ 2.05
(s, 3H), 3.32 (s, 3H), 3.36 (d, 1H), 3.46-3.60 (m, 6H), 3.73 (m,
3H), 3.87 (m, 4H), 4.05 (m, 2H), 4.17 (m, 3H), 4.29-4.43 (d,
3H), 4.46-4.58 (m, 5H), 4.61 (d, 1H, J ) 12.08 Hz), 4.67 (m,
2H), 4.75 (d, 1H, J ) 11.72 Hz), 7.19-7.39 (m, 25H); 13C, δ
20.80, 49.79, 61.79, 63.82, 63.84, 64.41, 65.36, 69.76, 72.12,
72.66, 72.74, 72.92, 73.56, 75.32, 75.38, 77.71, 79.21, 79.54,
84.21, 84.69, 84.85, 85.56, 104.09, 104.38, 104.62, 127.54-
138.20, 171.25. Sodium methoxide (3 drops, 1 M in MeOH)
was added to a solution of compound 15 (22 mg, 24 µmol) in
CH2Cl2-MeOH 1:1 (1 mL). After stirring for 1 h, the reaction
was carefully neutralized with Dowex 50 (H+) ion-exchange
resin, filtered, and concentrated. The residue was dissolved
in MeOH-EtOAc (5:1, 4 mL). Amberlite resin IR-45 (OH-)
resin (30 mg) and palladium on activated carbon were added.
The mixture was hydrogenolyzed at 110 psi overnight, filtered
twice through Celite, and concentrated. Lyophilization of the
concentrate gave methyl â-D-fructofuranosyl-(2f6)-â-D-fructo-
furanosyl-(2f6)-â-D-fructofuranoside (16) (9 mg, 17 µmol,
73%). [R]D -35 (c 0.97, CH3OH). NMR (CD3OD + 1 drop
D2O): 13C, δ 49.99, 61.51, 61.95, 62.25, 64.03, 64.48, 64.52,
76.53, 77.37, 77.62, 78.55, 78.61, 78.76, 81.72, 81.92, 83.07,
105.23, 105.50 (double intensity); 1H, δ 3.34 (s, 3H), 3.58-3.95
(15H), 4.03 (t, J ) 8 Hz, 1H), 4.04 (t, J ) 8 Hz, 1H), 4.06 (t, J
) 8 Hz, 1H), 4.14 (d, J ) 8 Hz, 1H), 4.15 (2d, J ) 8 Hz, 2H).
Anal. Calcd for C19H34O16‚3H2O: C, 39.9; H, 7.04. Found: C,
40,1; H, 7.18.
diluted with CH2Cl2, filtered through Celite, and concentrated.
The residue was purified on silica gel (toluene-EtOAc 12:1)
to afford methyl 6-O-acetyl-3-O-benzyl-1,4-O-(1,1,3,3-tetraiso-
propyldisiloxane-1,3-diyl)-â-D-fructofuranosyl-(2f1)-3,4,6-tri-
O-benzyl-â-D-fructofuranoside (17) (92 mg, 93 µmol, 86%).
NMR (CDCl3): 1H, δ 0.76-1.10 (m, 28H), 1.19 (s, 3H), 3.38 (s,
3H), 3.52 (m, 2H), 3.83-4.32 (m, 10H), 4.49-4.59 (m, 7H), 4.67
(d, 1H, J ) 12.08 Hz), 4.85 (d, 1H, J ) 12.44 Hz), 4.29 (d, 1H,
J ) 11.71 Hz), 7.18-7.37 (m, 20H); 13C, δ 12.67, 13.18, 13.59,
13.62, 17.12, 17.16, 17.19, 17.22, 17.29, 17.36, 20.81, 49.32,
62.62, 63.17, 64.95, 71.46, 72.32, 73.02, 73.12, 73.28, 78.86,
79.22, 81.99, 84.09, 85.04, 86.40, 103.94, 109.72, 127.43-
138.64, 170.71. To a solution of compound 17 (82 mg, 82 µmol)
in DMF (1.5 mL) was added TASF in DMF (1.3 M, 0.18 mL,
0.24 mmol). After stirring for 1 h, the reaction was diluted
with EtOAc (50 mL) and washed with water buffer solution
(pH ) 7, 30 mL). The aqueous layer was extracted with EtOAc
(3 × 10 mL), and the combined organic layers were dried and
concentrated, and the residue was purified by silica gel
chromatography (chloroform-MeOH 18:1) to afford methyl
6-O-acetyl-3-O-benzyl-â-D-fructofuranosyl-(2f1)-3,4,6-tri-O-
benzyl-â-D-fructofuranoside (18) (57 mg, 74 µmol, 93%). NMR
(CDCl3): 1H, δ 2.03 (s, 3H), 3.36 (s, 3H), 3.57-3.60 (m, 4H),
3.78 (s, 2H), 3.82-3.91 (m, 1H), 3.99 (m, 2H), 4.10 (m, 2H),
4.19(m, 1H), 4.26 (m, 2H), 4.51-4.61 (m, 6H), 4.75 (t, 2H),
7.20-7.32 (m, 20 H); 13C, δ 20.79, 49.96, 63.09, 64.17, 64.37,
70.82, 72.44, 72.84, 72.93, 73.29, 75.72, 78.43, 78.74, 83.55,
85.32, 85.55, 103.91, 104.18, 127.61-138.30, 171.08. 4,4’-
Dimethoxytrityl chloride (24 mg, 76 µmol) was added to a
solution of 18 (30 mg, 40 µmol) and 4-DMAP (2-4 mg, 16 µmol)
in pyridine (1.5 mL). The reaction mixture was stirred
overnight at 60 °C. MeOH (3 mL) was then added, the mixture
was concentrated and coevaporated with toluene, and the
crude product was dried overnight at reduced pressure. The
residue was dissolved in pyridine-CH2Cl2 (1:1, 4 mL) under
argon. The solution was cooled (0 °C) and benzoyl chloride (20
µL, 0.173 mmol) in CH2Cl2 (0.1 mL) was added. The mixture
was stirred for 3 h at room temperature, diluted with CH2Cl2
(20 mL), washed with aqueous saturated NaHCO3 and water,
dried, concentrated, and dried at reduced pressure. TFA (1 mL,
1% in CH2Cl2) was added dropwise to a solution of the residue
and triethylsilane (8 µL, 50 µmol) in CH2Cl2 (0.8 mL). After
20 min aqueous saturated NaHCO3 (2 mL) and then CH2Cl2
(10 mL) were added. The organic phase was separated, dried
and concentrated. The residue was purified on a silica gel
column (toluene-EtOAc 8:1) to afford methyl 6-O-acetyl-4-O-
benzoyl-3-O-benzyl-â-D-fructofuranosyl-(2f1)-3,4,6-tri-O-ben-
zy l-â-D-fructofuranoside (19) (20 mg, 24 µmol, 60% after three
steps). NMR (CDCl3): 1H, δ 2.01 (s, 3H), 3.36 (s, 3H), 3.62-
3.72 (m, 2H), 3.88-4.04 (m, 4H); 4.17-4.34 (m, 6H), 4.38-
4.60 (m, 7H), 4.67 (d, 1H, J ) 12.45 Hz), 4.74 (d, 1H, J ) 12.45
Hz), 5.59 (m, 1H), 7.19-7.99 (m, 25H); 13C, δ 20.85, 49.96,
62.90, 63.14, 65.37, 70.30, 71.84, 72.04, 72.62, 73.50, 78.69,
79.63, 81.76, 82.08, 83.78, 88.21, 103.84, 104.24, 127.58-
138.26, 162.50, 170.69. The acceptor 19 (8 mg, 9.27 µmol), the
donor 11 (5.5 mg, 9.27 µmol), and 2,6-di-tert-butyl-4-meth-
ylpyridine (1-2 mg, 9.27 µmol) were dissolved in CH2Cl2 (1
mL) together with crushed molecular sieves. The mixture was
stirred at room temperature and under argon atmosphere.
After 10 min, DMTST (20 mg, 77 µmol) was added and the
mixture was additionally stirred for 40 min and then quenched
by adding triethylamine (3-5 drops). The mixture was diluted
with CH2Cl2, filtered through Celite, and concentrated, and
the residue was purified on silica gel (toluene-EtOAc 8:1) to
yield methyl 6-O-acetyl-3-O-benzyl-1,4-O-(1,1,3,3-tetraisopro-
pyldisiloxane-1,3-diyl)-â-D-fructofuranosyl-(2f1)-6-O-acetyl-4-
O-benzoyl-3-O-benzyl-â-D-fructofuranosyl-(2f1)-3,4,6-tri-O-
benzyl-â-D-fructofuranoside (20) (8.7 mg, 6.21 µmol, 67%).
NMR (CDCl3): 1H, δ 0.97-1.08 (m, 28H), 1.97 (s, 3H), 2.00 (s,
3H), 3.35 (s, 3H), 3.47 (d, 1H, J ) 11.72 Hz), 3.55-3.75 (m,
3H), 3.89-4.06 (m, 9H), 4.18-4.37 (m, 5H), 4.38-4.46 (m, 3H),
4.47-4.60 (m, 5H), 4.65-4.87 (m, 4H), 5.61 (m, 1H), 7.29-
Meth yl 6-O-Acetyl-3-O-ben zyl-â-D-fr u ctofu r an osyl-(2f1)-
4-O-ben zoyl-3-O-ben zyl-â-D-fr u ctofu r a n osyl-(2f1)-3,4,6-
tr i-O-ben zyl-â-D-fr u ctofu r a n osid e (21). The acceptor 6 (60
mg, 0.10 mmol), the donor 11 (77 mg, 0.13 mmol) and 2,6-di-
tert-butyl-4-methylpyridine (26 mg, 0.13 mmol) were dissolved
in CH2Cl2 (2 mL) together with crushed molecular sieves (4
Å, 0.3 g). The mixture was stirred at room temperature and
under argon atmosphere for 10 min before DMTST (83 mg,
0.32 mmol) was added. The mixture was additionally stirred
for 40 min, quenched by adding triethylamine (0.15 mL),
J . Org. Chem, Vol. 67, No. 24, 2002 8461

Oscarson and Sehgelmeble
8.13 (m, 30H); 13C, δ 12.92, 13.49, 13.77, 13.87, 14.40, 17.34-
17.61, 20.94, 20.99, 49.79, 62.48, 63.58, 63.72, 64.19, 64.95,
71.28, 72.27, 72.59, 72.94, 73.10, 73.42, 73.72, 77.85, 79.01,
79.85, 81.99, 82.29, 82.78, 83.75, 85.34, 104.10, 104.47, 109.91,
127.80-138.30, 165.52, 170.61, 171.01. Trisaccharide 20 (8.7
mg, 6.21 µmol) was dissolved in DMF (1 mL), and TASF (25
µL, 1.3 M in DMF) was added. The reaction was stirred for 30
min, diluted with EtOAc (20 mL), and washed with water
buffer solution (pH ) 7, 10 mL). The aqueous layer was
extracted with EtOAc (3 × 5 mL), and the combined organic
layers were dried and concentrated. Column chromatography
of the residue (toluene-EtOAc 1:1) gave 21 (6 mg, 5.3 µmol,
85%). [R]D -48° (c 0.47, CH3OH). NMR (CDCl3): 1H, δ 1.98 (s,
3H), 2.02 (s, 3H), 3.34 (s, 3H), 3.55 (m, 4H), 3.77-4.63 (m,
23H), 4.70-4.83 (m, 3H), 5.58 (t, 1H), 7.12-8.12 (m, 30H); 13C,
δ 20.66, 20.75, 49.63, 62.36, 63.81, 64.02, 64.24, 71.11, 72.42,
72.49, 72.94, 72.97, 73.25, 75.96, 76.48, 76.70, 77.47, 78.46,
78.96, 82.42, 83.58, 84.77, 85.23, 103.84, 104.24, 104.29,
127.20-138.50, 165.52, 170.61, 170.98. Anal. Calcd for
neutralized with Dowex 50 (H+) ion-exchange resin, filtered,
and concentrated to yield methyl 3-O-benzyl-â-D-fructofuran-
osyl-(2f1)-3-O-benzyl-â-D-fructofuranosyl-(2f1)-3,4,6-tri-O-
benzyl-â-D-fructofuranoside. NMR (CDCl3): 13C, δ 49.72, 61.05,
62.18, 62.30, 62.93, 63.41, 65.27, 72.56, 72.69, 73.00, 73.03,
73.21, 73.74, 75.02, 79.08, 81.76, 83.12, 83.21, 84.28, 84.55,
84.82, 103.44, 103.74, 104.01. The residue was dissolved in
MeOH-EtOAc-water (5:1:1, 2 mL). Amberlite resin IR-45
(OH-) resin (30 mg) and palladium on activated carbon were
added. The mixture was hydrogenolyzed at 110 psi overnight,
filtered twice through Celite, concentrated, and purified using
Cartridges max-clean C18, 600 mg, from Alltech. Lyophiliza-
tion of the concentrate gave 22 (4 mg, 8 µmol, 58%). [R]D -19
(c 0.25, H2O). NMR (D2O): 1H, δ 3.34 (s, 3H), 3.62-3.89 (15H),
4.05 (t, J ) 8 Hz, 1H), 4.10 (2t, J ) 8 Hz, 2H), 4.19 (d, J ) 8
Hz, 1H), 4.20 (d, J ) 8 Hz, 1H), 4.22 (d, J ) 8 Hz, 1H). MALDI-
TOF MS: calcd for C19H34O16 518.2, found 541.0 [M + Na],
556.9 [M + K].
C
65H72O19: C, 67.46; H, 6.27. Found: C, 67.22; H, 6.41.
Ack n ow led gm en t. We thank the Swedish Natural
Science Research Council for financial support.
Met h yl â-D-F r u ct ofu r a n osyl-(2f1)-â-D-fr u ct ofu r a n o-
syl-(2f1)-â-D-fr u ctofu r a n osid e (22). Compound 20 (15.6
mg, 13.7 µmol) was dissolved in THF (0.5 mL) and treated with
TBAF (50 µL, 50 µmmol) for 1 h. CH2Cl2 (10 mL) was added
and the organic phase was washed with water, dried, and
concentrated. The product was dissolved in MeOH:CH2Cl2 (4:
1, 1 mL) and NaOMe (1M in MeOH) was added (pH ) 10-
11). After stirring for 15 min, the reaction was carefully
Su p p or tin g In for m a tion Ava ila ble: 13C NMR spectra of
compounds 2-5, 9-18, and 21 and 1H NMR spectra of
compounds 6, 11, 12, 15, 16, 21, and 22. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O020341Q
8462 J . Org. Chem., Vol. 67, No. 24, 2002