Convenient conversion of wheat hemicelluloses pentoses (d-xylose and l-arabinose) into a common intermediate

Article abstract of DOI:10.1016/j.carres.2007.07.010

The transformation of d-xylose and l-arabinose, the two major components of wheat straw and bran, into a unique multifunctional, optically pure, five-carbon synthon has been achieved. The synthetic sequence requires three steps: suitable protection of the

Full text of DOI:10.1016/j.carres.2007.07.010

Carbohydrate Research 342 (2007) 2450–2455
Note
Convenient conversion of wheat hemicelluloses pentoses
(D-xylose and L-arabinose) into a common intermediate
Ariane Bercier, Richard Plantier-Royon* and Charles Portella*
Laboratoire Re´actions Se´lectives et Applications, Associe´ au CNRS (UMR 6519), Universite´ de Reims,
Faculte´ des Sciences, BP 1039, F-51687 Reims, France
Received 19 March 2007; received in revised form 6 July 2007; accepted 12 July 2007
Available online 21 July 2007
Abstract—The transformation of D-xylose and L-arabinose, the two major components of wheat straw and bran, into a unique multi-
functional, optically pure, five-carbon synthon has been achieved. The synthetic sequence requires three steps: suitable protection of
the hydroxyl groups of the pentoses, introduction of an iodide at the C-5 position and zinc-mediated opening of the furanose ring
leading to the formation of a common substituted pent-4-enal.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Hemicelluloses; Pentoses; D-Xylose; L-Arabinose; Iodination; Bernet–Vasella reaction
Hemicelluloses are the second most abundant plant
material after cellulose. These carbohydrate polymers
represent a complex group of structurally different poly-
saccharides that exist in the cell walls closely associated
with cellulose. In spite of their abundance, hemicellu-
loses have not been as effectively utilized as starch or cel-
lulose. Hemicelluloses from wheat straw and bran
represent about 25% of the dry matter and are mainly
composed of two pentoses: D-xylose, the major one,
and L-arabinose. As a part of a research programme
devoted to the valorization of hemicelluloses, from frac-
tionation to fine chemistry, we were interested in the
chemical transformation of these two pentoses to higher
added-value products.
toses. The chosen method was the zinc-mediated ring
opening of halogenated carbohydrates at the primary
position introduced by Bernet and Vasella.1 From 5-
iodo-D-xylofuranosides and L-arabinofuranosides with
different protecting groups at C-2 and C-3 positions, this
reaction should lead, as previously observed for various
halogenated pentofuranosides,2–6 to the same c,d-unsat-
urated aldehyde whatever the starting pentose (Chart 1).
In this paper, we report the chemical transformations
of the two pentoses into the suitably protected 5-deoxy-
5-iodo carbohydrates from D-xylose and L-arabinose
separately and, as a model, from an equimolar mixture,
and their conversion into the corresponding pent-4-enal
derivatives via a Vasella-type reaction.
D-Xylose and L-arabinose are carbohydrates diastereo-
isomers at C-4. The approach targets the removal of
the chirality on C-4 position to afford a common opti-
cally pure synthon susceptible of various applications
in organic chemistry. Ideally, such a transformation
could be applied directly to a mixture of the two pen-
O
O
OP2
OP1
OP2
I
OP3
OP3
D-xylose
or
*
Corresponding authors. Tel.: +33 326 913 308; fax: +33 326 913 166
(R.P.R.); tel.: +33 326 913 234; fax: +33 326 913 166 (C.P.); e-mail
addresses: richard.plantier-royon@univ-reims.fr; charles.portella@
univ-reims.fr
L-arabinose
Chart 1. Retrosynthetic scheme for the formation of the common
intermediate.
0008-6215/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2007.07.010

A. Bercier et al. / Carbohydrate Research 342 (2007) 2450–2455
2451
Our approach requires the formation of a similar
intermediate from D-xylose and L-arabinose. Moreover,
introduction of different protecting groups on the
hydroxyl groups at C-2 and C-3 could allow further
selective reactions on these two positions. We chose to
carry out the following reaction sequence: selective pro-
tection of the primary hydroxyl groups by a bulky group
to obtain pentofuranose derivatives and formation of
the acetal in the 1,2-position in a second step.
35 ratio was obtained for 6a (D-xylose)/6b (L-arabinose)
as determined by H NMR.
As carefully detailed by Furstner, the zinc-induced
¨
1
ring-opening reactions of 6-deoxy-6-halopyranose or 5-
deoxy-5-halofuranose derivatives with metal–graphite
reagents depends on various parameters such as steric
and configurational effects.14 For 5-deoxy-5-iodopento-
furanoses, the reaction rate as well as the structure of
the product formed strongly depends on the configura-
tion (D-xylo vs D-ribo) and substitution pattern of the
parent sugar.
In a recent paper, we reported that reaction of the D-
xylose derived compound 6a with activated zinc3–5 was
unsuccessful whatever the reaction conditions.15 Com-
pound 6a proved to be inert; even the simple reduction
of the carbon–iodine bond, which was previously
observed using the Zn/Ag–graphite complex,14 did not
occur. Surprisingly, the same reaction carried out on
the epimeric L-arabinose derivative 6b with activated
zinc under sonication at 40 ꢁC in a 4:1 THF–water
mixture afforded the target pent-4-enal. The difference
in the reactivity of these two iodo pentofuranoses in
the reductive elimination reaction with activated zinc
was studied in full details.15
Starting from the known compounds 1a–2a7 and 1b8–
2b,9 the remaining free hydroxyl group was then benzyl-
ated, using classical conditions,10 to afford the fully pro-
tected pentofuranoses 3a–4a7 with 87–96% yields in the
D-xylo series and 3b11–4b with 84–90% yields in the
L-arabino series (Scheme 1). For this benzylation step,
D-xylo derivatives proved to react faster than the L-
arabino ones, as observed for the selective protection
of the primary hydroxyl group. Deprotection of the sily-
lated ethers was classically achieved using an excess of
trihydrated n-Bu4NF in THF while deprotection of the
triphenylmethyl ethers was performed in mild acidic
conditions (60% aqueous HOAc) at 50 ꢁC. Finally,
iodination of compounds 5a7 and 5b11 was easily carried
out12 giving the target 5-iodo compounds 6a13 and 6b
with 82–88% yields (Scheme 1).
Therefore, the mixture of the 1,2-O-isopropylidene
derivatives 6a,b was transformed in a mixture of the
methyl D-xylofuranosides and methyl L-arabinofurano-
sides 7a,b (a/b 40:60) by acidic methanolysis. The reduc-
tive elimination being compatible with unprotected
hydroxyl group, the reaction was performed from this
mixture to afford the unique pent-4-enal 8 isolated as
its oxime ether 9 (4:1 isomeric mixture) with a 88% over-
all yield (Scheme 2). The remaining free hydroxyl group
of the iodo D-xylo derivative 7a (prepared separately)
was protected either by a triethylsilyl group (TES) or a
methoxyethoxymethyl group (MEM) to give the corre-
sponding pentofuranosides 10a and 11a with 61% and
72% yield, respectively. Finally, reaction of these two
compounds with zinc in the above described condi-
tions resulted in the formation of the expected c-enals
12 and 13, which were purified and isolated with
91% and 78% yield, respectively (Scheme 2). These reac-
tions were monitored by ESIMS, no product resulting
from a reduction of the carbon–iodine bond was
detected and the two anomers exhibited a similar
reactivity.
In conclusion, a five-step reaction sequence has been
achieved for the transformation of the two major com-
ponents of wheat hemicelluloses, D-xylose and L-arabi-
nose into a unique enantiopure five-carbon synthon.
The synthesized substituted pent-4-enals represent
versatile polyfunctionalized building-blocks with two
well-defined stereogenic centres bearing differentiated
hydroxyl groups. The transformation of these synthons
to higher added-value compounds is currently under
investigation and will be reported in due course.
Overall yields for these five-step reaction sequence
were 38% (Method A) and 32% (Method B) for D-xylose
and 31% (Method A) and 29% (Method B) for L-
arabinose.
The feasibility of our concept was checked by apply-
ing this procedure to a mixture of pentoses. From an
equimolar mixture of D-xylose and L-arabinose consid-
ered as a model, the mixture of the iodo epimers 6a
and 6b was obtained with a 28% overall yield (5 steps)
via the 5-O-silyl protected derivatives. According to
the lower reactivity of the L-arabino derivatives, a 65/
O
O
a
PO
PO
O
O
CMe2
CMe2
O
HO
O
BnO
P = TBDPS, 1a: 56%, 1b: 53%
P = TBDPS, 3a: 96%, 3b: 90%
P = Tr,
b
2a: 54%, 2b: 55%
P = Tr,
4a: 87%, 4b: 84%
O
O
c
HO
I
O
O
CMe2
CMe2
O
O
BnO
BnO
method A, 5a: 81%, 5b: 80%
method B, 5a: 79%, 5b: 77%
6a: 88%, 6b: 82%
Scheme 1. Reagents and conditions: (a) NaH, 10% TBAI, BnBr, THF;
(b) method A: TBAFÆ3H2O, THF, rt; method B: HOAc–H2O 3:2,
50 ꢁC, 6 d; (c) I2, PPh3, imidazole, toluene, 70 ꢁC.

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A. Bercier et al. / Carbohydrate Research 342 (2007) 2450–2455
O
O
a
OMe
OH
I
I
O
CMe2
O
BnO
BnO
6a + 6b
7a + 7b
b
OBn
N
O
c
b
d
O
OMe
7a
I
BnO
OH
BnO
OP
BnO
OP
9
P = H, 8 not isolated
P = TES, 10a
P = MEM, 11a
P = TES, 12
P = MEM, 13
Scheme 2. Reagents and conditions: (a) MeOH, AcCl cat., 100%; (b) activated Zn (10 equiv), THF–H2O 4:1, 40 ꢁC, ))), 12: 91%, 13: 78%; (c) TES-Cl
˚
or MEM-Cl, pyridine, rt, 10a: 61%, 11a: 72%; (d) BnONH2ÆHCl, 4 A mol. sieves, anhyd THF, 9: 88% (2 steps).
1. Experimental
1.1. General methods
ture. After 12 h for D-xylo derivatives and 24 h for
L-arabino derivatives (1:9 EtOAc–petroleum ether),
MeOH was added to the reaction mixture to decompose
excess benzyl bromide. The reaction mixture was evapo-
rated under diminished pressure at 40 ꢁC to remove the
solvents. The resulting oil was diluted with ethyl acetate,
washed with water, dried over Na2SO4 and concentrated
to dryness. Compounds 3a,7b11 and 4a,7b were purified
on a silica gel column (1:9 EtOAc–petroleum ether) to
give pale yellow oils.
All air- and moisture-sensitive reactions were carried out
under an argon atmosphere. Tetrahydrofuran (THF)
was distilled over Na/benzophenone before use. Optical
rotations were recorded using a Perkin–Elmer 241
polarimeter with a thermally jacketed 10 cm cell in the
specified solvents. Elementary analyses were taken on
a Perkin–Elmer CHN 2400 elementary analysis instru-
ment. Low-resolution mass spectra (ESIMS) were
recorded on a ThermoFinnigan Trace MS spectrometer.
High resolution mass spectra (HRESIMS) were per-
formed on a Q-TOF Micro micromass positive ESI
(CV = +30 V). All reported NMR spectra were
recorded with a Bruker AC 250 at 250 MHz (1H) and
62.5 MHz (13C) in CDCl3 as the solvent. Chemical shifts
are reported as d values relative to CHCl3, peak defined
at d = 7.27 ppm (1H NMR) or d = 77.00 ppm (13C
NMR). Analytical thin-layer chromatography was
performed using commercially prepared silica gel pre-
coated plates and visualization was effected with short
wavelength UV light or by spraying with an alcoholic
solution of phosphomolybdic acid followed by heating.
Preparative flash silica gel chromatography was per-
formed using E. Merck Kieselgel 60 (40–63 lm).
1.2.1.
3-O-Benzyl-1,2-O-isopropylidene-5-O-triphenyl-
22
methyl-b-L-arabinofuranose (4b). (0.122 g, 84%); ½aꢀD
1
ꢁ55.2 (c 1.5, CHCl3); H NMR (CDCl3): d 7.67–7.52
(m, 6H, Harom.), 7.41–7.18 (m, 14H, Harom.), 5.94 (d,
1H, J1,2 3.7 Hz, 1-H), 4.62–4.45 (m, 4H, 2 · Hbenzyl, H-
2, H-3), 4.12 (br s, 1H, H-4), 3.65–3.48 (m, 2H, H-5a,
H-5b), 1.59 (s, 3H, CH3 isopropylidene), 1.49 (s, 3H,
CH3 isopropylidene); 13C NMR (CDCl3): d 143.9, 137.4
and 137.3 (Cq.arom.), 129.1, 128.9, 128.5, 128.3, 127.9,
127.6, 127.5 and 126.9 (CHarom.), 112.2 (Cq isopropylidene),
105.8 (C-1), 87.1 (CPh3), 84.4 (C-2), 80.5 (C-3), 79.8
(C-4), 72.9 (CH2Ph), 62.8 (C-5), 27.4 and 26.1 (2 ·
CH3 isopropylidene); HRESIMS m/z: [(M+Na)+] calcd
for C34H34O5Na, 545.2304; found, 545.2297.
1.3. General method for the preparation of compounds
6a and 6b
1.2. General method for the preparation of compounds
3a,b and 4a,b
To a mixture of compounds 5a7 (5.5 g, 19.6 mmol) or
5b11 (0.5 g, 1.9 mmol) in toluene (20 mL/ mmol), triphen-
ylphosphine (1.5 equiv) and imidazole (3.5 equiv) were
slowly added and, after 10 min, iodine (1.5 equiv) by
small portions. The soln was stirred at 70 ꢁC until start-
ing material disappeared (3:7 EtOAc–petroleum ether).
The soln was then poured into a satd aq NaHCO3 soln
(20 mL/mmol) and stirred during 5 min. The excess
Compounds 1a,b or 2a,b (0.160 g, 0.37 mmol) were
dissolved in dry THF (2 mL, 5 mL/mmol), and sodium
hydride (60% in mineral oil, 0.75 mmol, 30 mg), n-
tetrabutylammonium iodide (0.04 mmol, 15 mg) and
benzyl bromide (0.55 mmol, 96 mg, 61 lL) were added.
The mixture was stirred under argon, at room tempera-

A. Bercier et al. / Carbohydrate Research 342 (2007) 2450–2455
2453
iodine was removed by addition of a satd aq Na2S2O4
soln until the organic layer became clear. Then, the
organic layer was separated and the aqueous soln was
extracted with toluene. Organic layers were dried over
Na2SO4 and solvents were removed. The triphenylphos-
phine oxide was crystallized in a 1:9 Et2O–petroleum
ether mixture and filtrated. Solvents were removed and
the residue was purified on a silica gel column (3:7
EtOAc–petroleum ether) to give compounds 6a13 and
6b.
Calcd for C13H17O4I: C, 42.86; H, 4.67. Found: C,
42.97; H, 4.63.
1.4.2. Methyl 3-O-benzyl-5-deoxy-5-iodo-2-O-triethyl-
silyl-a,b-D-xylofuranoside (10a). To a soln of com-
pound 7a (0.206 g, 0.57 mmol) in dry pyridine (4 mL),
at 0 ꢁC, under argon, was added slowly triethylchloros-
ilane (0.86 mmol, 0.129 g, 145 lL). The reaction was
then stirred at room temperature until starting material
disappeared (1:4 EtOAc–petroleum ether). Pyridine was
evaporated and the residue was dissolved in CH2Cl2
(20 mL) and washed with water (2 · 10 mL). The organ-
ic layer was dried over Na2SO4 and solvents were evap-
orated. The residue was purified on a silica gel column
(15:85 EtOAc–petroleum ether) to give 10a as a yellow
oil.
1.3.1. 3-O-Benzyl-5-deoxy-5-iodo-1,2-O-isopropylidene-
b-L-arabinofuranose (6b). (pale yellow solid, 0.57 g,
20
82%); mp 85–86 ꢁC; ½aꢀD +13.5 (c 0.26, CHCl3); 1H
NMR (CDCl3): d 7.30–7.23 (m, 5H, Harom.), 5.90 (d,
1H, J1,2 3.7 Hz, H-1), 4.58 (d, 1H, JA,B 11.7 Hz, Hbenzyl),
4.58 (d, 1H, J2,1 3.7 Hz, H-2), 4.55 (d, 1H, JA,B 11.7 Hz,
(0.176 g, 65%, a/b ratio: 44:56 determined by GC); 1H
NMR (CDCl3): d 7.32–7.25 (m, 5H, Harom.), 4.87 (d,
0.4H, J1a,2 4.1 Hz, H-1 a-anomer), 4.83 (br s, 0.6H, H-
1 b-anomer), 4.80–4.42 (m, 3H, H-4, 2 · Hbenzyl), 4.27
(m, 1H, H-2), 4.09 (dd, 0.4H, J3,4 5.1, J3,2 6.2 Hz, H-
3), 3.85 (dd, 0.6H, J3,4 2.2, J3,2 5.2 Hz, H-3), 3.48–3.23
(m, 5H, H-5a, H-5b, OCH3), 0.94 (t, 5H, J 7.6 Hz,
CH3), 0.92 (t, 4H, J 7.6 Hz, CH3), 0.63–0.57 (m, 6H,
3 · CH2); 13C NMR (CDCl3): d 138.4 and 138.2
(Cq.arom.), 129.0, 128.5, 128.4 and 128.2 (CHarom.),
111.4 (C-1b), 102.9 (C-1a), 84.4 and 84.1 (C-3), 82.7
and 80.2 (C-4), 78.2 (C-2), 73.5 and 73.4 (CH2Ph),
56.6 and 56.2 (OCH3), 7.4 (CH2CH3), 5.3 and 5.2
(CH2CH3), 4.5 and 4.2 (C-5); HRESIMS m/z:
[(M+Na)+] calcd for C19H31O4ISiNa, 501.0934; found,
501.0933; Anal. Calcd for C19H31O4ISi: C, 47.70; H,
6.48. Found: C, 47.47; H, 6.55.
H
benzyl), 4.30 (br t, 1H, J4,5a = J4,5b 7.5 Hz, H-4), 4.07 (s,
1H, H-3), 3.36–3.30 (m, 2H, H-5a, H-5b), 1.46 (s, 3H,
CH3 isopropylidene), 1.24 (s, 3H, CH3 isopropylidene); 13C
NMR (CDCl3): d 137.0 (Cq.arom.), 128.5, 128.0 and
127.9 (CHarom.), 112.7 (Cq isopropylidene), 106.5 (C-1),
85.6 (C-3), 84.6 (C-2), 83.8 (C-4), 71.6 (CH2Ph), 27.0
and 25.9 (2 · CH3 isopropylidene), 6.2 (C-5); HRESIMS
m/z: [(M+Na)+] calcd for C15H19O4INa, 413.0226;
found, 413.0216; Anal. Calcd for C15H19O4I: C, 46.15;
H, 4.87. Found: C, 46.18; H, 4.91.
1.4. General method for the preparation of compounds
7a and 7b
Compound 6a (1.5 g, 3.85 mmol) or a mixture 6a + 6b
was dissolved in MeOH (50 mL, 13 mL/mmol). Acetyl
chloride (2 mL, 0.028 mmol) was slowly added at 0 ꢁC.
The mixture was warmed to room temperature and stir-
red for 8 h. A saturated aqueous NaHCO3 soln was
added until pH 7. The solvents were evaporated and
the residue was dissolved in CH2Cl2 (100 mL), washed
twice with water (2 · 30 mL) and dried over Na2SO4.
The solvent was removed to give 7a or a mixture of
7a + 7b without any purification as a yellow oil.
1.4.3. Methyl 3-O-benzyl-5-deoxy-5-iodo-2-O-methoxy-
ethoxymethyl-a,b-D-xylofuranoside (11a). To a soln of
compound 7a (0.196 g, 0.54 mmol) in dry pyridine
(4 mL), at 0 ꢁC, under argon, was slowly added meth-
oxyethoxymethyl chloride (0.81 mmol, 0.101 g, 93 lL).
The reaction was stirred at room temperature until start-
ing material disappeared (3:7 EtOAc–petroleum ether).
Pyridine was evaporated, the residue was dissolved in
CH2Cl2 (20 mL) and washed with water (2 · 5 mL).
The organic layer was dried over Na2SO4 and solvents
were evaporated. The residue was purified on a silica
gel column (25:75 EtOAc–petroleum ether) to give 11a
as a colourless oil.
1.4.1. Methyl 3-O-benzyl-5-deoxy-5-iodo-a,b-D-xylofur-
anoside (7a). (1.34 g, 96%, a/b ratio: 42:58 determined
by GC); 1H NMR (CDCl3): d 7.40–7.20 (m, 5H, Harom.),
5.06 (d, 0.4H, J1a,2 4.3 Hz, H-1 a-anomer), 5.05 (br s,
0.6H, H-1 b-anomer), 4.84–4.41 (m, 3H, H-2, 2 ·
H
benzyl), 4.49 (ddd, 1H, J4,3 2.7, J4,5a 5.9, J4,5b 9.3 Hz,
(0.182 g, 75%, a/b ratio: 41:59 determined by GC); 1H
NMR (CDCl3): d 7.35–7.26 (m, 5H, Harom.), 5.02–4.46
(m, 4H, H-1, H-4, 2 · Hbenzyl), 4.24 (br s, 1H, H-2),
3.76–3.33 (m, 15H, H-3, H-5a, H-5b, 3 · CH2,
2 · OCH3); 13C NMR (CDCl3): d 138.0 (Cq.arom.),
127.8, 127.4, 127.3, 127.2 and 127.0 (CHarom.), 109.4
(C-1b), 101.5 (C-1a), 95.0 (OCH2O), 83.0 and 82.4 (C-
3), 81.5 and 81.4 (C-4), 78.6 and 77.8 (C-2), 72.0 and
71.4 (CH2Ph), 71.1 and 66.1 (OCH2), 58.3 and 55.3
H-4), 4.27 (br s, 1H, H-3), 3.55–3.22 (m, 5H, H-5a, H-
5b, OCH3); 13C NMR (CDCl3): d 137.9 and 137.8
(Cq.arom.), 128.9, 128.8, 128.4, 128.3 and 128.2 (CHarom.),
113.0 (Cq isopropylidene), 110.1 (C-1b), 102.6 (C-1a), 83.9
and 83.8 (C-3), 82.3 and 79.9 (C-2), 79.5 and 76.7
(C-4), 73.1 and 72.6 (CH2Ph), 56.5 and 56.4 (OCH3),
5.0 and 2.1 (C-5); HRESIMS m/z: [(M+Na)+] calcd
for C13H17O4INa, 387.0069; found, 387.0062; Anal.

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A. Bercier et al. / Carbohydrate Research 342 (2007) 2450–2455
(OCH3), 3.9 and 1.0 (C-5); HRESIMS m/z: [(M+Na)+]
calcd for C17H25O6INa, 475.0594; found, 475.0605.
inate zinc and solvents were evaporated. The residue
was purified on a neutralized silica gel column (1:4
EtOAc–petroleum ether) to give 12 or 13 as a colourless
oil.
1.5. General method for the Bernet–Vasella reaction
1.5.1. Zinc activation. Zinc dust was stirred in a 3 N
aqueous HCl soln (0.5 mL/mmol of zinc) during 5
min, then filtered and washed with water (0.5 mL/
mmol), EtOH (0.5 mL/mmol) and ether (0.5 mL/mmol).
Finally, the material was dried under high vacuum with
a heatgun until the powder became pale grey.
1.5.5. (2R,3S)-3-Benzyloxy-2-triethylsilyloxypent-4-enal
23
(12). (0.189 g, 91%); ½aꢀD +26.3 (c 1.8, CHCl3); 1H
NMR (CDCl3): d 9.66 (s, 1H, H-1), 7.37–7.26 (m, 5H,
H
arom.), 5.91 (ddd, 1H, J4,3 6.8, J4,5cis 10.7, J4,5trans
17.4 Hz, H-4), 5.38–5.30 (m, 2H, H-5a, H-5b), 4.66 (d,
1H, JA,B 12.1 Hz, Hbenzyl), 4.37 (d, 1H, JA,B 12.1 Hz,
H
benzyl), 4.10–4.04 (m, 2H, H-2, H-3), 0.91 (t, 9H, J
7.7 Hz, CH3), 0.63 (q, 6H, J 7.7 Hz, CH2); 13C NMR
(CDCl3): d 203.5 (C-1), 138.3 (Cq.arom.), 134.6 (C-4),
129.0, 128.5 and 128.3 (CHarom.), 120.3 (C-5), 81.5 (C-
3), 80.4 (C-2), 71.1 (CH2Ph), 7.3 (CH2CH3), 5.3
(CH2CH3); HRESIMS m/z: [(M+Na)+] calcd for
C18H28O3SiNa, 343.1705; found, 343.1716.
1.5.2. Reaction with activated zinc, preparation of com-
pound 9. To a soln of 5-iodo pentofuranosides 7a + 7b
in a 4:1 THF–water mixture (5 mL/mmol) was added
activated zinc dust (10 equiv). The reaction was soni-
cated at 40 ꢁC until starting material disappeared. The
mixture was filtered through cotton to eliminate zinc
and solvents were evaporated. The residue was immedi-
ately dissolved in dry THF (9 mL, 16 mL/mmol) with
1.5.6. (2R,3S)-3-Benzyloxy-2-methoxyethoxymethyloxy-
1
˚
4 A molecular sieves (0.19 g). The mixture was flushed
pent-4-enal (13). (0.111 g, 78%); H NMR (CDCl3): d
with argon and benzylhydroxylamine hydrochloride
was added (1.14 mmol, 182 mg). After 8 h, molecular
sieves were filtered and the solvent evaporated. The
residue was dissolved in CH2Cl2 (10 mL), washed
twice with water (2 · 5 mL), dried over Na2SO4 and
concentrated. The residue was purified on a silica gel
column (3:7 EtOAc–petroleum ether) to afford 9 as a
yellow oil.
9.68 (1H, s, 1-H), 7.36–7.26 (m, 5H, Harom.), 5.95–5.86
(m, 1H, H-4), 5.38–5.30 (m, 2H, H-5a, H-5b), 4.93–
4.76 (m, 2H, OCH2O), 4.63 (d, 1H, JA,B 12.0 Hz,
Hbenzyl), 4.35 (1H, d, JA,B 12.0 Hz, Hbenzyl), 4.11–4.06
(m, 2H, H-2, H-3), 3.36 (s, 3H, OCH3), 3.79–3.72 (m,
2H, OCH2), 3.76–3.33 (m, 2H, OCH2); 13C NMR
(CDCl3): d 202.1 (C-1), 137.8 (Cq.arom.), 134.1 (C-4),
128.9, 128.6, 128.0 and 127.4 (CHarom.), 120.5 (C-5),
96.5 (OCH2O), 84.1 (C-3), 80.0 (C-2), 71.9 (OCH2),
71.1 (CH2Ph), 60.8 (OCH2), 59.4 (OCH3).
1.5.3.
(2R,3S)-3-Benzyloxy-2-hydroxypent-4-enal
O-benzyloxime 9. (0.146 g, 88%, 80:20 mixture of iso-
mers determined by GC); IR (film); m 3440, 3083, 3063,
3031, 2920, 2848, 1026, 928, 734 and 697 cmꢁ1 1H
;
Acknowledgements
NMR (CDCl3): d 7.47 (d, 0.8H, J1,2 5.5 Hz, H-1 major
isomer), 7.38–7.32 (m, 10H, Harom.), 6.82 (d, 0.2H, J1,2
5.5 Hz, H-1 minor isomer), 5.82–5.76 (m, 1H, H-4),
5.40–5.29 (m, 2H, H-5), 5.10 (s, 0.8H, Hbenzyl oxime),
5.07 (s, 0.2H, Hbenzyl oxime), 4.66 (d, 1H, JA,B 11.7 Hz,
This work was supported by the ‘Contrat de Plan
´
Etat-Region’ in Europol’Agro framework (GLYCOVAL
´
program). The authors are grateful to the ‘Region
Champagne-Ardenne’ and C.N.R.S. for a doctoral
fellowship (A.B.). We also thank the A.R.D. company
for the generous gift of the starting materials D-xylose
and L-arabinose, H. Baillia for his help in obtaining
some of the NMR spectra and D. Harakat for the mass
spectra.
Hbenzyl), 4.38 (d, 1H, JA,B 11.7 Hz, Hbenzyl), 4.32–4.29
(m, 1H, H-2), 3.98 (t, 0.2H, J3,4 7.5, J3,2 7.5 Hz, H-3
minor isomer), 3.90 (t, 0.8H, J3,2 7.5, J3,4 7.5 Hz, H-3
major isomer), 2.88 (s, 1H, OH); 13C NMR (CDCl3):
149.8 (C-1), 138.3, 138.0 and 137.9 (Cq.arom.), 134.8 and
134.5 (C-4), 129.1, 129.0, 128.9, 128.7, 128.6 and 128.5
(CHarom.), 121.4 and 120.5 (C-5), 82.4 and 81.6 (C-3),
78.6 and 76.9 (CH2Ph oxime), 72.2 (C-2), 72.1 (CH2Ph);
HRESIMS m/z: [(M+Na)+] calcd for C19H21O3NNa,
334.1419; found, 334.1411.
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