De novo synthesis of uronic acid building blocks for assembly of heparin oligosaccharides

Article abstract of DOI:10.1002/chem.200700141

An efficient de novo synthesis of uronic acid building blocks is described. The synthetic strategy relies on the stereoselective elongation of thio-acetal protected dialdehydes 12a and 17. The dialdehydes are prepared from D-xylose, a cheap and commercial

Full text of DOI:10.1002/chem.200700141

DOI: 10.1002/chem.200700141
De Novo Synthesis of Uronic Acid Building Blocks for Assembly of Heparin
Oligosaccharides
Alexander Adibekian, Pascal Bindschädler, Mattie S. M. Timmer, Christian Noti,
Nina Schützenmeister, and Peter H. Seeberger*[a]
Abstract: An efficient de novo synthe-
sis of uronic acid building blocks is de-
scribed. The synthetic strategy relies on
the stereoselective elongation of thio-
tive MgBr2·OEt2-mediated Mukaiyama
aldol addition to C4-aldehyde 12a is
performed to obtain d-glucuronic acid
building block 16, whereas l-iduronic
acid building block 22 is prepared by
MgBr2·OEt2-mediated cyanation of C5-
aldehyde 17. Synthesis of a heparin dis-
accharide demonstrates the utility of
the de novo strategy for the assembly
of glycosaminoglycan oligosaccharides.
A
Keywords: carbohydrates · de novo
17. The dialdehydes are prepared from
d-xylose, a cheap and commercially
available source. A highly stereoselec-
synthesis
·
heparin
·
oligosaccharides · uronic acids
Introduction
Intriguing strategies for the de novo synthesis of monosac-
charides have been reported in the past two decades.[2]
Sharpless and Masamune[3] reported the syntheses of eight
different hexoses by asymmetric epoxidation. More recently,
proline-catalyzed aldol reactions served to rapidly construct
partially protected monosaccharides.[4] Still, none of these el-
egant approaches delivered carbohydrate building blocks
suitable for the synthesis of oligosaccharides.
Heparin, a linear, highly sulfated polysaccharide and the
most acidic naturally occurring biopolymer, is composed of
a-1,4-linked repeating disaccharide units containing uronic
acid and d-glucosamine (GlcN). The uronic acid monosac-
charides are l-iduronic acid (IdoA) and less frequently
(about 10%) d-glucuronic acid (GlcA). A typical heparin
disaccharide bears O-sulfation at C2 of the uronic acid, at
C6 and more rarely also at C3 of glucosamine. In addition,
the glucosamine nitrogen can be sulfated or acetylated.[5]
Heparin isolated from natural sources is very heterogeneous.
Nevertheless, heparins play a key role in regulating the bio-
logical activity of several proteins in the coagulation cascade
along with many other pathological processes including cell
growth, virus entry, tumor metastasis and inflammatory pro-
cesses.[6]
The chemical synthesis of oligosaccharides requires suitably
protected monosaccharide building blocks that are tradition-
ally synthesized from unprotected sugars through a series of
protection and deprotection maneuvers.[1] One fundamental
difficulty of this process is the differentiation of up to five
chemically similar hydroxyl groups in hexoses that require
temporary protecting groups as well as selective masking of
the anomeric hydroxyl group. Consequently, protocols for
the preparation of carbohydrate building blocks rely on up
to 20 synthetic steps[1] making this process time consuming
and expensive. Dissection of carbohydrate building blocks
into linear fragments reduces the number of hydroxyl
groups and avoids temporary protection of the anomeric hy-
droxyl. The de novo strategy is convergent and minimizes
the number of synthetic steps. It is possible to prepare sever-
al structurally related carbohydrate building blocks from
one common linear precursor by varying the conditions for
the stereoselective construction of the carbon skeleton.
[a] A. Adibekian, P. Bindschädler, Dr. M. S. M. Timmer, C. Noti,
N. Schützenmeister, Prof. Dr. P. H. Seeberger
Laboratory for Organic Chemistry
The modular assembly of heparins[7] requires large quanti-
ties of differentially protected monosaccharides. While the
synthesis of d-glucosamine building blocks from cheap, com-
mercially available d-glucosamine is straightforward,[8] the
procurement of orthogonally protected uronic acids is the
highest synthetic hurdle on the way to heparin oligosacchar-
ides. The synthesis of IdoA building blocks represents an ex-
Swiss Federal Institute of Technology (ETH) Zürich
Wolfgang-Pauli-Strasse 10, HCI F312, 8093 Zürich (Switzerland)
Fax : (+41)44-633-1235
E-mail: seeberger@org.chem.ethz.ch
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
4510
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 4510 – 4522

FULL PAPER
traordinary challenge, since iduronic acid itself is not com-
mercially available. Syntheses of iduronic acid building
blocks from a variety of starting materials including idose,[9]
glucose[10] and glycals,[11] have been developed. While l-
idose is too expensive to serve as starting material, syntheses
from alternative starting materials require the inversion of
the C5 stereogenic center of a d-gluco configured sugar.
Fewmethods employed for this inversion have shown com-
plete selectivity for the desired configuration. Syntheses
from idose to procure iduronic acid building blocks have
been reported[9] but remain lengthy and involve several
steps that produce multiple products. Although a plethora
of other syntheses of glucuronic and iduronic acid building
blocks is known,[8,12] no concise, stereoselective route to
both orthogonally protected uronic acids from one common
advanced intermediate has been reported to date.
Recently, we developed a de
blocks: d-glucuronic acid A, l-iduronic acid B and d-glucos-
amine C (Scheme 1). A proper choice of protecting groups
in the synthesis of uronic acid building blocks is of para-
mount importance for the control of glycosidation events
and selective sulfations in the assembly of heparins.[7] Thus,
we selected the pivaloyl group as the acyl group (PG1) for
anchimeric assistance to form selectively the desired trans-
glycosidic bonds. In addition, pivaloate esters can be hydro-
lyzed in anticipation of O-sulfation[15] prior to cleavage of
benzyl ethers that were chosen as permanent protecting
groups (PG2). For protection of carboxylic acids (PG4) w e
planned to use methyl esters that can be removed together
with other acyl groups. Finally, we decided to use levulinic
esters[16] as temporary protecting groups PG3 for the C4-hy-
droxyl groups on both building blocks, as Lev esters are or-
thogonal to all other masking groups.
novo synthesis of fully func-
tionalized uronic acids.[13] We
used l-arabinose as the start-
ing material for the synthesis
of different C4 aldehydes that
were elongated by Mukaiya-
ma-type aldol reactions[14] to
give uronic acid building
blocks. While d-glucuronic
acid was efficiently prepared
in overall yield of 16%, the
route to the l-iduronic acid,
more abundant in heparin,
yielded only 6% overall, due
to lowselectivity in the aldol
addition step. Here, we report
a selective and high yielding
route to d-glucuronic acid and
l-iduronic acid building blocks.
The key steps are the diaste-
reoselective elongations of two
monoprotected
dialdehydes
that are both derived from d-
xylose as a cheap, commercial-
ly available starting material.
A C4 aldehyde is elongated by
an aldol reaction to furnish
glucuronic acid. Cyanation of a
Scheme 1. Retrosynthetic analysis of heparin oligosaccharides (P=protecting group; PG1 =Piv, PG2 =Bn,
PG3 =Lev, PG4 =Me).
C5 aldehyde provides iduronic acid. The highly diastereose-
lective carbonyl additions were studied in detail and allowed
us to postulate possible transition states. Finally, the synthet-
ic utility of the newstrategy is demonstrated by construction
of a selectively O-sulfated and N-acetylated heparin disac-
charide.
IdoA and GlcA are epimers with respect to C5 in the pyr-
anose ring. Therefore, our retrosynthetic analysis focused on
means of introducing the C5 stereocenter at a late stage of
the synthesis. Synthesis of common intermediate F would be
followed by divergence to both targets. The pathway to the
glucuronic acid building block relies on the oxidative cleav-
age of diol F to aldehyde D. A chelate-controlled 2,3-anti-
selective aldol reaction,[17] C4 protection as levulinic ester
and concluding cyclization will deliver d-gluco-thioglycoside
A. En route to the iduronic acid building block, C5-alde-
hyde E will be prepared by oxidation of the primary hydrox-
yl of diol F. Subsequently, syn-selective chelate-controlled
Results and Discussion
Synthetic strategy: Dissection of a model heparin oligosac-
charide reveals three different monosaccharide building
Chem. Eur. J. 2007, 13, 4510 – 4522
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4511

P. H. Seeberger et al.
Table 1. Lewis acid mediated reaction of acetal 3 to form thioacetal 4[a]
.
cyanation, methanolysis of the nitrile via a Pinner reaction
and final cyclization is expected to furnish the desired l-ido-
configured thioglycoside B. Glucosamine building block C
will be derived using previously established methods.[8d]
Entry
Lewis acid
equiv EtSH
Yield 4 [%][b]
1
2
3
4
5
6
7
SnCl4
TiCl4
BF3·OEt2
BF3·OEt2
BF3·OEt2
ZnCl2
3
3
3
64
37
70
81
67
85
91
6
Synthesis of the building blocks: The first goal of our syn-
thetic approach was the preparation of diol F, the key com-
pound on the way to both uronic acids. Monoacetal 1 was
readily available from d-xylose on hundreds of gram scale[18]
(Scheme 2). Protection of the primary alcohol with triphe-
nylchloromethane in pyridine proceeded smoothly to give
alcohol 2. Benzylation of the secondary hydroxyl with
benzyl bromide, sodium hydride and catalytic amount of
TBAI afforded fully protected d-xylofuranose 3 in quantita-
tive yield over two steps.
20
20
20
ZnBr2
[a] All reactions were carried out in CH2Cl2 (0.3m) at 08C. [b] Isolated
yield.
was obtained in quantitative yield. An X-ray structure of
7[40] revealed that the pivaloyl group did not migrate during
isopropylidene cleavage with acid.
We had planned for the N-
iodosuccinimide-mediated cyc-
lization of thioacetals[13] to be
the final step in the synthesis
of both uronic acid thioglyco-
sides. The reaction was tested
on a compound bearing both
pivaloyl and levulinoyl protect-
ing groups. For this purpose,
the primary hydroxyl on diol 7
was selectively protected as tri-
phenylmethyl
ether
(Scheme 4). The secondary hy-
droxyl was subjected to
esterification conditions using
levulinic acid, N,N’-diisopropyl
carbodiimide (DIPC) and 4-di-
Scheme 2. Synthesis of thioacetal 4: a) TrCl, pyridine, quant.; b) BnBr, NaH, TBAI (cat.), DMF, quant.
At this stage, we investigated the one-pot Lewis acid
mediated cleavage of the trityl protecting group and con-
comitant opening of the anomeric acetal 3 with ethane thiol
methylaminopyridine (DMAP) to give ester 9 in quantita-
tive yield over two steps. For the cleavage of triphenylmeth-
yl ether, various acidic conditions were tested, since the lev-
ulinoyl group exhibited a tendency to migrate to the pri-
mary hydroxyl. Optimal reaction conditions employed TFA
and triethylsilane in dichloromethane to afford primary al-
cohol 10 in 90% yield. Finally, the cyclization of thioacetal
as nucleophile to obtain monobenzylated thioacetal
4
(Table 1). Screening a variety of different Lewis acids and
reaction conditions allowed access to triol 4 (Scheme 2) as
the major product in moderate yield by using hard Lewis
acids such as SnCl4, TiCl4 or BF3·OEt2 and three equivalents
of thiol (entries 1–3). An increased yield of 81% was ob-
served by employing BF3·OEt2 and six equivalents of EtSH
(entry 4), as well as by careful controlling of reaction time.
Gratifyingly, the use of mild Lewis acid ZnBr2 and large
excess of ethane thiol improved the yield further to give
91% of thioacetal 4 (entry 7). Unambiguous confirmation of
the structure of 4 was based on the X-ray analysis of single
crystals (CCDC-633131).[40]
In order to selectively introduce an acyl protecting group
at the C2 hydroxyl, an acetonide was installed on triol 4
using thermodynamic conditions (Scheme 3). The dioxolane
ring was formed selectively under agency of 15 mol% of
pTsOH and acetone at room temperature to afford alcohol
5 in 93% yield. Subsequent protection of the free hydroxyl
using pivaloyl chloride and DMAP furnished the fully pro-
tected thioacetal 6 in quantitative yield. After treatment
with 75% acetic acid in water at 508C, the desired diol 7
Scheme 3. Synthesis of diol 7: a) pTsOH, acetone, 93%; b) PivCl,
DMAP, CH2Cl2, 08C, quant.; c) AcOH/H2O, 50 8C, quant.
4512
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 4510 – 4522

Heparin Oligosaccharides
FULL PAPER
Table 2. Mukaiyama-type aldol reactions with aldehydes 12a and 12b.[a]
Scheme 4. Synthesis of d-xylopyranose building block 11: a) TrCl, pyri-
dine, 90%; b) LevOH, DIPC, DMAP, CH2Cl2, quant.; c) TES, TFA,
CH2Cl2, 90%; d) NIS, TFA, CH2Cl2, 08C, 92 % (a/b 1:1).
Entry Enol ether Aldehyde Lewis acid
T [8C] I/J/K [%][b]
[c]
1
2
3
4
5
6
7
8
G
G
G
G
G
G
G
G
G
H
G
12b
12b
12b
12b
12b
12b
12b
12b
12b
12b
12a
TiCl4
ꢀ78
RT
0
ꢀ78
RT
0
–
10 proceeded smoothly with N-iodosuccinimide (NIS) and
one equivalent of TFA at 08C to furnish orthogonally pro-
tected d-xylopyranose thioglycoside[19,20] 11 as a separable
1:1 mixture of a and b anomers in 92% yield. Building
block 11 is useful[21] for the construction of b-glycosidic link-
ages found in the tetrasaccharide core of glycosaminogly-
cans linking xylose to the serine/threonine residues of the
proteoglycan core protein.[22]
BF3·OEt2
BF3·OEt2
BF3·OEt2
ZnCl2
ZnCl2
ZnCl2
MgBr2·OEt2
MgBr2·OEt2
MgBr2·OEt2
MgBr2·OEt2
1:1:1 (74)
1:1:1 (93)
[d]
–
10:4:– (66)
10:5:– (72)
10:7:– (87)
10:2:– (99)
1:–:– (98)
1:–:– (96)
1:–:– (85)
ꢀ78
[e]
[e]
[e]
[e]
0
9
10
11
ꢀ78
ꢀ78
ꢀ78
Next, we explored the route to the d-glucuronic acid
building block. Oxidative cleavage of diol 7 with sodium pe-
riodate in a THF/water mixture afforded C4-aldehyde 12a
in 82% yield (Scheme 5). Aldehyde 12a was purified by
silica gel column chromatography and could be stored for
days without significant decomposition.
[a] All reactions were carried out with 1.5 equiv of ketene acetal and
1.5 equiv of Lewis acid in toluene (0.2m). [b] Isolated yields. [c] Decom-
position of the aldehyde was observed. [d] No reaction was observed.
[e] Excess MgBr2·OEt2 (3 equiv) was used due to its low solubility in tol-
uene.
1
sides and analysis of the H NMR coupling constants[13] the
isomers were identified as the d-gluco (I), l-ido (J) and l-
altro (K) configurations. The lowselectivity is in agreement
with recent results by Evans,[24] who reported the BF3·OEt2-
mediated addition of enol silanes to syn-a,b-bisalkoxy alde-
hydes. The absence of the d-galacto isomer can be explained
assuming a sterically demanding Si,Si attack in a non-chelat-
ing, open transition state. Next, ZnCl2 was used as a chelat-
ing Lewis acid (entries 5–7). The best selectivity was ob-
tained at room temperature, giving I and J in a ratio of 10:4
and moderate yield of 66%. Use of ZnCl2 at lowtempera-
tures improved yields but decreased selectivity (entries 6
and 7). The use of MgBr2·OEt2 at ꢀ788C led to exclusive
formation of isomer I in quantitative yield. Interestingly,
when the (Z)-ketene acetal H was used, the same result was
obtained (entry 10). After applying these conditions to alde-
hyde 12a, again only isomer I was formed in 85% yield
(entry 11).
Scheme 5. Synthesis of the d-glucuronic acid building block 16: a) NaIO4,
H2O/THF, 82%; b) LevOH, DIPC, DMAP, CH2Cl2, quant.; c) HF py,
THF, quant.; d) NIS, TFA, CH2Cl2, 88% (a/b 1:1).
Nowthe stage was set for the chelation controlled Mu-
kaiyama-type aldol addition to aldehyde 12a. Yamamotoꢁs
ketene acetals[23] G and H were chosen as nucleophiles
(Table 2), since they are equipped with an acid-cleavable
TBS protecting group in the a-position. To identify optimal
reaction conditions, the (E)-ketene acetal G was used in
combination with aldehyde 12b (entries 1–9), that is avail-
able in five steps from l-arabinose.[13] The use of TiCl4 as ac-
tivator led to the decomposition of the aldehyde even at low
temperatures (entry 1). Aldol addition with non-chelating
Lewis acid BF3·OEt2 at 08C (entry 3) was high yielding
(93%), but three different diastereomers were formed in a
1:1:1 ratio. After conversion to the corresponding thioglyco-
Transmetallation of both enol silanes[25] to magnesium
enolate would enable formation of a cyclic transition state
and explain the high selectivity of these transformations. To
investigate this mechanistic assumption, both ketene acetals
were treated with MgBr2·OEt2 in [D8]toluene at ꢀ788C.
Even after warming to room temperature neither changes in
1H NMR signals of both nucleophiles nor appearance of
1
characteristic H NMR signals of TMS-Br or TBS-Br were
observed. Based on these results we exclude the possibility
of transmetallation and assume that the MgBr2·OEt2-medi-
Chem. Eur. J. 2007, 13, 4510 – 4522
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4513

P. H. Seeberger et al.
ated[26] Mukaiyama aldol reaction between ketene acetal G
or H and aldehyde 12a or 12b proceeds via an open transi-
tion state, where MgBr2 chelates the formyl oxygen and the
benzyloxy oxygen of the aldehyde (Figure 1). The nature of
the protecting group on oxygen at C3 plays a minor role in
this process, as both aldehydes react in a similar way. The Si
attack on the aldehyde is prohibited by the bulky rest R on
C2 of the aldehyde. The face selectivity on nucleophiles is
determined by steric repulsion between the bromide ligands
on magnesium and bulky substituents of ketene acetals G
and H. According to Heathcock,[27] this repulsion is mini-
mized in synclinal transition structures TS1 and TS2, as well
as in antiperiplanar transition structures TS3 and TS4. Both
TS3 and TS4 are disfavored compared with TS1 and TS2,
since increased steric repulsion is caused by a sterically de-
manding substituent R. The topological rule for preferred
gauche relationship of the donor and acceptor p systems in
a variety of C,C-bond forming reactions proposed by See-
bach[28] additionally favors TS1 and TS2. Thus, the d-gluco
diastereomer is formed with high selectivity using both
ketene acetals.
Aldol product 13 was masked as the corresponding levuli-
noyl ester (Scheme 5). The silyl ether was cleaved under
mild conditions using HF·pyridine in THF to furnish the C5-
alcohol 15 in quantitative yield over two steps. Finally, NIS-
mediated thioacetal cyclization led to the formation of the
desired d-glucuronic acid thioglycoside 16 as a separable 1:1
mixture of both anomers in 88% yield. At this stage, the
NOE correlations served to confirm the d-gluco configura-
tion on b-thioglycoside 16a (Figure 2). 1-Thio d-glucuronic
Figure 2. Diagnostic NOE correlations for donor 16a.
acids have recently been demonstrated to be efficient glyco-
sylating agents in the assembly of glycosaminoglycans.[8f]
The next target in our synthetic endeavor was the l-idur-
onic acid building block. We planned to prepare a C5 alde-
hyde and elongate it via a cyanation reaction (Scheme 6). A
number of procedures for the oxidation of alcohol 10 to al-
dehyde 17 were tested, but all failed either due to oxidation
of the sulfur or epimerization of the aldehyde during the re-
action. Finally, we found that a mild procedure based on
DMSO in combination with sulfur trioxide pyridine complex
and DIPEA, known as the Parikh–Doering oxidation,[29]
gave the desired aldehyde 17 in excellent yield of 94%.
Next, the chelate-controlled cyanation of aldehyde 17 was
explored. Chelating halide salts in combination with trime-
thylsilyl cyanide as a safe source of cyanide[30] were used to
selectively obtain the l-ido-configured product. The most in-
teresting results of this investigation are summarized in
Table 3. The mixtures of d-gluco- and l-ido diastereomers
were separated and analyzed after cleavage of the levulinoyl
protecting group, as partial migration took place during the
cyanation. No product was obtained when hard Lewis acids
such as BF3·OEt2 or TiCl4 were used, since rapid decomposi-
tion of the aldehyde occured even at ꢀ788C (entries 1 and
2). Use of CuBr2 at ꢀ208C
gave a mixture of cyanohy-
drins with a slight preference
for the isomer 18a in 82%
yield (entry 4). It was possible
to determine the relative con-
figuration of cyanohydrin 18a
by X-ray analysis[40] to confirm
the desired l-ido configuration
(Figure 3). When ZnI2 was
used, cyanation of the levuli-
noyl ketone as side reaction
resulted in lowyields of 32–
57% (entries 5–7). Again, use
of MgBr2·OEt2 as chelating ac-
tivator[30,31] proved to be the
method of choice and furnish-
ed the l-ido isomer with 8:1
diastereoselectivity and 82%
yield at 08C (entry 9). The
syn-preference of this transfor-
mation is in accordance with
Reetzꢁ model for chelate-con-
trolled additions of cyanosi-
lanes to aldehydes.[30,32]
Figure 1. Possible transition states for MgBr2·OEt2-mediated aldol reaction.
4514
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 4510 – 4522

Heparin Oligosaccharides
FULL PAPER
Scheme 6. Synthesis of l-iduronic acid building blocks 21 and 22: a)
SO3·Py, DMSO, DIPEA, 94%; b) AcCl, MeOH, toluene, 70%; c) 1)
LevOH, DIPC, DMAP, CH2Cl2, 08C; 2) NIS, CH2Cl2, 80% over two
steps (a/b 1:1); d) 1) LevOH, DIPC, DMAP, CH2Cl2, 08C; 2) BTI, aq.
NaHCO3, CH3CN; then TFA, 508C; 3) Cl3CCN, DBU, CH2Cl2, 77%
over three steps (a/b 1:1).
Figure 3. ORTEP plot of cyanohydrin 18a.
Table 3. Cyanation–deprotection sequence with aldehyde 17.[a]
Scheme 7. Cyclization and protection of diol 19 to b-l-iduronic acid fura-
nose 20: a) NIS, CH2Cl2, 81%; b) LevOH, DIPC, DMAP, CH2Cl2, 08C,
88%.
Entry
Lewis acid
T [8C]
18a/18b (Yield/%)[b]
[c]
1
2
3
4
5
6
7
8
BF3·OEt2
TiCl4
CuBr2
CuBr2
ZnI2
ꢀ78
ꢀ78
RT
ꢀ20
RT
ꢀ20
ꢀ20
RT
0
–
–
[c]
an alternative glycosylating agent in 77% yield using Storkꢁs
dethioacetalization with bis(trifluoroacetoxy)iodobenzene
(BTI)[35] followed by the reaction of the formed hemiacetal
with DBU and trichloroacetonitrile.
2:1 (87)
3:1 (82)
5:1 (32)[d]
8:1 (57)[d]
8:1 (52)[d]
6:1 (84)
ZnI2
ZnI2
[e]
[g]
[g]
[g]
MgBr2·OEt2
MgBr2·OEt2
MgBr2·OEt2
Synthesis of a heparin disaccharide: We applied the method-
ology described here to the synthesis of O-sulfated and N-
acetylated heparin disaccharide 32 (Scheme 8). In the first
step the IdoA building block was coupled with a linker bear-
ing a protected amine group in the terminal position. This
modification allows, after the sulfation and global deprotec-
tion, for the immobilization of the disaccharide on a glass
slide to prepare heparin arrays.[36] An N-(benzyl)benzyloxy-
carbonylamino linker was selected, for its compatibility with
oligosaccharide assembly.[37] Glycosidation of IdoA building
block 23 with N-(benzyl)benzyloxycarbonyl-5-amino-pen-
tane-1-ol catalyzed by TMSOTf in CH2Cl2 at ꢀ208C fol-
lowed by cleavage of the levulinoyl group furnished alcohol
25.[36b] Coupling with 2-azidoglucopyranose building block[8d]
26 using these conditions afforded disaccharide 27 in 81%
yield and complete a-selectivity for the newly constructed
glycosidic linkage. With the fully protected heparin disac-
charide in hand, we laid out the deprotection strategy. Sapo-
nification removes the acyl protecting groups on IdoA and
GlcN as well as hydrolyzes the methyl ester. O-Sulfation
9
10
8:1 (82)
[f]
ꢀ20
–
[a] All reactions were carried out with 1.1 equiv of TMSCN and 1.2 equiv
of Lewis acid in CH2Cl2 (0.1m). The diastereomeric ratio was determined
after removal of the partially migrated levulinoyl protecting group.
[b] Isolated yields. [c] Decomposition of the aldehyde was observed.
[d] Cyanation of the levulinoyl ketone was observed. [e] 3 equiv of Lewis
acid were used. [f] No reaction was observed. [g] Excess MgBr2·OEt2
(3 equiv) was used due to its low solubility in CH2Cl2.
Nitrile 18a readily underwent the Pinner reaction
(Scheme 6) when treated with an excess of hydrochloric acid
in toluene and methanol as the nucleophile.[33] Subsequent
hydrolysis furnished methyl ester 19 in 70% yield. The NIS-
mediated cyclization of diol 19 delivered exclusively the b-
furanose form of l-iduronic acid (Scheme 7). Serendipitous-
ly, protection with levulinic acid at 08C gave selectively the
4-O-Lev thioacetal, that was cyclized with NIS in CH2Cl2 to
furnish l-iduronic acid thioglycoside 22 in 80% yield over
two steps. Known[34] trichloroacetimidate 23 was prepared as
Chem. Eur. J. 2007, 13, 4510 – 4522
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4515

P. H. Seeberger et al.
places sulfate groups on position 2 of iduronic acid and posi-
tion 6 of glucosamine. The azide is reduced via a Staudinger
reaction before N-acetylation. Finally, hydrogenolysis will
remove all permanent protection from the desired heparin
disaccharide. Treatment of 27 with lithium hydroperoxide
followed by addition of an aqueous solution of KOH and
MeOH afforded the partially protected disaccharide 28 in
85% yield. O-Sulfation was conducted with SO3·Et3N in
DMF at 558C[38] and furnished double sulfated compound 29
in 82% yield. The azido group was reduced using PMe3 in
THF[39] to give amine 30 in 87% yield. Subsequent N-acety-
lation gave 31 quantitatively. Finally, hydrogenolytic cleav-
age of the benzyl and benzyloxycarbonyl groups furnished
the selectively sulfated heparin disaccharide 32 in quantita-
tive yield.
building blocks of d-xylose as well as d-glucuronic and l-
iduronic acids from a readily available common intermedi-
ate. Our de novo synthesis is based on the use of linear syn-
thetic intermediates, thus no anomeric protection is necessa-
ry and a/b mixtures of anomers are not formed during the
synthesis. The de novo synthesis of further carbohydrate
building blocks is currently under investigation und will be
reported in due course.
ExperimentalSection
Generalinformation : All chemicals used were reagent grade and used as
supplied except where noted. Dichloromethane (CH2Cl2), toluene and
tetrahydrofuran (THF) were purified by a Cycle-Tainer Solvent Delivery
System. Pyridine and triethylamine
were distilled over CaH2 prior to use.
Analytical thin layer chromatography
(TLC) was performed on Merck silica
gel 60 F254 plates (0.25 mm). Com-
pounds were visualized by UV irradi-
ation or dipping the plate in an ani-
saldehyde solution followed by heat-
ing. Flash column chromatography
was carried out using forced flow of
the indicated solvent on Fluka Kiesel-
gel 60 (230–400 mesh). Gel filtration
chromatography was carried out
using Sephadex LH-20 from Amer-
sham Biosciences.
1H and 13C NMR spectra were record-
ed on a Varian VXR-300 (300 MHz)
or Bruker DRX500 (500 MHz) spec-
trometer. High-resolution mass spec-
tra (MALDI-HRMS) were performed
by the MS-service at the Laboratory
for Organic Chemistry (ETH Zürich).
ESI MS were run on an Agilent 1100
Scheme 8. Assembly and sulfation of heparin disaccharide 32: a) TMSOTf (cat.), CH2Cl2, ꢀ208C, 76% (a/b
95:5); b) H2NNH2·H2O, Py/AcOH, CH2Cl2, 96%; c) 25, TMSOTf (cat.), CH2Cl2, ꢀ258C, 4 Š MS, 81%; d)
LiOH, H2O2; KOH, MeOH, 85%; e) SO3·Et3N, DMF, 558C, 82%; f) PMe3, THF, NaOH, 87%; g) Ac2O, Et3N,
MeOH, quant.; h) H2, Pd/C, quant.
Series LC/MSD instrument. IR spec-
tra were recorded on a Perkin-Elmer
1600 FTIR spectrometer. Optical ro-
tations were measured using
Perkin-Elmer 241 polarimeter.
a
1,2-O-Isopropylidene-5-O-triphenyl-
Conclusion
methyl-a-d-xylofuranoside (2): Triphenylmethyl chloride (30 g,
107.69 mmol) was added at 08C to solution of diol (18.6 g,
a
1
In summary, we developed a de novo synthesis for d-glucur-
onic- and l-iduronic acid building blocks. Common inter-
mediate 7 was obtained from d-xylose 1 in six steps and
85% yield. From this diol precursor, d-xylose thioglycoside
11 was afforded in four steps via a NIS-mediated cyclization
in 75% yield. d-Glucuronic acid 16 was prepared in five
97.9 mmol) in pyridine (150 mL). The mixture was stirred at room tem-
perature for 12 h and the solvent was removed in vacuo. The residue was
purified by flash chromatography (hexanes/ethyl acetate 2:1) to give 2
(44.7 g, quant.) as a white foam. Rf = 0.4 (hexanes/ethyl acetate 3:7);
[a]RDT =54.4 (c=1, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.57–7.19
(m, 15H), 6.04 (d, J=3.7 Hz, 1H), 4.55 (d, J=3.7 Hz, 1H), 4.38–4.23 (m,
2H), 3.58 (m, 2H), 3.30 (brs, 1H), 1.55 (s, 3H), 1.36 ppm (s, 3H);
13C NMR (75 MHz, CDCl3): d = 143.2, 128.4, 128.0, 127.2, 111.5, 104.9,
87.5, 85.1, 78.6, 76.2, 61.9, 27.0, 26.3 ppm; IR (thin film on NaCl): n˜ =
3458, 3008, 1491, 1448, 1263, 1074, 908 cmꢀ1; MALDI-HRMS: m/z: calcd
for C27H28O5Na: 455.1829, found: 455.1833 [M+Na]+.
steps and 61% yield, including
a
highly selective
MgBr2·OEt2-mediated aldol addition as key transformation.
MgBr2·OEt2-mediated cyanation and subsequent Pinner re-
action served as key steps to synthesize l-iduronic acid 22 in
eight steps and 30% yield. All transformations could be per-
formed on a multigram scale without noticeable loss of yield
or selectivity. The synthetic utility of the iduronic acid build-
ing block was demonstrated by construction of an O-sulfat-
ed and N-acetylated heparin disaccharide 32.
1,2-O-Isopropylidene-3-O-benzyl-5-O-triphenylmethyl-a-d-xylofurano-
side (3): Alcohol 2 (14.8 g, 34.2 mmol) was dissolved in DMF (100 mL)
and cooled to 08C. Sodium hydride (1.5 g, 60% in oil, 37.6 mmol), benzyl
bromide (4.5 mL, 37.6 mmol) and TBAI (cat.) were added and the mix-
ture was allowed to stir at room temperature for 12 h. The reaction was
quenched with sat. aq. NH4Cl and concentrated in vacuo. The residue
was taken in ethyl acetate, washed with water and brine, dried over
MgSO4 and concentrated in vacuo. The resulting residue was purified by
flash chromatography (hexanes/ethyl acetate 20:1 ! 10:1) to give 3
The chemistry presented here offers a convenient and
high-yielding route for the preparation of suitably protected
4516
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 4510 – 4522

Heparin Oligosaccharides
FULL PAPER
(18.5 g, quant.) as a pale yellowoil. Rf = 0.7 (hexanes/ethyl acetate 3:7);
[a]RDT =ꢀ26.8 (c=1, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.56–7.11
(m, 20H), 5.97 (d, J=3.8 Hz, 1H), 4.68–4.59 (m, 2H), 4.53–4.43 (m, 2H),
4.07 (d, J=3.1 Hz, 1H), 3.63 (dd, J=9.3, 5.8 Hz, 1H), 3.38 (dd, J=9.3,
6.8 Hz, 1H), 1.59 (s, 3H), 1.38 ppm (s, 3H); 13C NMR (75 MHz, CDCl3):
d = 143.8, 137.4, 128.7, 128.3, 127.7, 127.6, 127.5, 126.9, 111.6, 86.9, 82.5,
79.5, 72.0, 61.4, 27.0, 26.4 ppm; IR (thin film on NaCl): n˜ =3007, 1731,
1448, 1346, 1163, 1077, 1010, 899, 859 cmꢀ1; MALDI-HRMS: m/z: calcd
for C34H34O5Na: 545.2298, found: 545.2304 [M+Na]+.
2-O-Pivaloyl-3-O-benzyl-d-xylose di(ethylthio)acetal (7): Acetonide 6
(21.8 g, 46.3 mmol) was dissolved in 50% aq. AcOH (500 mL). The mix-
ture was allowed to stir at 508C for 3 h. The solvent was removed in
vacuo and the residue was coevaporated twice with toluene. The resulting
colorless oil 7 (19.9 g, quant.) was analytically pure and was used for the
next step without further purification. Rf = 0.5 (hexanes/ethyl acetate
2:3); [a]RDT =ꢀ34.8 (c=1, CHCl3); 1H NMR (300 MHz, CDCl3): d
=
7.38–7.22 (m, 5H), 5.49 (dd, J=6.2, 4.5 Hz, 1H), 4.77 (d, J=11.4 Hz,
1H), 4.60 (d, J=11.4 Hz, 1H), 4.09 (d, J=4.5 Hz, 1H), 4.02 (dd, J=6.2,
3.7 Hz, 1H), 3.79 (dd, J=8.9, 5.0 Hz, 1H), 3.65–3.53 (m, 2H), 2.81–2.58
3-O-Benzyl-d-xylose di(ethylthio)acetal (4): Acetonide
3 (314 mg,
(m, 4H), 1.30–1.19 ppm (m, 15H); 13C NMR (75 MHz, CDCl3): d
=
0.6 mmol) was dissolved in CH2Cl2 (2.4 mL) and cooled to 08C. EtSH
(0.75 mL, 12 mmol) and ZnBr2 (676 mg, 3 mmol) were added and the
mixture was stirred at 08C for 75 min. The reaction was quenched by
adding 5% aq. ammonium hydroxide and the resulting slurry was diluted
with CH2Cl2 and 1m aq. HCl. The phases were separated and the aque-
ous layer extracted with CH2Cl2 (2”). The combined organic layers were
dried over MgSO4, concentrated and purified by flash chromatography
(cyclohexane/ethyl acetate 7:3 ! pure ethyl acetate) to afford 4 (189 mg,
177.6, 137.6, 128.4, 127.8, 127.6, 79.0, 74.8, 73.8, 71.5, 63.7, 51.7, 39.2, 27.5,
25.6, 25.4, 14.4 ppm; IR (thin film on NaCl): n˜ =3559, 2973, 1726, 1479,
1278, 1151 cmꢀ1
;
MALDI-HRMS: m/z: calcd for C21H34O5S2Na:
453.1740, found: 453.1748 [M+Na]+.
2-O-Pivaloyl-3-O-benzyl-5-O-triphenylmethyl-d-xylose di(ethylthio)ace-
tal(8) : Triphenylmethyl chloride (16.7 g, 60 mmol) was added portion-
wise at 08C to a solution of diol 7 (17.3 g, 40.2 mmol) in pyridine
(200 mL). The mixture was stirred at room temperature for 24 h and the
solvent was removed in vacuo. The residue was purified by flash chroma-
tography (hexanes/ethyl acetate 20:1 ! 6:1) to give 8 (24.3 g, 90%) as a
pale yellowfoam. Rf = 0.7 (hexanes/ethyl acetate 3:7); [a]RDT =ꢀ8.9 (c=
1, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.70–7.11 (m, 20H), 5.70
(dd, J=7.0, 4.0 Hz, 1H), 4.76 (d, J=11.1 Hz, 1H), 4.51–4.42 (m, 2H),
4.27 (d, J=4.0 Hz, 1H), 4.25–4.17 (m, 1H), 3.52 (dd, J=8.9, 5.5 Hz, 1H),
3.22 (d, J=8.4 Hz, 1H), 3.02–2.82 (m, 2H), 2.80–2.71 (m, 2H), 1.50–
1.32 ppm (m, 15H); 13C NMR (75 MHz, CDCl3): d = 177.4, 146.9, 143.7,
128.6, 127.8, 127.2, 86.9, 82.1, 78.4, 75.1, 74.0, 70.5, 64.1, 39.2, 27.6, 26.0,
25.6, 14.8, 14.6 ppm; IR (thin film on NaCl): n˜ =3007, 1724, 1448, 1363,
91%) as a colorless oil. Rf
=
0.5 (ethyl acetate); [a]RDT =27.3 (c=1,
CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.40–7.27 (m, 5H), 4.79 (d,
J=11.3 Hz, 1H), 4.72 (d, J=11.3 Hz, 1H), 4.07 (dd, J=4.8, 2.5 Hz, 1H),
4.04 (d, J=7.7 Hz, 1H), 3.95–3.77 (m, 3H), 3.72–3.59 (m, 1H), 3.39 (d,
J=4.8 Hz, 1H), 2.90 (d, J=5.8 Hz, 1H), 2.83 (dd, J=8.3, 4.5 Hz, 1H),
2.77–2.55 (m, 4H), 1.22 (t, J=7.4, 3H), 1.21 ppm (t, J=7.4 Hz, 3H);
13C NMR (75 MHz, CDCl3): d = 137.9, 128.4, 128.1, 127.8, 78.4, 74.5,
71.9, 70.9, 62.9, 55.4, 25.2, 24.4, 14.6, 14.5 ppm; IR (thin film on NaCl):
n˜ =3451, 3007, 2930, 1454, 1391, 1264, 1091, 1052, 876 cmꢀ1; MALDI-
HRMS: m/z: calcd for C16H26O4S2Na: 369.1165, found: 369.1159
[M+Na]+.
1277, 1152, 1077, 632 cmꢀ1
;
MALDI-HRMS: m/z: calcd for
3-O-Benzyl-4,5-O-isopropylidene-d-xylose
di(ethylthio)acetal
(5):
C40H48O5S2Na: 695.2835, found: 695.2828 [M+Na]+.
pTsOH (422 mg, 2.22 mmol) was added to a solution of triol 4 (5.12 g,
14.78 mmol) in acetone (100 mL). The mixture was stirred at room tem-
perature for 12 h and the reaction was quenched with sat. aq. NaHCO3.
The suspension was filtered and the solvent was removed under reduced
pressure. The residue was purified by flash chromatography (hexanes/
ethyl acetate 10:1) to give 5 (5.31 g, 93%) as a colorless oil. Rf = 0.7
(hexanes/ethyl acetate 3:2); [a]RDT =49.3 (c=1, CHCl3); 1H NMR
(300 MHz, CDCl3): d = 7.44–7.19 (m, 5H), 4.94 (d, J=11.3 Hz, 1H),
4.72 (d, J=11.3 Hz, 1H), 4.52–4.41 (m, 1H), 4.06 (dd, J=8.1, 6.4 Hz,
1H), 3.99 (d, J=8.2 Hz, 1H), 3.94 (dd, J=7.0, 2.0 Hz, 1H), 3.75 (d, J=
7.9 Hz, 1H), 3.47 (ddd, J=7.9, 5.6, 2.1 Hz, 1H), 3.14 (d, J=5.6 Hz, 1H),
2.72–2.54 (m, 4H), 1.45 (s, 3H), 1.37 (s, 3H), 1.23 (t, J=7.4, 3H),
2-O-Pivaloyl-3-O-benzyl-4-O-levulinoyl-5-O-triphenylmethyl-d-xylose
di(ethylthio)acetal (9): Levulinic acid (6.79 g, 58.5 mmol) was dissolved
in CH2Cl2 (500 mL), followed by the addition of DMAP (7.15 g,
58.5 mmol). The mixture was cooled to 08C and N,N’-diisopropyl carbo-
diimide (DIPC) (9.23 mL, 5.85 mmol) was added. After 10 min alcohol 8
(26.5 g, 39 mmol) in CH2Cl2 (40 mL) was added dropwise. The mixture
was stirred at room temperature for 4 h. After dilution with CH2Cl2
(100 mL) the mixture was washed with sat. aq. NH4Cl and dried over
MgSO4. The solvent was removed in vacuo and the residue was purified
by silica gel chromatography (hexanes/ethyl acetate 4:1) to give 9 (2.96 g,
quant.) as a white foam. Rf = 0.5 (hexanes/ethyl acetate 3:7); [a]DRT
=
ꢀ15.2 (c=1, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.45–7.10 (m,
20H), 5.35–5.28 (m, 1H), 5.23 (d, J=5.6 Hz, 1H), 4.70 (d, J=11.5 Hz,
1H), 4.57–4.49 (m, 2H), 4.06 (d, J=5.4 Hz, 1H), 3.23 (m, 2H), 2.81–2.47
(m, 8H), 2.13 (s, 3H), 1.28 (t, J=7.4 Hz, 3H), 1.22–1.12 ppm (m, 12H);
13C NMR (75 MHz, CDCl3): d = 205.8, 177.2, 172.1, 138.4, 128.1, 127.2,
127.0, 76.9, 75.0, 74.4, 72.4, 61.0, 52.0, 39.1, 37.8, 28.2, 27.5, 25.9, 25.1,
25.0, 18.2, 14.3 ppm; IR (thin film on NaCl): n˜ =3007, 1727, 1490, 1448,
1279, 1152, 1075, 1032, 899, 632 cmꢀ1; MALDI-HRMS: m/z: calcd for
C45H54O7S2Na: 793.3203, found: 793.3194 [M+Na]+.
1.20 ppm (t, J=7.4 Hz, 3H); 13C NMR (75 MHz, CDCl3): d
= 138.3,
128.2, 128.1, 127.6, 109.3, 78.7, 77.7, 74.1, 72.3, 66.0, 55.5, 26.8, 25.7, 25.1,
24.2, 14.7, 14.5 ppm; IR (thin film on NaCl): n˜ =3007, 2930, 1454, 1381,
1248, 1075, 852 cmꢀ1; MALDI-HRMS: m/z: calcd for C19H30O4S2Na:
409.1478, found: 409.1471 [M+Na]+.
2-O-Pivaloyl-3-O-benzyl-4,5-O-isopropylidene-d-xylose di(ethylthio)ace-
tal(6) : Alcohol 5 (20 g, 51.7 mmol) was dissolved in CH2Cl2 (250 mL)
and cooled to 08C. Pivaloyl chloride (8.5 mL, 69 mmol) was added drop-
wise, followed by portionwise addition of DMAP (12.8 g, 103.5 mmol).
After stirring at 08C for 60 min sat. aq. NH4Cl (50 mL) was added and
the phases were separated. The aqueous layer was extracted with
CH2Cl2, and the combined organic layers were washed with brine and
dried over MgSO4. The solvent was removed in vacuo and the residue
was purified by silica gel chromatography (hexanes/ethyl acetate 5:1) to
give 6 (26.2 g, quant.) as a colorless oil. Rf = 0.8 (hexanes/ethyl acetate
2-O-Pivaloyl-3-O-benzyl-4-O-levulinoyl-d-xylose di(ethylthio)acetal (10):
Compound 9 (3.5 g, 4.54 mmol) was dissolved in CH2Cl2 (200 mL) and
cooled to 08C. Triethylsilane (14.5 mL, 91 mmol) was added, followed by
dropwise addition of trifluoroacetic acid (13.5 mL, 182 mmol). After
5 min the solution was adjusted to pH 5 by careful addition of sat. aq.
NaHCO3. The organic layer was separated, washed with brine and dried
over MgSO4. The solvent was removed in vacuo and the residue was pu-
rified by silica gel chromatography (hexanes/ethyl acetate 3:1 ! 2:3) to
give 10 (2.16 g, 90%) as a colorless oil. Rf = 0.6 (hexanes/ethyl acetate
7:3); [a]RDT =ꢀ15.4 (c=1, CHCl3); 1H NMR (300 MHz, CDCl3): d
=
7.39–7.20 (m, 5H), 5.13 (dd, J=7.3, 3.6 Hz, 1H), 4.90 (d, J=11.7 Hz,
1H), 4.72 (d, J=11.7 Hz, 1H), 4.23 (t, J=7.2, 1H), 4.16 (d, J=7.3 Hz,
1H), 4.05 (dd, J=6.9, 3.6 Hz, 1H), 3.97 (dd, J=8.5, 6.4 Hz, 1H), 3.76
(dd, J=8.5, 7.3 Hz, 1H), 2.76–2.50 (m, 4H), 1.44 (s, 3H), 1.34 (s, 3H),
1.26–1.17 ppm (m, 15H); 13C NMR (75 MHz, CDCl3): d = 177.1, 138.5,
128.1, 127.4, 127.3, 109.3, 78.8, 77.2, 74.3, 72.7, 65.9, 51.9, 39.1, 27.4, 26.6,
25.5, 24.8, 24.5, 14.5, 14.2 ppm; IR (thin film on NaCl): n˜ =2976, 1723,
1479, 1372, 1278, 1155, 1067, 854 cmꢀ1; MALDI-HRMS: m/z: calcd for
C24H38O5S2Na: 493.2058, found: 493.2061 [M+Na]+.
2:3); [a]RDT =ꢀ20.3 (c=1, CHCl3); 1H NMR (300 MHz, CDCl3): d
=
7.36–7.20 (m, 5H), 5.33 (d, J=5.5 Hz, 1H), 5.10 (t, J=4.7, 4.4 Hz, 1H),
4.77 (d, J=11.7 Hz, 1H), 4.67 (d, J=11.7 Hz, 1H), 4.34 (d, J=5.3 Hz,
1H), 4.04 (d, J=5.8 Hz, 1H), 3.72–3.67 (m, 2H), 2.82–2.35 (m, 8H), 2.13
(s, 3H), 1.28–1.15 ppm (m, 15H); 13C NMR (75 MHz, CDCl3): d = 206.9,
177.4, 172.4, 138.0, 128.2, 127.5, 127.2, 77.0, 74.7, 74.6, 72.5, 61.4, 52.0,
39.1, 38.1, 29.9, 29.8, 28.3, 27.4, 25.1, 25.0, 14.5, 14.4 ppm; IR (thin film
on NaCl): n˜ =2973, 1722, 1479, 1367, 1152, 1152, 1048 cmꢀ1; MALDI-
Chem. Eur. J. 2007, 13, 4510 – 4522
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4517

P. H. Seeberger et al.
HRMS: m/z: calcd for C26H40O7S2Na: 551.2108, found: 551.2104
[M+Na]+.
0.96–0.87 (m, 9H), 0.07–0.05 ppm (m, 6H); 13C NMR (75 MHz, CDCl3):
d = 177.4, 172.1, 137.9, 128.2, 127.4, 126.8, 74.6, 73.7, 73.4, 73.1, 52.0,
51.9, 51.9, 51.8, 39.1, 27.4, 25.7, 25.8, 25.6, 25.2, 18.2, 14.3, ꢀ4.8,
ꢀ5.1 ppm; IR (thin film on NaCl): n˜ =3556, 3008, 2956, 2951, 2859, 1729,
1602, 1455, 1397, 1363, 1260, 1150, 840 cmꢀ1; MALDI-HRMS m/z calcd
for C29H50O7S2SiNa: 625.2659, found: 625.2649 [M+Na]+.
Ethyl2- O-pivaloyl-3-O-benzyl-4-O-levulinoyl-a/b-d-xylopyranoside (11):
A solution of alcohol 10 (110 mg, 208 mmol) in CH2Cl2 (4.2 mL) was
treated with TFA (15.5 mL, 208 mmol) and NIS (51.5 mg, 229 mmol),
stirred for 5 min at room temperature and cooled to 08C. The reaction
was quenched by dropwise additon of saturated aqueous sodium thiosul-
fate solution (4.2 mL) and stirred for further 5 min at 08C. Saturated
aqueous NaHCO3 (0.8 mL) was added and the mixture was allowed to
warm to room temperature. After diluting with CH2Cl2, the phases were
separated and the aqueous layer was extracted with CH2Cl2. The com-
bined organic layers were dried over MgSO4, filtered, concentrated and
purified by flash chromatography (hexanes/ethyl acetate 1:1) to afford 11
(90 mg, 92%, as a pale yellowoil) as 1:1 a/b mixture.
b Anomer (11a): Rf = 0.5 (hexanes/ethyl acetate 2:3); [a]RDT =ꢀ9.7 (c=
1, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.37–7.23 (m, 5H), 5.05 (d,
J=7.2 Hz, 1H), 4.93 (dd, J=7.6, 4.5 Hz, 1H), 4.71 (d, J=11.6 Hz, 1H),
4.64 (d, J=11.7 Hz, 1H), 4.60 (d, J=7.3 Hz, 1H), 4.28 (dd, J=11.8,
4.5 Hz, 1H), 3.70 (d, J=7.2 Hz, 1H), 3.36 (dd, J=11.9, 7.7 Hz, 1H),
2.77–2.37 (m, 6H), 2.17 (s, 3H), 1.30–1.19 ppm (m, 12H); 13C NMR
Methyl2- O-pivaloyl-3-O-benzyl-4-O-levulinoyl-5-O-tert-butyldimethylsil-
yl-d-glucuronate di(ethylthio)acetal (14): LevOH (13 mg, 0.11 mmol) was
dissolved in CH2Cl2 (0.4 mL) and DMAP (13 mg, 0.11 mmol) was added
and stirred for 15 min. The reaction was cooled to 08C, DIPC (14 mg,
0.11 mmol) and alcohol 13 (43 mg, 0.07 mmol) in CH2Cl2 (1 mL) were
added and stirred for 20 h at room temperature. The solution was diluted
with CH2Cl2 (20 mL), washed with sat. NH4Cl and brine, and dried over
MgSO4. The solvent was evaporated and the residue was purified by
silica gel chromatography (CH2Cl2) to give 14 (52 mg, quant.) as a pale
yellowoil (52 mg, quant.). Rf = 0.3 (hexanes/ethyl acetate 4:1); [a]DRT
=
ꢀ10.4 (c=1, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.37–7.20 (m,
5H), 5.36 (dd, J=6.1, 4.8 Hz, 1H), 5.21 (dd, J=6.1, 4.8 Hz, 1H), 4.79 (d,
J=11.9 Hz, 1H), 4.70 (d, J=11.9 Hz, 1H), 4.55 (dd, J=5.9, 4.8 Hz, 1H),
4.48 (d, J=4.8 Hz, 1H), 4.14 (d, J=6.2 Hz, 1H), 3.73 (s, 3H), 2.81–2.34
(m, 8H), 2.12 (s, 3H), 1.34–1.15 (m, 15H), 0.97–0.79 (m, 9H), 0.07 (s,
3H), 0.06 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d = 205.9, 177.2,
171.5, 170.7, 138.4, 128.1, 127.1, 126.4, 77.4, 77.0, 76.6, 76.2, 74.6, 74.4,
72.2, 71.6, 52.2, 52.0, 39.1, 37.9, 29.8, 28.0, 27.4, 25.7, 25.0, 24.8, 23.6, 18.2,
14.3, ꢀ4.8, ꢀ5.2 ppm; IR (thin film on NaCl): n˜ =3011, 2972, 2030, 1720,
1523, 1456, 1363, 1157, 1081, 929, 840 cmꢀ1; MALDI-HRMS: m/z: calcd
for C34H56O9S2SiNa: 723.3027, found: 723.3034 [M+Na]+.
(75 MHz, CDCl3): d
= 206.0, 176.6, 171.7, 137.8, 128.3, 128.2, 127.6,
127.4, 127.3, 83.5, 78.5, 73.6, 70.2, 70.1, 64.2, 38.8, 37.8, 29.9, 29.8, 29.7,
27.8, 27.1, 24.5, 14.9 ppm; IR (thin film on NaCl): n˜ =2970, 2930, 1721,
1456, 1429, 1363, 1265, 1153, 1070 cmꢀ1; MALDI-HRMS: m/z: calcd for
C19H28O5SNa: 489.1918, found: 489.1916 [M+Na]+.
a Anomer (11b): Rf = 0.7 (hexanes/ethyl acetate 2:3); [a]RDT =23.1 (c=1,
CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.39–7.23 (m, 5H), 5.44 (d,
J=4.7 Hz, 1H), 4.98–4.84 (m, 2H), 4.76 (d, J=11.5 Hz, 1H), 4.66 (d, J=
11.6 Hz, 1H), 4.01–3.77 (m, 3H), 2.76–2.36 (m, 6H), 2.17 (s, 3H), 1.32–
1.18 ppm (m, 12H); 13C NMR (75 MHz, CDCl3): d = 205.9, 177.2, 171.7,
137.8, 128.3, 128.2, 127.6, 127.4, 127.3, 83.5, 81.8, 74.4, 73.6, 72.1, 70.4,
60.7, 38.8, 37.8, 29.9, 29.8, 29.7, 27.9, 27.2, 24.5, 14.9 ppm; IR (thin film
on NaCl): n˜ =2929, 1721, 1602, 1456, 1429, 1363, 1280, 1153, 1028,
909 cmꢀ1; MALDI-HRMS: m/z: calcd for C19H28O5SNa: 489.1918, found:
489.1916 [M+Na]+.
Methyl2- O-pivaloyl-3-O-benzyl-4-O-levulinoyl-d-glucuronate di(ethylth-
io)acetal(15) : Silyl ether 14 (217 mg, 0.31 mmol) was dissolved in THF
(3 mL) and HF·pyridine complex (55 mL, 0.62 mmol) was added drop-
wise. The solution was stirred for 12 h at room temperature, cooled to
08C and quenched with sat. aq. NaHCO3. The mixture was diluted with
ethyl acetate (20 mL), washed with sat. aq. NaHCO3 and brine, and dried
over MgSO4. The solvent was removed in vacuo and the residue was pu-
rified by silica gel chromatography (hexanes/ethyl acetate 1:1) to give al-
cohol 15 (181 mg, quant.) as colorless oil. Rf
= 0.8 (ethyl acetate);
2-O-Benzyl-3-O-pivaloyl-l-threo-dialdose
di(ethylthio)acetal
(12a):
[a]RDT =ꢀ11.3 (c=1, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.37–7.26
(m, 5H), 5.44 (dd, J=6.2, 5.0 Hz, 1H), 5.27 (dd, J=5.9, 4.8 Hz, 1H), 4.77
(d, J=11.4 Hz, 1H), 4.71 (d, J=11.4 Hz, 1H), 4.44 (dd, J=6.2, 4.8 Hz,
1H), 4.36 (dd, J=7.5, 5.9 Hz, 1H), 3.98 (d, J=5.0 Hz, 1H), 3.76 (s, 3H),
3.25 (d, J=7.5 Hz, 1H), 2.83–2.43 (m, 8H), 2.17 (s, 3H), 1.32–1.17 ppm
(m, 15H); 13C NMR (75 MHz, CDCl3): d = 206.5, 177.7, 172.8, 172.5,
138.1, 128.5, 127.7, 127.4, 77.1, 73.6, 75.3, 72.9, 69.5, 51.8, 39.3, 37.8, 29.9,
28.1, 27.5, 25.5, 25.2, 14.4 ppm; IR (thin film on NaCl): n˜ =3690, 2929,
1733, 1602, 1456, 1374, 1277, 1151 cmꢀ1; MALDI-HRMS: m/z: calcd for
C28H42O9S2Na: 609.2163, found: 609.2169 [M+Na]+.
NaIO4 (39 mg, 0.18 mmol) in H2O (0.5 mL) was added to a solution of
diol (71 mg, 0.16 mmol) in THF (2 mL) at room temperature. After stir-
ring for 2 h, the mixture was diluted with hexanes (20 mL) and washed
with sat. aq. NaHCO3 and brine. The phases were separated and the or-
ganic layer was dried over MgSO4. The solvent was removed in vacuo
and the residue was purified by silica gel chromatography (hexanes/ethyl
acetate 9:1) to give 12a as pale yellowoil (52 mg, 82%). Rf = 0.8 (hex-
anes/ethyl acetate 7:3); [a]RDT =ꢀ4.3 (c=1, CHCl3); 1H NMR (300 MHz,
CDCl3): d = 9.70 (d, J=0.8 Hz, 1H), 7.41–7.29 (m, 5H), 5.39 (dd, J=6.5,
4.2 Hz, 1H), 4.79 (d, J=11.5 Hz, 1H), 4.65 (d, J=11.5 Hz, 1H), 4.33 (dd,
J=4.2, 0.8 Hz, 1H), 4.19 (d, J=6.5 Hz, 1H), 2.75–2.53 (m, 4H), 1.29–
1.18 ppm (m, 15H); 13C NMR (75 MHz, CDCl3): d = 199.6, 177.2, 137.0,
128.4, 128.0, 127.9, 82.1, 73.7, 73.6, 51.1, 38.9, 27.1, 25.0, 24.9, 14.2,
14.0 ppm; IR (thin film on NaCl): n˜ =2975, 2931, 2873, 1732, 1479, 1455,
Methyl(ethyl2- O-pivaloyl-3-O-benzyl-4-O-levulinoyl-1-thio-a/b-d-gluco-
pyranosid)uronate (16): A solution of alcohol 15 (63 mg, 107 mmol) in
CH2Cl2 (1 mL) was treated with TFA (8 mL, 107 mmol) and NIS (27 mg,
118 mmol), stirred for 5 min at room temperature and cooled to 08C. The
reaction was quenched by dropwise additon of sat. aq. sodium thiosulfate
solution (4.2 mL) and stirred for further 5 min at 08C. Sat. aq. NaHCO3
was added to adjust pH 5 and the mixture was allowed to warm to room
temperature. After diluting with CH2Cl2, the phases were separated and
the aqueous layer was extracted with CH2Cl2. The combined organic
layers were dried over MgSO4, filtered, concentrated and purified by
flash chromatography (hexanes/ethyl acetate 4:1) to afford 15 (49 mg,
88%, as a pale yellowoil) as 1:1 a/b mixture.
b Anomer (16a): Rf = 0.6 (hexanes/ethyl acetate 1:1); [a]RDT =25.4 (c=
0.5, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.37–7.20 (m, 5H), 5.27–
5.11 (m, 2H), 4.67 (d, J=11.4 Hz, 1H), 4.62 (d, J=11.5 Hz, 1H), 4.46 (d,
J=10.0 Hz, 1H), 3.97 (d, J=9.9 Hz, 1H), 3.81 (d, J=9.2 Hz, 1H), 3.73 (s,
3H), 2.84–2.30 (m, 6H), 2.15 (s, 3H), 1.32–1.16 ppm (m, 12H); 13C NMR
1398, 1369, 1278, 1145, 1051 cmꢀ1
C16H26O4S2H: 399.1658, found: 399.1658 [M+H]+.
; MALDI-HRMS: m/z: calcd for
Methyl2-
O-pivaloyl-3-O-benzyl-5-O-tert-butyldimethylsilyl-d-glucuro-
nate di(ethylthio)acetal (13): Ketene acetal G (62 mg, 0.23 mmol) was
dissolved in toluene (1.2 mL) and MgBr2·OEt2 (116 mg, 0.45 mmol) was
added. The solution was stirred for 15 min at room temperature and
cooled to ꢀ788C. Aldehyde 12a (60 mg, 0.15 mmol) in CH2Cl2 (1.2 mL)
was added dropwise and stirred for 4 h at ꢀ788C. The solution was
warmed to room temperature and stirred for another 2 h. The mixture
was diluted with CH2Cl2 (20 mL), washed with sat. aq. NaHCO3 and
brine, and dried over MgSO4. The solvent was removed in vacuo and the
residue was purified by silica gel chromatography (hexanes/ethyl acetate
9:1) and gave aldol product 13 (77 mg, 85%) as colorless oil. Rf = 0.5
(hexanes/ethyl acetate 4:1); [a]RDT =ꢀ28.3 (c=1, CHCl3); 1H NMR
(300 MHz, CDCl3): d = 7.30 (m, 5H), 5.49 (dd, J=6.1, 4.8 Hz, 1H), 4.79
(d, J=11.4 Hz, 1H), 4.72 (d, J=11.4 Hz, 1H), 4.28 (d, J=7.0 Hz, 1H),
4.22 (dd, J=6.2, 2.2 Hz, 1H), 4.06 (d, J=4.8 Hz, 1H), 3.89 (ddd, J=9.1,
7.0, 2.1 Hz, 1H), 3.75 (s, 3H), 2.88–2.53 (m, 4H), 1.28–1.20 (m, 15H),
(75 MHz, CDCl3): d
= 205.8, 176.4, 171.1, 167.3, 137.6, 128.2, 127.6,
127.3, 83.6, 81.0, 77.1, 74.0, 71.0, 70.2, 52.7, 38.6, 37.6, 29.6, 27.5, 27.0,
23.6, 14.6 ppm; IR (thin film on NaCl): n˜ =3662, 3036, 2923, 1744, 1600,
1456, 1364, 1282, 1149, 1092 cmꢀ1
;
MALDI-HRMS: m/z: calcd for
C26H36O9SNa: 524.2080, found: 524.2072 [M+Na]+.
4518
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 4510 – 4522

Heparin Oligosaccharides
FULL PAPER
a Anomer (16b): Rf = 0.7 (hexanes/ethyl acetate 1:1); [a]RDT =ꢀ1.4 (c=
1, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.29 (m, 5H), 5.75 (d, J=
4.8 Hz, 1H), 5.21 (d, J=7.7 Hz, 1H), 4.99 (dd, J=8.1, 4.8 Hz, 1H), 4.74
(d, J=11.4 Hz, 1H), 4.68 (d, J=7.9 Hz, 1H), 4.64 (d, J=11.5 Hz, 1H),
3.88 (d, J=7.8 Hz, 1H), 3.69 (s, 3H), 2.72–2.36 (m, 6H), 2.17 (s, 3H),
1.32–1.22 ppm (m, 12H); 13C NMR (75 MHz, CDCl3): d = 205.9, 177.2,
171.5, 168.4, 137.5, 128.3, 127.7, 127.4, 80.6, 77.1, 71.4, 70.0, 52.6, 38.6,
37.5, 29.8, 29.6, 27.6, 27.0, 24.5, 14.8 ppm; IR (thin film on NaCl): n˜ =
3670, 2922, 1730, 1656, 1433, 1364, 1280, 1158 cmꢀ1; MALDI-HRMS:
m/z: calcd for C26H36O9SNa: 524.2080, found: 524.2072 [M+Na]+.
0.51 mmol) in toluene (5 mL) and silica gel (1.16 g), followed by drop-
wise addition of acetyl chloride (0.41 mL). The mixture was warmed to
room temperature, stirred for 20 h and cooled again to 08C. Water
(5 mL) was added dropwise at 08C, and the mixture was warmed to
room temperature overnight. The reaction was quenched by addition of
sat. aq. NaHCO3, the phases were separated and the aqueous phase was
extracted with CH2Cl2. The combined organic layers were dried over
MgSO4. The solvent was removed in vacuo and the residue was purified
by flash chromatography (cyclohexane/ethyl acetate 1:1) to give 19
(173 mg, 70%) as a colorless oil. Rf = 0.7 (hexanes/ethyl acetate 1:1);
[a]RDT =ꢀ29.7 (c=1, CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.44–7.27
(m, 5H), 5.43 (dd, J=5.7, 4.9 Hz, 1H), 4.84 (d, J=11.3 Hz, 1H), 4.71 (d,
J=11.2 Hz, 1H), 4.30 (dd, J=5.3, 2.8 Hz, 1H), 4.25 (d, J=5.1 Hz, 1H),
4.14 (d, J=6.1 Hz, 1H), 4.07 (ddd, J=8.1, 5.6, 2.8 Hz, 1H), 3.66 (s, 3H),
3.10 (d, J=5.4 Hz, 1H), 2.80–2.57 (m, 4H), 1.59 (brs, 1H), 1.31–1.20 ppm
(m, 15H); 13C NMR (75 MHz, CDCl3): d = 177.5, 173.1, 137.8, 128.3,
127.6, 127.5, 78.6, 74.8, 73.1, 72.4, 70.7, 52.8, 51.8, 39.2, 27.4, 25.0, 14.4,
14.3 ppm; IR (thin film on NaCl): n˜ =3544, 2972, 1731, 1429, 1367, 1277,
2-O-Levulinoyl-3-O-benzyl-4-O-pivaloyl-d-xylo-dialdose di(ethylthio)ace-
tal(17) : SO3·Py complex (1.12 g, 7.0 mmol) was added to a solution of al-
cohol 10 (930 mg, 1.76 mmol) in CH2Cl2 (18 mL) at 08C, followed by the
addition of DIPEA (2.1 mL, 12.3 mmol). The mixture was stirred for
5 min and dimethyl sulfoxide (1.7 mL, 24.6 mmol) was added dropwise.
After stirring at 08C for 15 min, the solution was diluted with CH2Cl2
(100 mL) and brine (25 mL) was added. The phases were separated and
the organic layer was washed with brine and dried over MgSO4. The sol-
vent was removed in vacuo and the residue was purified by flash chroma-
tography (hexanes/ethyl acetate 5:1) to give 17 (871 mg, 94%) as a
1148 cmꢀ1
found: 511.1787 [M+Na]+.
; MALDI-HRMS: m/z: calcd for C23H36O7S2Na: 511.1795,
yellowoil. Rf
=
0.4 (hexanes/ethyl acetate 7:3); [a]RDT =3.7 (c=1,
Methyl(ethyl2-
O-pivaloyl-3-O-benzyl-1-thio-b-l-idofuranosyl)uronate
CHCl3); 1H NMR (300 MHz, CDCl3): d = 9.52 (s, 1H), 7.38–7.24 (m,
5H), 5.41 (d, J=5.5 Hz, 1H), 5.28 (d, J=4.6 Hz, 1H), 4.75 (d, J=
11.3 Hz, 1H), 4.66 (d, J=11.1 Hz, 1H), 4.61–4.57 (m, 1H), 4.00 (d, J=
5.7 Hz, 1H), 2.91–2.54 (m, 8H), 2.18 (s, 3H), 1.29–1.17 ppm (m, 15H);
13C NMR (75 MHz, CDCl3): d = 205.9, 195.9, 176.8, 171.7, 137.1, 128.3,
127.9, 127.6, 77.4, 76.3, 74.6, 72.0, 51.6, 39.1, 37.9, 29.8, 27.8, 27.4, 25.4,
25.2, 14.4, 14.3 ppm; IR (thin film on NaCl): n˜ =3008, 1736, 1455, 1366,
(20): A solution of diol 19 (136 mg, 278 mmol) in CH2Cl2 (5.6 mL) at
room temperature was treated with NIS (75 mg, 334 mmol) and stirred
for 15 min at room temperature. The reaction was quenched by the addi-
ton of sat. aq. sodium thiosulfate solution (10 mL), stirred for 10 min at
room temperature, then diluted with CH2Cl2. The organic layer was sepa-
rated, washed with brine and dried over MgSO4. After concentration, the
residue was purified by flash chromatography (cyclohexane/ethyl acetate
17:3 ! 4:1) to afford 20 (96 mg, 81%) as a pale yellowoil. Rf = 0.5 (cy-
clohexanes/ethyl acetate 3:2); [a]RDT =113.3 (c=1, CHCl3); 1H NMR
(300 MHz, CDCl3): d = 7.39–7.28 (m, 5H), 5.71 (d, J=5.6 Hz, 1H), 5.37
(t, J=5.3 Hz, 1H), 4.77 (d, J=12.1 Hz, 1H), 4.59 (d, J=11.8 Hz, 1H),
4.56 (dd, J=6.8, 2.5 Hz, 1H), 4.84 (m, 1H), 4.36 (dd, J=6.7, 4.8 Hz, 1H),
3.76 (s, 3H), 3.21 (d, J=3.7, 1H), 2.62 (q, J=7.4 Hz, 2H), 1.27–1.21 (m,
3H), 1.24 ppm (s, 9H); 13C NMR (75 MHz, CDCl3): d = 177.2, 172.2,
136.9, 128.5, 128.1, 127.7, 86.1, 81.4, 78.0, 77.8, 72.8, 70.1, 52.7, 38.8, 27.2,
25.3, 15.2 ppm; IR (thin film on NaCl): n˜ =3537, 2978, 2933, 1736, 1479,
1275, 1147 cmꢀ1
;
MALDI-HRMS: m/z: calcd for C26H38O7S2Na:
549.1951, found: 549.1946 [M+Na]+.
4-O-Benzyl-5-O-pivaloyl-6,6-di(ethylthio)-l-idonitrile (18a) and 4-O-
benzyl-5-O-pivaloyl-6,6-di(ethylthio)-d-gluconitrile (18b): Aldehyde 17
(1.49 g, 2.84 mmol) was dissolved in CH2Cl2 (28 mL) and cooled to 08C.
MgBr2·OEt2 (2.93 g, 11.36 mmol) was added and the mixtute was stirred
vigorously for 5 min. Then trimethylsilyl cyanide (416 mL, 3.12 mmol) was
added dropwise over 10 min. The mixture was warmed to room tempera-
ture overnight before it was quenched with brine. The solution was dilut-
ed with CH2Cl2 (100 mL), washed with brine and dried over MgSO4.
After concentration, the residue was filtered through silica gel (hexanes/
ethyl acetate 2:1) and concentrated again. The resulting yellowoil was
dissolved in CH2Cl2 (28 mL). Hydrazine acetate (314 mg, 3.41 mmol) in
MeOH (28 mL) was added dropwise and the mixture was stirred for 12 h
at room temperature. The solvent was removed in vacuo and two nitriles
were separated by silica gel chromatography (hexanes/ethyl acetate 10:1
! 5:1) to give 18a (943 mg, 73%) as a yellowsolid and 18b (117 mg,
9%) as a yellowoil.
Nitrile (18a): Rf = 0.7 (hexanes/ethyl acetate 1:1); [a]RDT =ꢀ35.2 (c=1,
CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.40–7.27 (m, 5H), 5.46 (dd,
J=5.9, 4.4 Hz, 1H), 4.81 (d, J=11.3 Hz, 1H), 4.66 (d, J=11.4 Hz, 1H),
4.50 (d, J=5.7 Hz, 1H), 4.18 (dd, J=5.9, 3.8 Hz, 1H), 4.06 (d, J=4.4 Hz,
1H), 3.96 (dd, J=5.7, 3.7 Hz, 1H), 2.84–2.55 (m, 4H), 1.33–1.17 ppm (m,
15H); 13C NMR (75 MHz, CDCl3): d = 178.1, 136.9, 128.6, 128.1, 127.8,
117.9, 77.2, 75.0, 73.8, 72.1, 62.3, 51.2, 39.1, 27.2, 25.4, 25.3, 14.2,
14.0 ppm; IR (thin film on NaCl): n˜ =3553, 2977, 1729, 1479, 1397, 1264,
1148 cmꢀ1; MALDI-HRMS: m/z: calcd for C22H33NO5S2Na: 478.1692,
found: 478.1682 [M+Na]+.
1456, 1398, 1367, 1144, 1041 cmꢀ1
; MALDI-HRMS: m/z: calcd for
C21H30O7SNa: 449.1604, found: 449.1602 [M+Na]+.
Methyl(ethyl2- O-pivaloyl-3-O-benzyl-5-O-levulinoyl-1-thio-b-l-idofura-
nosyl)uronate (21): Furanose 20 (96 mg, 225 mmol) in CH2Cl2 (2 mL) was
added dropwise to a solution of levulinic acid (30 mL, 293 mmol), DMAP
(36 mg, 293 mmol) and DIPC (42 mL, 270 mmol) in CH2Cl2 (2.5 mL) at
08C. The mixture was stirred for 4 h at room temperature, diluted with
CH2Cl2 (50 mL), washed with sat. aq. NH4Cl, dried over MgSO4 and con-
centrated. The residue was purified by flash chromatography (cyclohex-
ane/ethyl acetate 3:2) to afford 21 (104 mg, 88%) as a pale yellowoil. Rf
=
0.4 (cyclohexane/ethyl acetate 3:2); [a]RDT =58.6 (c=1, CHCl3);
1H NMR (300 MHz, CDCl3): d = 7.37–7.21 (m, 5H), 5.67 (d, J=5.5 Hz,
1H), 5.48 (d, J=4.4 Hz, 1H), 5.29 (t, J=5.1 Hz, 1H), 4.71 (dd, J=6.0,
3.6 Hz, 1H), 4.67 (d, J=11.6 Hz, 1H), 4.50 (d, J=11.7 Hz, 1H), 4.33 (dd,
J=6.7, 4.6 Hz, 1H), 3.69 (s, 3H), 2.75–2.56 (m, 6H), 2.14 (s, 3H), 1.29–
1.20 ppm (m, 12H); 13C NMR (75 MHz, CDCl3): d = 205.7, 177.2, 171.3,
168.2, 136.9, 128.3, 127.8, 127.6, 85.7, 80.9, 76.6, 76.6, 72.8, 70.4, 52.6, 38.8,
37.9, 29.8, 28.0, 27.1, 25.4, 15.2 ppm; IR (thin film on NaCl): n˜ =3008,
2978, 2932, 1740, 1478, 1436, 1364, 1281, 1152, 1044 cmꢀ1; MALDI-
HRMS: m/z: calcd for C26H36O9SNa: 547.1972, found: 547.1977
[M+Na]+.
Nitrile (18b): Rf = 0.8 (hexanes/ethyl acetate 1:1); [a]RDT =17.1 (c=1,
CHCl3); 1H NMR (300 MHz, CDCl3): d = 7.39–7.26 (m, 5H), 5.50 (dd,
J=6.5, 4.1 Hz, 1H), 4.81 (d, J=11.2 Hz, 1H), 4.66 (d, J=11.3 Hz, 1H),
4.37 (d, J=7.3 Hz, 1H), 4.22 (dd, J=6.5, 2.6 Hz, 1H), 4.06 (d, J=4.1 Hz,
1H), 3.97 (dd, J=7.3, 2.7 Hz, 1H), 2.88–2.53 (m, 4H), 1.36–1.12 ppm (m,
15H); 13C NMR (75 MHz, CDCl3): d = 178.0, 137.1, 128.6, 128.2, 127.9,
118.9, 74.9, 74.0, 71.4, 62.9, 51.2, 39.1, 27.2, 25.6, 25.4, 14.2, 14.1 ppm; IR
(thin film on NaCl): n˜ =3555, 2975, 1728, 1479, 1397, 1277, 1148,
1072 cmꢀ1; MALDI-HRMS: m/z: calcd for C22H33NO5S2Na: 478.1692,
found: 478.1684 [M+Na]+.
Methyl(ethyl2-
O-pivaloyl-3-O-benzyl-4-O-levulinoyl-1-thio-a/b-l-ido-
pyranosyl)uronate (22): Levulinic acid (36 mg, 0.31 mmol) was dissolved
in CH2Cl2 (3 mL), followed by the addition of DMAP (38 mg,
0.31 mmol). The mixture was cooled to 08C and DIPC (49 mL,
0.31 mmol) was added. After 10 min, diol 19 (133 mg, 0.26 mmol) in
CH2Cl2 (2 mL) was added dropwise. The mixture was stirred at 08C for
2.5 h, then diluted with CH2Cl2 (50 mL), washed with sat. aq. NH4Cl and
dried over MgSO4. The solvent was removed in vacuo and the crude
product was coevaporated with toluene and again dissolved in CH2Cl2
(3 mL). NIS (65 mg, 0.29 mmol) was added and stirred for 15 min. Then
Methyl2- O-pivaloyl-3-O-benzyl-l-iduronate di(ethylthio)acetal (19):
MeOH (1.16 mL) was added at 08C to a mixture of nitrile 18 (230 mg,
Chem. Eur. J. 2007, 13, 4510 – 4522
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4519

P. H. Seeberger et al.
sat. aq. sodium thiosulfate (3 mL) was added and the mixture stirred for
10 min. The mixture was diluted with CH2Cl2 (100 mL) and the phases
were separated. The organic layer was washed with brine and dried over
MgSO4. The solvent was removed in vacuo and the residue was purified
by silica gel chromatography (hexanes/ethyl acetate 20:1 ! 8:1) to give
21 as 1:1 a/b mixture (114 mg, 80%, colorless oil). Rf = 0.3 (hexanes/
30 min, the reaction mixture was quenched with triethylamine, concen-
trated and the residue was purified by column chromatography (hexanes/
ethyl acetate 9:1) to yield disaccharide 27 (106 mg, 81%) as a colorless
oil. [a]RDT =10.2 (c=1, CHCl3); 1H NMR (500 MHz, CDCl3): d = 7.39–
7.25 (m, 25H), 5.20–5.17 (brd, 2H), 5.07–5.05 (m, 2H), 4.98–4.97 (t, J=
4.4 Hz, 2H), 4.88–4.72 (m, 6H), 4.62–6.60 (d, J=11.1 Hz, 1H), 4.51–4.49
(brd, 2H), 4.37–4.34 (dd, J=2.2, 10.1 Hz, 1H), 4.22–4.19 (dd, J=4.1,
12.2 Hz, 1H), 4.16–4.13 (m, 1H), 3.99–3.96 (m, 2H), 3.92–3.88 (dd, J=
8.8, 10.2 Hz, 1H), 3.80 (s, 3H), 3.75–3.70 (brm, 1H), 3.56–3.53 (dd, J=
8.9, 9.9 Hz, 1H), 3.51–3.41 (brm, 1H), 3.31–3.29 (dd, J=3.6, 10.2 Hz,
1H), 3.29–3.16 (brm, 2H), 2.03 (s, 3H), 1.61–1.31 (m, 6H), 1.24 ppm (s,
9H); 13C NMR (75 MHz, CDCl3); mixture of rotamers: d = 177.6, 170.7,
170.0, 156.6/156.3, 138.2, 137.9, 137.8, 137.7, 137.1/137.0, 128.8–127.4, 99.1,
98.5, 80.2, 77.9, 76.0, 75.6, 75.3, 75.0, 74.2, 73.2, 70.2, 70.1, 69.8. 69.2/69.1,
67.4, 63.6, 62.7, 52.5, 50.7/50.4, 47.3/46.4, 39.0, 28.2/27.7, 27.4, 23.5,
21.1ppm; IR (thin film on NaCl): n˜ =3007, 2937, 2871, 2109, 1733, 1687,
1
ethyl acetate 3:2); H NMR (300 MHz, CDCl3): d = 7.42–7.25 (m, 10H),
5.40 (s, 1H), 5.27 (d, J=2.3 Hz, 1H), 5.24–5.19 (m, 2H), 5.01 (d, J=
2.0 Hz, 1H), 5.00–4.97 (m, 1H), 4.97–4.94 (m, 1H), 4.81–4.75 (m, 2H),
4.72–4.65 (m, 2H), 4.55 (d, J=1.8 Hz, 1H), 3.79 (s, 3H), 3.78 (s, 3H),
3.73–3.71 (m, 2H), 2.84–2.47 (m, 16H), 2.18 (s, 3H), 2.17 (s, 3H), 1.34–
1.19 ppm (m, 24H); 13C NMR (75 MHz, CDCl3): d = 205.8, 177.6, 177.2,
171.8, 171.6, 168.9, 167.8, 137.1, 136.9, 128.4, 128.3, 128.0, 127.7, 127.6,
127.4, 82.7, 82.1, 74.3, 73.5, 72.9, 72.7, 72.5, 68.3, 68.0, 66.9, 66.4, 52.3,
52.2, 38.6, 37.6, 29.6, 27.8, 27.7, 27.1, 27.0, 26.9, 26.5, 25.8, 14.8 ppm; IR
(thin film on NaCl): n˜ =3586, 3032, 1740, 1602, 1364, 1150, 1071 cmꢀ1
;
1492, 1451, 1364, 1143 cmꢀ1
;
MALDI-HRMS: m/z: calcd for
MALDI-HRMS: m/z: calcd for C26H36O9SNa: 547.1972, found: 547.1965
[M+Na]+.
C61H72O15N4Na: 1123.489, found: 1123.486 [M+Na]+.
N-(Benzyl)-benzyloxycarbonyl-5-aminopentyl (2-azido-3,4-di-O-benzyl-2-
deoxy-a-d-glucopyranosyl)-(1!4)-3-O-benzyl-a-l-idopyranosyluronic
acid (28): H2O2 (30%, 0.9 mL) and 1n solution of LiOH (1.5 mL) were
added at 08C to a solution of disaccharide 27 (85 mg, 77 mmol) in THF
(2.6 mL). After stirring for 16 h at room temperature, the mixture was
cooled to 08C and MeOH (4.5 mL) and 3m aq. solution of KOH
(2.7 mL) were added. After stirring for additional 16 h at room tempera-
ture, the reaction mixture was neutralized with IR-120-H+ amberlite
resin, filtered and concentrated. The residue was purified by Sephadex
LH-20 chromatography (MeOH/CH2Cl2 1:1) to afford 28 (63 mg, 85%)
Methyl2-
O-pivaloyl-3-O-benzyl-4-O-levulinoyl-a/b-l-idopyranosyluro-
nate trichloroacetimidate (23): Levulinic acid (124 mg, 1.07 mmol) was
dissolved in CH2Cl2 (10 mL), followed by the addition of DMAP
(132 mg, 1.07 mmol). The mixture was cooled to 08C and DIPC (169 mL,
1.07 mmol) was added. After 10 min diol 19 (474 mg, 0.97 mmol) in
CH2Cl2 (10 mL) was added dropwise. The mixture was stirred at 08C for
2.5 h, then diluted with CH2Cl2 (100 mL), washed with sat. aq. NH4Cl
and dried over MgSO4. The solvent was removed in vacuo and the crude
product was dissolved in CH3CN (20 mL). Water was added (5 mL), fol-
lowed by addition of bis(trifluoroacetoxy)iodobenzene (1.43 g,
3.3 mmol). After 5 min, NaHCO3 was added (700 mg) and stirred for an-
other 30 min at room temperature. The solvent was removed and water
was added (30 mL), followed by dropwise addition of TFA (30 mL). The
mixture was stirred for 30 min at 508C and the solvent was removed
again. The resulting colorless oil was coevaporated with toluene, dis-
solved in CH2Cl2/trichloroacetonitrile 2:1 (18 mL) and cooled to 08C.
DBU (14 mL) was added, and the reaction was allowed to warm to room
temperature over 30 min. The solvent was removed in vacuo, and the res-
idue was purified by silica gel chromatography (hexanes/ethyl acetate
2:1) to give 23 as a/b mixture (461 mg, 77%) as a colorless oil. The ana-
lytical data were in agreement with those reported in the literature.[33]
as
a
colorless oil. [a]RDT =ꢀ13.2 (c=1, CHCl3); 1H NMR (300 MHz,
CDCl3): d = 7.38–7.25 (m, 25H), 5.17 (brs, 2H), 5.02 (s, 1H), 4.92–4.78
(m, 5H), 4.72–4.45 (m, 6H), 4.21 (s, 1H), 3.86–3.44 (m, 9H), 3.21–3.09
(brd, 2H), 1.51–1.27 ppm (m, 6H); 13C NMR (75 MHz, CDCl3); mixture
of rotamers: d
= 171.2, 156.8/156.3, 137.9, 137.6, 137.5, 137.4, 137.8/
137.6, 128.6–127.2, 101.9, 95.8, 77.8, 75.8, 74.9, 73.1, 72.4, 71.9, 71.7, 68.4,
67.3, 66.5, 65.8, 63.9, 61.6, 50.6/50.3, 47.1/46.2, 29.7, 29.1, 27.9/27.5,
23.4 ppm; IR (thin film on NaCl): n˜ =3513, 3005, 2923, 2102, 1687, 1497,
1451, 1364, 1128 cmꢀ1;MALDI-HRMS: m/z: calcd for C53H60O4N4Na:
983.4055, found: 983.4053 [M+Na]+.
5-Aminopentyl(2-acetamido-2-deoxy-6- O-sulfo-a-d-glucopyranosyl)-(1!
4)-2-O-sulfo-a-l-idopyranosyluronate (32): SO3·Et3N complex (44 mg,
0.24 mmol) was added to a solution of disaccharide 28 (23 mg, 24 mmol)
in anhydrous pyridine (2.7 mL). After stirring for 4 h at room tempera-
ture, the reaction was quenched with triethylamine (0.3 mL) and diluted
with MeOH (1 mL) and CH2Cl2 (1 mL). The solution was purified by Se-
phadex LH-20 chromatography (MeOH/CH2Cl2 1:1). The fractions that
contained the sulfated disaccharide were pooled and evaporated to dry-
ness to give 29 (24 mg, 82%) as a colorless oil. 1H NMR (300 MHz,
N-(Benzyl)-benzyloxycarbonyl-5-aminopentyl (methyl 2-O-pivaloyl-3-O-
benzyl-a-l-idopyranosyluronate (25): Trichloroacetimidate 23 (280 mg,
0.45 mmol)
and
N-(benzyl)-benzyloxycarbonyl-5-aminopentan-1-ol
(730 mg, 2.2 mmol) coevaporated five times with toluene and dried under
high vacuum. The starting materials were dissolved in CH2Cl2 and cooled
to ꢀ208C, then TMSOTf (16 mL, 0.09 mmol) was added and the reaction
was allowed to warm to ꢀ108C over 30 min. Quenching with triethyla-
mine at ꢀ258C and removal of the solvent followed by purification by
column chromatography (hexanes/ethyl acetate 9:1) yielded the product
24 (266 mg, 76% as 95:5 a/b mixture) as a colorless oil. N-Benzyloxycar-
bonyl-5-aminopentyl (methyl 2-O-pivaloyl-3-O-benzyl-4-O-levulinoyl-a-
l-idopyranosyluronate 24 (160 mg, 0.2 mmol) was dissolved in CH2Cl2
(1.5 mL). Pyridine (0.49 mL) and acetic acid (0.32 mL) were added, fol-
lowed by the addition of hydrazine monohydrate (20 mL, 0.41 mmol).
The reaction mixture was stirred for 90 min at room temperature,
quenched with acetone and evaporated to dryness. Glycoside 25 (135 mg,
96%) was isolated after purification by column chromatography (hex-
anes/ethyl acetate 4:1) as a colorless oil. The analytical data of the a
anomer were in agreement with those reported in the literature.[35b]
1H NMR (300 MHz, CDCl3): d = 7.33–7.15 (m, 15H), 5.16 (d, J=4.8 Hz,
2H), 4.96 (s, 1H), 4.89 (s, 1H), 4.82 (s, 1H), 4.78 (dd, J=11.7, 57.6 Hz,
1H), 4.59 (dd, J=11.7, 57.6 Hz, 1H), 4.45 (brs, 2H), 4.05–4.01 (m, 1H),
3.79–3.65 (m, 5H), 3.43–3.38 (m, 1H), 3.21–3.13 (m, 2H), 2.67 (d, J=
12.1 Hz, 1H), 1.63–1.19 ppm (m, 15H).
CD3OD): d
= 7.37–7.19 (m, 25H), 5.47–5.07 (m, 4H), 4.85–4.72 (m,
7H), 4.63–4.59 (d, J=11.8 Hz, 1H), 4.49–4.45 (m, 3H), 4.36–4.32 (dd, J=
2.8, 8.1 Hz, 1H), 4.25 (brs, 1H), 4.21–4.17 (m, 1H), 4.11 (brs, 1H), 3.97–
3.89 (m, 2H), 3.69–3.63 (m, 2H), 3.40–3.36 (m, 1H), 3.21–3.17 (m, 2H),
1.55–1.23 ppm (m, 6H); ESI-MS: m/z: calcd for C53H57O19N4S2: 1117.3,
found: 1119.3 [M+2H]2ꢀ
.
Compound 29 (23 mg, 21 mmol) was dissolved in THF (3.5 mL) and treat-
ed with a 0.1m aqueous solution of NaOH (0.4 mL). Then, 1m solution of
PMe3 in THF (42 mL) was added and the reaction was allowed to stir for
4 h. The reaction mixture was neutralized with 0.1m aq. HCl, concentrat-
ed and the residue was eluted from a Sephadex LH-20 chromatography
column with MeOH/CH2Cl2 1:1 to afford 30 (21 mg, 87%) as a colorless
oil. ESI-MS: m/z: calcd for C53H59O19N2S2: 1091.3, found: 1093.3
[M+2H]2ꢀ
.
To a solution of 30 (20 mg, 18 mmol) in MeOH (1 mL), triethylamine
(10 mL) and acetic anhydride (5 mL) were added. After stirring for 1 h at
room temperature, the reaction mixture was purified by Sephadex LH-20
chromatography (MeOH/CH2Cl2 1:1). The fractions containing the disac-
charide were pooled and evaporated to dryness. The residue was convert-
ed into the sodium salt by elution from a column of Dowex 50WX4-Na+
N-(Benzyl)-benzyloxycarbonyl-5-aminopentyl (6-O-acetyl-2-azido-3,4-di-
O-benzyl-2-deoxy-a-d-glucopyranosyl)-(1!4)-methyl(3- O-benzyl-2-O-
pivaloyl-a-l-idopyranosid)uronate (27): TMSOTf (1m solution in CH2Cl2,
40 mL) was added at ꢀ258C, to a solution of acceptor 25 (135 mg,
0.24 mmol) and imidate 26 (82 mg, 0.12 mmol) in CH2Cl2 (2.6 mL). After
1
with MeOH/H2O 9:1 to give 31 (21 mg, quant.) as a white solid. H NMR
4520
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 4510 – 4522

Heparin Oligosaccharides
FULL PAPER
(300 MHz, CD3OD): d = 7.34–7.16 (m, 25H), 5.18–5.11 (m, 3H), 4.84–
4.68 (m, 8H), 4.61–4.29 (m, 7H), 4.18–4.09 (m, 3H), 3.86–3.79 (m, 2H),
3.68–3.57 (m, 2H), 3.22–3.11 (m, 2H), 2.02 (s, 3H), 1.74–1.28 ppm (m,
6H); ESI-MS: m/z: calcd for C55H61O20N2S2: 1133.3, found: 1135.2
[11] P. Schell, H. A. Orgueira, S. Roehrig, P. H. Seeberger, Tetrahedron
Lett. 2001, 42, 3811–3814.
[12] a) W. Ke, D. M. Whitfield, M. Gill, S. Larocque, S.-H. Yu, Tetrahe-
dron Lett. 2003, 44, 7767–7770; b) O. Gavard, Y. Hersant, J. Alais,
V. Duverger, A. Dilhas, A. Bascou, D. BonnaffØ, Eur. J. Org. Chem.
2003, 3603–3620; c) A. Lubineau, O. Gavard, J. Alais, D. BonnaffØ,
Tetrahedron Lett. 2000, 41, 307–311; d) A. Dilhas, D. BonnaffØ, Car-
bohydr. Res. 2003, 338, 681–686; e) R. Ojeda, J. L. de Paz, M.
Martín-Lomas, J. M. Lassaletta, Synlett 1999, 1316–1318; f) S.-C.
Hung, S. R. Thopate, F.-C. Chi, S.-W. Chang, J.-C. Lee, C.-C. Wang,
Y.-S. Wen, J. Am. Chem. Soc. 2001, 123, 3153–3154.
[13] M. S. M. Timmer, A. Adibekian, P. H. Seeberger, Angew. Chem.
2005, 117, 7777–7780; Angew. Chem. Int. Ed. 2005, 44, 7605–7607.
[14] a) T. Mukaiyama, K. Banno, K. Narasaka, J. Am. Chem. Soc. 1974,
96, 7503–7509; b) T. Mukaiyama, Org. React. 1982, 28, 203–331.
[15] For use of pivaloate esters in heparin synthesis, see: a) R. Ojeda, J.-
L. de Paz, M. Martín-Lomas, Chem. Commun. 2003, 2486–2487;
b) J. L. de Paz, M. Martín-Lomas, Eur. J. Org. Chem. 2005, 1849–
1858.
[M+2H]2ꢀ
.
A solution of 31 (21 mg, 18 mmol) in MeOH/H2O (2 mL + 1 mL) was
stirred under H2-atmosphere in the presence of 10% Pd/C. After 24 h,
the suspension was filtered and concentrated to give 32 (11 mg, quant.)
1
as a white solid. H NMR (300 MHz, D2O): d = 5.11–5.09 (m, 2H), 4.55–
4.54 (m, 1H), 4.33–4.21 (m, 4H), 4.03–3.95 (m, 3H), 3.75–3.61 (m, 3H),
3.56–3.52 (m, 1H), 3.07–2.97 (m, 2H), 2.05 (s, 3H), 1.74–1.61 (m, 4H),
1.47–1.41 ppm (m, 2H); ESI-MS: m/z: calcd for C19H31O18N2S2: 639.1,
found: 641.5 [M+2H]2ꢀ
.
Acknowledgements
This research was supported by ETH Zürich, a KekulØ Fellowship from
the Fonds der Chemischen Industrie (to A.A.) and a Niels-Stensen Post-
doctoral Fellowship (to M.T.). We thank Professor Dieter Seebach for
helpful discussions and Dr. W. Bernd Schweizer for X-ray analysis.
[16] J. H. van Boom, P. M. J. Burgers, Tetrahedron Lett. 1976, 17, 4875–
4878.
[17] For 2,3-anti-selective aldol reactions, see: a) H. Danda, M. M.
Hansen, C. H. Heathcock, J. Org. Chem. 1990, 55, 173–181; b) C.
Gennari, A. Bernardi, L. Colombo, C. Scolastico, J. Am. Chem. Soc.
1985, 107, 5812–5813; c) I. Paterson, J. G. Cumming, J. D. Smith,
R. A. Ward, Tetrahedron Lett. 1994, 35, 441–444; d) C. J. Cowden, I.
Paterson, Org. React. 1997, 51, 1–200; e) D. A. Evans, M. G. Yang,
M. J. Dart, J. L. Duffy, A. S. Kim, J. Am. Chem. Soc. 1995, 117,
9598–9599; f) E. J. Corey, W. Li, G. A. Reichard, J. Am. Chem. Soc.
1998, 120, 2330–2336.
[1] a) T. Ogawa, Chem. Soc. Rev. 1994, 23, 397–407; b) S. J. Danishef-
sky, M. T. Bilodeau, Angew. Chem. 1996, 108, 1482–1522; Angew.
Chem. Int. Ed. Engl. 1996, 35, 1380–1419; c) T. Hudlicky, D. A. En-
twistle, K. K. Pitzer, A. J. Thorpe, Chem. Rev. 1996, 96, 1195–1220.
[2] For reviews on de novo synthesis of carbohydrates, see: a) R. R.
Schmidt, Pure Appl. Chem. 1987, 59, 415–424; b) A. Kirschning, M.
Jesberger, K.-U. Schçning, Synthesis 2001, 507–540.
[18] É. Bozó, S. Boros, J. Kuszmann, E. Gµcs-Baitz, L. Pµrkµnyi, Carbo-
hydr. Res. 1998, 308, 297–310.
[3] S. Y. Ko, A. W. M. Lee, S. Masamune, L. A. Reed, K. B. Sharpless,
F. J. Walker, Science 1983, 220, 949–951.
[19] Unlike monosaccharides containing the C5 substituent, the two OH
groups at C3 and C4 of xylopyranose are nearly equivalent in reac-
tivity. The necessary differentiation of the OH groups in the report-
ed syntheses[20] proved difficult and required tin ether chemistry.
[20] a) H. B. Mereyala, V. R. Kulkarni, Carbohydr. Res. 1989, 187, 154–
158; b) S. David, S. Hanessian, Tetrahedron 1985, 41, 643–663;
c) E. R. Palmacci, O. J. Plante, M. C. Hewitt, P. H. Seeberger, Helv.
Chim. Acta 2003, 86, 3975–3990.
[21] a) J. Tamura, Y. Miura, H. H. Freeze, J. Carbohydr. Chem. 1999, 18,
1–14; b) J. G. Allen, B. Fraser-Reid, J. Am. Chem. Soc. 1999, 121,
468–469.
[22] K. Prydz, K. T. Dalen, J. Cell Sci. 2000, 113, 193–205.
[23] K. Hattori, H. Yamamoto, J. Org. Chem. 1993, 58, 5301–5303.
[24] D. A. Evans, V. J. Cee, S. J. Siska, J. Am. Chem. Soc. 2006, 128,
9433–9441.
[25] Some Lewis acids such as TiCl4 and Bu2BOTf are known to form
the corresponding metal enolates by metal exchange with silyl eno-
lates: a) I. Kuwajima, E. Nakamura, Acc. Chem. Res. 1985, 18, 181–
187; b) M. Sodeoka, K. Ohrai, M. Shibasaki, J. Org. Chem. 1995, 60,
2648–2649.
[26] For magnesium halide mediated aldol reactions, see: a) K. Takai,
C. H. Heathcock, J. Org. Chem. 1985, 50, 3247–3251; b) J. Uenishi,
H. Tomozane, M. Yamato, Tetrahedron Lett. 1985, 26, 3467–3470;
c) A. Bernardi, S. Cardani, L. Colombo, G. Poli, G. Schimperna, C.
Scolastico, J. Org. Chem. 1987, 52, 888–891.
[27] C. H. Heathcock, S. K. Davidsen, K. T. Hug, L. A. Flippin, J. Org.
Chem. 1986, 51, 3027–3037.
[28] D. Seebach, J. Golinski, Helv. Chim. Acta 1981, 64, 1413–1423.
[29] a) J. R. Parikh, W. v. E. Doering, J. Am. Chem. Soc. 1967, 89, 5505–
5507; b) D. A. Evans, D. H. B. Ripin, D. P. Halstead, K. R. Campos,
J. Am. Chem. Soc. 1999, 121, 6816–6826.
[4] a) A. B. Northrup, D. W. C. MacMillan, Science 2004, 305, 1752–
1755; b) D. Enders, C. Grondal, Angew. Chem. 2005, 117, 1235–
1238; Angew. Chem. Int. Ed. 2005, 44, 1210–1212; c) J. Casas, M.
Engqvist, I. Ibrahem, B. Kaynak, A. Córdova, Angew. Chem. 2005,
117, 1367–1369; Angew. Chem. Int. Ed. 2005, 44, 1343–1345; d) D.
Enders, C. Grondal, M. Vrettou, G. Raabe, Angew. Chem. 2005,
117, 4147–4151; Angew. Chem. Int. Ed. 2005, 44, 4079–4083.
[5] a) B. Casu, U. Lindahl, Adv. Carbohydr. Chem. Biochem. 2001, 57,
159–206.
[6] a) H. E. Conrad, Heparin-Binding Proteins, Academic Press, San
Diego, CA, 1998; b) I. Capila, R. J. Linhardt, Angew. Chem. 2002,
114, 426–450; Angew. Chem. Int. Ed. 2002, 41, 390–412; c) R.
Raman, V. Sasisekharan, R. Sasisekharan, Chem. Biol. 2005, 12,
267–277; d) C. Noti, P. H. Seeberger, Chem. Biol. 2005, 12, 731–
756.
[7] For a comprehensive reviewon the synthesis of heparins, see:
B. K. S. Yeung, P. Y. C. Chong, P. A. Petillo, J. Carbohydr. Chem.
2002, 21, 799–865.
[8] For the synthesis of d-glucosamine building blocks and their applica-
tion to synthesis of heparin see: a) J.-L. de Paz, J. Angulo, J.-M. Las-
saletta, P. M. Nieto, M. Redondo-Horcajo, R. M. Lozano, G. GimØ-
nez-Gallego, M. Martín-Lomas, ChemBioChem 2001, 2, 673–685;
b) C. Tabeur, J.-M. Mallet, F. Bono, J.-M. Herbert, M. Petitou, P.
Sinaþ, Bioorg. Med. Chem. 1999, 7, 2003–2012; c) L. Poletti, M.
Fleischer, C. Vogel, M. Guerrini, G. Torri, L. Lay, Eur. J. Org.
Chem. 2001, 2727–2734; d) H. A. Orgueira, A. Bartolozzi, P. Schell,
R. E. J. N. Litjens, E. R. Palmacci, P. H. Seeberger, Chem. Eur. J.
2003, 9, 140–169; e) J.-C. Lee, X.-A. Lu, S. S. Kulkarni, Y.-S. Wen,
S.-C. Hung, J. Am. Chem. Soc. 2004, 126, 476–477; f) J. D. C. CodØe,
B. Stubba, M. Schiattarella, H. S. Overkleeft, C. A. A. van Boeckel,
J. H. van Boom, G. A. van der Marel, J. Am. Chem. Soc. 2005, 127,
3767–3773.
[30] M. T. Reetz, K. Kesseler, A. Jung, Angew. Chem. 1985, 97, 989–990;
Angew. Chem. Int. Ed. Engl. 1985, 24, 989–991.
[31] D. E. Ward, M. J. Hrapchak, M. Sales, Org. Lett. 2000, 2, 57–60.
[32] M. T. Reetz, Angew. Chem. 1984, 96, 542–555; Angew. Chem. Int.
Ed. Engl. 1984, 23, 556–569.
[9] C. Tabeur, F. Machetto, J.-M. Mallet, P. Duchaussoy, M. Petitou, P.
Sinaþ, Carbohydr. Res. 1996, 281, 253–276.
[10] L. Rochepeau-Jobron, J.-C. Jacquinet, Carbohydr. Res. 1997, 303,
395–406.
Chem. Eur. J. 2007, 13, 4510 – 4522
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4521

P. H. Seeberger et al.
[33] J.-F. Berrien, J. Royer, H.-P. Husson, J. Org. Chem. 1994, 59, 3769–
3774.
[34] G. J. S. Lohman, D. K. Hunt, J. A. Hçgermeier, P. H. Seeberger, J.
Org. Chem. 2003, 68, 7559–7561.
under mild acidic conditions as described in P. Westerduin, J. E. M.
Basten, M. A. Broekhoven, V. de Kimpe, W. H. A. Kuijpers,
C. A. A. van Boeckel, Angew. Chem. 1996, 108, 339–342; Angew.
Chem. Int. Ed. Engl. 1996, 35, 331–333.
[35] G. Stork, K. Zhao, Tetrahedron Lett. 1989, 30, 287–290.
[36] a) J. L. de Paz, C. Noti, P. H. Seeberger, J. Am. Chem. Soc. 2006,
128, 2766–2767; b) C. Noti, J. L. de Paz, L. Polito, P. H. Seeberger,
Chem. Eur. J. 2006, 12, 8664–8686.
[37] a) T. K.-K. Mong, H.-K. Lee, S. G. Durón, C.-H. Wong, Proc. Natl.
Acad. Sci. USA 2003, 100, 797–802; b) Y. Wang, X. Huang, L.-H.
Zhang, X.-S. Ye, Org. Lett. 2004, 6, 4415–4417.
[39] P. B. Alper, M. Hendrix, P. Sears, C.-H. Wong, J. Am. Chem. Soc.
1998, 120, 1965–1978.
[40] CCDC-633131 (4), -633132 (7), and -633133 (18a) contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[38] When partial N-sulfation of the carbamate moiety was detected
during O-sulfation, the N-sulfate group was selectively removed
Received: January 26, 2007
Published online: April 20, 2007
4522
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 4510 – 4522