Synthesis and NMR spectroscopic analysis of acylated pentasaccharide fragments of mycobacterial arabinogalactan

Article abstract of DOI:10.1039/c0ob00423e

The mycolyl-arabinogalactan (mAG) complex, a large glycolipid composed of arabinofuranose and galactofuranose monosaccharides and mycolic acid lipids, provides mycobacteria with substantial protection from their environment. It has been proposed that the

Full text of DOI:10.1039/c0ob00423e

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PAPER
Synthesis and NMR spectroscopic analysis of acylated pentasaccharide
fragments of mycobacterial arabinogalactan†
Chunjuan Liu, Michele R. Richards and Todd L. Lowary*
Received 14th July 2010, Accepted 8th September 2010
DOI: 10.1039/c0ob00423e
The mycolyl–arabinogalactan (mAG) complex, a large glycolipid composed of arabinofuranose and
galactofuranose monosaccharides and mycolic acid lipids, provides mycobacteria with substantial
protection from their environment. It has been proposed that the presence of flexible furanose rings in
the mAG facilitates the packing of the hydrophobic mycolic acids, forming a dense protective barrier of
low permeability. In a previous article, we probed this “flexible scaffold hypothesis” through the
synthesis and NMR analysis of di- and trisaccharide fragments of the mAG acylated with linear fatty
acids. However, we saw few conformational changes due to the presence of the acyl chains. We proposed
that branched pentasaccharide glycolipids 5–8 might exhibit larger changes due to the presence of more
acyl chains, and studies with these compounds are described here. The carbohydrate portion of 5–8 was
synthesized in a 1 + 2 + 2 manner. First, the monosaccharide diol was treated with an excess of
appropriately protected thioglycoside donor to give a trisaccharide, which, following selective
deprotection to a diol, was converted to the pentasaccharide in a one-pot glycosylation. The resulting
differentially protected pentasaccharide 20 gave glycolipids 5–8 upon removal of the protecting groups
at the primary positions, acylation, and hydrogenolysis. The conformations of 5–8 were probed using
NMR spectroscopy, and chemical shift selective filtering 1D-TOCSY spectra allowed for the
determination of all the ring coupling constants. It was found that the addition of four fatty acids to the
parent pentasaccharide had little effect on the conformation of the compounds in solution.
containing glycolipids (e.g., 1 and 2, Fig. 1), which were designed
Introduction
as model compounds for portions of the nonreducing end of the
mAG complex (3, Fig. 2).3,4 Motivated by the unusual structure of
Mycobacterial diseases, including tuberculosis and leprosy, remain
important health concerns given their widespread occurrence
this glycan, which is composed nearly entirely of furanose rings,
worldwide1 and the emergence of strains resistant to front-line
this study was undertaken to probe the effect of acylation on the
antibiotics used to treat these infections.2 Mycobacteria possess
conformation of the arabinofuranose rings in these glycolipids. It
an unusual, densely packed, and impermeable cell wall structure
has been proposed that the inherent flexibility of the furanoside
that both prevents the passage of antibiotics into the organism
rings in the structure facilitates tight packing of the mycolic acids
and allows it to evade the immune system of the infected
of mAG leading to the impermeable barrier that protects the
host.3 The largest structural component of the cell wall is the
mycolyl–arabinogalactan (mAG) complex, which is composed of
a polysaccharide esterified at the non-reducing terminus with long
chain lipids termed mycolic acids (vide infra).4 The dense packing
of the mycolic acids at the outer region of the cell wall complex
leads to the impermeability of the structure.
organism from its environment.6,7 Testing of this “flexible scaffold
hypothesis” is important as it may lead to an understanding of the
In a previous paper,5 we reported the synthesis and con-
formational analysis of di- and trisaccharide arabinofuranose-
Alberta Ingenuity Centre for Carbohydrate Science and Department of
Chemistry, The University of Alberta, Gunning-Lemieux Chemistry Centre,
Edmonton, Alberta, Canada. E-mail: tlowary@ualberta.ca; Fax: 780-492-
7705; Tel: 780-492-1861
† Electronic supplementary information (ESI) available: General ex-
perimental methods, 1D-ge-CSSF-TOCSY and 1D-ge-CSSF-DPFGSE-
NOESY spectra used in the conformational analysis; details on the
1
equations used to determine the rotamer populations in Table 2, and H
and 13C NMR spectra of new compounds. See DOI: 10.1039/c0ob00423e
Fig. 1 Model di- and trisaccharide glycolipids 1 and 2.
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Fig. 2 (left) Hexasaccharide motif (3) found at the non-reducing end of the mycolyl–arabinogalactan (mAG) complex. (right) Examples of mycolic acids
found in Mycobacterium tuberculosis.
factors that stabilize the mycobacterial cell wall macrostructure.
Such knowledge may lead to improved therapies for the treatment
of mycobacterial diseases through identification of key residues
in the structures whose biosynthesis could be targeted via novel
inhibitors. We postulated that if this hypothesis is correct, then the
conformations of oligosaccharide fragments of the mAG lacking
acylation should differ from those in which this modification is
present.
The results of the investigations with these di- and trisaccharides
indicated that acylation with linear, long-chain fatty acids did
not substantially influence the conformation of the five-membered
rings in these structures nor rotation about the C4–C5 bond, which
is immediately adjacent to the site of acylation. In addition, on
1
the basis of H and 13C NMR chemical shift data, acylation did
not lead to significant differences in the conformation about the
glycosidic linkages in 1 and 2.5 These results led us to postulate
that a more pronounced effect may be observed in glycolipids
with structures more similar to the non-reducing terminus of the
Fig. 3 Compounds 4–8 are the target pentasaccharides with the rings
labeled to facilitate comparison with 3.
mAG; i.e., those that possess a larger number of monosaccharide
residues and acyl chains, or those that are functionalized with
branched acyl groups that more closely resemble the mycolic
acids. In this paper, we extend our investigations to a series
of pentasaccharide glycolipids (Fig. 3) that are models of the
terminal branched structure of mAG (3). These investigations,
when coupled to those with more complicated analogues (e.g.,
those with lipids incorporating b-hydroxy groups and branching)
will allow us to address, in a systematic fashion, the effect of
various lipid structural motifs on carbohydrate conformation
in these glycolipids. We describe here the synthesis of target
acylated pentasaccharides 5–8 and conformational analysis of
these compounds.
the installation of the acyl chains. For this purpose, we chose
as the key intermediate pentasaccharide 9 (Scheme 1), which
could be acylated and then debenzylated leading to the target
glycolipids. Shown in Scheme 1 is the retrosynthetic analysis of 9.
We envisioned a convergent strategy in which the key steps would
be two glycosylation reactions of mono- or trisaccharide diols with
an excess of a suitably protected donors. Thus, treatment of 139
with an excess of 12 and subsequent debenzoylation would give
trisaccharide diol 11, which could be converted by coupling with
an excess of 1010,11 and removal of the p-methoxybenzyl ethers. As
described earlier for the preparation of acylated disaccharides such
as 1,5 the key issue in the preparation of 9 was the stereoselective
introduction of the two b-arabinofuranoside motifs. The use of 10
follows our earlier work in which the O-5 protecting group was
shown to influence the b-selectivity in the glycosylations leading
to disaccharide 1.5
Results and discussion
Preparation of pentasaccharides 4 and 9
The unacylated parent pentasaccharide (4) was synthesized
as described previously.8 The route used for the synthesis of
5–8 required a different protecting group strategy to allow for
The preparation of trichloroacetimidate 12 is shown in
Scheme 2. First, the known crystalline 1,2,5-orthoester 1512 was
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Scheme 1 Retrosynthesis of protected pentasaccharide 9.
Scheme 2 Synthesis of trichloroacetimidate 12.
prepared in four steps13,14 from the easily accessed methyl glycoside
14.15 Subsequent benzylation and ring-opening by treatment with
allyl alcohol afforded intermediate 16 in 72% over six steps from
14. Installation of the PMB ether at the O-5 position of 16 was
achieved by reaction with the p-methoxybenzyl trichloroacetimi-
date and lanthanum triflate16 to give fully protected 17. These mild
conditions allowed the protection of the alcohol in the presence of
the base-sensitive benzoate ester. Deprotection of the crude allyl
ether with palladium chloride and methanol gave the reducing
sugar 18 in a 1.8 : 1 a : b ratio in 84% yield over two steps, which was
converted to trichloroacetimidate 12 in situ. One of the attractive
features of this route is that many of the intermediates do not need
extensive purification; only two of the compounds – 16 and 18 –
were purified by chromatography. Next, the target pentasaccharide
9 could be assembled by coupling the building blocks together as
illustrated in Scheme 3. After generating trichloroacetimidate 12 in
situ, the donor was immediately reacted with diol 139 and TMSOTf
at 0 ◦C, which gave an 84% yield of trisaccharide 19. Conversion of
19 into the diol 11 was achieved under the usual sodium methoxide
conditions, which provided the product in 82% yield. With 11
in hand, it was coupled with excess donor 1010,11 to form the
pentasaccharide in 86% yield. As expected, the product was a
mixture of stereoisomers, in which the ratio of desired isomer to the
others was 5.9 : 1. Although the desired product was the major one,
separation by chromatography was difficult. We also tried other
donors; however, none improved stereoselectivity or purification.
In particular, the use of thioglycosides with a benzoate ester,
TMDMS ether, or allyl ether at O-5 gave poorer b-selectivity
than the 5-O-PMB ether donor 10.5 Analogous protecting group
effects have been observed in other studies on stereoselective
arabinofuranosylation.11,17
We postulated that the manipulation of the protecting groups
at the four primary positions from PMB ethers to TBDMS would
be helpful for the separation. Hence, installation of the TBDMS
ethers proceeded in 59% yield over three steps including the
glycosylation, treatment with TFA to remove the PMB ethers, and
then protection as silyl ethers. At this stage, the desired isomer 20
could be readily separated from the other isomers. The removal of
TBDMS ethers was done by treatment of TBAF in THF, which
provided 9 in 88% yield.
1
A combination of H and 13C NMR spectroscopy was used
1
to establish the structure of 9. The H NMR spectrum indicated
the presence of two b-arabinofuranosyl anomeric hydrogens at
5.04 ppm (doublet, J = 4.6 Hz) and 4.97 ppm (doublet, J = 4.6 Hz)
that were correlated (HMQC) to the resonances in 13C NMR
spectrum at 100.4 and 100.1 ppm, respectively. In addition, three
signals of the a-linked residues appeared at 5.10 ppm (doublet,
J = 1.4 Hz), 5.07 ppm (apparent singlet), and 4.91 ppm (doublet,
J = 1.5 Hz), which could be correlated to three resonances in the
13C NMR spectrum at 106.0, 105.9, 106.8 ppm, respectively.
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Scheme 3 Synthesis of protected pentasaccharide 9.
Scheme 4 Synthesis of target glycolipids 5–8.
Synthesis of target glycolipids 5–8
acid in the presence of N,N¢-dicyclohexylcarbodiimide (DCC).
Acylated compounds 21–24 were deprotected using palladium
hydroxide on carbon under a hydrogen atmosphere to give the
target compounds 5–8 in 25%–75% yield over two steps, as
shown in Scheme 4. In these hydrogenation reactions a 1 : 1
mixture of dichloromethane and methanol was used as the solvent
system, and the concentration was kept low (below 0.01 M)
to minimize partially deprotected intermediates from forming
micelles. We envisioned that the formation of such structures
would hinder complete cleavage of the benzyl ethers. In the case
of the preparation of 8, the yield of the hydrogenolysis was
As was reported for the di- and trisaccharide analogs,5 we chose
fatty acids or fatty acyl chlorides that were commercially available
for our initial acylation reactions. Butyryl chloride, decanoyl
chloride, palmitoyl chloride, and behenic acid (due to the lack
of commercial availability of behenoyl chloride) were used in the
esterification reaction. Each member of this homologous series
differs from the next by six carbon atoms.
The coupling reactions were carried out by treatment of tetraol
9 with an acid chloride and pyridine, or by reaction with behenic
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4
Table 1 2JH,H,3JH,H, and JH,H (Hz) for pentasaccharide 4 and pentasac-
nevertheless low, which may be due to the adsorption of the
amphiphilic compound onto the carbon-supported catalyst.
charide glycolipids 5–8a
Ring
B
Coupling
4b
5b
5c
6c
7c
8c
NMR analysis for the measurement of coupling constants.
3JH-1,H-2
4JH-1,H-3
3JH-2,H-3
3JH-3,H-4
3JH-4,H-5R
3JH-4,H5S
2JH-5R,H5S
3JH-1,H-2
4JH-1,H-3
3JH-2,H-3
3JH-3,H-4
3JH-4,H5R
3JH-4,H-5S
2JH-5R,H5S
3JH-1,H-2
4JH-1,H-3
3JH-2,H-3
3JH-3,H-4
3JH-4,H5R
3JH-4,H-5S
2JH-5R,H5S
3JH-1,H-2
4JH-1,H-3
3JH-2,H-3
3JH-3,H-4
3JH-4,H5R
3JH-4,H-5S
2JH-5R,H5S
3JH-1,H-2
4JH-1,H-3
3JH-2,H-3
3JH-3,H-4
3JH-4,H5R
3JH-4,H-5S
2JH-5R,H5S
1.5
0.6
3.0
6.2
5.0
3.1
1.5
0.6
3.1
6.2
4.8
3.0
1.5
0.5
2.9
6.0
4.7
2.8
1.6
0.7
2.8
6.0
4.6
2.9
1.5
0.6
2.9
6.0
4.4
2.9
1.5
0.6
3.0
6.2
4.4
2.8
Because the acylated compounds 5–8 were not soluble in water
or water–methanol mixtures, NMR spectra of 4–8 were acquired
using a solution of target compound in CD3OD or 1 : 1 CDCl3–
CD3OD, the choice being dictated by solubility of the compound.
Theassignment process was similar to thatdescribed for the related
di- and trisaccharide derivatives,5 using the “structural reporter
group” concept.18 The a- and b-arabinofuranosides have distinct
and well-resolved signals in the anomeric region of the 1H NMR
spectrum, and the stereochemistry of glycosidic linkages can easily
-11.3
-11.3
-11.3 -11.4 -11.4 -11.5
C
D
E
F
2.2
0.0
4.9
7.8
2.7
5.0
1.9
0.5
4.4
7.3
3.3
6.0
2.2
0.0
4.4
6.8
3.1
6.1
2.0
0.0
4.4
6.8
3.1
6.2
2.0
0.0
4.4
6.8
3.2
6.2
2.0
0.0
4.2
6.6
3.2
6.3
3
be determined from the JH-1,H-2 magnitude. For the a-isomer,
-12.2
-11.8
-11.6 -11.5 -11.5 -11.4
3JH-1,H-2 = 0–2 Hz; whereas for b-isomer, 3JH-1,H-2 = 3–5 Hz.19
To overcome the spectral overlap of the ring protons in the pen-
tasaccharides, the variable time version of the gradient-enhanced
chemical shift selective filtering (ge-CSSF) technique8,20,21 was
used; 1D-ge-CSSF-TOCSY and 1D-ge-CSSF-DPFGSE-NOESY
spectra were used to provide coupling constants and ring assign-
ments, respectively. In addition, to confirm the magnitudes of all
coupling constants, all of the 1D 1H NMR spectra were simulated
2.4
0.0
5.2
7.9
2.8
5.1
2.1
0.0
4.5
7.8
3.0
5.7
2.4
0.0
5.0
7.8
3.1
6.1
2.5
0.0
5.1
7.9
3.2
5.9
2.4
0.0
5.0
7.9
3.2
5.9
2.4
0.0
5.0
7.8
3.3
5.9
-12.3
-12.0
-11.9 -12.0 -12.0 -12.0
4.4
0.0
7.9
6.5
3.2
6.4
4.2
0.0
8.2
7.2
4.0
7.2
4.5
0.0
7.6
6.9
3.1
7.2
4.5
0.0
8.1
7.2
3.4
7.2
4.9
0.0
8.2
7.2
3.4
7.2
4.5
0.0
7.7
6.9
3.1
7.2
2
3
using the program WinDNMR22 to extract accurate JH,H, JH,H
,
4
or JH,H values. An example of the 1D-ge-CSSF-TOCSY is
shown for 5 in Fig. 4, while the remainder can be found in the
Supporting Information, together with representative examples of
the 1D-ge-CSSF-DPFGSE-NOESY spectra. Additional details
for obtaining the CSSF spectra and analyzing the data be found
in the Supporting Information. The coupling constants for the
target glycolipids are shown in Table 1, and their 1H and 13C NMR
chemical shifts can also be found in the Supporting Information.
Assignment of H-5R and H-5S was based on comparison with
previous literature,23,24 and 2JH-5R,H-5S was assumed to be negative.25
No broadening of signals was observed at the concentrations used
for the NMR measurements, suggesting that the compounds are
not aggregating.
-11.9
-1.7
-11.7 -11.8 -11.7 -11.8
4.4
0.0
8.0
6.6
3.2
6.4
4.2
0.0
8.3
7.3
3.8
7.4
4.5
0.0
7.7
6.9
3.2
7.4
4.6
0.0
8.2
6.8
3.3
7.3
4.7
0.0
8.3
6.8
3.3
7.3
4.6
0.0
7.9
6.9
3.2
7.4
-12.0
-11.7
-1.7 -11.7 -11.7 -11.9
a Couplings derived from 1D-ge-CSSF-TOCSY20,21 spectra and simula-
tions in WinDNMR.22 b CD3OD as solvent. c 1 : 1 CD3OD–CDCl3 as
solvent.
Table 2 Calculated C-4–C-5 rotamer distributions for pentasaccharides,
4–8
As can be seen from the data presented in Table 1, the values for
3JH-1,H-2, 4JH-1,H-3, 3JH-2,H-3, and 3JH-3,H-4 did not change significantly
upon acylation of O-5, indicating that addition of a lipid chain
had little effect on the ring conformation, a finding that was
also observed with the smaller di- and trisaccharide fragments.
In addition, all of the coupling constants for 5 were minimally
affected by changing the solvent from CD3OD to 1 : 1 CD3OD–
CDCl3, clearly demonstrating that the solvent did not affect
ring conformation. The NOE signals for 4 and 5 are also not
significantly different from each other or from the hexasaccharide
3 taken in D2O,8 indicating the conformation about the glycosidic
linkages is not affected by solvent or by the presence of O-5
Ring
C
Rotamer
4a
5a
5b
6b
7b
8b
gg
gt
tg
gg
gt
tg
gg
gt
tg
gg
gt
tg
53%
47%
0%
51%
48%
1%
32%
61%
7%
32%
61%
7%
53%
43%
4%
54%
44%
2%
54%
44%
2%
33%
57%
10%
27%
60%
13%
52%
45%
3%
57%
41%
2%
28%
57%
15%
28%
59%
14%
51%
45%
4%
57%
41%
2%
28%
57%
15%
28%
59%
14%
49%
46%
5%
55%
41%
4%
33%
57%
10%
27%
60%
13%
D
E
F
64%
39%
-3%
18%
57%
25%
17%
60%
23%
3
acyl groups. For rings C, D, E, and F, values for JH-4,H-5R and
3JH-4,H-5S appeared to change more significantly upon acylation,
thus we analyzed the rotamer populations about the C-4–C-5
bond (Fig. 5), as reported previously for the acylated di- and
tri-saccharides. Table 2 shows the rotamer populations for rings
C, D, E, and F in 4–8, and full details of this analysis can be found
in the Supporting Information.
For the a-linked residues of the unacylated pentasaccharide
4, rings C and D, both rotamers with O-4 and O-5 gauche to
one another are about equally populated to the exclusion of the
a CD3OD as solvent. b 1 : 1 CD3OD–CDCl3 as solvent.
rotamer with these atoms trans to each other: 53% gg: 47% gt: 0%
tg for ring C and 51% gg: 48% gt: 1% tg for ring D. These results
are consistent with the gauche effect,26 which would be expected to
favor the gt and gg rotamers about this bond. Acylation has little
effect on the conformation of the C-4–C-5 bond for rings C and
D of 5–8. For these compounds, the average populations for ring
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Fig. 4 Chemical shift selective filtering TOCSY spectra for 5. The spectra were recorded at 300 K on a 600 MHz spectrometer with 1 : 1 CD3OD–CDCl3
as a solvent. Spectrum a is an expansion of the 1D 1H spectrum; b through f show 1D-ge-CSSF-TOCSY20,21 spectra of each ring with an arrow indicating
the irradiation frequency. The mixing time (mix) and frequency difference (D) between the irradiated peak and its nearest neighbor that were used to each
spectrum are also indicated: b) ring D, selectively irradiated at 5.12 ppm, mix = 0.2 s, D = 3.1 Hz; c) ring C, selectively irradiated at 5.08 ppm, mix = 0.2 s,
D = 11.6 Hz; d) ring E, selectively irradiated at 5.03 ppm, mix = 0.16 s, D = 3.3 Hz; e) ring F, selectively irradiated at 5.01 ppm, mix = 0.16 s, D = 3.3 Hz; f)
ring B, selectively irradiated at 3.69 ppm, mix = 0.12 s, D = 1.4 Hz.
Conclusions
In conclusion, we have synthesized the differentially protected,
branched pentasaccharide 20 from the non-reducing end of my-
cobacterial mAG complex, which allowed for selective function-
alization at the O-5 positions. Highlights of the synthesis included
the preparation of a trichloroacetimidate arabinofuranose donor
Fig. 5 Rotamers about the C-4–C-5 bond for pentasaccharides 5–8.
12 that required minimal purification. The use of this donor
allowed the a-linkages to be synthesized in a one-pot protocol
C are 52 2% gg: 44 1% gt: 4 1% tg, and for ring D are 57
3% gg: 41 2% gt: 1 2% tg.
in 84% yield and excellent selectivity. Both b-(1→2)-linkages were
also synthesized in one pot in high yield and good selectivity
through the use of a thioglycoside donor (10) with a PMB group
on O-5.
For the b-linked rings of 4, residues E and F, the C-4–C-5
rotamer populations are identical, and the gt rotamer is more
populated than the gg rotamer: 32% gg: 61% gt: 7% tg. Unlike
the a-linked rings, acylation at O-5 seems to have an effect on the
conformation; the gg and gt populations both decrease, while the
tg population doubles. For compounds 5–8, the average rotamer
distributions for ring E is 28 6% gg: 57 0% gt: 15 6% tg, and
the averages for ring F are 25 4% gg: 60 1% gt: 15 4% tg.
The increase in the tg conformation is somewhat surprising, but
upon closer inspection, it appears that this rotamer may allow for
a hydrogen bond to form from the hydroxyl at C-3 to the carbonyl
oxygen, which had also been observed in the di- and trisaccharide.5
The proton–proton coupling constants of the target glycolipids
were determined through the use of chemical shift selective filtering
1D-TOCSY spectra and the aid of simulations. Acylation at
O-5 did not alter the ring conformation but did change the
rotamer distribution for the b-linked rings E and F, possibly
to accommodate an intramolecular hydrogen bond between the
carbonyl group of acyl group and the hydroxyl group at C-3. When
these results are compared to those reported for the analogous
di- and tri-saccharide structures, it appears that the presence of a
linear acyl chain does not substantially influence the conformation
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of the molecule. We conclude that lipids with branched acyl chains
may have more of an effect on ring conformation than the linear
lipid chains we have chosen to study to date.
1 : 1, dH) 5.12 (d, 1H, J1D,2D = 2.5 Hz, H-1D), 5.08 (d, 1 H, J1C,2C =
2.0 Hz, H-1C), 5.03 (d, 1 H, J1F,2F = 4.4 Hz, H-1F), 5.00 (d, 1 H,
J1E,2E = 4.6 Hz, H-1E), 4.76 (d, 1 H, J1B,2B = 1.2 Hz, H-1B), 4.32–4.02
(m, 14 H, H-5Ea, H-5Fa, H-5Fb, H-5Eb, H-2B, H-2C, H-2D, H-
5Da, H-5Ca, H-5Db, H-5Cb, H-3F, H-3E, H-4B), 4.00–3.88 (m,
10 H, H-2F, H-2E, H-3D, H-3C, H-3B, H-4D, H-4C, H-4E, H-4F,
H-5Ba), 3.69 (dd, 1 H, J4B,5Bb = 2.8 Hz, J5Ba,5Bb = 11.4 Hz, H-5Bb),
3.34 (s, 3 H, OCH3), 2.36–2.28 (m, 8 H, CH2 ¥ 4), 1.62–1.54 (m, 8
H, acyl CH2 ¥ 4), 1.34–1.16 (m, 48 H, acyl CH2 ¥ 24), 0.90–0.80
(m, 12 H, acyl CH3 ¥ 4); 13C NMR (125 MHz, CDCl3, dC) 175.6(5)
(C O), 175.6(4) (C O), 175.5(0) (C O ¥ 2), 110.5 (C-1B), 107.5
(C-1C), 107.2 (C-1D), 103.3 (C-1E), 103.2 (C-1F), 90.2 (C-2C),
89.8 (C-2D), 84.9 (C-3B), 82.9 (C-2B), 81.9 (C-4B), 81.7 (C-3E),
81.5 (C-3F), 81.4(4) (C-4D), 81.1 (C-4C), 78.5(3) (C-4E), 78.4(7)
(C-4F), 77.3 (C-2E), 77.1 (C-2F), 76.7(8) (C-3D), 76.7(6) (C-3C),
67.8 (C-5B), 67.2 (C-5E), 67.0 (C-5F), 64.9 (C-5D), 64.7 (C-5C),
56.0 (OCH3), 35.3(1) (acyl CH2), 35.2(9) (acyl CH2), 35.2(7) (acyl
CH2), 33.1(5) (acyl CH2), 33.1(4) (acyl CH2), 30.7(4) (acyl CH2),
30.7(3) (acyl CH2), 30.7(0) (acyl CH2), 30.6(2) (acyl CH2), 30.5(9)
(acyl CH2), 30.5(6) (acyl CH2), 30.5(5) (acyl CH2), 30.5(4) (acyl
CH2), 30.4(4) (acyl CH2), 30.4(1) (acyl CH2), 30.4(0) (acyl CH2),
26.1(5) (acyl CH2), 26.1(2) (acyl CH2), 23.9 (acyl CH2), 15.0 (acyl
CH3). ESIMS: m/z calcd for [C66H116O25Na]+: 1331.7698. Found:
1331.7692.
Experimental
General procedure for hydrogenolysis leading to 5–8
To a solution of starting material (0.01 mmol) in CH2Cl2 (1 mL)
and CH3OH (1 mL), 20% Pd(OH)2–C (0.15–0.20 fold by weight)
was added at room temperature. The reaction was stirred under a
positive pressure of hydrogen for 12 h. The resulting mixture was
filtered through Celite and concentrated. The crude residue was
purified on Iatrobeads with CH2Cl2–CH3OH as the eluent.
General procedure for acylation using carboxylic acid chlorides
leading to 21–23
To a solution of the alcohol (0.06 mmol) in CH2Cl2 (2 mL) and
pyridine (0.05 mL), the carboxylic acid chloride (0.15 mmol)
was added at 0 ◦C. The reaction was kept stirring for 2 h and
quenched by the addition of CH3OH. The resulting solution was
concentrated and the residue was purified by chromatography (4 : 1
hexanes–EtOAc) to obtain the acylated compound.
Methyl 5-O-butyryl-b-D-arabinofuranosyl-(1→2)-5-O-butyryl-a-
D-arabinofuranosyl-(1→3)-[5-O-butyryl-b-D-arabinofuranosyl-
(1→2)-5-O-butyryl-a-D-arabinofuranosyl-(1→5)]-a-D-
arabinofuranoside (5)
Methyl 5-O-palmitoyl-b-D-arabinofuranosyl-(1→2)-5-O-
palmitoyl-a-D-arabinofuranosyl-(1→3)-[5-O-palmitoyl-b-D-
arabinofuranosyl-(1→2)-5-O-palmitoyl-a-D-arabinofuranosyl-
(1→5)]-a-D-arabinofuranoside (7)
Isolated 82% as a colorless oil: Rf 0.13 (10 : 1 CH2Cl2–CH3OH);
[a]D +33.1 (c 0.9, CHCl3);1H NMR (500 MHz, CDCl3–CD3OD,
1 : 1, dH) 5.12 (d, 1H, J1D,2D = 2.4 Hz, H-1D), 5.07 (d, 1 H, J1C,2C
=
Isolated 87% as a colorless oil: Rf 0.27 (1 : 2 hexane–EtOAc); [a]D
+25.6 (c 0.5, CHCl3);1H NMR (500 MHz, CDCl3–CD3OD, 1 : 1,
dH) 5.12 (d, 1H, J1D,2D = 2.4 Hz, H-1D), 5.08 (d, 1 H, J1C,2C = 1.9 Hz,
1.9 Hz, H-1C), 5.03 (d, 1 H, J1F,2F = 4.4 Hz, H-1F), 5.00 (d, 1 H,
J1E,2E = 4.4 Hz, H-1E), 4.76 (d, 1 H, J1B,2B = 1.2 Hz, H-1B), 4.33–
4.26 (m, 2 H, H-5Ea, H-5Fa), 4.26–4.02 (m, 12 H, H-5Fb, H-5Eb,
H-2B, H-2C, H-2D, H-5Da, H-5Ca, H-5Db, H-5Cb, H-3F, H-3E,
H-4B), 4.02–3.88 (m, 10 H, H-2F, H-2E, H-3D, H-3C, H-3B, H-
4D, H-4C, H-4E, H-4F, H-5Ba), 3.70 (dd, 1 H, J4B,5Bb = 3.0 Hz,
J5Ba,5Bb = 11.4 Hz, H-5Bb), 3.27 (s, 3 H, OCH3), 2.34–2.30 (m, 8 H,
acyl CH2 ¥ 4), 1.67–1.58 (m, 8 H, acyl CH2 ¥ 4), 0.96–0.90 (m, 12
H, acyl CH3 ¥ 4); 13C NMR (125 MHz, CDCl3, dC) 175.2 (C O ¥
2), 175.1(1) (C O), 175.0(0) (C O), 110.5 (C-1B), 107.6 (C-
1C), 107.2 (C-1D), 102.9 (C-1E), 102.8 (C-1F), 89.7 (C-2C), 89.4
(C-2D), 84.6 (C-3B), 82.6 (C-2B), 82.0 (C-4B), 81.6 (C-3E), 81.5
(C-3F), 81.4(4) (C-4D), 81.3(8) (C-4C), 78.6 (C-4E, C-4F), 77.4
(C-2E), 77.2 (C-2F), 76.8(1) (C-3D), 76.7(6) (C-3C), 67.9 (C-5B),
66.9 (C-5E, C-5F), 64.7 (C-5D), 64.6 (C-5C), 55.3 (OCH3), 36.8(4)
(acyl CH2), 36.8(3) (acyl CH2), 19.4(5) (acyl CH2), 19.4(1) (acyl
CH2), 14.0(3) (acyl CH3), 13.9(8) (acyl CH3). ESIMS: m/z calcd
for [C42H68O25Na]+: 995.3942. Found: 995.3957.
H-1C), 5.02 (d, 1 H, J1F,2F = 4.4 Hz, H-1F), 5.00 (d, 1 H, J1E,2E
=
4.5 Hz, H-1E), 4.76 (d, 1 H, J1B,2B = 1.2 Hz, H-1B), 4.32–4.02 (m, 14
H, H-5Ea, H-5Fa, H-5Fb, H-5Eb, H-2B, H-2C, H-2D, H-5Da, H-
5Ca, H-5Db, H-5Cb, H-3F, H-3E, H-4B), 4.02–3.88 (m, 10 H, H-
2F, H-2E, H-3D, H-3C, H-3B, H-4D, H-4C, H-4E, H-4F, H-5Ba),
3.70 (dd, 1 H, J4B,5Bb = 2.8 Hz, J5Ba,5Bb = 11.4 Hz, H-5Bb), 3.34 (s, 3 H,
OCH3), 2.38–2.26 (m, 8 H, acyl CH2 ¥ 4), 1.66–1.52 (m, 8 H, acyl
CH2 ¥ 4), 1.40–1.06 (m, 96 H, acyl CH2 ¥ 48), 0.90–0.80 (m, 12 H,
acyl CH3 ¥ 4); 13C NMR (125 MHz, CDCl3, dC) 175.6(5) (C O),
175.6(3) (C O), 175.5(3) (C O), 175.4(9) (C O), 110.5 (C-1B),
107.5 (C-1C), 107.2 (C-1D), 103.4 (C-1E), 103.3 (C-1F), 90.3 (C-
2C), 89.9 (C-2D), 84.8 (C-3B), 82.9 (C-2B), 81.9 (C-4B), 81.7
(C-3E), 81.5 (C-3F), 81.4(4) (C-4D), 81.1 (C-4C), 78.5(3) (C-4E),
78.4(7) (C-4F), 77.3 (C-2E), 77.1 (C-2F), 76.7(5) (C-3D), 76.7(3)
(C-3C), 67.7 (C-5B), 67.1 (C-5E), 67.0 (C-5F), 65.0 (C-5D), 64.7
(C-5C), 56.0 (OCH3), 35.3(1) (acyl CH2), 35.2(9) (acyl CH2), 33.2
(acyl CH2), 30.9(6) (acyl CH2), 30.9(3) (acyl CH2), 30.9(2) (acyl
CH2), 30.8(3) (acyl CH2), 30.8(1) (acyl CH2), 30.7(8) (acyl CH2),
30.7(7) (acyl CH2), 30.6(6) (acyl CH2), 30.6(3) (acyl CH2), 30.6(0)
(acyl CH2), 30.5(9) (acyl CH2), 30.5(1) (acyl CH2), 30.4(8) (acyl
CH2), 30.4(5) (acyl CH2), 30.4(3) (acyl CH2), 26.2 (acyl CH2), 26.1
(acyl CH2), 23.9 (acyl CH2), 15.1 (acyl CH3). ESIMS: m/z calcd
for ESIMS: m/z calcd for [C90H164O25Na]+: 1648.1459. Found:
1648.1454.
Methyl 5-O-decanoyl-b-D-arabinofuranosyl-(1→2)-5-O-decanoyl-
a-D-arabinofuranosyl-(1→3)-[5-O-decanoyl-b-D-arabinofuranosyl-
(1→2)-5-O-decanoyl-a-D-arabinofuranosyl-(1→5)]-a-D-
arabinofuranoside (6)
Isolated 68% as a colorless oil: Rf 0.22 (10 : 1 CH2Cl2–CH3OH);
[a]D +34.7 (c 0.2, CHCl3);1H NMR (500 MHz, CDCl3–CD3OD,
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Methyl 5-O-behenoyl-b-D-arabinofuranosyl-(1→2)-5-O-behenoyl-
a-D-arabinofuranosyl-(1→3)-[5-O-behenoyl-b-D-arabinofuranosyl-
(1→2)-5-O-behenoyl-a-D-arabinofuranosyl-(1→5)]-a-D-
arabinofuranoside (8)
82.9 (C-3D), 82.6 (C-3C), 82.0(1) (C-4F), 81.9 (7) (C-4D), 80.9
(C-3B), 80.6 (C-4E), 80.5 (C-4C), 80.0 (C-4B), 72.6(7) (PhCH2O),
72.6(6) (PhCH2O), 72.5(8) (PhCH2O), 72.5(2) (PhCH2O), 72.4
(PhCH2O), 72.2 (PhCH2O), 72.1 (PhCH2O), 65.1 (C-5B), 63.5
(C-5C), 63.2 (C-5D), 62.7 (C-5E), 62.6 (C-5F), 54.9 (OCH3).
ESIMS: m/z calcd for [C75H86O21Na]+: 1345.5554. Found:
1345.5558.
Isolated 40% as a colorless oil: Rf 0.36 (1 : 1 hexane–EtOAc); [a]D
+7.2 (c 0.3, CHCl3);1H NMR (500 MHz, CDCl3–CD3OD, 1 : 1,
dH) 5.12 (d, 1H, J1D,2D = 2.2 Hz, H-1D), 5.08 (d, 1 H, J1C,2C = 1.8 Hz,
H-1C), 5.03 (d, 1 H, J1F,2F = 4.5 Hz, H-1F), 5.00 (d, 1 H, J1E,2E
=
4.4 Hz, H-1E), 4.76 (d, 1 H, J1B,2B = 0.7 Hz, H-1B), 4.32–4.02 (m,
24 H, H-5Ea, H-5Fa, H-5Fb, H-5Eb, H-2B, H-2C, H-2D, H-5Da,
H-5Ca, H-5Db, H-5Cb, H-3F, H-3E, H-4B, H-2F, H-2E, H-3D,
H-3C, H-3B, H-4D, H-4C, H-4E, H-4F, H-5Ba), 3.70 (dd, 1 H,
J4B,5Bb = 2.7 Hz, J5Ba,5Bb = 11.4 Hz, H-5Bb), 3.34 (s, 3 H, OCH3),
2.40–2.24 (m, 8 H, acyl CH2 ¥ 4), 1.70–1.50 (m, 8 H, acyl CH2 ¥
4), 1.40–1.00 (m, 144 H, acyl CH2 ¥ 72), 0.90–0.76 (m, 12 H, acyl
CH3 ¥ 4); 13C NMR (125 MHz, CDCl3, dC) 175.7 (C O), 175.6
(C O), 175.5(3) (C O), 175.4(9) (C O), 110.5 (C-1B), 107.5 (C-
1C), 107.3 (C-1D), 103.4 (C-1E), 103.3 (C-1F), 90.3 (C-2C), 89.9
(C-2D), 84.8 (C-3B), 82.9 (C-2B), 81.9 (C-4B), 81.7 (C-3E), 81.5
(C-3F), 81.4(3) (C-4D), 81.1 (C-4C), 78.6 (C-4E), 78.5 (C-4F), 77.3
(C-2E), 77.1 (C-2F), 76.7(2) (C-3D), 76.6(9) (C-3C), 67.7 (C-5B),
67.1 (C-5E), 67.0 (C-5F), 65.0 (C-5D), 64.7 (C-5C), 56.0 (OCH3),
35.3(3) (acyl CH2), 35.3(1) (acyl CH2), 35.2(8) (acyl CH2), 33.2
(acyl CH2), 30.9(8) (acyl CH2), 30.9(4) (acyl CH2), 30.8(6) (acyl
CH2), 30.8(4) (acyl CH2), 30.8(1) (acyl CH2), 30.8(0) (acyl CH2),
30.6(4) (acyl CH2), 30.5(0) (acyl CH2), 30.4(7) (acyl CH2), 30.4(5)
(acyl CH2), 26.2 (acyl CH2), 26.1 (acyl CH2), 23.9 (acyl CH2), 15.1
(acyl CH3). ESIMS: m/z calcd for [C114H212O25Na]+: 2004.5215.
Found: 2004.5210.
Methyl 3-O-benzyl-5-O-p-methoxybenzyl-a-D-arabinofuranosyl-
(1→3)-[3-O-benzyl-5-O-p-methoxybenzyl-a-D-arabinofuranosyl-
(1→5)]-2-O-benzyl-a-D-arabinofuranoside (11)
To a solution of compound 19 (342 mg, 0.38 mmol) in 1 : 1
CH3OH–CH2Cl2 (3 mL) a solution of NaOCH3 in CH3OH was
added until a pH of 11 was obtained. The reaction mixture was
stirred at room temperature for 2 h, neutralized with AcOH,
and concentrated. Chromatography of the residue (1 : 2 hexane–
EtOAc) gave 11 (287 mg, 82%) as a colorless syrup: Rf 0.15 (1 : 1
hexane–EtOAc); [a]D +111.1 (c 0.4, CHCl3);1H NMR (600 MHz,
CDCl3, dH) 7.34–7.17 (m, 19 H, Ar), 6.87–6.84 (m, 4 H, Ar), 5.08
(s, 1 H, H-1D), 5.06 (s, 1 H, H-1C), 4.81 (d, 1 H, J1B,2B = 1.3 Hz, H-
1B), 4.62–4.49 (m, 6 H, PhCH2O), 4.44–4.38 (m, 4 H, PhCH2O),
4.30–4.28 (m, 2 H, H-3B, H-4C), 4.25 (ddd, 1 H, J3D,4D = J4D,5Da
=
2.6 Hz, J4D,5Db = 2.9 Hz, H-4D), 4.16 (ddd, 1 H, J1C,2C = 1.2 Hz,
J2C,OH = 9.1 Hz, J2C,3C = 2.1 Hz, H-2C), 4.12–4.08 (m, 2 H, H-4B,
H-3D), 3.98–3.94 (m, 2 H, H-2B, H-5Ba), 3.82–3.78 (m, 8 H, H-
2D, H-3C, PMBOCH3 ¥ 2), 3.73 (dd, 1 H, J4B,5Bb = 2.7 Hz, J5Ba,5Bb
=
11.7 Hz, H-5Bb), 3.58–3.55 (m, 2 H, H-5Ca, H-5Da), 3.46–3.42
(m, 2 H, H-5Cb, H-5Db), 3.36 (d, 1 H, J = 10.2 Hz, OH), 3.35–
3.33 (m, 4 H, OH, OCH3); 13C NMR (125 MHz, CDCl3, dC)
159.5 (Ar), 159.4 (Ar), 138.0(3) (Ar), 137.9(5) (Ar), 137.6 (Ar),
129.5 (Ar ¥ 3), 129.4 (Ar), 129.2 (Ar), 128.3(9) (Ar ¥ 3), 128.3(5)
(Ar ¥ 3), 127.9 (Ar ¥ 3), 127.7(9) (Ar ¥ 2), 127.7(6) (Ar ¥ 3),
127.6(5) (Ar ¥ 2), 127.6(0) (Ar ¥ 3), 127.5(8) (Ar ¥ 2), 113.9(6)
(Ar ¥ 2), 113.9(0) (Ar ¥ 2), 109.2 (C-1C), 108.1 (C-1D), 107.1
(C-1B), 88.5 (C-2B), 85.3 (C-2D), 84.8 (C-3C), 83.7 (C-4D), 82.6
(C-4C), 80.7 (C-4B), 79.5 (C-3B), 78.3 (C-2C), 77.6 (C-3D), 73.4
(PhCH2O), 73.3 (PhCH2O), 72.0 (PhCH2O), 71.9 (PhCH2O), 71.7
(PhCH2O), 69.5 (C-5C, C-5D), 65.8 (C-5B), 55.3 (PMBOCH3 ¥
2), 54.8 (OCH3). ESIMS: m/z calcd for [C53H62O15Na]+: 961.3981.
Found: 961.3978.
Methyl 2,3-di-O-benzyl-b-D-arabinofuranosyl-(1→2)-3-O-benzyl-
a-D-arabinofuranosyl-(1→3)-[2,3-di-O-benzyl-b-D-
arabinofuranosyl-(1→2)-3-O-benzyl-a-D-arabinofuranosyl-
(1→5)]-2-O-benzyl-a-D-arabinofuranoside (9)
To a solution of 20 (189 mg, 0.10 mmol) in THF (6 mL) was
added TBAF (0.50 mL, 1.0 M in THF) at rt. The mixture was
stirred for 12 h and concentrated. The residue was purified by
chromatography (10 : 1 CH2Cl2–CH3OH) to afford 9 (124 mg,
88%) as a colorless oil: Rf 0.13 (1 : 3 hexane–EtOAc); [a]D +15.9
(c 0.2, CHCl3);1H NMR (500 MHz, CDCl3, dH) 7.38–7.22 (m,
35 H, Ar), 5.10 (d, 1 H, J1D,2D = 1.4 Hz, H-1D), 5.07 (s, 1 H,
H-1C), 5.04 (d, 1 H, J1E,2E = 4.6 Hz, H-1E), 4.97 (d, 1 H, J1F,2F
=
Allyl 2-O-benzoyl-3-O-benzyl-a-D-arabinofuranoside (16)
4.6 Hz, H-1F), 4.91 (d, 1 H, J1B,2B = 1.5 Hz, H-1B), 4.73–4.67 (m,
2 H, PhCH2O), 4.65–4.61 (m, 2 H, PhCH2O), 4.60–4.42 (m, 10
H, PhCH2O), 4.33–4.29 (m, 2 H, H-2C, H-4E), 4.28–4.18 (m, 4
H, H-2D, H-3F, H-3E, H-3B), 4.13–3.94 (m, 10 H, H-3C, H-3D,
H-2E, H-2B, H-2F, H-4B, H-4F, H-4C, H-4D, H-5Ba), 3.80–3.62
(m, 5 H, H-5Bb, H-5Ca, H-5Da, H-5Ea, H-5Fa), 3.60–3.50 (m,
4 H, H-5Db, H-5Cb, H-5Eb, H-5Fb), 3.35 (s, 3 H, OCH3); 13C
NMR (125 MHz, CDCl3, dC) 138.0(2) (Ar), 137.9(8) (Ar), 137.8
(Ar), 137.7 (Ar), 137.5(2) (Ar ¥ 2), 137.4(7) (Ar), 128.6 (Ar ¥
2), 128.5 (Ar ¥ 2), 128.4(3) (Ar ¥ 5), 128.4(2) (Ar ¥ 5), 128.3(9)
(Ar ¥ 2), 128.1 (Ar ¥ 2), 128.0 (Ar ¥ 2), 127.9 (Ar), 127.8(4)
(Ar), 127.8(2) (Ar), 127.7(9) (Ar), 127.7(8) (Ar), 127.7(6) (Ar ¥ 2),
127.7(0) (Ar ¥ 5), 127.6(8) (Ar ¥ 3), 106.8 (C-1B), 106.0 (C-1D),
105.9 (C-1C), 100.4 (C-1E), 100.1 (C-1F), 88.7 (C-2B), 86.2 (C-
2C), 85.8 (C-2D), 84.0 (C-2E, C-2F), 83.1 (C-3E), 83.0 (C-3F),
To a solution of 14 (5.00 g, 10.5 mmol) in acetic acid (25 mL)
a 33% HBr solution in acetic acid (25 mL) was added. The
reaction was stirred for 6 h at room temperature and diluted
with CH2Cl2 (200 mL). The clear solution was then washed with
cold saturated aqueous NaHCO3 solution (4 ¥ 200 mL) and
brine (200 mL), dried (MgSO4) and filtered. To this solution
molecular sieves (10 g), triethylamine (6.65 mL, 47.7 mmol) and
CH3OH (2 mL, 49.4 mmol) were added. After 12 h stirring,
the mixture was concentrated, diluted with CH2Cl2 (200 mL)
and washed with water (3 ¥ 200 mL) and brine (200 mL). The
solution was dried (MgSO4), filtered and evaporated to yield
the orthoester. To a solution of this orthoester in 1 : 1 CH2Cl2–
CH3OH (150 mL) a solution of NaOCH3 in CH3OH (2.5 mL,
1M) was added. The reaction was stirred at 40 ◦C for 4 h and
172 | Org. Biomol. Chem., 2011, 9, 165–176
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concentrated. The residue was diluted with CH2Cl2 (200 mL),
washed with water (50 mL), dried and concentrated to provide
the crude deprotected orthoester. To a solution of the crude
orthoester (4.26 g, 7.89 mmol) in CH2Cl2 (79 mL) molecular sieves
(5 g) was added. The mixture was stirred for 30 min at room
temperature and cooled to 0 ◦C. To this solution camphorsulfonic
acid (26 mg, 0.078 mmol) was added. After TLC indicated the
completion of reaction, triethylamine was added. Then the mixture
was filtered and concentrated to give the crude 1,2,5-o◦rthoester
15. After the residue was dissolved in DMF (39 mL) 0 C, NaH
(473 mg, 60% dispersion in oil, 11.8 mmol) and BnBr (1.41 mL,
11.8 mmol) were added subsequently. The reaction mixture was
stirred for 2 h and the reaction was quenched by the addition of
CH3OH. The mixture was diluted with CH2Cl2 (70 mL), washed
with water (70 mL) and brine (70 mL), dried and concentrated.
After the residue was dissolved in CH2Cl2 (39 mL), molecular
sieves (4 g) and allyl alcohol (2.68 mL, 39.5 mmol) were added.
The reaction mixture was stirred at room temperature for 30 min
and cooled to 0 ◦C and then a solution of TMSOTf (0.14 mL,
0.79 mmol, 0.1 in CH2Cl2 v/v) was added. The solution was
allowed to stir for 10 min and the reaction was quenched by the
addition of triethylamine. The mixture was filtered, concentrated
and purified by chromatography (2 : 1 hexane–EtOAc) to give
16 (2.92 g, 72% over 6 steps) as a colorless syrup: Rf 0.21 (2 : 1
hexane–EtOAc); [a]D +94.5 (c 1.0, CHCl3);1H NMR (500 MHz,
CDCl3, dH) 8.06–8.00 (m, 2 H, Ar), 7.62–7.57 (m, 1 H, Ar), 7.48–
7.44 (m, 2 H, Ar), 7.38–7.24 (m, 5 H, Ar), 5.99–5.91 (m, 1 H,
CH2 CH CH2O), 5.43 (d, 1 H, J1,2 = 1.6 Hz, H-2), 5.38–5.33 (m,
1 H, CH2 CH CH2O), 5.21–5.20 (m, 2 H, CH2 CH CH2O,
H-1), 4.84 (d, 1 H, J = 12.1 Hz, PhCH2O), 4.63 (d, 1 H, J =
12.1 Hz, PhCH2O), 4.30–4.26 (m, 2 H, CH2 CH CH2O, H-
4), 4.13–4.08 (m, 2 H, CH2 CH CH2O, H-3), 3.88 (ddd, 1
H, J4,5a = 3.5 Hz, J5a,5b = 12.2 Hz, J5a,OH = 4.5 Hz, H-5a), 3.67
(ddd, 1 H, J4,5b = 3.5 Hz, J5a,5b = 12.2 Hz, J5b,OH = 8.2 Hz,
H-5b), 1.97 (dd, 1 H, J5a,OH = 4.5 Hz, J5b,OH = 8.2 Hz, OH);
13C NMR (125 MHz, CDCl3, dC) 165.4 (C O), 137.6 (Ar),
133.9 (Ar), 133.4 (Ar), 129.7 (Ar ¥ 2), 129.4 (Ar), 128.5 (Ar ¥
2), 128.4 (Ar ¥ 2), 127.9(3) (Ar ¥ 2), 127.8(6) (CH2 CH-
CH2O), 117.6 (CH2 CH–CH2O), 105.2 (C-1), 83.2 (C-4), 82.9
(C-3), 82.2 (C-2), 72.5 (PhCH2O), 68.0 (CH2 CH–CH2O), 62.0
(C-5). ESIMS: m/z calcd for [C22H24O6Na]+: 407.1465. Found:
407.1463.
give the reducing sugar 18 (1.42 g, 84% over two steps) in a 1.8 : 1
a:b ratio as colorless oil: Rf 0.26 (3 : 1 hexane–EtOAc); [a]D -11.7
(c 0.6, CHCl3); ESIMS: m/z calcd for [C27H28O7Na]+: 487.1727.
Found: 487.1726. a isomer: 1H NMR (500 MHz, CDCl3, dH) 7.96–
7.92 (m, 2 H, Ar), 7.46–7.40 (m, 3 H, Ar), 7.36–7.28 (m, 5 H, Ar),
7.18–7.14 (m, 2 H, Ar), 6.81–6.77 (m, 2 H, Ar), 5.51 (dd, 1 H,
J1,2 = 0.8 Hz, J1,OH = 7.5 Hz, H-1), 5.37 (d, 1 H, J1,2 = 0.8 Hz, H-2),
4.81 (d, 1 H, J = 12.1 Hz, PhCH2O), 4.68 (d, 1 H, J = 12.1 Hz,
PhCH2O), 4.56–4.52 (m, 1 H, H-4), 4.50–4.42 (m, 2 H, PhCH2O),
4.05 (ddd, 1 H, J1,3 = 1.1 Hz, J2,3 = 1.0 Hz, J3,4 = 3.5 Hz, H-3), 3.77
(s, 3 H, PMBOCH3), 3.60–3.50 (m, 2 H, H-5a, H-5b), 3.37 (d, 1
H, J2,OH = 7.5 Hz, OH); 13C NMR (125 MHz, CDCl3, dC) 165.4
(C O), 159.2 (Ar), 137.1 (Ar), 133.4 (Ar), 129.9 (Ar), 129.8 (Ar),
129.3 (Ar ¥ 2), 129.2 (Ar), 128.4(9) (Ar ¥ 2), 128.4(7) (Ar ¥ 3), 128.0
(Ar ¥ 3), 113.7 (Ar ¥ 2), 101.1 (C-1), 82.8 (C-3), 82.7 (C-4), 80.7
(C-2), 73.0 (PhCH2O), 72.3 (PhCH2O), 69.3 (C-5), 55.2 (OCH3).
b isomer: 1H NMR (500 MHz, CDCl3, dH) 8.02–7.98 (m, 2 H, Ar),
7.61–7.56 (m, 3 H, Ar), 7.36–7.28 (m, 5 H, Ar), 7.25–7.22 (m, 2 H,
Ar), 6.88–6.85 (m, 2 H, Ar), 5.61 (dd, 1 H, J1,2 = 4.7 Hz, J1,OH
=
10.3 Hz, H-1), 5.28 (dd, 1 H, J1,2 = 4.7 Hz, J2,3 = 5.4 Hz, H-2), 4.69
(d, 1 H, J = 11.9 Hz, PhCH2O), 4.58–4.52 (m, 2 H, PhCH2O),
4.50–4.42 (m, 2 H, PhCH2O, H-3), 4.24 (ddd, 1 H, J3,4 = 3.0 Hz,
J4,5a = 3.1 Hz, J4,5b = 4.6 Hz, H-4), 3.95 (d, 1 H, J2,OH = 10.3 Hz,
OH), 3.79 (s, 3 H, PMBOCH3), 3.66 (dd, 1 H, J4,5a = 3.1 Hz, J5a,5b
=
10.3 Hz, H-5a), 3.60–3.50 (m, 1 H, H-5b); 13C NMR (125 MHz,
CDCl3, dC) 165.7 (C O), 159.5 (Ar), 137.5 (Ar), 133.3 (Ar), 129.7
(Ar ¥ 4), 129.6 (Ar ¥ 2), 129.5 (Ar), 129.0 (Ar), 128.4 (Ar ¥ 2),
127.9 (Ar), 127.8 (Ar ¥ 2), 114.0 (Ar ¥ 2), 95.8 (C-1), 80.8 (C-3,
C-4), 80.2 (C-2), 73.5 (PhCH2O), 72.1 (PhCH2O), 70.1 (C-5), 55.2
(OCH3).
Methyl 2-O-benzoyl-3-O-benzyl-5-O-p-methoxybenzyl-a-D-
arabinofuranosyl-(1→3)-[2-O-benzoyl-3-O-benzyl-5-O-p-
methoxybenzyl-a-D-arabinofuranosyl-(1→5)]-2-O-benzyl-a-D-
arabinofuranoside (19)
To a solution of alcohol 18 (443 mg, 0.95 mmol) and CCl3CN
(0.29 mL, 2.86 mmol) in CH2Cl2 (19 mL) was added DBU
(0.029 mL, 0.19 mmol). The reaction was stirred at rt for 4 h.
The solvent was evaporated and the residue was quickly filtered
through a short column of silica gel. The resulting solution was
then concentrated to give the imidate derivative 12, which was
used immediately in the next step. To a mixture of imidate residue,
˚
13 (101 mg, 0.40 mmol) and 4 A molecular sieves (700 mg) in
2-O-Benzoyl-3-O-benzyl-5-O-p-methoxybenzyl-D-arabinofuranose
CH2Cl2 (10 mL) was added a solution of TMSOTf (86 mL, 0.1 in
CH2Cl2 v : v) dropwise at 0 ◦C. After stirring at this temperature for
10min, the reaction was quenched bythe additionoftriethylamine.
The solution was then diluted with CH2Cl2 (30 mL) and filtered
through Celite. The filtrate was concentrated and purified by
chromatography (2 : 1 hexane–EtOAc) to afford 19 (382 mg, 84%)
as a white solid: Rf 0.23 (2 : 1 hexane–EtOAc); [a]D +68.0 (c 0.6,
CHCl3); 1H NMR (500 MHz, CDCl3, dH) 7.98–7.94 (m, 4 H, Ar),
7.60–7.54 (m, 2 H, Ar), 7.42–7.38 (m, 4 H, Ar), 7.32–7.10 (m,
19 H, Ar), 6.77–6.74 (m, 4 H, Ar), 5.46 (d, 1 H, J1C,2C = 1.3 Hz,
H-2C), 5.34 (d, 1 H, J1D,2D = 1.1 Hz, H-2D), 5.30 (s, 1 H, H-1C),
5.26 (s, 1 H, H-1D), 4.94 (d, 1 H, J1B,2B = 1.5 Hz, H-1B), 4.80–
4.74 (m, 2 H, PhCH2O), 4.60–4.54 (m, 4 H, PhCH2O), 4.48–4.42
(m, 2 H, PhCH2O), 4.42–4.34 (m, 2 H, H-4C, PhCH2O), 4.32–
4.28 (m, 2 H, H-3B, H-4D), 4.24–4.20 (m, 1 H, H-4B), 4.06–3.98
(18)
To a solution of PMBOH (0.92 mL, 7.36 mmol) in CH2Cl2
(36 mL), DBU (0.22 mL, 1.47 mol) and CCl3CN (3.69 mL,
36.79 mmol) were added. The solution was stirred at room temper-
ature for 2 h, passed though a short silica plug, and concentrated.
The resulting residue and 17 (1.41 g, 3.68 mmol) were dissolved in
toluene (42 mL) and La(OTf)3 (50 mg, 0.085 mmol) was added.
The reaction mixture was stirred for 5 h, the reaction was quenched
by the addition of few drops of acetic acid, and the solution was
concentrated. To a solution of this residue in CH3OH (65 mL),
PdCl2 (131 mg, 0.74 mmol) was added. The reaction mixture
was stirred for 5 h, neutralized by the addition of triethylamine,
and filtered through Celite. The filtrate was concentrated and the
residue was purified by chromatography (6 : 1 hexane–EtOAc) to
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(m, 4 H, H-2B, H-5Ba, H-3D, H-3C), 3.82 (dd, 1 H, J4B,5Bb = 2.7 Hz,
J5Ba,5Bb = 11.4 Hz, H-5Bb), 3.80–3.72 (m, 6 H, PMBOCH3 ¥ 2),
3.64–3.50 (m, 4 H, H-5Da, H-5Ca, H-5Db, H-5Cb), 3.36 (s, 3 H,
OCH3); 13C NMR (125 MHz, CDCl3, dC) 165.3 (C O), 165.2
(C O), 159.1 (Ar ¥ 2), 137.9 (Ar), 137.8 (Ar), 137.7 (Ar), 133.3
(Ar), 133.2 (Ar), 130.2 (Ar), 130.1 (Ar), 129.8(1) (Ar ¥ 2), 129.7(8)
(Ar ¥ 2), 129.6 (Ar), 129.5 (Ar), 129.2(4) (Ar ¥ 2), 129.2(0) (Ar ¥
2), 129.2(0) (Ar ¥ 2), 128.3(9) (Ar ¥ 2), 128.3(8) (Ar ¥ 2), 128.2(9)
(Ar ¥ 4), 128.2(4) (Ar ¥ 2), 127.8(4) (Ar ¥ 2), 127.8(2) (Ar ¥ 4),
127.6(4) (Ar), 127.6(1) (Ar), 127.5(3) (Ar), 113.7 (Ar ¥ 4), 107.1
(C-1B), 106.2 (C-1C), 105.6 (C-1D), 88.3 (C-2B), 83.6 (C-3C), 83.2
(C-3D), 82.4 (C-3B), 82.2 (C-4C), 82.1 (C-2D), 81.7 (C-2C), 80.6
(C-4D), 80.1 (C-4B), 73.0(2) (PhCH2O), 73.0(0) (PhCH2O), 72.1
(PhCH2O), 72.0 (PhCH2O), 71.9 (PhCH2O), 69.0 (C-5C), 68.8
(C-5D), 66.0 (C-5B), 55.2(0) (PMBOCH3), 55.1(9) (PMBOCH3),
54.9 (OCH3). ESIMS: m/z calcd for [C67H70O17Na]+: 1169.4505.
Found: 1169.4509.
NMR (125 MHz, CDCl3, dC) 138.5 (Ar), 138.4 (Ar), 138.3 (Ar),
138.2 (Ar), 137.9 (Ar), 137.8 (Ar), 137.7 (Ar), 128.4(0) (Ar ¥ 2),
128.3(7) (Ar ¥ 4), 128.3(2) (Ar ¥ 2), 128.2(9) (Ar ¥ 2), 128.2(6)
(Ar ¥ 2), 128.2(1) (Ar ¥ 2), 127.9(2) (Ar ¥ 2), 127.8(5) (Ar ¥ 2),
127.7(9) (Ar), 127.7(3) (Ar ¥ 4), 127.6(8) (Ar), 127.6(1) (Ar ¥ 2),
127.5(9) (Ar ¥ 2), 127.5(5) (Ar), 127.4(8) (Ar ¥ 3), 127.4(6) (Ar ¥ 2),
127.3(7) (Ar), 107.0 (C-1B), 106.5 (C-1C), 104.9 (C-1D), 100.3 (C-
1E), 100.0 (C-1F), 88.2 (C-2B), 85.9 (C-2C), 85.4 (C-2D), 84.5 (C-
3E), 84.2(2) (C-2E), 84.1(7) (C-3F), 84.1(4) (C-3C), 84.1(1) (C-2F),
84.0 (C-3D), 83.2 (C-4D), 82.7 (C-4C), 82.2 (C-4F), 82.1 (C-4E),
81.2 (C-4B), 80.1 (C-3B), 72.3(3) (PhCH2O), 72.2(7) (PhCH2O),
72.2(1) (PhCH2O), 72.1(8) (PhCH2O), 72.0(7) (PhCH2O), 72.0(6)
(PhCH2O), 71.7 (PhCH2O), 65.8 (C-5B), 65.5 (C-5C), 65.4 (C-
5D), 63.2 (C-5E), 63.1 (C-5F), 54.7 (OCH3), 25.9(8) (t-Butyl CH3 ¥
4), 26.0 (t-Butyl CH3 ¥ 6), 25.9 (t-Butyl CH3 ¥ 6), 18.4 (t-Butyl
C ¥ 2), 18.3 (t-Butyl C ¥ 2), -5.1(8) (Si CH3), -5.2(4) (Si CH3),
-5.2(6) (Si CH3 ¥ 2), -5.3(0) (Si CH3 ¥ 2), -5.3(1) (Si CH3 ¥
2). ESIMS: m/z calcd for [C99H142O21Na]+: 1801.9013. Found:
1801.9016.
Methyl 2,3-di-O-benzyl-5-O-tert-butyldimethylsilyl-b-D-
arabinofuranosyl-(1→2)-3-O-benzyl-5-O-tert-butyldimethylsilyl-
a-D-arabinofuranosyl-(1→3)-[2,3-di-O-benzyl-5-O-tert-
butyldimethylsilyl-b-D-arabinofuranosyl-(1→2)-3-O-benzyl-5-O-
tert-butyldimethylsilyl-a-D-arabinofuranosyl-(1→5)]-2-O-benzyl-
a-D-arabinofuranoside (20)
Methyl 2,3-di-O-benzyl-5-O-butyryl-b-D-arabinofuranosyl-
(1→2)-3-O-benzyl-5-O-butyryl-a-D-arabinofuranosyl-(1→3)-[2,3-
di-O-benzyl-5-O-butyryl-b-D-arabinofuranosyl-(1→2)-3-O-
benzyl-5-O-butyryl-a-D-arabinofurano-syl-(1→5)]-2-O-benzyl-a-
D-arabinofuranoside (21)
To a mixture of 11 (567 mg, 0.60 mmol), 10 (823 mg, 1.45 mmol),
˚
and 4 A molecular sieves (1.3 g) in CH2Cl2 (20 mL) was added
N-iodosuccinimide◦(352 mg, 1.56 mmol) and AgOTf (16 mg,
Isolated 92% as a colorless oil: Rf 0.19 (4 : 1 hexane–EtOAc); [a]D
+13.7 (c 0.3, CHCl3);1H NMR (500 MHz, CDCl3, dH) 7.37–7.20
(m, 35 H, Ar), 5.13 (s, 1H, H-1C), 5.12 (d, 1 H, J1E,2E = 4.5 Hz, H-
1E), 5.07 (s, 1 H, H-1D), 4.96 (d, 1 H, J1F,2F = 4.4 Hz, H-1F), 4.85
(d, 1 H, J1B,2B = 1.0 Hz, H-1B), 4.72–4.64 (m, 4 H, PhCH2O), 4.62–
4.44 (m, 9 H, PhCH2O), 4.43 (m, 1 H, PhCH2O), 4.40–4.38 (m, 1
H, H-2C), 4.34 (dd, 1 H, J1D,2D = 1.1 Hz, J2D,3D = 2.9 Hz, H-2D),
4.30–4.04 (m, 16 H, H-3B, H-5Fa, H-5Ea, H-5Fb, H-5Eb, H-4F,
H-4E, H-3F, H-3E, H-5Da, H-5Ca, H-5Db, H-5Cb, H-4D, H-4C,
H-4B), 4.01–3.92 (m, 6 H, H-2B, H-5Ba, H-2F, H-2E, H-3D, H-
3C), 3.78 (dd, 1 H, J4B,5Bb = 2.2 Hz, J5Ba,5Bb = 12.0 Hz, H-5Bb),
3.35 (s, 3 H, OCH3), 2.29–2.14 (m, 8 H, acyl CH2 ¥ 4), 1.64–
1.50 (m, 8 H, acyl CH2 ¥ 4), 0.92–0.80 (m, 12 H, acyl CH3 ¥ 4);
13C NMR (125 MHz, CDCl3, dC) 173.3 (C O), 173.1(8) (C O),
173.1(5) (C O ¥ 2), 137.9 (Ar), 137.8 (Ar), 137.7(5) (Ar), 137.7(1)
(Ar), 137.5(2) (Ar), 137.5(0) (Ar), 137.4(1) (Ar), 128.5(1) (Ar ¥ 2),
128.4(8) (Ar ¥ 2), 128.4(3) (Ar ¥ 2), 128.4(2) (Ar ¥ 3), 128.4(0)
(Ar ¥ 2), 128.3(5) (Ar ¥ 2), 128.3(1) (Ar ¥ 2), 128.1 (Ar), 128.0(0)
(Ar ¥ 2), 127.9(6) (Ar ¥ 2), 127.8(4) (Ar), 127.8(0) (Ar), 127.7(8)
(Ar), 127.7(4) (Ar ¥ 3), 127.7(0) (Ar ¥ 2), 127.6(7) (Ar ¥ 2), 127.6(3)
(Ar ¥ 5), 106.9 (C-1B), 106.6 (C-1C), 105.3 (C-1D), 100.6 (C-1E),
100.3 (C-1F), 88.3 (C-2B), 85.9 (C-2C), 85.6 (C-2D), 84.2 (C-
3C), 84.1 (C-3D), 83.7(1) (C-2E), 83.6(9) (C-2F), 82.5(5) (C-3E),
82.4(6) (C-3F), 81.0 (C-4B), 80.4 (C-4F), 80.2 (C-4E), 79.8 (C-3B),
78.9 (C-4C), 78.7 (C-4D), 72.5(1) (PhCH2O), 72.4(7) (PhCH2O),
72.4(2) (PhCH2O), 72.4(1) (PhCH2O), 72.3(0) (PhCH2O), 72.2(8)
(PhCH2O), 71.8 (PhCH2O), 66.0 (C-5C), 65.9 (C-5D), 65.5 (C-
5B), 63.5(4) (C-5E), 63.4(7) (C-5F), 54.7 (OCH3), 35.8(7) (acyl
CH2), 35.8(6) (acyl CH2), 35.8(4) (acyl CH2), 18.2(8) (acyl CH2),
18.2(6) (acyl CH2), 13.6(3) (acyl CH3), 13.6(0) (acyl CH3), 13.5(8)
(acyl CH3). ESIMS: m/z calcd for [C91H110O25Na]+: 1625.7228.
Found: 1625.7215.
◦
0.06 mmol) at -60 C. The solution was warmed to -40 C over
a period of 1 h and the reaction was quenched by the addition
of triethylamine. The solution was then diluted with CH2Cl2
(30 mL) and filtered through Celite. The filtrate was concentrated
and purified by chromatography (4 : 1 hexane–EtOAc) to afford a
mixture of pentasaccharides (947 mg, 86%) as a colorless oil. To a
solution of this mixture (947 mg, 0.52 mmol) in CH2Cl2 (51 mL)
trifluoroacetic acid (1.04 mL) was added dropwise. After TLC
indicated the completion of the reaction, the resulting solution was
neutralized by the addition of triethylamine. The reaction mixture
was then concentrated and the residue purified by chromatography
(10 : 1 CH2Cl2–CH3OH) to give a syrup, that was redissolved in
CH2Cl2 (51 mL). TBDMSCl (162 mg, 1.07 mmol), imidazole
(244 mg, 3.58 mmol) and DMAP (44 mg, 3.58 mmol) were added
and the reaction mixture was stirred at rt overnight before the
reaction was quenched by the addition of CH3OH. The reaction
mixture was then concentrated and purified by chromatography
(6 : 1 hexane–EtOAc) to afford 20 (645 mg, 59%) over three steps
as a colorless oil: Rf 0.26 (4 : 1 hexane–EtOAc) [a]D -8.9 (c 0.3,
CHCl3);1H NMR (500 MHz, CDCl3, dH) 7.34–7.20 (m, 35 H, Ar),
5.14 (d, 1 H, J1E,2E = 4.5 Hz, H-1E), 5.13 (d, 1 H, J1C,2C = 1.0 Hz,
H-1C), 5.09 (s, 1 H, H-1D), 5.00 (d, 1 H, J1F,2F = 4.4 Hz, H-1F),
4.86 (d, 1 H, J1B,2B = 1.0 Hz, H-1B), 4.72–4.44 (m, 14 H, PhCH2O),
4.39 (dd, 1 H, J1C,2C = 1.0 Hz, J2C,3C = 3.0 Hz, H-2C), 4.33 (dd, 1
H, J1D,2D = 1.0 Hz, J2D,3D = 2.9 Hz, H-2D), 4.25 (dd, 1 H, J2B,3B
=
3.0 Hz, J3B,4B = 6.8 Hz, H-3B), 4.18–4.06 (m, 5 H, H-4B, H-4C,
H-3E, H-3F, H-4D), 4.03–3.92 (m, 8 H, H-2F, H-2E, H-2B, H-
5Ba, H-3D, H-3C, H-4F, H-4E), 3.79 (dd, 1 H, J4B,5Bb = 2.3 Hz,
J5Ba,5Bb = 12.0 Hz, H-5Bb), 3.77–3.66 (m, 8 H, H-5Da, H-5Ca, H-
5Ea, H-5Fa, H-5Db, H-5Cb, H-5Eb, H-5Fb), 3.29 (s, 3 H, OCH3),
0.92–0.84 (m, 36 H, t-BuCH3), 0.06–0.00 (m, 24 H, SiCH3); 13C
174 | Org. Biomol. Chem., 2011, 9, 165–176
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Methyl 2,3-di-O-benzyl-5-O-decanoyl-b-D-arabinofuranosyl-
(1→2)-3-O-benzyl-5-O-decanoyl-a-D-arabinofuranosyl-(1→3)-
[2,3-di-O-benzyl-5-O-decanoyl-b-D-arabinofuranosyl-(1→2)-3-O-
benzyl-5-O-decanoyl-a-D-arabino-furanosyl-(1→5)]-2-O-benzyl-
a-D-arabinofuranoside (22)
(m, 8 H, acyl CH2 ¥ 4), 1.34–1.19 (m, 96 H, acyl CH2 ¥ 48),
0.92–0.87 (m, 12 H, acyl CH3 ¥ 4); 13C NMR (125 MHz, CDCl3,
dC) 173.5 (C O), 173.4 (C O), 173.3 (C O ¥ 2), 137.8(7) (Ar),
137.8(6) (Ar), 137.7(5) (Ar), 137.7(2) (Ar), 137.5(1) (Ar), 137.4(8)
(Ar), 137.3(9) (Ar), 128.5(2) (Ar ¥ 2), 128.4(9) (Ar ¥ 2), 128.4(3)
(Ar ¥ 3), 128.4(0) (Ar ¥ 2), 128.3(5) (Ar ¥ 2), 128.3(1) (Ar ¥
2), 128.0(5) (Ar), 128.0(3) (Ar ¥ 2), 127.9(8) (Ar ¥ 3), 127.8(4)
(Ar), 127.8(1) (Ar), 127.7(7) (Ar), 127.7(6) (Ar ¥ 2), 127.7(3) (Ar),
127.6(8) (Ar ¥ 2), 127.6(5) (Ar ¥ 3), 127.6(3) (Ar ¥ 3), 127.6(2)
(Ar ¥ 2), 106.9 (C-1B), 106.6 (C-1C), 105.2 (C-1D), 100.6 (C-1E),
100.3 (C-1F), 88.3 (C-2B), 85.8 (C-2C), 85.4 (C-2D), 84.3 (C-
3C), 84.2 (C-3D), 83.7(1) (C-2E), 83.6(9) (C-2F), 82.6(9) (C-3E),
82.5(9) (C-3F), 81.1 (C-4B), 80.4 (C-4F), 80.2 (C-4E), 79.9 (C-3B),
78.9 (C-4C), 78.7 (C-4D), 72.5(0) (PhCH2O), 72.4(9) (PhCH2O),
72.4(3) (PhCH2O ¥ 2), 72.3 (PhCH2O ¥ 2), 71.8 (PhCH2O), 66.0(0)
(C-5C), 65.9(4) (C-5D), 65.5 (C-5B), 63.6 (C-5E), 63.5 (C-5F),
54.7 (OCH3), 34.0(3) (acyl CH2), 34.0(1) (acyl CH2), 33.9(8) (acyl
CH2), 33.9(6) (acyl CH2), 33.9(3) (acyl CH2), 29.7(1) (acyl CH2),
29.6(8) (acyl CH2), 29.6(4) (acyl CH2), 29.5(6) (acyl CH2), 29.4(9)
(acyl CH2), 29.3(7) (acyl CH2), 29.2(8) (acyl CH2), 29.2(1) (acyl
CH2), 29.1(5) (acyl CH2), 24.8 (acyl CH2), 22.7 (acyl CH2), 14.1
(acyl CH3). ESIMS: m/z calcd for [C135H206O25Na]+: 2298.4746.
Found: 2298.4740.
Isolated 79% as a colorless oil: Rf 0.23 (4 : 1 hexane–EtOAc); [a]D
+12.4 (c 0.3, CHCl3);1H NMR (600 MHz, CDCl3, dH) 7.37–7.20
(m, 35 H, Ar), 5.13 (s, 1H, H-1C), 5.12 (d, 1 H, J1E,2E = 4.4 Hz, H-
1E), 5.07 (s, 1 H, H-1D), 4.96 (d, 1 H, J1F,2F = 4.3 Hz, H-1F), 4.85 (d,
1 H, J1B,2B = 0.9 Hz, H-1B), 4.73–4.65 (m, 4 H, PhCH2O), 4.62–4.57
(m, 3 H, PhCH2O), 4.55–4.44 (m, 6 H, PhCH2O), 4.40–4.39 (m, 2
H, PhCH2O, H-2C), 4.34 (dd, 1 H, J1D,2D = 1.1 Hz, J2D,3D = 2.8 Hz,
H-2D), 4.30–4.04 (m, 16 H, H-3B, H-5Fa, H-5Ea, H-5Fb, H-5Eb,
H-4F, H-4E, H-3F, H-3E, H-5Da, H-5Ca, H-5Db, H-5Cb, H-4D,
H-4C, H-4B), 4.02–3.92 (m, 6 H, H-2B, H-5Ba, H-2F, H-2E, H-
3D, H-3C), 3.79 (dd, 1 H, J4B,5Bb = 2.2 Hz, J5Ba,5Bb = 12.0 Hz, H-5Bb),
3.30 (s, 3 H, OCH3), 2.28–2.14 (m, 8 H, acyl CH2 ¥ 4), 1.60–1.38
(m, 8 H, acyl CH2 ¥ 4), 1.32–1.18 (m, 48 H, acyl CH2 ¥ 24),
0.92–0.86 (m, 12 H, acyl CH3 ¥ 4); 13C NMR (125 MHz, CDCl3,
dC) 173.5 (C O), 173.4 (C O), 173.3 (C O ¥ 2), 137.8(8) (Ar),
137.8(7) (Ar), 137.7(7) (Ar), 137.7(4) (Ar), 137.5(2) (Ar), 137.5(0)
(Ar), 137.4 (Ar), 128.5(1) (Ar ¥ 2), 128.4(9) (Ar ¥ 2), 128.4(2) (Ar ¥
3), 128.4(0) (Ar ¥ 2), 128.3(4) (Ar ¥ 2), 128.3(1) (Ar ¥ 2), 128.0(4)
(Ar), 128.0(2) (Ar ¥ 2), 127.9(6) (Ar ¥ 3), 127.8(3) (Ar), 127.8(0)
(Ar), 127.7(7) (Ar), 127.7(5) (Ar ¥ 2), 127.7(2) (Ar), 127.6(7) (Ar ¥
2), 127.6(4) (Ar ¥ 3), 127.6(3) (Ar ¥ 3), 127.6(1) (Ar ¥ 2), 106.9
(C-1B), 106.6 (C-1C), 105.3 (C-1D), 100.6 (C-1E), 100.3 (C-1F),
88.3 (C-2B), 85.8 (C-2C), 85.5 (C-2D), 84.3 (C-3C), 84.2 (C-3D),
83.7(2) (C-2E), 83.7(0) (C-2F), 82.7 (C-3E), 82.6 (C-3F), 81.1 (C-
4B), 80.4 (C-4F), 80.3 (C-4E), 79.8 (C-3B), 78.9 (C-4C), 78.7 (C-
4D), 72.5(1) (PhCH2O), 72.4(8) (PhCH2O), 72.4(3) (PhCH2O ¥
2), 72.3 (PhCH2O ¥ 2), 71.8 (PhCH2O), 66.0 (C-5C), 65.9 (C-5D),
65.5 (C-5B), 63.6 (C-5E), 63.5 (C-5F), 54.7 (OCH3), 34.0(3) (acyl
CH2), 34.0(1) (acyl CH2), 33.9(9) (acyl CH2), 33.9(6) (acyl CH2),
31.8(8) (acyl CH2), 31.8(5) (acyl CH2), 29.4(7) (acyl CH2), 29.4(1)
(acyl CH2), 29.3(3) (acyl CH2), 29.3(2) (acyl CH2), 29.2(8) (acyl
CH2), 29.2(5) (acyl CH2), 29.1(8) (acyl CH2), 29.1(3) (acyl CH2),
24.8 (acyl CH2), 22.6 (acyl CH2), 14.1 (acyl CH3). ESIMS: m/z
calcd for [C115H158O25Na]+: 1962.0984. Found: 1962.0986.
Methyl 5-O-behenoyl-2,3-di-O-benzyl-b-D-arabinofuranosyl-
(1→2)-5-O-behenoyl-3-O-benzyl-a-D-arabinofuranosyl-(1→3)-[5-
O-behenoyl-2,3-di-O-benzyl-b-D-arabinofuranosyl-(1→2)-5-O-
behenoyl-3-O-benzyl-a-D-arabino-furanosyl-(1→5)]-2-O-benzyl-
a-D-arabinofuranoside (24)
To a solution of alcohol (0.10 mmol) in CH2Cl2 (3 mL), behenic
acid (131 mg, 0.38 mmol), DCC (79 mg, 0.38 mol) and DCC
(5 mg) were added at 0 ◦C. The reaction was kept stirring for 4 h
and quenched by the addition of CH3OH. The resulting solution
was concentrated and the residue was purified by chromatography
(10 : 1 hexanes–EtOAc) to obtain a 63% yield of 24 as a white
solid: Rf 0.32 (6 : 1 hexane–EtOAc); [a]D +7.3 (c 0.6, CHCl3);1H
NMR (600 MHz, CDCl3, dH) 7.36–7.20 (m, 35 H, Ar), 5.13 (s,
1H, H-1C), 5.11 (d, 1 H, J1E,2E = 4.4 Hz, H-1E), 5.06 (s, 1 H,
H-1D), 4.96 (d, 1 H, J1F,2F = 4.4 Hz, H-1F), 4.85 (s, 1 H, H-1B),
4.72–4.64 (m, 4 H, PhCH2O), 4.62–4.56 (m, 3 H, PhCH2O), 4.55–
4.43 (m, 6 H, PhCH2O), 4.42–4.38 (m, 2 H, PhCH2O, H-2C),
4.35–4.32 (m, 1 H, H-2D), 4.30–4.04 (m, 16 H, H-3B, H-5Fa, H-
5Ea, H-5Fb, H-5Eb, H-4F, H-4E, H-3F, H-3E, H-5Da, H-5Ca,
H-5Db, H-5Cb, H-4D, H-4C, H-4B), 4.00–3.92 (m, 6 H, H-2B,
H-5Ba, H-2F, H-2E, H-3D, H-3C), 3.78 (dd, 1 H, J4B,5Bb = 2.1 Hz,
J5Ba,5Bb = 11.9 Hz, H-5Bb), 3.30 (s, 3 H, OCH3), 2.30–2.14 (m, 8
H, acyl CH2 ¥ 4), 1.60–1.46 (m, 8 H, acyl CH2 ¥ 4), 1.40–1.10 (m,
144 H, acyl CH2 ¥ 72), 0.92–0.84 (m, 12 H, acyl CH3 ¥ 4); 13C
NMR (125 MHz, CDCl3, dC) 173.5 (C O), 173.4 (C O), 173.3
(C O ¥ 2), 137.8(8) (Ar), 137.8(7) (Ar), 137.7(7) (Ar), 137.7(4)
(Ar), 137.5(3) (Ar), 137.5(0) (Ar), 137.4(1) (Ar), 128.5(1) (Ar ¥ 2),
128.4(8) (Ar ¥ 2), 128.4(2) (Ar ¥ 4), 128.3(9) (Ar ¥ 2), 128.3(4)
(Ar ¥ 2), 128.3(0) (Ar ¥ 2), 128.1 (Ar ¥ 2), 128.0 (Ar ¥ 2), 127.8(2)
(Ar), 127.7(9) (Ar), 127.7(5) (Ar ¥ 2), 127.7(1) (Ar), 127.6(6) (Ar ¥
2), 127.6(4) (Ar ¥ 4), 127.6(2) (Ar ¥ 4), 127.6(1) (Ar ¥ 2), 106.9
(C-1B), 106.6 (C-1C), 105.3 (C-1D), 100.6 (C-1E), 100.3 (C-1F),
88.3 (C-2B), 85.8 (C-2C), 85.4 (C-2D), 84.3 (C-3C), 84.2 (C-3D),
83.7(3) (C-2E), 83.7(1) (C-2F), 82.7 (C-3E), 82.6 (C-3F), 81.1
Methyl 2,3-di-O-benzyl-5-O-palmitoyl-b-D-arabinofuranosyl-
(1→2)-3-O-benzyl-5-O-palmitoyl-a-D-arabinofuranosyl-(1→3)-
[2,3-di-O-benzyl-5-O-palmitoyl-b-D-arabinofuranosyl-(1→2)-3-O-
benzyl-5-O-palmitoyl-a-D-arabinofuranosyl-(1→5)]-2-O-benzyl-a-
D-arabinofuranoside (23)
Isolated 69% as a colorless oil: Rf 0.43 (4 : 1 hexane–EtOAc); [a]D
+9.8 (c 0.3, CHCl3);1H NMR (600 MHz, CDCl3, dH) 7.37–7.20 (m,
35 H, Ar), 5.16 (s, 1H, H-1C), 5.14 (d, 1 H, J1E,2E = 4.5 Hz, H-1E),
5.03 (s, 1 H, H-1D), 4.96 (d, 1 H, J1F,2F = 4.4 Hz, H-1F), 4.86 (d, 1
H, J1B,2B = 0.8 Hz, H-1B), 4.72–4.65 (m, 4 H, PhCH2O), 4.61–4.57
(m, 3 H, PhCH2O), 4.55–4.44 (m, 6 H, PhCH2O), 4.42–4.39 (m, 2
H, PhCH2O, H-2C), 4.34 (dd, 1 H, J1D,2D = 1.1 Hz, J2D,3D = 2.8 Hz,
H-2D), 4.30–4.04 (m, 16 H, H-3B, H-5Fa, H-5Ea, H-5Fb, H-5Eb,
H-4F, H-4E, H-3F, H-3E, H-5Da, H-5Ca, H-5Db, H-5Cb, H-4D,
H-4C, H-4B), 4.02–3.93 (m, 6 H, H-2B, H-5Ba, H-2F, H-2E, H-
3D, H-3C), 3.79 (dd, 1 H, J4B,5Bb = 2.1 Hz, J5Ba,5Bb = 11.9 Hz, H-5Bb),
3.30 (s, 3 H, OCH3), 2.28–2.14 (m, 8 H, acyl CH2 ¥ 4), 1.58–1.48
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(C-4B), 80.4 (C-4F), 80.3 (C-4E), 79.9 (C-3B), 78.9 (C-4C), 78.7
(C-4D), 72.5(0) (PhCH2O), 72.4(7) (PhCH2O), 72.4(2) (PhCH2O ¥
2), 72.3 (PhCH2O ¥ 2), 71.8 (PhCH2O), 66.0(0) (C-5C), 65.9 (C-
5D), 65.5 (C-5B), 63.6 (C-5E), 63.5 (C-5F), 54.7 (OCH3), 34.0(4)
(acyl CH2), 34.0(1) (acyl CH2), 33.9(9) (acyl CH2), 33.9(7) (acyl
CH2), 29.7(2) (acyl CH2), 29.6(7) (acyl CH2), 29.5(7) (acyl CH2),
29.5(0) (acyl CH2), 29.3(7) (acyl CH2), 29.2(9) (acyl CH2), 29.2(1)
(acyl CH2), 29.1(6) (acyl CH2), 24.8(3) (acyl CH2), 24.8(1) (acyl
CH2), 22.7 (acyl CH2), 14.1 (acyl CH3). ESIMS: m/z calcd for
[C163H254O25Na]+: 2634.8502. Found: 2634.8496.
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This work was supported by the Alberta Ingenuity Centre for
Carbohydrate Science and the Natural Sciences and Engineering
Research Council of Canada. M.R.R. is supported by an AHFMR
Ph.D. studentship. We thank Dr Sara Duncan (AstraZeneca,
UK) for sending us the pulse sequences for the CSSF NMR
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