Synthesis of the complete series of mono acetates of N-acetyl-d-neuraminic acid

Article abstract of DOI:10.1039/c1ob06348k

The short syntheses of each of the mono-acetates of N-acetyl-d-neuraminic acid are reported. These are important molecules for studying the mechanism and function of enzymes which utilise Neu5Ac as a substrate. However, until now these molecules were not

Full text of DOI:10.1039/c1ob06348k

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PAPER
Synthesis of the complete series of mono acetates of N-acetyl-D-neuraminic
acid†
Paul A. Clarke,*a Nimesh Mistrya and Gavin H. Thomasb
Received 8th August 2011, Accepted 30th September 2011
DOI: 10.1039/c1ob06348k
The short syntheses of each of the mono-acetates of N-acetyl-D-neuraminic acid are reported. These
are important molecules for studying the mechanism and function of enzymes which utilise Neu5Ac as
a substrate. However, until now these molecules were not available as pure compounds and instead had
to be studied as mixtures. Neu4,5Ac2 and Neu5,8Ac2 were synthesised from a common precursor in 2
and 4 steps respectively, while Neu2,4Ac2 and Neu5,7Ac2 were synthesised in 3 and 4 steps respectively
from another common precursor. Both precursors could be easily prepared in 3 steps from Neu5Ac
itself. Importantly, no scrambling of the anomeric stereochemistry was detected throughout the course
of these syntheses.
As well as the common sialic acid Neu5Ac, many organisms
contain Neu5Ac derivatives that are O-acylated, which have also
been linked with distinct biological functions, such as recognition
sites for influenza C virus and human coronoviruses that bind
to 9-O-acetylated Neu5Ac (Neu5,9Ac2 2).3 Bacteria have also
been show to incorporate acylated Sias into the lipopolysaccharide
and capsule, and more recently to use O-acylated sialic acids as
Introduction
N-Acetyl-D-neuraminic acid 1 (Neu5Ac) is the most common of
the sialic acids (Sias) that play important roles in cell biology.
Sias are found as the terminal sugar in numerous glycoproteins
and glycolipids where they confer a negative charge to the cell
surface and play specific roles in recognition of other cell types.
The most high-profile function of sialic acid is as a substrate for the
sialic acid cleaving neuraminidases of influenza A and B,1 which
are essential enzymes for the infection cycle of the virus. Sias are
also important nutrient for many pathogenic bacteria and some
bacteria and parasites such as Trypanosoma cruzi can utilise sialic
acid to decorate their own cells surface.2 Neu5Ac that has been
taken into bacterial cells is catabolised by an N-acetylneuraminate
lyase (NanA) which cleaves Neu5Ac into N-acetylmannosamine
and pyruvate (Fig. 1).2a
nutrients. Hence these bacteria require sialate O-acetylesterases,
at least one of which is know to act on free sialic acids.4 As there
are now a range of eukaryotic, bacterial and viral enzymes that
have been identified that act on acylated Sias as substrates, precise
chemical tools to understand their mechanisms and specificity are
needed.
Since the inception of these studies in the 1980s, the O-acylated
Sias (Fig. 2) used have generally been from biological sources,
and this has complicated and limited the scope of possible
investigations. Specifically, the majority of work is carried out
on O-acylated neuraminic acids isolated from bovine submax-
illary mucin or other highly sialylyated protein preparation.5
The isolation procedure generally involves hydrolysis of the
glycoconjugates with 0.5 M formic acid at 80 ◦C, which can
Fig. 1 Conversion of Neu5Ac to N-acylmannosamine and pyruvate by
Neu5Ac lyase.
aDepartment of Chemistry, University of York, Heslington, York, UK, YO10
5DD. E-mail: paul.clarke@york.ac.uk; Fax: +44 1904 322516; Tel: +44
1904 322614
bDepartment of Biology, University of York, Heslington, York, UK, YO10
5DD
† Electronic supplementary information (ESI) available: Experimental
details and spectroscopic characterisation for all compounds not reported
in the experimental section. Copies of 1H and 13C NMR spectra of all new
compounds. See DOI: 10.1039/c1ob06348k
Fig. 2 Mono-O-acetates of Neu5Ac.
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lead to hydrolysis of the acetates and acetate migration. The
subsequent purification procedure of dialysis, ethereal extraction
and ion exchange chromatography also leads to partial (30–60%)
hydrolysis of the acetate groups.5 It should be noted that this
procedure only provides a mixture of O-acylated neuraminic
acids (both mono and per-acylated) and not purified samples
of individual O-acylated neuraminic acids. The mixture can be
assayed by HPLC to give a trace where the peaks are assigned
to individual O-acylated neuraminic acids without any further
authentication of their structure.6 To our knowledge the only O-
acylated neuraminic acids to be definitively characterised are the
9-OAc derivative of Neu5Ac (Neu5,9Ac2 2), which is commercially
available and the 4-OAc derivative of Neu5Ac (Neu4,5Ac2 3)
which, along with 2, has been synthesised previously.7 It would
seem that the assignment of the other traces in the HPLC of
mixed O-acylated neuraminic acids is tenuous at best. Therefore,
any studies reported on the use of O-acylated neuraminic acids
as substrates in enzyme assays (with the exception of 2) use
this mixture of O-acylated neuraminic acids rather than specific
individual molecules and are hence open to possible interpretation
errors.
In order to try and avoid these problems we chose two
common intermediates which could be used as staging points
for our syntheses: 8 which could be used for the synthesis of
both 3 and 4; and 9 which could be used for the synthesis of
both 5 and 6 (Fig. 3). While this would, if successful, obviate
the potential problem of competing acetate hydrolysis during
the late stage removal of the methyl ester, it would also mean
carrying an unprotected carboxylic acid group through a number
of synthetic transformations, something which had not been
attempted previously in Neu5Ac chemistry. We anticipated that
this strategy was worth pursuing as it should simplify the synthesis
substantially.
We recently became aware of this limitation when we decided
to investigate the effect of mono-O-acylated neuraminic acids on
a specific N-acetylneuraminate lyase. Realising the limitations
inherent in this current ‘state-of-the-art’, and that the lack of
authentic characterised standards of individual mono-O-acylated
neuraminic acids would severely limit our study and complicate
the interpretation of results, we embarked upon a program for the
unambiguous synthesis and characterisation of each of the mono-
O-acylated neuraminic acids 2–6 shown in Fig. 2. We reasoned
that this would provide a valuable set of standards, not only for
ourselves, but also for others investigating the ability of enzymes
to process mono-O-acylated neuraminic acids.
Fig. 3 Common synthetic strategy for the syntheses of 3, 4, 5 and 6.
Our investigations commenced with the synthesis of 8, the
common intermediate en route to 3 and 4 (Scheme 1). Neu5Ac 1
was quantitatively converted into its methyl ether 10 by the action
of MeOH and acid resin,11a which was in turn converted into
the benzylidine acetal 11. Benzylidine acetal 11 was transformed
smoothly into 8 by saponification of the methyl ester using
the Me3SnOH conditions developed by Nicolaou et al.,12 thus
removing the difficult problem of the selective saponification of a
methyl ester in the presence of an O-acetate. With 8 in hand, its
conversion into both 3 and 4 could be attempted.
Results and discussion
An investigation of the literature showed that there were published
routes to both 2 and 3. While the synthesis of 2 was achieved in 1
step from Neu5Ac 1,7 the synthesis of 3 took a not unreasonable
5 steps.7 In another report the attempted synthesis of 5 was
aborted due to acylation at 2-OH, and so the authors settled
for the synthesis of the a-methyl glycoside of methyl N, 7-O-
diacetylneuriminate 7 (Fig. 2).8a We were determined to overcome
these difficulties and devise syntheses of 3–6 which could be used
to produce useful quantities of material for biological evaluation in
the most expedient manner possible. One point of concern was that
most of the Neu5Ac chemistry literature protects the carboxylic
acid function as an ester as the first step in the synthesis and then
carries it through to the end. Some reports do not even attempt
to deprotect the ester at the end of the synthetic sequence,8,9 or
if they do it involves the simultaneous removal of the acetates on
the hydroxyl groups.10 This generates two problems, firstly that to
access our desired molecules the ester will have to be removed at
some point and the conditions for its removal will probably not be
compatible with O-acylation at any of the hydroxyl groups, and
secondarily, that scrambling of the a- and b-anomers has been
shown to occur in a number of systems where the carboxylic acid
is protected as an ester and the 2-OH ‘activated’.10a,11
Scheme 1 Reagents and conditions: (i) MeOH, acidic resin, rt, 100%; (ii)
PhCHO, TsOH, DMF, rt, 42%; (iii) Me3SnOH, CH2Cl2, rt, 55%.
Benzylidine acetal 8 was converted into 3 in two steps (Scheme
2). Treatment of 8 with Ac2O, pyridine and DMAP gave 12 in a
respectable 64% yield. This demonstrated that the 4-OH can be
acylated in the presence of the 8-OH. The previous synthesis of
3 exploited the selective acylation of 4-OH in the presence of the
most hindered 7-OH, where the 8-OH and 9-OH were protected
as an acetonide.7 The target, Neu4,5Ac2 3, was revealed by the
quantitative hydrogenolysis of benzylidine acetal 12, using 10%
Pd/C in MeOH. This completed the synthesis of 3 in 5 steps.
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Scheme 4 Reagents and conditions: (i) Ac2O, py, DMAP, CH2Cl2, rt, 55%;
(ii) 60% AcOH, 82%; (iii) TBAF, THF/H2O, rt, 87%; (iv) TESOTf, Et2O,
MeCN, -20 ◦C, 67%; (v) Ac2O, py, rt, 75%; (vi) 60% AcOH, 72%; (vii)
TBAF, THF/H2O, rt, 81%.
Scheme 2 Reagents and conditions: (i) Ac2O, py, DMAP, CH2Cl2, rt, 64%;
(ii) 10% Pd/C, H2, MeOH, 100%; (iii) TBSCl, im, DMF, rt, 67%; (iv) Ac2O,
py, DMAP, CH2Cl2, rt, 75%; (v) 10% Pd/C, H2, MeOH, 100%; (vi) TBAF,
THF/H2O, rt, 81%.
as the b-anomer. The TBS-ether was removed by the action of
TBAF in THF in 87% to give the desired Neu2,5Ac2 6. This
completed the synthesis of the previously unreported 6 in only 6
steps. The conversion of 9 into Neu5,7Ac2 5 commenced with the
TES-protection of the anomeric 2-OH with TESOTf at -20 ◦C
to give 18 in 67% yield (Scheme 4). Again we were able to effect
the derivatisation of the 2-OH, in the presence of the 7-OH with
a bulky silylating reagent, without anomerisation. The free 7-OH
was then acylated with Ac2O in pyridine to give 19 in 75% yield.
Once again the acetonide was removed in 72% yield by the action of
60% AcOH which remarkably left the 2-OTES hemiketal intact.
Removal of the both silyl groups was achieved with TBAF in
THF and provided the desired Neu5,7Ac2 5 in 81% yield. This
completed the synthesis of previously unknown 5 in 7 steps.
With four of the mono-acetates synthesised the series was
completed with the synthesis of Neu5,9Ac2 2 according the
procedure of Ogura et al., which involved stirring 1 with trimethyl
orthoacetate and TsOH.7
Neu5,8Ac2 4 was prepared from the same intermediate 8 by
TSB-ether formation at the more reactive 4-OH to give 13 in 67%
yield. Acylation of the 8-OH of 13 with Ac2O, pyridine and DMAP
provided 14 in 75% yield. The benzylidine acetal was removed by
hydrogenolysis over 10% Pd/C and the resulting compound was
treated with TBAF in THF to remove the silyl ether to reveal
the desired Neu5,8Ac2 4 in 81% yield. This provided previously
unknown 4 in 7 steps (Scheme 2).
With the syntheses of Neu4,5Ac2 3 and Neu5,8Ac2 4 complete,
we next turned our attention to the synthesis of 9, the precursor
for our planned syntheses of Neu5,7Ac2 5 and Neu2,5Ac2 6. The
synthesis of 9 proceeded according to Scheme 3. Methyl ester 10
was converted into acetonide 15 in 71% yield by the action of 2,2-
DMP, acetone and TsOH.7 Acetonide 15 was then silylated at the
4-OH with TBSCl, imidazole in DMF in 82% yield. The desired
staging post 9 was revealed by saponification the methyl ester with
Me3SnOH in CH2Cl2 in a 58% yield.
Conclusions
We have developed the first unambiguous and selective syntheses
of each of the previously unreported mono-O-acetates of Neu5Ac
1. Our syntheses utilises common synthetic intermediates which
are accessible in only 3 steps from Neu5Ac 1. These intermediates
contain an unprotected carboxylic acid function which allowed
us to complete the syntheses Neu2,5Ac2 6 (3 steps), Neu5,7Ac2 5
(4 steps) and Neu5,8Ac2 4 (4 steps) and the previously reported
Neu4,5Ac2 3 (2 steps) without concern for competing acetate
removal or migration, which has been problematic in other
studies. We have also shown that in competing acylation and
silylation reactions the reactivity of 4-OH > 8-OH > 2-OH and
4-OH > 2-OH > 7-OH, thus enabling future protecting group
manipulations to be planned. Importantly, our syntheses do not
suffer from epimerisation of the anomeric position, even when
the 2-OH is activated as an acetate or masked as a TES-ether.
Such anomerisation has been problematic in earlier work on the
synthesis of Neu5Ac derivatives. Our syntheses have uncovered
some surprising functional group compatibilities, selectivities and
reactivities, and the brevity of these syntheses enables the multi-
milligram production of 3–6 of a purity suitable to be used as
standards in biochemical assays.
Scheme 3 Reagents and conditions: (i); 2,2-DMP, acetone, TsOH, rt, 71%;
(ii) TBSCl, im, DMAP, rt, 82%; (iii) Me3SnOH, CH2Cl2, rt, 58%.
With 9 in hand we could now examine its conversion to
Neu2,5Ac2 6 and Neu5,7Ac2 5 (Scheme 4). Of the two free
hydroxyl groups present in 9, it was difficult to predict which
of either the 2-OH or 7-OH would be the most reactive to the
acylation conditions. The 7-OH is subject to the steric congestion
imposed by the pyranose and acetonide rings, while 2-OH is
effectively a tertiary alcohol. When we treated 9 with Ac2O,
pyridine and DMAP we found that the anomeric 2-OH was
acylated preferentially in 55% yield, with no sign of acylation
of the 7-OH. Remarkably, treatment of this 2-OAc with 60%
AcOH gave 17 in 82% yield, with the 2-OAc untouched and still
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5-Acetamido-4-O-acetyl-3,5-dideoxy-7,9-O-benzylidene-D-
glycero-D-galacto-nonulopyranosic acid (12)
Experimental
General methods
To a solution of 8 (40 mg, 0.10 mmol) in CH2Cl2 (2 mL) stirring
at room temperature under a N2 atmosphere was treated with
Ac2O (10 mL, 0.11 mmol), pyridine (12 mL, 0.15 mmol) and
DMAP (18 mg, 0.15 mmol). The reaction was stirred for 18 h
then partitioned between CH2Cl2 (20 mL) and a saturated aqueous
solution of NH4Cl (20 mL). The organic layer was washed with
brine (20 mL), dried (MgSO4) and concentrated in vacuo to give
an orange oil that was purified by flash column chromatography
using a 99 : 1 to 9 : 1 CH2Cl2:MeOH gradient to give a white solid
(28 mg, 64%). [a]D25 - 15 (c 1.0, MeOH); mp: 195–197 ◦C; nmax
(NaCl) 3450–3287 (br), 2972, 2722, 1772, 1756, 1623, 1561 cm-1;
dH (400 MHz, DMSO-d6): 8.07 (1H, d, J = 8.5 Hz, H-10), 7.56–
7.54 (2H, m, Ph), 7.39–7.38 (1H, m, Ph), 7.34–7.33 (2H, m, Ph),
6.44 (1H, d, J = 2.0 Hz, O-H2), 5.25 (1H, s, H-14), 4.35 (1H, d,
J = 5.5 Hz, O-H8), 4.21–4.14 (2H, m, H-4 + H-9), 3.75 (1H, d,
J = 11.5 Hz, H-6), 3.66–3.58 (2H, m, H-7+H-9), 3.54–3.76 (2H,
m, H-5 + H-8), 2.10 (1H, dd, J = 12.0, 5.0 Hz, H-3eq), 1.94 (3H, s,
H-20), 1.87 (3H, s, H-12), 1.75 (1H, dd, J = 12.0, 12.0 Hz, H-3ax)
ppm; dC (100 MHz, DMSO-d6) 172.0, 171.3, 168.1, 136.1, 134.5,
129.5, 129.2, 100.7, 95.3, 77.2, 71.5, 70.9, 70.5, 69.7, 53.1, 40.0,
22.5, 21.4 ppm; LRMS (ESI): m/z 440 (M+ + H), 462 (M+ + Na);
HRMS: found (M+ + H) 440.1473 C20H26NO10 requires 440.1478.
For general experimental details, including information on solvent
purification and the spectrometers used in this research as well
as for procedures, spectroscopic and crystallographic data not
reported below, see ESI.†
Methy 5-acetamido-3,5-dideoxy-7,9-O-benzylidene-D-glycero-D-
galacto-nonulopyranosonate (11)
To a solution of N-acetyl neuraminic acid methyl ester 10 (100 mg,
0.323 mmol) stirring at room temperature under a N2 atmosphere
was added benzaldehyde (37.7 mg, 0.355 mmol) followed by p-
toluenesulfonic acid (5 mg). The reaction was stirred for 20 h
then was concentrated in vacuo and purified by flash column
chromatography using a 0–5% MeOH:CH2Cl2 gradient to afford
a white solid (55.8 mg, 42%). [a]2D5 -24 (c 1.0, MeOH); mp: 199–
201 ◦C; nmax (NaCl) 3435–3325 (br), 2954, 1749, 1620, 1559 cm-1;
dH (400 MHz, DMSO-d6): 8.11 (1H, d, J = 8.5 Hz, H-10), 7.56–
7.54 (2H, m, Ph), 7.39–7.38 (1H, m, Ph), 7.34–7.33 (2H, m, Ph),
6.44 (1H, d, J = 2.0 Hz, O-H2), 5.19 (1H, s, H-15), 4.85 (1H, d,
J = 6.5 Hz, O-H4), 4.35 (1H, d, J = 5.5 Hz, O-H8), 4.19–4.15
(1H, m, H-9), 3.84 (1H, ddd, J = 11.0, 11.0, 5.5 Hz, H-4), 3.74
(1H, d, J = 11.5 Hz, H-6), 3.70 (3H, s, H-14), 3.65–3.55 (2H, m,
H-7+H-9), 3.51–3.46 (2H, m, H-5 + H-8), 2.02 (1H, dd, J = 12.0,
5.0 Hz, H-3eq), 1.89 (3H, s, H-12), 1.75–1.68 (1H, m, H-3ax) ppm;
dC (100 MHz, DMSO-d6) 172.0, 170.3, 136.2, 134.4, 129.6, 129.2,
100.6, 95.2, 77.1, 71.5, 70.5, 69.7, 65.6, 53.1, 52.4, 40.0, 22.6 ppm;
LRMS (ESI): m/z 412 (M+ + H), 434 (M+ + Na); HRMS: found
(M+ + H) 412.1532 C19H26NO9 requires 412.1529.
5-Acetamido-3,5-dideoxy-4-O-acetyl-D-glycero-D-galacto-
nonulopyranosic acid (3)
To a solution of 12 (20 mg, 0.046 mmol) in MeOH (3 mL) was
added 10% Pd/C (10 mg, 50% wt). The reaction was stirred at
room temperature andplacedunder vacuo then purged with H2 (via
balloon). This procedure was repeated twice before the reaction
was stirred for 2 h. The reaction was filtered through Celite and the
solids washed with MeOH (20 mL). The combined organics were
concentrated in vacuo to give a colourless oil (16 mg, quant). dH
(400 MHz, DMSO-d6): 8.08 (1H, d, J = 10.0 Hz, H-10), 6.74 (1H,
d, J = 2.0 Hz, O-H2), 4.56 (1H, d, J = 6.0 Hz, O-H7), 4.34 (1H, d,
J = 5.5 Hz, O-H8), 4.25 (1H, t, J = 6.0 Hz, O-H9), 4.21–4.18 (1H,
m, H-4), 3.73 (1H, dd, J = 10.5, 1.5 Hz, H-6), 3.60 (1H, br d, J =
6.0 Hz, H-9), 3.53–3.46 (1H, m, H-8), 3.50 (1H, ddd, J = 10.5, 10.0,
10.0 Hz, H-5), 3.33 (1H, dd, J = 11.0, 7.0 Hz, H-9), 3.21 (1H, d, J =
8.0 Hz, H-7), 2.10 (1H, dd, J = 12.0, 5.0 Hz, H-3eq), 1.95 (3H, s,
H-15), 1.89 (3H, s, H-12), 1.75 (1H, dd, J = 12.0, 12.0 Hz, H-3ax)
ppm; dC (100 MHz, DMSO-d6): 171.8, 171.5, 168.1, 94.7, 70.8,
70.4, 69.8, 69.2, 63.6, 53.1, 39.9, 22.7, 21.5 ppm. Other structural
data matched that reported in the literature.
5-Acetamido-3,5-dideoxy-7,9-O-benzylidene-D-glycero-D-galacto-
nonulopyranosic acid (8)
To a solution of 11 (250 mg, 0.608 mmol) in CH2Cl2 (10 mL)
stirring at room temperature under a N2 atmosphere was added
SnMe3OH (549 mg, 3.04 mmol). The reaction was stirred for 48 h
and was concentrated in vacuo to give a yellow oil. The crude
material was purified by flash column chromatography using a
9 : 1 CH2Cl2:MeOH gradient to give a white solid (132 mg, 55%).
[a]2D5 - 19 (c 1.0, MeOH); mp: 191–193 ◦C; nmax (NaCl) 3442–3307
(br), 2974, 2746, 1744, 1618, 1565 cm-1; dH (400 MHz, DMSO-d6):
8.11 (1H, d, J = 8.5 Hz, H-10), 7.56–7.54 (2H, m, Ph), 7.39–7.38
(1H, m, Ph), 7.34–7.33 (2H, m, Ph), 6.44 (1H, d, J = 2.0 Hz, O-
H2), 5.19 (1H, s, H-14), 4.84 (1H, d, J = 6.5 Hz, O-H4), 4.34 (1H,
d, J = 5.5 Hz, O-H8), 4.19-4.15 (1H, m, H-9), 3.84 (1H, ddd, J =
12.0, 11.0, 5.0 Hz, H-4), 3.74 (1H, d, J = 11.5 Hz, H-6), 3.66–
3.54 (2H, m, H-7+H-9), 3.51–3.46 (2H, m, H-5 + H-8), 1.98 (1H,
dd, J = 12.0, 5.0 Hz, H-3eq), 1.89 (3H, s, H-12), 1.70 (1H, dd,
J = 12.0, 12.0 Hz, H-3ax) ppm; dC (100 MHz, DMSO-d6) 172.0,
171.3, 136.2, 134.6, 129.5, 129.2, 100.6, 95.0, 77.2, 71.5, 70.5, 69.7,
65.5, 53.1, 40.0, 22.6 ppm; LRMS (ESI): m/z 398 (M+ + H), 420
(M+ + Na); HRMS: found (M+ + H) 398.1379 C18H24NO9 requires
398.1373.
5-Acetamido-4-O-tert-butyldimethylsilyl-3,5-dideoxy-7,9-O-
benzylidene-D-glycero-D-galacto-nonulopyranosic acid (13)
Imidazole (170 mg, 2.5 mmol) and tert-butyldimethylsilyl chloride
(151 mg, 1.0 mmol) were added to a solution of 8 (200 mg,
0.5 mmol) in DMF (5 mL) at 0 ◦C. The solution was stirred
at room temperature for 16 h. The solvent was removed in vacuo
then was partitioned between CH2Cl2 (50 mL) and H2O (50 mL).
The aqueous layer was extracted with CH2Cl2 (2x 50 mL) and
the combined organics were washed with brine (150 mL), dried
(MgSO4) and concentrated to give a yellow oil. The crude material
was purified by flash column chromatography using a 0% to 5%
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MeOH : CH2Cl2 gradient to give a white solid (170 mg, 67%). [a]D25
- 9 (c 1.0, MeOH); mp: 192–194 ◦C; nmax (NaCl) 3439–3321 (br),
2976, 2740, 1748, 1621, 1570 cm-1; dH (400 MHz, DMSO-d6): 8.06
(1H, d, J = 8.5 Hz, H-10), 7.57–7.54 (2H, m, Ph), 7.39–7.36 (1H,
m, Ph), 7.34–7.32 (2H, m, Ph), 6.51 (1H, d, J = 2.0 Hz, O-H2),
5.18 (1H, s, H-14), 4.35 (1H, d, J = 5.5 Hz, O-H8), 4.19–4.15 (1H,
m, H-9), 4.06–4.02 (1H, m, H-4), 3.72 (1H, d, J = 12.0 Hz, H-6),
3.67–3.58 (2H, m, H-7 + H-9), 3.54–3.44 (2H, m, H-5 + H-8), 2.09
(1H, dd, J = 12.0, 5.0 Hz, H-3eq), 1.88 (3H, s, H-12), 1.75 (1H, dd,
J = 12.0, 12.0 Hz, H-3ax) 0.81 (9H, s, H-22), 0.04 (3H, s, H-21),
0.03 (3H, s, H-21) ppm; dC (100 MHz, DMSO-d6) d 171.9, 171.4,
136.0, 134.6, 129.5, 129.2, 100.5, 95.3, 77.2, 71.5, 70.5, 69.7, 69.3,
53.3, 40.0, 25.8, 22.6, 17.8, -4.3, -4.6 ppm; LRMS (ESI): m/z 512
(M+ + H), 534 (M+ + Na); HRMS: found (M+ + H) 512.2243
C24H38NO9Si requires 512.2238.
H-7), 2.10 (1H, dd, J = 12.0, 5.0 Hz, H-3eq), 1.95 (3H, s, H-15),
1.89 (3H, s, H-12), 1.75 (1H, dd, J = 12.0, 12.0 Hz, H-3ax) ppm;
dC (100 MHz, DMSO-d6) 171.8, 171.5, 168.1, 94.7, 70.8, 70.4,
69.8, 69.2, 63.6, 53.1, 39.9, 22.7, 21.5 ppm; LRMS (ESI): m/z 466
(M+ + H), 488 (M+ + Na); HRMS: found (M+ + H) 466.2027
C19H36NO10Si requires 466.2030.
5-Acetamido-3,5-dideoxy-8,9-O-isopropylidene-4-O-tert-
butyldimethylsilyl-D-glycero-D-galacto-nonulopyranosic acid (9)
To a solution of 16 (200 mg, 0.45 mmol) in CH2Cl2 stirring at
room temperature under a N2 atmosphere was added SnMe3OH
(164 mg, 0.91 mmol). The reaction was stirred for 18 h and
was concentrated in vacuo to give a yellow oil. The crude
material was purified by flash column chromatography using a
9 : 1 CH2Cl2:MeOH gradient to give a white solid (120 mg, 58%).
[a]2D5 -17 (c 1.0, MeOH); mp: 180–182 ◦C; nmax (NaCl) 3571, 3491–
3274 (br), 2731, 1752, 1620, 1575 cm-1; dH (400 MHz, DMSO-d6):
8.05 (1H, d, J = 9.0 Hz, H-10), 6.87 (1H, s, O-H2), 4.53 (1H, br
s, O-H7), 4.06–4.02 (1H, m, H-4), 3.98 (1H, dd, J = 12.0, 6.0 Hz,
H-8), 3.92–3.86 (2H, m, H-6 + H-5), 3.73 (1H, br d, J = 10.5 Hz,
H-9), 3.64 (1H, br d, J = 10.5 Hz, H-9), 3.51 (1H, br d, J = 6.0 Hz,
H-7), 2.02 (1H, dd, J = 12.0, 5.0 Hz, H-3eq), 1.84 (3H, s, H-12),
1.62 (1H, dd, J = 12.0, 12.0 Hz, H-3ax), 1.28 (3H, s, H-15), 1.23
(3H, s, H-15), 0.82 (9H, s, H-19), 0.04 (3H, s, H-17), 0.03 (3H, s,
H-17) ppm; dC (100 MHz, DMSO-d6): 171.8, 171.5, 107.5, 94.7,
76.1, 71.9, 68.4, 65.6, 65.2, 52.9, 39.9, 26.6, 25.8, 25.6, 22.6, 17.5,
-4.6, -4.8 ppm; LRMS (ESI): m/z 464 (M+ + H), 486 (M+ + Na);
HRMS: found (M+ + H) 464.2234 C20H38NO9Si requires 464.2238.
5-Acetamido-4-O-tert-butyldimethylsilyl-8-O-acetyl-3,5-dideoxy-
7,9-O-benzylidene-D-glycero-D-galacto-nonulopyranosic acid (14)
To a solution of 13 (150 mg, 0.29 mmol) in pyridine (5 mL)
stirring at room temperature under a N2 atmosphere was treated
with Ac2O (30 mL, 0.32 mmol. The reaction was stirred for 24 h
then concentrated in vacuo to give an orange oil that was purified
by flash column chromatography using a 1 : 1 to 3 : 1 EtOAc:
petroleum ether gradient to give a white solid (115 mg, 72%).
[a]2D5 - 15 (c 1.0, MeOH); mp: 188–190 ◦C; nmax (NaCl) 3572,
3489–3255 (br), 2966, 2749, 1776, 1750, 1626, 1571 cm-1; dH (400
MHz, DMSO-d6): 8.10 (1H, d, J = 8.5 Hz, H-10), 7.57–7.53 (2H,
m, Ph), 7.39–7.35 (1H, m, Ph), 7.36–7.32 (2H, m, Ph), 6.44 (1H,
d, J = 2.0 Hz, O-H2), 5.19 (1H, s, H-14), 4.21-4.18 (1H, m, H-9),
4.06–4.02 (1H, m, H-4), 3.99–3.95 (1H, m, H-8), 3.76 (1H, d, J =
12.0 Hz, H-6), 3.65–3.56 (2H, m, H-7 + H-9), 3.52 (1H, ddd, J =
12.0, 12.0, 12.0 Hz, H-5), 2.09 (1H, dd, J = 12.0, 5.0 Hz, H-3eq),
1.95 (3H, s, H-20), 1.89 (3H, s, H-12), 1.72 (1H, dd, J = 12.0,
12.0 Hz, H-3ax) 0.80 (9H, s, H-22), 0.04 (3H, s, H-21), 0.03 (3H, s,
H-21) ppm; dC (100 MHz, DMSO-d6) 171.9, 171.3, 169.9, 135.9,
134.6, 129.6, 129.2, 100.5, 95.3, 77.2, 72.4, 71.5, 70.5, 69.6, 53.1,
40.0, 25.8, 22.6, 20.7, 17.7, -4.3, -4.6 ppm; LRMS (ESI): m/z 554
(M+ + H), 576 (M+ + Na); HRMS: found (M+ + H) 512.2348
C26H40NO10Si requires 512.2343.
5-Acetamido-2-O-acetyl-3,5-dideoxy-4-O-tert-butyldimethylsilyl-
D-glycero-D-galacto-nonulopyranosic acid (17)
To a solution of 9 (40 mg, 0.086 mmol) in CH2Cl2 (2 mL) stirring
at room temperature under a N2 atmosphere was treated with
Ac2O (11 mg, 0.10 mmol), pyridine (14 mg, 0.17 mmol) and
DMAP (21 mg, 0.17 mmol). The reaction was stirred for 18 h
then partitioned between CH2Cl2 (20 mL) and a saturated aqueous
solution of NH4Cl (20 mL). The organic layer was washed with
brine (20 mL), dried (MgSO4) and concentrated in vacuo to give
an orange oil that was purified by flash column chromatography
using a 1 : 2 to 3 : 1 EtOAc: petroleum ether gradient to give◦a white
solid (24 mg, 55%). [a]D25 -24 (c 1.0, MeOH); mp: 167–169 C; nmax
(NaCl) 3570, 3450–3201 (br), 2738, 1770, 1756, 1617, 1570 cm-1;
dH (400 MHz, DMSO-d6): 8.05 (1H, d, J = 9.0 Hz, H-10), 4.53
(1H, br s, O-H7), 4.05–4.01 (1H, m, H-4), 3.96 (1H, dd, J = 12.0,
6.0 Hz, H-8), 3.91–3.84 (2H, m, H-6 + H-5), 3.74 (1H, br d, J =
10.5 Hz, H-9), 3.62 (1H, br d, J = 10.5 Hz, H-9), 3.55 (1H, br d, J =
6.0 Hz, H-7), 2.07 (1H, dd, J = 12.0, 5.0 Hz, H-3eq), 1.92 (3H, s,
H-21), 1.82 (3H, s, H-12), 1.65 (1H, dd, J = 12.0, 12.0 Hz, H-3ax),
1.29 (3H, s, H-15), 1.25 (3H, s, H-15), 0.81 (9H, s, H-19), 0.04 (3H,
s, H-17), 0.03 (3H, s, H-17) ppm; dC (100 MHz, DMSO-d6): 171.8,
171.4, 169.5, 107.3, 97.5, 76.0, 71.7, 68.4, 65.3, 65.2, 52.7, 40.0,
26.6, 25.6, 25.8, 22.5, 21.1, 17.5, -4.6, -4.8 ppm; LRMS (ESI):
m/z 506 (M+ + H), 528 (M+ + Na); HRMS: found (M+ + H)
464.2234 C22H40NO10Si requires 506.2343.
5-Acetamido-8-O-acetyl-3,5-dideoxy-D-glycero-D-galacto-
nonulopyranosic acid (4)
To a solution of 14 (80 mg, 0.144 mmol) in MeOH (5 mL) was
added 10% Pd/C (24 mg, 50% wt). The reaction was stirred at
roomtemperatureandplaced under vacuo then purged with H2 (via
balloon). This procedure was repeated twice before the reaction
was stirred for 5 h. The reaction was filtered through Celite and the
solids washed with MeOH (50 mL). The combined organics were
concentrated in vacuo to give a colourless oil (66 mg, quant). [a]D25
- 15 (c 1.0, MeOH); mp: 177–179 ◦C; nmax (NaCl) 3506–3246 (br),
2968, 2752, 1778, 1753, 1623, 1573 cm-1; dH (400 MHz, DMSO-
d6):): 8.08 (1H, d, J = 10.0 Hz, H-10), 6.74 (1H, d, J = 2.0 Hz,
O-H2), 4.84 (1H, d, J = 6.0 Hz, O-H4), 4.34 (1H, d, J = 5.5 Hz,
O-H8), 4.25 (1H, t, J = 6.0 Hz, O-H9), 4.21–4.18 (1H, m, H-4),
3.73 (1H, dd, J = 10.5, 1.5 Hz, H-6), 3.60 (1H, br d, J = 6.0 Hz, H-
9), 3.53–3.46 (1H, m, H-8), 3.50 (1H, ddd, J = 10.5, 10.0, 10.0 Hz,
H-5), 3.33 (1H, dd, J = 11.0, 7.0 Hz, H-9), 3.21 (1H, d, J = 8.0 Hz,
A solution of the above compound (10 mg, 0.02 mmol) in 60%
AcOH (1 mL) was stirred for 3 h at 60 ◦C. The mixture was
concentrated in vacuo to yield a brown solid which was purified
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by flash column chromatography using a 9 : 1 CH2Cl2 : MeOH
gradient to yield a white solid (7.5 mg, 82%). [a]2D5 -24 (c 1.0,
MeOH); mp: 151–153 ◦C; nmax (NaCl) 3462–3247 (br), 2741, 1771,
1758, 1622, 1564 cm-1; dH (400 MHz, DMSO-d6): d 8.09 (1H, d,
J = 8.5 Hz, H-10), 4.54 (1H, br s, O-H7), 4.35 (1H, br d, J = 5.0 Hz,
O-H8), 4.22 (1H, br s, O-H9), 4.05–4.01 (1H, m, H-4), 3.67 (1H,
dd, J = 10.5, 1.5 Hz, H-6), 3.62 (1H, br d, H-9), 3.55–3.48 (1H,
m, H-8), 3.50 (1H, ddd, J = 10.0, 10.0, 5.0 Hz, H-5), 3.29 (1H, dd,
J = 11.0, 7.0 Hz, H-9), 3.16 (1H, d, J = 8.0 Hz, H-7), 2.07 (1H, dd,
J = 12.5, 5.0 Hz, H-3eq), 1.92 (3H, s, H-19), 1.89 (3H, s, H-11),
1.67 (1H, dd, J = 13.0, 11.2 Hz, H-3ax), 0.81 (9H, s, H-17), 0.04
(3H, s, H-15), 0.03 (3H, s, H-15) ppm; dC (100 MHz, DMSO-d6)
171.8, 170.3, 169.5, 97.5, 70.5, 69.7, 69.1, 65.6, 63.6, 53.1, 40.0,
22.5, 21.1, 17.5, -4.6, -4.8 ppm; LRMS (ESI): m/z 466 (M+ + H),
488 (M+ + Na); HRMS: found (M+ + H) 466.2034 C19H36NO10Si
requires 466.2030.
H-9), 3.64 (1H, br d, J = 10.5 Hz, H-9), 3.49 (1H, br d, J = 6.0 Hz,
H-7), 2.10 (1H, dd, J = 12.0, 5.0 Hz, H-3eq), 1.82 (3H, s, H-12),
1.69 (1H, dd, J = 12.0, 12.0 Hz, H-3ax), 1.27 (3H, s, H-15), 1.22
(3H, s, H-15), 0.91 (9H, t, J = 8.0 Hz, H-21), 0.81 (9H, s, H-19),
0.50 (6H, q, J = 8.0 Hz), 0.04 (3H, s, H-17), 0.03 (3H, s, H-17)
ppm; dC (100 MHz, DMSO-d6): 171.8, 171.4, 107.3, 95.9, 76.1,
71.9, 68.5, 65.4, 65.0, 53.1, 40.0, 26.7, 25.8, 25.6, 22.6, 17.5, 6.9,
4.9, -4.6, -4.8 ppm; LRMS (ESI): m/z 578 (M+ + H), 600 (M+
+ Na); HRMS: found (M+ + H) 578.3107 C26H52NO9Si2 requires
578.3102.
5-Acetamido-7-O-acetyl-3,5-dideoxy-8,9-O-isopropylidene-2-O-
triethylsilyl-4-O-tert-butyldimethylsilyl-D-glycero-D-galacto-
nonulopyranosic acid (19)
To a solution of 18 (100 mg, 0.173 mmol) in pyridine (2 mL)
stirring at room temperature under a N2 atmosphere was treated
with Ac2O (33 mL, 0.347 mmol. The reaction was stirred for 18 h
then partitioned between CH2Cl2 (20 mL) and a saturated aqueous
solution of NH4Cl (20 mL). The organic layer was washed with
brine (20 mL), dried (MgSO4) and concentrated in vacuo to give
an orange oil that was purified by flash column chromatography
using a 1 : 2 to 3 : 1 EtOAc : petroleum ether gradient to give a white
solid (80 mg, 75%). [a]D25 -22 (c 1.0, MeOH); mp: 174–176 ◦C; nmax
(NaCl) 3564, 2716, 1773, 1750, 1630, 1569 cm-1; dH (400 MHz,
DMSO-d6): 7.91 (1H, d, J = 9.0 Hz, H-10), 4.05–4.01 (1H, m,
H-4), 3.98 (1H, dd, J = 12.0, 6.0 Hz, H-8), 3.91–3.84 (2H, m, H-6
+ H-5), 3.74 (1H, br d, J = 10.5 Hz, H-9), 3.70 (1H, d, J = 6.0 Hz,
H-7), 3.64 (1H, br d, J = 10.5 Hz, H-9), 2.08 (1H, dd, J = 12.0,
5.0 Hz, H-3eq), 1.90 (3H, s, H-15), 1.82 (3H, s, H-12), 1.65 (1H,
dd, J = 12.0, 12.0 Hz, H-3ax), 1.28 (3H, s, H-17), 1.24 (3H, s,
H-17), 0.90 (9H, t, J = 8.0 Hz, H-19), 0.81 (9H, s, H-21), 0.50 (6H,
q, J = 8.0 Hz, H-22), 0.04 (3H, s, H-19), 0.03 (3H, s, H-19) ppm;
dC (100 MHz, DMSO-d6): 171.8, 171.5, 171.3, 107.3, 97.8, 76.1,
71.7, 70.4, 70.0, 65.6, 53.1, 39.9, 26.6, 25.7, 25.4, 22.5, 17.5, 6.9,
4.9, -4.6, -4.8 ppm; LRMS (ESI): m/z 620 (M+ + H), 642 (M+
+ Na); HRMS: found (M+ + H) 620.3200 C28H54NO9Si2 requires
620.3208.
5-Acetamido-2-O-acetyl-3,5-dideoxy-D-glycero-D-galacto-
nonulopyranosic acid (6)
To a solution of 17 (7.5 mg, 0.016 mmol) in THF (1 mL) and
H2O (1 mL) stirring at 0 ◦C was added 1.0 M TBAF in THF
(80 mL, 0.08 mmol). The reaction was stirred for 18 h then was
concentrated in vacuo to give a yellow oil. The crude material was
purified by flash column chromatography using a 3 : 1 CH2Cl2 :
MeOH gradient to give a white solid (4.8 mg, 87%). [a]2D5 -31 (c
1.0, MeOH); mp: 189–191 ◦C; nmax (NaCl) 3435–3311 (br), 2729,
1767, 1750, 1620, 1565 cm-1; dH (400 MHz, DMSO-d6): d 8.09
(1H, d, J = 8.5 Hz, H-10), 4.78 (1H, br s, O-H4), 4.54 (1H, br s,
O-H7), 4.35 (1H, br d, J = 5.0 Hz, O-H8), 4.24 (1H, br s, O-H9),
3.82 (1H, ddd, J = 10.5, 10.5, 5.0 Hz, H-4), 3.74 (1H, dd, J = 10.5,
1.5 Hz, H-6), 3.58 (1H, br d, H-9), 3.54–3.45 (1H, m, H-8), 3.50
(1H, ddd, J = 10.0, 10.0, 5.0 Hz, H-5), 3.29 (1H, dd, J = 11.0,
7.0 Hz, H-9), 3.15 (1H, d, J = 8.0 Hz, H-7), 2.07 (1H, dd, J = 12.5,
5.0 Hz, H-3eq), 1.92 (3H, s, H-19), 1.89 (3H, s, H-11), 1.70 (1H, dd,
J = 13.0, 11.2 Hz, H-3ax) ppm; dC (100 MHz, DMSO-d6) 172.0,
170.3, 169.5, 97.4, 70.3, 69.6, 69.1, 65.6, 63.6, 53.3, 39.8, 22.6, 21.2
ppm; LRMS (ESI): m/z 352 (M+ + H), 374 (M+ + Na); HRMS:
found (M+ + H) 352.1160 C13H22NO10Si requires 352.1165.
5-Acetamido-3,5-dideoxy-8,9-O-isopropylidene-2-O-triethylsilyl-
4-O-tert-butyldimethylsilyl-D-glycero-D-galacto-nonulopyranosic
acid (18)
5-Acetamido-7-O-acetyl-3,5-dideoxy-D-glycero-D-galacto-
nonulopyranosic acid (5)
A solution of 19 (70 mg, 0.11 mmol) in 60% AcOH (2 mL)
was stirred for 2 h at 60 ◦C. The mixture was concentrated in
vacuo to yield a brown solid which was purified by flash column
chromatography using a 9 : 1 CH2Cl2 : MeOH gradient to yield
a white solid (47 mg, 72%). [a]2D5 -13 (c 1.0, MeOH); mp: 184–
186 ◦C; nmax (NaCl) 3551, 3418–3265 (br), 2716, 1769, 1751, 1630,
1571 cm-1; dH (400 MHz, DMSO-d6): 8.04 (1H, d, J = 9.0 Hz, H-
10), 4.34 (1H, d, J = 5.5 Hz, O-H8), 4.24 (1H, t, J = 6.0 Hz, O-H9),
4.06–4.01 (1H, m, H-4), 3.90–3.84 (2H, m, H-6 + H-5), 3.63–3.57
(2H, m, H-7 + H-9), 3.51–3.46 (1H, m, H-8), 3.26 (1H, dd, J =
17.5, 6.0 Hz, H-9), 2.09 (1H, dd, J = 12.0, 5.0 Hz, H-3eq), 1.90
(3H, s, H-15), 1.82 (3H, s, H-12), 1.65 (1H, dd, J = 12.0, 12.0 Hz,
H-3ax), 0.90 (9H, t, J = 8.0 Hz, H-21), 0.78 (9H, s, H-19), 0.52 (6H,
q, J = 8.0 Hz, H-20), 0.04 (3H, s, H-17), 0.03 (3H, s, H-17) ppm; dC
(100 MHz, DMSO-d6): 171.9, 171.5, 171.3, 97.7, 71.7, 70.4, 69.8,
65.7, 63.6, 53.1, 40.0, 25.7, 22.6, 17.5, 6.9, 4.9, -4.6, -4.8 ppm;
A solution of 9 (200 mg, 0.428 mmol) in Et2O (5 mL) and
MeCN (5 mL) stirring at -78 ◦C under a N2 atmosphere was
treated with pyridine (172 mL, 2.68 mmol) followed by TESOTf
(193 mL, 0.856 mmol). The reaction was stirred at -20 ◦C for 16 h
then quenched with a saturated aqueous solution of NaHCO3
(50 mL) and extracted with EtOAc (3x 50 mL). The combined
organics were washed with brine (150 mL), dried (MgSO4) and
concentrated in vacuo to give a colourless oil. Purification by flash
column chromatography using a 95 : 5 to 9 : 1 to 1 : 1 petroleum
ether : EtOAc gradient afforded the desired compound as a white
◦
solid (165 mg, 67%). [a]2D5 -15 (c 1.0, MeOH); mp: 163–165 C;
nmax (NaCl) 3427–3227 (br), 2722, 1755, 1630, 1572 cm-1; dH (400
MHz, DMSO-d6): 7.91 (1H, d, J = 9.0 Hz, H-10), 4.55 (1H, br s,
O-H7), 4.05–4.01 (1H, m, H-4), 3.99 (1H, dd, J = 12.0, 6.0 Hz,
H-8), 3.93–3.87 (2H, m, H-6 + H-5), 3.74 (1H, br d, J = 10.5 Hz,
534 | Org. Biomol. Chem., 2012, 10, 529–535
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LRMS (ESI): m/z 580 (M+ + H), 602 (M+ + Na); HRMS: found
(M+ + H) 580.2888 C25H50NO9Si2 requires 580.2895.
Notes and references
1 J. N. Varghese, J. L. McKimm-Breschkin, J. B. Caldwell, A. A. Kortt
and P. M. Colman, Proteins: Struct., Funct., Genet., 1992, 14, 327.
2 (a) E. Severi, D. W. Hood and G. H. Thomas, Microbiology, 2007, 153,
2817; (b) A. C. C. Frasch, Parasitol. Today, 2000, 16, 282.
3 G. V. Srinivasan and R. Schauer, Glycoconjugate J., 2008, 26, 935.
4 S. M. Steenbergen, J. L. Jirik and E. R. Vimr, J. Bacteriol., 2009, 191,
7134.
5 A. Varki and S. Diaz, Anal. Biochem., 1984, 137, 236.
6 S. Hara, M. Yamaguchi, Y. Takemori, K. Furuhata, H. Ogura and M.
Nakamura, Anal. Biochem., 1989, 179, 162.
7 (a) H. Ogura, K. Furuhata, S. Sata, K. Anazawa, M. Itoh and Y. Shitori,
Carbohydr. Res., 1987, 167, 77; (b) A. Hasegawa, T. Murase, M. Ogawa,
H. Ishida and M. Kiso, J. Carbohydr. Chem., 1990, 9, 415.
8 (a) K. Anazawa, K. Furuhata and H. Ogura, Chem. Pharm. Bull., 1988,
36, 4976; (b) A. Hasegawa, T. Murase, M. Ogawa, H. Ishida and M.
Kiso, J. Carbohydr. Chem., 1990, 9, 429.
To a solution of the above compound (35 mg, 0.06 mmol) in
◦
THF (1 mL) and H2O (1 mL) stirring at 0 C was added 1.0 M
TBAF in THF (300 mL, 0.30 mmol). The reaction was stirred for
20 h then was concentrated in vacuo to give a yellow oil. The crude
material was purified by flash column chromatography using a
3 : 1 CH2Cl2 : MeOH gradient to give a white solid (17 mg, 81%).
[a]2D5 -35 (c 1.0, MeOH); mp: 185–187 ◦C; nmax (NaCl) 3441–3297
(br), 2739, 1775, 1753, 1618, 1561 cm-1; dH (400 MHz, DMSO-d6):
8.08 (1H, d, J = 8.0 Hz, H-10), 6.70 (1H, d, J = 2.0 Hz, O-H2),
4.84 (1H, d, J = 6.0 Hz, O-H4), 4.34 (1H, d, J = 5.5 Hz, O-H8),
4.25 (1H, t, J = 6.0 Hz, O-H9), 3.82 (1H, ddd, J = 10.5, 10.5,
5.0 Hz, H-4), 3.74 (1H, dd, J = 10.5, 1.5 Hz, H-6), 3.61–3.55 (2H,
m, H-7 + H-9), 3.54–3.45 (1H, m, H-8), 3.53 (1H, ddd, J = 10.0,
10.0, 10.0 Hz, H-5), 3.30 (1H, dd, J = 11.0, 7.0 Hz, H-9), 2.07
(1H, dd, J = 12.5, 5.0 Hz, H-3eq), 1.92 (3H, s, H-15), 1.89 (3H, s,
H-12), 1.70 (1H, dd, J = 13.0, 11.0 Hz, H-3ax) ppm dC (100 MHz,
DMSO-d6): 171.8, 171.5, 171.3, 94.7, 70.4, 69.8, 69.2, 65.7, 63.6,
53.1, 22.6, 21.4 ppm; LRMS (ESI): m/z 352 (M+ + H), 374 (M+ +
Na); HRMS: found (M+ + H) 352.1160 C13H22NO10Si requires
352.1165.
9 C.-S. Yu, K. Niikura, C.-C. Lin and C.-H. Wong, Angew. Chem., Int.
Ed., 2001, 40, 2900.
10 For representative examples see: (a) H. Ogura, H. Fujita, K. Furuhata,
M. Itoh and Y. Shitori, Chem. Pharm. Bull., 1986, 34, 1479; (b) K.
Furuhata, K. Anazawa, M. Itoh, Y. Shitori and H. Ogura, Chem.
Pharm. Bull., 1986, 34, 2725; (c) S. Sato, S. Fujita, K. Furuhata, H.
Ogura, S. Yoshimura, M. Itoh and Y. Shitori, Chem. Pharm. Bull.,
1987, 35, 4043; M. Hartman and E. Zbiral, Tetrahedron Lett., 1990, 31,
2875.
11 (a) R. Martin, K. L. Witte and C.-H. Wong, Bioorg. Med. Chem., 1998,
6, 1283; (b) M. J. Kiefel, J. C. Wilson, S. Bennett, M. Gredley and M.
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Acknowledgements
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We thank the Wellcome Trust VIP fund for financial support of
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This journal is
The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 529–535 | 535
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