Synthesis of phosphorylated 3,4-branched trisaccharides corresponding to LPS inner core structures of Neisseria meningitidis and Haemophilus influenzae

Article abstract of DOI:10.1016/j.carres.2010.03.006

2-(N-Benzyloxycarbonyl)aminoethyl 7-O-acetyl-6-O-allyl-2-O-benzoyl-4-O- benzyl-3-O-chloroacetyl-Lglycero- α-D-manno-heptopyranosyl-(1→3)-[2, 3,4,6-tetra-O-benzoyl-β-D-glucopyranosyl-(1→4)]-6,7-di-O-acetyl-2-O- benzyl-L-glycero-α-D-manno-heptopyranoside, a

Full text of DOI:10.1016/j.carres.2010.03.006

Carbohydrate Research 345 (2010) 1331–1338
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Synthesis of phosphorylated 3,4-branched trisaccharides corresponding to LPS
inner core structures of Neisseria meningitidis and Haemophilus influenzae
Johan D. M. Olsson a, Stefan Oscarson b,
*
a Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
b Centre for Synthesis and Chemical Biology, UCD School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
2-(N-Benzyloxycarbonyl)aminoethyl 7-O-acetyl-6-O-allyl-2-O-benzoyl-4-O-benzyl-3-O-chloroacetyl-L-
Received 15 January 2010
Received in revised form 1 March 2010
Accepted 4 March 2010
glycero-
O-acetyl-2-O-benzyl-
a
-
D
-manno-heptopyranosyl-(1?3)-[2,3,4,6-tetra-O-benzoyl-b-
D-glucopyranosyl-(1?4)]-6,7-di-
L
-glycero- -manno-heptopyranoside, a spacer-equipped protected derivative of
a-D
the common 3,4-branched diheptoside trisaccharide structure of the lipopolysaccharide core of Neisseria
meningitidis and Haemophilus influenzae has been synthesized. The protecting group pattern installed
allows regioselective introduction of phosphoethanolamine residues in the 3- and 6-position of the sec-
ond heptose unit in accordance with native structures. From this intermediate the 3-and 6-monophos-
phoethanolamine as well as the non-phosphorylated deprotected trisaccharides have been synthesized
to be used in evaluation of antibody binding specificity and in investigation of the substrate specificity
of glycosyl transferases involved in the biosynthesis of LPS core structures.
Available online 7 March 2010
Keywords:
Oligosaccharide synthesis
Thioglycosides
Lipopolysaccharides
Phosphoethanolamine
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
elongation of this trisaccharide unit, for example, the transferase
introducing the (1?2)-linked a-D-GlcNAcp unit in N. meningitidis.
The structures of the conserved parts of the lipopolysaccharides
from Neisseria meningitidis (Fig. 1) and Haemophilus influenzae
(Fig. 2) show significant similarity, the main differences being
The gene coding for this transferase has been identified and cloned,
but it is still not known if large substrates are needed to get high
activity or if phosphorylated or non-phosphorylated substrates
are preferred by the enzyme. Investigations such as these will be
greatly facilitated with the help of the synthesized derivatives.8
the substitution in the 4-position of Kdo (N. meningitidis:
a-D-
Kdop; H. influenzae: PPEtN) and in the 2-position of the second
heptose unit (N. meningitidis:
a-D-GlcNAcp; H. influenzae: L-a-D-
Hepp).1–5 Another difference is the phosphoethanolamine substitu-
tion of the second heptose unit, which in H. influenzae is almost
exclusively in the 6-position, whereas in N. meningitidis it is mainly
in the 3-position, although 6- and 3,6-disubstitution have also
been identified.
2. Results and discussion
In our earlier syntheses of tetrasaccharide structures from N.
menigitidis and H. influenzae we have utilized a 7-O-benzyl-6-O-
chloroacetyl-3,4-O-(20,30-dimethoxybutane-20,30-diyl)-2-O-p-meth
To in detail evaluate the specificity of antibodies raised against
these native structures, well-defined synthetic structures are al-
most a necessity. As part of a programme involving synthesis of
core LPS structures for the development of LPS-based glycoconju-
gate vaccines,6,7 we now report on the synthesis of regioselectively
phosphorylated structures of the common 3,4-branched trisaccha-
oxybenzyl-1-thio-L-glycero-a-D-manno-heptapyranoside donor for
the introduction of the second heptose unit.6,7 This protection
group pattern allowed for continued substitution with glycans in
the 2-position, after selective removal of the p-methoxybenzyl
group, and also introduction of a phosphoethanolamine moiety
in the 6-position after removal of the chloroacetyl group. However,
since the target molecules this time only contain 3- and 6-substi-
tutions and it is not possible to remove the BDA-acetal prior to
the removal of the p-methoxybenzyl group a new protecting group
pattern was developed for the heptosyl donor (Scheme 1).
ride L-a-D-Hepp-(1?3)-[b-D-Glc-(1?4)]-L-a-D-Hepp found in N.
meningitidis and H. influenzae LPS, the 3-O-phosphoethanolamine
derivative 18 and the 6-O-phosphoethanolamine derivative 19 as
well as the non-phosphorylated trisaccharide 20. These synthetic
derivatives will also be useful in establishing the substrate specific-
ity of various glycosyltransferases involved in the biosynthetic
The known ethyl 4-O-benzyl-2,3-O-isoproylidene-1-thio-a-D-
mannopyranoside9 (1) was prepared and its transformation into
a heptose derivative was accomplished as before, first a Swern oxi-
dation to give the 6-aldehyde followed by a Barbier reaction with
benzyloxymethyl chloride.10 This afforded the thioheptosides 2
* Corresponding author. Tel.: +353 17162318; fax: +353 17162501.
E-mail address: stefan.oscarson@ucd.ie (S. Oscarson).
0008-6215/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2010.03.006

1332
J. D. M. Olsson, S. Oscarson / Carbohydrate Research 345 (2010) 1331–1338
and 3 in good yield but with low stereoselectivity. A total yield of
56% with a -ratio of 4:5 was obtained. To utilize also the unde-
sired 6- -stereoisomer 2, this compound was transformed into the
6- -isomer 3 via a Mitsunobu reaction with p-nitro-benzoic acid
present in the donor.6,7,12,13 Interestingly, the 1,2-isopropylidene
acetal has in a recent publication been found also to be -directing,
D
/L
a
D
but this investigation involved mannuronic acid donors and other
L
acceptors.14
and subsequent deacylation in an overall yield of 57%. For tempo-
rary protection of the 6-position an allyl group was selected and
introduced (?5, 94%). In spite of the double bond function, allyl
groups are normally orthogonal to thiophilic promoters. Two
routes to the target structures were now investigated, one involv-
ing the use of thioglycoside 5 directly as a donor and a subsequent
selective protection release of the 3-position at the trisaccharide
level, and another one comprising the latter protecting group
manipulation performed already at the monosaccharide stage to
give a thioglycoside donor 7 protected in the 3- and 6-position
with orthogonal temporary protecting groups.
To introduce an orthogonal temporary protecting group in the
3-position, the isopropylidene acetal was removed by acid hydro-
lysis from compound 5 to yield the 2,3-diol 6 (96%, Scheme 1).
As a temporary protecting group, a chloroacetyl group was selected
and for the protection of the 2-position we hypothesized that a
participating group was required, considering the stereoselectivity
problems discussed with donor 5. Hence, the 3-O-CA-2-O-Bz deriv-
ative 7 was prepared through tin activation of 6 followed by chlo-
roacetylation and subsequent benzoylation in a 72% overall yield.
BnO
AllO
O
Thus, donor 5 was coupled using DMTST as promoter to the disac-
charide acceptor 8, earlier developed by us as an efficient acceptor to
obtain these quite elusive 3,4-branched structures (Scheme 2).10,11
O
O
BnO
O
OBn
OBn
O
O
O
SEt
O
AcO
Diethyl ether was used as solvent to improve
gle stereoisomer 9 was obtained in a 52% yield. Because of the man-
no-configuration of the donor we expected this to be the -product,
a-selectivity and a sin-
AllO
i
5
O
OBn
OBz
OBz
a
O
O
BzO
but no conclusive evidence could be obtained from NMR data. The
OBz
shifts of the anomeric carbon (d 101.2 ppm) and proton (d
O
AcO
OBz
OH
O
1
9
4.66 ppm) rather suggested a b-linkage, and the JC1–H1 of 167 Hz
OBn
was not diagnostic without the value of the other anomer for pur-
poses of comparison. Finally, the configuration was established by
transforming the trisaccharide 9 (hydrolysis of the isopropylidene
acetal followed by selective chloroacetylation of the 3-OH) into an
already synthesized derivative where we had both anomers for com-
parison. This proved that exclusively the b-linked product (C-1 d
102.2 (1JC1–H1 161 Hz), H-1 d 4.43) had been formed in the glycosyl-
ation; therefore, this approach was abandoned. The complete stere-
oselectivity was a surprise, but our experience when coupling
various heptosyl donors with a non-participating group in the 2-po-
sition to acceptor 8 is that a large ratio of b-anomer is always formed
O
BzO
BzO
O
8
BnO
AllO
OBz
OBz
O
BnO
CAO
ii
O
AcO
OBz
BnO
AllO
BnO
CAO
O
O
OBz
O
OBn
O
BzO
BzO
O
10
OBz
SEt
7
Scheme 2. Synthesis of trisaccharides 9 and 10. Reagents: (i) DMTST, Et2O, 52%; (ii)
Me2S2, Tf2O, CH2Cl2, 70%.
and to obtain
a-selectivity the
a-directing 3,4-BDA acetal has to be
β-D-Glc
α-D-Kdop
PEtN
|
3 or 6
1
↓
4
2
↓
4
α-D-GlcNAcp-(1→2)-L-α-D-Hepp-(1→3)-L-α-D-Hepp-(1→5)-α-D-Kdop-(2→6)-LipidA
Figure 1. Conserved structure of N. meningitidis LPS.
β-D-Glc
PEtN
|
6
1
↓
4
PPEtN
|
4
L-α-D-Hepp-(1→2)-L-α-D-Hepp-(1→3)-L-α-D-Hepp-(1→5)-α-D-Kdop-(2→6)-LipidA
Figure 2. Conserved structure of H. influenzae LPS.
BnO
HO
BnO
HO
BnO
AllO
BnO
AllO
HO
O
OH
O
OBz
O
O
O
v
i
vi, vii
O
O
O
BnO
BnO
BnO
BnO
BnO
O
O
O
HO
+
CAO
SEt
SEt
SEt
SEt
SEt
6
5
7
iv
1
3
2
BnO
AllO
BnO
ii
O
O
iii
p-NO2BzO
O
BnO
O
BnO
O
O
SEt
SEt
4
Scheme 1. Synthesis of heptosyl thioglycosides 5 and 7. Reagents: (i) (a) (COCl)2, DMSO, DIPEA, CH2Cl2; (b) BnOCH2Cl, Mg, HgBr2, I2, THF, 56% (2:3 4:5) over two steps; (ii) p-
nitrobenzoic acid, PPh3, DIAD, THF, 77%; (iii) NaOMe, MeOH–CH2Cl2 (2:1), 74%; (iv) AllBr, NaH, DMF, 94%; (v) (a) AllBr, NaH, DMF; (b) 80% HOAc (aq), 90% over two steps; (vi)
(a) Bu2SnO, toluene; (b) chloroacetyl chloride, toluene, 82%; (vii) BzCl, pyridine, CH2Cl2, 88%.

J. D. M. Olsson, S. Oscarson / Carbohydrate Research 345 (2010) 1331–1338
1333
Coupling of donor 7 with acceptor 8, using the stronger promoter
pyl phosphoramidite6 and tetrazole followed by m-CPBA oxidation
gave the phosphotriesters 16 and 17 in 80% and 73% yields, respec-
tively. The Boc-protection of the ethanolamino group provides
orthogonality to the spacer amino group protection to allow selec-
tive activation and conjugation of the latter.
Deprotection of derivative 16 in three steps, deallylation fol-
lowed by catalytic hydrogenolysis and Zemplen deacylation, and
of derivative 17 in two steps, deacylation and catalytic hydrogen-
olysis, gave the two target structures 18 and 19 in 49% and 76%
yield, respectively. Deprotection of 14 as described for compound
16 gave the nonposphorylated trisaccharide 20 in 75% yield.
In conclusion, an effective synthesis of a regioselectively pro-
tected spacer equipped trisaccharide intermediate 13 has been
developed and its transformation into phosphoethanolamine con-
taining structures corresponding to N. meningitidis and H. influen-
zae LPS core structures has been performed.
system Me2S2–Tf2O15 and CH2Cl2 as solvents, now efficiently affor-
ded thetrisaccharide 10 in70% yieldandwith completea-selectivity
(JC1–H1 = 172 Hz; 13C 96.9 ppm; 1H 5.19 ppm) (Scheme 2).
The spacer moiety and the phosphoethanolamine residues could
now be introduced using methodology already developed during
synthesis of the tetrasaccharide structures.6,7 ScOTf3-promoted ace-
tolysis of the 1,6-anhydro bridge afforded the anomeric acetate 11
(75%), which was converted to the ethyl thioglycoside by treatment
with ethanethiol and BF3ꢀdiethyl etherate (?12, 69%) (Scheme 3).
NIS–AgOTf-promoted glycosylation between donor 12 and CBz-pro-
tected ethanolamine gave the spacer-equipped trisaccharide 13 in
77% yield and with complete a-selectivity, although a non-partici-
pating benzyl group is present in the 2-position of the donor.
From derivative 13 now various phosphorylation patterns can be
easily accomplished, 3-mono, 6-mono and 3,6-diphosphorylation,
and obviously also the non-phosphorylated trisaccharide can be ob-
tained. Removal of the monochloroacetate by NH3–MeOH treatment
yielded the 30-OH derivative 14 (90%), whereas deallylation through
Ir-catalyzed rearrangement followed by NIS-promoted hydrolysis of
the obtained enol ether afforded the 60-OH compound 15 (73%)
(Scheme 4). The phosphoethanolamino groups were introduced
using phosphoramidite chemistry. Treatment of derivatives 14 and
15 with (2-tert-butyloxycarbonyl aminoethyl)benzyl N,N-diisopro-
3. Experimental
3.1. General methods
Normal work-up means drying the organic phase with MgSO4
(s) or Na2SO4 (s), filtering and evaporation of the solvent in vacuo
BnO
AllO
OBz
O
AcO
OBz
AcO
AcO
OBz
AcO
BnO
OBn
O
OBn
O
O
O
BzO
BzO
BzO
BzO
CAO
O
O
i
iii
O
O
OBz
OBz
O
AcO
OBz
O
O
CAO
BnO
O
CAO
BnO
R
NHCbz
O
OBn
O
O
OBz
BzO
BzO
OBz
AllO
AllO
O
AcO
AcO
OBz
13
10
11 R = OAc
12 R = SEt
ii
Scheme 3. Synthesis of spacer trisaccharide 13. Reagents: (i) Sc(OTf)3, Ac2O, 75%; (ii) EtSH, BF3ꢀOEt2, CH2Cl2, 69%; (iii) N-(benzyloxycarbonyl) aminoethanol, NIS, AgOTf,
CH2Cl2–Et2O (2:1), 77%.
AcO
AcO
HO
HO
OBz
OH
OBn
O
OH
O
O
O
BzO
BzO
OBn
P
O
HO
HO
OH
P
O
O
O
iv
O
O
OBz
OH
O
O
O
O
O
O
NHCbz
NH2
iii
BnO
HO
O
O
OBz
OH
AllO
HO
BocHN
BocHN
AcO
HO
16
18
AcO
AcO
OBz
OBn
O
O
HO
HO
OH
BzO
BzO
O
OH
O
O
HO
HO
O
OBz
O
iv
O
O
R2O
BnO
R1O
AcO
OH
NHCbz
O
O
HO
HO
HO
NH2
OBz
O
20
OH
13 R1 = All, R2 = CA
14 R1 = All, R2 = H
15 R1 = H, R2 = CA
HO
i
ii
HO
HO
OH
AcO
OBz
OH
O
iii
AcO
OBn
O
O
HO
HO
BzO
BzO
O
O
O
v
O
O
OH
OBz
HO
HO
O
CAO
BnO
O
NH2
NHCbz
O
O
O
BocHN
O
OH
OBz
O
O
P
HO
P
BnO
O
O
HO
AcO
19
17
BocHN
Scheme 4. Synthesis of target structures 18–20. Reagents: (i) NH3 (satd) MeOH–CH2Cl2 (2:1), 90%; (ii) (a) H2 (g), [bis(methyldiphenylphosphine)](1,5-cyclooctadine) Ir(I)PF6,
THF; (b) NIS, H2O, 73%; (iii) (a) (2-tert-butyloxycarbonyl aminoethyl)benzyl N,N-diisopropyl phosphoramidite, tetrazole, CH2Cl2; (b) m-CPBA, CH2Cl2, 0 °C (for 16 80% and for
17 73%); (iv) (a) H2 (g), [bis(methyldiphenylphosphine)](1,5-cyclooctadine) Ir(I)PF6, THF; (b) NIS, H2O; (c) Pd–C (10%), H2 (g), 0.1 M HCl (aq), EtOAc–MeOH (1:1); (d) NaOMe,
MeOH (for 18 49% and for 20 74% over four steps); (v) (a) Pd–C (10%), H2 (g), 0.1 M HCl (aq), EtOAc–MeOH (1:1); (b) NaOMe, MeOH, 76% over two steps.

1334
J. D. M. Olsson, S. Oscarson / Carbohydrate Research 345 (2010) 1331–1338
at ꢁ35 °C. CH2Cl2 was distilled over calcium hydride and collected
onto 4 A pre-dried MS. Thin Layer Chromatography (TLC) was car-
ried out on 0.25 mm pre-coated silica-gel plates (Merck Silica-Gel
60 F254); detected with UV-abs (254 nm) and/or by charring with
8% sulfuric acid or AMC (ammonium molybdate (10 g) and cerium
sulfate (2 g) dissolved in 10% H2SO4 (200 mL)) followed by heating
to ꢁ250 °C. FC means Flash Column chromatography using silica
gel (Amicon, (0.040–0.063 mm)). 1H NMR, 31P NMR and 13C NMR
spectra were performed on a Varian or Bruker instrument (300,
400 or 500 MHz) at 25 °C unless otherwise stated. Chemical shifts
are given in parts per million relative to solvent peaks in CDCl3 (d
77.17 for 13C and d 7.26 for 1H) and in D2O (d 4.79 for 1H) or TMS (d
0.00 for 13C NMR and 1H NMR. For 31P NMR 85% aq H3PO4 (d 0.00
was used as an external reference.
J = 7.6, 9.2 Hz), 3.85 (dd, 1H, J = 7.2, 10.0 Hz), 3.99 (dd, 1H, J = 1.6,
10.0 Hz), 4.18–4.23 (m, 2H), 4.31 (dd, 1H, J = 6.0, 7.2 Hz), 4.53 (ben-
zylic d, 1H, Jgem = 12.0 Hz), 4.70 (benzylic d, 1H, Jgem = 12.0 Hz), 4.67
(benzylic d, 1H, Jgem = 11.2 Hz), 4.93 (benzylic d, 1H, Jgem = 11.2 Hz),
5.57 (s, 1H), 7.28–7.39 (10H, Ar-H); HRMS calcd for C26H35O6S
[M+H]+ 475.2154; found 475.2140.
3.3. Ethyl 4,7-di-O-benzyl-2,3-O-isopropylidene-6-O-p-
nitrobenzoyl-1-thio-L-glycero-a-D-manno-heptopyranoside (4)
PPh3 (0.324 g, 1.23 mmol) and para-nitrobenzoic acid (0.206 g,
1.23 mmol) were added to a solution of 2 (0.293 g, 0.62 mmol) in
THF (5 mL). DIAD (0.242 mL, 1.23 mmol) was subsequently added
dropwise. The resulting reaction mixture was stirred for 3 h
whereafter the solvent was evaporated. FC (toluene?toluene–
EtOAc 39:1?19:1) gave 4 (0.298 g, 0.48 mmol, 77%). Rf = 0.68 (tol-
3.2. Ethyl 4,7-di-O-benzyl-2,3-O-isopropylidene-1-thio-
D-
glycero- -manno-heptopyranoside (2) and ethyl 4,7-di-O-
a-
D
uene–EtOAc 9:1); [
a]
+88 (c 1.0, CHCl3); 13C NMR (100 MHz,
D
benzyl-2,3-O-isopropylidene-1-thio-
heptopyranoside (3)
L
-glycero-
a
-
D
-manno-
CDCl3): d 14.4, 24.3, 26.6, 28.2, 67.4, 67.9, 71.0, 72.6, 73.3, 74.9,
76.5, 78.8, 80.0, 109.6, 123.6 (2C), 127.7 (2C), 127.8, 127.8, 128.4
(2C), 128.5 (2C), 128.7 (2C), 129.1, 131.0 (2C), 137.6, 137.9,
150.7, 163.9; 1H NMR (400 MHz, CDCl3): d 1.26 (t, 3H, J = 7.2 Hz),
1.39 (s, 3H), 1.45 (s, 3H), 2.51 (dq, 1H, J = 7.2, 12.8 Hz), 2.66 (dq,
1H, J = 7.2, 12.8 Hz), 3.58 (dd, 1H, J = 5.4, 10.0 Hz), 3.75 (dd, 1H,
J = 6.4, 9.6 Hz), 3.83 (dd, 1H, J = 6.4, 9.6 Hz), 4.25 (dd, 1H, J = 0.8,
5.6 Hz), 4.35–4.39 (m, 2H), 4.45 (benzylic d, 1H, Jgem = 11.2 Hz),
4.54 (benzylic d, 1H, Jgem = 11.6 Hz), 4.61 (benzylic d, 1H,
Jgem = 11.6 Hz), 4.82 (benzylic d, 1H, Jgem = 11.2 Hz), 5.65 (s, 1H),
5.83 (ddd, 1H, J = 1.6, 6.4, 6.4 Hz), 7.10–7.36 (m, 10H), 8.18 (d,
2H, J = 8.8 Hz), 8.26 (d, 2H, J = 8.8 Hz); HRMS calcd for C33H37NO9S:
[M+H]+ 624.2267; found 624.2257.
Oxalyl chloride (0.230 mL, 2.64 mmol) was dissolved in dry
CH2Cl2 (3 mL) and cooled to ꢂ60 °C. DMSO (0.375 mL, 5.28 mmol)
in dry CH2Cl2 (3 mL) was added dropwise. After stirring for 10 min,
ethyl 4-O-benzyl-2,3-O-isopropylidene-1-thio-a-D-mannopyrano-
side9 (1, 0.851 g, 2.40 mmol) dissolved in dry CH2Cl2 (5 mL) was
added dropwise and the stirring was continued for an additional
60 min at ꢂ60 °C followed by the addition of DIPEA (2.06 mL,
12.0 mmol). The mixture was slowly brought to rt, diluted with
CH2Cl2 (15 mL), washed with H2O (30 mL) and subjected to normal
work-up to yield the corresponding aldehyde, which was used with-
out further purification. Magnesium (0.408 g, 16.8 mmol, activated),
HgBr2 (cat.) and I2 (cat.) were dissolved in dry THF (4 mL). Benzyl-
oxymethyl chloride (1.67 mL, 7.20 mmol, 60%) was measured in a
dropping funnel and a small amount (ꢁ0.200 mL) was added drop-
wise to the magnesium mixture until the exothermic reaction
started and the purple-brown colour disappeared. After the initial
increase in temperature the reaction temperature was kept at
25 °C by immediately cooling of the mixture. The crude aldehyde
dissolved in dry THF (10 mL) was added to the dropping funnel con-
taining the benzyloxymethyl chloride. This aldehyde reagent solu-
tion was carefully added dropwise to the magnesium mixture over
45 min, strictly keeping the reaction temperature at 25–28 °C. After
completed addition, the mixture was stirred for 14 h at rt, then di-
luted with Et2O (30 mL), washed with NH4Cl (satd, 100 mL) and sub-
jected to normal work-up. FC (toluene–EtOAc 19:1?14:1?9:1)
Synthesis of 3 from 4: NaOMe (cat.) was added to a stirred solu-
tion of 4 (0.204 g, 0.33 mmol) in MeOH–CH2Cl2 (2:1, 6 mL). After
8 h the reaction mixture was neutralized with Dowex-H+ ion ex-
change resins, filtered and concentrated. FC (toluene–EtOAc
19:1?9:1) of the residue gave 2 (0.115 g, 0.24 mmol, 74%).
3.4. Ethyl 6-O-allyl-4,7-di-O-benzyl-2,3-O-isopropylidene-1-
thio-L-glycero-a-D-manno-heptopyranoside (5)
Compound 3 (0.289 g, 0.61 mmol) was dissolved in dry DMF
(6 mL) and allyl bromide (0.105 mL, 1.21 mmol) was added. This
solution was added dropwise at 0 °C to a slurry of NaH (0.048 g,
1.21 mmol, 60%) in DMF (2 mL). After 45 min, MeOH (2 mL) was
added and the solution was diluted with toluene (50 mL). The organ-
ic phase was washed with H2O (40 mL) and subjected to normal
work-up followed by FC (toluene?toluene–EtOAc?toluene–EtOAc
1:0?19:1?9:1) to give 5 (0.293 g, 0.570 mmol, 94%). Rf = 0.68 (tol-
uene–EtOAc 9:1); 13C NMR (100 MHz, CDCl3): d 14.5, 24.3, 26.6, 28.2,
69.4, 70.7, 72.7, 72.9, 73.5, 75.5, 75.7, 76.8, 79.1, 80.2, 109.6, 116.7,
127.7 (2C), 127.7 (2C), 128.0 (2C), 128.4 (2C), 128.5 (2C), 135.2,
138.3, 138.6; 1H NMR (400 MHz, CDCl3): d 1.23 (t, 3H, J = 7.2 Hz),
1.37 (s, 3H), 1.56 (s, 3H), 2.41–2.63 (m, 2H), 3.61 (dd, 1H, J = 6.4,
9.6 Hz), 3.72 (dd, 1H, J = 6.4, 9.6 Hz), 3.87 (dd, 1H, J = 7.2, 10.0 Hz),
3.93 (dd, 1H, J = 6.0, 12.4 Hz), 4.00 (ddd, 1H, J = 1.5, 6.4, 6.4 Hz),
4.07 (dd, 1H, J = 1.6, 10.0 Hz), 4.19 (dd, 1H, J = 1.5, 5.6 Hz), 4.26 (dd,
1H, J = 6.0, 12.4 Hz), 4.43 (dd, 1H, J = 6.4, 6.4 Hz), 4 52 (s, 2H), 4.56
(benzylic d, 1H, Jgem = 11.6 Hz), 4.97 (benzylic d, 1H, Jgem = 11.6 Hz),
5.09 (dd, 1H, J = 1.5, 10.4 Hz), 5.21 (dd, 1H, J = 1.5, 17.2 Hz), 5.59 (s,
1H), 5.87 (m, 1H), 7.25–7.37 (m, 10H); HRMS calcd for C29H38O6S:
[M+Na]+ 537.2281; found 537.2298.
afforded first the
by the -heptoside 3 (0.354 g, 0.75 mmol, 31%).
Compound 2 ( -heptoside): Rf = 0.44 (toluene–EtOAc 6:1);
+106 (c 1.0, CHCl3); 13C NMR (100 MHz, CDCl3): d 14.3, 24.1,
D-D-heptoside 2 (0.283 g, 0.60 mmol, 25%) followed
L-D
D-D
[a]
D
26.4, 28.0, 68.6, 71.0, 72.2, 72.8, 73.5, 76.5, 77.9, 78.6, 79.6,
109.5, 127.6, 127.8 (2C), 127.9, 128.2 (2C), 128.4 (2C), 128.5 (2C),
137.7, 138.2; 1H NMR (400 MHz, CDCl3): d 1.27 (t, 3H, J = 7.6 Hz),
1.39 (s, 3H), 1.56 (s, 3H), 2.49–2.72 (m, 2H), 3.56–3.63 (m, 2H),
3.73 (dd, 1H, J = 7.6, 8.4 Hz), 4.10–4.14 (m, 2H), 4.21 (d, 1H,
J = 5.2 Hz), 4.34 (dd, 1H, J = 5.2, 6.0 Hz), 4.52 (benzylic d, 1H,
Jgem = 12.5 Hz), 4.52 (benzylic d, 1H, Jgem = 12.5 Hz), 4.62 (benzylic
d, 1H, Jgem = 11.2 Hz), 4.95 (benzylic d, 1H, Jgem = 11.2 Hz), 5.55 (s,
1H), 7.28–7.40 (m, 10H); HRMS calcd for C26H35O6S [M+H]+
475.2154; found 475.2169.
Compound 3 (L-D-heptoside): Rf = 0.36 (toluene–EtOAc 6:1); [a]
D
+108 (c 1.0, CHCl3); 13C NMR (100 MHz, CDCl3): d 14.4, 24.3, 26.6,
28.1, 68.0, 68.7, 71.8, 73.4, 73.5, 75.7, 76.6, 78.8, 80.1, 109.5, 127.8,
127.8, 127.9 (2C), 128.1 (2C), 128.4 (2C), 128.5 (2C), 138.0, 138.4;
1H NMR (400 MHz, CDCl3): d 1.24 (t, 3H, J = 7.6 Hz), 1.37 (s, 3H),
1.53 (s, 3H), 2.17 (br s, 1H), 2.47 (dq, 1H, J = 7.6, 13.2 Hz), 2.59 (dq,
1H, J = 7.6, 13.2 Hz), 3.52 (dd, 1H, J = 5.2, 9.2 Hz), 3.62 (dd, 1H,
3.5. Ethyl 6-O-allyl-4,7-di-O-benzyl-1-thio-L-glycero-a-D-
manno-heptopyranoside (6)
Compound 3 (0.184 g, 0.387 mmol) was treated as described
above to give compound 5. The resulting oil was dissolved in 80%

J. D. M. Olsson, S. Oscarson / Carbohydrate Research 345 (2010) 1331–1338
1335
AcOH (aq, 8 mL) and the mixture was heated to 80 °C. After 2 h the
solvent was evaporated and toluene (2 ꢃ 10 mL) was co-evapo-
rated twice from the residue. FC (toluene–EtOAc?toluene–EtOAc
2:1?1:1) gave diol 6 (0.166 g, 0.348 mmol, 90%) as a colourless
1.35 (s, 3H), 1.56 (s, 3H), 1.96 (s, 3H), 3.46 (m, 1H), 3.53 (dd, 1H,
J = 3.6, 9.2 Hz), 3.74–3.84 (m, 4H), 3.89–3.93 (m, 3H), 3.98 (dd,
1H, J = 6.0, 12.4 Hz), 4.02–4.05 (m, 2H), 4.09–4.25 (m, 5H), 4.31–
4.41 (m, 3H), 4.52–4.70 (m, 5H), 4.87 (benzylic d, 1H,
Jgem = 11.2 Hz), 4.86 (benzylic d, 1H, Jgem = 10.4 Hz), 4.99 (dd, 1H,
J = 1.2, 10.4 Hz), 5.15 (dd, 1H, J = 1.2, 17.6 Hz), 5.19 (d, 1H,
J = 8.0 Hz), 5.27 (s, 1H), 5.54 (dd, 1H, J = 8.0, 9.6 Hz), 5.71 (dd, 1H,
J = 10.0, 10.0 Hz), 5.84–5.95 (m, 2H), 7.19–7.53 (m, 27H), 7.83–
7.87 (m, 4H), 7.92 (dd, 2H, J = 1.6, 8.8 Hz), 8.01 (d, 2H, J = 7.6 Hz).
oil. Rf = 0.39 (toluene–EtOAc 1:1); [
a
]
D
+130 (c 1.0, CHCl3); 13C
NMR (125 MHz, CDCl3): d 14.6, 24.7, 70.5, 71.3, 72.4, 72.7, 72.8,
73.4, 74.4, 75.5, 75.8, 84.1, 117.3, 127.6 (2C), 127.7, 127.7 (2C),
127.8, 128.4 (2C), 128.5 (2C), 134.9, 138.0, 138.6; 1H NMR
(500 MHz, CDCl3): d 1.20 (t, 3H, J = 7.5 Hz), 2.44–2.59 (m, 2H),
3.63 (dd, 1H, J = 6.0, 10.0 Hz), 3.74 (dd, 1H, J = 6.0, 10.0 Hz), 3.85–
3.92 (m, 2H), 3.95–4.03 (m, 3H), 4.13 (d, 1H, J = 8.0 Hz), 4.30 (m,
1H), 4.51 (s, 2H), 4.67 (benzylic d, 1H, Jgem = 12.0 Hz), 4.90 (benzylic
d, 1H, Jgem = 12.0 Hz), 5.14 (dd, 1H, J = 1.5, 10.5 Hz), 5.25 (dd, 1H,
J = 1.5, 17.5 Hz), 5.31 (s, 1H), 5.93 (m, 1H), 7.27–7.36 (m, 10H);
HRMS calcd for C26H34O6S: [M+H]+ 475.2154; found 475.2133.
3.8. 6-O-Allyl-2-O-benzoyl-4,7-di-O-benzyl-3-O-chloroacetyl-
glycero- -manno-heptopyranosyl-(1?3)-[2,3,4,6-tetra-O-
benzoyl-b- -glucopyranosyl-(1?4)]-7-O-acetyl-1,6-anhydro-2-
O-benzyl- -glycero- -manno-heptopyranose (10)
L-
a-D
D
L
a-D
Tf2O (51
l
L, 0.302 mmol) was added at 0 °C to a solution of
3.6. Ethyl 6-O-allyl-2-O-benzoyl-4,7-di-O-benzyl-3-O-
Me2S2 (30
lL, 0.330 mmol) in dry CH2Cl2 (0.5 mL). After 30 min
chloroacetyl-1-thio-
L
-glycero-
a
-
D
-manno-heptopyranoside (7)
the Tf2O–Me2S2 mixture was added dropwise at ꢂ60 °C and under
Ar to a stirred (10 min) solution of 7 (0.052 g, 0.079 mmol) and 8
(0.050 g, 0.055 mmol) in Et2O (4 mL). After 60 min (ꢂ60 °C?rt),
A mixture of Bu2SnO (0.177 g, 0.713 mmol) and 6 (0.282 g,
0.594 mmol) in dry toluene (5 mL) was refluxed for 60 min and then
cooled to ꢂ35 °C at which temperature ClAcCl (0.057 mL,
0.713 mmol) was added. After stirring for 15 min, the mixture was
diluted with toluene (10 mL), washed with brine (10 mL) and sub-
jected to normal work-up. FC (toluene–EtOAc?toluene–EtOAc
3:1?2:1) gave the corresponding 3-O-chloroacetyl derivative
(0.269 g, 0.488 mmol, 82%). This was dissolved in dry CH2Cl2
(7 mL) and pyridine (0.807 mL, 10.0 mmol) was added. The mixture
was cooled to 0 °C and BzCl (0.581 mL, 5.0 mmol) was added. After
90 min, additional CH2Cl2 (10 mL) was added and the solution was
washed with 1 M HCl (aq, 25 mL) and subjected to normal work-
up. FC (toluene?toluene–EtOAc?toluene–EtOAc?toluene–EtOAc
1:0?39:1?19:1?9:1) afforded 7 (0.274 g, 0.429 mmol, 88%).
Et3N (300 lL) was added and the mixture was diluted with CH2Cl2
(5 mL), washed with H2O (10 mL) and subjected to normal work-
up. FC (toluene–EtOAc 9:1?6:1) gave 10 (0.058 g, 0.039 mmol,
70%). Rf = 0.63 (toluene–EtOAc 2:1); [
a]
ꢂ22 (c 1.0, CHCl3); 13C
D
NMR (125 MHz, CDCl3): d 21.0, 40.8, 62.3, 64.9, 69.2, 70.3, 71.6,
71.7, 72.1, 72.5, 72.6, 72.7, 72.7, 72.9, 73.3, 73.4, 73.6, 74.6, 74.7,
74.9, 75.5, 75.7, 76.8, 96.9 (JCH = 172 Hz), 100.1 (JCH = 175 Hz),
100.5 (JCH = 161 Hz), 115.8, 127.6–130.2 (Ar-C), 133.2, 133.4,
133.4, 133.5, 133.6, 135.5, 137.6, 138.3, 138.4, 165.1, 165.2,
165.8, 166.0, 166.1, 166.5, 171.0; 1H NMR (500 MHz, CDCl3): d
2.07 (s, 3H), 3.44–3.48 (m, 2H), 3.79–4.02 (m, 8H), 4.18–4.47 (m,
11 H), 4.53 (dd, 1H, J = 6.0, 6.0 Hz), 4.60 (benzylic d, 1H,
Jgem = 11.0 Hz), 4.69 (benzylic d, 1H, Jgem = 11.0 Hz), 4.71 (dd, 1H,
J = 3.0, 12.0 Hz), 5.10 (d, 1H, J = 8.5 Hz), 5.15 (dd, 1H, J = 1.5,
10.5 Hz), 5.19 (s, 1H), 5.32 (s, 1H), 5.33 (dd, 1H, J = 1.5, 18.0 Hz),
5.50–5.51 (m, 2H), 5.53 (dd, 1H, J = 8.5, 10.0 Hz), 5.76 (dd, 1H,
J = 9.5, 9.5 Hz), 5.92 (dd, 1H, J = 9.5, 9.5 Hz), 5.96 (m, 1H), 7.14–
7.58 (m, 30H), 7.82 (dd, 2H, J = 1.5, 8.5 Hz), 7.86 (dd, 2H, J = 1.5,
9.0 Hz), 7.92–7.96 (m, 4H), 8.07 (dd, 2H, J = 1.5, 8.5 Hz); HRMS
calcd for C83H79ClO24 [M+Na]+ 1517.4542; found 1517.4460.
Rf = 0.65 (toluene–EtOAc 6:1); [a]
+19 (c 1.0, CHCl3); 13C NMR
D
(125 MHz, CDCl3): d 14.6, 25.0, 40.5, 70.1, 71.8, 71.9, 72.1, 73.1,
73.5, 74.8, 74.9, 75.3, 82.0, 116.4, 127.5–130.0 (Ar-C), 133.5, 135.0,
138.0, 138.1, 165.6, 166.3; 1H NMR (500 MHz, CDCl3): d 1.23 (t, 3H,
J = 7.5 Hz), 2.52–2.64(m, 2H), 3.69 (dd, 1H, J = 6.5, 9.0 Hz), 3.75 (ben-
zylic d, 1H, Jgem = 14.5 Hz), 3.82 (dd, 1H, J = 6.5, 9.0 Hz), 3.83 (ben-
zylic d, 1H, Jgem = 14.5 Hz), 4.00 (dd, 1H, J = 5.5, 13.0 Hz), 4.09 (dd,
1H, J = 6.5, 6.5 Hz), 4.29–4.33 (m, 2H), 4.42 (dd, 1H, J = 5.5,
13.0 Hz), 4.54 (s, 2H), 4.66 (benzylic d, 1H, Jgem = 11.0 Hz), 4.72 (ben-
zylic d, 1H, Jgem = 11.0 Hz), 5.21 (dd, 1H, J = 1.5, 10.0 Hz), 5.34 (dd, 1H,
J = 1.5, 18.0 Hz), 5.42–5.44 (m, 2H), 5.62 (dd, 1H, J = 1.5, 3.5 Hz), 6.00
(m, 1H), 7.26–7.34 (m, 10H), 7.46 (dd, 2H, J = 7.5, 7.5 Hz), 7.60 (t, 1H,
J = 7.5 Hz), 8.09 (d, 2H, J = 7.5 Hz); HRMS calcd for C35H39ClO8S
[M+Na]+ 677.1946; found 677.1912.
3.9. 7-O-Acetyl-6-O-allyl-2-O-benzoyl-4-O-benzyl-3-O-
chloroacetyl-
[2,3,4,6-tetra-O-benzoyl-b-
acetyl-2-O-benzyl- -glycero-a-D
L
-glycero-
a-
D
-manno-heptopyranosyl-(1?3)-
-glucopyranosyl-(1?4)]-1,6,7-tri-O-
-manno-heptopyranoside (11)
D
L
Sc(OTf)3 (3 mg, 0.006 mmol) was added to a stirred solution
of 10 (63 mg, 0.042 mmol) in Ac2O (5 mL). After 2.5 h, the mix-
ture was cooled to 0 °C and MeOH (2 mL) was added dropwise.
The mixture was concentrated, and the residue was co-evapo-
rated with toluene (2 ꢃ 5 mL), whereafter FC (toluene–EtOAc
6:1) gave 11 (48 mg, 0.032 mmol, 75%). Rf = 0.61 (toluene–EtOAc
3.7. 6-O-Allyl-4,7-di-O-benzyl-2,3-O-isopropylidene-
b- -manno-heptopyranosyl-(1?3)-[2,3,4,6-tetra-O-benzoyl-b-
glucopyranosyl-(1?4)]-7-O-acetyl-1,6-anhydro-2-O-benzyl-
glycero- -manno-heptopyranose (9)
L-glycero-
D
D-
L
-
a
-D
2:1); [a]
+10 (c 1.0, CHCl3); 13C NMR (125 MHz, CDCl3): d 20.4,
D
Compounds
5
(0.034 g, 0.066 mmol) and
8
(0.037 g,
20.5, 20.8, 20.9, 40.8, 61.6 (2C), 61.9, 63.8, 67.8, 70.3, 70.4, 71.6,
71.6, 72.2 (3C), 72.9, 73.0, 73.7, 73.9, 74.1, 74.3, 74.7, 75.2, 91.0,
99.5, 100.5, 116.8, 127.7–130.5 (Ar-C), 132.9, 133.1, 133.3, 133.4,
133.5, 134.6, 137.3, 138.1, 164.8, 165.4, 165.6, 165.7, 166.1,
166.6, 168.7, 170.0, 170.4, 170.8; 1H NMR (500 MHz, CDCl3): d
1.67 (s, 3H), 1.71 (s, 3H), 2.00 (s, 3H), 2.15 (s, 3H), 3.60–3.67
(m, 3H), 3.84–4.17 (m, 10H), 4.33–4.44 (m, 4H), 4.63 (benzylic
d, 1H, Jgem = 13.0 Hz), 4.65 (benzylic d, 1H, Jgem = 11.0 Hz), 4.70
(dd, 1H, J = 3.5, 12.0 Hz), 4.77 (benzylic d, 1H, Jgem = 13.0 Hz),
4.84 (benzylic d, 1H, Jgem = 11.0 Hz), 4.91 (d, 1H J = 8.0 Hz), 5.26
(dd, 1H, J = 1.5, 9.5 Hz), 5.34 (dd, 1H, J = 6.5, 6.5 Hz), 5.43 (dd,
1H, J = 1.5, 17.5 Hz), 5.50 (dd, 1H, J = 9.0, 9.0 Hz), 5.53 (d, 1H,
J = 1.0 Hz), 5.71 (dd, 1H, J = 3.0, 9.5 Hz), 5.83–5.90 (m, 2H), 5.98
0.041 mmol) were dissolved in dry Et2O (3 mL) followed by the
addition of 4 A MS. After stirring under an Ar-atmosphere for
30 min, the mixture was cooled to 0 °C and DMTST (0.032 g,
0.123 mmol) was added. After 2 h (0 °C?rt), Et3N (0.150 mL) was
added and the mixture was filtered through Celite and concen-
trated. FC (toluene–EtOAc 6:1?3:1) of the residue gave
9
(0.029 g, 0.021 mmol, 52%). 13C NMR (100 MHz, CDCl3): d 21.0,
26.4, 27.3, 63.2, 65.2, 69.7, 71.6, 72.1, 72.3, 72.5, 72.7, 72.9, 72.9,
73.6, 73.8, 74.0, 74.1, 74.9, 75.5, 75.9, 76.1, 78.8, 79.7, 100.8
(JCH = 161 Hz), 101.1 (JCH = 176 Hz), 101.2 (JCH = 167 Hz), 111.3,
117.8, 127.8–130.0, 133.4, 133.5, 133.7, 135.3, 138.3, 138.5,
165.2, 165.4, 166.0, 166.3, 170.7; 1H NMR (400 MHz, CDCl3): d

1336
J. D. M. Olsson, S. Oscarson / Carbohydrate Research 345 (2010) 1331–1338
(s, 1H), 5.98–6.04 (m, 2H), 6.15 (d, 1H, J = 1.5 Hz), 7.24–7.55 (m,
24 H), 7.68 (t, 1H, J = 7.5 Hz), 7.78 (dd, 2H, J = 1.5, 7.5 Hz), 7.95
(dd, 2H, J = 1.0, 8.0 Hz), 8.00 (d, 2H, J = 8.0 Hz), 8.05 (dd, 1H,
J = 1.0, 8.0 Hz), 8.28 (d, 1H, J = 7.5 Hz); HRMS calcd for
1H, Jgem = 13.2 Hz), 4.63 (benzylic d, 1H, Jgem = 11.2 Hz), 4.67
(dd, 1H, J = 3.6, 12.0 Hz), 4.74 (benzylic d, 1H, Jgem = 13.2 Hz),
4.81 (benzylic d, 1H, Jgem = 11.2 Hz), 4.82 (d, 1H, J = 8.0 Hz),
4.89 (m, 1H), 5.01 (s, 2H), 5.25 (dd, 1H, J = 1.6, 10.8 Hz), 5.34
(dd, 1H, J = 6.8, 6.8 Hz), 5.41 (dd, 1H, J = 1.6, 17.2 Hz), 5.45–5.49
(m, 2H), 5.68 (dd, 1H, J = 3.2, 10.0 Hz), 5.81–6.03 (m, 5H),
7.10–7.54 (m, 24H), 7.63 (m, 1H), 7.75 (dd, 2H, J = 1.2, 8.4 Hz),
7.92 (dd, 2H, J = 1.2, 8.0 Hz), 7.97 (dd, 2H, J = 1.2, 8.4 Hz), 8.03
(dd, 2H, J = 1.6, 8.4 Hz), 8.26 (dd, 2H, J = 1.2, 8.4 Hz); HRMS calcd
for C90H90ClNO29 [M+Na]+ 1706.5179; found 1706.5152.
C
82H81ClO28 [M+Na]+ 1571.4495; found 1571.4488.
3.10. Ethyl 7-O-acetyl-6-O-allyl-2-O-benzoyl-4-O-benzyl-3-O-
chloroacetyl- -glycero- -manno-heptopyranosyl-(1?3)-
[2,3,4,6-tetra-O-benzoyl-b- -glucopyranosyl-(1?4)]-6,7-tri-O-
-glycero- -manno-
L
a-D
D
acetyl-2-O-benzyl-1-thio-
L
a-D
heptopyranoside (12)
3.12. 2-(N-Benzyloxycarbonyl) aminoethyl 7-O-acetyl-6-O-allyl-
EtSH (20
l
L, 0.27 mmol) and BF3ꢀOEt2 (68
l
L, 0.54 mmol)
2-O-benzoyl-4-O-benzyl-
(1?3)-[2,3,4,6-tetra-O-benzoyl-b-
L
-glycero-
a
-
D
-manno-heptopyranosyl-
-glucopyranosyl-(1?4)]-6,7-
di-O-acetyl-2-O-benzyl-L-glycero-a-D-manno-heptopyranoside
were added to a solution of 11 (42 mg, 0.027 mmol) in dry
CH2Cl2 (3 mL). After stirring for 3 h (reaction monitored by MS)
at 27 °C under Ar, the mixture was diluted with CH2Cl2 (5 mL),
washed with NaHCO3 (satd) (10 mL) and subjected to normal
work-up followed by FC (toluene–EtOAc 6:1?9:2) to give 12
D
(14)
MeOH saturated with NH3 (2 mL) was added dropwise to a
cooled (0 °C) solution of 13 (15 mg, 0.009 mmol) in CH2Cl2
(1 mL). After stirring for 90 min at 0 °C, the solvent was evapo-
rated and FC (toluene–EtOAc 2:1) of the residue gave 14
(29 mg, 0.019 mmol, 69%). Rf 0.55 (toluene–EtOAc 3:1); [a]
D
+21 (c 1.0, CHCl3); 13C NMR (125 MHz, CDCl3): d 14.7, 20.3,
20.9, 20.9, 25.0, 40.8, 61.0, 61.5, 63.8, 68.0, 69.8, 70.2, 70.4,
71.3 (2C), 71.6, 72.0, 72.2, 72.9, 72.9, 73.7, 74.0, 74.1, 75.1
(2C), 75.5, 82.6, 99.3, 100.5, 116.6, 127.7–128.8 (Ar-C), 129.2,
129.2, 129.8–130.4 (Ar-C), 132.8, 133.0, 133.2, 133.2, 133.4,
134.7, 137.7, 138.2, 164.6, 165.3, 165.5, 165.6, 166.0, 166.5,
170.0, 170.4, 170.7; 1H NMR (500 MHz, CDCl3): d 1.15 (t, 3H,
J = 7.5 Hz), 1.66 (s, 3H), 1.75 (s, 3H), 2.15 (s, 3H), 2.37–2. 49
(m, 2H), 3.74–4.01 (m, 10H), 4.08 (dd, 1H, J = 6.5, 11.0 Hz),
4.13 (m, 1H), 4.31–4.40 (m, 3H), 4.54 (dd, 1H, J = 6.5, 11.0 Hz),
4.62 (benzylic d, 1H, Jgem = 13.0 Hz), 4.66 (benzylic d, 1H,
Jgem = 11.5 Hz), 4.71 (dd, 1H, J = 3.5, 12.0 Hz), 4. 78 (benzylic d,
1H, Jgem = 13.0 Hz), 4.82 (benzylic d, 1H, Jgem = 11.5 Hz), 4.87–
4.91 (m, 2H), 5.26 (d, 1H, J = 10.5 Hz), 5.31 (s, 1H), 5.41–5.50
(m, 3H), 5.53 (s, 1H), 5.72 (dd, 1H, J = 3.0, 10.5 Hz), 5.84–5.87
(m, 2H), 5.96–6.05 (m, 2H), 7.13–7.43 (m, 22H), 7.49 (t, 1H,
J = 7.5 Hz), 7.54 (t, 1H, J = 7.5 Hz), 7.67 (t, 1H, J = 7.5 Hz), 7.77
(dd, 2H, J = 1.0, 7.5 Hz), 7.94 (dd, 2H, J = 1.5, 8.0 Hz), 7.99 (d,
2H, J = 8.0 Hz), 8.08 (dd, 2H, J = 8.0 Hz), 8.28 (d, 2H, J = 8.0 Hz);
(13 mg, 0.008 mmol, 90%). Rf = 0.66 (toluene–EtOAc 1:1); [a]
D
+3 (c 1.0, CHCl3); 13C NMR (125 MHz, CDCl3): d 19.2 (2C), 20.0,
39.6, 60.0, 62.1, 62.3, 65.4, 66.0, 66.9, 68.7, 69.0 (2C), 70.2,
70.4, 70.7, 70.9, 71.4, 71.9 (2C), 72.6, 72.8, 73.7, 73.8 (2C),
74.2, 97.5, 98.7, 99.5, 115.5, 126.5–129.4 (Ar-C), 132.0, 132.2,
132.3, 133.6, 133.7, 135.7, 136.7, 138.1, 155.6, 163.5, 164.3,
164.5, 165.0, 165.5, 168.8, 169.5, 170.0; 1H NMR (500 MHz,
CDCl3): d 1.61 (s, 6H), 2.28 (s, 3H), 2.76 (m, 1H), 3.05 (m, 1H),
3.27–3.67 (m, 8H), 3.85–4.44 (m, 11H), 4.58–4.86 (m, 4H),
5.00–5.07 (m, 3H), 5.19–5.46 (m, 5H), 5.57 (dd, 1H, J = 9.0 Hz),
5.81–6.01 (m, 5H), 7.16–7.55 (m, 30H), 7.83 (d, 2H, J = 7.5 Hz),
8.00 (d, 2H, J = 7.5 Hz), 8.03–8.07 (m, 4H), 8.26 (d, 2H,
J = 7.5 Hz); HRMS calcd for
found 1630.5512.
C
88H89NO28 [M+Na]+ 1630.5463;
3.13. 2-(N-Benzyloxycarbonyl) aminoethyl 7-O-acetyl-2-O-
benzoyl-4-O-benzyl-3-O-chloroacetyl- -glycero- -manno-
heptopyranosyl-(1?3)-[2,3,4,6-tetra-O-benzoyl-b-
glucopyranosyl-(1?4)]-6,7-di-O-acetyl-2-O-benzyl-
-manno-heptopyranoside (15)
L
a-D
HRMS calcd for
1571.4487.
C
82H83ClO26
S
[M+Na]+ 1573.4474; found
D-
L
-glycero-a-
D
3.11. 2-(N-Benzyloxycarbonyl) aminoethyl 7-O-acetyl-6-O-allyl-
2-O-benzoyl-4-O-benzyl-3-O-chloroacetyl- -glycero-
manno-heptopyranosyl-(1?3)-[2,3,4,6-tetra-O-benzoyl-b-
glucopyranosyl-(1?4)]-6,7-di-O-acetyl-2-O-benzyl- -glycero-
-manno-heptopyranoside (13)
L
a
-
D-
A solution of 13 (14 mg, 8.2
gassed and placed under an argon atmosphere. [Bis(methyldiphe-
nylphosphine)](1,5-cyclooctadine) Ir(I)PF6 (0.7 mg, 0.82 mol)
was added and the solution was again degassed but now placed
under a H2-atmosphere. After stirring for 5 min, the H2 was re-
placed by Ar and the stirring was continued for 15 min whereafter
lmol) in dry THF (2.5 mL) was de-
D-
L
a-
l
D
Compound 12 (16 mg, 0.010 mmol) and N-Cbz-2-aminoetha-
nol (5 mg, 0.026 mmol) were dissolved in dry CH2Cl2–Et2O (2:1,
1.5 mL) followed by the addition of 4 A MS. After stirring for
30 min under an Ar-atmosphere the mixture was cooled to
0 °C and NIS (4 mg, 0.018 mmol) and AgOTf (cat.) were added.
NIS (18 mg, 82 lmol) and H2O (0.400 mL) were added. After an
additional 10 min, the solution was diluted with CH2Cl2 (6 mL),
washed with Na2S2O3 (10% aq, 10 mL) and subjected to normal
work-up followed by FC (toluene–EtOAc 2:1) to afford 15 (10 mg,
After stirring for 30 min (0 °C?rt), Et3N (70
l
L) was added and
6.0
l
mol, 73%). Rf = 0.68 (toluene–EtOAc 1:1); [
a
]
+2 (c 1.0,
D
the mixture was diluted with CH2Cl2 (5 mL), filtered through Cel-
ite, washed with Na2S2O3 (10% aq, 8 mL) and subjected to nor-
mal work-up. FC (toluene–EtOAc 6:1?3:1) gave 13 (13 mg,
CHCl3); 13C NMR (125 MHz, CDCl3): d 20.2, 20.3, 20.8, 40.5, 40.7,
60.7, 63.6, 65.1, 66.5, 66.9, 67.7, 69.6, 70.2, 71.3, 72.2, 72.4, 72.8,
73.3, 73.5, 74.9 (2C), 75.3, 79.2, 98.2, 99.2, 100.4, 127.9–130.1
(Ar-C), 132.8, 133.0, 133.2, 133.3, 133.5, 136.6, 137.4, 137.9,
156.6, 164.9, 165.2, 165.4, 166.0, 166.4, 169.8, 170.6, 171.3; 1H
NMR (500 MHz, CDCl3): d 1.59 (s, 6H), 2.15 (s, 3H), 3.09 (m, 1H),
3.35 (m, 2H), 3.51–3.54 (m, 4H), 3.78–4.11 (m, 11H), 4.28 (dd,
1H, J = 10.0, 10.0 Hz), 4.54 (benzylic d, 1H, Jgem = 13.0 Hz), 4.63
(dd, 1H, J = 3.5, 12.0 Hz), 4.70 (benzylic d, 1H, Jgem = 13.0 Hz), 4.73
(benzylic d, 1H, Jgem = 11.5 Hz), 4.78–4.85 (m, 3H), 5.01 (s, 2H),
5.32 (m, 1H), 5.49–5.52 (m, 2H), 5.67 (d, 1H, J = 10.0 Hz), 5.81–
5.91 (m, 2H), 7.17–7.54 (m, 30H), 7.76 (d, 2H, J = 7.5 Hz), 7.92 (d,
2H, J = 7.5 Hz), 7.96 (d, 2H, J = 6.0 Hz), 8.04 (d, 2H, J = 8.5 Hz),
0.0077 mmol, 77%). Rf = 0.69 (toluene–EtOAc 1:1); [
a]
ꢂ7 (c
D
1.0, CHCl3); 13C NMR (125 MHz, CDCl3): d 20.2, 20.3, 20.9, 40.6,
40.8, 60.7, 60.9, 63.2, 63.8, 66.6, 67.0, 67.8, 69.7, 70.3, 70.4,
71.3, 71.8, 72.2, 72.3, 72.9, 73.0, 73.7, 73.8, 74.1, 75.0, 75.1
(2C), 98.4. 99.4, 100.5, 116.6, 127.7–128.7 (Ar-C), 129.1, 129.2,
129.2, 129.7–130.4 (Ar-C), 132.9, 133.0, 133.3, 133.3, 133.4,
134.6, 136.7, 137.7, 138.2, 156.6, 164.7, 165.4, 165.5, 165.6,
166.0, 166.6, 169.8, 170.7, 171.1; 1H NMR (400 MHz, CDCl3): d
1.59 (s, 3H), 1.61 (s, 3H), 2.13 (s, 3H), 3.08 (m, 1H), 3.32 (m,
2H), 3.51–3.66 (m, 3H), 3.83–4.37 (m, 12 H), 4.58 (benzylic d,

J. D. M. Olsson, S. Oscarson / Carbohydrate Research 345 (2010) 1331–1338
1337
8.22 (d, 2H, J = 8.0 Hz); HRMS calcd for C87H86ClNO29 [M+Na]+
1660.4866; found 1660.4929.
sphere. After stirring for 5 min, the H2 was replaced by Ar and the
stirring was continued for 15 min whereafter NIS (12 mg,
56.0 lmol) and H2O (0.400 mL) were added. After an additional
3.14. 14 2-(N-Benzyloxycarbonyl) aminoethyl 7-O-acetyl-6-O-
allyl-3-O-[benzyl-2-(tert-butyloxycarbonylaminoethyl)-
10 min, the solution was diluted with CH2Cl2 (4 mL), washed with
Na2S2O3 (10% aq, 6 mL) and subjected to normal work-up followed
by FC (toluene–EtOAc 2:1). The product was directly dissolved in
EtOAc–MeOH (1:1) (2 mL) followed by the addition of 0.1 M HCl
phosphono]-2-O-benzoyl-4-O-benzyl-
heptopyranosyl-(1?3)-[2,3,4,6-tetra-O-benzoyl-b-
glucopyranosyl-(1?4)]-6,7-di-O-acetyl-2-O-benzyl-
-manno-heptopyranoside (16)
L-glycero-a-D-manno-
D
-
L-glycero-
a
-
(aq) (84 lL) and Pd–C (10%) (cat.). The mixture was stirred under
D
H2 (110 psi) for 14 h, filtered, concentrated and purified by FC
(EtOAc–MeOH–H2O, 7:2:1). The resulting product was dissolved
in MeOH (1.5 mL) and the pH was adjusted to 10 by the addition
of NaOMe (from a 0.1 M in MeOH stock solution). After stirring
for 14 h at 27 °C, the solution was cooled to 0 °C and neutralized
with Dowex-H+ ion exchange resins, filtered and concentrated. Re-
versed phase silica gel chromatography (H2O?H2O–MeOH 1:1)
Tetrazole (3 mg, 0.0043 mmol) was added to a solution of (2-
tert-butyloxycarbonyl aminoethyl)benzyl N,N-diisopropyl phos-
phoramidite6 (17 mg, 0.043 mmol) and 14 (14 mg, 0.009 mmol)
in dry CH2Cl2 (1.5 mL). After stirring for 90 min, the solution was
cooled to 0 °C and m-CPBA (6 mg, 0.026 mmol) was added. After
an additional 10 min at 0 °C, the solution was diluted with CH2Cl2
(4 mL), washed with NaHCO3 (satd, 10 mL) and subjected to nor-
mal work-up. FC (toluene–EtOAc 3:1?2:1) yielded 16 (14 mg,
0.0072 mmol, 80%) as an inseparable diastereomeric mixture.
Rf = 0.25 (toluene–EtOAc 2:1); 13C NMR (125 MHz, CDCl3): d 20.2,
20.3, 20.6, 28.3, 28.3, 40.5, 40.7, 60.7, 63.3, 63.4, 64.4, 66.5, 66.8,
66.8, 67.3, 67.8, 69.2, 69.4, 69.5, 69.6, 69.7, 70.8, 71.0, 71.3, 71.6,
72.1–72.4 (several carbons), 72.8, 72.9, 73.6, 73.8, 74.9, 75.0,
78.9, 79.0, 79.2, 98.3, 98.4, 99.3, 99.4, 100.0, 116.5, 127.5–130.4
(Ar-C), 132.8, 132.9, 133.0, 133.1, 133.2, 133.3, 133.4, 134.5,
135.6, 135.8, 136.6, 137.5, 137.7, 138.2, 155.7, 156.0, 156.6,
164.6, 164.4, 165.4, 165.5, 165.6, 166.0, 166.1, 169.8, 170.6,
170.6, 171.0; 31P NMR (decoupled, 162 Hz, CDCl3): d ꢂ1.64,
ꢂ1.02; HRMS calcd for C102H109N2O33P [M+Na]+ 1943.6542; found
1943.6540.
and freeze-drying of the product gave 18 (2.3 mg, 2.7 lmol, 49%);
13C NMR (125 MHz, D2O): d 27.7 (3C), 39.5, 40.7 (J = 7.5 Hz), 61.2,
61.5 (J = 5.0 Hz), 62.6, 62.9, 68.0, 68.8, 69.0, 69.6, 69.8, 70.0, 70.2,
70.7, 71.8, 73.0, 73.8 (2C), 75.7, 76.1, 76.3 (J = 5.0 Hz), 99.6, 100.7,
102.6 (Note: Cq and C(O) from –NHBoc not detected); 1H NMR
(500 MHz, D2O): d 1.36 (s, 9H), 2.96–2.98 (m, 2H), 3.21 (dd, 1H,
J = 8.0, 9.5 Hz), 3.23–3.43 (m, 8H), 3.52–3.76 (m, 8H), 3.85–4.06
(m, 7H), 4.18–4.24 (m, 2H), 4.48 (d, 1H, J = 8.0 Hz), 4.78 (d, 1H,
J = 1.5 Hz), 5.28 (s, 1H); 31P NMR (decoupled, 162 Hz, D2O): d
0.09; HRMS calcd for C29H55N2O23P [M+H]+ 831.3006; found
831.3051.
3.17. 2-Aminoethyl 6-O-[2-(tert-butyloxycarbonylaminoethyl)-
phosphono]-
L-glycero-
a-
D
-manno-heptopyranosyl-(1?3)-[b-
D-
glucopyranosyl-(1?4)]-
L
-glycero- -manno-heptopyranoside
a-D
(19)
3.15. 2-(N-Benzyloxycarbonyl) aminoethyl 7-O-acetyl-6-O-
[benzyl-2-(tert-butyloxycarbonylaminoethyl)-phosphono]-2-O-
Compound 17 (4 mg, 2.5
(1:1) (2 mL) followed by the addition of 0.1 M HCl (aq) (50 l
l
mol) was dissolved in EtOAc–MeOH
L)
benzoyl-4-O-benzyl-3-O-chloroacetyl-
heptopyranosyl-(1?3)-[2,3,4,6-tetra-O-benzoyl-b-
glucopyranosyl-(1?4)]-6,7-di-O-acetyl-2-O-benzyl-
-manno-heptopyranoside (17)
L
-glycero-
a
-
D
-manno-
-
D
and Pd–C (10%) (cat.). The mixture was stirred under H2 (110 psi)
for 14 h, filtered, concentrated and purified by FC (EtOAc–MeOH–
H2O, 7:2:1). The resulting product was dissolved in MeOH
(1.0 mL) and the pH was adjusted to 10 by the addition of NaOMe
(from a 0.1 M in MeOH stock solution). After stirring for 16 h, the
solution was cooled to 0 °C and neutralized with Dowex-H+ ion ex-
change resins, filtered and concentrated. Reversed phase silica gel
chromatography (H2O?H2O–MeOH 1:1) and freeze-drying of the
L-glycero-a-
D
Tetrazole (3 mg, 4.2
butyloxycarbonyl aminoethyl)benzyl N,N-diisopropyl phospho-
ramidite6 (16 mg, 42
mol) and 17 (14 mg, 8.4 mol) in dry CH2Cl2
(1 mL). After stirring for 60 min, the solution was cooled to 0 °C
and m-CPBA (6 mg, 2.6 mol) was added. After an additional
lmol) was added to a solution of (2-tert-
l
l
l
product gave 19 (1.6 mg, 1.9 l
mol, 76%). 13C NMR (125 MHz,
10 min (0 °C), the solution was diluted with CH2Cl2 (6 mL), washed
with NaHCO3 (satd, 8 mL) and subjected to normal work-up. FC
(toluene–EtOAc 3:1?2:1?1:1) gave 17 (12 mg, 6.2 lmol, 73%) as
CDCl3): d 27.7, 39.2, 40.7 (J = 10 Hz), 60.6, 61.5, 62.4, 63.4, 65.0,
66.0, 67.9, 69.6, 69.7, 69.9, 70.4, 70.8, 71.0, 73.4 (J = 6.5 Hz), 73.5,
73.8, 73.9, 75.6, 76.3, 99.8, 101.5, 102.5 (Note: Cq and C(O) from
–NHBoc not detected); 1H NMR (400 MHz, D2O): d 1.45 (s, 9H),
3.25–3.37 (m, 6H), 3.44–3.59 (m, 3H), 3.70–3.99 (m, 14 H), 4.11–
4.17 (m, 3H), 4.26 (dd, 1H, J = 9.4, 9.4 Hz), 4.51 (m, 1H), 4.56 (d,
1H, J = 8.0 Hz), 4.87 (d, 1H, J = 1.5 Hz), 5.31 (d, 1H, J = 0.8 Hz); 31P
an inseparable diastereomeric mixture. Rf = 0.55 (toluene–EtOAc
1:1); 13C NMR (125 MHz, CDCl3): d 20.1, 20.8, 21.0, 28.3, 28.4,
29.7, 40.5, 40.6, 40.8 60.4, 60.6, 63.3, 63.6, 65.1, 66.5, 67.1, 67.3,
67.7, 69.4–70.5 (several carbons), 72.1, 72.5, 72.9, 73.6, 74.1,
74.7, 74.9, 79.6, 98.3, 99.0, 100.4, 127.5–128.8 (Ar-C), 129.7,
129.7, 129.9, 130.0, 130.2, 132.8, 133.0, 133.2, 133.3, 133.4,
133.5, 136.6, 137.4, 138.1, 155.7. 155.9, 156.6, 164.8, 165.3,
165.4, 165.6, 166.0, 166.4, 166.5, 169.7, 170.6, 170.8; 31P NMR
(decoupled, 162 Hz, CDCl3): d ꢂ0.87, ꢂ1.08; HRMS calcd for
NMR (decoupled, 162 Hz, D2O):
C
d 0.62; HRMS calcd for
29H55N2O23P [M+H]+ 831.3006; found 831.3023.
3.18. 2-Aminoethyl
L
-glycero-
a
-
D
-manno-heptopyranosyl-
-glycero- -manno-
(1?3)-[b- -glucopyranosyl-(1?4)]-
D
L
a-D
C
101H106ClN2O34P [M+Na]+ 1979.5945; found 1979.5931.
heptopyranoside (20)
3.16. 2-Aminoethyl 3-O-[2-(tert-butyloxycarbonylaminoethyl)-
A solution of 14 (7 mg, 4.30 lmol) in dry THF (1.5 mL) was de-
phosphono]-
glucopyranosyl-(1?4)]-
(18)
L
-glycero-
a
-
D
-manno-heptopyranosyl-(1?3)-[ b-
D
-
gassed and placed under an argon atmosphere. [Bis(methyldiphe-
nylphosphine)](1,5-cyclooctadine) Ir(I)PF6 (cat.) was added and
the solution was again degassed but now placed under a H2-atmo-
sphere. After stirring for 5 min, the H2 was replaced by Ar and the
stirring was continued for 15 min whereafter NIS (10 mg,
L
-glycero- -manno-heptopyranoside
a-D
A solution of 16 (11 mg, 5.60 lmol) in dry THF (2 mL) was de-
gassed and placed under an argon atmosphere. [Bis(methyldiphe-
nylphosphine)](1,5-cyclooctadine) Ir(I)PF6 (cat.) was added and
the solution was again degassed but now placed under a H2-atmo-
43.0 lmol) and H2O (0.300 mL) were added. After an additional
10 min, the solution was diluted with CH2Cl2 (5 mL), washed with
Na2S2O3 (10% aq, 6 mL) and subjected to normal work-up followed

1338
J. D. M. Olsson, S. Oscarson / Carbohydrate Research 345 (2010) 1331–1338
by FC (toluene–EtOAc 2:1). The product was directly dissolved in
EtOAc–MeOH (1:1, 2 mL) followed by the addition of 0.1 M HCl
(aq, 76 lL) and Pd–C (10%, cat.). The mixture was stirred under
References
1. Andersen, S. R.; Kolberg, J.; Hoiby, E. A.; Namork, E.; Caugant, D. A.; Froholm, L.
O.; Jantzen, E.; Bjune, G. Microb. Pathog. 1997, 23, 139–155.
2. Cox, A. D.; Li, J. J.; Brisson, J. R.; Moxon, E. R.; Richards, J. C. Carbohydr. Res. 2002,
337, 1435–1444.
3. Richards, J. C.; Cox, A. D.; Schweda, E. K. H.; Martin, A.; Hood, D. W.; Moxon, E.
R. Adv. Exp. Med. Biol. 2001, 491, 515–524. and references cited therein.
4. Yildirim, H. H.; Hood, D. W.; Moxon, E. R.; Schweda, E. K. H. Eur. J. Biochem.
2003, 270, 3153–3167. and references cited therein.
5. Moxon, E. R.; Hood, D. W.; Saunders, N. J.; Schweda, E. K. H.; Richards, J. C.
Philos. Trans. R. Soc. London, Ser. B 2002, 357, 109–116.
6. Mannerstedt, K.; Segerstedt, E.; Olsson, J.; Oscarson, S. Org. Biomol. Chem. 2008,
6, 1087–1091.
H2 (110 psi) for 10 h, filtered, concentrated and purified by FC
(EtOAc–MeOH–H2O, 7:2:1). The resulting product was dissolved
in MeOH (2 mL) and the pH was adjusted to 10 by the addition
of NaOMe (from a 0.1 M in MeOH stock solution). After stirring
for 16 h, the solution was neutralized with Dowex-H+ ion exchange
resins, filtered and concentrated. Reversed phase silica gel chroma-
tography (H2O) and freeze-drying of the product gave 20 (2.0 mg,
3.2 l
mol, 74%); 13C NMR (125 MHz, D2O): d 39.2, 61.5, 62.4, 62.7,
7. Olsson, J. D. M.; Oscarson, S. Tetrahedron: Asymmetry 2009, 20, 879–886.
8. Wakarchuk, W.; Schur, M. J.; St. Michael, F.; Li, J.; Eichler, E.; Whitfield, D.
Glycobiology 2004, 14, 537–546.
9. Boons, G. J. An approach Towards the Development of a Synthetic Vaccine
Against Neisseria meningitides. Ph.D. Thesis, Leiden University, 1991.
10. Bernlind, C.; Oscarson, S. J. Org. Chem. 1998, 63, 7780–7788.
11. Segerstedt, E.; Mannerstedt, K.; Johansson, M.; Oscarson, S. J. Carbohydr. Chem.
2004, 23, 443–452.
12. Olsson, J. D. M. Synthesis of Bacterial Oligosaccharides from N. meningitidis and
Mechanistic Details of Stereoselective Glycosylations Using a Novel Bicyclic
Donor. Ph.D. Thesis, Stockholm University, 2009.
13. Crich, D.; Cai, W.; Dai, Z. J. Org. Chem. 2000, 65, 1291–1297.
14. Codee, J. D. C.; deJong, A. R.; Dinkelaar, J.; Overkleeft, H. S.; van der Marel, G. A.
Tetrahedron 2009, 65, 3780–3788.
66.1, 67.9, 68.7, 69.7, 69.8, 69.9, 70.7, 70.8, 71.7, 73.5, 73.7, 74.1,
75.6, 76.3 (2C), 99.8, 101.5, 102.5; 1H NMR (500 MHz, D2O): d
3.11–3.14 (m, 2H), 3.20 (dd, 1H, J = 8.0, 9.5 Hz), 3.25 (dd, 1H,
J = 9.0, 9.0 Hz), 3.37 (m, 1H), 3.42 (dd, 1H, J = 9.0, 9.0 Hz), 3.51
(dd, 1H, J = 6.0, 12.0 Hz), 3.56–3.71 (m, 9H), 3.77–3.79 (m, 2H),
3.88 (dd, 1H, J = 2.0, 12.0 Hz), 3.95–4.06 (m, 4H), 4.16 (dd, 1H,
J = 10.0, 10.0 Hz), 4.47 (d, 1H, J = 8.0 Hz), 4.77 (d, 1H, J = 1.0 Hz),
5.18 (d, 1H, J = 1.5 Hz); HRMS calcd for C22H41NO18 [M+Na]+
630.2216; found 630.2239.
Acknowledgement
15. Tatai, J.; Fugedi, P. Org. Lett. 2007, 9, 4647–4650.
We thank the Swedish Research Council and Science Founda-
tion Ireland (Grant Number 08/IN.1/B2067) for financial support.