β-Selective glucosylation in the absence of neighboring group participation: influence of the 3,4-O-bisacetal protecting system

Article abstract of DOI:10.1016/j.tet.2007.03.128

A 3,4-O-bisacetal 2,6-di-O-benzyl protected thioglucoside is converted to the corresponding glucosyl triflate with 1-benzenesulfinyl piperidine and trifluoromethanesulfonic anhydride. The moderate to excellent β-selectivity exhibited with this glucosyl tr

Full text of DOI:10.1016/j.tet.2007.03.128

Tetrahedron 63 (2007) 5042–5049
b-Selective glucosylation in the absence of neighboring group
participation: influence of the 3,4-O-bisacetal protecting system
*
David Crich, Venkataraman Subramanian and Thomas K. Hutton
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607-7061, USA
Received 11 January 2007; revised 16 March 2007; accepted 21 March 2007
Available online 27 March 2007
Abstract—A 3,4-O-bisacetal 2,6-di-O-benzyl protected thioglucoside is converted to the corresponding glucosyl triflate with 1-benzenesul-
finyl piperidine and trifluoromethanesulfonic anhydride. The moderate to excellent b-selectivity exhibited with this glucosyl triflate with
a range of alcohols is generally higher than that observed with the more electronically disarmed corresponding 3,4-O-carbonate, for which
a possible reason is advanced.
Ó 2007 Elsevier Ltd. All rights reserved.
OBn
1. Introduction
OMe
O
O
OBn
O
OBn
Ph
O
O
Ph
O
O
O
O
O
O
BnO
The use of cyclic protecting groups to restrict conforma-
tional mobility can have dramatic effects on the stereoselec-
tivity of glycosylation reactions.1 This is illustrated by the
glycosyl triflates 1, 2, 3, and 4, as generated from the corre-
sponding thioglycosides with either 1-benzenesulfinyl piper-
idine (BSP) and triflic anhydride, or with benzenesulfinyl
triflate, or from the corresponding sulfoxides with triflic
anhydride, typically in the presence of a hindered base
such as 2,6-di-tert-butyl-4-methylpyridine or 2,4,6-tri-tert-
butylpyrimidine (TTBP).2–5 With 1, b-mannosides are ob-
tained in a highly selective manner,6–8 an observation that
is attributed to the restriction of the C5–C6 bond to the
most deactivating trans-gauche (tg) conformation, with the
antiperiplanar C5–O5 and C6–O6 bonds,9,10 by the presence
of the benzylidene acetal.11 This rationale is borne out by 2,
which is highly a-selective under the same reactions condi-
tions.12 Donor 3 is also highly a-selective,12 a fact that we
attribute to the imposition of a half-chair conformation on
the pyranose ring by the cis-fused carbonate and which is
sufficient to override the b-directing effect of the benzyl-
idene acetal.12,13 The 3,4-di-O-carbonate 4 on the other
hand, which was investigated in L-6-deoxy-mannose (or
L-rhamnose series), shows moderate b-selectivity.14
OTf
OTf
OMe
OTf
1
2
O
3
O
OTf
t-Bu
S
O
N
N
N
O
O
OBn
t-Bu
t-Bu
O
4
BSP
TTBP
Different results are observed in the gluco-series wherein the
benzylidene protected system 5 is a-selective,15 the 2,3-
di-O-carbonate 6 moderately b-selective,16 and the 3,4-di-
O-carbonate 7 somewhat unselective.16 The 3-deoxy manno
and gluco donors 8 and 10,17 as well as their 3-deoxy-3-
fluoro counterparts 9 and 11,18 are all somewhat unselective
prompting us to suggest that a key interaction in determining
stereoselectivity in this series of glycosylation reactions is
that between the C2–O2 and C2–O3 bonds.17,18
OBn
O
OBn
O
Ph
O
O
O
BnO
O
O
O
BnO
BnO
O
O
BnO
OTf
OTf
OTf
O
5
7
6
OBn
O
Ph
O
Ph
O
O
O
O
X
X
Keywords: Glycosylation; Bisacetal; Glycosyl triflate; Stereoselectivity;
Protecting group.
BnO
OTf
OTf
* Corresponding author. Tel.: +1 312 996 5189; fax: +1 312 996 0431;
e-mail: dcrich@uic.edu
10: X = H
11: X = F
8: X = H
9: X = F
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.03.128

D. Crich et al. / Tetrahedron 63 (2007) 5042–5049
5043
Here we describe our investigations of the influence of
the bisacetal type protecting group on glycosylation stereo-
selectivity in the gluco-series through the use of thio-
glycosides 12 and 14, and the corresponding triflates 13
and 15.
triflates to be complete within minutes at ꢀ60 ꢁC, with 13
characterized by an anomeric hydrogen resonating at
d 6.10, and 15 exhibiting the corresponding signal at
d 6.06. In variable temperature NMR experiments both 13
and 15 were found to undergo decomposition around
ꢀ5 ꢁC. Quenching of the 2,3-bisacetal protected triflate 15
with isopropanol gave the corresponding glucoside 16 in
good yield, but with a disappointing anomeric selectivity
of 3:1 in favor of the b-anomer (Table 1, entry 1). The 3,4-
bisacetal protected triflate 13, on the other hand, gave the
b-glucoside 17 exclusively and in excellent yield (Table 1,
entry 2). On the basis of these results no further couplings
were undertaken in the 2,3-bisacetal series, however, a series
of glycosylations were carried out with the preformed 3,4-
bisacetal protected triflate 13 (Table 1, entries 3–10).
OMe
OMe
O
OBn
O
X
O
O
O
O
BnO
BnO
X
BnO
OMe
OMe
12: X = β-SPh
13: X = α-OTf
14: X = β-SPh
15: X = α-OTf
2. Results
With 3b-cholestanol 18 as acceptor the b-glucoside 19 was
formed exclusively (Table 1, entry 3), and a comparable
result was observed with 1-adamantanol (Table 1, entry 4).
With the glucose 4-OH acceptor 22 a ratio of 4:1 in favor
of the b-glucoside 23 was observed (Table 1, entry 5). In
view of this result, the poor ratio observed on coupling to
the less hindered glucose 6-OH acceptor 24 was surprising
Thioglycosides 12 and 14 were prepared as previously
described16 and converted to the corresponding triflates 13
and 15 in the standard manner with BSP and trifluoro-
methanesulfonic anhydride,19,20 in the presence of TTBP21
at ꢀ60 ꢁC. Experiments conducted in deuteriochloroform
in the NMR spectrometer revealed the formation of both
Table 1. Glycosylation of thioglycosides 12 and 14
Entry
Donor
Acceptor
Product
b:a ratiob
Yielda (%)
OMe
SPh
OMe
O
O
O
O
O
O
O
1
3:1
78
BnO
BnO
HO
BnO
MeO
OMe
BnO
OMe
14
12
12
16
MeO
OBn
O
OBn
O
O
O
O
O
O
SPh
2
3
b only
72
70
OBn
OBn
HO
OMe
OMe
17
C8H17
C8H17
MeO
OBn
O
MeO
OBn
O
O
O
SPh
b only
OBn
O
O
OMe
O
HO
OBn
OMe
MeO
18
19
MeO
MeO
OBn
O
OBn
O
O
O
O
O
O
SPh
SPh
HO
4
5
b only
60
80
OBn
OBn
OMe
OMe
20
12
21
OBn
MeO
OBn
O
OBn
BnO
O
O
O
O
O
HO
O
O
O
BnO
4:1
BnO
OBn
BnO
BnO
BnO
OMe
OMe
OMe
OMe
12
23
22
MeO
OBn
O
MeO
OH
O
OBn
O
O
O
O
O
O
BnO
BnO
SPh
O
BnO
6
BnO
3:1
76
OBn
BnO
OMe
BnO
OMe
BnO
OMe
OMe
12
24
25
(continued)

5044
D. Crich et al. / Tetrahedron 63 (2007) 5042–5049
Table 1. (continued)
Entry
7
Donor
Acceptor
Product
b:a ratiob
Yielda (%)
MeO
MeO
MeO
MeO
OBn
O
OBn
HO
Me
NHCO2CH2Ph
O
NHCO2CH2Ph
CO2Me
O
O
O
Me
27
O
SPh
SPh
SPh
O
2:1
82
CO2Me
OBn
BnO
OMe
OMe
26
12
12
12
OMe
O
OMe
O
MeO
OBn
O
OBn
O
HO
O
O
O
O
O
O
O
O
O
8
9
1.5:1
1.5:1
78
75
O
OBn
OBn
OMe
OMe
29
28
OBn
O
MeO
OBn
O
O
O
O
O
O
O
HO
HO
O
O
O
O
OBn
OBn
31
OMe
OMe
OMe
OMe
30
MeO
OBn
O
MeO
OBn
O
O
O
O
O
O
O
O
SPh
10
a onlyc
70
BnO
O
O
O
O
OBn
OMe
OMe
OMe
OMe
12
30
31
a
Isolated yields.
Determined by the crude 1H NMR analysis.
Reaction was performed with NIS/TfOH activation.
b
c
(Table 1, entry 6). With the threonine derivative 26 the selec-
tivity fell to 2:1 in favor of the b-anomer (Table 1, entry 7),
and with either the L- or D-rhamnose 4-OH acceptors 28
and 30,22,23 respectively, the b:a selectivity was only 1.5:1
(Table 1, entries 8 and 9). In the b-mannosylation reactions
conducted previously with donor 1, as well as in b-rhamno-
sylation reactions with 4, and, importantly, b-selective glu-
cosylations with 6 and 7, the secondary glucosyl acceptor
22 performs less well than the L-rhamnosyl acceptor 28
and the primary glucosyl acceptor 24, perhaps suggesting
that diastereoselective matching and/or mismatching plays
a significant role in some of these glycosylation reac-
tions.24–26 Finally, donor 12 was activated with N-iodosucci-
nimide/trifluoromethanesulfonic acid combination27 in the
presence of acceptor 30, when the disaccharide 31 was ob-
tained with complete a-selectivity (Table 1, entry 10). The
contrast in selectivity between entries 9 and 10 of Table 1
underlines the importance of the preformation of the gluco-
syl triflate 13 in the chemistry reported here. The change in
selectivity on going from the BSP/trifluoromethanesulfonic
anhydride activation method to promotion with N-iodosucci-
nimide and trifluoromethanesulfonic acid, or its silver salt,
parallels similar observations made with a range of other
thioglycosides in our laboratory.28,29
mannose series when thioglycoside 33 was reduced cleanly
to 34.12 Activation of 32 with BSP and triflic anhydride at
ꢀ60 ꢁC in dichloromethane, the standard conditions applied
for glycosylation of 12, followed by addition of acceptor 22
gave disaccharide 35 as a 1:1 mixture of a- and b-anomers in
50% yield. The methoxy groups in the bisacetal protecting
system of 12, therefore, play a significant role in determining
the stereoselectivity of the glycosylation reaction.
BnO
OBn
OMe
OBn
O
O
O
O
SPh
O
O
BnO
OMe
SPh
32
33
OBn
O
BnO
OBn
OBn
O
O
O
O
O
O
O
BnO
BnO
BnO
SPh
OMe
34
35
3. Discussion
The b-selectivity observed with the 3,4-O-bisacetal protected
glucosyl triflate 13 is significant in so far as it contrasts with
the a-selectivity observed earlier12 with the corresponding a-
selective 3,4-O-bisacetal protected mannosyl triflate 2. Even
more significant, however, is the improved b-selectivity ob-
served with triflate 13 over and above that has seen previ-
ously16 with the corresponding 3,4-O-carbonate 7 as the
more disarmed31,32 carbonate was expected to be the more
b-selective donor. Applying our standard mechanistic hy-
pothesis for these glycosyl triflate based glycosylations,
To probe the influence of the methoxy groups in the bisacetal
system on the stereoselectivity of glycosylations, thioglyco-
side 12 was treated with sodium cyanoborohydride and HCl
in THF,30 when 32 was obtained in excellent yield, as a single
diastereomer. The diequatorial disposition of the methyl
groups in 32 follows from the mechanism of reduction and
is supported by nuclear Overhauser measurements. The
analogous stereoselectivity was previously observed in the

D. Crich et al. / Tetrahedron 63 (2007) 5042–5049
5045
OBn
OBn
OBn
OMe
O
OMe
OMe
O
O
O
O
O
O
O
O
BnO
BnO
BnO
OMe
OTf
OMe
OMe
OTf
OTf
13
CIP
β-selective
SSIP
α-selective
Scheme 1. Glycosylation mechanism illustrating the influence of the 3,4-O-bisacetal group.
which is based on the classical Lemieux mechanism,33 and
for which we have provided substantial evidence,7,34,35 the
explanation must be found in the effect of the protecting
groups on the equilibria between the covalent a-triflates,
a transient contact ion pair (CIP) comprised of the glycosyl
oxacarbenium ions and the triflate counter ion, and a related
solvent separated ion pair (SSIP). In this hypothesis the cova-
lent a-triflate serves as a reservoir for the transient CIP,
which, with the triflate shielding the a-face from which it
has just departed, is the source of the b-glycosides. In the
SSIP the anomeric effect takes over, leading to the formation
of the a-glycosides. b-Selectivity is the result of a protecting
system that destabilizes the glycosyl oxacarbenium shifting
the whole series of equilibria toward the covalent glycosyl
triflate and thereby decreasing the concentration of the
SSIP. a-Selectivity is the result of a higher concentration of
the SSIP arising from increased glycosyl cation stability. In
the case of triflate 13 (Scheme 1), as the covalent triflate
collapses to the CIP with its glycosyl oxacarbenium ion in
and remote protecting groups can sometimes have major
effects on reactivity.
5. Experimental
5.1. General experimental
NMR spectra were recorded in CDCl3 solution, with
chemicals shifts in parts per million downfield from tetra-
1
methylsilane at 500 and 125 MHz for H and 13C, respec-
tively. Specific rotations were measured in CHCl3 at room
temperature. Mass spectra were recorded with electrospray
ionization.
5.2. General procedure for glycosylation using the
BSP/TTBP/Tf2O system
To a stirred solution of phenyl 2,6-O-benzyl-3,4-O-
(2,3-dimethoxybutane-2,3-diyl)-1-thio-b-D-glucopyranoside
4
a conformation approximating to a H3 half-chair,36,37 the
˚
(1 equiv), BSP (1.1 equiv), TTBP (1.5 equiv), and 4 A mo-
C2–O2 bond necessarily rotates down below the nominal
pyranose plane leading to an increased steric interaction
with the methoxy group of the bisacetal. We argue that it is
this increased steric interaction, which is absent in the corre-
sponding mannosyl triflate 2, that destabilizes the glycosyl
cation sufficiently to bring about the observed b-selectivity.
With the 2,3-O-bisacetal protected triflate 15 this interaction
is absent in the derived oxacarbenium ion, whether it adopts
the 4H3 or the closely related, isoenergetic 3E conformer,36,37
and the chemistry reverts to the more normal pattern with the
morehighlydisarmed2,3-O-carbonatebeingmore b-selective
than the acetal.
lecular sieves in CH2Cl2 (0.05 M in substrate) at ꢀ60 ꢁC
under an Ar atmosphere was added Tf2O (1.2 equiv). After
stirring for 30 min at the same temperature, a solution of gly-
cosyl acceptor (1.5 equiv) in CH2Cl2 (0.02 M in acceptor)
was added slowly at ꢀ60 ꢁC. The reaction was further stirred
for 3 h at the same temperature and then allowed to reach
room temperature before dilution with dichloromethane, fil-
tration, and washing with excess CH2Cl2. The organic layer
was then washed with saturated sodium bicarbonate solu-
tion, followed by saturated sodium chloride solution, then
was dried over sodium sulfate, evaporated to dryness, and
purified by silica gel column chromatography using
EtOAc/hexanes as eluant to afford the corresponding b and
a glucopyranosides.
Strong support for this hypothesis is provided by the loss of
stereoselectivity on glycosylation of the des-methoxy sys-
tem 32, when there is no longer a destabilizing steric inter-
action between the O2 protecting group and the cyclic
protecting group spanning O3 and O4. Once again, it is
appropriate to note the contrast with the mannose series
wherein both the standard donor 33 and the des-methoxy
analog 34 were a-selective.
5.2.1. Isopropyl 4,6-di-O-benzyl-2,3-O-(2,3-dimethoxy-
[a]1D7
butane-2,3-diyl)-b-D-glucopyranoside
(16b).
1
ꢀ103.0 (c 1.0); H NMR d: 1.19 (d, J¼6.0 Hz, 3H), 1.27
(d, J¼6.0 Hz, 3H), 1.32 (s, 3H), 1.36 (s, 3H), 3.29 (s, 3H),
3.30 (s, 3H), 3.48–3.55 (m, 2H), 3.60 (t, J¼9.5 Hz, 1H),
3.65–3.68 (m, 1H), 3.74 (d, J¼10.5 Hz, 1H), 3.88 (t,
J¼9.5 Hz, 1H), 3.95–3.98 (m, 1H), 4.53 (d, J¼8.0 Hz,
1H), 4.56 (s, 2H), 4.60 (d, J¼12.0 Hz, 1H), 4.92 (d, J¼
11.0 Hz, 1H), 7.23–7.33 (m, 10H); 13C NMR d: 17.7, 17.8,
22.3, 23.5, 47.8, 47.9, 69.4, 69.5, 72.5, 73.4, 74.0, 74.9, 75.0,
75.6, 99.3, 99.4, 99.5, 127.5, 127.6, 127.7, 128.0, 128.3,
128.4, 138.3, 138.4; HRMS calcd for C29H40O8Na
[M+Na]+: 539.2615, found 539.2610.
4. Conclusion
Although several b-selective glucosylation reactions have
been developed recently relying on the use of non-traditional
methods of neighboring group participation,38–40 the chem-
istry described here, together with that of the 2,3-O-carbon-
ate 6, provides a rare example of such a reaction that
completely avoids such types of participation. The increased
b-selectivity of 13, as compared to the more electronically
disarmed 6, illustrates how subtle conformational effects
5.2.2. Isopropyl 4,6-di-O-benzyl-2,3-O-(2,3-dimethoxy-
butane-2,3-diyl)-a-D-glucopyranoside (16a). [a]1D7 +10.0
(c 1.0); 1H NMR d: 1.18 (d, J¼6.0 Hz, 3H), 1.22

5046
D. Crich et al. / Tetrahedron 63 (2007) 5042–5049
(d, J¼6.5 Hz, 3H), 1.32 (s, 3H), 1.35 (s, 3H), 3.26 (s, 3H),
3.30 (s, 3H), 3.63 (d, J¼10.0 Hz, 1H), 3.75–3.79 (m, 3H),
3.85 (d, J¼9.5 Hz, 1H), 3.91–3.93 (m, 1H), 4.19 (t, J¼
10.0 Hz, 1H), 4.76 (d, J¼8.5 Hz, 1H), 4.49 (d, J¼7.0 Hz,
1H), 4.64 (d, J¼12.5 Hz, 1H), 4.91 (d, J¼11.5 Hz, 1H),
4.93 (d, J¼4.0 Hz, 1H), 7.19–7.36 (m, 10H); 13C NMR d:
17.7, 18.1, 21.3, 23.1, 47.8, 47.9, 68.3, 68.5, 69.7, 70.5,
70.6, 73.4, 75.0, 75.3, 95.2, 99.3, 99.7, 127.6, 127.7,
127.9, 128.1, 128.3, 138.2, 138.5; HRMS calcd for
C29H40O8Na [M+Na]+: 539.2615, found 539.2610.
3H), 4.87 (d, J¼11.5 Hz, 1H), 5.06 (d, J¼11.5 Hz, 1H),
7.37–7.19 (m, 25H); 13C NMR d: 17.6, 17.8, 47.9, 48.0,
55.3, 66.2, 68.2, 68.4, 70.0, 73.1, 73.2, 73.4, 73.6, 74.1,
74.7, 75.3, 78.9, 79.6, 80.5, 98.4, 99.6, 102.8, 127.0,
127.2, 127.3, 127.4, 127.5, 127.6, 127.7, 127.8, 127.9,
128.1, 128.4, 138.0, 138.4, 138.7, 138.9, 139.7; HRMS calcd
for C54H64O13Na [M+Na]+: 943.4239, found 943.4260.
5.2.7. Methyl 2,3,6-tri-O-benzyl-4-O-[2,6-di-O-benzyl-
3,4-O-(2,3-dimethoxybutane-2,3-diyl)-a-D-glucopyrano-
syl]-a-D-glucopyranoside (23a). [a]1D7 +82.5 (c 0.8); H
1
5.2.3. Isopropyl 2,6-di-O-benzyl-3,4-O-(2,3-dimethoxy-
butane-2,3-diyl)-b-D-glucopyranoside (17b). White solid,
mp 98 ꢁC; [a]1D7 +94.0 (c 1.0); 1H NMR d: 1.23 (d, J¼6.0 Hz,
3H), 1.29 (s, 3H), 1.31 (d, J¼6.5 Hz, 3H), 1.35 (s, 3H), 3.19
(s, 3H), 3.30 (s, 3H), 3.41 (dd, J¼8.7 and 7.5 Hz, 1H), 3.61–
3.68 (m, 3H), 3.77–3.81 (m, 2H), 3.98–4.00 (m, 1H), 4.46 (d,
J¼7.5 Hz, 1H), 4.61 (q, J¼4.0 Hz, 2H), 4.77 (d, J¼11.0 Hz,
1H), 4.86 (d, J¼11.5 Hz, 1H), 7.25–7.28 (m, 2H), 7.30–7.35
(m, 6H), 7.39–7.40 (m, 2H); 13C NMR d: 17.7, 17.8, 22.3,
23.7, 47.9, 48.0, 66.4, 68.7, 72.5, 72.7, 73.5, 73.7, 74.7,
79.2, 99.5, 102.6, 127.4, 127.5, 127.7, 128.2, 128.3, 138.5,
139.0; HRMS calcd for C29H40O8Na [M+Na]+: 539.2615,
found 539.2618.
NMR d: 1.28 (s, 3H), 1.30 (s, 3H), 3.17 (s, 3H), 3.27 (s,
3H), 3.38 (s, 3H), 3.52 (dd, J¼9.5 and 3.5 Hz, 2H), 3.55–
3.59 (m, 2H), 3.68 (d, J¼9.0 Hz, 1H), 3.76–3.83 (m, 4H),
3.94 (t, J¼9.5 Hz, 1H), 4.02 (t, J¼9.0 Hz, 1H), 4.11 (t,
J¼9.5 Hz, 1H), 4.38 (d, J¼12.0 Hz, 1H), 4.47–4.58 (m,
6H), 4.67 (d, J¼12.5 Hz, 1H), 4.81–4.88 (m, 3H), 5.66 (d,
J¼4.0 Hz, 1H), 7.16–7.31 (m, 25H); 13C NMR d: 17.7,
17.9, 47.9, 48.0, 55.2, 65.8, 67.8, 69.4, 69.6, 70.4, 73.3,
73.3, 73.5, 73.7, 74.1, 74.4, 76.3, 80.1, 81.8, 97.7, 98.1,
99.3, 99.4, 126.8, 126.9, 127.3, 127.4, 127.5, 127.6, 127.8,
128.1, 128.2, 128.2, 128.4, 138.0, 138.1, 138.3, 138.6,
139.2; HRMS calcd for C54H64O13Na [M+Na]+: 943.4239,
found 943.4258.
5.2.4. 3b-Cholestanyl 2,6-di-O-benzyl-3,4-O-(2,3-di-
methoxybutane-2,3-diyl)-b-D-glucopyranoside (19b).
5.2.8. Methyl 2,3,6-tri-O-benzyl-6-O-[2,6-di-O-benzyl-
3,4-O-(2,3-dimethoxybutane-2,3-diyl)-b-D-glucopyrano-
1
1
White solid, mp 128 ꢁC; [a]1D7 +84.0 (c 0.75); H NMR d:
syl]-a-D-glucopyranoside (25b). [a]1D7 +61.1 (c 1.65); H
0.59–0.63 (m, 1H), 0.65 (s, 3H), 0.83 (s, 3H), 0.86–1.39
(m, 36H), 1.47–1.57 (m, 4H), 1.64–1.73 (m, 2H), 1.80–
1.81 (m, 1H), 1.96–1.98 (m, 2H), 3.19 (s, 3H), 3.30 (s,
3H), 3.40 (dd, J¼9.5 and 7.5 Hz, 1H), 3.61–3.67 (m, 4H),
3.78 (t, J¼9.5 Hz, 2H), 4.50 (d, J¼7.5 Hz, 1H), 4.60 (q, J¼
4.0 Hz, 2H), 4.77 (d, J¼11.5 Hz, 1H), 4.86 (d, J¼11.5 Hz,
1H), 7.24–7.33 (m, 8H), 7.39–7.41 (m, 2H); 13C NMR d:
12.1, 12.3, 17.7, 17.8, 18.7, 21.3, 22.6, 22.8, 23.8, 24.2,
28.0, 28.3, 28.8, 29.7, 32.1, 34.8, 35.5, 35.6, 35.8, 36.2,
37.1, 39.5, 40.1, 42.6, 44.8, 47.8, 47.9, 54.4, 56.3, 56.5,
66.5, 68.7, 72.5, 73.5, 73.7, 74.7, 79.4, 99.5, 102.4, 127.4,
127.5, 127.8, 128.2, 128.3, 138.5, 139.0; HRMS calcd for
C53H80O8Na [M+Na]+: 867.5751, found 867.5758.
NMR d: 1.28 (s, 3H), 1.32 (s, 3H), 3.17 (s, 3H), 3.29
(s, 3H), 3.33 (s, 3H), 3.47–3.59 (m, 4H), 3.65–3.69 (m,
3H), 3.75–3.79 (m, 3H), 3.97 (t, J¼9.5 Hz, 1H), 4.15 (d, J¼
11.0 Hz, 1H), 4.35 (d, J¼7.0 Hz, 1H), 4.51 (d, J¼11.0 Hz,
1H), 4.58 (d, J¼6.0 Hz, 2H), 4.62 (d, J¼3.5 Hz, 1H),
4.65–4.69 (m, 3H), 4.78 (dd, J¼12.5 and 4.5 Hz, 1H), 4.82
(s, 2H), 4.96 (d, J¼11.0 Hz, 1H), 7.13–7.36 (m, 25H); 13C
NMR d: 13.8, 13.9, 44.0, 44.1, 51.3, 62.3, 64.7, 64.8, 66.0,
69.0, 69.5, 69.6, 70.1, 70.9, 71.0, 71.8, 73.9, 74.1, 74.8,
75.9, 78.2, 94.2, 95.7, 100.1, 123.4, 123.5, 123.6, 123.7,
123.8, 123.9, 124.0, 124.1, 124.3, 124.4, 124.5, 124.6, 134.4,
134.5, 134.6, 134.9, 135.1; HRMS calcd for C54H64O13Na
[M+Na]+: 943.4239, found 943.4208.
5.2.5. 1-Adamantyl 2,6-di-O-benzyl-3,4-O-(2,3-di-
methoxybutane-2,3-diyl)-b-D-glucopyranoside (21b).
5.2.9. Methyl 2,3,6-tri-O-benzyl-6-O-[2,6-di-O-benzyl-
3,4-di-O-(2,3-dimethoxybutane-2,3-diyl)-a-D-glucopyr-
anosyl]-a-D-glucopyranoside (25a). [a]1D7 +81.0 (c 0.5);
1H NMR d: 1.27 (s, 3H), 1.32 (s, 3H), 3.18 (s, 3H), 3.24
(s, 3H), 3.29 (d, J¼8.0 Hz, 1H), 3.33 (s, 3H), 3.39
(dd, J¼10.0 and 4.0 Hz, 1H), 3.57–3.69 (m, 4H), 3.73–
3.77 (m, 3H), 3.89–3.96 (m, 2H), 4.19 (t, J¼10.0 Hz, 1H),
4.49–4.57 (m, 4H), 4.63–4.70 (m, 3H), 4.78–4.86 (m, 3H),
4.93 (d, J¼11.0 Hz, 1H), 5.03 (d, J¼4.0 Hz, 1H), 7.16–
7.34 (m, 25H); 13C NMR d: 17.7, 17.9, 47.8, 47.9, 54.9,
65.6, 66.2, 68.1, 68.9, 69.8, 70.5, 72.8, 73.3, 73.4, 75.0,
75.7, 76.6, 77.9, 80.2, 82.1, 97.8, 97.9, 99.4, 99.5, 127.2,
127.3, 127.4, 127.5, 127.6, 127.8, 127.9, 128.0, 128.2,
128.3, 128.4, 128.4, 138.2, 138.3, 138.5, 138.9, 139.0;
HRMS calcd for C54H64O13Na [M+Na]+: 943.4239, found
943.4227.
1
[a]1D7 +85.0 (c 1.0); H NMR d: 1.28 (s, 3H), 1.34 (s, 3H),
1.59–1.62 (m, 6H), 1.81–1.84 (m, 3H), 1.91–1.93 (m, 3H),
2.14 (s, 3H), 3.19 (s, 3H), 3.29 (s, 3H), 3.39 (dd, J¼9.5
and 7.5 Hz, 1H), 3.59–3.63 (m, 3H), 3.78–3.80 (m, 2H),
4.59 (s, 2H), 4.69 (d, J¼7.5 Hz, 1H), 4.75 (d, J¼11.5 Hz,
1H), 4.87 (d, J¼1.5 Hz, 1H), 7.24–7.27 (m, 2H), 7.29–7.34
(m, 6H), 7.39–7.41 (m, 2H); 13C NMR d: 17.6, 17.8, 30.7,
36.3, 42.7, 47.9, 66.7, 69.0, 72.7, 73.3, 73.4, 74.7, 75.2,
79.2, 96.5, 99.5, 127.3, 127.4, 127.8, 128.1, 128.2, 138.5,
139.1; HRMS calcd for C36H48O8Na [M+Na]+: 631.3241,
found 631.3243.
5.2.6. Methyl 2,3,6-tri-O-benzyl-4-O-[2,6-di-O-benzyl-
3,4-O-(2,3-dimethoxybutane-2,3-diyl)-b-D-glucopyrano-
1
syl]-a-D-glucopyranoside (23b). [a]1D7 +72.0 (c 1.0); H
NMR d: 1.27 (s, 3H), 1.34 (s, 3H), 3.19 (s, 3H), 3.29 (s, 3H),
3.37 (s, 3H), 3.43–3.47 (m, 4H), 3.53–3.58 (m, 1H), 3.68–
3.81 (m, 5H), 3.88–3.92 (m, 2H), 4.34 (d, J¼12.5 Hz, 1H),
4.43 (q, J¼7.5 Hz, 2H), 4.49–4.60 (m, 4H), 4.71–4.78 (m,
5.2.10. N-Benzyloxycarbonyl 2,6-di-O-benzyl-3,4-O-(2,3-
dimethoxybutane-2,3-diyl)-b-D-glucopyranosyl-L-threo-
1
nine methyl ester (27b). [a]1D7 +66.9 (c 1.3); H NMR
d: 1.28 (d, J¼6.5 Hz, 6H), 1.34 (s, 3H), 3.18 (s, 3H), 3.29

D. Crich et al. / Tetrahedron 63 (2007) 5042–5049
5047
1
(s, 3H), 3.34–3.37 (m, 1H), 3.50–3.51 (m, 1H), 3.65 (s, 3H),
3.67–3.78 (m, 4H), 4.34 (dd, J¼9.0 and 3.5 Hz, 1H), 4.38 (d,
J¼7.5 Hz, 1H), 4.41–4.43 (m, 1H), 4.50 (q, J¼12.0 Hz, 2H),
4.77 (s, 2H), 5.13 (dd, J¼17.5 and 12.5 Hz, 2H), 5.76 (d,
J¼9.0 Hz, 1H), 7.23–7.37 (m, 15H); 13C NMR d: 17.7,
17.8, 47.9, 48.0, 52.4, 58.8, 65.6, 67.1, 68.2, 72.6, 73.6,
73.7, 74.8, 75.0, 78.6, 99.6, 101.8, 127.5, 127.6, 127.8,
128.1, 128.3, 128.5, 136.4, 138.2, 138.6, 156.8, 170.8;
HRMS calcd for C39H49NO12Na [M+Na]+: 746.3147, found
746.3166.
(c 1.0); H NMR d: 1.26 (s, 3H), 1.28 (s, 3H), 1.33 (d, J¼
6.0 Hz, 3H), 1.34 (s, 3H), 1.46 (s, 3H), 3.19 (s, 3H), 3.29
(s, 3H), 3.37 (s, 3H), 3.45–3.51 (m, 2H), 3.58–3.61 (m, 1H),
3.67–3.82 (m, 5H), 4.09 (d, J¼5.5 Hz, 1H), 4.32 (t, J¼
6.5 Hz, 1H), 4.55–4.62 (m, 3H), 4.79 (s, 2H), 4.82 (s, 1H),
7.27–7.38 (m, 10H); 13C NMR d: 17.6, 17.8, 17.9, 26.2,
28.0, 47.9, 48.0, 54.8, 64.6, 66.0, 68.4, 72.9, 73.4, 73.9, 74.8,
75.8, 79.3, 82.2, 98.2, 99.5, 99.6, 103.3, 108.9, 127.4, 127.5,
127.6, 127.8, 128.2, 128.2, 138.4, 138.7; HRMS calcd for
C36H50O12Na [M+Na]+: 697.3194, found 697.3191.
5.2.11. N-Benzyloxycarbonyl 2,6-di-O-benzyl-3,4-O-(2,3-
dimethoxybutane-2,3-diyl)-a-D-glucopyranosyl-L-threo-
5.2.15. Methyl 4-O-[2,6-di-O-benzyl-3,4-O-(2,3-di-
methoxybutane-2,3-diyl)-a-D-glucopyranosyl]-2,3-O-iso-
propylidene-a-D-rhamnopyranoside (31a). [a]1D7 +132.0
1
nine methyl ester (27a). [a]1D7 +100.0 (c 1.0); H NMR
1
d: 1.28 (d, J¼6.0 Hz, 6H), 1.31 (s, 3H), 3.17 (s, 3H), 3.25
(s, 3H), 3.54 (s, 3H), 3.64 (dd, J¼11.0 and 2.0 Hz, 2H),
3.67–3.72 (m, 1H), 3.74 (d, J¼10.0 Hz, 1H), 3.93–3.96
(m, 1H), 4.07 (t, J¼10.0 Hz, 1H), 4.24–4.25 (m, 1H),
4.32–4.33 (m, 1H), 4.54 (dd, J¼12.0 and 6.5 Hz, 2H), 4.66
(d, J¼12.0 Hz, 1H), 4.77 (d, J¼12.0 Hz, 1H), 4.86 (d, J¼
3.5 Hz, 1H), 5.07–5.14 (m, 2H), 5.96 (d, J¼8.0 Hz, 1H),
7.23–7.34 (m, 15H); 13C NMR d: 17.6, 17.8, 19.2, 47.9,
52.3, 58.9, 65.9, 66.9, 67.9, 69.3, 70.2, 73.4, 73.5, 75.7,
76.2, 98.9, 99.5, 99.6, 1274, 127.5, 127.7, 127.9, 128.0,
128.2, 128.4, 136.4, 138.0, 138.5, 156.7, 171.0; HRMS calcd
for C39H49NO12Na [M+Na]+: 746.3147, found 746.3171.
(c 1.0); H NMR d: 1.29 (s, 3H), 1.30 (d, J¼6.5 Hz, 3H),
1.34 (s, 3H), 1.35 (s, 3H), 1.53 (s, 3H), 3.19 (s, 3H), 3.32
(s, 3H), 3.34 (s, 3H), 3.55–3.65 (m, 3H), 3.69–3.78 (m,
3H), 3.91–3.92 (m, 1H), 4.04–4.08 (m, 2H), 4.33 (t, J¼
6.0 Hz, 1H), 4.56 (q, J¼8.5 Hz, 2H), 4.84 (s, 1H), 4.77–
4.81 (m, 2H), 5.59 (d, J¼4.0 Hz, 1H), 7.24–7.32 (m, 8H),
7.41–7.42 (m, 2H); 13C NMR d: 17.7, 18.0, 18.5, 26.3,
28.0, 47.9, 48.1, 54.7, 63.7, 66.2, 67.9, 69.4, 69.8, 73.2,
73.6, 76.0, 76.4, 78.5, 78.6, 96.5, 98.1, 99.4, 99.6, 109.2,
127.4, 127.5, 127.6, 128.2, 128.3, 138.1, 138.9; HRMS calcd
for C36H50O12Na [M+Na]+: 697.3194, found 697.3198.
5.3. Activation of donor 12 with N-iodosuccinimide/
trifluoromethanesulfonic acid
5.2.12. Methyl 4-O-[2,6-di-O-benzyl-3,4-O-(2,3-di-
methoxybutane-2,3-diyl)-b-D-glucopyranosyl]-2,3-O-iso-
propylidene-a-L-rhamnopyranoside (29b). [a]1D7 +47.0
To a stirred 0.05 M solution of 12 and acceptor 30
(1.5 equiv) in dry dichloromethane under argon was added
N-iodosuccinimide (1.2 equiv) at 0 ꢁC, followed by trifluoro-
methanesulfonic acid (0.1 equiv). After stirring for 0.5 h at
0 ꢁC, the reaction mixture was then diluted with dichloro-
methane and washed with saturated aqueous sodium bi-
carbonate. The combined organic portion was washed with
aqueous sodium thiosulfate and then brine, dried over
sodium sulfate, and evaporated to dryness. Purification by
silica gel chromatography gave 31a in 70% yield, with spec-
troscopic data identical to those described above.
1
(c 0.85); H NMR d: 1.28 (s, 3H), 1.31 (s, 3H), 1.32 (d,
J¼6.5 Hz, 3H), 1.34 (s, 3H), 1.45 (s, 3H), 3.21 (s, 3H),
3.29 (s, 3H), 3.36 (d, J¼9.5 Hz, 1H), 3.39 (s, 3H), 3.57–
3.55 (m, 1H), 3.66–3.63 (m, 1H), 3.77–3.69 (m, 4H), 3.82
(t, J¼10.0 Hz, 1H), 4.07 (d, J¼6.0 Hz, 1H), 4.21 (t, J¼
6.5 Hz, 1H), 4.56 (d, J¼12.0 Hz, 1H), 4.62 (d, J¼12.5 Hz,
1H), 4.77 (d, J¼12.0 Hz, 1H), 4.84 (d, J¼11.5 Hz, 2H),
4.94 (d, J¼6.5 Hz, 1H), 7.40–7.41 (m, 2H), 7.25–7.32 (m,
8H); 13C NMR d: 17.6, 17.7, 17.8, 26.4, 27.8, 47.9, 48.0,
54.8, 64.3, 66.1, 68.2, 72.4, 73.5, 73.8, 74.3, 75.9, 77.9,
78.2, 79.1, 98.1, 99.6, 101.7, 109.2, 127.2, 127.4, 127.5,
128.0, 128.3, 138.5, 139.3; HRMS calcd for C36H50O12Na
[M+Na]+: 697.3194, found 697.3176.
5.4. Phenyl 2,6-di-O-benzyl-3,4-O-(butane-2,3-diyl)-
1-thio-b-D-glucopyranoside (32)
5.2.13. Methyl 4-O-[2,6-di-O-benzyl-3,4-O-(2,3-di-
methoxybutane-2,3-diyl)-a-D-glucopyranosyl]-2,3-O-iso-
propylidene-a-L-rhamnopyranoside (29a). [a]1D7 +88.0
Sodium cyanoborohydride (0.33 g, 15.0 mmol) was added
to a stirred solution of donor 12 (0.2 g, 1.0 mmol) in THF
(10.0 mL) under an inert atmosphere. The solution was
cooled to 0 ꢁC and 2.0 M HCl in diethyl ether was added un-
til the pH was 3–4. The reaction mixture was stirred at room
temperature for 24 h, maintaining the same pH, then was
quenched by the addition of saturated NaHCO3.The aqueous
phase was extracted with EtOAc (50 mL) and the organic
layer was washed with water and then brine. After drying
over sodium sulfate, the extracts were evaporated to dryness
and purified by column chromatography using EtOAc/hex-
anes as eluant to give 32 (0.13 g, 70%). [a]1D7 ꢀ4.7 (c 1.0);
1H NMR d: 1.10 (d, J¼6.0 Hz, 3H), 1.17 (d, J¼6.0 Hz,
3H), 3.30–3.39 (m, 3H), 3.43 (t, J¼9.5 Hz, 1H), 3.54 (t, J¼
9.0 Hz, 1H), 3.58 (d, J¼8.0 Hz, 1H), 3.65 (dd, J¼11.0 and
4.5 Hz, 1H), 3.82 (d, J¼10.0 Hz, 1H), 4.55 (d, J¼12.0 Hz,
1H), 4.63 (d, J¼12.5 Hz, 1H), 4.72 (d, J¼9.5 Hz, 1H),
4.76 (d, J¼11.0 Hz, 1H), 4.83 (d, J¼11.0 Hz, 1H), 7.58–
7.60 (m, 2H), 7.45–7.47 (m, 2H), 7.23–7.37 (m, 11H); 13C
1
(c 0.37); H NMR d: 1.22 (s, 3H), 1.29 (d, J¼6.5 Hz, 3H),
1.30 (s, 3H), 1.35 (s, 3H), 1.39 (s, 3H), 3.21 (s, 3H), 3.31 (s,
3H), 3.33 (s, 3H), 3.61–3.67 (m, 2H), 3.69–3.73 (m, 2H),
3.74–3.76 (m, 1H), 3.92 (t, J¼10.0 Hz, 1H), 4.04 (d,
J¼5.5 Hz, 1H), 4.10–4.17 (m, 3H), 4.57 (s, 2H), 4.69 (d,
J¼12.0 Hz, 1H), 4.81 (s, 1H), 4.90 (d, J¼12.0 Hz, 1H),
4.99 (d, J¼3.5 Hz, 1H), 7.25–7.35 (m, 10H); 13C NMR d:
17.4, 17.8, 18.0, 26.3, 28.1, 48.0, 48.1, 54.6, 64.8, 65.7,
67.3, 68.8, 70.5, 73.6, 74.1, 75.9, 80.8, 97.9, 98.8, 99.5,
99.6, 108.8, 127.4, 127.5, 127.8, 128.2, 128.3, 138.2,
138.7; HRMS calcd for C36H50O12Na [M+Na]+: 697.3194,
found 697.3183.
5.2.14. Methyl 4-O-[2,6-di-O-benzyl-3,4-O-(2,3-di-
methoxybutane-2,3-diyl)-b-D-glucopyranosyl]-2,3-O-iso-
propylidene-a-D-rhamnopyranoside (31b). [a]1D7 +78.0

5048
D. Crich et al. / Tetrahedron 63 (2007) 5042–5049
2. Crich, D.; Lim, L. B. L. Org. React. 2004, 64, 115–251.
3. Crich, D. Chemistry of Glycosyl Triflates: Synthesis of b-
Mannopyranosides. In Glycochemistry: Principles, Synthesis,
and Applications; Wang, P. G., Bertozzi, C. R., Eds.; Dekker:
New York, NY, 2001; pp 53–75.
NMR d: 17.3, 17.4, 68.8, 73.4, 73.9, 75.1, 77.6, 77.7, 77.8,
82.9, 87.2, 127.4, 127.5, 127.6, 127.7, 128.2, 128.3, 128.8,
132.1, 133.7, 138.4, 138.5; HRMS calcd for C30H34O5S:
C30H34O5S [M+Na]+: 529.2019, found 529.2019.
4. Crich, D. J. Carbohydr. Chem. 2002, 21, 663–686.
5. Review on bisacetal chemistry: Ley, S. V.; Baeschlin, D. K.;
Dixon, D. J.; Foster, A. C.; Ince, S. J.; Priepke, H. W. M.;
Reynolds, D. J. Chem. Rev. 2001, 101, 53–80.
6. Crich, D.; Sun, S. J. Org. Chem. 1997, 62, 1198–1199.
7. Crich, D.; Sun, S. J. Am. Chem. Soc. 1997, 119, 11217–
11223.
5.5. Glycosylation of des-methoxy donor 32
Activation of 32 according to the standard BSP protocol and
treatment with acceptor 22 gave 35 (50%) as a 1:1 a/b mix-
ture. Column chromatography on silica gel eluting with
EtOAc/hexanes gave 35b and 35a.
8. Crich, D.; Sun, S. Tetrahedron 1998, 54, 8321–8348.
9. Rao, V. S. R.; Qasba, P. K.; Balaji, P. V.; Chandrasekaran, R.
Conformation of Carbohydrates; Harwood Academic:
Amsterdam, 1998.
10. Grindley, T. B. Structure and Conformation of Carbohydrates.
Glycoscience: Chemistry and Chemical Biology; Fraser-Reid,
B., Tatsuta, K., Thiem, J., Eds.; Springer: Berlin, 2001;
Vol. 1, pp 3–51.
11. Jensen, H. H.; Nordstrom, M.; Bols, M. J. Am. Chem. Soc.
2004, 126, 9205–9213.
12. Crich, D.; Cai, W.; Dai, Z. J. Org. Chem. 2000, 65, 1291–
1297.
13. Crich, D.; Vinod, A. U.; Picione, J.; Wink, D. J. ARKIVOC
2005, 339–344.
14. Crich, D.; Vinod, A. U.; Picione, J. J. Org. Chem. 2003, 68,
8453–8458.
15. Crich, D.; Cai, W. J. Org. Chem. 1999, 64, 4926–4930.
16. Crich, D.; Jayalath, P. J. Org. Chem. 2005, 70, 7252–7259.
17. Crich, D.; Vinogradova, O. J. Org. Chem. 2006, 71, 8473–
8480.
18. Crich, D.; Li, L. J. Org. Chem. 2007, 72, 1681–1690.
19. Crich, D.; Smith, M. J. Am. Chem. Soc. 2001, 123, 9015–
9020.
5.5.1. Methyl 2,3,6-tri-O-benzyl-4-O-[2,6-di-O-benzyl-
3,4-O-(butane-2,3-diyl)-b-D-glucopyranosyl]-a-D-gluco-
pyranoside (35b). [a]D21 +20.0 (c 0.45); 1H NMR d: 1.07 (d,
J¼6.0 Hz, 3H), 1.15 (d, J¼5.5 Hz, 3H), 3.29–3.33 (m, 4H),
3.37 (s, 3H), 3.39–3.46 (m, 4H), 3.58 (d, J¼10.5 Hz, 1H),
3.65 (d, J¼9.5 Hz, 1H), 3.69 (d, J¼11.5 Hz, 1H), 3.82
(d, J¼3.0 Hz, 1H), 3.86 (t, J¼9.0 Hz, 2H), 3.91 (d, J¼
10.0 Hz, 1H), 4.37–4.49 (m, 5H), 4.55 (d, J¼3.5 Hz, 1H),
4.59 (d, J¼12.0 Hz, 1H), 4.69 (d, J¼12.0 Hz, 1H), 4.76
(dd, J¼11.0 and 7.5 Hz, 1H), 4.83 (d, J¼11.5 Hz, 1H),
5.06 (d, J¼11.0 Hz, 1H), 7.21–7.41 (m, 25H); 13C NMR d:
17.3, 17.4, 55.3, 68.2, 68.5, 69.9, 73.1, 73.3, 73.7, 74.2, 74.3,
74.5, 75.3, 77.5, 78.9, 79.6, 80.5, 80.9, 98.4, 102.6, 127.1,
127.2, 127.4, 127.5, 127.6, 127.7, 127.7, 127.8, 128.0, 128.1,
128.2, 128.4, 138.0, 138.4, 138.8, 138.9, 139.6; HRMS calcd
for C52H60O11: C52H60O11 [M+Na]+: 883.4028, found
883.4021.
5.5.2. Methyl 2,3,6-tri-O-benzyl-4-O-[2,6-di-O-benzyl-
3,4-O-(butane-2,3-diyl)-a-D-glucopyranosyl]-a-D-gluco-
1
pyranoside (35a). [a]D21 +21.0 (c 0.50); H NMR d: 1.06
(d, J¼6.0 Hz, 3H), 1.13 (d, J¼6.0 Hz, 3H), 3.27–3.45 (m,
4H), 3.37 (s, 3H), 3.49–3.55 (m, 2H), 3.64–3.74 (m, 3H),
3.76 (t, J¼9.5 Hz, 1H), 3.84–3.87 (m, 1H), 3.93 (t, J¼
10.0 Hz, 1H), 4.03 (t, J¼9.0 Hz, 1H), 4.32 (d, J¼12.5 Hz,
1H), 4.48 (q, J¼9.5 Hz, 2H), 4.54–4.60 (m, 5H), 4.67 (d,
J¼12.0 Hz, 1H), 4.78 (d, J¼12.0 Hz, 1H), 4.82 (d, J¼
11.5 Hz, 1H), 4.94 (d, J¼11.5 Hz, 1H), 5.74 (d, J¼3.5 Hz,
1H), 7.18–7.33 (m, 25H); 13C NMR d: 17.3, 17.5, 55.1,
67.3, 69.5, 69.8, 73.1, 73.2, 73.3, 73.4, 73.5, 73.7, 74.3,
75.9, 77.3, 77.9, 80.3, 82.0, 97.7, 97.9, 126.8, 127.0,
127.4, 127.4, 127.5, 127.5, 127.7, 127.9, 128.1, 128.2,
128.3, 128.4, 138.0, 138.2, 138.3, 138.4, 139.1; HRMS calcd
for C52H60O11: C52H60O11 [M+Na]+: 883.4028, found
883.4027.
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We thank the NIH (GM 62160) for support of this work
and Dr. Mitesh Patel for the synthesis of the D-rhamnopyr-
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