Synthesis of Asialo GM1. New insights in the application of sulfonamidoglycosylation in oligosaccharide assembly: Subtle proximity effects in the stereochemical governance of glycosidation

Article abstract of DOI:10.1021/ja9724957

The total synthesis of asialo GM₁ (1a) has been accomplished. Using related chemistry, the methyl glycoside of the asialo compound (1b) has also been synthesized. These kinds of compounds have been identified as potential ligands for bacterial and viral infection sites. A simpler structure, which has also been identified for its infection attracting structure in the context of glycopeptides and glycolipids (methyl glycoside 2), has also been synthesized. The key common phase in the syntheses involves the sulfonamidoglycosidation reaction which is used to create a β-linkage leading to a ga1NAc residue joined to the C₄ hydroxyl group of a galactose unit either as a monosaccharide (see compound 2) or as C₄' in the context of a lactosyl moiety. During the course of these studies there was encountered an unusual 'proximal hydroxyl' directing effect. Thus, when C₄ on the galactose ring of an azaglycosylating donor bears a free hydroxyl (see, for instance, compound 13), β-glycoside formation predominates. When this hydroxyl group is blocked, the process tends in the direction of α-glycoside formation (see compound 32). These findings were explained as arising from a critical intramolecular hydrogen bond between the C₄ axial hydroxyl of the galactose donor and its proximal pyranosidal ring oxygen. This interaction stabilizes conformations from which β-glycosidation predominates.

Full text of DOI:10.1021/ja9724957

1588
J. Am. Chem. Soc. 1998, 120, 1588-1599
Synthesis of Asialo GM1. New Insights in the Application of
Sulfonamidoglycosylation in Oligosaccharide Assembly: Subtle
Proximity Effects in the Stereochemical Governance of Glycosidation
Ohyun Kwon† and Samuel J. Danishefsky*,†,‡
Contribution from the Department of Chemistry, HaVemeyer Hall, Columbia UniVersity,
New York, New York 10027, and Laboratory for Bioorganic Chemistry, The Sloan-Kettering
Institute for Cancer Research, 1275 York AVenue, Box 106, New York, New York 10021
ReceiVed July 23, 1997X
Abstract: The total synthesis of asialo GM1 (1a) has been accomplished. Using related chemistry, the methyl
glycoside of the asialo compound (1b) has also been synthesized. These kinds of compounds have been
identified as potential ligands for bacterial and viral infection sites. A simpler structure, which has also been
identified for its infection attracting structure in the context of glycopeptides and glycolipids (methyl glycoside
2), has also been synthesized. The key common phase in the syntheses involves the sulfonamidoglycosidation
reaction which is used to create a â-linkage leading to a galNAc residue joined to the C4 hydroxyl group of
a galactose unit either as a monosaccharide (see compound 2) or as C4′ in the context of a lactosyl moiety.
During the course of these studies there was encountered an unusual “proximal hydroxyl” directing effect.
Thus, when C4 on the galactose ring of an azaglycosylating donor bears a free hydroxyl (see, for instance,
compound 13), â-glycoside formation predominates. When this hydroxyl group is blocked, the process tends
in the direction of R-glycoside formation (see compound 32). These findings were explained as arising from
a critical intramolecular hydrogen bond between the C4 axial hydroxyl of the galactose donor and its proximal
pyranosidal ring oxygen. This interaction stabilizes conformations from which â-glycosidation predominates.
Background
Scheme 1. Target Structures
It is now becoming clear that carbohydrate substructures of
human cell surface glycoproteins or glycolipids constitute
important binding sites for a variety of bacterial and viral
infections.1,2 From this perspective alone there would be a clear
biological rationale for undertaking the synthesis of the title
structure, asialo GM1. One of the major causes of morbidity
and mortality of victims of cystic fibrosis (CF) is infection of
the lungs by microorganisms, particularly Pseudomonas aerugi-
nosa.3,4 Al Awquati and co-workers found that CF bronchial
and pancreatic epithelia reversibly bind P. aeruginosa. Strong
evidence was brought to bear to the effect that asialo GM1 (1a,
see Scheme 1), which is bound through a hydrophobic attraction
to the apical membrane of CF epithelia, is a likely binding site
for P. aeruginosa and that its increased abundance contributes
to bronchial bacterial invasion. These findings also underscore
the need to synthesize glycosides of the type 1b where the core
carbohydrate is retained, but the ceramide attachment is replaced
by simple glycosidic linkages. The synthetic carbohydrate
ligands should not be membrane bound. In suitably bioaVailable
form, they could serVe as “decoys” to preVent or clear up
bacterial infection. The understanding of how glycolipid
“ligands” interact with protein receptors in infectious bacteria
could well benefit from an insight as to structure activity
relationships (SAR) of the carbohydrate domain. An early
report from Krivan5 suggests that the interior galNAcâ1-4gal
disaccharide 2 functions as a recognition locus for a variety of
common pathogenic attachments such as occur in influenza and
pneumonia as well as CF-directed infection.3
† Columbia University.
‡ The Sloan-Kettering Institute for Cancer Research.
X Abstract published in AdVance ACS Abstracts, December 15, 1997.
(1) Ida¨npa¨a¨n-Heikkila¨, I.; Simon, P. M.; Vullo, T.; Cahill, P.; Sokol,
K.; Tuomanen, E. J. Infect. Dis., in Press.
(2) Cundell, D. R.; Tuomanen, E. Microb. Pathog. 1994, 17, 361-374.
(3) Imundo, L.; barasch, J.; Prince, A.; Al-Awqati, Q. Proc. Natl. Acad.
Sci. U.S.A. 1995, 92, 3019-3023.
(4) Barasch, J.; Kiss, B.; Prince, A.; Saiman, L.; Gruenert, D.; Al-Awqai,
Q. Nature 1991, 352, 70-73. Barasch, J.; Al-Awqati, Q. J. Cell. Sci. (Suppl.)
1993, 17, 229- 233.
(5) Krivan, H. C.; Roberts, D. D.; Ginsberg, V. Proc. Natl. Acad. Sci.
U.S.A. 1988, 85, 6157- 6161.
S0002-7863(97)02495-5 CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/04/1998

Synthesis of Asialo GM1
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1589
Scheme 2. Overall Synthetic Plan
Insights gained from the development of a stereoselective
the B and C rings. In this key connection (see boldface arrow
in Scheme 1), the sole axial oxygen center attached to the lactose
is glycosidically linked in a â-sense to a galNAc residue, which
through its C3 hydroxyl is, in turn, linked (â) to a terminal
galactose. Applying the logic of glycal assembly to this strategic
bond,8 and bearing in mind the biological thrust as expressed
in goal iv above, we would hope to couple the generalized AB
glycal (cf. 3) with CD glycal (4) leading to an ABCD glycal 5.
Continuing in the retrosynthetic vein, we first consider the
CD sector. Of course, the bicyclic glycal 3, in principle,
corresponds to a lactose or lactal derivative. Therefore one
might have started from the readily available lactose. However,
as discussed earlier,9 we had not yet developed a satisfactory
method to distinguish the sole C4′ axial hydroxyl as the specific
glycosidation site starting with lactal. Therefore, it would be
necessary for us to fashion a system of the type 3, through
synthesis, possibly from monocylcic glycals.
An important subgoal would be a system of the type 5, which
we termed as an “asialo GM1 glycal”. We were confident that
glycal 5 could be advanced to reach asialo GM1 (1a) or to probe
structures of the type 1b. The synthetic “gestalt” which
governed our experiments is broadly programmed in Scheme
2.
We first describe the synthesis of the azaglycosyl donor 13
(Scheme 3). The sequence started with triacetylgalactal 6, which
was converted to galactal and then to the mono-TIPS derivative
7 (TIPS ) triisopropylsilyl). This having been accomplished,
the hydroxyl groups at C3 and C4 were engaged as a cyclic
carbonate (see compound 8).9 The olefin linkage was epoxi-
6,7
synthetic route to asialo GM1
would undoubtedly find
application in the preparation of glycosides of the type 1b and
of the basic Krivan motif 2. In addition to the obvious biological
ramifications of the asialo GM1 problem, there were significant
chemical issues to be faced if we were to adapt our general
strategy of glycal assembly8 to the synthetic problem at hand.
Hence, the problem area was attractive to us in that it combined
questions of high interest to our laboratory at the level of
chemistry, with potential applications of consequence in anti-
infective strategies.
On the basis of these broad considerations, we summarized
the specific goals of our project to be (i) a total synthesis of
asialo GM1 in a concise fashion, (ii) the investigation of the
range of applicability of sulfonamidoglycosylation to the
assembly of complex and biologically useful oligosaccharides,
(iii) the application of the lessons of these investigations to the
assembly of analogues based on the Krivan ligand 2, and (iv)
the evaluation of the concept of using fully synthetic, circulating
glycosides incorporating the motifs of 1 and 2 as potential
antagonists of bacterial invasion in keeping with the findings
of Tuomanen,2 Al Awquati,3 and Krivan.5
From a chemical standpoint, the most provocative structural
feature of asialo GM1 as a target for synthesis is the union of
(6) (a) Sugimoto, M.; Horisaki, T.; Ogawa, T. Glycoconjugate J. 1985,
2, 11-15. (b) Sabesan, S.; Lemieux, R. U. Can. J. Chem. 1984, 62, 644-
654. (c) Paulsen, S.; Paal, M.; Hadamczyk, D.; Steiger, K.-M. Carbohydr.
Res. 1984, 131, c1-c5. Paulsen, S.; Paal, M. Carbohydr. Res. 1985. 137,
39-62.
(7) (a) Sugimoto, M.; Numata, M.; Koike, K.; Nakahara, Y.; Ogawa, T.
Carbohydr. Res. 1986, 156, c1. (b) Hasegawa, A.; Ishida, H.; Nagahama,
T.; Kiso, M. J. Carbohydr. Chem. 1993, 12, 703-718. (c) Stauch, T.;
Greilich, U.; Schmidt, R. R. Liebigs Ann. Chem. 1995, 2101-2111.
(8) Danishefsky, S. D.; Bilodeau, M. T. Angew. Chem., Int. Ed. Engl.
1996, 35, 1380-1419.
(9) Bilodeau, M. T.; Park, T. K.; Hu, S.; Randolph, J. T.; Danishefsky,
S. J.; Livingston, P. O.; Zhang, S. J. J. Am. Chem. Soc. 1995, 117, 7, 7840.
Park, T. K.; Kim, I. J.; Hu, S.; Bilodeau, M. T.; Randolph, J. T.; Kwon,
O.; Danishefsky, S. J. J. Am. Chem. Soc. 1996, 118, 11488.

1590 J. Am. Chem. Soc., Vol. 120, No. 7, 1998
Kwon and Danishefsky
Scheme 3a
a Reagents: (a) NH3/MeOH; (b) TIPSCl, Im, DMF, 74% (two steps); (c) 1,1′-carbonyldiimidazole (CDI), 4-dimethylaminopyridine (DMAP),
CH2Cl2, 97%; (d) dimethyldioxirane, CH2Cl2, 0 °C; (e) 7, ZnCl2, THF, -78 °C to room temperature (rt), 78%; (f) tert-butyldimethylsilyl chloride
(TBSCl), Im, DMF, 0 °C to rt, quantitative; (g) I(sym-coll)2ClO4, PhSO2NH2, 4 Å MS, CH2Cl2, 0 °C; (h) EtSH, LHMDS, DMF, -40 °C to rt, 42%
(two steps).
Scheme 4a
dized through the action of dimethyldioxirane,8 thereby affording
epoxide 9. The latter coupled smoothly with 6-O-TIPS-D-
galactal (7)10 under the influence of zinc chloride, specifically
at C3, to provide compound 10. Of the two hydroxyl groups in
this substance, the one which is equatorial (C2′ of the gal-gal
residue) underwent selective silylation (see compound 11). From
this point, it was possible to introduce the 2â-iodo-1R-
phenylsulfonamido arrangement through the reaction of 11 with
benzenesulfonamide in the presence of bis(sym-collidinyl)-
iodonium perchlorate.11 Previous experience8 had taught us that,
with a hindered glycosyl acceptor, a system of the type 12 would
not be effective as a glycosyl donor. Fortunately, methodology
was already on hand for dealing with this type of situation in a
complex setting.12 In the event, reaction of 12 with lithium
ethanethiolate gave rise to the donor system 13, which was to
function in a coupling reaction with a suitably differentiated
lactal derivative (cf. 3).
The specific lactal which we settled upon to correspond to
the generalized structure 3 was the pentabenzyl compound 20
(Scheme 4), in which only the axial 4′ hydroxyl group is
available to function as a glycosyl acceptor site. Actually, this
very compound had been prepared as part of a synthesis of the
human breast tumor antigen.9 In the chemistry practiced here,
some small variations were introduced with the view of allowing
us to explore a range of new lactal analogues, which were not
available via the previous protocols. We proceeded as fol-
lows: The cyclic carbonate epoxide 9, synthesized as shown
above from galactal, again served admirably for our purposes.
This compound coupled smoothly under guidance by anhydrous
zinc chloride with 3,6-O-dibenzyl-D-glucal (14), itself prepared
in one step from the selective 2-fold benzylation of D-glucal,
as shown. In this fashion we gained concise access to 15. The
latter underwent clean benzylation at its C2′ hydroxyl group,
thus affording 16. At this stage it proved possible to cleave
the TIPS protecting group and to benzylate the resultant 17,
a Reagents: (a) NaOMe, MeOH; (b) (i) (Bu3Sn)2O, PhH, Dean-
Stark; (ii) BnBr, tetrabutylammonium bromide (TBABr), 86% (overall);
(c) ZnCl2, THF, -78 °C to rt, 86%; (d) NaH, BnBr, DMF, 90%; (e)
tetrabutylammonium fluoride (TBAF), AcOH, THF, 90%; (f) NaH,
BnBr, DMF, 0 °C to rt, 81%; (g) K2CO3, MeOH, 89%; (h) (i)
(Bu3Sn)2O, toluene, Dean-Stark; (ii) BnBr, tetrabutylammonium iodide
(TBAI), quantitative.
thus providing 18 as shown. Further cleavage of the cyclic
carbonate gave 19, in which the C3′ and C4′ are free. While
this constellation in 19 could be exploited for other reasons, in
the case at hand, we took recourse to stannylidine-mediated
selective benzylation13 to afford the desired 20.
We first describe the total synthesis of the focusing target,
asialo GM1 (1a)6 and then relate the results of some interesting
and important accessory studies. Coupling of 13 and 20 could
be carried out under mediation by methyl triflate under the
conditions shown, to give the desired â-glycoside 21 (71% yield)
(Scheme 5), as well as a 6% yield of the R-anomer (22). Glycal
(10) Danishefsky, S. J.; Behar, V.; Randolph, J. T.; Lioyd, K. O. J. Am.
Chem. Soc. 1995, 117, 5701-5711.
(11) Griffith, D. A.; Danishefsky, S. J. J. Am. Chem. Soc. 1990, 112,
5811-5819.
(12) Griffith, D. A. Ph.D. Thesis, Yale University, 1992.

Synthesis of Asialo GM1
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1591
Scheme 5a
a Reagents: (a) MeOTf, 4 Å MS, Et2O/CH2Cl2 2:1, 0 °C, 71-84% R-H (R-H:â-H ) 13:1); (b) dimethyldioxirane, 4 Å MS, CH2Cl2, 0 °C; (c)
24, ZnCl2, THF, -50 °C to rt, 60% R-H, 6% â-H; (d) H2, Lindlar’s catalyst, palmitic anhydride, EtOAc, rt, 89%; (e) TBAF, AcOH, THF, 82%; (f)
Na, NH3, THF, -78 to -33 °C; MeOH, -78 °C to rt; (g) Ac2O, pyridine, 75% (overall); (h) NaOMe, MeOH, 89%.
21 was to function as the specific equivalent of the hypothesized
generalized structure 5. All of our subsequent schemes were
to pass through this kind of structure. The assignment of
sterochemistry at the B-C glycoside linkage for these two
compounds was initially based on extensive NMR analysis
(including COSY, Hetcor, and J-res techniques) which identified
the critical ring C anomeric protons to be as formulated.
Coupling reactions, similar to that of 13 + 20 using a
1â-(thioethyl)-2R-sulfonamidogalactose-type donor, had been
studied previously in our laboratory.9 Their outcomes have been
shown to be quite dependent on protecting group patterns8 and
are also markedly sensitive to the choice of reaction conditions.
We shall return to issues pertinent to the 2 + 2 coupling shortly.
We first report the synthesis of asialo GM1 (1a) from the
tetracyclic glycal 21. The sequence commenced with its
reaction with dimethyldioxirane to generate oxirane 23. The
latter, on reaction with azido alcohol 24,14 under mediation by
anhydrous zinc chloride, afforded a 60% yield of 25. There
was also obtained a 6% yield of the isomer 26. At this stage,
the formulation of stereochemistry at the pre-ceramide linkage
of glycosides 25 and 26 was based to a considerable extent on
well-established analogies rather than on unambiguous data on
the compounds themselves. The azide linkage of 25 suffered
reduction with Lindlar catalyst, and the resulting amine was
palmitoylated to give rise to 27.
The concluding deprotection sequence commenced with
desilylation (see compound 28). This step was followed by
debenzylation and peracetylation to provide homogeneous 29
in 75% yield. Finally, cleavage of all acyl bonds afforded an
89% yield of asialo GM1 (1a). Of course, there was no actual
sample of asialo GM1 (bearing the N-palmitoyl group in the
ceramide domain) available to us. Our assignment of the
structure was based on the extensive NMR analysis of the
intermediates en route to the final structure, on the close
correspondence on the four anomeric protons with NMR data
in the recent literature,15 and on the basis of the anomeric 13C-
(13) Davis, S.; Hanessian, S. Tetrahedron 1985, 41, 643-663.
(14) Schmidt, R. R.; Zimmermann, P. Tetrahedron Lett. 1986, 27, 481-
484. Zimmermann, P.; Schmidt, R. R. Liebigs Ann. Chem. 1988, 663-
667.
(15) Gasa, S.; Mitsuyama, T.; Makita, A. J. Lipid Res. 1983, 24, 174-
182.
(16) Podlasek, C. A.; Wu, J.; Stripe, W. A.; Bondo, P. B.; Serianni, A.
S. J. Am. Chem. Soc. 1995, 117, 8635-8644.

1592 J. Am. Chem. Soc., Vol. 120, No. 7, 1998
Kwon and Danishefsky
Scheme 6a
a Reagents: (a) NaH, BnBr, DMF, 82%; (b) I(sym-coll)2ClO4, PhSO2NH2, 4 Å MS, CH2Cl2, 0 °C, 80%; (c) EtSH, LHMDS, DMF, -40 °C to
rt, 84%; (d) 20, MeOTf, 4 Å MS, THP, 0 °C, 39% â-H, 4% R-H.
1H spin-coupling constants16 (measuring 160.9, 158.2, 160.0,
and 159.1). This structure is also supported by the agreement
of its high-resolution mass spectrum with theory. (FAB-HRMS
calcd for C6H110O23N2Na 1249.7400, found 1249.7420).
Prior to our discovery that donor 13 functioned well with
acceptor 20 to produce a highly favorable ratio of â:R glycosides
of tetracyclic product (cf. 21 and 22), we had evaluated other
versions of subtype glycal 4 as potential glycosyl donors. One
such study commenced with bicyclic diol 10. In this variation,
both hydroxyl groups were benzylated through the action of
sodium hydride and benzyl bromide to produce bicyclic glycal
30 (Scheme 6). The latter was converted, in 80% yield, to
iodosulfonomide 31 in the usual way. “Rollover” 8 of the
sulfonamido function through the action of ethanethiol (depro-
tonated through the action of lithium hexamethyldisilazide
(LHMDS)) gave rise to compound 32. This compound differs
from the previously noted donor 20 by the presence of a benzyl
group (instead of a TBS group) on the C2 hydroxyl of the
terminal galactose and a benzyl group rather than a free hydroxyl
group at C4 of the donor ring.
The coupling of compound 32 and acceptor 20 was studied
in some detail. Interestingly, through the use THF as solvent,
a 20:1 ratio of R:â glycosides (see 33 and 34) was obtained.
However, since the yield in this experiment was only reproduced
with difficulty due to the polymerization of tetrahydrofuran
under the conditions (methyl triflate) of the coupling, we did
not pursue the finding in detail. The experimental problem was
alleviated through the use of tetrahydropyran (THP) as the
solvent. A 10:1 ratio of 34 to 33 was obtained, this time in
43% yield. Attempted recourse to other solvent systems, such
as ether-methylene chloride led to mixtures, in which the
desired product 33 was favored, though only in ratios of
approximately ∼1.5:1. The criteria for distinguishing the
stereochemistry at the B:C connecting point between 33 and
34 were similar to those discussed above for glycals 21 and
22.
systems (38 and 42). The former would have the natural asialo
GM1 stereochemistry in the merger of the B and C rings. In
the latter structure, an unnatural glycosdic arrangement would
be present. Glycals 33 and 34 served as the starting materials
for the synthesis of methyl glycosides 38 and 42.
Epoxidation of glycal 33 through the action of dimethyldiox-
irane, followed by methanolysis, gave rise to 35 (Scheme 7),
albeit in a disappointing 43% yield. The deprotection phase
was conducted as above. Desilylation with TBAF (see com-
pound 36) was followed by reductive debenzylation (Na/NH3),
methanolysis, and peracetylation. By following these steps,
compound 37 was obtained in 80% yield. Finally, cleavage of
all the acetate functions afforded the â-methyl glycoside 38.
It is, eventually, our intention to pinpoint the structural
dependencies for bacterial binding to ligands related to asialo
GM1 in the structures which lack the cell anchoring. Therefore,
we also processed the tetracyclic glycal 34 which was epimeric
at the ring B-ring C glycosidic bond. This compound, at the
stereochemical level, departs from the central galNAcâ1-4gal
motif (see structure 2) identified by Krivan as a bacterial binding
domain.5 The synthesis of the epi-asialo GM1 system com-
menced with the glycal 34. This compound was advanced using
protocols which are closely related to those described above.
Epoxidation of 34 with dimethyldioxirane, followed by metha-
nolysis, led to methyl glycoside 39, this time in a more
respectable 64% yield. Deprotection of the two primary TIPS
groups gave rise to diol 40. The next phase involved cleavage
of the sulfonamide group, followed by exhaustive acylation (see
compound 41). Methanolysis of all of the oxygen bound
acetates led to methyl glycoside 42.
We proceeded to the synthesis of the disaccharide glycal 52
(Scheme 8). From such an intermediate we were confident that
we could reach the methyl glycoside 57 that embodies the basic
stereochemical motif identified by Krivan5 in a variety of
bacterial binding carbohydrate ligands. Once again, the effort
began from galactal and proceeded through the mono-TIPS
compounds (see structure 7). An additional silicon protecting
group was introduced at the C3 alcohol, in the context of the
3,6-O-di-TIPS-D-galactal derivative 43. The axial hydroxyl
group in 43 was acetylated (see structure 44). Once again, it
We shall return to the matter of the sharp dependency of the
stereochemistry of the azaglycosylation reaction on the nature
of C4 hydroxyl group of the galactose donor ring. We first
describe the sequences leading to the methyl glycoside goal

Synthesis of Asialo GM1
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1593
Scheme 7a
a Reagents: (a) dimethyldioxirane, CH2Cl2, 0 °C; MeOH, ZnCl2, THF, 43% for 35, 64% for 39; (b) TBAF, AcOH, THF, quantitative for 36,
93% for 40; (c) Na, NH3, THF, -78 to -33 °C; MeOH, -78 °C to rt; (d) Ac2O, pyridine, 80% for 37, 29% for 41; (e) NaOMe, MeOH, 99%.
proved possible to add iodobenzenesulfonamide to the glycal
linkage, even in the presence of the unprotected alcohol at C4,
thereby leading to trans-diaxial iodosulfonamide 45. Rear-
rangement and thiolative trapping gave rise to potential donor
46. In this compound, surprisingly, the TIPS group had
migrated from C3 to C4. Apparently, the presence of the
sulfonamide group, either due to hydrogen bonding or due to
steric congestion, favors the presence of a free OH at C3, even
though the bulky silyl group takes up residence on the axial
alcohol. Seemingly, the conditions of thiolate induced rear-
rangement of 45 trigger the equilibration of the silyl group from
C3 to C4 .
to its fully deprotected methyl glycoside 57 (Scheme 9). The
latter would be useful for the re-evaluation of the Krivan
concept.5
Reaction of glycal 52 with dimethyldioxirane and subsequent
methanolysis supplied â-methyglycoside 53 in 64% yield
accompanied by 17% of the R-methyl glycoside. The depro-
tection protocol followed the previous sequence for the asialo
GM1 methyl glycoside. Treatment of 53 with TBAF resulted
in cleavage of all the silyl groups. The benzyl and sulfonamido
groups were discharged by sodium in ammonia (see compound
55). Exhaustive acetylation afforded the purifiable peracetate
56. Deacetylation of all of the oxygen-bound acetates afforded
methyl glycoside 57.
Since we preferred to work in the series where C3 was
protected, we returned to the derived acetate 44. We were able
to carry out the addition of iodobenzenesulfonamide to the glycal
linkage to provide 49. Under the impact of lithium ethanethi-
olate (generated through the reaction of ethanethiol and LH-
MDS), the potential donor system 48, with the acetate still in
place, was obtained. Attempted deprotection of acetyl group
using potassium cyanide or potassium carbonate facilitated TIPS
group migration, providing 46 rather than desired 49. However,
it was possible to cleave this function through the action of
lithium aluminum hydride in ether, without triggering silyl
movement to afford donor 49. It would seem that, in the
reaction of 45, either the LHMDS base or the ethanethiolate
mediates this still mysterious rearrangement.
The strong preference for the formation of â-galactoside in
azaglycosidations with galactosyl donors possessing a C4 free
hydroxyl group appears to be quite general.8,9 Where C4 is
protected, competition from R-azagalactoside formation can be
very serious. For instance, in the course of the asialo GM1
glycal synthesis described above, the ratio of â:R glycoside
changed from 1:10 with donor 32, containing a C4 O-benzyl
protecting group, to 13:1 for donor 13, in which the C4 hydroxyl
group is unprotected. Moreover, the â:R ratio increased from
3:1 for a C4 acetyl donor (48) to 11:1 in the case of donor 49,
in which this group is free. Similarly, in the synthesis of the
MBr1 antigen,9 the directionality of the glycosidation is reversed
from 5:1, favoring R-glycoside for the C4 O-acetyl protected
donor, to 10:1 â:R for a corresponding case where the C4
hydroxyl in the galactal-derived donor is free.
Donors 48 and 49 were coupled to acceptor 50, in turn
prepared from D-galactal by stannylidene-induced dibenzylation.
These glycosidations led to disaccharides 51 (R/â ) 1:3) and
52 (R/â ) 1:11) as the major products, respectively. These
results again highlight the dramatic dependency of the stereo-
chemistry of glycosidation of such galactose-based donors on
the C4 protecting group. Before we discuss this issue in detail,
we first describe the conversion of “galNAcâ1-4gal” glycal 52
In analyzing this striking difference, we start with some
assumptions about the nature of glycosidation reactions,17,18 as
applied to the cases at hand. It seems reasonable that â-gly-
coside would be produced from a conventional neighboring
group participation of the C2 sulfonamide, leading to a structure
of the type 59 (Scheme 10). Inversion of configuration at C1
in 59 by the nucleophilic acceptor gives rise to â-galactoside
product 60. At the other limit, there can be considered a
structure of the type 61 corresponding to an anomeric “onium”
(17) Paulson, H. Angew. Chem., Int. Ed. Engl. 1982, 21, 155.
(18) Berresi, F.; Hindsgaul, O. J. Carbohydr. Chem. 1996, 14, 1043.

1594 J. Am. Chem. Soc., Vol. 120, No. 7, 1998
Kwon and Danishefsky
Scheme 8a
Scheme 9a
a Reagents: (a) dimethyldioxirane, 4 Å MS, CH2Cl2, 0 °C; MeOH,
64% (+17% of isomer); (b) TBAF, THF, 0 °C; (c) Na, NH3, THF,
-78 to -33 °C; NH4Cl; (d) Ac2O, pyridine, DMAP, 82% (three steps);
(e) NaOMe, MeOH, 44%.
generally attributable to intramolecular hydrogen bonding. For
example compounds 11, 13, 21, 43, 49, and 52 contain such
absorbances at 3569, 3537, 3534, 3558, 3570, and 3569 cm-1
,
respectively. By contrast, the compounds that have hydroxyl
groups in other placements exhibit broad absorption patterns
in the region characteristic of intermolecular hydrogen bonding.
In addition to the observations arising from these experiments,
NMR measurements presented supporting data strongly sug-
gesting the pyranose ring oxygen to be the intramolecular
hydrogen-bonding acceptor sites for the C4-free hydroxyl in the
galactose-derived pyranoses.21 For instance, in the proton NMR
spectrum of 3,6-di-O-TIPS-D-galactal (43), the free hydroxyl
hydrogen appears as a triplet and shows two cross peaks
corresponding to H4 and H5 in its COSY spectrum. Since
compound 43 contains a secondary alcohol, only the “virtual”
bond between the C4 axial hydroxyl and the pyranose ring
oxygen through strong hydrogen bonding explains the triplet
in the proton NMR spectrum and two cross peaks for the
hydroxyl hydrogen in the COSY spectrum. A similar pattern
of cross peaks for the C4 hydroxyl proton arising from
J-coupling to H4 and H5 is observed throughout the thiogly-
cosides (13 and 49), precursor glycals (11 and 43), and
azaglycosidation products (21 and 53).
a Reagents: (a) TIPSCl, imidazole, DMF, 62% (+7% of 7); (b)
Ac2O, pyridine, DMAP, 89%; (c) I(sym-coll)2ClO4, PhSO2NH2, 4 Å
MS, CH2Cl2, 0 °C, 93% for 47; (d) EtSH, LHMDS, DMF, -40 to
-15 °C, 88% for 48, 52% for 46 (two steps); (e) LAH, Et2O, 0 °C,
78%; (f) (i) (Bu3Sn)2O, PhH, Dean-Stark; (ii) BnBr, TBABr, 80%;
(g) MeOTf, 4 Å MS, Et2O/CH2Cl2 2:1, 67% for 52.
species. It seems probable, on stereoelectronic grounds, that a
species of the type 61 would be discharged by axial attack of
a glycosyl acceptor.
In these terms it follows that any structural feature of the
molecule which tends to favor a confomer of the type 58 would
be likely to lead to â-glycoside formation. In such a structure,
participation from the ring oxygen to expel an equatorial
anomeric group, en route to an onium species, would appear to
be stereoelectronically attenuated. By contrast, conformers
related to 6219 in which the pyranose oxygen is well disposed
to participate in expulsion of an axial C1 leaving group might
favor onium ion formation, resulting in weakening the â-se-
lectivity. Given such a framework of analysis, there remains a
need to explain why the distribution among these modalities is
affected to such a significant extent by the state of the C4
â-oxygen.
Intramolecular hydrogen bonding between axial hydroxyl
groups and ring oxygens in six-membered rings has previously
been reported. Wilson22 demonstrated through microwave
spectroscopy that 1,3-dioxan-5-ol exists in a chair conformation
with the hydroxyl group occupying axial position with an
intramolecular hydrogen bond of the O-H- - -O type (Scheme
11).
In studying the infrared spectra of several of the compounds
in this series, we observed some suggestive phenomena. The
spectra of the donor thioglycosides 13 and 49, their precursor
glycals 11 and 43, and their derived coupling products 21 and
52 exhibited weak and sharp bands in the OH stretching region,20
(20) Silverstein, R. M.; Bassler, G. C.; Morill, T. C. Spectroscopic
identification of organic compounds; John Wiley & Sons: New York, 1991;
pp 96, 101.
(21) Intramolecular hydrogen bonding between C4 axial amido nitrogen
and the pyranose ring oxygen has been suggested by ab initio calculation
after submission of this manuscript. See: Miljkovic´, M.; Yeagley, D.;
Deslongchamps, P.; Dong, Y. L. J. Org. Chem. 1997, 62, 7597-7604.
(22) Alonso, J. L.; Wilson, E. B. J. Am. Chem. Soc. 1980, 102, 1248-
1251.
(19) Conformer 58 could well be more stable than 62. However, if overall
glycosidation through the latter is faster, glycosidation via 58, which lacks
participation from the pyranose oxygen, formation of R-product will be
competitive or even dominant.

Synthesis of Asialo GM1
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1595
Scheme 10
Hz), 4.72-4.68 (2H, m), 4.65 (1H, d, J ) 7.2 Hz), 4.55 (1H, m), 4.08
(1H, dd, J ) 9.6, 5.6 Hz), 3.96-3.82 (6H, m), 3.33 (1H, d, J ) 3.2
Hz, OH), 3.27 (1H, d, J ) 2.8 Hz), 1.16-1.04 (42H, m); 13C NMR
(100 MHz, CDCl3) δ 154.45, 145.75, 99.27, 77.83, 76.59, 74.27, 72.04,
71.62, 70.86, 64.52, 62.57, 61.60, 17.84, 11.78; HRMS (FAB) calcd
for C31H58O10Si2Na (M + Na+) 669.3466, found 669.3491.
Scheme 11
As discussed earlier, the competition between neighboring
group participation by C2 sulfonamide versus onium ion
formation could well be governing the stereocontrol in the 1â-
(thioethyl)-2R-sulfonamidoglycosylation reaction. Given those
terms, and given the arguments presented above, the preferred
â-galactosidation in the case of the C4-free hydroxyl can be
explained. An intramolecular hydrogen bond between this
hydroxyl and the pyranosidal oxygen would help to (i) stabilize
the chair conformation in which the sulfonamide groups are
equatorial and (ii) destabilize onium ion contributions (see
structure type 61) which favor R-glycoside formation as
discussed above in Scheme 10.
This type of argument, suggesting the possibility of exploiting
subtle changes in resident functions to influence glycosyl donor
conformations, thereby controlling the stereochemical outcome
of glycosidation, has broad implications and ramifications.
Ongoing studies are directed to the further exploration of this
theme as well as to the evaluation of the central biological
concept of using carbohydrates as decoys for bacterial invasion.
Synthesis of Disaccharide Glycal 11. To a solution of the glycal
10 (665 mg, 1.03 mmol) and imidazole (420 mg, 6.16 mmol) in
anhydrous DMF (7.0 mL) at 0 °C was added tert-butyldimethylsilyl
chloride (465 mg, 3.08 mmol). The mixture was slowly warmed to rt
and stirred overnight. It was diluted with EtOAc and poured into water
(50 mL) and extracted with 3:1 hexane/EtOAc (3 × 50 mL). Combined
extracts were washed with brine, dried over MgSO4, and concentrated.
Flash column chromatography using 20:1-10:1 hexane/EtOAc afforded
11 (782 mg, quant.) as a white foam: [R]23D -39.2° (c 1.10, CHCl3);
FTIR (neat) 3569, 2943, 2866, 1819, 1809, 1651, 1464, 1384, 1367,
1240, 1142, 1114, 1071, 1034, 882, 838, 782, 668 cm-1; 1H NMR (500
MHz, CDCl3) δ 6.36 (1H, dd, J ) 6.3, 1.5 Hz, H1), 4.89 (1H, dd, J )
7.8, 1.5 Hz, H4′), 4.72 (1H, d, J ) 5.0 Hz, H1′), 4.63-4.59 (2H, m,
H2, H3′), 4.42 (1H, m, H3), 4.09 (1H, br s, H4), 4.00 (1H, dd, J )
8.8, 6.4 Hz), 3.96 (1H, dt, J ) 1.5, 6.9 Hz, H5′), 3.88-3.81 (5H, m),
2.76 (1H, d, J ) 1.8 Hz, OH), 1.11-1.02 (42H, m), 0.87 (9H, s), 0.12
(3H, s), 0.10 (3H, s); 13C NMR (125 MHz, CDCl3) δ 154.25, 145.26,
99.69, 77.58, 76.99, 73.71, 72.60, 71.15, 70.84, 63.45, 61.63, 61.48,
25.49, 17.81, 11.77, 11.71, -4.77, -5.10; HRMS (FAB) calcd for
C37H72O10Si3Na (M + Na+) 738.4331, found 738.4336.
Synthesis of Ethanethiosulfonamide 13. To a stirred mixture of
the glycal 11 (480 mg, 0.630 mmol), benzenesulfonamide (297 mg,
1.89 mmol), and freshly activated powdered 4 Å MS (500 mg) in dry
Experimental Procedures23
Synthesis of Disaccharide Glycal 10. 3,4-O-Cyclic carbonate-6-
O-TIPS-D-galactal (8) (1.00 g, 3.04 mmol) was azeotropically dried
using benzene before being dissolved in dry CH2Cl2 (5 mL) under
nitrogen. The solution was cooled to 0 °C, treated with dimethyldiox-
irane (73 mL, ∼3.65 mmol), and stirred for 40 min, at which time
TLC analysis indicated no trace of starting material. The solvent was
evaporated by a stream of dry argon to give the epoxide 9, which was
dried in Vacuo for 1 h. To the epoxide 9, under nitrogen, was added
via cannula a solution of 6-O-TIPS-D-galactal (7) (1.38 g, 4.57 mmol)
in dry THF (10 mL). The resulting solution was cooled to -78 °C,
and ZnCl2 (5.0 mL, 1.0 M in ether) was added. The mixture was
maintained at -78 °C for 2 h and then allowed to slowly warm to
room temperature and stirred for additional 12 h. The reaction was
quenched using saturated NaHCO3 solution (50 mL) and partioned
between water (50 mL) and EtOAc (3 × 100 mL). The collected
organic layer was washed with brine, dried over Na2SO4, and
concentrated in Vacuo. Flash column chromatography using 3:1 hexane/
EtOAc gave 10 (1.53 g, 78%) as a white foam: [R]23D -36.4° (c 1.24,
CHCl3); FTIR (neat) 3451, 2943, 2866, 1799, 1647, 1464, 1383, 1238,
1163, 1114, 1070, 1031, 882, 786, 685, 656 cm-1; 1H NMR (400 MHz,
CDCl3) δ 6.54 (1H, dd, J ) 6.4, 1.6 Hz), 4.85 (1H, dd, J ) 6.4, 2.0
(23) General Experimental Procedures: All commercial materials were
used without further purification unless otherwise noted. The following
solvents were distilled under positive pressure of dry argon immediately
before use: THF and ether from sodium-benzophenone ketyl and CH2Cl2
from CaH2. All the reactions were performed under argon atmosphere. NMR
(1H, 13C) spectra were recorded on Bruker AMX-400 MHz, Bruker
Advanced DMX-500 MHz, and Varian VXR-400 MHz referenced to CDCl3
(1H NMR, δ 7.26; 13C NMR, δ 77.00), CD3OD (1H NMR, δ 4.78; 13C
NMR, δ 49.05), DMSO-d6 (1H NMR, δ 2.49; 13C NMR, δ 39.7), and D2O
(1H NMR, δ 4.63) peaks unless otherwise stated. Assignment of each peak
(NH or OH peak) in 1H NMR is based on D2O exchange experiments.
Also, decoupling experiment, Hetcor, J-res, magnitude COSY, selective
COSY, and/or ROESY experiments. LB ) 0.1 Hz was used before Fourier
transformation for all of the 125 MHz 13C NMR. IR spectra were recorded
with a Perkin-Elmer Paragon 1000 FTIR spectrometer, and optical rotations
were measured with a Jasco DIP-370 or DIP-1000 digital polarimeter using
a 10 cm path length cell. Low- and high-resolution mass spectral analyses
were performed with a JEOL JMS-DX-303HF mass spectrometer. Analytical
thin-layer chromatography was performed on E. Merck silica gel 60 F254
plates (0.25 mm). Flash column chromatography was performed using the
indicated solvent on E. Merck silica gel 60 (40-63 mm) or Sigma H-Type
silica gel (10-40 mm) for normal phase and EM Science LiChroprep RP-
18 (15-25 mm) for reverse phase.

1596 J. Am. Chem. Soc., Vol. 120, No. 7, 1998
Kwon and Danishefsky
CH2Cl2 (6 mL) at 0 °C was added I(sym-coll)2ClO4 (1.18 g, 2.52 mmol).
The resulting mixture was stirred for 30 min in the dark at 0 °C and
treated with Na2S2O3 solution (6 mL). The filtrate was washed with
Na2S2O3 solution and CuSO4 solution, dried over MgSO4, and
concentrated in Vacuo. The bulk of the benzenesulfonamide was
precipitated by dissolving the crude product in a minimum amount of
7:1 hexane/EtOAc solution (8 mL). The crude product (520 mg) was
subjected to the next reaction without further purification.
mg, 0.34 mmol) in dry THF (1.0 mL) was added to it, and then the
resulting mixture was cooled to -60 °C. Anhydrous zinc chloride was
added (41 µL, 1.0 M in ether), and the resultant solution was slowly
warmed to rt as the dry ice melted and stirred overnight. The reaction
mixture was poured into ice water (5 mL), neutralized with NaHCO3
solution (5 mL), and extracted with 2:1 hexane/EtOAc (3 × 10 mL).
Collected extracts were washed with brine, dried over MgSO4, and
concentrated. Flash column chromatography using 9:1-7:1-6:1-4:1
hexane/EtOAc provided 25 (43 mg, 60%) accompanied by isomer 26
(4 mg, 6%): [R]24D -14.1° (c 1.12, CHCl3); FTIR (neat) 3542, 3238,
To a solution of ethanethiol (184 µL, 2.49 mmol) in anhydrous DMF
(2.5 mL) at -40 °C were added LHMDS (995 µL, 1.0 M in THF) and
a solution of iodosulfonamide 12 (520 mg, crude) in DMF (2.5 mL).
The reaction was stirred for 1 h at -40 °C, slowly warmed to -10 °C
for 1 h, poured into ice, neutralized with NH4Cl solution (50 mL), and
extracted with 2:1 hexane/EtOAc solution (3 × 50 mL). Combined
extracts were washed with brine, dried over MgSO4, and concentrated
under reduced pressure. Flash column chromatography using 10:1-
2927, 2112, 1797, 1455, 1365, 1323, 1165, 1085, 877, 735, 696 cm-1
;
1H NMR (500 MHz, CDCl3) δ 7.90 (2H, d, J ) 7.8 Hz), 7.38-7.15
(33H, m), 5.99 (1H, d, J ) 2.9 Hz), 5.76 (1H, dt, J ) 15.4, 6.7 Hz),
5.42 (1H, dd, J ) 15.4, 8.6 Hz), 5.09-4.92 (4H, m), 4.82 (1H, d. J )
10.7 Hz), 4.68-4.52 (5H, m), 4.38-4.18 (7H, m), 4.01-3.91 (5H, m),
3.86-3.82 (2H, m), 3.79-3.74 (2H, m), 3.71-3.66 (3H, m), 3.62-
3.55 (2H, m), 3.53-3.43 (4H, m), 3.39 (1H, dd, J ) 9.3, 2.9 Hz), 3.34
(1H, dt, J ) 7.4, 3.1 Hz), 3.28-3.21 (4H, m), 2.92 (1H, br s), 2.43
(1H, br s), 2.09 (2H, app q, J ) 6.5 Hz), 1.43-1.25 (22H, m), 1.12-
1.02 (42H, m), 0.91 (9H, s), 0.88 (3H, t, J ) 6.8 Hz), 0.25 (3H, s),
0.16 (3H, s); 13C NMR (125 MHz, CDCl3) δ 155.72, 138.58, 138.50,
138.32, 138.25, 138.20, 138.11, 137.91, 137.18, 132.61, 129.06, 128.71,
128.59, 128.36, 128.33, 128.32, 128.28, 128.22, 128.12, 128.01, 127.78,
127.74, 127.64, 127.55, 127.52, 127.46, 127.33, 127.28, 125.83, 103.36,
102.79, 101.65, 82.93, 82.60, 81.63, 80.28, 79.36, 76.43, 75.63, 75.53,
75.28, 74.59, 74.31, 73.52, 73.40, 73.24, 73.06, 72.69, 69.97, 68.80,
68.69, 68.68, 67.99, 67.69, 65.52, 64.17, 61.76, 60.80, 56.20, 32.37,
31.90, 29.68, 29.67, 29.66, 29.64, 29.63, 29.45, 29.34, 29.19, 29.02,
25.59, 22.67, 17.93, 17.91, 17.89, 17.67, 14.10, 11.90, 11.84, -4.49,
-5.31 (four unresolved carbons); HRMS (FAB) calcd for C115H168O24N4-
SSi3Na (M + Na+) 2128.0970, found 2128.0930.
7:1 hexane/EtOAc gave 13 (259 mg, 42%) as a white foam: [R]23
D
-43.6° (c 1.78, CHCl3); FTIR (neat) 3537, 3263, 2943, 2866, 2360,
1794, 1456, 1332, 1256, 1162, 1112, 1084, 1031, 882, 838, 784, 686,
1
592 cm-1; H NMR (500 MHz, CDCl3) δ 7.93-7.48 (5H, m), 5.39
(1H, s, H4′), 5.09 (1H, d, J ) 9.1 Hz, H1′), 4.67 (1H, d, J ) 8.8 Hz,
H2′), 4.52 (1H, d, J ) 6.3 Hz, NH), 4.48 (1H, s, H3′), 4.31 (1H, d, J
) 10.2 Hz, H1), 4.25 (1H, dd, J ) 9.0, 5.4 Hz), 4.09 (1H, s, H4), 3.92
(1H, dd, J ) 9.6, 7.2 Hz), 3.85 (1H, dd, J ) 9.6, 5.4 Hz), 3.81-3.74
(3H, m), 3.53 (1H, dt, J ) 6.5, 9.9 Hz, H2), 3.47 (1H, t, J ) 6.3 Hz),
2.90 (1H, s, OH), 2.40 (1H, dq, J ) 12.4, 7.4 Hz), 2.20 (1H, dq, J )
12.4, 7.4 Hz), 1.12-1.05 (42H, m), 0.90 (9H, s), 0.24 (3H, s), 0.19
(3H, s); 13C NMR (125 MHz, CDCl3) δ 153.66, 139.93, 132.79, 128.83,
127.96, 100.89, 83.50, 81.70, 79.46, 73.75, 72.84, 68.90, 68.11, 61.82,
61.77, 55.00, 25.58, 23.59, 17.92, 17.89, 17.71, 14.39, 11.87, 11.86,
-4.67, -5.23; HRMS (FAB) calcd for C45H83O12NS2Si3Na (M + Na+)
1000.4560, found 1000.4580.
Synthesis of the Tetrasaccharide 27. A flask containing the azide
25 (79 mg, 0.038 mmol), palmitic anhydride (38 mg, 0.076 mmol),
and Lindlar’s catalyst (160 mg) was evacuated and vented to a hydrogen
atmosphere twice. Ethyl acetate (3.0 mL) was added, and the mixture
was stirred under hydrogen atmosphere for 12 h. The reaction was
filtered through a short pad of silica gel, concentrated, and flash
chromatographed using 4:1-3:1 hexane/EtOAc to afford 27 (78 mg,
89%): [R]27D +17.4° (c 1.06, CHCl3); FTIR (neat) 3538, 3296, 2926,
2855, 1798, 1634, 1455, 1364, 1330, 1125, 1169, 1085, 888, 737, 696
cm-1; 1H NMR (500 MHz, CDCl3) δ 7.90 (2H, d, J ) 7.5 Hz), 7.55-
7.16 (33H, m), 6.08 (1H, d, J ) 8.8 Hz), 5.99 (1H, d, J ) 3.3 Hz),
5.70 (1H, dt, J ) 15.4, 6.8 Hz), 5.37 (1H, dd, J ) 15.4, 8.4 Hz), 5.10-
5.07 (2H, m), 4.97 (2H, AB, J ) 11.1 Hz, ∆ν ) 41.8 Hz, OCH2Ar),
4.96 (1H, d, J ) 11.2 Hz), 4.78 (2H, AB, J ) 10.8 Hz, ∆ν ) 33.8 Hz,
OCH2Ar), 4.65-4.51 (5H, m), 4.35-4.17 (7H, m), 4.00-3.96 (2H,
m), 3.93 (1H, t, J ) 9.2 Hz), 3.88-3.72 (6H, m), 3.66 (1H, d, J ) 9.8
Hz), 3.62-3.57 (2H, m), 3.55-3.41 (4H, m), 3.37-3.32 (2H, m), 3.29-
3.21 (4H, m), 2.93 (1H, br s), 2.15-2.04 (4H, m), 1.40-1.25 (48H,
m), 1.16-1.03 (42H, m), 0.92 (9H, s), 0.89 (6H, t, J ) 6.9 Hz), 0.26
(3H, s), 0.18 (3H, s); 13C NMR (125 MHz, CDCl3) δ 173.25, 155.72,
138.60, 138.53, 138.46, 138.33, 138.20, 137.91, 137.18, 137.14, 132.59,
129.05, 128.71, 128.57, 128.35, 128.31, 128.28, 128.22, 128.14, 128.00,
127.79, 127.75, 127.72, 127.57, 127.53, 127.48, 127.46, 127.31, 127.29,
126.80, 104.26, 103.35, 102.76, 101.63, 82.90, 82.76, 81.64, 80.27,
79.67, 76.55, 76.42, 75.51, 75.36, 75.25, 74.54, 74.32, 73.52, 73.36,
73.35, 73.22, 73.05, 72.69, 70.16, 69.67, 68.79, 68.66, 68.13, 67.67,
65.52, 61.77, 60.78, 56.19, 52.31, 36.96, 32.30, 31.91, 29.69, 29.67,
29.65, 29.54, 29.50, 29.43, 29.34, 29.33, 29.26, 29.22, 25.73, 25.59,
22.67, 17.93, 17.90, 17.89, 17.67, 14.10, 11.90, 11.83, -4.49, -5.32
(13 unresolved carbons); HRMS (FAB) calcd for C131H200O25N2SSi3-
Na (M + Na+) 2340.3370, found 2340.3410.
Synthesis of a GM1 Tetrasaccharide Glycal 21. A mixture of
thioglycoside 13 (124 mg, 0.127 mmol) and lactal 20 (96 mg, 0.127
mmol) was azeotroped three times with anhydrous benzene and placed
under high vacuum overnight. Freshly activated 4 Å MS (1.10 g) was
added to the mixture, and that was taken up in dry CH2Cl2 (1.0 mL)
and dry ether (2.0 mL), stirred for 5 min at rt, and cooled to 0 °C.
After the mixture was stirred for 5 min at 0 °C, MeOTf (72 µL, 0.64
mmol) was added dropwise. The reaction was stirred for 9 h at 0 °C,
and then Et3N (230 µL) was added. The reaction mixture was filtered
through a Celite pad and concentrated. Purification by flash column
chromatography using 9:1-6:1-4:1 hexane/EtOAc afforded 21 (152
mg, 71%) as a white foam accompanied by R-isomer 22 (12 mg, 6%):
[R]23 -19.6° (c 1.12, CHCl3); FTIR (neat) 3534, 3268, 3027, 2941,
D
2866, 1792, 1651, 1457, 1366, 1331, 1247, 1164, 1084, 1031, 885,
1
747, 702, 600 cm-1; H NMR (500 MHz, CDCl3) δ 7.89 (2H, d, J )
7.5 Hz), 7.41-7.21 (28H, m), 6.53 (1H, d, J ) 6.2 Hz), 5.55 (1H, d,
J ) 4.2 Hz), 5.16 (1H, s), 5.07 (1H, d, J ) 9.1 Hz), 4.97-4.93 (3H,
m), 4.79 (1H, d, J ) 10.6 Hz), 4.67-4.63 (2H, m), 4.58-4.47 (5H,
m), 4.43 (1H, d, J ) 7.2 Hz), 4.39-4.24 (5H, m), 4.15 (1H, t, J ) 3.6
Hz), 4.09 (1H, t, J ) 3.8 Hz), 3.96-3.93 (2H, m), 3.89-3.83 (2H, m),
3.79-3.75 (2H, m), 3.66 (1H, dd, J ) 10.6, 4.1 Hz), 3.58 (1H, dd, J
) 9.1, 5.0 Hz), 3.53-3.44 (3H, m), 3.38-3.28 (3H, m), 3.23 (1H, dd,
J ) 7.2, 5.6 Hz), 3.17 (1H, dd, J ) 9.9, 2.3 Hz), 3.01 (1H, d, J ) 2.3
Hz), 1.13-1.03 (42H, m), 0.93 (9H, s), 0.29 (3H, s), 0.20 (3H, s); 13
C
NMR (125 MHz, CDCl3) δ 155.96, 144.72, 138.45, 138.22, 138.12,
138.05, 137.21, 132.66, 129.16, 128.75, 128.47, 128.41, 128.37, 128.34,
128.28, 128.09, 127.74, 127.69, 127.66, 127.58, 127.50, 127.48, 127.41,
102.79, 102.72, 101.01, 99.29, 81.62, 81.12, 79.74, 75.85, 75.70, 75.30,
75.26, 74.72, 73.57, 73.29, 73.24, 73.16, 73.06, 72.76, 70.91, 69.65,
69.25, 68.71, 67.82, 67.77, 65.58, 61.96, 60.90, 55.92, 25.61, 17.93,
17.90, 17.69, 11.89, 11.84, -4.50, -5.30 (three unresolved aromatic
resonances); HRMS (FAB) calcd for C90H127O21NSSi3Na (M + Na+)
1696.7830, found 1696.7860.
Synthesis of the Tetrasaccharide 25. To a stirred mixture of the
glycal 21 (57 mg, 0.034 mmol) and freshly activated powdered 4 Å
MS (60 mg) in anhydrous CH2Cl2 (3.0 mL) at 0 °C was added
dimethyldioxirane (822 µL, 0.05 M in acetone). After 30 min, the
reaction was contcentrated with a stream of argon and further dried
under vacuum for 10 min. A solution of the azido alcohol 2414 (183
Synthesis of Asialo GM1 (1a). A solution of 27 (88 mg, 0.038
mmol) in THF (380 µL) was treated with glacial AcOH (44 µL) and
TBAF (1.1 mL, 1.0 M in THF) and stirred for 12 h at rt. The reaction
was poured into ice cold NaHCO3 solution (10 mL) and extracted with
EtOAc (3 × 10 mL). The combined organic phases were dried over
MgSO4, concentrated, and flash chromatographed using 10:10:1 hexane/
EtOAc/MeOH to afford 28 (59 mg, 82%).
To liquid ammonia (∼7 mL) at -78 °C were added Na (∼100 mg)
and a solution of 28 (59 mg, 0.031 mmol) in anhydrous THF (0.7 mL).

Synthesis of Asialo GM1
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1597
The resulting dark blue solution was allowed to reflux for 30 min and
cooled to -78 °C again. MeOH (3.0 mL) was added to it, and the
solution was stirred overnight at rt. The reaction was neutralized by
adding Dowex 58×8-200 ion-exchange resin (∼2.5 g), filtered through
a sintered glass funnel, and concentrated to be put under vacuum for
1 h. It was dissolved in anhydrous pyridine (∼1.5 mL) and cooled to
0 °C, and acetic anyhydride (0.5 mL) was added to it. The resultant
solution was stirred overnight at rt. The resultant material was poured
into water (15 mL) and extracted with EtOAc (3 × 15 mL). Collected
extracts were washed with saturated CuSO4 solution, dried over MgSO4,
and concentrated. Flash column chromatography using 20:10:1-30:
15:2 hexane/EtOAc/MeOH provided 29 (42 mg, 75% for two steps).
HRMS (FAB) calcd for C98H125O21NSSi2Na (M + Na+) 1762.7900,
found 1762.7900.
For 34: [R]18 +27.69° (c 1.52, CHCl3); FTIR (neat) 3506, 3200,
D
3032, 2942, 2866, 1813, 1651, 1497, 1454, 1367, 1337, 1247, 1211,
1
1164, 1097, 1038, 999, 910, 823., 792, 734, 697, 592, 458 cm-1; H
NMR (400 MHz, CDCl3) δ 7.78 (2H, d, J ) 7.3 Hz), 7.77-7.21 (38H,
m), 6.49 (1H, dd, J ) 7.0, 0.9 Hz), 6.20 (1H, d, J ) 9.0 Hz), 5.07 (1H,
app s), 5.03 (1H, d, J ) 3.5 Hz), 4.92-4.68 (8H, m), 4.62-4.57 (3H,
m), 4.54 (1H, d, J ) 7.6 Hz), 4.14 (1H, app s), 4.08 (1H, d, J ) 2.6
Hz), 3.96 (1H, dd, J ) 11.0, 2.1 Hz), 3.93-3.80 (5H, m), 3.68-3.60
(3H, m), 3.39 (1H, t, J ) 6.8 Hz), 3.33 (1H, dd, J ) 9.8, 2.7 Hz), 3.10
(1H, dd, J ) 3.1, 1.1 Hz), 1.14-1.00 (21H, m), 0.95-0.92 (21H, m);
13C NMR (75 MHz, CDCl3) δ 153.75, 145.48, 141.49, 139.48, 138.34,
138.26, 137.92, 137.89, 137.06, 132.32, 129.01, 128.63, 128.43, 128.37,
128.32, 128.26, 128.15, 127.93, 127.98, 127.77, 127.74, 127.69, 127.64,
127.60, 127.58, 127.56, 127.49, 126.94, 104.65, 103.17, 100.91, 99.64,
80.30, 79.63, 78.84, 76.19, 76.09, 75.06, 74.60, 74.40, 74.08, 73.55,
73.43, 73.21, 73.18, 73.02, 72.60, 72.26, 72.13, 71.88, 71.63, 70.46,
68.41, 67.61, 67.40, 61.16, 60.43, 59.96, 17.98, 17.95, 17.93, 17.88,
11.84, 11.78 (five unresolved aromatic resonances); HRMS (FAB) calcd
for C98H125O21NSSi2Na (M + Na+) 1762.7900, found 1762.7930.
Synthesis of the Tetrasaccharides 35 and 39. The tetrasaccharide
glycal 33 (122 mg, 0.0699 mmol) in dry CH2Cl2 (0.7 mL) at 0 °C was
treated with dimethyldioxirane (1.7 mL, ∼0.0839 mmol) and stirred at
0 °C for 30 min, after which time the mixture was concentrated by
passing a stream of argon over the solution and put under vacuum for
1 h. The resulting epoxide was dissolved in dry THF (0.5 mL) and
anhydrous MeOH (0.7 mL), cooled to -78 °C, and treated with ZnCl2
(84 µL, 1.0 M in ether). The mixture was slowly warmed to rt and
stirred overnight. After dilution with EtOAc, the solution was poured
into ice, neutralized with NaHCO3 solution (20 mL), and extracted with
2:1 hexane/EtOAc solution (3 × 20 mL). The extracts were dried over
MgSO4, concentrated, and subjected to flash chromatography using
3:1-2:1 hexane/EtOAc to yield the methyl glycoside 35 (54 mg,
43%): [R]20D -11.6° (c 0.62, CHCl3); FTIR (neat) 3460, 3225, 3030,
2941, 2865, 1812, 1497, 1453, 1363, 1209, 1162, 1095, 1063, 1028,
A solution of 29 (39 mg, 0.022 mmol) in anhydrous MeOH (0.8
mL) was treated with NaOMe (6 mg, 0.11 mmol) and stirred overnight
at rt. The reaction was neutralized with Dowex 50 × 8-200 (∼50
mg), filtered, and concentrated. Flash column chromatography on RP-
18 silica gel using 15%-10%-5% water in MeOH provided asialo
GM1 (1a) (24 mg, 89%).
TLC with 2:1:1 n-BuOH/
EtOH/H2O: Rf ) 0.56; [R]24D -1.45° (c 0.25, 1:1 CHCl3/MeOH); FTIR
(neat) 3390, 2918, 2850, 2358, 1652, 1634, 1068 cm-1; 1H NMR (400
MHz, DMSO-d6) δ 7.50 (2H, d, J ) 7.6 Hz), 5.51 (1H, dt, J ) 15.2,
6.6 Hz), 5.33 (1H, dd, J ) 15.3, 7.0 Hz), 5.27 (1H, br s), 5.14 (1H, br
s), 4.87 (2H, br s), 4.78 (1H, br s), 4.61-4.37 (7H, m), 4.54 (1H, d, J
) 8.3 Hz, anomeric H), 4.20 (1H, d, J ) 7.4 Hz, anomeric H), 4.19
(1H, d, J ) 7.6 Hz, anomeric H), 4.14 (1H, d, J ) 7.7 Hz, anomeric
H), 3.99-3.96 (2H, m), 3.85-3.73 (7H, m), 3.64-3.59 (4H, m), 3.50-
3.19 (5H, m), 3.02 (1H, t, J ) 8.1 Hz), 2.00 (2H, t, J ) 7.3 Hz), 1.91
(2H, bum), 1.81 (3H, s), 1.44-1.22 (48H, m), 0.84 (6H, t, J ) 6.8
Hz); 13C NMR (100 MHz, DMSO-d6) δ 171.72, 170.65, 131.37, 104.42,
103.72, 103.45, 102.51, 80.78, 79.62, 76.37, 75.28, 75.22, 74.75, 74.39,
74.32, 73.17. 72.97, 70.73, 70.62, 69.14, 68.04, 67.25, 60.51, 60.42,
60.31, 60.30, 59.92, 52.88, 51.67, 40.05, 39.84, 39.64, 39.43, 39.22,
39.01, 38.80, 35.54, 31.71, 31.24, 29.09, 29.04, 28.99, 28.97, 28.73,
28.71, 28.66, 25.34, 23.24, 22.04, 13.86 (10 unresolved carbons);
HRMS (FAB) calcd for C60H110O23N2Na (M + Na+) 1249.7400, found
1249.7420.
1
882, 752, 696, 593 cm-1; H NMR (400 MHz, CDCl3) δ 7.83 (2H,
Synthesis of Asialo GM1 Tetrasaccharide Glycal 33 and Its
Isomer 34. A mixture of thioglycoside 32 (60 mg, 0.057 mmol) and
the lactal 20 (44 mg, 0.057 mmol) was azeotroped three times with
anhydrous benzene and placed under high vacuum overnight. Freshly
activated 4 Å MS (520 mg) was added to the mixture and the material
was taken up in anhydrous THP (1.5 mL), stirred for 5 min at rt, and
cooled to 0 °C. After the mixture was stirred for 5 min at 0 °C, MeOTf
(32 µL, 0.29 mmol) was added dropwise. The reaction was stirred for
8 h at 0 °C and then Et3N (100 µL) was added. The reaction mixture
was filtered through a Celite pad and concentrated. Purification by
flash column chromatography using 25:1-15:1-7:1 benzene/EtOAc
provided separation between products from acceptor left. Further
purification by HPLC using 15% EtOAc in hexane (UV 260 nm)
afforded 34 (39 mg, 39%) and 33 (4 mg, 4%).
m), 7.42-7.13 (37H, m), 6.97 (1H, t, J ) 7.3 Hz), 6.01 (1H, d, J )
4.2 Hz), 5.07-4.82 (7H, m), 5.03 (1H, d, J ) 3.5 Hz), 4.76 (1H, dd,
J ) 8.6, 3.0 Hz), 4.68-4.51 (5H, m), 4.40-4.14 (6H, m), 4.03-3.82
(9H, m), 3.76-3.55 (5H, m), 3.56 (3H, s), 3.53-3.46 (4H, m), 3.42
(1H, dd, J ) 9.5, 3.2 Hz), 3.38-3.30 (2H, m), 3.27-3.21 (2H, m),
2.47 (1H, d, J ) 1.3 Hz), 1.19-1.07 (21H, m), 1.03-0.99 (21H, m);
13C NMR (125 MHz, CDCl3) δ 153.86, 139.65, 138.99, 138.72, 138.50,
138.26, 138.02, 137.74, 137.39, 132.28, 128.90, 128.68, 128.66, 128.50,
128.46, 128.34, 128.28, 128.27, 128.23, 128.18, 127.65, 127.92, 127.79,
127.76, 127.74, 127.72, 127.59, 127.55, 127.48, 127.34, 127.19, 126.86,
104.57, 103.68, 103.56, 102.81, 83.82, 82.62, 81.56, 80.27, 76.25, 75.92,
75.52, 75.26, 74.80, 74.68, 74.35, 73.57, 73.42, 73.25, 73.22, 73.12,
73.10, 73.07, 72.63, 70.68, 68.51, 68.05, 61.05, 60.90, 56.97, 56.50,
17.98, 17.97, 17.94, 11.90, 11.82 (three unresolved carbon resonances);
HRMS (FAB) calcd for C99H129O23NSSi2Na (M + Na+) 1810.8110,
found 1810.8100.
For 33: [R]18 -26.56° (c 3.37, CHCl3); FTIR (neat) 3258, 3032,
D
2942, 2866, 1814, 1732, 1649, 1497, 1462, 1360, 1248, 1211, 1163,
1
1098, 1028, 911, 883., 793, 735, 697, 597, 458 cm-1; H NMR (400
Compound 39 was prepared in a fashion identical to that for 34.
For 39: [R]21D +18.4° (c 1.19, CHCl3); FTIR (neat) 3449, 3194, 3064,
2944, 2866, 1810, 1607, 1496, 1463, 1368, 1335, 1266, 1210, 1088,
919, 883, 791, 748, 695, 664, 580 cm-1; 1H NMR (500 MHz, CDCl3)
δ 7.78 (2H, d, J ) 7.7 Hz), 7.44 (1H, t, J ) 7.5 Hz), 7.38 (2H, t, J )
7.2 Hz), 7.35-7.18 (35H, m), 6.08 (1H, d, J ) 8.6 Hz), 4.99 (1H, d,
J ) 3.3 Hz), 4.93-4.87 (3H, m), 4.82-4.78 (3H, m), 4.72-4.62 (5H,
m), 4.51-4.41(6H, m), 4.31 (1H, d, J ) 12.1 Hz), 4.18-4.13 (3H,
m), 4.09 (1H, br s), 4.00 (1H, d, J ) 2.3 Hz), 3.96-3.92 (2H, m),
3.88-3.75 (5H, m), 3.72 (1H, t, J ) 8.9 Hz), 3.66-3.62 (2H, m), 3.59-
3.47 (4H, m), 3.53 (3H, s), 3.39-3.35 (2H, m), 3.26 (1H, app t, J )
7.0 Hz), 3.22 (1H, dd, J ) 9.9, 2.5 Hz), 2.30 (1H, d, J ) 1.1 Hz),
1.10-1.04(21H, m), 0.95 (21H, s); 13C NMR (125 MHz, CDCl3) δ
153.71, 141.24, 139.39, 138.78, 138.36, 138.17, 137.90, 137.72, 137.12,
132.38, 129.06, 128.58, 128.47, 128.41, 128.31, 128.25, 128.20, 128.08,
128.01, 127.95, 127.82, 127.76, 127.71, 127.69, 127.59, 127.53, 127.50,
127.46, 127.40, 127.34, 127.00, 126.92, 104.46, 103.44, 102.94, 100.08,
81.86, 80.91, 79.47, 79.41, 76.18, 75.95, 75.34, 75.26, 75.25, 75.06,
MHz, CDCl3) δ 7.89 (2H, d, J ) 7.6 Hz), 7.47-7.21 (38H, m), 6.56
(1H, d, J ) 6.2 Hz), 5.59 (1H, d, J ) 5.0 Hz), 5.15 (1H, app s), 5.11
(1H, d, J ) 11.4 Hz), 5.01-4.92 (3H, m), 4.88 (1H, dd, J ) 8.5, 1.4
Hz), 4.83 (1H, dd, J ) 8.5, 2.6 Hz), 4.75 (2h, app t, J-10.5 Hz), 4.62-
4.51 (4H, m), 4.45 (1H, d, J ) 7.3 Hz), 4.41-4.34 (3H, m), 4.32 (1H,
d, J ) 8.3 Hz), 4.26 (1H, d, J ) 3.0 Hz), 4.19-4.15 (2H, m), 4.08
(1H, app t, J ) 6.9 Hz), 3.97-3.88 (3H, m), 3.85 (1H, d, J ) 3.0 Hz),
3.79 (1H, dd, J ) 9.3, 8.2 Hz), 3.69 (1H, dd, J ) 10.6, 4.1 Hz), 3.63-
3.58 (2H, m), 3.54 (1H, dd, J ) 8.5, 4.2 Hz), 3.50-3.36 (4H, m),
3.30-3.27 (2H, m), 1.19-1.12 (21H, m), 1.03 (21H, s); 13C NMR (75
MHz, CDCl3) δ 153.89, 144.66, 139.66, 139.11, 138.48, 138.41, 138.19,
138.01, 137.85, 137.32, 132.54, 129.07, 128.70, 128.58, 128.40, 128.31,
128.26, 128.22, 127.88, 127.87, 127.84, 127.76, 127.70, 127.69, 127.56,
127.45, 127.35, 126.94, 104.20, 102.95, 102.81, 99.38, 82.96, 81.08,
79.63, 76.00, 75.97, 75.77, 75.40, 75.20, 74.68, 74.56, 73.46, 73.31,
73.22, 73.16, 73.11, 73.10, 72.62, 71.09, 70.58, 69.74, 69.18, 67.76,
61.19, 56.25, 17.94, 17.92, 11.87, 11.80 (eight unresolved resonances);

1598 J. Am. Chem. Soc., Vol. 120, No. 7, 1998
Kwon and Danishefsky
74.63, 74.60, 73.50, 73.25, 73.12, 72.98, 72.81, 72.77, 72.49, 71.91,
71.73, 70.63, 68.11, 67.15, 61.20, 60.54, 56.97, 54.31, 18.03, 17.96,
17.92, 17.87, 11.83, 1179; HRMS (FAB) calcd for C99H129O23NSSi2-
Na (M + Na+) 1810.8110, found 1810.8110.
OCH2Ar), 4.23 (1H, m), 4.00-3.97 (2H, m), 3.73 (1H, dd, J ) 9.7,
2.7 Hz), 3.61-3.57 (4H, m), 3.44-3.38 (2H, m), 2.10 (3H, s, CH3-
CO), 1.09-1.06 (21H, m), 1.00 (21H, app d, J ) 0.7 Hz); 13C NMR
(75 MHz, CDCl3) δ 169.56, 144.78, 140.48, 138.10, 137.15, 131.95,
128.73, 128.40, 128.33, 128.25, 128.15, 127.76, 127.59, 127.38, 102.42,
98.49, 75.36, 74.65, 74.02, 73.20, 71.64, 71.46, 71.35, 70.21, 69.03,
61.06, 57.77, 20.91, 18.34, 18.30, 17.85, 17.83, 12.95, 11.76; HRMS
(FAB) calcd for C52H79O11NSSi2K (M + K+) 1020.4550, found
1020.4570.
Asialo GM1 Methyl Glycosides 38 and 42. A solution of
peracetylated â-methyl glycoside of asialo GM1 37 (18 mg, 0.015
mmol) in anhydrous MeOH (0.6 mL) was treated with NaOMe (3.6
mg) and stirred overnight at rt. After diluted with MeOH, the reaction
was neutralized with Dowex 50×8-200 (∼50 mg), filtered, and
concentrated. Flash column chromatography on LiChroprep RP-18
(from Merck) using 40%-10% water in MeOH and subsequent size-
exclusion chromatography on Lipophilic Sephadex LH-20 (from Sigma)
using MeOH afforded 38 (11 mg, 99%) For 3: [R]19D -12.8° (c 0.71,
MeOH); FTIR (neat) 3356, 2891, 1636, 1559, 1375, 1312, 1234, 1156,
Synthesis of Disaccharide Glycal 52. A stirred mixture of
thioglycoside 49 (98 mg, 0.15 mmol), galactal 50 (48 mg, 0.15 mmol),
and freshly activated powdered 4 Å MS (730 mg) in dry CH2Cl2 (1.0
mL) and dry ether (2.0 mL) at 0 °C was treated with MeOTf (82 µL,
0.73 mmol). The reaction was stirred for 8 h at 0 °C, filtered through
a pad of Celite after addition of Et3N (260 µL), and concentrated. Flash
column chromatography using 25:1-15:1 benzene/EtOAc provided 52
1
1116, 1051, 891, 763, 668 cm-1; H NMR (400 MHz, D2O) δ 4.65
(1H, d, J ) 8.4 Hz), 4.41 (1H, d, J ) 7.6 Hz), 4.40 (1H, d, J ) 8.0
Hz), 4.37 (1H, d, J ) 8.1 Hz), 4.12 (1H, d, J ) 2.6 Hz), 4.06 (1H, d,
J ) 2.1 Hz), 4.00-3.93 (2H, m), 3.86-3.83 (2H, m), 3.77-3.67 (7H,
m), 3.64-3.47 (5H, m), 3.53 (3H, s, OMe), 3.37 (1H, dd, J ) 9.7, 7.8
Hz), 3.25 (1H, t, J ) 8.4 Hz), 2.00 (3H, s, NAc); 13C NMR (100 MHz,
CD3OD) δ 174.83, 106.67, 105.30, 105.24, 104.20, 82.09, 81.05, 77.72,
77.64, 76.82, 76.53, 76.46, 76.32, 76.17, 74.75, 74.55, 72.57, 70.36,
70.30, 69.81, 69.73, 62.72, 61.91, 61.65, 57.37, 53.53, 23.52; HRMS
(FAB) calcd for C27H47O21NNa (M + Na+) 744.2538, found 744.2548.
Compound 42 was prepared in an identical fashion from 41.
(92 mg, 67%) accompanied by its R-anomer (8.4 mg, 6.2%): [R]21
D
-51.7° (c 2.09, CHCl3); FTIR (neat) 3569. 3264, 2942, 2866, 1648,
1454, 1341, 1236, 1212, 1161, 1110, 1058, 995, 882, 807, 752, 684,
1
594, 561, 459 cm-1; H NMR (500 MHz, CDCl3) δ 7.87-7.23 (15H,
m), 6.10 (1H, dd, J ) 6.3, 0.98 Hz, H1), 5.71 (1H, d, J ) 4.7 Hz,
NH), 4.67 (1H, app d, J ) 6.3 Hz, H2), 4.59 (2H, AB, J ) 11.5 Hz,
∆ν ) 164 Hz, CH2Ar), 4.45 (2H, s, CH2Ar), 4.36 (1H, d, J ) 8.4 Hz,
H1′), 4.22 (1H, app s), 3.95-3.91 (4H, m), 3.63-3.59 (2H, m, H6′,
H3′), 3.56 (1H, dd, J ) 9.9, 5.7 Hz), 3.49 (1H, dd, J ) 9.9, 6.4 Hz),
3.34 (1H, dd, J ) 8.2, 4.8 Hz, H5′), 3.29 (1H, td, J ) 8.8, 4.8 Hz,
H2′), 2.45 (1H, app s, OH), 1.20-0.98 (42H, m); 13C NMR (125 MHz,
CDCl3) δ 144.92, 139.98, 137.99, 136.96, 132.03, 128.74, 128.50,
128.33, 128.32, 128.31, 128.23, 127.61, 127.48, 102.55, 98.44, 75.65,
75.40, 74.96, 73.19, 71.88, 71.44, 71.33, 68.98, 68.05, 60.76, 57.21,
18.30, 18.26, 17.85, 17.82, 13.02, 11.75; HRMS (FAB) calcd for
C50H77O10NSSi2Na (M + Na+) 962.4704, found 962.4722.
â-Methyl Glycoside of GalNAcâ1-4Gal (57). A stirred mixture
of 52 (42 mg, 0.044 mmol) and flame-dried powdered 4 Å MS (50
mg) in dry CH2Cl2 (0.1 mL) at 0 °C was treated with dimethyldioxirane
(0.6 mL, ∼0.044 mmol). After 15 min, the reaction mixture was
concentrated with a stream of argon. The residue was further dried
under vacuum and then dissolved in anhydrous MeOH (1.0 mL) and
dry THF (1.0 mL). The mixture was stirred overnight. The product
was filtered through a pad of Celite, concentrated, and subjected to
flash column chromatography using 30% EtOAc in hexane to give
methyl glycosides 53 and its isomer (combined weights 36 mg, 81%,
R/â ∼3.7:1): 1H NMR (500 MHz, CDCl3) δ 7.81 (2H, d, J ) 7.2 Hz),
7.44-7.28 (14H, m), 4.98 (1H, d, J ) 6.4 Hz), 4.78 (2H, AB, J )
11.3 Hz, ∆ν ) 174 Hz), 4.53 (2H, AB, J ) 12.0 Hz, ∆ν ) 17.7 Hz),
4.36 (1H, d, J ) 8.3 Hz), 4.03 (1H, d, J ) 7.7 Hz), 3.99-3.94 (3H,
m), 3.71-3.66 (2H, m), 3.58-3.43 (5H, m), 3.55 (3H, s), 3.34 (1H, t,
J ) 8.2 Hz), 3.26 (1H, dd, J ) 8.4, 5.2 Hz), 2.51 (1H, s), 2.27 (1H, d,
J ) 1.6 Hz), 1.04-0.98 (42H, m).
The methyl glycosides (36 mg, 0.036 mmol) were dissolved in THF
(0.36 mL), cooled to 0 °C, and treated with TBAF (144 µL, 1.0 M in
THF). The resulting solution was warmed to rt and stirred overnight.
The reaction was only completed after addition of more TBAF (432
µL, 1.0 M in THF) and further stirring for 48 h. NaHCO3 (48 mg,
0.58 mmol) was added. The mixture was filtered through Celite,
concentrated, and purified by flash column chromatography using 10:
10:1 hexane/EtOAc/MeOH to yield desilylated methyl glycosides 54
and its isomer (24 mg, quantitative): 1H NMR (500 MHz, CDCl3) δ
7.76 (2H, d, J ) 7.2 Hz), 7.48 (1H, t, J ) 7.2 Hz), 7.42 (2H, t, J ) 7.2
Hz), 7.33-7.20 (10H, m), 4.76 (2H, AB, J ) 11.5 Hz, ∆ν ) 130 Hz),
4.43 (2H, AB, J ) 16.8 Hz, ∆ν ) 19.8 Hz), 4.20 (1H, d, J ) 8.1 Hz),
4.00 (1H, d, J ) 7.6 Hz), 3.79 (1H, d, J ) 3.0 Hz), 3.73-3.67 (2H,
m), 3.59 (1H, dd, J ) 11.6, 4.9 Hz), 3.46-3.27 (6H, m), 3.45 (3H, s),
3.19-3.16 (6H, m).
A 10 mL flask, fitted with a dry ice condenser, was charged with
anhydrous ammonia (∼5 mL) and Na (∼50 mg). The above-described
desilylated methyl glycoside mixture (24 mg, 0.036 mmol) in dry THF
(0.7 mL) was added at -78 °C. The resulting dark blue solution was
allowed to reflux for 30 min, cooled to -78 °C, and NH4Cl (119 mg)
was added. The ammonia was allowed to evaporate and the THF was
removed by passing a stream of argon over the solution and the residue
For 42: [R]19 +67.6° (c 0.62, MeOH); FTIR (neat) 3366, 2931,
D
1
1636, 1558, 1376, 1322, 1224, 1116, 1045, 886, 704, 633 cm-1; H
NMR (400 MHz, D2O) δ 4.69 (1H, d, J ) 3.5 Hz), 4.31 (2H, m), 4.26
(1H, t, J ) 6.4 Hz), 4.22 (1H, d, J ) 8.1 Hz), 4.17 (1H, dd, J ) 11.4,
3.9 Hz), 4.10 (1H, s), 3.88 (1H, d, J ) 10.4 Hz), 3.83-3.80 (2H, m),
3.71 (1H, br s), 3.64 (1H, dd, J ) 12.7, 4.5 Hz), 3.58-3.40 (9H, m),
3.38 (3H, s), 3.33 (1H, t, J ) 8.8 Hz), 3.15 (1H, d, J ) 1.7 Hz), 3.12
(1H, t, J ) 8.3 Hz), 1.87 (3H, s); 13C NMR (100 MHz, CD3OD) δ
173.12, 105.40, 104.39, 104.24, 99.37, 79.89, 77.93, 77.07, 76.14, 75.75,
75.51, 75.45, 73.88, 73.77, 73.56, 71.52, 71.44, 70.86, 69.27, 68.92,
61.57, 60.92, 60.34, 56.30, 49.43, 21.84 (one unresolved carbon);
HRMS (FAB) calcd for C27H47O21NNa (M + Na+) 744.2538, found
744.2537.
Synthesis of Sulfonamidothioglycoside 49. A solution of 48 (827
mg, 1.15 mmol) in dry ether (23 mL) at -15 °C was treated with LAH
(1.15 mL, 1.0 M in ether). TLC analysis showed incomplete consump-
tion of 48 after 2 h, and more LAH (0.5 mL) was added. Additional
LAH (0.25 mL) was added to complete the reaction, and it caused
formation of byproduct. Reaction was diluted with EtOAc (50 mL)
and stirred vigorously with half-saturated Rochelle salt solution (50
mL) until it showed clear separation between two layers. Aqueous
layer was extracted with EtOAc (2 × 50 mL). The collected organic
phases were washed with brine, dried over MgSO4, and concentrated.
Flash column chromatography using benzene-50:1 benzene/EtOAc
afforded 49 (608 mg, 78%): [R]22D -20.5° (c 5.86, CHCl3); FTIR (neat)
3570, 3288, 2942, 2866, 1720, 1462, 1382, 1327, 1259, 1159, 1108,
1015, 884, 798, 686, 594 cm-1; 1H NMR (500 MHz, CDCl3) δ 7.86-
7.41 (5H, m), 4.51 (1H, d, J ) 7.9 Hz, NH), 4.28 (1H, d, J ) 10.2 Hz,
H1), 4.05 (1H, d, J ) 2.7 Hz, H4), 3.94 (1H, dd, J ) 9.4, 3.0 Hz, H3),
3.80 (1H, dd, J ) 9.6, 5.3 Hz, H6), 3.64 (1H, td, J ) 9.7, 8.1 Hz, H2),
3.44 (1H, dd, J ) 6.8, 6.0 Hz, H5), 2.44-2.33 (3H, m, OH, SCH2),
1.18-0.98 (45H, m); 13C NMR (125 MHz, CDCl3) δ 141.92, 132.15,
128.45, 127.36, 84.28, 78.21, 75.64, 68.48, 61.68, 57.05, 23.96, 18.21,
18.15, 17.81, 17.78, 14.16, 12.86, 11.78; HRMS (FAB) calcd for
C32H61O6NS2Si2K (M + K+) 714.3116, found 714.3085.
Synthesis of Disaccharide Glycal 51. Reaction between thiogly-
coside 48 (100 mg, 0.139 mmol) and galactal 50 (46 mg, 0.139 mmol)
according to the procedure used in preparation of 21 followed by flash
column chromatography using 10:1-9:1-5:1 hexane/EtOAc gave 51
(70 mg, 51%) accompied by R-isomer (22 mg, 16%): [R]21D -53.01°
(c 1.05, CHCl3); FTIR (neat) 3025, 2923, 1942, 1870, 1802, 1746, 1668,
1601, 1493, 1372, 1181, 1154, 1069, 1028, 965, 907, 842, 757, 700,
1
620, 541 cm-1; H NMR (400 MHz, CDCl3) δ 7.90-7.87 (2H, m),
7.49-7.26 (13H, m), 6.14 (1H, dd, J ) 6.4, 1.7 Hz), 5.58 (1H, dd, J
) 5.2 Hz), 5.40 (1H, d, J ) 1.9 Hz), 4.68 (1H, dt, J ) 6.4, 1.8 Hz),
4.62 (2H, AB, J ) 11.8 Hz, ∆ν ) 113 Hz, OCH2Ar), 4.50 (2H, s,

Synthesis of Asialo GM1
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1599
was further concentrated under vacuum for 1 h. The material was
dissolved in anhydrous pyridine (1.5 mL) and treated with Ac2O (0.5
mL) and catalytic DMAP. The solution was stirred for 12 h and then
the contents were poured into water (15 mL) and extracted with EtOAc
(3 × 15 mL). The combined extracts were washed with brine, dried
over MgSO4, and concentrated. Flash column chromatography using
EtOAc afforded peracetylated methyl glycoside of GalNAcâ1-4Gal (19
mg, 82% overall, â/R 3.7:1).
provided 57 (4 mg, 44%): [R]28D -12.1° (c 0.18, MeOH); FTIR (MeOH
1
film) 3338, 1643, 1056 cm-1; H NMR (500 MHz, CD3OD) δ 4.52
(1H, d, J ) 8.5 Hz), 4.00 (1H, d, J ) 7.7 Hz), 3.90 (1H, d, J ) 2.1
Hz), 3.77 (1H, dd, J ) 11.2, 7.7 Hz), 3.75 (1H, t, J ) 9.5 Hz), 3.69
(1H, dd, J ) 11.2, 8.1 Hz, H3), 3.64 (1H, d, J ) 2.7 Hz), 3.58 (1H,
dd, J ) 11.2, 4.2 Hz, H6), 3.52-3.48 (2H, m), 3.46 (1H, dd, J ) 10.5,
3.3 Hz), 3.41-3.39 (2H, m), 3.37 (3H, s, OMe), 3.31 (1H, dd, J )
9.7, 7.8 Hz); 13C NMR (125 MHz, CD3OD) δ 175.18, 105.88, 104.33,
78.31, 76.94, 75.57, 74.89, 74.70, 72.64, 69.56, 62.67, 61.37, 57.20,
55.53, 23.02; HRMS (FAB) calcd for C15H27O11NNa (M + Na+)
420.1482, found 420.1490.
For â-anomer 56: [R]20D -18.7° (c 0.66, CHCl3); FTIR (neat) 1748,
1
1370, 1229, 1047 cm-1; H NMR (500 MHz, CDCl3) δ 5.91 (1H, dd,
J ) 11.3, 3.4 Hz, H3′), 5.70 (1H, d, J ) 6.9 Hz, NH), 5.38 (1H, d, J
) 3.2 Hz, H4′), 5.25 (1H, dd, J ) 10.4, 7.9 Hz, H2), 5.13 (1H, d, J )
8.2 Hz, H1′), 4.94 (1H, dd, J ) 10.5, 2.7 Hz, H3), 4.37 (1H, d, J )
7.9 Hz, H1), 4.31 (1H, dd, J ) 11.8, 5.5 Hz, H6), 4.28 (1H, dd, J )
11.8, 6.5 Hz, H6), 4.13 (1H, d, J ) 2.5 Hz, H4), 4.05 (2H, app d, J )
6.6 Hz, 2H6′) 3.91 (1H, t, J ) 6.6 Hz, H5′), 3.74 (1H, t, J ) 6.0 Hz,
H5), 3.51 (3H, s, OMe), 3.35 (1H, dt, J ) 11.2, 7.6 Hz, H2′), 2.13
(3H, s, CH3CO), 2.10 (3H, s, CH3CO), 2.07(3H, s, CH3CO), 2.04 (3H,
s, CH3CO), 2.03 (3H, s, CH3CO), 1.99 (3H, s, CH3CO), 1.98 (3H, s,
CH3CO); 13C NMR (125 MHz, CDCl3) δ 171.28, 170.88, 170.54,
170.44, 170.11, 169.72, 169.59, 101.82, 98.86, 73.19, 72.87, 72.07,
70.37, 69.05, 67.97, 66.94, 63.07, 61.44, 57.00, 53.60, 23.45, 20.81,
20.75, 20.65, 20.64, 20.61, 20.60; HRMS (FAB) calcd for C27H39O17-
NNa (M + Na+) 672.2115, found 672.2134.
Acknowledgment. This research was supported by the
National Institutes of Health (Grant Nos. AI 16943 and
HL25848). O.K. gratefully acknowledges the Kanagawa Acad-
emy of Science and Technology for a graduate fellowship. We
thank Dr. G. Sukenick of MSKCC and Drs. V. and B.
Parmakovich of Columbia University for mass spectral mea-
surements.
Supporting Information Available: Experimental proce-
dures and 1H NMR spectra for 45 and 47, 1H NMR spectra and
LRMS for 17, 31, and 36, and spectral data (1H NMR, 13C
NMR, FTIR, and HRMS) for compounds 14, 16, 18-20, 30,
32, 37, 41, 43, 44, 46, 48, and 50 (14 pages). See any current
masthead page for ordering and Internet access instructions.
A solution of 56 (13 mg, 0.020 mmol) in anhydrous MeOH (0.8
mL) was treated with NaOMe (4.4 mg, 0.082 mmol) and stirred
overnight. After diluted with MeOH, the reaction was neutralized with
Dowex 50×8-200 (∼50 mg, Aldrich), filtered, and concentrated. Flash
chromatography on RP-18 silica gel using 40%-10% water in MeOH
JA9724957