sidic bond may also confer upon the ligand the capacity to
preferentially stimulate proinflammatory functions in the
responding T cell population. Indeed, a C-glycoside analogue
of R-galactosylceramide (R-GalCer) enhances proinflamma-
tory T cell response as compared to natural R-GalCer.6
Whether this is a general phenomenon occurring also with
other types of glycolipid antigens and lipid-specific T cell
populations is not known.
Scheme 1. Preparation of the â-C-Glycoside 6
We have shown that sulfatide (1a), a â-D-galactosyl-
ceramide sulfated at position 3 of galactose, is one of the
mammalian endogenously derived self-antigens presented by
CD1 proteins.7 Sulfatide 1a is a natural ligand for all human
CD1 family members and is presented by all CD1 molecules
to specific T cells. Furthermore, the response to sulfatide is
very frequent in Multiple Sclerosis patients (our unpublished
results) and also occurs in mice during experimental allergic
encephalomyelitis (EAE), a model of autoimmune brain
disease.8
To investigate whether the substitution of the anomeric
oxygen with a methylene affects the proinflammatory T cell
responses also with sulfatide as the model antigen, we
prepared 1b, the C-glycoside isosteric analogue of sulfatide
1a. This modification might confer novel binding conforma-
tions in the active site of CD1 molecules or might influence
the binding capacity to CD1.9,10
Here we describe the synthesis of the C-sulfatide 1b and
show that this analogue is less stimulatory than sulfatide 1a.
The easy and highly stereoselective synthesis of the sulfatide
analogue 1b is based on the preparation of the â-C-galactosyl
ceramide 2, previously described by Dondoni et al. in an
alternative synthetic approach,11 followed by regioselective
sulfation of galactose.
The key features of our approach to the skeleton of â-C-
GalCer 2 are a [2,3]-Wittig sigmatropic rearrangement for
the construction of the â-C-glycoside12 and a Horner-
Wadsworth-Emmons olefination for the installation of the
carbon unsaturated chain.
glucosidic compound.12b The dianionic [2,3]-Wittig re-
arrangement of 4 was carried out by treatment with excess
LDA at -78 °C, followed by reaction of the crude with
diazomethane to afford the R-hydroxy ester 5 as a single
isomer, as clearly shown by the single set of peaks observed
in the 1H and 13C NMR spectra. The Z geometry of the newly
formed double bond was established by a NOE experiment,
which showed an effect of 5% on the H-2 atom of galactose
on irradiation of the vinylic hydrogen. Due to its acidic
lability, compound 5 was promptly hydrogenated with Pt(C)
in methanol to give compound 6 in high yield. The
configuration of the new stereocenter at position 1 of
galactose, generated after double bond reduction, was found
1
to be â through the H NMR coupling constant of 9 Hz
between H-1 and H-2 of galactose. Moreover, compound 6
was used to establish the absolute configuration of the
stereocenter at C-2 previously formed in the [2,3]-Wittig
1
rearrangement. The analysis of the H NMR spectra of its
(R)- and (S)-MTPA esters14 (see the Supporting Information)
allowed us to unequivocally assign the absolute configuration
at C-2 as S and confirmed the stereoisomeric purity and the
complete transmission of stereochemical information to this
new stereocenter during the rearrangement.
The stereochemistry at C-2 of compound 6 requires the
introduction of a masked amino functionality at that position
with retention of configuration. Therefore we decided to
employ a Mitsunobu reaction with methanesulfonic acid as
nucleophile on compound 6 (Scheme 2), followed by reaction
with sodium azide. Mitsunobu mesylation was performed
on compound 6 under the condition reported by Lawless et
al.15 followed by treatment with sodium azide in DMF, which
Starting from known 2,3,4,6-tetra-O-benzyl-1-C-vinyl-R-
D-galactopyranose 3,13 galactoside 4 was obtained (Scheme
1) exclusively as the R-anomer in 90% yield by using a
protocol reported in the literature for the corresponding
(11) Dondoni, A.; Perrone, D.; Turturici, E. J. Org. Chem. 1999, 64,
5557-5564.
(6) (a) Schmieg, J.; Yang, G.; Franck, R. W.; Tsuji, M. J. Exp. Med.
2003, 198, 1631-1641. (b) Yang, G.; Schmieg, J.; Tsuji, M.; Franck, R.
W. Angew. Chem., Int. Ed. 2004, 43, 3818-3822. (c) Chen, G.; Schmieg,
J.; Tsuji, M.; Franck, R. W. Org Lett. 2004, 6, 4077-80.
(7) Shamshiev, A.; Gober, H. J.; Donda, A.; Mazorra, Z.; Mori, L.; De
Libero, G. J. Exp. Med. 2002, 195, 1013-1021.
(12) (a) Tomooka, K.; Nakamura, Y.; Takeshi, N. Synlett 1995, 4, 321-
322. (b) Lay, L.; Meldal, M.; Nicotra, F.; Panza, L.; Russo, G. Chem.
Commun. 1997, 15, 1469-1470.
(13) Li, X.; Ohtake, H.; Takahashi, H.; Ikegami, S. Tetrahedron 2001,
57, 4297-4309.
(8) Jahng, A.; Maricic, I.; Aguilera, C.; Cardell, S.; Halder. R. C.; Kumar,
V. J. Exp. Med. 2004, 199, 947-957.
(14) (a) Dale, J. A.; Mosher, H. S. J. Am. Chem. Soc. 1973, 95, 512-
519. (b) Devijver, C.; Salmoun, M.; Daloze, D.; Braekman, J. C.; De Weerdt,
W. H.; De Kluijver M. J.; Gomez, R. J. Nat. Prod. 2000, 63, 978-980. (c)
Chun, J.; Byun, H.-S.; Arthur, G.; Bittman, R. J. Org. Chem. 2003, 68,
355-39.
(9) Espinosa, J. F.; Montero, E.; Vian, A.; Garcia, J. L.; Dietrich, H.;
Schmidt, R. R.; Martin-Lomas, M.; Imberty, A.; Can˜ada, F. J.; Jimenez-
Barbero, J. J. Am. Chem. Soc. 1998, 120, 1309-1318.
(10) Postema, M. H. D.; Piper, J. L.; Betts, R. L. Synlett 2005, 9, 1345-
1358.
(15) Lawless, L. J.; Blackburn, A. G.; Ayling, A. J.; Perez-Payan, M.
N.; Davis, A. P. J. Chem. Soc., Perkin Trans. 1 2001, 11, 1329-1341.
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