Focus on the controversial activation of human iNKT cells by 4-deoxy analogue of KRN7000

Article abstract of DOI:10.1021/jm900290r

4-Deoxy-α-GalCer analogues are considered weaker agonists than KRN7000 for the stimulation of human iNKT cells, but this remains strongly debated. In this work, we described a strategy toward 4-deoxy-α-GalCers with, as a key step, a metathesis reaction al

Full text of DOI:10.1021/jm900290r

4960 J. Med. Chem. 2009, 52, 4960–4963
DOI: 10.1021/jm900290r
Focus on the Controversial Activation of Human iNKT Cells by 4-Deoxy Analogue of KRN7000
†,‡
Vivien Lacone, Julie Hunault, Muriel Pipelier, Virginie Blot, Thomas Lecourt, Jezabelle Rocher,
†
†
†
‡
^
Anne-Laure Turcot-Dubois, Severine Marionneau, Jean-Yves Douillard, Monique Clement, Jacques Le Pendu,*
ꢀ
§
§
,
ꢀ
ꢀ
Marc Bonneville, Laurent Micouin,‡ and Didier Dubreuil*,†
†
ꢀ
ꢀ
ꢁ
ꢀ
ꢀ
Universite de Nantes, CNRS, Chimie et Interdisciplinarite: Synthese, Analyse, Modelisation (CEISAM), UMR CNRS 6230, Faculte des
ꢁ
‡
ꢀ
Sciences et des Techniques, 2 Rue de la Houssiniere, BP 92208, 44322 Nantes Cedex 3, France, UMR 8638 CNRS-Universite Paris Descartes,
ꢀ
Laboratoire de Chimie Therapeutique, Faculte des Sciences Pharmaceutiques et Biologiques, 4 Avenue de l’Observatoire, 75270 Paris Cedex 06,
France, Centre Rene Gauducheau, Centre Regional de Lutte Contre le Cancer Nantes-Atlantique, 44805 Saint-Herblain Cedex, France, and
ꢀ
§
ꢀ
ꢀ
INSERM, U892, Universiteꢀ de Nantes, Institut de Biologie, 9 Quai Moncousu, 44093 Nantes Cedex, France
Received March 7, 2009
4-Deoxy-R-GalCer analogues are considered weaker agonists than KRN7000 for the stimulation of
human iNKT cells, but this remains strongly debated. In this work, we described a strategy toward
4-deoxy-R-GalCers with, as a key step, a metathesis reaction allowing sphingosine modifications from a
single ethylenic R-galactoside precursor. The 4-deoxy-KRN7000 derivative 2, described here, induced
potent cytokinic responses, comparable to those of KRN7000, both from human iNKT cells in vitro and
from their murine counterpart in vivo.
Introduction
therapeutic potential, extensive structure-activity rela-
tionship (SAR) studies have been conducted to optimize
R-GalCersactivity. Initial studiesby Koezuka and co-workers
focused on the ceramide portion of the molecule and led to the
synthetic 20-deoxy-GalCer analogue (KRN7000, 1) as a po-
tential candidate for clinical application (Chart 1).6 Advances
in the elucidation of SARs for a number of synthetic
KRN7000 analogues have been widely reviewed in recent
update publications.7 We focused here on 4-deoxy-GalCer
analogues of KRN7000. Those latter derivatives, devoid of
4-OH group, failed to stimulate human iNKT lymphocytes
when presented by CD1d-transfected Hela cells.8 However,
subsequent data obtained from mouse iNKT cells indicated
that 4-deoxy-R-GalCer was an active agonist, albeit weaker,
than parent KRN7000.9 Crystal structure of the ternary
complex of human NKT TCR with CD1d and KRN7000
highlighted the involvement of the 3 and 4 hydroxyl groups on
the phytosphingosinescaffold through concomitant hydrogen
bonding with CD1d Asp80 residue and an additional H-bond
between the donating Arg95 of the CDR3R-loop and the
3-OH group of the glycolipidic ligand.10 Nevertheless, these
studies did not identify a specific interaction between the
4-OH group and the hCD1d binding domains. This contra-
dicts the assumption, postulated for now a decade, that this
position could be responsible for a loss of activity in the
human context. A comparison between human and mouse
empty CD1d crystal structures confirmed that the A0 and C0
hydrophobic binding pockets were superimposable in size and
shape.11 From these observations, it was admitted that R-
GalCer should adopt a similar conformation in both CD1d
molecules. Thus, evenif a somewhatmore potent activationof
mouse NKT cells by KRN7000, versus its 4-deoxy analogue,
has been attributed to an increased stability of the ternary
complex, the structural information available to date does not
fit well with the loss of IFN-γ and IL-4 stimulation with
4-deoxy R-GalCers mentioned in the human context. In the
Natural killer T cells (NKTa) are a subset of T cells, which
play a major role at regulating immune responses.1 A major
subpopulation of the CD1d restricted T lymphocytes, called
iNKT cells, can elicit a proinflammatory response through the
secretion of T helper 1 (Th1) cytokines (IFN-γ, TNF-R) or an
immunomodulatory response when releasing Th2 cytokines
(IL-4, IL-10). Disruption of the balance between Th1 and Th2
cytokines is involved in a broad range of diseases, and
therapeutic strategies could imply its restoration through in
vivo modulation of NKT cells.2 iNKT cells stimulation is
mediated by the formation of a ternary complex between the
semi-invariant T cell receptor (VR24JR18 human TCR and
VR14JR18 for mouse) at the surface of the lymphocyte and the
CD1d membrane protein of antigen presenting cells (APCs),
complexed with a glycolipid.3 Surprisingly, while the first
sugar unit of all mammalian glycolipids is in β-anomeric
position, the first active glycolipid antigens (e.g., agelasphin
9b), isolated from the marine sponge Agelas mauritianus, were
identified as R-galactosylceramides (R-GalCers) by the Kirin
Brewery Company in 1993.4 Recently, various R-glucuronyl-
ceramides (R-GluCers, GSL-1) and iso-globotrioside (iGb3-
GalR3Galβ4Glcβ-Cer) have also been shown to stimulate
both human and mouse NKT cells.5 Because of their strong
*To whom correspondence should be addressed. For D.D.: phone,
þ33 2 51 12 54 20; fax, þ33 2 51 12 54 02; E-mail, Didier.Dubreuil@
univ-nantes.fr. For J.L.P.: jlependu@nantes.inserm.fr.
a Abbreviations: IL, interleukin; IFN-γ, interferon γ; TNF-R, tumor
necrosis factor R; NKT, natural killer T; hiNKT, human iNKT; Th, T
helper; APC, antigen presenting cell; TCR, T cell receptor; CD, cluster
of differentiation; hCD1d, human CD1d; SAR, structure-activity
relationship; ip, intraperitoneal; R-GalCer, R-galactosylceramide;
R-GluCer, R-glucuronylceramide; iGb3, iso-globotrioside; DMAP, N,
N-dimethylaminopyridine; Boc, tert-butyloxycarbonyl; DMEM, Dul-
becco’s modified Eagle’s medium; MTT, 3-(4,5-dimethylthiazol-2-yl)-
2,5-diphenyl tetrasodium bromide; FCS, fetal calf serum; ELISA,
enzyme-linked immunosorbent assay.
r
pubs.acs.org/jmc
Published on Web 07/06/2009
2009 American Chemical Society

Brief Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 15 4961
present work, we propose to investigate the in vitro activity on
human iNKT cells, in complement to the in vivo activity in
mice, of the 20,4-dideoxy-R-galactosylceramide 2.
2 was prepared following our original strategy as illustrated
in Scheme 2. Because of an unsuitable removal of Boc group
during the glycosidic coupling of the R-fluoro-galactopyra-
nosyl donor 4 with the alcohol acceptor 3, using Mukaiyama
procedure,16 the target glycoside 5r was in first attempt
isolated in a modest 30% yield (Scheme 2). To overcome this
side degradation, the crude glycosidic mixture 5r,β was
submitted to another Boc2O, Et3N treatment, and the silyl
protecting group was removed (85%) subsequently from the
allylic alcohols, anticipating a steric crowding of the terminal
olefin. This procedure significantly improved the yield of
isolated galactoside 6r to 40% over three steps from the
ethylenic intermediate 3, while the anomer 6β was present in
only 20% yield. Olefin metathesis, in the presence of Grubbs
II catalyst,17 on the free allylic alcohol 6r was then efficiently
performed with tetradecene in refluxing dichloromethane to
give 7 in 77% yields. The synthesis was then completed by
removal of the N-Boc protecting group, acylation of the
resulting hydrochloride amine, with 4-nitrophenyl hexaco-
sanoate, in the presence of Et3N and catalytic DMAP (44%
yield over two steps), prior hydrogenation of the intermedi-
ate 8, to furnish the targeted 4-deoxy-KRN7000 analogue 2
in 67% yield.
Chemistry. To reinvestigate the ambiguous influence of
the 4-OH group in CD1d recognition inducing human iNKT
cell stimulation, we first focused our efforts on developing an
original and efficient access toward a variety of 20,4-dideoxy-
R-GalCer derivatives A (Scheme 1).12,13 Until now, all the
strategies developed to synthesize deoxy R-GalCers analo-
gues suffered from the constraint of building the variable
sphinganine fragments from a specific chiral pool at an early
step of the synthesis for each proposed variation.14 We deal
with the possibility of introducing both the sphingosine and
acyl chains of the glycosylceramide in the last few steps of the
synthesis. Thus, as a key step of our retrosynthetic approach
(Scheme 1), the sphingosine fragment would be completed
using an olefin cross metathesis process from a same pre-
cursor C to provide a variety of R-galactosylsphingosines B.
This original procedure widens the access to a large range of
4-deoxy-R-GalCer analogues A, from a galactosyl donor E
and the ethylenic aminodiol D.
The required acceptor D (P=TBDPS, compound 3) was
prepared through diasterereoselective aldol reaction with
slight modifications of the procedure described in the litera-
ture15 from commercially available glycinethylester hydro-
chloride and (þ)-(1R,2R,5R)-2-hydroxy-3-pinanone in 36%
yield over six steps.13 The targeted 4-deoxy-Galcer analogue
Results and Discussion
First, we assessed NKT cell cytokine responses after
4-deoxy-R-GalCer 2 stimulation in vivo in order to determine
precisely the ability of this compound to induce the release
of key immunomediators TNF-R, IFN-γ, and IL-4 in mice
(A, B, and C of Figure 1, respectively, of Supporting In-
formation). The kinetics of cytokine release were followed at
various antigen concentrations (10, 50, 100, and 1000 μg/kg)
at further times after ip injection. TNF-R and IL-4 were
detected at their highest level 4 h after ip injection for each
concentration, whereas IFN-γ secretion peaked at 18 h after
Chart 1. Structure of KRN7000 and Targeted 4-Deoxy-R-Gal-
Cer Analogue 2
Scheme 1. Retrosynthetic Approach to 4-Deoxy KRN7000 Analogues
Scheme 2. Synthesis of 4-Deoxy KRN7000 Analogue 2 from 3a
a Conditions: (a) AgClO4, SnCl2, THF/Et2O, 0 °C, 30 min (5r 30% and 5β 18%); (b) TBAF, THF, RT, 24h, 85% from pure 5r (c) one-pot procedure:
(a), then Boc2O, Et3N, DMF, RT, 12h then (b) (6r 40% and 6β 20%, from 3); (d) Grubbs second generation catalyst 5%, C12H25-CHdCH2, CH2Cl2,
reflux, 24h, 77%; (e) HClg, THF, RT, 1h; (f) para-nitrophenyl hexacosanoate, Et3N, cat. DMAP, 44% (over 2 steps); (g) H2, Pd/C 10%, THF/MeOH,
RT, 72h, 67%.

4962 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 15
Laco^ne et al.
Figure 1. Relative potencies of KRN7000 and 4-deoxy-KRN 2 to stimulate TNF-R (A), IFN-γ (B), and IL-4 (C) releases by a human VR24
iNKT cell line stimulated for 6 h, by CD1d-transfected Hela cells loaded with increasing concentrations of KRN7000 (-9-) or 2 (-O-).
Results are shown as means of triplicates from one representative experiment out of three. The mean half-maximal effective concentrations for
eliciting a TNF-R response (EC50) of tested compounds are given in nM ( SD (Mann-Whitney two-tailed test p=0.12). (A). Cytokine release
in cell culture supernatants was determined by a cellular assay (TNF-R) or ELISA (IFN-γ, IL-4).
injection. The kinetic profiles appeared identical to those of
KRN7000 (100 μg/kg), and there were no significant differ-
ences between the various 2 concentration groups, with the
exception of the IFN-γ amount (Figure 1B of Supporting
Information), whichwas higher at 1000μg/kgthan at10μg/kg
of 2 (P < 0.05). Thus, we confirmed that the in vivo activity of
4-deoxy-R-GalCer 2 did not differ from that of KRN7000 and
correlated with previous results of Kronenberg,9 showing that
in mice both antigens had the same activity in terms of the
IFN-γ and IL-2 production at two time points (2 and 14 h).
We further assessed cytokine responses after in vitro sti-
mulation by compound 2 of human iNKT cells. When loaded
on control cells devoid of CD1d, 2 failed to stimulate the
iNKT cell line at concentrations as high as 20 μM because
TNF-R, IFN-γ, or IL-4 productions always remained at
background levels (Figure 2 of Supporting Information). By
contrast, when loaded on CD1d expressing Hela cells, analo-
gue 2 proved as active as KRN7000 in stimulating TNF-R
release because the mean half-maximal effective concentra-
tions (EC50) to elicit a response of each glycolipid were not
significantly different (2.7 ( 0.57 nM vs 5.0 ( 1.1 nM)
(Figure 1). Compound 2 also stimulated a clear production
of IFN-γ and IL-4 cytokines from human CD1d-transfected
Hela cells, and at each of the concentrations tested, KRN7000
induced only slightly higher responses but not significantly
different (p>0.05). Noticeably, 2 proved more difficult to
solubilize than KRN7000 and optimal results were obtained
following prolonged solubilization times, a couple of hours in
DMSO at 37 °C, prior to overnight loading onto presenting
cells.
Experimental Section
Chemical shifts are quoted in ppm, and values of coupling
constants (J) are given in Hz. The compound tested (2) is >95%
pure by elemental analysis.
Preparation of 7. Compound 6r (327 mg, 0.44 mmol), in dry
CH2Cl2 (22 mL), was reacted under reflux for 24 h with
tetradecene (1.11 mL, 4.41 mmol) and Grubbs II catalyst
(18 mg, 0.02 mmol). Purification by flash chromatography on
silica gel (petroleum ether/EtOAc 85:15) afforded 7 as a color-
less oil (309 mg, 77%); [R]25 þ31.4 (c 0.7, CHCl3). H NMR
1
D
(300 MHz, CDCl3) δ 7.37-7.28 (m, 20H), 5.66 (dt, J=15.4, 6.8,
1H), 5.45 (m, 2H, H4), 4.96 and 4.58 (AB syst, J=11.4, 2H), 4.87
and 4.73 (AB syst, J=11.8, 2H), 4.83-4.75 (m, 3H), 4.50 and
4.41 (AB syst, J=11.8, 2H), 4.20 (m, 1H, H3), 4.07 (dd, J=10.0,
3.6, 1H), 4.03 (m, 1H), 3.95-3.86 (m, 3H), 3.70 (m, 2H), 3.60-
3.49 (m, 3H, 2.01 (m, 2H), 1.48 (s, 9H), 1.29 (s, 20H), 0.91 (t, J=
6.7, 3H). 13C NMR (75 MHz, CDCl3) δ 155.7, 138.6-137.8,
132.8, 129.5, 128.4-127.5, 98.9, 79.5, 79.3, 75.7, 74.8, 74.5, 74.2,
74.0, 73.6, 72.8, 69.7, 69.3, 68.6, 53.6, 32.4, 31.9, 29.7-29.1, 28.4,
22.7, 14.2. HRMS (ESIþ): calcd for C56H77NNaO9 [M þ Na]þ
930.5496; found 930.5466.
Preparation of 8. Compound 7 (130 mg, 0.14 mmol) was
dissolved in dry THF (15 mL), and HCl gas was bubbled until
total consumption of starting material. THF was evaporated to
remove excess of HCl, and the crude was dissolved in THF
(6 mL) in the presence of 4-nitrophenyl hexacosanoate (74 mg,
0.14 mmol), triethylamine (24 μL, 0.17 mmol), and a catalytic
amount of DMAP. After 16 h, the reaction mixture was diluted
with saturated aqueous NaHCO3 solution (10 mL). The aqu-
eous layer was extracted with Et2O (2 ꢀ15 mL). The organic
layers were combined, dried over MgSO4, and concentrated.
Flash chromatography on silica gel (petroleum ether/EtOAc
86:14) afforded 8 as white solid (75 mg, 44% over 2 steps);
[R]25D þ27.5 (c 1.2, CHCl3); mp 80-81 °C. 1H NMR (300 MHz,
CDCl3) δ 7.37-7.24 (m, 20H), 6.45 (d, J=8.1, 1H), 5.65 (dt, J=
15.6, 6.9, 1H), 5.41 (dd, J=15.6, 5.4, 1H), 4.91 and 4.55 (AB syst,
J=11.4, 2H), 4.87 and 4.70 (AB syst, J=11.7, 2H), 4.75 (m, 3H),
4.47 and 4.37 (AB syst, J=11.4, 2H), 4.14 (m, 1H), 4.03 (dd, J=
10.2, 3.6, 1H), 4.01 (m, 2H), 3.89-3.82 (m, 4H), 3.69 (dd, J=
10.2, 3.3, 1H), 3.50 (m, 2H), 2.12 (t, J=7.5, 2H), 1.98 (m, 2H),
1.60-1.10 (m, 66H), 0.88 (t, J=6.3, 6H). 13C NMR (75 MHz,
CDCl3) δ 173.4, 138.4 -137.6, 133.0, 129.1, 128.4-127.5, 99.1,
79.2, 75.8, 74.8, 74.4, 74.2, 74.0, 73.6, 72.7, 69.8, 69.1, 68.7,
52.8, 36.7, 32.4, 32.0, 29.7, 29.4, 25.8, 22.4, 14.2. HRMS
(ESIþ): calcd for C77H119NNaO8 [MþNa]þ 1208.8833; found
1208.8866.
Conclusions
In conclusion, in vitro data indicated that a 4-deoxy
analogue can be nearly as active as KRN7000 to stimulate
hiNKT cells. The removal of an hydroxyl group may have
decreased the solubility of the 4-deoxy-R-GalCer analogues,
explaining why earlier reports suggested that such compounds
had more severely decreased potency. This data paves the
route to a novel potent series of immunostimulating agents
easier to prepare than KRN7000. Several 4-deoxy analogues
of KRN7000 bearing modified sphingosine moieties have
been prepared following the exposed strategy, and details of
their synthesis and their biological evaluation will be reported
elsewhere.
Preparation of 2. Compound 8 (64 mg, 54 μmol) was dissolved
in MeOH (5 mL) and THF (2.5 mL) in the presence of palladium

Brief Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 15 4963
on activated carbon (64 mg). The mixture was stirred under H2
for 3 days, and the mixture was filtered through celite washed
with hot MeOH and CHCl3. The filtrate was concentrated, and
the residue was purified on silica gel (CHCl3/MeOH 100:0 to
95:5) to provide 2 as a white solid (30 mg, 67%); [R]25D þ32.7 (c
1.0, pyridine); mp 170-171 °C. 1H NMR (300 MHz, pyridine) δ
8.56 (d, J=8.7, 1H), 5.46 (d, J=3.9, 1H), 5.10 (m, 5H), 4.74 (m,
1H), 4.65 (dd, J=9.9, 3.9, 1H), 4.57-4.29 (m, 8H), 2.48 (t, J=
7.2, 2H), 1.95 -1.82 (m, 6H), 1.26 (s, 66H), 0.87 (t, J=6.3, 6H).
13C NMR (75 MHz, pyridine) δ 173.4, 102.1, 73.1, 71.9, 71.6,
71.0, 70.5, 69.6, 62.7, 54.9, 36.8, 35.1, 32.1, 30.0, 29.6, 26.6,
26.4, 22.9, 14.3. HRMS (ESIþ): calcd for C49H97NNaO8 [Mþ
Teneberg, S.; Wang, D. C.; Proia, R. L.; Levery, S. B.; Savage, P. B.;
Teyton, L.; Bendelac, A. Lysosomal glycosphingolipid recognition by
NKT cells. Science 2004, 306, 1786–1789.
(6) Morita, M.; Motoki, K.; Akimoto, K.; Natori, T.; Sakai, T.; Sawa,
E.; Yamaji, K.; Koezuka, Y.; Kobayashi, E.; Fukushima, H.
Structure-activity relationship of R-galatosylceramides against
B16-bearing mice. J. Med. Chem. 1995, 38, 2176–2187.
(7) (a) Savage, P. B.; Teyton, L.; Bendelac, A. Glycolipids for natural
killer T cells. Chem. Soc. Rev. 2006, 35, 771–779. (b) Wu, D.; Fujio,
M.; Wong, C.-H. Glycolipids as immunostimulating agents. Bioorg.
Med. Chem. 2008, 16, 1073–1083.
(8) Brossay, L.; Naidenko, O.; Burdin, N.; Matsuda, J.; Sakia, T.;
Kronenberg, M. Cutting edge: structural requirements for galac-
tosylceramide recognition by CD1-restricted NK T cells. J. Im-
munol. 1998, 161, 5124–5128.
(9) Sidobre, S.; Hammond, K. J. L.; Benazet-Sidobre, L.; Maltsev, S.
D.; Richardson, S. K.; Ndonye, R. M.; Howell, A. R.; Sakai, T.;
Besra, G. S.; Porcelli, S. A.; Kronenberg, M. The T cell antigen
receptor expressed by V alpha 14i NKT cells has a unique mode of
glycosphingolipid antigen recogniton. Proc. Natl. Acad. Sci. U.S.
A. 2004, 101, 12254–12259.
Na]þ 850.7112; found 850.7154. Anal. (C49H97NO8 H2O)
3
Calcd: C, 69.54; H, 11.79; N, 1.66. Found: C, 69.45; H, 11.86;
N, 1.74.
Acknowledgment. This work was supported by the
^
ꢀ
“Canceropole Grand-Ouest”, a grant from the “Region des
Pays de la Loire-Molecular and therapeutic targets-CIM-
ATH program”, the CNRS, INSERM, and ARC.
(10) Borg, N. A.; Wun, K. S.; Kjer-Nielsen, L.; Wilce, M. C. J.; Pellici,
D. G.; Koh, R.; Besra, G. S.; Bharadwaj, M.; Godfrey, D. I.;
McCluskey, J.; Rossjohn, J. CD1d-lipid-antigen recognition by the
semi-invariant NKT T-cell receptor. Nature 2007, 448, 44–49.
(11) Godfrey, D. I.; McCluskey, J.; Rossjohn, J. CD1d antigen pre-
sentation: treats for NKT cells. Nat. Immunol. 2005, 6, 754–756.
(12) Ndonye, R. M.; Izmirian, D. P.; Dunn, M. F.; Yu, K. O. A.;
Porcelli, S. A.; Khurana, A.; Kronenberg, M.; Richardson, S. K.;
Howell, A. R. Synthesis and evaluation of sphinganine analogues
of KRN7000 and OCH. J. Org. Chem. 2005, 70, 10260–10270.
Supporting Information Available: Experimental procedure
6r, biological methods; in vivo secretion of TNF-R, IFN-γ, and
IL-4 in mice after ip injection of KRN7000 and 2 at different
concentrations; negative control with untransfected Hela cells;
complete refs for 2, 3, 5, 9, 10, 12, 14. This material is available
free of charge via the Internet at http://pubs.acs.org.
^
(13) Dubreuil, D.; Pipelier, M.; Micouin, L.; Lacone, V.; Bonneville,
M.; Le Pendu, J. R-Galactoceramide analogs, their methods of
manufacture, intermediate compounds useful in these methods and
pharmaceutical compositions containing them. Patent PCT/
IB2007/004270, 2007; PCT/IB2006/0039292006.
References
(1) (a) Bendelac, A.; Savage, P. B.; Teyton, L. The biology of NKT
cells. Annu. Rev. Immunol. 2007, 25, 297–336.
(14) See Supporting Information for references on the synthesis of
(2) Yu, K. O. A.; Porcelli, S. A. The diverse functions of CD1d-
restricted NKT cells and their potential for immunotherapy. Im-
munol. Lett. 2005, 100, 42–55.
(3) Moody, D. B. How a T cell sees sugar. Nature 2007, 448, 36–37.
(4) Natori, T.; Morita, M.; Akimoto, K.; Koezuka, Y. Agelasphins,
novel antitumor and immunostimulatory cerebrosides from the
marine sponge Agelas Mauritianus. Tetrahedron 1994, 50, 2771–
2784.
sphinganine fragments from chiral pool.
(15) (a) Vo-hoang, Y.; Micouin, L.; Ronet, C.; Gachelin, G.; Bonin, M.
Total enantioselective synthesis and in vivo biological evaluation of
a novel fluorescent BODIPY R-galactosylceramide. ChemBio-
Chem 2003, 4, 27–33. (b) Cai, Y.; Ling, C.-C.; Bundle, D. R. A general,
efficient and stereospecific route to sphingosine, sphinganines, phyto-
sphingosines and their analogs. Org. Biomol. Chem. 2006, 4, 1140–
1146.
(5) (a) Mattner, J.; DeBord, K. L.; Ismail, N.; Goff, R. D.; Cantu, C.
III; Zhou, D.; Saint-Mezard, P.; Wang, V.; Gao, Y.; Yin, N.;
Hoebe, K.; Schneewind, O.; Walker, D.; Beutler, B.; Teyton, L.;
Savage, P. B.; Bendelac, A. Exogenous and endogenous glycolipid
antigens activate NKT cells during microbial infections. Nature
2005, 434, 525–529. (b) Zhou, D. P.; Mattner, J.; Cantu, C.; Schrantz,
N.; Yin, N.; Gao, Y.; Sagiv, Y.; Hudspeth, K.; Wu, Y. P.; Yamashita, T.;
(16) Mukaiyama, T.; Murai, Y.; Shoda, S. An efficient method for
glucosylation oh hydroxy compounds using glucopyranosyl fluor-
ide. Chem. Lett. 1981, 431–432.
(17) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Synthesis and
activity of a new generation of ruthenium-based olefin metathesis
catalysts coordinated with 1,3-dimesityl-4,5-dihydroimidazol-2-
ylidene ligands. Org. Lett. 1999, 1, 953–956.