Synthesis of β-D-galactosyl ceramide methylene isostere

Article abstract of DOI:10.1021/jo990398l

The methylene isostere of the glycosphingolipid β-D-galactosyl N- palmitoyl C₁₈ ceramide has been synthesized by a linear reaction sequence starting from a β-linked D-galactopyranosyl aldehyde. First, this sugar aldehyde was converted into a me

Full text of DOI:10.1021/jo990398l

J . Org. Chem. 1999, 64, 5557-5564
5557
Syn th esis of â-D-Ga la ctosyl Cer a m id e Meth ylen e Isoster e
Alessandro Dondoni,* Daniela Perrone, and Elisa Turturici
Dipartimento di Chimica, Laboratorio di Chimica Organica, Universita` di Ferrara, Via Borsari 46,
44100 Ferrara, Italy
Received March 4, 1999
The methylene isostere of the glycosphingolipid â-D-galactosyl N-palmitoyl C18 ceramide has been
synthesized by a linear reaction sequence starting from a â-linked D-galactopyranosyl aldehyde.
First, this sugar aldehyde was converted into a methylenephosphorane which in turn was coupled
with N-Boc serinal acetonide. The double bond of the resulting olefin was reduced and the oxazolidine
ring was cleaved and oxidized to give a C-glycosyl N-Boc R-amino butanal (three-carbon chain
elongation). Then, an additional C15 carbon chain was installed by addition of lithium 1-pentadecyne
to the above glycosyl amino aldehyde. The syn/anti ratio (70:30) of the resulting mixture of amino
alcohols was reversed (5:95) by an oxidation-reduction sequence to achieve the same stereochem-
istry as in the hydrophilic head of D-erythro-sphingosines. The major product was subjected to the
reduction of the triple bond with LiAlH4 to give the olefin with E geometry. Finally the N-amide
group was installed by reaction with palmitoyl chloride and the O-benzyl protective groups of the
sugar moiety were removed by treatment with lithium in liquid NH3-THF. The final product was
characterized as the O-acetyl derivative.
The simplest modification that can be made in natural
oligosaccharides and glycoconjugates to obtain chemically
and enzymatically resistant analogues is the replacement
of the oxygen atom of the glycosidic linkage with a
methylene group.1,2 These isosteres are precious tools for
the studies at molecular level of the role that carbohy-
drates play in numerous biological processes3 and for the
explorative work in drug discovery.4 Quite surprisingly
this concept has been much less applied to glycosphin-
golipids (GSLs). Natural glycosphingolipids constitute a
large family of O-glycoconjugates most of which can be
represented by the general formula shown in Figure 1.
These molecules contain two basic structural motifs: a
ceramide, i.e., a sphingoid base (sphingosine or sphin-
ganine) N-acylated with a fatty acid chain (stearoyl or
F igu r e 1.
palmitoyl), and an oligosaccharide, among which D-
glucose, D-galactose, D-lactose, and sialic acid are the
glycosphingolipids as cell membrane main constituents
has been recognized in “essentially all aspects of cell
regulations”6 including cell growth and differentiation,
cell-cell recognition, and adhesion.5a,7 Glycosphingolipids
are also known to be involved in various lipid storage
diseases.8 To further explore the functions of these
compounds as well as find new therapeutic approaches
and because of the difficulty of isolation from natural
sources in homogeneous form, various glycosphingolipids
have been prepared in recent years.9 Also, the synthesis
most common components. The structural variation in
all these portions gives rise to a great variety of chemi-
cally distinct glycosphingolipids.5 The biological role of
(1) For C-disaccharides, see: (a) Wang, Y.; Goekjian, P. G.; Ryck-
man, D. M.; Miller, W. H.; Babirad, S. A.; Kishi, Y. J . Org. Chem. 1992,
57, 482-489. (b) Dietrich, H.; Schmidt, R. R. Liebigs Ann. Chem. 1994,
975-981. (c) Mallet, A.; Mallet, J . M.; Sinay¨, P. Tetrahedron: Asym-
metry 1994, 5, 2593-2608. (d) Skrydstrup, T.; Maze´as, D.; Elmouchir,
M.; Doisneau, G.; Riche, C.; Chiaroni, A.; Beau, J . M. Chem. Eur. J .
1997, 3, 1342-1356. (e) Dondoni, A.; Zuurmond, H. M.; Boscarato A.
J . Org. Chem. 1997, 62, 8114-8124. For C-trisaccharides, see: (f)
Haneda, T.; Goekjian, P. G.; Kim, S. H.; Kishi, Y. J . Org. Chem. 1992,
57, 490-498. (g) Sutherlin, D. P.; Armstrong, R. W. J . Am. Chem. Soc.
1996, 118, 9802-9803. (h) Sutherlin, D. P.; Armstrong, R. W. J . Org.
Chem. 1997, 62, 5267-5283. For (1f6)-C-oligosaccharides, see: (i)
Dondoni, A.; Kleban, M.; Zuurmond, H.; Marra, A. Tetrahedron Lett.
1998, 39, 7991-7994.
(2) For C-glycosyl amino acids, see: Dondoni, A.; Marra, A.; Massi,
A. J . Org. Chem. 1999, 64, 933-944 and references therein.
(3) (a) Varki, A. Glycobiology 1993, 3, 97-130. (b) Lee, Y. C.; Lee,
R. T. Acc. Chem. Res. 1995, 28, 321-327. (c) Dwek, R. A. Chem. Rev.
1996, 96, 683-720.
(4) Mulligan, M. S.; Paulson, J . C.; De Frees, S.; Zheng, Z.-L.; Lowe,
J . B., Ward, P. A. Nature 1993, 364, 149-151.
(6) Merrill, A. H., J r.; Sweeley, C. C. In Biochemistry of Lipids,
Lipoproteins and Membranes; Vance, D. E., Vance, J . E., Eds.; Elsevier
Science B. V.: Amsterdam, The Netherlands, 1996; Chapter 12, pp
309-339.
(7) (a) Hakamori, S.-I. Biochem. Soc. Trans. 1993, 21, 583-595. (b)
Merrill, A. H., J r.; Hannun, Y. A.; Bell, R. M. In Advances in Lipid
Research, Vol. 25, Sphingolipids Part A: Functions and Breakdown
Products; Bell, R. M., Hannun, Y. A., Merrill, A. H., J r., Eds.; Academic
Press: San Diego, CA, 1993; pp 1-23. (c) Schwarz, A.; Rapaport, E.;
Hirschberg, K.; Futerman, A. H. J . Biol. Chem. 1995, 270, 10990-
10998.
(8) For instance, Tay-Sachs desease is a hereditary human desease
in which at least one step in sphingolipid degradation is deficient thus
leading to the accumulation of lipids in the lysosomes of the cells and
to their destruction. For a short account, see: Kolter, T. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 1955-1959.
(5) (a) Hakomori, S.-I. Sphingolipid Biochemistry. In Handbook of
Lipid Research; Kanfer, J . N., Hakomori, S., Eds.; Plenum: New York,
1983; Vol. 3, pp 1-150. (b) Li, Y.-T.; Li, S.-C. Adv. Carbohydr. Chem.
Biochem. 1882, 40, 235.
10.1021/jo990398l CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/07/1999

5558 J . Org. Chem., Vol. 64, No. 15, 1999
Dondoni et al.
of GSL analogues10 is a topic of current interest because
these compounds have proven to be potent enzyme
inhibitors. Nevertheless no syntheses of genuine meth-
ylene isosteres of glycosphingolipids have been reported
so far. The compound constituted by glucopyranose
R-linked to a long-chain saturated amino alcohol recently
described by Gurjar and Reddy11 should be considered a
nonisosteric analogue of a C-glucosylsphinganine since
the carbon tether holding the sugar and the saturated
aglycone moiety is lacking one carbon atom in respect to
the natural products. The C-lactosylceramide reported
by Schmidt and co-workers12 shows a carbon-carbon
bond between the two monosaccharide moieties while the
natural O-glycosidic linkage still holds the ceramide.
Hence, we report here on the total synthesis of the
methylene isostere (Gal-CH2-Cer, 2) of the natural
glycosphingolipid â-D-galactosyl N-palmitoyl C18 ceramide
(Gal-O-Cer, 1). Since 1 has recently been shown to be a
receptor for HIV binding in cells lacking the principal
CD4 cellular receptor,13 the methylene isostere 2 may act
as an inhibitor against HIV infection. A nonisosteric
analogue of 1 that proved to block efficiently the interac-
tion of recombinant HIV-1 gp 120 with 1 was considered
to be a potential inhibitor of the first step of the infection
process.14
primary hydroxy group of sphingosine into a functional
group capable of a fair degree of reactivity toward a sugar
derivative to give either an R- or â-C-glycosidic linkage.
These manipulations may especially affect the quite
sensitive allylic alcohol function of sphingosine17 to
produce partially epimerized mixtures. Therefore, suit-
able protection of the amino and the secondary hydroxy
group of sphingosine is crucial. A second point of concern
is the stereocontrol at the anomeric center of the sugar,
a nontrivial problem in C-glycoside synthesis.18 Guided
by the bond disconnection shown in Figure 1, we planned
a synthetic approach to 2 through two sequential carbon-
chain elongation reactions starting from a C1-function-
alized galactose derivative. To this aim we considered the
O-tetrabenzyl formyl C-galactoside 3 readily available
from the corresponding galactolactone by the thiazole-
based formylation methodology developed in our labora-
tory.19,20 We envisaged an initial assembly via Wittig
olefination of 3 with a methylenephosphorane bearing a
group that was susceptible of conversion into a glycinal
moiety (Scheme 1). The configurational stability of 3
under the Wittig coupling conditions14,21 secured the
â-linked stereochemistry at the anomeric carbon of the
galactoside moiety. The coupling of 3 with the oxazoli-
dinone methylenephosphorane derived from 4, a â-alanyl
anion equivalent described by Sibi and Renhowe,22 af-
forded in our hands the alkene 5 as a mixture of E and
Z isomers in lower yield (20%) than that reported by
others (34%).14 A similar reaction carried out with the
ylide derived from the oxazoline bearing phosphonium
salt23 6, afforded the corresponding alkene 7 in a more
satisfactory chemical yield (50%). The complexity of the
NMR spectrum of this product suggested the presence
of a mixture of compounds, presumably olefins with E
and Z geometry and epimers with opposite configuration
at the stereocenter of the heterocyclic ring. Accordingly,
subsequent reduction of the olefin carbon-carbon double
bond with diimide,24 opening of the oxazoline ring by HCl
promoted hydrolysis, and acetylation of the resulting
alcohol with Ac2O-pyridine-DMAP gave the ester 8
which proved to be a mixture of R and S epimers in 1:1
ratio by NMR analysis.
Resu lts a n d Discu ssion
Natural O-glycosylceramides as well as glycosphin-
golipids in general are currently prepared by O-glycosyl-
ation of either suitably protected sphingosine or ceramide
derivatives.9 This convergent approach takes advantage
of the availability of sphingosines with many structural
variations15 and the numerous and well-established
methods of O-glycoside synthesis.16 The same approach
may not be equally practical for C-glycosylceramide
synthesis. This would require the transformation of the
(9) Synthetic methods for glycosphingolipids have been reviewed:
(a) Gigg, J .; Gigg, R. Topics in Current Chemistry; Springer-Verlag:
Berlin, Heidelberg, 1990; Vol. 154, pp 77-139. (b) Hasegawa, A.; Kiso,
M. In Preparative Carbohydrate Chemistry; Hanessian S., Ed.; M.
Dekker: New York, 1997; pp 357-379. For selected recent papers, see:
(c) Nicolaou, K. C.; Caulfield, T. J .; Kataoka, H.; Stylianides, N. A. J .
Am. Chem. Soc. 1990, 112, 3693-3695. (d) Peterson, M. A.; Polt, R. J .
Org. Chem. 1993, 58, 4309-4314. (e) Gervay, J .; Peterson, J . M.;
Oriyama, T.; Danishefsky, S. J . J . Org. Chem. 1993, 58, 5465-5468.
(f) Bilodeau, M. T.; Park, T. K.; Hu, S.; Randolph, J . T.; Danishefsky,
S. J .; Livingston, P. O.; Zhang, S. J . Am. Chem. Soc. 1995, 117, 7840-
7841. (g) Liu, K. K.-C.; Danishefsky, S. J . Chem. Eur. J . 1996, 2, 1359-
1362. (h) Castro-Palomino, J . C.; Ritter, G.; Fortunato, S. R.; Reinhardt,
S.; Old, L. J .; Schmidt, R. R. Angew. Chem., Int. Ed. Engl. 1997, 36,
1998-2001. (i) Wilstermann, M.; Magnusson, G. J . Org. Chem. 1997,
62, 7961-7971. (j) Kamitakahara, H.; Suzuki, T.; Nishigori, N.; Suzuki,
Y.; Kanie, O.; Wong, C.-H. Angew. Chem., Int. Ed. Engl. 1998, 37,
1524-1528. (k) Takikawa, H.; Muto, S.; Mori, K. Tetrahedron 1998,
54, 3141-3150.
(10) (a) Hasegawa, A.; Morita, M.; Kojima, Y.; Ishida, H.; Kiso, M.
Carbohydr. Res. 1991, 214, 43-53. (b) Abe, A.; Inokuchi, J .-i; J imbo,
M.; Shimeno, H.; Nagamatsu, A.; Shayman, J . A.; Shukla, G. S.; Radin
N. S. J . Biochem. 1992, 111, 191-196. (c) Ogawa, S.; Tsunoda, H.;
Inokuchi, J .-i J . Chem. Soc., Chem. Commun. 1994, 1317-1318. (d)
Carson, K. G.; Ganem, B.; Radin, N. S.; Abe, A.; Shayman, J . A.
Tetrahedron Lett. 1994, 35, 2659-2662. (e) J efford, C. W.; McNulty,
J .; Lu, Z.-H. J . Chem. Soc., Chem. Commun. 1995, 123-124. (f)
Tsunoda, H.; Ogawa, S. Liebigs Ann. 1995, 267-277. (g) Mitchell, S.
A.; Oates, B. D.; Razavi, H.; Polt, R. J . Org. Chem. 1998, 63, 8837-
8842.
(15) For recent syntheses of sphingosines and excellent reviews of
the earlier literature, see: (a) Dondoni, A.; Perrone, D.; Turturici, E.
J . Chem. Soc., Perkin Trans. 1997, 2389-2393. (b) Nugent, T. C.;
Hudlicky, T. J . Org. Chem. 1998, 63, 510-520. (c) Hoffman, R. V.; Tao,
J . J . Org. Chem. 1998, 63, 3979-3985. (d) Kumar, P.; Schmidt, R. R.
Synthesis 1998, 33-35. (d) Andre´s, J . M.; Pedrosa, R. Tetrahedron:
Asymmetry 1998, 9, 2493-2498. (e) Hertweck, C.; Goerls, H.; Boland,
W. J . Chem. Soc., Chem. Commun. 1998, 1955-1956.
(16) Veeneman, G. H. In Carbohydrate Chemistry; Boons, G.-J ., Ed.;
ITP: London, 1998; Chapter 4, pp 98-167.
(17) Kisic, A.; Tsuda, M.; Kulmacz, R. J .; Wilson, W. K.; Schroepfer,
G. J ., J r. J . Lipid Res. 1995, 36, 787-803.
(18) (a) Postema, M. H. D. C-Glycoside Synthesis; CRC Press: Boca
Raton, FL, 1995. (b) Levy, E. D.; Tang. C. In Tetrahedron Organic
Chemistry Series, Vol. 13, The Chemistry of C-Glycosides; Baldwin, J .
E., Magnus, P. D., Eds.; Elsevier Science Ltd.: Oxford, U.K., 1995. (c)
Bertozzi, C.; Bednarski, M. In Modern Methods in Carbohydrate
Synthesis; Khan, S. H., O’Neill, R. A., Eds.; Harwood Academic
Publishers: Amsterdam, The Netherlands, 1996; Chapter 14, pp 316-
351.
(19) Dondoni, A.; Scherrmann, M.-C. J . Org. Chem. 1994, 59, 6404-
6412.
(11) Gurjar, M. K.; Reddy, R. Carbohydr. Lett. 1997, 2, 293-298.
(12) Dietrich, H.; Regele-Mayer, C.; Schmidt, R. R. Carbohydr. Lett.
1994, 1, 115-122.
(13) Harouse, J . M.; Bhat, S.; Spitalnik, S.; Laughlin, M.; Stefano,
K.; Silberberg, F.; Gonzalez-Scarano, F. Science 1991, 253, 320-323.
(14) Bertozzi, C. R.; Cook, D. G.; Kobertz, W. R.; Gonzalez-Scarano,
F.; Bednarski, M. D. J . Am. Chem. Soc. 1992, 114, 10639-10641.
(20) For an overview on the thiazole-based synthesis of aldehydes,
see: Dondoni, A. Synthesis 1998, 1681-1706.
(21) Dondoni, A.; Zuurmond, H. M.; Boscarato, A. J . Org. Chem.
1997, 62, 8114-8124.
(22) Sibi, M. P.; Renhowe, P. A. Tetrahedron Lett. 1990, 31, 7407-
7410.

â-D-Galactosyl Ceramide Methylene Isostere
J . ORG. CHEM., VOL. 64, NO. 15, 1999 5559
Sch em e 1a
Sch em e 2a
a
Reagents and conditions: (a) AcOH, H2O. (b) (COCl)2, DMSO,
i-Pr2EtN, CH2Cl2, -78 °C.
bond of the resulting mixture of E and Z olefins as
described,25 afforded the alkyloxazolidine 14 in ca. 50%
yield. The removal of the acetonide protective group
under standard conditions (AcOH-H2O, 4:1) transformed
14 into the N-Boc amino alcohol 15 which in turn was
converted into the aldehyde 16 by Swern oxidation.27
While the Wittig coupling between 12 and 13 worked well
on a small scale (1 mmol) as reported,25 the same reaction
carried out with 5 mmol or more of reagents (1.5 g of 13)
followed by deacetonization, afforded the S amino alcohol
1
15 containing 10-15% of the R isomer as shown by H
NMR analysis.28 The isolation of pure 15 was carried out
by conversion of the mixture of amino alcohol epimers
into p-nitrobenzoyl esters and separation by medium-
pressure column chromatography. The alcohol 15 was
liberated from the ester in almost quantitative yield by
basic treatment and then oxidized to the aldehyde 16.
The stereochemical purity of 16 was confirmed by reduc-
tion (NaBH4, 0 °C, 90%yield) to the alcohol 15 and
analysis of the NMR spectrum of the latter.
Having developed a gram-scale synthesis of the R-ami-
no aldehyde 16, we turned out to the next step of the
synthetic plan that involved the attachment of the
lipophilic unsaturated carbon-chain corresponding to the
sphingosine moiety. For this purpose we initially con-
sidered adding of a lithium alkylacetilide to 16 and
reducing the triple to a double bond as described in
various sphingosine syntheses.29 We were aware that
because of the single protection of the amino group of
16, the addition of the organometal would very likely
proceed with syn selectivity30 to give the undesired amino
alcohol as major product. In the event, we were ready to
a
Reagents and conditions: (a) n-BuLi, THF, -78 °C. (b)
TsNHNH2, AcONa, DME, 85 °C. (c) HCl (2 M), THF. (d) Ac2O,
pyridine, DMAP.
Because of the above unsatisfactory results, we decided
to capitalize on a more efficient Wittig olefination that
was recently reported from our laboratory25 as the result
of a parallel research. This involved the ylide of the sugar
phosphonium iodide 12 (Scheme 2) and the quite common
protected D-serinal 13. The phosphonium salt 12 was
prepared25 from the formyl C-galactoside 3 (three steps,
66% yield) while the aldehyde 13 was obtained from
D-serine by a recently improved method.26 Thus, coupling
of these reagents and diimide reduction of the double
(23) The phosphonium iodide 6 was prepared from the 4-(car-
bomethoxy)-2-phenyloxazoline 9 through alcohol 10 and iodide 11 (see
the Experimental Section). In turn, compound 9 was prepared starting
from D-serine as described for its L-enantiomer (Tkaczuk, P.; Thornton,
E. R. J . Org. Chem. 1981, 46, 4393-4398).
(26) Dondoni, A.; Perrone, D. Synthesis 1997, 527-529. Dondoni,
A. Perrone, D. Org. Synth. 1999, 77, in press.
(27) Tidwell, T. T. Synthesis 1990, 857-870.
(28) The two epimers could not be revealed by 1H NMR analysis at
room temperature since the spectrum was very complex due to the
presence of geometrical isomers and rotamers. A less complex spectrum
was obtained at 120 °C due to the coalescence of signals.
(29) (a) Radunz, H.-E.; Devant, R. M.; Eiermann, V. Liebigs Ann.
Chem. 1988, 1103-1105. (b) Garner, P.; Park, J . M.; Malecki, E. J .
Org. Chem. 1988, 53, 4395-4398. (c) Herold, P. Helv. Chim. Acta 1988,
71, 354-362. (d) Nimkar, S.; Menaldino, D.; Merrill, A. H.; Liotta, D.
Tetrahedron Lett. 1988, 29, 3037-3040.
(24) Hart, D. J .; Hong, W.-P.; Hsu, L.-Y. J . Org. Chem. 1987, 52, 2,
4665-4673.
(25) Dondoni, A.; Marra, A.; Massi, A. Tetrahedron 1998, 54, 2827-
2832.

5560 J . Org. Chem., Vol. 64, No. 15, 1999
Dondoni et al.
Sch em e 3
Sch em e 4a
a
Reagents and conditions: (a) HCl/dioxane (4.8 M). (b) Im2CO,
THF.
Ta ble 1. Red u ction of th e Keton e 19 w ith Meta l
Hyd r id es to a n ti-18 a n d syn -18 Am in o Alcoh olsa
additive
hydride (equiv) (equiv)
temp. yield
18
solvent
°C
(%)b (anti:syn)c
NaBH4 (5)
THF/MeOH 4:1 -60
CeCl3 (1) EtOH -60
60
90
60
24
43
90
65
60:40
73:27
70:30
48:52
78:22
95:5
NaBH4 (5)
Red-Al (1)d
THF
THF
THF
THF
-78
-78
-78
-78
-78
LABOH (1)e
DIBAH (3)f
L-Selectride (2)g
apply an oxidation-reduction sequence for hydroxy group
inversion developed in our laboratory some years ago.31,32
This synthetic scheme had to be adopted because several
attempts to prepare an amino aldehyde of type 16 with
a double protected amino group that could undergo anti
selective organometal addition30 were unsuccessful. For
example, the acetylation of 15 with Ac2O-pyridine-
DMAP at 90 °C gave after 6 h the O-acetyl ester while
the NHBoc group remained unaltered.
L-Selectride (2)g ZnBr2 (1) THF
85:15
a
All reactions were carried out with 50 mg of ketone 19.
Isolated chemical yields of mixtures of a n ti-18 and syn -18.
b
c Diastereomeric ratios were determined by 1H NMR analysis of
d
the crude mixture. Sodium bis(2-methoxyethoxy)aluminum hy-
dride. e Lithium tri-tert-butoxyaluminum hydride. f Diisobutyl-
g
aluminum hydride. Litium tri-sec-butylborohydride.
With the alkyne a n ti-18 in hand, the stereoselective
hydrogenation of the triple bond and the replacement of
the NBoc with the N-palmitoyl group remained to be
carried out. Thus, removal of the tert-butoxycarbonyl
group with HCl in dioxane gave the amino alcohol 21 in
90% isolated yield (Scheme 5). Given the conditions
employed for the reduction of the triple bond in earlier
sphingosine syntheses involving alkyne intermediates,29a,b
we first considered the reduction of 21 with lithium in
liquid ammonia. It was expected that under these condi-
tions also deprotection of the benzyl ether groups of the
galactose moiety would take place. Hence the hydrogena-
tion of 21 was carried out with excess lithium in liquid
ammonia/THF at -45 °C for 2 h. After the evaporation
of ammonia, the crude residue was treated with palmitoyl
chloride in the presence of sodium acetate to complete
the construction of the ceramide moiety. Acetylation of
the crude reaction mixture with Ac2O in pyridine afforded
a mixture of products constituted by the peracetylated
galactosyl ceramide isostere 2a and an unseparable
byproduct in 45% overall yield from 21. We looked for
improved conditions in this final stage of the synthesis.
Mindful of the excellent results of Liotta and co-workers
in a classical sphingosine synthesis,29d the reduction of
the triple bond of 21 was carried out using lithium
aluminum hydride in refluxing dimethoxyethane (DME).
After 3 h we could consistently obtain a yield of 65% of
isolated O-tetrabenzyl galactopsychosine isostere 22.34
The elaboration of this compound allowed the isolation
of two differentially protected target products 2a and 2b.
The installation of the palmitoyl chain on the amino
group of 22 afforded the O-tetrabenzylgalactosyl ceram-
ide isostere 2b (80% yield) whose debenzylation and
Thus, the addition of excess lithium 1-pentadecyne 17
to the R-amino aldehyde 16 (Scheme 3) afforded the
alcohol 18 (65% yield) as a mixture of S (syn adduct) and
R isomer (anti adduct) in 70:30 ratio as judged by 1H
NMR analysis. The same ratio of isomers was obtained
on carrying the reaction in the presence of the complex-
destroying agent hexamethylphosphoramide (HMPA),33
while the overall yield dropped to a lower value (35%).
The stereochemistry of these isomers was assigned
following the conversion of crude 18 into a mixture of
oxazolidinones 20a and 20b (70:30 ratio) and comparison
of the H-3′ and H-4′ coupling constant values as well as
by NOE measurements (Scheme 4). Being the amino
alcohol 18 constituted by a mixture of diastereomers with
a predominance of the undesired syn product, we turned
to the hydroxy group inversion. For this purpose crude
18 was oxidized to the ketone 19 (90% yield) by the Swern
method, and the carbonyl of the resulting ynone was
subjected to reduction by various metal hydrides (Table
1). The optimal reagent was found to be lithium tri-sec-
butylborohydride (L-selectride) which afforded the de-
sired amino alcohol a n ti-18 with high diastereoselectivity
(dr g 95%) and high isolated chemical yield (90%). The
stereochemistry of this compound was unequivocally
assigned through its oxazolidinone derivative 20b.
(30) It has been amply documented that addition reactions of
organometals to chiral R-amino aldehydes lead to syn or anti amino
alcohols depending on whether the amino group is singly or doubly
protected, respectively. For reviews of our research in this area and
leading references to the work of other groups, see: ref 20. Dondoni,
A.; Perrone, D. Aldrichimica Acta 1997, 30, 35-46.
(31) Dondoni, A.; Fantin, G.; Fogagnolo, M.; Medici, A.; Pedrini, P.
J . Org. Chem. 1989, 54, 702-706.
(32) For a recent application of this method in rare sugar synthesis,
see: Dondoni, A.; Marra, A.; Massi, A. J . Org. Chem. 1997, 62, 6261-
6267.
(33) Mulzer, J .; Pietschmann, C.; Buschmann, J .; Luger, P. J . Org.
Chem. 1997, 62, 3938-3943.
(34) Interest for debenzylated galactosylpsychosine isostere may
arise from the potential inhibitory activity of rgp120-GalCer binding
as shown by the O-linked analogue. See ref 14.

â-D-Galactosyl Ceramide Methylene Isostere
J . ORG. CHEM., VOL. 64, NO. 15, 1999 5561
Sch em e 5a
a
Reagents and conditions: (a) HCl/dioxane (4.8 M). (b) Li/NH3, THF, -45 °C. (c) C15H31COCl, AcONa, THF. (d) Ac2O, pyridine. (e)
LiAlH4, DME, 85 °C.
anhydrous THF (14.0 mL) was added a solution of 937 (1.70 g,
exhaustive acetylation produced pure 2a in 55% isolated
8.28 mmol) in anhydrous THF (10.0 mL). The mixture was
stirred for 15 min, warmed to room temperature, and then
treated with an aqueous phosphate buffer (pH 7, 15.0 mL) and
filtered through Celite. The aqueous phase was extracted with
yield. Key structural features of 2a and 2b that were
substantiated by H NMR analysis were the â-anomeric
1
linkage (J 1,2 ) 9.0 Hz) and the olefin with E geometry (J
) 15.0 Hz). The absolute and relative configuration at
AcOEt, and the combined organic phases were dried and
the stereocenters bearing the amino and hydroxy groups
concentrated to give 10 (1.10 g, 80%) as a white solid: mp 100-
1
were sufficiently demonstrated in the precursors of these
compounds.
101 °C; [R]D -82 (c 0.7, CHCl3); H NMR δ 3.20 (s, 1 H, OH),
3.67 (dd, 1 H, J ) 3.6, 11.6 Hz), 3.99 (dd, 1 H, J ) 2.9, 11.6
Hz), 4.35 (dd, 1 H, J ) 5.4, 6.2 Hz), 4.38-4.48 (m, 1 H), 4.49
(dd, 1 H, J ) 5.4, 8.7 Hz), 7.30-7.50 (m, 3 H), 7.80-7.90 (m,
2 H); 13C NMR δ 63.4, 68.7, 68.1, 126.9, 128.1, 131.3, 165.5.
Anal. Calcd for C10H11NO2: C, 67.78; H, 6.25; N, 7.90. Found:
C, 67.59; H, 6.27; N, 7.87.
In conclusion, the first synthesis of a carbon-linked
isostere of natural galactosyl ceramide was accomplished
in 12 steps from the sugar phosphorane 12 in 4% overall
yield. The linear synthetic scheme constitutes a model
that should be amenable to the preparation of an array
of galactosyl ceramides by changing either the alkyne in
the condensation reaction with the aldehyde 16 or the
fatty acid chloride in the amide bond formation. Moreover
since other sugar phospshoranes are available in our
laboratory, a combinatorial approach to various glycosyl
ceramide isosteres may become of interest.
(R)-4-(Iod om eth yl)-2-p h en yl-2-oxa zolin e (11). A mixture
of alcohol 10 (1.00 g, 5.64 mmol), PPh3 (4.30 g, 16.4 mmol),
imidazole (1.50 g, 22.4 mmol), and iodine (3.57 g, 14.0 mmol)
in anhydrous toluene (200 mL) was heated to 80 °C for 30 min.
The resulting suspension was filtered, and the solution was
washed with 5% aqueous Na2S2O3 and with saturated aqueous
NaHCO3. The organic phase was dried, filtered, and concen-
trated. Chromatography on silica gel of the crude residue with
toluene/AcOEt (100:5) gave 11 (1.30 g, 80%) as a yellow
1
Exp er im en ta l Section
syrup: [R]D +50.3 (c 0.9, CHCl3); H NMR δ 3.24 (dd, 1 H, J
) 7.8, 10.1 Hz), 3.50 (dd, 1 H, J ) 3.9, 10.1 Hz), 4.18-4.26
(m, 1 H), 4.46-4.58 (m, 2 H), 7.28-7.55 (m, 3 H), 7.90-8.00
(m, 2 H); 13C NMR δ 10.8, 67.2, 73.2, 127.3, 128.4, 131.7, 133.8,
165.2. Anal. Calcd for C10H10NOI: C, 41.81; H, 3.51; N, 4.88.
Found: C, 41.73; H, 3.52; N, 4.84.
All moisture-sensitive reactions were performed under a
nitrogen atmosphere using oven-dried glassware. Solvents
were dried over standard drying agent35 and freshly distilled
prior to use. Flash column chromatography36 was performed
on silica gel 60 (230-400 mesh), under positive pressure from
a compressed air line. Medium-pressure chromatography was
performed on silica gel 60 (230-240 mesh). Reactions were
monitored by TLC on silica gel 60 F254 with detection by
charring with alcoholic solutions of ninhydrin or sulfuric acid.
After extractive workup, organic solutions were dried over Na2-
SO4, filtered through a cotton plug, and evaporated under
reduced pressure. Melting points were determined with a
capillary apparatus and are uncorrected. Optical rotations
were measured at 20 ( 2 °C. IR spectra were recorded using
a Perkin-Elmer 1310 spectrometer. 1H (300 MHz) and 13C (75
MHz) NMR spectra were recorded at room temperature in
CDCl3 solutions, unless otherwise specified. Assignments were
aided by homo- and heteronuclear two-dimensional experi-
ments. MALDI-TOF mass spectra were acquired using R-cy-
ano-4-hydroxycinnamic acid as the matrix.
(R )-4-(2-P h e n y l-2-o x a zo lin in y l)m e t h y lt r ip h e n y l-
p h osp h on iu m iod id e (6). A mixture of 11 (1.20 g, 4.18 mmol)
and PPh3 (4.39 g, 16.7 mmol) was heated to 120 °C for 1 h;
then, to the still hot reaction mixture was added toluene (10.0
mL). After the reaction was cooled to room temperature, Et2O
(10.0 mL) was added. The precipitate was filtered, washed with
Et2O, and dried under vacuum to give the phosphonium salt
6 (2.00 g, 90%) as a white solid: mp 104-105 °C; [R]D -18.8
1
(c 0.6, CHCl3); H NMR δ 3.25-4.42 (m, 1 H), 4.69-4.85 (m,
3 H), 5.10 (dt, 1 H, J ) 3.0, 15.0 Hz), 7.20-8.00 (m, 20 H); 13
C
NMR δ 31.2, 61.5, 73.8, 118.2, 119.4, 126.5, 128.2, 130.2, 131.9,
133.9, 134.8, 164.7. Anal. Calcd for C28H25NOPI: C, 61.21; H,
4.58; N, 2.54. Found: C, 61.39; H, 4.57; N, 2.54.
Met h yl-5,9-a n h yd r o-6,7,8,10-t et r a -O-b en zyl-2,3,4-t r i-
deoxy-1-O-acetyl-2-N-ben zoylam in o-D-th r eo-L-ga la cto-(an d
L-ta lo)-d econ a te (8). To a stirred, cold (-78 °C) mixture of
phosphonium salt 6 (0.60 g, 1.08 mmol), powdered 4-Å molec-
ular sieves (0.50 g) and anhydrous THF (10.0 mL) was added
n-BuLi (0.68 mL, 1.08 mmol of a 1.6 M solution in hexanes).
(S)-4-(Hyd r oxym eth yl)-2-p h en yl-2-oxa zolin e (10). To a
cold (-50 °C) suspension of LiAlH4 (0.35 g, 9.12 mmol) in
(35) Perrin, D. D.; Armarego, W. L. Purification of Laboratory
Chemicals; Pergamon: New York, 1988.
(36) Still, W. C.; Kahn, M.; Mitra, A. J . Org. Chem. 1978, 43, 2923.
(37) See the reference cited in note 23.

5562 J . Org. Chem., Vol. 64, No. 15, 1999
Dondoni et al.
After 15 min, the resulting red-colored suspension was treated
with a solution of the aldehyde 319 (0.2 g, 0.36 mmol) in
anhydrous THF (2.0 mL). The mixture was allowed to warm
to -20 °C in a period of 2 h and then treated with aqueous
phosphate buffer (pH 7) and filtered through Celite. The
organic phase was dried and concentrated. Chromatography
on silica gel of the crude residue with cyclohexane/AcOEt (3:
1) containing Et3N (1‰) gave the olefin 7 (0.13 g, 50%). To a
stirred and warmed (85 °C) solution of this mixture (0.12 g,
0.17 mmol) and p-toluensulfonhydrazide (0.06 g, 0.34 mmol)
in dimethoxyethane (2.0 mL) was added an aqueous solution
of AcONa (1 M, 0.5 mL) in four portions over 2 h. After an
additional 4 h at 85 °C, the reaction mixture was diluted with
H2O (2.0 mL) and extracted with Et2O. The organic phase was
concentrated, and the crude residue was dissolved in aqueous
HCl (2 M, 2.0 mL) and stirred for 16 h at room temperature.
The solution was extracted with Et2O, and the combined
organic phases were washed with H2O, dried, and concen-
trated. To a solution of the crude residue in pyridine (2.0 mL)
and Ac2O (2.0 mL) was added DMAP (cat.). The resulting
mixture was stirred at room temperature for 14 h and then
concentrated. Chromatography on silica gel of the crude
residue with cyclohexane/AcOEt (4:1) gave 8 (0.06 g, 50%) as
To a suspension of the p-nitrobenzoyl ester of 15 (2.69 g,
3.12 mmol) in anhydrous MeOH (50.0 mL) was added at room
temperature a solution of MeONa (5%, 0.72 g of Na, 31.2
mmol) in MeOH (14.4 mL). The solution was stirred for 15
min and then diluted with AcOH (2.40 mL) and concentrated.
Chromatography on silica gel of the crude residue with
cyclohexane/AcOEt (2:1) containing Et3N (1‰) gave the alcohol
15 (2.22 g, 90%) as a white solid: mp 92-93 °C; [R]D -11.8 (c
1.8, CHCl3); 1H NMR δ 1.42 (s, 9 H), 1.50-1.52 (m, 3 H), 1.72-
1.93 (m, 1 H, H-3b), 2.61-2.70 (s, 1 H, OH), 3.20 (ddd, 1 H,
J 4a,5 ) J 5,6 ) 8.0, J 4b,5 ) 2.7 Hz, H-5), 3.43-3.70 (m, 8 H), 3.88
(dd, 1 H, J 7,8 ) 2.6, J 8,9 ) 0.5 Hz, H-8), 4.41 and 4.47 (2d, 2 H,
J ) 12.0 Hz, PhCH2), 4.64 and 4.94 (2d, 2 H, J ) 11.3 Hz,
PhCH2), 4.65-4.70 (m, 1 H, NH), 4.68 and 4.76 (2d, 2 H, J )
12.0 Hz, PhCH2), 4.65 and 4.95 (2d, 2 H, J ) 11.3 Hz, PhCH2),
7.40 and 7.80 (m, 20 H); 13C NMR δ 27.0, 27.8, 28.3, 53.0, 60.4,
66.5, 69.1, 72.2, 73.4, 73.6, 74.4, 75.4, 77.2, 78.6, 79.3, 84.8,
127.6, 127.8, 127.9, 128.2, 128.4, 137.8, 138.2, 138.6, 156.7.
Anal. Calcd for C43H53O8N: C, 72.54; H, 7.50; N, 1.96. Found:
C, 72.79; H, 7.58; N, 2.20.
5,9-An h yd r o-6,7,8,10-t et r a -O-b en zyl-2,3,4-t r id eoxy-2-
(ter t-b u t oxyca r b on yla m in o)-D-th r eo-L-ga la cto-d ecit ose
(16). To a cold (-78 °C) solution of oxalyl chloride (0.16 g, 1.26
mmol) in anhydrous CH2Cl2 (3.0 mL) was added a solution of
DMSO (0.20 g, 2.52 mmol) in anhydrous CH2Cl2 (1.20 mL).
The mixture was stirred for 30 min at -78 °C; then, a solution
of alcohol 15 (0.60 g, 0.84 mmol) in anhydrous CH2Cl2 (1.80
mL) was added. The reaction was stirred for 1 h, and then
N,N-diisopropylethylamine (0.88 mL, 5.05 mmol) was added.
After warming the reaction to 0 °C over 10 min, the mixture
was treated with cold (0 °C) aqueous HCl (1 M, 3.0 mL). The
solution was extracted with CH2Cl2, and the combined organic
phases were washed with aqueous phosphate buffer (pH 7),
dried, and concentrated. Chromatography on silica gel of the
crude residue with cyclohexane/AcOEt (3:1) containing Et3N
(1‰) gave the aldehyde 16 (0.54 g, 90%) as a syrup: [R]D +7.3
(c 1.0, MeOH); 1H NMR (DMSO-d6, 120 °C) δ 1.40 (s, 9 H),
1
a mixture of 2S and 2R epimers in ca. 1:1 ratio (by H NMR
analysis): 1H NMR (selected data) δ 5.85 (d, 0.5 H, J ) 8.2
Hz, NH), 5.95 (d, 0.5 H, J ) 8.2 Hz, NH); MALDI-TOF MS
781.1 (M+ + Na), 797.1 (M+ + K).
5,9-An h yd r o-6,7,8,10-t et r a -O-b en zyl-2,3,4-t r id eoxy-2-
(ter t-bu toxycar bon ylam in o)-D-th r eo-L-ga la cto-decitol (15).
The reaction was carried out as described in ref 25 starting
from the phosphonium salt 12 (6.0 g, 6.50 mmol) and the
aldehyde 13 (1.50 g, 6.50 mmol) to give the oxazoline derivative
14 (2.80 g, 52%) as a syrup. A solution of this compound (5.0
g, 6.65 mmol) in AcOH/H2O (5:1, 42.0 mL) was stirred at room
temperature for 24 h and then concentrated. Chromatography
on silica gel of the crude residue with cyclohexane/AcOEt (2:
1) containing Et3N (1‰) afforded compound 15 (4.25 g, 90%)
contaminated by its 2R epimer (85:15 ratio by 1H NMR
analysis). Attempts to separate these epimers by flash chro-
matography failed. To a solutions of these epimers (4.25 g) in
anhydrous pyridine (45.0 mL) was added p-nitrobenzoyl
chloride (1.83 g, 9.88 mmol). The mixture was stirred for 14 h
at room temperature and then concentrated. Purification of
the crude residue by medium-pressure chromatography (6 atm)
with toluene/AcOEt (10:1) gave as the first eluate the p-
nitrobenzoyl ester of 15 (2.69 g, 76%) as a light yellow solid:
1.40-1.96 (m, 4 H), 3.25 (ddd, 1 H, J 4a,5 ) J 5,6 ) 9.0, J 4b,5
2.8 Hz, H-5), 3.50-3.66 (m, 4 H), 3.69 (dd, 1 H, J 6,7 ) 9.0, J 7,8
) 3.0 Hz, H-7), 3.78-3.87 (m, 1 H, H-2), 4.40 (dd, 1 H, J 8,9
)
)
0.5 Hz, H-8), 4.47 and 4.53 (2 d, 2 H, J ) 12.0 Hz, PhCH2),
4.56 and 4.84 (2 d, 2 H, J ) 11.9 Hz, PhCH2), 4.63 and 4.82 (2
d, 2 H, J ) 11.5 Hz, PhCH2), 4.66 and 4.78 (2 d, 2 H, J ) 11.9
Hz, PhCH2), 6.63 (d, 1 H, J ) 7.5 Hz, NH), 7.20-7.40 (m, 20
H), 9.45 (d, 1 H, J ) 0.7 Hz, H-1); 13C NMR δ 25.1, 28.3, 31.0,
59.5, 69.1, 72.2, 73.5, 73.6, 74.4, 75.4, 76.6, 76.9, 78.4, 79.1,
127.5, 127.6, 127.8, 127.9, 128.2, 128.4, 137.8, 138.2, 156.0,
200.5; MALDI-TOF MS 733.1 (M+ + Na), 749.1 (M+ + K).
Anal. Calcd for C43H51NO8: C, 72.75; H, 7.24; N, 1.97. Found:
C, 72.73; H, 7.22; N, 2.10.
1
mp 80-81 °C; [R]D -8.3 (c 0.8, CHCl3); H NMR δ 1.40 (s, 9
H), 1.56-1.80 (m, 3 H), 1.80-1.98 (m, 1 H), 3.22 (ddd, 1 H,
J 4a,5 ) J 5,6 ) 8.0, J 4b,5 ) 2.8 Hz, H-5), 3.47-3.71 (m, 5 H), 3.98
(dd, 1 H, J 7,8 ) 2.5, J 8,9 ) 0.5 Hz, H-8), 3.96-3.99 (m, 1 H,
H-2), 4.22 (dd, 1 H, J 1a,2 ) 5.0, J 1a,1b ) 11.0 Hz, H-1a), 4.29
(dd, 1 H, J 1b,2 ) 4.5, H-1b), 4.40 and 4.43 (2 d, 2 H, J ) 12.0
Hz, PhCH2), 4.53 (d, 1 H, J ) 9.0 Hz, NH), 4.64 and 4.94 (2 d,
2 H, J ) 11.3 Hz, PhCH2), 4.68 and 4.76 (2 d, 2 H, J ) 12.0
Hz, PhCH2), 4.65 and 4.95 (2 d, 2 H, J ) 11.5 Hz, PhCH2),
7.20-7.40 (m, 20 H), 8.15-8.29 (m, 4 H); 13C NMR δ 27.6, 27.9,
28.3, 30.0, 49.4, 69.1, 72.2, 73.5, 73.6, 75.4, 76.6, 78.6, 79.1,
79.4, 84.4, 123.1, 127.7, 128.0, 128.4, 135.4, 137.9, 138.2, 155.5.
3′(S)-N-(ter t-Bu toxycar bon ylam in o)-4′(S)(an d (R))-n on -
a d ec-5′-yn -4′-olyl 2,3,4,6-Tetr a -O-ben zyl-â-C-D-ga la ctop y-
r a n osid e (18). To a stirred, cold (-20 °C) mixture of 1-pen-
tadecyne (0.23 g, 3.53 mmol), powdered 4-Å molecular sieves
(0.20 g), and anhydrous THF (18.0 mL) was added n-BuLi (2.20
mL, 3.52 mmol of a 1.6 M solution in hexanes). The resulting
white suspension was stirred at this temperature for 30 min
and then cooled to -50 °C over a period of 10 min. A solution
of the aldehyde 16 (0.50 g, 0.70 mmol) in anhydrous THF (3.0
mL) was added dropwise, and the resulting mixture was
stirred at -50 °C for 2 h and then quenched with aqueous
phosphate buffer (pH 7) and allowed to warm to room tem-
perature. The white suspension was filtered through a pad of
Celite, and the phases were separated. The aqueous phase was
extracted with AcOEt, and the combined organic layers were
dried and concentrated. Chromatography on silica gel of the
crude residue with cyclohexane/AcOEt (3:1) gave 18 (0.65 g,
65%) as a 70:30 mixture of epimers syn -18 and a n ti-18 (by
Anal. Calcd for C50H56N2O11
: C, 69.75; H, 6.56; N, 3.25.
Found: C, 69.56; H, 6.77; N, 3.29. The second eluate was the
2R epimer (0.53 g, 13%) as a syrup: 1H NMR δ 1.40 (s, 9 H),
1.40-1.45 (m, 1 H), 1.61-1.82 (m, 2 H), 1.90-2.10 (m, 1 H),
3.20 (ddd, 1 H, J 4a,5 ) J 5,6 ) 8.0, J 4b,5 ) 2.8 Hz, H-5), 3.45-
3.71 (m, 5 H), 3.97 (dd, 1 H, J 7,8 ) 2.5, J 8,9 ) 0.5 Hz, H-8),
3.96-3.98 (m, 1 H, H-2), 4.20 (dd, 1 H, J 1a,1b ) 12.0, J 1a,2
)
6.5 Hz, H-1a), 4.30 (dd, 1 H, J 1b,2 ) 5.0 Hz, H-1b), 4.42 and
4.45 (2 d, 2 H, J ) 12.0 Hz, PhCH2), 4.63 and 4.93 (2 d, 2 H,
J ) 11.3 Hz, PhCH2), 4.67-4.69 (m, 1 H, NH), 4.68 and 4.77
(2 d, 2 H, J ) 12.0 Hz, PhCH2), 4.65 and 4.95 (2 d, 2 H, J )
11.5 Hz, PhCH2), 7.22-7.40 (m, 20 H), 8.15-8.25 (m, 4 H);
13C NMR δ 27.7, 28.3, 29.7, 49.6, 70.0, 72.2, 74.4, 74.5, 75.5,
76.1, 76.6, 78.7, 79.2, 84.8, 120.8, 126.6, 127.8, 128.4, 131.5,
137.9, 138.6, 144.4, 155.4.
1
1H NMR analysis): H NMR δ 0.82-0.87 (m, 3 H), 1.20-1.50
(m, 20 H), 1.40-1.52 (m, 11 H), 1.54-1.70 (m, 3 H), 1.88-
2.00 (m, 1 H), 2.15 (dt, 1 H, J ) 1.0, 4.5 Hz), 2.70 (d, 0.7 H, J
) 4.6 Hz, OH), 3.08 (d, 0.3 H, J ) 6.4 Hz, OH), 3.40-3.70 (m,
5 H), 3.97 (dd, 1 H, J 3,4 ) 2.4, J 4,5 ) 0.5 Hz, H-4), 4.25-4.33
(m, 0.7 H, H-4′), 4.41 and 4.47 (2 d, 2 H, J ) 12.0 Hz, PhCH2),
4.38-4.42 (m, 0.3 H, H-4′), 4.43 and 4.94 (2 d, 2 H, J ) 12.0

â-D-Galactosyl Ceramide Methylene Isostere
J . ORG. CHEM., VOL. 64, NO. 15, 1999 5563
Hz, PhCH2), 4.64 and 4.94 (2 d, 2 H, J ) 12.0 Hz, PhCH2),
4.68 and 4.75 (2 d, 2 H, J ) 12.0 Hz, PhCH2), 7.20-7.40 (m,
20 H); 13C NMR δ 14.3, 18.8, 22.7, 28.1, 29.2, 29.4, 30.0, 56.3,
65.8, 69.1, 72.3, 73.5, 73.7, 75.5, 76.7, 79.1, 79.4, 84.8, 86.2,
127.6, 127.8, 127.9, 128.2, 128.4, 137.9, 138.3, 138.7, 156.5.
Oxa zolid in on es 20a a n d 20b. The mixture of epimers 18
(0.13 g, 0.14 mmol) was dissolved in a solution of HCl in
dioxane (4.8 M, 3.0 mL) and water (0.50 mL). The solution
was stirred at room temperature for 14 h and then concen-
trated. To the residue dissolved in anhydrous THF (2.0 mL)
was added N,N′-carbonyldiimidazole (0.03 g, 0.21 mmol) at 0
°C; then the resulting mixture was stirred for 45 min at room
(3′S,4′R)-N-(ter t-Bu toxyca r bon yla m in o)n on a d ec-5′-yn -
4′-olyl 2,3,4,6-Tetr a-O-ben zyl-â-C-D-galactopyr an oside (a n -
ti-18). To a cold (-78 °C) stirred solution of 19 (0.40 g, 0.44
mmol) in anhydrous THF (2.5 mL) was added L-selectride
(lithium tri-sec-butylborohydride, 0.87 mL, 0.87 mmol, of a 1
M solution in THF). After 30 min at this temperature, the
reaction was quenched with MeOH, allowed to warm to room
temperature, and partitioned between Et2O and saturated
aqueous NaCl. The combined organic phases were dried and
concentrated. Chromatography on silica gel of the crude
residue with cyclohexane/AcOEt (3:1) containing Et3N (1‰)
gave a n ti-18 (0.36 g, 90%, dr g 95% by 1H NMR analysis):
[R]D -13.2 (c 0.5, CHCl3); IR cm-1 2400; 1H NMR δ 0.82-0.93
(m, 3 H, CH3), 1.20-1.70 (m, 20 H), 1.43 (s, 9 H), 1.40-1.52
(m, 2 H, 2 H-8′), 1.54-1.70 (m, 3 H), 1.88-2.00 (m, 1 H, H-2′b),
2.15 (dt, 2 H, J ) 1.0, 4.5, Hz, 2 H-7′), 3.06 (d, 1 H, J ) 6.4
Hz, OH), 3.22 (ddd, 1 H, J 1,1′a ) J 1,2 ) 9.0, J 1,1′b ) 2.6 Hz, H-1),
3.47-3.68 (m, 5 H), 3.68-3.80 (m, 1 H, H-3′), 3.97 (dd, 1 H,
J 3,4 ) 2.5, J 4,5 ) 0.5 Hz, H-4), 4.41 and 4.47 (2 d, 2 H, J ) 12.0
Hz, PhCH2), 4.38-4.44 (m, 1 H, H-4′), 4.63 and 4.94 (2 d, 2 H,
J ) 11.5 Hz, PhCH2), 4.64 and 4.94 (2 d, 2 H, J ) 12.0 Hz,
PhCH2), 4.68 and 4.75 (2 d, 2 H, J ) 12.0 Hz, PhCH2), 4.70-
4.78 (m, 1 H, NH), 7.20-7.40 (m, 20 H); 13C NMR δ 14.1, 18.7,
22.7, 28.4, 28.9, 29.4, 29.7, 31.9, 55.8, 69.1, 73.5, 73.6, 74.5,
75.5, 77.2, 77.4, 77.7, 79.1, 79.4, 79.7, 84.8, 87.3, 127.5, 127.6,
127.8, 127.9, 128.1, 128.2, 128.4, 137.9, 138.3, 138.7, 156.9;
MALDI-TOF MS: 941.3 (M+ + Na), 957.5 (M+ + K). Anal.
Calcd for C58H79NO8: C, 75.86; H, 8.67; N, 1.52. Found: C,
76.09; H, 8.51; N, 1.59.
1
temperature and concentrated. The H NMR spectrum of the
crude residue revealed a mixture of 20a and 20b in ca. 70:30
ratio. Chromatography on silica gel of this mixture with
cyclohexane-AcOEt (2:1) afforded first 20a (0.07 g, 63%) as a
syrup and then 20b (0.03 g, 27%) contaminated by a small
amount of 20a .
20a : [R]D -43.1 (c 0.9, CHCl3); 1H NMR (DMSO-d6, 120 °C)
δ 0.82-0.92 (m, 3 H, CH3), 1.30 (s, 20 H), 1.40-1.53 (m, 2 H),
1.54-1.95 (m, 4 H), 2.20 (dt, 2 H, J 4′,7′ ) 2.0, J 7′,8′ ) 7.0 Hz, 2
H-7′), 3.24 (ddd, 1 H, J 1,1′a ) J 1,2 ) 8.0, J 1,1′b ) 2.8 Hz, H-1),
3.50-3.78 (m, 5 H), 3.68 (dd, 1 H, J 2,3 ) 9.5, J 3,4 ) 2.8 Hz,
H-3), 4.40 (dd, 1 H, J 4,5 ) 0.5 Hz, H-4), 4.47 and 4.55 (2 d, 2
H, J ) 12.0 Hz, PhCH2), 4.56 and 4.84 (2 d, 2 H, J ) 11.9 Hz,
PhCH2), 4.63 and 4.81 (2 d, 2 H, J ) 11.0 Hz, PhCH2), 4.66
and 4.78 (2 d, 2 H, J ) 11.5 Hz, PhCH2), 4.72 (dt, 1 H, J 3′,4′
)
6.0 Hz, H-4′), 7.20-7.40 (m, 21 H); 13C NMR δ 14.1, 18.7, 22.6,
29.1, 29.2, 29.6, 31.9, 32.9, 61.2, 69.2, 73.1, 73.3, 74.2, 75.3,
75.5, 76.5, 77.0, 78.6, 80.4, 84.6, 89.3, 89.0, 128.1, 128.3, 128.4,
128.5, 137.4, 138.0, 158.1; MALDI-TOF MS 867.5 (M+ + Na),
883.2 (M+ + K). Anal. Calcd for C54H69NO7: C, 76.83; H, 8.59;
N, 1.65. Found: C, 76.69; H, 8.70; N, 1.62.
(3′S,4′R)-3′-Am in on on a d ec-5′-yn -4′-olyl 2,3,4,6-Tetr a -O-
ben zyl-â-C-D-ga la ctop yr a n osid e (21). A solution of HCl in
dioxane (4.8 M, 2.0 mL) and water (0.5 mL) was added at room
temperature to a n ti-18 (0.30 g, 0.33 mmol). The mixture was
stirred overnight and then concentrated. The residue was
dissolved in saturated aqueous NaHCO3 and then extracted
with CH2Cl2, dried, and concentrated. Chromatography on
silica gel of the crude residue with CH2Cl2/MeOH/NH4OH (95:
5:1) gave 21 (0.24 g, 90%): 1H NMR δ 0.80-0.92 (m, 3 H, CH3),
1.25 (s, 22 H), 1.40-1.50 (m, 2 H), 1.50-1.70 (m, 2 H, 2 H-1′),
2.00-2.20 (m, 2 H, 2 H-2′), 2.75 (m, 1 H, OH), 3.15-3.27 (m,
20b: 1H NMR (DMSO-d6, 120 °C): δ 0.82-0.92 (m, 3 H,
CH3), 1.20-1.30 (s, 20 H), 1.40-1.53 (m, 2 H), 1.54-1.95 (m,
4 H), 2.19 (dt, 2 H, J 4′,7′ ) 2.0, J 7′,8′ ) 7.0 Hz, 2 H-7′), 3.25
(ddd, 1 H, J 1,1′a ) J 1,2 ) 8.0, J 1,1′b ) 2.8 Hz, H-1), 3.50-3.69
(m, 5 H), 3.68 (dd, 1 H, J 2,3 ) 9.5, J 3,4 ) 2.8, Hz, H-3), 4.42
(dd, 1 H, J 4,5 ) 0.5 Hz, H-4), 4.48 and 4.54 (2 d, 2 H, J ) 12.0
Hz, PhCH2), 4.57 and 4.84 (2 d, 2 H, J ) 11.9 Hz, PhCH2),
4.64 and 4.81 (2 d, 2 H, J ) 11.0 Hz, PhCH2), 4.66 and 4.78 (2
d, 2 H, J ) 11.5 Hz, PhCH2), 5.21 (dt, 1 H, J 3′,4′ ) 8.0 Hz,
H-4′), 7.08 (s, 1 H, NH), 7.20-7.40 (m, 20 H).
1 H, H-1), 3.46-3.70 (m, 6 H), 3.97 (d, 1 H, J 3,4 ) 2.5, J 4,5
)
0.5, H-4), 4.38-4.44 (m, 1 H, H-4′), 4.41 and 4.48 (2 d, 2 H, J
) 12.0 Hz, PhCH2), 4.62 and 4.93 (2 d, 2 H, J ) 11.5 Hz,
PhCH2), 4.68 and 4.75 (2 d, 2 H, J ) 12.0 Hz, PhCH2), 4.68
and 4.93 (2 d, 2 H, J ) 12.0 Hz, PhCH2), 7.20-7.40 (m, 20 H);
13C NMR δ 14.1, 18.7, 22.7, 28.8, 29.3, 29.7, 30.8, 31.9, 55.0,
55.7, 65.9, 69.1, 73.7, 74.4, 75.5, 76.2, 76.6, 78.9, 79.0, 79.5,
84.9, 86.7, 127.5, 127.8, 127.9, 128.2, 128.4, 137.9, 138.4, 138.7.
(3′S,4′R)-3′-Am in o-(E)-n on adec-5′-en -4′-olyl 2,3,4,6-Tetr a-
O-ben zyl-â-C-D-ga la ctop yr a n osid e (22). To a solution of 21
(0.20 g, 0.24 mmol) in anhydrous dimethoxyetane (5.0 mL) was
added LiAlH4 (0.90 g, 24.4 mmol). The mixture was heated to
85 °C, stirred at this temperature for 3 h, then cooled to room
temperature, and treated with aqueous KOH (4 M, 5.0 mL).
The white suspension was filtered through a pad of Celite and
concentrated. Chromatography on silica gel of the crude
residue with CH2Cl2/MeOH/NH4OH (94:5:1) gave 22 (0.13 g,
3′S-N-(ter t-Bu toxyca r bon yla m in o)n on a d ec-5′-yn -4′-on -
yl 2,3,4,6-Tet r a -O-b en zyl-â-C-D-ga la ct op yr a n osid e (19).
To a cold (-78 °C) solution of oxalyl chloride (0.10 g, 0.82
mmol) in anhydrous CH2Cl2 (2.0 mL) was added a solution of
DMSO (0.13 g, 1.63 mmol) in anhydrous CH2Cl2 (1.0 mL). The
solution was stirred at -78 °C for 30 min, and then a solution
of alcohol 18 (0.50 g, 0.54 mmol) in anhydrous CH2Cl2 (2.0 mL)
was added. After the reaction solution had been stirred at this
temperature for 1 h, N,N′-diisopropylethylamine (0.42 g, 3.27
mmol) was added. The mixture was allowed to warm to 0 °C
over 10 min and treated with cold (0 °C) aqueous HCl (1 M,
2.0 mL). The solution was extracted with CH2Cl2, and the
combined organic phases were washed with aqueous phos-
phate buffer (pH 7), dried, and concentrated. Chromatography
on silica gel of the crude residue with cyclohexane/AcOEt (4:
1) containing Et3N (1‰) gave the ketone 19 (0.45 g, 90%) as a
syrup: [R]D +8.4 (c 0.6, CHCl3); IR (NaCl) cm-1 2220, 1654;
1H NMR (DMSO-d6, 120 °C) δ 0.82-0.94 (m, 3 H, CH3), 1.25
(s, 20 H), 1.39 (s, 9 H), 1.40-1.60 (m, 2 H), 1.65-1.80 (m, 1
H), 1.80-1.94 (m, 2 H), 2.12-2.20 (m, 1 H, H-1′), 2.30-2.40
(m, 2 H, 2 H-7′ ), 3.24 (ddd, 1 H, J 1,1′a ) J 1,2 ) 9.0, J 1,1′b ) 2.8
1
65%) as a syrup: [R]D +12.4 (c 0.9, MeOH); H NMR δ 0.84-
0.94 (m, 3 H, CH3), 1.28 (s, 22 H), 1.40-1.64 (m, 3 H), 1.82-
2.05 (m, 3 H), 2.79 (ddd, 1 H, J 2′a,3′ ) 8.3, J 2′b,3′ ) 4.6, J 3′,4′
)
4.1 Hz, H-3′), 3.21 (ddd, 1 H, J 1,1′a ) J 1,2 ) 9.2, J 1,1′b ) 2.1 Hz,
H-1), 3.44-3.72 (m, 5 H), 3.95 (dd, 1 H, J 3,4 ) 2.5, J 4,5 ) 0.5
Hz, H-4), 3.98 (dd, 1 H, J 4′,5′ ) 6.4 Hz, H-4′), 4.42 and 4.51 (2
d, 2 H, J ) 11.9 Hz, PhCH2), 4.63 and 4.94 (2 d, 2 H, J ) 11.5
Hz, PhCH2), 4.64 and 4.96 (2 d, 2 H, J ) 10.7 Hz, PhCH2),
4.68 and 4.76 (2 d, 2 H, J ) 11.5 Hz, PhCH2), 5.39 (dd, 1 H,
J 5′,6′ ) 15.1 Hz, H-5′), 5.69 (ddd, 1 H, J 6′,7′a ) J 6′,7′b ) 6.8 Hz,
H-6′), 7.20-7.40 (m, 20 H); 13C NMR δ 14.1, 22.7, 29.3, 29.4,
29.5, 29.7, 31.9, 32.4, 55.7, 69.1, 73.5, 73.7, 74.4, 75.4, 76.6,
77.4, 78.9, 79.6, 84.9, 127.5, 127.7, 127.9, 128.1, 128.2, 128.4,
134.1, 137.9, 138.4, 138.6. Anal. Calcd for C53H73NO6: C, 77.85;
H, 8.69, N, 1.71. Found: C, 77.79; H, 8.70; N, 1.70.
Hz, H-1), 3.50-3.64 (m, 4 H), 3.68 (dd, 1 H, J 2,3 ) 9.5, J 3,4
2.8 Hz, H-3), 3.92-4.00 (m, 1 H, H-3′), 4.04 (dd, 1 H, J 4,5
)
)
0.5 Hz, H-4), 4.47 and 4.53 (2 d, 2 H, J ) 12.0 Hz, PhCH2),
4.56 and 4.84 (2 d, 2 H, J ) 11.5 Hz, PhCH2), 4.63 and 4.81 (2
d, 2 H, J ) 11.0 Hz, PhCH2), 4.66 and 4.78 (2 d, 2 H, J ) 11.5
Hz, PhCH2), 6.58 (s, 1 H, NH), 7.20-7.40 (m, 20 H); 13C NMR
δ 14.1, 19.0, 22.6, 27.6, 28.3, 28.9, 29.3, 29.4, 29.6, 31.9, 61.0,
62.1, 68.8, 72.2, 73.5, 74.4, 75.5, 78.7, 79.1, 79.6, 84.7, 97.8,
127.5, 127.6, 128.2, 128.4, 137.9, 138.1, 138.2, 155.4, 187.0.
Anal. Calcd for C58H77NO8: C, 76.03; H, 8.47; N, 1.53. Found:
C, 76.21; H, 8.29; N, 1.58.
(3′S,4′R)-3′-N-(p en t a d eca n oyla m in o)-(E)-n on a d ec-5′-
en -4′-olyl 2,3,4,6-Tetr a -O-ben zyl-â-C-D-ga la ctop yr a n osid e
(2b). To a solution of 22 (0.10 g, 0.12 mmol) in anhydrous THF

5564 J . Org. Chem., Vol. 64, No. 15, 1999
Dondoni et al.
(5.0 mL) was added slowly aqueous AcONa (0.10 g, 12 mmol
in 4 mL of H2O) and palmitoyl chloride (0.04 mL, 0.12 mmol).
The mixture was stirred for 1 h at room temperature and then
diluted with saturated aqueous NaHCO3 and extracted with
Et2O. The combined organic phases were dried and concen-
trated. Chromatography on silica gel of the crude residue with
cyclohexane/AcOEt (3:1) containing Et3N (1‰) gave 2b (0.13
AcOEt (2:1) containing Et3N (1‰) gave 2a (23.7 mg, 55%) as
a yellow syrup: [R]D -6.4 (c 0.5, CHCl3); 1H NMR δ 0.80-
0.98 (m, 6 H, 2 CH3), 1.28 (s, 46 H), 1.40-1.78 (m, 5 H), 1.98-
2.20 (m, 5 H), 1.98 (s, 3 H, CH3), 2.04 (s, 3 H, CH3), 2.05 (s, 6
H, 2 CH3), 2.15 (s, 3 H, CH3), 3.42 (ddd, 1 H, J 1,1′a ) J 1,2 ) 9.0,
J 1,1′b ) 2.5 Hz, H-1), 3.82-3.88 (m, 1 H, H-6a), 4.05 (dd, 1 H,
J 5,6b ) 6.5, J 6a,6b ) 11.0 Hz, H-6b), 4.10-4.22 (m, 2 H, H-3′,
1
g, 80%): [R]D -20 (c 0.5, CHCl3); H NMR δ 0.83-0.92 (m, 6
H-5), 5.06 (dd, 1 H, J 2,3 ) 9.0 Hz, H-2), 5.19 (dd, 1 H, J 3′,4′
)
H, 2 CH3), 1.25 (s, 46 H), 1.40-1.70 (m, 5 H), 1.90-2.05 (m, 3
H), 2.10 (dt, 2 H, J ) 1.6, 9.1 Hz), 3.18 (ddd, 1 H, J 1,1′a ) J 1,2
) 9.0, J 1,1′b ) 2.5 Hz, H-1), 3.44-3.60 (m, 3 H), 3.60 (dd, 1 H,
J 2,3 ) 8.8 Hz), 3.64 (dd, 1 H, J 3,4 ) 2.3 Hz, H-3), 3.82 (d, 1 H,
J ) 5.1 Hz, OH), 3.85-3.94 (m, 1 H, H-3′), 3.96 (dd, 1 H, J 4,5
) 0.5 Hz, H-4), 4.04-4.15 (m, 1 H, H-4′), 4.42 and 4.48 (2d, 2
H, J ) 11.8 Hz, PhCH2), 4.62 and 4.94 (2 d, 2 H, J ) 10.7 Hz,
PhCH2), 4.61 and 4.94 (2 d, 2 H, J ) 11.8 Hz, PhCH2), 4.69
4.5, J 4′,5′ ) 7.0 Hz, H-4′), 5.27-5.31 (m, 1 H, H-4), 5.35 (dd, 1
H, J 5′,6′ ) 14.8, H-5′), 5.39-5.44 (m, 1 H, H-3), 5.76 (ddd, 1 H,
J 6′,7′a ) J 6′,7′b ) 6.5 Hz, H-6′), 6.90-6.94 (m, 1 H, NH); 13C NMR
δ 14.1, 20.6, 20.7, 20.8, 21.2, 22.7, 25.9, 27.3, 29.0, 29.4, 29.5,
29.7, 31.9, 32.4, 36.9, 50.6, 61.5, 71.3, 71.4, 72.5, 74.1, 123.9,
136.7, 170.0, 170.1, 170.2, 170.4, 173.0, 178.5; MALDI-TOF
MS 931 (M+ + Na), 947 (M+ + K). Anal. Calcd for: C51H89
-
NO12: C, 67.45; H, 9.87; N, 1.54. Found C, 67.32; H, 9.72; N,
1.46.
and 4.76 (2 d, 2 H, J ) 11.8 Hz, PhCH2), 5.35 (dd, 1 H, J 5′,4′
)
6.0, J 5′,6′ ) 15.5 Hz, H-5′), 5.67 (ddd, 1 H, J 6′,7′a ) J 6′,7′b ) 6.5
Hz, H-6′), 5.78 (d, 1 H, J ) 7.4 Hz, NH), 7.20-7.40 (m, 20 H);
13C NMR δ 14.1, 22.7, 26.0, 28.5, 29.3, 29.7, 31.9, 32.4, 36.6,
55.6, 62.6, 69.1, 73.5, 73.6, 74.5, 75.9, 76.1, 76.6, 79.0, 79.5,
84.8, 127.5, 127.7, 127.8, 127.9, 128.2, 133.8, 137.7, 138.2,
175.0; MALDI-TOF MS 1082.2 (M+ + Na), 1098.4 (M+ + K).
Anal. Calcd for C69H103NO7: C, 78.35; H, 9.74; N, 1.32. Found
C, 78.48; H, 9.62; N, 1.31.
(3′S,4′R)-4′-O-Acet yl-3′-N-(p en t a d eca n oyla m in o)-(E)-
n on a d ec-5′-en -4′-olyl 2,3,4,6-Tetr a -O-a cetyl-â-C-D-ga la c-
top yr a n osid e (2a ). To cold (-45 °C) stirred liquid ammonia
(2.0 mL) were added a solution of 2b (0.05 g, 0.05 mmol) in
anhydrous THF (2.0 mL) and lithium (24.0 mg). The deep blue
solution was stirred at -45 °C for 2 h while the blue color
persisted. Ethanol was added, and the ammonia was allowed
to evaporate. The mixture was concentrated, and the residue
was dissolved in pyridine (2.0 mL) and Ac2O (2.0 mL), stirred
for 14 h at room temperature, and then concentrated. Chro-
matography on silica gel of the crude residue with cycloexane/
Syn th esis of 2a fr om 21. The reduction with lithium in
liquid ammonia was carried out as described above starting
from 21 (0.05 g, 0.06 mmol). After the mixture had been
concentrated, the residue was treated with palmitoyl chloride
as described for 2b. The crude residue was dissolved in a
solution of pyridine (2.0 mL) and Ac2O (2.0 mL), stirred for 14
h at room temperature, and then concentrated. Chromatog-
raphy on silica gel of the crude residue with cyclohexane/
AcOEt (2:1) and Et3N (1‰) gave 2a contaminated by small
amounts of uncharacterized byproducts (25.0 mg, 45% overall
yield).
Ack n ow led gm en t. Generous financial support from
MURST-COFIN-98 (Italy), is gratefully acknowledged.
We thank Mr. P. Formaglio (University of Ferrara) for
NMR measurements.
J O990398L