Synthesis of α- and β-carbon-linked serine analogues of the P(k) trisaccharide

Article abstract of DOI:10.1021/jo991096m

The synthesis of glycopeptide ligands for a range of biomedically relevant carbohydrate-binding proteins is a topic of great importance to the glycobiology community. This task is impeded by the inherent instability of glycosyl linkages to serine/threonine, the normal sites of O-glycosylation in proteins. We have previously developed methodology for the preparation of C- glycosylated serines based on catalytic asymmetric hydrogenation of the corresponding enamide esters with the DuPHOS-Rh⁺ catalysts. Here we report further development of the methodology in the preparation of the C-glycosyl serine analogue of the pk trisaccharide (α-Gal(1→4)β-Gal(1→4)β-Glc-CH₂- serine); we require these ligands for our continuing investigations of the binding subunit of the shiga-like toxin. Catalytic asymmetric hydrogenation was used to prepare both α- and β-C-glycosides in the R and S serine series. We report here on the tolerance of the DuPHOS catalysts toward acetate, benzoate, and benzyl hydroxyl protecting groups. Additionally, we have developed an amino acid protecting group strategy compatible with both asymmetric hydrogenation and solid-phase peptide synthesis. In the course of our studies, we have also developed a new methodology for regioselective reductive cleavage of benzylidene protecting groups.

Full text of DOI:10.1021/jo991096m

J . Org. Chem. 1999, 64, 9153-9163
9153
Syn th esis of r- a n d â-Ca r bon -Lin k ed Ser in e An a logu es of th e P k
Tr isa cch a r id e
Sheryl D. Debenham, J ennifer Cossrow, and Eric J . Toone*
Department of Chemistry, Levine Science Research Center, Duke University,
Durham, North Carolina 27708
Received J uly 8, 1999
The synthesis of glycopeptide ligands for a range of biomedically relevant carbohydrate-binding
proteins is a topic of great importance to the glycobiology community. This task is impeded by the
inherent instability of glycosyl linkages to serine/threonine, the normal sites of O-glycosylation in
proteins. We have previously developed methodology for the preparation of C-glycosylated serines
based on catalytic asymmetric hydrogenation of the corresponding enamide esters with the
DuPHOS-Rh+ catalysts. Here we report further development of the methodology in the preparation
of the C-glycosyl serine analogue of the Pk trisaccharide (R-Gal(1f4)â-Gal(1f4)â-Glc-CH2-serine);
we require these ligands for our continuing investigations of the binding subunit of the shiga-like
toxin. Catalytic asymmetric hydrogenation was used to prepare both R- and â-C-glycosides in the
R and S serine series. We report here on the tolerance of the DuPHOS catalysts toward acetate,
benzoate, and benzyl hydroxyl protecting groups. Additionally, we have developed an amino acid
protecting group strategy compatible with both asymmetric hydrogenation and solid-phase peptide
synthesis. In the course of our studies, we have also developed a new methodology for regioselective
reductive cleavage of benzylidene protecting groups.
In tr od u ction
ligands for both lectins and antibodies. A second general
strategy for the preparation of high-affinity ligands
involves the use of multivalency. Lectins are seldom
found in vivo as monomeric species; rather they are
aggregated into higher order oligomers. A reasonable
suggestion following from this observation is that Nature
has solved the “tight binding” problem through multiva-
lency. From this premise a wide range of high-affinity
multivalent carbohydrate ligands have been prepared for
myriad carbohydrate-binding proteins.4
Protein-carbohydrate interaction plays a central role
in biological recognition. In addition to myriad functions
in normal human biology, an array of pathological
recognition events are mediated by protein-carbohydrate
interaction.1 In the earliest phases of infection by a
variety of viral, parasitic, mycoplasmal, and bacterial
infections a pathogen recognizes and adheres to its host
through a protein-carbohydrate interaction. Because of
the importance of carbohydrate-mediated recognition, the
development of high-affinity soluble ligands designed to
inhibit pathogens-host adhesion is an area of intense
activity. The development of such inhibitors has been
frustrated to date by the exceptionally weak affinities
with which native, monovalent saccharides adhere to
their protein receptors; such interactions typically pro-
ceed with millimolar to micromolar dissociation con-
stants. Much contemporary glycoscience thus seeks
general strategies for overcoming this weak native af-
finity.
Two strategies have been explored toward this goal.
The first involves modification of the monovalent ligand
in a search for adventitious contacts between various
pendant moieties and the protein, either in or out of the
binding site. Some of the most successful demonstrations
of this strategy have been offered by Wong and co-
workers,2 who have shown that much of the specificity
of an oligosaccharide binding event is provided by a single
monosaccharide.3 Derivatized monosaccharides, prepared
randomly and identified with high throughput screens,
thus act as effectively as the parent oligosaccharide as
Toward the development of high-affinity ligands for
carbohydrate-binding proteins of immediate concern for
human health, we sought to prepare libraries of bivalent,
peptide-linked oligosaccharide ligands. Our rationale for
this exercise was to access the advantages of both
adventitious contacts between linker and protein outside
the binding site and multivalency. From this perspective,
peptides are attractive tethers for several reasons. First,
the amide linkage is robust to both chemical and enzy-
matic degradation, especially following the incorporation
of nonproteinaceous amino acids. Second, the peptide
backbone provides sufficient flexibility for optimal place-
ment of saccharide recognition epitopes within the car-
bohydrate-binding sites while at the same time providing
sufficient rigidity to reduce the conformational entropy
barrier encountered during restriction of the linker region
during binding. Third, a wide range of functionalities are
available with even the 20 proteinaceous amino acids in
the search for favorable interactions between ligand and
protein. Finally, the facile and well-developed synthetic
(3) For other examples see: (a) Simanek, E. E.; McGarvey, G. J .;
J abionowski, J . A.; Wong, C.-H. Chem. Rev. 1998, 98, 833-862. (b)
Hummer, G.; Nilsson, U.; Hof, S.; Hindsgaul, O. Abstr. Pap. Am. Chem.
Soc. 1998, 215, U112, Part 1.
(1) Dwek, R. A. Chem. Rev. 1996, 96, 683-720 and references
therein.
(2) Wong, C.-H.; Moris-Varas, F.; Hung, S.-C.; Marron, T. G.; Lin,
C.-C.; Gong, K. W.; Weitz-Schmidt, G. J . Am. Chem. Soc. 1997, 119,
8152-8158.
(4) For a review of the synthesis and binding studies of multivalent
glycoconjugates see: Roy, R. Curr. Opin. Struct. Biol. 1996, 6, 692-
702.
10.1021/jo991096m CCC: $18.00 © 1999 American Chemical Society
Published on Web 11/20/1999

9154 J . Org. Chem., Vol. 64, No. 25, 1999
Debenham et al.
methodology available for peptide synthesis allows rapid
preparation of ligands on solid supports.
reported for the production of C-glycosyl amino acids with
both natural and unnatural stereochemistry at the
R-amino acid center.11 We have previously reported
methodology based on catalytic asymmetric hydrogena-
tion of glycosylated enamides to produce the carbon-
linked glycosyl serines in either R or S stereochemistry
from a common starting material.12 In our original
communication amino acids were produced N-protected
as the tert-butyl carbamates and carboxyl protected as
the methyl esters; such protection is incompatible with
solid-phase synthesis. Here, we extend our methodology
beyond monosaccharides to produce gram quantities of
the Pk trisaccharide protected as the TMSE esters and
tert-butyl carbamates, appropriate for solid-phase glyco-
peptide synthesis. Finally, we report the use of triethyl-
silane/BF3‚Et2O for the selective conversion of a 4,6-di-
O-benzylidene protecting group to the corresponding 6-O-
benzyl ether. This methodology represents a significant
improvement over the widely used methodology involving
NaBCNH3 and HClg.13
We have previously reported the preparation of biva-
lent, peptide-linked ligands for the plant lectin con-
canavalin A.5 This work demonstrated that “shaving”
protocols effectively generate beads with low-density,
spatially segregated recognition sequences on the bead
surface that enforce exclusive intramolecular binding but
with high-density interior sequences suitable for sequenc-
ing by mass spectroscopic techniques.6 We are now
utilizing this strategy in a search for high-affinity ligands
for the shiga-like toxin (SLT). The shiga and shiga-like
toxins are members of a group of bacterial two-component
toxins that includes the heat labile and cholera toxins.
The proteins are structurally and mechanistically related
to the diphtheria and pertussis toxins, and to the toxic
plant lectins abrin and ricin. All members of this group
produce their toxic effects by recognizing and adhering
to host cell surfaces through a multimeric lectin recogni-
tion subdomain. Following endocytosis, a second, enzy-
matically active, subdomain is transported to the cytosol,
where it exerts its toxic effects.7
Resu lts a n d Discu ssion
The shiga toxin and shiga-like toxins bind the Pk
trisaccharide recognition domain of the glycolipid recep-
tor globotriosylceramide (R-Gal(1f4)â-Gal(1f4)âGlc-O-
cer).8 Originally isolated from Shigella dysenteria, the
toxin is now secreted by several strains of Escherichia
coli; to date more than 25 strains of SLT-producing
Escherichia have been identified in North America. The
most notorious of these, E. coli O157, produces a set of
symptoms functionally equivalent to those of shigellosis,
primarily a unique hemmorrhagic colitis. In children and
elderly patients, occasional progression to hemolytic
uremic syndrome and kidney failure is a complication of
the disease; the renal toxicity is thought to reflect the
high concentration of glycolipid receptor on kidney tis-
sue.9 There is currently no treatment for the disease
following the onset of symptoms, although high-affinity
mimics of the cell surface glycolipid receptor might serve
as effective therapeutic agents even following the onset
of bloody diarrhea.
A prerequisite for the synthesis of peptide-linked
ligands is access to sufficient quantities of Pk trisaccha-
ride-derivatized amino acid suitably protected for solid-
phase glycopeptide synthesis. Naturally occurring O-gly-
copeptides and proteins are glycosylated through either
serine or threonine. To avoid problems associated with
the instability of the O-glycosyl serine linkage, we instead
sought to utilize the C-linked analogue R-Gal(1f4)â-Gal-
(1f4)âGlc-CH2-serine.10 A variety of methods have been
P r ep a r a tion of th e r-An a logu e of th e P k Tr isa c-
ch a r id e. The two key aspects of the synthetic strategy
are disconnection of the trisaccharide and installation of
a moiety that facilitates incorporation of a C-glycoside
into the amino acid backbone. Several syntheses of the
Pk trisaccharide have been reported; all make the key
bond disconnection at the R-galactose(1f4)lactose link-
age.14 Our strategy toward the amino acid component
involves asymmetric hydrogenation of an enamide pre-
cursor. The enamide is prepared as the E/Z mixture by
Horner-Emmons olefination of a C-glycosyl aldehyde, in
turn prepared from the corresponding C-allyl glycoside
by ozonolysis. With these considerations in mind, we
chose to functionalize lactose as the C-allyl derivative
prior to installation of the terminal galactose residue.
Although the naturally occurring ligand possesses the
â-configuration at the glucosyl anomeric center, we
sought to produce all four diastereomers at the C-glycosyl
anomeric and the R-amino acid centers. We first consid-
ered synthesis of the two diastereomers of the R-C-
glycosyl compound, a route that requires preparation of
the R-C-allyl lactoside. A variety of methodologies have
been developed for the preparation of R-C-glycosides; we
considered both acid-catalyzed and radical additions to
R-C-allyl lactose.15 Gannis and co-workers16 report that
(11) (a) Ben, R. N.; Orellana, A.; Arya, P. J . Org. Chem. 1998, 63,
4817-4820. (b) Dondoni, A.; Marra, A.; Massi, A. Chem. Commun.
1998, 1741-1742. (c) Urban, D.; Skrydstrup, T.; Beau, J . M. Chem.
Commun. 1998, 955-956. (d) Dondoni, A.; Marra, A.; Massi, A.
Tetrahedron 1998, 54, 2827-2832. (e) Fuchss, T.; Schmidt, R. R.
Synthesis 1998, 753-758. (f) Arya, P.; Ben, R. N.; Qin, H. P.
Tetrahedron Lett. 1998, 39, 6131-6134. (g) Lay, L.; Meldal, M.; Nicotra,
F.; Panza, L.; Russo, G. Chem. Commun. 1997, 1469-1470. (h)
Burkhart, F.; Hoffmann, M.; Kessler, H. Angew. Chem., Int. Ed. Engl.
1997, 36, 1191-1192. (i) Dorgan, B. J .; J ackson, F. W. Synlett 1996,
859-861. (j) Sutherlin, D. P. Stark, T. M.; Hughes, R.; Armstrong, R.
W. J . Org. Chem. 1996, 61, 8350-8354. (k) Kessler, H.; Wittmann,
V.; Ko¨ck, M.; Kottenhahn, M. Angew. Chem., Int. Ed. Engl. 1992, 31,
902-904.
(5) Debenham, S. D.; Toone, E. J . J . Org. Chem., submitted for
publication.
(6) Va´gner, J .; Barany, G.; Lam, K. S.; Krchn˜a´k, V.; Sepetov, N. F.;
Ostrem, J . A.; Strop, P.; Lebl, M. Proc. Natl. Acad. Sci. U.S.A. 1996,
93, 8194-8199.
(7) O’Brien, A. D.; Tesh, V. L.; Donohue-Rolfe, A.; J ackson, M. P.;
Olsnes, S.; Sandvig, K.; Lindberg, A. A.; Keusch, G. T. Curr. Top.
Microbiol. Immun. 1992, 180, 65-94.
(8) Brown, J . E.; Echeverria, P.; Lindberg, A. A. Rev. Infect. Dis.
1991, 13, S298-S303.
(9) Arbus, G. S. Kidney Int. 1997, 58, S91-S96.
(10) (a) Bertozzi, C. R.; Hoeprich, P. D.; Bednarski, M. D. J . Org.
Chem. 1992, 57, 6092-6094 and references therein. (b) Large, D. G.;
Bradshaw, I. J . In Glycopeptides and Related Compounds: Synthesis,
Analysis, and Applications; Large, D. G., Warren, C. D., Eds.; Marcel
Dekker: New York, Basel, Hong Kong, 1997; pp 311-313. (c) Waka-
hayashi, K.; Pigman, W. Carbohydr. Res. 1974¸ 34, 3-14. (d) Manger,
I. D.; Rademacher, T. W.; Dwek, R. A. Biochemistry 1992, 31, 10724-
10732.
(12) Debenham, S. D.; Debenham, J . S.; Burk, M. J .; Toone, E. J . J .
Am. Chem. Soc. 1997, 119, 9897-9898.
(13) Garegg, P. J .; Hultberg, H. Carbohydr. Res. 1981, 93, C10-
C11
(14) Zhang, Z.; Magnusson, G. J . Org. Chem. 1996, 61, 2383-2393.
(15) Levy, D. E.; Tang, C. The Chemistry of C-Glycosides; Tetrahe-
dron Organic Chemistry Series Vol. 13; Elsevier Science Inc.: New
York, 1995; pp 42-70 and 175-195 and references therein.

Serine Analogue of the Pk Trisaccharide
J . Org. Chem., Vol. 64, No. 25, 1999 9155
Sch em e 1. Syn th esis of r-Tr isa cch a r id e
Sch em e 2. Syn th esis of th e r-Tr isa cch a r id e
Accep tor 7a
En a m id e Ester 17a
a
Conditions: (a) allyl phenyl sulfone, (Bu3Sn)2, PhH, hν, 53%;
(b) K2CO3, MeOH, 99%; (c) PhCHO, formic acid, 61%; (d) BzCl,
pyridine, 100%; (e) TFA, H2O 80%; (f) 2.0 equiv of BzCl, pyridine,
2 days, 100%.
a
(a) 7, 0.25 equiv of TMSOTf, CH2Cl2, 60%; (b) O3, then Me2S,
75%; (c) 16, TMG, THF, -78 °C; 65%; (d) (R,R)-Et-DuPHOS, THF,
90 psi of H2.
treatment of peracetylated lactose with BF3‚Et2O and
allyltrimethylsilane provides the required C-allyl lacto-
side 2 in 55% yield. In our hands the reaction was
complicated by low yields (<30%) and significant con-
tamination by the â-isomer. We thus turned to the radical
protocol of Magnusson and co-workers.17 Photochemically
initiated allylation of acetobromolactose (1) with allyl
phenyl sulfone and bistributyltin afforded the desired
R-analogue 2 exclusively, but in only moderate yield
(∼50%). Alterations of reaction conditions failed to sig-
nificantly improve the yield. Removal of the acetate
protecting groups was effected in quantitative yield with
K2CO3 in methanol (Scheme 1).
Sch em e 3. Syn th esis of TCE- or TMSE-P r otected
P h osp h on a te Ester a
With the installation of the R-C-allyl moiety complete,
it was necessary to differentially functionalize the dis-
accharide in preparation for addition of the terminal
R-galactosyl residue. Installation of the 4′,6′-di-O-ben-
zylidene by treatment of C-allyl lactoside 3 with benzal-
dehyde and formic acid followed by perbenzoylation
provided 5 in 61% yield for the two steps. Removal of
the benzylidene and selective benzoylation of the primary
hydroxyl provided the lactose-derived acceptor 7 in 24%
overall yield from lactose (Scheme 1). Coupling of the C4′
axial hydroxyl with perbenzylated galactosyl trichloro-
acetimidate 818 with TMSOTf promotion in dichlo-
romethane provided 9 in 66% yield (Scheme 2). Finally,
ozonolysis of the terminal furnished the required alde-
hyde in 78% yield.
Our previously reported strategy next required Hor-
ner-Emmons olefination to a glycine O-methyl ester-
derived phosphonate.12 While the methyl ester is com-
patible with hydrogenation, orthogonal deprotection
considerations render the product unsuitable for solid-
phase synthesis. Accordingly, we explored alternate
protecting group strategies.
a
Conditions: (a) 2,2,2-trichloroethanol, DMAP, DCC, 75%; (b)
2-(trimethylsilyl)ethanol, DMAP, DCC, 50%; (c) PCl3, then P(OMe)3,
88%; (d) 30% HBr/AcOH, then Boc2O, <8%. (e) Pd/C, H2, Boc2O,
MeOH, 98%.
deprotection. With these considerations in mind, trichlo-
roethyl esters (TCE) were investigated for carboxyl
protection. The TCE group is stable to both organic acids
and amine bases, permitting subsequent utilization of
either Boc or Fmoc amino protecting groups.19 The TCE
ester was installed using standard DCC coupling to
provide 11 in 71% yield.20,21 Treatment of 11 with PCl3
followed by P(OMe)3 afforded the ester 12 in 88% yield
(Scheme 3).
Catalytic asymmetric hydrogenation using the Du-
PHOS ligands requires amide or carbamate protection
of the enamide nitrogen.22 The conditions required for
amide hydrolysis preclude the use of amide protecting
groups. Although the phosphonate ester is initially
(19) (a) Woodward, R. B.; Heusler, K.; Gosteli, J .; Naegeli, P.;
Oppolzer, W.; Ramage, R.; Ranganathan, S.; Vorbruggen, H. J . Am.
Chem. Soc. 1966, 88, 852-4. (b) Carson, J . F. Synthesis 1979, 24-25.
(20) Preparation of methyl R-(dimethoxyphosphoryl)-N-tert-butyl-
oxycarbonylglycinate has been previously reported. (a) Zoller, U.; Ben-
Ishai, D. Tetrahedron 1975, 31, 863-6. (b) Schmidt, U.; Griesser, H.;
Leitenberger, V.; Lieberknecht, A.; Mangold, R.; Meyer, R.; Riedl, B.
Synthesis 1992, 487-490.
Ideal protecting groups for the enamide precursor
should be stable to phosphonate ester preparation (PCl3/
P(OMe)3), not interfere with asymmetric catalytic hydro-
genation, and be cleavable in the presence of carbohy-
drate acetate protecting groups. Additionally, the carboxyl
protecting group should be stable to tert-butyl carbamate
(21) Hamada, Y.; Kondo, Y.; Shibata, M.; Shioiri, T. J . Am. Chem.
Soc. 1989, 111, 669-673.
(22) (a) Burk, M. J .; Feaster, J . E.; Nugent, W. A.; Harlow, R. L. J .
Am. Chem. Soc. 1993, 115, 10125-10138. (b) Burk, M. J .; Harper, T.
G. P.; Kalberg, C. S. J . Am. Chem. Soc. 1995, 117, 4423-4424. (c) Burk,
M. J .; Gross, M. F.; Martinez, J . P. J . Am. Chem. Soc. 1995, 117, 9375-
9376. (d) Burk, M. J .; Wang, Y. M.; Lee, J . R. J . Am. Chem. Soc. 1996,
118, 5142-5143.
(16) Giannis, A.; Sandhoff, K. Tetrahedron Lett. 1985, 26, 1479-
1482.
(17) Ponten, F.; Magnusson, G. J . Org. Chem. 1996, 61, 7463-7466.
(18) Wegmann, B.; Schmidt, R. R. J . Carbohydr. Chem. 1987, 6,
357-375.

9156 J . Org. Chem., Vol. 64, No. 25, 1999
Debenham et al.
Sch em e 4. Syn th esis of th e r-Tr isa cch a r id e Glycosyla ted Ser in e Der iva tives 21 a n d 22a
a
(a) K2CO3, MeOH, 96%; (b) Ac2O, pyridine, DMAP, 93%; (c) O3, then Me2S, 75%; (d) 16, TMG, THF, -78 °C; 65%; (e) [(COD)Rh-
((S,S)-Et-DuPHOS)]+OTf-, 90 psi of H2, THF, 98% yield, >95% de; (f) [(COD)Rh-((R,R)-Et-DuPHOS)]+OTf-, 90 psi of H2, THF, 88%
yield, >95% de.
Sch em e 5. Syn th esis of â-Accep tor 27a
prepared N-protected as the benzyl carbamate, a protec-
tion strategy compatible with solid-phase peptide syn-
thesis was required. Accordingly, the Cbz amine protect-
ing group was converted to the corresponding tert-butyl
carbamate. Selective hydrogenolysis of benzyl carbamates
in the presence of TCE esters is not feasible due to
palladium/halogen exchange. Alternatively, cleavage of
the Cbz group was effected with HBr/HOAc. Immediate
treatment of the free amine with di-tert-butyl dicarbonate
(Boc2O) provided 13 in less than 8% yield. Numerous
attempts to increase the yield of this transformation were
unsuccessful, and the method was abandoned.
We next considered (trimethylsilyl)ethyl (TMSE) car-
boxyl protection. Conversion of 10b to the corresponding
TMSE ester 14 with (trimethylsilyl)ethanol and DCC
(Scheme 1) proceeded in 50% isolated yield. Conversion
a
Conditions: (a) (i) Rh(PPh3)3Cl, DABCO, (ii) HgO, HgCl2, 67%;
(b) DMSO, Ac2O, 95%; (c) allyl magnesium bromide, THF, 89%;
(d) Et3SiH, BF3Et2O, 73%.
to the phosphonate ester followed by catalytic hydro-
genolysis in the presence of Boc2O furnished the phos-
diastereomer 22, again in >95% stereoisomeric purity
(Scheme 4).
phonate ester 16 in 28% overall isolated yield for the
P r ep a r a tion of th e â-An a logu e of th e P k Tr isa c-
three steps. This phosphonate is both stable to all
ch a r id e. A parallel synthetic strategy that was utilized
for the successful synthesis of the R-C-glycosyl serine was
adopted for preparation of the â-analogue; accordingly,
conditions required for completion of the C-glycosyl serine
synthesis and appropriately protected for peptide syn-
thesis. We note parenthetically that reaction of the free
amine with Fmoc-chloroformate would produce the cor-
a synthesis of â-C-allyl lactose was required. Several
methods are available for installation of carbon function-
responding Fmoc-protected derivative.
ality to glycosides with exclusive equatorial selectivity.15
Horner-Emmons olefination of the unstable C-glycosyl
Our approach to this species followed the report of Kishi
that Grignard addition to a perbenzylated sugar lactone
followed by deoxygenation of the resulting hemiketal
aldehyde with phosphonate 16 at -78 °C furnished
enamide ester 17. Unfortunately, catalytic asymmetric
yields â-carbon-linked glycosides.24 To adapt this meth-
hydrogenation with either (R,R)-Et-DuPHOS or (R,R)-
Me-DuPHOS catalysts in THF at 90 psi of H2 failed
odology to our synthesis, the protected lactose-lactone
25 was required.
Allyl lactoside was converted to the 4′,6′-di-O-ben-
completely.22 Variation of solvent and reaction time also
failed to produce any reduced product (Scheme 2).
Our initial report of catalytic asymmetric hydrogena-
tion of glycosylated enamides utilized acetylated monosac-
charides. Accordingly, we decided to return to the less
sterically demanding protecting group. Methanolysis of
9 followed by immediate acetylation provided 19 in 89%
yield for the two steps. Ozonolysis of the alkene followed
by immediate Horner-Emmons olefination of the result-
ant aldehyde afforded 20 (Scheme 4).
With diminished steric bulk, enamide ester 20 was
reduced smoothly using the (S,S)-Et-DuPHOS catalyst
at 90 psi of H2 in THF for 48 h, providing the glycosylated
R-amino acid derivative 21 in 88% yield and >95%
diastereomeric excess.23 Alternatively, hydrogenation
with the R enantiomer of the catalyst provided the R
zylidene and perbenzylated to yield 23 according to
literature protocol.25 Removal of the allyl glycoside was
affected by treatment with Wilkinson’s catalyst (Rh-
[(PPh3)3]+Cl-) and diazabicyclo[2.2.2]octane (DABCO)
followed by HgO/HgCl2 hydrolysis of the vinyl ether
(Scheme 5).
Reducing sugar 24 was oxidized to the corresponding
lactone 25 in 98% yield with DMSO and acetic anhy-
dride.26 Treatment with allylmagnesium bromide in THF
at -78 °C produced the â-C-allyl lactose derivative 26
as an interconverting mixture of anomers.24,27 Deoxygen-
ation of the hemiketal with triethylsilane and BF3‚Et2O
(24) Lewis, M. D.; Cha, J . K.; Kishi, Y. J . Am. Chem. Soc. 1982,
104, 4976-4978.
(25) Dasgupta, R.; Anderson, L. Carbohydr. Res. 1994, 264, 155-
(23) Diastereomeric excess was determined by 1H NMR (300 or 400
MHz). The Si(CH3)3 and Boc peaks are almost baseline resolved in all
cases.
160.
(26) Kuzuhara, H.; Fletcher, H. G. J . Org. Chem. 1967, 32, 2531-
2534.

Serine Analogue of the Pk Trisaccharide
J . Org. Chem., Vol. 64, No. 25, 1999 9157
Sch em e 6. Syn th esis of â-Tr isa cch a r id e Glycosyla ted Ser in e Der iva tives 30 a n d 31a
a
Conditions: (a) 8, TMSOTf, Et2O, 64%; (b) O3, then Me2S, 69%; (c) 16, TMG, THF, -78 °C, 84%; (d) (R,R)-Et-DuPHOS, THF, 90 psi
of H2, 98% yield, >95% de; (e) (S,S)-Et-DuPHOS, THF, 90 psi of H2, 98% yield, >95% de.
Sch em e 7. Dep r otection of th e Ca r boxylic Acid s
proceeded smoothly with concomitant reduction of the
benzylidene to directly afford the desired acceptor 27.
Although literature precedent exists for the reduction of
a benzylidene with Et3SiH and TFA, we are unaware of
prior use of BF3‚Et2O in this regard.28 Indeed, TFA
catalysis failed to effect the selective benzylidene reduc-
tion on galactose-derivated substrates. We are currently
exploring the scope of these reaction conditions and will
report our results in due course.
34 a n d 35a
Coupling of acceptor 27 with the galactosyl trichloro-
acetimidate donor 8 in diethyl ether provided the per-
benzylated trisaccharide 28 in 84% yield. Use of dichlo-
romethane as a solvent resulted in minor contamination
of 28 with the â-isomer. Ozonolysis of the C-allyl glyco-
side and Horner-Emmons olefination as before provided
enamide ester 29 for catalytic asymmetric hydrogenation
(Scheme 6).
Asymmetric hydrogenation with the (R,R)-Et-DuPHOS
catalyst in THF afforded the R diastereomer 30 in
excellent yield and selectivity (>95% de). The S diaste-
reomer 31 was also isolated in >95% de after hydrogena-
tion with the S enantiomer of the catalyst. Alternatively,
catalytic hydrogenation of the acetylated â-trisaccharide
enamide under the same conditions proceeds with a
diastereomeric excess of only 52%. This result was
somewhat surprising in light of the previous observation
that the perbenzoylated derivative of the R-anomer failed
to react under equivalent hydrogenation conditions. In
contrast, asymmetric hydrogenation of peractylated
monosaccharides proceeds in excellent diastereoselectiv-
ity (>95%). Apparently a complex and subtle interplay
of steric and electronic effects control diastereoselectivi-
ties during RhDuPHOS-catalyzed hydrogenations, and
a thorough exploration of substrate-catalyst interactions
is required to achieve high stereoselectivity.
To complete the synthesis of a trisaccharide derivative
compatible with solid-phase peptide synthesis, the benzyl
ether protecting groups were removed and replaced with
acetates, producing both the R (32) and S (33) diaster-
eomers in good yield. Finally, removal of the TMSE ester
with TBAF provided the free carboxylic acids 34 and 35,
ready for peptide coupling (Scheme 7).
In conclusion, we have utilized catalytic asymmetric
hydrogenation methodology to produce four diastereo-
mers of the Pk trisaccharide as the C-glycosyl serine
derivative. The synthesis is concise and expeditious, and
a
Conditions: (a) Pd/C, MeOH/THF, 90 psi of H2, then Ac2O,
pyridine, 76% (32R), 66% (33S); (b) TBAF, 88% (34R), 99% (35S).
amenable to scale-up. Our development of a novel phos-
phonate ester provides C-glycosyl serines appropriately
protected for solid-phase peptide synthesis. Using the
reported methodology, we have prepared C-glycosyl
amino acid derivatives suitable for peptide synthesis on
a multigram scale. Additionally, the tolerance of the
DuPHOS-Rh catalyst was tested with respect to three
various hydroxyl protecting groups. The complex results
of this study reveal that no simple prescription for
effective hydrogenation exists. Finally, we have reported
a novel synthetic methodology for the regioselective
reduction of the 4,6-di-O-benzylidene protecting group.
We are currently evaluating the activity of the C-glycosyl
serine adducts as ligands for the SLT and will report our
results in due course.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were conducted under an
inert argon atmosphere. THF and diethyl ether were distilled
from sodium benzophenone ketyl. Dichloromethane was dis-
tilled from calcium hydride. Methanol was distilled from
magnesium. Solutions of compounds in organic solvents were
dried over sodium sulfate prior to rotary evaporation. DMF
was 99.5% pure and anhydrous (Amresco). Benzyl bromide was
filtered through alumina prior to use. TLC plates were
Kieselgel 60 F254 (Merck Art. 5554). Carbohydrate compounds
were visualized on TLC by charring with H2SO4/EtOH/H2O
(1:10:10). Flash column chromatography was done with silica
gel 60 (230-400 mesh, Merck). Although not technically
correct, compounds are named as derivatives of the corre-
sponding O-glycosides for ease of identification.
(27) (a) Czernecki, S.; Ville, G. J . Org. Chem. 1989, 54, 610-612.
(b) Lewis, M. D.; Cha, J . K.; Kishi, Y. J . Am. Chem. Soc. 1982, 104,
4976-4978.
(28) DeNinno, M. P.; Etienne, J . B.; Duplantier, K. C. Tetrahedron
Lett. 1995, 36, 669-672.

9158 J . Org. Chem., Vol. 64, No. 25, 1999
Debenham et al.
P r ep a r a tion of th e Tr isa cch a r id e r-Accep tor . 1-(O-
(2,3,4,6-Tetr a -O-a cetyl-â-D-ga la ctop yr a n osyl)-(1f4)-2,3,6-
tr i-O-a cetyl-r-D-glu cop yr a n osyl)-2-p r op en e (2). To a so-
lution of acetobromolactose 1 (2.40 g, 3.40 mmol) in toluene
(7.0 mL) and CH2Cl2 (2.0 mL) were added allyl phenyl sulfone
(3.0 equiv, 1.6 mL) and bistributyltin (1.4 equiv, 2.42 mL). The
solution was degassed with argon for 30 min before being
irradiated with a mercury lamp for 15 h. The solution was
concentrated and purified via chromatography eluting with 1:1
petroleum ether/EtOAc. 2 (1.19 g, 53%) was isolated as a white
17.2 Hz, 1H), 4.98-4.95 (dd, J ) 0.8, 10.6 Hz, 1H), 4.89-4.87
(d, J ) 8.4 Hz, 1H), 4.48-4.45 (dd, J ) 2.4, 11.4 Hz, 1H), 4.41-
4.35 (ddd, J ) 3.3, 3.9, 12.3 Hz, 1H), 4.32-4.28 (m, 1H), 4.13-
4.09 (t, J ) 8.0 Hz, 1H), 4.00-3.95 (m, 1H), 3.87-3.83 (dd, J
) 1.2, 12.4 Hz, 1H), 3.61-3.58 (dd, J ) 2.0, 12.0 Hz, 1H), 3.00
(s, 1H), 2.73-2.65 (m, 1H), 2.42-2.35 (m, 1H); 13C NMR (100
MHz, CDCl3) δ 188.88, 166.11, 165.57, 164.88, 161.07, 137.42,
133.32, 133.21, 133.08, 132.96, 129.88, 129.65, 129.60, 129.56,
128.90, 128.76, 128.50, 128.42, 128.34, 127.92, 126.33, 117.84,
101.69, 100.59, 77.47, 73.10, 72.63, 72.25, 71.81, 71.76, 69.58,
69.46, 68.07, 66.47, 62.84, 34.02, 30.43. Anal. Calcd for
1
foam: Rf ) 0.52 (1:1 EtOAc/petroleum ether); H NMR (600
MHz, CDCl3) δ 5.74-5.64 (m, 1H), 5.37-5.34 (m, 2H), 5.15-
5.09 (m, 3H), 4.99-4.97 (dd, J ) 5.2, 8.6 Hz, 1H), 4.96-4.96
(m, 1H), 4.51-4.50 (d, J ) 7.6 Hz, 1H), 4.35-4.33 (dd, J )
2.4, 11.6 Hz, 1H), 4.18-4.15 (dd, J ) 5.2, 10.5 Hz, 1H), 4.14-
4.08 (m, 3H), 3.90-3.88 (br t, J ) 6.8 Hz, 1H), 3.82-3.79 (m,
1H), 3.63-3.60 (t, J ) 7.6 Hz, 1H), 2.52-2.44 (m, 1H), 2.30-
2.17 (m, 1H), 2.11 (s, 3H), 2.05 (s, 3H), 2.02 (s, 3H), 2.01 (br s,
6H), 2.01 (s, 3H), 1.92 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
170.37, 170.31, 170.05, 169.99, 169.86, 169.53, 169.11, 133.02,
117.71, 101.27, 76.52, 71.43, 70.95, 70.67, 69.98, 69.73, 66.66,
62.21, 60.83, 30.97, 20.83, 20.77, 20.70, 20.58, 20.46.
C
57H50O15: C, 70.22; H, 5.17. Found: C, 70.15; H, 5.21.
1-((2,3-Di-O-ben zoyl-â-D-ga la ctop yr a n osyl)-(1f4)-2,3,6-
tr i-O-ben zoyl-r-D-glu cop yr a n osyl)-2-p r op en e (6). To a
solution of 5 (171.6 mg, 0.1765 mmol) in CH2Cl2 (2.0 mL) were
added water (2 drops) and trifluoroacetic acid (204 µL, 2.65
mmol). The reaction mixture was stirred at 25 °C for 5 h,
diluted with CH2Cl2, washed with water and saturated aque-
ous NaHCO3, dried (MgSO4), and concentrated. Purification
via flash chromatography eluting with a gradient of 1:9 to 2:8
EtOAc/CH2Cl2 provided 6 as a white foam (124.8 mg, 80%):
Rf ) 0.40 (1:1 EtOAc/petroleum ether); [R]20 +86.2° (c 1.00,
D
1-(â-D-Ga la ctop yr a n osyl-(1f4)-r-D-glu cop yr a n osyl)-2-
p r op en e (3). To a 1.0 M solution of NaOCH3 at 0 °C was
added a solution of 2 (1.858 g, 2.82 mmol) in anhydrous MeOH
(6.0 mL). The reaction mixture was stirred at 25 °C for 15 h
and then quenched by the addition of Dowex acid resin until
the pH was neutral by pH paper. The solution was filtered
and concentrated in vacuo to yield 3 as a pale yellow foam
(1.1 g), which was used without further purification: 1H NMR
(400 MHz, D2O) δ 5.73-5.65 (m, 1H), 5.08-5.04 (br d, J ) 9.0
Hz, 1H), 5.01-4.98 (br d, J ) 9.0 Hz, 1H), 4.31-4.29 (d, J )
7.6 Hz, 1H), 3.96-3.91 (ddd, J ) 3.0, 3.8, 12.6 Hz, 1H), 3.78-
3.77 (d, J ) 3.2 Hz, 1H), 3.74-3.37 (m, 12H), 2.39-2.24 (m,
2H); 13C NMR (100 MHz, D2O) δ 134.43, 117.43, 102.83, 79.04,
75.27, 74.75, 72.45, 71.63, 71.15, 70.85, 70.63, 68.44, 60.91,
60.09, 28.86. HRMS m/e calcd for M + Na 389.152597, found
389.1424.
CHCl3); 1H NMR (400 MHz, CDCl3) δ 8.05-8.02 (m, 4H), 7.91-
7.89 (m, 5H), 7.57-7.52 (m, 4H), 7.47-7.37 (m, 6H), 7.33-
7.27 (m, 4H), 7.22-7.18 (m, 2H), 6.04-6.00 (t, J ) 7.6 Hz, 1H),
5.78-5.67 (m, 2H), 5.41-5.38 (dd, J ) 4.8, 7.8 Hz, 1H), 5.14-
5.11 (dd, J ) 3.2, 10.0 Hz, 1H), 5.07 (s, 1H), 4.98-4.95 (d, J )
10.0 Hz, 1H), 4.88-4.86 (d, J ) 8.0 Hz, 1H), 4.52-4.48 (dd, J
) 6.4, 11.8 Hz, 1H), 4.44-4.40 (m, 2H), 4.22-4.21 (d, J ) 2.8
Hz, 1H), 4.15-4.10 (m, 1H), 4.03-4.00 (t, J ) 6.8 Hz, 1H),
3.54-3.44 (m, 3H), 2.89 (br s, 1H), 2.73-2.65 (m, 1H), 2.43-
2.03 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 165.88, 165.74,
165.47, 165.16, 133.56, 133.49, 133.23, 133.06, 129.84, 129.75,
129.59, 129.53, 129.39, 129.12, 128.99, 128.90, 128.62, 128.55,
128.29, 128.22, 117.84, 101.98, 76.90, 74.56, 71.29, 70.76,
70.54, 70.11, 69.67, 67.91, 62.73, 62.25, 31.42. Anal. Calcd for
C
50H46O15: C, 67.70; H, 5.23. Found: C, 67.63; H, 5.30.
1-((2,3,6-Tr i-O-b en zoyl-â-D-ga la ct op yr a n osyl)-(1f4)-
1-((4,6-O-Ben zylid en e-â-D-ga la ct op yr a n osyl)-(1f4)-r-
D-glu cop yr a n osyl))-2-p r op en e (4). Benzaldehyde and formic
acid were freshly distilled prior to use. To a solution of 3 (77.6
mg, 0.212 mmol) in 99% formic acid (175 µL) was added
benzaldehyde (375 µL). The reaction mixture was stirred for
45 min at 25 °C. After removal of formic acid by rotary
evaporation, NEt3 (0.5 mL) was added. The remaining solvents
were removed in vacuo. The compound was purified via flash
chromatography eluting with 8:1 EtOAc/MeOH, affording 4
as a colorless oil (58.5 mg, 61% yield): Rf ) 0.56 (1:4 MeOH/
CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 7.46-7.14 (m, 5H),
5.74-5.65 (m, 1H), 5.40 (s, 1H), 5.17 (br s, 1H), 5.06-5.01 (m,
2H), 4.52 (br s, 1H), 4.43-4.41 (d, J ) 8.0 Hz, 1H), 4.25 (br s,
1H), 4.16-4.13 (d, J ) 12.0 Hz, 1H), 4.00-3.83 (m, 4H), 3.67-
3.53 (m, 4H), 3.40-3.38 (d, J ) 8.4 Hz, 1H), 3.31 (s, 1H), 2.30
(br s, 1H); 13C NMR (100 MHz, CDCl3) δ 137.18, 134.67, 129.26,
129.00, 128.49, 128.18, 126.31, 125.26, 116.90, 102.38, 101.34,
75.53, 75.14, 73.161, 72.03, 71.17, 69.07, 66.94, 61.57, 28.89.
Anal. Calcd for C22H30O10‚H2O: C, 55.94; H, 6.83. Found: C,
55.43; H, 6.79.
2,3,6-tr i-O-ben zoyl-r-D-glu cop yr a n osyl)-2-p r op en e (7). To
a solution of 6 (148.4 mg, 0.168 mmol) in pyridine (6.0 mL) at
0 °C was added 4-(dimethylamino)pyridine (3.2 mg, 15 mol
%). Benzoyl chloride (19.5 µL, 0.168 mmol) was added drop-
wise. The solution was stirred for 3 h at 0 °C and 15 h at 25
°C. At this time, TLC (1:1 petroleum ether/EtOAc) showed
approximately 50% conversion to product. A second equivalent
of benzoyl chloride was added, and the reaction mixture was
allowed to stir at 25 °C for 20 h. Benzoyl chloride (40 µL, 2.0
eq) was added, and the reaction was stirred for 24 h. After
dilution with CH2Cl2 the organic layer was washed with water,
1 M HCl, and saturated aqueous NaHCO3, dried, and concen-
trated. Purification via flash chromatography eluting with 1:1
petroleum ether/EtOAc provided 7 as a white foam (186.7 mg,
100%). Rf ) 0.6 (1:1 petroleum ether/EtOAc); [R]20 +67.8° (c
D
1.00, CHCl3); 1H NMR (400 MHz, CDCl3) δ 8.02-7.91 (m, 10H),
7.57-7.19 (m, 20H), 6.00-5.96 (t, J ) 8.9 Hz, 1H), 5.83-5.68
(m, 2H), 5.49-5.45 (dd, J ) 5.8, 9.2 Hz, 1H), 5.24-5.21 (dd, J
) 3.1, 10.2 Hz, 1H), 5.12-5.08 (d, J ) 17.1 Hz, 1H), 5.00-
4.97 (d, J ) 10.3 Hz, 1H), 4.90-4.88 (d, J ) 7.9 Hz, 1H), 4.55-
4.45 (m, 3H), 4.27-4.22 (m, 2H), 4.17-4.07 (m, 2H), 3.84-
3.79 (m, 2H), 2.90 (br s, 1H), 2.79-2.71 (m, 1H), 2.43-2.39
(m, 1H); 13C NMR (100 MHz, CDCl3) δ 165.94, 165.80, 165.72,
165.53, 165.36, 165.02, 133.30, 133.25, 133.17, 133.11, 133.05,
132.98, 129.75, 129.72, 129.52, 129.48, 128.96, 128.82, 128.76,
128.37, 128.27, 128.23, 128.21, 117.70, 101.49, 76.75, 74.28,
74.28, 72.66, 72.06, 71.11, 70.53, 70.08, 69.64, 66.69, 62.80,
62.17, 30.49. Anal. Calcd for C57H50O16: C, 69.08; H, 5.09.
Found: C, 68.99; H, 5.37.
1-((2,3-Di-O-ben zoyl-4,6-ben zylid en e-â-D-ga la ctop yr a -
n osyl)-(1f4)-2,3,6-t r i-O-b en zoyl-r-D-glu cop yr a n osyl)-2-
p r op en e (5). To a solution of 4 (740.2 mg, 1.63 mmol) in dry
pyridine (11.0 mL) was added 4-(dimethylamino)pyridine (40
mg, 20 mol %). After the reaction mixture was cooled to 0 °C,
benzoyl chloride (1.9 mL, 16.3 mmol) was added dropwise. The
reaction was stirred for 24 h, during which time the solution
warmed to 25 °C. After dilution with CH2Cl2, the organic layer
was washed with water, 1 M HCl, and saturated aqueous
NaHCO3 and dried (MgSO4). Recrystallization from petroleum
ether/EtOAc yielded 5 as a pale yellow solid (1.592 g, 100%):
1-((2,3,4,6-Tetr a-O-ben zyl-r-D-galactopyr an osyl)-(1f4)-
(2,3,6-tr i-O-ben zoyl-â-D-ga la ctop yr a n osyl)-(1f4)-2,3,6-tr i-
O-ben zoyl-r-D-glu cop yr a n osyl)-2-p r op en e (9). 7 and 8
were azeotroped with toluene (3 × 5 mL) and dried in vacuo
for 15 h prior to use. Molecular sieves (4 Å) (∼20 mg) were
added to each flask. To a solution of acceptor 7 (77.0 mg, 0.078
mmol) in CH2Cl2 (2 mL, 0.04 M) at -5 °C was added TMSOTf
(0.25 equiv, 3.9 µL). A solution of donor 8 (104.6 mg, 2 equiv)
Rf ) 0.73 (1:1 EtOAc/petroleum ether); [R]20 +69.1° (c 1.01,
D
CHCl3); 1H NMR (400 MHz, CDCl3) δ 8.04-7.83 (m, 10H),
7.55-7.25 (m, 18H), 7.15-7.11 (t, J ) 7.6 Hz, 2H), 6.02-5.97
(t, J ) 8.0 Hz, 1H), 5.81-5.76 (dd, J ) 8.4, 10.4 Hz, 1H), 5.71-
5.62 (m, 2H), 5.36-5.32 (dd, J ) 5.6, 9.6 Hz, 1H), 5.30 (s, 1H),
5.19-5.15 (dd, J ) 4.0, 10.6 Hz, 1H), 5.11-5.06 (dd, J ) 1.6,

Serine Analogue of the Pk Trisaccharide
J . Org. Chem., Vol. 64, No. 25, 1999 9159
in CH2Cl2 (5.2 mL, 0.015 M) was added via cannula over 1.5
h. After the addition, TMSOTf (0.1 equiv, 2 µL) was added
and the solution warmed to 25 °C over 6 h. Following the
addition of NaHCO3, the solution was filtered and concen-
trated. Purification via flash chromatography eluting with 3:1
petroleum ether/EtOAc (Rf ) 0.3) afforded 9 as a white foam
toluene and dried in vacuo for 15 h prior to use. 14 (3.641 g,
10.7 mmol) was dissolved in toluene (135 mL) and heated to
70 °C before the addition of PCl3 (1.0 equiv, 0.934 mL). The
reaction was stirred for 15 h before the dropwise addition of
P(OMe)3 (1.0 equiv, 1.26 mL). The reaction was stirred for 2 h
before removal of the solvent by rotary evaporation. The
residue was dissolved in CH2Cl2, washed with saturated
NaHCO3, dried (MgSO4), and concentrated. Purification via
flash chromatography eluting with a gradient of 2:1 to 1:1
petroleum ether/EtOAc provided 15 (3.826 g, 88%) as a
colorless oil: Rf ) 0.10 (1:2 EtOAc/petroleum ether); 1H NMR
(400 MHz, CDCl3) δ 7.50-7.45 (m, 5H), 5.75-5.73 (br d, J )
8.0 Hz, 1H), 5.28-5.27 (m, 2H), 5.06-4.98 (dd, J ) 9.2, 14.8
Hz, 1H), 4.47-4.42 (m, 2H), 3.97 (s, 2H), 3.94 (s, 1H), 3.93 (s,
2H), 3.91 (s, 1H), 1.41-1.17 (m, 2H), 0.179 (s, 9H); 13C NMR
(100 MHz, CDCl3) δ 166.65, 155.55, 135.78, 128.21, 128.44,
128.04, 67.48, 65.14, 54.02, 53.96, 52.90, 51.43, 18.25, -1.68.
Anal. Calcd for C17H28NO7PSi: C, 48.91; H, 6.76; N, 3.36.
Found: C, 48.85; H, 6.82; N, 3.31.
2-(Tr im et h ylsilyl)et h yl r-(Dim et h oxyp h osp h or yl)-N-
ter t-bu tyloxyca r bon ylglycin a te (16). To a solution of 15
(95.3 mg, 0.228 mmol) in anhydrous MeOH (3.0 mL) was added
Boc2O (1.5 equiv, 75 mg). The solution was degassed with
argon for 20 min before the addition of 10% Pd/C (5 mol %,
12.1 mg). The vessel was pressurized to 90 psi of H2 and stirred
vigorously for 15 h. The reaction was filtered through Celite
and concentrated. Purification via flash chromatography elut-
ing with a gradient of 1:1 to 2:1 EtOAc/petroleum ether
provided 16 (60.6 mg, 98%) as a white solid: Rf ) 0.60 (1:1
EtOAc/petroleum ether), visualized with KMnO4; 1H NMR (400
MHz, CDCl3) δ 5.33-5.31 (br d, J ) 8.0 Hz, 1H), 4.82-4.74
(dd, J ) 9.2, 22.4 Hz, 1H), 4.27-4.23 (m, 2H), 3.79 (s, 2H),
3.78 (s, 1H), 3.76 (s, 2H), 3.75 (s, 1H), 1.39 (s, 9H), 1.03 (m,
2H), -0.01 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 166.91, 80.73,
64.97, 53.93, 53.86, 52.48, 51.01, 28.10, 17.26, -1.67. Anal.
Calcd for C14H30NO7PSi: C, 43.98; H, 7.89; N, 3.54. Found:
C, 43.98; H, 7.90; N, 3.54.
1-((2,3,4,6-Tetr a -O-ben zyl-r-D-ga la ctop yr a n osyl)-(1f4)-
(â-D-ga la ctop yr a n osyl)-(1f4)-r-D-glu cop yr a n osyl)-2-p r o-
p en e (18). To a solution of 9 (275.2 mg, 0.182 mmol) in
anhydrous MeOH (2.0 mL) and THF (2.5 mL) was added K2-
CO3 (20 mg, 0.8 equiv). The reaction was stirred at 25 °C for
15 h, filtered through Celite, and concentrated. Purification
via flash chromatography eluting with 15% MeOH/85% CH2-
Cl2 afforded 18 as a colorless oil (154.6 mg, 96%): Rf ) 0.7
(20% MeOH/80% CH2Cl2); [R]20D 13.2 (c 0.80, CHCl3); 1H NMR
(400 MHz, CD3OD) δ 7.31-7.14 (m, 20H), 5.83-5.73 (m, 1H),
5.06-5.01 (d, J ) 17.2 Hz, 1H), 4.98-4.96 (d, J ) 10 Hz, 1H),
4.93-4.92 (d, J ) 2.4 Hz, 1H), 4.76-4.62 (m, 5H), 4.46-4.29
(m, 5H), 3.95-3.85 (m, 5H), 3.81-3.66 (m, 5H), 3.64-3.52 (m,
5H), 3.5-3.39 (m, 5H); 13C NMR (100 MHz, CD3OD) δ 140.00,
139.60, 139.42, 136.43, 134.20, 130.45, 129.56, 129.40, 129.29,
129.20, 129.10, 128.78, 128.61, 116.98, 105.40, 101.21, 82.02,
80.24, 79.82, 77.67, 76.87, 76.65, 76.25, 75.88, 74.82, 74.71,
74.37, 73.57, 72.83, 72.70, 72.59, 71.33, 69.78, 62.25, 62.04,
30.53; HRMS m/e calcd for (M + H)+ 889.3932, found 889.4040.
1-((2,3,4,6-Tetr a -O-ben zyl-r-D-ga la ctop yr a n osyl)-(1f4)-
(2,3,6-tr i-O-a cetyl-â-D-ga la ctop yr a n osyl)-(1f4)-2,3,6-tr i-
O-a cetyl-r-D-glu cop yr a n osyl)-2-p r op en e (19). To a solution
of 18 (141.8 mg, 0.160 mmol) in pyridine (3.5 mL) were added
Ac2O (0.20 mL, 12 equiv) and DMAP (0.5 equiv, 17 mg). The
reaction was stirred for 15 h, diluted with CH2Cl2, and washed
with 1 M HCl and saturated NaHCO3. Purification via flash
chromatography eluting with 2:1 petroleum ether/EtOAc
(66.6 mg, 60%): Rf ) 0.6 (1:1 petroleum ether/EtOAc); [R]20
D
+53.1° (c 1.10, CHCl3); 1H NMR (400 MHz, CDCl3) δ 8.11-
7.01 (m, 50H), 5.94-5.89 (t, J ) 9.2 Hz, 1H), 5.81-5.65 (m,
2H), 5.51-5.47 (dd, J ) 5.8, 9.5 Hz, 1H), 5.37-5.34 (dd, J )
3.1, 15.2 Hz, 1H), 5.26-5.23 (d, J ) 11.6 Hz, 1H), 5.19 (s, 1H),
5.13-5.05 (m, 1H), 4.98-4.93 (m, 1H), 4.83-4.81 (d, J ) 7.5
Hz, 1H), 4.75-4.38 (m, 8H), 4.33-3.93 (m, 9H), 3.65-3.62 (t,
J ) 6.4 Hz, 1H), 3.29-3.24 (t, J ) 8.8 Hz, 1H), 2.93-2.90 (dd,
J ) 4.0, 8.8 Hz, 1H), 3.26-3.23 (m, 2H), 2.75-2.67 (m, 1H),
2.42-2.38 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 165.71,
165.66, 165.63, 165.34, 164.57, 139.21, 138.82, 138.44, 137.75,
133.23, 133.16, 132.98, 130.12, 129.69, 129.56, 128.41, 128.34,
128.22, 128.16, 128.14, 128.07, 127.95, 127.92, 127.58, 127.50,
127.41, 127.37, 127.32, 127.71, 127.01, 117.64, 104.00, 100.98,
81.50, 79.25, 75.86, 75.09, 74.88, 74.78, 73.91, 73.26, 73.18,
72.88, 72.77, 72.52, 72.29, 72.08, 70.87, 70.50, 70.28, 69.91,
68.19, 62.94, 62.78, 30.43, 20.90, 14.08. HRMS m/e calcd for
(M - H)+ 1511.5505, found 1511.5471.
2,2,2 Tr ich lor oeth yl r-Meth oxy-N-ben zyloxyca r bon -
ylglycin a te (11). 10a (167.6 mg, 0.701 mmol), 2,2,2-trichlo-
roethanol (1.2 equiv, 83.4 µL), and DMAP (0.5 equiv, 42.9 mg)
were dissolved in CH2Cl2 (3.5 mL) and cooled to 0 °C. DCC
(1.2 equiv, 173.4 mg) was added, and the reaction was allowed
to warm to 25 °C over 15 h. The reaction was filtered through
Celite, diluted with CH2Cl2, washed with 1.0 N HCl, water,
and saturated Na2CO3, and dried. Purification via column
chromatography eluting with 2:1 petroleum ether/EtOAc af-
forded 11 as a pale yellow oil (190 mg, 75%): 1H NMR (400
MHz, CDCl3) δ 7.38-7.32 (m, 5H), 6.04-6.02 (br d, J ) 8.0,
1H), 5.49-5.46 (d, J ) 7.2, 1H), 5.15 (s, 2H), 4.81 (s, 2H), 3.50
(s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.09, 155.46, 135.56,
128.49, 128.31, 128.10, 93.97, 80.55, 74.49, 67.42, 56.56.
2,2,2-Tr ich lor oeth yl r-(Dim eth oxyp h osp h or yl)-N-ben -
zyloxyca r bon ylglycin a te (12). 11 was azeotroped with
toluene and dried in vacuo for 15 h prior to use. 11 (5.00 g,
13.5 mmol) was dissolved in PhCH3 (135 mL), and the solution
was heated to 70 °C. PCl3 (1 equiv, 1.18 mL) was added, and
the solution was stirred at 70 °C for 15 h. P(OMe)3 (1 equiv,
1.60 mL) was added, and the reaction was stirred for 2 h before
removal of solvent by rotary evaporation. The residue was
diluted with CH2Cl2 and washed with water, saturated aque-
ous NaHCO3, and brine. The organic layer was dried (MgSO4)
and concentrated. Recrystallization from EtOH yielded 12
(3.726 g, 71% yield) as a white solid: 1H NMR (400 MHz,
CDCl3) δ 7.39-7.30 (m, 5H), 5.80-5.78 (br d, J ) 6.0 Hz, 1H),
5.15 (s, 2H), 5.12-5.07 (m, 1H), 5.03-5.01 (d, J ) 8.0 Hz, 1H),
4.90-4.87 (d, J ) 12.0 Hz, 1H), 4.80-4.77 (d, J ) 12.0 Hz,
1H), 3.85 (s, 1H), 3.84 (s, 2H), 3.82 (s, 1H), 3.81 (s, 2H); 13C
NMR (100 MHz, CDCl3) δ 135.64, 128.52, 128.34, 128.12,
75.01, 74.57, 67.75, 54.28, 54.03, 52.77, 51.29.
2-(Tr im eth ylsilyl)eth yl r-Meth oxy-N-ben zyloxyca r bo-
n ylglycin a te (14). 10b was azeotroped with toluene and dried
under high vacuum for 15 h prior to use. To a solution of 10b
(325 mg, 1.36 mmol), DMAP (0.5 equiv, 140 mg), and 2-(tri-
methylsilyl)ethanol (2 equiv, 0.400 mL) in CH2Cl2 (0.2 M, 7
mL) at 0 °C was added DCC (1.2 equiv, 199 mg). The reaction
was allowed to warm to 25 °C over 15 h. The solution was
filtered through Celite, concentrated, and purified via flash
chromatography eluting with 3:1 petroleum ether/EtOAc to
afford 14 (224.8 mg, 50%) as a colorless oil: Rf ) 0.5 (1:3
provided 19 (169.5 mg, 93%) as a colorless foam: Rf ) 0.6 (1:1
1
petroleum ether/EtOAc); [R]20 41.9 (c 1.00, CHCl3); H NMR
D
1
EtOAc/petroleum ether); H NMR (400 MHz, CDCl3) δ 7.36-
(400 MHz, CDCl3) δ 7.43-7.22 (m, 20H), 5.78-5.68 (m, 1H),
5.34-5.30 (t, J ) 9.2 Hz, 1H), 5.18-5.08 (m, 3H), 5.01-4.97
(dd, J ) 5.6, 9.2 Hz, 1H), 4.93-4.90 (d, J ) 11.2 Hz, 1H), 4.83-
4.75 (m, 4H), 4.69-4.66 (d, J ) 11.6 Hz, 1H), 4.57-4.55 (d, J
) 11.2 Hz, 1H), 4.51-4.36 (m, 5H), 4.31-4.27 (m, 2H), 4.21-
4.16 (m, 2H), 4.13-4.03 (m, 2H), 3.99-3.98 (d, J ) 2.4 Hz,
1H), 3.79-3.75 (m, 1H), 3.69-3.60 (m, 4H), 3.45-3.42 (m, 2H),
2.61-2.45 (m, 1H), 2.37-2.22 (m, 1H), 2.09 (s, 3H), 2.05 (s,
3H), 2.03 (s, 3H), 2.02 (s, 3H), 1.92 (s, 3H), 1.87 (s, 3H); 13C
7.29 (m, 5H), 6.03-6.01 (br d, J ) 9.2 Hz, 1H), 5.33-5.30 (br
d, J ) 9.2 Hz, 1H), 5.14 (s, 2H), 4.27-4.25 (m, 2H), 3.45 (s,
3H), 1.06-1.02 (m, 2H), 0.042 (s, 9H); 13C NMR (100 MHz,
CDCl3) δ 167.51, 155.62, 135.71, 128.43, 128.19, 128.03, 80.66,
67.18, 64.51, 56.07, 17.15, -1.69; HRMS (FAB) calcd for (M +
Na)+ C15H23NO5SiNa 348.1243, found 348.1237.
2-(Tr im et h ylsilyl)et h yl r-(Dim et h oxyp h osp h or yl)-N-
ben zyloxyca r bon ylglycin a te (15). 14 was azeotroped with

9160 J . Org. Chem., Vol. 64, No. 25, 1999
Debenham et al.
NMR (100 MHz, CDCl3) δ 170.66, 170.39, 170.32, 169.87,
169.81, 169.80, 138.78, 138.71, 138.12, 137.93, 133.13, 128.41,
128.29, 128.26, 128.20, 128.09, 128.05, 127.95, 127.62, 127.59,
127.37, 127.29, 117.63, 101.31, 101.26, 79.17, 76.58, 75.86,
75.40, 74.91, 74.58, 74.12, 73.29, 72.82, 72.52, 72.37, 71.70,
70.11, 69.90, 67.56, 62.30, 61.19, 30.72, 20.79, 20.73, 20.68,
20.57. Anal. Calcd for C61H72O22: C, 64.20; H, 6.36. Found:
C, 63.93; H, 6.41.
[R]20 +50.2° (c 1.01, CHCl3); 1H NMR (300 MHz, CDCl3) δ
D
7.25-7.01 (m, 20H), 5.12-5.07 (t, J ) 9.0 Hz, 1H), 5.00-4.98
(d, J ) 7.5 Hz, 1H), 4.97-4.94 (d, J ) 7.5 Hz, 1H), 4.80-4.77
(m, 1H), 4.75-4.71 (d, J ) 11.4 Hz, 1H), 4.64-4.47 (m, 6H),
4.40-4.36 (d, J ) 11.4 Hz, 1H), 4.27-4.22 (m, 7H), 4.18-4.18
(d, J ) 2.4 Hz, 1H), 4.13-4.01 (m, 3H), 3.97-3.87 (m, 7H),
3.81-3.80 (d, J ) 2.7 Hz, 1H), 3.54-3.40 (m, 5H), 3.27-3.23
(dd, J ) 4.8, 8.4 Hz, 1H), 1.93 (s, 3H), 1.87 (s, 3H), 1.85 (s,
3H), 1.83 (s, 3H), 1.74 (s, 3H), 1.68 (s, 3H), 1.26 (s, 9H), 0.85-
0.79 (m, 2H), -0.14 (s, 9H); 13C NMR (75 MHz, CDCl3) δ
172.07, 170.36, 170.02, 169.53, 169.44, 168.41, 154.96, 138.58,
138.50, 137.91, 137.74, 128.23, 128.04, 127.89, 127.85, 127.74,
127.38, 127.08, 101.25, 101.18, 79.66, 79.07, 76.38, 75.76,
75.31, 74.82, 74.52, 74.03, 73.18, 72.75, 72.44, 72.31, 71.93,
69.96, 69.45, 67.48, 63.70, 62.11, 61.11, 53.17, 28.49, 28.23,
2-(Tr im eth ylsilyl)eth yl 1-((2,3,4,6-Tetr a -O-ben zyl-r-D-
ga la ct op yr a n osyl)-(1f4)-(2,3,6-t r i-O-a cet yl-â-D-ga la ct o-
p yr a n osyl)-(1f4)-2,3,6-tr i-O-a cetyl-r-D-glu cop yr a n osyl)-
2-en e-2-(N-ter t-bu tyloxyca r bon yl)bu ten oa te (20). 19 was
dried under high vacuum for 15 h prior to use. To a solution
of 19 (114.6 mg, 0.127 mmol) in distilled CH2Cl2 (8.0 mL) and
anhydrous MeOH (4.0 mL) was added solid NaHCO3 (∼200
mg). The solution was cooled to -78 °C under argon. O3 was
bubbled through the solution until a blue color persisted for
10 min. The solution was then purged with O2 for 15 min
followed by argon for 15 min. Me2S (0.50 mL) was added to
the reaction and allowed to warm to 25 °C over 15 h. The
solution was filtered through Celite and concentrated. Puri-
fication via flash chromatography eluting with 1:1 petroleum
ether/EtOAc provided the aldehyde (108.7 mg, 75%) as a white
foam: Rf ) 0.25 (1:1 petroleum ether/EtOAc); (select NMR
data) 13C NMR (100 MHz, CDCl3) δ 198.67, 170.62, 170.26,
169.88, 169.77, 169.62, 168.65, 138.74, 138.66, 138.07, 137.86,
137.29, 132.56, 129.66, 128.39, 128.34, 128.22, 128.17, 128.15,
128.06, 128.01, 127.9., 127.85, 127.71, 127.60, 127.57, 127.34,
127.23, 101.28, 100.95, 79.11, 79.04, 76.79, 76.07, 75.91, 75.79,
75.29, 74.87, 74.53, 74.13, 73.44, 73.25, 72.74, 72.67, 72.55,
72.46, 72.26, 71.50, 71.22, 69.57, 69.45, 69.02, 67.50, 67.31,
66.95, 62.06, 61.76, 61.15, 60.99, 20.73, 20.52, 18.98. 16 was
azeotroped with toluene (3 × 15 mL) and stored under high
vacuum for 15 h prior to use. To a solution of 16 (695 mg, 1.5
equiv) in THF (15.0 mL) at -78 °C was added TMG (1.5 equiv,
228 µL). The solution was stirred at -78 °C for 10 min before
the addition of the aldehyde (1.377 g, 1.21 mmol) in THF (15.0
mL) via cannula. After 4 h, the reaction was diluted with CH2-
Cl2, washed with 1 N HCl and saturated NaHCO3, dried, and
concentrated. Purification via chromatography eluting with a
gradient of 2:1 to 1:1 to 1:2 petroleum ether/EtOAc provided
20 (1.080 g, 65%) as a colorless film: Rf ) 0.6 (1:1 petroleum
21.72, 20.73, 20.58, 17.39, -1.53. Anal. Calcd for C72H95NO25
-
Si‚H2O: C, 60.87; H, 6.88; N, 0.99. Found: C, 60.77; H, 6.79;
N, 1.02.
(2R)-(Tr im et h ylsilyl)et h yl 1-((2,3,4,6-Tet r a -O-b en zyl-
r-D-ga la ctop yr a n osyl)-(1f4)-(2,3,6-tr i-O-a cetyl-â-D-ga la c-
topyr an osyl)-(1f4)-2,3,6-tr i-O-acetyl-r-D-glu copyr an osyl)-
2-(N-ter t-bu tyloxyca r bon yl)bu ta n oa te (22). In a drybox,
[(COD)Rh-((R,R)-Et-DuPHOS)]+OTf- catalyst precursor (1
mg, 0.0014 mmol) and 20 (25.0 mg, 0.018 mmol) were dissolved
in deoxygenated anhydrous THF (3.0 mL) in a Fischer-Porter
tube. The reaction vessel was pressurized with 90 psi of H2
after five vacuum/H2 cycles and stirred at 25 °C for 48 h. The
vessel was then depressurized and the mixture concentrated.
The product was purified via flash chromatography eluting
with 3:1 petroleum ether/EtOAc to yield 22 as a colorless oil
(22 mg, 88%, >95% de): Rf ) 0.5 (1:1 EtOAc/petroleum ether);
[R]20 +42.2° (c 0.93, CHCl3) 1H NMR (400 MHz, CDCl3) δ
D
7.41-7.17 (m, 20H), 5.14-5.06 (m, 2H), 4.91-4.89 (d, J ) 11.2
Hz, 1H), 4.82-4.81 (d, J ) 2.0 Hz, 1H), 4.77-4.73 (m, 2H),
4.64-4.57 (m, 6H), 4.55-4.52 (d, J ) 10.8 Hz, 1H), 4.47-4.37
(m, 6H), 4.28-4.24 (dd, J ) 5.2, 8.8 Hz, 1H), 4.21-4.14 (m,
5H), 4.05-4.01 (m, 5H), 3.96-3.95 (d, J ) 2.8 Hz, 1H), 3.65-
3.58 (m, 5H), 3.42-3.39 (dd, J ) 4.8, 12.4 Hz, 1H), 2.11 (s,
3H), 2.02 (s, 6H), 2.00 (s, 3H), 1.85 (s, 3H), 1.54 (s, 3H), 1.42
(s, 9H), 1.01-0.96 (m, 2H), 0.03 (s, 9H); 13C NMR (100 MHz,
CDCl3) δ 170.73, 170.45, 170.36, 170.09, 169.80, 168.78, 138.84,
138.77, 138.17, 137.96, 128.42, 128.33, 128.30, 128.25, 128.15,
128.11, 128.03, 127.69, 127.65, 127.44, 127.38, 101.38, 101.14,
79.14, 76.89, 76.00, 75.42, 74.97, 74.66, 74.22, 73.95, 73.35,
72.87, 72.57, 72.34, 72.05, 69.66, 69.55, 67.61, 63.71, 62.49,
61.10, 53.42, 28.33, 28.14, 27.50, 20.85, 20.73, 20.63, 17.40,
-1.53. Anal. Calcd for C72H95NO25Si‚H2O C, 60.87; H, 6.88;
N, 0.99. Found: C, 60.98; H, 6.78; N, 1.01.
ether/EtOAc); [R]20 33.6 (c 1.20, CHCl3); 1H NMR (400 MHz,
D
CDCl3) δ 7.98-7.13 (m, 20H), 6.40 (br s, 2H), 5.15-5.10 (m,
2H), 4.93-4.90 (d, J ) 11.2 Hz, 1H), 4.84-4.79 (m, 2H), 4.78-
4.74 (m, 2H), 4.69-4.66 (d, J ) 11.6 Hz, 1H), 4.57-4.54 (d, J
) 11.2 Hz, 1H), 4.46-4.39 (m, 2H), 4.28-4.24 (m, 2H), 4.16-
4.04 (m, 4H), 3.98-3.97 (d, J ) 2.1 Hz, 1H), 3.97-3.86 (m,
4H), 3.68-3.60 (m, 2H), 3.57-3.54 (m, 3H), 3.44-3.41 (dd, J
) 5.2, 8.6 Hz, 2H), 2.49-2.42 (m, 2H,), 2.39-2.29 (m, 2H), 2.14
(s, 3H), 1.044 (s, 3H), 2.040 (s, 3H), 2.03 (s, 3H), 1.87 (s, 3H),
1.86 (s, 3H), 1.45 (s, 9H), 1.07-1.02 (m, 2H) 0.05 (s, 9H); 13C
NMR (100 MHz, CDCl3) δ 170.70, 170.54, 170.33, 170.02,
169.80, 168.76, 164.65, 153.08, 138.82, 138.75, 138.16, 137.94,
129.74, 128.42, 128.61, 128.29, 128.23, 128.14, 128.10, 128.01,
127.67, 127.64, 127.42, 127.35, 101.36, 101.12, 80.44, 79.12,
76.83, 76.47, 75.97, 75.37, 74.95, 74.62, 74.19, 73.71, 73.34,
72.82, 72.55, 72.34, 71.53, 69.64, 69.56, 67.59, 63.72, 62.29,
61.08, 29.96, 29.68, 28.15, 20.84, 20.77, 20.68, 20.60, 17.35,
-1.53; HRMS m/e calcd for C72H92NO25Si (M - H)+ 1398.5727,
found 1398.5756. Anal. Calcd for C72H93NO25Si‚H2O: C, 60.96;
H, 6.75; N, 0.99. Found: C, 60.75; H, 6.82; N, 0.96.
(2,3-Di-O-ben zyl-4,6-O-ben zylid en e-â-D-ga la ctop yr a n o-
syl)-(1f4)-2,3,6-tr i-O-ben zyl-r,â-D-glu cop yr a n ose (24). A
solution of 23 (15.6 g, 16.0 mmol) in EtOH (70 mL), toluene
(30 mL), and water (10 mL) was heated to 70 °C. Rh(PPh3)3Cl
(0.1 equiv, 1.6 g) and DABCO (0.25 equiv, 475 mg) were added.
The reaction was heated to reflux for 24 h. The mixture was
cooled to 25 °C and concentrated. Filtration through a short
plug of SiO2 followed by concentration provided an orange foam
that was dissolved in wet acetone (0.1 M, 170 mL). HgO (0.04
equiv, 150.0 mg) was added followed by HgCl2 (0.25 equiv, 1.15
g). The reaction was stirred at 25 °C for 24 h before dilution
with CH2Cl2. The organic layer was washed with water and
saturated aqueous KI, dried, and concentrated. Purification
via flash chromatography eluting with 2:1 petroleum ether/
EtOAc afforded 24 as a colorless foam (10.0 g, 67% yield): Rf
(2S)-(Tr im eth ylsilyl)eth yl 1-((2,3,4,6-Tetr a -O-ben zyl-r-
D-ga la ctop yr a n osyl)-(1f4)-(2,3,6-tr i-O-a cetyl-â-D-ga la cto-
p yr a n osyl)-(1f4)-2,3,6-tr i-O-a cetyl-r-D-glu cop yr a n osyl)-
2-(N-ter t-bu tyloxyca r bon yl)bu ta n oa te (21). In a drybox,
[(COD)Rh-((S,S)-Et-DuPHOS)]+OTf- catalyst precursor (1
mg, 0.0014 mmol) and 20 (25.0 mg0.018 mmol) were dissolved
in deoxygenated anhydrous THF (3.0 mL) in a Fischer-Porter
tube. The reaction vessel was pressurized with 90 psi of H2
after five vacuum/H2 cycles and stirred at 25 °C for 48 h. The
vessel was then depressurized and the mixture concentrated.
The product was purified via flash chromatography eluting
with 3:1 petroleum ether/EtOAc to yield 21 as a colorless oil
(25 mg, 98%, >95% de): Rf ) 0.5 (1:1 EtOAc/petroleum ether);
) 0.20 (1:2 EtOAc/petroleum ether); [R]20 +20.7° (c 1.00,
D
CHCl3); 1H NMR (400 MHz, CDCl3) δ 7.51-7.16 (m, 30H),
5.45-5.44 (d, J ) 6.4 Hz, 1H), 5.24-5.16 (m, 2H), 4.89-4.71
(m, 6H), 4.69-4.61 (m, 2H), 4.54-4.48 (t, J ) 12.0 Hz, 1H),
4.40-4.34 (dd, J ) 7.6, 17.2 Hz, 1H), 4.26-4.18 (m, 2H), 4.00-
3.91 (m, 3H), 3.85-3.72 (m, 2H), 3.66-3.52 (m, 2H), 3.38-
3.30 (m, 2H), 2.91-2.90 (m, 1H); 13C NMR (100 MHz, CDCl3)
δ 138.96, 138.79, 138.71, 138.46, 138.36, 138.28, 138.18,
138.09, 138.03, 128.77, 128.68, 128.48, 128.33, 128.28, 128.21,
128.15, 128.04, 128.01, 127.93, 127.75, 127.72, 127.64, 127.61,
127.48, 127.37, 127.22, 126.48, 108.85, 102.88, 102.80, 101.27,
97.91, 97.23, 91.15, 82.83, 82.70, 79.97, 79.53, 79.38, 79.24,

Serine Analogue of the Pk Trisaccharide
J . Org. Chem., Vol. 64, No. 25, 1999 9161
78.70, 77.55, 77.39, 77.01, 76.69, 75.83, 75.62, 75.20, 74.78,
73.60, 73.51, 72.92, 71.50, 70.21, 68.86, 68.27, 66.23, 63.76,
60.34. Anal. Calcd for C54H56O11‚2H2O: C, 70.71; H, 6.60.
Found: C, 70.80; H, 6.29.
127.67, 127.60, 127.56, 127.49, 127.32, 127.21, 116.88, 102.43,
85.39, 81.02, 80.87, 79.42, 79.26, 78.75, 75.26, 75.02, 73.45,
73.02, 72.84, 72.02, 68.36, 68.24, 66.14, 36.05.
1-((2,3,4,6-Tetr a -O-ben zyl-r-D-ga la ctop yr a n osyl)-(1f4)-
(2,3,6-tr i-O-ben zyl-â-D-ga la ctop yr a n osyl)-(1f4)-2,3,6-tr i-
O-ben zyl-â-D-glu cop yr a n osyl)-2-p r op en e (28). 8 and 27
were azeotroped with toluene and dried under vacuum for 15
h prior to use. To a solution of 27 (114.7 mg, 0.127 mmol) in
Et2O (3.1 mL) at 0 °C were added 4 Å molecular sieves (25
mg) and TMSOTf (0.25 equiv, 6.3 µL). A suspension of 8 (2
equiv, 170.4 mg) and 4 Å molecular sieves (50 mg) in Et2O
(8.5 mL) was added over 1 h. The reaction was warmed to 25
°C and stirred for an additional 4 h. The reaction was quenched
by the addition of NEt3, filtered through Celite, and concen-
trated. Purification via chromatography eluting with 5:1
petroleum ether/EtOAc afforded 28 (115 mg, 64%) as a
colorless foam: 1H NMR (400 MHz, CDCl3) δ 7.46-7.03 (m,
50H), 5.94-5.73 (m, 1H), 5.20-5.17 (d, J ) 10.8 Hz, 1H), 5.11-
5.03 (m, 2H), 4.86-4.66 (m, 8H), 4.63-4.29 (m, 10H), 4.19-
4.13 (m, 1H), 4.10-3.82 (m, 7H), 3.73-3.46 (m, 7H), 3.37-
3.22 (m, 6H), 3.19-3.15 (dd, J ) 4.8, 8.4 Hz, 1H), 2.56-2.53
(m, 1H,), 2.30-2.23 (m, 1H); 13C NMR (100 MHz, CDCl3) δ
139.23, 138.97, 138.90, 138.80, 138.77, 138.69, 138.56, 138.10,
134.93, 128.75, 128.55, 128.52, 128.36, 128.26, 128.09, 127.96,
127.89, 127.83, 127.80, 127.73, 127.59, 127.56, 127.46, 127.40,
127.35, 127.11, 116.84, 102.73, 100.63, 93.59, 85.14, 83.43,
81.70, 81.13, 80.85, 79.56, 79.45, 79.34, 78.80, 78.72, 76.06,
75.27, 75.19, 75.10, 75.02, 74.86, 73.72, 73.56, 73.45, 73.18,
73.08, 73.03, 72.76, 72.44, 72.20, 69.73, 69.49, 68.99, 68.37,
67.93, 36.10.
(2,3-Di-O-ben zyl-4,6-O-ben zylid en e-â-D-ga la ctop yr a n o-
syl)-(1f4)-2,3,6-tr i-O-ben zyl-D-glu cu r on ic Acid (25). To a
solution of DMSO (3.6 mL) and Ac2O (2.5 mL) was added 24
(10.0 g, 11.4 mmol), and the solution was stirred at 25 °C for
20 h. The reaction was diluted with CH2Cl2, washed with
water, dried (MgSO4), and concentrated to provide 25 as a
colorless foam (9.5 g, 95%), which was used without further
purification: Rf ) 0.2 (1:2 EtOAc/petroleum ether); [R]20
D
+50.8° (c 0.99, CHCl3); 1H NMR (400 MHz, CDCl3) δ 7.55-
7.18 (m, 30H), 5.47 (s, 1H), 4.85-4.83 (d, J ) 6.0 Hz, 1H),
4.82-4.80 (d, J ) 5.2 Hz, 1H), 4.77 (s, 1H), 4.73 (s, 1H), 4.71
(s, 1H), 4.68 (s, 1H), 4.61-4.56 (m, 3H), 4.49-4.46 (d, J ) 11.6
Hz, 1H), 4.43-4.41 (d, J ) 7.6 Hz, 1H), 4.36-4.33 (d, J ) 12.0
Hz, 1H), 4.23-4.2 (dd, J ) 4.0, 9.0 Hz, 1H), 4.13-4.09 (m,
3H), 4.06-4.06 (d, J ) 3.4 Hz, 1H), 3.90-3.86 (dd, J ) 1.6,
12.4 Hz, 1H), 3.80-3.75 (m, 2H), 3.73-3.72 (d, J ) 3.6 Hz,
1H), 3.64-3.61 (dd, J ) 2.4, 10.8 Hz, 1H), 3.45-3.42 (dd, J )
3.6, 9.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 168.76, 166.31,
138.49, 138.17, 137.86, 137.69, 136.76, 128.88, 128.36, 128.31,
128.25, 128.22, 128.11, 128.07, 127.97, 127.84, 127.74, 127.70,
127.64, 127.58, 127.54, 127.51, 126.39, 103.53, 101.15, 79.76,
76.27, 78.28, 77.91, 76.64, 75.32, 73.37, 73.16, 73.08, 72.91,
71.61, 68.87, 67.96, 66.33, 22.07.
1-H yd r oxy-1-((2,3-d i-O-b en zyl-4,6-O-b en zylid en e-â-D-
ga la ctop yr a n osyl)-(1f4)-2,3,6-tr i-O-ben zyl-â-D-glu cop y-
r a n osyl)-2-p r op en e (26). 25 was azeotroped with toluene and
stored under vacuum for 15 h prior to use. To a solution of 25
(12.1 g, 13.7 mmol) in THF (137 mL) at -78 °C was added a
solution of 1.0 M allylmagnesium bromide (1.5 equiv, 21.0 mL).
The solution was stirred for 2 h at -78 °C. Water was added
and the mixture allowed to stir for 20 min before extraction
with EtOAc. Purification via flash chromatography eluting
with 2:1 petroleum ether/EtOAc afforded 26 (11.2 g, 89% yield)
as a colorless oil: Rf ) 0.6 (1:2 EtOAc/petroleum ether); 1H
NMR (400 MHz, CDCl3) δ 7.49-7.16 (m, 30H), 5.91-5.80 (m,
1H), 5.46 (s, 1H), 5.34-5.31 (d, J ) 10.8 Hz, 1H), 5.17-5.15
(d, J ) 10.0 Hz, 1H), 5.13-5.09 (d, J ) 17.2 Hz, 1H), 5.01-
4.98 (d, J ) 11.2 Hz, 1H), 4.81 (s, 2H), 4.73 (s, 2H), 4.69-4.66
(m, 4H), 4.65-4.63 (d, J ) 11.2 Hz, 1H), 4.60-4.57 (d, J )
12.0 Hz, 1H), 4.52-4.50 (d, J ) 7.6 Hz, 1H), 4.38-4.35 (d, J
) 12.4 Hz, 1H), 4.29-4.26 (d, J ) 12.4 Hz, 1H), 4.08-3.87
(m, 6H), 3.80-3.75 (m, 1H), 3.60-3.57 (d, J ) 11.6 Hz, 1H),
3.47-3.45 (d, J ) 8.8 Hz, 1H), 3.42-3.39 (dd, J ) 4.0, 9.8 Hz,
1H), 2.89 (br s, 1H); 13C NMR (400 MHz, CDCl3) δ 132.36,
128.96, 128.81, 128.32, 128.17, 128.04, 128.00, 127.89, 127.67,
127.45, 127.31, 126.57, 119.80, 102.72, 101.45, 97.43, 82.15,
80.79, 79.50, 78.90, 75.97, 75.35, 73.86, 72.93, 71.72, 71.60,
68.97, 68.12, 66.38, 43.07. Anal. Calcd for C57H60O11: C, 74.31;
H, 6.57. Found: C, 74.02; H, 6.59.
2-(Tr im eth ylsilyl)eth yl 1-((2,3,4,6-Tetr a -O-ben zyl-r-D-
ga la ctop yr a n osyl)-(1f4)-(2,3,6-tr i-O-ben zyl-â-D-ga la cto-
p yr a n osyl)-(1f4)-2,3,6-tr i-O-ben zyl-â-D-glu cop yr a n osyl)-
2-en e-2-(N-ter t-bu tyloxyca r bon yl)bu ten oa te (29). To a
solution of 28 (90.1 mg, 0.063 mmol) in CH2Cl2 (8.0 mL) and
anhydrous MeOH (4.0 mL) was added NaHCO3 (100 mg). The
solution was cooled to -78 °C, and O3 was bubbled through
until a blue color persisted for 10 min. The solution was purged
with O2 for 10 min and argon for 20 min before addition of
Me2S (1.0 mL). The reaction was allowed to warm to 25 °C
over 15 h, then filtered, and concentrated. Purification via
chromatography eluting with a gradient of 5:1 to 4:1 petroleum
ether/EtOAc provided the aldehyde (63.4 mg, 69%) as a clear
oil. The aldehyde was used immediately (Rf ) 0.2 (4:1
petroleum ether/EtOAc)). 16 was azeotroped with toluene and
stored under high vacuum for 15 h prior to use. To a solution
of 16 (946.0 mg, 1.3 equiv) in THF (19.0 mL) at -78 °C was
added tetramethylguanidine (312 µL, 1.3 equiv). The mixture
was stirred for 15 min before the addition of a solution of the
aldehyde (2.719 g, 1.90 mmol) in THF (19.0 mL). The solution
was warmed to 25 °C. After 5 h, the reaction was diluted with
CH2Cl2, washed with 1 N HCl and saturated NaHCO3, dried
(MgSO4), and concentrated. Purification via chromatography
eluting with 4:1 petroleum ether/EtOAc afforded 29 (2.702 g,
84%) as a colorless foam: Rf ) 0.4 (4:1 petroleum ether/EtOAc);
1-((2,3,6-Tr i-O-b en zyl-r-D-ga la ct op yr a n osyl)-(1f4)-
(2,3,6-tr i-O-ben zyl-â-D-glu cop yr a n osyl)-2-p r op en e (27). 26
(3.44 g, 3.7 mmol) was azeotroped with toluene and stored
under vacuum for 15 h prior to use. To a solution of 26 in CH2-
Cl2 (0.08 M, 45.0 mL) at -78 °C were added Et3SiH (3.55 mL,
6 equiv) and BF3‚Et2O (1.89 mL, 4 equiv). The reaction was
stirred at -78 °C for 5 h. Saturated aqueous NaHCO3 was
added, and the solution was extracted with CH2Cl2. Purifica-
tion via flash chromatography eluting with 3:1 petroleum
ether/EtOAc provided 27 (2.463 g, 73%) as a colorless amor-
phous solid: Rf ) 0.5 (1:3 EtOAc/petroleum ether); [R]20D +8.5°
[R]20 +12.6° (c 1.05, CHCl3); 1H NMR (300 MHz, CDCl3) δ
D
7.41-7.01 (m, 50H), 6.55 (s, 1H), 6.36 (br s, 1H), 5.17-5.13
(d, J ) 11.1 Hz, 1H), 5.04-5.02 (d, J ) 3.6 Hz, 1H), 4.84-
4.65 (m, 6H), 4.57-4.53 (d, J ) 12.0 Hz, 1H), 4.49-4.39 (m,
6H), 4.34-4.29 (m, 4H), 4.23-4.17 (m, 2H), 4.14-4.04 (m, 4H),
4.02-3.79 (m, 7H), 3.63-3.51 (m, 4H), 3.49-3.43 (t, J ) 8.7
Hz, 1H), 3.33-3.31 (m, 2H), 3.28-3.24 (dd, J ) 2.4, 9.9 Hz,
1H), 3.21-3.13 (m, 3H), 2.66-2.59 (m, 1H), 2.39-2.30 (m, 1H),
1.39 (s, 9H), 1.26-1.00 (m, 2H), 0.02 (s, 9H); 13C NMR (75
MHz, CDCl3) δ 164.72, 153.09, 138.94, 138.79, 138.58, 138.50,
138.38, 138.20, 138.03, 137.90, 129.59, 128.64, 128.25, 128.14,
127.98, 127.69, 127.61, 127.46, 127.32, 126.98, 102.64, 100.56,
84.71, 81.56, 80.60, 80.19, 79.43, 78.91, 78.45, 75.23, 75.07,
74.82, 73.71, 73.36, 73.16, 73.06, 72.41, 72.11, 69.46, 68.24,
67.85, 63.48, 30.37, 28.27, 17.37, -1.34. Anal. Calcd for
1
(c 0.69, CHCl3); H NMR (400 MHz, CDCl3) δ 7.42-7.18 (m,
30H), 5.96-5.85 (m, 1H), 5.13-5.10 (d, J ) 10.8 Hz, 1H), 5.06-
5.04 (d, J ) 10.8 Hz, 1H), 4.82-4.79 (d, J ) 11.2 Hz, 1H),
4.77-4.75 (d, J ) 11.2 Hz, 1H), 4.72-4.64 (m, 3H), 4.60-4.59
(d, J ) 4.8 Hz, 1H), 4.58-4.56 (d, J ) 6.0 Hz, 2H), 4.49-4.44
(m, 2H), 4.42-4.41 (d, J ) 4.4 Hz, 1H), 4.39-4.38 (d, J ) 4.0
Hz, 1H), 4.01-3.97 (m, 2H), 3.38-3.79 (dd, J ) 3.6, 7.6 Hz,
1H), 3.69-3.58 (m, 4H), 3.51-3.47 (dd, J ) 5.2, 9.6 Hz, 1H),
C
102H117NO19Si: C, 72.53; H, 6.98; N, 0.83. Found: C, 72.52;
H, 7.02; N, 0.92.
3.39-3.25 (m, 6H), 2.59-2.54 (m, 1H), 2.32-2.25 (m, 1H); 13
C
(2R)-(Tr im et h ylsilyl)et h yl 1-((2,3,4,6-Tet r a -O-b en zyl-
r-D-ga la ct op yr a n osyl)-(1f4)-(2,3,6-t r i-O-b en zyl-â-D-ga -
la ctop yr a n osyl)-(1f4)-2,3,6-tr i-O-ben zyl-â-D-glu cop yr a -
NMR (400 MHz, CDCl3) δ 139.09, 138.54, 138.40, 138.25,
137.90, 134.78, 128.38, 128.32, 128.29, 128.19, 127.84, 127.76,

9162 J . Org. Chem., Vol. 64, No. 25, 1999
Debenham et al.
1
n osyl)-2-en e-2-(N-ter t-bu tyloxyca r bon yl)bu ta n oa te (30).
In a drybox, [(COD)Rh-((R,R)-Et-DuPHOS)]+OTf- catalyst
precursor (1 mg, 0.0014 mmol) and 29 (940 mg, 0.56 mmol)
were dissolved in deoxygenated anhydrous THF (3 mL) in a
Fischer-Porter tube. The reaction vessel was pressurized to
90 psi of H2 after five vacuum/H2 cycles and stirred at 25 °C
for 48 h. The vessel was then depressurized and the mixture
concentrated. The product was purified via flash chromatog-
raphy eluting with 3:1 petroleum ether/EtOAc to yield 30 as
a clear oil (920 mg, 98%, >95% de): Rf ) 0.4 (4:1 petroleum
ether/EtOAc); [R]20D +16.5° (c 1.00, CHCl3); 1H NMR (300 MHz,
CDCl3) δ 7.31-6.87 (m, 50H), 5.01-4.97 (d, J ) 11.0 Hz, 1H),
4.92-4.89 (d, J ) 8.5 Hz, 1H), 4.88-4.87 (d, J ) 3.3 Hz, 1H),
4.69-4.50 (m, 9H), 4.39-4.35 (d, J ) 12.0 Hz, 1H), 4.32-4.25
(m, 6H), 4.24-4.20 (d, J ) 9.9 Hz, 1H), 4.24-4.12 (m, 5H),
4.04-3.79 (m, 6H), 3.75-3.74 (t, J ) 2.1 Hz, 1H), 3.71-3.70
(d, J ) 2.7 Hz, 1H), 3.68-3.63 (m, 2H), 3.50-3.36 (m, 4H),
3.35-3.33 (d, J ) 6.3 Hz, 1H), 3.30-3.27 (d, J ) 8.7 Hz, 1H),
3.18-3.12 (m, 2H), 3.10-3.09 (d, J ) 2.4 Hz, 1H), 3.06 (br s,
1H), 2.99-2.97 (m, 4H), 1.22 (s, 9H), 0.82-0.75 (m, 2H); -0.16
(s, 9H); 13C NMR (75 MHz, CDCl3) δ 172.69, 170.97, 155.23,
138.99, 138.77, 138.61, 138.35, 138.25, 138.08, 137.87, 128.64,
128.14, 127.98, 127.70, 127.61, 127.46, 127.34, 126.97, 102.59,
100.62, 84.91, 81.61, 81.26, 79.58, 79.42, 79.16, 78.87, 75.26,
75.09, 74.83, 74.75, 73.68, 73.28, 73.15, 73.02, 72.37, 72.09,
69.41, 68.31, 67.79, 63.56, 60.42, 53.62, 28.95, 28.39, 27.83,
21.16, 17.43, 14.31, -1.38. Anal. Calcd for C102H119NO19Si: C,
72.44; H, 7.09; N, 0.83. Found: C, 72.44; H, 7.17; N, 0.87.
(2S)-(Tr im eth ylsilyl)eth yl 1-((2,3,4,6-Tetr a -O-ben zyl-r-
D-ga la ctop yr a n osyl)-(1f4)-(2,3,6-tr i-O-ben zyl-â-D-ga la c-
topyr an osyl)-(1f4)-2,3,6-tr i-O-ben zyl-â-D-glu copyr an osyl)-
a colorless foam: [R]20 +28.2° (c 1.07, CHCl3); H NMR (300
D
MHz, CDCl3) δ 5.52-5.51 (d, J ) 3.0 Hz, 1H), 5.36-5.31 (dd,
J ) 3.0, 10.5 Hz, 1H), 5.22-5.21 (d, J ) 3.9 Hz, 1H), 5.17-
5.06 (m, 4H), 4.79-4.70 (m, 2H), 4.52-4.47 (t, J ) 5.4 Hz, 1H),
4.43-4.34 (m, 3H), 4.20-4.03 (m, 8H), 3.78-3.77 (d, J ) 1.8
Hz, 1H), 3.69-3.63 (m, 2H), 3.55-3.44 (m, 2H), 3.39-3.34 (m,
2H), 2.10 (s, 3H), 2.08 (s, 3H), 2.06 (s, 3H), 2.05 (s, 3H), 2.04
(s, 3H), 2.02 (s, 3H), 2.00 (s, 3H), 1.98 (s, 3H), 1.94 (s, 3H),
1.60-1.43 (m, 4H), 1.39 (s, 9H), 0.96-0.89 (m, 2H), 0.00 (s,
9H);13C NMR (75 MHz, CDCl3) δ 172.3, 170.3, 170.25, 170.1,
170.0, 169.9, 169.7, 169.6, 169.2, 101.1, 99.4, 81.2, 79.7, 76.7,
76.574.4, 72.5, 72.3, 72.1, 71.7, 68.3, 68.1, 67.7, 66.7, 63.7, 62.7,
61.9, 61.1, 53.428.4, 28.2, 27.5, 20.9, 20.8, 20.7, 20.6, 17.4, 14.3,
-1.4. Anal. Calcd for C52H79NO29Si: C, 51.61; H, 6.58; N, 1.16.
Found: C, 51.53; H, 6.53; N, 1.08.
(2S)-(Tr im eth ylsilyl)eth yl 1-((2,3,4,6-Tetr a -O-a cetyl-r-
D-ga la ctop yr a n osyl)-(1f4)-(2,3,6-tr i-O-a cetyl-â-D-ga la cto-
p yr a n osyl)-(1f4)-2,3,6-tr i-O-a cetyl-â-D-glu cop yr a n osyl)-
2-en e-2-(N-ter t-bu tyloxycar bon yl)bu tan oate (33). A solution
of 31 (822.9 mg, 0.49 mmol) in THF (2.0 mL) and anhydrous
MeOH (2.0 mL) was degassed with argon for 15 min. Ten
percent Pd/C (75 mg) was added and the vessel pressurized
to 90 psi of H2 after five vacuum cycles. The reaction was
stirred for 4 days, filtered through Celite, and concentrated
(Rf ) 0.7 (5:3:1 EtOAc/MeOH/H2O)). The residue was dissolved
in pyridine (4.0 mL, 0.1 M). Ac2O (15 equiv, 0.60 mL) was
added and the reaction stirred for 15 h at 25 °C. The mixture
was diluted with CH2Cl2, washed with water, 1.0 N HCl, and
saturated NaHCO3, dried (MgSO4), and concentrated. Purifi-
cation via chromatography eluting with a gradient of 1:1 to
2:1 EtOAc/petroleum ether provided 33 (382.6 mg, 66%) as a
2-en e-2-(N-ter t-bu tyloxyca r bon yl)bu ta n oa te (31). In
a
colorless foam: [R]20 +46.0° (c 1.18, CHCl3); 1H NMR (300
D
drybox, [(COD)Rh-((S,S)-Et-DuPHOS)]+OTf- catalyst precur-
sor (1 mg, 0.0014 mmol) and 29 (940 mg, 0.56 mmol) were
dissolved in deoxygenated anhydrous THF (3.0 mL) in a
Fischer-Porter tube. The reaction vessel was pressurized to
90 psi of H2 after five vacuum/H2 cycles, and the mixture was
stirred at 25 °C for 48 h. The vessel was depressurized and
the mixture concentrated. The product was purified via flash
chromatography eluting with 3:1 petroleum ether/EtOAc to
MHz, CDCl3) δ 5.53-5.52 (d, J ) 2.4 Hz, 1H), 5.36-5.31 (dd,
J ) 3.0, 11.1 Hz, 1H), 5.15-4.98 (m, 4H), 4.94-4.93 (d, J )
3.6 Hz, 1H), 4.76-4.66 (m, 2H); 4.47-4.35 (m, 4H), 4.18-3.96
(m, 8H), 3.72-3.65 (m, 3H), 3.52-3.48 (m, 1H), 3.39-3.33 (m,
1H), 2.08 (s, 3H), 2.06 (s, 3H), 2.05 (s, 3H), 2.03 (s, 3H), 2.01
(s, 6H), 2.00 (s, 3H), 1.99 (s, 3H), 1.98 (s, 3H), 1.93 (s, 3H),
1.83-1.56 (m, 4H), 1.38 (s, 9H), 0.97-0.92 (m, 2H), -0.01 (s,
9H); 13C NMR (75 MHz, CDCl3) δ 172.4, 170.4, 170.2, 169.8,
169.5, 169.2, 168.6, 101.0, 99.5, 76.8, 76.7, 76.3, 74.4, 72.8, 72.0,
71.7, 68.9, 68.8, 67.8, 67.1, 63.6, 62.5, 61.3, 60.2, 53.1, 28.3,
yield 31 as a colorless oil (922 mg, 98%, >95% de): Rf ) 0.4
1
(4:1 petroleum ether/EtOAc); [R]20 +1.5° (c 1.00, CHCl3); H
D
NMR (300 MHz, CDCl3) δ 7.23-6.90 (m, 50H), 5.01-4.97 (d,
J ) 10.8 Hz, 1H), 4.89-4.87 (d, J ) 3.6 Hz, 1H), 4.82-4.79
(d, J ) 8.4 Hz, 1H), 4.69-4.50 (m, 6H), 4.38-4.27 (m, 7H),
4.24-4.19 (d, J ) 12.6 Hz, 1H), 4.17-4.12 (m, 2H), 4.03-3.94
(m, 2H), 3.91-3.89 (m, 2H), 3.85-3.79 (m, 3H), 3.75-3.74 (t,
J ) 2.1 Hz, 1H), 3.71-3.71 (d, J ) 2.4 Hz, 1H), 3.67-3.66 (d,
J ) 3.6 Hz, 1H), 3.64-3.62 (d, J ) 3.3 Hz, 1H), 3.48-3.27 (m,
8H), 3.18-3.12 (m, 1H), 3.08-2.93 (m, 6H), 1.69-1.64 (m, 4H),
1.25 (s, 9H), 0.80-0.74 (m, 2H), -0.17 (s, 9H); 13C NMR (75
MHz, CDCl3) δ 172.70, 138.99, 138.78, 138.61, 138.36, 138.16,
137.88, 128.67, 128.25, 128.15, 127.98, 127.71, 127.63, 127.53,
127.46, 127.35, 126.97, 102.59, 100.64, 84.96, 81.61, 81.15,
79.58, 79.53, 79.43, 79.21, 79.12, 78.52, 75.18, 74.94, 74.83,
74.75, 74.01, 73.69, 73.57, 73.30, 73.15, 73.03, 72.37, 72.09,
69.42, 68.30, 67.79, 63.56, 53.49, 29.78, 28.61, 28.41, 27.77,
17.42, -1.39. Anal. Calcd for C102H119NO19Si‚H2O: C, 71.75;
H, 7.03; N, 0.82. Found: C, 71.41; H, 7.00; N, 0.79.
(2R)-(Tr im eth ylsilyl)eth yl 1-((2,3,4,6-Tetr a -O-a cetyl-r-
D-ga la ctop yr a n osyl)-(1f4)-(2,3,6-tr i-O-a cetyl-â-D-ga la cto-
p yr a n osyl)-(1f4)-2,3,6-tr i-O-a cetyl-â-D-glu cop yr a n osyl)-
2-en e-2-(N-ter t-bu tyloxycar bon yl)bu tan oate (32). A solution
of 30 (833.5 mg, 0.49 mmol) in THF (2.0 mL) and anhydrous
MeOH (2.0 mL) was degassed with argon for 15 min. Ten
percent Pd/C (∼75 mg) was added and the vessel pressurized
to 90 psi of H2 after five vacuum cycles. The reaction was
stirred for 4 days and was then filtered through Celite and
concentrated (Rf ) 0.7 (5:3:1 EtOAc/MeOH/H2O)). The residue
was dissolved in pyridine (5.0 mL, 0.1 M). Ac2O (15 equiv, 0.7
mL) was added and the reaction stirred for 15 h at 25 °C. The
mixture was diluted with CH2Cl2, washed with water, 1.0 N
HCl, and saturated NaHCO3, dried (MgSO4), and concentrated.
Purification via chromatography eluting with a gradient of 1:1
to 2:1 EtOAc/petroleum ether provided 32 (511.6 mg, 76%) as
27.9, 27.1, 20.7, 20.5, 17.4, -1.5. Anal. Calcd for C52H79NO29
-
Si: C, 51.61; H, 6.58; N, 1.16. Found: C, 51.48; H, 6.52; N,
1.21.
(2R)-1-((2,3,4,6-Tet r a -O-a cet yl-r-D-ga la ct op yr a n osyl)-
(1f4)-(2,3,6-tr i-O-acetyl-â-D-galactopyr an osyl)-(1f4)-2,3,6-
tr i-O-acetyl-â-D-glu copyr an osyl)-2-en e-2-(N-ter t-bu tyloxy-
ca r bon yl)bu ta n oic Acid (34). To a solution of 32 (524.7 mg,
0.43 mmol) in THF (5.0 mL) was added 1.0 M TBAF (1.70 mL).
The reaction was stirred at 25 °C for 4 h, diluted with CH2-
Cl2, washed with 1 N HCl, dried (MgSO4), and concentrated.
Purification via flash chromatography eluting with 4:1 EtOAc/
petroleum ether provided 34 (425.0 mg, 88%) as a pale yellow
foam: Rf ) 0.8 (4:1 EtOAc/petroleum ether); 1H NMR (300
MHz, CDCl3) δ 5.54-5.53 (d, J ) 3.0 Hz, 1H), 5.37-5.32 (dd,
J ) 3.0, 11.1 Hz, 1H), 5.21-5.19 (m, 1H), 5.16-5.02 (m, 5H),
4.94-4.93 (d, J ) 3.6 Hz, 1H), 4.77-4.67 (m, 2H), 4.48-4.41
(m, 4H), 4.21-4.19 (m, 1H), 4.16-4.00 (m, 6H), 3.97-3.96 (d
J ) 2.1 Hz, 1H), 3.74-3.65 (m, 2H), 3.54-3.49 (m, 1H), 3.40-
3.35 (m, 1H), 2.08 (s, 3H), 2.07 (s, 3H), 2.04 (s, 3H), 2.02 (s,
3H), 2.01 (s, 3H), 2.00 (s, 3H), 1.997 (s, 3H), 1.995 (s, 3H), 1.98
(s, 3H), 1.94 (s, 3H), 1.39 (s, 9H); 13C NMR (75 MHz, CDCl3)
δ 176.3, 170.5, 170.3, 169.9, 169.6, 169.3, 168.7, 101.0, 99.5,
76.8, 76.4, 74.4, 72.8, 72.1, 71.8, 69.0, 68.9, 67.9, 67.0, 62.6,
61.4, 60.3, 28.3, 27.4, 21.0, 20.8. Anal. Calcd for C47H67NO29
C, 50.86; H, 6.08; N, 1.26. Found: C, 50.64; H, 6.17; N, 1.32.
:
(2S)-1-((2,3,4,6-Tet r a -O-a cet yl-r-D-ga la ct op yr a n osyl)-
(1f4)-(2,3,6-tr i-O-acetyl-â-D-galactopyr an osyl)-(1f4)-2,3,6-
tr i-O-acetyl-â-D-glu copyr an osyl)-2-en e-2-(N-ter t-bu tyloxy-
ca r bon yl)bu ta n oic Acid (35). To a solution of 33 (377.4 mg,
0.31 mmol) in THF (5.0 mL) was added 1.0 M TBAF (1.2 mL).
The reaction was stirred at 25 °C for 4 h, diluted with CH2-
Cl2, washed with 1 N HCl, dried (MgSO4), and concen-

Serine Analogue of the Pk Trisaccharide
J . Org. Chem., Vol. 64, No. 25, 1999 9163
trated. Purification via flash chromatography eluting with 4:1
EtOAc/petroleum ether provided 35 (351.7 mg, 99%) as a
colorless foam: Rf ) 0.8 (4:1 EtOAc/petroleum ether); 1H NMR
(300 MHz, CDCl3) δ 5.55-5.54 (d, J ) 3.3 Hz, 1H), 5.37-5.33
(dd, J ) 3.3, 11.1 Hz, 1H), 5.17-5.03 (m, 4H), 4.95-4.94 (d, J
) 3.6 Hz, 1H), 4.78-4.68 (m, 2H), 4.49-4.32 (m, 5H), 4.20-
3.98 (m, 8H), 3.75-3.67 (m, 3H), 3.55-3.48 (m, 2H), 3.41-
3.37 (m, 1H), 2.09 (s, 3H), 2.07 (s, 3H), 2.04 (s, 3H), 2.02 (s,
9H), 2.01 (s, 3H), 2.00 (s, 3H), 1.99 (s, 3H), 1.94 (s, 3H), 1.40
(s, 9H); 13C NMR (75 MHz, CDCl3) δ 175.9, 170.5, 170.3, 170.2,
170.0, 169.9, 169.5, 169.3, 168.7, 155.6, 101.0, 99.5, 80.1, 76.9,
76.7, 76.4, 74.4, 72.8, 72.0, 71.8, 69.0, 68.8, 67.9, 67.1, 62.5,
61.3, 60.3, 53.0, 28.3, 27.4, 27.0, 21.0, 20.9, 20.8, 20.6. Anal.
Calcd for C47H67NO29: C, 50.86; H, 6.08; N, 1.26. Found: C,
50.83; H, 6.20; N, 1.27.
Ack n ow led gm en t. This work was supported by the
National Institutes of Health (Grant RO1GM57179).
S.D.D. acknowledges support from the Biological Chem-
istry Program at Duke University (Grant T32GM08858).
J .C. acknowledges the National Science Foundation
Research Experiences for Undergraduates and the
Howard Hughes Program at Duke University for finan-
cial support. We gratefully acknowledge a gift of Du-
PHOS ligands from Dr. M. Burk, Chiroscience, U.K.
J O991096M