Stereoselective synthesis of conformationally constrained glycosylated amino acids using an enzyme-catalyzed desymmetrization

Article abstract of DOI:10.1021/jo020532t

As part of an effort to probe the mechanism by which glycosyltransferases recognize glycoproteins and assemble the core structures of O-linked oligosaccharides, constrained glycopeptides, compounds 2 and 3, based on the α-N-acetylgalactosaminyl serine substructure 1, were designed. In this paper we describe a stereoselective preparation of protected versions of these compounds. A pig liver esterase-catalyzed enzymatic desymmetrization of a diacetate substrate, 10, was employed as a key component in the synthesis.

Full text of DOI:10.1021/jo020532t

Ster eoselective Syn th esis of Con for m a tion a lly Con str a in ed
Glycosyla ted Am in o Acid s Usin g a n En zym e-Ca ta lyzed
Desym m etr iza tion
J onathan W. Lane and Randall L. Halcomb*
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215
halcomb@colorado.edu
Received August 12, 2002
As part of an effort to probe the mechanism by which glycosyltransferases recognize glycoproteins
and assemble the core structures of O-linked oligosaccharides, constrained glycopeptides, compounds
2 and 3, based on the R-N-acetylgalactosaminyl serine substructure 1, were designed. In this paper
we describe a stereoselective preparation of protected versions of these compounds. A pig liver
esterase-catalyzed enzymatic desymmetrization of a diacetate substrate, 10, was employed as a
key component in the synthesis.
1. In tr od u ction
Glycosylation is a ubiquitous posttranslational modi-
fication of proteins and is associated with a number of
processes both within cells and at cell surfaces. These
include protein transport, cell adhesion, and signal
transduction.1 Aberrant glycosylation of cellular proteins
and glycolipids is associated with various diseases,
including cancerous and inflammatory conditions.2 There-
fore, an understanding on a molecular level of the
structural features of glycoproteins that are recognized
by various enzymes and receptors would be valuable in
developing inhibitor-based strategies to control carbo-
hydrate-mediated cellular processes. This fundamental
understanding could, in turn, lead to new therapeutic
strategies for conditions that are characterized by ab-
normal glycosylation.
F IGURE 1. Thomsen-Freidenreich antigen.
The concept of aberrant glycosylation of proteins is
exemplified by the presence of large quantities of the
Thomsen-Freidenreich antigen (T antigen; Figure 1) on
the surface of many types of tumor cells, specifically
highly metastatic cells.3 The T antigen lacking any
additional sugar units is often referred to as Core 1 and
represents the O-linked oligosaccharides,1 a common
class of glycoproteins. The foundation of Core 1 is
comprised of the prevalent R-N-acetylgalactosaminyl
serine glycoconjugate substructure 1 (Figure 2), and
F IGURE 2. R-N-Acetylgalactosaminyl serine glycoconjugate
substructure and corresponding constrained glycopeptide tar-
gets.
assembly of the Core 1 disaccharide from 1 is mediated
by a â-1,3-galactosyltransferase (Core 1 GalTase) en-
zyme.4 This particular transferase was chosen for de-
tailed study in our group.
The ground-state conformations of small glycopeptides
have been studied in some detail by NMR spectroscopy;5
however, relatively little is known about the conforma-
tions that are recognized by various enzymes and recep-
tors. The preferred torsional angle about the exocyclic
(1) (a) Kornfeld, R.; Kornfeld, S. Annu. Rev. Biochem. 1985, 54, 631.
(b) Rademacher, T. W.; Parekh, R. B.; Dwek, R. A. Annu. Rev. Biochem.
1988, 57, 785. (c) Varki, A. Glycobiology 1993, 3, 97. (d) Dwek, R. A.
Chem. Rev. 1996, 96, 683.
(2) Hakomori, S.-I. Adv. Cancer Res. 1989, 52, 257.
(3) (a) Springer, G. F. Science 1984, 224, 1198. (b) Kurosaka, A.;
Nakajima, H.; Funakoshi, I.; Matsuyama, M.; Nagayo, T.; Yamashita,
I. J . Biol. Chem. 1983, 258, 11594. (c) Fukuda, M.; Carlsson, S. R.;
Klock, J . C.; Dell, A. J . Biol. Chem. 1986, 261, 12796. (d) Fung, P. Y.
S.; Madej, M.; Koganty, R. R.; Longenecker, B. M. Cancer Res. 1990,
50, 4308. (e) Capon, C.; Leroy, Y.; Wieruszeski, J .-M.; Ricart, G.;
Strecker, G.; Montreuil, J .; Fournet, B. Eur. J . Biochem. 1989, 182,
139. (f) Hounsell, E. F.; Lawson, A. M.; Feeney, J .; Gooi, H. C.;
Pickering, N. J .; Stoll, M. S.; Lui, S. C.; Feizi, T. Eur. J . Biochem. 1985,
148, 367.
(4) (a) Anderson, G. N.; Ericsson, L. C. J . Biol. Chem. 1981, 256,
9633. (b) Mendicino, J .; Sivakami, S.; Davila, M.; Chandrasekaran, E.
V. J . Biol. Chem. 1982, 257, 3987. (c) Cheng, P.-W.; Bona, S. J . Biol.
Chem. 1982, 257, 6251. (d) Brockhausen, I.; Mo¨ller, G.; Pollex-Kru¨ger,
A.; Rutz, V.; Paulsen, H.; Matta, K. L. Biochem. Cell. Biol. 1992, 70,
99.
10.1021/jo020532t CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/23/2003
1348
J . Org. Chem. 2003, 68, 1348-1357

Synthesis of Glycosylated Amino Acids
SCHEME 1. Selective Syn th esis Str a tegy for Con str a in ed Glycop ep tid es
C1-O bond (φ) of the carbohydrate moiety in the ground
state is somewhat rigid, as predicted by the exoanomeric
effect (Figure 2).6 However, other torsional angles within
the side chain, including ø2, are somewhat more flexible,
as illustrated in 1. Significant research has gone into
designing conformational constraints into various amino
acid and peptide motifs to probe bioactive conformations.7
However, conformationally restricted glycopeptides are
relatively unexplored.8
In an effort to probe the mechanism by which glycosyl-
transferases recognize glycoproteins and assemble the
core structures of O-linked oligosaccharides, a series of
conformationally constrained glycopeptides was chosen
for synthesis.9 These targets were designed in an effort
to represent the accessible low-energy conformations
about ø2 of the native structure 1, and will ultimately be
incorporated into peptides for evaluation as substrates
for, or inhibitors of, Core 1 GalTase. Among those chosen
was compound 2 in which the R-carbon (CR) of the amino
acid component of the structure is incorporated into a
six-membered ring and exhibits the natural L-serine
configuration. The ø2 torsional angle is effectively con-
strained in one of the two possible gauche conformations,
and the C1-O bond is locked into the low-energy exo-
anomeric orientation. The unnatural D-serine configura-
tion could also be useful in our studies, and is represented
by the similarly constrained analogue 3 (Figure 2).
Through our previous strategy,10 fully protected ver-
sions of constrained glycopeptides 2 and 3 were success-
fully synthesized, albeit with low overall diastereoselec-
tivity. In an effort to preferentially obtain one amino acid
configuration over the other and to more readily secure
the quantities of diastereomerically pure material neces-
sary for biological evaluation and structural studies, a
more selective synthesis was desired.
The first-generation synthesis strategy was designed
to establish the desired anomeric orientation at the
spiroketal center through a thermodynamic spiroketal-
ization event.11 Furthermore, it was predicted that dia-
stereomeric preferences inherent within this same proc-
ess would afford an excess of the natural L-serine
configuration at CR in a diastereotopic group-selective
cyclization. Although the strategy was relatively success-
ful in producing the correct stereochemistry at the
spiroketal center, it failed to yield an excess of either the
L- or D-serine configuration.10
Therefore, we pursued an alternate synthesis strategy
(Scheme 1) in which a differentially protected chiral
alkyne, 5, representing the R,R-disubstituted R-amino
acid component of the target glycopeptide, would undergo
a nucleophilic addition to the carbohydrate lactone 4.9,10
Selective deprotection of the resulting product 6 followed
by reduction of the internal alkyne would provide the
spiroketal precursor 7. This method has the advantage
of setting the configuration at CR prior to ring closure,
and circumvents any dependence on the spiroketalization
process itself to provide diastereoselection at the amino
acid stereocenter. Selective thermodynamic spiroketal-
ization of the free primary hydroxyl group in 7 should
accomplish the original goal of installing the correct
anomeric configuration. Deprotection and subsequent
oxidation of the other hydroxyl group in 7 followed by
further manipulations should provide either 2 or 3,
selectively, depending on the stereochemical configura-
tion of 5. The successful implementation of this second-
generation route is reported here.
(5) (a) Kirnarsky, L.; Prakash, O.; Vogen, S. M.; Nomoto, M.;
Hollingsworth, M. A.; Sherman, S. Biochemistry 2000, 39, 12076. (b)
Wu, W.; Pasternack, L.; Huang, D.-H.; Koeller, K. M.; Lin, C.-C.; Seitz,
O.; Wong, C.-H. J . Am. Chem. Soc. 1999, 121, 2409. (c) O’Connor, S.
E.; Imperiali, B. Chem. Biol. 1998, 5, 427. (d) Liang, R.; Andreotti, H.;
Kahne, D. J . Am. Chem. Soc. 1995, 117, 10395. (e) Meyer, B. Top. Curr.
Chem. 1990, 154, 141.
(6) (a) J uarista, E.; Cuevas, G. Tetrahedron 1992, 48, 5019. (b)
Deslongchamps, P. Stereoelectronic Effects in Organic Chemistry;
Pergamon: New York, 1983.
(7) (a) Degrado, W. F. Design of Peptides and Proteins. Advances
in Protein Chemistry; Academic Press: New York, 1988; Vol. 39, p 51.
(b) Hruby, V. J .; Al-Obeidi, F.; Kazmierski, W. Biochem. J . 1990, 268,
249. (c) Toniolo, C. Int. J . Pept. Protein Res. 1990, 35, 287. (d) Hruby,
V. J .; Bonner, G. G. In Methods in Molecular Biology; Pennigton, M.
W., Dunn, B. M., Eds.; Humana Press: Totowa, NJ , 1994; Vol. 35, pp
201-240. (e) Obrecht, D.; Altorfer, M.; Robinson, J . A. Adv. Med. Chem.
1999, 4, 1. (f) Goodman, M.; Shao, H. Pure Appl. Chem. 1996, 68, 1303.
For more examples of constraining ø2, see: Gibson, S. E.; Guillo, N.;
Tozer, M. J . Tetrahedron 1999, 55, 585.
(8) (a) Bock, K.; Duus, J . Ø.; Hindsgaul, O.; Lindh, I. Carbohydr.
Res. 1992, 228, 1. (b) Sabesan, S.; Neira, S.; Davidson, F.; Duus, J . Ø.;
Bock, K. J . Am. Chem. Soc. 1994, 116, 1616. (c) Wilstermann, M.;
Kononov, L. O.; Nilsson, U.; Ray, A. K.; Magnusson, G. J . Am. Chem.
Soc. 1995, 117, 4742. (d) Davis, B. G. J . Chem. Soc., Perkin Trans. 1
2000, 2137. (e) Navarre, N.; vanOijen, A. H.; Boons, G. J . Tetrahedron
Lett. 1997, 38, 2023. (f) Geyer, A.; Muller, M.; Schmidt, R. R. J . Am.
Chem. Soc. 1999, 121, 6312. (g) Alibes, R.; Bundle, D. R. J . Org. Chem.
1998, 63, 6288.
The stereoselective construction of R,R-disubstituted
R-amino acids has attracted a great deal of attention in
the synthesis community for some time, and numerous
(9) Koviach, J . L.; Chappell, M. D.; Halcomb, R. L. J . Org. Chem.
2001, 66, 2318.
(10) Lane, J . W.; Halcomb, R. L. Tetrahedron 2001, 57, 6531.
(11) Perron, R.; Albizati, K. F. Chem. Rev. 1989, 89, 1617.
J . Org. Chem, Vol. 68, No. 4, 2003 1349

Lane and Halcomb
elegant methods have been developed.12 This attention
is undoubtedly due to inherent structural challenges of
these compounds as well as their notable effects on
biological activity.13 These quaternary amino acids have
been utilized in studies of enzyme mechanisms14 and as
enzyme inhibitors15 and have been found to exert a strong
influence on the conformation of peptides into which they
are incorporated.16 Many of these compounds are natu-
rally occurring, including a number that are present as
substructures of natural products. Specifically, the R-sub-
stituted serine unit, a structural feature embedded in our
targets, has been investigated in the design of peptides12b
and is contained within natural products such as myrio-
cin, (+)-lactacystin, (+)-conagenin, and sphingofungin
E.17
F IGURE 3. Dialkyl malonate PLE desymmetrization sub-
strates.
mal byproducts and mild reaction conditions. In light of
the study by Nagao and co-workers, we determined that
a similar enzymatic desymmetrization would be ap-
propriate for the synthesis of our chiral nucleophilic
addition precursor 5. The mild nature of the procedure
would tolerate sensitive protecting groups, and enantio-
selectivities were predicted to be relatively high on the
basis of similarities between our substrates and those in
the work reported earlier.17a
Traditionally, R-substituted serines were prepared
through a number of standard methods including re-
arrangements of chiral trichloroacetimidates,17b,18 alkyl-
ation of chiral enolates,19 and ring-opening of chiral
aziridines.20 Additionally, several enzymatic resolution
strategies have been developed to produce R,R-disubsti-
tuted amino acids in enantiomerically pure form from
racemic mixtures.12b However, to our knowledge only one
type of enzyme-catalyzed desymmetrization strategy for
constructing these compounds has been reported.17a,21
This strategy, based on the hydrolytic enzymatic desym-
metrization of R-alkyl aminomalonate derivatives, was
first utilized by Fukuyama and co-workers in their total
synthesis of (-)-tantazole B.21 Fukuyama’s method was
subsequently employed in a recent effort by Nagao and
co-workers.17a The latter study detailed a synthesis of
R-substituted serines based on the enantioselective en-
zymatic hydrolysis of a series of diethyl R-alkyl-R-
(benzyloxycarbonylamino)malonates using pig liver es-
terase (PLE) or rabbit liver esterase (RLE).17a
2. Resu lts a n d Discu ssion
Several dialkyl R-alkynyl-R-(tert-butoxycarbonylamino)-
malonates of the general structure 8 (Figure 3) were
constructed.24 Unfortunately, subjection of these sub-
strates 8 to PLE under a variety of reaction conditions
failed to yield any of the desired desymmetrized hydroly-
sis products. Only starting material and traces of un-
identified byproducts were recovered from these reac-
tions.
These unanticipated results prompted us to refocus our
efforts on obtaining and desymmetrizing a diacetate
substrate bearing functionality similar to that in 8. Like
diesters, diacetates are known to be effective precur-
sors for PLE desymmetrization protocols.22 Furthermore,
such compounds should be readily available through
chemistry developed in our first-generation synthesis.10
The enantioenriched alcohol product would be presum-
ably more convenient to purify than the corresponding
carboxylic acid afforded by an ester hydrolysis, and
should be more readily amenable to protecting group
installation as well.
We were delighted to find that the configuration of the
amino acid component 5 could indeed be established
through a PLE-catalyzed enzymatic desymmetrization of
the symmetric diacetate 9 (Scheme 2). Diacetate 9 was
obtained from acetylation of the diol 11, which was an
intermediate in the first-generation synthesis strategy.10
Employing acetonitrile as a cosolvent, the monoacetate
10 was routinely produced in good yield with enantio-
meric excesses of 80% as measured by chiral GC. The
overhydrolyzed product 11 was easily recovered and
recycled. The highlights of these studies are detailed in
the abbreviated table in Scheme 2.
The important role of enzymes in organic synthesis is
well-documented,22,23 and the advantages include mini-
(12) For reviews on the synthesis of quaternary R-alkylated R-amino
acids, see: (a) Williams, R. M. Synthesis of Optically Active R-Amino
Acids; Pergamon Press: Oxford, 1989. (b) Wirth, T. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 225. (c) Cativiela, C.; Dias-de-Villegas, M. D.
Tetrahedron: Asymmetry 1998, 9, 3517. (d) Cativiela, C.; Dias-de-
Villegas, M. D. Tetrahedron: Asymmetry 2000, 11, 645.
(13) (a) Barrett, G. C. Amino Acids, Peptides and Proteins; The
Chemical Society: London, 1980; Vol. 13, p 1. (b) Hunt, S. In Chemistry
and Biochemistry of the Amino Acids; Barrett, G. C., Ed.; Chapman
and Hall: London, 1985; p 55. (c) Coppala, G. M.; Schuster, H. F.
Asymmetric Synthesis: Construction of Chiral Molecules using Amino
Acids; Wiley: New York, 1987. (d) Williams, R. M. In Organic
Chemistry Series Volume 7: Synthesis of Optically Active R-Amino
Acids; Baldwin, J . E., Magnus, P. D., Eds.; Pergamon: Oxford, 1989.
(14) Walsh, J . J .; Metzler, D. E.; Powell, D.; J acobson, R. A. J . Am.
Chem. Soc. 1980, 102, 7136.
(15) J ung, H. J . In Chemistry and Biochemistry of the Amino Acids;
Barrett, G. C., Ed.; Chapman and Hall: London, 1985; p 227.
(16) (a) Balaram, P. Curr. Opin. Struct. Biol. 1992, 2, 845. (b)
Giannis, A.; Kolter, T. Angew. Chem., Int. Ed. Engl. 1993, 32, 1244.
(c) Burgess, K.; Ho, K.-K.; Pal, B. J . Am. Chem. Soc. 1995, 117, 3808.
(d) Paradisi, M. P.; Torrini, I.; Zecchini, G. P.; Lucente, G.; Gavuzzo,
E.; Mazza, F.; Pochetti, G. Tetrahedron 1995, 51, 2379.
(17) (a) Sano, S.; Hayashi, K.; Miwa, T.; Ishii, T.; Fujii, M.; Mima,
H.; Nagao, Y. Tetrahedron Lett. 1998, 39, 5571 and references therein.
(b) Oishi, T.; Ando, K.; Inomiya, K.; Sato, H.; Iida, M.; Chida, N. Org.
Lett. 2002, 4, 151.
The stereochemistry of 10 could not be assigned
unambiguously at this point. However, this information
was later determined through subsequent transforma-
tions (see below), and the major enantiomer was found
(22) Wong, C.-H.; Whitesides, G. M. Enzymes in Synthetic Organic
Chemistry; Elsevier: New York, 1994.
(18) Hatakeyama, S.; Matsumoto, H.; Fukuyama, H.; Mukugi, Y.;
Irie, H. J . Org. Chem. 1997, 62, 2275.
(19) (a) Seebach, D.; Aebi, J . D. Tetrahedron Lett. 1984, 25, 2545.
(b) Scho¨llkopf, U. Pure Appl. Chem. 1983, 55, 1799.
(20) Davis, F. A.; Zhang, Y.; Rao, A.; Zhang, Z. Tetrahedron 2001,
57, 6345.
(21) Fukuyama, T.; Xu, L. J . Am. Chem. Soc. 1993, 115, 8449.
(23) Ohno, M.; Otsuka, M. Organic Reactions: Chiral Synthons by
Ester Hydrolysis Catalyzed by Pig Liver Esterase; Wiley: New York,
1989; pp 1-55.
(24) (a) Kober, R.; Hammes, W.; Steglich, W. Angew. Chem., Int.
Ed. Engl. 1982, 21, 203. (b) von der Brueck, D.; et al. Tetrahedron
1972, 28, 791.
1350 J . Org. Chem., Vol. 68, No. 4, 2003

Synthesis of Glycosylated Amino Acids
SCHEME 2. Su ccessfu l Desym m etr iza tion of 9
SCHEME 3. Diver gen t Syn th esis of 13 a n d 15
to possess the (S)-configuration shown in Scheme 2. It is
typically more difficult to predict the stereoselectivities
of enzyme-catalyzed transformations of acyclic substrates
such as 9 than of their cyclic counterparts due to the
greater conformational mobilities of open-chain com-
pounds in the relevant active sites.25 This stereochemical
outcome was, however, in agreement with a study
conducted by Norin and co-workers concerning the de-
symmetrization of a series of acyclic malonates.26 Re-
gardless, a judicious protecting group installation strat-
egy in the construction of the nucleophilic addition
precursor 5 would eventually provide selective access to
either configuration at CR independent of the desym-
metrization outcome.
The synthesis of the nucleophilic amino acid which
would ultimately bear the D-serine configuration com-
menced with the protection of the free hydroxyl group of
the enantiomerically enriched alkyne 10 as the 3,4-
dimethoxybenzyl (DMB) ether to give compound 12
(Scheme 3). Previous attempts to incorporate the more
standard 4-methoxybenzyl (PMB) protecting group into
our synthesis were unsuccessful due to difficulties as-
sociated with installation and later removal of this group.
The relatively mild, acid-catalyzed protection employed
a modification of a recent protocol by Mukaiyama and
co-workers.27 Conditions for this transformation were
optimized in an effort to avoid significant racemization
of 10 through acetate migration. A racemization of a
similar substrate was documented recently.28 Removal
of the acetate protecting group of 12 under mild condi-
tions followed by silyl protection of the resulting free
hydroxyl group gave the appropriately protected alkyne
13 in good yield.
Alternatively, the benzyl and silyl protecting groups
were successfully installed in reverse order to provide the
enantiomer of 13, compound 15, which would ultimately
bear the L-serine configuration. Initial protection of the
free primary hydroxyl group in 10 provided the silyl ether
14. The acetate protecting group on 14 was then removed
under mild conditions in an effort to avoid silyl migration.
Subsequent protection of the resulting free primary
hydroxyl group as the DMB ether gave 15 in good yield
(Scheme 3). Enantiomeric ratios of both 13 and 15 were
determined by 1H NMR analysis of their respective
diastereomeric (R)-MTPA esters,29 and were found to be
ca. 9:1 in each case. The MTPA esters were prepared by
esterification of the free primary hydroxyl groups af-
forded by desilylation of 13 and 15. This important
analysis verified the successful suppression of any race-
mization pathways.
Following the successful preparation of 13 and 15, we
were positioned to execute a convergent coupling between
(27) Nakano, M.; Kikuchi, W.; Matsuo, J -i.; Mukaiyama, T. Chem.
Lett. 2001, 424.
(28) Akai, S.; Naka, T.; Fujita, T.; Takebe, Y.; Tsujino, T.; Kita, Y.
J . Org. Chem. 2002, 67, 411.
(29) (a) Dale, J . A.; Mosher, H. S. J . Am. Chem. Soc. 1973, 95, 512.
(b) Sullivan, G. R.; Dale, J . A.; Mosher, H. S. J . Org. Chem. 1973, 38,
2143.
(25) Toone, E. J .; Werth, M. J .; J ones, J . B. J . Am. Chem. Soc. 1990,
112, 4946.
(26) Bjorkling, F.; Boutelje, J .; Gatenbeck, S.; Hult, K.; Norin, T.;
Szmulik, P. Tetrahedron 1985, 41, 1347.
J . Org. Chem, Vol. 68, No. 4, 2003 1351

Lane and Halcomb
SCHEME 4. Syn th esis of th e Con str a in ed Glycop ep tid e Bea r in g th e D-Con figu r a tion
SCHEME 5. Syn th esis of th e Con str a in ed Glycop ep tid e Bea r in g th e L-Con figu r a tion
the respective amino acid and carbohydrate components
of our targets. The incorporation of the D-serine config-
uration was accomplished in good overall yields without
significant difficulties. Addition of a 3-fold excess of the
dianion of 13 to the lactone 169 afforded a hemiketal
intermediate (Scheme 4). However, removal of unreacted
13 at this point using conventional chromatography was
only partially successful. Therefore, the product mixture
including unreacted 13 was subjected to acidic deprotec-
tion conditions to produce 17. Then, desilylated 13 could
be easily removed by chromatography and recycled. All
intermediates following the acetylide addition and prior
to the spiroketal were comprised of two major dia-
stereomers, which were presumed to be anomers at C1
of the sugar. Partial reduction of the alkyne group of 17
to the cis-alkene and acid-catalyzed spiroketalization
were performed in a one-pot reaction to give one major
product, confirming an excess of one configuration at CR.
Removal of the silyl protecting groups followed by per-
acetylation afforded 18 in good overall yield and purity.
Reduction of the azide and olefin functional groups in
18 occurred with unexpected simultaneous removal of the
dimethoxybenzyl group to provide the acetamide 19. A
two-step oxidation sequence then provided the desired
acid 20 in excellent yield and purity.
To selectively obtain the L-serine configuration, experi-
ments were conducted to incorporate 15 through the
usual acetylide addition to 16. The addition as well
as the subsequent removal of the primary TBS pro-
tecting group were successful, and two major anomers
were again observed, each of which, as before, consisted
of one major configuration at CR. Unfortunately, at-
tempts to carry out the ensuing spiroketalization led to
complicated product mixtures. 1H NMR analysis of these
mixtures suggested that the tert-butylcarbamate (BOC)
protecting group was lost in the majority of products. Our
previous strategy entailed the successful spiroketaliza-
tion of a similar compound which lacked the DMB
group.10 Therefore, we hypothesized that the DMB pro-
tecting group was adversely affecting the spiroketaliza-
tion in this instance. The loss of the BOC protecting
group was possibly facilitated by the relief of unfavor-
1352 J . Org. Chem., Vol. 68, No. 4, 2003

Synthesis of Glycosylated Amino Acids
the synthesis. This route enables production of quantities
of material necessary for incorporation into peptides and
for subsequent biological evaluation and structural stud-
ies.
4. Exp er im en ta l Section
F IGURE 4. â-Anomer 24.
1
Gen er a l Meth od s. H and 13C NMR spectra are reported
in parts per million (δ) relative to the peaks for CHCl3 (7.24
and 77.23 ppm, respectively) or CD3OD (3.31 and 49.15 ppm,
respectively) as the internal standard.
able steric interactions with the tert-butyldiphenylsilyl
(TBDPS) protecting group at O6 of the sugar. The notion
seemed reasonable since molecular models of this spiro-
ketal suggested that these two large protecting groups
would be in close proximity to each other. This same
interaction would not be present in a spiroketal bearing
the D-serine configuration. Options to replace the DMB
protecting group with smaller groups, as well as alterna-
tive reaction conditions for the spiroketalization, were
explored, but were found to have little effect on the
outcome of the reaction. Therefore, an alternate protect-
ing group pattern was developed in which no unfavorable
interactions between these positions would be present.
To be specific, a protecting group that could be removed
prior to spiroketalization was installed on O6 of the
carbohydrate component.
The revised route commenced with the addition of a
3-fold excess of the dianion of 15 to the modified lactone
21,9,30 affording a hemiketal intermediate (Scheme 5).
The ensuing deprotection was executed on this interme-
diate, which was contaminated with unreacted 15. The
mixture was subjected to acidic conditions as before to
successfully liberate the two desired primary hydroxyl
groups and give 22. Desilylated 15 was removed and
recycled at this point. The intermediate 22, which now
lacked an O6 protecting group on the sugar, was sub-
jected to the one-pot hydrogenation/spiroketalization
reaction conditions employed for 17. Although the desired
spiroketal was produced, yields were low, and signifi-
cant amounts of byproducts which lacked the DMB
protecting group were also obtained. More successful
conditions involved initial hydrogenation of 22 in the
presence of a mild acid to give the intermediate cis-
alkene. The catalyst was then removed, and the mixture
was treated with a stronger acid to induce spiroketal-
ization. Protecting group manipulations as before gave
compound 23 and the â-anomer 24 (see Figure 4) in good
combined overall yield. The stereochemistry of 24 was
verified through NOESY experiments. Attempts to equili-
brate the â-anomer to the R-anomer at any point after
the cyclization were unsuccessful. Reduction of 23 under
the usual conditions gave compound 25. Oxidation of the
primary alcohol provided the carboxylic acid 26. The
structures of both 20 and 26 were confirmed by conver-
sion to their corresponding methyl esters, whose struc-
tures were previously established.10
(1,1-Bis(acetoxym eth yl)pr op-2-yn yl)car bam ic Acid ter t-
Bu tyl Ester (9). Diol 1110 (2.850 g, 13.24 mmol, 1.0 equiv)
was dissolved in 30 mL of a 2:1 pyridine/Ac2O solution at rt,
and DMAP (81 mg, 0.66 mmol, 0.05 equiv) was added in one
portion. The resulting mixture was stirred for 12 h and was
then concentrated on a high-vacuum (0.1 Torr) rotary evapora-
tor to give a dark orange oil. The oil was chromatographed on
silica gel (3:1 hexanes/EtOAc) to give 9 as a powdery white
solid (3.708 g, 12.40 mmol, 94%) after drying under high
vacuum (0.1 Torr) for several days. IR (thin film): 3283, 2978,
1748 cm-1 1H NMR (500 MHz, CDCl3): δ 4.97 (s, 1H), 4.38
.
(AB, J ) 11.1 Hz, ∆ν ) 11.1 Hz, 4H), 2.39 (s, 1H), 2.09 (s, 6H)
1.44 (s, 9H). 13C NMR (125 MHz, CDCl3): δ 170.6, 154.1, 81.1,
80.0, 73.5, 64.9, 53.4, 28.5, 21.0. TLC (SiO2, 50% EtOAc/
hexanes): Rf ) 0.65. Mp: 73-75 °C. HRMS (m/z): calcd for
C
14H21NO6 (M + H)+ 300.1447, found 300.1438. Anal. Calcd
for C14H21NO6: C, 56.18; H, 7.07; N, 4.68. Found: C, 55.99;
H, 6.82; N, 4.78.
(S)-(1-Acet oxym et h yl-1-h yd r oxym et h ylp r op -2-yn yl)-
ca r ba m ic Acid ter t-Bu tyl Ester (10). Three separate reac-
tions were individually and simultaneously prepared in the
following manner. A 100 mL round-bottomed flask was loaded
with 37 mL of phosphate buffer (pH 6.5, 0.1 M) followed by
4.6 mL of CH3CN. To this stirring mixture at rt was added
PLE (lyophilized powder (20 units/mg of solid), 67 mg) followed
by 9 (300 mg, 1.0 mmol). The three solutions were each stirred
for 3 h, then saturated with excess NaCl(s), and allowed to
stir for an additional 5 min. The three resulting mixtures were
combined upon filtration through Celite with EtOAc washings.
The biphasic filtrate was concentrated on a high-vacuum (0.1
Torr) rotary evaporator with toluene azeotropes as necessary
to remove excess water, and the resulting residue was dis-
solved in acetone. This mixture of product and insoluble
inorganic salts was filtered, with additional acetone washings
as necessary, and the resulting organic filtrate was concen-
trated to give an oil. The oil was chromatographed on silica
gel (1:1 hexane/EtOAc and then EtOAc) to give 10 as a clear
oil (516 mg, 2.02 mmol, 67% conversion, 94% yield based on
recovered 11). Compound 10 was determined to be a 9:1 ratio
of enantiomers in favor of the (S)-configuration by chiral GC
(Beta Dex 120). [R]28D: +8.06 (c 3.00, CHCl3). IR (thin film):
3290, 2978, 1719 cm-1. 1H NMR (500 MHz, CDCl3): δ 5.10 (s,
1H), 4.37 (AB, J ) 11.3 Hz, ∆ν ) 11.2 Hz, 2H), 3.80 (s, 2H),
2.42 (s, 1H), 2.11 (s, 3H), 1.44 (s, 9H). 13C NMR (125 MHz,
CDCl3): δ 171.1, 154.9, 80.9, 80.8, 73.6, 65.5, 64.6, 55.2, 28.4,
20.9. TLC (SiO2, 50% EtOAc/ hexanes): Rf ) 0.41. HRMS (m/
z): calcd for C12H19NO5 (M + H)+ 258.1341, found 258.1347.
Anal. Calcd for C12H19NO5: C, 56.02; H, 7.44; N, 5.44. Found:
C, 56.35; H, 7.20; N, 5.32.
2-(3,4-Dim eth oxyben zyloxy)-3-n itr op yr id in e. In a modi-
fied literature procedure,27 KOH (2.832 g, 50.50 mmol, 12.0
equiv) and K2CO3 (1.744 g, 12.62 mmol, 3.0 equiv) were
dissolved in 60 mL of toluene. 3,4-Dimethoxybenzyl alcohol
(3.184 g, 18.93 mmol, 4.5 equiv) in 20 mL of toluene was then
added rapidly by syringe to the stirring mixture, followed by
2-chloro-3-nitropyridine (2.000 g, 12.62 mmol, 3.0 equiv). After
the resulting mixture was stirred for 2 min, tris(3,6-dioxa-
heptylamine) (0.40 mL, 1.26 mmol, 0.3 equiv) was added
dropwise, and the resulting brown solution was stirred for 3
h. The reaction mixture was then immediately filtered through
Celite with toluene washings as necessary. The filtrate was
3. Con clu sion
In conclusion, stereoselective syntheses of protected
versions of two constrained glycopeptides, 2 and 3, were
developed. A PLE-catalyzed enzymatic desymmetrization
of the diacetate 10 was employed as a key component in
(30) (a) Crich, D.; Ritchie, T. J . J . Chem. Soc., Perkin Trans. 1 1990,
4, 945. (b) Rollin, P.; Sinay¨, P. Carbohydr. Res. 1981, 98, 139. (c)
Mlynarski, J .; Banaszek, A. Tetrahedron 1999, 55, 2785.
J . Org. Chem, Vol. 68, No. 4, 2003 1353

Lane and Halcomb
subsequently concentrated on a high-vacuum (0.1 Torr) rotary
evaporator, and the crude yellow oil was chromatographed on
silica gel (3:1 and then 1:1 hexanes/EtOAc) to give a yellow
solid which was recrystallized in hexanes/benzene. The product
was isolated as yellow, needlelike crystals (2.565 g, 8.84 mmol,
phase was extracted with 2 × 50 mL of EtOAc. The combined
organic phases were dried (MgSO4), filtered, and concentrated
to give a crude oil. This product was subsequently dissolved
in 8 mL of a solution of ammonia in MeOH (1 M), and the
resulting solution was stirred at rt for 12 h. The reaction
mixture was then concentrated to give a crude oil which was
chromatographed on silica gel (3:1 hexanes/EtOAc) to give the
product as a clear oil (948 mg, 2.86 mmol). TLC (SiO2, 25%
EtOAc/hexanes): Rf ≈ 0.35. This product was subsequently
dissolved in 19 mL of CH2Cl2. To this mixture was added
2-(3,4-dimethoxybenzyloxy)-3-nitropyridine (332 mg, 1.14 mmol,
0.4 equiv) followed by camphorsulfonic acid (17 mg, 0.07 mmol,
0.025 equiv), and the resulting mixture was stirred for 1 h at
rt. At this time, the above additions of 2-(3,4-dimethoxy-
benzyloxy)-3-nitropyridine (332 mg, 1.14 mmol, 0.4 equiv)
followed by camphorsulfonic acid (17 mg, 0.07 mmol, 0.025
equiv) were repeated. Shortly after this second addition, a
white precipitate formed. After 1 h, the addition/stirring
sequence was repeated three more times as above. Upon
completion of the final 1 h stirring period, additional cam-
phorsulfonic acid (17 mg, 0.07 mmol, 0.025 equiv) was added
to ensure complete reaction, and the mixture was stirred for
an additional 12 h. The mixture was diluted with 50 mL of
CH2Cl2 and quenched wth 25 mL of saturated aq NH4Cl. The
phases were separated, and the aq phase was extracted with
2 × 50 mL of CH2Cl2. The combined organic phases were dried
(MgSO4), filtered, and concentrated to give a crude yellow oil.
This oil was chromatographed on silica gel (3:1 hexanes/
EtOAc) to give 15 as a clear oil (970 mg, 2.02 mmol, 62% from
10). Compound 15 was determined to be a 9:1 ratio of
enantiomers in favor of the (R)-configuration through deriva-
tization to the corresponding Mosher’s esters.29 [R]28D: -1.97
70%). IR (thin film): 3080, 2831, 1600 cm-1 1H NMR (500
.
MHz, CDCl3): δ 8.38 (dd, J ) 4.8, 1.8 Hz, 1H), 8.26 (dd, J )
7.9, 1.8 Hz, 1H), 7.09 (d, J ) 1.8 Hz, 1H), 7.04-7.00 (m, 1H),
7.02 (d, J ) 7.9 Hz, 1H), 6.84 (d, J ) 8.1 Hz, 1H), 5.50 (s, 2H),
3.89 (s, 3H) 3.86 (s, 3H). 13C NMR (125 MHz, CDCl3): δ 156.2,
151.8, 149.2, 149.0, 135.3, 134.4, 128.7, 120.5, 116.9, 111.2,
111.1, 69.0, 56.1, 56.0. TLC (SiO2, 25% EtOAc/hexanes): Rf )
0.16. Mp: 90-92 °C. HRMS (m/z): calcd for C14H14N2O5
290.0903, found 290.0894. Anal. Calcd for C14H14N2O5: C,
57.93; H, 4.86; N, 9.65. Found: C, 58.32; H, 4.89; N, 9.78.
(S )-[1-(t er t -Bu t yld im e t h ylsila n yloxym e t h yl)-1-(3,4-
d im eth oxyben zyloxym eth yl)p r op -2-yn yl]ca r ba m ic Acid
ter t-Bu tyl Ester (13). Monoacetate 10 (9:1 ratio of enanti-
omers, 777 mg, 3.02 mmol, 1.0 equiv) was dissolved in 25 mL
of CH2Cl2 at rt. To this mixture was added 2-(3,4-dimethoxy-
benzyloxy)-3-nitropyridine (435 mg, 1.51 mmol, 0.5 equiv)
followed by a solution of camphorsulfonic acid (17 mg, 0.08
mmol, 0.025 equiv) in 1 mL of CH2Cl2, and the resulting
mixture was stirred for 1.5 h at rt. The above additions of
2-(3,4-dimethoxybenzyloxy)-3-nitropyridine (435 mg, 1.51 mmol,
0.5 equiv) followed by a solution of camphorsulfonic acid (17
mg, 0.08 mmol, 0.025 equiv) in 1 mL of CH2Cl2 were then
repeated. Shortly after this second addition, a white precipitate
formed. After 1.5 h, the addition/stirring sequence was re-
peated. Upon completion of the final 1.5 h stirring period,
additional camphorsulfonic acid (17 mg, 0.08 mmol, 0.025
equiv) in 1 mL of CH2Cl2 was added to ensure complete
reaction, and the mixture was stirred for an additional 12 h.
The mixture was diluted with 50 mL of CH2Cl2 and quenched
with 25 mL of saturated aq NH4Cl. The phases were separated,
and the aq phase was extracted with 2 × 50 mL of CH2Cl2.
The combined organic phases were dried (MgSO4), filtered, and
concentrated to give a crude yellow oil. This crude oil was
chromatographed on silica gel (3:1 hexanes/EtOAc) to give the
product as a clear oil. TLC (SiO2, 25% EtOAc/hexanes): Rf ≈
0.30. This product was subsequently dissolved in 8 mL of a
solution of ammonia in MeOH (1 M), and the resulting solution
was stirred at rt for 12 h. The reaction mixture was then
concentrated to give the crude product (800 mg, 2.18 mmol),
which was redissolved in 15 mL of DMF at rt. Imidazole (592
mg, 8.72 mmol, 4.0 equiv) and tert-butyldimethylchlorosilane
(1.314 g, 8.72 mmol, 4.0 equiv) were then successively added
to the solution, and the resulting mixture was heated to 45
°C and stirred for 12 h. The reaction mixture was then cooled
to rt and concentrated on a high-vacuum (0.1 Torr) rotary
evaporator. The residue was dissolved in a mixture of 50 mL
of EtOAc and 25 mL of saturated aq NH4Cl. The phases were
separated, and the aq phase was extracted with 2 × 50 mL of
EtOAc. The combined organic phases were dried (MgSO4),
filtered, and concentrated to give a crude product. This product
was chromatographed on silica gel (3:1 hexanes/EtOAc) to give
13 as a clear oil (840 mg, 1.75 mmol, 59% from 10). Compound
13 was determined to be a 9:1 ratio of enantiomers in favor of
the (S)-configuration through derivatization to the correspond-
ing Mosher’s esters.29 [R]28D: +2.98 (c 2.00, CHCl3).
(c 2.00, CHCl3). IR (thin film): 3437, 2951, 2854, 1724 cm-1
.
1H NMR (500 MHz, CDCl3): δ 6.88-6.79 (m, 3H), 5.02 (s, 1H),
4.53 (s, 2H), 3.87-3.78 (m, 2H), 3.86 (s, 3H), 3.85 (s, 3H), 3.74
(d, J ) 9.3 Hz, 1H), 3.59 (d, J ) 9.3 Hz, 1H), 2.33 (s, 1H), 1.41
(s, 9H) 0.85 (s, 9H), 0.04 (s, 6H). 13C NMR (125 MHz, CDCl3):
δ 154.6, 149.2, 148.8, 130.6, 120.6, 111.2, 110.0, 82.7, 80.0, 73.6,
72.0, 71.0, 64.8, 56.1, 56.0, 55.0, 28.6, 26.0, 18.4, -5.1, -5.2.
TLC (SiO2, 25% EtOAc/hexanes): Rf ) 0.37. HRMS (m/z):
calcd for C25H41NO6Si (M + H)+ 480.2781, found 480.2758.
Anal. Calcd for C25H41NO6Si: C, 62.60; H, 8.62; N, 2.92.
Found: C, 62.93; H, 8.53; N, 2.99.
(R)-MTP A Der iva tive of 15. All (R)-MTPA derivatives
were prepared according to published procedures.29 Products
were purified by silica gel column chromatography (3:1 hex-
anes/EtOAc) to give quantitatively the (R)-MTPA esters of 13
and 15. 1H NMR analysis indicated a 9:1 ratio of diastereomers
on the basis of integration of the alkyne protons. The minor
diastereomer of the MTPA ester of 13 was identical to the
major diastereomer produced from the derivatization of 15 and
1
vice versa. H NMR (500 MHz, CDCl3): δ 7.57-7.48 (m, 2H),
7.41-7.32 (m, 3H), 6.84-6.76 (m, 3H), 4.99 (s, 1H), 4.74 (d, J
) 10.5 Hz, 1H), 4.56 (d, J ) 10.5 Hz, 1H), 4.41 (AB, J ) 11.7
Hz, ∆ν ) 16.5 Hz, 2H), 3.86 (s, 6H), 3.55 (s, 2H), 3.50 (s, 3H),
2.37 (s, 1H), 1.41 (s, 9H). MS (m/z): calcd for C29H34NO8F3 (M
+ Na)+ 604, found 604.
(R)-MTP A Der iva tive of 13. 1H NMR analysis of the
1
product indicated a 9:1 ratio of diastereomers. H NMR (500
MHz, CDCl3): δ 7.52-7.47 (m, 2H), 7.41-7.32 (m, 3H), 6.85-
6.78 (m, 3H), 4.98 (s, 1H), 4.66 (AB, J ) 10.5 Hz, ∆ν ) 14.3
Hz, 2H), 4.46 (s, 2H), 3.86 (s, 6H), 3.59 (AB, J ) 9.5 Hz, ∆ν )
15.8 Hz, 2H), 3.48 (s, 3H), 2.34 (s, 1H), 1.40 (s, 9H). MS (m/z):
calcd for C29H34NO8F3 (M + Na)+ 604, found 604.
Com p ou n d 17. To a solution of 13 (1.167 g, 2.44 mmol, 3.0
equiv) in 24.4 mL of anhydrous THF at rt was added hexa-
methylphosphoramide (1.70 mL, 9.74 mmol, 12.0 equiv). The
mixture was cooled to -78 °C, and n-butyllithium (1.52 M in
hexanes, 3.36 mL, 5.12 mmol, 6.3 equiv) was added slowly.
The resulting pale yellow mixture was stirred for 1.5 h at -78
°C, after which a solution of 169 (543 mg, 0.81 mmol, 1.0 equiv)
in 8.1 mL of anhydrous THF was added slowly by cannula.
(R )-[1-(t er t -Bu t yld im e t h ylsila n yloxym e t h yl)-1-(3,4-
d im eth oxyben zyloxym eth yl)p r op -2-yn yl]ca r ba m ic Acid
ter t-Bu tyl Ester (15). Monoacetate 10 (9:1 ratio of enanti-
omers, 850 mg, 3.30 mmol, 1.0 equiv) was dissolved in 22 mL
of DMF at rt. Imidazole (446 mg, 6.60 mmol, 2.0 equiv) and
tert-butyldimethylchlorosilane (988 mg, 6.60 mmol, 2.0 equiv)
were then sucessively added to the solution, and the resulting
mixture was heated to 45 °C and stirred for 12 h. The reaction
mixture was then cooled to rt and concentrated on a high-
vacuum (0.1 Torr) rotary evaporator. The resulting residue was
dissolved in a mixture of 50 mL of EtOAc and 25 mL of
saturated aq NH4Cl. The phases were separated, and the aq
1354 J . Org. Chem., Vol. 68, No. 4, 2003

Synthesis of Glycosylated Amino Acids
The mixture was stirred for an additional 25 min at -78 °C
and was then quenched with 1 mL of H2O, followed by 1 mL
of saturated aq NH4Cl. The heterogeneous mixture was
warmed to rt and was then diluted with 50 mL of EtOAc and
an additional 35 mL of saturated aq NH4Cl. The phases were
separated, and the aq phase was extracted with 2 × 50 mL of
EtOAc. The combined organic phases were dried (MgSO4),
filtered, and concentrated. The concentrated solution was
chromatographed on silica gel (9:1 and then 3:1 hexanes/
EtOAc) to give a mixture of unreacted 13 and addition product.
TLC (products) (SiO2, 25% EtOAc/ hexanes): Rf values ∼0.44-
0.50. This mixture of 13 and the addition products could be
quantitatively separated by HPLC if desired, but was typically
carried on without purification.
in one portion, and the mixture was stirred for 5 h at rt. The
solution was concentrated on a high-vacuum (0.1 Torr) rotary
evaporator, and the resulting oil was chromatographed on
silica gel (1:1 hexane/EtOAc) to give the product mixture as a
clear foam. The product was further purified by HPLC (silica
gel, 1:1 hexanes/EtOAc). Compound 18 was isolated as a clear
foam (273 mg, 0.40 mmol, 53% from 17) in greater than 90%
purity. [R]28D: +31.5 (c 1.85, CHCl3). IR (thin film): 2968, 2105,
1747, 1703 cm-1. 1H NMR (500 MHz, CDCl3): δ 6.86-6.76 (m,
3H), 6.42 (d, J ) 10.1 Hz, 1H), 5.71 (d, J ) 10.1 Hz, 1H), 5.43-
5.33 (m, 1H), 5.38 (dd, J ) 10.9, 3.4 Hz, 1H), 4.97 (s, 1H), 4.44
(AB, J ) 11.8 Hz, ∆ν ) 10.8 Hz, 2H), 4.25 (t, J ) 6.6 Hz, 1H),
4.15-4.00 (m, 2H), 3.97 (d, J ) 11.5 Hz, 1H), 3.85 (s, 3H),
3.84 (s, 3H), 3.79 (d, J ) 11.5 Hz, 1H), 3.72-3.82 (m, 1H),
3.62 (d, J ) 9.5 Hz, 1H), 3.48 (d, J ) 10.9 Hz, 1H), 2.13 (s,
3H) 2.03 (s, 3H), 1.97 (s, 3H), 1.38 (s, 9H). 13C NMR (125 MHz,
CDCl3): δ 170.6, 170.3, 170.0, 155.2, 149.1, 148.8, 134.0, 130.6,
127.0, 120.4, 111.1, 111.0, 96.6, 79.9, 73.7, 70.3, 68.6, 67.9, 67.6,
65.3, 61.6, 61.0, 56.1, 56.0, 51.4, 28.5, 20.8 (3H). TLC (SiO2,
50% EtOAc/hexanes): Rf ) 0.33. HRMS (m/z): calcd for
The above mixture was dissolved in 20 mL of an 8:1:1 AcOH/
H2O/MeOH solution. Two drops of aqueous HCl solution (2 N)
was then added to the mixture, and the resulting solution was
stirred for 2 h at rt. The reaction was then diluted with excess
toluene, and the resulting biphasic mixture was concentrated
on a high-vacuum (0.1 Torr) rotary evaporator at a tempera-
ture not exceeding 30 °C. The resulting crude oil was im-
mediately chromatographed on silica gel (3:1 and then 1:1
hexanes/EtOAc) to give 17 as a foam (574 mg, 0.56 mmol, 68%
from 16). Desilylated 13 was recovered as a clear oil (547 mg,
1.49 mmol). Compound 17 was isolated as an inseparable
mixture comprised of a major product bearing the D-configu-
ration at CR, observed to be a 1:1 mixture of anomers, and a
minor product believed to be an anomeric mixture of the
L-configuration at CR, as determined by 1H NMR. [R]28D: +22.5
(c 2.25, CHCl3). IR (thin film): 3417, 2955, 2854, 2109, 1713
cm-1. 1H NMR (500 MHz, CDCl3): δ 7.65-7.57 (m, 4H), 7.42-
7.31 (m, 6H), 6.86-6.76 (m, 3H), 5.34-5.23 (m, 1H), 4.52-
4.42 (m, 2H), 4.08-3.57 (m, 17H), 1.43-1.35 (s (minor), δ 1.40;
s (major), δ 1.382; s (major), δ 1.377; s (minor), δ 1.368; s
(minor), δ 1.365; total 9H), 1.07-1.00 (s (minor), δ 1.06; s
(major), δ 1.03; s (major), δ 1.02; total 9H), 0.97-0.76 (s
(major), δ 0.943; s (minor), δ 0.935; s (major), δ 0.93; s (minor),
δ 0.90; s (minor), δ 0.89; s (major), δ 0.81; s (major), δ 0.80; s
(minor), δ 0.782; s (minor), δ 0.780; total 18H), 0.19-0.10 (s
(minor), δ 0.17; s (major), δ 0.16; s (major), δ 0.15; s (major),
δ 0.14; s (major), δ 0.13; s (major), δ 0.11; s (minor), δ 0.10; s
(minor), δ 0.09; s (minor), δ 0.07; s (major), δ 0.03; s (minor),
δ 0.02; s (major), δ -0.01; s (minor), δ -0.016; s (minor), δ
-0.019; s (minor), δ -0.08; total 12H). 13C NMR (125 MHz,
CDCl3): δ 155.7, 154.9, 149.3, 149.2, 149.1, 149.0, 135.9, 135.8,
135.7, 133.7, 133.6, 133.5, 133.4, 130.1, 130.0, 129.9, 129.8,
127.9, 127.8, 127.7, 120.8, 120.7, 111.3, 111.2, 111.1, 94.8, 92.3,
84.8, 82.2, 80.7, 76.0, 73.9, 73.8, 73.6, 73.4, 72.4, 72.2, 71.5,
71.1, 70.9, 67.8, 67.2, 66.7, 63.0, 62.3, 56.1, 55.1, 29.9, 28.5,
28.4, 27.1, 27.0, 26.6, 26.5, 26.4, 26.3, 19.4, 19.3, 18.7, 18.6,
13.9, -3.4, -3.5, -3.7, -3.8, -4.3, -4.4, -4.5, -4.6. TLC (SiO2,
25% EtOAc/ hexanes): Rf ) 0.13. MS (m/z): calcd for
C
31H42N4O13 678.2748, found 678.2771.
Com p ou n d 19. Compound 18 (182 mg, 0.27 mmol) was
dissolved in 12 mL of a 20:1 EtOAc/Ac2O solution, and 10%
Pd/C (91 mg) was added to the mixture. The flask was
evacuated under aspirator vacuum and refilled with hydrogen
three times, and then the mixture was stirred under hydrogen
(1 atm) for 6 h. The mixture was then filtered through Celite,
and concentrated to give an oil. The oil was chromatographed
on silica gel (EtOAc) to give 19 as a white foam (87 mg, 0.16
mmol, 59%). [R]28D: +66.6 (c 0.70, CHCl3). IR (thin film): 3397,
2968, 1741, 1654 cm-1. 1H NMR (500 MHz, CDCl3): δ 5.81 (s,
1H), 5.32 (d, J ) 3.2 Hz, 1H), 5.15 (dd, J ) 11.1, 3.4 Hz, 1H),
4.94 (s, 1H), 4.34 (t, J ) 10.7 Hz, 1H), 4.12 (dd, J ) 11.1, 7.1
Hz, 1H), 4.06 (dd, J ) 11.3, 6.0 Hz, 1H), 4.03-3.98 (m, 1H),
3.71 (d, J ) 10.9 Hz, 1H), 3.65 (d, J ) 11.3 Hz, 1H), 3.56-
3.46 (m, 1H), 3.50 (d, J ) 11.7 Hz, 1H), 2.14 (s, 3H), 2.08-
2.01 (m, 1H), 2.03 (s, 3H), 2.00 (s, 3H), 1.96 (s, 3H), 1.77 (dt,
J ) 15.3, 4.8 Hz, 1H), 1.72-1.60 (m, 3H), 1.40 (s, 9H). 13C NMR
(100 MHz, CDCl3): δ 171.3, 170.7, 170.6, 170.5, 156.2, 98.9,
80.7, 69.1, 67.5, 67.4, 67.3, 65.4, 62.1, 54.1, 51.0, 28.6, 25.7,
23.4, 23.2, 21.0, 20.9 (2H). TLC (SiO2, 100% EtOAc): Rf ) 0.34.
HRMS (m/z): calcd for C24H38N2O12 (M + H)+ 547.2503, found
547.2489.
Com p ou n d 20. To a solution of 19 (58 mg, 0.11 mmol, 1.0
equiv) in 2.2 mL of CH2Cl2 at rt was added NaHCO3 (68 mg)
followed by Dess-Martin periodinane (90 mg, 0.21 mmol, 2.0
equiv). The reaction mixture was stirred for 9 h, after which
it was quenched with 2 mL of a Na2S2O3 solution (25 g of
Na2S2O3 per 100 mL). After being stirred for 15 min, the
mixture was diluted with 15 mL of CH2Cl2 and 15 mL of H2O.
The phases were separated, and the aq phase was extracted
with 2 × 10 mL of CH2Cl2. The combined organic phases were
dried (Na2SO4), filtered, and concentrated. The resulting
product was dissolved in 3.5 mL of 4:1 tBuOH/H2O. NaH2PO4
(31 mg, 0.22 mmol, 2.0 equiv), 2-methyl-2-butene (2.0 M in
THF, 0.22 mL, 0.44 mmol, 4.2 equiv), and finally NaClO2 (58
mg, 0.64 mmol, 6.0 equiv) were successively added, and the
solution was stirred at rt for 12 h. The reaction mixture was
then diluted with 15 mL of H2O and 15 mL of EtOAc. The
phases were separated, and the aq phase was extracted with
2 × 10 mL of EtOAc. The combined organic phases were
washed with 10 mL of brine, dried (Na2SO4), filtered, and
concentrated to give an oil. The oil was chromatographed on
silica gel (EtOAc and then 95:5 EtOAc/AcOH) to give 20 as a
white foam (53 mg, 0.09 mmol, 89%). [R]28D: +80.7 (c 1.15,
MeOH). IR (thin film): 3354, 2974, 1736, 1654 cm-1. 1H NMR
(500 MHz, CD3OD): δ 8.03 (d, J ) 9.9 Hz, 1H), 7.12 (s, 1H),
5.39 (d, J ) 3.4 Hz, 1H), 5.16 (dd, J ) 11.1, 3.2 Hz, 1H), 4.32-
4.23 (m, 1H), 4.22 (dd, J ) 10.5, 7.5 Hz, 1H), 4.18-4.13 (m,
1H), 4.13-4.07 (m, 1H), 3.96 (AB, J ) 11.3 Hz, ∆ν ) 30.7 Hz,
2H), 2.19 (dt, J ) 13.7, 4.6 Hz, 1H), 2.15 (s, 3H), 2.08-1.86
(m, 2H), 2.05 (s, 3H) 2.00 (s, 3H), 1.93 (s, 3H), 1.55-1.47 (m,
C
53H82N4O11Si3 (M + Na)+ 1057, found 1057.
Com p ou n d 18. To a solution of 17 (779 mg, 0.75 mmol,
1.0 equiv) in 53 mL of EtOAc was added 10% Pd/C (512 mg)
followed by camphorsulfonic acid (175 mg, 0.75 mmol, 1.0
equiv). The flask was evacuated under aspirator vacuum and
refilled with hydrogen three times, and then the mixture was
stirred under hydrogen (1 atm) for 22 h. The mixture was then
filtered through Celite and quenched with 2 mL of triethyl-
amine. The solution was concentrated to give an oil, which
was chromatographed on silica gel (3:1 hexanes/EtOAc) to give
the product mixture as a clear foam (557 mg, 0.55 mmol). TLC
(SiO2, 50% EtOAc/hexanes): Rf ≈ 0.66. This product was
dissolved in 11 mL of THF, and tetrabutylammonium fluoride
(1.0 M in hexanes, 2.74 mL, 2.74 mmol, 5.0 equiv) was added
dropwise. The solution was stirred at rt for 12 h, after which
the reaction mixture was chromatographed on silica gel
(EtOAc and then 9:1 EtOAc/MeOH). The product was isolated
as a clear foam. TLC (SiO2, 90% EtOAc/MeOH): Rf ≈ 0.52.
The product mixture was taken up in 9 mL of a 2:1 pyridine/
Ac2O solution. A catalytic amount of DMAP was then added
J . Org. Chem, Vol. 68, No. 4, 2003 1355

Lane and Halcomb
1H), 1.44 (s, 9H). 13C NMR (100 MHz, CD3OD): δ 174.4, 172.6,
171.1, 171.0, 170.7, 156.1, 98.1, 79.3, 69.4, 67.7, 67.4, 63.1, 62.2,
56.4, 50.7, 27.6, 25.4, 24.7, 21.5, 19.4 (2H), 19.3. TLC (SiO2,
EtOAc with 2% AcOH): Rf ) 0.17. HRMS (m/z): calcd for
believed to be an anomeric mixture of the D-configuration at
1
CR by H NMR. [R]28D: +38.6 (c 1.45, CHCl3). IR (thin film):
1
3430, 2952, 2105, 1638 cm-1. H NMR (500 MHz, CDCl3): δ
6.84-6.77 (m, 3H), 5.64-5.26 (s (major), δ 5.55; s (minor), δ
5.49; s (minor), δ 5.33; s (major), δ 5.30; total 1H), 4.56-4.41
(m, 2H), 4.20-3.40 (m, 19H), 1.43-1.34 (s (major), δ 1.40; s
(minor), δ 1.39; s (major), δ 1.38; total 9H), 0.95-0.82 (s
(major), δ 0.92; s (major), δ 0.91; s (minor), δ 0.90; s (major),
δ 0.87; s (major), δ 0.86; s (minor), δ 0.85; total 18H), 0.16-
0.01 (s (minor), δ 0.17; s (major), δ 0.16; s (minor), δ 0.15; s
(minor), δ 0.14; s (minor), δ 0.13; s (major), δ 0.12; s (major),
δ 0.106; s (minor), δ 0.099; s (major), δ 0.082; s (minor), δ 0.075;
s (major), δ 0.04; s (minor), δ 0.03; s (major), δ 0.02; total 12H).
13C NMR (125 MHz, CDCl3): δ 155.3, 149.3, 149.2, 149.1,
149.0, 130.1, 129.9, 120.8, 120.7, 111.3, 111.0, 95.6, 95.1, 93.1,
92.1, 85.1, 82.4, 80.9, 80.6, 76.6, 76.4, 74.8, 73.9, 73.8, 73.3,
72.3, 72.2, 71.7, 71.6, 71.3, 71.0, 67.4, 66.4, 64.6, 64.2, 63.3,
62.9, 56.1, 56.0, 55.7, 55.2, 30.8, 28.7, 28.6, 28.5, 26.6, 26.5,
26.4, 26.3, 26.2, 26.1, 18.8, 18.7, 18.6, 13.9, -2.7, -3.2, -3.3,
-3.4, -4.0, -4.1, -4.2, -4.3, -4.4, -4.5, -4.6. TLC (SiO2, 50%
EtOAc/hexanes): Rf ) 0.16. HRMS (m/z): calcd for C37H64N4O11-
Si2 796.4110, found 796.4110.
C
24H36N2O13 (M + H)+ 561.2296, found 561.2294.
2-Azid o-3,4,6-tr i-O-(ter t-bu tyld im eth ylsilyl)-2-d eoxy-D-
ga la cton o-1,5-la cton e (21). Following a published proce-
dure,9 KHMDS (0.5 M in toluene, 4.9 mL, 2.4 mmol, 1.1 equiv)
was added slowly to a solution of 3,4,6-tri-O-(tert-butyldi-
methylsilyl)-2-deoxy-D-galactono-1,5-lactone30 (1.135 g, 2.22
mmol, 1.0 equiv) in 22.2 mL of THF at -78 °C. The reaction
mixture was stirred for 45 min at -78 °C and was then cooled
to -96 °C. A solution of trisyl azide (756 mg, 2.44 mmol, 1.1
equiv) in 7.9 mL of THF at -78 °C was then added by cannula.
The resulting pale yellow mixture was stirred for 5 min at -96
°C. AcOH (0.25 mL) was then added dropwise, and the solution
subsequently became bright yellow. The reaction mixture
warmed to rt over 1 h, after which the color somewhat
dissipated. The reaction mixture was slowly warmed to 30 °C
and stirred for an additional 20 min. After being cooled to rt,
the solution was concentrated, and the residue was filtered
through a short plug of silica gel (20:1 hexanes/EtOAc) to
remove major impurities. The resulting clear oil was chro-
matographed on silica gel (40:1 and then 3:1 hexanes/EtOAc)
to give 21 as a white crystalline solid (717 mg, 1.31 mmol,
59%) after drying under high vacuum (0.1 Torr) for several
days. [R]28D: +63.8 (c 2.05, CHCl3). IR (thin film): 2925, 2849,
Com p ou n d s 23 a n d 24. Compound 22 (198 mg, 0.25 mmol,
1.0 equiv) was dissolved in 20 mL of a 9:1 EtOAc/AcOH
solution, and 10% Pd/C (15 mg) was added. The flask was
evacuated under aspirator vacuum and refilled with hydrogen
three times, and then the mixture was stirred under hydrogen
(1 atm) for 5 h. The mixture was filtered through Celite, and
the filtrate was concentrated on an aspirator pressure rotary
evaporator followed by a high-vacuum (0.1 Torr) rotary
evaporator. The resulting oil was dissolved in 20 mL of a
p-toluenesulfonic acid monohydrate/EtOAc (1 mg/mL) solution,
and the mixture was stirred for 12 h at rt. The reaction was
quenched with 1 mL of triethylamine, and the solution was
concentrated to give an oil. The oil was chromatographed on
silica gel (1:1 and then hexanes/EtOAc) to give the product
mixture as a clear foam (143 mg, 0.18 mmol). TLC (SiO2, 50%
EtOAc/ hexanes): Rf values ∼0.79-0.62. This product was
dissolved in 4 mL of THF, and tetrabutylammonium fluoride
(1.0 M in hexanes, 0.90 mL, 0.74 mmol, 4.0 equiv) was added
dropwise. The solution was stirred at rt for 12 h, after which
the mixture was chromatographed on silica gel (EtOAc and
then 9:1 EtOAc/MeOH). The product was isolated as a clear
foam. TLC (SiO2, 90% EtOAc/MeOH): Rf ≈ 0.52. The product
mixture was taken up in 6 mL of a 2:1 pyridine/Ac2O solution.
A catalytic amount of DMAP was then added in one portion,
and the mixture was stirred for 5 h at rt. The solution was
concentrated on a high-vacuum (0.1 Torr) rotary evaporator,
and the resulting oil was chromatographed on silica gel (1:1
hexanes/EtOAc) to give the product mixture as a clear foam.
The purified product was further purified by HPLC (silica gel,
1:1 hexanes/EtOAc). Compound 23 was isolated as a clear foam
(67 mg, 0.10 mmol, 40% from 22) in greater than 90% purity.
Compound 24 was isolated as a clear foam (21 mg, 0.03 mmol,
12% from 22) in greater than 90% purity.
1
2116, 1747 cm-1. H NMR (500 MHz, CDCl3): δ 4.26 (d, J )
9.9 Hz, 1H), 4.15 (m, 1H), 4.10 (ddd, J ) 8.3, 6.0, 0.8 Hz, 1H),
3.78-3.69 (m, 3H), 0.92 (s, 9H), 0.88 (s, 9H), 0.86 (s, 9H), 0.16
(s, 3H), 0.14 (s, 3H), 0.13 (s, 3H), 0.11 (s, 3H), 0.05 (s, 6H). 13
C
NMR (125 MHz, CDCl3): δ 168.5, 80.3, 73.6, 69.4, 63.6, 60.2,
26.2, 26.1, 26.0, 18.7, 18.6, 18.3, -3.7, -3.9, -4.5, -4.9, -5.1,
-5.2. TLC (SiO2, 5% EtOAc/hexanes): Rf ) 0.24. mp 58-60
°C. HRMS (m/z): calcd for C24H51N3O5Si3 (M + H)+ 546.3215,
found 546.3239. Anal. Calcd for C24H51N3O5Si3: C, 52.80; H,
9.42; N, 7.70. Found: C, 53.19; H, 9.10; N, 7.75.
Com p ou n d 22. To a solution of 15 (1.018 g, 2.05 mmol, 2.5
equiv) in 20.5 mL of anhydrous THF at rt was added hexa-
methylphosphoramide (1.42 mL, 8.19 mmol, 10.0 equiv). The
mixture was then cooled to -78 °C, and n-butyllithium (1.52
M in hexanes, 2.83 mL, 4.30 mmol, 5.2 equiv) was added
slowly. The resulting pale yellow mixture was stirred for 1.5
h at -78 °C, after which a solution of 21 (446 mg, 0.82 mmol,
1.0 equiv) in 8.2 mL of anhydrous THF was added slowly by
cannula. The mixture was stirred for an additional 25 min at
-78 °C and was then quenched with 1 mL of H2O, followed
by 1 mL of saturated aq NH4Cl. The heterogeneous mixture
was warmed to rt and was then diluted with 50 mL of EtOAc
and an additional 35 mL of saturated aq NH4Cl. The phases
were separated, and the aq phase was extracted with 2 × 50
mL of EtOAc. The combined organic phases were dried
(MgSO4), filtered, and concentrated. The concentrated solution
was chromatographed on silica gel (9:1 and then 3:1 hexanes/
EtOAc) to give a mixture of unreacted 15 and the addition
product. TLC (products) (SiO2, 25% EtOAc/hexanes): Rf values
∼0.44-0.50. This mixture of 15 and the addition products
could be quantitatively separated by HPLC if desired, but was
typically carried on without further purification.
The above mixture was dissolved in 20 mL of an 8:1:1 AcOH/
H2O/MeOH solution. Two drops of aqueous HCl solution (2 N)
was then added to the mixture, and the resulting solution was
stirred for 2 h at rt. The reaction was then diluted with excess
toluene, and the resulting biphasic mixture was concentrated
on a high-vacuum (0.1 Torr) rotary evaporator at a tempera-
ture not exceeding 30 °C. The resulting oil was immediately
chromatographed on silica gel (1:1 hexanes/EtOAc and then
EtOAc) to give 22 as a foam (435 mg, 0.55 mmol, 67% from
21). Desilylated 15 was recovered as a clear oil (413 mg, 1.12
mmol). Compound 22 was isolated as an inseparable mixture
comprised of a major product bearing the L-configuration at
CR (1:1 mixture of anomers), as well as a minor product
Da ta for Com p ou n d 23. [R]28D: +67.4 (c 3.75, CHCl3). IR
1
(thin film): 2968, 2105, 1747, 1714 cm-1. H NMR (500 MHz,
CDCl3): δ 6.88-6.78 (m, 3H), 6.06 (s, 1H), 5.64 (s, 1H), 5.42-
5.30 (m, 1H), 5.34 (dd, J ) 10.9, 3.2 Hz, 1H), 5.04 (s, 1H), 4.45
(AB, J ) 11.5 Hz, ∆ν ) 55.3 Hz, 2H), 4.22 (t, J ) 6.8 Hz, 1H),
4.16-3.98 (m, 3H), 3.86 (s, 3H), 3.84 (s, 3H), 3.76 (d, J ) 10.3
Hz, 1H), 3.67 (d, J ) 8.5 Hz, 1H), 3.55 (d, J ) 10.9 Hz, 1H),
3.31 (d, J ) 6.4 Hz, 1H), 2.11 (s, 3H) 2.02 (s, 3H), 1.99 (s, 3H),
1.36 (s, 9H). 13C NMR (125 MHz, CDCl3): δ 170.6, 170.3, 170.0,
154.2, 149.2, 149.0, 136.2, 130.1, 126.2, 120.8, 111.3, 111.0,
96.1, 79.8, 73.7, 70.4, 69.0, 67.7, 67.6, 61.8, 61.3, 60.7, 56.1,
56.0, 52.5, 28.4, 20.8 (3H). TLC (SiO2, 50% EtOAc/hexanes):
Rf ) 0.38. HRMS (m/z): calcd for C31H42N4O13 678.2748, found
678.2763.
Da ta for Com p ou n d 24. [R]28D: +36.3 (c 0.95, CHCl3). IR
1
(thin film): 2974, 2110, 1747, 1703 cm-1. H NMR (400 MHz,
CDCl3): δ 6.85-6.77 (m, 3H), 6.50 (d, J ) 10.2 Hz, 1H), 6.00
1356 J . Org. Chem., Vol. 68, No. 4, 2003

Synthesis of Glycosylated Amino Acids
(d, J ) 10.4 Hz, 1H), 5.39-5.33 (m, 1H), 4.95-4.87 (m, 2H),
4.45 (s, 2H), 4.11-4.01 (m, 4H), 3.98-3.91 (m, 1H), 3.86 (s,
3H), 3.85 (s, 3H), 3.83-3.89 (m, 1H), 3.67 (AB, J ) 9.5 Hz, ∆ν
) 36.0 Hz, 2H), 2.14 (s, 3H) 2.02 (s, 3H), 1.96 (s, 3H), 1.37 (s,
9H). 13C NMR (100 MHz, CDCl3): δ 170.5, 170.3, 170.0, 155.0,
149.2, 148.9, 135.2, 130.5, 122.0, 120.5, 111.1, 111.0, 97.6, 80.0,
73.7, 70.4, 69.7, 69.2, 66.6, 66.3, 63.4, 61.4, 56.1, 56.0, 51.7,
28.5, 20.9, 20.8, 20.7. TLC (SiO2, 50% EtOAc/hexanes): Rf )
0.28. HRMS (m/z): calcd for C31H42N4O13 678.2748, found
678.2750.
THF, 0.16 mL, 0.32 mmol, 4.2 equiv), and finally NaClO2 (41
mg, 0.46 mmol, 6.0 equiv) were successively added, and the
solution was stirred at rt for 12 h. The reaction mixture was
then diluted with 10 mL of H2O and 15 mL of EtOAc. The
phases were separated, and the aq phase was extracted with
2 × 10 mL of EtOAc. The combined organic phases were
washed with 10 mL of brine, dried (Na2SO4), filtered, and
concentrated to give a crude oil. The oil was chromatographed
on silica gel (9:1 EtOAc/MeOH and then 90:8:2 EtOAc/MeOH/
AcOH) to give 26 as a white foam (39 mg, 0.07 mmol, 90%).
[R]28D: +57.9 (c 1.05, MeOH). IR (thin film): 3424, 2979, 1736,
Com p ou n d 25. Compound 23 (114 mg, 0.17 mmol) was
dissolved in 7 mL of a 20:1 EtOAc/Ac2O solution, and 10% Pd/C
(57 mg) was added to the mixture. The flask was evacuated
under aspirator vacuum and refilled with hydrogen three
times, and then the mixture was stirred under hydrogen (1
atm) for 12 h. A second portion of 10% Pd/C (28 mg) was added,
and the stirring under hydrogen was continued for an ad-
ditional 12 h. The mixture was then filtered through Celite,
and concentrated to give an oil. The oil was chromatographed
on silica gel (EtOAc and then 9:1 EtOAc/MeOH) to give 25 as
a white foam (53 mg, 0.10 mmol, 58%). [R]28D: +80.4 (c 0.85,
CHCl3). IR (thin film): 3430, 2974, 1747, 1643 cm-1. 1H NMR
(500 MHz, CDCl3): 5.86 (d, J ) 10.1 Hz, 1H), 5.34 (dd, J )
3.2, 1.0 Hz, 1H), 5.12 (dd, J ) 11.1, 3.4 Hz, 1H), 4.49 (s, 1H),
4.34 (t, J ) 10.5 Hz, 1H), 4.15 (dd, J ) 11.1, 6.6 Hz, 1H), 4.06
(dd, J ) 11.1, 6.9 Hz, 1H), 4.03-3.96 (m, 2H), 3.85 (d, J )
11.7 Hz, 1H), 3.68 (d, J ) 11.9 Hz, 1H), 3.38 (d, J ) 10.9 Hz,
1H), 2.13 (s, 3H), 2.04 (s, 3H), 1.96 (s, 3H), 1.95 (s, 3H), 1.86-
1.63 (m, 5H), 1.39 (s, 9H). 13C NMR (100 MHz, CDCl3): δ 171.0,
170.7, 170.6, 170.5, 156.1, 98.3, 80.9, 69.3, 67.4, 67.2, 63.6, 62.9,
61.8, 53.4, 50.7, 28.5, 27.1, 25.9, 23.5, 21.0, 20.9 (2H). TLC
(SiO2, 100% EtOAc): Rf ) 0.20. HRMS (m/z): calcd for
1643 cm-1 1H NMR (400 MHz, CD3OD): δ 7.89 (d, J ) 8.9
.
Hz, 1H), 5.39 (d, J ) 3.2 Hz, 1H), 5.16 (dd, J ) 11.2, 3.3 Hz,
1H), 4.35 (d, J ) 10.8 Hz, 1H), 4.30-4.08 (m, 4H), 3.46 (d, J
) 11.0 Hz, 1H), 2.14 (s, 3H), 2.16-2.08 (m, 1H), 2.06 (s, 3H),
2.04-1.92 (m, 1H), 1.95 (s, 3H) 1.93 (s, 3H), 1.87 (dt, J ) 13.5,
4.1 Hz, 1H), 1.64-1.55 (m, 1H), 1.42 (s, 9H). 13C NMR (100
MHz, CD3OD): δ 176.2, 174.1, 172.4, 172.3, 172.0, 157.2, 99.3,
80.8, 70.8, 69.0, 68.6, 65.8, 63.3, 56.3, 52.0, 28.8, 28.6, 27.7,
22.7, 20.8, 20.7, 20.6. TLC (SiO2, 90:8:2 EtOAc/MeOH/AcOH):
Rf ) 0.09. HRMS (m/z): calcd for C24H36N2O13 (M + H)+
561.2296, found 561.2318.
Ack n ow led gm en t. This research was supported by
an NSF Career Award (Grant CHE-9733765). R.L.H.
also thanks the Camille and Henry Dreyfus Founda-
tion (Camille Dreyfus Teacher-Scholar Award), Pfizer
(J unior Faculty Award), and Novartis (Young Investiga-
tor Award) for support. This work was facilitated by a
500 MHz NMR spectrometer that was purchased partly
with funds from an NSF Shared Instrumentation Grant
(CHE-9523034). Bob Barkley (University of Colorado)
is thanked for obtaining the mass spectra. Rich Shoe-
maker (University of Colorado) is thanked for his
assistance in performing the NMR studies.
C
24H38N2O12 (M + H)+ 547.2503, found 547.2494.
Com p ou n d 26. To a solution of 25 (42 mg, 0.08 mmol, 1.0
equiv) in 1.5 mL of CH2Cl2 at rt was added NaHCO3 (48 mg)
followed by Dess-Martin periodinane (64 mg, 0.15 mmol, 2.0
equiv). The reaction mixture was stirred for 9 h, after which
it was quenched with 1 mL of a Na2S2O3 solution (25 g of
Na2S2O3 per 100 mL). After being stirred for 15 min, the
mixture was diluted with 15 mL of CH2Cl2 and 15 mL of H2O.
The phases were separated, and the aq phase was extracted
with 2 × 10 mL of CH2Cl2. The combined organic phases were
dried (Na2SO4), filtered, and concentrated. The resulting
product was dissolved in 2.5 mL of 4:1 tBuOH/H2O. NaH2PO4
(22 mg, 0.16 mmol, 2.0 equiv), 2-methyl-2-butene (2.0 M in
Su p p or tin g In for m a tion Ava ila ble: 1H and 13C spectra
for 9, 10, 2-(3,4-dimethoxybenzyloxy)-3-nitropyridine, 15, the
(R)-MTPA derivative of 15 (1H only), the (R)-MTPA derivative
of 13 (1H only), and 17-26. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O020532T
J . Org. Chem, Vol. 68, No. 4, 2003 1357