Synthesis of C-5 analogs of N-acetylneuraminic acid via indium-mediated allylation of N-substituted 2-amino-2-deoxymannoses

Article abstract of DOI:10.1021/jo9614856

This paper presents a short synthesis of new analogs of N-acetylneuraminic acid (Neu5Ac) varied structurally at C-5. The synthetic strategy includes indium-mediated coupling reactions between ethyl 2-(bromomethyl)acrylate and N-derivatized mannosamines, and the ozonolysis of the resulting enoates. The main advantage of this indium-mediated allylation for the synthesis of neuraminic acids comes from the efficient, stereoselective C-C bond formation, which affords predominantly the correct diastereomer having a threo relationship between the newly generated hydroxyl group and the C-2 amide group of mannosamine. By this approach, Neu5Boc (4a), Neu5Gly (4b), Neu5 (6-NHCbz)hexanoyl (4c), and Neu5 (1-naphthyl)acetyl (4d) were prepared in three steps (overall ~ 50%). In addition, several N-substituted neuraminic acids were synthesized by N-acylation of the amino functionality of neuraminic acid (5b), which was obtained by deprotecting the N-Boc group of Neu5Boc (4a). These analogs include Neu5BrAc (6a), Neu5acryloyl (6b), Neu5benzoyl (6c) and Neu5benzoyl-4-benzoyl (6d). The N-acylation method is especially suited for synthesis of neuraminic acids bearing substituents that can not tolerate ozonolysis or that are unstable (photo)chemically. Finally, we illustrate the utility of synthetic neuraminic acids by converting 4c to a derivative of 2-deoxy-2,3-didehydroneuraminic acid (8c), a precursor to inhibitors of neuraminidases.

Full text of DOI:10.1021/jo9614856

J . Org. Chem. 1996, 61, 8739-8745
8739
Syn th esis of C-5 An a logs of N-Acetyln eu r a m in ic Acid via
In d iu m -Med ia ted Allyla tion of N-Su bstitu ted
2-Am in o-2-d eoxym a n n oses
Seok-Ki Choi, Shelly Lee, and George M. Whitesides*
Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street,
Cambridge, Massachusetts 02138
Received August 1, 1996X
This paper presents a short synthesis of new analogs of N-acetylneuraminic acid (Neu5Ac) varied
structurally at C-5. The synthetic strategy includes indium-mediated coupling reactions between
ethyl 2-(bromomethyl)acrylate and N-derivatized mannosamines, and the ozonolysis of the resulting
enoates. The main advantage of this indium-mediated allylation for the synthesis of neuraminic
acids comes from the efficient, stereoselective C-C bond formation, which affords predominantly
the correct diastereomer having a threo relationship between the newly generated hydroxyl group
and the C-2 amide group of mannosamine. By this approach, Neu5Boc (4a ), Neu5Gly (4b), Neu5-
(6-NHCbz)hexanoyl (4c), and Neu5(1-naphthyl)acetyl (4d ) were prepared in three steps (overall
∼50%). In addition, several N-substituted neuraminic acids were synthesized by N-acylation of
the amino functionality of neuraminic acid (5b), which was obtained by deprotecting the N-Boc
group of Neu5Boc (4a ). These analogs include Neu5BrAc (6a ), Neu5acryloyl (6b), Neu5benzoyl
(6c) and Neu5benzoyl-4-benzoyl (6d ). The N-acylation method is especially suited for synthesis of
neuraminic acids bearing substituents that can not tolerate ozonolysis or that are unstable (photo)-
chemically. Finally, we illustrate the utility of synthetic neuraminic acids by converting 4c to a
derivative of 2-deoxy-2,3-didehydroneuraminic acid (8c), a precursor to inhibitors of neuraminidases.
In tr od u ction
as the most ubiquitous analog, N-glycolylneuraminic acid
(Neu5glycolyl), and other O-acetylated analogs (4-O-
acetylNeu5Ac, 9-O-acetylNeu5Ac). Neu5Ac and its ana-
logs are expressed as R-O-sialosides on the surface of
mammalian cells as a component essential to gan-
This paper describes an efficient synthesis of a physi-
ologically important carbohydrate, neuraminic acid (Neu),1
with varying substituents at C-5, and its derivatives
related to 2-deoxy-2,3-didehydroneuraminic acid (Neu2en).
The crucial step of this approach is the In-mediated,
nucleophilic addition of an allylic anion equivalent to
N-derivatives of 2-amino-2-deoxymannose (2-mannosa-
mine). The coupling reaction proceeds well in an aqueous
medium, and its efficiency has been consistently high
among a number of substrates presenting common
functional groups such as free OH, N-Boc, and N-Cbz
groups.
A significant number of cellular events are mediated
by a variety of carbohydrate-linked proteins and lipid
molecules (glycoconjugates).2 Neuraminic acids or sialic
acids refer to a class of structurally unique, natural
carbohydrates that occur as a sugar element, terminating
in glycoproteins and glycolipids.3 There are about 30
natural sialic acids, substituted differently at positions
C-4 to C-9, including N-acetylneuraminic acid (Neu5Ac)
gliosides,2c glycoconjugates,2a and sialyl Lewis x,4 and also
occur as a linear homopolymer (polysialic acid, >50-mer).5
Carbohydrates of this class mediate numerous cellular
recognition events4 in cell migration and adhesion,6
immune responses,7 tumor metastasis,8 and the develop-
ment of neural cells.9 In addition, these cellular moieties
constitute a characteristic ligand commonly recognized
* Author to whom correspondence should be addressed. Tel: (617)-
495-9430; Fax: (617)-495-9857. Internet: gwhitesides@gmwgroup.
harvard.edu.
(4) (a) Magnani, J . L.; Nilsson, B.; Brockhaus, M.; Zopf, D.; Steplews-
ki, Z.; Koprowski, H.; Ginsburg, V. Cancer Res. 1983, 43, 5489. (b)
Danishefsky, S. J .; Koseki, K.; Griffith, D. A.; Gervay, J .; Peterson, J .
M.; McDonald, F. E.; Oriyama, T. J . Am. Chem. Soc. 1992, 114, 8331.
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M. Proc. Natl. Acad. Sci. U.S.A. 1995, 92, 7031.
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663. (b) Lasky, L. A. Annu. Rev. Physiol. 1995, 57, 827.
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M.-E. d.; Schnaar, R. L.; Mahoney, J . A.; Hartnell, A.; Bradfield, P.;
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X Abstract published in Advance ACS Abstracts, November 15, 1996.
(1) The IUPAC name for neuraminic acid is 5-amino-3,5-dideoxy-
D-glycero-R-D-galacto-2-nonulosonic acid.
(2) For review, see: (a) Horowitz, M. I.; Pigman, W. The Glycocon-
jugates; Academic Press: New York, 1977-1985; Vols. 1-4. (b)
Karlsson, K.-A. Curr. Opin. Struct. Biol. 1995, 5, 622. (c) Wiegandt,
H. In Glycolipids; Wiegandt, H., Ed.; Elsevier: New York, 1985; Vol.
10, p 199. (d) Varki, A. Glycobiology 1993, 3, 97.
(3) (a) Corfield, A. P.; Schauer, R. In Sialic Acids, Chemistry,
Metabolism and Function; Schauer, R., Ed.; Springer Verlag: New
York, 1982; Vol. 10, pp 5-39. (b) Vliegenthart, J . F. G.; Kamerling, J .
P. In Sialic Acids, Chemistry, Metabolism and Function; Schauer, R.,
Ed.; Springer Verlag: New York, 1982; Vol. 10, pp 59-76. (c) Roy, R.;
Laferrie`re, C. A.; Pon, R. A.; Gamian, A. In Methods in Enzymology
(Neoglycoconjugates. Part B. Biomedical Applications); Lee, Y. C., Lee,
R. T., Eds.; Academic Press, Inc: San Diego, 1994; Vol. 247, pp 351-
361.
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1994, 369, 160.
S0022-3263(96)01485-5 CCC: $12.00 © 1996 American Chemical Society

8740 J . Org. Chem., Vol. 61, No. 25, 1996
Choi et al.
by many infectious pathogens such as viruses (influ-
enza,10 polyoma,11 rota,12 Sendai13), bacteria, and para-
sites.14 In general, the adsorption of pathogens to target
cells, the initial step of infection, results from the binding
of pathogenic surface proteins to the sialosides on the
cellular surface.2b,15
or zinc)-mediated, nucleophilic addition of a carbanion
to a carbonyl equivalent adds a useful process that leads
to higher carbon sugars (eq 1). This C-C forming,
coupling reaction has been applied to nonsugar alde-
hydes/ketones,25b,28 aldimines,29 and aldoses.25ab,28f,30 In
Synthetic analogs of Neu have helped to unravel
mechanisms of sialic acid-dependent processes. These
analogs have been involved in structure-activity
studies,3b,16 to study the specificities of distinct sialocon-
jugates in virus infectivity,17 cellular adhesion,18 and
sialidase resistance.19 They have been tested also as
inhibitors of pathogens.20 Particularly, analogs of Neu
with a fluorescent or photosensitive group at position C-5
(along with C-9)21 have been used as molecular probes
in in vivo detection of sialylated glycans,22 and in
enhancing the sensitivity of sialyltransferase assay,23 and
in characterization of new Neu-binding receptors and
neuraminidases.24
In contrast to the significance and diversity of physi-
ological roles of sialic acids, the use of synthetic Neu has
been limited, partially due to a lack of efficient synthetic
methods. A number of chemical25 and chemoenzymatic26
syntheses of Neu have been developed. These synthetic
methods constitute a valuable route to Neu, especially
non-natural Neu which is otherwise unavailable by
isolation from natural sources.25c,27 As a methodology
important to carbohydrate synthesis, metal (indium, tin,
general, this metal-mediated reaction gives high chemical
yields, unrestrained reaction scales (milli- to multigram
synthesis), and good regio/stereoselectivity. Unlike many
organometallic reactions, this reaction is insensitive to
the presence of moisture and proceeds well in aqueous
media, rendering the protection of the hydroxyl groups
of carbohydrate substrates unnecessary.
Recently, Gordon et al.25a and Chan et al.25b demon-
strated the efficiency of In-mediated reactions by syn-
thesizing per-acetylated or unprotected Neu5Ac starting
from a commercially available N-acetylmannosamine.
The present study extends the scope of In coupling to the
synthesis of Neu by demonstrating a general synthesis
of C-5 analogs of Neu. We believe that the present
method provides a valuable alternative to other syn-
thetic25,26 and isolation27 approaches in preparation of
Neu, useful in designing syntheses of complex carbohy-
drates.
Resu lts a n d Discu ssion
(12) Me´ndez, E.; Arias, C. F.; Lo´pez, S. J . Virol. 1993, 67, 5235.
(13) Dallocchio, F.; tomasi, M.; Bellini, T. Biochem. Biophys. Res.
Commun. 1995, 208, 36.
Scheme 1 describes a three-step synthesis of N-acy-
lated derivatives of Neu (4a -d ; Neu5R). The synthesis
began with N-derivatization of 2-mannosamine, which
was performed by neutralization of 1 with NaOMe in
MeOH, and by treatment with (Boc)2O or N-hydroxysuc-
cinimide esters (N-Cbz-glycine, 6-(NH-Cbz)hexanoic acid,
and 1-naphthaleneacetic acid). The reaction afforded
N-Boc or N-acylmannosamines (2a -d ) in 85-90% yields.
A similar treatment with dansyl chloride afforded N-
dansylmannosamine (2e). Each derivative (2a -d ) con-
sisted of two epimers (C-1) with an average ratio of R/â
∼ 3/1 on the basis of the 1H-NMR spectrum. We
proceeded with mixtures of epimers for the next step,
because the two isomers are in equilibrium with the same
aldehyde, which then reacts with indium reagent.
The In-mediated reaction for C-C bond formation was
performed by warming (∼55 °C) a vigorously stirred
suspension of indium powder (∼4 equiv), ethyl 2-(bro-
momethyl)acrylate (∼6 equiv)31 and unprotected man-
nosamines (2a -e) in an acidic medium (0.1 M HCl/EtOH
∼1/7 v/v). The reaction afforded enoates (3a -e): Scheme
1; R ) COOC(CH3)3 (88%), COCH2NHCbz (82%), CO-
(CH2)5NHCbz (81%), COCH2-1-C10H7 (68%), SO2-1-C10H6-
5-NMe2 (70%), COCH3 (90%25a). This heterogeneous
reaction was run in an acidic medium rather than a
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Cockle, S. A.; Klein, M. H.; Read, R. J . Nature Struct. Biol. 1994, 1,
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Miller, L. H. Science 1994, 264, 1941.
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Pritchet, T.; Milks, G.; Sabesan, S. Pure Appl. Chem. 1984, 56, 797.
(b) Brossmer, R.; Gross, H. J . In Methods in Enzymology (Neoglyco-
conjugates. Part B. Biomedical applications); Lee, Y. C., Lee, R. T.,
Eds.; Academic Press, Inc.: San Diego, 1994; Vol. 247, pp 153-176.
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Virology 1987, 160, 502. (b) Machytka, D.; Kharitonenkov, I.; Isecke,
R.; Hetterich, P.; Brossmer, R.; Klein, R. A.; Klenk, H.-D.; Egge, H.
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Am. Chem. Soc. 1994, 116, 1616.
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M. Bioorg. Med. Chem. Lett. 1993, 3, 747. (b) Murakami, M.; Ikeda,
K.; Achiwa, K. Carbohydr. Res. 1996, 280, 101.
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coconjugates. Part B. Biomedical Applications); Lee, Y. C., Lee, R. T.,
Eds.; Academic Press, Inc.: San Diego, 1994; Vol. 247, pp 177-193.
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K.; Feeney, R. E.; Brossmer, R. Biochemistry 1989, 28, 7386. (b) Gross,
H. J .; Brossmer, R. Eur. J . Biochem. 1988, 177, 583.
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U.; Verheijen, F. W. J . Biol. Chem. 1990, 265, 10801. (b) Mirelis, P.;
Brossmer, R. Bioorg. Med. Chem. Lett. 1995, 5, 2809.
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H. Angew. Chem., Int. Ed. Engl. 1990, 29, 823.
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L.; Ichikawa, Y.; Wong, C.-H. J . Am. Chem. Soc. 1992, 114, 10138. (c)
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Synthesis of C-5 Analogs of N-Acetylneuraminic Acid
J . Org. Chem., Vol. 61, No. 25, 1996 8741
tography.25a Here, the chemical shifts and coupling
constants of the two C-3 protons (Hax and Heq) of Neu
are influenced characteristically by the stereochemistry
of the hydroxyl group substituted at C-4.27,33
Sch em e 1a
We estimated the ratio (threo/erythro or S/ R) between
the two diastereomers (3) by integration of distinct
olefinic signals in the 1H-NMR spectrum. For substrates
2a -c, the S/ R ratio was 3.5-4.0, but with 2d and 2e,
the selectivity was low, ∼1.5 and ∼1.0, respectively. The
preferential formation of the threo product was observed
also in other indium (or tin)-mediated allylations with
aldoses bearing a C-2 hydroxyl group.28d,f,30a,b,d The
molecular basis of the stereochemical outcome of this
reaction (from N-substituted mannosamines) has not
been clearly established, but a model was proposed on
the basis of Cram-type chelation.25a,28f This mechanism
suggests a formation of a five-membered chelate between
In(R) and an aldose (via coordination of the metal to
aldehyde oxygen and amide nitrogen), and the attack of
an allylic nucleophile to an aldehyde of this complex,
preferentially from the less-hindered side.25a,28f According
to this model, the structural and functional properties
of N-substituents should influence the efficiency of
formation of the chelate as well as the approach of a
nucleophile. We believe that the low selectivity observed
from 2d (naphthalenylacetyl) and 2e (N-sulfonamide)
may be related to these factors.
The efficiency of ozonolysis of the enoates was almost
quantitative from 1H-NMR spectroscopy, but the yields
of 4 (Neu5R), after purification of the crude product by
chromatography (silica gel, 10% MeOH/CH2Cl2 to 5%
HCOOH/30% MeOH/CH2Cl2), were ∼65-70% (4a -c) and
27% (4d ). It is noteworthy that unprotected 4 was
isolated directly, without having to convert it to the
peracetylated Neu5R.25a The direct isolation might have
reduced the yield due to incomplete chromatographic
recovery of polar Neu5R adsorbed to silica gel. Addition-
ally, certain functional groups (aromatic, dansyl) under-
went partial or complete decomposition under the ozo-
nolysis conditions. This decomposition was observed for
enoates 3d (27% for 4d ) and 3e (0%). Accordingly, the
present method is limited to enoates with N-substituents
stable to ozonolysis.
Derivatives of Neu that were unsuitable for prepara-
tion by Scheme 1 could be prepared by N-derivatization
of the amino group of Neu. There are several methods,
either chemical25c or chemoenzymatic,26d,34 for synthesis
of N-deacetylated Neu. Scheme 2 summarizes an alter-
native approach for the synthesis of Neu and its N-
acylation, complementary to previous methods. The
treatment of 4a with TFA/CH2Cl2 (or 1.0 M HCl/MeOH)
removed the N-Boc group quantitatively, but afforded
undesired product(s), believed to be imines. Therefore,
we acetylated 4a exhaustively by use of Ac2O in pyridine
and then deprotected the N-Boc group of 5a . Product 5b
was allowed to react with acid chlorides in the presence
of i-Pr2NEt as base. This N-acylation afforded Neu5R
(6a -d ; 36-60%) containing N-COCH2Br, COCHdCH2,
or COC6H4-4-COC6H5); these species can not be prepared
according to Scheme 1.
a
(1) NaOMe, (Boc)2O, or X-COR, MeOH, rt, 24 h; (2) In, ethyl
R-bromomethacrylate, EtOH, 0.1 M HCl, 55 °C, 36 h; (3) O3,
MeOH, -78 °C, 30 min; then HCO2H, H2O2, H2O, rt, 90 min.
neutral solvent, because the presence of a small amount
of HCl increased the rate and efficiency of the coupling
reaction.25a,30b The scale of the reaction could be varied
within a laboratory scale (0.1 mg to g5 g of man-
nosamines) without noticeable change in yield.
The success of this reaction is ascribed to the selective
reactivity of indium toward allylic halides and to its
inability to reduce the aldehyde function.28,29,32 Clearly,
the products resulted from a nucleophilic addition of an
allylic anion equivalent (as a ligand chelated to In28c) to
an aldehyde of 2. Each addition reaction resulted in
formation of a mixture composed of two diastereomers 3
(threo/erythro or S/ R) at the newly generated carbon
center (marked *). In most cases, the major isomer could
not be cleanly separated by flash column chromatography
(silica gel; 5-20% MeOH/CH2Cl2), but its purity could
be increased to g90% after repeated (g2) chromatogra-
phy.
The stereochemistry at the chiral center of the major
isomer was determined unambiguously as S after ozo-
nolysis (Scheme 1: O3, MeOH, -78 °C) of 3. Compound
4 (R ) COCH3; Neu5Ac), obtained by this method, was
indistinguishable from authentic Neu5Ac25c,27 isolated
from edible bird nests, with respect to 1H- and 13C-NMR
spectroscopy, mass spectrometry, and thin layer chroma-
The methods described in Schemes 1 and 2 represent
a convenient route to various C-5 analogs of Neu, such
(33) Schreiner, E.; Zbiral, E.; Kleineidam, R. G.; Schauer, R. Liebigs
Ann. Chem. 1991, 129.
(32) Beuchet, P.; Marrec, N. L.; Mosset, P. Tetrahedron Lett. 1992,
33, 5959.
(34) Sparks, M. A.; Williams, K. W.; Lukacs, C.; Schrell, A.; Priebe,
G.; Spaltenstein, A.; Whitesides, G. M. Tetrahedron 1993, 49, 1.

8742 J . Org. Chem., Vol. 61, No. 25, 1996
Choi et al.
Sch em e 2a
Sch em e 3a
a
(1) Ac2O, pyridine, 69%; (2) TFA, CH2Cl2, rt, quantitative; (3)
BrCH2COBr, i-Pr2NEt, CH2Cl2, rt, 12 h, 60%; (4) CH2dCHCOCl,
i-Pr2NEt, CH2Cl2, 36%; (5) C6H5COCl, i-Pr2NEt, CH2Cl2, 58%; (6)
C6H5COC6H4COCl, i-Pr2NEt, CH2Cl2, 60%.
a
(1) Ac2O, pyridine, 48 h, 72%; (2) CF3SO3SiMe3, MeCN, 50 °C,
2.5 h, 73%; (3) Me3SiN3, t-BuOH, 80 °C,4 h, 81%; (4) LiOH, MeOH,
H2O, rt, 12 h, 62%; (5) CF3SO3H, TFA, 0 °C, 30 min, 33%.
as amino acid conjugates (4b, 4c), and (photo)chemically
cross-linkable (6a , 6b, 6d ) analogs. These functional
Neu5R may be potentially useful as (photo)affinity-
labeled or fluorescent Neu in photolabeling studies21-24,35
of sialic acid-dependent cellular processes.
disclosed, In-mediated allylation of unprotected carbo-
hydrates in aqueous ethanol.25a,30b The strategy is limited
slightly by the cost of indium and 2-amino-2-deoxyman-
nose, but its efficiency is comparable to that of the
(chemo)enzymatic syntheses of sialic acids26a,39 or its
isolation from bird nests.25c,27 Particularly, the present
method is a versatile means of introducing various
chemical functionalities such as amino acids, (photo)-
affinity-labels or fluorescent tags to position C-5 of
neuraminic acid.
Scheme 3 summarizes a synthesis of analogs of 2-deoxy-
2,3-dehydroneuraminic acid (Neu2en).33,36 Neu2en be-
longs to a class of inhibitors of neuraminidase,37 an
enzyme that catalyzes the hydrolytic cleavage of C(2)-O
bond of R-O-sialosides. Sialic acid 4c was acetylated
exhaustively. Product 4c′ was converted to oxazole 7 by
treatment with TMSOTf according to literature meth-
ods.33,38 This oxazole was transformed to Neu2en 8a by
treatment with TMSN3, which resulted in ring-opening
and the substitution of azide nucleophile at position C-4
with an inversion of stereochemistry.33,38 The hydrolysis
and deprotection of N-Cbz group led to unprotected
Neu2en 8c. This example illustrates the use of a
synthetic Neu as a precursor to an analog of azido-
substituted dehydroneuraminic acid. Additionally, the
analog contains an ꢀ-amino linker group tethered to C-5;
this linker may be useful in tethering an additional probe
for studies of the active site of neuraminidases.24a
Exp er im en ta l Section
Gen er a l. Tetrahydrofuran (THF) was distilled from sodium
benzophenone ketyl. Methylene chloride (CH2Cl2) was dis-
tilled after refluxing over CaH2. Indium (In) metal (99.99%;
Aldrich) was used as received in powder form. Thin layer
chromatography (TLC) was performed on silica gel precoated
glass plates (E. Merck, Darmstadt). Flash column chroma-
tography was performed on silica gel 60F254 (230-400 mesh,
E. Merck). Ozonolysis was performed with an ozone generator
(Griffin Technics Inc).
Typ ica l P r oced u r e for N-Der iva tiza tion of 2-Am in o-
2-d eoxym a n n ose Hyd r och lor id e. To a solution of 2-amino-
2-deoxy-D-mannopyranose hydrochloride (1) (2.0 g, 9.3 mmol)
and NaOMe (0.56 g, 10.4 mmol) in 80 mL of MeOH were added
N-Cbz-glycine N-hydroxysuccinimide ester (3.4 g, 11.1 mmol)
and Et3N (1.3 mL, 9.3 mmol). After stirring for 30 h at rt, the
reaction mixture was concentrated in vacuo to yield a pale
yellow oil. This thick oily residue was flash chromatographed
on silica gel (300 g) by eluting with 5% MeOH/CH2Cl2 and then
20% MeOH/CH2Cl2. The desired product 2b, containing a
mixture of two epimers (R/â ), was obtained as a light yellow,
semicrystalline oil (3.1 g, 90%). Rf ) 0.5 (20% MeOH/CH2-
Cl2). 1H-NMR (400.14 MHz, CD3OD): δ (ppm) 7.35-7.27 (m,
5H), 5.05 (s, 2H), 4.44 (d, 0.3H, J ) 4.2 Hz), 4.32-4.30 (d, 0.7H,
J ) 4.5 Hz), 4.04-4.0 (dd, 1H, J ) 4.6, 9.7 Hz), 3.88 (s, 2H),
3.86-3.68 (m, 4H), 3.62-3.57 (t, 0.7H, J ) 9.5 Hz), 3.50-3.46
(t, 0.3H, J ) 9.5 Hz); 13C-NMR (100.61 MHz, CD3OD): δ (ppm)
Con clu sion s
We presented a short synthesis of analogs of (dehydro)-
neuraminic acids. The synthesis relies on the previously
(35) (a) Gross, H. J .; Bu¨nsch, A.; Paulson, J . C.; Brossmer, R. Eur.
J . Biochem. 1987, 168, 595. (b) Warner, T. G. Biochem. Biophys. Res.
Commun. 1987, 148, 1323. (c) Warner, T. G.; Lee, L. A. Carbohydr.
Res. 1988, 176, 211.
(36) (a) Itzstein, M. v.; Wu, W.-Y.; Kok, G. B.; Pegg, M. S.; Dyason,
J . C.; J in, B.; Phan, T. V.; Smythe, M. L.; White, H. F.; Oliver, S. W.;
Colman, P. M.; Varghese, J . N.; Ryan, D. M.; Cameron, J . M.; Penn,
C. R. Nature 1993, 363, 418. (b) Zbiral, E.; Schreiner, E.; Christian,
R.; Kleineidam, R. G.; Schauer, R. Liebigs Ann. Chem. 1989, 159.
(37) (a) Colman, P. M. Protein Sci. 1994, 3, 1687. (b) Air, G. M.;
Laver, W. G. Proteins 1989, 6, 341.
(38) Itzstein, M. v.; Wu, W.-Y.; J in, B. Carbohydr. Res. 1994, 259,
301.
(39) For review, see: DeNinno, M. P. Synthesis 1991, 583.

Synthesis of C-5 Analogs of N-Acetylneuraminic Acid
J . Org. Chem., Vol. 61, No. 25, 1996 8743
177.09, 172.38, 137.73, 129.20, 128.74, 128.53, 94.38, 74.07,
70.40, 68.33, 67.48, 62.00, 54.79, 47.50, 44.47, 25.87, 8.90; FAB-
MS (NBA/NaI): m/ z 393 [M + Na]+; HRMS: calcd for
C16H22N2O8Na 393.1272, found 393.1274.
(dd, 1H, J ) 5.8, 12.5 Hz), 3.41-3.39 (d, 1H, J ) 8.4 Hz), 3.13-
3.09 (t, 2H, J ) 6.8 Hz), 2.52-2.47 (dd, 1H, J ) 7.9 Hz), 2.44-
2.40 (dd, 1H, J ) 5.3 Hz), 2.35-2.32 (m, 2H), 1.67-1.60 (m,
2H), 1.30-1.25 (t, 3H, J ) 7.1 Hz); 13C-NMR (100.61 MHz,
CD3OD): δ (ppm) 177.31, 168.57, 129.40, 128.89, 128.72,
128.18, 72.52, 72.05, 69.67, 67.27, 65.18, 61.90, 54.66, 41.61,
38.10, 36.87, 30.58, 27.42, 14.48; FAB-MS (NBA/NaI): m/ z
563 [M + Na]+; HRMS: calcd for C26H40N2O10Na 563.2578,
found 563.2581.
2a : 89%; Rf ) 0.6 (30% MeOH/CH2Cl2); 1H-NMR (250.13
MHz, CD3OD): δ (ppm) 5.01 (s, 1H), 4.00-3.92 (m, 2H), 3.85-
3.69 (m, 2H), 3.62-3.35 (m, 2H), 1.44 (s, 9H); 13C-NMR (101.61
MHz, CD3OD): δ (ppm) 95.30, 95.10, 80.36, 78.24, 74.52, 73.43,
70.64, 68.41, 68.11, 62.23, 62.12, 56.33, 28.73; FAB-MS
(NBA/NaI): m/ z 302 [M + Na]+; HRMS: calcd for C11H21NO7-
Na 302.1214, found 302.1216.
3d (R ) COCH2-1-C10H7): 68% (S/ R ∼ 1.5/1). Rf ) 0.72
(20% MeOH/CH2Cl2). 1H-NMR (300.14 MHz, CD3OD):
δ
2c: 89%; Rf ) 0.6 (20% MeOH/CH2Cl2); 1H-NMR (300.14
MHz, CD3OD): δ (ppm) 7.34-7.27 (m, 5H), 5.05 (s, 2H), 4.99
(d, H1R, J ) 1.4 Hz), 4.38 (dd, H2â), 4.29-4.27 (dd, H2R, J )
1.4, 4.7 Hz), 4.03-3.98 (dd, H3R, J ) 4.7, 9.6 Hz), 3.85-3.73
(m, 3H), 3.62-3.55 (t, H4R, J ) 9.6 Hz), 3.53-3.48 (t, 2H, J )
6.8 Hz), 2.33-2.24 (quin, 1.5H, J ) 7.3 Hz), 2.18-2.16 (t, 0.5H,
J ) 7.2 Hz), 1.65-1.57 (quin, 2H, J ) 7.3 Hz), 1.52-1.45 (quin,
2H, J ) 7.2 Hz), 1.40-1.32 (quin, 2H, J ) 7.3 Hz); 13C-NMR
(100.61 MHz, CD3OD): δ (ppm) 176.54, 158.48, 138.34, 129.47,
129.36, 128.79, 128.50, 94.68, 73.40, 70.55, 68.43, 66.96, 62.18,
54.79, 41.49, 36.60, 30.42, 27.30, 26.40; FAB-MS (NBA/NaI):
m/ z 449 [M + Na]+; HRMS: calcd for C20H30N2O8Na1 449.1898,
found 449.1900.
(ppm) 8.05-7.95 (m, 2H), 7.86-7.73 (m, 2H), 7.54-7.37 (m,
3H), 6.07-6.04 (two s, 1H), 5.50-5.32 (two s, 1H), 4.10-4.04
(q, 2H, J ) 7.9 Hz), 3.85-3.45 (m, 6H), 2.59-2.48 (m, 2H),
1.29-1.26 (t, 3H, J ) 7.9 Hz); FAB-MS (NBA/NaI): m/ z 484
[M + Na]+; HRMS: calcd for C24H31NO8Na 484.1946, found
484.1947.
3e (R ) SO2-1-C10H6-5-NMe2): 80% (S/ R ∼ 1/1). 1H-NMR
(399.88 MHz, CD3OD): δ (ppm) 8.54-8.52 (d, 1H, J ) 7.6 Hz),
8.42-8.3 (m, 1H), 8.23-8.20 (m, 1H), 7.59-7.45 (m, 2H), 7.29-
7.23 (m, 1H), 5.60 and 5.85 (d, 1H, J ) 1.6 Hz), 5.29 (d, 1H, J
) 1.6 Hz), 4.07-4.03 (q, 2H, J ) 7.0 Hz), 3.92-3.85 (m, 1H),
3.81-3.31 (m, 6H), 2.86 (two S, 6H), 2.44-2.39 (dd, 0.5H, J )
3.0, 14.1 Hz), 2.08-2.02 (dd, 0.5H, J ) 9.7, 14.1 Hz), 1.71-
1.66 (dd, 0.5H, J ) 3.0, 14.1 Hz), 1.58-1.52 (dd, 0.5H, J )
9.7, 14.1 Hz), 1.22-1.17 (t, 3H, J ) 7.0 Hz); 13C-NMR (100.55
MHz, CD3OD): δ (ppm) 168.33, 153.41/153.30, 139.0/138.73,
137.87/137.55, 131.14/130.89, 129.48/129.24, 128.40, 127.72/
127.35, 124.33, 120.57, 116.45, 116.32, 115.65, 94.63, 73.30,
72.28, 71.16, 70.05, 69.18, 65.34, 62.69, 60.53, 59.29, 37.26,
14.44; FAB-MS (NBA/NaI): m/ z 549 [M + Na]+, 526 [M]+;
HRMS: calcd for C24H34N2O9SNa 549.1881, found 549.1883.
Typ ica l P r oced u r e for Ozon olysis. Compound 3b (R )
COCH2NHCbz; 1.1 g, 2.27 mmol) was solubilized in 50 mL of
MeOH, after which the solution was cooled to -78 °C. Ozone
gas was bubbled into the methanolic solution while stirring it
at -78 °C. After 30 min, the ozone bubbling was stopped, and
a mixture of H2O (10 mL), 30% H2O2 (5 mL), and HCO2H (2
mL) was added to the solution. The mixture was gradually
warmed to rt while stirring it for 90 min under air. The clear
solution was concentrated in vacuo to yield a pale yellow foam.
The crude product was purified by flash column chromatog-
raphy on silica gel (50 g) by eluting with 10% MeOH/CH2Cl2
and then 5% HCO2H/30% MeOH/CH2Cl2. The product 4b was
obtained as a white foam (0.72 g, 65%). Rf ) 0.76 (20% MeOH/
CH2Cl2). 1H-NMR (399.88 MHz, CD3OD): δ (ppm) 7.38-7.29
(m, 5H), 5.11 (s, 2H), 4.38-4.32 (q, 2H, J ) 7.1 Hz), 4.17-
4.10 (m, 2H), 3.96-3.78 (m, 4H), 3.88 (s, 2H), 3.73-3.70 (t,
1H, J ) 6.6 Hz), 2.33-2.29 (dd, 1H, J ) 4.9, 12.7 Hz), 1.78-
1.72 (t, 1H, J ) 12.7 Hz), 1.36-1.32 (t, 3H, J ) 7.1 Hz); 13C-
NMR (100.55 MHz, CD3OD): δ (ppm) 174.18, 173.77, 159.70,
137.85, 129.45, 129.04, 128.84, 96.96, 73.35, 72.07, 69.20,
67.97, 67.08, 64.61, 63.81, 57.87, 45.15, 40.89, 14.22; FAB-MS
(NBA/NaI): m/ z 509 [M + Na]+; HRMS: calcd for C21H30N2O11-
Na 509.1745, found 509.1747.
2d : 85%; Rf ) 0.72 (30% MeOH/CH2Cl2); 1H-NMR (250
MHz, CD3OD): δ (ppm) 8.08-8.01 (br d, 1H, J ) 15.4 Hz),
7.87-7.84 (dd, 1H, J ) 2.0, 8.1 Hz), 7.79-7.76 (dd, 1H, J )
2.0, 7.4 Hz), 7.55-7.38 (m, 4H), 5.04 (s, 1H), 4.44 (br d, 0.3 H,
J ) 4.6 Hz), 4.31-4.29 (dd, 0.7 H, J ) 1.3, 4.6 Hz), 4.13-4.08
(d, 1H, J ) 11.3 Hz), 4.05-4.0 (dd, 1H, J ) 4.6, 9.6 Hz), 3.82-
3.78 (m, 2H), 3.62-3.58 (m, 1H), 2.65-2.61 (m, 2H); 13C-NMR
(100.55 MHz, CD3OD): δ (ppm) 175.07, 174.55, 171.38, 135.29,
133.67, 133.61, 129.61, 128.84, 128.75, 127.24, 126.75, 126.54,
125.0, 94.79, 73.47, 70.56, 62.38, 55.31, 47.82, 29.92, 26.24;
FAB-MS (NBA/NaI): m/ z 370 [M + Na]+; HRMS: calcd for
C18H21NO6Na 370.1265, found 370.1266.
Typ ica l P r oced u r e of In -Med ia ted Allyla tion .25a,b To
a solution of 2b (2.3 g, 6.22 mmol) and ethyl 2-(bromomethyl)-
acrylate31 (7.2 g, 37.3 mmol) in 60 mL of EtOH and 9 mL of
0.1 M HCl was added slowly indium powder (3.2 g, 27.9 mmol)
at rt. After stirring for 10 min, the mixture was gradually
heated to 55 °C and stirred vigorously for 2 d at the same
temperature. At the conclusion of the reaction, the mixture
was divided into six plastic centrifuge bottles (15 mL) and spun
(2000 rpm) for 1 h, after which a homogeneous solution was
separated from the indium reagent (white paste). The clear
supernatants were combined and concentrated to a colorless
oil. The residue was chromatographed on silica gel (400 g) by
eluting with 5% MeOH/CH2Cl2 and then 20% MeOH/CH2Cl2.
The desired product 3b (R ) COCH2NHCbz) was obtained as
a colorless oil in 82% (S/ R ∼4/1) yield (2.47 g). Rf ) 0.76 (20%
MeOH/CH2Cl2). 1H-NMR (250.13 MHz, CD3OD): δ (ppm)
7.36-7.28 (m, 5H), 6.20 (br s, 1H), 5.68 (br s, 1H), 5.12 (s, 2H),
4.36-4.28 (m, 1H), 4.19-4.13 (q, 2H, J ) 7.0 Hz), 3.84 (s, 2H),
3.88-3.65 (m, 5H), 2.52-2.38 (m, 2H), 1.34-1.24 (t, 3H, J )
7.0 Hz); 13C-NMR (100.55 MHz, CD3OD): δ (ppm) 173.66,
168.52, 137.99, 129.35, 128.91, 128.81, 128.60, 73.15, 71.09,
69.32, 68.61, 63.96, 61.98, 54.89, 49.84, 37.83, 14.43, 9.33; FAB-
MS (NBA/NaI): m/ z 507 [M + Na]+; HRMS: calcd for
C22H32N2O10Na 507.1953, found 507.1955.
3a (R ) COOC(CH3)3): 88% (S/ R ∼ 3.5/1). Rf ) 0.87 (30%
MeOH/CH2Cl2). 1H-NMR (250.13 MHz, CD3OD): δ (ppm)
6.22-6.21 (d, 1H, J ) 1.5 Hz), 5.68 (d, 1H, J ) 1.5 Hz), 4.31-
4.26 (t, 1H, J ) 6.5 Hz), 4.23-4.15 (q, 2H, J ) 7.1 Hz), 3.98-
3.52 (m, 6H), 2.50-2.47 (br d, 2H), 1.44 (s, 9H), 1.32-1.26 (t,
3H, J ) 7.1 Hz); 13C-NMR (100.55 MHz, CD3OD): δ (ppm)
168.57, 158.89, 138.25, 136.17, 95.05, 80.93, 73.19, 70.58,
68.25, 64.16, 61.96, 37.83, 28.64; FAB-MS (NBA/NaI): m/ z
416 [M + Na]+; HRMS: calcd for C17H31NO9Na 416.1895,
found 416.1897.
4a : White foam. 70%. 1H-NMR (300.14 MHz, CD3OD): δ
(ppm) 4.31-4.22 (q, 2H, J ) 7.1 Hz), 4.02-3.52 (m, 7H), 2.29-
2.23 (dd, 1H, J ) 4.9, 12.3 Hz), 1.87-1.79 (t, 1H, J ) 12.3
Hz), 1.43 (s, 9H), 1.33-1.28 (t, 3H, J ) 7.1 Hz); FAB-MS
(NBA/NaI): m/ z 418 [M + Na]+; HRMS: calcd for C16H29NO10
Na 418.1687, found 418.1689.
-
4c: White foam. 65%. Rf ) 0.68 (20% MeOH/CH2Cl2). 1H-
NMR (300.14 MHz, CD3OD): δ (ppm) 7.33-7.27 (m, 5H), 5.05
(s, 2H), 4.27-4.22 (q, 2H, J ) 6.9 Hz), 4.13-4.09 (m, 1H, H4),
4.03-4.01 (dd, 1H, J ) 10.3 Hz, H6), 3.85-3.81 (t, 1H, J )
10.2, H5), 3.77-3.75 (dd, 1H, J 8,9' ) 3.5 Hz, J 9,9' ) 8.6 Hz, H9),
3.67-3.64 (m, 1H, H8), 3.60-3.58 (dd, 1H, J ) 5.8 Hz, H9'),
3.58-3.56 (dd, 1H, J 7,8 ) 6.9 Hz, H7), 3.12-3.09 (t, 2H, J )
6.9 Hz), 2.29-2.27 (t, 2H, J ) 7.5 Hz), 2.26-2.23 (dd, 1H, J 3eq,4
) 4.9 Hz, J 3eq,3ax ) 11.4 Hz, H3eq), 1.86-1.81 (t, 1H, J ) 11.4
Hz, H3ax), 1.67-1.62 (quin, 2H), 1.52-1.47 (quin, 2H), 1.37-
1.34 (m, 2H), 1.33-1.28 (t, 3H, J ) 6.9 Hz); 13C-NMR (100.55
MHz, CD3OD): δ (ppm) 192.05, 178.11, 171.76, 129.43, 128.92,
128.71, 96.56, 72.07, 71.66, 70.12, 67.66, 67.28, 64.69, 63.14,
54.09, 41.58, 40.79, 40.15, 36.93, 30.50, 27.29, 26.64, 14.31;
3c (R ) CO(CH2)5NHCbz): 81% (S/ R ∼ 4/1). Rf ) 0.73 (20%
MeOH/CH2Cl2). 1H-NMR (300.14 MHz, CD3OD): δ (ppm)
7.33-7.27 (m, 5H), 6.21 (d, 1H, J ) 1.3 Hz), 5.69 (br s, 1H),
5.04 (s, 2H), 4.31-4.28 (t, 1H, J ) 6.4 Hz), 4.19-4.15 (q, 2H,
J ) 7.4 Hz), 3.96-3.94 (d, 1H, J ) 9.8 Hz), 3.89-3.87 (d, 1H,
J ) 9.8 Hz), 3.83-3.81 (m, 1H), 3.79-3.75 (m, 2H), 3.61-3.58

8744 J . Org. Chem., Vol. 61, No. 25, 1996
Choi et al.
FAB-MS (NBA/NaI): m/ z 565 [M + Na]+, 543 [M + H]+;
1H, J ) 4.9, 13.3 Hz), 2.14-1.90 (m, 16H), 1.27-1.23 (t, 3H,
J ) 7.2 Hz); FAB-MS (NBA/NaI): m/ z 623 [M + Na]+, 582
[M - Et]+.
HRMS: calcd for C25H38N2O11Na 565.2371, found 565.2373.
4d : Pale brown oil. 27%. Rf ) 0.47 (15% MeOH/CH2Cl2).
1H-NMR (300.14 MHz, CD3OD): δ (ppm) 8.23-8.09 (m, 2H),
7.85-7.73 (m, 2H), 7.64-7.35 (m, 3H), 4.32-4.20 (q, 2H, J )
7.1 Hz), 4.18-4.04 (m, 4H), 3.99-3.62 (m, 5H), 2.34-2.28 (dd,
1H, J ) 4.87, 12.87 Hz, H3eq), 1.83-1.75 (t, 1H, J ) ∼12.3 Hz,
H3ax), 1.33-1.26 (t, 3H, J ) 7.1 Hz); FAB-MS (glycerol): m/ z
464 [M + H]+.
Acetyla tion of 4c. Compound 4c (1.7 g, 3.13 mmol) and
Ac2O (20 mL) in 40 mL of pyridine was stirred for 48 h at rt.
After concentration of the reddish reaction mixture, a pale
yellow foam was obtained and purified with flash silica gel
(100 g) chromatography eluting with 10% MeOH/CH2Cl2. The
penta-O-acetylated product (4c′) was obtained in 72% yield
(1.70 g) as light yellow oil. Rf ) 0.62 (10% MeOH/CH2Cl2).
1H-NMR (300.13 MHz, CDCl3): δ (ppm) 7.35-7.27 (m, 5H),
5.48-5.46 (m, 1H), 5.36-5.29 (m, 1H), 5.25-5.22 (m, 1H), 5.08
(s, 2H), 5.05-5.02 (m, 1H), 4.49-4.43 (dd, 1H, J ) 2.5, 12.4
Hz), 4.30-4.20 (q, 2H, J ) 7.0 Hz), 4.19-4.12 (m, 2H), 3.18
(br s, 2H), 2.65-2.61 (dd, 1H, J ) 5.1, 8.8 Hz), 2.57-2.50 (m,
2H), 2.13-2.01 (m, 15H), 1.58-1.49 (m, 4H), 1.29-1.15 (m, 5H);
13C-NMR (100.55 MHz, CDCl3): δ (ppm) 173.38, 170.75,
170.52, 170.29, 168.34, 128.42, 127.99, 77.39, 77.07, 76.75,
72.74, 71.45, 68.40, 67.86, 66.44, 62.36, 62.11, 48.89, 40.68,
36.17, 35.71, 29.35, 26.01, 24.65, 20.66, 13.71; FAB-MS
(NBA/NaI): m/ z 775 [M + Na]+; HRMS: calcd for C35H48N2O16-
Na 775.2898, found 775.2897.
Acetyla tion of 4a . Ac2O (20 mL) was added to 4a (3.0 g,
7.59 mmol) in 20 mL of pyridine. After 48 h stirring at rt, the
volatile solvents were removed by evaporation. The pale red
oil was purified with flash silica gel (200 g) chromatography
by eluting with 10% MeOH/CH2Cl2. The product 5a was
obtained as a pale yellow oil in 69% yield (3.17 g). 1H-NMR
(250.13 MHz, CD3OD): δ (ppm) 5.47-5.43 (dd, 1H, J ) 2.4,
4.0 Hz), 5.14-5.04 (m, 2H), 4.48-4.42 (dd, 1H, J ) 2.6, 12.4
Hz), 4.27-4.16 (q, 2H, J ) 7.1 Hz), 4.12-4.05 (dd, 1H, J )
6.1, 12.4 Hz), 3.77-3.62 (m, 1H), 2.55-2.48 (m, 1H), 2.11-
1.95 (multiple s, 15H), 1.30-1.24 (t, 3H, J ) 7.1 Hz); FAB-
MS (NBA/NaI): m/ z 628 [M + Na]+; HRMS: calcd for
C
26H39NO15Na 628.2215, found 628.2217.
Syn th esis of 7. Compound 4c′ (1.5 g, 1.99 mmol) was
solubilized in anhyd MeCN (20 mL), followed by dropwise
addition of trimethylsilyl trifluoromethanesulfonate (0.65 mL,
4.21 mmol) at rt. The mixture was stirred at 50 °C for 2.5 h
under a stream of N2. After cooling to 0 °C, Na2CO3 (0.85 g)
was added to the reaction mixture followed by stirring for 30
min at 0 °C. The solid material was filtered through a pad of
Celite and washed with 20 mL of CH2Cl2. The filtrates were
combined and concentrated in vacuo prior to flash silica gel
(100 g) chromatography by eluting with 10% MeOH/CH2Cl2.
The desired product with Rf of 0.54 (10% MeOH/CH2Cl2) was
obtained as a pale yellow oil in 73% yield (0.92 g). 1H-NMR
(250.13 MHz, CD3OD): δ (ppm) 7.34-7.20 (m, 5H), 6.36-6.35
(d, 1H, J ) 4.1 Hz), 5.60-5.56 (dd, 1H, J ) 2.5, 5.9 Hz), 5.39-
5.36 (ddd, 1H, J ) 2.5, 6.1 Hz), 4.98-4.93 (dd, 1H, J ) 4.1,
8.6 Hz), 4.86 (s, 2H), 4.59-4.54 (dd, 1H, J ) 2.5, 12.4 Hz),
4.29-4.20 (q, 2H, J ) 7.2 Hz), 4.27-4.21 (m, 1H), 4.05-3.97
(t, 1H, J ) 7.4 Hz), 3.55-3.50 (dd, 1H, J ) 2.5, 9.8 Hz), 3.17-
3.12 (t, 2H, J ) 6.7 Hz), 2.36-2.30 (t, 1H, J ) 7.4 Hz), 2.01-
1.96 (m, 4H), 1.35-1.20 (m, 2H), 1.31-1.26 (t, 3H, J ) 7.2
Hz); 13C-NMR (100.55 MHz, CDCl3): δ (ppm) 170.63, 170.50,
170.00, 169.60, 138.31, 128.64, 127.99, 127.77, 127.43, 107.18,
72.08, 70.79, 69.34, 66.44, 62.04, 61.79, 43.67, 42.83, 40.78,
39.97, 29.13, 27.89, 26.24, 25.33, 24.32, 23.15, 20.81, 14.10;
FAB-MS (NBA/NaI): m/ z 655 [M + Na]+, 633 [M + H]+;
HRMS: calcd for C31H40N2O12Na 655.2476, found 655.2479.
Syn th esis of 8a . To oxazoline 7 (0.85 g, 1.34 mmol)
dissolved in t-BuOH (15 mL) was added trimethylsilyl azide
(0.71 mL, 5.35 mmol). After being stirred at 80 °C for 4 h
under N2 atmosphere, the mixture was concentrated in vacuo
to yield a red oil, which was purified with flash silica gel (70
g) chromatography eluting with 10% MeOH/CH2Cl2. The
product was obtained in 81% (0.74 g) as a pale red oil. Rf )
0.66 (10% MeOH/CH2Cl2). 1H-NMR (300.14 MHz, CD3OD):
δ (ppm) 7.34-7.23 (m, 5H), 5.91-5.90 (d, 1H, J ) 2.4 Hz),
5.42-5.40 (dd, 1H, J ) 1.8, 4.6 Hz), 5.28-5.24 (m, 3H), 4.62-
4.59 (dd, 1H, J ) 3.5, 12.4 Hz), 4.42-4.41 (dd, 1H, J ) 1.9,
10.6 Hz), 4.3-4.14 (m, 4H), 4.11-4.06 (t, 1H, J ) 10.6 Hz),
3.20-3.18 (br m, 2H), 2.17-1.93 (m, 11H), 1.64-1.54 (quin,
2H, J ) 7.3 Hz), 1.50-1.44 (quin, 2H, J ) 7.3 Hz), 1.29-1.23
(m, 5H); 13C-NMR (100.55 MHz, CD3OD): δ (ppm) 173.33,
170.47, 170.22, 170.13, 161.05, 145.35, 138.24, 128.57, 128.40,
128.20, 127.86, 127.34, 107.62, 67.81, 66.38, 62.10, 61.65,
58.31, 47.62, 43.54, 35.30, 26.17, 23.06, 20.64, 13.91; FAB-MS
(NBA/NaI): m/ z 698 [M + Na]+, 633 [M - N3]+.
Dep r otection of N-Boc of 5a . To compound 5a (1.9 g, 3.15
mmol) dissolved in 20 mL of anhyd CH2Cl2 was added TFA
(10 mL) at 0 °C. After stirring for 2 h at the same temperature
and evaporation of the mixture, a pale red oil was obtained.
The residue was solubilized in 10 mL of MeOH, followed by
evaporation: this procedure was repeated five times to remove
free TFA. The crude product 5b was dried in vacuo and used
in the next step without further purification. Rf ) 0.84 (20%
MeOH/CH2Cl2). 1H-NMR (399.88 MHz, CD3OD): δ (ppm)
5.42-5.40 (br d, 1H, J ) 8.5 Hz), 5.31-5.2 (m, 2H), 4.47-
4.46 (br d, 1H, J ) 12.7 Hz), 4.32-4.12 (m, 3H), 4.20-4.18 (q,
2H, J ) 7.1 Hz), 2.65-2.61 (m, 1H, H3eq), 2.2-2.0 (m, 16H),
1.26-1.23 (t, 3H, J ) 7.1 Hz); 13C-NMR (100.55 MHz, CD3-
OD): δ (ppm) 173.74, 171.65, 170.91, 169.78, 166.96, 98.09,
71.25, 70.43, 69.43, 68.56, 67.50, 63.62, 50.96, 35.95, 20.94-
20.55 (m), 14.22; FAB-MS (NBA/NaI): m/ z 506 [M + H]+;
HRMS: calcd for C21H32NO13 506.1872, found 506.1874.
Typ ica l P r oced u r e for N-a cyla tion of 5b. To compound
5b (0.2 g, 0.32 mmol) dissolved in anhyd CH2Cl2 (5 mL) was
added i-Pr2NEt (0.25 mL) and 4-benzoylbenzoyl chloride (0.12
g, 0.49 mmol). After stirring for 12 h at rt, MeOH (5 mL) was
added to the mixture while stirring it. The evaporation of
volatile solvents afforded a pale red oily residue, which was
purified with flash column chromatography (20 g silica gel)
by eluting with 10% MeOH/CH2Cl2. Product 6d (0.14 g, 60%)
was obtained as an oil. Rf ) 0.66 (10% MeOH/CH2Cl2). 1H-
NMR (250.13 MHz, CD3OD): δ (ppm) 8.24-8.07 (m, 2H),
7.88-7.77 (m, 4H), 7.66-7.63 (br d, 1H), 7.57-7.51 (t, 2H, J
) 7.7 Hz), 5.45-5.05 (m, 4H), 4.44-4.33 (m, 1H), 4.25-4.17
(q, 2H, J ) 7.1 Hz), 4.14-4.0 (m, 2H), 2.58-2.50 (m, 1H), 2.10-
1.9 (m, 16H), 1.30-1.23 (t, 3H, J ) 7.1 Hz); FAB-MS (NBA/
NaI): m/ z 736 [M + Na]+.
6a : Pale red oil (60%). 1H-NMR (250.13 MHz, CD3OD): δ
(ppm) 5.40-5.36 (dd, 1H, J ) 2.2, 6.6 Hz), 5.3-5.2 (m, 1H),
5.1-5.07 (m, 1H), 4.46-4.4 (dd, 1H, J ) 2.5, 12.5 Hz), 4.28-
4.17 (q, 2H, J ) 7.0 Hz), 4.13-4.0 (m, 2H), 3.71 (s, 2H), 2.52-
2.50 (dd, 1H), 2.15-1.84 (m, 16H), 1.34-1.23 (t, 3H, J ) 7.0
Hz); FAB-MS (NBA/NaI): m/ z 649 [M + Na]+.
6b: Pale red oil (36%). 1H-NMR (300.14 MHz, CD3OD): δ
(ppm) 6.24-6.05 (m, 2H), 5.68-5.65 (dd, 1H, J ) 3.1, 8.7 Hz),
5.38-5.35 (dd, 1H, J ) 2.4, 6.3 Hz), 5.27-5.22 (m, 2H), 5.10-
5.05 (double t, 1H, J ) 2.4, 6.3 Hz), 4.46-4.4 (dd, 1H, J ) 2.4,
12.4 Hz), 4.27-4.18 (q, 2H, J ) 7.2 Hz), 4.15-4.05 (m, 2H),
2.57-2.52 (dd, 1H, J ) 5.1, 13.4 Hz), 2.10-1.90 (m, 16H),
1.38-1.33 (t, 3H, J ) 7.0 Hz); FAB-MS (NBA/NaI): m/ z 582
[M + Na]+.
6c: Pale red oil (58%). 1H-NMR (300.14 MHz, CD3OD): δ
(ppm) 8.03-8.0 (dd, 2H, J ) 1.3, 6.5 Hz), 7.58-7.55 (dd, 1H,
J ) 1.3, 6.5 Hz), 7.48-7.42 (t, 2H, J ) 6.5 Hz), 5.40-5.37 (dd,
1H, J ) 2.4, 6.4 Hz), 5.36-5.23 (m, 2H), 5.12-5.07 (double t,
1H, J ) 2.4, 6.4 Hz), 4.44-4.4 (dd, 1H, J ) 2.5, 12.3 Hz), 4.25-
4.20 (q, 2H, J ) 7.2 Hz), 4.13-4.02 (m, 2H), 2.57-2.52 (dd,
Hyd r olysis of 8a . To a solution of MeOH (5 mL) containing
0.7 g (1.04 mmol) of compound 8a was added LiOH‚H2O (0.26
g, 6.20 mmol) dissolved in H2O (10 mL). After stirring for 12
h at rt, the reaction mixture was acidified to pH ∼ 4 by adding
cation exchange resin (Dowex 50W-X8; hydrogen form). The
resins were filtered off, and the filtrate was evaporated prior
to flash column chromatography with silica (10 g), eluting with
5% MeOH/CH2Cl2 to 3% HCO2H/30% MeOH/CH2Cl2. From
fractions with Rf ) 0.31 (3% HCO2H/20% MeOH/CH2Cl2), 0.34

Synthesis of C-5 Analogs of N-Acetylneuraminic Acid
J . Org. Chem., Vol. 61, No. 25, 1996 8745
g (62%) of 8b was obtained as an oil (the oily residue was
converted to powder after being dissolved in water and
lyophilization). 1H-NMR (300.14 MHz, CD3OD): δ (ppm)
7.34-7.30 (m, 5H), 5.89-5.78 (d, 1H, J ) 2.3 Hz), 5.05 (s, 2H),
4.32-4.24 (m, 2H), 4.18-4.14 (t, 1H, J ) 9.5 Hz), 3.91-3.89
(m, 2H), 3.13-3.08 (t, 2H, J ) 7.1 Hz), 2.30-2.25 (t, 2H, J )
7.1 Hz), 1.66-1.64 (m, 2H), 1.51-1.49 (m, 2H), 1.38-1.35 (m,
2H); 13C-NMR (100.55 MHz, CD3OD): δ (ppm) 177.14, 168.57,
158.85, 150.04, 138.38, 129.41, 128.89, 128.69, 77.20, 67.27,
63.74, 59.44, 41.59, 40.13, 37.06, 30.53, 30.05, 27.33, 26.66,
26.47; FAB-MS (glycerol): m/ z 560 [M + K]+, 544 [M + Na]+;
HRMS: calcd for C23H31N5O9Na 544.2018, found 544.2019.
Dep r otection of N-Cbz Gr ou p of 8b. Compound 8b (0.2
g, 0.384 mmol) was dissolved in CF3CO2H/CH2Cl2 (1/1; 2 mL)
containing anisole (62 mg, 0.576 mmol), followed by addition
of CF3SO3H (0.34 mL, 3.84 mmol) at 0 °C. After stirring for
30 min at 0 °C, 3 mL of water was added to the reaction
mixture. This aqueous mixture was washed with CH2Cl2 (3
× 5 mL), neutralized with Na2CO3, and evaporated to a solid
material. The solid residue was extracted with MeOH (10 mL).
The extract was concentrated before being applied to a flash
silica gel (10 g) column, which was eluted with 5% MeOH/
CH2Cl2 to 3% HCO2H/50% MeOH/CH2Cl2. The product 8c was
obtained as a pale red oil (50 mg, 33%). This oily material,
after being dissolved in water and lyophilization, was con-
verted to a pale brown solid (hygroscopic). Rf ) 0.31 (5%
HCO2H/30% MeOH/CH2Cl2). 1H-NMR (500.14 MHz, D2O): δ
(ppm) 5.61 (d, 1H, J ) 1.7 Hz), 4.23-4.18 (t, 2H, J ) 10.7 Hz,
H4, H5), 4.11-4.08 (t, 1H, J ) 10.0 Hz, H6), 3.84-3.81 (m, 1H,
H8), 3.79-3.75 (dd, 1H, J ) 11.8 Hz, H9), 3.56-3.52 (pseudo
t, 2H, H7, H9′), 3.07-3.04 (t, 2H, J ) 5.8 Hz), 2.24-2.21 (t, 1.3
H, J ) 6.8 Hz), 2.13-2.11 (t, 0.7 H, J ) 6.8 Hz), 1.56-1.53
(m, 2H), 1.45-1.40 (m, 2H), 1.26-1.20 (m, 2H); 13C-NMR
(100.61 MHz, D2O/CD3OD): δ (ppm) 103.93, 76.22, 69.15,
64.13, 60.26, 40.20, 36.77, 29.03, 26.63, 25.90, 22.73; FAB-MS
(negative ion mode): m/ z 386 [M - 1]-.
Ack n ow led gm en t. This work has been supported
by NIH Grant GM 30367. NMR spectra were obtained
in the Harvard University NMR Laboratory which has
been supported in part by NIH Grant (1-SIO-RR04870-
01) and NSF Grant (CHE88-140195). We thank Dr. A.
Tyler and Ms. J . Lynch for performing mass spectrom-
etry at The Harvard University Chemistry Department
Mass Spectrometry Facility which has been supported
by Grants from NSF (CHE-9020043) and NIH (SIO-
RR06716).
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
spectra of compounds 2a -e, 3a -e, 4a -d , 5a , 6a ,c,d , 7, and
8a -c (22 pages). This material is contained in libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
J O9614856