Sialoside clusters as potential ligands for siglecs (sialoadhesins)

Article abstract of DOI:10.1139/v02-053

Clusters of O- and S-linked α-sialosides with valencies of two to four were constructed to serve as potential multivalent inhibitors towards sialoadhesins (siglecs). Thus, O- and S-prop-2-ynyl α-sialosides (3, 7), together with 4-iodophenyl sialoside 5 were prepared from acetochloroneuraminic acid derivative 1 using silver salicylate and propargyl alcohol for 3 and phase-transfer catalysis for 5 and 7, respectively. Oxidative acetylenic homocoupling of 3 and 7 under Glaser conditions (CuCl, O₂) provided 1,3-diynes 8 and 9 in 83-86% yields. Palladium catalyzed cross-coupling of O-prop-2-ynyl sialoside 3 with 5 using Pd₂(dba)₃ and PPh₃ gave nonsymmetrical dimer 10 (82%). Alternatively, symmetrical clusters were then prepared as above under Sonogashira cross-coupling conditions with 1,4-diiodobenzene (11), 1,3,5-triodobenzene (14), and finally 1,2,4,6-tetraiodobenzene (17) to provide both O- and S-linked dimers 12 (93%) and 13 (88%), trimers 15 (81%) and 16 (76%), while only O-linked tetramer 18 was prepared in 87% yield. Finally, treatment of the O-linked prop-2-ynyl sialoside 3 with Grubbs' metathesis catalyst Cl₂Ru(PCy₃)₂=CHPh (19) gave, as expected, benzeneannulation regioisomeric trimers 20a, 20b in 68% yield.

Full text of DOI:10.1139/v02-053

908
Sialoside clusters as potential ligands for siglecs
(sialoadhesins)
Zhonghong Gan and René Roy
Abstract: Clusters of O- and S-linked ꢀ-sialosides with valencies of two to four were constructed to serve as potential
multivalent inhibitors towards sialoadhesins (siglecs). Thus, O- and S-prop-2-ynyl ꢀ-sialosides (3, 7), together with 4-
iodophenyl sialoside 5 were prepared from acetochloroneuraminic acid derivative 1 using silver salicylate and propargyl
alcohol for 3 and phase-transfer catalysis for 5 and 7, respectively. Oxidative acetylenic homocoupling of 3 and 7 un-
der Glaser conditions (CuCl, O2) provided 1,3-diynes 8 and 9 in 83–86% yields. Palladium catalyzed cross-coupling of
O-prop-2-ynyl sialoside 3 with 5 using Pd2(dba)3 and PPh3 gave nonsymmetrical dimer 10 (82%). Alternatively, sym-
metrical clusters were then prepared as above under Sonogashira cross-coupling conditions with 1,4-diiodobenzene
(11), 1,3,5-triodobenzene (14), and finally 1,2,4,6-tetraiodobenzene (17) to provide both O- and S-linked dimers 12
(93%) and 13 (88%), trimers 15 (81%) and 16 (76%), while only O-linked tetramer 18 was prepared in 87% yield.
Finally, treatment of the O-linked prop-2-ynyl sialoside 3 with Grubbs’ metathesis catalyst Cl2Ru(PCy3)2=CHPh (19)
gave, as expected, benzeneannulation regioisomeric trimers 20a, 20b in 68% yield.
Key words: siglec, sialoadhesins, sialic acid, Sonogashira, palladium cross-coupling.
Résumé : On a préparé une série d’agrégats d’ꢀ-sialosides liés par l’oxygène ou le soufre et de valence allant de deux
à quatre qui pourraient éventuellement servir d’inhibiteurs multivalents vis-à-vis des sialoadhésines (siglecs). On a ainsi
préparé les ꢀ-sialosides de O- et de S-prop-2-ynyle (3, 7) ainsi que le sialoside de 4-iodophényle (5) à partir du dérivé
1 de l’acide acétochloroneuraminique, en utilisant le salicylate d’argent et l’alcool propargylique pour le composé 3 et
une catalyse de transfert de phase pour les composés 5 et 7 respectivement. L’homocouplage acétylénique oxydant des
composés 3 et 7 dans des conditions de Glazer (CuCl, O2) a permis d’obtenir les composés 8 et 9 avec des rendements
allant de 83 à 86%. Un couplage croisé catalysé par le palladium du sialoside de O-prop-2-ynyle 3 avec le composé 5,
à l’aide de Pd2(dba)3 et de PPh3, fournit le dimère non symétrique 10 (82%). De façon alternative, des agrégats
symétriques ont alors été préparés de la façon mentionnée ci-dessus, en utilisant les conditions de couplage croisé de
Sonagashira et du 1,4-diiodobenzène (11), du 1,3,5-triiodobenzène (14) et finalement du 1,2,4,6-tétraiodobenzène (17);
on a ainsi obtenu des produits liés par l’oxygène et le soufre dont les dimères 12 (93%) et 13 (88%) et les trimères 15
(81%) et 16 (76%) ainsi que le produit 18 (87%) un tétramère lié uniquement à l’oxygène. Enfin, le traitement du
sialoside de prop-2-ynyle lié à l’oxygène, 3, avec le catalyseur de métathèse de Grubbs, Cl2Ru(PCy3)2=CHPh (19),
conduit, tel que prévu, aux trimères de benzèneannellation régioisomérique 20a, 20b avec un rendement de 68%.
Mots clés : siglec, sialoadhésines, acide sialique, Sonogashira, couplage croisé au palladium.
Gan and Roy 916
Introduction
animal lectins that mediate cell adhesion and signaling, rec-
ognize sialoconjugates. Several siglecs are expressed on
cells of the innate immune system and sialoadhesin (or
siglec-1) is found on macrophages and has been implicated
in lymphocyte adhesion and myeloid cell development (3).
Although siglecs are known to possess only one carbohy-
drate recognition domain (CRD) (4), multivalent sialosides
have been shown to dramatically increase their inhibitory
potency towards sialoadhesin (5). Given the importance of
multivalent glycoforms in the study of carbohydrate–protein
interactions at the molecular level (6) and their potential
Sialic acid is a generic term representing over 40 different
structures derived from neuraminic acid, a nine-carbon
amino acid sugar (1). The most prevalent member, N-
acetylneuraminic acid, is usually present as a capping resi-
due on natural glycoproteins and glycolipids. As such, it
plays the role of a “terminal elaboration factor” (2) and is
thus well-suited in mediating molecular recognition at the
cell surface, a property well exploited by several pathogens
(1). Conversely, siglecs, a subgroup of immunoglobulin-type
Received 9 October 2001. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 9 July 2002.
Dedicated to the late Raymond U. Lemieux, an outstanding pioneer in carbohydrate chemistry.
Z. Gan and R. Roy.1 Department of Chemistry, Center for Research in Biopharmaceuticals, University of Ottawa, Ottawa, ON
K1N 6N5, Canada.
1Corresponding author (e-mail: rroy@science.uottawa.ca).
Can. J. Chem. 80: 908–916 (2002)
DOI: 10.1139/V02-053
© 2002 NRC Canada

Gan and Roy
909
Scheme 1.
HO
AcO
CO2Me
O
OAc
AcO
AcHN
2
O
Silver salicylate, rt
69%
AcO
AcO
Cl
OAc
3
AcO
AcHN
O
CO2Me
HO
I
AcO
CO2Me
O
OAc
AcO
AcO
AcHN
4
TBAHS
1 M Na2CO3, EtOAc, rt
1
O
I
AcO
55%
5
°
(i) NaOMe/MeOH, -40 C, 30 min
AcO
+
(ii) H resin, -40 C, 15 min
°
CO2Me
SAc
OAc
AcO
CO2Me
S
AcO
OAc
O
(iii) propargyl bromide, Et3N, 1 h
AcO
O
AcHN
AcHN
85%
AcO
AcO
6
7
Scheme 2.
OAc
AcO
AcO
CO2Me
S
CO2Me
OAc
O
OAc
CuCl, O2
X
NHAc
AcO
AcHN
AcO
AcHN
AcO
O
TMEDA
DMF, 40°C
O
OAc
X
AcO
MeO2C
OAc
AcO
7
8 X = S
9 X = O
roles in receptor clustering, we propose herein the synthesis
of sialic acid clusters using a variety of metal-catalyzed
cross-coupling strategies (7).
thioacetate derivative 6, itself obtained from 1 under PTC
conditions (10). Chemoselective de-S-acetylation of 6 under
low-temperature Zemplén conditions followed by low-
temperature quenching by acidic (H+) resin generated a
sialic acid thiol intermediate (10, 11). The thiol intermediate
was then coupled to propargyl bromide to give 7 in 85%
yield as previously observed from other glycosyl thio-
acetates (12) (Scheme 1).
Results and discussion
The syntheses of the requisite prop-2-ynyl ꢀ-sialosides 3,
5, and 7 necessary for the palladium-catalyzed homo- and
cross-coupling reactions are depicted in Scheme 1. Prop-2-
ynyl ꢀ-O-sialoside 3 was readily accessible from ꢁ-
acetochloroneuraminic acid 1 using propargyl alcohol in the
presence of silver salicylate. The Koenigs–Knorr glycosyl-
ation occurred with complete stereocontrol giving rise to the
ꢀ form as previously observed for analogous cases (8). The
pure product can be obtained by recrystalizing the crude
sample from ethanol (69%). 4-Iodophenyl ꢀ-sialoside 5 was
also prepared from 1 using improved phase-transfer catalysis
(PTC) conditions developed in our laboratory (9). The syn-
thesis of aryl ꢀ-sialosyl derivatives was achieved at room
temperature in a two-phase system using ethyl acetate, 1 M
sodium carbonate, and tetrabutylammonium hydrogensulfate
as phase-transfer catalyst. The reaction was entirely
stereoselective and provided 5 in 55% yield. Prop-2-ynyl
ꢀ-thiosialoside 7 was synthesized from the corresponding
The syntheses of homo-coupling symmetrical diynes can
be accomplished by using the Glaser or alternative methods
(13). Thus, oxygen was bubbled through a solution of prop-
2-ynyl ꢀ-sialoside 3, copper(I) chloride, and TMEDA in
DMF at 40°C for 2 h. The desired dimer (9) was obtained in
1
86% yield. The structure of (9) was confirmed from its H
NMR spectrum which did not contain a signal with a chemi-
cal shift close to ꢂ 2.24 ppm, the position of the acetylenic
proton in the spectrum of the monomer. The mass spectrum
of compound (9) gave a M+ + 1 peak at 1057.2 Da. This pro-
cedure was also successfully applied to prop-2-ynyl ꢀ-thio-
sialoside 7 to afford the corresponding dimer 8 in 83% yield
(Scheme 2).
According to our previous studies (14), the use of
Sonogashira cross-coupling conditions modified by removal
of the copper(I) iodide cocatalyst, can eliminate the formation
© 2002 NRC Canada

910
Can. J. Chem. Vol. 80, 2002
Scheme 3.
AcO
AcO
CO2Me
O
CO2Me
O
OAc
OAc
AcO
AcHN
AcO
AcO
AcHN
AcO
+
O
O
I
5
3
Pd2(dba)3, PPh3
DMF/Et3N
°
h, 60 C , 82%
4
AcO
CO2Me
O
OAc
OAc
AcO
NHAc
O
O
O
AcHN
OAc
AcO
AcO
MeO2C
OAc
10
was sequentially hydrolyzed with NaOMe in methanol fol-
lowed by 0.1 M NaOH to provide water-soluble 13a.
Scheme 4.
AcO
Encouraged by the successful synthesis of divalent
sialoside derivatives by the Sonogashira reaction, we further
expanded this reaction toward the synthesis of larger clus-
ters. As already mentioned, the formation of symmetrical
diynes as minor by-products that cause purification prob-
lems can be avoided using CuI. However, CuI is a particu-
larly effective co-catalyst which allows the reaction to occur
at room temperature. Without CuI, the reaction has to be ac-
complished at higher temperatures and longer reaction times
are required. Since sialic acid trimers and tetramers are eas-
ily separated from their corresponding symmetrical diynes,
the addition of CuI was employed to help the reactions to
occur smoothly and rapidly with more hindered tri- or tetra-
iodobenzenes.
1,3,5-Triiodobenzene (14) was prepared from 1,3,5-
tribromobenzene following a known procedure (16). Treat-
ment of 1,3,5-tribromobenzene with KI, I2, and Ni powder in
refluxing DMF afforded 1,3,5-triiodobenzene in 52% yield.
Direct polyiodination of benzene with periodic acid and io-
dine in sulfuric acid at room temperature (rt) provided
1,2,4,6-tetraiodobenzene (17) in good yield (73%) (17).
CO2Me
X
OAc
AcO
AcHN
AcO
O
I
I
+
3 X = O
7 X = S
11
Pd2(dba)3, PPh3
o
DMF/Et3N, 60 C
OR
RO
CO2R1
X
OR
RO
NHAc
OR
OR
RO
AcHN
X
O
O
RO
R1O2C
12 X = O, R = Ac, R1 = Me (93%)
13 X = S, R = Ac, R1 = Me (88%)
13a X = S, R = R1 = H
(i) NaOMe, MeOH
(ii) 0.1M NaOH
of symmetrical diyne. This new protocol was thus used for
the treatment of prop-2-ynyl ꢀ-sialoside 3 (1.1 equiv) and 4-
iodophenyl O-ꢀ-sialoside 5 (1 equiv) using tris(dibenzyl-
ideneacetone)dipalladium(0) (Pd2(dba)3) as catalyst at 60°C
to afford cross-coupling dimer 10 in 82% yield. As ex-
pected, no symmetrical diyne (9) was found (Scheme 3).
Similarly, treatment of 3 with 1,4-diiodobenzene (11, 1 equiv)
under the above reaction conditions provided dimer 12 in
93% yield (Scheme 4). Again, no symmetrical diyne (9) was
observed. The distinction between the homodimer (9) and
the crossdimer 12 can be clearly distinguished from two
marked differences between their respective 13C NMR spec-
tra. The acetylene peaks of the crossdimer 12 were shifted
downfield at ꢂ 86.2 and at 85.6 ppm compared with those of
the homodimer (9) at ꢂ 74.7 and at 70.1 ppm and the spectra
of 12 contained peaks in the aromatic region while those of
9 did not. Previous results showed that thioethers could also
undergo cross-coupling with aryl halides under Sonogashira
conditions (15). Thus, prop-2-ynyl ꢀ-thiosialosides 7 reacted
with 1,4-diiodobenzene in the presence of Pd2(dba)3 at 60°C
to afford dimer 13 in 88% yield. Fully protected dimer 13
Prop-2-ynyl ꢀ-sialoside
3 was treated with 1,3,5-
triiodobenzene (14) (Pd2(dba)3, CuI, PPh3, DMF–Et3N, rt,
1 h) to give trimer 15 (81%). Trimer 15 was readily sepa-
rated from a small amount of symmetrical diyne (9) as a by-
product by silica gel chromatography. Trimer 16 was analo-
gously prepared from prop-2-ynyl ꢀ-thiosialoside 7 in 76%
yield (Scheme 5).
Treatment of prop-2-ynyl ꢀ-sialoside 3 with 1,2,4,6-
tetraiodobenzene (17) using the above conditions gave O-
linked tetramer 18 in 87% yield (Scheme 6). Because of the
steric hindrance, the reaction with tetraiodobenzene needed
longer reaction time for completion (4 h). The structure for
1
18 was confirmed by its H NMR and 13C NMR spectra and
from the molar mass determined by FAB-MS.
Grubbs’ catalyst 19 can also be used to catalyze intermo-
lecular cyclotrimerization of three terminal alkynes accord-
ing to our previous findings (18). Prop-2-ynyl ꢀ-sialoside 3
was treated with Grubbs’ catalyst 19 in refluxing 1,2-dichloro-
ethane for 24 h. The desired regioisomeric trisubstituted
© 2002 NRC Canada

Gan and Roy
911
Scheme 5.
OAc
AcHN
AcO
OAc
OAc
O
AcO
CO2Me
X
OAc
CO2Me
AcO
AcHN
AcO
X
O
Pd2(dba)3, CuI
PPh3, DMF/Et3N
RT, 1h
3 X = O
7 X = S
I
I
X
MeO2C
OAc
NHAc
OAc
X
O
OAc
AcO
AcO
O
MeO2C
I
AcO
OAc
14
AcHN
AcO
15 X = O 81%
16 X = S 76%
Scheme 6.
AcO
OAc
AcO
AcHN
AcO
NHAc
AcO
AcO
CO2Me
O
OAc
OAc
AcO
CO2Me
O
O
OAc
OAc
AcHN
AcO
O
O
Pd2(dba)3, CuI
CO2Me
O
PPh3, DMF/Et3N
4h, rt, 87%
3
I
MeO2C
I
I
O
OAc
NHAc
OAc
O
OAc
O
AcO
AcO
O
I
MeO2C
AcO
17
OAc
AcHN
AcO
18
benzene derivatives 20a, 20b were isolated as a mixture of
1,2,4-(20a) and 1,3,5-(20b) regioisomers in 68% yield
(Scheme 7). The reaction was found to be highly
regioselective in favor of the 1,2,4-regioisomer 20a over that
of 20b (4.5:1). The regioisomeric structures and the ratio
novel procedure is therefore complementary to that using
dicobalt octacarbonyl [Co2(CO)8] (19).
Experimental section
1
were determined from the H NMR spectrum by comparing
General methods
the data of analogous products reported in the literature (18,
19). The aromatic protons for the 1,2,4-isomer 20a appeared
at ꢂ 7.27 ppm (d, J = 7.8 Hz), 7.23 (s), and 7.19 (d, J =
7.8 Hz) and for the symmetrical 1,3,5-isomer 20b as a sin-
glet at ꢂ 7.14 ppm. The 13C NMR showed aromatic carbon
signals at 136.4, 135.4, 135.0 ppm (quaternary carbons) and
128.7, 127.9, 127.1 ppm (tertiary carbons) for the 1,2,4-
isomers and those for 1,3,5-isomer appeared at 137.2 ppm
(quaternary carbon) and at 126.4 ppm (tertiary carbon). This
1H and 13C NMR were recorded on a Bruker AMX500
spectrometer at 500 MHz for protons and 125.7 MHz for
carbons, respectively. Proton chemical shifts (ꢂ) are given
relative to internal chloroform (7.24 ppm) for CDCl3. For
carbon spectra, chemical shifts were given relative to CDCl3
(77.0 ppm). Spectral analyses were performed as first-order
approximations and were based on correlation spectroscopy
(COSY), heteronuclear multiple quantum coherence
(HMQC), and one- and two-dimensional distortionless
© 2002 NRC Canada

912
Can. J. Chem. Vol. 80, 2002
Scheme 7.
AcO
CO2Me
O
OAc
AcO
AcHN
AcO
O
3
PCy3
ClCH2CH2Cl
reflux, 24 h
Ph
Cl
Cl
Ru
PCy3
19
AcO
AcO
CO2Me
O
CO2Me
O
OAc
OAc
AcO
AcHN
AcO
AcO
AcHN
AcO
O
O
OAc
OAc
O
NHAc
O
NHAc
O
O
+
MeO2C
MeO2C
OAc
OAc
OAc
AcO
AcO
MeO2C
O
MeO2C
OAc
O
OAc
OAc
AcO
AcO
AcO
AcO
O
O
OAc
AcHN
OAc
AcHN
20a (major)
20b (minor)
enhancement by polarization transfer (DEPT) experiments.
Optical rotations were measured on a PerkinElmer 241
polarimeter. FAB-MS spectra were recorded on a Kratos
Concepts IIH with Cs+ beam and are not high resolution un-
less stated otherwise. Thin layer chromatography (TLC) was
performed using silica gel 60-F254 glass plates. Reagents
used for developing plates include ceric sulfate (1% w/v)
and ammonium sulfate (2.5% w/v) in 10% (v/v) aqueous
sulfuric acid, iodine, dilute aqueous potassium permanga-
nate, and UV light. TLC plates were heated to approxi-
mately 150°C when necessary. Purifications were performed
by gravity or flash chromatography on silica gel 60 (230–
400 mesh, E. Merck no. 9385). Solvents were evaporated
under reduced pressure using a Büchi rotary evaporator con-
nected to a water aspirator. All chemicals used in the experi-
ments were of reagent grade. Solvents were purified by the
published procedures.
(840 mg, 69%) as a colorless solid: mp 162–164°C; [ꢀ]D
+69.4° (c 0.5, CH3CN). HR-MS calcd. for C23H32N1O13(MH+)
(m/z): 530.1874; found: 530.1895. H NMR (CDCl3) ꢂ: 5.44
(d, 1H, J5,NH = 9.0 Hz, NH), 5.34 (m, 1H, H-8), 5.25 (dd,
1H, J6,7 = 1.3 Hz, J7, 8 = 8.3 Hz, H-7), 4.80 (m, 1H, H-4),
1
4.35 (dd, 1H, J = 15.7 Hz, -OCH2Cϵ), 4.22 (dd, 1H, J9a,9b
=
12.4 Hz, J8,9a = 2.7 Hz, H-9a), 4.10 (dd, 1H, -OCH2Cϵ),
4.04–3.97 (m, 3H, H-5, H-6, H-9b), 3.75 (s, 3H, OCH3),
2.57 (dd, 1H, J3a,3e = 12.8 Hz, J3e,4 = 4.6 Hz, H-3e), 2.39
(dd, 1H, J = 2.4 Hz, -CϵCH), 2.09, 2.07, 1.98, 1.96, 1.81 (s,
15H, OAcs, NHAc), 1.91 (dd, 1H, J3a,4 = 12.5 Hz, H-3a).
13C NMR (CDCl3) ꢂ: 170.8–170.0 (O=Cs), 167.8 (C-1), 98.2
(C-2), 78.9 (-CϵCH), 74.4 (-CϵCH), 72.6 (C-6), 68.8 (C-4),
68.4 (C-8), 67.2 (C-7), 62.3 (C-9), 52.8 (OCH3), 52.7
(-OCH2Cϵ), 49.2 (C-5), 37.8 (C-3), 23.0, 21.0, 20.9, 20.7,
20.6 (NHAc, OAcs).
Methyl (4-iodophenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-
3,5-dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosid)
onate (5)
Methyl (prop-2-ynyl 5-acetamido-4,7,8,9-tetra-O-acetyl-
3,5-dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosid)
onate (3)
To a solution of freshly prepared acetochloroneuraminic
acid 1 (680 mg, 1.33 mmol) in EtOAc (20 mL) was added a
solution of p-iodophenol (587 mg, 2.67 mmol) and TBAHS
(453 mg, 1.33 mmol) in 1 M Na2CO3 (20 mL). The mixture
was stirred vigorously for 1 h at room temperature and next
diluted with EtOAc (20 mL). The organic phase was sepa-
rated and washed with brine. The organic phase was dried
over Na2SO4 and concentrated under reduced pressure. The
residue was purified by silica gel column chromatography
using CH2Cl2–EtOH (30:1, v/v) as eluent to give compound
5 (509 mg, 55%) as a white solid, mp 88–90°C; [ꢀ]D +10.8°
(c 1.0, CHCl3). FAB-MS calcd. for C26H32IO13N1: 693.45;
To a solution of freshly prepared ꢁ-acetochloroneuraminic
acid 1 (1.18 g, 2.31 mmol) in dry propargyl alcohol (20 mL)
containing 4 Å molecular sieves (2 g) was added freshly pre-
pared silver salicylate (0.85 g, 3.47 mmol). The reaction was
stirred for 2 h under nitrogen at room temperature in the
dark. The slurry was filtered over Celite, washed with di-
chloromethane, and evaporated to dryness. The residue was
dissolved in dichloromethane (30 mL). The organic solution
was successively washed with sat. NaHCO3 solution, 5%
Na2S2O3 solution, and brine. The organic phase was dried
over Na2SO4 and concentrated under reduced pressure. The
crude syrup was crystallized from ethanol to afford pure 3
1
found: 694.1 ([M + 1]+, 33.9%). H NMR (CDCl3) ꢂ: 7.49
© 2002 NRC Canada

Gan and Roy
913
(d, 2H, J = 8.8 Hz, aromatic H), 6.76 (d, 2H, aromatic H),
5.58 (bs, 1H, NH), 5.29 (m, 2H, H-7, H-8), 4.87 (m, 1H,
PPh3 (0.1 mmol). The solution was stirred at 60°C under ni-
trogen atmosphere for 2 h. The solution was diluted with
CH2Cl2 (20 mL), and then washed successively with 5%
HCl and brine. The organic phase was dried over Na2SO4
and concentrated under vacuum. The residue was purified by
silica gel column chromatography.
H-4), 4.38 (d, 1H, J5,6 = 10.8 Hz, H-6), 4.21 (d, 1H, J9a,9b
=
12.6 Hz, H-9a), 4.09–4.01 (m, 2H, H-9b, H-5), 3.59 (s, 3H,
OCH3), 2.62 (dd, 1H, J3a,3e = 12.9 Hz, J3e,4 = 4.6 Hz, H-3e),
2.14 (dd, 1H, J3a,4 = 12.5 Hz, H-3a), 2.08, 2.06, 1.99, 1.97,
1.84 (s, 15 H, OAcs, NHAc). 13C NMR (CDCl3) ꢂ: 170.8–
170.0 (O=Cs), 168.0 (C-1), 153.7, 138.2, 121.8, 87.1 (aro-
matic C), 99.8 (C-2), 73.4 (C-6), 69.1 (C-8), 68.6 (C-4),
67.3 (C-7), 62.0 (C-9), 52.9 (OCH3), 49.2 (C-5), 38.1 (C-3),
23.0, 20.9, 20.7, 20.6 (NHAc, OAcs).
1,3,5-Triiodobenzene (14)
1,3,5-Tribromobenzene (1.10 g, 3.5 mmol), KI (3.50 g,
21 mmol), Ni powder (2.00 g), I2 (5.10 g), and DMF
(12.5 mL) were added into a 50 mL round-bottomed flask.
The flask was evacuated on the vacuum line at 0°C for
15 min. The mixture was refluxed under N2 for 3 h. After
cooling, the solution was poured into a separation funnel.
The flask was washed with 3% aq HCl (50 mL) and CH2Cl2
(50 mL) until all material, except for Ni powder, was trans-
ferred into the separation funnel. The CH2Cl2 layer was sep-
arated, and the aqueous layer was extracted with CH2Cl2.
The combined organic phase was washed with distilled wa-
ter and dried over Na2SO4. The solvent was evaporated,
leaving a light-brown crude product. This was further puri-
fied by sublimation at 60°C overnight. The residue was sub-
limed at 120–140°C to afford compound 15 (0.83 g,
52%).13C NMR (CDCl3) ꢂ: 144.4, 95.2 (lit. (16) value).
Methyl (prop-2-ypnyl 5-acetamido-4,7,8,9-tetra-O-acetyl-
3,5-dideoxy-2-thio-D-glycero-ꢀ-D-galacto-2-nonulopyra-
nosid) onate (7)
To a solution of thioacetate sialoside 6 (220 mg,
0.40 mmol) in dry methanol (10 mL), cooled to –40°C, was
added a 1 M solution of sodium methoxide (380 L,
0.38 mmol). The mixture was stirred at –40°C under nitro-
gen for 30 min. The solution was then neutralized with
Amberlite IR-120 H+ resin at –40°C for 15 min. The solu-
tion was filtered. To the filtrate were added prapargyl bro-
mide (80% in toluene, 67 L, 0.60 mmol) and triethyl amine
(112 L, 0.8 mmol). The solution was stirred at room tem-
perature for 1 h. The solution was poured then into water
and exacted by dichloromethane (3 × 10 mL). The combined
organic layers were washed with 5% HCl and brine. The or-
ganic phase was dried over Na2SO4 and concentrated under
reduced pressure. The compound 7 (185 mg, 85%) was puri-
fied by recrystallization from CH2Cl2–hexanes as white sol-
ids, mp 186 to 187°C; [ꢀ]D +51° (c 0.2, CH3CN). HR-MS
calcd. for C23H32NO12S (MH+) (m/z): 546.1645; found:
546.1653. 1H NMR (CDCl3) ꢂ: 5.37 (m, 1H, H-8), 5.31–5.27
1,2,4,5-Tetraiodobenzene (17)
H5IO6 (1.59 g, 6.97 mmol) was dissolved with stirring in
conc. H2SO4 (25 mL), iodine (5.20 g, 20.5 mmol) was
crushed and added to the clear solution. After 30 min of stir-
ring, the dark mixture was placed in an ice bath. Benzene
(0.95 g, 12.20 mmol) was then added slowly. The reaction
was allowed to stir at room temperature for 2 days. The mix-
ture was poured onto crushed ice. The resulting solid was
collected by suction filtration and washed well with metha-
nol to remove iodine. The crude lavender powder was crys-
tallized from 2-methoxyethanol, giving white needles 17
(5.16 g, 73%), mp 253 to 254°C (lit. (17) value mp 253°C).
1H NMR (CDCl3) ꢂ: 7.98 (s, 2H, aromatic H).
(m, 2H, NH, H-7), 4.84 (m, 1H, H-4), 4.25 (dd, 1H, J9a,9b
=
12.5 Hz, J8,9a = 2.7 Hz, H-9a), 4.08–3.99 (m, 2H, H-9b,
H-5), 3.84 (dd, 1H, J5,6 = 10.8 Hz, J6,7 = 2.2 Hz, H-6), 3.79
(s, 3H, OCH3), 3.41, 3.40 (d, 2H, J = 2.6 Hz, -SCH2C=),
2.69 (dd, 1H, J3a,3e = 12.7 Hz, J3e,4 = 4.6 Hz, H-3e), 2.14 (t,
1H, -CϵCH), 2.13, 2.09, 2.00, 1.99, 1.83 (s, 15H, OAcs),
1.95 (dd, 1H, J3a,4 = 12.3 Hz, H-3a). 13C NMR (CDCl3) ꢂ:
170.8–170.0 (O=Cs), 168.0 (C-1), 82.7 (C-2), 79.5 (-CϵCH),
74.2 (C-6), 70.6 (-CϵCH), 69.4 (C-4), 68.4 (C-8), 67.2 (C-7),
62.2 (C-9), 53.0 (OCH3), 49.2 (C-5), 37.4 (C-3), 23.1, 21.1,
20.7, 20.7 (NHAc, OAcs), 16.8 (-SCH2Cϵ).
General procedure for the homo-coupling of acetylenic
sialic acid derivatives (3, 7)
In a mixture of propargyl glycoside (0.2 mmol), CuCl
(0.06 mmol), and TMEDA (0.12 mmol) in DMF (5 mL) was
bubbled O2 at 40°C. Then the brownish green solution was
poured into water (50 mL). The mixture was extracted with
CH2Cl2 (3 × 20 mL). The combined organic phases were
washed with 5% HCl and brine, dried overNa2SO4, and con-
centrated under vacuum. The residue was purified by silica
gel column chromatography CH2Cl2–MeOH (20:1, v/v) as
eluent.
General procedure for the homo-coupling of acetylenic
thiosugar by Glaser reaction
In a mixture of thiosugar (1 mmol), CuCl (0.3 mmol), and
TMEDA (0.6 mmol) in N,N-dimethylformamide (10 mL)
was bubbled O2 at 40°C for 2 h. Then the brownish green
solution was poured into water (100 mL). The mixture was
extracted with CH2Cl2 (3 × 20 mL). The combined organic
phases were washed with brine, dried over Na2SO4, and con-
centrated under vacuum. The residue was purified by silica
gel column chromatography.
1,6-Di-S-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosylonate)-
hex-2,4-di-yne (8)
Reaction time: 3 h; yield: 83%; mp 131 to 132°C, [ꢀ]D
+131.7° (c 0.6, CHCl3). FAB-MS calcd.: 1089.12; found:
1
1089.2 (M+, 12.2%). H NMR (CDCl3) ꢂ: 5.40 (d, 2H, J5,NH
=
=
General procedure for the cross-coupling of acetylenic
thiosugar by Sonogashira reaction
To acetylenic thiosugar (1 mmol) and 1,4-diiodobenzene
(0.45 mmol) in a degassed solution of DMF and Et3N
(5 mL, 1:1, v/v) were added Pd2(dba)3 (0.05 mmol) and
10.1 Hz, NH), 5.33 (m, 2H, H-8), 5.25 (dd, 2H, J6,7
2.2 Hz, J7,8 = 8.6 Hz, H-7), 4.80 (m, 2H, H-4), 4.20 (dd, 2H,
J9a,9b = 12.5 Hz, J8,9a = 2.7 Hz, H-9a), 4.02 (dd, 2H, J8,9b
=
5.5 Hz, H-9b), 3.99 (ddd, 2H, J4,5 = 10.6 Hz, H-5), 3.83 (dd,
2H, J5,6 = 10.8 Hz, H-6), 3.78 (s, 6H, OCH3), 3.51 (ABq,
© 2002 NRC Canada

914
Can. J. Chem. Vol. 80, 2002
2H, J = 16.9 Hz, -SCH2Cϵ), 3.38 (ABq, 2H, -SCH2Cϵ), 2.65
(dd, 2H, J3a,3e = 12.6 Hz, J3e,4 = 4.6 Hz, H-3e), 2.11, 2.07,
matic C), 99.9 (C-2>), 98.0 (C-2), 85.6 (-OCH2CϵC-), 83.8
(-OCH2CϵC-), 73.4 (C-6>), 72.6 (C-6), 69.1 (C-8>), 68.9 (C-4),
68.6 (C-4>), 68.4 (C-8), 67.3 (C-7>), 67.2 (C-7), 62.3 (C-9),
62.0 (C-9>), 53.6 (-OCH2Cϵ), 52.9 (OCH3, OCH3>), 49.2
(C-5, C-5>), 38.2 (C-3>), 37.9 (C-3), 23.1, 21.0, 20.9, 20.7,
1.98, 1.96, 1.81 (s, 30H, OAcs, NHAc), 1.89 (dd, 2H, J3a,4
=
12.2 Hz, H-3a). 13C NMR (CDCl3) ꢂ: 170.7–170.0 (O=Cs),
167.9 (C-1), 82.5 (C-2), 74.2 (-SCH2CϵC-), 74.1 (C-6), 69.3
(C-4), 68.2 (C-8), 67.1 (C-7, -SCH2CϵC-), 62.2 (C-9), 53.3
(OCH3), 49.1 (C-5), 37.4 (C-3), 23.0, 21.1, 20.7, 20.6, 20.6
(NHAc, OAcs), 17.6 (-SCH2Cϵ). Anal. calcd. for C46H60N2O24S2:
C 50.73, H 5.55, N 2.57; found: C 50.83, H 5.69, N 2.56.
20.6 (NHAcs, Oacs). Anal. calcd. for C49H62N2O26
:
C 53.75, H 5.71, N 2.56; found: C 53.63, H 5.76, N 2.59.
General procedure for the cross-coupling of acetylenic
sialic acid derivatives with 1,4-diiodobenzene (11)
1,6-Di-O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosylonate)-
hex-2,4-di-yne (9)
To a degassed solution of the prop-2-ynyl sialosides (3, 7)
(0.2 mmol) and 1,4-diiodobenzene (11) (30 mg, 91 mol) in
DMF–Et3N (4 mL, 1:1) were added Pd2(dba)3 (9.2 mg,
10 mol) and PPh3 (10.5 mg, 40 mol). The mixture was
stirred under N2 at 60°C. The solution was poured into water
(50 mL). The mixture was extracted with CH2Cl2 (3 × 10 mL).
The combined organic phases were washed with 5% HCl
and brine, dried over Na2SO4, and concentrated under vac-
uum. The residue was purified by silica gel column chroma-
tography using CH2Cl2–MeOH (20:1, v/v) as eluent.
Reaction time: 2 h; yield: 86%; mp 118–120°C, [ꢀ]D
+23.0° (c 1.0, CHCl3). FAB-MS calcd.: 1057.0; found:
1
1057.2 (M+, 2.3%). H NMR (CDCl3) ꢂ: 5.39–5.31 (m, 4H,
NH, H-8), 5.24 (dd, 2H, J6,7 = 1.7 Hz, J7,8 = 8.6 Hz, H-7),
4.80 (m, 2H, H-4), 4.36 (ABq, 2H, J = 16.2 Hz, -OCH2Cϵ),
4.22 (ABq, 2H, -OCH2Cϵ), 4.21 (dd, 2H, J9a,9b = 12.4 Hz,
J8,9a = 2.7 Hz, H-9a), 4.03–3.98 (m, 6H, H-5, H-6, H-9b),
3.76 (s, 6H, OCH3), 2.55 (dd, 2H, J3a,3e = 12.8 Hz, J3e,4
=
4.6 Hz, H-3e), 2.09, 2.08, 1.98, 1.97, 1.81 (s, 30 H, OAcs,
NHAc), 1.88 (dd, 2H, J3a,4 = 12.6 Hz, H-3a). 13C NMR
(CDCl3) ꢂ: 170.8–169.9 (O=Cs), 167.7 (C-1), 97.9 (C-2),
74.7 (-OCH2CϵC-), 72.6 (C-6), 70.1 (-OCH2CϵC-), 68.8
(C-4), 68.2 (C-8), 67.1 (C-7), 62.3 (C-9), 53.1 (-OCH2Cϵ),
52.9 (OCH3), 49.2 (C-5), 37.7 (C-3), 23.0, 21.0, 20.7, 20.7,
20.6 (NHAc, OAcs). Anal. calcd. for C46H60N2O26: C 52.26,
H 5.72, N 2.65; found: C 51.92, H 5.75, N 2.65.
1,4-Bis-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosyloxyonate
prop-2-ynyl)benzene (12)
Reaction time: 2 h; yield: 93%; mp 119–121°C, [ꢀ]D
+18.8° (c 0.5, CHCl3). FAB-MS calcd.: 1133.09; found:
1
1133.3 (M+, 3.6%). H NMR (CDCl3) ꢂ: 7.31 (s, 4H, aro-
matic H), 5.56–5.36 (m, 4H, NH, H-8), 5.27 (dd, 2H, J6,7
=
2.0 Hz, J7,8 = 8.5 Hz, H-7), 4.83 (m, 2H, H-4), 4.36 (ABq,
2H, J = 15.8 Hz, -OCH2Cϵ), 4.33 (ABq, 2H, -OCH2Cϵ),
4.25 (dd, 2H, J9a,9b = 12.4 Hz, J8,9a = 2.8 Hz, H-9a), 4.12–
4.00 (m, 6H, H-5, H-6, H-9b), 3.74 (s, 6H, OCH3), 2.60 (dd,
2H, J3a,3e = 12.8 Hz, J3e,4 = 4.6 Hz, H-3e), 2.11, 2.08, 1.99,
Methyl [4-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosyloxyonate
prop-2-ynyl) phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-
3,5-dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosid]
onate (10)
1.98, 1.83 (s, 30H, OAcs, NHAc), 1.96 (dd, 2H, J3a,4
=
12.8 Hz, H-3a). 13C NMR (CDCl3) ꢂ: 170.8–170.0 (O=Cs),
167.9 (C-1), 131.6, 122.6 (aromatic C), 98.1 (C-2), 86.2
(-OCH2CϵC-), 85.6 (-OCH2CϵC-), 72.6 (C-6), 68.8 (C-4),
68.4 (C-8), 67.2 (C-7), 62.3 (C-9), 53.5 (-OCH2Cϵ), 52.9
(OCH3), 49.3 (C-5), 37.9 (C-3), 23.1, 21.1, 20.8, 20.7, 20.6
(NHAc, OAcs). Anal. calcd. for C52H64N2O26: C 55.12,
H 5.69, N 2.47; found: C 54.82, H 5.75, N 2.49.
To a degassed solution of the propargyl sialic acid 3
(58.7 mg, 0.11 mmol) and iodophenyl sialic acid 5 (70 mg,
0.1 mmol) in DMF–Et3N (4 mL, 1:1) were added Pd2(dba)3
(5.0 mg, 5.5 mol) and PPh3 (5.8 mg, 22 mol). The mixture
was stirred under N2 at 60°C for 4 h. The solution was
poured into water (50 mL). The mixture was extracted with
CH2Cl2 (3 × 10 mL). The combined organic phases were
washed with 5% HCl and brine, dried over Na2SO4, and
concentrated under vacuum. The residue was purified by sil-
ica gel column chromatography using CH2Cl2–MeOH (20:1,
v/v) as eluent to afford dimer (91 mg, 82%): mp 120 to
1,4-Bis-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosylthioonate
prop-2-ynyl)benzene (13)
Reaction time 3 h; yield: 88%; mp 134–136°C, [ꢀ]D +95°
(c 0.7, CHCl3). FAB-MS calcd.: 1165.22; found: 1165.2
1
121°C, [ꢀ]D +20° (c 0.5, CHCl3). H NMR (CDCl3) ꢂ: 7.29
1
(d, 2H, J = 8.6 Hz, aromatic H), 6.93 (d, 2H, aromatic H),
5.47–5.25 (m, 6H, NH, NH>, H-7, H-7>, H-8, H-8>), 4.89 (m,
1H, H-4>), 4.82 (m, 1H, H-4), 4.55 (ABq, 2H, J = 15.6 Hz,
-OCH2Cϵ), 4.41 (dd, 1H, J5>,6> = 10.3 Hz, J6>,7> = 1.1 Hz,
(M+, 3.5%). H NMR (CDCl3) ꢂ: 7.23 (s, 4H, aromatic H),
5.50 (d, 2H, J5,NH = 9.9 Hz, NH), 5.36 (m, 2H, H-8), 5.26
(dd, 2H, J6,7 = 1.6 Hz, J7,8 = 8.3 Hz, H-7), 4.81 (m, 2H, H-4),
4.23 (dd, 2H, J9a,9b = 12.4 Hz, J8,9a = 2.4 Hz, H-9a), 4.04–
3.98 (m, 4H, H-9b, H-5), 3.83 (dd, 2H, J5,6 = 10.7 Hz, H-6),
3.71 (s, 6H, OCH3), 3.63 (ABq, 2H, J = 16.9 Hz,
H-6>), 4.29 (ABq, 2H, -OCH2Cϵ), 4.25 (dd, 1H, J9a,9b
=
12.4 Hz, J8,9a = 2.8 Hz, H-9a), 4.23 (d, 1H, J9a>,9b> = 12.6 Hz,
H-9a>), 4.10–4.02 (m, 5H, H-5, H-5>, H-6, H-9b, H-9b>),
-SCH2Cϵ), 3.58 (ABq, 2H, -SCH2Cϵ), 2.67 (dd, 2H, J3a,3e
=
3.75 (s, 3H, OCH3), 3.57 (s, 3H, OCH3>), 2.64 (dd, 1H, J3a>,3e>
12.9 Hz, J3e>,4> = 4.6 Hz, H-3e>), 2.60 (dd, 1H, J3a,3e
12.8 Hz, J3e,4 = 4.6 Hz, H-3e), 2.17 (dd, 1 H, J3a>,4
=
=
=
12.6 Hz, J3e,4 = 4.5 Hz, H-3e), 2.12, 2.05, 1.96, 1.95, 1.81
(s, 30H, OAcs, NHAc), 1.93 (dd, 2H, J3a,4 = 12.2 Hz, H-3a).
13C NMR (CDCl3) ꢂ: 170.7–170.0 (O=Cs), 168.0 (C-1),
131.4, 122.8 (aromatic C), 86.6 (C-2), 82.3 (-SCH2CϵC-),
81.8 (-SCH2CϵC-), 74.2 (C-6), 69.4 (C-4), 68.5 (C-8), 67.2
(C-7), 62.2 (C-9), 53.1 (OCH3), 49.1 (C-5), 37.5 (C-3), 23.0,
21.1, 20.7, 20.7, 20.6 (NHAc, OAcs), 18.0 (-SCH2Cϵ).
12.6 Hz, H-3a>), 2.12, 2.09, 2.08, 2.07, 2.00, 1.99, 1.99,
1.98, 1.85, 1.83 (s, 30 H, OAcs, NHAcs), 1.96 (dd, 1H, J3a, 4
=
12.5 Hz, H-3a). 13C NMR (CDCl3) ꢂ: 170.9–169.9 (O=Cs),
168.0 (C-1>), 167.9 (C-1), 154.0, 133.0, 119.4, 117.8 (aro-
© 2002 NRC Canada

Gan and Roy
915
Anal. calcd. for C52H64N2O24S2: C 50.73, H 5.55, N 2.57;
found: C 50.83, H 5.69, N 2.56.
9.9 Hz, NH), 5.36 (m, 3H, H-8), 5.27 (dd, 3H, J6,7
=
2.2 Hz, J7,8 = 8.3 Hz, H-7), 4.83 (m, 3H, H-4), 4.24 (dd, 3H,
J9a,9b = 12.5 Hz, J8,9a = 2.6 Hz, H-9a), 4.05–3.99 (m, 6H,
H-9b, H-5), 3.85 (dd, 3H, J5,6 = 10.8 Hz, H-6), 3.72 (s, 9H,
OCH3), 3.59 (s, 6H, -SCH2Cϵ), 2.68 (dd, 3H, J3a,3e = 12.6 Hz,
J3e,4 = 4.6 Hz, H-3e), 2.13, 2.07, 1.98, 1.97, 1.82 (s, 45H,
OAcs, NHAc), 1.93 (dd, 3 H, J3a,4 = 12.0 Hz, H-3a). 13C NMR
(CDCl3) ꢂ: 170.8–170.0 (O=Cs), 168.0 (C-1), 134.1,
123.5 (aromatic C), 86.3 (C-2), 82.7 (-SCH2CϵC-), 81.0
(-SCH2CϵC-), 74.2 (C-6), 69.4 (C-4), 68.6 (C-8), 67.2
(C-7), 62.2 (C-9), 53.1 (OCH3), 49.1 (C-5), 37.5 (C-3), 23.0,
21.1, 20.7, 20.7, (NHAc, OAcs), 17.8 (-SCH2Cϵ). Anal.
calcd. for C75H93N3O36S3: C 52.72, H 5.49, N 2.46; found:
C 52.75, H 5.67, N 2.45.
Fully deprotected divalent sialoside (13a)
To peracetylated sialoside 13 (75 mg, 0.064 mmol) dis-
solved in MeOH (2 mL) was added 1 M NaOMe in MeOH
(1 mL) and the solution was stirred at 25°C. After 4 h,
MeOH was removed and 0.1 N NaOH (5 mL) was added.
The mixture was stirred at 25°C overnight. The solution was
treated with Amberlite IR-120 H+ resin for 10 min, and
filtrered. The filtrate was then freeze-dried to afford com-
pound 13a in quantitative yield: [ꢀ]D +32.7° (c 2.6, H2O).
MS (ES+) calcd. for C34H44N2O16S2: 800.86; found: 801.1
([M + 1]+). 1H NMR (D2O) ꢂ: 7.10 (s, 4H, aromatic H), 2.75
(dd, 2H, J3a,3e = 12.4 Hz, J3e,4 = 4.5 Hz, H-3e), 1.91 (s, 6H,
NHAc), 1.80 (dd, 2H, J3a,4 = 12.2 Hz, H-3a). 13C NMR
(D2O) ꢂ: 175.4 (C=O), 170.8 (C-1), 131.3, 122.7 (aromatic
C), 88.2 (-SCH2CϵC-), 83.4 (C-2), 82.5 (-CH2CϵC-), 75.4
(C-6), 71.7 (C-4), 68.8 (C-8), 69.5 (C-7), 63.2 (C-9), 52.1
(C-5), 40.2 (C-3), 22.5 (NHAc), 18.3 (-SCH2Cϵ).
1,2,4,6-Tetrakis-(methyl 5-acetamido-4,7,8,9-tetra-O-
acetyl-3,5-dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopy-
ranosyloxyonate prop-2-ynyl)benzene (18)
To a degassed solution of the prop-2-ynyl sialoside 3
(100 mg, 0.19 mmol) and 1,2,4,5-tetraiodobenzene (17)
(25 mg, 43 mol) in DMF–Et3N (4 mL, 1:1) were added
Pd2(dba)3 (8.6 mg, 9.4 mol), CuI (3.6 mg, 18.9 mol), and
PPh3 (9.9 mg, 37.7 mol). The mixture was stirred under N2
at room temperature for 4 h. The solution was poured into
water (50 mL). The mixture was extracted with CH2Cl2 (3 ×
10 mL). The combined organic phases were washed with 5%
HCl and brine, dried over Na2SO4, and concentrated under
vacuum. The residue was purified by silica gel column chro-
matography using CH2Cl2–MeOH (10:1, v/v) as eluent to af-
ford tetramer 18 (82 mg, 87%): [ꢀ]D +25.6° (c 0.5, CHCl3).
FAB-MS calcd.: 2188.08; found: 1696.6 [M+-C20H28NO13 -H,
General procedure for the cross-coupling of acetylenic
sialic acid derivatives with 1,3,5-triiodobenzene (14)
To a degassed solution of the propargyl sialic acid
(0.2 mmol) and 1,3,5-triiodobenzene (14) (27.8 mg,
61 mol) in DMF–Et3N (4 mL, 1:1) were added Pd2(dba)3
(9.2 mg, 10 mol), CuI (3.8 mg, 20 mol), and PPh3
(10.5 mg, 40 mol). The mixture was stirred under N2 at
room temperature for 1 h. The solution was poured into wa-
ter (50 mL). The mixture was extracted with CH2Cl2 (3 ×
10 mL). The combined organic phases were washed with 5%
HCl and brine, dried over Na2SO4, and concentrated under
vacuum. The residue was purified by silica gel column chro-
matography using CH2Cl2–MeOH (15:1, v/v) as eluent.
1
0.7%). H NMR (CDCl3) ꢂ: 7.44 (s, 2H, aromatic H), 5.47
(d, 4H, J5,NH = 8.4 Hz, NH), 5.37 (m, 4H, H-8), 5.28 (dd,
4H, J6,7 = 1.8 Hz, J7,8 = 8.4 Hz, H-7), 4.82 (m, 4H, H-4),
4.58 (ABq, 4H, J = 16.1 Hz, -OCH2Cϵ), 4.40 (ABq, 4H,
-OCH2Cϵ), 4.25 (dd, 4H, J9a,9b = 12.5 Hz, J8,9a = 2.6 Hz,
H-9a), 4.07–3.98 (m, 12H, H-5, H-6, H-9b), 3.75 (s, 12H,
OCH3), 2.60 (dd, 4H, J3a,3e = 12.8 Hz, J3e,4 = 4.6 Hz, H-3e),
2.12, 2.08, 1.98, 1.97, 1.82 (s, 60 H, OAcs, NHAc), 1.93
(dd, 4H, J3a,4 = 12.5 Hz, H-3a). 13C NMR (CDCl3) ꢂ: 170.8–
170.0 (O=Cs), 167.8 (C-1), 136.1, 124.8 (aromatic C), 98.1
(C-2), 90.7 (-OCH2CϵC-), 83.1 (-OCH2CϵC-), 72.5 (C-6),
68.8 (C-4), 68.4 (C-8), 67.1 (C-7), 62.3 (C-9), 53.4 (-OCH2Cϵ),
52.9 (OCH3), 49.3 (C-5), 37.8 (C-3), 23.0, 21.0, 20.7, 20.7,
20.6 (NHAc, OAcs). Anal. calcd. for C98H122N4O52: C 53.75,
H 5.71, N 2.56; found: C 53.46, H 5.67, N 2.50.
1,3,5-Tris-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosyloxyonate
prop-2-ynyl)benzene (15)
Yield: (81%); mp 129–132°C, [ꢀ]D +16.2° (c 0.5, CHCl3).
1
FAB-MS calcd.: 1660.59; found: 1660.5 (M+, 1.5%). H NMR
(CDCl3) ꢂ: 7.37 (s, 3H, aromatic H), 5.40–5.37 (m, 6H, NH,
H-8), 5.28 (dd, 3H, J6,7 = 1.9 Hz, J7,8 = 8.5 Hz, H-7), 4.82
(m, 3H, H-4), 4.53 (ABq, 3H, J = 15.9 Hz, -OCH2Cϵ), 4.28
(ABq, 3H, -OCH2Cϵ), 4.24 (dd, 3H, J9a,9b = 12.6 Hz, J8,9a
=
2.7 Hz, H-9a), 4.08–4.00 (m, 9H, H-5, H-6, H-9b), 3.74 (s,
9H, OCH3), 2.60 (dd, 3H, J3a,3e = 12.8 Hz, J3e,4 = 4.6 Hz,
H-3e), 2.12, 2.09, 1.99, 1.98, 1.83 (s, 45H, OAcs, NHAc),
1.95 (dd, 3H, J3a,4 = 12.8 Hz, H-3a). 13C NMR (CDCl3) ꢂ:
171.1–170.0 (O=Cs), 167.8 (C-1), 134.6, 123.2 (aromatic
C), 98.1 (C-2), 85.8 (-OCH2CϵC-), 84.2 (-OCH2CϵC-),
72.6 (C-6), 68.8 (C-4), 68.3 (C-8), 67.2 (C-7), 62.4 (C-9),
53.4 (-OCH2Cϵ), 52.9 (OCH3), 49.3 (C-5), 37.9 (C-3), 23.1,
21.1, 20.8, 20.7, 20.6 (NHAc, Oacs). Anal. calcd. for
C75H93N3O39: C 54.25, H 5.64, N 2.53; found: C 54.55, H 5.63,
N 2.50.
1,3,4- and 1,3,5-Tris-(methyl 5-acetamido-4,7,8,9-tetra-O-
acetyl-3,5-dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyrano-
syloxyonate methylene)benzene (20a, 20b)
To a solution of the prop-2-ynyl sialoside 3 (100 mg,
0.19 mmol) in dry 1,2-dichloroethane (4 mL) was added ru-
thenium catalyst 19 (8 mg, 9.7 mol). The mixture was
refluxed under N2 for 24 h. The solution was evaporated un-
der vacuum. The residue was purified by silica gel column
chromatography using CH2Cl2–MeOH (10:1, v/v) as eluent
to afford two isomers 20a, 20b (68 mg, 68%) (1,2,4- and
1,3,5-Tris-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-
dideoxy-D-glycero-ꢀ-D-galacto-2-nonulopyranosylthioonate
prop-2-ynyl)benzene (16)
1
1,3,5-regioisomers, 9:2). H NMR (CDCl3) ꢂ: 7.27 (d, 1H,
Yield: (76%); [ꢀ]D +104.7° (c 0.3, CHCl3). FAB-MS
J = 7.8 Hz, H-Ar), 7.23 (s, 1H, H-Ar), 7.19 (d, 1H, H-Ar),
7.14 (s, 1H, H-Ar for the sym. isomer), 3.69, 355, 3.54 (s,
OMe), 3.68 (s, OMe for the syn. isomer), 2.64–2.55 (m, 3H,
calcd.: 1708.63; found: 1708.9 (M+, 2.5%). 1H NMR
(CDCl3) ꢂ: 7.26 (s, 3H, aromatic H), 5.53 (d, 3H, J5,NH
=
© 2002 NRC Canada

916
Can. J. Chem. Vol. 80, 2002
H-3e). 13C NMR (CDCl3) ꢂ: 170.9–168.1 (C=Os), 137.2,
126.4 (Ar for sym. Isomer), 136.4, 135.4, 135.0, 128.7,
127.9, 127.1 (Ar), 98.6, 98.3, 98.3 (C-2), 72.5, 72.4, 72.3
(C-6), 69.4 (C-4), 68.5, 68.4 (C-8), 67.3, 67.2 (C-7), 66.5,
64.3, 64.1 (CH2), 62.3, 62.2, 62.1 (C-9>), 52.6, 52.5, 52.5
(OCH3), 49.4 (C-5), 38.0, 38.0, 37.9 (C-3), 23.1 (NHAc),
21.1, 20.8, 20.7, 20.7 (Oacs).
7. R. Roy, S.K. Das, R. Dominique, M.C. Trono, F. Hernández-
Mateo, and F. Santoyo-González. Pure Appl. Chem. 71, 565
(1999).
8. R. Roy and C.A. Lafferière. Can. J. Chem. 68, 2045 (1990).
9. D. Carrière, S.J. Meunier, F.D. Tropper, and R. Roy. J. Mol.
Catal. A: Chem. 154, 9 (2000).
10. R. Roy, D. Zanini, S.J. Meunier, and A. Romanowska. ACS
Symp. Ser. 560, 104 (1994).
11. A. Hasegawa, J. Nakamura, and M. Kiso. J. Carbohydr. Chem.
5, 11 (1986).
Conclusions
12. Z. Gan and R. Roy. Tetrahedron Lett. 41, 1155 (2000).
13. (a) C. Glaser. Ann. Chem. Pharm. 154, 137 (1870). For a re-
view and representative examples see: (b) P. Siemsen, R.C.
Livingston, and F. Diederich. Angew. Chem. Int. Ed. Engl. 39,
2632 (2000); (c) A.S. Hay. J. Org. Chem. 27, 3320 (1962);
(d) G. Eglinton and A.R. Galbraith. Chem. Ind. (London), 737
(1956); (e) G. Eglinton. J. Chem. Soc. 889 (1959).
In summary, the palladium-catalyzed Sonogashira reaction
has been successfully applied for the synthesis of sialic acid
clusters of restricted conformational mobility. The procedure
is general, high yielding, compatible with the easily remov-
able acetate protecting group, and the sialic acid clusters
were isolated in excellent yields. The reactions are applica-
ble to thioglycosides. The choice for these “rigidified” scaf-
folds is based on the assumption that lesser entropic penalty
will be paid upon binding with the siglecs, as previously
observed by isothermal titration calorimetry (ITC) for analo-
gous mannoside clusters upon binding to the phytohemag-
glutinin concanavalin A (20).
14. (a) R. Roy, S.K. Das, F. Hernández-Mateo, F. Santoyo-
González, and Z. Gan. Synthesis, 1049 (2001); (b) B. Liu and
R. Roy. J. Chem. Soc. Perkin Trans. 1, 773 (2001).
15. For examples of Glaser and Sonogashira reactions using
organosulfur compounds see: (a) T.J.J. Müller Tetrahedron
Lett. 40, 6563 (1999); (b) M. Fossatelli, A.C.T.H. van der
Kerk, S.F. Vasilevsky, and L. Brandsma. Tetrahedron Lett. 33,
4229 (1992); (c) T.X. Nee and G.M. Whitesides. J. Org. Chem.
53, 2489 (1988); (d) U. Fritzsche and S. Hunig. Tetrahedron
Lett. 13, 4831 (1972). For reviews on general palldium cross-
couplings, see: (e) K. Sonogashira. In Comprehensive organic
synthesis. Vol. 3. Edited by B.M. Trost and I. Fleming. Pergamon
Press, New York. 1991. pp. 521–549; (f ) L. Brandsma, S.F.
Vasilevsky, and H.D. VerKruijsse. In Application of transition
metal catalysts in organic synthesis. Springer, Berlin. 1998.
pp. 67–83; (g) K. Sonogashira. In Metal-catalyzed cross-
coupling reactions. Edited by F. Diederich and P.J. Stang.
Wiley–VCH, Weinheim, Germany. 1998. pp. 203–229.
16. U. Schöberl, T.F. Magnera, R.M. Harrison, F. Fleischer,
J.L. Pflug, P.F.H. Schwab, X. Meng, D. Lipiak, B.C. Noll,
V.S. Allured, T. Rudaleige, S. Lee, and J. Michl. J. Am. Chem.
Soc. 119, 3907 (1997).
Acknowledgment
Support of this work by the Natural Sciences and Engi-
neering Research Council of Canada (NSERC) is gratefully
acknowledged.
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© 2002 NRC Canada