Synthesis of the unique trisaccharide repeating unit, isolated from lipopolysaccharides Rhizobium leguminosarum bv. trifolii 24, and its analogue

Article abstract of DOI:10.1016/S0008-6215(97)10073-8

The synthesis of trisaccharide: 6-d-α-L-Talp(1→2)-α-L-Rhap(l →5)- DHA, and its analogue: 6-d-α-L-Talp(1→2)-β-L-Rhaf(1→5)DHA is described. In the first step a disaccharide, composed of 6-d-L-Talp and L-Rhap was obtained. This, in turn, was converted to the corresponding 1- trichloroacetimidate and coupled with DHA alcohol to afford the required trisaccharide. Its analogue was achieved by the conversion of the above disaccharide to the glycosyl bromide, involving the rhamnopyranose ring scission, followed by condensation with DHA in Koenigs-Knorr procedure.

Full text of DOI:10.1016/S0008-6215(97)10073-8

Carbohydrate Research 306 (1998) 379±385
Synthesis of the unique trisaccharide repeating
unit, isolated from lipopolysaccharides
Rhizobium leguminosarum bv. trifolii 24,
and its analogue
Anna Banaszek
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
Received 22 June 1997; accepted 4 November 1997
Abstract
The synthesis of trisaccharide: 6-d-ꢀ-l-Talp(1!2)-ꢀ-l-Rhap(1!5)-DHA, and its analogue: 6-d-
ꢀ-l-Talp(1!2)-ꢁ-l-Rhaf(1!5)DHA is described. In the ®rst step a disaccharide, composed of
6-d-l-Talp and l-Rhap was obtained. This, in turn, was converted to the corresponding 1-tri-
chloroacetimidate and coupled with DHA alcohol to a€ord the required trisaccharide. Its analogue
was achieved by the conversion of the above disaccharide to the glycosyl bromide, involving the
rhamnopyranose ring scission, followed by condensation with DHA in Koenigs-Knorr procedure.
# 1998 Elsevier Science Ltd. All rights reserved
Keywords: Trisaccharides; DHA; 6-d-l-Talose; l-Rhamnopyranose
1. Introduction
units, composed of solely rare sugars: 3-deoxy-d-
lyxo-heptulosaric acid (DHA), 6-deoxy-l-Tal, and
l-Rha (Fig. 1). Synthetic approaches to this tri-
saccharide were not described, however, shortly
after isolation of DHA [5] we elaborated a method
of preparation of this particularly attractive sugar
[6] as well as 6-deoxy-l-Tal [7].
Gram-negative bacteria belonging to the genus
Rhizobium have the unique ability to induce N2
®xing nodules on roots of legumes by a complex
multistep interaction between the microsymbiont
and its host plant [1]. Experimental evidence sug-
gests that the conversion from the bacteria to
nitrogen-®xing bacteroides involves the alteration
of their antigenic speci®ty [2]. In order to get a
deeper insight into the precise role of the carbohy-
drate chain in R. leguminosarum bv. trifolii and its
exo mutant AR20 [3], a detailed structural analy-
sis of their lypopolysaccharides (LPS) was per-
formed [4]. It was found that their O-speci®c longer
chain consists of unusual trisaccharide repeating
2. Results and discussion
A retrosynthetic analysis of the target compound
suggested a preparation in the ®rst step of the dis-
accharide 3a (Scheme 1). Assuming the structural
similarity of 6-deoxy-sugar units, both the required
glycosydic acceptor 1c and glycosydic donor 2d
0008-6215/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved
PII S0008-6215(97)10073-8

380
A. Banaszek/Carbohydrate Research 306 (1998) 379±385
4a. Disaccharide 4a thus formed was considered as
a kinetic product of dealkylation of 1-OH and
4-OH groups in the Rhap unit, with spontaneous
ring scission, followed by acetylation [13]. To
overcome this undesired transformation, the benzyl
groups in 3a were removed and the product, after
acetylation and deprotection of the anomeric
hydroxyl group with TFA in CH2Cl2, was
converted to the trichloroacetimidate 5b [14]
(Scheme 1).
Fig. 1.
The required glycosyl partner 7b (Scheme 2) was
prepared from the heptulosonic acid 6a [6], the 5,7-
OH groups of which were selectively blocked [15]
as O-isopropylidene derivative 6b. This, in turn,
was benzylated at the 4-O-position with BnBr/
Ag2O (Scheme 2). After removal of O-iso-
propylidene protection, the primary 7-OH group in
6e was oxidized using NaOCl/TEMPO [16] to
a€ord 7a. Esteri®cation of 7-CO2H group with
methanol, promoted by Me3SiCl [6] furnished the
acceptor 7b.
could be prepared from the common substrate i.e.
tert-butyl l-Rhap 1b. Thus, the glycosyl acceptor
1c was readily obtained by a selective protection of
1b, analogous to the reported procedure [8]. Pre-
paration of the glycosyl donor 2d was performed
by a conversion of 1b to 2a in a known reaction
sequence [9]. Subsequent hydrolysis of the tert-
butyl group with TFA in CH2Cl2 under the condi-
tions applied for the hydrolysis of a tert-butyl ester
[10], then acetylation and reaction with DCMME
[11] a€orded the required chloride 2d.
Coupling of the trichloroacetimidate 5b with the
.
acceptor 7b promoted by BF3 OEt2 a€orded solely
Ideally suited to construct the ꢀ-(1!2)-trans
linkage was a classical procedure involving AgOTf-
sym. collidine as promoters [12]. Disaccharide 3a
thus obtained was isolated in 72% yield as a sole
product. For the conversion of 3a to the glycosyl
donor, needed for condensation with DHA accep-
tor, removal of the anomeric tert-butyl group was
necessary. With this aim, acetolysis using TFA±
Ac2O (1:15, 0 ꢀC!rt) was attempted. However,
despite the mild reaction conditions, acetolysis was
accompanied by transformation of Rhap ring to
the furanose one giving rise to 1-O-acetyl derivative
the ꢀ-coupled trisaccharide 8a. This, in turn, was
subjected to hydrogenolysis, followed by acetyla-
tion, leading to the fully O-acetylated derivative 8c.
Thus, the ®rst synthesis of the Rhizobium tri-
saccharide in a protected form was achieved.
Having in hand the disaccharide 4a it was of
interest to accomplish the synthesis of an analo-
gous trisaccharide, containing the Rha unit in the
furanose form. Additionally, we were stimulated
by the absence of information in literature on the
use of a Rhaf donor for condensation with sugar
acceptors. It is worth noting that hexofuranoses
have been identi®ed as components of the bacterial
LPSs [17].
For the formation of an interglycosidic
linkage leading to the ``new'' trisaccharide the
Koenigs±Knorr procedure was employed. Thus,
Scheme 1. (a) AgOTf, sym. collidine, (b) TFA, Ac2O; (c)
TFA, CH2Cl2.
Scheme 2. (a) NaOCl, TEMPO; TEMPO=2,2,6,6,-tetramethyl-
piperidine 1-oxyl, radical.

A. Banaszek/Carbohydrate Research 306 (1998) 379±385
381
disaccharide bromide 4b obtained in the reaction
of 4a with TiBr4 [15] was condensed with the DHA
alcohol 6b in the presence of Hg(CN)2. The reac-
tion proceeded smoothly, furnishing the sole tri-
saccharide 9a (Scheme 3) with the new glycosidic
linkage assigned to the ꢁ-con®guration. It is known
that the NMR data i.e. chemical shifts and cou-
pling constants for establishing ꢀ or ꢁ-con®gura-
tion of the manno type anomers, especially those of
furanosides, are uncertain due to their great con-
formational diversity [18a]. Fortunately, the per-O-
acetylated derivative of this trisaccharide 9c was
crystalline, so allowing to con®rmation of the
structure by the X-ray analysis [13].
A creation of the ꢁ-glycosidic linkage between
the bromide 4b and alcohol 7b deserves some
notes. According to the knowledge on a particu-
larly disfavoring creation of the cis-glycosidic link-
age in furanosides: manno, rhamno, lyxo [18] we
could expect a selective formation of the trans ꢀ-
glycoside. The creation of the opposite ꢁ-cis link-
age implicit so far.
pyranosyl bromide (17.2 g, 45 mmol) in CH2Cl2
(50 mL) at 5 ꢀC under argon. The mixture was
stirred for 1 h at room temperature, then ®ltered
and puri®ed by chromatography (hexane±AcOEt,
17:3), yield: 12.5 g (76%): mp 71±73 ꢀC; [ꢀ]d 54.6ꢀ
1
(c 2.32, CHCl3); H NMR (C6D6): ꢂ 5.81 (dd, 1H,
H-3), 5.55 (5, 1H, H-4), 5.47 (dd, 1H, H-2), 5.20 (d,
1H, H-1), 4.20 (pq, 1H, H-5), 1.72, 1.69, 1.68, (3s,
3Â3H, Ac), 1.24 (d, 3H, CH3), 1.04 (s, 9H, t-Bu);
J1,2 1.9, J2,3 3.3, J3,4 10.0, J4,5 9.9, J5,6 9.8, J5,3
1.8 Hz; Anal. Calcd for C16H26O8 (346.37): C
55.48%, H 7.57%, Found C 55.13%, H 7.46%.
Further transformation of 1a to 1c was per-
formed according to the procedure described for
an analogous methyl glycoside [8].
t-Butyl a-l-rhamnopyranoside (1b).ÐCharacter-
istic data: mp 45±46 ꢀC; [ꢀ]d 79.8ꢀ (c 1.2, CHCl3);
Anal. Calcd for C10H20O5 (220.26): C 54.53%, H
9.15%, Found C 54.36%, H 9.16%.
t-Butyl 3,4-di-O-benzyl-6-deoxy-a-l-rhamno-
pyranoside (1c).ÐCharacteristic data: colourless
syrup; [ꢀ]d
46.5ꢀ (c 1.3, CHCl3); 1H NMR
(200 MHz, C6D6): ꢂ 7.05±7.35 (m, 10H, 2ÂPh),
5.27 (s, 1H, H-1), 4.85 (d, 1H, Bn), 4.52 (d, 1H,
Bn), 4.36 (s, 2H, Bn), 4.12 (pq, 1H, H-5), 3.88 (m,
2H, H-2, H-4), 3.58 (t, 1H, H-3), 2.4 (bs, 1H, OH),
1.8 (d, 3H, CH3), 1.11 (s, 9H, t-Bu); J1,2 ꢁ0, J2,3
ꢁ1.8, J3,4 9.1, J4,5 9.6, J5,6 6.2 Hz; 1H NMR
(CDCl3): ꢂ 7.28±7.38 (m, 10H, Ph), 5.07 (d, 1H, H-
1), 4.88 (d, 1H, Bn), 4.66±4.73 (m, 2H, Bn), 4.63 (d,
1H, Bn), 3.93 (pq, 1H, H-5), 3.85±3.90 (m, 2H, H-
2, H-4), 3.42 (t, 1H, H-3), 2.4 (d, 1H, OH), 1.27 (d,
3H, CH3), 1.22 (s, 9H, t-Bu); J1,2 0.7, J3,4 9.5, J4,5
9.6, J5,6 6.2, J2,OH 2.1 Hz; Anal. Calcd for
C24H32O5 (400.5): C 71.97%, H 8.05%, Found C
71.63%, H 8.12%.
3. Experimental
General methods.ÐOptical rotations were mea-
sured with JASCO DIP Digital Polarimeter at
room temperature. 1H NMR spectra were recorded
on Bruker AM-500 (500 MHz) with Me4Si as
internal standard. Mass spectra were taken on a
AMD-604 mass spectrometer. Reactions were
monitored by TLC on silica (Merck alu-plates
(0.2 mm)). Reaction products were puri®ed by ¯ash
chromatography, using Merck's Kieselgel 60 (240±
400 mesh or 70±230 mesh).
t-Butyl 2,3,4-tri-O-acetyl-a-l-rhamnopyranoside
(1a).ÐTo a mixture of t-butyl alcohol (7.2 mL,
79 mmol), Hg(CN)2 (15 g, 59.5 mmol) and mole-
cular sieves 3A (10 g) in CH2Cl2 (100 mL), was
added a solution of 2,3,4-tri-O-acetyl-ꢀ-l-rhamno-
t-Butyl 2,3,4-tri-O-acetyl-6-deoxy-a-l-talopyrano-
side (2a).ÐPrepared from 1b analogously to the
described procedure for methyl glycoside [9].
Characteristic data: mp 122 ꢀC; [ꢀ]d 72.3ꢀ (c 1.0,
1
CHCl3); H NMR (CDCl3): ꢂ 5.31 (t, 1H, H-3),
5.15 (m, 1H, H-2), 5.12 (d, 1H, H-1), 4.91 (ddd,
1H, H-4), 4.31 (pq, 1H, H-5), 2.15, 2.14, 1.99 (3s,
3Â3H, Ac), 1.25 (s, 9H, t-Bu), 1.17 (d, 3H, CH3);
J1,2 1.6, J2,3=J3,4 3.7, J4,5 1.7, J4,2 1.0, J5,6 6.6 Hz;
Anal. Calcd for C16H26O8 (346.37): C 55.48%, H
7.57%, Found C 55.25%, H 7.46%.
1,2,3,4,-Tetra-O-acetyl-6-deoxy-a-l-talopyranose
(2c).ÐA solution of 3a (0.52 g, 1.5 mmol) in anhy-
drous CH2Cl2 (30 mL) was stirred with TFA
(15 mL) at room temperature until TLC (hexane±
Et2O, 3:7) showed disappearance of the substrate.
.
Scheme 3. (a) Hg(CN)2, CH2Cl2, rt; (b) BF3 OEt2, CH2Cl2,
40 ꢀC.

382
A. Banaszek/Carbohydrate Research 306 (1998) 379±385
Evaporation left a syrup which was treated with
Ac2O-Py. After usual work-up the product was
puri®ed by chromatography to yield 0.31 g (62%)
3H, Bn), 4.31 (pq, 1H, H-5), 3.90 (dd, 1H, H-3),
3.85 (pq, 1H, H-5), 3.75 (t, 1H, H-2), 3.46 (t, 1H,
H-4), 2.15, 2.10, 1.99 (3s, 3Â3H, Ac), 1.27 (d, 3H,
of 2c: mp 97 ꢀC; [ꢀ]d 72.3ꢀ (c 0.26, CHCl3); H
1
0
CH3), 1.2 (d, 3H, CH3 ), 1.19 (s, 9H, t-Bu); J2,3 3.0,
0 0 0 0 0 0
J2 ,3 =J3 ,4 3.8, J3,4 9.3, J4,5 9.5, J4 ,5 1.1, J5,6 6.3,
NMR (CDCl3): ꢂ 6.13 (d, 1H, H-1), 5.32 (t, 1H, H-
3), 5.20 (m, 1H, H-2), 5.09 (ddd, 1H, H-4), 4.22
(pq, 1H, H-5), 2.7, 2.16, 2.14, 2.0 (4s, 4Â3H, Ac),
1.22 (d, 3H, CH3); J1,2 1.5, J2,3 3.7, J3,4 3.7, J4,5
1.0, J5,6 6.5 Hz; Anal. Calcd for C14H20O9 (332.30):
C 50.60%, H 6.07%, Found C 50.48%, H 6.14%.
2,3,4,-Tri-O-acetyl-6-deoxy-a-l-talopyranosyl
chloride (2d).ÐTo a solution of 2c (0.664 g,
2 mmol) in anhydrous CH2Cl2 (5 mL) were added
DCMME (Cl2CHOCH3) (0.89 mL, 10 mmol) and
freshly fused ZnCl2 (13 mg) under argon. The
reaction mixture was stirred at room temperature
until all starting material was consumed (TLC,
hexane±Me2CO, 17:3) and the single faster moving
product was formed. The mixture was diluted with
dry toluene, ®ltered through Celite and con-
centrated. The residue was eluted from a short
column of silica gel to give 0.49 g (79.5%) of 2d as
a syrup.
0
0
J5 ,6 6.6 Hz; HRMS (LSIMS): Calcd for C36H48O12
[M+Na]+ m/z 695.3044, Found m/z 695.3051.
t-Butyl 2-O-(2,3,4-tri-O-acetyl-6-deoxy-a-l-talo-
pyranosyl)-3,4-di-O-acetyl-a-l-rhamnopyranoside
(3c).ÐA solution of 3a (0.67 g, 1 mmol) in EtOH
(15 mL) was stirred with Pd/C (0.2 g) overnight.
After ®ltration, and evaporation of the solvent the
residue was acetylated with Ac2O/Py, to a€ord 3c
(0.48 g, 83%): [ꢀ]d 72.9ꢀ (c 0.9, CHCl3); 1H NMR
(C6D6): ꢂ 5.65 (dd, 1H, H-3), 5.53 (t, 1H, H-4), 5.48
(t, 1H, H-30), 5.40 (dt, 1H, H-40), 5.30 (m, 1H, H-
20), 5.21 (d, 1H, H), 5.07 (d, 1H, H-10), 4.20 (pq,
1H, H-50), 4.17 (pq, 1H, H-5), 4.8 (q, 1H, H-2),
1.99, 1.83, 1.69, 1.68, 1.66 (5s, 5Â3H, Ac), 1.25 (d,
0
3H, CH3), 1.11 (s, 9H, t-Bu), 1.0 (d, 3H, CH3 ); J1,2
0
0
0
0
0
0
0
1.9, J1 ,2 1.3, J2,3 3.4, J2 ,3 =J3 ,4 3.7, J3,4 9.9, J4 ,5
0
0
0
1.1, J5,6 6.3, J5 ,6 6.5 Hz; HRMS (LSIMS): Calcd
for C26H40O14 [M+Na]+ m/z 599.2315, Found m/z
599.2316.
t-Butyl 2-O-(2,3,4-tri-O-acetyl-6-deoxy-a-l-talo-
pyranosyl)-3,4-di-O-benzyl-a-l-rhamnopyranoside
(3a).ÐTo a stirred suspension of AgOTf (0.46 g,
1.8 mmol) in dry CH2Cl2 (3 mL) was added a mix-
ture of glycosyl donor 2d (0.49 g, 1.55 mmol), gly-
cosyl acceptor 1c (0.44 g, 1.25 mmol), and sym.-
collidine (1.65 mL 1 M solution in CH2Cl2,
1.25 mmol) at 40 ꢀC under argon. After stirring
for 0.5 h at this temperature (TLC, hexane±
Me2CO, 4:1; hexane±Et2O-MeOH, 1:1:0.05) the
reaction mixture was diluted with CH2Cl2 and ®l-
tered through a Celite. The ®ltrate was washed
with aqueous solution of saturated NaHCO3,
Na2S2O3 and H2O. The organic phase was dried
with MgSO4, evaporated and the residue was pur-
i®ed by chromatographꢀy to give amorphous 3a
(0.57 g, 73%): [ꢀ]d 61.4 (c 0.8, CHCl3); 1H NMR
(C6D6): ꢂ 7.5±7.35 (m, 10H, 2Ph), 5.67 (m, 1H, H-
40), 5.61 (t, 1H, H-30), 5.29 (m, 1H, H-20), 5.28 (d,
1H, H-10), 5.23 (d, 1H, H-1), 4.93, 4.59, 4.51, 4.42
(4d, 4Â1H, 2Bn), 4.23 (pq, 1H, H-50), 4.11 (pq, 1H,
H-5), 4.08 (dd, 1H, H-3), 3.95 (t, 1H, H-2), 3.77 (t,
1H, H-4), 1.83, 1.73, 1.72 (3s, 3Â3H, Ac), 1.39 (d,
2-O-(2,3,4-Tri-O-acetyl-6-deoxy-a-l-talopyrano-
syl)-3,4-di-O-acetyl-a-l-rhamnopyranose (5a).ÐA
solution of 3c (0.58 g, 1 mmol) in CH2Cl2 (3 mL)
was stirred with TFA (1.5 mL) for 4 h at room
temperature. Evaporation followed by ®ltration
through silica gel (hexane±Me2CO, 7:3) a€orded 5a
(0.42 g, 82%): mp 73 ꢀC; [ꢀ]d
34.8ꢀ (c 0.52,
CHCl3).
2-O-(2,3,4-Tri-O-acetyl-6-deoxy-a-l-talopyrano-
syl)-3,4-di-O-acetyl-a-l-rhamnopyranosyl trichloro-
acetimidate (5b).ÐTo a solution of 5a (0.26 g,
0.5 mmol) and Cl3CCN (0.5 mL, 4.45 mmol) in dry
CH2Cl2 (15 mL) was added DBU (0.47 mL,
0.51 mmol) at 20 ꢀC under argon. After stirring
for 10 min, the mixture was directly poured on
silica gel, and eluted with hexane±Et2O (1:1) to give
5b (0.29 g, 82%) as a colourless syrup: [ꢀ]d 51.7ꢀ
1
(c 1.0, CHCl3); H NMR (CDCl3): ꢂ 8.68 (s, 1H,
NH), 6.25 (d, 1H, H-1), 5.29 (t, 1H, H-30), 5.26
(dd, 1H, H-3), 5.22±5.24 (m, 1H, H-40), 5.13±5.17
(m, 2H, H-20, H-4), 4.98 (d, 1H, H-10), 4.29
(pq, 1H, H-50), 4.27 (q, 1H, H-2), 4.06 (pq, 1H, H-
0
3H, CH3), 1.18 (s, 9H, t-Bu), 1.06 (d, 3H, CH3 );
5), 2.16, 2.14, 2.09, 2.06, 2.0 (5s, 5Â3H, Ac), 1.27
0
0
0
0
0
0
0
J1,2 2.0, J1 ,2 1.4, J2,3 3.0, J2 ,3 =J3 ,4 3.6, J3,4 9.3,
0
(d, 3H, CH3), 1.23 (d, 3H, CH3 ); J1,2 2.0, J1 ,2 1.0,
0
1
0
0
0
0
0
0
0
J2,3 3.3, J3,4 9.7, J4,5 9.8, J4 ,5 1.0, J5,6 6.3, J5 ,6
0
J4,5 9.3, J4 ,5 1.1, J5,6 6.3, J5 ,6 6.5 Hz; H NMR
(CDCl3): ꢂ 7.24±7.34 (m, 10H, 2Ph), 5.32 (t, 1H,
H-30), 5.29 (dt, 1H, H-40), 5.19 (m, 1H, H-20), 5.1
(bs, 2H, H-1, H-10), 4.88 (d, 1H, Bn), 4.61±4.72 (m,
6.6 Hz.
Methyl (methyl 3-deoxy-5,7-O-isopropylidene-a-
d-lyxo-hept-2-ulopyranosid)onate (6b).ÐA mixture

A. Banaszek/Carbohydrate Research 306 (1998) 379±385
383
of 6a [6] (0.354 g, 1.5 mmol), dimethoxypropane
(2 mL), DMF (3 mL), and CSA (15 mg) was stirred
for 3 h at room temperature, then the mixture was
neutralized with TEA (0.2 mL) and evaporated
with toluene. Puri®cation by chromatography
(hexane±Me2CO, 3:2) gave 6b (0.38 g, 92%) as a
crystalline product: mp 53 ꢀC; [ꢀ]d +61.3ꢀ (c 0.63,
J4,5 3.2, J6,7 1.8, J6,7a 2.2, J7,7a 12.8 Hz; HRMS
(LSIMS): Calcd for C25H30O7 [M+Na]+ m/z
465.1889, Found m/z 465.1889.
Methyl (methyl 4-O-benzyl-3-deoxy-a-d-lyxo-
hept-2-ulopyranosid)onate (6e).ÐA solution of 6c
(0.183 g, 0.5 mmol) and CSA (5 mg) in a mixture of
CH2Cl2±MeOH (6 mL, 2:1) was stirred for 1 h at
room temperature (TLC, hexane±Me2CO, 3:2)
NaHCO3 was added and stirring was continued for
15 min. Filtration through a Celite followed by
evaporꢀation a€orded crystalline 6e (0.152 g, 93%):
1
CHCl3); H NMR (CDCl3): ꢂ 4.48 (ddd, 1H, H-4),
4.18 (dd, 1H, H-5), 3.79±3.82 (m, 1H, H-6), 3.78 (s,
3H, CO2CH3), 3.70±3.71 (m, 2H, H-7, H-7a), 3.70
(bs, 1H, OH), 3.26 (s, 3H, OCH3), 2.63 (dd, 1H, H-
3eq), 1.90 (dd, 1H, H-3ax), 1.43, 1.36 (2s, 2Â3H, i-
Pr),; J3ax,3eq 15.1, J3ax,4 3.5, J3eq,4 4.7, J4,5 7.2, J5,6
1.9, J6,7 1.9 Hz; HRMS (LSIMS): Calcd for
C12H20O7 [M+Na]+ m/z 299.1106, Found m/z
299.1104.
ꢀ
1
mp 47 C; [ꢀ]d +49.9 (c 0.61, CHCl3); H NMR
(CDCl3): ꢂ 7.30±7.37 (m, 5H, Ph), 4.57±4.62 (m,
2H, Bn), 4.01±4.05 (m, 1H, H-5), 3.89 (ddd, 1H, H-
4), 3.84±3.87 (m, 1H, H-6), 3.81 (s, 3H, CO2CH3),
3.67 (ddd, 2H, H-7, H-7a), 3.23 (s, 3H, OCH3),
2.8±2.86 (bs, 1H, 7-OH), 2.69 (bs, 1H, 5-OH), 2.23
(ddd, 1H, H-3eq), 2.03 (dd, 1H, H-3ax); J3ax,3eq
12.8, J3ax,4 11.6, J3eq,4 5.0, J3eq,5 0.9, J7,6 1.3, J7a,6
1.2, J7a,7b 4.3, J4,5 3.0 Hz; HRMS (LSIMS): Calcd
for C16H22O7 [M+Na]+ m/z 349.1263, Found m/z
349.1264.
Methyl
(methyl
4-O-benzyl-3-deoxy-5,7-O-
isopropylidene-a-d-lyxo-hept-2-ulopyranosid)onate
(6c), and benzyl (methyl 4-O-benzyl-3-deoxy-5,7-
O-isopropylidene-a-d-lyxo-hept-2-ulopyranosid)-
onate (6d).ÐA suspension of 6b (0.184 g,
0.66 mmol), BnBr (0.3 mL, 2.53 mmol) and a
freshly prepared Ag2O (0.58 g, 2.5 mmol) in a mix-
ture of MeCN±DMF (2:1, 6 mL) was stirred over-
night at room temperature. The suspension was
diluted with Et2O, ®ltered, poured into aq.
NaHCO3, and extracted with Et2O. The organic
layer was washed with aq. Na2S2O3, dried, and
evaporated. The residue was applied to a silica gel
column. Elution with hexane±Et2O (1:2) gave 6c
(0.17 g, 71%): mp 108 ꢀC; [ꢀ]d +63.8ꢀ (c 0.55,
1,7-Dimethyl (methyl 4-O-benzyl-3-deoxy-a-d-
lyxo-hept-2-ulopyranosid)arate (7b).ÐTo a solu-
tion of 6e (0.2 g, 0.6 mmol) in CH2Cl2 (2 mL) satu-
rated aq. NaHCO3 (5 mL), KBr (8 mg), and
TEMPO (8 mg) were added. The mixture was
cooled in the ice-bath, then NaOCl (4.1 mL) was
added dropwise with stirring. After 1 h the solvents
were evaporated and the residue was ®ltered
through a silica gel column (CH2Cl2±MeOH, 10:1).
Evaporation left a syrup which was redissolved in
dry MeOH, treated with 1 M solution of Me3SiCl
in CH2Cl2 and stirred overnight. The reaction
mixture was concentrated, and puri®ed by chro-
marography (CH2Cl2±Me2CO, 95:5) to yield 7b
1
CHCl3); H NMR (CDCl3): ꢂ 7.26±7.36 (m, 5H,
Ph), 4.63 (d, 1H, Bn), 4.57 (d, 1H, Bn), 4.10±4.12
(m, 1H, H-5), 4.05 (d, 1H, H-7a), 3.96 (d, 1H, H-
7), 3.88 (ddd, 1H, H-4), 3.81 (s, 3H, CO2CH3),
3.34±3.36 (m, 1H, H-6), 3.21 (s, 3H, OCH3), 2.1±
2.22 (m, 2H, H-3ax, H-3eq), 1.49, 1.46, (2s, 2(3H, i-
Pr); J3ax,3eq 12.5, J3ax,4 11.5, J3eq,4 5.2, J4,5 3.2, J5,6
2.4, J6,7 1.7, J6,7a 2.1, J7,7a 12.8 Hz; HRMS
(LSIMS): Calcd for C19H26O7 [M+Na]+ m/z
389.1576, Found m/z 389.1577. As a side product
was isolated the product of transesteri®cation of
carbomethoxy group leading to the carbobenzy-
loxy derivative 6d in 4.8% yield (14 mg): mp 73±
74 ꢀC; [ꢀ]d +43.0ꢀ (c 1.59, CHCl3); 1H NMR
(CDCl3): ꢂ 7.27±7.40 (m,5H, Ph), 5.20 (d, 1H,
OCH2Ph), 4.59 (d, 1H, OCH2), 4.56 (d, 1H,
OCH2Ph), 4.30 (d, 1H, OCH2Ph), 4.10 (m, 1H, H-
5), 4.04 (dd, 1H, H-7a), 3.97 (dd, 1H, H-7), 3.87
(ddd, 1H, H-4), 3.35 (m, 1H, H-6), 3.19 (s, 3H,
OCH3), 2.12±2.24 (m, 2H, H-3ax, H-3eq), 1.47, 1.45
(2s, 2Â3H, i-Pr); J3ax,3eq 12.4, J3ax,4 11.8, J3eq,4 4.9,
(0.18 g, 82%): [ꢀ]d +56.6ꢀ (c 0.41, CHCl3); H
1
NMR (CDCl3): ꢂ 7.1±7.4 (m, 5H, Ph), 4.61 (s, 2H,
Bn), 4.36 (d, 1H, H-5), 4.27 (d, 1H, H-6), 3.97
(ddd, 1H, H-4), 3.86, 3.84 (2s, 2Â3H, CO2CH3),
3.26 (s, 3H, OCH3), 2.25 (ddd, 1H, H-3eq), 2.09
(dd, 1H, H-3ax), 1.92 (bs, 1H, OH); J3ax,3eq 12.9,
J3ax,4 11.6, J3eq,4 5.1, J3eq,5 0.9, J4,5 3.0, J5,6 1.5 Hz;
HRMS (LSIMS): Calcd for C17H22O8 [M+Na]+
m/z 377.1212, Found m/z 377.1220.
1,7-dimethyl (2,3,4-tri-O-acetyl-6-deoxy-a-l-talo-
pyranosyl)-(1!2)-(3,4-di-O-acetyl-a-l-rhamno-
pyranosyl)-(1!5)-(methyl 4-O-benzyl-3-deoxy-a-
d-lyxo-hept-2-ulopyranosid)arate (8a).ÐA mixture
of alcohol 7b (65 mg, 0.177 mmol), tri-
chloroacetimidate 5b (118 mg, 0.177 mmol) and
molecular sieves 3 A (100 mg) in CH2Cl2 (2 mL),

384
A. Banaszek/Carbohydrate Research 306 (1998) 379±385
was stirred for 1 h under argon. The mixture was
(0.1 mL), and the reaction mixture was stirred
overnight at room temperature. After addition of
dry NaHCO3 and evaporation with toluene the
product was puri®ed by chromatography (hexane±
Et2O, 1:1) to yield 4a (86 mg, 71%): syrup; [ꢀ]d
ꢀ
.
cooled to 40 C and a solution of BF3 OEt2
(1.77 mL, 1 M solution in CH2Cl2) was added.
After stirring for 15 min at ambient temperature
(TLC, CH2Cl2±MeOH, 95:5) the mixture was neu-
tralized with pyridine, ®ltered, and concentrated.
Puri®cation by chromatography a€orded tri-
saccharide 8a (118 mg, 78%) as a sole product:
amorphous powder; [ꢀ]d 21.5ꢀ (c 0.55, CHCl3);
1H NMR (CDCl3): ꢂ 5.14±5.19 (m, 2H, H-200, H-
300), 4.8 (dt, 1H, H-400), 4.7±5.2 (m, 2H, H-30, H-40),
4.83 (d, 1H, H-100), 6.63, 4.55 (2d, 2Â1H, Bn), 4.49
(bs, 1H, H-5), 4.27 (d, 1H, H-6), 4.11 (dd, 1H, H-
20), 3.97 (ddd, 1H, H-4), 3.92 (pq, 1H, H-500), 3.86,
3.85 (2s, 2Â3H, CO2CH3), 3.82 (pq, 1H, H-50),
3.24 (s, 3H, OCH3), 2.27 (dd, 1H, H-3eq), 1.98±2.18
(m, 1H, H-3ax), 2.11, 2.10, 2.03, 2.02, 2.0 (5s,
42.8ꢀ (c 0.9, CHCl3); H NMR (C6D6): ꢂ 7.1±7.6
1
(m, 5H, Ph), 6.50 (d, 1H, H-1), 5.56 (t, 1H, H-5),
5.44 (t, 1H, H-30), 5.41 (dt, 1H, H-20), 4.47 (d, 1H,
Bn), 4.41 (d, 1H, Bn), 4.17 (dd, 1H, H-4), 3.99 (dd,
1H, H-2), 3.98 (dq, 1H, H-50), 3.82 (t, 1H, H-3),
1.80, 1.75, 1.72, 1.63, 1.62 (5s, 5Â3H, Ac), 1.50 (d,
0
0
3H, CH3 ), 1.04 (d, 3H, CH3); J1,2 3.4, J1 ,2 1.0, J2,3
0
0
4.6, J2 ,3 3.7, J3,4 4.6, J3 ,4 3.6, J4,5 6.4, J4 ,5 1.4,
0
0
0
0
0
0
0
J5,6 6.4, J5 ,6 6.6 Hz; Anal Calcd for C29H38O14
(610.61) ): C 56.99%, H 6.27%, Found C 57.12%,
H 6.11%.
2-O-(2,3,4-Tri-O-acetyl-6-deoxy-a-l-talopyrano-
syl)-5-O-acetyl-3-O-benzyl-a-l-rhamnofuranosyl
bromide (4b).ÐTo a solution of 4a (0.3 g,
0
00
5Â3H, Ac), 1.22 (d, 3H, CH3 ), 0.90 (d, 3H, CH3 );
0
0
00 00
0
0
00 00
J1 ,2 2.1, J1 ,2 1.0, J2 ,3 3.2, J2 ,3 3.3, J3ax,3eq 12.7,
0
J4,3ax 11.8, J4,3eq 4.7, J4,5 2.5, J3 ,4 9.9, J3 ,4 3.9,
0
00 00
0.5 mmol) in a mixture of dry CH2Cl2±AcOH
(5:0.5, 5.5 mL) was added TiBr4 (0.3 g) under
argon. The mixture was stirred for 1 h at room
temperature, then dry AcONa was added, and
stirring was continued for few minutes. Filtration,
followed by evaporation with toluene left a syrup,
immediately used for the condensation reaction.
1,7-dimethyl (2,3,4-tri-O-acetyl-6-deoxy-a-l-talo-
pyranosyl)-(1!2)-(5-O-acetyl-2-O-benzyl-b-l-
rhamnofuranosyl)-(1!5)-(methyl 4-O-benzyl-3-
deoxy-a-d-lyxo-hept-2-ulopyranosid)arate (9a).ÐA
mixture of alcohol 7b (65 mg, 0.177 mmol),
Hg(CN)2 (45 mg, 0.177 mmol) and molecular sieves
3A (0.2 g) was stirred for 1 h under argon. Bromide
4b (from above experiment) in CH2Cl2 was added
dropwise and stirring was continued for 3 h. The
mixture was diluted with CH2Cl2 ®ltered through a
Celite, and the ®ltrate was washed with aq. KI,
then H2O. Puri®cation by chromatography (hex-
ane±Et2O-MeOH, 1:1:0.01) a€orded 9a (0.112 g,
0
0
00 00
0
0
00 00
J4 ,5 9.9, J4 ,5 1.2, J5,6 1.4, J5 ,6 6.3, J5 ,6 6.6 Hz;
HRMS (LSIMS): Calcd for C39H52O21 [M+Na]+
m/z 879.2899, Found m/z 879.2902.
1,7-dimethyl (2,3,4-tri-O-acetyl-6-deoxy-a-l-talo-
pyranosyl)-(1!2)-(3,4-di-O-acetyl-a-l-rhamno-
pyranosyl)-(1!5)-(methyl 4-O-acetyl-3-deoxy-a-
d-lyxo-hept-2-ulopyranosid)arate (8c).ÐA mixture
of 8a (43 mg, 0.5 mmol), in EtOH and the catalyst
Pd/C (20 mg) was stirred overnight under H2. Fil-
tration through a Celite, then evaporation gave 8b
(TLC, hexane±Me2CO, 3:2) which was subjected to
acetylation (Ac2O-Py, 1:1, 1 mL). Usual work-up
a€orded 9c (31 mg, 78%): mp 93±94 ꢀC; [ꢀ]d 2.4ꢀ
1
(c 0.72, CHCl3); H NMR (C6D6): ꢂ 5.54 (dd, 1H,
H-30), 5.46±5.49 (m, 2H, H-5, H-40), 5.38 (dt, 1H,
H-400), 5.32 (ddd, 1H, H-4), 5.26 (t, 1H, H-200), 5.22
(d, 1H, H-10), 5.05 (d, 1H, H-100), 4.56 (t, 1H, H-
300), 4.31 (t, 1H, H-20), 2.20±4.26 (m, 2H, H-50, H-
500), 4.14 (d, 1H, H-6), 3.70, 3.30 (2s, 2Â3H,
CO2CH3), 3.11 (s, 3H, OCH3), 2.46 (t, 1H, H-3ax),
2.35 (dddd, 1H, H-3eq), 1.96, 1.81, 1.78,01.69, 1.66,
ꢀ
1
70%) as a syrup: [ꢀ]d +26.2 (c 0.4, CHCl3); H
NMR (C6D6): ꢂ 7.05±7.25 (m, 5H, Ph), 5.74 (m,
1H, H-400), 5.64±5.71 (m, 2H, H-50, H-300), 5.44 (dt,
1H, H-200), 5.39 (d, 1H, H-10), 4.83 (pq, 1H, H-500),
4.58-4.64 (m, 3H, unresolved), 4.44±4.51 (m, 2H,
Bn), 3.96 (d, 1H, H-6), 3.94 (t, 1H, H-300), 3.87
(ddd, 1H, H-4), 3.84 (dd, 1H, H-30), 3.62 (t, 1H, H-
20), 3.75, 3.43 (2s, 2Â3H, CO2CH3), 3.02 (s, 3H,
OCH3), 2.64 (t, 1H, H-3ax), 2.56 (dd, 1H, H-3eq),
1.89, 1.76, 1.69, 1.62 (4s, 4Â3H, Ac), 1.54 (d, 3H,
1.61 (6s, 6Â3H, Ac), 1.32 (d, 3H, CH3 ), 1.05 (d,
00
0
0
00 00
0
0
00 00
3H, CH3 ); J1 ,2 2.2, J1 ,2 1.4, J2 ,3 3.1, J2 ,3 2.5,
0
J3ax,3eq 12.7, J3ax,4 12.3, J3eq,4 5.0, J3eq,5 0.7, J3 ,4
0
00 00
0
0
9.7, J3 ,4 3.8, J4,5 2.6, J4 ,5 9.5, J4 ,5 0.5, J5,6 1.4,
00 00
0
0
00 00
J5 ,6 1.3, J5 ,6 1.6 Hz; HRMS (LSIMS): Calcd for
C34H48O22 [M+Na]+ m/z 831.2535, Found m/z
831.2535.
2-O-(2,3,4-Tri-O-acetyl-6-deoxy-a-l-talopyrano-
syl)-1,5-di-O-acetyl-3-O-benzyl-6-deoxy-a-l-rhamno-
furanose (4a).ÐA solution of 3a (0.124 g,
0.2 mmol) in Ac2O (4 mL) was treated with TfOH
00
0
0
0
00 00
CH3 ), 1.34 (d, 3H, CH3 ); J1 ,2 4.4, J2 ,3 3.6,
0
J3ax,3eq 12.7, J3ax,4 11.8, J3eq,4 4.6, J4 ,5 8.0, J3 ,4
0
0
0
0
0
0
0
5.6, J4 ,5 8.1, J5 ,6 6.3, J5 ,6 6.6 Hz; HRMS
00 00

A. Banaszek/Carbohydrate Research 306 (1998) 379±385
(LSIMS): Calcd for C44H56O20 [M+Na]+ m/z
References
927.3362, Found m/z 927.3260.
385
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l-rhamnofuranosyl)-(1!5)-(methyl 4-O-acetyl-3-
deoxy-a-d-lyxo-hept-2-ulopyranosid)arate(9c).ÐTo
a solution of 9a (94 mg, 0.1 mmol) in EtOH Pd/C
was added and the reaction mixture was stirred
overnight under hydrogen. After ®ltration and
evaporation of the solvent the residue was acety-
lated with Ac2O±Py (1:1, 3 mL). Usuall work-up,
then chromatography (hexane±Et2O, 1:1) gave 9c
(67 mg, 83%) as crystals: mp 213 ꢀC; [ꢀ]d +48.7ꢀ (c
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1
0.97, CHCl3); H NMR (C6D6): ꢂ 5.79±5.81 (m,
1H, H-400), 5.63 (t, 1H, H-300), 5.42 (dt, 1H, H-200),
5.32±5.36 (m, 2H, H-4, H-50), 5.30 (dd, 1H, H-40),
5.14 (d, 1H, H-10), 5.09 (d, 1H, H-100), 4.79 (d, 1H,
H-5), 4.72 (pq, 1H, H-500), 4.03 (bs, 1H, H-6), 3.79
(t, 1H, H-30), 3.6 (dd, 1H, H-20), 3.57, 3.35 (2s,
2Â3H, CO2CH3), 2.98 (s, 3H, OCH3), 2.57 (t, 1H,
H-3ax), 2.40 (dd, 1H, H-3eq), 2.11, 2.08, 1.86, 1.75,
0
1.72, 1.60 (6s, 6Â3H, Ac), 1.53 (d, 3H, CH3 ), 1.33
00
0
0
00 00
0
0
00 00
(d, 3H, CH3 ); J1 ,2 4.9, J1 ,2 1.2, J2 ,3 9.4, J2 ,3
0
3.6, J3ax,3eq 12.6, J3ax,4 12.4, J3eq,4 4.5, J4 ,5 10.3,
0
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00 00
0
0
00 00
J4 ,5 1.8, J5,6 2.3, J5 ,6 6.2, J5 ,6 6.4 Hz; HRMS
(LSIMS): Calcd for C34H48O22 [M+Na]+ m/z
831.2535, Found m/z 831.2533.
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The author would like to thank Ms I. Kazi-
mierczak for the technical assistance. Financial
support by Grant 2.P303.146.04 from KBN is
gratefully acknowledged.