Synthesis of an L-rhamnose tetrasaccharide, the common and major structure of the repeating unit of the O-antigenic polysaccharide of a strain of Klebsiella pneumoniae and Pseudomonas holci

Article abstract of DOI:10.1016/S0008-6215(01)00258-0

A tetrasaccharide, α-L-Rhap-(1 → 3)-α-L-Rhap-(1 → 2)-α-L-Rhap-(1 → 2)-L-Rhap, the common and major structure of the repeating unit of the O-antigenic polysaccharide of a strain of Klebsiella pneumoniae and Pseudomonas holci was synthesized as its methyl and octyl glycosides. Selective 3-O-glycosylation of allyl α-L-rhamnopyranoside with 2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl trichloroacetimidate gave allyl 2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl-(1 → 3)-α-L-rhamnopyranoside (3). Benzoylation, deallylation, and trichloroacetimidation afforded 2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl-(1 → 3)-2,4-di-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (6). Self condensation of 3,4-di-O-benzoyl-β-L-rhamnopyranose 1,2-methyl orthoester or 1,2-octyl orthoester gave methyl or octyl 2-O-acetyl-3,4-di-O-benzoyl-α-L-rhamnopyranosyl-(1 → 2)-3,4-di-O-benzoyl-α-L-rhamnopyranoside (16 or 17), and subsequent selective deacetylation gave the disaccharide acceptor (18 or 19). Coupling of 6 with 18 (or 19), followed by deacylation in ammonia-saturated methanol, produced the target tetrasacharide.

Full text of DOI:10.1016/S0008-6215(01)00258-0

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Carbohydrate Research 336 (2001) 229–235
Note
Synthesis of an -rhamnose tetrasaccharide, the common
L
and major structure of the repeating unit of the
O-antigenic polysaccharide of a strain of Klebsiella
pneumoniae and Pseudomonas holci
Jianjun Zhang, Yuliang Zhu, Fanzuo Kong*
Research Center for Eco-En6ironmental Sciences, Academia Sinica, PO Box 2871, Beijing 100085, PR China
Received 8 August 2001; accepted 18 September 2001
Abstract
A tetrasaccharide, a-
of the repeating unit of the O-antigenic polysaccharide of a strain of Klebsiella pneumoniae and Pseudomonas holci
was synthesized as its methyl and octyl glycosides. Selective 3-O-glycosylation of allyl a- -rhamnopyranoside with
2,3,4-tri-O-acetyl-a- -rhamnopyranosyl trichloroacetimidate gave allyl 2,3,4-tri-O-acetyl-a- -rhamnopyranosyl-(1“
3)-a- -rhamnopyranoside (3). Benzoylation, deallylation, and trichloroacetimidation afforded 2,3,4-tri-O-acetyl-a-
-rhamnopyranosyl trichloroacetimidate (6). Self condensation of
-rhamnopyranose 1,2-methyl orthoester or 1,2-octyl orthoester gave methyl or octyl 2-O-acetyl-
-rhamnopyranosyl-(1“2)-3,4-di-O-benzoyl-a- -rhamnopyranoside (16 or 17), and subsequent
L
-Rhap-(1“3)-a-
L
-Rhap-(1“2)-a-
L
-Rhap-(1“2)-L-Rhap, the common and major structure
L
L
L
L
L-
rhamnopyranosyl-(1“3)-2,4-di-O-benzoyl-a-
L
3,4-di-O-benzoyl-b-
3,4-di-O-benzoyl-a-
L
L
L
selective deacetylation gave the disaccharide acceptor (18 or 19). Coupling of 6 with 18 (or 19), followed by
deacylation in ammonia-saturated methanol, produced the target tetrasacharide. © 2001 Elsevier Science Ltd. All
rights reserved.
Keywords: Oligosaccharide; Rhamnose; Antigen
The tetrasaccharide, a-
L
-Rhap-(1“3)-a-
L
-
latter one has a 3-acetylamino-3,6-dideoxy-a-
-galactopyranosyl residue attached to the 3-
Rhap-(1“2)-a- -Rhap-(1“2)-
L
L
-Rhap, is the
D
common and major structure of the repeating
units of the O-antigenic polysaccharide of a
strain of Klebsiella pneumoniae strain1 and
Pseudomonas holci.2 The former repeating unit
contains one more a-(1“2)-linked
nose residue at the reducing end, while the
O-position of the rhamnose unit reducing end.
For investigation of the oligosaccharide’s
structure–bioactivity relationships, we present
herewith the synthesis of the target
tetrasaccharide.
L
-rham-
As outlined in Scheme 1, condensation of
2,3,4-tri-O-acetyl-a-
L
-rhamnopyranosyl
tri-
chloroacetimidate (2) with unprotected allyl
a- -rhamnopyranoside (1) selectively gave al-
lyl 2,3,4-tri-O-acetyl-a- -rhamnopyranosyl-
(1“3)-a- -rhamnopyranoside (3) in satis-
L
* Corresponding author. Tel.: +86-10-62936613; fax:
+86-10-62923563.
E-mail address: fzkong@mail.rcees.ac.cn (F. Kong).
L
L
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(01)00258-0

230
J. Zhang et al. / Carbohydrate Research 336 (2001) 229–235
6. The disaccharide acceptor was readily pre-
pared by the method of self-condensation of
the orthoester 12 or 13.6 Thus 3,4-di-O-ben-
factory yield (64.3%). Keeping the tempera-
ture below −10 °C during the addition of
TMSOTf was necessary in order to avoid
byproduct formation. We rationalized that the
good regioselectivity is owing to the formation
of 3-O-linked orthoester disaccharide, fol-
lowed by an intramolecular rearrangement.3
The (1“3) linkage was confirmed by benzoy-
zoyl-b-
1,2-octyl (13) orthoesters were prepared by the
sequential reaction of tri-O-acetyl-a-
L
-rhamnopyranose 1,2-methyl (12) and
L
-
rhamnopyranosyl bromide (7) with methanol
and octanol, respectively, then Zemple´n deac-
ylation, and conventional benzoylation. Self-
condensation of the orthoesters 12 or 13
promoted by TMSOTf was carried out readily
giving the disaccharides 16 (68.8%) or 17
(70.0%), respectively, as the major product
and the monosaccharides 14 (10.7%) or 15
(11.4%) as the minor one. This chemoselectiv-
ity means that the self-condensation of the
orthoesters is indeed an effective method for
the preparation of a-(1“2)-linked rhamnose
disaccharides. Selective deacetylation7 of 16 or
1
lation of 3, and the H NMR spectrum of the
1
resultant 4 showed a H NMR spectrum iden-
tical to that reported in the literature.4 Com-
pared to our previously reported method for
preparation of a-(1“3)-linked rhamnose dis-
accharide with an unprotected rhamnoside as
the acceptor via isolated orthoester intermedi-
ate,4 the present technique is simpler. Deally-
lation with PdCl2, followed by trichloro-
acetimidation with CCl3CN in the presence of
DBU or K2CO3,5 gave the disaccharide donor
,
Scheme 1. Reagents and conditions: (a) TMSOTf, CH2Cl2, 4 A MS, N2, −20 °C to rt, 4 h; (b) BzCl–pyridine (dry); (c) PdCl2,
CH2Cl2, 2 h; (d) CCl3CN, DBU or K2CO3, CH2Cl2 8 h; (e) lutidine, CH2Cl2, ROH, 4 A MS, 4 h; (f) MeONa, MeOH; (g)
CH3OH, CH3COCl (0.1%, v/v); (h) NH3, MeOH.
,

J. Zhang et al. / Carbohydrate Research 336 (2001) 229–235
231
17 with CH3COCl–methanol afforded the dis-
accharide acceptor, methyl 3,4-di-O-benoyl-a-
(v/v) H2SO4 in MeOH or by UV detection.
Column chromatography was conducted by
elution of a column (8×100 mm, 16×240
mm, 18×300 mm, 35×400 mm) of silica gel
(100–200 mesh) and EtOAc–petroleum ether
(bp 60–90 °C) as the eluent. Analytical LC
was performed with a Gilson HPLC consist-
ing of a pump (model 306), a stainless steel
column packed with silica gel (Spherisorb
SiO2, 10×300 mm or 4.6×250 mm), a differ-
ential refractometer (132-RI Detector), and a
UV–vis detector (model 118). EtOAc–
petroleum ether (bp 60–90 °C) was used as
the eluent at a flow rate of 1–4 mL/min.
Solutions were concentrated at a temperature
B60 °C under diminished pressure.
L
-rhamnopyranosyl-(1“2)-3,4-di-O-benzoyl-
a-
benzoyl-a-
O-benzoyl-a-
L
-rhamnopyranoside (18) or octyl 3,4-di-O-
-rhamnopyranosyl-(1“2)-3,4-di-
-rhamnopyranoside (19). We
L
L
were gratified to find that the self-condensa-
tion of the orthoester with a long-chain fatty
acid alcohol as the aglycone moiety ran
smoothly giving the corresponding disaccha-
ride in good yield. This can be an efficient and
concise method for the preparation of a-(1“
2)-linked manno- and rhamnopyranose disac-
charides with a long-chain fatty acid at the
reducing end. With the disaccharide donor 6
and the disaccharide acceptor 18 or 19 at
hand, the tetrasaccharide 20 or 21 was readily
constructed in dichloromethane in the pres-
ence of TMSOTf. Finally deacylation of 20 or
21 in ammonia-saturated methanol gave the
target tetrasaccharide 22 or 23, and their
bioassays are in progress and will be reported
in due course.
Allyl 2,3,4-tri-O-acetyl-h-
syl-(1“3)-2,4-di-O-benzoyl-h-
noside (4).—2,3,4-Tri-O-acetyl-a-
pyranosyl trichloroacetimidate (1) (4.350 g, 10
mmol) and allyl a- -rhamnopyranoside (2)
L
-rhamnopyrano-
-rhamnopyra-
-rhamno-
L
L
L
(2.04 mg, 10 mmol) were dried together under
high vacuum for 2 h, then dissolved in anhyd
CH2Cl2 (40 mL). TMSOTf (60 mL, 0.2 equiv)
was added dropwise at −25 °C with N2 pro-
tection. The reaction mixture was stirred for 3
h, during which time the temperature was
gradually raised to ambient temperature. Then
the mixture was neutralized with triethylamine
and concentrated to dryness under reduced
pressure to afford the crude allyl 2,3,4-tri-
In summary, a very concise and efficient
synthesis of methyl or octyl a-
osyl-(1“3)-a-
rhamnopyranosyl-(1“2)-a-
L
-rhamnopyran-
-rhamnopyranosyl-(1“2)-a-
-rhamnopyrano-
L
L
-
L
side was achieved in a regio- and stereoselec-
tive way. Because of its simplicity and effi-
ciency, this method could be used for
construction of higher rhamnose oligosaccha-
rides with a-(1“3)- and a-(1“2)-linkages.
O-acetyl-a-
L
-rhamnopyranosyl-(1“3)-a- -
L
rhamnopyranoside (3). To the solution of
crude 3 in pyridine (20 mL), BzCl (3.5 mL, 30
mmol) was added dropwise, and the mixture
was stirred overnight at rt. TLC (3:1
petroleum ether–EtOAc) indicated that the
reaction was complete. Ice water was added,
and the mixture was diluted with CH2Cl2,
washed with 1 N HCl, water, and satd aq
NaHCO3. The organic layer was combined,
dried, and concentrated. Purification of the
crude product by column chromatography
(3:1 petroleum ether–EtOAc) gave 4 (4.400 g,
64.3% for two steps) as a syrup: [h]D +62° (c
1.0, CHCl3), lit.4 [h]D +64° (c 1.5, CHCl3).
1. Experimental
General methods.—Melting points were de-
termined with a ‘Mel-Temp’ apparatus. Opti-
cal rotations were determined with
a
Perkin–Elmer model 241-MC automatic po-
larimeter for solutions in a 1-dm, jacketed cell.
1H NMR spectra were recorded with Varian
XL-400 and Varian XL-200 spectrometers, for
solutions in CDCl3 with tetramethylsilane
(Me4Si) as the internal standard. Chemical
shifts are expressed in ppm downfield from the
internal Me4Si absorption. Mass spectra were
recorded with a VG PLATFORM mass spec-
trometer using the ESI mode. Thin-layer chro-
matography (TLC) was performed on Silica
Gel HF with detection by charring with 30%
1
Compound 4 gave H NMR data identical to
those reported in the literature.4
2,3,4-Tri-O-acetyl-h-
(1“3)-2,4-di-O-benzoyl-h-
2,2,2-trichloroacetimidate (6).—To a solution
L
-rhamnopyranosyl-
L
-rhamnopyranosyl

232
J. Zhang et al. / Carbohydrate Research 336 (2001) 229–235
and subjected to column chromatography to
give 9 (1.8 g, 78.6%) as a syrup: [h]D +13.5°
(c 1.2, CHCl3). 1H NMR (CDCl3): l 5.37 (d, 1
H, J1,2 2.2 Hz, H-1), 5.09 (dd, 1 H, J2,3 3.9, J3,4
9.9 Hz, H-3), 5.04 (dd, 1 H, J3,4=J4,5=9.9
Hz, H-4), 4.55 (dd, 1 H, J1,2 2.2, J2,3 3.9 Hz,
H-2), 3.53–3.40 (m, 3 H, H-5, OCH2C7H15),
2.09 (s, 3 H, CH3CO), 2.04 (s, 3 H, CH3CO),
1.71 (s, 3 H, CH3CO3), 1.53–0.84 (m, 18 H,
H-6, C7H15CH2O); 13C NMR (CDCl3, 100
MHz): l 14.1, 17.6, 20.8, 20.8, 22.7, 24.8, 26.1,
29.2, 29.3, 29.5, 31.6, 62.7, 69.2, 70.5, 70.8,
76.6, 97.2, 124.2, 169.8, 169.8, 170.5. Anal.
Calcd for C20H.34O8: C, 59.68; H, 8.52. found:
C, 59.56; H, 8.50.
of allyl 2,3,4-tri-O-acetyl-a-
L
-rhamnopyran-
-rhamnopy-
osyl-(1“3)-2,4-di-O-benzoyl-a-
L
ranoside (4) (684 mg, 1 mmol) in 90% AcOH
(10 mL) containing AcONa (293 mg, 3 mmol)
was added PdCl2 (89 mg, 0.5 mmol), and the
mixture was stirred for 12 h, at the end of
which time TLC (2:1 petroleum ether–EtOAc)
indicated that the reaction was complete. The
mixture was diluted with CH2Cl2 (30 mL) and
washed with water and satd aq NaHCO3. The
organic layer was concentrated, and the
residue was passed through a short silica gel
column with 2:1 petroleum ether–EtOAc as
the eluent to give crude 2,3,4-tri-O-acetyl-a-
rhamnopyranosyl-(1“3)-2,4-di-O-benzoyl-
a,b- -rhamnopyranose (5) (620 mg, 96%).
L
-
L
3,4-Di-O-benzoyl-1,2-O-methoxyethylidene-
Compound 5 was dissolved in CH2Cl2 (10
mL), and CCl3CN (0.2 ml, 2 mmol) and DBU
(27 mL, 0.18 mmol) were added. The reaction
mixture was stirred for 2 h, at the end of
which time TLC (2:1 petroleum ether–EtOAc)
indicated that the reaction was complete. Con-
centration of the reaction mixture, followed
by purification of the crude product on a silica
gel column with 2:1 petroleum ether–EtOAc
as the eluent, furnished the disaccharide donor
6 (710 mg, 90%) as a syrup: [h]D +4.3° (c 1.3,
i-
L
-rhamnopyranose (12).—A mixture of
-rhamnopyranosyl bro-
2,3,4-tri-O-acetyl-a-
L
mide (7) (2.0 g, 5.7 mmol), 2,4-lutidine (0.8
mL, 7.2 mmol), and tetrabutylammonium
bromide (0.8 g, 2.4 mmol) in CH2Cl2 (1 mL)
was stirred at rt, and anhyd MeOH (0.5 mL,
12 mmol) was added. The reaction mixture
was stirred for 24 h. TLC (1:1 petroleum
ether–EtOAc) indicated that the reaction was
complete. The reaction mixture was concen-
trated and subjected to column chromatogra-
phy to give crude product 8 (1.6 g, 93%).
According to the standard method, compound
8 (1.5 g, 4.9 mmol) was deacetylated with
MeONa in MeOH to give 10, and then 10 was
benzoylated with BzCl in pyridine to furnish
12 in quantitative yield. Flash chromatogra-
phy (3:1 petroleum ether–EtOAc) of the
residue gave pure 12 (1.98 g, 93.8%) as a
1
CHCl3). H NMR (CDCl3): l 8.80 (s, 1 H,
CNHCCl3), 8.18–7.43 (m, 10 H, 2 Bz-H), 6.44
(d, 1 H, J1,2 1.9 Hz, H-1), 5.62 (dd, 1 H, J1,2
1.9, J2,3 3.2 Hz, H-2), 5.59 (dd, 1 H, J3,4=
J4,5=9.8 Hz, H-4), 5.09 (dd, 1 H, J2%,3% 3.2,
J3%,4% 9.8 Hz, H-3%), 4.94–4.91 (m, 2 H, H-1%,
H-2%), 4.89 (dd, 1 H, J3%,4%=J4%,5%=9.8 Hz,
H-4%), 4.49 (dd, 1 H, J2,3 3.4, J3,4 9.8 Hz, H-3),
4.22 (m, 1 H), 3.93 (m, 1 H), 1.94 (s, 3 H,
CH3CO), 1.87 (s, 3 H, CH3CO), 1.82 (s, 3 H,
CH3CO), 1.35 (d, 3 H, J 6.2 Hz), 1.07 (d, 3 H,
J 6.3 Hz). Anal. Calcd for C34H.36Cl3NO14: C,
51.75; H 4.60. Found: C, 51.56; H, 4.58.
1
syrup: [h]D +100.9° (c 1.3, CHCl3). H NMR
(CDCl3): l 8.01–7.36 (m, 10 H, 2 Bz-H),
5.54–5.45 (m, 3 H), 4.82 (dd, 1 H, J1,2 2.5,
J2,33.6 Hz, H-2), 3.66 (m, 1 H, H-5), 3.26 (s, 3
H, OCH3), 1.79 (s, 3 H, CCH3), 0.89 (d, J5,6
6.6 Hz, 3 H, H-6). Anal. Calcd for C23H24O8:
C, 64.48; H, 5.65. Found: C, 64.29; H, 5.66.
3,4-Di-O-benzoyl-1,2-O-octoxyethylidene-i-
3,4-Di-O-acetyl-1,2-O-octoxyethylidene-i-
rhamnopyranose (9).—A mixture of 2,3,4-tri-
O-acetyl-a- -rhamnopyranosyl bromide (7)
L
-
L
(2.0 g, 5.7 mmol), 2,4-lutidine (0.8 mL, 7.2
mmol), and tetrabutylammonium bromide
(0.8 g, 2.4 mmol) in anhyd CH2Cl2 (10 mL)
was stirred at rt, and C8H17OH (0.95 mL, 6
mmol) was added. The reaction mixture was
stirred for 24 h. TLC (1:1 petroleum ether–
EtOAc) indicated that the reaction was com-
plete. The reaction mixture was concentrated
L
-rhamnopyranose (13).—According to the
standard method, compound 9 (2.0 g, 5.0
mmol) was deacetylated with MeONa in
MeOH to give 11, and then 11 was benzoy-
lated with BzCl in pyridine to furnish 13 in
quantitative yield. Flash chromatography (4:1
petroleum ether–EtOAc) of the residue gave
pure 13 as a syrup (2.5 g, 95%): [h]D +91.2°

J. Zhang et al. / Carbohydrate Research 336 (2001) 229–235
233
1
for 2 h, neutralized with Et3N and filtered,
then the filtrate was concentrated. Purification
of the product by column chromatography
(5:1 petroleum ether–EtOAc) gave a syrup 17
(616 mg, 70.0%) as the main product and a
syrupy 15 (60 mg, 11.4%) as the minor
product. For compound 17: [h]D +62° (c 1.0,
(c 1.3, CHCl3). H NMR (CDCl3): l 8.01–
7.36 (m, 10 H, 2 Bz-H), 5.54–5.46 (m, 3 H,
H-1, H-3, H-4), 4.80 (dd, 1 H, J1,2 2.5, J2,3 3.6
Hz, H-2), 3.76 (m, 1 H, H-5), 3.46 (m, 2 H,
OCH2C7H15), 1.79 (s, 3 H, CCH3), 1.52–0.83
(m, 18 H, H-6, OCH2C7H15). Anal. Calcd for
C30H38O8: C, 68.42; H, 7.27. Found C, 68.45;
H, 7.32.
1
CHCl3). H NMR (CDCl3): l 8.03–7.33 (m,
Methyl
rhamnopyranosyl-(1“2)-3,4-di-O-benzoyl-h-
-rhamnopyranoside (16).—To a solution of
2-O-acetyl-3,4-di-O-benzoyl-h-
L
-
20 H, 4 Bz-H), 5.85 (dd, 1 H, J 3.4, J 10.0
Hz), 5.77 (dd, 1 H, J 3.2, J 10.0 Hz), 5.68 (dd,
1 H, J1%,2% 1.8, J2%,3% 3.1 Hz, H-2%), 5.63 (dd, 1 H,
J 9.8 Hz), 5.54 (dd, 1 H, J 9.8 Hz), 4.98 (d, 1
H, J 1.7 Hz), 4.95 (d, 1 H, J 1.8 Hz), 4.28 (m,
2 H), 4.11 (m, 1 H), 3.65 (m, 2 H), 2.05 (s, 3
H, COCH3), 1.70–1.32 (m, 21 H); 13C NMR
(CDCl3, 100 MHz): l 14.1, 17.6, 17.8, 20.8,
22.7, 26.2, 29.3, 29.5, 29.5, 31.9, 66.9, 67.5,
68.3, 69.7, 69.9, 71.3, 71.7, 72.1, 98.7, 99.7,
165.2, 165.4, 165.7, 165.8, 169.8. Anal. Calcd
for C50H.56O14: C, 68.17; H, 6.41. Found: C,
68.33; H, 6.39. For compound 15: [h]D +15°
L
compound 12 (856 mg, 2 mmol) in anhyd
CH2Cl2 (20mL) was added TMSOTf (18 mL,
0.1 mmol) in the presence of 4 A molecular
,
sieves under an N2 atmosphere at −20 °C.
The mixture was slowly raised to rt and stirred
for 2 h, neutralized with Et3N and filtered,
then the filtrate was concentrated. Purification
of the product by column chromatography
(3:1 petroleum ether–EtOAc) gave syrupy 16
(538 mg, 68.8%) as the main product and a
syrupy 14 (46 mg, 10.7%) as the minor
product. For compound 16: [h]D +53° (c 1.3,
1
(c 0.3, CHCl3). H NMR (CDCl3): l 7.98–
7.34 (m, 10 H, 2 Bz-H), 5.71 (dd, 1 H, J2,3 3.5,
J3,4 10.1 Hz, H-3), 5.54 (dd, 1 H, J3,4=J4,5 =
10.1 Hz, H-4), 5.46 (dd, 1 H, J1,2 1.7, J2,3 3.4
Hz, H-2), 4.85 (d, 1 H, J1,2 1.7 Hz, H-1), 4.12
(m,1 H, H-5), 3.64–3.60 (m, 2 H), 2.15 (s, 3
H, CH3CO), 1.70–0.88 (m, 18 H). 13C NMR
(CDCl3, 100 MHz): l 14.2, 17.7, 21.0, 22.7,
26.2, 29.4, 29.4, 29.5, 29.5, 31.9, 66.6, 68.5,
70.1, 70.4, 71.8, 97.6, 165.5, 165.8, 170.1.
Anal. Calcd for C30H38O8: C, 68.42; H, 7.27.
Found: C, 68.17; H, 7.25.
1
CHCl3). H NMR (CDCl3): l 8.00–7.35 (m,
20 H, 4 Bz-H), 5.80 (dd, 1 H, J 3.3, J 9.8 Hz),
5.76 (dd, 1 H, J 3.1, J 10.0 Hz), 5.66 (dd, 1 H,
J1%,2% 1.8, J2%,3% 3.1 Hz, H-2%), 5.63 (dd, 1 H, J
9.8 Hz), 5.55 (dd, 1 H, J 9.8 Hz), 4.97 (d, 1 H,
J 1.7 Hz), 4.86 (d, 1 H, J 1.8 Hz), 4.30–4.24
(m, 2 H), 4.10 (m, 1 H), 3.49 (s, 3 H, OCH3),
2.04 (s, 3 H, COCH3), 1.40 (d, 3 H, J 6.3 Hz),
1.32 (d, 3 H, J 6.4 Hz). Anal. Calcd for
C43H42O14: C, 65.97; H, 5.41. Found: C, 65.76;
H, 5.38. For compound 14: [h]D +55.1° (c
Methyl 3,4-di-O-benzoyl-h-
L
-rhamnopyran-
-rhamnopy-
1
1.3, CHCl3). H NMR (CDCl3): l 7.98–7.34
osyl-(1“2)-3,4-di-O-benzoyl-h-
L
(m, 10 H, 2 Bz-H), 5.69 (dd, 1 H, J2,3 3.5, J3,4
10.1 Hz, H-3), 5.54 (dd, 1 H, J3,4=J4,5=10.1
Hz, H-4), 5.46 (dd, 1 H, J1,2 1.6, J2,3 3.5 Hz,
H-2), 4.75 (d, 1 H, J1,2 1.6 Hz, H-1), 4.11 (m,
1 H, H-5), 3.47 (s, 3 H, OCH3), 2.16 (s, 3 H,
CH3CO), 1.34 (d, 3 H, J5,6 6.3 Hz, H-6). Anal.
Calcd for C23H.24O8: C, 64.48; H, 5.65. Found:
C, 64.32; H, 5.64.
ranoside (18).—To a solution of 16 (782 mg, 1
mmol) in anhyd MeOH (50 mL) was added
acetyl chloride (1.5 mL) at 0 °C. The solution
was sealed in a flask and stirred at rt until
TLC (2:1 petroleum ether–EtOAc) showed
that the starting material disappeared. The
solution was neutralized with Et3N, then con-
centrated to dryness. The residue was passed
through a short silica gel column to give 18
(688 mg, 93.0%): [h]D +99° (c 1.6, CHCl3).
1H NMR (CDCl3): l 7.98–7.36 (m, 20 H, 4
Bz-H), 5.73–5.69 (m, 2 H), 5.64–5.58 (m, 2
H), 5.05 (d, 1 H, J 1.4 Hz), 4.89 (d, 1 H, J 1.5
Hz), 4.45 (dd, 1 H, J 1.5, J 3.4 Hz), 4.33 (dd,
1 H, J 1.4, J 3.3 Hz), 4.30–4.07 (m, 2 H), 3.48
(s, 3 H, CH3O), 2.20–1.80 (br, 1 H, OH),
Octyl
rhamnopyranosyl-(1“2)-3,4-di-O-benzoyl-h-
-rhamnopyranoside (17).—To a solution of
2-O-acetyl-3,4-di-O-benzoyl-h- -
L
L
compound 13 (1.052 g, 2 mmol) in anhyd
CH2Cl2 (20 mL) was added TMSOTf (18 mL,
,
0.1 mmol) in the presence of 4 A molecular
sieves under an N2 atmosphere at −20 °C.
The mixture was slowly raised to rt and stirred

234
J. Zhang et al. / Carbohydrate Research 336 (2001) 229–235
3 H, OCH3), 1.98 (s, 3 H, CH3CO), 1.95 (s, 3
1.40–1.30 (m,
C41H40O13: C, 66.48; H, 5.44. Found: C, 66.59;
H, 5.46.
Octyl 3,4-di-O-benzoyl-h-
osyl-(1“2)-3,4-di-O-benzoyl-h-
6
H). Anal. Calcd for
H, CH3CO), 1.89 (s, 3 H, CH3CO), 1.49 (d, 3
H, J 6.1 Hz), 1.44 (d, 3 H, J 6.1 Hz), 1.11 (d,
3 H, J 6.1 Hz), 1.01 (d, 3 H, J 6.1 Hz); 13C
NMR (CDCl3, 100 MHz): l 17.1, 17.3, 17.6,
17.7, 20.5, 20.5, 20.7, 55.2, 66.6, 67.2, 67.5,
67.6, 68.5, 69.5, 70.5, 71.1, 71.1, 71.6, 71.8,
71.9, 71.9, 73.1, 74.6, 76.7, 77.7, 99.1, 99.3,
100.0, 100.8, 165.3, 165.4, 165.4, 165.5, 165.7,
165.9, 169.2, 169.3, 170.0. Anal. Calcd for
C73H74O26: C, 64.12; H, 5.46. Found: C, 64.32;
H, 5.45.
L
-rhamnopyran-
-rhamnopy-
L
ranoside (19).—To a solution of 17 (880 mg, 1
mmol) in anhyd MeOH (50 mL) was added
acetyl chloride (1.5 mL) at 0 °C. The solution
was sealed in a flask and stirred at rt until
TLC (3:1 petroleum ether–EtOAc) showed
that the starting material disappeared. The
solution was neutralized with Et3N, then con-
centrated to dryness. The residue was passed
through a short silica gel column to give 19
(730 mg, 87.1%): [h]D +79° (c 1.3, CHCl3).
1H NMR (CDCl3): l 8.01–7.36 (m, 20 H, 4
Bz-H), 5.76–5.70 (m, 2 H), 5.62–5.55 (m, 2
H), 5.04 (d, 1 H, J 1.5 Hz), 4.96 (d, 1 H, J 1.5
Hz), 4.43 (dd, 1 H, J 1.5, J 3.5 Hz), 4.32 (dd,
1 H, J 1.5, J 3.3 Hz), 4.12 (m, 1 H), 3.65 (m,
Octyl 2,3,4-tri-O-acetyl-h-
osyl-(1“3)-2,4-di-O-benzoyl-h-
ranosyl-(1“2)-3,4-di-O-benzoyl-h-
pyranosyl-(1“2)-3,4-di-O-benzoyl-h-
L
-rhamnopyran-
-rhamnopy-
-rhamno-
-rham-
L
L
L
nopyranoside (21).—The disaccharide donor 6
(788 mg, 1 mmol) and the disaccharide accep-
tor 19 (838 mg, 1 mmol) were dried together
under high vacuum for 2 h, then dissolved in
anhyd CH2Cl2 (10 mL). TMSOTf (15 mL, 0.08
equiv) was added dropwise at −20 °C with
N2 protection. The reaction mixture was
stirred for 2 h, during which time the reaction
temperature was gradually allowed to rise to
ambient temperature. Then the mixture was
neutralized with triethylamine and concen-
trated to an oily residue. Purification by
column chromatography (2:1 petroleum
ether–EtOAc) gave 21 (1.140 g, 77.9%): [h]D
13
2 H), 1.68–0.88 (m, 21 H); C NMR (CDCl3,
100 MHz): l 14.1, 17.6, 17.7, 22.7, 26.2, 29.3,
29.4, 29.5, 31.9, 66.7, 67.4, 68.2, 69.7, 71.5,
71.7, 72.0, 72.2, 98.8, 101.4, 165.3, 165.6,
165.8, 165.9. Anal. Calcd for C48H54O13: C,
68.72; H, 6.49. Found: C, 68.85; H, 6.48.
Methyl 2,3,4-tri-O-acetyl-h-
osyl-(1“3)-2,4-di-O-benzoyl-h-
ranosyl-(1“2)-3,4-di-O-benzoyl-h-
pyranosyl - (1“2) - 3,4 - di - O - benzoyl - h -
L
-rhamnopyran-
-rhamnopy-
-rhamno-
L
L
L
-
1
+74° (c 1.0, CHCl3). H NMR (CDCl3): l
rhamnopyranoside (20).—The disaccharide
donor 6 (788 mg, 1 mmol) and the disaccha-
ride acceptor 18 (740 mg, 1 mmol) were dried
together under high vacuum for 2 h, then
dissolved in anhyd CH2Cl2 (10 mL). TMSOTf
(15 mL, 0.08 equiv) was added dropwise at
−20 °C with N2 protection. The reaction mix-
ture was stirred for 2 h, during which time the
reaction temperature was gradually allowed to
rise to ambient temperature. Then the mixture
was neutralized with triethylamine and con-
centrated to an oily residue. Purification by
column chromatography (2:1 petroleum
ether–EtOAc) gave 20 (970 mg, 71.0%): [h]D
8.06–7.33 (m, 30 H, 6 Bz-H), 5.87 (dd, 1 H, J
3.2, J 10.2 Hz), 5.65–5.58 (m, 3 H), 5.45 (dd,
1 H, J 1.4, J 3.3 Hz), 5.29 (dd, 1 H, J 10.2
Hz), 5.10 (d, 1 H, J 1.3 Hz), 5.04 (dd, 1 H, J
3.4, J 9.8 Hz), 4.94–4.88 (m, 4 H), 4.77 (d, 1
H, J 1.4 Hz), 4.39 (dd, 1 H, J 3.3, J 9.9 Hz),
4.35–4.33 (m, 2 H), 4.24–4.22 (m, 1 H), 4.22–
4.20 (m, 1 H), 3.96–3.94 (m, 1 H), 3.89–3.74
(m, 2 H), 3.53–3.51 (m, 1 H), 1.91 (s, 3 H,
CH3CO), 1.87 (s, 3 H, CH3CO), 1.82 (s, 3 H,
CH3CO), 1.72–1.64 (m, 2 H), 1.43–1.24 (m,
16 H), 1.03 (d, 3 H, J 6.1 Hz), 0.93–0.86 (m,
6 H); 13C NMR (CDCl3, 100 MHz): l 14.1,
17.1, 17.3, 17.6, 17.7, 20.5, 20.5, 20.7, 22.7,
26.1, 26.2, 29.3, 29.4, 29.5, 31.8, 67.0, 67.2,
67.5, 67.6, 68.2, 68.5, 69.5, 70.5, 71.1, 71.7,
71.8, 71.9, 72.0, 73.1, 74.6, 77.0, 77.7, 98.9,
99.1, 99.3, 100.8, 165.3, 165.4, 165.5, 165.7,
165.9, 166.5, 169.2, 169.2, 170.0. Anal. Calcd
for C80H88O26: C, 65.56; H, 6.05. Found: C,
65.79; H, 6.04.
1
+94° (c 1.9, CHCl3). H NMR (CDCl3): l
8.06–7.33 (m, 30 H, 6 Bz-H), 5.92 (dd, 1 H, J
3.2, J 10.0 Hz), 5.67–5.48 (m, 4 H), 5.40 (dd,
1 H, J 9.9 Hz), 5.18 (d, 1 H, J 1.6 Hz, H-1),
5.11 (dd, 1 H, J 3.1, J 10.1 Hz), 5.02–4.92 (m,
5 H), 4.48–4.41 (m, 3 H), 4.30 (m, 1 H), 4.18
(m, 1 H), 4.01 (m, 1 H), 3.94 (m, 1 H), 3.57 (s,

J. Zhang et al. / Carbohydrate Research 336 (2001) 229–235
235
4.02 (dd, 1 H, J 1.5, J 3.3 Hz), 3.98 (dd, 1 H,
J 1.6, J 3.3 Hz), 3.82–3.30 (m, 15 H), 1.62–
Methyl h-
rhamnopyranosyl-(1“2)-h-
syl-(1“2)-h- -rhamnopyranoside (22).—Tet-
L
-rhamnopyranosyl-(1“3)-h-
L
-
L
-rhamnopyrano-
13
1.53 (m, 2 H), 1.31–0.86 (m, 25 H); C NMR
L
(CD3OD, 100 MHz): l 98.4, 100.9, 101.9,
102.1, 78.5, 77.8, 77.5, 31.2, 28.7, 28.6, 28.5,
25.5, 21.9, 16.3, 16.2, 16.1, 16.0, 12.6. MS
(m/z) Calcd for C32H58O17: 714.5 [M]. Found:
737.5 [M+Na].
rasaccharide 20 (680 mg, 0.5 mmol) was dis-
solved in a satd methanolic ammonia (5 mL).
After 48 h at rt, the reaction mixture was
concentrated, and the residue was purified by
chromatography on Sephadex LH-20 (MeOH)
to afford 22 as a foamy solid (248 mg, 80.5%):
[h]D +46° (c 1.3, CH3OH). 1H NMR
(CD3OD): l 5.08 (d, 1 H, J 1.3 Hz,), 5.05 (d,
1 H, J 1.4 Hz), 4.94 (d, 1 H, J 1.3 Hz), 4.67 (d,
1 H, J 1.3 Hz), 4.06 (dd, 1 H, J 1.3, J 3.2 Hz),
4.03 (dd, 1 H, J 1.4, J2,3 3.1 Hz), 3.98 (dd, 1
H, J 1.5, J 3.2 Hz), 3.79–3.30 (m, 16 H),
Acknowledgements
This work was supported by The Chinese
Academy of Sciences (Projects KJ952J1510
and KIP-RCEES9904) and by The National
Natural Science Foundation of China
(Projects 29802009, 39970864, and 30070815).
13
1.29–1.23 (m, 12 H); C NMR (CD3OD, 100
MHz): l 99.7, 100.9, 101.9, 102.1, 78.3, 77.8,
77.5, 53.4, 16.3, 16.3, 16.2, 16.0. MS (m/z)
Calcd for C25H44O17: 616 [M]. Found: 639
[M+Na].
References
Octyl h -
rhamnopyranosyl-(1“2)-h-
syl-(1“2)-h- -rhamnopyranoside (23).—Tet-
L
- rhamnopyranosyl - (1“3) - h -
L
-
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-rhamnopyrano-
L
rasaccharide 21 (732 mg, 0.5 mmol) was dis-
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concentrated, and the residue was purified by
chromatography on Sephadex LH-20 (MeOH)
to afford 23 as a foamy solid (284 mg, 79.6%):
[h]D +36° (c 1.3, MeOH); 1H NMR
(CD3OD): l 5.09 (d, 1 H, J 1.3 Hz), 5.05 (d, 1
H, J 1.3 Hz), 4.92 (d, 1 H, J 1.6 Hz), 4.77 (d,
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