Regioselective glycosylation of glucosamine and galactosamine derivates using O-pivaloyl galactosyl donors

Article abstract of DOI:10.1515/znb-2003-0808

Penta-O-pivaloyl-galactopyranose and tetra-O-pivaloyl-galactopyranosyl bromide after electrophilic activation reacted with 6-O-protected 2-azido-galactosides to give the precursor structures of the Thomsen-Friedenreich antigen disaccharide with high regioselectivity, but low yield. With 4,6-O-benzylidene protected 2-azidogalactosides and 2-O-pivaloyl phenylthio galactosides, T-antigen disaccharides of this type were obtained in good yields. Glycosylation reactions of 4,6-O-benzylidene protected glucosamine derivatives with O-pivaloyl protected galactosyl bromide efficiently gave lactolactosamine disaccharides. Even a thioglycoside was efficiently galactosylated by this method resulting in the formation of a disaccharide thioglycoside useful itself as a potential glycosyl donor.

Full text of DOI:10.1515/znb-2003-0808

Regioselective Glycosylation of Glucosamine and Galactosamine
Derivates Using O-Pivaloyl Galactosyl Donors
Mathias Oßwald, Uwe Lang, Siglinde Friedrich-Bochnitschek, Waldemar Pfrengle,
and Horst Kunz
Institut fu¨r Organische Chemie der Universita¨t Mainz,
Duesbergweg 10 – 14, D-55128 Mainz, Germany
Reprint requests to Prof. Dr. H. Kunz. Fax: +49 6131 39-24786. E-mail: hokunz@uni-mainz.de
Z. Naturforsch. 58b, 764 – 774 (2003); received April 17, 2003
Penta-O-pivaloyl-galactopyranose and tetra-O-pivaloyl-galactopyranosyl bromide after elec-
trophilic activation reacted with 6-O-protected 2-azido-galactosides to give the precursor structures of
the Thomsen-Friedenreich antigen disaccharide with high regioselectivity, but low yield. With 4,6-O-
benzylidene protected 2-azidogalactosides and 2-O-pivaloyl phenylthio galactosides, T-antigen disac-
charides of this type were obtained in good yields. Glycosylation reactions of 4,6-O-benzylidene pro-
tected glucosamine derivatives with O-pivaloyl protected galactosyl bromide efficiently gave lacto-
lactosamine disaccharides. Even a thioglycoside was efficiently galactosylated by this method result-
ing in the formation of a disaccharide thioglycoside useful itself as a potential glycosyl donor.
Key words: O-Pivaloyl Galactosyl Donors, Glycosylation Reactions, T Antigen
Regioselective galactosylation of glucosamine galactal [9] and subsequent conversion of the obtained
derivatives is a key step in the synthesis of Lewisx, azidonitrate into an anomeric mixture of the methyl 2-
Lewisa [1] or Globo H antigen structures [2]. Similar azido-galactosides 3a/b [10]. Selective O-6 protection
regioselective galactosylation reactions are required in of 3a/b was achieved by pivaloylation to give 4a/b or
syntheses of Gal(1-3)Gal [3], Thomsen-Friedenreich tritylation to furnish 5a/b (Scheme 2).
(T) antigen [4] and sialyl T antigen [5] structures.
In many cases, trichloroacetimidates have been used
as the glycosyl donors in these conversions [1 – 4].
Enzymatic galactosylations [5 – 6] have also been
applied successfully.
We report on results obtained with O-pivaloyl
protected galactosyl donors in the synthesis of β(1-
3)-linked galactosyl galactosamine and glucosamine
derivatives. In analogy to the corresponding glucose
derivatives [7], penta-O-pivaloyl-β-D-galactopyranose
1 and 2,3,4,6-tetra-O-pivaloyl-α-D-galactopyranosyl
bromide
2 [8] were obtained from galactose
(Scheme 1).
Scheme 2.
In order to obtain a monofunctional acceptor,
3a/b were converted into the corresponding 4,6-O-
benzylidene acetals 6a/b.
Scheme 1.
Regioselective galactosylation of 6-O-pivaloyl-2-
The galactosamine derived glycosyl acceptors were azido-galactosides 4a/b was carried out using penta-
prepared via azidonitration of the O-acetyl-protected O-pivaloylgalactose 1 activated by either catalytic (A)
c
0932–0776 / 03 / 0800–0764 $ 06.00 ꢀ 2003 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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M. Oßwald et al. · Regioselective Glycosylation of Glucosamine and Galactosamine Derivates
765
galactosides. Auge´ and Veyrie`res [11] investigated the
reaction of 3,4-O-stannylene derivatives of galacto-
sides with O-acetyl-protected galactosyl bromide and
observed the formation of mixtures containing the
trisaccharides as the major components (galactosyla-
tion at O-3 and O-4). With O-benzyl-galactosyl bro-
mide regioselective monogalactosylation at O-3 of
1,2,6-tri-O-benzyl protected galactose was achieved.
However, the undesired α-linked disaccharide always
was the prevailing stereoisomer.
Since the 3,4-O-stannylene derivative of 3a/b re-
acted with galactosyl bromide 2 to give a mix-
ture of products, a 6-O-protected acceptor was used.
The 6-O-pivaloyl group is supposed to interfere
with stannylene-directed glycosylations because of its
coordinating abilities. Therefore, 6-O-trityl-2-azido-
galactosides 5a/b were investigated in this study. Af-
ter treatment with equimolar amounts of dibutyltin
oxide in methanol, the 3,4-O-stannylene derivatives
5a/b-Sn were dried in high vacuum and then reacted
with 2 equiv. of tetrabutylammonium iodide and 1.5
equiv. of galactosyl bromide 2 in boiling dioxane
(Scheme 5).
Scheme 3.
or equimolar amounts (B) of trimethylsilyl trifluo-
romethanesulfonate (TMS triflate, Scheme 3).
Both reactions proceeded slowly in dichloro-
methane in the presence of molecular sieves. Af-
ter 2 days at room temperature the reaction was
stopped by addition of triethylamine. With catalytic
trimethylsilyl trifluoromethanesulfonate (TMSOTf),
regioselective formation of β(1- 3)galactosyl-2-azido-
galactoside 8a/b (40% α : β = 4:5) was observed. The
pure β-anomer 8b (23%) was obtained by recrystalli-
sation from ethyl acetate. In the presence of equimo-
lar TMSOTf the 4-O-trimethylsilyl derivatives of the
β(1-3)galactosyl-2-azido galactosides 9a/b were iso-
lated after working-up under exclusion of water. In
this latter reaction the corresponding β(1-4) linked dis-
accharide was formed as a minor product in a ratio
of 1:15.
It is noteworthy that an analogous reaction of the O-
acetylated galactose 10 with the 6-O-benzoyl deriva-
tive 11 of 3a gave a mixture of the β(1-3)- (12) and
β(1-4)-galactosyl-azido-galactosides (13) in a ratio of
8:1 (Scheme 4).
Scheme 5.
According to TLC monitoring, the 1,3-linked disac-
charide 14a/b was formed with high selectivity. How-
ever, the removal of tin-containing impurities required
repeated chromatography. Therefore, the yield of suf-
ficiently pure galactosyl(β1-3)-2-azido-galactosides
14a/b was low.
Scheme 4.
Separation of the regioisomeric disaccharides
proved to be difficult. Comparison of reactions dis-
played in Schemes 3 and 4 illustrate the regiodiffer-
entiating effects of the O-pivaloyl protection in both
glycosyl donor and acceptor.
A similar result was obtained with 2,3,4,6-tetra-O-
pivaloyl-α-D-glucopyranosyl bromide 15 [7] as the
As an alternative concept of regiodifferentiation O- glycosyl donor. Again, only repeated purification re-
pivaloylated galactosyl bromide 2 was used in re- sulted in the isolation of the pure glucosyl(β1-3)-2-
action with 3,4-O-stannylene derivatives of azido- azido-α-galactoside 16.
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M. Oßwald et al. · Regioselective Glycosylation of Glucosamine and Galactosamine Derivates
Scheme 6.
It had to be concluded that a regioselective galac-
tosylation of 2-azido galactosides using O-pivaloyl-
protected galactosyl donors preventing additional pro-
tecting group manipulations can be achieved either
directly or via a stannylene intermediate. However,
the yields of the desired galactosyl(β1-3)-2-azido-
galactosides are unsatisfying. It should be briefly out-
lined that the precursors 8, 9 and 10 of the Thomsen-
Friedenreich antigen can be converted into disac-
charide donors suitable for conjugation with serine
or threonine derivatives [10,12]. Removal of the O-
pivaloyl groups from disaccharide 14a/b was achieved
by Zemple´n transesterification with cata◦lytic amounts
of sodium methoxide in methanol at 30 C. The crude
product was treated with acetic anhydride/sodium ac-
etate to furnish the O-acetylated galactosyl-2-azido-
galactoside isolated after purification as crystals en-
riched in the α anomer 17 (Scheme 6).
Scheme 7.
tion reaction and no accompanying alkylation at O-6
was observed.
After conversion of the 3-O-protected thiogalacto-
sides 20, 21 into their 4,6-O-benzylidene acetals 22,
23, pivaloylation of the 2-OH function furnished the
thiogalactosyl donors 24 and 25.
Thiogalactoside 24 was activated with dimethyl-
methylthiosulfonium triflate (DMTST) [14] and re-
acted with galactoside 6a as the acceptor to form the
galactosyl(β1-3)-2-azido-galactoside 26. The analo-
gous reaction of phenylthio galactoside 25 with accep-
tor 6b gave the precursor disaccharide 27 of T anti-
gen in good yield. Both disaccharides 26 and 27 offer
possibilities of selective deprotection and diversifica-
tion in a number of positions. They also can be trans-
formed into glycosyl donors of type 18 according to
known procedures [10,13]. It is worth mentioning that
Acetolysis [13] of 17 using◦acetic anhydride/conc.
sulfuric acid (100:1) at −25 C resulted in the for-
mation of the α-acetate 18, which can be converted
into the corresponding glycosyl bromide according to
known procedures [10, 13].
In addition to the regioselective galactosylation, pre- the bicyclic thiogalactoside donors 24 and 25 show en-
cursors of the T antigen saccharide have also been hanced reactivity compared to O- pivaloylated mono-
prepared by galactosylation of 4,6-O-benzylidene-2- cyclic analogues. Thus, reaction of 6b with 21a pre-
azido-galactosides 6 using thioglycosides [14] as the pared in order to characterise 21 gave only 25% of
glycosyl donors. To obtain galactosyl thioglycosides, the corresponding disaccharide under identical reac-
which can be differentiated in all positions [15], tion conditions.
phenylthio galactoside 19 was prepared from peracety-
From the results of the reactions shown in Scheme
lated galactose with thiophenol in the presence of 8 it is concluded, that reactions of 2-O-pivaloylated
boron trifluoride etherate [16] and subsequent treat- glycosyl donors produce the desired disaccharides
ment with catalytic NaOMe in methanol. It was sub- with high β-selectivity. Orthoester formation was not
jected to regioselective 3-O-benzylation or allylation observed, which facilitates purification of the prod-
via its 3,4-O-stannylenederivative [17,18] to give com- ucts. The reactions of monofunctionalized acceptors
pounds 20 or 21, respectively (Scheme 7). It is remark- (Scheme 8) give higher yields than the regioselective
able that the thioglycoside does not affect this alkyla- glycosylations shown in the Schemes 3 and 5.
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M. Oßwald et al. · Regioselective Glycosylation of Glucosamine and Galactosamine Derivates
767
Scheme 10.
Scheme 8.
2 with ethyl thioglycoside 33 of the 4,6-benzylidene-
protected N-phthaloyl glucosamine gave the lacto- lac-
tosamine derivative 34. In order to prevent anomerisa-
tion of the product, this galactosylation was promoted
by silver triflate in the presence of Huenig’s base. In
fact, the β-selectivity of the reaction was higher than
20:1. Due to the neutral conditions, some amounts
of the corresponding orthoester were formed which
could be readily separated by chromatography.The ob-
tained lacto-lactosamine thioglycoside 34 can directly
be used for further glycosylations as will be described
elsewhere.
As a consequence of these experiences, monofunc-
tional glucosamine acceptors were investigated in reac-
tions with O-pivaloylated galactosyl donors to furnish
lacto-lactosamine derivatives. Besides galactosyl bro-
mide 2 the O-pivaloylated O-galactosyl trichloroace-
timidates 28a/b [19] were used as the donors in reac-
tions with the glycofurano-oxazoline 30 obtained from
N-acetylglucosamine 29 by treatment with an excess
of boron trifluoride etherate in acetone (Scheme 9).
The outlined examples of reactions show that O-
pivaloyl protected galactosyl donors despite their re-
duced reactivity are useful in galactosylations of
monofunctional glycosyl acceptors of both the glu-
cosamine and the galactosamine series. They can also
be applied in regioselective glycosylation reactions of
acceptors with 3,4-diol structure. In these cases, the
yields of disaccharides are lower obviously due to the
sterical demand and reduced reactivity of the pivaloy-
lated galactosyl donors.
Scheme 9.
Due to its acid-sensitivity, glucofurano-oxazoline30
was not stable under glycosylation conditions, neither
with galactosyl bromide 2 in the presence of silver tri-
flate/collidine nor with trichloroacetimidates activated
by boron trifluoride.
However, pivaloyl protected galactosyl bromide 2
reacted with benzyl 2-acetamido-4,6-O-benzylidene-
2-deoxy-glucopyranoside 31 [20] in the presence
of silver triflate/tetramethyl urea [21] to give the
lacto-lactosamine disaccharides 32a/b in high yield
(Scheme 10).
Experimental Section
Optical rotation values were recorded on a Perkin Elmer
241 polarimeter and calculated for λ = 589 nm.
Analytical TLC was performed on aluminium-backed
TLC plates coated with Silica Gel 60 F254 (E. Merck, Darm-
stadt, Germany), detection by UV of λ = 254 nm and by
a solution of 2 N H2SO4/0.2% 3-methoxyphenol (1:2) in
ethanol. Column chromatography was carried out using sil-
ica gel (63 – 200 µm), flash-chromatography on silica gel
(40 – 63 µm) purchased from E. Merck, Darmstadt, Ger-
many. NMR spectra were recorded on a Bruker WT 200
spectrometer (200 MHz 1H and 50.3 MHz 13C) and a Bruker
AM 400 spectrometer (400 MHz 1H and 100.6 MHz 13C).
The two anomers can readily be separated by chro-
matography, and the desired β-anomer was isolated in
high yield. In a similar reaction galactosyl bromide HPLC was performed using a LKB (Pharmacia) 2150 unit
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768
M. Oßwald et al. · Regioselective Glycosylation of Glucosamine and Galactosamine Derivates
Methyl 2-azido-2-deoxy-6-O-triphenylmethyl-α/β-D-galac-
with diode-array detection and a Lichrospher 100 RP 18 col-
umn (250×4 mm) of Bischoff. Water/methanol served as the
eluent.
topyranoside (5a/b)
To a solution of (3a/b) [10] (2.0 g, 9 mmol) in pyri-
dine (30 ml), triphenylchloromethane (2.5 g, 9.2 mmol) and
4-dimethylamino-pyridine (DMAP, 0.4 g, 3.2 mmol) were
added. The solutio◦n was stirred at room temp. for 3 d, fi-
nally heated to 40 C for 2 h and then diluted with toluene
(100 ml). After evaporation of the solvents in vacuo, the
residue was dissolved in diethyl ether (100 ml). The solu-
tion was extracted with water (50 ml), 1 N HCl (50 ml) and
water, dried with MgSO4, and the solvent was evaporated in
vacuo. Yield: 3.2 g (77%), mixture of anomers α : β = 1:3.
Flash-chromatography in petroleum ether/ethyl acetate (5:1)
Melting points have been measured using a Dr. Totolli ap-
paratus (Bu¨chi) and are uncorrected.
2,3,4,6-Tetra-O-pivaloyl-α-D-galactopyranosyl bromide (2)
To
a
solution of 1,2,3,4,6-penta-O-pivaloyl-β-D-
galactopyranose (1) [22] (44 g, 73 mmol) in dry
dichloromethane (60 ml) a solution of hydrogen bro-
mide in acetic acid (33%, 72 ml) was added dropwise
at 0 ◦C. After stirring for 12 h at room temp., toluene
(400 ml) was added, and the solvents were evaporated in
vacuo. Codistillation in vacuo with toluene (400 ml) and
with diethyl ether (400 ml) was repeated. The remaining
crude product was dissolved in diethyl ether (500 ml). The
solution was carefully washed with sat. sodium bicarbonate
solution, dried with MgSO4, and the solvent evaporated in
vacuo. After recrystallisation the pure crystalline galactosyl
bromide (2) was isolated.
◦
gave the pure β-anomer: m.p. 144 – 145 C; [α]2D2 = −2.7
(c 1, CHCl3); Rf = 0.48 (light petroleum/ethyl acetate 2:1). –
1H NMR (DMSO- d6): δ = 7.41 – 7.23 (m, 15 H, Ph), 5.32
(d, 1H, J3,OH = 5.6 Hz, 3-OH), 4.74 (m, 1H, 4-OH), 4.19
(d, 1H, J1,2 = 7.9 Hz, 1-H). 3.66, 3.61 (2 × m, 2 × 1H,
4-H, 5-H), 3.41 (dd, 1H, J2,3 = 10.3 Hz, J3,4 = 3.6 Hz, 3-
H), 3.34 (dd, 1H, J2,3 = 10.2 Hz, 2-H), 3.19 (dd, 1H, J6,5
=
Yield: 34 g (80%); m. p. 91 – 92◦C; [α]D22 = +159.5 (c 1,
CHCl3); Rf = 0.57 (light petroleum/diethyl ether 5:1). – 1H
NMR (CDCl3): δ = 6.65 (d, 1H, J1,2 = 4.0 Hz, 1-H), 5.52
(dd, 1H, J3,4 = 3.3 Hz, J4,5 = 2.1 Hz, 4-H), 5.47 (dd, 1H,
J2,3 = 10.5 Hz, 3-H), 5.00 (dd, 1H, J2,1 = 4.0 Hz, 2-H), 4.50
ꢀ
ꢀ
7.1 Hz, J6,6 = 9.2 Hz, 6-H), 3.03 (dd, 1H, J6 ,5 = 4.9 Hz,
6’-H); [α-anomer: δ = 4.77 (d, 1H, J1,2 = 3.7 Hz, 1-H)]. –
C26H27N3O5 (461.5): calcd. C 67.67, H 5.91, N 9.11; found
C 67.85, H 5.86, N 9.35.
Methyl 2-azido-4,6-O-benzylidene-2-deoxy-α/β-D-galacto-
pyranoside (6a/b)
ꢀ
(m, 1H, 5-H), 4.11 (dd, 1H, J6,6 = 11.3 Hz, J6,5 = 7.0 Hz,
ꢀ
6-H), 4.04 (dd, 1H, J6 ,5 = 6.7 Hz, 6’-H), 1.25-1.10 (4 × s,
36H, Piv.). – C26H43BrO9 (579.5): calcd. C 53.89, H 7.48;
found C 53.96, H 7.35.
To a solution of (3a/b) [10] (1.5 g, 6.8 mmol) and ben-
zaldehyde dimethylacetal (1.2 ml, 7.9 mmol) in dimethyl-
formamide (10 ml) 0.4 g of p- toluenesulfonic acid was
Methyl 2-azido-2-deoxy-6-pivaloyl-α/β-D-galacto-
pyranoside (4a/b)
◦
added. The solution was kept at 35 C for 3 h. Triethy-
lamine (1 ml, 10 mmol) was then added. The solvent was
evaporated, the residue dried in high vacuum, and then pu-
rified by flash-chromatography in light petroleum/ethyl ac-
etate 1:5. Yield: 1.7 g (81%), colourless crystals, mixture of
anomers (1:1); C14H17N3O5 (307.3): calcd. C 54.72, H 5.57,
N 13.67; found C 54.72, H 5.49, N 13.53. For a sample
the anomers have been separated by column chromatogra-
phy (eluent: light petroleum/ethyl acetate, 1:2). α-anomer
To
a solution of methyl 2-azido-2-deoxy-α/β-D-
galactopyranoside (3a/b) [10] (5.0 g, 23 mmol) in pyridine
(100 ml) at −15 ◦C pivaloyl chloride (1.5 ml, 12 mmol) was
added. The solution was stirred at this temperature for 12 h,
then additional 3 ml of pivaloyl chloride (24 mmol) were
added. After 48 h the solution was brought to room temper-
ature. Pyridine was evaporated in vacuo. After codistillation
with toluene (50 ml) in vacuo, the residue was dissolved in
(6a): m. p. 119 – 120 ◦C; [α]D22 = +183.7 (c 1, CHCl3); Rf
=
dichloromethane (100 ml) and washed with sat. NaHCO3 so- 0.52. – 1H NMR (DMSO-d6): δ = 7.42 (m, 5H, Ph), 5.59
lution. After evaporation of the solvent in vacuo, drying in (s, 1H, CHPh), 5.43 (d, 1H, J3OH = 7.2 Hz, 3-OH), 4.85
high vacuum and recrystallisation from light petroleum/ethyl (d, 1H, J1,2 = 3.4 Hz, 1-H), 4.20 (d, 1H, J3,4 = 3.2 Hz,
acetate (10:1), the pure product was obtained as colourless 4-H), 4.05 (m, 2H, 6,6’-H), 3.96 (m, 1H, 3-H), 3.63 (m,
crystals: Yield: 3.5 g (51%); ratio of anomers 1:1; Rf = 0.38 1H, 5-H), 3.53 (dd, 1H, J2,3 = 10.8 Hz, 2-H). 3.32 (s, 3H,
(α anomer), 0.32 (β anomer) in light petroleum/ethyl acetate OCH3). – 13C NMR (DMSO-d6): δ = 99.72 (CHPh), 98.93
2:1. – C12H21N3O6 (303.3): calcd. C 47.52, H 6.98, N 13.85; (C-1). β-anomer (6b): m. p. 168 – 169 ◦C; [α]D22 = −3.5 (c 1,
1
found C 47.70, H 6.99, N 13.27. – For an analytical sample CHCl3); Rf = 0.75. – H NMR (DMSO-d6): δ = 7.43 (m,
the anomers were separated: α anomer: m.p. 48 ◦C, [α]D22
=
5H, Ph), 5.59 (s, 1H, CHPh), 5.47 (d, 1H, J3OH = 7.0 Hz,
+120.0 (c 1.2, CHCl3). – 1H NMR (CDCl3): δ = 4.80 (d, 1H, 3-OH), 4.26 (d, 1H, J1,2 = 8.1 Hz, H-1), 4.10 (d, 1H, J3,4
J1,2 = 3.5 Hz, 1-H); β-anomer: m.p. 88 – 90 ◦C, [α]D22 = +43.5 3.4 Hz, 4-H), 4.06 (m, 2H, 6,6’-H), 3.56 (m, 1H, 3-H), 3.53
(c 1, CHCl3). – 1H NMR: δ = 4.13 (d, 1H, J1,2 =7.7 Hz, 1-H). (m, 1H, 5-H), 3.44 (s, 3H, OCH3), 3.41 (dd, 1H, J2,3
=
=
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M. Oßwald et al. · Regioselective Glycosylation of Glucosamine and Galactosamine Derivates
769
8.1 Hz, 2-H). – 13C NMR (DMSO-d6): δ = 101.76 (C-1), 7.9 Hz, 1- H), 3.92 (dd, 0.3H, J3,4 = 2.8 Hz, J1/2 = 1.0 Hz,
99.74 (CHPh).
4-H), 3.42 (s, OCH3).
Treatment with aqueous methanol quantitatively converts
9a/b into 8a/b.
Methyl 2-azido-2-deoxy-6-O-pivaloyl-3-O-(2,3,4,6-tetra-
O-pivaloyl-β-D-galactopyranosyl)-β-D-galactopyrano-
side (8b)
Methyl 2-azido-6-O-benzoyl-2-deoxy-3-O-(2,4,6-tetra-O-
acetyl-β-D-galactopyranosyl)-4-O-trimethylsilyl-β-D-
galactopyranoside (12)
To a solution of 4a/b (1.30 g, 4.28 mmol) and 1 (2.7 g,
4.4 mmol) in dry dichloromethane (50 ml) 2.0 g of molec-
˚
ular sieves (4 A) were added. After stirring the mixture for
To methyl 2-azido-6-O-benzoyl-2-deoxy-β-D-galacto-
pyranoside [23] (11) (0.10 g, 0.31 mmol), penta-O-acetyl-β-
D-galactopyranose (10) (0.12 g, 0.31 mmol) and molecular
1 h, a catalytic amount (0.05 ml) of trimethylsilyl trifluo-
romethanesulfonate was added. The mixture was stirred for
additional 48 h. After addition of triethylamine (0.15 ml,
0.8 mmol), filtration, washing with water (50 ml) and dry-
ing with MgSO4, the solvent was evaporated. The residue
was extracted with ethyl acetate, the solution was filtered
through silica gel, and the solvent was evaporated to give
1.45 g (42%) of the crude mixture of anomers (8a/b). Dis-
solution of the material in aqueous ethyl acetate resulted in
the precipitation of the β- anomer (8b) as colourless crys-
tals: Yield: 0.91 g (27%); m. p. 206 – 208 ◦C; [α]D22 = +15.8
(c 1, CHCl3); Rf = 0.55 (light petroleum/ethyl acetate 5:1). –
˚
sieves 4 A in dichloromethane (2 ml), trimethylsilyl triflate
(0.6 ml, 69 mg, 0.31 mmol) was added. After stirring for 24 h
at room temp. triethylamine (40 mg, 0.4 mmol) and addi-
tional 0.08 ml (0.4 mmol) of TMS triflate were added, and the
stirring was continued for 12 h. After filtration and evapora-
tion, purification was carried out by chromatography in light
petroleum/ethyl acetate (2:1) to give 12 which according to
the 400 MHz 1H NMR spectrum in CDCl3 contained the re-
gioisomer 13 in a ratio of 8:1 (δ = 0.19, M3Si). Yield: 145 mg
(62%); colourless oil; [α]2D2 = +12.3 (c 0.4, CHCl3); Rf
=
1H NMR (CDCl3): δ = 5.38 (dd, 1H, J3,4 = 3.3 Hz, J4,5
=
0.53 (toluene, acetone 9:2). – 1H NMR (CDCl3): Signals of
2.0 Hz, 4’-H), 5.23 (dd, 1H, J2,3 = 10.5 Hz, J2,1 = 7.9 Hz,
2’-H), 5.09 (dd, 1H, 3’-H), 4.78 (d, 1H, 1’-H), 4.29 (m, 2H,
6a,6b−H), 4.12 (d, 1H, J1,2 = 8.0 Hz, 1-H), 4.01 (m, 3H, 5’-
12: δ = 8.0 (m, 2H, o-benzoyl), 7.55 (m, 1H, p-benzoyl),
7.43 (m, 2H, m-benzoyl), 5.36 (dd, 1H, J3,4 = 3.3 Hz, J4,5
=
0.8 Hz, 4’-H), 5.24 (dd, 1H, J1,2 = 7.8 Hz, J2,3 = 10.5 Hz,
2’-H), 4.98 (dd, 1H, 3’- H), 4.72 (d, 1H, 1’-H), 4.45 (dd, 1H,
ꢀ
ꢀ
H, 6a ,6b −H), 3.90 m, 1H, 4-H), 3.58 (m, 2H, H-5, 2-H),
3.37 (dd, 1H, J2,3 = 10.2 Hz, J3,4 = 3.2 Hz, 3-H), 2.60 (‘s’,
1H, 4-OH).
J5,6a = 6.2 Hz, J6a,6b = 11.0 Hz, 6a-H), 4.36 (dd, 1H, J5,6b
=
6.3 Hz, 6b-H), 4.13 (d, 1H, J1,2 = 8.2 Hz, 1-H), 4.07 (m, 3H,
H-6’, 4-H), 3.83 (m, 1H, 5’-H), 3.68 (t, 1H, 5-H), 3.55 (dd,
Methyl 2-azido-deoxy-6-O-pivaloyl-3-O-(2,3,4,6-tetra-O-
pivaloyl-β-D-galactopyranosyl)-4-O-trimethylsilyl-α/β-
D-galactopyranoside (9a/b)
1H, J1,2 = 8.2 Hz, J2,3 = 10.2 Hz, 2-H), 3.29 (dd, 1H, J3,4
=
3.0 Hz, 3-H), 2.10, 2.06, 1.96 (3 × s, 12H, OAc), 0.17 (s,
9H, Me3Si).
The galactosylation was performed as described for (8a/b)
or (8b), respectively, with (4a/b) (0.35 g, 1.15 mmol), 1
(0.70 g, 0.16 mmol) and molecular sieves 4 A (1 g) in
Stannylene-directed glycosylation
General procedure
˚
dichloromethane (20 ml). After 1 h under argon atmosphere,
0.2 ml (1.1 mmol) of trimethylsilyl triflate was added via
a syringe, and the mixture was stirred for 2 days. Triethy-
lamine (0.16 ml, 1.16 mmol) was added, the mixture filtered
and evaporated to dryness. The residue was dissolved in light
petroleum/ethyl acetate (20:1) and purified by chromatogra-
phy in this solvent. Yield: 0.31 g (32%), mixture of anomers
The carefully dried acceptor 5a/b (0.66 – 5.2 mmol) and
1.1 equiv. of di-n-butyltin oxide were heated in boiling
methanol. After clearance of the solution heating was con-
tinued for 2 h. Then, the solvent was evaporated in vacuo,
followed by codistillation with toluene twice. Finally, the
remaining tin-complex 5a/b-Sn was dried in high vacuum.
The dry complex 5a/b-Sn, 1.5 equivalents of the glyco-
(2:1): α-anomer: Rf = 0.68, β-anomer Rf = 0.60 (light
1
petroleum/ethyl acetate 5:1). – H NMR (CDCl3): a) com- syl bromide, 2 equivalents of dry tetrabutylammonium io-
˚
mon signals of 9a/b: δ = 5.40 (dd, 1H, J3,4 = 3.3 Hz, J4,5
=
dide, and freshly activated molecular sieves 4 A in dry 1,4-
1.0 Hz, 4’-H), 5.33 (dd, 1H, J1,2 = 8.0 Hz, J2,3 = 10.4 Hz, dioxane were heated under reflux and argon atmosphere for
2’-H), 5.06 (dd, 1H, 3’-H), 4.78 (d, 1H, 1’-H), 4.15 (m, 2H, 15 h (monitoring by TLC). The solvent was evaporated in
ꢀ
6a,6a’-H), 4.04 (dd, 1H, J5,6b = 6.2 Hz, J6a,6b = 11.2 Hz, 6b - vacuo and the remaining residue was extracted with ethyl
H), 3.85 (t, 1H, J5,6 = 6.3 Hz, 5’-H), 0.16 (s, 9H, Si(CH3)3). acetate. The tin-containing insoluble amounts were filtered
Signals of α-anomer (9a): δ = 4.83 (d, 0.6H, J1,2 = 3.4 Hz, off. The solution was evaporated to dryness, and the residue
1-H), 4.09 (dd, 0.6H, J3,4 = 2.7 Hz, J4,5 1.0 Hz, 4-H), 3.40 (s, purified by flash-chromatography in light petroleum/ethyl
OCH3). Signals of β-anomer (9b): δ = 4.42 (d, 0.3H, J1,2
=
acetate (20:1).
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M. Oßwald et al. · Regioselective Glycosylation of Glucosamine and Galactosamine Derivates
Methyl 2-azido-2-deoxy-3-O-(2,3,4,6-tetra-O-pivaloyl-β-D-
galactopyranosyl)-6-O-triphenylmethyl-α/β-D-galacto-
pyranoside (14a/b)
with acetic anhydride (20 ml) and sodium acetate under re-
flux for 2 h. Acetic anhydride was evaporated in vacuo,
the residue was dissolved in diethyl ether, and the solution
washed with 0.1 N NaHCO3 solution, dried with MgSO4
and evaporated in vacuo to give the crude oily product 17.
Yield: 0.43 g (65%). Purification by flash-chromatography
in light petroleum/ethyl acetate (4:1) gave (17) as crystals
enriched in the α-anomer (α : β > 8:1): yield 0.30 g (45%);
m.p. 75 – 78 ◦C, [α]D22 = +48.2 (c 1, CHCl3); Rf = 0.50 (light
petroleum/ethyl acetate 2:1). – 1H NMR (DMSO-d6): δ =
7.32 – 7.22 (m, 15H, C(Ph)3), 5.23 (d, 1H, J3,4 = 3,3 Hz, 4-
The disaccharide was synthesised according to the gen-
eral procedure from 5a/b (2.4 g, 5.2 mmol) and galactosyl
bromide (2) (4.5 g, 7.7 mmol) in dry dioxane (150 ml) to
give 14a/b: Yield: 0.9 g (18%), mixture of anomers (α : β =
1.5:1) as colourless crystals, m. p. 72 – 74 ◦C; [α]D22 = + 27.9
(c 1, CHCl3); Rf = 0.52 (light petroleum/ethyl acetate 5:1). –
1H NMR (CDCl3): δ = 7.38 (m, 30H, Ph3C), 5.28 – 5.22
(m, 4H, α + β 4’-H, 3’-H), 5.09 – 5.03 (m, 2H, α + β 2’-
H), 4.98 – 4.92 (m, 3H, α 1-H, α + β 1’-H), 4.66 (d, 1H,
J4,OH = 5.8 Hz, α 4-OH), 4.58 (d, 1H, J4,OH = 5.8 Hz, β
4-OH), 4.42 (d, 1H, J1,2 = 7.1 Hz, β 1-H), 4.31 – 4.26 (m,
2H, α + β 5’-H), 3.99 – 3.79 (m, 10H, α + β 3-H, α + β
4-H, α + β 5-H, α + β 6’-H), 3.55 (dd, 1H, J1,2 = 3.5 Hz,
J2,3 = 10.9 Hz, α 2-H), 3.53 (s, 3H, β OCH3), 3.48-3.44
(m, 4H, β H-2, α OCH3), 3.25 (m, 2H, α + β 6a-H), 2.95
(m, 2H, α +β 6b-H), 1.21 – 1.03 (m, 72H, α +β C(CH3)3).
C52H69N3O14 (960.1): calcd. C 65.05, H 7.24, N 4.38; found
C 65.58, H 7.56, N 4.02.
H), 5.20 (d, 1H, J3,4 = 3.5 Hz, 4’-H), 5.11 (dd, 1H, J2,3
8.4 Hz, 3’-H), 4.96 (d, 1H, J1,2 = 3,6 Hz, 1-H), 4.90 – 4.85
(m, 2H, 1’-H, 2’-H), 4.12 (m, 1H, 5’-H), 4.05 (dd, J2,3
=
=
10.8 Hz, 1H, 3-H), 4.02 (m, 1H, 5-H), 3.93 – 3.85 (m, 2H, 6-
H), 3.61 (dd, 1H, J2,3 = 10.9 Hz, 2-H), 3.45 (s, 3H, OCH3),
2.93 – 2.91 (m, 2H, 6-H), 2.07 – 1.81 (5 × s, 15H, CH3). –
C42H47N3O15 (833.8): calcd. C 60.50, H 5.68, N 5.04; found
C 60.33, H 5.74, N 4.78.
2-Azido-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-β-D-galacto-
pyranosyl)-1,4,6-tri-O-acetyl-α/β-D-galactopyranose (18)
Methyl 2-azido-2-deoxy-3-O-(2,3,4,6-tetra-O-pivaloyl-β-D-
glucopyranosyl)-6-O-triphenylmethyl-α-D-galactopyrano-
side (16)
To a solution of 17◦(200 mg, 0.24 mmol) in a◦cetic an-
hydride (9 ml) at −20 C, 8 ml of a cooled (−20 C) mix-
ture of acetic anhydride/conc. H2SO4 (100:1) was added. A
yellow colour results from cleavage of the trityl ether. Af-
ter 24 h, dichloromethane (150 ml) was added. The solution
was washed with 0.1 N NaHCO3 solution and with water,
dried with MgSO4, and the solvent was evaporated in vacuo.
The residue was purified by flash- chromatography in light
petroleum/ethyl acetate 3:1. Yield: 120 mg (76%), colourless
crystals, mixture of anomers, α : β = 8:1; m.p. 137 – 138 ◦C;
[α]2D2 = +57.5 (c 1, CHCl3); Rf = 0.73 (light petroleum/ethyl
acetate 1:1). – 1H NMR (CDCl3) α-anomer: δ = 6.22 (d, 1H,
J1,2 = 3.7 Hz, 1-H), 5.43 (d, 1H, J3,4 = 3.1 Hz, 4-H), 5.24 (d,
1H, J3,4 = 3.0 Hz, 4’-H), 5.14 (dd, 1H, J2,3 = 10.0 Hz, 3’-H),
4.98 (d, 1H, J1,2 = 7.9 Hz, 1’-H), 4.92 (dd, 1H, 2’-H), 4.22 –
4.16 (m, 2H, 5-H, 5’-H), 4.11 (dd, 1H, J2,3 = 10.9 Hz, 3-H),
4.06 – 3.97 (m, 3H, 2-H, 6’-H), 3.92 (dd, 1H, J5,6a = 6.7 Hz,
J6a,6b = 11.1 Hz, 6a-H), 3.83 (dd, 1H, J5,6b = 7.2 Hz, 6b-H),
2.10 – 1.91 (7 times s, 21H, CH3). Signals of β- anomer: δ =
4.55 (d, 1H, J1,2 = 8.0 Hz, 1-H), 3.34 (dd, 1H, J2,3 = 10.5 Hz,
2-H). C26H35N3O17 (661.6): calcd. C 47.20, H 5.33, N 6.35;
found C 47.03, H 5.26, N 6.36.
This compound was obtained according to the general
procedure from 5a/b (0.30 g, 0.65 mmol) and 0.60 g
(10 mmol) of 2,3,4,6-tetra-O-pivaloyl-α-D-glucopyranosyl
bromide [7] (15) in dry 1,4-dioxane (20 ml). After chro-
matography the pure α-anomer (16) was isolated: 125 mg
(20%), colourless oil; [α]2D2 = +96.8 (c 1, CHCl3); Rf = 0.55
(light petroleum/ethyl acetate 5:1). – 1H NMR (DMSO-d6):
δ = 7.30 (m, 15H, CPh3), 5.33 (t, 1H, J3,4 = J4,5 = 9.4 Hz,
4’-H), 5.03 (d, 1H, J1,2 = 7.9 Hz, 1’-H), 4.92 – 4.87 m, 3H,
H-1, 2’-H, 3’-H), 4.60 (d, 1H, J4,OH = 5.1 Hz, 4-OH), 4.13 –
4.02 (m, 2H, 6’-H), 3.94 – 3.77 (m, 4H, 3-H, 4-H, 5-H, 5’-H),
3.51 (dd, 1H, J1,2 = 3.5 Hz, J2,3 = 11.0 Hz, 2-H), 3.42 (s, 3H,
OCH3), 3.24 (dd, 1H, J5,6a = 7.8 Hz, J6a,6b = 9.5 Hz, 6a-H),
2.98 (dd, 1H, J5,6b = 3.7 Hz, 6b-H), 1.10 – 0.99 (4 × s, 36H,
CCCH3)3). – C52H69N3O14 (960.1): calcd. C 65.05, H 7.24,
N 4.38; found C 65.58, H 7.12, N 4.56.
Methyl 4-O-acetyl-2-azido-2-deoxy-3-O-(2,3,4,6-tetra-O-
acetyl-β-D-galactopyranosyl)-6-O-triphenylmethyl-α-D-
galactopyranoside (17)
Selective 3-O-alkylation of phenylthio galactoside (19)
Treatment of 14a/b (0.75 g 0.78 mmol) with a solution
of sodium methanolate (from 25 mg sodium) in methanol
(20 ml) at 35 C for 12 h, neutralisation with acidic ion-
General procedure
◦
exchange resin Lewatit CNP 80, filtration and evaporation of
Phenyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-galactopyrano-
the solvent gave the crude depivaloylated compound [0.45 g, side [16] (5.0 g, 11.3 mmol) was deacetylated by stirring with
◦
92%, m.p. 80 – 84 C; [α]2D2 = +20 (c 1, CHCl3)] as a mix- methanol (100 ml) and 5 ml of 0.1 M sodium methanolate
ture of anomers, α : β = 1.2:1. This product was then heated in methanol at room temp. until completion of the reac-
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771
tion (TLC monitoring, about 4 h). Neutralisation with ion- (50 Torr) for 3 h. After addition of triethylamine (1 ml,
exchange resin Lewatit CNP, filtration and evaporation of the 9.9 mmol) the solvents were evaporated, the residue dried in
solvent gave phenyl 1-thio-galactopyranoside (19) in a form high vacuum and purified by flash-chromatography in ethyl
sufficiently pure for further conversion. Yield: 2.5 g (77%), acetate. Yield: 2.1 g (54%), colourless crystals, m. p. 154 –
◦
◦
m.p. 97 – 101 C, [α]2D2 = −52.1 (c 1, MeOH), Rf = 0.37 155 C; [α]2D2 = +15.8 (c 0.5, CHCl3); Rf = 0.83 (ethyl ac-
etate). 1H NMR (DMSO-d6): δ = 5.57 (s, 1H, CHPh), 5.37
(CH2Cl2/MeOH 1:1).
A
suspension of phenyl thio-galactoside (19) (9 –
(d, 1H, J2,OH = 6.0 Hz, 2-OH), 4.69 (d, 1H, J1,2 = 9.4 Hz,
1-H), 4.33 (d, 1H, J3,4 = 3.2 Hz, 4-H), 3.64 (s, 1H, 5-H),
3.57 (m, 1H, 2-H), 3.44 (dd, 1H, J2,3 = 9.2 Hz, J3,4 = 3.1 Hz,
3-H). – C22H24O5S (400.5): calcd. C 65.98, H 6.04, S 8.01;
found C 65.74, H 6.14, S 8.70.
18 mmol) and di-n-butyltin oxide (1.5 equivalents) in
methanol (100 ml) was heated under reflux for 3 h. The sol-
vent was evaporated in vacuo and the amorphous residue was
dried in high vacuum. To this crude product dissolved in 1,4-
dioxane (100 ml) at 80 ◦C, tetrabutylammonium iodide (1 g)
and an excess (2 to 10-fold) of the alkyl bromide were added.
The mixture was then heated under reflux until the TLC mon-
itoring (ethyl acetate) showed complete consumption of 19.
After evaporation of the solvents, the residue was purified by
flash-chromatography in ethyl acetate.
Phenyl 3-O-benzyl-4,6-O-benzylidene-1-thio-β-D-galacto-
pyranoside (23)
The compound was prepared from 21 (3.0 g, 8.3 mmol)
and α, α-dimethoxy-toluene (3.4 ml, 22.2 mmol) in
dimethyl formamide (50 ml) in the presence of p-
toluenesulfonic acid (0.5 g) as was described for (22). Flash-
chromatography in ethyl acetate gave (23) in a yield of 3.3 g
Phenyl 3-O-allyl-1-thio-β-D-galactopyranoside (20)
(88%) as colourless crystals; m. p. 159 – 160 C; [α]D22
+13.8 (c 1, CHCl3); Rf = 0.86 (light petroleum/ethyl acetate
1:5). – 1H NMR (DMSO4-d6): δ = 5.58 (s, 1H, CHPh), 5.39
(d, 1H, J2,OH = 6.0 Hz, 2-OH), 4.72 (d, 1H, J1,2 = 9.4 Hz,
1-H), 4.40 (d, 1H, J3,4 = 3.1 Hz, 4-H), 3.53 (dd, 1H, J2,3
9.2 Hz, 3-H). – C26H26O5S (450.5): calcd. C 69.31, H 5.82,
S 7.12; found C 69.26, H 5.84, S 7.24.
=
◦
This compound was obtained from crude 19 (2.5 g,
9.1 mmol) and 3.4 g (13.7 mmol) of Bu2SnO via reaction
of the stannylene intermediate with allyl bromide (10 ml,
115 mmol) in dioxane. Yield: 2.6 g (87%), colourless crys-
tals; m.p. 112 – 114 C; [α]2D2 = −18.0 (c 1, CHCl3); Rf
=
◦
=
0.55 (ethyl acetate). – 1H NMR (DMSO-d6): δ = 7.45 – 7.17
(m, 5H, SPh), 5.91 (m, 1H, −CH=), 5.32 (dd, 1H, Jtrans
17.5 Hz, = CH2trans), 5.30 (d, 1H, J2,OH = 6.2 Hz, 2-OH),
5.09 (dd, 1H, Jcis = 10.4 Hz, = CH2cis), 4.67 (t, 1H, J6a,OH
=
Phenyl 3-O-benzyl-2,4,6-tri-O-pivaloyl-1-thio-β-D-galacto-
pyranoside (21a)
=
J6b,OH = 5.3 Hz, 6-OH), 4.59 (d, 1H, J1,2 = 9.7 Hz, 1-H), 3.22
(dd, 1H, 1H, J2,3 = 9.1 Hz, J3,4 = 3.1 Hz, 3-H). – C15H20O5
S (312.4): calcd. C 57.68, H 6.45, S 10.26; found C 57.62,
H 6.47, S 9.84.
To a solution of (21) (3.6 g, 9.9 mmol) in pyridine was
added pivaloyl chloride (15 ml, 12 mmol). The mixture was
stirred at room temp. for 24 h, diluted with toluene (100 ml),
and the solvents were evaporated in vacuo. The residue was
dissolved in diethyl ether (100 ml), washed with 0.1 N HCl
(50 ml), sat. NaHCO3 solution (50 ml), and water and was
dried with MgSO4. After evaporation of the solvent, the
syrupy residue was purified by flash-chromatography in light
petroleum/ethyl acetate (7:1) and gave the tri-O-pivaloyl
compound 21a instead of an expected mono pivaloyl deriva-
tive. Yield: 1.4 g (23%), colourless crystals, m.p. 82 – 83 ◦C;
[α]2D2 = +25.3 (c 1, CHCl3); Rf = 0.63 (light petroleum/ethyl
Phenyl 3-O-benzyl-1-thio-β-D-galactopyranoside (21)
The compound was synthesised according to the general
procedure from 19 (4.4 g, 16.1 mmol) and 6.0 g (24.1 mmol)
of Bu2SnO and treatment of the stannylene intermediate with
benzyl bromide (5.5 g, 32.2 mmol) to yield 21, 3.6 g (61%),
colourless crystals, m.p. 150 ◦C; [α]D22 = +26.0 (c 1, CHCl3);
Rf = 0.39 (CHCl3/MeOH 3:1). – 1H NMR (DMSO-d6): δ =
7.50 – 7.28 (m, 10H, SPh, CPh), 5.39 (d, 1H, J2,OH = 6.2 Hz,
2-OH), 4.71 – 4.55 (m, 5H, H-1, 4-OH, OH-6, OCH2Ph),
3.99 (m, 1H, 4-H), 3.32 (dd, 1H, J2,3 = 9.0 Hz, J3,4 = 3.0 Hz,
3-H). – C19H22O5S (362.4): calcd. C 62.97, H 6.12, S 8.85;
found C 60.70, H 6.06, S 8.11 (the compound contains Sn-
impurities).
acetate 5:1). – 1H NMR (DMSO-d6): δ = 5.23 (d, 1H, J3,4
=
2.7 Hz, 4-H), 5.07 (d, 1H, J1,2 = 10.1 Hz, 1-H), 4.98 (t,
1H, J2,3 = 9.8 Hz, 2-H), 3.95 (dd, 1H, 3-H), 1.13 – 1.05 (3
× s, 27H, C(CH3)3). – C34H46O8S (614.8): calcd. C 66.43,
H 7.54, S 5.21; found C 66.40, H 7.27, S 4.97.
Pivaloylation of 4,6-O-benzylidene-thio-galacto-
pyranosides
Phenyl 3-O-allyl-4,6-O-benzylidene-1-thio-galactopyrano-
side (22)
A solution of 20 (3.0 g, 9.6 mmol), α, α-dimethoxy-
To the phenyl 4,6-O-benzylidene-thio-galactopyranoside
toluene (1.7 ml, 11.1 mmol) and p-toluenesulf◦onic acid in (ca. 0.5 mmol) in pyridine (20 ml) pivaloyl chloride (1.5 g,
dimethylformamide (50 ml) was stirred at 35 C in vacuo 12 mmol) was added. After stirring for 20 h, pyridine
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M. Oßwald et al. · Regioselective Glycosylation of Glucosamine and Galactosamine Derivates
was evaporated in vacuo, two codistillations with toluene (s, 1H, 5’-H), 3.59 (s, 1H, 5-H), 3.47 (s, 3H, OCH3), 3.44
(10 ml) were carried out, the residue was dissolved in di- (dd, J1,2 = 8.1 Hz, J2,3 = 10.6 Hz, 2-H). – 13C NMR (DMSO-
ethyl ether (50 ml) and the solution was washed with 2 N d6): δ = 101.98 (C-1), 100.63 and 99.62 (2 × CHPh), 99.28
HCl (30 ml), sat. NaHCO3 solution (30 ml) and water. After (C-1’). – C39H45N3O11 (731.8): calcd. C 64.01, H 6.22,
drying with MgSO4 and evaporation of the solvent in vacuo, N 5.74; found C 63.87, H 6.16, N 6.00.
the crude product was purified by flash-chromatography in
Methyl 2-azido-3-O-(3-allyl-4,6-O-benzylidene-2-O-
pivaloyl-β-D-ga1actopyranosyl)-4,6-O-benzylidene-2-
deoxy-α-D-galactopyranoside (26)
light petroleum/ethyl acetate (4:1).
Phenyl 3-O-allyl-4,6-O-benzylidene-2-O-pivaloyl-1-thio-β-
D-galactopyranoside (24)
In analogy to the preparation of 27, compound 26 was
synthesised from 24 (1.30 g, 1.23 mmol), 6a (0.38 g,
The compound was obtained according to the general
1.23 mmol) and 2.6 g (1.0 mmol) DMTST. Yield: 0.45 g
procedure from 22 (1.5 g, 4.7 mmol). Yield: 2.0 g (87%),
◦
(66%); colourless solid, m.p. 186 – 188 C; [α]2D2 = +147.7
◦
colourless crystals, m. p. 132 – 133 C; [α]2D2 = −9.5 (c 1,
(c 1, CHCl3); Rf = 0.29 (light petroleum/ethyl acetate 1:2). –
1H NMR (CDCl3): δ = 5.55 (s, 1H, CHPh), 5.53 (s, 1H,
CHPh’), 5.35 (dd, 1H, J1,2 = 7.9 Hz, J2,3 = 10.1 Hz, 2’-H),
4.92 (d, 1H, J1,2 = 3.3 Hz, 1-H), 4.88 (d, 1H, J1,2 = 7.9 Hz,
CHCl3); Rf = 0.83 (light petroleum/ethyl acetate 1:2). –
1H NMR (DMSO-d6): δ = 5.61 (S, 1H, CHPh), 5.06 – 4.97
(m, 2H, 1-H, 2-H), 4.46 (d, 1H, J3,4 = 3.2 Hz, 4-H). –
13C NMR (DMSO-d6): δ = 132.91(Cipso of SPh), 116.29
(=CH2), 99.79 (CHPh), 84.24 (C-1). – C27H32O6S (484.6):
calcd. C 66.92, H 6.66, S 6.62; found C 66.94, H 6.57, S 6.68.
1’-H), 4.44 (d, 1H, J3,4 = 3.1 Hz, 4’-H), 3.77 (dd, 1H, J1,2
=
3.3 Hz, J2,3 = 10.7 Hz, 2-H), 3.59 (dd, 1H, 3’-H), 3.44 (s, 3H,
OCH3). – 13C NMR (CDCl3): δ = 101.05 (C-1’), 100.66,
100.35 (2 × CHPh), 99.97 (C-1). – C35H43N3O11 (681.7):
calcd. C 61.66, H 6.36, N 6.16; found C 61.67, H 6.28,
N 6.11.
Phenyl 3-benzyl-4,6-O-benzylidene-2-O-pivaloyl-1-thio-β-
D-galactopyranoside (25)
The compound was obtained according to the general pro-
cedure from 23 (0.30 g, 0.66 mmol). Yield: 0.2 g (59%),
colourless crystals, m. p. 153 – 154 ◦C; [α]D22 = −4.1 (c 0.5,
CHCl3); Rf = 0.43 (light petroleum/ethyl acetate 1:2). – 1H
NMR (DMSO-d6): δ = 5.64 (s, 1H, CHPh), 5.07 (t, 1H,
J1,2 = J2,3 = 9.8 Hz, 2-H), 5.01 (d, 1H, 1-H), 4.54 (d, 1H,
J3,4 = 3.2 Hz, 4-H), 3.85 (dd, 1H, J2,3 = 9.3 Hz, 3-H), 3.77 (s,
1H, 5-H). – 13C NMR (DMSO-d6): δ = 132.91 (Cipso, SPh),
99.81 (CHPh), 84.21 (C-1). – C31H34O6S (534.7): calcd.
C 69.64, H 6.41, S 6.00; found C 69.62, H 6.45, S 6.34.
O-(2,3,4,6-Tetra-O-pivaloyl-α/β-D-galactopyranosyl)
trichloroacetimidate (28a/b)
2,3,4,6-Tetra-O-pivaloyl-D-galactopyranose:
Pivalo-
ylbromogalactose 2 (1.5 g, 2.59 mmol) was dissolved
in acetone (10 ml) and water (0.18 ml). At 0 ◦C silver
carbonate was added. After stirring for 30 min. and filtration
through silica gel, the solvent was evaporated in vacuo to
give the crude tetra-pivaloylgalactose quantitatively: 1.3 g,
[α]2D2 = +51.9 (c 1, CHCl3).
The compound was carefully dried. To this compound
(0.8 g, 1.56 mmol) in dichloromethane (5 ml), trichloroace-
tonitrile (0.46 ml, 4.6 mmol) was added dropwise. Subse-
Methyl 2-azido-(3-O-benzyl-4,6-O-benzylidene-2-O-
pivaloyl- βD-galactopyranosyl)-4,6-O-benzylidene-2-
deoxy-β-D-galactopyranoside (27)
To a suspension of 25 (1.3 g, 2.4 mmol), 6b (0.6 g, quently, dried potassium carbonate (0.36 g) was added. Af-
R
ter stirring for 24 h and filtration through Celiteꢀ, the sol-
˚
1.95 mmol) and molecular sieves 4 A in dry dichloromethane
vent was evaporated in vacuo, and the product was purified
(30 ml) under argon atmosphere, 2,6-di-tert-butyl-pyridine
(0.5 ml, 2.5 mmol) and dimethyl methylthiosulfonium triflu- by chromatography in light petroleum/ethyl acetate (7:1) to
give 28a/b (α : β = 1:3) as a colourless solid. Yield: 0.89 g
(86%), Rf = 0.50, α-anomer (28a), 0.38, β-anomer (28b)
(light petroleum/ethyl acetate 6:1). C18H44NO10Cl3 (661.0):
calcd. C 50.88, H 6.71, N 2.12; found C 51.16, H 6.65,
N 2.38.
oromethanesulfonate (DMTST) [24] (0.52 g, 2 mmol) were
added. After stirring for 2 h at room temperature, filtration
R
through Celiteꢀ and evaporation of the solvent from the fil-
trate, the crude product was dissolved in ethyl acetate. After
dropwise addition of light petroleum, the crystalline product
27 precipitated. Yield: 1.17 g (82%); m. p. > 250 ◦C; [α]D22
=
For further identification, the anomers were separated by
column chromatography: α-anomer (28a): [α]2D2 = +80.4
+47.9 (c 1, CHCl3); Rf = 0.48 (light petroleum/ethyl acetate
1:2).- H NMR (DMSO-d6): δ = 5.66 (s, 1H, CHPh), 5.62 (c 1, CHCl3); 1H NMR (CDCl3): δ = 8.64 (s, 1H, NH), 6.59
1
(s, 1H, CH’Ph), 5.02 (dd, 1H, J1,2 = 8.1 Hz, J2,3 = 10.1 Hz, (d, 1H, J1,2 = 3.7 Hz, 1-H), 5.56 (dd, 1H, J3,4 = 3.2 Hz, J4,5
=
2’-H), 4.84 (d, 1H, 1’-H), 4.41 (d, 1H, J1,2 = 8.0 Hz, 1-H), 1.1 Hz, 4-H), 5.53 (dd, 1H, J2,3 = 10.6 Hz, 3-H), 5.39 (dd,
4.37 (d, 1H, J3,4 = 3.4 Hz, 4-H), 3.81 (dd, 1H, J2,3 = 10.1 Hz, 1H, 2-H). β-anomer (28b): [α]2D2 = +6.7 (c 1, CHCl3); – 1H
J3,4 = 3.5 Hz, 3’-H), 3.70 (dd, 1H, J2,3 = 10.5 Hz, 3-H), 3.66 NMR (CDCl3): δ = 8.67 (s, 1H, NH), 5.94 (d, 1H, J1,2
=
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773
8.2 Hz, 1-H), 5.48 – 5.43 (m, 2H, 4-H, 2-H), 5.19 (dd, 1H, acetate 1:1). – 1H NMR (CDCl3) δ = 5.68 (d, 1H, J = 6.7 Hz,
J2,3 =10.3 Hz, J3,4 = 3.3 Hz, 3-H).
NH), 5.54 (s, 1H, CHPh), 5.29 (dd, 1H, J3,4 = 3.3 Hz, J4,5 =
2.4 Hz, 4’-H), 5.19 (d, 1H, J1,2 = 3.4 Hz, 1-H), 5.10 (dd,
1H, J1,2 = 7.5 Hz, J2,3 = 10.3 Hz, 2’-H), 5.02 (dd, 1H, 3’-
H), 4.84 (d, 1H, J1,2 = 7.5 Hz, 1’-H), 4.66 and 4.43 (2 ×
2-Methyl-4,5-(5,6-isopropylidene-α-D-glucofurano)-∆2-
oxazoline (30)
d, 2x1H, Jgem = 11.5 Hz, CH2-Ph), 4.23 (dd, 1H, J5,6a
=
To a stirred solution of N-acetyl-glucosamine [25] (29)
(6.6 g, 30 mmol) in dry acetone (300 ml) at 0 ◦Cboron tri-
fluoride etherate (1.32 ml, 3.5 equivalents) was added drop-
wise. After stirring for some hours at room temp., 29 was
completely dissolved. After stirring for 24 h, the deeply red
solution was poured into 2 N sodium hydroxide solution
(250 ml). The solution was extracted with chloroform (5
× 100 ml), the combined organic layers were dried with
MgSO4, and the solvents were evaporated in vacuo. Purifi-
cation of the brown oil was achieved by chromatography
in toluene/ethanol (6:1) on 300 g of silica gel. This chro-
matography was repeated and gave 30 as a colourless oil.
Yield: 4.2 g (60%), [α]2D2 = −3.3 (c 1, CHCl3); Rf = 0.51
4.2 Hz, J6a,6b = 9.9 Hz, 6a-H), 4.14 (m, 1H, 2-H), 4.03-3.93
(m, 3H, H-3, 6’-H), 3.86 (m, 1H, 5-H), 3.80 – 3.70 (m, 2H, H-
4, 6b-H), 3.67 (m, 1H, 5-H). – 13C NMR (CDCl3): δ = 100.4
(C-1’), 97.4 (C-1). – C48H67NO15 (898.1): calcd. C 64.20,
H 7.52, N 1.56; found C 64.04, H 7.65, N 1.78.
α-anomer (32a): Yield: 0.57 g (17%); colourless oil,
[α]2D2 = +73.9 (c 1, CHCl3; Rf = 0.56 (light petroleum/ethyl
acetate 1:1). – 1H NMR (CDCl3): δ = 5.89 (s, 1H, NH), 5.66
(d, 1H, J1,2 = 3.5 Hz, 1’-H), 5.44 (m, 2H, 4’-H, CHPh), 5.28
(dd, 1H, J3,4, 3.0 Hz, J2,3 = 10.5 Hz, 3’-H), 5.22 (dd, 1H,
J2,3 = 10.9 Hz, 2’-H), 4.86 (d, 1H, J1,2 = 3.9 Hz, 1-H), 4.68
(d, 1H, Jgem = 12 Hz, CH2a-Ph), 4.49 (m, 2H, CH2bPh, 5’-H),
4.42 (m, 1H, 2-H), 4.20 (dd, 1H, J3,4 = 10.3 Hz, J4,5 = 4.8 Hz,
4-H), 4.13 (dd, 1H, J5,6a = 8.2 Hz, J6a,6b = 11.4 Hz, 6a’-
1
(toluene/ethanol 3:1). H NMR (CDCl3): δ = 6.10 (d, 1H,
J1,2 = 5.1 Hz, 1-H), 4.43 (s, 1H, OH), 4.37 (m, 1H, 2-H),
4.30 – 4.25 (m, 2H, 3-H, 5-H), 4.06 (dd, 1H, J5,6a = 6.2 Hz,
J6a,6b = 8.8 Hz, 6a-H), 3.95 (dd, 1H, J5,6b = 4.9 Hz, 6b-H),
3.67 (dd, 1H, J4,5 = 7.8 Hz, J3,4 = 2.8 Hz, 4-H), 1.96 (d, 3H,
5JCH3,H−2 = 1.2 Hz, CH3-oxazoline), 1.35 and 1.28 (2 × s, 2
× 3H, CH3-isopropylidene); 13C NMR (CDCl3): δ = 167.0
(C=N), 109.3 (isopropylidene), 107.1 (C-1), 81.8 (C-2), 14.0
(CH3-CN). – C11H17NO5 (243.26): calcd. C 54.31, H 7.04,
N 5.76; found C 54.31, H 7.38, N 5.69.
H), 4.04 (dd, 1H, J2,3 = 9.0 Hz, 2-H), 3.92 (dd, 1H, J5,6b
=
6.3 Hz, 6b’-H), 3.86 (m, 1H, 5-H), 3.75 – 3.64 (m, 2H, 6-
H). – 13C NMR (CDCl13): δ = 97.1 (C-1), 96.0 (C-1’). –
C48H67NO15 (898.1): calcd. C 64.04, H 7.52, N 1.56; found
C 64.93, H 7.60, N 1.77.
Ethyl 4,6-O-benzylidene-2-deoxy-2-phthalimido-3-O-
(2,3,4,6-tetra-O-pivaloyl-β-D-galactopyranosyl)-1-thio-
β-D-glucopyranoside (34)
Benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-3-O-
(2,3,4,6-tetra-O-pivaloyl-β-D-galactopyranosyl)-α-D-
glucopyranoside (32b) and the corresponding (- - -α-D-
galactopyranosyl)-α-D-glucopyranoside (32a)
To a solution of ethyl 4,6-O-benzylidene-2-deoxy-2-
phthalimido-1-thio-β-D-glucopyranoside [26] (33) (5 g,
11.3 mmol) and ethyldiisopropylamine (Huenig’s base,
2.6 ml, 15.2 mmol) in dry dichloromethane (250 ml) un-
˚
In a brown glass flask under argon atmosphere, ben-
zyl 2-acetamido-4,6-O- benzylidene-2-deoxy-α-D-gluco-
pyranoside [20] (31) (1.5 g, 3.76 mmol) and pivalobro-
mogalactose 2 (2.9 g, 5 mmol) were dissolved in dry
der argon atmosphere molecular sieves 4 A were added. Af-
ter stirring for 30 min silver triflate (3.9 g, 15.2 mmol) was
added, and subsequently a solution of 2 (8.5 g, 14.7 mmol)
in dry dichloromethane (100 ml). After 6 h additional AgOTf
(1.95 g, 7.6 mmol), Huenig’s base (1.3 ml, 7.6 mmol)
and subsequently (2) (4.25 g, 7.3 mmol) dissolved in
dichloromethane (50 ml) were added. The stirring was con-
˚
dichloromethane (30 ml). Molecular sieves 4 A were added
◦
to the stirred solution. After cooling to 10 C, silver tri-
flate (1.3 g, 5 mmol) and tetramethyl urea (TMU, 1.35 g,
12 mmol) dissolved in dry dichloromethane (20 ml) were
added dropwise. The mixture was stirred at room temp. for
6 h, then additional galactosyl bromide 2 (1.45 g, 2.5 mmol),
AgOTf (0.65 g, 2.5 mmol) and TMU (0.7 g, 6 mmol) were
added. After 28 h the conversion was complete, the mixture
R
tinued for 24 h. The mixture was filtered through Celiteꢀ,
the solution washed with water (100 ml), 2 N HCl (300 ml),
sat. NaHCO3 solution (300 ml) and water and dried with
MgSO4. The solvent was evaporated in vacuo and the residue
was purified in two portions by chromatography on silica
gel (200 g) in light petroleum/ethyl acetate (8:1) to give 34.
Yield: 7.7 g (72%); colourless amorphous solid; [α]2D2 = +2.8
(c 1, CHCl3); Rf = 0.59 (light petroleum/ethyl acetate 2.5:1).
The separated α-anomer (ratio α : β < 1:22, HPLC) has
Rf = 0.61. – 1H NMR (CDCl3): δ = 5.53 (s, 1H, CHPh),
5.26 (d, 1H, J1,2 = 10.6 Hz, 1-H), 5.20 (dd, 1H, J3,4 = 3.1 Hz,
R
was filtered through Celiteꢀ, the filtrate dried with MgSO4
and the solvent evaporated in vacuo. Purification and sepa-
ration was achieved by chromatography on silica gel (300 g)
in light petroleum/ethyl acetate (2:1). If necessary, a second
chromatography in light petroleum/ethyl acetate (3:1) is car-
ried out.
β-anomer (32b): Yield: 2.63 g (79%); colourless oil; J4,5 = 0.8 Hz, 4’-H), 4.93 (dd, 1H, J2,3 = 10.3 Hz, J1,2
=
[α]2D2 = +34.5 (c 1, CH Cl3); Rf = 0.51 (light petroleum/ethyl 7.6 Hz, 2’-H), 4.88-4.82 (m, 2H, 3’-H, 3-H), 4.66 (d, 1H,
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M. Oßwald et al. · Regioselective Glycosylation of Glucosamine and Galactosamine Derivates
1’-H), 4.45 (t, 1H, 2- H), 4.36 (dd, 1H, J5,6a = 4.8 Hz, J6a,6b
=
As a by-product, the corresponding orthoester was iso-
10.4 Hz, 6a-H), 3.99 (m, 2H, 6’-H), 3.88 – 3.78 (m, 2H, 4-H, lated: [α]2D2 = +7.1 (c 1, CHCl3); Rf = 0.64 (light
petroleum/ethyl acetate 2:1). – 1H NMR (CDCl3): δ = 5.41
6b-H), 3.67 (m, 1H, 5-H), 3.55 (m, 1H, 5’-H), 2.69 – 2.58 (m,
2H, CH2S). – 13C NMR (CDCl3): δ = 101.8 (CHPh), 98.8
(d, 1H, J1,2 = 4.0, 1’-H), 5.37 (d, 1H, J1,2 = 10.6 Hz, 1-H).
(C-1’), 82.0(C-1). – C49H65NO15S (940.0): calcd. C 62.61,
–
13C NMR (CDCl3): δ = 129.8 (CO3-orthoester), 101.1
H 6.97, N 1.49; found C 62.62, H 7.00, N 1.52.
(CHPh), 95.8 (C-1’), 81.9 (C-1).
[13] a) H. Paulsen, M. Paal, Carbohydr. Res. 135, 71 (1984);
b) H. Paulsen, S. Peters, T. Bielfeldt, M. Meldal,
K. Bock, Carbohydr. Res. 268, 17 (1995).
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Carbohydr. Res. 310, 157 (1998); b) T. Mu¨ller, G. Hum-
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[18] Y. Tsuda, M. E. Haque, K. Yoshimoto, T. Kikuchi,
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