A novel general route for the synthesis of C-glycosyl tyrosine analogues.

Article abstract of DOI:10.1002/1521-3765(20020415)8:8<1872::AID-CHEM1872>3.0.CO;2-A

A general method for the synthesis of C-glycosyl amino acids is described here. The stereoisomerically pure tyrosine analogues alpha-L-4 and beta-L-6 are prepared in reasonable overall yields from allyl derivatives 10 and 11. The key step is a benzannulation procedure which is employed in the creation of the aromatic ring that bears the amino acid function.

Full text of DOI:10.1002/1521-3765(20020415)8:8<1872::AID-CHEM1872>3.0.CO;2-A

FULL PAPER
A Novel General Route for the Synthesis of C-Glycosyl Tyrosine Analogues
Elisabetta Brenna,* Claudio Fuganti, Piero Grasselli, Stefano Serra, and
Sabrina Zambotti[a]
Abstract: A general method for the synthesis of C-glycosyl amino acids is described
here. The stereoisomerically pure tyrosine analogues a-l-4 and b-l-6 are prepared in
Keywords: amino acids ¥ annulation
reasonable overall yields from allyl derivatives 10 and 11. The key step is a
¥ C-glycosides ¥ glycopeptides
benzannulation procedure which is employed in the creation of the aromatic ring that
bears the amino acid function.
easily applied to prepare other tyrosine analogues that have
different glycan moieties, or to vary the spacer units between
Introduction
It has been established that glycopeptides play a central role
in biological recognition processes,[1] and there is increasing
interest in their employment as pharmaceuticals. This ap-
proach is limited by the inherent instability of the O-glycosyl
linkage in vivo: The lifetime of glycopeptide drugs could be
increased by thwarting the enzymatic cleavage of the glycan
from the peptide backbone. It has been observed that
resistance to enzymatic hydrolysis could be achieved either
the sugar and the amino acid. As a matter of fact, for the
formation of the functionalised aromatic ring we employed a
benzoannulation procedure we had previously optimised,[8]
and had already applied to the synthesis of C-glycoside 7.[9]
by preparing non-natural O-glycosyl amino acids,[2] by sub-
[3]
À
À
À
stituting the glycosidic C O bonds with C C or C S bonds,
or by replacing the sugar moiety with a cyclohexane ring
which bears suitable hydroxylic functions.[4]
The syntheses of several anomeric C-glycosyl a-amino acids
have been recently reviewed.[5] In the case of derivatives of
the aromatic series, only one paper is devoted to the
preparation of C-glycosyl tyrosines of the general structure
type 1, which possess a methylene group instead of the
phenolic oxygen of tyrosine.[6] Prior to this work, a series of
phenylalanine-containing C-glycosides of structure type 2,
which are based on a two-carbon alkyne-linkage, had been
prepared.[7]
In this paper we report on the preparation of a- and b-C-
glucosyl tyrosine analogues 3 6, which have a hydroxyl
function on the aromatic ring. The extra phenolic group is a
consequence of the chemistry used to build the arene, but it
can be conveniently exploited for further derivatisation of the
substrate with a sugar moiety. We have devised a quite general
route for the synthesis of derivative 3 6, which could be
[a] Dr. E. Brenna, Prof. C. Fuganti, Prof. P. Grasselli,
Dr. S. Serra, Dr. S. Zambotti
Dipartimento di Chimica del Politecnico
Centro CNR per lo Studio delle Sostanze Organiche Naturali
Via Mancinelli 7, 20131 Milano (Italy)
Fax : (‡39)0223-993-080
Results and Discussion
Synthesis of the aromatic moiety: In the known examples of
C-glycosyl tyrosine of structural formula 1 the aromatic
E-mail: brenna@dept.chem.polimi.it
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Chem. Eur. J. 2002, 8, No. 8

1872 1878
moiety was introduced with the formation of the crucial
C-glycoside linkage by the addition of an organozinc species
to a glucal derivative. The authors observed that the a/b
selectivity associated with this C-glycosylation method dra-
matically depended on the nature of the sugar component. We
preferred a different approach (Scheme 1), which is based on
the formation of the aromatic ring after the establishment of
the anomeric linkage, in order to optimise a general synthetic
path to both a- and b-C-glycosyl amino acids. We took
advantage of our experience in the reaction of 3-alkoxycar-
ketal. The reaction of allylmagnesium chloride with the
lactone 13 in THF, which is followed by treatment with
Et3SiH, gave the b-allyl glucoside 11 with 99% stereoselec-
tivity (1H NMR)[12] (Scheme 2).
The derivatives 12 and 13 were prepared from methyl a-d-
glucopyranoside according to the known routes,[14] as shown in
Scheme 2.
Compounds 10 and 11 were manipulated separately
through conventional organic reactions to provide the mono-
ester and monoacid derivatives 8 and 9 (Scheme 3), respec-
bonyl-3,5-hexadienoic
acids
with ethyl chloroformate in
THF in the presence of triethyl-
amine. This reaction gave 3-hy-
droxy-benzoate ester deriva-
tives from a benzoannulation
mechanism. The application of
this synthetic scheme required
the preparation of monoester
monoacid derivatives 8 and 9,
as shown in Scheme 1. The a-
and b-allyl glucosides 10 and 11,
which have a well-defined con-
figuration at the anomeric car-
bon atom, were envisaged as
suitable precursors of the key
OBn
OBn
O
O
BnO
BnO
BnO
BnO
BnO
BnO
10
NHCOCH3
BnO
CH2CH
3, 4
COOH
OBn
OBn
O
O
BnO
BnO
benzoannulation
procedure
BnO
BnO
BnO
BnO
8
HO
COOEt
COOH
COOEt
23
intermediates
(Scheme 1).
8
and
9
OBn
O
COOH
OBn
BnO
BnO
O
benzoannulation
procedure
BnO
BnO
Two common reactions of
sugar chemistry that allow high
stereochemical control on the
configuration of the anomeric
carbon atom were employed
(see Scheme 2). From the meth-
odologies for the preparation of
a-C-glycosides,[10] we chose the
acid-catalysed addition report-
ed by Giannis et al.[11] Treat-
ment of acetyl derivative 12
with allyltrimethylsilane in ace-
tonitrile in the presence of BF3 ¥
Et2O at 48C afforded 10 with
high stereoselectivity (>99%,
1H NMR)[12] (Scheme 2). The
reaction requires the presence
of an acyl group at the anome-
ric carbon atom and is applica-
ble to a variety of glycopyrano-
sides and to disaccharides.[11]
Several methods are availa-
ble for the installation of car-
bon functionality to glycosides
with exclusive equatorial selec-
tivity.[10] We chose the approach
of Kishi et al.,[13] which consists
of a Grignard addition to a
perbenzylated sugar lactone,
and which is followed by deoxy-
genation of the resulting hemi-
COOEt
OBn
OBn
9
HO
COOEt
24
OBn
OBn
O
BnO
BnO
O
BnO
BnO
NHCOCH3
CH2CH
COOH
OBn
BnO
OBn
11
5, 6
Scheme 1. Synthetic procedure to derivatives 3 6.
OBn
O
OBn
O
v
BnO
BnO
BnO
BnO
BnO
BnO
OAc
12
10
iii
OBn
O
OBn
O
OH
i
ii
BnO
BnO
O
BnO
BnO
HO
HO
BnO
BnO
OH
OMe
OH
OMe
iv
OBn
OBn
O
OBn
O
O
vi
vii
OH
BnO
BnO
BnO
BnO
BnO
BnO
BnO
OBn
BnO
O
11
13
Scheme 2. i) Benzyl chloride, KOH, dioxane; ii) H2SO4, 4n acetic acid; iii) Ac2O, pyridine; iv) CrO3, H2SO4;
v) allyltrimethylsilane, BF3 ¥ Et2O, acetonitrile, 48C; vi) allylmagnesium chloride; vii) Et3SiH, BF3 ¥ Et2O.
Chem. Eur. J. 2002, 8, No. 8
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1873

E. Brenna et al.
FULL PAPER
lithium aluminum hydride re-
duction to afford alcohols 29
and 30, which were immediate-
ly brominated with PPh3 and
NBS in order to provide com-
pounds 25 and 26, respectively.
The reaction of 25 and 26 with
diethyl acetamidomalonate in
DMF solution with NaH as a
base, proceeded rapidly and
produced high yields. Treat-
ment of 31 and 32 with sodium
hydroxide in refluxing ethanol
gave a 1:1 mixture of the two
possible diastereoisomeric N-
acetamido acids, both in the a-
ˆ
Scheme 3. i) ozone, CH2Cl2/MeOH 1:1 v/v, then PPH3; ii) PPh3 CHCOOEt, toluene; iii) DIBAL, toluene,
À788C; iv) manganese(iv)oxide, CH2Cl2; v) betaine 22, CH2Cl2; vi) ethyl chloroformate, Et3N, THF.
tively. Ozonolysis of both C-allyl glucosides in methanol/
methylene chloride (1:1 v/v) gave the aldehydes 14 and 15,
after the reaction was quenched with triphenylphosphine.
Compounds 14 and 15 were condensed with (triphenyl-l5-
phosphanylidene)-acetic ethyl ester to afford the unsaturated
ethyl esters 16 and 17. Reduction with diisobutyl aluminum
hydride and oxidation of allylic alcohols 18 and 19 with
manganese(iv) oxide in methylene chloride gave unsaturated
aldehydes 20 and 21, which were treated with betaine 22[15] to
introduce the last functionalised double bond and obtain the
monoester monoacid derivatives 8 and 9. The E-configuration
was assigned to this new double bond on the basis of previous
studies on the stereochemistry of the Wittig reaction of
betaine 22 with aldehydes.[15b,c] This reaction gives 3-(E)-
alkylidenesuccinic acid derivatives with high diastereoselec-
tivity.
(3 and 4) and in b-series (5 and 6). Separation of a-d-3 from its
diastereoisomer a-l-4 and of b-d-5 from its diastereoisomer
b-l-6 was thus required.
Enzymatic deacylation: The two mixtures of a-d,l- and b-d,l-
stereoisomeric N-acetamides were submitted separately to
enzymic deacetylation at 258C in the presence of acylase I
from Aspergillus species; the pH was maintained at 7.8 by
addition of 0.02m NaOH. The reactions were monitored by
NMR spectroscopy. The signals of the methyl group of the
acetamido moieties appeared at: CH3CONH d(3) ˆ 1.83,
d(4) ˆ 1.86 for the a-stereoisomers, d(5) ˆ 1.80, d(6) ˆ 1.82
for the b-stereoisomers. When no further evolution in the
ratio of the two integrals was observed, the enzymatic
reactions were stopped (48 h in both cases).
Compounds 8 and 9 rapidly underwent reaction with ethyl
chloroformate in THF in the presence of triethylamine to
provide the desired aromatic derivatives 23 and 24 in high
yields.
Acylase I is a widely applicable enzymatic catalyst for the
kinetic resolution of unnatural and rare a-amino acids.[17] It
promotes the hydrolysis of N-acetylated amino acids with l-
configuration and accepts substrates that have a wide range of
structure and functionality.[17] Thus, the two N-acetyl l-amino
acids 4 and 6, both with diastereomeric excess (de) >99%
(1H NMR), were recovered from the water phase after
suitable treatment with acetic anhydride at pH 8 (see
Experimental Section). The two unreacted N-acetyl d-amino
acids 3 and 5 were found to contain 24 and 13%, respectively,
of the corresponding l epimer. The stereoisomers 3 6 were
converted into the corresponding methyl esters by diazo-
methane treatment for optical and spectroscopic character-
isation.
Synthesis of the amino acid functionality: In the synthesis of 1,
the introduction of the amino acid moiety was achieved using
the so-called Jackson method, involving a Pd0-mediated
coupling with an enantiomerically pure zinc reagent which
already bears the amino acid function.[6] Amino acid deriv-
atives in diastereoisomerically pure form were obtained, but
we found that the efficiency of the transformation was
extremely sensitive to reaction conditions. We chose a differ-
ent approach based on the reaction of the bromo derivatives
25 and 26 with diethyl acetami-
do malonate[16] (Scheme 4).
This implied a further step to
separate the d and l stereo-
isomers of both the a and b
series.
The phenolic group was pro-
tected as a benzyl ether by
reaction of compounds 23 and
24 with potassium carbonate
and benzyl bromide in acetone
solution. These derivatives 27
and 28 were then submitted to
Scheme 4. i) K2CO3, benzyl bromide, acetone; ii) LiAlH4, THF; iii) PPh3, NBS, THF; iv) diethyl acetamido-
malonate, NaH, DMF; v) NaOH, ethanol.
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C-Glycosyl Tyrosine Analogues
1872 1878
hexane/ethyl acetate 7:3 v/v. Compound 10 was isolated as a white solid
(43.16 g, 89%). M.p. 608C (lit.[18] 64 658C), [a]2D0 ˆ 34.2 (c ˆ 1.02 in
CHCl3);[18] [a]D ˆ 36.5, c ˆ 2.19 in CHCl3); 1H NMR (250 MHz, CDCl3,
Conclusion
A general method for the synthesis of C-glycosyl amino acid
was developed, and here described for the preparation of
stereoisomerically pure tyrosine analogues a-l-4 and b-l-6 in
reasonable overall yields from allyl derivatives 10 and 11.
The application of the annulation procedure allowed us to
build the aromatic ring, after the anomeric linkage had been
created under strict stereochemical control through well-
established reactions of carbohydrate chemistry. Thus, the
glycosyl moiety can be easily modulated and both a- and b-
derivatives can be prepared as single diastereoisomers.
The method is very flexible and can be applied to the
synthesis of other C-glycosyl amino acids with different
spacers between the sugar moiety and the aromatic amino
acid. For example, it is possible to increase or decrease the
number of the methylene units that separate the sugar moiety
from the pseudo-tyrosine fragment. The key step is the
preparation of the unsaturated aldehydes to be submitted to
condensation with the betaine 22, in order to afford the
monoester monoacid substrates for benzoannulation proce-
dure. Indeed, the application of the same sequence to
derivative 7 allows us to successfully prepare b-C-glucosyl-3-
hydroxyphenylalanine.
ˆ
258C, TMS): d ˆ 7.5 7.0 (m, 20H; 4C6H5), 5.82 (m, 1H; CH CH2), 5.11
ˆ
(dd, J ˆ 13, 1.7 Hz, 1H; CH CHH), 5.06 (dd, J ˆ 6, 1.7 Hz, 1 H;
ˆ
CH CHH), 5.00 4.40 (m, 8H; 4CH2Ph), 4.13 (m, 1H; H-Canomeric),
ˆ
3.90 3.50 (m, 6H; sugar moiety), 2.47 (m, 2H; CH2CH CH2); elemental
analysis calcd (%) for C37H40O5 (564.7): C 78.69, H 7.14; found: C 78.64, H
7.20.
1-(2,3,4,6-Tetra-O-benzyl-b-d-glucopyranos-1-yl)-2-propene (11): Lactone
13 was azeotroped with toluene prior to use.
A 2 m solution of
allylmagnesium chloride in THF (70 mL, 0.139 mol) was added to a
solution of lactone 13 (50.0 g, 0.093 mol) in THF (300 mL) at À788C. The
reaction mixture was stirred at À788C for 2 h, treated with a 5% NH4Cl
solution, and extracted with ethyl acetate. The residue, which consisted
mainly of 1-hydroxy-1-(2,3,4,6-tetra-O-benzyl-d-glucopyranosyl)-2-pro-
pene, (49.1g, 91%) was azeotroped with toluene and used as obtained.
Et3SiH (29.3 g, 0.252 mol) and BF3 ¥ Et2O (21.3 mL) were added to a
solution of 1-hydroxy-1-(2,3,4,6-tetra-O-benzyl-d-glucopyranosyl)-2-pro-
pene (49.1g, 0.084 mol) in methylene chloride (400 mL) at À788C. The
reaction was stirred at À788C for 12 h. Saturated aqueous NaHCO3 was
added, and the reaction mixture extracted with CH2Cl2. The solid residue
was recrystallised from hexane/ethyl acetate (95:5 v/v) to give derivative 11
(37.1g, 78%). M.p. 85 8C (lit.: 91 92 8C)[19]; [a]D20 ˆ 15.6 (c ˆ 1.11 in CHCl )
3
(lit.: [a]D20 ˆ 13.5)[19]; 1H NMR (250 MHz, CDCl3, 258C, TMS): d ˆ 7.4 7.0
ˆ
ˆ
(m, 20H; 4C6H5), 5.94 (m, 1H; CH CH2), 5.20 5.00 (m, 2H; CH CH2),
5.00 4.50 (m, 8H; 4CH2Ph), 3.80 3.50 (m, 4H; sugar moiety), 3.41(ddd,
J ˆ 9.4, 4.1, 2.2 Hz, 1 H; sugar moiety), 3.34 (m, 2H; sugar moiety), 2.60 (m,
ˆ
ˆ
1H; CHHCH CH2), 2.32 (m, 1H; CHHCH CH2); elemental analysis
calcd (%) for C37H40O5 (564.7): C 78.69, H 7.14; found: C 78.73, H 7.22.
The mechanism of the cyclisation route implies the
introduction of a hydroxyl group onto the aromatic ring. This
functional group can be exploited to derivatise the C-glucosyl
4-(2,3,4,6-Tetra-O-benzyl-a-d-glucopyranos-1-yl)-but-2-enoic ethyl ester
(16):[20] A solution of allyl derivative 10 (43.0g, 0.076 mol), in CH2Cl2/
MeOH (1:1 v/v, 150 mL) was treated with ozone at À788C. The reaction
mixture was quenched with triphenylphosphine, warmed to room temper-
ature, and concentrated. The resulting aldehyde 14 was used immediately.
A solution of 14 and of (triphenyl-l5-phosphanylidene)-acetic acid ethyl
ester (40 g, 0.114 mol) in toluene (100 mL) was heated under reflux for 2 h.
The residue was chromatographed and eluted with hexane/ethyl acetate 8:2
v/v to afford ester derivative 16 (24.3 g, 50%). [a]2D0 ˆ 46.6 (c ˆ 1.20 in
CHCl3); 1H NMR (250 MHz, CDCl3, 258C, TMS): d ˆ 7.4 7.1(m, 20H;
À
amino acid with other sugar moieties through a C O
anomeric linkage, in order to investigate the effects of this
double glycosylation. The hydroxylic function can also be
removed, after deprotection by hydrogenolysis, by reduction
of the O-tetrazole derivative,[8] in order to provide carbon-
linked analogue of natural glycoamino acids.
ˆ
4C6H5), 6.95 (dt, J ˆ 6.4, 16.0 Hz, 1H; CH2CH CH), 5.90 (d, J ˆ 16.0 Hz,
ˆ
1H; CH2CH CH), 5.00 4.40 (m, 8H; 4CH2Ph), 4.15 (m ‡ q, J ˆ 7.1Hz,
3H; H-Canomeric, COOCH2CH3), 3.80 3.50 (m, 6H; sugar moiety), 2.62 (m,
Experimental Section
ˆ
2H; CH2CH CH2), 1.26 (t, J ˆ 7 Hz, 3H; COOCH2CH3); elemental
analysis calcd (%) for C40H44O7 (636.8): C 75.45, H 6.96; found: C 75.68,
H 7.08.
General remarks: Acylase I from Aspergillus species (Sigma) was em-
ployed in this work. H NMR spectra were recorded on a Bruker AC-250
(250 MHz, H), or on a Bruker ARX 400 (400 MHz, 1H), or on a Bruker
1
1
4-(2,3,4,6-Tetra-O-benzyl-b-d-glucopyranos-1-yl)-but-2-enoic ethyl ester
(17): The same procedure was used to convert derivative 11 (37 g,
0.066 mol) via aldehyde 15 into ester 17 (22.9 g, 55%). [a]2D0 ˆ À31.3 (c ˆ
Avance 500 (500 MHz, 1H) spectrometer. A pH-Stat 718 Stat Titrino
Metrohm was used to perform enzymatic deacylation. Optical rotations
were measured on a Dr. Kernchen Propol digital automatic polarimeter.
Microanalyses were determined on a Analyzer 1106 Carlo Erba. All the
chromatographic separations were carried out on silica gel columns. In the
NMR assignment, the aromatic ring, which is built by benzannulation, is
referred to as benzene ring A. The numbering of its carbon atoms used in
the NMR description is as specified in the name of the compound itself.
1
1.15 in CHCl3); H NMR (250 MHz, CDCl3, 258C, TMS): d ˆ 7.4 7.1(m,
ˆ
20H; 4C6H5), 6.97 (dt, J ˆ 7.4, 15.7 Hz, 1H; CH2CH CH), 5.82 (d, J ˆ
ˆ
15.7 Hz, 1H; CH2CH CH), 4.90 4.75 (m, 4H; 2CH2Ph), 4.65 4.45 (m,
4H; 2CH2Ph), 4.12 (q, J ˆ 7 Hz, 2H; COOCH2), 3.70 3.55 (m, 4H, sugar
ˆ
moiety), 3.40 3.20 (m, 3H; sugar moiety); 2.63 (m, 1H; CHHCH CH2),
ˆ
2.35 (m, 1H; CHHCH CH2), 1.26 (t, J ˆ 7 Hz, 3H; COOCH2CH3);
elemental analysis calcd (%) for C40H44O7 (636.7): C 75.45, H, 6.96; found:
C 75.53, H 7.11.
2,3,4,6-Tetra-O-benzyl-a-d-glucopyranose was prepared from commercial
starting material, methyl a-d-glucopyranoside, by following the procedure
in ref. [14a]. Acetylation of this derivative in acetic anhydride and pyridine
gave 12.[14b] 2,3,4,6-Tetra-O-benzyl-a-d-glucopyranose was oxidised to
2,3,4,6-tetra-O-benzyl-d-glucono-d-lactone (13) by treatment with Jones
reagent in acetone solution, rather than through the use of DMSO in acetic
anhydride as reported in ref. [14c].
4-(2,3,4,6-Tetra-O-benzyl-a-d-glucopyranos-1-yl)-but-2-en-1-ol (18):[20]
A
1.5 m diisobutyl aluminum hydride in toluene (76 mL, 0.114 mol) was
added dropwise to a solution of the ester, 16 (24.0 g, 0.038 mol), in toluene
(200 mL) at À788C. The reaction was warmed to 258C, treated with water,
filtered through a Celite cake, and extracted with ethyl acetate. The residue
was chromatographed, and eluted with hexane/ethyl acetate 6:4 v/v to give
the allylic alcohol 18 (19.4 g, 86%). M.p. 738C; [a]2D0 ˆ 42.2 (c ˆ 1.26 in
CHCl3) (lit.: [a]2D0 ˆ 44.2, c ˆ 1.56 in CHCl3)[20]; 1H NMR (250 MHz, CDCl3,
1-(2,3,4,6-Tetra-O-benzyl-a-d-glucopyranos-1-yl)-2-propene (10): Allyltri-
methylsilane (19.6 g, 0.172 mol) and boron trifluoride etherate (44 mL,
0.344 mol) were added successively to a solution of derivative 12 (50.0 g,
0.086 mol) in acetonitrile (300 mL) under nitrogen atmosphere at 48C.
After 24 h at 48C, the reaction mixture was poured into a saturated solution
of sodium hydrogen carbonate and extracted with methylene chloride. The
organic phase was dried (Na2SO4) and concentrated under reduced
pressure to give a residue which was chromatographed, eluted with
ˆ
258C, TMS): d ˆ 7.4 7.0 (m, 20H; 4C6H5), 5.70 (m, 2H; CH CH), 5.00
4.35 (m, 8H; 4CH2Ph), 4.15 4.00 (m‡d, J ˆ 5 Hz, 3H; H-Canomeric
,
ˆ
CH2OH), 3.90 3.45 (m, 6H; sugar moiety), 2.47 (m, 2H; CH2CH CH);
elemental analysis calcd (%) for C38H42O6 (594.7): C 76.74, H 7.12; found: C
76.61, H 7.18.
Chem. Eur. J. 2002, 8, No. 8
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1875

E. Brenna et al.
FULL PAPER
4-(2,3,4,6-Tetra-O-benzyl-b-d-glucopyranos-1-yl)-but-2-en-1-ol (19): The
same procedure was used on compound 17 (22.0 g, 0.034 mol) to give
allylic alcohol 19 (18.1 g, 88%): [a]2D0 ˆ 0.4 (c ˆ 1.38 in CHCl3); 1H NMR
(250 MHz, CDCl3, 258C, TMS): d ˆ 7.4 7.1(m, 20H; 4C 6H5), 5.73 (m, 2H;
12 h, diluted with water and extracted with ethyl acetate. The residue was
crystallised from hexane/ethyl acetate 9:1, to afford the benzyl ether-
protected derivative 27 (8.75 g, 85%). M.p. 828C; [a]2D0 ˆ 71( c ˆ 1.01 in
1
CHCl3); H NMR (400 MHz, CDCl3, 258C, TMS): d ˆ 7.61(d, J ˆ 1.5 Hz,
ˆ
CH CH), 4.95 4.75 (m, 4H; 2CH2Ph), 4.70 4.50 (m, 4H; 2CH2Ph), 4.04
1H; H-C2 of benzene ring A), 7.55 (dd, J ˆ 8, 1.5 Hz, 1 H; H-C6 of benzene
ring A), 7.45 7.10 (m, 26H; 5C6H5, H-C5 of benzene ring A), 5.10 (s, 2H;
PhCH2O-C3 of benzene ring A), 4.92 (d, J ˆ 11 Hz, 1H; CHHPh), 4.81(d,
J ˆ 11 Hz, 1H; CHHPh), 4.77 (d, J ˆ 11 Hz, 1H; CHHPh), 4.56 (m, 1H;
H-Canomeric), 4.53 4.30 (m, 7H; 5CHHPh, COOCH2CH3), 3.85 (m, 2H;
sugar moiety), 3.75 (dd, J ˆ 6, 9 Hz, 1H; H-C2 of the sugar moiety), 3.60
3.45 (m, 3H; sugar moiety), 3.28 (dd, J ˆ 3.2, 14.5 Hz, 1H; CHH-Canomeric),
2.99 (dd, J ˆ 11, 14.5 Hz, 1H; CHH-Canomeric), 1.39 (t, J ˆ 7 Hz, 3H;
COOCH2CH3); elemental analysis calcd (%) for C51H52O8 (792.9): C
77.25, H 6.61; found: C 77.46, H 6.75.
(d, J ˆ 6.4 Hz, 2H; CH2OH), 3.80 3.50 (m, 4H; sugar moiety), 3.40 (ddd,
J ˆ 9.8, 4.4, 2.2 Hz, 1H; H-C5 sugar moiety), 3.31(m, 2H; sugar moiety),
ˆ
ˆ
2.56 (m, 1H; CHH CH CH), 2.28 (m, 1H; CHHCH CH); elemental
analysis calcd (%) for C38H42O6 (594.7): C 76.74, H 7.12; found: C 76.85, H
7.05.
7-(2,3,4,6-Tetra-O-benzyl-a-d-glucopyranos-1-yl)-3-ethoxycarbonyl-hep-
ta-3,5-dienoic acid (8):
A mixture of the allylic alcohol 18 (19.0 g,
0.032 mol) and manganese(iv)oxide (1.5 equiv) in methylene chloride
(100 mL) was heated under reflux for 3 h. The reaction mixture was
filtered, and the dissolved aldehyde 20 was used immediately. Betaine 22[15]
(19.7 g, 0.048 mol) was added directly to the aldehyde solution, and the
reaction mixture was heated under reflux for 3 h, concentrated under
reduced pressure, and chromatographed. Elution with hexane/ethyl acetate
1:1 v/v gave the unsaturated acid 8 (14.7 g, 64%). [a]2D0 ˆ 50.3 (c ˆ 1.18 in
CHCl3); 1H NMR (250 MHz, CDCl3, 258C, TMS): d ˆ 7.6 6.9 (m, 21H;
4-(2,3,4,6-Tetra-O-benzyl-b-d-glucopyranos-1-ylmethyl)-3-benzyloxyben-
zoic ethyl ester (28): The same procedure was used to transform derivative
24 (8.0 g, 0.011 mol) into compound 28 (7.56 g, 87%). M.p. 1078C; [a]D20
ˆ
À2.2 (c ˆ 1.96 in CHCl3); 1H NMR (250 MHz, CDCl3, 258C, TMS): d ˆ
7.7 7.1(m, 28H; 3 Â benzene ring A, 5C6H5), 5.13 (m, 2H; PhCH2O-C3 of
benzene ring A), 5.0 4.40 (m, 8H; 4CH2Ph), 4.34 (q, J ˆ 7 Hz, 2H;
COOCH2CH3), 3.80 3.30 (m, 8H; 7 Â sugar moiety, CHH-Canomeric), 2.72
(dd, J ˆ 9.5, 14 Hz, 1H; CHH-Canomeric), 1.39 (t, J ˆ 7 Hz, 3H;
COOCH2CH3); elemental analysis calcd (%) for C51H52O8 (792.9): C
77.25, H 6.61; found: C 77.08, H 6.43.
ˆ
ˆ
ˆ
ˆ
4C6H5, CH CHCH ), 6.36 (dd, J ˆ 11, 15 Hz, 1H; CH CHCH ), 6.18 (dt,
ˆ
ˆ
J ˆ 6, 15 Hz, 1H; CH CHCH ), 5.00 4.40 (m, 8H; 4CH2Ph), 4.17 (m,
3H; H-Canomeric, COOCH2CH3), 3.80 3.25 (m, 8H; 6 Â sugar moiety,
CH2COOH), 2.61(m, 2H;
COOCH2CH3); elemental analysis calcd (%) for C44H48O9 (720.8): C
C
H2-Canomeric), 1.29 (t, J ˆ 7 Hz, 3H;
1-(2,3,4,6-Tetra-O-benzyl-a-d-glucopyranos-1-ylmethyl)-2-benzyloxy-4-
hydroxymethylbenzene (29): A solution of ester 27 (8.50 g, 0.011 mol) in
THF (10 mL) was added dropwise to a suspension of LiAlH4 (1.25 g,
0.033 mol) in THF (100 mL), and the temperature was maintained below
208C. The reaction mixture was stirred at room temperature for 1h. The
usual work-up afforded a solid residue, which was recrystallised from
hexane/ethyl acetate 8:2 v/v to give the alcohol 29 (7.34 g, 89%). M.p.
1028C; [a]2D0 ˆ 63.3 (c ˆ 1.12 in CHCl3); 1H NMR (250 MHz, CDCl3, 258C,
TMS): d ˆ 7.7 7.1(m, 26H; 1  benzene ring A, 5C6H5), 6.95 (d, J ˆ
1.15 Hz, 1 H; H-C of benzene ring A), 6.81(dd, J ˆ 1.15, 8 Hz, 1 H; H-C
73.31, H 6.71; found: C 73.41, H 6.87.
7-(2,3,4,6-Tetra-O-benzyl-b-d-glucopyranos-1-yl)-3-ethoxycarbonyl-hep-
ta-3,5-dienoic acid (9): The same procedure was used to convert the allylic
alcohol 19 (18 g, 0.030 mol) into 9, an unsaturated acid (13.3 g, 61%).
[a]2D0 ˆ À2.3 (c ˆ 0.44 in CHCl3); 1H NMR (250 MHz, CDCl3, 258C, TMS):
d ˆ 7.6 6.9 (m, 21H; 4C6H5, vinylic), 6.30 (m, 2H; vinylic), 5.00 4.50 (m,
8H; 4CH2Ph), 4.24 (m, 2H; COOCH2CH3), 3.80 3.25 (m, 9H; 7 Â sugar
moiety, CH2COOH), 2.70 (m, 1H; CHH-Canomeric), 2.42 (m, 1H; CHH-
Canomeric), 1.31 (t, J ˆ 7 Hz, 3H; COOCH2CH3); elemental analysis calcd
(%) for C44H48O9 (720.8): C 73.31, H 6.71; found: C 73.21, H 6.64.
3
5
of benzene ring A), 5.06 (s, 2H; PhCH2O-C2 of benzene ring A), 5.0 4.30
(m, 11H; 4CH2Ph, H-Canomeric, CH2OH), 3.90 3.45 (m, 6H; sugar moiety),
3.25 (dd, J ˆ 3, 14.5 Hz, 1H; CHH-Canomeric), 2.92 (dd, J ˆ 12, 14.5 Hz, 1H;
CHH-Canomeric); elemental analysis calcd (%) for C49H50O7 (750.9): C 78.37,
H 6.71. found: C 78.19, H 6.56.
4-(2,3,4,6-Tetra-O-benzyl-a-d-glucopyranos-1-ylmethyl)-3-hydroxybenzo-
ic ethyl ester (23): Ethyl chloroformate (2.47 g, 0.023 mol) was dropped
into a solution of the unsaturated acid 8 (14.0 g, 0.019 mol) in THF (35 mL).
Et3N (2.32 g, 0.023 mol) was added, and the temperature maintained below
208C. The reaction mixture was stirred at room temperature for 30 min,
poured into diluted HCl, and extracted with ethyl acetate. The residue was
chromatographed and eluted with hexane/ethyl acetate 9:1 v/v to give
compound 23 (9.20 g, 69%). M.p. 1188C; [a]2D0 ˆ 49.3 (c ˆ 1.03 in CHCl3);
1H NMR (400 MHz, CDCl3, 258C, TMS): d ˆ 7.50 (m, 2H; benzene
ring A), 7.4 7.1(m, 20H; 4C 6H5), 7.09 (d, J ˆ 8 Hz,1H; H-C5 of benzene
ring A), 7.05 (brs, 1H; OH), 4.90 4.40 (m, 8H; 4CH2Ph), 4.34 (q, J ˆ 7 Hz,
2H; COOCH2CH3), 4.27 (m, 1H; H-Canomeric), 4.02 (dt, J ˆ 8.1, 3.5 Hz, 1 H;
H-C5 of the sugar moiety), 3.85 (t, J ˆ 8.1Hz, 1H; sugar moiety), 3.71(dd,
J ˆ 8.1, 5.1 Hz, 1 H; H-C2 of the sugar moiety), 3.63 (d, J ˆ 3.5 Hz, 2H;
CH2OBz of the sugar moiety), 3.58 (t, J ˆ 8.1Hz, 1H; sugar moiety), 3.10
(dd, J ˆ 9.7, 14.7 Hz, 1H, CHH-Canomeric), 2.97 (dd, J ˆ 3, 14.7 Hz, 1H;
CHH-Canomeric), 1.37 (t, J ˆ 7 Hz, 3H; COOCH2CH3); elemental analysis
calcd (%) for C44H46O8 (702.8): C 75.19, H 6.60; found: C 75.31, H 6.71.
1-(2,3,4,6-Tetra-O-benzyl-b-d-glucopyranos-1-ylmethyl)-2-benzyloxy-4-
hydroxymethyl benzene (30): The same procedure was used to convert the
ester derivative 28 (7.0 g, 8.84 mmol) to the alcohol 30 (6.03 g, 91%). M.p.
1
738C; [a]2D0 ˆ À2.2 (c ˆ 1.0 in CHCl3); H NMR (250 MHz, CDCl3, 258C,
TMS): d ˆ 7.5 7.1(m, 26H; 1  benzene ring A, 5C6H5), 6.91(d, J ˆ
1.15 Hz, 1 H; H-C of benzene ring A), 6.81(dd, J ˆ 1.15, 8 Hz, 1 H; H-C
3
5
of benzene ring A), 5.10 (s, 2H; PhCH2O-C2 of benzene ring A), 4.90 4.35
(m, 10H; 4CH2Ph, CH2OH), 3.80 3.25 (m, 8H; 7 Â sugar moiety, CHH-
Canomeric), 2.67 (dd, J ˆ 9.7, 14.6 Hz, 1H; CHH-Canomeric); elemental analysis
calcd (%) for C49H50O7 (750.9): C 78.37, H 6.71; found: C 78.49, H 6.87.
1-(2,3,4,6-Tetra-O-benzyl-a-d-glucopyranos-1-ylmethyl)-2-benzyloxy-4-
bromomethyl benzene (25): NBS (2.49 g, 0.014 mol) was added to a
solution of alcohol 29 (7.0 g, 9.33 mmol) and PPh3 (3.67 g, 0.014 mol) in
THF (50 mL), while the temperature was kept below 308C. The reaction
mixture was stirred at room temperature for 2 h and concentrated.
Bromomethyl derivative 25 (6.22 g, 82%) was recovered by chromatog-
raphy and eluted with hexane/ethyl acetate 8:2 v/v. M.p. 938C; [a]2D0 ˆ 47.4
4-(2,3,4,6-Tetra-O-benzyl-b-d-glucopyranos-1-ylmethyl)-3-hydroxybenzo-
ic ethyl ester (24): The same procedure was used to convert the unsaturated
acid 9 (13.0 g, 0.018 mol) into its aromatic derivative 24 (8.23 g, 65%). M.p.
1088C; [a]2D0 ˆ 12.2 (c ˆ 0.98 in CHCl3); 1H NMR (400 MHz, CDCl3, 258C,
TMS): d ˆ 7.88 (s, 1H; OH), 7.60 (d, J ˆ 2 Hz, 1H; H-C2 of benzene ring A),
7.49 (dd, J ˆ 8, 2 Hz, 1H; H-C6 of benzene ring A), 7.4 7.1(m, 20H;
4C6H5), 7.02 (d, J ˆ 8 Hz, 1H; H-C5 of benzene ring A), 5.00 4.75 (m, 4H;
2CH2Ph), 4.65 4.45 (m, 4H; 2CH2Ph), 4.36 (q, J ˆ 7 Hz, 2H;
COOCH2CH3), 3.75 3.55 (m, 5H; sugar moiety), 3.48 (m, 1H; sugar
moiety), 3.33 (t, J ˆ 8.5 Hz, 1H; sugar moiety), 3.09 (dd, J ˆ 2.7, 14.7 Hz,
1H; CHH-Canomeric), 2.92 (dd, J ˆ 7.8, 14.7 Hz, 1H; CHH-Canomeric), 1.38 (t,
J ˆ 7 Hz, 3H; COOCH2CH3); elemental analysis calcd (%) for C44H46O8
(702.8): C 75.19, H 6.60; found: C 75.09, H 6.48.
1
(c ˆ 1.05 in CHCl3); H NMR (400 MHz, CDCl3, 258C, TMS): d ˆ 7.4 7.1
(m, 26H; 1  benzene ring A, 5C6H5), 6.94 (d, J ˆ 1.15 Hz, 1 H; H-C of
3
benzene ring A), 6.84 (dd, J ˆ 1.15, 8 Hz, 1 H; H-C of benzene ring A), 5.05
5
(s, 2H, PhCH2O-C2 of benzene ring A), 4.92 (d, J ˆ 11 Hz, 1H; CHHPh),
4.81(d, J ˆ 11 Hz, 1H; CHHPh), 4.76 (d, J ˆ 11 Hz, 1H, CHHPh), 4.60
4.30 (m, 8H; 5CHHPh, H-Canomeric, CH2Br), 3.85 (m, 2H; sugar moiety),
3.74 (m, 1H; sugar moiety), 3.85 (m, 3H; sugar moiety), 3.23 (dd, J ˆ 3.4,
14.7 Hz, 1H; CHH-Canomeric), 2.93 (dd, J ˆ 12, 14.7 Hz, 1H; CHH-Canomeric);
elemental analysis calcd (%) for C49H49BrO6 (813.8): C 73.32, H 6.07, Br
9.82; found: C 73.44, H 6.19, Br 9.67.
4-(2,3,4,6-Tetra-O-benzyl-a-d-glucopyranos-1-ylmethyl)-3-benzyloxyben-
zoic ethyl ester (27): Benzyl bromide (2.52 g, 0.020 mol) was added to a
mixture of derivative 23 (9.20 g, 0.013 mol) and potassium carbonate
(2.71g, 0.020 mol) in acetone (50 mL). The reaction mixture was stirred for
1-(2,3,4,6-Tetra-O-benzyl-b-d-glucopyranos-1-ylmethyl)-2-benzyloxy-4-
bromomethyl benzene (26): According to the same procedure alcohol 30
(5.90 g, 7.87 mmol) was transformed into bromo derivative 26 (5.05 g,
1
79%). M.p. 1108C; [a]2D0 ˆ À7.1( c ˆ 0.88 in CHCl3); H NMR (250 MHz,
1876
¹ WILEY-VCH Verlag GmbH, 69451Weinheim, Germany, 2002
0947-6539/02/0808-1876 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 8

C-Glycosyl Tyrosine Analogues
1872 1878
CDCl3, 258C, TMS): d ˆ 7.5 7.1(m, 26H; 1  benzene ring A, 5C6H5), 6.98
(m, 2H; benzene ring A), 5.09 (s, 2H; PhCH2O-C2 of benzene ring A),
4.90 4.40 (m, 10H, 4CH2Ph, CH2Br), 3.80 3.30 (m, 8H; 7 Â sugar moiety,
CHH-Canomeric), 2.66 (dd, J ˆ 9.4, 14.5 Hz, 1H, CHH-Canomeric); elemental
analysis calcd (%) for C49H49BrO6 (813.8): C 73.32; H 6.07, Br 9.82; found:
C 73.56, H 6.12, Br 9.98.
methyl ester for spectroscopic characterisation. 1H NMR (500 MHz,
CDCl3, 258C, TMS): d ˆ 7.35 7.05 (m, 25H; 5C6H5), 6.99 (d, J ˆ 7.6 Hz,
1H; H-C5 of benzene ring A), 6.56 (d, J ˆ 1.2 Hz, 1 H; H-C2 of benzene
ring A), 6.49 (dd, J ˆ 1.2, 7.6 Hz, 1 H; H-C6 of benzene ring A), 5.73 (d, J ˆ
7.5 Hz, 1H; NH), 4.95 (s, 2H; PhCH2O-C3 of benzene ring A), 4.86 (d, J ˆ
11 Hz, 1H; CHHPh), 4.80 4.60 (m, 3H; 2CHHPh, CHNH), 4.50 4.25 (m,
6H; 5CHHPh, H-Canomeric), 3.78 (m, 2H; sugar moiety), 3.68 (dd, J ˆ 6,
9.4 Hz, 1H; sugar moiety), 3.61 (s, 3H; COOC H3), 3.54 (m, 2H; sugar
moiety), 3.44 (m, 1H; sugar moiety), 3.15 (dd, J ˆ 3, 14.7 Hz, 1H; CHH-
Canomeric), 2.99 (m, 2H; CH2CHNH), 2.84 (dd, J ˆ 11.6, 14.7 Hz, 1H; CHH-
Canomeric), 1.83 (s, 3H, NHCOCH3).
2-Acetamido-2-[3-benzyloxy-4-(2,3,4,6-tetra-O-benzyl-a-d-glucopyranos-
1-ylmethyl)benzyl] malonic diethyl ester (31): Diethyl acetamidomalonate
(2.39 g, 0.011 mol) was added to a suspension of NaH (0.42 g, 60% in
mineral oil, 0.011 mol) in DMF (20 mL). After 20 min, the bromo
derivative 25 (6.0 g, 7.38 mmol) in DMF (5 mL) was added dropwise. The
reaction mixture was stirred at room temperature for 2 h, poured into water
and extracted with ethyl acetate. The residue was chromatographed and
eluted with hexane/ethyl acetate 8:2 v/v, and pure derivative 31 (4.83 g,
69%) was obtained after recrystallisation from hexane/ethyl acetate 8:2
v/v. M.p. 618C; [a]2D0 ˆ 37.6 (c ˆ 1.03 in CHCl3); 1H NMR (500 MHz,
CDCl3, 258C, TMS): d ˆ 7.4 7.0 (m, 25H; 5C6H5), 7.05 (d, J ˆ 7.5 Hz, 1H,
The aqueous phase was concentrated in vacuo and the residue was
acetylated according to a modified Schotten Baumann procedure. It was
dissolved in water at pH 8 (KOH), treated with an excess of acetic
anhydride. After 24 h the reaction mixture was concentrated, diluted with
water, and extracted with ethyl acetate. The residue was recrystallised from
isopropanol, to afford the diastereoisomerically pure (de > 99% from
1H NMR spectrum of the corresponding methyl ester) derivative a-l-4
(0.970 g, 32%). M.p. 1418C; elemental analysis calcd (%) for C53H55NO9
(850.0): C 74.89, H 6.52, N 1.65; found: C 74.70, H 6.88, N 1.98.
H-C5 of benzene ring A), 6.55 (d, J ˆ 1.15 Hz, 1 H; H-C of benzene ring A),
2
6.52 (s, 1H; NH), 6.50 (dd, J ˆ 1.15, 7.5 Hz, 1 H; H-C of benzene ring A),
6
4.98 (s, 2H; PhCH2O-C3 of benzene ring A), 4.93 (d, J ˆ 11 Hz, 1H;
CHHPh), 4.81(d, J ˆ 11 Hz, 1H; CHHPh), 4.77 (d, J ˆ 11 Hz, 1H;
CHHPh), 4.55 4.30 (m, 10H; H-Canomeric, 5CHHPh, 2COOCH2CH3),
3.85 ( m, 2H; sugar moiety), 3.75 (dd, J ˆ 6, 9.5 Hz, 1H; sugar moiety),
3.70 3.60 (m, 4H; 2  sugar moiety, CH2CNH), 3.49 (dd, J ˆ 2, 11 Hz, 1H;
sugar moiety), 3.21(dd, J ˆ 3, 14.7 Hz, 1H; CHH-Canomeric), 2.90 (dd, J ˆ
11.6, 14.7 Hz, 1H; CHH-Canomeric), 1.92 (s, 3H; NHCOCH3), 1.30 1.25 (m,
6H; 2COOCH2CH3); elemental analysis calcd (%) for C58H63NO11 (950.1):
C 73.32, H 6.68, N 1.47; found: C 73,47, H 6.56, N 1.23.
Treatment with diazomethane in CH2Cl2/Et2O converted derivative 4 into
the corresponding methyl ester for optical and spectroscopic character-
1
isation: [a]D ˆ 53.6 (c ˆ 0.5 in CHCl3); H NMR (500 MHz, CDCl3, 258C,
TMS): d ˆ 7.35 7.0 (m, 25H; 5C6H5), 6.99 (d, J ˆ 7.6 Hz, 1H; H-C5 of
benzene ring A), 6.56 (d, J ˆ 1.2 Hz, 1 H; H-C2 of benzene ring A), 6.49 (dd,
J ˆ 1.2, 7.6 Hz, 1 H; H-C6 of benzene ring A), 5.75 (d, J ˆ 7.5 Hz, 1H ; N H),
4.94 (s, 2H; PhCH2O-C3 of benzene ring A), 4.86 (d, J ˆ 11 Hz, 1H;
CHHPh), 4.80 4.60 (m, 3H; 2CHHPh, CHNH), 4.50 4.25 (m, 6H;
5CHHPh, H-Canomeric), 3.78 (m, 2H; sugar moiety), 3.68 (dd, J ˆ 6, 9.4 Hz,
1H; sugar moiety), 3.60 (s, 3H, COOCH3), 3.53 (m, 2H, sugar moiety), 3.44
(m, 1H; sugar moiety), 3.15 (dd, J ˆ 3, 14.7 Hz, 1H; CHHCanomeric), 2.99 (m,
2H; CH2CHNH), 2.84 (dd, J ˆ 11.6, 14.3 Hz, 1H; CHH-Canomeric), 1.86 (s,
3H; NHCOCH3).
2-Acetamido-2-[3-benzyloxy-4-(2,3,4,6-tetra-O-benzyl-b-d-glucopyranos-
1-ylmethyl)benzyl] malonic diethyl ester (32): The same procedure was
used to convert derivative 26 (4.90 g, 6.03 mmol) into compound 32 (3.72 g,
65%). M.p. 76 778C; [a]2D0 ˆ À4.3 (c ˆ 1.07 in CHCl3); 1H NMR
(500 MHz, CDCl3, 258C, TMS): d ˆ 7.35 7.1(m, 26H; 5C 6H5, 1  ben-
zene ring A), 6.44 (m, 3H; 2 Â benzene ring A, NH), 4.94 (m, 2H;
PhCH2O-C3 of benzene ring A), 4.81(m, 3H; 3 C HHPh), 4.75 (d, J ˆ
11 Hz, 1H; CHHPh), 4.62 (d, J ˆ 11 Hz, 1H; CHHPh), 4.52 (d, J ˆ 11 Hz,
1H; CHHPh), 4.45 (d, J ˆ 11 Hz, 1H; CHHPh), 4.37 (d, J ˆ 11 Hz, 1H;
CHHPh), 4.0 4.25 (m, 4H, 2COOCH2CH3), 3.70 3.25 (m, 10H; 7 Â sugar
moiety, CH2CNH, CHH-Canomeric), 2.57 (dd, J ˆ 9.8, 15 Hz, 1H; CHH-
N-Acetamido-3-benzyloxy-4-(2,3,4,6-tetra-O-benzyl-b-d-glucopyranos-1-
ylmethyl)-d-phenylalanine (5) and N-acetamido-3-benzyloxy-4-(2,3,4,6-
tetra-O-benzyl-b-d-glucopyranos-1-ylmetyl)-l-phenylalanine (6): The
same procedure was used to produce diastereoisomerically pure (de
>99%) b-l-6 (0.485 g, 36%), after recrystallisation from isopropanol, and
the derivative b-d-5 (0.512 g, 38%) with impurity of 13% of diaster-
Canomeric), 1.83 (s, 3H; NHCOCH3), 1.25 1.15 (m, 6H; 2COOCH CH3);
eoisomer
6 from the 1:1 mixture of derivatives 5 and 6 (1.35 g,
2
1.59 mmmol). The reaction was monitored by 1H NMR from signals of
the methyl group of the acetamido moiety: CH3CONH d(5) ˆ 1.80 and
d(6) ˆ 1.82. b-d-5 (de 74%). M.p. 1458C; elemental analysis calcd (%) for
C53H55NO9 (850.0): C 74.89, H 6.52, N 1.65; found: C 74.98, H 6.45, N 1.34.
elemental analysis calcd (%) for C58H63NO11 (950.1): C 73.32, H 6.68, N
1.47; found: C 73,25, H 6.79, N 1.59.
N-Acetamido-3-benzyloxy-4-(2,3,4,6-tetra-O-benzyl-a-d-glucopyranos-1-
ylmethyl)-d,l-phenylalanine (3, 4): A mixure of derivative 31 (4.60 g,
4.85 mmol) and NaOH (0.290 g, 7.28 mmol) in ethanol (35 mL) was heated
under reflux for 5 h. After the usual work-up, a 1:1 mixture (1H NMR of the
corresponding methyl ester) of diastereoisomeric derivatives 3 and 4 was
recovered (3.21g, 78%).
Treatment with diazomethane in CH2Cl2/Et2O converted derivative 5 (de
74%) into the corresponding methyl ester for spectroscopic character-
isation: 1H NMR (500 MHz, CDCl3, 258C, TMS): d ˆ 7.35 7.1(m, 26H;
5C6H5, 1  benzene ring A), 6.51(m, 2H; benzene ring A), 5.71(d, J ˆ
8.5 Hz, 1H; NH), 4.97 (m, 2H; PhCH2O-C3 of benzene ring A), 4.85 4.72
(m, 5H, 4 CHHPh, CHNH), 4.62 (d, J ˆ 11 Hz, 1H; CHHPh), 4.53 (d, J ˆ
11 Hz, 1H; CHHPh), 4.43 (d, J ˆ 11 Hz, 1H; CHHPh), 4.36 (d, J ˆ 11 Hz,
1H; CHHPh), 3.66 3.22 (m, 11H; 7 Â sugar moiety, COOCH3, CHH-
N-Acetamido-3-benzyloxy-4-(2,3,4,6-tetra-O-benzyl-b-d-glucopyranos-1-
ylmethyl)-d,l-phenylalanine (5, 6): The same procedure gave derivative 32
(2.20 g, 2.23 mmol) in a 1:1 mixture (1H NMR of the corresponding methyl
ester) of diastereoisomeric derivatives 5 and 6 (1.48 g, 75%).
C
anomeric), 2.96 (m, 2H; CH2CHNH), 2.59 (m, 1H; CHH-Canomeric), 1.80 (s,
N-Acetamido-3-benzyloxy-4-(2,3,4,6-tetra-O-benzyl-a-d-glucopyranos-1-
ylmethyl)-d-phenylalanine (3) and N-acetamido-3-benzyloxy-4-(2,3,4,6-
tetra-O-benzyl-a-d-glucopyranos-1-ylmethyl)-l-phenylalanine (4): The
enzyme, acylase I, (500 mg) was added to a suspension of the 1:1 mixture
of derivatives 3 and 4 (3.0 g, 3.53 mmol) in water/isopropanol 6:1(35 mL).
The pH was kept at 7.8 by addition of NaOH (0.02m) by a pH-Stat. The
reaction mixture was stirred at room temperature for 48 h, and monitored
by 1H NMR spectroscopy. Samples of the reaction mixture were acidified,
extracted with ethyl acetate, treated with diazomethane in Et2O, and
concentrated under reduced pressure. The signals of the methyl group of
the acetamido moiety were monitored: CH3CONH d(3) ˆ 1.83, d(4) ˆ 1.86.
When no further evolution was observed, the mixture was acidified by
addition of 1n HCl, and filtered. The filtrate was extracted with ethyl
acetate. The organic phase afforded a-d-3 (1.04 g, 35%) with 24% of the a-
l-4 diastereoisomer (1H NMR of the corresponding methyl ester). M.p.
1238C; elemental analysis calcd (%) for C53H55NO9 (850.0): C 74.89, H
6.52, N 1.65; found: C 74.57, H 6.78, N 1.33. Treatment with diazomethane
in CH2Cl2/Et2O converted derivative 3 (de 52%) into the corresponding
3H, NHCOCH3). b-l-6 (de >99%). M.p. 1608C; elemental analysis calcd
(%) for C53H55NO9 (850.0): C 74.89, H 6.52, N 1.65; found: C 75.01, H 6.48,
N 1.79.
Treatment with diazomethane in CH2Cl2/Et2O converted derivative 6 (de
99%) into the corresponding methyl ester for optical and spectroscopic
characterisation: [a]D ˆ À4 (c ˆ 0.5 in CHCl3); 1H NMR (500 MHz,
CDCl3, 258C, TMS): d ˆ 7.35 7.1(m, 26H; 5C H5, 1H benzene ring A),
6
6.51(m, 2H; benzene ring A), 5.74 (d, J ˆ 8.5 Hz, 1H; NH), 4.97 (m, 2H;
PhCH2O-C3 of benzene ring A), 4.85 4.72 (m, 5H; 4CHHPh, CHNH),
4.62 (d, J ˆ 11 Hz, 1H; CHHPh), 4.53 (d, J ˆ 11 Hz, 1H; CHHPh), 4.43 (d,
J ˆ 11 Hz, 1H; CHHPh), 4.36 (d, J ˆ 11 Hz, 1H; CHHPh), 3.68 3.21(m,
11 H; 7Â sugar moiety, COOCH3, CHH-Canomeric), 2.99 (m, 2H; CH2-CH-
NH), 2.96 (m, 1H; CHH-Canomeric), 1.82 (s, 3H; NHCOCH3).
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Received: October 29, 2001[F3640]
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0947-6539/02/0808-1878 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 8