Ritter-type reaction of C-(1-bromo-1-deoxy-d-glycopyranosyl)formamides and its application for the synthesis of oligopeptides incorporating anomeric α-amino acids

Article abstract of DOI:10.1016/j.carres.2011.07.001

O-Peracetylated or -perbenzoylated C-(1-bromo-1-deoxy-d-glycopyranosyl) formamides of d-gluco, d-galacto, and d-arabino configuration were reacted with Ag(I)-salts or HgO in nitrile solvents to give N-acyl-1-cyano-d- glycopyranosylamines with an axial C-N

Full text of DOI:10.1016/j.carres.2011.07.001

Carbohydrate Research 346 (2011) 2104–2112
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Carbohydrate Research
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Ritter-type reaction of C-(1-bromo-1-deoxy-D-glycopyranosyl)formamides
and its application for the synthesis of oligopeptides incorporating anomeric
a-amino acids
⇑
Katalin Czifrák, Viktor Gyóllai, Katalin E. Kövér, László Somsák
Department of Organic Chemistry, University of Debrecen, POB 20, H-4010 Debrecen, Hungary
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 May 2011
Received in revised form 29 June 2011
Accepted 1 July 2011
Available online 13 July 2011
O-Peracetylated or -perbenzoylated C-(1-bromo-1-deoxy-
-galacto, and -arabino configuration were reacted with Ag(I)-salts or HgO in nitrile solvents to give
N-acyl-1-cyano- -glycopyranosylamines with an axial C–N bond at the anomeric centre. In the presence
of HgBr2, Hg(CN)2, or InCl3 the anomer of the above glycosylamine with an equatorial C–N bond was also
isolated or detected. In CH3NO2 solutions as few as 5–10 equiv of the nitrile were sufficient to get accept-
able yields for the products. Under similar conditions N-substituted C-(2,3,4,6-tetra-O-acetyl-1-bromo-1-
D
-glycopyranosyl)formamides of
D-gluco,
D
D
D
Keywords:
Ritter-reaction
2-Bromo-2-deoxy-hept(hex)-2-
ulopyranosonamide
2-Amino-2-deoxy-hept(hex)-2-
ulopyranosononitrile
deoxy-b-
D
-galactopyranosyl)formamides gave anomeric spiro-oxazoline derivatives which, upon mild
-amino acids.
Ó 2011 Elsevier Ltd. All rights reserved.
acidic hydrolysis, opened up to di- and tripeptides of anomeric
a
Anomeric a-amino acid
Oligopeptide
1. Introduction
Thus, in the presence of non-participating 2-substituents, axial
N-glycopyranosylamides were obtained from type II intermediates
on the action of water,5 and N,N-bis-acylamide products were
formed with several aromatic carboxylic acids6–8 and amino
acids9–11 as external nucleophiles. Carboxylic acids were also used
as internal nucleophiles for the synthesis of several anomeric
b-amino acid and peptide derivatives.12–15 Further internal
O-nucleophiles, such as a 2-O-Zn salt obtained from a 1,2-epox-
ide16 and a 2-O-benzyl group17 gave 1,2-annelated oxazolines,
while the CH2OH appendage of heptulopyranose18 or fructopyra-
nose19 derivatives furnished spiro-oxazolines, each with an axial
C–N bond at the anomeric carbon. 2-N-Substituents were also
observed to attack the axial glycosyl-nitrilium ion and furnished
1,2-annelated imidazolines.20,21
Ritter-type reactions involve combination of a carbocation (car-
benium ion) with a nitrile (generally applied in high excess or as
the solvent) to give a nitrilium ion which, after ensuing transforma-
tions by nucleophiles, may furnish carboxamides as well as hetero-
cycles.1,2 Glycosyl-nitrilium ions (II formed from glycosylium ions I
and nitriles, Scheme 1) are known to play important roles in direct-
ing the stereoselectivity of glycosylation reactions towards the
formation of equatorial glycosides.3 On the other hand, attack of var-
ious external or internal nucleophiles onto glycosyl-nitrilium ions
lead to several types of products rendering these transformations
highly valuable in the carbohydrate field as well. Protecting groups
in the sugar moieties can have a bearing on the configuration of gly-
cosyl-nitrilium ions which tend to be axial (II) in the presence of
non-participating protective groups demonstrated by NMR and
computational methods4 as well as by the structure of the end-
products (vide infra). However, participating protection of the
substituent in position 2 may force the formation of equatorial
glycosyl-nitrilium ions (III). In these cases high equatorial selectivity
can be observed in the products but, interestingly, exclusive axial
selectivities were also reported in some transformations.
With participating substituents next to the anomeric carbon,
the outcome of the reactions is less predictable. With amino acids
as well as aromatic carboxylic acids as external nucleophiles
2-deoxy-2-phthalimido22 and 2-deoxy-2-tetrachlorophthalimido11
D-glucopyranosyl derivatives gave equatorial N,N-bis-acylamide
type products. Starting from O-perbenzoylated -glucose, the
D
equatorial amide was formed in low yield accompanied by several
by-products in the presence of water as the nucleophile.23 Under
similar conditions O-peracetylated
-mannose each gave mixtures of axial and equatorial amides with
a large excess of the latter. To explain this for the -mannose
case, equilibration of the amides was invoked.24 The internal
D-glucose, D-galactose, and
D
D
⇑
Corresponding author. Tel.: +36 52 512 900/22348; fax: +36 52 512 744.
E-mail address: somsak@tigris.unideb.hu (L. Somsák).
0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2011.07.001

K. Czifrák et al. / Carbohydrate Research 346 (2011) 2104–2112
2105
cyano-D-glycopyranosylamines in the presence of Ag2CO3 in ni-
O
non-partici-
pating PG
participating
triles as solvents.27 In this paper, a detailed investigation of this
reaction and its extension to the synthesis of some oligopeptide
PG
I
R
PGO
C
N
derivatives with an anomeric a-amino acid moiety are presented.
R-CN
O
N
O
2. Results and discussion
PG =
PGO
O
PG
C
protecting
group
A Ritter-type reaction of C-(2,3,4,6-tetra-O-acetyl-1-bromo-1-
deoxy-b-
-galactopyranosyl)formamide28 (1, Table 1, entry 1)
III
R
D
II
R
was first observed during an attempted exchange of the bromine
to fluorine by AgF in dry CH3CN. Under such conditions, widely ap-
plied for the synthesis of glycosyl fluoride derivatives (see Refs.
29–31 and references cited therein), an unexpected product, actu-
ally compound 2 was isolated in 70% yield instead of the expected
C
N
O
O
O
Nu
N
C
R
Nu
PGO
PG
C-(2,3,4,6-tetra-O-acetyl-1-deoxy-1-fluoro-a-D-galactopyranosyl)-
formamide. In the presence of Ag2CO3 1 was transformed to 2 in a
very clean reaction (entry 2), while AgOTf gave the same result un-
der significantly shorter reaction time (entry 6). The new product
crystallized out during removal of the solvent after the usual work-
up, did not exhibit characteristic fluoride couplings, had one
exchangeable proton, and five methyl resonances in its 1H NMR
spectrum, and showed a CN signal in the 13C NMR spectrum. Vici-
nal proton–proton couplings indicated that the sugar ring adopted
a 4C1 conformation. The CN resonance appeared as a pseudo triplet
in the proton coupled carbon spectrum with ꢀ3 Hz splittings due
to couplings with H-2 and the NH protons. This allowed us to
deduce the equatorial orientation for the CN group based on the
3JH-2,CN coupling in the 4C1 conformation.32–34
Nu =
external or internal
nucleophile
product with
product with
axial C-N bond
equatorial C-N bond
(e.g. α-
D
-gluco type)
(e.g. β-D-gluco type)
may be preponderant
Scheme 1.
nucleophile CH2OH group of a 3-O-benzoyl D-fructopyranose deriv-
ative gave only one spiro-oxazoline with an axial C–N bond.19
Unprotected sugars were reported to give 1,2-cis configured
N-glycosylamides in liquid HF with both furanoid and pyranoid
Some other promoters3 were also tried to perform this transfor-
mation. HgO (entry 7) gave similar results to those obtained with
silver salts, but in the presence of HgBr2, HgO–HgBr2, Hg(CN)2,
and InCl3 (entries 8, 12, 13, and 17, respectively) a second product
identified as 3, the anomer of 2, was also detected and isolated
from the mixtures. Appearance of 435 in the reaction conducted
rings depending on the sugar configuration.25
D-Glucose was con-
verted to N-b-D-glucopyranosylamides with several nitriles in the
presence of TMSOTf–AgClO4 under mechanochemical conditions.26
Some years ago we reported on the facile transformation of
C-(1-bromo-1-deoxy-D-glycopyranosyl)formamides into N-acyl-1-
Table 1
Reaction of C-(2,3,4,6-tetra-O-acetyl-1-bromo-1-deoxy-b-D-galactopyranosyl)formamide (1) with CH3CN under various conditions
OAc
OAc
O
OAc
OAc
OAc
OAc
OAc
O
OAc
Promoter (1 eq.)
CH3CN
H
H
O
O
CONH2
CN
CONH2
NHCOCH3
AcO
AcO
AcO
AcO
+
2
+
2
1
1
AcO
CH3NO2, rt
in the dark
AcO
AcO
AcO
NHCOCH3
Br
CN
OH
2
3
4
1
Entry
Promoter
CH3CN (equiv)
Reaction time
Product ratio (%) by 1H NMR
2
3
4
1
2
3
4
5
6
7
8
AgF
Ag2CO3
As solvent
As solvent
10
5
1.5
As solvent
As solvent
As solvent
3 d
3 d
5 d
7 d
12 d
1 min
8 h
1 d
1 d
1 d
1 d
16 h
1 d
1 d
1 d
1 d
1 d
1 d
1 d
1 d
70a,b
100
77
68
30
100
100
72
41
30
24
91
84
63
53
52
83
59
—
—
—
—
—
—
23
32
55c
—
—
—
26
36c
46c
—
AgOTf
HgO
HgBr2
—
—
28
33
25
17
9
9
10
5
10
11
12
13
14
15
16
17
18
19
20
1.5
As solvent
As solvent
10
5
1.5
As solvent
10
5
HgO–HgBr2
Hg(CN)2
8
8
13
16
10
17
29
14
24
13c
21c
23c
—
InCl3
12
15
27c
71
35
1.5
a
b
c
Isolated yield.
C-(2,3,4,6-Tetra-O-acetyl-1-fluoro-
Together with an unidentified product in ꢀ10–15% ratio.
a-D-galactopyranosyl)formamide was isolated in ꢀ3% yield from the mother liquor.

2106
K. Czifrák et al. / Carbohydrate Research 346 (2011) 2104–2112
with Hg(CN)2 (entry 13) must be due to traces of water in the sol-
vent. The structure of 3 was proven by NMR spectra showing char-
acteristics similar to those of 2, except for the appearance of the CN
resonance as a pseudo triplet type with ꢀ6 Hz coupling constants.
Thus, the 3JH-2,CN couplings for 2 and 3 support the gauche and the
antiperiplanar arrangements, respectively, of the nuclei involved in
the 4C1 conformation, and provide thereby unequivocal evidence
for the anomeric configuration of these compounds.32–34
acceptable to good yields. In each compound the cyano group
occupies an equatorial position as shown by the JH-2,CN couplings
in the range of 2.2–3.2 Hz indicating the incorporation of the nitrile
reagent in an axial direction.
3
This Ritter-type reaction was also investigated with N-substi-
tuted C-(2,3,4,6-tetra-O-acetyl-1-bromo-1-deoxy-b-D-galactopyr-
anosyl)formamides 1932 and 20 (Scheme 2). Compound 20 was
prepared from pentachlorophenyl C-(2,3,4,6-tetra-O-acetyl-1-bro-
Having in mind the extension of this reaction to nitriles not
applicable as solvents, several co-solvents were tried. In the pres-
ence of 5 equiv of CH3CN the transformation of 1 was either incom-
plete or gave complex product mixtures in CH2Cl2, 1,4-dioxane,
HMPT, and benzene (in the light of their reactivity alcohols, esters,
ketones,36 and sulfoxides36 were not considered as solvents). How-
ever, in CH3NO2 rather clean reactions were observed: with the
mercury(II) salts and InCl3 (entries 9–11, 14–16, and 18–20,
respectively) 2 and 3 were detected and, due to traces of water
in the solvent CH3NO2, 4 also appeared in increasing ratios as the
amount of CH3CN decreased. A conceivable anomerization of 2 to
3 was excluded by experiments conducted with pure 2 or 3 in
CH3NO2 in the presence of 2 equiv of HgBr2 or Hg(CN)2 showing
no change of these compounds even at elevated temperatures such
as 100 °C. On the other hand, with Ag2CO3 only 4 was observed as a
by-product (entries 3–5). Thus, CH3NO2 and silver salts facilitate
the use of nitriles in smaller excess maintaining the axial selectiv-
ity of the reaction.
mo-1-deoxy-b-D-galactopyranosyl)formate and L-alanine methyl-
ester according to the procedure described for 19.32 Bromides 19
and 20 were each reacted with 1 equiv of Ag2CO3 in CH3CN as
the solvent to give the spiro-oxazoline derivatives 21 and 23 in
good and modest yield, respectively. The reaction of 19 with
10 equiv of the solid benzyloxycarbonylamino-acetonitrile was
performed in CH3NO2 in the presence of 1 equiv of Ag2CO3 to give
the spiro compound 22.
The structure of compounds 21–23 was established by NMR
methods. The absence of exchangeable protons as well as reso-
nances characteristic for imidate type carbons (155.8–158.2 ppm)
were in accordance with the spirocyclic structures. Spectra for 22
exhibited two series of resonances indicating the presence of E/Z
isomers along the C-5 = N bond, while for 21 and 23 only one iso-
mer was present. This configurational issue was not investigated
further. The 4C1 conformation of the sugar rings was unequivocally
assigned with the use of vicinal proton–proton coupling constants
(see Section 3). The configuration of the anomeric carbon was
established on the basis of three-bond heteronuclear couplings be-
tween H-2 and the exocyclic imine type carbon C-5 attached to C-1
of the sugar part (parent monosaccharide numbering). These cou-
plings were measured using a sensitivity enhanced gradient long-
range 13C–1H correlation experiment (G-HSQMBC),39 and values
around 3 Hz indicated gauche arrangement of the relevant atoms
in the 4C1 conformation.
Next the extension of the reaction to other nitriles applied as
solvents and to starting C-(1-bromo-1-deoxy-D-glycopyrano-
syl)formamides 5,37 6,38 and 735 besides 1 was investigated
(Table 2). In these experiments Ag2CO3 was used because of the
cost, stability, and easy handling of the reagent. The results show
that under these conditions several O-acyl protected 1-acylamino-
1-deoxy-D-glycopyranosyl cyanides 8–18 can be obtained in
Table 2
Preparation of O-peracylated N-acyl-1-cyano-D-glycopyranosylamines
CONH2
CN
O
O
R-CN as solvent
(RO)n
(RO)n
Ag2CO3 (1 eq.), rt
in the dark
Br
NHCOR
2, 8-18
1, 5-7
Starting compound
R
Yield (%)
Product
OAc
CH3–
CH3CH2–
CH2@CH–
CH2@CH–CH2-
2 (76)
8 (74)
9 (57)
10 (62)
11 (24)
OAc
OAc
OAc
O
O
CONH2
CN
AcO
AcO
AcO
AcO
CH3OCH2–
Br
NHCOR
1
CH3–
CH3CH2–
12 (36)a
13 (53)
OAc
O
OAc
O
AcO
AcO
CONH2
CONH2
CN
AcO
AcO
AcO
AcO
Br
NHCOR
5
CH3–
CH3CH2–
(CH3)3C–
14 (78)33
15 (57)
16 (27)
OBz
O
OBz
O
BzO
BzO
BzO
BzO
CN
BzO
BzO
Br
NHCOR
6
CH3–
CH2@CH–
17 (41)
18 (43)
Br
NHCOR
CN
OAc
CONH2
OAc
O
O
OAc
OAc
OAc
OAc
7
a
With 2 equiv AgF.

K. Czifrák et al. / Carbohydrate Research 346 (2011) 2104–2112
2107
a and b
19
25 (51%)
OAc
OAc
OAc
OAc
OAc
O
OAc
O
R1
H
H
N
O1
c or d
CONHR1
CONHR1
b
AcO
AcO
AcO
5
2
A2cO
1
1
O
AcO
AcO
NHCOR2
N
Br
R2
R1
R1
R2
CH3
c
d
c
19 CH2CO2CH3
21 (65%) CH2CO2CH3
22 (29%) CH2CO2CH3
23 (43%) CH(CH3)CO2CH3 CH3
24 (55%)
CH2NHCO2CH2Ph 25 (29%)
26 (27%)
20 CH(CH3)CO2CH3
Scheme 2. Reagents and conditions: (a) 1 equiv AgOTf, 10 equiv PhCH2OCONHCH2CN, CH3NO2, in the dark, rt; (b) 1 equiv CF3CO2H or CH3CO2H, 2 equiv H2O, CH2Cl2, rt; (c)
1 equiv Ag2CO3, CH3CN, in the dark, rt; (d) 1 equiv Ag2CO3, 10 equiv PhCH2OCONHCH2CN, CH3NO2, in the dark, rt.
Spiro-oxazolines 21–23 were opened up by mild acidic hydroly-
sis to peptide derivatives 24–26, respectively. Carrying out the Rit-
ter-reaction of 19 with benzyloxycarbonylamino-acetonitrile and
the hydrolysis of the intermediate spiro-derivative in a continuous
operation improved the overall yield of 25 to 51% for the two steps.
For 24–26 the NMR structural elucidation showed the presence
of amide carbonyls (166.1–167.3 ppm) instead of imidate type car-
subsequent tautomerization of C result in the end-products 2,
and 8–18. In the presence of promoters other than silver salts for-
mation of 3 was also observed. Since the anomeric interconversion
of 2 and 3 was excluded, this can be accounted for by neighbouring
group participation of the acyl protecting groups of O-2 as illus-
trated by E resulting in an equatorial attack of the nitrile. Glyco-
syl-nitrilium ion A may then follow similar transformations as
those starting with G, and end up with 3 as the isolable product.
We have no explanation for the finding that with silver salts no
compounds of type 3 were formed.
3
bons. The JH-2,CONHR1 couplings were obtained from experiments
as above, and the 2.4–2.9 Hz values were indicative of the equato-
rial position of the CONHR1 moiety. To corroborate this configura-
tional assignment dipeptide 29, the anomeric pair of 24, was also
synthesised (Scheme 3). Azide 2732 was reduced by Raney-Ni to
glycosylamine 28. In this reaction the formation of anomers or
anomerisation of the formed glycosylamine cannot be excluded,
however, the product 28 isolated from the crude mixture by crys-
In conclusion, a Ritter-type reaction of a series of O-peracylated
C-(1-bromo-1-deoxy-
promoted by silver salts gave access to N-acyl-1-cyano-
anosylamines which can be regarded as anomeric -amino acid
derivatives40–43 and new derivatives of artificial ketoses.44 The
reaction was extended to N-substituted C-(1-bromo-1-deoxy-b-
D-glycopyranosyl)formamides and nitriles
D-glycopyr-
a
tallization existed in the b-
D
-anomeric configuration as revealed by
D-
3
the JH-2,CONHR1 of 5.8 Hz coupling. Conventional acetylation of 28
by AcCl in pyridine gave a mixture of 24 and 29 (possibly due to
anomerisation of 28 under the reaction conditions) which could
galactopyranosyl)formamides which gave anomeric spiro-oxazo-
line derivatives. In each of these compounds the newly formed
C–N bond at the anomeric carbon was axially oriented in spite of
the participating protecting groups at the equatorial O-2. Mild
acidic hydrolysis of the spiro-oxazolines led to di- and tripeptides
3
be separated by column chromatography. For 29 the JH-2,CONHR1
coupling was 5.3 Hz, and thus these heteronuclear three-bond cou-
pling values for the anomeric pairs 24 and 29 proved the configu-
ration of the anomeric carbon in both compounds.
incorporating anomeric a-amino acids, thereby complementing re-
ported synthetic methods for this class of sugar–peptide deriva-
The formation of the new compounds by nitrile incorporation
can be explained following the mechanistic proposal shown in
Scheme 4. A promoter facilitates removal of a bromide ion from
the substrates (1, 5–7, 19, 20) to give glycosylium ion B. Axial at-
tack of a nitrile may give glycosyl-nitrilium ion represented by res-
onance forms F and G. Intramolecular nucleophilic attack by the
amide carbonyl oxygen may lead to spirocyclic intermediate H
which, on losing a proton, gives spiro-oxazolines 21–23 as well
as D. Tautomeric ring opening of the oxazoline in D and a
tives.45–50
3. Experimental
3.1. General methods
Melting points were measured in open capillary tubes or on a
Kofler hot-stage and are uncorrected. Optical rotations were deter-
mined with a Perkin–Elmer 241 polarimeter at room temperature.
OAc
OAc
OAc
OAc
H
O
O
CONHCH2CO2CH3
AcO
CONHCH2CO2CH3
AcO
2
1
AcO
AcO
Br
NHCOCH3
19
24 (15%) 3JH-2,CO 2.4 Hz
a
OAc
OAc
OAc
OAc
O
OAc
O
OAc
O
H
c
b
N3
NH2
NHCOCH3
AcO
AcO
AcO
2
1
AcO
AcO
AcO
CONHCH2CO2CH3
27 (65%)
CONHCH2CO2CH3
28 (79%)
CONHCH2CO2CH3
29 (15%) 3JH-2,CO 5.3 Hz
Scheme 3. Reagents and conditions: (a) 2 equiv NaN3, DMSO, rt; (b) ꢀ2 equiv Raney-Ni, H2, EtOAc, 70 °C; (c) 2 equiv CH3COCl, pyridine, rt.

2108
K. Czifrák et al. / Carbohydrate Research 346 (2011) 2104–2112
NR1
O
O
O
NHCOR2
O
O
CONHR1
CN
or
RCO
O
RCO
O
RCO
O
RCO
O
NHCOR2
N
CN
Br
R2
3
1, 5-7, 19, 20
2, 8-18
21-23
promoter -Br
R2
NH
O
O
O
O
O
N
N
CONHR1
OH
RCO
O
RCO
O
RCO
O
RCO
O
CONHR1
-H
N
N
R2
R2
A
B
C
D
-H
R2-CN
R1 = H
R2
NHR1
O
NHR1
O
N
CONHR1
O
O
O
O
O
CONHR1
RCO
RCO
RCO
O
N
N
N
O
O
O
R2
R
G
E
F
H
R2
R2
Scheme 4.
NMR spectra were recorded with Bruker 200 (200/50 MHz for
1H/13C), Bruker 360 (360/90 MHz for 1H/13C) or Avance DRX 500
(500/125 MHz for 1H/13C) spectrometers. Chemical shifts are refer-
enced to Me4Si (1H), or to the residual solvent signals (13C). TLC
was performed on DC-Alurolle Kieselgel 60 F254 (Merck), and the
plates were visualised under UV light and by gentle heating. For
column chromatography Kieselgel 60 (Merck, particle size 0.063–
0.200 mm) was used. Organic solutions were dried over anhydrous
MgSO4 and concentrated under diminished pressure at 40–50 °C
(water bath). CH3CN, CH3NO2 were distilled from P2O5, other ni-
triles, AgOTf, and AgF were purchased from Sigma-Aldrich and
used without further purification. Ag2CO3 was prepared from
AgNO3 and K2CO3, and dried over P2O5.
3JH-2,CN = ꢀ3.0), 77.7 (C-1), 67.7, 67.5, 67.3, 66.7 (C-2–C-5), 60.6
(C-6), 22.9 (NHCOCH3), 20.3 (2), 20.5 (2) (CH3); Anal. Calcd for
C17H22N2O10 (414.36): C, 49.28; H, 5.35; N, 6.76. Found: C,
48.27; H, 5.43; N, 6.35.
3.2.2. N-Acetyl-2,3,4,6-tetra-O-acetyl-1-cyano-b-D-galactopyr-
anosylamine (2-acetamido-3,4,5,7-tetra-O-acetyl-2-deoxy-b-
D-
galacto-hept-2-ulopyranosononitrile) (3)
Compound 1 (0.50 g, 1.10 mmol) was dissolved in a mixture of
dry CH3NO2 (5 mL), CH3CN (10 equiv) was added, and the solution
was stirred with freshly activated molecular sieves overnight.
HgBr2 (0.50 g, 1.39 mmol) was added in one portion. The mixture
was stirred at rt until complete disappearance of the starting mate-
rial (TLC, 3:1 EtOAc–hexane) (2–3 days). It was then diluted with
CHCl3, filtered through a Celite pad, and the filtrate was concen-
trated under diminished pressure. The residue was dissolved in
CHCl3 and washed several times with 1 M KBr solution in order
to remove mercury salts. The crude oil was purified by column
chromatography (1:1?3:1 EtOAc–hexane) to give pure products:
2 (0.08 g, 20%), 3 (0.15 g, 33%), and 4 (0.07 g, 15%).
3.2. General procedure for the preparation of O-peracylated
N-acyl-1-cyano-D-glycopyranosylamines) (2-acylamino-2-
deoxy-hept(hex)-2-ulopyranosononitriles) (2, 8–18)
An O-peracylated C-(1-bromo-1-deoxy-D-glycopyranosyl)form-
amide (1,28 5,37 6,38 or 7,35 0.25 mmol) was dissolved in a nitrile
(1 mL), and silver carbonate (0.07 g, 0.25 mmol) or silver fluoride
(0.063 g, 0.50 mmol) was added in one portion. The mixture was
stirred at rt in the dark until complete disappearance of the start-
ing material (2–3 days, TLC 3:1 EtOAc–hexane). It was then diluted
with acetone (9 mL), filtered through a Celite pad, the filter cake
was washed with acetone (3 mL), and the filtrate was concen-
trated. The residue was purified by column chromatography or
crystallisation to give pure products.
Compound 3 was obtained as white crystals. Mp 161–163 °C;
[a]
+262 (c 0.17, CHCl3); 1H NMR (CDCl3, 360 MHz): d (ppm)
D
7.21 (s, 1H, NH), 5.53 (dd, 1H, J3,4 3.1 Hz, J4,5 1.3 Hz, H-4), 5.41
(dd, 1H, J2,3 10.5 Hz, J3,4 3.1 Hz, H-3), 5.22 (d, 1H, J2,3 10.5 Hz, H-
0
2), 4.44 (t, 1H, J5,6 6.8 Hz, J5,6 6.8 Hz, H-5), 4.21–4.16 (m, 2H, H-6,
H-60), 2.21, 2.16, 2.06 (2), 2.01 (4s, 15H, OCOCH3, NHCOCH3); 13C
NMR (CDCl3, 90 MHz): d (ppm) 171.7 (NHCOCH3), 170.1, 169.6,
3
169.3 169.1 (CO), 111.9 (CN, JH-2,CN = ꢀ5.8 Hz), 79.9 (C-1), 71.2,
68.5 (2), 66.1 (C-2–C-5), 60.2 (C-6), 23.1 (NHCOCH3), 20.5, 20.4,
20.3, 20.2 (CH3); Anal. Calcd for C17H22N2O10 (414.36): C, 49.28;
H, 5.35; N, 6.76. Found: C, 48.77; H, 5.23; N, 6.00.
3.2.1. N-Acetyl-2,3,4,6-tetra-O-acetyl-1-cyano-a-D-galactopyran-
osylamine (2-acetamido-3,4,5,7-tetra-O-acetyl-2-deoxy-
a-D-
galacto-hept-2-ulopyranosononitrile) (2)
Prepared from 1 (0.51 g, 1.12 mmol) in CH3CN according to
Section 3.2. Reaction time 2 d, purification by column chromatog-
raphy (1:3 EtOAc–CHCl3), yield 0.35 g (76%) white crystals.
3.2.3. N-Propanoyl-2,3,4,6-tetra-O-acetyl-1-cyano-
pyranosylamine (3,4,5,7-tetra-O-acetyl-2-deoxy-2-propan-
amido- -galacto-hept-2-ulopyranosononitrile) (8)
a-D-galacto-
a
-D
Mp: 155–156 °C; [
a
]
D
+49 (c 1.15, CHCl3); 1H NMR (CDCl3,
Prepared from 1 (0.05 g, 0.11 mmol) in CH3CH2CN according to
Section 3.2. Reaction time 2 d, purification by column chromatog-
raphy (1:3 EtOAc–CHCl3), yield 0.035 g (74%) white crystals. Mp:
360 MHz): d (ppm) 7.90 (s, 1H, NH), 5.75 (d, 1H, J2,3 10.7 Hz, H-
2), 5.30 (dd, 1H J2,3 10.7 Hz, J3,4 3.4 Hz, H-3), 5.27 (dd, 1H, J3,4
3.4 Hz, J4,5 1.1 Hz, H-4), 4.26 (t, 1H, J5,6 6.0 Hz, J5,6 6.0 Hz, H-5),
186–187 °C; [a]
+55 (c 0.91, CHCl3); 1H NMR (CDCl3, 360 MHz):
0
D
4.10–4.08 (m, 2H, H-6, H-60), 2.20, 2.19 (2), 2.03, 1.99 (4s,
15H, OCOCH3, NHCOCH3); 13C NMR (CDCl3, 90 MHz): d (ppm)
171.2 (NHCOCH3), 170.3, 170.0, 169.7 168.2 (CO), 114.7 (CN,
d (ppm) 7.68 (s, 1H, NH), 5.76 (d, 1H, J2,3 10.6 Hz, H-2), 5.30 (dd,
1H, J2,3 10.6 Hz, J3,4 3.4 Hz, H-3), 5.38 (dd, 1H, J3,4 3.4 Hz, J4,5
0
1.0 Hz, H-4), 4.26 (t, 1H, J5,6 6.6 Hz, J5,6 6.6 Hz, H-5), 4.10 (m, 2H,

K. Czifrák et al. / Carbohydrate Research 346 (2011) 2104–2112
2109
H-6, H-60), 2.42 (q, 2H, J 7.3 Hz, J 7.3 Hz, CH2), 2.20, 2.17, 2.02, 1.98
3.2.7. N-Acetyl-2,3,4,6-tetra-O-acetyl-1-cyano-
sylamine (2-acetamido-3,4,5,7-tetra-O-acetyl-2-deoxy-
gluco-hept-2-ulopyranosononitrile) (12)
a
-
D
-glucopyrano-
(4s, 12H, OCOCH3), 1.21 (t, 3H, J 7.3 Hz, J 7.3 Hz, CH3); 13C NMR
(CDCl3, 90 MHz): d (ppm) 174.5 (NHCOCH2CH3), 170.3, 170.0,
a-D-
3
169.7 168.1 (CO), 114.8 (CN, JH-2,CN = ꢀ3.0), 77.6 (C-1), 67.6 (2),
Prepared from 5 (0.60 g, 1.32 mmol) in CH3CN with AgF accord-
ing to Section 3.2. Reaction time 1 d, purification by column chro-
matography (1:1?3:1 EtOAc–hexane), yield 0.20 g (36%) white
67.4, 67.3, 66.7 (C-2–C-5), 60.6 (C-6), 28.9 (NHCOCH2CH3), 20.3
(2), 20.5 (2) (CH3), 8.9 (NHCOCH2CH3); Anal. Calcd for
C18H24N2O10 (428.39): C, 50.47; H, 5.65; N, 6.54. Found: C, 50.41;
crystals. Mp 179–181 °C; [
a]
+57 (c 1.01, acetone); 1H NMR
D
H, 5.93; N, 6.67.
((CD3)2CO, 200 MHz): d (ppm) 8.72 (s, 1H, NH), 5.52 (d, 1H, J2,3
10.0 Hz, H-2), 5.42 (dd, 1H, J3,4 4.5 Hz, J4,5 2.4 Hz, H-4), 5.16 (dd,
0
1H, J2,3 9.8 Hz, J3,4 4.5 Hz, H-3), 4.31 (dd, 1H, J6,6 12.3 Hz, J5,6
3.2.4. N-Propenoyl-2,3,4,6-tetra-O-acetyl-1-cyano-a-D-galacto-
pyranosylamine (3,4,5,7-tetra-O-acetyl-2-deoxy-2-propen-
6.0 Hz, H-6), 4.02 (dd, 1H, J6,6 12.3 Hz, J5,6 6.0 Hz, H-60), 2.11,
0
2.10, 2.02, 1.99, 1.96 (5s, 15H, NHCOCH3, OCOCH3); 13C NMR
amido- -galacto-hept-2-ulopyranosononitrile) (9)
a-D
((CD3)2CO, 50 MHz): d (ppm) 170.7 (NHCOCH3), 170.4, 170.2,
Prepared from 1 (0.05 g, 0.11 mmol) in CH2CHCN according to
Section 3.2. Reaction time 2 d, purification by column chromatog-
raphy (1:3 EtOAc–CHCl3), yield 0.03 g (57%) white crystals. Mp:
3
169.8, 168.9 (CO), 115.9 (CN, JH-2,CN = ꢀ3.0 Hz), 78.1 (C-1), 71.5,
71.1, 69.2, 68.5 (C-2–C-5), 61.8 (C-6), 22.9 (NHCOCH3), 20.5, 20.4
(2), 20.3(CH3); Anal. Calcd for C17H22N2O10 (414.364): C, 49.28;
H, 5.35; N, 6.76. Found: C, 48.52; H, 5.60; N, 6.70.
158–160 °C; [a]
+61 (c 0.80, CHCl3); 1H NMR (CDCl3, 360 MHz):
D
d (ppm) 7.20 (s, 1H, NH), 6.51 (d, 1H, J 7.3 Hz, CH2), 6.29 (dd, 1H,
J 7.3 Hz, J 6.9 Hz, CH), 5.86 (d, 1H, J 6.9 Hz, CH2), 5.78 (d, 1H, J2,3
10.6 Hz, H-2), 5.25 (dd, 1H, J2,3 10.6 Hz, J3,4 2.8 Hz, H-3), 5.39 (dd,
3.2.8. N-Propanoyl-2,3,4,6-tetra-O-acetyl-1-cyano-
pyranosylamine (3,4,5,7-tetra-O-acetyl-2-deoxy-2-propan-
amido- -gluco-hept-2-ulopyranosononitrile) (13)
a-D-gluco-
0
1H, J3,4 2.8 Hz, J4,5 1.1 Hz, H-4), 4.23 (t, 1H, J5,6 6.6 Hz, J5,6 6.6 Hz,
a
-D
0
0
H-5), 4.18 (dd, 1H, J6,6 10.7 Hz, J5,6 6.6 Hz, H-6), 4.09 (dd, 1H, J6,6
Prepared from 5 (0.31 g, 0.69 mmol) in CH3CH2CN according to
Section 3.2. Reaction time 3 d, purification by column chromatog-
raphy (1:3 EtOAc–CHCl3), yield 0.16 g (53%) white crystals from
10.7 Hz, J5,6 6.6 Hz, H-6), 2.20, 2.16, 2.02, 1.99 (4s, 12H, OCOCH3);
13C NMR (CDCl3, 90 MHz): d (ppm) 170.3 (NHCOCH@CH2), 170.1,
170.0, 169.7, 168.1 (CO), 130.2 (CH@CH2), 128.8 (CH@CH2), 114.5
+25 (c 0.61, CHCl3); 1H NMR (CDCl3,
3
EtOAc. Mp: 187–189 °C; [a]
D
(CN, JH-2,CN = ꢀ3.2), 78.2 (C-1), 68.1, 67.7, 67.6, 66.7 (C-2–C-5),
200 MHz): d (ppm) 6.97 (s, 1H, NH), 5.57 (d, 1H, J2,3 9.8 Hz, H-2),
5.31 (dd, 1H, J3,4 4.4 Hz, J4,5 1.1 Hz, H-4), 5.16 (dd, 1H, J2,3 9.8 Hz,
J3,4 4.4 Hz, H-3), 4.29 (dd, 1H, J6,6 12.5 Hz, J5,6 6.0 Hz, H-6), 4.00
60.6 (C-6), 20.5 (2), 20.4 (2) (CH3); Anal. Calcd for C18H22N2O10
(426.37): C, 50.70; H, 5.20; N, 6.57. Found: C, 49.93; H, 5.12; N,
6.39.
0
0
0
(dd, 1H, J6,6 12.5 Hz, J5,6 6.0 Hz, H-6), 3.96 (t, 1H, J5,6 6.0 Hz, J5,6
6.0 Hz, H-5), 2.42 (q, 2H, J 7.3 Hz, J 7.2 Hz, CH2CH3), 2.16, 2.11,
2.03 (2) (3s, 12H, OCOCH3), 1.21 (t, 3H, J 7.3 Hz, J 7.2 Hz, CH2CH3);
13C NMR (CDCl3, 50 MHz): d (ppm) 173.4 (NHCOCH2CH3), 170.3,
3.2.5. N-(But-3-enoyl)-2,3,4,6-tetra-O-acetyl-1-cyano-
topyranosylamine (3,4,5,7-tetra-O-acetyl-2-(but-3-enamido)-2-
deoxy- -galacto-hept-2-ulopyranosononitrile) (10)
a-D-galac-
a-D
3
169.8, 168.7, 167.6 (CO), 114.1 (CN, JH-2,CN = ꢀ3.0 Hz), 76.0 (C-1),
Prepared from 1 (0.10 g, 0.22 mmol) in CH2CHCH2CN according
to Section 3.2. Reaction time 2 d, purification by column chroma-
tography (1:3 EtOAc–CHCl3), yield 0.06 g (62%) white crystals.
70.1, 69.8, 68.2, 66.9 (C-2–C-5), 60.6 (C-6), 28.7 (CH2CH3), 20.2,
20.1, 20.0, 19.9 (CH3), 8.4 (CH2CH3); Anal. Calcd for C18H24N2O10
(428.391): C, 50.47; H, 5.65; N, 6.54. Found: C, 50.03; H, 5.52; N,
6.23.
Mp: 149–150 °C; [
a
]
D
+57 (c 0.88, CHCl3); 1H NMR (CDCl3,
360 MHz): d (ppm) 6.85 (s, 1H, NH), 5.99 (m, 1H, CH), 5.38 (d,
1H, J2,3 10.7 Hz, H-2), 5.40–5.35 (m, 2H, H-3, H-4), 5.14 (m, 2H,
CH2), 4.20 (m, 3H, H-5, H-6, H-60), 3.19 (d, 2H, J 7.3 Hz, CH2),
2.20, 2.16, 2.03, 2.00 (4s, 12H, OCOCH3); 13C NMR (CDCl3,
90 MHz): d (ppm) 170.3 (NHCOCH2CH@CH2), 170.0, 169.9 167.8,
167.7 (CO), 129.9 (NHCOCH2CH@CH2), 120.5 (NHCOCH2CH@CH2),
3.2.9. N-Propanoyl-2,3,4,6-tetra-O-benzoyl-1-cyano-
pyranosylamine (3,4,5,7-tetra-O-benzoyl-2-deoxy-2-propan-
amido- -gluco-hept-2-ulopyranosononitrile) (15)
a-D-gluco-
a
-D
Prepared from 6 (0.30 g, 0.43 mmol) in CH3CH2CN according to
Section 3.2. Reaction time 2 d, purification by column chromatog-
raphy (1:3 EtOAc–CH2Cl2), yield 0.17 g (57%) white crystals. Mp:
3
114.4 (CN, JH-2,CN = ꢀ3.1 Hz), 78.0 (C-1), 68.0, 67.7, 67.6, 66.6 (C-
2–C-5), 60.7 (C-6), 41.0 (NHCOCH2CH@CH2) 20.5 (2), 20.4, 20.3
(CH3); Anal. Calcd for C19H24N2O10 (440.40): C, 51.82; H, 5.49; N,
6.36. Found: C, 51.34; H, 5.43; N, 6.55.
239–241 °C;
[
a]
+62.0 (c 1.03, CHCl3); 1H NMR (CDCl3,
D
360 MHz): d (ppm): 8.00–7.08 (m, 20H, ArH), 7.71 (s, 1H, NH),
6.88 (pseudo t, 1H, J 9.8 Hz, J 9.2 Hz, H-3 or H-4), 6.36 (d, 1H, J2,3
9.8 Hz, H-2), 5.82 (pseudo t, 1H, J 9.8 Hz, J 9.2 Hz, H-3 or H-4),
4.46–4.40 (m, 3H, H-5, H-6, H-60), 2.40 (pseudo q, 2H, J 7.2 Hz, J
5.2 Hz, CH2), 1.10 (pseudo t, 3H, J 7.2 Hz, J 5.2 Hz, CH3); 13C NMR
(CDCl3, 90 MHz): d (ppm): 166.1 (NHCOCH2CH3), 166.1, 165.8,
3.2.6. N-Methoxyacetyl-2,3,4,6-tetra-O-acetyl-1-cyano-
topyranosylamine (3,4,5,7-tetra-O-acetyl-2-deoxy-2-methoxy-
acetamido- -galacto-hept-2-ulopyranosononitrile) (11)
a-D-galac-
a-D
3
Prepared from 1 (0.10 g, 0.22 mmol) in CH3OCH2CN according
to Section 3.2. Reaction time 2 d, purification by column chroma-
tography (1:3 EtOAc–CHCl3), yield 0.02 g (24%) white crystals.
164.8, 164.7 (CO), 134.0–127.4 (benzoyl ArC), 114.8 (CN, JH-
2,CN, = ꢀ2.2 Hz), 77.8 (C-1), 71.4, 70.8, 69.2, 68.5 (C-2–C-5), 62.0
(C-6), 29.0 (NHCOCH2CH3), 8.10 (NHCOCH2CH3); Anal. Calcd for
Mp: 149–151 °C; [
a
]
D
+29 (c 1.22, CHCl3); 1H NMR (CDCl3,
C38H32N2O10 (676.69): C, 67.45; H, 4.77; N, 4.14. Found: C, 67.10;
360 MHz): d (ppm) 7.34 (s, 1H, NH), 5.78 (d, 1H, J2,3 10.9 Hz, H-
2), 5.41 (dd, 1H, J3,4 3.2 Hz, J4,5 1.1 Hz, H-4), 5.11 (dd, 1H, J2,3
10.9 Hz, J3,4 3.2 Hz, H-3), 4.22–4.05 (m, 3H, H-5, H-6, H-60), 4.04
(d, 1H, J 6.9 Hz, CH2), 3.97 (d, 1H, J 6.9 Hz, CH2), 3.49 (s, 3H,
OCH3), 2.21, 2.17, 2.03, 2.01 (4s, 12H, OCOCH3); 13C NMR (CDCl3,
90 MHz): d (ppm) 170.4 (NHCOCH2OCH3), 170.1, 169.9 169.3,
H, 4.36; N, 4.01.
3.2.10. N-Pivaloyl-2,3,4,6-tetra-O-benzoyl-1-cyano-a-D-gluco-
pyranosylamine (3,4,5,7-tetra-O-benzoyl-2-deoxy-2-pival-
amido- -gluco-hept-2-ulopyranosononitrile) (16)
a
-D
Prepared from 6 (0.20 g, 0.28 mmol) in (CH3)3CCN according to
Section 3.2. Reaction time 2 d, purification by column chromatog-
raphy (1:2 EtOAc–Hexane), yield 0.06 g (27%) white crystals and
3
167.7 (CO), 114.1 (CN, JH-2,CN = ꢀ3.0), 77.8 (C-1), 71.6 (NHCO-
CH2OCH3), 68.1, 67.8, 67.5, 66.4 (C-2–C-5), 60.5 (C-6), 59.3 (NHC-
OCH2OCH3), 20.6 (2), 20.4, 20.3 (CH3); Anal. Calcd for
C18H24N2O11 (444.39): C, 48.65; H, 5.44; N, 6.30. Found: C, 50.00;
H, 5.70; N, 6.47.
compound 4 (0.05 g, 27%). Mp: 226–229 °C; [
a]
D
+37 (c 0.98,
CHCl3); 1H NMR (CDCl3, 360 MHz): d (ppm): 8.10–7.24 (m, 20H,
ArH), 6.85 (s, 1H, NH), 6.13 (d, 1H, J2,3 9.8 Hz, H-2), 5.70 (pseudo

2110
K. Czifrák et al. / Carbohydrate Research 346 (2011) 2104–2112
0
t, 2H, J 9.8 Hz, J 9.2 Hz in each, H-3, H-4), 4.62 (dd, 1H, J6,6 12.5 Hz,
(d, 3H, J 6.8 Hz, CH(CH3)); 13C NMR (CDCl3, 125 MHz) d (ppm):
172.5 (COOCH3), 170.2, 169.8, 169.7, 169.1 (CO), 164.2 (CONH,
3JH-2,CONHCH2CO2Me = 2.2 Hz), 94.3 (C-1), 73.3, 69.7, 66.4, 66.4 (C-2–
C-5), 60.5 (C-6), 52.5 (COOCH3), 48.0 (CH), 20.8, 20.7, 20.5, 20.4
(CH3), 17.6 (CH(CH3). Anal. Calcd for C19H26N1Br1O12 (540.32): C,
42.24; H, 4.85; N, 2.59; Br, 14.79. Found: C, 41.80; H, 4.68; N,
2.44; Br, 15.10.
J5,6 2.6 Hz, H-6), 4.46 (dd, 1H, J6,6 12.6 Hz, J5,6 5.9 Hz, H-60), 4.34
0
0
0
(ddd, 1H, J4,5 9.8 Hz, J5,6 5.9 Hz, J5,6 2.6 Hz, H-5), 1.33 (s, 9H,
C4H9); 13C NMR (CDCl3, 90 MHz): d (ppm): 177.6 (NHCOC(CH3)3),
166.0, 165.9, 164.9, 163.5 (CO), 133.5–127.6 (benzoyl ArC), 114.4
3
(CN, JH-2,CN = ꢀ2.6 Hz), 77.8 (C-1), 71.6, 70.6, 69.6, 68.5 (C-2–C-
5), 67.0 (NHCOC(CH3)3), 62.2 (C-6), 27.2 (NHCOC(CH3)3) Anal. Calcd
for C40H36N2O10 (704.74): C, 68.17; H, 5.15; N, 3.97. Found: C,
68.00; H, 4.86; N, 4.11.
3.4. N-[(1R)-2,3,4,6-Tetra-O-acetyl-1,5-anhydro-D-galactitol-
spiro[1.4]-2-methyl-2-oxazolin-5-ylidene]glycine methylester
(21)
3.2.11. N-Acetyl-2,3,4-tri-O-acetyl-1-cyano-b-D-arabinopyrano-
sylamine (2-acetamido-3,4,5-tri-O-acetyl-2-deoxy-b-D-arabino-
hex-2-ulopyranosononitrile) (17)
Compound 1932 (0.20 g, 0.38 mmol) was dissolved in dry CH3CN
(2 mL) and Ag2CO3 (1.1 equiv) was added. The solution was stirred at
rt in the dark until complete transformation of the starting material
(4 d, TLC 3:1 EtOAc–hexane). The mixture was filtrated on a Celite
pad and the solvent was removed from the filtrate. The obtained
crude product was purified by column chromatography (3:1
EtOAc–hexane) to give 21 (0.09 g, 65%) as a colourless oil, Rf = 0.39
Prepared from 7 (0.14 g, 0.36 mmol) in CH3CN according to Sec-
tion 3.2. Reaction time 2 d, purification by column chromatography
(1:1?3:1 EtOAc–Hexane), yield 0.05 g (41%) white crystals from
CH2Cl2–Et2O. Mp: 170–172 °C; [
(CDCl3, 360 MHz): d (ppm) 8.53 (s, 1H, NH), 5.69 (d, 1H, J2,3
a
]
ꢁ29 (c 1.07, CHCl3); 1H NMR
D
9.6 Hz, H-2), 5.34 (dd, 1H, J2,3 9.6 Hz, J3,4 5.0 Hz, H-3), 5.30 (ddd,
1H, J3,4 5.0 Hz, J4,5 2.5 Hz, J4,5 1.6 Hz, H-4), 4.06 (dd, 1H, J6,6
(3:1 EtOAc–hexane), [
a]
D
+0.1 (c 0.44, CHCl3); 1H NMR (CDCl3,
0
0
0
13.5 Hz, J5,6 2.5 Hz, H-5), 3.80 (dd, 1H, J6,6 13.5 Hz, J5,6 1.6 Hz, H-
50), 2.13 (2), 2.08, 1.96 (3s, 12H, OCOCH3, NHCOCH3); 13C NMR
(CDCl3, 90 MHz): d (ppm) 170.9 (NHCOCH3), 170.1, 169.8, 168.2
360 MHz): d (ppm): 5.70 (d, 1H, J2,3 10.6 Hz, H-2), 5.56 (dd, 1H, J3,4
4.0 Hz, J4,5 <1 Hz, H-4), 5.46 (dd, 1H, J2,3 10.6 Hz, J3,4 4.0 Hz, H-3),
0
4.62 (ddd, 1H, J5,6 6.6 Hz, J5,6 6.6 Hz, J4,5 <1 Hz, H-5), 4.25 (s, 2H,
3
0
0
(CO), 114.7 (CN, JH-2,CN = ꢀ3.1 Hz), 78.0 (C-1), 67.9, 66.9, 66.8 (C-
CH2), 4.19 (dd, 1H, J6,6 11.9 Hz, J5,6 6.6 Hz, H-6), 4.10 (dd, 1H, J6,6
11.9 Hz, J5,6 6.6 Hz, H-60), 3.77 (s, 3H, OCH3), 2.25 (s, 3H, CH3),
2.19, 2.03, 2.01, 1.97 (4s, 12H, OCOCH3); 13C NMR (CDCl3,
125 MHz): d (ppm): 170.4, 170.2, 170.0, 168.7 (CO), 165.3 (C@N),
0
2–C-4), 61.6 (C-5), 23.0 (CH3), 20.7, 20.5, 20.4 (CH3); Anal. Calcd
for C14H18N2O8 (342.30): C, 49.12; H, 5.30; N, 8.18. Found: C,
50.10; H, 5.57; N, 8.33.
3
158.2 (C@N, JH-2,C@NCH2COOCH3 = ꢀ3.1 Hz), 95.7 (C-1), 70.8, 69.5,
3.2.12. N-Propenoyl-2,3,4-tri-O-acetyl-1-cyano-b-
D-arabinopyr-
68.3, 67.9 (C-2–C-5), 61.4 (C-6), 52.1 (OCH3), 50.3 (CH2), 20.7, 20.5,
20.5, 20.4 (OCOCH3), 14.9 (CH3); Anal. Calcd for C20H26N2O12
(486.44): C, 49.38; H, 5.39; N, 5.76. Found: C, 49.55; H, 5.56; N, 5.80.
anosylamine (3,4,5-tri-O-acetyl-2-deoxy-2-propenamido-b-
arabino-hex-2-ulopyranosononitrile) (18)
D-
Prepared from 7 (0.31 g, 0.81 mmol) in CH2CHCN according to
Section 3.2. Reaction time 2 d, purification by column chromatog-
raphy (1:1?3:1 EtOAc–hexane), yield 0.12 g (43%) as a colourless
3.5. N-[(1R)-2,3,4,6-Tetra-O-acetyl-1,5-anhydro-D-galactitol-
spiro[1.4]-2-benzyloxycarbonylaminomethyl-2-oxazolin-5-
ylidene]glycine methylester (22)
syrup. Rf = 0.28 (1:1 EtOAc–hexane); [
a]
ꢁ28 (c 1.06, CHCl3); 1H
D
NMR (CDCl3, 200 MHz): d (ppm) 6.90 (s, 1H, NH), 6.51 (d, 1H, J
7.5 Hz, CH2), 6.29 (dd, 1H, J 7.5 Hz, J 6.9 Hz, CH), 5.86 (d, 1H, J
7.5 Hz, CH2), 5.77 (d, 1H, J2,3 8.8 Hz, H-2), 5.28 (dd, 1H, J2,3 8.8 Hz,
Compound 19 (0.17 g, 0.33 mmol) was dissolved in dry CH3NO2
(3 mL), NCCH2NHCOOCH2Ph (10 equiv) and Ag2CO3 (1.1 equiv)
were added. The mixture was stirred in the dark at rt for 6 d. After
completion of the reaction (TLC, 3:1 EtOAc–hexane) the mixture
was filtered on a Celite pad and the solvent was removed. The
crude oil was purified by column chromatography (3:1 EtOAc–hex-
ane) to give 0.04 g (29%) of 22 (1:1 mixture of two isomers) as a
colourless oil. Rf = 0.29 (EtOAc); 1H NMR (CDCl3, 360 MHz): d
(ppm): 7.44–7.32 (m, 5H, Ph), 7.01 (s, 1H, NH), 5.71 (d, 1H,
J2,310.6 Hz, H-2), 5.58–5.52 (m, 2H, H-4, H-40), 5.48-5.30 (m, 3H,
H-20, H-3, H-30), 5.20-5.14 (m, 2H, CH2), 4.60–4.62 (m, 2H, H-5,
H-50), 4.32–4.04 (m, 10H, H-6a, H-6a0, H-6b, H-6b0, CH2a, CH2b,
CH2Ph), 3.79 (s, 3H, OCH3), 2.19, 2.17, 2.13, 2.11, 2.03, 2.01, 1.99,
1.97 (8s, 24H, OCOCH3); 13C NMR (CDCl3, 125 MHz): d (ppm):
170.5, 170.3, 170.1 (2), 169.9, 169.4, 168.8 (2) (CO), 168.2
(CO2CH3), 165.1 (C@N), 157.1, 157.0 (CO2CH2Ph), 135.9–128.2 (aro-
matics), 95.3 (C-1), 94.1 (C-10), 73.6, 71.0, 69.8, 69.5, 68.3, 67.9,
67.5, 66.6 (C-2–C-5 and C-20–C-50), 71.0 (CH2), 60.7 (C-6), 60.4
0
J3,4 3.5 Hz, H-3), 5.24 (ddd, 1H, J3,4 3.5 Hz, J4,5 2.6 Hz, J4,5 1.2 Hz,
H-4), 4.05–3.94 (m, 2H, H-5, H-50), 2.18, 2.17, 2.06 (3s, 9H,
OCOCH3); 13C NMR (CDCl3, 50 MHz):
d
(ppm) 170.0
(NHCOCH@CH2), 169.6, 168.3, 165.6 (CO), 129.7 (CH2@CH), 128.9
3
(CH2@CH), 114.5 (CN, JH-2,CN = ꢀ3.1 Hz), 78.1 (C-1), 67.7, 66.9,
66.7 (C-2–C-4), 61.6 (C-5), 23.0 (CH3), 20.7, 20.5, 20.4 (CH3); Anal.
Calcd for C15H18N2O8 (354.31): C, 50.85; H, 5.12; N, 7.91. Found: C,
50.30; H, 5.37; N, 8.13.
3.3. N-(2,3,4,6-Tetra-O-acetyl-1-bromo-1-deoxy-b-
anosylcarbonyl)]- -alanine methylester (N-(3,4,5,7-tetra-O-
acetyl-2-bromo-2-deoxy- -galacto-hept-2-ulopyranosonoyl)-
D-galactopyr-
L
a-D
L
-alanine methylester) (20)
Pentachlorophenyl C-(2,3,4,6-tetra-O-acetyl-1-bromo-1-deoxy-
D
-galactopyranosyl)formate32 (0.30 g, 0.43 mmol) was dissolved
b-
0
0
in dry 1,4-dioxane (3 mL) and methyl
L
-alaninateꢂHCl (2 equiv),
(C-60), 52.6 (OCH3), 52.2 (OCH3 ), 41.2 (2) (CH2, CH2 ), 20.9 (6),
and Et3N (2 equiv) were added. The reaction mixture was stirred
at rt and monitored by TLC (1:1 EtOAc–hexane). After completion
of the reaction the solvent was removed. The obtained crude prod-
uct was purified by column chromatography (1:1 EtOAc–hexane)
to give 0.18 g (73%) 20 as colourless oil. Rf = 0.24 (1:1 EtOAc–hex-
20.5 (CH3)
3.6. N-[(1R)-2,3,4,6-Tetra-O-acetyl-1,5-anhydro-
D
-galactitol-
spiro[1.4]-2-methyl-2-oxazolin-5-ylidene]-
ester (23)
L-alanine methyl-
ane); [
a] +83 (c 0.73, CHCl3); IR mmax (CHCl3): 3380, 2958, 1758,
D
1678, 1374, 1262, 1070 cmꢁ1
;
1H NMR (CDCl3, 360 MHz)
d
Compound 20 (0.60 g, 1.10 mmol) was dissolved in dry CH3CN
(10 mL) and Ag2CO3 (1.1 equiv) was added. After stirring for 4 d
in the dark the mixture was filtered on a Celite pad and the solvent
was removed. The obtained crude product was purified by column
chromatography (3:1 EtOAc–hexane) to give 0.24 g (43%) 23 as a
(ppm): 7.15 (t, 1H, J = 6.8, 6.8 Hz, NH), 5.54 (dd, 1H, J3,4 3.2 Hz,
J4,5 1.6 Hz, H-4), 5.42 (d, 1H, J2,3 10.0 Hz, H-2), 5.32 (dd, 1H, J
2,3
10.0 Hz, J3,4 3.2 Hz, H-3), 4.60–4.48 (m, 4H, H-5, H-6, H-60, CH),
3.79 (s, 3H, OCH3), 2.18, 2.12, 2.09, 1.98 (4s, 12H, OCOCH3), 1.45

K. Czifrák et al. / Carbohydrate Research 346 (2011) 2104–2112
2111
colourless oil. Rf = 0.19 (1:1 EtOAc–hexane), [
a
]
D +1 (c 0.41, CHCl3);
3.7.3. N-(1-Acetamido-2,3,4,6-tetra-O-acetyl-1-deoxy-b-
topyranosylcarbonyl)-
3,4,5,7-tetra-O-acetyl-2-deoxy-
osonoyl)- -alanine methylester) (26)
D
-galac-
1H NMR (CDCl3, 360 MHz): d (ppm): 5.65 (d, 1H, J2,310.6 Hz, H-2),
5.54 (dd, 1H, J3,4 4.0 Hz, J4,5 <1 Hz, H-4), 5.42 (dd, 1H, J2,3 10.6 Hz,
L
-alanine methylester (N-(2-acetamido-
a-D
-galacto-hept-2-ulopyran-
0
J3,4 4.0 Hz, H-3), 4.58 (ddd, 1H, J5,6 6.6 Hz, J5,6 6.6 Hz, J4,5 <1 Hz,
L
0
H-5), 4.42 (q, 1H, J 6.9 Hz, J 6.4 Hz, CH), 4.18 (dd, 1H, J6,6 11.9 Hz,
Prepared from 23 (0.05 g, 0.10 mmol) according to Section 3.7.
Purified by column chromatography (3:1 EtOAc–hexane), yield
J5,6 6.6 Hz, H-6), 4.11 (1H, J6,6 11.9 Hz, J5,6 6.6 Hz, H-60), 3.70 (s,
0
0
3H, OCH3), 2.24 (s, 3H, CH3), 2.20, 2.03, 2.01, 1.99 (4s, 12H,
0.015 g (29%) of 26 as colourless oil. Rf = 0.15 (EtOAc); [a] +69.0
D
OCOCH3), 1.48 (d, 3H,
J
6.4 Hz, CH(CH3)); 13C NMR (CDCl3,
(c 0.40, CHCl3); 1H NMR (CDCl3, 360 MHz): d (ppm): 7.28 (t, 1H, J
5.8 Hz, J 5.8 Hz, NH), 6.27 (s, 1H, NH), 5.46–5.42 (m, 2H, H-2, H-
4), 5.19 (dd, 1H, J2,3 10.6 Hz, J3,4 3.3 Hz, H-3), 4.52 (q, 1H, J 6.8 Hz,
125 MHz): d (ppm): 171.3, 170.4, 170.2, 169.9 (CO), 165.2 (C@N),
3
155.8 (C@N, JH-2,C@NCH– = ꢀ3.3 Hz), 95.5 (C-1), 70.6, 69.5, 68.4,
0
67.9 (C-2–C-5), 61.3 (C-6), 56.6 (CH), 52.0 (OCH3), 20.6, 20.5,
20.4, 20.3 (OCOCH3), 18.2 (CH(CH3), 14.9 (CH3); Anal. Calcd for
J 6.4 Hz, CH), 4.35 (dd, 1H, J6,6 11.9 Hz, J5,6 6.6 Hz, H-6), 4.25
0
0
(ddd, 1H, J5,6 6.6 Hz, J5,6 6.6 Hz, J4,5 0.9 Hz, H-5), 4.14 (1H, dd, J6,6
11.9 Hz, J5,6 6.6 Hz, H-60), 3.79 (s, 3H, OCH3), 2.23, 2.10, 2.07,
0
C21H28N2O12 (500.44): C, 51.12; H, 5.70; N, 6.26. Found: C, 50.85;
H, 5.52; N, 5.96.
2.06, 2.00 (5s, 15H, OCOCH3, NHCOCH3), 1.46 (d, 3H, J 6.4 Hz,
CH(CH3)); 13C NMR (CDCl3, 125 MHz): d (ppm): 173.1, 171.3,
171.0, 170.7 (CO), 170.5 (CO2CH3), 168.9 (NHCOCH3), 166.7
3.7. General procedure for the hydrolysis of spiro-oxazolines
21–23 to oligopeptides 24–26
3
(CONHCH2, JH-2,CONHCH2COOCH3 = ꢀ2.4 Hz), 83.9 (C-1), 69.2, 68.9,
67.4 (2) (C-2–C-5), 60.8 (C-6), 52.8 (OCH3), 48.9 (CH), 24.0
(NHCOCH3), 20.9, 20.6, (2), 20.5 (CH3), 18.4 (CH(CH3)); Anal. Calcd
for C21H30N2O13 (518.45): C, 49.90; H, 5.72; N, 5.60. Found: C,
49.63; H, 5.56; N, 5.44.
Compounds 21–23 each was dissolved in CH2Cl2 (1 mL/
0.1 mmol), CF3COOH or AcOH (1 equiv) and water (2 equiv) were
added. The mixture was stirred at rt until disappearance of the
starting material (TLC, 3:1 EtOAc–hexane). It was then diluted with
CH2Cl2 and washed with satd aq NaHCO3 solution (2 ꢃ 5 mL),
water (5 mL), dried, and the solvent removed. The obtained syrup
was purified by column chromatography.
3.8. N-(2,3,4,6-Tetra-O-acetyl-1-amino-1-deoxy-
a-D-galactopyr-
anosylcarbonyl)glycine methylester (N-(3,4,5,7-tetra-O-acetyl-
2-amino-2-deoxy-b-D-galacto-hept-2-ulopyranosonoyl)glycine
methylester) (28)
3.7.1. N-(1-Acetamido-2,3,4,6-tetra-O-acetyl-1-deoxy-b-
topyranosylcarbonyl)glycine methylester (N-(2-acetamido-3,4,
5,7-tetra-O-acetyl-2-deoxy- -galacto-hept-2-ulopyranos-
onoyl)glycine methylester) (24)
D-galac-
Azide 2732 (0.10 g, 0.20 mmol) was dissolved in dry EtOAc (5 mL)
and Raney-Ni (ꢀ0.2 g, 2 equiv) was added to the solution. The mix-
ture was stirred at 70 °C and monitored by TLC (3:1 EtOAc–hexane).
After completion of the reaction the mixture was filtered on a Celite
pad and the solvent was removed. The obtained syrup was crystal-
lised from EtOH to give 0.07 g (79%) of 28 as a white crystalline
a-D
Prepared from 21 (0.05 g, 0.10 mmol) according to General pro-
cedure 3.7. Purified by column chromatography (9:1 EtOAc–
MeOH), yield (0.02 g, 55%) of 24 as a colourless syrup. Rf = 0.42
(9:1 EtOAc–hexane); [
a
]
D
+69 (c 0.38, CHCl3); 1H NMR (CDCl3,
product. Mp: 123–126 °C; [a]
D +77 (c 1.06, CHCl3); 1H NMR (CDCl3,
360 MHz): d (ppm): 7.28 (t, 1H, J 5.8 Hz, J 5.8 Hz, NH), 6.37 (s, 1H,
NH), 5.45 (d, 1H, J2,3 10.6 Hz, H-2), 5.56 (dd, 1H, J3,4 3.3 Hz, J4,5
1.1 Hz, H-4), 5.22 (dd, 1H, J2,3 10.6 Hz, J3,4 3.3 Hz, H-3), 4.33–3.98
(m, 5H, H-5, H-6, H-60, CH2), 3.78 (s, 3H, OCH3), 2.20, 2.09 (2),
2.06, 1.99 (4s, 15H, OCOCH3, NHCOCH3); 13C NMR (CDCl3,
125 MHz): d (ppm): 170.9, 170.5, 170.1, 169.5 (CO), 170.1 (CO2CH3),
168.6 (NHCOCH3), 167.3 (CONHCH2, 3JH-2,CONHCH2COOCH3 = ꢀ2.4 Hz),
83.7 (C-1), 68.7, 68.4, 67.0 (2) (C-2–C-5), 60.8 (C-6), 52.3 (OCH3),
41.3 (CH2), 23.5 (NHCOCH3), 20.6 (3), 20.5 (CH3); Anal. Calcd for
360 MHz): d (ppm): 7.53 (t, 1H, J 5.3 Hz, J 5.3 Hz, NH), 5.62 (dd, 1H,
J2,3 11.0 Hz, J3,4 3.2 Hz, H-3), 5.50 (dd, 1H, J3,4 3.2 Hz, J4,5 <1 Hz, H-4),
0
5.24 (d, 1H, J2,3 11.0 Hz, H-2), 5.13 (ddd, 1H, J5,6 6.3 Hz, J5,6 6.3, J4,5
<1 Hz, H-5), 4.18 (dd, 1H, J 18.4 Hz, J 5.3 Hz, CH2), 4.10 (dd, 1H,
0
0
0
J6,6 11.5 Hz, J5,6 6.3 Hz, H-6), 4.02 (dd, 1H, J6,6 11.0 Hz, J5,6 6.3 Hz,
H-60), 3.95 (dd, 1H, J 18.4 Hz, J 5.3 Hz, CH2), 3.78 (s, 3H, OCH3);
2.29 (s, 2H, NH2), 2.16, 2.12, 2.04, 1.95 (4s, 12H, OCOCH3); 13C
NMR (CDCl3, 125 MHz): d (ppm): 170.4 (CO2CH3), 170.3, 170.1,
3
169.8, 169.6 (CO), 169.5 (CONH, JH-2,CONHCH2COOCH3 = ꢀ5.8 Hz),
C20H28N2O13 (504.45): C, 47.62; H, 5.59; N, 5.55. Found: C, 47.44;
86.5 (C-1), 71.3, 70.4, 68.9, 68.0 (C-2–C-5), 62.0 (C-6), 52.3
H, 5.36; N, 5.65.
(COOCH3), 40.7 (CH2), 20.6 (2), 20.5 (2) (CO); Anal. Calcd for
C18H26N2O12 (462.41): C, 46.75; H, 5.67; N, 6.06. Found: C, 46.45;
3.7.2. N-(2,3,4,6-Tetra-O-acetyl-1-deoxy-1-Z-glycylamido-b-
D
-
H, 5.76; N, 5.90.
galactopyranosylcarbonyl)glycine methylester (N-(3,4,5,7-tetra-
O-acetyl-2-deoxy-2-Z-glycylamido- -galacto-hept-2-
a-
D
3.9. N-(1-Acetamido-2,3,4,6-tetra-O-acetyl-1-deoxy-a-D-galac-
ulopyranosonoyl)glycine methylester) (25)
topyranosylcarbonyl)glycine methylester (N-(2-acetamido-3,4,
Prepared from 22 (0.04 g, 0.06 mmol) according to Section 3.7.
Purified by column chromatography (9:1 EtOAc–MeOH), yield
0.01 g (27%) of 24 as a colourless oil. Rf = 0.13 (5:1 EtOAc–hexane);
5,7-tetra-O-acetyl-2-deoxy-b- -galacto-hept-2-ulopyrano-
sonoyl)glycine methylester) (29)
D
[
a]
D
+58 (c 0.160, CHCl3); 1H NMR (CDCl3, 360 MHz): d (ppm):
Compound 28 (0.26 g, 0.56 mmol) was dissolved in dry pyridine
(5 mL) and AcCl (0.08 mL, 1.12 mmol) was added. The mixture was
stirred at rt overnight and monitored by TLC (99:1 EtOAc–MeOH).
The volatiles were then removed, followed by co-evaporations
with PhCH3 (2x5 mL). The residue was dissolved in EtOAc
(10 mL) and washed with water. The water phase was washed with
EtOAc (5 ꢃ 10 mL). The combined organic phase was dried, the sol-
vent removed, and the residue purified by column chromatography
(99:1 EtOAc–MeOH) to give 0.045 g, (15%) of compound 29 as a
colourless oil in the first fraction (Rf = 0.23, 99:1 EtOAc–MeOH)
and 0.045 g (15%) of compound 24 as the second fraction
(Rf = 0.31, 99:1 EtOAc–MeOH).
7.38–7.32 (m, 5H, ArH), 7.30 (s, 1H, NH), 7.18 (s, 1H, NH), 5.51 (s,
1H, NH), 5.46 (d, 1H, J2,3 10.6 Hz, H-2), 5.44 (dd, 1H, J3,4 3.4 Hz,
J4,5 1.1 Hz, H-4), 5.19 (dd, 1H, J2,3 10.6 Hz, J3,4 3.4 Hz, H-3), 5.12–
5.08 (m, 2H, CH2), 4.29–3.86 (m, 5H, H-5, H-6, H-60, CH2), 3.77 (s,
3H, OCH3), 2.20, 2.06, 2.05, 1.95 (4s, 12H, OCOCH3); 13C NMR
(CDCl3, 125 MHz): d (ppm): 170.6, 170.2, 170, 169.9 (2), 169.5,
168.8, 168.7 (CO2CH3, NHCOCH2, NHCO2, CO), 166.7 (CONCH2,
3JH-2,CONHCH2COOCH3 = ꢀ2.9 Hz); 156.8 (–CO2CH2Ph), 133.0–128.6
(aromatics), 83.8 (C-1), 69.2, 68.5, 67.1 (2) (C-2–C-5), 67.1 (CH2),
65.6 (CH2), 60.8 (C-6), 52.4 (OCH3), 41.4 (2) (CH2), 20.6 (6), 20.5
(2) (CH3); Anal. Calcd for C28H35N3O15 (653.60): C, 51.46; H, 5.40;
N, 6.43. Found: C, 51.65; H, 5.56; N, 6.72.

2112
K. Czifrák et al. / Carbohydrate Research 346 (2011) 2104–2112
16. Gordon, D. M.; Danishefsky, S. J. J. Org. Chem. 1991, 56, 3713–3715.
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D +153 (c 0.078, CHCl3); 1H NMR
(CDCl3, 360 MHz): d (ppm): 7.86 (t, 1H, J 5.8 Hz, J 5.8 Hz, NH), 7.06
(s, 1H, NH), 5.63 (dd, 1H, J2,3 10.5 Hz, J3,4 3.3 Hz, H-3), 5.47 (dd, 1H,
J3,4 3.3 Hz, J4,5 1.0 Hz, H-4), 5.23 (d, 1H, J2,3 10.5 Hz, H-2), 4.60
17. Pavia, A. A.; Ungchhun, S. N.; Durand, J. L. J. Org. Chem. 1981, 46, 3158–3160.
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20. Marra, A.; Sinaÿ, P. Carbohydr. Res. 1990, 200, 319–337.
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22. Handlon, A. L.; Fraser-Reid, B. J. Am. Chem. Soc. 1993, 115, 3796–3797.
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28. Kiss, L.; Somsák, L. Carbohydr. Res. 1996, 291, 43–52.
29. Shimizu, M.; Togo, H.; Yokoyama, M. Synthesis 1998, 799–822.
30. Yokoyama, M. Carbohydr. Res. 2000, 327, 5–14.
0
(pseudo t, 1H, J5,6 6.7 Hz, J5,6 6.4 Hz, H-5), 4.14–3.05 (m, 4H, H-6,
H-60, CH2), 3.74 (s, 3H, OCH3), 2.15, 2.14, 2.02, 2.01, 1.96 (5s,
15H, OCOCH3, NHCOCH3); 13C NMR (CDCl3, 125 MHz): d (ppm):
172.7, 170.2 (3), 169.6 (CO, COOCH3), 169.3 (NHCOCH3), 166.3
3
(CONHCH2, JH-2,CONHCH2COOCH3 = ꢀ5.3 Hz), 85.8 (C-1), 71.1, 70.1,
68.1, 67.2 (C-2–C-5), 61.2 (C-6), 52.4 (OCH3), 41.1 (CH2), 24.1
(NHCOCH3), 20.9, 20.6 20.5 (2) (CH3); Anal. Calcd for C20H28N2O13
(504.45): C, 47.62; H, 5.59; N, 5.55. Found: C, 47.14; H, 5.31; N,
5.25.
31. Gyóllai, V.; Somsák, L.; Györgydeák, Z. Tetrahedron 1998, 54, 13267–13276.
32. Czifrák, K.; Szilágyi, P.; Somsák, L. Tetrahedron: Asymmetry 2005, 16, 127–141.
33. Czifrák, K.; Kovács, L.; Kövér, K. E.; Somsák, L. Carbohydr. Res. 2005, 340, 2328–
2334.
Acknowledgements
This work was supported by the Hungarian Scientific Research
Fund (Grant OTKA NK 68578) as well as by the TÁMOP 4.2.1/B-
09/1/KONV-2010007 project co-financed by the European Union
and the European Social Fund.
34. Májer, G.; Borbás, A.; Illyés, T. Z.; Szilágyi, L.; Bényei, A. C.; Lipták, A. Carbohydr.
Res. 2007, 342, 1393–1404.
}
35. Osz, E.; Sós, E.; Somsák, L.; Szilágyi, L.; Dinya, Z. Tetrahedron 1997, 53, 5813–
5824.
}
36. Somsák, L.; Kovács, L.; Gyóllai, V.; Osz, E. Chem. Commun. 1999, 591–592.
37. Somsák, L.; Kovács, L.; Tóth, M.; Osz, E.; Szilágyi, L.; Györgydeák, Z.; Dinya, Z.;
}
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