Homologation of methyl 2-azido- and 2-acetamido-3,4-di-O-benzyl-2-deoxy-D-hexopyranosides with allyloxymethylmagnesium chloride

Article abstract of DOI:10.1016/S0008-6215(01)00078-7

Methyl 2-azido-2-deoxy-hexodialdo-1,5-pyranosides of the α-, β-D-gluco and α-D-manno configuration as well as methyl 2-acetamido-2-deoxy-hexodialdo-1,5-pyranosides of the α- and β-D-gluco configuration, protected at positions 3 and 4 with O-benzyl groups

Full text of DOI:10.1016/S0008-6215(01)00078-7

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Carbohydrate Research 332 (2001) 225–234
Note
Homologation of methyl 2-azido- and
2-acetamido-3,4-di-O-benzyl-2-deoxy- -hexopyranosides
D
with allyloxymethylmagnesium chloride
Barbara Grzeszczyk, Aleksander Zamojski*
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44, PL-01-224 Warsaw, Poland
Received 12 January 2001; accepted 6 March 2001
Dedicated to Professor Gerard Descotes on the occasion of his 68th birthday and in appreciation of his
achievements in carbohydrate chemistry
Abstract
Methyl 2-azido-2-deoxy-hexodialdo-1,5-pyranosides of the a-, b-
D
-gluco and a-
D-manno configuration as well as
-gluco configuration, protected at positions
methyl 2-acetamido-2-deoxy-hexodialdo-1,5-pyranosides of the a- and b-
D
3 and 4 with O-benzyl groups were reacted with an excess of allyloxymethylmagnesium or (phenyldimethylsi-
lyl)methylmagnesium chlorides to afford mixtures of C-6 stereoisomeric heptopyranosides. Configuration of the
1
products separated by column chromatography was assigned by H NMR data. © 2001 Elsevier Science Ltd. All
rights reserved.
Keywords: Methyl 2-azido-3,4-di-O-benzyl-2-deoxy-a-, -b-
D
-gluco- and -a-D-manno-heptopyranosides; Methyl 2-acetamido-3,4-di-
O-benzyl-2-deoxy-a- and -b-
D
-gluco-heptopyranosides; Allyloxymethylmagnesium chloride; (Phenyldimethylsilyl)methyl-
magnesium chloride; Homologation reaction
taining 2-azido- or 2-acetamido-2-deoxy
groupings.
A convenient route to higher homologs of
hexoses consists in reaction of properly pro-
tected dialdo-1,5-pyranosides with C1 Grig-
nard reagents of the type ROCH2MgCl or
R3SiCH2MgCl followed by chromatographic
separation of the resulting stereoisomeric hep-
tosides.1–4 The homologation reaction is com-
patible with a variety of protecting groups
including ethers, acetals1–3 and esters.4 In this
paper, we present our results on chain-elonga-
tion reactions of methyl hexopyranosides con-
Natural 2-amino-2-deoxy-heptoses are only
scarcely known. G. Weise et al.5 found,
among the sugars of Anacystis nidulans cell
wall LPS, a minor component to which was
assigned the structure of a 2-amino-2-deoxy-
heptose with the
configuration. 2,6-Diamino-2,3,4,6,7-pentade-
oxy- -ribo-heptopyranose (purpurosamine B,
2) was found as a component of the aminogly-
D
-glycero-
D
-gulo(ido?) (1)
D
8
coside antibiotic gentamycin C2.6
D
-7 and LD
-
forms of this sugar have been obtained by
synthesis.
* Corresponding author. Tel.: +48-22-6323221; fax: +48-
22-6326681.
E-mail address: awzam@icho.edu.pl (A. Zamojski).
Methyl
2-azido-3,4-di-O-benzyl-2-deoxy-
-gluco (3 and
hexopyranosides of a- and b-
D
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(01)00078-7

226
B. Grzeszczyk, A. Zamojski / Carbohydrate Research 332 (2001) 225–234
318.5 nm indicator of the LD configuration for
the glycero moiety (Fig. 1).11 6,7-Diols 23 and
24 were next acetylated to yield 6,7-di-O-ace-
tyl derivatives 26 and 27, respectively. The
results of chain elongation of aldehydes 6–8,
17 and 18 are collected in Table 1.
The configuration of the methyl heptosides
obtained was assigned on the basis of similar-
ity of coupling constants J5,6, J6,7a, and J6,7b in
4), and a- -manno (5) configuration have been
D
selected for the homologation experiments.
For conversion to the corresponding dialdo-
1,5-pyranosides (6–8), the Dess–Martin9 oxi-
dant proved to be the most efficient. Reaction
of the freshly prepared aldehydes (6–8) with
allyloxymethylmagnesium chloride occurred
smoothly at low temperature and afforded
mixtures of diastereoisomeric methyl hep-
tosides in 58–60% overall yield. Both mixtures
(9, 10 and 11, 12) stemming from the a- and
1
the H NMR spectra with the analogous data
of heptosides of established configuration ob-
tained earlier or with the CD spectra (Fig. 1).
For compounds 11 and 12, the configurational
assignments are tentative, based on the obser-
vation of predominance of the DD stereoiso-
mer over the LD counterpart in reactions of
methyl
hexodialdo-1,5-pyranosides
with
alkoxymethylmagnesium chloride.3
b-
rated by simple-column chromatography. The
-manno alde-
D
-gluco substrates (6 and 7) could be sepa-
In summary, chain-elongation reactions
with allyloxymethylmagnesium chloride led to
the expected heptosides in moderate yields.
Although the separation of diastereoisomers
formed could be effected by simple chro-
matography, in some cases difficulties were
encountered. Also, the stereoselectivities of
these reactions were rather low, furnishing the
DD stereoisomer in a light predominance over
the LD form. Only in the case of 2-acetamido-
2-deoxy aldehyde (17), the LD stereoisomer
dominated over the DD partner. The chain-
elongation reactions with the silyl reagent
were superior, affording single diastereoiso-
meric (LD) heptosides in good yields.
mixture obtained from the a-
D
hyde 8 resisted separation. However, after
acetylation both 6-O-acetyl derivatives (13,
14) were separated and characterized (Scheme
1).
From methyl 2-acetamido-3,4-di-O-benzyl-
2-deoxy-a- and b- -glucopyranosides (15 and
D
16) the corresponding hexodialdo-1,5-pyran-
osides (17 and 18) were prepared and reacted
with
allyloxymethylmagnesium
chloride.
From both reaction mixtures of diastereoiso-
meric heptosides, 19 (59%) and 20 (52%) were
obtained. Their separation into compo-
nents — directly after the reaction, as 6-O-
acetyl derivatives, after de-allylation, and as
6,7-di-O-acetyl derivatives — was unsuccess-
ful. Their NMR spectral and MS data charac-
terized these mixtures only in part. Both
aldehydes, 17 and 18, were also reacted with
(phenyldimethyl)silylmethylmagnesium chlo-
ride to furnish single heptosides (21 and 22,
1
The H NMR spectrum of the aldehyde 18
3
deserves a short comment. The J coupling
constants recorded are not typical for a com-
pound of the b- -gluco configuration: J1,2 3.2,
D
J2,3 4.3, and J3,4 4.2 Hz point at an equilibrium
4
1
of both chair forms, C1 and C4. Epimeriza-
tion of the formyl group at C-5 was excluded
by reduction of 18 back to the substrate 16.
respectively) of
L
-glycero-
D
-gluco configura-
MM calculations (SYBYL,
MMFF-9412) indi-
tion in good yields. Oxidation of 21 and 22
(peroxyacetic acid, 0 °C) resulted in removal
of the silyl group and formation of methyl
heptosides 23 and 24, respectively. However,
when 21 was oxidized with the same reagent
at −10 °C, a ‘dimeric’ product 25 was ob-
tained.10 The configuration of 23 and 24 was
confirmed as LD on the basis of the CD
spectra which showed a negative E band at
cated a small strain energy difference between
both chair forms with a small preference for
1
1
the C4 conformer. The H NMR spectrum of
the aldehyde 18 has been recorded earlier in
literature and all coupling constants were
found in agreement.13 It is possible that the
hydrated form of the aldehyde 18 is responsi-
ble for these abnormalities. The elemental
analysis values point at a hemihydrate. Never-

B. Grzeszczyk, A. Zamojski / Carbohydrate Research 332 (2001) 225–234
227
1
theless, in the H NMR spectrum of 18 a peak
of the aldehyde proton is present at l 9.80.
1. Experimental
3
Non-typical J values were also noted by
Optical rotations were measured with a
JASCO DIP 360 automatic polarimeter at
Paulsen14 for the b anomer of the aldehyde 8.
Scheme 1.

228
B. Grzeszczyk, A. Zamojski / Carbohydrate Research 332 (2001) 225–234
Fig. 1. CD spectra for compounds 23 and 24.
Table 1
The results of chain-elongation reactions of methyl 2-azido- (6–8) and 2-acetamido- (17, 18) -3,4-di-O-benzyl-2-deoxy-hexodialdo-
1,5-pyranosides
Aldehyde no.
AllOCH2MgCl
Compound no.
PhMe2SiCH2MgCl
Compound no.
DD (%)
Compound no.
LD (%)
LD (%)
6
7
8
17
18
9
11
34.4
34.7
37.8
10
12
24.4
22.7
11.1
13 a
14 a
19 (59%) b
21
22
70
63
20 (51.7%) b
a 6-O-Acetyl derivatives.
b Unresolved mixture of stereoisomers.
2092 °C. NMR spectra were recorded with
Varian Gemini AC-200 (200 MHz) or Bruker
AM-500 (500 MHz) spectrometers in CDCl3
solutions with Me4Si as an internal standard
carried out on a Shimadzu instrument: central
unit C-R4A, pump unit LC-8A, UV-detector
STD 250-6A on a column LiChroCART®
250-10 with ChiraSpher® NT (5 mm) (E.
Merck). CD spectra were measured with
JASCO 715 CD spectrometer for solutions of
heptose 6,7-diols 23 and 24 in Me2SO which
the (CH3COO)4Mo2 complex was added (mo-
lar ratio 1.25:1).
1
unless otherwise noted. H signals of aromatic
groups occurred at the expected chemical
shifts and are omitted in the description of
spectra. 13C NMR spectra were recorded in
the DEPT 135 mode. TLC was performed on
Silica Gel HF-254 ready plates and column
chromatography on Silica Gel 230–400 or
70–230 mesh (E. Merck). Mass spectra
(LSIMS, positive mode) were recorded on an
AMD-604 mass spectrometer and on a Per
Septive Biosystems Mariner™ mass spectrom-
eter (ESI/TOF, positive mode). HPLC was
Methyl 2-azido-3,4-di-O-benzyl-2-deoxy-a-
and -b-
-glucopyranosides (3 and 4),14,15 and
D
methyl 2-azido-3,4-di-O-benzyl-2-deoxy-a- -
D
mannopyranoside (5)16 were obtained by azi-
donitration of 3,4,6-tri-O-acetyl-1,5-anhydro-
2-deoxy-
D
-arabino-hex-1-enitol and the subse-
quent conventional steps.14 Methyl 2-acetam-

B. Grzeszczyk, A. Zamojski / Carbohydrate Research 332 (2001) 225–234
229
stereoisomers J6,5 3.5–4.2, J6,7A ꢀ7.0, J6,7B
3.5–4.0 Hz, and for -glycero- -gluco
stereoisomers J6,5B1.5, J6,7Aꢀ8.0, J6,7B 4.9–
5.3 Hz.3 The values of analogous coupling
constants were used also for configurational
ido-3,4-di-O-benzyl-2-deoxy-a- and -b- -glu-
D
L
D
copyranosides (15 and 16) were prepared ac-
cording to literature.17,18
Methyl 2-azido-3,4-di-O-benzyl-2-deoxy-h-
-gluco-hexodialdo-1,5-pyranoside (6).—To a
D
determination of the
D
- and
L
-glycero- -
D
solution of 3 (0.297 g) in CHCl2 (15 mL), the
Dess–Martin periodinane reagent9 (0.379 g)
was added and the solution was stirred 17 min
at rt. The reaction mixture was diluted with
CH2Cl2 (20 mL) and saturated aq solutions of
Na2S2O3 (20 mL) and NaHCO3 (25 mL) were
added. The mixture was stirred for 15 min, the
organic layer was separated, dried, and con-
centrated to dryness. The residue (0.350 g)
was purified by chromatography in 1:1“1:2
manno stereoisomers 13 and 14.19
Compound 9: Yield (34.4%), colorless oil,
[h]D +68° (c 1.2, CHCl3); H NMR: l 5.91–
1
5.81 (m, 1 H, CH2ꢀCH), 5.25–5.12 (m, 2 H,
CH2ꢀCH), 4.95–4.69 (2×ABq, 4 H, 2×
CH2Ph), 4.78 (d, 1 H, J1,2 3.6 Hz, H-1), 4.05
(ddd, 1 H, H-6), 3.99 (dd, 1 H, J3,4 8.8, J3,2
10.2 Hz, H-3), 3.96–3.93 (m,
2
H,
CH2ꢁCHꢀCH2), 3.82 (dd, 1 H, J5,6 3.6, J5,4
10.0 Hz, H-5), 3.64 (dd, 1 H, H-4), 3.52 (dd, 1
H, J7A,6 6.8, J7A,7B 9.9 Hz, H-7A), 3.50 (dd, 1
H, J7B,6 4.0 Hz, H-7B), 3.43 (s, 3 H, OCH3),
3.38 (dd, 1 H, H-2), 2.68 (d, 1 H, JOH,6 3.5 Hz,
OH); 13C NMR: l 134.47 (CH2ꢀCH), 117.34
(CH2ꢀCH), 98.45 (C-1), 81.02, 79.23, 72.35,
70.59 (C-3, 4, 5, 6), 75.51, 74.72 (2×CH2Ph),
72.35 (CH2ꢀCHꢁCH2O), 70.62 (C-7), 63.80
(C-2), 55.25 (OCH3); LSIMS HRMS for
1
hexane–EtOAc to yield 6 (0.279 g, 95%). H
NMR (200 MHz): l 9.66 (d, 1 H, J6,5 0.4 Hz,
CHO).
Methyl 7-O-allyl-2-azido-3,4-di-O-benzyl-
2-deoxy-
D
- and -
L
-glycero-h- -gluco-heptopy-
D
ranosides (9 and 10).—To dry magnesium
turnings (0.097 g, 4.06 mmol) under freshly
distilled THF (0.1 mL), sublimed HgCl2 (50
mg) was added and a few drops of neat pure
allyloxymethyl chloride, freshly distilled be-
fore the reaction, were added while lowering
the temperature to ca. −10 to −15 °C.
When formation of the Grignard reagent has
started, the rest of allyloxymethyl chloride
(0.433 g, 4.06 mmol) in THF (2 mL) was
added at −18 to −20 °C, and stirring was
continued for 2 h. The temperature was then
lowered to −30 °C and a solution of alde-
hyde 6 (0.233 g, 0.59 mmol) in abs THF (3
mL) was dropped in. The mixture was stirred
at −20 °C for 1.5 h and slowly brought to rt
while stirring for another 12 h. A cold (0 °C)
aq satd solution of NH4Cl (20 mL) was added
and the products were extracted with ether.
Ether extract was dried, concentrated to dry-
ness and the residue was chromatographed
with 3:2 hexane–EtOAc to give a mixture of 9
and 10 (0.162 g, 59%). Proportion of
diastereoisomers 9 and 10 was determined to
C25H31N3O6+Na+
([M+Na]+)
Calcd:
492.21106. Found: 492.21145.
Compound 10: Yield (24.2%), colorless oil,
1
[h]D +61° (c 1.0, CHCl3); H NMR: l 5.94–
5.85 (m, 1 H, CH2ꢀCH), 5.31–5.16 (m, 2 H,
CH2ꢀCH), 4.91–4.73 (2×ABq, 4 H, 2×
CH2Ph), 4.79 (d, 1 H, J1,2 3.5 Hz, H-1), 4.13–
4.09 (m, 1 H, H-6), 4.06–4.00 (m, 2 H,
CH2ꢁCHꢀCH2), 3.97 (dd, 1 H, J3,4 9.0, J3,2
10.1 Hz, H-3), 3.79 (dd, 1 H, J4,5 9.9 Hz, H-4),
3.72 (bd, 1 H, J5,6B1, H-5), 3.60 (dd, 1 H,
J7A,6 7.9, J7A,7B 9.4 Hz, H-7A), 3.50 (dd, 1 H,
J7B,6 5.4 Hz, H-7B), 3.39 (dd, 1 H, H-2), 3.37
(s, 3 H, OCH3), 2.04 (d, 1 H, JOH,6 6.6 Hz,
OH); 13C NMR: l 134.38 (CH2ꢀCH), 117.33
(CH2ꢀCH), 98.77 (C-1), 80.46, 77.73, 69.96,
67.37 (C-3, 4, 5, 6), 75.45, 75.09 (2×CH2Ph),
72.30 (CH2ꢀCHꢁCH2O), 71.19 (C-7), 63.56
(C-2), 55.11 (OCH3); LSIMS HRMS for
C25H31N3O6+Na+
([M+Na]+)
Calcd:
1
be 1.4:1 on the basis of H NMR spectral
492.21106. Found: 492.20958.
OMe signals. The mixture was separated by
HPLC using 4:1 hexane–EtOAc as eluent.
The configuration of stereoisomeric methyl
heptosides 9, 10 was determined by compari-
Methyl 2-azido-3,4-di-O-benzyl-2-deoxy-i-
-gluco-hexodialdo-1,5-pyranoside (7).—The
D
procedure used was analogous to the one de-
scribed for 6. Alcohol 4 (0.353 g) was con-
3
1
son of coupling constants J of protons at
verted to 7 (0.324 g, 92%), H NMR: l 9.68
C-6, -7A, and -7B. For
D
-glycero- -gluco
D
(d, 1 H, J5,6 0.9 Hz, CHO).

230
B. Grzeszczyk, A. Zamojski / Carbohydrate Research 332 (2001) 225–234
H-3), 3.53 (s, 3 H, OCH3), 3.46 (t, 1 H, J4,3 9.1
Methyl 7-O-allyl-2-azido-3,4-di-O-benzyl-
2-deoxy- -glycero- and - -glycero-i- -gluco-
heptopyranosides (11 and 12).—The procedure
used was analogous to the one described for 9
and 10. Starting from aldehyde 7 (0.264 g), 11
(0.108 g, 34.7%), and 12 (0.071 g, 22.7%) were
obtained.
Hz, H-4), 3.37 (dd, 1 H, H-2), 3.34 (dd, 1 H,
D
L
D
13
J5,6 1.5, J5,4 9.7 Hz, H-5); C NMR: l 134.47
(CH2ꢀCH), 117.33 (CH2ꢀCH), 103.06 (C-1),
83.12, 77.14, 74.00, 67.55, 66.24 (C-2, 3, 4, 5,
6), 75.52, 75.36 (2×CH2Ph), 72.32 (CH2ꢀ
CHꢁCH2O), 70.92 (C-7), 57.03 (OCH3);
LSIMS HRMS for C25H31N3O6+Na+
([M+Na]+) Calcd: 492.21106. Found
492.21023.
Compound 11: White solid, mp 40–41 °C,
1
[h]D −11.3° (c 1.3, CHCl3); H NMR: l
5.91–5.82 (m, 1 H, CH2ꢀCH), 5.26–5.13 (m,
2 H, CH2ꢀCH), 4.93–4.69 (2×ABq, 4 H,
2×CH2Ph), 4.18 (d, 1 H, J1,2 8.0 Hz, H-1),
4.09–4.04 (m, 1 H, H-6), 3.97–3.93 (m, 2 H,
CH2ꢁCHꢀCH2), 3.63 (dd, 1 H, J4,3 8.8, J4,5 9.6
Hz, H-4), 3.56–3.42 (m, 4 H, H-3, -5, -7A,
-7B), 3.55 (s, 3 H, OCH3), 3.36 (dd, 1 H, J2,3
9.8 Hz, H-2); 13C NMR: l 134.5 (CH2ꢀCH),
117.3 (CH2ꢀCH), 103.05 (C-1), 83.60, 78.74,
74.77, 71.44 (C-3, 4, 5, 6), 75.56, 74.77 (2×
CH2Ph), 72.33 (CH2ꢀCHꢁCH2O), 70.62 (C-7),
66.43 (C-2), 57.10 (OCH3); LSIMS HRMS
for C25H31N3O6+Na+ ([M+Na]+) Calcd:
492.21106. Found 492.21054. Anal. Calcd for
C25H31N3O6: C, 63.95; H, 6.66; N, 8.95.
Found: C, 63.95; H, 6.62; N, 8.81.
Stereoisomer 12 was characterized also as
the 6-O-acetyl derivative 12Ac obtained as a
1
colorless oil, [h]D −65° (c 1.0, CHCl3); H
NMR: l 5.90–5.81 (m, 1 H, CH2ꢀCH), 5.46
(ddd, 1 H, J6,5 1.5 Hz, H-6), 5.28–5.15 (m, 2
H, CH2ꢀCH), 4.94–4.41 (2×ABq, 4 H, 2×
CH2Ph), 4.16 (d, 1 H, J1,2 8.0 Hz, H-1), 4.04–
3.95 (m, 2 H, CH2ꢁCHꢀCH2), 3.64 (dd, 1 H,
J7A,6 7.5, J7A,7B 9.5 Hz, H-7A), 3.62 (dd, 1 H,
J7B,6 6.6 Hz, H-7B), 3.57 (s, 3 H, OCH3), 3.57
(dd, 1 H, H-5), 3.52 (t, 1 H, J4,3 8.2, J4,5 9.3
Hz, H-4), 3.48 (t, 1 H, J3,2 9.6 Hz, H-3), 3.40
(t, 1 H, H-2), 2.09 (s, 3 H, COCH3); 13C
NMR:
l
134.35
(CH2ꢀCH),
117.22
(CH2ꢀCH), 103.26 (C-1), 83.67, 76.77, 72.37,
68.46, 66.31 (C-2, -3, -4, -5, -6), 66.92 (C-7),
75.64, 75.14, 72.14 (2×CH2Ph, CH2ꢀCHꢁ
CH2O), 57.17 (OCH3), 21.01 (COCH3);
LSIMS HRMS for C27H33N3O7+Na+
([M+Na]+) Calcd: 534.22162. Found
534.22292.
Stereoisomer 11 was also characterized as
the 6-O-acetyl derivative 11Ac obtained as a
1
colorless oil, [h]D −33° (c 0.6, CHCl3); H
NMR: l 5.88–5.79 (m, 1 H, CH2ꢀCH), 5.41
(ddd, 1 H, J6,5 1.9 Hz, H-6), 5.24–5.11 (m, 2
H, CH2ꢀCH), 4.90–4.71 (2×ABq, 4 H, 2×
CH2Ph), 4.15 (d, 1 H, J1,2 8.0 Hz, H-1), 3.97–
3.88 (m, 2 H, CH2ꢁCHꢀCH2), 3.65 (t, 1 H, J4,3
9.8, J4,5 8.9 Hz, H-4), 3.65 (dd, 1 H, J7A,6 6.1,
J7A,7B 10.2 Hz, H-7A), 3.57 (s, 3 H, OCH3),
3.54 (dd, 1 H, J7B,6 6.3 Hz, H-7B), 3.45 (dd, 1
H, H-2), 3.43 (t, 1 H, J3,2 9.9 Hz, H-3), 2.05 (s,
Methyl 2-azido-3,4-di-O-benzyl-2-deoxy-h-
D
-manno-hexodialdo-1,5-pyranoside (8).—The
procedure used was analogous to the one de-
scribed for 6. Alcohol 5 (0.513 g) was con-
1
verted to 8 (0.497 g, 96%), H NMR l: 9.72
(d, 1 H, J5,6 1.1 Hz, CHO).
3
H, COCH3); 13C NMR:
l
134.38
Methyl 6-O-acetyl-7-O-allyl-2-azido-3,4-di-
(CH2ꢀCH), 117.16 (CH2ꢀCH), 102.87 (C-1),
83.53, 78.06, 74.70, 71.25, 66.25 (C-2, -3, -4,
-5, -6), 67.50 (C-7), 75.67, 74.67, 72.07 (2×
CH2Ph, CH2ꢀCHꢁCH2O), 56.99 (OCH3),
21.06 (COCH3); ESI HRMS for C27H33-
N3O7+Na+ ([M+Na]+) Calcd: 534.2216.
Found 534.2198.
O-benzyl-2-deoxy-
D
-glycero- and -
L
-glycero-
h-D
-manno-heptopyranosides (13 and 14).
—The procedure was analogous to the one
described for 9 and 10. Starting from aldehyde
8 (0.436 g), an inseparable diastereomeric mix-
ture of methyl heptosides (0.308 g, 60%) was
obtained. This mixture was acetylated in the
conventional manner (Ac2O–Py) and the 6-O
acetyl derivatives 13 and 14 were separated by
column chromatography using 2:1 hexane–
EtOAc as eluent.
Compound 12: Colorless oil, [h]D +34° (c
1
0.6, CHCl3); H NMR: l 5.94–5.83 (m, 1 H,
CH2ꢀCH), 5.30–5.14 (m, 2 H, CH2ꢀCH),
4.89–4.73 (2×ABq, 4 H, 2×CH2Ph), 4.17
(d, 1 H, J1,2 8.1 Hz, H-1), 4.14–3.95 (m, 3 H,
H-6, CH2ꢁCHꢀCH2), 3.59 (t, 1 H, J3,2 7.2 Hz,
Compound 13: Colorless oil, [h]D −38.2° (c
1
1.2, CHCl3); H NMR: l 5.90–5.80 (m, 1 H,

B. Grzeszczyk, A. Zamojski / Carbohydrate Research 332 (2001) 225–234
231
ing the temperature −10 to −15 °C. When
the formation of the Grignard reagent had
started, the rest of allyloxymethyl chloride
(0.494 g, 4.64 mmol) in THF (2 mL) was
added at −18 to −20 °C, and stirring was
continued for 2 h. The temperature was then
lowered to −30 °C and a solution of alde-
hyde 17 (0.340 g, 0.77 mmol) in abs THF (10
mL) was dropped in. The mixture was stirred
at −20 °C for 2 h. A cold (0 °C) aq satd
solution of NH4Cl (20 mL) was added and the
products were extracted with CH2Cl2. The
organic extract was dried, concentrated to
dryness, and the residue was chro-
matographed with 1:1 hexane–acetone to give
a mixture of diastereoisomers 19 (0.235 g,
59%). The approximate proportion of
diastereoisomeric heptosides in 19 was deter-
CH2ꢀCH), 5.44 (ddd, 1 H, J6,5 2.0 Hz, H-6),
5.26–5.12 (m, 2 H, CH2ꢀCH), 4.96–4.65 (2×
ABq, 4 H, 2×CH2Ph), 4.33 (d, 1 H, J1,2 1.2
Hz, H-1), 3.99–3.89 (m, 2 H, CH2ꢁCHꢀCH2),
3.88 (dd, 1 H, H-2), 3.86 (t, 1 H, H-4), 3.68
(dd,1 H, J7A,6 5.4, J7A,7B 10.4 Hz, H-7A), 3.64
(dd, 1 H, J3,4 9.6, J3,2 3.6 Hz, H-3), 3.61 (dd, 1
H, J7B,6 6.7 Hz, H-7B), 3.47 (dd, 1 H, J5,4 9.9
Hz, H-5), 3.51 (s, 3 H, OCH3), 2.04 (s, 3 H,
COCH3); 13C NMR: l 134.52 (CH2ꢀCH),
117.02 (CH2ꢀCH), 100.46 (C-1), 81.57, 75.22,
74.48, 71.58 (C-3, 4, 5, 6), 74.99, 72.29, 72.03
(2×CH2Ph, CH2ꢀCHꢁCH2O), 67.70 (C-7),
61.49 (C-2), 56.97 (OCH3); 21.09 (COCH3);
LSIMS HRMS for C27H33N3O7+Na+
([M+Na]+) Calcd: 534.22162. Found:
534.22315
Compound 14: Colorless oil, [h]D −71.2° (c
1
1
1.6, CHCl3); H NMR: l 5.89–5.80 (m, 1 H,
mined to be 1:1.5 on the basis of H NMR
CH2ꢀCH), 5.50 (ddd, 1 H, H-6), 5.27–5.12
(m, 2 H, CH2ꢀCH), 4.87–4.45 (2×ABq, 4 H,
2×CH2Ph), 4.35 (d, 1 H, J1,2 1.1 Hz, H-1),
4.03–3.93 (m, 2 H, CH2ꢁCHꢀCH2), 3.90 (dd,
1 H, J2,3 3.1 Hz, H-2), 3.72 (t, 1 H, J4,5 8.7 Hz,
H-4), 3.69 (dd, 1 H, J3,4 8.6 Hz, H-3), 3.67
(dd, 1 H, J7A,6 7.6, J7A,7B 9.5 Hz, H-7A), 3.62
(dd, 1 H, J7B,6 6.5 Hz, H-7B), 3.52 (s, 3 H,
OCH3), 3.50 (dd, 1 H, J5,6 1.5 Hz, H-5), 2.18
(s, 3 H, COCH3); 13C NMR: l 134.64
(CH2ꢀCH), 117.32 (CH2ꢀCH), 101.16 (C-1),
81.83, 73.51, 73.17, 68.70 (C-3, 4, 5, 6), 75.64,
72.47, 72.34 (2×CH2Ph, CH2ꢀCHꢁCH2O),
67.25 (C-7), 61.84 (C-2), 57.26 (OCH3), 21.26
(COCH3); LSIMS HRMS for C27H33N3O7+
Na+ ([M+Na]+) Calcd: 534.22162. Found:
534.22051.
spectrum. Some selected data from the spec-
trum of 19 are listed below: inter alia l 4.61
(d, 1 H, J1,2 3.6 Hz) and 4.67 (d, 1 H, J1,2 3.7
Hz): two H-1, 4.07 (ddd, 1 H, J6,5 3.9 Hz) and
4.11 (ddd, 1 H, J6,5 0.9, J6,7A 7.2, J6,7B 6.2 Hz):
two H-6, 3.54 (dd, 1 H, J7A,6 6.6, J7A,7B 9.9 Hz,
H-7A), 3.50 (dd, 1 H, J7B,6 3.7 Hz, H-7B) and
3.58 (dd, 1 H, J7A,7B 9.4 Hz, H-7A), 3.50 (dd,
1 H, H-7B): two pairs of H-7, 3.38 (s, 3 H)
13
and 3.28 (s, 3 H): two OCH3; C NMR: inter
alia l 98.61 and 98.87 (two C-1).
Other signals 5.94–5.83 (m, 2 H, 2×
CH2ꢀCH), 5.29–5.13 (m, 4 H, 2×CH2ꢀCH),
4.94–4.60 (4×ABq, 8 H, 4×CH2Ph), 4.05–
3.95 (m, 4 H, 2×CH2ꢁCHꢀCH2), 3.74–3.63
(m, 4 H, H-3, 2×H-4, H-5); LSIMS HRMS
for C27H35NO7+Na+ ([M+Na]+) Calcd
508.23112. Found 508.23022.
Methyl 2-acetamido-3,4-di-O-benzyl-2-de-
oxy - h -
D
- gluco - hexodialdo - 1,5 - pyranoside
Methyl
2-acetamido-3,4-di-O-benzyl-2,7-
-glycero-h-
(17).—The procedure used was analogous to
the one described for 6. Alcohol 15 (0.831 g)
was converted to the aldehyde 17 (0.800 g,
dideoxy-7-(phenyldimethylsilyl)-
L
D
-
gluco-heptopyranoside (21).—To dry magne-
sium turnings (0.105 g 4.36 mmol) and sub-
limed HgCl2 (50 mg) in freshly distilled dry
THF (7 mL) was added dropwise
(chloromethyl)dimethylphenylsilane (0.805 g,
4.36 mmol). The mixture was heated until the
reaction started. The remaining solution of
(chloromethyl)dimethylphenylsilane in THF
was now added dropwise at such rate as to
maintain a gentle reflux. After the Grignard
reagent formation was complete the tempera-
ture was lowered to −20 °C and a solution of
1
97%). H NMR: l 9.66 (d, 1 H, J6,5 1.2 Hz,
CHO).
Methyl 2-acetamido-7-O-allyl-3,4-di-O-ben-
zyl-2-deoxy-
D
-glycero- and -
L
-glycero-h- -
D
gluco-heptopyranoside (19).—To dry mag-
nesium turnings (0.111 g 4.64 mmol) under
freshly distilled THF (0.1 mL) sublimed HgCl2
(50 mg) was added and a few drops of neat
pure allyloxymethyl chloride (freshly distilled
before the reaction) were added while lower-

232
B. Grzeszczyk, A. Zamojski / Carbohydrate Research 332 (2001) 225–234
Hz, H-5), 3.68 (dd, 1 H, J7B,6 4.7 Hz, H-7B),
3.30 (s, 3 H, OCH3), 1.82 (s, 3 H, COCH3);
13C NMR: l 98.77 (C-1), 79.71, 78.01, 71.78,
68.83 (C-3, C-4, C-5, C-6), 75.15, 74.73 (2×
CH2Ph), 64.80 (C-7), 55.09 (OCH3), 52.42
(C-2), 23.35 (COCH3); LSIMS HRMS
for C24H31NO7+H+ ([M+H]+) Calcd:
446.21788. Found: 446.21798.
aldehyde 17 (0.300 g, 0.726 mmol) in abs THF
(15 mL) was added dropwise and stirring was
continued for 2 h. A cold (0 °C) aq satd
solution of NH4Cl (20 mL) was added and the
products were extracted with CH2Cl2. The
organic extract was dried, concentrated to
dryness, and the residue was purified by
column chromatography with 1:1 hexane–ace-
tone to give 21 (0.287 g, 70%) as a white solid,
mp 113–114 °C, [h]D +78.2° (c 0.8, CHCl3);
1H NMR: l:5.23 (d, 1 H, JNH,2 9.2 Hz, NH),
4.88–4.59 (2×ABq, 4 H, 2×CH2Ph), 4.66
(d, 1 H, J1,2 3.6 Hz, H-1), 4.14 (ddd, 1 H, J2,3
10.4 Hz, H-2), 4.05 (dt, 1 H, J6,7A 10.7, J6,7B
3.5, J6,5 B1.0 Hz, H-6), 3.70 (t, 1 H, J4,5 9.5,
J4,3 9.2 Hz, H-4), 3.63 (dd, 1 H, H-3), 3.35
(dd, 1 H, H-5), 3.27 (s, 3 H, OCH3), 1.82 (s, 3
H, COCH3), 1.36 (dd, 1 H, J7A,7B 14.9 Hz,
H-7A), 0.90 (dd, 1 H, H-7B); 13C NMR: l
98.69 (C-1), 80.04, 78.71, 74.69, 66.70 (C-3, -4,
-5, -6), 75.29, 74.67 (2×CH2Ph), 55.00
(OCH3), 52.52 (C-2), 23.39 (COCH3), 21.47
(C-7); LSIMS HRMS for C32H41NO6Si+
Na+ ([M+Na]+) Calcd: 586.26009. Found:
586.26243. Anal. Calcd for C32H41NO6Si: C,
68.17; H, 7.52; N, 2.19. Found: C, 68.10; H,
7.54; N, 2.29.
Methyl 2-acetamido-6,7-di-O-acetyl-3,4-di-
O-benzyl-2-deoxy-
L
-glycero-h- -gluco-hepto-
D
pyranoside (26).—Compound 23 was acety-
lated in the conventional manner (Ac2O–Py)
to give 26 as a colorless oil, [h]D +48° (c 1.2,
1
CHCl3); H NMR: l 5.59 (ddd, 1 H, J6,5 1.3,
J6,7A 6.7, J6,7B 8.1 Hz, H-6), 5.29 (d, 1 H, JNH,2
9.4 Hz, NH), 4.87–4.44 (2×ABq, 4 H, 2×
CH2Ph), 4.67 (d, 1 H, H-1), 4.27 (ddd, 1 H,
J2,1 3.6, J2,3 10.5 Hz, H-2), 4.28–4.25 (m, 2 H,
H-7A, H-7B), 3.82 (t, 1 H, J5,4 10.0 Hz, H-5),
3.72 (dd, 1 H, J3,4 8.8 Hz, H-3), 3.55 (dd,1 H,
H-4), 3.31 (s, 3 H, OCH3), 2.15, 2.04, 1.84
(3×s, 9 H, 3×COCH3); 13C NMR: l 98.77
(C-1), 80.59, 77.41, 69.01, 67.88 (C-3, -4, -5,
-6), 75.23, 75.13 (2×CH2Ph), 62.16 (C-7),
55.05 (OCH3), 52.25 (C-2), 23.37, 20.87, 20.68
(3×COCH3); LSIMS HRMS for C28H35-
NO9+Na+ ([M+Na]+) Calcd: 552.22095.
Found: 552.22173.
Methyl 2-acetamido-3,4-di-O-benzyl-2-de-
oxy -
L
- glycero - h -
D
- gluco - heptopyranoside
Methyl 2-acetamido-3,4-di-O-benzyl-2-de-
(23).—To a solution of 21 (100 mg, 0.98
mmol) in AcOH (1.5 mL) were added KBr
(0.025 g) and CH3COONa (0.184 g). The mix-
ture was cooled to 0 °C and stirred with exclu-
sion of light. AcOH (0.97 mL of a 30%
solution in AcOH) was added to the mixture.
After stirring for 2 h at 0 °C the mixture was
brought to rt. An aq 15% solution of Na2S2O5
was added to reduce the remaining peroxy-
acetic acid. The product was extracted with
CH2Cl2 and the organic extract was washed
with water, aq 10% NaHCO3 and water again,
dried, and concentrated. The residue was
chromatographed with 1:2 hexane–EtOAc to
yield 23 (73 mg, 96%) as a colorless oil, [h]D
oxy - i -
D
- gluco - hexodialdo - 1,5 - pyranoside
(18).—To a solution of alcohol 16 (0.603 g) in
CH2Cl2 (40 mL), the Dess–Martin periodinane
reagent (0.738 g) was added and the solution
was stirred 5 days at 32 °C. The reaction
mixture was diluted with CH2Cl2 (20 mL), a
saturated aq solution of Na2S2O3 (20 mL) and
a saturated aq solution of NaHCO3 (25 mL)
were added. After the mixture was stirred for
15 min, the organic layer was separated, dried,
and concentrated to dryness. The residue
(0.621 g) was purified by chromatography
with 1:1 hexane–acetone to yield 18 (0.415 g,
69%); mp 197–198 °C, [h]D −22.3° (c 0.4,
1
CHCl3); H NMR: l 9.80 (d, 1 H, J6,5 0.3 Hz,
1
+105° (c 1.2, CHCl3); H NMR: l 5.23 (d, 1
CHO), 6.45 (d, 1 H, JNH,2 8.9 Hz, NH), 4.71
(d, 1 H, J1,2 3.2 Hz, H-1), 4.70–4.53 (2×ABq,
4 H, 2×CH2Ph), 4.28 (d, 1 H, J5,4 3.4 Hz,
H-5), 4.19 (ddd, 1 H, J2,3 4.3 Hz, H-2), 3.98 (t,
1 H, J4,3 4.2 Hz, H-4), 3.76 (t, 1 H, H-3), 3.53
(s, 3 H, OCH3), 1.82 (s, 3 H, COCH3); 13C
NMR: l 101.5 (C-1), 79.03, 75.46, 73.42 (C-3,
H, JNH,2 9.2 Hz, NH), 4.87–4.66 (2×ABq, 4
H, 2×CH2Ph), 4.67 (d, 1 H, J1,2 3.6 Hz, H-1),
4.17 (ddd, 1 H, J2,3 10.6 Hz, H-2), 3.97 (bt, 1
H, H-6), 3.83 (t, 1 H, J3,4 9.4 Hz, H-3), 3.54
(dd, 1 H, J7A,6 6.3, J7A,7B 11.3 Hz, H-7A), 3.69
(t, 1 H, H-4), 3.65 (dd, 1 H, J5,6 1.5, J5,4 10.0

B. Grzeszczyk, A. Zamojski / Carbohydrate Research 332 (2001) 225–234
233
(CD3OD): l 4.83–4.34 (m, 6 H, H-1, NH,
2×CH2Ph), 3.96 (ddd, J5,6 1.4, J6,7A 6.9, J6,7B
8.2 Hz, H-6), 3.81 (dd, 1 H, J4,3 8.6, J4,5 8.5
Hz, H-4), 3.78 (dd, 1 H, J3,4 9.0, J3,2 9.6 Hz,
H-3), 3.62–3.71 (m, 3 H, H-5, H-7A, H-7B),
3.45 (s, 3 H, OCH3), 1.88 (s, 3 H, COCH3);
13C NMR (CD3OD): l 102.15 (C-1), 82.97,
77.92, 73.52, 68.97 (C-3, -4, -5, -6), 74.64,
74.48 (2×CH2Ph), 62.42 (C-7), 55.53, 55.25
(OCH3, C-2), 21.62 (COCH3); LSIMS HRMS
for C24H31NO7+Na+ ([M+Na]+) Calcd:
468.19982. Found: 468.20018.
-4, -5), 73.05, 71.96 (2×CH2Ph), 57.08
(OCH3), 49.17 (C-2), 23.53 (COCH3); LSIMS
HRMS for C23H27NO6 +H+ ([M+H]+)
Calcd: 414.19166. Found: 414.19263. Anal.
Calcd for C23H27NO6·1/2 H2O: C, 65.39; H,
6.68; N, 3.32. Found: C, 65.08; H, 6.81; N,
3.61.
Methyl 2-acetamido-7-O-allyl-3,4-di-O-ben-
zyl-2-deoxy-
D
-glycero- and -
L
-glycero-i- -
D
gluco-heptopyranosides (20).—Starting from
aldehyde 18 (0.327 g), an inseparable
diastereomeric mixture of heptosides (20,
0.199 g, 52%) was obtained in the form of a
colorless oil. The proportion of stereoisomers
in 20 was close to 1:1 on the basis of 1H NMR
Methyl 2-acetamido-6,7-di-O-acetyl-3,4-di-
O-benzyl-2-deoxy-
L
-glycero-i- -gluco-hepto-
D
pyranoside (27).—Compound 24 was acety-
lated in the conventional manner (Ac2O/Py) to
give 27 as a colorless oil, [h]D +13.0° (c 1.0,
1
data. Selected data from the H NMR spec-
trum are given below: inter alia l 4.74 (d, 1 H,
J1,2 8.1 Hz) and 4.64 (d, 1 H, J1,2 7.4 Hz): two
H-1, 3.45 (s, 3 H) and 3.44 (s, 3 H): two
OCH3; 13C NMR: l 101.31, 101.06 (2×C-1);
LSIMS HRMS for C27H35NO7 +Na+ ([M+
Na]+) Calcd: 508.23112. Found 508.23075.
1
CHCl3); H NMR: l 5.58–5.47 (m, 2 H, NH,
H-6), 4.89–4.42 (2×ABq, 4 H, 2×CH2Ph),
4.74 (d, 1 H, J1,2 7.9 Hz, H-1), 4.38 (dd, 1 H,
J7A,6 6.0, J7A,7B 11.1 Hz, H-7A), 4.21 (dd, 1 H,
J7B,6 7.1 Hz, H-7B), 4.18 (t, 1 H, H-3), 3.59
(bd, 1 H, J5,4 9.8 Hz, H-5), 3.53 (t, 1 H, J4,3
8.7 Hz, H-4), 3.47 (s, 3 H, OCH3), 3.34 (ddd,
1 H, J2,NH 8.2, J2,3 9.1 Hz, H-2), 1.87 (s, 3 H,
COCH3); 13C NMR: l 101.99 (C-1), 81.08,
77.68, 72.68, 68.15 (C-3, -4, -5, -6), 74.94,
74.92 (2×CH2Ph), 62.09 (C-7), 57.43, 56.86
(OCH3, C-2), 23.58 (COCH3), 20.95, 20.74
(COCH3); LSIMS HRMS for C28H35NO9+
Na+ ([M+Na]+) Calcd: 552.22095. Found:
552.22372
Methyl
2-acetamido-3,4-di-O-benzyl-2,7-
-glycero-i-
dideoxy-7-(phenyldimethylsilyl)-
L
D
-
gluco-heptopyranoside (22).—The procedure
used was analogous to the one described for
21. Starting from aldehyde 18 (0.495 g), 22
(0.426 g, 63%) was obtained as a colorless oil,
[h]D −10.6° (c 1.01, CHCl3); 1H NMR: l 5.43
(d, 1 H, JNH,2 7.8 Hz, NH), 4.87–4.60 (2×
ABq, 4 H, 2×CH2Ph), 4.58 (d, 1 H, J1,2 8.2
Hz, H-1), 4.10–4.02 (m, 1 H, H-6), 4.00 (t, 1
H, J3,4 9.3 Hz, H-3), 3.67 (t, 1 H, J4,5 9.1 Hz,
H-4), 3.45 (s, 3 H, OCH3), 3.31 (ddd, 1 H, J2,3
9.9 Hz, H-2), 3.12 (d, 1 H, J5,6B1.0 Hz, H-5),
1.85 (s, 3 H, COCH3), 1.35 (dd, 1 H, J7A,6 9.2,
J7A,7B 14.7 Hz, H-7A), 1.10 (dd, 1 H, J7B,6 5.6
1,3-Di-[methyl 2-acetamido-3,4-di-O-ben-
zyl-2,7-dideoxy-
L
-glycero-h- -gluco-heptopy-
D
ranos - 7 - yl] - 1,1,3,3 - tetramethyl - disiloxane
(25).—The procedure used was analogous to
the one described for 23 except for the temper-
ature (−10 °C). From 21 (93 mg) 25 (80 mg,
50%) was obtained as a white solid; mp 212–
13
Hz, H-7B), 0.36, 0.34 (2s, 6 H, (CH3)2Si); C
NMR: l 101.09 (C-1), 80.48, 78.97, 77.90,
67.01 (C-3, -4, -5, -6), 74.91, 74.67 (2×
CH2Ph), 57.22, 55.89 (OCH3, C-2), 23.59
(COCH3), 22.04 (C-7), −2.05, −2.56
(CH3)2Si; LSIMS HRMS for C32H41NO6Si+
Na+ ([M+Na]+) Calcd: 586.26009 Found:
586.26274.
1
214 °C, [h]D +63° (c 0.7, CHCl3); H NMR:
l 5.27 (d, 1 H, JNH,2 9.1 Hz, NH), 4.92–4.64
(2×ABq, 4 H, 2×CH2Ph), 4.69 (d, 1 H, J1,2
3.6 Hz, H-1), 4.17 (ddd, 1 H, J2,3 10.1 Hz,
H-2), 3.73 (t, 1 H, J4,5 9.4, J4,3 9.1 Hz, H-4),
3.67 (dd, 1 H, H-3), 3.40 (dd, 1 H, J5,6 1.0 Hz,
H-5), 3.31 (s, 3 H, OCH3), 1.83 (s, 3 H,
COCH3), 0.89 (dd, 1 H, J7A,6 7.5 Hz, H-7A),
0.69 (dd, 1 H, J7B,6 3.6, J7B,7A 14.8 Hz, H-7B),
0.19, 0.17 (2 s, 6 H, [(CH3)2Si]); 13C NMR: l
98.89 (C-1), 80.38, 78.84, 774.72, 62.01 (C-3,
-4, -5, -6), 75.46, 75.39 (2×CH2Ph), 55.24,
Methyl 2-acetamido-3,4-di-O-benzyl-2-de-
oxy -
L
- glycero - i -
D
- gluco - heptopyranoside
(24).—The procedure used was analogous to
the one described for 23. From 22 (107 mg),
24 (50 mg, 59%) was obtained as a colorless
1
oil, [h]D −42.8° (c 0.8, CH3OH); H NMR

234
B. Grzeszczyk, A. Zamojski / Carbohydrate Research 332 (2001) 225–234
4. Grzeszczyk, B.; Zamojski, A. Coll. Czech. Chem. Com-
mun. 2000, 65, 610–620.
5. Weise, G.; Drews, G.; Jann, B.; Jann, K. Arch. Microbiol.
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University of Tokyo Press: Tokyo, 1975; pp. 77–111.
7. Honda, Y.; Suami, T. Bull. Chem. Soc. Jpn. 1981, 54,
2825–2826.
55.21 (2×OCH3), 52.86, 52.82 (2×C-2), 2×
23.59 (2×COCH3), 22 99 (C-7), 0.73, 0.42
[(CH3)2Si]; ESI HRMS for C52H72N2O13Si2+
Na+ ([M+Na]+) Calcd: 1011.4474. Found:
1011.4465. Anal. Calcd for C52H72N2O13Si2: C,
63.13; H, 7.34; N, 2.83. Found: C, 63.07; H,
7.51; N, 2.72.
8. Chmielewski, M.; Konowal, A.; Zamojski, A. Carbohydr.
Res. 1979, 70, 275–282.
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Acknowledgements
10. Stepowska, H.; Zamojski, A. Tetrahedron 1999, 55,
Support of this work by a Grant No. 3
TO9A 066 12 from the State Committee for
Scientific Research (KBN) is gratefully ac-
knowledged. We thank Dr Jadwiga Frelek for
CD measurements. We thank also Ms Anna
Kelner for performing the azidonitration reac-
5519–5538.
11. Frelek, J.; Geiger, M.; Voelter, W. Curr. Org. Chem.
1999, 3, 145–174.
12. PC SPARTAN PLUS 2000, Wavefunction, Inc., Irvine, CA
92612, USA.
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