Synthesis and biological evaluation of a small library of nojirimycin-derived bicyclic iminosugars

Article abstract of DOI:10.1016/j.carres.2007.04.002

Novel nojirimycin-derived bicyclic structures, containing cyclic carbamate, urea and guanidine moieties have been synthesised starting from suitably protected α-C-vinylnojirimycin and α-C-allylnojirimycin, respectively, and their biological activity against different glycosidases and as antibacterial agents tested.

Full text of DOI:10.1016/j.carres.2007.04.002

Carbohydrate Research 342 (2007) 1813–1830
Synthesis and biological evaluation of a small library
of nojirimycin-derived bicyclic iminosugars
Laura Cipolla,* Marcos Reis Fernandes, Maria Gregori,
Cristina Airoldi and Francesco Nicotra
Department of Biotechnology and Biosciences, University of Milano-Bicocca, P.za della Scienza 2, 20126 Milano, Italy
Received 22 February 2007; received in revised form 4 April 2007; accepted 9 April 2007
Available online 18 April 2007
Abstract—Novel nojirimycin-derived bicyclic structures, containing cyclic carbamate, urea and guanidine moieties have been syn-
thesised starting from suitably protected a-C-vinylnojirimycin and a-C-allylnojirimycin, respectively, and their biological activity
against different glycosidases and as antibacterial agents tested.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Iminosugars; Nojirimycin; Glycosidases; Enzyme inhibitors; Glucuronidase; Antibacterial
1. Introduction
structures are responsible for their potent activity,
mimicking the flattened-chair transition state of the
enzymatic reaction.1e,8 In addition, it was demon-
strated1e that the interaction between a heteroatom pos-
sessing a protonable lone pair suitably positioned in the
molecule can influence the inhibitory activity. In connec-
tion with the design of more fine-tuned inhibitors,
numerous syntheses of these alkaloids have been
reported.9 The design of non-natural bicyclic imino-
sugars has driven the synthesis of a number of different
innovative structures.10
We report herein the synthesis of a variety of novel
nojirimycin-derived bicyclic analogs, the six-membered
ring of which has a flattened-chair conformation as a
result of its fusion with the second ring. An innovative
feature of these bicyclic structures is the introduction
of pharmacophoric groups, such as cyclic carbamate,
urea and guanidine moieties. Cyclic carbamates such
as 1,3-oxazolidin-2-ones and 1,3-oxazinan-2-ones are
important target molecules: oxazolidinones are relevant
pharmacophores in antibiotics against highly resistant
Gram-positive bacteria,11 while 1,3-oxazinan-2-ones
are important heterocycles present in several biologi-
cally active natural products such as maytansine and
its analogues,12 and are investigated as anti-cancer
drugs.12 In addition, ring-annulated 2-oxazolidinones
Polyhydroxylated alkaloids, usually referred to as imino-
sugars, display a wide range of interesting biological
activities, suggesting their potential use in the treatment
of a number of diseases. Mainly, they are known for
their inhibitory activity towards carbohydrate-process-
ing enzymes,1 suggesting their use in different therapeu-
tic applications, such as treatment of diverse viral
infections,2 that is, human immunodeficiency virus
(HIV),2a–d human hepatitis B virus (HBV),2b,d,e human
hepatitis C (HCV),2f,g bovine viral diarrhoea virus
(BVDV),2g Japanese encephalitis virus (JEV)2h and den-
gue virus,2h as well as cancer,3 diabetes,4 tuberculosis,5
malaria5b and lysosomal storage diseases.6 Due to the
tremendous potential of iminosugars, in the last several
years a variety of monocyclic and bicyclic iminosugars
have been synthesised7 or isolated from natural sour-
ces.1b In particular, the core structure of a bicyclic imino-
sugar may contain various heterocyclic rings, such as
the [4.3.0] indolizine system, or the [3.3.0] pyrrolizidine
system. It has been suggested that their rigid, bicyclic
*
Corresponding author. Tel.: +39 02 6448 3460; fax: +39 02 6448
3565; e-mail: laura.cipolla@unimib.it
0008-6215/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2007.04.002

1814
L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
can be used as precursors of iminosugar structures.13
The urea pharmacophore is present in several molecules
with therapeutic applications,14 as far as the guanidi-
nium group is included in many natural and unnatural
derivatives, displaying an array of potent, selective and
specific biological activities.15 Preliminary biological
evaluation of the synthesised compounds focused on
glycosidase inhibition and antibacterial activity.
O
O
CH2NH2
HO
HO
BnO
H
N
N
H
OH
BnO
OBn
OH
OBn
a
5
1
d
O
O
CH2R
BnO
BnO
Cbz
N
BnO
N
b
2. Results and discussion
H
OBn
BnO
c
OBn
To generate a small library of bicyclic iminosugars, five-
or six-membered rings were fused to nojirimycin. Carba-
mate, urea, and guanidine functionality was introduced
on the nitrogen atom, and amino, hydroxyl or carbox-
ylic groups were positioned on the bicyclic scaffolds.
Cyclic carbamates (1,3-oxazolidin-2-ones and 1,3-oxaz-
inan-2-ones), cyclic ureas (1,3-diazolidin-2-ones and
1,3-diazinan-2-ones) and cyclic guanidines (2-imino-
1,3-diazolidines and 2-imino-1,3-diazinanes) have been
synthesised from key compounds a-C-allyl nojirimycin
1,16 and a-C-vinyl nojirimycin; the different position of
the double bond afforded the six-membered or the
five-membered nojirimycin-fused ring, respectively.
OBn
OBn
2
3: R = I
4: R = N3
e
O
O
CH2N3
O
O
O
CH2R'
RO
N
g
N
R
H
H
OBn
BnO
f
OBn
BnO
OBn
6 R = Ac
7 R = H
OBn
8: R = H, R' = N3
9: R = OH, R' = N3
h
i
2.1. Synthesis of oxazolidinones and oxazinanones
O
O
CH2NH2
O
a-C-Allyl nojirimycin 116 was protected as carbobenzyl-
oxy derivative 2 (58% yield, Scheme 1), with benzyl chlo-
roformate and diisopropylethylamine (DIPEA), to
allow an iodocyclisation reaction between the double
bond and the benzyloxy group in position 2 producing
a cyclic iodoether, as already reported for allyl-C-glyco-
sides.17 However, when compound 2 was reacted with
iodine at 10 ꢁC, a iodocyclisation reaction18 occurred,
affording the bicyclic iododerivative 3 (92% yield, de
>95% in favour of S isomer). The stereochemical
outcome of the reaction was determined by NOESY
experiments on derivative 6.
N
HO
H
HO
OH
OH
10
Scheme 1. Reagents and conditions. (a) CbzCl, DIPEA, dry MeCN,
58%; (b) I2, dry CH2Cl2, 0 ꢁC, 92%; (c) NaN3, n-Bu4NI, dry CH2Cl2,
88%; (d) H2, Pd(OH)2/C, 1:1 MeOH–H2O, AcOH, quantitative yield;
(e) Ac2O, TFA, 72%; (f) dry MeOH, cat. Na, 95%; (g) IBX, DMSO; (h)
NaPO4H2.2H2O, NaClO2, CH3CN, 72% over two steps; (i) H2,
Pd(OH)2/C, 1:1 acetone–H2O, AcOH, quantitative yield.
The nojirimycin-fused 1,3-oxazinan-2-one 3 was then
further functionalised. Nucleophilic substitution of
iodine with tetrabutylammonium iodide and sodium
azide in dry N,N-dimethylformamide afforded the azido-
bicyclic derivative 4 (reflux, 88% yield). Then, com-
pound 4 was submitted to selective acetolysis of the
primary benzyloxy group19 using a mixture of acetic
anhydride in trifluoroacetic acid obtaining compound
6 (72% yield). NOESY experiments on acetate 6 allowed
the determination of the absolute configuration of the
stereocentre generated in the iodocarbamoylation reac-
tion, which was S. Oxazinanone 6 was further function-
alised with a carboxyl group as follows. Compound 6
IBX in dimethylsulfoxide,21 that was directly trans-
formed into azido acid derivative 9 (NaPO4H2Æ2H2O,
NaClO2, CH3CN, 72% yield over two steps).22 Com-
pounds 4 and 9 were finally deprotected by hydrogenol-
ysis, with simultaneous reduction of the azido function
to the corresponding amino group yielding compounds
5 and 10, respectively.
Looking at the second ring potentiality, we thought
that the five-membered 1,3-oxazolidin-2-one fused to
the nojirimycin moiety could be of great interest. Start-
ing from commercially available 2,3,4,6-tetra-O-benzyl-
D-glucopyranose, the corresponding glucosyl benzyl-
amine 1116a was formed in quantitative yields by reaction
with benzylamine and catalytic camphor-10-sulfonic
acid (CSA).
´
was deacetylated under Zemplen conditions (Na,
MeOH)20 affording alcohol 7 (95% yield). Alcohol 7
was then oxidised to the intermediate aldehyde 8 with

L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
1815
Reaction of 11 (Scheme 2) with vinylmagnesium bro-
mide (1 M in THF) afforded the open-chain amino alco-
hol 12 (63% yield, 70% de). The stereochemistry of the
newly formed stereocentre was determined only after
ring closure by reductive amination. To oxidise the
hydroxyl group of 12 into the corresponding ketone,
protection of the nitrogen was needed.16a Compound
12 was therefore reacted with fluorenylmethyl chlorofor-
mate and diisopropylethylamine in dry acetonitrile,
affording the Fmoc-protected amino alcohol 13 in quan-
titative yields. Oxidation of 13 with IBX in dry DMSO
afforded compound 14 in 97% yield. Finally, in a two-
step procedure, hydrolysis of the Fmoc protecting
group, using diethylamine in dry acetonitrile, to the
labile intermediate 15, followed by intramolecular
reductive amination (triacetoxyborohydride, glacial ace-
tic acid) afforded the C-vinyl nojirimycin derivative 16
(65% yield over two steps, 60% de). 1H NMR and
NOESY analysis of 16 allowed the determination of
the absolute configuration of the stereocentres derived
from the previous Grignard reaction and the cyclisation
reaction. J values between H-2/H-3, H-3/H-4 and H-4/
H-5 (9.5 Hz) showed that the nojirimycin ring adopts
cate the D-configuration at C-5, while the J values
between H-1/H-2 (5.5 Hz), suggest the a orientation of
the vinyl group.
To further proceed to the bicyclic oxazolidinone
derivative, selective debenzylation of the tertiary nitro-
gen of the ring was performed, by oxidative cleavage
with ceric ammonium nitrate (CAN),16b affording the
N-deprotected compound 17. Carbamoylation of crude
17 with benzyl chloroformate afforded compound 18
(CbzCl, DIPEA in dry CH3CN, 54% yield over two
steps), the reaction of which at 0 ꢁC with iodine in dry
dichloromethane afforded, as expected, the bicyclic iodo
derivative 19 (84% yield, de >95%). 1H NMR and
NOESY experiments allowed the determination of the
absolute configuration of the new stereocentre, which
in this case was R.
The oxazolidinone 19 was further functionalised first
by nucleophilic substitution of the iodide with an azido
function (tetrabutylammonium iodide and sodium azide
in dry DMF, reflux) affording azido derivative 20 in 97%
yield. The primary hydroxyl group at C-6 of compound
20 was selectively debenzylated by acetolysis (Ac2O,
TFA)19 to give the acetylated compound 22 in 74%
4
20
´
a C1 chair conformation; in addition, NOESY experi-
yield. Deacetylation at C-6, under Zemplen conditions
ments and J values between H-4 and H-5 (9.5 Hz) indi-
afforded alcohol 23 (78% yield). Finally, a two-step
OBn
BnO
R
N
BnO
H
O
OBn
O
e
OBn R
N
c
O
NHBn
OBn R
N
a
BnO
Bn
BnO
f
OBn
BnO
b
Bn
BnO
OBn
OBn
OBn
OBn
12: R = H
13: R = Fmoc
OBn
14: R = Fmoc
15: R = H
16: R = Bn
17: R = H
18: R = Cbz
11
d
g
O
O
O
O
O
O
R
O
RO
BnO
N
N
CH2N3
CH2N3
N
CH2R
m
k
h
H
H
H
BnO
OBn
BnO
OBn
BnO
i
OBn
OBn
OBn
OBn
22: R = Ac
23: R = H
24: R = H
25: R = OH
19: R = I
20: R = N3
l
n
o
j
O
O
O
O
HO
O
HO
HO
N
CH2NH2
N
CH2NH2
H
H
HO
OH
OH
OH
OH
26
21
Scheme 2. Reagents and conditions. (a) CH2@CHMgBr, dry THF, 63%; (b) FmocCl, DIPEA, dry MeCN, quantitative yield; (c) IBX, DMSO, 97%;
(d) DEA, dry MeCN; (e) NaBH(OAc)3, Na2SO4, AcOH, 65% over two steps; (f) CAN, 5:1 THF–H2O; (g) CbzCl, DIPEA, dry MeCN, 54% over two
steps; (h) I2, 0 ꢁC, dry CH2Cl2, 84%; (i) NaN3, n-Bu4NI, dry CH2Cl2, 97%; (j) H2, Pd(OH)2/C, 1:1 MeOH–H2O, AcOH, quantitative yield; (k) Ac2O,
TFA, 74%; (l) dry MeOH, cat. Na, 78%; (m) IBX, DMSO; (n) NaPO4H2Æ2H2O, NaClO2, MeCN, 83% over two steps; (o) H2, Pd(OH)2/C, 1:1
acetone–H2O, AcOH, quantitative yield.

1816
L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
O
H
O
O
O
O
O
O
O
N
Ph
O
NH
H
AcO
BnO
BnO
BnO
BnO
BnO
BnO
b
CH2Br
N
N
a
N
N
c
N
a
b
17
H
H
3
H
BnO
OBn
BnO
OBn
OBn
OBn
OBn
OBn
29
OBn
OBn
OBn
OBn
33
32
28
27
d
O
O
d
NH
HO
HO
NH
H
BnO
CH2NH2
CH2N3
N
N
O
d
c
O
O
O
O
H
OH
HO
OH
30
N
BnO
OBn
N
31
35
OH
H
OBn
H
34
HO
OH
OH
Scheme 4. Reagents and conditions. (a) Benzyl isocyanate, dry DME,
80 ꢁC, 94%; (b) NBS 2 equiv, dry CH2Cl2, 0 ꢁC, 65%; (c) NaN3, dry
DMF, 79%; (d) H2, Pd(OH)2/C, AcOH, 1:1 MeOH–H2O, quantitative
yield.
OH
OH
Scheme 3. Reagents and conditions. (a) n-Bu4NOH, CH3CN, 98%; (b)
Ac2O, TFA, 59%; (c) dry MeOH, cat. Na, 70%; (d) H2, Pd(OH)2/C,
AcOH, 1:1 MeOH–H2O, quantitative yield.
uct originates from the nucleophilic attack of the nitro-
gen on the activated double bond; no traces of the
product derived from the competing attack by the car-
bonyl oxygen could be detected. It is worth noting that
during the cyclisation reaction the loss of the N-benzyl
group was observed. 1H NMR and NOESY experiments
allowed the determination of the absolute configuration
of the new stereocentre, which was S. Further function-
alisation of the urea ring involved nucleophilic substitu-
tion of the bromine by an azido functionality to give
derivative 34 (sodium azide, 79% yield), followed by
complete deprotection and reduction to the correspond-
ing amine 35 by hydrogenolysis (quantitative yield).
oxidation procedure (IBX in DMSO to aldehyde 24,
then NaPO4H2Æ2H2O, NaClO2, CH3CN, 83% yield over
two steps) afforded azido acid derivative 25. Derivatives
20 and 25 were finally deprotected by hydrogenolysis,
with simultaneous reduction of the azido function to
the corresponding amino group to compounds 21 and
26, respectively.
To introduce greater structural variation in the second
ring, functionalisation with a hydroxyl group was
attempted. Treatment of compound 3 with tetrabutylam-
monium hydroxide afforded compound 27 as the only
product (Scheme 3), resulting from a b-elimination reac-
tion, instead of the expected nucleophilic substitution
product. With compound 27 in our hands, acetolysis
was performed, affording compound 28 (59% yield),
2.3. Synthesis of 2-imino-1,3-diazolidines and 2-imino-
1,3-diazinanes (cyclic guanidines)
which gave, as expected, isomerisation of the double
20
´
bond. Methanolysis under Zemplen conditions affor-
A cyclic guanidine functionality was also introduced on
the nojirimycin ring (Scheme 5). Vinyl-C-nojirimycin 17
was reacted with N,N0-di-Boc-thiourea in the presence
of mercuric chloride,24 affording directly the cyclic pro-
tected guanidine derivative 37, which was submitted
without purification to the subsequent reaction. Double
nucleophilic displacement, first with iodine to derivative
38 (46% yield over two steps), secondly with sodium
azide (61% yield), afforded derivative 39. The stereo-
chemistry of the newly generated stereocentre was deter-
mined by NOESY experiments on derivative 39.
Hydrolysis of the carbamate protecting groups with tri-
fluoroacetic acid to guanidine 40 (86% yield), followed
by hydrogenolysis afforded compound 41 (quantitative
yield). Attempts to oxidise the primary hydroxyl group
of 41 with TEMPO25 failed.
ded bicycle 29, formed by intramolecular attack of the
free hydroxyl group on the carbonyl group. Derivatives
27 and 29 were finally deprotected by hydrogenolysis, to
generate bicyclic iminosugars 30 and 31, respectively.
Reduction of the double bond in 27 was diastereoselec-
tive (quantitative yield, de >98%) giving the stereoiso-
mer with the R configuration at the newly generated
1
stereocentre, as determined by H NMR spectroscopy.
2.2. Synthesis of 1,3-diazolidin-2-ones and 1,3-diazinan-2-
ones (cyclic ureas)
To generate a small iminosugar library, variations of the
functionality in the second ring were made. First, a 1,3-
diazolidin-2-one was synthesised (Scheme 4). Vinyl-C-
nojirimycin 17 was reacted with benzyl isocyanate,23
affording urea 32 in 94% yield. Treatment of 32 with
N-bromosuccinimide in dry dichloromethane afforded
the five-membered cyclic urea 33. The cyclisation prod-
A guanidine functionality was also considered for the
synthesis of six-membered bicyclic structures. Thus,
treatment of 1 with N,N0-di-Boc-thiourea in the pres-
ence of mercuric chloride,24 afforded a mixture of two

L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
1817
BocN
BnO
Inhibition of α-Glucosidase (yeast)
BocN
BnO
NBoc
CH2R
NBoc
CH2HgCl
41
35
31
30
26
21
10
5
N
N
a
H
17
H
b
BnO
OBn
BnO
37
OBn
OBn
OBn
38: R = I
39: R = N3
c
DNJ
d
0
20
40
60
80
100
HN
HN
BnO
Inhibition (%)
NH
H
NH
H
HO
CH2NH2
e
CH2N3
N
N
Inhibition of β-Glucuronidase (bovine liver)
41
35
31
HO
OH
BnO
OBn
OBn
40
OH
41
30
26
21
10
Scheme 5. Reagents and conditions. (a) N,N0-di-Boc-thiourea, HgCl2,
Et3N, dry DMF; (b) I2, CH2Cl2, 46% over two steps; (c) NaN3, dry
DMF, 100 ꢁC, 61%; (d) 4:1 CF3COOH–H2O, 86%; (e) H2, Pd(OH)2/C,
AcOH, 1:1 MeOH–H2O, quantitative yield.
5
DNJ
Boc
0
10
20
30
40
50
BocN
BnO
BocN
BnO
N
CH2HgCl
NHBoc
O
Inhibition (%)
+
N
N
a
Figure 1. Inhibition of a-glucosidase and b-glucuronidase by bicyclic
1
CH2HgCl
H
iminosugars.
BnO
BnO
OBn
OBn
OBn
42
43
irimycin (56% inhibition, IC50 180 lM). In particular,
compounds 10 and 26 were the most active with 89%
(IC50 126 lM) and 82% (IC50 140 lM) inhibition,
respectively. Compound 21 and 31 showed 72% and
69% inhibition corresponding to 103 and 148 lM IC50,
respectively. Compounds 5 (23% inhibition), 10 (47%
inhibition, IC50 218 lM), 21 (11% inhibition) and 26
(45% inhibition, IC50 259 lM) proved to inhibit b-glucu-
ronidase, the best inhibitors being those possessing the
carboxylic function at C-6 of the nojirimycin ring, as
expected (IC50 were determined only for most significant
inhibitors). None of the synthesised compounds resulted
active against b-glucosidase.
Compounds 5, 10, 21, 26, 30 and 31 were also tested in
antibacterial assays against Enterococcus faecium (Gram
positive), Staphylococcus aureus (Gram positive), Esche-
richia coli (Gram negative) and Pseudomonas aeruginosa
(Gram negative). However none showed antibacterial
activity.
Scheme 6. Reagents and conditions. (a) N,N0-di-Boc-thiourea, HgCl2,
Et3N, dry DMF.
different bicyclic structures 42 and 43 (Scheme 6), which
slowly decomposed. Different reaction conditions were
tested in order to selectively obtain only one compound,
without any significant improvement.
2.4. Biological evaluation
Fully deprotected iminosugars were assayed as glyco-
sidase inhibitors against commercially available
a-glucosidase (yeast), b-glucosidase (almond) and b-
glucuronidase (bovine liver). b-Glucuronidase was also
tested because it is a target enzyme for anticancer che-
motherapy.26 To examine the potential of each member
of the library as glycosidase inhibitor, preliminary
screening assays at a fixed concentration (200 lM) of
potential inhibitors were carried out. The inhibitory
activity is shown as a percentage at the fixed concentra-
tion; inhibition data are summarised in Figure 1. The
inhibitory activity against the corresponding p-nitro-
phenyl glycosides was estimated by measuring p-nitro-
phenol absorbance at 405 nm. 1-Deoxynojirimycin
(DNJ) was used as the reference inhibitor. For com-
pounds showing an interesting inhibitory effect, IC50
was also determined.
3. Experimental
3.1. General methods
All solvents were dried over molecular sieves, for at least
24 h prior to use. When dry conditions were required, the
reaction was performed under Ar atmosphere. Thin-layer
chromatography (TLC) was performed on Silica Gel 60
F254 plates (Merck) with detection with UV light when
possible, or charring with a solution containing concd
H2SO4–EtOH–H2O in a ratio of 5:45:45 or a solution
Compounds 10, 21, 26 and 31, all featuring a cyclic
carbamate group were active against a-glucosidase, with
inhibition potency higher then the reference 1-deoxynoj-

1818
L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
containing (NH4)6Mo7O24 (21 g), Ce(SO4)2 (1 g), concd
H2SO4 (31 mL) in H2O (500 mL). Flash column chroma-
tography was performed on silica gel 230–400 mesh
(Merck). NMR spectra were recorded at 400 MHz (1H)
and at 100.57 MHz (13C) on a Varian Mercury instru-
ment. Chemical shifts are reported in parts per million
downfield from TMS as an internal standard; J values
are given in Hz. Numbering refers to parent monosaccha-
ride. Mass spectra were recorded on a MALDI2 Kom-
pakt Kratos instrument, with gentisic acid (DHB) as
the matrix. Optical rotations were measured at room
strains: Escherichia coli, Pseudomonas aeruginosa,
Staphylococcus aureus and Enterococcus faecium. The
test strains were grown for 17–18 h at 37 ꢁC in LB
broth27 and then diluted in the same medium to
OD600 = 0.05. The bacteria (100 lL) were then inocu-
lated in a microtitre plate containing serial dilutions
(250–0.12 lg/mL) of the compound in 100 lL. The
microtitre plates were incubated 18–20 h at 37 ꢁC and
the MIC was defined as the lowest concentration of test
compound that inhibited bacterial growth.
temperature with a Kruss-Optronic P3002 polarimeter.
3.4. (2R,3R,4R,5S,6R)-N-(Benzyloxycarbonyl)-3,4,5-
tris(benzyloxy)-2-benzyloxymethyl-6-(prop-2-enyl)piperi-
dine (2)
¨
[a]D values are given in 10ꢀ1 deg cm2 gꢀ1
.
3.2. General procedures for enzymatic assays
To a solution of compound 1 (0.133 g, 0.24 mmol) in dry
CH3CN (3 mL), DIPEA (0.168 mL, 0.98 mmol) and
CbzCl (0.184 mL, 1.31 mmol) were added. After 4 h
the solvent was evaporated under reduced pressure.
The crude residue was purified by flash chromatography
(petroleum ether–EtOAc, 85:15), affording compound 2
(0.096 g, 58%) as a yellowish oil. Due to conformational
equilibrium between the two chair conformations, broad
Inhibitory activity was determined spectrophotometri-
cally, measuring the residual hydrolytic activities of
the glycosidases against the corresponding p-nitrophenyl
a- or b-D-glucopyranoside, and b-D-glucuronide.
a-Glucosidase from yeast, b-glucosidase from almond
and b-glucuronidase from bovine liver were used for
the enzymatic assays. All enzymes and p-nitrophenyl
glycosides were purchased from Sigma. Each experiment
was carried out in triplicate.
1
signals displayed at room temperature H NMR spec-
trum; to have sharp and resolved signals for unam-
biguous assignments, the spectrum was recorded at
The enzymatic assays were prepared as follow: (a) a-D-
glucosidase: 0.94 U/mL in phosphate buffer (0.5 M with
0.244 M K2HPO4 and 0.256 M KH2PO4, pH 6.5); (b)
b-D-glucosidase: 1.2 U/mL in citrate buffer 0.3 M, pH
5.0; (c) b-D-glucuronidase: 120 U/mL in acetate buffer
13.6 M, pH 5.0; (d) p-nitrophenyl glycosides (1 mM)
were dissolved in water; (e) 1 mM stock solution of inhib-
itors in water were used for the determination of percent-
age of inhibition with a 200 lM concentration of the
inhibitor in the assay cuvette; various inhibitor’s concen-
trations (50–400 lM) were used to determine IC50 values.
Each glycosidase assay was performed by preparing
1 mL samples in cuvettes, containing 0.2 mL of buffer,
0.1 mL of enzyme solution and 0.2 mL of water or stock
solution with the inhibitor and finally each cuvette was
filled up to a total volume of 0.9 mL with distilled water.
The mixture was incubated for 10 min at 37 ꢁC, the reac-
tion was started by adding 0.1 mL of the glycoside solu-
tion. After 30 min, 0.1 mL of saturated aqueous
solution of Na2CO3 was added and the absorbance of
p-nitrophenate was measured at 405 nm. The percentage
inhibition was calculated by the formula (A ꢀ B)/
A · 100, where A is the p-nitrophenol resulting from the
enzymatic hydrolysis without inhibitor and B is that in
the presence of the inhibitor. The IC50 value is the con-
centration of inhibitor at 50% of enzyme activity.
22
40 ꢁC. ½aꢁD +8.6 (c 0.6, CHCl3); 1H NMR (CDCl3;
40 ꢁC): d 7.41–7.25 (m, 25H, Ph), 5.94–5.88 (m, 1H, H-
20), 5.19 (br s, 2H, NCOOCH2Ph), 5.03 (d, 1H,
J3 a;2 ¼ 17:3 Hz, H-30a), 4.95 (d, 1H, J3 b;2 ¼ 10:1 Hz,
H-30b), 4.73–4.50 (m, 8H, OCHPh), 4.47–4.41 (m, 1H,
H-1), 4.32 (dt, 1H, J5,6 = 8.9 Hz, J5,4 = 3.8 Hz, H-5),
4.05 (dd, 1H, J4,5 = 3.8 Hz, J4,3 = 2.1 Hz, H-4), 3.95
0
0
0
0
(br d, 1H, J3,2 = 8.0 Hz, H-3), 3.82 (dd, 1H, J2,3
8.0 Hz, J2,1 = 5.4 Hz, H-2), 3.73 (br dd, 1H, J6a,5
=
=
8.9 Hz, J6a,6b = 3.8 Hz, H-6a), 3.64 (t, 1H, J = 8.9 Hz,
H-6b), 2.73–2.58 (m, 2H, H-10); 13C NMR (CDCl3): d
156.20 (CO), 138.54, 138.46, 138.43, 138.05, 136.66
(Cquat. arom.), 136.84 (20-C), 128.75–127.72 (CH arom),
116.29 (C-30), 81.81, 80.92, 77.38 (C-2, C-3, C-4), 73.30,
73.30, 72.85, 72.60, 72.01, 67.67 (OCH2Ph, C-6), 54.92,
54.92 (C-1, C-5), 34.50 (C-10); MALDI-MS m/z 721
[M+Na]+; 737 [M+K]+; C45H47NO6 requires 697.86;
Anal. Calcd for C45H47NO6: C, 77.45; H, 6.79; N, 2.01.
Found: C, 77.49; H, 6.81; N, 1.99.
3.5. (3S,4aR,5S,6R,7R,8R)-5,6,7-Tris(benzyloxy)-8-
((benzyloxy)methyl)-hexahydro-3-(iodomethyl)pyr-
ido[1,2-c][1,3]oxazin-1(3H)-one (3)
To a solution of compound 2 (0.597 g, 0.855 mmol) in
dry CH2Cl2 at 0 ꢁC (10 mL), I2 was added (0.434 g,
1.71 mmol). After 3 h the reaction was quenched by
the addition of aq sodium thiosulfate until a colourless
solution was obtained, and then the mixture was ex-
tracted with CH2Cl2. The organic layer was dried over
3.3. Antibacterial assays
Minimal inhibitory concentration (MIC) of the synthes-
ised compounds was determined against four bacterial

L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
1819
Na2SO4, filtered and concentrated to dryness. The crude
residue was purified by flash chromatography (petro-
leum ether–EtOAc, 7:3), affording compound 3 as a yel-
C-5), 54.10 (C-30), 30.13 (C-10); MALDI-MS m/z 649
[M+H]+; 672 [M+Na]+; 688 [M+K]+; C38H40N4O6
requires 648.75; Anal. Calcd for C38H40N4O6: C,
70.35; H, 6.21; N, 8.64. Found: C, 70.25; H, 6.23; N,
8.65.
22
1
lowish oil (0.795 g, 92%). ½aꢁD ꢀ12.2 (c 1.0, CHCl3); H
NMR (CDCl3): d 7.35–7.28 (m, 20H, Ph), 4.78–4.74 (dt,
1H, J5,6 = 6.5 Hz, J5,4 = 3.5 Hz, 5-H), 4.62 (d, 1H,
J = 12.1 Hz, OCHPh), 4.58 (d, 1H, J = 12.2 Hz,
OCHPh), 4.47 (d, 1H, J = 11.8 Hz, OCHPh), 4.43 (d,
1H, J = 12.2 Hz, OCHPh), 4.38 (d, 1H, J = 11.8 Hz,
OCHPh), 4.33 (d, 1H, J = 13.9 Hz, OCHPh), 4.30 (d,
1H, J = 13.9 Hz, OCHPh), 4.26 (d, 1H, J = 12.1 Hz,
OCHPh), 4.01–3.95 (m, 1H, H-20), 3.79 (t, 1H,
J = 3.5 Hz, H-4), 3.72–3.68 (m, 1H, H-1), 3.66 (t, 1H,
J = 3.5 Hz, H-3), 3.63 (dd, 1H, J6a,6b = 9.8 Hz,
J6a,5 = 6.5 Hz, H-6a), 3.59 (dd, 1H, J6b,6a = 9.8 Hz,
3.7. (3S,4aR,5S,6R,7R,8R)-3-(Aminomethyl)-hexahydro-
5,6,7-trihydroxy-8-(hydroxymethyl)pyrido[1,2-c][1,3]oxa-
zin-1(3H)-one (5)
To a solution of 4 (0.050 g, 0.077 mmol) in MeOH
(2 mL), Pd(OH)2/C (0.050 g) and two drops of AcOH
were added. The flask was purged three times with Ar
and then filled with H2. After 48 h, the catalyst was
removed by filtration, and the filtrate concentrated un-
der reduced pressure, affording compound 5 as a yellow-
0
0
J6b,5 = 6.5 Hz, H-6b), 3.27 (dd, 1H, J3 a;3 b ¼ 10:4 Hz,
22
J3 a;2 ¼ 3:5 Hz, H-30a), 3.25 (br s, 1H, H-2), 3.10 (dd,
ish oil in quantitative yield. ½aꢁD ꢀ8.5 (c 1.00, MeOH);
0
0
1H, J3 b;3 a ¼ 10:4 Hz, J3 b;2 ¼ 7:5 Hz, H-30b), 2.09
1H NMR (D2O): d 4.77–4.71 (m, 1H, H-20), 4.62 (br t,
0
0
0
0
0
0
(ddd, 1H, J1 a;1 b ¼ 13:3 Hz, J = 11.2 Hz, J = 2.0 Hz,
1H, H-5), 4.02 (ddd, 1H, J = 9.8 Hz, J = 4.8 Hz, J1,2
1.6 Hz, H-1), 3.98 (dd, 1H, J6a,6b = 11.8 Hz, J6a,5
8.5 Hz, H-6a), 3.90 (dd, 1H, J3,4 = 3.2 Hz, J3,2
=
=
=
H-10a), 1.95 (ddd, 1H, J1 b;1 a ¼ 13:3 Hz, J = 6.2 Hz,
J = 2.0 Hz, H-10b); 13C NMR (CDCl3): d 153.99 (CO),
138.31, 138.19, 137.57, 137.57 (Cquat. arom.), 128.75–
127.84 (CH arom.), 74.94, 74.58, 74.01, 72.18 (C-2, C-
3, C-4, C-20), 73.15, 72.67, 72.34, 72.25, 67.35 (OCH2Ph,
C-6), 53.90, 49.70 (C-1, C-5), 30.13 (C-10), 6.23 (C-30);
MALDI-MS m/z 735 [M+H]+; 757 [M+Na]+; 773
[M+K]+; C38H40INO6 requires 733.63; Anal. Calcd for
C38H40INO6: C, 62.21; H, 5.50; N, 1.91. Found: C,
62.16; H, 6.79; N, 1.94.
0
0
1.6 Hz, H-3), 3.87 (dd, 1H, J4,3 = 3.2 Hz, J4,2 = 1.6 Hz,
H-4), 3.72 (dd, 1H, J6b,6a = 11.8 Hz, J6b,5 = 5.1 Hz, H-
6b), 3.53 (t, 1H, J = 1.6 Hz, H-2), 3.15 (dd, 1H,
J3 a;3 b ¼ 13:7 Hz, J3 a;2 ¼ 8:5 Hz, H-30a), 3.09 (dd, 1H,
0
0
0
0
J3 b;3 a ¼ 13:7 Hz, J3 b;2 ¼ 3:3 Hz, H-30b), 2.20 (br ddd,
0
0
0
0
1H, H-10a), 2.02 (ddd, 1H, J1 b;1 a ¼ 13:5 Hz, J1 b;1
¼
0
0
0
4:8 Hz, J1 b;2 ¼ 1:7 Hz, H-10b); 13C NMR (D2O): d
153.36 (CO), 69.73, 69.51, 69.03, 67.82 (C-2, C-3, C-4,
C-20), 60.19, 48.54 (C-1, C-5), 59.73, 59.17 (C-6, C-30),
26.24 (C-10); MALDI-MS m/z 285 [M+Na]+; 301
[M+K]+; C10H18N2O6 requires 262.26; Anal. Calcd for
C10H18N2O6: C, 45.80; H, 6.92; N, 10.68. Found: C,
45.84; H, 6.91; N, 10.75.
0
0
3.6. (3S,4aR,5S,6R,7R,8R)-3-(Azidomethyl)-5,6,7-
tris(benzyloxy)-8-((benzyloxy)methyl)-hexahydro-
pyrido[1,2-c][1,3]oxazin-1(3H)-one (4)
To a solution of compound 3 (0.583 g, 0.795 mmol) in
dry DMF (10 mL), n-Bu4NI (0.147 g, 0.398 mmol) and
NaN3 (0.103 g, 1.59 mmol) were added and the reaction
mixture heated to reflux. After 2 h, the solvent was evap-
orated, under reduced pressure. The crude residue was
purified by flash chromatography (petroleum ether–
EtOAc, 65:35), affording compound 4 as yellowish oil
3.8. ((3S,4aR,5S,6R,7R,8R)-3-(Azidomethyl)-5,6,7-
tris(benzyloxy)-octahydro-1-oxopyrido[1,2-c][1,3]oxazin-
8-yl)methyl acetate (6)
To compound 4 (0.120 g, 0.185 mmol), a mixture of
Ac2O–TFA, 4:1 (0.128 M) was added. After 9 h, the
reaction was neutralised with a satd aq NaHCO3, and
extracted with EtOAc. Then, the organic phase was sub-
mitted to vacuum evaporation and flash chromatogra-
phy (petroleum ether–EtOAc, 5:5) affording compound
22
(0.697 g, 88%). ½aꢁD ꢀ9.6 (c 1.0, CHCl3); 1H NMR
(CDCl3): d 7.38–7.21 (m, 20H, Ph), 4.86–4.81 (m, 1H,
H-5), 4.73–4.31 (m, 8H, 4 · OCH2Ph), 4.21–4.15 (m,
1H, H-20), 3.89 (t, 1H, J = 3.6 Hz, H-4), 3.87–3.78 (m,
1H, H-1), 3.76 (t, 1H, J = 3.6 Hz, H-3), 3.71–3.66 (m,
22
6 as a yellowish oil (0.082 g, 72%). ½aꢁD ꢀ18.2 (c 0.8,
1
0
0
0
0
2H, H-6), 3.46 (dd, 1H, J3 a;3 b ¼ 12:3 Hz, J3 a;2
¼
CHCl3); H NMR (C6D6): d 7.27–7.01 (m, 15H, Ph),
5:2 Hz, H-30a), 3.40 (dd, 1H, J3 b;3 a ¼ 12:3 Hz,
5.42 (dd, 1H, J5,6a = 10.0 Hz, J5,6b = 4.2 Hz, H-5), 4.83
(dd, 1H, J6a,6b = 11.3 Hz, J6a,5 = 10.0 Hz, H-6a), 4.66
and 4.22 (ABq, 2H, J = 11.6 Hz, OCH2Ph), 4.41 and
4.04 (ABq, 2H, J = 11.6 Hz, OCH2Ph), 4.17 and 4.07
(ABq, 2H, J = 11.8 Hz, OCH2Ph), 3.94 (dd, 1H,
J6b,6a = 11.6 Hz, J6b,5 = 4.2 Hz, H-6b), 3.88–3.83 (m,
0
0
J3 b;2 ¼ 5:2 Hz, H-30b), 3.34 (dd, 1H, J2,3 = 3.6 Hz,
0
0
0
0
J2,1 = 2.6 Hz, H-2), 2.28 (ddd, 1H, J1 a;1 b ¼ 13:9 Hz,
J = 11.6 Hz, J = 1.5 Hz, H-10a), 1.74 (ddd, 1H,
J1 b;1 a ¼ 13:9 Hz, J = 6.3 Hz, J = 1.9 Hz, H-10b); 13C
NMR (CDCl3): d 154.07 (CO), 138.33, 138.21, 137.61,
137.58 (Cquat. arom.), 129.1–127.8 (CH arom.), 75.08,
74.84, 73.26, 72.33 (C-2, C-3, C-4, C-20), 73.15, 72.73,
72.39, 72.22 (OCH2Ph), 67.39 (C-6), 53.93, 49.77 (C-1,
0
0
1H, H-20), 3.74 (ddd, 1H, J1;1 a ¼ 10:6 Hz, J1;1 b
¼
0
0
6:5 Hz, J1,2 = 1.7 Hz, H-1), 3.70 (br t, 1H, J = 3.1 Hz,
H-3), 3.48 (br s, 1H, H-4), 3.01 (br s, 1H, H-2), 2.65

1820
L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
(dd, 1H, J3 a;3 b ¼ 12:8 Hz, J3 a;2 ¼ 6:0 Hz, H-30a), 2.56
3.10. (3S,4aR,5S,6R,7R,8S)-3-(Azidomethyl)-5,6,7-
tris(benzyloxy)-octahydro-1-oxopyrido[1,2-c][1,3]oxa-
zine-8-carboxylic acid (9)
0
0
0
0
(dd, 1H, J3 b;3 a ¼ 12:8 Hz, J3 b;2 ¼ 4:8 Hz, H-30b), 2.01
0
0
0
0
(q, 1H, J = 12.8 Hz, H-10a), 1.78 (s, 3H, CH3CO), 1.02
0
0
0
0
0
(ddd, 1H, J1 b;1 a ¼ 12:8 Hz, J1 b;1 ¼ 6:5 Hz, J1 b;2
¼
1:7 Hz, H-10b); 13C NMR (CDCl3): d 171.31 (CO),
154.15 (C-40), 137.82, 137.47, 137.25 (Cquat. arom.),
128.84–127.98 (CH arom.), 73.77, 73.18, 72.19, 72.18
(C-2, C-3, C-4, C-20), 72.77, 72.25, 71.77, 61.60
(OCH2Ph, C-6), 54.06 (C-30), 53.52, 48.54 (C-1, C-5),
26.84 (C-10), 21.39 (CH3CO); MALDI-MS m/z
601 [M+H]+; 624 [M+Na]+; 640 [M+K]+; C33H36-
N4O7 requires 600.62; Anal. Calcd for C33H36N4O7: C,
65.99; H, 6.04; N, 9.33. Found: C, 65.95; H, 6.00; N,
9.34.
Alcohol 7 (0.072 g, 0.129 mmol) was dissolved in dry
DMSO (1.3 mL), and IBX (0.180 g, 0.644 mmol) was
added. After 6 h, the reaction was diluted with water,
the precipitate filtered off, and the mixture extracted
with Et2O. Usual work up afforded aldehyde 8, which
was submitted to the subsequent reaction without any
further purification. Aldehyde 8 was dissolved in
CH3CN (1.6 mL), then 1.25 M aq NaH2PO4Æ2H2O
(1.0 mL) and NaClO2 (0.116 g, 1.29 mmol) were added.
After 6 h, the reaction mixture was concentrated, the
residue suspended in CH2Cl2, the precipitate filtered
off, and the solvent evaporated under reduced pressure.
Purification by flash chromatography (EtOAc/EtOH,
NOESY experiments on acetate 6 allowed the deter-
mination of the absolute configuration of the stereocen-
tre generated in the iodocarbamoylation reaction,
22
1
which was S. H NMR coupling constants, in agree-
9:1) afforded azido acid 9 (0.053 g, 72%). ½aꢁD ꢀ23.8 (c
1
ment with some molecular mechanics calculations,
1.0, CHCl3); H NMR (C6D6): d 7.20–6.85 (m, 15H,
1
showed that the nojirimycin ring has C4 chair confor-
Ph), 5.82 (br s, 1H, H-5), 4.70–4.35 (m, 6H, 3 · OCH2-
Ph), 4.32–4.18 (m, 1H, H-20), 4.17–4.00 (m, 2H, H-1,
H-4), 3.80 (br s, 1H, H-3), 3.13 (br s, 1H, H-2), 2.78–
2.60 (m, 2H, H-30), 2.52 (br s, 1H, OH), 2.22–2.03 (m,
2H, H-10); 13C NMR (CDCl3): d 166.12, 155.80 (CO),
137.95, 137.40, 137.40 (Cquat. arom.), 131.10–127.08
(CH arom.), 74.33, 74.33, 74.08, 73.83 (C-2, C-3, C-4,
C-20), 72.18, 72.09, 71.80 (OCH2Ph), 54.19, 46.12 (C-1,
C-5), 50.43 (CH2N3), 30.48 (C-10); MALDI-MS m/z
573 [M+H]+; 595 [M+Na]+; 611 [M+K]+; C31H32N4O7
requires 572.61; Anal. Calcd for C31H32N4O7: C,
65.02; H, 5.63; N, 9.78. Found: C, 64.98; H, 5.65; N, 9.81.
mation, with some distortion and flattening of the chair
around the C2–C3–C4 region, producing the lowering
of the couplings, even below 3 Hz. In this case, there
is a major conformer around C5–C6, because we have
one large and one small coupling for H-5/H-6a and
H-5/H-6b.
3.9. (3S,4aR,5S,6R,7R,8R)-3-(Azidomethyl)-5,6,7-
tris(benzyloxy)-hexahydro-8-(hydroxymethyl)pyrido-
[1,2-c][1,3]oxazin-1(3H)-one (7)
To a solution of 6 (0.050 g, 0.083 mmol) in dry MeOH
(0.6 mL), catalytic Na was added. After 2 h, the reaction
was neutralised with 5% aq HCl, and the solvent evapo-
rated. Purification by flash chromatography (petroleum
ether–EtOAc, 25:75) afforded compound 7 as a yellow-
3.11. (3S,4aR,5S,6R,7R,8S)-3-(Aminomethyl)-octa-
hydro-5,6,7-trihydroxy-1-oxopyrido[1,2-c][1,3]oxazine-8-
carboxylic acid (10)
22
1
ish oil (0.046 g, 95%). ½aꢁD ꢀ24.4 (c 0.7, CHCl3); H
NMR (C6D6): d 7.35–7.05 (m, 15H, Ph), 4.66–4.66 (m,
1H, H-5), 4.62 (d, 1H, J = 12.4 Hz, OCHPh), 4.58 (d,
1H, J = 12.2 Hz, OCHPh), 4.45 (d, 1H, J = 11.9 Hz,
OCHPh), 4.43 (m, 3H, OCH2Ph, H-20), 4.30 (d, 1H,
J = 11.6 Hz, OCHPh), 3.90–3.80 (m, 1H, H-1), 3.75
(d, 2H, J = 6.0 Hz, H-6), 3.70 (dd, 1H, J3,4 = 3.0 Hz,
J3,2 = 2.7 Hz, H-3), 3.62 (dd, 1H, J4,3 = 3.0 Hz,
J4,5 = 2.8 Hz, H-4), 3.39–3.38 (m, 2H, H-30), 3.25
To a solution of 9 (0.037 g, 0.065 mmol) in acetone–
H2O, 1:1 (2 mL), Pd(OH)2/C (0.030 g) and two drops
of AcOH were added. The flask was purged three times
with Ar and then filled with H2. After 48 h, the solids
were removed by filtration, and the filtrate was concen-
trated under reduced pressure, affording compound 10
22
as a yellowish oil in quantitative yield. ½aꢁD ꢀ8.2 (c
1
1.0, MeOH); H NMR (D2O): d 4.73–4.61 (m, 1H, H-
20), 4.51 (d, 1H, J5,4 = 2.5 Hz, H-5), 4.28 (br t, 1H, H-
0
0
0
0
(br s, 1H, H-2), 2.32 (dd, 1H, J1 a;1 b ¼ 13:4 Hz,
4), 3.96 (ddd, 1H, J1;1 a ¼ 13 Hz, J1;1 b ¼ 5:6 Hz,
0
0
0
0
J1 a;2 ¼ 11:0 Hz, H-1’a), 1.72 (dd, 1H, J1 b;1 a
¼
J1,2 = 1.8 Hz, H-1), 3.78 (t, 1H, J = 7.1 Hz, H-3), 3.51
13:4 Hz, J1 b;2 ¼ 5:5 Hz, H-10b); 13C NMR (CDCl3): d
155.08 (CO), 138.08, 137.49, 137.26 (Cquat. arom.),
131.10–127.07 (CH arom.) 74.36, 73.43, 73.02 (C-2, C-
3, C-4, C-20), 72.79, 72.24, 72.20 (OCH2Ph), 61.49 (C-
6), 56.43, 49.64 (C-1, C-5), 54.12 (CH2N3), 30.15 (C-
10); MALDI-MS m/z 559 [M+H]+; 581 [M+Na]+; 597
[M+K]+; C31H34N4O6 requires 558.62; Anal. Calcd for
C31H34N4O6: C, 66.65; H, 6.13; N, 10.03. Found: C,
66.60; H, 6.10; N, 10.04.
(br s, 1H, H-2), 3.15 (dd, 1H, J3 a;3 b ¼ 13:4 Hz,
0
0
0
0
J3 a;2 ¼ 3:2 Hz, H-30a), 3.09 (dd, 1H, J3 b;3 a ¼ 13:4 Hz,
0
0
0
0
J3 b;2 ¼ 8:6 Hz, H-30b), 2.03–1.91 (m, 2H, H-10); 13C
NMR (D2O): d 180.28, 169.45 (CO), 107.43 (C-20),
70.00, 69.25, 67.95 (C-2, C-3, C-4), 61.18 (C-5), 49.99
(C-1), 47.95 (C-30), 26.56 (C-10); MALDI-MS m/z 278
[M+H]+; 299 [M+Na]+; 315 [M+K]+; C10H16N2O7 re-
quires 276.24; Anal. Calcd for C10H16N2O7: C, 43.48;
H, 5.84; N, 10.14. Found: C, 43.45; H, 5.86; N, 10.17.
0
0

L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
1821
3.12. (2R,3R,4R,5S,6R)-6-(Benzylamino)-1,3,4,5-tetra-
kis(benzyloxy)oct-7-en-2-ol (12)
requires 880.08; Anal. Calcd for C58H57NO7: C, 79.15;
H, 6.53; N, 1.59. Found: C, 79.07; H, 6.50; N, 1.61.
Compound 11 (3.15 g, 5.0 mmol) was dissolved in 1 M
vinylmagnesium bromide in THF (25 mL, 25 mmol).
After 48 h, the reaction was quenched by the addition
of a satd aq soln of NH4Cl and extracted with EtOAc.
Usual workup and flash chromatography (petroleum
ether–EtOAc, 75:25 + 0.5% Et3N) afforded compound
3.14. (3R,4R,5S,6R)-6-[N-Benzyl-N-(fluoren-9-ylmeth-
oxycarbonyl)-amino]-1,3,4,5-tetrakis(benzyloxy)oct-8-en-
2-one (14)
To a solution of compound 13 (0.100 g, 0.110 mmol) in
DMSO (1 mL), IBX (0.130 g, 0.450 mmol) was added.
After 21 h, the reaction was diluted with H2O, filtered
and extracted with Et2O. After usual workup and flash
chromatography (petroleum ether–EtOAc, 8:2) resulted
compound 14 as a yellowish oil (0.097 g, 97%). Due to
conformational equilibria of the open-chain ketone,
1H NMR showed unclear resolution, and is not
reported, whereas 13C NMR refers to the major con-
22
12 as yellowish oil (2.06 g, 63%, 70% de). ½aꢁD ꢀ5.1 (c
1
0.7, CHCl3); H NMR (C6D6): d 7.40–7.21 (m, 20H,
Ph), 5.81–5.70 (m, 1H, H-2), 5.22 (d, 1H, J1a,2
=
10.3 Hz, H-1a), 5.00 (d, 1H, J1b,2 = 17.3 Hz, H-1b),
4.87 (d, 1H, J = 10.1 Hz, OCHPh), 4.84 (d, 1H,
J = 10.7 Hz, OCHPh), 4.74 (d, 1H, J = 11.2 Hz,
OCHPh), 4.66 (d, 1H, J = 13.5 Hz, OCHPh), 4.6 (d,
1H, J = 11.6 Hz, OCHPh), 4.58–4.55 (m, 2H,
2 · OCHPh), 4.35 (d, 1H, J = 11.4 Hz, OCHPh), 4.27
(dd, 1H, J5,4 = 7.2 Hz, J5,6 = 3.2 Hz, H-5), 4.16–4.14
(m, 1H, H-7), 3.87 (d, 1H, J = 13.1 Hz, NHCHPh),
3.86–3.84 (m, 1H, H-4), 3.68–3.63 (m, 2H, H-8), 3.58
(dd, 1H, J = 6.3 Hz, J = 3.1 Hz, H-6), 3.54 (d, 1H,
J = 13.3 Hz, NHCHPh), 3.09 (dd, 1H, J = 3.4 Hz,
J = 8.3 Hz, H-3); 13C NMR (CDCl3): d 140.67, 138.85,
138.59, 138.33, 138.28 (Cquat. arom.), 138.27 (C-2),
128.86–126.99 (CH arom.), 117.59 (C-1), 83.26, 79.88,
78.13 (C-4, C-5, C-6), 75.40, 75.10, 73.81, 73.25, 71.89
(OCH2Ph, C-8), 71.04 (C-7), 61.36 (C-3), 50.79
(NCH2Ph); MALDI-MS m/z 659 [M+H]+; 681
[M+Na]+; 697 [M+K]+; C43H47NO5 requires 657.84;
Anal. Calcd for C43H47NO5: C, 78.51; H, 7.20; N,
2.13. Found: C, 78.47; H, 7.19; N, 2.13.
22
former at equilibrium. ½aꢁD ꢀ3.9 (c 0.7, CHCl3); 13C
NMR (C6D6): d 229.90, 165.70 (CO), 144.06, 144.06,
143.99, 141.51, 138.56, 137.77, 137.62, 137.62, 137.32
(Cquat. arom.), 134.45 (C-2), 129.31–120.21 (CH arom.),
119.25 (C-1), 80.98, 80.01, 79.50 (C-4, C-5, C-6), 75.41,
74.81, 73.94, 73.31, 73.31 (OCH2Ph, C-8), 65.48
(CH2Fmoc), 60.14 (C-3), 51.00 (NCH2Ph), 47.88 (CH
Fmoc); MALDI-MS m/z 901 [M+Na]+; C58H55NO7
requires 878.06; Anal. Calcd for C58H55NO7: C, 79.34;
H, 6.31; N, 1.60. Found: C, 79.29; H, 6.25; N, 1.50.
3.15. (2R,3R,4R,5S,6R)-N-Benzyl-3,4,5-tris(benzyloxy)-
2-benzyloxymethyl-6-(eth-2-enyl)piperidine (16)
To a solution of compound 14 (2.04 g, 2.32 mmol) in dry
CH3CN (18 mL), diethylamine (2 mL) was added. After
2 h, the solvent was evaporated to dryness and crude 15
directly submitted to the subsequent reaction. To a solu-
tion of crude 15 in dry DCE (30 mL) cooled to ꢀ35 ꢁC
were sequentially added glacial AcOH (1.33 mL,
23.2 mmol), anhydrous Na2SO4 (13.2 g, 92.8 mmol)
and finally NaHB(OAc)3 (1.97 g, 9.28 mmol). After
19 h, satd aq NaHCO3 was added to neutrality; the sus-
pension was then filtered, the mixture extracted with
CH2Cl2. Usual work up followed by flash chromatogra-
phy (toluene + 0.2% Et3N) afforded compound 16 as a
yellowish oil (0.960 g, 64% over two steps, 60% de).
3.13. (2R,3R,4R,5S,6R)-6-[N-Benzyl-N-(fluoren-9-
ylmethoxycarbonyl)amino]-1,3,4,5-tetrakis(benzyl-
oxy)oct-8-en-2-ol (13)
To a solution of compound 12 (2.6 g, 3.13 mmol) in dry
CH3CN (30 mL), DIPEA (0.64 mL, 3.76 mmol) and
FmocCl (1.6 g, 6.26 mmol) were added. After 6 h, the
solvent was evaporated under reduced pressure; purifi-
cation by flash chromatography (petroleum ether–
EtOAc, 75:25 + 0.5% Et3N) afforded compound 13 as
a colourless oil (2.75 g, 99%). Due to conformational
22
1
½aꢁD +29.1 (c 0.6, CHCl3); H NMR (CDCl3): d 7.24–
7.07 (m, 25H, Ph), 5.92 (dt, 1H, J = 16.6 Hz,
1
J = 10.0 Hz, H-10), 5.33 (dd, 1H, J2 a;1 ¼ 10:0 Hz,
0
0
equilibria of the open-chain alcohol, H NMR showed
unclear resolution, and is not reported, whereas 13C
NMR refers to the major conformer at equilibrium.
J2 a;2 b ¼ 2:0 Hz, H-20a), 5.02 (dd, 1H, J2 b;1 ¼ 16:6 Hz,
0
0
0
0
J2 b;2 a ¼ 2:0 Hz, H-20b), 4.90 and 4.69 (ABq, 2H,
J = 10.9 Hz, OCH2Ph), 4.84 and 4.44 (ABq, 2H, J =
10.7 Hz, OCH2Ph), 4.39 and 4.33 (ABq, 2H,
J = 11.6 Hz, OCH2Ph), 4.29 (br s, 2H, OCH2Ph), 3.96
and 3.48 (ABq, 2H, J = 13.6 Hz, NCH2Ph), 3.74 (dd,
1H, J3,2 = 9.5 Hz, J3,4 = 3.8 Hz, H-3), 3.67 (dd, 1H,
J6a,6b = 10.5 Hz, J6a,5 = 3.4 Hz, H-6a), 3.63 (dd, 1H,
J6b,6a = 10.5 Hz, J6b,5 = 1.9 Hz, H-6b), 3.59 (t, 1H,
J = 9.5 Hz, H-4), 3.57 (dd, 1H, J2,3 = 9.5 Hz,
0
0
22
½aꢁD +7.9 (c 0.8, CHCl3); 13C NMR (C6D6): d 156.52
(CO), 144.42, 144.38, 141.62, 141.59, 139.17, 139.14,
139.01, 138.96, 138.66 (Cquat. arom.), 135.45 (C-2),
128.61–119.92 (CH arom.), 118.32 (C-1), 80.89, 80.34,
79.16 (C-4, C-5, C-6), 75.27, 74.81, 74.13, 73.58, 71.91
(OCH2Ph, 8-C), 71.75 (C-7), 67.15 (CH2Fmoc), 62.22
(C-3), 51.90 (NCH2Ph), 47.97 (CH Fmoc); MALDI-
MS m/z 903 [M+Na]+; 919 [M+K]+; C58H57NO7

1822
L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
0
J2,1 = 5.5 Hz, H-2), 3.34 (dd, 1H, J1;1 ¼ 9:2 Hz,
J1,2 = 5.5 Hz, H-1), 2.89 (br d, 1H, J5,4 = 9.5 Hz, H-5);
13C NMR (CDCl3): d 140.22, 139.28, 139.28, 138.65,
138.24 (Cquat. arom.), 131.16 (C-10), 130.71–126.86
(CH arom.), 121.78 (C-20), 84.12, 80.22, 79.64 (C-2,
C-3, C-4), 75.74, 75.64, 73.32, 72.08, 68.04 (OCHPhO,
C-6), 60.61, 59.61 (C-1, C-5), 52.63 (NCH2Ph); MALDI-
MS m/z 641 [M+H]+; 664 [M+Na]+; C43H45NO4
requires 639.82; Anal. Calcd for C43H45NO4: C, 80.72;
H, 7.09; N, 2.19. Found: C, 80.77; H, 7.05; N, 2.21.
From J values between H-2/H-3, H-3/H-4 and H-4/
H-5 (9.5 Hz) the nojirimycin ring has the 4C1 conforma-
tion. In addition, from the NOESY experiments and
from the J values between H-4/H-5 a D-configuration
at C-5 after the ring closure was determined, while the
J values between H-1/H-2, allowed the assignment of
the a-vinyl appendage obtained in the Grignard reaction
on the glycosyl amine.
(petroleum ether–EtOAc, 85:15) afforded the carboben-
zyloxy derivative 18 as a yellowish oil (1.02 g, 54% over
two steps). Due to conformational equilibrium between
the two chair conformations, broad signals displayed at
room temperature 1H NMR; in order to have sharp and
resolved signals for unambiguous assignments the spec-
22
trum was recorded at 55 ꢁC. ½aꢁD +36.4 (c 0.72,
1
CHCl3); H NMR (C6D6; 55 ꢁC): d 7.23–6.98 (m, 25H,
Ph), 6.41–6.32 (m, 1H, H-10), 5.40 (d, 1H,
J2 a;1 ¼ 17:1 Hz, H-20a), 5.20 (d, 1H, J2 b;1 ¼ 10:3 Hz,
H-20b), 5.15 and 5.05 (Abq, 2H, J = 12.5 Hz,
NCOOCH2Ph), 4.91 (br t, 1H, J = 6.0 Hz, H-1), 4.74–
4.71 (m, 1H, H-5), 4.50–4.30 (m, 8H, 4 · OCH2Ph),
4.14 (dd, 1H, J = 2.5 Hz, J = 1.4 Hz, H-4), 3.95 (br d,
1H, J3,2 = 8.0 Hz, H-3), 3.83 (dd, 1H, J2,3 = 8.0 Hz,
J2,1 = 6.0 Hz, H-2), 3.70 (dd, 1H, J6a,6b = 9.0 Hz,
J6a,5 = 3.9 Hz, H-6a), 3.62 (t, 1H, J = 9.0 Hz, H-6b);
13C NMR (CDCl3): d 155.86 (CO), 138.43, 138.41,
138.24, 137.95, 136.66 (Cquat. arom.), 133.95 (C-10),
128.70–127.68 (CH arom.), 119.62 (C-20), 81.76, 79.85,
77.49 (C-2, C-3, C-4), 73.33, 73.33, 72.61, 72.46, 71.42,
67.73 (OCH2Ph, C-6), 56.27, 55.03 (C-1, C-5); MAL-
DI-MS m/z 707 [M+Na]+; 723 [M+K]+; C44H45NO6 re-
quires 683.83; Anal. Calcd for C44H45NO6: C, 77.28; H,
6.63; N, 2.05. Found: C, 77.24; H, 6.61; N, 2.02.
0
0
0
0
3.16. (2R,3R,4R,5S,6R)-3,4,5-Tris(benzyloxy)-2-benzyl-
oxymethyl-6-(eth-2-enyl)piperidine (17)
To a solution of C-vinyl derivative 16 (0.956 g,
1.49 mmol) in a 5:1 THF–H2O mixture (40 mL) CAN
was added (3.28 g, 5.98 mmol) portionwise. After 4 h,
satd aq NaHCO3 was added to basic pH. The suspension
was filtered, extracted with Et2O and usual work up affor-
ded 0.800 g of crude 17. An analytical sample was puri-
fied by flash chromatography (petroleum ether–EtOAc,
3.18. (1R,5R,6R,7S,8S,8aS)-6,7,8-Tris(benzyloxy)-5-
((benzyloxy)methyl)-tetrahydro-1-(iodomethyl)-1H-oxaz-
olo[3,4-a]pyridin-3(5H)-one (19)
22
1
8:2 + 0.5% Et3N). ½aꢁD +34.6 (c 1.0, CHCl3); H NMR
(CDCl3): d 7.25–7.05 (m, 20H, Ph), 6.24–6.16 (m, 1H,
To a solution of compound 18 (0.342 g, 0.500 mmol) in
dry CH2Cl2 at 0 ꢁC (17 mL), I2 (0.254 g, 1.00 mmol) was
added. After 4 h, the reaction was quenched by the addi-
tion of H2O and sodium thiosulfate until the solution
became colourless, then the mixture was extracted with
CH2Cl2. The organic layer was dried over Na2SO4, fil-
tered and concentrated to dryness. The crude residue
was purified by flash chromatography (petroleum
ether–EtOAc, 75:25), affording bicyclic compound 19
10-H), 5.36 (d, 1H, J2 a;1 ¼ 16:8 Hz, H-20a), 5.33 (d, 1H,
0
0
J2 b;1 ¼ 9:3 Hz, H-20b), 4.92 and 4.77 (Abq, 2H,
J = 10.8 Hz, OCH2Ph), 4.85 and 4.43 (Abq, 2H, J =
10.7 Hz, OCH2Ph), 4.70 and 4.65 (ABq, 2H, J =
11.5 Hz, OCH2Ph), 4.51 and 4.47 (Abq, 2H,
J = 10.0 Hz, OCH2Ph), 3.84 (br s, 1H, 1-H), 3.71–3.65
0
0
(m, 3H, H-2, H-3, H-6a), 3.51 (br dd, 1H, J6b,6a
=
9.0 Hz, J6b,5 = 5.9 Hz, H-6b), 3.40 (br t, 1H, H-4),
3.13–3.08 (m, 1H, H-5), 2.01 (br s, 1H, NH); 13C NMR
(CDCl3): d 139.07, 138.57, 138.54, 138.24 (Cquat. arom.),
134.43 (C-10), 128.75–127.17 (CH arom.), 117.98 (C-20),
83.97, 82.20, 80.86 (C-2, C-3, C-4), 76.01, 75.56, 73.62,
72.76, 70.75 (OCH2Ph, C-6), 56.28, 53.80 (C-1, C-5);
MALDI-MS m/z 551 [M+H]+; 573 [M+Na]+; C36H39-
NO4 requires 549.71; Anal. Calcd for C36H39NO4: C,
78.66; H, 7.15; N, 2.55. Found: C, 78.60; H, 7.10; N, 2.55.
22
as a yellowish oil (0.323 g, 90%). ½aꢁD ꢀ34.2 (c 0.8,
1
CHCl3); H NMR (CDCl3): d 7.30–7.16 (m, 20H, Ph),
4.62 (d, 1H, J = 11.7 Hz, OCHPh), 4.59 (d, 1H,
J = 11.8 Hz, OCHPh), 4.88 (dt, 1H, J = 10.1 Hz,
J1 ;1 ¼ 4:6 Hz, H-10), 4.55–4.38 (m, 5H, 5 · OCHPh),
0
4.27 (d, 1H, J = 11.9 Hz, OCHPh), 4.23–4.19 (m, 1H,
H-5), 3.80 (t, 1H, J = 2.8 Hz, H-3), 3.77 (t, 1H,
0
J = 2.8 Hz, H-4), 3.73 (dd, 1H, J1;1 ¼ 4:6 Hz,
J1,2 = 2.8 Hz, H-1), 3.65 (dd, 1H, J6a,6b = 9.5 Hz,
J6a,5 = 7.5 Hz, H-6a), 3.59 (dd, 1H, J6b,6a = 9.5 Hz,
J6b,5 = 6.1 Hz, H-6b), 3.41 (t, 1H, J = 2.8 Hz, H-2),
3.17. (2R,3R,4R,5S,6R)-N-(Benzyloxycarbonyl)-3,4,5-
tris(benzyloxy)-2-benzyloxymethyl-6-(eth-2-enyl)piperi-
dine (18)
3.22 (dd, 1H, J2 a;2 b ¼ 10:1 Hz, J2 a;1 ¼ 3:9 Hz, H-20a),
3.08 (t, 1H, J = 10.1 Hz, H-20b); 13C NMR (CDCl3): d
156.78 (CO), 138.23, 138.04, 137.43, 137.43 (Cquat.
arom.), 128.80–127.81 (CH arom.), 74.45, 73.81, 73.67,
71.97 (C-2, C-3, C-4, C-10), 73.30, 72.69, 72.32, 71.70,
67.63 (OCH2Ph, C-6), 57.17, 52.49 (C-1, C-5), 7.09 (C-
0
0
0
0
To a solution of crude 17 (0.800 g) in dry CH3CN
(15 mL), DIPEA (0.33 mL, 1.9 mmol) and CbzCl
(0.36 mL, 2.54 mmol) were added. After 4 h, the solvent
was evaporated to dryness. Flash chromatography

L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
1823
20); MALDI-MS m/z 743 [M+Na]+; 759 [M+K]+;
C37H38INO6 requires 719.60; Anal. Calcd for C37H38-
INO6: C, 61.76; H, 5.32; I, 17.63; N, 1.95. Found: C,
61.81; H, 5.29; I, 17.58; N, 1.94.
(D2O): d 156.45, 71.25, 69.10, 69.04, 67.98 (C-2, C-3,
C-4, C-10), 60.16, 59.24 (C-6, C-20), 59.06, 54.11 (C-1,
C-5) MALDI-MS m/z 271 [M+Na]+; C9H16N2O6 re-
quires 248.23; Anal. Calcd for C9H16N2O6: C, 43.55;
H, 6.50; N, 11.29. Found: C, 43.65; H, 6.43; N, 11.31.
1H NMR and NOESY experiments allowed the deter-
mination of the absolute configuration of the new ste-
reocentre, which in this case was R.
3.21. ((1S,5R,6R,7S,8S,8aR)-1-(Azidomethyl)-6,7,8-
tris(benzyloxy)-hexahydro-3-oxo-1H-oxazolo[3,4-a]pyri-
din-5-yl)methyl acetate bicyclic oxazolidinone azido
acetyl derivative (22)
3.19. (1S,5R,6R,7S,8S,8aR)-1-(Azidomethyl)-6,7,8-
tris(benzyloxy)-5-((benzyloxy)methyl)-tetrahydro-1H-
oxazolo[3,4-a]pyridin-3(5H)-one (20)
Compound 20 (0.181 g, 0.285 mmol) was dissolved in a
4:1 Ac2O–TFA mixture (0.128 M). After 24 h, the
reaction was neutralised with satd aq NaHCO3, and
extracted with EtOAc; the organic phase was dried over
Na2SO4, filtered and concentrated to dryness. Flash
chromatography (petroleum ether–EtOAc, 7:3) afforded
acetylated compound 22 as a yellowish oil (0.123 g,
To a solution of iodide 19 (0.85 g, 0.117 mmol) in dry
DMF (2 mL), n-Bu4NI (0.021 g, 0.058 mmol) and
sodium azide (0.015 g, 0.234 mmol) were added and the
reaction heated at reflux for 2 h. Evaporation of the sol-
vent, followed by purification by flash chromatography
(petroleum ether–EtOAc, 7:3) afforded azide 20 as a yel-
22
22
1
1
lowish oil (0.072 g, 97%). ½aꢁD ꢀ61.0 (c 0.7, CHCl3); H
NMR (CDCl3): d 7.23–7.04 (m, 20H, Ph), 4.61 (d, 1H,
J = 11.9 Hz, OCHPh), 4.59 (d, 1H, J = 11.9 Hz,
OCHPh), 4.47 (q, 1H, J = 4.9 Hz, H-10), 4.42 (s, 2H,
OCH2Ph), 4.41 (d, 1H, J = 11.9 Hz, OCHPh), 4.38 (d,
1H, J = 10.9 Hz, OCHPh), 4.24 (d, 1H, J = 11.8 Hz,
OCHPh), 4.23 (d, 1H, J = 11.9 Hz, OCHPh), 4.22–
4.17 (m, 1H, 5-H), 3.81 (dd, 1H, J4,3 = 3.4 Hz,
74%). ½aꢁD ꢀ77.0 (c 0.7, CHCl3); H NMR (CDCl3): d
7.62–7.02 (m, 15H, Ph), 4.58 (d, 1H, J = 11.9 Hz,
OCHPh), 4.58 (d, 1H, J = 12.0 Hz, OCHPh), 4.52–
4.46 (m, 2H, H-6a, H-10), 4.40 (d, 1H, J = 12.1 Hz,
OCHPh), 4.36 (d, 1H, J = 12.0 Hz, OCHPh), 4.30 (d,
1H, J = 12.0 Hz, OCHPh), 4.30–4.27 (m, 1H, H-5),
4.23 (d, 1H, J = 11.8 Hz, OCHPh), 3.94 (dd, 1H,
J6b,6a = 11.4 Hz, J6b,5 = 4.8 Hz, H-6b), 3.89 (dd, 1H,
J4,5 = 3.2 Hz, H-4), 3.77 (dd, 1H, J3,4 = 3.4 Hz, J3,2
=
=
J = 4.7 Hz, J = 2.9 Hz, H-1), 3.80 (dd, 1H, J3,2
2.9 Hz, J3,4 = 2.2 Hz, H-3), 3.45 (dd, 1H, J4,3 = 2.2 Hz,
=
0
3.0 Hz, H-3), 3.73 (dd, 1H, J1;1 ¼ 4:7 Hz, J1,2
0
0
1.6 Hz, H-1), 3.65 (dd, 1H, J6a,6b = 9.7 Hz, J6a,5 = 7.6
J4,5 = 2.0 Hz, H-4), 3.38 (dd, 1H, J2 a;2 b ¼ 12:9 Hz,
J2 a;1 ¼ 5:3 Hz, H-20a), 3.32–3.28 (m, 2H, H-2, H-20b),
2.00 (s, 3H, COCH3); 13C NMR (CDCl3): d 171.09,
156.82 (CO); 137.54, 137.28, 137.06 (Cquat. arom.),
128.91–122.86 (CH arom.), 73.17, 72.52, 72.20, 71.96
(C-2, C-3, C-4, C-10), 73.04, 71.94, 71.69 (OCH2Ph),
61.26 (C-6), 53.19 (C-20), 53.20, 52.17 (C-1, C-5), 21.27
(CH3CO); MALDI-MS m/z 610 [M+Na]+; 624
[M+K]+; C32H34N4O7 requires 586.63; Anal. Calcd for
C32H34N4O7: C, 65.52; H, 5.84; N, 9.55. Found: C,
65.55; H, 5.90; N, 9.50.
0 0
Hz, H-6a), 3.58 (dd, 1H, J6b,6a = 9.7 Hz, J6b,5
=
0
0
6.0 Hz, H-6b), 3.33 (dd, 1H, J2 a;2 b ¼ 13:0 Hz,
J2 a;1 ¼ 5:0 Hz, H-20a), 3.30 (dd, 1H, J2,3 = 3.0 Hz,
0
0
0
0
J2,1 = 1.6 Hz, H-2), 3.24 (dd, 1H, J2 b;2 a ¼ 13:0 Hz,
J2 b;1 ¼ 4:9 Hz, H-20b); 13C NMR (CDCl3): d 156.85
(CO), 138.27, 138.04, 137.39, 137.36 (Cquat. arom.),
128.81–127.84 (CH arom.), 74.43, 73.22, 73.19. 71.82
(C-2, C-3, C-4, C-10), 73.37, 72.69, 72.39, 71.60
(OCH2Ph), 67.66 (C-6), 54.08, 52.52 (C-1, C-5), 53.26
(C-20); MALDI-MS m/z 658 [M+Na]+; 674 [M+K]+.
C37H38N4O6 requires 634.72; Anal. Calcd for
C37H38N4O6: C, 70.01; H, 6.03; N, 8.83. Found: C,
69.98; H, 6.00; N, 8.90.
0
0
3.22. (1S,5R,6R,7S,8S,8aR)-1-(Azidomethyl)-6,7,8-
tris(benzyloxy)-tetrahydro-5-(hydroxymethyl)-1H-oxaz-
olo[3,4-a]pyridin-3(5H)-one (23)
3.20. (1S,5R,6R,7S,8S,8aS)-1-(Aminomethyl)-tetra-
hydro-6,7,8-trihydroxy-5-(hydroxymethyl)-1H-oxazolo-
[3,4-a]pyridin-3(5H)-one bicyclic (21)
To compound 22 (0.123 g, 0.21 mmol) in dry MeOH
(3 mL), a catalytic amount of Na was added. After
3 h, 5% aq HCl was added to neutrality, and the solvent
evaporated. Flash chromatography (petroleum ether–
EtOAc, 45:55) afforded deacetylated compound 23 as
To a solution of 20 (0.046 g, 0.072 mmol) in MeOH
(2 mL), Pd(OH)2/C (0.046 g) and two drops of AcOH
were added. The flask was purged three times with Ar
and then filled with H2. After 48 h, the solids were re-
moved by filtration, and the filtrate was concentrated
under reduced pressure, affording compound 21 as a yel-
lowish oil in quantitative yield. Due to conformational
22
a yellowish oil (0.090 g, 78%). ½aꢁD ꢀ22.9 (c 0.6, CHCl3);
1H NMR (CDCl3): d 7.29–7.04 (m, 15H, Ph), 4.62 (d,
1H, J = 11.9 Hz, OCHPh), 4.61 (d, 1H, J = 11.9 Hz,
OCHPh), 4.47–4.42 (m, 3H, OCH2Ph, H-10), 4.45 (d,
1H, J = 11.9 Hz, OCHPh), 4.37 (d, 1H, J = 11.9 Hz,
OCHPh), 4.26 (d, 1H, J = 11.9 Hz, OCHPh), 4.03–
3.98 (m, 1H, H-5), 3.84–3.81 (m, 2H, H-3, H-1), 3.78
1
equilibria, the H NMR showed broad signals, and is
22
not reported. ½aꢁD ꢀ4.2 (c 1.0, MeOH); 13C NMR

1824
L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
22
(dd, 1H, J6a,6b = 11.6 Hz, J6a,5 = 5.0 Hz, H-6a), 3.76
(dd, 1H, J6b,6a = 11.6 Hz, J6b,5 = 6.2 Hz, H-6b), 3.61
(dd, 1H, J = 3.8 Hz, J = 3.5 Hz, H-4), 3.43 (dd, 1H,
and is not reported. ½aꢁD ꢀ1.7 (c 1.0, MeOH); 13C NMR
(D2O): d 192.93 (COOH), 74.39, 72.63, 70.33, 69.78 (C-
2, C-3, C-4, C-10), 61.89, 57.64 (C-1, C-5), 61.76 (C-6),
50.95 (C-20); MALDI-MS m/z 285 [M+Na]+; 301
[M+K]+; C9H14N2O7 requires 262.22; Anal. Calcd for
C9H14N2O7: C, 41.22; H, 5.38; N, 10.68. Found: C,
41.27; H, 5.41; N, 10.63.
J2 a;2 b ¼ 13:0 Hz, J2 a;1 ¼ 5:0 Hz, H-20a), 3.37 (dd, 1H,
0
0
0
0
J2 b;2 a ¼ 13:0 Hz, J2 b;1 ¼ 4:7 Hz, H-20b), 3.32 (dd, 1H,
J = 2.5 Hz, J = 2.3 Hz, H-2); 13C NMR (CDCl3): d
157.67 (CO), 137.71, 137.19, 136.29 (Cquat. arom.),
128.99–128.09 (CH arom.), 74.55, 73.58, 73.47, 73.05
(C-2, C-3, C-4, C-10), 73.01, 72.60, 71.58 (OCH2Ph),
62.00 (C-6), 54.99, 54.48 (C-1, C-5), 53.39 (C-20); MAL-
DI-MS m/z 568 [M+Na]+; 584 [M+K]+; C30H32N4O6
requires 544.60; Anal. Calcd for C30H32N4O6: C,
66.16; H, 5.92; N, 10.29. Found: C, 66.00; H, 5.90; N,
10.25.
0
0
0
0
3.25. (4aR,5S,6R,7R,8R)-5,6,7-Tris(benzyloxy)-8-((benz-
yloxy)methyl)-hexahydro-3-methylenepyrido[1,2-c]-
[1,3]oxazin-1(3H)-one (27)
To a solution of 3 (0.359 g, 0.489 mmol) in CH3CN
(5.5 mL), n-Bu4NOH (0.815 mL, 1.222 mmol) was
added. After 4 h, the reaction was extracted with
EtOAc; usual workup and flash chromatography (petro-
leum ether–EtOAc, 75:25) afforded compound 27 as a
3.23. (1S,5S,6R,7R,8S,8aR)-1-(Azidomethyl)-6,7,8-
tris(benzyloxy)-hexahydro-3-oxo-1H-oxazolo[3,4-a]-
pyridine-5-carboxylic acid (25)
22
yellowish oil (0.292 g, 98%). ½aꢁD +14.4 (c 0.2, CHCl3);
1H NMR (CDCl3): d 7.35–7.15 (m, 20H, Ph), 4.84 (m,
1H, H-5), 4.70 (d, 1H, J = 12.0 Hz, OCHPh), 4.67 (d,
To a solution of alcohol 23 (0.069 g, 0.126 mmol) in dry
DMSO (1.2 mL), IBX (0.176 g, 0.630 mmol) was added.
After 6 h, H2O was added, the precipitate filtered off,
and the mixture extracted with Et2O. After usual work-
up, crude product 24 was directly submitted to the sub-
sequent reaction. To a solution of crude aldehyde 24
(0.126 mmol) in CH3CN (1.6 mL) a 1.25 M aq solution
of NaH2PO4Æ2H2O (1.0 mL) and NaClO2 (114 mg,
1.26 mmol) were added. After 7 h, the reaction mixture
was concentrated, the residue suspended in CH2Cl2
and filtered, and the solvent evaporated under reduced
pressure. Flash chromatography (EtOAc–EtOH, 9:1)
afforded the amino acid derivative 25 as a yellowish oil
(0.059 g, 83% over two steps). Due to conformational
0
0
1H, J = 11.8, OCHPh), 4.63 (d, 1H, J3 a;3 b ¼ 1:4 Hz,
H-30a), 4.57 (d, 1H, J = 12.0 Hz, OCHPh), 4.52 (d,
1H, J = 11.9 Hz, OCHPh), 4.51 (s, 1H, OCHPh), 4.46
(s, 1H, OCHPh), 4.45 (d, 1H, J = 11.8 Hz, OCHPh),
4.39 (d, 1H, J = 11.7 Hz, OCHPh), 4.21 (d, 1H,
J3 b;3 a ¼ 1:4 Hz, H-30b), 3.92 (t, 1H, J = 3.9 Hz, H-4),
3.77 (m, 2H, H-1, H-3), 3.75 (dd, 1H, J6a,6b = 9.8 Hz,
J6a,5 = 7.0 Hz, H-6a), 3.69 (dd, 1H, J6b,6a = 9.8 Hz,
J6b,5 = 6.0 Hz, H-6b), 3.45 (t, 1H, J = 3.0 Hz, H-2),
0
0
2.74 (dd, 1H, J1 a;1 b ¼ 14:6 Hz, J1 a;1 ¼ 6:5 Hz, H-10a),
0
0
0
0
2.56 (dd, 1H, J1 b;1 a ¼ 14:6 Hz, J1 b;1 ¼ 6:3 Hz, H-10b);
13C NMR (CDCl3): d 151.85 (CO), 151.46 (C-20),
138.28, 138.18, 137.70, 137.65 (Cquat. arom.), 128.77–
127.74 (CH arom.), 92.904 (C-30), 76.74 (C-2), 75.91
(C-3), 72.74 (C-4), 73.23, 73.05, 72.52, 72.47 (OCH2Ph),
67.70 (C-6), 55.24 (C-5), 49.06 (C-1), 27.74 (C-10); MAL-
DI-MS m/z 607 [M+H]+; 629 [M+Na]+; 645 [M+K]+;
C38H39NO6 requires 605.72; Anal. Calcd for
C38H39NO6: C, 75.35; H, 6.49; N, 2.31. Found: C,
75.23; H, 6.50; N, 2.34.
0
0
0
0
1
equilibria, the H NMR showed broad signals, and is
22
not reported. ½aꢁD ꢀ41.3 (c 1, CHCl3); 13C NMR
(CDCl3): d 188.12 (COOH), 167.89 (CO), 137.91,
137.38, 137.17 (Cquat. arom.), 129.08–126.27 (CH
arom.), 74.07, 73.17, 71.86, 71.28 (C-2, C-3, C-4, C-10),
72.22, 71.86, 71.58 (OCH2Ph), 54.89, 54.89 (C-1, C-5),
52.57 (C-20); MALDI-MS m/z 582 [M+Na]+; 598
[M+K]+; C30H30N4O7 requires 558.58; Anal. Calcd for
C30H30N4O7: C, 64.51; H, 5.41; N, 10.03. Found: C,
64.51; H, 5.41; N, 10.03.
3.26. ((4aR,5S,6R,7R,8R)-5,6,7-Tris(benzyloxy)-
1,4a,5,6,7,8-hexahydro-3-methyl-1-oxopyrido[1,2-c]-
[1,3]oxazin-8-yl)methyl acetate (28)
3.24. (1S,5S,6R,7R,8S,8aS)-1-(Aminomethyl)-hexahy-
dro-6,7,8-trihydroxy-3-oxo-1H-oxazolo[3,4-a]pyridine-5-
carboxylic acid (26)
Compound 27 (0.262 g, 0.432 mmol) was dissolved in a
4:1 mixture of Ac2O–TFA (0.128 M). After 24 h, the
reaction was neutralised with satd aq NaHCO3, and
extracted with EtOAc; the organic phase was dried over
Na2SO4, filtered and concentrated to dryness. Flash
chromatography (petroleum ether–EtOAc, 7:3) afforded
acetate 28 as a yellowish oil (0.141 g, 59%). ½aꢁ2D2 +20.9 (c
To a solution of 25 (0.047 g, 0.084 mmol) in 1:1 ace-
tone–H2O (2 mL), Pd(OH)2/C (0.047 g) and two drops
of AcOH were added. The flask was purged three times
with Ar and then filled with H2. After 48 h, the solids
were removed by filtration, and the filtrate was concen-
trated under reduced pressure, affording compound 26
as a yellowish oil in quantitative yield. Due to confor-
mational equilibria, the 1H NMR showed broad signals,
1
0.6, CHCl3); H NMR (CDCl3): d 7.32–7.15 (m, 15H,
Ph), 4.98 (m, 1H, H-5), 4.71 (d, 1H, J = 12.0 Hz,
OCHPh), 4.62 (d, 1H, J = 12.2 Hz, OCHPh), 4.51 (d,
1H, J = 12.0 Hz, OCHPh), 4.51 (m, 1H, H-10), 4.48

L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
1825
(dd, 1H, J6a,6b = 11.6 Hz, J6a,5 = 8.3 Hz, H6-a), 4.44 (d,
1H, J = 11.6 Hz, OCHPh), 4.43 (d, 1H, J = 12.2 Hz,
OCHPh), 4.36 (d, 1H, J = 11.9 Hz, OCHPh), 4.31 (m,
under reduced pressure, affording compound 30 as a yel-
22
lowish oil in quantitative yield. ½aꢁD +12.6 (c 0.5,
1
MeOH); H NMR (D2O): d 4.36 (m, 1H, H-20), 4.31
1H, H-1), 4.18 (dd, 1H, J6b,6a = 11.6 Hz, J6b,5
=
(m, 1H, H-5), 3.83 (dd, 1H, J6a,6b = 12.1 Hz,
J6a,5 = 9.8 Hz, H-6a), 3.83 (m, 1H, H-1), 3.77 (m, 2H,
4.9 Hz, H-6b), 3.75 (t, 1H, J = 3.1 Hz, H-3), 3.58 (t,
1H, J = 3.05 Hz, H-4), 3.24 (br t, 1H, H-2), 2.02 (s,
3H, H-30), 1.85 (s, 3H, CH3Ac); 13C NMR (CDCl3): d
170.86 (COAc), 151.09 (CO), 149.10 (C-20), 138.06,
137.89, 137.35 (Cquat. arom.), 128.75–127.80 (CH
arom.), 95.50 (C-10), 75.58 (C-2), 74.70 (C-3), 72.52
(C-4), 72.84, 72.47, 71.91 (OCH2Ph), 60.94 (C-6),
53.30 (C-5), 50.25 (C-1), 21.25 (C-30), 18.90 (CH3Ac);
MALDI-MS m/z 559 [M+H]+; 581 [M+Na]+; 597
[M+K]+; C33H35NO7 requires 557.63; Anal. Calcd for
C33H35NO7: C, 71.08; H, 6.33; N, 2.51. Found: C,
71.11; H, 6.45; N, 2.54.
H-3,
H-4),
3.59
(dd,
1H,
J6b,6a = 12.1 Hz,
J6b,5 = 4.7 Hz, H-6b), 3.53 (t, 1H, J = 1.9 Hz, H-2),
1.94 (m, 2H, H-10), 1.21 (d, 3H, J = 5.9 Hz, H-30); 13C
NMR (D2O): d 160.94 (CO), 75.46, 72.41, 72.06, 70.32
(C-2, C-3, C-4, C-20), 62.26, 51.50 (C-1, C-5), 61.68
(C-6), 32.87 (C-10), 22.42 (C-30); MALDI-MS m/z 270
[M+Na]+; C10H17NO6 requires 247.25; Anal. Calcd
for C10H17NO6: C, 48.58; H, 6.93; N, 5.67. Found: C,
48.55; H, 6.91; N, 5.70. NOESY experiments on com-
pound 30 allowed the determination of the absolute
configuration of the stereocentre generated in the hydro-
genation of the double bond, which was R.
3.27. (5R,6S,7R,8R,8aR)-6,7,8-Tris(benzyloxy)-tetra-
hydro-5-(2-oxopropyl)-1H-oxazolo[3,4-a]pyridin-3(5H)-
one (29)
3.29. (5R,6S,7R,8R,8aR)-Tetrahydro-6,7,8-trihydroxy-5-
(2-oxopropyl)-1H-oxazolo[3,4-a]pyridin-3(5H)-one (31)
To compound 28 (0.180 g, 0.323 mmol) in dry MeOH
(2.3 mL) a catalytic amount of Na was added. After
3 h, 5% aq HCl was added to neutrality, and the solvent
evaporated. Flash chromatography (petroleum ether–
EtOAc, 6:4) afforded deacetylated compound 29 as a
To a solution of 29 (0.030 g, 0.12 mmol) in MeOH
(2 mL), Pd(OH)2/C (0.030 g) and two drops of AcOH
were added. The flask was purged three times with Ar
and then filled with H2. After 48 h, the solids were re-
moved by filtration, and the filtrate was concentrated
under reduced pressure, affording compound 31 as a yel-
22
white solid (0.110 g, 70%); mp 137–139 ꢁC; ½aꢁD +65.3
22
(c 0.3, CHCl3); 1H NMR (CDCl3): d 7.36–7.23 (m,
15H, Ph), 4.95 (d, 1H, J = 10.1 Hz, OCHPh), 4.88 (d,
1H, J = 11.4 Hz, OCHPh), 4.77 (d, 1H, J = 10.9 Hz,
OCHPh), 4.76 (m, 1H, H-1), 4.65 (s, 2H, OCH2Ph),
4.60 (d, 1H, J = 11.5 Hz, OCHPh), 4.23 (dd, 1H,
J6a,6b = 9.0 Hz, J6a,5 = 7.9 Hz, H-6a), 3.79 (dd, 1H,
J6b,6a = 9.0 Hz, J6b,5 = 3.8 Hz, H6-b), 3.66 (m, 3H,
H-2, H-3, H-5), 3.36 (dd, 1H, J = 9.6 Hz, J = 8.4 Hz,
lowish oil in quantitative yield. ½aꢁD +4.4 (c 0.80, H2O);
1H NMR (CDCl3): d 4.31 (m, 2H, H-1, H-3), 4.17 (dd,
1H, J4,3 = 9.4 Hz, J4,5 = 4.2 Hz, H-4), 3.62 (dt, 1H,
J5,6 = 10.3 Hz, J5,4 = 4.2 Hz, H-5), 3.52 (dd, 1H,
J2,3 = 9.5 Hz, J2,1 = 6.2 Hz, H-2), 3.35 (t, 1H,
J = 9.0 Hz, H-6a), 3.27 (t, 1H, J = 9.8 Hz, H-6b), 2.89
(dd, 1H, J1 a;1 b ¼ 17:3 Hz, J1 a;1 ¼ 4:0 Hz, H-10a), 2.61
0
0
0
(dd, 1H, J1 b;1 a ¼ 17:3 Hz, J1 b;1 ¼ 9:9 Hz, H-10b), 2.07
(s, 3H, CH3); 13C NMR (CDCl3): d 214.56 (CO ketone),
161.22 (CO), 75.81, 75.46, 72.31 (C-2, C-3, C-4), 69.26
(C-6), 56.51, 52.52 (C-1, C-5), 41.72 (C-10), 32.45
(CH3); MALDI-MS m/z 246 [M+H]+; 284 [M+K]+;
C10H15NO6 requires 245.23; Anal. Calcd for
C10H15NO6: C, 48.98; H, 6.17; N, 5.71. Found: C,
48.90; H, 6.25; N, 5.78.
0
0
0
0
0
0
0
H-4), 2.98 (dd, 1H, J1 a;1 b ¼ 15:6 Hz, J1 a;1 ¼ 5:7 Hz,
H-10a), 2.50 (dd, 1H, J1 b;1 a ¼ 15:6 Hz, J1 b;1 ¼ 8:7 Hz,
H-10b), 2.14 (s, 3H, C-30); 13C NMR (CDCl3): d
205.21 (COCH3), 156.62 (CO), 138.83, 137.70, 137.50
(Cquat. arom.), 128.84–128.04 (CH arom.), 81.85, 79.07
(C-2, C-3), 80.54 (C-4), 77.65, 77.33, 77.02 (OCH2Ph),
66.22 (C-6), 53.65 (C-5), 48.28 (C-1), 41.46 (C-10),
30.32 (C-30); MALDI-MS m/z 517 [M+H]+; 539
[M+Na]+; C31H33NO6 requires 515.60; Anal. Calcd
for C31H33NO6: C, 72,21; H, 6,45; N, 2,72. Found: C,
72.11; H, 6.45; N, 2.64.
0
0
0
0
3.30. (2R,3R,4R,5S,6R)-N-Benzyl-3,4,5-tris(benzyloxy)-
2-((benzyloxy)methyl)-6-vinylpiperidine-1-carboxamide
(32)
3.28. (3R,4aR,5S,6R,7R,8R)-Hexahydro-5,6,7-trihydr-
oxy-8-(hydroxymethyl)-3-methylpyrido[1,2-c][1,3]oxa-
zin-1(3H)-one (30)
To compound 17 (0.100 g, 0.18 mmol) in dry DME
(2.5 mL), benzyl isocyanate (0.4 mL, 0.36 mmol) was
added and the reaction mixture heated to reflux. After
2 h, the solvent was evaporated under reduced pressure.
The crude residue was purified by flash chromatography
(petroleum ether–EtOAc, 8:2), affording compound 32
To a solution of 27 (0.050 g, 0.08 mmol) in MeOH
(2 mL), Pd(OH)2/C (0.050 g) and two drops of AcOH
were added. The flask was purged three times with Ar
and then filled with H2. After 48 h, the solids were re-
moved by filtration, and the filtrate was concentrated
22
(0.117 g, 94%) as a yellowish oil. ½aꢁD +38.7 (c 1.0,
1
CHCl3); H NMR (CDCl3): d 7.33–7.19 (m, 25H, Ph),
0
0
0
0
6.17 (ddd, 1H, J1 ;2 b ¼ 17:6 Hz, J1 ;2 a ¼ 10:5 Hz,

1826
L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
J1 ;1 ¼ 7:4 Hz, H-10), 5.63 (t, 1H, J = 5.3 Hz, NH), 5.31
experiments allowed the determination of the absolute
configuration of the new stereocentre, which in this case
was S.
0
(dd, 1H, J2 a;1 ¼ 10:5 Hz, J2 a;2 b ¼ 1:3 Hz, H-20a), 5.29
0
0
0
0
(dd, 1H, J2 b;2 a ¼ 17:6 Hz, J2 b;2 a ¼ 1:3 Hz, H-20b),
4.72 (d, 1H, J = 11.5 Hz, OCHPh), 4.64 (d, 1H,
J = 11.4 Hz, OCHPh), 4.59 (d, 1H, J = 12.1 Hz,
OCHPh), 4.52 (d, 1H, J = 11.4 Hz, OCHPh), 4.56 (d,
1H, J = 12.1 Hz, OCHPh), 4.55 (d, 1H, J = 10.2 Hz,
OCHPh), 4.51 (d, 1H, J = 11.8 Hz, OCHPh), 4.42 (d,
1H, J = 11.8 Hz, OCHPh), 4.58–4.54 (m, 1H, H-1),
4.40–4.35 (m, 3H, NCH2Ph, H-5), 3.95 (dd, 1H,
J3,4 = 3.8 Hz, J3,2 = 2.3 Hz, H-3), 3.86 (dd, 1H,
J2,1 = 5.7 Hz, J2,3 = 2.3 Hz, H-2), 3.80 (br t, 1H, H-4),
3.78 (dd, 1H, J6a,6b = 9.7 Hz, J6a,5 = 4.9 Hz, H-6a),
3.64 (dd, 1H, J6b,6a = 9.7 Hz, J6b,5 = 7.4 Hz, H-6b);
13C NMR (CDCl3): d 158.41 (CO), 139.52, 138.46,
138.24, 138.09, 138.00 (Cquat. arom.), 135.06 (C-10),
128.77–127.78 (CH arom.), 119.63 (C-20), 83.33, 79.83,
78.94 (C-2, C-3, C-4), 73.41, 73.03, 72.79, 72.08, 71.89,
70.79 (CH2Ph, C-6), 56.58, 54.76 (C-1, C-5); MALDI-
MS m/z 706 [M+Na]+; 721 [M+K]+; C44H46N2O5
requires 682.85; Anal. Calcd for C44H46N2O5: C, 77.39;
H, 6.79; N, 4.10. Found: C, 77.59; H, 6.81; N, 4.10.
0
0
0
0
3.32. (1R,5R,6R,7R,8S,8aR)-1-(Azidomethyl)-6,7,8-
tris(benzyloxy)-5-((benzyloxy)methyl)-hexahydro-
imidazo[1,5-a]pyridin-3(5H)-one (34)
To a solution of bromide 33 (0.128 g, 0.19 mmol) in dry
DMF (2.3 mL), sodium azide (0.050 g, 0.76 mmol) was
added and the reaction heated at reflux for 24 h. Evap-
oration of the solvent, followed by purification by flash
chromatography (petroleum ether–EtOAc, 6:4) afforded
22
azide 34 as a yellowish oil (0.095 g, 79%). ½aꢁD +13.3 (c
1
0.2, CHCl3); H NMR (CDCl3): d 7.24–7.09 (m, 20H,
Ph), 4.66 (d, 1H, J = 12.0 Hz, OCHPh), 4.626 (d, 1H,
J = 12.7 Hz, OCHPh), 4.49 (d, 1H, J = 11.8 Hz,
OCHPh), 4.49–4.45 (m, 1H, H-10), 4.45–4.35 (m, 3H,
3 · OCHPh), 4.31–4.20 (m, H-5), 4.294 (d, 1H,
J = 11.7 Hz, OCHPh), 4.24 (d, 1H, J = 12 Hz,
OCHPh), 3.94 (t, 1H, J = 4.4 Hz, H-4), 3.82 (dd, 1H,
J6a,6b = 9.4 Hz, J6a,5 = 7.2 Hz, H-6a), 3.77 (dd, 1H,
J3,4 = 4.4 Hz, J3,2 = 2.8 Hz, H-3), 3.67 (dd, 1H, J6b,6a
=
3.31. (1S,5R,6R,7R,8S,8aR)-6,7,8-Tris(benzyloxy)-5-
((benzyloxy)methyl)-1-(bromomethyl)-hexahydro-
imidazo[1,5-a]pyridin-3(5H)-one (33)
9.4 Hz, J6b,5 = 4.7 Hz, H-6b), 3.64 (br t, 1H, H-1), 3.34
(t, 1H, J = 2.6 Hz, H-2), 3.19 (m, 2H, H-20); 13C NMR
(CDCl3): d 153.64 (CO), 138.70, 138.45, 137.64, 137.60
(Cquat. arom), 128.74–127.41 (CH arom), 76.30, 76.11,
74.36, 72.87 (C-2, C-3, C-4, C-10), 73.40, 72.82, 72.55,
71.53 (OCH2Ph), 67.37 (C-6), 50.02 (C-20), 55.56,
53.14 (C-1, C-5); MALDI-MS m/z 657 [M+Na]+; 673
[M+K]+; C37H39N5O5 requires 633.74; Anal. Calcd for
C37H39N5O5: C, 70.12; H, 6.20; N, 11.05. Found: C,
69.98; H, 6.20; N, 11.09.
To a solution of 32 (0.353 g, 0.517 mmol) in dry CH2Cl2
(8 mL) cooled to ꢀ20 ꢁC, NBS (0.184 g, 1.03 mmol) was
added. After 6 h, the reaction was quenched by the addi-
tion of H2O and sodium thiosulfate until the solution
became colourless, then the mixture was extracted with
CH2Cl2. The organic layer was dried over Na2SO4, fil-
tered and concentrated to dryness. The crude residue
was purified by flash chromatography (petroleum
ether–EtOAc, 6:4), affording compound 33 as a yellow-
3.33. (1R,5R,6R,7R,8S,8aR)-1-(Aminomethyl)-hexa-
hydro-6,7,8-trihydroxy-5-(hydroxymethyl)imidazo-
[1,5-a]pyridin-3(5H)-one (35)
22
ish oil (0.225 g, 65%). ½aꢁD ꢀ9.4 (c 1.0, CHCl3); IR
(neat); m 1694 cmꢀ1 (carbonyl); 1H NMR (CDCl3): d
7.24–7.04 (m, 20H, Ph), 4.68 (d, 1H, J = 11.8 Hz,
OCHPh), 4.62 (d, 1H, J = 11.8 Hz, OCHPh), 4.58 (m,
1H, H-10), 4.49 (s, 1H, OCHPh), 4.43 (d, 1H,
J = 11.8 Hz, OCHPh), 4.38–4.26 (m, 4H, 3 · OCHPh,
H-5), 4.30 (d, 1H, J = 13.0 Hz, OCHPh), 3.90 (t, 1H,
J = 4.2 Hz, H-4), 3.79 (m, 3H, H-1, H-3, H-6a), 3.67
(dd, 1H, J6b,6a = 9.4 Hz, J6b,5 = 5.1 Hz, H-6b), 3.42 (t,
To a solution of 34 (0.050 g, 0.079 mmol) in MeOH
(2 mL), Pd(OH)2/C (0.050 g) and two drops of AcOH
were added. The flask was purged three times with Ar
and then filled with H2. After 48 h, the solids were re-
moved by filtration, and the filtrate was concentrated
under reduced pressure, affording compound 35 as a yel-
22
0
0
1H, J = 2.5 Hz, H-2), 3.31 (dd, 1H, J2 a;2 b ¼ 10:4 Hz,
lowish oil in quantitative yield. ½aꢁD +14.8 (c 0.2, H2O);
J2 a;1 ¼ 4:5 Hz, H-20a), 3.23 (dd, 1H, J2 b;2 a ¼ 10:4 Hz,
1H NMR (D2O): d 5.40 (m, 1H, H-5), 4.76–4.62 (m, 1H,
H-10), 4.23 (dd, 1H, J4,5 = 5.8 Hz, J4,3 = 2.2 Hz, H-4),
3.90 (t, 1H, J = 3.5 Hz, H-2), 3.79 (m, 2H, H-1, H-3),
3.62 (dd, 1H, J6a,6b = 13.5 Hz, J6a,5 = 3.9 Hz, H-6a),
3.42 (dd, 1H, J6b,6a = 13.5 Hz, J6b,5 = 1.8 Hz, H-6b),
2.77–2.70 (m, 2H, H-20); 13C NMR (D2O): d 165.72
(CO), 77.25, 75.57, 74.22, 71.53 (C-2, C-3, C-4), 62.48
(C-6), 58.36, 51.08 (C-1, C-5), 42.45 (C-10), 38.72 (C-
20); MALDI-MS m/z (MALDI-MS) 270 [M+Na]+;
C9H17N3O5 requires 247.25; Anal. Calcd for
0
0
0
0
J2 b;1 ¼ 7:8 Hz, H-20b); 13C NMR (CDCl3): d 153.61
(CO), 138.74, 138.68, 138.46, 137.66 (Cquat. arom),
126.18–128.84 (CH arom), 74.90, 75.12, 76.24, 76.34
(C-2, C-3, C-4, C-10), 73.39, 72.77, 72.63, 71.64
(OCH2Ph), 67.39 (C-6), 57.35, 53.26 (C-1, C-5), 29.99
(C-20); MALDI-MS m/z 694 [M+Na]+; 710 [M+K]+;
C37H39BrN2O5 requires 671.62; Anal. Calcd for
C37H39BrN2O5: C, 66.17; H, 5.85; Br, 11.90; N, 4.17.
Found: C, 66.21; H, 5.80; Br, 11.82; N, 4.11. NOESY
0
0

L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
1827
C9H17N3O5: C, 43.72; H, 6.93; N, 17.00. Found: C,
43.81; H, 6.80; N, 17.08.
compound 38 as a yellowish oil (0.082 g, 46% over two
22
1
steps). ½aꢁD +17.2 (c 0.2, CHCl3); H NMR (CDCl3): d
7.34–7.23 (m, 20H, Ph), 4.71 (d, 1H, J = 11.5 Hz,
OCHPh), 4.65 (d, 1H, J = 12.0 Hz, OCHPh), 4.63 (s,
2H, OCH2Ph), 4.52 (d, 1H, J = 11.5 Hz, OCHPh),
4.46–4.37 (m, 2H, H-5, H-10), 4.44 (d, 1H,
J = 11.7 Hz, OCHPh), 4.41 (d, 1H, J = 11.6 Hz,
OCHPh), 4.32 (d, 1H, J = 11.7 Hz, OCHPh) 4.07 (dd,
1H, J = 6.7 Hz, J = 5.7 Hz, H-4), 3.95–3.78 (m, 3H,
H-6a, H-3, H-1), 3.62–3.59 (m, 2H, H-6b, H-2), 3.47
3.34. (2R,3S,4R,5R,6R)-2-Allyl-N-benzyl-3,4,5-tris(benz-
yloxy)-6-((benzyloxy)methyl)piperidine-1-carboxamide
(36)
To compound 1 (0.100 g, 0.18 mmol) in dry DME
(2.5 mL), benzyl isocyanate (0.04 mL, 0.36 mmol) was
added and the reaction mixture heated to reflux. After
2 h, the solvent was evaporated under reduced pressure.
The crude residue was purified by flash chromatography
(petroleum ether–EtOAc, 8:2), affording compound 36
(dd, 1H, J2 a;2 b ¼ 9:6 Hz, J2 a;1 ¼ 3:02 Hz, H-20a), 3.08
0
0
0
0
(dd, 1H, J2 b;1 ¼ 10:7 Hz, J2 b;2 a ¼ 9:7 Hz, H-20b), 1.50
(s, 9H, CH3Boc), 1.492 (s, 9H, CH3Boc); 13C NMR
(CDCl3): d 159.43 (CN), 149.54, 150.37 (CO), 138.28,
138.24, 137.86, 137.65 (Cquat. arom.), 128.94–128.48
(CH arom.), 83.089, 79.134 (Cquat. Boc), 79.90 (C-3),
78.53 (C-2), 73.45 (C-4), 73.86, 73.55, 73.30, 72.51
(OCH2Ph), 67.62 (C-6), 58.46 (C-5), 57.99 (C-1), 53.51
(C-10), 28.73, 28.68, 28.62, 28.51, 28.50, 28.34 (CH3Boc),
8.47 (C-20); MALDI-MS m/z 941 [M+Na]+; 957
[M+K]+; C47H56IN3O8 requires 917.87; Anal. Calcd
for C47H56IN3O8: C, 61.50; H, 6.15; I, 13.83; N, 4.58.
Found: C, 61.39; H, 6.18; I, 13.88; N, 4.56.
0
0
0
0
22
(0.125 g, 99%) as a yellowish oil. ½aꢁD +22.1 (c 1.0,
CHCl3); 1H NMR (CDCl3): d 7.21–7.15 (m, 25H,
Ph), 6.32 (t, 1H, J = 5.3 Hz, NH), 5.76 (dddd,
0
0
0
0
0
0
1H, J2 ;3 a ¼ 16:4 Hz, J2 ;3 b ¼ 10:0 Hz, J2 ;1 b ¼ 8:2 Hz,
J2 ;1 a ¼ 6:1 Hz, H-20), 4.91 (m, 2H, H-30), 4.64 (d, 1H,
J = 11.3 Hz, OCHPh), 4.61 (d, 1H, J = 11.3 Hz,
OCHPh), 4.583 (d, 1H, J = 11.3 Hz, OCHPh), 4.54 (d,
1H, J = 11.3 Hz, OCHPh), 4.50 (d, 1H, J = 11.4 Hz,
OCHPh), 4.48 (d, 1H, J = 11.3 Hz, OCHPh), 4.23 (m,
2 · OCH2Ph, H-1), 3.76 (m, 3H, H-2, H-3, H-4), 3.70
(m, 1H, H-5), 3.62 (m, 2H, H-6), 2.53 (dt, 1H,
0
0
J1 a;1 b ¼ 14:4 Hz, J = 6.1 Hz, H-10a), 2.36 (dt, 1H,
3.36. tert-Butyl (1R,5R,6R,7R,8S,8aR)-2-(tert-butoxy-
carbonyl)-1-(azidomethyl)-6,7,8-tris(benzyloxy)-5-((benz-
yloxy)methyl)-hexahydroimidazo[1,5-a]pyridin-3(5H)-
ylidenecarbamate (39)
0
0
J1 b;1 a ¼ 14:4 Hz, J = 8.2 Hz, H-10b); 13C NMR
0
0
(CDCl3):
d 158.31 (CO), 139.49, 138.42, 138.19,
138.04, 137.95 (Cquat. arom.), 135.03 (C-20), 128.73–
127.34 (CH arom), 119.57 (C-30), 82.33, 79.80, 77.78
(C-2, C-3, C-4), 73.38, 73.33, 73.01, 72.76, 71.87, 70.77
(OCH2Ph, C-6), 55.55, 54.72 (C-1, C-5), 45.37 (C-10);
MALDI-MS m/z 698 [M+H]+; 720 [M+Na]+; 736
[M+K]+; C45H48N2O5 requires 696.87; Anal. Calcd for
C45H48N2O5: C, 77,56; H, 6,94; N, 4,02. Found: C,
77.76; H, 6.69; N, 4.17.
To a solution of iodide 38 (0.134 g, 0.146 mmol) in dry
DMF (1.6 mL), sodium azide (0.038 g, 0.584 mmol)
was added and the reaction heated at reflux for 24 h.
Evaporation of the solvent, followed by purification by
flash chromatography (petroleum ether–EtOAc, 8:2)
22
afforded azide 39 as a yellowish oil (0.074 g, 61%). ½aꢁD
1
ꢀ13.8 (c 0.5, CHCl3); H NMR (CDCl3): d 7.34–7.14
3.35. tert-Butyl (1S,5R,6R,7R,8S,8aR)-2-(tert-butoxy-
carbonyl)-6,7,8-tris(benzyloxy)-5-((benzyloxy)methyl)-
hexahydro-1-(iodomethyl)imidazo[1,5-a]pyridin-3(5H)-
ylidenecarbamate (38)
(m, 20H, Ph), 4.68 (d, 1H, J = 11.5 Hz, OCHPh), 4.66
(d, 1H, J = 11.9 Hz, OCHPh), 4.61 (s, 2H, OCH2Ph),
4.48 (d, 1H, J = 11.5 Hz, OCHPh), 4.43 (d, 1H,
J = 12.8 Hz, OCHPh), 4.38 (d, 1H, J = 12.4 Hz,
OCHPh), 4.33 (d 1H, J = 11.6 Hz, OCHPh), 4.27
0
0
0
0
0
To a solution of 17 (0.107 g, 0.195 mmol) in dry DMF
(1 mL) cooled to 0 ꢁC, di-Boc-thiourea (0.108 g,
0.39 mmol), Et3N (0.54 mL, 0.39 mmol) and HgCl2
(0.106 g, 0.39 mmol) were added sequentially. After
4 h, EtOAc was added and the precipitate filtered on a
Celite pad. After usual workup, crude 37 was directly
submitted to the subsequent reaction. To a solution of
crude 37 (0.195 mmol) in dry CH2Cl2 (4.2 mL), I2
(0.990 g, 0.390 mmol) was added. After 3 h, the reaction
was quenched by the addition of H2O and sodium thio-
sulfate until the solution became colourless, then the
mixture was extracted with CH2Cl2. The organic layer
was dried over Na2SO4, filtered and concentrated to dry-
ness. The crude residue was purified by flash chromato-
graphy (petroleum ether–EtOAc, 8:2), affording bicyclic
(ddd, 1H, J1 ;2 b ¼ 8:9 Hz, J1 ;2 a ¼ 3:9 Hz, J1 ;1 ¼
2:6 Hz, H-10), 3.99 (m, 2H, H-5, H-4), 3.79 (m, 3H,
H-6a, H-3, H-1), 3.61 (dd, 1H, J6b,6a = 6.6 Hz,
0
0
J6b,5 = 4.1 Hz, H-6b), 3.59 (dd, 1H, J2 a;2 b ¼ 10:5 Hz,
J2 a;1 ¼ 3:9 Hz, H-20a), 3.53 (t, 1H, J = 3.7 Hz, H-2),
0
0
3.29 (dd, 1H, J2 b;2 a ¼ 10:5 Hz, J2 b;1 ¼ 8:9 Hz, H-20b),
1.51 (s, 18H, CH3Boc); 13C NMR (CDCl3): d 159.53
(CN), 150.71, 149.67 (CO), 138.27, 138.25, 137.79,
137.61 (Cquat. arom.), 128.70–127.77 (CH arom.),
83.07, 79.12 (Cquat. Boc), 79.34, 77.78, 73.24 (C-2, C-3,
C-4), 73.64, 73.43, 73.36, 72.17 (4 · OCH2Ph), 67.60
(C-6), 56.36, 55.37, 53.28 (C-1, C-5, C-10), 30.13 (C-
20); MALDI-MS m/z 857 [M+Na]+; 873 [M+K]+;
C47H56N6O8 requires 832.98; Anal. Calcd for
C47H56N6O8: C, 67.77; H, 6.78; N, 10.09. Found: C,
0
0
0
0

1828
L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
67.80; H, 6.75; N, 10.09; NOESY experiments on azide
39 allowed the determination of the absolute configura-
tion of the stereocentre generated in the cyclisation,
which was S.
3.39. (3aR,5R,6R,7R,7aS)-[(6,7-Bis-benzyloxy-5-benzyl-
oxymethyl-2-chloromercuriomethyl-hexahydro-furo[3,2-
b]pyridin-4-yl)-tert-butoxycarbonylimino-methyl]-car-
bamic acid tert-butyl ester (42) and tert-butyl
(4aR,5S,6R,7R,8R)-2-(tert-butoxycarbonyl)-5,6,7-
tris(benzyloxy)-8-((benzyloxy)methyl)-3-(chloro-
mercuriomethyl)-octahydropyrido[1,2-f]pyrimidin-1-
ylidenecarbamate (43)
3.37. (1R,5R,6R,7R,8S,8aR)-1-(Azidomethyl)-6,7,8-
tris(benzyloxy)-5-((benzyloxy)methyl)-hexahydroimid-
azo[1,5-a]pyridin-3(5H)-imine (40)
Compound 39 (0.098 g, 0.116 mmol) was dissolved in a
4:1 TFA–H2O mixture. After 1 h, the reaction was neu-
tralised with satd aq NaHCO3, and extracted with
EtOAc. The organic phase was dried over Na2SO4, fil-
tered and concentrated to dryness. Flash chromatogra-
phy (petroleum ether–EtOAc, 75:25) afforded azide 40
To a solution of 1 (0.041 g, 0.07 mmol) in dry DMF
(0.35 mL) cooled to 0 ꢁC, di-Boc-thiourea (0.019 g,
0.07 mmol), Et3N (0.02 mL, 0.14 mmol) and HgCl2
(0.019 g, 0.07 mmol) were added sequentially. After
24 h, EtOAc was added and the precipitate filtered on
a Celite pad. Usual workup and flash chromatography
(petroleum ether–EtOAc, 85:15) afforded compound 42
(0.015 g) and 43 (0.018 g) as a yellowish oils.
22
as a yellowish oil (0.063 g, 86%). ½aꢁD ꢀ20.4 (c 0.4,
1
CHCl3); H NMR (CDCl3): d 7.72–7.10 (m, 20H, Ph),
1
4.56 (d, 1H, J = 12.0 Hz, OCHPh), 4.48 (d, 1H,
J = 12.0 Hz, OCHPh), 4.43 (d, 1H, J = 12.0 Hz,
OCHPh), 4.40 (s, 2H, OCH2Ph), 4.33 (d, 1H,
J = 11.7 Hz, OCHPh), 4.28 (d, 1H, J = 12.0 Hz,
OCHPh), 4.26 (d, 1H, J = 11.8 Hz, OCHPh), 3.89 (m,
0
Compound 42. H NMR (CDCl3): d 7.24–7.17 (m,
15H, Ph), 4.75 (m, 1H, H-5), 4.62 (d, 1H, J = 11.7 Hz,
OCHPh), 4.58 (d, 1H, J = 11.8 Hz, OCHPh), 4.52 (m,
1H, H-20), 4.49 (d, 1H, J = 11.4 Hz, OCHPh), 4.44 (d,
1H, J = 11.4 Hz, OCHPh), 4.37 (d, 1H, J = 11.8 Hz,
OCHPh), 4.34 (d, 1H, J = 11.8 Hz, OCHPh), 4.00 (dd,
1H, J2,3 = 8.5 Hz, J2,1 = 6.4 Hz, H-2), 3.91 (br t, 1H,
H-4), 3.65 (m, 2H, H-3, H-6a), 3.53 (t, 1H, J = 3.5 Hz,
1H, H-10), 3.84 (m, 1H, H-5), 3.72 (dd, 1H, J1;1
4:6 Hz, J1,2 = 2.3 Hz, H-10), 3.67 (dd, 1H, J3,4
¼
=
4.4 Hz, J3,2 = 2.3 Hz, H-3), 3.50 (m, 2H, H-6), 3.45 (t,
1H, J = 4.4 Hz, H-4), 3.32 (t, 1H, J = 2.3 Hz, H-2),
3.28 (d, 2H, H-20); 13C NMR (CDCl3): d 159.66 (CN),
137.18, 137.01, 136.92, 136.73 (Cquat. arom.), 128.90–
127.82 (CH arom.), 74.54, 73.47, 73.32 (C-2, C-3, C-4),
73.72, 72.93, 72.63, 72.06 (OCH2Ph), 57.84, 55.20,
54.61 (C-1, C-5, C-10), 53.19 (C-6), 30.16 (C-20); MAL-
DI-MS m/z 656 [M+Na]+; 671 [M+K]+; C37H40N6O4
requires 632.75; Anal. Calcd for C37H40N6O4: C,
70.23; H, 6.37; N, 13.28. Found: C, 70.27; H, 6.41; N,
13.30.
0
H-6b), 3.45 (ddd, 1H, J1;1 a ¼ 12:3 Hz, J1,2 = 6.4 Hz,
0
0
0
J1;1 b ¼ 2:4 Hz), 2.58 (ddd, 1H, J1 a;2 ¼ 2:5 Hz,
J1 a;1 b ¼ 10:9 Hz, J1 a;1 ¼ 12:3 Hz, H-10a), 1.92 (dd,
0
0
0
1H, J1 b;2 ¼ 4:1 Hz, J1 b;1 a ¼ 10:9 Hz, H-10b), 1.69 (m,
2H, H-30), 1.45 (s, 9H, CH3Boc), 1.44 (s, 9H, CH3Boc);
MALDI-MS m/z 952 [M+H]+; 990 [M+K]+.
C41H52ClHgN3O8 requires 950.91.
0
0
0
0
1
Compound 43. H NMR (CDCl3): d 7.31–7.23 (m,
20H, Ph), 4.91 (m, 1H, H-5), 4.78 (d, 1H, J = 11.3 Hz,
OCHPh), 4.76 (d, 1H, J = 11.6 Hz, OCHPh), 4.67 (m,
1H, H-20), 4.65 (d, 1H, J = 11.8 Hz, OCHPh), 4.61 (d,
1H, J = 11.3 Hz, OCHPh), 4.60 (d, 1H, J = 11.6 Hz,
OCHPh), 4.41 (d, 1H, J = 11.8 Hz, OCHPh), 4.39 (d,
1H, J = 11.5 Hz, OCHPh), 4.29 (d, 1H, J = 11.5 Hz,
3.38. (1R,5R,6R,7R,8S,8aR)-1-(Aminomethyl)-octa-
hydro-5-(hydroxymethyl)-3-iminoimidazo[1,5-a]pyridine-
6,7,8-triol (41)
0
0
OCHPh), 4.03 (ddd, 1H, J1;1 a ¼ 10:0 Hz, J1;1 b
9:7 Hz, J1,2 = 3.2Hz, H-1), 3.95 (t, 1H, J = 7.6 Hz, H-
4), 3.84 (m, 2H, H-3, H-6a), 3.73 (dd, 1H, J6b,6a
10.1 Hz, J6b,5 = 4.3 Hz, H-6b), 3.51 (t, 1H, J = 3.2 Hz,
¼
To a solution of 40 (0.054 g, 0.08 mmol) in MeOH
(2 mL), Pd(OH)2/C (0.050 g) and two drops of AcOH
were added. The flask was purged three times with Ar
and then filled with H2. After 48 h, the solids were re-
moved by filtration, and the filtrate was concentrated
under reduced pressure, affording compound 41 as a yel-
=
0
0
0
H-2), 2.54 (ddd, 1H, J1 a;1 b ¼ 13:3 Hz, J1 a;1 ¼ 10:0 Hz,
J1 a;2 ¼ 5:4 Hz, H-10a), 2.25 (t, 1H, J = 12.3 Hz, H-
0
0
30a), 1.69 (m, 1H, H-10b), 1.59 (dd, 1H, J3 b;3 a
¼
0
0
22
12:3 Hz, J3 b;2 ¼ 4:5 Hz, H-30b), 1.61 (s, 9H, CH3Boc),
1.52 (s, 9H, CH3Boc); MALDI-MS m/z 1042 [M+H]+;
1080 [M+K]+; C48H58ClHgN3O8 requires 1041.03.
0
0
lowish oil in quantitative yield. ½aꢁD +6.8 (c 0.2, H2O);
1H NMR (D2O): d 4.29 (m, 1H, H-10), 4.10 (dd, 1H,
0
J1;1 ¼ 5:4 Hz, J1,2 = 2.2 Hz, H-1), 3.86 (m, 2H, H-5,
H-6a), 3.74 (m, 2H, H-2, H-3), 3.61 (m, 2H, H-4, H-
6b), 3.23 (m, 2H, H-20); 13C NMR (D2O): d 165.57
(CN), 72.18, 71.81, 70.65 (C-2, C-3, C-4), 63.98, 62.13,
62.06 (C-5, C-1, C-10), 57.74 (C-6), 49.13 (C-20); MAL-
DI-MS m/z 269 [M+Na]+; 285 [M+K]+; C9H18N4O4
requires 246.26; Anal. Calcd for C9H18N4O4: C, 43.89;
H, 7.37; N, 22.75. Found: C, 43.91; H, 7.41; N, 22.70.
Acknowledgements
The authors acknowledge the European Community’s
Human Potential Programme under contract HPRN-
CT-2002-00173, [GLYCIDIC SCAFFOLDS], and the

L. Cipolla et al. / Carbohydrate Research 342 (2007) 1813–1830
1829
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Michael, J. P. Nat. Prod. Rep. 1997, 14, 21–41; (d)
Takahata, H.; Momose, T. In The Alkaloids; Cordell, G.
A., Ed.; Academic: San Diego, 1993; Vol. 44,.
`
Ministero dell’Universita e della Ricerca under contract
´
MIUR-PRIN 2005 No. 2005037725, Dr. Jesus Jimenez-
Barbero for his contribution to conformational analysis,
and Professor Alessandra Polissi for antibacterial
tests.
9. For a recent review on the synthesis of swainsonine and its
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