Intramolecular cyclization of alkoxyaminosugars: Access to novel glycosidase inhibitor families

Article abstract of DOI:10.1039/c2ob25213a

We report the synthesis of two novel families of iminosugars as glycosidase inhibitors involving an intramolecular cyclization between an N-alkoxyamino group and a latent aldehyde of a reducing sugar as the key step. Using this methodology we have prepare

Full text of DOI:10.1039/c2ob25213a

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PAPER
Intramolecular cyclization of alkoxyaminosugars: access to novel glycosidase
inhibitor families†
Elisa Martínez-Castro,a Alejandro González-Benjumea,a Óscar López,a Inés Maya,a Eleuterio Álvarezb and
José G. Fernández-Bolaños*a
Received 27th January 2012, Accepted 29th March 2012
DOI: 10.1039/c2ob25213a
We report the synthesis of two novel families of iminosugars as glycosidase inhibitors involving an
intramolecular cyclization between an N-alkoxyamino group and a latent aldehyde of a reducing sugar as
the key step. Using this methodology we have prepared the hitherto unknown bicyclic polyhydroxylated
N-(methoxy, benzyloxy)anhydroazepanes and N-benzyloxy-D-xylonojirimycin; all these novel
compounds turned out to be moderate β-glucosidase inhibitors in a pH-dependent manner.
Introduction
Glycoconjugates, either natural or synthetic, exert a great variety
of biological activities, including many of therapeutic interest,
where nature of the sugar and its linkage strongly modulate the
pharmacology and pharmacokinetic properties of the
molecule.1,2
The importance of carbohydrates in the borderline between
Chemistry, Biochemistry and Medicinal Chemistry has stimu-
lated the development of a vast number of synthetic3 and biosyn-
thetic4,5 tools for carrying out glycosylation reactions in which
the sugar appendages are incorporated into different scaffolds in
chemo- and stereoselective fashions.3
Scheme 1 Neoglycosylation reaction from O-alkyl oximes.12
reaction we isolated the first examples of zwitterionic alkoxya-
mino cyanoboranes 3 as the major components.
Boronated alkoxyamines turned out to be excellent cyanobor-
ane transfer agents, and also good glycosyl acceptors in neogly-
corandomization reactions with reducing unprotected
carbohydrates 4 to afford neoglycosides 5.
To our knowledge, no intramolecular reaction involving an
alkoxyamino group and a latent aldehyde moiety has been
reported up to the moment.
Among the arsenal of processes devoted for the preparation of
neoglycoconjugates it is worth mentioning the one known as
neoglycorandomization,6,7 a robust methodology which involves
a chemoselective ligation of fully unprotected reducing sugars
with an alkoxyamine-appended aglycon without any prior acti-
vation.8 This process has received great attention and has been
successfully applied to the preparation of glycorandomized
libraries of compounds with notable biological activities, such as
antitumoral agents9,10 and antibiotics.11 In this context, we have
recently reported12 the preparation of functionalized N-alkoxy-
amines 2 by reduction of O-alkyloximes 1 with sodium
cyanoborohydride in glacial acetic acid (Scheme 1); in this
Results and discussion
Herein we describe the synthesis of carbohydrate-derived N-
alkoxyamines and their intramolecular cyclization involving a
latent aldehyde of a reducing sugar under acidic conditions in
order to afford unprecedented polyhydroxylated N-alkoxyanhy-
droazepanes and reducing polyhydroxylated N-alkoxypiperi-
dines, two novel families of iminosugars with potential
glycosidase inhibition properties.
aDepartamento de Química Orgánica, Facultad de Química,
Universidad de Sevilla, c/Profesor García González 1, E-41012 Seville,
Spain. E-mail: bolanos@us.es; Fax: +34 954624960;
Tel: +34 954550996
bInstituto de Investigaciones Químicas “Isla de la Cartuja”, CSIC-USE,
Américo Vespucio 49, 41092 Seville, Spain
†Electronic supplementary information (ESI) available: Crystallographic
data of compound 12, 1H and 13C NMR of new compounds. CCDC
864830. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2ob25213a
Following the procedure previously developed in our research
group,12 we accomplished the preparation of galactose-derived
4220 | Org. Biomol. Chem., 2012, 10, 4220–4228
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alkoxyamines 10, 11 starting from their O-alkyloxime counter-
parts 8, 9 (Scheme 2).
Oxidation of commercially available di-O-isopropylidene-pro-
the alkoxyamino moiety; thus boron-containing derivatives 3
(Scheme 1), where the cyanoborane is located on unbranched
haloalkyl alkoxyamines, are the major components of the
NaBH3CN-mediated reduction. On the contrary, 12 and 13 are
minor compounds in the mixtures due to the higher steric hin-
drance of the pyranose moiety; these compounds are highly
polar, with a lower chromatographical mobility on TLC than the
alkoxyamino counterparts 10 and 11 (see Experimental), and they
are only slightly soluble in CH2Cl2 and very soluble in MeOH.
The zwitterionic structure of adduct 12 was confirmed by
X-ray diffraction; Fig. 1 depicts the ORTEP drawing of 12
showing thermal ellipsoids at the 50% probability level. From
the ORTEP it can be deduced that 12 has the S configuration at
the N-atom, showing a gauche relationship between the B–CN
bond and N–C6 and N–O bonds. The fact that the crystal struc-
ture of 12 only shows the S isomer might be due to a selective
crystallization from the diastereoisomeric mixture in solution.
Tentatively, we suggest that the major isomer in solution corre-
sponds to the S derivative.
tected galactopyranose
6
with Dess–Martin periodinane
afforded13 aldehyde 7 in good yield; condensation of crude 7
with O-benzyl and O-methyl hydroxylamine hydrochlorides
furnished O-benzyl and O-methyloximes 8 and 9, as a non-
resolved mixture of E and Z isomers in a 1 : 1 ratio, as deduced
from NMR spectra (Scheme 2). The assignment of both isomers
is based on the deshielding observed for H-6 of the E isomer
(ca. 0.7 ppm for both, methyl and benzyl derivatives); a similar
situation was found for a D-xylo-configured oxime.12
Both O-alkyloximes were reduced using NaBH3CN in glacial
acetic acid to furnish a separable mixture of the D-galacto-confi-
gured alkoxyamines 10 and 11 (77 and 62% yields, respect-
ively), together with their zwitterionic cyanoborane adducts 12
and 13 as minor compounds (10 and 23% yields, respectively).
The outcome of this reaction clearly indicates that the ratio of the
aminocyanoborane adducts is strongly affected by the nature of
We accomplished the deprotection of 10 using aqueous TFA
for 4 days at rt to furnish transient 6-benzyloxyamino-6-deoxy-
galactose 14, which turned out to be an interesting substrate to
study neoglycosylation reactions. NMR analysis of the crude
Scheme 2 Preparation of D-galacto-configured N-alkoxyamines and
their boronated counterparts.
Fig. 1 ORTEP drawing of 12.
Scheme 3 Intermolecular neoglycosylation reaction vs. intramolecular cyclization for compound 10.
This journal is © The Royal Society of Chemistry 2012
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reaction revealed that signals corresponding to the anomeric
mixture of the expected fully unprotected derivative 14 disap-
peared at acidic medium giving access to a new single
compound.
Such unexpected transformation can be explained considering
the simultaneous presence of an alkoxyamino group and a latent
aldehyde in 14; thus, the neoglycosylation reaction involving
such functional groups in acidic medium could furnish an oligo-
meric or polymeric structure, like 15. Alternatively, an intramole-
cular cyclization to afford polyhydroxylated azepane 16 could
take place instead (Scheme 3).
Spectroscopical data showed the new compound to be oxaza-
bicyclo-octane 19, the first example of a polyhydroxylated
N-alkoxyanhydroazepane. These results suggest that intermole-
cular neoglycosylation reaction was not favoured for unprotected
substrate 14. Nevertheless, azepane itself 16 was not detected;
compound 16 probably evolved to bicyclic derivative 19 via an
acid-catalyzed dehydration at anomeric position of protonated
compound 17, and subsequent nucleophilic attack of OH-5 on
C-2 of the transient iminium cation 18 (Scheme 3).
time, followed by per-acetylation under standard conditions
(Scheme 5) to give 21 as a non-resolved mixture of α/β anomers
in a 1 : 3.3 ratio. Subsequent deprotection of 21 using methanolic
NaOMe allowed removal of the O-acetyl groups to furnish N-
acetyl derivative 22 as an α/β mixture. E/Z stereoisomers for the
acetamido group due to the restriction of free rotation around the
N–C bond were detected by NMR.
N-Methoxyamine 11 was deprotected (Scheme 6), yielding to
the corresponding azabicyclo-octane 23 in excellent yield (85%).
The bicyclic structure of compounds 19 and 23 was evidenced
from their 1H NMR data; four-bond long-range couplings
(Table 1) between protons H-1 and H-3eq (1.3 Hz), H-1 and H-5
(0.5 Hz), H-3eq and H-5 (2.1 and H 1.9 Hz) via a planar W
pathway is in agreement with the chair conformation of the 1,3-
oxazinane rings. Another four-bond long-range coupling was
also found for H-5 and H-7 (1.0 Hz); these couplings are also
supported by 2D-COSY experiments. The structure of these
bicyclic compounds was further confirmed by 2D-NOESY
experiments, showing a strong correlation between H-3ax and
H-6. Furthermore, coupling constants found for both compounds
also discard the possible 2,6-anhydroazepane structure 20, which
could have been obtained by cyclization involving hydroxyl on
C-6.
The only structure similar to 19 found in the literature was
reported by Wong and co-workers14 as a transient intermediate
(8-oxa-2-aza-4,6,7-trihydroxybicyclo[3.2.1]octane)
in
the
reduction of 6-azido-D-galactopyranose, which could not be iso-
lated, and was only detected by NMR spectroscopy. Such com-
pound readily evolved in solution under reduction conditions to
the corresponding tetrahydroxylated azepane.
Cyclization involving hydroxyl groups on C-3 or C-4 on
derivative 18 would lead to highly strained bicyclic compounds
(bearing unstable three and four-membered rings), and such
compounds are not detected; furthermore, cyclization through
hydroxyl group on C-6 is not either favoured, probably due to
repulsive 1,3-diaxial interactions involving the hydroxyl group
on C-4 and the aminomethylene bridge in compound 20
(Scheme 4).
Bicyclic anhydroazepanes 19 and 23 exhibited an extraordi-
nary high stability, in contrast with the few related compounds
reported so far in the literature;14 such stability could maybe be
explained considering the reduced basicity of N-alkoxyamines,
which reduces the facility of undergoing a ring-opening reaction.
Stimulated by these results, we also attempted the preparation
of 6-membered N-alkoxyiminosugars starting from D-xylo-
In order to confirm the presence of the fully unprotected 6-
alkoxyamino derivative 14 as an intermediate in the formation of
19, we accomplished the acidic deprotection of 10 for a shorter
Scheme 6 Synthesis of N-methoxyanhydroazepane 23.
Table 1 Selected NMR data for compounds 19 and 23a
Compound H-1
4J1,3eq 4J1,5 H-3eq 4J3eq,5 H-3ax J3ax,4
19
23
4.96 1.3
5.02 1.3
0.5
0.5
3.29
3.34
2.1
1.9
2.98
2.99
11.2
11.1
a δ in ppm, J in Hz.
Scheme 4 Another potential intramolecular cyclization on iminium
ion 18.
Scheme 5 Trapping of 6-benzyloxyamino galactopyranose as transient intermediate in intramolecular cyclization.
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Scheme 8 Synthesis of N-benzyloxy-D-xylonojirimycin 33.
Scheme 7 Synthesis of D-xylo-configured 5-alkoxyamines and their
cyanoboronated adducts.
configured aldehyde 25, readily obtained from commercially-
available mono-O-isopropylidene-D-glucofuranose 24 by oxi-
dative degradation of the side chain with NaIO4 (Scheme 7).15
Treatment of 25 with O-benzyl and O-methylhydroxylamine
in pyridine furnished O-alkyloximes 2612 and 27 from good to
almost quantitative yields, and as a 2 : 1 E/Z ratio. Reduction of
such alkyloximes with NaBH3CN in glacial acetic acid afforded
the expected alkoxyamines 28 and 29,12 together with their cya-
noboronated adducts 30 and 31, as minor compounds, in a
similar fashion as already observed for D-galacto derivatives 12
and 13.
The conversion of D-xylo-configured derivatives 28 and 29
into iminosugars involves the removal of the protective group
under acidic conditions. Nevertheless, the deprotection reaction
turned out to be more tricky than previously anticipated; stan-
dard treatment with aqueous TFA under the same conditions
used for the deprotection of 10 and 11 gave complex mixtures.
Some other procedures used for the removal of isopropylidene
moieties, such as treatment with AcOH–H2O, NaI/CeCl3/SiO2 or
(CF3CO)2O/I2/FeCl3 also furnished very complex mixtures. The
extensive decomposition observed under all these conditions
came from the N–O bond cleavage, followed by subsequent
side-reactions.
Scheme 9 Proposed degradation for the attempted N-methoxy-D-xylo-
nojirimycin 34.
neoglycosylation reaction, and no bicyclic derivatives, indicating
that in this case, fused bicyclic structures with an anhydro scaf-
fold are not stable, unlike their D-galacto counterparts.
We also tried to extend this strategy to methoxyamino deriva-
tive 29; nevertheless, attempts of deprotection under acidic con-
ditions failed, including the mild conditions derived from the use
of the Amberlite IR-120(H+) resin. In all the cases an extensive
decomposition was observed, and the expected compound 34
was observed only as a minor compound, which in turn easily
decomposed in solution. NMR spectra proved the lability of the
methoxyamino functionality under acidic conditions, and
suggested that N–O bond cleavage takes part even prior to the
isopropylidene removal.
We suggest that the degradation of the methoxyamino group
of 29 occurs by protonation of the amino group, followed by het-
erolytic cleavage of the N–O bond, releasing the corresponding
amino compound and formaldehyde (Scheme 9).
A similar situation, although to a lesser extent, was also
observed in the preparation of benzyloxy derivative 33, as the
crude reaction of the acidic deprotection released a smell of
benzaldehyde.
To our delight, treatment of N-benzyloxy derivative 28 with
acidic Amberlite IR-120(H+) resin under very mild conditions
(room temperature for 2 h) led to the formation of N-benzyloxy-
D-xylonojirimycin 33 via an intramolecular cyclization reaction
involving the benzyloxyamino group and the latent aldehyde in
the transient fully unprotected intermediate 32 (Scheme 8).
N-Benzyloxy-piperidine 33 was obtained in a 31% yield, after
crystallization from the crude reaction medium; it is the first
1
example of a reducing N-alkoxyiminosugar. H NMR spectrum
Enzymatic inhibition studies
of 33 showed it to exist exclusively as the α-anomer in solution,
as suggested by the small value of the J2,3 coupling constant
(3.0 Hz); such observation can be explained considering the fact
that iminosugar derivatives exhibit stronger anomeric effects
than carbohydrates bearing an endocyclic oxygen atom, due to
the stronger electron-donating effect of the nitrogen atom when
compared with oxygen.16
We have evaluated the inhibitory properties of unprotected imi-
nosugar derivatives 19, 23 and 33 against nine commercially
available glycosidases and glycogen phosphorylase type b from
rabbit muscle; Ki values are depicted in Table 2.
These data indicate that bicyclic derivative 19, despite having
a very different structure compared with enzyme substrates, exhi-
bits a moderate inhibition against β-glucosidase, although seven
times stronger than methoxy counterpart 23. These results could
1
Furthermore, H NMR spectra of the crude product did not
show any oligomers, so discarding any intermolecular
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Table 2 Inhibitory activities of compounds 19, 23 and 33a at pH 6.8
β-glucosidase inhibitors in a pH-dependent manner, and one of
them also a moderate inhibitor of glycogen phosphorylase
type b.
Compound enzyme
19
23
33
α-Glucosidase (Baker’s yeast)
α-Glucosidase (rice)
β-Glucosidase (almonds)
N.I.b
N.I.
660
N.I.
N.I.
4810
N.I.
N.I.
N.I.
146c
N.I.
N.I.
N.I.
N.I.
N.I.
N.I.
Experimental
β-Galactosidase (E. coli)
N.I.
N.I.
N.I.
N.I.
N.I.
N.I.
447
N.I.
N.I.
N.I.
N.I.
N.I.
N.I.
N.I.
General procedures
β-Galactosidase (Aspergillus niger)
α-Galactosidase (green coffee beans)
α-Manosidase (Jack beans)
β-Manosidase (Helix pomatia)
α-L-Fucosidase (bovine kidney)
Glycogen phosphorylase b (rabbit muscle)
Optical rotations were measured with a Jasco P-2000 polarimeter
and IR spectra (KBr disks) were obtained with FT-IR Bomem
MB-120 and FT-IR JASCO-410 spectrophotometers. 1H (300
and 500 MHz) and 13C (75.5 and 125.7 MHz) NMR spectra
were recorded on Bruker Avance-300 and Avance-500 spec-
trometers at rt. The assignments of 1H and 13C signals were
confirmed by homonuclear COSY and heteronuclear 2D corre-
lated spectra, respectively. Mass spectra (CI and LSI) were
recorded on Micromass AutoSpec-Q mass spectrometer with a
resolution of 1000 or 10 000 (10% valley definition). For LSI
spectra, ions were produced by a beam of xenon atoms and Cs+
ions, respectively, using thioglycerol as matrix and NaI as addi-
tive. TLC was performed on aluminium pre-coated sheets
(E. Merck Silica Gel 60 F254); spots were visualized by UV
light, by charring with 10% H2SO4 in EtOH or with 3% ninhy-
drin in EtOH. Column chromatography was performed using
E. Merck Silica Gel 60 (40–63 μm). Microanalyses were per-
formed at the Instituto de Investigaciones Químicas “Isla de la
Cartuja” US-CSIC, using an elemental analyzer LECO Truspec
CHN/CHNS.
Enzymatic assays were carried out in a Hitachi U-2900 spec-
trophotometer. Commercially-available α-glucosidase (baker’s
yeast), β-glucosidase (almonds), α-galactosidase (green coffee
beans), β-galactosidase (E. coli), β-galactosidase (Aspergillus
oryzae), α-mannosidase (Jack beans), β-mannosidase (Helix
pomatia), α-L-fucosidase (bovine kidney) and glycogen phos-
phorylase type b (rabbit muscle) were used as received, without
further purification. Assays were accomplished as described pre-
viously.18 Each glycosidase assay was performed by preparing
ten 2-mL samples in PS cuvettes containing 0.1 M phosphate
buffer (pH 6.8) and the appropriate substrate solution. The con-
centration of the substrates ranged from 0.25 to 4.0 Km. Water or
inhibitor solution plus water were also added up to a constant
volume of 1.9 mL for the Km or the Ki measurement, respect-
ively. Reaction was started by adding 0.1 mL of dilute enzyme
solution at 25 °C and the formation of the p-nitrophenolate was
monitored for 2 min by measuring the increase of absorbance at
400 nm.
d
—
a Ki expressed in μM; b No inhibition; c At pH 5.0; d Not tested.
be explained considering favourable hydrophobic interactions
involving the benzyl residue and hydrophobic residues of the
enzyme active site. Furthermore, the existence of three hydroxyl
groups on 19 might enable hydrogen-bonding interactions with
polar motifs of the active site of the enzyme.
N-Benzyloxy polyhydroxylated piperidine 33 showed no inhi-
bition against the tested glycosidases at pH 6.8. Given that
N-alkoxyamines are less basic than the parent amines, we also
tested compound 33 against β-glucosidase at a lower pH (5.0) in
order to increase the concentration of its protonated form, which
might better interact with the carboxylic residues of the enzyme
active site. Under these conditions, a remarkable increase in inhi-
bition was observed, changing from no inhibition at pH 6.8 to
exhibit a moderate Ki value (146 μM) at pH 5.0, 4.5 times the
activity shown by 19. N-Benzyloxy piperidine 33 might at lower
pH values lose the pseudo-anomeric hydroxyl group to furnish a
transient iminium cation resembling an oxocarbenium ion of the
enzyme substrate that could interact with the active site of the
enzyme; this would explain the absence of activity at higher pH
values. Moreover, the absence of an exocyclic hydroxymethyl
group on C-6 of 33 would explain a relatively low activity
against β-glucosidase. Bicyclic oxabicyclo-octanes 19 and 23
when tested at lower pH, showed a decrease in activity; in this
case the highly stable structure of both compounds precludes at
pH 5.0 the formation of azepane-based iminium cation 18,
whose conformational flexibility would presumably allow a
stronger interaction with the enzyme active site and thus, higher
activity.
Moreover, anhydroazepane 19 also displayed moderate inhi-
bition of glycogen phosphorylase b (Ki 447 μM), an interesting
target for controlling the level of sugar in blood.17
Initial rates were calculated from the slopes of each reaction
and were used to obtain two Hanes plots ([S]/V vs. [S]), one
with and another without inhibitor. Inhibition constants (Ki)
were obtained from the formula Ki = [I]/(Km′/Km − 1), were [I]
is the inhibitor concentration in the cuvette and Km and Km′ are
the enzymatic Michaelis–Menten constants in the absence and in
the presence of the inhibitor, respectively.
Glycogen phosphorylase activities were assayed in the direc-
tion of glycogen synthesis19 by using commercial glycogen
phosphorylase b (rabbit muscle, 10 μg ml−1) at 30 °C in the
presence of 1% oyster glycogen, α-D-glucose-1-phosphate,
1 mM AMP, with or without inhibitors at pH 6.8 (50 mM
triethanolamine/HCl, 1 mM dithiothreitol and 1 mM EDTA
Conclusions
In conclusion, using acid catalysis, we have carried out the first
examples of intramolecular cyclizations between N-alkoxyamino
groups and latent aldehydes of reducing sugars to afford novel
iminosugar derivatives. Following this methodology, we
accessed two novel families of iminosugars: polyhydroxylated
N-alkoxyanhydroazepanes and reducing N-benzyloxy-D-xylono-
jirimycin. Such compounds turned out to be moderate
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buffer). Pi concentration was determined using the method devel-
oped by Taussky and Shorr.20 Hanes plots were built using the
initial velocity from each reaction, as indicated above for
glycosidases.
(C(CH3)2); 9E: δ 147.8 (C-6), 109.8 (C(CH3)2), 73.4 (C-4), 70.8
(C-3), 70.4 (C-2), 66.7 (C-5), 62.4 (OCH3); 9Z δ 148.9 (C-6),
109.1 (C(CH3)2), 71.4 (C-4), 70.7 (C-3), 70.3 (C-2), 63.9 (C-5),
61.9 (OCH3); LSI-MS m/z 310 ([M + Na]+, 60%); HRLSI-MS
calcd for C13H21NNaO6 ([M + Na]+): 310.1267; found:
310.1247; Anal. calcd for C13H21NO6: C, 54.35; H, 7.37; N,
4.88, found: C, 54.37; H, 7.37; N, 5.06.
(E- and Z)-1,2:3,4-Di-O-isopropylidene-α-D-galacto-hexodialdo-
1,5-pyranose-6-O-benzyloxime (8E and 8Z)
To a solution of 1,2:3,4-di-O-isopropylidene-α-D-galacto-hexo-
dialdo-1,5-pyranose 7 (270 mg, 1.05 mmol) in pyridine (4 mL)
was added O-benzylhydroxylamine hydrochloride (200 mg,
1.25 mmol, 1.2 equiv.), and the mixture was stirred at rt for 5 h.
Then it was concentrated to dryness and the residue was dis-
solved in EtOAc (50 mL) and washed with H2O (3 × 50 mL);
the organic layer was dried over MgSO4, filtered and the filtrate
was concentrated to dryness. The residue was purified by
column chromatography (1 : 5 EtOAc–hexane) to give 8 as a
6-Benzyloxyamino-6-deoxy-1,2:3,4-di-O-isopropylidene-α-D-
galactopyranose (10) and N-benzyloxy-N-(6-deoxy-1,2:3,4-di-O-
isopropylidene-α-D-galactopyranos-6-yl)amine-cyanoborane (12)
To a solution of (E- and Z)-1,2:3,4-di-O-isopropylidene-α-D-
galacto-hexodialdo-1,5-pyranose-6-O-benzyloxime 8 (383 mg,
1.05 mmol) in AcOH (2 mL) at 0 °C was added NaBH3CN
(140 mg, 2.23 mmol, 2.2 equiv.), and the corresponding mixture
was stirred at rt for 1.5 h. Then it was concentrated to dryness
and the residue was dissolved in EtOAc (60 mL) and washed
with H2O (3 × 50 mL); the organic layer was dried over MgSO4,
filtered and the filtrate was concentrated to dryness. The residue
was purified by column chromatography (1 : 10 → 1 : 2 EtOAc–
hexane) to give a separable mixture of 10 and 12.
1
1 : 1 E/Z diastereoisomeric mixture, as deduced from H NMR:
340 mg, 86%; RF 0.31 (1 : 2 EtOAc–hexane 1 : 2); [α]2D3 −69
(c 0.7, CH2Cl2); IR νmax 2989, 2929, 1641, 1451, 1375, 1256,
1
1211, 1070, 1014, 896, 872, 701 cm−1; H NMR (300 MHz,
CDCl3) δ 7.29 − 7.19 (m, 10H, Ar-H), 5.49, 5.48 (2d, 1H each,
J1,2 = 4.6 Hz, H-1), 5.09 (m, 2H, PhCH2), 5.04 (s, 2H, PhCH2),
4.27 (m, 2H, H-2), 1.49, 1.44, 1.39, 1.27 (4s, 24H, C(CH3)2);
8E: δ 7.42 (d, 1H, J5,6 = 6.8 Hz, H-6), 4.85–4.56 (m, 1H, H-3),
4.37 (dd, 1H, J4,5 = 1.9 Hz, J5,6 = 6.8 Hz, H-5), 4.21 (dd, 1H,
J3,4 = 7.8 Hz, H-4); 8Z: δ 6.72 (d, 1H, J5,6 = 4.5 Hz, H-6), 4.91
(dd, 1H, J4,5 = 1.8 Hz, J5,6 = 4.5 Hz, H-5), 4.85–4.56 (m, 2H,
H-4, H-3); 13C-NMR (75.5 MHz, CDCl3) δ 137.6, 137.3, 128.4,
128.2, 127.9 (Ar-C), 109.7, 109.6, 108.9 (×2) (C(CH3)2), 96.2
(C-1), 76.4, 76.1 (PhCH2), 70.7, 70.5 (C-3), 70.3, 70.2 (C-2),
26.13, 26.0, 25.9, 25.0, 24.9, 24.4, 24.3 (C(CH3)2); 8E: δ 148.2
(C-6), 73.2 (C-4), 66.7 (C-5); 8Z: δ 149.5 (C-6), 71.3 (C-4),
63.9 (C-5); LSI-MS m/z 364 ([M + H]+, 15%); HRLSI-MS calcd
for C19H26NO6 ([M + H]+): 364.1760, found: 364.1787.
Eluted first was 10: 295 mg, 77%; RF 0.51 (1 : 2 EtOAc–
hexane); [α]2D3 −16 (c 0.8, CH2Cl2); IR νmax 3275, 2984, 1607,
1
1454, 1377, 1308, 1254, 1170, 997, 907, 799, 620 cm−1; H
NMR (300 MHz, CDCl3) δ 7.25 (m, 5H, Ar-H), 5.46 (d, 1H,
J1,2 = 4.9 Hz, H-1), 4.65 (s, 2H, PhCH2), 4.52 (dd, 1H, J2,3
=
2.3 Hz, J3,4 = 7.9 Hz, H-3), 4.24 (dd, 1H, H-2), 4.13 (m, 1H,
H-5), 4.05 (dd, 1H, J4,5 = 1.6 Hz, H-4), 3.02 (m, 2H, H-6a,
H-6b), 1.44, 1.36, 1.26 (×2) (4s, 3H each, 4C(CH3)2); 13C-NMR
(75.5 MHz, CDCl3) δ 138.2, 128.4, 128.3, 127.8 (Ar-C), 109.4,
108.9 (C(CH3)2), 96.5 (C-1), 76.0 (PhCH2), 72.1 (C-4), 71.0
(C-3), 70.9 (C-2), 64.1 (C-5), 52.4 (C-6), 26.1 (×2), 25.2, 24.5
(C(CH3)); LSI-MS m/z 366 ([M + H]+, 15%); HRLSI-MS calcd
for C19H28NO6 [M + H]+: 366.1917, found: 366.1916.
Eluted second was 12:‡ 42 mg, 10%, RF 0.27 (1 : 2 EtOAc–
hexane); [α]2D4 −15 (c 0.8, CH2Cl2); IR νmax 3320, 3057, 2985,
2434, 1685, 1459, 1377, 1303, 1254, 1168, 1002, 896, 753,
(E- and Z)-1,2:3,4-Di-O-isopropylidene-α-D-galacto-hexodialdo-
1,5-pyranose-6-O-methyloxime (9E and 9Z)
1
695 cm−1; H NMR (300 MHz, CDCl3) δ 7.46–7.33 (m, 5H,
To a solution of 1,2:3,4-di-O-isopropylidene-α-D-galacto-hexo-
dialdo-1,5-pyranose 7 (258 mg, 1.00 mmol) in pyridine (3 mL)
was added O-methylhydroxylamine hydrochloride (100 mg,
1.20 mmol, 1.2 equiv.), and the mixture was stirred at rt for 12 h.
Then it was concentrated to dryness and the residue was purified
by column chromatography (1 : 15 → 1 : 7 EtOAc–hexane) to
give 9 as a 1.25 : 1 E/Z diastereoisomeric mixture, as deduced
Ar-H), 6.82 (d, 1H, JNH,H-6 = 8.2 Hz, NH), 5.54 (d, 1H, J1,2
=
4.9 Hz, H-1), 5.23, 4.96 (2d, 1H each, JH,H = 9.9 Hz, PhCH2),
4.63 (dd, 1H, J2,3 = 2.3 Hz, J3,4 = 7.9 Hz, H-3), 4.37 (dd, 1H,
H-2), 4.29 (m, 1H, H-5), 4.12 (dd, 1H, J4,5 = 1.7 Hz, H-4), 3.52
(m, 2H, H-6a, H-6b), 2.00 (brs, 2H, BH2), 1.42, 1.38, 1.34, 1.32
(4s, 3H each, C(CH3)2); 13C-NMR (75.5 MHz, CDCl3) δ 132.8,
129.4, 129.2, 128.9 (Ar-C), 110.1, 109.4 (C(CH3)2), 96.3 (C-1),
74.2 (PhCH2), 70.8 (×2), 70.7 (C-2, C-3, C-4), 62.0 (C-5), 57.0
(C-6), 26.1, 26.0, 25.0, 24.3 (C(CH3)); Anal. calcd for
C20H29BN2O6: C, 59.42; H, 7.23; N, 6.93, found: C, 59.35; H,
7.24; N, 6.79.
1
from H NMR: 261 mg, 91%; RF 0.75 (2 : 1 EtOAc–hexane);
[α]2D3 −129 (c 1.0, CH2Cl2); IR νmax 1694, 1314, 1260, 1064,
999, 866, 797, 718, 630 cm−1 1H NMR (300 MHz, CDCl3)
;
δ 3.89, 3.85 (2s, 3H each, OCH3), 1.55, 1.45, 1.33, 1.32 (4s, 3H
each, C(CH3)2); 9E: δ 7.38 (d, 1H, J5,6 = 6.8 Hz, H-6), 5.53 (d,
1H, J1,2 = 4.5 Hz, H-1), 4.62 (dd, 1H, J2,3 = 3.8 Hz, J3,4 = 7.9
Hz, H-3), 4.41 (dd, 1H, J4,5 = 2.0 Hz, H-5) 4.33 (dd, 1H, H-2),
4.26 (dd, 1H, H-4); 9Z: δ 6.71 (d, 1H, J5,6 = 4.6 Hz, H-6), 5.55
(d, 1H, J1,2 = 4.5 Hz, H-1), 4.90 (dd, 1H, J4,5 = 1.9 Hz, H-5),
‡Crystal data for 12: C20H29BN2O6, M = 404.26, monoclinic, a =
8.5632(3) Å, b = 11.8122(4) Å, c = 10.9084(4) Å, α = 90.00°, β =
91.6900(10)°, γ = 90.00°, V = 1102.91(7) Å3, T = 173(2) K, space
group P2(1), Z = 2, μ(MoKα) = 0.089 mm−1, 15 535 reflections
measured, 3469 independent reflections (Rint = 0.0188). The final R1
values were 0.0339 (I > 2σ(I)). The final wR(F2) values were 0.0863
(I > 2σ(I)). The final R1 values were 0.0368 (all data). The final wR(F2)
values were 0.0889 (all data). The goodness of fit on F2 was 1.033.
4.60 (dd, J2,3 = 2.6 Hz, J3,4 = 6.6 Hz, H-3), 4.52 (dd, 1H, J4,5
=
2.0 Hz, H-4), 4.32 (dd, 1H, H-2); 13C-NMR (75.5 MHz, CDCl3)
δ 96.3 (C-1, C-1), 26.3, 26.2, 26.1, 26.0, 25.1, 25.0, 24.6, 24.5
This journal is © The Royal Society of Chemistry 2012
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6-Deoxy-1,2:3,4-di-O-isopropylidene-6-methoxyamino-α-D-
galactopyranose (11) and N-(6-deoxy-1,2:3,4-di-O-isopropylidene-
α-D-galactopyranos-6-yl)-N-methoxyamine-cyanoborane (13)
Ar-H), 4.96 (ddd, 1H, J1,5 = 0.5 Hz, J1,3e = 1.3 Hz, J1,7 = 5.9
Hz, H-1), 4.70, 4.67 (2d, 1H each, JH,H = 11.3 Hz, PhCH2), 4.15
(d, 1H, J5,6 ≈ 0 Hz, J6,7 = 2.4 Hz, H-6), 4.14 (ddd, 1H, J5,7
=
1.0 Hz, J6,7 = 2.4, J1,7 = 5.9 Hz, H-7), 4.07 (ddd, 1H, J4,5 = 4.4
Hz, J3e,4 = 6.0 Hz, J3a,4 = 11.2 Hz, H-4), 3.91 (m, 1H, H-5),
3.29 (dddd, 1H, J1,3e = 1.3 Hz, J3e,5 = 2.1 Hz, J3e,4 = 6.0 Hz,
To a solution of (E- and Z)-1,2:3,4-di-O-isopropylidene-α-D-
galacto-hexodialdo-1,5-pyranose-6-O-methyloxime 9 (236 mg,
0.82 mmol) in AcOH (4 mL) at 0 °C was added NaBH3CN
(129 mg, 2.06 mmol, 2.5 equiv.), and the corresponding mixture
was stirred at rt for 12 h. Then it was concentrated to dryness
and the residue was purified by column chromatography (1 : 5 →
1 : 2 EtOAc–hexane) to give a separable mixture of 11 and 13.
Eluted first was 11: 147 mg, 62%; RF 0.43 (1 : 2 EtOAc–
hexane); [α]2D6 −17 (c 1.0, CH2Cl2); IR νmax 2991, 2928, 1459,
J3a,3e = 14.9 Hz, H-3e), 2.98 (dd, 1H, J3a,4 = 11.2 Hz, J3a,3e
=
14.9 Hz, H-3a); 13C-NMR (75.5 MHz, CD3OD) δ 138.8, 129.9,
129.3, 128.9 (Ar-C), 92.6 (C-1), 86.0 (C-5), 81.3 (C-7), 77.3
(C-6), 76.0 (PhCH2), 62.5 (C-4), 53.9 (C-3); LSI-MS m/z 290
([M + Na]+, 18%); HRLSI-MS calcd for C13H17NNaO5 ([M +
Na]+): 290.1004, found: 290.0995.
1
1381, 1245, 1201, 1173, 1061, 993, 891, 862 cm−1; H NMR
(300 MHz, CDCl3) δ 5.54 (d, 1H, J1,2 = 5.0 Hz, H-1), 4.62 (dd,
1H, J2,3 = 2.4 Hz, J3,4 = 7.8 Hz, H-3), 4.32 (dd, 1H, H-2), 4.18
(m, 1H, H-4), 4.15 (m, 1H, H-5), 3.13 (dd, 1H, J5,6a = 3.8 Hz,
J6a,6b = 14.0 Hz, H-6a), 3.54 (s, 3H, OCH3), 3.05 (dd, 1H, J5,6b
= 8.6 Hz, H-6b), 1.55, 1.44, 1.34 (×2) (4s, 3H each, C(CH3)2);
13C-NMR (75.5 MHz, CDCl3) δ 109.6, 108.0 (C(CH3)2), 96.6
(C-1), 72.3 (C-4), 71.1 (C-3), 70.9 (C-2), 64.1 (C-5), 61.7
(OCH3), 52.1 (C-6), 26.2, 26.1, 25.3, 24.6 (C(CH3)2); LSI-MS
m/z 290 ([M + H]+, 100%); HRLSI-MS calcd for C13H24NO6
([M + H]+): 290.1580, found: 290.1560.
1,2,3,4-Tetra-O-acetyl-6-(N-acetyl-N-benzyloxy)amino-6-deoxy-α
and β-D-galactopyranose (21)
A solution of 6-benzyloxyamino-6-deoxy-1,2:3,4-di-O-isopropy-
lidene-α-D-galactopyranose 10 (102 mg, 0.28 mmol) in a 4 : 1
TFA–H2O mixture (1 mL) was kept at rt for 3.5 h. Then it was
concentrated to dryness, and the residue was dissolved in a 1 : 1
Ac2O–Py mixture (3 mL) and DMAP (8 mg, 0.065 mmol, 0.23
equiv.) was added. The corresponding solution was kept at rt for
12 h; after that, water was slowly added at 0 °C and concentrated
to dryness. The residue was dissolved in EtOAc (40 mL) and
washed with H2O (3 × 30 mL); the organic layer was dried over
MgSO4, filtered and concentrated to dryness. The residue was
purified by column chromatography (1 : 5 → 1 : 2 EtOAc–
hexane) to give 21 as a non-resolved anomeric mixture, as
Eluted second was 13, obtained as a non-resolved 10 : 1 dia-
stereoisomeric mixture: 61 mg, 23%; RF 0.26 (1 : 2 EtOAc–
hexane); [α]2D5 +23 (c 0.8, CH2Cl2); IR νmax 3021, 2435, 1381,
1254, 1254, 1213, 1164, 1098, 1071, 1007, 909, 879, 852,
1
766 cm−1; H NMR (300 MHz, CDCl3) major diastereoisomer:
1
deduced from H NMR: 90.1 mg, 65%; RF 0.7 (1 : 1 EtOAc–
δ 6.46 (brd, 1H, JNH,H6 = 2.3 Hz, NH), 5.52, (d, 1H, J1,2 = 4.9
Hz, H-1), 4.65 (dd, 1H, J2,3 = 2.3 Hz, J3,4 = 7.8 Hz, H-3), 4.38
(dd, 1H, H-2), 4.29 (m, 1H, H-5), 4.14 (dd, 1H, J4,5 = 1.7 Hz,
H-4), 3.85 (s, 3H, OCH3), 3.43–3.37 (m, 2H, H-6a, H-6b), 1.53,
1.43 1.35, 1.33 (4s, 3H each, C(CH3)2); minor diastereoisomer:
δ 6.71 (brd, 1H, JNH,H = 8.0 Hz, NH), 5.49 (d, 1H J1,2 = 4.9 Hz,
H-1), 4.60 (dd, 1H, J2,3 = 2.5 Hz, J3,4 = 7.9 Hz, H-3), 4.36 (dd,
1H, H-2), 4.11 (m, 1H, H-5), 4.20 (dd, 1H, J4,5 = 1.9 Hz, H-4),
3.82 (s, 3H, OCH3), 3.48–3.33 (m, 2H, H-6a, H-6b), 2.00 (brs,
2H, BH2), 1.56, 1.50, 1.47, 1.46 (4s, 3H each, C(CH3)2);
13C-NMR (75.5 MHz, CDCl3) major diastereoisomer: δ 110.3,
109.6 (C(CH3)2), 96.3 (C-1), 71.0 (C-2), 70.8 (C-3, C-4), 62.1
(C-5), 61.0 (OCH3), 56.7 (C-6), 26.0, 25.9, 25.1, 24.4 (C
(CH3)2); minor diastereoisomer: δ 109.7, 108.9 (C(CH3)2), 96.0
(C-1), 71.2 (C-4), 70.7 (C-3), 70.6 (C-2), 63.8 (C-5), 59.4
(OCH3), 56.4 (C-6), 26.1 (×2), 25.2, 24.6 (C(CH3)2); LSI-MS
hexane); IR νmax 2934, 1753, 1670, 1433, 1371, 1221, 1055,
1
954, 740, 701 cm−1; H NMR (500 MHz, CDCl3) δ 7.37 (m,
5H, Ar-H); 21α: δ 6.35 (brs, 1H, H-1), 5.38 (m, 1H, H-4),
5.30–5.28 (m, 2H, H-2, H-3), 4.82, 4.78 (2d, 1H each, JH,H
=
10.6 Hz, PhCH2), 4.42 (t, 1H, J4,5 ≈ 0 Hz, J5,6a = J5,6b = 6.9 Hz,
H-5), 3.84–3.82 (m, 1H, H-6a), 3.62 (m, 1H, H-6b), 2.12, 2.07,
2.03, 2.00, 1.98 (5s, 3H each, 5Ac); 21β: δ 5.63 (d, 1H, J1,2
8.3 Hz, H-1), 5.31 (dd, 1H, J2,3 = 10.4 Hz, H-2), 5.28 (d, 1H,
3,4 = 3.5 Hz, J4,5 ∼ 0 Hz, H-4), 5.03 (dd, 1H, H-3), 4.81 (s, 2H,
=
J
PhCH2), 4.05 (t, 1H, J5,6a = J5,6b = 6.3 Hz, H-5), 3.96 (m, 1H,
H-6a), 3.63 (dd, 1H, J6a,6b = 14.5 Hz, H-6b), 2.13, 2.06, 2.03
(×2), 1.96 (5s, 3H each, Ac); 13C-NMR (75.5 MHz, CDCl3) δ
134.4, 129.3, 129.2, 128.9 (Ar-C), 20.9 (×2), 20.8, 20.7, 20.4
(Ac); 21α: δ 170.3, 170.2, 170.0 (×2), 169.1 (CvO), 89.8
(C-1), 76.9 (PhCH2), 67.8 (C-5), 67.7 (C-2, C-3), 65.6 (C-4),
53.5 (C-6); 21β: δ 170.3, 170.0, 169.5 (×2), 169.2 (CvO), 92.4
(C-1), 77.0 (PhCH2), 71.0 (C-5), 70.1 (C-3), 67.9 (C-2), 67.2
(C-4), 46.6 (C-6); LSI-MS m/z 518 ([M + Na]+, 5%);
HRLSI-MS calcd for C23H29NNaO11 ([M + Na]+): 518.1638,
found: 518.1610.
m/z 351 ([M
+
Na]+, 40%); HRLSIMS calcd for
C14H25BN2NaO6 ([M + Na]+): 351.1703, found: 351.1714.
(1S,4R,5S,6R,7R)-2-Benzyloxy-8-oxa-2-azabicyclo[3.2.1]octane-
4,6,7-triol (19)
A solution of 6-benzyloxyamino-6-deoxy-1,2:3,4-di-O-isopropy-
lidene-α-D-galactopyranose 10 (508 mg, 1.39 mmol), in a 1 : 1
TFA–H2O mixture (1.2 mL) was stirred at rt 4 days; after that it
was concentrated to dryness and the residue was purified by
column chromatography (5 : 1 EtOAc–MeOH) to give 19:
256 mg, 69%; RF 0.6 (5 : 1 EtOAc–MeOH); [α]2D3 +52 (c 0.6,
MeOH); IR νmax 3350, 1643, 1493, 1454, 1197, 1046, 969, 745,
6-(N-Acetyl-N-benzyloxy)amino-6-deoxy-D-galactopyranose (22)
To a solution of 1,2,3,4-tetra-O-acetyl-6-(N-acetyl-N-benzyloxy)
amino-6-deoxy-D-galactopyranose 21 (50 mg, 0.1 mmol) in
MeOH (3 mL) was added a 0.5 M methanolic NaOMe solution
(0.3 mL, 0.15 mmol) and the mixture was stirred at rt for
45 min. After that, the reaction was neutralized with Amberlite
IR-120(H+) resin, filtered and the filtrate was concentrated to
1
702 cm−1; H NMR (500 MHz, CD3OD) δ 7.30–7.26 (m, 5H,
4226 | Org. Biomol. Chem., 2012, 10, 4220–4228
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dryness to give pure 22: 28.4 mg, 87%; RF 0.17 (5 : 1 EtOAc–
MeOH); [α]2D2 +50 (c 0.4, MeOH); IR νmax 3530, 2853, 1690,
7.50 (d 1H, J4,5 = 5.2 Hz, H-5), 6.00 (d, 1H, J1,2 = 3.0 Hz, H-1),
4.70 (dd, 1H, J3,4 = 2.6 Hz, H-4), 4.36 (t, 1H, J2,3 = 2.4 Hz,
H-3), 3.90 (s, 3H, OCH3); 27Z: δ 6.83 (d, 1H, J4,5 = 3.3 Hz,
H-5), 5.98 (d, 1H, J1,2 = 4.6 Hz, H-1), 5.06 (t, 1H, J3,4 = 3.2 Hz,
H-4), 4.60–4.55 (m, 1H, H-3), 3.93 (s, 3H, OCH3); 13C-NMR
(75.5 MHz, CDCl3) 27E: δ 146.3 (C-5), 112.2 (C(CH3)2), 105.2
(C-1), 85.1 (C-2), 77.4 (C-4), 76.3 (C-3), 62.3 (OCH3), 26.9,
26.4 (C(CH3)2); 27Z: δ 148.5 (C-5), 112.1 (C(CH3)2), 104.8
(C-1), 85.2 (C-2), 78.0 (C-4), 75.9 (C-3), 62.6 (OCH3), 27.1,
26.3 (C(CH3)2); LSI-MS m/z 218 ([M + H]+, 70%); HRLSI-MS
calcd for C9H16NO5 ([M + H]+): 218.1031, found: 218.1028;
Anal. calcd for C9H15NO5: C, 49.76; H, 6.96; N, 6.45, found: C,
49.75; H, 7.11; N, 6.19.
1504, 1397, 1200, 1043, 967, 734, 701 cm−1
;
1H-NMR
(300 MHz, CD3OD) δ 7.42–7.33 (m, 5H, Ar-H), 5.14 (d, 1H,
J1,2 = 3.1 Hz, H-1α), 5.01–4.90 (m, 4H, CH2Ph), 4.39 (m, 1H,
H-1β), 4.33 (m, 1H, H-5α), 4.10–3.88 (m, 5H, H-2α, H-3α,
H-4α, H-4β, H-5β), 3.80–3.71 (m, 4H, H-6aα, H-6bα, H-6aβ,
H-6bβ), 3.46 (m, 2H, H-2β, H-3β), 2.05 (s, 6H, NAc); 13C-NMR
(75.5 MHz, CD3OD) δ 130.8, 130.7, 130.0, 129.7 (Ar-C), 98.8
(C-1β), 94.3 (C-1α), 77.6, 77.2 (CH2Ph), 74.9 (C-3β), 73.6
(C-2β), 72.6 (C-5β), 71.5 (C-3α), 71.1 (C-2α), 70.8 (C-4β), 70.3
(C-4α), 68.0 (C-5α), 20.6 (NAc); LSI-MS m/z 350 ([M + Na]+,
35%); HRLSI-MS calcd for C15H21NNaO7 ([M + Na]+):
350.1216, found: 350.1228.
5-Deoxy-1,2-O-isopropylidene-5-methoxyamino-α-D-xylofuranose
(29) and N-(5-deoxy-1,2-O-isopropylidene-α-D-xylofuranos-5-yl)-
N-methoxyamino-cyanoborane (31)
(1S,4R,5S,6R,7R)-2-Methoxy-8-oxa-2-azabicyclo[3.2.1]octane-
4,6,7-triol (23)
A solution of 6-deoxy-1,2:3,4-di-O-isopropylidene-6-methoxya-
mino-α-D-galactopyranose 11 (259 mg, 0.89 mmol) in 9 : 1
TFA–H2O (0.9 mL) was stirred at rt for 4 days. Then it was neu-
tralized with Amberlite IRA-68 resin, filtered and washed with
water and methanol. The combined filtrates were concentrated to
dryness and the residue was purified by column chromatography
(EtOAc → 5 : 1 EtOAc–MeOH) to give 23: 145 mg, 85%; RF
0.39 (5 : 1 EtOAc–MeOH); [α]2D3 +67 (c 0.8, MeOH); IR νmax
3364, 1662, 1444, 1197, 1139, 1046, 1022, 1003, 843, 794,
To a solution of (E- and Z)-1,2-O-isopropylidene-α-D-xylo-pen-
todialdo-1,4-furanose-5-O-methyloxime 27 (1.12 g, 5.17 mmol)
was added NaBH3CN (877 mg, 13.96 mmol, 2.7 equiv.), and the
mixture was stirred at rt for 7 h. Then it was concentrated to
dryness and the residue was dissolved in EtOAc (50 mL) and
washed with H2O (3 × 50 mL); the organic layer was dried over
MgSO4, filtered and the filtrate was concentrated to dryness. The
residue was purified by column chromatography (1 : 5 → 1 : 1
EtOAc–hexane) to give a separable mixture of 29 and 31.
1
716 cm−1; H NMR (500 MHz, CD3OD): δ 5.02 (ddd, 1H, J1,5
Eluted first was 29: 564 mg, 50%; RF 0.31 (1 : 2 EtOAc–
= 0.5 Hz, J1,3e = 1.3 Hz, J1,7 = 5.9 Hz, H-1, H-1), 4.20 (ddd,
1H, J5,7 = 1.0 Hz, J6,7 = 2.4 Hz, J1,7 = 5.9, H-7), 4.18 (d, 1H,
J5,6 ∼ 0 Hz, J6,7 = 2.4, H-6), 4.06 (ddd, 1H, J4,5 = 4.3 Hz, J3e,4
= 6.0 Hz, J3a,4 = 11.2 Hz, H-4), 3.94 (m, 1H, H-5), 3.52 (s, 3H,
hexane); [α]2D3 +130 (c 0.7, CH2Cl2); IR νmax 3398, 2981, 1567,
1201, 1054, 1006, 976, 849, 789, 635 cm−1
;
1H NMR
(300 MHz, CD3OD) δ 5.86 (d, 1H, J1,2 = 3.7 Hz, H-1), 4.48 (d,
1H, J2,3 ∼ 0 Hz, H-2), 4.10 (d, 1H, J3,4 = 2.7 Hz, H-3), 4.32 (m,
1H, H-4), 3.52 (s, 3H, OCH3), 3.19 (dd, 1H, J4,5a = 4.8 Hz,
J5a,5b = 13.5 Hz, H-5a), 3.06 (dd, 1H, J4,5b = 7.3 Hz, H-5b),
1.44, 1.29 (2s, 3H each, C(CH3)2); 13C-NMR (75.5 MHz,
CD3OD) δ 112.8 (C(CH3)2), 106.2 (C-1), 87.0 (C-2), 79.1 (C-4),
76.3 (C-3), 61.7 (OCH3), 51.0 (C-5), 27.2, 26.6 (C(CH3)2);
LSI-MS m/z 242 ([M + Na]+, 25%); HRLSI-MS m/z calcd for
C9H17NNaO5 ([M + Na]+): 242.1014, found: 242.0992.
Eluted second was 31: 133 mg, 10%; RF 0.23 (1 : 2 EtOAc–
hexane); [α]2D3 −64 (c 0.9, CH2Cl2); IR νmax 3394, 2991, 2938,
2439, 1459, 1371, 1226, 1075, 1008 cm−1; 1H NMR (300 MHz,
CD3OD) δ 5.92 (d, 1H, J1,2 = 3.4 Hz, H-1), 4.51 (d, 1H, J2,3 ∼ 0
Hz, H-2), 4.51 (dt, 1H, J3,4 = J4,5a = 2.8 Hz, J4,5b = 8.7 Hz,
H-4), 4.11 (d, 1H, H-3), 3.58 (dd, 1H, J5a,5b = 14.2 Hz, H-5a),
4.52 (s, 3H, OCH3), 3.26 (dd, 1H, H-5b), 1.47, 1.30 (s, 3H each,
C(CH3)2); 13C-NMR (75.5 MHz, CD3OD) δ 113.2 (C(CH3)2),
106.4 (C-1), 87.2 (C-2), 76.3 (C-4), 76.2 (C-4), 76.1 (C-3), 60.3
(C-5), 56.2 (OCH3), 27.3, 26.6 (C(CH3)2); CI-MS m/z 259
([M + H]+, 10%); HRCI-MS m/z calcd for C10H20BN2O5
([M + H]+): 259.1837, found: 259.1843.
OCH3), 3.34 (dddd, 1H, J1,3e = 1.3 Hz, J3e,5 = 1.9 Hz, J3e,4
=
6.0 Hz, J3e,3a = 14.9 Hz, H-3e), 2.99 (dd, 1H, J3a,4 = 11.2 Hz,
J3e,3a = 14.9 Hz, H-3a); 13C-NMR (75.5 MHz, CD3OD) δ 92.9
(C-1), 86.0 (C-5), 81.2 (C-7), 77.3 (C-6), 63.3 (C-4), 60.2
(OCH3), 53.2 (C-3); CIMS m/z 192 ([M + H]+, 100%);
HRCI-MS calcd for C7H14NO5 ([M + H]+): 192.0872, found:
192.0866; Anal. calcd for C7H13NO5: C, 43.98; H, 6.85; N,
7.33, found: C,43.95; H, 7.00; N, 7.20.
(E- and Z)-1,2-O-Isopropylidene-α-D-xylo-pentodialdo-1,4-
furanose-5-O-methyloxime (27E and 27Z)
To a solution of 1,2-O-isopropylidene-α-D-xylo-pentodialdo-l,4-
furanose 25 (425 mg, 2.26 mmol) in pyridine (4 mL) was added
O-methylhydroxylamine hydrochloride (226 mg, 2.71 mmol, 1.2
equiv.) and the mixture was stirred at rt for 16 h. Then it was
concentrated to dryness and the residue was dissolved in EtOAc
(50 mL) and washed with H2O (3 × 30 mL). The organic layer
was dried over MgSO4 and filtered, and the filtrate was concen-
trated to dryness, and the residue was purified by column chrom-
atography (1 : 10 → 1 : 2 EtOAc–hexane) to give 27 as a 2 : 1
E/Z diastereoisomeric mixture, as deduced from 1H NMR.
(2R,3R,4S,5R)-1-Benzyloxy-2,3,4,5-tetrahydroxypiperidine (33)
Yield: 440 mg, 90%; RF: 0.71 (27E) and 0.60 (27Z) (1 : 2
To a solution of 5-benzyloxyamino-5-deoxy-1,2-O-isopropyli-
dene-α-D-xylofuranose 28 (100 mg, 0.32 mmol), in a 2 : 1
CH3CN–H2O mixture (3 mL) was added Amberlite IR-120(H+)
resin (135 mg) and the mixture was stirred at rt for 2 h. Then,
EtOAc–hexane); [α]D26 −64 (c 1.0, CH2Cl2); IR νmax 3398, 2981,
2938, 1381, 1254, 1206, 1158, 1075, 1012, 852, 779, 639 cm−1
;
1H NMR (300 MHz, CDCl3) δ 4.60–4.55 (m, 2H, H-2); 27E:
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 4220–4228 | 4227

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3 F. Nicotra, L. Cipolla, F. Peri, B. La Ferla and C. Redaelli, Adv. Carbo-
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the resin was filtered off, and the residue was concentrated to
dryness and crystallized from CH3CN, to give 33 in the α-pyra-
nose form exclusively. Yield: 25.2 mg, 31%; RF 0.10 (AcOEt);
1
IR νmax 3409, 119, 1061, 1012, 881, 745, 702 cm−1; H NMR
5 R. W. Gantt, P. Peltier-Pain and J. S. Thorson, Nat. Prod. Rep., 2011, 28,
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(500 MHz, DMSO-d6 and a drop of D2O) δ 7.31–7.26 (m, 5H,
Ar-H), 4.59 (d, 1H, J2,3 = 3.0 Hz, H-2), 4.05 (s, 2H, PhCH2),
3.25–3.22 (m, 2H, H-4, H-5), 3.13 (dd, 1H, J3,4 = 9.5 Hz, H-3),
2.86 (m, 2H, H-6a, H-6b); 13C-NMR (125.5 MHz, DMSO-d6
and a drop of D2O) δ 138.4, 129.4, 129.0, 128.6 (Ar-C), 84.5
(C-2), 74.3 (PhCH2), 74.0 (C-4), 71.4 (C-3), 69.1 (C-5), 52.1
(C-6); LSIMS m/z 278 ([M + Na]+ 2%); HRLSI-MS calcd for
C12H17NNaO5 [M + Na]+: 278.5632, found: 278.5124.
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Acknowledgements
We thank the Dirección General de Investigación of Spain
(CTQ2008 02813) and Junta de Andalucía (FQM 134) for
financial support. E.M.-C. also thanks MICINN for the award of
a fellowship.
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4228 | Org. Biomol. Chem., 2012, 10, 4220–4228
This journal is © The Royal Society of Chemistry 2012