Polyhydroxylated homoazepanes and 1-deoxy-homonojirimycin analogues: Synthesis and glycosidase inhibition study

Article abstract of DOI:10.1039/b609000a

The Johnson-Claisen rearrangement of d-gluco and l-ido-derived allylic orthoesters afforded γ,δ-unsaturated ester that on ester reduction, epoxidation, regioselective oxirane opening by sodium azide and hydrogenation led to sugar amino alcohols - immediat

Full text of DOI:10.1039/b609000a

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Polyhydroxylated homoazepanes and 1-deoxy-homonojirimycin analogues:
synthesis and glycosidase inhibition study†
Shankar D. Markad,a Narayan S. Karanjule,a Tarun Sharma,b Sushma G. Sabharwalb and Dilip D. Dhavale*a
Received 26th June 2006, Accepted 7th August 2006
First published as an Advance Article on the web 22nd August 2006
DOI: 10.1039/b609000a
The Johnson–Claisen rearrangement of D-gluco and L-ido-derived allylic orthoesters afforded
c,d-unsaturated ester that on ester reduction, epoxidation, regioselective oxirane opening by sodium
azide and hydrogenation led to sugar amino alcohols—immediate precursors for
1-deoxy-homonojirimycin 3a,b and polyhydroxylated homoazepanes 4a,b. Our synthetic approach and
glycosidase inhibitory activity is reported.
ring oxygen of D-glucose is replaced by a nitrogen atom,3
Introduction
whereas in 1-deoxynojirimycin 1b (and other 1-deoxyazasugars),
Glycobiology is an emerging research field at the frontier of
the hemiacetalic functionality is replaced by an aminomethylene
chemistry, enzymology and biology. Many important biological
group. The latter modification improved the glycosidase inhibitory
activity and some of them are therapeutically useful.3b,4–6 In
iminosugars the absolute configuration at each stereocentre is
crucial for its biological activity and therefore many stereoselective
syntheses of 1-deoxynojirimycin 1b and analogues have been
described to date.7,8
processes, wherein glycosidases play a crucial role, are being un-
covered leading to the possibility of finding new therapeutic targets
for the treatment of various diseases such as obesity, diabetes, viral
infection including AIDS and cancer.1 Most glycosidase inhibitors
share two common structural features: (i) a basic nitrogen atom
that at physiological pH mimics the positive charge formed during
the hydrolysis of the glycosidic bond and (ii) an array of hydroxyl
groups in a conformationally restricted motif which selectively
fit into the enzyme active site.2 The iminosugar structure is the
obvious choice as their polyhydroxylated nitrogen containing ring
skeleton is identical to that of sugars and thus mimics the enzyme.
The parent molecule of iminosugars (also called as azasugars)
namely nojirimycin 1a (Fig. 1) is the compound in which the
The one carbon ring homologues of 1b are polyhydroxylated
azepanes 2a,b and 4c,d (Fig. 1)9–11 which are glycosidase inhibitors
and potential DNA minor groove binding ligands (MGBL) due to
the flexibility of the seven-membered ring.12 Thus, the development
of new azasugars and azepanes opened a dynamic research
field at the interface between glycobiology and synthetic organic
chemistry. In this regard, we have recently reported the synthesis
of tetrahydroxy perhydroazaazulenes.13 Our approach hinges on
the Johnson–Claisen rearrangement of D-glucose derived allylic
alcohols 5a,b using trimethyl orthoacetate and propionic acid,
to give c,d-unsaturated ester 6 (Scheme 1). Conversion of methyl
ester 6 to an azidomethyl group and epoxidation gave 7. Reductive
5-exo-tet-cyclization of 7 under Staudinger conditions led to 8
that on opening of the 1,2-acetonide functionality followed by
reductive aminocyclization afforded perhydroazaazulenes 9.
Fig. 1 Nojirimycin and azepane analogues.
aGarware Research Centre, Department of Chemistry, University of Pune,
Pune, 411 007, India. E-mail: ddd@chem.unipune.ernet.in; Fax: +91-20-
2569-1728; Tel: +91-20-2560-1225-584
Scheme 1 Synthesis of perhydroazaazulenes.
bDivision of Biochemistry, Department of Chemistry, University of Pune,
Pune, 411 007, India
In continuation of our investigations in the area of
iminosugars,14 we thought of exploiting the Johnson–Claisen rear-
rangement product 6 in the synthesis of an altogether new 1-deoxy-
D-altro-homonojirimycin 3a, 1-deoxy-L-gluco-homonojirimycin
3b and the corresponding ring homologated polyhydroxylated
† Electronic supplementary information (ESI) available: The detailed
experimental procedures for preparation of compounds 11, 12a,b, 13a,b
and 14a,b and copies of 1H and 13C NMR spectra of compounds 4a, 4b,
4a·HCl, 4b·HCl, 3a, 3b, 3a·HCl, 3b·HCl, 11, 12a,b, 13a,b, 14a,b and 15a,b.
See DOI: 10.1039/b609000a
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homoazepanes 4a and 4b, and studied their glycosidase inhibitory
activity. Our results are described herein.
Results and discussion
The c,d-unsaturated ester 6 was obtained by the Johnson–Claisen
rearrangement of D-glucose derived allylic alcohols 5a and/or 5b
in 90% yield. Reduction of the ester functionality in 6 by LAH
followed by benzylation gave benzyl ether 11 which on treatment
with m-CPBA afforded a diastereomeric mixture of epoxides 12a
and 12b in a 2 : 1 ratio. The appreciable difference in the Rf values
allowed us to separate the epoxides by column chromatography.
The formation of 12a as a major product could be due to the
six-membered hydrogen bonding of m-CPBA with the oxygen of
C3-OBn and the delivery of oxygen from the b-face; whereas the
five-membered hydrogen bonding of m-CPBA with the furanose
oxygen and attack from the a-face gave 12b as a minor product.
Based on this the absolute configurations at the newly generated
C5,C6-stereocentres were assigned as 5R,6S for 12a and 5S,6R for
12b.15
The utility of 12a,b was initially demonstrated in the formation
of homoazepanes 4a,b respectively. Thus, regioselective epoxide
ring opening of 12a and 12b at C6, with lithium azide in DMF,
afforded exclusively 6-azido compounds 13a and 13b, respectively,
in high yield16 (Scheme 2). The appearance of a double doublet
at ∼d 4.2 corresponding to H5 and a multiplet at d 3.42–3.58
for H6 in 13a/13b indicated the regioselective formation of 6-
azido compounds. In the subsequent step, removal of –OBn
groups and reduction of the azide functionality in 13a, using
ammonium formate in the presence of 10% Pd/C, followed
by selective Cbz protection afforded N-Cbz protected amino
alcohol 14a as a white solid in 76% yield. Compound 14a on
reaction with TFA–water (to cleave the 1,2-acetonide function-
ality) followed by reductive aminocyclization, using ammonium
formate in the presence of 10% Pd/C in methanol, followed
by chromatographic purification afforded 1,6,7,8-tetradeoxy-1,6-
imino-(2S,3R,4R,5R,6R)-L-glycero-D-gluco-nonitol 4a as a thick
oil. The free base was treated with MeOH–HCl to give 4a as
a hydrochloride salt. The same sequence of reactions with 12b
gave 1,6,7,8-tetradeoxy-1,6-imino-(2S,3R,4R,5S,6S)-D-glycero-L-
ido-nonitol 4b and its hydrochloride salt 4b·HCl (Scheme 2).
Compounds 13a/13b and 14a/14b were characterized by spectral
and analytical techniques and the data were found to be in
agreement with the structures.
Scheme 2 Reagents and conditions: (a) LAH, THF, 0 ◦C, 1 h; (b) NaH,
BnBr, TBAI, THF, 0 ◦C to rt, 8 h; (c) m-CPBA, CH2Cl2, 0 ◦C to 25 ◦C,
24 h; (d) NaN3, LiCl, DMF, 100 ◦C, 8 h; (e) (i) HCOONH4, 10% Pd/C,
MeOH, 80 ◦C, 1 h; (ii) CbzCl, NaHCO3, MeOH–H2O, 0 ◦C to rt, 12 h; (f)
(i) TFA–H2O (2 : 1), 0 ◦C to rt, 2.5 h; (ii) HCOONH4, 10% Pd/C, MeOH,
80 ◦C, 1 h; (g) MeOH–HCl, rt, 3 h.
Thus, targeting the synthesis of 1-deoxy-homonojirimycin ana-
logues 3a,b, the free hydroxyl groups in 14a were protected as
acetates by treatment with acetic anhydride and pyridine to afford
triacetyl derivative 15a (Scheme 3). In the next step, cleavage of the
1,2-acetonide functionality in 15a (TFA–water), treatment with
Although the spectral data of homoazepanes 4a and 4b were
found to be consistent with the structures, the configurational
assignments at each stereocentre in 4a and 4b were tentatively
made, stereocentres C2/C3/C4 are the same as in the D-glucose
and C5/C6 by knowing the stereochemistry of epoxides 12a
1
and 12b. The H NMR spectra of 4a and 4b did not give any
supportive information on the conformational and configura-
tional assignment due to the flexibility in seven-membered ring
systems.9–11 As an alternative, we thought of converting 12a/12b
to the corresponding six-membered piperidine derivatives 3a/3b
(by chopping the anomeric carbon), wherein the configurational
assignment at each carbon atom will be clearly evident from
the six-membered cyclic chair structure, by either 4C1 or 1C4
conformation, and the same configurational assignments would
be applicable to the homoazepanes 4a,b.
Scheme 3 Reagents and conditions (a) Ac2O, Py, DMAP, 8 h; (b) (i)
TFA–H2O (2 : 1), 0 ◦C to rt, 2.5 h; (ii) NaIO4, acetone–water (9 : 1),
0 ◦C, 30 min; (iii) H2, 10% Pd/C, MeOH, 80 psi, 12 h; (iv) HCl–CH3OH
(9 : 1), 80 ◦C, 3 h; (c) aq. NH3, MeOH, rt, 15 min.
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sodium metaperiodate (to cleave the anomeric carbon atom) and
hydrogenation in the presence of 10% Pd/C in methanol afforded
a mixture of tetra-O-acetyl- and tri-O-acetyl-O-formyl-1-deoxy-
D-altro-homonojirimycins.17 One pot removal of O-acetyl and O-
formyl groups using methanolic hydrogen chloride afforded the
hydrochloride salt of the 1-deoxy-D-altro-homonojirimycin 3a as
a sticky gum, which on treatment with methanolic ammonia and
purification afforded 3a as a thick liquid.
Similarly, 14b gave 1-deoxy-L-gluco-homonojirimycin 3b as a
thick liquid. Compound 15b was characterized by spectral and
analytical techniques and the data were found to be in agreement
with the structure.
constant of 12.6 Hz indicated the axial orientation of H2. H3
and H4 appeared as two triplets with large coupling constants
(J2,3 = J3,4 = J4,5 = 9.6 Hz) indicating the relative axial orientation
of these protons and the 1C4 conformation of 3b with 4S,5S
absolute configurations at the newly generated stereocentres. Thus,
the stereochemistry assigned to 3a and 3b on the basis of the
1
stereochemistry of 15a and 15b was confirmed by the H NMR
of 3a and 3b. Because the formation of 3a and 3b involves the
loss of the corresponding anomeric carbon of 15a and 15b, the
configurational assignments at each carbon atom of 3a and 3b
provided proof for the stereochemistry of homoazepanes 4a and
4b at four stereocentres.
Conformational analysis
Glycosidase inhibitory study
4
1
The six-membered iminosugars are known to exist in C1 or C4
The glycosidase inhibitory activity against a-glucosidase, b-
glucosidase, b-galactosidase, and a-mannosidase for compounds
3a,b and 4a–d was studied and the IC50 values are summarized
in Table 1. Compounds 3a and 3b were found to be selective
b-glucosidase inhibitors. Asano et al.18 have reported 1-deoxy-
D-altro-nojirimycin 3c as a non-selective glycosidase inhibitor.
However, the structurally similar, two carbon homologated 1-
deoxy-D-altro-homonojirimycin 3a showed selective b-glucosidase
inhibition in millimolar concentration. Chida et al.19 have reported
1-deoxy-L-gluco-nojirimycin 3d with an IC50 value of 74 lg
mL−1 (0.454 mM) against b-glucosidase, while 1-deoxy-L-gluco-
homonojirimycin 3b showed selective b-glucosidase inhibition
(IC50 = 45.0 lM) with a ten fold increase in the activity. This
effect could be attributed to the two carbon homologation at
C5. The synthesis of polyhydroxylated azepanes 4c and 4d was
reported earlier by us.11b Herein we report their biological activity
and compare their values with the activities of newly synthesised
two carbon homologated compounds 4a and 4b. Compound 4a
was found to be a a-glucosidase inhibitor, whereas 4c inhibit both
b-glucosidase and b-galactosidase in millimolar concentrations.
Compound 4b inhibit a-glucosidase and b-glucosidase whereas
compound 4d is active against b-glucosidase and b-galactosidase
in millimolar concentrations.
conformations.11b In order to determine the conformations of
1
3a and 3b, we studied their H NMR spectra and the coupling
constant information was obtained by decoupling experiments. In
the 1H NMR spectrum of 3a, the appearance of two doublets of
doublets, corresponding to H1a and H1e with one large geminal
coupling constant (J1a,1e = 13.8 Hz) and small vicinal coupling
constants (J1a,2e = 3.6 Hz and J1e,2e = 2.7 Hz) indicated the
equatorial orientation of H2 and this fact was confirmed by the
appearance of H2 as a doublet of doublets of doublets with small
coupling constants (J2e,1a = 4.8 Hz, J2e,1e = 2.7 Hz and J2e,3e
=
3.0 Hz). The relative disposition of H2 and H3 is trans as in the
starting compound 15a the corresponding H3 and H4 are trans
and the same stereochemistry is maintained in 3a. Therefore, H3
is assumed to be equatorial and confirmed by its appearance as
a doublet of doublets with small J values (J3e,4a = 4.8 Hz and
J3e,2e = 3.0 Hz). H4, however, appeared as doublet of doublets
with one large coupling constant (J4a,5a = 9.0 Hz) indicating a
di-axial relation between H4 and H5. The doublet of triplets
corresponding to H5 with a large (J4a,5a = 9.0 Hz) coupling
constant confirmed the di-axial orientation of H4/H5. This fact
clearly indicated the 4C1 conformation (Fig. 2) of 3a with 4R,5R
absolute configurations at the newly generated stereocentres. In
the 1H NMR spectrum of 3b, the appearance of one of the
doublet of doublets corresponding to H1 with a large coupling
Conclusions
We have demonstrated the utility of c,d-unsaturated ester 6 em-
ploying Johnson–Claisen rearrangement for the synthesis of ho-
moazepanes 4a,b and 1-deoxy-homonojirimycin 3a,b analogues,
which involves ester reduction, benzyl ether protection, epoxida-
tion, regioselective nucleophilic ring opening by azide, hydrogenol-
ysis and N-Cbz protection protocol. The ready availability
Fig. 2 Conformations of 3a,b.
Table 1 IC50 values in mMa
Compounds
a-Glucosidase (yeast)
b-Glucosidase (almonds)
b-Galactosidase (bovine testes)
a-Mannosidase (jack bean)
4a
4c
4b
4d
3a
3b
10.4
ND
17.3
ND
NI
602.2
21.6
7.3
69.1
7.6
NI
44.3
NI
45.8
NI
NI
NI
ND
NI
48.4
NI
NI
NI
0.045
a NI: No inhibition under our assay conditions. ND: Not determined. Values are the average of three sets of assays performed.
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of reagents, high yielding steps and good regioselectivity in the
process give easy access for the synthesis of different types of
otherwise difficult azasugars required for glycosidase inhibition
study. Another interesting aspect of the present route is that
we have converted D-glucose to 3b, which is an L-glucose. Thus
we have converted D-glucose to L-glucose by simple organic
transformations and chopping of the anomeric carbon atom,
which alters the numbering. We also studied compounds for their
glycosidase inhibition and found that compound 3b is a selective
b-glucosidase inhibitor in the lM range and compounds 3a, 4a
and 4b are selective b-glucosidase inhibitors in the mM range.
1,6,7,8-Tetradeoxy-1,6-imino-(2S,3R,4R,5S,6S)-D-glycero-L-
ido-nonitol (4b). Compound 14b (0.10 g, 0.243 mmol) was
reacted with TFA–H2O (3 cm3, 2 : 1) followed by ammonium
formate (0.092 g, 1.46 mmol) and 10% Pd/C (0.05 g) as described
in the synthesis of 4a to afford 4b (0.046 g, 90%) as a sticky
gum (Found: C, 48.85; H, 8.65. Calcd for C9H19NO5: C, 48.86;
H, 8.66%); Rf 0.52 (methanol); [a]2D5 +2.7 (c 0.75 in CH3OH);
mmax.(nujol)/cm−1 3200–3600 (broad band); dH (300 MHz; D2O)
1.58–1.89 (3H, m, H7a,b and H8a), 1.98–2.12 (1H, m, H8b), 3.27
(1H, dd, J 14.1 and 6.6 Hz, H1a) 3.35 (1H, dd, J 14.1 and 3.3 Hz,
H1b), 3.24–3.36 (1H, m, H6), 3.65 (2H, t, J 6.3 Hz, CH2OH),
3.58–3.67 (1H, m, H3), 3.69 (1H, t, J 7.5 Hz, H4), 3.78 (1H, t,
J 7.5 Hz, H5), 4.01 (1H, ddd, J 9.6, 6.6 and 3.3 Hz, H2); dC
(75 MHz; D2O) 29.9, 29.7 (C7/C8), 48.8, 62.5 (C1/C6), 63.6,
70.4, 73.5, 77.7, 78.1 (C2/C3/C4/C5/C9).
Experimental
General methods
1,6,7,8-Tetradeoxy-1,6-imino-(2S,3R,4R,5R,6R)-L-glycero-D-
gluco-nonitol hydrochloride (4a·HCl). To a solution of 4a in
methanol (2 cm3) was added a drop of concentrated hydrochloric
acid and the resulting reaction mixture was stirred for 15 min
Melting points were recorded with a melting point apparatus and
are uncorrected. IR spectra were recorded with FTIR as a thin film
or in nujol mull or using KBr pellets and are expressed in cm−1. 1H
(300 MHz) and 13C (75 MHz) NMR spectra were recorded using
CDCl3 and/or D2O as solvent(s). Chemical shifts are reported
in d units (ppm) with reference to TMS as an internal standard
and J values are given in Hz. Decoupling and DEPT experiments
confirmed the assignments of the signals. Elemental analyses were
carried out with a C,H analyzer. Optical rotations were measured
using a polarimeter at 25 ◦C. Thin layer chromatography was
performed on pre-coated plates (0.25 mm, silica gel 60 F254).
Column chromatography was carried out with silica gel (100–
200 mesh). The reactions were carried out in oven-dried glassware
under dry N2. Methanol, pyridine and THF were purified and
dried before use. Distilled n-hexane and ethyl acetate were used for
column chromatography. Sodium azide, lithium chloride, benzyl
chloroformate and m-chloroperbenzoic acid were purchased from
Merck. 10% Pd/C was purchased from Aldrich and/or Fluka.
After decomposition of the reaction with water, the work-up
involves washing of the combined organic layers with water, then
brine, drying over anhydrous sodium sulfate and evaporation of
solvent under reduced pressure.
◦
at 25 C. The solvent was evaporated on a rotary evaporator to
afford 4a·HCl as a semisolid in quantitative yield (Found: C, 41.91;
H, 7.81. Calcd for C9H20ClNO5: C, 41.94; H, 7.82%); [a]2D5 +46.7
(c 0.3 in CH3OH); mmax.(nujol)/cm−1 3200–3600 (broad band); dH
(300 MHz; D2O) 1.64–1.86 (3H, m, H7a,b and H8a), 1.88–2.02
(1H, m H8b), 3.67 (2H, t, J 4.5 Hz, CH2OH), 3.47–3.56 (1H, m,
H1a), 3.57–3.74 (3H, m, H1b, H5 and H6), 3.91–4.25 (2H, m, H3
and H2), 4.14 (1H, d, J 5.1 Hz, H4); dC (75 MHz; D2O) 26.5, 28.1
(C7/C8), 44.2, 59.9, 61.0 (C1/C6/C9), 69.7, 71.3, 73.1 (strong)
(C2/C3/C4/C5).
1,6,7,8-Tetradeoxy-1,6-imino-(2S,3R,4R,5S,6S)-D-glycero-L-
ido-nonitol hydrochloride (4b·HCl). The reaction of compound
4b with concentrated hydrochloric acid as described in the prepa-
ration of 4a·HCl afforded 4b·HCl in quantitative yield (Found: C,
41.97; H, 7.79. Calcd for C9H20ClNO5: C, 41.94; H, 7.82%); [a]D25
+4.0 (c 0.5 in CH3OH); mmax.(nujol)/cm−1 3200–3600 (broad band);
dH (300 MHz; D2O) 1.74–1.93 (3H, m, H7a,b and H8a), 2.01–2.14
(1H, m, H8b), 3.32 (1H, dd, J 14.4 and 6.9 Hz, H1a), 3.33–3.41
(1H, m, H6), 3.40 (1H, dd, J 14.4 and 3.0 Hz, H1b), 3.66 (2H,
t, J 6.0 Hz, CH2OH), 3.69 (1H, d, J 7.5 Hz, H3), 3.73 (1H, d,
J 7.5 Hz, H5), 3.83 (1H, t, J 7.5 Hz, H4), 4.05 (1H, ddd, J 9.3,
6.9 and 3.0 Hz, H2); dC (75 MHz; D2O) 26.7, 27.4 (C7/C8), 46.2,
60.1, 61.3 (C1/C6/C9), 67.6, 70.8, 75.7, 75.9 (C2/C3/C4/C5).
1,6,7,8-Tetradeoxy-1,6-imino-(2S,3R,4R,5R,6R)-L-glycero-D-
gluco-nonitol (4a). A solution of 14a◦(0.10 g, 0.243 mmol) in
TFA–H2O (3 cm3, 2 : 1) was stirred at 25 C for 2.5 h. Trifluroacetic
acid was co-evaporated with benzene to furnish a thick liquid. To a
solution of the above product in methanol was added ammonium
formate (0.092 g, 1.46 mmol) and 10% Pd/C (0.05 g) and the
reaction mixture was refluxed for an hour. The catalyst was filtered
through a pad of celite and washed with methanol. The filtrate was
concentrated to get a thick liquid, which on column purification
(chloroform–methanol–25% aqueous ammonia = 8 : 1.9 : 0.1)
afforded 4a (0.048 g, 94%) as a semisolid (Found: C, 48.88; H,
8.64. Calcd for C9H19NO5: C, 48.86; H, 8.66%); Rf 0.58 (methanol);
[a]D25 +3.1 (c 0.65 in CH3OH); mmax.(nujol)/cm−1 3200–3600 (broad
band); dH (300 MHz; D2O) 1.62–1.81 (3H, m, H7a,b and H8a),
1.82–1.98 (2H, m, H8b and H1a), 3.30–3.38 (2H, m, H6 and
H1a), 3.45 (1H, dd, J 6.6, 4.8 Hz, H4), 3.64 (2H, t, J 5.4 Hz,
CH2OH), 3.86–3.97 (2H, m, H2/H5), 4.11 (1H, d, J 5.1 Hz,
H3); dC (75 MHz; D2O) 25.6, 28.9 (C7/C8), 46.6, 62.2, 63.2
(C1/C6/C9), 72.1, 73.7, 75.1, 75.2 (C2/C3/C4/C5).
3,5,9-Tri-O-acetyl-6-(N-benzoxycarbonylamino)-6,7,8-trideoxy-
1,2-O-isopropylidene-a-D-glycero-D-gluco-nona-1,4-furanose (15a).
To an ice-cooled solution of 14a (0.50 g, 1.22 mmol) in
dry pyridine (1.5 cm3) was added acetic anhydride (2.48 g,
24.33 mmol). After stirring for 8 h at room temperature, ice-water
(2 cm3) was added and the reaction mixture was extracted with
chloroform (3 × 15 cm3). Usual workup and chromatographic
purification (n-hexane–ethyl acetate = 9 : 1) afforded triacetyl
derivative 15a (0.64 g, 98%) as a white solid (Found: C, 58.11;
H, 6.59. Calcd for C26H35NO11: C, 58.09; H, 6.56%); Rf 0.49
(20% ethyl acetate–n-hexane); [a]2D5 +20.7 (c 0.68 in CHCl3); mp
110–112 ◦C (ethyl acetate–n-hexane = 1 : 9); mmax.(KBr)/cm−1
3300–3400 (broad band), 1742, 1671, 1529, 1450, 1375 and 1240;
dH (300 MHz; CDCl3; Me4Si) 1.31 (3H, s, CH3), 1.50 (3H, s, CH3),
1.61–1.85 (4H, m, H7a,b and H8a,b), 2.00 (3H, s, COCH3), 2.04
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(3H, s, COCH3), 2.05 (3H, s, COCH3), 4.04–4.16 (3H, m, H9a,b
and H6), 4.32 (1H, dd, J 9.6 and 3.0 Hz, H4), 4.44 (1H, d, J
3.6 Hz, H2), 4.89 (1H, d, J 9.6 Hz, exchanges with D2O, NH),
5.05 (1H, dd, J 9.6 and 2.7 Hz, H5), 5.09 (2H, ABq, J 12.3 Hz,
OCH2Ph), 5.28 (1H, d, J 3.0 Hz, H3), 5.90 (1H, d, J 3.6 Hz, H1),
7.25–7.35 (5H, m, ArH’s); dC (75 MHz; CDCl3; Me4Si) 20.7, 20.8,
21.0 (3 × COCH3), 25.4, 26.2 (2 × CH3), 26.7, 26.8 (C7/C8),
52.5, 63.9 (C6/C9), 66.8 (C4), 71.3 (OCH2Ph), 75.0, 77.0, 82.7
(C2/C3/C5), 105.0 (C1), 112.2 (OCO), 127.8 (strong), 128.3
(strong), 136.2 (ArC’s), 156.0 (NHCO), 169.4, 169.8, 170.9 (3 ×
COCH3).
4.14–4.21 (1H, m, H2); dC (75 MHz; D2O) 25.7, 27.5 (C6/C7),
44.3, 55.5 (C1/C5), 61.2 (C9), 66.2, 67.2, 68.8 (C2/C3/C4).
1,5,6,7-Tetradeoxy-1,5-imino-(2R,3S,4S,5S)-L-gluco-octitol hy-
drochloride (3b·HCl). The reaction of 15b (0.20 g, 0.37 mmol)
with TFA–H2O (2 : 1, 3 cm3) and NaIO4 (0.093 g, 0.43 mmol)
followed by hydrogenation in the presence of 10% Pd/C (0.08 g),
using the same reaction conditions as described in the synthesis
of 3a·HCl afforded 3b·HCl (0.048 g, 56% overall) as a semisolid
(Found: C, 42.23; H, 7.99. Calcd for C8H18ClNO4: C, 42.20;
H, 7.97%); Rf 0.62 (methanol); [a]2D5 −22.2 (c 0.45 in CH3OH);
mmax.(nujol)/cm−1 3200–3600 (broad band); dH (300 MHz; D2O)
1.56–1.80 (3H, m, H6a,b and H7a), 1.94–2.14 (1H, m, H7b),
2.93 (1H, t, J 12.0 Hz, H1a), 3.14 (1H, ddd, J 9.6, 6.9 and
3.6 Hz, H5), 3.45 (1H, t, J 9.6 Hz, H3), 3.47 (1H, dd, J 12.0
and 5.1 Hz, H1b), 3.48 (1H, t, J 9.6 Hz, H4), 3.62 (2H, t, J 5.7 Hz,
CH2OH), 3.77 (1H, ddd, J 12.0, 9.6 and 5.1 Hz, H2); dC (75 MHz;
D2O) 28.3, 29.5 (C6/C7), 48.6 (C5), 61.4, 63.5, 69.3, 73.5, 78.5
(C1/C2/C3/C4/C8).
3,5,9-Tri-O-acetyl-6-(N-benzoxycarbonylamino)-6,7,8-trideoxy-
1,2-O-isopropylidene-b-L-glycero-L-ido-nona-1,4-furanose (15b).
The reaction of 14b (0.50 g, 1.22 mmol) with acetic anhydride
(2.48 g, 28.72 mmol) and dry pyridine (1.5 cm3) as described in
the synthesis of 15a afforded 15b (0.63 g, 95%) as a thick liquid
(Found: C, 58.07; H, 6.53. Calcd for C26H35NO11: C, 58.09; H,
6.56%); Rf 0.44 (20% ethyl acetate–n-hexane); [a]2D5 −5.0 (c 0.4 in
CHCl3); mmax.(neat)/cm−1 3300–3500 (broad band), 1735, 1600,
1400 and 1377; dH (300 MHz; CDCl3; Me4Si) 1.32 (3H, s, CH3),
1.52 (3H, s, CH3), 1.42–1.52 (1H, m, H7a), 1.57–1.69 (3H, m,
H7b and H8a,b), 2.05 (3H, s, COCH3), 2.07 (3H, s, COCH3),
2.09 (3H, s, COCH3), 3.79–3.89 (1H, m, H6), 4.06 (2H, t, J
6.3 Hz, CH2OAc), 4.43 (1H, dd, J 6.0 and 3.9 Hz, H4), 4.52
(1H, d, J 3.9 Hz, H2), 5.06 (2H, s, OCH2Ph), 5.11 (1H, d, J 9.3,
exchanges with D2O, NH), 5.17 (1H, dd, J 6.0 and 4.2 Hz, H5),
5.19 (1H, d, J 3.9 Hz, H3), 5.90 (1H, d, J 3.9 Hz, H1), 7.26–7.34
(5H, m, ArH’s); dC (75 MHz; CDCl3; Me4Si) 20.8, 21.0, 21.1 (3 ×
COCH3), 25.1, 26.4, 26.9 (strong) (2 × CH3 and C7/C8), 51.4,
51.5, 63.7 (C5/C6/C9), 66.8 (C4), 72.3 (OCH2Ph), 77.2, 83.8
(C2/C3), 104.3 (C1), 112.5 (OCO), 127.9 (strong), 128.0, 128.4
(strong), 136.3 (ArC’s), 155.9 (NHCO), 169.9, 170.1, 170.9 (3 ×
COCH3).
1,5,6,7-Tetradeoxy-1,5-imino-(2R,3S,4R,5R)-D-altro-octitol (3a).
A solution of 3a·HCl (0.05 g, 0.18 mmol) in methanol and 25%
aqueous ammonia (2:1, 3 cm3) was stirred at room temperature
for 15 min. The solvent was evaporated on a rotary evaporator
to afford a thick liquid, which on purification by column chro-
matography (chloroform–methanol–25% aqueous ammonia = 8 :
1.9 : 0.1) afforded 3a (0.035 g, 83%) as a thick liquid (Found:
C, 50.27; H, 8.97. Calcd for C8H17NO4: C, 50.25; H, 8.96%); Rf
0.49 (methanol); [a]D25 +26.7 (c 0.68 in CH3OH); mmax.(nujol)/cm−1
3200–3600 (broad band); dH (300 MHz; D2O) 1.48–1.82 (3H, m,
H6a,b and H7a), 1.83–1.94 (1H, m, H7b), 2.89 (1H, dd, J 13.8
and 3.6 Hz, H1a), 3.00 (1H, dt, J 9.0 and 4.2 Hz, H5), 3.09 (1H,
dd, J 13.8 and 2.7 Hz, H1b), 3.64 (2H, t, J 6.3 Hz, CH2OH), 3.77
(1H, dd, J 9.0 and 3.0 Hz, H4), 3.92 (1H, dd, J 4.8 and 3.0 Hz,
H3), 3.97 (1H, ddd, J 4.8, 3.6 and 2.7 Hz, H2); dC (75 MHz; D2O)
26.5, 27.9 (C6/C7), 44.5, 55.2 (C1/C5), 61.6 (C8), 68.1, 69.1, 70.1
(C2/C3/C4).
1,5,6,7-Tetradeoxy-1,5-imino-(2R,3S,4R,5R)-D-altro-octitol hy-
drochloride (3a·HCl). A solution of 15a (0.20 g, 0.37 mmol) in
TFA–H2O (2 : 1, 3 cm3) was stirred at 25 ◦C for 2.5 h. Trifluroacetic
acid was co-evaporated with benzene to furnish a thick liquid. To
a cooled solution of hemiacetal (0.18 g, 0.36 mmol) in acetone–
water (10 cm3, 5 : 1) was added sodium metaperiodate (0.09 g,
0.43 mmol) and stirred for half an hour. The reaction mixture
was quenched by adding ethylene glycol (0.1 cm3). Acetone was
removed under reduced pressure and the residue obtained was
extracted with chloroform (3 × 15 cm3). Usual workup and column
purification (n-hexane–ethyl acetate = 8 : 2) afforded aldehyde,
which was directly subjected for hydrogenation in methanol (8 cm3)
and 10% Pd/C (0.08 g) under 80 psi for 12 h. The catalyst was
filtered through a pad of celite, washed with methanol and the
filtrate was concentrated to get a gummy solid that was directly
subjected for deacetylation using MeOH–HCl (5 cm3, 9 : 1) under
reflux conditions for 3 h. The reaction mixture was cooled to
room temperature and freeze-dried to get 3a·HCl (0.051 g, 60%
overall) as a semisolid (Found: C, 42.21; H, 7.96. Calcd for
C8H18ClNO4: C, 42.20; H, 7.97%); Rf 0.64 (methanol); [a]2D5 +29.6
(c 0.68 in CH3OH); mmax.(nujol)/cm−1 3200–3600 (broad band); dH
(300 MHz; D2O) 1.64–1.85 (3H, m, H6a,b and H7a), 1.98–2.16
(1H, m, H7b), 3.21 (1H, dd, J 13.2 and 3.6 Hz, H1a), 3.32–3.42
(2H, m, H1b and H5), 3.68 (2H, t, J 5.7 Hz, CH2OH), 3.98 (1H,
dd, J 9.6 and 3.0 Hz, H4), 4.02 (1H, dd, J 4.5 and 3.0 Hz, H3),
1,5,6,7-Tetradeoxy-1,5-imino-(2R,3S,4S,5S)-L-gluco-octitol (3b).
The reaction of 3b·HCl (0.047 g, 0.21 mmol) with 25% aque-
ous ammonia as described for 3a and column purification
(chloroform–methanol–25% aqueous ammonia = 8 : 1.9 : 0.1)
afforded 3b (0.03 g, 76%) as a thick liquid (Found: C, 50.28; H,
8.94. Calcd for C8H17NO4: C, 50.25; H, 8.96%); Rf 0.47 (methanol);
[a]D25 −22.2 (c 0.45 in CH3OH); mmax.(nujol)/cm−1 3200–3600 (broad
band); dH (300 MHz; D2O) 1.54–1.82 (3H, m, H6a,b and H7a),
1.98–2.12 (1H, m, H7b), 2.78 (1H, dd, J 12.6 and 11.4 Hz, H1a),
2.93 (1H, ddd, J 9.6, 7.8 and 3.9 Hz, H5), 3.35 (1H, t, J 9.6 Hz,
H3), 3.36 (1H, dd, J 12.6 and 4.5 Hz, H1b), 3.42 (1H, t, J 9.6 Hz,
H4), 3.64 (2H, t, J 6.0 Hz, CH2OH), 3.70 (1H, ddd, J 11.4, 9.6
and 4.5 Hz, H2); dC (75 MHz; D2O) 26.5, 27.3 (C6/C7), 47.1 (C5),
59.2 (C1), 61.4, 68.2, 72.4, 76.9 (C2/C3/C4/C8).
Procedure for inhibition assay
Inhibition potencies of 4a–d and 3a,b were determined by
measuring the residual hydrolytic activities of the glycosidases.
Glycosidases namely a-mannosidases (jack bean), a-glucosidase
(baker’s yeast), b-glucosidase (almond) and b-galactosidase
(bovine testes) were purchased from Sigma Chemicals Co.
USA. Substrates (purchased from Sigma Chemicals Co. USA)
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p-nitrophenyl-b-D-glucopyranoside, p-nitrophenyl-a-D-glucopy-
ranoside of 2 mM concentration, were prepared in 0.025 M citrate
buffer with pH 6.0, and p-nitrophenyl-a-D-mannopyranoside, of
2 mM concentration, was prepared in 0.025 M citrate buffer with
pH 4.5. The test compound (of various concentrations of 0.5 lM to
1 mM) was preincubated with the enzyme, buffered at its optimal
pH, for 30 min at 25 ◦C. The enzyme reaction was initiated by the
addition of 100 lL of substrate. Controls were run simultaneously
in the absence of test compound. The reaction was terminated at
the end of 10 min by the addition of 0.05 M borate buffer (pH 9.8)
and absorbance of the liberated p-nitrophenol was measured at
405 nm with a Shimadzu Spectrophotometer UV-1601.20
V. D. Chaudhari and J. N. Tilekar, Tetrahedron Lett., 2003, 44, 7321;
(c) S. Moutel, M. Shipman, O. R. Martin, K. Ikeda and N. Asano,
Tetrahedron: Asymmetry, 2005, 16, 487.
10 Selected syntheses of tetrahydroxy azepanes: (a) H. Paulsen and K.
Todt, Chem. Ber., 1967, 100, 512; (b) R. Dax, B. Gaigg, B. Grassberger,
B. Koelblinger and A. E. Stuetz, J. Carbohydr. Chem., 1990, 9, 479;
(c) B. B. Lohray, Y. Jayamma and M. Chatterjee, J. Org. Chem., 1995,
60, 5958; (d) X. Qian, F. Moris-Varas and C. Wong, Bioorg. Med.
Chem. Lett., 1996, 6, 1117; (e) F. Moris-Varas, X. Qian and C. Wong,
J. Am. Chem. Soc., 1996, 118, 7647; (f) P. R. Andreana, T. Sanders, A.
Janczuk, J. I. Warrick and P. G. Wang, Tetrahedron Lett., 2002, 43, 6525;
(g) C. C. Joseph, H. Regeling, B. Zwanenburg and G. J. F. Chittenden,
Tetrahedron, 2002, 58, 6907; (h) J. Fuentes, C. Gasch, D. Olano, M. A.
Pradera, G. Repetto and F. J. Sayago, Tetrahedron: Asymmetry, 2002,
13, 1743; (i) J. N. Tilekar, N. T. Patil, H. S. Jadhav and D. D. Dhavale,
Tetrahedron, 2003, 59, 1873; (j) G. F. Painter, P. J. Eldridge and A.
Falshaw, Bioorg. Med. Chem., 2004, 12, 225.
11 Pentahydroxy azepanes: (a) H. Li, Y. Bleriot, C. Chantereau, J. Mallet,
M. Sollogoub, Y. Zhang, E. Rodriguez-Garcia, P. Vogel, J. Jimenez-
Barbero and P. Sinay, Org. Biomol. Chem., 2004, 2, 1492; (b) D. D.
Dhavale, S. D. Markad, N. S. Karanjule and J. PrakashaReddi, J. Org.
Chem., 2004, 69, 4760; (c) K. Martinez-Mayorga, J. L. Medina-Franco,
S. Mari, F. J. Canada, E. Rodriguez-Garcia, P. Vogel, H. Li, Y. Bleriot,
P. Sinay and J. Jimenez-Barbero, Eur. J. Org. Chem., 2004, 20, 4119;
(d) H. Li, Y. Bleriot, J. Mallet, Y. Zhang, E. Rodriguez-Garcia, P. Vogel,
S. Mari, J. Jimenez-Barbero and P. Sinay, Heterocycles, 2004, 64, 65.
12 H. A. Johnson and N. R. Thomas, Bioorg. Med. Chem. Lett., 2002, 12,
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Acknowledgements
We are grateful to Prof. M. S. Wadia and Dr K. G. Marathe
for helpful discussions. We are thankful to CSIR, New Delhi for
financial support. SDM and NSK are thankful to CSIR, New
Delhi for Senior Research Fellowships. We gratefully acknowledge
UGC, New Delhi for a grant to purchase a high field (300 MHz)
NMR facility.
13 S. D. Markad, N. S. Karanjule, T. Sharma, S. G. Sabharwal, V. G.
Puranik and D. D. Dhavale, Org. Biomol. Chem., 2006, 4, 2549.
14 (a) D. D. Dhavale, N. N. Saha and V. N. Desai, J. Org. Chem., 1997,
62, 7482; (b) V. N. Desai, N. N. Saha and D. D. Dhavale, J. Org.
Chem., 1999, 64, 1715; (c) V. N. Desai, N. N. Saha and D. D. Dhavale,
Chem. Commun., 1999, 1719; (d) N. N. Saha, V. N. Desai and D. D.
Dhavale, Tetrahedron, 2001, 57, 39; (e) N. T. Patil, J. N. Tilekar and
D. D. Dhavale, J. Org. Chem., 2001, 66, 1065; (f) N. T. Patil, J. N.
Tilekar and D. D. Dhavale, Tetrahedron Lett., 2001, 42, 747; (g) D. D.
Dhavale, N. T. Patil, S. John and S. G. Sabharwal, Bioorg. Med. Chem.,
2002, 10, 2155; (h) D. D. Dhavale, N. N. Saha, V. N. Desai and J. N.
Tilekar, ARKIVOC, 2002, (VIII), 91.
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3680 | Org. Biomol. Chem., 2006, 4, 3675–3680
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