Synthesis of l-3-epi-isofagomine, its homo-, n-butyl and bicyclic analogues from d-glucose as glycosidase inhibitors

Article abstract of DOI:10.1016/j.tetlet.2013.09.102

Synthesis of l-3-epi-isofagomine, its homo-, n-butyl derivatives and its bicyclic analogue as potent glycosidase inhibitor has been achieved from readily available d-glucose. Inhibition of some commercially available glycosidases was also carried out with

Full text of DOI:10.1016/j.tetlet.2013.09.102

Accepted Manuscript
Synthesis of L-3-epi-isofagomine, its homo-, n-butyl and bicyclic analogues
from D-glucose as glycosidase inhibitors
Asadulla Mallick, A.P. John Pal, Yashwant D. Vankar
PII:
S0040-4039(13)01667-5
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.09.102
TETL 43602
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
30 July 2013
19 September 2013
20 September 2013
Please cite this article as: Mallick, A., John Pal, A.P., Vankar, Y.D., Synthesis of L-3-epi-isofagomine, its homo-,
n-butyl and bicyclic analogues from D-glucose as glycosidase inhibitors, Tetrahedron Letters (2013), doi: http://
dx.doi.org/10.1016/j.tetlet.2013.09.102
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
Synthesis of L-3-epi-isofagomine, its homo-,
n-butyl and bicyclic analogues from D-
glucose as glycosidase inhibitors
Leave this area blank for abstract info.
Asadulla Mallick, A. P. John Pal, Yashwant D.
Vankar*

1
Tetrahedron Letters
journal homepage: www.els evier.com
Synthesis of L-3-epi-isofagomine, its homo-, n-butyl and bicyclic analogues from D-
glucose as glycosidase inhibitors
Asadulla Mallick, A. P. John Pal, Yashwant D. Vankar*
Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India
ARTICLE INFO
ABSTRACT
Article history:
Received
Synthesis of L-3-epi-isofagomine, its homo-, n-butyl derivatives and its bicyclic analogue as
potent glycosidase inhibitor has been achieved from readily available D-glucose. Inhibiton of
some commercially available glycosidases was also carried out with the newly synthesized
inhibitors which showed reasonably good inhibitions (9.4-198.2 µM). One of them (compound
11) showed selective inhibition of β−galactosidase.
Received in revised form
Accepted
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Azasugars
Iminosugars
Piperidines
Bicyclic azasugars
Glycosidase
for synthetic studies as they represent challenging bicyclic
scaffolds and possess good therapeutic potential.15-17
Considering the importance of isofagomine, and these bicyclic
azasugars, newer approaches to procure such molecules and
their analogues are still needed to facilitate the discovery of
potential selective glycosidase inhibitors.
In the recent past, azasugars (or iminosugars) and their
analogues have shown enormous therapeutic applications1,2 in
diseases such as diabetes,3 cancers,4 HIV,5 lysosomal storage
disorders,6 etc. Azasugars are polyhydroxylated compounds
where anomeric carbon is replaced by a nitrogen atom, while if
the ring oxygen is replaced by nitrogen atom then they are
called iminosugars.7 In 1966, Inouye et al. isolated nojirimycin
1 (Figure 1) from the strains of Streptomyces8 as the first
naturally occurring polyhydroxylated piperidine iminosugar
which was found to be both an α- and a β-glucosidase
inhibitor.1a Its stable congener 1-deoxynojirimycin (DNJ) 2a
was originally synthesized by Paulsen et. al.9 in 1966. Later on
in 1976, DNJ was isolated from the root of Mulberry trees by
Murai et al.10 The N-butyl derivative of DNJ (Zavesca) 2b is
being used as a drug for the Gaucher’s disease whereas N-
hydroxyethyl DNJ (Glyset) 2c is used for the treatment of type
Recently, we reported the synthesis of isofagomine 3 and related
biologically active molecules from carbohydrate based starting
materials.18 Likewise, we have also reported the synthesis of
bicyclic azasugars such as L-(+)-swainsonine
5 and (+)-
lentiginosine
6
from carbohydrate building blocks.19 In
continuation with our interest in developing newer approaches for
the synthesis of glycosidase inhibitors,20 we report in this paper the
synthesis of L-3-epi-isofagomine and its homo-, n-butyl and
bicyclic analogues from D-glucose.
II diabetes.11 Isofagomine
3
is another important
polyhydroxylated compound designed by Bols et al. which
shows selective and strong inhibition against β-glucosidase
(sweet almonds) with Ki of 110 nM.12 It is known to rectify the
conformation of misfolded β-glucocerebrosiadse and thus it
could be useful in treating certain types of Gaucher’s disease.13
Furthermore, L-3-epi-isofagomine 4 has also been synthesized
and it shows selective inhibition against β-galactosidase [IC50
=
469 µM, rat intestine lactase].14 Similarly, polyhydroxylated
indolizidine alkaloids such as (+)-swainsonine 5, (+)-
lentiginosine 6 and (+)-castanospermine 7 are also good targets
Figure 1. Monocyclic piperidine based and bicyclic indolizidine
based imino / azasugars.
* Corresponding author. Tel.:+91 512 259 7169
E-mail: vankar@iitk.ac.in (Y. D. Vankar)

2
Our retrosynthetic analysis (Scheme 1) illustrates that these
target monocyclic and bicyclic azasugar derivatives could be
reduced to simpler intermediate 9 which could be obtained
from D-glucose. Thus, our synthesis originated from compound
15 which was obtained from 1,2:5,6-di-O-isopropylidene
protected glucose following a literature procedure21 (Scheme
2). The 5,6-O-isopropylidene unit in compound 15 was
selectively removed by the treatment with dilute acid at room
temperature. The corresponding diol, so generated, was
subjected to selective tosylation with TsCl, pyridine in the
presence of DMAP to give compound 8 in 88% yield over two
steps. The formation of compound 8 was ascertained by the
appearance of a sharp singlet peak around δ 2.42 corresponding
to the tosyl group in its 1H NMR spectrum. Reduction of azide
group of compound 8, to the corresponding amine followed by
hydrogenolysis in presence of Pd(OH)2/C in methanol that
yielded the tosylate salt 16 as colourless crystals.22 Typically,
the formation of cyclic compound 16 was confirmed by the
disappearance of the sharp band corresponding to azide at 2102
cm-1 in IR spectrum. As an additional proof, the stereochemical
outcome of compound 16 was confirmed by X-ray crystal
structure (cf. experimental section). This protonated amine salt
16 upon benzyl carbamate protection afforded the Cbz-
protected amine 17 in 90% yield which typically showed a
strong absorption peak at 1696 cm-1 in its IR spectrum and a
peak at δ 156.4 in the 13C NMR spectrum for the carbamate
group. The free hydroxyl group in compound 17 was converted
to the benzyl ether functionality by treatment with benzyl
bromide in presence of NaH to give compound 9 in 91% yield.
Originally, we attempted to synthesize 19 from 9 by acetonide
deprotection followed by oxidative cleavage with NaIO4 and
reduction with NaBH4. But the overall yield was very poor in
this series of reactions (22% yield over three steps). However,
the yield was remarkably improved by changing the sequence
of reactions. Thus, 1,2-O-isopropylidene ring was then
removed by treatment with trifluoroacetic acid/water to give the
corresponding hemiketal which upon reduction with NaBH4 in
methanol furnished the triol 18 in good yield. Formation of the
triol was confirmed by the devoid of the peaks at δ 1.50 and
1.31 (methyl groups of acetonide moiety) in 1H NMR spectrum
and appearance of [M + Na]+ peak at 424.1739 (calculated)
Scheme 1. Retrosynthetic analysis of the various azasugars
in its high resolution mass spectrum, along with other spectral
characteristics. The 1,2-diol moiety in compound 18 was converted
to the corresponding aldehyde by oxidative cleavage with NaIO4,
followed by reduction with NaBH4 to yield compound 19. The
global deprotection of 18 and 19 by hydrogenolysis using
Pd(OH)2/C in methanol furnished tetra-ol 10 and triol 4,
respectively. The spectral data of compound 4 was found to be in
agreement with the reported data.14a The triol 18 was converted
to the corresponding acetate 20 (Scheme 3) in 96% yield which
was characterized by a sharp absorption band at 1742 cm-1 in IR
spectrum. The benzyl carbamate functionality was removed by
hydrogenolysis to give the corresponding secondary amine
which was converted to its N-butyl derivative by condensation
with butyraldehyde in presence of NaCNBH3 to afford 22. The
absence of an absorption band at 1702 cm-1 in its IR spectrum
and the appearance of a peak at δ 0.90 as a triplet (J = 7.3 Hz)
1
for three hydrogens of the methyl group in H NMR spectrum,
apart from other spectral details (cf. experimental section),
confirmed the formation of 22. Furthermore, the stereochemical
outcome of compound 22 was supported by COSY and NOE
experiments. Thus, in NOE experiment (Fig. 2), no
enhancement of signal for H-5 at δ 2.16 was observed
.
.
Scheme 2. Synthesis of L-3-epi-isofagomine and its analogue

3
upon irradiation of signal for H-4 at around δ 4.95 which
suggests that H-5 and H-4 are in trans diaxial orientation. This
was further proved by irradiation of proton from side chain (-
CHOAc-) at δ 5.28 which showed 0.9% of NOE enhancement
of H-4 proton. No enhancement of signals in NOE was
observed by irradiation of the signals for either H-3 at δ 3.80 or
H-5 for each other. This also indicated that H-3 and H-5 are
trans oriented. Similar NOE observations were made for
compound 23 also. The acetate functionalities in triacetate 22
were removed by treatment with NaOMe. Finally, the
hydrogenolysis of the benzyl group furnished the final
compound 11 in 82% yield. Similarly, the diol 19 was
converted to 12 following the same sequence of reactions as
employed for the synthesis of 11 from 18 in good yields
(overall 53%). For the synthesis of bicyclic analogue 14, the
triol 18 was selectively converted to its primary tosyl derivative
13 (Scheme 4) by treatment with p-TsCl and n-Bu2SnO in the
presence of triethylamine.23 The Cbz-deprotection and
cyclization was achieved by hydrogenation in presence of
Pd(OH)2/C to get final compound 14 in 82% yield.
Figure 2. NOE enhancement signal for the compounds 22 and 23.
Scheme 4. Synthesis of bicyclic analogue.
The biological activities of compounds 10, 11, 12 and 14
were tested against few commercially available glycosidases24
and the results are shown in Table 1. None of these compounds
showed significant inhibitory activity against α-glucosidase
(rice). Compound 10 was found to be active against α-
Table 1. IC50 (µM) values for synthesized polyhydroxylated
compounds 10, 11, 12and 14.[a]
Enzyme
pH
10
11
NI
12
14
glucosidase,
β-glucosidase,
α-galactosidase
and
β-
galactosidase in µM range. Compound 12 was also found to be
active against α-glucosidase, β-galactosidase and α-
mannosidase. Likewise, compound 14 also did not show much
selectivity, though the inhibitions were in low micromolar
range. However, compound 11 showed selective and potent
inhibition against β-galactosidase with 158.5 µM IC50 value.
α-Glucosidase (yeast)
β-Glucosidase (almonds)
5
6.5 1 198.2
70.4
NI
NI
86.0
9.4
4.6
64.5
14.4
25.2
NI
NI
NI
α-Galacosidase (coffee beans)
6.5
7.3
4.6
4.6
NI
β-Galactosidase (bovine liver)
α-Mannosidase (Jack beans)
α-Glucosidase (rice)
158.5 22.6 31.4
NI
NI
61.5 NI
NI NI
NI
OH
R
H
OAc R
H
BnO
BnO
Ac2O, Et3N
OH
OAc
DMAP, DCM,
12 h, rt
[a] NI: no inhibition at 3 mM concentration; enzyme inhibition was carried
out at optimal pH of the enzyme at 37 0C.
N
N
Cbz
Cbz
18
19
20
R=CH2OH
R=H
R=CH2OAc, 96%
21
R=H, 89%
R
H
OAc
In conclusion, we have reported the synthesis of L-3-epi-
isofagomine, its homo-, n-butyl derivatives and its bicyclic
analogue as potential glycosidase inhibitors from chiral synthon
1,2:5,6-di-O-isopropylidene-α-glucofuranose via very effective
pathways. Further variations in structural features of compound
11 could improve its inhibition potency against β-galactosidase.
Also, further variations in structural features of compounds 10,
12 and 14, could lead to improve their selectivity.
BnO
OAc
1. Pd(OH)2/C, MeOH, 30 min.
N
2. NaCNBH3, Butyraldehyde
pH=6, 4 h, rt
22
23
R=CH2OAc, 78%
R=H, 70%
R
H
OH
Acknowledgments
HO
OH
1. NaOMe, MeOH
2. H2, Pd(OH)2/C, H+/MeOH
3 days, rt, 82%
We thank the Department of Science and Technology, New
Delhi, for the J. C. Bose National Fellowship to YDV
(JCB/SR/S2/JCB-26/2010) and the Council of Scientific and
Industrial Research, New Delhi for a research grant (Grant No.:
02(0124)/13/EMR-II)]. A.M. thanks CSIR, New Delhi for senior
research fellowship.
N
11
12
R=CH2OH, 82%
R=H, 85%
References and notes
1.
(a) Compain, P. E.; Martin, O. R. Iminosugars: From Synthesis to
Therapeutic Applications, Wiley-VCV, Weinheim, 2007; (b) Stutz, A.
E. Iminosugars as Glycosidase Inhibitors. Nojirimycin and Beyond,
Wiley-VCH, Weinheim, 1999.
Scheme 3. Synthesis of n-butyl derivative of L-3-epi-isofagomine and
its analogue
2.
(a) Asano, N.; Nash, R. J.; Molyneux, R. J.; Fleet, G. W. J.
Tetrahedron: Asymmetry 2000, 11, 1645-1680; (b) Vinni, H.;

4
Lillelund, H. H.; Jensen, L. X.; Bols, M. Chem. Rev. 2002, 102, 515-
554; (c) Pearson, M. S. M.; Mathé-Allainmat, M.; Fargeas, V.;
Lebreton, J. Eur. Org. Chem. 2005, 11, 2159-2191; (d) Dragutan, I.;
Dragutan, V.; Demonceau, A. RSC Adv. 2012, 2, 719-736 and
reference therein.
3.
4.
5.
Somsak, L.; Nagya, V.; Hadady, Z.; Dosca, T.; Gergely, P. Curr.
Pharm. Des. 2003, 9, 1177–1189.
Weiss, M.; Hettmer, S.; Smith, P.; Ladish, S. Cancer Res. 2003, 63,
3654–3658.
(a) Karlsson, G. B.; Butters, T. D.; Dwek, R. A.; Platt, F. M. J. Biol.
Chem. 1993, 268, 570–576; (b) Groopmann, J. E. Rev. Infect. Dis.
1990, 12, 931–937; (c) Ratner, L.; Hayden, N. V.; Dedera, D. Virology
1991, 181, 180-192.
6.
(a) Platt, F. M.; Neises, G. R.; Reinkensmeier, G.; Townsend, M. J.;
Perry, V. H.; Proia, R. L.; Winchester, B.; Dwek, R. A.; Butters, T. D.
Science 1997, 276, 428-431; (b) Winchester, B.; Fleet, G. W. J.
Glycobiology 1992, 2, 199-210; (c) Asano, N. Glycobiology 2003, 13,
93R-104R.
7.
8.
9.
McNaught, A. D. Pure & Appl. Chem. 1996, 68, 1919-2008.
Inouye, S.; Tsuruoka, T.; Niida, T. J. Antibiotics 1966, 19, 288-292.
Paulsen, H. Angew. Chem. Int. Ed. Engl. 1966, 5, 495-511.
10. Yagi, M.; Kouno, T.; Aoyagi, Y.; Murai, H. Nippon Nogei Kagaku
Kaisi 1976, 50, 571-572.
11. (a) Fattorusoo E.; Scafati, O. T. Modern Alkaloids, Wiley-VCH. New
York, 2008, 111-133; (b) Compain, P. M.; Martin, O. R. Curr. Top.
Med. Chem. 2003, 3, 541-560; (c) Dwek, R. A.; Butters, T. D.; Platt, F.
M.; Zitzman, N. Nat. Rev. Drug Discov. 2002, 1, 65-75.
12. (a) Jespersen, T. M.; Dong, W.; Sierks, M. R.; Skrydstrup, T.; Lundt,
I.; Bols, M.; Angew.Chem. Int. Ed. Engl. 1994, 33, 1778-1779; (b)
Bülow, A.; Plesner, I. W.; Bols. M. J. Am. Chem. Soc. 2000, 122,
8567–8568
13. Dulsat, C.; Mealy, N. Drugs of the Future 2009, 34, 23-26.
14. (a) Cruse, F. P. da; Horne, G.; Fleet, G. W. J. Tetrahedron Lett, 2008,
49, 6812-6815, (b) Kato, A.; Miyauchi, S.; Kato, N.; Nash, R. J.;
Yoshimura, Y.; Nakagome, I.; Hirono, S.; Takahata, H.; Adachi, I.
Bioorg. Med. Chem. 2011, 19, 3558-68.
15. (a) Sun, J. Y.; Zhu, M. Z.; Wang, S. W.; Miao, S.; Xie, Y. H.; Wang, J.
B. Phytomedicine 2007, 14, 353–359; (b) Goss, P. E.; Reid, C. L.;
Bailey, D.; Dennis, J. W. Clin. Can. Res. 1997, 3, 1077– 1086; (c)
Goss, P. E.; Baker, M. A.; Carver, P. J.; Dennis, J. W. Clin. Can. Res.
1995, 1, 935–944; (d) Lagana, A.; Goetz, J. G.; Nabi, I. R.; Cheung,
P.; Raz, A.; Dennis, J. W. Mol. Cell Biol. 2006, 26, 3181–3193.
16. Murphy, P. V.; Cronin, L. Org. Lett. 2005, 7, 2691–2693.
17. Cardona, F.; Moreno, G.; Guarna, F.; Vogel, P.; Schetz, C.; Merino,
P.; Goti, A. J. Org. Chem. 2005, 70, 6552–6555.
18. (a) Gupta, P.; Dharuman, S.; Vankar, Y. D. Tetrahedron:Asymmetry
2010, 21, 2966-2972; (b) Reddy, Y. S.; Kancharla, P. K.; Roy, R.;
Vankar, Y. D. Org. Biomol. Chem. 2012, 10, 2760-2773.
19. Alam, M. A.; Kumar, A.; Vankar, Y. D. Eur. J. Org. Chem. 2008, 29,
4972-4980; (b) Alam, M. A.; Vankar, Y. D. Tetrahedron Lett, 2008,
49, 5534-5536.
20. Jayakanthan, K.; Vankar, Y. D. Org. Lett. 2005, 7, 5441-5444; (b)
Reddy, B. G.; Vankar, Y. D. Angew. Chem. Int. Ed. 2005, 44, 2001-
2004; (c) Lahiri. R.; Kokatla, H. P.; Vankar, Y. D. Tetrahedron Lett.
2011, 52, 781-786.
21. Filichev, V. V.; Pedersen, E. B.; Tetrahedron 2001, 57, 9163-9168; (b)
Huang, B.G.; Bobek, M. Carbohydrate Research 1998, 308, 319-328.
22. Austin, G. N.; Baird, P. D.; Fleet, G. W. J.; Peach, J. M.; Smith, P. W.;
Watkin, D. J. Tetrahedron 1987, 43, 3095-3108
23. Martinelli, M. J.; Nayyar, N. K.; Moher, E. D.; Dhokte, U. P.; Pawlak,
J. M.; Vaidyanathan. R. Org. Lett. 1999, 1, 447-445; (b) Shimada, Y.;
Usuda, K.; Okabe, H.; Suzuki, T.; Matsumoto, K. Tetrahedron:
Asymmetry 2009, 20, 2802-2808.
24. All the enzymes and corresponding substrates were purchased from
Sigma Chemicals Co.