Hydroxymethyl-Branched Polyhydroxylated Indolizidines: Novel Selective α-Glucosidase Inhibitors

Article abstract of DOI:10.1021/acs.orglett.5b01505

α,α-Disubstituted piperidines and conformationally constrained polyhydroxylated indolizidines bearing a hydroxymethyl substituent in position 8a were synthesized from a readily available l-sorbose-derived ketonitrone. Diastereoselective vinylation under t

Full text of DOI:10.1021/acs.orglett.5b01505

Letter
pubs.acs.org/OrgLett
Hydroxymethyl-Branched Polyhydroxylated Indolizidines: Novel
Selective α‑Glucosidase Inhibitors
Julien Boisson,†,‡ Amel
ia Thomasset, Emilie Racine, Pascale Cividino,†,‡
†,‡
†,‡
́
†
,‡
†,‡
§
,†,‡
Thomas Banchelin Sainte-Luce, Jean-Franco
̧
is Poisson, Jean-Bernard Behr, and Sandrine Py*
†Univ. Grenoble Alpes, DCM, F-38000 Grenoble, France
‡CNRS, DCM, F-38000 Grenoble, France
§Universite
Exactes et Naturelles, BP 1039, 51687 Reims Cedex 2, France
́ ́
de Reims Champagne-Ardenne, Institut de Chimie Moleculaire de Reims (ICMR), CNRS UMR 7312, UFR Sciences
*
S Supporting Information
ABSTRACT: α,α-Disubstituted piperidines and conformationally constrained polyhydroxylated indolizidines bearing a
hydroxymethyl substituent in position 8a were synthesized from a readily available L-sorbose-derived ketonitrone.
Diastereoselective vinylation under two sets of complementary conditions allowed access to both configurations of the newly
formed quaternary stereocenter. Subsequent N-allylation and ring-closing metathesis afforded 8a-branched indolizidines in high
yield. The newly prepared iminosugars demonstrated highly potent inhibition of α-glucosidases. Most interestingly, compound
9b exhibits very high selectivity toward this class of enzymes, with an unusual mode of binding.
lycosidase inhibition is a valuable therapeutic strategy for
G
the treatment of metabolic disorders, cancer, and viral
1
infections. Intense research on glycosidase inhibition by
2
iminosugars is ongoing in both academic laboratories and
3
pharmaceutical companies. However, the main limitation of
glycosidase inhibition as a therapeutic approach is the ubiquity
of this class of enzymes in living organisms, and therefore the
inherent difficulty of selective inhibition without affecting
normal cell functions. It is thus a timely challenge to design
glycosidase inhibitors that are not only potent but also highly
selective toward specific enzymes. In this letter, we describe the
synthesis of novel polyhydroxylated indolizidines bearing a C-
Figure 1. Analogues of DNJ as α-glucosidase inhibitors.
8
a quaternary center, among which a potent and highly
7
the active site of specific glycosidases. As examples, α,α-
selective inhibitor of α-glucosidase has been identified.
Deoxynojirimycin (DNJ, Figure 1) was the first iminosugar
to be recognized as a potent inhibitor of glucosidases from
disubstituted piperidine 1 is a slightly better inhibitor of human
α-glucosidase (IC = 1 μM) than DNJ (IC = 1.44 μM), and
α,α-disubstituted piperidine 2 (IC50 = 32 nM) inhibits rice α-
glucosidase more selectively than DNJ. In a combination of
both approaches, we envisioned the synthesis of novel
quaternary castanospermine analogues bearing a hydroxymeth-
yl substituent in position 8a. The latter may mimic the
hydroxymethyl in position 6 of a glucosyl residue and could
improve affinity and/or selectivity for glucosidases. The
synthesis of compounds containing a quaternary stereocenter
remains a challenging endeavor, and only two reports on the
8
50
50
4
various animal, plant, or microbial sources. Castanospermine, a
9
natural polyhydroxylated indolizidine isolated from Castano-
spermum australe, share the same inhibition profile and might
be considered as a conformationally restricted analogue of
5
DNJ. In the search for more potent and selective glycosidase
inhibitors, the design of constrained analogues of chemical
leads has been a classical approach. To reach this goal, a first
method consists in introducing a second cycle on the parent
structure to reduce its conformational mobility and adjust the
6
substituent’s orientation. Another method aims at building
quaternary centers to afford C-branched iminosugars featuring
an additional substituent, which may improve the affinity for
Received: May 27, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b01505
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 1. Preparation of Nitrone 5 and Stereodivergent Vinylation
synthesis of 8a-substituted polyhydroxylated indolizidines are
cooled to −78 °C. After reduction with zinc, only piperidine 6b
1
0
21
described.
In continuation of our interest in the synthesis of glycosidase
was isolated in 86% yield (Scheme 1).
The observed diastereoselectivity (trans-addition with vinyl-
magnesium bromide only and cis-addition in the presence of
1
1
inhibitors, we have previously reported the synthesis of a six-
membered ring ketonitrone from D-fructose, which was used
ZnCl as a Lewis acid) is in accordance with the models
2
12
8
17b
for the synthesis of deoxymannojirimycin. To synthesize the
targeted castanospermine analogues, we thought to start from
nitrone 5, of the D-gluco configuration, which could be prepared
from readily available L-sorbose. The previous route to
synthesize such ketonitrones was significantly improved by
proposed by Davis et al. and Cheng et al. for nucleophilic
additions to endocyclic CN bonds (Scheme 2). In the
Scheme 2. Stereoselectivity of Vinylation
13
direct activation of the primary alcohol to a bromide: 1,3,4,5-
14
tetra-O-benzyl-L-sorbopyranose (3) was treated with PPh3·
Br and pyridine, in refluxing THF, to yield 4 in 87% yield. The
2
latter was next converted into nitrone 5 in a single step, by
treatment with an excess of hydroxylamine hydrochloride and
triethylamine, in THF. Nitrone 5 was thus obtained in only 2
steps from 3, with a 70% overall yield (Scheme 1).
The first approach to prepare indolizidines from ketonitrones
1
5
using SmI -mediated umpolung being unsuccessful, a strategy
2
involving ring closing metathesis to build up the five-membered
ring fused to the piperidine moiety was chosen, requiring
diastereoselective addition of a vinyl group to nitrone 5. The
addition of organometallics to five-membered polyalkoxylated
aldonitrones has been amply described to occur with good
absence of an additive, the Grignard addition is sterically
controlled, with a favored attack opposite to the benzyloxy
group at C3, yielding a N-hydroxypiperidine of (S)-
configuration at C2. In the presence of a Lewis acid, we
hypothesize the dominance of stereoelectronic control, favoring
axial attack of the nucleophile in a chairlike transition state
forming with the development of an antiperiplanar nonbonding
doublet at the nitrogen atom and pyramidalization of the
electrophilic carbon atom. This can explain the prevalent
formation of the N-hydroxypiperidine of (R)-configuration at
C2 when a Lewis acid efficiently coordinates nitrone 5.
16
stereoselectivities. In contrast, the addition of organometallics
to six-membered aldonitrones proceeds with lower selectiv-
1
7
ities and such reactions have never been reported on
ketonitrones.
After a screening of solvents (see Supporting Information
(SI)), we found that vinylmagnesium bromide added on
nitrone 5 in high yields, with the best selectivity in
dichloromethane at −78 °C (dr = 85:15). Reduction of the
crude mixture of the resulting unseparable hydroxylamines with
Next, vinylpiperidines 6a and 6b were converted to dienes 7a
82%) and 7b (81%) respectively (Scheme 3). Ring closing
1
8
zinc and acetic acid afforded piperidines 6a and 6b (Scheme
(
1
9
), which were separated by chromatography (overall yield:
1%). The configuration of their quarternary center was
Scheme 3. N-Allylation of Piperidines 6a and 6b
assigned unambiguously by NMR (see SI).
With the aim to invert the selectivity and favor isomer 6b, the
addition of vinylmagnesium bromide to nitrone 5 was
1
9
performed in the presence of various additives. Both Et AlCl
2
20
and MgBr ·OEt are known to tune, and in some cases to
2
2
invert, the diastereoselectivity of addition of organometallics to
α-alkoxy-substituted nitrones. However, these additives gave
unsatisfactory results in this case (6a/6b ≈ 75:25; see SI). In
contrast, complexation of nitrone 5 with TMSOTf, Zn(OTf) ,
2
or ZnCl prior to addition of vinylmagnesium bromide resulted
2
in inversion of diastereoselectivity (6a/6b ≈ 20:80; see SI).
Most satisfyingly, the desired (2R)-vinyl-N-hydroxypiperidine
was formed as a single diastereoisomer when nitrone 5
metathesis proceeded smoothly in the presence of 5 mol % of
Grubbs II catalyst, in refluxing dichloromethane, yielding 8a
(85%) from 7a and 8b (93%) from 7b (Scheme 4).
Hydrogenation of the double bond and benzyl deprotection
(
solution in dichloromethane) was added to an equimolar
mixture of ZnCl and vinylmagnesium bromide previously
were effected in one step (5 bar of H , Pearlman’s catalyst,
2
2
B
DOI: 10.1021/acs.orglett.5b01505
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 4. Elaboration of Tetrahydroxylated Indolizidines
Scheme 6. Synthesis of Tetrahydroxylated N-Propyl α,α-
Disubstituted Piperidines
a panel of commercially available glycosidases under a standard
29
protocol, and percent inhibition was evaluated at 1 mM
concentration of inhibitor (Table 1). In case of complete
inactivation (>96%) at this concentration, IC50 values were
determined further.
HCl) to afford the 8a-branched tetrahydroxy indolizidines 9a
(
80%) and 9b (89%).
Dihydroxylation of the double bond in 8b was next studied.
Osmylation of 8b under classical conditions (cat. OsO ,
4
,
a b
2
2
Table 1. Inhibitory Activity against Glycosidases
NMO) afforded only 20% of the cis-diol 10b as a single
isomer (see SI for configuration assignment). One of the
isolated byproducts was the lactam 11b (14%), resulting from
enzyme
9a
9b
12b
13a
13b
α-glucosidase S. cerevisiae
α-glucosidase rice
80%
99%
89%
10%
NI
82%
100%
NI
71%
96%
95%
NI
95%
2
3
allylic oxidation. To circumvent this side reaction, the
osmylation was next performed in the presence of acids.
c
d
e
f
96%
20%
19%
10%
10%
90%
99%
47%
7%
6%
NI
β-glucosidase almond
β-galactosidase A. orizae
α-mannosidase Jack beans
β-mannosidase H. pomatia
α-rhamnosidase A. niger
Introduction in the reaction media of Ti(OiPr) (1.4 equiv) or
4
NI
6%
NI
HCl (1.1 equiv) resulted in only a slight yield improvement
NI
(
27% and 38% respectively). To avoid isolation of the rather
NI
NI
4%
unstable alkene 8b, one-pot metathesis/dihydroxylation was
also attempted,
53%
24%
NI
b
NI
2
4,25
with no success. At last, inspired by the
a
Expressed as % inhibition at 1 mM concentration of drug. NI means
recent work of Jarosz, we decided to treat 8b with a
stoichiometric amount of osmium tetraoxide in the presence
of TMEDA to form a stable complex, which was next converted
c
d
no inhibition. IC = 2.2 μM. IC = 0.052 μM, K = 31 nM, K ′ = 67
50
50
i
i
e
f
nM. IC50 = 1.5 μM. IC = 2.3 μM.
50
26
into the expected diol upon treatment with ethylene diamine.
All the synthesized C-branched iminosugars were found to
exhibit inhibitory potency against glycosidases, and in some
cases the inhibition revealed to be selective toward the two α-
glucosidases tested (Table 1). In particular, indolizidine 9b, the
structure that fits best with that of DNJ or castanospermine,
was the most active (IC50 = 52 nM, rice α-glucosidase).
Interestingly, as revealed by Lineweaver−Burk plots (see SI), a
mixed inhibition pattern was observed for 9b (K = 31 nM, K ′ =
Under these conditions, the diol 10b was isolated in an
improved yield of 62% (Scheme 5). Finally, 10b was converted
Scheme 5. Dihydroxylation of 8b
i
i
6
7 nM), in sharp contrast with the more standard competitive
behavior of DNJ or castanospermine. Moreover, and
strinkingly, compound 9b is a highly selective inhibitor of α-
glucosidases, in contrast to DNJ and castanospermine that are
also inhibitors of β-glucosidases. The discovery of a novel,
noncompetitive mode of inhibition of α-glucosidases could be
of great interest and should open new opportunities in the
development of drugs with more specific action. Further studies
are currently underway to unravel the specificity of the mode of
interaction of compound 9b with α-glucosidases and will be
reported in due course.
ASSOCIATED CONTENT
Supporting Information
■
to 12b (91%) by hydrogenolysis. Application of these
dihydroxylation conditions to the isomer 8a only led to
complex mixtures of products, from which the expected diol
could not be isolated.
With the aim to evaluate the importance of the constrained
bicyclic scaffold on the activity and selectivity of our products
toward glycosidases, N-allylated piperidines 7a and 7b were
also converted into tetrahydroxy α,α-disubstituted piperidines
*
S
Characterization data, full experimental procedures, and copies
1
13
of H and C NMR spectra of all new compounds. The
Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.orglett.5b01505.
AUTHOR INFORMATION
Corresponding Author
■
1
3a (60%) and 13b (49%), following a two-step sequence
27 28
*E-mail: sandrine.py@ujf-grenoble.fr.
Notes
involving diimide reduction and debenzylation (Scheme 6).
The inhibitory activity of compounds 9a, 9b, and 12b and
their monocyclic analogues 13a and 13b was evaluated against
The authors declare no competing financial interest.
C
DOI: 10.1021/acs.orglett.5b01505
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(
16) For general reviews, see: (a) Merino, P.; Tejero, T. Synlett 2011,
ACKNOWLEDGMENTS
■
2
011, 1965−1977. (b) Merino, P. C. R. Chim. 2005, 8, 775−788.
J.B. and E.R. are grateful to the Universite
doctoral allocation. Dr. Alice Kanazawa, DCM Grenoble, is
thanked for fruitful discussions. Martine Fayolle and Jerome
Blu, DCM Grenoble, are thanked for large-scale preparation of
nitrone 5. We also acknowledge support from ICMG FR 2607,
Grenoble, through which NMR and MS analyses have been
performed.
́
de Grenoble for a
(
(
c) Lombardo, M.; Trombini, C. Curr. Org. Chem. 2002, 6, 695−713.
d) Lombardo, M.; Trombini, C. Synthesis 2000, 2000, 759−774.
́
(e) Merino, P.; Franco, S.; Merchan, F. L.; Tejero, T. Synlett 2000,
442−454. For vinylation of nitrones, see: (f) Cardona, F.; Moreno,
G.; Guarna, F.; Vogel, P.; Schuetz, C.; Merino, P.; Goti, A. J. Org.
Chem. 2005, 70, 6552−6555. (g) Delso, I.; Tejero, T.; Goti, A.;
Merino, P. Tetrahedron 2010, 66, 1220−1227. (h) Kaliappan, K. P.;
Das, P.; Chavan, S. T.; Sabharwal, S. G. J. Org. Chem. 2009, 74, 6266−
6
(
274.
17) (a) Archibald, G.; Lin, C.-P.; Boyd, P.; Barker, D.; Caprio, V. J.
REFERENCES
■
Org. Chem. 2012, 77, 7968−7980. (b) Chan, T.-H.; Chang, Y.-F.; Hsu,
(
1) (a) Zechel, D. L.; Withers, S. G. Acc. Chem. Res. 2000, 33, 11−18.
b) Lopez, O. M.-M.; Martos, S.; Gonzalez-Benjumea, A. Carbohydr.
J.-J.; Cheng, W.-C. Eur. J. Org. Chem. 2010, 2010, 5555−5559.
(
(
c) Zhao, H.; Wang, W.-B.; Nakagawa, S.; Jia, Y.-M.; Hu, X.-G.; Fleet,
Chem. 2012, 38, 215−262. (c) Gloster, T. M. Biochem. Soc. Trans.
012, 40, 913−928.
2) (a) Compain, P.; Martin, O. R. Iminosugars: From synthesis to
therapeutic applications; Wiley: Chichester, U.K., 2007. (b) Horne, G.;
Wilson, F. X.; Tinsley, J.; Williams, D. H.; Storer, R. Drug Discovery
Today 2011, 16, 107−118. (c) Nash, R. J.; Kato, A.; Yu, C.-Y.; Fleet,
G. W. J. Future Med. Chem. 2011, 3, 1513−1521.
3) Bras, N. F.; Cerqueira, N. M. F. S. A.; Ramos, M. J.; Fernandes, P.
A. Expert Opin. Ther. Pat. 2014, 24, 857−874.
4) Asano, N.; Oseki, K.; Kizu, H.; Matsui, K. J. Med. Chem. 1994, 37,
701−3706.
5) (a) Hohenschutz, D. L.; Bell, E. A.; Jewess, P. J.; Leworthy, D. P.;
Pryce, R. J.; Arnold, E.; Clardy, J. Phytochemistry 1981, 20, 811−814.
b) Molyneux, R. J.; Roitman, J. N.; Dunnheim, G.; Szumilo, T.;
G. W. J.; Wilson, F. X.; Nash, R. J.; Kato, A.; Yu, C.-Y. Chin. Chem.
Lett. 2013, 24, 1059−1063.
(
Lett. 2003, 5, 1773−1776.
(
Asymmetry 2000, 11, 2339−2346. (b) Lombardo, M.; Fabbroni, S.;
Trombini, C. J. Org. Chem. 2001, 66, 1264−1268. (c) Delso, I.; Marca,
E.; Mannucci, V.; Tejero, T.; Goti, A.; Merino, P. Chem. - Eur. J. 2010,
2
(
18) Cicchi, S.; Bonanni, M.; Cardona, F.; Revuelta, J.; Goti, A. Org.
19) (a) Shibata, T.; Uemae, K.; Yamamoto, Y. Tetrahedron:
(
1
(
1
(
6, 9910−9919. See also ref 17c.
20) (a) Giovannini, R.; Marcantoni, E.; Petrini, M. J. Org. Chem.
995, 60, 5706−5707.
21) Notably, when ZnCl or Et AlCl was used as an additive, excess
(
3
(
2
2
vinylmagnesium bromide was necessary for complete conversion of
nitrone 5. While transmetalation could be considered between the
Grignard reagent and these additives, divinylzinc failed to react with
nitrone 5 at −78 °C and led to poor diastereoselectivities at higher
temperatures.
(
Elbein, A. D. Arch. Biochem. Biophys. 1986, 251, 450−457. (c) Pandey,
G.; Dumbre, S. G.; Pal, S.; Khan, M. I.; Shabab, M. Tetrahedron 2007,
6
3, 4756−4761. (d) San
Chasseraud, M.; Ahidouch, A.; Mellet, C. O.; Ouadid-Ahidouch, H.;
Fernandez, J. M. G. Chem. Commun. 2010, 46, 5328−5330.
6) (a) Borges de Melo, E.; da Silveira Gomes, A.; Carvalho, I.
́ ́
chez-Fernandez, E. M.; Rísquez-Cuadro, R.;
(
22) Wang, N.; Zhang, L.-H.; Ye, X.-S. Org. Biomol. Chem. 2010, 8,
639−2649.
23) (a) Sletten, E. M.; Liotta, L. J. J. Org. Chem. 2006, 71, 1335−
343. (b) Hottin, A.; Wright, D. W.; Steenackers, A.; Delannoy, P.;
Dubar, F.; Biot, C.; Davies, G. J.; Behr, J.-B. Chem. - Eur. J. 2013, 19,
526−9533.
24) (a) Beligny, S.; Eibauer, S.; Maechling, S.; Blechert, S. Angew.
́
2
(
1
(
Tetrahedron 2006, 62, 10277−10302. (b) Behr, J.-B.; Gainvors-Claisse,
A.; Belarbi, A. Nat. Prod. Res. 2006, 20, 1308−1314. (c) Arora, I.;
Kashyap, V. K.; Singh, A. K.; Dasgupta, A.; Kumar, B.; Shaw, A. K. Org.
Biomol. Chem. 2014, 12, 6855−6868. For a recent review on bicyclic
iminosugars, see: Lahiri, R.; Ansari, A. A.; Vankar, Y. D. Chem. Soc. Rev.
013, 42, 5102−5118.
7) Furneaux, R. H.; Gainsford, G. J.; Mason, J. M.; Tyler, P. C.;
Hartley, O.; Winchester, B. G. Tetrahedron 1997, 53, 245−268.
8) Maughan, M. A. T.; Davies, I. G.; Claridge, T. D. W.; Courtney,
S.; Hay, P.; Davis, B. G. Angew. Chem., Int. Ed. 2003, 42, 3788−3792.
9) Pawar, N. J.; Parihar, V. S.; Chavan, S. T.; Joshi, R.; Joshi, P. V.;
Sabharwal, S. G.; Puranik, V. G.; Dhavale, D. D. J. Org. Chem. 2012,
7, 7873−8782.
10) (a) Langlois, N.; Le Nguyen, B. K.; Retailleau, P.; Tarnus, C.;
9
(
Chem., Int. Ed. 2006, 45, 1900−1903. (b) For a recent application in
iminosugar synthesis, see: Malik, M.; Ceborska, M.; Witkowski, G.;
Jarosz, S. Tetrahedron: Asymmetry 2015, 26, 29−34.
2
(
(
25) Scholte, A. A.; An, M. H.; Snapper, M. L. Org. Lett. 2006, 8,
759−4762.
26) Malik, M.; Witkowski, G.; Ceborska, M.; Jarosz, S. Org. Lett.
(
4
(
(
2
(
(
013, 15, 6214−6217.
27) Marsh, B. J.; Carbery, D. R. J. Org. Chem. 2009, 74, 3186−3188.
7
(
28) Pd- or Raney-Ni-catalyzed hydrogenation/hydrogenolysis of 7a
yielded significant amounts of N-deallylation products.
Salomon, E. Tetrahedron: Asymmetry 2006, 17, 53−60. (b) Duran-
Lara, E. F.; Shankaraiah, N.; Geraldo, D.; Santos, L. S. J. Braz. Chem.
Soc. 2009, 20, 813−819.
(29) Gossan, D.; Alabdul Magid, A.; Kouassi-Yao, P.; Behr, J.-B.;
Ahibo, A.; Djakoure, L.; Harakat, D.; Voutquenne-Nazabadioko, L.
Phytochemistry 2015, 109, 76−83.
(
11) (a) Behr, J.-B.; Chevrier, C.; Defoin, A.; Tarnus, C.; Streith, J.
, Y. J.
Tetrahedron 2003, 59, 543−553. (b) Desvergnes, S.; Py, S.; Vallee
́
Org. Chem. 2005, 70, 1459−1462. (c) Masson, G.; Philouze, C.; Py, S.
Org. Biomol. Chem. 2005, 3, 2067−2069. (d) Ceccon, J.; Greene, A. E.;
Poisson, J.-F. Org. Lett. 2006, 8, 4739−4742. (e) Laroche, C.; Behr, J.-
B.; Szymoniak, J.; Bertus, P.; Schutz, C.; Vogel, P.; Plantier-Royon, R.
Bioorg. Med. Chem. 2006, 14, 4047−4054. (f) Ceccon, J.; Danoun, G.;
Greene, A. E.; Poisson, J.-F. Org. Biomol. Chem. 2009, 7, 2029−2031.
(
g) Danoun, G.; Ceccon, J.; Greene, A. E.; Poisson, J.-F. Eur. J. Org.
Chem. 2009, 2009, 4221−4224.
12) Racine, E.; Bello, C.; Gerber-Lemaire, S.; Vogel, P.; Py, S. J. Org.
Chem. 2009, 74, 1766−1769.
13) Chery, F.; Cronin, L.; O'Brien, J. L.; Murphy, P. V. Tetrahedron
004, 60, 6597−6608.
14) Helleur, R.; Rao, V. S.; Perlin, A. S. Carbohydr. Res. 1981, 89,
3−90. See Supporting Information for modification of the original
experimental procedures described in this paper.
15) Racine, E.; Py, S. Org. Biomol. Chem. 2009, 7, 3385−3387.
(
(
2
(
8
(
D
DOI: 10.1021/acs.orglett.5b01505
Org. Lett. XXXX, XXX, XXX−XXX