Synthesis and glycosidase inhibition potency of all-trans substituted 1-C-perfluoroalkyl iminosugars

Article abstract of DOI:10.1016/j.carres.2018.05.004

Synthetic analogues of the naturally occurring iminosugar homoDMDP, which feature a perfluoroalkyl group at the pseudo-anomeric position, have been synthesized from the corresponding sugar-derived cyclic aldonitrone. The new fluorinated iminosugars as wel

Full text of DOI:10.1016/j.carres.2018.05.004

CarbohydrateResearch464(2018)2–7
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Synthesis and glycosidase inhibition potency of all-trans substituted 1-C-
perfluoroalkyl iminosugars
Fabien Massicot, Richard Plantier-Royon∗∗, Jean-Luc Vasse, Jean-Bernard Behr∗
Université de Reims Champagne-Ardenne, Institut de Chimie Moléculaire de Reims (ICMR), CNRS UMR 7312, UFR Sciences Exactes et Naturelles, BP 1039, F-51687
Reims Cedex 2, France
A R T I C L E I N F O
A B S T R A C T
Keywords:
Iminosugar
homoDMDP
Perfluoroalkyl chain
Glycosidase inhibition
Synthetic analogues of the naturally occurring iminosugar homoDMDP, which feature a perfluoroalkyl group at
the pseudo-anomeric position, have been synthesized from the corresponding sugar-derived cyclic aldonitrone.
The new fluorinated iminosugars as well as homoDMDP and its 6-deoxy counterpart were evaluated for their
inhibitory activity against a panel of glycosidases. While the replacement of the (1′,2′)-dihydroxyethyl sub-
stituent of homoDMDP with –C4F9 proved detrimental for enzyme binding, introduction of a –C3F7 moiety tuned
the inhibitory activity spectrum selectively towards α-fucosidase and α-glucosidase from yeast.
1. Introduction
physico-chemical properties such as solubility, basicity or bioavail-
ability [9]. The role of fluorine substitution in structure-activity re-
Iminosugars have been reported for fifty years as potent inhibitors
of carbohydrate processing enzymes such as glycoside hydrolases,
glycosyltransferases or glycogen phosphorylase [1]. A number of these
nitrogen-in-the-ring carbohydrate mimics are naturally occurring but
[2], in parallel, many synthetic approaches were developed to fill the
library of analogues [3]. Among the five families of natural iminosugars
(polyhydroxy-piperidines, -pyrrolidines, -pyrrolizidines, -nortropanes
and -indolizidines), pyrrolidines such as DMDP 1, DAB 1′ and their
homologues (compounds 2 and 3 in Fig. 1 but also broussonetines [4],
which contain a C13 lipophilic side-chain) are particularly widespread
[5]. Interestingly, the inhibitory potency of homologues of DAB is
clearly dependent on the nature of the side-chain. For instance, while
lationships has been largely reviewed and exemplified with a series of
biologically relevant pharmacophores [10]. With iminosugars, some
studies focused on the replacement of one OH group by F, with limited
success though [11]. Recently, first series of iminosugar C-glycosides
with a polyfluoroalkyl side chain such as 4–7 (Fig. 1) have been de-
signed and synthesized to inhibit glycosidases or glycosyltransferases.
While 6,6-difluoro-homoDMDP 4 decreased slightly the activity of α-
glucosidase from yeast and rice (no inhibition on other glycosidases),
trifluoro-homoDMDP 5 was mostly active against β-glucosidase from
almond [7], whereas difluoromethylphosphono-iminosugar 6 was in-
active to inhibit chitin synthase [12] (a glycosyl transferase) or glyco-
sidases [13]. The fuco-configured perfluoropropyl C-glycoside 7 was a
moderate inhibitor of fucosidase (74% inhibition at 250 μM) [9b].
Nevertheless, the prediction of the activity of homoDMDP analogues
bearing a fluorinated chain remains elusive, so that the extension of the
library of fluorinated homoDMDP analogues may be of interest to
identify new active and/or specific targets.
DAB is
a
modest inhibitor of trehalase from porcine kidney
displays strong affinity
(IC50 = 61 μM) [6], homoDMDP
2
(IC50 = 5.0 μM) for the same isoform and 3 shows no significant in-
hibition [7]. Mimicry of the natural substrate (for instance, α-D-gluco-
pyranosyl-1,1-α-D-glucopyranoside in the case of trehalase) by imino-
sugar C-glycosides might place the extra substituent into the aglycon
subsite, giving rise to favorable (increasing inhibition potency) or un-
favorable (decreasing potency) interactions [8]. Thus, the synthesis of
new iminosugar C-glycosides with unprecedented side-chains would
help identifying more potent and more specific inhibitors of ther-
apeutically relevant glycosidases. In this regard, the introduction of
fluorine atoms or fluoroalkyl groups into the structures of iminosugars
has been initiated to tune both their inhibition profile and their
Herein, we report the synthesis of new analogues of homoDMDP
8a,b, which feature a perfluoroalkyl chain at the C-1 position (carbo-
hydrate numbering) and their inhibitory activities against a range of
commercial glycosidases in comparison with iminosugars 2 and 3,
which were assayed under the same conditions.
∗
Corresponding author.
Corresponding author.
∗∗
E-mail addresses: richard.plantier-royon@univ-reims.fr (R. Plantier-Royon), jb.behr@univ-reims.fr (J.-B. Behr).
https://doi.org/10.1016/j.carres.2018.05.004
Received 26 April 2018; Received in revised form 9 May 2018; Accepted 9 May 2018
0008-6215/©2018ElsevierLtd.Allrightsreserved.

F. Massicot et al.
CarbohydrateResearch464(2018)2–7
Fig. 1. Structures of iminosugars structurally related to homoDMDP.
Scheme 1. Synthesis of iminosugars 2 and 3 [15,16]. Reagents and conditions. i: vinylMgBr, THF, 0 °C, 91%; ii: MsCl, NEt3, CH2Cl2, 91%; iii: OsO4, NMO, acetone/
water, 80% (dr: 4/6); iv: acetone, TsOH, 89%; v: BnNH2, 120 °C, 69%; vi: 80% HCOOH then H2, Pd(OH)2/C, 70%; vii: BnNH2, CH2Cl2, 4 Å MS, quant.; viii: allylMgCl,
THF, 0 °C, 91%; ix: MsCl, pyr., 79%; x: H2SO4, O3, then NaBH4, MeOH, 74%; xi: HCOONH4, 10% Pd/C, MeOH, reflux, 40%.
2. Synthesis of homoDMDP and its analogues
equivalents) to secure complete conversion, affording the expected
hydroxylamines 16a and 16b in 62% and 69% respectively after pur-
ification on silica gel (ethyl acetate/petroleum ether, 1/9, v/v). Sur-
prisingly, no conversion was observed when Et2O was replaced by THF
as the solvent during the process. Nucleophilic additions of organo-
metallics to nitrone 15 usually occur with good stereoselectivities af-
fording the (1S) configured hydroxylamine as the major diastereoi-
somer [20]. The same observation accounted here for the addition of
the perfluoroalkyl species. Only one isomer was isolated, arising from
exclusive nucleophilic attack at the less hindered Re side, as controlled
by the bulky substituents at C-2 and C-4. The configuration of the newly
formed stereogenic center was confirmed by HOESY experiments. The
relative cis position of the perfluoroalkyl chain with regard to H-2 and
H-4 in 16b was deduced from the corresponding correlations (Fig. 2).
The configuration of 16a was attributed by analogy.
Iminosugar C-glycosides 2 and 3 were obtained either from 2,3,5-
tri-O-benzyl-L-xylofuranose or from glycosylamine 12 following re-
ported procedures as depicted in Scheme 1 [14–16].
Sugar-derived cyclic nitrones represent appropriate building-blocks
for the introduction of various substituents on an iminosugar scaffold
through 1,3-dipolar cycloaddition or nucleophilic addition of organo-
metallic reagents [17]. The stereochemical outcome of these reactions
is typically controlled by the stereocenter next to the electrophilic
carbon and substantial diastereoisomeric excesses are usually obtained.
To access homoDMDP analogues, the D-arabino configured nitrone 15
was required (Scheme 2), which was prepared in four steps from 2,3,5-
tri-O-benzyl-L-xylose, according to the reported procedure [18]. With
nitrone 15 in hands, we investigated the addition step of a per-
fluoroalkyl organometallic nucleophile. Perfluoroalkyl Grignard re-
agents such as C3F7MgBr or C4F9MgBr are unstable species which de-
compose above −30 °C and thus need to be prepared in situ [19]. Here,
a pre-formed solution of perfluoroalkyl Grignard was obtained by ad-
dition of EtMgBr to C3F7I or C4F9I in Et2O at −45 °C. Nitrone 15, so-
lubilized in a minimal volume of THF, was added and the mixture was
left to react for 1 h. An excess of the organometallic was needed (2.5
Deprotection and N-O reduction of pyrrolidines 16 was finalized
next.
A two-step procedure was experienced starting with 16b.
Treatment of 16b with BCl3 afforded the expected debenzylated hy-
droxylamine in only 24% yield [21]. Reduction of 17b was effected
next with sulfurous acid, giving the targeted homoDMDP analogue 8b
in 38% yield. Alternatively, concomitant debenzylation and hydro-
genolysis were carried out successfully after prolonged reaction time
Scheme 2. Synthesis of fluorinated iminosugars 8a,b. i: H2N-OTBDPS, MgSO4, PPTS, PhMe, 100 °C, 30 min; ii: MsCl, NEt3, CH2Cl2, 0 °C to rt, 30 min; iii: TBAF, THF,
0 °C, 5 min; iv: NH2OH-HCl, NaHCO3, MeOH-H2O, rfx 16 h; v: I-CnF2n+1, EtMgBr, Et2O, – 45 °C, 30 min; vi: H2, Pd/C, HCl 6 M, rt, 48 h.
3

F. Massicot et al.
CarbohydrateResearch464(2018)2–7
Table 1
Inhibitory activity against glycosidases.a,b
Enzyme
2
3
8a
8b
DAB (1′)
α-glucosidase ricec
α-glucosidase S.
cerevisiae
79%d
84%e
12% 33%
63% 99%
IC50
6%
9%
IC50 = 0.15 μMh
IC50 = 250 μMh
=
6.2 μM
β-glucosidase almond 96%
67% 90%g
60% IC50 = 250 μMh
IC50
=
0.41 μM
β -glucosidase A. niger 36%
NI
11%
31%
NI
β -galactosidase A.
orizae
91%f
25%
26%
13%
15% 31%
19% 40%
20% 20%
α-mannosidase Jack
bean
α-rhamnosidase A.
niger
α-fucosidase bovine
kidney
NI
IC50 = 320 μMh
23%
9%
NI
99%
IC50
NIh
=
56 μM
a
b
Expressed as % inhibition at 1 mM concentration of inhibitor. NI means no
c
d
e
f
inhibition at 1 mM. Assayed at pH 5.2. 34% at 100 μM. 36% at 100 μM.
47% at 100 μM. 33% at 100 μM.h taken from Ref. [7].
g
Fig. 2. Two-dimensional heteronuclear (HOESY) correlations for 16b.
(48 h) using Pd/C in the presence of 6 M HCl, affording 8a and 8b in
44% and 47% yields respectively. The low polarity and poor protona-
tion ability of perfluorinated iminosugars 7 allowed easy purification
by silica gel chromatography with ethyl acetate as the eluent. The all-
trans configuration of mannitol-derived 8a,b was confirmed here by the
characteristic coupling constants of such systems (J1,2, J2,3, J3,4 above
6 Hz) [22].
3. Glycosidase inhibition assays
The strong interaction of iminosugars with glycoenzymes has at-
tracted great attention in medicinal chemistry. Indeed, the depletion of
glycoenzyme's activity with iminosugar inhibitors or the control of the
native conformation of glycosidases with iminosugar chaperones were
experienced in the study or the therapy of several disorders [23].
Nevertheless, the lack of selectivity of iminosugars usually hampers
their medical use, the inhibition of the targeted enzyme being accom-
panied by undesirable inhibitions of isoforms that display essential
biological roles. Selectivity might be induced by an additional sub-
stituent at the pseudo-anomeric position [24]. In the case of DAB 1′ and
its analogues, the insertion of CF2 or CF3 on the side chain affords
analogues such as 4 or 5, which display retained or even increased
biological potential towards certain glycosidases [7]. With highly
fluorinated compounds 8a,b it is possible to go further in the analysis of
structure-activity relationships. To this aim, iminosugars 8a,b were
tested against a panel of glycosidases in parallel with the non-fluori-
nated analogues 2 and 3. Inhibition of rice α-glucosidase, yeast α-glu-
cosidase, almond β-glucosidase, β-glucosidase from Aspergillus niger, β-
galactosidase from Aspergillus oryzae, Jack bean α-mannosidase, bovine
liver α-fucosidase and α-rhamnosidase from Aspergillus niger was first
evaluated at 1 mM concentration of inhibitor (Table 1). When almost
complete inhibition (> 95%) occurred at this high concentration, IC50
(the concentration of inhibitor affording half initial rate of the con-
sidered glycosidase) was determined further. In the case where in-
hibition rate was between 80% and 95%, additional assay was con-
ducted at a concentration of 100 μM. According to the literature,
heptafluoropropylpyrrolidines (pKa = 4.5–4.6) are significantly less
basic than DMDP (pKa = 7.2), which impacts the protonation state of
the iminosugar in biological medium [9b]. Thus, all the assays were
performed at buffered pH = 5.7, to ensure proper enzyme activity and,
at least partial, protonation at nitrogen. Glycosidases are particularly
sensitive to pH, as examplified on Fig. 3 with α-glucosidase from yeast:
changing the pH from 6.9 to 6.2 or 5.7 results in significant loss in
Fig. 3. α-glucosidase catalysed release of pNP from α-pNP-Glc at different pH.
initial rate as reflected by the decrease in absorbance due to released p-
nitrophenolate [25]. However, at pH 5.7, α-glucosidase from yeast is
still sufficiently active to perform the biological assays. Another border
line case was α-glucosidase from rice, which was significantly more
active at pH 5.2 than pH 5.6. Thus, contrarily to all the other tested
glycosidases, the isoform from rice was assayed at pH 5.2.
As reported in Table 1, homoDMDP 2 was a potent inhibitor of β-
glucosidase from almond (IC50 = 0.41 μM) and had some effect on the
other tested glucosidases, though to a lesser extent [26]. This was ac-
companied by a strong inhibition of β-galactosidase at 1 mM, which
decreased rapidly (only 47% remaining inhibition at 100 μM). For its
part, 6-deoxy-homoDMDP elicited only weak inhibition at 1 mM con-
centration towards yeast α-glucosidase and β-glucosidase from almond.
Interestingly, the biological behaviour of fluorinated homoDMDP ana-
logues 8a,b differed significantly from their model 2. Whereas (C4F9)
substituted 8b had almost no effect on the tested glycosidases (only
60% inhibition of β-glucosidase from almond), iminosugar 8a proved
strongly active against α-glucosidase from yeast (IC50 = 6.2 μM) and α-
fucosidase (IC50 = 56 μM). It is commonly admitted that favorable IC50
(ie, below 100 μM) might be obtained only for iminosugars showing
almost complete inhibition (> 95%) at 1 mM concentration. This is
ensured here with control assays at 100 μM, conducted when % in-
hibition is in the borderline range 80–95%, actually providing inhibi-
tion rates < 50% in each case at this concentration.
As observed earlier with gem-difluoromethylene or trifluoromethyl
substituted iminosugars 4,5, the electronic impact of the perfluorinated
4

F. Massicot et al.
CarbohydrateResearch464(2018)2–7
substituent as well as its hydrophobic character might influence the
conformation of the molecule and spatial distribution of hydroxyl
groups [27], which would lead to unexpected inhibition profile. This is
clearly evidenced here with 8a, which displays strong inhibition of
yeast α-glucosidase, an enzyme that is usually sparsely impacted by
homoDMDP analogues. Iminosugar 8a is also a strong inhibitor of α-
fucosidase, which is uncommon for DMDP-scaffolded pyrrolidines.
Moreover, a C4F9 substituent seems to be the upper limit of fluorine
introduction since an almost complete loss in inhibition potency was
observed with analogue 8b.
perfluoroalkyl iodide (2.2 mmol) in dry Et2O (6 mL) at −45 °C. The
mixture was stirred for 40 min. A solution of nitrone 15 (150 mg,
0.877 mmol) in THF/Et2O (0.6 mL/1.5 mL) was added dropwise during
15 min and the mixture was stirred for 1 h after which the temperature
was raised slowly to −15 °C. A solution of sat. NH4Cl was then added
and the mixture was extracted with Et2O (3 ✕ 15 mL). The organic
layers were dried (MgSO4), concentrated and purified by column
chromatography (EtOAc/Petroleum ether: 1/9) to yield pure hydro-
xylamine 16a,b.
6.2.1. (1S)-N-hydroxy-2,3,5-tri-O-benzyl-1-C-heptafluoropropyl-1,4-
dideoxy-1,4-imino-D-arabinitol 16a
4. Conclusions
(62%, colourless oil): Rf = 0.25 (EtOAc/Petroleum ether: 1/9);
[α]D20 = −14.3 (c 1, CHCl3); 1H NMR (600 MHz, CDCl3): δ 3.66–3.73
(m, 2H, H-4 and H-5a), 3.96–4.02 (m, 2H, H-1 and H-5b), 4.17 (dd, 1H,
In conclusion, homoDMDP analogues with a perfluoroalkyl chain at
the pseudo anomeric position were prepared using a stereoselective
nucleophilic addition of fluorinated Grignard reagents onto a cyclic
nitrone in the key step of the synthetic sequence. These two fluorinated
iminosugars with a perfluoropropyl or a perfluorobutyl chain were
tested against a panel of glycosidases. While the replacement of the
dihydroxyethyl side-chain of homoDMDP by –C4F9 proved deleterious
for enzyme binding, introduction of a –C3F7 moiety afforded potent and
selective inhibition of α-fucosidase and α-glucosidase from yeast.
Nevertheless, concerning iminosugars, the impact of fluorine atoms on
their glycosidase inhibition potencies is so far difficult to predict.
Indeed, introduction of fluoroalkyl chains might deeply influence hy-
drophobicity or electron density partitioning of the molecule, as well as
pKa of the amine, as previously described [9b]. As a consequence, in-
tramolecular interactions (conformation) and intermolecular glycosi-
dase-inhibitor interactions (binding) might be deeply affected to afford
new and rather unexpected inhibition profiles.
J4,5 4.5 Hz, J4,3 3.5 Hz, H-3), 4.24 (dd, 1H, J3,4 3.5 Hz, J3,2 3.5 Hz, H-2),
4.39 (d, 1H, JHa,Hb 11.5 Hz, CHaHb-Ph), 4.48 (d, 1H, JHb,Ha 11.5 Hz,
CHaHb-Ph), 4.51 (d, 1H, JHa’,Hb’ 12 Hz, CHa’Hb’-Ph), 4.52 (s, 2H, CH2-
Ph), 4.56 (d, 1H, JHb’,Ha’ 12 Hz, CHa’Hb’-Ph), 5.25 (s, 1H, OH),
7.28–7.34 (m, 15H, 3 Ph); 13C NMR (150 MHz, CDCl3) δ 65.81 (C-5),
69.17 (C-4), 72.19 (CH2), 72.29 (CH2), 72.64 (dd, JC,F 18.7 Hz and
25.7 Hz, C-1), 73.33 (CH2), 82.37 (C-3), 83.11 (C-2), 107.18–111.45
(m, CF3 and 2 x CF2), 127.81–128.58 (m, Ar), 137.29 (Cquat), 137.64
(Cquat), 138.11 (Cquat); 19F NMR (470 MHz, CDCl3): δ −80.49 (t, 3F, JF,F
10.4 Hz, CF3), −116.83 (dm, 1F, JF,F 284 Hz), −121.48 (dm, 1F, JF,F
284 Hz), −125.35 (ddd, 1F, JF,F 290 Hz, 11.6 Hz and 4.6 Hz), −126.4
(ddd, 1F, JF,F 290 Hz, 11.5 Hz and 2.7 Hz); HRMS- ESI+ (m/z): [M
+Na]+ calcd for C29H28NO4F7Na: 610.1804; found 610.1807.
6.2.2. (1S)-N-hydroxy-2,3,5-tri-O-benzyl-1-C-nonafluorobutyl-1,4-
dideoxy-1,4-imino-D-arabinitol 16b
5. Acknowledgements
(69%, colourless oil): Rf = 0.25 (EtOAc/Petroleum ether: 1/9);
[α]D20 = −11.8 (c 1, CHCl3); 1H NMR (500 MHz, CDCl3): δ 3.73–3.79
(m, 2H, H-4 and H-5a), 4.05–4.14 (m, 2H, H-1 and H-5b), 4.26 (dd, 1H,
This work was supported by the Structure Fédérative de Recherche
CAP-SANTE. The authors warmly thank Anthony Robert, Dominique
Harakat, Agathe Martinez, Maléotane NDiaye and Guillaume Bonneau
for experimental and technical assistance. We are also thankful to
Professor Halima Ouadid-Ahidouch and to Professor Ahmed Ahidouch,
as well as to Drs. Sandrine Py and Albert Defoin for ongoing discussions
and collaborations concerning iminosugars.
J4,5 4.0 Hz, J4,3 3.0 Hz, H-3), 4.34 (dd, 1H, J3,4 3.3 Hz, J3,2 3.3 Hz, H-2),
4.47 (d, 1H, JHa,Hb 11.5 Hz, CHaHb-Ph), 4.56 (d, 1H, JHb,Ha 11.5 Hz,
CHaHb-Ph), 4.58 (d, 1H, JHa’,Hb’ 11.7 Hz, CHa’Hb’-Ph), 4.59 (s, 2H, CH2-
Ph), 4.63 (d, 1H, JHb’,Ha’ 11.7 Hz, CHa’Hb’-Ph), 5.92 (s, 1H, OH),
7.33–7.42 (m, 15H, 3 Ph); 13C NMR (125 MHz, CDCl3) δ 65.80 (C-5),
69.07 (C-4), 72.10 (CH2), 72.25 (CH2), 72.82 (dd, JC,F 18.7 Hz and
25.0 Hz, C-1), 73.22 (CH2), 82.42 (C-3), 83.19 (C-2), 106.67–121.29
(m, CF3 and 3 x CF2), 127.79–128.50 (m, Ar), 137.30 (Cquat), 137.66
(Cquat), 138.04 (Cquat); 19F NMR (470 MHz, CDCl3): δ −80.85 (t, 3F, JF,F
9.5 Hz, CF3), −116.48 (dm, 1F, JF,F 284 Hz), −120.41 (dm, 1F, JF,F
284 Hz), −121.96 (dm, 1F, JF,F 298 Hz), −122.76 (dm, 1F, JF,F
298 Hz), −125.29 (dm, 1F, JF,F 294 Hz), −126.37 (dm, 1F, JF,F
294 Hz); HRMS- ESI+ (m/z): [M+H]+ calcd for C30H29NO4F9:
638.1953; found 638.1948.
6. Experimental section
6.1. General methods
Reactants and reagents were purchased from Aldrich and Sigma and
were used without further purification. Silica gel F254 (0.2 mm) was
used for TLC plates, detection being carried out by spraying with an
alcoholic solution of phosphomolybdic acid or an aqueous solution of
KMnO4 (2%)/Na2CO3 (4%), followed by heating. Flash column chro-
matography was performed over silica gel M 9385 (40–63 μm) Kieselgel
60. NMR spectra were recorded on Bruker AC 250 (250 MHz for 1H,
62.5 MHz for 13C and 235 MHz for 19F), 500 (500 MHz for 1H, 125 MHz
for 13C and 470 MHz for 19F) or 600 (600 MHz for 1H, 150 MHz for 13C)
spectrometers. Chemical shifts are expressed in parts per million (ppm)
and were calibrated to the residual solvent peak for 1H and 13C spectra
and to CCl3F peak for 19F spectra. Coupling constants are in Hz and
splitting pattern abbreviations are: br, broad; s, singlet; d, doublet; t,
triplet; m, multiplet. Optical rotations were determined at 20 °C with a
Perkin-Elmer Model 241 polarimeter in the specified solvents. High
Resolution Mass Spectra (HRMS) were performed on Q-TOF Micro
micromass positive ESI (CV = 30 V).
6.3. Synthesis of perfluoroalkyliminosugars 8a,b
A solution of 16a (80 mg, 0.136 mmol) in MeOH (4 mL) and 6 M
HCl (0.8 mL) was hydrogenated in the presence of Pd/C (10%) (40 mg)
under H2 (1 bar). After 24 h, more Pd-C (40 mg) was added and the
solution was stirred for additional 24 h. The catalyst was then removed
by filtration over Celite® and the solution was concentrated. The re-
sulting crude product was diluted in MeOH, neutralized with Amberlyst
A-26 (HO−) resin and purified by column chromatography (ethyl
acetate) to yield 8a as colorless oil (18 mg, 44%).
6.3.1. (1S)-1-C-heptafluoropropyl-1,4-dideoxy-1,4-imino-D-arabinitol 8a
20
Rf = 0.27 (EtOAc); [α]D = +15.2 (c 0.8, MeOH); 1H NMR
(250 MHz, CD3OD): δ 2.90 (ddd, 1H, J5,4 8.5 Hz, J5,6a 4.2 Hz, J5,6b
3.2 Hz, H-4), 3.65 (dd, 1H, JHa’,Hb’ 11.5 Hz J5,6 4.2 Hz, H-5a), 3.65–3.80
(m, 1H, H-1), 3.70 (dd, 1H, JHa’,Hb’ 11.6 Hz J5,6 3.2 Hz, H-5b), 3.84 (dd,
1H, J4,5 8.5 J4,3 6.7 Hz, H-3), 4.27 (t, 1H, J3,4 J3,2 6.7 Hz, H-2); 13C NMR
6.2. Synthesis of perfluoroalkylhydroxylamines 16a,b
A solution of EtMgBr (3 M, 0.73 mL, 2.2 mmol) was added to
5

F. Massicot et al.
CarbohydrateResearch464(2018)2–7
(62.5 MHz, CD3OD) δ 61.1 (C-5), 62.8 (dd, JC,F 20.3 Hz and 24.3 Hz, C-
1), 64.3 (C-4), 78.5 (C-2), 78.5 (C-3), 108.0–129.0 (m, CF3, 2 ✕ CF2);
19F NMR (235 MHz, CDCl3): δ −82.4 (t, 3F, JF,F 9.9 Hz, CF3), −122.4
(dm, 1F, JF,F 276 Hz), −125.2 (dm, 1F, JF,F 276 Hz), −127.1 (d, 1F, JF,F
7.5 Hz), −127.3 (d, 1F, JF,F 7.5 Hz); HRMS- ESI+ (m/z): [M+H]+ calcd
for C9H11NO3F9: 352.0595; found 352.0597.
A solution of 16b (209 mg, 0.328 mmol) in MeOH (5 mL) and 6 M
HCl (1.0 mL) was hydrogenated in the presence of Pd/C (10%) (50 mg)
under H2 (1 bar). After 24 h, more Pd-C (50 mg) was added and the
solution was stirred for additional 24 h. The catalyst was then removed
by filtration over Celite® and the solution was concentrated. The re-
sulting crude product was diluted in MeOH, neutralized with Amberlyst
A-26 (HO−) resin and purified by column chromatography (ethyl
acetate) to yield 8b as colorless oil (54 mg, 47%).
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20
(250 MHz, CD3OD): δ 2.87 (ddd, 1H, J5,4 9.0 Hz, J5,6a 4.2 Hz, J5,6b
3.2 Hz, H-4), 3.63 (dd, 1H, JHa’,Hb’ 11.6 Hz J5,6 4.2 Hz, H-5a), 3.65–3.80
(m, 1H, H-1), 3.70 (dd, 1H, JHa’,Hb’ 11.6 Hz J5,6 3.2 Hz, H-5b), 3.81 (dd,
1H, J4,5 9.0 J4,3 6.8 Hz, H-3), 4.24 (t, 1H, J3,4 J3,2 6.8 Hz, H-2); 13C NMR
(62.5 MHz, CD3OD) δ 61.3 (C-5), 62.9 (dd, JC,F 20.0 Hz and 24.5 Hz, C-
1), 64.4 (C-4), 78.6 (C-2), 78.6 (C-3), 105.0–127.0 (m, CF3, 3 ✕ CF2);
19F NMR (235 MHz, CDCl3): δ −82.6 (t, 3F, JF,F 9.9 Hz, CF3), −122.0
(dm, 1F, JF,F 280 Hz), −123.4 to −123.6 (m, 2F), −124.6 (dm, 1F, JF,F
280 Hz), −127.4 (tm, 2F, JF,F 13.9 Hz); HRMS- ESI+ (m/z): [M+H]+
calcd for C8H11NO3F7: 302.0627; found 302.0634.
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6.4. Glycosidase assay
α-Glucosidases (from rice and yeast), β-glucosidases (from almond
and A. niger), β-galactosidase (from A. oryzae), α-mannosidase (from
Jack bean), α-rhamnosidase (from A. niger), α-fucosidase (from bovine
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Chemical Co. In a typical experiment, the glycosidase (0.013 U/mL)
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Percentage of inhibition was calculated as follows:
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Asample
Acontrol
⎛
⎞
⎟
⎜
%I= 1−
×100
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⎝
⎠
In cases where inhibition was above 95%, IC50 values were de-
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Appendix A. Supplementary data
Supplementary data related to this article can be found at http://dx.
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7