Regiospecific formation of sugar-derived ketonitrone towards unconventional: C -branched pyrrolizidines and indolizidines

Article abstract of DOI:10.1039/c9ob01419e

The synthesis of unprecedented branched pyrrolizidines and indolizidines was accomplished via nitrone chemistry. The required ketonitrone, a known intermediate usually obtained as a mixture of regioisomers, was prepared in a pure form from d-arabinose by

Full text of DOI:10.1039/c9ob01419e

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Journal Name
ARTICLE
Regiospecific formation of sugar-derived ketonitrone towards
unconventional C-branched pyrrolizidines and indolizidines
Received 00th January 20xx,
Accepted 00th January 20xx
Fabien Massicot,a Gatien Messire,a Alexis Vallée,a Jean-Luc Vasse,a Sandrine Py b and Jean-Bernard
Behr*a
DOI: 10.1039/x0xx00000x
www.rsc.org/
The synthesis of unprecedented branched pyrrolizidines and indolizidines was accomplished via nitrone chemistry. The
required ketonitrone, a known intermediate usually obtained as a mixture of regioisomers, was prepared in a pure form
from D-arabinose by a sequence of oximation/reduction/oxidation steps. Nucleophilic vinylation or allylation followed by
ring-closing metathesis of the corresponding N-allylpyrrolidines furnished the targeted iminosugars, which proved potent
and selective inhibitors of alpha-glucosidase from rice (GH31 family).
6a,b, which encompass the same structural outlines as 2 and
3. Hence, iminosugars 5,6 might be regarded as constrained
analogues of DAB 7, a potent but not selective inhibitor of
Introduction
Carbohydrate-derived cyclic nitrones are particularly well-
designed building blocks for the construction of complex
polyhydroxylated nitrogen heterocycles.1 Due to their ease of
formation, stability and high reactivity, polyalkoxylated
aldonitrones have been widely used in the synthesis of five-,
six-, or seven-membered iminosugars via nucleophilic addition
or 1,3-dipolar cycloaddition.2,3 In contrast, cyclic ketonitrones
derived from carbohydrates have been much less used.
Beyond a possible drop in reactivity due to the additional
substituent at the electrophilic center, the main reason for the
underutilization of ketonitrones in iminosugar synthesis is the
lack of convenient methods for their preparation.4 However,
six-membered ketonitrones such as 1 have been prepared
recently in a straightforward manner by using a ketose, namely
L-sorbose, as carbohydrate precursor.5 Nitrone 1 proved to be
a pivotal intermediate in the synthesis of indolizidine 2 and
quinolizidine 3 (Figure 1), a new series of constrained
analogues of DNJ (4).5,6 Both compounds 2 and 3 were shown
highly potent and selective inhibitors of α-glucosidases,
especially that from the GH31 family. The significant difference
in selectivity, when compared to the standard DNJ (4), was
predominantly attributed to quaternarization at C-6
(carbohydrate numbering) and to additional interactions in the
vicinity of enzyme catalytic site induced by the annulated ring.
To gain a better view on the influence of this particular motif
we intended to prepare pyrrolizidines 5a,b and indolizidines
glycosidases.7 DAB and its derivatives also display potent
inhibition of other biologically relevant enzymes such as N-
acetylgalactosamine-6-sulfatase,8 glycogen phosphorylase,9
arabinofuranosyl transferase,10 chitin synthase11 or DNA
polymerase.12 Branched-chain pyrrolizidines and indolizidines
such as 5 or 6 are infrequent, contrarily to regioisomers (i.e.
compound 8, Figure 1), which have been extensively studied
and are widespread in nature.13
O
n
H
N
N
N
HO
HO
HO
HO
BnO
BnO
steps
OBn
OH
OH
OH
OH
OBn
1
DNJ, 4 : 0.035 M 6
2 : 0.052 M (n=1) 5
3 : 0.047 M (n=2) 6
n
n
O
N
N
N
HO
HO
HO
HO
HO
HO
this work
OH
5b (n=1)
6b (n=2)
OH
5a (n=1)
6a (n=2)
OH
10
HO
H
N
N
HO
HO
HO
HO
HO
HO
N
H
HO
OH
OH
DAB, 7
hyacinthacine A2,
8
a. Univ. Reims Champagne-Ardenne, ICMR, CNRS UMR 7312, FR Condorcet CNRS
3417, 51687 Reims Cedex 2, France.
OH
9
Figure 1 Structures of iminosugars/nitrones 1-10 and activities (IC50) against rice
α-glucosidase.
b. Univ. Grenoble Alpes, DCM, F-38000 Grenoble, France; CNRS CNRS, DCM, F-
38000 Grenoble, France.
E-mail: jb.behr@univ-reims.fr
Electronic Supplementary Information (ESI) available: copies of 1H- and 13C-NMR
spectra of all compounds, NOESY spectra for 5b, 6a, 6b, 20b and 21b See
DOI: 10.1039/x0xx00000x
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To the best of our knowledge, only a few examples of which would afford the ketonitrone as the only product, to
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DOI: 10.1039/C9OB01419E
pyrrolizidines bearing a quaternary center at the ring junction avoid tedious separation of the mixture of regioisomers 12/10.
have been described in the literature, such as compound 9 To this goal, we experienced a possible sequence starting from
prepared in ten steps from a D-glucose thiocyanate scaffold.14 2,3,5-tri-O-benzyl-D-arabinose 13, involving oximation
/
/
Unfortunately, the biological activity of 9 has not been oxidation of alcohol
/ selective reduction of oxime
reported. To access targeted compounds 5,6, ketonitrone 10 deprotection steps. The obtained δ-oxo hydroxylamine A
appeared as an adequate synthon when following a parallel would spontaneously cyclize to target 10 (Scheme 1).
strategy to that used for 2 and 3. Five-membered ketonitrones Alternatively, the reduction of oxime could be effected prior to
such as 10 are invariably prepared by oxidation of the oxidation of the alcohol, affording A in a same manner.
corresponding N-hydroxypyrrolidine precursors, a method O-Protected oxime 1517 was obtained in good yield simply by
yielding mixtures of regioisomers.15,16 In some cases, refluxing aldose 13 and TBDPSO-NH2 in toluene in the
regioisomeric products are difficult to separate and further presence of MgSO4 and PPTS (Scheme 2). Subsequent
transformations must be conducted on the mixture, oxidation with Dess-Martin periodinane afforded ketone 16 in
restraining their use in multistep synthesis.
84% yield. Selective reduction of the C=N bond proved
Thus, we present herein a new synthetic route to nitrone 10, possible with sodium cyanoborohydride, without affecting
enabling its isolation as a unique regioisomer, and its C=O. However, the intermediate nitrone 10 which formed in
transformation into pyrrolizidines 5a,b and indolizidines 6a,b. the reaction mixture after spontaneous removal of the silyl
The glycosidase inhibition profile of 5,6 as well as that of their group underwent further reduction, so that a 50/50 mixture of
monocyclic model 7 was evaluated on a panel of commercial hydroxylamines 11a,b was isolated after standard work-up.
enzymes to provide additional information on the potential of
BnO
BnO
these new constrained iminosugars.14b,c
BnO
BnO
i
ii
iii
O
OH
13
11a,b
Results and discussion
Nitrone 10 has been synthesized in the recent literature by
C O
Ox.
C N
Red.
BnO
BnO
N
N
TBDPSO
TBDPSO
15
16
regioselective
oxidation
of
D-arabino
configured
hydroxylamine 11a.16 A number of reagents have been
evaluated to increase selectivity during dehydrogenation of Scheme 2 oxidation/reduction strategy to access nitrone 10.
Reaction conditions: i) H2N-OTBDPS, PPTS, PhMe (89%); ii) Dess-Martin periodinane,
CH2Cl2 (84%); iii) NaBH3CN, MeOH-HCl (60%).
11a. Hypervalent iodine oxidants afford mainly aldonitrone
12a (5:1 ratio and 89% yield with IBX for instance).16b Aerobic-
oxidation of 11a in the presence of a gold catalyst gave a
mixture of aldonitrone/ketonitrone in a 39/61 ratio (89%
yield).16c The L-xylo configurated hydroxylamine 11b is also a
possible precursor of 10.
Inversion of oxidation/reduction steps was envisioned next. In a
first set of experiments, oxime 15 was reduced with NaBH3CN in a
slightly acidic methanolic solution (Scheme 3). However, various
assays at different pH or with a range of co-solvents invariably
afforded O-deprotected hydroxylamine 17 as the major product, in
an optimized 81% yield. Meanwhile, intermediate 17 was obtained
in a more efficient manner after direct oximation of tri-O-benzyl-
arabinose 13 with NH2OH, HCl and reduction with NaBH3CN (95%
for the two steps). Selective protection of the NH-OH hydroxyl in 17
was effected next in order to minimize the possible oxidation to
oxime during upcoming carbonyl formation. Thus, treatment of 17
with either TBDPS-Cl or PhCOOH/CDI afforded hydroxylamines 18
or 19 in 77% and 83% yields, respectively.
BnO
R1
R1
R2
N
R2
N
BnO
BnO
BnO
BnO
BnO
[Ox]
OH
+
O
N
O
BnO
12a
12b
11a : R1=CH2OBn, R2=H
11b : R1=H, R2=CH2OBn
10
BnO
BnO
a
BnO
BnO
BnO
BnO
BnO
BnO
i (81%)
OH
BnO
BnO
NH2OR
O
15
13
BnO
BnO
BnO
BnO
C N
Red.
O
OH
OH
iii
iv
b
BnO
OH
10
C O
Ox.
N
ii, i
OR
HN
NH
NH
13
14
HO
17
OH
(95%)
RO
c
A
18 : R=TBDPS
19 : R=C(O)Ph
a) oxidation of alcohol; b) reduction of oxime; c) deprotection
Scheme 3 synthesis of nitrone 10 by reduction/oxidation of oximes.
Reaction conditions: i) NaBH3CN, MeOH-HCl; ii) NH2OH.HCl, MeONa, MeOH; iii) for 18,
TBDPS-Cl, NEt3, CH2Cl2 (77%) and for 19, PhCOOH, carbonyldiimidazole, CH2Cl2 (83%);
iv) CrO3-H2SO4 (Jones reagent), acetone, –20 °C (40% from 18, 54% from 19).
Scheme 1 possible synthetic access to ketonitrone 10.
Oxidation of 11b has not been reported yet, but the treatment
of its enantiomer with either hypervalent iodine reagents16b or
with the system air/Ru catalyst16a gave unsatisfactory results
with either low ratio of ketonitrone or low yields. For this
reason, we focused on a possible new synthetic access to 10,
A number of oxidizing reagents were tested next on 17, 18 or 19 to
produce nitrone 10 or a possible O-protected precursor A (Scheme
1). Thus, pyridinium dichromate, 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone, 2-iodoxybenzoic acid, Dess-Martin periodinane,
2 | J. Name., 2012, 00, 1-3
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tetrapropylammonium perruthenate, or Swern and Moffat produced, which were separated by silica gel chromatography at
oxidation protocols proved unsuccessful to this aim, giving rise this stage (20a/20b), or more easily at the nDeOxtI:s1t0e.p10(3V29ie1/wCa/9A2rOt1icBbl0e)1O.4nT1lhi9nEee
either to very low conversion or to oxidation at both the secondary configurations of both isomers were assigned unambiguously by
alcohol and the hydroxylamine function. However, to our delight NMR (see SI). Whatever the temperature or the additive used, the
the strongly acidic Jones oxidizing reagent allowed selective 2,3-trans isomers 20b and 21b were obtained as major products.
oxidation of the secondary alcohol and NH-O-deprotection at the However, the modulation of the reaction conditions makes it
same time, affording the expected nitrone 10 in 40% and 54% yield possible to increase the ratio of the 2,3-cis epimers 20a or 21a. The
from 18 or 19 respectively. Under these same conditions no nitrone obtained results lead to the following observations: a) nucleophilic
was isolated starting from unprotected hydroxylamine 17.
attack occurs mainly from the Re face of 10, affording the 2,3-trans
isomers 20b and 21b as major products; b) unsurprisingly, better
control occurs when lowering the temperature (entries 1,2 or 8-10),
increasing the ratio of major isomers b vs a; c) unlike what could be
observed with the addition of Grignard reagents to six-membered
ketonitrone 1,5,6 ZnCl2 as the additive, premixed with the Grignard
reagent, had no significant effect on the stereoselectivity of
allylation (entry 7) and it completely annihilated the reactivity of
vinylmagnesium bromide (entry 3); d) Et2AlCl as an additive slightly
disfavoured the Re attack, which improved the yield of isomer a
(entry 5 or 10); e) a vinyl aluminum is not the reactive species in the
presence of Et2AlCl, since a control experiment including initial
transmetallation did not produce any product (entry 11). The
stereoselectivity of the reaction observed here is in agreement with
former results from the literature. Indeed, although organometallic
additions onto six-membered nitrones where reported to favor the
formation of a 2,3-cis isomer,18 it is agreed that steric control occurs
in all cases with five-membered nitrones, affording the 2,3-trans
adducts with excellent selectivities.2,19 Here, in the absence of
additive, the C-3 OBn substituent induces direct steric hindrance
promoting attack of the Grignard reagent from the Re face. In the
presence of diethylaluminum chloride, competition may occur
between Grignard reagent and Lewis acid to occupy the less
hindered side, one situation giving classically the 2,3-trans isomer,
the other one affording the 2,3-cis product.20 No further attempts
were conducted to improve or invert selectivity since each isomer
had to be used in the next steps.
Targeted pyrrolizidines 5 and indolizidines 6 might be obtained next
starting with ketonitrone 10, by following the strategy that was
exploited for the synthesis of 2 and 3 from ketonitrone 1.5,6 A key
nucleophilic vinylation or allylation is required as the first step to
produce the pivotal quaternary center. To this aim, nitrone 10 was
subjected to addition of vinylmagnesium bromide and
allylmagnesium bromide under various conditions of temperature
and in the presence of a Lewis acid (Table 1).2i,j
Table 1 nucleophilic addition of Grignard reagent to nitrone 10a
O
BnO
H
H
1)
RMgCl
solvent
R
N
N
N
BnO
BnO
2
5
R
3
4
T°, additive
BnO
BnO
BnO
OBn
OBn
OBn
2) Zn, AcOH
10
20a: R=vinyl
21a: R=allyl
20b: R=vinyl
21b: R=allyl
Entry
R
additive
T (°C)
yieldb
drc
a:b
1
2
vinyl
vinyl
vinyl
vinyl
vinyl
allyl
allyl
allyl
allyl
allyl
allyl
allyl
none
none
–78 °C
0 °C
55%
52%
9 : 91
21 : 79
–
d
e
3
ZnCl2
–78 °C
–78 °C
–30 °C
–78 °C
–78 °C
–78 °C
–50 °C
–30 °C
–30 °C
0 °C
–
4
Et2AlClf
Et2AlClf
none
59%
55%
72%
75%
80%
78%
83%
28 : 72
31 : 69
10 : 90
13 : 87
18 : 82
23 : 77
35 : 65
–
Completion of the synthesis of pyrrolizidines 5 and indolizidines 6
was accomplished via N-allylation of 20 or 21 with allylbromide to
produce pyrrolidines 22 or 23 respectively in good yield (Scheme 4).
Subsequent ring-closing metathesis was performed in refluxing
dichloromethane using Grubb’s II catalyst (5 mol%) to give the
sterically congested bicyclic systems 24 and 25.21 Finally,
hydrogenation of the double bond and removal of benzyl protecting
groups were effected at once under hydrogen atmosphere in the
presence of Pd/C in an acidic medium. After neutralization with ion
exchange resin, pyrrolizidines 5a,b and indolizidines 6a,b were
purified by standard chromatography using CHCl3/MeOH/NH4OH
(6/4/1) as the eluent and were subjected next to enzyme inhibition
assays.
5
6
d
7
ZnCl2
8
Et2AlClf
Et2AlClf
Et2AlClf
Et2AlCld
Et2AlClf
9
10
11
12
e
–
37%
34 : 66
a Reactions performed in CH2Cl2 (without Lewis acid or in the presence of ZnCl2)
b
or in Et2O (when using Et2AlCl) with 2.5 equiv. of Grignard reagent. Isolated
yield (chromatography on silica gel). c Diastereoisomeric ratios were determined
d
from 1H-NMR analysis of the crude reaction mixture. Lewis acid and Grignard
reagent were pre-mixed together before addition of 10. e No reaction occurred. f
Et2AlCl (4 equiv.) was premixed with 10 in Et2O at the reaction temperature
during 15 min before addition of Grignard reagent.
Due to the instability of the formed hydroxylamines, the reaction
sequence combined nucleophilic addition of the organometallic and
reduction of N-OH with Zn in acetic acid to afford pyrrolidines
20,21. As shown in Table, both possible stereoisomers were
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5
DOI: 10.1039/C9OB01419E
N
7a
BnO
BnO
N
Table 2 Reported inhibitory activities of DAB and of some known bicyclic
BnO
ii
iii
3
analogues against various α-glucosidases.a
i
2
5
5a
20a
1
2
3
4
85%
48%
83%
BnO
OBn
OBn
α-glucosidase
yeast
(IC50
rice
A. niger
(IC50)
BnO
BnO
OBn
OBn
22a
24a
)
(IC50
)
H
N
HO
0.33 µM [7c]
0.15 µM [7e]
1.2 µM [7f]
120 µM [7f]
250 µM [23]
218 µM [7c]
16 µM [7a]
400 µM [7f]
N
N
iii
ii
BnO
i
5b
20b
HO
91%
52%
51%
OH
7
BnO
22b
24b
H
N
HO
no inhib. [22]
no inhib. [22]
100 µM [22]
5
HO
N
8a
N
BnO
BnO
BnO
OH
ii
iii
3
6a
6b
26
1
2
40%
83%
OH
BnO
OBn
OBn
BnO
OBn
N
21a
+
HO
23a
25a
i
ca 1 mM [11c]
ca 1 mM [11c]
4.5 µM [11d]
90%
H
21b
HO
OH
N
27
N
iii
BnO
ii
S
N-nBu
54%
51%
BnO
BnO
OBn
[Ki=183 µM] [7b]
not determined
[Ki=419 µM] [7b]
N
23b
25b
Scheme 4 synthesis of iminosugars 5a,b and 6a,b.
Reaction conditions: i) Allyl-Br, K2CO3, KI cat., CH3CN; ii) CH2Cl2, Grubbs II cat., reflux; iii)
H2, Pd/C, MeOH-HCl 6M.
HO
OH
28
a Corresponding references in brackets.
Biological evaluation
In turn, the hydroxymethyl substituent is preserved in the
structure of 5,6 emerging either on one side of the bicyclic
iminosugars (isomers a) or on the other (isomers b). Enzymatic
assays were performed on a series of commercial glycosidases
(-glucosidase from rice and from yeast, -glucosidase from
almond, -glucosidase and -rhamnosidase from A. niger, -
galactosidase from A. orizae, -mannosidase and -N-
acetylglucosaminidase from Jack bean, -galactosidase from
green coffee bean and -fucosidase from bovine kidney) to
assess potency and selectivity of these new compounds (Table
3). Owing to some inhomogeneity in the published inhibition
data of DAB, notably towards α-glucosidase from rice (Table
2), a prepared sample of this compound was tested under the
same conditions than 5,6 to ensure accurate correlation
resulting from strictly identical experimental conditions. To
this end, DAB (7) was prepared by hydrogenation of nitrone
12a according to the reported procedure.24 A first set of
biological assays afforded the % inhibition of a given enzyme
induced by 1 mM of the tested iminosugar. In cases where
inhibition was greater than 95%, IC50 values were determined
further by assaying decreasing concentrations of inhibitor.
Total annihilation (>95%) of enzyme activity at 1 mM
concentration is generally a prerequisite for high inhibition
potencies, usually in the micromolar range. On the opposite,
%inhibition below this threshold are typical of modest or poor
inhibitors with half maximal inhibitory concentrations usually
above 100 µM. Former results from our laboratories have
always followed this empirical rule.
The iminosugar 1,4-dideoxy-1,4-imino-D-arabinitol (DAB, 7)
entails a coveted structural framework due its specific
hydroxyl distribution, closely related to that of glucose at C-
3,4,6. As a consequence, DAB and some derivatives have
strong affinities for enzymes operating with glucosides or
glucoconjugates, and strong inhibition has been disclosed
towards α-glucosidase from yeast or glycogen phosphorylase
for instance.7,9 However, the flexibility of the five-membered
ring as well as structural similarities of DAB with other
biologically relevant carbohydrates such as arabinose or
mannose induce potent inhibition of other series of enzymes,
reducing the potential of 7 as a therapeutic agent due to
possible deleterious cross-inhibition.
Thus, introduction of additional substituents into the 5-
membered ring is usually achieved with the aim of increasing
potency and/or selectivity towards a specific enzymatic
activity. Modification of the DAB scaffold towards bicyclic
structures has already been envisioned, giving rise to inhibitors
with various properties (Table 2). Hence, the spirocyclopropyl
substituent in 26 annihilates the inhibition potency of DAB
towards α-glucosidases from rice or yeast.22 A fused cycle such
as in pyrrolizidine 27 had likewise a deleterious effect against
these same enzymes.11c-d,17 Surprisingly, an increase in
inhibition was observed towards amyloglucosidase from A.
niger, making pyrrolizidine 27 a powerful and highly selective
inhibitor of this isozyme. Incorporation of the hydroxymethyl
substituent into a thioimidate cycle as in 28 proved also
detrimental for inhibition, irrespective of the glucosidase.7b
4 | J. Name., 2012, 00, 1-3
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Table 3 Glycosidase Inhibition potencies of prepared compounds a,b
being more active than DAB itself. InterestinglyV,ie6waArtsichleoOwnleinde
exclusive inhibition of this enzyme amonDgOtIh: o10s.e10t3e9s/Cte9dO,Ba0l1l4t1h9eE
others being almost unaffected at 1 mM. Pyrrolizidine 5a
showed cross-inhibition of yeast α-glucosidase (IC50=15 µM)
but was inactive against all the other tested enzymes. Thus
compounds 5a and 6a show an activity comparable to DAB
towards α-glucosidases, but proved much more selective for
these specific hydrolases. This behaviour is very similar to that
of homologues 2 and 3 (Figure 1) by analogy with the
monocyclic model DNJ. The C-branched fused cycle in these
compounds seems easily tolerated by α-glucosidases
(particularly that from rice) but induces a steric clash in the
catalytic site of ß-glucosidases, which might contribute to their
excellent selectivity when compared to the monocyclic
counterparts. Nevertheless, pyrrolizidine 5a and indolizidine
6a are significantly less potent inhibitors of rice α-glucosidase
(an enzyme from the GH-31 family) than homologues 2 and 3.
The latter feature an incremental OH group, corresponding to
2-OH of glucose. This additional hydroxyl, also present in the
structure of DNJ, is certainly a pivotal binding element that
reinforces protein-inhibitor interactions up to two orders of
magnitude (IC50 ca. 50 nM for 2,3 or DNJ;5,6 IC50 ca. 5-10 µM
for 5a, 6a or DAB). This is in agreement with results from the
literature, where stabilization of protein-inhibitor complex by
one binding OH was estimated at 2.5 kcal/mol, decreasing the
binding constant by a factor of 70 at 298 K.26
Enzyme
5a
6a
5b
6b
DAB
-glucosidase
98%
99%
53%
90%
99%
(7.8 µM)
(rice)
(9.3 µM)
(4.2 µM)
-glucosidase
100%
57%
47%
28%
100%
(0.69
µM)
(Sac. cerevisiae)
(15 µM)
-glucosidase
(almond)
19%
18%
58%
15%
30%
6%
NI
11%
NI
26%
9%
10%
37%
–22%c
11%
24%
NI
95%
(79 µM)
-glucosidase
(Asp. niger)
96%
(62 µM)
-galactosidase
(Asp. orizae)
13%
9%
76%
-mannosidase
(Jack bean)
23%
29%
NI
97%
(49 µM)
-rhamnosidase
(Asp. niger)
7%
34%
11%
14%
37%
-galactosidase
NI
(green coffee)
-GlcNAc-ase
(Jack bean)
8%
–11%c
22%
15%
16%
6%
-fucosidase
66%
64%
(bovine kidney)
a
% inhibition at 1 mM of inhibitor (IC50 in brackets, determined when >95%
b
inhibition); NI means no impact on enzyme activity (less than 5% inhibition
or activation); c negative values mean activation of enzyme activity.
In our assay (Table 3), DAB proved to be highly active towards
α-glucosidase from rice (>95% at 1 mM, IC50=7.8 µM),
significantly more potent than described in some papers (Table
2). The corresponding hydrochloride (obtained by addition of
aqueous HCl to DAB, then evaporation) was tested likewise
and afforded the same potent inhibition value. Furthermore,
another sample of DAB 7, prepared independently by an
alternative method,25 provided strictly identical performances.
This discrepancy with some literature results is puzzling, but
might be due to disparity in enzyme sources. In agreement
with results from the literature,7b,c,e,f DAB proved also very
active against other glycosidases. It displayed IC50=0.69 µM
against α-glucosidase from yeast, and potent inhibition of ß-
glucosidases (almond: IC50=79 µM, A. niger: IC50=62 µM) or α-
mannosidase (IC50=49 µM). In spite of few structural
differences, pyrrolizidines 5a,b and indolizidines 6a,b displayed
significantly varied behaviour. First of all, the position of the
free hydroxymethyl substituent proved crucial to maintain
inhibition potency. Indeed 5b and 6b, which are structurally
related to L-sugars, proved almost inactive against all tested
enzymes. Marginal effect was obtained with indolizidine 6b,
which causes 90% inhibition of rice α-glucosidase at 1 mM
concentration. But, as expected, this activity decreased rapidly
with concentration and only 46% inhibition was maintained at
100 µM (i.e., IC50>100 µM). Epimers 5a,6a for their part,
proved to be potent inhibitors of α-glucosidase from rice
(IC50=9.3 µM and IC50=4.2 µM respectively), indolizidine 6a
Conclusions
In conclusion, we report here the synthesis of a new series of
pyrrolizidines 5a,b and indolizidines 6a,b as branched bicyclic
analogues of the known DAB 7. As expected, the D-configured
iminosugars 5a and 6a displayed potent inhibition of rice α-
glucosidase (IC50=9.3 µM for 5a and 4.2 µM for 6a),
comparable to that of DAB (IC50=7.8 µM). Moreover,
iminosugars 5a,6a proved much more selective than their
monocyclic analogue, DAB being also a potent inhibitor of ß-
glucosidases and of α-mannosidase. These results are in
agreement with former results from the literature, showing
that six-membered homologues with
a carbon-branched
substituent retain strong inhibition potencies towards α-
glucosidase from the GH31 family. Conversely, this distinctive
structural feature abolishes recognition by other enzymes,
giving rise to highly selective inhibitors. Work is in progress to
understand the high selectivity of branched bicyclic
iminosugars on a molecular level and to evaluate these
compounds on other GH31 α-glucosidases of therapeutic
relevance.
Experimental SECTION
General methods
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J. Name., 2013, 00, 1-3 | 5
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Organic & Biomolecular Chemistry
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Journal Name
Reactants and reagents were purchased from standard suppliers 7.72‒7.81 (5H, m, 5 Ar-H); 13C NMR (CDCl3, 500 VMiewHAzr)ticδle O1n9lin.4e
DOI: 10.1039/C9OB01419E
(Sigma-Aldrich, Alfa-Aesar, Fisher Scientific) and were used without (C(CH3)3), 19.5 (C(CH3)3 ), 71.2 (Ph-CH2), 73.1 (Ph-CH2), 73.4 (Ph-
further purification. All reactions were conducted under Ar CH2), 73.5 (CH), 74.2 (Ph-CH2), 74.4 (Ph-CH2), 74.5 (Ph-CH2), 74.7
atmosphere using anhydrous solvents, air- or moisture-sensitive (Ph-CH2), 75.9 (CH), 84.0 (CH), 84.2 (CH), 127.7-128.7 (25 x Ar-C),
reagents and products were stored at ‒20°C under Ar. Silica gel 129.9-130.0 (Si-Ar-Cpara), 133.0 (Ar-CIV), 133.2 (Ar-CIV), 133.3 (Ar-CIV),
F254 (0.2 mm) was used for TLC plates, detection being carried out 134.9 (Si-Ar-CIV), 135.6‒135.7 (Si-Ar-Cmeta, Si-Ar-Cortho), 153.2 (C-1),
by spraying with an alcoholic solution of phosphomolybdic acid or 156.0 (C-1), 206.3 (C=O), 206.4 (C=O); m/z calcd for C42H451NO5NaSi
an aqueous solution of KMnO4 (2%) / Na2CO3 (4%), followed by [M + Na]+ 694.2965, found 694.2961
heating. Reactions were monitored either by TLC. Column
chromatography was performed over silica gel M 9385 (40‒63 m)
(2R,3R,4R)-1,3,4-tris(benzyloxy)-5-hydroxyamino-pentan-2-ol
(17): To a solution of 2,3,5-tri-O-benzyl-D-arabinose 13 (10 g, 23.8
mmol, 1.0 equiv.) in dry methanol (60 mL) under argon was added
Kieselgel 60. NMR spectra were recorded on Bruker AC 250 (250
1
1
MHz for H, 62.5 MHz for 13C), 500 (500 MHz for H, 125 MHz for
13C) or 600 (600 MHz for 1H, 150 MHz for 13C) spectrometers.
Chemical shifts are expressed in parts per million (ppm) and were
calibrated to deuterated or residual non-deuterated solvent peaks
for 1H and 13C spectra. Coupling constants are in Hz and splitting
pattern abbreviations are: br, broad; s, singlet; d, doublet; t, triplet;
m, multiplet. DEPT 1D NMR experiment, COSY, HSQC, and HMBC 2D
NMR experiments were used to confirm the NMR peak assignments
for all compounds. Optical rotations were determined at 20 °C with
hydroxylamine hydrochloride (3.31 g, 47.6 mmol, 2 equiv.) and
sodium methoxide (1.93 g, 35.7 mmol, 1.5 equiv.). The resulting
solution was stirred at room temperature for 2 h then concentrated
in vacuum. The residue was dissolved in CH2Cl2 (40 mL) and the
mixture was washed with water (3 x 10 mL), dried (MgSO4) and
concentrated under reduced pressure. The residue was dissolved in
THF (150 mL), and sodium cyanoborohydride (2,99 g, 47,6 mmol, 2
equiv.) was added. Two drops of methyl orange were added as the
indicator and a concentrated HCl/methanol (v/v = 1/3) mixture was
carefully added to the solution at room temperature to maintain
the pH value between 3 and 4. After completion of the reaction
(characterized by persistence of the red color of the solution), the
resulting mixture was concentrated in vacuo. The residue was
dissolved in ethyl acetate (50 mL) and washed with 1 N NaOH
solution (2 x 10 mL) and then brine (2 x 20 mL). After drying
(MgSO4) and concentration under reduced pressure, the crude
product was purified by flash chromatography (silica gel, petroleum
ether/EtOAc 12:1 to 1:1) to afford hydroxylamine 17 (9.88g, 95% for
a
Perkin-Elmer Model 241 polarimeter, in chloroform or in
methanol. High Resolution Mass Spectra (HRMS) were performed
on Q-TOF Micro micromass positive ESI (CV = 30 V).
(2R,3R,4R)-2,3,5-tris(benzyloxy)-4-hydroxypentanal
O-(tert-
butyldiphenylsilyl) oxime (15): To a solution of 2,3,5-tri-O-benzyl-D-
arabinose 13 (12.6 g, 30 mmol, 1.0 equiv.) in dry toluene (120 mL)
under argon was added MgSO4 (14.4 g, 120 mmol, 4.0 equiv.). The
suspension was heated to reflux and stirred 5 min, then O-tert-
butyldiphenylsilylhydroxylamine (12.2 g, 45 mmol, 1.5 equiv.) and
pyridinium p-toluenesulfonate (251 mg, 1 mmol, 0.033 equiv.) were
added. The mixture was stirred at this temperature for 30 min then
cooled at room temperature. The suspension was passed through a
pad of celite and rinsed with toluene. The filtrate was washed with
a saturated aqueous solution of sodium bicarbonate (2 x 20 mL) and
then brine (20 mL). After drying (MgSO4) and concentration under
reduced pressure, the crude product was purified by flash
chromatography (silica gel, petroleum ether/EtOAc 1:12 to 1:5) to
afford known 1517,27 (mixture of Z an E diastereomers, 18 g, 89 %)
as a pale-yellow oil.
[훼]2퐷0
2 steps) as a yellow oil.
+19 (c 1 in CHCl3); νmax/cm-1 3399,
1
3063, 2913, 1737, 1496, 1244, 1210, 1090, 1028; H NMR (CDCl3,
500 MHz) δ 3.10‒3.20 (2H, m, H-5, H-5’), 3.65‒3.72 (3H, m, H-1, H-
1’, H-3), 4.00‒4.03 (1H, m, H-2), 4.09‒4.11 (1H, m, H-4), 4.51‒4.71
(6H, m, 3 x Ph-CH2), 7.25‒7.34 (15H, m, 15 Ar-H); 13C NMR (CDCl3,
500 MHz) δ 53.8 (C-5), 70.5 (C-2), 71.3 (C-1), 73.4 (Ph-CH2), 73.4
(Ph-CH2), 73.7 (Ph-CH2), 75.9 (C-4), 78.3 (C-3), 127.7‒128.4 (15 x Ar-
C), 137.9 (Ar-CIV), 137.9 (Ar-CIV), 138.1 (Ar-CIV); m/z calcd for
C26H31NO5Na [M + Na]+ 460.2100, found 460.2105.
(7R,8R,9R)-7,8,10-tris(benzyloxy)-2,2-dimethyl-3,3-diphenyl-4-
oxa-5-aza-3-siladecan-9-ol (18): To a stirred solution of (2R,3R,4R)-
2,3,5-tris(benzyloxy)-1-hydroxyamino-pentan-2-ol 17 (1 g, 2.3
mmol, 1 equiv.) in dry CH2Cl2 (25 mL) at room temperature under
argon was added dropwise triethylamine (690 mg, 2.53 mmol, 1.1
equiv.). The mixture was stirred at this temperature for 1h and tert-
butyldiphenylchlorosilane (680 mg, 2.2 mmol, 2.2 equiv.) was
added. The resulting mixture was stirred at room temperature
overnight and then concentrated in vacuo. The residue was
dissolved in THF (10 mL), passed through a pad of celite and rinsed
with THF (3 x 5 mL). EtOAc (25 mL) was added to the filtrate and the
(2R,3S)-2,3,5-tris(benzyloxy)-4-oxopentanal
O-(tert-
butyldiphenylsilyl) oxime (16): To a solution of 15 (2.69 g, 4 mmol,
1.0 equiv.) in dry CH2Cl2 (40 mL) under argon was added Dess-
Martin periodinane (1.86 g, 4.4 mmol, 1.1 equiv.). The resulting
solution was stirred 1h at room temperature then washed with a
saturated aqueous solution of sodium bicarbonate (2 x 20 mL) and
brine (20 mL). After drying (MgSO4) and concentration under
reduced pressure, the crude product was purified by flash
chromatography (silica gel, petroleum ether/EtOAc 1:19) to afford
16 (mixture of Z and E diastereomers, 2.25 g, 84 %) as a pale-yellow
oil. νmax/cm-1 3066, 3032, 2933, 2859, 1735, 1455, 1428, 1243,
mixture was washed with
a saturated aqueous solution of
ammonium chloride (10 mL) and then brine (10 mL). After drying
(MgSO4) and concentration under reduced pressure, the crude
product was purified by flash chromatography (silica gel, petroleum
ether/EtOAc 1:9 to 1:4) to afford 18 (1.19 g, 77 %) as a yellow oil.
1
[훼]2퐷0
1112; H NMR (CDCl3, 500 MHz) δ 1.17 (9H, s, C(CH3)3), 4.16‒4.66
+ 27 (c 1 in CHCl3); νmax/cm-1 3476, 3031, 2931, 2858, 1454,
(10H, m, H-2, H-3, H-5, 3 x Ph-CH2), 7.12‒7.40 (21H, m, 20 Ar-H),
1428, 1109, 1028; 1H NMR (CDCl3, 250 MHz) δ 1.11 (9H, s, 3 x CH3),
6 | J. Name., 2012, 00, 1-3
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ARTICLE
2.95‒3.16 (2H, m, H-6), 3.64‒3.68 (3H, m, H-8, H-10), 3.90‒3.97 and concentration under reduced pressure, the crude product was
View Article Online
DOI: 10.1039/C9OB01419E
(1H, m, H-9), 4.20‒4.26 (1H, m, H-7), 4.50‒4.73 (6H, m, 3 x Ph-CH2), purified by flash chromatography (silica gel, petroleum ether/EtOAc
[훼]20
7.20‒7.42 (21H, m, 21 x Ar-H), 7.65‒7.73 (4H, m, 4 x Ar-H); 13C NMR
(CDCl3, 250 MHz) δ 19.2 (C-2), 27.5 (3 x CH3), 54.2 (C-6), 70.8 (C-9),
71.1 (C-10), 73.6 (Ph-CH2), 73.7 (2 x Ph-CH2), 75.2 (C-7), 77.7 (C-8),
127.6‒128.6 (15 x Ar-C), 129.7 (2 x Si-Ar-Cpara), 133.9 (2 x Si-Ar-CIV),
135.7 (4 x Si-Ar-Cmeta), 135.8 (4 x Si-Ar-Cortho), 138.0 (Ar-CIV), 138.1
(Ar-CIV), 138.2 (Ar-CIV); m/z calcd for C42H50NO5Si [M + H]+ 676.3458,
found 676.3450.
1:9 to 1:1) to afford 10 as a brown oil.
‒ 62 (c 1 in CHCl3);
퐷
νmax/cm-1 3412, 3053, 3030, 2860, 1606, 1496, 1453, 1236, 1089; 1H
NMR (CDCl3, 250 MHz) δ 3.90‒3.95 (1H, m, H-2), 4.15‒4.18 (1H, m,
H-3), 4.36‒4.42 (2H, m, H-2’, H-6), 4.49 (s, 2H, Ph-CH2), 4.61 (s, 2H,
Ph-CH2), 4.66‒4.74 (3H, m, H-6’, Ph-CH2), 4.82‒4.84 (1H, m, H-4),
7.27‒7.41 (15H, m, 15 x Ar-H); 13C NMR (CDCl3, 250 MHz) δ 62.6 (C-
6), 67.5 (C-2), 71.7 (Ph-CH2), 72.6 (Ph-CH2), 73.7 (Ph-CH2), 76.6 (C-3),
83.9 (C-4), 127.9‒128.7 (15 x Ar-C), 136.9 (Ar-CIV), 137.3 (Ar-CIV),
137.5 (Ar-CIV), 144.3 (C-5); m/z calcd for C26H28NO4 [M + H]+
418.2018, found 418.2012.
(2R,3R,4R)-5-(benzoyloxyamino)-1,3,4-tris(benzyloxy)-pentan-2-
ol (19): A stirred solution of benzoic acid (307 mg, 2.52 mmol, 1.1
equiv.) in dry CH2Cl2 (20 mL) under argon was cooled to 0 °C and
carbonyldiimidazole (408 mg, 2.52 mmol, 1.1 equiv.) was added.
The mixture was stirred at this temperature for 30 min and 17•HCl
(1.09 g, 2.29 mmol, 1 equiv., previously prepared by addition of a
0,5 M hydrogen chloride solution in MeOH to 17, stirring for 30
minutes and concentration under reduced pressure) was added.
The ice-bath was removed, and the reaction mixture was stirred at
room temperature overnight. The resulting mixture was then
passed through a pad of celite and rinsed with CH2Cl2 (3 x 10 mL).
The filtrate was washed with a saturated aqueous solution of
sodium bicarbonate (10 mL) and then brine (10 mL). After drying
(MgSO4) and concentration under reduced pressure, the crude
product was purified by flash chromatography (silica gel, petroleum
ether/EtOAc 1:9 to 1:4) to afford 19 (1.03 g, 83 %) as a yellow oil.
General procedure for the addition of Grignard reagent to
nitrone 10 and for the reduction of the obtained hydroxylamine to
amine: To a well-stired solution of nitrone 10 (1 equiv.) in dry Et2O
(50 mL) under argon cooled at ‒30 °C was added dropwise a 1.0 M
solution of diethylaluminum chloride in hexanes (4 equiv.). The
mixture was stirred at this temperature for 30 min. and the
Grignard reagent (2.5 equiv.) was added dropwise. The resulting
solution was stirred at the same temperature for 4 h then was
quenched with a saturated aqueous solution of ammonium chloride
(20 mL). The organic layer was separated, and the aqueous layer
was extracted with CH2Cl2 (3 x 10 mL). The combined organic
extracts were washed with brine, dried (MgSO4) and concentrated
under reduced pressure to afford a mixture of two hydroxylamines,
[훼]2퐷0
+15.9 (c 1 in CHCl3); νmax/cm-1 3470, 3030, 2867, 1721, 1453, which were used in the next step without purification.
1271, 1089, 1027; 1H NMR (DMSO-d6, 500 MHz) δ 3.26‒3.31 (1H, m,
H-5), 3.36‒3.41 (1H, m, H-5’), 3.60 (1H, dd, J = 5.4, 10 Hz, H-1),
3.67‒3.70 (2H, m, H-1’, H-3), 3.90‒3.95 (1H, m, H-2), 4.03‒4.07 (1H,
m, H-4), 4.52 (2H, d, J = 2.6 Hz, Ph-CH2-O-CH2), 4.57 (2H, s, Ph-CH2),
4.64 (2H, s, Ph-CH2), 5.05 (1H, d, J = 6 Hz, OH), 7.25‒7.38 (15H, m,
15 x Ar-H), 7.54 (2H, dd, J = 7.8, 7.8 Hz, CO-Ar-Hmeta), 7.68 (1H, dd, J
= 7.5, 7.5 Hz, CO-Ar-Hpara), 7.92 (2H, dd, J = 8.4, 1.3 Hz, CO-Ar-Hortho),
8.38 (1H, dd, J = 6.2, 4.5 Hz, NH); 13C NMR (DMSO-d6, 500 MHz) δ
52.6 (C-5), 69.3 (C-2), 72.0 (C-1), 72.4 (Ph-CH2), 72.7 (Ph-CH2), 73.5
(Ph-CH2), 75.9 (C-4), 79.8 (C-3), 127.4‒128.2 (15 x Ar-C), 128.4 (CO-
Ar-CIV), 128.8 (CO-Ar-Cortho), 128.9 (CO-Ar-Cmeta), 133.4 (CO-Ar-Cpara),
138.5 (Ar-CIV), 138.6 (Ar-CIV), 138.7 (Ar-CIV), 165.4 (CO); m/z calcd
for C23H35NO6Na [M + Na]+ 564.2362, found 564.2368.
To a well-stirred solution of activated zinc powder (10 equiv.) in
AcOH (10 mL) was added copper acetate monohydrate (0.1 equiv.).
The mixture was stirred at 30 °C for 1 h until copper colour
disappeared. A solution of the two diastereomeric hydroxylamines
(1 equiv.) in AcOH (10 mL) was added, and the reaction mixture was
stirred at 30 °C overnight. Solvent was removed in vacuum, the
residue was neutralized with a saturated solution of NaHCO3 and
washed three times with EtOAc. The organic layers were combined,
washed with brine, dried (MgSO4) and concentrated under reduced
pressure. The crude product was purified by flash chromatography
(silica gel, petroleum ether/EtOAc 1:19 to 1:4) to afford pyrrolidines
as yellow oils.
(2R,3R,4R)-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-2-
General procedure for the preparation of (3R,4R)-3,4-
vinylpyrrolidine (20a) and (2S,3R,4R)-3,4-bis(benzyloxy)-2-
(benzyloxymethyl)-2-vinylpyrrolidine (20b): According to the
general method described above, the reaction of vinylmagnesium
bromide and nitrone 10 (1.2 g, 2.91 mmol) afforded amines 20a and
20b (20a:20b = 31:69 from NMR analysis of the crude product),
which were separated by flash chromatography to afford pure
amines 20a (213 mg) then 20b (475 mg) as yellow oils. The overall
yield for the two steps was 55 %.
bis(benzyloxy)-5-(benzyloxymethyl)-3,4-dihydro-2H-pyrrole
1-
oxide (10): To a stirred solution of alcohol 18 or 19 (1.5 mmol, 1
equiv.) in dry acetone (20 mL) under argon at ‒20 °C was added
dropwise a freshly prepared 1.43 M Jones reagent (1.26 mL, 1.8
mmol, 1.2 equiv. of CrO3, prepared by addition of 12 mL of
concentrated sulfuric acid to a stirred solution of 6 g CrO3 in 30 mL
water). The resulting solution was stirred at this temperature for
1h, then another portion of Jones reagent (0.31 mL, 0.45 mmol, 0.3
equiv.) was added. After 30 min., the solution was quenched with
isopropanol (5 mL) and diluted with EtOAc (20 mL). The mixture was
successively washed with a 1 N HCl solution (2 x 10 mL), a 1 N NaOH
solution (2 x 10 mL) and then brine (10 mL). After drying (MgSO4)
(2R,3R,4R)-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-2-
[훼]20
vinylpyrrolidine (20a):
‒ 19.0 (c 0.2 in CHCl3); νmax/cm-1 3336,
퐷
1
3089, 3063, 3030, 2861, 1605, 1496; H NMR (CDCl3, 250 MHz) δ
2.91 (1H, dd, J = 4.3, 12.2 Hz, H-5), 3.23‒3.35 (2H, m, H-5’, BnO-
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Journal Name
CHaHb), 3.48 (1H, d, J = 9.5 Hz, BnO-CHaHb), 4.04‒4.10 (1H, m, H-4), 138.4 (Ar-CIV), 138.7 (Ar-CIV), 138.8 (Ar-CIV); m/z calcdVfioewr ACr2ti9cHle3O4NnlOine3
4.15‒4.1 8 (1H, m, H-3), 4.41‒4.70 (6H, m, 3 x Ph-CH2), 5.25 (1H, dd, [M + H]+ 444.2539, found 444.2549.
DOI: 10.1039/C9OB01419E
J = 1.5, 11 Hz, CHaHb=CH), 5.47 (1H, dd, J = 1.5, 17.5 Hz, CHaHb=CH),
General procedure for the N-allylation of pyrrolidine: To a well-
stired solution of pyrrolidines 20 or 21 (1 equiv.) in dry CH3CN (20
mL) under argon was added potassium carbonate (1.7 equiv.), allyl
bromide (1.6 equiv.) and a catalytic amount of potassium iodide.
The mixture was stirred during 6.5 h at 82 °C then a saturated
aqueous solution of sodium bicarbonate was added. The organic
layer was separated, and the aqueous layer was extracted with
CH2Cl2 (3 x 10 mL). The combined organic extracts were washed
with brine, dried (MgSO4) and concentrated under reduced
pressure. The crude product was purified by flash chromatography
(silica gel, petroleum ether/EtOAc 1:49) to afford N-allyl
pyrrolidines as yellow oils.
6.04 (1H, dd, J = 11, 17.5 Hz, CH2=CH), 7.28‒7.33 (15H, m, 15 x Ar-
H); 13C NMR (CDCl3, 250 MHz) δ 48.5 (C-5), 67.6 (C-2), 72.0 (Ph-CH2),
72.5 (BnO-CH2), 72.7 (Ph-CH2), 73.4 (Ph-CH2), 85.4 (C-4), 86.6 (C-3),
115.4 (CH2=CH), 127.7‒128.5 (15 x Ar-C), 136.5 (CH2=CH), 138.2 (Ar-
CIV), 138.4 (Ar-CIV), 138.7 (Ar-CIV); m/z calcd for C28H32NO3 [M + H]+
430.2382, found 430.2389.
(2S,3R,4R)-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-2-
[훼]20
vinylpyrrolidine (20b):
‒ 31.0 (c 1 in CHCl3); νmax/cm-1 3347,
퐷
1
3089, 3063, 3029, 2862, 1607, 1496; H NMR (CDCl3, 250 MHz) δ
2.77 (1H, s br, NH), 2.96 (1H, dd, J = 4.5, 11.2 Hz, H-5), 3.34 (1H, dd,
J = 7.1, 11.2 Hz, H-5’), 3.62 (1H, d, J = 9.5 Hz, BnO-CHaHb), 3.66 (1H,
d, J = 9.5 Hz, BnO-CHaHb), 4.00 (1H, d, J = 4.1 Hz, H-3), 4.14‒4.20
(1H, m, H-4), 4.51 (2H, d, J = 2.1 Hz, Ph-CH2), 4.59 (2H, d, J = 2.5 Hz,
Ph-CH2), 4.66 (2H, d, J = 2.2 Hz, Ph-CH2), 5.21 (1H, d, J = 10.5 Hz,
CHaHb=CH), 5.38 (1H, d, J = 17.5 Hz, CHaHb=CH), 6.04 (1H, dd, J =
10.5, 17.5 Hz, CH2=CH), 7.35 (15H, m, 15 x Ar-H); 13C NMR (CDCl3,
250 MHz) δ 48.8 (C-5), 67.0 (C-2), 71.7 (BnO-CH2, Ph-CH2), 72.7 (Ph-
CH2), 73.5 (Ph-CH2), 84.5 (C-4), 89.8 (C-3), 114.1 (CH2=CH),
(127.5‒128.4 (15 x Ar-C), 138.3 (Ar-CIV), 138.4 (Ar-CIV), 138.5 (Ar-
CIV), 141.3 (CH2=CH); m/z calcd for C28H32NO3 [M + H]+ 430.2382,
found 430.2392.
(2R,3R,4R)-1-allyl-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-2-
vinylpyrrolidine (22a): According to the above general method, the
N-allylation of vinylpyrrolidine 20a (150 mg, 0.35 mmol) afforded N-
[훼]20
allyl vinylpyrrolidine 22a (139 mg, 85%) as yellow oil.
‒ 20.0 (c
퐷
1 in CHCl3); νmax/cm-1 3089, 3062, 3029, 2865, 1638, 1604, 1500,
1
1451; H NMR (CDCl3, 600 MHz) δ 2.83 (1H, dd, J = 6, 9.5 Hz, H-5),
3.09‒3.16 (3H, m, H-5’, CH2=CH-CH2-N), 3.53 (1H, d, J = 9.6 Hz, BnO-
CHaHb), 3.56 (1H, d, J = 9.6 Hz, BnO-CHaHb), 4.08‒4.11 (1H, m, H-4),
4.22 (1H, d, J = 5.6 Hz, H-3), 4.28‒4.34 (1H, m, H-4), 4.45‒4.53 (4H,
m, 2 x Ph-CH2), 4.57 (1H, d, J = 12 Hz, Ph-CHaHb), 4.62 (1H, d, J = 12
Hz, Ph-CHaHb), 5.05 (1H, d, J = 10 Hz, CHaHb=CH-CH2-N), 5.16 (1H, d,
(2R,3R,4R)-2-allyl-3,4-bis(benzyloxy)-2-
(benzyloxymethyl)pyrrolidine (21a) and (2S,3R,4R)-2-allyl-3,4- J = 16 Hz, CHaHb=CH-CH2-N), 5.27‒5.30 (2H, m, CH2=CH), 5.79‒5.88
bis(benzyloxy)-2-(benzyloxymethyl)pyrrolidine (21b): According to (2H, m, CH2=CH, CH2=CH-CH2-N), 7.28‒736 (15H, m, 15 x Ar-H); 13C
general method, the reaction of allylmagnesium bromide and NMR (CDCl3, 250 MHz) δ 51.8 (CH2=CH-CH2-N), 53.8 (C-5), 68.8 (C-
nitrone 10 (1.2 g, 2.91 mmol) afforded amines 21a and 21b 2), 70.44 (BnO-CH2), 71.8 (Ph-CH2), 72.4 (Ph-CH2), 73.5 (Ph-CH2),
(21a:21b = 35:65 from NMR analysis of the crude); they were 82.4 (C-4), 86.9 (C-3), 116.2 (CH2=CH-CH2-N), 116.5 (CH2=CH),
partially separated by flash chromatography to afford a mixture of 127.5‒128.4 (15 x Ar-C), 135.7 (CH2=CH), 137.0 (CH2=CH-CH2-N),
amines 21a and 21b (970 mg) then pure amine 21b (100 mg) as 138.4 (Ar-CIV), 138.5 (Ar-CIV), 138.8 (Ar-CIV); m/z calcd for C31H36NO3
yellow oils. The overall yield for the two steps was 83 %.
[M + H]+ 470.2695, found 470.2689.
(2R,3R,4R)-2-allyl-3,4-bis(benzyloxy)-2-
(2S,3R,4R)-1-allyl-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-2-
(benzyloxymethyl)pyrrolidine (21a): (from mixture of 21a/21b) 13C vinylpyrrolidine (22b): According to the above general method, the
NMR (CDCl3, 250 MHz) δ 36.3 (CH2=CH-CH), 48.8 (C-5), 65.5 (C-2), N-allylation of vinylpyrrolidine 20b (215 mg, 0.5 mmol) afforded N-
[훼]20
71.7, 72.4, 72.6, 73.3 (4 x Ph-CH2), 85.4 (C-4), 87.3 (C-3), 117.9
(CH2=CH), (127.5‒128.5 (15 x Ar-C), 134.9 (CH2=CH), 138.3 (Ar-CIV),
138.4 (Ar-CIV), 138.6 (Ar-CIV).
allyl vinylpyrrolidine 22b (213 mg, 91%) as yellow oil.
‒ 57 (c 1
퐷
in CHCl3); νmax/cm-1 3087, 3063, 3029, 2863, 1640, 1604, 1498,
1455; H NMR (CDCl3, 250 MHz) δ 2.99‒3.15 (2H, m, H-5, CH2=CH-
1
CHaHb-N), 3.22‒3.29 (1H, m, H-5’), 3.48 (1H, dm, J = 14 Hz CH2=CH-
CHaHb-N), 3.71 (1H, d, J = 9.8 Hz, BnO-CHaHb), 3.88 (1H, d, J = 9.8 Hz,
BnO-CHaHb), 4.06 (1H, d, J = 5.6 Hz, H-3), 4.40‒4.48 (1H, m, H-4),
4.53‒4.61 (4H, m, 2 x Ph-CH2), 4.75 (2H, s, Ph-CH2), 5.10‒5.36 (4H,
m, CH2=CH, CH2=CH-CH2-N), 5.82‒5.97 (2H, m, CH2=CH, CH2=CH-
CH2-N), 7.32 (15H, m, 15 x Ar-H); 13C NMR (CDCl3, 250 MHz) δ 51.9
(CH2=CH-CH2-N), 56.2 (C-5), 68.7 (C-2), 70.05 (BnO-CH2), 71.7 (Ph-
CH2), 72.7 (Ph-CH2), 73.6 (Ph-CH2), 82.4 (C-4), 91.2 (C-3), 115.3
(CH2=CH), 115.8 (CH2=CH-CH2-N), 127.3‒128.3 (15 x Ar-C), 137.1
(CH2=CH-CH2-N), 138.6 (Ar-CIV), 138.7 (Ar-CIV), 138.8 (Ar-CIV), 140.9
(CH2=CH); m/z calcd for C31H36NO3 [M + H]+ 470.2695, found
470.2687.
(2S,3R,4R)-2-allyl-3,4-bis(benzyloxy)-2-
[훼]20
(benzyloxymethyl)pyrrolidine (21b):
‒ 15 (c 1 in CHCl3);
퐷
νmax/cm-1 3089, 3063, 3030, 2861, 1635, 1496, 1453; 1H NMR
(CDCl3, 250 MHz) δ 2.05 (1H, s br, NH), 2.44 (2H, d, J = 7.3 Hz,
CH2=CH-CH2), 2.95 (1H, dd, J = 4.5, 11.5 Hz, H-5), 3.31 (1H, dd, J =
6.5, 11.5 Hz, H-5’), 3.49 (1H, d, J = 9.5 Hz, BnO-CHaHb), 3.55 (1H, d, J
= 9.5 Hz, BnO-CHaHb), 3.83 (1H, d, J = 3.5 Hz, H-3), 4.05‒4.11 (1H, m,
H-4), 4.41‒4.65 (6H, m, 3 x Ph-CH2), 5.01‒5.08 (2H, m, CH2=CH),
5.72‒5.89 (1H, m, CH2=CH), 7.24‒7.32 (15H, m, 15 x Ar-H); 13C NMR
(CDCl3, 250 MHz) δ 40.2 (CH2=CH-CH), 48.9 (C-5), 65.6 (C-2), 71.2
(BnO-CH2), 71.7 (Ph-CH2), 72.5 (Ph-CH2), 73.5 (Ph-CH2), 84.8 (C-4),
88.0 (C-3), 118.2 (CH2=CH), 127.5‒128.5 (15 x Ar-C), 134.3 (CH2=CH),
8 | J. Name., 2012, 00, 1-3
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Page 9 of 12
Organic & Biomolecular Chemistry
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Journal Name
ARTICLE
(2R,3R,4R)-1,2-diallyl-3,4-bis(benzyloxy)-2-
(1R,2R,7aR)-1,2-bis(benzyloxy)-7a-(benzyloxymethyl)-2,3,5,7a-
View Article Online
DOI: 10.1039/C9OB01419E
(benzyloxymethyl)pyrrolidine (23a) and (2S,3R,4R)-1,2-diallyl-3,4- tetrahydro-1H-pyrrolizine (24a): According to general method, the
bis(benzyloxy)-2-(benzyloxymethyl)pyrrolidine (23b): According to metathesis of vinylpyrrolidine 22a (112 mg, 0.24 mmol) afforded
[훼]20
‒ 12 (c 0.57 in CHCl3); νmax/cm-1
the above general method, the N-allylation of the mixture of
pyrrolidine 21a and 21b (353 mg, 0.8 mmol, 21b:22b = 55:65)
afforded N-allyl pyrrolidines 23a and 23b, which were separated by
flash chromatography to afford 23b (226 mg) then 23a (123 mg) as
yellow oils. The overall yield was 90 %. (23b can also be prepared
from pure 21b with comparable yield).
24a (52mg, 48 %) as yellow oil.
퐷
1
3063, 3029, 2915, 2854, 1695, 1498, 1455, 1066; H NMR (CDCl3,
500 MHz) δ 2.69 (1H, dd, J = 5.0, 11.1 Hz, H-3), 3.12 (1H, dd, J = 4.1,
11.1 Hz, H-3’), 3.26‒3.30 (2H, m, H-5, BnO-CHaHb), 3.36 (1H, d, J =
8.7 Hz, BnO-CHaHb), 3.81‒3.86 (2H, m, H-5’, H-2), 4.00 (1H, d, J = 2.8
Hz, H-1), 4.34 (2H, s, Ph-CH2), 4.39 (1H, d, J = 12.1 Hz, PhCHaHb),
4.45 (1H, d, J = 12.1 Hz, PhCHaHb), 4.54 (2H, s, Ph-CH2), 5.77 (1H, d, J
= 5.8 Hz, H-7), 5.85‒5.86 (1H, m, H-6), 7.16‒7.25 (15H, m, 15 x Ar-
H); 13C NMR (CDCl3, 500 MHz) δ 58.2 (C-3), 62.6 (C-5), 71.4 (Ph-CH2),
72.2 (Ph-CH2), 73.5 (Ph-CH2), 76.1 (BnO-CH2), 82.8 (C-2), 83.0 (C-7a),
84.8 (C-1), 127.5‒128.5 (15 x Ar-C), 128.4 (C-6), 129.8 (C-7), 138.4
(Ar-CIV), 138.6 (Ar-CIV), 138.7 (Ar-CIV); m/z calcd for C29H32NO3 [M +
H]+ 442.2382, found 442.2369.
(2R,3R,4R)-1,2-diallyl-3,4-bis(benzyloxy)-2-
[훼]2퐷0
(benzyloxymethyl)pyrrolidine (23a):
‒ 19 (c 1 in CHCl3);
νmax/cm-1 3087, 3065, 3031, 2865, 1639, 1604, 1498, 1451; H NMR
(CDCl3, 250 MHz) δ 2.30‒2.48 (2H, m, CH2=CH-CH2), 2.78‒2.84 (1H,
m, H-5), 3.19‒3.25 (1H, m, H-5’), 3.31‒3.35 (2H, m, CH2=CH-CH2-N),
3.42-3.51 (2H, m, BnO-CH2), 4.11‒4.19 (2H, m, H-4, H-5), 4.42‒4.81
(6H, m, 3 x Ph-CH2), 5.01‒5.22 (4H, m, CH2=CH-CH2, CH2=CH-CH2-N),
5.77‒5.93 (1H, m, CH2=CH-CH2), 5.95‒6.12 (1H, m, CH2=CH-CH2-N),
1
(1R,2R,7aS)-1,2-bis(benzyloxy)-7a-(benzyloxymethyl)-2,3,5,7a-
7.35 (15H, m, 15 x Ar-H); 13C NMR (CDCl3, 250 MHz) δ 35.8 (CH2=CH- tetrahydro-1H-pyrrolizine (24b): According to general method, the
CH2), 52.0 (CH2=CH-CH2-N), 54.2 (C-5), 67.0 (C-2), 71.9 (Ph-CH2), 72.7 metathesis of vinylpyrrolidine 22b (110 mg, 0.23 mmol) afforded
[훼]20
‒ 41 (c 1 in CHCl3); νmax/cm-1
(Ph-CH2), 73.1 (BnO-CH2), 73.4 (Ph-CH2), 82.2 (C-4), 87.6 (C-3), 116.0
(CH2=CH-CH2-N), 116.8 (CH2=CH), 127.4‒128.4 (15 x Ar-C), 136.4
(CH2=CH), 137.3 (CH2=CH-CH2-N), 138.6 (Ar-CIV), 138.6 (Ar-CIV),
139.0 (Ar-CIV); m/z calcd for C32H38NO3 [M + H]+ 484.2852, found
484.2847.
24b (54 mg, 52 %) as yellow oil.
퐷
1
3061, 3029, 2916, 2854, 1695, 1499, 1455, 1066; H NMR (CDCl3,
250 MHz) δ 2.55 (1H, dd, J = 8.0, 9.4 Hz, H-3), 3.36‒3.49 (3H, m, H-
3’, H-5, BnO-CHaHb), 3.58 (1H, d, J = 9.3 Hz, BnO-CHaHb), 3.87‒3.94
(2H, m, H-5’, H-1), 4.25 (1H, m, H-2), 4.54‒4.68 (6H, m, 3 x Ph-CH2),
5.75‒5.82 (2H, m, H-6, H-7), 7.28‒7.31 (15H, m, 15 x Ar-H); 13C NMR
(CDCl3, 250 MHz) δ 57.4 (C-3), 63.0 (C-5), 72.3 (Ph-CH2), 73.2 (Ph-
CH2), 73.6 (Ph-CH2), 73.8 (BnO-CH2), 80.2 (C-7a), 82.4 (C-2), 87.6 (C-
1), 127.3‒128.5 (15 x Ar-C), 127.9 (C-6), 131.7 (C-7), 138.6 (Ar-CIV),
138.6 (Ar-CIV), 138.9 (Ar-CIV); m/z calcd for C29H32NO3 [M + H]+
442.2382, found 442.2386.
(2S,3R,4R)-1,2-diallyl-3,4-bis(benzyloxy)-2-
[훼]2퐷0
(benzyloxymethyl)pyrrolidine (23b):
‒ 36 (c 1 in CHCl3);
νmax/cm-1 3087, 3064, 3029, 2865, 1639, 1605, 1498, 1450; H NMR
(CDCl3, 250 MHz) δ 2.28 (2H, d, J = 6.8, CH2=CH-CH2), 2.98‒3.18 (3H,
m, H-5, CH2=CH-CHaHb-N), 3.46‒3.50 (2H, m, CH2=CH-CHaHb-N, BnO-
CHaHb), 3.67 (1H, d, J = 10.85 Hz, BnO-CHaHb), 4.02 (1H, d, J = 5.3 Hz,
H-3), 4.30‒4.37 (1H, m, H-4), 4.45‒4.78 (6H, m, 3 x Ph-CH2),
1
(1R,2R,8aR)-1,2-bis(benzyloxy)-8a-(benzyloxymethyl)-
4.96‒5.12 (3H, m, CH2=CH-CH2, CHaHb=CH-CH2-N), 5.26 (1H, d, J = 1,2,3,5,8,8a-hexahydroindolizine (25a): According to general
17 Hz, CHaHb=CH-CH2-N), 5.80‒5.99 (2H, m, CH2=CH-CH2, CH2=CH- method, the metathesis of pyrrolidine 23a (126 mg, 0.27 mmol)
[훼]2퐷0
CH2-N), 7.28‒7.37 (15H, m, 15 x Ar-H); 13C NMR (CDCl3, 250 MHz) δ
36.4 (CH2=CH-CH2), 51.7 (CH2=CH-CH2-N), 56.0 (C-5), 67.3 (C-2), 71.5
(BnO-CH2), 71.8 (Ph-CH2), 72.3 (Ph-CH2), 73.5 (Ph-CH2), 82.3 (C-4),
86.8 (C-3), 115.9 (CH2=CH-CH2-N), 117.4 (CH2=CH), 127.3‒128.4 (15
x Ar-C), 134.5 (CH2=CH), 137.2 (CH2=CH-CH2-N), 138.5 (Ar-CIV), 139.0
(Ar-CIV), 139.1 (Ar-CIV); m/z calcd for C32H38NO3 [M + H]+ 484.2852,
found 484.2846.
afforded 25a (50 mg, 40 %) as yellow oil.
‒ 19.0 (c 0.25 in
CHCl3); νmax/cm-1 3063, 3030, 2915, 2853, 1695, 1498, 1455, 1068;
1H NMR (CDCl3, 250 MHz) δ 1.89 (1H, dm, J = 18.1 Hz, H-8), 2.31
(1H, dm, J = 18.1 Hz, H-8’), 2.97 (1H, dd, J = 3.2, 10.0 Hz, H-3), 3.13
(1H, dm, J = 18.0, H-5), 3.26 (1H, dd, J = 7.2, 10 Hz, H-3’), 3.36‒3.50
(3H, m, H-5’, BnO-CH2), 4.07‒4.13 (1H, m, H-2), 4.18 (1H, d, J = 3.2
Hz, H-1), 4.40‒4.60 (6H, m, 3 x Ph-CH2), 5.60‒5.78 (2H, m, H-6, H-7),
7.26‒7.36 (15H, m, 15 x Ar-H); 13C NMR (CDCl3, 250 MHz) δ 23.5 (C-
8), 45.4 (C-5), 55.2 (C-3), 62.4 (C-8a), 68.2 (BnO-CH2), 71.5 (Ph-CH2),
72.2 (Ph-CH2), 73.4 (Ph-CH2), 82.6 (C-2), 86.9 (C-1), 123.5 (C-6 or C-
7), 124.1 (C-6 or C-7), 123.52‒128.4 (15 x Ar-C), 138.3 (Ar-CIV), 138.6
(Ar-CIV), 138.8 (Ar-CIV); m/z calcd for C30H33LiNO3 [M + Li]+ 462.2620,
found 462.2625.
General procedure for the metathesis of pyrrolidine: To a well-
stirred solution of pyrrolidine 22 or 23 (1 equiv.) in dry and degazed
(30 min of argon bubbling) CH2Cl2 (10 mL) under argon was added
second generation Grubbs catalyst (0.05 equiv). The mixture was
stirred overnight at 40°C then second generation Grubbs catalyst
(0.05 equiv) was added additionally. After another 6 h, the resulting
mixture was cooled at room temperature, passed through a pad of
celite and rinsed with Et2O (3 x 5 mL). Finally, the mixture was
concentrated under reduced pressure. The crude product was
purified by flash chromatography (silica gel, petroleum ether/EtOAc
1:3) to afford target compounds as yellow oils.
(1R,2R,8aS)-1,2-bis(benzyloxy)-8a-(benzyloxymethyl)-
1,2,3,5,8,8a-hexahydroindolizine (25b): According to general
method, the metathesis of pyrrolidine 23b (232 mg, 0.5 mmol)
[훼]2퐷0
afforded 25b (120 mg, 54%) as yellow oil.
‒ 17.8 (c 0.5 in
CHCl3); νmax/cm-1 3061, 3029, 2914, 2854, 1695, 1499, 1456, 1065;
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
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Organic & Biomolecular Chemistry
Page 10 of 12
ARTICLE
Journal Name
1H NMR (CDCl3, 250 MHz) δ 2.24 (2H, s br, H-8), 2.98 (1H, dd, J = 4.2, Hz, H-5’), 3.54 (1H, dd, J = 9.2, 11.3 Hz, H-3’), 3.70 (2H, s, BnO-CH2),
View Article Online
13
DOI: 10.1039/C9OB01419E
9.3 Hz, H-3), 3.21 (1H, d, J = 17.8, H-5), 3.30 (1H, d, J = 17.8, H-5’), 3.95 (1H, d, J = 5.7 Hz, H-1), 4.25‒4.29 (1H, m, H-2); C NMR (D2O,
3.53 (1H, dd, J = 8.0, 9.3 Hz, H-3’), 3.62 (1H, d, J = 8.9 Hz, BnO- 500 MHz) δ 17.5 (C-6), 18.5 (C-7), 20.7 (C-8), 43.7 (C-5), 53.2 (C-3),
CHaHb), 3.80 (1H, d, J = 8.9 Hz, BnO-CHaHb), 3.87 (1H, d, J = 2.9 Hz, 60.4 (BnO-CH2), 63.6 (C-8a), 74.1 (C-2), 82.0 (C-1); m/z calcd for
H-1), 4.30‒4.36 (1H, m, H-2), 4.50 (2H, s, Ph-CH2), 4.57 (2H, d, J = C9H18NO3 [M + H]+ 188.1287, found 188.1289.
1.1 Hz, Ph-CH2), 4.72 (2H, d, J = 2.7 Hz, Ph-CH2), 5.67‒5.80 (2H, m,
H-6, H-7), 7.32‒7.43 (15H, m, 15 x Ar-H); 13C NMR (CDCl3, 250 MHz)
δ 28.2 (C-8), 45.9 (C-5), 56.8 (C-3), 62.4 (C-8a), 69.3 (BnO-CH2), 71.4
(Ph-CH2), 72.0 (Ph-CH2), 73.4 (Ph-CH2), 82.5 (C-2), 89.6 (C-1), 123.7
(C-6 or C-7), 124.0 (C-6 or C-7), 127.2‒128.3 (15 x Ar-C), 138.3 (Ar-
CIV), 138.6 (Ar-CIV), 138.7 (Ar-CIV); m/z calcd for C30H33LiNO3 [M + Li]+
462.2620, found 462.2628.
(1R,2R,8aS)-8a-(hydroxymethyl)indolizidine-1,2-diol
(6b): According to general method, the hydrogenolysis of
unsaturated indolizidine 25b (95 mg, 0.21 mmol) afforded 6b
[훼]20
1
(20 mg, 51 %) as brown solid.
‒ 11.7 (c 0.4 in MeOH); H
퐷
NMR (D2O, 500 MHz) δ 1.39‒1.42 (1H, m, H-6), 1.53‒1.72 (5H,
m, H-6’, H-7, H-8), 2.74‒2.77 (1H, m, H-5), 2.82‒2.88 (1H, m, H-
5’), 2.95‒2.99 (1H, m, H-3), 3.20‒3.25 (1H, m, H-3’), 3.74 (1H,
d, J = 11.8 Hz, BnO-CHaHb), 3.78‒3.83 (2H, m, H-1, BnO-CHaHb),
4.18‒4.22 (1H, m, H-2); 13C NMR (D2O, 500 MHz) δ 18.9 (C-6),
19.0 (C-7), 25.0 (C-8), 44.9 (C-5), 54.7 (C-3), 59.2 (BnO-CH2),
64.5 (C-8a), 76.1 (C-2), 84.4 (C-1); m/z calcd for C9H18NO3 [M +
H]+ 188.1287, found 188.1279.
General procedure for the hydrogenolysis of unsaturated
pyrrolizidines and indolizidines : To a well-stirred solution of
unsaturated pyrrolizidines or indolizidines (0.1 mmol) in dry MeOH
(5 mL) was added 20% Pd/C (25 mg) and HCl (6 M, 1 mL). The
suspension was stirred 48 h under hydrogen (1 atm) then filtered
over celite. The celite was rinsed with MeOH and the filtrate was
neutralized with Amberlist A-26 (OH-) resin. Finally, the solution was
concentrated under reduced pressure and the residue was purified
by flash chromatography (silica gel, CHCl3/MeOH/NH4OH 6/4/1) to
afford the compounds as brown solids.
Enzymatic assay: all the enzymes were purchased from Sigma
Chemical Co. In a typical experiment, the glycosidase (0.013 U/mL)
was pre-incubated at 33 °C for 5 min in the presence of the inhibitor
in 50 mM acetate buffer (pH 5.6, except for rice α-glucosidase pH
5.1 and yeast α-glucosidase pH 6.2). The reaction was started by
addition of the appropriate substrate (p-nitrophenyl glycoside, 1
mM concentration) to a final volume of 250 µl. The reaction was
stopped after 10-15 min (depending on the enzyme) by addition of
350 µL of 0.4 M Na2CO3. The released p-nitrophenolate was
quantified spectrophotometrically at 415 nm with a microplate
reader (300 µL of the reaction mixture in a well, OD ca 0.7 for the
control, without inhibitor). In cases where inhibition was greater
than 95%, IC50 values were determined further after assaying
decreasing concentrations of inhibitor (typically 5 concentrations
around IC50). All the assays were done in duplicate (less than 10%
variability in each case).
(1R,2R,7aR)-7a-(hydroxymethyl)pyrrolizidine-1,2-diol
(5a):
According to general method, the hydrogenolysis of unsaturated
pyrrolizidine 24a (40 mg, 0.09 mmol) afforded 5a (13 mg, 83 %) as
[훼]20
brown solid.
+ 11.0 (c 0.36 in MeOH); 1H NMR (D2O, 500 MHz)
퐷
δ 1.59‒1.64 (1H, m, H-7), 1.75‒1.87 (2H, m, H-6), 1.98‒2.03 (1H, m,
H-7’), 2.77‒2.81 (1H, m, H-5), 2.94‒3.01 (2H, m, H-3), 3.08‒3.13
(1H, m, H-5’), 3.49 (1H, d, J = 11.5 Hz, BnO-CHaHb), 3.55 (1H, d, J =
11.5 Hz, BnO-CHaHb), 3.92 (1H, d, J = 5.1 Hz, H-1), 4.15‒4.19 (1H, m,
H-2); 13C NMR (D2O, 500 MHz) δ 24.6 (C-6), 28.4 (C-7), 55.7 (C-5),
56.2 (C-3), 65.0 (BnO-CH2), 74.5 (C-2), 77.8 (C-7a), 78.0 (C-1); m/z
calcd for C8H16NO3 [M + H]+ 174.1130, found 174.1124.
(1R,2R,7aS)-7a-(hydroxymethyl)pyrrolizidine-1,2-diol
(5b):
Conflicts of interest
“There are no conflicts to declare”.
According to general method, the hydrogenolysis of unsaturated
pyrrolizidine 24b (54 mg, 0.12 mmol) afforded 5b (10 mg, 51 %) as
[훼]20
brown solid.
+ 8.3 (c 0.21 in MeOH); 1H NMR (D2O, 500 MHz) δ
퐷
2.00‒2.07 (1H, m, H-7), 2.13‒2.25 (3H, m, H-7’, H-6), 3.08 (1H, dd, J
= 7.2, 12.4 Hz, H-3), 3.38‒3.42 (1H, m, H-5), 3.54‒3.59 (1H, m, H-5’),
3.68 (1H, d, J = 12.5, BnO-CHaHb), 3.86 (1H, dd, J = 6.1, 12.4 Hz, H-3’)
3.96 (1H, d, J = 12.5, BnO-CHaHb), 4.13 (1H, d, J = 6.1 Hz, H-1),
4.39‒4.43 (1H, m, H-2); 13C NMR (D2O, 500 MHz) δ 23.6 (C-6), 32.3
(C-7), 55.4 (C-3), 56.5 (C-5), 60.9 (BnO-CH2), 73.8 (C-2), 80.0 (C-1),
81.1 (C-7a); m/z calcd for C8H16NO3 [M + H]+ 174.1130, found
174.1134.
Acknowledgements
The authors would like to thank the CNRS and Univ. Reims
Champagne Ardenne for financial support. GM is grateful to
URCA and GRAND REIMS for a doctoral allocation. We also
thank Karine Machado, Anthony Robert and Dr. Dominique
Harakat for their help in structural determination of new
compounds.
(1R,2R,8aR)-8a-(hydroxymethyl)indolizidine-1,2-diol
(6a):
Notes and references
According to general method, the hydrogenolysis of unsaturated
indolizidine 25a (45 mg, 0.10 mmol) afforded 6a (15 mg, 83 %) as
1
(a) R. Matute, S. Garcia-Vinuales, H. Hayes, M. Ghirardello, A.
Daru, T. Tejero, I. Delso and P. Merino, Curr. Org. Synth.,
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1.31‒1.43 (3H, m, H-8, H-6), 1.46‒1.55 (1H, m, H-7), 1.64‒1.75 (2H,
m, H-6’, H-7’), 2.62‒2.70 (2H, m, H-5, H-3), 2.79 (1H, td, J = 3.0, 13.5
10 | J. Name., 2012, 00, 1-3
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25 D. LeNouen, A. Defoin and J.-B. Behr, ChemistrySelect, 2016,
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BnO
n
n
BnO
BnO
N
N
HO
HO
HO
HO
4 steps
N
O
OH
potent and selective
n=1,2 : inhibitors of -glucosidase (rice)
OH
weak
12 | J. Name., 2012, 00, 1-3
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