Synthesis and fucosidase inhibitory study of unnatural pyrrolidine alkaloid 4-epi-(+)-codonopsinine

Article abstract of DOI:10.1021/jo200176u

The total synthesis of enantiopure 4-epi-(+)-codonopsinine was achieved in 10 steps starting from d-ribose as a chiral building block. The key step involved a highly stereoselective nucleophilic addition of a Grignard reagent to a protected ribosylamine.

Full text of DOI:10.1021/jo200176u

NOTE
pubs.acs.org/joc
Synthesis and Fucosidase Inhibitory Study of Unnatural
Pyrrolidine Alkaloid 4-epi-(þ)-Codonopsinine
Alexis Kotland,† Fabien Accadbled,† Koen Robeyns,‡ and Jean-Bernard Behr*,†
†Institut de Chimie Molꢀeculaire de Reims (ICMR), UFR Sciences, CNRS, BP 1039, 51687 Reims Cedex 2, France
‡Institute of Condensed Matter and Nanosciences (IMCN), Universitꢀe Catholique de Louvain (UCL), B^atiment Lavoisier, place Louis
Pasteur 1, 1348 Louvain-la-Neuve, Belgium.
S Supporting Information
b
ABSTRACT: The total synthesis of enantiopure 4-epi-(þ)-codonopsinine
was achieved in 10 steps starting from D-ribose as a chiral building block. The
key step involved a highly stereoselective nucleophilic addition of a Grignard
reagent to a protected ribosylamine. Synthesis of the N-desmethyl derivative
and its p-tolyl analogue was also accomplished, and the compounds were
assayed against R-fucosidase.
atural polyhydroxylated pyrrolidines are secondary meta-
bolites that have been isolated from a great variety of plants
The biological potential of fuco-pyrrolidines that incorporate a
hydrophobic substituent at C2 has been recently exemplified by
us and others.8 The biological evaluation of such compounds
suggest that the aryl moiety might be a major player in enzyme
recognition and that a 2(S) configuration induces the best
interactions in the fucosidase active site. Among the numerous
methods devoted to the preparation of five-membered imino-
cyclitols,9 the stereoselective addition of an organometallic
reagent to a glycosylamine is straightforward and occurs usually
with high selectivity.9a As depicted in Figure 2, target compounds
3ꢀ5 could be synthesized by such a method, using a protected
5-deoxyribosylamine as the starting material.10 Indeed, D-ribose
features the adequate hydroxyl distribution to reach the targeted
L-fuco configuration. Furthermore, the 5-hydroxy group of
D-ribose could be easily removed to lead, after inversion of
configuration, to the required 5(S)-methyl substituent.
Combining different methods from literature, 5-deoxyribose 8
was prepared in four steps and 59% overall yield (Scheme 1).
First, acetonation of D-ribose was achieved by treatment with
acetone in the presence of sulfuric acid.11 The crude product was
tosylated selectively at the primary hydroxyl by addition of one
equivalent of TsCl in pyridine for 16 h at room temperature.12
Under these conditions, sulfonyl ester 6 was obtained as a colorless
oil in 80% yield after purification by flash chromatography over
silica gel (Et2O/petroleum ether, 7:3). Treatment of 6 with sodium
iodide in dioxane/DMF at 80 °C for 3 h yielded 5-iodoribose
derivative 7 (82%, white solid). Reductive dehalogenation was
accomplished by hydrogenation at 1 atm over Pd/C in the presence
of NEt3.13 Purification by silica gel chromatography (Et2O/
petroleum ether, 5:5) yielded deoxyribose 8 as a colorless oil.
The corresponding p-methoxybenzylglycosylamine 9 formed
quantitatively after stirring hemiacetal 8 with commercial
N
and microorganisms.1 On a structural point of view, these five-
membered-ring alkaloids can be regarded as sugar mimics in
which the ring oxygen has been replaced by nitrogen. This
alteration, although slight, greatly impacts the biological proper-
ties since iminosugars bind much more efficiently to glycosidases
than the parent carbohydrate substrates, thus acting as potent
inhibitors.2 Since glycosidases are involved in a number of
pathological events, interest in iminosugars has increased over
the past decades. The inhibition of R-L-fucosidase, an enzyme
responsible for the trimming of fucosides located on the cell
surface, was recently envisioned as a therapeutic option for the
treatment of inflammation, cancer or viral infection.3 Pyrroli-
dines such as 14 or 25 (Figure 1), which feature the fucose sub-
stitution pattern, are potent inhibitors of fucosidase (Ki = 5 nM
and 8 nM, respectively).
Interestingly, a new class of polyhydroxypyrrolidines was
discovered, which incorporates an aryl moiety at C2 (Figure 1).
(ꢀ)-Codonopsinine and its analogue (ꢀ)-codonopsine, both
isolated from Codonopsis clematidae, were found to exhibit
antibiotic activity and hypotensive activity.6 Their hydroxy-
lated congeners radicamine A and radicamine B were isolated
from Lobelia chinensis Lour, a herb used in Chinese folk
medicine.7 Due to their intriguing molecular structures and
promising biological activities, the synthesis of new 2-aryl
polyhydroxylated pyrrolidines with structural diversities is of
interest. Plagiaring Nature, we wished to explore the potential
of new fuco-configurated codonopsinine analogues and test
their ability to inhibit fucosidase. Thus, we present herein the
synthesis, X-ray characterization, and biological evaluation of
4-epi-(þ)-codonopsinine 3 as well as the syntheses and anti-
fucosidase activities of the N-desmethyl and p-tolyl analogues,
4 and 5.
Received: January 26, 2011
Published: April 15, 2011
r
2011 American Chemical Society
4094
dx.doi.org/10.1021/jo200176u J. Org. Chem. 2011, 76, 4094–4098
|

The Journal of Organic Chemistry
NOTE
Scheme 2. Synthesis of Iminosugars 3ꢀ5
Figure 1. Structures of polyhydroxypyrrolidines.
glycosylamine 9, which is very sensitive to hydrolysis, was used
as such in the next step.
Organometallics usually add to protected aldoses14 or glyco-
sylamines9 in a straightforward manner to yield the correspond-
ing alditols or aminoalditols. The reaction requires an excess of
reagent (one equivalent being consumed by neutralization of the
acidic proton from the substrate) and occurs usually with high
selectivity. Interestingly, the stereochemical outcome of the
reaction is identical in both the aldose or aldimine series. More-
over, the nature of the protecting groups deeply impacts the
diastereoisomeric ratio. In the ribose series, a 2,3-O-isopropyli-
dene give rise mainly to 1,2-anti product,15 whereas OBn protecting
groups afford the syn diastereoisomer as the major adduct.16
In our case, addition of paramethoxyphenylmagnesium bro-
mide to 9 was performed in THF at room temperature, and
consumption of the starting material occurred over 4 h. The 1H
and 13C NMR spectra of the crude reaction mixture definitely
disclosed formation of a single addition product. Purification by
silica gel chromatography (AcOEt/petroleum ether, 3:7) yielded
10a as a colorless oil in 52% yield. The modest yield of the
reaction might be attributed to the high tendency of glycosyla-
mines to hydrolyze back to the corresponding hemiacetal, giving
rise to quantitative amounts of nonisolated side products. The
configuration of the newly formed stereocenter was established
by NOE experiments on subsequent pyrrolidine 11a and was
firmly ascertained on the basis of X-ray crystallographic analysis
of final compound 3. As anticipated, the nucleophilic addition
proceeded with anti selectivity providing aminoalcohol 10a with
Figure 2. Retrosynthetic pathway for the synthesis of 3ꢀ5.
Scheme 1. Synthesis of Deoxyribose 8
p-methoxybenzylamine for 24 h at room temperature in the
presence of 4Å molecular sieves (Scheme 2). The excess amine
was removed by evaporation under reduced pressure, and
4095
dx.doi.org/10.1021/jo200176u |J. Org. Chem. 2011, 76, 4094–4098

The Journal of Organic Chemistry
NOTE
Table 1. Inhibition of r-L-Fucosidase by Iminosugars 3ꢀ5
compound
% inhibition at 0.1 mM
IC50 (μM)
Ki (μM)
3
4
5
89
96
99
5.9
0.81
0.058
0.054
0.0095
0.010
a drop in affinity by 2 orders of magnitude.18 However, the aryl
moiety seems not to be detrimental for binding, and compounds
4 and 5 are among the most potent inhibitors of fucosidase
described to date.
Figure 3. X-ray structure of 4-epi-(þ)-codonopsinine 3.
In summary, a short and stereoselective synthesis of 4-epi-
codonopsinine 3 was developed, starting from D-ribose. The key
step, i.e. the addition of a Grignard reagent to a protected
ribosylamine, yielded only the anti isomer. The structure of 3
was firmly ascertained on the basis of X-ray crystallographic
analysis. Two derivatives, i.e. the N-desmethyl compound 4 and
its p-tolyl analogue 5, were also prepared, and the compounds
exhibited very strong inhibition toward R-L-fucosidase, with Ki’s
in the nanomolar range. Due to their unique hydrophobic
character, these aryl-polyhydroxypyrrolidines could be a re-
sponse to the poor cellular bioavailability of the most common
fucosidase inhibitors with therapeutic potential like that of 1 or 2.
the 1(S) configuration. Mesylation was then carried out under
our standard conditions (MsCl, pyridine, room temperature)16
affording pyrrolidine 11a in 63% isolated yield via an in situ
nucleophilic displacement of the intermediary sulfonic ester.
This sequence brought about inversion of configuration at C-4
of starting aminoalcohol, affording the expected 5(S) configura-
tion in the pyrrolidine framework.
The removal of the N-paramethoxybenzyl group proved
somewhat tricky and afforded 12a in only 46% yield. N-methyla-
tion was then performed under the acidic EschweilerꢀClarke
conditions (HCOOH/HCHO) in the aim of deprotecting
simultaneously the isopropylidene acetal.17 However, the acet-
onide was resistant, and a mixture of fully deprotected 3 (24%)
and its precursor 13 (40%) were obtained in 64% global yield,
which were separated by column chromatography. Subsequent
treatment of 13 with 1 M hydrochloric acid was necessary to
obtain 4-epi-codonopsinine 3 (75% yield). After neutralization
(Amberlyst A-26, OHꢀ form), pyrrolidine 3 was purified by silica
gel chromatography (AcOEt/CH2Cl2/MeOH, 4:4:2) and was
crystallized from chloroform for X-ray analysis. The structure
(see Figure 3) shows the compound in a 3E conformation with
atom C-3 out of the plane of the other four atoms. The planar
aromatic ring is twisted relative to the pyrrolidine ring by ∼90°.
The absolute configuration at C-2 and C-5 could be firmly
assigned as 2(S),5(S).
The N-desmethyl derivative 4 was prepared in 73% yield by
acidic treatment of pyrrolidine 12a and was purified by ion
exchange chromatography (Dowex 50WX8, elution with 0.8 M
NH4OH). The p-tolyl iminosugar 5 was prepared following a
similar reaction sequence. Here again, addition of p-tolylmagne-
sium bromide to glycosylamine 9 was completely selective and
afforded aminoalcohol 10b in 52% yield. Subsequent cyclization
(MsCl in pyridine, 78% yield), hydrogenolysis (H2, Pd/C, 46%
yield) and acetonide deprotection (aq. HCl, 73% yield) were
performed under the conditions stated for 10a to afford pyrro-
lidine 5 as a colorless oil.
New aryl-iminosugars 3ꢀ5 were assayed for their inhibitory
activity toward R-L-fucosidase from bovine kidney (Table 1). A
strong inhibition occurred with 3ꢀ5 at 100 μM concentration
(Table 1). IC50’s and Ki’s were determined from Dixon plots, by
assaying at least five dilutions. Iminosugars 3ꢀ5 were highly
potent inhibitors of fucosidase, the N-desmethyl derivatives 4
and 5 being significantly more active (IC50 = 58 nM and 54 nM,
respectively) than epi-codonopsinine 3 (IC50 = 5.9 μM). All
three compounds dispayed a competitive inhibition pattern
according to LineweaverꢀBurk plots, with inhibition constants
around 10 nM for 4 and 5 (Table 1). Title compound 4-epi-(þ)-
codonopsinine displayed an inhibition constant Ki = 0.8 μM. As
observed by others, the N-Me supplementary substituent induces
’ EXPERIMENTAL SECTION
General Details. All reactions were performed under argon. The
solvents were dried and distilled prior to use. Grignard reagents were
purchased from standard commercial sources. 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 p-anisaldehyde or an
aqueous solution of KMnO4 (2%)/Na2CO3 (4%), followed by heating.
Flash column chromatography was performed over silica gel M 9385
(40ꢀ63 μm) Kieselgel 60. NMR spectra were recorded on a 250 MHz
(250 MHz for 1H, 62.5 MHz for 13C). Chemical shifts are expressed in
parts per million (ppm) using TMS as internal standard. Coupling
constants are in hertz, and splitting pattern abbreviations are br, broad; s,
singlet; d, doublet; t, triplet; q, quartet; m, multiplet. IR spectra were
recorded with an IRTM plus MIDAC spectrophotometer and are
expressed in cmꢀ1. 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).
General Method for the Synthesis of Aminoalcohols 10a,b.
Arylmagnesium bromide (10 mL of a commercial 1M solution, 10 mmol)
was added to a stirred solution of glycosylamine 9 (0.746 g, 2.55 mmol) in
THF (5 mL) at0 °C, and theresulting mixture was left to reactatrtfor 7 h.
Saturated NH4Cl was then added, and the solution was extracted with
Et2O (3 ꢁ 20 mL) . The combined organic layers were dried (MgSO4)
and evaporated, and the crude aminoalcohol was purified by FC (EtOAc/
petroleum ether, 3:7) to give pure 10 as a colorless oil (0.522 g, 52%, for
10a).
(1S,2S,3R,4R)-N-(4-Methoxybenzyl)-1-[4-methoxyphenyl]-2,3-O-iso-
propylidene-pentan-2,3-diol (10a): as a colorless oil: Rf = 0.28 (PE/
EtOAc, 7:3); [R]20 = ꢀ12.9 (c 1.16, CHCl3); IR (film) νmax 2990,
D
2935, 2837, 1612, 1516, 1251 (cmꢀ1); 1H NMR (CDCl3, 250 MHz) δ
1.22 (3 H, s), 1.24 (3 H, s), 1.35 (3 H, d, J = 5.9 Hz), 3.49 (2 H, s),
3.70ꢀ3.93 (8 H, m), 4.03 (1 H, dd, J = 5.2, 9.4 Hz), 4.26 (1 H, dd, J = 5.2,
10.1 Hz), 6.81 (2 H, d, J = 8.4 Hz), 6.95 (2 H, d, J = 8.4 Hz), 7.12 (2 H, d,
J = 8.4 Hz), 7.18 (2 H, d, J = 8.4 Hz); 13C NMR (62.5 MHz; CDCl3) δ
20.7 (CH3), 25.6 (CH3), 28.1 (CH3), 50.2 (CH2), 55.4 (CH3), 55.5
(CH3), 61.3 (CH), 65.0 (CH), 80.0 (CH), 83.3 (CH), 108.4 (C), 114.2
(ArꢀCH), 114.4 (ArꢀCH), 128.9 (ArꢀCH), 130.3 (ArꢀCH), 132.7
4096
dx.doi.org/10.1021/jo200176u |J. Org. Chem. 2011, 76, 4094–4098

The Journal of Organic Chemistry
NOTE
(ArꢀC), 159.1 (ArꢀC), 159.3 (ArꢀC); ESI-HRMS: calcd for
C23H32NO5 ([M þ H]þ) 402.2280; found 402.2276.
the crude hydrochloride obtained after acidic treatment could be
neutralized with Amberlite A-25 (OHꢀ) to give pyrrolidine 3 as the
free base in almost pure form (75%).
(1S,2S,3R,4R)-N-(4-Methoxybenzyl)-1-tolyl-2,3-O-isopropylidene-
pentan-2,3-diol (10b): as a colorless oil: Rf = 0.30 (PE/EtOAc, 7:3);
(2S,3S,4R,5S)-2-[4-Methoxyphenyl]-5-methylpyrrolidine-3,4-diol
(4): as a colorless oil from 11a following deprotection procedures A and
B: [R]20D = ꢀ56.1 (c 0.2, CH3OH); 1H NMR (D2O, 250 MHz) δ 1.29
(3 H, d, J = 6.9 Hz), 3.70ꢀ3.82 (4 H, m), 4.17 (1 H, t, J = 3.8 Hz), 4.30 (1
H, d, J = 9.6 Hz), 4.49 (1 H, dd, J = 3.8, 9.6 Hz), 7.02 (2 H, d, J = 8.4 Hz),
7.40 (2 H, d, J = 8.4 Hz); 13C NMR (62.5 MHz; D2O) δ 10.9 (CH3),
54.6 (CH3), 55.9 (CH), 61.9 (CH), 71.3 (CH), 75.5 (CH), 114.0
(ArꢀCH), 125.3 (ArꢀC), 128.7 (ArꢀCH), 159.0 (ArꢀC); ESI-
HRMS: calcd for C12H18NO3 ([M þ H]þ) 224.1287; found 224.1282.
(2S,3S,4R,5S)-2-Tolyl-5-methylpyrrolidine-3,4-diol (5): as a colorless
oil from 11b following deprotection procedures A and B: [R]20D = ꢀ
48.6 (c 0.37, CH3OH); 1H NMR (D2O, 250 MHz) δ 1.12 (3 H, d, J = 6.9
Hz), 2.29 (3 H, s), 3.48ꢀ3.54 (1 H, m), 4.00ꢀ4.08 (2 H, m), 4.24 (1 H,
dd, J = 4.0, 9.0 Hz), 7.21 (2 H, d, J = 8.1 Hz), 7.28 (2 H, d, J = 8.1 Hz);
13C NMR (62.5 MHz; D2O) δ 16.2 (CH3), 22.4 (CH3), 57.1 (CH),
66.1 (CH), 76.4 (CH), 81.8 (CH), 129.5 (ArꢀCH), 131.0 (ArꢀC),
131.7 (ArꢀCH), 140.3 (ArꢀC); ESI-HRMS: calcd for C12H18NO2
([M þ H]þ) 208.1338; found 208.1344.
[R]20 = ꢀ9.1 (c 1, CHCl3); IR (film) νmax 2989, 2933, 2862, 1613,
D
1515, 1250 (cmꢀ1); 1H NMR (CDCl3, 250 MHz) δ 1.12 (3 H, s), 1.18
(3 H, s), 1.30 (3 H, d, J = 5.9 Hz), 2.39 (3 H, s), 3.48 (2 H, bs),
3.70ꢀ3.90 (5 H, m), 4.02 (1 H, dd, J = 5.4, 9.2 Hz), 4.30 (1 H, dd, J = 5.4,
10.1 Hz), 6.80 (2 H, d, J = 8.6 Hz), 7.10ꢀ7.30 (6 H, m); 13C NMR (62.5
MHz; CDCl3) δ 20.8 (CH3), 21.6 (CH3), 25.7 (CH3), 28.3 (CH3), 50.4
(CH2), 55.7 (CH3), 61.8 (CH), 65.2 (CH), 80.2 (CH), 83.5 (CH),
108.7 (C), 114.4 (ArꢀCH), 127.9 (ArꢀCH), 129.9 (ArꢀCH), 130.5
(ArꢀCH), 137.7 (ArꢀC), 137.8 (ArꢀC), 159.5 (ArꢀC); ESI-HRMS:
calcd for C23H32NO4 ([M þ H]þ) 386.2331; found 386.2349.
General Method for the Synthesis of Iminosugars 11a,b.
Methanesulfonyl chloride (87 μL, 2 equiv) was added to a stirred
solution of aminoalcohol 10 (0.418 g, 1.04 mmol) in pyridine (3.6 mL)
at 0 °C, and the resulting mixture was left to react at rt for 16 h. The
reaction was quenched with water and the solution was extracted twice
with CH2Cl2. The combined organic layers were dried (MgSO4),
evaporated and the crude pyrrolidine was purified by FC (Et2O/
petroleum ether, 3:7) to give pure 11 as a colorless oil (0.251 g, 63%
for 11a).
Procedure for N-Methylation. (2S,3S,4R,5S)-N-Methyl-2-[4-
methoxy-phenyl]-3,4-O-isopropylidene-5-methyl-pyrrolidine-3,4-diol
(13). Pyrrolidine 12a (84 mg, 0.32 mmol) was dissolved in formic acid
(0.7 mL) and formaldehyde (1.4 mL of a 37% solution in water). The
resulting mixture was heated to 80 °C until complete consumption of the
starting compound. Then, an aq solution of K2CO3 (20 mL) was added,
and the resulting solution was extracted with CH2Cl2 (4 ꢁ 15 mL). The
combined organic fractions were dried over anhydrous MgSO4, filtered,
and concentrated to yield a crude, yellow residue. Purification by flash
chromatography (Et2O/petroleum ether: 6:4 then Et2O) afforded 13
(36 mg, 40%) and fully deprotected 3 (18 mg, 24%). Compound 13: Rf =
(2S,3S,4R,5S)-N-(4-Methoxybenzyl)-2-[4-methoxyphenyl]-3,4-O-iso-
propylidene-5-methylpyrrolidine-3,4-diol (11a): as a colorless oil: Rf =
0.40 (PE/EtOAc, 7:3); [R]20D = þ56.8 (c 0.5, CHCl3); IR (film) νmax
2978, 2935, 2835, 1612, 1513, 1379, 1247 (cmꢀ1); 1H NMR (CDCl3,
250 MHz) δ 1.09 (3 H, d, J = 6.5 Hz), 1.36 (3 H, s), 1.60 (3 H, s), 3.19 (1
H, d, J = 13.9 Hz), 3.22ꢀ3.30 (1 H, m), 3.57 (1 H, d, J = 13.9 Hz), 3.70
(6 H, s), 3.95 (1 H, d, J = 2.3 Hz), 4.59 (1 H, dd, J = 2.3, 6.7 Hz), 4.78 (1
H, t, J = 6.7 Hz), 6.75ꢀ6.85 (4 H, m), 7.07 (2 H, d, J = 8.5 Hz), 7.20 (2 H,
d, J = 8.5 Hz); 13C NMR (62.5 MHz; CDCl3) δ 10.6 (CH3), 25.2
(CH3), 26.3 (CH3), 49.6 (CH2), 55.2 (CH3), 55.2 (CH3), 57.1 (CH),
69.1 (CH), 80.9 (CH), 86.3 (CH), 112.5 (C), 113.5 (ArꢀCH), 113.7
(ArꢀCH), 129.2 (ArꢀCH), 129.5 (ArꢀCH), 131.5 (ArꢀC), 131.7
(ArꢀC), 158.3 (ArꢀC), 158.9 (ArꢀC); ESI-HRMS: calcd for
C23H30NO4 ([M þ H]þ) 384.2175; found 384.2187.
0.34 (PE/Et2O, 4:6); [R]20 = þ30.0 (c 0.5, CHCl3); IR (film) νmax
D
1
2976, 2934, 2836, 1611, 1512, 1249 (cmꢀ1); H NMR (CDCl3, 250
MHz) δ 1.03 (3 H, d, J = 6.5 Hz), 1.25 (3 H, s), 1.51 (3 H, s), 1.98
(3 H, s), 3.03 (1 H, quin), 3.70 (3 H, s), 3.90 (1 H, bs), 4.55 (1 H, d, J =
6.7 Hz), 4.72 (1 H, t, J = 6.7 Hz), 6.75 (2 H, d, J = 8.6 Hz), 6.99 (2 H, d,
J = 8.6 Hz); 13C NMR (62.5 MHz; CDCl3) δ 11.2 (CH3), 24.7 (CH3),
26.1 (CH3), 35.1 (CH3), 55.2 (CH3), 60.6 (CH), 71.6 (CH), 81.2
(CH), 85.6 (CH), 111.9 (C), 113.7 (2 ꢁ ArꢀCH), 129.5 (2 ꢁ Arꢀ
CH), 131.5 (ArꢀC), 158.3 (ArꢀC); ESI-HRMS: calcd for C16H24NO3
([M þ H]þ) 278.1756; found 278.1763.
(2S,3S,4R,5S)-N-(4-Methoxybenzyl)-2-tolyl-3,4-O-isopropylidene-5-
methylpyrrolidine-3,4-diol (11b). Following the same procedure, 11b
was obtained as a colorless oil (78%): Rf = 0.60 (PE/EtOAc, 7:3);
[R]20D = þ63.8 (c 1.16, CHCl3); IR (film) νmax 2977, 2933, 2834, 1611,
1512, 1246 (cmꢀ1); 1H NMR (CDCl3, 250 MHz) δ 1.01 (3 H, d, J = 6.3
Hz), 1.26 (3 H, s), 1.51 (3 H, s), 2.25 (3 H, s), 3.11 (1 H, d, J = 13.9 Hz),
3.20ꢀ3.24 (1 H, m), 3.49 (1 H, d, J = 13.9 Hz), 3.70 (3 H, s), 3.90 (1 H,
d, J = 2.1 Hz), 4.51 (1 H, dd, J = 2.1, 6.3 Hz), 4.68 (1 H, t, J = 6.1 Hz),
6.78 (2 H, d, J = 8.4 Hz), 6.95ꢀ7.20 (6 H, m); 13C NMR (62.5 MHz;
CDCl3) δ 12.1 (CH3), 22.5 (CH3), 26.5 (CH3), 27.6 (CH3), 51.0
(CH2), 56.6 (CH3), 58.5 (CH), 70.8 (CH), 82.3 (CH), 87.7 (CH),
113.7 (C), 114.9 (ArꢀCH), 129.7 (ArꢀCH), 130.4 (ArꢀCH), 130.6
(ArꢀCH), 133.0 (ArꢀC), 138.0 (ArꢀC), 138.4 (ArꢀC), 159.7
(ArꢀC); ESI-HRMS: calcd for C23H30NO3 ([M þ H]þ) 368.2226;
found 368.2220.
Deprotection of 13 (36 mg, 0.13 mmol) following procedure B gave 3
(23 mg, 75%) as colorless crystals: mp = 81 °C; Rf = 0.28 (CH2Cl2/
EtOAc/MeOH, 7:4:2); [R]20D = þ7 (c 0.34, CH3OH); 1H NMR (D2O,
250 MHz) δ 1.09 (3 H, d, J = 6.7 Hz), 2.10 (3 H, s), 3.00 (2 H, bs),
3.38ꢀ3.45 (1 H, m), 3.56 (1 H, d, J = 4.4 Hz), 3.81 (3 H, s), 4.00 (1 H,
dd, J = 4.4, 6.2 Hz), 4.25 (1 H, t, J = 6.2 Hz), 6.88 (2 H, d, J = 8.4 Hz),
7.20 (2 H, d, J = 8.4 Hz); 13C NMR (62.5 MHz; CDCl3) δ 8.8 (CH3),
34.8 (CH3), 55.3 (CH3), 61.1 (CH), 71.7 (CH), 73.5 (CH), 78.4 (CH),
113.9 (ArꢀCH), 129.0 (ArꢀCH), 132.9 (ArꢀC), 159.0 (ArꢀC); ESI-
HRMS: calcd for C13H20NO3 ([M þ H]þ) 238.1443; found 238.1441.
General Methods for Pyrrolidine Deprotection. Procedure
A: removal of N-4-methoxybenzyl group was achieved by hydrogenation
of pyrrolidine 11 (0.16 mmol) over Pd/C (50 mg) in 3 mL MeOH for
48 h. The resulting suspension was filtered over a pad of Celite washed
several times with MeOH. Evaporation of the solvent gave a colorless oil,
which was purified by silica gel chromatography (Et2O/petroleum ether,
6:4) to give pure 12a,b in 46% yield.
’ ASSOCIATED CONTENT
Supporting Information. Copies of NMR spectra (1H-,
S
b
13C) for all new compounds, crystallographic data for 3, Dixon
plots for fucosidase inhibitory assays. This material is available
free of charge via the Internet at http://pubs.acs.org.
Procedure B: acetonide hydrolysis was performed by stirring a
solution of 12 or 13 (0.1 mmol) in 1 M HCl (0.5 mL) for 24 h at rt.
After evaporation, the crude product was applied to a column of Dowex
50WX8. The resin was washed with distilled water and then eluted with
0.8 M NH4OH to give pure pyrrolidines 4 or 5 in 73% yield. Alternately,
’ AUTHOR INFORMATION
Corresponding Author
jb.behr@univ-reims.fr
4097
dx.doi.org/10.1021/jo200176u |J. Org. Chem. 2011, 76, 4094–4098

The Journal of Organic Chemistry
NOTE
’ ACKNOWLEDGMENT
(16) Behr, J.-B.; Mvondo-Evina, C.; Phung, N.; Guillerm, G. J. Chem.
Soc., Perkin Trans. I 1997, 1597–1601.
(17) Nguyen, T. X.; Kobayashi, Y. J. Org. Chem. 2008,
73, 5536–5541.
(18) Asano, N.; Kizu, H.; Oseki, K.; Tomioka, E.; Matsui, K.;
Okamoto, M.; Baba, M. J. Med. Chem. 1995, 38, 2349–2356.
We thank Professor Bernard Tinant for helpful discussion, the
technical platform (Aurꢀelien Lebrun, Dominique Harakat, and
Sylvie Lanthony) for their assistance, and Elodie Geba and
Pac^ome Sientzoff (Opꢀeration “Lycꢀeens Chercheurs”) for their
contagious enthusiasm. This research was supported by the
french CNRS and the University of Reims Champagne Ardenne.
’ REFERENCES
(1) (a) Watson, A. A.; Fleet, G. W. J.; Asano, N.; Molyneux, R. J.;
Nash, R. J. Phytochemistry 2001, 56, 265–293. (b) Asano, N.; Nash, R. J.;
Molyneux, R. J.; Fleet, G. W. J. Tetrahedron: Asymmetry 2000,
11, 1645–1680.
(2) Iminosugars as Glycosidase Inhibitors: Nojirimycin and Beyond;
St€utz, A. E., Ed.; Wiley-VCH: Weinheim, Germany, 1999.
(3) (a) Robina, I.; Moreno-Vargas, A. J.; Carmona, A. T.; Vogel, P.
Curr. Drug Metabol. 2004, 5, 329–361. (b) Shimanek, E.; McGarvey,
E. J.; Jablonowski, J. A.; Wong, C.-H. Chem. Rev. 1998, 98, 833–862.
(c) Padro, M.; Castillo, J. A.; Gomez, L.; Joglar, J.; Clapes, P.; de Bolos,
C. Glycoconj. J. 2010, 27, 277–285.
(4) Ak, A.; Prudent, S.; LeNou€en, D.; Defoin, A.; Tarnus, C. Bioorg.
Med. Chem. Lett. 2010, 20, 7410–7413.
(5) Chevrier, C.; LeNou€en, D.; Neuburger, M.; Defoin, A.; Tarnus,
C. Tetrahedron Lett. 2004, 45, 5363–5366.
(6) (a) Mathkalikova, S. F.; Malikov, V. M.; Yunusov, S. Y. Khim.
Prir. Soedin 1969, 5, 30–32. Chem. Abstr. 1969, 71, 13245z.
(b) Mathkalikova, S. F.; Malikov, V. M.; Yunusov, S. Y. Khim. Prir.
Soedin 1969, 5, 606–607. Chem. Abstr. 1970, 73, 25712d.
(7) Shibano, M.; Tsukamoto, D.; Masuda, A.; Tanaka, Y.; Kusano, G.
Chem. Pharm. Bull. 2001, 49, 1362–1365.
(8) (a) Moreno-Clavijo, E.; Carmona, A. T.; Vera-Ayoso, Y.;
Moreno-Vargas, A.; Bello, C.; Vogel, P.; Robina, I. Org. Biomol. Chem.
2009, 7, 1192–1202. (b) Behr, J.-B. Tetrahedron Lett. 2009, 50, 4498–4501.
(c) Palmer, A. M.; J€ager, V. Eur. J. Org. Chem. 2001, 2547–2558. (d) For a
library of β-N-acetylglucosaminidase inhibitors with hydrophobic substit-
uents at C2, see: Liu, J.; Numa, M. M. D.; Liu, H.; Huang, S. J.; Sears, P.;
Shikhman, A. R.; Wong, C.-H. J. Org. Chem. 2004, 69, 6273–6283. (e) For
analogous R-mannosidase inhibitors with antitumor activity, see: Fiaux,
H.; Popowycz, F.; Favre, S.; Sch€utz, C.; Vogel, P.; Gerber-Lemaire, S.;
Juillerat-Jeanneret, L. J. Med. Chem. 2005, 48, 4237–4246.
(9) (a) Behr, J.-B.; Plantier-Royon, R. Recent Res. Dev. Org. Chem.
2006, 10, 23–52. (b) Compain, P.; Chagnault, V.; Martin, O. R.
Tetrahedron: Asymmetry 2009, 20, 672–711. (c) Stocker, B. L.; Danger-
field, E. M.; Win-Mason, A. L.; Haslett, G. W.; Timmer, M. S. M. Eur. J.
Org. Chem. 2010, 1615–1637.
(10) For the synthesis of natural (ꢀ)-codonopsinine, see: (e) Reddy,
J. S.; Rao, B. V. J. Org. Chem. 2007, 72, 2224–2227. and references cited
therein. For recent syntheses of other 2-aryl-pyrrolidines, see:
(a) Su, J.-K.; Jia, Y.-M.; He, R.; Rui, P.-X.; Han, N.; He., X.; Xiang, J.;
Chen, X.; Zhu, J.; Yu, C.-Y. Synlett 2010, 1609–1616. (b) Tsou, E.-L.;
Chen, S.-Y.; Yang, M.-H.; Wang, S.-C.; Cheng, T.-R. R.; Cheng, W.-C.
Bioorg. Med. Chem. 2008, 16, 10198–10204. (c) Ribes, C.; Falomir, E.;
Carda, M.; Marco, J. A. J. Org. Chem. 2008, 73, 7779–7782. (d) Merino,
P.; Delso, I.; Tejero, T.; Cardona, F.; Marradi, M.; Faggi, E.;
Parmeggiani, C.; Goti, A. Eur. J. Org. Chem. 2008, 2929–2947.
(11) Defoin, A.; Joubert, M.; Henchel, J.-M.; Strehler, C.; Streith, J.
Synthesis 2000, 1637.
(12) Attia, M. I.; Timmermann, M.; H€oger, P.; Herdeis, C. Eur. J.
Org. Chem. 2007, 3669–3675.
(13) Jensen, H. H.; Jensen, A.; Hazell, R. G.; Bols, M. J. Chem. Soc.,
Perkin Trans. 1 2002, 1190–1198.
(14) Behr, J.-B.; Guillerm, G. Tetrahedron Lett. 2007, 48, 2369–2372.
(15) (a) Boschetti, A.; Nicotra, F.; Panza, L.; Russo, G. J. Org. Chem.
1988, 53, 4181–4185. (b) Rao, J. P.; Rao, B. V.; Swarnalatha, J. L.
Tetrahedron Lett. 2010, 51, 3083–3087.
4098
dx.doi.org/10.1021/jo200176u |J. Org. Chem. 2011, 76, 4094–4098