Stereomeric pyrrolidinopentoses bearing an imidazole ring - Synthesis, chiroptical properties, and evaluation as potential sugar-mimic glycosidase inhibitors

Article abstract of DOI:10.1002/1099-0690(200202)2002:4<702::AID-EJOC702>3.0.CO;2-Y

The syntheses of the imidazolo-pyrrolidino-pentoses ent-2 (Larabino), 3 (D-xylo), 4 (D-lyxo), ent-4 (L-lyxo), and 5 (D-ribo) are reported, completing the series of all eight possible stereomers. The corresponding five linear imidazolo sugar precursors were prepared by nucleophilic addition of C(4)-metallated imidazole derivatives to the appropriately configured and protected aldotetroses. Cyclisation of the resulting linear imidazolo-carbohydrates was performed by means of intramolecular Walden inversion processes, followed by deprotection to afford the five target imidazolo-sugars. Three of the four D-configured stereomers proved to be good to moderate glycosidase inhibitors, as determined by Michaelis-Menten kinetics.

Full text of DOI:10.1002/1099-0690(200202)2002:4<702::AID-EJOC702>3.0.CO;2-Y

FULL PAPER
Stereomeric Pyrrolidinopentoses Bearing an Imidazole Ring ؊ Synthesis,
Chiroptical Properties, and Evaluation as Potential Sugar-Mimic Glycosidase
Inhibitors
[a]
[a]
[a]
[b]
´
´
´
Theophile Tschamber,* Herve Siendt, Celine Tarnus, Dariusz Deredas,
Andrzej Frankowski,[b] Sylviane Kohler,[c] and Jacques Streith*[a]
Keywords: Azasugars / Carbohydrates / Circular dichroism / Glycosidase inhibition / Imidazolo-pyrrolidinopentoses
The syntheses of the imidazolo-pyrrolidino-pentoses ent-2 (
L
-
linear imidazolo-carbohydrates was performed by means of
intramolecular Walden inversion processes, followed by de-
arabino), 3 ( -xylo), 4 ( -lyxo), ent-4 ( -lyxo), and 5 ( -ribo)
D
D
L
D
are reported, completing the series of all eight possible ste- protection to afford the five target imidazolo-sugars. Three
reomers. The corresponding five linear imidazolo sugar pre- of the four -configured stereomers proved to be good to
D
cursors were prepared by nucleophilic addition of C(4)-
metallated imidazole derivatives to the appropriately config-
ured and protected aldotetroses. Cyclisation of the resulting
moderate glycosidase inhibitors, as determined by
Michaelis−Menten kinetics.
Introduction
structure of the substrate (or, alternately, of its pyrroline
mimic) Ϫ in its flattened transition state Ϫ and the en-
zyme’s active site.[5,6]
Polyhydroxylated alkaloids that mimic the structures of
monosaccharides are now believed to be widespread in
plants and in microorganisms. These sugar mimics inhibit
glycosidases by virtue of their structural resemblance to the
sugar moiety of the natural substrates. In 1988, the polyhy-
droxypyrroline nectrisine (1) was isolated as an immunomo-
dulator from the culture broth of the fungus Nectria lu-
cida[1] and later shown to be a powerful inhibitor of α-glu-
cosidase and, to a lesser extent, of α-mannosidase.[2,3] Nat-
urally occurring five-membered glycosidase inhibitors,
In a recent article dealing with glycosidase-catalyzed hy-
drolysis mechanisms of polysaccharides Ϫ their building
blocks being piperidinoses Ϫ Zechel and Withers reviewed
the finely tuned action of these enzymes and postulated that
polysaccharide hydrolases give rise to transition states pos-
sessing pronounced oxocarbonium character Ϫ and there-
fore flattened half-chair conformations Ϫ both with re-
taining and with inverting glycosidases.[7]
In 1989 we set out to incorporate an imidazole ring into
comprising several dozen polyhydroxylated pyrrolidines a furano-pentose, the azole moiety being intended to induce
(i.e., pyrrolidines, indolizidines, and pyrrolizidines[4]), are, as a flattening of the envelope conformation of the attached
a rule, saturated heterocycles. To the best of our knowledge, pyrrolidinose moiety. The natural product nectrisine (1) was
nectrisine (1), which bears an imine functionality in a five- the reference and model compound for this research pro-
membered azasugar ring, is the only exception so far found ject. The first substance we synthesized along these lines
in nature. The pyrroline double bond, which brings about was the -xylo-imidazolo sugar ent-3, the 3D structure and
a flattening of the envelope conformation of that ring, in absolute configuration of which had been ascertained by
azasugar 1 would seem to mimic the transition state of the NMR spectroscopy and by single-crystal X-ray diffraction
sugar moiety of the enzymeϪsubstrate complex. Therefore, analysis.[8] Tested against a dozen human liver glycosidases,
one may surmise that its 3D structure is in agreement with ent-3 proved to be inactive as a glycosidase inhibitor.[9]
Pauling’s prediction of close complementarity between the Nevertheless, having previously established that some imid-
azolo-piperidino-pentoses of type 30 Ϫ which are structural
[a]
isomers of pyrrolidino-pentose ent-3 (see below: Scheme 6)
Ϫ were selective and sometimes quite potent glycosidase
inhibitors,[10] we surmised that some stereomers of ent-3
might show similar inhibitory properties. This assumption
turned out to be true, as demonstrated here for some of
the eight possible stereomers, the syntheses of which are
described below.
´
´
Ecole Nationale Superieure de Chimie, Universite de Haute-
Alsace,
3, rue Alfred Werner, 68093 Mulhouse, France
Fax: (internat.) ϩ 33-3/89336860
E-mail: J.Streith@uha.fr
[b]
[c]
Institute of Organic Chemistry, Technical University,
ul. Zwirki 36, 90924 Lodz, Poland
Optical Spectroscopy, Hoffmann-La Roche AG,
Grenzacherstrasse, 4070 Basel, Switzerland
702
WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ193X/02/0204Ϫ0702 $ 17.50ϩ.50/0 Eur. J. Org. Chem. 2002, 702Ϫ712

Stereomeric Pyrrolidinopentoses Bearing an Imidazole Ring
FULL PAPER
In a preceding publication we reported the synthesis of compound (97%), together with small amounts of 8 (3%), in
the -arabino (2) and the -ribo (ent-5) stereomers, as well 97% overall yield. O-Benzylation of 7 gave 10, acid-induced
as a second and more efficient synthesis of ent-3.[11] Here deprotection of which (HCl/THF) provided the crystalline
we describe the detailed syntheses of the five remaining ste- compound 11. Bis(tritylation) of this yielded 12, which was
1
reomers (Scheme 1). H and 13C NMR spectra, as well as treated with Tf2O (in pyridine/CH2Cl2), resulting in imme-
CD spectra corroborated the expected absolute configura- diate intramolecular Walden inversion. The resulting bicyc-
tions for all eight stereomers. Finally, inhibition assays of lic bis(trityl)imidazolium ion intermediate, which was nei-
these imidazolo-sugars Ϫ 2 to 5 and ent-2 to ent-5 Ϫ ther isolated nor characterized, was treated with acid (HCl)
against six commonly encountered glycosidases are re- to remove the trityl protecting groups, which provided 13.
ported.
Debenzylation of this gave the desired -arabino compound
1
ent-2, the H and 13C NMR spectra of which proved to be
identical to and superimposable on those of 2. Further-
more, the chiroptical properties of ent-2 and of the known
-arabino product 2 proved their 3D mirror image struc-
tures (Table 1; Figure 1).
Xylose Series 3/ent-3
Retrosynthetic analysis of the -xylo stereomer 3 re-
quired the linear imidazolo--arabino derivative 14 as the
Scheme 1. Nectrisine (1) and imidazolopyrrolidinoses 2 to 5 and
ent-2 to ent-5
Results
Synthesis of Imidazolo-Pyrrolidinoses
Arabinose Series 2/ent-2
Synthesis of the -arabino-pyrrolidinose stereomer 2 had
already been described by us in a preceding publication.[11]
Retrosynthetic analysis of its enantiomer ent-2 (Scheme 2)
required the -threo derivative 6 Ϫ a compound that we
had prepared previously[12] Ϫ as the chiral starting material
and an imidazol-4-yl anion, the preparation of which had
been described and discussed in detail elsewhere.[13Ϫ15] Suf-
fice it to say that a solution of EtMgBr in diethyl ether had
to be added to 4-iodo-1-tritylimidazole in dry CH2Cl2 to
give the C(4)-metallated imidazole building block, which
was not isolated. Treatment of this with 6 provided the dias-
tereomeric -xylo (7; 30%) and -lyxo (8; 70%) adducts
(overall yield: 89%), which were not separated. Since it was
the minor adduct 7 that was needed for the preparation of
target molecule ent-2, the mixture of adducts 7 and 8 was
oxidized (activated MnO2, CH2Cl2, room temp.) to the cor-
responding ketone 9 (87%), reduction of which (-Se-
Scheme 2. Reagents and conditions: a) 1) 4-iodo-1-tritylimidazole,
EtMgBr/Et2O, CH2Cl2, 2) ϩ 6 in CH2Cl2; b) MnO2, CH2Cl2; c) -
Selectride, THF, Ϫ50 °C; d) NaH, BnBr, TBAI, THF, 40 °C; e) 4
 HCl/THF (1:3), reflux, 6 h; f) TrCl, NEt3, DMAP cat., CH2Cl2,
reflux, 4 h; g) 1) Tf2O, CH2Cl2, Ϫ70 °C to 0 °C, then MeOH and
concentration, 2) 6  HCl, dioxane, 55 °C, 3 h; h) H2, Pd(OH)2/C,
lectride, THF, Ϫ50 °C) afforded the desired 7 as the major EtOH/AcOH (3:2)
Eur. J. Org. Chem. 2002, 702Ϫ712
703

T. Tschamber, J. Streith et al.
FULL PAPER
chiral precursor (Scheme 3). The synthesis of this com-
pound had already been described in a previous publica-
tion.[10] The primary alcohol of 14 was selectively silylated
(TBDPSCl/imidazole/DMF) to provide 15. Walden inver-
sion occurred at once when Tf2O was added to 15 in pyrid-
ine, the secondary triflate intermediate undergoing spontan-
eous intramolecular nucleophilic attack by the nearest imid-
azole nitrogen atom to give 16. After the standard workup,
-xylo derivative 16 was isolated and partly deprotected by
fluoride ion (TBAF/THF) to give 17, which was debenzyl-
ated by catalytic hydrogenolysis to yield the desired -xylo
target molecule 3.
Scheme 3. Reagents and conditions: a) 1) imidazole, DMF,
TBDPSCl, 2) ϩ 14 in DMF, room temp., 14 h; b) Tf2O, pyridine,
CH2Cl2, Ϫ78 °C, to room temp.; c) TBAF, THF, room temp.; d)
H2 (30 bar), Pd(OH)2/C, MeOH/AcOH
Scheme 4. Reagents and conditions: a) 1) imidazole, TBDPSCl,
DMF, 2) ϩ 18 in DMF; b) Tf2O, CH2Cl2, Ϫ78 °C to room temp.;
c) TBAF, THF, room temp.; d) H2 (30 bar), Pd(OH)2/C, MeOH/
AcOH; e) 1) 15, nBuLi, THF, Ϫ78 °C, 15 min, 2) ϩ 22 in THF,
Ϫ78 °C to room temp.; f) 1) NaH, THF, TBAI cat, BnBr, 40 °C,
2) ϩ 6  HCl at room temp., then 45 °C, 14 h
The synthesis of the -xylo enantiomer ent-3 had already
been described previously[8,11] and its 3D structure demon-
strated by single-crystal X-ray diffraction analysis.[8] The 1H
and 13C NMR spectra of 3 proved to be identical to, and
therefore superimposable on, those of ent-3. Furthermore,
the chiroptical properties were in perfect agreement with
the expected 3D mirror image relationship of the enantiom-
eric pair 3/ent-3 (Table 1, Figure 1).
The retrosynthetic analysis of the -lyxo stereomer ent-4
was identical to the preceding one, albeit obviously in the
enantiomeric series (Scheme 4). The starting material was
the -erythro compound 22, a known and easily prepared
product.[16,17] Nucleophilic addition of the known lithio de-
rivative of imidazole 23[18] to 22 provided the minor -arab-
ino product 24 (25%) and the major -ribo diastereomer 25
(75%) in 88% overall yield. Adduct 25 was O-benzylated
and the acid-sensitive protection groups of the ensuing
(fully protected) intermediate were removed with HCl, to
afford ent-18. From this, ent-19 was formed, and eventually
the pyrrolidinose derivatives ent-20 and ent-21 were ob-
tained. Standard deprotection of the latter gave the -lyxo
derivative ent-4, the chiroptical properties of which demon-
strated its mirror image relationship with the -lyxo ste-
reomer 4 (Table 1, Figure 1).
Lyxose Series 4/ent-4
Retrosynthetic analysis of the -lyxo stereomer required
the linear imidazolo--ribo derivative precursor 18, the syn-
thesis of which we had already described in a previous pub-
lication.[10] The linear synthetic sequence was very similar
to the one that we used for the preparation of the -xylo
compound 3. The primary alcohol of 18 was selectively sily-
lated (TBDPSCl/imidazole/DMF) to afford 19. Intramolec-
ular Walden inversion occurred at once when Tf2O was ad-
ded to 19 in pyridine, the intermediate secondary triflate
undergoing nucleophilic attack by the nearest nitrogen
atom of the imidazole moiety. After the standard workup,
-lyxo derivative 20 was isolated and treated with TBAF to
Ribose Series 5/ent-5
Retrosynthetic analysis of the -ribo stereomer 5 required
give 21, which was debenzylated by hydrogenolysis to yield the linear imidazolo--lyxo-diol derivative 26 as the chiral
the -lyxo stereomer 4 (Scheme 4).
precursor (Scheme 5). This diol, the synthesis of which had
704
Eur. J. Org. Chem. 2002, 702Ϫ712

Stereomeric Pyrrolidinopentoses Bearing an Imidazole Ring
FULL PAPER
already been described in a previous publication,[10] was se- and Figure 1), it followed that ent-2 and 2 were enantiom-
lectively silylated (TBDPSCl/imidazole/DMF) at the prim- eric entities.
ary alcohol to provide 27. Intramolecular Walden inversion
Similar arguments could be put forward to demonstrate
occurred spontaneously when Tf2O was added to 27 in pyr- the absolute configuration of the newly synthesized imida-
idine, the intermediate secondary triflate spontaneously un- zolo-sugar 3: i) compound 3 had 1H and 13C NMR spectra
dergoing SN2 attack by the nearest N atom. After the identical to and superimposable on those of the known ste-
standard workup, -ribo derivative 28 was isolated. Treat- reomer ent-3,[8,11] ii) the chiroptical data of 3 were of oppos-
ment of the latter with fluoride ion (TBAF/THF) gave 29, ite sign to and the mirror image of those of ent-3 ([α]D
which was debenzylated by catalytic hydrogenolysis to give values: Table 1; CD spectra: Figure 1). It followed that 3
the -ribo 5 target molecule (Scheme 5).
and ent-3 were enantiomeric entities. Note furthermore that
the absolute configuration of ent-3 had already been ascer-
tained in a previous publication, by a single-crystal X-ray
diffraction analysis.[8]
Analogously, NMR and chiroptical arguments permitted
the absolute -ribo configuration of 5 to be demonstrated
by comparison with the known -ribo configuration of
ent-5.[11]
As to the opposite enantiomers in the lyxo series, neither
of which was known, their 1H and 13C NMR spectra proved
to be identical and superimposable; furthermore they ap-
peared to be quite different from those of the other three
pairs of enantiomers. In addition, the synthetic flow sheet
of 4 (-lyxo) was straightforward (Scheme 4); since starting
material 18 had been demonstrated to be -ribo-configured
(see above and Scheme 3), it followed that the target molec-
ule 4 existed in the -lyxo configuration after the intramole-
cular Walden inversion; hence, the -lyxo configuration for
ent-4, as deduced i) from its 1H and 13C NMR spectra,
which proved to be identical to and superimposable on
those of 4, ii) from its CD spectrum, which was the mirror
image of that of ent-4 (Figure 1), and iii) from its rotatory
power, which was of the same magnitude as, but of opposite
sign to, that of ent-4 (Table 1).
Scheme 5. Reagents and conditions: a) 1) imidazole, TBDPSCl,
CH2Cl2, NEt3, DMAP cat, 2) ϩ 26 in DMF; b) Tf2O, pyridine,
CH2Cl2, Ϫ25 °C; c) TBAF, THF, room temp.; d) H2, Pd(OH)2/
C, AcOH
The synthesis of the -ribo enantiomer ent-5 had already
1
been described by us in a previous publication.[11] The H
and 13C NMR spectra of 5 and ent-5 proved to be identical
and superimposable. Furthermore, their chiroptical proper-
ties permitted their 3D mirror image relationship to be
demonstrated unambiguously (Table 1 and Figure 1).
Chiroptical data, particularly circular dichroism (CD)
spectra, proved to be of great help, since they enabled mir-
ror image relationships to be demonstrated between oppos-
ite enantiomers, as described above (Figure 1). The sign of
Spectral Properties and Structure Analyses
The structural and configurational assignments of all the long-wavelength Cotton effect (CE), which appeared at
eight imidazolo-pyrrolidinopentoses 2 to 5 and ent-2 to ent- 210Ϫ212 nm, seemed to be determined by the absolute con-
5 could be achieved without ambiguity thanks to the com- figuration of the asymmetric center C(7), connected directly
1
bination of H/13C NMR spectroscopy, circular dichroism to the imidazole chromophore, the (7R) configuration giv-
(CD spectra: Figure 1), and rotatory power data ([α]2D0 ing rise to a positive CE and the (7S) form to a negative
values: Table 1).
one, as observed in all instances (Figure 1). The same cor-
The -arabino-configured imidazolo-pyrrolidino-pentose relation between the sign of the long-wavelength CE and
2 had already been synthesized.[11] That 2 occurs in the - the absolute configuration of carbon atom C(8) Ϫ also dir-
arabino configuration is due to the fact that it had been ectly connected to the imidazole chromophore Ϫ had also
obtained from -sorbose, in which the configurations of been observed with the analogous and isomeric imidazolo-
carbon atoms C(3) and C(4) had been retained,[19] whereas piperidino-pentose isomers of type 30 (Scheme 6), the (8R)
C(5) had undergone a Walden inversion during the intram- configuration producing a positive CE and (8S) a negative
olecular cyclisation step.[11] These three consecutive asym- one.[10] Similarly, Vasella and co-workers published some
metric carbon atoms of -sorbose correspond to carbon CD data for pyrrolo-piperidino-hexose derivatives, and
atoms C(7), C(6), and C(5), respectively, in compound 2;[11] showed that the -manno-pyrrolo-piperidino-hexose 31,
as for carbon atom C(2) of -sorbose, it had been incorpor- which is (8R)-configured, appeared with a pronounced pos-
ated into the imidazole ring of 2 as described in a previous itive CE, whereas its (8S)-configured -gluco diastereomer
publication.[19] Since the newly synthesized stereomer ent-2 32 appeared with a negative CE (Scheme 6).[20]
had 1H and 13C NMR spectra identical to and superimpos-
Furthermore, the imidazolo-pyrrolidino-tetroses 33 (-er-
able on those of 2, and since furthermore the chiroptical ythro), ent-33 (-erythro), and 34 (-threo), the syntheses of
data of ent-2 were the mirror image of those of 2 (Table 1 which we had described previously (the -threo enantiomer
Eur. J. Org. Chem. 2002, 702Ϫ712
705

T. Tschamber, J. Streith et al.
FULL PAPER
Let us now compare the CD spectra of -erythro-tetrose
33 and of -ribo-pentose 5. Each had a pronounced nega-
tive long-wavelength CE at 214 nm (and a very pronounced
positive CE at 199 nm). The 214-nm band of 5 was slightly
broadened when compared to the corresponding band of
33, the broadening effect obviously being due to the super-
position of two CEs with different amplitudes but the same
sign. That is to say that stereomeric imidazolo-pyrrolidino-
pentoses with opposite CIP notations for C(5) and C(7)
produce two CEs with the same sign in their CD spectra.
As a consequence, the longest-wavelength and less pro-
nounced CE (with an estimated λmax ϭ 226 nm) is hidden
beneath the stronger band, the λmax of which appears at
213Ϫ214 nm, this being observed with -xylo (3) and with
-ribo (5) stereomers, as well as with their respective enanti-
omers (Figure 1).
Scheme 6. Imidazolopiperidinose 30, pyrrolopiperidinoses 31 and
32, and imidazolopyrrolidinoses 33, ent-33, and 34
Enzymatic Assays
ent-34 has not been prepared),[11] showed similar CD spec-
All eight imidazolo-pyrrolidino-pentoses in Scheme 1
tra, a (7R) configuration giving rise to a positive long-wave- have been evaluated as potential inhibitors of six commer-
length CE and (7S) to a negative one. Their C(5) carbon cially available glycosidases, and the results compiled in
atoms being devoid of hydroxymethylene groups, these Table 2. All imidazolo sugars that were active proved to be
three imidazolo-pyrrolidino-tetroses represent reference competitive inhibitors.
compounds when it comes to comparative CD spectral in-
The -arabino stereomer 2 was a good and selective in-
terpretations with respect to the pentose homologues de- hibitor of Jack bean α--mannosidase (Ki ϭ 5 µ). The -
scribed here (those of Figure 1). To illustrate that point, let xylo stereomer 3 proved to be an even better inhibitor of
us compare the CD spectra of -threo-tetrose 34 and of - Escherichia coli β--galactosidase (Ki ϭ 0.2 µ determined
arabino-pentose 2. Each had a pronounced positive CE (34: by Morrisson treatment),[21] albeit the association occurred
∆ε ϭ ϩ4.45 at 212 nm; 2: ∆ε ϭ ϩ4.10 at 210.5 nm), most at a rather reduced rate. Nevertheless, 3 turned out to be
probably as a consequence of their (8R) and (7R) configura- nonselective, since it also inhibited baker’s yeast α--glucos-
tions, respectively. Furthermore, each showed a negative CE idase and green coffee bean α--galactosidase (see Table 2).
at shorter wavelength (34: ∆ε ϭ Ϫ3.90 at 198 nm; 2: ∆ε ϭ Similarly, -lyxo stereomer 4 was a nonselective and gener-
Ϫ2.23 at 197 nm). Last but not least, an additional negative ally a poor inhibitor of the same three glycosidases. The -
CE appeared at higher wavelength, but only for imidazolo- ribo stereomer 5 was totally inactive with any of the six gly-
pentose 2 (∆ε ϭ Ϫ0.75 at 225.5 nm), the CD spectrum of cosidases.
imidazolo-tetrose 34 being devoid of such an analogous
As to the four stereomers of the -series, these were inact-
long-wavelength CE. It is reasonable to assume that this ive with the exception of ent-3, which was a poor inhibitor
long-wavelength CE band appearing with 2 is due to the of Jack bean α--mannosidase.
asymmetric carbon atom C(5R), which bears the CH2OH
Imidazolo-pyrrolidino-tetroses 33 (-erythro), ent-33 (-
group. We note that the two longest-wavelength CE bands erythro), and 34 (-threo) had already been evaluated as
of imidazolo-pyrrolidino-pentoses Ϫ i.e., at λ ϭ 210Ϫ212 potential inhibitors with the same six glycosidases. They
nm (strong band) and λ ϭ 225Ϫ226 nm (weak band) Ϫ can had turned out to be inactive, with only -threo derivative
clearly be distinguished in the CD spectra when of opposite 34 showing poor inhibition with an α-mannosidase.[11]
sign [i.e., when C(5) and C(7) have the same CIP notation],
as observed in - and -arabino and in - and -lyxo azasu- it is fair to say that the (R) configuration at C(5) seems
gar derivatives (Figure 1). to be mandatory for some inhibition to be attained; this
Within the rather limited scope of only six glycosidases,
Table 1. Rotatory power data ([α]2D0 values) for the eight stereomers 2 to 5 and ent-2 to ent-5
2 (-arabino)
3 (-xylo)
4 (-lyxo)
5 (-ribo)
ϩ9
ϩ41
ϩ12
ϩ70
(c ϭ 1.0, H2O)
ent-2 (-arabino)
Ϫ8
(c ϭ 0.6, EtOH)
ent-3 (-xylo)
Ϫ41
(c ϭ 0.6, MeOH)
ent-4 (-lyxo)
Ϫ12
(c ϭ 1.0, MeOH)
ent-5 (-ribo)
Ϫ58
(c ϭ 1.0, H2O)
(c ϭ 0.75, EtOH)
(c ϭ 0.75, MeOH)
(c ϭ 1.0, MeOH)
706
Eur. J. Org. Chem. 2002, 702Ϫ712

Stereomeric Pyrrolidinopentoses Bearing an Imidazole Ring
FULL PAPER
Table 2. Inhibition constants (IC50) in µ measured at 22 °C; NI ϭ
no inhibition at [I] ϭ 1 m; ([S] ϭ KM); %: percentage of inhibition
at 1 m; (1) slow association; (2) slow association, Ki with Mor-
risson treatment
zymes’ active sites. Beyond that, it would seem to be rather
risky to deduce any rational interpretation in terms of con-
figuration and functional complementarity between the im-
idazolo sugars described here and the chiral 3D structures
of the enzymes’ active sites.
Experimental Section
General: Flash chromatography (FC): silica gel (Merck 60;
230Ϫ400 mesh). TLC: silica gel on aluminium sheets (Merck 60
HF254); the spots were viewed under UV or by heating with a ther-
mogun after spraying with a solution of KMnO4 (20 g) and
Na2CO3 (40 g) in H2O (1 L) or a solution of phosphomolybdic
acid (5% in 96% EtOH). M.p.: Kofler hot-bench or Büchi-SMP
apparatus; corrected values. Optical rotations were all measured at
ϩ20 °C: SchmidtϪHaensch Polartronic Universal polarimeter. CD
Figure 1. Circular dichroism of the imidazolopyrrolidinoses
observation goes along with the second prerequisite, that
the ϪCH2OH handle must be present in these -series com-
pounds in order to obtain a proper docking into the en- spectra were measured in H2O solution between 185 and 400 nm
Eur. J. Org. Chem. 2002, 702Ϫ712 707

T. Tschamber, J. Streith et al.
FULL PAPER
under nitrogen with a Jobin Yvon CD6 Dichrograph (∆ε values) at
7.22Ϫ7.38 [20 H, H-arom], 7.46 [d, 1 H, C(4Ј)-H], 7.82 [d, 1 H,
the research center of the Roche pharmaceutical division in Basel, C(2Ј)-H], J2Ј,4Ј ϭ 1.3, J2,3 ϭ 5.0, J3,4a ϭ 6.7, J3,4b ϭ 6.7. 13C NMR
1
Switzerland. H and 13C NMR spectra: 250 MHz and 62.9 MHz,
(CDCl3, 62.9 MHz): δ ϭ 25.2 and 25.8 [2 ϫ CH3 acetonide], 65.4
[C(4)], 72.4 [CH2Ph], 75.9 [CPh3], 76.1 [C(3)], 81.8 [C(2)], 109.4
respectively; Bruker ACF 250 spectrometer at 300 K. Internal refer-
1
ences for H NMR: SiMe4 (δ ϭ 0.00), CDCl3 (δ ϭ 7.26), CD3OD [C(CH3)2], 127.4Ϫ129.3 [C-arom], 137.2 and 138.5 (Cs of Ph], 139.3
(δ ϭ 3.30), [D4]TSP for spectra in D2O (δ ϭ 0.00); for 13C NMR: [C(2Ј)], 141.3 [Cs of CPh3), 192.9 [C(1)]. C36H34N2O4 (558.65): C
CDCl3 (δ ϭ 77.03), CD3OD (δ ϭ 49.02); δ in ppm and J in Hz.
HR-MS were measured with an MAT-311 or with a Zabspec TOF
spectrometer at the University of Rennes. Microanalyses were car-
ried out by the Service Central de Microanalyses of the CNRS,
69390 Vernaison, France. ‘‘MeOH ϩ NH3’’ stands for a solution
of pure MeOH saturated at room temp with NH3 (ex gas form).
77.39, H 6.13, N 5.01; found C 77.2, H 6.1, N 5.2.
Imidazolo- -xylo Derivative 7: A solution of -Selectride (1 , 12.8
mL, 12.8 mmol) in THF was added dropwise at Ϫ78 °C to a stirred
solution of 9 (4.75 g, 8.50 mmol) in anhydrous THF (80 mL). The
reaction was monitored by TLC (EtOAc/cyclohexane, 1:1). After 1
h at Ϫ50 °C, the solution was quenched with MeOH (20 mL), and
then allowed to warm up to room temp. and concentrated to near
dryness in vacuum. The residue was taken up in CH2Cl2 (50 mL).
D
Enzymatic Assays: Glycosidases [α-mannosidase (EC 3.2.1.24)
from Jack beans, β-mannosidase (EC 3.2.1.25) from snails, α-gluco-
sidase (EC 3.2.1.20) from baker’s yeast, β-glucosidase (EC 3.2.1.21) The organic solution was washed with a saturated solution of
from almonds, α-galactosidase (EC 3.2.1.22) from green coffee be-
ans, β-galactosidase from Escherichia coli (EC 3.2.1.23)], and their
corresponding substrates were purchased from Sigma Co. Spectro-
NH4Cl (100 mL) and the aq. phase was extracted with CH2Cl2 (3
ϫ 50 mL). The combined organic phases were dried (MgSO4), fil-
tered, concentrated to dryness, and purified by chromatography
photometric assays were performed at the optimum pH for each (EtOAc/cyclohexane, 1:1) to give a mixture of 7 ϩ 8 (4.61 g, 97%)
enzyme,[22] with p-nitrophenyl-α--mannopyranoside as a substrate
for α-mannosidase (Km ϭ 2 m, pH ϭ 4.5), p-nitrophenyl-β--
mannopyranoside for β-mannosidase (Km ϭ 1.3 m, pH ϭ 4.0), p-
nitrophenyl-α--glucopyranoside for α-glucosidase (Km ϭ 0.3 m,
pH ϭ 7), p-nitrophenyl-β--glucopyranoside for β-glucosidase
in a 97:3 ratio, as determined by reverse phase HPLC (Chiracel
OD-R column, eluent: MeOH/H2O, 95:5). H NMR (CDCl3, 250
MHz) of 7: δ ϭ 1.30 and 1.41 [2 s, 6 H, 2 ϫ CH3 acetonide], 2.8
[slarge, OH], 3.74 [t, 1 H, HaϪC(4)], 3.93 [dd, 1 H, HbϪC(4)], 3.95
[dd, 1 H, HϪC(2)], 4.27 [dt, 1 H, HϪC(3)], 4.51 and 4.68 [AB, 2 H,
J ϭ 11.4, CH2Ph], 4.73 [d, 1 H, HϪC(1)], 6.89 [s, 1 H, HϪC(4Ј)],
1
(Km ϭ 2 m, pH ϭ 5.0), and p-nitrophenyl-β--galactoside (Km
ϭ
0.3 m, pH ϭ 7) and p-nitrophenyl-α--galactoside (Km ϭ 0.3 m, 7.07Ϫ7.34 [m, 20 H, H-arom], 7.45 [s, 1 H, HϪC(2Ј)], J1,2 ϭ 3.5,
pH ϭ 6.5) as substrates for the corresponding galactosidases. The
J
2,3 ϭ 6.2, J3,4a ϭ 6.3, J3,4b ϭ 7.7, J4a,4b ϭ 8.2. HR-MS: [M ϩ H]ϩ
release of p-nitrophenol was measured continuously at 405 nm to ion 561.2747 (C36H37N2O4, calcd. 561.2753).
determine initial velocities. All kinetics were performed at 25 °C
Imidazolo-D-xylo Derivative 11: A suspension of NaH in oil (50%,
and the reaction was started by the addition of enzyme in a 1-mL
assay medium (acetate buffer 50 m, or phosphate buffer 20 m
according to the desired pH value) using substrate concentrations
around the Km value of each enzyme. The Ki values were deter-
mined for the most potent inhibitors, by the Dixon graphical pro-
cedure.[23,24]
1.15 g, excess) was added at 0 °C to a stirred solution of almost
pure 7 (as obtained above: 4.54 g, 8.10 mmol) in anhydrous THF
(80 mL) under argon. When the evolution of H2 had ceased, Bu4NI
(ca. 30 mg) and BnBr (1.16 mL, 1.67 g, 9.72 mmol) were added,
the vigorously stirred solution was heated at 40 °C for 12 h and
allowed to cool to room temp., and MeOH (5 mL) was added
slowly. The solution was concentrated to dryness, the residue was
taken up in EtOAc (80 mL), and the resulting solution was washed
Coupling Reaction between an Imidazole Grignard Reagent and the
D-Threose Derivative 6: A solution of EtMgBr in Et2O (3 , 12.6
mL, 37.9 mmol) was added under argon at room temp. to a stirred with H2O and then with brine and concentrated to dryness, to af-
solution of 4-iodo-1-tritylimidazole (15.16 g, 34.8 mmol)[14] in an-
ford 10 as a crude product that was neither purified nor character-
hydrous CH2Cl2. After 15 min, a solution of aldehyde 6 (7.90 g, ized. Crude product 10 was dissolved in 4  HCl/THF, 1:3 (40 mL)
31.6 mmol)[13Ϫ15] in anhydrous CH2Cl2 (45 mL) was added to the
and heated at reflux for 6 h. THF was evaporated in vacuum, the
stirred mixture and left to react at room temp., the reaction being aqueous phase was extracted with Et2O (2 ϫ 50 mL), and the or-
monitored by TLC (EtOAc/cyclohexane, 7:3). After 2 h, the reac-
tion was quenched with a saturated aq. solution of NH4Cl (100
ganic phase was washed with 2  HCl (2 ϫ 50 mL). The combined
aqueous phases were basified with some solid K2CO3 and extracted
mL) and the organic phase was separated, dried (MgSO4), filtered, with CH2Cl2. The resulting organic solution was dried (MgSO4),
and concentrated to dryness in vacuo. The crude residue was puri-
fied by chromatography (EtOAc/cyclohexane, 7:3, then 8:2), the
filtered, and concentrated to dryness, and the crude residue was
purified by chromatography (CH2Cl2/MeOH ϩ NH3, 9:1) to afford
two diastereomers 7 and 8 as well as trace amounts of imidazole 11 as a crystalline compound (890 mg, 30%). M.p. 114 °C (EtOAc).
1
not being separated (all together: 15.83 g, ca. 81% of 7 ϩ 8).
[α]2D0 ϭ ϩ47 (c ϭ 2, MeOH). H NMR (CD3OD, 250 MHz): δ ϭ
3.33 [td, 1 H, C(3)-H], 3.49Ϫ3.56 [m, 2 H, 2 ϫ C(4)-H], 3.96 [dd,
1 H, C(2)-H], 4.36 and 4.47 [AB, 2 H, J ϭ 11.6, CH2Ph], 4.67 and
4.94 [AB, 2 H, J ϭ 11.0, CH2Ph], 4.83 [d, 1 H, C(1)-H], 7.10 [s, 1
H, C(2Ј)-H], 7.19Ϫ7.37 [m, 10 H, H-arom], 7.73 [s, 1 H, C(4Ј)-H],
J1,2 ϭ 8.2, J2,3 ϭ 2.0, J3,4 ϭ 6.3. 13C NMR (CD3OD, 62.9 MHz):
δ ϭ 64.5 [C(4)], 71.9 [CH2Ph], 72.8 [C(3)], 76.6 [CH2Ph], 78.0
[C(1)], 82.5 [C(2)], 128.5Ϫ129.4 [C-arom and C-imidazole], 137.1
[C-arom], 140.3 [C-imidazole].
Imidazolo Ketone Derivative 9: Precipitated activated MnO2 (20 g)
was added under argon at room temp. to a stirred solution of the
above mixture of 7 ϩ 8 (4.00 g, 7.13 mmol) in CH2Cl2 (45 mL).
After 90 min, the reaction mixture was filtered through a small
column of silica gel and the column was washed several times with
EtOAc. The mixed organic phases were concentrated to dryness
and the crude residue was purified by chromatography (EtOAc/
cyclohexane, 4:6), to provide ketone 9 as a colorless foam (3.45 g,
87%), which was recrystallised. M.p. 126 °C (EtOAc/cyclohexane).
Imidazolo-D-xylo Derivative 12: DMAP (ca. 10 mg), anhydrous
[α]2D0 ϭ Ϫ50 (c ϭ 2, CHCl3). 1H NMR (CDCl3, 250 MHz): δ ϭ Et3N (920 µL, 6.51 mmol, 3 equiv.), and TrCl (1.51 g, 5.43 mmol,
1.27 and 1.30 [2s, 6 H, 2 CH3 acetonide], 3.94 [dd, 1 H, C(4)-Ha], 2.5 equiv.) were added under argon to a stirred solution of 11 (800
4.00 [dd, 1 H, C(4)-Hb], 4.50 and 4.70 [AB, 2 H, J ϭ 11.7, CH2Ph], mg, 2.17 mmol) in CH2Cl2 (24 mL). This solution was heated at
4.55 [td, 1 H, C(3)-H], 4.72 [d, 1 H, C(2)-H], 7.04Ϫ7.12 and reflux for 4 h, allowed to cool to room temp., and washed with
708
Eur. J. Org. Chem. 2002, 702Ϫ712

Stereomeric Pyrrolidinopentoses Bearing an Imidazole Ring
FULL PAPER
brine, and the aqueous phase was extracted with CH2Cl2 (2 ϫ 25
mL). The combined organic solutions were dried (MgSO4), filtered,
and concentrated to dryness, and the crude residue was purified by
chromatography (EtOAc/cyclohexane, 2:8) to provide compound
MeOH ϩ NH3, 98:2). Some H2O (10 mL) was added and the mix-
ture was extracted with CH2Cl2, and the organic phase was washed
with a saturated NH4Cl solution to remove pyridine. It was then
dried (MgSO4), filtered, and concentrated to dryness, and the re-
sulting slightly yellow oil was purified by chromatography (Et2O/
12 (1.044 g, 56%) as a colorless oil. [α]2D0 ϭ ϩ25 (c ϭ 2, MeOH).
1
The H NMR (CDCl3, 250 MHz) and 13C NMR (CDCl3) spectra MeOH ϩ NH3, 99:1, then 98:2) to give 16 (178 mg, 51%) as a
of 12 proved to be identical to, and therefore superimposable on,
colorless foam. [α]2D0 ϭ ϩ20 (c ϭ 0.85, CH2Cl2). 1H NMR (CDCl3):
δ ϭ 0.98 [s, 9 H, ϪOSiPh2C(CH3)3], 3.82 [dd, 1 H, C(8)-Hb], 3.94
[dd, 1 H, C(8)-Ha], 4.57 [td, 1 H, C(5)-H], 4.61 [dd, 1 H, C(6)-H],
4.51 and 4.66 [AB, 2 H, J ϭ 11.8, ϪOCH2Ph], 4.61 and 4.74 [AB,
2 H, J ϭ 11.6, ϪOCH2Ph], 4.95 [dd, 1 H, C(7)-H], 6.99 [s, 1 H,
C(1)-H], 7.19Ϫ7.66 [m, 21 H, H-arom and C(3)-H], J1,7 ϭ 0.5,
J5,6 ϭ 6.4, J5,8a ϭ 6.2, J5,8b ϭ 3.3, J6,7 ϭ 3.4, J8a,8b ϭ 11.0. HR-
MS: [M ϩ H]ϩ ion 589.2881 (C37H41N2SiO3, calcd. 589.2886).
those of the known product ent-12.[11]
L
-arabino-Imidazolo-Pyrrolidinose Derivative 13: Tf2O (570 µL, 3.45
mmol, 3 equiv.) was added dropwise at Ϫ70 °C to a stirred solution
of 12 (978 mg, 1.15 mmol) and pyridine (370 µL, 4.63 mmol, 4
equiv.) in anhydrous CH2Cl2 (25 mL), the temperature slowly rising
to 0 °C. After 2 h, MeOH was added, the solution was concentrated
in vacuo, the residue was taken up in dioxane (40 mL), some 6 
HCl (ca. 3.5 mL) was added slowly at room temp., and the resulting
solution was stirred at 55 °C for 3 h and basified at room temp.
with solid Na2CO3 (ca. 4 g). The resulting mixture was filtered,
concentrated to dryness and purified by chromatography (CHCl3/
D-xylo-Imidazolo-Pyrrolidinose Derivative 17: A solution of TBAF
in THF (1 , 0.75 mL, 0.75 mmol) was added at room temp. under
argon to a stirred solution of 16 (170 mg, 0.29 mmol) in anhydrous
THF (3 mL). After 4 h, conversion was complete according to TLC
(CH2Cl2/MeOH ϩ NH3, 9:1). Some H2O (5 mL) was added and
the aqueous solution was extracted with CH2Cl2. The organic
phase was washed with a saturated aq. solution of Na2SO4 to re-
move the tetrabutylammonium salts, dried (MgSO4), and concen-
trated to dryness, and the resulting viscous yellow oil was purified
by chromatography (CH2Cl2/MeOH ϩ NH3, 95:5, then 90:10) to
EtOH, 9.5:0.5) to give 13 (330 mg, 82%) as a colorless oil. [α]2D0
ϭ
ϩ24 (c ϭ 0.6, CHCl3). The 1H (CDCl3) and 13C NMR (CDCl3)
spectra of 13 proved to be identical to, and therefore superimpos-
able on, those of the known ent-13.[11]
L
-arabino-Imidazolo-Pyrrolidinose ent-2: A stirred solution of 13
1
(300 mg, 0.86 mmol) in EtOH/AcOH, 3:2 (10 mL) was put under
H2 for 3 d in the presence of Pd(OH)2/C (350 mg) at room temp.
The suspension was filtered through Clarcel, the solution was con-
centrated to near dryness in vacuum, the residue was taken up in
MeOH, and the resulting solution was percolated over Amberlite
IRA-400 (OHϪ) beads and concentrated to dryness. The residue
was purified by chromatography (Et2O/MeOH ϩ NH3, 7:3) to af-
ford ent-2 (72 mg, 49%) as colorless crystals. M.p.dec 220Ϫ221 °C
yield 17 (98 mg, 97%) as a colorless foam. H NMR (CDCl3): δ ϭ
3.86 [dd, 1 H, C(8)-Hb], 3.97 [dd, 1 H, C(8)-Ha], 4.55 [td, 1 H,
C(5)-H], 4.66 [dd, 1 H, C(6)-H], 4.56 and 4.68 [AB, 2 H, J ϭ 11.5,
OCH2Ph], 4.59 and 4.71 [AB, 2 H, J ϭ 11.9, OCH2Ph], 4.90 [d, 1
H, C(7)-H], 6.86 [br s, 1 H, C(1)-H], 7.25Ϫ7.38 [m, 10 H, H-arom],
7.55 [br s, 1 H, C(3)-H], J5,6 ϭ 6.4, J5,8a ϭ 4.0, J5,8b ϭ 6.6, J6,7
ϭ
3.3, J8a,8b ϭ 11.9. 13C NMR (CDCl3): δ ϭ 59.9 [C(5)], 60.9 [C(8)],
71.1 [OCH2Ph], 72.7 [OCH2Ph], 76.5 [C(7)], 88.5 [C(6)], 122.2
[C(1)], 127.8Ϫ128.5 [10 C, C-arom], 131.3 and 133.2 [C(3) and
C(7a)], 137.0 and 137.3 [2 C’s-arom].
(MeOH). [α]2D0 ϭ Ϫ8 (c ϭ 1, H2O) {2: [α]2D0 ϭ ϩ9 (c ϭ 1, H2O)[11]
(see Table 1). CD spectra for 2 and ent-2: Figure 1. The 1H and 13
}
C
NMR spectra of ent-2 were identical to, and therefore superimpos-
able on, those of the known -arabino stereomer 2.[11] C7H10N2O3
(170.17): C 49.40, H 5.92, N 16.46; found C 49.7, H 6.0, N 16.3.
D
-xylo-Imidazolo-Pyrrolidinose 3: A stirred solution of 17 (98 mg,
0.28 mmol) in MeOH (2 mL) and AcOH (1 mL) was put under H2
pressure (30 bar) in the presence of 20% Pd(OH)2/C (75 mg) at
room temp. After 4 d, the suspension was centrifuged and the cata-
lyst was rinsed several times with hot MeOH under sonication. The
combined organic solutions were concentrated in vacuum, sequen-
tially percolated over Clarcel and Amberlite IRA-400 (OHϪ) beads
to remove acetic acid, and concentrated to dryness, and the re-
sulting crude oil was purified by chromatography (CHCl3/MeOH/
MeOH ϩ NH3, 8:1:1, then 7:2:1) to give 3 (32 mg, 67%) as a color-
less powder. [α]2D0 ϭ ϩ41 (c ϭ 0.60, EtOH) (see Table 1). CD spec-
tra of 3 and ent-3: Figure 1. The 1H NMR (CD3OD) and 13C NMR
(CD3OD) spectra proved to be identical to, and therefore superim-
posable on, those of the known -xylo enantiomer ent-3.[8,11] HR-
MS: [M ϩ H]ϩ ion 171.0775 (C7H11N2O3, calcd. 171.0770).
Imidazolo-L-arabino Derivative 15: A solution of imidazole (125
mg, 1.7 mmol) in anhydrous DMF (4 mL) was treated with tert-
butyldiphenylsilyl chloride (310 µL, 1.1 mmol) at room temp. for
15 min. To this solution was added a solution of 14 (310 mg, 0.85
mmol)[10] in DMF (8 mL). After 14 h at room temp., conversion
was complete as determined by TLC (Et2O/MeOH ϩ NH3, 98:2).
Water (10 mL) was added, and the aq. phase was extracted with
Et2O. The organic solution was washed with a saturated aqueous
solution of NH4Cl (15 mL) to remove imidazole and DMF, dried
(MgSO4), filtered, and concentrated to dryness, and the resulting
crude foam was purified by chromatography (Et2O/MeOH ϩ NH3,
1
98:2, then 95:5) to give 15 (360 mg, 70%) as a colorless resin. H
NMR (CDCl3): δ ϭ 1.06 [s, 9 H, ϪOSiPh2C(CH3)3], 3.76 [dd, 1 H,
C(4)-Hb], 3.80 [dd, 1 H, C(2)-H], 3.82 [dd, 1 H, C(4)-Ha], 3.95 [dt,
1 H, C(3)-H], 4.24 and 4.45 [AB, 2 H, J ϭ 11.9, OCH2Ph], 4.25
and 4.47 [AB, 2 H, J ϭ 11.2, OCH2Ph], 4.82 [d, 1 H, C(1)-H], 7.03
[s, 1 H, C(4Ј)-H], 7.05Ϫ7.12 [m, 2 H, H-arom], 7.18Ϫ7.50 [m, 14
H, H-arom], 7.58 [s, 1 H, C(2Ј)-H], 7.58Ϫ7.66 [m, 4 H, H-arom],
J1,2 ϭ 3.0, J2,3 ϭ 6.6, J3,4a ϭ J3,4b ϭ 4.8, J4a,4b ϭ 10.4.
Imidazolo-L-ribo Derivative 19: A solution of imidazole (120 mg,
1.76 mmol) in anhydrous DMF (4 mL) was treated with tert-butyl-
diphenylsilyl chloride (300 µL, 1.08 mmol) at room temp. for 15
min. To this solution was added a solution of the known compound
18 (300 mg, 0.88 mmol)[10] in DMF (8 mL). After 14 h at room
temp., conversion was complete as determined by TLC (Et2O/
MeOH ϩ NH3, 98:2). Water (20 mL) was added, and the reaction
mixture was extracted with Et2O. The organic solution was washed
with a saturated aqueous solution of NH4Cl (30 mL) to remove
D-xylo-Imidazolo-Pyrrolidinose Derivative 16: Tf2O (250 µL, 1.5
mmol, 2.5 equiv.) was added at Ϫ78 °C to a solution of 15 (360
mg, 0.59 mmol) and anhydrous pyridine (250 µL, 3 mmol, 5 equiv.) imidazole and DMF, dried (MgSO4), filtered, and concentrated to
in anhydrous CH2Cl2 (7 mL). After 15 min, the reaction mixture dryness, and the resulting crude foam was purified by chromato-
was allowed to warm to room temp. and became deep red. After 6 graphy (Et2O/MeOH ϩ NH3, 98:2, then 95:5) to give 19 (392 mg,
h, conversion seemed to be complete according to TLC (Et2O/
77%) as a colorless resin. 1H NMR (CDCl3): δ ϭ 1.06 [s, 9 H,
Eur. J. Org. Chem. 2002, 702Ϫ712
709

T. Tschamber, J. Streith et al.
FULL PAPER
OSiPh2C(CH3)3], 3.43 [m, 1 H, C(3)-H], 3.72 [dd, 1 H, C(4)-Hb],
3.80 [dd, 1 H, C(4)-Ha], 3.99 [dd, 1 H, C(2)-H], 4.38 and 4.50 [AB,
then 7:2:1) to give 4 (95 mg, 55%) as a slightly gray powder that
could not be crystallized. [α]2D0 ϭ ϩ12 (c ϭ 0.6, MeOH) (see
2 H, J ϭ 11.9, OCH2Ph], 4.53 and 4.85 [AB, 2 H, J ϭ 10.9, Table 1). CD spectrum: Figure 1. 1H NMR (CD3OD, 250 MHz):
OCH2Ph], 4.91 [d, 1 H, C(1)-H], 7.08 [s, 1 H, C(4Ј)-H], 7.10Ϫ7.50 δ ϭ 3.83 [dd, 1 H, C(8)-Hb], 3.95 [dd, 1 H, C(8)-Ha], 4.48 [br m, 1
[m, 16 H, H-arom], 7.54 [s, 1 H, C(2Ј)-H], 7.57Ϫ7.66 [m, 4 H, H-
H, C(5)-H], 4.72 [dd, 1 H, C(6)-H], 4.90 [d, 1 H, C(7)-H], 6.97 [br
arom], J1,2 ϭ 2.6, J2,3 ϭ 8.7, J3,4a ϭ 3.4, J3,4b ϭ 5.2, J4a,4b ϭ 10.4. s, 1 H, C(1)-H], 7.71 [br s, 1 H, C(3)-H], J5,6 ϭ 6.3, J5,8a ϭ 2.8,
J5,8b ϭ 6.4, J6,7 ϭ 5.1, J8a,8b ϭ 11.6. 13C NMR (CD3OD, 100.6
MHz): δ ϭ 61.5 [C(8)], 62.3 [C(5)], 65.9 [C(7)], 76.9 [C(6)], 122.2
[C(1)], 133.0 [C(3)], 137.6 [C(7a)]. HR-MS: [M ϩ H]ϩ ion 171.0771
(C7H11N2O3, calcd. 171.0770).
D
-lyxo-Imidazolo-Pyrrolidinose Derivative 20: Tf2O (300 µL, 1.48
mmol, 2.5 equiv.) was added at Ϫ78 °C to a solution of 19 (380
mg, 0.64 mmol) and anhydrous pyridine (300 µL, 3.2 mmol) in
anhydrous CH2Cl2 (8 mL). After 15 min, the reaction mixture was
allowed to warm to room temp. and became deep red. After 6 h,
conversion seemed to be complete according to TLC (Et2O/MeOH
ϩ NH3, 98:2). Water (15 mL) was added, the mixture was extracted
with CH2Cl2, and the organic phase was washed with a saturated
NH4Cl solution to remove pyridine. It was then dried (MgSO4),
filtered, and concentrated to dryness, and the resulting slightly yel-
low oil was purified by chromatography (Et2O/MeOH ϩ NH3,
99:1, then 98:2) to give 20 (220 mg, 58%) as a colorless foam.
Coupling Reaction between the C(4)-Lithio Derivative of Imidazole
23 and D-erythro-Aldehyde 22: A solution of nBuLi in hexane (1.6
, 11.8 mL, 18.9 mmol, 1.1 equiv.) was added under argon at Ϫ78
°C to a stirred solution of imidazole 23 (6.05 g, 20.9 mmol) in
anhydrous THF (50 mL), whereupon the solution became red.
After 15 min, a solution of the known compound 22 (4.25 g, 17.0
mmol)[17,18,21] in anhydrous THF (40 mL) was added dropwise, and
the reaction mixture was monitored by TLC (EtOAc/cyclohexane,
3:7). After 90 min, the solution was allowed to warm to room
temp., H2O (30 mL) was added, the reaction mixture was extracted
with CH2Cl2, and the organic phase was dried (MgSO4), filtered,
and concentrated to dryness to afford an orange-colored syrup that
consisted of the two diastereomers 24 (minor product) and 25 (ma-
jor product) in a 1:3 ratio. These two compounds were separated
by careful chromatography (EtOAc/cyclohexane, 2:8, then 3:7) to
provide the -arabino (24; 2.02 g) and the -ribo diastereomer (25;
6.03 g) (total yield of 24 ϩ 25: 88%).
1
[α]2D0 ϭ Ϫ56 (c ϭ 1.0, CH2Cl2). H NMR (CDCl3): δ ϭ 1.02 [s, 9
H, OSiPh2C(CH3)3], 3.92Ϫ4.02 [m, 2 H, C(8)-Ha and C(8)-Hb],
4.47 [dd, 1 H, C(6)-H], 4.44 and 4.49 [AB, 2 H, J ϭ 9.6, OCH2Ph],
4.37 and 4.59 [AB, 2 H, J ϭ 11.7, OCH2Ph], 4.68 [ddd, 1 H, C(5)-
H], 4.73 [d, 1 H, C(7)-H], 7.06 [br s, 1 H, C(1)-H], 7.09Ϫ7.40 [m,
16 H, H-arom], 7.55Ϫ7.62 [m, 2 H, H-arom], 7.75 [br s, 1 H, C(3)-
H], J5,6 ϭ 7.1, J5,8a ϭ 5.4, J5,8b ϭ 8.6, J6,7 ϭ 5.0. 13C NMR
(CD3OD): δ ϭ 61.3 [C(5)], 65.3 [C(8)], 70.5 [C(7)], 71.3 [OCH2Ph],
73.1 [OCH2Ph], 83.2 [C(6)], 124.0 [C(1)], 128.7Ϫ129.5 [16 C, C-
arom], 130.9 and 131.1 [2 C, C-arom], 133.8 [br s, C(7a)], 134.1 [2
C, C’s-arom], 134.3 [br s, C(3)], 136.5 and 136.7 [2 C, C-arom],
138.7 and 139.0 [2 C, C’s-arom]. HR-MS: [M ϩ H]ϩ ion 589.2885
(C37H41N2SiO3, calcd. 589.2886).
D
-arabino Stereomer 24: Its 1H and 13C NMR spectra (CDCl3)
proved to be identical to and therefore superimposable on those of
ent-24, the synthesis and spectral properties of which had already
been described in a previous publication.[10]
D-lyxo-Imidazolo-Pyrrolidinose Derivative 21: A solution of TBAF
D
-ribo Stereomer 25: Its 1H and 13C NMR spectra proved to be
in THF (1 , 2.8 mL, 2.8 mmol, 2.5 equiv.) was added at room
temp. under argon to a stirred solution of 20 (630 mg, 1.07 mmol)
in anhydrous THF (9 mL). After 4 h, conversion was complete
according to TLC (CH2Cl2/MeOH ϩ NH3, 9:1). Some H2O (5 mL)
was added and the reaction mixture was extracted with CH2Cl2.
The organic phase was washed with a saturated aq. solution of
Na2SO4 to remove the tetrabutylammonium salts, dried (MgSO4),
and concentrated to dryness, and the resulting viscous yellow oil
was purified by chromatography (CH2Cl2/MeOH ϩ NH3, 95:5) to
yield 21 (355 mg, 95%) as a colorless foam. 1H NMR (CDCl3): δ ϭ
3.95 [dd, 1 H, C(8)-Hb], 4.01 [dd, 1 H, C(8)-Ha], 4.37 [dd, 1 H,
C(6)-H], 4.46 [td, 1 H, C(5)-H], 4.42 and 4.65 [AB, 2 H, J ϭ 12.5,
OCH2Ph], 4.65 [d, 1 H, C(7)-H], 4.53 and 4.72 [AB, 2 H, J ϭ 12.0,
OCH2Ph], 6.88 [br s, 1 H, C(1)-H], 7.23Ϫ7.38 [m, 10 H, H-arom],
identical to and therefore superimposable on those of ent-25, the
synthesis and spectral properties of which had also been described
in the same publication.[10]
Imidazolo-D-ribo Derivative ent-18: A suspension of NaH in oil
(60%, 1.34 g, ca. 33 mmol, 3 equiv.), and a catalytic amount of
Bu4NI (50 mg) were added under argon at room temp. to a stirred
solution of 25 (6.00 g, 11.1 mmol) in anhydrous THF (150 mL).
The mixture was heated at 35 °C for 30 min, whereupon it turned
red. BnBr (1.6 mL, 13.5 mmol, 1.2 equiv.) was added to this stirred
solution, and the solution was heated at 40 °C for 15 h. The fully
protected intermediate formed according to TLC (EtOAc/cyclohex-
ane, 3:7), was neither isolated nor characterized. After the reaction
mixture had cooled to room temp., H2O (15 mL) and 6  HCl (30
mL) were added and the solution was heated at 45 °C for 14 h.
Having been allowed to cool to room temp., the reaction mixture
was extracted with CH2Cl2 in order to remove polar impurities.
The aq. phase was neutralized with ammonia and extracted with
CH2Cl2, the organic phase was dried (MgSO4), filtered, and con-
centrated to dryness, and the crude residue was purified by chroma-
tography (CH2Cl2/MeOH ϩ NH3, 98:2, then 95:5, and eventually
7.55 [br s, 1 H, C(3)-H], J5,6 ϭ 7.3, J5,8a ϭ 4.2, J5,8b ϭ 7.2, J6,7
ϭ
5.0, J8a,8b ϭ 11.9. 13C NMR (CDCl3): δ ϭ 59.6 [C(5)], 61.2 [C(8)],
68.0 [C(7)], 69.7 [OCH2Ph], 71.6 [OCH2Ph], 81.0 [C(6)], 123.2
[C(1)], 127.6Ϫ128.3 [10 C, C-phenyl], 131.2 [C(7a)], 132.5 [C(3)],
136.8 [1 C, C’s-phenyl], 136.9 [1 C, C’s-phenyl].
D-lyxo-Imidazolo-Pyrrolidinose 4: A stirred solution of 21 (355 mg,
1.01 mmol) in MeOH (4 mL) and AcOH (2 mL) was put under H2
pressure (30 bar) in the presence of 20% Pd(OH)2/C (ϩ 30% H2O)
at room temp., the reaction being monitored by TLC (CH2Cl2/
MeOH ϩ NH3, 2:1). After 7 d, conversion seemed to be complete.
The suspension was centrifuged and the catalyst was rinsed several
times with hot MeOH under sonication. The combined organic
solutions were concentrated in vacuum, sequentially percolated
over Clarcel and Amberlite IRA-400 (OHϪ) beads to remove acetic
acid, and then concentrated to dryness. The resulting crude oil was
90:10) to provide ent-18 (1.74 g, 47%) as a colorless resin. [α]2D0
ϭ
ϩ48 (c ϭ 0.6, MeOH). The H (CDCl3) and 13C NMR (CD3OD)
spectra proved to be identical to, and therefore superimposable on,
those of 18.[10] HR-MS: [M ϩ Na]ϩ ion 391.1636 (C21H24N2O4Na,
calcd. 391.1634).
1
Imidazolo-D-ribo Derivative ent-19: This compound was produced
by the same procedure as for 19, starting from imidazole (600 mg,
8.84 mmol) in anhydrous DMF (30 mL), tert-butyldiphenylsilyl
purified by chromatography (CHCl3/MeOH/MeOH ϩ NH3, 8:1:1, chloride (1.70 g, 6.2 mmol, 1.4 equiv.), and ent-18 (1.63 g, 4.42
710 Eur. J. Org. Chem. 2002, 702Ϫ712

Stereomeric Pyrrolidinopentoses Bearing an Imidazole Ring
FULL PAPER
mmol). Workup followed by chromatography gave ent-19 (1.53 g,
to afford 28 (173 mg, 71%) as a colorless foam. 1H NMR
57%) as a colorless foam. The 1H and 13C NMR spectra proved (CD3OD): δ ϭ 1.02 [s, 9 H, OSiPh2C(CH3)3], 3.95 [dd, 1 H, C(8)-
to be identical to, and therefore superimposable on, those of 19
(see above).
Hb], 4.21 [dd, 1 H, C(8)-Ha], 4.40 [ddd, 1 H, C(5)-H], 4.47 [dd, 1
H, C(6)-H], 4.52 and 4.64 [AB, 2 H, J ϭ 12.1, OCH2Ph], 4.45 and
4.69 [AB, 2 H, J ϭ 11.8, OCH2Ph], 4.95 [d, 1 H, C(7)-H], 7.06 [s,
1 H, C(1)-H], 7.26Ϫ7.57 [m, 20 H, H-arom], 7.62 [s, 1 H, C(3)-H],
J5,6 ϭ 7.3, J5,8a ϭ 2.4, J5,8b ϭ 4.3, J6,7 ϭ 4.8, J8a,8b ϭ 11.6.
L
-lyxo-Imidazolo-Pyrrolidinose Derivative ent-20: This compound
was produced by the same procedure as above for the preparation
of 20, starting from ent-19 (1.53 g, 2.51 mmol), pyridine (1.1 mL,
6.7 mmol, 5 equiv.), CH2Cl2 (32 mL), and Tf2O (1.1 mL, 6.7 mmol,
2.5 equiv.). Workup followed by chromatography gave ent-20 (683
mg, 46%) as a colorless foam. [α]2D0 ϭ ϩ63 (c ϭ 1.1, CH2Cl2). The
1H and 13C NMR were identical to, and therefore superimposable
on, those of 20 (see above).
D-ribo-Imidazolo-Pyrrolidinose Derivative 29: This compound was
produced by the same procedure as for ent-21 in Scheme 4, starting
from 28 (270 mg, 0.46 mmol) in THF (15 mL) under argon and a
solution of TBAF in THF (1 , 1.6 mL, 1.6 mmol). Standard
workup followed by chromatography (Et2O/MeOH ϩ NH3, 95:5,
then 90:10) provided 29 (158 mg, 95%) as a foam, which crystal-
lized. M.p. 148 °C (EtOAc). [α]2D0 ϭ ϩ151 (c ϭ 1.0, MeOH). 1H
NMR (CD3OD): δ ϭ 3.74 [dd, 1 H, C(8)-Hb], 4.18 [dd, 1 H, C(8)-
Ha], 4.30Ϫ4.42 [m, 2 H, C(5)-H and C(6)-H], 4.51 and 4.64 [AB, 2
H, J ϭ 11.2, OCH2Ph], 4.60 and 4.75 [AB, 2 H, J ϭ 11.6,
OCH2Ph], 4.91 [d, 1 H, C(7)-H], 7.02 [br s, 1 H, C(1)-H], 7.25Ϫ7.42
L
-lyxo-Imidazolo-Pyrrolidinose Derivative ent-21: This compound
was produced by the same procedure as above for the preparation
of 21, starting from ent-20 (680 mg, 1.15 mmol), THF (10 mL)
under argon, and TBAF in THF (1 , 2.9 mL). Workup followed
by chromatography gave ent-21 (365 mg, 91%) as a colorless oil.
1
The H and 13C NMR spectra were identical to, and therefore su-
[m, 10 H, H-arom], 7.77 [br. s, 1 H, C(3)-H], J5,8a ϭ 2.4, J5,8b
ϭ
6.0, J6,7 ϭ 4.5, J8a,8b ϭ 11.8. 13C NMR (CD3OD): δ ϭ 61.8 [C(5)],
63.2 [C(8)], 70.4 [OCH2Ph], 71.4 [OCH2Ph], 73.3 [C(7)], 83.8 [C(6)],
123.9 [C(1)], 129.0, 129.3, 129.5 [10 C, C-arom], 132.9 [C(3)], 134.7
[C(7a)], 138.9 [C’s-phenyl], 139.0 [C’s-phenyl]. HR-MS: [M]ϩ ion
350.1645 (C21H22N2O3, calcd. 350.1630). C21H22N2O3 (350.40): C
71.98, H 6.33, N 8.00; found C 71.9, H 6.1, N 8.2.
perimposable on, those of 21 (see above).
L
-lyxo-Imidazolo-Pyrrolidinose ent-4: This compound was pro-
duced by the same procedure as above for the preparation of 4,
starting from ent-21 (150 mg, 0.43 mmol) in MeOH (4 mL) and
AcOH (2 mL) under H2 pressure (30 bar) in the presence of 20%
Pd(OH)2/C. After 4 d, workup and chromatography afforded ent-
4 (46 mg, 63%) as a colorless powder. [α]2D0 ϭ Ϫ12 (c ϭ 0.75,
MeOH) (see Table 1). CD spectra of 4 and ent-4: see Figure 1. The
1H NMR and 13C NMR spectra were identical to those of 4 (see
above). HR-MS: [M ϩ H]ϩ ion 171.0770 (C7H11N2O3, calcd.
171.0770).
D-ribo-Imidazolo-Pyrrolidinose 5: This compound was produced by
a procedure similar to that used for 4 and ent-4 (see above), starting
from 29 (212 mg, 0.61 mmol) in AcOH (20 mL) under H2 pressure
(1 bar, though) in the presence of 20% Pd(OH)2/C (ϩ 30% H2O).
After 28 h, the reaction seemed to be complete, as monitored by
TLC (Et2O/MeOH ϩ NH3, 6:4). Workup followed by chromato-
graphy (Et2O/MeOH ϩ NH3, 70:30) provided 5 (84 mg, 82%) as
colorless crystals. M.p.dec 198Ϫ199 °C (MeOH). [α]2D0 ϭ ϩ70 (c ϭ
1.0, MeOH) (see also Table 1). CD spectrum: see Figure 1. The
1H (D2O) and 13C NMR (CD3OD) spectra were identical to, and
therefore superimposable on, those of ent-5, the synthesis and spec-
tral properties of which had already been described in a previous
publication.[11] C7H10N2O3 (170.17): C 49.40, H 5.92, N 16.46;
found C 49.6, H 6.0, N 16.5.
Imidazolo-L-lyxo Derivative 27: A solution of imidazole (135 mg,
1.98 mmol) in anhydrous CH2Cl2 (15 mL) was treated with
TBDPSCl (430 µL, 1.65 mmol) in the presence of Et3N (250 µL,
1.8 mmol) and catalytic amounts of DMAP (6 mg) for 15 min at
room temp. To this solution was added a solution of the known
compound 26 (501 mg, 1.36 mmol)[10] in CH2Cl2 (5 mL). After 3
h at room temp., conversion was complete, as monitored by TLC
(Et2O/MeOH ϩ NH3, 95:5). Water (10 mL) was added and the aq.
phase was extracted with CH2Cl2, and the organic phase was
washed with a saturated aq. solution of NH4Cl (20 mL) to remove
imidazole, dried (MgSO4), filtered, and concentrated to dryness,
and the resulting crude foam was purified by chromatography
(Et2O/MeOH ϩ NH3, 98:2, then 95:5) to afford 27 (715 mg, 87%)
as a colorless, viscous foam. 1H NMR (CD3OD): δ ϭ 1.04 [s, 9
H, OSiPh2C(CH3)3], 3.60Ϫ3.75 [m, 2 H, C(4)-Ha and C(4)-Hb],
4.05Ϫ4.20 [m, 2 H, C(2)-H and C(3)-H], 4.07 and 4.32 [AB, 2 H,
J ϭ 11.0, OCH2Ph], 4.36 and 4.47 [AB, 2 H, J ϭ 11.5, OCH2Ph],
4.73 [d, 1 H, C(1)-H], 6.95Ϫ7.00 [m, 2 H, H-arom], 7.09 [s, 1 H,
C(4Ј)-H], 7.15Ϫ7.41 [m, 14 H, H-arom], 7.62Ϫ7.66 [m, 4 H, H-
arom], 7.72 [s, 1 H, C(2Ј)-H], J1,2 ϭ 8.2.
L
-ribo-Imidazolo-Pyrrolidinose ent-5: This compound has already
been described.[11] Rotatory power: Table 1. CD spectrum: Fig-
ure 1.
Acknowledgments
We thank the EU PECO Copernicus program (ERBCI-
PACT930232), and the Franco-Polish Polonium program (no.
98249) for having furthered the bilateral scientific exchange ende-
avors by the Lodz and the Mulhouse research groups. We also wish
to thank the Fondation pour l’Ecole de Chimie de Mulhouse for
`
an 18-month visiting scientist research grant to A. F., the Ministere
D-ribo-Imidazolo-Pyrrolidinose Derivative 28: Tf2O (205 µL, 1.24
mmol, 3 equiv.) was added at Ϫ25 °C to a solution of 27 (250 mg, de l’Enseignement et de la Recherche for a Ph.D. grant to H. S.,
0.41 mmol) and anhydrous pyridine (200 µL, 2.5 mmol, 6 equiv.)
in anhydrous CH2Cl2 (10 mL). After 30 min, the solution was al-
as well as the Polish Academy of Sciences for its financial support
for part of this work (grant C.P.B.P. 01.13.1.4). We express our
lowed to warm to room temp., the reaction being monitored by sincere thanks to Dr. Bryan Winchester, Institute of Child Health,
TLC (Et2O/MeOH ϩ NH3, 98:2). After 1 h, the mixture was University of London, and Dr. Sylviane Picasso, Institute of Or-
treated with saturated aq. NaHCO3 (5 mL) and the resulting me- ganic Chemistry, University of Lausanne, for some preliminary gly-
dium was extracted with CH2Cl2. The organic phase was dried
(MgSO4), filtered, and concentrated to dryness, and the crude res-
cosidase inhibition assays. And last but not least, the continuous
support of the Centre National de la Recherche Scientifique
idue was purified by chromatography (Et2O/MeOH ϩ NH3, 98:2), (UMR-7015) is gratefully acknowledged.
Eur. J. Org. Chem. 2002, 702Ϫ712
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Received July 23, 2001
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[O01359]
712
Eur. J. Org. Chem. 2002, 702Ϫ712