Pseudoamide-Type Pyrrolidine and Pyrrolizidine Glycomimetics and Their Inhibitory Activities against Glycosidases

Article abstract of DOI:10.1021/jo0499221

Coupling reaction of (2R,3R,4R,5R)-2,5-hydroxy-methyl-3,4-dihydroxypyrrolidine (DMDP) with isothiocyanates afforded the corresponding thiourea adducts, which were transformed into isourea-type bicyclic oxapyrrolizidine glycomimetics by mercury(II) oxide-assisted intramolecular sulfur displacement. Cyclic carbamate and thiocarbamate analogues were also prepared by direct carbonylation or thiocarbonylation of DMDP. Evaluation of the glycosidase inhibitory properties demonstrated that remarkable specificities in enzyme inhibition can be achieved upon modifications on the pseudoaglyconic side chain and on the nature of the sp²-hybridized endocyclic ring nitrogen.

Full text of DOI:10.1021/jo0499221

iminocyclitols of the homoazasugar4 (aza-C-glycoside)
family, of which (2R,3R,4R,5R)-2,5-hydroxymethyl-3,4-
dihydroxypyrrolidine (DMDP, 1) is one of the most
prominent representatives,5 have gained special impor-
tance. Homoazasugars usually retain the same type of
biological activity of the parent azasugar while exhibiting
a higher stability as compared with the corresponding
aminoacetal counterparts (aza-O-glycosides). Moreover,
the pyrrolidine ring of these compounds adopts confor-
mations that resemble well the twisted half-chair con-
formation of the incipient oxocarbenium cation postulated
as the transition state of enzymatic glycoside hydrolysis.
However, the strong inhibitory activity of pyrrolidine
glycomimetics is frequently accompanied by low enzyme
specificity. Thus, compound 1 inhibits simultaneously
several R and â-glycosidases, which represents a serious
limitation for the above-mentioned applications. A higher
enzyme specificity has been reported for the related
pyrrolizidine azasugar australine (2),6 probably due to
the spatial requirements imposed by the rigid bicyclic
structure. Nevertheless, the bridgehead location of the
nitrogen atom in pyrrolizidines prevents incorporation
of pseudoaglyconic N-substituents, a strategy that has
been exploited in monocyclic azasugars to identify more
potent and specific glycosidase inhibitors suitable for
clinical trials.1,7
P seu d oa m id e-Typ e P yr r olid in e a n d
P yr r olizid in e Glycom im etics a n d Th eir
In h ibitor y Activities a ga in st Glycosid a ses
M. Isabel Garc´ıa-Moreno,† David Rodr´ıguez-Lucena,†
Carmen Ortiz Mellet,*,† and
J ose´ M. Garc´ıa Ferna´ndez*,‡
Departamento de Qu´ımica Orga´nica, Facultad de Qu´ımica,
Universidad de Sevilla, E-41071 Sevilla, Spain, and
Instituto de Investigaciones Qu´ımicas, CSIC, Ame´rico
Vespucio 49, Isla de la Cartuja, E-41092 Sevilla, Spain
jogarcia@iiq.csic.es; mellet@us.es
Received J anuary 13, 2004
Abstr a ct: Coupling reaction of (2R,3R,4R,5R)-2,5-hydroxy-
methyl-3,4-dihydroxypyrrolidine (DMDP) with isothiocya-
nates afforded the corresponding thiourea adducts, which
were transformed into isourea-type bicyclic oxapyrrolizidine
glycomimetics by mercury(II) oxide-assisted intramolecular
sulfur displacement. Cyclic carbamate and thiocarbamate
analogues were also prepared by direct carbonylation or
thiocarbonylation of DMDP. Evaluation of the glycosidase
inhibitory properties demonstrated that remarkable speci-
ficities in enzyme inhibition can be achieved upon modifica-
tions on the pseudoaglyconic side chain and on the nature
of the sp2-hybridized endocyclic ring nitrogen.
Recently, we found that a subtle change in the struc-
ture of azasugars, by replacing the sp3 ring nitrogen atom
with a pseudoamide-type nitrogen (urea, thiourea, car-
bamate, thiocarbamate, isourea) with substantial sp2
character, led to a new group of glycosidase inhibitors
(“sp2-azasugars”)8 with high anomer selectivity.9 Interest-
ingly, this electronic feature is also present in the natural
Glycosyl hydrolases represent an important class of
biocatalysts involved in the metabolism of carbohydrates
and in the assembly of specific oligosaccharide structures
which, in turn, play an essential role in biological
communication, including fertilization, infection, the
inflammatory response, cell adhesion, and cancer me-
tastasis. Consequently, specific inhibitors of such en-
zymes show high promise as probes for structure/function
studies of enzymatic catalysis and as chemotherapeutic
drugs for the treatment of viral infections, cancer, and
metabolic disorders such as diabetes.1
In the past decade, the natural and synthetic polyhy-
droxyalkaloids termed generically iminosugars (“azasug-
ars”),2 nitrogen in the ring carbohydrate mimics, have
emerged as the most important class of reversible gly-
cosidase inhibitors.3 Among them, the five-membered
(3) For recent reviews on iminosugar glycosidase inhibitors, see: (a)
Asano, N. Curr. Top. Med. Chem. 2003, 3, 471. (b) Lillelund, V. H.;
J ensen, H. H.; Liang, X.; Bols, M. Chem. Rev. 2002, 102, 515. (c)
Watson, A. A.; Fleet, G. W. J .; Asano, N.; Molyneux, R. J .; Nash, R. J .
Phytochemistry 2001, 56, 265. (d) Asano, N.; Nash, R. J .; Molyneux,
R. J .; Fleet, G. W. J . Tetrahedron: Asymmetry 2000, 11, 1645. (e)
Elbein, A. D.; Molyneux, R. J . Alkaloid Glycosidase Inhibitors. In
Comprehensive Natural Products Chemistry; Barton, D., Nakanishi,
K., Meth-Cohn, O., Eds.; Elsevier: Oxford, 1999; Vol. 3, p 129. (f)
Simmonds, M. S. J .; Kite, G. C.; Porter, E. A. Taxonomic Distribution
of Iminosugars in Plants and Their Biological Activities. In Iminosug-
ars as Glycosidase Inhibitors; Stu¨tz, A., Ed.; Wiley-VCH: Weinheim,
Germany, 1999; p 8. (g) Ossor, A.; Elbein, A. D. Glycoprotein Processing
Inhibitors. In Carbohydrates in Chemistry and Biology; Ernst, B., Hart,
G. W., Sinay¨, P., Eds.; Wiley-VCH: Weinheim, Germany, 2000; Part
II, Vol. 3, p 513.
* To whom correspondence should be addressed. (C.O.M.) Phone:
+34 954557150. Fax: +34 954624960. (J .M.G.F.) Phone: +34
954489559. Fax: 954460564.
(4) (a) Martin, O. R. Toward Azaglycosyl Compounds and Homoaza-
glycosides. In Carbohydrate Mimics. Concepts and Methods; Chapleur,
Y., Ed.; Wiley-VCH: Weinheim, Germany, 1998; p 259. (b) Wong, C.-
H-; Provencher, L.; Porco, J . A., J r.; J ung, S.-H.; Wang, Y.-F.; Chen,
L.; Wang, R.; Steensma, D. H. J . Org. Chem. 1995, 60, 1492.
(5) Evans, S. V.; Fellows, L. E.; Shing, T. K. M.; Fleet, G. W. J .
Phytochemistry 1985, 24, 1953.
(6) (a) Molyneux, R. J .; Benson, M.; Wong, R. Y.; Tropea, J . E.;
Elbein, A. D. J . Nat. Prod. 1988, 51, 1198-1206. (b) Kato, A.; Kano,
E.; Adachi, I.; Molyneux, R. J .; Watson, A. A.; Nash, R. J .; Fleet, G.
W. J .; Wormald, M. R.; Kizu, H.; Ikeda, K.; Asano, N. Tetrahedron:
Asymmetry 2003, 14, 325.
(7) van den Broek, L. A. G. M. Azasugars: Chemistry and Their
Biological Activity as Potential Anti-HIV Drugs. In Carbohydrates in
Drug Design; Witczak, Z. J ., Nieforth, K. A., Eds.; Marcel Dekker: New
York, 1997; p 471.
(8) By analogy with the trivial name “azasugar”, we are using here
the term “sp2-azasugar” to refer to glycomimetics where the endocyclic
oxygen atom has been replaced by a nitrogen atom with substantial
sp2 character, typically a pseudoamide-type nitrogen.
† Universidad de Sevilla.
‡ Instituto de Investigaciones Qu´ımicas.
(1) For recent leading reviews, see: (a) N. Asano, N. Glycobiology
2003, 13, 93R. (b) Greimel, P.; Spreitz, J .; Stu¨tz, A. E.; Wrodnigg, T.
M. Curr. Top. Med. Chem. 2003, 3, 513. (c) Butters, T. M.; Dwek, R.
A.; Platt, F. M. Curr. Top. Med. Chem. 2003, 3, 561. (d) Vasella, A.;
Davies, G. J .; Bo¨hm, M. Curr. Opin. Chem. Biol. 2002, 6, 619. (e)
Heightman, T. D.; Vasella, A. Angew. Chem., Int. Ed. 1999, 38, 750.
(f) Sears, P.; Wong, C.-H. Chem. Commun. 1998, 1161. (g) Dwek, R.
A. Chem. Rev. 1996, 96, 683.
(2) Although the term “azasugar” is widely used in the literature to
refer to glycomimetics where the endocyclic oxygen atom has been
replaced by nitrogen, the term is not strictly correct according to the
IUPAC-IUMB nomenclature recommendations for carbohydrates, the
accepted term being “iminosugar”. “Azahexose” would actually imply
that a carbon atom has been exchanged for a nitrogen atom. See:
McNaught, A. D. Pure Appl. Chem. 1996, 68, 1919.
10.1021/jo0499221 CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/21/2004
3578
J . Org. Chem. 2004, 69, 3578-3581

trehalase inhibitor trehazolin (3),10 where the occurrence
of the cyclic isourea function and the aglyconic glucopy-
ranosyl substituent results in remarkable enzyme speci-
ficity. We hypothesized that by incorporating this func-
tional group onto a preformed pyrrolidine template, new
bicyclic pseudoamide-type inhibitors endowed with the
advantages of trehalozoids and pyrrolizidines could be
generated.
SCHEME 1a
a
Reagents and conditions: (i) BzCl, pyridine, 0 °C to rt, 4 h;
(ii) 50% aq AcOH, 50 °C, 3 h; (iii) 1.1 equiv of BzCl, pyridine,
CH2Cl2, -65 °C, 1.5 h; (iv) PPh3, I2, imidazole, toluene, 70 °C, 16
h; (v) NaN3, HMPT, 80 °C; (vi) (a) NaOMe, MeOH, (b) 9:1 TFA-
water; (vii) 10% Pd/C, 4 bar, 24 h.
Since a rational design and synthesis to afford desired
inhibition is often extremely difficult, due to the limited
information regarding the structure of the active site, we
have centered on synthetic methodologies that would be,
eventually, amenable to combinatorial library strate-
gies.11 In a first approach, we decided to focus on creating
a small, but diverse, group of compounds to test as
potential glycosidase inhibitors, thus minimizing the risk
that none of a series of compounds is inhibitory. DMDP
has been selected as a suitable core to prove the potential
of this concept to generate enzyme specificity, due to their
broad and strong glycosidase inhibitory activity. More-
over, the C2-symmetric structure of 1 makes it attractive
in ring-closing schemes involving one of the hydroxy-
methyl substituents characteristic of the homoazasugar
skeleton. Its synthesis was accomplished on a multigram
scale from D-fructose 1,2:4,5-di-O-acetonide (4) by a
modification of the method reported by Tatiboue¨t et al.12
involving benzoylation of the OH-3 to give 5, selective
removal of the 4,5-O-isopropylidene group, and regiose-
lective benzoylation of the equatorial OH-4 to give 7.
Replacement of OH-5 was accomplished using a double-
inversion strategy involving azide addition to 5-deoxy-
5-iodo-L-sorbopyranose derivative 8.13 Deprotection of the
hydroxy groups and final catalytic hydrogenation af-
forded 1 (Scheme 1).14
cycles, generated from hydroxycarbodiimide precursors,
to suitably located aldehyde groups.15 This approach is,
however, unsuitable for accessing the corresponding aza-
C-glycoside homologues. Instead, a two-step transforma-
tion was devised for assembling the bicyclo[3.3.0]octane
framework from 1 involving (i) nucleophilic addition of
the pyrrolidine nitrogen to an isothiocyanate electrophile
and (ii) mercury(II) oxide-assisted sulfur displacement
by one of the primary hydroxyl groups in the thiourea
adduct. Both reactions proceed with total chemoselectiv-
ity, avoiding the use of protecting groups in the DMDP
core. The first step provides, directly, sp2-azasugars in
the pyrrolidine series, while the second step affords
trehazoloid-pyrrolizidine hybrid structures. Thus, reac-
tion of 1 with phenyl isothiocyanate and 2,3,4,6-tetra-O-
acetyl-â-D-glucopyranosyl isothiocyanate16 gave the cor-
responding thiocarbamoyl pyrrolidines 11 and 12, re-
spectively, the pseudodisaccharide derivative 12 being
further deacetylated to the fully unprotected compound
13. The subsequent ring-closing reaction led to the
corresponding phenylimino and glucopyranosylimino fused
oxazolidine-pyrrolidine derivatives 14 and 15 (Scheme
2).
Previous syntheses of bicyclic isourea glycomimetics
having a bridgehead nitrogen, in the aza-O-glycoside
series, relied on the intramolecular nucleophilic addition
of the endocyclic N-atom of 2-amino-2-oxazoline hetero-
The DMDP-derived thioureas 11-13 exhibited a de-
generate chemical exchange process in their NMR spectra
due to slow rotation about the endocyclic nitrogen-
thiocarbonyl bond in the NMR time scale.17 This process
becomes slow enough to break the symmetry of the
pyrrolidine ring and to allow structure confirmation at
temperatures below ambient (5-10 °C). Such an effect
is absent in the case of the bicyclic compounds.
(9) (a) Garc´ıa-Moreno, M. I.; Benito, J . M.; Ortiz Mellet, C.; Garc´ıa
Ferna´ndez, J . M. J . Org. Chem. 2001, 66, 7604. (b) D´ıaz Pe´rez, V. M.;
Garc´ıa-Moreno, M. I.; Ortiz Mellet, C.; Fuentes, J .; Garc´ıa Ferna´ndez,
J . M.; D´ıaz Arribas, J . C.; Can˜ada, F. J . J . Org. Chem. 2000, 65, 136.
(c) J ime´nez Blanco, J . L.; D´ıaz Pe´rez, V. M.; Ortiz Mellet, C.; Fuentes,
J .; Garc´ıa Ferna´ndez, J . M.; D´ıaz Arribas, J . C.; Can˜ada, F. J . Chem.
Commun. 1997, 1969.
(10) For reviews on trehazolin and close analogues (“trehazoloids”),
see: (a) Berecibar, A.; Grandjean C.; Siriwardena, A. Chem. Rev. 1999,
99, 779. (b) Kobayashi, Y. Carbohydr. Res. 1999, 315, 3.
(11) For recent reports on combinatorial synthetic strategies applied
to the identification of selctive glycosidase inhibitors in the pyrrolidine
azasugar series, see: (a) Gerber-Lemaire, S.; Popowycz, F.; Rodrı´guez-
Garc´ıa, E.; Carmona Asenjo, A. T.; Robina, I.; Vogel, P. ChemBioChem
2002, 3, 466. (b) Saotome, C.; Wong, C.-H.; Kanie, O. Chem. Biol. 2001,
8, 1061-1070. (c) Takebayashi, M.; Hiranuma, S.; Kanie, Y.; Kajimoto,
T.; Kanie, O.; Wong, C.-H. J . Org. Chem. 1999, 64, 5280.
(14) For alternative recent syntheses of DMDP, see: (a) Donohoe,
T. J .; Headley, C. E.; Cousins, R. P. C.; Cowley, A. Org. Lett. 2003, 5,
999. (b) Dondoni, A.; Giovannini, P. P.; Perrone, D. J . Org. Chem. 2002,
67, 7003. (c) Izquierdo, I.; Plaza, M. T.; Franco, F. Tetrahedron:
Asymmetry 2002, 13, 1503. (d) Le merrer, Y.; Poitout, L.; Depezay,
J .-C.; Dosbaa, I.; Geoffroy, S.; Foglietti, M.-J . Bioorg. Med. Chem. 1997,
5, 519.
(15) (a) Garc´ıa-Moreno, M. I.; D´ıaz Pe´rez, P.; Ortiz Mellet, C.; Garc´ıa
Ferna´ndez, J . M. J . Org. Chem. 2003, 68, 8890. (b) Garc´ıa-Moreno,
M. I.; D´ıaz Pe´rez, P.; Ortiz Mellet, C.; Garc´ıa Ferna´ndez, J . M. Chem.
Commun. 2002, 848.
(12) Tatiboue¨t, A.; Lefoix, M.; Nadolny, J .; Martin, O. R.; Rollin, P.;
Yang, J .; Holman, G. D. Carbohydr. Res. 2001, 333, 327.
(13) 5-Azido-5-deoxy-D-fructopyranose derivatives have also been
obtained from L-sorbose, an alternative starting material for DMDP
synthesis; see: (a) Murphy, D. J . Chem. Soc. C 1967, 1732. (b)
Kuzuhara, H.; Emoto, S. Tetrahedron Lett. 1973, 14, 5051.
(16) Camarasa, M. J .; Ferna´ndez-Resa, P.; Garc´ıa-Lo´pez, M. T.; de
las Heras, F. G.; Me´ndez-Castrillo´n, P. P.; San Fe´lix, A. Synthesis 1984,
509.
(17) For a discussion of the structural properties and reactivity of
sugar thioureas, see: Ortiz Mellet, C.; Garc´ıa Ferna´ndez, J . M. Adv.
Carbohydr. Chem. Biochem. 1999, 55, 35.
J . Org. Chem, Vol. 69, No. 10, 2004 3579

TABLE 1. Glycosid a se In h ibitor y Activities (Ki, µM) for P seu d oa m id e-Typ e P yr r olid in es 11 a n d 13 a n d P yr r olizid in es
14, 15, 17, a n d 19, in Com p a r ison w ith Da ta for th e P a r en t Aza su ga r s 1 a n d 2
compound
enzyme
118
218
11
72
9.2
39
13
14
15
17
19
R-glucosidase (yeast)a
0.73
1.7
3.3
2.5
355
2.9
2.1
n.i.b
n.i.
n.d.d
n.d.
n.d.
28
n.i.
334
n.i.
n.i.
n.i.
n.i.
n.i.
>1000
465
153
341
n.i.
n.i.
n.i.
n.i.
251
20
132
340
644
29
n.i.
n.i.
n.i.
408
433
347
72
n.i.
n.i.
n.i.
â-glucosidase (almonds)c
â-glucosidase/â-galactosidase (bovine liver)c
isomaltase (yeast)a
28
trehalase (pig kidney)e
n.i.
>1000
n.i.
invertase (yeast)b
n.i.
170
n.i.
249
amyloglucosidase (Aspergillus niger)f
1.5
a
b
d
pH 6.8. n.i. ) no inhibition detected. c pH 7.3. n.d. ) not determined. e pH 6.0. f pH 4.5.
SCHEME 2a
kidney), which is in agreement with the configurational
specificity of the parent azasugars 1 and 2.
Iminosugars are thought to be good, but rather non-
specific, inhibitors of glucosidases because they mimic the
incipient glycosyl cation involved in the mechanism of
action of both R- and â-glycosidases, as a result of the
heterocyclic nitrogen atom being protonated at physi-
ological pH. In N-thiocarbonyl compounds such as 11 and
13, the basicity is drastically decreased (by 14 pK units)
as compared to the corresponding amine, while keeping
a positive charge density resulting from delocalization
of the lone electron pair into the thiocarbonyl group.17
This scenario is probably closer to that encountered in
the transition state of enzymatic glycoside hydrolysis at
the endocyclic oxygen atom region,19 which was expected
to result in improved enzyme specificities. Actually,
compound 11 is a rather good competitive inhibitor of
â-glucosidase and isomaltase (Ki 9.2 and 28 µM, respec-
tively) and only a moderate inhibitor of R-glucosidase and
â-glucosidase/â-galactosidase, indicative of a reverse, and
20-fold higher, selectivity as compared to DMDP for these
particular enzymes. In sharp contrast with 1, no inhibi-
tion was detected for invertase and amyloglucosidase at
mM concentration. The pseudoaglyconic substituent
proved to have a decisive role in the biological activity.
Thus, replacement of the aromatic group into a â-D-
glucopyranosyl residue (13) virtually eliminated any
interaction with the assayed glycosidases.
a
Reagents and conditions: (i) PhNCS, pyridine, rt, 24 h; (ii)
2,3,4,6-tetra-O-acetyl-â-D-glucopyranosyl isothiocyanate, pyridine,
rt, 24 h; (iii) NaOMe, MeOH; (iv) HgO, MeCN, rt, 24 h; (v) (a)
triphosgene, 10% aq NaHCO3, toluene, 5 h, (b) Ac2O, pyridine;
(vi) (a) CS2, DCC, DMF, -10 °C to rt, 16 h, (b) Ac2O, pyridine.
To broaden the range of DMDP-derived sp2-azasugar
glycomimetics for structure/activity studies, the prepara-
tion of the carbonyl and thiocarbonyl pyrrolizidine de-
rivatives 17 and 19 seemed attractive. Their preparation
was accomplished in a straightforward manner by direct
carbonylation and thiocarbonylation of 1 with triphos-
gene and carbon disulfide/dicyclohexylcarbodiimide, re-
spectively. Purification was better effected on the corre-
sponding triacetates 16 and 18, which after conventional
catalytic transesterification afforded the fully unprotected
compounds in pure form (Scheme 2). All compounds here
reported were found to be stable for months as solids or
as aqueous solutions in a refrigerator.
A further increase in enzyme specificity was observed
for the bicyclic carbamate and thiocarbamate derivatives
17 and 19, which can be considered as conformationally
restricted N-(thio)carbonyl pyrrolidines. Thus, 17 and 19
retained the isomaltase inhibitory activity while they
were 1 order of magnitude weaker inhibitors of â-glu-
cosidase. The enzyme specificity was also strongly de-
(18) Ekhart, C. W.; Fechter, M. H.; Hadwiger, P.; Mlaker, E.; Stu¨tz,
A. E.; Tauss, A., Wrodnigg, T. M. Tables of Glycosidase Inhibitors with
Nitrogen in the Sugar Ring and Their Inhibitory Activities. In
Iminosugars as Glycosidase Inhibitors; Stu¨tz, A., Ed.; Wiley-VCH:
Weinheim, Germany, 1999; p 253.
(19) Theoretical and experimental studies indicate that true transi-
tion state analogues must be essentially neutral or zwitterionic at
physiological pH to keep specificity against the target enzyme. See:
(a) Legler, G. Glycosidase Inhibition by Basic Sugar Analogues and
the Transition State of Enzymatic Glycoside Hydrolysis. In Iminosug-
ars as Glycosidase Inhibitors; Stu¨tz, A., Ed.; Wiley-VCH: Weinheim,
1999; p 31 (b) J eong, J .-H.; Murray, B. W.; Takayama, S.; Wong, C.-
H. J . Am. Chem. Soc. 1996, 118, 4227. (c) Legler, G.; Finken, M.-T.
Carbohydr. Res. 1996, 292, 103. (d) Ble´riot, Y.; Genre-Grandpierre,
A.; Imberty, A.; Tellier, C. J . Carbohydr. Chem. 1996, 15, 985. (e) Deng,
H.; Chan, A. W.-Y.; Bagdasianan, C. K.; Estupin˜a´n, B.; Ganem, B.;
Callender, R. H.; Scharamm, V. L. Biochemistry 1996, 35, 6037. (f)
Ernert, P.; Vasella, A.; Weber, M.; Rupitz, K.; Withers, S. G. Carbohydr.
Res. 1993, 250, 113.
The inhibitory activities of the new pseudoamide-type
pyrrolidine and pyrrolizidine azasugar mimics 11, 13 and
14, 15, 17, 19 for R-glucosidase (yeast), â-glucosidase
(almonds), â-glucosidase/â-galactosidase (bovine liver,
cytosolic), isomaltase (yeast), trehalase (pig kidney),
invertase (yeast), and amyloglucosidase (Aspergillus ni-
ger) are summarized in Table 1. None of the prepared
compounds inhibited R-galactosidase (green coffee beans),
R-mannosidase (J ack beans), and R-fucosidase (bovine
3580 J . Org. Chem., Vol. 69, No. 10, 2004

pendent on the nature of the sp2-hybridized bridgehead
nitrogen. Thus, the more basic isourea-type pyrrolizidine
analogues 14 and 15 were 10-fold weaker inhibitors of
isomaltase. Interestingly, the glucopyranosyl derivative
15 turned to be a good inhibitor of porcine trehalase
(Ki 20 µM), with virtually no inhibition of any other of
the tested glycosidases.
In summary, the concept demonstrated herein of
modifying the glycosidase inhibitory properties of pyrro-
lidine homoazasugars through the incorporation of the
key ring nitrogen into linear or cyclic pseudoamide
functionalities provides a new direction to the develop-
ment of highly selective glycosidase inhibitors. The
methodology allows the efficient introduction of molecular
diversity by modifying the configuration of the homoaza-
sugar core, the nature of the pseudoaglyconic substituent
or the basicity of the pseudoamide group. The high
efficiency of the proposed transformations, in combination
with the abundance of commercially available isothio-
cyanate reagents, makes the approach particularly well
suited for combinatorial library schemes. Work in that
direction is currently underway in our laboratories.
Ack n ow led gm en t. We thank the Ministerio de
Ciencia y Tecnolog´ıa for financial support (Grant
No. BMC2001-2366-CO3-03) and the Ministerio de
Educacio´n, Cultura y Deportes, for a doctoral fellowship
(D.R.-L.).
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal details, full purification and characterization data for the
prepared compounds, and experimental procedure for deter-
mination of glycosidase inhibition constants (Ki). This material
is available free of charge via the Internet at http://pubs.acs.org.
J O0499221
J . Org. Chem, Vol. 69, No. 10, 2004 3581