A new structural motif for the design of potent glucosidase inhibitors [12]

Full text of DOI:10.1021/ja005746b

998
J. Am. Chem. Soc. 2001, 123, 998-999
A New Structural Motif for the Design of Potent
Glucosidase Inhibitors
Kelly S. E. Tanaka,‡ Geoffrey C. Winters,
Raymond J. Batchelor, Frederick W. B. Einstein, and
Andrew J. Bennet*
Department of Chemistry, Simon Fraser UniVersity
8888 UniVersity DriVe, Burnaby
British Columbia V5A 1S6, Canada
Figure 1. Structures of various glucosidase inhibitors and of the
glucopyranosyl oxacarbenium ion.
ReceiVed October 31, 2000
Scheme 1. Synthesis of the Bicyclo[4.1.0]heptane Compounds
7 and 8
An important field in glycobiology involves the design and
synthesis of glycosidase inhibitors with potential therapeutic
applications,1 such as the treatment of metabolic disorders,2
cancer,3 and AIDS.4 Retaining glucosidases hydrolyze sugar acetal
linkages via a glucosylated enzyme intermediate5 resulting in
retention of configuration at the anomeric center. Both glucosy-
lation and deglucosylation occur via transition states (TSs) that
have oxacarbenium ion character5-7 and a distorted six-membered
ring.8 Although no single compound effectively inhibits all
glucosidases,6,9 all inhibitors possess functionalities that mimic
certain features of the glucosyl oxacarbenium ion (1). For instance,
1-deoxynojirimicin (2),10 isofagomine (3),11 and validamine (4)12
mimic charge development at the TS by incorporating a basic
nitrogen atom in place of O-5, C-1, and O-1, respectively (Figure
1).
(a) DBU, DPPA, toluene, room temperature; (b) PPh3, pyridine,
NH4OH, room temperature; (c) pyridine, AcCl, toluene, room temperature;
(d) ZnMe2, CH2I2, toluene, -10 °C; (e) 10% Pd-C H2 (12 psi), MeOH;
(f) KOH, MeOH:H2O (1:1).
Conformationally restricted compounds, e.g., nojiritetrazole
(5),13 where the fused tetrazole ring forces the six-membered ring
into a half-chair conformation, are potent inhibitors. Also,
compounds such as valienamine (6) potentially mimic both the
charge and the ring distortion of the TS. Since several different
sequence-based families of enzyme exist that are capable of
hydrolyzing an R-glucoside linkage,14 it is not too surprising that
no single structural class of compounds yields tight binding
inhibitors for all R-glucosidases.15 Thus, constant motivation exists
for the design of new structural motifs to be used as a basis for
potent glycosidase inhibitors.16
The current report details the synthesis and biological activity
for the two bicyclo[4.1.0]heptane derivatives 7 and 8, the first
example of bicyclo[4.1.0]heptane carbocyclic glucosidase inhibi-
tors (Scheme 1). In addition, compound 7 is the tightest binding
yeast R-glucosidase inhibitor reported to date.
Conversion of the known alcohol 917 to azide 10 proceeded in
a 68% yield with DPPA (diphenylphosphoryl azide) in the
presence of DBU.18 After reducing 10 with PPh3 in aqueous
pyridine,19 acetylation gave acetamide 11 in a yield of 97% from
10. The cyclopropyl group was introduced quantitatively by using
Furakawa’s protocol,20 to give a 1:1 ratio of 12 and 13.21
While both compounds have the same stereochemistry at four
stereocenters, the 1R (12) and the 1S (13) diastereomers are
stereochemically related to D-glucose and L-idose, respectively.
The diastereomers were separated by column chromatography (see
Supporting Information for details). After removal of the O-benzyl
group (10% Pd-C and H2) the acetamido groups were hydrolyzed
with KOH (1.5 equiv) in refluxing MeOH:H2O (1:1 v/v). After
neutralization with H+ ion-exchange resin, the final compounds
were eluted from the resin with 1 N NH4OH. The resultant syrups
were crystallized as their HCl salts from acidic methanol (1.5
equiv of HCl) by the addition of acetone. The yields of 7 and 8
(from 14 and 15) were 46% and 33%, respectively.
‡ Current address: Department of Biochemistry, Albert Einstein College
of Medicine, Bronx, NY 10461.
(1) Asano, N.; Nash, R. J.; Molyneux, R. J.; Fleet, G. W. J. Tetrahedron
Asymmetry 2000, 11, 1645.
(2) Clissold, S. P.; Edwards, C. Drugs 1988, 35, 214.
(3) Humphries, M. J. Cancer Res., 1986, 46, 5212. Nishimura, Y.; Satoh,
T.; Adachi, H.; Kondo, S.; Takeuchi, T.; Azetaka, M.; Fukuyasu, H.; Iizuka,
Y. J. Med. Chem. 1997, 40, 2626.
(4) Karpas, A.; Fleet, G. W. J.; Dwek, R. A.; Petursson, S.; Namgoong, S.
K.; Ramsden, N. G.; Jacob, G. S.; Rademacher, T. W. Proc. Natl. Acad. Sci.
U.S.A. 1988, 85, 9229. Karlsson, G. B.; Buttlers, T. D.; Dwek, R. A.; Platt,
F. M. J. Biol. Chem. 1993, 268, 570.
(5) Koshland, D. E., Jr. Biol. ReV. 1953, 28, 416. Withers, S. G.; Street, I.
P. J. Am. Chem. Soc. 1988, 110, 8551. Sinnott, M. L. Chem. ReV. 1990, 90,
1171.
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J. D.; Withers, S. G. Curr. Opin. Struct. Biol. 1994, 4, 885. Withers, S. G.
Pure Appl. Chem. 1995, 67, 1673. Huang, X.; Tanaka, K. S. E.; Bennet, A.
J. J. Am. Chem. Soc. 1997, 119, 11147.
(7) Zechel, D. L.; Withers, S. G. Acc. Chem. Res. 2000, 33, 11.
(8) Strynadka, N. C. J.; James, M. N. G. J. Mol. Biol. 1991, 220, 401.
(9) Asano, N.; Nishida, M.; Kato, A.; Kizu, H.; Matsui, K.; Shimada, Y.;
Itoh, T.; Baba, M.; Watson, A. A.; Nash, R. J.; de Q. Lilley, P. M.; Watkin,
D. J.; Fleet, G. W. J. J. Med. Chem. 1998, 41, 2565. Oki. T.; Matsui, T.;
Osajima, Y. J. Agric. Food Chem. 1999, 47, 550.
(10) Inouye, S.; Tsuruoka, T.; Niida, T. J. Antibiot. 1966, 19, 288.
(11) Jespersen, T. M.; Dong, W.; Sierks, M. R.; Skrydstrup, T.; Lundt, I.;
Bols, M. Angew. Chem., Int. Ed. Engl. 1994, 41, 2565.
(12) Kameda, Y.; Horii, S. J. Chem. Soc., Chem. Commun. 1972, 746.
(13) Ermert, P.; Vasella, A. HelV. Chim. Acta 1991, 74, 2043.
(14) Henrissat, B.; Czjzek, M.; Darbon, H.; Mosbah, A.; Receveur, V.;
Roig-Zamboni, V. AFMB ActiVity Report 1996-1999 1999, 47.
(15) This correlation was recently pointed out by Zechel and Withers for
â-glucosidases (ref 7).
The configuration of both diastereomers was confirmed by
single-crystal X-ray diffraction experiments. Structural diagrams
(16) For a recent example see: Le, V.-D.; Wong, C.-H. J. Org. Chem.
2000, 65, 2399.
(17) Fukase, H.; Horii, S. J. Org. Chem. 1992, 57, 3651.
(18) Thompson, A. S.; Humphrey, G. R.; DeMarco, A. M.; Mathre, D. J.;
Grabowski, E. J. J. Org. Chem. 1993, 58, 5886.
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(20) Furakawa, J.; Kawabata, N.; Nishimura, J. Tetrahedron 1968, 24, 53.
(21) Two diagnostic doublets for the diastereomers appear in the 1H NMR
spectrum at δ 3.05 ppm (H-8A) for 12 and δ 2.77 ppm (H-8A) for 13 (see
Supporting Information for full characterization of 12 and 13).
10.1021/ja005746b CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/16/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 5, 2001 999
Table 1. Inhibition Kinetic Parametersa,b
Ki (µM) for competitive inhibition
enzyme
2c
4d
6d
18
NRe
7
8
14
15
yeast R-glucosidase
rice R-glucosidase
15 ( 1
0.0024 ( 0.0004
580
0.107 ( 0.015
103 ( 8
820 ( 70
2640 ( 330
4100 ( 490
800 ( 100
NRe
NIf
NIg
a All kinetic measurements were made by using the same experimental protocol as that reported in ref 22. b The kinetic data were fit to a
standard competitive inhibition equation. c Reference 22. d IC50 ref 23. e Not reported. f No inhibition observed at 1.3 mM. g No inhibition observed
at 1.2 mM.
Figure 3. Lineweaver-Burk plot for inhibition of yeast R-glucosidase
by 7.
The Lineweaver-Burk plot (Figure 3) for inhibition of
4-nitrophenyl R-D-glucoside hydrolysis catalyzed by yeast R-glu-
cosidase on the addition of 7 shows that this compound binds
competitively to the active site of the enzyme. Moreover, the
measured Ki value (107 nM) for inhibition of yeast R-glucosidase
by compound 7 is, to the best of our knowledge, lower than all
previously reported values.
The comparison between 6 and 7 is particularly interesting since
these compounds are structurally very similar, the ∼170-fold (12.7
Figure 2. Molecular structures of the 1R (top) and 1S (bottom)
diastereomeric cations; 50% enclosure ellipsoids are shown. All hydrogen
atoms and the chloride ion for both structures are excluded for clarity.
kJ/mol) difference in binding of these compounds to the yeast
enzyme could result from one or both of the following factors:
(1) the introduction of a more favorable hydrogen bond(s) between
7’s hydroxymethyl group and the active site or (2) the addition
of an extra hydrophobic interaction between the cyclopropyl CH2
group and the enzyme’s active site. Finally, a comparison between
amine 7 and acetamide 14 supports the current idea that a positive
charge greatly enhances inhibitor potency,7 although other factors
such as hydrogen bonding may contribute to the 26 kJ/mol
difference in the free energy of binding.
for the two diastereomers (7 and 8) are shown in Figure 2. Both
the 1R24 (7) and the 1S25 (8) diastereomers adopt half-chair
conformations with the most marked difference between the two
isomers being the relative orientation of the cyclopropyl ring and
the hydroxymethyl substituent at C1 (IUPAC numbering scheme,
Figure 2).
Amines 7 and 8, and their corresponding acetamido compounds
14 and 15, were tested as inhibitors against two commercially
available R-glucosidase enzymes. Measured Ki values for these
four bicyclo[4.1.0]heptane derivatives and the reported values for
2, 4, and 6 are listed in Table 1.
In summary, a new class of tight-binding competitive R-glu-
cosidase inhibitors has been synthesized and this structural motif
will be of utility in the design of other glycosyl transferring
enzyme inhibitors.
Acknowledgment. The authors gratefully acknowledge the Natural
Sciences and Engineering Research Council of Canada for financial
support of this work.
(22) Tanaka, K. S. E.; Bennet, A. J. Can J. Chem. 1998, 76, 431.
(23) Kameda, Y.; Asano, N.; Yoshikawa, M.; Takeuchi, M.; Yamaguchi,
T.; Matsui, K.; Horii, S.; Fukase, H. J. Antibiot. 1984, 37, 1301.
(24) Crystal structure of (1R,2R,3S,4S,5S,6S)-5-ammonio-1-hydroxymethyl-
2,3,4-bicyclo[4.1.0]heptanetriol chloride: colorless plate; C8H16ClNO4; mono-
clinic, space group P21; Z ) 2; a ) 7.2170(9) Å; b ) 9.1308(11) Å; c )
7.6440(10) Å; â ) 102.427(10)°; V ) 491.91(11) Å3; T 293 K; RF ) 0.026;
GoF ) 1.34.
(25) Crystal structure of (1S,2R,3S,4S,5S,6R)-5-ammonio-1-hydroxymethyl-
2,3,4-bicyclo[4.1.0]heptanetriol chloride: colorless blade; C8H16ClNO4; ortho-
rhombic, space group P212121; Z ) 4; a )7.7355(13) Å; b ) 6.6838(13) Å;
c ) 19.6814(39) Å; V ) 1017.6 Å3; T ) 293 K.; RF ) 0.033; GoF ) 1.24.
Supporting Information Available: Preparation and tables giving
the full spectroscopic characterization of compounds 7, 8, and 10-15,
tables of experimental details, positional parameters, and thermal
parameters for the X-ray analyses of 7 and 8 (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
JA005746B