Amplification of the inhibitory activity of miglitol by monofluorination

Article abstract of DOI:10.1016/j.bmcl.2009.08.012

Selective monofluorination of the α-glycosidase inhibitor and antidiabetic agent Miglitol at position C(2) creates an competitive inhibitor of five times higher activity than the parent compound. Its screening against a panel of human cell lines showed a

Full text of DOI:10.1016/j.bmcl.2009.08.012

Bioorganic & Medicinal Chemistry Letters 19 (2009) 5673–5674
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Amplification of the inhibitory activity of miglitol by monofluorination
*
Erik Prell, René Csuk
Martin-Luther-Universität Halle-Wittenberg, NF II, Organische Chemie, Kurt-Mothes-Str. 2, D-06120 Halle (Saale), Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Selective monofluorination of the a-glycosidase inhibitor and antidiabetic agent Miglitol at position C(2)
Received 20 July 2009
Revised 3 August 2009
Accepted 4 August 2009
Available online 7 August 2009
creates an competitive inhibitor of five times higher activity than the parent compound. Its screening
against a panel of human cell lines showed a low cytotoxicity therefore making this compound an inter-
esting candidate for further clinical investigations.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Miglitol
Fluorination
Glycosidase-inhibitor
Imino sugar
Miglitol (GlysetTM) (1) is used, alone or with other drugs, to treat
type-2 diabetes in people whose diabetes cannot be controlled by
dietalone. Miglitol (Fig. 1)slowsdownthebreakdownandadsorption
of table sugar and other oligosaccharides in the small intestine, there-
foreresultinginloweredbloodsugarlevelsfollowingmeals. Itacts1 as
a competitive inhibitor of a-glucosidases, and —in addition—1 sup-
presses the postprandial increase in interleukin-6 and increases
active glucagon-like peptide 1 secretion.
dichloromethane for 3 h at room temperature gave 70% of fluori-
nated 6.
Compound 6 was successively deprotected: First, the benzyli-
dene acetal and the trityl group were cleaved off by treatment8
of compound 6 with acetyl chloride in methanol; this resulted in
an almost quantitative yield of 7 that was hydrogenated9 for 24 h
in the presence of palladium on charcoal at 40 °C to yield com-
pound 8 (ca. 100 mg) in 68% yield after chromatographic work-up.
Total sales for 1 in the USA were approx. 22 Mill $ for 2007 with a
total annual growth of 267% compared to 2006. The daily doses,
however, arehigh(50–300 mg/d). Inaddition, miglitolaswellasvar-
ious N-alkylated derivatives have become pharmacological agents
to treat metabolic disorders, for example, Gaucher’s disease.2 There-
fore, it seemed of interest to look out for compounds being stronger
competitive inhibitors of a-glucosidases than miglitol.
Inspection of models and interpreting in-silico docking experi-
ments3 suggested that a miglitol derivative bearing an epimeric
fluorine substituent at position C(2) should bind more strongly to
the active site of the a-glucosidase (from baker’s yeast).
To corroborate this theory we set out for a synthesis (Scheme 1)
of this target compound. Since 1 is commercially available we
decided to start our synthetic approach from miglitol (1).
Thus, starting material 1 was treated with benzaldehyde in the
presence4 of anhydrous ZnCl2 to yield 90% of the corresponding
benzylidene acetal 2. Tritylation5 of 2 gave 3 whose benzylation
with benzylbromide in the presence of bis(tri-n-butyltin)oxide6
afforded a mixture of the monobenzylated compounds 4 and 5 in
a 5:1 ratio. Reaction of monobenzylated 4 with DAST7 in dry
Scheme 1. Reactions and conditions: (a) benzaldehyde, ZnCl2, 50 °C, 48 h, 90%; (b)
TrCl, pyridine, DMAP, 50 °C, 48 h, 83%; (c) bis(tri-n-butyltin)oxide, toluene, BnBr,
90 °C, 5d, 4:5 = 5:1, together 65%; (d) DAST, dichloromethane, 25 °C, 3 h, 70%; (e)
MeOH, AcCl, 25 °C, 5d, quant.; (f) MeOH, Pd/C (10%), H2, 40 °C, 24 h, 68%.
* Corresponding author. Tel.: +49 345 5525660; fax: +49 345 5527030.
E-mail address: rene.csuk@chemie.uni-halle.de (R. Csuk).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.08.012

5674
E. Prell, R. Csuk / Bioorg. Med. Chem. Lett. 19 (2009) 5673–5674
and Cn3D free software; docking simulation were run using
a
modified
algorithm. GOLD (Jones, G.; Willett, P.; Glen, R. C.; Leach, A. R.; Taylor, R. J. Mol.
Biol. 1997, 267, 727). Crystal structure data were obtained from the PDB
structures 3D3I and 2JKE: Kurakata, Y.; Uechi, A.; Yoshida, H.; Kamitori, S.;
Sakano, Y.; Nishikawa, A.; Tonozuka, T. J. Biol. Chem. 2008, 381, 116 and Gloster,
T. M.; Turkenburg, J. P.; Potts, J. R.; Henrisat, B.; Davies, G. J. Chem. Biol. 2008, 15,
1058; for comparative 3-D-QSAR studies: Saqib, U.; Siddiqi, M. I. Int. J. Integr.
Biol. 2009, 5(1), 13; a similar in-silico approach—although on HIV-1 integrase
inhibitors—has been described by Savarino: Savarino, A. Retrovirology 2007, 4,
21.
Figure 1. Structure of antidiabetic miglitol (1).
Biological screening of compounds 1 and 8 was performed using
4. Wessel, H. P. J. Carbohydr. Chem. 1988, 7, 263.
5. Bernotas, R. C.; Pezzone, M. A.; Ganem, B. Carbohydr. Res. 1987, 167, 305.
6. Dasgupta, F.; Garegg, P. J. Synthesis 1994, 1121.
a 4-nitrophenolate-based assay10 starting from the corresponding
glucoside and the a-glucosidase from baker’s yeast. Whereas migl-
7. Middleton, W. J. J. Org. Chem. 1975, 40, 574.
itol shows an IC50 of 9.9 mM in this test for compound 811 an IC50
of 2.1 mM was observed—therefore showing an approx. fivefold
stronger inhibition of the enzyme. Evaluation of the enzyme kinet-
ics revealed 8 as a competitive inhibitor of the enzyme. Biological
8. Khare, D. P.; Hindsgaul, O.; Lemieux, R. U. Carbohydr. Res. 1985, 136, 285.
9. Gilham, P. T.; Khorana, H. G. J. Am. Chem. Soc. 1959, 81, 4647.
10. Conchie, J.; Gelman, A. L.; Levvy, G. A. Biochem. J. 1967, 103, 609. measurement
was performed in microtiter plates using
a Spectrafluor Plus instrument
working at k = 415 nm applying concentration of the glucoside 0.5, 0.67, 1.0
screening revealed 8 as a strong competitive inhibitor against a
a
-
and 2.0 mM and 0.22–0.24 U/ml of the enzyme..
11. Selected analytical data for 4: oil,
½
a D
ꢀ
¼ ꢁ5:69 (c 0.44, CHCl3); 1H NMR
glucosidase. Screening of 8 against a panel of human cell lines
showed a low cytotoxicity of 8 therefore making this compound
an interesting candidate for further clinical investigations.
(400 MHz, CDCl3): d = 7.50–7.20 (m, 25H, H-aromat.), 5.54 (s, 1H, CH-
= 11.5, CH020 OBn), 4.65 (d, 1H, JH ,H = 11.5,
00 ,H0
0
0 0
benzylidene), 5.00 (d, 1H, JH
CH0 OBn), 4.50 (dd, 1H, J6 ,5 = 4.3, J6 = 10.5, H-600), 3.74–3.56 (m, 3H, H-2, H-
00
00 ,60
60, 2H-4), 3.36 (dd, 1H, J3,2 = 9.0, J3,4 = 9.0, H-3), 3.19–3.16 (m, 2H, H-200, H-2e0 ),
2.98 (dd, 1H, J1 ,2 = 5.1, J1 = 11.0, H-100), 2.76 (ddd, 1H, JH-1
= 5.9e, JH-1
0 0 , H-
0 0
0 0 ,10
0 0 , H-20
e
Acknowledgments
= 13.9, H-100), 2.62–2.51 (m, 2H, H-10e, H-5), 2.21 (dd, 1H,
00
200
,
H-10
= 5.9, JH-1
2
+
J1 ,2 = 10.7, J1 ,1 = 11.0, H-10) ppm; MS (ESI–MeOH): m/z (%) = 628.1 ([M+H] ,
0
0
00
100), 650.3 ([M+Na]+, 11), 1254.7 ([M2+H]+, 5), 1277.0 ([M2+Na]+, 14); selected
Many thanks are due to Dr. Claudia Korb for enzymatic screen-
ing, Dr. Dieter Ströhl for many NMR spectra, Dr. Ralph Kluge for
ESI-MS measurements and Mr. Stefan Schwarz for screening the
human cell lines.
analytical data for 8:
½
a D
ꢀ
¼ ꢁ65:77 (c 0.06, MeOH); 1H NMR (500 MHz,
0 0
0
CD3OD): d = 4.40 (dddd, 1H, J2,1 = 4.2, J2,3 = 7.1, J2,1 = 9.1, J2,F = 49.5, H-2), 3.94
(dd, 1H, J6 ,5 = 2.7, J6 = 12.1, H-600), 3.90 (dd, 1H, J6 ,5 = 2.5, J6 ,6 = 12.1, H-60),
0 0
0
0
0 0
0 0 ,60
3.74 (ddd, 1H, JH-2
= 4.5, JH-2
0 0
= 7.5, JH-2
= 11.3, H-20e0), 3.71 (ddd,
00 , H-10
0 0, H-10 0
0 0, H-20
1H, JH-2 , H-1 = 3.7, JH-2 , H-1 = 7.6, JH-2 , H-2 = 11.3, H-20e), 3.49–3.44 (m, 2H, H-3,
0
0
0
0
0 0
H-4), 3.40 (ddd, 1H, J1 ,2 = 4.2, J1 = 10.9, J1 ,F = 13.6, H-100), 3.14 (ddd, 1H, JH-
0 0
0 0
0 0 ,10
= 7.6, JH-1
= 7.5, JH-1
= 4.5, JH-1 ,
= 12.6, H-100), 2.78 (ddd, 1H, JH-1 ,
References and notes
0 0
0 0
0
100
,
H-20
,
-H-20 0
,
H-10
H-
e
= 12.6, H-10e0), 2.65 (ddd, 1H, J1 ,2 = 9.1,
20
H-200
H-10 0
0
0
0
= 3.7, JH-1 ,
J1 ,1 = 10.9, J1 ,F = 14.2, H-10), 2.50 (m, 1H, H-5) ppm; 13C NMR (100 MHz,
0
0 0
0
1. Arakawa, M.; Ebato, C.; Mita, T.; Fujitani, Y.; Shimizu, T.; Watada, H.; Kawamori,
R.; Hirose, T. Metab. Clin. Exp. 2008, 57, 1299.
2. Mahuran, D. J.; Tropak, M. B.; Buttner, E. D.; Blanchard, J. E.; Brown, E. D. U.S.
Patent 2009075960 A1, 2009; Chem. Abstr. 2009, 150, 345565.
3. Visualization was performed using the CAChe 4.0 software from Oxford
molecular; structural superimpositions were conducted using the SWISS PDB
1
2
CD3OD): d = 90.4 (d, J2,F = 175.7, C2), 77.3 (d, J3,F = 18.0, C3), 70.6 (d,
3J4,F = 10.4, C4), 67.5 (C5), 59.3 (ethylene-C2), 58.4 (C6), 54.8 (ethylene-C1),
2
54.0 (d, J1,F = 26.6, C1) ppm; 19F NMR (188 MHz, CD3OD): d = ꢁ195.21 (m, 1F,
F) ppm; MS (ESI–MeOH): m/z (%) = 200.5 ([cluster]2+, 6), 210.3 ([M+H]+, 100),
232.3 ([M+Na]+, 16), 250.3 ([M+Na,H2O]+, 28).