C-glucopyranosyl-1,2,4-triazoles as new potent inhibitors of glycogen phosphorylase

Article abstract of DOI:10.1021/ml4001529

Glycogen phosphorylase inhibitors are considered as potential antidiabetic agents. 3-(β-d-Glucopyranosyl)-5-substituted-1,2,4-triazoles were prepared by acylation of O-perbenzoylated N¹-tosyl-C-β-d-glucopyranosyl formamidrazone and subsequent r

Full text of DOI:10.1021/ml4001529

Letter
pubs.acs.org/acsmedchemlett
C‑Glucopyranosyl-1,2,4-triazoles As New Potent Inhibitors of
Glycogen Phosphorylase
†
‡
‡
,†
́
Eva Bokor, Tibor Docsa, Pal Gergely, and Laszlo Somsak*
́
́
́
́
†Department of Organic Chemistry, University of Debrecen, POB 20, H-4010 Debrecen, Hungary
‡Department of Medical Chemistry, Medical and Health Science Centre, University of Debrecen, Egyetem ter
Hungary
́
1, H-4032 Debrecen,
S
* Supporting Information
ABSTRACT: Glycogen phosphorylase inhibitors are consid-
ered as potential antidiabetic agents. 3-(β-D-Glucopyranosyl)-
5-substituted-1,2,4-triazoles were prepared by acylation of O-
perbenzoylated N1-tosyl-C-β-D-glucopyranosyl formamidrazone and subsequent removal of the protecting groups. The best
inhibitor was 3-(β-D-glucopyranosyl)-5-(2-naphthyl)-1,2,4-triazole (Ki = 0.41 μM against rabbit muscle glycogen phos-
phorylase b).
KEYWORDS: 1,2,4-Triazole, C-glucopyranosyl derivative, bioisoster, glycogen phosphorylase, inhibitor
nhibitors of enzymes are among classics of medicinal
naphthoyl)-β-D-glucopyranosylamine (1 R = 2-naphthyl) was
Ichemistry, and many drug molecules’ activity is due to the best inhibitor,18 which also served as a lead structure for
decreasing the efficiency of these catalytic proteins.1 In a
chemical biological approach, finding an enzyme inhibitor is the
bioisosteric replacements. As illustrated in Chart 1, enzymatic
tests21 as well as crystallographic studies19 revealed high
similarity of amide (1) and 1,2,3-triazole (2) type inhibitors
both in binding strength and structural features of the enzyme−
inhibitor complexes. Kinetic tests of bioisosteric oxadiazoles22,23
3−5 demonstrated that the constitution of the heterocycle had
a strong bearing on the inhibition: the most efficient inhibitor
in these series was 5-(β-D-glucopyranosyl)-3-(2-naphthyl)-
1,2,4-oxadiazole (5), which had a similar efficiency to that of 1.
Other investigations on C-glucopyranosyl heterocycles with
condensed rings showed that benzothiazole 7 was much less
efficient than benzimidazole 8.24 An X-ray crystallographic
study of the RMGPb−8 complex revealed a specific H-bond
between NH of the heterocycle and the main chain CO of
His377,25 and the stronger binding of 8 was attributed to this
interaction, which cannot exist in the case of 7.
result of a good match of the biological and chemical spaces
represented by a binding site of an enzyme and a small
molecule, respectively, fitting to each other with considerable
strength. Among several methods to design inhibitors,
bioisosteric replacement of structural elements of existing
molecules is widely applied and in many cases results in higher
activity or other advantageous property of the new compound.2
Glycogen phosphorylase (GP) is the main regulatory enzyme
of glycogen metabolism. GP, catalyzing the rate determining
step of glycogen degradation in the liver by phosphorolysis, is
directly responsible for the regulation of blood glucose levels.
Therefore, GP has been a validated target in combating
noninsulin-dependent or type 2 diabetes mellitus (T2DM), and
its inhibitors are considered as potential antidiabetic agents.
The biochemical and pharmacological background of this
research has been thoroughly summarized in several reviews of
the past decade; therefore, the reader is kindly referred to those
papers.3−5 Furthermore, possible application of GP inhibitors
in intervention of other diseased states associated with GP
activity (e.g., cardiovascular disorders,6 ischemic lesions,7,8 and
tumorous growth7) has also been under investigations.
On the basis of these preliminaries, synthesis and study of
1,2,4-triazoles of type 6 were envisaged anticipating that the H-
bond donor capacity of this heterocycle would result in
stronger inhibitors of GP.
3-Glycosyl-5-substituted-1,2,4-triazoles were described in the
literature mainly with furanoid rings in reactions of C-
glycofuranosyl (thio)formimidates with hydrazide or amidra-
zone reagents26−28 or transforming a 2,5-anhydro-D,L-allono-
lactone derivative with aminoguanidine.29 3-Glycopyranosyl-5-
substituted-1,2,4-triazoles could not be located in the literature;
the only C-glycopyranosyl-1,2,4-triazoles were 1,3,5-trisubsti-
tuted derivatives obtained from glycosyl cyanides with 1-aza-2-
azoniaallene salts30 or with hydrazonoyl chlorides in the
presence of Yb(OTf)3.31
Several classes of compounds9,10 were shown to be inhibitors
of GP. The most widely studied group of molecules is that of
glucose derivatives,11,12 which bind primarily to the active site
of GP.13 The best glucose derivatives are submicromolar
inhibitors of rabbit muscle GPb, the prototype of GPs.14
Glucopyranosylidene-spiro-thiohydantoin (Ki = 29.8 μM
against rat liver GP) was shown to exert considerable in vivo
blood sugar diminishing activity.15
N-Acyl-β-D-glucopyranosylamines (compounds 1 in Chart 1)
were among the first GP inhibitors,16 and many analogous
derivatives were investigated.17−20 In this series, N-(2-
Received: April 22, 2013
Accepted: May 17, 2013
© XXXX American Chemical Society
A
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ACS Medicinal Chemistry Letters
Letter
Chart 1. Selected Inhibitors of Glycogen Phosphorylase and
Their Efficiency
Scheme 1. Synthesis of 3-(β-D-Glucopyranosyl)-5-
substituted-1,2,4-triazoles (6)
a
a
a
b
c
From 10. From 11a. The crude mixture obtained from amidrazone
d
10 and acetoxyacetyl chloride was treated by TBAF. From 12b.
3-(β-D-Glucopyranosyl)-5-substituted-1,2,4-triazoles 6 were
assayed against RMGPb as described earlier,35 and the kinetic
results, showing the compounds to be competitive inhibitors,
are summarized in Table 1. Methyl (6a) and hydroxymethyl
(6c) derivatives proved weak inhibitors in the micromolar
a
b
Ki [μM] against RMGPb for R = 2-naphthyl. A Ki value of 2.4 μM
was measured independently by Oikonomakos and co-workers.22
a
Table 1. Inhibition of RMGPb by Compounds 6 and
Comparison to Other Nonclassical Bioisosteres
Synthesis of the desired 3-glucopyranosyl-5-substituted-1,2,4-
triazoles of type 6 was planned by adaptation of a literature
protocol32 in which acylation of N1-tosylamidrazones gave 3,5-
disubstituted-1-tosyl-1,2,4-triazoles. Removal of the N-tosyl
group was foreseen under conditions usually applied for N-
desulfonylation of nitrogen heterocycles.33
To start the syntheses, O-perbenzoylated β-D-glucopyranosyl
formimidate34 9 was reacted with tosylhydrazide to give the
necessary tosylamidrazone 10 in good yield (Scheme 1).
Reaction of 10 with acetyl chloride furnished tosyl-triazole 11a,
which was N-detosylated by tetrabutylammonium fluoride
(TBAF) to 12a. With acetoxyacetyl chloride 10 gave a mixture
of 11b and 12b indicating that the N-tosyl group is prone to
splitting off under the acylation conditions. The crude mixture
of 11b and 12b was treated with TBAF to produce 12b in 61%
yield for the two steps. Acylations of 10 with aromatic acid
chlorides were accompanied by complete N-detosylation
thereby simplifying the preparation of 12d−f, which were
obtained in good yields. Removal of the O-acyl protecting
groups was effected under Zemplen
compounds 6a and 6c−f in good to excellent yields.
́
conditions to give test
a
b
Ki [μM] Calculated from the IC50 value by using a web-based tool.36
B
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ACS Medicinal Chemistry Letters
Letter
(7) Henke, B. R.; Sparks, S. M. Glycogen phosphorylase inhibitors.
Mini-Rev. Med. Chem. 2006, 6, 845−857.
range and were significantly less efficient than the parent
amides 1a and 1c, respectively. Appending unsubstituted
aromatic groups to the 1,2,4-triazole ring as in 6d and 6f led
to a remarkable strengthening of the inhibition. While 1,2,4-
oxadiazoles 5d and 5f were practically equipotent with the
corresponding amides 1d and 1f, triazoles 6d and 6f inhibited
the enzyme by ∼1 order of magnitude stronger, respectively.
This indicated that the possibility for the formation of a H-
bond was advantageous for the binding, rendering compound
6f to one of the most efficient glucose analogue inhibitors of
GP known to date. Introduction of a t-butyl substituent in the
4-position of the phenyl group as in 6e resulted in a much
weaker inhibitor. This observation may reveal that the active
site of GP, where these compounds may bind to, can not
accommodate a bulky aliphatic moiety.
Further studies to establish the binding peculiarities of these
inhibitors by X-ray crystallographic investigation of the
enzyme−inhibitor complexes as well as molecular dockings to
predict other efficient derivatives based on this skeleton are in
progress.
In conclusion, a new method was elaborated for the synthesis
of hitherto unknown 3-(β-D-glucopyranosyl)-5-substituted-
1,2,4-triazoles. These compounds inhibited rabbit muscle
GPb, and the 5-(2-naphthyl) derivative with its submicromolar
inhibition proved one of the best inhibitors of the enzyme.
(8) Guan, T.; Qian, Y. S.; Tang, X. Z.; Huang, M. H.; Huang, L. F.;
Li, Y. M.; Sun, H. B. Maslinic acid, a natural inhibitor of glycogen
phosphorylase, reduces cerebral ischemic injury in hyperglycemic rats
by GLT-1 up-regulation. J. Neurosci. Res. 2011, 89, 1829−1839.
́
́ ́ ́
(9) Somsak, L.; Czifrak, K.; Toth, M.; Bokor, E.; Chrysina, E. D.;
Alexacou, K. M.; Hayes, J. M.; Tiraidis, C.; Lazoura, E.; Leonidas, D.
D.; Zographos, S. E.; Oikonomakos, N. G. New inhibitors of glycogen
phosphorylase as potential antidiabetic agents. Curr. Med. Chem. 2008,
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glycogen phosphorylase. Mini-Rev. Med. Chem. 2010, 10, 1139−1155.
(11) Praly, J. P.; Vidal, S. Inhibition of glycogen phosphorylase in the
context of type 2 diabetes, with focus on recent inhibitors bound at the
active site. Mini-Rev. Med. Chem. 2010, 10, 1102−1126.
(12) Somsak, L. Glucose derived inhibitors of glycogen phosphor-
́
ylase. C. R. Chim. 2011, 14, 211−223.
(13) Chrysina, E. D.; Chajistamatiou, A.; Chegkazi, M. From
structure-based to knowledge-based drug design through X-ray protein
crystallography: sketching glycogen phosphorylase binding sites. Curr.
Med. Chem. 2011, 18, 2620−2629.
(14) Chrysina, E. D. The prototype of glycogen phosphorylase. Mini-
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́ ́
(15) Docsa, T.; Czifrak, K.; Huse, C.; Somsak, L.; Gergely, P. The
̈
effect of glucopyranosylidene-spiro-thiohydantoin on the glycogen
metabolism in liver tissues of streptozotocin-induced and obese
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(16) Watson, K. A.; Mitchell, E. P.; Johnson, L. N.; Cruciani, G.; Son,
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ASSOCIATED CONTENT
* Supporting Information
Representative synthetic procedures, enzyme kinetic measure-
ments, and compound characterization. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
̋
(17) Somsak
́
, L.; Kovac
́
s, L.; Tot
́
h, M.; Osz, E.; Szilag
́
yi, L.;
AUTHOR INFORMATION
Corresponding Author
*(L.S.) Tel: +3652512900, ext. 22348. Fax: +3652512744. E-
mail: somsak@tigris.unideb.hu.
Gyorgydeak, Z.; Dinya, Z.; Docsa, T.; Tot
́
́
h, B.; Gergely, P. Synthesis
̈
■
of and a comparative study on the inhibition of muscle and liver
glycogen phosphorylases by epimeric pairs of D-gluco- and D-
xylopyranosylidene-spiro-(thio)hydantoins and N-(D-glucopyranosyl)
amides. J. Med. Chem. 2001, 44, 2843−2848.
Funding
́
(18) Gyorgydeak, Z.; Hadady, Z.; Felfoldi, N.; Krakomperger, A.;
̈
̈
This work was supported by the Hungarian Scientific Research
Fund (OTKA CK77712, CNK80709, and PD105808) as well
́ ́ ́
Nagy, V.; Toth, M.; Brunyanszky, A.; Docsa, T.; Gergely, P.; Somsak,
L. Synthesis of N-(β-D-glucopyranosyl)- and N-(2-acetamido-2-deoxy-
β-D-glucopyranosyl) amides as inhibitors of glycogen phosphorylase.
Bioorg. Med. Chem. 2004, 12, 4861−4870.
́
́
as TAMOP 4.2.1./B-09/1/KONV-2010-0007 and TAMOP-
4.2.2.A-11/1/KONV-2012-0025 projects implemented through
the New Hungary Development Plan, cofinanced by the
European Social Fund. T.D. thanks the Hungarian Academy of
́
(19) Chrysina, E. D.; Bokor, E.; Alexacou, K.-M.; Charavgi, M.-D.;
Oikonomakos, G. N.; Zographos, S. E.; Leonidas, D. D.;
́
Oikonomakos, N. G.; Somsak, L. Amide-1,2,3-triazole bioisosterism:
́
Sciences for a Janos Bolyai research fellowship.
the glycogen phosphorylase case. Tetrahedron: Asymm. 2009, 20, 733−
Notes
740.
The authors declare no competing financial interest.
́ ́
(20) Konya, B.; Docsa, T.; Gergely, P.; Somsak, L. Synthesis of
heterocyclic N-(β-D-glucopyranosyl)carboxamides for inhibition of
glycogen phosphorylase. Carbohydr. Res. 2012, 351, 56−63.
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