Rational design, synthesis, and structure–activity relationships of 5-amino-1H-pyrazole-4-carboxylic acid derivatives as protein tyrosine phosphatase 1B inhibitors

doi:10.1016/j.bmc.2016.10.012

Bioorganic & Medicinal Chemistry

Volume 25, Issue 1, 1 January 2017, Pages 67-74

https://doi.org/10.1016/j.bmc.2016.10.012 Get rights and content

Abstract

A series of novel amino-carboxylic based pyrazole as protein tyrosine phosphatase 1B (PTP1B) inhibitors were designed on the basis of structure-based pharmacophore model and molecular docking. Compounds containing different hydrophobic tail (1,2-diphenyl ethanone, oxdiadizole and dibenzyl amines) were synthesized and evaluated in PTP1B enzymatic assay. Structure–activity relationship based optimization resulted in identification of several potent, metabolically stable and cell permeable PTP1B inhibitors.

Graphical abstract

Introduction

Protein tyrosine phosphatase 1B (PTP1B) is an intracellular protein expressed in insulin responsive tissues including the classical insulin targeted tissues such as liver, muscle and fat.¹ PTP1B plays an important role in insulin receptor signaling.² PTP1B dephosphorylates the insulin receptor during its biosynthesis in endoplasmic reticulum as well as after it has been stimulated by the insulin, and thus play a central role in negative regulation of insulin signaling pathway.³ Out of several negative regulators, PTP1B has gained importance because of its specificity and in vivo validation in animal models of diabetes.

The discovery of potent, selective, cell permeable and orally bioavailable PTP1B inhibitors is a challenging medicinal chemistry objective. PTP1B inhibitors need to have good cellular penetration, as target is intracellular, and orally available drug is desired. This is formidable task because of the physical nature of this target. Most of the small PTP1B inhibitors bear highly charged phosphonates⁴ or multiple acid and peptide functionalities⁵ due to which they show poor cell permeability and oral bioavailability. Out of several small molecule PTP1B inhibitors, only three small molecule PTP1B inhibitors entered clinical trials (Fig. 1) and finally discontinued due to insufficient efficacy and unwanted side effects. In our earlier communications we have reported cell permeable and orally bio-available PTP inhibitors. The journey was started with designing of ‘heterocyclic based carboxylic acids’ that resembles as ‘head group’ and followed by synthesis of the compounds containing ‘hydrophobic tail’.⁶

Section snippets

Inhibitor design

Multiple chemotypes and their co-crystal structures are known in the literature for PTP1B inhibitors. We have shortlisted (Fig. 2) different head group pharmacophores which have been successfully used to design PTP1B inhibitors.⁷

The active site of PTP1B has evolved to accommodate phosphotyrosine (p-Tyr) residue which contains two negative charges at physiological pH. Hence the inhibitors developed against PTP1B were also having negative charges to compete with p-Tyr. But these inhibitors are

Chemistry

In our previous article⁶ we have reported the discovery of isoxazole carboxylic acid-based potent, selective and orally bio-available PTP1B inhibitors. Herein, our aim was to discover novel ‘5-Amino-1H-pyrazole-4-carboxylic acid’ as pharmacophore which is connected to an aromatic ring (phenyl) which in turn connected to a hydrophobic tail group through a methylene or alkyl amine group. 1,2-Diphenyl ethanone, benzylphenyl-1,2,4-oxadiazole and dibenzyl amine group has been selected as hydrophobic

Results and discussion

All the derivatives (8a–j, 11a–f and 16a–i) were evaluated in fluorescence based kinetic assay as per the procedure described in our earlier publication.⁶

Simple unsubstituted compound 8a showed poor activity against PTP1B enzyme assay. To explore SAR, small hydrophobic group like –F was incorporated in the phenyl ring (R³ or R⁵), but it also did not improve activity (8b–c). A variety of other di-para-substituents were also significantly less active (8d–f). Further optimization revealed that

Conclusion

In summary, a series of ‘amino-carboxylic based pyrazole’ was discovered as novel pharmacophore by structure-based pharmacophore model and molecular docking analysis. In comparison to most of the existing PTP1B inhibitors, our designed molecules contain small molecular weight, non-phosphonate head groups. Functional groups such as 1,2-diphenyl ethanone, oxdiadizole and dibenzyl amines were selected as hydrophobic tail. A series of compounds containing these hydrophobic tails were synthesized

General synthetic methods

The purity of compounds was determined by HPLC. 1H nuclear magnetic resonance (NMR) spectra were recorded in the deuterated solvents specified on a Varian 400 spectrometer operating at 400. The signal of the deuterated solvent was used as internal reference. Chemical shifts (δ) are given in ppm and are referenced to residual not fully deuterated solvent signal. Coupling constants (J) are given in Hz. Chemical shifts are reported in parts per million (δ) from the tetramethylsilane resonance in

Acknowledgements

Authors are grateful to Drs. Kasim A. Mookhtiar and Venkata P. Palle for their support, management of Advinus Group for encouragement. Analytical departments are being acknowledged for their help during this work. We thank Dr. Anup Ranade for managing intellectual property. Advinus publication no. ADV-A-035.

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Rational design, synthesis, and structure–activity relationships of 5-amino-1H-pyrazole-4-carboxylic acid derivatives as protein tyrosine phosphatase 1B inhibitors

Abstract

Graphical abstract

Introduction

Section snippets

Inhibitor design

Chemistry

Results and discussion

Conclusion

General synthetic methods

Acknowledgements

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Bioorg. Med. Chem. Lett.

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Nature

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Eur. J. Biochem.

Expert Opin. Investig. Drugs