Potent non-peptidyl inhibitors of protein tyrosine phosphatase 1B

Azido-Functionalized Aromatic Phosphonate Esters in RPOSS-Cage-Supported Lanthanide Ion (Ln = La, Nd, Dy, Er) Coordination

Within this work, a modified preparation of diethyl 4-azidobenzylphosphonate (L1) is presented and the family of 4- or 4'-azido-substituted aromatic phosphonate esters is increased by three new ligand platforms: diisopropyl 4-azidobenzylphosphonate (L2), diisopropyl ((4'-azido-[1,1'-biphenyl]-4-yl)methyl)phosphonate (L3), and diisopropyl 4-azido-2,3,5,6-tetrafluorobenzylphosphonate (L4), which exhibit an anomalous splitting of the N₃ stretching vibrations. Subsequent coordination to the in situ generated ^RPOSS (polyhedral oligomeric silsesquioxane)-cage-supported lanthanide precursors [(Ln{^RPOSS})₂(THF)_m] (P1-P6) (Ln = La, Nd, Dy, Er; R = iBu, Ph; m = 0, 1) yields complexes of the general formula [Ln{^RPOSS}(L1-L4)_n(S1)_x(THF)_m] (1-30) (n = 2, 3; x = 0, 1; m = 0-2) retaining the azide unit for future semiconductor surface immobilization. Because the latter compounds are mostly oils or viscous waxes, preliminary solution-state structure elucidations via DOSY-ECC-MW estimations have been carried out which are in accordance with ¹H NMR integral ratios as well as solid-state structures, where available. Moreover, the optical properties of the Nd, Dy, and Er derivatives of complexes 1-30 are examined in the visible and NIR spectral regions, where applicable.

The development of protein tyrosine phosphatase1B inhibitors defined by binding sites in crystalline complexes

Protein tyrosine phosphatase1B (PTP1B), a significant negative regulator in insulin and leptin signaling pathways, has emerged as a promising drug target for Type II diabetes mellitus and obesity. Numerous potent PTP1B inhibitors have been discovered within both academia and pharmaceutical industry. However, nearly all medicinal chemistry efforts have been severely hindered because a vast majority of them demonstrate poor membrane permeability and low-selectivity, especially over T-cell protein tyrosine phosphatase (TCPTP). To search the rules about the selectivity over TCPTP and membrane permeability of PTP1B inhibitors, based on the PTP1B/inhibitor crystal complexes, the development PTP1B inhibitors defined as AB, AC, ABC and ADC types have been concluded in the review.

Substrate Activity Screening (SAS) and Related Approaches in Medicinal Chemistry

Substrate activity screening (SAS) was presented a decade ago by Ellman and co-workers as a straightforward methodology for the identification of fragment-sized building blocks for enzyme inhibitors. Ever since, SAS and variations derived from it have been successfully applied to the discovery of inhibitors of various families of enzymatically active drug targets. This review covers key achievements and challenges of SAS and related methodologies, including the modified substrate activity screening (MSAS) approach. Special attention is given to the kinetic and thermodynamic aspects of these methodologies, as a thorough understanding thereof is crucial for successfully transforming the identified fragment-sized hits into potent inhibitors.

Bidentate inhibitors of protein tyrosine phosphatases

SIGNIFICANCE

Protein tyrosine phosphatases (PTPs) are important enzymes that are involved in the regulation of cellular signaling. Evidence accumulated over the years has indicated that PTPs present exciting opportunities for drug discovery against diseases such as diabetes, cancer, autoimmune diseases, and tuberculosis. However, the highly conserved and partially positive charge of the catalytic sites of PTPs is a major challenge in the development of potent and highly selective PTP inhibitors.

RECENT ADVANCES

Here, we examine the strategy of developing bidentate inhibitors for selective inhibition of PTPs. Bidentate inhibitors are small-molecular-weight compounds with the ability to bind to both the active site and a non-conserved secondary phosphate binding site. This secondary phosphate binding site was initially discovered in protein tyrosine phosphatase 1B (PTP1B), and, hence, most of the bidentate inhibitors reported in this review are PTP1B inhibitors.

CRITICAL ISSUES

Although bidentate inhibition is a good strategy for developing potent and selective inhibitors, the cell membrane permeability and pharmacokinetic properties of the inhibitors are also important for successful drug development. In this review, we will also summarize the various efforts made toward the development of phosphotyrosine (pTyr) mimetics for increasing cellular permeability.

FUTURE DIRECTIONS

Even though the secondary phosphate binding site was initially found in PTP1B, structural data have shown that a secondary binding site can also be found in other PTPs, albeit with varying degrees of accessibility. Along with improvements in pTyr mimetics, we believe that the future will see an increase in the number of orally bioavailable bidentate inhibitors against the various classes of PTPs.

Nano-rod ZnO as a novel and reusable catalyst for C−P bond formation and hydrophosphonation of isatin derivatives under solvent-free conditions

A highly efficient method for the synthesis of α1-oxindole-α-hydroxyphosphonates via nano-rod ZnO catalyzed hydrophosphonation of isatin derivatives was developed. The reaction products are in excellent yields using the catalytic system nano-rod ZnO (25 mol%) under solvent-free conditions at room temperature. The catalyst can be reused several times without any significant loss of its activity.

Oxime-based click chemistry in the development of 3-isoxazolecarboxylic acid containing inhibitors of Yersinia pestis protein tyrosine phosphatase, YopH

The pathogenicity of Yersinia pestis relies on several effector proteins including YopH, a protein tyrosine phosphatase (PTP). We previously screened a library of analogues based on the ubiquitous PTP substrate para-nitrophenylphosphate (pNPP) and found that incorporation of a 3-phenyl substituent to give 6-nitro-[1,1'-biphenyl]-3-yldihydrogen phosphate (1) enhanced affinity. Herein we report the conversion of 1 from a substrate into an inhibitor by replacing the hydrolysable phosphoryl group with a 3-isoxazolecarboxylic acid moiety and by introduction of an aminooxy group and subsequent diversification using oxime-based click chemistry. This approach led to the identification of non-promiscuous bidentate YopH inhibitors with affinity in the low micromolar range.

Utilization of nitrophenylphosphates and oxime-based ligation for the development of nanomolar affinity inhibitors of the Yersinia pestis outer protein H (YopH) phosphatase

Our current study reports the first K(M) optimization of a library of nitrophenylphosphate-containing substrates for generating an inhibitor lead against the Yersinia pestis outer protein phosphatase (YopH). A high activity substrate identified by this method (K(M) = 80 μM) was converted from a substrate into an inhibitor by replacement of its phosphate group with difluoromethylphosphonic acid and by attachment of an aminooxy handle for further structural optimization by oxime ligation. A cocrystal structure of this aminooxy-containing platform in complex with YopH allowed the identification of a conserved water molecule proximal to the aminooxy group that was subsequently employed for the design of furanyl-based oxime derivatives. By this process, a potent (IC(50) = 190 nM) and nonpromiscuous inhibitor was developed with good YopH selectivity relative to a panel of phosphatases. The inhibitor showed significant inhibition of intracellular Y. pestis replication at a noncytotoxic concentration. The current work presents general approaches to PTP inhibitor development that may be useful beyond YopH.

Vanillic acid derivatives from the green algae Cladophora socialis as potent protein tyrosine phosphatase 1B inhibitors

A novel vanillic acid derivative (1) and its sulfate adduct (2) were isolated from a green algae, Cladophora socialis. The structures of 1 and 2 were elucidated from NMR and HRESIMS experiments. Both compounds showed potent inhibitory activity against protein tyrosine phosphatase 1B (PTP1B), an enzyme involved in the regulation of insulin cell signaling. Compounds 1 and 2 had IC50 values of 3.7 and 1.7 microM, respectively.

Design, synthesis, and discovery of stilbene derivatives based on lithospermic acid B as potent protein tyrosine phosphatase 1B inhibitors

Dihydroxy stilbene derivatives were designed based on lithospermic acid B and were prepared from 4-(chloromethyl)benzoic acid. The inhibitory activities of the novel compounds against protein tyrosine phosphatase 1B (PTP1B) were evaluated. 3,4-Dihydroxy stilbene carbonyl compounds (7, 11b, 27b) inhibited PTP1B with IC50 values comparable to molybdate, while the conjugation-extended compound (15b) showed inhibition 3-fold better than preclinical RK682. The introduction of electron withdrawing groups or amides into the second phenyl ring, or extension of the conjugation into the stilbene molecule may increase stability of the generated radicals.

Probing acid replacements of thiophene PTP1B inhibitors

The following account describes our systematic effort to replace one of the carboxylate groups of our diacid thiophene PTP1B inhibitors. Active hits were validated using enzymatic assays before pursuing efforts to improve the potency. Only when the C2 carboxylic acid was replaced with another ionizable functional group was reversible and competitive inhibition retained. Use of a tetrazole ring or 1,2,5-thiadiazolidine-3-one-1,1-dioxide as a carboxylate mimetic led to the discovery of two unique starting series that showed improved permeability (PAMPA) and potency of the order of 300nM. The SAR from these efforts underscores some of the major challenges in developing small molecule inhibitors for PTP1B.

Molecular dynamics simulations of interaction between protein-tyrosine phosphatase 1B and a bidentate inhibitor

AIM

To investigate the dynamic properties of protein-tyrosine phosphatase (PTP) 1B and reveal the structural factors responsible for the high inhibitory potency and selectivity of the inhibitor SNA for PTP1B.

METHODS

We performed molecular dynamics (MD) simulations using a long time-scale for both PTP1B and PTP1B complexed with the inhibitor SNA, the most potent and selective PTP1B inhibitor reported to date. The trajectories were analyzed by using principal component analysis.

RESULTS

Trajectory analyses showed that upon binding the ligand, the flexibility of the entire PTP1B molecule decreases. The most notable change is the movement of the WPD-loop. Our simulation results also indicated that electrostatic interactions contribute more to PTP1B-SNA complex conformation than the van der Waals interactions, and that Lys41, Arg47, and Asp48 play important roles in determining the conformation of the inhibitor SNA and in the potency and selectivity of the inhibitor. Of these, Arg47 contributed most. These results were in agreement with previous experimental results.

CONCLUSION

The information presented here suggests that potent and selective PTP1B inhibitors can be designed by targeting the surface residues, for example the region containing Lys41, Arg47, and Asp48, instead of the second phosphate binding site (besides the active phosphate binding site).

Discovery and structure–activity relationships of novel sulfonamides as potent PTP1B inhibitors

A series of novel sulfonamides containing a single difluoromethylene-phosphonate group were discovered to be potent inhibitors of protein tyrosine phosphatase 1B. Structure-activity relationships around the scaffold were investigated, leading to the identification of compounds with IC50 or Ki values in the low nanomolar range. These sulfonamide-based inhibitors exhibit 100 and 30 times higher inhibitory activity than the corresponding tertiary amines and carboxamides, respectively.

Synthesis of functionalized acetophenones as protein tyrosine phosphatase 1B inhibitors

Protein tyrosine phosphatase 1B (PTP1B) is an enzyme that plays a critical role in down-regulating insulin signaling through dephosphorylation of the insulin receptor. Studies have shown that PTP1B knock-out mice showed increased insulin sensitivity in muscle and liver as well as resistance to obesity. A series of functionalized acetophenones were synthesized and evaluated for their PTP1B inhibitory activity. Some of the screened compounds displayed good inhibitory activity.

Recent advances in protein tyrosine phosphatase 1B inhibitors

Type 2 diabetes and obesity are characterised by insulin and leptin resistance. Studies suggest that these may be due to defects in the insulin and leptin signalling pathways. Over the last decade, a considerable body of evidence has been amassed indicating that protein tyrosine phosphatase 1B (PTP1B) is involved in the downregulation of insulin and leptin signalling. Consequently, compounds that inhibit PTP1B have potential as therapeutics for treating Type 2 diabetes and obesity. This review covers recent advances in PTP1B inhibitors with an emphasis on recent attempts to create potent, selective and cell-permeable small-molecule inhibitors.

Protein tyrosine phosphatases: their role in insulin action and potential as drug targets

Protein tyrosine phosphatases (PTPases) are the enzymes responsible for the selective dephosphorylation of tyrosine residues. PTPases function to regulate a wide array of biological responses mediated by growth factors and other stimuli by balancing the cellular level of phosphotyrosine in concert with their counterparts, protein tyrosine kinases. The important roles which PTPases play in regulating intracellular signalling and, ultimately, biological function along with the recent availability of information regarding their structural features has highlighted them as potential targets for pharmacological modulation. This is demonstrated by the increased level of activity directed towards the identification of novel small-molecule PTPase inhibitors. The rationale and potential utility of this drug discovery approach is discussed here, with particular emphasis on its application for the treatment of insulin resistance and Type 2 diabetes.

Alpha,alpha-difluoro-beta-ketophosphonates as potent inhibitors of protein tyrosine phosphatase 1B

A novel series of inhibitors that contain an aryl alpha,alpha-difluoro-beta-ketophosphonate group has been synthesized and evaluated against protein tyrosine phosphatase 1B. These compounds exhibit strong inhibitory activity, the best of which has a K(i) value of 0.17 microM. These results demonstrate that aryl alpha,alpha-difluoro-beta-ketophosphonates are powerful phosphotyrosine mimetics for the development of potent PTP inhibitors.

Structure-based prediction of free energy changes of binding of PTP1B inhibitors

The goals were (1) to understand the driving forces in the binding of small molecule inhibitors to the active site of PTP1B and (2) to develop a molecular mechanics-based empirical free energy function for compound potency prediction. A set of compounds with known activities was docked onto the active site. The related energy components and molecular surface areas were calculated. The bridging water molecules were identified and their contributions were considered. Linear relationships were explored between the above terms and the binding free energies of compounds derived based on experimental inhibition constants. We found that minimally three terms are required to give rise to a good correlation (0.86) with predictive power in five-group cross-validation test (q2 = 0.70). The dominant terms are the electrostatic energy and non-electrostatic energy stemming from the intra- and intermolecular interactions of solutes and from those of bridging water molecules in complexes.

The development of potent non-peptidic PTP-1B inhibitors

The SAR from our peptide libraries was exploited to design a series of potent deoxybenzoin PTP-1B inhibitors. The introduction of an ortho bromo substituent next to the difluoromethylphosphonate warhead gave up to 20-fold increase in potency compared to the desbromo analogues. In addition, these compounds were orally bioavailable and active in the animal models of non-insulin dependent diabetes mellitus (NIDDM).

Discovery of novel PTP1b inhibitors

A small library of 19 compounds was designed based on unique structural features of PTP1b. Utilizing electrospray ionization mass spectrometry (ESI-MS) to provide binding information about complexes of enzyme and small molecule ligands, two classes of lead compounds were discovered.

Structure-based design and discovery of novel inhibitors of protein tyrosine phosphatases

Protein tyrosine phosphatases (PTPs) are important in the regulation of signal transduction processes. Certain enzymes of this class are considered as potential therapeutic targets in the treatment of a variety of diseases such as diabetes, inflammation, and cancer. However, many PTP inhibitors identified to date are peptide-based and contain a highly charged phosphate-mimicking component. These compounds usually lack membrane permeability and this limits their utility in the inhibition of intracellular phosphatases. In the present study, we have used structure-based design and modeling techniques to explore catalytic-site directed, reversible inhibitors of PTPs. Employing a non-charged phosphate mimic and non-peptidyl structural components, we have successfully designed and synthesized a novel series of trifluoromethyl sulfonyl and trifluoromethyl sulfonamido compounds as PTP inhibitors. This is the first time that an uncharged phosphate mimic is reported in the literature for general, reversible, and substrate-competitive inhibition of PTPs. It is an important discovery because the finding may provide a paradigm for the development of phosphatase inhibitors that enter cells and modify signal transduction.

Crystal structure of PTP1B complexed with a potent and selective bidentate inhibitor

Protein-tyrosine phosphatase 1B (PTP1B) has been implicated as an important regulator in several signaling pathways including those initiated by insulin and leptin. Potent and specific PTP1B inhibitors could serve as useful tools in elucidating the physiological functions of PTP1B and may constitute valuable therapeutics in the treatment of several human diseases. We have determined the crystal structure of PTP1B in complex with compound 2, the most potent and selective PTP1B inhibitor reported to date. The structure at 2.15-A resolution reveals that compound 2 simultaneously binds to the active site and a unique proximal noncatalytic site formed by Lys-41, Arg-47, and Asp-48. The structural data are further corroborated by results from kinetic analyses of the interactions of PTP1B and its site-directed mutants with compound 2 and several of its variants. Although many of the residues important for interactions between PTP1B and compound 2 are not unique to PTP1B, the combinations of all contact residues differ between PTP isozymes, which provide a structural basis for potent and selective PTP1B inhibition. Our data further suggest that potent, yet highly selective, PTP1B inhibitory agents can be acquired by targeting the area defined by residues Lys-41, Arg-47, and Asp-48, in addition to the previously identified second aryl phosphate-binding pocket.

Synthesis of [difluoro-(3-alkenylphenyl)-methyl]-phosphonic acids on non-crosslinked polystyrene and their evaluation as inhibitors of PTP1B

A series of [difluoro-(3-alkenylphenyl)-methyl]-phosphonates were prepared on non-crosslinked polystyrene, a soluble polymer support. After cleavage from the support, the resulting phosphonic acids were examined for inhibition with protein tyrosine phosphatase 1B. Compound 20, bearing an alpha,beta-unsaturated allyl ester moiety, was the most potent of this series of compounds, being a reversible, competitive inhibitor with a K(i) of 8.0+/-1.4 microM.

alpha-bromoacetophenone derivatives as neutral protein tyrosine phosphatase inhibitors: structure-Activity relationship

A series of alpha-haloacetophenone derivatives was tested for inhibition of protein tyrosine phosphatases SHP-1 and PTP1B. The results show that the bromides are much more potent than the corresponding chlorides, whereas the phenyl ring is remarkably tolerant to modifications. Derivatization of the phenyl ring with a tripeptide Gly-Glu-Glu resulted in a potent, selective inhibitor against PTP1B.

Divalent and trivalent alpha-ketocarboxylic acids as inhibitors of protein tyrosine phosphatases

Protein tyrosine phosphatases (PTPases) are important targets for the treatment of insulin resistance in patients with type II diabetes and as antibacterial agents. As a result, there is a growing interest in the development of potent and specific inhibitors for these enzymes. This paper describes a series of inhibitors that contain two or three alpha-ketocarboxylic acid groups that are designed to form multiple contacts with residues inside or near the active site of phosphatases. The inhibitors have been assayed against three PTPases: the Yersinia PTPase, PTP1B, and LAR. The best of the inhibitors has IC(50) values against the Yersinia PTPase and PTP1B of 0.7 and 2.7 microM, respectively. These divalent and trivalent compounds are significantly more potent than their corresponding monovalent analogues. In addition, they show good selectivity for PTP1B and the Yersinia PTPase as compared to LAR.

Synthesis and PTP1B inhibition of 1,2-naphthoquinone derivatives as potent anti-diabetic agents

A new series of 1,2-naphthoquinone derivatives was synthesized by various synthetic methods and evaluated for their ability to inhibit protein tyrosine phosphatase 1B (PTP1B). 1,2-Naphthoquinone derivatives with substituent at R(4) position showed submicromolar inhibitory activity, and compound 24 demonstrated 10- to 60-fold selectivity against the tested phosphatases. Also, several 4-aryl-1,2-naphthoquinone derivatives with substituents at R(3), R(6), R(7), or/and R(8) showed submicromolar inhibitory activity and good plasma stability.

The difluoromethylenesulfonic acid group as a monoanionic phosphate surrogate for obtaining PTP1B inhibitors

Three peptides, 7-9, bearing sulfono(difluoromethyl)phenylalanine (F(2)Smp, 2), a nonhydrolyzable, monoanionic phosphotyrosine mimetic, were prepared and evaluated as PTP1B inhibitors. The most effective inhibitor was the nonapeptide, ELEF(F(2)Smp)MDYE-NH(2), (9) which exhibited a K(i) of 360 nM. A comparison of F(2)Smp-bearing peptides 7 [DADE(F(2)Smp)LNH(2), K(i)=3.4 microM] and 8 [EEDE(F(2)Smp)LNH(2), K(i)=0.74 microM] with their phosphono(difluoromethyl)phenylalanine (F(2)Pmp)-bearing analogues indicated that F(2)Smp is not as effective a pTyr mimetic as F(2)Pmp by 100- to 130-fold. Although F(2)Smp is not as effective as F(2)Pmp, a comparison of peptide 7 with analagous peptides bearing other monoanionic pTyr mimetics recently reported in the literature indicates that F(2)Smp is about 65-fold more effective than any other non-hydrolyzable, monanionic pTyr mimetic reported to date. To further assess the difluoromethylenesulfonic acid (DFMS) group as a monoanionic phosphate mimetic, a series of 24 nonpeptidyl biaryl compounds bearing the DFMS group were prepared using polymer-supported methodologies and screened for PTP1B inhibition. Several of these compounds were selected for further study and their IC(50)'s compared to their difluoromethylenephosphonic (DFMP) analogues. The differences in IC(50)'s between the DFMS and DFMP non-peptidyl compounds was not as great as with the F(2)Smp- and F(2)Pmp-bearing peptides. Possible reasons for this and its implication to the design of small molecule PTP1B inhibitors is discussed.

Investigation of potential bioisosteric replacements for the carboxyl groups of peptidomimetic inhibitors of protein tyrosine phosphatase 1B: identification of a tetrazole-containing inhibitor with cellular activity

Protein tyrosine phosphatases (PTPs) constitute a diverse family of enzymes that, together with protein tyrosine kinases, control the level of intracellular tyrosine phosphorylation, thus regulating many cellular functions. PTP1B negatively regulates insulin signaling, in part, by dephosphorylating key tyrosine residues within the regulatory domain of the beta-subunit of the insulin receptor, thereby attenuating receptor kinase activity. Inhibitors of PTP1B would therefore have the potential of prolonging the phosphorylated (activated) state of the insulin receptor and are anticipated to be a novel treatment of the insulin resistance characteristic of type 2 diabetes. We previously reported a series of small molecular weight peptidomimetics as competitive inhibitors of PTP1B, with the most active analogues having K(i) values in the low nanomolar range. Furthermore, we confirmed that the O-carboxymethyl salicylic acid moiety is a remarkably effective novel phosphotyrosine mimetic. Because of the low cell permeability of this compound class, it was important to investigate the possibility of replacing one or both of the remaining carboxyl groups while maintaining PTP1B inhibitory activity. The analogues described herein further support the importance of an acidic functionality at both positions of the tyrosine head moiety. An important discovery was the ortho tetrazole analogue 29 (K(i) = 2.0 microM), which was equipotent to the dicarboxylic acid analogue 2 (K(i) = 2.0 microM). Solution of the X-ray cocrystal structure of the ortho tetrazole analogue 29 bound to PTP1B revealed that the tetrazole moiety is well-accommodated in the active site and binds in a fashion similar to the ortho carboxylate analogue 2 reported previously. This novel monocarboxylic acid analogue revealed significantly higher Caco-2 cell permeability as compared to all previous compounds. Furthermore, compound 29 exhibited modest enhancement of insulin-stimulated 2-deoxyglucose uptake by L6 myocytes.

Protein tyrosine phosphatases: structure and function, substrate specificity, and inhibitor development

Protein tyrosine phosphatases (PTPs) are signaling enzymes that control a diverse array of cellular processes. Malfunction of PTP activity is associated with a number of human disorders. Recent genetic and biochemical studies indicate that PTPs represent a novel platform for drug discovery. Detailed knowledge of PTP substrate specificity and the wealth of structural data on PTPs provide a solid foundation for rational PTP inhibitor design. This review summarizes a correlation of PTP structure and function from mutagenesis experiments. The molecular basis for PTP1B and MKP3 substrate recognition is discussed. A powerful strategy is presented for creating specific and high-affinity bidentate PTP inhibitors that simultaneously bind both the active site and a unique adjacent site. Finally, recent advances in the development of potent and selective inhibitors for PTP1B and Cdc25 are described.

Structure of protein tyrosine phosphatase 1B in complex with inhibitors bearing two phosphotyrosine mimetics

Protein tyrosine phosphatases (PTPases) are signal-transducing enzymes that dephosphorylate intracellular proteins that have phosphorylated tyrosine residues. It has been demonstrated that protein tyrosine phosphatase 1B (PTP1B) is an attractive therapeutic target because of its involvement in regulating insulin sensitivity (Elcheby et al. Science 1999, 283, 1544-1548). The identification of a second binding site in PTP1B (Puius et al., Proc. Natl. Acad. Sci. U.S.A.1997, 94, 13420-13425) suggests a new strategy for inhibitor design, where appropriate compounds may be made to simultaneously occupy both binding sites to gain much higher affinity and selectivity. To test this hypothesis and gain further insights into the structural basis of inhibitor binding, we have determined the crystal structure of PTP1B complexed with two non-peptidyl inhibitors, 4 and 5, both of which contain two aryl difluoromethylenephosphonic acid groups, a nonhydrolyzable phosphate mimetic. The structures were determined and refined to 2.35 and 2.50 A resolution, respectively. Although one of the inhibitors seems to have satisfied the perceived requirement for dual binding, it did not bind both the active site and the adjacent noncatalytic binding site as expected. The second or distal phosphonate group instead extends into the solvent and makes water-mediated interactions with Arg-47. The selectivity of the more potent of these two inhibitors, as well as four other inhibitors bearing two such phosphate mimetics for PTP1B versus seven other PTPases, was examined. In general, selectivity was modest to good when compared to PTPases Cdc25a, PTPmeg-1, PTPbeta, and CD45. However, selectivity was generally poor when compared to other PTPases such as SHP-1, SHP-2, and especially TCPTP, for which almost no selectivity was found. The implications these results have concerning the utility of dual-binding inhibitors are discussed.

alpha-Ketocarboxylic acid-based inhibitors of protein tyrosine phosphatases

A series of aryl alpha-ketocarboxylic acids was synthesized and investigated as inhibitors for the protein tyrosine phosphatase from Yersinia enterocolitica. IC(50) values for these compounds range from 79 to 2700 microM. Larger aromatic groups, and aromatic groups with high electron density, lead to more potent inhibitors. In general, the related aryl alpha-hydroxycarboxylic acids show lower activity.

Potent Reversible Inhibitors of the Protein Tyrosine Phosphatase CD45

The cytosolic portion of CD45, a major transmembrane glycoprotein found on nucleated hematopoietic cells, contains protein tyrosine phosphatase activity and is critical for T-cell receptor-mediated T-cell activation. CD45 inhibitors could have utility in the treatment of autoimmune disorders and organ graft rejection. A number of 9,10-phenanthrenediones were identified that reversibly inhibited CD45-mediated p-nitrophenyl phosphate (pNPP) hydrolysis. Chemistry efforts around the 9,10-phenanthrenedione core led to the most potent inhibitors known to date. In a functional assay, the compounds were also potent inhibitors of T-cell receptor-mediated proliferation, with activities in the low micromolar range paralleling their enzyme inhibition. It was also discovered that the nature of modification to the phenanthrenedione pharmacophore could affect selectivity for CD45 over PTP1B (protein tyrosine phosphatase 1B) or vice versa.

Protein tyrosine phosphatase-1B in diabetes

A role for protein tyrosine phosphatases in the negative regulation of insulin signaling and a putative involvement in the insulin resistance associated with type 2 diabetes have been postulated since their discovery. The recent demonstration that mice lacking the protein tyrosine phosphatase-1B (PTP-1B) have enhanced insulin sensitivity validates this. Furthermore, when fed a high fat diet, these mice maintained insulin sensitivity and were resistant to obesity, suggesting that inhibition of PTP-1B activity could be a novel way of treating type 2 diabetes and obesity. This commentary reviews our current knowledge of PTP-1B in insulin signaling and its role in diabetes and discusses the development of potent and selective PTP-1B inhibitors.

Protein-tyrosine phosphatases: structure, mechanism, and inhibitor discovery

Protein-tyrosine kinases (PTKs) and their associated signaling pathways are crucial for the regulation of numerous cell functions including growth, mitogenesis, motility, cell-cell interactions, metabolism, gene transcription, and the immune response. Since tyrosine phosphorylation is reversible and dynamic in vivo, the phosphorylation states of proteins are governed by the opposing actions of PTKs and protein-tyrosine phosphatases (PTPs). In this light, both PTKs and PTPs play equally important roles in signal transduction in eukaryotic cells, and comprehension of mechanisms behind the reversible pTyr-dependent modulation of protein function and cell physiology must necessarily encompass the characterization of PTPs as well as PTKs. In spite of the large number of PTPs identified to date and the emerging role played by PTPs in disease, a detailed understanding of the role played by PTPs in signaling pathways has been hampered by the absence of PTP-specific agents. Such PTP-specific inhibitors could potentially serve as useful tools in determining the physiological significance of protein tyrosine phosphorylation in complex cellular signal transduction pathways and may constitute valuable therapeutics in the treatment of several human diseases. The goal of this review is therefore to summarize current understandings of PTP structure and mechanism of catalysis and the relationship of these to PTP inhibitor development. The review is organized such that enzyme structure is covered first, followed by mechanisms of catalysis then PTP inhibitor development. In discussing PTP inhibitor development, nonspecific inhibitors and those obtained by screening methods are initially presented with the focus then shifting to inhibitors that utilize a more structure-based rationale.

Synthesis and characterization of a novel class of protein tyrosine phosphatase inhibitors

Nonpeptidyl aryloxymethylphosphonates were prepared and evaluated as protein tyrosine phosphatase inhibitors. The results suggest that aryloxymethylphosphonates are effective nonhydrolyzable phosphotyrosine surrogates and provide further insight into the molecular mechanisms by which phosphate mimics inhibit phosphatase function.

Synthesis and biological evaluation of alpha,alpha-difluorobenzylphosphonic acid derivatives as small molecular inhibitors of protein-tyrosine phosphatase 1B

A series of alpha,alpha-difluorobenzylphosphonic acids having a hydrophobic functional group were prepared via the Stille coupling reaction from halogenated alpha,alpha-difluorobenzylphosphonates. Evaluation of inhibitory activity toward protein tyrosine phosphatase (PTP 1B) revealed that the ethynyl, phenylethynyl and (E)-styryl groups on the benzene nuclei increased the inhibitory activity of alpha,alpha-difluorobenzylphosphonic acid. Inhibitory activities significantly increased upon introducing both (E)-styryl and bis-methylsulfonamide functional groups onto the benzene nuclei of alpha,alpha-difluorobenzylphosphonic acid.