Structure–Activity Relationship and Rational Design of 3,4-Dephostatin Derivatives as Protein Tyrosine Phosphatase Inhibitors

Eco-friendly methoximation of aromatic aldehydes and ketones using MnCl2.4H2O as an easily accessible and efficient catalyst

Methoximes are important as a class of intermediates and products, among fine chemicals and specialties. The development of a new, facile and efficient method for their synthesis is reported. The methoximes were properly accessed from the corresponding aromatic aldehydes and ketones in good to excellent yields, under mild conditions, employing the inexpensive and environmentally friendly MnCl2.4H2O as a catalyst (at low loading and without the addition of ligand), in EtOH at 50°C. The scope of the process was systematically assessed.

Endoplasmic reticulum stress causes insulin resistance by inhibiting delivery of newly synthesized insulin receptors to the cell surface

Accumulation of unfolded proteins in the endoplasmic reticulum (ER) causes ER stress and activates a signaling network known as the unfolded protein response (UPR). Here we characterize how ER stress and the UPR inhibit insulin signaling. We find that ER stress inhibits insulin signaling by depleting the cell surface population of the insulin receptor. ER stress inhibits proteolytic maturation of insulin proreceptors by interfering with transport of newly synthesized insulin proreceptors from the ER to the plasma membrane. Activation of AKT, a major target of the insulin signaling pathway, by a cytosolic, membrane-bound chimera between the AP20187-inducible FV2E dimerization domain and the cytosolic protein tyrosine kinase domain of the insulin receptor was not affected by ER stress. Hence, signaling events in the UPR, such as activation of the JNK mitogen-activated protein (MAP) kinases or the pseudokinase TRB3 by the ER stress sensors IRE1α and PERK, do not contribute to inhibition of signal transduction in the insulin signaling pathway. Indeed, pharmacologic inhibition and genetic ablation of JNKs, as well as silencing of expression of TRB3, did not restore insulin sensitivity or rescue processing of newly synthesized insulin receptors in ER-stressed cells. [Media: see text].

CH-π hydrogen bonds in biological macromolecules

This is a sequel to the previous Perspective "The CH-π hydrogen bond in chemistry. Conformation, supramolecules, optical resolution and interactions involving carbohydrates", which featured in a PCCP themed issue on "Weak Hydrogen Bonds - Strong Effects?": Phys. Chem. Chem. Phys., 2011, 13, 13873-13900. Evidence that weak hydrogen bonds play an enormously important role in chemistry and biochemistry has now accumulated to an extent that the rigid classical concept of hydrogen bonds formulated by Pauling needs to be seriously revised and extended. The concept of a more generalized hydrogen bond definition is indispensable for understanding the folding mechanisms of proteins. The CH-π hydrogen bond, a weak molecular force occurring between a soft acid CH and a soft base π-electron system, among all is one of the most important and plays a functional role in defining the conformation and stability of 3D structures as well as in many molecular recognition events. This concept is also valuable in structure-based drug design efforts. Despite their frequent occurrence in organic molecules and bio-molecules, the importance of CH-π hydrogen bonds is still largely unknown to many chemists and biochemists. Here we present a review that deals with the evidence, nature, characteristics and consequences of the CH-π hydrogen bond in biological macromolecules (proteins, nucleic acids, lipids and polysaccharides). It is hoped that the present Perspective will show the importance of CH-π hydrogen bonds and stimulate interest in the interactions of biological macromolecules, one of the most fascinating fields in bioorganic chemistry. Implication of this concept is enormous and valuable in the scientific community.

First-in-class small molecule inhibitors of the single-strand DNA cytosine deaminase APOBEC3G

APOBEC3G is a single-stranded DNA cytosine deaminase that comprises part of the innate immune response to viruses and transposons. Although APOBEC3G is the prototype for understanding the larger mammalian polynucleotide deaminase family, no specific chemical inhibitors exist to modulate its activity. High-throughput screening identified 34 compounds that inhibit APOBEC3G catalytic activity. Twenty of 34 small molecules contained catechol moieties, which are known to be sulfhydryl reactive following oxidation to the orthoquinone. Located proximal to the active site, C321 was identified as the binding site for the inhibitors by a combination of mutational screening, structural analysis, and mass spectrometry. Bulkier substitutions C321-to-L, F, Y, or W mimicked chemical inhibition. A strong specificity for APOBEC3G was evident, as most compounds failed to inhibit the related APOBEC3A enzyme or the unrelated enzymes E. coli uracil DNA glycosylase, HIV-1 RNase H, or HIV-1 integrase. Partial, but not complete, sensitivity could be conferred to APOBEC3A by introducing the entire C321 loop from APOBEC3G. Thus, a structural model is presented in which the mechanism of inhibition is both specific and competitive, by binding a pocket adjacent to the APOBEC3G active site, reacting with C321, and blocking access to substrate DNA cytosines.

Aliphatic C−H/π Interactions: Methane−Benzene, Methane−Phenol, and Methane−Indole Complexes

Noncovalent C-H/pi interactions are prevalent in biochemistry and are important in molecular recognition. In this work, we present potential energy curves for methane-benzene, methane-phenol, and methane-indole complexes as prototypes for interactions between C-H bonds and the aromatic components of phenylalanine, tyrosine, and tryptophan. Second-order perturbation theory (MP2) is used in conjunction with the aug-cc-pVDZ and aug-cc-pVTZ basis sets to determine the counterpoise-corrected interaction energy for selected complex configurations. Using corrections for higher-order electron correlation determined with coupled-cluster theory through perturbative triples [CCSD(T)] in the aug-cc-pVDZ basis set, we estimate, through an additive approximation, results at the very accurate CCSD(T)/aug-cc-pVTZ level of theory. Symmetry-adapted perturbation theory (SAPT) is employed to determine the physically significant components of the total interaction energy for each complex.

Formylchromone derivatives as irreversible and selective inhibitors of human protein tyrosine phosphatase 1B. Kinetic and modeling studies

A series of formylchromone derivatives were synthesized as PTP1B inhibitors and some of them were potent against PTP1B with IC50 values as low as 1.0 microM. They exhibited remarkable selectivity for PTP1B over other human PTPases. Kinetic studies revealed that formylchromone derivatives are irreversible and active site-directed inhibitors. Molecular modeling study identified the orientation of the inhibitor bound at the active site of PTP1B.

Formylchromone derivatives as a novel class of protein tyrosine phosphatase 1B inhibitors

Formylchromone inhibits a human protein tyrosine phosphatase PTP1B with a IC(50) value of 73 microM. The chemical reactivity of formylchromone was adjusted by substitution at various positions of the formylchromone skeleton. In an initial assessment of the structure-activity relationship, the most potent inhibitor showed an IC(50) of 4.3 microM against PTP1B and strong or medium selectivity against other human PTPases, LAR and TC-PTP. This compound, however, was not selective against microbial PTPases, YPTP1 and YOP. The potency and selectivity of the formylchromone derivatives expecting further improvements provides a novel pharmacophore for the design of drugs for the treatment of type 2 diabetes and obesity.

Molecular design and biological activities of protein-tyrosine phosphatase inhibitors

Protein-tyrosine kinase (PTKase) and protein-tyrosine phosphatase (PTPase) regulate the intracellular signal transduction in various biological processes. PTPase often negatively regulates the intracellular protein-tyrosine phosphorylation. PTPases are considered to be involved in the etiology of diabetes mellitus and neural diseases, such as Alzheimer's disease and Parkinson's disease. Therefore, PTPase inhibitors should be useful tools to study the role of PTPases in these diseases and other biological phenomena, and they hopefully may be developed into chemotherapeutic agents. We first discovered a naturally occurring PTPase inhibitor, dephostatin, in 1993. Later, we developed stable and safe dephostatin analogues by a molecular design approach employing the concept of CH/pi interaction. We prepared Et-3,4-dephostatin as a stable analogue and found it to inhibit PTP-1B and SHPTP-1 PTPases selectively. Et-3,4-dephostatin increased the tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 (IRS-1), with or without insulin, in differentiated 3T3-L1 mouse adipocytes. It also increased the phosphorylation and activation of Akt. The analogue also enhanced translocation of glucose transporter 4 (GLUT4) from the cytoplasm to the membrane and 2-deoxyglucose transport. It also showed an in vivo antidiabetic effect in terms of reducing the high blood glucose level in KK-Ay mice after oral administration. Since Et-3,4-dephostatin contains a nitrosamine moiety, we designed nitrosamine-free dephostatin analogues employing the concept of CH/pi interaction. Then, we synthesized methoxime- and hexyl-methoxime-3,4-dephostatin as nitrosamine-free analogues. These analogues also showed antidiabetic activity in vivo and illustrate the utility of the CH/pi interaction molecular design approach.

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.

Antidiabetic effect of a nitrosamine-free dephostatin analogue, methoxime-3,4-dephostatin, in db/db mice

Et-3,4-dephostatin, a protein-tyrosine phosphatase (PTPase) inhibitor, potentiates insulin-dependent signal transduction and shows an antidiabetic effect in mice. However, it contains a nitrosamine moiety that is often mutagenic and carcinogenic. Therefore, we previously designed and synthesized methoxime-3,4-dephostatin as a nitrosamine-free analogue of dephostatin. In the present paper, we studied in situ and in vivo antidiabetic effects of this PTPase inhibitor. Methoxime-3,4-dephostatin induced 2-deoxyglucose transport by mouse 3T3-L1 adipocytes and rat L6 myocytes without insulin. It also inhibited glucagon-induced glucose release from primary culture rat hepatocytes. When hepatocytes were prepared from starved rats, methoxime-3,4-dephostatin did not inhibit the release of glucose, indicating that the chemical may act on glycogenolysis. Oral administration of methoxime-3,4-dephostatin for 3-7 days inhibited the increase in the blood glucose level in type-2 diabetes model db/db mice. It also decreased food and water intakes of mice, but showed no liver or blood toxicity.

Potentiation of insulin-related signal transduction by a novel protein-tyrosine phosphatase inhibitor, Et-3,4-dephostatin, on cultured 3T3-L1 adipocytes

We previously isolated dephostatin from Streptomyces as a novel inhibitor of CD45-associated protein-tyrosine phosphatase. We prepared Et-3,4-dephostatin as a stable analogue and found it to inhibit PTP-1B and SHPTP-1 protein-tyrosine phosphatases selectively but not to inhibit CD45 and leukocyte common antigen-related phosphatase ones effectively. Et-3,4-dephostatin increased the tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 with or without insulin in differentiated 3T3-L1 mouse adipocytes. The increase of tyrosine phosphorylation by Et-3,4-dephostatin was more prominent in 6-h than in 30-min incubation. It also increased phosphorylation and activation of Akt with or without insulin. Et-3,4-dephostatin also enhanced translocation of glucose transporter 4 from the cytoplasm to the membrane and 2-deoxy-glucose transport. Et-3,4-dephostatin-induced glucose uptake was inhibited by SB203580, a p38 inhibitor, but not by PD98059, a MEK inhibitor, or by cycloheximide as insulin-induced uptake. Interestingly, although LY294002, a phosphatidylinositol 3-kinase inhibitor, inhibited the insulin-induced glucose uptake completely, it only partially inhibited the Et-3,4-dephostatin-induced uptake. It also blocked insulin-induced glucose transporter 4 translocation but not the Et-3,4-dephostatin-induced one. The increase in c-Cbl tyrosine phosphorylation caused by Et-3,4-dephostatin was stronger than that in insulin receptor phosphorylation. These observations indicate that a phosphatidylinositol 3-kinase-independent pathway involving c-Cbl is more important in Et-3,4-dephostatin-induced glucose uptake than in insulin-induced uptake. Et-3,4-dephostatin showed an in vivo antidiabetic effect in terms of reducing the high blood glucose level in KK-A(y) mice after oral administration. Thus, Et-3,4-dephostatin potentiated insulin-related signal transductions in cultured mouse adipocytes and showed an antidiabetic effect in mice.

Sulfonylated aminothiazoles as new small molecule inhibitors of protein phosphatases

Based on a previously identified lead structure, SC-alphaalphadelta9, we have developed a versatile new chemical scaffold that can be readily modified to generate libraries of both Tyr and dual specificity phosphatase inhibitors with reduced molecular weight and lipophilicity. The most potent analogue identified to date, aminothiazole 8z, inhibits the dual specificity phosphatase Cdc25B with a Ki of 4.6+/-0.4 microM and a Hill coefficient of 2.