Thiuram disulfides as pseudo-irreversible inhibitors of lymphoid tyrosine phosphatase

Visible-Light-Driven Iodine-Catalyzed Synthesis of Unsymmetrical Disulfides via Oxidative Coupling

Herein, a facile and environmentally friendly oxidative coupling reaction to obtain unsymmetrical disulfide compounds, without using metal or organic dyes as photocatalyst and only using a catalytic amount of iodine, was developed. Oxygen is used as oxidant in the reaction and the substrate scope is wide. A gram-scale synthesis also highlights the synthetic practicality of this photochemical strategy. Moreover, our mechanistic studies support the formation of disulfide products through free-radical coupling.

Diaryl dithiocarbamates: synthesis, oxidation to thiuram disulfides, Co(III) complexes [Co(S2CNAr2)3] and their use as single source precursors to CoS2

Air and moisture stable diaryl dithiocarbamate salts, Ar₂NCS₂Li, result from addition of CS₂ to Ar₂NLi, the latter being formed upon deprotonation of diarylamines by ⁿBuLi. Oxidation with K₃[Fe(CN)₆] affords the analogous thiuram disulfides, (Ar₂NCS₂)₂, two examples of which (Ar = p-C₆H₄X; X = Me, OMe) have been crystallographically characterised. The interconversion of dithiocarbamate and thiuram disulfides has also been probed electrochemically and compared with that established for the widely-utilised diethyl system. While oxidation reactions are generally clean and high yielding, for Ph(2-naphthyl)NCS₂Li an ortho-cyclisation product, 3-phenylnaphtho[2,1-d]thiazole-2(3H)-thione, is also formed, resulting from a competitive intramolecular free-radical cyclisation. To demonstrate the coordinating ability of diaryl dithiocarbamates, a small series of Co(III) complexes have been prepared, with two examples, [Co{S₂CN(p-tolyl)₂}₃] and [Co{S₂CNPh(m-tolyl)}₃] being crystallographically characterised. Solvothermal decomposition of [Co{S₂CN(p-tolyl)₂}₃] in oleylamine generates phase pure CoS₂ nanospheres in an unexpected phase-selective manner.

Rational design of a SHP-2 targeted, fluorogenic peptide substrate

Protein tyrosine phosphatase (PTP) targeted, peptide based chemical probes are valuable tools for studying this important family of enzymes, despite the inherent difficulty of developing peptides targeted towards an individual PTP. Here, we have taken a rational approach to designing a SHP-2 targeted, fluorogenic peptide substrate based on information about the potential biological substrates of SHP-2. The fluorogenic, phosphotyrosine mimetic phosphocoumaryl aminopropionic acid (pCAP) provides a facile readout for monitoring PTP activity. By optimizing the amino acids surrounding the pCAP residue, we obtained a substrate with the sequence Ac-DDPI-pCAP-DVLD-NH₂ and optimized kinetic parameters (k_cat = 0.059 ± 0.008 s^-1, K_m = 220 ± 50 µM, k_cat/K_m of 270 M^-1s^-1). In comparison, the phosphorylated coumarin moiety alone is an exceedingly poor substrate for SHP-2, with a k_cat value of 0.0038 ± 0.0003 s^-1, a K_m value of 1100 ± 100 µM and a k_cat/K_m of 3 M^-1s^-1. Furthermore, this optimized peptide has selectivity for SHP-2 over HePTP, MEG1 and PTPµ. The data presented here demonstrate that PTP-targeted peptide substrates can be obtained by optimizing the sequence of a pCAP containing peptide.

Interrogating Protein Phosphatases with Chemical Activity Probes

Protein phosphatases, while long overlooked, have recently become appreciated as drivers of both normal- and disease-associated signaling events. As a result, the spotlight is now turning torwards this enzyme family and efforts geared towards the development of modern chemical tools for studying these enzymes are well underway. This Minireview focuses on the evolution of chemical activity probes, both optical and covalent, for the study of protein phosphatases. Small-molecule probes, global monitoring of phosphatase activity through the use of covalent modifiers, and targeted fluorescence-based activity probes are discussed. We conclude with an overview of open questions in the field and highlight the potential impact of chemical tools for studying protein phosphatases.

Lazaroids U83836E and U74389G are potent, time-dependent inhibitors of caspase-1

Caspase-1 is involved in inflammatory processes and is overactive in autoimmunity and autoinflammation. Antioxidant small molecules also play a role in the immune response by decreasing inflammation. An 84-membered library of pro- and antioxidant small molecules was screened for potential inhibitors of caspase-1. Thirteen compounds were discovered to reduce the activity of caspase-1 below 30%. The most potent inhibitors were lazaroid antioxidant molecules, U83836E (B8) and U74389G (B9), displaying apparent Ki values of 48.0 and 50.0 nm, respectively. Both demonstrated a time-dependent and reversible inhibition.

Covalent inhibition of the lymphoid tyrosine phosphatase

Covalent inhibitors of lymphoid tyrosine phosphatase (LYP) were identified from a screen of the NIH Molecular Libraries Small Molecules Repository (MLSMR). Both of the two lead compounds identified have phosphotyrosine-mimetic benzoic acid moieties as well as electrophilic acrylonitrile groups. Inhibition kinetics of both compounds are consistent with covalent modification of the enzyme, with nanomolar KI and reciprocal millisecond kinact values, representing the best efficiency ratios (kinact /KI ) among currently reported covalent LYP inhibitors. Covalent inhibitors can provide longer efficacy and better selectivity than more conventional noncovalent inhibitors, and these lead compounds are an important step toward the development of protein tyrosine phosphatase (PTP)-targeted covalent therapeutic compounds.