Tao Pei

Preparation and incorporation into small peptides and combinatorial libraries of phosphohistidine analogs for study of prokaryotic two-component signal transduction systems

Two component signaling systems are involved in a rich variety of responses to the extracellular environment (including antimicrobial peptide production, osmosensing/ osmoregulation, virulence factor production, sporulation, xenobiotic metabolism, cell-wall production, antibiotic resistance, and chemotaxis), primarily in prokaryotes [1], They are composed of a first protein, usually bearing a membrane-spanning region, containing a ~250 amino acid histidine kinase domain having catalytic activity for autophosphorylation by ATP of a histidine residue in the cytoplasmic domain. Autophosphorylation occurs between two juxtaposed subunits of a kinase dimer. A ~120 amino acid domain in the cytosolic response regulator protein bears an aspartate residue to which transfer of the phosphate group from the phosphohistidine in the first protein is catalyzed. Response regulators may bear DNA-binding domains that can activate downstream responses, for example as transcription factors or repressors. The chemistry of phosphohistidine intermediates in the histidine kinases signal transduction cascade is not well known. Even such simple issues as phosphorylation of nitrogen at the 1 or 3 position are obscure, and are made difficult to address by the intrinsic hydrolytic instability of phosphohistidines. We have prepared stable analogs of both phosphohistidines for incorporation into novel reagents to address basic questions about the function of two-component signaling systems. These phosphohistidine analogs have been incorporated into small peptides and used in solid-phase syntheses. Other groups have recently reported syntheses of phosphohistidine analogs as well [2].

Palladium-catalyzed cyclization of alkenyl β-keto esters in the presence of chlorotrimethylsilane

PdCl2(CH3CN)2 catalyzed the cyclization of alkenyl beta-keto esters in the presence of a stoichiometric amount of SiMe3Cl to form 2-carboalkoxycyclohexanones in good yield with excellent regioselectivity.