No abstract

N-Boc derivatives of Leu, Met, Thr, Trp, and Pro, the properties of which resemble those of the respective α-amino acid residues present in proteins, rapidly oxidize in the presence of 3,3-dimethyldioxirane to give different products depending on the structure of the oxidizable group in the side chain. A high regioselectivity for the oxygen atom insertion into the γ-CH bond of Leu residues with respect to the weaker α-CH bond was observed. A position selectivity in the oxidation of peptides containing more than one Leu residue was also found.

For-Thp-Leu-Ain-OMe and for-Met-delta(z)Leu-Phe-OMe are two conformationally restricted fMLP-OMe analogues able to discriminate between different biological responses of human neutrophils. In this paper, we demonstrate that the former peptide, which evokes only chemotaxis, does not alter human neutrophil Ca2+ levels. In contrast, for-Met-delta(z)Leu-Phe-OMe, which induces superoxide anion release and degranulation but not chemotaxis, significantly increases the cation concentration. The chelation of Ca2+ in both extracellular and intracellular media abolishes O2- production triggered by for-Met-delta(z)Leu-Phe-OMe, while the same procedure does not affect neutrophil chemotaxis towards for-Thp-Leu-Ain-OMe. We therefore suggest that chemotaxis, unlike superoxide anion release, is independent of Ca2+ enhancement in human neutrophils.

No abstract

The reaction of 2,3‐diaminopyridine (DAP) with alkyl chloroformates and dialkyl dicarbonates is affected by the nature of the acylating agent and the acylation conditions. Mono and dicarbamates of DAP were obtained using chloroformates, while the formation of alkoxycarbonyl derivatives of imidazo[4,5‐b]pyridin‐2‐one was observed when the reaction with dicarbonates was performed at room temperature in THF‐pyridine. Our procedure for the synthesis of imidazopyridin‐2‐ones represents an improvement over the previous methods which require rather severe conditions. The revised structure for a monoacetyl derivative of the above bicyclic system is also reported.