Biosynthesis of the Carbonylmethylene Structure Found in the Ketomemicin Class of Pseudotripeptides

We recently discovered novel pseudotripeptides, the ketomemicins, which possess a C‐terminal pseudodipeptide connected with a carbonylmethylene instead of an amide bond, through heterologous expression of gene clusters identified in actinobacteria. The carbonylmethylene structure is a stable isostere of the amide bond and its biological significance has been shown in several natural and synthetic products. Despite the biological importance of these compounds, little is known about how the carbonylmethylene structure is biosynthesized. In this work, we fully characterized the biosynthetic machinery of the pseudodipeptide. An aldolase, dehydratase, PLP‐dependent glycine‐C‐acetyltransferase, and dehydrogenase were involved in the formation of the pseudodipeptide, with malonyl‐CoA and phenylpyruvate as starter substrates.     

Peptide N‐Amination Supports β‐Sheet Conformations

The conformational heterogeneity of backbone N‐substituted peptides limits their ability to adopt stable secondary structures. Herein, we describe a practical synthesis of backbone aminated peptides that readily adopt β‐sheet folds. Data derived from model N‐amino peptides suggest that extended conformations are stabilized through cooperative steric, electrostatic, and hydrogen‐bonding interactions.