β- and γ-Di- and Tripeptides as Potential Substrates for the Oligopeptide Transporter hPepT1

Organophotoredox-Catalyzed Synthesis of Unnatural α/β Amino Acids and Peptides via Deaminative Three-Component Coupling

Herein, we disclose an expedient visible-light-mediated, organophotoredox-catalyzed multicomponent synthesis of unnatural amino acids using a Katritzky salt, glyoxal derivatives, and substituted anilines. Mechanistically, an alkyl radical is generated from the Katritzky salt via a deaminative process that undergoes addition to the in situ-generated imine to furnish α-amino acids in a moderate diastereoisomeric ratio. For the first time, we have demonstrated this deaminative protocol to access substituted β-amino acids from α-amino acid-derived Katritzky salts. Furthermore, α-amino amides are also generated from the corresponding 2-oxoacetamide derivatives.

Per Artursson's Major Contributions to the Caco-2 Cell Literature in Pharmaceutical Sciences

This edition of the Journal of Pharmaceutical Sciences is dedicated to the wonderful career of Per Artursson from the Uppsala University. My Commentary focusses on Per's major contributions to the Caco-2 cell literature over the past 30 years. Two especially influential papers have been cited more than 1000 times out of a total citation count of almost 30,000 and a h-index of 93 (Google Scholar), making Per one of the most cited and influential Pharmaceutical scientists of his generation. The Caco-2 field to which Per contributed so many advances has informed the community on key areas including predictive drug fluxes across the intestine, metabolism by intestinal epithelia, the role of transporters during flux, enantiomer-selective flux, excipient interaction with tight junctions, and nanoparticle uptake by enterocytes. In this pioneering work, Per has been careful to emphasise that Caco-2 monolayers have limitations and are a model of the human small intestine where observations must be backed up with in vitro tissue and in vivo work. Throughout, he has paid great attention to detail in methodology, as reflected by co-authorship of two Nature Protocols on Caco-2 assays. The article briefly assesses some of the most important milestones in Per's published Caco-2 research.

Chiral alpha-aminoxy acid/achiral cyclopropane alpha-aminoxy acid unit as a building block for constructing the alpha N-O helix

The monomer 1 derived from achiral 1-(aminoxy)cyclopropanecarboxylic acid (OAcc) and oligopeptides 2-9 consisting of a chiral alpha-aminoxy acid and an achiral alpha-aminoxy acid such as OAcc were synthesized and their structures characterized. The eight-membered-ring intramolecular hydrogen bond, namely the alpha N-O turn, was formed between adjacent residues independent of their chirality. However, the helix formation was sequence-dependent. Dipeptide 2 bearing chiral alpha-aminoxy acid (d-OAA) at the N-terminus and achiral OAcc at the C-terminus preferentially adopted a right-handed 1.8(8) helical structure, but dipeptide 3 (OAcc-d-OAA) did not. Theoretical calculation results, in good agreement with experimental ones, revealed that the biased handedness of alpha N-O turn found in OAcc residue depends on its preceding chiral residue. It was then found that the helical conformation was destroyed in the case of oligopeptides 6 and 7 [OAA-(OAcc)(n), n = 2, 3]. The crystal structure of tripeptide 8 ((i)PrCO-d-OVal-OAcc-d-OVal-NH(i)Bu) further disclosed the helical structure formed by three consecutive homochiral alpha N-O turns. This study has uncovered achiral aminoxy acid residues such as the OAcc unit as a useful building block to be incorporated into chiral aminoxy peptides to mimic chiral helix structure.