Synthesis and characterisation of D-amino acid-based oligopeptides for use as probes of the influence of molecular structure on the paracellular route of gastrointestinal drug uptake

A series of peptides based on D-amino-acids, and with an N-terminal D-phenylalanine residue, was synthesised by solution methods using t-butoxycarbonyl amino protection. These peptides were designed to resist metabolism in the gastrointestinal tract and to serve as probes of the effects of molecular shape and charge on the paracellular route of drug uptake in the gut. The peptides were characterised by NMR spectroscopy, FAB mass spectrometry, optical rotation and purified by HPLC.