Simplified Pepstatins:  Synthesis and Evaluation of N-Terminally Modified Analogues

Abstract

The promising strategy of gastric ulcer healing with perorally administered epidermal growth factor (EGF) is so far strongly limited by the pepsinic degradation of this therapeutic polypeptide in the stomach. The incorporation of EGF in a bioadhesive polymer-pepsin inhibitor conjugate used as drug carrier matrix, however, might provide sufficient protection toward pepsinic degradation. The synthesis of appropriate pepsin inhibitors represents a prerequisite for the development of such polymer-inhibitor conjugates. The presented study demonstrates that modifications at the N-terminus of simplified analogues of pepstatin which can be synthesized in a simple and straight way result only in slight variations of the inhibitory activity. These analogues display only 10-fold reduced inhibitory activity, compared to pepstatin A, when bearing a greater N-terminal group like isovaleryl, Boc, or Cbz. Compounds which are substituted at the N-terminus by a shorter N-acyl group like propionyl or cyclopropylcarbonyl show further reduced activity (0.01, compared to pepstatin A). The presence of an amide or a urethane moiety at the N-terminus has no considerable effect on enzyme inhibition. Therefore, the N-terminus of these analogues is able to be modified forming a covalent bond to various bioadhesive polymers via a suitable functionality.

Oral protein delivery: Current status and future prospect

“…This systems could reduce presystemic metabolism of protein drugs, exclude the undesired disturbance in digestion of nutritive proteins due to the reduced dilution effects of inhibitors, exclude systemic toxic side effects of inhibitors, specifically target the sites in the GI tract, and reduce dose requirements for enzyme inhibitors [38]. Extensive costs for certain enzyme inhibitors, however, should be considered to guarantee affordable production costs in large-scale production of such conjugates [39].…”

Peptidyl Fluoro-Ketones as Proteolytic Enzyme Inhibitors

“…We have investigated modifications of peptstatin A as an approach to developing inhibitors of plasmepsin II. Pepstatin A is a natural inhibitor of peptidic aspartate proteases such as pepsin [46], renin [47], HIV-1 [48], and HIV-2 [49] proteases. Pepstatin A is also a strong inhibitor of plasmepsin II (IC 50 = 0.44 nM) and plasmepsin IV (IC 50 = 0.61 nM) but it is non selective towards the human cathepsin D (IC 50 = 0.64 nM).…”

Synthesis and cathepsin D inhibition of peptide-hydroxyethyl amine isosteres with cyclic tertiary amines

“…All of theses proteases are inhibited by pepstatin A [16][17][18], a pentapeptide like compound which contains two unusual/3-amino acid statines [(3S,4S)-4-amino-3-hydroxy-6-methylheptanoic acid]. Pepstatin, which contains a reactive hydroxyl group, forms the tetrahedral intermediate by reacting with the essential carboxyl group in the active site of the proteinase.…”