Bioactivatable Pseudotripeptidization of Cyclic Dipeptides To Increase the Affinity toward Oligopeptide Transporter 1 for Enhanced Oral Absorption: An Application to Cyclo(l‑Hyp‑l‑Ser) (JBP485)

The cyclic dipeptides generally present lower affinity toward intestinal oligopeptide transporter 1 (PEPT1) than the linear dipeptides. JBP485 (cyclo­(l-Hyp-l-Ser)) is a low-affinity substrate of PEPT1 with poor oral bioavailability. However, JBP923 (l-Hyp-l-Ser) is a high-affinity substrate of PEPT1 with high oral absorption. We hypothesize that the bioactivatable pseudo-tripeptidization prodrug strategy is promising to increase the affinity of cyclic dipeptides toward PEPT1. To test our hypothesis, we design five amino acid ester prodrugs of JBP485. Compared with JBP485, the optimal prodrug (JBP485-3-CH2-O-valine, J3V) demonstrates improved affinity of PEPT1, oral bioavailability in rats and beagle dogs. Moreover, J3V can dose-dependently protect against liver injury. Additionally, J3V is stable in the gastrointestinal tract, beneficial to the PEPT1-mediated membrane transport, and is bioactivated in the enterocytes and hepatic cells, essential to elicit its bioactivity. In summary, the bioactivatable pseudo-tripeptidization strategy shows potential in increasing affinity of PEPT1 to enhance oral bioavailability of cyclic dipeptides.