Improving Oral Bioavailability of Peptides by Multiple N‐Methylation: Somatostatin Analogues

Abstract

Full methyl jacket? A complete library of the N‐methylated somatostatin cyclopeptidic analogue Veber–Hirschmann peptide cyclo(‐PFwKTF‐) has been prepared with the aim of improving its bioavailability. Several analogues from the library were found to bind to the somatostatin receptor in the nanomolar range and one of them shows a significant oral bioavailability of 10 %. Conformational analysis shows that N‐methylation is allowed at specific positions without affecting the bioactive conformation.

Exploring experimental and computational markers of cyclic peptides: Charting islands of permeability

“…Indeed, N-methylation of a cyclic peptide agonist of somatostatin improved its oral bioavailability without significantly modifying its biological activity and selectivity [12]. In some cases, N-methylation does not increase membrane permeability and arbitrarily increasing the number of N-methyl modifications is not reflected by the sought-after increase in permeability [13].…”

Towards the Development of Cell Permeable Macrocyclic Scaffolds: Probing the Structural Requirements for Enhancing Cellular Uptake

“…For the study, the cyclic peptide motif c[Xaa 5 A first series of N-methylated analogs was prepared by standard solid phase peptide synthesis on 2'-chlorotrityl polystyrene resin using the procedure described by Biron, et al for selective N-methylation on solid support and HATU as coupling reagent [10]. After cleavage from the resin with a HFIP solution, the N-methylated peptides were successively cyclized with PyBOP, deprotected with a solution of TFA and labeled on the lysine side chain with a dansyl moiety in solution to afford analogs 2-6.…”

“…Other amide bonds are free to interact with water and bring an energetic cost to cross the membrane in a passive way. N-Methylation of free amide bonds (not involved in IHB) is a promising approach to improve cellular uptake [5,6]. Another approach is to use peptoid residues (N-substituted glycines) to replace and mimic peptide bonds.…”

N-Methylated sst2 Selective Somatostatin Cyclic Peptide Analogue as a Potent Candidate for Treating Neurogenic Inflammation

“…13 We have previously shown that multiple N-methylation of the peptidic backbone in cyclic peptides induces remarkable physicochemical properties, that is, increased metabolic stability and enhanced absorption through the intestinal wall with an overall increase in oral bioavailability. 11 Thus, we synthesized a focused library of multiply N-methylated seglitide, where only the externally oriented (or solvent exposed) amide bonds were selectively N-methylated. This biased library was synthesized based on our previous experience with cyclic RGD hexapeptides 14 and SST analogues, where Nmethylation of the solvent exposed amide bonds (which are not involved in any interaction with the receptor) retained the bioactive conformation, showing significant biological activity.…”

“…In the case of these cyclic hexapeptide analogues of SST, N-methylation at Lys 9 either retains or increases the affinity of the resulting analogue by reinforcing the bioactive conformation of the cyclic peptide by two additional γ-turns. 11 However, in case of 4 and 5, Nmethylations at D-Trp 8 and Phe 11 , respectively, result in subtle loss of bioactive conformation by disrupting the stabilizing γ-turns, but this loss is compensated by the N-methylation at Lys 9 , showing a better affinity and selectivity profile. On the contrary, this is not the case for 6, where both of the γ-turns are destabilized by N-methylations at D-Trp 8 and Phe 11 , resulting in a lower affinity, which could not be compensated by additional N-methylation at Lys 9 as observed in the tetra-N-methylated analogue 7.…”