Hybrid Cyclobutane/Proline-Containing Peptidomimetics: The Conformational Constraint Influences Their Cell-Penetration Ability

Abstract

A new family of hybrid β,γ-peptidomimetics consisting of a repetitive unit formed by a chiral cyclobutane-containing trans-β-amino acid plus a Nα-functionalized trans-γ-amino-l-proline joined in alternation were synthesized and evaluated as cell penetrating peptides (CPP). They lack toxicity on the human tumoral cell line HeLa, with an almost negligible cell uptake. The dodecapeptide showed a substantial microbicidal activity on Leishmania parasites at 50 µM but with a modest intracellular accumulation. Their previously published γ,γ-homologues, with a cyclobutane γ-amino acid, showed a well-defined secondary structure with an average inter-guanidinium distance of 8–10 Å, a higher leishmanicidal activity as well as a significant intracellular accumulation. The presence of a very rigid cyclobutane β-amino acid in the peptide backbone precludes the acquisition of a defined conformation suitable for their cell uptake ability. Our results unveiled the preorganized charge-display as a relevant parameter, additional to the separation among the charged groups as previously described. The data herein reinforce the relevance of these descriptors in the design of CPPs with improved properties.

Bio-Membrane Internalization Mechanisms of Arginine-Rich Cell-Penetrating Peptides in Various Species

“…In order to increase the transduction efficiency and stability of the cargoes and to decrease the rate of biodegradability, various strategies of modifications on CPPs were deployed. They include, but are not limited to, the use of D-form amino acid replacements on β or γ sides [37], cisor trans-γ-amino acid modification on branches [38], and non-standard amino acid substitutions [39]. However, various modifications of the primary sequences of CPPs, types of cargoes for delivery, combination manners of cargoes, and even concentrations of CPPs were also important factors in contributing to alternative entry routes into cells [27,30,31,34,38,40].…”

β‐N‐Heterocyclic Cyclobutane Carboximides: Synthesis through a Tandem Base‐Catalyzed Amidation/aza‐Michael Addition Protocol and Facile Transformations

“…[1] Short oligomers of ACBCs may adopt helical, [2] ribbon, [3] or strand architectures, [4] or macromolecular assemblies. [5] Other molecules incorporating ACBC units have been used as organogelators, [6] metal catalyst ligands, [6b] cellpenetrating agents, [7] peptidenucleic acids, [8] or inhibitors of protein-protein interactions. [9] The most common synthetic approach for preparing ACBC derivatives is via a [2 + 2] cycloaddition reaction, achieved in thermal, [10] photochemical, [11] metal-catalyzed [12] or multi-component [13] modes.…”

Direct Access to Unnatural Cyclobutane α-Amino Acids through Visible Light Catalyzed [2+2]-Cycloaddition

“…In this regard, cyclobutane amino acids (CBAAs) have evolved as an interesting class of derivatives for the development of new classes of strained, conformational restricted peptide mimetics for medical applications as well as diverse uses as synthetic building blocks or catalysts. − As a result, many efforts have been set to the synthesis of cyclobutane α-, − β-, − and γ-amino acids − (Scheme a). However, although some derivatives exhibit potent biological activities, − cyclobutane α-amino acids have recently received much less attention, which might be due to a lack of efficient, straightforward approaches for their preparation. − …”