Solid-Phase Peptide Macrocyclization and Multifunctionalization via Dipyrrin Construction

Peptide Multifunctionalization via Modular Construction of Trans-AB2C Porphyrin on Resin

Peptide multifunctionalization is a crucial technique to develop peptide-based agents for various purposes. Porphyrin-peptide conjugates are a class of popular multifunctional peptides renowned for their multifunctional and multimodal properties. However, the tedious synthetic works for porphyrin building blocks are involved in most previous studies. In this work, a modular solid-phase synthetic approach is reported to construct trans-AB2C porphyrin on peptide chains without presynthesized porphyrin building blocks. The products from this approach, which inherit both functionalities from the porphyrins and the modules employed for constructing porphyrins, show potential in biomedical and biomaterial applications. Furthermore, by extending this synthetic approach, the first example of "resin-to-resin" reaction is reported to link two peptides together along the construction of porphyrin motifs to give porphyrin-peptide conjugates with two different peptide chains.

Facile Peptide Macrocyclization and Multifunctionalization via Cyclen Installation

Cyclen-peptide bioconjugates are usually prepared in multiple steps that require individual preparation and purification of the cyclic peptide and hydrophilic cyclen derivatives. An efficient strategy is discovered for peptide cyclization and functionalization toward lanthanide probe via three components intermolecular crosslinking on solid-phase peptide synthesis with high conversion yield. Multifunctionality can be conferred by introducing different modular parts or/and metal ions on the cyclen-embedded cyclopeptide. As a proof-of-concept, a luminescent Eu3+ complex and a Gd3+-based contrasting agent for in vitro optical imaging and in vivo magnetic resonance imaging, respectively, are demonstrated through utilizing this preparation of cyclen-embedded cyclic arginylglycylaspartic acid (RGD) peptide.

A fluorescent electrophile for CLIPS: self indicating TrkB binders

Combination of cysteine-containing peptides with electrophiles provides efficient access to cyclo-organopeptides. However, there are no routes to intrinsically fluorescent cyclo-organopeptides containing robust, brilliant fluorophores emitting at wavelengths longer than cellular autofluorescence. We show such fluorescent cyclo-organopeptides can be made via SNAr reactions of cysteine-containing peptides with a BODIPY system. Seven compounds of this type were prepared to test as probes; six contained peptide sequences corresponding to loop regions in brain-derived neurotrophic factor and neurotrophic factor 4 (BDNF and NT-4) which bind tropomyocin receptor kinase B (TrkB). Cellular assays in serum-free media indicated two of the six key compounds induced survival of HEK293 cells stably transfected with TrkB whereas a control did not. The two compounds inducing cell survival bound TrkB on those cells (Kd ∼40 and 47 nM), illustrating how intrinsically fluorescent cyclo-organopeptides can be assayed for quantifiable binding to surface receptors in cell membrane environments.

5,10,15,20-Tetrakis(pentafluorophenyl)porphyrin as a Functional Platform for Peptide Stapling and Multicyclisation

Polyfluorinated aromatic reagents readily react with thiolates via nucleophilic aromatic substitution (SN Ar) and provide excellent scaffolds for peptide cyclisation. Here we report a robust and versatile platform for peptide stapling and multicyclisation templated by 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, opening the door to the next generation of functional scaffolds for 3D peptide architectures. We demonstrate that stapling and multicyclisation occurs with a range of non-protected peptides under peptide-compatible conditions, exhibiting chemoselectivity and wide-applicability. Peptides containing two cysteine residues are readily stapled, and the remaining perfluoroaryl groups permit the introduction of a second peptide in a modular fashion to access bicyclic peptides. Similarly, peptides with more than two cysteine residues can afford multicyclic products containing up to three peptide 'loops'. Finally, we demonstrate that a porphyrin-templated stapled peptide containing the Skin Penetrating and Cell Entering (SPACE) peptide affords a skin cell penetrating conjugate with intrinsic fluorescence.

Modulating Secondary Structure Motifs Through Photo-Labile Peptide Staples

Peptide-protein interactions (PPIs) are facilitated by the well-defined three-dimensional structure of bioactive peptides, interesting compounds for the development of new therapeutic agents. Their secondary structure and thus their propensity to engage in PPIs can be influenced by the introduction of peptide staples on the side chains. In particular, light-controlled staples based on azobenzene photoswitches and their structural influence on helical peptides have been studied extensively. In contrast, photolabile staples bearing photocages as a structural key motif, have mainly been used to block supramolecular interactions. Their influence on the secondary structure of the target peptide is under-investigated. Thus, in this study we use a combination of spectroscopic techniques and in silico simulations to systematically study a series of helical peptides with varying length of the photo-labile staple to obtain a detailed insight into the structure-property relationship in such photoresponsive biomolecules.

Differential Peptide Multi-Macrocyclizations at the Surface of a Helical Foldamer Template

Hybrid sequences comprising a peptide with several Cys residues and an aromatic foldamer helix with several chloroacetamide functions at its surface were synthesized. Such products may in principle form numerous macromulticyclic thioether products by intramolecularly combining all Cys residues and all chloroacetamide functions. However, we show that the reactive sites on the structurally defined helix can be placed at such locations that the peptide selectively stitches itself to form a series of different macrocycles within mostly one preferred product. Reactions were monitored by HPLC and products with two, three or four macrocycles were identified using LC-MS and NMR. The series of selective macrocyclizations define a sort of reaction trail where reaction sites otherwise identical are involved successively because of their precise positioning in space. The trails can be predicted to a large extent based on structural considerations and the assumption that smaller macrocycles form faster.

Biocompatible and Selective Generation of Bicyclic Peptides

Bicyclic peptides possess superior properties for drug discovery; however, their chemical synthesis is not straightforward and often neither biocompatible nor fully orthogonal to all canonical amino acids. The selective reaction between 1,2-aminothiols and 2,6-dicyanopyridine allows direct access to complex bicyclic peptides in high yield. The process can be fully automated using standard solid-phase peptide synthesis. Bicyclization occurs in water at physiological pH within minutes and without the need for a catalyst. The use of various linkers allows tailored bicyclic peptides with qualities such as plasma stability, conformational preorganization, and high target affinity. We demonstrate this for a bicyclic inhibitor of the Zika virus protease NS2B-NS3 as well as for bicyclic versions of the α-helical antimicrobial peptide aurein 1.2.

Versatile Synthesis of Multivalent Porphyrin-Peptide Conjugates by Direct Porphyrin Construction on Resin

Multifunctional porphyrin-peptide conjugates with different propensities for self-assembly into various supramolecular nanoarchitectures play important roles in advanced materials and biomedical research. However, preparing prefunctionalized core porphyrins by traditional low-yielding statistical synthesis and purifying them after peptide ligation through many rounds of HPLC purification is tedious and unsustainable. Herein, we report a novel integrated solid-phase synthetic protocol for the construction of porphyrin moieties from simple aldehydes and dipyrromethanes on resin-bound peptides directly to form mono-, cis/trans-di-, and trivalent porphyrin-peptide conjugates in a highly efficient and controllable manner; moreover, only single final-stage HPLC purification of the products is needed. This efficient strategy enables the rapid, greener, and substrate-controlled diversity-oriented synthesis of multivalent porphyrin-(long) peptide conjugate libraries for multifarious biological and materials applications.