Calculating Resin Functionalization in Solid-Phase Peptide Synthesis Using a Standardized Method based on Fmoc Determination

Immobilization of KR-12 on a Titanium Alloy Surface Using Linking Arms Improves Antimicrobial Activity and Supports Osteoblast Cytocompatibility

Implant-associated infections pose significant challenges due to bacterial resistance to antibiotics. Recent research highlights the potential of immobilizing antimicrobial peptides (AMPs) onto implants as an alternative to conventional antibiotics for the prevention of bacterial infection. While various AMP immobilization methodologies have been investigated, they lack responsiveness to biological cues. This study proposes an enzyme-responsive antimicrobial coating for orthopedic devices using KR-12, an AMP derived from Cathelicidin LL-37, coupled with the Human Elastin-Like Polypeptide (HELP) as a biomimetic and stimuli-responsive linker, while mimicking the extracellular matrix (ECM). During implantation, these customized interfaces encounter the innate immune response triggering elastase release, which degrades HELP biopolymers, enabling the controlled release of KR-12. After coupling KR-12 with HELP to titanium surfaces, the antimicrobial activity against four pathogenic bacterial strains (Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa) was assessed, revealing an inhibition ratio of bacterial adhesion and colonization exceeding 92% for all tested strains, compared with surfaces functionalized with KR-12 only. It is thought that the enhanced antimicrobial activity was due to the improved mobility of KR-12 when coupled with HELP. Furthermore, the prepared coatings boosted the adhesion and proliferation of human osteoblasts, confirming the cytocompatibility. These findings suggest the potential for smart coatings that combine the antimicrobial functions of AMPs with HELP's biological properties for use in a variety of settings, including medical devices.

Towards green, scalable peptide synthesis: leveraging DEG-crosslinked polystyrene resins to overcome hydrophobicity challenges

Diethylene glycol dimethacrylate (DEG)-crosslinked polystyrene (PS) resin offers a promising alternative to traditional divinyl benzene (DVB)-PS resin for solid-phase peptide synthesis (SPPS), particularly for challenging sequences with hydrophobic or bulky amino acids. DEG-PS resin's reduced hydrophobicity and enhanced flexibility improve synthesis efficiency, yielding peptides up to 28 residues with higher purities and yields compared to DVB-PS. In various syntheses, DEG-PS outperformed DVB-PS resin, with higher purities and yields for challenging peptides such as ABC analogue (73.2%, 58.3% vs. 72.5%, 46.3%) and Thymosin (58.4%, 48.6% vs. 54.0%, 39.2%). In addition, DEG-PS resin effectively suppressed common side reactions, such as dipeptide formation, typically encountered with Wang PS-based resins. Incorporating green chemistry principles, DEG-PS enabled the synthesis of complex peptides with satisfactory results using environmentally friendly solvents and reagents. Three challenging peptides; β (34-42), Jung and Redemann (JR), and ABRF 1992 - were synthesized on DEG-PS resin, achieving purities of 41.4%, 41.0%, and 68.0%, and yields of 50.5%, 52.6%, and 56.2%, respectively. These findings highlight DEG-PS resin's advantages for classical, green, and automated SPPS, offering superior performance and scalability for industrial applications.

Abiotic Foldamer Quaternary Structures

Abiotic aromatic foldamer sequences have been previously shown to fold in helix-turn-helix motifs in organic solvents. Using simple computational tools, a new helix-turn-helix motif was designed that bears additional hydrogen bond donor OH groups to promote its aggregation into a genuine, trimeric, abiotic quaternary structure. This sequence was synthesized and its self-assembly in solution was investigated by Nuclear Magnetic Resonance (NMR), Circular Dichroism (CD) and Molecular Dynamics (MD) simulations. The existence of two stable discrete aggregates was evidenced, one assigned to the initially designed trimer, the other to a dimer including multiple water molecules. The two species may be quantitatively interconverted upon changing the water content of the solution or the temperature. These results represent important steps in the design of protein-like abiotic architectures.

The Influence of Disulfide, Thioacetal and Lanthionine-Bridges on the Conformation of a Macrocyclic Peptide

Cyclisation of peptides by forming thioether (lanthionine), disulfide (cystine) or methylene thioacetal bridges between side chains is established as an important tool to stabilise a given structure, enhance metabolic stability and optimise both potency and selectivity. However, a systematic comparative study of the effects of differing bridging modalities on peptide conformation has not previously been carried out. In this paper, we have used the NMR deconvolution algorithm, NAMFIS, to determine the conformational ensembles, in aqueous solution, of three cyclic analogues of angiotensin(1-7), incorporating either disulfide, or non-reducible thioether or methylene thioacetal bridges. We demonstrate that the major solution conformations are conserved between the different bridged peptides, but the distribution of conformations differs appreciably. This suggests that subtle differences in ring size and bridging structure can be exploited to fine-tune the conformational properties of cyclic peptides, which may modulate their bioactivities.

Domain Swapping in Abiotic Foldamers

Foldamer sequences that adopt tertiary helix-turn-helix folds mediated by helix-helix hydrogen bonding in organic solvents have been previously reported. In an attempt to create genuine abiotic quaternary structures, i.e. assemblies of tertiary structures, new sequences were prepared that possess additional hydrogen bond donors at positions that may promote an association between the tertiary folds. However, a solid state structure and extensive solution state investigations by Nuclear Magnetic Resonance (NMR) and Circular Dichroism (CD) show that, instead of forming a quaternary structure, the tertiary folds assemble into stable domain-swapped dimer motifs. Domain swapping entails a complete reorganization of the arrays of hydrogen bonds and changes in relative helix orientation and handedness that can all be rationalized.

Development of New Leishmanicidal Compounds via Bioconjugation of Antimicrobial Peptides and Antileishmanial Guanidines

Leishmaniasis refers to a collection of diseases caused by protozoa from the Leishmania genus. These diseases, along with other parasitic afflictions, pose a significant public health issue, particularly given the escalating number of at-risk patients. This group includes immunocompromised individuals and those residing in impoverished conditions. The treatment of leishmaniasis is crucial, particularly in light of the mortality rate associated with nontreatment, which stands at 20-30,000 deaths per year globally. However, the therapeutic options currently available are limited, often ineffective, and potentially toxic. Consequently, the pursuit of new therapeutic alternatives is warranted. This study aims to design, synthesize, and evaluate the leishmanicidal activity of antimicrobial peptides functionalized with guanidine compounds and identify those with enhanced potency and selectivity against the parasite. Accordingly, three bioconjugates were obtained by using the solid-phase peptide synthesis protocol. Each proved to be more potent against intracellular amastigotes than their respective peptide or guanidine compounds alone and demonstrated higher selectivity to the parasites than to the host cells. Thus, the conjugation strategy employed with these compounds effectively contributes to the development of new molecules with leishmanicidal activity.

On the Utility of Chemical Strategies to Improve Peptide Gut Stability

Inherent susceptibility of peptides to enzymatic degradation in the gastrointestinal tract is a key bottleneck in oral peptide drug development. Here, we present a systematic analysis of (i) the gut stability of disulfide-rich peptide scaffolds, orally administered peptide therapeutics, and well-known neuropeptides and (ii) medicinal chemistry strategies to improve peptide gut stability. Among a broad range of studied peptides, cyclotides were the only scaffold class to resist gastrointestinal degradation, even when grafted with non-native sequences. Backbone cyclization, a frequently applied strategy, failed to improve stability in intestinal fluid, but several site-specific alterations proved efficient. This work furthermore highlights the importance of standardized gut stability test conditions and suggests defined protocols to facilitate cross-study comparison. Together, our results provide a comparative overview and framework for the chemical engineering of gut-stable peptides, which should be valuable for the development of orally administered peptide therapeutics and molecular probes targeting receptors within the gastrointestinal tract.

The breaking beads approach for photocleavage from solid support

Photocleavage from polystyrene beads is a pivotal reaction for solid phase synthesis that relies on photolabile linkers. Photocleavage from intact porous polystyrene beads is not optimal because light cannot penetrate into the beads and the surface area exposed to irradiation is limited. Thus, hazardous, technically challenging and expensive setups are used for photocleavage from intact beads. We developed a new concept in which grinding the beads during or prior to irradiation is employed as an essential part of the photocleavage process. By grinding the beads we are exposing more surface area to the light source, hence, photocleavage can be performed even using a simple benchtop LED setup. This approach proved very efficient for photocleavage of various model compounds including fully protected oligosaccharides.