Chemical Modification of Microcin J25 Reveals New Insights on the Stereospecific Requirements for Antimicrobial Activity.

In this study, microcin J25, a potent antimicrobial lasso peptide that acts on Gram-negative bacteria, was subjected to a harsh treatment with a base in order to interrogate its stability and mechanism of action and explore its structure-activity relationship. Despite the high stability reported for this lasso peptide, the chemical treatment led to the detection of a new product. Structural studies revealed that this product retained the lasso topology, but showed no antimicrobial activity due to the epimerization of a key residue for the activity.

A Lasso-Inspired Bicyclic Peptide: Synthesis, Structure and Properties.

The chemical synthesis of a bicycle inspired by the natural lasso peptide sungsanpin using a combination of solid-phase and in-solution chemistries is described. The bicyclic-derived topoisomer was designed by introducing a covalent linkage between the ring and the loop, which allowed the tying of these two parts of the peptide, rendering the bicyclic structure. Several structural techniques, such as MS fragmentation, ion-mobility and NMR spectroscopic analysis were used to characterize the bicycle.

Investigation of the Biosynthesis of the Lasso Peptide Chaxapeptin Using an E. coli-Based Production System.

Lasso peptides are natural products belonging to the family of ribosomally synthesized and posttranslationally modified peptides (RiPPs) and are defined by their unique topology. Even though lasso peptide biosynthetic gene clusters are found in many different kinds of bacteria, most of the hitherto studied lasso peptides were of proteobacterial or actinobacterial origin. Despite this, no E.

Lasso peptides: chemical approaches and structural elucidation.

The discovery and development of novel constrained peptides that combine the advantages of therapeutic proteins with those of small molecules has partially prompted the re-emergence of peptides as therapeutics. In this regard, lasso peptides are characterized by both the selectivity and potency of larger protein biologics but with no or low immunogenicity, and the stability and bioavailability of small molecules. Moreover, the diverse functionality of lasso peptides and their extraordinary stability against chemical, thermal and proteolytic degradation make them attractive candidates for drug discovery.

Synthesis of complex head-to-side-chain cyclodepsipeptides.

Cyclodepsipeptides are cyclic peptides in which at least one amide link on the backbone is replaced with an ester link. These natural products present a high structural diversity that corresponds to a broad range of biological activities. Therefore, they are very promising pharmaceutical candidates.

The road to the synthesis of "difficult peptides".

The last decade has witnessed a renaissance of peptides as drugs. This progress, together with advances in the structural behavior of peptides, has attracted the interest of the pharmaceutical industry in these molecules as potential APIs. In the past, major peptide-based drugs were inspired by sequences extracted from natural structures of low molecular weight.

A new quinoxaline-containing peptide induces apoptosis in cancer cells by autophagy modulation.

The synthesis of a new small library of quinoxaline-containing peptides is described. After cytotoxic evaluation in four human cancer cell lines, as well as detailed biological studies, it was found that the most active compound, RZ2, promotes the formation of acidic compartments, where it accumulates, blocking the progression of autophagy. Further disruption of the mitochondrial membrane potential and an increase in mitochondrial ROS was observed, causing cells to undergo apoptosis.

Single-molecule kinetics and footprinting of DNA bis-intercalation: the paradigmatic case of Thiocoraline.

DNA bis-intercalators are widely used in molecular biology with applications ranging from DNA imaging to anticancer pharmacology. Two fundamental aspects of these ligands are the lifetime of the bis-intercalated complexes and their sequence selectivity. Here, we perform single-molecule optical tweezers experiments with the peptide Thiocoraline showing, for the first time, that bis-intercalation is driven by a very slow off-rate that steeply decreases with applied force.

Semipermanent C-terminal carboxylic acid protecting group: application to solubilizing peptides and fragment condensation.

The 2-methoxy-4-methylsulfinylbenzyl alcohol (Mmsb-OH) safety-catch linker has been described as a useful tool to overcome two obstacles in peptide synthesis: the solubility and fragment condensation of peptides. The incorporation of the linker into an insoluble peptide target, thereby allowing the conjugation of a poly-Lys as a "solubilizing tag", notably enhanced the solubility of the peptide. The selective conditions that remove that linker favored its incorporation as a semipermanent C-terminal protecting group, thereby allowing fragment condensation of peptides.

2-Methoxy-4-methylsulfinylbenzyl: a backbone amide safety-catch protecting group for the synthesis and purification of difficult peptide sequences.

The use of 2-methoxy-4-methylsulfinylbenzyl (Mmsb) as a new backbone amide-protecting group that acts as a safety-catch structure is proposed. Mmsb, which is stable during the elongation of the sequence and trifluoroacetic acid-mediated cleavage from the resin, improves the synthetic process as well as the properties of the quasi-unprotected peptide. Mmsb offers the possibility of purifying and characterizing complex peptide sequences, and renders the target peptide after NH4 I/TFA treatment and subsequent ether precipitation to remove the cleaved Mmsb moiety.

Linear versus branched poly-lysine/arginine as polarity enhancer tags.

The design and synthesis of Lys- and Arg-containing peptides as solubilizing tags were studied to evaluate their influence on polarity. The relevance of spatial arrangement of polar groups, in α- or ε-amino positions, was confirmed by chromatographic analysis of a rational PolyLys-based synthesized structure. The most promising of the solubilizing tags here analyzed was conjugated to a commercial water-insoluble drug (indomethacin) as proof of concept.

Thioester Bonds of Thiocoraline Can Be Replaced with NMe-Amide Bridges without Affecting Its DNA-Binding Properties.

In the search for new drug candidates for DNA recognition, affinity and sequence selectivity are two of the most important features. NMe-azathiocoraline, a synthetic antitumor bisintercalator derived from the natural marine product thiocoraline, shows similar potency to the parent compound, as well as possessing enhanced stability. Analysis of the DNA-binding selectivity of NMe-azathiocoraline by DNase I footprinting using universal substrates with all 136 tetranucleotides and all possible symmetrical hexanucleotide sequences revealed that, although this ligand binds to all CpG steps with lower affinities than thiocoraline, it displays additional binding to AT-rich sites.

Stellatolides, a new cyclodepsipeptide family from the sponge Ecionemia acervus: isolation, solid-phase total synthesis, and full structural assignment of stellatolide A.

The marine environment is a rich source of metabolites with potential therapeutic properties and applications for humans. Here we describe the first isolation, solid-phase total synthesis, and full structural assignment of a new class of cyclodepsipeptides from the Madagascan sponge Ecionemia acervus that shows in vitro cytotoxic activities at submicromolar concentrations. Seven structures belonging to a new family of compounds, given the general name stellatolides, were characterized.

Rescuing biological activity from synthetic phakellistatin 19.

Phakellistatins is one of the families of Pro-rich cyclic peptides whose synthetic counterparts have revealed cytotoxicities that differ greatly from those displayed by their corresponding natural ones. This is also the case of the last member isolated from this family, phakellistatin19, an octacyclopeptide containing three Pro moieties and a high percentage of apolar residues. Exhaustive NMR studies on the synthetic and natural phakellistatin 19 have been performed in order to find a plausible explanation for this intriguing behavior.

The first total synthesis of the cyclodepsipeptide pipecolidepsin A.

Pipecolidepsin A is a head-to-side-chain cyclodepsipeptide isolated from the marine sponge Homophymia lamellosa. This compound shows relevant cytotoxic activity in three human tumour cell lines and has unique structural features, with an abundance of non-proteinogenic residues, including several intriguing amino acids. Although the moieties present in the structure show high synthetic difficulty, the cornerstone is constituted by the unprecedented and highly hindered γ-branched β-hydroxy-α-amino acid D-allo-(2R,3R,4R)-2-amino-3-hydroxy-4,5-dimethylhexanoic acid (AHDMHA) residue, placed at the branching ester position and surrounded by the four demanding residues L-(2S,3S,4R)-3,4-dimethylglutamine, (2R,3R,4S)-4,7-diamino-2,3-dihydroxy-7-oxoheptanoic acid, D-allo-Thr and L-pipecolic acid.

Orthogonal chemistry for the synthesis of thiocoraline-triostin hybrids. Exploring their structure-activity relationship.

The natural compounds triostin and thiocoraline are potent antitumor agents that act as DNA bisintercalators. From a pharmaceutical point of view, these compounds are highly attractive although they present a low pharmacokinetic profile, in part due to their low solubility. Synthetically, they represent a tour de force because no robust strategies have been developed to access a broad range of these bicyclic (depsi)peptides in a straightforward manner.

"Head-to-side-chain" cyclodepsipeptides of marine origin.

Since the late 1980s, a large number of depsipeptides that contain a new topography, referred to as "head-to-side-chain" cyclodepsipeptides, have been isolated and characterized. These peptides present a unique structural arrangement that comprises a macrocyclic region closed through an ester bond between the C-terminus and a β-hydroxyl group, and terminated with a polyketide moiety or a more simple branched aliphatic acid. This structural pattern, the presence of unique and complex residues, and relevant bioactivity are the main features shared by all the members of this new class of depsipeptides, which are reviewed herein.

Understanding acid lability of cysteine protecting groups.

Cys-disulfide bonds contribute to the stabilization of peptide and protein structures. The synthesis of these molecules requires a proper protection of Cys residues, which is crucial to prevent side-reactions and also to achieve the correct Cys connectivity. Here we undertook a mechanistic study of a set of well-known acid-labile Cys protecting groups, as well other new promising groups, in order to better understand the nature of their acid-lability.

Handles for Fmoc solid-phase synthesis of protected peptides.

Protected peptide fragments are valuable building blocks for the assembly of large peptide sequences through fragment condensation approaches, whereas protected peptides are typically synthesized for the preparation of amide-bridge cyclic peptides in solution. Efficient synthesis of both protected peptides and protected peptide fragments by solid-phase peptide synthesis methodology requires handles that attach the growing peptides to the polymeric support and can be cleaved under appropriate conditions, while maintaining intact the side-chain protecting groups. Here, we provide an overview of attachment methods described in the literature for the preparation of protected peptides using Fmoc/tBu chemistry, including the most commonly used acid-labile linkers along with the most recent and sophisticated.

Constella™(EU)-Linzess™(USA): the last milestone in the long journey of the peptide linaclotide and its implications for the future of peptide drugs.

Irritable bowel syndrome with constipation (IBS-C) and chronic idiopathic constipation (CIC) are highly prevalent gastrointestinal disorders associated with health, economical and social problems. Recently, after a long journey of preclinical studies and clinical trials, linaclotide, a first-in-class GC-C receptor peptide agonist, has received the approval in the USA and Europe for the treatment of IBS-C and CIC. This article provides an overview of clinical, economic and biological aspects of IBS-C and CIC and covers the current and emerging therapeutic agents for treating these conditions.

Eco-friendly combination of the immobilized PGA enzyme and the S-Phacm protecting group for the synthesis of Cys-containing peptides.

Enzyme-labile protecting groups have emerged as a green alternative to conventional protecting groups. These groups introduce a further orthogonal dimension and eco-friendliness into protection schemes for the synthesis of complex polyfunctional organic molecules. S-Phacm, a Cys-protecting group, can be easily removed by the action of a covalently immobilized PGA enzyme under very mild conditions.

Acid-labile Cys-protecting groups for the Fmoc/tBu strategy: filling the gap.

To address the existing gap in the current set of acid-labile Cys-protecting groups for the Fmoc/tBu strategy, diverse Fmoc-Cys(PG)-OH derivatives were prepared and incorporated into a model tripeptide to study their stability against TFA. S-Dpm proved to be compatible with the commonly used S-Trt group and was applied for the regioselecive construction of disulfide bonds.

Polymers and drug delivery systems.

In the treatment of health related dysfunctions, it is desirable that the drug reaches its site of action at a particular concentration and that this therapeutic dose range remains constant over a sufficiently long period of time to alter the process. However, the action of pharmaceutical agents is limited by various factors, including their degradation, their interaction with other cells, and their incapacity to penetrate tissues as a result of their chemical nature. For these reasons, new formulations are being studied to achieve a greater pharmacological response; among these, polymeric systems of drug carriers are of high interest.