Solid-phase synthesis of biaryl bicyclic peptides containing a 3-aryltyrosine or a 4-arylphenylalanine moiety.

A methodology for the solid-phase synthesis of biaryl bicyclic peptides containing a Phe-Phe, a Phe-Tyr or a Tyr-Tyr motif has been devised. This approach comprises two key steps. The first one involves the cyclization of a linear peptidyl resin containing the corresponding halo- and boronoamino acids via a microwave-assisted Suzuki-Miyaura cross coupling. This step is followed by the macrolactamization of the resulting biaryl monocyclic peptidyl resin leading to the formation of the expected biaryl bicyclic peptide. This study provides the first solid-phase synthesis of this type of bicyclic compounds being amenable to prepare a diversity of synthetic or natural biaryl bicyclic peptides.

Synthesis and Biological Evaluation of Ru(II) and Pt(II) Complexes Bearing Carboxyl Groups as Potential Anticancer Targeted Drugs.

The synthesis and characterization of Pt(II) (1 and 2) and Ru(II) arene (3 and 4) or polypyridine (5 and 6) complexes is described. With the aim of having a functional group to form bioconjugates, one uncoordinated carboxyl group has been introduced in all complexes. Some of the complexes were selected for their potential in photodynamic therapy (PDT). The molecular structures of complexes 2 and 5, as well as that of the sodium salt of the 4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine ligand (cptpy), were determined by X-ray diffraction. Different techniques were used to evaluate the binding capacity to model DNA molecules, and MTT cytotoxicity assays were performed against four cell lines. Compounds 3, 4, and 5 showed little tendency to bind to DNA and exhibited poor biological activity. Compound 2 behaves as bonded to DNA probably through a covalent interaction, although its cytotoxicity was very low. Compound 1 and possibly 6, both of which contain a cptpy ligand, were able to intercalate with DNA, but toxicity was not observed for 6. However, compound 1 was active in all cell lines tested. Clonogenic assays and apoptosis induction studies were also performed on the PC-3 line for 1. The photodynamic behavior for complexes 1, 5, and 6 indicated that their nuclease activity was enhanced after irradiation at λ = 447 nm. The cell viability was significantly reduced only in the case of 5. The different behavior in the absence or presence of light makes complex 5 a potential prodrug of interest in PDT. Molecular docking studies followed by molecular dynamics simulations for 1 and the counterpart without the carboxyl group confirmed the experimental data that pointed to an intercalation mechanism. The cytotoxicity of 1 and the potential of 5 in PDT make them good candidates for subsequent conjugation, through the carboxyl group, to "selected peptides" which could facilitate the selective vectorization of the complex toward receptors that are overexpressed in neoplastic cell lines.

Multivalent display of the antimicrobial peptides BP100 and BP143.

Carbohydrates are considered as promising templates for the display of multiple copies of antimicrobial peptides. Herein, we describe the design and synthesis of chimeric structures containing two or four copies of the antimicrobial peptides KKLFKKILKYL-NH(2) (BP100) and KKLfKKILKYL-NH(2) (BP143) attached to the carbohydrate template cyclodithioerythritol (cDTE) or α-D-galactopyranoside (Galp). The synthesis involved the preparation of the corresponding peptide aldehyde followed by coupling to an aminooxy-functionalized carbohydrate template. After purification, the multivalent display systems were obtained in high purities (90-98%) and in good yields (42-64%). These compounds were tested against plant and human pathogenic bacteria and screened for their cytotoxicity on eukaryotic cells. They showed lower MIC values than the parent peptides against the bacteria analyzed. In particular, the carbopeptides derived from cDTE and Galp, which contained two or four copies of BP100, respectively, were 2- to 8-fold more active than the monomeric peptide against the phytopathogenic bacteria. These results suggest that preassembling antimicrobial peptides to multimeric structures is not always associated with a significant improvement of the activity. In contrast, the carbopeptides synthesized were active against human red blood cells pointing out that peptide preassembly is critical for the hemolytic activity. Notably, peptide preassembly resulted in an enhanced bactericidal effect.

Solid-Phase Synthesis of Biaryl Cyclic Lipopeptides Derived from Arylomycins.

An efficient approach for the solid-phase synthesis of N-methylated tailed biaryl cyclic lipopeptides based on the structure of arylomycins was established. Each of these analogues incorporates an N-terminal linear lipopeptide attached to a biaryl cyclic tripeptide containing a Phe-Tyr, a Tyr-Tyr, or a His-Tyr linkage. This methodology first involved an intramolecular Suzuki-Miyaura arylation of a linear peptidyl resin incorporating the corresponding halogenated amino acid at the N-terminus and a boronotyrosine at the C-terminus. After N-methylation of the resulting biaryl cyclic peptidyl resin, the N-methylated lipopeptidyl tail was then assembled. The biaryl cyclic lipopeptides were purified and characterized.

A nucleus-directed bombesin derivative for targeted delivery of metallodrugs to cancer cells.

We have synthesized a set of bombesin derivatives with the aim of exploring their tumor targeting properties to deliver metal-based chemotherapeutics into cancer cells. Peptide QRLGNQWAVGHLL-NH2 (BN3) was selected based on its high internalization in gastrin-releasing peptide receptor (GRPR)-overexpressing PC-3 cells. Three metallopeptides were prepared by incorporating the terpyridine Pt(II) complex [PtCl(cptpy)]Cl (1) (cptpy = 4'-(4-carboxyphenyl)-2,2':6,2″-terpyridine) at the N-terminus of BN3 or at the NƐ- or Nα-amino group of an additional Lys residue (1-BN3, Lys-1-BN3 and 1-Lys-BN3, respectively). 1-Lys-BN3 displayed the best cytotoxic activity (IC50: 19.2 ±â€¯1.7 µM) and similar ability to intercalate into DNA than complex 1. Moreover, the polypyridine Ru(II) complex [Ru(bpy)2)(cmbpy)](PF6)2 (2) (bpy = 2,2'-bipyridine; cmbpy = 4-methyl-2,2'-bipyridine-4'-carboxylic acid), with proven activity as photosensitizer, was coupled to BN3 leading to metallopeptide 2-Lys-BN3. Upon photoactivation, 2-Lys-BN3 displayed 2.5-fold higher cytotoxicity against PC-3 cells (IC50: 7.6 ±â€¯1.0 µM) than complex 2. To enhance the accumulation of the drugs into the cell nucleus, the nuclear localization signal (NLS) PKKKRKV was incorporated at the N-terminus of BN3. NLS-BN3 displayed higher cellular internalization along with nuclear biodistribution. Accordingly, metallopeptides 1-NLS-BN3 and 2-NLS-BN3 showed increased cytotoxicity (IC50: 12.0 ±â€¯1.1 µM and 2.3 ±â€¯1.1 µM). Interestingly, the phototoxic index of 2-NLS-BN3 was 8-fold higher than that of complex 2. Next, the selectivity towards cancer cells was explored using 1BR3.G fibroblasts. Higher selectivity indexes were obtained for 1-NLS-BN3 and 2-NLS-BN3 than for the unconjugated complexes. These results prove NLS-BN3 effective for targeted delivery of metallodrugs to GRPR-overexpressing cells and for enhancing the cytotoxic efficacy of metal-based photosensitizers.

Antimicrobial peptides incorporating non-natural amino acids as agents for plant protection.

The control of plant pathogens is mainly based on copper compounds and antibiotics. However, the use of these compounds has some limitations. They have a high environmental impact and the use of antibiotics is not allowed in several countries. Moreover, resistance has been developed to these pathogens. The identification of new agents able to fight plant pathogenic bacteria and fungi will represent an alternative to currently used antibiotics or pesticides. Antimicrobial peptides are widely recognized as promising candidates, however naturally occurring sequences present drawbacks that limit their development. These include susceptibility to protease degradation and low bioavailability. To overcome these problems, research has focused on the introduction of unnatural amino acids into lead peptide sequences. In particular, we have improved the biological profile of antimicrobial peptides active against plant pathogenic bacteria and fungi by incorporating triazolyl, biaryl and D-amino acids into their sequence. These modifications and their influence on the biological activity are summarized.