Synthetic approaches to nucleopeptides containing all four nucleobases, and nucleic acid-binding studies on a mixed-sequence nucleo-oligolysine

Willardiine and Its Synthetic Analogues: Biological Aspects and Implications in Peptide Chemistry of This Nucleobase Amino Acid

Willardiine is a nonprotein amino acid containing uracil, and thus classified as nucleobase amino acid or nucleoamino acid, that together with isowillardiine forms the family of uracilylalanines isolated more than six decades ago in higher plants. Willardiine acts as a partial agonist of ionotropic glutamate receptors and more in particular it agonizes the non-N-methyl-D-aspartate (non-NMDA) receptors of L-glutamate: ie. the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) and kainate receptors. Several analogues and derivatives of willardiine have been synthesised in the laboratory in the last decades and these compounds show different binding affinities for the non-NMDA receptors. More in detail, the willardiine analogues have been employed not only in the investigation of the structure of AMPA and kainate receptors, but also to evaluate the effects of receptor activation in the various brain regions. Remarkably, there are a number of neurological diseases determined by alterations in glutamate signaling, and thus, ligands for AMPA and kainate receptors deserve attention as potential neurodrugs. In fact, similar to willardiine its analogues often act as agonists of AMPA and kainate receptors. A particular importance should be recognized to willardiine and its thymine-based analogue AlaT also in the peptide chemistry field. In fact, besides the naturally-occurring short nucleopeptides isolated from plant sources, there are different examples in which this class of nucleoamino acids was investigated for nucleopeptide development. The applications are various ranging from the realization of nucleopeptide/DNA chimeras for diagnostic applications, and nucleoamino acid derivatization of proteins for facilitating protein-nucleic acid interaction, to nucleopeptide-nucleopeptide molecular recognition for nanotechnological applications. All the above aspects on both chemistry and biotechnological applications of willardine/willardine-analogues and nucleopeptide will be reviewed in this work.

carba-Nucleopeptides (cNPs): A Biopharmaceutical Modality Formed through Aqueous Rhodamine B Photoredox Catalysis

Exchanging the ribose backbone of an oligonucleotide for a peptide can enhance its physiologic stability and nucleic acid binding affinity. Ordinarily, the eneamino nitrogen atom of a nucleobase is fused to the side chain of a polypeptide through a new C-N bond. The discovery of C-C linked nucleobases in the human transcriptome reveals new opportunities for engineering nucleopeptides that replace the traditional C-N bond with a non-classical C-C bond, liberating a captive nitrogen atom and promoting new hydrogen bonding and π-stacking interactions. We report the first late-stage synthesis of C-C linked carba-nucleopeptides (cNPs) using aqueous Rhodamine B photoredox catalysis. We prepare brand-new cNPs in batch, in parallel, and in flow using three long-wavelength photochemical setups. We detail the mechanism of our reaction by experimental and computational studies and highlight the essential role of diisopropylethylamine as a bifurcated two-electron reductant.

Cell Membrane-Coated Oil in Water Nano-Emulsions as Biomimetic Nanocarriers for Lipophilic Compounds Conveyance

Recently, we developed ultra-stable oil in water nano-emulsions (O/W NEs), able to carry both internal and external cargos (Somes), such as lipophilic compounds and hydrophilic coatings, respectively, that we call here NEsoSomes. O/W NEs are an excellent bioengineering tool for drug and molecules delivery, due to their ability to dissolve a large number of hydrophobic compounds and protect them from hydrolysis and degradation under biological conditions. At present, no report is available on the combination of cell membrane coatings with such nanocarriers, probably due to their typical instability feature. Since then, we have reported, for the first time, a new cell membrane (CM)-coated nanomaterial composed of membranes extracted from glioblastoma cancer cells (U87-MG) deposited on NEsoSomes, through a liquid-liquid interface method, to produce highly controllable membrane caked nano-capsules, namely CM-NEsoSomes. CM-NEsoSomes were physically characterized by dynamic light scattering (DLS) over time and their correct morphology was analyzed by confocal and transmission electron microscopy (TEM) microscopy. Moreover, CM-NEsoSomes biocompatibility was tested on the healthy model cell line, performing cell cytotoxicity and uptake assay, showing nanocarriers uptake by cells with no induced cytotoxicity.

From Prebiotic Chemistry to Supramolecular Biomedical Materials: Exploring the Properties of Self-Assembling Nucleobase-Containing Peptides

Peptides and their synthetic analogs are a class of molecules with enormous relevance as therapeutics for their ability to interact with biomacromolecules like nucleic acids and proteins, potentially interfering with biological pathways often involved in the onset and progression of pathologies of high social impact. Nucleobase-bearing peptides (nucleopeptides) and pseudopeptides (PNAs) offer further interesting possibilities related to their nucleobase-decorated nature for diagnostic and therapeutic applications, thanks to their reported ability to target complementary DNA and RNA strands. In addition, these chimeric compounds are endowed with intriguing self-assembling properties, which are at the heart of their investigation as self-replicating materials in prebiotic chemistry, as well as their application as constituents of innovative drug delivery systems and, more generally, as novel nanomaterials to be employed in biomedicine. Herein we describe the properties of nucleopeptides, PNAs and related supramolecular systems, and summarize some of the most relevant applications of these systems.

Nucleoside Analogs and Nucleoside Precursors as Drugs in the Fight against SARS-CoV-2 and Other Coronaviruses

Coronaviruses (CoVs) are positive-sense RNA enveloped viruses, members of the family Coronaviridae, that cause infections in a broad range of mammals including humans. Several CoV species lead to mild upper respiratory infections typically associated with common colds. However, three human CoV (HCoV) species: Severe Acute Respiratory Syndrome (SARS)-CoV-1, Middle East Respiratory Syndrome (MERS)-CoV, and SARS-CoV-2, are responsible for severe respiratory diseases at the origin of two recent epidemics (SARS and MERS), and of the current COronaVIrus Disease 19 (COVID-19), respectively. The easily transmissible SARS-CoV-2, emerging at the end of 2019 in China, spread rapidly worldwide, leading the World Health Organization (WHO) to declare COVID-19 a pandemic. While the world waits for mass vaccination, there is an urgent need for effective drugs as short-term weapons to combat the SARS-CoV-2 infection. In this context, the drug repurposing approach is a strategy able to guarantee positive results rapidly. In this regard, it is well known that several nucleoside-mimicking analogs and nucleoside precursors may inhibit the growth of viruses providing effective therapies for several viral diseases, including HCoV infections. Therefore, this review will focus on synthetic nucleosides and nucleoside precursors active against different HCoV species, paying great attention to SARS-CoV-2. This work covers progress made in anti-CoV therapy with nucleoside derivatives and provides insight into their main mechanisms of action.

Discovery of Nucleic Acid Binding Molecules from Combinatorial Biohybrid Nucleobase Peptide Libraries

Nature has three biopolymers: oligonucleotides, polypeptides, and oligosaccharides. Each biopolymer has independent functions, but when needed, they form mixed assemblies for higher-order purposes, as in the case of ribosomal protein synthesis. Rather than forming large complexes to coordinate the role of different biopolymers, we dovetail protein amino acids and nucleobases into a single low molecular weight precision polyamide polymer. We established efficient chemical synthesis and de novo sequencing procedures and prepared combinatorial libraries with up to 100 million biohybrid molecules. This biohybrid material has a higher bulk affinity to oligonucleotides than peptides composed exclusively of canonical amino acids. Using affinity selection mass spectrometry, we discovered variants with a high affinity for pre-microRNA hairpins. Our platform points toward the development of high throughput discovery of sequence defined polymers with designer properties, such as oligonucleotide binding.

Nucleobase morpholino β amino acids as molecular chimeras for the preparation of photoluminescent materials from ribonucleosides

Bioinspired smart materials represent a tremendously growing research field and the obtainment of new building blocks is at the molecular basis of this technology progress. In this work, colloidal materials have been prepared in few steps starting from ribonucleosides. Nucleobase morpholino β-amino acids are the chimera key intermediates allowing Phe-Phe dipeptides' functionalization with adenine and thymine. The obtained compounds self-aggregate showing enhanced photoluminescent features, such as deep blue fluorescence and phosphorescence emissions.

Synthesis, Antiproliferative Activity, and DNA Binding Studies of Nucleoamino Acid-Containing Pt(II) Complexes

We here report our studies on the reaction with the platinum(II) ion of a nucleoamino acid constituted by the l-2,3-diaminopropanoic acid linked to the thymine nucleobase through a methylenecarbonyl linker. The obtained new platinum complexes, characterized by spectroscopic and mass spectrometric techniques, were envisaged to exploit synergistic effects due to the presence of both the platinum center and the nucleoamino acid moiety. The latter can be potentially useful to protect the complexes from early deactivation, as well as to facilitate their cell internalization. The biological activity of the complexes in terms of antiproliferative effects was evaluated in vitro on different cancer cell lines and healthy cells, showing the best results on human cervical adenocarcinoma (HeLa) cells along with good selectivity for cancer over normal cells. In contrast, the metal-free nucleoamino acid did not show any cytotoxicity on both normal and cancer cell lines. Finally, the ability of the novel Pt(II) complexes to bind various DNA model systems was investigated by circular dichroism (CD) spectroscopy and polyacrylamide gel electrophoresis analyses proving that the newly obtained compounds can potentially target DNA, similarly to other well-known anticancer Pt complexes, with a peculiar G-quadruplex vs. duplex selectivity.

Biological macromolecule binding and anticancer activity of synthetic alkyne-containing L-phenylalanine derivatives

Herein, we described the synthesis of two L-phenylalanines α-derivatized with a terminal alkyne moiety whose structures differed by phenyl ring halogen substitution (two o-Cl in 1 vs. one p-Br in 2) and investigated their effect on biological macromolecules and living cells. We explored their interaction with quadruplex DNA (G4 DNA), using tel₂₆ and c-myc as models, and bovine serum albumin (BSA). By CD spectroscopy, we found that 1 caused minor tel26 secondary structure changes, leading also to a slight thermal stabilization of this hybrid antiparallel/parallel G4 structure, while the c-myc parallel topology remained essentially unchanged upon 1 binding. Other CD evidences showed the ability of 1 to bind BSA, while molecular docking studies suggested that the same molecule could be housed into the hydrophobic cavity between sub-domains IIA, IIB, and IIIA of the protein. Furthermore, preliminary aggregation studies, based on concentration-dependent spectroscopic experiments, suggested the ability of 1 to aggregate forming noncovalent polymeric systems in aqueous solution. Differently from 1, the bromine-modified compound was able to bind Cu(II) ion, likely with the formation of a CuL₂ complex, as found by UV spectroscopy. Finally, cell tests excluded any cytotoxic effect of both compounds toward normal cells, but showed slight antiproliferative effects of 2 on PC3 cancerous cells at 24 h, and of 1 on both T98G and MDA-MB-231 cancer cells at 48 h.

Synthesis and nucleic acid binding evaluation of a thyminyl l-diaminobutanoic acid-based nucleopeptide

Herein we present the synthesis of a l-diaminobutanoic acid (DABA)-based nucleopeptide (3), with an oligocationic backbone, realized by solid phase peptide synthesis using thymine-bearing DABA moieties alternating in the sequence with free ones. CD studies evidenced the ability of this oligothymine nucleopeptide, well soluble in aqueous solution, to alter the secondary structure particularly of complementary RNA (poly rA vs poly rU) and inosine-rich RNAs, like poly rI and poly rIC, and showed its preference in binding double vs single-stranded DNAs. Furthermore, ESI mass spectrometry revealed that 3 bound also G-quadruplex (G4) DNAs, with either parallel or antiparallel topologies (adopted in our experimental conditions by c-myc and tel₂₂, respectively). However, it caused detectable changes only in the CD of c-myc (whose parallel G4 structure was also thermally stabilized by ~3 °C), while leaving unaltered the antiparallel structure of tel₂₂. Interestingly, CD and UV analyses suggested that 3 induced a hybrid mixed parallel/antiparallel G4 DNA structure in a random-coil tel₂₂ DNA obtained under salt-free buffer conditions. Titration of the random-coil telomeric DNA with 3 gave quantitative information on the stoichiometry of the obtained complex. Overall, the findings of this work suggest that DABA-based nucleopeptides are synthetic nucleic acid analogues potentially useful in antigene and antisense strategies. Nevertheless, the hexathymine DABA-nucleopeptide shows an interesting behaviour as molecular tool per se thanks to its efficacy in provoking G4 induction in random coil G-rich DNA, as well as for the possibility to bind and stabilize c-myc oncogene in a G4 structure.

Prebiotic Peptides: Molecular Hubs in the Origin of Life

The fundamental roles that peptides and proteins play in today's biology makes it almost indisputable that peptides were key players in the origin of life. Insofar as it is appropriate to extrapolate back from extant biology to the prebiotic world, one must acknowledge the critical importance that interconnected molecular networks, likely with peptides as key components, would have played in life's origin. In this review, we summarize chemical processes involving peptides that could have contributed to early chemical evolution, with an emphasis on molecular interactions between peptides and other classes of organic molecules. We first summarize mechanisms by which amino acids and similar building blocks could have been produced and elaborated into proto-peptides. Next, non-covalent interactions of peptides with other peptides as well as with nucleic acids, lipids, carbohydrates, metal ions, and aromatic molecules are discussed in relation to the possible roles of such interactions in chemical evolution of structure and function. Finally, we describe research involving structural alternatives to peptides and covalent adducts between amino acids/peptides and other classes of molecules. We propose that ample future breakthroughs in origin-of-life chemistry will stem from investigations of interconnected chemical systems in which synergistic interactions between different classes of molecules emerge.

Synthesis, DNA binding studies, and antiproliferative activity of novel Pt(II)-complexes with an L-alanyl-based ligand

An artificial alanine-based amino acid {(S)-2-amino-3-[4-propyl-3-(thiophen-2-yl)-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl]propanoic acid, here named TioxAla}, bearing a substituted triazolyl-thione group on the side chain and able to bind RNA biomedical targets, was here chosen as a valuable scaffold for the synthesis of new platinum complexes with potential dual action owing to the concomitant presence of the metal centre and the amino acid moiety. Three new platinum complexes, obtained from the reaction of TioxAla with K₂PtCl₄, were characterized by mass spectrometry, nuclear magnetic resonance and UV-vis spectroscopy: one compound (Pt1, bis-{(S)-2-amino-3-[4-propyl-3-(thiophen-2-yl)-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl]propanoate-O,S} platinum(II)) consisted of two amino acid units coordinating the Pt(II) ion; the other two, Pt2 [potassium dichloro-{(S)-2-amino-3-[4-propyl-3-(thiophen-2-yl)-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl]propanoate (O,S)} platinum(II)] and Pt3 [potassium dichloro-{(S)-2-amino-3-[4-propyl-3-(thiophen-2-yl)-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl]propanoate (O,N)} platinum(II)], were isomers bearing one TioxAla unit, and two chlorides as Pt-ligands. Pt coordination involved preferentially the amino, carboxylic and thione functions of TioxAla. By preliminary antiproliferative assays, a moderate cytotoxic activity on cancer cells was observed only for Pt2 and Pt3, while no anticancer activity was found for both the chloride-free complex (Pt1) and TioxAla. This cytotoxicity, however lower than that of cisplatin, well correlated with the marked ability, here found only for Pt2 and Pt3 complexes, to bind DNA sequences either in random coil or in structured forms (duplex and G-quadruplex), as verified by spectroscopic and spectrometric analysis.

Benzodifurans for biomedical applications: BZ4, a selective anti-proliferative and anti-amyloid lead compound

AIM

Our goal is to evaluate benzodifuran-based scaffolds for biomedical applications.

METHODOLOGY

We here explored the anticancer and anti-amyloid activities of a novel compound (BZ4) in comparison with other known benzodifuran analogs, previously studied in our group, and we have explored its ability to interact with different DNA model systems.

RESULTS

BZ4 shows antiproliferative activity on different cancer cells; does not affect noncancerous control cells and alters the aggregation properties of β-amyloid, as ascertained by circular dichroism, fluorescence spectroscopy and scanning electron microscopy analysis. An overall, qualitative picture on the mechanistic aspects related to the biological activities is discussed in light of the dynamic light scattering, UV, circular dichroism and fluorescence data, as well as of the metal ion-binding properties of BZ4.

Discovery of a novel small molecular peptide that disrupts helix 34 of bacterial ribosomal RNA

Despite the advances in modern medicine, antibiotic resistance is a persistent and growing threat to the world. Thus, the discovery and development of novel antibiotics have become crucial to combat multi-drug resistant pathogens. The goal of our research is to discover a small molecular peptide that can disrupt the synthesis of new ribosomes. Using the phage display technique, we have discovered a 7-mer peptide that binds to the second strand of 16S h34 RNA with a dissociation constant in the low micromolar range. Binding of the peptide alters RNA structure and inhibits the binding of the ribosomal RNA small subunit methyltransferase C (RsmC) enzyme that methylates the exocyclic amine of G1207. The addition of this peptide also increases the lag phase of bacterial growth. Introduction of chemical modifications to increase the binding affinity of the peptide to RNA, its uptake and stability can further improve the efficacy of the peptide as an antibiotic agent against pathogenic bacteria.

Discovery of a novel heptapeptide that disrupts RNA–RNA and RNA–protein interactions in bacterial ribosome.

Novel insights into nucleoamino acids: biomolecular recognition and aggregation studies of a thymine-conjugated L-phenyl alanine

This article deals with the synthesis in solid phase and characterization of a nucleoamino amide, based on a phenylalaninamide moiety which was N-conjugated to a thymine nucleobase. In analogy to the natural nucleobase-amino acid conjugates, endowed with a wide range of biological properties, the nucleoamino amide interacts with single-stranded nucleic acids as verified in DNA- and RNA-binding assays conducted by CD and UV spectroscopies. These technologies were used to show also that this conjugate binds serum proteins altering significantly their secondary structure, as evidenced by CD and UV using BSA as a model. The biomolecular recognition seems to rely on the ability of the novel compound to bind aromatic and heteroaromatic moieties in protein and nucleic acids, not hindered by its propensity to self-assemble in aqueous solution, behavior suggested by dynamic light scattering (DLS) and CD spectroscopy in concentration- and temperature-dependent experiments. Finally, the high stability in human serum concurs to define the picture of the nucleoamino amide: this enzymatically stable drug candidate could interfere with protein and single-stranded nucleic acid-driven biological processes, particularly those associated with mRNA poly(A) tail, and its self-assembling nature, in analogy to other L-Phe-based systems, discloses new scenarios in drug delivery technology.

DNA- and RNA-binding ability of oligoDapT, a nucleobase-decorated peptide, for biomedical applications

Background

Nucleobase-bearing peptides and their interaction with DNA and RNA are an important topic in the development of therapeutic approaches. On one hand, they are highly effective for modulating the nucleic-acid-based biological processes. On the other hand, they permit to overcome some of the main factors limiting the therapeutic efficacy of natural oligonucleotides, such as their rapid degradation by nucleases.

Methods and results

This article describes the synthesis and characterization of a novel thymine-bearing nucleoamino acid based on the l-diaminopropionic acid (l-Dap) and its solid phase oligomerization to α-peptides (oligoDapT), characterized using mass spectrometry, spectroscopic techniques, and scanning electron microscopy (SEM) analysis. The interaction of the obtained nucleopeptide with DNA and RNA model systems as both single strands (dA₁₂, rA₁₂, and poly(rA)) and duplex structures (dA₁₂/dT₁₂ and poly(rA)/poly(rU)) was investigated by means of circular dichroism (CD) and ultraviolet (UV) experiments. From the analysis of our data, a clear ability of the nucleopeptide to bind nucleic acids emerged, with oligoDapT being able to form stable complexes with both unpaired and double-stranded DNA and RNA. In particular, dramatic changes in the dA₁₂/dT₁₂ and poly(rA)/poly(rU) structures were observed as a consequence of the nucleopeptide binding. CD titrations revealed that multiple peptide units bound all the examined nucleic acid targets, with T_Ldap/A or T_Ldap/A:T(U) ratios >4 in case of oligoDapT/DNA and ~2 in oligoDapT/RNA complexes.

Conclusion

Our findings seem to indicate that Dap-based nucleopeptides are interesting nucleic acid binding-tools to be further explored with the aim to efficiently modulate DNA- and RNA-based biological processes.

Synthesis of O-Amino Sugars and Nucleosides

Nucleic acids and carbohydrates are essential biomolecules involved in numerous biological and pathological processes. Development of multifunctional building blocks based on nucleosides and sugars is in high demand for the generation of novel oligonucleotide mimics and glycoconjugates for biomedical applications. Recently, aminooxyl-functionalized compounds have attracted increasing research interest because of their easy derivatization through oxime ligation or N-oxyamide formation reactions. Various biological applications have been reported for O-amino carbohydrate- and nucleoside-derived compounds. Here, we report our efforts in the design and synthesis of glyco-, glycosyl, nucleoside- and nucleo-aminooxy acid derivatives from readily available sugars and amino acids, and their use for the generation of N-oxyamide-linked oligosaccharides, glycopeptides, glycolipids, oligonucleosides and nucleopeptides as novel glycoconjugates or oligonucleotide mimics. Delicate and key points in the synthesis will be emphasized.

Insight into the binding of a non-toxic, self-assembling aromatic tripeptide with ct-DNA: Spectroscopic and viscositic studies

The report describes the synthesis, self-association and DNA binding studies of an aromatic tripeptide H-Phe-Phe-Phe-OH (FFF). The peptide backbone adopts β-sheet conformation both in solid and solution. In aqueous solution, FFF self-assembles to form nanostructured aggregates. Interactions of this peptide with calf-thymus DNA (ct-DNA) have been studied using various biophysical techniques including ultraviolet (UV) absorption spectroscopy, fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The value of mean binding constant calculated from UV and fluorescence spectroscopic data is (2.914 ± 0.74) x 103 M-1 which is consistent with an external binding mode. Fluorescence intercalator displacement (FID) assay, iodide quenching study, viscosity measurement and thermal denaturation study of DNA further confirm the groove binding mode of peptide, FFF with ct-DNA. MTT cell survival assay reveals very low cytotoxicity of the peptide toward human lung carcinoma cell line A549.

Nucleic acid binding and other biomedical properties of artificial oligolysines

In the present study, we report the interaction of an artificial oligolysine (referred to as AOL) realized in our laboratory with targets of biomedical importance. These included polyinosinic acid (poly rI) and its complex with polycytidylic acid (poly I:C), RNAs with well-known interferon-inducing ability, and double-stranded (ds) DNA. The ability of the peptide to bind both single-stranded poly rI and ds poly I:C RNAs emerged from our circular dichroism (CD) and ultraviolet (UV) studies. In addition, we found that AOL forms complexes with dsDNA, as shown by spectroscopic binding assays and UV thermal denaturation experiments. These findings are encouraging for the possible use of AOL in biomedicine for nucleic acid targeting and oligonucleotide condensation, with the latter being a key step preceding their clinical application. Moreover, we tested the ability of AOL to bind to proteins, using serum albumin as a model protein. We demonstrated the oligolysine-protein binding by CD experiments which suggested that AOL, positively charged under physiological conditions, binds to the protein regions rich in anionic residues. Finally, the morphology characterization of the solid oligolysine, performed by scanning electron microscopy, showed different crystal forms including cubic-shaped crystals confirming the high purity of AOL.