Muraymycin-derived nucleoside-peptide antibiotics: potential lead structures for novel antimicrobial agents

En esta conferencia se describe el mecanismo de acción de una nueva clase de antibióticos tipo nucleósidos denominados muraimicinas, caracterizados por la presencia de una cadena peptídica unida al fragmento nucleosídico. Dada la importancia de identificar nuevos antibióticos efectivos frentes a cepas bacterianas resistentes a los antibióticos actuales, este nueva clase de compuestos representan una prometedora línea de acción contra estas bacterias, actuando sobre una nueva enzima implicada en la biosíntesis de la pared celular, la translocasa I. Así, se describe la síntesis de análogos de muraimicinas y sus correspondientes actividades antibióticas que llevó a la caracterización de un nuevo análogo sintético como potente inhibidor de esta enzima (rango nM) y con un perfil biológico muy prometedor para un posible futuro desarrollo farmacéutico.Vicerrectorado de Investigación y Transferencia de la Universidad de Málaga; y Departamento de Química Orgánica. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Cellular Targeting of Oligonucleotides by Conjugation with Small Molecules

Drug candidates derived from oligonucleotides (ON) are receiving increased attention that is supported by the clinical approval of several ON drugs. Such therapeutic ON are designed to alter the expression levels of specific disease-related proteins, e.g., by displaying antigene, antisense, and RNA interference mechanisms. However, the high polarity of the polyanionic ON and their relatively rapid nuclease-mediated cleavage represent two major pharmacokinetic hurdles for their application in vivo. This has led to a range of non-natural modifications of ON structures that are routinely applied in the design of therapeutic ON. The polyanionic architecture of ON often hampers their penetration of target cells or tissues, and ON usually show no inherent specificity for certain cell types. These limitations can be overcome by conjugation of ON with molecular entities mediating cellular ‘targeting’, i.e., enhanced accumulation at and/or penetration of a specific cell type. In this context, the use of small molecules as targeting units appears particularly attractive and promising. This review provides an overview of advances in the emerging field of cellular targeting of ON via their conjugation with small-molecule targeting structures

Unexpected Seven-Membered Ring Formation for Muraymycin-Type Nucleoside-Peptide Antibiotics

Naturally occurring nucleoside-peptide antibiotics such as muraymycins or caprazamycins are of major interest for the development of novel antibacterial agents. However, the synthesis of new analogues of these natural products for structure–activity relationship (SAR) studies is challenging. In our synthetic efforts towards a muraymycin-derived nucleoside building block suitable for attachment to a solid support, we came across an interesting side product. This compound resulted from an undesired Fmoc deprotection with subsequent cyclization, thus furnishing a remarkable caprazamycin-like seven-membered diazepanone ring

Aminoribosylated Analogues of Muraymycin Nucleoside Antibiotics

Nucleoside antibiotics are uridine-derived natural products that inhibit the bacterial membrane protein MraY. MraY is a key enzyme in the membrane-associated intracellular stages of peptidoglycan biosynthesis and therefore considered to be a promising, yet unexploited target for novel antibacterial agents. Muraymycins are one subclass of such naturally occurring MraY inhibitors. As part of structure-activity relationship (SAR) studies on muraymycins and their analogues, we now report on novel derivatives with different attachment of one characteristic structural motif, i.e., the aminoribose moiety normally linked to the muraymycin glycyluridine core unit. Based on considerations derived from an X-ray co-crystal structure, we designed and synthesised muraymycin analogues having the aminoribose attached (via a linker) to either the glycyluridine amino group or to the uracil nucleobase. Reference compounds bearing the non-aminoribosylated linker units were also prepared. It was found that the novel aminoribosylated analogues were inactive as MraY inhibitors in vitro, but that the glycyluridine-modified reference compound retained most of the inhibitory potency relative to the unmodified parent muraymycin analogue. These results point to 6′-N-alkylated muraymycin analogues as a potential novel variation of the muraymycin scaffold for future SAR optimisatio

Solid Phase-Supported Synthesis of Muraymycin Analogues

Naturally occurring muraymycin nucleoside antibiotics represent a promising class of novel antimicrobials as they inhibit MraY, an enzyme involved in bacterial cell wall biosynthesis. The synthesis of muraymycins and their analogues is challenging as it involves multi‐step routes, thus hampering detailed structure‐activity relationship (SAR) studies. In this work, we report a novel solid phase‐based synthetic strategy for accessing muraymycin analogues via a modular approach, thereby enabling a more efficient access to structural variations, particularly of the muraymycin peptide moiety. The efficiency of this new method was exemplified in an alanine scan of the peptide unit. The inhibitory in vitro activities of the resultant analogues towards MraY provided novel SAR insights. Overall, this new synthetic method for the preparation of muraymycin analogues might support the development of these antibacterial agents towards potential drug candidates

Merging Natural Products: Muraymycin-Sansanmycin Hybrid Structures as Novel Scaffolds for Potential Antibacterial Agents

To overcome bacterial resistances, the need for novel antimicrobial agents is urgent. The class of so‐called nucleoside antibiotics furnishes promising candidates for the development of new antibiotics, as these compounds block a clinically unexploited bacterial target: the integral membrane protein MraY, a key enzyme in cell wall (peptidoglycan) biosynthesis. Nucleoside antibiotics exhibit remarkable structural diversity besides their uridine‐derived core motifs. Some sub‐classes also show specific selectivities towards different Gram‐positive and Gram‐negative bacteria, which are poorly understood so far. Herein, the synthesis of a novel hybrid structure is reported, derived from the 5′‐defunctionalized uridine core moiety of muraymycins and the peptide chain of sansanmycin B, as a new scaffold for the development of antimicrobial agents. The reported muraymycin–sansanmycin hybrid scaffold showed nanomolar activity against the bacterial target enzyme MraY, but displayed no significant antibacterial activity against S. aureus, E. coli, and P. aeruginosa

Towards Zwitterionic Oligonucleotides with Improved Properties: the NAA/LNA-Gapmer Approach

Oligonucleotides (ON) are promising therapeutic candidates, for instance by blocking endogenous mRNA (antisense mechanism). However, ON usually require structural modifications of the native nucleic acid backbone to ensure satisfying pharmacokinetic properties. One such strategy to design novel antisense oligonucleotides is to replace native phosphate diester units by positively charged artificial linkages, thus leading to (partially) zwitterionic backbone structures. Herein, we report a “gapmer” architecture comprised of one zwitterionic central segment (“gap”) containing nucleosyl amino acid (NAA) modifications and two outer segments of locked nucleic acid (LNA). This NAA/LNA‐gapmer approach furnished a partially zwitterionic ON with optimised properties: i) the formation of stable ON‐RNA duplexes with base‐pairing fidelity and superior target selectivity at 37 °C; and ii) excellent stability in complex biological media. Overall, the NAA/LNA‐gapmer approach is thus established as a strategy to design partially zwitterionic ON for the future development of novel antisense agents

Synthesis of an Antimicrobial Enterobactin-Muraymycin Conjugate for Improved Activity Against Gram-Negative Bacteria

Overcoming increasing antibiotic resistance requires the development of novel antibacterial agents that address new targets in bacterial cells. Naturally occurring nucleoside antibiotics (such as muraymycins) inhibit the bacterial membrane protein MraY, a clinically unexploited essential enzyme in peptidoglycan (cell wall) biosynthesis. Even though a range of synthetic muraymycin analogues has already been reported, they generally suffer from limited cellular uptake and a lack of activity against Gram-negative bacteria. We herein report an approach to overcome these hurdles: a synthetic muraymycin analogue has been conjugated to a siderophore, i. e. the enterobactin derivative EntKL, to increase the cellular uptake into Gram-negative bacteria. The resultant conjugate showed significantly improved antibacterial activity against an efflux-deficient E. coli strain, thus providing a proof-ofconcept of this novel approach and a starting point for the future optimisation of such conjugates towards potent agents against Gram-negative pathogens

Muraymycin Nucleoside Antibiotics: Structure-Activity Relationship for Variations in the Nucleoside Unit

Muraymycins are a subclass of naturally occurring nucleoside antibiotics with promising antibacterial activity. They inhibit the bacterial enzyme translocase I (MraY), a clinically yet unexploited target mediating an essential intracellular step of bacterial peptidoglycan biosynthesis. Several structurally simplified muraymycin analogues have already been synthesized for structure–activity relationship (SAR) studies. We now report on novel derivatives with unprecedented variations in the nucleoside unit. For the synthesis of these new muraymycin analogues, we employed a bipartite approach facilitating the introduction of different nucleosyl amino acid motifs. This also included thymidine- and 5-fluorouridine-derived nucleoside core structures. Using an in vitro assay for MraY activity, it was found that the introduction of substituents in the 5-position of the pyrimidine nucleobase led to a significant loss of inhibitory activity towards MraY. The loss of nucleobase aromaticity (by reduction of the uracil C5-C6 double bond) resulted in a ca. tenfold decrease in inhibitory potency. In contrast, removal of the 20 -hydroxy group furnished retained activity, thus demonstrating that modifications of the ribose moiety might be well-tolerated. Overall, these new SAR insights will guide the future design of novel muraymycin analogues for their potential development towards antibacterial drug candidates

Symmetric Grothendieck polynomials, skew Cauchy identities, and dual filtered Young graphs

Symmetric Grothendieck polynomials are analogues of Schur polynomials in the K-theory of Grassmannians. We build dual families of symmetric Grothendieck polynomials using Schur operators. With this approach we prove skew Cauchy identity and then derive various applications: skew Pieri rules, dual filtrations of Young's lattice, generating series and enumerative identities. We also give a new explanation of the finite expansion property for products of Grothendieck polynomials