Synthesis of Peptidoglycan Units with UDP at the Anomeric Position

Synthesis of a Borrelia burgdorferi-Derived Muropeptide Standard Fragment Library

The interplay between the human innate immune system and bacterial cell wall components is pivotal in understanding diseases such as Crohn's disease and Lyme arthritis. Lyme disease, caused by Borrelia burgdorferi, is the most prevalent tick-borne illness in the United States, with a substantial number of cases reported annually. While antibiotic treatments are generally effective, approximately 10% of Lyme disease cases develop persistent arthritis, suggesting a dysregulated host immune response. We have previously identified a link between the immunogenic B. burgdorferi peptidoglycan (PG) and Lyme arthritis and showed that this pathogen sheds significant amounts of PG fragments during growth. Here, we synthesize these PG fragments, including ornithine-containing monosaccharides and disaccharides, to mimic the unique composition of Borrelia cell walls, using reproducible and rigorous synthetic methods. This synthetic approach allows for the modular preparation of PG derivatives, providing a diverse library of well-defined fragments. These fragments will serve as valuable tools for investigating the role of PG-mediated innate immune response in Lyme disease and aid in the development of improved diagnostic methods and treatment strategies.

Optimizations of lipid II synthesis: an essential glycolipid precursor in bacterial cell wall synthesis and a validated antibiotic target

Lipid II is an essential glycolipid found in bacteria. Accessing this valuable cell wall precursor is important both for studying cell wall synthesis and for studying/identifying novel antimicrobial compounds. Herein, we describe optimizations to the modular chemical synthesis of lipid II and unnatural analogues. In particular, the glycosylation step, a critical step in the formation of the central disaccharide unit (GlcNAc-MurNAc), was optimized. This was achieved by employing the use of glycosyl donors with diverse leaving groups. The key advantage of this approach lies in its adaptability, allowing for the generation of a wide array of analogues through the incorporation of alternative building blocks at different stages of synthesis.

Antibiotics and Antibiotic Resistance-Mur Ligases as an Antibacterial Target

The emergence of Multidrug Resistance (MDR) strains of bacteria has accelerated the search for new antibacterials. The specific bacterial peptidoglycan biosynthetic pathway represents opportunities for the development of novel antibacterial agents. Among the enzymes involved, Mur ligases, described herein, and especially the amide ligases MurC-F are key targets for the discovery of multi-inhibitors, as they share common active sites and structural features.

Glycosides and Glycoconjugates of the Diterpenoid Isosteviol with a 1,2,3-Triazolyl Moiety: Synthesis and Cytotoxicity Evaluation

Several glycoconjugates of the diterpenoid isosteviol (16-oxo-ent-beyeran-19-oic acid) with a 1,2,3-triazolyl moiety were synthesized, and their cytotoxicity was evaluated against some human cancer and normal cell lines. Most of the synthesized compounds demonstrated weak inhibitory activities against the M-HeLa and MCF-7 human cancer cell lines. Three lead compounds, 54, 56 and 57, exhibited high selective cytotoxic activity against M-HeLa cells (IC₅₀ = 1.7-1.9 μM) that corresponded to the activity of the anticancer drug doxorubicin (IC₅₀ = 3.0 μM). Moreover, the lead compounds were not cytotoxic with respect to a Chang liver human normal cell line (IC₅₀ > 100 μM), whereas doxorubicin was cytotoxic to this cell line (IC₅₀ = 3.0 μM). It was found that cytotoxic activity of the lead compounds is due to induction of apoptosis proceeding along the mitochondrial pathway. The present findings suggest that 1,2,3-triazolyl-ring-containing glycoconjugates of isosteviol are a promising scaffold for the design of novel anticancer agents.

Iron-Binding and Anti-Fenton Properties of Novel Amino Acid-Derived Cyclic Imide Dioximes

We present a novel route for the preparation of amino acid-derived cyclic imide dioxime derivatives. Readily accessible amino acids were conveniently converted to their corresponding cyclic imide dioximes in simple synthetic steps. The aim of this work was to describe and compare the iron-chelating and antioxidant properties of synthesized compounds in relation to their molecular structure, and in particular, which of those features are essential for iron(II)-chelating ability. The glutarimide dioxime moiety has been established as an iron(II)-binding motif and imparts potent anti-Fenton properties to the compounds. Compound 3 was shown to strongly suppress hydroxyl radical formation by preventing iron cycling via Fe-complexation. These findings provide insights into the structural requirements for achieving anti-Fenton activity and highlight the potential use of glutarimide dioximes as antioxidants.

Synthesis and cytotoxicity of the conjugates of diterpenoid isosteviol and N-acetyl-D-glucosamine

A series of conjugates of diterpenoid isosteviol (16-oxo-ent-beyeran-19-oic acid) and N-acetyl-D-glucosamine was synthesised and their cytotoxicity against several human cancer cell lines (M-Hela, MCF-7, Hep G2, Panc-1, PC-3), as well as normal human cell lines (WI-38, Chang liver) was assayed. Most of the conjugates were found to be cytotoxic against the mentioned cancer cell lines in the range of IC₅₀ values 13-89 µM. Two lead compounds 14a and 14b showed selective cytotoxicity against M-Hela (IC₅₀ 13 and 14 µM) that was two times as high as the cytotoxicity of the anti-cancer drug Tamoxifen in control (IC₅₀ 28 µM). It was found that cytotoxic activity of the lead compounds against M-Hela cells is due to induction of apoptosis.

Synthesis and anti-cancer activities of glycosides and glycoconjugates of diterpenoid isosteviol

A series of glycosides and glycoconjugates of diterpenoid isosteviol (16-oxo-ent-beyeran-19-oic acid) with various monosaccharide residues were synthesized and their cytotoxicity against some human cancer and normal cell lines was assayed. Most of the synthesized compounds demonstrated moderate to significant cytotoxicity against human cancer cell lines M-HeLa and MCF-7. Three lead compounds exhibited selective cytotoxic activities against M-HeLa (IC50 = 10.0-15.1 μM) that were three times better than the cytotoxicity of the anti-cancer drug Tamoxifen (IC50 = 28.0 μM). Moreover, the lead compounds were not cytotoxic with respect to the normal human cell line Chang liver (IC50 > 100 μM), whereas Tamoxifen inhibited the viability of normal human Chang liver cells with an IC50 value of 46.0 μM. It was determined that the cytotoxicity of the lead compounds was due to induction of apoptosis proceeding along the mitochondrial pathway. The cytotoxic activity of the synthesized compounds substantially depended on the nature of the monosaccharide residue and its position, that is, whether the monosaccharide residue was attached directly to the isosteviol skeleton or was moved away from it by means of a polymethylene linker.

Enterococcus faecium secreted antigen A generates muropeptides to enhance host immunity and limit bacterial pathogenesis

We discovered that Enterococcus faecium (E. faecium), a ubiquitous commensal bacterium, and its secreted peptidoglycan hydrolase (SagA) were sufficient to enhance intestinal barrier function and pathogen tolerance, but the precise biochemical mechanism was unknown. Here we show E. faecium has unique peptidoglycan composition and remodeling activity through SagA, which generates smaller muropeptides that more effectively activates nucleotide-binding oligomerization domain-containing protein 2 (NOD2) in mammalian cells. Our structural and biochemical studies show that SagA is a NlpC/p60-endopeptidase that preferentially hydrolyzes crosslinked Lys-type peptidoglycan fragments. SagA secretion and NlpC/p60-endopeptidase activity was required for enhancing probiotic bacteria activity against Clostridium difficile pathogenesis in vivo. Our results demonstrate that the peptidoglycan composition and hydrolase activity of specific microbiota species can activate host immune pathways and enhance tolerance to pathogens.

Synthesis of 1-C-Glycoside-Linked Lipid II Analogues Toward Bacterial Transglycosylase Inhibition

Preparation of Lipid II analogues containing an enzymatically uncleavable 1-C-glycoside linkage between the disaccharide moiety and the pyrophosphate- or pyrophosphonate-lipid moiety is described. The synthesis of a common 1-C-vinyl disaccharide intermediate has been developed that allows easy preparation of both an elongated sugar-phosphate bond and a sugar-phosphonate moiety, which are coupled with the polyprenyl phosphate to give the desired molecules. Inhibition studies show how a subtle structural modification results in dramatically different potency toward bacterial transglycosylase (TGase), and the results identify Lipid II-C-O-PP (IC50 =25 μM) as a potential TGase inhibitor.