A robust synthesis of N-glycolyl muramyl dipeptide via azidonitration/reduction

Recent Advances in the Synthesis and Biological Applications of Peptidoglycan Fragments

The biosynthesis, breakdown, and modification of peptidoglycan (PG) play vital roles in both bacterial viability and in the response of human physiology to bacterial infection. Studies on PG biochemistry are hampered by the fact that PG is an inhomogeneous insoluble macromolecule. Chemical synthesis is therefore an important means to obtain PG fragments that may serve as enzyme substrates and elicitors of the human immune response. This review outlines the recent advances in the synthesis and biochemical studies of PG fragments, PG biosynthetic intermediates (such as Park's nucleotides and PG lipids), and PG breakdown products (such as muramyl dipeptides and anhydro-muramic acid-containing fragments). A rich variety of synthetic approaches has been applied to preparing such compounds since carbohydrate, peptide, and phospholipid chemical methodologies must all be applied.

Beyond GalNAc! Drug delivery systems comprising complex oligosaccharides for targeted use of nucleic acid therapeutics

Nucleic Acid Therapeutics (NATs) are establishing a leading role for the management and treatment of genetic diseases following FDA approval of nusinersen, patisiran, and givosiran in the last 5 years, the breakthrough of milasen, with more approvals undoubtedly on the way. Givosiran takes advantage of the known interaction between the hepatocyte specific asialoglycoprotein receptor (ASGPR) and N-acetyl galactosamine (GalNAc) ligands to deliver a therapeutic effect, underscoring the value of targeting moieties. In this review, we explore the history of GalNAc as a ligand, and the paradigm it has set for the delivery of NATs through precise targeting to the liver, overcoming common hindrances faced with this type of therapy. We describe various complex oligosaccharides (OSs) and ask what others could be used to target receptors for NAT delivery and the opportunities awaiting exploration of this chemical space.

Temporary ether protecting groups at the anomeric center in complex carbohydrate synthesis

The synthesis of a carbohydrate building block usually starts with introduction of a temporary protecting group at the anomeric center and ends with its selective cleavage for further transformation. Thus, the choice of the anomeric temporary protecting group must be carefully considered because it should retain intact during the whole synthetic manipulation, and it should be chemoselectively removable without affecting other functional groups at a late stage in the synthesis. Etherate groups are the most widely used temporary protecting groups at the anomeric center, generally including allyl ethers, MP (p-methoxyphenyl) ethers, benzyl ethers, PMB (p-methoxybenzyl) eithers, and silyl ethers. This chapter provides a comprehensive review on their formation, cleavage, and applications in the synthesis of complex carbohydrates.

Synthetic mycobacterial molecular patterns partially complete Freund's adjuvant

Complete Freund's adjuvant (CFA) has historically been one of the most useful tools of immunologists. Essentially comprised of dead mycobacteria and mineral oil, we asked ourselves what is special about the mycobacterial part of this adjuvant, and could it be recapitulated synthetically? Here, we demonstrate the essentiality of N-glycolylated peptidoglycan plus trehalose dimycolate (both unique in mycobacteria) for the complete adjuvant effect using knockouts and chemical complementation. A combination of synthetic N-glycolyl muramyl dipeptide and minimal trehalose dimycolate motif GlcC14C18 was able to upregulate dendritic cell effectors, plus induce experimental autoimmunity qualitatively similar but quantitatively milder compared to CFA. This research outlines how to substitute CFA with a consistent, molecularly-defined adjuvant which may inform the design of immunotherapeutic agents and vaccines benefitting from cell-mediated immunity. We also anticipate using synthetic microbe-associated molecular patterns (MAMPs) to study mycobacterial immunity and immunopathogenesis.

Versatility of glycals in synthetic organic chemistry: coupling reactions, diversity oriented synthesis and natural product synthesis

Glycals, 1,2-unsaturated sugar derivatives, are versatile starting materials for the synthesis of natural products and the generation of novel structural features in Diversity Oriented Synthesis (DOS). The versatility of glycals in synthesis emanates, among others, from the presence of the ring oxygen and the enol-ether type unsaturation, the different types of stable conformations they can adopt depending on the nature of the protecting groups present and the ease with which the protecting groups of the three hydroxy groups could be tailored to suite for a desired manipulation. This review summarizes the literature on the different transformations of the endo glycals into biologically relevant compounds such as chromans, thiochromans, chromenes, thiochromenes, peptidomimetics, bridged benzopyrans etc., as well as on the use of glycals as chiral building blocks for the synthesis of various natural products such as aspicilin, reblastatin, diospongins, decytospolides, osmundalactones, paclitaxel, isatisine, d-fagomine, and spliceostatin, reported post 2014.

Convergent Synthesis of Novel Muramyl Dipeptide Analogues: Inhibition of Porphyromonas gingivalis-Induced Pro-inflammatory Effects by High Doses of Muramyl Dipeptide

Porphyromonas gingivalis (P.g.)-induced TNF-α can be affected by muramyl dipeptide (MDP) in a biphasic concentration-dependent manner. We found that in P.g.-exposed macrophages, treatment with 10 μg/mL of MDP (MDP-low) up-regulated TNF-α by 29%, while 100 μg/mL or higher (MDP-high) significantly decreased it (16% to 38%). MDP-high was found to affect the ubiquitin-editing enzyme A20 and activator protein 1 (AP1). An AP1 binding site was found in the promoter region of A20. A20 promoter activity was up-regulated after transfection of AP1 cDNA in cells. Four analogues of MDP (3-6) were prepared through a convergent strategy involving the synthesis of two unique carbohydrate fragments, 7a and 7b, using the peptide coupling reagents, EDCI and HOAt. Analogue 4 improved MDP function and P.g.-induced activities. We propose a new signaling pathway for TNF-α induction activated after exposing macrophages to both P.g. and MDP-high or analogue 4.

Synthesis of glycoaminooxy acid and N-oxyamide-linked glycolipids

Synthesis of orthogonally protected glycoaminooxy acid and fully deprotected N-oxyamide-linked novel glycolipids is reported.

Synthesis of Diverse N-Substituted Muramyl Dipeptide Derivatives and Their Use in a Study of Human NOD2 Stimulation Activity

A flexible synthetic strategy toward the preparation of diverse N-substituted muramyl dipeptides (N-substituted MDPs) from different protected monosaccharides is described. The synthetic MDPs include N-acetyl MDP and N-glycolyl MDP, known NOD2 ligands, and this methodology allows for structural variation at six positions, including the muramic acid, peptide, and N-substituted moieties. The capacity of these molecules to activate human NOD2 in the innate immune response was also investigated. It was found that addition of the methyl group at the C1 position of N-glycolyl MDP significantly enhanced the NOD2 stimulating activity.

Peptidoglycan Modifications Tune the Stability and Function of the Innate Immune Receptor Nod2

Natural modifications of peptidoglycan modulate the innate immune response. Peptidoglycan derivatives activate this response via the intracellular innate immune receptor, Nod2. To probe how these modifications alter the response, a novel and efficient carbohydrate synthesis was developed to allow for late-stage modification of the amine at the 2-position. Modification of the carbohydrate was found to be important for stabilizing Nod2 and generating the proper response. The native Nod2 ligands demonstrate a significant increase in the cellular stability of Nod2. Moreover, changing the identity of the natural ligands at the carbohydrate 2-position allows for the Nod2-dependent immune response to be either up-regulated or down-regulated. The ligand structure can be adjusted to tune the Nod2 response, suggesting that other innate immune receptors and their ligands could use a similar strategy.