One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate ...

Vanderbilt University

We previously discovered a positive allosteric modulator (PAM) of the metabotropic glutamate receptor subtype 5 (mGlu(5)) termed 4 N-{4-chloro-2-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]phenyl}-2-hydroxybenzamide (CPPHA) that elicits receptor activation through a novel allosteric site on mGlu(5), distinct from the classical mGlu(5) negative allosteric modulator (NAM) MPEP allosteric site. However, a shallow structure-activity relationship (SAR), poor physiochemical properties, and weak PAM activity at rat mGlu(5) limited the utility of CPPHA to explore allosteric activation of mGlu(5) at a non-MPEP site. Thus, we performed a functional high-throughput screen (HTS) and identified a novel mGlu(5) PAM benzamide scaffold, exemplified by VU0001850 (EC(50) = 1.3 μM, 106% Glu(max)) and VU0040237 (EC(50) = 350 nM, 84% Glu Max). An iterative parallel synthesis approach delivered 22 analogues, optimized mGlu(5) PAM activity to afford VU0357121 (EC(50) = 33 nM, 92% Glu(max)), and also revealed the first non-MPEP site neutral allosteric ligand (VU0365396). Like CPPHA, PAMs within this class do not appear to bind at the MPEP allosteric site based on radioligand binding studies. Moreover, mutagenesis studies indicate that VU0357121 and related analogues bind to a yet uncharacterized allosteric site on mGlu(5), distinct from CPPHA, yet share a functional interaction with the MPEP site.

Discovery of a Novel Chemical Class of mGlu(5) Allosteric Ligands with Distinct Modes of Pharmacology.

Herein we report the discovery, synthesis and evaluation of a series of N-Aryl-bicyclo[2.2.1]heptane-2-carboxamides as selective KCNQ2 (K(v)7.2) and KCNQ4 (K(v)7.4) channel openers. The best compound, 1 (ML213) has an EC(50) of 230 nM (KCNQ2) and 510 nM (KCNQ4) and is selective for KCNQ2 and KCNQ4 channels versus a large battery of related potassium channels, as well as affording modest brain levels. This represents the first report of unique selectivity profile for KCNQ2 and KCNQ4 over the other channels (KCNQ1/3/5) and as such should prove to be a valuable tool compound for understanding these channels in regulating neuronal activity.

Discovery, Synthesis, and Structure Activity Relationship of a Series of N-Aryl- bicyclo[2.2.1]heptane-2-carboxamides: Characterization of ML213 as a Novel KCNQ2 and KCNQ4 Potassium Channel Opener.

Progress toward the total synthesis of bielschowskysin is described including introduction of the quaternary C12 and neighboring C13 stereocenters.

Progress toward the total synthesis of bielschowskysin.

Professional health bodies such as the World Health Organization (WHO), the American Academy of Pediatrics (AAP), and the U.S. Department of Health and Human Services (HHS) recommend breast milk as the sole source of food during the first year of life. This position recognizes human milk as being uniquely suited for infant nutrition. Nonetheless, most neonates in the West are fed alternatives by 6 months of age. Although inferior to human milk in most aspects, infant formulas are able to promote effective growth and development. However, while breast-fed infants feature a microbiota dominated by bifidobacteria, the bacterial flora of formula-fed infants is usually heterogeneous with comparatively lower levels of bifidobacteria. Thus, the objective of any infant food manufacturer is to prepare a product that results in a formula-fed infant developing a breast-fed infant-like microbiota. The goal of this focused review is to discuss the structure, synthesis, and function of carbohydrate additives that play a role in governing the composition of the infant microbiome and have other health benefits.

Infant food applications of complex carbohydrates: Structure, synthesis, and function.

Human milk oligosaccharides (HMOs) are the third largest macromolecular component of breast milk and offer infants numerous health benefits, most of which stem from the development of a healthy microbiome. Characterization, quantification, and chemical derivatization of HMOs remains a frontier issue in glycobiology due to the challenge of isolating appreciable quantities of homogenous HMOs from breast milk. Herein, we report the synthesis of the human milk tetrasaccharide lacto-N-tetraose (LNT). LNT is ubiquitous in human breast milk as it is a core structure common to longer-chain HMOs and many glycolipids.

Synthesis of lacto-N-tetraose.

A series of carbohydrate 2-azido-1-nitrate-esters, protected at the C-3, C-4, and C-6 positions, were hydrolyzed thermally under reagent free conditions. This preliminary result was extended to direct exchange of the 1-nitrate-ester modality for alcohol, alkoxy, and azide coupling partners with minimal purification. While direct glycosylation of nitrate esters ultimately proved unsuccessful, we have demonstrated that an anomeric nitrate-ester can be converted directly to a trichloroacetimidate in a short and simple one-pot procedure, bypassing lower yielding two-step sequences.

Direct, microwave-assisted substitution of anomeric nitrate-esters.

Streptococcus agalactiae (Group B Streptococcus, GBS) is a Gram-positive bacterial pathogen that causes invasive infections in both children and adults. During pregnancy, GBS is a significant cause of infection of the fetal membranes (chorioamnionitis), which can lead to intra-amniotic infection, preterm birth, stillbirth, and neonatal sepsis. Recently, breastfeeding has been thought to represent a potential mode of GBS transmission from mother to newborn, which might increase the risk for late-onset sepsis. Little is known, however, about the molecular components of breast milk that may support or prevent GBS colonization. In this study, we examine how human milk oligosaccharides (HMOs) affect the pathogenesis of GBS. HMOs from discrete donor samples were isolated and profiled by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Growth and biofilm assays show that HMOs from mothers of specific milk groups can modulate the growth and biofilm formation of GBS. High-resolution field-emission gun scanning electron microscopy (SEM) and confocal laser scanning microscopy confirmed the quantitative biofilm assays and demonstrated cell arrangement perturbations in bacterial cultures treated with specific oligosaccharides. These findings demonstrate that HMOs affect the growth and cell biology of GBS. Finally, this study provides the first example of HMOs functioning as antibiofilm agents against GBS.

Human Milk Oligosaccharides Exhibit Antimicrobial and Antibiofilm Properties against Group B Streptococcus.

A one-pot, metal-free procedure has been developed to synthesize unsymmetrical organoselenides. In the first step of the reaction, arylation of potassium selenocyanate (KSeCN) with an iodonium reagent proceeds in the absence of a metal catalyst to produce an arylselenocyanate. In the second step, treatment with sodium borohydride unmasks a second selenium nucleophile that engages an aliphatic electrophile, iodonium reagent, or glycosyl halide. The procedure represents an umpolung approach to the synthesis of aryl-selenides.

Metal-Free Synthesis of Unsymmetrical Organoselenides and Selenoglycosides.

Each year over 3 million people die from infectious diseases with most of these deaths being poor and young children who live in low- and middle-income countries. Infectious diseases emerge for a multitude of reasons. On the social front, reasons include a breakdown of public health standards, international travel, and immigration (for financial, civil, and social reasons). At the molecular level, the modern rise of infectious diseases is tied to the juxtaposition of drug-resistant pathogens and a lack of new antimicrobials. The consequence is the possibility that humankind will return to the preantibiotic era wherein millions of people will perish from what should be trivial illnesses. Given the stakes, it is imperative that the chemistry community take leadership in delivering new antibiotic leads for clinical development. We believe this can happen through innovation in two areas. First is the development of novel chemical scaffolds to treat infections caused by multidrug-resistant pathogens. The second area, which is not exclusive to the first, is the generation of antibiotics that do not cause collateral damage to the host or the host's microbiome. Both can be enabled through advances in chemical synthesis. It is with this general philosophy in mind that we hypothesized human milk oligosaccharides (HMOs) could serve as novel chemical scaffolds for antibacterial development. We provide herein a personal account of our laboratory's progress toward the goal of using HMOs as a defense against infectious diseases.

The Human Milk Glycome as a Defense Against Infectious Diseases: Rationale, Challenges, and Opportunities.

In a previous study, we reported that human milk oligosaccharides (HMOs) isolated from five donor milk samples possessed antimicrobial and antibiofilm activity against Streptococcus agalactiae, also known as Group B Streptococcus or GBS. Herein, we present a broader evaluation of the antimicrobial and antibiofilm activity by screening HMOs from 14 new donors against three strains of GBS and two of the ESKAPE pathogens of particular interest to child health, Staphylococcus aureus and Acinetobacter baumannii. Growth and biofilm assays showed that HMOs from these new donors possessed antimicrobial and antibiofilm activity against all three strains of GBS, antibiofilm activity against methicillin-resistant S. aureus strain USA300, and antimicrobial activity against A. baumannii strain ATCC 19606.

Antimicrobial and Antibiofilm Activity of Human Milk Oligosaccharides against Streptococcus agalactiae, Staphylococcus aureus, and Acinetobacter baumannii.

Steven D. Townsend

Department of Chemistry,
Institute of Chemical-Biology

Vanderbilt University

One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

Steven D. Townsend

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Chemistry,Institute of Chemical-Biology

Vanderbilt University

One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

Department of Chemistry,
Institute of Chemical-Biology