Study of the mechanism of enantioseparation of macrocyclic glycopeptide-based chiral stationary phases

The purpose of this research has been to investigate the mechanisms of chiral separations in HPLC. The goal was to develop a method of interrogating chiral separations that is applicable to all CSPs. This dissertation focuses on the development and application of this approach. The macrocyclic glycopeptide CSPs were used to experimentally test our model/approach and to provide proof of principle;The linear solvation energy relationship (LSER), developed by Kamlet, Taft, and Abraham, was selected for its ability to de-convolute the interactions a solute experiences in a biphasic system. The LSER model has a term for each type of interaction that a solute can experience or participate in. These include interactions through polarizable n and pi electrons (eE), dipolar interactions (sS), hydrogen bond acceptance ( aA) and donation (bB), and dispersion forces ( vV). Each term has a component for the system\u27s ability to participate in the specified interaction, the lower case variables which are called system constants, and a component for the solutes ability to participate in the specified interaction, the upper case variables called solute descriptors;We obtained system constants for the macrocyclic glycopeptide CSPs in the reverse phase mode and the normal phase mode. With knowledge of the system constants, it is possible to determine the solute descriptors of each enantiomer. This is achieved using multiple linear regression analysis, with the system constants of a CSP as the independent variables, and the logarithm of the retention factor of one enantiomer as the dependent variable. The solute descriptors for each enantiomer are determined, and the differences in the solute descriptors reveal the relative importance of each intermolecular interaction in generating enantioselectivity;We applied this method of analysis to the reverse phase mode separations with the teicoplanin CSP. Several neutral compounds and amino acids were eluted and the solute descriptors for each enantiomer were determined. The statistical fits of the regression were excellent. It was found that steric repulsions and ion-dipole interactions had the strongest influence on enantioselectivity, with both types of hydrogen bonding having a weak influence on enantioselectivity. Dipolar interactions were found to be unimportant in generating enantioselectivity

Studies toward the syntheses of tetrahydroswertianolin and puniceaside B

Tetrahydroxanthones are a family of natural products with chemically interesting functional groups and a diverse array of reported biological activities. The dissertation research described herein has been focused on the synthesis of tetrahydroswertianolin, a glycosylated tetrahydroxanthone, and puniceaside B, a heterodimeric, glycosylated tetrahydroxanthone. To the best of our knowledge, there have been no published reports on the total synthesis of either natural product. We have targeted tetrahydroswertianolin and puniceaside B in hopes of developing a divergent method to easily access a variety of tetrahydroxanthone cores for natural product and analogue synthesis. Our efforts to develop a cascade reaction toward the tetrahydroxanthone core and the stepwise route that we simultaneously pursued will be presented. A scalable synthetic route to the tetrahydroxanthone core of tetrahydroswertianolin and the aromatic xanthone core of puniceaside B was accomplished. An asymmetric route to the tetrahydroxanthone precursor was also developed.2019-02-14T00:00:00

Ferrocene Bioconjugates

In this review we present our recent contribution to the field of bioorganometallic chemistry of ferrocene. Ferrocene conjugates with biomolecules have been synthesized and characterized using IR and NMR (1H, 13C, COSY, NOESY, HMBC) spectroscopy, ESI-MS and HRMS. The bioconjugates of ferrocene with resveratrol (2) and mannose (10, 11, 14 and 15) were biologically evaluated for their potential inhibitory effect on HepG2 cancer cells (2) and E. coli adherence to the bladder epithelium (10, 11, 14 and 15). The oxalamide-bridged ferrocene 17 was sub¬jected to conformational analysis in solution and in the solid state, and tested for its gelation and cytotoxic activity. The mono- (30–32, 36–38, 42–45) and disubstituted ferrocene conjugates with natural amino acids (21–28, 33–35, 39–41, 48, 49, 62–65, 69–72) were subjected to the detailed conformational and DFT analyses in order to determine the turn-inducing potential of ferrocene scaffolds in the corresponding peptidomimetics. This work is licensed under a Creative Commons Attribution 4.0 International License

En detaljert studie i substrat posisjonering i familie 18 kitinaser

Chitin is a linear polymer consisting of β-1,4-linked N-acetyl-glucosamine (GlcNAc; A) units tightly packed in a crystalline structure. It is produced by living organisms in large quantities per year and is a structural component of fungi, insects and crustaceans. A soluble derivative of chitin, chitosan, is obtained by deacetylation of the chitin polymer, resulting in a hetero-polymer consisting of N-acetyl-glucosamine and glucosamine (GlcN; D) units. Despite, the large amounts of chitin produced, it does not accumulate in nature because it is broken down efficiently by a group of enzymes known as chitinases. Chitin turnover is of considerable economic interest, and inhibition of chitinases is a desirable target in the development of fungicides, pesticides and therapeutics. The primary goal of the work described in this thesis was to study the binding of chitin, fragments of chitin (chitooligosaccharides), and chitosan to different chitinases to gain an insight into the mechanisms behind chitin degradation. Papers I and II describe a detailed thermodynamic characterization of binding of Nacetylated chitooligosaccharides and the pseudosaccharide allosamidin to ChitinaseB (ChiB) from Serratia marcescens, providing new insights into the contributory factors of ligand-binding. Remarkably, binding of chitooligosaccharides was found to be driven exclusively by entropy despite several conserved stacking interactions between the ligand and the active site. Paper III describes a study of the role of the conserved tryptophan in subsite −3 and a putative “+3” binding site by comparing how ChitinaseA (ChiA) from Serratia marcescens and its −3 subsite mutant ChiA-W167A interact with chitooligosaccharides and chitosan. The results reported in this paper highlight the importance of Trp167 for ligand binding and suggest there are important interactions between the enzyme and the ligand which have not been studied previously. Humans possess two active and highly conserved family 18 chitinases, acidic mammalian chitinase (AMCase) and chitotriosidase (HCHT), which are believed to be a part of the human immune system. Papers IV and V deal with the productive and non-productive binding of HCHT, and compare preferences of substrate positioning for HCHT and AMCase. The results help to elucidate the mechanisms of ligand binding to human chitinases and have important implications for the future design of AMCase inhibitors. Inhibitor development requires efficient and fast screening methods to identify strongly binding molecules. Paper VI describes a novel method using infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI MS) for rapid and robust detection of noncovalent complexes, which is a promising tool in the search for efficient chitinase inhibitors.Kitin er en lineær polymer bestående av β-1,4-linkede N-acetyl-glukosamin (GlcNAc; A) enheter tett pakket i en krystallinsk struktur. Kitin er en viktig strukturell komponent i sopp, insekter og skalldyr og blir produsert i enorme mengder årlig. Kitosan er et vannløslig derivat av kitin som fremstilles ved deacetylering av kitin polymeren til en hetro-polymer bestående av N-acetylglukosamin og glukosamin (GlcN; D) enheter. Til tross for de enorme mengdene kitin som produseres årlig akkumulerer ikke kitin i naturen. Dette skyldes en mengde proteiner som effektivt bryter ned kitin, kjent som kitinaser. Nedbrytning av kitin er av stor økonomisk interesse og inhibering av kitinaser er ønskelig for utvikling av nye fungicider, persticider og medisiner. Målet med dette prosjektet har vært å studere bindingen av kitin, kitin fragmenter (kitooligosakkarider) og kitosan til forskjellige kitinaser for og beder å forstå mekanismene bak nedbrytningen av kitin. Artikkel I og II gir en detaljert termodynamisk karakterisering av bindingen av Nacetylerte kitooligosakkarider og pseudosakkaridet allosamidin til KitinaseB (ChiB) fra Serratia marcescens, noe som gir et nytt innblikk i hvilke faktorer som bidrar til ligand binding. Det ble observert at binding av kitooligosakkarider i all hovedsak ble drevet av entropi, til tross for at flere konserverte interaksjoner mellom liganden og enzymet i det aktive setet. I artikkel III blir betydningen av den konserverte tryptofan i subsete −3 og det antatte ”+3” bindingsetet studert ved å sammenlikne hvordan KitinaseA (ChiA) fra Serratia marcescens og dens subsete −3 mutant ChiA-W167A binder til kitosan og kitooligosakkarider. Resultatene fra dette studiet understreker betydningen til Trp167 når det kommer til binding av ligander og retter ny oppmerksomhet mot interaksjoner mellom enzymet og liganden utenfor det definerte aktive setet. Mennesker har to aktive, svært konserverte familie 18 kitinaser, acidic mammalian chitinase (AMCase) and chitotriosidase (HCHT), som antas å være en del av det humane immun systemet. I artikkel IV og V har vi studert både produktive og ikke-produktive bindinger til HCHT og preferanser for substratbinding er sammenliknet med den for AMCase. Dette gir en ny innsikt i bindings mekanismer hos humane kitinaser og gir verdifull informasjon for videre design av AMCase inhibitorer. Utviklingen av nye inhibitorer krever effektive og raske metoder for screening av molekyler som binder strekt til enzymet. Artikkel VI beskriver en ny metode for rask og robust deteksjon av ikke-kovalente komplekser ved hjelp av infrarød matrix assisert laser desorption ioniserings masse spektrometri (IR-MALDI-MS). Denne metoden har et stort potensial i jakten på effektive kitinase inhibitorer.Norges Forskningsrå

Chemical Synthesis: New Methods for O-Glycosylation and the Preparation of Organic Thin Films

This dissertation focuses on the diverse use of chemical synthesis. Herein, I will discuss the use of synthetic organic chemistry for the modification surfaces and the synthesis of small molecules. Chapter One is an introduction to the realm of surface chemistry. I have highlighted some key methods for surface modification. Additionally, methods to characterize the as-formed thin films are also outlined. In Chapter Two, I discuss the use of visible-light photoredox catalysis in the nanoscale lithography of Au(111) surfaces. Blue LED irradiation of solutions of NBDT in the presence of Ru(bpy)32+ results in the formation of p-nitrophenyl radicals that graft onto Au. Further reaction of the grafted arenes with aryl radicals results in oligomerization to polyphenylene structures with resulting film thicknesses that are dependent on both the initial concentration of diazonium salt and the duration of the grafting procedure. Grafting onto Au(111) coated with SiO2 mesospheres (d = 500 nm) prior to mesospheres removal results in the production of nanopatterned surfaces wherein each nanopore represents the former location of a mesosphere. Chapter Three focuses on the a novel use of visible light photoredox catalysis for organic thin film formation with nanoscale lithography of Au(111) surfaces. Irradiation of solutions of phthalimide esters with blue LEDs in the presence of the Ru(bpy)3Cl2 results in the formation of carbon centered radicals that form organic thin films. We propose that a series of additional reactions of the grafted aliphatic chains with alkyl radicals results in oligomerization and the formation of multilayers. Chapter Four is a brief discussion of the significance of oligosaccharide synthesis. The development of efficient and stereoselective methods for glycosylation is a synthetic challenge. Thioglycosides are inert to many glycosylation methods and are bench top stable. Their stability to common carbohydrate protecting group manipulations makes thioglycosides ideal glycosyl donors or acceptors. Traditionally, the activation of thioglycosides requires heavy metals, halogen electrophiles, or stoichiometric thiophilic reagents. In contrast, our method discussed in Chapter 5 requires catalytic Bronsted acid for the remote activation of a thioglycoside donor. Under these conditions, O-glycosylation formation and release of a tetrahydrothiophene aglycon is swift and high yielding

An Intramolecular Method for the Formation of Glycosidic Bonds

The improved understanding of carbohydrate functions in biological systems has increased the demand for well-characterized and pure carbohydrates in biomedical research. Chemical synthesis is the most feasible method to satisfy the scientific demand despite the inherent challenges of the glycosylation reaction. Therefore, it is essential to investigate novel methods for the formation of glycosidic bonds. In this work, an intramolecular method was developed using a thio-methylene-silyl linker to tether a glycosyl donor and acceptor. The glycosylation conditions resulted in the formation of both anomeric isomers with a preference for the inversion pathway, which is inconsistent with an entirely intermolecular glycosylation mechanism. More specifically, the ⍺ anomer of the thio-methylene-silyl tethered glycosyl donor and acceptor formed glycosyl products in up to 70% yield (1:2.8 ⍺: β stereoselectivity) and the corresponding β anomer formed glycosyl products in up to 76% yield (2.2:1 ⍺: β stereoselectivity). A detailed study of the mechanism of the reaction was conducted using competition experiments, crossover experiments, and computational work. In a double-labeled crossover experiment, the ⍺ glycosylation product was produced by an intramolecular pathway 33% of the time and an intermolecular pathway the remaining 67%. Correspondingly, the β product is formed 38% by an intramolecular pathway and 62% by an intermolecular pathway. During the study, insight was gained regarding how intramolecular glycosylation proceeds and how novel linkers could improve stereoselectivity in glycosylation

The Synthesis of Functionalized Glycosides: Coordination Chemistry, Antiparasitic Activity, Precursors to Conformationally Constrained Macrocyclic Architectures and Photophysical Properties

The research presented in this thesis focuses on the synthesis of functional glycosides and the investigation of their properties. This included the study of their ability to form metal complexes and the study of the antiparasitic activity of both the free glycosides and metal complexes, the use of glycosides to serve as precursors to conformationally constrained macrocyclic molecules and a preliminary investigation of the photophysical properties of a collection of glycosidic compounds. Two novel classes of glycosylated chelators were synthesized and characterized; one containing a dinitrogen aminopyridyl chelating motif and another containing a dinitrogen/oxygen phenoxy-iminopyridyl metal binding unit. The ability of these compounds to form stable metal complexes with several metals (Cu(II), Zn(II) and Fe(II)) was investigated and the coordination complexes obtained were characterized. The anti-chagasic and anti-leishmanial activity of a selection of these compounds were evaluated in collaboration with the group of Prof André Luis Souza dos Santos at the Microbiology Institute Paulo de Góes in Universidade Federal do Rio de Janeiro (UFRJ), in addition to their toxicity towards mammalian macrophage cells. Several compounds with antiparasitic activity with excellent selectivity indexes were identified. From the analysis of these preliminary investigations, structural features were identified that appear to be necessary for their antiparasitic activity. Preliminary investigations into the probably mode of action involving the study of the susceptibility of the glycosylated compounds to enzymatic hydrolysis by β-glycosidase were carried out. The toxicity of the most potent compounds was also investigated using the Galleria Mellonella model. The use of carbohydrates as scaffolds to synthesize conformationally constrained macrocycles was also explored. To this end, several galactosyl donors were synthesized and their reactivity towards glycosylation with a serine derivative and 2- chloroethanol was investigated. Two different synthetic strategies were compared to highlight the intramolecular glycosylation as the most suitable route for macrocyclization. Finally, the photophysical properties of a collection of glycosides and structural analogues was examined. This involved the synthesis of a family of substituted iminopyridyl compounds and the preliminary analysis of their fluorescent properties. Based on these studies, a plausible explanation for the fluorescent behaviour of glycoside functionalised iminopyridyl compounds is proposed

Enantiomeric separations using macrocyclic glycopeptide based chiral stationary phases, an application and mechanism study

The purpose of this dissertation was to further investigate the mechanism by which macrocyclic glycopeptides are able to separate enantiomers and to try to develop and expand their application in high performance liquid chromatography (HPLC) and other related separation techniques. A unique application of enantiomeric separations for chiral sulfoxides using macrocyclic glycopeptide chiral stationary phases (CSPs) was first demonstrated. Furthermore, another successful enantiomeric separation of a series of biologically active racemic analogues of dihydrofurocoumarin was done using this class of CSPs. The macrocyclic glycopeptides proved to be exceptionally selective for many classes of chiral compounds. Enantiomeric recognition mechanism was discussed and investigated. The last part of this dissertation presented an absolute configuration determination approach using exciton coupling chirality method. This method was extended as a general method for determination of the absolute configuration of dihydrofuroangelicins bearing a variety of C-8 substituted double bonds, synthesized in the racemic form and resolved through enantioselective chromatography

Cation Clock Reactions For The Determination Of Relative Reaction Kinetics In Glycosylation Reactions

This dissertation presents the development of cyclization reactions as clocks for the determination of the molecularity of glycosylation reactions in individual pyranoside systems and extends it to the arabinofuranoside systems. It also describes the development of selective hydrogenolytic cleavage of naphthylmethyl ethers in the presence of sulfides. The first part of chapter one gives an overview of the significance of glycochemistry and the challenges involved. The second part describes some selected glycosylation methods and extends this to the general mechanistic studies of glycosylation. This is followed by the discussion of the general clock reactions in literature which initiates a further discussion of the concept of cyclization as a clock for probing reaction mechanism and providing specific previous studies as well as the limitations involved and finally proposes the possible solution. The second chapter discusses the cation clock method based on the intramolecular Sakurai reaction to probe the concentration dependence of representative O- and C-glycosylation reactions from glycosyl trichloroacetimidate donors on activation by trimethylsilyl triflate. The 4,6-O-benzylidene-directed β-mannosylation, and both α and β-glucosylation demonstrated to proceed with a strong dependence on the concentration of the acceptor alcohol, whereas the α-mannosylation is much less concentration dependent. In the third chapter, the further development of the concept cation clock reactions for the determination of relative reaction kinetics in arabinofuranosylation is discussed. The use of intramolecular hydroxyl groups as candidates for clock reactions has been shown, leading to the formation of cyclic clock products in both 3,5-O-di-tert-butylsilylene and 3,5-di-O-benzyl arabinofuranoside series. In the study, formation of the β-arabinofuranoside is more concentration dependent than the α-isomers in the 3,5-O-di-tert-butylsilylene protected donor. The unselective formation of both, β and α-O-glycosides in the 3,5-di-O-benzyl protected arabinofuranosides is also understood in terms of a more of SN1-like mechanism with a strong nucleophile. Chapter four discusses the use of the cation clock method to determine the influence of acceptor nucleophilicity on the arabinofuranosylation mechanism. The use of acceptors of varying nucleophilicity, revealed that 3,5-di-tert-butylsilylene protected arabinofuranosylation is likely to occur vial a loose SN2 mechanism from each of the two rapidly equilibrating glycosyl triflate. In chapter five, hydrogenolytic cleavage of naphthylmethyl ethers in the presence of sulfides is described. The series of model thioethers or thioglycosides protected with combinations of benzyl ethers and 2-naphthylmethyl ethers, that the latter are readily cleaved selectively under hydrogenolytic conditions in the presence of the frequently catalyst-poisoning sulfides. Finally, chapter six documents the experimental procedures and characterization data for the synthesized compound