Synthesis, Diol Binding and Structural Elucidation of a Novel Class of Boronic Acid Hydrazone &amp; Understanding the RG-II Dimer via synthesis of RG-II glycosyl residues and Quantifying Their Binding Interactions With Boric Acid Using 11B NMR Spectroscopy

Lukulay, Philip Sheku

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Year:: 2016
Contributor:: Lukulay, Philip Sheku (creator); Basu, Amit (Advisor); Delaney, Sarah (Reader); Seto, Christopher (Reader); Brown University. Department of Chemistry (sponsor)
Genre:: theses
Subject:: carbohydrate detection; boronic acids; diol binding; rhamnogalacturonan II; apiose; 11B NMR
Extent:: 9, 235 p.
DOI: https://doi.org/10.7301/Z0P55KX1

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Abstract:: Boronic acids are a special class of organic compounds that have been extensively utilized in a wide array of applications due to the unique properties associated with the boron atom. Alkylamino groups attached at the ortho position to phenylboronic acids hold a special place in the design of boronic acids for diol recognition as such systems have been shown to increase the rate of boronate ester formation. We were interested in using imino-type boronic acids as a new scaffold to study diol binding. From a synthetic standpoint, the imino boronate type systems offer an advantage since their formation is fast, offer greater stability under physiological conditions and relatively devoid of the challenging purification observed in the ortho-amino-type systems as a result of the zwitterionic property associated with the B-N moiety. In this work first part of this thesis, we report on the synthesis of boronic acid acylhydrazones as new compounds to study diol recognition. These novel classes of compounds were observed to have high binding affinities for diols when compared to phenylboronic acid. UV-Vis pH titration and 11B NMR studies showed that the origin of the high binding affinities was as a result of a pKa lowering effect of the proximal boronic acid moiety. We also observed that solvent influences the pKa our boronic acid acylhydrazones with protic solvents reducing the pKa while the opposite effect was observed in aprotic solvents. X-Ray Crystallography and 1H referenced-DOSY also showed that our boronic acid acylhydrazones can undergo several structural interconversions depending on solvent conditions employed. The second part of this thesis focuses on Rhamnogalacturonan II (RG-II), which is a complex pectin polysaccharide found in the primary cell wall of vascular plants where it exists predominantly as a dimer that is cross-linked via a 1:2 boronate-diol diester. This crosslinking occurs via apiose residues present on each of the respective RG-II monomers. In this work, 11B NMR spectroscopy was used to identify and quantify borate ester complexes formed between selected RG-II monomers and boric acid in order to understand the intrinsic binding preference for apiose over other glycosyl residues found in RG-II.
Notes:: Thesis (Ph. D.)--Brown University, 2016

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Lukulay, Philip Sheku, "Synthesis, Diol Binding and Structural Elucidation of a Novel Class of Boronic Acid Hydrazone & Understanding the RG-II Dimer via synthesis of RG-II glycosyl residues and Quantifying Their Binding Interactions With Boric Acid Using 11B NMR Spectroscopy" (2016). Chemistry Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0P55KX1

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Chemistry Theses and Dissertations

Theses and Dissertations for the Chemistry department.
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Synthesis, Diol Binding and Structural Elucidation of a Novel Class of Boronic Acid Hydrazone & Understanding the RG-II Dimer via synthesis of RG-II glycosyl residues and Quantifying Their Binding Interactions With Boric Acid Using 11B NMR Spectroscopy