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Title: C-Alkyl inositol phosphates for use in receptor-ligand engineering
Author: Swarbrick, Joanna
ISNI:       0000 0004 2678 2389
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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The phosphatidylinositol phosphates (PIPns) and inositol phosphates (IPns) are intricately involved in cell signalling. They bind to a vast array of proteins, which results in a host of physiological responses. Therefore it is difficult to determine the precise downstream effects of an individual protein-phosphoinositide interaction. Perturbations of these networks occur in pathological conditions such as cancer and diabetes increasing the need to understand these systems. Receptor-Ligand Engineering (RLE) may provide the tools to map these interactions. Chemical modification of the small PIPn or IPn ligand and complementary mutation of binding site amino acids is used to create a unique protein-ligand binding pair. Once the modified protein is engineered into the cell line, the dose dependent effects of its stimulation with the complementary ligand can be studied in isolation from signal pathway cross-talk. Phosphatidylinositol 4,5-diphosphate [PtdIns(4,5)P2 / PIP2] and phosphatidylinositol 3,4,5-triphosphate [PtdIns(3,4,5)P3 / PIP3] analogues with C-alkyl groups replacing the axial inositol C-Hprotons would be suitable ligands for RLE. To date, no such analogues are known in the literature. The key challenges in preparation of such compounds are selective protection and deprotection of the myo-inositol hydroxyls, introduction of new inositol C-substituents with retention of myostereochemistry,and phosphorylation of an unnatural tertiary centre. 4-C-Alkyl IP3 and 4-C-alkyl IP4 analogues were chosen as targets to explore the chemical limitations of analogue synthesis. Orthoesters simultaneously tied up the 1-, 3- and 5-O differentiating between the remaining three hydroxyls in a rigid structure. Oxidation of the isolated 4-OH to the inos-4-ose and selective reintroduction of the myo-geometry by addition of dimethylsulfoxonium methylide generated the key exo-methylene oxide intermediate. Lithium alkyl cyanocuprates were employed to open the exo-methylene oxide introducing primary, -secondary, and -tertiary alkyl and aryl protrusions. 4-C-Alkyl triols were prepared by regiocontrolled DIBAL-H reduction of the orthobenzoate to a benzyl ether, directed by the 4-C-alkyl protrusion. The corresponding 4-C-alkyltetrols were obtained by acidic hydrolysis of the orthobenzoate and cleavage of the resultant benzoate ester. All polyols were then phosphorylated and globally deprotected to generate the final series of 4-C-alkyl IP3 and IP4 analogues. Some initial investigations were also performed to extend this methodology to prepare 4-and 5-C-alkyl derivatives from a common precursor.
Supervisor: Gaffney, Piers Sponsor: EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral