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Date of Award

2006

Document Type

Thesis - Pacific Access Restricted

Degree Name

Master of Science (M.S.)

Department

Chemistry

First Advisor

Larry O. Spreer

First Committee Member

Andreas Franz

Second Committee Member

Charles M. McCallum

Third Committee Member

Silvio Rodriguez

Abstract

A radioisotope of rubidium, 82Rb is used in positron emission tomography. Neutral crown ethers and cryptands have been studied as carrier ligands for Rb+ but exhibit low ion carrying capacity and high toxicity. The present study involved investigating a lariat ether containing an ionizable phosphoryl moiety and a lipophilic sidearm. This kind of molecule is expected to be ionized at physiological pH. It should be able to form neutral complexes with Rb+ and may be able to cross the blood-brain barrier.

Molecular modeling of crown ether-alkali metal cation complexes indicates that a macrocycle containing more than 18 but less than 21 atoms can incorporate Rb+ ion in its cavity. Molecular modeling of some of the complexes of phospho-lariat ethers with rubidium using the Spartan'02 software package revealed that a lariat ether containing 20 member macrocycle will probably form the most stable complex with Rb+ion. Also, it was thought that more flexibility could be imparted to the macrocycle if it contains propyleneoxy units instead of ethyleneoxy units which form most crown ethers. Molecular modeling of two phospho-lariat ethers with 16 and 20 membered rings revealed that 20 membered macrocycle may be a better choice due to the side arm's participation in the complexation with Rb+ to a greater extent. Molecular modeling was used to find the bond angles and bond distances in this molecule.

The synthesis to obtain ionizable phospho-bipodands was performed using subsequent benzylation, phosphorylation and hydrogenation steps. The characterization of products was done using HPLC, NMR and ESI-MS techniques. The synthetic scheme used was demonstrated to be plausible and could be used to obtain ionizable phoshobipodands. Extraction using solid phase anion exchange columns proved to be a good clean up procedure for obtaining pure bipodand. This bipodand could be used as a precursor for synthesizing an ionizable 20 membered lariat ether.

Pages

119

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