Date of Thesis

Spring 2019

Thesis Type

Honors Thesis (Bucknell Access Only)

Degree Type

Bachelor of Science

Major

Cell Biology/Biochemistry

First Advisor

Michael R. Krout

Second Advisor

Timothy G. Strein

Third Advisor

David S. Rovnyak

Keywords

Synthesis, Bile Salts, Chiral Separations, Capillary Electrophoresis, Nuclear Magnetic Resonance

Abstract

Bile salts are naturally occurring steroidal compounds that are synthesized in the liver and secreted into the gastrointestinal tract to assist in emulsifying lipids in food. Bile salts have also been used in analytical chemistry as chiral selectors, but the structural dynamics of bile salts remains elusive. Above a certain concentration, the critical micelle concentration (CMC), bile salt monomers aggregate to form micelles, and some bile salt micelles have the ability to discriminate between chiral isomers. The Strein/Rovnyak group has investigated this chiral selection mechanism with various bile acids, including deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA) and have discovered that the presence of a C12 hydroxyl group is required for chiral selection. To study the importance of this C12 hydroxyl group, a 4-step synthesis of novel bile acid 12-methoxy deoxycholic acid (12-moDCA) was carried out with a 52.7% overall yield to support analytical work on the chiral recognition mechanism of 12-moDCA micelles. A chiral probe molecule,1,1’-binaphthyl-2,2’-diyl hydrogen phosphate (BNDHP) was used in these experiments to reveal chiral selectivity in 12-moDC micelles. Through analysis using micellar electrokinetic capillary chromatography (MEKC) and nuclear Overhauser effect spectroscopy (NOESY), 12-moDCA micelles were found to discriminate BNDHP enantiomers, indicating that a hydrogen bond donor at C12 is not necessary in forming a micelle with chiral recognition abilities.

Another structural feature on bile salts that has proven significant is the length and composition of the C17 side chain. Previous studies with taurodeoxycholic acid (TDCA), a bile acid with an elongated and functionalized C17 chain, has shown improved chiral recognition abilities over DCA, which has a shorter C17 chain. To study this, glyco-conjugates of DCA, cholic acid (CA) and 12-moDCA were synthesized to elongate and functionalize the C17 chain of these bile acids. MEKC and various 1D and 2D nuclear magnetic resonance (NMR) data show that the C17 side chain interacts differently with (R)- vs. (S)-BNDHP while glyco-conjugated micelles form at lower CMCs, suggesting that the elongated C17 chain helps to drive micelle formation and chiral recognition.

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