Master of Science (MS)
Semester of Degree Completion
This research work comprised two projects. The first one mainly focused on the synthesis of 12 alanine derivatives and analysis of their interactions with β-cyclodextrin through 1H NMR titration. And the other project was an investigation of the conjugation effect of alkynones in its addition reactions with tributyltin hydride.
The synthesis of the alanine derivatives involved methyl esterification of alanine and then the substitution of an NH hydrogen with a benzoyl group. A total of 4 different substitution groups, labeled as the "A" groups, were introduced on the para-position of the benzoyl's phenyl group. Since alanine has one chiral center, we synthesized D-, L- and the racemic derivatives of alanine bearing these A groups, respectively. A total of 12 alanine derivatives were synthesized.
These 12 alanine derivatives, which differ in their specific chirality or A groups, were later used as guest molecules for the study of their interactions with the host molecule, β-cyclodextrin. NMR titrations were carried out incrementally to study whether or not the host molecule can recognize guest molecules as non-solvent molecules and also, whether or not the host molecule can differentiate between the D- and L- enantiomers of the guest molecules. The 1H NMR titration experiments showed that all the guest molecules were recognized by the host molecule as indicated by the fact that upon mixing with the host molecule, the chemical shifts of hydrogens on the benzene ring of the guest molecules changed. What's more, the hydrogens on the benzene ring of the D-isomer of the guest molecule with A being a nitro group (NO2) exhibited greater changes in the aromatic proton area than its enantiomer. The other three types of guest molecules with their A groups being H, CH3, OCH3 respectively, did not show this type of chirality recognition or the recognition phenomenon was not obvious at all.
The second project involved the addition reaction of alkynones with tributyltin hydride. Two different reaction conditions and two different starting materials were used . At first, tributyltin hydride was added to a solution of 1-phenyl-2-propyn-1-one to undergo an addition reaction that was expected to be consistent with Markovnicov's rule and yield an alkene with geminal hydrogens. However, unexpectedly, a new dimeric product, 1,6-diphenyl-2,4-hexadiene-1,6-dione, was isolated in a very low yield with the major product being the trans alkene derived from the addition of the tributyltin to the triple bond. When using an icebath to cool the reaction solution down to 0 °C before the addition of tributyltin hydride, and stirring the reaction mixture for a longer time, no products with geminal hydrogen or alkenes with cis-configuration were isolated, nor was 2,3-bis(methylene )-1,4-diphenyl-1,4-butanedione detected. The product isolated was still a trans alkene. However, when this procedure (with icebath and longer reaction time) was tried out with an ester, phenyl 2-propiolate, the expected alkene product with geminal hydrogen was obtained.
Yang, Guang, "Investigation of β-Cyclodextrin's Ability in Differentiating Chiral Guest Molecules and Synthesis of 1,6-diphenyl-2,4-hexadiene-1,6-dione" (2015). Masters Theses. 2360.