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Cyclobutane amino acids and peptidomimetics, parallel catalyst screening for aziridination
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This thesis describes two projects: (i) syntheses and conformational studies of cyclobutane amino acids and peptidomimetics; and, (ii) parallel screening of catalysts for asymmetric aziridination. Syntheses and conformational studies of nonnatural amino acids and peptide mimetics are important in synthetic and medicinal chemistry. Recent discovery of naturally occurring cyclobutane amino acids has raised considerable interest in the syntheses and biological studies of these types of compounds. This thesis will demonstrate asymmetric syntheses of cyclobutane amino acids, incorporation of these compounds into designed peptidomimetics, and conformational studies of the tripeptide mimics of these cyclobutane amino acids and an octapeptide containing these acids. From the first project, the following conclusions were formulated: the cyclobutane amino acids and their derivatives can be synthesized and incorporated into peptidomimetics; Crystal structures of the tripeptide mimics show extended conformations; and, the octapeptide synthesized in this study adapts an P-hairpin secondary structure, as evidenced by CD and 2D NMR. The second project is parallel catalyst screening for aziridination of olefins. Since aziridines are versatile intermediates for syntheses of biologically important compounds, such as amino acids, efforts to discover a catalytic system for aziridination are desirable. Copper and rhodium catalyzed asymmetric aziridination of olefins had previously been reported by others. High yields and high enantiomeric excess with the ylides Phl=NTs and PhI=NNs have been obtained. For metal-catalyzed aziridination, since there are only two aziridinating reagents available, we were interested in developing new nitrogen ylides. The aziridination section describes how known preparations of various nitrogen ylides and how catalysts screening using high throughput screening methodology. Microtitre plates were used to screen various metal catalysts, ylides, substrates, and solvents at different temperatures. Preliminary results from the plates indicates that Doyle's catalysts gave satisfactory yields of aziridine. Repeatable large scale aziridination catalyzed by Doyle's catalysts are optimized and reported.
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Includes bibliographical references: p. 150-155.
Issued also on microfiche from Lange Micrographics.
Li, Shih-ming (1996). Cyclobutane amino acids and peptidomimetics, parallel catalyst screening for aziridination. Master's thesis, Texas A&M University. Available electronically from
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