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I. Synthesis of β-Sitosterol and Phytosterol Esters; II. New Methodology for Singlet Oxygen Generation from 1,1-Dihydroperoxides Derivatives
Phytosterols are steroid compounds structurally similar with cholesterol and vary in the nature of carbon side chain. β-Sitosterol is commercially available in preparative amount only as mixtures with other phytosterols. New semipreparative synthesis of pure β-sitosterol and sidechain-modified phytosterols is discussed in this dissertation. This new synthesis is achieved via a temporary masking of the stigmasterol 5,6-alkene as an epoxide. Following performance of the desired modification, the alkene is regenerated through a mild deoxygenation. Preparation of phytosterol esters for cholesterol metabolism study is also discussed in this dissertation. Singlet oxygen (1O2) is the lowest excited state of oxygen molecule. Due to its special properties, 1O 2 has been widely used as the oxidant in chemistry, biology, and medicine. In the past decades, two major generation methods have been developed, photosensitization and chemical generation. However, most of the reported chemical generations require the water-rich media, which is associated with short 1O 2 lifetime as a major drawback. Therefore, there is a need for 1O2 generation from organic solvents. The investigation of fragmentation of monoactivated derivatives of 1,1-dihydroperoxides is discussed in this dissertation. This previously unobserved fragmentation can be conducted in various organic solvents and generate high yield of 1O 2. This reaction is general for a range of skeletal frameworks and activating groups, and can be applied directly to 1,1-dihydroperoxides via in situ activation. Kinetic and mechanistic investigation suggests it involving rate-limiting formation of a peroxyanion, which decompose to generate 1O 2 via Grob-like process.
Hang, Jiliang, "I. Synthesis of β-Sitosterol and Phytosterol Esters; II. New Methodology for Singlet Oxygen Generation from 1,1-Dihydroperoxides Derivatives" (2012). ETD collection for University of Nebraska - Lincoln. AAI3503477.