Browsing by Subject "total synthesis"
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Item Beta-Lactones as Synthetic Vehicles in Natural Product Synthesis: Total Syntheses of Schulzeines B & C and Omphadiol, and Studies toward the Total Syntheses of Scabrolides A & B and Sinulochmodin C(2012-02-14) Liu, Gang?-Lactones are a class of structurally unique compounds. The versatile reactivity patterns offered by ?-lactones have enable chemists to utilize them as powerful synthetic vehicles in complex molecule synthesis. In the total syntheses of the naturally occurring, ?-glucosidase inhibitors schulzeines B & C, a readily available trichloromethyl ?-lactone was used as a versatile masked surrogate for bishomoserine aldehyde, which led to a highly efficient construction of the core structures through a pivotal Pictet-Spengler condensation and a Corey-Link reaction. The first total synthesis of (+)-omphadiol was achieved in ten steps from (R)-carvone. This synthesis features a three-step synthesis of a bicyclic ?-lactone, which constitutes the key intermediate for the highly stereocontrolled introduction of the six contiguous stereogenic centers in the natural product. In efforts toward the total syntheses of scabrolides A & B and sinulochmodin C via transannular C-H insertions, ?-lactones served as the key intermediates for the synthesis of complex macrocyclic model substrates. These model studies provided valuable insights into the reactivity and selectivity issues for transannular C-H insertion reactions.Item Large scale total synthesis of apoptolidinone and progress towards the total synthesis of ammocidin(2009-05-15) Liu, QingsongApoptolidin 1.1 was isolated in 1997 by Hayakawa and co-workers from a soil bacterium Nocardiopsis sp. during screening for specific apoptosis inducers. The primary biological test revealed that this polyketide macrolide induced apoptosis in cells transformed with the adenovirus type E1A oncognene, but not normal cells. This dissertation describes the latest studies in understanding of apoptolidin?s biological activity mechanism and previous contributions towards its total synthesis. Synthesizing apoptolidinone 1.26 by an intra-molecular Horner-Wadsworth-Emmons approach featuring a Suzuki coupling, cross metathesis and two diastereoselective aldol reactions is discussed. 15 mg apoptolidinone is prepared via our previously developed intramolecular Suzuking coupling approach. Ammocidin 3.1, which was found to induce apoptosis in Ba/F3-v12 cells in an IL- 3 free medium, is a specific apoptosis inducer discovered by Hayakawa and co-workers in 2001 from Saccharothrix sp. AJ9571. A strategy featuring Suzuki coupling, cross metathesis, Yamaguchi macrolactonization and three asymmetric aldol reactions was applied to the total synthesis of ammocidinone 3.6, the aglycone of ammocidin. The preparation of the key building blocks was discussed in the following chapter: aldehyde 3.8 (C14-C19) was synthesized via Sharpless asymmetric epoxidation; ethyl ketone 3.9? (C20-C28) was prepared via Kobayashi and Crimmins?s asymmetric aldol methodologies; aldehyde 3.14 (C7-C13) was generated by Brown crotylation and cross metathesis.Item Studies towards the total synthesis of the macrocyclic diamine alkaloid haliclonacyclamine C(Texas A&M University, 2005-11-01) Qu, TaoMarine sponges produce a series of complex polycyclic diamine alkaloids which appear to have a common biogenesis from simple bis-pyridine macrocycles. These structurally novel secondary metabolites are presumably biosynthetically produced by the controlled ionic coupling of macrocyclic 3-alkyl piperidines leading to 3,4??-linked bis-piperidines (ii). Included among these diamine marine alkaloids is haliclonacyclamine C (i) which serves as our synthetic target. Chapter I in this thesis provides background information describing biological activity and proposed biosynthetic pathways to these important diamine marine alkaloids. Chapter II details progress towards the total synthesis of haliclonacyclamine C. The focus of Chapter II will be on our successful construction of the 3,4??-linked bispiperidine central core (ii) highlighted by the use of palladium-mediated C-C bond forming processes. The stereoselective hydrogenation of a coupled product will also be discussed.