THESIS
2008
xv, 86 p. : ill. ; 30 cm
Abstract
Diels-Alder reaction, a former [4+2] cycloaddition is one of the most amazing reactions known to mankind and it is widely used in the total synthesis of natural products. In nature, a significant number of natural products seem to be Diels-Alder like adducts and this leads to chemists questioning whether Diels-Alder reaction can happen in nature and whether an enzyme (known as Diels-Alderase) is present to catalyze such reactions. Our collaborators from Kunming isolated natural products known as Longphyllineside A-C and Disculponeatin A-B and they resemble Diels-Alder adducts. In chapter 2, we show that the possible Diels-Alder pathway for the biosynthesis of Longphyllineside A is supported by density functional theory calculations of model reactions. The calculated region- and stereo-c...[
Read more ]
Diels-Alder reaction, a former [4+2] cycloaddition is one of the most amazing reactions known to mankind and it is widely used in the total synthesis of natural products. In nature, a significant number of natural products seem to be Diels-Alder like adducts and this leads to chemists questioning whether Diels-Alder reaction can happen in nature and whether an enzyme (known as Diels-Alderase) is present to catalyze such reactions. Our collaborators from Kunming isolated natural products known as Longphyllineside A-C and Disculponeatin A-B and they resemble Diels-Alder adducts. In chapter 2, we show that the possible Diels-Alder pathway for the biosynthesis of Longphyllineside A is supported by density functional theory calculations of model reactions. The calculated region- and stereo-chemistry of the Diels-Alder reaction corresponds to the formation of Longphyllineside A as kinetic product, but not thermodynamic product. The study of Disculponeatin A is presented in chapter 3. Our study shows that the calculated NMR data of S isomer matches the experimental data reasonably well. In addition, the S isomer is obtained via Diels-Alder dimerization with the lowest activation barrier, albeit it is the kinetic product as compared to the R isomer. However, its calculated relatively high activation barrier indicates that a metal ion either in solution or from an enzyme may be necessary to coordinate to three closing carbonyl groups in the transition state that leads to the formation of the S isomer, lowering down its activation barrier significantly. A brief theoretical study on the proposed Diels-Alder reaction pathway leading to Lovastatin has also been performed, which is given in chapter 4. Finally, in chapter 5, an allyl-In(I) tetramer is proposed as the reactive intermediate in the allylation reaction of carbonyl compounds in aqueous solution. This species is able to reproduce the experimentally observed
1H NMR chemical shift, reactivity, secondary kinetic isotope effect, and diastereoselectivity of indium-mediated allylation reactions.
Post a Comment