Studies in the synthesis and isolation of natural products.

摘要

Two synthetic strategies towards the Lycopodium alkaloid nankakurine A were described. Attempts toward a tandem cyclization to construct the tetracyclic core of the natural product were discussed. While the tandem cyclization event was not observed, a tricyclic product was isolated. This product was elaborated to substrates for an intramolecular hydroamination to obtain the natural product. In the course of these studies, a structural revision of nankakurine A upon the isolation of nankakurine B prompted us to revise our retrosynthesis of the natural product. Progress towards a revised retrosynthesis of the nankakurines utilizing an intramolecular enamine/imminium ion condensation reaction was described.;One approach to the synthesis of the antibiotic platensimycin was detailed. This approach utilized an intramolecular Diels-Alder (IMDA) reaction to assemble the core of the natural product. Three IMDA substrates were synthesized from (+)-carvone using a Petasis/hydroboration sequence. These substrates were tested in both inverse and normal electron demand IMDA reactions.;The use of triflic anhydride in the activation of enones was developed into two new methods for the synthesis of vinyl triflates. The first method that was developed involved the activation of enones with triflic anhydride with concomitant arylation, a reaction termed a Friedel-Crafts triflation. A second method utilizing the conjugate addition of allylstannanes with concomitant triflation also was developed. Products from this reaction were used as substrates for an intramolecular Heck cyclization to provide rapid access to polycyclic systems.;The agricultural bacterium Xylella fastidiosa is the causative agent for diseases of grape, citrus, almond, and alfalfa plants, which cause devastating economic losses worldwide. The pathogen regulates its lifestyle in a density dependent fashion using a diffusible signaling factor (DSF). The isolation and characterization of two putative X. fastidiosa DSFs was described, and a preliminary investigation of their biological activity in Xylella was discussed.