ABSTRACT
This chapter presents assignments of almost all of the polyethers together with their application to structural studies. One of the structural features of most polyether antibiotics is the repetition of similar partial structures in the molecules, which results in complicated C NMR spectra with many methylene and methine signals crowded in a narrow region. In addition to structural investigation, the methodology will further enable one to study important problems associated with the mechanisms of action of the polyether antibiotics, such as interaction with metal cations in solution. Subtle conformational changes of the antibiotics caused by complex formation will be amply reflected in their C NMR spectra. C NMR spectroscopy is well known to be a very useful tool for the structural elucidation of natural products. This is also true with the polyether antibiotics, especially when good crystals suitable for x-ray analysis are not obtainable, as evidenced in case of narasin.
