The biosynthesis of amphotericin B.

The polyene antibiotic and natural product amphotericin B is produced by Streptomyces nodosus, together with its co-metabolite amphotericin A. Polyene antibiotics are used in the treatment of fungal diseases, despite their potent human toxicity. Information on the biosynthetic pathway would provide us with the basic information to produce less toxic analogues. An investigation into the biosynthesis of amphotericin B was undertaken which involved a variety of methods and techniques. Attempted incorporation of precursors into the metabolite was a major part of this work, with the feeding of [13C1]- and [13C2]-acetates and diethyl [13C1]malonate, with any incorporation being detected by NMR and mass spectrometry. The synthesis of the deuteriated (2S,3S)-3-hydroxy-2-[13C3]methyl[3-13C]butanoyl N-acetylcysteamine thioester was undertaken, which was consequently fed to cultures of S. nodosus. An investigation of growth and production of amphotericin B from cultures of S. nodosus was carried out in order to determine the optimum time for the feeding of precursors. An examination of extracts of the culture broth also provided information on co-metabolites and possible putative intermediates present, which, although only a brief introductory study, indicated the potential importance of such investigations. Some evidence for the proposed mode of biosynthesis of amphotericin B was found, although there was no detection of incorporation of the administered deuteriated thioester. The background work into the growth of Streptomyces nodosus and production of amphotericin B that was carried out in this study will form the basis for any future investigations into the biosynthesis of this important metabolite.