The fungi are a kingdom of organisms as complex and diverse as plants and animals with an estimated 1.5 million species, of which only about 10% have been named and described. The diversity of fungi is reflected in the diversity of fungal metabolites which are the products of secondary metabolism. The biosynthetic pathways are also diverse including polyketides, sesquiterpenes and diterpenes, diketopiperazines, cyclic peptides, -lactams and combinations of these pathways. Many of these compounds have biological activity which may be harmful, such as mycotoxins and phytotoxins, or beneficial such as antibiotics and other pharmaceuticals. The structure of many of these relatively low molecular weight compounds has often been a challenge to the natural products chemist but the continuing development of mass spectroscopy, nuclear magnetic resonance spectrometry with increasingly sophisticated methods of chromatography have led to the continuing discovery of novel fungal metabolites.

Key Concepts:

• Fungal secondary metabolism is both diverse and distinct.
  
• Secondary metabolism is linked to primary metabolism by a common pool of intermediates such as acetyl-CoA, mevalonate and amino acids.
  
• Penicillins, cephalosporins and griseofulvin are widely used antibiotics.
  
• Mycotoxins such as aflatoxin, ochratoxin and patulin are controlled in human foodstuffs by legislation.
  
• The majority of plants have endophytic fungi some of which produce useful metabolites.