text: A variety of organisms including bacteria, fungi, and plants, produce small molecule secondary metabolites also known as natural products, which play a role in cell signaling, pigmentation and in defense against predation. Secondary metabolites are a rich source of biologically active compounds and hence are often used as research tools and leads for drug discovery. Examples of secondary metabolites include:
  * Alkaloids
  * Glycosides
  * Lipids
  * Nonribosomal peptides, such as actinomycin-D
  * Phenazines
  * Natural phenols (including flavonoids)
  * Polyketide
  * Terpenes and terpenoids, including steroids
  * Tetrapyrroles.