precursors

In science, a precursor is a substance that participates in the formation of another substance. In chemistry and biochemistry, precursors act as starting materials, intermediates, or building blocks from which target molecules are synthesized. The term emphasizes that the precursor is transformed or consumed in the reaction step that yields the final product.

Chemical synthesis often proceeds through a sequence of precursors, each contributing specific fragments to the product’s structure. Examples include salicylic acid as a precursor to acetylsalicylic acid (aspirin) in classic pharmaceutical production, and simple sugars or amino acids that function as precursors to more complex metabolites and biomolecules.

In biology, precursors are often endogenous compounds that feed into metabolic pathways. Glucose and other monosaccharides serve as precursors to many cellular products, while amino acids act as precursors to proteins. Precursors can also be exogenous, obtained from diet or environment and used in biosynthetic processes.

Regulatory frameworks applicable to precursors exist in chemistry and pharmacology because some substances can be diverted for illicit drug manufacture. Authorities may require licensing, tracking, reporting, or controlled access to certain precursors to prevent misuse while allowing legitimate research and industry.

Beyond chemistry and biology, the idea of a precursor appears in materials science, where a precursor compound or film is converted into a final material, such as precursors used in ceramics or semiconductor fabrication.