The Nobel Prize in Chemistry 2021 was awarded to Benjamin List and David McMillan for their innovation in molecular construction, known as “asymmetric organocatalysis”. German scientist Benjamin List of the Max Planck Institute and Scotland-born scientist David MacMillan of Princeton University, independent of each other, developed a new type of catalyst.
Catalyst is a substance that speeds up a chemical reaction without being consumed in the overall reaction (It is chemically unchanged at the end of the reaction). All catalysts belonged to one of the two groups of metals and enzymes before the year 2000. Metals often act as catalyst efficiently, since they are able to easily give or take electrons to reactants. However, they show a low tolerance to oxygen and moisture, and are also expensive. In addition, some metal catalysts are toxic “heavy metals” that negatively affect the environment and people’s health.
The second type of catalysts are biological catalysts, known as enzymes. Enzymes are the proteins that catalyze biochemical reactions. All living organisms require these biomolecules for syntheses and break down reactions. Enzymes are extremely selective catalysts, which means that they are capable to choose a single substance, named substrate, from thousands of compounds.
Organocatalysis, which is the use of small organic molecules to catalyze organic transformations, is a new and fundamental tool, specifically in the synthesis of chiral molecules. It was in early 2000 that organocatalysis was conceptualized and introduced as an effective field of research by two papers: one from Benjamin List and his research group on enamine catalysis, and the other from David McMillan and his research group on iminium catalysis.
Compared to both metals and enzymes, organocatalysis has several advantages:
- First, these organic molecules are not sensitive to oxygen and moisture, so it is not necessary to use special equipment, complicated experimental techniques and dry reagents.
- Second, there are various organic molecules (such as amino acids, carbohydrates and hydroxy acids), which can be naturally obtained from biological materials. Thus, they are cheap and available, even in large-scale industrial manufacturing.
- Third, these small organic molecules are not toxic. This makes them safe and environmentally friendly.
Several aspects of organocatalysts drew the attention of research groups. It began to be used in various synthesis projects and represented benefits for asymmetric reactions. The greatest application of organocatalysis has been in medicinal chemistry. It has been used in academic research and pharmaceutical companies to construct new drugs.
This huge innovation changed the field of catalysis and brought new insights to chemical synthesis.