For over 100 years, pharmaceutical companies have used flat, ring-shaped structures known as aromatic rings to help drugs attach to specific sites in the body. These rings, such as benzene rings, are commonly found in medicines and are easy to produce. However, their flat and rigid shape can make it challenging for them to fit well into the complex, three-dimensional shapes of biological targets. Additionally, these rings can have issues like poor solubility in water and unintended interactions with other parts of the body. As a result, researchers are exploring ways to replace these flat structures with more flexible, three-dimensional ones that could lead to more effective and targeted drugs. A team led by Varinder Aggarwal at the University of Bristol has developed a new method to overcome a major obstacle in creating these 3D structures. The challenge comes from a natural chemical rule known as the rule-of-five, which dictates that molecules prefer to react in a specific way. This preference has made it difficult for scientists to create the diverse 3D structures that could be useful in drug development. The team started with simple, nitrogen-containing molecules called 1,5-dienes, which are relatively easy to obtain. These molecules have a chemical group attached to the nitrogen that can be altered to control how they react when forming a ring. The researchers then introduced a light-absorbing photocatalyst and exposed the mixture to blue light. The photocatalyst absorbed the light and transferred its energy to the molecule. An acetyl group attached to the nitrogen guided the molecule to form a ring in a different, more desirable way, resulting in a rigid three-dimensional structure. To test the potential of their method, the team created a 3D version of a part of an experimental drug designed to improve cognitive function. They also performed additional chemical reactions on the 3D structures, adding and modifying different chemical groups to show that these structures can be customized for various uses. The researchers believe their approach could open up new possibilities in drug development. They predict that their method will inspire new strategies for creating complex, three-dimensional molecular structures that could lead to the discovery of more effective medicines and other innovative applications.