Diastereomer
Diastereomers are stereoisomers that are not mirror images of each other and have different physical and chemical properties. They arise in molecules with two or more chiral centres, where configurations differ at some but not all centres.
What are diastereomers?
Diastereomers are a class of stereoisomers that are not enantiomers—meaning they are not mirror images of one another. This distinction arises in molecules containing two or more chiral centres. When the configuration at one or more chiral centres differs while at least one remains the same, the resulting isomers are diastereomers. Unlike enantiomers, diastereomers exhibit different melting points, boiling points, solubilities, and reactivities, which makes them separable by conventional techniques such as chromatography or recrystallisation.
How do diastereomers differ from enantiomers?
The key difference lies in their spatial relationship: enantiomers are non-superimposable mirror images, while diastereomers are not. Enantiomers have identical physical properties except for their interaction with plane-polarised light (optical activity) and chiral environments. Diastereomers, however, have distinct physical and chemical properties, which is crucial in pharmaceutical development where one diastereomer may be therapeutically active while another is inactive or even toxic.
Why are diastereomers important in drug development?
In medicinal chemistry, the synthesis of chiral molecules often produces mixtures of diastereomers. Because each diastereomer can have different biological activity, pharmacokinetics, and toxicity profiles, it is essential to control or separate them during manufacturing. Regulatory agencies such as the MHRA, EMA, and FDA require rigorous characterisation of stereoisomeric impurities. Techniques like HPLC, NMR, and chiral chromatography are routinely used to assess and purify diastereomeric mixtures to ensure product safety and efficacy.
Related concepts
Diastereomer separation is critical in quality control, particularly in the production of active pharmaceutical ingredients (APIs). The use of chiral auxiliaries, asymmetric synthesis, and chiral stationary phases in HPLC are standard strategies to manage diastereomeric purity. Regulatory frameworks such as ICH Q6A and ISO 17025 guide the analytical validation of methods used to detect and quantify diastereomers in pharmaceuticals.