Scientist explains how drugs with the same chemical properties can have drastically different effects

My research has focused on one such compound found in red grapes and peanuts, resveratrol. It has been a scientific mystery why clinical trials on using resveratrol to treat Alzheimer’s disease have had inconsistent results. Turns out, it may be because two different forms were used – while one may help with cognition and memory, the other may be toxic to the nervous system.

Isomers and amino acids

Many drugs have the same atoms and bonds but are arranged differently in space. These drugs are called chiral compounds – meaning they exist as two non-superimposable mirror images. For example, your hands are also non-superimposable mirror images of each other. Although they look the same, they don’t overlap when you put one on top of the other.

Usually, these mirror-image versions have very similar properties because they share the same elements and bonds. But the way they are arranged in space can drastically change the effects they have in the body. Just as you wouldn’t be able to fit a left-handed glove on your right hand, a left-handed version of a drug wouldn’t be able to fit into a target in the body shaped to fit a right-handed molecule.

Chiral molecules come in two versions, or isomers, defined by their optical activity. This means that if you shine polarized light on a chiral molecule, one will rotate the light to the left (indicated by the prefix L-, or levorotatory) while the other will rotate it to the right (indicated by the prefix D, or dextrorotatory).

Amino acids, the building blocks of proteins, are chiral molecules. Living organisms primarily make proteins from amino acids with L configurations. The D configuration, however, has many other functions in nature. Bacteria, for example, use D configuration amino acids to make their cell walls. Mammals use D configuration amino acids as messengers in their nervous and endocrine systems.

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