A chiral molecule: shape matters in its effects

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The Astaxanthin molecule has two asymmetric carbons located at the 3 and 3’ positions of the benzenoid ring. The hydroxyl groups that are attached to these asymmetric carbons can be oriented in space in different ways. If the OH group is projected below the plane of the molecule it is said to be in S configuration. The R configuration results if the projection is above the plane. Astaxanthin is then called a chiral molecule, which has three configurations, (3S, 3’S), (3R, 3’S) and (3R, 3’R), called enantiomers. Chiral isomers show different chemical behavior when reacting with other chiral molecules, just as a left hand interacts differently with left and right-handed gloves.

Chiral asymmetry exists in all biologically active molecules of animals like enzymes, nucleotides, amino acids, DNA, proteins, and carbohydrates. The three different Astaxanthin enantiomers can
produce marked differences in biological activities such as toxicology, pharmacology, or metabolism. The animal body acts as a chiral selector and will interact and metabolize each enantiomer to generate different physiological responses. One isomer may produce the desired therapeutic activity, while the other may be inactive or in worst cases produce undesired or toxic effects.