Allenic carotenoids function

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Functional groups include allene, acetylene, hydroxy, methoxy, epoxy, keto, aldehyde, carboxylate, lactone, acyl ester, glycoside, glycosyl ester and sulphate. Carotenoids with elements other than oxygen directly attached to the carbon skeleton have not been found in Nature. 

Most carotenoids are xanthophylls, not carotenes. These compounds are formed by the introduction of one or more oxygen functions into the molecule. Other modifications of carotenoids involve the formation of allenic and acetylenic groups, additions to the polyene chain, and the loss of carbon atoms. Little is known concerning the biosynthesis of these compounds. 

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