This very diverse group of compounds is presumably generated by an oxidative cleavage of the carotenoid (tetraterpenoids
, [C.sub.40]) molecule between the [C.sub.9] and [C.sub.10] positions, yielding apocarotenoids (also called norisoprenes) with 13 carbon atoms.
Carotenoids, the C40 tetraterpenoids
derived from head-to-tail condensation of eight isoprenoid units, are notable for their wide distribution, structural diversity, and various functions.
The chemical structure of lutein ([C.sub.40][H.sub.56][O.sub.2]) consists of 40-carbon, hence known as tetraterpenoids
, with alternating single and double carbon-carbon bonds with attached methyl side groups.
Carotenoids are tetraterpenoids
naturally occurring in plants and other photosynthetic organisms.