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The terpenoids, also known as isoprenoids, are a class of naturally occurring organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeably with "terpenes", terpenoids contain additional functional groups , usually containing oxygen. [ 1 ]
In general, carotenoids absorb wavelengths ranging from 400 to 550 nanometers (violet to green light). This causes the compounds to be deeply colored yellow, orange, or red. Carotenoids are the dominant pigment in autumn leaf coloration of about 15-30% of tree species, [3] but many plant colors, especially reds and purples, are due to polyphenols.
Commonly, terpenes contain 2, 3, 4 or 6 isoprene units; the tetraterpenes (8 isoprene units) form a separate class of compounds called carotenoids; the others are rare. The basic unit isoprene itself is a hemiterpene. It may form oxygen-containing derivatives such as prenol and isovaleric acid analogous to terpenoids.
Tetraterpenoids (including many carotenoids) are tetraterpenes that have been chemically modified, as indicated by the presence of oxygen-containing functional groups. Phytoene is biosynthesized via the head-to-head condensation of two GGPP molecules. [2] One group of tetraterpenes, and possibly the most studied one, is the carotenoids pigments ...
Xanthophylls are carotenoids with molecules containing oxygen, such as lutein and zeaxanthin. Carotenes are carotenoids with molecules that are unoxygenated, such as α-carotene, β-carotene and lycopene. [22] In plants, carotenoids can occur in roots, stems, leaves, flowers, and fruits. Carotenoids have two important functions in plants.
Carotenes are produced in a general manner for other terpenoids and terpenes, i.e. by coupling, cyclization, and oxygenation reactions of isoprene derivatives. Lycopene is the key precursor to carotenoids. It is formed by coupling of geranylgeranyl pyrophosphate and geranyllinally pyrophosphate. [18]
Carotenoids are the most common group of pigments found in nature. [18] Over 600 different kinds of carotenoids are found in animals, plants, and microorganisms. Marine animals are incapable of making their own carotenoids and thus rely on plants for these pigments. Carotenoproteins are especially common among marine animals.
[4] [5] Phytochemicals under research can be classified into major categories, such as carotenoids [6] and polyphenols, which include phenolic acids, flavonoids, stilbenes or lignans. [5] Flavonoids can be further divided into groups based on their similar chemical structure, such as anthocyanins , flavones , flavanones , isoflavones , and ...