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The terpenoids ( ), sometimes called isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from one another not only in functional groups but also in their basic carbon skeletons. These lipids can be found in all classes of living things, and are the largest group of natural products. About 60% of known natural products are terpenoids. Plant terpenoids are used extensively for their aromatic qualities and play a role in traditional herbal remedies. Terpenoids contribute to the scent of eucalyptus, the flavors of cinnamon, cloves, and ginger, the yellow color in sunflowers, and the red color in tomatoes. Well-known terpenoids include citral, menthol, camphor, salvinorin A in the plant ''Salvia divinorum'', the cannabinoids found in cannabis, ginkgolide and bilobalide found in ''Ginkgo biloba'', and the curcuminoids found in turmeric and mustard seed. The steroids and sterols in animals are biologically produced from terpenoid precursors. Sometimes terpenoids are added to proteins, e.g., to enhance their attachment to the cell membrane; this is known as isoprenylation. ==Structure and classification== Terpenes are hydrocarbons resulting from the combination of several isoprene units. The isoprene unit has the formula CH2=C(CH3)CH=CH2. Terpenoids can be thought of as modified terpenes, wherein methyl groups have been moved or removed, or oxygen atoms added. (Some authors use the term "terpene" more broadly, to include the terpenoids.) Just like terpenes, the terpenoids can be classified according to the number of isoprene units used: * Hemiterpenoids, 1 isoprene unit (5 carbons) * Monoterpenoids, 2 isoprene units (10C) * Sesquiterpenoids, 3 isoprene units (15C) * Diterpenoids, 4 isoprene units (20C) (e.g. ginkgolides) * Sesterterpenoids, 5 isoprene units (25C) * Triterpenoids, 6 isoprene units (30C) (e.g. sterols) * Tetraterpenoids, 8 isoprene units (40C) (e.g. carotenoids) * Polyterpenoid with a larger number of isoprene units Terpenoids can also be classified according to the number of cyclic structures they contain. The Salkowski test can be used to identify the presence of terpenoids. Meroterpenes are any compound, including many natural products, having a partial terpenoid structure. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Terpenoid」の詳細全文を読む スポンサード リンク
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