Isoprenoid definition

Figure 8. C q isoprenoid tiophenes as indicators of palaeosalinity structures, definition of the isoprenoid thiophene ratio (ITR) and some typical distributions (based on peak heights in m/z 308 mass chromatograms) in sediments and petroleums. Description of the samples is given elsewhere (16).

Figure 14. (a) Depth profile of isoprenoid thiophene ratio (ITR) for the Jurf ed Darawish oil shale, (b) Definition of ITR. 

Spom, Roberts and Goodman81 have recently provided a broad overview of the field of the retinoids, based on the IUPAC-IUB Joint commission definition that Retinoids are a class of compounds consisting of four isoprenoid units joined in a head-to-tail manner. (The work was updated in 1994) Whereas there is only a handful of naturally occurring retinoids using this definition, more than a thousand man-made retinoids are known. The IUPAC-IUB bulletin recommended that the term, retinal, not be used as a chemical designation but be reserved as an adjective referring to the retina. They suggested that retinaldehyde be used instead in scientific literature as the name of chemical related to vision. 

Interest in enzyme stereospecificity and the stereochemistry of prochiral centres, such as the methylene groups of mevalonic acid, has necessitated more precise definitions of the stereochemistry of the various molecules involved and of the enzymological consequences. The use of multiply labelled mevalonic acid in terpenoid and steroid biosynthesis has been reviewed by Hanson. The Proceedings of the 1970 Phytochemical Society symposium have been published. They include a general discussion of terpenoid pathways of biosynthesis by Clayton and specific chapters on monoterpenoids, diterpenoids, eedysones, carotenoids, isoprenoid quinones, and chromanols. Other reviews concerning biosynthesis have appeared on furanocoumarins, indole alkaloids, monoterpenoids, and diterpenoids. ... 

The term lipids is defined as those organic compounds that are insoluble in water, soluble in organic solvents (e.g., chloroform, ether), contain hydrocarbon groups as primary parts of the molecule, and are present in or derived from living organisms. Compound classes covered in this definition include fatty acids (FA), acylglycerols, FA esters (e.g., waxes), and isoprenoid hydrocarbons. Other compounds also included are often considered as belonging to different classes, such as carotenoids, sterols, and the vitamins A, D, E, and K. 

Definition Unsat. branched chain isoprenoid hydrocarbon found in shark liver oil Empiricai C30H50... 

The general pathway of isoprenoid biosynthesis was elucidated largely through studies of the biosynthesis of sterols in yeast and higher animals. It was shown that specifically labeled [ CJacetate was incorporated in specific patterns into cholesterol. A variety of branched C5 compounds, notably j8,jS-dimethylacrylate, were also tested as possible isoprenoid precursors. Incorporation of label was observed, but the results were not definitive. The key... 

Retinoids have been defined as a class of compounds consisting of four isoprenoid units (H2C=C(CH3)-CH=CH2) joined in a head-to-tail manner. The retinoid molecule can be divided into three parts a trimethylated cyclohexene ring, a conjugated tetraene side chain, and a polar carbon-oxygen functional group. Retinol (I), retinaldehyde (II), and retinoic acid (III), as well as their derivatives whose structures are shown in Structure 1 (/), are included by this definition. 

Hemiterpenes, by definition, consist of only one isopentane unit and are, thus, the simplest members of terpenoids. The basic building blocks of isoprenoids, namely IPP and DMAPP, must be universally present in green plants, being the progenitors of the phytyl side chain of chlorophyll, which is essential for biological activity (Sect. 8.1.4). These do not appear to be accumulated by plants (3), though the related prenyl alcohol (3,3-dimethylallyl alcohol, 9) and its isomer isoprene alcohol (10) have been found to occur in a few essential oils (229). Isoprene (11) itself is an important emittant of pine forests (165). 

The ketone subfraction is dominated markedly by a monounsatura-ted C40 isoprenoid ketone (84), the structure of which is not still definitely established with respect to the location of the unsaturation three diunsaturated C40 ketones (85)-(87) were also identified. In addition this subfraction comprises C11-C22 isoprenoid ketones, the most important of which is the compound (88). 

---