Terpenoids hemiterpenoids

Hemiterpenoids are produced from the isoprenyl diphosphate DMAPP. All other terpenoids are produced from DMAPP and IPP via longer-chain prenyl diphosphate intermediates formed by prenyl transferases. Prenyl transferases (20) catalyze the formation of geranyl diphosphate (GPP), famesyl diphosphate (FPP), and geranylgeranyl diphosphate (GGPP) from one molecule of DMAPP and one, two, or three molecules of IPP, respectively (Fig. 1). Isoprenyl diphosphates are the substrates for all TPS, which lead to the hemiterpenoids, monoterpenoids, sesquiterpenoids, and diterpenoids, which will be highlighted with selected examples in the following sections. 

Several reviews have appeared, on such topics as steroid and terpenoid biogenesis, hemiterpenoid alkaloids,indole alkaloids (monoterpenoids), ophiobolins (sesterterpenoids), sterols in Digitalis, oestrogens, plant tri-terpenoids, and carotenoids. ... 

Terpenoid Synthesis from Isoprene.—Co-oxidation of thiophenol and isoprene with oxygen yields the synthons (9) and (10) in useful yields and the isoprene epoxide (11) is a useful hemiterpenoid synthon with carbanions. ... 

The generic name terpene was originally applied to the hydrocarbons found in turpentine, the suffix ene indicating the presence of olefinic bonds. Each of these materials contain two isoprene units, hence ten carbon atoms. Related materials containing 20 carbon atoms are named as diterpenes. The relationship to isoprene was discovered later, by which time the terms monoterpene and diterpene were well established. Hence the most basic members of the family, i.e. those containing only one isoprene unit, came to be known as hemiterpenoids. Table 1.1 shows various sub-divisions of the terpenoid family based on this classification. It also shows two specific sub-groups of terpenoid materials, namely, the carotenoids and the steroids. Steroids and carotenoids are sub-groups of the triterpenoids and tetraterpenoids, respectively, as will be explained later. 

The alkaloids of this chapter are classified according to the classification of terpenoids, namely hemiterpenoid alkaloids (alkaloids with a C5 unit), monoterpenoid alkaloids (alkaloids with a Cjo unit), sesquiterpenoid alkaloids (alkaloids with a C15 unit), diterpenoid alkaloids (alkaloids with a C20... 

It is clear from the mechanism shown in Figure 6.14 that terpenoid structures will always contain a multiple of ve carbon atoms when they are rst formed. The rst terpenoids to be studied contained 10 carbon atoms per molecule and were called monoterpenoids. This nomenclature has remained and so those with 5 carbon atoms are known as hemiterpenoids those with 15, sesquiterpenoids those with 20, diterpenoids and so on. In general, only the hemiterpenoids, monoterpenoids, and... 

Hemiterpenoids are used mostly as intermediates in the synthesis of other terpenoids. The main exceptions are some esters of prenol that impart fruity top-notes in perfumery. Prenyl acetate (58), R = Me) and benzoate (58), R = Ph) are the two most important of these. 

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