Iridoids secologanin type

Fig. 103. Formation of secologanin type iridoids from loganin...

B, Iridoid Indole Alkaloids. Most jS-carbolines are derived from tryptamine and the iridoid secologanin (D 6.1.2). In dependence on the structure of the iridoid part alkaloids of the Corynanthe-Strychnos type as well as of the Aspidosperma and Iboga types may be distinguished. The latter are formed by rearrangement of the iridoid part which is shown schematically in Fig. 259 and in detail in Fig. 261. 

Secologanin (1) of Fig. (1) is the most important representative of the iridoids (la), a special type of cyclopentanoid monoterpenes. (1) belongs the subclass of secoiridoids (lb), in which the bond C-7-C-8 is cleaved [1]. The number of known iridoids is more than 650 [2], The biosynthesis of iridoids like that of other monoterpenes starts from two C5 units (lc) whose precursor was considered to be mevalolactone [3], However, recently it was proved that the biosynthesis of some classes of terpenoids [4,5], and specially of secologanin [6] runned from 1-deoxy-D-xylulose-5-phosphate as an alternative or even main route. 

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