Iridoid monoterpenes indole alkaloids

Formation of Deoxyloganic Acid from Geraniol Formation of 8-e/ i-Deoxyloganin and Related Iridoids Iridoids Derived from 10-Hydroxycitronellol Conversion of Loganin to Secologanin Secologanin as a Precursor for Indole Alkaloids Distribution of Iridoid Monoterpenes Biological Activity... 

Monoterpene and indole alkaloids are frequently derived from iridoid monoterpene precursors (Inouye, 1991). 

Loganin (6) is a key intermediate in the biosynthetic pathway leading to other iridoid monoterpenes as well as complex indole alkaloids. Many of these additional compounds are derived by conversion of this bicyclic iridoid monoter-pene into secologanin (18). The mechanism by which ring cleavage occurs to yield secologanin is not well understood, but apparently the cleavage happens after oxidation of the... 

The order Gentianales (Apocynaceae, Gentianaceae, Lo-ganiaceae, Rubiaceae, and Theligonaceae) contains normal iridoid monoterpenes and secoiridoids, as well as iridoid-derived alkaloids in families other than the Asclepiadaceae. Multiple types of alkaloids are found in the Apocynaceae (indole and steroidal types), the Loganiaceae, and Rubiaceae (emetine, quinine, and indole types). 

T.a. are biosynthesized from mevalonic acid, but the origin of the nitrogen is not known. They therefore differ from the iridoid, isoquinoline and indole alkaloids, in which a monoterpene is linked to an amino acid. 

This is an example of a bicyclic ring system with the fusion of benzene and pyridine rings. Biosynthetically they are related to indole alkaloids since both groups are derived from the same two precursors, tryptophan and loganin—a monoterpene iridoid (Samuelsson 1992). 

The procedure has been utilised to synthesise the hydroxyloganin, the key ring intermediate in the metabolism of iridoids to secoiridoids and subsequently to indole and related alkaloids having this monoterpenic part. 

This is a very large group of alkaloids whose basic structure contains a pyrrole ring fused to a benzene ring. Biosynthesis of pure indoles involves the amino acid tryptophan as precursor, while that of a major subgroup of the indoles, including the Catharanthus and Rauwolfia alkaloids, involves a second precursor— the monoterpene iridoid loganin. 

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