Tetracyclic diterpenes-kauranes

Kauranes and Gibberellic Acids.— The parent tetracyclic diterpene from which the gibberellic acids are derived, is enf-kaurene (62). Several workers have... 

Four structural types of diterpenes are known from Helianthus labdanes, kauranes, atisiranes and trachylobanes (Figure 2), with the tetracyclic kaurane type being the most widespread in the genus. The majority of Helianthus diterpenes have an Ol-oriented carboxylic acid function attached to carbon 4. 

Diterpenes (C20) can be linear as in the phytol part of chlorophyll or mono- to tetracyclic.87 Very well researched are the tricyclic taxanes of which taxol A from the Taxus baccata tree inhibits cell division and has found use in anticancer treatment. Certain labdanes inhibit blood platelet aggregation and kaurane norditer-pene glycosyl ester atractylosides from the Mediterranean thistle block the ATP/ADP translocation - such diterpenes are very toxic when ingested. Ubiquitous plant-derived kaurane-type diterpenes are the plant hormones (gibberellins) or defense substances (phytoalexins). 

In 2014, Canesi s group also reported on a remarkable application of their chemistry that enabled them to develop an asymmetric synthesis of the tetracyclic main core of kaurane diterpenes [131]. The phenolic non-conjugated enyne 249 was elaborated to fulfill the reactivity and stereochemistry requirements of the intended oxidative cationic polycyclization [132], in tandem with apinacolic transposition. After chlorination of the benzylic alcohol of 249 with inversion of configuration, the use of BTI rapidly promoted this dearomative tandem process, which thus... 

---