Diterpenes casbene

Takahashi and coworkers [170] synthesized the antifungal diterpene casbene (287) by using carbene-olefin coupling for ring closure. As shown in Scheme 96, the... 

Dudley, M.W., Dueber, M.T. and West, C.A. (1986) Biosynthesis of the macrocyclic diterpene casbene in castor bean (Ricinus communis L.) seedlings changes in enzyme levels induced by fungal infection and intracellular localization of the pathway. Plant Physiol., 81, 335-42. 

Pborbol and Its Relatives.— The Euphorbiaceae are a rich source of diterpenes. The hydrocarbon casbene (126), which is clearly related to the macrocyclic diterpene cembrene, has been isolated from Ricinus communis It may also be related to the parent hydrocarbon of the phorbol group of diterpenoids. 

Although not directly involved as odour-active food components, diterpenes are widespread in the plant kingdom, where they mainly occur as components of resins of conifers and juices of the aster (sunflower) family (Asteraceae) and spurge family (Euphorbiaceae) plants. Diterpenic hydrocarbons are precursors of numerous diterpenoids, many of which are biologically active substances. More than 3000 different diterpenoid structures have been defined, aU of which appear to be derived from geranylgeranyl diphosphate. Like monoterpenes and sesquiterpenes, diterpenes are mostly cycHc compounds. Examples of diterpenoid hydrocarbons (8-9) are tri-cychc hydrocarbon (-)-ent-kaur-16-ene, tetracycHc hydrocarbon (-)-abieta-7(8),13(14)-diene and macrocycHc compounds cem-brene, casbene and taxa-4,11-diene. 

SCHEME 8.4 Postulated biosynthesis of complex casbene diterpene families and biomimetic synthesis of ingenol by Baran et al. [13]. 

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