Diterpene 19-carboxylic derivatives

The tricyclic diterpene carboxylic acid, abietic acid, is widely distributed (see Chap. 8.1) and commonly available commercially. Fisher implicated it in a case of allergic contact dermatitis because it is the major constituent of violinist s resin (58). It is also found in colophony and pine resins, on which Karlberg et al. (92) performed a dermatological study. Wahlberg (182) studied dermatitis caused by abietic acid and colophony. Abietic acid derivatives are also common, so some derivatives (161) of it have also been studied, notably dihydroabietyl alcohol (49). A white powder from the bark of Betula sp. causes skin eruptions in mill workers... 

Terpenes are are a class of compounds whose chemical structures are based on a number of isoprene units , derived from the hydrocarbon CH2=C(CH3)-CH=CH2 they may themselves be hydrocarbons, but may also contain alcohol (OH), aldehyde/ketone (CO) and carboxylic acid (COOH) groups. Monoterpenes are Cm compounds derived from two isoprene units, sesquiterpenes (Cu) are derived from three isoprene units, diterpenes (C20) from four and tritepenes (C30) from six. Terpenes are widespread in plants, where they are largely responsible for the odor, and they are the major constituents of plant-derived essential oUs . Among the best known terpenes are 3-pinene (turpentine), camphor, menthol and citroneUal (aU monoterpenes) and farnesol (a sesquiterpene that is a constituent of the essential oils of many plants). Certain terpenes have important biological roles vitamin A, for example, is a diterpene, and steroid hormones have a structure related to triterpenes (and are biosynthesized by a similar route). 

A totally different synthesis of the diterpene alkaloids has been reported by Masamune (102-104). The carboxylic acid CCXCII was converted via the bromo ketone CCXCIII to the tetrahydropyranyl ethers CCXCIV. Hydrogenolysis of the latter gave the corresponding phenols CCXCV. Base treatment of CCXCV effected cyclization of only one isomer to furnish a dienone ether (CCXCVI). Catalytic hydrogenation of the benzoate (CCXCVII) gave the tetrahydro cis-fused derivative... 

Regardless of its origin (gum, wood or tall oil), rosin is mainly composed (90-95 pa- cent) of diterpenic mono-carboxylic acids, commonly known as resin acids whose generic formula is C19H29COOH. The remaining components are essentially made up of neutral compounds, the nature of which depends on the specific origin of the rosin [5]. The most common resin acids found in pine rosin are derived from the three basic tricyclic carbon skeletons abietane, pimarane and isopimarane and the less common bicyclic labdane skeleton (Fig. 4.1). 

---