Pimaranes and Isopimaranes

Pine trees such as Firms silvestris (Pinaceae), which are wide-spread in Europe, contain pimarane derivatives, e.g. (+)-8(14),15-pimaradiene-3,18-diol, 8(14),15-pimaradien-18-al also referred to as eryptopinone, and 8(14),15-pimaradien-18-oie aeid denoted as pimaric acid, isolated from Ameriean rosin and belonging to the 

Isopimaranes occur in some pine (Pinaceae) and juniper species (Cupressaceae). Examples include 7,15-isopimaradiene and 8,15-isopimaradien-18-oic acid (A -isopimaric acid) from Pinus silvestris as well as 8(14),15-isopimaradiene-3,18-diol and 8,15-isopimaradiene-3,7,19-triol from Juniperus thurifera. 

Representatives of podocarpanes include podocarpinol in Podocarpus totara, and podocarpic acid, the dominant acidic constituent of podocarpus resin obtained from Javanese P. cupressina (Cupressaceae), as well as the bitter-tasting phenolic compounds nimbiol and nimbione. These are found in the bark and isolated from neem oil expressed from the seed-kernels of the Indian neem tree Azadirachta indica (Meliaceae). Extracts of this bark are added to some mouthwashes and skin creams neem oil is used as an agricultural insect repellant and antifeedant. 

9(ll)-parguerene-2a,7a,16-triol in the alga Laurencia obtusa. The wood of Erythroxylon monogynum (Araliaceae) contains derivatives of erythroxylane and devadarane such as (+)-4(18)-erythroxylene-15,16-diol and (-)-devadarane-15,16-diol. 

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With very few exceptions, the pine resin acids belong to four basic skeletal classes abietane, pimarane, isopimarane, and labdane (Fig. 7). The acids of the abietane, pimarane and isopimarane series have a isopropyl or methyl/ethyl group in the carbon-13 position and a single carboxyl group in the carbon-18 position, and differ only in the number and location of the carbon-carbon double bonds (the most common have two carbon-carbon double bonds). The acids of labdane series are less common and contain one carboxyl group in the carbon-19 position. 

Fig. 9. Common acids of the pimarane and isopimarane skeletal class (pimaric-type acids) (see p. 269 in [18 ).

The common pine resin acids based on the pimarane and isopimarane skeletal (pimaric-type acids) are shown in Fig. 9. The pimarane and isopimarane acids series differ only in the methyl group position in the carbon-13 position. Isopimaric and sandaracopimaric acids differ in the location of the carbon-carbon double bond. 

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). 

In general, very little has been written about diterpenes from the Latin American Celastra-ceaeas these structures are not often found. Abietriene type diterpenes have been the general rule in the Celastraceae although the chemical study of the minor constituents of Orthosphenia mexicana and Rzedowskia tolantonguensis did enable pimarane type diterpenes to be isolated and chemically characterized [43,45] and the second of these species afforded a series of new diterpenes with an isopimarane skeleton, described for the first time in the Celastraceae. 

A group of diterpenes with the pimarane skeleton (1). In R, the methyl group at C-10 is cis to the ethyl group at C-13, whereas in the isopimaranes it is in the transposition. Both enantiomers of not only the R but also of the isopimaranes occur in nature. R are formed by a further cyclization of the labdane skeleton. Examples are annonalide, momilactones A and B (both growth inhibitors for plants ), leucophleol and ent-8(14),15-pimaradiene. In the past the R were also known as sandaracopimaranes. 

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