Isopimaranes

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. 

The Brazilian plant Vellozia bicolor contains the isopimarane diterpene 12-chloroillifunone C (436). The corresponding epoxide, which is also found in this plant, is not converted to 436 under the isolation conditions (623). Teuracemin (437), a novel weo-clerodane diterpene, was isolated from Teucrium racemosum and is the 7-hydroxy derivative of the known tafricanin A (624). Examination of fresh plant material revealed the presence of 437. The new weo-clerodane ajugarin-I chlorohydrin (438) has been characterized from the Indian plant Ajuga parviflora... 

Cyclic diterpanes with two (labdane), three (abietane, isopimarane and rimuane) or four rings (e i-beyerane, e i-kaurane and phyllocladane) can be particularly abundant where there has been a significant contribution from gymnospermous resins, such as in coals (Fig. 5.28 Aplin et al. 1963 Noble et al. 1985, 1986 Weston et al. 1989 Otto Simoneit 2001). 

Fig. 5.28 Examples of cyclic diterpanes generally abundant in mature woody-gymnospermous kerogen. 18-Nor- and 19-nor-isopimaranes can also be abundant, deriving from norisopimaroid precursors.

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. 

Again from Southern Spain, S. reverchonii contained derivatives of em-beyerane, ent-atisane, em-isopimarane [55] the new 12-acetyl-jativatriol (124), and the eight already known lagascol (157), lagascatriol... 

VIII. Diterpenoids having ent-isopimarane (group H) and abietane (group I) skeletons... 

Table 6. C-NMR Chemical Shifts for Ent-isopimaranes (group H) and Abietanes (group I)... 

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. 

C20H28O2, Mr 300.44, pale-yellow gum, [a]p -3.0 (CHCI3). A diterpene of the cleistanthane group, isolated from the roots of Cunuria spruceana (Euphorbi-aceae). S. exhibits antitumor properties. The cleistan-thanes are formed biosynthetically from pimaranes or isopimaranes by migration of an ethyl group. 

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. 

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). 

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