Abietane skeleton

The structures and nomenclature for the common pine resin acids based on the abietane skeleton (abietic-type acids) are given in Fig. 8. The abietic, neoabietic, palustric and levopimaric acids differ only in tbe location of tbeir two double bonds. All double bonds are endocyclic, except in the neoabietic acid in which one is exocyclic. 

In 2011, Hartwig and coworkers reported the total synthesis of taiwaniaquinol B (55, Scheme 11.9), a member of a family of diterpenoids that are derived from the abietane skeleton [36]. A key aspect of the Hartwig synthesis of taiwaniaquinol B was the use of the iridium-catalyzed borylation reaction to accomplish the C(5) functionalization of resorcinol derivative 53. This regioselectivity for the overall bromination is complementary to that which would be obtained using a standard electrophilic aromatic substitution (EAS) reaction. In the transformation of 53 to 54, a sterically controlled borylation was first accomplished, which was then followed by treatment of the boronic ester intermediate with cupric bromide to... 

Figure 3.17 shows the mass profile of the resinous material collected from the Roman amphora. It shows the presence of abietane skeleton diterpenoids due to the occurrence of the peaks at m/z 315, 299, 285, 253 and 239. Furthermore, a high degree of oxidation of the resin was ascertained by the abundance of peaks at m/z 315 and 253, deriving from 7-oxo-dehydroabietic acid, and those at m/z 331 and 329, from highly oxidised tricyclic diterpenoid molecules. Finally, the presence of retene was evidenced by the peaks at m/z 234 and 219. The results showed that a pitch from Pinaceae had been in the amphora. 

Terpenoids are susceptible to a number of alterations mediated by oxidation and reduction reactions. For example, the most abundant molecule in aged Pinus samples is dehydroabietic acid [Structure 7.10], a monoaromatic diterpenoid based on the abietane skeleton which occurs in fresh (bleed) resins only as a minor component. This molecule forms during the oxidative dehydrogenation of abietic acid, which predominates in rosins. Further atmospheric oxidation (autoxidation) leads to 7-oxodehydroabietic acid [Structure 7.11]. This molecule has been identified in many aged coniferous resins such as those used to line transport vessels in the Roman period (Heron and Pollard, 1988 Beck et al., 1989), in thinly spread resins used in paint media (Mills and White, 1994 172-174) and as a component of resin recovered from Egyptian mummy wrappings (Proefke and Rinehart, 1992). 

Parallel analyses by IR, thin-layer chromatography (TLC), and gas chromatography-mass spectrometry (GC-MS) of organic remains adhering to shards of ancient amphoras excavated in the harbor of Carthage (Tunisia) identified these remains as pine pitches. Capillary GC of methylated acid fractions showed abietic acid, dehydroabietic acid, and 7-ketodehydroabietic acid as the principal components. Two-dimensional TLC of untreated ether extracts revealed abietic acid in 12 of 31 samples and dehydroabietic acid in 26 of 31 samples. IR spectra of solid, raw samples indicated the presence of isopropyl groups, characteristic of the abietane skeleton, in 80% of the samples. Rapid and convenient analysis by TLC and IR was, in most cases, sufficient to identify pine resin products even after extensive pyrolytic and oxidative degradation. 

About 80% of the diterpene acids of the genus Finns have an abietane skeleton, with abietic acid (structure 3) as the predominant component. Other diterpene acids have a pimarane skeleton (structure 4). All compounds with the abietane skeleton are distinguished by the presence of an isopropyl group. 

Abietane skeleton, 375, 378 Abietic acid disproportionation, 375 loss in manufacture of pine pitch, 377 oxidation, 375 structure, 371... 

Diterpenoids from Salvia and Rosmarinus belong to two main groups abietane and clerodane. In general, the diterpenoids with abietane skeletons usually occur in Asiatic and European species, whereas the most common diterpenoids in South American species are of the clerodane type (Al-Hazimi and Miana, 1994). 

Cryptotanshinone is a quinoid diterpene with a nor-abietane skeleton isolated from roots of the Iranian medicinal plant Perouskia abronatoides L. which exhibited leishmanicidal activity in vitro. These findings provide a rationale for the traditional use of the roots in Iran as a constituent of poultices for treatment of cutaneous leishmaniasis [199], More recently, Valderrama et al. [200] synthesized several eurylfurylquinones and hydroquinones from activated monosubstituted 1,4-benzoquinones and studied their in vitro activities against Leishmania amazonensis. 

More than 200 diterpenes with an abietane skeleton are reported to exist naturally Numerous representatives oeeur in conifers. Selected examples include palustra-diene, also referred to as (-)-8,13-abietadiene, from the pine tree Pintds palustris, from the so-called berries of the sade tree Juniperus sabina (Cupressaceae) and other species of juniper trees, (-)-abietenol from the pine Pinus silvestris and the fir Abies sibirica, (-)-abietic aeid belonging to the resin acids of turpentine and wide-spread in conifers such as various pines Pinus), larch trees Larix) and firs Abies), as well as (+)-palustric acid from the balm and the roots of Pinus palustris, isolated from gum rosin. 

The C20H36 tricyclic diterpanes are also called diterpane resins, derived from the abietane skeleton. Fichtelite (C19H34), which belongs to the same family, is presumed to be the result of decarboxylation of the abietic acid. The MS of these relate to individual structures (see Figure 10a-e ). 

The abietane skeleton is shared by four resin acids (Fig. 4.2), namely abietic, neoabietic, palustric and levopi-maric acids. The structures of these compounds, generally known as abietadienoic acids, diffa- only in the position of the conjugated double bond system, which is an important feature of this group of resin acids, because it... 

The abietane skeleton that Ruzicka excluded from the phytol rule (444) can... 

In addition to the /-abietane skeleton, other tricyclic e /-pimarane derived ring skeletons have been reported (Figure 15) Cleistanthanes and isocleistan-thanes were detected in Brickellia eupatoriedes (JP) and erythroxanes were identified in Helichrysum refluxum (450). The absolute configuration (5R, lOR) of the Brickellia cleistanthanes is identical to that reported for the cleistanthanes of the Euphorbiaceae, but antipodal to those (5S, lOS) of the Velloziaceae (Vellozia) (Figure 16 [p. 428] 427). 

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