7 oxodehydroabietic acid

However, in many archaeological samples pimarane diterpenoids are often absent, and of the abietane compounds only dehydroabietic acid remains. In fact, dehydroabietic acid is present as a minor component in the fresh resins, but its abundance increases on ageing at the expense of the abietadienic acids since the latter undergo oxidative dehydrogenation to the more stable aromatic triene, dehydroabietic acid [2,18]. If oxygen is available, dehydroabietic acid can be oxidized to 7-oxodehydroabietic acid and 15-hydroxy-7-oxodehydroabietic acid. Since these diterpenoid compounds are often the dominant components in archaeological samples [95,97], they are considered characteristic for the presence of Pinaceae resins. 

Figure 2.15 APCI (+) mass spectrum of the lipid extract obtained from a ceramic vessel recovered from the thirteenth century church of Sant Antimo in Piombino (Central Italy) (a). TheAPCI MS/MS spectrum obtained by selecting ions at m/z 315 (b). The latter made it possible to determine that ions at m/z 315 are due to protonated 7 oxodehydroabietic acid. (Adapted from ref. [29])...

When ions at m/z 315 are isolated and submitted to CID, the product ion spectrum shown in Figure 2.15(b) is obtained. Productions at m/z 300,297,273 and 269 can be attributed to losses of a methyl radical, water, cyclopropane and formic acid, respectively. These decompositions, together with other information and a more detailed study of the MS [2] spectrum, enable the identification of the compound with [M+H]+ at m/z 315 as proto-nated 7-oxodehydroabietic acid. 

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). 

Structure 7.10 Dehydroabietic acid Structure 7.11 7-Oxodehydroabietic acid... 

FIGURE 36.12 Pyrogram obtained by THM-GC/MS from Roman Caecuban wine from an amphorae recovered in the shipwreck Madrague de Giens. N-Sim, norsimonelUte Ret, retene PIM, pimaric acid DAB, dehydroabietic acid ABT, abietic acid OAB, 7-oxodehydroabietic acid [118]. 

Fig. 2. Chemical structures of identified oxidation products in colophony, a 15-hydroperoxyabietic acid, b i3,i4(a)-epoxyabietic acid, c i3,i4(p)-epoxyabietic acid, d di(dehydroabietic acid 15-yl) peroxide, e 15-hydroperoxydehydroabietic acid, f 7-oxodehydro-abietic acid, g 15-hydroxydehydroabietic acid, h 15-hydroxy-/-oxodehydroabietic acid, i i3(p), i4(p)-dihydroxyabietic acid, j 12-hydroxyabietic acid, k 8,i2-peroxo-7,8-dihydroabietic acid...

The low-temperature ozonolysis of podocarpa-8,1 l,13-trien-12-ol (59) to form the lactol (60) has been re-examined54 and the importance of slightly acidic reaction conditions has been noted. The conversion of podocarpic acid into 19-hydroxypodocarpa-8(14)-en-13-one has been described.55 The C-12 oxygen function was removed by hydrogenolysis of the 12-toluene-p-sulphonate. Details of the nitration of methyl 7-oxodehydroabietate have appeared.56 The conformational analysis of the ring C diene, levopimaric acid, has been discussed57 in terms of a folded conformation. 

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