Terpenoids triterpenoid resins

Triterpenoids (C30 compounds) are the most ubiquitous of the terpenoids and are found in both terrestrial and marine flora and fauna (Mahato et al., 1992). Diterpenoids and triterpenoids rarely occur together in the same tissue. In higher plants, triterpenoid resins are found in numerous genera of broad-leaved trees, predominantly but not exclusively tropical (Mills and White, 1994 105). They show considerable diversity in the carbon skeleton (both tetracyclic and pentacyclic structures are found) which occur in nature either in the free state or as glycosides, although many have either a keto or a hydroxyl group at C-3, with possible further functional groups and/or double bonds in the side-chains. 

A range of modem resin samples from the Dipterocarpaceae, Pinaceae and Burseraceae families (Table I), encompassing both diterpenoid and triterpenoid resins, have been examined using GC and GC-MS to act as reference materials against which to compare results from the archaeological samples. Wherever possible, the higher terpenoid peaks have been identified by comparison with previously published data. 

The lipophilic fraction, extractable with nonpolar solvents (ethyl ether, dichloromethane, etc.) consists mainly of fats, waxes, terpenes and terpenoids, and higher aliphatic alcohols (cf. Sections 5.3.1 and 5.3.2). Terpenes, resin acids, and sterols are located in the resin canals present in the bark and also occur in the cork cells and in the pathological exudate (oleore-sin) of wounded bark. Triterpenoids are abundant in bark /3-sitosterol occurs in waxes, as an alcohol component, and the cork cells in the outer bark (periderm) of birch contain large amounts of betulinol (cf. Fig. 5-6). 

Wood resin is considerably changed during the pulping process. The fatty acid esters of sterols and triterpenoid alcohols in hardwoods (waxes) are saponified very slowly. Unsaturated compounds, e.g., fatty acids, resin acids, and other higher terpenoids, are polymerized to high molecular weight compounds, which also give rise to "pitch problems."... 

Terpenes are flammable unsaturated hydrocarbons, existing in liquid form. They are found in essential oils, resins or oleoresins. They are used as intermediate for the synthesis of sesquitrepenes and terpenoids. They are classified as mono, di or triterpenoids. 

The terpenoids can be defined as a group of natural products whose structure may be divided into isoprene units (13). Isoprene, or isopentenyl, is a C5 (five carbon atom) compound, which can be viewed as the terpenoid building block (Figure 2). Both the lower terpenoids (monoterpenoids and sesquiterpenoids) and the higher terpenoids (diterpenoids and triterpenoids) are built up from multiples of these isoprene units. When freshly exuded, resins tend to be liquid or semi-liquid, as they contain either one or the other of the two higher terpenoids in solution in a mixture of the more volatile lower terpenoids. 

Where residues exhibited a terpenoid component, these were most commonly triterpenoid in nature, although in a few cases some sesquiterpenoids also survived. Closer examination of the mass spectra of terpenoid components of the archaeological samples showed similarities with the compounds found in modem resins of the Dipterocarpaceae family. 

However, the samples from Noen U-Loke do not demonstrate a clear-cut correspondence to the modem Dipterocarp resins as neither hydroxydammarenone (G), which is not detected at all in these samples, nor ursolic aldehyde (J2) dominate. Instead, a-amyrin (D) is the usually largest peak by far. Although this is the case, the composition of the archaeological material is quite dissimilar to the triterpenoid Canarium resin, but does exhibit a range of the terpenoid components present in Dipterocarp resins suggesting that this family may be the botanical source of die resin used as a coating on these ceramics. 

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