Mononuclear phenolic compounds from

The mononuclear phenol compounds isolated from lichens can be subdivided into three major categories, namely the orsellinic acid, the phloroacetophenone and the phthalide derivatives. These are discussed in turn. 

A mononuclear phenolic compound tentatively assigned the structure of ethyl 2-hydroxy-4-methoxy-6-pentylbenzoate (106) has been isolated by SoLBERG from Icmadophila ericetorum 305) but the possibility that this compound may be an artefact of the ethanolic work-up procedure is not discussed. 

Vanadium(V) alkoxides have been known since 1913,69 and in Table 2 we show some of the known alkoxides, the parent alcohol, and the nature of the complex in organic solvents and in aqueous solution. Alkoxides have been prepared from methanol, ethanol, isopropanol, t-butanol, silsequioxanes, cyclopentanol, cyclohexanol, norborneol, adamantanol, phenol, and other alcohols (see Table 2).70- 0 The simple complexes associate in organic solvents and dimerization in the presence of alkoxide is observed with the isopropanol complex.70 The more sterically hindred alcohols are less reactive and do not hydrolyze completely in the presence of small amounts of water.73 The first simple alkoxide to be structurally characterized was the methoxide complex (14) and the vanadium was found to be a six-coordinate dinuclear species however, the structure of this compound did not refine very well.91 This was the first report of the diamond core V—O—V—0 unit, albeit associated with two six-coordinate vanadium atoms. The diamond core V—O—V—O (11), which has since then been found to be a typical structural unit for these complexes, was distinctly asymmetric revealing a difference in the interactions between the two mononuclear parts of the molecule. The first monodentate alkoxide found to contain... 

Several new classes of compounds have been discovered in lichens during this period. For example six diphenyl ethers have been isolated and it would appear that they may arise biogenetically either by catabolism of the more common depsidones or by direct phenolic oxidation resulting in carbon-oxygen coupling of the mononuclear aromatic units [e.g. in leprolomin 118)]. A novel group of nonacyclic diketopiperazines have been isolated 14) and it would appear that these compounds are derived biogenetically from the aromatic amino-acid, tyrosine. 

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