Total Synthesis of Depsides

Total synthesis has provided a definitive method for structural elucidation of all groups of depsides and provides a useful alternative to the classical hydrolytic degradation procedure. Further, in cases where complex mixtures of homologous depsides or simply lack of lichen material make isolation of the new depside impractical, t.l.c. comparisons of synthetic material with the natural mixtures has enabled the identity of a number of new depsides to be established (44, 45). 

The use of the newer condensing reagents trifluoroacetic anhydride or dicyclohexylcarbodiimide has streamlined the synthesis of the depside linkage from the appropriately substituted benzoic acid and phenol. Where necessary the phenolic and carboxyl groups of the precursors are protected by O-benzylation until after depside-ester bond formation has been achieved. Catalytic hydrogenolysis of the so-formed 0-benzyldepside esters subsequently gives the natural depsides. 

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