Identification and Detection of Depsides Without Isolation

Further refinements of analytical t.l.c. procedures for detecting and comparing depsides in lichen extracts have been reported by C. F. Culberson and coworkers 64), 66), 86). Moreover two-dimensional t.l.c. is useful in microchemical studies on mixtures difficult to resolve by the standardized one-dimensional method (55). 

Although further transformations of the hydrolysis products (e.g. decarboxylation, lactonisation) are sometimes observed under these conditions, in general they cause no confusion. Although such experiments do not provide absolute proof of structure without isolation and characterisation of the new depsides and the hydrolysis products they certainly do provide compelling evidence for them. In a number of cases the structures assigned by this method have subsequently been confirmed by comparisons of natural and synthetic material 111, 120). 

High performance liquid chromatography (h.p.l.c.) has also been effectively employed as an analytical tool in examining depsides and their hydrolysis products in microextracts (67, 73, 87). The major advantage of this technique is that it yields quantitative information about the components present in crude extracts. 

Such Rp correlations were also used to tentatively identify 4-0-de-methylimbricaric acid (247) ((55), 4-0-demethylmicrophyllinic acid (248) ((55), 4-0-demethylglomellic acid (249) (72), 4-0-demethyl glomelliferic acid (250) (72), and 4-O-demethylloxodellic acid (251) (72). The trace quantities present precluded the isolation and further investigation of these depsides. 

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