Correlations of the structures of some natural products containing orcinol or phloroglucinol nuclei, and related compounds, support the hypothesis that the molecules are elaborated, at least in part, by the head-to-tail linkage of acetate units. Chemical and biochemical evidence is cited in support of the hypothesis.

The general problem of the biosynthesis of depsides and depsidones is considered. Feeding experiments using sodium acetate isotopically labelled in the carboxyl group have demonstrated that the mould Penicillium griseofulvum Dierckx (Raistrick's strain P68) elaborates 2-hydroxy-6-methylbenzoic acid (VII) by the head-to-tail linkage of acetic acid units in accord with the hypothesis of Birch and Donovan (1953). This demonstration constitutes the first definite support for the hypothesis based on bio- chemical experiments.

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Me*14C0,H, when fed to a strain of Penicilliuwa griseofulvuin Dierckx, This result A preliminary leads to griseofulvin with the isotopic distribution shown in (I).supports the general validity of the acetic acid hypothesis. account of some of this work has already appeared.1 STRUCTURAL evidence reviewed in Part I suggested-that the skeletons of many natural phenolic compounds are derived, at least in part, by the head-to-tail linkage of acetic

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