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Dehydrogenation of rosenonolactone, a metabolite of Trichotheciuin roseunz Link, and of dihydroisorosenonolactone gives 1 : 7-dimethyl-and 9-hydroxy-1 : 7-dimethyl-phenanthrene, a result which, in conjunction with the composition and properties of the lactones, shows that they are diterpenoid derivatives having the same nucleus. Rosenono-and isorosenono-lactone and their derivatives are y-lactones, an examination of which in conjunction with earlier work 1 enables provisional structures t o be ascribed to the metabolite and its degradation products.

Rosololactone, C,oH3003, from the mycelium of T . roseurn Link, is a diterpenoid y-lactone containing a secondary hydroxyl group and a vinyl residue and on dehydrogenation yields 1 : 7-dimethylphenanthrene. Dehydration of dihydrorosololactone readily gives a dienoic acid, dihydrorosenic acid, which on hydrogenation is converted into tetrahydrorosenic acid. Lactonisation of this acid yields a mixture of allo-and neo-hydroxyrosanoic y-lactone identical with the two y-lactones from iso(?)ros-11 : 12-en-16-oic acid (Part XXXI l ) , thereby establishing a close structural affinity between rosoloand rosenono-lactone.IN addition to the major constituent, rosenonolactone, the mycelium of Trichothecium Yoseum Link contains a minor metabolite which in Part VI was designated rosonolactone. The present communication details an investigation on the chemistry and structure of this compound which has the formula, C20H3003. Since the metabolite, which appears

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