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The metabolite, mitorubrin, elaborated by the phytotoxic fungus, Penicitlium rubrum, has been synthesised.

The routes of biosynthesis, in appropriate moulds, of the substances named in the title have been examined by means of feeding experiments with 14C-labeUed acetic and formic acids. SOME previous papers dealt with a speculative examination of the biosynthetic origins of plant and mould products from acetic acid by head-to-tail linkage, or from acetic acid and methionine. These predictions have been confirmed by direct experiment with CH3*14C02H in two cases 2*3 where the molecule can arise from a straight chain of acetic acid units joined by head-to-tail linkage, and in one case (mycophenolic acid) 4 5 where methionine is also involved. We have now extended our researches to trace the origins of molecules which can only arise from branched carbon chains. From previous work there seem to be three Iikely modes of origin : (A) From acetic acid, by head-to-tail linkage in a straight chain with the introduction of C, units from the C, pool (choline, methionine etc.). (B) From acetic acid by production of branched chains employing head-to-tail linkage. (C) By the isoprene route formally similar to (B) but with a definite intermediate in the form of mevalonic acid.Mycophenolic acid *J is an interesting example of the working of routes (A) and (C) in one compound; no example of route (B) had, before the present work, been demonstrated.

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