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The biosynthetic origin of the carbon and oxygen atoms of the novel fungal secondary metabolite 1 was studied. Incorporation studies with single and multiple labelled 13C precursors indicated that the major portion of the molecule was derived from two polyketide chains madeup of acetate units. One of the chains had benzoic acid (which can be derived from phenylalanine) as a starter unit. The remaining carbons were derived from a four-carbon unit related to succinate and from methionine.Studies with [l-13C,18O2]acetate and 18O2 indicated that five of the oxygens, including both of the heterocyclic oxygens, were derived from atmospheric oxygen. The oxygens at the two ester carbonyls were derived from acetate.

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The isolation and structure determination by 1H and 1 3C NMRand MSof24 novel squalestatins from cultures of Phoma sp. C2932 is described.