Feeding experiments with [1-C-13]-, [1,2-C-13(2)]-, and [1-C-13,O-18(2
)]acetate as well as a fermentation under an O-18-enriched atmosphere
resulted in information regarding the biosynthetic origin of all carbo
n and of the oxygen atoms of the landomycin A aglycon moiety as well a
s of the direction of the incorporation of the decaketide chain. Only
two of the six oxygens in landomycinone seem to originate from the ace
tate building blocks. This raises questions about current hypotheses f
or the formation of multicyclic aromatic polyketides. Some unusual pre
aromatic deoxygenation steps early in the biosynthesis have been propo
sed. As an additional result of the biosynthetic investigations, the s
tructure of landomycin A and thus of all other landomycins were revise
d concerning the position of the phenol-glycosidically linked deoxysac
charide chain from 2 to 1.