Abstract: Feeding of [l-I3C] acetate to cultures of Streptomyces cinnamonensis gave monensin A labeled at carbons 7, 9, 13, 19, and 25, as established by 13C NMR analysis. Similarly, incorporation of [l-13C] propionate resulted in enrichment of carbons 1, 3, 5, 11, 17, 21, and 23. Further incorporations of [1, 2-I3C2] acetate,[1, 2-13C2] propionate,[2-13C] propionate, and [2, 3-13C2] succinate and analysis by 13C NMR, including extensive ...