The ^<13>C-NMR spectra (Fig.3 a-e) of sclerin which was obtained by feeding formate-^<13>C, acetate-1-^<13>C and -2-^<13>C and malonate-2-^<13>C respectively to the culture of Sclerotinia sclerotiorum, indicated a good participation of those compounds to the biosynthesis of sclerin (I). The spectra also clarified the positions of incorporation of ^<13>C-atom of those labeled precursors in the molecule of I. The spectrum in Fig. 3-e particularly showed that I should not be derived from two polyketomethylene chains contrary to the hypothesis proposed previously, since ^<13>C from malonate was strongly labeled C_4 of the aromatic ring of I. The result indicated that I must be derived through one chain of polyketomethylene. From the result shown in Fig.5, the source of "extra methyl" of aureothin (IX) was confirmed to be the methyl of propionate, and two carbons at C_6 and C_7 of IX were demonstrated being derived from an acetate through "Route B" in Fig. 4. The propionamide moiety of aureothiicin (XI) has simultaneously been ascertained to be formed by the direct incorporation of propionate.
