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Incorporation of sodium [I -l3C, '802]acetate by Penicillium multicolor into multicoianic, multicolic, and multicolosic acids, (I), ( 2 ) , and (3), respectively, has given samples which when derivatised and examined by spin echo Fourier transform (S.E. F.T.) 3C n.m.r. spectroscopy show 80-induced l3C-satellites, confirming the previously proposed biosynthetic pathway involving oxidative fission of the P-ketide derived intermediate 6-pentylresorcylate ( 8 ) and establishing that lactonisation of the tetronic acid ring occurs by displacement from the C -I carboxy-group by the C-4 enolic oxygen, rather than by lactol formation. lsO-Induced changes in the l3C-chernical shifts of directly attached carbon atoms have recently been shown to provide an extremely valuable addition to the armoury of n.m.r. techniques available for the investigation of biosynthetic path-

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