Further studies on the biosynthesis of granaticin

Experiments with cerulenin-inhibited cultures of S. violaceoruber showed conversion of dihydrogranaticin (II) into granaticin (I), but not vice versa, confirming an earlier conclusion that II is the biosynthetic precursor of I. Feeding of CH3(13)C18O2Na followed by 13C-NMR analysis of the product by the 18O shift method indicated the expected incorporation of 18O at carbons 1, 11 and 13 of I and showed that the oxygen of the pyran ring originates from C-3 and not from C-15. Analysis of I biosynthesized from 13C2H3COONa by 13C[1H, 2H] triple resonance NMR spectroscopy showed the incorporation of one atom of deuterium each at C-2 and C-4. C-16 carried a maximum of 2, not 3, atoms of deuterium. These results are discussed in terms of biosynthetic mechanisms.