In conclusion, we have characterised the structure and biosynthesis of burnettiene A (1) from A. burnettii, which has been shown to be a biosynthetically talented fungus harbouring a large number of BGCs. Interestingly, 1 contains one of the longest polyketide chain (tridecaketide) known to form decalin structures. A. burnettii also produces the unusually long tetradecaketide burnettramic acids. Compared to fusarielin A (Fig. ), where the decalin core is highly oxidised, 1 has the branched chains highly oxidised with a methyl ester and carboxylic acid moieties. We have also investigated the biosynthesis of 1 by evaluating truncated gene cluster variants. This led to the isolation and characterisation of the intermediates preburnettienes A and B (3 and 2). We also identified the functions of the tailoring enzymes BueF and BueE.