Mass spectrometric studies on the intrinsic stability of destruxin E from Metarhizium anisopliae

Destruxins are of current interest as bioactive agents. They are cyclic hexadepsipeptides produced by fungi, the most common destruxins, A, B and E, differing in the structure of a side chain. Before they can be widely used, the potential risk of destruxins and their metabolites entering the human food chain must to be assessed; thus, knowledge of the structures of their degradation products is essential. Here we report a study aimed at identifying, by tandem mass spectrometry and accurate mass analysis, the products resulting from thermally and temporally induced degradation of destruxin E. The degradation products fell into two groups: those with relatively simple modifications of the side chain and those involving much more complex rearrangements. The structures of most of the degradation products were deduced from the MS data, with the major product being destruxin E diol: significantly, this compound had previously been reported to have only been produced as a metabolic product of enzyme action rather than as a simple degradation product as demonstrated here.