Structural studies on minor enniatins from Fusarium sp. VI 03441: Novel N-methyl-threonine containing enniatins

A strain of a yet unidentified Fusarium sp. produced in addition to enniatins A1, B and B1 a number of minor enniatins. The strain formed a well supported clade with strains identified as Fusarium acuminatum (Gibberella acuminata) in phylogenetic analyses using the TEF-1α gene sequences. Two of the minor enniatins were easily recognised as hydroxylated species on the basis of their fragment ion spectra. The hydroxylation could be traced to one of the amino acid moieties using multiple-stage ion trap mass spectrometry. Different approaches for acetylation of the isolated compounds and complete hydrolysis supported the elucidation of the amino acid moiety as 3-hydroxy-2-methylamino-butyric acid, which is equivalent with N-methyl-threonine. The primary structures of the two enniatins were tentatively determined to be cyclo[Hiv-N-Me-Val-Hiv-N-Me-Val-Hiv-N-Me-Thr] and cyclo[Hiv-N-Me-Leu-Hiv-N-Me-Val-Hiv-N-Me-Thr]. The two depsipeptides represent new analogues and were named enniatin P1 and P2, respectively.