Biosynthesis of tetraoxygenated phenylphenalenones in Wachendorfia thyrsiflora

Abstract

The biosynthetic origin of 1,2,5,6-tetraoxygenated phenylphenalenones and the sequence according to which their oxygen functionalities are introduced during the biosynthesis in Wachendorfia thyrsiflora were studied using two approaches. (1) Oxygenated phenylpropanoids were probed as substrates of recombinant W. thyrsiflora polyketide synthase 1 (WtPKS1), which is involved in the diarylheptanoid and phenylphenalenone biosynthetic pathways, (2) Root cultures of W. thyrsiflora were incubated with (13)C-labelled precursors in an (18)O2 atmosphere to observe incorporation of the two isotopes at defined biosynthetic steps. NMR- and HRESIMS-based analyses were used to unravel the isotopologue composition of the biosynthetic products, lachnanthoside aglycone and its allophanyl glucoside. Current results suggest that the oxygen atoms decorating the phenalenone tricycle are introduced at different biosynthetic stages in the sequence O-1→O-2→O-5. In addition, the incubation of W. thyrsiflora root cultures with (13)C-labelled lachnanthocarpone established a direct biosynthetic precursor-product relationship with 1,2,5,6-tetraoxygenated phenylphenalenones.