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Abstract:
Phenylbenzoisochromenone glucosides (oxa-phenylphenalenone
glucosides) occurring in some phenylphenalenone-producing plants of
the Haemodoraceae undergo conversion to phenylbenzoisoquinolindiones
(aza-phenylphenalenones) in extracts of Xiphidium caeruleum. Precursordirected
biosynthetic experiments were used to generate a series of new
phenylbenzoisoquinolindiones from native phenylbenzoisochromenone glucosides
and external amines, amino acids, and peptides. Intermediates of the
conversion were isolated, incubated with cell-free extracts, and exposed to
reactions under oxidative or inert conditions, respectively, to elucidate the
entire pathway from phenylbenzoisochromenones to phenylbenzoisoquinolindiones.
An intermediate in this pathway, a reactive hydroxylactone/aldehyde,
readily binds not only to amines in vitro but may also bind to the N-terminus
of biogenic peptides and proteins of herbivores and pathogens in vivo. The
deactivation of biogenic amino compounds by N-terminal modification is
discussed as the key reaction of a novel phenylphenalenone-based plant defense mechanism. According to these data, the
ecological function of phenylphenalenone-type compounds in the Haemodoraceae, subfamily Haemodoroideae, has been substantiated.
