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Abstract

We investigated the organ-specific phytochemistry of the inflorescences, leaves at different stages of senescence,
and roots of Xiphidium caeruleum (Haemodoraceae) and elucidated the structure of six undescribed compounds.
Among these, a phenylcarbamoylnaphthoquinone (PCNQ), representing the first member of a class of undescribed
phenylphenalenone-derived nitrogenous compounds, was identified and its spontaneous formation
elaborated. Starting from phenylbenzoisochromenone glucosides, the reaction cascade proceeds through oxidative
decarboxylation and several oxidation steps to an anhydride, which is further converted to a carboxyphenylnaphthoquinone.
In the presence of amino acids, this carboxy-phenylnaphthoquinone readily reacts to
PCNQs. Hence, the carboxy-phenylnaphthoquinone was hypothesized to be involved in plant defense because of
its reactivity towards amino acids. It was also hypothesized that reduced levels of the corresponding glucosidic
phenylbenzoisochromenone precursors in older leaves may foster pathogen-driven senescence.