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Stereo‐ and Regioselective Phyllobilane Oxidation in Leaf Homogenates of the Peace Lily ( Spathiphyllum wallisii) : Hypothetical Endogenous Path to Yellow Chlorophyll Catabolites
Author(s) -
Vergeiner Clemens,
Ulrich Markus,
Li Chengjie,
Liu Xiujun,
Müller Thomas,
Kräutler Bernhard
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201404783
Subject(s) - endogeny , chemistry , chlorophyll , botany , methanol , biochemistry , stereochemistry , organic chemistry , biology
In senescent leaves, chlorophyll typically is broken down to colorless and essentially photo‐inactive phyllobilanes, which are linear tetrapyrroles classified as “nonfluorescent” chlorophyll catabolites (NCCs) and dioxobilane‐type NCCs (DNCCs). In homogenates of senescent leaves of the tropical evergreen Spathiphyllum wallisii , when left at room temperature and extracted with methanol, the major endogenous, naturally formed NCC was regio‐ and stereoselectively oxidized (in part) to a mixture of its 15‐hydroxy and 15‐methoxy derivative. In the absence of methanol in the extract, only the 15‐OH‐NCC was observed. The endogenous oxidation process depended upon molecular oxygen. It was inhibited by carbon monoxide, as well as by keeping the leaf homogenate and extract at low temperatures. The remarkable “oxidative activity” was inactivated by heating the homogenate for 10 min at 70 °C. Upon addition of a natural epimeric NCC ( epi NCC) to the homogenate of senescent or green Sp. wallisii leaves at room temperature, the exogenous epi NCC was oxidized regio‐ and stereoselectively to 15‐OH‐ epi NCC and 15‐OMe‐ epi NCC. The identical two oxidized epi NCCs were also obtained as products of the oxidation of epi NCC with dicyanodichlorobenzoquinone (DDQ). Water elimination from 15‐OH‐ epi NCC occurred readily and gave a known “yellow” chlorophyll catabolite (YCC). The endogenous oxidation process, described here, may represent the elusive natural path from the colorless NCCs to yellow and pink coloured phyllobilins, which were found in (extracts of) some senescent leaves.