Abstract
In cold extracts of senescent leaves of the plum tree (Prunus domestica ssp. domestica), six colorless non‐fluorescent chlorophyll catabolites (NCCs) were characterized, named Pd‐NCCs. In addition, several minor NCC fractions were tentatively classified. The structure of the most polar one of the NCCs, named Pd‐NCC‐32, featured an unprecedented twofold glycosidation pattern. Three of the NCCs are also functionalized at their 32‐position by a glucopyranosyl group. In addition, two of these glycosidated NCCs carry a dihydroxyethyl group at their 18‐position. In the polar Pd‐NCC‐32, the latter group is further glycosidated at the terminal 182‐position. Four other major Pd‐NCCs and one minor Pd‐NCC were identified with five NCCs from higher plants known to belong to the ‘epi’‐series. In addition, tentative structures were derived for two minor fractions, classified as yellow chlorophyll catabolites, which represented (formal) oxidation products of two of the observed Pd‐NCCs. The chlorophyll catabolites in leaves of plum feature the same basic structural pattern as those found in leaves of apple and pear trees.
Highlights
In view of a surprising stereochemical diversity observed in natural dioxobilin-type NCCs (DNCCs), we suggested an earlier branching-point in the ‘PaO/phyllobilin’ pathway of Chl-breakdown.[9][39] a P450-enzyme catalyzing deformylation of FCCs was identified,[40] which converts FCCs (1-formyl-19-oxobilin-type or ‘type-I’ phyllobilins) to corresponding 1,19-dioxobilin-type FCCs (DFCCs), opening the pathway to ‘type-II’ phyllobilins.[9][40][41] Under weakly acidic conditions, the latter are indicated to isomerize stereoselectively to corresponding DNCCs.[41]
In the context of investigations of Chl-catabolites in domestic agricultural plants, we have studied the nature of such phyllobilins in stone fruit and report here our work on the Chl-catabolites in leaves of the plum tree (Prunus domestica ssp. domestica)
Five major and nine minor colorless nonfluorescent chlorophyll catabolites (NCCs) were provisionally identified in extracts of senescent leaves of plum trees on the basis of their characteristic UV-absorbance properties, using analytical HPLC (Fig. 2)
Summary
About 25 years ago, chlorophyll (Chl) breakdown and the appearance of the fall colors were still a stunning mystery.[1][2] In 1991, a first colorless Chl degradation product from a higher plant was described, the ‘nonfluorescent’ Chl-catabolite (NCC) Hv-NCC-1 from senescent leaves of barley (Hordeum vulgare).[3][4] Structural identification of Hv-NCC-1 as a 1-formyl-19-oxobilintype linear tetrapyrrole[3] opened the door to the structure-guided discovery of the ‘PaO/phyllobilin’ pathway of Chl-breakdown.[5 – 9] As we know oxidative cleavage of the Chl macroring generates1-formyl-19-oxobilins and sets the stage for the formation of various bilin-type catabolites of Chl,[10][11] or ‘phyllobilins’.[7 – 9] The ‘early’ stages of Chl-breakdown, which take place in the chloroplasts, furnish one of two epimeric primary ‘fluorescent’ Chl-catabolites (pFCCs), with species-dependent configuration of their formation.[11][12] pFCCs are rapidly hydroxylated to 32OH-pFCC (probably still in the chloroplast).[7]. Five major and nine minor colorless NCCs were provisionally identified in extracts of senescent leaves of plum trees on the basis of their characteristic UV-absorbance properties, using analytical HPLC (Fig. 2). Senescent plum tree leaves were extracted with cold MeOH (to avoid significant NCC oxidation, see [28]), and the extract was separated by semi-preparative HPLC.
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