A pink colored dioxobilin-type phyllobilin from breakdown of chlorophyll

Abstract

In senescent leaves of higher plants, colorless chlorophyll (Chl) catabolites typically accumulate that belong to one of two major types, classified as formyloxobilin-type or dioxobilin-type phyllobilins (PBs). Natural yellow and pink colored formyloxobilin-type PBs are also known, named YCCs and PiCCs, respectively. A dioxobilin-type yellow Chl catabolite (DYCC) was recently prepared by partial synthesis, characterized by spectroscopic means and also identified in grapevine leaves. Here, we report the first dioxobilin-type pink Chl catabolite (DPiCC) from its partial synthesis from the DYCC. The DPiCC had similar structural features and absorption characteristics (in the visible spectral region) as the natural PiCC, its formyloxobilin-type analogon. In contrast to the effectively racemic PiCC, the DPiCC is an optically active pigment with a stable new asymmetric carbon center.

In Search of Bioactivity – Phyllobilins, an Unexplored Class of Abundant Heterocyclic Plant Metabolites from Breakdown of Chlorophyll

“…The complexes of 13 with the closed shell transition metal ions Zn (II) and Cd(II) were strongly red fluorescent, signaling the presence of such transition metal ions down beyond the nM range (Scheme 6). [34] Preliminary investigations with the DPiCC 16 have indicated a similar capacity for metal complexation, [37] as is known for the PiCCs. [34] Bi-or tridentate binding of transition metal ions by phyllochromobilins modifies their reactivity.…”

“…[33b] A related set of PBs, as represented by the type-I phyllochromobilins 12 and 13, is available from oxidation of DNCCs, the type-II phyllobilanes. Hence, oxidation of the DNCC 14 by the ubiquitous 'oxidative activity' furnished the DYCC 15, [36] a proto-type-II yellow PB, which is readily oxidized further in the presence of air to the corresponding type-II PrB, the DPiCC 16 [37] (see Scheme 3). The conversion of the polar phylloleucobilins to phylloxanthobilins and phylloroseobilins is difficult to rationalize by being a mere detoxification process.…”

A Blue Zinc Complex of a Dioxobilin‐Type Pink Chlorophyll Catabolite Exhibiting Bright Chelation‐Enhanced Red Fluorescence

“…The blue Zn(II) complex 2 has provisionally been detected previously as a reaction intermediate in the synthesis of 1 from the corresponding DYCC, where 1 was obtained by de-complexation of the presumed Zn(II) complex 2 in a phosphate buffer. [14] The Zn complex 2 exhibited pseudo molecular ions at m/z 691. S1).…”

“…[16,17] Here, we describe a first representative metal chelate of an optically active type-II PrB, of the pink DPiCC 1. [14] The blue Zn(II) complex ZnDPiCC (2) was obtained nearly quantitatively by treatment of a solution of 1 in MeCN with Zn(acac) 2 under Ar at room temperature (Scheme 2). Work-up of the blue solution of the Zn(II) complex 2 furnished the ZnDPiCC 2 as dark blue powder in a yield of 94 %.…”

“…[13] We have recently also discovered related dioxobilin-type (or type-II) PChBs (Scheme 1). [14] The dioxobilintype PBs [7][8][9] carry the same two oxo-functions at the cleavage site of the porphyrinoid macrocycle, as do the heme-derived bilins. [1b,15] The increased structural similarity of type-II PChBs with natural bilins supports the consideration of such PChBs as candidates for physiological functions in the plants [1b,16] and other interesting biological activity.…”