Biladienones from the photooxidation of a meso-gem-disubstituted phlorin: crystal and molecular structures of the 3N + O coordinated nickel(II) and copper(II) complexes

meso-Diketopyripentaphyrin and Diketopyrihexaphyrin as Macrocyclic Tripyrrinone Ligands for NiII Ions

We report expanded porphyrins with pyridine rings and two neighboring carbonyl groups, which allow Ni^II ions to coordinate to the tripyrrinone-type NNNO coordination structure with Ni-O bonds. The selectivity of tripyrrinone is superior to other pyrrolic or pyridinic cavities of expanded porphyrins. Introduction of α-carbonyl pyridine next to the tripyrrolic conjugated structure is a powerful strategy for regioselective metalation of flexible expanded porphyrinoids.

Synthesis of a doubly SO2-fused phlorin: Tuning the structure and properties by the SO2 groups

A doubly SO2-fused phlorin 4 has been synthesized by the [2 + 2] condensation of dipyrromethanecarbinol 2 and SO2-fused dipyrromenthane 3 in the presence of TFA, followed by DDQ oxidation. The SO2-fused phlorin 4 has been characterized by absorption, fluorescence, mass and NMR spectra, as well as X-ray analysis. Compared to the [Formula: see text]-unsubstituted phlorin 5, the SO2-fused phlorin 4 exhibits a red-shifted absorption spectrum (around 12 nm), a more distorted molecular conformation, as well as nice photostability even with an electron-donating meso-3,5-di-tert-butylphenyl group. The titration of 4 and 5 with TBAF has been monitored by absorption spectroscopy. The deprotonated phlorin 4 shows a peak at 870 nm which is red shifted by 26 nm compared to that of deprotonated 5.

Transition metal complexes of phyllobilins - a new realm of bioinorganic chemistry

Phyllobilins may function as natural ligand molecules for biologically important transition metal ions, giving complexes with remarkable chemical and photophysical properties.

Natural cyclic tetrapyrroles feature outstanding capacity for binding transition metal ions, furnishing Nature with the important metallo-porphyrinoid ‘Pigments of Life’, such as heme, chlorophyll (Chl) and vitamin B₁₂. In contrast, linear tetrapyrroles are not generally ascribed a biologically relevant ability for metal-binding. Indeed, when heme or Chl are degraded to natural linear tetrapyrroles, their central Fe- or Mg-ions are set free. Some linear tetrapyrroles are, however, effective multi-dentate ligands and their transition metal complexes have remarkable chemical properties. The focus of this short review is centred on such complexes of the linear tetrapyrroles derived from natural Chl-breakdown, called phyllobilins. These natural bilin-type compounds are massively produced in Nature and in highly visible processes. Colourless non-fluorescing Chl-catabolites (NCCs) and the related dioxobilin-type NCCs, which typically accumulate in leaves as ‘final’ products of Chl-breakdown, show low affinity for transition metal-ions. However, NCCs are oxidized in leaves to give less saturated coloured phyllobilins, such as yellow or pink Chl-catabolites (YCCs or PiCCs). YCCs and PiCCs are ligands for various biologically relevant transition metal-ions, such as Zn(ii)-, Ni(ii)- and Cu(ii)-ions. Complexation of Zn(ii)- and Cd(ii)-ions by the effectively tridentate PiCC produces blue metal-complexes that exhibit an intense red fluorescence, thus providing a tool for the sensitive detection of these metal ions. Outlined here are fundamental aspects of structure and metal coordination of phyllobilins, including a comparison with the corresponding properties of bilins. This knowledge may be valuable in the quest of finding possible biological roles of the phyllobilins. Thanks to their capacity for metal-ion coordination, phyllobilins could, e.g., be involved in heavy-metal transport and detoxification, and some of their metal-complexes could act as sensitizers for singlet oxygen or as plant toxins against pathogens.

Blue transition metal complexes of a natural bilin-type chlorophyll catabolite

Natural pink degradation products of chlorophyll occur in de-greened leaves. They form blue transition metal complexes, some of which show intensive red fluorescence and may serve as highly sensitive reporters of transition metals in plants.

Synthesis of biladienone and bilatrienone by coupled oxidation of tetraarylporphyrins

Tetraarylbiladien-ab-ones bearing various substituents (R) in the para position of the phenyl groups were preprared by coupled oxidation of tetraarylporphyrin iron complexes. The yields of 5,10,15-triaryl-19-aroyl-15-hydroxybiladien-ab-ones were 74% (R=H), 85% (R=OMe), 44% (R=COOMe), and 28% (R=CN). Kinetic studies of the iron porphyrin oxidation revealed that the reaction is accelerated by an electron-withdrawing substituent with the Hammett reaction constant rho=0.295. 5,10,15-Triaryl-19-aroyl-15-hydroxybiladien-ab-ones undergo the acid-catalyzed elimination reaction either by acetic acid or by mesoporous silica to afford 5,10,15-triaryl-19-aroylbilatrien-abc-one. The elimination reaction in acetic acid is accelerated by an electron-donating substituent with the Hammett reaction constant rho=-1.48.

Dipyrromethane + dipyrromethanedicarbinol routes to an electron deficient meso-substituted phlorin with enhanced stability

Two dipyrromethane + dipyrromethanedicarbinol routes to a meso-substituted phlorin bearing electron-withdrawing pentafluorophenyl substituents (TpFPPhl) were investigated in an attempt to obtain a phlorin with enhanced stability toward light and air and to explore the application of dipyrromethanecarbinol chemistry to the preparation of phlorins. For each route, a systematic survey of reaction parameters for the two-step, one-flask reaction leading to TpFPPhl was performed. The analytical-scale reactions were monitored for yield of TpFPPhl by HPLC. Sharp differences were observed in the yield of TpFPPhl afforded by the two synthetic routes. The most promising reaction condition (TFA catalysis, 100 mM) was performed on a preparative scale providing TpFPPhl in a yield of 45% (189 mg). The stability of the electron-deficient phlorin in dilute solution upon exposure to light and air was probed in a number of solvents, and decomposition was monitored by UV-vis spectroscopy and HPLC. Many of the solutions of TpFPPhl were found to be quite stable for periods of approximately 8 h, with decomposition requiring exposure periods of several days. Taken together, this work contributes an efficient synthesis of a meso-substituted phlorin of practical stability and provides further insights toward the adaptation of dipyrromethanecarbinol chemistry to the preparation of diverse porphyrinoids.

Synthesis and electrochemistry of undeca-substituted metallo-benzoylbiliverdins

The high-yield preparation of metallo-benzoylbiliverdins 9, 10, and 11 from either oxidation of dodeca-substituted porphyrin 6 in the presence of NaNO2/TFA and air followed by metalation or by reaction of the Ni(II) or Cu(II) complexes of 6 with m-chloroperoxybenzoic acid in pyridine under air is reported. The X-ray structures of complexes 9 and 10 and the electrochemistry and spectroelectrochemistry of metallo-benzoylbiliverdins 9-11 are presented and discussed.

Synthesis of N-Confused Phlorins via an Addition/Cyclization Pathway

The syntheses of N-confused phlorins are provided by reactions of N-confused porphyrins with nitrilimines and with dialkyl acetylenedicarboxylate. Both reactions involve zwitterionic intermediates and proceed through an addition/cyclization pathway.

A facile and versatile preparation of bilindiones and biladienones from tetraarylporphyrins

Bilindiones and biladienones carrying aryl groups at the meso positions were prepared using coupled oxidation reactions of iron tetraarylporphyrins in 20-63% yield.

Regioselective oxidative liberation of aryl-substituted tripyrrinone metal complexes from N-confused porphyrin

[reaction: see text] A Cu(II) complex of the first aryl-substituted tripyrrinone derivative, 14-benzoyl-5,10-diphenyl-1-oxo-tripyrrinato copper(II) (3-Cu) was obtained in the reaction of N-confused tetraphenylporphyrin (NCTPP) and Cu(OAc)(2) in refluxing toluene, and subsequent treatment with acid afforded a free tripyrrolic ligand that could bind a variety of transition metals.