Heptaphyrins: expanded porphyrins with seven heterocyclic rings

Expanded porphyrins containing seven pyrrole/heterocyclic rings linked in a cyclic fashion are termed heptaphyrins. The number of π-electrons in heptaphyrins depends on the number ofmeso carbon bridges used to link the heterocyclic rings, accordingly heptaphyrins with 28π-electrons and 30π-electrons are reported to date. Both condensation reactions of the appropriate precursors and acid-catalysed oxidative coupling reactions have been utilized to synthesise the heptaphyrins. The 30π heptaphyrins exhibit rich structural diversity where some of the heterocyclic rings in the macrocycle undergo a 180° ring flipping. An overview of the synthetic methods employed for the synthesis of heptaphyrins, their spectroscopic properties, structural behaviour and aromatic properties are highlighted in this paper

Core modified oxybenziporphyrins: new aromatic ligands for metalcarbon bond activation

Successful syntheses of two new aromatic core modified oxybenziporphyrins by a simple 3 + 1 methodology and the first aromatic core modified oxybenziporphyrin palladium complex are reported

Novel heteroatom containing rubyrins

Synthesis of rubyrins containing two or three heteroatoms (O, S, Se) in the core is accomplished using modified diols and tetrapyrromethanes. Substitution of heteroatoms leads to significant reductions in HOMO-LUMO gap and easier oxidations and reductions reflecting the changes in electronic structure of the rubyrin skeleton

Carboplatin derivatives with superior antitumor activity compared to the parent compound

A series of new carboplatin derivs. was synthesized by introducing fluoro, chloro, bromo and hydroxy substituents into the cyclobutane ring. The carboxylic acid groups were used for the complexation with platinum(II) fragments bearing two ammonia and (RR/SS)-trans-1,2-diaminocyclohexane ligands, resp., as non-leaving groups. The antiproliferative activity of the new carboplatin analogs differing in the cyclobutanedicarboxylato ligands and the type of platinum fragment were studied in tests with J82 bladder cancer cells and SK-OV-3 as well as cisplatin-resistant NIH:OVCAR-3 ovarian cancer cells. The most active compds. were the 3-fluoro, 3-chloro and 3,3-difluoro derivs. of carboplatin. NMR spectroscopy showed that cis-diammine(3-chloro-1,1-cyclobutanedicarboxylato)platinum(II) was hydrolyzed much faster than carboplatin explaining its higher cytostatic activity

meso-Aryl sapphyrins with heteroatoms; synthesis, characterization, spectral and electrochemical properties

The synthesis, characterization and spectral properties of six new meso-aryl core modified sapphyrins are described. An efficient approach involving an acid catalyzed condensation of bithiophene diol 1 and modified tripyrranes 2a–2e allows preparation of the desired meso-aryl sapphyrins in 16–36% yield. The product distribution and the isolated yield were found to be dependent on the nature of the acid catalyst (Lewis acid or protic acid) and its concentration. Protic acid catalyst exclusively gave the expected sapphyrins while two additional products, an 18? tetraphenylporphyrin and a 26? modified rubyrin, were isolated under Lewis acid catalysis. An analysis of proton NMR and absorption spectral data suggests that in free base sapphyrins, the heterocyclic ring opposite to the bithiophene unit is inverted as in N-5 meso-aryl sapphyrin and the degree of inversion is dependent on the nature of the heterocyclic ring. The energy optimized structure calculated from the semi-empirical method substantiates such a conclusion. Protonation of sapphyrins generates respective mono- and dications and the heterocyclic ring retains an inverted structure in contrast to normal N-5 sapphyrins. The triplet excited lifetimes for free base and protonated derivatives are similar both under argon saturated and air equilibrated conditions, indicating that the triplet state quenching by oxygen is minimal. Cyclic voltammetric studies reveal easier reductions and harder oxidations relative to meso-aryl porphyrins and the ?redox observed for 3d suggests significant reduction of the HOMO–LUMO energy gap consistent with the large red shift observed for the Soret band

Characterization of a new meso-aryl rubyrin isomer: [26]hexaphyrin (1.1.1.0.1.0) with an inverted heterocyclic ring

The synthesis and characterization of new aromatic 26π macrocycles obtained from the acid catalyzed 4+3 coupling reaction of core modified tripyrrane and tetrapyrrane are described

Ground and excited state dynamics of core-modified normal and expanded porphyrins

Singlet and triplet excited state data on two new core-modified expanded porphyrins and their protonated derivatives are reported. Absorption spectral studies indicate a gradual red shift of the absorption bands upon sulfur substitution into the core. The singlet lifetimes for expanded S3-sapphyrin and S4-rubyrin decrease steadily relative to STPPH and S2TPP owing to a higher rate of intersystem crossing. Furthermore, the protonated derivatives of S3-sapphyrin and S4-rubyrin encapsulate fluoride ions into their cavities with binding constants of 807 and 48 M-1 respectively. However, the triplet lifetime for S3-sapphyrin is longer (58.80 μs) than for normal thiaporphyrins (STPPH, 37.45 μs; S2TPP, 20.96 μs), suggesting that it could be very well suited for photosensitizing triplet oxygen.</p

N-confused expanded porphyrin: first example of a modified sapphyrin with an inverted N-confused pyrrole ring

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Inverted meso-aryl porphyrins with heteroatoms; characterization of thia, selena, and oxa N-confused porphyrins

Synthesis and characterization of inverted porphyrins containing S, Se, and O are reported. A simple 3 + 1 MacDonald-type condensation using modified tripyrrane containing the N-confused ring and diols afforded various N-confused porphyrins 6a-f in 19-30% yield. The single-crystal X-ray structure of 6b shows a ruffled conformation with tilt angles of 21.11&#176; and 31.23&#176; for the N-confused ring and the adjacent pyrrole ring III, respectively, revealing its severe nonplanarity. Significant changes in C&#945;-C&#946;, C&#946;-C&#946;, and C&#945;-X bond lengths are observed in 6b relative to free thiophene and pyrrole, suggesting the altered delocalization pathway in the modified N-confused porphyrins. The two molecules in the unit cell show a cyclophane-type noncovalent dimer with a face to face orientation of two N-confused pyrrole rings as a result of the presence of weak N-HN and C-HN intermolecular hydrogen bonds involving pyrrole-NH, the N atom of the N-confused ring, and the C atom of the pyrrole ring. A detailed 1H and 13C NMR study by 1D and 2D methods allowed assignments of all the peaks in the free base and protonated forms. NMR studies reveal the presence of three different tautomeric forms in solution for 6c in CDCl3 at low temperature. UV-visible studies reveal absorption band shifts upon heteroatom substitution, and the magnitudes of these shifts are dependent on the nature of the heteroatom. In all cases both monoprotonated and diprotonated species have been identified, and on addition of acid, the first proton goes to the outer N2 atom of the N-confused ring