Main Strategies for the Synthesis of meso-Arylporphyrins

meso-Arylporphyrins as most accessible tetrapyrrole macroheterocycles have always been the focus of attention from researchers concerned with practically useful properties of these compounds. The first syn­theses of meso-arylporphyrins date back to about 90 years ago. Up to now, the yields of these compounds have been improved from 5 to 80%. The present review analyzes different ways and strategies for the synthesis of meso-aryl-substituted porphyrins. The most efficient methods that can be scaled up to an industrial level have been identified.

Creation from Confusion and Fusion in the Porphyrin World─The Last Three Decades of N-Confused Porphyrinoid Chemistry

Confusion is a novel concept of isomerism in porphyrin chemistry, delivering a steady stream of new chemistry since the discovery of N-confused porphyrin, a porphyrin mutant, in 1994. These days, the number of confused porphyrinoids is increasing, and confusion and associated fusion are found in various fields such as supramolecular chemistry, materials chemistry, biological chemistry, and catalysts. In this review, the birth and growth of confused porphyrinoids in the last three decades are described.

Encapsulation of Gold Nanorods with Porphyrins for the Potential Treatment of Cancer and Bacterial Diseases: A Critical Review

Cancer and bacterial diseases have been the most incidental diseases to date. According to the World Health Report 2018, at least every family is affected by cancer around the world. In 2012, 14.1 million people were affected by cancer, and that figure is bound to increase to 21.6 million in 2030. Medicine therefore sorts out ways of treatment using conventional methods which have been proven to have many side effects. Researchers developed photothermal and photodynamic methods to treat both cancer and bacterial diseases. These methods pose fewer effects on the biological systems but still no perfect method has been synthesized. The review serves to explore porphyrin and gold nanorods to be used in the treatment of cancer and bacterial diseases: porphyrins as photosensitizers and gold nanorods as delivery agents. In addition, the review delves into ways of incorporating photothermal and photodynamic therapy aimed at producing a less toxic, more efficacious, and specific compound for the treatment.

Two-Step, One-Flask Synthesis of an N-Confused Porphyrin Bearing Pentafluorophenyl Substituents

A two-step, one-flask reaction of pyrrole and pentafluorobenzaldehyde was investigated as a streamlined synthetic route to an N-confused porphyrin bearing pentafluorophenyl substituents previously prepared by a stepwise route. A survey of acid catalysts, acid catalyst concentration, DDQ quantity, and reaction time was performed with monitoring by HPLC. The targeted N-confused porphyrin was observed from many reaction conditions. The best condition afforded the N-confused porphyrin in an isolated yield of 10-12% (245-281 mg), providing improved access to this interesting porphyrinoid.

Synthesis of tetraferrocenylporphyrin and new metal complexes: Searching for reliable synthetic procedures

The tetraferrocenylporphyrin synthetic procedure was performed varying different reaction conditions. Mg, Mn, Pd and Cd complexes were synthesized and preliminarily studied. The results obtained show that the synthetic procedure strongly depends on catalyst, solvent and reagents concentration, even more than what observed with similar tetraarylporphyrins; concentration of substrates plays an important role in determining the outcome of the reactions.

Synthetic transformations of porphyrins – Advances 2002-2004

Contemporary methods for the modification of porphyrins are presented. In association with the Third International Conference on Porphyrins and Phthalocyanines (ICPP-3) a survey of current method developments and reactivity studies is made. The review focuses on synthetic transformations of porphyrins currently in use for various applications and on functional group transformations. A brief survey of important developments covers selectively the literature from late 2001 to early 2004.

Solvent-free synthesis of meso- tetraarylporphyrins in air: product diversity and yield optimization

The scope and optimization of a solvent-free method for the rapid preparation and facile purification of technologically important meso-substituted aryl porphyrins, such as 5,10,15,20-tetraphenylporphyrin is presented. This one-step method involves heating the aromatic aldehyde to ~200°C in a vial fitted with a septum-lined cap, followed by addition of the pyrrole and maintaining the temperature for about 20 minutes. The dioxygen in air serves as the oxidant. Present results show that the addition of benzoic acid as a catalyst improves the yield of 5,10,15,20-tetraphenylporphyrin from 22% to 32% and of para halogenated phenylporphyrins from 10% to ~25%. Herein is also presented an examination of the many factors that influence the yield, the ease of purification, and the ability to scale up the reaction. Since the tarry by-products from this method are much less soluble than in most other synthetic strategies, much less solvent is required for purification; simple extraction is often sufficient. This method can be scaled in the lab to > 300 mg, and provides an attractive route to many meso-substituted porphyrins because of its minimal waste generation in terms of both solvent and chromatography support.

Synthetic routes to meso-patterned porphyrins

Synthetic meso-substituted porphyrins offer significant attractions compared with naturally occurring beta-substituted porphyrins. The attractions include the rectilinear arrangement of the four meso substituents and potential synthetic amenability from pyrrole and simple acyl reactants, thereby avoiding the cumbersome syntheses of beta-substituted pyrroles. In practice, however, the classical methods for the synthesis of meso-substituted porphyrins were characterized by high-temperature reactions, limited scope of substituents, and statistical mixtures accompanied by laborious chromatography if porphyrins bearing two different types of substituents were sought. Such methods left unrealized the tremendous utility of meso-substituted porphyrins across the enormously broad field of porphyrin science, which touches pure chemistry; energy, life and materials sciences; and medicine. This Account surveys a set of strategies, developed over a generation, that provide rational access to porphyrins bearing up to four distinct meso substituents. A "2 + 2" route employs a dipyrromethane-1,9-dicarbinol and a dipyrromethane (bearing ABC- and D-substituents, respectively) in a two-step, one-flask process of acid-catalyzed condensation followed by oxidation at room temperature to form the free base "ABCD-porphyrin." A "bilane" route relies on the acid-catalyzed reaction of a 1-acyldipyrromethane (CD substituents) and a 9-bromodipyrromethane-1-carbinol (AB substituents) to form the corresponding 19-acyl-1-bromobilane. Reaction of the latter compound in the presence of MgBr(2), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and toluene at reflux exposed to air affords the corresponding magnesium(II) porphyrin. The two routes are complementary, both in scope and in implementation. A suite of methods also affords trans-A(2)B(2)-porphyrins by reaction of a dipyrromethane and an aldehyde, self-condensation of a dipyrromethane-1-carbinol, or self-condensation of a 1-acyldipyrromethane. These new routes are also useful for preparing sparsely substituted porphyrins, which bear fewer than four meso substituents (e.g., trans-AB-porphyrins, A-porphyrins). Because of their compact size and the ability to incorporate hydrophilic or amphipathic groups, such molecules are ideal for biological applications. The success of these new synthetic strategies has relied on a number of advances including (1) the development of simple yet efficient routes to dipyrromethanes, acyldipyrromethanes, and dipyrromethane-carbinols, (2) the identification of acid catalysts and reaction conditions for condensations of pyrromethane species without accompanying acidolysis (which underlies scrambling and formation of a mixture of porphyrin products), (3) the development of analytical methods to rapidly screen for scrambling and to characterize the distribution of oligopyrromethanes and macrocycles, (4) selection and refinement of synthetic methods to increase yields and to limit or avoid use of chromatography, thereby achieving scalability to multigram levels, and (5) exploitation of discoveries concerning the fundamental chemistry of pyrrolic species. With these developments, the prior era of porphyrin synthesis has been supplanted with rational routes that proceed under very mild conditions and afford a single porphyrin bearing up to four distinct meso substituents. The meso substituents encompass a very wide range of molecular complexity. The resulting porphyrins can serve as building blocks in the construction of model systems, as components of molecular materials, and as surrogates for naturally occurring tetrapyrrole macrocycles.

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.

De Novo Synthesis of Stable Tetrahydroporphyrinic Macrocycles: Bacteriochlorins and a Tetradehydrocorrin

[structures: see text] Bacteriochlorins (tetrahydroporphyrins) are attractive for diverse photochemical applications owing to their strong absorption in the near-infrared spectral region, as exemplified by the bacterial photosynthetic pigment bacteriochlorophyll a, yet often are labile toward dehydrogenation to give the chlorin. Tetradehydrocorrins (ring-contracted tetrahydroporphyrins) are attractive for studies of catalysis analogous to that of vitamin B12. An eight-step synthesis toward such tetrahydroporphyrinic macrocycles begins with p-tolualdehyde and proceeds to a dihydrodipyrrin-acetal (1) bearing a geminal dimethyl group and a p-tolyl substituent. Self-condensation of 1 in CH3CN containing BF3 x OEt2 at room temperature afforded a readily separable mixture of two free base bacteriochlorins and a free base B,D-tetradehydrocorrin. Each bacteriochlorin contains two geminal dimethyl groups to lock-in the bacteriochlorin hydrogenation level, p-tolyl substituents at opposing (2,12) beta-positions, and the absence (H-BC) or presence (MeO-BC) of a methoxy group at the 5- (meso) position. The B,D-tetradehydrocorrin (TDC) lies equidistant between the hydrogenation levels of corrin and corrole, is enantiomeric, and contains two geminal dimethyl groups, 2,12-di-p-tolyl substituents, and an acetal group at the pyrroline-pyrrole junction. Examination of the effect of the concentrations of 1 (2.5-50 mM) and BF3 x OEt2 (10-500 mM) revealed a different response surface for each of H-BC, MeO-BC, and TDC, enabling relatively selective preparation of a given macrocycle. The highest isolated yield of each was 49, 30, and 66%, respectively. The macrocycles are stable to routine handling in light and air. The bacteriochlorins display characteristic spectral features; for example, H-BC exhibits near-IR absorption (lambda(Qy) = 737 nm, epsilon(Qy) = 130,000 M(-1) cm(-1)) and emission (lambda(em) = 744 nm, phi(f) = 0.14). In summary, this simple entry to stable bacteriochlorins and tetradehydrocorrins should facilitate a wide variety of applications.