Editorial - Ingenta Connect

19 downloads 330 Views 63KB Size Report
from a search engine (Web of KnowledgeSM-Thomson Reuters®) the hits obtained (approximate value) indicate a steady growth on the number of publications ...
Editorial

Current Organic Synthesis, 2014, Vol. 11, No. 1 1

Editorial Tetrapyrrolic Macrocycles: Synthesis and Prospects Cyclic tetrapyrrolic based molecules are macrocycles in which four functionalized pyrrole units are bridged to form a highly chemically stable extended -electron system. This apparently straightforward definition conceals a vast world of scientific knowledge that traversed time. For instance, porphyrins are the most representative class of this type of molecules, as they are ubiquitous in nature. Some cyclic tetrapyrroles are the active cores of some compounds with crucial biochemical roles in living systems, such as hemoglobin and chlorophyll. On the other hand, phthalocyanines are exclusively obtained from synthetic procedures and widely used as pigments in textiles, polymers and paints. The realization of synthetic methods for preparing both types of compounds occurred at similar times. While the synthetic mesotetraphenylporphyrin was firstly synthesized by Rothemund in 1935 [1], Linstead used for the first time the term phthalocyanine in 1934 [2], after several accidently prepared bluish pigments without structural assignment [3]. Having started in equally promising environments, both types of macrocycles had however different growth rates. After direct retrieval from a search engine (Web of KnowledgeSM-Thomson Reuters®) the hits obtained (approximate value) indicate a steady growth on the number of publications involving those macrocycles, having the porphyrin “sub-family” a more representative growing (Fig. 1).

9000 8000

Porphyrins Phthalocyanines

Nr of Publications

7000 6000 5000 4000 3000 2000 1000 0 1940

1950

1960

1970

1980

1990

2000

2010

Years Fig. (1). Approximate number of publications (porphyrin type-grey bar and phthalocyanine type-black bar) since 1934 until 2012 inclusive. (Source: Web of KnowledgeSM-Thomson Reuters®).

It is no surprise that the dramatic increase on reports involving tetrapyrrolic macrocycles around the late 90’s was due to a spread in the diverse applications from these materials. From the traditional applications of porphyrins and phthalocyanines in biomimetics, dyes or catalysts, the synthetic developments on their preparation lead into new applications in multiple fields, already well documented [4]. This special issue, devoted to covering these new synthetic developments also intends to give insight on new emerging fields of application for these old, yet actual and exciting compounds. The review article by Vicente et al. [5] is a great example of the work carried out in the development of synthetic procedures to conveniently prepare a vast array of porphyrins, reviewing the widely used methodology which has been utilized to synthesize tetrapyrrole macrocycles in the porphyrin series from monopyrrole precursors, the MacDonald [2+2] porphyrin synthesis, the [3+1] route from tripyrrolic intermediates and from a,c-biladiene salts, as well as several selected porphyrin reactivity profiles. Corroles, [6] now considered an independent class of molecules within the largest family of tetrapyrrolic compounds, are here reviewed, particularly the preparation of meso-triaarylcorroles and their functionalization, namely via cycloaddition transformations, along with a description of the nonlinear optical (NLO) properties of a series of metal-free and gallium corroles with different peripheral substituents. Also related to porphyrins, as one of their reduced forms, chlorins are here reviewed by De Oliveira et al. [7], where the most relevant synthetic methodologies that have been developed over the last decades are covered. As chlorins are by far the most abundant and important porphyrinoid type compounds, bearing in mind their occurrence in Nature (consider chlorophyll), this special type of compounds are also covered, regarding their principal natural sources. Changing to the totally synthetic members of the tetrapyrrolic macrocycles, glycosylated phthalocyanines and their preparation methodologies are here reviewed by Hanack et al. [8], giving an insight on the preparation of this specific type of macrocycles, prepared aiming utilization in biological systems.

2

Current Organic Synthesis, 2014, Vol. 11, No. 1

Editorial

Nakagaki et al. [9] review extensively the utilization of metalloporphyrins immobilized on silica and modified silica as catalysts in heterogeneous processes, which is advocated by the “Green Chemistry” principles, in the idealization and production of more efficient, selective, and preferably recyclable catalysts to develop technological processes. Synthetic routes for the preparation of such catalyst are here carefully covered. Still bearing in mind the utilization of environmentally friendly processes, Piñeiro et al. [10] contributes here with a paper describing past and current microwave assisted methodologies for the synthesis of porphyrins and porphyrin derivatives, including porphyrin precursors such as dipyrromethanes, covering solventless and solution reactions. As biomedical applications of tetrapyrrolic macrocycles are one of the most endeavored topics in recent years, Tomé et al. [11] reviews the synthesis and biological applications of porphyrins and phthalocyanines decorated with dendrimers, focusing the design of dendrimers with modulated size, shape, branching length/density and surface functionality. Finally, also the potential application of tetrapyrrolic macrocycles in medical imaging technologies is also reviewed in this Special Issue, [12] for recent developments involving tetrapyrrolic-based sensitizers for cancer detection, with emphasis on positron emission tomography, fluorescence imaging and magnetic resonance imaging technologies, arising from their displayed intrinsic affinity for tumor localization and their well-portrayed photophysical and photosensitizing properties, which can lead to their potential use as sensitizers in a variety of in vivo imaging technologies. Without any doubt, the synthesis and applications of tetrapyrrolic macrocycles still render knowledge to ensure steady growth and interest. Many applications were naturally left outside this special issue topic, since it would be too broad to cover, but it is hoped that the diverse topics covered in this special issue of Current Organic Synthesis will provide valuable information to readers of the journal. Lastly, as a guest editor for this special issue, I am indebted for the valuable and excellent contributions from my colleagues, as well as to all other colleagues, acting as referees, for their comments. A final sincere acknowledgment is also due to Ms. Arsala Saeed (Assistant Manager Publications at Bentham Science Publishers) for her invaluable assistance in the organization of this issue. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

Rothemund, P. Formation of porphyrins from pyrrole and aldehydes. J. Am. Chem. Soc., 1935, 57, 2010-2011. Linstead, R.P. Phthalocyanines. Part I. A new type of synthetic colouring matters. J. Chem. Soc., 1934, 1016-1017. (a) Braun, A.; Tcherniac, J. Über die Produkte der Einwirkung von Acetanhydrid auf Phthalamid. Ber. Dtsch. Chem. Ges., 1907, 40, 2709-2714; (b) Diesbach, H.; von der Weid, E. Quelques sels complexes des o-dinitriles avec le cuivre et la pyridine. Helv. Chim. Acta, 1927, 10, 886-888. Handbook of Porphyrin Science, Kadish, K.M.; Smith, K.M.; Guilard, R., Eds.; Vols 1-30, World Scientific Press: Singapore, 2010-2012. Vicente, M.G.H.; Smith, K.M. Syntheses and functionalizations of porphyrin macrocycles. Curr. Org. Synth., 2014, 11, 3-28. Santos, C.I.M.; Barata, J.F.B.; Calvete, M.J.F.; Vale, L.S.H.P.; Dini, D.; Meneghetti, M.; Neves, M.G.P.M.S.; Faustino, M.A.F.; Tomé, A.C.; Cavaleiro J.A.S. Synthesis and functionalization of corroles. An insight on their nonlinear optical absorption properties. Curr. Org. Synth., 2014, 11, 29-41. Oliveira, K.T.; Momo, P.B.; de Assis, F.F.; Ferreira, M.A.B.; Brocksom T.J. Chlorins: natural Sources, synthetic developments and main applications. Curr. Org. Synth., 2014, 11, 42-58. Hanack, M.; Crucius, G.; Ziegler T. Glycosylated metal phthalocyanines. Curr. Org. Synth., 2014, 11, 59-66. Nakagaki, S.; Ferreira, G.K.B.; Marçal, A.L.; Ciuffi K.J. Metalloporphyrins immobilized on silica and modified silica as catalysts in heterogeneous processes. Curr. Org. Synth., 2014, 11, 67-88. Pineiro, M. Microwave-assisted synthesis and reactivity of porphyrins. Curr. Org. Synth., 2014, 11, 89-109. Figueira, F.; Pereira, P.M.R.; Silva, S.; Cavaleiro, J.A.S.; Tomé J.P.C. Porphyrins and phthalocyanines decorated with dendrimers: synthesis and biomedical applications. Curr. Org. Synth., 2014, 11, 110-126. Calvete, M.J.F.; Simões, A.V.C.; Henriques, C.A.; Pinto, S.M.A.; Pereira, M.M. Tetrapyrrolic macrocycles: potentialities in medical imaging technologies. Curr. Org. Synth., 2014, 11, 127-140.

Mário J. F. Calvete (Guest Editor) Coimbra Chemistry Centre Department of Chemistry Faculty of Science and Technology University of Coimbra Rua Larga 3004-535 Portugal E-mail: [email protected]