Masked Imidazolyl−Dipyrromethanes in the Synthesis of Imidazole-Substituted Porphyrins

Abstract

Imidazole-substituted metalloporphyrins are valuable for studies of self-assembly and for applications where water solubility is required. Rational syntheses of porphyrins bearing one or two imidazol-2-yl or imidazol-4-yl groups at the meso positions have been developed. The syntheses employ dipyrromethanes, 1-acyldipyrromethanes, and 1,9-diacyldipyrromethanes bearing an imidazole group at the 5-position. The polar, reactive imidazole unit was successfully masked by use of (1) the 2-(trimethylsilyl)ethoxymethyl (SEM) group at the imidazole pyrrolic nitrogen, and (2) a dialkylboron motif bound to the pyrrole of the dipyrromethane and coordinated to the imidazole imino nitrogen. The nonpolar nature of such doubly masked imidazolyl-dipyrromethanes facilitated handling. Selected masked dipyrromethanes were characterized by 11B and 15N NMR spectroscopy. Five distinct methods were examined to obtain trans-A2B2-, trans-AB2C-, and trans-AB-porphyrins. Each porphyrin contained one or two SEM-protected imidazole units. The SEM group could be removed with TBAF or HCl. Two zinc(II) porphyrins and a palladium(II) porphyrin bearing a single imidazole moiety were prepared and subjected to alkylation (with ethyl iodide, 1,3-propane sultone, or 1,4-butane sultone) to give water-soluble imidazolium- porphyrins. This work establishes the foundation for the rational synthesis of a variety of porphyrins containing imidazole units.

New Route to ABCD-Porphyrins via Bilanes

“…43 On the basis of the gHSQC spectra, the values of the NH one-bond coupling constant ( 1 J N-H ) ranged from -96 to -100 Hz for each bilane, which are consistent with those reported for shorter homologues (i.e., dipyrromethanes 42 ).…”

Modifications of Porphyrins and Hydroporphyrins for their Solubilization in Aqueous Media

“…Lindsey and co-workers prepared porphyrins with one or two meso-imidazolyl groups by starting from imidazole-functionalized dipyrromethane precursors [95,96]. Mono-imidazolyl porphyrin 58 was alkylated with various alkylating reagents.…”

“…The resulting imidazolium porphyrins were studied for their use in photodynamic therapy. The zwitterionic imidazolium sulfonate porphyrin 60Zn, for example, is the product obtained when butanesultone was used as the alkylating reagent (Scheme 15) [95].…”

Synthesis and photodynamic activity of new imidazole substituted pyropheophorbide-a derivatives

“…Meanwhile, a large number of porphyrins bearing imidazole have been prepared for materials chemistry and the life sciences on account of numerous specifi c characteristics of imidazole substituent [20,21]. Imidazole is not only a vital constituent in biological structures [22,23], where it is involved in electron transfer in photosynthesis, nucleic acid bases, and amino acids, but also presents in many fungicides and antifungal, antiprotozoal, and antihypertensive medications [24] as well as in the anticancer medication mercaptopurine, which combats leukemia by interfering with DNA activities [25].…”