De Novo Synthesis of Bacteriochlorins Bearing Four Trideuteriomethyl Groups by Haoyu Jing Qun Tang David F. Bocian & Jonathan S. Lindsey

Author:Haoyu Jing, Qun Tang, David F. Bocian & Jonathan S. Lindsey
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Tags: Site-specific introduction of isotopes in tetrapyrrole macrocycles provides the foundation for probing physicochemical features germane to photosynthetic energy-transduction processes, but has chiefly been done with porphyrins rather than the more biologically relevant hydroporphyrin analogues of native photosynthetic pigments. A prior study incorporated pairwise 13C or 15N atoms in the skeleton of a bacteriochlorin containing a gem-dimethyl group in each pyrroline ring. Here, a complementary effort is reported that installs deuterium atoms in substituents at the perimeter of a bacteriochlorin. Thus, perdeuteriated 3-methyl-2,4-pentanedione was converted in an 8-step synthesis via the intermediacy of tert-butyl 5-formyl-3,4-bis(trideuteriomethyl)pyrrole-2-carboxylate to the 2,3,12,13-tetrakis(trideuteriomethyl)-8,8,18,18-tetramethylbacteriochlorin (BC-2). The fidelity of isotope substitution was maintained throughout the synthesis. Resonance Raman spectroscopy of the copper chelate (CuBC-2) revealed that addition of the four -pyrrolic substituents alone is not sufficient to account for the vibronic complexity observed for the copper chelate of bacteriochlorophyll a (CuBChl a). The increased vibronic activity exhibited by the natural pigments and CuBChl a must arise from the increased structural complexity of the macrocycle., bacteriochlorophyll; isotopic labeling; photosynthesis; pyrrole synthesis; resonance Raman spectroscopy


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