Synthesis of zinc 20-substituted bacteriochlorophyll-d analogs and their chlorosomal self-aggregation

Hitoshi Tamiakia, Ayaka Wadaa
aGraduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan

Zinc complexes of methyl 31-demethyl-bacteriopheophorbides-d possessing a 2-(un)substituted ethynyl or ethenyl group at the 20-position were prepared through palladium-catalyzed cross-coupling of their 20-bromide with the corresponding alkyne or alkene (see below) [1]. The synthetic zinc 20-substituted 3-hydroxymethyl-131-oxo-chlorins self-aggregated in an aqueous micellar solution to give similar large oligomers as self-aggregates of bacteriochlorophylls in the core part of the main light-harvesting antenna (chlorosome) of photosynthetic green bacteria [2]. The zinc 20-ethynyl-chlorin fully gave the self-aggregates, but its 202-substitution disturbed the self-aggregation. The 20-(2-phenyl)ethenyl moieties induced the formation of relatively smaller oligomers as well as residual monomers due to their steric bulkiness.


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