PORPHYRIN BUILDING-BLOCKS FOR MODULAR CONSTRUCTION OF BIOORGANIC MODEL SYSTEMS

We outline a modular building block strategy for the covalent assembly of porphyrin-containing model systems. Molecular design issues for the synthesis of porphyrin dimers, dye-porphyrin dyads, and multi-porphyrin arrays have been used to guide the development of this approach. The major design constraints are to achieve directed coupling of free base and/or metalloporphyrin building blocks in dilute solution under non-acidic non-metalating conditions. A set of 24 porphyrin building blocks has been synthesized. The porphyrins are prepared by reaction of substituted benzaldehydes with pyrrole using the two-step one-flask room temperature porphyrin synthesis. Routes to 7 substituted aldehydes are described. Each porphyrin bears one or four functional groups, and many also are facially-encumbered in order to achieve increased solubility. 12 functional groups that meet the design criteria include those that can be reacted directly in coupling reactions such as active esters, alpha-chloroacetamido, benzoyl, and iodo groups, and others that require deprotection prior to coupling, such as phthalimidomethyl, FMOC-prolyl, trimethylsilylethynyl, dithiolane, methoxycarbonyl, and trimethylsilylethoxycarbonyl groups. The synthesis of 13 porphyrin dimers and dye-porphyrin dyads has been explored as a testbed for refining strategies for the synthesis of molecular devices containing multiple porphyrins and other components. The coupling strategies investigated have yielded dimers or dyads with subunits linked by amide, butadiyne, ethyne, or thiourea groups. This building block approach should enable rapid assembly of architecturally-defined porphyrin-based model systems.