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Syntheses of derivatized capped iron(II) porphyrin complexes and their interaction with CO and O₂

University of British Columbia

The affinity of hemoglobin for CO relative to O₂ is decreased compared to simple iron-porphyrin systems mainly due to electronic effects. Hydrogen-bond formation with the His E7 residue of hemoglobin has been revealed to stabilize the bound dioxygen. This thesis describes the development of a series porphyrin models, benzene-4/4 (49a), benzene-5/5 (49b), amidobenzene-4/4 (49c) and amidobenzene-5/5 (49d) capped porphyrins, which serve as simple models to imitate the hydrogen bonding in hemoglobin. The chain linked bis pyrroles 38 were synthesized by Friedel-Crafts acylation of the benzene and nitrobenzene diacid chain derivatives with two equivalents of the β-unsubstituted pyrrole 36, followed by diborane reduction of the ketonic groups. After the nitro functions were transformed to the acetamides, modification of the ethyl ester functions of 38a, 38b and 39 via the benzylesters 40, the carboxypyrroles 41 and the α-unsubstituted pyrroles 42 afforded the important bis formyl pyrroles 43. The cyanoacrylate protected formyl pyrrole derivatives 44 were subjected to monochlorination at the α-methyl groups followed by condensation with two equivalents of the α-unsubstituted pyrrole 46 to give dipyrromethane dimers 47. Strong aqueous alkali caused saponification of the two ester groups and deprotection of the formyl functions to give 48. The α formyl-α′-unsubstituted dipyrromethane dimer, resulting from the thermal decarboxylation of 48, was cyclized to produce the porphyrin 49 in acidic medium. The interactions of CO and O₂ with the heme derivatives, Fe[superscript]Ⅱ(porphyrin)(DcIm), have been studied. The CO binding constant of the amide substituted heme is two foldlarger than that of the non-amide substituted heme. In contrast, the low temperature (-45°C) O₂ binding constants of the hemes have shown a 6-8 fold increase from nonamide to amide substituted hemes, probably because of a hydrogen bonding between the amide function and bound dioxygen similar to the hydrogen bonding in hemoglobin. [formula omitted]

Text

2011-02-03

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http://hdl.handle.net/2429/31030

Chemistry

University of British Columbia

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