Graham M. F. Bisset

meso-Methylporphyrins and -chlorins

Abstract Two efficient synthetic routes to meso-methylporphyrins and -chlorins are described. In the first, meso-formylporphyrins and -chlorins are reduced to the corresponding meso-hydroxymethyl derivatives, and after zinc chelation and treatment with acetic anhydride in pyridine, the resulting meso-acetoxymethylporphyrins are reduced to meso-methyl with sodium borohydride or by catalytic hydrogenation. The second route is more efficient in that copper(II) meso-formylporphyrins and -chlorins can be reduced directly with tetra n-butylammonium borohydride in hot 1,2-dichloroethane to give the copper(II) meso-methyl analog. Using the procedures developed herein, a formal total synthesis of the meso-pheophorbide from Chlorobium chlorophyll “660” band 6 is decribed, and certain photooxidation and electrophilic deuteration problems in the meso-methylchlorin series are clarified.

Polyformylation of copper(II) porphyrins

Abstract Vilsmeier formylation of copper(II) octaethylporphyrin (1) is shown to yield the copper(II) complexes of meso-monoformyloctaethylporphyrin, meso-α,β- and meso-α,γ-diformyloctaethylporphyrins, meso-α,β,γ-triformyloctaethylporphyrin, and meso-α,β,γ,δ-tetraformyloctaethylporphyrin. There is therefore no difference in regioselectivity of meso-diformylation between the octaethylporphyrin and etioporphyrin-I series.

meso(Methine) functionalization of octa-alkylporphyrins

meso-Acetoxymethylocta-alkylporphyrins [e.g.(1), (7), and (8)] react with a variety of nucleophiles such as alcohols (to give the corresponding alkoxymethylporphyrins), amines (yielding aminomethylporphyrins), and Grignard reagents (to give meso-alkylporphyrins). Treatment of the meso-acetoxymethylporphyrins with thiol reagents accomplishes reduction to give the meso-methylporphyrin rather than the sulphide. Making use of these meso-functionalization reactions, potential cytochrome P450 models and a model for the tense form of hemoglobin are synthesized.

On the partial synthesis of optically pure bacteriopheophorbides -C and -D

Abstract Methyl bacteriopheophorbides-c or -d (obtained by partial synthesis, or by Markownikoff hydration of methyl pyropheophorbide-a, respectively) are obtained as a mixture of the (R,S) diastereomers at the 2(1-hydroxyethyl) group; these can be efficiently and completely separated using reverse phase high performance liquid chromatography (HPLC). Purity of the resolved mixture is demonstrated by 360 MHz NMR spectra.

Recent studies on The chlorobium chlorophylls (bacteriochlorophylls-C).

Abstract 1. 1. Methods for introduction of methyl groups into the meso positions of porphyrins and chlorins are described. 2. 2. Acetoxymethyl groups at the meso positions of porphyrins and chlorins are shown to be highly reactive towards nucleophiles. 3. 3. A partial synthesis of a methyl pheophorbide related to bacteriochlorophyll-c is described.

Polyformylation of copper(II) complexes of octa-alkylporphyrins

Vilsmeier formylation of copper(II) octaethylporphyrin (1) affords the copper(II) complexes of α-formyloctaethylporphyrin, α,γ- and α,β-diformyloctaethylporphyrins, α,β,γ-triformyloctaethylporphyrin, and α,β,γ,δ-tetraformyloctaethylporphyrin [(13), (2), (3), (14), and (15), respectively]. Similar results are obtained when copper(II) etioporphyrin-I (5) is formylated. It therefore appears that there exists no difference in regioselectivity in the diformylation reactions between the copper(II) octaethyl- and copper(II) etioporphyrin-I series. Earlier work which indicated that in the octaethylporphyrin series there is a preference for formation only of the copper(II)α,γ-diformylporphyrin (2) is suggested to be a result of preferential crystallization of the least-soluble α,γ-compound from an almost equal mixture of the two isomers.