Aggregation of 2,3-dihydroxy-etiochlorin I. An amphiphilic model compound for photodynamic therapy and green heme d.

The crystal structure of 2,3-dihydroxy-etiochlorin I has been determined to obtain information on its aggregation behavior. Cis-dihydroxychlorins serve as model compounds for green heme d and show promising photonecrotic activity in photodynamic therapy. The compound shows strong aggregation in the solid state facilitated by intramolecular hydrogen bonding between one hydroxy group and pyrrole nitrogens of neighboring molecules. This novel type of aggregation leads to chain-type aggregates in the crystal. The title compound 4 crystallized in the monoclinic space group Ia (Z = 4) with unit cell dimensions a = 9.902(4) A, b = 26.430(9) A, c = 10.823(5), beta = 104.47(3) A, V = 2743(2) A3. The structure was refined to an R-value of 0.097 on the basis of 1150 reflections with F > 4.0 sigma (F) (130 K).

Regioselective photoreduction of zinc(II) porphyrins to give chlorins.

The ascorbic acid/organic base photoreduction of zinc(II) porphyrins was investigated. It was established that certain substituents can direct the photoreduction to the site of the macrocycle to which they are attached. For example, zinc(II) vinylporphyrins (8, 12, 16, 20) are photoreduced with cis stereochemistry on the ring bearing the vinyl group to give the corresponding chlorins. Zinc(II) acetylporphyrins (22, 24) were likewise reduced to chlorins such that cis-hydrogenation took place on the ring bearing the acetyl group. Zinc(II) formylporphyrins 33 also appear to reduce at the ring bearing the formyl group. When the zinc(II) acrylic porphyrin 28 was photoreduced, reduction did take place at the ring bearing the acrylic side chain, but migration of the acrylate double bond was very rapid, and the product isolated was the corresponding porphyrin propionate 30. Reduction of a zinc(II) porphyrin 35 bearing both a vinyl group and a nuclear carboxylic ester took place at the ring bearing the carboxylic ester. The reaction provides a general method for regioselective synthesis of chlorins from zinc(II) porphyrins without any evidence of formation of over-reduction products characteristic of many other procedures for formation of chlorins from porphyrin precursors.