The crystallographic structure of the photooxidized product of hypocrellin A and the study of the photodynamic action mechanism.

In attempting to study the phototherapeutic action and the photosensitized oxygenation mechanism, we have determined the crystal structure of the main oxidized product of hypocrellin A (HA). It was crystallized in monoclinic system with space group P2(1). The cell data are: a = 10.030(3), b = 8.877(3), c = 15.764(5)A, beta = 104.50(2) degrees, Z = 2. The crystal structure has been determined by direct method and refined to a final R of 0.055 based on the 1408 observed reflections with I greater than 2.5 sigma (I). The photooxidized product is composed of a heptacyclic aliphatic hydrocarbon connecting with two alpha-naphthoquinone derivatives as its skeletal molecule. No peroxidic linkage has been found. On the basis of the crystal structure determined, we have deduced part of the process of formation of the oxide, i. e. firstly, the peroxide was formed by photocycloaddition of oxygen molecule to Hypocrellin A, then thermodissociation took place to form a stable oxide.