Abstract
Four chlorophyll derivatives (pheophytins) were isolated from silkworm excreta by column and thin-layer chromatography and their structures were elucidated by spectroscopy. Among them, two substances, 132-hydroxy (132-R, S) pheophytin a and pheophytin b, have in vitro cytostatic activity against hepatoma tissue culture (HTC) cells. The methyl ester derivatives of pheophorbides showed cytotoxic effects towards the tumor cells under illumination. This can be explained by photodynamic destruction of HTC cells by singlet oxygen, as has already been shown in the case of hematoporphyrin. The observation that natural pheophytins have cytostatic effects even in the dark suggests that there is another biological mechanism for the action of these chlorophyll derivatives.
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