Chemistry and biochemistry of chinese drugs. VII. Cytostatic pheophytins from silkworm excreta, and derived photocytotoxic pheophorbides.

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Abstract
Four chlorophyll derivatives (pheophytins) were isolated from silkworm excreta by column chromatography and TLC; their structures were elucidated by spectroscopy. Among them, 2 substances, 132-hydroxy (132-R,S) pheophytin a and pheophytin b, have in vitro cytostatic activity against [rat Morris] 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 for 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.