ISOPIMPINELLIN IS NOT PHOTOTOXIC IN A CHICK SKIN ASSAY

Synthetic isopimpinellin (5,8-dimethoxypsoralen), confirmed to contain as impurities only trace quantities at most of psoralen, bergapten (5 -methoxypsoralen) and xanthotoxin (8-methoxypsoralen), is not phototox ic when tested in a chick skin bioassay system. These findings are at variance with earlier studies showing isopimpinellin to be phototoxic against chick skin and support the conclusion that isopimpinellin is p hotobiologically inactive. As recently proposed by others, the several reports of isopimpinellin photoactivity are most likely attributable to contamination by small amounts of highly active psoralens such as b ergapten or xanthotoxin.