A series of nitrocoumarin and nitrochromene derivatives have been prepared and shown to inhibit the phosphatidylinositol-specific phospholipase C (PLC)(ICW C 10 pg/mL) isolated from human melanoma. The inhibition of PLC by nitrocoumarin 4a was time-dependent and irreversible. The inhibition of PLC was shown to interfere with inositide metabolism in whole cells (I&= 4 pg/mL) in a manner consistent with their proposed mode of activity. Finally, the ...