Inhibition of guinea-pig complement by derivatives of benzamidine. I. Effect of p-nitrophenylureido derivative of m-(m-phenoxypropoxy)benzamidine on guinea-pig complement component haemolytic activity.

Derivatives of benzamidine have been shown to be potent inhibitors of whole guinea-pig complement. Among these compounds the -[-(-nitrophenylureido) phenoxypropoxy] benzamidine (NPUPPB) was the most potent complement inhibitor synthesized. NPUPPB blocked the addition of C1 to EAC4. It had no effect on the stability of EAC4 or the decay rate of EAC42. It also blocked the addition of C2 to EAC14. No effect of the inhibitor was found when C3 was added to EAC142. A profound inhibition occurred when either C[unk]567 was added to EAC1423 or when C5 was added to EAC1423. A slight though possibly insignificant effect occurred when C6 or C7 were added to EAC4235 and EAC42356. No effect occurred when C8 and C9 were added to the heat-stable intermediate EAC43567. NPUPPB is a potent though poorly soluble competitive inhibitor of complement activity.