2886-83-1 N,N'-Diethylene-N''-(5-methyl-1,3,4-thiadiazol-2-yl)phosphoramide NSC 528988 P,P-Bis(1-aziridinyl)-N-(5-methyl-1,3,4-thiadiazol-2-yl)phosphinic amide S 261 S-261