Abstract The present invention comprises compounds of the formula ##STR1## and the biologically acceptable acid addition salts thereof, wherein R 1 represents hydrogen or lower alkyl having 1 to 4 carbon atoms; R 2 represents an alkylene having 2 to 4 carbon atoms; R 3 represents amino or guanidino; R 4 represents nitrophenyl, methylnitrophenyl, dinitropheyl, naphthyl, or nitronaphtyl; m is 2 or 3; and n is 3 or 4. The compounds of the present invention are analytical reagents useful for measuring proteolytic enzymes such as thrombin and trypsin. The enzymatic hydrolysis of the invention compounds provides a chromogenic amine by which the proteolytic enzyme concentration can be determined spectrophotometrically.