Highly sensitive peptide‐4‐methylcoumaryl‐7‐amide substrates for blood‐clotting proteases and trypsin

Seventy‐four peptide amides of 7‐amino‐4‐methylcoumarine (Mec) of the type Boc‐Xaa‐Yaa‐Arg‐NH‐Mec were newly synthesized and tested to find specific substrates for blood‐clotting proteases and trypsin. The Xaa and Yaa residues of these substrates have been replaced by 12 and 15 different amino acids, respectively. Among these peptides, the followings were found to be most sensitive substrates for individual enzymes: Boc‐Asp(OBzl)‐Pro‐Arg‐NH‐Mec (kcat= 160 s−1, Km= 11 μM, kcat/Km=15000000 M−1 s−1) for human α‐thrombin, Z‐< Glu‐Gly‐Arg‐NH‐Mec(kcat= 19 s−1, Km= 59 μM, kcat/Km= 320000 M−1 s−1) for bovine factor Xa, Boc‐Gln‐Gly‐Arg‐NH‐Mec (kcat= 5.8 s−1, Km= 140 μM, kcat/Km= 42000) for bovine factor XIIa, Boc‐Asp(OBzl)‐Ala‐Arg‐NH‐Mec (kcat= 9.2 s−1, Km= 120 μM, kcat/Km= 77000 M−1 s−1) for bovine activated protein C, and Boc‐Gly‐Phe‐Arg‐NH‐Mec (kcat= 29 s−1, Km= 230 μM, kcat/Km= 130000 M−1 s−1) for bovine plasma kallikrein. Moreover, Boc‐Glu(OBzl)‐Ala‐Arg‐NH‐Mec (kcat= 46 s−1, Km= 370 μM, kcat/Km= 120000 M−1 s−1) was newly found as a good substrate for human factor XIa. Bovine trypsin effectively hydrolyzed peptide‐NH‐Mec substrates containing Ala and Pro at the P2 site. The most reactive substrate was Boc‐Gln‐Ala‐Arg‐NH‐Mec (kcat= 120 s−1, Km= 6.0 μM, kcat/Km= 20000000 M−1 s−1).