Isocoumarins are potent mechanism-based heterocyclic irreversible inhibitors for a variety of
serine proteases. Most
serine proteases are inhibited by the general
serine protease inhibitor 3,4-dichloroisocoumarin, whereas
isocoumarins containing hydrophobic 7-acylamino groups are potent inhibitors for human
leukocyte elastase and those containing 7-alkylureidogroups are inhibitors for procine
pancreatic elastase.
Isocoumarins containing basic side chains that resemble
arginine are potent inhibitors for
trypsin-like
enzymes. A number of 3-alkoxy-4-chloro-7-guanidinoisocoumarins are potent inhibitors of bovine
thrombin, human
factor Xa, human
factor XIa, human
factor XIIa, human
plasma kallikrein, porcine
pancreatic kallikrein, and bovine
trypsin. Another cathionic derivative, 4-chloro-3-(2-isothiureidoethoxy)
isocoumarin, is less reactive toward many of these
enzymes but is an extremely potent inhibitor of human
plasma kallikrein. Several guanidinoisocoumarins have been tested as
anticoagulants in human plasma and are effective at prolonging the prothrombin time. The mechanism of inhibition by this class of heterocyclic inactivators involves formation of an acyl
enzyme by reaction of the active site
serine with the
isocoumarin carbonyl group.
Isocoumarins with 7-amino or 7-guanidino groups will then decompose further to
quinone imine methide intermediates, which react further with an active site residue (probably His-57) to form stable inhibited
enzyme derivatives.
Isocoumarins should be useful in further investigations of the physiological function of
serine proteases and may have future therapeutic utility for the treatment of
emphysema and coagulation disorders.