Abstract: Peptides which act as inhibitors or substrates of thrombin are provided.

Abstract: This invention provides peptides of the formula ##STR1## wherein X is H, CH.sub.3 or an N-protecting group;Y is(1) C.sub.3 -C.sub.9 alkyl optionally substituted by C.sub.1 -C.sub.4 alkoxy,(2) C.sub.5 -C.sub.10 aryl optionally substituted by C.sub.1 -C.sub.4 alkoxy,(3) C.sub.5 -C.sub.10 alkylaryl optionally substituted by C.sub.1 -C.sub.4 alkoxy,(4) (CH.sub.2).sub.n --Q or ##STR2## wherein Q is H, amino, amidino, imidizole, guanidino or isothioureido and n is 1-5;Z is COR.sub.1, ##STR3## wherein: R.sub.1 is H, OH, CH.sub.2 Cl, CH.sub.2 --CH.sub.2 --CO-pip, CF.sub.2 --CF.sub.2 --CO-pip, CH.sub.2 --CH(CH.sub.3)--CO-pip, CF.sub.2 --CF(CF.sub.3)--CO-pip, CH.sub.2 --CH.sub.2 --CO-Pro-NHEt, CF.sub.2 --CF.sub.2 --CO-Pro-NHEt or a chromophoric group,R.sub.2 and R.sub.3 may be the same or different and are selected from the group consisting of OH, OR.sub.6 and NR.sub.6 R.sub.7, wherein R.sub.6 and R.sub.7 may be the same or different and are selected from the group consisting of C.sub.1-10 alkyl, phenyl or C.sub.6 -C.

Abstract: Peptides which act as inhibitors or substrates of thrombin are derived from the formula: D-Phe-Pro-Arg or its analogues, wherein Phe is substituted by (a), wherein Ar.sub.1 or Ar.sub.2 are the same or different and are selected from the group consisting of phenyl, thienyl, pyridyl, naphthyl, thionaphtyl, indolyl and saturated groups corresponding to these, optionally substituted by up to three groups selected from C.sub.1 -C.sub.3 alkyl and C.sub.1 -C.sub.3 alkoxy, L.sub.1 and L.sub.2 are the same of different and are selected from the group consisting of CH.sub.2, C.sub.2 --C.sub.2, O-CH.sub.2, S-CH.sub.2, Ar-L taken together optionally means H, diphenyl-methyl, fluorenyl or saturated groups corresponding to these, but one of the Ar-L cannot be H when the other [CH.sub.2 ].sub.n -Q, (c) where Q=H, amino, amidino, imidazole, guanidino or isothioureido and n=1-5, preferably 3-5, or C.sub.3 -C.sub.9 alkyl and C.sub.5 -C.sub.