This invention provides novel compounds, pharmaceutical compositions and methods of treating thrombotic disorders in mammals, the compounds having the formula (I), wherein: Ar is phenyl, naphthyl, furanyl, benzofuranyl, indolyl, pyrazolyl, oxazolyl, fluorenyl, phenylcycloalkane where the cycloalkane can be cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl and Ar can be optionally substituted by one or more groups selected from C1-C6 alkyl, C1-C6 alkoxy, hydroxy, phenyl-(CH2)0-6-, phenyl-(CH2)0-6O-,C3-C6 cycloalkyl, -(CH2)-C3-C6 cycloalkyl, halogen, C1-C3 perflouroalkyl and C1-C3 perfluoroalkoxy where phenyl can be substituted with from one or more groups selected from C1-C6 alkyl, C1-C6 alkoxy, phenyl, halogen, trifluoromethyl and trifluoromethoxy; R1 is hydrogen, C1-C6 alkyl or phenyl-(CH2)1-6- where phenyl can be substituted with C1-C6 alkyl, C1-C6 alkoxy, halo, trifluoromethyl and trifluoromethoxy; R2 and R3 are H, C1-C6 alkyl, phenyl-(CH2)0-3-, halo and C1-C3 perfluoroalkyl where phenyl can be substituted with C1-C6 alkyl, C1-C6 alkoxy, halo, trifluoromethyl and trifluoromethoxy; R4 is -CHR5CO2H or -CH2-tetrazole where R5 is H or benzyl; and n = 0 or 1; or a pharmaceutically acceptable salt or ester form thereof.