The invention relates to heterocyclic derivatives of formula (I), wherein R.sup.2 is amino, a group OR.sup.4 or a group --Y--R.sup.5 where R.sup.4 is hydrogen or C.sub.1-4alkyl, Y is C.sub.1-4alkylene, R.sup.5 is hydrogen, halo, hydroxy, C.sub.1-2alkoxy, C.sub.1-2alkoxyC.sub.1-2alkoxyC.sub.1-4, or a group NR.sup.7R.sup.8 where R.sup.7 and R.sup.8 are independently selected from hydrogen, C.sub.1-2alkyl, hydroxyC.sub.1-2alkyl or alkoxyC.sub.1-2alkyl, or R.sup.7 and R.sup.8 together with the nitrogen atom to which they are attached form a saturated 5-6-membered heterocyclic ring which optionally contains an additional heteroatom; n is one or two and each R.sup.1 is independently selected from halo, haloC.sub.1-2alkyl, hydroxy, oxo, amino, C.sub.1-2alkylamino or di-C.sub.1-2dialkylamino; or a pharmaceutically acceptable salt thereof. These compounds possess antithrombotic and anticoagulant properties and are accordingly useful in methods of treatment of humans or animals. The invention also relates to processes for the preparation of the heterocyclic derivatives, to pharmaceutical compositions containing them and to their use in the manufacture of medicaments for use in the production of an antithrombotic or anticoagulant effect. ##STR00001##