The invention generally relates to compounds of the formula I, which are in equilibrium with their 4-hydroxy tautomers, and their pharmaceutically acceptable salts: ##STR1## where n is 0 to 2; A is S, CH.sub.2, O, NH or Se, and when n is 0, A is not CH.sub.2, and when n is 1, A is not CH.sub.2 or NH; X is a substituted or unsubstituted C.sub.1 -C.sub.3 alkyl, C.sub.2 -C.sub.3 alkenyl, C.sub.2 -C.sub.3 alkynyl or amino, or sulfur or oxygen; Ar is a substituted or unsubstituted monocyclic carbocycle or heterocycle, or fused or nonfused polycyclic carbocycle or heterocycle; and R.sub.1 and R.sub.2 are hydrogen or a moiety that forms together with the attached CO.sub.2 a readily hydrolyzable ester group. These compounds and their salts are useful as inhibitors of GARFT or as antiproliferative agents. The invention also pertains to pharmaceutical compositions and methods employing such compounds as GARFT inhibitors or antiproliferative agents. The invention also relates to compounds useful as intermediates for preparing such compounds, and to their synthesis.