Compounds of formula 1: wherein R1 is alkyl, cycloalkyl, aryl, aralkyl, heteroaryl, or heteroaralkyl, substituted with 0–3 substituents selected from lower alkyl, halo, hydroxy, lower alkoxy, amino, lower alkyl-amino, and nitro; R2 is hydroxy, amino, or lower alkoxy; R3 is H, lower alkyl, lower acyl, lower alkoxy-acyl, or amino-acyl; R4 is H or lower alkyl; and pharmaceutically acceptable salts and esters thereof; are effective inhibitors of GSK3.