Compounds, pharmaceutically acceptable salts, and compositions thereof of the general formula: wherein Ar is aryl and heteroaryl; R1, R2, R3, and R4 are hydrido, alkyl, cyano, heteroaryl, hydroxy, amino, acylamino, halo, alkoxy, aryloxy, carboxyamido, alkenyl, cycloalkyl, heterocyclyl, acyl, acyloxy, carboalkoxy, carboxy, thio, sulfinyl, sulfonyl and sulfoxy, R5, R6, R7, and R8 are hydrido and lower alkyl; and Het is a nitrogen-containing heterocyclic ring.