The invention provides compounds of formula (I), 1 prodrugs and stereoisomers thereof, and the pharmaceutically acceptable salts of the compounds, prodrugs, and stereoisomers, wherein R.sup.1, R.sup.2, R.sup.3, HET, n, Q, X, Y, and Z are as described herein; compositions thereof; and uses thereof in treating diabetic complications including diabetic neuropathy, diabetic nephropathy, diabetic microangiopathy, and the like.