1. Contribution from the Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Weaver-Densford Hall, 308 Harvard Street SE, Minneapolis, Minnesota 55455-0343, Department of Pharmaceutical Chemistry, The University of Kansas, 2095 Constant Avenue, Lawrence, Kansas 66047, and GlaxoSmithKline Pharmaceuticals, P.O. Box 1539, 709 Swedeland Road, King of Prussia, Pennsylvania 19406-0939