1. Department of Medicinal Chemistry, Victorian College of Pharmacy, Monash University, 381 Royal Parade, Parkville, Victoria 3052, Australia, Department of Molecular Pharmacology, Neurobiology Unit, Roche Bioscience, 3401 Hillview Avenue, R2-101, Palo Alto, California 94304, Department of Medicinal Chemistry and Systems Pharmacology Unit, GlaxoWellcome Research Group, Gunnels Road, Stevenage, Hertfordshire SG1 2NY, U.K., and Tripos Inc., 1699 South Hanley Road, St. Louis, Missouri 63144