1. Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milano, Italy, Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, Department of Chemistry, Texas A&M University, College Station, Texas 77843, and Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-1065