1. Department of Chemistry, University of Puerto Rico, P.O. Box 23346, Río Piedras, Puerto Rico 00931, Departments of Pharmacology and Otolaryngology, School of Medicine, University of Puerto Rico, P.O. Box 365067, San Juan, Puerto Rico 00936-5067, and Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842