1. Department of Chemistry and Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, V6T 1Z1, Canada, Department of Chemistry, University of California, Davis, California 95616, Department of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84112, and Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0820