1. Contribution from the Department of Pharmaceutical Sciences, 528 Shapero Hall, Wayne State University, Detroit, Michigan 48202, Department of Chemistry, Wayne State University, Detroit, Michigan 48202, Department of Biochemistry, Parke-Davis Pharmaceutical Research, 2800 Plymouth Road, Ann Arbor, Michigan 48105, and Department of Biochemistry and Cell Biology, SUNY Stony Brook, 312 Life Sciences Building, Stony Brook, New York 11794