1. Department of Chemistry, Pomona College, Claremont, California 91711, Departments of Chemistry and Pharmacy, Birla Institute of Technology and Science, Pilani 333031, India, Pharmacia & Upjohn, 301 Henrietta Street, Kalamazoo, Michigan 49007, and Biochemical Virology Laboratory, Lindsley F. Kimball Research Institute of The New York Blood Center, 310 E. 67th Street, New York, New York 10021