1. Department of Medicinal Chemistry, Isis Pharmaceuticals, 2280 Faraday Avenue, Carlsbad, California 92008, Department of Biological Chemistry, Merck Research Laboratories, P.O Box 4, West Point, Pennslyvania 19486, and Department of Medicinal Chemistry, Merck Research Laboratories, P.O. Box 2000, Rahway, New Jersey 07065