1. Contribution from the Discovery Chemistry Research and Technologies, Lilly Research Labs, Lilly Corporate Center, Eli Lilly & Company, Indianapolis, Indiana 46285, Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, and Pharmaceutical Product Development, Lilly Research Labs, Lilly Corporate Center, Eli Lilly & Company, Indianapolis, Indiana 46285