1. Contribution from the Laboratory of Tumor Vaccinology, Clinical Immunology Service, Department of Medicine, the Laboratory for Bioorganic Chemistry, and the Organic Synthesis Core Laboratory, Sloan-Kettering Institute for Cancer Research, 1275 York Avenue, New York, New York 10021, and Department of Chemistry, Columbia University, Havemeyer Hall, 3000 Broadway, New York, New York 10027