1. Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford U.K., OX1 3TA, Drexel Institute for Biotechnology & Virology Research, Drexel University, College of Medicine, 700 East Butler Avenue, Doylestown, Pennsylvania 18901, and Oxford Glycosciences Ltd, The Forum, 86 Milton Park, Abingdon, Oxfordshire U.K., OX14 4RY