1. Departments of Organic Chemistry and Analytical Chemistry, Universidad Complutense de Madrid, E-28040 Madrid, Spain, Biocompatibles Ltd., Farnham Business Park, Weydon Lane, Farnham, Surrey GU9 8QL, U.K., and Institute for Bioprocessing and Analytical Measurement Techniques, Rosenhof, D-37308 Heiligenstadt, Germany