1. Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.
2. The Department of Life Sciences (DLS), Aberystwyth University, Wales SY23 3DA, U.K.
3. GlaxoSmithKline R&D, Stevenage, Hertfordshire SG1 2NY, U.K.
4. Department of Chemistry & Biochemistry, University of California Los Angeles, 607 Charles E. Young Drive East, P.O. Box 951569, Los Angeles, California 90095-1569, United States