1. Dyson Perrins Laboratory, Oxford Centre for Molecular Sciences, University of Oxford, South Parks Road, Oxford OX1 3QY, U.K., Evotec OAI, 151 Milton Park, Abingdon, OX14 4SD, U.K., and Chemical Crystallography, 9 Parks Road, University of Oxford, Oxford, OX1 3PD, U.K.