Department of Pharmaceutical Chemistry, University of California, San Francisco, USA. scooter@cgl.ucsf.edu|Department of Pharmaceutical Chemistry, University of California, San Francisco, USA. scooter@cgl.ucsf.edu|Department of Pharmaceutical Chemistry, University of California, San Francisco, USA. scooter@cgl.ucsf.edu|Department of Pharmaceutical Chemistry, University of California, San Francisco, USA. scooter@cgl.ucsf.edu