1. Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0343, Department of Anesthesiology, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0818, Clinical Research Institute of Montreal, 110 Pine Avenue West, Montreal, Quebec, H2W 1R7, Canada, and Adolor Corporation, 371 Phoenixville Pike, Malvern, Pennsylvania 19355