Acknowledgment. The authors are indebted to Dr. WC Randall and his staff for elemental analyses, Mr. YC Lee for determination of pK, values, Mr. WR McGaughran for NMR and IR spectra, and Miss M. Galavage and Miss EM Babiarz for expert technical assistance with the biological assays. We thank Dr. R. Hirschmann and Dr. JM Sprague for helpful discussions and encouragement throughout the course of this investigation.
