(32) SD Nelson, JR Mitchell, JA Timbrell, WR Snodgrass, and GB Corcoran, Science, 193, 901 (1976).(33) SS Tate, R. Sweet, FH McDowell, and A. Meister, Proc. Natl. Acad. Sci. USA, 68, 2121 (1971).(34) Sale of this material has been discontinued by its major supplier owing to its explosive proper tie^.^^ We prepared this material in small-scale quantities by the method of Carpino et