. "23-ethyl-17,20-dioxa-4,14,23,26-tetraazahexacyclo[24.6.1.17,14.02,6.08,13.027,32]tetratriaconta-1(33),2(6),7(34),8(13),9,11,27(32),28,30-nonaene-3,5-dione" . "18b" . . . . . . . . . . .