Chemistry of Renieramycins. Part 2. Partial Reduction and Nucleophilic Substitution of Hexahydro-1,5-imino-4-oxo-3-benzazocine-7,10-dione: Promising Method to Construct Renieramycin J from Renieramycin G via Renieramycin E

The conversion of 1,2,3,4,5,6,7,10-octahydro-9-methoxy-3,8,11trimethyl-1,5-imino-3-benzazocine-4,7,10-trione (8) to the corresponding alkylated compound at C-21 position (11) as an ABC ring model of renieramycin J (1j) is described.This is a promising method for converting renieramycin G (1g) into 1j via renieramycin E (1e).As part of our search for new metabolites via the isolation and characterization of biologically active compounds from Thai marine animals, we recently reported the isolation and structural elucidation of renieramycins J-L (1j-l) from a Thai sponge, Xestospongia sp., in the vicinity of Sichang Island. 2 It is interesting to note that these natural products have an acetone residue at C-21.One possible pathway to generate these compounds is shown in Scheme I which involves partial reduction of type I compound (such as renieramycin G (1g) 3 ) to give type II compound (such as renieramycin E (1e) 4 ), into which an acetone nucleophile can be substituted at the C-21 position 5 stereoselectively to give type IV compound (such as renieramycin J (1j)) via type III compound.We report here the preparation of the ABC ring model ( 11) from readily available lactam (8) via α-amino nitrile (10a).