diluted with ethyl acetate and washed with water twice 1n hydrochloric acid twice 1n sodium hydroxide twice and brine dried over anhydrous magnesium sulfate and concentrated to a yellow solid the solid was chromatographed flash silica gel lps 1 benzene ethyl acetate 92 8 to yield the title compound as a colorless solid 460 mg 0 78 mmol tlc r f 0 25 isomer b r f 0 31 isomer a silica gel benzene ethyl acetate 9 1 a solution of n 3s 1 1 dimethylethoxy carbonyl amino 2 4 methoxyphenyl methyl thio 1 oxo 4 phenylbutyl l leucine 1 1 dimethylethyl ester 638 mg 1 06 mmol trifluoroacetic acid 14 ml and anisole 1 0 ml was stirred under argon for 1 hour the solution was cooled to 0 u00b0 c and treated with mercuric trifluoroacetate 498 mg 1 1 eq and stirring continued at 0 u00b0 c for 1 hour the reaction was then concentrated to red oil diluted with ether 10 ml and hexane was added to form a colorless precipitate the solid was triturated in the ether hexane solution collected by filtration washed with hexane and dried under argon to yield a colorless solid the solid was taken into 80 aqueous acetic acid 25 ml and hydrogen sulfide was bubbled through the solution for 30 minutes the black reaction mixture was filtered through a pad of celite followed by a millipore filter teflon the filtrate was concentrated and the colorless residue diluted with degassed double distilled water 20 ml and 1n hydrochloric acid 1 5 ml 1 5 eq the mixture was filtered millipore metricel and the clear colorless filtrate was lyophilized twice to yield the.