sub 5 c sub 2 str154 str155 str156 h 34 h sub 3 c str157 h sub 3 c str158 h 35 h sub 3 c str159 str160 str161 h 36 h sub 3 c str162 h sub 3 c str163 h 37 str164 str165 h sub 3 c str166 h 38 str167 str168 h sub 3 c str169 h 39 str170 str171 h str172 h sub 3 c 40 str173 str174 h sub 3 c str175 h 41 str176 str177 h str178 h sub 3 c 42 str179 str180 h sub 3 c str181 h the r 1 protecting groups in examples 20 to 26 the r 3 protecting group in example 29 and r 5 protecting group in example 35 are removed as the last step in the synthesis the 4 azidoproline of example 30 when treated with the reducing agent will yield a 4 aminoproline product the r 6 ester groups shown in examples 37 to 42 are not removed 1 n 3s 3 benzoylamino 2 4 methoxyphenyl methyl thio 4 phenylbutyl l alanyl l proline isomer a is treated with the reagent listed below in col i to give the product shown in col ii str182 deprotection by treatment with mercuric trifluoroacetate yields the desired final product __________________________________________________________________________examplecol i r sub.