l proline t butyl ester 0 5 g was mixed with 4 5 ml of 5 5 n methanolic ammonia at room temperature under nitrogen for one hour to remove the acetyl group the solvent was then removed at 25 u00b0 c with a rotary evaporator after the product was taken up in methanol and reevaporated twice more in the rotary evaporator the clear oily residue was dissolved in ethyl ether washed twice with 5 potassium bisulphate and once with saturated nacl dried over mgso 4 and filtered residual solvent was removed in vacuo to yield a clear oily product migrating as a single spot on thin layer chromatography in three separate solvent systems the t butyl ester protecting group was removed by reaction with trifluoroacetic acid in anisole by substituting 2 acetylthiopropanoic acid 3 acetylthio 2 d methylpropanoic acid or 3 acetylthio 2 d l methylpropanoic acid for the 3 acetylthiopropanoic acid in example 2 and substantially following the procedures of examples 2 and 3 the following compounds are obtained by removing the t butyl ester protecting group with trifluoroacetic acid in anisole as a first step the dicyclohexylamine salt can be formed to assist in the resolution of isomers the acetyl protecting group can be removed in a second step using methanolic ammonia as described in example 3 l 3 4 dehydroproline u03b4 3.