employed include those well known in the art for example urethane protecting substituents such as benzyloxycarbonyl 34 cbz 34 tert butyloxycarbonyl 34 boc 34 and the like boc is preferred for protecting the alpha amino group in the amino acids undergoing reaction at the carboxyl end of said amino acid the boc protecting group is easily removed using tfa as mentioned above or other acids such as hcl 3m in dioxane the epsilon amino group of lys can be protected by the cbz group or preferably by 2 cl cbz group the oh of tyr is protected preferably using the 2 6 cl 2 bzl group although the bzl group may be used where the tyr residue is toward the n terminal side of the desired sequence the oh group of thr and ser can be protected by the bzl group arg is protected with the nitro group glu and asp are protected as their benzyl esters his is protected as its dnp derivative cys is protected as the acm derivative these groups are relatively stable to the action of tfa used to remove the boc group at each step after the peptide sequence is formed these protecting groups except for acm and dnp can be removed by the action of hf or by hydrogenation the dnp group is removed preferably by the action of thiophenol 10 in dmf as a final resin program although this reaction may be run in solution with the.