Extended chain derivatives of somatostatin

Claim 1

A process for preparing a peptide of formula I ##STR139## in which R 1 is hydrogen, H-Gly or H-Leu and R 2 is hydrogen or carboxyl, which comprises: oxidizing a linear peptide of formula ##STR140## in which R 3 is Boc, Boc-Gly or Boc-Leu and R 2 is hydrogen or carboxyl with iodine or thiocyanogen to obtain the corresponding cyclic disulfide derivative of formula ##STR141## in which R 2 and R 3 are as defined herein and subsequently removing all remaining protecting groups under moderately acidic conditions to obtain the corresponding peptide of formula I; or followed by subjecting said linear peptide to treatment with either mercuric acetate, mercuric chloride, silver acetate or silver nitrate to remove selectively the sulfhydryl protecting groups to obtain the mercuric or disilver salt, respectively, of the corresponding disulfhydryl derivative; converting the latter salt to its corresponding free disulfhydryl derivative by treatment with hydrogen sulfide, oxidizing said last-named disulfhydryl derivative by treatment with oxygen, 1,2-diiodoethane, sodium or potassium ferricyanide or iodine to obtain the corresponding cyclic disulfide derivative and removing the remaining protecting groups under moderately acidic conditions and isolating the desired peptide of formula I.