Synthesis of a Protected Cyclic Disulphide Octapeptide A6‐13 of the (Ala12)‐Sheep Insulin‐A‐Chain
The synthesis of a protected (Ala12)‐sheep insulin‐A‐chain octapeptide with a 6,11‐disulphide ring using the combination of A6,11‐S‐trityl/A 7‐S‐diphenylmethyl thiol protecting groups is described. For the formation of the cyclic disulphide octapeptide 2 the linear octapeptide, Boc‐Cys(Trt)Cys(Dpm)AlaGlyValCys(Trt)Ala‐Leu‐OH (1), is prepared by a 4 + 4‐ as well as a 3 + 2 + 3‐fragment condensation scheme followed by treatment with iodine in methanol. Most of the peptide coupling reactions were performed using the azide technique obtaining the intermediate peptide fragments in good yields. For the characterization of the cyclic disulphide peptide 2 the 13C‐n.m.r.‐spectroscopy was used in combination with other usual methods.