Synthesis of human pancreatic growth hormone-releasing factor and two omission analogs by segment-coupling method in aqueous solution

Polypeptide synthesis by the thioester method

A novel method for polypeptide synthesis, in which partially protected peptide thioesters are used as building blocks, has been developed. Partially protected peptide thioesters are easily prepared by solid-phase methodology. The thioester moiety is converted to an active ester in the presence of a silver compound such as AgNO(3) or AgCl and an active ester component such as 1-hydroxybenzotriazole or 3,4-dihydro-3-hydro-4-oxo-1,2, 3-benzotriazine. Segment condensation can be accomplished using partially protected peptide segments. The consecutive condensation of the partially protected peptide segments is realized by the selective removal of the 9-flourenylmethoxycarbonyl group, for terminal amino protection, after segment condensation has been achieved. In this method, large peptide segments can easily be used. Thus, the products obtained by the thioester method can be separated from by-products by reverse phase high performance liquid chromatography, even when no purification process was performed during the prior segment condensation procedures. This indicates that proteins that have no specific features such as enzymatic or biological activities can be obtained after isolation, solely based on their chromatographic profiles. Thus, the thioester method will provide a new basis for protein studies including phosphorylated and glycosylated polypeptides.

Total synthesis of S-carbamoylmethyl bovine apocytochrome c by segment coupling

Three peptide segments corresponding to the complete sequence of the 104 amino acid protein bovine apocytochrome c were synthesized by the solid-phase method. The peptides Ac-[Cys(Cam)14,17, GlyS23]-apocytochrome c-(1-23) (I), CF3CO-[GlyS60]-apocytochrome c-(24-60) (II), and CF3CO-apocytochrome c-(61-104) (III) were purified by chromatography on CM-cellulose, partition chromatography and/or HPLC. Each of the peptides was reacted with citraconic anhydride to block all of the lysine side chains, and the 61-104 peptide was treated with 10% hydrazine to remove the trifluoroacetyl group, to give the corresponding peptides Ia, IIa, and IIIa. Peptides IIa and IIIa were coupled together by reaction with silver nitrate/N-hydroxysuccinimide to give the 24-104 sequence. After removal of the trifluoroacetyl group from the amino terminus, peptide Ia was also coupled. Treatment of the peptide mixture with aqueous acetic acid removed the citraconyl groups, and purification by chromatography on CM-cellulose and HPLC gave a 0.6% yield of [Cys(Cam)14,17]-apocytochrome c. The synthetic product was shown to be identical to a sample derived from native bovine cytochrome c by paper or gel electrophoresis, HPLC and by chymotryptic or tryptic map.