Insulinotropic peptide synthesis using solid and solution phase combination techniques

The present invention relates to the preparation of insulinotropic peptides that are synthesized using a solid and solution phase ("hybrid") approach. Generally, the approach includes synthesizing three different peptide intermediate fragments using solid phase chemistry. Solution phase chemistry is then used to add additional amino acid material to the third fragment which is then coupled to the second fragment and then the first fragment in solution. Alternatively, a different second fragment is coupled to the first fragment in the solid phase. Then, solution phase chemistry is then used to add additional amino acid material to a different third fragment. Subsequently, this different third fragment is coupled to the coupled first and different second fragment in the solution phase. The use of a pseudoproline in one of the fragments eases solid phase synthesis of that fragment and also eases subsequent solution phase coupling of this fragment to the other fragments. The present invention is very useful for forming insulinotropic peptides such as GLP-1(7-36) and its natural and non-natural counterparts.