A process for preparing insulin compounds

A process for preparing insulin compounds and its analogs or derivatives from their corresponding precursors of insulin, which are represented by the formula: ** ** Formula wherein R is hydrogen or a cleavable amino acid chemistry or enzymatically or peptide cleavable chemically or enzymatically comprising at least two amino acid residues, R1 is OH or an amino acid residue, or Y1-Y2 in which Y is an amino acid residue, residues A1 to A21 correspond to the a chain of insulin and the residues B1-B27 correspond to the B chain of insulin, including substitution, deletion and / or additions thereof, R2 is Z1-Z2 wherein Z1 is selected from Pro, Lys, Asp and Z2 is selected from Lys or Pro or Glu or Z1-Z2-Z3 wherein Z1 is selected from Pro, Lys, Asp and Z2 is selected from Lys or Pro or Glu and Z3 is threonine or a peptide moiety of at least three amino acid residues, with the proviso that the amino acid corresponding to B30 is threonine, and X is a polypeptide that connects the A chain to the B chain and cleavable enzymatically without affecting either the A chain or the B chain, having at least two amino acids in the the first and last amino acid are lysine or arginine, such precursors are defined by an amino acid sequence that is at least 85% homologous to the amino acid sequences set forth in SEQ ID NO 1, 2, 3, 4, 5, 6, 7, 8 and 9, which comprises treating said precursor with trypsin and carboxypeptidase used in combination and concurrently, wherein the reaction is carried out in a pH range of 8 to 9, and wherein the ratio of the relative concentration of trypsin relative to carboxypeptidase is from 5: 1 to 50: 1 and the relative amount of trypsin to that of the insulin precursor is from 1:10 to 1: 100.