A first aspect of the invention relates to a polypeptide compound of formula (I): A-C-B   (I) wherein: A is the A chain of insulin or a functional derivative or variant thereof; B is the B chain of insulin or a functional derivative or variant thereof; C is a peptide of the formula: (X1)p—(X2)n—(X3)q wherein: each X1 and X3 is independently a basic amino acid; each X2 is independently a natural or unnatural amino acid; p is 1 or 2; q is 0, 1 or 2; n is 0, 1, 2 or 3. Further aspects of the invention relate to pharmaceutical compositions comprising said polypeptide compound, and therapeutic uses thereof. Another aspect relates to the use of said polypeptide compounds in the preparation of insulin and derivatives thereof.