Disclosed is a process for the preparation of formula (Ia) or a pharmaceutically acceptable salt, ester, tautomer, solvate or amide thereof, wherein reacting a compound of formula (Xa) with a compound of formula (XIa) in the presence of a peptide coupling agent, in an organic solvent or mixture of organic solvents, to yield the corresponding compound of formula (Ia). Further disclosed is a process for the preparation of formula (Ib) or a pharmaceutically acceptable salt, ester, tautomer, solvate or amide thereof, wherein reacting a compound of formula (Xb) with a compound of formula (XIb) in the presence of a peptide coupling agent, in an organic solvent or mixture of organic solvents, to yield the corresponding compound of formula (Ib).
