Synthesis of prostate specific membrane antigen (PSMA) ligands

A method for synthesizing a compound of formula (I), or a pharmaceutically acceptable salt thereof, using solid phase synthesis:

• wherein said method comprises all of the following steps:
• a) contacting a supported compound of formula (II)
• with a compound of formula (III)
• to provide a supported compound of formula (IV)
• b) contacting the supported compound of formula (IV) with a deprotecting agent to provide a supported compound of formula (V)
• c) contacting the supported compound of formula (V) with a compound of formula (VI)
• to provide a supported compound of formula (VII)
• d) contacting the supported compound of formula (VII) with a deprotecting agent to provide a supported compound of formula (VIII)
• e) contacting the supported compound of formula (VIII) with a compound (IX)
• to provide a supported compound of formula (X)
• f) contacting the supported compound of formula (X) with a cleavage reagent, and optionally with a deprotecting agent, to provide the compound of formula (I), or a pharmaceutically acceptable salt thereof;
• wherein
• PG, PG1, PG4, PG5 and PG6 are each independently a carboxyl protecting group;
• L is a linker;
• PG2 and PG3 are each independently an amino protecting group;
• R1 and R2 are each independently H, an activating ester group, and
• LG is a leaving group selected from the group consisting of imidazole, halogens and activating ester groups.