Patent ID: 8921566

Claim:
A process for the preparation of a compound of formula (3): or a salt thereof, comprising the step of: a) reacting a lactone of formula (4): with a sulfonating agent to form a compound of formula (5): or a salt thereof; b) reacting the compound of formula (5) or a salt thereof with a sulfur-bearing nucleophile, optionally followed by deprotection, to form a compound of formula (6): or a salt thereof; c) reacting the compound of formula (6) or a salt thereof with a disulfide compound to form the compound of formula (3), wherein: Q′ is a linear, branched or cyclic alkyl having 1 to 10 carbon atoms, phenyl, ortho or para-nitrophenyl, dinitrophenyl, pyridyl or nitropyridyl; and R a , R b , R c , R d and R e , each independently, is H or a linear, branched or cyclic alkyl having 1 to 10 carbon atoms.