Efficient and practical protection of the catechol residue of 3,4-dihydroxyphenylalanine (DOPA) derivative as acetonide

The acetonide formation of 3,4-dihydroxyphenylalanine (DOPA) derivative was realized under efficient and practical reaction conditions: the reaction of the methyl ester of DOPA in acetone-i-PrOH in the presence of 5 mol% of TsOH afforded the catechol side chain protected DOPA as an acetonide in quantitative yield; the workup procedure is a simple evaporation of the solvents. This methodology allows an access to the reaction in large scale.