Electroreductive Cleavage of 2-Methylene-9,10-anthraquinone (Maq) Esters of Carboxylic Acids and N-Substituted Carbamic Acids: Protecting Groups for Carboxylic Acids and Primary Amines

Article abstract of DOI:10.1021/jo00197a021

The 2-methylene-9,10-anthraquinone (Maq) ester of γ-(benzyloxycarbonylamino)butyric acid (3a) and the Maq ester of N-(3-benzyloxycarbonylpropyl)carbamic acid (4) were synthesized as possible γ-aminobutyric acid (GABA) delivery systems.Electrochemical reduction of these Maq esters at -0.5 V (SCE) in 50percent aqueous THF buffer (pH 7.0) produced their corresponding anthrahydroquinones, which failed to give detectable cleavage products after several hours.In contrast, reduction of 3a and 4 in DMF at -0.9 V (-1.2 V) produced their radical anions (dianions), which formed theMaq cleavage products 2-methyl-9,10-anthraquinone and 2-(hydroxymethyl)-9,10-anthraquinone in combined yields of >80percent.Comparable yields of the other cleavage products, the GABA esters, were also found.This work demonstrates that electrochemical reduction can be used as an alternative method for deprotection of Maq esters of carboxylic acids used in the synthesis of peptides.In addition, the synthesis of 4 and its reductive cleavage shows that Maq esters of carbamates can serve as protecting groups of primary amines.