Novel α-amino squaric acid analogs were synthesized by initial addition reaction of a dianion enolate generated from N-Boc aminoacid tert-butyl ester to squaric acid diisopropyl ester, and subsequent decarboxylation of the resulting carboxylic acid moiety.
The synthesis of an amino acid analogue bearing a squaryl group as a carboxylic acid surrogate (sq-AA; 2) has been developed. Aminomalonate equivalent 6 was used as a nucleophilic synthon whose alkylation or conjugateaddition reaction followed by deprotection and decarboxylation reaction gave sq-AAs.