Synthesis of Amino-Acid Conjugates of 18β-Glycyrrhetic Acid Methyl Ester 3-O-Hemisuccinate

Hybrid molecules based on 18β-glycyrrhetic acid (GLA), i.e., conjugates of GLA methyl ester 3-O-hemisuccinate with methyl/ethyl esters of L-amino acids (isoleucine, leucine, phenylalanine), were synthesized in 50–55% yields using N-hydroxysuccinimide–N,N′-dicyclohexylcarbodiimide. The conjugate with L-leucine methyl ester (5) showed pronounced antiviral activity against human adenovirus type 5.