Synthesis and structural characterization of novel biologically active and thermally stable poly(ester-imide)s containing different natural amino acids linkages

Starting from the natural α-amino-acid L-tyrosine, a potentially bioactive diphenolic molecule, N,N′-(pyromellitoyl)-bis-L-tyrosine dimethyl ester (8), was prepared in three steps using protecting groups to block the NH₂ and COOH of tyrosine. A facile and rapid polycondensation reaction of diol 8 with several optically active diacid chlorides such as N,N′-(pyromellitoyl)-bis-(L-α-amino) diacid chlorides derived from L-phenyalanine, L-leucine, L-methionine, L-valine and L-alanin was developed under microwave irradiation. The polymerization reactions proceeded rapidly and was completed within 12 min, producing a series of novel poly(ester-imide)s (PEI)s in good yields and moderate inherent viscosities of 0.41–0.51 dL/g. The obtained polymers were characterized by means of FT-IR, ¹H-NMR, elemental and thermogravimetric analysis techniques. In addition, in vitro toxicity test and biodegradability behavior of the diphenolic 8 and obtained PEIs were investigated in culture media and soil burial degradation. The outcome showed that synthesized diol 8 and its derived polymers are biologically active and biodegradable under natural environment.