A new diacid monomer 9 was synthesized in five steps. Starting from the reaction of L-leucine with phthalic anhydride in acetic acid provided (2S)-4-methyl-2-phthalimidylpentanoic acid (3) in good yield. The compound 3 was converted to (2S)-4-methyl-2-phthalimidylpentanoyl chloride (4) by reaction with thionyl chloride. The resulting acid chloride 4 was reacted with p-aminobenzoic acid (5) in dry tetrahydrofuran and (2S)-4-(4-methyl-2-phthalimidylpentanoyl-amino)benzoic acid (6) was obtained. Then, it was converted to (2S)-4-(4-methyl-2-phthalimidylpentanoylamino)benzoyl chloride (7) by treatment with thionyl chloride. The reaction of acid chloride 7 with 5-aminoisophthalic acid in dry N,N-dimethylacetamide (DMAc) gave (2S)-4-[(4-methyl-2-phthalimidylpentanoylamino)-benzoylamino]isophthalic acid (9) in high yield. The step-growth polymerization of this diacid with several aromatic diols, such as bisphenol-A (10a), phenolphthalein (10b), 1,5-naphthalenediol (10c), hydroquinone (10d), bisphenyl-2,2'-diol (10e), 4,4'-dihydroxydiphenyl sulfone (10f), 4,4'-dihydroxydiphenyl sulfide (10g), and 1,8-dihydroxyanthraquinone (10h), was carried out in a system of tosyl chloride, pyridine, and N,N-dimethylformamide (DMF) to give a series of new optically active polyesters (PE)s with good yield and moderate inherent viscosity ranging from 0.29 to 0.43 dL/g. All of the aforementioned polymers were fully characterized by FTIR and specific rotation. Some structural characterization was performed by H-1 NMR and elemental analysis. These polymers are readily soluble in amide-type solvents such as DMF, DMAc, dimethyl sulfoxide, and protic solvents such as sulfuric acid. Thermal gravimetry analysis showed that the 10% weight loss temperature in a nitrogen atmosphere was more than 360 degrees C, which indicates that the resulting PEs have a good thermal stability as well as excellent solubility. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2942-2949, 2008