Biodegradable polyesters derived from amino acids

New optically active polyesters derived from amino acids by replacement of the backbone amino groups for hydroxyl residues are presented. The polyesters described are the following: poly (L)HO Asp(COOH)-OH, poly(L)HOGlu(COOH)-OH, poly(L)HOSer(OH)-OH, poly(L)HOThr(OH)-OH, poly(L)HOLys(OH)-OH, and poly(HOAa(X)(OH)-co-LA) and some other copolymers of a-hydroxy acids. The polymers were prepared via (a) direct condensation in bulk employing several catalysts as PTSA, boric acid, Mukaiyama's reagent, stannous chloride dihydrate, (b) acyl halide activation, and (c) microwaveassisted polymerization. The obtained polymers reached a molecular weight between 1000 and 4000. The highest molecular weight attained employing polycondensation methods in solution, was either by utilizing polyacid, or metal catalyst (boric acid and stannous chloride respectively). Applying oxalyl chloride for chain extension also showed to be an efficient method. On the other hand, the microwave-assisted polymerization exhibited significant advantages and polymerization could be implemented with lack of solvent (neat). The polymers were characterized by several methods (GPC, CD, DSC, solubility), and tested for their degradability and biocompatibility to cell growth. Most of the polymers displayed a linear correlation between their calculated log P values and their experimental contact angles parameters. Transition glass temperatures (T_g) of copolymers with various compositions of LA were correlated to either Gordon Taylor equation or to a three parameters modified Kwei equation. The circular dichroism spectra (CD) of several homo and copolymers were measured. In general, CD curves of the homopolymers of HOSer, HOGlu, HOThr, HO Asp, and HOLys(OH) revealed a significant ester maxima approximately at 205-220 nm while the copolymers of HOSer with HOPhe displayed an additional cotton effect band at 200.6-201.5 nm. This is accounted for polymer rotational isomers and not to a different ππ* transition at lower wavelength.