Biocatalytic synthesis of polyesters from sugar-based building blocks using immobilized Candida antarctica lipase B

The synthesis of linear ester oligomers (LEOs) and cyclic ester oligomers (CEOs) from non-activated succinic acid (A) in combination with di-anhydro hexitols (B, DAH) in a toluene based medium using immobilized Candida antarctica lipase B (CAL B), was studied. The conversion is highest for isomannide and decreases in the order isomannide > isosorbide ≫ isoidide. These experimental results were corroborated by substrate-imprinted docking indicating that the hydroxyl group oriented inwards the “V”-shaped plane of the DAHs (endo-hydroxyl) is preferred over the outwards oriented hydroxyl group (exo-hydroxyl) by CAL B. The maximum conversions under optimized conditions were 88.2% and 93.7% for succinic acid and isomannide, respectively. MALDI-TOF detected products at 24 h were a mixture of cyclic (35.1%) and linear ester oligomers (64.9%). Cyclic ester oliogomers were the most abundant products during the first 8 h of reaction (32.5–48.7%), where the first cyclic of the series (CEO1) was the most predominant cyclic product (23–40%).