Insight into lipase-catalyzed formation of macrocyclic oligoesters

A detailed study of a mild lipase-catalyzed route to cyclic ester oligomers based on diester and diol monomers is provided. A systematic variation of acyl donor and acceptor substrates enabled us to relate cyclization to their structural elements and elucidate the role of the immobilized Candida antarctica lipase B (Novozym 435) in this process. Moreover, its potential for optimization and as a tool for the production of cyclic oligoesters as monomers was investigated. For instance, a series of cyclic oligoesters of di-, tri-, tetra- and pentaethylene terephthalate was obtained in excellent purities (>99%) and conversions. Furthermore, 2,5- and 2,6-pyridinodicarboxylate combined with diethylene glycol yielded high amounts of cyclic oligoesters. Also cyclic oligoesters of propylene terephthalate were produced in good purity (84%) in toluene at moderate temperature (70 °C at 285 mbar). In some cases the cyclic dimer with rotational C2 symmetry was preferentially obtained.