Studies on asymmetric synthesis of bicyclomycin precursors. A chemoenzymatic route to chiral 2,5-diketopiperazines and 2-oxa-bicyclo[4.2.2]decane-8,10-diones

A novel asymmetric route to bicyclomycin analogues, 2-oxa-bicyclo[4.2.2]decane-8,10-diones, is described. The key chiral synthons 3-(ω-hydroxyalkyl)-2,5-diketopiperazines 3a-c were obtained via enzymatic kinetic resolution of their respective acetates 2a-c using hydrolases (up to >98% ee, E > 200). The chiral 2,5-diketopiperazines were then transformed into their bicyclic derivatives in a stereospecific manner. Circular dichroism and NMR studies were performed to determine the absolute and relative configuration of the obtained products. The biocatalytic approach gave high stereoselectivities in comparison to the chiral pool synthesis from glutamic acid (58% ee) and thus demonstrated the ability of hydrolases to discriminate a remote stereocenter.