Chemoenzymatic Total Synthesis of the Proposed Structures of Putaminoxins B and D

Different enzymatic and nonenzymatic approaches were tested and compared to afford enantiopure homoallylic and allylic alcohols as building blocks in a total synthesis showcase. Thereby, highly enantioselective alcohol dehydrogenases and the P450 BM3 monooxygenase variant A74G L188Q were compared to classical asymmetric reagent-controlled allyl additions. Thus, the first total syntheses of the proposed structures for putaminoxins B/D and their respective enantiomers were accomplished. Detailed spectroscopic analysis of the newly synthesized compounds unraveled a discrepancy with respect to the reported structures of putaminoxins B/D. Furthermore, it was demonstrated that total synthesis is generally required for unequivocal assignment of configuration, because purely comparative NMR studies and judgment by analogy can lead to false predictions.