Bacillus stearothermophilus acetylacetoin synthase: A new catalyst for C–C bond formation

The synthesis of α-hydroxy-1,3-diketones 2 and 3 from the corresponding 1,2-diketones with Bacillus stearothermophilus ATCC2027 acetylacetoin synthase (AAS) was described. The enzyme catalyzed the condensation of the dialkyl- or alkyl-aryl-1,2-diketones 1 with the elimination of a carboxylic acid moiety. The reactions were carried out using either one diketone both acting as donor and acceptor (homo-coupling) or with two different reacting species (cross-coupling). The homo-coupling reactions of the asymmetric dialkyl-1,2-diketones 1c–d afforded a mixture of the regioisomers 2 (30–42%, ee 67–70%) and 3 (19–25%), while only the 1,3-diketones 2a (57%), 2b (60%), and 2e (45%, ee 76%) were obtained using 2,3-butanedione 1a, 3,4-hexanedione 1b, and 1-phenyl-1,2-propanedione 1e, respectively. The cross-coupling reactions of the diketones 1a and 1b, and 1b and 1e were carried out using various ratios of the donor and the acceptor. In both cases the only cross-coupling product was 3-ethyl-3-hydroxy-2,4-hexanedione 4 (62%, ee 91%).