Enzymatic process for the resolution of enantiomeric mixtures of beta-lactams

#The present invention relates to enzymatic processes for the resolution of enantiomeric mixtures of β-lactams useful in the preparation of taxanes.

#The taxane family of terpenes, of which taxol and docetaxel are members, has attracted considerable interest in both the biological and chemical arts. Such taxanes may be prepared through a variety of semi-synthetic routes. In one, a β-lactam is coupled to a derivative of 10-deacetylbaccatin III to form a sidechain at the C-13 position of the derivative. As the stereochemistry of these taxanes may affect their pharmaceutical activity, methods allowing efficient stereospecific preparation of the intermediate β-lactam, as well as the final taxane products, have been the subject of investigation.

#Brieva et al. (Brieva, R.; Crich, J. Z. and Sih, C. J., J. Org. Chem. 1993,58, 1068) reported that racemic β-lactam underwent selective kinetic hydrolysis with several Pseudomonas lipases and two penicillinases. Pseudomonas lipases used by Brieva et al. include P-30, AK and K-10.

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#To a 4-L Erlenmeyer flask equipped with a mechanical stirrer was added a solution of 62 g (0.205 mol) of recrystallized racemic β-lactam in 1.0 L of toluene. The solid was completely dissolved by warming with a 40° C. water bath and then cooling to ambient temperature. To a 1-L graduated cylinder was added 87.1 g (0.5 mol) of K2HPO4, and 4.9 g (0.036 mol) of KH2PO4 diluted to the 1000 mL mark with RO water and mixed to dissolve completely. A beef liver suspension was prepared by adding 20 g of frozen beef liver (Premium Select Brand, Nebraskaland, Inc., New York) to a blender and then adding the pH 8 buffer to make a total volume of 1 L. The mixture was blended to make a homogeneous suspension which was then added directly to the toluene solution. The mixture was stirred for 22 h at ambient temperature. The layers were separated and the aqueous layer was extracted with 1 L of ethyl acetate. The organic layers were combined and concentrated to give 67 g of white powder. The powder was recrystallized from 600 mL of hot absolute ethanol to give 23.4 g (0.078 mol, 38%) of optically pure β-lactam (+)-m.p. 153-155° C.; [a]20589=+38.1° (MeOH, c=0.7).

#As noted previously, others have reported successful application of pig liver acetone powder (PLAP), bovine liver acetone powder (BLAP) and chicken liver acetone powder (CLAP), in the resolution of numerous chiral secondary alcohols. The application of a BLAP biphasic enzymatic resolution procedure to (±)-1a resulted in 37% yield of the hydroxy β-lactam (−)-2a and a 33% yield of the acetoxy β-lactam (−)-1a after 3 h at room temperature (Scheme 1). 3