S)-N-Boc-3-hydroxypiperidine (S-NBHP) is a useful synthon for the synthesis of pharmaceutical intermediates including ibrutinib, the API of the newly approved drug Imbruvica, for the treatment of lymphoma. To our knowledge, there are no published biotransformation methods scalable to prepare S-NBHP. We report here the development of an efficient process catalyzed by recombinant ketoreductase (KRED) to reduce N-Boc-piperidin-3-one to obtain optically pure S-NBHP. The process has been optimized and demonstrated to have commercial potential with 100 g/L of substrate concentration, product of >99% ee with under 5% of enzyme loading (w/w). ■ INTRODUCTIONA large number of natural and unnatural bioactive molecules have one or more piperidine rings. 1 There are many active pharmaceutical ingredients (API) which also contain this moiety. 2 The hydroxyl group on the C3-position would introduce a chiral carbon atom and may significantly affect the bioactivity of the molecule. 3 As a result, chiral hydroxypiperidines and their derivatives are important synthons used in the pharmaceutical industry.Several methods have been reported for the synthesis of chiral piperidines including classic diastereomeric resolution, 4 asymmetric synthesis, 5 and asymmetric reduction, for example, of 4-oxo-piperidine-3-carboxylic acid esters followed by multistep conversions (Scheme 1). 6 All these methods suffered from low yields or lengthy synthesis. Lacheretz et al. reported the bioreduction of cyclic 3-oxo-amines using the tissue of Daucus carota, where six piperidin-3-one derivatives could be reduced to S-alcohols with varying enantioselectivity. 7 Among the substrates, the reduction of N-Boc-piperidin-3-one showed the highest enantioselectivity, giving (S)-N-Boc-3-hydroxypiperidine (S-NBHP) with 95% optical purity. Unfortunately the reaction is not practical due to low substrate concentration (3 mM), high catalyst concentration (23%, m/v), moderate chiral purity (95% ee) and low yield (73%).Ketoreductase (KRED)-mediated biotransformation has been applied more and more widely in pharmaceutical industry nowadays. 8 In general, there are two strategies to locate a KRED for practical application. On the one hand, the discovery of new natural KRED biocatalysts using activity screening and genome mining continues to enlarge the substrate spectrum. 9 On the other hand, enzyme engineering technologies including directed evolution and semirational and rational design can engineer KREDs with high efficiency and stability. 10 Directed evolution and rational design as the most important technique of protein engineering have emerged to be powerful tools for manipulating protein properties with numerous successful stories. 11 The availability of highly diversified KRED libraries makes it increasingly possible to discover biocatalysts to meet the metrics of industrial processes. Here we report such a work to screen and apply recombinant KREDs to catalyze the asymmetric preparation of S-NBHP on an industrial scale. ■ RESULTS AND DISCUSSIONThe target enz...

Temsirolimus is an intravenous drug for the treatment of renal cell carcinoma that can be prepared using enol acyl donors, which is not favorable in process development. An improved enzymatic process to prepare temsirolimus has been developed employing lipase‐catalyzed regioselective acylation of rapamycin with environmentally friendly acyl donors. After screening of common commercial lipases and none‐enol acyl donors, it was found that p‐nitrophenyl 2,2,5‐trimethyl‐1,3‐dioxane‐5‐carboxylate reacted as efficient acyl donor when catalyzed by immobilized Thermomyces lanuginose lipase. By optimizing the process conditions (i.e., reaction temperature, solvents, and additives), the reaction time was significantly shortened while the reaction conversion reached 95.4% in methyl tert‐butyl ether after 48 h at 50°C using the new acyl donors. This work demonstrated a cost‐effective, efficient, and scalable process to synthesize temsirolimus.