Synthesis of 2-Keto-d- and l-gluconic Acid via Stereoselective Direct Aldol Reactions

Enantioselective Hydroboration of Ketones Catalyzed by Rare-Earth Metal Complexes Containing Trost Ligands

Four chiral dinuclear rare-earth metal complexes [REL¹]₂ (RE = Y(1), Eu(2), Nd(3), La (4)) stabilized by Trost proligand H₃L¹ (H₃L¹ = (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-methylphenol) were first prepared, and all were characterized by X-ray diffraction. Complex 4 was employed as the catalyst for enantioselective hydroboration reaction of substituted ketones, and the corresponding secondary alcohols with excellent yields and high ee values were obtained using reductant HBpin. The same result was also achieved using the combination of lanthanium amides La[N(SiMe₃)₂]₃ with Trost proligand H₃L¹ in a 1:1 molar ratio. The experimental findings and DFT calculation revealed the possible mechanism of the enantioselective hydroboration reaction and defined the origin of the enantioselectivity in the current system.

Production of 2-keto-gluconic acid from glucose by immobilized Pseudomonas plecoglossicida resting cells

2-Keto-d-gluconic acid (2KGA) is an important organic acid derived from d-glucose and is used to produce the food antioxidant erythorbic acid. To improve the 2KGA production performance and cell reusability, various carriers such as calcium alginate, k-carrageenan, chitosan, and poly(vinyl alcohol)-alginate were evaluated to immobilize Pseudomonas plecoglossicida JUIM01 resting cells. Calcium alginate was shown to be a suitable carrier since the immobilized cells had the highest number of reuse times and produced the highest 2KGA concentration of 171.77 g/L, with a productivity of 3.58 g/L·h and conversion ratio of 98.38%. The cell concentration, cultivation temperature, aeration rate and initial glucose concentration were further optimized in a 5-L airlift bioreactor to obtain the best 2KGA production performance by calcium alginate-immobilized P. plecoglossicida cells. Under the optimal conditions including a cell concentration of 4.0 g/L, glucose concentration of 126.0 g/L, temperature of 34 °C and aeration rate of 2.8 L/min, 134.45 g/L 2KGA was produced by alginate-immobilized P. plecoglossicida cells within 30 h, with a total productivity of 4.48 g/L·h and yield of 1.07 g/g (conversion ratio of over 99.0%). The immobilized cells maintained a stable conversion capacity after nine reuses and 25 days of storage at 4 °C, which indicated that calcium alginate immobilization of P. plecoglossicida cells had industrial practicability for 2KGA production.

Total synthesis of pipecolic acid and 1-C-alkyl 1,5-iminopentitol derivatives by way of stereoselective aldol reactions from (S)-isoserinal

A short synthesis of iminosugars and pipecolic acid derivatives has been realized through aldol addition of a pyruvate, a range of ketones and (S)-isoserinal, followed by catalytic reductive intramolecular amination. The stereoselective aldol reaction was achieved successfully by using tertiary amines or di-zinc aldol catalysts, thus constituting two parallel routes to optically pure products with good yields and high diastereoselectivities. These carbohydrate analogues may be the inhibitors of potent glycosidases and glycosyltransferases.