Synthesis of Optically Active α-Hydroxy Acids by Kinetic Resolution Through Lipase-Catalyzed Enantioselective Acetylation

Abstract

The lipase‐catalyzed acetylation of a broad spectrum of racemic 2‐hydroxy acids 1 to their 2‐acetoxy acids 2 was shown to proceed with high enantioselectivity. Thus, the microbial lipases, in particular from Candidaantarctica and Burkholderiaspecies, are convenient biocatalysts for the synthesis of optically active 2‐hydroxy acids in excellent enantioselectivity (ee values up to > 99%). The absolute configurations of the 2‐hydroxy acids 1 were assigned by comparison of the gas‐chromatographic data with that of literature‐known reference compounds, or by means of the exciton‐coupled circular dichroism method (ECCD) on their bichromophoric 2‐naphthoate 9‐anthrylmethyl derivatives 3. These results establish that (S)‐2‐hydroxy acids 1 were preferentially acetylated by microbial lipases.

Bridging racemic lactate esters with stereoselective polylactic acid using commercial lipase catalysis

“…R′ = Et as in the case of MHBA (compare entries 1a and 2a). This observation is in agreement with the established empirical rule, which suggests that the size of the substituents is crucial for the enantioselectivity of CRL: 78,79,86,87,[94][95][96][97][98] a larger size difference between R′ and OH results in a higher enantioselectivity due to a larger difference in free energy between the transition states of the two enantiomers.…”

“…The screening was carried out under dilute conditions in analogy with reported procedures. 55,78,[81][82][83] Under the mild aqueous conditions, only LA and methanol were analyzed as products. The reactions were buffered and performed at room temperature to avoid non-stereoselective background hydrolysis.…”

“…[69][70][71][72] Frequently applied in organic synthesis, lipases have been demonstrated to be particularly valuable in kinetic resolution of alcohols, carboxylic acids, esters, and amines 56,57,[73][74][75][76][77] but examples on resolution of α-hydroxy esters are very rare. 78,79 Experimental Reactions were carried out in 10 mL thick glass walled crimp cap vials. In a typical experiment a known amount of ester (Sigma-Aldrich or derived from lactide) (e.g.…”

High pressure study of a highly energetic nitrogen-rich carbon nitride, cyanuric triazide

“…2. The full pattern refinement yielded lattice parameter values close to those published in the literature 15 (Table I). Table I.…”

“…CTA presents a high level of nitrogen content at 82% per atomic weight. First-principles theory simulations predict two high pressure phase transitions for cyanuric triazide 14 starting from the room condition phase, a hexagonal (P3) structure 15 (Figs. 1(a) and 1(b)).…”