Kinetic Resolution Of Primary Alcohols Research Articles

Dynamic Kinetic Resolution of Primary Alcohols with an Unfunctionalized Stereogenic Center in the β‐Position.

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Dynamic Kinetic Resolution of Primary Alcohols with an Unfunctionalized Stereogenic Center in the β‐Position

AbstractPrimary alcohols with an unfunctionalized stereogenic center in the β‐position undergo an enzyme‐ and metal‐catalyzed dynamic kinetic resolution (DKR). The in situ racemization of the primary alcohol, required for the DKR, takes place via: (i) ruthenium‐catalyzed dehydrogenation of the alcohol, (ii) enolization of the aldehyde formed, and (iii) ruthenium‐catalyzed readdition of hydrogen to the aldehyde. The present method widens the scope of metal‐ and enzyme‐catalyzed DKR, which has so far been limited to α‐chiral alcohol and amine derivatives.

Kinetic resolution of primary alcohols having remote stereogenic centers: lipase mediated kinetic resolution of (±)-3-chloro-3-arylpropanols

Kinetic resolutions of (±)-3-chloro-3-arylpropanols by lipase mediated acetylation are described for the first time. Acetylation with CCL provided the best enantioselectivity amongst the enzymes used. Enantiomerically enriched products were obtained with up to 78% ee after two successive lipase-catalyzed acetylations. Different substituents on the aromatic ring and bromide, instead of chloride, on the substrates were found to have no drastic influence on the enantioselectivity of the reaction.

Enzymatic kinetic resolution of primary alcohols by direct esterification in solvent-free system

Direct enzymatic esterification catalyzed by immobilized Candida antarctica lipase B (CALB) and Rhizomucor miehei lipase (RML) was evaluated for kinetic resolution of some primary alcohols with a chiral center at the next carbon atom: 2-methoxy-2-phenylethanol ( 1), 2-phenyl-1-propanol ( 2) and 1-phenyl-1,2-ethanediol ( 3). The reactions were performed in solvent-free system with removal of water at low pressure. CALB was superior to RML in both reaction rates and enantioselectivity. The influence of acid species on enantioselectivity of CALB was studied on esterification of 1. In a series of free fatty acids, the highest enantioselectivity value was obtained for decanoic acid. Among other acid species investigated, 4-oxopentanoic acid gave the best results. The position of the double bond in pentenoic acid affected the reaction rate and enantioselectivity. Enantioselectivity of CALB increased significantly with reducing the reaction temperature. Direct esterification for kinetic resolution of 2 and 3 was also investigated. RML has a stricter substrate selectivity towards both: the acid and alcohol. Lowering the reaction temperature had no effect on enantioselectivity.

Highly enantioselective kinetic resolution of primary alcohols of the type Ph-X-CH(CH 3)-CH 2OH by Pseudomonas cepacia lipase: effect of acyl chain length and solvent

Although lipase from Pseudomonas cepacia (PCL) shows high enantioselectivity towards many secondary alcohols, it usually exhibits only low to moderate enantioselectivity towards primary alcohols. To increase this enantioselectivity, we optimised the reaction conditions for the PCL-catalysed hydrolysis of esters of three chiral primary alcohols: 2-methyl-3-phenyl-1-propanol 1, 2-phenoxy-1-propanol 2 and solketal 3. The enantioselectivity towards 1-acetate increased from E=16 to 38 upon changing the solvent from ethyl ether/phosphate buffer to 30% n-propanol in phosphate buffer and increased again to E ≥190 upon changing the substrate from 1-acetate to 1-heptanoate. The same changes increased the enantioselectivity towards alcohol 2 from E=17 to 70, but did not significantly increase the enantioselectivity towards alcohol 3. The best solvent was similar to the solvent used to crystallise the open form of PCL and likely stabilises the open form of PCL. This stabilisation may increase the enantioselectivity by removing kinetic contributions from a non-enantioselective lid-opening step. We determined the kinetic contribution of the lid-opening step by measuring the interfacial activation of PCL. The activation energy for the PCL-catalysed hydrolysis of ethyl acetate was at least 2.6 kcal/mol lower in the presence of a water–organic solvent interface.

Enhancement of the Efficiency of the Low Temperature Method for Kinetic Resolution of Primary Alcohols by Optimizing the Organic Bridges in Porous Ceramic‐Immobilized Lipase.

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Enhancement of the Efficiency of the Low Temperature Method for Kinetic Resolution of Primary Alcohols by Optimizing the Organic Bridges in Porous Ceramic-Immobilized Lipase

For the enhancement of enantioselectivity and acceleration of the reaction rate in the lipase-catalyzed resolution of primary alcohols, the use of a very low reaction temperature (−30 °C) and an immobilized lipase on organic bridges-coated porous ceramic support was found to be highly effective. Furthermore, the structure of the organic bridges greatly influenced the temperature effect between ln E and 1/T as well as the reaction rate. Among the organic bridges examined in the resolution of (±)-2-hydroxymethyl-1,4-benzodioxane, the 6-(2-methylpropanoyloxy)hexylsilanetrioxyl bridge was the best choice for both the E value and the reaction rate at −30 °C.