Poly(octadecyl acrylate) exists in a crystalline state at room temperature. This crystalline state was formed even after being grafted onto silica through the terminal group of the polymer. When this polymer-grafted silica (SiI-ODAn) was used as a reversed phase liquid chromatography packing material, better selectivity for diastereomerized phenylethylamines derivatized by (S)-(-)-(2,3-naphthalenedicarboximidyl)propionyl fluoride was observed at room temperature than was observed for simple octadecylated silica (aDS). On the other hand, increasing temperature reduced the selectivity to be close to that of ODE Additional experiments showed the better selectivity derived from SiI-ODAn was due to both the highly-oriented structure of the polymer and the carbonyl-rc interaction with the diastereomer. A theoretical investigation of this carbonyl-rc interaction is also described briefly.mainly as an organic stationary phase in RPLC. However, since the hydrophobicity difference between diastereomers is rather small, a D S usually shows low selectivity. Therefore, we focus on the fact that the above-mentioned diastereomerizing reagents have chromophoric groups which can work as a ~-~ interaction source. From these considerations, we applied poly(long-chain alkyl acrylate)grafted silicas (Sil-ODAn and Sil-DCAn) as packing materials for diastereomer separation in an RPLC mode. These polymeric organic phases have been developed by us [8 10] and are very attractive for the following reasons: (1) they have many carbonyl groups that act as ~-electron sources and (2) they undergo a temperature-induced crystalline-to-isotropic phase transition as schematically illustrated in Figure 1. In this paper, we wish to report that diastereomeric separation can be enhanced through high orientation of the carbonyl groups on silica.Original
Enantiomer separation has been often realized with reversed phase liquid chromatography using diastereomerizing reagents with simply-hydrophobized silica. The present study demonstrates that diastereomer selectivity can be enhanced through highly-oriented organic phase produced by achiral poly(octadecyl acrylate)-grafted on silica and a carbonyl-π interaction due to the acrylate moiety is effective as the driving force for the selectivity enhancement.
Abstract:The stereoselective reduction of an aromatic α-keto amide with actinomycete strains was investigated. It was found that 2-chlorobenzoylformamide was reduced to the corresponding 2-chloromandelamide by mesophilic and thermophilic strains of actinomycetes. Among the strains tested, the reduction of 2-chlorobenzoylformamide by Streptomyces thermocyaneoviolaceus (one of thermophilic strains) in the presence of glycerol as an additive produced only (S)-2-chloromandelamide in 99% conversion with 99% enantiomeric excess (e.e.). On the other hand, the reduction by Streptomyces thermocarboxydovorans NBRC16324 at 45 °C or Thermoactinomyces vulgaris NBRC15851 cultivated in a soluble starch-based medium gave the corresponding (R)-hydroxy amide (conversion, 99%; 99% e.e.). Mesophilic and other thermophilic actinomycete strains also catalyzed the reduction to the corresponding (R)-hydroxy amide with 85%-99% e.e. Thus, the syntheses of both enantiomers of 2-chloromandelamide was achieved though the reduction of 2-chlorobenzoylformamide with different actinomycete strains.
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