Asymmetric catalysis ester hydrolysis

Hatano et al.l39 found that the poly(L-lysine)-Cu(II) complex exerted asymmetrically selective catalysis on the hydrolysis of phenylalanine ester, whereas Cu ions and bis(bipyridyl)Cu had no catalytic activity. The great stability of the intermediate PLL-Cu complex with the D-ester was considered responsible for the catalytic activity. 

An interesting variation of the catalysis by poly(amino acids) was reported by Hatano et al. (141). Several metal ions and their complexes are known to be effective catalysts for the hydrolysis of amino acid esters, in wdiich coordination of substrates to the metal ion renders nucleophilic attack by H2O more facile 142). Hatano et al. found ttat D-phenylalanine methyl ester 20 was catalytically hydrolyzed by poly-L-lysine-Cu(II) complex 3 to 4 times more efficiently than the L-iso-mer. The rate difference arose from the lower enthalpy of activation for the D-sub-strate. At die same time, the circular dichroism data indicated that formation of the catalj t-substrate complex was more favorable with the D-ester than with the L-ester (74J). Ap endy, poly-L-lysine helped form an asymmetrically selective binding site. 

The key structural feature of POST-1 - the presence of dangling pyridine groups in the channels - affords a unique opportunity to perform asymmetric heterogeneous catalysis. Thus, potentially, any base catalyzed reactions (e.g., esterification or hydrolysis) can be performed with POST-1. Moreover, chiral pores should induce a degree of enantioselectivity in the final product mixture. The catalytic activity of POST-1 in the transesterification reaction was examined. Although the reaction of 16 and ethanol in the presence of POST-1 in carbon tetrachloride produced ethyl acetate in 11% yield, little or no transesterification occured without POST-1 or with the iV-methylated POST-1 (Sect. 2.2). The post chemical modification of the pyridine groups in POST-1 proves the role of free pyridine moiety in transesterification reaction. Transesterification of ester 16 with bulkier alcohols such as isobutanol, neopentanol, and 3,3,3-triphenyl-l-propanol occurs at a much slower rate under otherwise identical reaction conditions. Such size selectivity suggests that catalysis mainly occurs in the channels. 

On the basis of the previous results. Park, Jew, and co-workers [101] developed in 2009 an efficient synthetic methodology for enantiomerically pure a-alkyl-a,3-diaminopropionic acid. They described the asymmetric PTC alkylation of Af(l)-Boc-2-phenyl-2-imidazoline-4-carboxylic acid /cr/-butyl esters (52) with propargyl, allyl, and substituted benzyl bromides under catalysis with the binaphthalene-derived PTC XXV (Scheme 8.19). Alkylated products were obtained in high yields with excellent enantioselectivities and their acidic hydrolysis furnished corresponding optically active a-alkyl-a,(3-diaminopropionic acids. Another example of PTC alkylation of heterocyclic compounds, namely 1-cyanotetrahydro-(3-carbolines using a binaphthyl-modified V-spiro-type catalyst L, was reported by Maruoka and co-workers [103]. 

A recent example has been described by Brown et al. who have studied the KR of p-nitrophenyl esters of the d- and i-N-tert-butoxycarbonyl derivatives of glutamine and phenylalanine with ethanol or methanol promoted by chiral lanthanide complexes, providing enantioselectivities of up to 99% ee [302]. On the other hand, an enantioselective hydrolysis of phenylalanine derivatives was reported in 1986, providing a perfect enantiomer discrimination (s> 1000), as a result of catalysis with a tripeptide [303]. In 2007, Maruoka et al. reported the KR of differently a,a-disubstituted a-siloxy aldehydes based on an asymmetric rearrangement into the corresponding chiral acyloins using axially chiral organoaluminium Lewis acids, which provided selectivity factors of up to 39.5... 

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