Synthesis of a tetradecapeptide corresponding to sequence 90-103 of bovine adrenodoxin.

Kawasaki, Koichi; Kawasaki, Chiye; Maeda, Mitsuko; Okada, Yoshio

doi:10.1248/cpb.28.2105

Cited by 4 publications

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“…Coming to the methionine ester 9a, it is to be noted that the older preparation in refluxing benzene has a 56% yield and is supported by melting point and optical rotation as analytical data (Kawasaki 1980), while the more recent one in refluxing toluene has a 75% yield but provides neither melting point nor optical rotation (Fayad 2015). In both cases, the enantiomeric excess is an unknown issue.…”

Section: Resultsmentioning

confidence: 99%

“…On the other hand, histidine, asparagine, glutamine and threonine benzyl esters tosylates are just cited as reactants (Kempf 1991;Zhao 2009;Abiko 1983;Nishizawa 1977;Bose 1982) but, to the best of our knowledge, their preparations have never been individually described, while those of tryptophan and arginine are, in different respects, problematic (Arai 1983;Magnus 1989;Biondini 2010;Dorman 1976) and cysteine benzyl ester tosylate is unknown. Of the remaining proline and methionine benzyl esters tosylates, for which one and two preparations with only partial characterizations are reported respectively (Dai 2009;Kawasaki 1980;Fayad 2015), we decided to include methionine (9). Therefore, we have considered the preparation of the benzyl esters tosylates 1a-8a and, in addition, the methionine benzyl ester tosylate 9a, after verifying that literature methods prescribe, for the nine esters, the use of refluxing benzene, toluene, carbon tetrachloride or benzyl alcohol itself regardless of safety and of racemization and provide very few or no analytical data on the enantiomer systems formed by the products and on their enantiomeric composition (Chart 2).…”

Section: Introductionmentioning

confidence: 99%

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One-step preparation of enantiopure l- or d-amino acid benzyl esters avoiding the use of banned solvents

2017

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The enantiomers of amino acid benzyl esters are very important synthetic intermediates. Many of them are currently prepared by treatment with benzyl alcohol and p-toluenesulfonic acid in refluxing benzene or carbon tetrachloride, to azeotropically remove water, and then precipitated as tosylate salt by adding diethyl ether. Here, we report a very efficient preparation of eight L- or D-amino acid benzyl esters (Ala, Phe, Tyr, Phg, Val, Leu, Lys, Ser), in which these highly hazardous solvents are dismissed using cyclohexane as a water azeotroping solvent and ethyl acetate to precipitate the tosylate salt. With some work-up modifications and lower yield, the procedure can be applied also to methionine. Chiral HPLC analysis shows that all the benzyl esters, including the highly racemizable ones such as those of phenylglycine, tyrosine and methionine, are formed enantiomerically pure under these new reaction conditions thus validating the solvents replacement. Contrariwise, toluene cannot be used in place of benzene or carbon tetrachloride because leading to partially or totally racemized amino acid benzyl esters depending on the polar effect of the amino acid α-side chain as expressed by Taft's substituent constant (σ*).

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

One-step preparation of enantiopure l- or d-amino acid benzyl esters avoiding the use of banned solvents

2017

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ChemInform Abstract: SYNTHESIS OF A TETRADECAPEPTIDE CORRESPONDING TO SEQUENCE 90‐103 OF BOVINE ADRENODOXIN

Kawasaki¹,

Kawasaki²,

Maeda³

et al. 1980

Chemischer Informationsdienst

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Preparation of enantiopure methionine, arginine, tryptophan, and proline benzyl esters in green ethers by Fischer–Speier reaction

et al. 2018

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The simplest way to prepare the tosylate salts of amino acid benzyl esters, whose enantiomers are very important synthetic intermediates, is treatment of amino acid with benzyl alcohol and p-toluenesulfonic acid in a refluxing water-azeotroping solvent (Fischer-Speier esterification). However, to this day, the literature proposes only hazardous solvents, such as benzene, carbon tetrachloride, and chloroform, which must be absolutely avoided, or solvents, such as toluene and benzyl alcohol, which cause racemization because of too high boiling water azeotropes. On the other hand, the alternative successful use of cyclohexane, which we have recently reported for several amino acid benzyl esters, is inapplicable or not very efficient for 'problematic' amino acid such as tryptophan, arginine, and methionine, for which, indeed, the simple Fischer-Speier esterification is not described or poorly exemplified in the literature. Therefore, more polar solvents, in particular the green ethers CPME, TAME, and Me-THF, were selected and first considered for the preparation of methionine benzyl ester, previously accomplished in cyclohexane with modest yield. After discarding CPME and TAME, because causing racemization and decomposing under acidic conditions, respectively, we focused on Me-THF. In this ether, the benzyl esters of Met, Arg, and Trp could be obtained in good yield and, as proved by chiral HPLC or H NMR analysis, enantiomerically pure. The procedure was successfully extended to proline benzyl ester, which could be prepared enantiomerically pure and in quantitative yield both in cyclohexane and in Me-THF, thus avoiding the recently reported use of carbon tetrachloride.

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Synthesis of a tetradecapeptide corresponding to sequence 90-103 of bovine adrenodoxin.

Cited by 4 publications

References 0 publications

One-step preparation of enantiopure l- or d-amino acid benzyl esters avoiding the use of banned solvents

One-step preparation of enantiopure l- or d-amino acid benzyl esters avoiding the use of banned solvents

ChemInform Abstract: SYNTHESIS OF A TETRADECAPEPTIDE CORRESPONDING TO SEQUENCE 90‐103 OF BOVINE ADRENODOXIN

Preparation of enantiopure methionine, arginine, tryptophan, and proline benzyl esters in green ethers by Fischer–Speier reaction

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