Studies on the constituents of Helleborus purpurascens: use of derivatives from calix[6]arene, homooxacalix[3]arene and homoazacalix[3]arene as extractant agents for amino acids from the aqueous extract.

Abstract

The task of this work was to investigate the extraction capacity of various calixarenes for free and esterified amino acids from aqueous acid phases. Furthermore, this method was applied to aqueous extracts of Helleborus purpurascens. Generally, it is known that calixarenes can be used as extractants for ammonium compounds due to π-cation and lone pair cation interactions. As first, tert-Butyl-calix[6]arene and derivatives thereof were used. They had already proven their worth in previous investigations. In addition, tert-Butyl-hexahomooxa-calix[3]arene was used also, which can also enter into lone pair cation interactions. In addition to these well-known calixarenes, new calixarenes were produced and tested. Based on the tert-Butyl-hexahomooxa-calix[3]arene, a phosphor(III)bridged derivative was prepared, combining the three aromatic hydroxyl groups to a phosphite. As a seldom-described class of calixarenes, tert-Butyl-hexahomoaza-calix[3]arene derivatives were used. The nitrogen analogues of tert-Butyl-hexahomooxa-calix[3]arene could be produced as N-benzyl derivatives. The structure of the esterified carboxymethylated derivative of N,N',N″-Tribenzyl-tert-Butyl-hexahomoaza-calix[3]arene could be verified by X-ray structure analysis. It crystallized as a partial cone. The extraction capacity of the described calixarenes was investigated for amino acids from aqueous acidic solutions into an organic phase. For the testing were chosen asparagine, aspartic acid, tyrosine, tryptophane, phenylalanine and pipecolinic acid and their methyl esters. The amino acids and their methyl esters were dissolved in water at different pH values. The calixarenes were dissolved in dichloromethane (DCM) or chloroform. After this preparation, the aqueous acidic amino acid solutions were mixed with the solutions and shaken intensively. In addition, blank values were determined by extracting the aqueous stock solutions of the amino acids and their methyl esters with pure solvents. To determine the extraction rate, the phases were separated and each analysed using GC-FID, partially GC-MS(EI). The evaluation is performed in two ways. On the one hand the depletion in the aqueous phase and on the other hand the content in the organic phase was determined.