Cysteine sulfoxide derivatives in Petiveria alliacea.

Two diastereomers of S-benzyl-L-cysteine sulfoxide have been isolated from fresh roots of Petiveria alliacea. Their structures and absolute configurations have been determined by NMR, MALDI-HRMS, IR and CD spectroscopy and confirmed by comparison with authentic compounds. Both the R(S) and S(S) diastereomers of the sulfoxide are present in all parts of the plant (root, stem, and leaves) with the latter diastereomer being predominant. Their total content greatly varied in different parts of the plant between 0.07 and 2.97 mg g(-1) fr. wt, being by far the highest in the root. S-Benzylcysteine has also been detected in trace amounts (<10 microg g(-1) fr. wt) in all parts of the plant. This represents the first report of the presence of S-benzylcysteine derivatives in nature.

Distribution of S-Alk(en)ylcysteine sulfoxides in some Allium species. Identification Of a new flavor precursor: S-ethylcysteine sulfoxide (Ethiin).

The content of S-alk(en)ylcysteine sulfoxides, important nonvolatile flavor precursors, was determined in 15 different Allium species by means of gas chromatography. The method employed is based on derivatization of S-alk(en)ylcysteine sulfoxides with ethyl chloroformate followed by their reduction with sodium iodide. The total content of S-alk(en)ylcysteine sulfoxides varied considerably in the wide range between 0.02 and 1.3% fresh weight. Not only the total content but also relative proportions of individual derivatives varied to a great extent. A novel S-alkylcysteine derivative, S-ethylcysteine sulfoxide (ethiin), not previously reported to occur in Allium species, was found in most of the samples examined in trace amounts. None of the other S-alk(en)ylcysteine sulfoxides, for example, isopropyl, (Z)-1-propenyl, butyl, or pentyl, were detected in any of the samples analyzed, limiting possible levels of each of these components to

Gas chromatographic determination of S-alk(en)ylcysteine sulfoxides.

A new GC method for determination of S-alk(en)ylcysteine sulfoxides, important secondary metabolites occurring in many plant genera, has been developed. The method is based on isolation of the amino acid fraction by ion-exchange chromatography followed by derivatization with ethyl chloroformate at ambient temperature and reduction of derivatized S-alk(en)ylcysteine sulfoxides by sodium iodide. The main advantages of the new method are its high sensitivity, excellent resolution capability, accuracy and reliability, as well as the possibility to identify unknown compounds by means of GC-MS. The content of alliin and other S-alk(en)ylcysteine sulfoxides was determined in nine different samples of garlic (Allium sativum L.) originating from the Czech Republic, France, and China. The total content of S-alk(en)ylcysteine sulfoxide pool ranged between 0.53 and 1.3% fresh weight, with S-allylcysteine sulfoxide (alliin) being predominant. A novel S-alkylcysteine derivative, S-ethylcysteine sulfoxide (ethiin), not previously reported to occur in Allium species, was found in some of the samples examined.

Volatile compounds thermally generated from S-propylcysteine and S-propylcysteine sulfoxide-aroma precursors of Allium vegetables.

Two nonvolatile flavor precursors occurring in Allium vegetables, S-propyl-L-cysteine and its sulfoxide, were heated in closed model systems at different temperatures (from 80 to 200 degrees C) in the presence of variable amounts of water (0-98%) for 1-60 min. It seems to be indisputable that thermally generated breakdown products of both S-propyl-L-cysteine and particularly S-propyl-L-cysteine sulfoxide can significantly participate in the aroma formation of culinary processed Alliumvegetables. Dipropyl disulfide, dipropyl trisulfide, propylthiol, and dipropyl thiosulfonate were identified as the predominant volatile compounds generated by thermal degradation of S-propylcysteine sulfoxide. Dipropyl disulfide and 2-(propylthio)ethylamine were the major breakdown products formed from S-propylcysteine. Substantial amounts of various alkyl- and alkylthio-substituted pyridines were also generated from both S-propylcysteine and its sulfoxide.