S-Allyl-L-cysteine sulfoxide

Nishimura and coworkers57-59 studied the y-radiolysis of aqueous solutions of sulfoxide amino acids. Sulfoxide amino acids are the precursors of the flavors of onions (S-propyl-L-cysteine sulfoxide, S-methyl-L-cysteine sulfoxide and S-(l-propenyl)-L-cysteine sulfoxide) and garlic (S-allyl-L-cysteine sulfoxide). In studies on sprout inhibition of onion by /-irradiation it was found that the characteristic flavor of onions became milder. In the y-radiolysis of an aqueous solution of S-propyl-L-cysteine sulfoxide (PCSO)57,58 they identified as the main products alanine, cysteic acid, dipropyl disulfide and dipropyl sulfide. In the radiolysis of S-allyl-L-cysteine sulfoxide (ACSO) they found that the main products are S-allyl-L-cysteine, cysteic acid, cystine, allyl alcohol, propyl allyl sulfide and diallyl sulfide. The mechanisms of formation of the products were partly elucidated by the study of the radiolysis in the presence of N20 and Br- as eaq - and OH radicals scavengers, respectively. 

Naturally occurring alliin, the major precursor to the garlic aroma, is (f c- s)-(+)-cysteine sulfoxide 26 (Scheme 10) with both a chiral carbon and chiral sulfur - probably the first such compound (note that sulforaphene - see earlier - was isolated more or less simultaneously with alliin). Hence there are four possible stereoisomers. The alliin level in garlic is significant 5-14 mg g fresh weight. 

SCHWiMMER, S. S-Allyl-L-cysteine sulfoxide lyase [Allium cepa (Onion)]. Methods Enzymol. 17 B, 475 (1971). 

Similar to the S-allyl-L-cysteine sulfoxide in garlic, the C-S lyase can also catalyze the flavor formation from the 5 -methyl-L-cysteine sulfoxide. Therefore, when garlic is cut or crushed, methyl sulfenic acid and allyl sulfenic acid can be produced from 5 -methyl-L-cysteine sulfoxide and S-allyl-L-cysteine sulfoxide, respectively (Figure 18.5). As sulfenic acids are quite reactive, methyl sulfenic acid and allyl sulfenic acid will quickly form the metiiyl 2-propenethiosulfinate and allyl methaneth-iosulfinate. With the similar reaction to that from diallyl thiosulfinate, these thiosulfinates produce allyl methyl disulfide and allyl methyl trisulfide. 

Akao, M., Shibuya, T., Shimada, S., Sakurai, H., and Kumagai, H. 2008. In vivo production of bioactive compounds from S-allyl-L-cysteine sulfoxide, garlic odor precursor, that inhibit platelet aggregation. J Clin Biochem Nutr Suppl 43 1-3. 

Ziegler, S.J. and Sticher, O. 1989. HPLC of S-alk(en)yl-I cysleine derivatives in garlic including quantitative determination of (+)-S-allyl-L-cysteine sulfoxide (alliin). PlantaMed 55(4) 372-328. 

The key precursor for garlic aroma is S-allyl-L-cysteine sulfoxide (alliin) which, as in onions, occurs in garlic bulbs together with S-methyl-and S-propyl-compounds. The allyl and propyl-compounds are assumed to be synthesized from serine and corresponding thiols ... 

Allyl chloride is presumed to be metabolized to allyl alcohol, which could then be further metabolized via two pathways to form either acrolein or glycidol, from which a variety of metabolites could result. Metabolites identified in rat urine are 3-hydroxy-propylmercapturic acid and allyl mercapturic acid and its sulfoxide. Allyl glutathione and S-allyl-L-cysteine have been detected in the bile of dosed rats. In-vitro metabolism of allyl chloride results in haem destruction in microsomal cytochrome P450 (lARC, 1985). 

Raw garlic per se 5-glutamyl-5-allyl-L-cysteines, 5-allyl-L-cysteine sulfoxides, allicin, adenosine Intact clove with the white or pink skin by simple pull off Precursor of allicin, methiin, (-t-j-S-ftrani-l-propenyO-L-cysteine sulfoxide, and cycloalliin... 

The flavor precursors, 5 -alk(en)yl-L-cysteine sulfoxides, themselves do not have any specific flavor. However, when garlic or onion cells are damaged by cutting or crushing and the 5 -alk(en)yl-L-cysteine sulfoxides meet the C-S lyase (alliinase), they are converted into various volatile sulfuric compounds. Stoll and Seebeck (1951) first proposed the production of diallyl thiosulfinate (allicin) from the 5 -allyl-L-cysteine sulfoxide (alliin) by the C-S lyase. Through the reaction catalyzed by the C-S lyase, 5 -alk(en)yl-L-cysteine sulfoxides yield alk(en)yl sulfenic acid and aminoacrylic acid, the latter being spontaneously degraded... 

Alkyl allyl sulfoxides start to racemize significantly only at temperatures above 50°C58-60. For example, ( + )-(S)-ally]-L-cysteine, the progenitor of the odorous part of garlic, did not undergo epimerization at sulfur during isolation and recrystallization61. 

Known active constituents of garlic (there are at least 35 other constituents whose actions are unknown) ajoene, allicin, aliin, allixin, allyl mercaptan, allyl methyl thiosulfmate, allyl methyl trisulfide, allyl propyl disulfide, diallyl disulfide, diallyl hepta sulfide, diallyl hexa sulfide, diallyl penta sulfide, diallyl sulfide, diallyl tetra sulfide, diallyl tri sulfide, dimethyl disulfide, dimethyl trisulfide, dirpopyl disulfide, methyl ajoene, methyl allyl thiosulfmate, propyline sulfide, 2-vinyl-4H-l, 3-tithiin, 3-vinyl-4H-1, 2dithiin, S-allyl cysteine sulfoxide, S-allyl mercapto, cysteine. 

The chemistry of garlic flavor parallels that of onion and Freeman and Whenham [72] established that any differences were due to qualitative and quantitative differences in the precursors present. The principle substrate is S-(2-propenyl)l-cysteine sulfoxide, which when acted upon by alliinase produces allyl thiosulflnate (allicin)... 

Alline S-Propenyl-cysteine sulfoxide 7-L-Glutamyl-S-allyl-cysteine... 

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