S-allyl-L-cysteine

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. 

In the case of ACSO it was found also that N20 addition reduces the yield of S-allyl-L-cysteine (ACS), indicating that this product is formed by eaq - but not by OH radicals. As a result it can be expected that KBr addition will not reduce the ACS yield. It was found that KBr not only does not reduce the yield of ACS, but it rather increases i ts formation. This is explained as due to ACS formation by reaction of eaq" with ACSO, and its disappearance by reaction with OH radicals to give back ACSO as it is known for the reaction with sulfides. The authors suggest the same reactions for PCSO and PCS (propyl-L-cysteine) although the yield of PCS was not determined. 

The observation that in the case of PCSO there is no formation of propanol while allyl alcohol is formed from ACSO agrees with the resonance stabilization of the allyl radical60 and hence weaker bond for S-allyl than for S-propyl. The yield of allyl alcohol from irradiation of ACSO is considerably greater than that from S-allyl-L-cysteine, probably due to energy delocalization by the four p electrons of the S atom. 

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). 

De Rooij BM, Boogaard PJ, Rijksen DA, et al. Urinary excretion of N-acetyl-S-allyl-L-cysteine upon garlic consumption by human volunteers. Arch Toxicol 1996 70 635-639. 

De Rooij et al. (1996) conducted a study to evaluate the urinary excretion ofM-acetyl-S-allyl-L-cysteine (allylmercapturic acid, ALMA). The importance of this study lies in the use of ALMA as a biomarker for occupational exposure... 

The totai annuai voiume of production of the 51 simpie aiiphatic and aromatic suifides and thiois is approximateiy 182 kg in Europe (European Fiavour and Fragrance Association, 2005), 80 kg in the United States of America (USA) (Flavor and Extract Manufacturers Association, 2006) and 3 kg in Japan (Japanese Flavor and Fragrance Manufacturers Association, 2002). in Europe, approximately 72% of the total volume is accounted for solely by diethyl trisulfide (No. 1701), whereas in the USA, (S)-1-methoxy-3-heptanethiol (No. 1671), ( )-isobutyl 3-methylthiobutyrate (No. 1677), methyl (methylthio)acetate (No. 1691), bis(1-mercaptopropyl)sulfide (No. 1709) and S-allyl-L-cysteine (No. 1710) account for 84% of the total volume of production. The daily per capita intake of each agent is reported in Table 1. Annual volumes of production of this group of flavouring agents are summarized in Table 2. 

For S-allyl-L-cysteine (No. 1710), the NOEL of 250 mg/kg bw per day from a 28-day study in rats (Kodera et al., 2002) provides an adequate margin of safety (>8 million) in relation to currently estimated levels of intake of this substance from use as a flavouring agent. 

Oral LDso values have been reported for 2 of the 51 substances evaluated in this group and are summarized in Table 3. In rats, oral LDso values of 682 and 9500-10 940 mg/kg bw have been reported for ethanethiol (No. 1659) and S-allyl-L-cysteine (No. 1710), respeotively, confirming the low acute toxicity of simple aliphatic and aromatic sulfides and thiols (Fairchild Stokinger, 1958 Kodera et al 2002). 

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). 

Suzuki, T., M. Sugii, T. Kakimoto, and N. Tsuboi Isolation of (-)-S-allyl-L-cysteine from garlic. Chem. Pharm. Bull. 9, 251 (1951). 

ViRTANEN, A. I., and I. Mattila y-L-glutamyl-S-allyl-L-cysteine in garlic (Allium sativum). Suom. Kemistilehti B34, 44 (1961). 

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. 

Suzuki, T., Sugii, M., and Kakimoto, T. 1962b. y-L-Glutamyl-S-allyl-L-cysteine, a new gama-glutamyl peptide in garlic. Chem Pharm Bull 70 345-346. 

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