Amino sulfenic acids

Onions contain an amino acid that is a positional isomer of alliin. When acted upon by alliinase it produces 2-propene sulfenic acid, which isomerizes to the lachrima-tory factor that brings tears to the eyes of onion cutters.c This, too, decomposes to form many other compounds.3... 

Carballal S, Alvarez B, Turell L, Both H, Freeman BA, Radi R (2007) Sulfenic acid in human serum albumin. Amino Acids 32 543-551... 

In onions, things start much the same way but the initial amino acid is not quite the same. The skeleton is the same as that of the garlic compound but the double bond is conjugated with the sulfoxide. Elimination and dimerization of the sulfenic acid produce an isomeric thiosulfinate. 

Poole LB, Karplus PA, Claiborne A. Protein sulfenic acids in redox signaling. Annu. Rev. Pharmacol. Toxicol. 2004 44 325-347. Pollegioni L, Piubelli L, Sacchi S, Pilone MS, Molla G. Physiological functions of D-amino acid oxidases from yeast to humans. Cell. Mol. Life Sci. 2007 64 1373-1394. 

Phenyldithioacetic acid (8) allows thioacylation of the 7-amino group in penicillanate (9) the resulting highly nucleophilic thioamide (10) gives intramolecular trapping of the sulfenic acid, RSOH, which is in thermal equilibrium with the thiazolidine 5-oxide moiety in (10 Scheme 2). ... 

Sulfenic acids (45) are generally quite unstable they easily dimerise and eliminate water to form thiol sulfinates (46) (Scheme 28). Several sulfenic acids have, however, been isolated and many of these are stabilised by hydrogen bonding to a carbonyl or amino group. The first sulfenic acid to be isolated was the anthraquinone derivative (47) in 1912. Sulfenic acids have been postulated as transient intermediates in many chemical and biochemical processes, e.g. the oxidation of thiol groups in proteins and the thermolysis of sulfoxides, including the acid-catalysed rearrangement of penicillin sulfoxides (48) to cephalosporins (49) (Scheme 29)... 

Stilbenes synthesis by Heck coupling, 43 Stille coupling aryl triflate + organylstannane, 42 Stobbe condensation, 58-59 Stork reagent, 328-329 Strain, steric. See Steric strain Strecker s synthesis of a-amino acids, 50, 301 L-Streptose synthesis, 267 Styrene. See Benzene, ethenyl-Succinic acid. See Butanedioic acid Succinimide. See 2,5-Pyrrolidinedione Sugars. See Monosaccharides Oligosaccharides inexpensive derivs. pr. (table), 263-264 Sulfafurazole, 307 Sulfamethoxazole, 308 Sulfenic acids, esters ... 

The actual presence of large amounts of cysteic acid in bleached hair had at one time been in doubt [55, 56]. It had been theorized that the cysteic acid found in bleached hair hydrolysates was formed by decomposition of intermediate oxidation products of cystine during hydrolysis prior to the analytical procedure [55]. However, differential infrared spectroscopy [4] and electron spectroscopy for chemical analysis by Robbins and Bahl [5] on intact unhydrolyzed hair have conclusively demonstrated the existence of relatively large quantities of cysteic acid residues in chemically bleached hair. Evidence for other sulfur acids (e.g., sulfinic or sulfenic acids) in bleached hair has not been provided. It is unlikely that these amino acids exist in high concentrations in hair because these species are relatively unstable. 

Sulfuric acid may be reduced to the level of sulfide and is then an important building stone of L-cysteine (see below). L-Cysteine, (S)- x-amino-/ -thiolpropionic acid, is one of the most important sulfur-containing substances in primary metabolism. The secondary products derived from L-cysteine may contain the sulfur in different states of oxidation. Of importance are sulfides (—S—), disulfides (—S—S— ), sulfenic acids (—S—OH), sulfoxides (—SO— ), sulfinic acids (—SO—OH) and sulfonic acids (—SO2—OH). 

Alliins are degraded to sulfenic acids and (X-amino acrylic acid (Fig. 190). oc-Aminoacrylic acid decomposes spontaneously to pyruvic acid and ammonia. 

The chemistry of the PPIs dictates reaction with electrophilic groups in amino adds after add-catalyzed conversion of the prodrug. The reactive group is the free SH of cysteine, which can then form a disulfide bond with the sulfenic acid or sulfenamide derivative of the PPI. In principle, cysteine disulfides can also react, but reformation of the native disulfide would eliminate the bound drug. 

In a weakly alkaline solution, isothiocyanate reacts with the a-amino group of cysteine (Figure 2.64). The reaction of isothiocyanates with cystine leads to the cleavage of disulfide bond (-S-S-) with the formation of cysteine sulfenic acid and a dithiocarbamic acid ester. Dehydration of this ester yields 5-amino-l,3-thiazine-4-one-3-thione derivative and elimination of hydrogen sulfide produces a cyclic 2-thiazoline-4-carboxylic acid derivative (Figure 2.65). Reaction of cystine with thiocyanates (R-S-C=N), formed by spontaneous isomerisation of isothiocyanates, produces disulfide Cys-S-S-R and -thiocyanoalanine, which cyclises to 2-thiazoline derivative (Figure 2.66). 

The (E)-(prop-l-en-l-yl)sulfenic acid derived from the related amino acid occurring in onion and known as isoaUiin behaves differently. It isomerises on catalysis with enzyme LF-lyase... 

When you slice an onion, you break cells, releasing what s inside and allowing amino acid sulfoxides to form sulfenic acids. Enzymes once kept apart now mix together, producing syn-propanethial-S-oxide, a volatile sulfur compound that reacts with the water in your eyes to form sulfuric acid. The sulfuric acid burns, stimulating your eyes to release tears to wash away the irritant. Cooking renders the compound inactive, but here are some tips that will help with the burn ... 

Rich, D., and J. P. Tam Synthesis of Dehydro Amino Acids and Peptides by Dehydrosulfenation. Rate Enhancement Using Sulfenic Acid Trapping Agents. J. Org. Chem. 42, 3815 (1977). 

The oxidation of co-ordinated cysteine ligands may also give a variety of products. The most usually encountered reactions involve the formation of sulfenate or sulfinate as above however, in some cases disulfide formation occurs in preference to oxygen transfer. In the example shown in Fig. 9-39, the formation of the disulfide is accompanied by decarboxylation of the amino acid ... 

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