Disulfides methyl methanethiosulfonate

Methyl methanethiosulfonate (MMTS) is a small reversible blocking agent for sulfhydryl groups (Thermo Fisher, Toronto Research). It reacts with free thiols to form a dithiomethane modification with release of sulfinic acid (Figure 1.122). The sulfinic acid component decomposes into volatile products, which don t affect the disulfide formed from the MMTS reaction Alkylthiosulfonates react rapidly with thiols under mild conditions at physiological pH. The MMTS compound is a liquid at 10.6 M concentration and is conveniently added to a reaction medium by pipette. Complete thiol modifications of available cysteine residues in proteins can... 

The most important flavour compound in raw onions is thiopropanal-S-ox-ide, the lachrymatory factor [145,146]. Other important flavour compounds are 3,4-dimethyl-2,5-dioxo-2,5-dihydrothiophene and alkyl alkane thiosulfonates such as propyl methanethiosulfonate and propyl propanethiosulfonate with a distinct odour of freshly cut onions [35, 36, 147]. Various thiosulfinates that have a sharp and pungent odour may also contribute to the flavour of onions. These compounds, however, are rapidly decomposed to a mixture of alkyl and alkenyl monosulfides, disulfides and trisulfides (Scheme 7.3) of which dipropyl disulfide, methyl ( )-propenyl disulfide, propyl ( )-propenyl disulfide, dipropyl trisulfide and methyl propyl trisulfide are the most important contributors to the aroma of raw and cooked onions (Table 7.5, Fig. 7.6) [148-150]. Recently, 3-mercapto-2-methylpentan-l-ol was identified in raw and cooked onions eliciting intense meat broth, sweaty, onion and leek-like odours [142, 151]. 

S-Methyl methanethiosulfonate is commercially available, but is expensive. Other preparation methods involve oxidation of thiols or disulfides by halogens or peroxides,3 reduction of sulfinyl halides5 (which have to be prepared) or sulfonyl halides with potassium iodide6 or copper/bronze7 as well as thermolysis of sulfonylhydrazines.8 Finally, a two-day procedure for the preparation of methyl methanethiosulfonate has been reported from dimethyl sulfoxide.9... 

Some volatile sulfur compounds were obtained from methionine and riboflavin after light irradiation under acidic conditions (Table I). Methyl mercaptan seems to be one of the important off-odor components. At this time, because of using the solvent extraction with dichloromethane, the amount of highly volatile methyl mercaptan seemed to be low. Therefore, we focused the other off-odor components, that is, methional, dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS) and methyl methanethiosulfonate (MMTS). In particular, DMTS is considered to be significant because of its extremely low threshold value. Figure 1 shows that the amount of DMDS and DMTS increased with decreasing pH value. 

---