Cysteine sulfoxides and volatile sulfur compounds from Allium tripedale.
Allium tripedale Trautv. belonging to the subgenus Nectaroscordum grows naturally in the mountainous areas of northwest Iran. Leaves have a very strong and somewhat unpleasant taste and are widely used by the local population as a spicy vegetable. Three new cysteine based compounds were identified in A. tripedale as the first examples of sulfur containing 1-butenyl derivatives in nature. The compounds have been described as o-phthaldialdehyde (OPA) derivatives and identified as (+)-S-(1-butenyl)-L-cysteine sulfoxide (homoisoalliin) and its gamma-glutamyl derivative as well as the gamma-glutamyl derivative of S-(1-butenyl)-L-cysteine (desoxyhomoisoalliin). These cysteine sulfoxides have been also found in Allium siculum Ucria. As volatile compounds, di-(1-butenyl)-disulfide and the cepaene-like compounds di-(1-S-sulfoxymethyl-butyl)-disulfide, 1-S-sulfoxymethyl-butyl-1'-S-sulfoxy-1-butenyl-butyl-disulfide and 1-S-sulfoxymethyl-butyl-1'-S-sulfoxybutyl-butyl-disulfide could be tentatively identified by various MS experiments. Primary products resulting from the alliinase reaction of homoisoalliin seem to be highly unstable and were rapidly converted to the volatile compounds listed above.