INTERMOLECULAR AND INTRAMOLECULAR ISOTOPIC CORRELATIONS IN SOME CYANOGENIC GLYCOSIDES AND GLUCOSINOLATES AND THEIR PRACTICAL IMPORTANCE

Sinalbin is a complex organic salt from white mustard. The delta C-13- values of the aromatic parts of the anion glucosinalbin (p-hydroxyphen ylacetic acid) and of the cation sinapin (sinapic acid) are identical (-32.2 parts per thousand) and both aromatic compounds are depleted by 6.4 parts per thousand with respect to the glucose moiety (-25.8 part s per thousand) bound in glucosinalbin. The delta C-13-value of the ch oline part of the molecule can be correlated to its metabolic origin f rom glucose. However, there is an unexpected dramatic C-13-enrichment in the first C-atom of glucosinalbin, originally the C-2 of tyrosine. This enrichment of approximately 11 parts per thousand relative to the mean value of the aglycone is found in the same position of four othe r glucosinolates and cyanogenic glycosides derived from phenylalanine or tyrosine. An isotope effect on the phenylalanine-ammonia-lyase reac tion is discussed as the most probable cause for this finding. In cont rast, sinigrin, the glucosinolate from black mustard, shows a relative C-13-depletion of 6.5 parts per thousand in the corresponding first C -atom of the aglycone allyl mustard oil. The proposed reason for this depletion is an isotope effect on an aldol reaction during the biosynt hetic introduction of this C-atom into the aglycone skeleton. Syntheti c allyl mustard oil is depleted by 14 parts per thousand in the same p osition relative to the delta C-13-value of the whole molecule, probab ly owing to an isotope effect on the first step of its chemical synthe sis, the binding of allyl amine to CS2. This difference can be used to detect adulterations of mustard. Copyright (C) 1996 Elsevier Science Ltd