The Possible Contribution of Isotope Effects on Ester- and Aldol Condensations to Isotope Discriminations and Isotopic Patterns of Natural Compounds

Abstract

Acetyl-CoA provides the C-2-units for the formation of many secondary compounds. The primary pattern of this intermediate is originating from glucose, further modifications are introduced by isotope effects on the pyruvate-dehydrogenase-reaction and on ester- and aldol-reactions in the course of the biosynthesis of secondary products. The overlap of these various effects is demonstrated through the pattern of some natural products. The partial pattern of limonene and pulegone, respectively, products from different origin are not identical, this is interpreted as a consequence of individual relative contributions of the above mentioned effects in the plants in question. On the other hand the distinct relative depletion in a position of sinigrin, a glucosinolate from Brassica nigra, originating from CH3 of acetate can be assigned to an isotope effect of the aldol reaction between a precursor and acetyl-CoA. An corresponding depletion has been measured in position 5 of citrate. Therefore the kinetic isotope effect on the citrate synthase reaction is studied in vitro at present.