THE POSSIBLE CONTRIBUTION OF ISOTOPE EFFECTS ON ESTER AND ALDOL CONDENSATIONS TO ISOTOPE DISCRIMINATIONS AND ISOTOPIC PATTERNS OF NATURAL COMPOUNDS

Acetyl-CoA provides the C-2-units for the formation of many secondary compounds. The primary pattern of this intermediate is originating fro m glucose, Further modifications are introduced by isotope effects on the pyruvate-dehydrogenase reaction and on ester-and aldol-reactions i n the course of the biosynthesis of secondary products. The overlap of these various effects is demonstrated through the pattern oi some nat ural products. The partial pattern of limonene and pulegone, respectiv ely, products from different origin are not identical, this is interpr eted as a consequence of individual relative contributions of the abov e mentioned effects in the plants in question. On the other hand the d istinct relative depletion in a position of sinigrin, a glucosinolate from Brassica nigra, originating from CH3 of acetate can be assigned t o an isotope effect of the aldol reaction between a precursor and acet yl-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.