Carbon isotope pattern in purine alkaloids a key to isotope discriminations in C 1 compounds

Abstract

The δ 13C- and δ 15N-values of caffeine and theobromine from various natural origins have been determined. In agreement with earlier findings, they permit distinction from corresponding synthetic products. For a 13C pattern analysis, the purine alkaloids were hydrolysed by means of 22.5 M H 2SO 4, and the relative 13C abundance of the fragments was analysed by GC-C-IRMS. The 13C pattern of natural purine alkaloids indicated an enrichment of 13C in the position 2 and 8, originating from the THF pool ( δ 13C = − 21,7‰ ) and a depletion in the methyl groups coming from the SAM pool ( δ 13 C = ⩽ − 39‰ ). The results suggest the existence of two separate C 1 pools and an isotope effect implied in the formation or transfer of CH 3 groups. The carbon isotope pattern of synthetic purine alkaloids was completely different from that of the natural alkaloids.