CARBON-ISOTOPE PATTERN IN PURINE ALKALOIDS A KEY TO ISOTOPE DISCRIMINATIONS IN C-1 COMPOUNDS

The delta(13)C- and delta(15)N-values of caffeine and theobromine from various natural origins have been determined. In agreement with earli er findings, they permit distinction from corresponding synthetic prod ucts. For a(13)C pattern analysis, the purine alkaloids were hydrolyse d by means of 22.5 M H2SO4, and the relative C-13 abundance of the fra gments was analysed by GC-C-IRMS. The C-13 pattern of natural purine a lkaloids indicated an enrichment of C-13 in the positions 2 and 8, ori ginating from the THF pool (delta(13)C = -21, 7 parts per thousand) an d a depletion in the methyl groups coming from the SAM pool (delta(13) C = less than or equal to -39 parts per thousand). The results suggest the existence of two separate C-1 pools and an isotope effect implied in the formation or transfer of CH3 groups. The carbon isotope patter n of synthetic purine alkaloids was completely different from that of the natural alkaloids.