Formation and identification of 4′-O-methyl-(-)-epigallocatechin in humans

The possible beneficial effects of tea consumption have attracted a great deal of attention. Many of the biological effects have been attributed to tea catechins, but the metabolic fate of these compounds is not clear. In the present study, a major metabolite observed in human blood and urine samples after green tea administration was identified as a O-methylated derivative of (-)-epigallocatechin (EGC) by comparison with products from chemical and enzymatic O-methylation of EGC. The structure of this metabolite was elucidated as 4′-O-methyl-(-)-epigallocatechin (4′-O-MeEGC) by ¹H and ¹³C NMR and heteronuclear multiple bond connectivity experiment. The human plasma level of 4′-O-MeEGC reached its peak value within the first 2 h following tea ingestion. Its maximum concentration was 4 to 6 times higher than that of EGC. The half-lives of EGC and 4′-O-MeEGC in the blood were 1.02 ± 0.07 and 4.39 ± 1.14 h, respectively. The amount of 4′-O-MeEGC excreted in urine was about 3 times higher than that of EGC, and 88% of 4′-O-MeEGC was excreted in urine within 8 h. The present structural information and concentration-time profile of this metabolite provide the basis for understanding the biotransformation of EGC and for future elucidation of its biological activities.