Identification of new diketopiperazines in roasted coffee

This paper reports on the identification of new diketopiperazines (DKPs) in roasted coffee. The roasted coffee was extracted with hot water and CHCl3 to achieve both a cleanup and a concentration of the DKPs. To get rid of the huge caffeine peak in both HPLC and GC analysis. this extract was cleaned up again by ion-exchange chromatography on Dowex 50x8 followed by gel chromatography on Sephadex G10. The identification was accomplished by HPLC-ESI-MS, HPLC-ESI-MS/MS, GC-EI-MS and by comparison with synthesised reference compounds. In roasted coffee the following DKPs were identified: cyclo(pro-gly), cyclo(pro-ala), cyclo(phe-val), cyclo(phe-leu), and cyclo(phe-ile). Except for cyclo(pro-gly), where only one isomer can be formed. each DKP was present in both possible isomeric forms.