Alkannin and shikonin (A/S) derivatives possessing a wide spectrum of biological activities have been found in roots of several Boraginaceous species [1,2]. As reviewed in [3], determination of monomeric A/S derivatives in commercial samples, root extracts and tissue cultures by HPLC has been described previously. Although the presence of oligomeric A/S derivatives has been confirmed by size exclusion chromatography, their analysis by HPLC has not been reported. Therefore, in the present study a rapid and simple HPLC-DAD-APCI-MS method was developed to detect and determine monomeric and oligomeric alkannins/shikonins simultaneously for the first time. Commercial samples of alkannin and shikonin were analyzed for the respective compounds and the structures of the oligomeric derivatives were identified based on their MS-spectra.
Under the experimental conditions applied monomeric A/S was detected at a retention time (r.t.) of 12.7min in the LC-MS chromatogram (with a molecular ion of m/z 288), while two other major peaks were observed at r.t. 20.3 and 20.6min, each of them showing a molecular ion at m/z 558 representing A/S dimers. In smaller proportions, three additional A/S dimers with m/z 574 (r.t. 17.8, 18.0, 18.1min) and four trimers (m/z 828; r.t 24.9–25.4min) were detected. The molecular ion at m/z 558 is in absolute accordance with the dimeric structure proposed recently by our group [4], representing the main dimeric component in the alkannin commercial sample. The proposed structures of the other oligomers detected will be discussed.
References: [1] Papageorgiou, V.P., Assimopoulou, A.N. et al. (1999) Angewandte Chemie, Int. Edition, 38(3): 270–301. [2] Papageorgiou V.P., Assimopoulou, A.N. et al. (2006) Current Organic Chemistry, 10(16): 2123–2142. [3] Papageorgiou V.P., Assimopoulou, A.N. et al. (2006) Current Organic Chemistry, 10(5): 583–622. [4] Spyros A., Assimopoulou, A.N. et al. (2005) Biomedical Chromatography, 19: 498–505.
