Transformation of naturally-occurring 1,9-trans-9,5-cis sweroside to all trans sweroside during acetylation of sweroside aglycone

From the rootstock of Scabiosa columbaria L. loganin and sweroside were iso lated. Sweroside showed moderate antibacterial activity. Pure sweroside was converted to the sweroside aglycone 1-acetoxy derivative (DABCO/Ac2O) afte r hydrolysis of the glucose unit. X-ray crystallography of the monoacetate showed unambiguously that it had been transformed to a new seco-iridoid hav ing the novel trans diaxial configuration for the protons on C-1, C-9 and C -5. The mechanism for the rearrangement is discussed. (C) 2001 Elsevier Sci ence Ltd. All lights reserved.