Secoiridoids and xanthones in the genus Centaurium

Two new acyl secoiridoid glucosides, named decentapicrins A and B, accumulating in the fruits of Centaurium littorale Gilmour spp. littorale, have been isolated by means of preparative column chromatography. Another new compound, named decentapicrin C, could also be detected but in minute amounts and was prepared from decentapicrin B. The close interrelation between these three compounds and the strongly bitter centapicrin (Ia) and desacetylcentapicrin (Ib), accumulating in the fruits of Centaurium erythraea R AFN. [1, 2], have been demonstrated by means of TLC analysis of the products obtained under alkaline treatment. Under these conditions not only hydrolysis, but also acyl migrations, took place. Decentapicrin A is partly converted into desacetylcentapicrin (Ib) and decentapicrin C; decentapicrin B is converted into decentapicrin C. On the basis of this chemical information and spectroscopical data ( (1)H-NMR, (13)C-NMR, UV and IR) the structures of decentapicrins A, B and C are postulated to be Ic, Id and Ie respectively. The single acylation at C (3)-OH and C (4)-OH of the glucose moiety as shown in the structures of decentapicrins A and B is new in iridoid chemistry. Unlike centapicrin (Ia) and desacetylcentapicrin (Ib) the new compounds decentapicrins A, B and C are only weak bitter principles like sweroside (I).