Pensteminoside, an unusual catalpol-type iridoid from Penstemon gentianoides HBK (Plantaginaceae)

The investigation of Penstemon gentianoides, afforded, in addition to plantarenaloside ( 2), globularisicin ( 3), luteolin ( 4), diosmetin ( 5), verbascoside ( 6) and martynoside ( 7); an unusual catalpol-type iridoid, pensteminoside [8- O- trans-cinnamoyl, 6-hydroxy, 1-[ β- D-glucopyranoside-6′- O-((4″-hydroxy)-cinnamoyl)]-catalpol ( 1)]. Its structure was elucidated by spectroscopic analyses, including high field NMR spectroscopy. From the MeOH and ethyl acetate extracts of aerial parts of Penstemon gentianoides HBK (Plantaginaceae) an unusual iridoid of the catalpol-type, was isolated and characterized as pensteminoside: (8- O- trans-cinnamoyl, 6-hydroxy, 1-[ β- D-glucopyranoside-6′- O-((4″-hydroxy)-cinnamoyl)]-catalpol) was isolated, along with the known iridoids: plantarelanoside and globularisicin, the flavone: luteolin and diosmetin, as well the phenylpropanoids, verbascoside and martynoside. Their structures were established by 1D and 2D NMR spectroscopic analyses.