Halohydrins and polyols derived from antirrhinoside: Structural revisions of muralioside and epimuralioside

Treatment of the iridoid glucoside antirrhinoside (1) with pyridinium chlor ide in dimethylformamide gave rise to the two possible trans-halohydrins, l inarioside (4) and isolinarioside (5). Pyridinium bromide gave the two anal ogous bromohydrins. It is shown that the iridoid glucosides 8-epi-muraliosi de from Linaria arcusangeli and 7,8-epi-antirrhinoside from Linaria dalmati ca are both identical with isolinarioside, and therefore, these names are r edundant. The structure of muralioside isolated from Cymbalaria muralis is revised to that of its 8-epimer (8), while the structure, of an isomeric, n ew iridoid glucoside from Paulownia tomentosa has been elucidated to be 7 b eta-hydroxyharpagide (3), the structure originally assigned to 8. In additi on, 7 alpha-hydroxyharpagide (2), the known product from the base-catalyzed hydrolytic opening of 1, has been isolated from Antirrhinum majus and thus shown to be a natural product.