Structure Elucidation of Purpurinidin from Salix purpurea Reveals an Undescribed Class of Pyranoanthocyanins─the Salicinocyanins

Plants from the family Salicaceae have been used as health-promoting products for more than 3,500 years. They contain various secondary metabolites such as anthocyanins and phenolic glycosides (salicinoids) derived from salicin, a prodrug of salicylic acid, one of the most commonly used drugs today. Anthocyanins, which are primarily found in berries and certain vegetables, are recognized for their wide range of health benefits. Although salicinoids are well-known, knowledge regarding the occurrence of anthocyanins in this plant family is limited. In the early 1970s, Bridle et al. discovered an unknown anthocyanin in the bark of Salix purpurea, which was named purpurinidin. As far as we know, however, the structure of purpurinidin has not been elucidated to date. In this work, we present the isolation and structure elucidation of compound 1 that we suspect to be the aforementioned purpurinidin, which reveals the existence of new group of anthocyanin- and salicinoid-derived pyranoanthocyanin-type compounds. We have named this new type of pyranoanthocyanins "salicinocyanins" to emphasize their chemical origins.