Dual-tautomerism separation method based on asymmetric transformation: Gram-scale preparation of high-purity punicalagin from pomegranate peel wastes

•A special orthogonal separation method named as DTS was developed.•Only an individual approach was used in the two-step purification of DTS.•Preparation efficiency of DTS was improved by asymmetrical transformation.•Low-temperature injection technique was used to maintain the stability of DTS.•Grams of punicalagin (99.5%) were prepared by DTS from pomegranate peel waste.