Isolation of a new disaccharide nucleoside from Helleborus caucasicus: structure elucidation and total synthesis of hellecaucaside A and its β-anomer

•A new disaccharide nucleoside was isolated from Helleborus caucasicus.•The structure of hellecaucaside A was determined by 1D/2D NMR, IR, and HRMS.•The stereoselective synthesis of hellecaucaside A and its β-anomer was achieved in good overall yields.•The synthesis of hellecaucaside A paves the way for the preparation of disaccharide nucleosides modified at C-5′.

Hellecaucaside A, a new disaccharide nucleoside featuring a 2′-O-α-d-ribofuranosyluridine skeleton and a 4-hydroxybenzoyl group at the 5′ position, was isolated from the underground part of Helleborus caucasicus. The structure of the compound was elucidated by means of chemical degradation and spectroscopic analyses, such as 1D/2D NMR, chiral-GC, and HRMS. The total synthesis of hellecaucaside A and its β-anomer was accomplished, unequivocally confirming the structure of the natural product.

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