Panthogenins A and B,two novel norergostanol steroids from Dioscorea panthaica

Two novel 27-norergostanol steroids,panthogenins A(1) and B(2),possessing unusual rings E and F featuring a ketal moiety at C-25 were isolated from rhizomes of Dioscorea panthaica.Their structures and relative configurations were elucidated by extensive spectroscopic methods including 1D and 2D NMR techniques,and the structure of panthogenin A was further confirmed by X-ray crystallography.Both compounds showed potent in vitro insulin sensitizing activity.