First Total Synthesis of Two New Diglycosides, Neohancosides A and B, from Cynanchum hancockianum.

Abstract Neohancosides A (1) and B (2) are monoterpene diglycosides isolated from Cynanchum hancockianum , which is a Chinese folk medicine having antitumor activity. First total synthesis of 1 and 2 , (3 R )-linaloyl and (3 R )-8-hydroxylinaloyl 3- O - β -d-xylopyranosyl-(1 → 6)-β-d-glucopyranosides were achieved stereoselectively using fluoride 12b as a glycosyl donor. The asymmetry of C-3 in 1 and 2 was introduced efficiently by separating diasteremers of (3 R ), (3 S )-linaloyl and (3 R ), (3 S )-8-benzoyloxylinaloyl 3- O -2,3,4-tri- O -benzoyl-β-d-glucopyranoside, 19 and 21 and 20 and 22 , respectively. Absolute configurations of 1 and 2 were determined by enzymatic degradation of synthetic intermediates 33 and 34 .