Ozonolysis of Protected Iridoid Glucosides

Scutellaria subvelutina was found to be an excellent source of the catalpol ester scutellarioside I (3) and this was chemically converted into 5,7-bisdeoxycynanchoside. The partially protected iridoid glucosides, 8,10:4’,6’-di-O-isopropylidene-5,7-bisdeoxycynanchoside (6) and ,3’,6’-tetra-O-benzoylantirrhinoside (10), as well as the fully protected 5,6-O-isopropylidene-2’,3’,4’,6’-tetra-O-acetylantirrhinoside (8a) were subjected to ozonolysis with reductive work-up using sodium borohydride. Using a large excess of reductant, the reaction mixtures from 6 and 8a were reduced completely to give the respective polysubstituted cyclopentanols, while reduction of the ozonolysis product from 10 could be stopped at the hemiacetal 11 by employing a smaller amount of reductant.