OZONOLYSIS OF PROTECTED IRIDOID GLUCOSIDES

Scutellaria subvelutina was found to be an excellent source of the cat alpol ester scutellarioside I (3) and this was chemically converted in to 5,7-dideoxycynanchoside. The partially protected iridoid glucosides , :4',6'-di-O-isopropylidene-5,7-dideoxycynanchoside (6) and 6,2',3 ', 6'-tetra-O-benzoyl antirrhinoside (10), as well as the fully protected opylidene-2',3',4',6'-tetra-O-acetylantirrhinoside (8a) were subjecte d to ozonolysis with reductive work-up using sodium tetrahydridoborate . Using a large excess of reductant, the reaction mixtures from 6 and 8a were reduced completely to give the respective polysubstituted cycl opentanols, while reduction of the ozonolysis product from 10 could be stopped at the hemiacetal 11 by employing a smaller amount of reducta nt.