Synthesis and structure revision of intensely sweet saponin, osladin

Abstract

The total synrhesis of compound 10, which is the reported structure of intensely sweet saponm oaladin, has been  completed.However, it is not as sweet as suggested Re-extraction of the sweet principle of rhizomes of the fern Polypodium vulgare (Polypodiaceae) and single crystal X-ray diffraction study revealed its real structure to be 27. We also found it to be only 500 tunes sweeter than sucrose as against 3,000 tones suggested elsewhere. Therefore, the tolal synthesis, of the real osladin was achieved from steroidal aldehyde 20 by using newly developed beta-selective and 2' hydroxyl group-discriminated glucosylation procedure and our original alpha-selective thermal rhamnosylation reaction. Synthetic osladin was also very sweet and thus we prove that osladin is the real sweet principle of the fern.