Osladin structure

Osladin, a steroidal saponin, was isolated as a sweet principle of the fem Polypodium vulgare L. (Polypodiaceae). Later, Nishizawa and Yamada.36 reinvestigated the structure of osladin and revised the stereochemistry at C-22, C-25, and C-26. Although osladin has been reported to be 3000 times sweeter than sucrose, this value was also... 

Three steroidal saponins, polypodosides, were isolated from the rhizomes of Polypodium glycyrrbiza DC. Eaton (Polypodiaceae).37,38 According to the corrected structure of osladin, the structure of polypodoside was also revised.39 Polypodoside A was shown to be highly sweet (600 times sweeter than sucrose). 

The steroidal saponin osladin (58) was isolated as a sweet principle from the fern Polypodium vulgare L. (Polypodiaceae) nearly 40 years ago [20,28]. However, the original structure proposed was later revised because the synthetic compound produced was not sweet at all [87]. The correct structure of osladin (58) was characterized by single crystal X-ray... 

Osladin (62) is a steroidal glycoside that is about 500-times sweeter than sucrose. It was isolated by the Czech chemists Jizba and Herout in 1967 [112] from the rhizomes of European fern Polypodium vulgare known for its very sweet taste. Its structure has been recently revised [113] by total synthesis. During the synthesis it was shown that minute changes in the structure result in total loss of the sweet taste. Thus, this is a t5 ical glycoside whose overall structure - including the glycosidic part - is crucial for the respective activity. 

Steroidal Saponins The fern genus, Polypodium, has so far yielded three sweet steroidal saponins, namely, osladin (45) and polypodosides A and B (46, 47). The first-named of these compounds was structurally determined without full stereochemistry as an isolate of P. 

Osladin (3) (revised structure) HO Qj j (500 limes swcein- than sucrose)... 

Therefore, we found following thing throughout the synthetic study. 1) We achieved the total synthesis of saponin 2 that was found not to be sweet. This suggests that 2 is not the structure of the natural saponin osladin. 2) We isolated natural osladin from the rhizomes of the fern, P. vulgare. A single crystal X-ray diffraction study of natural osladin shows that it is the stereoisomeric compound 3. Furthermore, osladin is only 500 times sweeter than sucrose. 3) A total synthesis of 3 was achieved and thus the sweet principle of this fern was proved to be osladin. ... 

Since the original sample of osladin and spectral data were not available, we isolated the rhizomal sweet principle of P. vulgare from plants collected in the southern part of Germany by Professors Y. Asakawa and H. Becker. Sweet components of the fern were extracted by ethanol. Successive chromatography and recrystallizations afforded pure sweet compound as colorless crystals (0.02% isolated yield). Since the sweet compound has a mp of 202-204 C (lit. 201-203 °C) and a molecular formula C45H74O17 suggested from HRMS (FAB), this is the same compound, osladin, which was isolated by Jizba and Herout. Both and NMR spectra of the natural osladin were not identical with those of synthetic 2. Thus, the structure of real osladin differs from that of 2. 

In the original paper on the structure determination of osladin, Jizbii, Dolejs, Herout, and Sorm, did not mention the intensity of the sweetness. Although osladin has been claimed to be 3000 times sweeter than sucrose by Ftirnsworth, reexamination of sweetness by Ajinomoto Co. suggests it is only 500 times sweeter. ... 

JiZBA, J., L. DolejS, V. Herout, and F. Sorm The Structure of Osladin - The Sweet Principle of the Rhizomes of Polypodium vulgare L. Tetrahedron Letters 1971, 1329. 

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