Saponins structure determination

COSTELLO, C.E., Application of tandem mass spectral approach to structural determination of saponins. In Advances in Experimental Medicine and Biology (G. R. Waller and K. Yamaski, eds.), 405, Plenum Publishing, New York. 1996, pp. 317-329... 

Levy, M., Zehavi, U., Naim, M., Polacheck, I. Isolation, structure determination, synthesis, and anti-fungal activity of a new native alfalfa-root saponin. Carbohydr Res 1989 193 115-123. 

Structure determination of sapogenins and saponins from genus Astragalus originally involves a combination of chromatographic, chemical and spectral methods nuclear magnetic resonance spectroscopy (NMR) with chemical transformation and enzymatic degradation, as well as MS (mass spectroscopy). 

Determination of the structure of the isolated pure saponins is usually approached by a combination of chemical and spectroscopic methods. However, the quantities of pure saponins isolated are often small (sometimes only a few milligrams) and there is always a need for highly sensitive, high-resolution and, if possible, non-degradative methods in order to aid the structural determination of a saponin. 

For smaller quantities of compounds more sensitive inverse detected techniques are available, such as HMQC ( IH-I C one bond correlation via heteronuclear multiple quantum coherence, analogous to HETCOR) and HMBC (proton detected heteronuclear multiple bond correlation spectroscopy) (15). The last provide, in addition to the intraresidue multiple bond correlations, interresidue correlations between the anomeric carbon and the aglycone protons.We follow this general strategy for the structural determination of tri terpenoid saponins of Bupleurum fruticosum (16) andArdisia japonica (9). 

The interesting biological properties shown by many saponins, coupled with improvements in spectroscopic methods of structure determination have led to the increased study of this class of compound. The following papers deal with saponins and prosapogenins which are based on known triterpenoids of the following groups dammarane-euphane,158 lupane,159 oleanane,160 and ursane.161... 

R76 N. P. Sahu and B. Achari, Advances in Structural Determination of Saponins and Terpenoid Glycosides , p. 315 R77 M. Liu and J. C. Lindon, Recent Advances in Editing and Selective Detection Methods for NMR Spectroscopy , p. 351... 

Structure determinations of the homogeneous saponins are usually carried out by a combination of chemical and spectroscopic methods. Extensive investigations of the aglycones demonstrated that most of them are spirostane derivatives or modified spirostanes. Furostanol glycosides have also been isolated and characterized, which according to Marker and Lopez (41) are precursors of sugar conjugates of spirostanes. 

Sahu NP, Achari B (2001) Advances in Structural Determination of Saponins and Terpenoid Glycosides. Curr Org Chem 5 315... 

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. 

FULL STRUCTURAL DETERMINATION OF SAPONINS. THE CLASSICAL METHOD... 

The structure determination of saponin components of Quillaja saponaria has been thoroughly reviewed [18]. The process of chemical degradation coupled with structure determination is outlined in Fig. 4. The combination of these chemical and spectroscopic methods has led to determination of the variety of structures discussed in this review. 

Among the active extracts, D. zingiberensis was selected for further study. Bioassay-guided fractionation has led to the isolation and structure determination of two steroidal saponins DZ (gracillin), Diosgenin-3-0- [a-L-Rhamnopyranosyl-(l- 2)] -O- [p-D-glucopyranolyl-(I —... 

Fig. 6. ES MS" spectra of the pentaglycosylated saponin 4 from the fruit methanolic extract of P. dodecandra (Phytotaccaceae). Sample (1 mg/ml) injected by a syringe pump (5pl/min) (infusion experiment). For LC/MS conditions, see experimental. This experiment allowed a sequential fragmentation of the saponin sugar chain (cleavage of only one sugar at each MS/MS step), clarifying the structural determination.

The structures of these saponins were determined through spectroscopic studies permethylation followed by hydrolysis as well as isolation of the genuine sapogenin through Smith degradation. 

Since 1958, Shibata and his successors have conducted chemical studies on the saponins of the crude drug. After many twists and turns, it was determined that the major saponins of Ginseng were not oleanane oligoglycosides which are very common in nature, but that the genuine sapogenins were represented by triterpenes of the dammarane type. This was the first example of the occurrence of dammarane saponins in nature. The complications encountered in the isolation and structure determination were mainly due to an unexpected acid catalyzed epimerization of the tertiary hydroxyl group on c-20 of the carbon skeleton which was followed by cyclization of the side chain. This undesirable reaction accompanied acid hydrolysis of the saponins to the sapogenins. 

Although TLC indicated the presence of a minor saponin named ginsenoside-Ra, little effort was devoted to its isolation and structure determination prior to 1981. Besso etal. showed that the minor saponin actually was a mixture of three saponins by means of reverse phase TLC on octadecyldimethylsilyl silica gel (52). Reverse phase column chromatography of Ra permitted separation into three saponins in 0.03%, 0.02% and 0.005% yield which were named ginsenosides-Rai, Ra2 and Ra3. 

Triterpenoid Saponins Phenolic Compounds Recent Methods of Structure Determination of Prenylated Phenols Biological Activities of Phenolic Constituents of Glycyrrhiza Species... 

Zou, K., Y.-Y Zhao, and R.-Y. Zhang Structure Determination of Two Saponins from Glycyrrhiza inflata Bat. Yaoxue Xuebao (Acta Pharm. Sinica, China), 29, 393 (1994) Chem. Abstr., 121, 251348f (1994). 

Hamburger M, Slacanin 1, Hostettmann K et al (1992) Acetylated saponins in mollusciddtd activity from Sapindus rarak unambiguous structure determination by proton nuclear magnetic resonance and quantitative analysis. Phytochem Anal 3 231-237 Hart KJ, Yanez-Ruiz DR, Duval SM et al (2008) Plant extracts to manipulate rumen fermentation. Anim Feed Sci Technol 147 8-35... 

In 2006, Milosavljevic and co-workers64 reported a study of the complete 4H and 13C NMR assignment of a new triterpenoid saponin, leucantho-side-A (13), from Cephalaria leucantha L. In the course of determining the structure and assigning the spectra, the authors made extensive use of the normal ensemble of 2D NMR experiments in use for the characterization of natural product structures HSQC, HMBC, DQF-COSY, TOCSY, and NOESY. The authors supplemented the aforementioned list of experiments with 2D /-resolved, DINE-(Double INEPT-Edited)-HSQC, and INADEQUATE spectra. The authors made no mention of the use of the connectivity information derived from the 1,1-ADEQUATE spectrum in the assembly of the triterpene nucleus of the molecule but reported extensive tabulations of the 1,1-ADEQUATE correlations that were used to sequence and assign the saccharide resonances of the tri- and di-saccharide sub-units, 14 and 15, respectively, linked to the triterpene nucleus. 

---