Oleanane, structure

The pentacyclic component at m/e 412 resembles the spectrum of oleanane (structure shown) or gammacerane. It is also similar to that of lupane (13, 15) but lacks the M-43 (369) fragment indicative of any isopropyl sidechain. Therefore, ring E is probably 6-member-ed, not 5-membered as in lupane or the hopanes. Although the mass spectrum is a slightly better match to gammacerane, the short GC retention time probably rules out gammacerane but not oleanane (13). 

Canonica, L., Russo, G, and A. Bonati Triterpenes of Glycyrrhiza glabra. 1. Two New Lactones with an Oleanane Structure. Gazz. Chim. Ital., 96, 772 (1966). 

Fig. 12 Structures of oleanane glycosides from chrysomelid beetles...

Ginsenosides with a few exceptions share a similar basic structure, consisting of a saturated 1,2-cyclopentanoperhydrophenanthrene (sterane or gonane) steroid nucleus. They are classified into two groups by the skeleton of aglycones, namely dammarane-type and oleanane-type. Ginsenosides... 

Smith GW, Fowell DT, Melsom BG, Grystal structure of 18a(H)-oleanane, Nature 228 355-356, 1970. 

The distribution and structural elucidation of saponins have been reviewed. Glucuronides with a free carboxy-group and carbohydrate residues at C-2 and C-4 are readily cleaved with acetic anhydride in refluxing pyridine to give the genuine aglycone (see Vol. 7, p. 145). Details of the mass spectra of a series of permethylated oleanane saponins have been discussed. 

Phytochemical studies of these species led to the isolation and structural characterization, by NMR and MS analysis, of many secondary metabolites, mainly flavonoids, and expecially flavonol glycosides, clerodane diterpenes, and triterpenes having the lupane, ursane, and oleanane skeletons. Particularly flavonoids and their glycosides have a chemotaxonomic interest in the genus and in general in the Chrysobalanaceae family. 

Astragalus genus is one of the richest source of cycloartane saponins. Oleanane type saponins are also found in Astragalus sp., but their occurrence is limited to structures common to Leguminosae. Fig (3) shows the naturally occurring cycloartanes and oleananes which have been isolated from different Astragalus species. 

Oleanane and cycloartane saponins can be isolated and structurally elucidated using similar techniques. A single chromatographic step is rarely sufficient to isolate a pure saponin from an extract. As a general rule, several preparative techniques are required to obtain the pure product. 

The structure of 27-(3,4-dihydroxycinnamoyloxy)oleanolic acid (101), from the root bark of Melianthus comosus, was confirmed by X-ray analysis of the related bromolactone diacetate.76 Cadambagenic acid (102) from the stem bark of Anthocephalus cadamba is a derivative of 18aH-oleanane.77 2a,3a,23-Trihydroxyolean-12-en-28-oic acid (103) and 2-hydroxy-3-oxo-24-noroleana-l,4,12-trien-28-oic acid (104) have been isolated from the fruit of Pseudopanax... 

The two different C31H54 pentacycles (m/e 426), one observed in BB2 extract and one in POWl extract had no M-29, M-43 or M-57 fragments. The m/e 205 was small, ruling out structures like lupan-3-one (16). Other differences also eliminate friedelan-3-one and oleanan-3-one type of structure ( 16). 

Arjungenin (107) from Terminalia arjuna is the C-19 epimer of tomentosic acid/ A new nortriterpenoid, norarjunolic acid (108), has been isolated from Akebia quinata where it occurs with arjunolic acid. The structure of the ketol (109), from the stems of Castanopsis lamontii, was confirmed by its partial synthesis from 14a,15a-epoxytaraxeran-3-one (110). Other new oleananes include phytolac-... 

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... 

The crystal structures of the triclinic and orthorhombic forms of 18aH-oleanane (147), from Nigerian crude petroleum, have been reported. Other crystal structures include meristropic acid methyl ester (148), hederagenin (149) from... 

Triptohypol F (18) showed the presence of one double bond, two methine carbons attached to an oxygen function and one methoxy group, according to the 13C NMR spectrum. From these data and its H NMR and MS spectra, it was assumed to be an oleanane-type triterpene. The location of the double bond and the hydroxyl and methoxy groups were determined by a HMBC experiment. The stereochemistry of the hydroxyl and methoxy groups were determined by a NOESY spectrum. According to these data the structure of (18) was established as showed above. 

The root of the Bupleurum species has been used in China as a traditional remedy for inflammatory diseases [20]. The main constituents of this drug are oligoglycosides of oleanane triterpenes called saikosaponin a-f. Saikosaponins cause a reduction in histamine secretion and enhance the anti-inflammatory actions of glucocorticoids [22]. Some of them have been shown to inhibit prostaglandin E2 production in the macrophage culture system [23]. It has recently been reported that the saikosaponins present in Heteromorpha trifoliata, which are structurally related to those of Bupleurum falcatum (saiko in Japanese), have anti-inflammatory activity. One in vivo study concluded that the isolated saikosaponins act by a mechanism close to that of steroids, but do not involve the glucocorticoid receptor [24]. 

The main kind of anti-inflammatory triterpenes isolated have oleanane, ursane, taraxastane, lupane and lanostane skeletons (Table 1). Some minor compounds such as hopane are included in other structural groups. Other anti-inflammatory triterpenes like the different cucurbitacins are not included in this review because of their high toxicity. 

Oleanane triterpenoids are the largest group within the triterpenes and encompass a huge number of active compounds. They are structurally classified as olean-12-ene (Table 2) and ll-keto-olean-12-ene (Table 3), directly derived from the oleanane skeleton. Other modifications give rise to the D C-friedooleananes (Table 4), friedelanes (D A-friedooleananes), 24-nor-D A-friedooleananes (Table 5) and 24,30-dinor-D A-friedooleananes (Table 6). The oleananes include glycyrrhetinic acid, probably the most widely studied triterpene. 

Since the initial reports of sweetness-inhibitory oleanane-type gymnemic acids from the leaves of Gymnema sylvestre, plant species of the family Asclepiadaceae have served as bountiful sources of sweetness-inhibitory compounds. The initial isolation and structural characterization of these compounds was very challenging, and these early investigations have been reviewed [19]. In 1989, gymnemic acids I-VI (90-95) were isolated with a common gymnemagenin (149) aglycone structure and a... 

Furthermore, from the knots of Wistaria brachybotrys, several kinds of oleanane type saponins (101 - 108) were isolated together with isoflavonoids. Of these saponins, wistariasaponins A, Bl, B2, C, D and G were found to be novel saponins, and their structures of sapogenols were elucidated by the long-range COSY spectra and difference NOE... 

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