Astragalus cycloartane

The side chain m. Astragalus cycloartane sapogenins and saponins may be of different type (Table 1) side chain with acyclic construction, or with tetrahydrofuranic ring at C-17 (20,24-epoxy cycloartane, the most rapresentative side chain as in cycloastragenol, 18), or with a tetrahydropyranic ring (20,25-epoxy and 16,23-epoxy cycloartane derivatives) and with two condenced epoxy ring (16P,23 16a,24-diepoxycycloartane compounds). All these chains influence the signals of the carbons and protons involved and that of the vicinal atoms [147,219]. 

Table 2. Astragalus species studied for their cycloartane and oleanane saponins... 

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. 

Fig. (3). Tetranor-cycloartane and oleanane triterpenoids isolated from Astragalus sp.

Table 3. Cycloartane saponins found in Astragalus species... 

Astragaloside II, a cycloartane triterpene glycoside isolated from the Egyptian Astragalus spinosus, was tested at minimum of five concentrations 10-fold dilution against a total of 60 human tumor cell lines derived from seven cancer types (lung, colon, melanoma, renal, ovarian, brain and leukemia). The results indicated that the colon cancer (SW-620) and the leukemias (CCRF-CEM, HL-60) were the most sensitive cell lines [98]... 

Cycloartane saponins seemingly contribute to the immunomodulatory properties of Astragalus, in fact, curculigosaponin G from Curculigo orchioides was reported to significantly promote the proliferation of spleen lymphocytes in mice compared to controls, without a marked influence on antibody formation [167]. 

About 130 saponins have been described in Astragalus spp. untill now. Table (2). D-xylose (xyl), D-glucose (g c), L-rhamnose (rha), L-arabinose (ara) represent the carbohydrate components of these glycosides pentoses are more frequent then hexoses. Apiose (apio), in the furanosic form, occurs only in cycloaraloside C, named also astrailienin A [140,61]. Glucuronic acid has been found only in pentacyclic triterpene saponins (as in soyasaponins). Astragalus saponins of cycloartane series... 

Several other activities are reported for Astragalus spp. the cycloartane saponins from A. sieversienus show an hypocholesterolemic action [219], while astramembrannin I, 87, and astrasieversianin I, 92 produce antileukocytopenic and anti-stress effects in mice [319]. Aqueous extract of A. membranaceus root causes significant stimulation of melanocyte proliferation using the sulphorhodamine B (SRB) test. This result supports the use of these extracts in traditional treatments of vitiligo [191]. 

Astragaloside II, a cycloartane triterpene oligoglycoside from Astragalus spinosus afforded close to 100% protection of T lymphocytes in vitro against cytopathic effects of HIV infection. The EC50of c.a. 2.5. 10 5 molar was difficult to achieve in vivo [148]. 

Among cycloartane glycosides from Astragalus Turkish species, only astragaloside I (88) was able to stimulate NF-kB expression in macrophages. This implies that they are critical structural features responsible for macrophage activation by saponins [71]. 

Gan LX, Han XB, Chen YQ (1986a) Astrasieversianins IX, XI and XV, cycloartane derived saponins from Astragalus sieversianus. Phytochemistiy 25(6) 1437-1441... 

Taxonomy Cycloartane Triterpenoids Astragalus dasyanthus Pall. (Leguminosae) [1]. 

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