Cycloartan

More recently (2006) we performed and reported quantitative structure-activity relationship (QSAR) modeling of the same compounds based on their atomic linear indices, for finding fimctions that discriminate between the tyrosinase inhibitor compounds and inactive ones [50]. Discriminant models have been applied and globally good classifications of 93.51 and 92.46% were observed for nonstochastic and stochastic hnear indices best models, respectively, in the training set. The external prediction sets had accuracies of 91.67 and 89.44% [50]. In addition to this, these fitted models have also been employed in the screening of new cycloartane compounds isolated from herbal plants. Good behavior was observed between the theoretical and experimental results. These results provide a tool that can be used in the identification of new tyrosinase inhibitor compounds [50]. 

Cong-Jun Li, Ying-He Li, Pei-Gen X, Tom JM, Watson WH, Krawiec M. An unusual cycloartane triterpenoid from Cimicifuga foetida. Phytochemistry 1996 42 489-494. 

In our study on the chemical constituents of Salvia frigida Boiss., we report here the isolation and identification of two oleanane type (componnd 1, 2) and two cycloartane type triterpenoids (compound 3,4) with the componnds a-amyrin 5 and P-sitoserol 6. The compounds have been characterized by UV/vix, IR, H NMR, NMR and MS spectroscopy. 

Zahid, M. et al.. New cycloartane and flavonol glycosides from Corchorus depressus, Helv. Chim. 

Esterification with a fatty acid or with ferulic acid at C-3 of triterpene alcohols exerted almost no influence on the activity as has been observed with lupane- (264/265) and cycloartane- (66/67, 72/73) type compounds and a C-3 monohydroxy triterpenoid (264/266). However, esterification at C-3 with a fatty acid reduced the inhibitory activity of some dihydroxy triterpenoids (138/139,140 202/203, 204 230/231 232/233, 234). 

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.

Cycloartanes are found in the plants in free states as well as in the glycosidic form. Over than 100 saponins, mainly derivatives of the 20(R),24(S) form of 90, 19 cyclolanost-24-ene-30-ol (cycloastragenol), named astragalosides or astraversianins, and more rarely the 20(S), 24(R) form (cyclogalegenin), named cyclogaleginosides and sieberosides have been so far isolated (Table 3). Some species also contain trihydroxyolean-12-ene saponins (Table 4). 

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. 

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

The hydrolytic studies are usually performed under acidic conditions, the major disadvantage with cycloartane saponins being cyclopropane ring opening and rearrangement. 

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]. 

The full paper on the synthesis of pollinastanol from cycloartanol has been published.21 The revision of stereochemistry at C-4 in the Buxus alkaloids, suggested by 13C chemical shift considerations,22 has been confirmed by X-ray analysis of the derivative (18) of cyclobuxidine F.23 Assignments of the 13C resonances of a series of cycloartanes have been reported.24... 

The natural occurrence of cycloartane triterpenoids has been reviewed.25 Acid hydrolysis of lyofolic acid, a glucoside from the leaves of Lyonia ovalifolia, afforded lyofoligenic acid (19) whose structure was established by X-ray analysis of the 3a-O-p-bromobenzoate methyl ester.26 The constitution of the genuine aglycone, protolyofoligenic acid (20), was confirmed by interrelation with cycloartenol.27... 

Other new cycloartanes include schizandronic acid (21) from the wood of Schiz-andra nigra28 and lithocarpolone (22), lithocarpidol (23), and 24-methylene-cycloartane-3 0,21-diol (24) from Lithocarpus polystachya.29... 

Abrusoside E dimethyl ester (cycloartane triterpene glycosides) Abrus precatorius (Fabaceae) [leal J Sweet... 

---