Triterpene glycosides, pentacyclic

The resistance of oats Avena sativa, Poaceae) to the take-all fungus Ophiobolus graminis is due to a fluorescent wot tip glycoside. This resistance factor, avenacin, has proven to be a mixture of four pentacyclic triterpene glycosides (5-8). Compounds (5 and 7), which possess anthranilic acid residues as a part of the molecule, have the greatest fungicidal properties (Fig. 24.3) (Harbome, 1986). 

The msyority of natural triterpenes are pentacyclic compounds. The next largest group are the tetracyclic triterpenes. There is also a smaller number of triterpenes with various other cyclic structures. The only important acyclic triterpene is squalene (and its 2,3-oxide as a metabolic intermediate). Most triterpenes are alcohols (3-OH). They are found free and as glycosides (saponins) (Karrer, 1958 Robinson, 1975) or esters. Free triterpenes are often components of resins, latex, or cuticle. Saponins are powerful surface-active agents and can cause lysis of red blood cells. Some of them have been... 

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... 

C30H52, Mr 412.74, 18a-0. mp. 210°C, [aJo +40.3° (CHCI3), a pentacyclic triterpene hydrocarbon occurring in crude oil. O. represents the saturated skeleton of /3- amyrin. Numerous related triterpenes are derived from O. e.g., the hydrocarbons II,l3(l8)-olea-nadiene, (C30H48O, Mr 424.71, mp. 226-227°C), 12-oleanene (C30H50, Mr 410.73, mp. 162-164°C), and 18-oleanene (mp. 174-175 °C) from polypody species (Polypodium), as well as various polyols (see table) that are widely distributed as glycosides ( sap-onins). 

---