24-Methylene cycloartenol

The sterols (0.6%) are mainly )8-sitosterol, camp-esterol and stigmasterol. The triterpenes (0.04%) include cycloartenol, cycloartanol, 24-methylene-cycloartenol and probably a-amyrin (Fedeli et aL, 1966). 

Fig. 3.44. Gas chromatographic separation of the triterpene alcohol fraction from coberine (A), cocoa butter (B) and cocoa butter +5% coberine (C) (according to Gegiou and Staphylakis, 1985). 7, lanos-terol 2, p-amyrine 3, butyrospermol 4, 24-methylene lanostenol 5, parkeol 6, cycloartenol 7, a-amyrine 8, lup-20(29)-en-3p-ol 9, 24-methylene cycloartenol 10, i// -taraxasterol 11, taraxasterol 12, cyclobranol...

Coumaric acid, para Frju (unriped) Cycloartenol, 24-methylene Fr ° Cycloartenol Fr ... 

As indicated previously, plant sterols are thought to be formed in most cases through cycloartenol which is often converted to 24-methylenecycloartenol, a substance present in grapefruit peel and in many other plants. The methylene carbon is donated by S-adenos-ylmethionine (AdoMet) as shown in Eq. 22-13, which implies a transient intermediate carbocation. Saturation of the side chain and oxidative demethylation similar to that shown in Fig. 22-8175 and introduction of a double bond176 leads to campesterol (Fig. 22-9). 

Obtusifoliol Gramisterol Cycloeucalenol Citrostadienol p-Amyrin a-Amyrin Cycloartenol 24-methylene cycloartanol Cyclobranol... 

A. Other Unaponifiable Compounds Cycloartenol, (3-amyrin, and 24-methylene cycloartanol are the major triterpenols, which constitute less than 1% of WGO. Hydrocarbons are minor components in the WGO unsaponifiable fraction (Table 7). According to Kuksis (42), 50% of the hydrocarbons was squalene and the reminder consisted of n-C29 alkanes. The presence of lutein and cryptoxanthin in WGO were first reported in 1935 and 1940, respectively (43, 44). Recently, Panfili et al. (45), reported that petroleum-ether-extracted WGO contained 25 ppm lutein, 23 ppm zeaxanthin, and 8 ppm (3-carotene. 

Rice bran Total 1055 mg/Kg campesterol (24%) stigmasterol (11%) sitosterol (52%) A -avenasterol (8%) 3 main unknown compounds in addition to obtusifoliol and gramisterol. cycloartenol and 24-methylene-cycloartanol present as y-oryzanoi (see text). 

Triterpenols and sterols are present as free or esterified with fatty acids (oleic acid and linoleic acid as the most relevant). Total content of triterpens is between 100-300 mg/100 g of oil. 24-Methylen-cycloartanol and cycloartenol are dominant. Erythrodiol, uvaol and triterpenic acids (ursolic, oleanolic acids etc) have been described in the imsaponifiable fraction of olive oil. The terpenoid fraction is complex and many constituents are still imdefined. 

Fig. 7. The formation of 24-methylene cycloartanol, cyclolaudenol and cyclosadol by methylation of cycloartenol.

Apart from 24-methylene cycloartanol (2-F) and cyclolaudenol (2-G), which in maize and barley embryos could give rise to 24a- and 24 -methyl sterols respectively, a further primary product of methylation, cyclosadol (2-T) has recently been foimd in maize and barley embryos. Its significance in the major pathway of sterol synthesis is still under investigation, but minor components such as 4-T and 8-T have also been reported in maize. The overall pattern of the type of compounds formed by the first attack of 5-adenosyl methionine on cycloartenol is outlined in Fig. 7. 

The next question is when in the biosynthetic pathway do the two methylations take place. As already indicated, experiments with enzyme preparations demonstrate that cycloartenol is the best substrate for the first methylation. However 24-methylene lophenol (5-F) and not 24-methylene cycloartanol (2-F), is the preferred substrate for the second methylation. This is formed by the pathway indicated in Fig. 8. 24-Methylene cycloartanol (2-F) is demethylated to cycloeucalenol (8-F) which is the substrate for cycloeucalenol obtusifoliol isomerase which opens the 9,19-cyclopropane ring to form obtusifoliol (13-F) demethylation at C-14 and isomerization... 

The isomerase does not act on cycloartenol or 24-methylene cycloartanol which explains the absence of lanosterol (1-A) and 24-methylene lanosterol (1-F) from photosynthetic tissues. 

Dimethylsterols (triterpene alcohols). The main triterpene alcohols present in olive oil are (3-amyrin, butyrospermol, cycloartenol and 24-methylene-cycloartanol (Figure 9.6). This sterol fraction is complex and many constituents are still unidentified. Itoh and his co-workers (1981) used argentation thin layer chromatography and GC-MS to identify minor 4,4-dimethylsterols present in olive oil and olive pomace oil ((3-residue oil). 

Dimethyl sterols (triterpene alcohols) Sample (j-Amyrin A8-Sterol a- Amyrin Cycloartenol A7-Sterol 24-Methylene cycloartanol Others... 

Sample Cycloartanol Cycloartenol 24-Methylene cycloartanol Others ... 

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