Triterpenes Unsaturated compounds

Diverse spectroscopic methods have been employed to characterise triterpenes. Ultraviolet (UV) and infrared (IR) spectroscopy are not very useful techniques in elucidating the structure of triterpenes, but the former gives information about compounds with conjugated double bonds and the latter may provide some information about substituents like the hydroxyl group, ester carbonyl group or a,p-unsaturate carbonyl. Other physical data may be of interest to characterise new compounds, but the use of modem spectroscopic methods of nuclear magnetic resonance (NMR) and mass spectroscopy (MS) are essential for the structural determination. 

Recently, the isolation of five new triterpenes from the Brazilian medicinal plant Maytenus krukovii (local name chuchuhuasi ), used for the treatment of skin cancer, was reported [77]. These triterpenes, named krukovines A-E (104-108), have an a,P-unsaturated ketone system in the C ring and are triterpenoids based on either a 3-oxooleanane or a 3-oxoursane skeletons, Fig. (32). The synthesis of krukovines A and B, has also been described, which not only confirmed the proposed structures for these compounds, but also provides sufficient material for biological activities [197]. 

In connection with the structure study of isodehydropanaxadiol (29) (see Chapter III), Ohsawa etal. 22, 23) earlier discovered a new cyclobro-mination of y,5-unsaturated alcohols under the influence of N-bromosuccinimide in CCI4. Thus (13) afforded stereospecifically the bromo compound (60), which on reduction with zinc in acetic acid at room temperature, regenerated (13). The structure of (60) was elucidated by X-ray analysis. The chirality of c-24 of ocotillol type triterpenes including betulafolienetriol-oxide-I (61) and -II (62) which are constituents of white birch leaves, was established by correlation with (60) as shown in Chart 14 113). Further investigation 111) disposed of a comment by Rao et al. 114) on this correlation. 

Croteau and Ronald (1983) and Coscia (1984) reviewed chromatographic studies on terpinoids. Those authors considered terpinoids as ubiquitous, structurally diverse, lipophilic compounds. Terpinoids exist in various polymeric forms of the unsaturated branch-chain pentane, isoprenol. Terpenes are characterized as hemi-prenes (C5), monoterpenes (Cio), sesquiterpenes (C15). diterpenes (C20), and triterpenes (Cjo)- A representative hemiprene (hemiterpene) is mevalonic acid, a precursor in the biosynthesis of isoprenoids. Monoterpenes contain numerous... 

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