Amyrin conditions

Stereoselective l.4-reduction oi the 1.3-butadiene system to olefin 57 lakes place tinder the conditions of the Birch reduction. Intramolecular protonation of the intermediate carbanion at the 18-position to give 57 occurs with high selectivity syn to the hydroxymethy-iene group Conversion into phosphoric acid derivative 58 and cleavage of the phosphoric acid amide group under (he conditions of the Bcnkeser reduction provides compound 5921 Fluonde ion causes the release of free p-amyrin (1) in a final step I Li, NH3(iyTllF (1/1.75), -78 C 93%. 

The production of pro-inflammatory substances is an important step during chronic painful inflammatory diseases and its inhibition is a target of novel analgesics. The resin of Protium kleinii is used in folk medicine for inflammatory skin conditions. Its effects seem to be mediated by several pentacyclic triterpenes such as amyrin and brein [92], The topical and systemic administration of the extract of P. kleinii and some of its triterpenes has antinociceptive and anti-inflammatory actions, accompanied by reduced neutrophil infiltration and cytokine... 

The three fernene isomers (409, 413, and 414), all of which are natural triterpenes, and various functionalized variants thereof, suffer rearrangement in the retro-biogenetic direction to -neohopene (412) (501, 504—506). Evidently A -fernene (413) is relatively resistant to the acidic conditions since mixtures of (412) and (413) are often obtained. Both A -and A -fernene (414 and 409) are converted to the A -isomer under relatively mild conditions. The apparent ease of migration of the double bond into the A position in this series contrasts with the rapid rearrangement of multiflorenyl acetate (372-OAc) to P-amyrin acetate (352, R = OAc) mentioned in the preceding section. 

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