Enzyme-catalysed formation of β-amyrin from a bicyclic isomer of 2,3-epoxysqualene

Total Synthesis of (+)-seco-C-Oleanane via Stepwise Controlled Radical Cascade Cyclization

“…In contrast to what we expected using radical chemistry, at this point, it should be noted that Van Tamelen et al described the racemic epoxide 16 , which was transformed into dl -δ-amyrin by treatment with stannic chloride–CH 3 NO 2 at 0 °C . In the same sense, the transformation of 16 by a cyclase from Pysum sativum led directly to β-amyrin (Scheme ). These results coincided with recent experimental , and theoretical data in that the carbocationic cyclization of polyprenes led to tricyclic structures without the intermediacy of mono- or bicyclic carbocations.…”

Camelliols A−C, Three Novel Incompletely Cyclized Triterpene Alcohols from Sasanqua Oil (Camellia sasanqua)

“…Sasanqua oil contains β-amyrin (25% of the triterpenes). It is interesting to note that a bicyclic squalene 2,3-oxide, possessing the same ring system (D/E ring) as 1 and 3 , afforded β-amyrin on enzymatic cyclization . Thus, 1 and 3 might be byproducts of the biosynthesis of β-amyrin.…”

Enzymatic cyclization of squalene and oxidosqualene to sterols and triterpenes

“…118 Finally, like lanosterol cyclase, 3-amyrin cyclase cyclized a bicyclic analogue of 2,3-oxidosquaIene 92. 119 In contrast, chemical cyclization of the same bicyclic substrate afforded 5-amyrin and not 3-amyrin.120 Further, corn (Zea mays) embryos cycloartenol cyclase cyclized 2,3-frans-l'-nor-2,3-oxidosqualene (64) (Chart V) to 31-norcycloartenol and 31-norlanosterol with a reduced yield, whereas it did not cyclize 2,3-cis-l'-nor- The first purification of plant OSC activities was achieved using cell suspension cultures of R. japonica which produce olean-12-ene-and urs-12-ene-type triterpenes as well as phytosterols. 23 Three different cyclase activities were present in the microsomal preparation which respectively catalyzed the cyclization of oxidosqualene into cycloartenol, /3-amyrin (olean-12-en-3/3-ol) and a-amyrin (urs-12-en-3/3-ol).…”