365456-22-0Relevant articles and documents
Squalene-Hopene Cyclase: On the Polycyclization Reactions of Squalene Analogues Bearing Ethyl Groups at Positions C-6, C-10, C-15, and C-19
Takahashi, Kazunari,Sasaki, Yusuke,Hoshino, Tsutomu
, p. 1477 - 1490 (2018)
Squalene-hopene cyclase (SHC) has been found to convert acyclic squalene into 6,6,6,6,5-fused pentacyclic triterpenes hopene and hopanol. The enzymatic reactions of squalene analogues bearing ethyl groups in lieu of methyl groups at positions C-6, C-10, C-15, and C-19 have been examined to investigate whether the larger ethyl substituents (a C1 unit increment) are accepted as substrates and to investigate how these substitutions affect polycyclization cascades. Analogue 6-ethylsqualene 19a did not cyclize, which indicates that substitution with the bulky group at C-6 completely inhibited the polycyclization reaction. In contrast, 19-ethylsqualene 19b afforded a wide spectrum of cyclization products, including mono-, bi-, tetra-, and pentacyclic products in a ratio of 6:6:1:2. The production of tetra- and pentacyclic scaffolds suggests that the reaction cavity for D-ring formation site is somewhat loosely packed and can accept the 19-ethyl group, and that a robust hydrophobic interaction exists between the 19-ethyl group and the binding site. In contrast to 19b, 10-ethylsqualene 20a and 15-ethylsqualene 20b afforded mainly mono- and bicyclic products, that is, the polycyclization cascade terminated prematurely at the bicyclic reaction stage. Therefore, the catalytic domains for the 10- and 15-methyl binding sites are tightly packed and cannot fully accommodate the Et substituents. The cyclization pathways followed by the ethyl-substituted substrates in the presence of SHC and lanosterol and β-amyrin synthases are compared.
Squalene-hopene cyclase: Insight into the role of the methyl group on the squalene backbone upon the polycyclization cascade. Enzymatic cyclization products of squalene analogs lacking a 26-methyl group and possessing a methyl group at C(7) or C(11)
Nakano, Shin-Ichi,Ohashi, Shumi,Hoshino, Tsutomu
, p. 2012 - 2022 (2007/10/03)
To provide deep insight into the polycyclization reaction of squalene, some analogs were synthesized and incubated with the cell-free homogenates of the recombinant Escherichia coli encoding the wild-type squalene cyclase. The presence of C(6)-Me leads to an efficient polycyclization cascade. Substitution of the C(14)-H and the C(18)-H with a methyl group halted the polycylization reaction at the tricyclic ring stage having a 6/6/6-fused ring system and the tetracycle with a 6/6/6/6-fused ring, respectively, both of which were produced according to a Markovnikov closure. Replacement of the C(7)-H and the C(11)-H with a methyl group led to no cyclization. These results, in conjunction with our previous reports, indicated that the methyl positions are important for bringing to completion of the normal polycylization reaction and further demonstrated that the precise steric bulk size at the methyl positions of squalene is critical to the correct folding and the strong binding of the substrate to the squalene cyclase.
New cyclization mechanism for squalene: A ring-expansion step for the five-membered C-ring intermediate in hopene biosynthesis
Hoshino, Tsutomu,Kouda, Masanori,Abe, Takamasa,Ohashi, Shumi
, p. 2038 - 2041 (2007/10/03)
Three triterpenes having the 6/6/5-fused tri- and 6/6/6/5-fused tetracyclic skeletons were isolated from an incubation mixture of the mutated F601A enzyme, these products being in accordance with a Markovnikov closure. Successful trapping of the tricyclic
