Squalene-Hopene Cyclase: Mechanistic Insights into the Polycyclization Cascades of Squalene Analogs Bearing Ethyl and Hydroxymethyl Groups at the C-2 and C-23 Positions
作者:Ikki Kaneko、Yuri Terasawa、Tsutomu Hoshino
DOI:10.1002/chem.201801668
日期:2018.8.1
Squalene‐hopene cyclase (SHC) catalyzes the conversion of squalene 1 into 6,6,6,6,5‐fused pentacyclic hopene 2 and hopanol 3. To elucidate the binding sites for the terminal positions of 1, four analogs, having the larger ethyl (Et) and the hydrophilic CH2OH groups at the 23E or 23Z positions of 1, were incubated with SHC. The analog with the Et group at the 23E position (23E‐Et‐1) yielded two tetra‐ and three pentacyclic
MEDINA, JULIO C.;KYLER, KEITH S., J. AMER. CHEM. SOC., 110,(1988) N 14, 4818-4821
作者:MEDINA, JULIO C.、KYLER, KEITH S.
DOI:——
日期:——
Cyclization cascade of the C33-bisnorheptaprenoid catalyzed by recombinant squalene cyclase
作者:Jun Cheng、Tsutomu Hoshino
DOI:10.1039/b823167b
日期:——
The enzymatic cyclization reaction of polyprenoid C33 by squalene–hopene cyclase (SHC) was investigated with the intention of creating an unnatural hexacyclic compound. The enzymatic products consisted of mono-, bi-, tri-, tetra- and pentacyclic skeletons; however, hexacyclic products were not generated, contrary to our expectations. The absence of a hexacyclic skeleton indicated that the entire carbon chain of C33 polyprene could not be included in the reaction cavity. Formation mechanisms of the products having mono- to pentacycles were discussed. Both chair/chair/boat conformation and chair/chair/chair conformations were formed for a tricycle, and both chair/chair/chair/boat conformation and chair/chair/chair/chair structures were constructed for a tetracycle. The pentacyclic product was created from the chair/chair/chair/chair/boat conformation. Squalene was folded in an all pre-chair conformation inside the reaction cavity to form the hopene skeleton. Therefore, the formation of a boat structure during the polycyclization reaction indicated that the molecule of polyprene C33 was folded improperly due to incorrect arrangement/positioning in the reaction cavity. The creation of the hexacyclic core failed; however, it should be noted that SHC possessed great potential to tolerate the elongated squalene analog C33, thus leading to the creation of novel compounds with C33.