54339-68-3Relevant articles and documents
Isomerization, but not oxidation, is suppressed by a single point mutation, E361Q, in the reaction catalyzed by cholesterol oxidase
Sampson, Nicole S.,Kass, Ignatius J.
, p. 855 - 862 (1997)
The putative active site base of cholesterol oxidase from Streptomyces has been removed by site-directed mutagenesis and the mutant enzyme characterized. When glutamate-361 is mutated to a glutamine, the isomerization chemistry catalyzed by cholesterol oxidase is suppressed and the intermediate cholest-5-ene-3-one is isolated. The specific activity for oxidation is 20-fold slower than the wild-type reaction, though the specific activity for isomerization is 10000-fold slower. Furthermore, incubation of cholest-5-ene-3-one with the E361Q cholesterol oxidase resulted in the production of cholest-4-ene-6β-hydroperoxy-3-one (6%), cholest-4-ene-3,6-dione (32%), cholest-4-ene-6β-ol-3-one (36%), and cholest-4-ene-6α-hydroperoxy-3-one/cholest-4-ene-6α-ol-3-one (13%), in addition to cholest-4-ene-3-one (13%). Measurement of reaction stoichiometry eliminated the possibility that H2O2 or the C4a-hydroperoxy flavin was the oxygenation agent. It is proposed that cholest-4-ene-6-hydroperoxy-3-one is the product of radical chain autoxidation and that cholest-4-ene-3,6-dione and cholest-4-ene-6-ol-3-one are decomposition products of the hydroperoxy steroid radical. The characterization of the E361Q mutant chemistry has illuminated the importance of intermediate sequestration in enzyme catalysis. The mutant enzyme will be used to obtain information about the structure of the enzyme in the presence of the reaction intermediate. Moreover, the altered activity of E361Q cholesterol oxidase will facilitate its application in studies of cell membranes.
P -TsOH-Catalyzed one-pot transformation of di- and trihydroxy steroids towards diverse A/B-ring oxo-functionalization
Sarkar, Antara,Das, Jayanta,Ghosh, Pranab
, p. 9051 - 9060 (2017/08/29)
A solid support-mediated p-TsOH-catalyzed milder transformative protocol was developed to furnish diverse ring-A and/or ring-B oxo-functionalized steroids. To furnish interesting isomers involving the A/B-ring of biomolecules in a one-pot approach, only solid supports (and not solution!) were found to be effective. p-TsOH/SiO2-oxidation of 4β-hydroxycholesterol, the major oxysterol in human circulation, into a mixture of cholest-4-en-3-one, cholest-4-ene-3,6-dione, and 5α-cholestane-3,6-dione was the starting point for the investigations herein. The reaction protocol was optimized in detail, and efforts were carried out toward gaining an understanding of the mechanistic aspects favoring the solid support, and a possible synergetic catalytic system involving p-TsOH and SiO2 was expected to be a key part. Application of the novel methodology to 4β,7α-dihydroxy steroids resulted in the desired diverse ketosteroids through oxidation/oxidative dehydration, which generalized the process as a facile multi-oxo-functionalization steroidal transformation.
Stereospecific oxidation of 3β-hydroxysteroids by persolvent fermentation with Pseudomonas sp. ST-200
Aono, Rikizo,Doukyu, Noriyuki
, p. 1146 - 1151 (2007/10/03)
Pseudomonas sp. strain ST-200 isolated from a humus soil effectively oxidizes cholesterol dissolved in organic solvents but not that suspended in the growth medium. The organism does not assimilate cholesterol. This organism oxidized a variety of 5α- or 5-ene-steroids dissolved in organic solvent. First, the 3β-OH group was oxidized to a ketone group. The 3α-OH group was scarcely oxidized. Successively, C-6 position of 5-ene-steroids was hydroxylated, and a double bond of 5-ene-steroids was transferred from Δ5 to Δ4. Then, the 6-OH group was oxidized to a ketone group. Persolvent fermentation with ST-200 would provide an effective, convenient, and stereospecific method to oxidize the C-3 and C-6 positions of steroids.
