516-86-9Relevant articles and documents
Effect of substrate features and mutagenesis of active site tyrosine residues on the reaction course catalysed by Trypanosoma brucei sterol C-24-methyltransferase
Liu, Jialin,Ganapathy, Kulothungan,Wywial, Ewa,Bujnicki, Janusz M.,Nwogwugwu, Chizaram A.,Nes, W. David
experimental part, p. 413 - 422 (2012/08/07)
TbSMT [Trypanosoma brucei 24-SMT (sterol C-24- methyltransferase)] synthesizes an unconventional 24-alkyl sterol product set consisting of Δ24(25)-, Δ24(28)- and Δ 25(27)-olefins. The C-methylation reaction requires Si(β)-face C-24-methyl addition coupled to reversible migration of positive charge from C-24 to C-25. The hydride shifts responsible for charge migration in formation of multiple ergostane olefin isomers catalysed by TbSMT were examined by incubation of a series of sterol acceptors paired with AdoMet (S-adenosyl- L-methionine). Results obtained with zymosterol compared with the corresponding 24-2H and 27-13C derivatives revealed isotopic-sensitive branching in the hydride transfer reaction on the path to form a 24-methyl-Δ24(25)-olefin product (kinetic isotope effect, kH/kD =1.20), and stereospecific CH3→ CH2 elimination at the C28 branch and C27 cis-terminal methyl to form Δ24(28)and Δ25(27) products respectively. Cholesta-5,7,22,24-tetraenol converted into ergosta-5,7,22,24(28)-tetraenol and 24β-hydroxy ergosta-5,7,23-trienol (new compound), whereas ergosta-5,24-dienol converted into 24-dimethyl ergosta-5,25(27)-dienol and cholesta-5,7,24-trienol converted into ergosta-5,7,25(27)-trienol, ergosta-5,7,24(28)-trienol, ergosta-5,7,24-trienol and 24 dimethyl ergosta-5,7,25(27)-trienol. We made use of our prior research and molecular modelling of 24-SMT to identify contact amino acids that might affect catalysis. Conserved tyrosine residues at positions 66, 177 and 208 in TbSMT were replaced with phenylalanine residues. The substitutions generated variable loss of activity during the course of the first C-1-transfer reaction, which differs from the corresponding Erg6p mutants that afforded a gain in C-2-transfer activity. The results show that differences exist among 24-SMTs in control of C-1- and C-2-transfer activities by interactions of intermediate and aromatic residues in the activated complex and provide an opportunity for rational drug design of a parasite enzyme not synthesized by the human host. The Authors Journal compilation
Synthesis of zymosterol, fecosterol, and related biosynthetic sterol intermediates
Dolle,Schmidt,Erhard,Kruse
, p. 278 - 284 (2007/10/02)
The first syntheses of sterol biosynthetic intermediates zymosterol(4), 4,4-dimethylzymosterol(5), cholesta-8,14,24-trien-3β-ol(6), the 4,4-dimethyl analogue 7, and fecosterol (8) are described in detail. Multigram quantities of key intermediates 16 and 17 were efficiently prepared from known enones 20 and 21 (eight steps, 35% overall yield). Novel entry into Δ8-sterols was achieved through regiospecific hydroboration/deoxygenation of the 8,14-diene systems. Sterols containing Δ24- or Δ(24(28))-olefins were obtained from C24-hydroxy intermediates either via dehydration using bis[α,α-bis(trifluoromethyl)benzenemethanolato]diphenylsulfur in CH2Cl2 or via Swern oxidation/Wittig olefination, respectively. In this way, 16 and 17 were converted to the desired Δ8,24-, Δ8,14,24-, and Δ(8,24(28))-sterols with high regiocontrol.
