14031-37-9Relevant academic research and scientific papers
Isomeric product detection in the heterogeneous reaction of hydroxyl radicals with aerosol composed of branched and linear unsaturated organic molecules
Nah, Theodora,Zhang, Haofei,Worton, David R.,Ruehl, Christopher R.,Kirk, Benjamin B.,Goldstein, Allen H.,Leone, Stephen R.,Wilson, Kevin R.
, p. 11555 - 11571 (2015/02/19)
(Figure Presented) The influence of molecular structure (branched vs linear) on product formation in the heterogeneous oxidation of unsaturated organic aerosol is investigated. Particle phase product isomers formed from the reaction of squalene (C30H50, a branched alkene with six C=C double bonds) and linolenic acid (C18H30O2, a linear carboxylic acid with three C=C double bonds) with OH radicals are identified and quantified using two-dimensional gas chromatography-mass spectrometry. The reactions are measured at low and high [O2] (～1% vs 10% [O2]) to understand the roles of hydroxyalkyl and hydroxyperoxy radical intermediates in product formation. A key reaction step is OH addition to a C=C double bond to form a hydroxyalkyl radical. In addition, allylic alkyl radicals, formed from H atom abstraction reactions by hydroxyalkyl or OH radicals play important roles in the chemistry of product formation. Functionalization products dominate the squalene reaction at ～1% [O2], with the total abundance of observed functionalization products being approximately equal to the fragmentation products at 10% [O2]. The large abundance of squalene fragmentation products at 10% [O2] is attributed to the formation and dissociation of tertiary hydroxyalkoxy radical intermediates. For linolenic acid aerosol, the formation of functionalization products dominates the reaction at both ～1% and 10% [O2], suggesting that the formation and dissociation of secondary hydroxyalkoxy radicals are minor reaction channels for linear molecules. The distribution of linolenic acid functionalization products depends upon [O2], indicating that O2 controls the reaction pathways of the secondary hydroxyalkyl radical. For both reactions, alcohols are formed in favor of carbonyl functional groups, suggesting that there are some key differences between heterogeneous reactions involving allylic radical intermediates and those reactions of OH radicals with simple saturated hydrocarbons.
Enzymatic cyclizations of squalene analogs with threo- And erythro-diols at the 6,7- or 10,11-positions by recombinant squalene cyclase. Trapping of carbocation intermediates and mechanistic insights into the product and substrate specificities
Abe, Takamasa,Hoshino, Tsutomu
, p. 3127 - 3139 (2007/10/03)
In order to trap the carbocation intermediates formed during the squalene cyclization cascade, squalene analogs with threo- and erythro-dioh at the 6,7- and 10,11-positions were incubated with the recombinant squalene cyclase from Alicyclobacillus acidocaldarius, leading to the construction of the triterpenes with tetrahydropyran, octahydrochromene, decahydronaphthalene with a carbonyl group, dodecahydrobenzo[f]chromene, tetradecahydronaphtho[2,1-b]oxepine and malabaricane skeletons, almost of which are novel compounds. These products indicate that 6-membered monocyclic, 6/6-fused bicyclic and 6/6/5-fused tricyclic cations were involved in the cyclization reaction in addition to acyclic cation. All the trapped cations were the stable tertiary cation, but not the secondary one, indicating that the polycyclization reaction proceeds with a Markovnikov closure. The product profiles revealed that the cyclization reactions proceeded with the product and substrate specificities in addition to enantioselectivity. Mechanistic insight into the observed stereochemical specificities indicated that the pre-organized chair-conformation of squalene-diols is tightly constricted by the cyclase and a free motion or a conformational change is not allowed in the reaction cavity, thus, the substrate and product specificities are dominantly directed by the least motion of the nucleophilic hydroxyl group toward the intermediary carbocation; a small rotation of the hydroxyl group afforded the cyclization products in a good yield, but a large rotation of the hydroxyl group gave a marginal or no detectable amount of products. The Royal Society of Chemistry 2005.
Antibodies mimic natural oxidosqualene-cyclase action in steroid ring a formation
Hasserodt, Jens,Janda, Kim D.,Lerner, Richard A.
, p. 40 - 45 (2007/10/03)
Cationic cyclizations are among the most demanding reactions that have been catalyzed by antibodies. These studies provided valuable mechanistic insights while opening up the possibility of formation of steroidal carbon frameworks. However, they have involved substrates that contained an aryl sulfonate group adjacent to a primary carbon center not observed in natural cationic cyclization processes. This paper presents an extension of our earlier work, now focusing on substrates analogous to those seen in triterpene biosynthesis. Three antibodies, 15D6, 20C7, and 25A10, have been generated by immunization with an 4-aza-steroid aminoxide hapten (termed HA8) that initiate the cationic cyclization of an oxidosqualene derivative and catalyze the formation of ring A of the lanosterol nucleus at neutral pH. Antibody HA8-25A10 kinetically resolved its racemic substrates. Design of the substrate was based on a dual-anchor model for specific binding that consists of displaying a functional group at the head (epoxide trigger) and the tail (amide functionality) of the otherwise hydrophobic poly-ene chain. The assay involved solubilization of the substrates with 0.2% surfactant. No ring formation was detected in the absence of antibody catalyst. The uncatalyzed epoxide hydrolysis was slow and did not deprive the antibody of substrate. Observations in the field of enzymic poly-ene cyclizations suggest that subtle changes in the substrate structure may well lead to multi-ring formation under the influence of the current catalyst.
