34310-88-8Relevant academic research and scientific papers
Photochemistry of bacteriochlorophylls in human blood plasma: 2. Reaction mechanism investigated by product analysis and deuterium isotope effect
Dandler, Joerg,Wilhelm, Brigitte,Scheer, Hugo
experimental part, p. 342 - 352 (2010/10/02)
Transmetalated (Pd) bacteriochlorophyll derivatives are currently being clinically tested as sensitizers for photodynamic therapy. Protocols using short delay times between injection and irradiation generate interest in the photochemistry of these pigments in the blood. Using near-infrared irradiation where these pigments absorb strongly, we have studied the mechanism of photo-oxidation in two lipoprotein fractions, low- and high-density lipoproteins, derived from human blood plasma that preferentially accumulate these pigments (Dandler et al. [2009] Photochem. Photobiol., 85, in press). Using quenchers of reactive oxygen species, and chemical reporters, in particular peroxides generated from cholesterol as an inherent component of the lipoproteins, a Type II mechanism generating singlet oxygen has been demonstrated for Pd- and Zn-bacteriopheophorbides. In homogeneous systems, accelerated bleaching in D2O, compared with H2O, supports this mechanism. An unusual deuterium isotope effect was observed, by contrast, in heterogeneous amphiphilic-water systems. In the early phase, and under high oxygen concentrations, again a positive D-isotope effect is observed which later, in a second phase, is reversed to a negative D-isotope effect. The latter cannot be explained by heterogeneous pigment populations in the amphiphilic system; we, therefore, conclude a mechanistic switch, and discuss a possible mechanism.
Sensitized photooxygenation of cholesterol and pseudo-cholesterol derivatives via singlet oxygen
Shuping, Wu,Zhiqin, Jiang,Heting, Li,Li, Yang,Daixun, Zeng
, p. 52 - 60 (2007/10/03)
3-Substituted cholesterols and 7-substituted pseudocholesterols undergo a facile photooxygenation sensitized by 9, 10-dicyanoanthracene (DCA) and lumiflavin (LF) to give similar, oppositely-positioned enol derivatives. Both steroids showed the same reaction pattern associated with the endocyclic 5- and 4-olefin units, respectively. The reaction was proposed to proceed via the ene reaction of singlet oxygen and subsequent rearrangement of the initially formed 5α-hydroperoxides.
Singlet-oxygen ene reaction with 3β-substituted stigmastanes. An alternative pathway for the classical Schenck rearrangement
Ponce, Maria A.,Ramirez, Javier A.,Galagovsky, Lydia R.,Gros, Eduardo G.,Erra-Balsells, Rosa
, p. 2351 - 2357 (2007/10/03)
The course of the singlet-oxygen ene reaction with stigmasta-5,22-dienes may be controlled if in the substrate a good leaving group as substituent is present at 3-C. Thus when the 5α-hydroperoxystigmasta-5,22-diene is formed instead of the well known allylic rearrangement to yield the 7α-hydroperoxystigmasta-5,22-diene isomer an intramolecular nucleophilic substitution can then occur yielding 5α-hydroxystigmasta-6,22-dien-3-one. Various stigmasta-5,22-dienes were chosen to elucidate which feature of the stigmastane is necessary to control the course of the reaction. Thus, 3β-F, 3β-Cl, 3β-Br, 3β-I and 3α-Br-stigmasta-5,22-dienes were firstly prepared and fully characterized in order to study their reaction with 1O2 under different experimental conditions. 3β-Acetoxy- and 3β-mesyloxy-stigmasta-5,22-diene derivatives were also prepared and studied.
Mass spectrometry characterization of the 5α-, 7α-, and 7β-hydroxy derivatives of β-sitosterol, campesterol, stigmasterol, and brassicasterol
Bortolomeazzi, Renzo,De Zan, Michela,Pizzale, Lorena,Conte, Lanfranco S.
, p. 3069 - 3074 (2007/10/03)
The 5α-hydroperoxides of β-sitosterol, campesterol, stigmasterol, and brassicasterol were obtained by photooxidation of the respective sterols in pyridine in the presence of hematoporphyrine as sensitizer. The reduction of the hydroperoxides gives the corresponding 5α-hydroxy derivatives. The 7α- and 7β-hydroperoxides of the sterols were obtained by allowing an aliquot of the 5α-hydroperoxides to isomerize to 7α-hydroperoxides, which in turn epimerize to 7β-hydroperoxides. The reduction gave the corresponding 7α- and 7β-hydroxy derivatives. The 5α-, 7α-, and 7β-hydroxy derivatives of β-sitosterol, campesterol, stigmasterol, and brassicasterol were identified by comparing thin-layer chromatography mobilities, specific color reactions, and mass spectral data with those of the corresponding hydroxy derivatives of cholesterol, which were synthesized in the same manner. The phytosterols had the same behavior to photooxidation as cholesterol and, moreover, the different phytosterols photooxidized at about the same rate. The mass spectra of the trimethylsilyl ethers of the hydroxy derivatives of the phytosterols investigated and of the corresponding hydroxy derivatives of cholesterol have the same fragmentation patterns and similar relative ion abundances.
The mechanisms of the rearrangements of allylic hydroperoxides: 5α-hydroperoxy-3β-hydroxycholest-6-ene and 7α-hydroperoxy- 3β-hydroxycholest-5-ene
Beckwith, Athelstan L. J.,Davies, Alwyn G.,Davison, Ian G. E.,Maccoll, Allan,Mruzek, Margaret H.
, p. 815 - 824 (2007/10/02)
The rearrangement of 5α-hydroperoxy-3β-hydroxycholest-6-ene in solution under 18O2, gives isotopically normal 7α-hydroperoxy-3β-hydroxycholest-5-ene, whereas the epimerization of this product to give 7β-hydroperoxy-3β-hydroxycholest-5-ene involves incorporation of 73-83% of 18O2 into the hydroperoxy group. These two reactions proceed through the corresponding hydroperoxyl radicals, which have different e.s.r. spectra and which therefore must exist as separate and distinct species. The former reaction shows a first-order dependence on hydroperoxide concentration, and a half-order dependence on t-butyl hyponitrite which was added as an initiator. It is suggested that the first reaction involves a sigmatropic [2,3]-rearrangement, whereas the second reaction proceeds through a dissociative mechanism.
Catalytic Oxygenation of Cholesterol with a Platinum Catalyst under Moderate Pressure of Oxygen
Sakamaki, Hiroshi,Take, Masa-aki,Akihisa, Toshihiro,Matsumoto, Taro,Ichinohe, Yoshiyuki
, p. 3023 - 3025 (2007/10/02)
The catalytic oxigenation of cholesterol 1 with a platinum black catalyst under moderate pressure (20-25 atm) of oxygen yielded eleven oxidation products, 3-13a.The reaction pathway of the catalytic oxygenation is discussed on the basis of the results for several reaction conditions.
CHEMISTRY OF SINGLET OXYGEN. 47. 9,10-DICYANOANTHRACENE-SENSITIZED PHOTOOXYGENATION OF ALKYL-SUBSTITUTED OLEFINS.
Araki,Dobrowolski,Goyne,Hanson,Zhi Qui Jiang,Lee,Foote
, p. 4570 - 4575 (2007/10/02)
9,10-Dicyanoanthracene (DCA) sensitizes the photooxygenation of 1-methylcyclohexene, 1,2-dimethylcyclohexene, and cholesterol in acetonitrile and benzene. For all three olefins, the products are the same as those formed by reaction with singlet oxygen. Th
Reactions of steroidal 4,5- and 5,6-epoxides with strong bases
Holland, Herbert L.,Jahangir
, p. 2165 - 2170 (2007/10/02)
A series of C-3 oxygenated and unsubstituted (4,5)α, (4,5)β, (5,6)α, and (5,6)β epoxy steroids has been prepared, and the reactions of these compounds with strong bases (potassium tert-butoxide, LDA, and LDEA) were investigated.Only LDEA gave rise to product formation; β elimination of the epoxide to give a β-hydroxy olefin was observed in this case.The regioselectivity of product formation is consistent with a mechanism of rearrangement involving removal of a hydrogen located syn to the epoxide oxygen.In some cases, a directing influence from a polar substituent (OH) of the starting material was also apparent.The (13)C nmr spectra of the steroidal epoxides used in this study were assigned; these data are diagnostic of the conformation of ring A of (4,5)α and (4,5)β epoxy steroids.
