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Ruthenium-decorated lipid vesicles: Light-induced release of [Ru(terpy)(bpy)(OH2)]2+ and thermal back coordination
Electrostatic forces play an important role in the interaction between large transition metal complexes and lipid bilayers. In this work, a thioether-cholestanol hybrid ligand (4) was synthesized, which coordinates to ruthenium(II) via its sulfur atom and intercalates into lipid bilayers via its apolar tail. By mixing its ruthenium complex [Ru(terpy)(bpy)(4)]2+ (terpy = 2,2′;6′,2′′-terpyridine; bpy = 2,2′-bipyridine) with either the negatively charged lipid dimyristoylphosphatidylglycerol (DMPG) or with the zwitterionic lipid dimyristoylphosphatidylcholine (DMPC), large unilamellar vesicles decorated with ruthenium polypyridyl complexes are formed. Upon visible light irradiation the ruthenium-sulfur coordination bond is selectively broken, releasing the ruthenium fragment as the free aqua complex [Ru(terpy)(bpy)(OH 2)]2+. The photochemical quantum yield under blue light irradiation (452 nm) is 0.0074(8) for DMPG vesicles and 0.0073(8) for DMPC vesicles (at 25 °C), which is not significantly different from similar homogeneous systems. Dynamic light scattering and cryo-TEM pictures show that the size and shape of the vesicles are not perturbed by light irradiation. Depending on the charge of the lipids, the cationic aqua complex either strongly interacts with the membrane (DMPG) or diffuses away from it (DMPC). Back coordination of [Ru(terpy)(bpy)(OH2)]2+ to the thioether-decorated vesicles takes place only at DMPG bilayers with high ligand concentrations (25 mol %) and elevated temperatures (70 °C). During this process, partial vesicle fusion was also observed. We discuss the potential of such ruthenium-decorated vesicles in the context of light-controlled molecular motion and light-triggered drug delivery.
Bonnet, Sylvestre,Limburg, Bart,Meeldijk, Johannes D.,Gebbink, Robertus J. M. Klein,Killian, J. Antoinette
p. 252 - 261
(2011)
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Development of Improved Synthetic Routes to Pixatimod (PG545), a Sulfated Oligosaccharide-Steroid Conjugate
The heparan sulfate (HS) mimetic pixatimod (PG545) is a highly potent inhibitor of angiogenesis, tumor growth, and metastasis currently in clinical trials for cancer. PG545 has also demonstrated potent antiviral activity against numerous HS-dependent viruses, including SARS-CoV-2, and shows promise as an antiviral drug for the treatment of COVID-19. Structurally, PG545 consists of a fully sulfated tetrasaccharide conjugated to the steroid 5α-cholestan-3β-ol. The reported synthesis of PG545 suffers from a low yield and poor selectivity in the critical glycosylation step. Given its clinical importance, new efficient routes for the synthesis of PG545 and analogues were developed. Particular attention was given to improving the key glycosylation step by using more stable protecting groups and optimized glycosyl donors.
Chhabra, Mohit,Ferro, Vito,He, Qi Qi,Wimmer, Norbert
p. 2420 - 2431
(2021/11/01)

Method for synthesizing cholesterol by taking BA as raw material
The invention discloses a method for synthesizing cholesterol by taking BA as a raw material. A plant source raw material 21-hydroxy-20-methylpregna-4-en-3-one, also known as Shuangjiangchun or BA is taken as a raw material, and the cholesterol is synthesized by the steps of oxidation, Wittig reaction, acetylation, reduction, selective hydrogenation reduction and the like. The raw materials for synthesizing cholesterol are plant sources, the price is low, the safety is high, the risk of pathogenic bacteria and virus infection is avoided, and the synthesis method is easy to operate, high in yield, few in side reaction, environmentally friendly, good in economical efficiency and convenient for industrial production; and the invention solves the safety problem of the existing cholesterol product and the problems of high cost, environmental unfriendliness and unsuitability for large-scale industrial production in the synthesis technology.
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(2021/08/14)

Electrochemical Borylation of Alkyl Halides: Fast, Scalable Access to Alkyl Boronic Esters
Herein, a fast, scalable, and transition-metal-free borylation of alkyl halides (X = I, Br, Cl) enabled by electroreduction is reported. This process provides an efficient and practical access to primary, secondary, and tertiary boronic esters at a high current. More than 70 examples, including the late-stage borylation of natural products and drug derivatives, are furnished at room temperature, thereby demonstrating the broad utility and functional-group tolerance of this protocol. Mechanistic studies disclosed that B2cat2 serves as both a reagent and a cathodic mediator, enabling electroreduction of difficult-to-reduce alkyl bromides or chlorides at a low potential.
Cao, Yangmin,Hu, Ping,Huang, Cheng,Liu, Zhao,Lu, Qingquan,Ma, Wan,Peng, Pan,Qi, Xiaotian,Wang, Bingbing
supporting information
p. 12985 - 12991
(2021/09/03)

Copper-Catalyzed and Indium-Mediated Methoxycarbonylation of Unactivated Alkyl Iodides with Balloon CO
This work emphasizes the synthesis of alkyl esters via Cu-catalyzed and In-mediated alkoxycarbonylation of unactivated alkyl iodides in the presence of In or InI. The reactions were suitable for the preparation of primary, secondary, and even tertiary alkyl esters, representing an exceptionally rare example for the creation of quaternary carbon centers upon formation of esters. The preliminary mechanistic studies indicated that alkyl radicals were involved, and Cu/In/CO played a cooperative role in the carbonylation event.
Chen, Yanchi,Su, Lei,Gong, Hegui
supporting information
p. 4689 - 4693
(2019/06/27)

Oxidative Deprotection of p-Methoxybenzyl Ethers via Metal-Free Photoredox Catalysis
An efficient and greener deprotection method for p-methoxybenzyl (PMB) ethers using a metal-free visible light photoredox catalyst and air and ammonium persulfate as the terminal oxidants is presented. Various functional groups and protecting groups were tolerated in the developed method to achieve good to excellent yields in short reaction times. Significantly, the developed method was compatible with PMB ethers derived from primary, secondary, and tertiary alcohols and a gram-scale reaction. Mechanistic studies support a proposed reaction mechanism that involves single electron oxidation of the PMB ether.
Ahn, Deok Kyun,Kang, Young Woo,Woo, Sang Kook
p. 3612 - 3623
(2019/03/11)

Ruthenium nanoparticles ligated by cholesterol-derived NHCs and their application in the hydrogenation of arenes
Herein we present ruthenium nanoparticles (Ru-NPs) stabilized with two rigid NHC ligands derived from cholesterol. The obtained nanoparticles were fully characterized and applied in the hydrogenation of various aromatic compounds under mild conditions. Interestingly, the more bulky ligand gives a slightly lower ligand coverage and a faster catalyst.
Rakers, Lena,Martínez-Prieto, Luis M.,López-Vinasco, Angela M.,Philippot, Karine,Van Leeuwen, Piet W. N. M.,Chaudret, Bruno,Glorius, Frank
supporting information
p. 7070 - 7073
(2018/07/05)

Addressable Cholesterol Analogs for Live Imaging of Cellular Membranes
Cholesterol is an essential component of most biological membranes and serves important functions in controlling membrane integrity, organization, and signaling. However, probes to follow the dynamic distribution of cholesterol in live cells are scarce and so far show only limited applicability. Herein, we addressed this problem by synthesizing and characterizing a class of versatile and clickable cholesterol-based imidazolium salts. We show that these cholesterol analogs faithfully mimic the biophysical properties of natural cholesterol in phospholipid mono- and bilayers, and that they integrate into the plasma membrane of cultured and primary human cells. The membrane-incorporated cholesterol analogs can be specifically labeled by click chemistry and visualized in live-cell imaging experiments that show a distribution and behavior comparable with that of endogenous membrane cholesterol. These results indicate that the cholesterol analogs can be used to reveal the dynamic distribution of cholesterol in live cells. Cholesterol is an important component of biological membranes, but probes recording its dynamic intracellular distribution are scarce. Rakers et al. developed cholesterol-derived imidazolium salts mimicking properties of natural cholesterol. Following specific labeling via click chemistry, one of the cholesterol analogs was shown to incorporate into cellular membranes equivalent to endogenous cholesterol.
Rakers, Lena,Grill, David,Matos, Anna L.L.,Wulff, Stephanie,Wang, Da,B?rgel, Jonas,K?rsgen, Martin,Arlinghaus, Heinrich F.,Galla, Hans-Joachim,Gerke, Volker,Glorius, Frank
p. 952 - 12,961
(2018/05/08)

Efficient Water Reduction with sp3-sp3 Diboron(4) Compounds: Application to Hydrogenations, H–D Exchange Reactions, and Carbonyl Reductions
A series of crystalline sp3-sp3 diboron(4) compounds were synthesized and shown to promote the facile reduction of water with dihydrogen formation. The application of these diborons as simple and effective dihydrogen and dideuterium sources was demonstrated by conducting a series of selective reductions of alkynes and alkenes, and hydrogen–deuterium exchange reactions using two-chamber reactors. Finally, as the water reduction reaction generates an intermediate borohydride species, a range of aldehydes and ketones were reduced by using water as the hydride source.
Flinker, Mathias,Yin, Hongfei,Juhl, René W.,Eikeland, Espen Z.,Overgaard, Jacob,Nielsen, Dennis U.,Skrydstrup, Troels
supporting information
p. 15910 - 15915
(2017/11/23)

An Alkyne Diboration/6π-Electrocyclization Strategy for the Synthesis of Pyridine Boronic Acid Derivatives
A new and efficient synthesis of pyridine-based heteroaromatic boronic acid derivatives is reported through a novel diboration/6π-electrocyclization strategy. This method delivers a range of functionalized heterocycles from readily available starting materials.
Mora-Radó, Helena,Bialy, Laurent,Czechtizky, Werngard,Méndez, María,Harrity, Joseph P. A.
p. 5834 - 5836
(2016/05/09)

Visible-Light-Promoted Activation of Unactivated C(sp3)-H Bonds and Their Selective Trifluoromethylthiolation
Selective functionalization of ubiquitous C(sp3)-H bonds using visible light is a highly challenging yet desirable goal in organic synthesis. The development of such processes relies on both rational design and serendipitous discoveries from innovative tools such as screening technologies. Applying a mechanism-based screening strategy, we herein report photoredox-mediated hydrogen atom transfer catalysis for the selective activation of otherwise unactivated C(sp3)-H bonds, followed by their trifluoromethylthiolation, which has high potential as a late-stage functionalization tool. The generality of this method is exhibited through incorporation of the trifluoromethylthio group in a large number of C(sp3)-H bonds with high selectivity without the need for an excess of valuable substrate.
Mukherjee, Satobhisha,Maji, Biplab,Tlahuext-Aca, Adrian,Glorius, Frank
supporting information
p. 16200 - 16203
(2016/12/27)

Marine and semi-synthetic hydroxysteroids as new scaffolds for pregnane X receptor modulation
In recent years many sterols with unusual structures and promising biological profiles have been identified from marine sources. Here we report the isolation of a series of 24-alkylated-hydroxysteroids from the soft coral Sinularia kavarattiensis, acting as pregnane X receptor (PXR) modulators. Starting from this scaffold a number of derivatives were prepared and evaluated for their ability to activate the PXR by assessing transactivation and quantifying gene expression. Our study reveals that ergost-5-en-3β-ol (4) induces PXR transactivation in HepG2 cells and stimulates the expression of the PXR target gene CYP3A4. To shed light on the molecular basis of the interaction between these ligands and PXR, we investigated, through docking simulations, the binding mechanism of the most potent compound of the series, 4, to the PXR. Our findings provide useful functional and structural information to guide further investigations and drug design.
Sepe, Valentina,Di Leva, Francesco Saverio,D'Amore, Claudio,Festa, Carmen,De Marino, Simona,Renga, Barbara,D'Auria, Maria Valeria,Novellino, Ettore,Limongelli, Vittorio,D'Souza, Lisette,Majik, Mahesh,Zampella, Angela,Fiorucci, Stefano
p. 3091 - 3115
(2014/07/08)

LIGHT INDUCED DRUG RELEASE
Photosensitive compounds for use in a method of treating a disease or condition are described. The photosensitive compounds have the formula R—Y, wherein R is a ruthenium complex and Y is at least one sulphur-containing photoreleasable group, and the compounds comprise at least one ruthenium-sulphur bond; or a pharmaceutically acceptable salt, solvate, ester or amide, such that upon influence of visible or near infra-red light (400-1400 nm) in vivo, said at least one ruthenium-sulphur bond is broken, thereby generating a pharmacologically active compound.
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Paragraph 0108; 0116

(2014/06/11)

Novel human umbilical vein endothelial cells (HUVEC)-apoptosis inhibitory phytosterol analogues: Insight into their structure-activity relationships
Design, synthesis and insight into the structure-activity relationships (SAR) of phytosterol analogues as novel antiapoptotic agents are described. In particular, the non-branched alkyl chain at C24 and the pseudosugar moiety at C3 hydroxyl group turned out crucial for the inhibition of human umbilical vein endothelial cells (HUVEC) apoptosis.
Lee, Sujin,Marharjan, Sony,Jung, Jong-Wha,Kim, Nam-Jung,Kim, Kyeojin,Han, Young Taek,Lim, Changjin,Choi, Hyun-Jung,Kwon, Young-Geun,Suh, Young-Ger
experimental part
p. 455 - 460
(2012/08/28)

Modification in the side chain of solomonsterol A: Discovery of cholestan disulfate as a potent pregnane-X-receptor agonist
Seven synthetic analogues of the PXR (pregnane-X-receptor) potent natural agonist solomonsterol A were prepared by total synthesis. Their activity toward PXR was assessed by transactivation and RT-PCR assays. The study discloses cholestan disulfate (8) as a new, simplified agonist of PXR. By in vitro studies on hepatic cells we have demonstrated that this compound is a potent PXR agonist and functional characterization in human macrophages and hepatic stellate cells provided evidence that cholestan disulfate (8) has the ability to modulate the immune response triggered by bacterial endotoxin as well as to counter-activate hepatic stellate cell activation induced by thrombin. Because inhibition of immune-driven circuits might have relevance in the treatment of inflammation and liver fibrosis, the present data support the development of cholestan disulfate (8) in preclinical models of inflammatory diseases. The Royal Society of Chemistry 2012.
Sepe, Valentina,Ummarino, Raffaella,D'Auria, Maria Valeria,Lauro, Gianluigi,Bifulco, Giuseppe,D'Amore, Claudio,Renga, Barbara,Fiorucci, Stefano,Zampella, Angela
experimental part
p. 6350 - 6362
(2012/09/05)

Novel approach to determining the absolute configurations at the C3-positions of various types of sterols based on an induced circular dichroism
Circular dichroism (CD) spectra of the 2,2′-binaphthyl ester derived from Δ5-sterols showed not bisignate CD but diagnostic CD bands at around 210 and 240 nm. These bands might be attributable to an interaction between an olefinic chromophore and a binaphthyl one. Various types of unsaturated sterols were thus derivatized followed by complete hydrogenation, to give saturated sterols. As a result, CD spectra of the binaphthyl derivatives of the saturated sterols showed bisignate curves centered at 240 nm (3S(β): positive chirality; 3R(α): negative one). This suggested a straightforward and practical method for discriminating the absolute stereogenic center at the C-3 positions of sterols based on an induced CD. This finding should contribute significantly to the analysis of metabolites of various types of sterols.
Fujiwara, Toshio,Taniguchi, Yuka,Katsumoto, Yukiteru,Tanaka, Takeyuki,Ozeki, Minoru,Iwasaki, Hiroki,Node, Manabu,Yamashita, Masayuki,Hosoi, Shinzo
p. 1198 - 1204
(2012/11/07)

Reliable and safe, gram-scale hydrogenation and hydrogenolysis of O-benzyl ether groups with in situ Pd0/C catalyst
Hydrogenation of alkenes, alkynes, and hydrogenolysis of O-benzyl ethers with Pd0/C catalyst generated in situ can be readily scaled up under safer conditions than with traditional procedures. The precise control of the palladium loading and the mild conditions developed allow the formation of a very active and reliable Pd0/C catalyst, leading to highly reproducible results. Georg Thieme Verlag Stuttgart - New York.
Felpin, Francois-Xavier,Fouquet, Eric
experimental part
p. 2893 - 2896
(2011/10/13)

Synthesis and crystal structure of [1,2,4]-triazolo-annulated 3-aza-A-homocholestane derivative: A novel pentaheterocyclic ring system
A novel pentaheterocyclic ring system derived from (5α)-cholestan-3- one, i.e. [1R-[1α(R*),3aβ,3bα,5aβ,12aα, 12bβ,14aα]]-1-(1,5-dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13, 14,14a-tetradecahydro-8,12a,14a-trimethyl-9-(2,4,6-trichlorophenyl) -cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-a]azepinium hexachloroantimonate (6) has been synthesized via the reverse-electron-demand 1,3-dipolar cycloaddition of the 1-aza-2-azoniaallene cation 4 to the triple bond of acetonitrile followed by ring enlargement. The structure of 6 was determined by NMR, IR and high-resolution mass spectra, and unequivocally confirmed by X-ray crystallographic analysis. The title compound crystallizes in monoclinic class under the space group P2-1 with a = 8.163(3) A, b = 11.214(4) A, c = 24.191(9) A, α = 90°, β = 97.740(5)°, and γ = 90°. The five-membered triazole ring is essentially planar and aromatic, while the seven-membered azepine ring is not planar, but adopts a chair-like conformation.
Bai, He-Xiang,Wang, Jing-Mei,Xia, Shi-Jing,Wang, Quan-Rui
body text
p. 316 - 321
(2011/10/05)

Radical chain reduction of alkylboron compounds with catechols
The conversion of alkylboranes to the corresponding alkanes is classically per-formed via protonolysis of alkylboranes. This simple reaction requires the use of severe reaction conditions, that is, treatment with a carboxylic acid at high temperature (>150 °C). We report here a mild radical procedure for the transformation of organoboranes to alkanes. 4-tert-Butylcatechol, a well-established radical inhibitor and antioxidant, is acting as a source of hydrogen atoms. An efficient chain reaction is observed due to the exceptional reactivity of phenoxyl radicals toward alkylboranes. The reaction has been applied to a wide range of organoboron derivatives such as B- alkylcatecholboranes, trialkylboranes, pinacolboronates, and alkylboronic acids. Furthermore, the so far elusive rate constants for the hydrogen transfer between secondary alkyl radical and catechol derivatives have been experimentally determined. Interestingly, they are less than 1 order of magnitude slower than that of tin hydride at 80 °C, making catechols particularly attractive for a wide range of transformations involving C-C bond formation.
Villa, Giorgio,Povie, Guillaume,Renaud, Philippe
supporting information; experimental part
p. 5913 - 5920
(2011/06/16)

A useful, reliable and safer protocol for hydrogenation and the hydrogenolysis of o-benzyl groups: The in situ preparation of an active Pd 0/C catalyst with well-defined properties
A simple, highly reproducible protocol for the hydrogenation of alkenes and alkynes and for the hydrogenolysis of O-benzyl ethers has been developed. The method features the in situ preparation of an active Pd0/C catalyst from Pd(OAc)2 and charcoal, in methanol. The mild reaction conditions (25°C) and low catalyst loading required (0.025 mol%), as well as the absence of contamination of the product by palladium residues (0/C: It's a kind of magic! A sustainable, simple and highly reproducible protocol for the hydrogenation of alkenes and alkynes (see scheme) and for the hydrogenolysis of O-benzyl ethers has been developed with an in situ generated Pd0/C catalyst. The homemade Pd0/C catalyst allows mild reaction conditions (25°C, 1 atm H2) and low catalyst loading (as low as 0.025 mol%), without any contamination of the product by palladium residues (4 ppb).
Felpin, Francois-Xavier,Fouquet, Eric
supporting information; experimental part
p. 12440 - 12445
(2011/01/05)

Novel and efficient synthesis and antifungal evaluation of 2,3-functionalized cholestane and androstane derivatives
Synthetic modifications of cholesterol and other traditional steroid molecules have become a promising area for the exploration and development of novel antifungal agents, especially with respect to the development of fatty-acid esters of steroids. In addition, 2,3-functionalized steroids are also compounds with potentially interesting biological properties and proper functionalization of 2,3-steroids can lead to the development of efficient syntheses of building blocks for novel fatty-acid esters of steroids. In this Letter, we outline a novel and efficient approach to the synthesis of 2,3-functionalized cholestane and androstane derivatives and present their promising preliminary antifungal activities against a number of fungal species.
Jursic, Branko S.,Upadhyay, Sunil Kumar,Creech, Clinton C.,Neumann, Donna M.
supporting information; experimental part
p. 7372 - 7375
(2011/02/23)

NOVEL SULFATED OLIGOSACCHARIDE DERIVATIVES
The invention relates to novel compounds that have utility as inhibitors of heparan sulfate-binding proteins; compositions comprising the compounds, and use of the compounds and compositions thereof for the antiangiogenic, antimetastatic, anti-inflammatory, antimicrobial, anticoagulant and/or antithrombotic treatment of a mammalian subject.
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(2009/05/28)

Microwave-assisted cross-coupling and hydrogenation chemistry by using heterogeneous transition-metal catalysts: An evaluation of the role of selective catalyst heating
The concept of specific microwave effects in solid/liquid catalytic processes resulting from the selective heating of a microwave-absorbing heterogeneous transition-metal catalyst by using 2.45 GHz microwave irradiation was evaluated. As model transformations Ni/C-, Cu/C-, Pd/C-, and Pd/ Al 2O3-catalyzed carbon-carbon/ carbon-heteroatom cross-couplings and hydrogenation reactions were investigated. To probe the existence of specific microwave effects by means of selective catalyst heating in these transformations, control experiments comparing microwave dielectric heating and conventional thermal heating at the same reaction temperature were performed. Although the supported metal catalysts were experimentally found to be strongly microwave absorbing, for all chemistry examples investigated herein no differences in reaction rate or selectivity between microwave and conventional heating experiments under carefully controlled conditions were observed. This was true also for reactions that use low-absorbing or microwave transparent solvents, and was independent of the microwave absorbtivity of the catalyst support material. In the case of hydrogenation reactions, the stirring speed was found to be a critical factor on the mass transfer between gas and liquid phase, influencing the rate of the hydrogenation in both microwave and conventionally heated experiments.
Irfan, Muhammed,Fuchs, Michael,Glasnov, Toma N.,Kappe, C. Oliver
supporting information; experimental part
p. 11608 - 11618
(2010/05/17)

Metal-dependent reaction tuning with cyclopentylmetal reagents: Application to the asymmetric synthesis of (+)-α-conhydrine and (S)-2-cyclopentyl-2- phenylgrycolic acid
The reaction profile of the cyclopentyl organometallic reagents with the aliphatic ketones can be tuned to reduction or addition by changing the metal atom. Cyclopentylmagnesium bromide (CPMB) reduces aromatic and aliphatic aldehydes and ketones to the corresponding alcohols without any C-C bond formation and shows good diastereoselectivity in the reduction of the substituted cyclic and polycyclic ketones as well as chiral α-oxygenated aliphatic ketones. However, in the presence of 10 mol% of ZnClα 2, the cyclopentylmagnesium halides follow a normal Grignard addition to the ketones to give tertiary alcohols with complete diastereoselectivity. The reductive as well as the addition protocols were used for the asymmetric synthesis of two medicinally important compounds, (+)-α-conhydrine and (S)-2-cyclopentyl-2-phenylglycolic acid.
Roy, Siddharth,Sharma, Anubha,Mula, Soumyaditya,Chattopadhyay, Subrata
experimental part
p. 1713 - 1722
(2009/09/07)

(BDP)CuH: A "hot" Stryker's reagent for use in achiral conjugate reductions
(Chemical Equation Presented) A ligand-modified, economical version of Stryker's reagent (SR) has been developed based on a bidentate, achiral bis-phosphine. Generated in situ, "(BDP)CuH" smoothly effects conjugate reductions of a variety of unsaturated substrates, including those that are normally unreactive toward SR. Substrate-to-ligand ratios typically on the order of 1000-10000:1 can be used leading to products in high yields.
Baker, Benjamin A.,Boskovic, Zarko V.,Lipshutz, Bruce H.
p. 289 - 292
(2008/09/19)

Method and apparatus for conducting microwave assisted organic reactions with gas-phase reactants
A method of accelerating the hydrogenation of organic compounds is provided. The method includes positioning an microwave transparent reaction vessel containing at least one reactant suitable for hydrogenation in a microwave cavity, purging the reaction vessel, charging the reaction vessel with hydrogen gas, and applying a continuous single mode of microwave radiation within the cavity and to the vessel and its contents for a time sufficient to effect a chemical change in the reactants.
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(2008/06/13)

A simple and efficient catalytic method for the reduction of ketones
A range of ketones was efficiently reduced in the presence of catalytic amounts of lithium isopropoxide in 2-propanol under microwave heating, with alcohol products being formed in yields up to 99%.
Ekstroem, Jesper,Wettergren, Jenny,Adolfsson, Hans
p. 1609 - 1613
(2008/02/11)

Deprotection of benzyl ethers using 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) under photoirradiation
The deprotection of benzyl ethers was effectively realized in the presence of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in MeCN under photoirradiation using a long wavelength UV light.
Rahim, Mohammad Abdur,Matsumura, Shuichi,Toshima, Kazunobu
p. 7307 - 7309
(2007/10/03)

The effects of added ammonium chloride in the reductive amination of some carbonyl compounds over Ru and Pd catalysts
The reductive amination of acetophenone, (+)-camphor, and 5α-cholestan-3-one over Ru and Pd metals as well as their carbon-supported catalysts gave corresponding amines together with alcohols as by-products. However, we found that the corresponding amines are selectively synthesized by the addition of ammonium chloride to the reaction system with depression of the formation of alcohol, as exemplified with acetophenone. Although alcohols are usually not formed over Pd with alicyclic ketones, the alcohols formation was effectively depressed over Ru in the presence of ammonium chloride. The effects of the additive on the stereoselectivity of the formation of amines are also discussed in the cases of (+)-camphor and 5α-cholestan-3-one.
Ikenaga, Tomoaki,Matsushita, Kumiko,Shinozawa, Junichi,Yada, Satoru,Takagi, Yuzuru
p. 2105 - 2109
(2007/10/03)

Al-isopropoxydiisobutylalane: A study of the effect of solvent on the rate and stereoselectivity of cyclic ketone reduction
The effect of solvent on the rate and stereoselectivity of cyclic ketone reduction by Al-isopropoxydiisobutylalane (DIBAiOPr) has been investigated. In dichloromethane, DIBAiOPr behaves as a bulky reducing agent, approaching the carbonyl group along an equatorial trajectory to produce the axial alcohol with > 10:1 stereoselectivity. In sharp contrast, reduction in toluene gives the complementary outcome, affording the thermodynamically more stable isomer with > 99:1 stereoselectivity.
Bahia, Perdip S.,Jones, Matthew A.,Snaith, John S.
p. 9289 - 9291
(2007/10/03)

A free radical method for reduction of cyclohexanones - Preferential formation of equatorial alcohols
Cyclohexanones react with 2-hydroselenobenzoic acid to afford spiro-[4H-3,1-benzoxaselenin-2,1′-cyclohexan]-4-ones. Stannane reduction and basic hydrolysis gives epimeric cyclohexanols, with the equatorial isomer predominating.
Clive, Derrick L. J.,Cheng, Hua
p. 1951 - 1961
(2007/10/03)

Cleavage of a p-cyanobenzyl group from protected alcohols, amines, and thiols using triethylgermyl sodium
Alcohols, amines, and thiols protected with a p-cyanobenzyl group can be easily and quantitatively deprotected using triethylgermyl sodium under mild conditions.
Yokohama, Yasuo,Takizawa, Shuichi,Nanjo, Masato,Mochida, Kunio
p. 1032 - 1033
(2007/10/03)

Collisionally-induced dissociation mass spectra of organic sulfate anions
The collisionally-induced dissociation mass spectra of a variety of organic sulfate ester anions are described and mechanistically rationalized. A cyclic syn-elimination pathway, analogous to that of the Cope elimination, is postulated for the commonly observed formation of bisulfate anion (HSO4-, m/z 97). Deuterium labeling experiments confirm that the proton transferred to oxygen during bisulfate elimination normally originates from the C-2 position, although examination of the spectra of polyfunctional steroids reveals that the proton abstracted may originate from more distant sites as well. Adamantyl, phenyl, and vinyl sulfate anions, which do not readily lend themselves to a cyclic syn-elimination, do not give rise to an m/z 97 ion. Instead, these sulfates undergo both heterolytic and homolytic S-O bond cleavages to yield an m/z M - 80 anion, resulting from loss of neutral SO3, as well as an ion at m/z 80, corresponding to SO3-·, respectively. Sulfates that can give rise to a resonance stabilized radical by homolytic C-O bond fission, as exemplified by benzyl and linalyl sulfates, can be recognized by the formation of an m/z 96 (SO4-·) ion.
Attygalle,Garcia-Rubio,Ta,Meinwald
p. 498 - 506
(2007/10/03)

Acceleration of the reduction of aldehydes and ketones using Mn(dpm)3 catalyst and phenylsilane in the presence of dioxygen
Saturated ketones and aldehydes are reduced to alcohols by phenylsilane and Mn(dpm)3(cat) in the presence of dioxygen.
Magnus, Philip,Fielding, Mark R
p. 6633 - 6636
(2007/10/03)

A new mild PTSA-catalyzed method for sulfate ester hydrolysis and acid-catalyzed rearrangement of 12-acetyl-diene-11-ol tetracyclic triterpenoids involving an angular methyl migration
Tetracyclic triterpenoids containing the 12-acetyl-Δ8,14-diene-ll-ol moiety undergo a series of acid-catalyzed rearrangements. The rearrangement products have been characterized, plausible mechanisms for the rearrangement have been elucidated and conditions have been developed to give high yields of the rearrangement products. A new and general PTSA·H2O and PPTS-catalyzed sulfate hydrolysis method has been developed. (C) 2000 Elsevier Science Ltd.
Singh
p. 6973 - 6976
(2007/10/03)

Phosphine effects in the copper(I) hydride-catalyzed hydrogenation of ketones and regioselective 1,2-reduction of α,β-unsaturated ketones and aldehydes. Hydrogenation of decalin and steroidal ketones and enones
The stereoselectivity and regioselectivity of the catalytic hydrogenation of ketones and α,β-unsaturated ketones and aldehydes using soluble copper(I) hydride catalysts have been investigated as a function of the ancillary phosphine ligand. While a relatively narrow range of aryldialkylphosphine ligands produce active hydrogenation catalysts, some ligands provide higher selectivity for 1,2-reduction of acyclic unsaturated carbonyl substrates than observed using the previously reported dimethylphenylphosphine-stabilized catalyst. The synthetic utility of this class of hydridic hydrogenation catalysts is illustrated by the hydrogenation of decalin and steroidal ketones and enones, the latter giving allylic alcohols with high selectivity. (C) 2000 Elsevier Science Ltd.
Chen, Jian-Xin,Daeuble, John F.,Stryker, Jeffrey M.
p. 2789 - 2798
(2007/10/03)

Rapid hydrogenation of unsaturated sterols and bile alcohols using microwaves
This paper describes an operationally simple, rapid hydrogenation of unsaturated sterols and bile alcohols in a domestic microwave oven. This has been achieved by the addition of catalytic amounts of Pd/C in methylene chloride/propylene glycol solvents in the presence of ammonium formate followed by microwave irradiation. It is suggested that this methodology will be helpful in the identification of saturated and unsaturated sterols with different side-chain structures in rare diseases: sitosterolemia, cerebrotendinous xanthomatosis (CTX), as well as atherosclerosis and diabetes mellitus. Sterols, such as cholesterol, campesterol, sitosterol, and bile alcohols with unsaturated side chains, were converted to their reduced congeners with high yield and purity.
Dayal,Ertel,Rapole,Asgaonkar,Salen
p. 451 - 454
(2007/10/03)

Potassium borohydride reductions of immobilised ketosteroids
Ketosteroids absorbed into various insoluble supports (powdered polyethylene, microporous 2% crosslinked polystyrene beads, macroporous highly crosslinked polystyrene beads, silica gel and alumina) call be reduced using aqueous potassium barohydride. The use of phase transfer catalysts generally raises yields. In the case of 6-ketosteriods the supported reactions often follow a stereochemical course significantly different from that of analogous reactions in solution. This is attributed to the adsorbtion of the steroid onto the inner surfaces of the supports. In these cases reduction of (he ketosteroid by alkoxyborohydrides is substantially suppressed and thus most of the reduction is brought about by BH4- itself, a relatively sterically undemanding reductant. The net result is that whilst reductions of 6-ketosteroids in solution by potassium borohydride typically gives the 69α- and 6β-alcohols in the ratio 15:85, with the supported steroid the ratios can be as high as 90:10.
Briggs, Josie C.,Hodge, Philip,Zhengpu, Zhang
p. 3943 - 3956
(2007/10/03)

The reaction of alkyl peroxy radicals
Secondary alkyl peroxy radicals generated from 4-phenyl-2-butyl-, 2-nonyl- and 3α-cholestanyl hydroperoxides at 45°C undergo Russell termination reactions in preference to non-terminating decomposition reactions. Non-terminating decomposition of 2-nonyl peroxy radicals afforded 2,5-nonanedione and 2,5-nonanediol due to intramolecular hydrogen abstraction reactions of alkoxy radicals. The radicals derived from 2-methyl-4-phenyl-2-butyl-, 2-methyl-5-phenyl-2-pentyl- and 2-methyl-6-phenyl-2-hexyl hydroperoxides afforded benzylic functionalized products due to intermolecular reactions. 2-Hexylperoxy radicals generated in excess alcohols ineffectively abstracted the α-hydrogens of alcohols. These results demonstrate the low reactivity of alkyl peroxy radicals.
Goosen, Andre,Kindermans, Sybrandus
p. 1 - 8
(2007/10/03)

Efficient method for inversion of secondary alcohols by reaction of chloromethanesulfonates with cesium acetate
Inversion of a variety of secondary alcohols using the (chloromethylsulfonyl)oxy group as a favorable leaving group with cesium acetate in the presence of 18-crown-6 has been performed to give the inverted acetates in high yields.
Shimizu, Takeshi,Hiranuma, Sayoko,Nakata, Tadashi
p. 6145 - 6148
(2007/10/03)

Oxidation of ethers to esters by photo-irradiation with benzil and oxygen
A novel method for the conversion of ethers to esters by photo-oxidation using benzil and molecular oxygen, and its plausible reaction mechanism participated by benzoylperoxy radical are described.
Seto, Hideharu,Yoshida, Keigo,Yoshida, Shigeo,Shimizu, Takeshi,Seki, Hiroshi,Hoshino, Mikio
p. 4179 - 4182
(2007/10/03)

Formation of ketones from alkyl nitrites in the solid state
Alkyl nitrites selectively afforded the corresponding ketones upon photoirradiation in the solid state. It was suggested by the X-ray crystallographic analysis that the cavity in crystal and the initial conformation of the nitroso group had an influence on the yield of the ketones.
Kinbara, Kazushi,Takezaki, Hiroshi,Kai, Akiyoshi,Saigo, Kazuhiko
p. 217 - 218
(2007/10/03)

Mechanism of cholesterol reduction to coprostanol by Eubacterium corpostanoligenes ASTCC 51222
The mechanism of reduction of cholesterol to coprostanol by Eubacterium coprostanoligenes ATCC 51222 was studied by incubating the bacterium with a mixture of α- and β-isomers of cholesterol.Coprostanol, isolated after incubation of cholesterol in a growth medium under anaerobic conditions, retained 97percent of the tritium originally presented in cholesterol.The majority of this tritium (64percent), however, was in the C-6 position in coprostanol, which showed that the conversion of cholesterol into coprostanol by E. coprostanoligenes involved the intermediate formation of 4-cholesten-3-one followed by the reduction of the latter to coprostanol.In resting cell assays in which washed bacterial cells were incubated with micellar cholesterol in phosphate buffer at 37 deg C, both 4-cholesten-3-one and coprostanone were produced in addition to coprostanol.Furthermore, 5-cholesten-3-one, 4-cholesten-3-one, and coprostanone were converted efficiently to coprostanol by E. coprostanoligenes.These results support the hypothesis that the major pathway for reduction of cholesterol by E. coprostanoligenes involves the intermediate formation of 4-cholesten-3-one followed by reduction of the latter to coprostanol through coprostanone as an intermediate. (Steroids 61:33-40, 1996) - Key words: dual-labeled cholesterol, coprostanol; cholesterol reduction; Eubacterium; NMR.
Ren, Dewei,Li, Ling,Schwabacher, Alan W.,Youbg, Jerry W.,Beitz, Donald C.
p. 33 - 40
(2007/10/03)

Syntheses and CD Studies of 5α-Cholesteno-, -- and -pyrimidines
Syntheses of 5α-cholesteno- (5a), - (12a), and pyrimidines (15a) have been achieved by using hydroxymethylene derivatives of relevant cholestanones prepared from cholesterol (1).Their CD spectra exhibit at least three Cotton effects between 300 to 200 nm, a first CD band around 290, a second one around 260 and a third one around 220 nm.A quadrant rule is developed and applied to the determination of the first CD band, while a helicity rule is applicable to the third CD band.The first band is positive in the series, whereas it is negative in the and the series.The third band is negative in all three series. - Key Words: Cholestenopyrimidines / Circular dichroism / Quadrant rule of cholestenopyrimidines
Hasan, Mashooda,Rashid, Naghmana,Khan, Khalid Mohammed,Snatzke, Guenther,Duddeck, Helmut,Voelter, Wolfgang
p. 889 - 896
(2007/10/02)

A Novel Methylation of Allylic Alcohols Using cis-Dichlorobis(triphenylphosphine)platinum(II)-Tin(II) Chloride Dihydrate Complex Catalyst
The reaction of allylic alcohols in benzene-methanol (3:2) solvent in the presence of cis-dichlorobis(triphenylphosphine)platinum(II)-tin(II) chloride dihydrate complex catalyst afforded allylic methyl ethers.The structure of the obtained compounds was identified by direct comparison with authentic sample.Cholest-4-en-3α-ol, with a quasi-axial hydroxy group, gave a quantitative yield of 3α-methoxycholest-4-ene.On the other hand, cholest-4-en-3β-ol, with a guasi-equatorial hydroxy group, yielded 3β-methoxycholest-4-ene preferentially, but also yielded 3α-methoxycompound as a by-product, lowering the selectivity of the reaction.
Sakamaki, Hiroshi,Kameda, Noriyuki,Iwadare, Tsukasa,Ichinohe, Yoshiyuki
p. 3491 - 3496
(2007/10/03)

Electrochemical preparation and some reactions of alkoxy triphenylphosphonium ions
The formation of an alkoxy triphenylphosphonium ion by anodic oxidation of Ph3P in the presence of an alcohol was investigated. When a CH2Cl2 solution of Ph3P, Ph3P-H·ClO4-, and an alcohol was subjected to constant-current electrolysis in an undivided cell equipped with a graphite anode and a Pt cathode, the 31P-NMR spectra of the resulting electrolyte showed that alkoxy triphenylphosphonium perchlorates (2) were formed in good to fair yields from primary and secondary aliphatic alcohols, while allylic and bencyclic alcohols were transformed to the corresponding alkyl phosphonium ions, and in the case of tertiary aliphatic alcohols, no formation of the corresponding alkoxy or alkyl phosphonium ions was recognized at all. The isolation of 2 thus formed was achieved in good yields by a simple procedure. For the electrolysis, Ph3P+H·BF4- could be utilized instead of the perchlorate salt, giving an alkoxy triphenylphosphonium tetrafluoroborate (3) from primary and secondary aliphatic alcohols. The reaction of the alkoxy phosphonium ion prepared from β- and α-cholestanol with various nucleophiles such as Bu4N+·X- (X = Br, Cl, F, N3, SCN), PhSH, and PhOH was examined. The results indicated that the reaction site of the phosphonium ions is dictated by the identity of the nucleophile. A soft nucleophile was apt to attack at the α-carbon, giving the corresponding SN2 reaction product in a good yield, while a hard one tended to react at the phosphorus of the phosphonium ion, leading to the regeneration of the cholestanol.
Maeda,Koide,Maki,Ohmori
p. 1076 - 1080
(2007/10/02)

Stereoselective Introduction of Hydroxyl Groups via Hydrazones
Reduction of tosylhydrazones by hydride reagents in wet alcohol gave predominantly alcohols whose stereochemistries are opposite to those of the major reduction products of the corresponding ketones with sodium borohydride.
Tada, Masahiro,Chiba, Kazuhiro,Izumiya, Koji,Tamura, Mihoko
p. 3532 - 3533
(2007/10/02)

Xanthic anhydrides: A novel and convenient source of alkoxythiocarbonyl and alkyl radicals
Upon irradiation with visible light, xanthic anhydrides 14 undergo a chain reaction leading to xanthates 17 and involving β-scission of the intermediate alkoxythiocarbonyl radical.
Forbes, Judith,Zard, Samir Z.
p. 8257 - 8266
(2007/10/02)

Selective Hydrogenations Promoted by Copper Catalysts. 2. Hydrogen-Transfer Reactions Leading to Stereoselective Hydrogenation of Δ5-3β-Sterols to 5β-Derivatives
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Ravasio, Nicolette,Gargano, Michele,Rossi, Michele
p. 1259 - 1261
(2007/10/02)

Epimerization of secondary alcohols by new homogeneous, low oxidation state metal catalysts: Carbon-hydrogen bond activation in rhenium alkoxide complexes (η5-C5R55)Re(NO)(PPh 5)(OCHRR′)
Diastereomerically pure secondary alcohols epimerize to mixtures of diastereomers in C6H5R at 65-90 °C in the presence of 10 mol % (η5-C5R5)Re(NO)(PPh3)(OCH 3) (1; R = H, Me). The methoxide ligand of 1 first exchanges with the alcohol substrate to give alkoxide complexes (η5-C5R5)Re(NO)(PPh 3)(OCHR′R″) (2). Authentic samples of diastereomerically and enantiomerically pure 2 are prepared, where OCHR′R″ is derived from (+)- and (-)-, exo- and endo-borneol. NMR data show that epimerization occurs first at rhenium (ca. 35 °C) and then at carbon (ca. 65 °C). Substitution reactions and rate experiments show that PPh3 initially dissociates from 2 with anchimeric assistance by alkoxide oxygen lone pairs. An intermediate with a trigonal-planar rhenium, which can either return to 2 (with epimerization at rhenium) or undergo β-hydride elimination to a ketone hydride complex (leading to epimerization at carbon), is proposed. Accordingly, rates of epimerization at carbon (but not rhenium) are strongly inhibited by added PPh3, and show a significant kH/kD.
Saura-Llamas, Isabel,Gladysz
p. 2136 - 2144
(2007/10/02)