- Regioselective opening of a cyclopropane ring by mercury(II) and transmetalation of the product with molybdenum. A novel, stereoelectronically controlled, skeletal rearrangement ans Grob-type fragmentation of organomolybdenum intermediates
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Organomercurial 2, arising by a regioselective ring-opening of cyclopropane derivative 1, can be transmetalated with Mo-reagents to initially generate complexes 3 and 7. While 3 reacts further via a stereoelectronically controlled cascade rearrangement to afford 6, complex 7 favors a Grob-type fragmentation leading to 9.
- Srogl, Jiri,Kocovsky, Pavel
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Read Online
- Novel synthesis of 5-hydroxy-5α-cholesta-2,7-dien-6-one and its criegee hydroxylation
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Cholesterol (1) is used to synthesize again 5α-hydroxy-2,7-dien-6-one (5) through the intermediates 2-4. cis-Hydroxylation of 5 with OsO4 and subsequent acetylation give steroids 6-8. Dehydration of 5α-hydroxy-6-ketone 6 forms the unsaturated compounds 9-11.
- Kovganko,Sokolov
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Read Online
- A mild method for the replacement of a hydroxyl group by halogen: 2. unified procedure and stereochemical studies
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N,N-Dimethyl- and N,N-diisopropyl-1-halo-2-methyl-l-propenylamines are readily available reagents for the mild deoxyhalogenation of alcohols and hydroxyacids. In this study we showed that the reactivity of the reagents can be tuned by varying the size of the alkyl groups on the reagents: the replacement of methyl by isopropyl groups led to a significant increase of reactivity. We then described a unified procedure for all deoxyhalogenations using the readily available α-chloroenamines as reagents with (bromination, iodination) or without (chlorination) an alkaline bromide or iodide. Finally, we showed that deoxyhalogenation reactions of secondary alcohols were highly stereospecific and generally occurred with inversion of configuration.
- Gati, Wafa,Munyemana, Fran?ois,Colens, Alain,Srour, Aladdin,Dufour, Mathilde,Vardhan Reddy, K. Harsha,Téchy, Brigitte,Rosse, Gérard,Schweiger, Ed,Qiao, Qi,Ghosez, Léon
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- A General Catalytic Method for Highly Cost- and Atom-Efficient Nucleophilic Substitutions
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A general formamide-catalyzed protocol for the efficient transformation of alcohols into alkyl chlorides, which is promoted by substoichiometric amounts (down to 34 mol %) of inexpensive trichlorotriazine (TCT), is introduced. This is the first example of a TCT-mediated dihydroxychlorination of an OH-containing substrate (e.g., alcohols and carboxylic acids) in which all three chlorine atoms of TCT are transferred to the starting material. The consequently enhanced atom economy facilitates a significantly improved waste balance (E-factors down to 4), cost efficiency, and scalability (>50 g). Furthermore, the current procedure is distinguished by high levels of functional-group compatibility and stereoselectivity, as only weakly acidic cyanuric acid is released as exclusive byproduct. Finally, a one-pot protocol for the preparation of amines, azides, ethers, and sulfides enabled the synthesis of the drug rivastigmine with twofold SN2 inversion, which demonstrates the high practical value of the presented method.
- Huy, Peter H.,Filbrich, Isabel
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supporting information
p. 7410 - 7416
(2018/04/30)
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- Ti-Catalyzed Radical Alkylation of Secondary and Tertiary Alkyl Chlorides Using Michael Acceptors
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Alkyl chlorides are common functional groups in synthetic organic chemistry. However, the engagement of unactivated alkyl chlorides, especially tertiary alkyl chlorides, in transition-metal-catalyzed C-C bond formation remains challenging. Herein, we describe the development of a TiIII-catalyzed radical addition of 2° and 3° alkyl chlorides to electron-deficient alkenes. Mechanistic data are consistent with inner-sphere activation of the C-Cl bond featuring TiIII-mediated Cl atom abstraction. Evidence suggests that the active TiIII catalyst is generated from the TiIV precursor in a Lewis-acid-assisted electron transfer process.
- Wu, Xiangyu,Hao, Wei,Ye, Ke-Yin,Jiang, Binyang,Pombar, Gisselle,Song, Zhidong,Lin, Song
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p. 14836 - 14843
(2018/11/10)
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- Dehalogenation of vicinal dihalo compounds by 1,1′-bis(trimethylsilyl)-1: H,1′ H-4,4′-bipyridinylidene for giving alkenes and alkynes in a salt-free manner
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We report a transition metal-free dehalogenation of vicinal dihalo compounds by 1,1′-bis(trimethylsilyl)-1H,1′H-4,4′-bipyridinylidene (1) under mild conditions, in which trimethylsilyl halide and 4,4′-bipyridine were generated as byproducts. The synthetic protocol for this dehalogenation reaction was effective for a wide scope of dibromo compounds as substrates while keeping the various functional groups intact. Furthermore, the reduction of vicinal dichloro alkanes and vicinal dibromo alkenes also proceeded in a salt-free manner to afford the corresponding alkenes and alkynes.
- Rej, Supriya,Pramanik, Suman,Tsurugi, Hayato,Mashima, Kazushi
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supporting information
p. 13157 - 13160
(2017/12/26)
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- METHOD OF CONVERTING ALCOHOL TO HALIDE
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The present invention relates to a method of converting an alcohol into a corresponding halide. This method comprises reacting the alcohol with an optionally substituted aromatic carboxylic acid halide in presence of an N-substituted formamide to replace a hydroxyl group of the alcohol by a halogen atom. The present invention also relates to a method of converting an alcohol into a corresponding substitution product. The second method comprises: (a) performing the method of the invention of converting an alcohol into the corresponding halide; and (b) reacting the corresponding halide with a nucleophile to convert the halide into the nucleophilic substitution product.
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Page/Page column 51; 181
(2017/01/02)
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- Formamides as Lewis Base Catalysts in SNReactions—Efficient Transformation of Alcohols into Chlorides, Amines, and Ethers
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A simple formamide catalyst facilitates the efficient transformation of alcohols into alkyl chlorides with benzoyl chloride as the sole reagent. These nucleophilic substitutions proceed through iminium-activated alcohols as intermediates. The novel method, which can be even performed under solvent-free conditions, is distinguished by an excellent functional group tolerance, scalability (>100 g) and waste-balance (E-factor down to 2). Chiral substrates are converted with excellent levels of stereochemical inversion (99 %→≥95 % ee). In a practical one-pot procedure, the primary formed chlorides can be further transformed into amines, azides, ethers, sulfides, and nitriles. The value of the method was demonstrated in straightforward syntheses of the drugs rac-Clopidogrel and S-Fendiline.
- Huy, Peter H.,Motsch, Sebastian,Kappler, Sarah M.
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supporting information
p. 10145 - 10149
(2016/08/16)
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- Hantzsch Ester as a Photosensitizer for the Visible-Light-Induced Debromination of Vicinal Dibromo Compounds
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The debromination of vicinal dibromo compounds to generate alkenes usually requires harsh reaction conditions and the addition of catalysts. Just recently the visible-light-induced debromination of vicinal dibromo compounds emerged as a possible alternative to commonly used methods, but the substrate scope of this reaction is limited and a photocatalyst is necessary for the successful conversion of the starting compounds. A catalyst-free visible-light-induced debromination of vicinal dibromo compounds with a base-activated Hantzsch ester as photosensitizer is reported. The method has a wide substrate scope and a broad functional-group compatibility.
- Chen, Wenxin,Tao, Huachen,Huang, Wenhao,Wang, Guoqiang,Li, Shuhua,Cheng, Xu,Li, Guigen
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supporting information
p. 9546 - 9550
(2016/07/14)
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- Synthesis and characterization of steroidal heterocyclic compounds, DNA condensation and molecular docking studies and their in vitro anticancer and acetylcholinesterase inhibition activities
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A facile, convenient and efficient approach for the synthesis of a new series of steroidal heterocyclic compounds (4-12) by reacting a mixture of compounds (1e-3e) with o-aminothiophenol/o-aminophenol/o-phenylenediamine is reported. The structural assignment of products is confirmed on the basis of IR, 1H NMR, 13C NMR, MS and analytical data. The compounds obey the Lipinski's 'Rule of Five' analysis based on computational prediction and pharmacokinetic properties. The anticancer activity has been tested in vitro against three cancer cell lines Hep3B (human hepatocellular carcinoma), MCF7 (human breast adenocarcinoma), HeLa (human cervical carcinoma) and one non-cancer normal cell i.e. PBMCs (peripheral blood mononuclear cell) by MTT assay. In addition, the synthesized compounds are also tested for their in vitro antioxidant activity by various reported methods in which compounds 10-12 exhibited good antioxidant activity. Nonenzymatic degradation of DNA has been investigated. The acetylcholinesterase (AChE) inhibitor activities of the steroidal derivatives are also evaluated using Ellman's method. Moreover, the application of compound 6 as a DNA gene transporter is evaluated by DNA condensation and ascertained by employing TEM and AFM, which illustrate that the compound 6 induces the condensation of CT-DNA. Molecular docking studies further characterize the interaction of the synthesized compounds with DNA. 2015
- Ali, Abad,Asif, Mohd,Khanam, Hena,Mashrai, Ashraf,Sherwani, Mohd Asif,Owais, Mohammad,Shamsuzzaman
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p. 75964 - 75984
(2015/09/28)
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- Selective reduction of α,β-unsaturated steroidal carbonyl compounds by NaBH4in presence of guanidine hydrochloride in dioxane
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A selective hydrogenation of α,β-unsaturated steroidal carbonyl compounds with NaBH4in the presence of guanidine hydrochloride in dioxane in good to excellent yields are described.
- Khan, Salman Ahmad,Asiri, Abdullah M.
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p. 6331 - 6334
(2015/02/19)
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- Synthesis of steroidal thiazolidinones as antibacterial agents based on the in vitro and quantum chemistry calculation
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Steroidal thiazolidinone derivatives were prepared from the reaction of steroidal thiosemicarbazones with ethyl bromoacetate in dioxane. Steroidal thiosemicarbazones were prepared by reacting thiosemicarbazide with steroidal ketones. The structures of these compounds were elucidated by IR, 1HNMR, 13CNMR, and mass spectral study, and their purities were confirmed by elemental analyses. The antibacterial activities of these compounds were evaluated by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria, and then the minimum inhibitory concentration of compounds were determined. The results showed that steroidal thiazolidinone derivatives are better in inhibiting growth as compared with steroidal thiosemicarbazone derivatives of both types of the bacteria. Compounds 7 and 8 are better antibacterial agents as compared with standard drug, Amoxicillin. Based on the quantum chemistry calculation at the DFT/6-31G*level, the frontier molecular orbitals and electrostatic potential of compounds 7 and 8 were also discussed.
- Khan, Salman A.,Asiri, Abdullah M.,Sharma, Kamlesh
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p. 1998 - 2004
(2013/07/26)
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- Stereoretentive chlorination of cyclic alcohols catalyzed by titanium(IV) tetrachloride: Evidence for a front side attack mechanism
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A mild chlorination reaction of alcohols was developed using the classical thionyl chloride reagent but with added catalytic titanium(IV) chloride. These reactions proceeded rapidly to afford chlorination products in excellent yields and with preference for retention of configuration. Stereoselectivities were high for a variety of chiral cyclic secondary substrates including sterically hindered systems. Chlorosulfites were first generated in situ and converted to alkyl chlorides by the action of titanium tetrachloride which is thought to chelate the chlorosulfite leaving group and deliver the halogen nucleophile from the front face. To better understand this novel reaction pathway, an ab initio study was undertaken at the DFT level of theory using two different computational approaches. This computational evidence suggests that while the reaction proceeds through a carbocation intermediate, this charged species likely retains pyramidal geometry existing as a conformational isomer stabilized through hyperconjugation (hyperconjomers). These carbocations are then essentially "frozen" in their original configurations at the time of nucleophilic capture.
- Mondal, Deboprosad,Li, Song Ye,Bellucci, Luca,Laino, Teodoro,Tafi, Andrea,Guccione, Salvatore,Lepore, Salvatore D.
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p. 2118 - 2127
(2013/04/10)
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- Synthesis and biological studies of steroidal pyran based derivatives
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Steroid based cancer chemotherapeutic agents of the type 2′-amino-3′-cyanocholest-6-eno[5,7-de]4H-pyrans (1c-3c) have been synthesized and characterized by the various spectroscopic and analytical techniques. The DNA binding studies of compounds (1c-3c) with CT DNA were carried out by UV-vis and fluorescence spectroscopy and gel electrophoresis. The compounds (1c-3c) bind to DNA preferentially through electrostatic and hydrophobic interactions with Kb values found to be 5.4 × 103, 2.3 × 103 M-1 and 1.97 × 103 M-1, respectively indicating the higher binding affinity of compound (1c) towards DNA. The molecular docking study suggested that the electrostatic interaction of compounds (1c-3c) in between the nucleotide base pairs is due to the presence of pyran moiety in steroid molecule. All the compounds (1c-3c) cleave supercoiled pBR322 DNA via hydrolytic pathway, as validated by T4 DNA ligase assay. The compounds (1c-3c) were screened for in vitro cytotoxicity against the cancer and non-cancer cells SW480, A549, HepG2, HeLa, MCF-7, HL-60, DU-145, NL-20, HPC and HPLF by MTT assay. The compounds (1c-3c) were tested for genotoxicity (comet assay) involving apoptotic degradation of DNA and was analyzed by agarose gel electrophoresis and visualized by ethidium bromide staining. The results revealed that compound (1c) has better prospectus to act as cancer chemotherapeutic candidate which warrants further in vivo anticancer investigations.
- Shamsuzzaman,Dar, Ayaz Mahmood,Khan, Yusuf,Sohail, Aamir
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- Electrochemical synthesis of glycoconjugates of 3β-hydroxy- Δ5-steroids by using non-activated sugars and steroidal thioethers
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A new protocol for the electrochemical synthesis of glycoconjugates is presented. Thioether derivatives of cholesterol and other sterols were subjected to anodic oxidation in the presence of a sugar alcohol affording glycoconjugates with the sugar linked to a steroid moiety by an ether bond. The isomeric 6β-3α,5α-cyclo-steroidal thioethers proved to be better sterol donors than the normal 3β-Δ5-steroidal thioethers.
- Tomkiel, Aneta M.,Brzezinski, Krzysztof,?otowski, Zenon,Siergiejczyk, Leszek,Wa?ejko, Piotr,Witkowski, Stanis?aw,Kowalski, Jan,P?oszyn?ska, Jolanta,Sobkowiak, Andrzej,Morzycki, Jacek W.
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p. 8904 - 8913
(2013/09/23)
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- A facile and green protocol for nucleophilic substitution reactions of sulfonate esters by recyclable ionic liquids [bmim][X]
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Ionic liquids [bmim][X] (X = Cl, Br, I, OAc, SCN) are highly efficient reagents for nucleophilic substitution reactions of sulfonate esters derived from primary and secondary alcohols. The counter anions (X-) of the ionic liquids, [bmim][X], effectively replace the sufonates affording the corresponding substitution products such as alkyl halides, acetates, and thiocyanides in excellent yields. The newly developed protocol is very environmentally attractive because the reactions use stoichiometric amounts of ionic liquids as sole reagents in most cases and do not require additional solvents, any other activating reagents, non-conventional equipment, or special precautions. Moreover, these ionic liquids can be readily recycled without loss of reactivity, making the whole process greener.
- Liu, Yajun,Xu, Yongnan,Jung, Sun Ho,Chae, Junghyun
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p. 2692 - 2698,7
(2012/12/12)
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- A facile and green protocol for nucleophilic substitution reactions of sulfonate esters by recyclable ionic liquids [bmim][X]
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Ionic liquids [bmim][X] (X = Cl, Br, I, OAc, SCN) are highly efficient reagents for nucleophilic substitution reactions of sulfonate esters derived from primary and secondary alcohols. The counter anions (X-) of the ionic liquids, [bmim][X], effectively replace the sufonates affording the corresponding substitution products such as alkyl halides, acetates, and thiocyanides in excellent yields. The newly developed protocol is very environmentally attractive because the reactions use stoichiometric amounts of ionic liquids as sole reagents in most cases and do not require additional solvents, any other activating reagents, non-conventional equipment, or special precautions. Moreover, these ionic liquids can be readily recycled without loss of reactivity, making the whole process greener. Georg Thieme Verlag KG Stuttgart · New York.
- Liu, Yajun,Xu, Yongnan,Jung, Sun Ho,Chae, Junghyun
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p. 2692 - 2698
(2013/01/15)
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- Synthesis and in vitro antibacterial activity of novel steroidal (6R)-spiro-1,3,4-thiadiazoline derivatives
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Novel steroidal (6R)-spiro-1,3,4-thiadiazoline derivatives were synthesized by the cyclization of steroidal thiosemicarbazones with acetic anhydride, screened in vitro against antibacterial activity using disc-diffusion method and the minimum inhibitory concentration. The results showed that steroidal thiadiazoline derivatives exhibited better antibacterial activity than the steroidal thiosemicarbazone derivatives. Chloro and acetoxy substituents on the 3β-position of the steroidal thiadiazoline ring increased the antibacterial activity. Among all the compounds, compound 7 and 8 were found better inhibitors of both types of bacteria (Gram-positive and Gram-negative) as compared to the respective drug amoxicillin. All the synthesized compounds were well characterized by spectroscopic methods such as IR, 1H-NMR, 13C-NMR mass, and elemental analysis and their stereochemistry was also discussed.
- Khan, Salman A.,Asiri, Abdullah M.
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p. 1452 - 1457
(2013/02/23)
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- Iron(III)-catalyzed halogenations by substitution of sulfonate esters
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A novel halogenation reaction from sulfonates catalyzed by iron(III) is described. The reaction can be performed as a stoichiometric or a catalytic version. This reaction provides a convenient strategy for the efficient access to structurally diverse secondary chlorides, bromides and iodides. The stereochemical course of the reaction is governed by the substrate and the experimental conditions. Secondary alcohols modified as quisylates or pysylates are substantially more reactive. Aliphatic quisylates proceed with overall inversion of configuration under catalytic conditions. Chemoselectivity in bismesylates was observed in favour of the secondary mesylate. Additionally, based on the experimental results, a possible catalytic cycle for the halogenation has been proposed.
- Ortega, Nuria,Feher-Voelger, Andres,Brovetto, Margarita,Padron, Juan I.,Martin, Victor S.,Martin, Tomas
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p. 963 - 972
(2011/06/20)
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- Catalytic phosphorus(V)-mediated nucleophilic substitution reactions: Development of a catalytic appel reaction
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Catalytic phosphorus(V)-mediated chlorination and bromination reactions of alcohols have been developed. The new reactions constitute a catalytic version of the classical Appel halogenation reaction. In these new reactions oxalyl chloride is used as a consumable stoichiometric reagent to generate the halophosphonium salts responsible for halogenation from catalytic phosphine oxides. Thus, phosphine oxides have been transformed from stoichiometric waste products into catalysts and a new concept for catalytic phosphorus-based activation and nucleophilic substitution of alcohols has been validated. The present study has focused on a full exploration of the scope and limitations of phosphine oxide catalyzed chlorination reactions as well as the development of the analogous bromination reactions. Further mechanistic studies, including density functional theory calculations on proposed intermediates of the catalytic cycle, are consistent with a catalytic cycle involving halo- and alkoxyphosphonium salts as intermediates.
- Denton, Ross M.,An, Jie,Adeniran, Beatrice,Blake, Alexander J.,Lewis, William,Poulton, Andrew M.
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experimental part
p. 6749 - 6767
(2011/10/02)
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- Synthesis and biological evaluation of some thiazolidinone derivatives of steroid as antibacterial agents
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Steroidal thiazolidinone derivatives were prepared by the multi-step reactions of steroid. It is prepared from steroidal thiosemicarbazones with ethyl bromoacetate in dioxane. Steroidal thiosemicarbazones were prepared by the reaction of thiosemicarbazide with steroidal ketones. The structures of these compounds were elucidated by IR, 1H NMR, Fab mass spectrometries and their purities were confirmed by elemental analyses. The antibacterial activity of these compounds was evaluated by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria and then the minimum inhibitory concentration (MIC) of compounds was determined. The results showed that steroidal thiazolidinone derivatives are better in inhibiting the growth as compared to steroidal thiosemicarbazone derivatives of both types of the bacteria (Gram-positive and Gram-negative). Compounds 7 and 8 are better antibacterial agents as compared to standard drug Amoxicillin.
- Khan, Salman Ahmad,Yusuf, Mohammed
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scheme or table
p. 2597 - 2600
(2009/10/09)
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- Practical synthesis of 3β-amino-5-cholestene and related 3β-halides involving i-steroid and retro-i-steroid rearrangements
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(Equation Presented) Derivatives of 3β-amino-5-cholestene (3β-cholesterylamine) are of substantial interest as cellular probes and have potential medicinal applications. However, existing syntheses of 3β-amino-5-cholestene are of limited preparative utility. We report here a practical method for the stereoselective preparation of 3β-amino-5- cholestene, 3β-chloro-5-cholestene, 3β-bromo-5-cholestene, and 3β-iodo-5-cholestene from inexpensive cholesterol. A sequential i-steroid/retro-i-steroid rearrangement promoted by boron trifluoride etherate and trimethylsilyl azide converted cholest-5-en-3β-ol methanesulfonate to 3β-azido-cholest-5-ene with retention of configuration in 93% yield.
- Sun, Qi,Cai, Sutang,Peterson, Blake R.
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scheme or table
p. 567 - 570
(2009/07/18)
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- Unusual electrochemical oxidation of cholesterol
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It has been found that cholesterol undergoes direct electrochemical oxidation on platinum electrode in dichloromethane. Voltammetric measurements show that the process is controlled by the rate of electron transfer and the height of the oxidation peak is linear vs. concentration of cholesterol. Preparative electrolysis with separated cathodic and anodic compartments afforded dicholesteryl ether in a relatively high material yield. Depending on electrolysis conditions (composition of supporting electrolyte and electrolytic cell construction) various by-products with a 3β-chloro, 3β-acetoxy, or 3β-acetylamino group were obtained.
- Kowalski, Jan,Lotowski, Zenon,Morzycki, Jacek W.,Ploszynska, Jolanta,Sobkowiak, Andrzej,Wilczewska, Agnieszka Z.
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p. 543 - 548
(2008/09/17)
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- Rapid conversion of hindered arylsulfonates to alkyl chlorides with retention of configuration
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Arylsulfonates of hindered secondary alcohols are converted to the corresponding alkyl chlorides very rapidly and in good yields in the presence of titanium tetrachloride at low temperatures. These reactions proceed with exclusive retention of configuration.
- Lepore, Salvatore D.,Bhunia, Anjan K.,Mondal, Deboprosad,Cohn, Pamela C.,Lefkowitz, Craig
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p. 3285 - 3286
(2007/10/03)
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- Chlorination of 3β-hydroxyl-5-Δ steroids with anhydrous ferric chloride
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Treatment of 3β-hydroxyl-5-Δ steroids with anhydrous FeCl 3 in CH2Cl2 afforded reasonable yields of the corresponding alkyl chlorides with a retention of configurations. The structures of the chlorine-exchanging products were determined by NMR and HRMS spectra. The absolute configurations were confirmed by X-ray crystal analysis of 3β-chloro-androst-5-en-17-one. The generality and scope of the reaction were also investigated.
- Liu, Feng-Wu,Liu, Hong-Min,Zhang, Yan-Bing,Zhang, Jing-Yu,Tian, Li-Huan
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p. 825 - 830
(2007/10/03)
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- Syntheses and structures of 3-stannylcholest-5-ene species
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The compounds, 3α- and 3β-triphenylstannylcholest-5-ene, 1 and 2 respectively, have been prepared stereospecifically in reactions of Ph3SnLi with cholesteryl methane- or toluene-p-sulfonates, and of Ph3SnCl with the Grignard reagent from cholesteryl chloride, respectively. Complete 1H and 13C NMR spectral assignments for 1 have been obtained using HMBC and HMQC techniques: these have been used to aid the 13C NMR spectral assignments for 2 and 3α- and 3β-(InPh3-nSn)cholest-5-enes (n = 1-2) (9-12). Crystal structure determinations of 3α-(IPh2Sn)cholest-5-ene 9 and 3α-(I2PhSn)cholest-5-ene 10 indicate distorted tetrahedral geometries about the tin centres in both compounds. The Sn-I bond lengths are 2.731(5) A in 9 and between 2.6979(12) and 2.7173(12) A in 10. Despite the similarity in the values (ca. 60°) of the dihedral angles, Sn-C(3)-C(2)-C(1) [C(1) aliphatic carbon] and Sn-C(3)-C(4)-C(5) [C(5) olefinic carbon], the values of 3J[119Sn-13C(1)] are about twice the 3J[119Sn-13C(5)] values in each of 1, 9 and 10; in contrast, 3J[119Sn-13C(1)] and 3J[119Sn-13C(5)] values are essentially the same in each of 2, 11 and 12 [Sn-C(3)-C(2)-C(1) and Sn-C(3)-C(4)-C(5) ca. 180°].
- Buchanan, Heather J.,Cox, Philip J.,Doidge-Harrison, Solange M. S. V.,Howie, R. Alan,Jaspars, Marcel,Wardell, James L.
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p. 3657 - 3664
(2007/10/03)
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- Syntheses and CD Studies of New Cholesteno- and -pyrimidines
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The syntheses of 5α- and 5β-cholest-3-enopyrimidines (7) and (7') could be achieved by using the hydroxymethylene derivative of cholestan-4-one (5) prepared from cholesterol (1).Their 2'-derivatives 7a-7d and 7'a-7'c were also synthesized. 5α-Cholest-6-enopyrimidine (13) was prepared by the reaction of 5α-cholestan-7-one (12) with tris(formylamino)methane.The CD spectra exhibit at least three Cotton effects between 300 and 210 nm, a first CD band around 290, a second one around 260, and a third one around 220 nm.An earlier developed quadrant rule can be applied to the determination of the sign of the first CD band, while the suggested helicity rule allows prediction of the third CD band. - Keywords: Cholestenopyrimidines / Circular dichroism / Quadrant rule of cholestenopyrimidines
- Hasan, Mashooda,Rashid, Naghmana,Khan, Khalid Mohammed,Perveen, Shahnaz,Snatzke, Guenther,et al.
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p. 1871 - 1876
(2007/10/03)
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- Corner Opening of Cyclopropanes by Mercury(II) and Thallium(III) and Transmetalation of the Intermediate Organomercurials. A Novel, Stereoselective Approach to Cyclobutanes and Cyclopropanes
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The reactivity of the two isoelectronic cations (Hg2+ and Tl3+) toward the cyclopropane rings is compared, and further evidence for the exclusive corner selectivity for Hg2+ is provided by isotope labeling.Cleavage of cyclopropyl derivative 1 with Hg(NO3)2, followed by KBr quenching, afforded the stable, rearranged organomercurial 3, whose transmetalation has been studied.Whereas reaction of 3 with Pd(II) afforded lactol 4, treatment with Me2CuLi resulted in the formation of cyclobutanol derivative (3 -> 29); analogous conjugate addition has also been accomplished (32 -> 35).Similarly, the organomercurial 22, obtained from 21 as the major product on the Hg(II)-mediated ring-opening, reacted with Me2CuLi or AlCl3 to give the ring-closure product 21.These reactions represent a novel method for the stereoselective construction of four- and three-membered rings.The stereochemistry of the key steps of these transformations has been established by using stereospecifically deuterated substrates 1b, 3b, 21b, and 22b.
- Kocovsky, Pavel,Srogi, Jiri,Pour, Milan,Gogoll, Adolf
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p. 186 - 197
(2007/10/02)
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- Radical cation reactions associated with the thiocarbonyl group
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The radical cation reactions of different thiocarbonyl compounds were examined. Compounds 7, 8, 11, 14 and 18 underwent a radical cation fragmentation in a photoinduced electron transfer (PET) reaction, in the presence of tris(4-bromophenyl)aminium hexachloroantimonate.
- Barton,Dalko,Gero
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p. 1883 - 1886
(2007/10/02)
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- A USEFUL METHOD FOR CONVERTING 2 ALCOHOLS TO THEIR CHLORIDES WITH RETENTION OF CONFIGURATION
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Xanthate esters of 2 alcohols are converted to their chlorides with retention of configuration in good yield by use of sulfuryl chloride.
- Kozikowski, A. P.,Lee, Jaemoon
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p. 3053 - 3056
(2007/10/02)
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- A simple Method for the Transformation of Steroidal Epoxides to Olefins
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5,6α-Oxido-5α-cholestane (1) and its 3β-substituted analogues (2-4) on silver nitrate-neutral alumina surface were readily converted to cholest-5-ene (5) and its 3β-substituted analogues (6-8) in 90-95percent yield.
- Shafiullah,Pathak, R. K.
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p. 668 - 669
(2007/10/02)
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- DEHALOGENATION OF α-HALOKETONES AND VIC-DIBROMIDES WITH NICKEL BORIDE
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α-Haloketones and vic-dibromides are converted to the corresponding ketones and alkenes respectively with nickel boride generated in situ from sodium borohydride and nickel chloride.
- Sarma, J.C.,Borbaruah, M.,Sharma, R.P.
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p. 4657 - 4660
(2007/10/02)
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- REACTION OF SOME TRISUBSTITUTED STEROID EPOXIDES WITH TRIPHENYLPHOSPHINE - IODINE DOMPLEX. DEOXYGENATION OF EPOXIDES
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Triphenylphosphine - iodine complex was found to be an effective reagent for deoxygenation of trisubstituted steroidal epoxides.The mechanism of the reaction is proposed.
- Paryzek, Zdzislaw,Wydra, Roman
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p. 2601 - 2604
(2007/10/02)
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- Sterochemical Aspects of Acid-Catalyzed Cyclopropane Ring-Opening Reactions. A Stereospecific Pathway to Crinosterol and Brassicasterol
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It is shown that the acid-catalyzed ring-opening of the two diastereoisomeric 23,24-methylenecholosterols 3 and 5 on treatment with gaseous HCl in acetic acid leads sterospecifically to the naturally occuring crinosterol (4) and brassicasterol (6), respectively (Scheme 1).This isomerization can be viewed as a biomimetic model of an in vivo methylation process of the type already known in plant sterol metabolism (cf. cycloeucalenol --> obtusifoliol, 1-->2).The synthetic application of this method provides a convenient labelling of sterol side chain for tracer experiments.The mechanistic features of the reaction with respect to its particular stereospecificity are discussed.
- Lang, Robert W.,Djerassi, Carl
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p. 407 - 418
(2007/10/02)
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- New Procedure for the Transformation of Alcohols to Alkyl Halides via Xanthate Esters and Free-Radical Intermediates
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O-Alkyl-S-methyl xanthates have been used to convert alcohols to alkyl halides via free-radical pathways.The xanthate esters were readily prepared in high yields and were converted in 8-80percent yields to the corresponding alkyl halides by (a) photolysis with 254-nm light in carbon tetrachloride or bromotrichloromethane and (b) by treatment with Cu(I)-Cu(II) halide in acetonitrile.The photochemical transformation gave low yields with highly aliphathic compounds due to carbon tetrachloride-mediated free-radical halogenation reactions.The transformation promoted by Cu(I)-Cu(II) halide competed with an electron-transfer oxidation process.The reaction could not be induced with AIBN or benzoyl peroxide or by treatment with molybdenum pentachloride.Mechanistic implications are discussed.
- Cristol, Stanley J.,Seapy, Dave G.
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p. 132 - 136
(2007/10/02)
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- REACTIONS IN DRY MEDIA: REACTIONS OF CHOLESTEROL AND CHOLESTANES ON SILICA BOUND FERRIC CHLORIDE CHOLESTANE-DIACHOLESTENE REARRANGEMENT
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Reaction of cholesterol with silica bound FeCl3 resulted in a mixture of 3β-cholesteryl chloride and dicholesteryl ether.5-cholestene and hydroxy-and halogeno-substituted cholestane derivatives gave on heating at 100 deg C with this reagent a 1:1 mixture of 20-epimeric diacholestenes.The 20(R)-isomer gave with meta-chloroperbenzoic acid 20(R)-α-epoxide, while the 20(S)-gave a mixture of 20(S)-α- and 20(S)-β-epoxides.5α,6β-Dihydrocholestane reacted with the FeCl3/SiO2 under milder conditions (50 deg C) to give 6β-hydroxy-20(R)-diacholestene, which was converted to the 20(R)-diacholestene.
- Tal, Daniel M.,Keinaen, Ehud,Mazur, Yehuda
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p. 4327 - 4330
(2007/10/02)
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