A simple and efficient chemoselective method for the catalytic deprotection of acetals and ketals using bismuth triflate

Bismuth triflate is a highly efficient catalyst (0.1-1 mol %) for the deprotection of acetals and ketals. The procedure is very facile and selective for acetals derived from ketones and conjugated aldehydes. tert-Butyldimethylsilyl ethers are stable to the reaction conditions. The highly catalytic nature of bismuth triflate and the use of a relatively nontoxic solvent system (THF/H(2)O) make this procedure particularly attractive for large-scale synthesis.     

CBr4-photoirradiation protocol for chemoselective deprotection of acid labile primary hydroxyl protecting groups

CBr₄-photoirradiation protocol was found to be a mild, highly efficient and selective method for deprotection of isopropylidene, benzylidene, triphenylmethyl and tert-butyldimethylsilyl protecting groups on sugar molecules. The conditions of this reaction can also be used to cleave peptides off from acid-labile resin linkers in solid-phase peptide synthesis.     

A mild and practical deprotection method for benzyl thioethers

A highly effective and mild deprotection method was developed for benzyl thioethers using dibutylmagnesium in the presence of a catalytic amount of titanocene dichloride. This methodology is applicable to both aromatic and aliphatic benzyl thioethers.     

A simple method for chemoselective phenol alkylation

A simple and effective method for chemoselective alkylation of phenol over carboxylic acid using a 40% aqueous solution of tetrabutylphosphonium hydroxide that affords the desired phenyl ethers in 82-99% yield is described.     

A mild copper catalyzed method for the selective deprotection of aryl allyl ethers

Copper boryl reagents enable the selective cleavage of aryl allyl ethers to the corresponding phenols in good to moderate yields.     

A mild and efficient method for the chemoselective deprotection of acetonides with lanthanum(III) nitrate hexahydrate

Acetonides are hydrolyzed selectively and efficiently with lanthanum(III) nitrate hexahydrate in acetonitrile. The method has good compatibility with other sensitive hydroxyl protecting groups such as trityl, TBDMS, THP, OAc, OBz and OBn.     

A novel and convenient chemoselective deprotection method for both silyl and acetyl groups on acidic hydroxyl groups such as phenol and carboxylic acid by using a nitrogen organic base, 1,1,3,3-tetramethylguanidine

[reaction: see text] 1,1,3,3-Tetramethylguanidine (TMG)(1), a nitrogen organic base, is a convenient and useful reagent for chemoselective deprotection of both silyl and acetyl groups on acidic hydroxyl groups such as phenol and carboxylic acid without affecting aliphatic silyl and acetyl groups. The chemoselectivity is dependent on the acidity of the hydroxyl group.     

A mild and chemoselective method for the deprotection of tert-butyldimethylsilyl (TBDMS) ethers using iron(III) tosylate as a catalyst

The most common method for the deprotection of TBDMS ethers utilizes stoichiometric amounts of tetrabutylammonium fluoride, n-Bu₄N⁺F⁻ (TBAF), which is highly corrosive and toxic. We have developed a mild and chemoselective method for the deprotection of TBDMS, TES, and TIPS ethers using iron(III) tosylate as a catalyst. Phenolic TBDMS ethers, TBDPS ethers and the BOC group are not affected under these conditions. Iron(III) tosylate is an inexpensive, commercially available, and non-corrosive reagent.     

SmI2/water/amine mediates cleavage of allyl ether protected alcohols: application in carbohydrate synthesis and mechanistic considerations

[reaction: see text]. SmI2/H2O/amine provides selective cleavage of unsubstituted allyl ethers in good to excellent yields. This method is therefore useful in deprotection of alcohols and carbohydrates.     

A practical ruthenium-catalyzed cleavage of the allyl protecting group in amides, lactams, imides, and congeners

A convenient methodology for the deprotection of N-allylic amide-like moieties was developed. The first examples accounting for the ruthenium-catalyzed deallylation of amides, lactams, imides, pyrazolidones, hydantoins, and oxazolidinones have been achieved by the sequential use of Grubbs carbene (isomerization step) and RuCl(3) (oxidation step). A variety of substrates, including enantiopure multifunctional beta- and gamma-lactams, can be employed.     

N-Iodosuccinimide (NIS) as a mild and highly chemoselective catalyst for deprotection of tert-butyldimethylsilyl ethers

A variety of alcoholic TBDMS (t-butyldimethylsilyl) ethers are easily removed in excellent yields by treatment with a catalytic amount of N-iodosuccinimide (NIS, 5 mol %) in methanol. This method is able to deprotect TBDMS ethers of alcohols in the presence of TBDMS ethers of phenols.     

A high loading sulfonic acid-functionalized ordered nanoporous silica as an efficient and recyclable catalyst for chemoselective deprotection of tert-butyldimethylsilyl ethers

A high loading sulfonic acid-functionalized ordered nanoporous silica efficiently catalyzes the deprotection of a variety of alcoholic TBDMS (tert-butyldimethylsilyl)ethers in methanol. The catalyst shows high thermal stability (up to 240 °C) and can be recovered and reused for at least seven reaction cycles without loss of reactivity. This method can be used to deprotect TBDMS ethers of alcohols in the presence of TBDMS ethers of phenols.     

A simple electrochemical method for the determination of hydroxyl free radicals without separation process

Generally speaking, measurement of hydroxylated radical products of salicylic acid requires a fussy separation process. In this study, we describe a simple method to electrochemically detect hydroxyl radicals (*OH) using 4-hydroxybenzoic acid (4-HBA) as the *OH trap. The *OH is generated by the Fenton reaction from iron (II) sulfate and hydrogen peroxide in a phosphate buffer solution. Experimental results show that our method can detect the OH with high sensitivity without any separation process. The differential pulse voltammetric responses show a linear dependence on the concentration of *OH in a range of 2.0x10(-6) and 1.0x10(-3)M with a determination limit down to 5.0x10(-7)M. As a demonstration, the kinetics of the Fenton reaction was mapped by measuring the reaction product of hydroxyl radical trapped by 4-HBA. The result is in good agreement with that reported previously. All the results show that the present approach could provide a simple, inexpensive and promising method for biomedicine and iatrology.     

A highly efficient and reusable mesoporous supported Co(II) catalyst for chemoselective deprotection of aryl acetates

Chemoselective deprotection of aryl acetates is successfully carried out in excellent yield using a mesoporous silica-supported (Salen) Co(II) catalyst. The catalyst shows high thermal stability and also can be recovered and reused at least 10 times without any significant loss of its catalytic activity. The present process is environmentally benign and economical.     

A new simple and sensitive fluorometric method for the determination of hydroxyl radical and its application

A simple and sensitive fluorometric method to detect the hydroxyl radical is described. This method employs the reaction between OH and dimethyl sulfoxide (DMSO) to generate quantitatively formaldehyde, which then reacts with ammonia and 1,3-cyclohexanedione (CHD) at pH 4.5. The product produces the characteristic fluorescence with its excitation and emission wavelength at 400.4 and 452.3 nm, respectively. The quantitative analysis of hydroxyl radical can be done through the determination of the fluorescence intensity. By the developed method, the scavenging abilities of some amino acids and flavonoids on hydroxyl radical are studied.     

A mild and selective method for the N-Boc deprotection by sodium carbonate

A cleavage of N-tert-butyloxycarbonyl protection by Na₂CO₃ is reported. The N-free products are obtained in excellent yields. The compatibility of the method with the presence of acidic or basic groups is demonstrated. The reactions were performed on indole, azaindole, indazole, pyrazole, indolinone, quinolinone, and oxazolone.     

B-bromo-9-borabicyclo[3.3.1]nonane. A convenient and selective reagent for ether cleavage

In methylene chloride solution, B-bromo-9-borabicyclo[3.3.1]nonane (BBr-9-BBN) readily cleaves, in excellent yield, a variety of ethers of representative structural types. The reagent can also be used for selective cleavage of one of the ether groups in a molecule containing more than one such group.     

A simple practical method for estimating activation sensitivities of different elements/isotopes with cyclotron produced neutrons

A simple method for estimating the activation sensitivity of an element/isotope, activated with cyclotron produced fast neutrons, has been developed. It uses the measured neutron spectra produced by bombarding a thick Be target with deuterons of different energies (15-54 MeV) and the measured/estimated neutron cross sections for the particular nuclear reaction. This method is applicable to all sorts of neutron spectra and all the elements/isotopes, whose cross sections/excitation functions in the relevant energy ranges, are available. We have applied this method to estimate the activation sensitivities of a number of lighter elements of biomedical interest. It is pointed out that this simple method is much cheaper, more convenient and quicker in estimating the activation sensitivities than experimental measurements - of course as long as the appropriate excitation functions are available.     

A sensitive and practical colorimetric test for polymer-supported hydroxyl and thiol groups

A new sensitive and practical colorimetric test for solid-supported hydroxyl and thiol groups is described. The assay is based on the direct labeling with low amounts of commercially available NF31 in the presence of DMAP at room temperature, resulting in easily detectable red beads.