An Efficient Deprotective Method for Allylic Alcohols Protected as Methoxyethoxymethyl (MEM) And Methoxymethyl (MOM) Ethers

Methoxyethoxymethyl ethers (MEM) and methoxymethyl ethers (MOM) of allylic alcohols are readily cleaved by pyridinium paratoluenesulfonate (PPTS) in 2-butanone or t-butyl alcohol. This procedure is also efficient for deprotection of benzylic and aliphatic alcohols.     

Methoxymethyl (MOM) group nitrogen protection of pyrimidines bearing C-6 acyclic side-chains

Novel N-methoxymethylated (MOM) pyrimidine (4-13) and pyrimidine-2,4-diones (15-17) nucleoside mimetics in which an isobutyl side-chain is attached at the C-6 position of the pyrimidine moiety were synthesized. Synthetic methods via O-persilylated or N-anionic uracil derivatives have been evaluated for the synthesis of N-1- and/or N-3-MOM pyrimidine derivatives with C-6 acyclic side-chains. A synthetic approach using an activated N-anionic pyrimidine derivative afforded the desired N,N-1,3-diMOM and N-1-MOM pyrimidines 4 and 5 in good yield. Introduction of fluorine into the side-chain was performed with DAST as the fluorinating reagent to give a N,N-1,3-diMOM pyrimidine 13 with a 1-fluoro-3-hydroxyisobutyl moiety at C-6. Conformational study of the monotritylated N-1-MOM pyrimidine 12 by the use of the NOE experiments revealed the predominant conformation of the compound to be one where the hydroxymethyl group in the C-6 side-chain is close to the N-1-MOM moiety, while the OMTr is in proximity to the CH(3)-5 group. Contrary to this no NOE enhancements between the N-1-MOM group and hydroxymethyl or fluoromethyl protons in 13 were observed, which suggested a nonrestricted rotation along the C-6 side-chain. Fluorinated N,N-1,3-diMOM pyrimidine 13 emerged as a model compound for development of tracer molecules for non-invasive imaging of gene expression using positron emission tomography (PET).     

A Facile Removal of the Tetrahydropyranyl Protecting Group from Alcohol Derivatives

The tetrahydropyranyl (THP) moiety has been frequently used as a protecting group for alcohols¹. There has been an occasional comment regarding difficulty in storing the derivatives, since any trace of acid will hydrolyze them². Also, as with any protecting group, one must be concerned with methods for its later removal³. In this report we describe a simple method for removing the THP protecting group under mild conditions and a procedure to store these derivatives.     

A New Protecting Group for Phenols: Phenylthiomethyl (PTM) Ethers

Hemithioacetals have previously found utility as protecting groups for alcohols and phenols. In particular, the protection of alcohols^2,3,4 and phenols⁵ as methylthiomethyl (MTM) ethers, and the facile hydrolysis of these ethers back to the parent alcohol or phenol have been reported. We now wish to report the use of phenylthiomethyl (PTM) ethers as phenolic protecting groups which may be differentiated from phenolic MTM ethers.     

Selective Removal of the o-Nitrophenylsulfenyl Protecting Group in Peptide Synthesis

2-Thiopyridone (2-mercaptopyridine, 1 ) was found to be a very suitable reagent for removing the N^α-o-nitrophenylsulfenyl (NPS-) group in both conventional and solid-support peptide synthesis. A 3- to 5-molar excess of the reagent together with an equivalent amount of glacial acetic acid in methanol, dimethylformamide, or methylene chloride produces the soluble, stable mixed disulfide, 2-nitrophenyl 2-pyridyl disulfide ( 2 ), and the N^α-deprotected amino-acid or peptide. The yields are quantitative in less than 5 min if all educts are dissolved, in about 20 to 30 min in solid-support synthesis. No modifications of either the indole side-chain of tryptophan or of a series of side-chain protecting groups, in particular of the t-butyl type, are produced. No adverse side-reactions (insoluble disulfides) were observed. The procedure is illustrated with a series of amino-acid derivatives and with the solid-support synthesis of [5-leucine]-enkephalin.     

(Butylthio)carbonyl Group: A New Protecting Group for the Guanine Residue in Oligoribonucleotide Synthesis

The protection of the O⁶-amide and N²-amino groups of guanosine with the (butylthio)carbonyl group is described. This group could be rapidly introduced in good yields and removed very easily under the conventional deprotective condition for theexo-amino acyl groups of other nucleoside bases.     

Deprotection of t-Butyldimethylsiloxy(TBDMS)Protecting Group

t-Butyldimethylsilyl(TBDMS)ether can be cleaved upon refluxing in acetone/H2O(95: 5)in the presence ora catalytic amount of copper(II)chloride dihydrate(5 mmol %).     

A General Method Based on the Use of N-Bromosuccinimide for Removal of the Thiophenyl Group at the Anomeric Position to Generate A Reducing Sugar with the Original Protecting Groups Still Present

Abstract

Efficient conversion of a range of different phenyl thioglycosides into their hemiacetals has been achieved by treatment with N-bromosuccinimide in aqueous acetone. The method is mild and general since it does not interfere with the presence of other protecting groups like acetate, benzyl, benzylidene acetal, tert-butyldiphenylsilyl groups, and the O-glycosidic bond (e.g. di-, tetra-, and pentasaccharide thioglycosides).     

Acridin-9-ylmethoxycarbonyl （Amoc）： A New Photochemically Removable Protecting Group for Alcohols

Synthesis and photochemistry of acridin-9-ylmethoxycarbonyl(Amoc)as a new photochemically removableprotecting group for alcohols were described.Three carbonates of alcohols 1—3 were synthesized throughcondensation of 9-hydroxymethylacridine and chloroformates of alcohols,including benzyl alcohol,phenethylalcohol and one galactose derivative.The photolysis of protected alcohols can efficiently release the correspondingalcohol in the efficiencies(Q_(u1)ε)of 100—200(quantum yield Q_(u1)=0.011—0.023,and molar absorptivity ε=9.1×10~3—9.8×10~3 mol~(-1)·L·cm~(-1))under 360 nm light.     

Deprotection of t-Butyldimethylsiloxy (TBDMS) Protecting Group with Catalytic Copper (II) Chloride Dihydrate

The protection of functional group is unavoidable in multi-step organic synthesis. Alongwith tetrahydropyranyl (THP) ethers, t-butyldimethylsilyl (TBDMS) ethers have beenwidely used for protecting hydroxyl groups. TBDMS ether is more stable to hydrolysisthan trimethylsilyl ether, but is still readily cleaved by a variety of selective conditionsl.The deprotection of TBDMS is usually under mild acidic conditions [AcOH/H,O/THF,3t l: l', or BF, Et,O/CHCI,', etc. '], or with a fluoride…     

(p-Phenylazophenyl)-Isopropyloxycarbonyl,a New Protecting Group for Peptide Synthesis

The preparation and properties of thirty two N(α)-[2-(p-phenylazophenyl)-isopropylcarbonyl]-amino-acids and derivatives are described. The new coloured protecting group (AZOC-) can be easily and selectively removed with mild acid treatment, much the same as the 2-(biphenyl)-isopropyloxycarbonyl (BPOC-)group. It is introduced via quite stable and yet reactive, crystalline intermediates, AZOC-OPh and AZOC-N₃.     

A facile method for the rapid and selective deprotection of methoxymethyl (MOM) ethers

We describe a rapid and efficient method for selective deprotection of methoxymethyl (MOM) ethers using ZnBr₂ and n-PrSH, which completely removed MOM from diverse MOM ethers of primary, secondary, and tertiary alcohols or phenol derivatives. The deprotection takes less than ten minutes with both high yield and selectivity in the presence of other protecting groups. In addition, the rapid deprotection of MOM ethers of tertiary hydroxyls in high yield with no epimerization allows MOM to be a suitable protecting group for tertiary alcohols.     

Asymmetric Cyclizative Dimerization of (ortho-Alkynyl Phenyl) (Methoxymethyl) Sulfides with Palladium(II) Bisoxazoline Catalyst

The first example of an asymmetric cyclization–dimerization of (ortho-alkynyl phenyl) (methoxymethyl) sulfides with a palladium(II) bisoxazoline (box) catalyst has been developed. The box ligand enhances the alkynophilicity of benzothienyl palladium(II) intermediate A and thus promotes coordination of the second alkyne substrate, leading to the dimerization. The characteristic properties of the box ligand were supported by density functional theory (DFT) calculations of the intermediate. Axially chiral bibenzothiophenes were obtained in good yields with good enantioselectivities.     

Poly(acrylamide-co-itaconic acid) as a Potential Ion-Exchange Sorbent for Effective Removal of Antibiotic Drug-Ciprofloxacin from Aqueous Solution

This study describes equilibrium and kinetic sorption studies to remove the antibiotic drug Ciprofloxacin (CF) from aqueous solutions using poly(acrylamide-co-itaconic acid) [poly(AAm-co-IA)] as polymeric cation exchanger sorbent material. The co-polymeric sorbent was prepared by free radical induced aqueous polymerization and was characterized by FTIR spectroscopy and TGA analysis. In addition, its physicochemical parameters were also determined. The various isotherm models, when applied to equilibrium sorption data at 28°C, followed the following order: Langmuir > Temkin > Freundlich, with the fair maximum sorption capacity (Q _o ) of 178.5 mg g^?1. The kinetic sorption data, obtained at 28°C, was applied to kinetic models such as pseudo first order equation, pseudo second order model and a simple Elovich model. Based on regression values, the order of fitness of these models was pseudo second order > pseudo first order > simple Elovich model. The second order adsorption coefficients k_2adswere found to be 58 × 10^?3, 52.7 × 10^?3, 34.01×10^?3 g/mg min for drug solutions with initial concentrations of 10, 20 and 30 mg L^?1 respectively The sorption mean free energy from the Dubinin–Raduschkevich (DR) isotherm was found to be nearly 8.839 kJ mol^?1 indicating an ion-exchange mechanism for drug uptake. The optimum pH value of sorbate solution for drug uptake was found to be around 6.0. Finally, the antibacterial action of drug was investigated and it was found that after adsorption there was a decrease in bacterial growth inhibition efficiency of drug solution.     

Mild cleavage of methoxymethyl (MOM) ethers with trimethylsilyl bromide

Trimethylsilyl bromide is an effective reagent for the deprotection of methoxymethyl ethers under mild conditions.