T-butyldimethylsilyl Research Articles

Structural Development of Silicon‐Containing Retinoids: Structure–Activity Relationship Study of the Hydrophobic Pharmacophore of Retinobenzoic Acids Using Silyl Functionalities

We designed and synthesized a series of retinobenzoic acids bearing various silyl functionalities in order to explore in detail the structure-activity relationship (SAR) at the hydrophobic moiety of retinoids. Among the synthesized compounds, 24 c bearing a t-butyldimethylsilyl (TBS) group at the hydrophobic site exhibited potent retinoid activity comparable to that of the lead compound Am555S (4). Compound 24 c exhibited transcription-promoting activity towards all three subtypes of retinoic acid receptor (RAR), but showed the highest activity towards RARγ, in contrast to the high RARα-selectivity of Am80 (3) and Am555S (4). The SARs presented here should be helpful in the development of subtype-selective retinoids, and in particular 24 c might be a promising lead compound for new RARγ ligands.

Synthesis of a protected ribonucleoside phosphoramidite-linked spin label via an alkynyl chain at the 5′ position of uridine

New, spin-labeled nucleosides, and an efficient synthetic route for a modified uridine amidite, were developed. The spin-labeled part was the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) group, which was linked via an alkynyl chain at the 5 position of uridine. Three typical protecting groups, the t-butyldimethylsilyl (TBDMS) group at 2′, the dimethoxytrityl (DMTr) group at 5′, and the phosphoramidite group at 3′, were introduced to produce an automated nucleic acid synthesizer. The TEMPO group at the 5 position in the uridine structure affected introduction of bulky protecting groups, such as the DMTr group at the 5′ position and the TBDMS group at the 2′ position. The electron paramagnetic resonance (EPR) data revealed a nitroxyl radical in the structure of synthetic nucleoside compounds; however, RNA produced by automated synthesis using a TEMPO-linked uridine phosphoramidite building block was EPR silent.

Fluoride-mediated polycondensation for the synthesis of polymers of intrinsic microporosity

A fluoride-mediated double SNAr polycondensation method was successfully developed to prepare high-molecular weight polymers of intrinsic microporosity (PIMs). The polymerization was conducted between a t-butyldimethylsilyl (TBS)-protected biscatechol monomer (2) and a widely used tetrafluoro monomer (3) in the presence of fluoride ion with excellent to quantitative yields. Three fluoride ion sources (i.e. KF, TBAF and CsF) were investigated, and all of them were effective as catalysts to give high-molecular weight linear products with good film forming property. Therefore, this method warrants its synthetic utility for PIM synthesis.

Preparation of Nano Silica Supported Sodium Hydrogen Sulfate: As an Efficient Catalyst for the Trimethyl, Triethyl and t‐Butyldimethyl Silylations of Aliphatic and Aromatic Alcohols in Solution and under Solvent‐free Conditions

AbstractNano silica supported sodium hydrogen sulfate has been prepared by mixing NaHSO4 with activated Nano silicagel. We wish to report a new method for the synthesis of trimethyl (TMS), triethyl (TES) and t‐butyldimethyl silyl (TBS) ethers from benzylic, allylic, propargylic alcohols, phenols, naphtholes and some of phenolic drugs in the solution and under solvent‐free conditions.

Chemoselective Deprotection of Aryl tert-Butyldimethylsilyl Ethers Promoted by Phosphates

A facile protocol to the chemoselective deprotection of aryl t-butyldimethylsilyl (TBDMS) ethers using Na3PO4 · 12H2O as promoter is described. From aryl TBDMS ethers to the corresponding phenols, the TBDMS group could be cleaved in the presence of 0.5 equivalent of Na3PO4 · 12H2O in dimethylformamide at room temperature with good to excellent yields in the presence of other common protecting and functional groups. K3PO4 · 3H2O was also found to be useful for the selective deprotection reaction. This is, to our knowledge, the first report on chemoselective deprotection of aryl TBDMS ethers using phosphates.

5-Fluoro-4-thiouridine phosphoramidite: New synthon for introducing photoaffinity label into oligodeoxynucleotides

The synthesis of phosphoramidite of 5-fluoro-4-thio-2′- O-methyluridine is described. An appropriate set of protecting groups was optimized including the 4-thio function introduced via 4-triazolyl as the 4-(2-cyanoethyl)thio derivative, and the t-butyldimethyl silyl for 2′ and 3′ hydroxyl protection, enabling efficient synthesis of the phosphoramidite. These protecting groups prevented unwanted side reactions during oligonucleotide synthesis. The utility of the proposed synthetic route was proven by the preparation of several oligonucleotides via automated synthesis. Photochemical experiments confirmed the utility of the synthon.

ChemInform Abstract: A Novel 1,3-Migration of the Trimethylsilyl Group from Oxygen to Carbon.

Abstract Condensation of 1-lithio-2-trimethylsiloxyethylene 1 with t-butyl(dimethyl)silyl triflate 2a leads to silylated enol ethers 4a or 4b according to the experimental conditions. The formation of 4b is due to a 1,3-migration of the trimethylsilyl group from oxygen to carbon of 1 . Condensation with chlorosilane 2b lead exclusively to 4b .

Novel derivatisation technique for the determination of chlorophenoxy acid type herbicides by gas chromatography–mass spectrometry

The analytical detection of chlorophenoxycarboxylic-acid-type herbicides (2,4-D, dichloprop, MCPA, etc.) in environmental samples is often a problem in instrumental analysis, as these compounds containing free carboxylic groups require chemical derivatisation prior to gas chromatographic (GC) methods. Nine chlorophenoxy-acid-type herbicide active ingredients have been derivatised successfully with trimethylsilyl N,N-dimethyl carbamate and t-butyldimethylsilyl N,N-dimethyl carbamate by forming their trimethylsilyl (TMS) and t-butyldimethylsilyl (TBDMS) esters, respectively. The detection and determination of the derivatives were performed by capillary gas chromatography-mass spectrometry. The study included determination of retention indices, mass spectral properties and comparison of derivatives produced. The mass spectra of TBDMS derivatives are usually dominated by very characteristic ions [M-57](+) resulting from the cleavage of t-butyl moiety during electron impact (EI) ionisation in the mass spectrometer. Limits of detection were 5 to 100 pg applying GC with EI-MS detection in full scan mode. The method, using SPE sample preparation, was applied for the analysis of 115 ground water and surface water samples collected in Békés County, Hungary in 2009.

Chemoselective Deprotection of Triethylsilyl Ethers

An efficient and selective method was developed for the deprotection of triethylsilyl (TES) ethers using formic acid in methanol (5–10%) or in methylene chloride 2–5%) with excellent yields. TES ethers are selectively deprotected to the corresponding alcohols in high yields using formic acid in methanol under mild reaction conditions. Other hydroxyl protecting groups like t-butyldimethylsilyl (TBDMS) remain unaffected.

Inhibition of tRNA-dependent ligase MurM from Streptococcus pneumoniae by phosphonate and sulfonamide inhibitors

Ligase MurM catalyses the addition of Ala from alanyl-tRNA Ala, or Ser from seryl-tRNA Ser, to lipid intermediate II in peptidoglycan biosynthesis in Streptococcus pneumoniae, and is a determinant of high-level penicillin resistance. Phosphorus-based transition state analogues were designed as inhibitors of the MurM-catalysed reaction. Phosphonamide analogues mimicking the attack of a lysine nucleophile upon Ala-tRNA Ala showed no inhibition of MurM, but adenosine 3′-phosphonate analogues showed inhibition of MurM, the most active being a 2′-deoxyadenosine analogue (IC 50 100 μM). Structure/function studies upon this analogue established that modification of the amino group of the aminoalkylphosphonate resulted in loss of potency, and modification of the adenosine 5′-hydroxyl group with either a t-butyl dimethyl silyl or a carbamate functional group resulted in loss of activity. A library of 48 aryl sulfonamides was also screened against MurM using a radiochemical assay, and two compounds showed sub-millimolar inhibition. These compounds are the first small molecule inhibitors of the Fem ligase family of peptidyltransferases found in Gram-positive bacteria.

Protecting Groups Transfer: Unusual Method of Removal of Tr and Tbdms Groups by Transetherification

The triphenylmethyl (Tr) group undergoes a transfer (transetherification or disproportionation) between the molecules of 5′-O-Tr-2′-deoxynucleosides in a process mediated by anhydrous sulfates of Cu+2, Fe+2, or Ni+2 to yield mixtures of 3′,5′-bis-O-Tr and 3′-O-Tr products. If phenylmethanol is present in a reaction medium, detritylation results with concomitant formation of phenylmethyl triphenylmethyl ether. The behavior of t-butyldimethylsilyl (TBDMS) group in 5′-O-TBDMS-2′-deoxynucleosides is exactly the same. Such type of transetherifications was not observed before for the O-Tr and O-TBDMS groups.

Molecularly defined (L)‐lactic acid oligomers and polymers: Synthesis and characterization

AbstractThe synthesis of (L)‐lactide oligomers from dimer to 64mer via an exponential growth strategy is described. By careful selection of orthogonal protective groups, the synthesis were conducted using a t‐butyldimethylsilyl (TBDMS) ether as the protective group of the hydroxyl group and benzyl (Bn) ester as the protective group of the carboxylic acid group. The yields of both the deprotection steps and coupling reactions using 1,3‐dicyclohexylcarbodiimide or 1‐[3‐(dimethylamino)propyl]‐3‐ethylcarbodiimide hydrochloride were high (70–100%) and the absence of a requirement for conducting the majority of reactions under an inert atmosphere permitted a robust and efficient synthetic strategy to be developed. This allowed monodisperse dimer, tetramer, octamer, 16mer, 32mer, and 64mer materials to be prepared in gram quantities and fully characterized using mass spectrometry and size exclusion chromatography. Evaluation of the thermal and physical properties using thermogravimetric analysis, differential scanning calorimetry, and small angle X‐ray scattering demonstrated a close correlation between the molecular structure of the well‐defined Poly(lactide) oligomers and their physical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5977–5990, 2008

Novel Synthetic Approach to Multibenzoylated Nucleosides

Abstract An improved and highly efficient synthetic approach to multibenzoylated nucleosides bearing free 5′‐hydroxyl groups is described here. By employing t-butyldimethylsilyl (TBDMS) rather than the more commonly used dimethoxytrityl (DMTr) as a temporary 5′‐OH protecting group of the starting nucleoside, this methodology provides the expected products in nearly quantitative yields, thereby substantially reducing the cost and effort of synthesis.

Molecularly Defined Caprolactone Oligomers and Polymers: Synthesis and Characterization

The synthesis of molecularly defined epsilon-caprolactone oligomers and polymers up to the 64-mer, via an exponential growth strategy, is described. By careful selection of orthogonal protecting groups, t-butyldimethylsilyl (TBDMS) ether for the hydroxyl group and benzyl (Bn) ester for the carboxylic acid group, a highly efficient synthetic strategy was developed with yields for both deprotection steps being essentially quantitative and for the coupling reactions using 1,3-dicyclohexylcarbodiimide (DCC), yields of 80-95% were obtained even at high molecular weights. This allows monodisperse dimers, tetramers, octamers, 16-mers, 32-mers and 64-mers to be prepared in gram quantities and fully characterized using mass spectroscopy, size exclusion chromatography (SEC), and IR and NMR spectroscopy. Thermal and physical properties were measured using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). These results conclusively show a distinct structure/property relationship with a close correlation between the number of repeat units and physical properties. In addition, a number of marked differences were observed on comparison with the parent poly(caprolactone) polymer.

A catalytic method for chemoselective detritylation of 5′-tritylated nucleosides under mild and heterogeneous conditions using silica sulfuric acid as a recyclable catalyst

A rapid, mild and highly efficient procedure for the chemoselective deprotection of triphenylmethyl (trityl, Tr), p-anisyldiphenylmethyl (monomethoxytrityl, MMT) and di-( p-anisyl)phenylmethyl (dimethoxytrityl, DMT) groups from nucleoside trityl ethers has been established. The deprotection was achieved at room temperature, using a catalytic amount of silica sulfuric acid (SSA) in acetonitrile. The trityl nucleosides were deprotected in 2–17 min without any depurination. These conditions are compatible with other acid sensitive hydroxyl protecting groups such as p-methoxybenzyl (PMB), isopropylidene, cyclohexylidene, di-( p-anisyl)methylidene, triisopropylsilyl (TIPS) and t-butyldimethylsilyl (TBDMS).

Exomethylene pyranonucleosides: Efficient synthesis and biological evaluation of 1-(2,3,4-trideoxy-2-methylene-β- d- glycero-hex-3-enopyranosyl)thymine

A new series of unsaturated pyranonucleosides with an exocyclic methylene group and thymine as heterocyclic base have been designed and synthesized. d-Galactose ( 1) was readily transformed in three steps into the corresponding 1-(β- d-galactopyranosyl)thymine ( 2). Selective protection of the primary hydroxyl group of 2 with a t-butyldimethylsilyl (TBDMS) group, followed by specific acetalation, and oxidation gave 1-(6- O- t-butyldimethylsilyl-3,4- O-isopropylidene-β- d- lyxo-hexopyranosyl-2-ulose)thymine ( 5). Wittig reaction of the ketonucleoside 5, deprotection and tritylation of the 6′-hydroxyl group gave 1-(2-deoxy-2-methylene-6- O-trityl-β- d- lyxo-hexopyranosyl)thymine ( 9). Exomethylene pyranonucleoside 9 was converted to the olefinic derivative 10, which after detritylation afforded the title compound 1-(2,3,4-trideoxy-2-methylene-β- d- glycero-hex-3-enopyranosyl)thymine ( 11). These novel synthesized compounds were evaluated for antiviral activity against rotaviral infection and cytotoxicity in colon cancer. As compared to AZT, compounds 1-(2-deoxy-2-methylene-β- d- lyxo-hexopyranosyl)thymine ( 7) and 1-(β- d- lyxo-hexopyranosyl-2-ulose)thymine ( 8) showed to be more efficient, in rotavirus infections and in treatment of colon cancer.

Operationally Simple and Efficient Workup Procedure for TBAF-Mediated Desilylation: Application to Halichondrin Synthesis

An operationally simple and efficient workup method for tetrabutylammonium fluoride (TBAF)-mediated t-butyldimethylsilyl (TBS) deprotection has been developed. The procedure includes addition of a sulfonic acid resin and calcium carbonate, followed by filtration and evaporation. This method eliminates the tedious aqueous-phase extraction process to remove excess TBAF and materials derived from TBAF, thereby making the protocol highly amenable to multiple TBS deprotections. Its efficiency and usefulness were demonstrated by using the transformation of 1a to 3a in the halichondrin synthesis. [reaction: see text].

Deprotection of a Silyl Group with Mesoporous Silica

The triethylsilyl (TES) group of silyl ethers of several types is selectively and easily removed in the presence of a t-butyldimethylsilyl (TBDMS) group with a mesoporous silica MCM-41/MeOH heterogeneous system. Comparison of the efficiency was carried out among several solvents, and among such promoters as common zeolites and ion-exchange resins. Furthermore, FSM-16, another mesoporous silica, was examined for the possibility of recycling by re-calcination at 400 degrees C after the reaction.

Novel Methodologies. Part 92. A Simple, Efficient and Highly Selective Deprotection of t‐Butyldimethylsilyl (TBDMS) Ethers Using Silica Supported Sodium Hydrogen Sulfate as a Heterogeneous Catalyst.

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A simple, efficient and highly selective deprotection of t-butyldimethylsilyl (TBDMS) ethers using silica supported sodium hydrogen sulfate as a heterogeneous catalyst

t-Butyldimethylsilyl (TBDMS) ethers have been efficiently and selectively deprotected using silica supported sodium hydrogen sulfate (NaHSO 4·SiO 2) as a heterogeneous catalyst at room temperature to regenerate the parent alcohols in high yields.