Tert-butyl Ester Groups Research Articles

Photolithographic Technique for Direct Photochemical Modification and Chemical Micropatterning of Surfaces

We describe a photolithographic method for the direct modification and micropatterning of the surface chemical structure of self-assembled monolayers. End-functional azobenzene alkanethiols are designed and synthesized so that, when self-assembled onto gold substrates, an acid-sensitive tert-butyl ester end group is positioned at the air−monolayer interface. Upon exposure to UV radiation in the presence of a photoacid generator, the tert-butyl ester groups are removed in the form of butylene gas to form surface carboxylic acid groups. The orientation of the monolayers and photochemical surface modification reactions are characterized by X-ray photoelectron spectroscopy measurements. The photochemical change from hydrophobic tert-butyl ester groups to hydrophilic carboxylic acid groups causes a significant change in wettability reflected in a water contact angle change from 89 to 28°, respectively. Surface chemical modifications may be patterned on a microscale by simply irradiating the self-assembled mono...

Routes to metallodendrimers: synthesis of isomeric neutral metallomacromolecules based on bis(2,2':6',2"-terpyridine)ruthenium(II) connectivity.

Routes for the syntheses of isomeric, zwitterionic, bisterpyridine-Ru(II)-based macromolecules are described. Access to these novel architectures is facilitated by the construction of terpyridine-modified, 1-->3 C-branched, ester-terminated building blocks. Constitutional isomers result from the interchangable placement of methyl and tert-butyl ester groups on both the branched framework near the Ru(II) centers and the termini of the branched construct. Water solubility is imparted to each isomer through selective transformation of the tert-butyl esters to their corresponding carboxylates. Along with the standard characterization techniques, electrochemical and spectroscopic data also support the structural formation.

Anion recognition and sensing by mono- and bis-urea substituted ferrocene receptors

New mono- and bis-urea substituted ferrocene receptors have been synthesised. Proton NMR anion coordination studies with chloride and dihydrogen phosphate reveal the presence of bulky tert-butyl ester group urea substitiuents disfavours H 2PO 4 − complexation and amplifies the recognition of Cl −. Electrochemical studies showed these urea ferrocene receptors electrochemically recognise H 2PO 4 − and Cl − and AcO − via perturbations of the respective ferrocene oxidation wave.

Stable Monopyrrole Atropisomers.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Thermal shaping of shell-crosslinked (SCK) nanoparticles, facilitated by nanoconfinement of fluid-like cores

The controlled manipulation of the shape of shell-crosslinked (SCK) nanoparticles is described as a novel methodology for the construction of complex nanostructured materials. The presence of a hydrophobic, fluid-like (low Tg) core domain in the SCK allows for substrate-induced shaping of the nanoparticle. The SCK nanoparticles are prepared by the self-assembly of poly(acrylic acid)-block-polyisoprene (PAA-b-PI) diblock copolymers into polymer micelles, followed by crosslinking of the hydrophilic shell layer via amidation reactions between the acrylic acid functionalities and 2,2′-(ethylenedioxy)bis(ethylamine). The synthesis of two amphiphilic diblock copolymers, one consisting of an unmodified PI block (PAA-b-PI, PI having 86% 4,1-microstructure, Tg(PI) = −75 °C) and the other composed of a hydrochlorinated PI block (PAA-b-PI(HCl), Tg(PI(HCl)) = 27 °C), the assembly of the copolymers into polymer micelles and the subsequent shell-crosslinking of the micelles into SCKs is described. The synthesis of a poly(tert-butyl acrylate)-block-polyisoprene (PtBA-b-PI) precursor via nitroxide-mediated radical polymerization (NMRP) and the subsequent methanesulfonic acid catalyzed cleavage of the precursor's tert-butyl ester groups is discussed. Treatment of poly(tert-butyl acrylate)-block-polyisoprene (PAA-b-PI) with HCl(g) is also described as a method for hydrolysis of the tert-butyl esters and for hydrochlorination of the unsaturated groups of PI to yield PAA-b-PI(HCl) in one step. The results of the analyses of solution properties are presented and these findings, in conjunction with transmission electron microscopy (TEM) and atomic force microscopy (AFM) size measurements, indicate spherical shapes for the SCKs in aqueous solution. Using a combination of TEM and AFM dimension determinations, an SCK containing a PI core (predominantly cis-4,1-repeat units) of Tg = −63 °C is shown to deform, at room temperature, from the solution-state spherical shape upon deposition onto a mica substrate. By contrast, deposition of an SCK containing a PI(HCl) core (Tg = 33 °C) shows little deformation at room temperature from spherical shape as determined by its particle aspect ratio of 1.4 (sphere = 1.0). Thermally-driven particle shape manipulation, behavior analogous to the processing of nanoscopic thermoplastic materials, is demonstrated with the hydrochlorinated SCK (PAA-b-PI(HCl)). A large decrease in the average AFM particle height of this SCK is found upon heating above the Tg of the hydrochlorinated PI core (33 °C). This finding demonstrates the major role played by the core (glassy vs. fluid-like) in defining the equilibrium shape of the SCK. Crosslinking within the core domain (in addition to the initial shell crosslinking) is also shown to dramatically increase the rigidity of the nanoparticles and prevent nanoparticle shape deformation when in contact with substrates.

Stable Monopyrrole Atropisomers

Malonic ester derivatives of ethyl and methyl 3,5-dimethyl-4-(1′-iodoneopentyl)-1H-pyrrole-2-carboxylate exhibit restricted rotation about the pyrrole C(4)–C(1′) bond due to the bulky 1′-tert-butyl and malonic ester groups and the ortho effect at C(4) of the sterically crowded 3,5-dimethylpyrrole. The malonates belong to a rare class of atropisomers with restricted rotation about an sp3–sp2 C–C bond, and they undergo diastereomeric separation by TLC and crystallization: the diastereomers are stable in solution at room temperature. A crystal of one of the diastereomers, suitable for X-ray crystallography, gave the relative configuration of the chiral axis and stereogenic center at C(1′). Dynamic NMR studies of the purified diastereomers provide kinetic and thermodynamic parameters associated with the atropisomerism: ΔG‡ = 132–134 kJ/mol (∼32 kcal/mol) at 383 K in C2D2Cl4 solvent.

Diastereoselective synthesis of S-tert-butyl-beta-(trifluoromethyl)isocysteine.

Both diastereoisomers of S-tert-butyl-beta-(trifluoromethyl)isocysteine have been synthesized stereoselectively by the sequential reactions of trifluoroacetimidoyl chloride with the lithium enolate of tert-butyl alpha-tert-butylthioacetate, followed by the diastereoselective reduction of the imino group with sodium borohydride in the presence of zinc(II) or di(ethylene glycol) dimethyl ether, and finally by the deprotection of N-aryl and tert-butyl ester groups.

Stereochemistry of the reductive amination of 4-oxoproline derivatives with glycine esters

An amination of 4-oxoproline derivatives with glycine methyl or benzyl ester and sodium cyanoborohydride led to the mixtures of corresponding diastereomeric 4-cis- and 4-trans-glycinoproline derivatives. We found that the ratio of diastereomers mainly depends on the structure of 4-oxoproline ester groups and, to a lesser extent, on the structure of N-acyl substituents. The best results were achieved with tert-butyl ester group; it ensured good yields of the amination products and the greatest prevalence of 4-cis-isomers. The structure of ester group in glycine molecule only scarcely affected the resulting ratio of N-(N-benzyloxycarbonylglycyl)-4-glycinoprolines. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2002, vol. 28, no. 6; see also http://www.maik.ru.

Soluble, High Molecular Weight Polysilsesquioxanes with Carboxylate Functionalities

AbstractHigh molecular weight polysilsesquioxanes with carboxylate functionalities were prepared by sol-gel polymerization of organotrialkoxysilanes bearing tert-butyl ester groups. Trialkoxysilyl-containing monomers of the type (RO)3Si(CH2)3C(O)OtBu (R = Me, Et) were prepared by hydrosilation of the corresponding vinylic tert-butyl esters CH3CHCH2C(O)OtBu. Acid- or base-catalyzed polymerization of the monomers leads to very high molecular weight polymers with relatively narrow polydispersities. The polymerization results in complete condensation of the alkoxy groups while the tert-butyl ester functionality remains fully intact. Partial or full deprotection of the tert-butyl group can easily be achieved to yield the corresponding carboxylic acid polymers. The ester and carboxylic acid functionalities of these new materials allow for their potential use in a variety of applications such as scavenging of heavy metals.

Shell Cross-Linked Nanoparticles Containing Hydrolytically Degradable, Crystalline Core Domains

Shell cross-linked knedel-like nanoparticles (SCKs) possessing an amphiphilic core−shell morphology consisting of a cross-linked shell and a hydrolytically degradable, crystalline core domain were synthesized from poly(e-caprolactone)-b-poly(acrylic acid) (PCL-b-PAA) amphiphilic diblock copolymers via a two-step process: self-assembly of PCL-b-PAA into polymer micelles followed by cross-linking of the hydrophilic shell layer via condensation reactions between the carboxylic acid functionalities of PAA and the amine groups of 2,2‘-(ethylenedioxy)bis(ethylamine). PCL-b-PAA was prepared from the selective hydrolysis of a poly(e-caprolactone)-b-poly(tert-butyl acrylate) (PCL-b-PtBA) precursor, which was synthesized by ring opening polymerization (ROP) of e-caprolactone (e-CL) followed by atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA). Selective hydrolysis of the tert-butyl ester groups of the PtBA block by reaction with trimethylsilyl iodide (TMSI), followed by reaction with aqueous...

Synthesis, electrochemistry, and interactions with beta-cyclodextrin of dendrimers containing a single ferrocene subunit located "off-center".

Two series of dendrimers containing a single ferrocene unit located in the focal point of these macromolecules have been synthesized and characterized. The first series of dendrimers has considerable lipophilic character, with tert-butyl ester groups located in their peripheral regions. In contrast, the second series of dendrimers was obtained by the hydrolysis of these peripheral ester groups, yielding water-soluble dendrimers with carboxylic acid groups in their surfaces. The electrochemical properties of these macromolecules were strongly affected by the dendritic groups attached to the ferrocene subunits. Host-guest interactions between the water-soluble dendrimers and the well-known receptor beta-cyclodextrin were also investigated. The dendritic groups were found to hamper markedly the formation of inclusion complexes between the cyclodextrin receptor and the dendrimer's ferrocene unit.

Synthesis and Characterization of Poly(dimethyl siloxane)−Poly[alkyl (meth)acrylic acid] Block Copolymers

Block copolymers containing dimethyl siloxane and carboxylic acid sequences were synthesized by group transfer polymerization (GTP) of various methacrylates and acrylates using silyl ketene acetal terminated poly(dimethylsiloxane) (PDMS) as initiator, followed by hydrolysis of the ester sequences to the free acid. The block copolymers were obtained with controlled molecular weight and narrow molecular weight distribution. The tert-butyl methacrylate (tBMA) and trimethyl silyl methacrylate (TMSMA) polymerized more slowly than corresponding acrylates. tert-Butyl and trimethyl silyl ester groups in the poly(meth)acrylate block could be quantitatively hydrolyzed. Most copolymers were contaminated by unincorporated homo-PDMS, which was efficiently removed by hexane or supercritical CO2 extraction. The solubility and thermal properties (DSC, TGA) were investigated for the hydrolyzed amphiphilic polymers.

Chemically Amplified Electron-Beam Photoresists

Two novel series of electron-beam photoresists possessing high sensitivity and contrast have been developed based on chemical amplification chemistry. The amplification process relies on the electron-beam-induced generation of acids derived from the decomposition of onium salts to catalytically deblock pendant tert-butyl ester groups along the backbone of a photoresist polymer or alternatively similar groups present in dissolution inhibitors.

Biodegradation of cyclic and substituted linear oligomers of poly(3-hydroxybutyrate).

Cyclic oligo(3-hydroxybutyrate), oligo(3-HB), was synthesized and purified, resulting in oligolides that contained three to seven (R)-3-hydroxybutyrate units (triolides up to heptolides). In addition, linear 3-HB octamers obtained as either tert-butyl or methyl esters were substituted with different end groups at the hydroxy end. The hydroxy terminus was replaced by either a benzyloxy, trifluoroacetoxy, crotonyloxy (S)-3-hydroxybutyryloxy, or fluorenylmethylcarbonyloxy (FMOC) group. P(3-HB) hairpin loops occurred on the surface of certain regions of the polymer, especially of lamellar crystallites. Cyclic 3-HB oligomers provide a model system for these loops. It is assumed that they provide attachment points for the depolymerizing enzymes. All of the (R)-oligolides tested were degraded except the (R)-triolide. Triolides were not degraded, suggesting that enzymatic attack was prevented presumably by steric hindrance on the rigid ring system. Unsubstituted linear octamers were degraded. Biodegradation was prevented when the hydroxy terminus was protected by the FMOC group, but was not dependent on a free hydroxy terminal group; all other protecting groups did not prevent degradation. Substitution of the carboxy end of a methyl or tert-butyl ester group did not influence biodegradation.

Selective Removal of an N-BOC Protecting Group in the Presence of a tert-Butyl Ester and Other Acid-Sensitive Groups

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSelective Removal of an N-BOC Protecting Group in the Presence of a tert-Butyl Ester and Other Acid-Sensitive GroupsFrank S. Gibson, Stephen C. Bergmeier, and Henry RapoportCite this: J. Org. Chem. 1994, 59, 11, 3216–3218Publication Date (Print):June 1, 1994Publication History Published online1 May 2002Published inissue 1 June 1994https://doi.org/10.1021/jo00090a045RIGHTS & PERMISSIONSArticle Views14399Altmetric-Citations102LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (327 KB) Get e-Alerts Get e-Alerts

The Effect of Bulky Ester Alkyl Substituents on Rate Constants of Radical Polymerization of Dialkyl Fumarates.

The radical polymerization of dialkyl fumarates bearing various ester alkyl groups was investigated to evaluate the propagation and termination rate constants (kp and kt) by means of electron spin resonance spectroscopy. It was revealed that the introduction of tert-butyl ester group promoted the polymerization reactivity not only the retardation of the termination, but also by the acceleration of the propagation despite of steric repulsion by the bulky substituents. The latter was interpreted by the stereospecific propagation leading to the diisotactic polymer formation.

Effect of .alpha.- and .beta.-ester alkyl groups on the propagation and termination rate constants for radical polymerization of dialkyl itaconates

Radical polymeriiations of seven dialkyl itaconates (DRIs) with methyl, isopropyl, or tert-butyl ester groups were carried out with dimethyl 2,2'-azobis(isobutyrate) in benzene at 60°C. The effects of the α- and β-ester alkyl substituents of the DRIs on the polymerization rate (R p ) and the propagation and termination'rate constants (k p and k t ) were examined. For a-substitution R p decreased with increasing bulkiness of the alkyl group, whereas the opposite was observed for β-substitution. ESR data revealed that K p decreases with bulkiness of the α-ester alkyl group in the order methyl> isopropyl> t-butyl

Meso and racemo Additions in Propagation for Radical Polymerization of Dialkyl Fumarates II. Determination of the Absolute Rate Constants

The propagation process in radical polymerization of dialkyl fumarates (DRF) was investigated. The propagation rate constants (kp) for some DRFs were determined by ESR spectroscopy. It was revealed that kp increased with the introduction of a bulky tert-butyl ester group in the following order: di-tert-butyl fumarate>methyl tert-butyl fumarate>dimethyl fumarate. The absolute rate constants for meso and racemo additions were elucidated by the combination of the kp and the probability of meso addition, which was determined by 13C NMR spectroscopy.

Syntheses of disaccharides with (1→4)-β glycosidic linkages related to the 4- and 6-sulfates and the 4,6-disulfates of chondroitin

The sodium salts of the 6′-sulfate 12, the 4′-sulfate 15 and the 4′,6′-disulfate 17 of benzyl 4- O-(β- d-galactopyranosyl)-β- d-glucopyranosiduronate 10 have been synthesized. Methyl [benzyl 2,3-di- O-benzoyl-4- O-(2,3-di- O-benzoyl-β- d-galactopyranosyl)-β- d-glucopyranosid]uronate ( 9) has been prepared as a key intermediate from benzyl 4′,6′- O-benzylidene-β- d-lactopyranoside ( 2). Protection of 2 at C-6 with the tert-butyldimethylsilyl group, followed by O-perbenzoylation and disilylation, gave benzyl 2,3-di- O-benzoyl-4- O-(2,3-di- O-benzoyl-4,6- O-benzylideneβ- d-galactopyranosyl)-β- d-glucopyranoside ( 7). Oxidation of the 6-position of 7 protocol to be difficult. However, 7 could be converted into the tert-butyl glucuronate 8 using chromium trioxide-pyridine and tert-butanol. Simultaneous hydrolysis of the benzylidene acetal and the tert-butyl ester groups, followed by esterification of the resulting free acid with diazomethane, yielded 9. Compound 9 was directly sulfated with sulfur trioxide-trimethylamine within 12 h to give the 6′-sulfate 11. The 4′,6′-disulfate 16 was accessible by running the reaction under the same conditions for 14 days. The 4′-sulfate 14 was obtained after protecting the 6′-OH group of 9 with benzoyl cyanide to give the 6′-benzoate 13 followed by sulfation under more vigorous reaction conditions. Deesterification of 9, 11, 14, and 16 was achieved by treatment with aqueous sodium hydroxide in tetrahydrofuran to give 10, 12, 15, and 17, respectively.

Deprotection of carboxylic esters assisted by hydrogen bonding network in phenolic media. Its application to β-lactam antibiotic syntheses

Deprotection of p-methoxybenzyl, diphenylmethyl, and tert-butyl ester groups, which is an essential step of β-lactam antibiotic synthesis, can be performed successfully by gentle heating in phenolic media.