Tert-butyl Ester Research Articles

Thermally induced transformation tert-butyl peroxyethyl esters of carboxylic acids

The features of thermolysis of tert-butyl peroxyethyl esters of carboxylic acids (CH₃)₃COOCH(CH₃)OC(O)R are investigated. Based on the identification of reaction products and the analysis of kinetic parameters, the fact of simultaneous transformation of four bonds (O–O, C–O, C–C and C–H) in a molecule with the formation of two molecules was proved for the first time [RC(O)OH and CO] and two free radicals [(CH₃)₃CO• and •CH₃], which, under experimental conditions, do not enter into a cross-break reaction, but detach the hydrogen atom from the solvent. Evidence of the coordinated (simultaneous) transformation of four bonds is the low (compared with the energy of bond dissociation) values of the activation energy and the pre-exponential multiplier, as well as negative values of the activation entropy.

Assessment of Conjugation Pathways in N-Methylporphyrins that Are Fused to Acenaphthylene, Phenanthrene, or Pyrene: Evidence for the Presence of Alternative Aromatic Circuits.

Acenaphtho-, phenanthro-, and pyrenopyrrole esters, readily available from Barton-Zard reactions of ethyl isocyanoacetate with nitroarenes, were reacted with methyl iodide and KOH in DMSO to give N-methylpyrroles and subsequent cleavage of the ester moieties was accomplished with KOH in ethylene glycol at 200 °C. Condensation with two equiv of an acetoxymethylpyrrole in refluxing acetic acid-2-propanol afforded a series of annulated tripyrranes. Cleavage of the terminal tert-butyl ester groups with trifluoroacetic acid, followed by condensation with a diformylpyrrole and oxidation with FeCl3, gave N-methyl acenaphtho-, phenanthro-, and pyrenoporphyrins. The N-methyl substituent effectively freezes the tautomeric equilibria to maximize interactions between the porphyrin nucleus and the fused aromatic substructures. Analysis of the proton NMR spectra provides evidence of the presence of extended aromatic circuits within these structures. Anisotropy of induced ring current (AICD) plots clearly shows the presence of 30π electron pathways in phenanthro- and pyrenoporphyrins that run around the exterior of the benzenoid fragments. These results demonstrate that N-alkylation can be used to relocate aromatic pathways in porphyrinoid systems.

Meso-Hydroxylmethyl-1,3,5,7-tetramethylBODIPY: A Visible-Light Photoremovable Protective Group for Carboxyl Groups

AbstractA meso-BODIPY-type photoremovable protecting group for carboxyl group is developed. BODIPYs are well-known for brilliant color, favorable to reaction monitoring and purification. meso-BODIPY esters are achieved via esterification in 44–89% yields, while deprotection is fulfilled under irradiation of blue LED bulb in the presence of photocatalyst and organic hydrogen donor in 43–95% yields. This method is applicable to a variety of acids, such as aromatic, heteroaromatic, alkyl, α,β-unsaturated carboxylic acids, etc. Our BODIPY-deprotective condition is almost neutral that both methyl and tert-butyl esters are compatible.

Copper-Catalyzed Direct Asymmetric Aldol Reaction of Glycine Schiff Bases to Access syn-β-Hydroxy-α-amino Esters.

This study reported a copper-catalyzed direct asymmetric aldol reaction between aldehydes and glycine Schiff bases with methyl, allyl, and tert-butyl esters. Additionally, this reaction afforded high yields of syn-β-hydroxy-α-amino esters with excellent enantio- and diastereoselectivities (93-99% ee, up to >99:1 dr). The aldol reaction accepted aromatic, linear aliphatic, and α-substituted aliphatic aldehydes.

Aquatic plants as whole-cell biocatalysts for preparing optically active β-hydroxy esters

We investigated the asymmetric reduction of β-keto esters using aquatic plants as whole-cell biocatalysts under darkness and illumination by fluorescent light. The (S)- β-hydroxy esters were obtained with high enantiomeric excess (ee) values. Regardless of the light conditions, the amount of (R)- β-hydroxy ester produced did not change significantly as the substrate concentration increased, whereas the yield of (S)- β-hydroxy ester increased substantially. Moreover, increasing the quantity of plants resulted in a significant increase in the production of (S)- β-hydroxy ester and a slight increase in the production of (R)- β-hydroxy ester, reducing the ee value. The reaction proceeded more efficiently for substrates bearing bulkier ester moieties, of which the tert-butyl ester gave the best results. Ultimately, we concluded that aquatic plants can be used as whole-cell biocatalysts for preparing optically active β-hydroxy esters. This result represents a new use of aquatic plants and contributes to the achievement of carbon neutrality.

Separation of enantiomers of chiral fullerene derivatives through enantioselective encapsulation within an adaptable helical cavity of syndiotactic poly(methyl methacrylate) with helicity memory.

Optically active left (M)- and right (P)-handed helical syndiotactic poly(methyl methacrylate)s (M- and P-st-PMMAs) with a helicity memory enantioselectively encapsulated the racemic C60 derivatives, such as 3,4-fulleroproline tert-butyl ester (rac-1) and tetraallylated C60 (rac-2), as well as the C60-bound racemic 310-helical peptides (rac-3) within their helical cavities to form peapod-like inclusion complexes and a unique "helix-in-helix" superstructure, respectively. The enantiomeric excess (ee) and separation factor (enantioselectivity) (α) of the analyte 1 (ee = 23%-25% and α = 2.35-2.50) encapsulated within the helical cavities of the M- and P-st-PMMAs were higher than those of the analytes 2 and 3 (ee = 4.3%-6.0% and α = 1.28-1.50). The optically pure (S)- and (R)-1 were found to more efficiently induce an excess one-handed helical conformation in the st-PMMA backbone than the optically pure (S)- and (R)-1-phenylethylamine, resulting in intense mirror-image vibrational circular dichroism (VCD) spectra in the PMMA IR regions. The excess one-handed helices induced in the st-PMMAs complexed with (S)- and (R)-1 were memorized after replacement with the achiral C60, and the complexes exhibited induced electric CDs in the achiral C60 chromophore regions.

Total synthesis of (±)−paralemnolin A

The first total synthesis of chlorinated tricyclic norsesquiterpenoid paralemnolin A in racemic form was achieved. The synthesis features chlorolactonization of a cyclohexene derivative having a tert-butyl ester, construction of the novel tricyclic skeleton by an intramolecular Reformatsky–Honda reaction, and methylenation of the carbonyl group of the lactone moiety with Tebbe reagent.

Florisil as an efficient reagent for deprotection of tert-butyl carbamates, carbonates and esters

Florisil (magnesium polysilicate) is an efficient and eco-friendly reagent for the deprotection of tert-butyl carbamates, carbonates, and ethers. Moderate to excellent yields could be achieved in the presence of other acid-sensitive groups. The separation of products is easy, and Florisil can be recycled several times without observing a decrease in yields.

Copper-Catalyzed Synthesis of Masked (Hetero)Aryl Sulfinates.

Catalysis using substoichiometric copper facilitates the synthesis of masked (hetero)aryl sulfinates under mild, base-free conditions from aryl iodides and the commercial sulfonylation reagent sodium 1-methyl 3-sulfinopropanoate (SMOPS). The development of a tert-butyl ester variant of the SMOPS reagent allowed the use of aryl bromide substrates. The sulfones thus generated can be unmasked and functionalized in situ to form a variety of sulfonyl-containing functional groups.

Endomorphin-2 analogs with C-terminal esterification display potent antinociceptive effects in the formalin pain test in mice

Previously, we have investigated three C-terminal esterified endomorphin-2 (EM-2) analogs EM-2-Me, EM-2-Et and EM-2-Bu with methyl, ethyl and tert-butyl ester modifications, respectively. These analogs produced significant antinociception in acute pain at the spinal and supraspinal levels, with reduced tolerance and gastrointestinal side effects. The present study was undertaken to determine the analgesic effects and opioid mechanisms of these three analogs in the formalin pain test. Our results demonstrated that intracerebroventricular (i.c.v.) administration of 0.67–20 nmol EM-2 analogs EM-2-Me, EM-2-Et and EM-2-Bu produced dose-dependent antinociceptive effects in both phase Ⅰ and phase Ⅱ of formalin pain. EM-2-Me and EM-2-Bu displayed more potent antinociception than morphine. Especially, EM-2-Bu exhibited the highest antinociception in phase Ⅱ of formalin pain, with the ED50 value being 2.1 nmol. Naloxone (80 nmol, i.c.v.) completely antagonized the antinociceptive effects of EM-2-Me, EM-2-Et and EM-2-Bu (20 nmol, i.c.v.) in both phase I and phase Ⅱ of formalin pain, suggesting a central opioid mechanism. Nevertheless, the antinociception induced by EM-2-Me might be involved in the release of dynorphin A, which subsequently acted on κ- opioid receptor. EM-2-Bu produced the antinociception probably by the direct activation of both μ- and δ-opioid receptors. EM-2-Me, EM-2-Et and EM-2-Bu also produced significant analgesic effects after peripheral administration, and the central opioid receptors were involved. Furthermore, EM-2-Bu had no influence on the locomotor activity after i.c.v. injection. The present investigation demonstrated that C-terminal esterified modifications of EM-2 will be beneficial for developing novel therapeutics in formalin pain.

A Simple and Powerful tert-Butylation of Carboxylic Acids and Alcohols

AbstractA simple and safe tert-butylation reaction was developed. Treatment of various free amino acids with 1.1 equivalents of bis(trifluoromethanesulfonyl)imide in tert-butyl acetate directly afforded tert-butyl esters with free amino groups quickly and in good yields. In addition, various carboxylic acids and alcohols without amino groups were converted into tert-butyl esters and ethers, respectively, in high yields in the presence of small catalytic amounts of bis(trifluoromethanesulfonyl)imide. All tert-butylation reactions of free amino acids, carboxylic acids, and alcohols proceeded much faster and in higher yields compared with conventional methods.

β-Lactam TRPM8 Antagonists Derived from Phe-Phenylalaninol Conjugates: Structure-Activity Relationships and Antiallodynic Activity.

The protein transient receptor potential melastatin type 8 (TRPM8), a non-selective, calcium (Ca2+)-permeable ion channel is implicated in several pathological conditions, including neuropathic pain states. In our previous research endeavors, we have identified β-lactam derivatives with high hydrophobic character that exhibit potent and selective TRPM8 antagonist activity. This work describes the synthesis of novel derivatives featuring C-terminal amides and diversely substituted N'-terminal monobenzyl groups in an attempt to increase the total polar surface area (TPSA) in this family of compounds. The primary goal was to assess the influence of these substituents on the inhibition of menthol-induced cellular Ca2+ entry, thereby establishing critical structure-activity relationships. While the substitution of the tert-butyl ester by isobutyl amide moieties improved the antagonist activity, none of the N'-monobencyl derivatives, regardless of the substituent on the phenyl ring, achieved the activity of the model dibenzyl compound. The antagonist potency of the most effective compounds was subsequently verified using Patch-Clamp electrophysiology experiments. Furthermore, we evaluated the selectivity of one of these compounds against other members of the transient receptor potential (TRP) ion channel family and some receptors connected to peripheral pain pathways. This compound demonstrated specificity for TRPM8 channels. To better comprehend the potential mode of interaction, we conducted docking experiments to uncover plausible binding sites on the functionally active tetrameric protein. While the four main populated poses are located by the pore zone, a similar location to that described for the N-(3-aminopropyl)-2-[(3-methylphenyl)methoxy]-N-(2-thienylmethyl)-benzamide (AMTB) antagonist cannot be discarded. Finally, in vivo experiments, involving a couple of selected compounds, revealed significant antinociceptive activity within a mice model of cold allodynia induced by oxaliplatin (OXA).

Rhodium-Catalyzed Asymmetric Arylation-Induced Glycolate Aldol Additions of Silyl Glyoxylates.

(Diene)Rh(I) complexes catalyze the stereoselective three-component coupling of silyl glyoxylates, arylboronic acids, and aldehydes to give glycolate aldol products. The participation of Rh-alkoxides in the requisite Brook rearrangement was established through two component Rh-catalyzed couplings of silyl glyoxylates with ArB(OH)2 to give silyl-protected mandelate derivatives. The intermediacy of a chiral Rh-enolate was inferred through enantioselective protonation using a chiral Rh-catalyst. Diastereoselective three-component couplings with aldehydes as terminating electrophiles to give racemic products were best achieved with a bulky aryl ester on the silyl glyoxylate reagent. Optimal enantioselective couplings were carried out with the tert-butyl ester variant using an anisole-derived enantiopure tricyclo[3.2.2.02,4 ]nonadiene ligand.

Rapeseed oil as feedstock for the polymeric materials via Michael addition reaction

Rapeseed oil was used to synthesize a Michael donor to obtain polymeric materials after nucleophilic polymerization via Michael reaction. Four different bio-polyols as precursors for the Michael donor monomer synthesis were synthesized from epoxidized rapeseed oil using an oxirane ring-opening reaction. Various alcohols such as methanol, butane-1,4-diol, 2,2′-oxydi(ethan-1-ol), and 2-ethyl-2-(hydroxymethyl)propane-1,3-diol were used to obtain bio-polyols with different OH group functionality. The transesterification reaction between the synthesised bio-polyol hydroxyl groups and tert-butyl acetoacetate ester introduced acetoacetate functional groups into their structure. The acid value, hydroxyl value, viscosity and moisture content of the synthesized polyols and corresponding acetoacetates were analyzed. Size-exclusion chromatography and Fourier transform infrared spectroscopy were used to study the chemical structure of polyols and acetoacetates. From developed acetoacetates and commercially available trimethylolpropane triacrylate, bio-based polymers were obtained via carbon-Michael reaction. The different chemical structures and functionalities of the synthesized bio-based monomers allowed for the development of polymer formulations with diverse cross-linking densities. The structural, physical and thermal properties of the developed polymers were analyzed using solid-state NMR, differential scanning calorimetry, dynamic mechanical analysis and thermal gravimetric analysis testing apparatus.

Tin(II) Chloride-Catalyzed Direct Esterification and Amidation of tert-Butyl Esters Using α,α-Dichlorodiphenylmethane Under Mild Conditions.

A practical one-pot synthesis of esters and amides from tert-butyl esters via acid chloride was developed. Reactions of tert-butyl esters with α,α-dichlorodiphenylmethane as the chlorinating agent and SnCl2 as catalyst-generated acid chloride intermediates in situ were subsequently used in reactions with a variety of alcohols and amines to afford the corresponding esters and amides in high yields under mild reaction conditions. This catalytic synthetic procedure offers an effective strategy for the facile esterification and amidation of tert-butyl esters.

Size Control and Biological Properties of PAMAM-Cored Multiarm Block Copolymers.

Size is one of the crucial factors influencing the biological properties of nanomedicines. However, the size control of nanomaterials is still very challenging, and the size effect on their biological properties is worth studying. Herein, we present the synthesis and size control of a series of multiarm block copolymers with the third-generation PAMAM (G3 PAMAM) as the core. The multiarm copolymers were synthesized by the ring-opening polymerization of N-carboxyanhydride of the l-glutamic acid-5-tert-butylester [Glu(OtBu)-NCA] monomer with the amine-terminated PAMAM as the initiator, followed by the synthesis of the poly(carboxybetaine) (PCB) block via the atom transfer radical polymerization of the 2-(dimethylamino)ethyl methacrylate monomer, the reaction with tert-butyl bromoacetate, and the deprotection of the tert-butyl ester groups. The polyglutamic acid (PGA) block provided abundant reactive groups for the functionalization of the multiarm block copolymers, and the PCB block imparted excellent water solubility and anti-protein adsorption capability. We synthesized three multiarm copolymers with diameters of 15, 24, and 41 nm, respectively, by tuning the polymerization degrees of the arms. Doxorubicin was coupled to the PGA block through the acylhydrazone linkage, which resulted in a pH-sensitive drug release and a drug loading of over 20%. We systematically investigated the size effects on their cellular uptake, cytotoxicity, endocytic pathway, biodistribution, tumor penetration, and antitumor activity. This work is helpful for the design of polymeric nano-drug carriers for tumor therapy.

The significance of notch signaling in the regulation of Тreg-lymphocyte differentiation in patients with infiltrative pulmonary tuberculosis

Data on the role of regulatory T lymphocytes (Treg) in the immunopathogenesis of tuberculosis are actively accumulating in the current literature. The overwhelming effect of Treg cells on the proliferation, functional activity of Th1 lymphocytes and antigen-presenting cells allows to consider this population as a possible target of modulation of the immune response in patients with tuberculosis. The Notch signaling pathway participates in the regulation of FoxP3 transcription factor expression and, therefore, is capable of supporting suppressor activity of Treg lymphocytes. A key role in the functioning of the Notch signaling cascade belongs to the enzyme γ-secretase that cleaves the intracellular domain of the receptor (Notch ICD), with the subsequent formation of a complex that regulates cell differentiation. The actively studied inhibitor of γ-secretase is DAPT – N-[N-(3.5-difluorophenacetyl)-L-alanyl]-S-phenylglycine tert-butyl ester). Mononuclear leukocytes isolated from the blood of patients with drug-sensitive and drug-resistant pulmonary tuberculosis by gradient centrifugation before the start of anti-tuberculosis therapy were used as the material for the study. The cells were cultured under conditions of stimulation with Mycobacterium tuberculosis antigens CFP10-ESAT6 or with the addition of γ-secretase inhibitor (DAPT) at doses of 5 μM/L and 10 μM/L in combination with CFP10-ESAT6 at 37 °C and 5% CO2 for 72 h to the incubation medium. The number of Treg lymphocytes was assessed by flow cytofluorimetry by determining the expression of the CD4 surface receptor (FITC) and the intracellular transcription factor FoxP3 (PE). In intact cell cultures of pulmonary tuberculosis patients, the relative number of Treg lymphocytes was statistically significantly (p < 0.001) higher than that of healthy donors. Stimulation of cells with CFP10-ESAT6 antigens was accompanied by an increase in the proportion of CD4+FoxP3+ cells in both groups of tuberculosis patients. Addition of γ-secretase inhibitor at a concentration of 5 μM/L to the incubation medium did not lead to statistically significant changes in the number of Treg lymphocytes. The increase in DAPT concentration up to 10 μM/L was accompanied by a decrease in the number of Treg lymphocytes in comparison with the corresponding indices upon stimulation with CFP10-ESAT6 antigens in all groups of the subjects. Regardless of cultivation conditions, the number of CD4+FoxP3+ cells in patients with drug-resistant mycobacteria exceeded their number in patients with drug-sensitive pulmonary tuberculosis. Inhibition of the Notch signaling pathway by a γ-secretase inhibitor (DAPT) at a concentration of 10 μM/L contributed to a decrease in the number of Treg lymphocytes in patients with drug-sensitive and drug-resistant pulmonary tuberculosis. Reduction of Treg lymphocyte number by γ-secretase inhibitor confirms the importance of Notch signaling cascade as a potential target for correction of Treg lymphocytes immunosuppressive activity and pathogenetic therapy of tuberculosis.

Convenient Preparation of <i>tert</i>-Butyl Amino Acid Esters from <i>tert</i>-Butanol

A preparation of tert-butyl esters of amino acid is described that proceeds from protected amino acids and tert-butanol using anhydrous magnesium sulfate and an excess of boron trifluoride diethyl etherate as additional reagents. The method affords tert-butyl esters in good yields and a variety of amino acid side chains and substituents tolerate the reaction conditions.

Triarylamminium Radical Cation Facilitates the Deprotection of tert-Butyl Groups in Esters, Ethers, Carbonates, and Carbamates.

We report a catalytic protocol for mild OtBu deprotection using two commercial reagents: the tris-4-bromophenylamminium radical cation, commonly known as magic blue (MB•+), and triethylsilane. Magic blue catalytically facilitates the cleavage of the C-O bond in tert-butyl carbamates, carbonates, esters, and ethers in a high isolated yield of up to 95%, and sacrificial triethylsilane accelerates the reaction. Without requiring high temperatures, transition metals, or strong acidic or basic catalysts, this method is suitable for structurally diverse compounds, including aliphatic, aromatic, and heterocyclic substrates.

Nickel-catalyzedN-arylation of optically pure amino acid esters with activated (hetero)aryl electrophiles

An efficient method for the C–N cross-coupling of (hetero)aryl (pseudo)halides with optically pure α-amino acid esters employing a commercially available nickel catalyst and weak inorganic base was developed. This is the first example of Ni-catalyzed N-arylation of amino acid esters without the use of electrochemistry, which was shown to effectively couple a variety of amino acid tert-butyl esters with (hetero)aryl chlorides, bromides, and tosylates in high yields and excellent enantioretention. Base-mediated racemization was revealed during control experiments, but increasing the steric bulk of the amino acid ester group limited the amount of racemization of the product.