Enzyme Aided Analysis of the Substituent Distribution along the Chain of Cellulose Acetates Regioselectively Modified by the Action of an Aspergillus niger Acetylesterase

Two cellulose acetates (CA) were regioselectively deacetylated by action of a pure Aspergillus niger acetylesterase from the carbohydrate esterase family 1. The action of acetyl esterase along the polymeric chain was monitored by a new enzyme-aided method. CA with and without esterase modification was hydrolysed with a pure endoglucanase. The fragments were deutero-acetylated and separated by preparative SEC in CHCl₃. The partial degree of substitution of the individual fragments was determined by ¹H-NMR spectroscopy. The investigation confirmed the uniform regioselective and regular deacetylation along the polysaccharide chain. The partial substitution in C₂ seemed to be of major importance for the enzyme's mode of action.     

13C-NMR spectra of substituted 1,4-dihydropyridines

It has been found that the electron shift in the C₍₂₎=C₍₃₎ bond, under the influence of the substituent attached to the nitrogen atom and the substituents in the 3- and 5-positions, occurs via a -inductive mechanism. 4-(1,4-Dihydropyridyl) functional groups behave as electron donating substituents via an inductive mechanism.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1232–1238, September, 1989.     

Sonogashira reaction of aryl halides with propiolaldehyde diethyl acetal catalyzed by a tetraphosphine/palladium complex

All-cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C₃H₅)]₂ efficiently catalyzes the Sonogashira reaction of propiolaldehyde diethyl acetal with a variety of aryl bromides and chlorides. A minor electronic effect of the substituents of the aryl bromide was observed. Similar reaction rates were observed in the presence of activated aryl bromides such as 4-trifluoromethylbromobenzene and deactivated aryl bromides such as bromoanisole. Turnover numbers up to 95,000 can be obtained for this reaction. Even aryl chlorides and heteroarylbromides or chlorides have been successfully alkynylated with this catalyst. Moreover, a wide variety of substituents on the aryl halide such as fluoro, trifluoromethyl, acetyl, benzoyl, formyl, nitro, dimethylamino or nitrile are tolerated.     

Formation of perfluorinated polyphenylenes by multiple pentafluorophenylation using C6F5Si(CH3)3

Pentafluorophenylation of perfluoroarenes with C₆F₅Si(CH₃)₃ was investigated by using NMR and MALDI-TOF-MS techniques. Successive multiple pentafluorophenylation easily occurred not only on the para-position but also on the ortho-positions to provide perfluorinated p-phenylene and m-phenylene compounds. The perfluoroarenes having electron-withdrawing substituents provided oligo- to poly-(phenylene)s depending on the added amounts of C₆F₅Si(CH₃)₃, while the perfluoroarenes having electron-donor substituents gave H(C₆F₄)_nF polymers produced from C₆F₅H, which was the decomposed product of C₆F₅Si(CH₃)₃.     

Synthesis and properties of C(9) and C(11) ethyl derivatives of 8-aza-D-homogonanes. The steric factor in the annelation of cyclic Schiff bases by β-triketones

We have studied the steric factors due to the substituents at C₍₁₎ of 3,4-dihydroisoquinolines and in the acyl segment of 2-acyl-1,3-cyclohexanediones that affect the annelation of cyclic Schiff bases by -triketones. Ethyl substituents at C₍₁₎ of 3,4-dihydroisoquinolines show about twice as much retarding effect on reaction rate and yield of desired products as does the replacement of acetyl by butanoyl in 2-acyl-1,3-cyclohexanediones. Derivatives that are ethylated at C₍₁₁₎ of aza-D-homogona-1,3,5(10),13-tetraen-12,17a-diones exist as a mixture of conformers hindered at the C ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1239–1245, September, 1993.     

Mode of action of acetylesterases associated with endoglucanases towards water-soluble and -insoluble cellulose acetates

A screening of commercial enzyme preparations for the capability ofcellulose acetate (CA) deacetylation revealed that such enzyme activity ismore common than could be anticipated. Enzyme-aided deacetylation of celluloseacetate was clearly a function of the degree of substitution (DS). Celluloseacetates up to a DS of 1.4 were deacetylated by a large number of enzyme mixes.Interestingly, none of the investigated enzyme preparations had the capabilityfor complete cellulose acetate deacetylation. Definitely most hydrolasepreparations investigated in our study deacetylated cellulose acetate with nopreference for a certain position, as could be confirmed by NMR spectroscopy.However, one acetyl esterase had a clear preference for the C2- andC3-positions, leaving the acetyl substituents at the C6-position intact.     

Triindolo-Truxene Derivatives: Design,Synthesis, and Fine-Tuning of Electronic Properties and Molecular Assembly through Molecular Engineering

Triindolo-truxene, a C₃-symmetric molecule with a large π-conjugated plane, has six methylene carbon atoms and three aromatic carbon atoms that can be facilely functionalized. Herein, butyl, carbonyl, cyano, and/or malononitrile groups were introduced at six methylene carbon atoms (6-, 14-, 22- or 8-, 16-, 24-positions) and/or three aromatic carbon atoms (2-, 10-, and 18-positions) of triindolo-truxene to produce eight derivatives. Their photophysical properties, electrochemical properties, and molecular assembly can be effectively modulated by substituents and substitution patterns. Incorporation of electron-deficient groups led to redshifts in both the absorption and emission of these derivatives and also lowered their HOMO and LUMO levels. Different substitution patterns resulted in the different intramolecular donor–acceptor interactions. Electron-deficient substituents at the methylene carbon atoms in the 6-, 14-, and 22-positions led to intramolecular charge transfer from the fluorene arms to the truxene core, whereas the corresponding substitutions at the methylene carbon atoms in the 8-, 16-, and 24-positions resulted in intramolecular charge transfer from the truxene core to the fluorene arms. The molecular packing in single crystals and molecular aggregation in solution are also influenced by the substituents and substitution patterns. This work provides a straightforward strategy to alter the properties of triindolo-truxene.     

DFT study of 1-, 4-, and 5-substituted 2-oxo-1,2,3,4-tetrahydropyrimidines: substituent steric and electronic effects,and ring flipping

Steric and the electronic effects caused by the substituents in the 1-, 4-, and 5-positions of substituted 2-oxo-1,2,3,4-tetrahydropyrimidines were investigated using density functional theory at the B3LYP/6-31++G(d,p) level. Results of this study show that the heterocyclic ring adopts a pseudo-boat conformation, in which the C₄ and N₁ atoms are deviated from ring planarity. The C₄-substituent occupies a pseudo-axial position and the space orientation of the substituent depends on the type and position of the additional substituent in this aryl group. The heights of the C₄ and N₁ atoms from the boat plane and the orientation of 5-CO moiety toward the heterocyclic ring depend on the electronic and steric effects of the substituents in the various positions. Ring flip calculations for 4-phenyl substituent explain the extreme steric effect caused by the substituent in the 1-position. These calculations indicate the more favored pseudo-axial orientation of the phenyl group over the equatorial orientation.     

Specific rearrangement reactions of acetylated lysine containing peptide bn (n = 4–7) ion series

Characterization of ε‐N‐acetylated lysine containing peptides, one of the most prominent post‐translational modifications of proteins, is an important goal for tandem mass spectrometry experiments. A systematic study for the fragmentation reactions of b ions derived from ε‐N‐acetyllysine containing model octapeptides (K_AcYAGFLVG and YAK_AcGFLVG) has been examined in detail. Collision‐induced dissociation (CID) mass spectra of b_n (n = 4–7) fragments of ε‐N‐acetylated lysine containing peptides are compared with those of N‐terminal acetylated and doubly acetylated (both ε‐N and N‐terminal) peptides, as well as acetyl‐free peptides. Both direct and nondirect fragments are observed for acetyl‐free and singly acetylated (ε‐N or N‐terminal) peptides. In the case of ε‐N‐acetylated lysine containing peptides, however, specific fragment ions (m/z 309, 456, 569 and 668) are observed in CID mass spectra of b_n (n = 4–7) ions. The CID mass spectra of these four ions are shown to be identical to those of selected protonated C‐terminal amidated peptides. On this basis, a new type of rearrangement chemistry is proposed to account for the formation of these fragment ions, which are specific for ε‐N‐acetylated lysine containing peptides. Consistent with the observation of nondirect fragments, it is proposed that the b ions undergo head‐to‐tail macrocyclization followed by ring opening. The proposed reaction pathway assumes that b_n (n = 4–7) of ε‐N‐acetylated lysine containing peptides has a tendency to place the K_Ac residue at the C‐terminal position after macrocyclization/reopening mechanism. Then, following the loss of CO, it is proposed that the marker ions are the result of the loss of an acetyllysine imine as a neutral fragment. Copyright © 2014 John Wiley & Sons, Ltd.     

13C NMR chemical shifts of benzophenone azine as a benchmark for configurational assignment of azines with aromatic substituents

An analysis of the ¹³C NMR spectral data and quantum chemical calculations for benzophenone azine shows that the shielding constant of the C _ipso atom of its molecule is stereo-specific. The characteristic difference in chemical shifts of the C _ipso atoms of the phenyl rings in the cis- and trans-positions with respect to the lone pair of the neighboring nitrogen atom is 2–3 ppm. The stereospecificity observed for chemical shifts was proposed to be used for the configurational assignment of azines containing aromatic substituents.     

Stereochemistry of nitrogen heterocycles. 69. 13C NMR spectra of stereoisomeric 10-methyl-5-oxygen-substituted trans-decahydroquinolines

The ¹³C NMR spectra of 5-keto- and 5a- and 5e-hydroxy-10-methyl- and 1,10-dimethyltrans-decahydroquinolines have been recorded and interpreted. The increments of the oxo and hydroxy groups in the 10-methyldecahydroquinoline and the isostructural 10-methyldecaline systems were compared. The difference between the increments of azacyclic and the carbocyclic systems appears- at the -positions relative to the electronegative substituents (C₍₇₎ and C₍₉₎) and at the antiperiplanar -positions relative to nitrogen (C₍₅₎ and C₍₇₎). The increments of the oxo and the equatorial hydroxy groups in the aza ring are more shielded than in the carbon ring (at C₍₇₎, 2 ppm; at C_(g), 1 ppm), while the increments of the axial hydroxy group are more deshielded (at C₍₅₎, 1.5–2.0 ppm; at C₍₉₎, 1.0–1.5 ppm). The more the respective carbon atoms of the heterocycle are hydrogenated, the stronger are the deshielding -effect and the shielding -effect of the methyl group on nitrogen.For Communication 68, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 60–65, January, 1990.     

Pd(II)-catalyzed deprotection of acetals and ketals containing acid sensitive functional groups

The pincer complex [Pd(C¹,O¹,N¹-L)(NCMe)]ClO₄ (L = monoanionic ligand resulting from deprotonation of the acetyl group of the dimethyl monoketal of 2,6-diacetylpyridine) is used for the high-yield and selective catalytic hydrolysis of aliphatic, aromatic, cyclic, and acyclic dimethyl-acetals, -ketals, and dioxolanes, even in the presence of large substituents. Other protecting groups, such as THP or TBDMS, or very acid-sensitive alcohols were not affected. The catalyst is easily prepared in high yield from Pd(AcO)₂ and 2,6-diacetylpyridinium perchlorate stable to air and moisture, easily and fully recoverable and reusable.     

Acetylation of DMSO:PF solutions of cellulose

Three different techniques for esterifying solutions of cellulose dissolved in mixtures of dimethyl sulfoxide (DMSO) and paraformaldehyde (PF) were evaluated and are herein described. The evaluation and development of suitable synthetic procedures and the characteristics of the resulting acetylated cellulose are reported. Glacial acetic acid (glacial HOAc), acetyl chloride (AcCl), and acetic anhydride (Ac₂O) were compared as acetylating agents for solutions of cellulose in DMSO:PF, and it was demonstrated that mixtures of pyridine (Py) and Ac₂O rapidly acetylated the cellulose to yield beige to amber acetone-soluble cellulose acetates which were partially oxidized. These thermoplastic resins exhibited softening points between 80 and 110°C and thermal stabilities (in nitrogen atmospheres) similar to those of native celluloses (350 to 375°C). Degree of acetyl substitution (DS) values ranged from 0 to 2.0 as a function of acetylation time.     

Synthèse de sucres aminès ramifiés II. Synthèse et réactions de spiro-aziridines. Communication préliminaire

Treatment of 3-C-cyano-1,2:5,6-di-O-isopropylidene-3-O-(toluene-p-sulfonyl)-α-D -allofurannose with AlLiH₄ or RMgX yields spiro-aziridines with two identical substituents on C(3′) (? H, ? CH₃, ? C₂H₅). Reactions of these products and their derivatives are briefly described. If the C(3′) substituents are protons, the aziridine ring is easily opened. In acidic media (HCl), an amino-sugar containing the branched chain ? CH₂Cl is produced; with hydrogenation, a ? CH₃ branched chain results. If the C(3′) substituents are methyl groups, the aziridine ring cannot be opened neither with HCl nor with hydrogen. The acetylated derivative of this latter compound rearranges to the corresponding allylamide with HCl. For both types of spiro-aziridine, the nitrous deamination leads to the corresponding alkene.     

Suzuki Coupling of Cyclopropylboronic Acid With Aryl Halides Catalyzed by a Palladium–Tetraphosphine Complex

The tetraphosphine all‐cis‐1,2,3,4‐tetrakis(diphenylphosphinomethyl)cyclopentane (Tedicyp) in combination with [Pd(C₃H₅)Cl]₂ affords a very efficient catalyst for the coupling of cyclopropylboronic acid with aryl bromides and aryl chlorides. Higher reactions rates were observed with aryl bromides than with aryl chlorides; however, even in the presence of 1–0.4% of catalyst, a few aryl chlorides gave the coupling products in good yields. A wide variety of substituents such as alkyl, methoxy, trifluoromethyl, acetyl, benzoyl, formyl, carboxylate, nitro, and nitrile on the aryl halides are tolerated. The coupling reaction of sterically very congested aryl bromides such as bromomesitylene or 2,4,6‐triisopropylbromobenzene also proceeds in good yields.     

Peracetylated α‐d‐glucopyranosyl fluoride and peracetylated α‐maltosyl fluoride

The X‐ray analyses of 2,3,4,6‐tetra‐O‐acetyl‐α‐d ‐glucopyranosyl fluoride, C₁₄H₁₉FO₉, (I), and the corresponding maltose derivative 2,3,4,6‐tetra‐O‐acetyl‐α‐d ‐glucopyranosyl‐(1→4)‐2,3,6‐tri‐O‐acetyl‐α‐d ‐glucopyranosyl fluoride, C₂₆H₃₅FO₁₇, (II), are reported. These add to the series of published α‐glycosyl halide structures; those of the peracetylated α‐glucosyl chloride [James & Hall (1969). Acta Cryst. A 25 , S196] and bromide [Takai, Watanabe, Hayashi & Watanabe (1976). Bull. Fac. Eng. Hokkaido Univ. 79 , 101–109] have been reported already. In our structures, which have been determined at 140 K, the glycopyranosyl ring appears in a regular ⁴C₁ chair conformation with all the substituents, except for the anomeric fluoride (which adopts an axial orientation), in equatorial positions. The observed bond lengths are consistent with a strong anomeric effect, viz. the C1—O5 (carbohydrate numbering) bond lengths are 1.381 (2) and 1.381 (3) Å in (I) and (II), respectively, both significantly shorter than the C5—O5 bond lengths, viz. 1.448 (2) Å in (I) and 1.444 (3) Å in (II).     

Tetraphosphine/palladium catalysed Suzuki cross-coupling reactions of aryl halides with alkylboronic acids

Through the use of [PdCl(C₃H₅)]₂/cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane as a catalyst, a range of aryl bromides and chlorides undergoes Suzuki cross-coupling with alkylboronic acids in good yields. Several alkyl substituents such as ethyl, n-butyl, n-octyl, isobutyl or 2,2-dimethylpropyl on the alkylboronic acids have been successfully used. The functional group tolerance on the aryl halide is remarkable; substituents such as fluoro, methyl, methoxy, acetyl, formyl, benzoyl, nitro or nitrile are tolerated. Furthermore, this catalyst can be used at low loading, even for reactions of sterically hindered aryl bromides.     

Migration of an acetyl group in glucosamine and glucose derivatives by the action of butyllithium. The synthesis of an N-acetylglucosamine 4-phosphate derivative

Conclusions The migration of the acetyl group from C⁴ to C⁶ occurs in partially acetylated derivatives of D-glucose and D-glucosamine upon reaction with butyllithium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2106-2109, September, 1987.     

Effect of bulky substitution on catalytic activity of a manganese salen complex used in biomimetic alkene epoxidation and alkane hydroxylation with sodium periodate

The catalytic activity of Mn(salen)Cl containing tert-pentyl groups at the 3,5-positions of the salen ligand in the epoxidation of alkenes and hydroxylation of alkanes was studied at room temperature, using sodium periodate as an oxygen source. The effects of various axial ligands were investigated in the epoxidation of cyclooctene. Imidazole, as a strong π-donor ligand, was the best axial ligand. The effect of different solvents was studied in the epoxidation of cyclooctene in CH₃CN/H₂O solvent mixture. The epoxidation reactions of cyclooctene by different oxygen donors including NaIO₄, Bu₄NIO₄, KHSO₅, H₂O₂, H₂O₂/urea, NaOCl and tert-BuOOH were also studied and NaIO₄ was selected as oxygen source. The presence of bulky substituents in the 3,5-positions of the salen ligand was found to increase the catalytic activity of this complex.     

Developing a Library of Mannose-Based Mono- and Disaccharides: A General Chemoenzymatic Approach to Monohydroxylated Building Blocks

Regioselective deprotection of acetylated mannose-based mono- and disaccharides differently functionalized in anomeric position was achieved by enzymatic hydrolysis. Candida rugosa lipase (CRL) and Bacillus pumilus acetyl xylan esterase (AXE) were immobilized on octyl-Sepharose and glyoxyl-agarose, respectively. The regioselectivity of the biocatalysts was affected by the sugar structure and functionalization in anomeric position. Generally, CRL was able to catalyze regioselective deprotection of acetylated monosaccharides in C6 position. When acetylated disaccharides were used as substrates, AXE exhibited a marked preference for the C2, or C6 position when C2 was involved in the glycosidic bond. By selecting the best enzyme for each substrate in terms of activity and regioselectivity, we prepared a small library of differently monohydroxylated building blocks that could be used as intermediates for the synthesis of mannosylated glycoconjugate vaccines targeting mannose receptors of antigen presenting cells.