Construction of Recombinant Escherichia coli Catalysts which Simultaneously Express an (S)‐Oxynitrilase and Different Nitrilase Variants for the Synthesis of (S)‐Mandelic Acid and (S)‐Mandelic Amide from Benzaldehyde and Cyanide

Recombinant Escherichia coli strains were constructed which simultaneously expressed the genes encoding the (S)‐oxynitrilase from cassava (Manihot esculenta) together with the wild‐type or a mutant variant of the arylacetonitrilase from Pseudomonas fluorescens EBC191 in a single organism under the control of a rhamnose‐inducible promoter. The whole cell catalysts obtained converted benzaldehyde and potassium cyanide in aqueous media at pH 5.2 mainly to (S)‐mandelic acid and/or (S)‐mandelic amide and synthesized only low amounts of the corresponding (R)‐enantiomers. The conversion of benzaldehyde and potassium cyanide (KCN) by a whole‐cell catalyst simultaneously expressing the (S)‐oxynitrilase and the wild‐type nitrilase resulted in a ratio of (S)‐mandelic acid to (S)‐mandelic amide of about 4:3. This could be explained by the strong nitrile hydratase activity of the wild‐type nitrilase with (S)‐mandelonitrile as substrate. The relative proportion of (S)‐mandelic amide formed in this system was significantly increased by coexpressing the (S)‐oxynitrilase with a carboxy‐terminally truncated variant of the nitrilase. This whole‐cell catalyst converted benzaldehyde and KCN to mandelic amide and mandelic acid in a ratio of about 9:1. The ee of the (S)‐mandelic amide formed was calculated to be >95%.     

Synthesis of 2‐Haloalkylpyridines via Cp*RuCl‐Catalyzed Cycloaddition of 1,6‐Diynes with α‐Halonitriles. Unusual Halide Effect in Catalytic Cyclocotrimerization

In the presence of 2–5 mol % Cp*RuCl (cod), various 1,6‐diynes reacted with α‐monohalo‐ and α,α‐dihalonitriles at ambient temperature to afford 2‐haloalkylpyridines in 42–93% isolated yields. The failure of acetonitrile, N,N‐dimethylaminoacetonitrile, phenylthioacetonitrile, and methyl cyanoacetate as nitrile substrate clearly showed that the α halogen substitution is essential for the present cycloaddition under mild conditions. The cycloaddition of unsymmetrical diynes bearing a substituent on one alkyne terminal gave 2,3,4,6‐substituted pyridines exclusively.     

Enzymatic Synthesis of Chiral Phenylalanine Derivatives by a Dynamic Kinetic Resolution of Corresponding Amide and Nitrile Substrates with a Multi‐Enzyme System

Mutant α‐amino‐ε‐caprolactam (ACL) racemase (L19V/L78T) from Achromobacter obae with improved substrate specificity toward phenylalaninamide was obtained by directed evolution. The mutant ACL racemase and thermostable mutant D ‐amino acid amidase (DaaA) from Ochrobactrum anthropi SV3 co‐expressed in Escherichia coli (pACLmut/pDBFB40) were utilized for synthesis of (R)‐phenylalanine and non‐natural (R)‐phenylalanine derivatives (4‐OH, 4‐F, 3‐F, and 2‐F‐Phe) by dynamic kinetic resolution (DKR). Recombinant E. coli with DaaA and mutant ACL racemase genes catalyzed the synthesis of (R)‐phenylalanine with 84% yield and 99% ee from (RS)‐phenylalaninamide (400 mM) in 22 h. (R)‐Tyrosine and 4‐fluoro‐(R)‐phenylalanine were also efficiently synthesized from the corresponding amide compounds. We also co‐expresed two genes encoding mutant ACL racemase and L ‐amino acid amidase from Brevundimonas diminuta in E. coli and performed the efficient production of various (S)‐phenylalanine derivatives. Moreover, 2‐aminophenylpropionitrile was converted to (R)‐phenylalanine by DKR using a combination of the non‐stereoselective nitrile hydratase from recombinamt E. coli and mutant ACL racemase and DaaA from E. coli encoding mutant ACL racemase and DaaA genes.     

Cross‐Linked Amorphous Nitrilase Aggregates for Enantioselective Nitrile Hydrolysis

A recombinant Escherichia coli strain was constructed which efficiently expressed the enantioselective nitrilase from Alcaligenes faecalis DSMZ 30030 as a hisitidine‐tagged enzyme variant under the control of a rhamnose inducible promoter. The enzyme was purified from cell extracts and used for the preparation of cross‐linked enzyme aggregates (CLEAs). The conditions for the preparation of the CLEAs were optimized using various organic solvents and cross‐linking agents and a procedure was developed which combined a precipitation with 85 % (v/v) isopropyl alcohol and a cross‐linking with 30 mM glutaraldehyde. Thus, about 80 % of the initial nitrilase activity could be incorporated into the CLEAs. The hydrolysis of racemic mandelonitrile to (R)‐mandelic acid was compared between the soluble nitrilase preparations and their CLEAs (nit‐CLEAs). The nitrilase activity in the CLEAs was at 30 °C and 60 °C about 5 times more stable than in the soluble preparations. The CLEAs could be reused 5 times with only about 10 % reduction in activity. The enantioselectivity of the nitrilase for the formation of (R)‐mandelic acid from racemic mandelonitrile decreased for both preparations with increasing temperatures (10 °C to 50 °C), but this effect was significantly less pronounced for the CLEAs. A detailed analysis of solvent effects on nitrilase enantioselectivity allowed thermodynamic insights into contributions from free energy component (activation enthalpy and entropy) to chiral preference of nitrilase in such non conventional media.     

Chemoenzymatic synthesis of chiral carboxylic acids via nitriles

BACKGROUND: Enantiomerically pure 1,4‐benzodioxane‐2‐carboxylic acid derivatives are useful building blocks for the synthesis of pharmaceuticals and biologically active compounds whose interaction with their biological target (enzyme, receptor) depends very much on the absolute configuration of the chiral carbon at the 2‐position. The aim of the present work is to investigate the route to racemic nitriles and the subsequent selective enzymatic hydrolysis by nitrilase to optically active 1,4‐benzodioxane‐2‐carboxylic acid and 6‐formyl‐1,4‐benzodioxane‐2‐carboxylic acid. RESULTS: A range of microbial nitrilases from Rhodococcus, Alcaligenes and Pseudomonas strains have been prepared and screened for the desired biotransformations using a chiral high performance liquid chromatography (HPLC) analytical method. The nitrilase from Alcaligenes faecalis ATCC 8750 showed the highest and the nitrilase from Rhodococcus rhodochrous NCIMB 11216 the lowest activity towards 2‐cyano‐6‐formyl‐1,4‐benzodioxane. Lyophilised cells of Rhodococcus R 312 gave the (R)‐1,4‐benzodioxane‐2‐carboxylic acid with high enantioselectivity after 25% conversion. Excellent enantioselectivities for the hydrolysis of both 2‐cyano‐1,4‐benzodioxane as well as 2‐cyano‐6‐formyl‐1,4‐benzodioxane have been achieved and the absolute configuration of 1,4‐benzodioxane‐2‐carboxylic acid was determined to be R by comparison with the specific rotation of commercially available (R)‐1,4‐benzodioxane‐2‐carboxylic acid. CONCLUSIONS: This new nitrilase‐catalysed kinetic resolution of 2‐cyano‐ and 2‐cyano‐6‐formyl‐1,4‐benzodioxane opens a mild route to optically active 1,4‐benzodioxane‐2‐carboxylic acids. As the formyl functional group would be damaged in chemical nitrile hydrolysis, nitrilase‐catalysed hydrolysis solves this synthetic bottleneck and advances nitrilase biocatalytic tools for the preparation of more complex 1,4‐benzodioxane‐2‐carboxylic acids. Copyright © 2007 Society of Chemical Industry     

Selective Hydrogenation of Amides using Ruthenium/ Molybdenum Catalysts

Recyclable, heterogeneous bimetallic ruthenium/molybdenum catalysts, formed in situ from triruthenium dodecacarbonyl [Ru₃(CO)₁₂] and molybdenum hexacarbonyl [Mo(CO)₆], are effective for the selective liquid phase hydrogenation of cyclohexylcarboxamide (CyCONH₂) to cyclohexanemethylamine (CyCH₂NH₂), with no secondary or tertiary amine by‐product formation. Variation of Mo:Ru composition reveals both synergistic and poisoning effects, with the optimum combination of conversion and selectivity at ca. 0.5, and total inhibition of catalysis evident at ≥1. Good amide conversions are noted within the reaction condition regimes 20–100 bar hydrogen and 145–160 °C. The order of reactivity of these catalysts towards reduction of different amide functional groups is primary>tertiary≫secondary. In situ HP‐FT‐IR spectroscopy confirms that catalyst genesis occurs during an induction period associated with decomposition of the organometallic precursors. Ex situ characterisation, using XRD, XPS and EDX‐STEM, for active Mo:Ru compositions, has provided evidence for intimately mixed ca. 2.5–4 nm particles that contain metallic ruthenium, and molybdenum (in several oxidation states, including zero).     

Efficient Biocatalytic Synthesis of Highly Enantiopure α-Alkylated Arylglycines and Amides

A number of racemic α-alkylarylglycine amides including 1-amino-1-carbamoyl-1,2,3,4-tetrahydronaphthalene underwent efficient biocatalytic hydrolysis under very mild conditions to afford the corresponding (S)-α-alkylarylglycines and (R)-α-alkylarylglycine amides in excellent yields with enantiomeric excesses higher than 99.5%. Both the reaction rate and enantioselectivity of biocatalytic kinetic resolution were strongly dependent upon the nature of the substituent and the substitution pattern on the benzene ring of the substrate. In contrast, no effective biotransformation of the Strecker nitrile derived from acetophenone was observed under the catalysis of a nitrile hydratase/amidase-containing microbial Rhodococcus sp. AJ270 whole-cell catalyst. Coupled with the chemical hydrolysis of amide, this biotransformation process provided efficient syntheses of α-substituted arylglycines in both enantiomeric forms from readily available racemic amides.     

Synthesis,Structure–Activity,and Structure–Stability Relationships of 2‐Substituted‐N‐(4‐oxo‐3‐oxetanyl) N‐Acylethanolamine Acid Amidase (NAAA) Inhibitors

N‐Acylethanolamine acid amidase (NAAA) is a cysteine amidase that preferentially hydrolyzes saturated or monounsaturated fatty acid ethanolamides (FAEs), such as palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), which are endogenous agonists of nuclear peroxisome proliferator‐activated receptor‐α (PPAR‐α). Compounds that feature an α‐amino‐β‐lactone ring have been identified as potent and selective NAAA inhibitors and have been shown to exert marked anti‐inflammatory effects that are mediated through FAE‐dependent activation of PPAR‐α. We synthesized and tested a series of racemic, diastereomerically pure β‐substituted α‐amino‐β‐lactones, as either carbamate or amide derivatives, investigating the structure–activity and structure–stability relationships (SAR and SSR) following changes in β‐substituent size, relative stereochemistry at the α‐ and β‐positions, and α‐amino functionality. Substituted carbamate derivatives emerged as more active and stable than amide analogues, with the cis configuration being generally preferred for stability. Increased steric bulk at the β‐position negatively affected NAAA inhibitory potency, while improving both chemical and plasma stability.     

Stereoselective Formation of 1,4‐Anhydro‐2‐C‐carboxytetritols in the Degradation of 1,5‐Anhydroribitol and 1,5‐Anhydroxylitol with Oxygen in Aqueous Alkali

Abstract

In addition to other acid products, degradation of 1,5‐anhydroribitol (5) and 1,5‐anhydroxylitol (6) with oxygen in 1.25 M NaOH produced diastereomeric 1,4‐anhydro‐2‐C‐carboxy‐D‐erythritol (7) and 1,4‐anhydro‐2‐C‐carboxy‐D‐threitol (8) and their enantiomers as major products. However, the ratio of the diastereomers differed for the two reactants. Thus, their formation could not proceed solely by benzilic acid‐type rearrangements through α‐dicarbonyl intermediates as typically proposed for formation of alkyl C‐carboxyfuranosides from alkyl glycopyranosides in similar reactions. The α‐dicarbonyl species that can form from 5 and 6 are identical. Potential mechanisms to account for stereoselective formation of 7 and 8 are presented.     

Selective hydrogenation of nitrile‐butadiene rubber catalyzed by thermoregulated phase transfer phosphine rhodium complex

Hydrogenation of polymer having C?C double bond can be carried out with the metal–organic complex as catalyst, which has the property of themoregulated phase transfer. In this study, a new complex RhCl[PPh[(OCH₂CH₂)_5≤n≤6CH₃]₂]₃ (Rh/AEOPP) was synthesized with a good yield, which was further used as catalyst to selectively hydrogenated nitrile‐butadiene rubber (HNBR). This is the first time that Rh/AEOPP complex was synthesized and applied in nitrile‐butadiene rubber (NBR) hydrogenation. The result shows that hydrogenation degree of product (HNBR) can be extended to 90%, when the condition is [Cat] = 3% (based the weight of NBR), L₂: Cat (Weight Ratio) = 2, [NBR] = 5% (based on the weight of xylene solution), P (H₂) = 1.5 MPa, T = 155°C, and t = 8 h. Also, by adjusting temperature, the catalyst could be easily separated from products with 89% catalyst complex recovery. In addition, ¹H‐NMR and infrared (IR) spectra showed that C?C double bonds in NBR was successfully hydrogenated without causing reduction of the CN group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crystallization and melting behavior of multi‐walled carbon nanotube‐reinforced nylon‐6 composites

The crystallization and melting behavior of neat nylon‐6 (PA6) and multi‐walled carbon nanotubes (MWNTs)/PA6 composites prepared by simple melt‐compounding was comparatively studied. Differential scanning calorimetry (DSC) results show two crystallization exotherms (T_{CC, 1} and T_{CC, 2}) for PA6/MWNTs composites instead of a single exotherm (T_{CC, 1}) for the neat matrix. The formation of the higher‐temperature exotherm T_{CC, 2} is closely related to the addition of MWNTs. X‐ray diffraction (XRD) results indicate that only the α‐phase crystalline structure is formed upon incorporating MWNTs into PA6 matrix, independently of the cooling rate and annealing conditions. These observations are significantly different from those for PA6 matrix, where the increase in cooling rate or decrease in annealing temperature results in the crystal transformation from α‐phase to γ‐phase. The crystallization behavior of PA6/MWNTs composites is also significantly different from those reported in PA6/nanoclay systems, probably due to the difference in nanofiller geometry between one‐dimensional MWNTs and two‐dimensional nanoclay platelets. The nucleation sites provided by carbon nanotubes seem to be favorable to the formation of thermodynamically stable α‐phase crystals of PA6. The dominant α‐phase crystals in PA6/MWNTs composites may play an important role in the remarkable enhancement of mechanical properties. Copyright © 2005 Society of Chemical Industry     

Potassium Phosphate‐Catalyzed Chemoselective Reduction of α‐Keto Amides: Route to Synthesize Passerini Adducts and 3‐Phenyloxindoles

A chemoselective reduction of α‐keto amides to biologically important α‐hydroxy amides (mandelamides) by polymethylhydrosiloxane (PMHS) using 5 mol% potassium phosphate (K₃PO₄) as catalyst has been developed. This transition metal‐free protocol discloses excellent chemoselectivity for the ketone reduction of α‐keto amides in the presence of other reducible functionalities like ketone, nitro, halides, nitrile and amide. Also, the chemoselectively reduced α‐hydroxy amide has been derivatized to isocyanide‐free Passerini adducts. The N‐alkyl‐α‐hydroxy amides have been successfully converted to 3‐phenyloxindole derivatives by treatment with methanesulfonyl cholride and triethylamine.

     

Optimization of nitrilase production from a new thermophilic isolate

A new thermostable nitrilase‐producing isolate identified as Streptomyces sp. MTCC 7546 has been studied extensively for the optimization of enzyme production operating in batch mode. The benzonitrile was observed as inducer of nitrilase production. The isolate showed maximum nitrilase production after 24 h of incubation at optimal conditions. The strain grows well on a variety of carbon sources and produces the nitrilase that catalyses the hydrolysis of nitriles to acids without formation of amides. The enzyme is mostly active against mono‐ and di‐aliphatic nitriles (10 mmol L^?1) at pH of 7.4 and at a temperature of 50 °C. Copyright © 2007 Society of Chemical Industry     

Application of a Recombinant Escherichia coli Whole‐Cell Catalyst Expressing Hydroxynitrile Lyase and Nitrilase Activities in Ionic Liquids for the Production of (S)‐Mandelic Acid and (S)‐Mandeloamide

The conversion of benzaldehyde and cyanide into mandelic acid and mandeloamide by a recombinant Escherichia coli strain which simultaneously expressed an (S)‐hydroxynitrile lyase (oxynitrilase) from cassava (Manihot esculenta) and an arylacetonitrilase from Pseudomonas fluorescens EBC191 was studied. Benzaldehyde exhibited a pronounced inhibitory effect on the nitrilase activity in concentrations ≥25 mM. Therefore, it was tested if two‐phase systems consisting of a buffered aqueous phase and the ionic liquid 1‐butyl‐1‐pyrrolidinium bis(trifluoromethanesulfonyl)imide (BMpl NTf₂) or 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMim PF₆) could be used for the intended biotransformation. The distribution coefficients of the substrates, intermediates and products of the reaction were determined and it was found that BMpl NTf₂ and BMim PF₆ were highly efficient as substrate reservoirs for benzaldehyde. The recombinant E. coli strain was active in the presence of BMpl NTf₂ or BMim PF₆ phases and converted benzaldehyde and cyanide into mandelic acid and mandeloamide. The two‐phase systems allowed the conversion of benzaldehyde dissolved in the ionic liquids to a concentration of 700 mM with product yields (=sum of mandelic acid and mandeloamide) of 87–100%. The cells were slightly more effective in the presence of BMpl NTf₂ than in the presence of BMim PF₆. In both two‐phase systems benzaldehyde and cyanide were converted into (S)‐mandeloamide and (S)‐mandelic acid with enantiomeric excesses ≥94%. The recombinant E. coli cells formed, in the two‐phase systems with ionic liquids and increased substrate concentrations, higher relative amounts of mandeloamide than in a purely aqueous system with lower substrate concentrations.     

Enantioselective Phase‐Transfer Catalytic α‐Benzylation and α‐Allylation of α‐tert‐Butoxycarbonyllactones

A new enantioselective α‐benzylation and α‐allylation of α‐tert‐butoxycarbonyllactones was devloped. α‐Benzylation and α‐allylation of α‐tert‐butoxycarbonylbutyrolactone and α‐tert‐butoxycarbonylvalerolactone under phase‐transfer catalytic conditions (50% cesium hydroxide, toluene, −60 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐NAS bromide (1 mol%) afforded the corresponding α‐substituted α‐tert‐butoxycarbonyllactones in very high chemical yields (up to 99%) and optical yields (up to 99% ee). The synthetic potential of this method has been successfully demonstrated by the asymmetric synthesis of unnatural α‐quaternary homoserines, 3‐alkyl‐3‐carboxypyrrolidine and 3‐alkyl‐3‐carboxypiperidine.     

Stereoselective Tandem Epoxidation–Alcoholysis/Hydrolysis of Glycals with Molybdenum Catalysts

Molybdenum catalysts are efficient and selective catalysts for the tandem epoxidation/alcoholysis or epoxidation/hydrolysis of glucal and galactal derivatives. In glucal derivatives the selectivity is mainly controlled by the allylic substituent at position 3 of the glycal, obtaining in general the products derived from the initial formation of the α‐epoxide (gluco) when this hydroxy group is protected, while products derived from the β‐epoxide (manno) are mainly obtained when it is unprotected. In galactal derivatives the estereoselectivity is always high to give the α‐epoxide (galacto) and independent of the protecting groups.     

Enzymatic Synthesis of Enantiopure α‐ and β‐Amino Acids by Phenylalanine Aminomutase‐Catalysed Amination of Cinnamic Acid Derivatives

The phenylalanine aminomutase (PAM) from Taxus chinensis catalyses the conversion of α‐phenylalanine to β‐phenylalanine, an important step in the biosynthesis of the N‐benzoyl phenylisoserinoyl side‐chain of the anticancer drug taxol. Mechanistic studies on PAM have suggested that (E)‐cinnamic acid is an intermediate in the mutase reaction and that it can be released from the enzyme's active site. Here we describe a novel synthetic strategy that is based on the finding that ring‐substituted (E)‐cinnamic acids can serve as a substrate in PAM‐catalysed ammonia addition reactions for the biocatalytic production of several important β‐amino acids. The enzyme has a broad substrate range and a high enantioselectivity with cinnamic acid derivatives; this allows the synthesis of several non‐natural aromatic α‐ and β‐amino acids in excellent enantiomeric excess (ee >99 %). The internal 5‐methylene‐3,5‐dihydroimidazol‐4‐one (MIO) cofactor is essential for the PAM‐catalysed amination reactions. The regioselectivity of amination reactions was influenced by the nature of the ring substituent.     

Preparation and characterization of chitosan/α‐zirconium phosphate nanocomposite films

Nano‐fillers play an important role in the final structure and properties of nanocomposites. The objective of the work presented here was to prepare nanocomposite films of chitosan/α‐zirconium phosphate using a casting process, with α‐zirconium phosphate (α‐ZrP) as nano‐filler and chitosan as matrix. The effects of α‐ZrP on the structure and properties of the nanocomposites were investigated. X‐ray diffraction patterns showed that α‐ZrP crystals were intercalated by n‐butylamine. The results from scanning electron microscopy and transmission electron microscopy indicated that α‐ZrP could be uniformly dispersed in the chitosan matrix when α‐ZrP loading in the composites was less than 2 wt%. A strong interaction between α‐ZrP and chitosan formed during the film‐forming process. Tensile testing showed that the tensile strength and elongation at break of nanocomposite films achieved maximum values of 61.6 MPa and 58.1%, respectively, when α‐ZrP loading was 2 wt%. The parameter B calculated from tensile yield stress according to the Pukanszky model was used to estimate the interfacial interaction between the chitosan matrix and α‐ZrP. Films with a loading of 2 wt% α‐ZrP had the highest B value (3.2), indicating the strongest interfacial interaction. The moisture uptake of the nanocomposites was reduced with addition of α‐ZrP. It can be concluded that α‐ZrP as nano‐filler in a chitosan matrix can enhance the mechanical properties of nanocomposites due to the strong interactions between α‐ZrP and chitosan. Copyright © 2010 Society of Chemical Industry     

Molecular Basis for the Stereoselective Ammoniolysis of N‐Alkyl Aziridine‐2‐Carboxylates Catalyzed by Candida antarctica Lipase B

Candida antarctica lipase B catalyzed the stereoselective ammoniolysis of N‐alkyl aziridine‐2‐carboxylates in tBuOH saturated with ammonia and yielded the (2S)‐aziridine‐2‐carboxamide and unreacted (2R)‐aziridine‐2‐carboxylate. Varying the N‐1 substituent on the aziridine ring changed the rate and stereoselectivity of the reaction. Substrates with a benzyl substituent or a (1′R)‐1‐phenylethyl substituent reacted approximately ten times faster than substrates with a (1′S)‐1‐phenylethyl substituent. Substrates with a benzyl substituent showed little stereoselectivity (E=5–7) while substrates with either a (1′R)‐ or (1′S)‐1‐phenylethyl substituent showed high stereoselectivity (D>50). Molecular modeling by using the current paradigm for enantioselectivity—binding of the slow enantiomer by an exchange‐of‐substituents orientation—could not account for the experimental results. However, modeling an umbrella‐like‐inversion orientation for the slow enantiomer could account for the experimental results. Steric hindrance between the methyl in the (1′S)‐1‐phenylethyl substituent and Thr138 and Ile189 in the acyl‐binding site likely accounts for the slow reaction. Enantioselectivity likely stems from an unfavorable interaction of the methine hydrogen with Thr40 for the slow enantiomer and from subtle differences in the orientations of the other three substituents. This success in rationalizing the enantioselectivity supports the notion that an umbrella‐like‐inversion orientation can contribute to enantioselectivity in lipases.     

Synthesis of polyethylene oxide end‐capped with perfluoroalkyl groups/polystyrene prototype brushes

Polystyrene (PS)/poly(ethylene oxide) (PEO) prototype brushes were prepared by alternating free‐radical copolymerization of methacryloyl‐terminated PS and α‐vinylbenzyl‐ω‐hydroxy or α‐vinylbenzyl‐ω‐perfluoroalkyl (R_f) PEO macromonomers with the addition of Lewis acid (SnCl₄). It was found from their dilute‐solution properties that PS/PEO end‐capped with R_f (PBR_f), and PS/PEO having OH groups at terminal ends (PBOH) prototype brushes formed a single molecule in benzene and aggregates in chloroform, respectively. However, the brush PBOH formed a single molecule in N,N‐dimethylformamide. Such aggregation behaviors seemed to be caused by the interaction between hydroxy groups of PEO chain ends. The brush PBOH was also converted into PBR_f‐type brush by chemical modification, using corresponding acid chloride. The substitution of R_f groups was ～70% due to slipping of terminal hydroxy groups into PEO internal domains. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 772–778, 2006