Presence Of Dicyclohexylcarbodiimide Research Articles

Crystallization behavior of poly(l-lactide)-poly(ethylene glycol) multiblock copolymers

Poly(l-lactide) (PLLA)-poly(ethylene glycol) (PEG) multiblock copolymers were synthesized by polyesterification reaction of dicarboxylated PLLA with PEG in the presence of dicyclohexylcarbodiimide and N-dimethylaminopyridine. Dicarboxylated PLLA was prepared by a direct condensation polymerization of l-lactic acid with predetermined amounts of succinic acid, which was used to provide PLLA with a carboxylated terminal group. DSC and X-ray diffractometry of the multiblock copolymer suggested that PLLA and PEG blocks were phase separated and the crystallization behavior of one block was markedly affected by the presence of the other block, and in particular by the block length of the other block. The longer the PLLA block, the lower the crystallinity and the melting temperature of the PEG block. Multiblock copolymers crystallized from the melt and those from the solution casting showed different crystallization behavior, even though the chemical structures and the molecular weights were the same. The crystallizability of the PLLA block was more affected by the crystallization method than that of the PEG block.

Functionalization of polyethylene oxide with 4-amino-N-(2-pyrimidinyl) benzene sulfonamide at one end

Polyethylene oxide (PEO) with 4-amino-N-(2-pyrimidinyl) benzene sulfon- amide (APBS; PEOas) at one end was used as a carrier polymer for attachment (via the hydroxyl end group) of drugs such as mustard. For this purpose, the amine group of PEOas was protected first by the formation of a Schiff's base; then protected PEOasOBr and PEOasONH2 were prepared. In order to attach N,N-dichloroethyl amine (DCEA) to the PEOasONH2, DCEA hydrogen chloride salt was reacted with maleic anhydride first, then the resulting N,N-dichloroethyl maleinamic acid (DCEMA) could react with protected PEOasONH2 continuously in the presence of dicyclohexylcarbodiimide (DCC). However, DCEMA is unstable; the chloroethyl group was rearranged to a corresponding ternary ammonium salt with a three-membered ring (DCEMAr). There- fore, the protected PEOasONH2 was coupled with the DCEMAr in the presence of DCC; then it attacked the nucleophilic center of the aniline group of the APBS end of the PEOas after deprotection. Thus, a PEO with higher molecular weight and wider distri- bution was formed due to the intermolecular addition of PEOas. © 1999 John Wiley & Sons,

Synthesis and characterization of poly(ethylene glycol)/poly( l-lactic acid) alternating multiblock copolymers

Thermoplastic hydrogels of alternating multiblock copolymers, consisting of poly(ethylene glycol) (PEG) and poly( l-lactic acid) (PLLA), were synthesized. Dicarboxylated oligomeric PLLAs were synthesized by the condensation reaction of l-lactic acid in the presence of succinic acid. Changing the feed ratio of l-lactic acid to succinic acid controlled PLLA molecular weights. Alternating multiblock copolymers with different block lengths of PEG and PLLA were obtained from the polycondensation reaction between PEG and dicarboxylated-PLLA in the presence of dicyclohexyl carbodiimide and N-dimethyl aminopyridine as catalysts. The chemical compositions of dicarboxylated PLLAs and multiblock copolymers were verified by 1H-NMR and FT-IR, and the molecular weight and distribution were measured by gel permeation chromatography. DSC thermograms showed that there existed a high degree of phase mixing, as well as microphase separation in the multiblock copolymer, demonstrated by a large T g peak from the amorphous phase-mixing domain and a small T m peak from crystalline microdomains of the PLLA component. The block copolymers with low molecular weights were water-soluble and clouded at a temperature which is associated with a lower critical solution temperature (LCST) phenomonon. However, the high molecular weight polymers could swell in water and their optical transparency was influenced by temperature. This observation can be attributed to an enhanced hydrophobic interaction between hydrophobic moieties in the polymer chains, caused by an increase in temperature. The weight swelling ratio (absorbed water/polymer) of the polymers was controlled by polymer composition and molecular weight. These block copolymers may offer potential for applications in drug delivery and various other biomedical projects.

Synthesis of optically active 1,4-benzoxazinones and 1,5-benzoxazepinones by regiocontrolled ring transformations of oxirane carboxylic acids and esters with aromatic o-hydroxyarylamines

Enantiopure diethyl oxirane dicarboxylate 1 reacts with o-aminophenols 2 either to 1,4-benzoxazin-2-ones 5 or to the 1,5-benzoxazepin-2-one 4 while a condensed 1,4-oxazin-3-one 6 was obtained with 2-amino-3-hydroxypyridine. On the other hand optical active oxirane carboxylic acids 7 react with o-aminophenols 8 in the presence of DCC (dicyclohexylcarbodiimide) or isobutyl chloroformiate affording oxirane carboxamides 9 that can be ring transformed to either 2,3-dihydro-4 H-1,4-benzoxazin-3-ones 10 or 3-hydroxy-2,3-dihydro-5 H-1,5-benzoxazepin-4-ones 11 depending on the reaction conditions.

Dicyclohexylcarbodiimide alters the pH dependence of violaxanthin de-epoxidation

The de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin in the xanthophyll cycle of higher plants is controlled by the pH of the thylakoid lumen. The influence of N,N′-dicyclohexylcarbodiimide (DCCD) on the pH dependence of the de-epoxidation reactions has been investigated in isolated pea thylakoids. In the presence of DCCD, the decrease in de-epoxidase activity at increasing pH was found to be shifted by about 0.3 pH units to more-alkaline pH values. This was paralleled by a less-pronounced cooperativity for the pH dependence of de-epoxidation. Comparative studies with antenna-depleted thylakoids from plants grown in intermittent light and with unstacked thylakoids indicated that binding of DCCD to antenna proteins is most probably not responsible for the altered pH dependence. Analyses of the zeaxanthin content of different antenna subcomplexes showed that the DCCD-induced de-epoxidation at high pH leads to zeaxanthin formation in all antenna proteins from both photosystems. Our data support the view that DCCD binding to the violaxanthin de-epoxidase may be responsible for the altered pH dependence.

Inulin polysaccharide having pendant amino acids: Synthesis and characterization

Inulin polysaccharide was esterified with N-protected α-amino acids (N,N′-di-benzylocarbonyl-L-lysine and N-benzylocarbonyl-glycine) under a mild condition (room temperature) and within short reaction times (6 h). The esterification reactions were conducted in the presence of dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine as a catalyst. The optimal reaction time (6 h) was determined by monitoring the concentration of free carboxylic acid of the N-protected amino acids during the reaction. The degree of substitution per fructose unit was 0.95 for inulin-lysine and 1.01 for inulin-glycine. The resulting biopolymer was deprotected by catalytic transfer hydrogenation method using 1,4-cyclohexadiene as an effective hydrogen donor. The structures, molecular weight, and thermal properties of the amino acid esters of inulin were determined by Fourier transform infrared spectroscopy, 1H and 13C NMR, UV, viscosity, and dicyclohexylcarbodiimide. This new modified inulin polysaccharide would have the potential as a biomaterial for biomedical applications. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 953–963, 1998

Synthesis and Characterization of Poly(Oxyethylene)S with (2-Benzoxazolon-3-yl)Acetyl End-Groups. Complex Formation with Polycarboxylic Acids

Chemical modification of poly(oxyethylene)s (MW from 600 Da to 3000 Da), leading to the obtaining of poly(oxyethylene)s with (2-benzoxazolon-3-yl)acetyl endgroups, is described. The corresponding diesters were synthesized in high yields-70—84% and degree of esterification-82—92% under mild conditions in the presence of dicyclohexylcarbodiimide and 4-dimethylaminopyridine as catalyst. The diesters were characterized by 1H-NMR, 13C-NMR and IR spectra, and SEC analysis. The relatively narrow molecular weight distribution was retained in the process of chemical modification. The complex formation between polyacrylic or polymeth-acrylic acids and (2-benzoxazolon-3-yl)acetyl derivatives of poly -(oxyethylene)s was studied in dilute aqueous solutions by potentio-metric titration and viscometry. The presence of (2-benzoxazolon-3-yl)acetyl end groups attached to the poly(oxyethylene)s chains results in a significant decrease of the critical poly(oxyethylene) chain length necessary for the formation of stable polymer-polymer complexes.

In vivo analysis of the effect of dicyclohexylcarbodiimide on electron and proton transfers in cytochrome bf complex of Chlorella sorokiniana.

The effect of N,N'-dicyclohexylcarbodiimide (DCCD) on electron and proton transfers within the cytochrome (cyt) bf complex has been analyzed in living cells of the green algae Chlorella sorokiniana under anaerobic conditions. DCCD induces a partial decoupling of the protomotive Q-cycle, in agreement with the conclusions of Wang and Beattie (1991) Arch. Biochem. Biophys. 291, 363-370. In the presence of 20 microM DCCD, we observe the development of a lag phase in the kinetics of the slow electrogenic phase associated with electron and proton transfers within the cyt bf complex. In the same conditions, the initial rate of cyt b and cyt f reduction is decreased by about 30%. We propose that in the absence of DCCD, a transmembrane movement of proton is coupled to the oxidation of plastoquinol at site Qo. In the presence of 20 microM DCCD, this redox-coupled proton pump is inhibited, and the kinetics of phase b and cyt b reduction become close to that predicted on the basis of a pure Q-cycle process. In agreement with this hypothesis, we observe that upon a weak-flash excitation, two charges are translocated through the membrane in addition to the charge translocated at the level of photosystem I. Part of this large electrogenic phase could be associated with the translocation of a proton from the stroma to the lumen. A tentative mechanism is discussed that remains in the frame of the Q-cycle but accounts for an additional proton-pumping process or for the partial decoupling observed in the presence of DCCD, as well.

The kinetics of zeaxanthin formation is retarded by dicyclohexylcarbodiimide

The de-epoxidation of violaxanthin to antheraxanthin (Anth) and zeaxanthin (Zeax) in the xanthophyll cycle of higher plants and the generation of nonphotochemical fluorescence quenching in the antenna of photosystem II (PSII) are induced by acidification of the thylakoid lumen. Dicyclohexylcarbodiimide (DCCD) has been shown (a) to bind to lumen-exposed carboxy groups of antenna proteins and (b) to inhibit the pH-dependent fluorescence quenching. The possible influence of DCCD on the de-epoxidation reactions has been investigated in isolated pea (Pisum sativum L.) thylakoids. The Zeax formation was found to be slowed down in the presence of DCCD. The second step (Anth --> Zeax) of the reaction sequence seemed to be more affected than the violaxanthin --> Anth conversion. Comparative studies with antenna-depleted thylakoids from plants grown under intermittent light and with unstacked thylakoids were in agreement with the assumption that binding of DCCD to antenna proteins is probably responsible for the retarded kinetics. Analyses of the DCCD-induced alterations in different antenna subcomplexes showed that Zeax formation in the PSII antenna proteins was predominantly influenced by DCCD, whereas Zeax formation in photosystem I was nearly unaffected. Our data support the suggestion that DCCD binding to PSII antenna proteins is responsible for the observed alterations in xanthophyll conversion.

Organofluorine compounds and fluorinating agents part 21: perfluoroalkylidene sugars by non-classical acetalation of pyranoses

Acetalations of methyl α- d-mannopyranoside ( 1), methyl 6- O-trityl-α- d-mannopyranoside ( 5), benzyl α- d-mannopyranoside ( 14), and methyl β- d-galactopyranoside ( 17) with perfluoroaldehydes (C 4F 9CH=O, C 6F 13CH=O, and C 8F 17CH=O) in the presence of dicyclohexylcarbodiimide (DCC) lead, under epimerization at the C-atom 3 of the corresponding pyranose moiety, to perfluoroalkylidene derivatives of α- d-altrosides ( 2–4, 6/7, 15) and of β- d-gulosides ( 18–20), respectively. After partial deprotection of 3 (or 15) and 18–20, respectively, the liquid crystalline, amphiphilic 3,4- O-perfluorohexylidene- d-altropyranoside ( 13) and 2,3- O-perfiuoroalkylidene- d-gulopyranosides 24–26 were obtained.

Tripodal trisamides based on nicotinic and picolinic acid derivatives

A number of polydentate arylamide ligands have been prepared by coupling various acyclic tripodal or linear polyamines with derivatives of nicotinic and picolinic acids. Two synthetic procedures were utilized; tris{[(2-hydroxynicotinyl)carbonyl]-2-aminoethyl}amine (H3NICTREN) was prepared by Method A, the HOSu/DCC method, and the other arylamides in this study were prepared by Method B, the CDI method. Method A involved the reaction of N-hydroxysuccinimide with 2-hydroxynicotinic acid (in the presence of dicyclohexylcarbodiimide (DCC) as a dehydrative coupling reagent) to form the succinimide ester, followed by reaction with TREN to yield H3NICTREN. Method B involved reaction of a carboxylic acid (2-hydroxynicotinic, 3-hydroxypicolinic, nicotinic, or picolinic acids) with carbonyldiimidazole (CDI) to form the N-acylimidazolide, followed by reaction with the amine (TREN, TAME, spermidine, or TRPN) to yield the desired arylamide. The X-ray structure of 1,1,1-tris{[(3-hydroxypicolinyl)carbonyl]-2-aminomethyl}ethane (H3PICTAME) was determined; crystals of H3PICTAME are monoclinic, a = 10.257(2), b = 15.572(3), c = 15.208(2) Å, β = 96.124(15)°, Z = 4, space group P21/a. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R = 0.041 and Rw = 0.038 for 2506 reflections with I >= 3 sigma (I). In the solid state, H3PICTAME contains an extensive hydrogen-bonding network, with eight intra- and one intermolecular H-bonds per molecule; the ligand is partially preorganized for metal ion chelation. The acid dissociation constants of H3NICTREN and those of 1,1,1-tris{[(2-hydroxynicotinyl)carbonyl]-2- aminomethyl}ethane (H3NICTAME) have been determined; pKa1 = 11.2 (10.68), pKa2 = 10.7 (10.58), pKa3 = 10.0 (9.71), and pKa4 = 6.25 for H3NICTREN (H3NICTAME); the high phenolic pKa's are consistent with the hydrogen bonding observed in the solid state.Key words: arylamide, hydrogen bonding, preorganization.

Organofluorine compounds and fluorinating agents Part 17: Sonochemical-forced preparation of perfluoroalkanals and their use for non-conventional acetalations of carbohydrates

The homologous 1-iodo-perfluoroalkanes 1a-1c and α,ω-dibromo-perfluoroalkanes 4a, 4b were carbonylated with DMF in the presence of Al/SnCl 2 Al/PbBr 2 under sonication in a short reaction time. The hydrated aldehydes 2a-2c and 5a, 5b respectively were obtained in good yields allowing dehydration to 3a-3c and 6a, 6b. Some of the fluorinated aldehydes were selected as substrates in a Wittig-Horner olefination assisted by ultrasound and in non-conventional acetalations of methyl α- l-rhamnopyranoside ( 9). Thus, ( E)-1-perfluorooctyl-2-phenylsulphonyl-ethene ( 8) was prepared from 3c and the phosphonate 7 by Wittig-Horner synthesis. Acetalations of 9 were carried out with the aldehydes ( 3a, 3b, 6a), hydrated aldehydes ( 2a, 2b), and the aldehyde hemiacetal 12 respectively, in the presence of dicyclohexylcarbodiimide (DCC). In all cases, a selective epimerization was observed at the C-atom 3 of the monosaccharide, i.e. polyfluoroalkylidenated 6-deoxy-α- l-altropyranosides 10,11,13, and 14 were obtained.

The ( η5-cyclopentadienyl)Fe(CO) 2 complex of the ( l)- and ( d)-tryptophan methyl ester N-anion: synthesis and acylation of the amino function

The photochemical reaction of ( η 5-C 5H 5)Fe(CO) 2I with ( l)- and ( d)-tryptophan methyl ester in the presence of diisopropylamine in benzene leads to complexation of the ( η 5-C 5H 5)Fe(CO) 2 moiety to the deprotonated indole nitrogen. This reaction takes place without detectable (< 1%) racemization at C α. The amino group of the complex formed was acylated by treatment with p-chlorobenzoic acid and Fmoc-( l)-leucine in the presence of dicyclohexylcarbodiimide.

Synthesis and characterization of poly[(2,6‐dimethyl‐1,4‐phenylene oxide)‐block‐isoprene] diblock copolymers

AbstractAs a first stage in the synthesis of a new class of thermoplastic elastomers, a suitable synthetic route for elastomeric tailor‐made diblock copolymers based on poly(2,6‐dimethyl‐1,4‐phenylene oxide), PPE, as the thermoplastic block and on 1,4‐polyisoprene, PIP, as the elastomeric block, is outlined. The 2,6‐dimethyl‐1,4‐phenylene oxide‐block‐isoprene diblock copolymers were synthesized via an amidation coupling route between the ammonium salt of PPE and the monocarboxylic acid of PIP in the presence of dicyclohexylcarbodiimide, DCC. Preliminary studies were focused on the synthesis of a welldefined low molar mass diblock copolymer (Mn = 10000) in order to facilitate the quantitative characterization by proton NMR spectroscopy. The developed amidation coupling route was successively applied to the synthesis of a similar diblock copolymer with a number‐average molar mass of 40000 in order to obtain optimum overall properties.

Spectrophotometric determination of acrivastine in urine and capsules

Three sensitive and accurate spectrophotometric methods are presented for the determination of the antihistaminic acrivastine (ACR) in capsules and urine. The first method utilizes the reaction of 2-nitrophenylhydrazine hydrochloride in presence of dicyclohexylcarbodiimide and pyridine. The violet colour of the resulting acid hydrazide is measured at 550 nm. The second method is based on alkaline oxidation of the drug with potassium permanganate and subsequent measurement of the formed manganate ion at 608 nm. The third method uses derivative spectrophotometry for the determination of ACR. The last method is extended to the in vitro determination of the drug in urine. All methods gave a relative standard deviation of less than 2%.

Chemical properties ofN-(amidomethy)- andN-(imidomethyl)glycine derivatives 2. Reactions at alkoxycarbonyl and carboxyl groups

N-(Aroylarnmomethylfglycine amides were synthesized by reactions ofN-(aroyllminomethyl) glycine esters with ammonia. Alkaline hydrolysis ofN-(amidomethyl)glycine,N-(irnidornethyl)glycine, andN-(amidomethyl)pheriylalariiiie esters afforded the correspondingN-(amidowthyVa-amirio acids- Reactions of the Last-mentioned compounds with ethyl esters of glycine, alanine, and phenylalanine in the presence of dicyclohexylcarbodiimide yielded dipeptides containingNh-amidomethyl substituents.

Synthesis of functional derivatives ofN-carboxamidomethyl- andN-phthalimidomethyl-a-amino acids and peptides by reaction of amides and nitriles of ?-amino acids with formaldehyde and primary amides or phthalimide

A direct method for the synthesis of functional derivatives ofN-carboxatnidomethyl- and N-phthalimidomethyl-a-amino acids by the reaction of nitriles and amides of α-amino acids (including peptides) with formaldehyde and NH-compounds (amides and imides) in DMF in the presence of TsOH was developed. The reactions of the compounds synthesized with acetic anhydride, tosyl chloride, and phcnylalanine benzylamide in the presence of dicyclohexylcarbodiimide affording the corresponding N-acyl and N-sulfonyl derivatives or peptides containing carboxamido- and phthalimidomethyl substituents at the terminal N-atom of the peptide chain, were studied.

Synthesis, reactivity and X-ray molecular structure of the activated ester complex [( η5-C 5H 4COONS)Co(CO) 2](NS ; N-succinimidyl)

The title compound [( η 5-C 5H 4COONS)Co(CO) 2] ( 2) was prepared in high yield (91%) by treatment of the organometallic carboxylic acid [( η 5-C 5H 4COOH)Co(CO) 2] ( 1) with N-hydroxysuccinimide in the presence of dicyclohexylcarbodiimide. The activated ester complex 2 was identified by spectroscopic methods, in addition its X-ray structure was determined. Compound 2 crystallizes in the triclinic space group P1 with a = 6.1880(8), b = 9.722(1), c = 10.869(1) Å, α = 83.37(1), β = 83.91(1) and γ = 86.30(1)°, V = 645(1) Å3 and Z = 2. The stability of the above species 2 and its reactivity as labelling agent for amines and amino-esters are investigated and discussed.

Highly Photostable Organic Fluorescent Pigments – A Simple Synthesis of N‐Arylpyrrolopyrrolediones (DPP)

AbstractN‐Arylpyrrolopyrrolediones 1b‐g are prepared by the condensation of the corresponding lactones 2 and 5 with arylamines in the presence of dicyclohexylcarbodiimide. Bright red dye pigments are obtained with an intense red to orange solid‐state fluorescence.

Hydrolytic release of herbicides from modified polyamides of tartrate derivatives

A group of polyamides containing free hydroxyl groups has been prepared by polycondensations of diethyl- l-tartrate with various diamines under mild conditions of room temperature and without using a solvent and a catalyst. Loading of polyamide derived from ethylene diamine and tartrate with 2,4-dichlorophenoxyacetic acid has been carried out by chemical modifications in the presence of dicyclohexylcarbodiimide (DCC). The effects of polymer backbone hydrophilicity, the medium pH and temperature on the hydrolysis rate of the polymers have also been investigated, although there is some uncertainty about the precise value of initial molecular weights of the polymer.