Controlled synthesis of O-glycopolypeptide polymers and their molecular recognition by lectins

The facile synthesis of high molecular weight water-soluble O-glycopolypeptide polymers by the ring-opening polymerization of their corresponding N-carboxyanhydride (NCA) in very high yield (overall yield > 70%) is reported. The per-acetylated-O-glycosylated lysine-NCA monomers, synthesized using stable glycosyl donors and a commercially available protected amino acid in very high yield, was polymerized using commercially available amine initiators. The synthesized water-soluble glycopolypeptides were found to be α-helical in aqueous solution. However, we were able to control the secondary conformation of the glycopolypeptides (α-helix vs nonhelical structures) by polymerizing racemic amino acid glyco NCAs. We have also investigated the binding of the glycopolypeptide poly(α-manno-O-lys) with the lectin Con-A using precipitation and hemagglutination assays as well as by isothermal titration calorimetry (ITC). The ITC results clearly show that the binding process is enthalpy driven for both α-helical and nonhelical structures, with negative entropic contribution. Binding stoichiometry for the glycopolypeptide poly(α-manno-O-lys) having a nonhelical structure was slightly higher as compared to the corresponding polypeptide which adopted an α-helical structure.     

Facile preparation of well-defined AB2 Y-shaped miktoarm star polypeptide copolymer via the combination of ring-opening polymerization and click chemistry

Well-defined AB2 Y-shaped miktoarm star polypeptide copolymer, PZLL-b-(PBLG)2, was synthesized via a combination of ring-opening polymerization (ROP) of alpha-amino acid N-carboxyanhydride (NCA) and click chemistry, where PZLL is poly(epsilon-benzyloxycarbonyl-L-lysine) and PBLG is poly(gamma-benzyl-L-glutamate). First, two types of primary-amine-containing initiators, N-aminoethyl 3,5-bis(propargyloxyl)-benzamide and 3-azidopropylamine, were synthesized and employed for the ROP of NCA, leading to the formation of dialkynyl-terminated PZLL and azide-terminated PBLG, dialkynyl-PZLL and PBLG-N3, respectively. The subsequent copper(I)-catalyzed cycloaddition reaction between dialkynyl-PZLL and slightly excess PBLG-N3 led to facile preparation of PZLL-b-(PBLG)2 Y-shaped miktoarm star polypeptide copolymer. The excess PBLG-N3 was scavenged off by reacting with alkynyl-functionalized Wang resin. The obtained Y-shaped miktoarm star polypeptide copolymer was characterized by gel permeation chromatograph (GPC), Fourier transform-infrared spectroscopy (FT-IR), and (1)H NMR. Moreover, after the hydrolysis of protecting benzyl and benzyloxycarbonyl groups of PZLL-b-(PBLG)2, water-soluble pH-responsive Y-shaped miktoarm star polypeptide copolymer, PLL-b-(PLGA)2, was obtained, where PLL is poly(L-lysine) and PLGA is poly(L-glutamic acid). It can self-assemble into PLGA-core micelles at acidic pH and PLL-core micelles at alkaline pH, accompanied with the coil-to-helix transition of PLGA and PLL sequences, respectively. The spontaneous pH-responsive supramolecular assembly of PLL-b-(PLGA)2 miktoarm star polypeptide copolymer has been investigated via a combination of (1)H NMR, laser light scattering (LLS), transmission electron microscopy (TEM), and circular dichroism (CD) spectroscopy.     

Block copolymerization of α-amino acid N-carboxyanhydride initiated by vinyl polymers having a terminal amino group and the characterization of the block copolymers

Poly(methyl methacrylate) and polystyrene having terminal amino groups were synthesized by the radical polymerization of those monomers in the presence of 2-mercaptoethylammonium chloride as a chain-transfer agent. By the terminal group analysis and the molecular weight determination of the polymers, 0.5–1.3 amino groups were found in a chain of poly(methyl methacrylate) and 0.5–2.5 amino groups in a chain of polystyrene. Using these polymers having a terminal amino group as an initiator, the block polymerization of α-amino acid N-carboxyanhydride (NCA) was carried out. In the polymerizations of Glu(OBzl) NCA and Lys(Z) NCA by the poly(methyl methacrylate) initiator, the terminal amino group underwent a nucleophilic addition reaction to NCA and initiated the polymerization, yielding A-B-type block copolymers in a high yield. The same was observed in the polymerizations of Gly(OBzl) NCA and Lys(Z) NCA by the polystyrene initiator. By eliminating the protecting groups of the side chains of the polypeptide segment, the block copolymers poly(methyl methacrylate)-poly(Glu), poly(methyl methacrylate)-poly(Lys), polystyrene-poly(Glu) and polystyrene-poly(Lys) were synthesized with little side reactions. The side chain amino groups of poly(Lys) segment in the poly(methyl methacrylate)-poly(Lys) block copolymers were sulphonated or stearoylated successfully.     

Water-soluble poly(L-serine)s with elongated and charged side-chains: synthesis, conformations, and cell-penetrating properties

Water-soluble poly(L-serine)s bearing long side-chain with terminal charge groups were synthesized via ring-opening polymerization of O-pentenyl-L-serine N-carboxyanhydride followed by thiol-ene reactions. These side-chain modified poly(L-serine)s adopt β-sheet conformation in aqueous solution with excellent stability against changes in pH and temperature. These water-soluble poly(L-serine) derivatives with charged side-chain functional groups and stable β-sheet conformations showed membrane-penetrating capabilities in different cell lines with low cytotoxicity.     

Synthesis and self-assembly of well-defined poly(amino acid) end-capped poly(ethylene glycol) and poly(2-methyl-2-oxazoline)

Poly(ethylene glycol) (PEG) and poly(2-methyl-2-oxazoline) (PMOx) are water-soluble, biocompatible polymers with stealth hemolytic activities. Poly(amino acid) (PAA) end-capped PEG and PMOx were prepared using amino-terminated derivatives of PEG and PMOx as macroinitiators for the ring-opening polymerization of γ-benzyl protected l-glutamate N-carboxyanhydride and S-benzyloxycarbonyl protected l-cysteine N-carboxyanhydride, respectively, in the presence of urea, at room temperature. The molecular weight of the PAA moiety was kept between M(n) = 2200 and 3000 g mol(-1). PMOx was polymerized by cationic ring-opening polymerization resulting in molecular weights of M(n) = 5000 and 10,000 g mol(-1), and PEG was a commercial product with M(n) = 5000 g mol(-1). Here, we investigate the self-assembly of the resulting amphiphilic block copolymers in water and the effect of the chemical structure of the block copolymers on the solution properties of self-assembled nanostructures. The PEG-block-poly(amino acid), PEG-b-PAA, and PMOx-block-poly(amino acid), PMOx-b-PAA, block copolymers have a narrow and monomodal molecular weight distribution (PDI < 1.3). Their self-assembly in water was studied by dynamic light scattering and fluorescence spectroscopy. In aqueous solution, the block copolymers associate into particles with hydrodynamic radii (R(H)) ranging in size from R(H) 70 to 130 nm, depending on the block copolymer architecture and the polymer molecular weight. Larger R(H) and critical association concentration values were obtained for copolymers containing poly(S-benzyloxycarbonyl-l-cysteine) compared to their poly(γ-benzyl-L-glutamate) analogue. FTIR investigations revealed that the poly(γ-benzyl-L-glutamate) block adopts a helical conformation, while the poly(S-benzyloxycarbonyl-L-cysteine) block exists as β-sheet.     

Recognition of novel lipopolypeptides with many pendent sugar residues by lectin

A lipid-polypeptide conjugate (lipo-polypeptide) was obtained by the ring-opening polycondensation of N-epsilon-Z-L-lysine N-carboxyanhydride (NCA) using 3-aminopropyl dioctadecylamine as initiator and subsequent deprotection. Maltose lactone was coupled with the lipo-polypeptide to give novel amphiphiles which carried many maltoamide residues as pendent groups. The sugar group-carrying amphiphiles incorporated in phospholipid liposomes were recognized by a lectin from Canavalia ensiformis (Con A), which was proven by the increase in turbidity of the liposome suspension after mixing with the lectin. The recognition was largely affected by the degree of polymerization of lysine residues and the surface density of the amphiphile in the liposomes. The association constant (K(ass)) of Con A with maltoamide residues on the liposome was much larger than those for small molecular weight sugars due to the "cluster effect".     

Synthesis and characterization of RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) triblock copolymer

Advances in tissue engineering require biofunctional scaffolds that can provide not only physical support for cells but also chemical and biological cues needed in forming functional tissues. To achieve this goal, a novel RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) (PEG-PLA-PGL/RGD) was synthesized in four steps (1) to prepare diblock copolymer PEG-PLA-OH and to convert its -OH end group into -NH(2) (to obtain PEG-PLA-NH(2)), (2) to prepare triblock copolymer PEG-PLA-PBGL by ring-opening polymerization of NCA (N-carboxyanhydride) derived from benzyl glutamate with diblock copolymer PEG-PLA-NH(2) as macroinitiator, (3) to remove the protective benzyl groups by catalytic hydrogenation of PEG-PLA-PBGL to obtain PEG-PLA-PGL, and (4) to react RGD (arginine-glycine-(aspartic amide)) with the carboxyl groups of the PEG-PLA-PGL. The structures of PEG-PLA-PGL/RGD and its precursors were confirmed by (1)H NMR, FT-IR, amino acid analysis, and XPS analysis. Addition of 5 wt % PEG-PLA-PGL/RGD into a PLGA matrix significantly improved the surface wettability of the blend films and the adhesion and proliferation behavior of human chondrocytes and 3T3 cells on the blend films. Therefore, the novel RGD-grafted triblock copolymer is expected to find application in cell or tissue engineering.     

Selective enzymatic degradation of self-assembled particles from amphiphilic block copolymers obtained by the combination of N-carboxyanhydride and nitroxide-mediated polymerization

Combining controlled radical polymerizations and a controlled polypeptide synthetic technique, such as N-carboxyanhydride (NCA) ring-opening polymerization, enables the generation of well-defined block copolymers to be easily accessible. Here we combine NCA polymerization with the nitroxide-mediated radical polymerization of poly(n-butyl acrylate) (PBA) and polystyrene (PS), using a TIPNO and SG1-based bifunctional initiator to create a hybrid block copolymer. The polypeptide block consists of (block) copolymers of poly(L-glutamic acid) embedded with various quantities of L-alanine. The formed superstructures (vesicles and micelles) of the block copolymers possessed varying degrees of enzyme responsiveness when exposed to elastase and thermolysin, resulting in controlled enzymatic degradation dictated by the polypeptide composition. The PBA containing block copolymers possessing 50% L-alanine in the polypeptide block showed a high degradation response compared to polymers containing lower L-alanine quantities. The particles stabilized by copolypeptides with L-alanine near the hydrophobic block showed full degradation within 4 days. Particles containing polystyrene blocks revealed no appreciable degradation under the same conditions, highlighting the specificity of the system and the importance of synthetic polymer selection. However, when the degradation temperature was increased to 70 °C, degradation could be achieved due to the higher block copolymer exchange between the particle and the solution. A number of novel biohybrid structures are disclosed that show promise as enzyme-responsive materials with potential use as payload release vehicles, following their controlled degradation by specific, target, enzymes.     

Isopeptide bonds in chemotactic tripeptides. Synthesis and activity of lysine-containing fMLF analogs.

In order to explore the properties of chemotactic N-formylpeptides containing isopeptide bonds within their backbones, a group of lysine-containing analogs of the prototypical chemotactic tripeptide N-formylmethionyl-leucyl-phenylalanine (fMLF) was synthesized. The new analogs were designed by adding to the HCO-Met or Boc-Met residue a dipeptide fragment made up of Lys and Phe residues joined through Lys N alpha or N epsilon bonds, in all possible combinations. Thus, the following six pairs of tripeptides were synthesized and examined for their bioactivity: RCO-Met-Lys(Z)-Phe-OMe (2a, b), RCO-Met-Lys(Z-Phe)-OMe (3a, b), Z-Lys(RCO-Met)-Phe-OMe (4a, b), Z-Phe-Lys(RCO-Met)-OMe (5a, b), RCO-Met-Phe-Lys(Z)-OMe (6a, b) and Z-Lys(RCO-Met-Phe)-OMe (7a, b), with R=OC(CH3)(3 )and R=H for compounds a and b, respectively. All the new models were characterized fully and their activity (chemotaxis, superoxide anion production and lysozyme release) on human neutrophils determined as agonists (compounds b) and antagonists (compounds a). All N-formyl derivatives 2b-7b are less potent than fMLF-OMe as chemoattractants, but compound 7b exhibits selective activity as superoxide anion producer. Derivatives 2a-7a do not show antagonistic activity towards fMLF induced chemotaxis and O(2)(-) production, however, all these compounds except 4a antagonize lysozyme release by 60%.     

Stimuli-responsive zwitterionic block copolypeptides: poly(N-isopropylacrylamide)-block-poly(lysine-co-glutamic acid)

Synthesis of novel zwitterionic block copolypeptides, poly(N-isopropylacrylamide)-block-poly(L-glutamic acid-co-L-lysine) [PNiPAM(n)(PLG(x)-co-PLLys(y))m , where n is the number-average degree of polymerization (DP(n)) of PNiPAM block, x and y are the mole fraction of glutamic acid and lysine residues, respectively, and m is the total DP(n) of the peptide block], and their stimuli-responsiveness to temperature and pH variation in aqueous solutions are described. Initiated with the amino-terminated poly(N-isopropylacrylamide) (PNiPAM(n)-NH2), ring-opening polymerization (ROP) of a mixture of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA), and Boc-L-lysine N-carboxyanhydride (BLLys-NCA) afforded the block copolypeptides PNiPAM(n)(PBLG(x)-co-PBLLys(y))m, with a poly(N-isopropylacrylamide) block together with a random copolypeptide block, which was then deprotected with HBr/trifluoroacetic acid into the double hydrophilic block copolypeptides, PNiPAM(n)(PLG(x)-co-PLLys(y))m. Their block ratios and lengths, as well as the amino acid residue ratios in the random copolypeptide block are varied (n = 360, x = 0.4-0.5, y = 0.4-0.6, and m = 220-252). The secondary structures of the copolypeptides in aqueous solution at different pH conditions were examined. Phase transitions in aqueous solutions induced by both pH and temperature variation were investigated by (1)H NMR spectroscopy. The transitions induced by temperature were also explored by turbidity measurements using UV/vis spectroscopy for their lower critical aggregation temperature (LCAT) determination. Furthermore, these aggregation processes were followed by dynamic light scattering measurements.     

Enhanced stability of polymeric micelles based on postfunctionalized poly(ethylene glycol)-b-poly(γ-propargyl L-glutamate): the substituent effect

One of the major obstacles that delay the clinical translation of polymeric micelle drug delivery systems is whether these self-assembled micelles can retain their integrity in blood following intravenous (IV) injection. The objective of this study was to evaluate the impact of core functionalization on the thermodynamic and kinetic stability of polymeric micelles. The combination of ring-opening polymerization of N-carboxyanhydride (NCA) with highly efficient "click" coupling has enabled easy and quick access to a family of poly(ethylene glycol)-block-poly(γ-R-glutamate)s with exactly the same block lengths, for which the substituent "R" is tuned. The structures of these copolymers were carefully characterized by (1)H NMR, FT-IR, and GPC. When pyrene is used as the fluorescence probe, the critical micelle concentrations (CMCs) of these polymers were found to be in the range of 10(-7)-10(-6) M, which indicates good thermodynamic stability for the self-assembled micelles. The incorporation of polar side groups in the micelle core leads to high CMC values; however, micelles prepared from these copolymers are kinetically more stable in the presence of serum and upon SDS disturbance. It was also observed that these polymers could effectively encapsulate paclitaxel (PTX) as a model anticancer drug, and the micelles possessing better kinetic stability showed better suppression of the initial "burst" release and exhibited more sustained release of PTX. These PTX-loaded micelles exerted comparable cytotoxicity against HeLa cells as the clinically approved Cremophor PTX formulation, while the block copolymers showed much lower toxicity compared to the cremophor-ethanol mixture. The present work demonstrated that the PEG-b-PPLG can be a uniform block copolymer platform toward development of polymeric micelle delivery systems for different drugs through the facile modification of the PPLG block.     

Synthesis of poly(epsilon-caprolactone)-b-poly(gamma-benzyl-L-glutamic acid) block copolymer using amino organic calcium catalyst

A biodegradable two block copolymer, poly(epsilon-caprolactone)-b- poly(gamma-benzyl-L-glutamic acid) (PCL-PBLG) was synthesized successfully by ring-opening polymerization of N-carboxyanhydride of gamma-benzyl-L-glutamate (BLG-NCA) with aminophenyl-terminated PCL as a macroinitiator. The aminophenethoxyl-terminated PCL was prepared via hydrogenation of a 4-nitrophenethoxyl-terminated PCL, which was novelly obtained from the polymerization of epsilon-caprolactone (CL) initiated by amino calcium 4-nitrobenzoxide. The structures of the block copolymer and its precursors from the initial step of PCL were confirmed and investigated by 1H NMR, FT-IR, GPC, and FT-ICRMS analyses and DSC measurements.     

Radiopaque organic-inorganic hybrids based on poly(D,L-lactide)

Hybrid organic-inorganic nanocomposites were prepared starting from alpha,omega-triethoxysilane-terminated poly(d,l-lactic acid) (PDLLA) to be used as potential radiopaque biocompatible coatings for medical devices. The synthesis of the organic phase precursors of given chain length was achieved via anionic polymerization of d,l-lactide using a bifunctional initiator and subsequent triethoxysilane functionalization of the end groups. PDLLA-based ceramers (ceramic polymers) were then synthesized by the sol-gel process at room temperature (rt) in the presence of different amounts of tetraethoxysilane. The rt-synthesized hybrids were then cured (at 80 or 130 degrees C), and their thermal and viscoelastic properties were investigated. All obtained hybrids were optically transparent, due to the nanometric dimension of the silica particles, and yielded clearly contrasted radiographic images.     

Synthesis and characterization of biotinylated forms of insulin-like growth factor-1: topographical evaluation of the IGF-1/IGFBP-2 AND IGFBP-3 interface

Activation of the insulin-like growth factor-1 (IGF)-1 receptor signaling pathways by IGF-1 and IGF-2 results in mitogenic and anabolic effects. The bioavailability of the IGFs is regulated by six soluble binding proteins, the insulin-like growth factor binding proteins (IGFBPs), which bind with approximately 0.1 nM affinity to the IGFs and often serve as endogenous antagonists of IGF action. To identify key domains of IGF-1 involved in the interaction with IGFBP-2 and IGFBP-3, we employed IGF-1 selectively biotinylated on residues Gly 1, Lys 27, Lys 65, and Lys 68. All monobiotinylated species of IGF-1 exhibited high affinity ( approximately 0.1-0.2 nM) for IGFBP-2 and IGFBP-3 in solid-phase-binding assays. However, different labeling intensities were observed in ligand blot analysis of IGFBP-2 and IGFBP-3. The N(epsilon)(Lys65/68)(biotin)-IGF-1 (N(epsilon)(Lys65/68b)-IGF-1) probe exhibited the highest signal intensity, while N(alpha)(Gly1b)-IGF-1 and N(epsilon)(Lys27b)-IGF-1 demonstrated significantly lower signals. When taken together, these results suggest that, once bound to IGFBP-2 or IGFBP-3, the biotin moieties of N(alpha)(Gly1b)-IGF-1 and N(epsilon)(Lys27b)-IGF-1 are inaccessible to NeutrAvidin-peroxidase, the secondary binding component. Ligand blots using IGF-1 derivatized with a long chain form of the N-hydroxysuccinimide biotin (NHS-biotin) to yield N(alpha)(Gly1)(LC-biotin)-IGF-1 and N(epsilon)(Lys27)(LC-biotin)-IGF-1 demonstrated increased signal intensity compared with their NHS-biotin counterparts. In BIAcore analysis, IGFBP-2 and IGFBP-3 bound only to the N(epsilon)(Lys65/68b)-IGF-1-coated flowcell of a biosensor chip, confirming the inaccessibility of Gly 1 and Lys 27 when IGF-1 is bound to IGFBP-2 and IGFBP-3. These data confirm the involvement of the IGFBP-binding domain on IGF-1 in binding to IGFBP-2 and IGFBP-3 and support involvement of the IGF-1R-binding domain in IGFBP binding.     

Helix formation in poly (N epsilon,N epsilon,N epsilon-trimethyl-L-lysine) and poly (L-lysine): dependence on concentration and molecular weight.

Helix formation in (Lys)n.HClO4 and poly(N epsilon,N epsilon,N epsilon-trimethyl-L-lysine).HClO4 +AD(LysMe3)n.HClO4+BD is dependent on peptide concentration and on molecular weight. For (LysMe3)n.HClO4 of degree of polymerization (DP) 2510 the midpoint of the coil-to-helix transition is 2 mM and for DP of 190 it is 5 mM. For (Lys)n.HClO4 the peptide concentration for half-helix is 30-60 times as high, and is only weakly dependent, if at all, on molecular weight. Helix formation is an intermolecular process. The use of methylated (Lys)n as the perchlorate permits study of the intermolecular coil-helix transition at low concentration, instead of the high concentration (ca. 1-2 M) required for (Lys)n.HBr. At constant peptide concentration helix content increases with added NaClO4. The higher the peptide concentration, the less NaClO4 is needed to induce helix.     

Synthesis and characterization of glycopolymer-polypeptide triblock copolymers

Glycopolymer-polypeptide triblock copolymers of the structure, poly(l-alanine)-b-poly(2-acryloyloxyethyl-lactoside)-b-poly(l-alanine) (AGA), have been synthesized by sequential atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP). Controlled free radical polymerization of 2-O-acryloyl-oxyethoxyl-(2,3,4,6-tetra-O-acetyl-beta-d-galactopyranosyl)-(1-4)-2,3,6-tri-O-acetyl-beta-d-glucopyranoside (AEL) by ATRP with a dibromoxylene (DBX)/CuBr/bipy complex system was used to generate a central glycopolymer block. Telechelic glycopolymers with diamino end groups were obtained by end group transformation and subsequently used as macroinitiators for ROP of l-alanine N-carboxyanhydride monomers (Ala-NCA). Gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy analysis demonstrated that copolymer molecular weight and composition were controlled by both the molar ratios of the Ala-NCA monomer to macroinitiator and monomer conversion and exhibited a narrow distribution (Mw/Mn = 1.06-1.26). FT-IR spectroscopy of triblock copolymers revealed that the ratio of alpha-helix/beta-sheet increased with poly(l-alanine) block length. Of note, transmission electron microscopy (TEM) demonstrated that selected amphiphilic glycopolymer-polypeptide triblock copolymers self-assemble in aqueous solution to form nearly spherical aggregates of several hundreds nanometer in diameter. Significantly, the sequential application of ATRP and ROP techniques provides an effective method for producing triblock copolymers with a central glycopolymer block and flanking polypeptide blocks of defined architecture, controlled molecular weight, and low polydispersity.     

L-Phe end-capped poly(L-lactide) as macroinitiator for the synthesis of poly(L-lactide)-B-poly(L-lysine) block copolymer

A poly(L-lactide)-b-poly(Nepsilon-(Z)-L-lysine) (PLLA-b-PZLys) block copolymer was synthesized through the ring-opening polymerization of Nepsilon-(Z)-lysine-N-carboxyanhydride using L-Phe-terminated PLLA as a macroinitiator. The L-Phe-terminated PLLA was prepared through a novel three-step process. First, the hydroxyl-terminated PLLA was synthesized through the ring-opening polymerization of L-lactide initiated by n-butanol under the existence of tin(II) ethylhexanoate. Subsequently, the complete capping of the hydroxyl end group of PLLA with BOC-L-Phe was achieved by using a mixed anhydride of BOC-L-Phe under the catalysis of 4-(1-pyrrolidinyl) pyridine. Finally, the free amino end group was obtained by removal of the t-butoxycarbonyl group through trifluoroacetic acid treatment under anhydrous condition. All these treatments were conducted under mild conditions, thus avoiding the breakdown of the PLLA backbone. Poly(L-lactide)-b-poly(L-lysine) block copolymer was produced after deprotection treatment of PLLA-b-PZLys. The structure of the block copolymer was confirmed by 1H NMR, IR, and GPC. Adjustment of the ratio of the NCA monomer to the macroinitiator could control the chain length of the PLys block.     

Novel amphiphilic poly(epsilon-caprolactone)-g-poly(L-lysine) degradable copolymers

As part of the search of novel degradable polymers, amphiphilic and cationic poly(epsilon-caprolactone)-g-poly(l-lysine) (PCL-g-PlL) copolymers have been synthesized following a grafting "onto" or a grafting "from" method both applied to a macropolycarbanionic PCL derivative. The first approach led to PCL-g-PZlL containing 36% of epsilon-caprolactone and 64% of N-epsilon-Z-l-lysine units, by reaction of activated poly(N-epsilon-Z-l-lysine) on the macropolycarbanion derived from PCL. The second route was based on the anionic ring opening polymerization of N-carboxyanhydride of N-epsilon-benzyloxycarbonyl-l-lysine initiated by the macropolycarbanion derived from PCL and led to a similar copolymer containing 45% of of epsilon-caprolactone and 55% of N-epsilon-Z-l-lysine units. After deprotection of the lysine units, PCL-g-PlL copolymers were obtained. These copolymers are water-soluble and form nanometric micelle-like objects with mean diameters between 60 and 500 nm in distilled water depending on the synthesis route.     

Enzymatic preparation of novel thermoplastic di-block copolyesters containing poly[(R)-3-hydroxybutyrate] and poly(epsilon-caprolactone) blocks via ring-opening polymerization

Enzymatic modification of a microbial polyester was achieved by the ring-opening polymerization of epsilon-caprolactone (CL) with low-molecular weight telechelic hydroxylated poly[( R)-3-hydroxybutyrate] (PHB-diol) as initiator and Novozym 435 (immobilized Candida antarctica Lipase B) as catalyst in anhydrous 1,4-dioxane or toluene. The ring-opening polymerization was investigated at different conditions with two different types of PHB-diols: PHB-diol(P), containing a primary OH and a secondary OH end groups, and PHB-diol(M), consisting of 91% PHB-diol(P) and 9% PHB-diol containing two secondary OH end groups. The reactions were followed by GPC analyses of the resulting polymers at different time points, and the optimal conditions were established to be 70 degrees C at a weight ratio of CL/enzyme/solvent of 8:1:24. The ring-opening polymerization of CL with PHB-diol(M) (Mn of 2380, NMR) at the molar ratio of 50:1 under the optimal conditions in 1,4-dioxane gave the corresponding poly[HB(56 wt %)-co-CL(44 wt %)] with Mn (NMR) of 3900 in 66% yield. Polymerization of CL and PHB-diol(P) ( Mn of 2010, NMR) at the same condition in toluene gave the corresponding poly[HB(28 wt %)-co-CL(72 wt %)] with Mn (NMR) of 7100 in 86% yield. Both polymers were characterized by (1)H and (13)C NMR and IR analyses as di-block copolyesters containing a PHB block with a secondary OH end group and a poly(epsilon-caprolactone) (PCL) block with a primary OH end group. NMR analyses and control experiments suggested no formation of random copolymers and no change of the PHB block during the reaction. The enzymatic ring-opening polymerization was selectively initiated by the primary OH group of PHB-diol, whereas the secondary OH group remained as an end group in the final polymers. The thermal properties of the di-block poly(HB-co-CL)s were analyzed by DSC, with excellent T g values for the elastomer domain: poly[HB(56 wt %)- co-CL(44 wt %)] with M n (NMR) of 3900 demonstrated a T g of -57 degrees C, Tm of 145, 123, and 53 degrees C; and poly[HB(28wt%)-co-CL(72wt%)] with Mn (NMR) of 7100 gave a Tg of -60 degrees C, Tm of 147 and 50 degrees C. Thus, the selective enzymatic ring-opening polymerization with PHB-diol as macro-initiator provides a new method for the preparation of PHB-based block copolymers as biomaterials with good thermoplastic properties and novel structures containing functional end groups.     

Organocatalytic Synthesis of Quinine-Functionalized Poly(carbonate)s

The ring-opening polymerization of substituted cyclic carbonates with 1-(3,5-bis-trifluoromethyl-phenyl)-3-cyclohexyl-thiourea (TU)/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) organocatalysts afford highly functionalized oligocarbonates. The fluorescent alkaloid quinine can be readily incorporated into the oligocarbonates either by initiation from quinine or by ring-opening polymerization of a quinine-functionalized cyclic carbonate (MTC-Q). Copolymerization of MTC-Q with a boc-protected guanidinium cyclic carbonate affords, after deprotection, highly water-soluble cationic copolymers functionalized with both quinine and pendant guanidinium groups. When multiple quinine groups are attached to the oligomers, they exhibit minimal fluorescence due to self-quenching. Upon hydrolysis, the fluorescence intensity increases, providing a potential strategy for monitoring the hydrolysis rates in real time.